676563-20-5Relevant academic research and scientific papers
Reactions of an arylrhodium complex with aldehydes, imines, ketones, and alkynones. New classes of insertion reactions
Krug, Christopher,Hartwig, John F.
, p. 4594 - 4607 (2008/10/09)
Organorhodium complexes of the general formula (DPPE)Rh(pyridine)(R) (R = p-tol (2a) and CH2SiMe3 (2b), DPPE = 1,2- bis(diphenylphosphino)ethane) were prepared from [(DPPE)-Rh(μ-Cl)] 2, pyridine, and p-tolyllithium or Me3SiCH 2MgCl. Complex 2a inserted the electron-poor aldimines (p-tol)CH=N(C6H4-p-CO2Me) (3a-Tol) and (Ph)CH-N(C6H4-p-CO2Me) (3a-Ph) to give amide complexes that were isolated directly or trapped with PEt3. In contrast, the reaction of aryl complex 2a with the electron-neutral and electron-rich imines PhCH = NPh (3b) and (p-tol)CH=N(C6H 4-p-OMe) (3c) did not form stable amide products. Instead, the amide from insertion of imines 3b or 3c underwent β-hydrogen elimination, followed by metalation of the resulting ketimine. The reaction of 2a with 3a-Ph was first order in arylrhodium complex and inverse first order in the concentration of pyridine. Aldehydes that cannot enolize, such as PhCHO and Me3CCHO, inserted into the Rh-aryl bond of 2a to form ketones and esters. The esters were formed from insertion of a second aldehyde into the Rh-O bond of an intermediate alkoxide, followed by β-hydride elimination. Complex 2a underwent proton transfer with acetophenone to give π-oxaallyl complex 24 and with water to generate toluene and the dimeric hydroxide [(DPPE)Rh(μ-OH)]2 (36). It also reacted with the tert-butyl-substituted ynone 25 to form a product that contained a metalated isobutyl group. Quenching the reaction between aryl complexes 2a and 3a-Ph with H2O instead of PEt3 also formed hydroxide 36 and the diarylmethylamine (Ph)(p-tol)CH-NH(C6H4-p-CO 2-Me) (35).
Imine Insertion into a Late Metal-Carbon Bond to Form a Stable Amido Complex
Krug, Christopher,Hartwig, John F.
, p. 2694 - 2695 (2007/10/03)
An arylrhodium(I) complex containing a labile dative ligand was prepared, and its reactivity toward aryl imines was investigated. The arylrhodium(I) complex (DPPE)Rh(C5H5N)(p-tol), 2, was isolated in 65% yield from [(DPPE)Rh(μ-Cl)]2, pyridine, and p-tolyllithium. Reaction of 2 with the aldimine (p-tol)CH=N(C6H4-p-CO2Me) (3a-Tol) gave the Rh amide insertion product 4 in 88% isolated yield. The solid-state structure of 4 was determined by single-crystal X-ray diffraction. The reaction of 2 with the electron-neutral and electron-rich aldimines (Ph)CH=NPh (3b) and (p-tol)CH=N(C6H4-p-OMe) (3c) also appeared to involve insertion, but the amido complexes formed from these insertions were not stable. Thus, reaction of 2 with 3b, followed by addition of Et3NHCl, gave the amine and ketimine products (Ph)(p-tol)CH?NHPh, 5, and (p-tol)(Ph)C=N(Ph), 6, in 25% and 50% yields. Several lines of data indicate that these products are formed by a sequence of transformations involving insertion of imine to give a Rh amide intermediate, β-hydrogen elimination, cyclometalation to form a bound imine and H2, and protonolysis of the metallacycle upon addition of Et3NHCl. Consistent with this proposal, the proposed metallacycle containing the ortho-metalated ketimine ligand (p-tol)2C=N(C6H4-p-OMe) was isolated and characterized by single-crystal X-ray diffraction. Copyright
