Preparation, characterisation, and reactions with phosphite donor ligands of the new cationic monoalkyne complexes [WI(CO)(NCMe){Ph2P(CH2)nPPh2}(η2-RC2R)][BF4](n= 1–6; R = Me or Ph). X-ray crystal structure of [WI(CO)-{P(OPri)3}{Ph2P(CH2)PPh2}(η2-MeC2Me)][BF4]0.5[OH]0.5·0.5H2O

Abstract

Reaction of the complexes [WI₂(CO){Ph₂P(CH₂)_nPPh₂}(η²-RC₂R)](n= l–6; R = Me or Ph) with 1 equivalent of Ag[BF₄] in acetonitrile at room temperature affords good yields of the highly coloured cationic alkyne compounds [WI(CO)(NCMe){Ph₂P(CH₂)_nPPh₂}(η²-RC₂R)][BF₄](1)–(12). The complex [WI(CO)(NCMe){Ph₂P(CH₂)PPh₂}(η²-MeC₂Me)][BF₄] reacts rapidly with 1 equivalent of P(OR′)₃(R′= Me, Et, Prⁱ, or Buⁿ) in CH₂CI₂ to afford the substituted products [WI(CO){P(OR′)₃}{Ph₂P(CH₂)PPh₂}(η₂-MeC₂Me)][BF₄](13)–(16). X-ray single crystallographic studies were carried out on the compound [WI(CO){P(OPrⁱ)₃}{Ph₂P(CH₂)PPh₂)(η²-MeC₂Me)]-[BF₄]_0.5[OH]_0.5·0.5[H₂O](15). Crystals of (15) are monoclinic space group P2₁/_n, Z= 8, in a unit cell of dimensions a= 19.494(18), b= 19.634(12), c= 25.063(15)Å, and β= 101.3(1)°. The structure was refined to R= 0.080 for 3 987 reflections above background. There are two cations in the asymmetric unit with equivalent geometry. The co-ordination geometry about the tungsten atoms may be considered to be octahedral, with as expected the but-2-yne ligand trans to the iodide ligand. Carbon-13 n.m.r. chemical shifts of the alkyne contact carbons suggest that the alkyne ligand is donating four-electrons to the metal in compounds (1)–(16). The barrier to but-2-yne rotation in (15) is ΔG^‡= 56.9 ± 0.5 kJ mol^–1.