Ortho phosphorylation of PPh3 to give a diphosphine and formation of a "butterfly" structure on a tetrairidium framework

Abstract

A brief thermolysis of the bis-phosphine-substituted tetrairidium cluster Ir-4(CO)(10)(PPh3)(2) (1) in chlorobenzene (CB) converts it rapidly to the diphosphine cluster Ir-4(CO)(7)(mu-CO)(3){kappa(2)- Ph2P(O-C6H4)PPh2} (2) in 53% yield, providing evidence for ortho phosphorylation at the tetrairidium cluster framework. Treatment of 2 with excess C-60 affords the "butterfly" Ir-4-C-60 complex Ir-4(CO)(6)(mu-CO){mu(3)-kappa(2)-Ph2P(o-C6H4)P(eta(1)-o-C6H4)}(mu(3)-eta(2):eta(2):eta(2)-C-60) (3) in 71% yield. Interestingly, compound 3 can be prepared directly from the thermolysis of 1 with excess C-60 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 kappa(2)-Ph2P(O-C6H4)PPh2 ligand chelating one of the basal iridium atoms. In contrast, complex 3 possesses a "butterfly" geometry in which the C-60 ligand is coordinated to the lower wing of the "butterfly" by an arene type mu(3)-eta(2):eta(2):eta(2)-C-60 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.