Ethylenediamine rhodium complexes

For the insertion of noble metal ions into phthalocyanine H2(Pc), the latter is favorably activated by transformation into its lithium derivative. Thus, reaction of Li2(Pc) with [Rh(COD)Cl]2 in a large excess of a donor solvent L yielded the Rh(II) complexes, Rh(Pc) L2 (L = Py, BuNH2, Bipy, Pyz) [119]. The formation of these Rh(II) species is very remarkable because Rh insertions normally yield either Rh(I) or Rh(III) derivatives. Recently, tris(ethylenediamine)-rhodium(III) iodide [Rh(en)3]I3 and phthalodinitrile have been used to prepare H [RhI2(Pc)] 2phthalodinitrile. This material was then transformed into [Rh(OH)2(Pc)] by treatment with first H2SQ4 and then KOH. Treatment of... 

The tris(ethylenediamine) chromium (III) ion was first resolved by Werner6 by means of sodium 3-nitro-(+)-camphor. What has been said concerning the resolution of the corresponding rhodium compound holds true of the chromium compound, except that for the chromium compound the solubility difference of the diastereoisomeric chloride (+)-tartrates is so small that a resolution via these diastereoisomers has not been achieved.5,6 The method reported here is essentially the same as the one described for the rhodium complex but with minor alterations... 

Werner resolved the tris oxalate using strychninium ion in 1912. Other effective resolving agents for the tris complex include (+ )-tris(l,10-phenanthroline)nickel(II), ( + )- or (- )-tris(ethylenediamine)cobalt(III) and (- )-tris(ethylenediamine)rhodium(III). The (- )-[Co(ox)3] ion has been studied by single-crystal methods and has the d configuration. It has been related to (-i-)-[Cr(ox)3] by X-ray powder photography, so its absolute configuration is also established as d by the more exact form of the rule of least-soluble diastereoisomers. ... 

Another very common type of optically-active complex has the general formula [M(AA)2X2]. In this system, it is important to note that the trans isomer has a plane of symmetry and cannot be optically active. Therefore, the cis structure for such a complex is conclusively demonstrated if the complex is shown to be optically active. This technique for proof of structure has often been used the identity of the cis and trans isomers of the complex dichlorobis(ethylenediamine)rhodium(m), structures XXTV, XXV, and XXVI, was determined by this technique. 

Metal salen complexes can adopt non-planar conformations as a result of the conformations of the ethane-1,2-diyl bridge. The conformations may have Cs or C2 symmetry, but the mixtures are racemic. Replacement of the ethylenediamine linker by chiral 1,2-diamines leads to chiral distortions and a C2 chiral symmetry of the complex due to the half-chair conformation of the 5-membered ring of the chelate. Depending on substitution at the axial positions of the salen complex, the symmetry may be reduced to Q, but as we have seen before in diphosphine complexes of rhodium (Chapter 4) and bisindenyl complexes of Group 4 metals (Chapter 10) substitution at either side leads to the same chiral complex. Figure 14.10 sketches the view from above the complex and a front view. 

The observation that IfH(en) > Kh(NH3) is qualitatively supported by the enthalpy and entropy changes associated with the first acid dissociation equilibrium (Table XXII). Increased hydrogen bond stabilization should contribute negatively to both AH°(Kal) and AS°(Kal), which is consistent with the observation for both chromium(III) and rhodium(III) that it is the ammine complexes which have the highest AH°(Kal) and AS°(Kal) values. The greater acid strength of the ethylenediamine systems is then due to a decrease of AH0, which is greater than the decrease of AS0. The AH°(Kai) and param-... 

The activation parameters for the ethylenediamine complexes of rhodium(III) and iridium(III) are also in keeping with an essentially dissociative mechanism. The observation that AHt(k-t) is larger than AHt(k 2) for iridium(III) has been rationalized in terms of stabilization of the aquahydroxo species by intramolecular hydrogen bond formation. Similarly, the observation for the rhodium(III) system that AHl(k ) < AHt(k-2) for ammonia, whereas A// (, ) AHt(k 2) for ethylenediamine may, in part, by rationalized in terms of the observed differences in the degree of intramolecular hydrogen bond stabilization of the aqua hydroxo species in the two systems [ZCH(en) > J h(NH3) see Table XXI]. 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

The platinum(IV), rhodium(III), and iridium(III) sepulchrates, dinitrosarcophaginates, and diaminosarcophaginates have been synthesized in high yields (45-65% for Pt(IV), 40% for Ir(III), and 90-100% for Rh(III)) starting from their tris-ethylenediaminates [94, 156, 157]. The rhodium (III) and iridium(III) complexes were prepared in a similar manner to that for cobalt (III) complexes, except of the elevated temperatures (Rh, 60°C Ir, 90°C) required for the quoted yields. Moreover, if chiral [Rh(en)3] cation was used initially, clathrochelate complexes were obtained in ca 100% chemical and chiral yields, despite the seven centres of chirality [157]. 

While the absolute configuration of transition metal catecholates has not been determined by x-ray diffraction, the assignments are based on several lines of reasoning. In particular, for both the rhodium(III) and chromium(III) complexes, that isomer precipitated by A-tris(ethylenediamine)cobalt(III) is assigned the A configuration. 

Treatment of aqueous solutions of bis(ethylenediamine)dichloro-rhodium(III) with sodium borohydride give solutions which the proton magnetic resonance spectrum shows to contain an Rh—H complex (t 31 p.p.m., J Rh—h 31 c.p.s.). Also, the infrared spectrum of the precipitated tetraphenyl boronate shows a band at 2100 cm-1 assigned to an Rh—H stretch. 

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