Bond order metal-phosphorus

The first two bands in the UPS of Ni(PF3)4 (Fig. 26) are remarkably similar to those of Ni(CO)4 and hence can be assigned to the 2 7 2 and 2 E ionic states, which are produced by electron elimination from the t2 and e MOs of predominantly Ni(3d) character (20). The UPS of Pd(PF3)4 and Pt(PF3)4 can be assigned analogously (Table XXVII and Fig. 26) (20). The heavy atom effect (172) is clearly operative in this triad in the sense that the relative intensities of the spectral peaks are in the order Pt > Pd > Ni. The next two bands in the UPS of Ni(PF3)4 correspond to the ionization of the metal-phosphorus a bonds of symmetries t2 and a,. The latter ionization is not detectable in the UPS of the heavier metal compounds and, presumably, is obscured by peaks of higher intensity. [Note that there are some differences between the preliminary reports (152, 182) and a subsequent full paper (20) regarding the spectra and assignments. For example, the weak 14.7 eV band of Ni(PF3)4 was not detected in one report (152). This band was detected in... 

Metal-phosphine bonds can generally be modeled in much the same way as any other metal-heteroatom bond. The fact that phosphines participate in x-backbonding (filled dn (metal) -> empty d or a (phosphorus) interaction) is only of importance for generic force field parameterization schemes, and half-integer bond orders have been used to describe the effect of x-back-donation[ 153). In the usually adopted empirical force field formalism, x-bonding effects, like most of the other structural/elec-tronic effects, are accommodated by the general parameter-fitting procedure (see Parts I and III). 

A = Alkali metal AE = Alkaline-earth metal a-P = Amorphous phosphorus CN = Mean coordination number (i(M-P) = Distance between M and P atom Distances between P atoms E = Element = Band gap M = Metal PBO = Pauling bond order (P) = Formal charge of a P atom (M) = Formal charge of a M atom R = Zr, Ftf, rare earth metal or actinoid metal RE = Rare earth element / cov = Covalent radius ... 

Note The [ CpM (jU-PRR ) (/U-CO)] series has phosphorus resonances that are deshielded by AS= 15-45ppm, compared to the respective values in the l CpM(CO)j2(/a-PRR )J series. This is attributed to the higher metal-metal bond order in the former complexes. 

O.OOSA) is indeed very similar to the free ligand value. On the other hand, the nickel-phosphorus distance (2.099 O.OOSA) is very much shorter than the values reported in other phosphine-nickel complexes, which suggests that the metal-phosphorus bond in Ni(PF3)4 may indeed have significant -character. A u-bond order of one has been estimated from the magnitude of the Co- P coupling constant in the [Co(PF3)4] ion (191). ... 

A variety of examples of remote intramolecular G-F bond activation have been discovered. All the recent examples involve fluorinated aromatic substituents that exhibit special reactivity including attack at the metal center. We divide the examples according to the atoms to which the fluoroaryl group is bonded, considering them in the order nitrogen, phosphorus, and sulfur. 

For example, due to the availability of a lone pair on trivalent phosphorus, a compound that features a bridging PR2 ligand can be represented in terms of simple resonance structures that feature two 2-center-2-electron bonds (Fig. 3). Thus, the bridging PRa ligand serves as a one-electron (M-X) donor to one metal and as a two-electron (M-<-L) donor to the other metal, such that it is overall a three-electron x-LX donor ligand. For such situations, the derived electron count at each metal center enables one to predict an M-M bond order that is in accord with theoretical calculations and the result is noncontroversial. 

Because of the reactive covalent bonds to halogen atoms, all of the trihalides of the group VA elements hydrolyze in water. It is found that the rates decrease in the order P > As > Sb > Bi, which agrees with the decrease in covalent bond character that results from the increase in metallic character of the central atoms. Not all of the trihalides react in the same way. The phosphorus trihalides react according to the equation... 

Our experience has shown that the hydrolysis of aluminium phosphide with cold water is the most suitable method for the laboratory preparation of phosphine. Here it is important that the aluminium phosphide be as pure as possible in order to avoid the formation of spontaneously inflammable phosphine. The presence of small quantities of diphosphine and also higher phosphines are responsible for this spontaneous inflammability 96.276-278) jj. gp, pears, however, that these are only formed when P—P bonds are already present in the phosphide. Accordingly the hydrolysis of aluminium phosphide, prepared from the elements with phosphorus in slight excess, always leads to spontaneously inflammable phosphine. The formation of diphosphine and higher phosphines from aluminium or alkaline earth metal phosphides, which contain excess phosphorus, can be easily understood when the lattices of these compounds are considered. 

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