Electron-Withdrawing Phosphine Compounds in Hydroformylation Reactions. 1. Syntheses and Reactions Using Mono- and Bis(p-toluenesulfonylamino) Phosphines

Abstract

The rhodium-catalyzed hydroformylation of 1-hexene has been examined in the presence of members of a new class of electron-withdrawing phosphorus ligands, the N-sulfonylphosphoramides. All of the phosphorus compounds in this initial study contain one or two p-toluenesulfonylamino (TsN) groups attached to the phosphorus atom, including three compounds that have been described previously, TosL (1), a monophosphorus compound with two TsN groups, diTosL (2), a diphosphorus compound with one TsN group on each phosphorus atom, and 3, a chiral amino acid-derived ligand with one TsN and one O-acyl group on phosphorus. In addition, two new chelating analogues of 1 containing two- and four-carbon bridges between the phosphorus atoms (5, 7), an analogue of 1 with an ethyl instead of a phenyl group on phosphorus (8), a nonchelating monophosphorus analogue of 2 (10), and a monophosphorus adduct of the ditosylate of o-phenylenediamine (12) have been synthesized and used in hydroformylations, and comparison reactions with PPh3 in THF, toluene, and CH2Cl2 have been run. The 13C NMR spectra of 5 and 7 and related diphosphorus compounds have been examined for evidence of false AA‘X spectra in which the chemical shifts of the nominally equivalent phosphorus atoms are split by the presence of a single 13C atom. The chelating compound 2 is by far the most effective hydroformylation ligand, giving high turnover frequencies (TOF) and linear to branched (n:i) ratios of the aldehyde product. Reactions of 2 run at a 1000:10:1 ratio of 1-hexene:2:Rh(acac)(CO)2 at 84 psi CO/H2 at 60 °C in THF gave TOF = 440 mol aldehyde/mol Rh/h and an n:i ratio of 10, and at 80 °C gave TOF = 760 and an n:i ratio of 15.8. Reactions with 2 were also run in toluene, giving similar results, and in CH2Cl2, giving rise to higher n:i ratios (up to 28.5) but also to faster catalyst deactivation. In the absence of chelation, 10 gave lower turnover frequencies (TOF) and linear-to-branched ratios (n:i), and 1 and 3 also gave lower TOF values and low n:i ratios similar to those of PPh3 and 10. The chelating analogues of 1, 5 and 7, were very poor ligands and gave n:i ratios characteristic of monophosphorus ligands. Compounds 8 and 12 inhibit all reaction.