Ir Complexes With Mixed‐Valent Bidentate Ligands: From Complex Synthesis to Catalytic Application

The bidentate ligands Ph 2 P(E)NHPPh 2 (E = S, Se) feature phosphorous atoms in two different oxidation states and provide the potential to tune chemical reactivity through the choice of donor E. The mononuclear complexes [Ir(COD){ κ 2 ‐P,E‐ Ph 2 P(E)NPPh 2 }] (E = S 1a , Se 1b ) were prepared from the dimer [IrClCOD] 2 (COD = 1,5‐cyclooctadiene) and the ligands Ph 2 P(E)NHPPh 2 (E = S, Se) in the presence of KO t Bu. Reaction of complexes 1a and 1b with CO afforded complexes [Ir(CO) 2 { κ 2 ‐P,E‐ Ph 2 P(E)NPPh 2 }] (E = S 2a , Se 2b ). The carbonylation of 1a was studied using UV‐vis absorption and Raman spectroscopies. A transient five‐coordinate intermediate [Ir(CO)(COD){ κ 2 ‐ P,S‐ Ph 2 P(S)NPPh 2 }] 1a‐I was observed. We support our findings with DFT calculations correlating the computed CO stretching frequencies with experimental values for this intermediate. The potential of complexes 1a , 1b , 2a , and 2b in the dehydrogenation of 2‐naphthylmethanol is explored, with dehydrogenation yielding 2‐naphthaldehyde and H 2 . This reactivity contrasts with the pathway reported earlier with other Ir catalysts, where additionally decarbonylation occurs. The yields with the COD derivatives, 1a and 1b , are moderate and higher than those of the carbonyl complexes, 2a and 2b . This difference highlights the effect of changing the ancillary ligands on the chemical behavior of the catalysts.