Perpendicular to parallel reorientation of a terminal alkyne on a mixed-metal triangle; synthesis and structural characterisation

Abstract

Reaction of [Fe2(CO)6(μ-η2-CCPh)(μ-PPh2)] 1 with [W2(CO)4(η5-C5H5)2] affords the coordinatively unsaturated 46-electron trinuclear Fe2W cluster [Fe2W(CO)5(η5-C5H5){μ3-η2-(⊥)-HCCPh}(μ-CO)(μ-PPh2)] 2, in which an Fe–W edge is perpendicularly-bridged by a terminal alkyne molecule. Treatment of 1 with [Mo2(CO)4(η5-C5H5)2] also gives a 46-electron cluster, [Fe2Mo(CO)5(η5-C5H5){μ3-η2-(⊥)-HCCPh}(μ-CO)(μ-PPh2)] 3, the molybdenum analogue of 2 and, in addition, the saturated 48-electron FeMo2 trinuclear cluster [FeMo2(CO)5(η5-C5H5)2{μ3-η2-(⊥)-CCPh}(μ-PPh2)] 4, in which an acetylide ligand perpendicularly bridges an Fe–Mo bond. The trimetallic FeWCo acetylide-bridged species, [FeWCo(CO)6(η5-C5H5){μ3-η2-(⊥)-CCPh}(μ-PPh2)] 5, is the unique product when 1 is treated with the WCo heterobimetallic complex [CoW(η5-C5H5)(CO)7], while the corresponding reaction of 1 with [CoMo(η5-C5H5)(CO)7], leads to 3 and the molybdenum analogue of 5, [FeMoCo(CO)6(η5-C5H5){μ3-η2-(⊥)-CCPh}(μ-PPh2)] 6. Carbonylation of 3 at elevated pressure (80 atm CO) results in a ⊥–‖ alkyne reorientation to give the 48-electron cluster, [Fe2Mo(CO)6(η5-C5H5){μ3-η2-(‖)-HCCPh}(μ-CO)(μ-PPh2)] 7, as the sole product. Conversion of 7 back to 3 has been shown to occur in solution at room temperature. Single crystal X-ray diffraction studies have been performed on 2, 3, 4, 6 and 7.