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Abstract

The silver aluminates AgAl[OC(CF3)(2)(R)](4) (R = H, CH3, CF3)
react with solutions of white phosphorus P-4 to give complexes
that bind one or two almost undistorted tetrahedral P-4
molecules in an eta(2) fashion: [Ag(P-
4)(2)](+)[Al(OC(CF3)(3))(4)](-) (1) containing the first
homoleptic metal-phosphorus cation, the molecular species (P-
4)AgAl[OC(CH3)(CF3)(2)](4) (2), and the dimeric Ag(mu,eta(2)-P-
4)Ag bridged {(P-4)AgAl[OC(CH3)(CF3)(2)]4}(2) (3). Compounds 1-
3 were characterized by variable-temperature (VT) P-31 NMR
spectroscopy (1 also by VT P-31 MAS-NMR spectroscopy), Raman
spectroscopy, and single-crystal X-ray crystallography. Other
Ag:P-4 ratios did not lead to new species, and this observation
was rationalized on thermodynamic grounds. The Ag(P-4)(2)(+)
ion has an almost planar coordination environment around the
Ag+ ion due to d(x2-y2)(Ag) --> sigma*(P-P) back-bonding.
Calculations (HF-DFT) on six Ag(P-4)(2)(-) isomers 4a-f showed
that the planar eta(2) form 4a is only slightly favored by 5.2
kJ mol(-1) over the tetrahedral eta(2) species 4b: eta(1)-P-4
and eta(3)-P-4 complexes are less favorable (27 - 76 kJ mol(-
1)). The bonding of the P-4 moiety in [RhCl-(eta(2) -P-
4)(PPh3)(2)], the only compound in which an eta(2) bonding mode
of a tetrahedral P-4 molecule has been claimed, must be
regarded as a tetraphosphabicyclobutane, and not as a
tetrahedro-P-4 complex, on the basis of the published NMR and
vibrational spectra, the calculated geometry of [RhCl(P-
4)(PH3)(2)] (10), the highly endothermic (385 kJ mol(-1))
calculated dissociation enthalpy of 10 into P-4 and
RhCl(PH3)(2) (11), as well as atoms in molecules (AIM) and
natural bond orbital (NBO) population analyses of 10 and the
Ag(P-4)(2)(+) ion. Therefore, 1-3 are the first examples of
species containing eta(2)-coordinated tetrahedral P-4
molecules.