Reactions of co-ordinated ligands. Part 24. The reaction of bis-(but-2-yne)carbonyl(η-cyclopentadienyl or η5-indenyl)molybdenum tetrafluoroborate with acetonitrile and phosphines; crystal structures of ...

Article abstract of DOI:10.1039/DT9810000873

Reaction of the compounds [Mo(CO)(RC₂R¹)₂(η-C₅H ₅ or η⁵-C₉H₇)][BF₄] with refluxing acetonitrile in the presence of the respective acetylene affords the compounds [Mo(NCMe)(RC₂R¹)₂(η-C₅H ₅ or η⁵-C₉H₇)][BF₄] where R = R¹ = Me; R = Bu^t, R¹ = H; R = Ph, R¹ = Me; R = Pr¹, R¹ = H. Treatment of [Mo(CO)(RC₂R¹)₂(η-C₅H ₅ or η⁵-C₉H₇)][BF₄] at room temperature in methylene chloride with PEt₃, PPh₃, or P(C₆H₁₁)₃ gives the monoacetylene compounds [Mo(CO)L(RC₂R¹)(η-C₅H₅ or η⁵-C₉H₇)][BF₄] [L = PEt₃, PPh₃, P(C₆H₁₁)₃; R = R¹ = Me; R = Bu^t, R¹ = H; R = Prⁱ, R¹ = H; R = Ph, R¹ = Me; or R = R¹ = C₆H₄Me-4]. Reaction of the acetonitrile complexes with the phosphines PEt₃, PMe₃, PMePh₂, Ph₂PCH=CHPPh₂, (Ph₂PCH₂)₂, or (Me₂PCH₂)₂ results in the displacement of both the acetonitrile and one acetylene ligand to form complexes of the type [MoL₂(RC₂R¹)-(η-C₅H₅ or η-⁵-C₉H₇)][BF₄]. X-Ray single-crystal crystallographic studies were carried out on the compounds [Mo(CO)(PEt₃)(MeC₂Me)(η⁵-C ₉H₇)][BF₄] and [Mo(PMe₃)₂(MeC₂Me)(η⁵-C ₉H₇)][BF₄]. Crystals of the former are monoclinic, space group P2₁/c, Z = 4, in a unit cell of dimensions a = 9.158(2), b = 14.726(2), c = 16.581(3) A, and β = 94.12(2)°. Crystals of the latter complex are also monoclinic, space group P2₁, Z = 2, in a unit cell of dimensions a = 8.661 (2), b = 10.293(2), c = 13.580(2) A, and β = 106.42(2)°. The structures have been refined to R 0.041 (R′ 0.045) and R 0.039 (R′ 0.048) for 4 329 and 2 052 respective reflections with I > 3σ(I). The molybdenum co-ordination in each cation may be described in terms of a pseudo-octahedral structure. The but-2-yne ligand adopts a similar conformation in both complexes lying approximately coplanar with either the Mo-CO or Mo-PMe₃ bond. Variable-temperature ¹H and ¹³C n.m.r. data are interpreted in terms of rotation of the acetylene. Examination of the ¹³C chemical shifts of the acetylene contact carbons suggests that in these complexes the acetylene ligand can act as a four-electron donor.