Reactions of an Arylrhodium Complex with Aldehydes, Imines, Ketones, and Alkynones. New Classes of Insertion Reactions

Abstract

Organorhodium complexes of the general formula (DPPE)Rh(pyridine)(R) (R ) p-tol (2a) and CH 2 SiMe 3 (2b), DPPE ) 1,2-bis(diphenylphosphino)ethane) were prepared from [(DPPE)-Rh(µ-Cl)] 2 , pyridine, and p-tolyllithium or Me 3 SiCH 2 MgCl. Complex 2a inserted the electronpoor aldimines (p-tol)CHdN(C 6 H 4 -p-CO 2 Me) (3a-Tol) and (Ph)CHdN(C 6 H 4 -p-CO 2 Me) (3a-Ph) to give amide complexes that were isolated directly or trapped with PEt 3 . In contrast, the reaction of aryl complex 2a with the electron-neutral and electron-rich imines PhCHd NPh (3b) and (p-tol)CHdN(C 6 H 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 Me 3 CCHO, 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 H 2 O instead of PEt 3 also formed hydroxide 36 and the diarylmethylamine (Ph)(p-tol)CH-NH(C 6 H 4 -p-CO 2 -Me) (35).

An umpolung strategy to react catalytic enols with nucleophiles

“…This leads to iridium enolate species A (represented as an η 3 -enolate in Fig. 5) 51 . Our hypothesis is that the role of the additive (KBF 4 ) is to increase the rate of the formation of iridium enolate species A.…”

Mechanistic study of the rhodium-catalyzed carboxylation of simple aromatic compounds with carbon dioxide

“…Therefore, we decided to prepare the tetracoordinated 16-electron complexes RhMe(PCy 3 )(dcype) 2 and RhPh(PCy 3 )(dcype) 3 as appropriate precursors of the 14-electron complexes ( Scheme 3 ). 14 2 and 3 were prepared in good yields through the treatment of [RhCl(dcype)] 2 with MeLi and PhLi, respectively in the presence of a stoichiometric amount of PCy 3 . 15 Their structures were determined using 1 H and 31 P NMR.…”

In Situ Synthesis of Neutral Dinuclear Rhodium Diphosphine Complexes [{Rh(diphosphine)(μ2‐X)}2]: Systematic Investigations

“…The m 2 -OH-bridged precursor 4 seems to be unsuitable for the in situ preparation of [{Rh(DPPE)(m 2 -OH)} 2 ], which is formed in only 4 % yield in THF at room temperature. [41] DIPAMP Upon addition of two equivalents of DIPAMP to 1 in THF at room temperature, a precipitate is formed that, analogously to DPPE, very likely is the ionic complex [Rh(DIPAMP) 2 ][Rh-(cod)(Cl) 2 ]. The complex is much more soluble than the DPPE analogue.…”