DFT investigation of H-2 activation by [M(NHPnPr(3))(' 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 (Delta G > 100 kJ mol(-1)), an observation that is relevant for the design and synthesis of novel biomimetic catalysts.