Rhodium isocyanides

Dimeric chloride initiators, 14 267 Dimeric fullerenes, 12 233, 252 Dimeric Lewis acids, 14 267 Dimeric rhodium isocyanide complexes, 19 648... 

A report has appeared of the results of energy-transfer and electron-transfer quenching experiments involving the A2 excited state of some binuclear rhodium isocyanide complexes, e.g. [Rh2(br)4], where br = 1,3-di-isocyanopropane, and [Rh2(TMB)4] , and TMB = 2,5-dimethyl-2,5-di-isocyanohexane. Detailed... 

An analogous mode of reaction is observed in the C-CN cleavage of ben-zonitriles with sUylmetal complexes [72]. For example, a silylrhodium complex initially forms an r -iminoacylrhodium complex (Scheme 1.55). The aryl group of the iminoacyl moiety migrates onto rhodium to form a rhodium isocyanide complex. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Lithium 1,2,4-triazolate with [Rh2( j,-Ph2PCH2PPh2)(CO)2( j.-Cl)]PFj. gives the A-framed complex 177 (L=L = CO) (86IC4597). With one equivalent of terf-butyl isocyanide, substitution of one carbon monoxide ligand takes place to yield 177 (L = CO, L = r-BuNC), whereas two equivalents of rerr-butyl isocyanide lead to the product of complete substitution, 177 (L = L = r-BuNC). The starting complex (L = L = CO) oxidatively adds molecular iodine to give the rhodium(II)-rhodium(II) cationic species 178. 

The most interesting work on the isocyanide complexes of the elements in this subgroup has been done with rhodium and iridium. For the most part, the work is involved with the oxidative addition reactions of d square-planar metal complexes. 

The preparations of a number of rhodium(I) complexes of isocyanides, some of them new, have been described. The newtetrakis(methyl isocyanide) complex, [Rh(CNCH3)4], was isolated as salts of various anions from reactions of RhClj -3H20 or [(l,S-CgH,2)RhCl]2 and this isocyanide ligand (11), and several [Rh(CNR)4]+ alkyl and aryl isocyanide complexes (R= Bu, Pr, /)-C6H4C1, /.-CSH4CH3, and P-C6H4OCH3) have... 

If RhCl3 SHjO and methyl isocyanide are reacted under mild conditions, and then 1 added, the rhodium(III) isocyanide complex Rh(CNCH3)3l3 is obtained (11). 

Alternatively, rhodium catalysts have been revealed to be effective for the coupling of two alkynes with an isocyanide to afford the iminocyclopentadienes 62 and 62 in high yield (Tab. 11.9) [36bj. The coordinating solvent dibutyl ether, in combination with por-tionwise addition of the isocyanides, is key to the success of this transformation. 

Tab. 11.9 Rhodium complex-catalyzed coupling of various diynes with isocyanide.

Finally, the recent synthesis of a series of two-dimensional isocyanide coordination polymers containing rhodium(I) could lead to the development of a new area of metal-containing polymers (50-52). 

Rhodium(I) or polymer supported rhodium(I) compounds catalyzed the formation ofFefCO - CNR L (x = 1 - 3 R = Bu, xylyl L = MA, citra-conic anhydride, acrylamide) (29, 30), and the dimer [CpFe(CO)2]2 catalyzed the stepwise substitution of carbonyl groups in CpFeI(CO)2 to give CpFeKCO - CNR) (x = 1,2 R = Bu, xylyl) in 60-80% yields. A nonchain free-radical mechanism was proposed for the latter reaction (28). The compounds CpFeX(CO)2 x(CNR)x (x = 1,2 X = halide, SiMe3) are known for a range of alkyl and aryl isocyanides (169-171). 

Reactions of isocyanides with metal-metal multiple-bonded dimers of molybdenum, rhenium, ruthenium, and rhodium have effected cleavage of... 

The ability of the cations [M(CNR)4]+ (M = Rh, Ir) to self-associate is a function of steric crowding in the molecule, and for bulky R groups monomeric species predominate. An estimate has been made of the steric size of isocyanides in terms of fan-shaped angles and as part of this study the structure of RhCl(CNC6H2Bu -2,4,6)3 has been elucidated (126). The structural determinations of a series of dimeric rhodium(I) isocyanide salts have been completed. An eclipsed configuration was found for [Rh2 CN (CH2)3NC)4](BPh4)2 NCMe (42)2 (287), whereas [Rh2(CNPh)8]-... 

A linear tetramer has recently been isolated from reactions on xylyl isocyanide with (CODRhCl)2 in methanol solution (32). An X-ray structural determination (279) has shown it to be 118 containing four rhodium... 

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