Transmission of Trans Effects in Dinuclear Complexes

The substitution of a terminal hydride ligand in the complexes [Ir2(μ-H)(μ-Pz)2H3(L)PiPr3)2] (L =
NCCH3 (1) or pyrazole (3)) by chloride provokes a significant change in the lability of the L ligand, despite
the fact that the substituted hydride and the L ligand lie in opposite extremes of the diiridium(III) complexes.
Detailed structural studies of complex 3 and its chloro-trihydride analogue [Ir2(μ-H)(μ-Pz)2H2Cl(HPz)(PiPr3)2] (4) have shown that this behavior is a consequence of the transmission of ligand trans effects from one
extreme of the molecule to the other, with the participation of the bridging hydride. Extended Hückel calculations
on model diiridium complexes have suggested that such trans effect transmissions are due to the formation of
molecular orbitals of σ symmetry extended along the backbones of the complexes. This is also an expected
feature for metal−metal bonded complexes. The feasibility of the transmission of ligand trans effects and
trans influences through metal−metal bonds and its relevance to the understanding of both the reactivity and
structures of metal−metal bonded dinuclear compounds have been substantiated through structural studies
and selected reactions of the diiridium(II) complexes [Ir2(μ-1,8-(NH)2naphth)I(CH3)(CO)2(PiPr3)2] (isomers 6
and 7) and their cationic derivatives [Ir2(μ-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2](CF3SO3) (isomers 8 and 9).