Stereochemistry and molecular rearrangements of some six-, seven-, and eight-coordinate chelates of early transition metals

This article is a review of the stereochemistry and molecular rearrangements of selected six-, seven-, and eight-coordinate chelates of early transition metals: primarily, metal β-diketonates, dithiocarbamates, and monothiocarbamates. Dihalobis(β-diketonato)metal complexes M(dik)2X2(M = Ti, Zr, or Hf) generally have an octahedral cis configuration, but Ti(acac)2I2 and V(dik)2X2 exist in solution as an equilibrium mixture of cis and trans isomers. Nuclear magnetic resonance (NMR) line-shape studies show that the dialkoxy complexes cis-Ti(dik)2(OR)2 rearrange by an intramolecular twisting mechanism whereas the closely related O,O−dimethyl dithiophosphates cis-Ti(Me2dtp)2(OR)2 undergo metal-ligand bond rupture. The seven-coordinate complexes Zr(acac)3Cl, Ti(S2CNMe2)3Cl, Ti(SOCNEt2)Cl, and CpM(S2CNMe2)3 (M = Ti, Zr, or Hf) have a pentagonal bipyramidal structure with the Cl or Cp ligand in an axial position. Eight-coordinate structures and stereoisomers are described