Tris amines, chromium complexes

Chromium(II) complexes of bipyridyls, terpyridyl and the phenanthrolines have been discussed in Section 35.2.2.1. Complexes of the ligands 2-aminomethylpyridine (pic, 2-picolyl-amine) and 8-aminoquinoline (amq), which have one heterocyclic and one amino nitrogen donor atom, have been prepared by methods similar to those in Scheme 10. The bis(amine) complexes are typical high-spin, distorted octahedral complexes, and the mono(amine) complexes, from their antiferromagnetic behaviour and reflectance spectra, are six-coordinate, halide-bridged polymers (Table 15).103 No tris(amine) complexes could be prepared so the attempt to find spin isomeric systems in octahedral chromium(II) systems was unsuccessful ([Cr(en)3]X2 are high-spin and [Cr(bipy)3]X3 and [CrX2(bipy)2] low-spin). 

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). 

It has been found4 that a good yield may be obtained rapidly by allowing the commercially available green chromic chloride, CrCl8-6H20, in methanol to boil under reflux with ethylenedi-amine in the presence of metallic zinc. The product, hydrated tris(ethylenediamine)chromium(III) chloride, is obtained as a solid and is readily purified. An exactly similar procedure may be used for the complex of 1,2-propanediamine. 

Tricarbonylchromium stabilized benzylic carbocations can be captured by a large variety of nucleophiles, such as alcohols, amines, thiols, nitriles, trimethylsilyl enol ethers, allylsilanes, electron-rich aromatics, dialkylzincs, and tri-alkylaluminums (eq 19). The relative stereochemistry formed during these reactions via carbocations in acyclic systems proceeds with net retention. Friedel-Crafts acylation of (styrene)chromium complexes has been explored via the benzylic cations (eq 20). Tricarbonylchromium-stabilized oxonium ions are also utilized for steroselective carbon-carbon bond forming reactions (eq 21). ... 

VC13 with primary amines gave similar derivatives containing one coordinated amide and one or more molecules of amine,64 but ethylenediamine186,187 and propylenediamine186 give [V(L)3]C13 (L = en, pn). These are isomorphous with the chromium(III) complexes the chlorine atoms are ionic, and the cations are tris-bidentate. 

Chromium(II) forms the trigonal bipyramidal complex [CrBr(Me6tren)]Br with the tripod ligand tris(2-dimethylaminoethyl)amine (Me6tren) (Section 35.3.4.3), and pyrazolyl-substituted ligands also form five-coordinate complex cations (Section 35.3.3.4.v see also Table 42). 

Chromium(II) complexes of the ligands l,l -methylenedipyrazole (11 H2Cpz2), l,l -methyl-enebis(3,5-dimethylpyrazole) (12 H2Cdmpz2), tris(l-pyrazolyl)methane (13 HCpz3),10S tris(l-pyrazolylethyl)amine (14 R = H, TPyEA)106,107 and tris(3,5-dimethyl-l-pyrazolylethyl)amine... 

Part A illustrates a general method of preparing a,0-unsaturated j8-keto amines (/3-keto imines cf. synthesis 13), a class of weakly acidic bidentate ligands. Part C illustrates the use of chromium(III) chloride-tris(tetrahydro-furan) in the synthesis of a chromium(III) complex under nonaqueous conditions. 

Alkyllithium addition to the (ti -arene) dicarbonylchromium imine chelates has been examined. Treatment of optically pure chelate (41) with methyllithium provides amine (42) with an enantiomeric excess of 94% (Scheme 5). No diastereoselectivity was reported for alkyllithium additions to (arene)tri-carbonylchromium complex (40). In the absence of additional examples, the generality of this chromium chelate methodology for asymmetric amine synthesis cannot be assessed. 

The voluntary withdrawal of chromated copper arsenate (CCA) as a wood preservative for domestic applications was driven by public concerns over its health and environmental profile. In its place have risen two competing systems, the amine copper quat (ACQ) system and the copper azole system. Both systems avoid using heavy metals such as chromium and arsenic and rely on the co-biocidal effects of copper and organic biocides. The elimination of CCA has created many opportunities for oleochemicals as preservative companies try to develop formulations that are not only environmentally friendly but can also match the preservative performance of CCA [66]. The ACQ system is based on didecyldimethyl ammonium bicarbonate and has produced a significant demand for ClO-based amine and quat. The azole systems use biocides such as tebuconazole and propiconazole in combination with copper ethanolamine complexes. Ethoxylated amines [67] and amine oxides [68] have been described as providing improved performance in azole-based systems. Other copper systems have employed ethoxylated diamines [69] and amine oxides [70] to enhance performance. 

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