Trifluorophosphine metal complexes,

The reductive fluorophosphination of metal halides in the presence of copper and hydrogen gas at high temperature and pressure offers a useful synthetic route for a number of hydrido trifluorophosphine metal complexes (method A). 

Often because of the close similarity in volatility and solubility of the mixed carbon trifluorophosphine metal complexes the best separative method involves gas chromatography. Vapor pressures and enthalpy of sublimation data for the complexes [M(PF3)(CO)5] (M = Cr, W) are comparable with the values for the corresponding hexacarbonyl complexes. 

A very large number of trifluorophosphine-metal complexes of this type are known, as evidenced by the number of entries in Table XV. The most widely used synthetic methods are displacement of PF3 from a... 

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... 

Dinuclear complexes have been made by photolysis of the related hydrido complex (vide infra) (method K) or by interaction of halogeno PF3-metal derivatives with the trifluorophosphine metallate salt (method L). 

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. 

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. 

Alkene Transition Metal Complexes Containing Trifluorophosphine... 

Oxidative addition of an allyl halide to a zero-valent complex (method D) or treatment of a trifluorophosphine metal late complex with an allylic halide followed by loss of PF3 (method E) have also been briefly reported. 

A particularly interesting example of CO displacement involves the photochemical reaction of the early transition metal complexes [M(>/5-C5H5)2(CO)2] (M = Ti, Zr, Hf) with PF3 (Scheme 10). In the case of (M = Hf) this complex represented the first hafnocene-phosphine complex to be reported. A slightly better synthetic route to the mono(trifluorophosphine)titanium(II) complex involves displacement of PEt3 from [Ti( /5-C5H5)2(CO)(PEt3)]. 

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. 

Alternatively, treatment of trifluorophosphine metallates with R3MC1 (method B) or via metal-metal bond cleavage reactions of dinuclear PF3 metal complexes with a group IV metal hydride R3MH (method C) have been useful synthetic methods, e.g.,... 

The small number of complexes of this type (listed in Table XVIII) have been obtained via the reaction of a trifluorophosphine metallate... 

Table 1. Trifluorophosphine-Hydride Complexes Prepared from Transition-Metal Salts...

Reductive fluorophosphination of metal halides in the presence of hydrogen will lead to some very stable complexes which contain covalently bound hydrogen (8.187) and (8.188). The proton can be removed from trifluorophosphine metal hydrides by weak bases, to form ionic trifluorophosphine metallates such as K Ir(PF3) . ... 

Trifluorophosphine complexes of transition metals. J. F. Nixon, Adv. Inorg, Chem. Radiochem., 1985,29,1 (368). 

Direct condensation of metal vapors with trifluorophosphine at -196°C provides a convenient alternative to the high-pressure route to metal-PF3 complexes. The reactions of Mo, Cr, Co, Ni, and Pd vapors with PF3 yield only one volatile product in each case, namely Mo(PF3)6 (132), Cr(PF3)6, Co2(PF3)g, Ni(PF3)4, and Pd(PF3)4 (128), respectively. The yields are good, 40-100% depending on the metal vapor used. Some defluorination of the PF3 accompanies the formation of Cr(PF3)6. No complex could be isolated from the manganese vapor-PF3 reaction, although some defluorination seems to have occurred. The reaction of iron and PF3 is complex,... 

Trifluorophosphine is a very convenient ligand in metal atom chemistry to use along with other ligands, e.g., in the stabilization of metal arene complexes (Section III,B). Reaction of a mixture of PF3 and PH3 with nickel vapor yields Ni(PF3)3PH3 and Ni(PF3)2(PH3)2 but no Ni(PH3)4. Attempts to make Ni(PH3)4 lead to hydrogen evolution from the ligand during or after condensation with the nickel vapor (128). 

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. 

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. 

Structural and/or spectroscopic investigations have shown that the local symmetries around the metal atoms in the M(PF3)4 (189,215), M(PF3)5(2), and M(PF3)6 compounds are Td, D3h, and Oh, respectively. Unfortunately theoretical studies on trifluorophosphine complexes are confined to CNDO/2 calculations on Ni(PF3)4, Fe(PF3)5, and Cr(PF3)6 (251). In view of the discussion of relaxation effects and basis set dependences presented in Section II the CNDO/2 results (Table XXVI) should be used only as a qualitative guide to spectral assignment. 

The pentacoordinate trifluorophosphine complexes behave similarly. Thus the difference in energy between the 2E and 2E" states, Ae e"> increases markedly in going from Fe(PF3)s to Ru(PF3)s. This increase is caused by the change in energy of the 2E state, which, in turn, results from changing from a 3d to a 4d metal orbital. 

Trifluorophosphine Complexes of Transition Metals John F. Nixon... 

In some cases H2 can interact directly with binary metal-trifluorophosphine complexes under mild conditions with or without addition of PF3 or UV irradiation (method B), and group IV hydrides have also been utilized (method C). 

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. 

Ionization Potentials (eV) of Transition Metal Trifluorophosphine and Hydridotrifluorophosphine Complexes. Data for... 

Dinuclear Transition Metal Trifluorophosphine Complexes Containing PF2-Bridging Ligands... 

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