Flexible coordination of bulky amidinates and guanidinates towards rhodium(i): conversion of kinetic to thermodymanic isomers

Reactions of the bulky amidinate and guanidinate salts K[(ArN)(2)CR] (R = Bu(t), NPr(i)(2) or N(C(6)H(11))(2); Ar = 2,6-diisopropylphenyl) with [{RhCl(eta(4)-COD)}(2)] (COD = 1,5-cyclooctadiene) lead to KCl elimination and the formation of the complexes, [Rh{(eta(5)-ArN)(ArN)CR}(COD)], in which the anionic ligand coordinates the rhodium centre in an unprecedented eta(5)-cyclohexadienyl mode. The thermal conversions of these complexes to their N,N'-chelated isomers, [Rh{kappa(2)-N,N'-(ArN)(2)CR}(COD)], were carried out and the kinetics of these processes have been shown to be first order. The rates of the isomerisations are inversely proportional to the size of the amidinate or guanidinate backbone substituent. Analogies between the ligating properties of the bulky amidinates and guanidinates used in the study, and those of beta-diketiminates are discussed.