Several organorhodium(I) complexes of the general formula (PPh(3))(2)(CO)RhR (R = p-tolyl, o-tolyl, Me) were isolated and were shown to insert aryl aldehydes into the aryl-rhodium(I) bond. Under nonaqueous conditions, these reactions provided ketones in good yield. The stability of the arylrhodium(I) complexes allowed these reactions to be run also in mixtures of THF and water. In this solvent system, diarylmethanols were generated exclusively. Mechanistic studies support the formation of ketone and diarylmethanol by insertion of aldehyde into the rhodium-aryl bond and subsequent beta-hydride elimination or hydrolysis to form diaryl ketone or diarylmethanol products. Kinetic isotope effects and the formation of diarylmethanols in THF/water mixtures are inconsistent with oxidative addition of the acyl carbon-hydrogen bond and reductive elimination to form ketone. Moreover, the intermediate rhodium diarylmethoxide formed from insertion of aldehyde was observed directly during the reaction. Its structure was confirmed by independent synthesis. This complex undergoes beta-hydrogen elimination to form a ketone. This alkoxide also reacts with a second aldehyde to form esters by insertion and subsequent beta-hydrogen elimination. Thus, reactions of arylrhodium complexes with an excess of aldehyde formed esters by a double insertion and beta-hydrogen elimination sequence.

The reaction of monomeric and dimeric rhodium(I) amido complexes with unactivated olefins to generate imines is reported. Transamination of {(PEt(3))(2)RhN(SiMePh(2))(2)} (1a) or its -N(SiMe(3))(2) analogue 1b with p-toluidine gave the dimeric [(PEt(3))(2)Rh(mu-NHAr)](2) (Ar = p-tolyl) (2a) in 80% isolated yield. Reaction of 2a with PEt(3) generated the monomeric (PEt(3))(3)Rh(NHAr) (Ar = p-tolyl) (3a). PEt(3)-ligated arylamides 2a and 3a reacted with styrene to transfer the amido group to the olefin and to form the ketimine Ph(Me)C=N(p-tol) (4a) in 48-95% yields. The dinuclear amido hydride (PEt(3))(4)Rh(2)(mu-NHAr)(mu-H) (Ar = p-tolyl) (5a) was formed from reaction of 2a in 95% yield, and a mixture of this dimeric species and the (PEt(3))(n)RhH complexes with n = 3 and 4 was formed from reaction of 3a in a combined 75% yield. Propene reacted with 2a to give Me(2)C=N(p-tol) (4b) and 5a in 90 and 57% yields. Propene also reacted with 3a to give 4b and 5a in 65 and 94% yields. Analogues of 2a and 3a with varied electronic properties also reacted with styrene to form the corresponding imines, and moderately faster rates were observed for reactions of electron-rich arylamides. Kinetic studies of the reaction of 3a with styrene were most consistent with formation of the imine by migratory insertion of olefin into the rhodium-amide bond to generate an aminoalkyl intermediate that undergoes beta-hydrogen elimination to generate a rhodium hydride and an enamine that tautomerizes to the imine.

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 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(mu-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, beta-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.

Organosilanes with the potentially coordinating group -N^CI-y^NlV^]") or -N(CH-,CH ? OMe) 2 have been prepared and characterized by proton, carbon, and silicon NMR"spectroscopy. None of the compounds showed evidence of hypervalency, suggesting that the conformationally-flexible bridging framework produces an unfavorable entropy of coordination. Abstracth3C η η N R CHa 409 Brought to you by | provisional account Unauthenticated Download Date | 6/3/15 5:50 PM