Divergent stereoisomers of molybdenum carbonyl complexes of NHC-based pincer ligands

The first molybdenum complexes of widely used NHC-based CNC and C<^>N<^>C pincer ligands are described, viz. [Mo(L)(CO)(3)] (L = 2,6-bis(mesityl-imidazolylidene)pyridine = CNC-Mes, 1; alpha,alpha'-(diimidazolylidene-dodecamethylene)lutidine = C<^>N<^>C-12, 2). These complexes have been thoroughly characterised in solution and the solid-state, revealing different stereochemical preferences of the tridentate ligands. In the case of flexible C<^>N<^>C-12 an uncommon lac-coordination geometry is observed, whilst the complex of rigid CNC-Mes adopts the expected mer-configuration. For the combination of donors associated with the ligands, DFT calculations establish preferential fac-coordination, however, within the CNC (Delta Delta G = +63.1 kJ.mol(-1)) and CAN'T (Delta Delta G = +20.0 kJ.mol(-1)) scaffolds this conformation is significantly destabilised relative to the mer-alternative. (C) 2017 Elsevier Ltd. All rights reserved.