Rhodium Complexes in P–C Bond Formation: Key Role of a Hydrido Ligand

Olefin
hydrophosphanation is an attractive route for the atom-economical
synthesis of functionalized phosphanes. This reaction involves the
formation of P–C and H–C bonds. Thus, complexes that
contain both hydrido and phosphanido functionalities are of great
interest for the development of effective and fast catalysts. Herein,
we showcase the excellent activity of one of them, [Rh­(Tp)­H­(PMe3)­(PPh2)] (1), in the hydrophosphanation
of a wide range of olefins. In addition to the required nucleophilicity
of the phosphanido moiety to accomplish the P–C bond formation,
the key role of the hydride ligand in 1 has been disclosed
by both experimental results and DFT calculations. An additional Rh–H···C
stabilization in some intermediates or transition states favors the
hydrogen transfer reaction from rhodium to carbon to form the H–C
bond. Further support for our proposal arises from the poor activity
exhibited by the related chloride complex [Rh­(Tp)­Cl­(PMe3)­(PPh2)] as well as from stoichiometric and kinetic studies.

烯烃氢膦化反应（hydrophosphanation）是实现官能化膦烷原子经济性合成的极具吸引力的路径。该反应涉及P-C键与H-C键的构建。因此，同时包含氢基（hydrido）与膦阴离子基（phosphanido）官能团的金属配合物，对于开发高效快速的催化剂具有重要研究价值。本文中，我们展示了其中一种配合物——[Rh(Tp)H(PMe3)(PPh2)] (1)——在多种烯烃的氢膦化反应中展现出的优异催化活性。除了膦阴离子基片段所需的亲核性可促成P-C键的形成之外，配合物1中氢配体的关键作用已通过实验结果与密度泛函理论（Density Functional Theory，DFT）计算得以阐明。部分中间体与过渡态中存在的额外Rh-H···C稳定作用，可促进氢从铑向碳原子的转移反应，进而完成H-C键的构建。相关氯化物配合物[Rh(Tp)Cl(PMe3)(PPh2)]所表现出的极低催化活性，以及化学计量与动力学研究结果，进一步佐证了我们的推论。