Dehydrogenation of Hydridoirida-β-diketones in Methanol: The Selective Formation of Mono- and Dinuclear Acyl Complexes

The hydridoirida-beta-diketone [IrH{(PPh2(o-C6H4CO))(2)H)Cl] (1) reacts with diimines (NN) or with pyridine (py) in refluxing methanol to undergo dehydrogenation. The reactions afford selectively the cis-acyl, trans-phosphane isomers of the cationic [Ir(PPh2(o-C6H4CO))(2)(NN)](+) {NN = 2,2'-bipyridine (2); R-N=C(CH3)-C(CH3)=N-R' [R = R' = NH2 (3); R = R' = OH (4); R = OH, R' = NH2 (5)]} or neutral [IrCl(PPh2(o-C6H4CO))(2)(py)] (6) derivatives. The reactions are faster for ligands containing amino substituents. Refluxing 1 in MeOH affords the formation of an equimolar mixture of dimer cationic species (Ir-2(mu-Cl)(mu-PPh2(o-C6H4CO))(2)(PPh2(o-C6H4CO))(2)](+) (7a and 7b) containing two acyls and a chloride as bridging groups. The isomers could be separated by fractional precipitation. Compound [3]Cl, containing amino substituents in the imino functionalities, catalyses the hydrogen transfer from 2-propanol to cyclohexanone to afford cyclohexanol. All the complexes were fully characterised spectroscopically. Single crystal X-ray diffraction analysis was performed on complexes 6 and [7b]ClO4.