Transition Metal Complexes of Chromium, Molybdenum, Tungsten, and Manganese Containing η1(S)-2,5-Dimethylthiophene, Benzothiophene, and Dibenzothiophene Ligands

Ultraviolet photolysis of hexanes solutions containing the complexes M(CO) 6 (M = Cr, Mo, W) or CpMn(CO) 3 (Cp = η 5 -C 5 H 5 ) and excess thiophene (T*) (T* = 2,5-dimethylthiophene (2,5-Me 2 T), benzothiophene (BT), or dibenzothiophene (DBT)) produces the η 1 ( S )-T* complexes (CO) 5 M(η 1 ( S )-T*) 1 − 8 or Cp(CO) 2 Mn(η 1 ( S )-T*) 9 − 11, respectively. However, when T* = DBT and M = Mo, a mixture of two products results, which includes (CO) 5 Mo(η 1 ( S )-DBT), 4a, and the π-complex (CO) 3 Mo(η 6 -DBT), 4b, as detected by 1 H NMR spectroscopy. Only the complexes (CO) 5 W(η 1 ( S )-DBT) ( 1 ), (CO) 5 Cr(η 1 ( S )-DBT) ( 5 ), and Cp(CO) 2 Mn(η 1 ( 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.