Rhodium, tetrakis reactions

Rhodium, tetrakis(trimethylphosphine)-reactions, 4, 926 Rhodium carboxylates, 4,903 chemotherapy, 4, 903 Rhodium complexes, 4. 901 acetylacetone synthesis, 2, 376 alkylperoxo... 

S. Baral, P. Hambright, A. Harriman, and P. Neta, Radiolytic Studies of the Redox Reactions and Alkylation of Rhodium Tetrakis(4-sulfonatophenyl)porphyrin in Aqueous Solutions, J. Phys. Chem., 89 (1985) 2037. 

As shown in the previous two sections, rhodium(n) dimers are superior catalysts for metal carbene C-H insertion reactions. For nitrene C-H insertion reactions, many catalysts found to be effective for carbene transfer are also effective for these reactions. Particularly, Rh2(OAc)4 has demonstrated great effectiveness in the inter- and intramolecular nitrene C-H insertions. The exploration of enantioselective C-H amination using chiral rhodium catalysts has been reported by several groups.225,244,253-255 Hashimoto s dirhodium tetrakis[A-tetrachlorophthaloyl-(A)-/ r/-leuci-nate], Rh2(derived rhodium complex, Rh2(i -BNP)4 48,244 afforded moderate enantiomeric excess for amidation of benzylic C-H bonds with NsN=IPh. 

Dirhodium(II) tetrakis(carboxamides), constructed with chiral 2-pyrroli-done-5-carboxylate esters so that the two nitrogen donor atoms on each rhodium are in a cis arrangement, represent a new class of chiral catalysts with broad applicability to enantioselective metal carbene transformations. Enantiomeric excesses greater than 90% have been achieved in intramolecular cyclopropanation reactions of allyl diazoacetates. In intermolecular cyclopropanation reactions with monosubsti-tuted olefins, the cis-disubstituted cyclopropane is formed with a higher enantiomeric excess than the trans isomer, and for cyclopropenation of 1-alkynes extraordinary selectivity has been achieved. Carbon-hydro-gen insertion reactions of diazoacetate esters that result in substituted y-butyrolactones occur in high yield and with enantiomeric excess as high as 90% with the use of these catalysts. Their design affords stabilization of the intermediate metal carbene and orientation of the carbene substituents for selectivity enhancement. 

Chiral rhodium(II) carboxamides are exceptional catalysts for highly enantio-selective intermolecular cyclopropenation reactions (50). With ethyl diazoacetate and a series of alkynes, use of dirhodium(II) tetrakis[methyl 2-pyrrolidone-5-(R)-carboxylate], Rh2(5R-MEPY)4, in catalytic amounts ( 1.0 mol %) results in the formation of ethyl eyelopropene-3-earboxylates (eq 4) with enantiomeric excesses... 

Tetrakis(trimethylphosphine)rhodium(I) chloride loses two trimethylphosphine ligands when allowed to react with PPh3 at elevated temperatures (equation 52). The ionic compound also undergoes a more complex reaction with benzene and sodium. In this a trimethylphosphine ligand is converted to a PMe2Ph ligand (equation 53).186 The geometry adopted by both these complexes... 

In contrast to olefins, little is known on catalytic hydroboration of conjugated dienes. Suzuki and Miyaura20 described a 1,4-addition of catecholborane to acyclic 1,3-dienes, catalyzed with tetrakis(triphenylphosphine)pa]ladium(0). An interesting Markovnikov type regioselectivity was observed in the enantioselective dihydroboration of (E)-1-phenyl-1,3-butadiene with catecholborane, catalyzed by chiral rhodium complexes.21 However, the scope of these reactions is not well known, and the choice of catalysts is very limited. 

In rhodium(II)-catalyzed intermolecular cyclopropanation reactions, chiral dirhodium(II) carb-oximidates provide only limited enantiocontrol. " Tetrakis(5-methoxycarbonyl-2-pyrrolidonato)dirhodium [18, Rh2(MEPY)J, in both enantiomeric forms of the carboxamide ligands, produces the highest enantioselectivities. As can be seen for the cyclopropanation of styrene with diazoacetates, a high level of double diastereoselectivity results from the combination of this chiral catalyst with /- or d-menthyl diazoacetate, but not with diazoacetates bearing other chiral residues.In terms of trans/cis selectivity and enantioselectivity for styrene giving 19 this catalyst is comparable to the Aratani catalysts, but they cannot match the high enantiocontrol of the chiral copper catalysts developed by Pfaltz, Masamune, and Evans vide supra). 

In cyclopropanation reactions with diazoacetamides and rhodium catalysts, diastereoselectivity is much more dependent on the catalyst than with diazoacetic esters (see Section 1.2.1.2.4.2.6.3.2.). Tetrakis(acetamido)dirhodium generally provides enhanced trans (anti) selectivity. For example, A,A -diisopropyl-2-phenylcyclopropane-l-carboxamide was obtained from a-diazo-A.Af-diisopropylacetamide and styrene as follows [catalyst, total yield, ratio (trans/cis)] RhjCOCOCjF l, 51%, 12 Rh2(OAc),, 53%, 64 Rh CNHAc), 47%, 112. 

Hashimoto and coworkers [69] have recently begun to explore the use of chiral rhodium catalysts in the intramolecular dipolar cycloadditirai reactions of indoles, and have applied their methodology to the synthesis of the Aspidosperma ring system. Thus, the cycloaddition of the cyclopropyl carbonyl ylides derived from cyclopropyl diazo-5-imido-3-ketoesters 135 upon treatment with dirhodium (11) tetrakis[Af-tetrachlorophthaloyl-(5)-ferf-leucinate] gave cycloadducts 136 along with the spiro[2.3]hexanes 137 in only moderate yields (Scheme 34). Although the reaction proceeds with exclusive endo diastereoselectivity, only moderate enantioselectivities of up to 66% enantiomeric excess (ee) could be obtained. 

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