Publications by authors named "Vincenzo Passarelli"

43 Publications

Impact of Green Cosolvents on the Catalytic Dehydrogenation of Formic Acid: The Case of Iridium Catalysts Bearing NHC-phosphane Ligands.

Inorg Chem 2021 Sep 24. Epub 2021 Sep 24.

Departamento Química Inorgánica-Instituto Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain.

The catalysts [Ir(COD)(κ-,,-PCP)]BF and [Ir(COD)(κ--PCO)]BF proved to be active in the solventless dehydrogenation of formic acid. The impact of various cosolvents on the activity was evaluated, showing an outstanding improvement of the catalytic performance of [Ir(COD)(κ--PCO)]BF] in "green" organic carbonates: namely, dimethyl carbonate (DMC) and propylene carbonate (PC). The TOF value for [Ir(COD)(κ--PCO)]BF increases from 61 to 988 h upon changing from solventless conditions to a 1/1 (v/v) DMC/HCOOH mixture. However, in the case of [Ir(COD)(PCP)]BF, only a marginal improvement from 156 to 172 h was observed under analogous conditions. Stoichiometric experiments allowed the identification of various key reaction intermediates, providing valuable information on their reactivity. Experimental data and DFT calculations point to the formation of dinuclear species as the catalyst deactivation pathway, which is prevented in the presence of DMC and PC.
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http://dx.doi.org/10.1021/acs.inorgchem.1c02132DOI Listing
September 2021

Iridium(i) complexes bearing hemilabile coumarin-functionalised N-heterocyclic carbene ligands with application as alkyne hydrosilylation catalysts.

Dalton Trans 2021 Aug 2;50(32):11206-11215. Epub 2021 Aug 2.

Departamento de Química Inorgánica-Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, CP. 50009, Zaragoza, Spain.

A set of iridium(i) complexes of formula IrCl(κC,η-ICou)(cod) or IrCl(κC, η-BzICou)(cod) (cod = 1,5-cyclooctadiene; Cou = coumarin; I = imidazolin-2-carbene; BzI = benzimidazolin-2-carbene) have beeen prepared from the corresponding azolium salt and [Ir(μ-OMe)(cod)] in THF at room temperature. The crystalline structures of 4b and 5b show a distorted trigonal bipyramidal configuration in the solid state with a coordinated coumarin moiety. In contrast, an equilibrium between this pentacoordinated structure and the related square planar isomer is observed in solution as a consequence of the hemilability of the pyrone ring. Characterization of both species by NMR was achieved at the low and high temperature limits, respectively. In addition, the thermodynamic parameters of the equilibrium, ΔH and ΔS, were obtained by VT H NMR spectroscopy and fall in the range 22-33 kJ mol and 72-113 J mol K, respectively. Carbonylation of IrCl(κC,η-BzICou)(cod) resulted in the formation of a bis-CO derivative showing no hemilabile behaviour. The newly synthesised complexes efficiently catalyze the hydrosilylation of alkynes at room temperature with a preference for the β-(Z) vinylsilane isomer.
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http://dx.doi.org/10.1039/d1dt01946eDOI Listing
August 2021

Preparation of Butadienylpyridines by Iridium-NHC-Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement.

Chemistry 2021 Aug 21;27(46):11868-11878. Epub 2021 Jun 21.

Departamento de Química Inorgánica Instituto de Síntesis Química y Catálisis Homogénea-ISQCH, Universidad de Zaragoza-CSIC, Facultad de Ciencias, 50009, Zaragoza, Spain.

Iridium(I) N-heterocyclic carbene complexes of formula Ir(κ O,O'-BHetA)(IPr)(η -coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(κ O,O'-BHetA)(η -coe) complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(κ O,O'-BHetA)(κ N,C-C H N)(IPr) through the iridium(I) intermediate Ir(κ O,O'-BHetA)(IPr)(η -C H N). The cyclometalated IrH(κ O,O'-acac)(κ N,C-C H N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z,E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z,3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6π-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction.
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http://dx.doi.org/10.1002/chem.202101414DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8453560PMC
August 2021

Ligand Lability Driven by Metal-to-Borane Pseudorotation: A Mechanism for Ligand Exchange.

Inorg Chem 2020 Dec 4;59(24):17958-17969. Epub 2020 Dec 4.

Instituto de Síntesis Química y Catálisis Homogénea-ISQCH, University of Zaragoza 12, 50009 Zaragoza, Spain.

The discovery of systems that interact with small molecules plays a vital facilitating role in the development of devices that show sensitivity to their surroundings and an ability to quickly relay chemical and physical information. Herein, we report on the reaction of [NiCl(dppe)] with decaborane that produces in usable yield a new 11-vertex nickelaborane, [7,7-(dppe)--7-NiBH] (), which shows interesting reactivity and functionality toward carbon monoxide and ethylisonitrile. This contribution describes the synthesis and full structural characterization of and its small-molecule EtNC and CO adducts, and , and delineates the dynamic molecular behavior of all of these species in solution. This information sets a foundation from which more advanced work on this and related metallaborane systems can be conceived and provides a more general reference to how NMR spectroscopy, combined with DFT calculations, can be used to analyze the precise locomotion of labile ligands around a metal center held within a borane cluster.
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http://dx.doi.org/10.1021/acs.inorgchem.0c02205DOI Listing
December 2020

Rhodium(I)-NHC Complexes Bearing Bidentate Bis-Heteroatomic Acidato Ligands as gem-Selective Catalysts for Alkyne Dimerization.

