Facial coordination

A large body of work with particular reference to the mimicry of mononuclear zinc enzymes has utilized tris(pyrazolyl)borate ligands. This ligand class offers a facial coordination mode of three pyrazole A-donors and can be functionalized in the three and five positions on the rings to increase steric bulk and vary the electronic properties of the ligand. The synthesis and complex formation with these ligands has been extensively reviewed.2,21 219... 

Reactions with Tridentate Facial Coordinating Ligands. . . 168... 

Reactions with Tridentate Facial Coordinating Ligands... 

Koyama Yoshino, 1972). This ligand will coordinate such that the metal-ion lies out of the mean plane of the donor atoms and, for example around one face (24) when occupying three coordination positions in an octahedral metal complex. This ligand system is thus restricted to facial coordination in contrast to corresponding open-chain derivatives [which, in principle, may coordinate in either a facial (25) or a meridional (26) manner]. 

The molecule [ReI(MQ+)(CO)3(dmb)]2+ has been a model system for studying intramolecular electron transfer over the last two decades. Here, MQ+ is the monodentate ligand Af-methyl-4,4/-bipyridinium, dmb is the bidentate ligand 4,4r-dimethyl-2,2r-bipyridine, and the three CO ligands are facially coordinated. Irradiation of this complex at room temperature in solution with near-UV light leads to a sequence of intramolecular electron-transfer events as shown in Fig. 7. 

Inspired by the 2-His-l-carboxylate facial triad our interest focused on the development of a new facially coordinating tripod ligand which... 

A control experiment with the unfunctionalized methyl bis(3,5-dimethylpyrazol-l-yl)acetate (51) showed no occupancy of the polymer sites and subsequently no A and A" signals but a typical IR spectrum of Merrifield polymer. Therefore, the results of our experiments prove a facial coordination of rhenium(I) by the monoanionic NJ), 0 tripod ligand as well as a solid phase fixation of the ligand and the resulting tricarbonyl complex (68). 

The facially coordinating l,4,7-tiimethyl-l,4,7-triazacyclononane (Cn) ligand forms stable methylrhodium(III) complexes, such as [Rh(Me)3Cn], [Rh(Me)2Cn]OTf and [Rh(Me)Cn](OTf)2 (OTf=trifluoromethanesulfonate) and the latter two have rich aqueous chemistry. When dissolved in water, [Rh(Me)Cn] readily coordinates two water molecules to form the... 

Nitridoosmium(VI) complexes containing facially coordinated polypyrazolyl ligands have been reported. [Os (N)(tpm)(Cl)2] (47) (tpm = tris(l-pyrazolyl)methane) is prepared in a manner... 

The IR spectrum in benzene shows three strong carbonyl bands at 1997.2, 1923.5, and 1903.5 cm-1 associated with the three facial coordinated carbon monoxides. In CH2C12 solution, the two lower-frequency bands appear as one strong broad band at 1911 cm-1, which is about the average of the two... 

Nickel(II) complexes with various saturated triaza macrocycles are six-coordinate in both the solid state and aqueous solution.2659,2663 In the bis complexes the ligands are facially coordinated (371) with normal Ni—N bond distances (about 210-214 pm). 1,2662... 

An oxo atom spans two Ru atoms and bonds to the facially coordinated [2.2]paracyclophane ring. It has been proposed that the carbide and oxo atoms are both derived from the same CO ligand. This seems reasonable given that pyrolysis of 204 affords 205 and C02 in quantitative yield. In contrast to the generation of 117 from 202 the transformation here appears to involve an intramolecular process.115... 

Hydrolysis of ML3(H20)33 + by reaction Eq. (1) gives dihydroxo-bridged species which may exist in several isomeric forms. For (L)3 = (NH3)3 there are five possible isomers if only facial coordination is considered then the number of isomers is reduced to two, the so-called cis and trans isomers (see Fig. 9). The ammonia, tame, and tacn chromium(III) complexes mentioned previously have all been isolated as their trans isomers. Similarly it has been found that... 

The remaining branched chain ligands (32)-(36) are restricted to facial coordination and, while MU + systems predominate, Co(tach)X3 are known,381,586,587 and there is no apparent reason why other mono(branched chain triamine) complexes cannot be prepared (Section 13.1.5.3). 

Copper and nickel Chromium and cobalt N -Np Na-Np Meridional/facial coordination Azo/hydrazone tautomerism Non-planarity due to azo/hydrazone tautomerism Formation of two copper and two nickel complexes by unsymmetrical o.o -dihydroxyazobenzenes78 Detection of isomeric 2 1 chromium complexes 79 proton magnetic resonance80 Isolation of isomeric 2 1 chromium and cobalt complexes 86 87 limited X-ray crystallographic89 90 Proton magnetic resonance80 Detection of five isomeric 2 1 chromium complexes of symmetrical o.o -dihydroxydiarylazo compounds... 

The molecular structures of dicarbonyl-A/4 CH-1,3-cycloheptadienetri-methylphosphinechromium(0) (38o) (Fig. 4) (57) and dicarbonyl-//4 CH-2,4-dimethyl-l,3-pentadienetrimethylphosphitechromium(0) (39n) (Fig. 5) (55) have been determined by X-ray structure analysis. In good approximation, the coordination spheres of the metal atoms of 38o and 39n are octahedral. Two carbonyls and one donor ligand occupy three facial coordination sites. 

Complexes of the ligand 1,3,5-triamino-1,3,5-trideoxy-cis-inositol and its derivatives. These ligands act as N3 donors towards both iron(II) and high-spin iron(III), although ring inversion could make a facially coordinating 03 donor set available (93,94). 

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