Desoxo molybdenum(IV) and tungsten(IV) bis(dithiolene) complexes: monomer-dimer interconversion involving reversible thiol bridge formation

Abstract

Two series of thiol-bridged dimeric desoxo molybdenum(IV) and tungsten(IV) bis(dithiolene) complexes, [Et₄N]₂[M^IV₂(SR)₂(mnt)₄] [M = Mo, R = (1) −Ph, (2) −CH₂Ph, (3) −CH₂CH₃, (4) −CH₂CH₂OH; M = W, R = (1a) −Ph, (2a) −CH₂Ph, (3a) −CH₂CH₃, (4a) −CH₂CH₂OH] and one monomeric desoxo complex, [Et₄N]₂[W^IV(SPh)₂(mnt)₂] (5a) are reported. These complexes are diamagnetic, and crystal structures of each of the complex (except 5a) exhibits a dimeric {M^IV₂(SR)₂} core without any metal-metal bond where each metal atom possesses hexa coordination. The M-SR distance ranges from 2.437 to 2.484 Å in molybdenum complexes and from 2.418 to 2.469 Å in tungsten complexes. These complexes display Mo-S(R)-Mo angles ranging from 92.84° to 96.20° in the case of 1-4 and W-S(R)-W angles ranging from 91.20° to 96.25° in the case of 1a-4a. Interestingly, both the series of Mo(IV) and W(IV) dimeric complexes respond to an unprecedented interconversion between the dimer and the corresponding hexacoordinated monomer upon change of pH. This pH-dependent interconversion establishes the fact that even the pentacoordinated Mo(IV) and W(IV) bis(dithiolene) moieties are forced to dimerize; these can easily be reverted back to the corresponding monomeric complex, reflecting the utility of dithiolene ligand in stabilizing the Mo(IV)/W(IV) moiety in synthesized complexes similar to the active sites present in native proteins.