Development of Five-Coordinate Zinc Mono- and Dithiolates as S-Donor Metalloligands: Formation of a Zn−W Coordination Polymer

The synthesis and isolation of mono- and dithiolate-bridged Zn(μ-SR)nW(CO)m (where n = 1, m = 5; n = 2, m = 4) species from the dimeric N,N′-bis(2-mercaptoethyl)-1,4-diazacycloheptanezinc(II), [Zn-1′]2, and the monomeric [N-(3-thiabutyl)-N′-(3-thiapentaneoate)-1,5-diazacycloheptane]zinc(II), Zn-1′-Ac, are described. Upon cleavage of the dimeric [Zn-1′]2 with Na+[ICH2CO2]−, the resulting Zn-1′-Ac product is isolated as a monomeric, five-coordinate Zn(N2SS′O) complex equipped with one available Zn-bound thiolate for further reactivity. Cleavage of [Zn-1′]2 with [Et4N]+Cl− afforded a monomeric intermediate, [Zn-1′-Cl]−, containing two Zn-bound thiolates. The zinc mono- and dithiolato complexes demonstrated reactivity toward labile-ligand tungsten carbonyl species, (THF)W(CO)5 and (pip)2W(CO)4, to yield respectively [(Zn-1′-Ac)W(CO)5]x and [(Zn-1′-Cl)W(CO)4]− complexes that were isolated and characterized spectroscopically and via X-ray diffraction. Upon binding to W(CO)5, the five-coordinate Zn(N2SS′O) complex becomes six-coordinate within the coordination polymer [(Zn-1′-Ac)W(CO)5]x, in which the acetate tether of each molecule provides an O donor to occupy the octahedral axial position of a neighboring moiety. The [(Zn-1′-Cl)W(CO)4]− dithiolate-bridged complex maintains a five-coordinate, square-pyramidal [Zn(N2S2Cl)]− center, utilizing a chloride as the apical donor and resulting in an overall anionic complex. The addition of CO(g) to the [(Zn-1′-Cl)W(CO)4]− complex was monitored by IR spectroscopy, which showed the emergence of [(Zn-1′-Cl)W(CO)5]−.