Ortho Phosphorylation of PPh3To Give a Diphosphine and Formation of a “Butterfly” Structure on a Tetrairidium Framework

Abstract

A brief thermolysis of the bis-phosphine-substituted tetrairidium cluster Ir4(CO)10(PPh3)2 (1) in chlorobenzene (CB) converts it rapidly to the diphosphine cluster Ir4(CO)7(μ-CO)3{κ2-Ph2P(o-C6H4)PPh2} (2) in 53% yield, providing evidence for ortho phosphorylation at the tetrairidium cluster framework. Treatment of 2 with excess C60 affords the “butterfly” Ir4−C60 complex Ir4(CO)6(μ-CO){μ3-κ2-Ph2P(o-C6H4)P(η1-o-C6H4)}(μ3-η2:η2:η2-C60) (3) in 71% yield. Interestingly, compound 3 can be prepared directly from the thermolysis of 1 with excess C60 in moderate yield (52%). Compounds 2 and 3 have been characterized by microanalysis, spectroscopy, and single-crystal X-ray diffraction studies. A molecular structure determination reveals that complex 2 adopts a regular tetrahedral geometry with three edge-bridging CO groups around the basal triangle and a diphosphine κ2-Ph2P(o-C6H4)PPh2 ligand chelating one of the basal iridium atoms. In contrast, complex 3 possesses a “butterfly” geometry in which the C60 ligand is coordinated to the lower wing of the “butterfly” by an arene type μ3-η2:η2:η2-C60 bonding mode. One unique feature of 3 is the presence of both ortho phosphorylated and ortho-metalated phenyl rings forming five-membered [Ir−P−C−C−P] and [Ir−Ir−P−C−C] metallocycles joined in a spiro union at the iridium−iridium-bridged phosphorus atom. A crossover experiment confirms that the conversion of 1 to 2 is intramolecular. Plausible reaction pathways for the formation of 2 and 3 are proposed.