The synthesis of novel N-heterocyclic α-diphenylphosphinoglycines

Synthetic amino acids are of interest in various fields of chemistry, biochemistry and pharmacy. The first experiments with a phosphanyl group were obtained by condensation of natural amino acids with secondary phosphanes and formaldehyde, usually forming bis(phosphanylmethyl) amino acids, and studied with respect to their use as ligands in rhodium-catalysed hydrogenation reactions and in complexes for radio-diagnostics. The use of primary phosphanes extended the range of N-phosphanylmethyl amino acids to various P,N-heterocyclic types. The incorporation of P-alkyl instead of Pphenyl groups led to an increase in the sensitivity of Nalkyl-α-phosphanylglycines. To obtain more stable α-phosphanyl amino acids we systematically varied the nitrogen substituents of the (diphenylphosphanyl)glycines and report here on the novel N-aryl derivatives 1, their synthesis, structure and properties, and the first examples of their transitionmetal complexes and their use in homogeneous catalysis.

A three-component one-pot reaction of diphenylphosphine, primary amine and glyoxylic acid hydrate in diethyl ether or methanol allowed an easy access to N-monosubstituted diphenylphosphinoglycines 1b-10b.

Fig. 1. Preparation of α,α-phosphinoaminoacids



The reaction of nickel (0) complexes with N-monosubstituted diphenylphosphinoglycines leads to the formation of a catalytically active form of the ethylene oligomerisation catalyst via oxidative addition to O-H or O-C bond of the used phosphorus ligand. The linear olefins with terminal methyl and vinyl groups are the main products of the catalytic ethylene oligomerisation process. The highest conversion of C2H4 into linear α-olefins was observed with N-C6H3-2,5-(COOMe)2 phosphinoglycinate ligand 5b. Since the conversion of ethylene with a nickel-based catalyst on the base of  N-(2-methoxybenzyl) diphenylphosphineglycine 4b showed of covertion of etheline about 75% of the preferential formation of hexene-1 (40%) and butene-1 (20%). Organonickel complex based on the base of N- (2-pyrazine) diphenylphosphineglycine 8b  to process about 96% of the loaded gas and analysis by gas chromatography showed 85% butene-1 in the condensed gas after catalyst reaction at the temperature about -25. The low part of the buten-1 was dissolved in the liquid oligomers .

Screening tests of the catalytic activity of the new phosphinoglycines in combination with complex [Ni0(COD)2] (where COD= 1,5 cyclooctadiene) led likewise to oligo/polymerization of ethylene with high selectivity for linear products with methyl and vinyl end groups. We showed However, the catalytic process requires use of the special techniques operated in inert conditions due limited stability of [Ni0(COD)2]. Moreover, this low stability of the metal complex precursor sometimes strongly limited a possibility of industrial application of the laboratory created catalytic systems based on the nickel complexes and P-C-C-O chelating ligands. Usually this problem can be solved by using of the chemical reducing reagents as NaH and others.

The aim of the research is to elaborated new processes of active nickel catalysts generation using electrochemical techniques. The generation of the active nickel catalysts will be performed by reaction of oxidative addition of synthesized new N-substituted α-diphenylphosphino-α-aminoacids to the electrochemically generated nickel(0) complexes as in case of previously described organonickel sigma-bonded complexes.

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