Niobium/Rhodium Bimetallic Complexes: Synthesis, Structure, and Catalytic Hydrosilylation of Acetophenone and Benzaldehyde

Reactions of a new imido phosphido complex, Cp2Nb(NBut)(PPh2) (1), with olefin complexes of rhodium afford two types of compounds. With [(μ-Cl)Rh(C2H4)2]2, an imido/phosphido-bridged complex, Cp(Cl)Nb(μ-NBut)(μ-PPh2)RhCp (2), characterized by NMR and X-ray diffraction, was prepared. Formation of 2 represents a rare example of a Cp/Cl exchange reaction in organometallic chemistry. When 1 reacts with [(μ-Cl)Rh(COD)]2, the target phosphido-bridged bimetallic complex Cp2Nb(NBut)(μ-PPh2)Rh(Cl)(COD) (4) is formed. The structure of this product was established by NMR and an X-ray diffraction study. Both 2 and 4 are catalyst precursors for hydrosilylation of benzaldehyde and acetophenone. The activity of the neutral complex 4 exceeds that of the cation [Cp2Nb(NBut)(PPh2)Rh(COD)]+ derived from 4 by chloride anion abstraction.

一种新型亚胺膦基配合物二(环戊二烯基（cyclopentadienyl，Cp）)铌（niobium，Nb）(=N叔丁基（tert-butyl，But）)(二苯基膦基（diphenylphosphino，PPh₂))（Cp₂Nb(=NBut)(PPh₂)，1）与铑烯烃配合物的反应可生成两类化合物。当与[(μ-氯)Rh(C₂H₄)₂]₂反应时，可成功制备得到一种亚胺基/膦基桥联配合物Cp(Cl)Nb(μ-N叔丁基)(μ-二苯基膦基)RhCp（2），该产物经核磁共振（nuclear magnetic resonance，NMR）与X射线衍射（X-ray diffraction）表征。配合物2的生成是有机金属化学（organometallic chemistry）中一类罕见的环戊二烯基/氯交换反应实例。当配合物1与[(μ-氯)Rh(环辛二烯（cyclooctadiene，COD）)]₂反应时，可生成目标膦基桥联双金属配合物Cp₂Nb(=N叔丁基)(μ-二苯基膦基)Rh(Cl)(COD)（4）。该产物的结构通过核磁共振与X射线衍射研究得以确证。配合物2与4均可用作苯甲醛与苯乙酮硅氢化反应（hydrosilylation）的催化剂前驱体。中性配合物4的催化活性优于通过脱除配合物4中氯离子所得到的阳离子[Cp₂Nb(N叔丁基)(二苯基膦基)Rh(COD)]⁺。