Metal-metal bonded compounds. VI. Rhodium-mercury bonded complexes [(diene)-{RNC(Y)NR'}2RhHgCl]2 containing interchanging metal-metal bridging and chelating amidino groups

Abstract

Complexes of the composition [(Diene)RNC(Y)NR'{2}RhHgCl] (Diene = 1, 5-cyclooctadiene, norbornadiene; Y = H; R' = CH(CH{3}){2}; R = CH{3}, CH(CH{3}){2}, p-CH{3}C{6}H{4}; R' = p-CH{3}CH{3}C{6}H{4} and Y = CH{3}, R = R$= p-CH{3}C{6}H{4}) have been isolated in almost quantitative yields from the reaction of [(Diene)RhCl]{2} with [HgRNC(Y)NR'{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(CH{3}){2}) the two N-aryl groups are bonded to Rh and situated cis to Hg. For small R groups (CH{3}) two isomers are observed, one with the two NCH{3} groups bonded to Rh and cis to Hg, and one with a NCH{3} and a N-aryl group bonded to Rh and situated cis to Hg.}1{}3{C NMR data show that for R' = p-CH{3}C{6}H{4} the complexes are fluxional. The process involves an interchange of the bridging and the chelating aminido groups via monodentate intermediates.