Silylation, Sulfidation, and Benzene-1,2-dithiolate Complexation Reactions of Oxo- and Oxosulfidomolybdates(VI) and -Tungstates(VI)

Abstract

The synthesis and structures of two types of molecules are presented: [MVIO3 - nSn(OSiR2R')]1- (M = Mo, n = 0-3; M = W, n = 3) and [MVIO2(OSiR2R')(bdt)]1- (M = Mo, W; bdt = benzene-1,2-dithiolate). For both types, R2R' are Me3, Pri3, Ph3, Me2But and Ph2But. The complete series of oxo/sulfido/silyloxo molybdenum complexes has been prepared. Complexes with n = 0 are readily prepared by the silylation of Ag2MoO4 and sustain mono- or disulfidation with Ph3SiSH to form a species with n = 1 and n = 2, respectively. Complexes with n = 3 are accessible by the silylation of [MOS3]2-. Structures of the representative series members [MoO3(OSiPh2But)]1-, [MoO2S(OSiPh3)]1-, [MoOS2(OSiPri3)]1-, [MoS3(OSiPh2But)]1-, and also [WS3(OSiMe2But)]1-, all with tetrahedral stereochemistry, are presented. Benzene-1,2-dithiolate complexes are prepared by the reaction of [MoO3(OSiR2R')]1-with the dithiol or by the silylation of previously reported [MO3(bdt)]2-. The structures of [MoO2(OSiPh2But)(bdt)]1- and [WO2(OSiPri3)(bdt)]1- conform to square-pyramidal stereochemistry with an oxo ligand in the apical position. The role of these complexes in the preparation of site analogues of the xanthine oxidoreductase enzyme family is noted. The sulfidation reactions reported here point to the utility of Ph3SiSH and Pri3SiSH as reagents for MoVI-based oxo-for-sulfido conversions.

Mechanism of molybdate insertion into pterin-based molybdenum cofactors

“…H 2 bdt) can labilize strong Mo-oxo bonds, resulting in the elimination of water and insertion of Mo into the dithiolene. 40 As a result, we suggest that in Cnx1E the MPT dithiolene supplies the two protons that are required to labilize one oxo ligand from MoO 4 2− and eliminate a water molecule. This proposal is based on (1) the need to deprotonate the dithiolene in order to coordinate Mo, (2) the immediate proximity of the two dithiolene S-H protons to a single terminal oxo ligand of molybdate, and (3) the relatively high acidity of the dithiolene protons compared to nearby amino acids.…”

“…Thus, the XAS intensity in the pre-edge region is expected to be a sensitive probe of the number of Mo-oxo bonds in Cnx1E bound Moco-AMP, providing a competitive advantage over X-ray crystallography in discerning terminal oxo ligands from hydroxide and aqua ligands. In order to more accurately assess the oxidation state and the number of oxo ligands bound to Mo in Cnx1E bound Moco-AMP, we have compared the enzyme XANES data with sodium molybdate, Na 2 MoO 4 ( 1 ), and three synthetic Mo(VI)-dithiolene analog complexes: [(bdt)MoO 3 ](NEt 4 ) 2 ( 2 ) 39 , [(bdt)MoO 2 (OSiPh 2 t Bu)](NEt 4 ) ( 3 ) 40 , and [(bdt)MoO 2 (OSiPh 3 )](NEt 4 ) ( 4 ) 41 (bdt = benzene-1,2-dithiolate) (see Supplementary Fig. 6 - 9 ).…”

“…10 ). The bond lengths (R) and the number of scatterers of a given atom type (N) determined from the Moco-AMP EXAFS analysis are compared with crystal structure values for trioxo model compound 2 39 , dioxo model compound 3 40 , and a dioxo computational model (listed in Supplementary Table 3 ). EXAFS parameters for various values of N at pH 6 and pH 8 are presented in Supplementary Tables 4 - 5 .…”

Aminobisphenolate supported tungsten disulphido and dithiolene complexes

“…[24][25][26][27][28][29] The nitrogen donor N8 is located trans to the terminal sulphido S1 with the relatively long W1-N8 bond (2.38-2.41 Å) most likely due to the structural trans effect of a multiple bonded sulphido ligand. 10,16,21,[30][31][32] Complexes 1S 2 and 4S 2 treated with diethyl acetylenedicarboxylate. (i) 1,2-C 2 H 4 Cl 2 , Lawesson's reagent, 60-80°C, 20 h (for 1S 2 -3S 2 ) (ii) 1,2-C 2 H 4 Cl 2 , P 2 S 5 , 20°C, 20 h (for 3S 2 and 4S 2 ).…”

“…typical for molecular tungsten sulphido complexes used as structural analogues of the oxidized sites in the xanthine oxidoreductase enzyme family. 10,16,21,[30][31][32] Complexes 1S 2 and 4S 2 treated with diethyl acetylenedicarboxylate. When dichloromethane solutions of disulphido complexes 1S 2 and 4S 2 were treated with a slight excess of diethyl acetylenedicarboxylate an immediate colour change from orange to green (1S 2 ) or dark red (4S 2 ) was observed (Scheme 2).…”