Chemistry 2020 Aug 7;26(43):9598-9608. Epub 2020 Jul 7.

Departamento de Química Inorgánica-Instituto de, Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, CP., 50009, Zaragoza, Spain.

A series of Rh(κ -BHetA)(η -coe)(IPr) complexes bearing 1,3-bis-hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(μ-Cl)(IPr)(η -coe)] with the corresponding anionic BHetA species. The Rh -NHC-BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head-to-tail enynes. Among them, the acetanilidato-based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h with complete selectivity for the gem-isomer. Investigation of the reaction mechanism supports a non-oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ -HBHetA species. However, in the presence of pyridine as additive, the identification of the common Rh H(C≡CPh) (IPr)(py) intermediate gives support for an alternative oxidative route.
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http://dx.doi.org/10.1002/chem.202001584DOI Listing
August 2020

Reversible Activation of Water by an Air- and Moisture-Stable Frustrated Rhodium Nitrogen Lewis Pair.

Chemistry 2019 Oct 20;25(60):13665-13670. Epub 2019 Aug 20.

Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.

[Cp*Rh(κ N,N',P-L)][SbF ] (Cp*=C Me ), bearing a guanidine-derived phosphano ligand L, behaves as a "dormant" frustrated Lewis pair and activates H and H O in a reversible manner. When D O is employed, a facile H/D exchange at the Cp* ring takes place through sequential C(sp )-H bond activation.
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http://dx.doi.org/10.1002/chem.201902452DOI Listing
October 2019

Zwitterionic Rhodium and Iridium Complexes Based on a Carboxylate Bridge-Functionalized Bis-N-heterocyclic Carbene Ligand: Synthesis, Structure, Dynamic Behavior, and Reactivity.

Inorg Chem 2018 May 6;57(9):5526-5543. Epub 2018 Apr 6.

Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea , Universidad de Zaragoza-CSIC, Facultad de Ciencias , C/Pedro Cerbuna, 12 , 50009 Zaragoza , Spain.

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp*MCl{(MeIm)CHCOO}] and [M(diene){(MeIm)CHCOO}] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; M = Rh, Ir; MeIm = 3-methylimidazol-2-yliden-1-yl; diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd)) were prepared from the salt [(MeImH)CHCOO]Br and suitable metal precursor. The solid-state structure of both types of complexes shows a boat-shaped six-membered metallacycle derived of the κC,C' coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp*M complexes, whereas in the M(diene) complexes it is at the flagpole position of the metallacycle. The complexes [Rh(diene){(MeIm)CHCOO}] (diene = cod, nbd) exist as two conformational isomers in dichloromethane, bowsprit and flagpole, that interconvert through the boat-to-boat inversion of the metallacycle. An inversion barrier of ∼17 kcal·mol was determined by two-dimensional exchange spectroscopy NMR measurements for [Rh(cod){(MeIm)CHCOO}]. Reaction of zwitterionic Cp*M complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp*MCl{(MeIm)CHCOOMe}] or [Cp*MCl{(MeIm)CHCOOH}] (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [M(diene){(MeIm)CHCOOMe}] (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic M(diene) complexes with methyl triflate. In contrast, reaction of [Ir(cod){(MeIm)CHCOO}] with HBF·EtO (Et = ethyl), CHOTf, CHI, or I gives cationic iridium(III) octahedral complexes [IrX(cod){(MeIm)CHCOO}] (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from κC,C' to κC,C',O coordination of the bis-NHC ligand accompanying the oxidative addition prevents the coordination of the anions eventually formed in the process that remain as counterions.
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http://dx.doi.org/10.1021/acs.inorgchem.8b00498DOI Listing
May 2018

Mechanistic insights into the tropo-inversion of the biphenyl moiety in chiral bis-amido phosphites and in their palladium(ii) complexes.

Dalton Trans 2018 Feb;47(7):2292-2305

Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Departamento de Química Inorgánica, Pedro Cerbuna 12, 50009 Zaragoza, Spain.

Chiral bis-amido phosphites L1 and L2 containing a diaminobiphenyl unit and a chiral alkoxy group derived from either (-)-menthol or 3-acetoxy deoxycholic methyl ester have been synthesised. Both L1 and L2 react with PdCl(NCPh) affording di- or mononuclear derivatives with formula trans-[Pd(μ-Cl)Cl(L)] (1a, L = L1; 1b, L = L2) or trans-PdCl(L) (2a, L = L1; 2b, L = L2) depending on the Pd : L molar ratio. The crystal structure of (M,P)-1a confirms the trans arrangement of the ligand L1 and shows an unusual puckering of the Pd(μ-Cl) core (θ 46°). Both the ligands L1 and L2 and their complexes (1 and 2) are fluxional in solution as a consequence of the tropo-inversion of the diaminobiphenyl unit. For L1, L2, 1a and 2a a combined study including variable temperature P{H} NMR spectroscopy and line shape analysis, Eyring plots and DFT calculations have shed light on the mechanism of the tropo-inversion.
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http://dx.doi.org/10.1039/c7dt04829gDOI Listing
February 2018

Metal as Source of Chirality in Octahedral Complexes with Tripodal Tetradentate Ligands.

