The electron-poorphosphines P{C6H3(CF3)(2)-3,5}(3) and P(C6F5)(3) do not mimic phosphites as ligands for hydroformylation. A comparison of the coordination chemistry of P{C6H3(CF3)(2)-3,5}(3) and P(C6F5)(3) and the unexpectedly low hydroformylation activity of their rhodium complexes

The fluoroaryl phosphines P{C6H3(CF3)(2)-3,5}(3) (L-a) and P(C6F5)(3) (L-b) form the complexes trans- [MCl2(L-a)(2)] and trans-[MCl2(L-b)(2)] (M = Pd or Pt) which have been isolated and fully characterised. 31 P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = L-b < L-a < PPh3. The crystal structure of trans-[PtCl2(L-a)(2)] is reported and reveals that the Pt-P bond lengths in trans-[PtCl2L2] are in the order L = L-b < L-a < PPh3. The equilibria established when [Pt(norbornene)(3)] is treated with L-a or L-b are investigated by P-31 and Pt-195 NMR spectroscopy and the species [PtLn(norbornene)(3-n)] (n = 1-3) identified. Ligands L-a and L-b appear to have similar affinities for platinum(0). The complexes trans-[MCl(CO)(L-a)(2)] and trans-[MCl(CO)(L-b)(2)] (M = Rh or Ir) have been synthesised and fully characterised; the values of m CO are comparable with those for analogous phosphite complexes. The ligands L-a, L-b, P(C6H2F3-3,4,5)(3) (L-c), P{C6H4(CF3)-2}(3) (L-d), PPh3 and P(OPh)(3) have been tested in rhodium-catalysed hydroformylation of 1-hexene and L-a, L-b, and PPh3 have been tested in rhodium-catalysed hydroformylation of 4-methoxystyrene. Ligands L-a, and L-b, have been shown to be stable under the hydroformylation catalysis conditions. For the 1-hexene reaction, the activity and selectivity for L-a and L-c are very similar to the PPh3 catalyst (TOF ca. 400 h(-1); n : iso 2.5-3.0) but for the sterically demanding L-b and L-d the activity and selectivity was much lower than with PPh3 (TOF ca. 15, n : iso ratio 0.6). Thus, the yield of heptanals obtained with the catalyst derived from L-a is 94% while under the same conditions with L-b only 6%. The TOF for the L-a/Rh catalyst was 5 times lower than for the P(OPh)(3)/Rh catalyst despite the superficially similar ligand electronic characteristics for L-a and P(OPh)(3).