Rhodium amido

Equation 9.85 shows the reaction of a similar rhodium-amido complex with unstrained olefins. In this case, the product is a free imine. The inverse order of the reaction in added phosphine and the zero order of the reaction in any free amine imply that the imine is formed by the sequence shown in Equation 9.86, involving olefin insertion, 3-hydrogen elimination (see Chapter 10), and tautomerization of the resulting enamine to the imine. 

Whatever the route to a rhodium dihydride alkene complex, the hydrogen must be transferred sequentially to the double bond. It had always been assumed that the first C-H bond is formed / to the amido-group, so that the more stable Rh-substrate chelate is formed. This is the alkylhydride isomer observed in stoichiometric NMR studies at low temperatures, and is supported by studies under catalytic turnover conditions, assuming a normal isotope effect... 

Derivatives of the steroids androstene and pregnene have been transformed directly into A-acyl amino acids by an orthogonal catalysis procedure, utilizing [RhCl(nbd)]2 and Co2(CO)8 (Scheme 11). The rhodium phosphine catalyst (generated in situ in the presence of syn-gas and phosphine) affects hydroformylation of the internal olefin to generate aldehyde. In the presence of Co2(CO)8, A-acyl amino acids are obtained as the major products. An unstable amido alcohol intermediate, formed by reaction of the amide with aldehyde, is proposed to undergo cobalt-catalyzed GO insertion to yield the desired A-acyl amino acid. 

Benzene—dienes, with pentarutheniums, 6, 986 Benzen/if/indenyl—amido complexes, with Ti(IV), 4, 438 j4-Benzenes with iridium, 7, 328 rhodium, 7, 181... 

The oxidation-reduction route was also used to prepare copolymers 53 of bis[bis(tri-methylsilyl)amido]germanium and acetylene derivatives130 (Scheme 27). Rhodium compounds such as [Rh(norbornadiene)Cl]2 were used as catalysts. In contrast to other polymers prepared from germylenes, the monomer-to-monomer ratio was not regular. Relatively low molecular weight polymers 53 (Mn = 1 x 103-104) were isolated. 

Prompted by our earlier work dealing with the internal dipolar cycloaddition reaction of mesoionic oxazolium ylides of type 74, we subsequently studied the rhodium(II) catalyzed reactions of the related a-diazo ketoamide system 154 <97JOC2001 04OL3241 05JOC2206>. Attack of the amido oxygen at the rhodium carbenoid produces a push-pull carbonyl ylide dipole (i.e., 155) that is isomeric with the isomiinchnone class of mesoionic betaines. 

In the total synthesis of (-)-conocarpan, the chiral 2,3-dihydrobenzo[b furan core was constructed by radical based intramolecular cyclization as shown below <07CC2151>. In addition, chiral 2-isopropeny 1-2,3-dihydrobenzo[6J furans and 2-amido-bcnzo b furans were be made by palladium-catalyzed reaction in the presence of Trost ligand, and the rhodium(I)-catalyzed cyclization, respectively <07JOC2857 07OL2361>. 

Amidocarbonylation is a recently developed, organometallic-catalyzed route to amino acid generation - particularly A(-acyl a-amino acids - using either aldehydes or alkenes as starting materials and synthesis gas as an integral building block. The two principal classes of reaction are illustrated in eqs. (1) and (2). Both syntheses offer the opportunity to introduce two functionalities, amido and carboxylate, simultaneously where an amide is the co-reactant. Homogeneous amidocarbonylation catalysts are typically cobalt carbonyl-based, or utilize transition-metal binary systems, e. g. cobalt-rhodium, cobalt-palladium, and cobalt-iron. 

The zirconocene bis(arylamido) complex 787 was obtained by the reaction of Cp2ZrCl2 with 2 equiv. of the lithium amide605 (Scheme 195). When the reaction is carried out in a 1 1 ratio, the monoamide zirconocene chloride is generated as the major product. Reaction of in situ-generated Cp 2Zr with 2-(methylmercapto)aniline yields monoamido zirconocene hydride 788, the spectroscopic data of which suggest an interaction between the S atom and the Zr center in this complex. The bis(amido) complex 787 serves as a precursor for the synthesis of amido rhodium and iridium complexes. 

Isomunchnone dipoles generated by the cyclization of rhodium carbenoid intermediates with adjacent amido groups have also been shown to undergo cycloaddition with both electron-rich and certain heteroaromatic 7i-bonds. For example, the catalytic decomposition of diazoimide 12 provided dipole 13 which subsequently added across the indole 7i-bond to give a cycloadduct possessing the aspidosperma alkaloid skeleton (Scheme 4) (95JOC6258). 

The cyclohexyl derivative of Diop, 4.5-bis(dicyclohexylphosphinomethyl)-2.2-dimethyT1.3-dioxolane (CyDiop). is a much better cocatalyst in rhodium complexes than Diop itself in the catalytic hydrogenation of oxo groups a to amido functions. 

Asymmetric hydrogenation of a-amidoacrylic acids and related olefins has been reported to proceed with high enantioselectivity in the presence of chiral ferrocenyl-phosphine-rhodium catalysts. Both ferrocenylmonophosphines [21, 24, 58] and ferrocenylbisphosphines [17, 59, 60] can produce A -acetylphenylalanine with >80 /o ee in the rhodium-catalyzed hydrogenation of a-acetoaminocinnamic acid or its esters (Scheme 2-42). The high selectivity is ascribed mainly to a characteristic structure of the olefinic substrate that has an amido group at the proper position... 

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