Inactivity of iridium–triphenylphosphine complexes for catalytic imine hydrogenation: formation of neutral, dihydrido- ortho -metallated species

摘要: Reactions of cis,trans,cis-[Ir(H)2(PPh3)2(MeOH)2]PF6 in MeOH with the imines Ph(R′)C=NR under 1 atm H2 precipitate neutral, Ir(III)-dihydrido complexes [Ir(H)2{RN=C(R′)(o-C6H4)}(PPh3)2], where R = alkyl or benzyl, and R′ Ph, H, Me; dihydrides are well characterized through elemental analysis, NMR IR data and, one case, imine Ph2C=NCH2Ph, an X-ray structure. These products formed via intermediate ortho-metallated species, exemplified by [Ir(H){PhCH2N=CPh(o-C6H4)}(PPh3)2(MeOH)]PF6 case Ph2C=NCH2Ph reaction; then reacts (via net heterolytic cleavage: → H− + H+) to give neutral dihydride HPF6 as co-product. The ‘unique’ PhCH=NPh, same conditions, does not form a instead is readily catalytically hydrogenated PhCH2N(H)Ph; remarkably, we have shown previously that this within corresponding Rh system no catalytic hydrogenation occurs because amine product ‘poisons’ centre coordination N-phenyl ring.