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

Abstract

Reactions of the bulky amidinate and guanidinate salts K[(ArN)₂CR] (R = Bu^t, NPrⁱ₂ or N(C₆H₁₁)₂; Ar = 2,6-diisopropylphenyl) with [{RhCl(η⁴-COD)}₂] (COD = 1,5-cyclooctadiene) lead to KCl elimination and the formation of the complexes, [Rh{(η⁵-ArN)(ArN)CR}(COD)], in which the anionic ligand coordinates the rhodium centre in an unprecedented η⁵-cyclohexadienyl mode. The thermal conversions of these complexes to their N,N′-chelated isomers, [Rh{κ²-N,N′-(ArN)₂CR}(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 β-diketiminates are discussed.