Phosphenium Versus Pro-Phosphide Character of P-<i>tert-</i>butyl-dicyclopropeniophosphine: Zwitterionic Palladate Complexes of a Dicationic Phosphido Ligand

With the view to enhancing the unique coordinating ability of the known phenyl-tetrakis­(diisopropylamino)­dicyclopropeniophosphine (Ph-DCP), replacement of the phenyl substituent by a <i>tert</i>-butyl substituent was envisaged. Both α-dicationic R-DCP phosphines, with R = Ph and ^<i>t</i>Bu, were prepared in 54%–55% yield by substitution of RPCl₂ with two equivalents of bis­(diisopropylamino)-dicyclopropenylidene (BAC) and metathesis with NaBF₄. This method is implicitly consistent with the representation of R-DCPs as BAC-phosphenium adducts. The R-DCP salts were found to coordinate hard and soft Lewis acids such as a promoted oxygen atom (in the singlet spin state) in the corresponding R-DCP oxides, and electron-rich transition-metal centers in η¹-R-DCP complexes with AuCl, PtCl₃^–, or PdCl₃^–, respectively. Coordination of Ph-DCP with PdCl₂, which is a more electron-deficient Pd­(II) center, leads to pentachlorinated dinuclear complexes [(Ph-DCP)­PdCl₂]₂Cl^–, where the dicoordinate Cl^– bridge screens the repelling pairs of positive charges from each other. The same behavior is inferred for the ^<i>t</i>Bu-DCP ligand, from which addition of an excess of (MeCN)₂PdCl₂ was found to trigger a heterolytic cleavage of the DCP–^<i>t</i>Bu bond, releasing ^<i>t</i>Bu⁺ and a dicationic phosphide, DCP^–: the latter is evidenced as a ligand in a tetranuclear complex ion [(μ²-DCP^–)­Pd₂Cl₄]₂, which, upon HCl treatment, dissociates to a doubly zwitterionic dipalladate complex. All the complexes were isolated in 82%–97% yield, and five of them were characterized by X-ray crystallography

Transition-Metal-Free α-Vinylation of Enolizable Ketones with β-Bromostyrenes

International audienceAn α-vinylation of enolizable ketones has been developed by using β-bromostyrenes and a KOtBu/NMP system. β,γ-Unsaturated ketones of E configuration were obtained in excellent yield and selectivity. Further synthetic possibilities are highlighted by one-pot functionalization via trapping of intermediate dienolates with alkyl, allyl, benzyl, and propargyl halides to generate quaternary centers. The reported transformation is believed to involve phenylacetylene and propargylic alcohol derivatives

Phosphenium Versus Pro-Phosphide Character of P-<i>tert-</i>butyl-dicyclopropeniophosphine: Zwitterionic Palladate Complexes of a Dicationic Phosphido Ligand

With the view to enhancing the unique coordinating ability of the known phenyl-tetrakis­(diisopropylamino)­dicyclopropeniophosphine (Ph-DCP), replacement of the phenyl substituent by a <i>tert</i>-butyl substituent was envisaged. Both α-dicationic R-DCP phosphines, with R = Ph and ^<i>t</i>Bu, were prepared in 54%–55% yield by substitution of RPCl₂ with two equivalents of bis­(diisopropylamino)-dicyclopropenylidene (BAC) and metathesis with NaBF₄. This method is implicitly consistent with the representation of R-DCPs as BAC-phosphenium adducts. The R-DCP salts were found to coordinate hard and soft Lewis acids such as a promoted oxygen atom (in the singlet spin state) in the corresponding R-DCP oxides, and electron-rich transition-metal centers in η¹-R-DCP complexes with AuCl, PtCl₃^–, or PdCl₃^–, respectively. Coordination of Ph-DCP with PdCl₂, which is a more electron-deficient Pd­(II) center, leads to pentachlorinated dinuclear complexes [(Ph-DCP)­PdCl₂]₂Cl^–, where the dicoordinate Cl^– bridge screens the repelling pairs of positive charges from each other. The same behavior is inferred for the ^<i>t</i>Bu-DCP ligand, from which addition of an excess of (MeCN)₂PdCl₂ was found to trigger a heterolytic cleavage of the DCP–^<i>t</i>Bu bond, releasing ^<i>t</i>Bu⁺ and a dicationic phosphide, DCP^–: the latter is evidenced as a ligand in a tetranuclear complex ion [(μ²-DCP^–)­Pd₂Cl₄]₂, which, upon HCl treatment, dissociates to a doubly zwitterionic dipalladate complex. All the complexes were isolated in 82%–97% yield, and five of them were characterized by X-ray crystallography