Synthesis and Structures of Bis(dithiolene)−Tungsten(IV) Complexes Related to the Active Sites of Tungstoenzymes

• Published in: Inorganic chemistry 2000-03, Vol.39 (6), p.1275-1281
• Main Authors: Sung, Kie-Moon, Holm, R. H
• Format: Article
• Language: English
• Subjects: Archaea - enzymology; Bacteria - enzymology; Binding Sites; Crystallography, X-Ray; Enzymes - chemistry; Enzymes - metabolism; Kinetics; Molecular Conformation; Molybdenum - chemistry; Molybdenum - metabolism; Organometallic Compounds - chemistry; Thermodynamics; Tungsten - chemistry; Tungsten - metabolism
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic991153u

Recent protein crystallographic results on tungsten enzymes and primary sequence relationships between certain molybdenum and tungsten enzymes provoke interest in the generalized bis(dithiolene) complexes [WIV(QR)(S2C2R‘2)2]1- and [WVIO(QR)(S2C2R‘2)2]1- (Q = O, S, Se) as minimal representations of enzyme sites. The existence and stability of W(IV) complexes have been explored by synthesis. Reaction of [W(CO)2(S2C2Me2)2] (1) with PhO- results in complete CO substitution to give [W(OPh)(S2C2Me2)2]1- (2). Reaction of 1 with PhQ- affords the monocarbonyls [W(CO)(QPh)(S2C2Me2)2]1- (Q = S (3), Se (5)). The use of sterically demanding 2,4,6-Pr i 3C6H2Q- also yields monocarbonyls, [W(CO)(QC6H2-2,4,6-Pr i 3)(S2C2Me2)2]1- (Q = S (4), Se (6)). The X-ray structures of square pyramidal 2 and trigonal prismatic 3−6 (with unidentate ligands cis) are described. The tendency to substitute one or both carbonyl ligands in 1 in the formation of [MIV(QAr)(S2C2Me2)2]1- and [MIV(CO)(QAr)(S2C2Me2)2]1- with M = Mo and W is related to the M−Q bond length and ligand steric demands. The results demonstrate a stronger binding of CO by W(IV) than Mo(IV), a behavior previously demonstrated by thermodynamic and kinetic features of zerovalent carbonyl complexes. Complexes 3−6 can be reversibly reduced to W(III) at approximately −1.5 V versus SCE. On the basis of the potential for 2 (−2.07 V), monocarbonyl ligation stabilizes W(III) by ∼500 mV. This work is part of a parallel investigation of the chemistry of bis(dithiolene)−molybdenum (Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263) and −tungsten complexes related to enzyme active sites.