Platinum(II) Acetimino Cyclometalated Complexes Derived from Room Temperature Ammonia Activation

Two Pt(II) rollover cyclometalated complexes, [Pt(bpyPh−H)(DMSO)Me] (1) and [Pt(bpyPh−H)(DMSO)Cl] (2), where bpyPh−H is the C3-deprotonated 6-phenyl-2,2’-bipyridine, were reacted with aqueous ammonia in acetone at room temperature. In the case of the electron-poor complex 2 simple substitution of DMSO by NH3 gave the amino complex [Pt(bpyPh−H)(NH3)Cl] (4), whereas the electron-rich complex 1 produced the rare acetimine complex [Pt(bpyPh−H)(HN=CMe2)Me] (3), which was isolated and characterized. Complex 3 is stable both in solution and in the solid state, in the presence of air and water. The result is noteworthy, as the condensation product of acetone and ammonia, acetimine, is not stable under mild conditions. The reaction likely requires a Pt(II) electron-rich complex and the presence of a carbon donor in trans position. An analogous reaction occurs with methylamine, allowing the synthesis of the secondary imine complex [Pt(bpyPh−H)(MeN=CMe2)Me], 5. Starting from this finding a series of cyclometalated acetimine complexes [Pt(N C)(HN=CMe2)Me] were isolated and characterized with other classical and rollover cyclometalated ligands with an array of different electronic and steric properties, indicating a possible extension of the reaction to various cyclometalated ligands. A preliminary study on the antimicrobial and antitumor properties of complex 3, taken as a model for this class, showed no significant effects against Gram-positive, Gram-negative bacteria, or yeasts, but found activity in vitro against HT29 colon cancer cell line.