Sulfurization and Selenization of the Halfsandwich Nitrosylmetal Complexes Cp*M(CO)2NO (M = Cr, Mo) and Cp*M(NO)I2 (M = Mo, W)

Abstract

The photo-induced decarbonylation of Cp*Cr(CO)2NO in acetonitrile solution in the presence of excess sulfur leads to the cyclo-pentasulfido complex Cp*Cr(NO)(S5) (1 a), while in the case of limited sulfur supply the binuclear bis(µ-disulfido) complex Cp*2Cr2(NO)2(µ-S2)2 (4a) is formed preferentially. The corresponding reaction with elemental selenium produces Cp*2Cr2(NO)2(µ-Se2)2 (4b), irrespective of the available amount of selenium. Photodecarbonylation of Cp*Mo(CO)2NO gives only the binuclear derivates Cp*2Mo2(NO)2(µ-E2) (E = S (5a), Se (5b)) which are also obtained by treating Cp*Mo(NO)I2 with H2S or H2Se, respectively. Nitrosyl loss predominates if the tungsten complex Cp*W(NO)I2 is reacted with H2S; in an argon atmosphere the products are Cp*W(S)(S2)(I) (7a) and Cp*2W2(S)2(µ-S)2 (8a), while in air some Cp*W(NO)(S5) (3a) and the oxo compounds Cp*W(O)(S2)I (7c), Cp*2W2(O)2(µ-S)2 (8c) and Cp*2W2(S)(O)(µ-S)2 (8d) are formed. The analogous reaction with H2Se leads to Cp*W(NO)(Se5) (3b), Cp*2W2(O)2(µ-Se)2 (9c) and Cp*2W2(Se)(O)(µ-Se)2 (9d), respectively. The binuclear tungsten complexes 8a,c,d and 9c,d contain a central W(µ-E)2W framework (E = S or Se) which is unaffected by air, while terminal sulfido and selenido ligands are quantitatively converted into the corresponding terminal oxo ligands in the presence of air in CH2C12 or THF solution. With the preparation of Cp*2W2(O)2(µ-E)2 (E = S (8c) and Se (9c)), the series of dioxo complexes containing a pair of monochalcogen bridges (E = O, S, Se, Te) has become complete. The new complexes have been characterized by their IR (v(NO)), 1H and 13C NMR (Cp*) spectra as well as by electron-impact mass spectrometry. According to the X-ray structure analyses, the binuclear compounds Cp*2Cr2(NO)2(µ-S2)2 (4a) and Cp*2Mo2(NO)2(µ-Se2)2 (5b) contain two 14-electron [Cp*M(NO)2] fragments which are connected by a pair of dichalcogen (η1,η2-E2) bridging ligands (M = Cr or Mo, E = S or Se). The central M2E2 four-membered ring is not planar, and the binuclear molecules are chiral.