Tetradentate

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

Eig. 1. Types of chelates where (1) represents a tetracoordinate metal having the bidentate chelant ethylenediamine and monodentate water (2), a hexacoordinate metal bound to two diethylenetriamines, tridentate chelants (3), a hexacoordinate metal having triethylenetetramine, a tetradentate chelant, and monodentate water and (4), a porphine chelate. The dashed lines iadicate coordinate bonds. 

Forma n dyes bear a formal resemblance to a2o dyes, since they contain an a2o group but have sufficient stmctural dissimilarities to be considered as a separate class of dyes. The most important forma2an dyes are the metal complexes, particularly copper complexes, of tetradentate forma2ans. They are used as reactive dyes for cotton (81) is a representative example. 

MeCN. The structure of the anion (Fig 24.4b) can be envisaged as a tridentate [ReHg] ligand coordinated to ReCtriphos)" ", and, since the metal atoms are only 259.4 pm apart, is said to involve an Re=Re triple bond (in which case the [ReHg] should be regarded as tetradentate and its Re atom as 10-coordinated). 

In all the compounds of known structure, ruthenium is 6-coordinate therefore, in complexes like Ru(EDTAH)(H20) [131], the acid is penta-dentate, with a free carboxylate group likewise, in K[Ru(EDTAH2)C12] and [Ru(EDTAH2)(dppm)] two of the carboxylates are protonated, so it is tetradentate. 

The most common catalysts for ATRP are complexes based on a copper(T) halide and nitrogen based ligand(s). Various ligands have been employed and those most frequently encountered are summarized in Table 9.5. Typically, four nitrogens coordinate to copper. The bidentate bipyridyl (bpy) ligands 132-133 are known to form a 2 1 complex. The tetradentate ligands are expected to form a 1 1 complex. 

Complexes of open chain tetradentate ligands containing heavy donor atoms. C. A. McAuliffe, Adv. Inorg. Chem. Radiochem., 1975,17,165-187 (58). 

Structural aspects of metal complexes with some tetradentate Schiff bases. M. Calligaris, G. Nardin and L. Randaccio, Coord. Chem. Rev., 1972, 7, 385-403 (56). 

Complexes of tetradentate ligands containing phosphorus and arsenic. L. M. Venanzi, Angew. Chem., Int. Ed. Engl., 1964,3, 453-460 (27). 

The spectra and structure of transition metal complexes with tetradentate macrocyclic ligands. K. B. Yatsimirskii and Y. D. Lampeka, Russ. Chem. Rev. (Engl. Transl), 1980, 49,1003-1020 (191). 

Cirunwald-Winstein analysis, 1,505 thiocyanates, 3, 729 thiourea, 3, 755 tricyanomethides, 3, 709 triethylenetetramine, 3, 722 tripod ligands tetradentate, 3,734... 

Formazan, l-(2-hydroxy-5-suIfophenyl)-3-phenyl-5-(2-carboxyphenyl)-zinc detection, 6, 83 Formazans cobalt complexes dyes, 6, 81 metal complexes bidentate, 6, 78 color photography, 6,111 dyes, 6, 77 tetradentate, 6, 81 tridentate, 6, 79... 

The same, distorted, octahedral geometry is also found in a number of monomeric diorganotin complexes having two bidentate ligands, such as MejSn(0-NMe-C0-Me)2 (379) and Me Sn(S-CS-NMei)2 (380), or one tetradentate group, such as Me2Sn(salen) (381). 

Most of the tetradentate equatorial ligands have a complex structure and, since their systematic names are often cumbersome, abbreviations and... 

Encapsulation in Y zeohte was also the method chosen to immobihze Mn complexes of C2-symmetric tetradentate hgands (Fig. 24) [75]. These materials were used as catalysts for the enantioselective oxidation of sulfides to sulfoxides with NaOCl. The lack of activity when the larger io-dosylbenzene was used as an oxidant was interpreted as an indication that the reaction took place inside the zeolite microporous system. Both the chemo- and enantioselectivity were dependent on the structure of the sulfide. (2-Ethylbutyl)phenylsulfide led to better results than methylphenylsulfide, although in all cases the enantioselectivity was low (up to 21% ee). 

There are very few examples of asymmetric synthesis using optically pure ions as chiral-inducing agents for the control of the configuration at the metal center. Chiral anions for such an apphcation have recently been reviewed by Lacour [19]. For example, the chiral enantiomerically pure Trisphat anion was successfully used for the stereoselective synthesis of tris-diimine-Fe(ll) complex, made configurationally stable because of the presence of a tetradentate bis(l,10-phenanthroline) ligand (Fig. 9) [29]. Excellent diastereoselectivity (>20 1) was demonstrated as a consequence of the preferred homochiral association of the anion and the iron(ll) complex and evidence for a thermodynamic control of the selectivity was obtained. The two diastereoisomers can be efficiently separated by ion-pair chromatography on silica gel plates with excellent yields. 

An iron complex-catalyzed enantioselective hydrogenation was achieved by Morris and coworkers in 2008 (Scheme 13) [49]. Reaction of acetophenone under moderate hydrogen pressure at 50°C catalyzed iron complex 12 containing a tetradentate diimi-nodiphosphine ligand in the presence of BuOK afforded 1-phenylethanol with 40% conversion and 27% ee. 

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