Influence of steric effect on the structural aspects of N,N′,N″-triarylguanidine derived six-membered [C,N] palladacycles

Abstract

Guanidine derived six-membered [C,N] palladacycles of the types [(C,N)Pd(μ-OC(O)R)]2 (1a–d), [(C,N)Pd(μ-Br)]2 (2a,b), cis-[(C,N)PdBr(L)] (3a–d, 4, and 5), and ring contracted guanidine derived five-membered [C,N] palladacycle, [(C,N)PdBr(CNXy)] (6) were prepared in high yield following the established methods with a view aimed at understanding the influence of the substituents on the aryl rings of the guanidine upon the solid state structure and solution behaviour of palladacycles. Palladacycles were characterised by microanalytical, IR, NMR and mass spectral data. The molecular structures of 1a, 1c, 2a, 2b, 3a, 3c, 3d, and 4–6 were determined by single crystal X-ray diffraction data. Palladacycles 1a and 1c were shown to exist as a dimer in transoid in–in conformation in the solid state but as a mixture of a dimer in major proportion and a monomer (κ2-O,O′-OAc) in solution as deduced from 1H NMR data. Palladacycles 2a and 2b were shown to exist as a dimer in transoid conformation in the solid state but the former was shown to exist as a mixture of a dimer and presumably a trimer in solution as revealed by a variable temperature 1H NMR data in conjunction with ESI-MS data. The cis configuration around the palladium atom in 3a, 3c, and 3d was ascribed to steric influence of the aryl moiety of NAr unit and that in 4–6 was ascribed to antisymbiosis. The solution behaviour of 3d was studied by a variable concentration (VC) 1H NMR data.