Insertions of ketones and nitriles into organorhodium(I) complexes and β-hydrocarbyl eliminations from rhodium(I) alkoxo and iminyl complexes

A series of tris(triethylphosphine)-ligated organorhodium(I) complexes were prepared, and their reactions with electron-poor arylnitriles and diarylketones were studied. [(PEt3)(3)Rh(Ar)] (Ar = phenyl (1a) or o-anisyl (1e)) reacted with an excess of electron-poor arylnitriles Ar'C N (Ar' = p-CF3C6H4 or 3,5-bis(CF3)C6H3) to form Rh(I) iminyl complexes [(PEt3)(3)Rh[N = CAr)(Ar')]} (2h-j). In contrast, 3,5-bis(CF3)C6H3CN did not insert into the M-C bond of the arylrhodium(I) complexes [(PEt3)(3)Rh(Ar)] (Ar = p-CF3C6H4 (If) or 3,5-bis(CF3)C6H3 (19)), Containing more electron-poor aryl groups. The kinetic data for nitrile insertions were most consistent with a pathway involving initial ligand dissociation, followed by a classic migratory insertion. The iminyl complexes 2i-j decomposed at higher temperatures via beta-aryl eliminations with selective migration of the more electron-poor aryl group 3,5-bis(CF3)C6H3 to form 1g and the corresponding nitriles. Migratory aptitudes of various aryl groups were assessed by studying beta-aryl eliminations from a variety of iminyl complexes. Kinetic data for these beta-aryl eliminations were most consistent with initial phosphine dissociation and carbon-carbon bond cleavage of the resulting 14-electron intermediate. Insertions of diarylketones Ar(Ar')C = O (Ar = 3,5-bis(CF3)C6H3, Ar' = Ph or 3,5-bis(CF3)C6H3)) into 1a also occurred, although the resulting Rh(I) alkoxides {(PEt3)(2)Rh[OC(Ph)(Ar)-(Ar')]} (3f-g) were not stable under the reaction conditions and could not be directly identified. Instead, a mixture of {(PEt3)(3)Rh[3,5-bis(CF3)C6H3]} (1g) and the ketone Ph(Ar')C = O (Ar' = Ph or 3,5-bis(CF3)C6H3)) were detected as the major products, indicating that decomposition of alkoxides 3f-g occurred by beta-elimination of the more electron-poor aryl group. Independent preparation of 3f-g and studies on their thermal decomposition with added PEt3 confirmed that selective beta-aryl elimination occurs to generate aryl complex 1g and the corresponding ketones. Analogous beta-aryl eliminations from bisphosphine rhodium(I) alkoxo complexes 3a-e and trisphosphine rhodium(I) alkoxo complexes 4b-e were also studied, and the kinetic results were most consistent with irreversible beta-phenyl elimination from bis(phosphine) alkoxo complexes. Insertion of 3,5-bis(CF3)C6H3CN into an alkylrhodium(I) complex [(PEt3)(3)Rh(Me)] (1h) did not occur; however, the electron-poor ketone Ar2C = O (Ar = 3,5-bis(CF3)C6H3)) inserted into 1h, as judged by the detection of the corresponding alcohol HOC(Me)[3,5-bis(CF3)C6H3)](2) as the major organic product after quenching with Et3N center dot HCl. Vinylrhodium(I) complex [(PEt3)(3)Rh-(CH = CH2)] (1i) also reacted with ketones of the type Ar2C = O (Ar = 3,5-bis(CF3)C6H3) to form a Rh(I) alkoxo complex (PEt3)2RhIOC(CH=CH2)[3,5-bis(CF3)C6H3]2) (3h), which was stabilized by the intramolecular coordination of the vinyl moiety to the rhodium center. The alkynylrhodium(I) complex [(PEt3)(3)Rh(C CPh)] (1j) did not react with ketones or nitriles. Instead, the propargylic alkoxides ((PEt3)(2)Rh[OC(R)(2)(C CPh)]} (R = Me or Ph) that would have resulted from insertion were shown to react rapidly in the presence of added PEt3 to form the alkynyl complex 1j and the corresponding ketones via beta-alkynyl eliminations.