Exploring the Transphobia Effect on Heteroleptic NHC Cycloplatinated Complexes

The synthesis of 1-(4-cyanophenyl)-1H-imidazol (1) has been carried out by an improved method. Then its corresponding imidazolium iodide salt, 2, has been used to prepare the N-heterocyclic carbene (NHC) cycloplatinated compound [{Pt­(μ-Cl)­(C∧C*)}2] (4) (HC∧C*-κC* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene) following a step-by-step protocol. The intermediate complex [PtCl­(η3-2-Me-C3H4) (HC∧C*-κC*)] (3) has also been isolated and characterized. Using 4 as precursor, several heteroleptic complexes of stoicheometry [PtCl­(C∧C*)­L] (L = PPh3 (5), pyridine (py, 6), 2,6-dimethylphenyl isocyanide (CNXyl, 7), and 2-mercapto-1-methylimidazole (MMI, 8)) and [Pt­(C∧C*)­LL′]­PF6 (L = PPh3, L′ = py (9), CNXyl (10), and MMI (11)) have been synthesized. Complexes 6–8 were obtained as a mixture of cis- and trans-(C*,L) isomers, while trans-(C*,L) isomer was the only one observed for complexes 5 and 9–11. Their geometries have been discussed in terms of the degree of transphobia (T) of pairs of trans ligands and supported by theoretical calculations. The trans influence of the two σ Pt–C bonds present in these molecules, Pt–CAr and Pt–C*(NHC), has been compared from the JPt–P values observed in the new complex [Pt­(C∧C*)­(dppe)]­PF6 (dppe = 1, 2-bis­(diphenylphosphino)­ethane, 12).