Rhodium silyl complexes structures

In 1998, Mitchell and Tilley described the synthesis of a new rhodium silyl complex <19980M2912>. Reaction of (Me3P)3RhCl with (THF)2LiSiHMes2 (Mes = 2,4,6-trimethylphenyl) in toluene resulted in formation of a light yellow solution, from which colorless crystals of compound 5 were isolated after work-up. The presence of both Rh-H (5 =—9.90) and Si-H (5 = 5.76) resonances in the NMR spectrum and five separate methyl signals suggested the structure 5 shown in Equation (31). 

Direct alkyne insertion into a Rh—Si bond has been observed for the intermediate rhodium silyl complex (dtbpm) Rh[Si(OEt)3] (PMe3) [dtbpm = di(ferf-butyl)phosphino methane] in the hydrosilylation of 2-butyne with triethoxysilane catalyzed by the rhodium alkyl complex (dtbpm)RhMe(PMc3). The crystal structure of (dtbpm)Rh[Si(OEt)3j (PMes) shows that the coordination around the Rh metal is planar with a Rh—Si bond length [2.325(2) A] similar to that found for the complex (Me3P)3RhH(C6F5) Si(OEt)3 (Table ll) . The proposed mechanism for the hydrosilylation reaction of 2-butyne with HSi(OEt)3 yielding mainly the E-isomer of MeCH=C(Me)Si(OEt)3 is outlined in Scheme 36. 

Our study on the synthesis, structure and catalytic properties of rhodium and iridium dimeric and monomeric siloxide complexes has indicated that these complexes can be very useful as catalysts and precursors of catalysts of various reactions involving olefins, in particular hydrosilylation [9], silylative couphng [10], silyl carbonylation [11] and hydroformylation [12]. Especially, rhodium siloxide complexes appeared to be much more effective than the respective chloro complexes in the hydrosilylation of various olefins such as 1-hexene [9a], (poly)vinylsiloxanes [9b] and allyl alkyl ethers [9c]. 

It has been reported that the chiral NMR shift reagent Eu(DPPM), represented by structure 19, catalyzes the Mukaiyama-type aldol condensation of a ketene silyl acetal with enantiose-lectivity of up to 48% ee (Scheme 8B1.13) [29-32]. The chiral alkoxyaluminum complex 20 [33] and the rhodium-phosphine complex 21 [34] under hydrogen atmosphere are also used in the asymmetric aldol reaction of ketene silyl acetals (Scheme 8BI. 14), although the catalyst TON is quite low for the former complex. 

The oxidatively cleavable linker/tag complex has broader application and is introduced into the polymeric support by a rhodium-catalyzed carbene insertion. The tags are liberated from the solid support by treatment with ceric ammonium nitrate. For analysis the released tags are first silylated and then separated by gas chromatography. Since the tags are electrophoric, they can be analyzed in subpicomole quantity by electron capture detection. The structure of the compound is deduced from the resulting chromatogram. 

The extent of asymmetric hydrosilylation depends strongly upon the structure of hydrosilanes employed in a similar manner to the cases of other chiral rhodium complex-catalyzed reactions with dimethylphenylsilane optical yields are generally more than several times as high as with trimethylsilane. Most remarkable is the fact that the addition of dimethylphenylsilane to pivalophenone gave the silyl ether of (iS)-2,2-dimethyH-phenylpropanol, while that of trimethylsilane led to the (R)-enantiomer. 

Trls(diphenylthiophosphinoyl)nethanide (C(P(S)Ph2)3 ) complexes of rhodium and Iridium have been prepared and the crystal structure of the iridium complex [Ir(co) 2 T)2-C(P(S)Ph2> 3-S,S ] reveals a bidentate S,S ligand-iridium interaction. The trihydride complex [IrHa(CO)(dppe)] reacts with primary, secondary, and tertiary silanes to yield mono- and bis(silyl)hydride complexes of the formulae [IrH2(SiRR 2) (CO)(dppe)] and [IrH(SiRR 2)2(CO)(dppe)] (SiRR 2 = SiPhs,... 

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