Strukturuntersuchungen an metallorganischen Chalkogenatokomplexen von Molybd�n und Wolfram. Die Molek�l- und Kristallstrukturen von Tricarbonyl-1-7-?-cycloheptatrienyl-tris-?-phenylselenodimolybd�n, ?7-C7H7Mo(?-Se(C6H5))3Mo(CO)3; Dicarbonyl-1-7-?-cycloheptatrienylphenyltelluromolybd�n, ?7-C7H7Mo(CO)2Te(C6H5), und Dicarbonyl-1-7-?-cycloheptatrienylphenylselenowolfram, ?7-C7H7W(CO)2Se(C6H5)

Structural, electrochemical and oxygen atom transfer properties of a molybdenum selenoether complex [Mo2O4(OC3H6SeC3H6O)2] and its thioether analogue [Mo2O4(OC3H6SC3H6O)2]

The first crystallographically characterized molybdenum(vi) selenoether complex [Mo(2)O(4)(OC(3)H(6)SeC(3)H(6)O)(2)] and its thioether analogue [Mo(2)O(4)(OC(3)H(6)SC(3)H(6)O)(2)] were synthesised. Their structural, electrochemical and oxygen atom transfer properties are compared. This is relevant for the molybdenum cofactors of the DMSO reductase family where the coordination of the active site metal occurs through O (serine/aspartate), S (cysteine) or Se (selenocysteine). Both structures are almost identical except for those parameters that are directly derived from the different sizes of the varied ligand atoms (Se and S). No trans influence was observed. The metal centered redox process (Mo(V)<-->Mo(VI)) is at slightly lower voltage for the sulfur than for the selenium complex. The selenium compound catalyses the oxygen atom transfer from DMSO to PPh(3) by a different mechanism and at a higher rate than the sulfur compound, which is an indication that cysteine and selenocysteine might be used for a purpose in the different molybdenum and tungsten cofactors.

Organometallic Selenolates. 5.(1) Synthesis and Complexing Properties of 2-Propene- and 2-Methyl-2-propeneselenolato Molybdenum and Tungsten Compounds. Crystal Structures of cp(CO)(3)WSeCH(2)C(CH(3))=CH(2), [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2), [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))W(CO)(5)], [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))Mo(CO)(5)], and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)]

2-Propene- and 2-methyl-2-propeneselenolato complexes of molybdenum(II) and tungsten(II) have been prepared via insertion of gray selenium into alkali-metal-molybdenum and -tungsten bonds and subsequent reaction with allyl and beta-methallyl chlorides. The complexes are monomeric in the solid state. The (beta-methallyl)molybdenum compound cp(CO)(3)MoSeCH(2)C(CH(3))=CH(2) (2) decomposes slowly in solution with CO loss and formation of the corresponding dimer [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2) (3), whose crystal structure has been determined (C(22)H(24)Mo(2)O(4)Se(2), monoclinic, P2(1)/c, a = 11.151(2) Å, b = 13.436(3) Å, c = 16.872(3) Å, beta = 102.42(2) degrees, Z = 4). A monomeric structure has been found for cp(CO)(3)WSeCH(2)C(CH(3))=CH(2) (5) (C(12)H(12)O(3)SeW, triclinic, P&onemacr;, a = 7.592(3) Å, b = 7.700(3) Å, c = 12.296(5) Å, alpha = 98.31(4) degrees, beta = 104.24(2) degrees, gamma = 108.49(3) degrees, Z = 2). Additionally, the complexing properties of the selenolato complexes have been investigated. The reactions of the molybdenum complexes cp(CO)(3)MoSeCH(2)CH=CH(2) (1) and (2) with the metal(0)-carbonyl complexes W(CO)(5)(THF), (CH(3)CN)(3)Mo(CO)(3), and (eta(6)-C(7)H(8))Mo(CO)(3) (C(7)H(8) = cycloheptatriene) led to the formation of [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))M(CO)(5)] (M = W (6), Mo (7)) and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8), respectively. 6 and 7 are isostructural and crystallize in the monoclinic space group P2(1)/n (6, C(17)H(12)MoO(8)SeW, a = 14.708(2) Å, b = 9.837(2) Å, c = 14.958(2) Å, beta = 103.030(10) degrees, Z = 4; 7, C(17)H(12)Mo(2)O(8)Se, a = 14.712(2) Å, b = 9.8670(10) Å, c = 14.982(2) Å, beta = 103.100(10) degrees, Z = 4), whereas [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8) crystallizes in the noncentrosymmetric orthorhombic space group Pna2(1) (C(16)H(10)Mo(2)O(8)Se, a = 18.638(4) Å, b = 9.707(2) Å, c = 11.169(3) Å, Z = 4). Furthermore, (77)Se-NMR spectra displayed chemical shifts consistent with earlier results on related complexes.