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Phosphenium Versus Pro-Phosphide Character of P-tert-butyl-dicyclopropeniophosphine: Zwitterionic Palladate Complexes of a Dicationic Phosphido Ligand
dataset
posted on 2016-10-21, 18:22 authored by Cleve
Dionel Mboyi, Carine Maaliki, Amelle Mankou Makaya, Yves Canac, Carine Duhayon, Remi ChauvinWith the view to enhancing the unique
coordinating ability of the
known phenyl-tetrakis(diisopropylamino)dicyclopropeniophosphine (Ph-DCP),
replacement of the phenyl substituent by a tert-butyl
substituent was envisaged. Both α-dicationic R-DCP phosphines,
with R = Ph and tBu, 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 tBu-DCP ligand, from which addition of an
excess of (MeCN)2PdCl2 was found to trigger
a heterolytic cleavage of the DCP–tBu bond, releasing tBu+ 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.