Guanidinato and amidinato complexes of iridium(I): synthesis O₂ and S₈ reactivity, and (alkene)peroxo- and (alkene)persulfidoiridium(III) intermediates

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, 4-MeC₆H₄, 4-MeOC₆H₄, 2,6-Me₂C₆H₃ or 2,6-ⁱPr₂C₆H₃; 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 d⁸ 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 ¹³C NMR chemical shifts of the alkene carbon atoms in the Ir^I(cod) complexes and the average CO stretching frequencies for the Ir^I(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}(cod)(O₂)], using multi-dimensional NMR and IR spectroscopy. The (alkene)persulfidoiridium(III) intermediate [Ir{PhNC(NMe₂)NPh}(cod)(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{π-PhNC(Me)NPh-κN:κN'}₂], with an amidinato ligand, were synthesized and characterized. In the reaction of the Ir^I(cod) complex with O₂, the corresponding (alkene)peroxoiridium(III) intermediate [Ir{PhNC(Me)NPh}(cod)(O₂)] was observed. The reactivity of this intermediate and its decay products is similar to that of [Ir{ArNC(NR₂)NAr}(cod)(O₂)], with the formation of 4-cycloocten-1-one being observed upon addition of cod. Mononuclear (alkene)rhodium(I) complexes, [Rh{PhNC(NMe₂)NPh}(cod)] and [Rh{PhNC(Me)NPh}(cod)], and a dinuclear complex, [{Rh(nbd)}₂{π-PhNC(NMe₂)NPh-κN:κN'}₂], were synthesized and characterized (where nbd = norbornadiene or bicyclo[2.2.1]hepta-2,5-diene). Investigation of the reactivity of these complexes with O₂ show they react very slowly or not at all.