METAL-METAL BONDED COMPOUNDS. VI. RHODIUM-MERCURY BONDED COMPLEXES 2RhHgCl>2 CONTAINING INTERCHANGING METAL-METAL BRIDGING AND CHELATING AMIDINO GROUPS

Article abstract of DOI:10.1016/S0022-328X(00)83042-9

Complexes of the composition <(Diene) 2RhHgCl> (Diene = 1,5-cyclooctadiene, norbornadiene; Y = H; R = R' = CH(CH3)2; R = CH3, CH(CH3)2, p-CH3C6H4; R' = p-CH3C6H4 and Y = CH3, R = R' = p-CH3C6H4) have been isolated in almost quantitative yields from the reaction of <(Diene)RhCl>2 with 2>.The structure in the solid state is probably dimeric, while in solution the compounds are definitely monomeric.NMR data show that the molecular configuration consists of a rhodium atom coordinated by a bidentate diene, a bidentate amidino group, a HgCl ligand and a N atom of an amidino group, which bridges the Rh-Hg bond.Various isomers are possible for compounds containing asymmetric amidino groups, depending on the size of the alkyl (R) group.For bulky R groups (CH(CH3)2) the two N-aryl groups are bonded to Rh and situated cis to Hg.For small R groups (CH3) two isomers are observed, one with the two NCH3 groups bonded to Rh and cis to Hg, and one with a NCH3 and a N-aryl group bonded to Rh and situated cis to Hg. 13C NMR data show that for R' = p-CH3C6H4 the complexes are fluxional.The process involves an interchange of the bridging and the chelating aminido groups via monodentate intermediates.