Transition metal complexes of chromium, molybdenum, tungsten, and manganese containing η1(S)-2,5-dimethylthiophene, benzothiophene, and dibenzothiophene ligands

Article abstract of DOI:10.1021/om990322f

Ultraviolet photolysis of hexanes solutions containing the complexes M(CO)₆ (M = Cr, Mo, W) or CpMn(CO)₃ (Cp = η⁵-C₅H₅) and excess thiophene (T*) (T* = 2,5-dimethylthiophene (2,5-Me₂T), benzothiophene (BT), or dibenzothiophene (DBT)) produces the η¹(S)-T* complexes (CO)₅M(η¹(S)-T*) 1-8 or Cp(CO)₂Mn(η¹(S)-T*) 9-11, respectively. However, when T* = DBT and M = Mo, a mixture of two products results, which includes (CO)₅Mo(η¹(S)-DBT), 4a, and the π-complex (CO)₃Mo(η⁶-DBT), 4b, as detected by ¹H NMR spectroscopy. Only the complexes (CO)₅W(η¹(S)-DBT) (1), (CO)₅Cr(η¹(S)-DBT) (5), and Cp(CO)₂Mn(η¹(S)-DBT) (9) were sufficiently stable (several days) to be isolated and characterized by elemental analyses. Rates of DBT ligand displacement by CO (1 atm) at room temperature decreased in the order 5 > 1 > 9. Single-crystal, X-ray structural determinations are reported for 1, 5, and 9. The tilt angle (θ) of the DBT ligand in these and related complexes is discussed in terms of π-back-bonding to the DBT ligand.