Monocyclopentadienyl pentafluorothiophenolate complexes of molybdenum and their interactions with thallium(I) ions; dynamic nuclear magnetic resonance studies and crystal and molecular structures of [TlMo(SC6F5)2L2(cp)](L = CO or SC6F5; cp =η5-C5H5)

Abstract

Reactions between [MoCl(CO)₃(cp)](cp =η⁵-C₅H₅) and Tl(SC₆F₅) afford the fully characterised complexes [TlMo(SC₆F₅)₂L₂(cp)][L = CO (1) or SC₆F₅(2)]. Complex (2) is formed by an oxidative substitution process and can also be obtained by reactions of Tl(SC₆F₅) with other molybdenum-(II), -(III), or -(IV) precursors. Molecular structures of crystalline complexes (1) and (2) have been determined by X-ray diffraction. Complex (1) contains units of [(cp)(OC)₂Mo(µ-SC₆F₅)₂Tl] in which Tl^I is co-ordinated by two S atoms (mean Tl–S 3.015 Å) and is close to one ortho-F atom of each C₆F₅ring (mean Tl ⋯ F 3.095 Å); intermolecular Tl ⋯ S interactions between individual units of (1) give this material an extended-chain structure in the solid state. Crystalline (2) contains discrete molecular units of [(cp) Mo(µ-SC₆F₅)₄Tl] in which Tl^I is co-ordinated by four S atoms (mean Tl–S 3.272 Å); these four S atoms, four closely associated o-F atoms, one from each C₆F₅ring (mean Tl ⋯ F 3.062 Å), and the Mo atom [Mo ⋯ Tl 3.402(3)Å] define a cavity in which the Tl^I is situated. The anion [Mo(SC₆F₅)₄(cp)]^– in (2) is acting as a polydentate ligand to Tl⁺. Variable-temperature ¹⁹F n.m.r. studies on complexes (1) and (2) in toluene, dichloromethane, and acetone solutions establish the occurrence both of restricted rotation of the C₆F₅ groups and of solvent-dependent ionic dissociation into Tl⁺ and [Mo(SC₆F₅)₂L₂(cp)]^–. Significant ionisation occurs in the polar solvent acetone, and this is supported by conductivity measurements. Reactions of complex (1) with tertiary phosphines give products [Mo(SC₆F₅)(CO)₂L(cp)][L = PMe₂Ph (3), PMePh₂(4), or PPh₃(5)] with ‘four-legged piano-stool’ geometry; these complexes are principally cis isomers although minor amounts of trans isomers were detected by ¹H n.m.r. spectroscopy in solutions of (3) and (5). Reaction of complex (2) with PPh₃ affords a species [TlMo(SC₆F₅)₄(PPh₃)₂(cp)] which variable-temperature ¹H, ¹⁹F, and ³¹P n.m.r. studies show to exist as a mixture of two interchanging forms in solution.