Trifluorophosphine Complexes of Transition Metals

Monofluorophos-Metal Complexes: Ripe for Future Discoveries in Homogeneous Catalysis

The discovery that cyclic (ArO)2PF can support Rh-catalysts for hydroformylation with significant advantages in tuning regioselectivity transformed the study of metal complexes of monofluorophos ligands from one of primarily academic interest to one with potentially important applications in catalysis. In this review, the syntheses of monofluorophosphites, (RO)2PF, and monofluorophosphines, R2PF, are discussed and the factors that control the kinetic stability of these ligands to hydrolysis and disproportionation are set out. A survey of the coordination chemistry of these two classes of monofluorophos ligands with d-block metals is presented, emphasising the bonding of the fluorophos to d-block metals, predominantly in low oxidation states. The application of monofluorophos ligands in homogeneous catalysis (especially hydroformylation and hydrocyanation) is discussed, and it is argued that there is great potential for monofluorophos complexes in future catalytic applications.

Ring size effects in cyclic fluorophosphites: ligands that span the bonding space between phosphites and PF3

The 5- to 8-membered cyclic fluorophosphites L5-8 have been prepared from the corresponding chlorophosphites which are derived from dihydroxyarenes or bis(trimethylsiloxy)arenes. Ligand L5 is very sensitive to hydrolysis but L6-8 are much more kinetically robust. The coordination chemistry of L5-8 has been explored with Mo(0), Pt(0) and Rh(i) and it is shown that the π-acceptor properties of L5-8 increase with decreasing ring size. The IR spectra and X-ray crystal structures of the [Mo(CO)4L2] complexes show that L5-8 lie between PF3 and P(OAr)3 in terms of their σ/π-bonding properties. The [PtL4] complexes are readily prepared from [Pt(nbe)3] and 4 equiv. of L5-8 whereas equilibrium mixtures of PtLx(nbe)y species form when 2 equiv. of L5-8 are added to [Pt(nbe)3]. The CO substitution reactions of [Rh2Cl2(CO)4] with L5-8 to give [Rh2Cl2L4] are evidence of the PF3-like ligand properties of L5-8. The trends in the properties of L5-8 are analysed in terms of their proximity to PF3 or P(OPh)3.

Formation of difluorosulfane complexes of the third row transition metals by sulfur-to-metal fluorine migration in trifluorosulfane metal complexes: the anomaly of trifluorosulfane iridium tricarbonyl

The stability of the experimentally known complex (Et3P)2Ir(CO)(Cl)(F)(SF3) of the third row transition metal iridium suggests that SF3 complexes of the third row transition metals might be viable species in contrast to the SF3 complexes of the first row transition metals previously studied by theoretical methods. However, the metal complexes [M](SF3) ([M] = Ta(CO)5, Re(CO)4, CpW(CO)2, CpOs(CO), and CpPt) containing three-electron donor tetrahedral SF3 ligands are thermodynamically disfavored relative to the isomeric [M](SF2)(F) derivatives with predicted energy differences ranging from -19 to -44 kcal/mol. The one exception is an Ir(SF3)(CO)3 isomer containing a one-electron donor pseudo-square-pyramidal SF3 ligand having essentially the same energy as the lowest energy Ir(SF2)(F)(CO)3 isomer. This, as well as the stability of the known (Et3P)2Ir(CO)(Cl)(F)(SF3), suggests that metal complexes containing one-electron donor pseudo-square-pyramidal SF3 ligands might be viable synthetic objectives in contrast to those containing three-electron donor tetrahedral SF3 ligands. The [M](SF2)(F) derivatives formed by sulfur-to-metal fluorine migration from isomeric [M](SF3) complexes are predicted to be viable toward SF2 dissociation to give the corresponding [M](F) derivatives. This suggests the possibility of synthesizing metal complexes of the difluorosulfane (SF2) ligand via the corresponding metal trifluorosulfane complexes with the SF3(+) cation as the ultimate source of the SF2 ligand. Such a synthetic approach bypasses the need for the very unstable SF2 as a synthetic reagent.

