Synthesis of cationic carbonyl cyclopentadienyl complexes of molybdenum and tungsten, and X-ray crystal structure of (acetone hydrazone)-tricarbonyl(η-cyclopentadienyl)tungsten hexafluorophosphate

Abstract

Substitution of the hydrazine ligand in [Mo(η-C₅H₅)(CO)₃(N₂H₄)]Cl with a range of commonly used tertiary phosphine and phosphite ligands (L) has provided a new high-yield route to [Mo(η-C₅H₅)(CO)₃L]⁺ cations for the majority, but not all, of the ligands used. With phosphonites, phosphinites, and smaller phosphines there is a competing reaction to give [Mo(η-C₅H₅)(CO)₂L₂]⁺ cations. Reaction of [W(η-C₅H₅)(CO)₃(N₂H₄)] Cl with PPh₃and PMePh₂ gives [W(η-C₅H₅)(CO)₃L]⁺(L = PPh₃ or PMePh₂) and [W(η-C₅H₅)(NCO)(CO)₂(PPh₃)], depending on the reaction conditions. The complexes [M(η-C₅H₅)(CO)₃(N₂H₄)]Cl (M = Mo or W) react with acetone to give the respective hydrazone cations [M(η-C₅H₅)(CO)₃(NH₂NCMe)]⁺, which are thermodynamically more stable than the hydrazine precursors; [Mo(η-C₅H₅)(CO)₃(NH₂NCMe₂)]⁺ is converted into [Mo(η-C₅H₅)(CO)₂-(solvent)₂]⁺ in-polar solvents at room temperature. The crystal and molecular structure of [W(η-C₅H₅)(CO)₃-(NH₂NCMe₂)][PF₆] has been determined from three-dimensional X-ray data collected by counter methods. The structure has been refined by full-matrix least-squares techniques to a final R(on _F) of 0.030, based on 2 141 reflections. The complex crystallises in the triclinic space group P with two molecules in a cell of dimensions a= 10.81 (2), b= 9.74(2), c= 8.47(2)Å, α= 113.3(1), β= 96.0(1), and γ= 95.1 (1)°. The tungsten atom is formally seven co-ordinate and the complex is best described as possessing the ‘piano-stool’ geometry. The major feature is the mode of bonding of the hydrazone ligand, which is shown to occur through the amino-nitrogen atom, in contradiction to current theories on the bonding of hydrazones to transition metals. Possible factors in-fluencing the relative stability of amino- or imino-nitrogen bonding are discussed.