title: Synthesis and structures of bis(dithiolene)-tungsten(IV) complexes related to the active sites of tungstoenzymes.
abstract: 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-Pri3C6H2Q- also yields monocarbonyls, [W(CO)(QC6H2-2,4,6-Pri3)(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)(SeC2Me2)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 approximately 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.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Sung
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
mesh_terms: D001105:Archaea / Q000201:enzymology*; D001419:Bacteria / Q000201:enzymology*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry*; D013816:Thermodynamics; D014414:Tungsten / Q000737:chemistry / Q000378:metabolism
chemical_list: D004798:Enzymes; D009942:Organometallic Compounds; D008982:Molybdenum; D014414:Tungsten