Reactions of co-ordinated ligands. Part 43. Alkyne linking reactions at dimetal centres. Synthesis and structures of [Mo2{µ-(σ,η3:η2:η3,σ-C8H4But4)}(η-C5H5)2], [Mo2{µ-(σ,η3:η3,σ-CHCHButC6H2But3)}(η-C5H5)2], and [FeMo(CO)2(C4Me2Ph2)(η-C5H5)2]

Abstract

Addition of Na[Fe(CO)₂(η-C₅H₅)] to a solution of [Mo(NCMe)(η²-Bu^tC₂H)₂(η-C₅H₅)][BF₄] in tetrahydrofuran affords the two complexes [Mo₂{µ-(σ,η³:η²:η³,σ-C₈H₄Bu^t₄)}(η-C₅H₅)₂](1) and [Mo₂{µ-(σ,η³:η³,σ-CHCHBu^tC₆H₂Bu^t₃)}(η-C₅H₅)₂](2), structurally identified by n.m.r.spectroscopy and single-crystal X-ray crystallography. In (1) a C₈ chain bridges the Mo ⋯ Mo vector [Mo(1)–Mo(2) 2.639(1)Å], the chain beginning and ending with σ bonds to Mo(2). Carbons C(1), C(2), C(3) and C(6), C(7), C(8) each form an η³-allylic interaction with Mo(1) with C(4) and C(5) bonded as an η²-alkene to Mo(2). In contrast, complex (2) can be described as a 5-vinyl substituted C₆‘fly-over’ complex where the C₈ ligand bonds via a C–Mo σ bond to Mo(2) and an η⁴-diene-like interaction to Mo(1). One of the carbons, C(2), symmetrically bridges the Mo₂ unit [Mo(1)–Mo(2) 2.705(5)Å]. The mechanism of formation of these complexes is discussed. An attempt to extend these reactions to [Mo(NCMe)(η²-PhC₂Me)₂(η-C₅H₅)][BF₄] and [Mo(NCMe)(η²-PhC₂Ph)₂(η-C₅H₅)][BF₄] resulted in the formation of the dinuclear complexes [FeMo(CO)₂(C₄Me₂Ph₂)(η-C₅H₅)₂](3) and [FeMo(CO)₂(C₄Ph₄)(η-C₅H₅)₂](4), the former being structurally characterised by X-ray crystallography.