Superweak complexes of tetrahedral P4 molecules with the silver cation of weakly coordinating anions

The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solns. of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 mols. in an h2 fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]- (1) contg. the 1st homoleptic metal-phosphorus cation, the mol. species (P4)AgAl[OCMe(CF3)2]4 (2), and the dimeric Ag(m,h2-P4)Ag bridged {(P4)AgAl[OC(H)(CF3)2]4}2 (3). Compds. 1-3 were characterized by variable-temp. (VT) 31P NMR spectroscopy (1 also by VT 31P MAS NMR spectroscopy), Raman spectroscopy, and single-crystal x-ray crystallog. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodn. grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to dx2-y2(Ag) -> s*(P-P) backbonding. Calcns. (HF-DFT) on six Ag(P4)2+ isomers showed that the planar h2 form is only slightly favored by 5.2 kJ mol-1 over the tetrahedral h2 species; h1-P4 and h3-P4 complexes are less favorable (27-76 kJ mol-1). The bonding of the P4 moiety in [RhCl(h2-P4)(PPh3)2], the only compd. in which an h2 bonding mode of a tetrahedral P4 mol. was claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, from the published NMR and vibrational spectra, the calcd. geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol-1) calcd. dissocn. enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in mols. (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the 1st examples of species contg. h2-coordinated tetrahedral P4 mols. [on SciFinder (R)]