Synthesis and dynamic nuclear magnetic resonance studies of pentafluorobenzenethiolate complexes of molybdenum and tungsten. The crystal and molecular structures of [W(SC6F5)3(CO)(η5-C5H5)]·0.5CH2Cl2and [N(PPh3)2][Mo(SC6F5)4(η5-C5H5)

Abstract

The reaction between [WBr3(CO)2(η5-C5H5)] and excess of Tl(SC6F5)(CH2Cl2, 20 °C) affords Tl[W(SC6F5)4(η5-C5H5)](2b) as the major product and [W(SC6F5)3(CO)(η5-C5H5)](3) as the minor product. Complex (3) has been structurally characterised as its 0.5 CH2Cl2 solvate by X-ray diffraction. Chiral molecules of [W(SC6F5)3(CO)(η5-C5H5)] adopt a distorted square-based ‘piano-stool’ geometry with the trans W–S bond [2.443 6(15)A] longer than the cis W–S bonds (mean 2.358 A). The SC6F5 ligands lie with S–C bonds approximately in the plane of the square base and, all C6F5 groups have the same rotational orientation about the central W atom. However, dynamic 19F n.m.r. studies of (3) reveal that two isomeric forms exist at low temperature due to different orientations of the SC6F5 ligands but these undergo exchange at ambient temperature as a result of rotation about the W–SC6F5 bonds or inversion at sulphur. Similar studies of complex (2b) established that apparent rotation of the SC6F5 groups is solvent dependent and occurs in conjunction with ionic dissociation into Tl+ and [W(SC6F5)4(η5-C5H5)]–. The TlI in (2b) and related complexes Tl[Mo(SC6F5)4(η5-C5H5)] and Tl[Mo(SC6F5)2(CO)2(η5-C5H5)] can be replaced by non-co-ordinating cations to give X+[M(SC6F5)4(η5-C5H5)]–[M = Mo, X = NBun4(4a) or N(PPh3)2(4b); M = W, X = NMe4] and N(PPh3)2+[Mo(SC6F5)2(CO)2(η5-C5H5)]– which also exhibit fluxional behaviour according to 19F n.m.r. studies. The structure of complex (4b), determined in the solid state by X-ray diffraction, comprises discrete ions [(Ph3P)N(PPh3)]+ and [Mo(SC6F5)]4[(η5-C5H5)]–. The complex anion has a ‘piano-stool’ geometry with a square base defined by four SC6F5 ligands (mean Mo–S 2.420 A) and the C6F5 groups form a ‘swastika-like’ arrangement about the square plane. Reactions of (2b) with tertiary phosphines (L) in CH2Cl2 at 20 °C afford 1:2 adducts Tl[W(SC6F5)4L2(η5-C5H5)][L = PPh3(6b), PMe2Ph (6c), or PEt3(6d)]. Dynamic 19F n.m.r. studies established a different structure for (6b) in solution compared to (6c) and (6d).