Abstract
BINAP aminophosphines are prevalent N,P-bidentate, chiral ligands for asymmetric catalysis. While modification via the BINAP-nitrogen linkage is well explored and has provided a diverse body of derivatives, modification of the other substituents of the phosphorous center is another avenue in generating new congeners of this important class of chiral ligands. Herein reported are new BINAP aryl aminophosphines with electron rich or deficient substituents on the aryl rings. This scalable synthesis converted readily available starting material, (S)-BINOL, to a key intermediate (S)-NOBIN, from which the final chiral aminophosphines were prepared via a palladium-catalyzed, phosphonylation reaction. The aryl substituents are able to modify the electronic properties of the phosphorous center as indicated by the range of 31P-NMR shifts of these new ligands. A computational analysis was performed to linearly quantitate contributions to the 31P-NMR shifts from both resonance and field effects of the substituents. This correlation may be useful for designing and preparing other related aminophosphines with varying ligand properties.
Highlights
Since the introduction of C2-symmetric phosphine ligands [1], much effort has been devoted to finding new chiral ligands for transition-metal catalysis [2,3,4]
The diphenyl substituents of MAP in this class are replaced with aryl substituents bearing electron rich or deficient groups. These phosphines exhibit a range of 31P-NMR chemical shifts. These new BINAP-based bidentate aminophosphines will lead to expanded applications in transition metal-complex formation and asymmetric catalysis
We report here syntheses of new bidentate BINAP aminophosphines derived from (S)-NOBIN
Summary
Since the introduction of C2-symmetric phosphine ligands [1], much effort has been devoted to finding new chiral ligands for transition-metal catalysis [2,3,4]. To expand the reaction scope of BINAP aminophosphines, new BINAP aminophosphines that can be readily diversified, as pioneered by the work of Kocovsky and co-workers in the synthesis of MAP (2-amino-2'-diphenylphosphino-1,1'-binaphthyl) [15], were reported. The diphenyl substituents of MAP in this class are replaced with aryl substituents bearing electron rich or deficient groups. These phosphines exhibit a range of 31P-NMR chemical shifts. These new BINAP-based bidentate aminophosphines will lead to expanded applications in transition metal-complex formation and asymmetric catalysis
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