Transition Metal Polyhydride Complexes. 11. Mechanistic Studies of the Cis to Trans Isomerization of the Iridium(III) Dihydride Ir(H)2(CO)L (L = C6H3(CH2P(H)2)2)

Density functional theory (B3LYP) has been used to investigate the mechanism of the cis−trans isomerization in Ir(H) 2 (CO)L (L = C 6 H 3 (CH 2 P(H 2 )) 2 ), a model for Ir(H) 2 (CO)L‘ (L‘ = C 6 H 3 (CH 2 P(i-Pr 2 )) 2 . This complex is initially formed as the cis isomer by bubbling H 2 through a benzene solution of Ir(CO)L‘ at room temperature. Over period of 18 h at 90 °C, the cis isomer quantitatively converts to the trans isomer ( Organometallics 1997, 16, 3786). Five possible mechanisms are examined in detail: (i) CO dissociation and reassociation; (ii) CO migratory insertion into the Ir−H bond and subsequent elimination; (iii) Ph−H reductive elimination to an arene intermediate and subsequent oxidative addition; (iv) phosphine dissociation, complex rearrangement, and phosphine reassociation; and (v) nondissociative trigonal twist. The preferred mechanism involves two consecutive trigonal twists in which the complex passes through a distorted octahedral intermediate.