J Am Chem Soc 2018 01 10;140(3):912-915. Epub 2018 Jan 10.

Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza , Pedro Cerbuna 12, 50009 Zaragoza, Spain.

The challenging control of the absolute configuration of chiral-at-metal complexes is efficiently achieved using the tripodal tetradentate ligand L. The optical resolution of rac-[RhCl(κC,N,N',P-L)] mediated by (S)-α-phenylglycine provides access to enantiopure complexes of general formula [Rh(κC,N,N',P-L)A(Solv)][SbF] that enantioselectively catalyze the Diels-Alder reaction between methacrolein and HCp with enantiomeric ratio of up to >99/1. The nature of the active species, the origin of the enantioselectivity and mechanistic details are disclosed by means of NMR spectroscopy and DFT studies.
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http://dx.doi.org/10.1021/jacs.7b12731DOI Listing
January 2018

A well-defined NHC-Ir(iii) catalyst for the silylation of aromatic C-H bonds: substrate survey and mechanistic insights.

Chem Sci 2017 Jul 5;8(7):4811-4822. Epub 2017 Apr 5.

Departamento Química Inorgánica - ISQCH , Universidad de Zaragoza - CSIC , Pedro Cerbuna 12 , 50009 Zaragoza , Spain . Email: ; Email:

A well-defined NHC-Ir(iii) catalyst, [Ir(H)(IPr)(py)][BF] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), that provides access to a wide range of aryl- and heteroaryl-silanes by intermolecular dehydrogenative C-H bond silylation has been prepared and fully characterized. The directed and non-directed functionalisation of C-H bonds has been accomplished successfully using an arene as the limiting reagent and a variety of hydrosilanes in excess, including EtSiH, PhMeSiH, PhMeSiH, PhSiH and (EtO)SiH. Examples that show unexpected selectivity patterns that stem from the presence of aromatic substituents in hydrosilanes are also presented. The selective bisarylation of bis(hydrosilane)s by directed or non-directed silylation of C-H bonds is also reported herein. Theoretical calculations at the DFT level shed light on the intermediate species in the catalytic cycle and the role played by the ligand system on the Ir(iii)/Ir(i) mechanism.
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http://dx.doi.org/10.1039/c6sc04899dDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5602144PMC
July 2017

The Stepwise Reaction of Rhodium and Iridium Complexes of Formula [MCl (κ C,N,N',P-L)] with Silver Cations: A Case of trans-Influence and Chiral Self-Recognition.

Chemistry 2017 Oct 18;23(58):14532-14546. Epub 2017 Sep 18.

Departamento de CatálisisyProcesos Catalíticos, Instituto de Síntesis QuímicayCatálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Departamento de Química Inorgánica, Pedro Cerbuna 12, 50009, Zaragoza, Spain.

Acetonitrile suspensions of the dichlorido complexes [MCl (κ C,N,N',P-L)] [M=Rh (1), Ir (2)] react with AgSbF in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ C,N,N',P-L)(NCMe) ][SbF ] (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ C,N,N',P-L)} (μ-Cl)][SbF ] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ C,N,N',P-L)(Solv)][SbF ] (Solv=H O, MeCN, 7-10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ C,N,N',P-L)(NCMe)(μ-Cl)} Ag][SbF ] in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ C,N,N',P-L)(NCMe)] through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods.
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http://dx.doi.org/10.1002/chem.201702711DOI Listing
October 2017

Stereospecific control of the metal-centred chirality of rhodium(iii) and iridium(iii) complexes bearing tetradentate CNN'P ligands.

Dalton Trans 2017 Jun;46(22):7332-7350

Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Departamento de Química Inorgánica, Pedro Cerbuna 12, 50009 Zaragoza, Spain.

Ligands LH1-LH3 have been prepared by two successive condensation/reduction steps. These ligands react with MCl (M = Rh, Ir) rendering the trichlorido complexes [MCl(κN,N',P-LH)] (M = Rh, LH = LH1 (1), LH2 (2), LH3 (3); M = Ir, LH = LH1, (4)) as racemic mixtures of fac and mer isomers. Only one of the two possible fac isomers was detected. The mer isomer of the rhodium compounds 1-3 quantitatively isomerizes to the more stable fac isomer, whereas the mer isomer of the iridium complex 4 does not. DFT calculations indicate a dissociative pathway for this isomerization. In the presence of acetate or trifluoroacetate, complexes 1-3 or 4, respectively, undergo cyclometallation of their free benzylic arm affording the corresponding dichlorido compounds [MCl(κC,N,N',P-L)] (M = Rh, L = L1 (5), L2 (6), L3 (7); M = Ir, L = L1 (8)). Only one of the three possible enantiomeric pairs of coordination isomers was detected. The configuration at the stereogenic centres, namely the metal and the iminic nitrogen atom is stereospecifically predetermined. DFT calculations reveal that the cyclometallation follows an acetate-assisted mechanism and indicate that the isolated isomers are the most stable. Complexes 1-8 have been characterized by analytical and spectroscopic means and by the determination of the crystal structures of the complexes 1, 3 and 5-8 by X-ray diffractometry.
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http://dx.doi.org/10.1039/c7dt01446eDOI Listing
June 2017

Temperature Dual Enantioselective Control in a Rhodium-Catalyzed Michael-Type Friedel-Crafts Reaction: A Mechanistic Explanation.

