The electron-poor phosphines P{C_6H_3(CF_3)_2-3,5}3 and P(C_6F_5)_3 do not mimic phosphites as ligands for hydroformylation.A comparison of the coordination chemistry of P{C_6H_3(CF_3)_2-3,5}3 and P(C_6F_5)_3 and the unexpectedly low hydroformylation

摘要

The fluoroaryl phosphines P{C_6H_3(CF_3)_2-3,5}_3(L_a)and P(C_6F_5)_3(L_b)form the complexes trans-[MCl_2(L_a)_2] and trans-[MCl_2(L_b)_2](M = Pd or Pt)which have been isolated and fully characterised.~31P NMR studies of competition experiments show that the stability of trans-[PdCl_2L_2] is in the order L = L_b < L_a < PPH_3.The crystal structure of trans-[PtCl_2(La)_2] is reported and reveals that the Pt-P bond lengths in trans-[PtCl_2L_2] are in the order L = L_b < L_a < PPh_3.The equilibria established when [Pt(norbornene)_3] is treated with L_a or L_b are investigated by ~31P and ~195Pt NMR spectroscopy and the species [PtL_n(norbornene)_(3-n)](n = 1-3)identified.Ligands L_a and L_b appear to have similar affinities for platinum(O).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 nu_CO are comparable with those for analogous phosphite complexes.The ligands L_a,L_b,P(C_6H_2F_3-3,4,5)_3(L_c),P{C_6H_4(CF_3)-2}_3(L_d),PPH_3 and P(OPh)_3 have been tested in rhodium-catalysed hydroformylation of 1-hexene and L_a,L_b,and PPH_3 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 PPH_3 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 PPH_3(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.