An electrochemical investigation on the reduction path of the arene complexes [CpM(arene)]2+ and [(η-9-SMe2-7,8-C2B9H10)M(arene)]2+ (M=Rh, Ir)

Journal of Solid State Electrochemistry (Impact Factor: 2.23). 11/2007; 11(12):1643-1653. DOI: 10.1007/s10008-007-0324-2

ABSTRACT The reduction behavior of the isoelectronic complexes [CpMIII(η6-C6R6)]2+ (M=Rh, Ir; R=H, Me) and [(η-9-SMe2-7,8-C2B9H10)MIII(η6-C6R6)]2+ (M=Rh, Ir; C6R6 = C6H6, C6H5OMe, C6H3Me3) has been studied by cyclic voltammetry and controlled potential coulometry in acetonitrile and propylene carbonate at 253
and 298K, respectively. The extent of chemical reversibility of the pertinent sequences Rh(III)/Rh(II)/Rh(I) and Ir(III)/Ir(I)
is highly dependent on both the nature of the solvent and the intrinsic electronic properties of the arene substituents. The
arene η6 coordination makes the derivatives in their lower oxidation states notably short lived, even if, in some cases, the use of
propylene carbonate improves their stability or causes the increase in their lifetimes before changing the arene coordination
from η6 to η4. Cations [(η-9-SMe2-7,8-C2B9H10)M(η6-C6R6)]2+ were obtained by the bromide abstraction from [(η-9-SMe2-7,8-C2B9H10)MBr2]2 with Ag+ in the presence of benzene and its derivatives. The structure of [(η-9-SMe2-7,8-C2B9H10)Ir(η6-C6H5OMe)](BF4)2 was determined by X-ray diffraction.

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    ABSTRACT: The reaction of (η5-C9H2Me5)Rh(1,5-C8H12) (1) with I2 gives the iodide complex [(η5-C9H2Me5)RhI2]2 (2). The solvate complex [(η5- C9H2Me5)Rh(MeNO2)3]2+ (generated in situ by treatment of 2 with Ag+ in nitromethane) reacts with benzene and its derivatives giving the dicationic arene complexes [(η5-9H2Me5)Rh(arene)]2+ [arene = C6H6 (3a), C6Me6 (3b), C6H5OMe (3c)]. Similar reaction with the borole sandwich compound CpRh(η5-C4H4BPh) results in the arene-type complex [CpRh(μ-η5:η6-C4H4BPh)Rh(η5-C9H2Me5)]2+ (4). Treatment of 2 with CpTl in acetonitrile affords cation [(η5-C9H2Me5)RhCp]+ (5). The structure of [3c](BF4)2 was determined by X-ray diffraction. The electrochemical behaviour of complexes prepared was studied. The rhodium-benzene bonding in series of the related complexes [(ring)Rh(C6H6)]2+ (ring = Cp, Cp*, C9H7, C9H2Me5) was analyzed using energy and charge decomposition schemes.
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    ABSTRACT: Reaction of (η-9-SMe2-7,8-Me2-7,8-C2B9H8)M(cod) with hydrohalic acids affords the 16-valence-electron complexes (η-9-SMe2-7,8-Me2-7,8-C2B9H8)MX2 (M = Rh, X = Cl (3a), Br (3b), I (3c); M = Ir, X = Cl (4a), Br (4b), I (4c)). According to X-ray analysis, 3a, 3b, 4b, and 4c have monomeric pseudocloso-structures with a long cage C⋯C distance (2.122, 1.985, 2.238, and 2.186 Å, respectively), in contrast to dimeric closo-structures of the cage-non-methylated analogs. The structural difference was explained using DFT calculations. 3b and 4b react with SMe2 and Tl[Tl(η-7,8-C2B9H11)] giving closo-metallacarboranes (η-9-SMe2-7,8-Me2-7,8-C2B9H8)M(SMe2)Br2 (M = Rh (5), Ir (6)) and (η-9-SMe2-7,8-Me2-7,8-C2B9H8)M(η-7,8-C2B9H11) (M = Rh (7), Ir (8)).
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