Chemistry 2016 Jul 27;22(31):11064-83. Epub 2016 Jun 27.

Departamento de Catálisis y Procesos Catalíticos, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC -, Universidad de Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.

By changing the temperature from 283 to 233 K, the S (99 % ee) or R (96 % ee) enantiomer of the Friedel-Crafts (FC) adduct of the reaction between N-methyl-2-methylindole and trans-β-nitrostyrene can be obtained by using (SRh ,RC )-[(η(5) -C5 Me5 )Rh{(R)-Prophos}(H2 O)][SbF6 ]2 as the catalyst precursor. This catalytic system presents two other uncommon features: 1) The ee changes with reaction time showing trends that depend on the reaction temperature and 2) an increase in the catalyst loading results in a decrease in the ee of the S enantiomer. Detection and characterization of the intermediate metal-nitroalkene and metal-aci-nitro complexes, the free aci-nitro compound, and the FC adduct-complex, together with solution NMR measurements, theoretical calculations, and kinetic studies have allowed us to propose two plausible alternative catalytic cycles. On the basis of these cycles, all the above-mentioned observations can be rationalized. In particular, the reversibility of one of the cycles together with the kinetic resolution of the intermediate aci-nitro complexes account for the high ee values achieved in both antipodes. On the other hand, the results of kinetic measurements explain the unusual effect of the increment in catalyst loading.
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http://dx.doi.org/10.1002/chem.201601301DOI Listing
July 2016

Postsynthetic modifications of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] with Lewis bases: cluster modular tuning.

Dalton Trans 2016 May;45(20):8622-36

Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, ES-50009 Zaragoza, Spain.

It has been demonstrated that the reaction of [2,2,2-(H)(PPh3)2-closo-2,1-RhSB8H8] () with PPh3 affords the boron substituted rhodathiaborane-PPh3 adduct, [6,6-(PPh3)2-9-(PPh3)-arachno-6,5-RhSB8H9] (). Building upon this reaction, we report herein that the 10-vertex hydridorhodathiaborane reacts with the Lewis bases, PCy3, py, 2-Mepy, 2-Etpy, 3-Mepy and 4-Mepy to form the rhodathiaborane-ligand adducts, [6,6-(PPh3)2-9-(L)-arachno-6,5-RhSB8H9], where L = PCy3 (), 2-Mepy (), 2-Etpy (), py (), 3-Mepy () or 4-Mepy (), and [8,9-μ-(H)-9-(PPh3)2-8-(L)-arachno-9,6-RhSB8H8], where L = py (), 3-Mepy () or 4-Mepy (). The selectivity of the reactions depended on the nature of the entering Lewis bases, affording the 6,5-isomers, , , and as single products for PPh3, PCy3, 2-Mepy and 2-Etpy; and mixtures of the 6,5-/9,6-regioisomers, /, / and / for py, 3-Mepy and 4-Mepy, respectively. The molecular structures of both regioisomers were characterized by X-ray diffraction analysis for the 6,5-isomers, and , and for the 9,6-isomers, and . Variable temperature NMR studies of the reaction between and PPh3 or 2-Mepy demonstrated that at low temperatures there is formation of the 9,6-species that subsequently isomerizes to the 6,5-regioisomer, indicating that for the more sterically hindered Lewis bases, PPh3, 2-Mepy and PCy3, the latter isomer is more stable and accessible through an intramolecular {Rh(PPh3)2} vertex flip. The formation of both isomers with py, 3-Mepy and 4-Mepy indicates that the kinetic and thermodynamic energies of the 6,5 and 9,6 rhodathiaborane-ligand adducts are similar for these Lewis bases. Lewis base bonding to exo-polyhedral boron vertices results in a change of the metal coordination from pseudo-octahedral Rh(iii) in to pseudo-square planar Rh(i) in the adducts. The chemistry described here highlights the remarkable structural flexibility of these polyhedral boron-containing compounds, their modular architecture and their easy postsynthetic modification.
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http://dx.doi.org/10.1039/c6dt00856aDOI Listing
May 2016

En route to phosphonato iridium(i) complexes: the decisive effect of an intramolecular hydrogen bond.

Dalton Trans 2016 Jan;45(3):951-62

Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, C/Pedro Cerbuna 12, ES-50009 Zaragoza, Spain.

