Cleavage of an aryl carbon–sulfur bond in hydride–thiolate complexes of molybdenum and tungsten. Crystal structures of [{Mo(SC6H2Pri3-2,4,6)(OMe)(PMePh2)}2(µ-S)2] and [{Mo(SC6H2Pri3-2,4,6)(OEt)(PEtPh2)}2(µ-S)2]

Abstract

The complexes [MoH(SC₆H₂Prⁱ₃-2,4,6)₃(Pr¹Ph₂)]1(R¹= Me or Et) in tetrahydrofuran (thf)–R²OH decomposed via cleavage of an aryl carbon–sulfur bond to give C₆H₃Prⁱ₃-1,3,5 and the complexes [{Mo(SC₆H₂Prⁱ₃-2,4,6)(OR²)(PR¹Ph₂)}₂(µ-S)₂]2(R²= Me or Et). Compounds 2a(R¹= R²= Me) and 2b(R¹= R²= Et) have been structurally characterised by X-ray diffraction and shown to be dimers with (µ-S)₂ bridging ligands derived from the thiolate ligands of the precursor complexes. The arene produced in these reactions has been detected by ²H NMR spectroscopy and by GC–mass spectrometry; C₆H₂(²H)Prⁱ₃-1,3,5 was observed from [MoH(SC₆H₂Prⁱ₃-2,4,6)₃(PR¹Ph₂)] in thf–MeO²H. The thermal reactivity of the complex [WH(SC₆H₂Me₃-2,4,6)₃(PMe₂Ph)₂]3 was studied by combined TGA–mass spectrometry. The temperature for TGA started at 50 °C and was increased at 3° min^–1 until 500 °C. Three events were seen at 200, 260 and 320 °C. At each, mesitylene, the hydrodesulfurisation product, was the major species detected by mass spectrometry; PMe₂Ph was also detected during the first event and HSC₆H₂Me₃-2,4,6 during the second and third events at low levels.