Rhodium or ruthenium units peripherally coordinated to carbosilane dendrimers functionalized with P-stereogenic monophosphines
摘要:
Carbosilane dendrimers containing P-stereogenic monophosphines as terminal groups, Dend-{CH2PPhR)(n)(R = 2-biphenylyl or 9-phenanthryt), were reacted with [RhCl(COD)](2) or [RUCl2(p-cymene)](2) to afford the corresponding chiral metalladendrimers Dend-{CH2PPhR(RhCl(COD))}(n) or Dend-{CH2PPhR(RuCl2(p-cymene))}(n), respectively. Attempts to obtain the first generation Ru-clendrimer for R = 2-biphenylyl proved unsuccessful, probably due to the steric hindrance of R. Complete characterization of these species was achieved by multinuclear NMR spectra, including 2D experiments, mass spectrometry, and optical rotation determinations. The catalytic properties of the rhodium dendrimers were tested in the hydrogenation of dimethylitaconate and those of the ruthenium derivatives in the asymmetric hydrogen transfer of acetophenone. The following model chiral compounds, (CH3)(3)Si{CH2PPhR(RhCl(COD))} and (CH3)(3)Si{CH2PPhR(RuCl2(p-cymene))}, were prepared in order to detect potential dendritic effects. All compounds were active in the catalytic conditions tested, but low or null e.e. were found. (c) 2006 Elsevier B.V. All rights reserved.
Carbosilane dendrimers peripherally functionalized with P-stereogenic diphosphine ligands and related rhodium complexes
摘要:
The first carbosilane dendrimer functionalized with P-stereogenic diphosphine ligands was prepared along with its cationic rhodium derivative. A mononuclear rhodium model compound was also synthesized. Both species were used as catalysts in the hydrogenation of dimethylitaconate and the results compared with those obtained with the related rhodium-containing P-stereogenic monophosphine dendrimers. (C) 2009 Elsevier B.V. All rights reserved.