Enantioselective synthesis of six-membered palladacycles having metal-bound stereogenic carbons: Isolation and reactivity of palladacycles containing readily accessible β-hydrogens

Journal of the American Chemical Society

Volumn 126, Issue 51, 2004, Pages 16820-16833

  Burke, Brenda J ^a   Overman, Larry E ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL BONDS; HYDROGEN; ORGANOMETALLICS; STEREOCHEMISTRY; SYNTHESIS (CHEMICAL); X RAY CRYSTALLOGRAPHY;

ENANTIOSELECTIVE SYNTHESIS; EPIMERIZATION; PALLADACYCLES; STEREOGENIC CARBONS;

PALLADIUM COMPOUNDS;

COORDINATION COMPOUND; HYDROGEN; PALLADIUM COMPLEX; PHOSPHINE DERIVATIVE; TRIFLUOROMETHANESULFONIC ACID;

ARTICLE; ENANTIOSELECTIVITY; EPIMERIZATION; HIGH TEMPERATURE; ROOM TEMPERATURE; STEREOCHEMISTRY; THERMOSTABILITY; X RAY CRYSTALLOGRAPHY;

CRYSTALLOGRAPHY, X-RAY; MAGNETIC RESONANCE SPECTROSCOPY; MOLECULAR STRUCTURE; NAPHTHALENES; ORGANOMETALLIC COMPOUNDS; OXAZOLONE; PALLADIUM; STEREOISOMERISM; TEMPERATURE; THERMODYNAMICS;

EID: 11244331624     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja045047p     Document Type: Article

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63. 2O). Palladacycle 10α was not isolated.
64. 4 caused β-hydride elimination to 4.
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66. 31P decoupling using low power continuous wave decoupling of the individual multiplets.
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72. 1H} NMR spectra of 13 and 14 obtained with these counterions matched those from TBP· HOTf.
73. 15N NMR spectra of 26. When the mixture of 13 and 26 was exposed to 1 equiv of TBP·HOTf, both led to Heck product 4. To circumvent the undesired formation of 26, a volatile acid was employed to transform palladacycle 3β to 13, thus obviating the need for purification of the product by column chromatography.
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87. 1H NMR spectra, provide strong evidence that suggests this is not the favored coordination mode. The benzyl carbon attached to the nitrogen of the N-benzyloxindole appears as a slightly broadened singlet in each carbon spectrum, and the benzyl hydrogens appear as a simple AB system. If the nitrogen was directly coordinated to palladium (structure B), it is anticipated that the benzyl carbon and benzyl protons would couple to the two phosphorus atoms in the bidentate ligands on palladium, giving doublets of doublets instead of the observed singlets. Additionally, in structure A the amide is fully conjugated, whereas in structure B it is not.
88. (a) Shultz, C. S.; Ledford, J.; DeSimone, J. M.; Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6351-6356.
89. (b) Malinoski, J. M.; White, P. S.; Brookhart, M. Organometallics 2003, 22, 621-623.
90. For spectroscopic characterization of several cationic diimine Pd(II) β-agostic complexes in the context of polymerization reactions, see: Shultz, L. H.; Tempel, D. J.; Brookhart, M. J. Am. Chem. Soc. 2001, 123, 11539-11555.
91. Perhaps hydrogen bonding of the ammonium salt to the oxindole carbonyl group disrupts coordination of the N-benzyloxindole ligand.
92. Cf., Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91-100.
93. A related thermodynamic preference of a six-membered chelate was observed in cationic Pd(diimine) complexes chelated by an ester carbonyl fragment; see ref 51.
94. (a) Brown, J. M.; Pérez-Torrente, J. J.; Alcock, N. W.; Clase, H. J. Organometallics 1995, 14, 207-213.
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96. (c) Hii, K. K.; Claridge, T. D. W.; Brown, J. M. Angew. Chem. 1997, 36, 984-987.
97. (d) Reference 50e.
98. This low barrier to migration is substantiated by DFT calculations in related cationic Pd(II) systems; see ref 50e.