Transmission of trans effects in dinuclear complexes

The substitution of a terminal hydride ligand in the complexes [Ir-2(mu -H) (mu -Pz)(2)H-3(L)(PPr3)-Pr-i)(2)] (L = NCCH3 (1) or pyrazole (3)) by chlori de provokes a significant change in the lability of the L ligand, despite t he fact that the substituted hydride and the L ligand lie in opposite extre mes of the diiridium(III) complexes. Detailed structural studies of complex 3 and its chloro-trihydride analogue [Ir-2(mu -H)(eta -Pz)(2)H2Cl(HPz)((PP r3)-Pr-i)(2)] (4) have shown that this behavior is a consequence of the tra nsmission of ligand trans effects from one extreme of the molecule to the o ther, with the participation of the bridging hydride. Extended Huckel calcu lations on model diiridium complexes have suggested that such trans effect transmissions are due to the formation of molecular orbitals of a symmetry extended along the backbones of the complexes. This is also an expected fea ture 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 str uctural studies and selected reactions of the diiridium(II) complexes [lr(2 )(mu -1,8-(NH)(2)naphth)I(CH3)(CO)(2)((PPr3)-Pr-i)(2)] (isomers 6 and 7) an d their cationic derivatives [lr(2)(mu -1,8-(NH)(2)naphth)(CH3)(CO)(2)((PPr 3)-Pr-i)(2)](CF3SO3) (isomers 8 and 9).