3 research outputs found
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-tetrakisÂ(diisopropylamino)Âdicyclopropeniophosphine (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 <sup><i>t</i></sup>Bu, were prepared in
54%–55% yield by substitution of RPCl<sub>2</sub> with two
equivalents of bisÂ(diisopropylamino)-dicyclopropenylidene (BAC) and
metathesis with NaBF<sub>4</sub>. 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 η<sup>1</sup>-R-DCP complexes with AuCl, PtCl<sub>3</sub><sup>–</sup>, or PdCl<sub>3</sub><sup>–</sup>, respectively. Coordination
of Ph-DCP with PdCl<sub>2</sub>, which is a more electron-deficient
PdÂ(II) center, leads to pentachlorinated dinuclear complexes [(Ph-DCP)ÂPdCl<sub>2</sub>]<sub>2</sub>Cl<sup>–</sup>, where the dicoordinate
Cl<sup>–</sup> bridge screens the repelling pairs of positive
charges from each other. The same behavior is inferred for the <sup><i>t</i></sup>Bu-DCP ligand, from which addition of an
excess of (MeCN)<sub>2</sub>PdCl<sub>2</sub> was found to trigger
a heterolytic cleavage of the DCP–<sup><i>t</i></sup>Bu bond, releasing <sup><i>t</i></sup>Bu<sup>+</sup> and
a dicationic phosphide, DCP<sup>–</sup>: the latter is evidenced
as a ligand in a tetranuclear complex ion [(ÎĽ<sup>2</sup>-DCP<sup>–</sup>)ÂPd<sub>2</sub>Cl<sub>4</sub>]<sub>2</sub>, 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-tetrakisÂ(diisopropylamino)Âdicyclopropeniophosphine (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 <sup><i>t</i></sup>Bu, were prepared in
54%–55% yield by substitution of RPCl<sub>2</sub> with two
equivalents of bisÂ(diisopropylamino)-dicyclopropenylidene (BAC) and
metathesis with NaBF<sub>4</sub>. 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 η<sup>1</sup>-R-DCP complexes with AuCl, PtCl<sub>3</sub><sup>–</sup>, or PdCl<sub>3</sub><sup>–</sup>, respectively. Coordination
of Ph-DCP with PdCl<sub>2</sub>, which is a more electron-deficient
PdÂ(II) center, leads to pentachlorinated dinuclear complexes [(Ph-DCP)ÂPdCl<sub>2</sub>]<sub>2</sub>Cl<sup>–</sup>, where the dicoordinate
Cl<sup>–</sup> bridge screens the repelling pairs of positive
charges from each other. The same behavior is inferred for the <sup><i>t</i></sup>Bu-DCP ligand, from which addition of an
excess of (MeCN)<sub>2</sub>PdCl<sub>2</sub> was found to trigger
a heterolytic cleavage of the DCP–<sup><i>t</i></sup>Bu bond, releasing <sup><i>t</i></sup>Bu<sup>+</sup> and
a dicationic phosphide, DCP<sup>–</sup>: the latter is evidenced
as a ligand in a tetranuclear complex ion [(ÎĽ<sup>2</sup>-DCP<sup>–</sup>)ÂPd<sub>2</sub>Cl<sub>4</sub>]<sub>2</sub>, 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