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

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.