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

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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 = But, 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 = But, 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.