Substituent groups in aryl- and arylalkylphosphanes: effects on coordination chemistry and catalytic properties

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>Thirty phosphane ligands were prepared and characterized. Aryl groups of the phosphane ligands were modified through change in functionality. The side chains were the following: trifluoromethylphenyl, selenomethylphenyl, 9-anthryl, alkyl-substituted aryl groups, and pyridyl and alkyl groups. In addition, three chromium carbonyl complexes of potentially bidentate arylphosphanes containing nitrogen heteroatoms were prepared and characterized. Characterization of the isolated complexes verified the monodentate coordination from phosphorus and two bidentate coordination modes, (P,N)-bound and (N,N')-bound.</p><p>Ligands and complexes were characterized by ¹H, ¹³C{¹H}, ³¹P{¹H}, and two-dimensional NMR spectroscopy, X-ray crystallography, and mass spectrometry. The ¹³C{¹H} and ³¹P{¹H} NMR spectra, and calculated cone angles of the <em>o</em>-alkyl-substituted aryl- and arylalkylphosphane ligands provided valuable parameters, which could be plotted against catalytic results in the search for correlations between the structures and catalytic behavior of ligands. Correlations were found between the parameters and the catalytic behavior of Rh-catalysts modified with the <em>o</em>-alkyl-substituted phenylphosphanes.</p><p>The research reported here was directed toward the preparation and characterization of phosphane ligands which would favor the formation of isobutanal in propene hydroformylation. The <em>o</em>-alkyl-substituted arylphosphanes, which were studied most throughly, gave the highest selectivity to isobutanal but at the cost of activity. Linear <em>n</em>-butanal was still the main product, though only barely. Alkyl substituents in meta position increased the activity of propene hydroformylation even up to the level with the reference ligand PPh₃, but, the selectivity decreased simultaneously.</p></div>