Pentacoordinated iridium(i) complexes of formula IrCl(SiNP)(tfbb) (1) and IrCl(HNP)2(tfbb) (2) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2; HNP = NH(4-C6H4CH3)PPh2) have been prepared and fully characterised. Both feature a distorted square pyramidal coordination polyhedron at the metal centre in the solid state and are fluxional in solution. Their reaction with trimethyl phosphite yields the derivatives [Ir(SiNP){P(OMe)3}(tfbb)]Cl ([3]Cl) and Ir{PO(OMe)2}(HNP)2(tfbb) (4). The course of the reaction between IrCl(HNP)2(tfbb) (2) and trimethyl phosphite was elucidated by NMR spectroscopy and DFT calculations, showing that the intermediate [Ir(HNP)2{P(OMe)3}(tfbb)](+) ((5+)) forms and further reacts with the chloride anion yielding the phosphonato derivative 4 and methyl chloride. The decisive role of the N-H group in the formation of the phosphonato ligand has been established by IR and NMR spectroscopic measurements and by DFT calculations.
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http://dx.doi.org/10.1039/c5dt04038hDOI Listing
January 2016

Intramolecular C-H oxidative addition to iridium(I) triggered by trimethyl phosphite in N,N'-diphosphanesilanediamine complexes.

Dalton Trans 2015 Nov 8;44(42):18596-606. Epub 2015 Oct 8.

Centro Universitario de la Defensa, Ctra. Huesca s/n, ES-50090 Zaragoza, Spain.

The reaction of [Ir(SiNP)(cod)][PF6] ([1][PF6]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2) with trimethyl phosphite affords the iridium(iii) derivatives of the formula [IrHClx(SiNP-H){P(OMe)3}2-x]((1-x)+) (x = 0, 3(+); x = 1, 6) containing the κ(3)C,P,P'-coordinated SiNP-H ligand (SiNP-H = Si(CH2)(CH3){N(4-C6H4CH3)PPh2}2). The thermally unstable pentacoordinated cation [Ir(SiNP){P(OMe)3}(cod)](+) (2(+)) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula [IrClx(SiNP){P(OMe)3}2-x]((1-x)+) (x = 0, 4(+); x = 1, 7) should be firstly obtained from 2(+) and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2(+) on the outcome of the C-H oxidative addition reaction has also been investigated.
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http://dx.doi.org/10.1039/c5dt02886hDOI Listing
November 2015

Intramolecular C-H oxidative addition to iridium(I) in complexes containing a N,N'-diphosphanosilanediamine ligand.

Inorg Chem 2014 Jan 7;53(2):972-80. Epub 2014 Jan 7.

Centro Universitario de la Defensa , Ctra. Huesca s/n, ES-50090 Zaragoza, Spain.

The iridium(I) complexes of formula Ir(cod)(SiNP)(+) (1(+)) and IrCl(cod)(SiNP) (2) are easily obtained from the reaction of SiMe2{N(4-C6H4CH3)PPh2}2 (SiNP) with [Ir(cod)(CH3CN)2](+) or [IrCl(cod)]2, respectively. The carbonylation of [1][PF6] affords the cationic pentacoordinated complex [Ir(CO)(cod)(SiNP)](+) (3(+)), while the treatment 2 with CO gives the cation 3(+) as an intermediate, finally affording an equilibrium mixture of IrCl(CO)(SiNP) (4) and the hydride derivative of formula IrHCl(CO)(SiNP-H) (5) resulting from the intramolecular oxidative addition of the C-H bond of the SiCH3 moiety to the iridium(I) center. Furthermore, the prolonged exposure of [3]Cl or 2 to CO resulted in the formation of the iridium(I) pentacoordinated complex Ir(SiNP-H)(CO)2 (6). The unprecedented κ(3)C,P,P' coordination mode of the [SiNP-H] ligand observed in 5 and 6 has been fully characterized in solution by NMR spectroscopy. In addition, the single-crystal X-ray structure of 6 is reported.
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http://dx.doi.org/10.1021/ic4024458DOI Listing
January 2014

A second rhodopsin-like protein in Cyanophora paradoxa: gene sequence and protein expression in a cell-free system.

J Photochem Photobiol B 2013 Aug 27;125:188-93. Epub 2013 Jun 27.

Istituto di Biofisica, CNR, Pisa, Italy.

Here we report the identification and expression of a second rhodopsin-like protein in the alga Cyanophora paradoxa (Glaucophyta), named Cyanophopsin_2. This new protein was identified due to a serendipity event, since the RACE reaction performed to complete the sequence of Cyanophopsin_1, (the first rhodopsin-like protein of C. paradoxa identified in 2009 by our group), amplified a 619 bp sequence corresponding to a portion of a new gene of the same protein family. The full sequence consists of 1175 bp consisting of 849 bp coding DNA sequence and 4 introns of 326 bp. The protein is characterized by an N-terminal region of 47 amino acids, followed by a region with 7 α-helices of 213 amino acids and a C-terminal region of 22 amino acids. This protein showed high identity with Cyanophopsin_1 and other rhodopsin-like proteins of Archea, Bacteria, Fungi and Algae. Cyanophosin_2 (CpR2) was expressed in a cell-free expression system, and characterized by means of absorption spectroscopy.
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http://dx.doi.org/10.1016/j.jphotobiol.2013.06.010DOI Listing
August 2013

Automatic and real time recognition of microalgae by means of pigment signature and shape.

Environ Sci Process Impacts 2013 Jul;15(7):1397-410

Istituto di Scienza e Tecnologia Informazione, CNR, Via Moruzzi 1, 56124 Pisa, Italy.

