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

A variety of α-hydroxy carboxylic acid salts [AgO2CC(OH)R1R2] react with SbPh3Cl21 to afford the cyclometalled complexes 4b–g. A single crystal X-ray analysis of (±)-4g reveals the presence of conformational diastereoisomers arising from the helical chirality of the SbPh3 propeller unit. Benzilic acid (R1=R2=Ph) however, reacts with 1 to afford the di-ester 3. To rationalise the steric impediment to cyclisation, the solid-state geometries of all known five coordinate dioxo cyclometallates possessing an integral XPh3 unit are presented, along with the accessible conformations for each structural alternative. Computer modelling and crystallographic correlations identify severe 1,3-transannular interactions within the fluxional species associated with the nascent cyclometallate of benzilic acid.