Guanidinato and amidinato complexes of iridium(I)

Abstract

A variety of mononuclear alkene complexes, [Ir{ArNC(NR2)NAr}(cod)], and dicarbonyl complexes, [Ir{ArNC(NR2)NAr}(CO)2] (where R = Me or Et; Ar = Ph, 4MeC6H4, 4-MeOC6H4, 2,6-Me2C6H3 or 2,6-Pr2C6H3; and cod = 1,5-cyclooctadiene), were synthesized from the neutral N,N-dialkyl-N′,N′′-diarylguanidines via deprotonation and transmetalation. These complexes were fully characterized by spectroscopic techniques and single-crystal X-ray diffraction. The single-crystal structure determinations show the guanidinato(1−) ligands coordinate the low valent d iridium(I) center in an N,N′-chelating binding mode, and the C−N bond lengths indicate a high degree of π-electron delocalization over the CN3 core. The C NMR chemical shifts of the alkene carbon atoms in the Ir(cod) complexes and the average CO stretching frequencies for the Ir(CO)2 complexes suggest that the guanidinato ligands function as stronger donors than related monoanionic, bidentate nitrogen-donor ligands. Intermediates in the reactions of the [Ir{ArNC(NR2)NAr}(cod)] complexes with O2 were identified and characterized as (alkene)peroxoiridium(III) species, [Ir{ArNC(NR2)NAr}(η-cod)(η-O2)], using multi-dimensional NMR and IR spectroscopy. The (alkene)persulfidoiridium(III) intermediate [Ir{PhNC(NMe2)NPh}(ηcod)(η-S2)] was identified and characterized in the reaction of [Ir{PhNC(NMe2)NPh}(cod)] with S8. It was determined that these intermediates are able to transfer oxygen or sulfur to simple organic molecules such as PPh3. The self-decay of the (alkene)peroxoiridium(III) intermediates leads to C−O bond formation and alkene oxidation, and upon addition of excess cod release of 4-cycloocten-1-one was observed. In addition, a mononuclear alkene complex, [Ir{PhNC(Me)NPh}(cod)], and a dinuclear tetracarbonyl complex, [{Ir(CO)2}2{μ-PhNC(Me)NPh-κN:κN'}2], with an amidinato ligand, were synthesized and characterized. In the reaction of the Ir(cod) complex with O2, the corresponding (alkene)peroxoiridium(III) intermediate