Phosphonium bis(glycolates) and phosphinoglycolates: Synthesis, solvolysis, oxidation to (thio)phosphinoylglycolates and use as ligands in Ni-catalyzed ethylene oligomerization

Secondary phosphines, glyoxylic acid hydrate and amines react to form organoammonium phosphonium bis(glycolates) 1a–d. In CD3OD solution, diphenylphosphonium bis(glycolates) undergo reversible solvolysis to phosphinoglycolates 2a,b and acetalic glyoxylic species. The P-dialkyl species 1c avoids this and maintains the phosphonium bis(glycolate) structure in CD3OD (cHex2P) or undergoes further solvolysis with partial formation of R2PH (R = tBu). Condensation to phosphinoglycines, e.g. 3b, observed for primary amines, does not take place with N-secondary amines at room temperature. Heating leads to condensation but is followed by decarboxylation as shown for the conversion of 2a to 4a. Because of the kinetic lability, the phosphonium compounds 1a–d are sensitive to oxidation by air, H2O2, or sulfur. The resulting phosphinoyl and thiophosphinoyl glycolates and glycolic acids 5–8 are kinetically stable. Precatalyst solutions formed from 1a, c, d and Ni(COD)2 in THF developed moderate to good activity in the oligo- or polymerization of ethylene to linear products containing methyl and vinyl end groups. Activity and molecular weights increased with the +I-effect of the P-substitutents. The solution structures of the novel compounds were elucidated by multinuclear NMR spectroscopy. For 7a a crystal structure analysis is also presented.

Secondary phosphines, glyoxylic acid hydrate and amines react with formation of organoammonium phosphonium bis(glycolates) 1a–d, which easily undergo solvolysis to phosphinoglycolates, oxidation to kinetically more stable (thio)phosphinoyl glycolates or with Ni(COD)2 formation of in situ precatalyst solutions for the oligomerization of ethylene. For Ph2P(S)CH(OH)COO− Et2NH2+ the crystal structure is reported.Figure optionsDownload as PowerPoint slideHighlights
► Organoammonium diorganophosphonium bis(glycolates), properties and solution structures are described.
► Solvolysis in CD3OD or in D2O solution leads to diorganophosphinoglycolates.
► Oxidation with H2O2 or S provides diorgano(thio)phosphinoylglycolates.
► With Ni(COD)2 catalysts for oligo/polymerization of ethylene are obtained.