Heteroatom-silicon multiple bonds

Recent advances in the chemistry of silicon-heteroatom multiple bonds... 

Recent advances in the chemistry of silicon-heteroatom multiple bonds 1065 B. Theoretical Calculations 1. Silanones and silanethiones... 

The protonation of organo-rare-earth metal species through a-bond metathesis plays a key role in many catalytic applications described below. The high reactivity of rare-earth metals for insertion of unsaturated carbon-carbon multiple bonds [18], in conjunction with smooth o-bond metathesis, allows to perform catalytic small molecule synthesis. This route is atom efficient, economic, and opens access to nitrogen-, phosphorous-, silicon-, boron-, and other heteroatom-containing molecules. The most important catalytic applications of organo-rare-earth metals involving the o-bond metathesis process will be discussed in this review. 

The hydrosilylation of carbon-heteroatom multiple bonds had received little attention until it was found in 1972 that Rh(PPh3)3Cl is an extremely effective catalyst for the hydrosilylation of carbonyl compounds. This is a new and unique reduction method since the resulting silicon-oxygen bond can easily be hydrolyzed. Other transition metal complexes including platinum, ruthenium , and rhodium also have good catalytic activity in the selective and asymmetric hydrosilylation of carbonyl compounds "". 

During the past three years, we have studied the reactions of thermally generated silicon atoms with low molecular weight reaetants. Reaction products were isolated in argon matrices and identified by means of IR spectroscopy, aided by calculated vibrational spectra. The method turned out to be very versatile and successful [1-4]. When the reactions of silicon atoms with unsaturated substrates are compared, a general sequence of products can be outlined as follows if a heteroatom is participating in the multiple bond, the silicon atom is bound to a lone pair in the primary product. This primary product can be isomerized photochemically to a cyclic silylene, the formal addition product of the Si atom to the Jt bond, which is the first product in case of substrates with C-C multiple bonds. Consecutive photoisomerizations lead to the formal insertion product of the Si atom into a C-H bond and, finally, to the product(s) of (successive) migration of H atoms to the Si atom. 

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