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

Helena Riihimäki

Department of Chemistry, University of Oulu

Abstract

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.

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 o-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 o-alkyl-substituted phenylphosphanes.

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 o-alkyl-substituted arylphosphanes, which were studied most throughly, gave the highest selectivity to isobutanal but at the cost of activity. Linear n-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.

Table of Contents
Acknowledgments
List of original papers
Symbols and abbreviations
1. Introduction
1.1. Phosphane ligands
1.2. Hydroformylation
2. Aims of the work
3. Synthetic work
3.1. Reagents
3.2. General procedure for preparation of phosphanes
3.2.1. Trifluoromethyl- and selenomethyl-substituted phenylphosphanes (I)
3.2.2. (9-Anthryl)phenylphosphanes (I)
3.2.3. Alkyl-substituted arylphosphanes (II, III, IV)
3.2.4. Alkyl-substituted pyridylphosphanes (III, V)
3.2.5. o-Alkyl-substituted arylalkylphosphanes (V)
3.3. Cr carbonyl derivatives of phosphane ligands containing nitrogen
4. Characterization
4.1. Instrumentation and measurements
4.2. Structure of phosphane ligands
4.2.1. 31P{1H} NMR spectra and cone angles
4.2.2. 1H and 13C{1H} NMR spectra
4.2.3. X-ray crystal structures
4.3. Structure of Cr carbonyl derivatives
4.3.1. NMR spectra
4.3.2. X-ray crystal structures
5. Hydroformylation
5.1. Trifluoromethyl- and selenomethyl-substituted phenylphosphanes (I)
5.2. Alkyl-substituted arylphosphanes and arylalkylphosphanes (II–V)
6. Conclusions
References
List of Tables
1. Yields, 31P NMR shifts (δP), and calculated cone angles (θ ) of ligands (L).
2. 13C NMR shifts (ppm) for the o-substituted phenyl rings of phosphane ligands 1, 5, 8, 13, and 14. R indicates the o-substituent of the phenyl ring. See Scheme 11 for numbering of carbon atoms.
3. 1H and 13C NMR shifts (ppm) and coupling constants (Hz) for the m-isopropyl-substituted phenylphosphane ligands 18–20. See Scheme 13 for numbering of hydrogen and carbon atoms.
4. 1H NMR shifts (ppm), multiplicities and coupling constants (Hz) for the isopropyl group directly bonded to phosphorus. See Scheme 14 for numbering of hydrogen and carbon atoms.
5. 13C NMR shifts (ppm) and coupling constants of doublets (Hz) for isopropyl and cyclohexyl groups directly bonded to phosphorus. See Scheme 14 for numbering of hydrogen and carbon atoms.
6. 1H and 13C NMR shifts (ppm) and coupling constants (Hz) for (o-N,N- dimethylaminophenyl)diphenylphosphane (L1), Cr(CO)4(L1), (p-thiomethylphenyl)­­bis(2-pyridyl)phosphane (L2), and Cr(CO)5(L2).
List of Figures
Scheme 1. Hydroformylation reaction.
Scheme 2. Reaction route for the preparation of substituted phosphanes.
Scheme 3. Schematic structures of (o-trifluoromethylphenyl)diphenylphosphane 1, tris­(o-tri­fluoro­methylphenyl)phosphane 2, (p-trifluoromethylphenyl)­diphenyl­phosphane 3, tris(p-tri­fluoro­methylphenyl)phosphane 4, and (o-seleno­methylphenyl)­diphenyl­phosphane 5.
Scheme 4. Schematic structures of (9-anthryl)diphenylphosphane 6 and bis(9-anthryl)­­phenylphosphane 7.
Scheme 5. Schematic structures of (o-methylphenyl)diphenylphosphane 8, bis(o-methyl­phenyl)­­phenylphosphane 9, (o-ethylphenyl)diphenylphosphane 10, bis(o-ethyl­phenyl)­phenyl­phosphane 11, (o-isopropylphenyl)diphenylphsophane 12, (o-cyclohexylphenyl)­diphenyl­phosphane 13, and (o-phenylphenyl)­diphenyl­phosphane 14.
