Rhodium ii

Halpem, E. Kimura, J. Molin-Case, and C. S. Wong, Chem. Comm., 1971, 1207. 

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The reaction of thiocarbonyl compounds with diazoalkanes (alkyl, aryl substituted) frequently gives good to excellent yields of thiiranes. The mechanism may involve addition of a carbene across the thiocarbonyl group, especially in the presence of rhodium(II) acetate... 

There are several examples of intramolecular reactions of monocyclic /3-lactams with carbenes or carbenoids most of these involve formation of olivanic acid or clavulanic acid derivatives. Thus treatment of the diazo compound (106) with rhodium(II) acetate in benzene under reflux gives (107), an intermediate in the synthesis of thienamycin (80H(14)1305, 80TL2783). 

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 rhodium(II) acetate catalyzed reaction of 2-(3-oxo-2-diazobutyryl)-1,2,3,4-tetrahydroisoquinoline in boiling toluene yielded 2-methyl-4,6,7,l 16-tetra-hydro[l, 3]oxazino[2,3-n]-isoquinoline-4-one in 72% yield (99TL8269). 

Until recently, well-authenticated cases of the rhodium(II) oxidation state were rare, with the exception of the dinuclear carboxylates. They fall into two main classes, although there are other rhodium(II) complexes ... 

Reaction of RhCl3.3H20 with bulky tertiary phosphines at room temperature or below generally leads to reduction to rhodium(II). 

The second class of rhodium(II) complexes is the dimers [71]. The dimeric... 

Figure 2.35 The lantern structure adopted by dimeric rhodium(II) carboxylates.

ESCA data support a rhodium(II) oxidation state in these compounds. Therefore, the Rh 3d5//2 binding energy is c. 309.2 eV in simple car-boxylates, midway between those in typical rhodium(I) complexes (c. 308.5 eV) and rhodium(III) complexes (c. 310.7 eV) [72],... 

The diamagnetism of all these rhodium(II) compounds indicates spin pairing via a metal-metal bond. 

Part of the upsurge in interest in rhodium(II) carboxylates since the early 1970s results from the discovery that they have potential as anti-tumour... 

Photolysis of the rhodium(III) complex of octaethylporphyrin gives a rhodium(II) dimer that readily undergoes addition reactions to afford rhodium(III) species (Figure 2.42). 

Figure 2.42 Synthesis of a dimeric rhodium(II) octaethylporphyrin complex.

The dinuclear rhodium(II) acetate is described in section 2.8.2 the dinuclear structure is retained on one-electron oxidation, but when ozone is used as the oxidant, a compound with a trinuclear Rh30 core is formed, analogous to those formed by Fe, Cr, Mn and Ru. (It can also be made directly from RhCl3.)... 

The rhodium(II) compound is a diamagnetic dimer with oxygen it forms a paramagnetic monomeric 02 adduct, probably a superoxide complex represented as (porph)Rh3+02. 

The iridium(II) complexes are rarer that those of rhodium(II). Iridium does not seem to form carboxylates Ir2(02CR)4 with the lantern structure complexes analogous to trans-RhX2 (PR3 )2 are not formed with bulky tertiary phosphines, probably because the greater strength of Ir-H bonds leads to IrHX2(PR3)2. 

Aryls have recently been synthesized [188], including a rare rhodium(II) compound (Figure 2.106). 

From a study of the decompositions of several rhodium(II) carboxylates, Kitchen and Bear [1111] conclude that in alkanoates (e.g. acetates) the a-carbon—H bond is weakest and that, on reaction, this proton is transferred to an oxygen atom of another carboxylate group. Reduction of the metal ion is followed by decomposition of the a-lactone to CO and an aldehyde which, in turn, can further reduce metal ions and also protonate two carboxyl groups. Thus reaction yields the metal and an acid as products. In aromatic carboxylates (e.g. benzoates), the bond between the carboxyl group and the aromatic ring is the weakest. The phenyl radical formed on rupture of this linkage is capable of proton abstraction from water so that no acid product is given and the solid product is an oxide. 

The chemistry, structure and metal-metal bonding in compounds of rhodium(II). T. R. Felthouse, Prog. Inorg. Chem., 1982, 29, 73-166 (353). 

Much of the early work into the rhodium(II)-catalysed formation of oxazoles from diazocarbonyl compounds was pioneered by the group of Helquist. They first reported, in 1986, the rhodium(II) acetate catalysed reaction of dimethyl diazomalonate with nitriles.<86TL5559, 93T5445, 960S(74)229> A range of nitriles was screened, including aromatic, alkyl and vinyl derivatives with unsaturated nitriles, cyclopropanation was found to be a competing reaction (Table 3). 

A series of catalysts was also screened in the reaction with benzonitrile to give methyl 2-phenyl-5-methoxyoxazole-4-carboxylate, with rhodium(II) acetate being the most effective (Table 4).<93T5445>... 

Helquist s work on the use of diazomalonate in the synthesis of oxazoles has been extended to other diazocarbonyl compounds in our own laboratory.<92TL7769, 94T3761> Thus it was found that sulfonyl-, phosphonyl- and cyano-substituted diazoesters gave the corresponding 4-functionalised oxazoles 30 in acceptable yield (Scheme 20). In many cases the yield of oxazole was significantly improved by the use of rhodium(II) trifluoroacetamide as catalyst. The 4-cyano-oxazole 30 (R = Me, Z = CN) proved interesting in that it allowed the formation of a bis-oxazole 31 by a second rhodium catalysed reaction (Scheme 20). 

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