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.