Microalgae are unicellular photoautotrophic organisms that grow in any habitat such as fresh and salt water bodies, hot springs, ice, air, and in or on other organisms and substrates. Massive growth of microalgae may produce harmful effects on the marine and freshwater ecological environment and fishery resources. Therefore, rapid and accurate recognition and classification of microalgae is one of the most important issues in water resource management. In this paper, a new methodology for automatic and real time identification of microalgae by means of microscopy image analysis is presented. This methodology is based on segmentation, shape features extraction, and characteristic colour (i.e. pigment signature) determination. A classifier algorithm based on the minimum distance criterion was used for microalgae grouping according to the measured features. 96.6% accuracy from a set of 3423 images of 24 different microalgae representing the major algal phyla was achieved by this methodology.
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http://dx.doi.org/10.1039/c3em00160aDOI Listing
July 2013

Tetraflagellochloris mauritanica gen. et sp. nov. (Chlorophyceae), a New Flagellated Alga from the Mauritanian Desert: Morphology, Ultrastructure, and Phylogenetic Framing.

J Phycol 2013 Feb 25;49(1):178-93. Epub 2012 Oct 25.

Istituto di Biofisica, CNR, Via Moruzzi 1, Pisa, 56124, Italy.

Morphological, ultrastructural, and molecular-sequence data were used to assess the phylogenetic position of a tetraflagellate green alga isolated from soil samples of a saline dry basin near F'derick, Mauritania. This alga can grow as individual cells or form non-coenobial colonies of up to 12 individuals. It has a parietal chloroplast with an embedded pyrenoid covered by a starch sheath and traversed by single parallel thylakoids, and an eyespot located in a parietal position opposite to the flagellar insertion. Lipid vacuoles are present in the cytoplasm. Microspectroscopy indicated the presence of chlorophylls a and b, with lutein as the major carotenoid in the chloroplast, while the eyespot spectrum has a shape typical of green-algal eyespots. The cell has four flagella, two of them long and two considerably shorter. Sequence data from the 18S rRNA gene and ITS2 were obtained and compared with published sequences for green algae. Results from morphological and ultrastructural examinations and sequence analysis support the placement of this alga in the Chlorophyceae, as Tetraflagellochloris mauritanica L. Barsanti et A. Barsanti, gen. et sp. nov.
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http://dx.doi.org/10.1111/j.1529-8817.2012.01232.xDOI Listing
February 2013

Fundamental questions and concepts about photoreception and the case of Euglena gracilis.

Integr Biol (Camb) 2012 Jan 14;4(1):22-36. Epub 2011 Nov 14.

Istituto di Biofisica, CNR, via Moruzzi 1, 56124 Pisa, Italy.

The ability to sense light can be considered the most fundamental and presumably the most ancient property of visual systems. This ability is the basis of phototaxis, one of the most striking behavioral responses of motile photosynthetic microorganisms (i.e. microalgae) to light stimuli, which allows them to move toward or away directional light. In order to fully exploit the information content of light (intensity, direction, distribution) microorganisms need proper perceiving devices, termed photoreceptors, which must act as sensors, to perceive wavelength and direction of light, as transducers, to convert the light signal into chemical and/or electrical information, but also as amplifiers and eventually as transmitters. This review describes the universal structural, behavioral and physiological features necessary for the proper functioning of these devices in algae, and how these features have been investigated by means of different analytical techniques such as for example microspectroscopy, digital fluorescence microscopy, two photons FLIM. The insight of the photoreceptive response mechanism is explained using the unicellular alga Euglena gracilis, in which the different structural, behavioral and physiological features combine to achieve a concerted, efficient response to light stimuli.
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http://dx.doi.org/10.1039/c1ib00115aDOI Listing
January 2012

Reactivity of novel N,N'-diphosphino-silanediamine-based rhodium(I) derivatives.

Inorg Chem 2011 Oct 22;50(20):9958-67. Epub 2011 Sep 22.

Centro Universitario de la Defensa, Ctra. Huesca s/n, ES-50090 Zaragoza, España.

The coordination abilities of the novel N,N'-diphosphino-silanediamine ligand of formula SiMe(2)(NtolPPh(2))(2) (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)](2) (2), [Rh(SiNP)(COD)][BF(4)] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)](2) (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CN(t)Bu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CN(t)Bu, respectively. Otherwise, PPh(3) and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh(3)) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CN(t)Bu even in excess. Otherwise, RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η(1)-C(3)H(5))(SiNP) (9a) and [Rh(acac)(η(3)-C(3)H(5))(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)](2) (2) and the CC coupling product 3-allylpentane-2,4-dione.
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http://dx.doi.org/10.1021/ic2004408DOI Listing
October 2011

Comparative study of [RuClCp(HdmoPTA-κP)(PPh3)][CF3SO3] and the heterobimetallic complexes [RuClCp(PPh3)-μ-dmoPTA-1κP:2κ2N,N'-M(acac-κ2O,O')2] (M=Co, Ni, Zn; dmoPTA=3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane).

Dalton Trans 2011 Apr 21;40(13):3237-44. Epub 2011 Feb 21.

Departamento de Química Inorgánica, Facultad de Química, Universidad de La Laguna, La Laguna, Tenerife, Spain.

