Cyclohexane-1,2-diamine metal complexes

Cyclodextrins classification, 920 Cyclohexane-1,2-diamine metal complexes, 34 C.yclohexanc-l,2-dione monooxime metal complexes, 273 Cyclohexane-1,3,5-triamine metal complexes, 50 Cyclohexanone oxime... 

Five- and six-membered rings formed by coordination of diamines with a metal ion have the stereochemical characteristics of cyclopentane and cyclohexane. The ethylenediamine complexes have puckered rings and the trimethylenediamine complexes have chair conformations. The methylene protons are nonequivalent in these nonplanar conformations, taking on the character of equatorial and axial substituents. They are made equivalent as the result of rapid conformational inversion at room temperature, just as in the alicyclic compounds (Fig. 7.1). This has been observed in nmr studies of planar and octahedral complexes of ethylenediamine-type ligands with a number of metals. 

The treatment of complex ion equilibria in solution is analogous to the treatment of weak acids. One of the best known chelators is the well-known EDTA (ethylene diamine tetraacetic acid). The metal stability constants for EDTA are very high, which indicates strong complexes. Various other compounds are available with high metal-stability constants for agricultural or environmental uses. Some of the more important ones are DPTA (diethylene triamine pentaacetic acid), CyDTA (cyclohexane diamine tetraacetic acid), EDDA [ethylene diamine di (0-hydroxyphenyl acetic acid], or Chel-138. 

Among several chiral cyclic and acyclic diamines, (R,R)-cyclohexane-l,2-diamine-derived salen ligand (which can adopt the gauche conformation) was most effective in providing high enantioselectivity [38]. Further, the introduction of substituents at the 3,4, 5 and 6 positions on the aromatic ring of catalyst 39c was not advantageous, and resulted in low enantioselectivity [32,37,39]. The metal ions from first-row transition metals - particularly copper(II) and cobalt(II) - that could form square-planar complexes, produced catalytically active complexes for the asymmetric alkylation of amino ester enolates [38]. 

The compounds that we will study are tris-bidentate complexes with trans-cyclohexane-1,2-diamine (see Section 17.6). We start from [Co(NH3)6]3+ (see Section 17.1). Using the usual tools in HyperChem, edit that complex so that it has six identical Co-N distances of 1.955 A and valence angles involving Co of 90° or 180°. Select the cobalt and the six nitrogen atoms with the select tool and save this structure make sure that the same name also appears as the MOMEC input structure (Setup/Files/Input). Open the module that allows you to compute the structure with the metal center and the six donor atoms fixed Execute/Rigid Geo-metry/Fixed Coordinates. Read File will mark the coordinates to be fixed, i.e., the x,y,z coordinates of the atoms that you have selected in HyperChem. The window shown in Fig. 17.20.1 will appear. 

Relatively soft, late transition-metal Lewis acids are also suitable catalysts for electrophilic fluorination. Indeed, the cationic chiral mthenium(II)-(15,25)-A,/V -bis(o-(diphenyl-phosphino)benzylidene)cyclohexane-1,2-diamine complex is a powerful catalyst for the enantioselective fluorination of (3-keto esters (Scheme 44.25). ... 

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