Hydrido-Silyl complexes

Given the ability of 14 electron fragments [(dtbpm)Pt(O)] and [(dcpm)Pt(O)] to activate C-H and C-Si bonds of inert organosilanes under very mild reaction conditions, it was of course no big surprise that Si-H activation reactions of silanes are possible as well. Hydrido-silyl complexes were formed in practically quantitative reactions if 14 or IS were used as precursors for the [(dtbpm)Pt(O)] fragment. Examples of Si-H insertion products, all stable, isolable compounds which could be fully characterized, are 25 - 27, and others have been made. 

Although we have assumed this complex to be a Pdn(hydrido)silyl complex it is plausible that this complex may be characterized as a Pd°-T 2-... 

Figure 8. Most stable styrene coordinated complexes. The styrene coordination energies are reported in kcal/mol. The coordination energies are reported as the energy of the tt-complex relative to the energy of the flee styrene molecule and the respective hydrido-silyl complexes.

Keywords Disilanes / Oxidative Addition / Phosphinoalkylsilanes / Chelate Assistance / Hydrido-Silyl Complexes... 

Hydrido-disilanyl complexes L M(H)(SiR2-SiR2H) are interesting because H2 elimination could support a possible 3-Si-H elimination and result in disilene complexes or products derived thereof Analogous to the synthesis of the well-known hydrido-silyl complexes... 

The, /si-H coupling constant is of special interest, because it is a versatile parameter to monitor the degree of oxidative addition. For uncoordinated silanes Vsi-H is about 200 Hz, as observed for Ic with 196.5 Hz. For hydrido silyl complexes without any Si,H interaction values below 20 Hz are observed. The coupling constants of 2a-c of 95-98 Hz are typical for three-center two-electron bonds. They are among the highest values found up to now, confirming that the oxidative addition is "frozen" in an early state. 

Although igw vary from 1.48-22 A in Table 11.1, the JSUI are always closer to those in OA products and more analogous to JHD in elongated H-H bonds (> 1 A). Furthermore, Jsm does not correlate with dSiH or even with the extent of OA.16 In some cases Jsm are nearly as low (22-26 Hz) as those in hydrido-silyl complexes yet dsm fall in the range of true a complexes. As will be discussed below, dsm often varies little with substituents at Si compared to №1. However, dmi is not a reliable indicator of either the presence or absence of a 3c-2e interaction because dMSi can be either longer or shorter than those in classical -Si bonds. 

P 1H NMR spectra show four signals consistent with an octahedral structure in which the silane is regarded as one ligand with the midpoint of one Si-H bond taking up a coordination site ds to CO. If these spedes were to be formulated as seven-coordinate hydrido-silyl complexes, they would undoubtedly be fluxional... 

Phosphine-substituted hydrido-silyl complexes [FeH(SiR)3(CO)sL] have been prepared by carbonyl substitution in cis-[FeH(SiR3)(CO)4] thus for example, reaction of 1 equivalent of dppm with cis-[FeH(Si(0He)3 (CO)4] leads to mer-[FeH(Si(OHe)3)(CO)3(dppm-P)] and the reaction of cis-[FeH(SiPh3)(CO)4] with Ph2P(CH2)4PPh2 (dppb) leads to mer-[FeH(SiPh3)(CO)3(dppb-P)]. ... 

HYDRIDO-SILYL COMPLEXES OF CHROMIUM WITH METAL-HYOROGEN-SILICON THREE-CENTER BONDS... 

On the metal side, an electronically imsaturated metal complex is required to which the Si—H bond can be added. 16-electron complexes can easily be created in situ by UV irradiation of metal carbonyl compounds, which results in the cleavage of one CO ligand. Hydrido-silyl complexes are formed when irradiation is done in the presence of a hydridosilane R4 jcSiHjc x= 1—4). Manganese complexes of the type (tj —CsRsKCOKL)... 

Mn(H)SiR3, (L = CO, PR3, P(OR)3, CNR) are particularly well investigated (4). In the extimple described here, ( / —C6Me6)Cr(CO)3 is employed as a metal carbonyl. This results in hydrido-silyl complexes, in which the Si—H interaction is slightly stronger than in the corresponding Mn complexes (5). 

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