Probing the Structure, Dynamics, and Bonding of Coinage Metal Complexes of White Phosphorus.

A series of cationic white phosphorus complexes of the coinage metals Au and Cu have been synthesised and characterised both in the solid state and in solution. All complexes feature a P4 unit coordinated through an edge P-P vector (η(2)-like), although the degree of activation (as measured by the coordinated P-P bond length) is greater in the gold species. All of the cations are fluxional on the NMR timescale at room temperature, but in the case of the gold systems fluxionality is frozen out at -90 °C. Electronic structure calculations suggest that this fluxionality proceeds via an η(1)-coordinated M-P4 intermediate.

Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+ centre.

A range of thio- and seleno-phosphonium cationic complexes [RE(PR'3)](+)[X](-) (R = Me, Ph; E = S, Se; X = GaCl4, SbF6) have been synthesised and structurally characterised. Reaction of [PhSPPh3][GaCl4] and [PhSePPh3][GaCl4] with P(t)Bu3 results in the ready transfer of the "RS(+)" and "RSe(+)" fragments from PPh3 to the stronger electron donor P(t)Bu3. NMR experiments combined with an Eyring analysis on the corresponding degenerate phosphine exchange reaction allowed the thermodynamic values for the phosphine exchange reaction of the sulfur cation (ΔH(‡) 18.7 ± 12.0 kJ mol(-1); ΔS(‡) -99.3 ± 36.3 J mol(-1) K(-1)) to be compared with the corresponding values (ΔH(‡) 2.4 ± 1.1 kJ mol(-1) and ΔS(‡) -58.1 ± 5.0 J mol(-1) K(-1)) for the [PhSePPh3](+) system. Importantly, the large negative entropy of activation and linear dependence on the rate of exchange are compatible with an SN2-type exchange process. This conclusion is supported by DFT calculations which confirm that the phosphine exchange process occurs via an associative mechanism. The rate of exchange was found to increase from sulfur to selenium and those with aryl substituents underwent exchange faster than those with alkyl substituents.

White phosphorus as a ligand for the coinage metals.

Reaction of equimolar quantities of MX (M = Au, Cu, X = Cl; M = Ag, X = OTf) and GaCl(3) in CH(2)Cl(2) with P(4) leads to phosphorus ligating a cationic coinage metal centre. For Cu and Ag, ion-contacted coordination polymers are formed; for Au, an ion-separated complex is observed that features the [Au(η(2)-P(4))(2)](+) cation, which is the first homoleptic Au-P(4) complex to be characterised in the condensed phase.