Trifluorophosphine complexes carbonyls

There are many similarities in the behavior of PF3 and CO as ligands. This is manifested by the existence of a large number of PF3 complexes of the transition metals (197, 226). Several UPS studies of such complexes have now appeared in the literature (20, 152, 169, 182, 221, 227). As pointed out in Section II, it is difficult to arrive at a completely unequivocal set of assignments for these compounds other than for the predominantly metal MOs. It is seen below, however, that one of the advantages of studying the UPS of the PF3 complexes is that many more ionizations pertinent to bonding discussions are discernible. Furthermore, trifluorophosphine complexes tend to be more thermally stable than their carbonyl counterparts. 

Transition metal carbonyl complexes can be suitable precursors, for example, treatment of hydrido complexes or their alkali salts with PF3 under UV irradiation followed if necessary by acidification of the reaction mixture (method E). Interestingly, vanadium forms the hydrido trifluorophosphine complex [VH(PF3)6], whereas with CO, the paramagnetic [V(CO)6] is formed. 

Several other tetranuclear complexes containing different metals have been obtained from the reaction between metal carbonyl and metal trifluorophosphine complexes (method E) or by intermolecular ligand-exchange reactions (method F) between tetranuclear complexes. The following structures have been proposed on the basis of 19F NMR and mass spectroscopic studies. 

A variety of synthetic routes to monoene and polyene tri-fluorophosphine-transition metal complexes have been devised. Direct photochemically induced reaction of a metal-PF3 complex with an activated alkene or diene (method A) has proved useful only for iron, the products being either [Fe(PF3)4(alkene)J or [Fe(PF3)3(diene)] (194). Mixed carbonyl-trifluorophosphine complexes of the type [Fe(PF3)x(CO)3 x(diene)] result from either thermal or photochemical reactions of dieneiron carbonyl complexes and PF3 (52, 53) (method B). The compounds are fluxional. 

The first reported arene-transition metal trifluorophosphine complex [Cr(i/6-C6H6)(PF3)3] was obtained by UV irradiation of [Cr(i/6-C6H6)(C0)3] with PF3 (method A), whereas the corresponding thermal reaction afforded instead the mixed carbonyl trifluorophos-... 

The thermal stabilities of the trifluorophosphine complexes are greater than those of their carbonyl analogues and they generally have a remarkable stability towards moisture and oxidising agents. These compounds are soluble to various extents in polar and non-polar solvents but not in water. 

The chemical and thermal stability of the fluorophosphine complexes is markedly increased in every case over the chlorophosphine complexes, none of the latter being volatile. The stability of the fluorophophine complexes as compared with the parent carbonyl is also noteworthy. While nickel carbonyl is distillable only with considerable decomposition, tetrakis(trifluorophosphine)nickel-(0) is far more stable on distillation at atmospheric pressure, and can also conveniently be handled in a high-vacuum system. 

Phosphorus trifluoride is a ligand that is used extensively in coordination chemistry. It substitutes readily into various metal carbonyl complexes using either thermal or photochemical techniques. As a ligand, it is unique in its similarity to carbon monoxide in lower-valent organometallic compounds. In its role as a model for CO, a number of studies are possible that cannot be done on the carbonyls themselves.1 The name normally used for PF3 in complexes is trifluorophosphine. 

Transition metal carbonyl chemistry originated with the discovery of [Ni(C0)4] in 1890. Although the first trifluorophosphine coordination complex was prepared the following year by Moissan (263) by treating... 

An interesting feature of hydrido transition metal-PF3 complexes is that apart from a few dinuclear systems (Section VI) only mononuclear systems are so far known and there is as yet no corresponding chemistry analogous to that of polynuclear carbonyl hydrido compounds. The trifluorophosphine metal hydrido compounds are usually highly acidic and can readily form metallate ions such as [M(PF3)m]x and [MH(PF3) r. 

More recently, decarbonylation of the bridging // -alkyne complex [Rh2(//5-C5H5)2(CO)2(CF3CCCF3)] with Me3NO gave the z/2-complex, which, when treated with PF3, afforded high yields of the i 1-alkyne mixed carbonyl-trifluorophosphine derivative (8), in which the ligands are mutually trans 103). 

Trifluorophosphine and carbon monoxide readily undergo ligand-exchange reactions in their transition metal complexes. The close similarity in bonding characteristics of the two ligands toward transition metals has been discussed extensively in several review articles (72,174,272) and the evidence will not be repeated here. Extensive vibrational spectroscopic studies have been made on mixed carbonyl-PF3 metal complexes (72,174) and force constant calculations have been carried out in some cases. 

Clark and co-workers have shown that trifluorophosphine can replace all the CO groups from certain metal carbonyl complexes (56, 58, 59). Other fluorophosphines behave similarly, the reactions usually being thermally or photochemically induced (320, 57, 121, 284, 287, 61). In the case of HCo(CO)4, however, substitution by PFg occurs rapidly and spontaneously even at —20°C (320). 

There is an interesting report of carbonyl substitution in the reaction between phosphorus pentafluoride and MeSiH2Co(CO)4 (114, 7). There is evidence that PF5 is reduced by the silicon-hydrogen bonds yielding HCo(CO)4, fluorosilane, and trifluorophosphine the latter subsequently displaces carbon monoxide from the hydridocarbonyl complex. 

Particularly stable complexes can be formed with PF3. Although the highly electronegadve F atoms significantly lower the ability of the phosphorus atom to donate its lone-pair electrons in o bond formation this is compensated by the Ji bonding capacity of the vacant d orbitals. Trifluorophosphine forms complexes analogous to those of carbon monoxide, for example, F3P BH3 and Ni(PF3)4 which can be compared with the very stable H3B CO and Ni(CO)4. A whole series of complexes of general formulae [M(PF3)where jc = 1 or 2, are known, which correspond to carbonyl complexes with similar formulae (8.173). 

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