High-Valent Pyrazolate-Bridged Platinum Complexes: A Joint Experimental and Theoretical Study.

Complexes [{Pt(C^C*)(μ-pz)}] (HC^C* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1-imidazol-2-ylidene , HC^C* = 1-phenyl-3-methyl-1-imidazol-2-ylidene ) react with methyl iodide (MeI) at room temperature in the dark to give compounds [{Pt(C^C*)Me(μ-pz)}(μ-I)]I (C^C* , C^C* ). The reaction of with benzyl bromide (BnBr) in the same conditions afforded [Br(C^C*)Pt(μ-pz)Pt(C^C*)Bn] (), which by heating in BnBr(l) became [{Pt(C^C*)Bn(μ-pz)}(μ-Br)]Br (). Experimental investigations and density functional theory (DFT) calculations on the mechanisms of these reactions from revealed that they follow a S2 pathway in the two steps of the double oxidative addition (OA). Based on the DFT investigations, species such as [(C^C*)Pt(μ-pz)Pt(C^C*)R]X (RX = MeI , BnBr ) and [(C^C*)Pt(μ-pz)Pt(C^C*)(R)X] (RX = MeI , BnBr ) were proposed as intermediates for the first and the second OA reactions, respectively. In order to put the mechanisms on firmer grounds, was prepared as [(C^C*)Pt(μ-pz)Pt(C^C*)Me]BF () and used to get I(C^C*)Pt(μ-pz)Pt(C^C*)Me, (C^C*)Pt(μ-pz)Pt(C^C*)(Me)I, and [{Pt(C^C*)Me(μ-pz)}(μ-I)]BF (). The single-crystal X-ray structures of , , , and along with the mono- and bi-dimensional H and Pt{H} NMR spectra of all the named species allowed us to compare structural and spectroscopic data for high-valent complexes with the same core [{Pt(C^C*)(μ-pz)}] but different oxidation states.