Silicon complexes with iridium

Several examples of oxidative addition reactions of compounds involving group (iv) elements, silicon and germanium, with iridium(i) complexes have been described and reviewed. In the reaction of silicon hydrides (CH3) (C2H50)3 SiH with bis(bis-l, 2-diphenylphosphinoethane)iridium(i), [Ir (diphos)2],... 

Silylene-based pincer ligands offer exciting reactivities in terms of transition metal complex formation and their applications in catalytic systems. The pincer complex [SiCSi)Ni(II) can be synthesized by oxidative addition of C—H bond of the corresponding [SiC(H)Si] ligand. [SiCSi]Ni(II) complex has been employed as catalyst for Ni-catalyzed Sonogashira reactions (8). Moreover bis(silylene) pincer complexes of iridium and rhodium reveal strong 5-donating ability of divalent silicon and have demonstrated selectivity in catalytic C—H borylation reactions with arenes (9). 

Iridium siloxide complexes show a similar activity. Catalytic tests performed in the presence of [ Ir( 4-OSiMe3)(cod) 2], with the use of trimethylvinylsilane and dimethylphenylsilane as reactants [59], gave the same type of silicon derivatives as those obtained by Murai and coworkers [58], but the siloxide iridium precursor used appeared to be more efficient under milder conditions. When the [Ir(cod)(PCy3)(OSiMe3)] was used rather than the binuclear iridium siloxide complex, Z-Me3SiCH2CH=CHOSiMe2Ph was obtained exclusively [59],... 

Burger. P. and Bergman, R.G. (1993) Facile intermolecular activation of carbon-hydrogen bonds in methane and other hydrocarbons and silicon-hydrogen bonds in silanes with the iridium(III) complex Cp (PMe3)Ir (CH3)(OTf). J. Am. Chem. Soc., 115 (22). 10462-10463. 

Interesting, optically acive complexes were obtained upon reaction of organosilicon hydrides. The reactions of R3SiH with transition metal complexes represent a key step in catalytic hydrosilylation reactions. Catalytic activation of silicon hydrides has been proposed to arise from an oxidative addition process to a transition metal centre. Such a process has been shown to be reversible via a reductive elimination step (equation 9). The stereochemistry of addition to an iridium complex was shown to occur in a cis fashion59 (equation 10). 

The iridium(V) fluoro complex [IrFj] has been prepared via reduction of [IrF ] with silicon or dihydrogen, In the gas phase, [IrFj] possesses D h symmetrywhile in the solid state, a fluoride-bridged polymeric structure with bridges mutually cis is indicated on the basis of and F NMR... 

Although oxidation reactions of this type are generally associated with square-planar four-co-ordinate complexes, there are several examples of oxidative addition to five-co-ordinate species. In these systems, however, the mechanism may also be termed as oxidative elimination since the product is six co-ordinate and one of the ligands is displaced. The mechanism of silicon hydride addition to hydridocarbonyltris(triphenyl-phosphine)iridium(i) has been described, the reaction... 

Fac-tris(trimethylphosphino)iridium(III) silane complexes of the form IrHX(PMe3)3 SiRR2 (X = H, D R = H, D, Cl, Ph R = Ph, t-Bu) have been prepared by the oxidative addition of SiXRRj to IrH(PMe3)4 with the loss of PMes. The exclusive formation of the facial isomers is attributed to a preferential cis addition of the R3Si—H moiety parallel to the P—Ir—P axis, yielding the cis hydride products in which the silicon is trans to a phosphine . ... 

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