Palladium(II) and platinum(II) 2-(methoxycarbonyl)ethylselenolates: Synthesis, spectroscopy, structures and their conversion into metal selenide

A diselenide, (MeOOCCH2CH2Se)2 (1) has been prepared by esterification of (HOOCCH2CH2Se)2 in methanol. The reductive cleavage of Se–Se bond in 1 by NaBH4 in methanol generates MeOOCCH2CH2SeNa. The latter in different stoichiometries reacts with [M2Cl2(μ-Cl)2(PR3)2] to give a variety of products of compositions [M2Cl2(μ-SeCH2CH2COOMe)2(PR3)2] (2); [M2Cl2(μ-Cl)(μ-SeCH2CH2COOMe)(PR3)2] (3); [Pd2(SeCH2CH2COOMe)2(μ-SeCH2CH2COOMe)2(PR3)2] (4);[Pd3Cl2(μ-SeCH2CH2COOMe)4(PR3)2] (5). Treatment of complexes 2 with [M2Cl2(μ-Cl)2(PR3)2] affords complexes 3 in nearly quantitative yield. The formation of various products in these reactions is sensitive to stoichiometric ratio of reactants employed. This enables interconversion of various complexes by manipulating mole ratios of appropriate starting materials. A homoleptic palladium complex, [Pd(SeCH2CH2COOMe)2]6 (6) was isolated from a reaction between Na2PdCl4 and MeOOCCH2CH2SeNa. All these complexes have been characterized by elemental analysis, IR, UV–Vis and NMR (1H, 13C, 31P, 77Se, 195Pt) spectroscopy. Structures of trans-[Pd2Cl2(μ-SeCH2CH2COOMe)2(PPh3)2] (2d), [Pt2Cl2(μ-Cl)(μ-SeCH2CH2COOMe)(PnPr3)2] (3e), [Pd3Cl2(μ-SeCH2CH2COOMe)4(PnPr3)2] (5) and [Pd(SeCH2CH2COOMe)2]6 (6) have been established unambiguously by X-ray crystallography. In these complexes, there are bridging selenolate ligands with their uncoordinated ester groups. Compound 6 has a centrosymmetric Pd6Se12 hexagon in which every two palladium atoms are bridged by selenolate ligands. Thermal behaviour of some complexes has been investigated. Pyrolysis of compound 2b in tributylphosphate at 195 °C gave Pd17Se15 nanoparticles which were characterized by XRD and EDAX.