Platinum Dithiolene Complexes of π-Coordinating and π-Interacting η4-Cyclobutadiene Ligands

Five new organometallic platinum dithiolene complexes of the eta(4)-cyclobutadiene ligand [(eta(4)-C4Me4)Pt(dithiolene)] (dithiolene = mnt (2), demedt (3), tdt (4), dddt (5), dmit (6)) and one platinum diselenolene complex, [(eta(4)-C4Me4)Pt(dsit)] (7), were prepared from [(eta(4)-C4Me4)Pt(Cl)-(mu-Cl)](2) (1) and Na-2(mnt), O=C(dcmedt), H(2)tdt, O=C(dddt), (NBu4)(2)[Zn(dmit)(2)] or (NEt4)(2)-[Zn(dsit)(2)], respectively. The (eta(4)-C4Me4)Pt complexes 2-7 were characterized by NMR, UV-vis spectra, and CV. Those H-1 and C-13 NMR spectra showed Pt-195 satellite Coupling at the C4Me4 (JP(J(Pt-H) = 13-15 Hz), at the C4Me4 J(Pt-C) = Ca. 100 Hz), and at the dithiolene carbons. The complexes having an electron-rich dichalcogenolene ligand (5-7) resulted in lower energy electronic absorption compared with the electron-poor series 2-4. The eta(4)-C4Me4 ligand was replaced by the nucleophilic substitution of bis(diphenylphosphino)ethane (DPPE) to form the square-planar [Pt(dithiolene)(dppe)] complex. 2, 3, and 5-7 were structurally determined by X-ray diffraction studies. All the molecules were monomeric, had two-legged piano-stool geometries, and were formal 16-electron complexes with the Nit (d(8)) center. The crystal structure of 2 showed an inversion-centered dyad. 5 had eta(4)-C4Me4 center dot center dot center dot dithiolene plane-to-plane interaction in the crystal to form a zigzag chain. 6 and 7 were isostructural to each other and had intermolecular interactions through eta(4)-C4Me4 center dot center dot center dot trithiocarbonate contacts to form a zigzag chain. The eta(4)-C4Me4 group behaves as a pi-coordinating ligand and pi-interacting ligand as well. Dithiolene and diselenolene ligands used in this work were as follows: mnt = maleonitrile-1,2-dithiolate, dcmedt = 1,2-dimethoxycarbonylene-1,2-dithiolate, tdt = toluene- 3,4-dithiolate, dddt = 5.6-dihydro-1,4-dithiine-2,3-dithiolate, dmit = 1,3-dithiol-2-thione-4,5-dithiolate, and dsit = 1,3-dithiol-2-thione-4,5-diselenolate.