III -Amine Complexes

Submitted by DAVID BERMAN, CARY BOKERMAN, and R. W. PARRY  

Checked by WILLIAM C. SEIDEL.f JOHN A. FETCHIN,t DAVID G. HOLAH.t and JOHN P. FACKLER, JR.f 

The synthesis of [Cr(NH3)6]Cl3 from anhydrous chromium(III) chloride and liquid ammonia in the presence of catalytic quan- 

Balthis and Bailar obtained tris(ethylenediamine)chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt(III) complexes. Mori described the preparation of hexaamminechromium(III) salts from the oxidation of chro-mium(II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic. Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer, in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product. The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

Approximately 2 g. of shredded asbestos slurried in 15 ml. of water is added to a solution containing 10 g. of sodium formate in about 30 ml. of water the solution is boiled gently, then about 80 ml. of a 5% platinum(II) chloride solution is added. The solution is boiled until the platinum has been deposited. 

---

Mechanisms of substitution of octahedral cobalt(III) amine complexes. C. K. Poon, Inorg. Chim. Acta, Rev., 1970, 4, 123-144 (131). 

Barraclough CG, Eawrance GA, Fay PA. 1978. Characterization of binuclear /r-peroxo and /Li-superoxo cobalt(III) amine complexes from Raman spectroscopy. Inorg Chem 17 3317. 

In the present study the surface chemistry of birnessite and of birnessite following the interaction with aqueous solutions of cobalt(II) and cobalt(III) amine complexes as a function of pH has been investigated using two surface sensitive spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The significant contribution that such an investigation can provide rests in the information obtained regarding the chemical nature of the neat metal oxide and of the metal oxide/metal ion adsorbate surfaces, within about the top 50 of the material surface. The chemical... 

In the final analysis, it may be that both conjugate base and bimolecular mechanisms are operative in the base hydrolysis of Cr(III) amine complexes (115). 

Complexes of (( Ir(III) are kinetically inert and undergo octahedral substitution reactions slowly. The rate constant for aquation of [IrBr(NH3)5]2+ [35884-02-7] at 298 K has been measured at -2 x 10-10 s-1 (168). In many cases, addition of a catalytic reducing agent such as hypophosphorous acid greatly accelerates the rate of substitution via a transient, labile Ir(H) species (169). Optical isomers can frequently be resolved, as is the case of ot-[IrCl2(en)2]+ [15444-47-0] (170). Ir(III) amine complexes are photoactive and undeigo rapid photosubstitution reactions (171). Other iridium complexes... 

The three different tetranuclear structures which have been observed in the crystalline state are the two compact structures 6 and 8 and the chain structure 7a. Structure 6 is found in [Co4(NH3),2(OH)6]C16-8H20 and its amine analogs (52 59). The analogous ammonia and ethylenediamine chromium(III) complexes Cr4(NH3)12(OH)66+ and Cr4(en)6(0H)66+ have been characterized quite recently (40, 41, 42, 60). Structure 7a has so far been observed (42) only in a chromium(III) amine complex, Cr4(en)6(OH)66+, but, as discussed in Section IV, both structures 7b and 7c are possible structures for the tetranuclear aqua chromium(III) species. Structure 8 is known from the so-called rhodoso complex, Cr4N12(OH)66+ [N12 = (NH3)12 or (en6] (61, 62). 

The circular dichroism (CD) spectra of optically active di-, tri-, and tetranuclear complexes of chromium(III) and cobalt(III) have been reported and used to establish the complexes absolute configurations (55 59, 111, 115, 116, 152-157). The changes in circular dichroism resulting from ion pairing have been studied for the tetranuclear hexol Co j(OH)2Co(NH,)4J, h+ and have been shown to be attributable to the vicinal effect of the chiral oxygen centers produced stereospecifically by the ion-pair formation (56). For a series of trinuclear cobalt (III) amine complexes, cis-Co(CN)2[(OH)2Co(N4)2 J3 +, it was shown that the main CD contributions due to the two chiral Co(OH)4(CN)2 and Co(N4)(OH)2 centers are additive (155). In the case of the related tetranuclear complex Co((OH)2Co(en)2J,< + this postulate of additivity of CD spectra proved unsatisfactory (57). 

From the values given in Table XIII it is noted that Kd is apparently much more sensitive to variation of the nonbridging ligands than to variation of the metal ion. It is seen that Kd for all the aqua metal ions lies within a relatively narrow range of about 103 5 M-1. In contrast, chromium(III) and cobalt(III) amine complexes have Kd values which vary by at least five orders of magnitude. 

For example, the r0 value for the Co-N bond in cobalt(III)-amine complexes is smaller in parameterization schemes where 1,3-nonbonded interactions between the ligating atoms are included, than in force fields where only L-M-L angle bending functions are used. This is because the 1,3-nonbonded interactions in such complexes are highly repulsive, promoting an extension of the Co-N bonds. Thus, a smaller value for the ideal Co-N bond is required in order to reproduce the experimentally ob-... 

Several recent publications are focused on allylic and benzylic tosylamida-tions of a range of unsaturated hydrocarbons with Phi = NTs [192-196]. Salen-Mn(III) complexes, Ru(II) and Mn(III)-porphyrins, and Ru(II)- and Ru(III)-amine complexes were employed as catalysts for this purpose, and issues pertaining to catalyst efficiency and enantioselectivity of tosylamidation were addressed. Examples are shown in Scheme 71 [192,193]. 

Hydrolysis of cobalt(III) amine complexes occurs by two routes. One route is pH-independent, which is usually measured in acidic conditions and is thus often termed acid hydrolysis or aquation. The second route, base hydrolysis, is usually first order in hydroxide ion and complex concentration, although under certain conditions the reaction may become independent of [OH ] or dependent on the general base (156). 

D.J. Williams, J.S. Kruger, A.F. McLeroy, A.P. Wilkinson, and J.C. Hanson, Iridium(III) Amine Complexes as High-stability Structure-directing Agents for the Synthesis of Metal Phosphates. Chem. Mater., 1999, 11, 2241-2249. 

For many electrochemical reactions, values of E, and hence k are unknown so that the intrinsic barrier cannot be obtained experimentally. For example, the reductions of substitutionally inert Co(III)-amine complexes to the corresponding Co(II) species are accompanied by rapid following steps to form [CofOHj) ] . Nevertheless, rate-potential data still can be obtained for such systems which are directly related to corresponding homogeneous redox reactions in thejollowing two ways. 

These reactions can be attributed to the excitation of charge-transfer states. High-energy UV irradiation (A < 200 nm) leads to high-quantum-yield photoreduction of Ru(III) amine complexes. Another photoredox-induced substitution is the result of exciting the intervalence charge-transfer band of the ion pair. ... 

---