Investigations on organoantimony compounds : XVII. Preparation and properties of heterocyclic trans-dichloro-β-diketonato-cis-diorganoantimony(V) compounds. Influence of stereochemistry on β-diketonate ligand exchange reactions in octahedral dichloro-β-diketonatodiorganoantimony(V) compounds

A series of heterocyclic trans-dichloro-β-diketonato-cis-diorganoantimony(V) compounds of the type R₂SbCl₂X (R₂ = (CH₂)₄, (CH₂)₅, o,o′−C₆H₄C₆H₄, o,o′−C₆H₄CH₂C₆H₄; X = Acac, Dpm) has been synthesized. The stereochemistry of these compounds has been deduced from PMR spectroscopic and molecular dipole moment data. Since the cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds R₂SbCl₂Acac (R = Me, Et, Ph) were known previously, a set of both cis- and trans-diorgano main group organometallic complexes has thus been made available, which allows a comparative study of the influence of stereochemistry on the strength of metal—ligand interactions in this type of octahedral d¹⁰ metal complex. β-Diketonate—ligand exchange reactions have been studied by PMR spectroscopy, and a marked influence of stereochemistry observed. trans-Dichloro-β-diketonato-cis-diorganoantimony(V) compounds undergo ligand exchange only slowly, if at all, whereas cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds react instantaneously. Both PMR chemical shift data and IR spectroscopic data point to the occurrence of a stronger antimony-β-diketonate interaction in trans-dichloro-β-diketonato-cis-diorganoantimony than in cis-dichloro-β-diketonato-trans-diorganoantimony compounds. This can be understood in terms of the hybridization of the antimony valence orbitals. The results are in line with the assumption that Sb---O bond rupture is the rate-determining step in β-diketonate ligand exchange.