DFT Investigation of H2 activation by [M(NHPnPr3)('S3')] (M = Ni, Pd). Insight into key factors relevant to the design of hydrogenase functional models

Density functional theory has been used to investigate the reaction between H(2) and Ni(NHPnPr(3))('S3')] or Pd(NHPnPr(3))('S3')], where 'S3' = bis(2-sulfanylphenyl)sulfide(2-), which are among the few synthetic complexes featuring a metal coordination environment similar to that observed in the NiFe] hydrogenase active site and capable of catalyzing H(2) heterolytic cleavage. Results allowed us to unravel the reaction mechanism, which is consistent with an oxidative addition-hydrogen migration pathway for Ni(NHPnPr(3))('S3')], whereas metathesis is also possible with Pd(NHPnPr(3))('S3')]. Unexpectedly, H(2) binding and activation implies structural reorganization of the metal coordination environment. It turns out that the structural rearrangement in Ni(NHPnPr(3))('S3')] and Pd(NHPnPr(3))('S3')] can take place due to the peculiar structural features of the Ni and Pd ligands, explaining the remarkable catalytic properties. However, the structural reorganization is the most unfavorable step along the H(2) cleavage pathway (DeltaG > 100 kJ mol(-1)), an observation that is relevant for the design and synthesis of novel biomimetic catalysts.