Formation of diphenylphosphanylbutadienyl complexes by insertion of two P-coordinated alkynylphosphanes into a Pt-C6F5 bond: Detection of intermediate and reaction products

Resumen

The reactions between cis[M(C6F5)2(PPh2 C≡CR)2] (M = Pt, Pd; R = Ph, tBu, Tol 2, 3) or cis-[Pt(C6F5)2(PPh2C≡ CR)(PPh2C≡CtBu)] (R = Ph 4, Tol 5) and cis-[Pt(C6F5)2(thf)2] 1 have been investigated. Whereas [M](PPh2C≡CtBu)2 ([M] = cis-M(C6F5)2) is inert towards 1, the analogous reactions starting from [M](PPh2C≡CR)2 or [Pt](PPh2C≡CR)(PPh2C≡CtBu) (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 6a,c, M = Pd 7a,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 PPh2C≡CR ligands into a Pt-C6F5 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(PPh2C≡ CR)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-κ C<sup/>: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(C6 F5)2] (16, 18) (x-ray, R = Ph, M = Pt) and, finally, to 1-pentafluorophenyl-2,3bis(diphenylphosphanyl)naphthalene mononuclear complexes (17, 19) by annulation of a phenyl or tolyl group.