Pyridine and related ligands

Steffen and E. D. Stephens, Inorg. Nuclear Chem. Letters, 1973, 9, 1011. 

Cabral, M. T. P. Leite, and M. F. Cabral, paper given at 16th International Coordination Chemistry Conference, Dublin, 1974. 

The formation of hydrated cobalt(n) complexes of pyridine carboxylic acids and the subsequent thermal decomposition to lower hydrates has been documented.82,83 Cobalt(n) halides react with 6-methylpicolinic acid (6-mpaH), picolinic acid (paH), nicotinic acid (naH), and pyridine-2,6-dicarboxylic acid (2,6-py) to form Co(6-mpa) (6-mpaH)X (X = Cl, Br, or NCS), Co(naH)nX2 (n = 2, X = Cl, Br n = 3, X = NCS), and Co(pa)(paH)X, EtOH (X = Cl, Br, or NCS) which are all probably octahedral.83 6-Methylpicolinic acid also formed Co(6-mpaH)4X2,2HX (X = Cl or Br) which were formulated [(6-mpaH)2H]2[CoX4], since the electronic spectra show absorptions characteristic of tetrahalogenocobaltate(n) ions.83 

Di-(2-pyridyl)ketoxime [dpkx (9)] forms tetrahedral Co(dpkx)Cl2,H20 and Co(dpkx)3Cl2, which may be octahedral but has fie = 2.1 BM, possibly due to Curie-Weiss dependence of the moment upon temperature.86 The bonding in these complexes is probably via one pyridyl-N and the oxime-N. Pyridine-4-carbaldehyde 

Bidentate behaviour has also been observed for 3-(2-pyridyl)-5,6-diphenyl-l,2,4-triazine in [CoL3](BF4)2 and [CoL2(H20)2](BF4)2, whilst 3- 2-(o-phen) -5,6-diphenyl-l,2,4-triazine (L ) is terdentate in [CoL2]X2 (X = Br, BF4, or NOa). The spin state of the cobalt is temperature dependent for both types of complex.92 

Pyridine and related ligands. The crystal structures of [M(py)2(N03)2] (M = Co, Cu, or Zn) have been determined and the overall molecular geometries are very similar for all three compounds. In all of these complexes the nitrate groups are co-ordinated in an assymetric bidentate manner, the degree of assymetry following the order Co Zn Cu. Cobalt complexes of the linear quinquedentate ligand pyDPT (75) have been isolated. They are [Co-(pyDPT)X]X,H20 (X = Cl, Br, 1, or NO3), [Co(pyDPT)](PF6)2, and 

X = NCS, n = 0 X = NO2, n = 1 X = I, n = 5 X = I, n = 2) have been reported. [Co(phen)3](xanthate)2 has been isolated from reaction of C0CI2, potassium xanthate, and phen in aqueous solution. The complexes C0LX2 (L = bipy or phen X = Cl or Br) have also been prepared.  

The eight-co-ordinate complex [Co(napy)4](C104)2 (napy = 1,8-naph-thapyridine) has been isolated and its structure discussed in terms of a distorted dodecahedral structure similar to that reported for the analogous iron(ii) compound. The related complex [Co(napy)2(N03)2] has also been reported and appears to be the first example of a neutral mixed-ligand eight-co-ordinate complex of this metal.  

When aqueous solutions of C0SO4 are treated with adenine (AdeH), the complex [C02(H2O) (Ade)2](AdeH)2(SO4)2,6H2O is obtained. The cation is centrosymmetric and contains unidentate Ade ligands co-ordinated via N-9.326a 2-Aminothiazole (atm) and 2-bromothiazole (brt) form the octahedral 

Complexes. Pyridine and related ligands. Recent Mossbauer studies suggested that [FeCl2(py)4] has a cis-octahedral structure however. X-ray studies have shown it to be isomorphous with trans-[MCl2(py)4] (M = Co or Ni). Magnetic and spectroscopic properties of [Fe(py)2(phen)(NCS)2] have been reported. An n.m.r. study of [FeL(PF )2] [L = (42)] shows the presence of both cis- and trans-isomers in solution.The methyl-substituted pyridyl-thiazoles (43) form the complexes [FeL2-X2],nH20 (X = Cl, Br, I. NO3, 

Forster and D. J. Dahm, fnorg. Chem., 1972, II. 918 P. Laigroz and 1. Bkouchc-Waksman. Bull. Soc. chim. France, 1972, 959. 

Tatehata. T. Kumamaru, and Y. Yamamoto. J. Inorg. Nuclear Chem., 1971, 33, 3427. 

The structure of bis(piperidine)-aPy5-tetraphenylporphinatoiron(ii) shows the complex to have an octahedral [FeN ] core. The 4 1 complex between 4-methylpyridine and iron(ii) phthalocyanine has only two 4-Mepy groups co-ordinated to the metal in a rrfl/j. -octahedral arrangement.The dimerization of iron(ii) phthalocyanine in DM SO has been studied and iron(ii) phthalocyanines have been used as n.m.r. shift reagents for amines. Although 

Kobayashi, F. Kurokawa, T. Ashida, N. Uyeda, and E. Suito, Chem. Comm., 1971, 1631. 

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Niobium and tantalum halides form adducts with various nitrogen donor ligands including aliphatic and aromatic amines nitriles, Schiffs bases and imidazoles (Table 5). The reactions of MXS with pyridine and related ligands such as bipy or phen depend critically on the reaction conditions. With py at low temperature MX5 (X = Cl, Br) yielded 1 1 adducts that are rapidly reduced to [MX4(py)2] on increasing the temperature, with formation of l-(4-pyridyl)pyridinium halide. Similarly, bipy and phen reduced the metal in MeCN to oxidation state +IV and formed monoadducts of type [MX bipy)] at room temperature, while at 0°C the same reactions yielded [NbCls(bipy)(MeCN)] and [TaX5(bipy)(MeCN)J (X = C1 or Br). NbBrs and Tals formed [MX5(bipy)2], which were formulated as the eight-coordinate [MX4(bipy)2]X.1 Reduction of the metal can however be prevented, even at room temperature,... 

Niobium and tantalum halides also fonn adducts with numerous N-donors. Their reactions with pyridine and related ligands (bipyridine, phenanthroline, 7-azaindole ) depend critically on the reaction conditions. Indeed, aromatic amines have a tendency to reduce the metal to oxidation state IV especially for niobium but the reduction can be prevented, even at rt, by an appropriate choice of the solvent (equations 2a-c). Imide adducts M(NR)Cl3L2 are obtained with primary or secondary amines. ... 

The cyclization of ort/zo-allyl phenols was reported by Murahashi in the late 1970s. The reaction of the 2-(2-cyclohexenyl)phenol (Equation 16.110) was one of the early examples of Wacker-type reactions with alcohol nucleophiles and has been re-investigated in more recent years with chiral catalysts. Intramolecular reactions of alkene-ols and alkenoic acids form cyclic ethers and lactones. These reactions were reported by Larock and by Annby, Andersson, and co-workers, and examples are shown in Equations 16.111 and 16.112. °° ° The use of DMSO as solvent was important to form the lactone products. More recently, reactions with alcohols were reported by Stoltz to form cyclic ethers by the use of pyridine and related ligands in toluene solvent. - The type of ligand, whether an additive or the solvent, is crucial to the development of these oxidative processes. However, the features of these ligands that lead to catalysis are not well understood at this time. 

Triosmium clusters with pyridines and related ligands... 

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