Ligand chemistry of alkylselenolates: an experimental and DFT study of the formation and structural characterization of [PtCl2−x(SeR)x(PPh3)2] (x = 1, 2; R = tBu, nBu)
Affiliations: Department of Chemistry, University of Oulu, PO Box 3000, FIN-90014 Oulu, Finland | Department of Chemistry, University of Joensuu, PO Box 111, FIN-90801 Joensuu, Finland
Abstract: cis-[Pt(SeR)2(PPh3)2] [R = tBu (1), nBu (2)] can be synthesized by the reaction of RSeLi with cis-[PtCl2(PPh3)2] in a molar ratio of 2:1. The reaction of equimolar amounts of cis-[PtCl2(PPh3)2] and RSeLi (R = tBu, nBu) produces a mixture containing cis-[Pt(SeR)2(PPh3)2] and [PtCl(SeR)(PPh3)2] [R = tBu (3), nBu (4)] in addition to unreacted cis-[PtCl2(PPh3)2]. The direct reaction of nBuLi with cis-[PtCl2(PPh3)2] affords cis-[Pt(nBu)2(PPh3)2] (6). The complexes were characterized by 31P{1H}, 195Pt{1H} and 77Se NMR spectroscopy, as well as by singlecrystal X-ray crystallography. Unlike the corresponding arylselenolato complexes, 1 and 2 do not isomerize from cis- to trans-isomers upon standing in solution. However, they are not stable. For example, 2 slowly forms dinuclear [Pt2(µ-SenBu)2(SenBu)2(PPh3)2] (5) due to the condensation of the mononuclear species. In the solid state, 1 and 2 crystallize as cis,antiisomers. It was furthermore observed that the n-butyl groups can adopt various conformations in different complexes. In order to model the structural properties and energetics of the mononuclear alkylselenolatoplatinum complexes, the geometries and relative stabilities of the isomers of [Pt(SeR)2(PH3)2], [PtCl(SeR)(PH3)2] and [Pt(R)2(PH3)2] (R = nBu, tBu) were studied by density functional theory (DFT) molecular orbital (MO) techniques. The calculations also provide insight into the pathway of the reaction from cis-[PtCl2(PPh3)2] to cis-[Pt(SeR)2(PPh3)2] involving two successive substitution steps of Cl− by RSe−.
