Edward I. Stiefel

Preparations and properties of tripodal and linear tetradentate N,S-Donor ligands and their complexes containing the MoO22+core

Abstract New linear and tripodal tetradentate ligands, LH 2 , are reported and their syntheses are described. The new linear ligands L = HSCH 2 CH 2 SCH 2 CH 2 NRCH 2 CR 2 SH, R = H, CH 3 ) and the new tripodal ligands N(CH 2 CH 2 SH) 2 CH 2 Z, Z = CH 2 NH 2 , CH 2 N(CH 3 ) 2 , CH 2 N(C 2 H 5 ) 2 , CH 2 SCH 3 and CO 2 - were synthesized. The known linear ligands HSCH 2 CH 2 NCH 3 (CH 2 ) n NCH 3 CH 2 CH 2 SH (n = 2, 3) and HSCR 2 CH 2 NHCH 2 CH 2 NHCH 2 CR 2 SH (R = H, CH 3 ) were also utilized. These ligands react with MoO 2 (acac) 2 in CH 3 OH to yield MoO 2 L complexes in high yield. Infra-red and 1 H nmr spectra provide evidence to supplement X-ray crystallographic results reported elsewhere for selected numbers of the series. Octahedral structures with cis MoO 2 2+ groupings are assigned. Solution 1 H nmr studies are consistent with a trans placement of the two thiolate donors in agreement with the X-ray studies.

Ligand and induced internal electron transfer pathways to new Mo–S and W–S dithiocarbamate complexes

Addition of tetra-alkylthiuram disulphides [R2NC(S)S–SC(S)NR2] to MOVIS42–, WVIS42– and MOVIO2S22–yields the new complexes MoV(S2)(S2CNR2)3 and WVIS(S2)(S2CNR2)2 and the known complex MoVIO(S2)(S2CNR2)2, respectively, revealing redox behaviour involving induced internal electron transfer and lignad electron transfer processes.

Proton and electron transfer in molybdenum complexes: Implications for molybdenum enzymes

Abstract The reaction of sodium molybdate with o -aminobenzenethiol in acidic aqueous ethanol leads to the isolation of Mo(SNHC 6 H 4 ) 3 , in which each coordinated amino group is singly deprotonated. This result, and others from the literature, are used to illustrate the change in the acidity of ligands coordinated to Mo as a function of both oxidation state and the number of bound oxo-groups. Thus, ligands which may be coordinated to Mo in enzymes may change their p K a values from less than to greater than the physiological pH as the oxidation state decreases. The Mo site may therefore have both proton and electron transfer capacity and since all substrate reactions involve the flow of both protons and electrons it is suggested that the Mo site couples the flow of electrons and protons. In line with this notion, simple mechanistic schemes are presented which explain a number of features of the action of Mo in enzymes. Analogies are drawn between Mo and Re chemistry and it is suggested that Re complexes and Re substituted enzymes (if and when prepared) may provide useful complementary information in the study of Mo chemistry.

Analogous reactivity of MoS42– and WSe42–: preparation of WSe2(Bui2NCS2)3 by an induced internal redox reaction

Addition of tetreaalkylthiuram disulfides R2NC(S)S–SC(S)NR2(R = Et and Bui) to WSe42– yields the new complexes WvSe2(R2NCS2)3, revealing that WSe42– undergoes induced internal electron transfer similar to that of MoS42–, but different from the reactivity of WS42–, as predicted by comparison of the lowest energy charge transfer transitions of the reactants.

Novel bonding mode for WS42–: synthesis and structure of [Mo2(O2CPh)2(WS4)2]2–

The synthesis of (Et4N)2[Mo2(O2CPh)2(WS4)2] is reported; the structure reveals a novel bonding mode for the tetrathiotungstate ligands which bridge two quadruply-bonded molybdenum atoms.