Synthesis of electron-withdrawing butane- and arene-sulfonylamino phosphines and use in rhodium-catalyzed hydroformylation

Abstract

Reaction of RSO₂N(H)CH₂CH₂N(H)SO₂R [R = Bu (1), 4-nitrobenzene (7), 1-naphthalene (9a), 2-naphthalene (9b)] with PhPCl₂ or EtPCl₂ gives monodentate phosphorus compounds 2 and 3 (R = Bu, PhP and EtP), and 8 (R = 4-nitrobenzene, PhP), and with Ph₂PCl gives the corresponding bidentate phosphine ligands Ph₂PN(SO₂R)CH₂CH₂N(SO₂R)PPh₂ [R = Bu (10), 4-nitrobenzene (11), 1- and 2-naphthalene (12a,b)]; similar reactions of N,N′-(1-butanesulfonyl)-2,2′-diaminobiphenyl (4) give monodentate 5 (PhP) and 6 (EtP) and N,N′-bis(diphenylphosphino)-N,N′-(1-butanesulfonyl)-2,2′-diaminobiphenyl (16). A monodentate analogue of 10 was also prepared, Ph₂PN(Et)SO₂Bu (14). Diphosphorus compounds with two butanesulfonylamino groups on phosphorus were also prepared from 1 and Cl₂P(CH₂)_nPCl₂ (n = 2, 4) to give 19 and 20. Details of the ¹³C NMR false AA′X systems are reported for 19 and 20. Rhodium-catalyzed hydroformylation reactions were run at 60 and 80 °C, at CO/H₂ pressures from 4–11 atm, and in THF, toluene, CH₂Cl₂, and dioxane. Results show that the highest ratios of linear (n) to branched (iso) aldehydes were obtained with arenesulfonamides (n∶iso > 10) while the bidentate alkanesulfonamide 10 gave a lower n∶iso ratio of 7.2 but the highest rate [k₁ = 1.98 h⁻¹, turnover frequency = 1130 mol aldehyde (mol Rh)⁻¹ h⁻¹] in THF at 80 °C. Both the rate and n∶iso ratio for 10 were found to increase with decreasing CO/H₂ pressure in THF and in toluene, although the rate change was small for toluene. Both the rate and n∶iso ratio for 10 also increased in CH₂Cl₂, but this was found not to be due to lower CO/H₂ concentrations in solution, on the basis of solubility measurements in THF and CH₂Cl₂.