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 but-2-ynecarbonyl(η5-indenyl)(triethylphosphine)molybdenum tetrafluoroborate and but-2-yne(η5-indenyl)bis(trimethylphosphine)molybdenum tetrafluoroborate

Abstract

Reaction of the compounds [Mo(CO)(RC₂R¹)₂(η-C₅H₅ or η⁵-C₉H₇)][BF₄] with refluxing acetonitrile in the presence of the respective acetylene affords the compounds [Mo(NCMe)(RC₂R¹)₂(η-C₅H₅ 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-C₅H₅ 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, Ph₂PCHCHPPh₂, (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-C₉H₇)][BF₄] and [Mo(PMe₃)₂(MeC₂Me)(η⁵-C₉H₇)][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)Å, 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)Å, 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.