Ligands tridentate

Coordination of the dianion [S4N4] as a tridentate ligand has been established in a few cases. The complexes IrCl(CO)(S4N4)PPh3 and... 

Cationic complexes of rran.s-chelating tridentate ligand, (/ ,/ )-4,6-dibenzo-furandiyl-2,2 -bis(4-phenyloxazoline), with transition metal(II) perchlorates as effective catalysts for asymmetric cycloaddition of nitrones 98YGK368. 

The cationic aqua complexes prepared from traws-chelating tridentate ligand, R,R-DBFOX/Ph, and various transition metal(II) perchlorates induce absolute enantio-selectivity in the Diels-Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazoli-dinone dienophiles. Unlike other bisoxazoline type complex catalysts [38, 43-54], the J ,J -DBFOX/Ph complex of Ni(C104)2-6H20, which has an octahedral structure with three aqua ligands, is isolable and can be stored in air for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. 

Attention has increasingly focused on neutral ligands diat can complex to cuprate reagetits dirougli soft beteroatoms sudi as sulfur and phosphorous fSclieme 3.50) [218-219]. Leyetidecker s bydroxyproline-derived tridentate ligand IS repre-... 

The tridentate ligands C, L and M are effective catalysts for the enantioselective addition of dialkylzincs to aromatic aldehydes16,17. In particular, ligands L and M qualify as members of the chemical enzyme (chemzyme) class of synthetic reagents17, since they function in a predictable, clear-cut mechanistic way. As demonstrated by X-ray diffraction, the actual catalyst is a monomeric zinc chelate 2 formed in toluene at 50 C by reaction of L or M with one equivalent of diethylzinc. 

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

The sulphoxide (SDE) acts as a tridentate ligand in the 1 2 complexes and as bidentate ligand in the 1 3 complexes shown in Scheme 19. 

The crystal structure of a mono(cyclopentadienyl)zirconium complex containing a novel Me2Si-linked bis(amidinate) ligand was reported (Scheme 203). In this compound the central Zr atom is octahedrally coordinated with the bis(amidi-nate) acting as a tridentate ligand. ... 

Recent studies have been directed towards the synthesis of heterocyclic hydrazones which have lower toxicities than thiosemicarbazones [44], It has been proposed that the hydrazinic N-H group is essential for activity since it might be involved in a crucial radical formation step important in the mechanism of RDR. This is supported by the loss of antileprotic activity for this series of compounds when the hydrazinic hydrogen is replaced by a methyl group [44]. The heterocyclic hydrazones, like thiosemicarbazones, behave as tridentate ligands. 

The S-methyldithiocarbazates of both 2-picolylphenylketone, 16, and 2,6-luti-dylphenylketone, 17, yielded high spin iron(Ill) complexes, [Fe(15-H)Cl2(H20)] and [Fe(16-H)Cl2(H20)] [144]. Both complexes involve a tridentate ligand bonding via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. 

S-methyldithiocarbazates of 2-formylquinoline, 18, and 1-formylisoquinoline, 19, have been found to act as anionic tridentate ligands with iron(III) forming [FeLj] [FeC ] on isolation from a dimethoxypropane-ethanol mixture [145]. No new spectral data was provided when [Fe(19-Fl)2] [FeCl4] was included in a more recent paper [146],... 

Methyl-3-formylpyrazole thiosemicarbazone, 40, yielded [Ni(40)2]A2 (A = Cl, Br, NO3, BF4, CIO4 and 1/2 SO4) from weakly acidic solution [190]. The molecule 40 bonds as a NNS tridentate ligand and all complexes behave as 1 2 electrolytes. Their electronic spectra are consistent with an octahedral stereochemistry and Dq values range from 1111-1190 cm and B values from 629 to 741 cm" ... 

Methyl-3-formylpyrazole A-phenylthiosemicarbazone, 45, coordinates as a deprotonated NNS tridentate ligand to form the diamagnetic, spin-paired [Ni(45-H)NCS] complex [200]. However, the complexes formed with other nickel(II) salts have stoichiometry [Ni(45)2]A2, where A = Cl, Br, NO3, CIO4, and BF4. These octahedral complexes NNS coordinated neutral hgands have Dq values between 1086 and 1150cm" ... 

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