Formation of Diphenylphosphanylbutadienyl Complexes by Insertion of Two P-Coordinated Alkynylphosphanes into a PtC6F5 Bond: Detection of Intermediate and Reaction Products

Resumen

The reactions between cis-[M(C6F5)2(PPh2CCR)2] (M=Pt, Pd; R=Ph, tBu, Tol 2, 3) or cis-[Pt(C6F5)2(PPh2CCR)(PPh2CCtBu)] (R=Ph 4, Tol 5) and cis-[Pt(C6F5)2(thf)2] 1 have been investigated. Whereas [M](PPh2CCtBu)2 ([M]=cis-M(C6F5)2) is inert towards 1, the analogous reactions starting from [M](PPh2CCR)2 or [Pt](PPh2CCR)(PPh2CCtBu) (R=Ph, Tol) afford unusual binuclear species [Pt(C6F5)(S)μ-{C(R′)C(PPh2)C(PPh2)C(R)(C6F5)}M(C6F5)2] (R=R′=Ph, Tol, M=Pt 6 a,c, M=Pd 7 a,c; M=Pt, R′=tBu, R=Ph 8, Tol 9) containing a bis(diphenylphosphanyl)butadienyl bridging ligand formed by an unprecedented sequential insertion reaction of two P-coordinated PPh2CCR ligands into a PtC6F5 bond. Although in solution the presence of coordinated solvent S (S=(thf)x(H2O)y) in 6, 7 is suggested by NMR spectroscopy, X-ray diffraction analyses of different crystals of the mixed complex [Pt(C6F5)μ-{C(tBu)C(PPh2)C(PPh2)C(Tol)(C6F5)}Pt(C6F5)2] 9 unequivocally establish that in the solid state the steric crowding of the new diphenylbutadienyl ligand formed stabilizes an unusual coordinatively unsaturated T-shaped 3-coordinated platinum(II) center. Structure determinations of the mononuclear precursors cis-[Pt(C6F5)2(PPh2CCR)2] (R=Ph, tBu, Tol) have been carried out to evaluate the factors affecting the insertion processes. The reactions of the platinum complexes 6 towards neutral ligands (L=CO, py, PPh2H, CNtBu) in a 1:1 molar ratio afford related diplatinum derivatives 10–13, whereas treatment with CNtBu (1:2 molar ratio) or 2,2′-bipy (1:1 molar ratio) results in the opening of the chelating ring to give cis,cis-[Pt(C6F5)(L)2μ-{1-κC1:2-κPP′-C(R)C(PPh2)C(PPh2)C(R)(C6F5)}Pt(C6F5)2] (14, 15). The unsaturated or solvento complexes are unstable in solution evolving firstly, through an unexpected formal 4-1 R (Ph, Tol) migration, to the intermediate diphosphanylbutadienyl isomer derivatives [Pt(C6F5)(S)μ-{C(C6F5)C(PPh2)C(PPh2)C(R)2}M(C6F5)2] (16, 18) (X-ray, R=Ph, M=Pt) and, finally, to 1-pentafluorophenyl-2,3-bis(diphenylphosphanyl)naphthalene mononuclear complexes (17, 19) by annulation of a phenyl or tolyl group.