Unravelling the role of precursors phosphine`s features in governing the reactivity of [MCl2(P-P)] (M = Pd, Pt) towards formation of thiolate complexes via S−S and S−C bond cleavage

Abstract

Group 10 thiolate complexes have been in the quest zone of research due to pertinent catalytic potential. The present work unravels the role of precursor phosphine`s feature in their reactivity towards 4,6-dimethylpyrimidine-2-thiol and subsequent thiolate complex. Synthesized thiolate complexes were thoroughly characterized using elemental analyses, NMR (1H, 13C{1H}, 31P{1H}), UV–Vis spectroscopy and Single Crystal X-ray diffraction analyses. Treatment of [MCl2(PPh3)2] (M = Pd, Pt) with two equivalents of NaSC4H(4,6-Me)N2 resulted in chelated [Pd{κ-S, κ-N: SC4H(4,6-Me)2N2}{SC4H(4,6-Me)2N2}(PPh3)] (1a) as well as an expected trans compound [Pt{SC4H(4,6-Me)2N2}2(PPh3)2] (1b). A similar reaction with the chelating phosphine ‘dppm’ (dppm = 1,1-bis(diphenylphosphino)methane) as an ancillary ligand resulted in the serendipitous product of composition [Pd2(µ2-S){SC4H(4,6-Me)2N2}2(µ2-dppm)2] (2a) depending upon competitive cleavage of S-S and S-C bond. The reaction of [PdCl2(dppe)] afforded a cis configured compound [Pd{2-SC4H(4,6-Me)2N2}2(dppe)] (2b). Contrary, the similar reaction of [PdCl2(dppp)] results in removal of ‘dppp’ (1,3-bis(diphenylphosphino)propane) yielding the chelated complex [Pd{κ-S, κ-N: SC4H(4,6-Me)2N2}2] (2c). Above all, the reactivity of 4,6-dimethylpyrimidine-2-thiol significantly differs compared to unsubstituted pyrimidyl, pyridyl analogue which has been attributed to the additional richness of electrons/activation in the ring which in turn facilitates competitive reactivity pattern of S-S and S-C bond. The virtue of such activation can easily be understood by the isolation of complex [Pd2(µ2-S){SC4H(4,6-Me)2N2}2(µ2-dppm)2] (2a). Rationalization of results via DFT calculation reveals that projection angle P-M-P (ranging from ∼75 to 92°) driven structural change in the chelating phosphine and associated degree of softness in ligand molecule played a crucial role in governing the resulting product of substitution reaction as dimeric, monomeric and chelated complexes. Thus, projection angle- driven geometrical and electronic structure and variation provide opportunity and direction to efficiently derive biologically as well as academically important complexes.