Platinum dithiolene complexes of π-coordinating and π-interacting η4-cyclobutadiene ligands

Article abstract of DOI:10.1021/om900222s

Five new organometallic platinum dithiolene complexes of the η⁴-cyclobutadiene ligand [(η⁴-C₄Me ₄)Pt(dithiolene)] (dithiolene = mnt (2), dcmedt (3), tdt (4), dddt (5), dmit (6)) and one platinum diselenolene complex, [(η⁴-C ₄Me₄)Pt(dsit)] (7), were prepared from [(η⁴-C₄Me₄)Pt(Cl)(w-Cl)]₂ (1) and Na₂(mnt), O=C(dcmedt), H₂tdt, O=C(dddt), (NBu ₄)₂[Zn(dmit)₂], or (NEt₄) ₂[Zn(dsit)₂], respectively. The (η⁴-C ₄Me₄)Pt complexes 2-7 were characterized by NMR, UV-vis spectra, and CV. Those ¹H and ¹³C NMR spectra showed ¹⁹⁵Pt satellite coupling at the C₄Me₄ (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 η⁴-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 Pt^II (d⁸) center. The crystal structure of 2 showed an inversion-centered dyad. 5 had η⁴-C₄Me₄- ... -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 η⁴-C₄Me₄- ... -trithiocarbonate contacts to form a zigzag chain. The η⁴-C ₄Me₄ group behaves as a π-coordinating ligand and a π-interacting ligand as well. Dithiolene and diselenolene ligands used in this work were as follows: mnt = maleonitrile-1,2-dithiolate, dcmedt = 1,2-dimethoxycarbonylethylene-1,2-dithiolate, tdt = toluene-3,4-dithiolate, dddt = 5,6-dihydrol,4-dithiine-2,3-dithiolate, dmit = 1,3-dithiol-2-thione-4,5- dithiolate, and dsit = 1,3-dithiol-2-thione-4,5diselenolate.