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Desoxo Molybdenum(IV) and Tungsten(IV) Bis(dithiolene) Complexes:  Monomer−Dimer Interconversion Involving Reversible Thiol Bridge Formation

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posted on 23.07.2007, 00:00 by Amit Majumdar, Kuntal Pal, Kowliki Nagarajan, Sabyasachi Sarkar
Two series of thiol-bridged dimeric desoxo molybdenum(IV) and tungsten(IV) bis(dithiolene) complexes, [Et4N]2[MIV2(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[WIV(SPh)2(mnt)2] (5a) are reported. These complexes are diamagnetic, and crystal structures of each of the complex (except 5a) exhibits a dimeric {MIV2(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 14 and W−S(R)−W angles ranging from 91.20° to 96.25° in the case of 1a4a. 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.