Rhodium or ruthenium units peripherally coordinated to carbosilane dendrimers functionalized with P-stereogenic monophosphines

Carbosilane dendrimers containing P-stereogenic monophosphines as terminal groups, Dend-{CH2PPhR}n (R = 2-biphenylyl or 9-phenanthryl), 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-dendrimer 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)3Si{CH2PPhR(RhCl(COD))} and (CH3)3Si{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.