Synthesis and structure of organoantimony (V) cyclometallates: transannular interactions and the barrier to cyclisation

A variety of alpha-hydroxy carboxylic acid salts [AgO2CC(OH)(RR2)-R-1] reac t with SbPh3Cl2 1 to afford the cyclometalled complexes 4b-g. A single crys tal X-ray analysis of(+/-)-4g reveals the presence of conformational diaste reoisomers arising from the helical chirality of the SbPh3 propeller unit. Benzilic acid (R-1 = R-2 = Ph) however, reacts with 1 to afford the di-este r 3. To rationalise the steric impediment to cyclisation, the solid-state g eometries of all known five coordinate dioxo cyclometallates possessing an integral XPh3 unit are presented, along with the accessible conformations f or each structural alternative. Computer modelling and crystallographic cor relations identify severe 1,3-transannular interactions within the fluxiona l species associated with the nascent cyclometallate of benzilic acid. (C) 2001 Elsevier Science B.V. All rights reserved.