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

ABSTRACT: Complexes [{Pt(C^C*)(μ-pz)}₂] (HC^C*_A = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene 1a, HC^C*_B = 1-phenyl-3-methyl-1H-imidazol-2-ylidene 1b) react with methyl iodide (MeI) at room temperature in the dark to give compounds [{Pt^IV(C^C*)Me(μ-pz)}₂(μ-I)]I (C^C*_A 2a, C^C*_B 2b). The reaction of 1a with benzyl bromide (BnBr) in the same conditions afforded [Br(C^C*_A)Pt^III(μ-pz)₂Pt^III(C^C*_A)Bn] (5a), which by heating in BnBr(l) became [{Pt^IV(C^C*_A)Bn(μ-pz)}₂(μ-Br)]Br (6a). Experimental investigations and density functional theory (DFT) calculations on the mechanisms of these reactions from 1a revealed that they follow a S_N2 pathway in the two steps of the double oxidative addition (OA). Based on the DFT investigations, species such as [(C^C*_A)Pt^III(μ-pz)₂Pt^III(C^C*_A)R]X (RX = MeI Int-Me, BnBr Int-Bn) and [(C^C*_A)Pt^II(μ-pz)₂Pt^IV(C^C*_A)(R)X] (RX = MeI Int'-Me, BnBr Int'-Bn) were proposed as intermediates for the first and the second OA reactions, respectively. In order to put the mechanisms on firmer grounds, Int-Me was prepared as [(C^C*_A)Pt^III(μ-pz)₂Pt^III(C^C*_A)Me]BF₄ (3a') and used to get [I(C^C*_A)Pt^III(μ-pz)₂Pt^III(C^C*_A)Me](4a), [(C^C*_A)Pt^II(μ-pz)₂Pt^IV(C^C*_A)(Me)I](Int'-Me), and [{Pt^IV(C^C*)Me(μ-pz)}₂(μ-I)]BF₄ (2a'). The single-crystal X-ray structures of 2a, 2b, 3a', and 5a along with the mono- and bi-dimensional ¹H and ¹⁹⁵Pt{¹H} 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)}₂] but different oxidation states.

SUBMITTER: Arnal L 

PROVIDER: S-EPMC9387385 | biostudies-literature | 2022 Aug

REPOSITORIES: biostudies-literature