Silicon—cobalt bonds

Cobalt-silicon bonds, in hydridocobalt complexes, 7, 5 Cobalt—tin bonds, in hydridocobalt complexes, 7, 5 Co-catalyst effects, in olefin polymerization, 4, 1111 (—)-Goccinine, via Alder-ene reactions, 10, 593 Co-condensation sites, in metal vapor synthesis technique,... 

Triethylsilylcobalt carbonyl was formed by Eq. (74) even under high pressures of carbon monoxide (60 atm, 200° C) so that carbon monoxide insertion into a cobalt-silicon bond does not readily occur... 

In view of the stability of the cobalt-silicon bond, ascribed to d-d back-bonding, this result is not surprising. 

An impressive synthesis of estrone (51) was reported by Vollhardt and coworkers. Cobalt-catalyzed cooligomerization of the diyne (49) with bis(trimethylsilyl)acetylene gave the estratrienone (50) in 71% yield. Introduction of the hydroxy substituent at C-3 was then cleverly achieved by selective proto-desilylation at C-2, followed by oxidation of the carbon-silicon bond using LTFA (Scheme 19). 

Zimgast M, Marschner C, Baumgartner J (2006) Cobalt-assisted silicon—silicon bond activation. Organometallics 25 4897... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

In summary, the four chemical systems described in this paper demonstrate the versatility and selectivity of electrochemical methods for synthesis and characterization of metal-carbon a-bonded metalloporphyrins. The described rhodium and cobalt systems demonstrate significant differences with respect to their formation, stability and to some extend, reactivity of the low valent species. On the other hand, properties of the electroche-mically generated mono-alkyl or mono-aryl germanium and silicon systems are similar to each other. 

Dimethyl(trimethylsilyl)phosphine (63) reacts with aluminium chlorides with cleavage of the silicon-phosphorus bond,58 as shown for aluminium trichloride. The same phosphine (63) reacts with the cobalt derivative (64) as shown.59... 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

Figure 6.3 Illustration of the three-coordinate complex [Co N(SiMe3)2 3]. Cobalt and nitrogen atoms are shown as black spheres, silicon atoms are grey and carbon atoms are given in white shadow. The Co-N bond length is 1.87A...

A related effect is that silicon-transition-metal compounds, once formed, undergo Si-M bond cleavage when dissolved in polar solvents (252,262,300,305,306,310). The products are often complex, but have been shown to include a cluster compound in one case involving cobalt (252). 

In the presence of ruthenium, rhodium and cobalt complexes that initially contain or generate M-H and M-Si bonds, the divinylderivatives of silicon com-... 

Silicon forms a variety of compounds containing clusters of transition metal atoms that exhibit a wide range of structures. DisUane reacts with Co2(CO)g to give the cobalt cluster (38) in which the silicon is coordinated to five Co atoms (equation 48). The Si-- Si distance of 2.817 A is too long for a bond (normally about 2.35 A) and the Si-Co distances average 2.336 A. ... 

Hydrolysis or condensation with allyl bromide showed retention of configuration to occur at silicon. However, products of low optical purity were obtained. It is difficult to know whether some racemisation had occurred in the silicon-cobalt bond cleavage or whether it is due to a low configurational stability of the silyl Grignard reagent. 

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