Rhodium complexes Schiff bases

Rhodium complexes with oxygen ligands, not nearly as numerous as those with amine and phosphine complexes, do, however, exist. A variety of compounds are known, iucluding [Rh(ox)3] [18307-26-1], [Rh(acac)3] [14284-92-5], the hexaaqua ion [Rh(OH2)3] [16920-31 -3], and Schiff base complexes. Soluble rhodium sulfate, Rh2(804 )3-a H2 0, exists iu a yellow form [15274-75-6], which probably coutaius [Rh(H20)3], and a red form [15274-78-9], which contains coordinated sulfate (125). The stmcture of the soluble nitrate [Rh(N03)3 2H20 [10139-58-9] is also complex (126). Another... 

Butyne-l,4-diol has been hydrogenated to the 2-butene-diol (97), mesityl oxide to methylisobutylketone (98), and epoxides to alcohols (98a). The rhodium complex and a related solvated complex, RhCl(solvent)(dppb), where dppb = l,4-bis(diphenylphosphino)butane, have been used to hydrogenate the ketone group in pyruvates to give lactates (99) [Eq. (15)], and in situ catalysts formed from rhodium(I) precursors with phosphines can also catalyze the hydrogenation of the imine bond in Schiff bases (100) (see also Section III,A,3). 

The main product is always the (R)-enantiomer of (28) 64). Employing other chiral catalysts, e.g. Schiff bases prepared from (S)-alaninemethyl ester or (S)-valinemethyl ester and 2-pyridinecarboxaldehyde in form of their rhodium complexes, in the same reaction, no or only very low asymmetric induction was observed. 

Beyond the 3+ oxidation state, rhodium forms a limited number of complexes in the 4+, 5+ and 6+ oxidation states. A recent review1221 gives an excellent summary of the chemistry of the higher oxidation state chemistry of Rh (as well as Ru, Os, Ir, Pd and Pt). For the 4+ oxidation state, the hexafluoro, hexachloro and trioxo dianions are well characterized. The known neutral species include RhF4 and some oxides. There are also scattered reports of Rhlv complexes containing substituted biguanides and Schiff base chelates. 

Some of the complexes produced thus may be made directly from rhodium trichloride, however. Interaction of the carbonyl chloride with a Schiff base (salen type) leads to metallomesogens (liquid crystals) such as (18-G-IV).2... 

Nonplanar or highly substituted Schiff bases also confer steric protection upon their rhodium(II) complexes. By contrast relatively simple thio ligands such as... 

The reaction of benzothiazoline 148 with RhCl(PPh3)3 gives rhodium(III) complex 149 as determined by X-ray diffraction <03CL1058>. The nickel(II) Schiff base complex 150 is also synthesized from the corresponding benzothiazoline <03BCJ127>. 

Palladium, rhodium and ruthenium complexes of the Schiff base salen are synthesized in the supercages of zeolite Y. The existence of intracrystalline transition metal-salen complexes is verified by a detailed physicochemical characterization. The catalytic properties of the prepared host/guest inclusion compounds are explored in the hydrogenation of hexene-(l) or an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l). 

It has recently been reported [58] that Schiff bases undergo rhodium(I) complex-catalyzed hydrosilylation under mild conditions, equation (25). 

An effective asymmetric reduction of Schiff bases to optically active secondary amines via catalytic hydrosilylation using (+)-DIOP-rhodium complex (6) has been... 

In Table 20 are listed results of asymmetric reduction of certain cyclic Schiff bases by the use of diphenylsilane-(+)-DIOP-rhodium complex combination, equation (26). The optical yields are significantly affected by the bulkiness of substituents R. 

Mesomorphic Schiff-bases can also complex two square planar cw-[M(C02)]-moities with M=rhodium or iridium [117]. The complexes, 51, show SmA behavior. 

The reaction of the free ligand Bu4salonphenH2 with [Rh(/it-Cl)(H2C=CH2)2]2 it th presence of NR4OH in refluxing ethanol yielded the Schiff-base rhodium complexes Rh(R)(Bii4salophen), with R = Et 277 and -Bu 278, respectively. The reaction of Rh(H)(Bu4salophen) with CO afforded the formyl complex Rh(CHO)(Bu4salophen) 279344... 

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