The synthesis of novel heterobimetallic derivatives of general formula [RuClCp(PPh(3))-μ-dmoPTA-1κP:2κ(2)N,N'-M(acac-κ(2)O,O')(2)] (M = Ni (3), Zn (4); dmoPTA = 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) is described. The preparations of the ruthenium-cobalt analogue (M = Co (2)) and the starting compound [RuClCp(HdmoPTA-κP)(PPh(3))](CF(3)SO(3)) have been revised and their yield improved. Similar to 2, the solid state structures of 3 and 4 show that the dmoPTA-P and the dmoPTA-N(CH(3)) atoms are involved in the coordination to the {RuCpCl(PPh(3))} and {M(acac)(2)} moieties, respectively. The size of the diffusing units is almost the same for the three binuclear complexes, indicating that they exhibit similar solution structures. The diamagnetic ruthenium-zinc derivative was fully characterized in solution at 193 K by NMR as two diastereomeric pairs of enantiomers (R-Ru, Δ-Zn; R-Ru, Λ-Zn; S-Ru, Δ-Zn; S-Ru, Λ-Zn). Finally, the electrochemical properties of the complexes have been investigated by cyclic voltammetry.
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http://dx.doi.org/10.1039/c0dt00571aDOI Listing
April 2011

Chemistry, physico-chemistry and applications linked to biological activities of β-glucans.

Nat Prod Rep 2011 Mar 17;28(3):457-66. Epub 2011 Jan 17.

Istituto di Biofisica, CNR, Via Moruzzi, Pisa, Italy.

β-Glucans is the common name given to a group of chemically heterogeneous polysaccharides. They are long- or short-chain polymers of (1-->3)-β-linked glucose moieties which may be branched, with the branching chains linked to the backbone by a (1-->6)-β linkage. β-(1-->3)-Glucans are widely distributed in bacteria, algae, fungi and plants, where they are involved in cell wall structure and other biological function. β-Glucans have been shown to provide a remarkable range of health benefits, and are especially important against the two most common conventional causes of death in industrialized countries, i.e. cardiovascular diseases (where they promote healthy cholesterol and blood glucose levels) and cancer (where they enhance immune system functions). This Highlight provides a comprehensive and up-to-date commentary on β-glucans, their chemistry, physico-chemistry, functional role in immunological responses, and possible applications as therapeutic tools. In addition, we discuss the mechanism behind their health benefits, which are not yet fully understood.
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http://dx.doi.org/10.1039/c0np00018cDOI Listing
March 2011

Rhodium(III)-catalyzed dimerization of aldehydes to esters.

Chemistry 2011 Jan 7;17(1):91-5. Epub 2010 Dec 7.

Departamento de Química de Coordinación y Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón (ICMA), C.S.I.C.-Universidad de Zaragoza, Pedro Cerbuna 12, 50009-Zaragoza, Spain.

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http://dx.doi.org/10.1002/chem.201002921DOI Listing
January 2011

A rhodopsin-like protein in Cyanophora paradoxa: gene sequence and protein immunolocalization.

Cell Mol Life Sci 2010 Mar 18;67(6):965-71. Epub 2009 Dec 18.

Istituto di Biofisica, CNR, Pisa, Italy.

Here, we report the DNA sequence of the rhodopsin gene in the alga Cyanophora paradoxa (Glaucophyta). The primers were designed according to the conserved regions of prokaryotic and eukaryotic rhodopsin-like proteins deposited in the GenBank. The sequence consists of 1,272 bp comprised of 5 introns. The correspondent protein, named Cyanophopsin, showed high identity to rhodopsin-like proteins of Archea, Bacteria, Fungi, and Algae. At the N-terminal, the protein is characterized by a region with no transmembrane alpha-helices (80 aa), followed by a region with 7alpha-helices (219 aa) and a shorter 35-aa C-terminal region. The DNA sequence of the N-terminal region was expressed in E. coli and the recombinant purified peptide was used as antigen in hens to obtain polyclonal antibodies. Indirect immunofluorescence in C. paradoxa cells showed a marked labeling of the muroplast (aka cyanelle) membrane.
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http://dx.doi.org/10.1007/s00018-009-0225-xDOI Listing
March 2010

MICROSPECTROPHOTOMETRY AS A METHOD TO IDENTIFY KLEPTOPLASTIDS IN THE NAKED FRESHWATER DINOFLAGELLATE GYMNODINIUM ACIDOTUM(1).

J Phycol 2009 Dec 29;45(6):1304-9. Epub 2009 Sep 29.

Istituto di Biofisica, Istituto Scienza Tecnologia Informazione, Area della Ricerca CNR, Via Moruzzi 1, 56124 Pisa, Italy.

A relatively small number of freshwater dinoflagellates are involved in symbiotic association with cryptophytes. The chloroplasts of the cryptophytes are retained by the dinoflagellate and give it the characteristic phycobilin pigmentation, either phycoerythrin or phycocyanin. The pigment characterization of the retained chloroplasts can give precise and accurate information about the type of cryptophyte preyed upon by the dinoflagellate. For this purpose, we performed microspectrophotometric evaluation of the pigments of Gymnodinium acidotum Nygaard and three different cryptophytes present in samples collected from a tributary of the river Arno, in Tuscany (Italy). The comparison of the different spectroscopic data allowed us to discriminate effectively among the cryptophytes preyed upon by the dinoflagellate.
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http://dx.doi.org/10.1111/j.1529-8817.2009.00751.xDOI Listing
December 2009

Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: the case of Euglena gracilis.