Metal-metal bonding in binuclear metal carbonyls with three bridging methylaminobis(difluorophosphine) ligands: iron, cobalt, and nickel derivatives

The [CH3N(PF2)2]3M2(CO)n (M = Fe, Co, Ni; n = 2, 1, 0) derivatives, in which a metal-metal bond is bridged by three CH3N(PF2)2 groups similar to the known very stable [CH3N(PF2)2]3Co2(CO)2, have been investigated by density functional theory. The lowest energy structures for the dicarbonyls [CH3N(PF2)2]3M2(CO)2 (M = Ni, Co, Fe) are predicted to be closed-shell singlets with metal-metal distances of approximately 3.94 A, approximately 2.80 A, and approximately 2.63 A, respectively, corresponding to the metal-metal bonds of orders 0, 1, and 2, required to give both metal atoms the favored 18-electron configurations. For the monocarbonyls [CH3N(PF2)2]3M2(CO) (M = Ni, Co, Fe), unsymmetrical structures with a carbonyl group terminally bonded to one metal are greatly preferred energetically over structures in which the carbonyl group bridges the pair of metal atoms. The lowest energy structures for [CH3N(PF2)2]3M2(CO) (M = Ni, Co, Fe) are singlet, triplet, and singlet states, respectively, with metal-metal distances of approximately 2.77 A, approximately 2.38 A, and approximately 2.13 A, respectively. These distances correspond to the metal-metal dative bonds of orders 1, 2, and 3, required to give both metal atoms the favored 18-electron configuration. Among the carbonyl-free species the iron compound [CH3N(PF2)2]3Fe2 is of particular interest since its very short Fe[double double bonds]Fe distance of approximately 2.02 A suggests the formal quadruple bond required to give both iron atoms the favored 18-electron configuration.

Unexpected direct iron-fluorine bonds in trifluorophosphane iron complexes: an alternative to bridging trifluorophosphane and difluorophosphido groups

The iron trifluorophosphane complexes [Fe(PF(3))(n)] (n=4, 5), [Fe(2)(PF(3))(n)] (n=8, 9), [H(2)Fe(PF(3))(4)], and [Fe(2)(PF(2))(2)(PF(3))(6)] have been studied by density functional theory. The lowest energy structures of [Fe(PF(3))(4)] and [Fe(PF(3))(5)] are a triplet tetrahedron and a singlet trigonal bipyramid, respectively. Both cis and trans octahedral structures were found for [H(2)Fe(PF(3))(4)] with the cis isomer lying lower in energy by approximately 10 kcal mol(-1). The lowest energy structure for [Fe(2)(PF(3))(8)] has two [Fe(PF(3))(4)] units linked only by an iron-iron bond of length 2.505 A consistent with the formal Fe=Fe double bond required to give both iron atoms the favored 18-electron configuration. In the lowest energy structure for [Fe(2)(PF(3))(9)] one of the iron atoms has inserted into a P-F bond of one of the PF(3) ligands to give a structure [(F(3)P)(4)Fe<--PF(2)Fe(F)(PF(3))(4)] with a bridging PF(2) group and a direct Fe-F bond. A bridging PF(3) group is found in a considerably higher energy [Fe(2)(PF(3))(9)] structure at approximately 30 kcal mol(-1) above the global minimum. However, this bridging PF(3) group keeps the two iron atoms too far apart (approximately 4 A) for the direct iron-iron bond required to give the iron atoms the favored 18-electron configuration. The preferred structure for [Fe(2)(PF(2))(2)(PF(3))(6)] has a bridging PF(2) group, as expected. However, this bridging PF(2) group bonds to one of the iron atoms through an P-Fe covalent bond and to the other iron through an F-->Fe dative bond, leaving an uncomplexed phosphorus lone pair.

The synthesis of tris(perfluoroalkyl)phosphines

Tris(perfluoroalkyl)phosphines, of interest as tunable alternatives to the carbon monoxide ligand, can be synthesised by the nucleophile mediated reaction of perfluoroalkyltrimethylsilanes with triphenylphosphite; the method can be extended to diphosphines.

Modular Synthesis of Fluorous Trialkylphosphines

A modular synthetic protocol was developed for the preparation of fluorous trialkylphosphines with a different number of methylene spacers and various lengths of the fluorous ponytails P[(CH(2))(A)R(FX)][(CH(2))(B)R(FY)][(CH(2))(C)R(FZ)] (A, B, C = 3 and 4; X, Y, Z = 4, 6, and 8). [reaction: see text]

Synthesis and spectroscopic characterization of bis(trifluorophosphinyl)-gold(I) undecafluorodiantimonate(V) [Au(PF3)2][Sb2F11]

The synthesis of [Au(PF3)2][Sb2F11], the first example of a linear, thermally stable metal bis(trifluorophosphine) complex is achieved by CO substitution of [Au(CO)2][Sb2F11] by PF3. The [Au(PF3)2]+ cation can also be generated by reductive phosphorylation by an excess of PF3 in fluorosulfuric acid. Spectroscopic characterization involves 19F and 31P NMR in HSO3F and SO2 solution including spectral simulation by the WIN-DAISY method and FT-IR and Raman spectra. Spectroscopic evidence suggests that the metal–ligand bond involves predominantly σ-bonding with drastically reduced π-back-donation. Key words: gold(I) complex, linear; gold(I) PF3 complex; 31P NMR; 19F NMR; vibrational spectra.