Reactions of co-ordinated ligands. Part 28. The reaction of nucleophilic reagents with the cationic bis(acetylene) molybdenum complexes [Mo(CO)(RC2R′)2(η-C5H5)][BF4]; X-ray crystal structures of [Mo{C(Me)C(Me)C(O)C(Me)CHMe}(CO)2(η-C5H5)] and [Mo{η3:η2-HButCCHC–O–C(O)C(But)CH}(CO)(η-C5H5)]

Abstract

Reaction of [Mo(CO)(η²-MeC₂Me)₂(η-C₅H₅)][BF₄] with lithium dimethylcuprate affords [Mo(CO)(η²-MeC₂Me)(σ-CMeCMe₂)(η-C₅H₅)], whereas reaction with K[BHBu^s₃] followed by treatment with CO gives [[graphic omitted])C(Me)CHMe}(CO)₂(η-C₅H₅)], which has been identified by X-ray crystallography. Crystals are monoclinic, space group P2₁/n, Z= 4, in a unit cell with a= 6.495(3), b= 16.902(9), c= 14.002(7)Å, β= 97.62(4)°. The structure has been refined to R= 0.025 (R′= 0.024) for 2 136 reflections (293 K) to 2θ < 55°(Mo-K_αX-radiation). The molybdenum atom is co-ordinated by an η-C₅H₅ ligand, two terminal linear carbonyl ligands, and a bidentate ligand derived from one CO, two but-2-yne molecules, and a hydride ligand. Reaction of CO with [Mo(CO)(η²-MeC₂Me)(σ-CMeCMe₂)(η-C₅H₅)] affords an analogous complex. A similar reaction between K[BHBu^s₃] and [Mo(CO)(η²-EtC₂Me)₂(η-C₅H₅)][BF₄] gives two analogous isomeric complexes, both isomers containing the vinyl group, C(Me)CHEt. In contrast [Mo(CO)(η²-Bu^tC₂H)₂(η-C₅H₅)][BF₄] affords the lactone complex [Mo{η³:η²-HBu^tCCH[graphic omitted]H}(CO)(η-C₅H₅)] characterised by X-ray crystallography. Crystals are monoclinic, space group P2₁/c(no. 14), Z= 4, in a unit cell with a= 11.935(7), b= 11.673(9), c= 13.674(9)Å, β= 105.93(5)°. The structure has been refined to R= 0.053 (R′= 0.052) for 2 526 reflections (230 K) to 2θ⩽ 50°(Mo-K_αX-radiation). The molybdenum atom is bound to an η-cyclopentadienyl ligand and a linear terminal CO. The remainder of the co-ordination sphere is taken up by an η³ : η² vinyl-substituted, unsaturated γ-lactone derived from one hydride, two carbonyls, and two Bu^tC₂H ligands. The structures of these complexes and the mechanism of their formation are discussed.