Biochem Biophys Res Commun 2009 Jul 18;385(2):176-80. Epub 2009 May 18.

Istituto Sistemi Complessi, CNR, Sesto Fiorentino, Italy.

In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A(498,) non fluorescent and B(462), fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A(498) becomes B(462)), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B(462) form acts as donor for the non-fluorescent A(498) form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.
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http://dx.doi.org/10.1016/j.bbrc.2009.05.034DOI Listing
July 2009

Synthesis and reactivity of the novel hydride derivative RhHCl(TIMP(3)) (HTIMP(3) = tris[1-(diphenylphosphino)-3-methyl-1H-indol-2-yl]methane).

Dalton Trans 2009 Apr 9(13):2290-7. Epub 2009 Feb 9.

Instituto Ciencia Molecular, Universidad de Valencia, Polígono La Coma, s/n 46980, Paterna, Valencia, Spain.

The reaction of HTIMP(3) (HTIMP(3) = tris[1-(diphenylphosphino)-3-methyl-1H-indol-2-yl]methane) with [RhCl(COD)](2) and Rh(acac)(CO)(2) produces RhHCl(TIMP(3)) (1H) and Rh(TIMP(3))(CO) (2), respectively, both exhibiting tetradentate kappaC,kappa(3)P-coordination of the TIMP(3) moiety. The reaction of RhHCl(TIMP(3)) with nucleophiles (L) in the presence of AgBF(4) or AgPF(6) produces different compounds depending on the nature of L. Indeed, cationic Lewis adducts of formula [RhH(L)(TIMP(3))](+) ((2H+)-(5H+)) are obtained when L is CO, CNCH(2)Ph, pyridine or CH(2)CHCN. On the other hand, when the incoming nucleophile is CH(3)COOH the hydride-free complex [Rh(CH(3)COO)(TIMP(3))](+) ((6+)) is obtained. Finally, the reaction of RhHCl(TIMP(3)) with PhCCPh and CH(2)CHCOOMe in the presence of AgPF(6) leads to the insertion products [Rh(PhCCHPh)(TIMP(3))](+) ((+)) and [Rh(CH(2)CH(2)COOMe)(TIMP(3))](+) ((8+)), respectively. The solid state structure has been determined by single crystal X-ray diffraction in selected cases (1H, (6+)).
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http://dx.doi.org/10.1039/b816185bDOI Listing
April 2009

Intervalent bis(mu-aziridinato)M(II)--M(I) complexes (M=Rh,Ir): delocalized metallo-radicals or delocalized aminyl radicals?

Chemistry 2008 ;14(35):10985-98

Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-UZ, Pedro Cerbuna 12, E-50009 Zaragoza, Spain.

Reactions of the methoxo complexes [{M(mu-OMe)(cod)}(2)] (cod=1,5-cyclooctadiene, M=Rh, Ir) with 2,2-dimethylaziridine (Haz) give the mixed-bridged complexes [{M(2)(mu-az)(mu-OMe)(cod)(2)}] [(M=Rh, 1; M=Ir, 2). These compounds are isolated intermediates in the stereospecific synthesis of the amido-bridged complexes [{M(mu-az)(cod)}(2)] (M=Rh, 3; M=Ir, 4). The electrochemical behavior of 3 and 4 in CH(2)Cl(2) and CH(3)CN is greatly influenced by the solvent. On a preparative scale, the chemical oxidation of 3 and 4 with [FeCp(2)](+) gives the paramagnetic cationic species [{M(mu-az)(cod)}(2)](+) (M=Rh, [3](+); M=Ir, [4](+)). The Rh complex [3](+) is stable in dichloromethane, whereas the Ir complex [4](+) transforms slowly, but quantitatively, into a 1:1 mixture of the allyl compound [(eta(3),eta(2)-C(8)H(11))Ir(mu-az)(2)Ir(cod)] ([5](+)) and the hydride compound [(cod)(H)Ir(mu-az)(2)Ir(cod)] ([6](+)). Addition of small amounts of acetonitrile to dichloromethane solutions of [3](+) and [4](+) triggers a fast disproportionation reaction in both cases to produce equimolecular amounts of the starting materials 3 and 4 and metal--metal bonded M(II)--M(II) species. These new compounds are isolated by oxidation of 3 and 4 with [FeCp(2)](+) in acetonitrile as the mixed-ligand complexes [(MeCN)(3)M(mu-az)(2)M(NCMe)(cod)](PF(6))(2) (M=Rh, [8](2+); M=Ir, [9](2+)). The electronic structures of [3](+) and [4](+) have been elucidated through EPR measurements and DFT calculations showing that their unpaired electron is primarily delocalized over the two metal centers, with minor spin densities at the two bridging amido nitrogen groups. The HOMO of 3 and 4 and the SOMO of [3](+) and [4](+) are essentially M--M d-d sigma*-antibonding orbitals, explaining the formation of a net bonding interaction between the metals upon oxidation of 3 and 4. Mechanisms for the observed allylic H-atom abstraction reactions from the paramagnetic (radical) complexes are proposed.
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http://dx.doi.org/10.1002/chem.200801615DOI Listing
January 2009
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