Configurational rearrangements in cis-M(AA) 2X 2, cis-M(AA) 2XY, and 3. The cis-M(AA) 2X 2 system - diastereotopic probe on the terminal AA groups [1, 2

Abstract

The series complexes Ti(dibm) 2X 2 [X = F, Cl, or Br; dibm = anion of diisobutyrylmethane], M(dibm) 2Cl 2 [M = Sn or Ge], and Ti(dpm) 2X 2 [X = F, Cl, or Br; dpm = anion of dipivaloylmethane] have been prepared and investigated by variable temperature nuclear magnetic resonance (NMR) spectroscopy. Except for Ti(dpm) 2F 2 and Ti(dpm) 2Cl 2, the above complexes have not been reported previously. NMR spectra indicate that these complexes possess the cis-diastereomeric configuration. Diastereotopic isopropyl methyl probes have been incorporated into the dibm ligand to follow the steric course of the configurational rearrangement taking place in these C 2-type complexes. The NMR spectra have been analyzed in terms of the permutational and topological and mechanistic analyses reported earlier. It is shown that the rearrangements can be rationalized in terms of the A 5 averaging set, and it is argued that the likely sole reaction pathway is a twist process about the two opposite C 3(i′) and C 3(‴) axes of the octahedral skeleton. Approximate rate constants for the configurational changes are reported: ligand labilization follows the order acac < dibm < dpm for the Ti(dik) 2Cl 2 complexes, and Cl < Br ∼ for the Ti(dibm) 2X 2 systems.