Group 11 Metal PSiP Chemistry

KO Bu as base. The preformed Ru hydride 27a was similarly inactive in the absence of added KO Bu, although 94% conversion was obtained in the hydrogenation of cyclohexanone when using 2mol% KO Bu (entry 6, Table 6.1). These preliminary results estabhsh the catalytic utility of such (PSiP) Ru complexes in ketone transfer hydrogenation. 

The synthesis of Ru complexes supported by the cyclohexylphosphino PSiP hgand analog 14 was subsequently pursued [41]. The tertiary silane 14 reacted 

Analogs of 29, 30, and 32 which have the central silyl X-group replaced by C(sp )-Me (29c-32c), phosphide (29p-32p), or amido (29n-32n) donor groups were also studied computationally [41]. The assessed natural bond orbital (NBO) charge distribution reveals the following order of descending donating abihty  

X = C(sp )-Me 32 n, X = N) directly correlates with the degree of electron deficiency at Ru and hence increases in the following order (kcalmol ) 32  

Y-shaped, while 46-syn is best described as T-shaped. Computational modeling studies suggest that the structure of 46-anti is the electronically preferred one, whereas that of 46-syn results from distortions provoked by sterics. Such small structural differences lead to more significant differences in reactivity between syn and anti isomers. Thus, syn isomers of 38, 46, and 47 form six-coordinate adducts with chlorinated solvents, CO, and P(OMe)j after coordination of the incoming hgand trans to Si. The anti isomers do not form detectable adducts with chlorinated solvents and coordinate CO or P(OMe)j either trans to Si (kinetic product) or trans to hydride (thermodynamic product). The equihbrium distribution of isomers for such six-coordinate adducts is dependent on the nature of the hahde ligand, such that in the case of CO adducts, the replacement of chloride by iodide inverts the stereochemistry of the reaction product and switches the CO coordination position from trans to hydride (98%) to trans to Si (100%). 

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Milstein and coworkers [43] have also contributed to group 10 metal PSiP chemistry, having attempted to stabilize Pt silanone (R2Si=0) species in the framework of a PSiP pincer. The attempted deprotonation of the silanol Pt" complex 120 with a strong base resulted in an unusual rearrangement process that afforded the dinuclear Pt hydride complex 125 (Scheme 6.26). A proposed... 

The published chemistry of group 8 metal PSiP complexes is thus far restricted to the synthesis of Ru" complexes. PSiP complexes of Ru" were first reported by Stobart and coworkers, who studied the complexation of the bis(phosphinoalkyl) silanes 1 and 5 with Ru carbonyl species. In an initial study, low yields of the 18-electron hydrido carbonyl complexes [K -(Ph2P(CH2)n)2SiMe]Ru(H)(CO)2 (17, n = 2 18, =3) were obtained upon reaction of either 1 or 5 with RUjICOljj (Scheme 6.5) [36]. Complex 18 was crystallographically characterized and featured... 

Our group has explored in detail the reactivity of 82 and the dicyclohexylphos-phino analog 84 (Scheme 6.19). These Pt chloride complexes were utiHzed as precursors for the synthesis of Pt alkyl complexes and cations of the type [(PSiP)Pt]", with the goal of accessing highly reactive metal complexes that would engage in E-H bond activation chemistry [77]. Indeed, square planar Pt alkyl and aryl complexes of the type (R -PSiP)PtR (85, R = Ph, R = CH2Ph 86,... 

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