Phosphinoorganosilane synthesis and Bis(phosphinoorgano)silyl complexes of ruthenium




Zhou, Xiaobing

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Hydrozirconation and subsequent phosphination have been developed into a versatile synthetic methodology leading to formation of phosphorus-carbon bonds. A family of phosphinoalkylsilane ligand precursors SiHMen(CH₂CH₂CH₂PPh₂)₃₋n (ChelH, I: n = 2; biPSiH, II: n = 1; triPSiH, III: n = 0) previously prepared via a photo-chemical route were synthesized in this way and the phosphination step has been shown to be dependent on steric factors. Similar methods have been used to obtain a group of new ligand precursors, the poly(silaalkyl)phosphines PPhn(CH₂CH₂CH₂PR₂)₃₋n (12: n = 1; 13: n = 0), which have been isolated and fully characterized. Analogues PPhn(o-C₆H₄SiMe₂H)₃₋n (21 : n = 1; 22: n = 0) containing more rigid benzylic backbones have been prepared from the corresponding (o-tolyl)phosphines via polylithiation and shown to exhibit temperature dependent NMR behavior. Poly(silaalkyl)phosphine coordination chemistry has been explored, yielding an unprecedented trans-bis(silyl) Pt(II) complex Pt[PhP(o-C₆H₄CH₂SiMe₂)₂]PPh₃ (25 ) which was isolated and characterized by using spectroscopic methods. The chemistry of [bis(diphenylphosphinopropyl)silyl] hydrido dicarbonyl ruthenium(II), RuH (biPSi)(CO)₂ (26), has been investigated in detail. The two diastereomers, syn and anti, were observed to exchange slowly with the two CO groups also scrambling at a comparable rate. A kinetic study of these two intramolecular isomerization processes suggests the involvement of dissociation and re-association of the chelate (biPSi) phosphines. Oxygen atom insertion into the Ru-Si bond of 26 occurs both in a hydrolysis process and direct oxidation by dioxygen. A labeling experiment suggests the former may involve a molecular dihydrogen intermediate, while the latter leads to insertion of oxygen atoms into both Ru-Si and Si-C bonds. Chlorination of 26 and subsequent thermal loss of a CO group afforded a novel l6e five coordinate Ru(II) species RuCl(biPSi)(CO) (42). Reaction of 42 with NaBH₄ or LiAlH₄ gave a mononuclear borohydride complex Ru(biPSi)(CO)(μ-η²-H₂BH₂) (43) or a rare hydrido anionic complex [fac-Ru(H)₂biPSi)(CO)]⁻ (44), both of which are extremely sensitive and have been identified in situ by using solution NMR spectroscopy. The silyl group in 26 was found to exert a stronger trans effect than hydride.



Phosphorus, Photochemistry