SYNTHESIS AND CHARACTERIZATION OF SINGLE-SOURCE MOLECULAR PRECURSORS TO BINARY METAL SULFIDES - BIS(DIETHYLDITHIOCARBAMATO)M(II) TRIALKYLPHOSPHINE (M=ZN AND CD) ADDUCTS

Monomeric, five-coordinate is(diethyldithiocarbamato)M(II)(trialkylpho sphine) complexes, 1 (M = Zn, alkyl = Me), 2 (M = Zn, alkyl = Et), 3 ( M = Cd, alkyl = Me), and 4 (M = Cd, alkyl = Et) have been synthesized by addition of trialkylphosphine ligands to toluene solutions of bis(d iethyldithiocarbamato)M(II) (M = Zn, and Cd). The bidentate ligand, 1, 2-bis(diethylphosphino)ethane (DEPE) reacted with bis(diethyldithiocar bamato)M(II) (M = Zn, Cd) and a 1:1 mixture of [(Et2NCS2)2Zn]2: [(Et2N CS2)2Cd]2 in toluene to form five-coordinate, dinuclear DEPE-bridged c omplexes, [(Et2NCS2)2M]2(mu-DEPE), 5 (M = Zn), 6 (M = Cd) and 7 [(Et2N CS2)2Zn](mu-Et2PCH2 CH2PEt2)[Cd(Et2NCS2)2], respectively. The composit ion and structure of all compounds was confirmed by elemental analyses , infra-red spectroscopy, H-1, C-13{H-1} and P-31{H-1} nuclear magneti c resonance (NMR) spectroscopy and in selected cases by X-ray crystall ography. Variable temperature P-31{H-1} and Cd-113{H-1} NMR showed tha t these complexes undergo a dynamic exchange process at room temperatu re involving M-P bond cleavage with activation parameters of DELTAH(do uble dagger) = 9 kcal mol-1 and DELTAS(double dagger) = -7 eu as deter mined by two independent measurements based on simulation of variable temperature P-31{H-1} and Cd-113{H-1} NMR data for 4. The solid-state structures of (Et2NCS2)2ZnPMe3 (1) and (Et2NCS2)2CdPEt3 (4) have been determined by single-crystal X-ray diffraction. The single crystal X-r ay diffraction structure of [(Et2NCS2)2Zn]2(mu-DEPE) . 2C7H8 (5) has b een reported earlier and confirmed the dinuclear nature showing that t he two zinc units were bridged by the DEPE ligand and not chelated. Th ermogravimetric analysis (TGA) of compounds 1-3 showed that the PR3 li gands dissociated prior to thermal decomposition. However, compound 4 exhibited a single weight loss to give crystalline CdS as determined b y X-ray powder diffraction, electron diffraction and transmission elec tron microscopy. The homobimetallic species, 5 and 6, also decomposed to give ZnS and CdS, respectively while the heterobimetallic species, 7, thermally decomposed to give crystalline Zn0.5Cd0.5S according to X -ray powder diffraction data.