Scheme 6. Schematic structures of (2,4,5-trimethyl­phenyl)diphenylphosphane 15, (2,5-di­methyl­­phenyl)­diphenylphosphane 16, and (2-methylnaphthyl)diphenylphosphane 17.
Scheme 7. Schematic structures of (m-isopropylphenyl)diphenylphosphane 18, bis(m-iso­propyl­­phenyl)­phenyl­phosphane 19, and tris(m-isopropylphenyl)phosphane 20.
Scheme 8. Schematic structures of (3-methyl-2-pyridyl)diphenylphosphane 21, (2,5-dimethyl­phenyl)­bis(3-pyridyl)phosphane 22, and (2,5-dimethylphenyl)bis(4-pyridyl)­phosphane 23.
Scheme 9. Schematic structures of (o-methylphenyl)diisopropylphosphane 24, (o-cyclohexyl­phenyl)­­diisopropyl­phosphane 25, (o-methylphenyl)dicyclohenylphosphane 26, (o-cyclohexyl­phenyl)­­dicyclo­hexyl­phosphane 27, bis(o-methylphenyl)­isopropyl­phosphane 28, (2-methyl­naphthyl)­­diisopropyl­phosphane 29, and (2-methylnaphthyl)­dicyclohexylphosphane 30.
Scheme 10. Schematic structures of (o-N,N-dimethylamino­phenyl)­diphenyl­phosphane L1, (p-thio­­­methyl­­­phenyl)­bis(2-pyridyl)­phosphane L2, and (p-methoxy­phenyl)­­bis(2-pyridyl)­phosphane L3 used as ligands in the preparation of chromium carbonyl derivatives.
Scheme 11. Numbering of hydrogen and carbon atoms in NMR measurements.
Scheme 12. Cone angle of the o-substituted phenylphosphanes (8, 10, 12, 13, 14) plotted as a function of the 13C NMR shifts of C1, C2, C3, and C7 (see Scheme 11). The o-substituent is shown in parentheses.
Scheme 13. Numbering of hydrogen and carbon atoms of ligands 18–20 in NMR measurements.
Scheme 14. Numbering of hydrogen and carbon atoms in NMR measurements. R means o-methyl- or o-cyclohexyl-substituted aryl ring.
1. Crystal structures of bis(o-methylphenyl)phenylphosphane 9, (m-isopropyl­phenyl)­diphenylphosphane 18, (2,5-dimethylphenyl)bis(4-pyridyl)­phosphane 23, and (o-cyclohexyl­phenyl)­­dicyclo­hexyl­phosphane 27.
Scheme 15. Numbering of hydrogen and carbon atoms of Cr complexes of (o-N,N-dimethyl­amino­phenyl)diphenylphosphane (L1), (p-thio­methylphenyl)­bis(2-pyridyl)­­phosphane (L2), and (p-­methoxy­­­phenyl)­bis(2-pyridyl)­­phosphane (L3).
2. Crystal structures of monodentate [Cr(CO)5(L2)] and bidentate [Cr(CO)4(L1)] and [Cr(CO)4(L3)] complexes.
Scheme 16. Selectivity to isobutanal plotted as a function of cone angle. The values are for o-substituted arylphosphanes. The substituent is shown in parentheses.
Scheme 17. Initial rates of propene hydroformylation reaction plotted as a function of cone angle. The values are for o-alkyl-substituted arylphosphanes. The substituent is shown in parentheses.
Scheme 18. Selectivity to isobutanal plotted as a function of 31P NMR shifts. The values are for o-alkyl-substituted arylphosphanes. The substituent is shown in parentheses.
Scheme 19. Initial rates of propene hydroformylation reaction plotted as a function of 31P NMR shifts. The values are for o-substituted arylphosphanes. The substituent is shown in parentheses.
Scheme 20. Selectivity to isobutanal plotted as a function of the 13C NMR shift of C7 (see Scheme 11 for numbering of carbons). The values are for o-substituted arylphosphanes. The substituent is shown in parentheses.
Scheme 21. Initial rates of propene hydroformylation reaction plotted as a function of the 13C NMR shift of C7 (see Scheme 11 for numbering of carbons). The values are for o-substituted arylphosphanes. The substituent is shown in parentheses.
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