Synthesis of Rhodium Complexes with Bulky Substituted Cyclopentadienyl Ligands. H/D Exchange Reactions and Silane Activation

Abstract

Rh(I) complexes of the type (η5-C5Me4R)Rh(olefin)2 have been successfully synthesized through a novel procedure that makes use of zincocenes, Zn(C5Me4R)2, as mild cyclopentadienyl transfer reagents. This method proves to be also practical for the preparation of (η5-C5Me4SiR3)Rh(olefin)2 derivatives with no degradation of the C−Si bond of the cyclopentadienyl ligand. Complexes (η5-C5Me4R)Rh(CH2═CHSiMe3)2 have been tested in hydrogen/deuterium scrambling reactions with deuterated benzene. As expected, complexes (η5-C5Me4R)Rh(CH2═CHSiMe3)2 (R = But, 3,5-But2C6H3) incorporate deuterium into the α and β sites of the vinyl silane ligand at faster rates than derivative (η5-C5Me5)Rh(CH2═CHSiMe3)2, but silyl-substituted cyclopentadienyl species (η5-C5Me4SiMe2R′)Rh(CH2═CHSiMe3)2 (R′ = Me, But) exchange hydrogen at β sites of the vinyl silane at slower rates, as a consequence of the steric effects exerted by the SiMe2R groups. Reaction of diolefin compounds (η5-C5Me4R)Rh(C2H4)2 with triethyl silane led to formation of Rh(V) complexes (η5-C5Me4R)Rh(H)2(SiEt3)2 along with carbosilane HEt2SiCH(Me)SiEt3.