M. Ghalib, J. Lach, O. S. Fomina
Jul 27, 2014
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0
Influential Citations
13
Citations
Journal
Polyhedron
Abstract
Abstract 1,3-Dialkyl-1,3-benzazaphospholine-2-carboxylic acids 2a , b can be conveniently prepared by metalation and alkylation of N -methyl- and N -neopentyl- o -phosphanylaniline in liquid ammonia and cyclocondensation of the resulting N , P -disecondary phosphanylanilines 1a , b with glyoxylic acid hydrate (GAH) in ether. The primary neopentylphosphanylaniline reacts with two equivalents of GAH and forms a phosphanylbis(amino acid) 3 with toluidine. α-Branched P -substituents induce strongly preferred formation of trans -diastereoisomers with R , R - and S , S -configuration at P and C2, as shown by a crystal structure analysis of 2a , whereas a P -neopentyl ( P -Np) group gives rise to trans / cis -diastereoisomeric mixtures. The trans -configuration exhibits the P lone-pair in cis -position to the COOH group, suitable for formation of five-membered chelate rings, as in diphenylphosphanylacetate nickel catalysts for ethylene oligomerization. Screening of 2a , b /Ni(COD) 2 solutions in THF by a batch procedure indeed showed formation of catalysts for conversion of ethylene to linear oligomers and waxy low-molecular weight polymers. The conversion depends strongly on the size of the N -alkyl group, being slow and limited for the N -Me catalyst 2a / Ni and much faster and more complete for the N -Np-substituted catalysts 2b / Ni and 2c / Ni ( N -Np, P - t Bu). Comparison of 2b / Ni with 2c / Ni shows that the more bulky P-substituent further increases the catalyst activity.