Nickel complexes pyridine

Transition Metal-Ligand Complex Formation - Nickel-Pyridine Complexes... 

Ordinary hydromagncsialion may be effected by the use of a nickel-pyridine complex like Ni(py)4Ch. even though it affords a mixture of rcgioisomcrie allylmagnesium reagents as determined by carboxylalion. giving two kinds of carboxylic acids (eq. 3.37) (5(). An alkoxybntadicne underwent the alkylation as well... 

Nickel halide complexes with amines give mixtures of linear polymer and cychc trimers (30). Nickel chelates give up to 40% of linear polymer (31). When heated with ammonia over cadmium calcium phosphate catalysts, propargyl alcohol gives a mixture of pyridines (32). 

Nickel, tris(l, 10-phenanthroline) racemization, 1,24. 466 solid state, 1, 467 structure, 1,64 Nickel complexes, 5,1-300 acetylacetone alcoholysis, 2, 380 pyridine complexes, 2, 386 solvolysis, 2,379 structure, 2,388 amidines... 

The electronic spectra of a range of dithio- and perthiocarboxylato-nickel(II) complexes and their pyridine adducts show the presence of a variety of structures in solution, but complete interpretation of the spectra was prevented by lack of a complete MO treatment of these complexes (378). 

Electrocatalysis with nickel-bpy complexes has been shown useful for synthetic applications,202,211 especially when used in combination with the sacrificial anode process in an undivided cell (Equation (45)).207,211 Under these very simple experimental conditions, efficient nickel catalysts can be also generated in the presence of the cheap pyridine ligand.212... 

Diynes react with nitriles and aldehydes in the presence of a nickel(0) complex to give pyridines and dienones, respectively (Scheme 93).448,448a,448b... 

Nickel(II) complexes of a variety of bidentate sulfoxide ligands have been reported (326,378,413) and [NiL3][C104]2 species reported where L is the unusual bidentate ligand 2-(ethysulfinyl)pyridine-iV-oxide. Bidentate 0,0-coordination via sulfoxide and pyridine-N-oxide donors is assigned from infrared data (63). 

A considerable number of nickel(II) complexes with pyridine and substituted pyridines have been reported so far. Selected examples are reported in Table 44. 

The most common stoichiometries found in nickel(H) pyridine and substituted pyridine complexes are NiX2L4 and NiX2L2 where X is a mononegative ion and L is pyridine or a substituted pyridine. Complexes of formula NipysX2 have been found to correspond to either [NiX2py4]-2py (X = NCS, NCO)818 or [Ni(N03)2py3]-3py.819... 

Table 45 Nickel(II) Complexes with Ligands Related to Pyridine...

Bis(pyrrole-2-aldiminato)nickel(II) complexes (125) are diamagnetic in the solid state when R = H, Pr, Pr and Et, and paramagnetic pseudotetrahedral when R = Bu. 1001-1003 In solution there exists an equilibrium between square planar and tetrahedral species when R = Pr1, Bus and Bu Such equilibria were also investigated for complexes of the type (126) obtained from the condensation reaction in basic media of o-aminobenzaldehyde and a number of diamines in the presence of nickel(II).1004-1007 Square planar complexes (127)1008,1009 and (128)1010 were obtained with deprotonated pyridinecarboxamide ligands. In these complexes the Ni—N (amide) bond distance (184-187 pm) is shorter than the Ni—N (pyridine) distance (192-195 pm). 

A number of representative nickel(II) complexes prepared with Schiff bases derived from pyridine-2-carbaldehyde, pyridine-2,6-dicarbaldehyde and related species are summarized in Table 98, together with some of their distinctive physicochemical properties and preparative routes. All of these complexes involve N and either O or S as donor atoms and exhibit various coordination numbers and geometries depending on the denticity of the ligands and on their steric and electronic requirements. 

Nickel(II) complexes of 8-hydroxyquinoline, HL, are well known from the viewpoint of analytical chemistry. The brown, diamagnetic complex ML2 has cis square planar coordination (342). The same coordination occurs in C6H6 and CHC13 solutions. In water, pyridine or dioxane, this complex is green and paramagnetic, as is the solid hydrate NiL2-2H20. 

The addition and dissociation of pyridine and substituted pyridine molecules to a planar nickel(II) complex with a quadridentate N202 ligand have been studied by the microwave temperature-jump technique in chlorobenzene solvent (38). The data were interpreted with the assumption of mechanism C (Fig. 7), i.e., that k65 is the smallest rate constant. Subsequently, however, 14N NMR was used to measure the rate of pyridine exchange from the octahedral complex (138). The rates are the same for the two different experiments within a factor of two. This observation excludes mechanism B and is consistent with either mechanism A or C. The rate constants have consequently been presented in Table VI as k64. 

As has been noted (29, 31), nickel(III) poly(pyridine) complexes may be prepared. Electron-exchange rates have been determined (15) from a series of cross-reactions. The rate of the electron transfer reaction has... 

The case of the hexa(pyridine) nickel(II) complex has been extensively debated in the early literature of NMR of paramagnetic complexes [17-21]. The shift pattern with a-H > y-H > (i-H (Fig. 2.11 and Table 2.3) was soon recognized to be predominantly of a-type. The ligand has a a MO system which has the correct symmetry to overlap with the dx2 y2 and dz2 orbitals. However, spin polarization can induce V2 spin density in the it system. Once some unpaired spin density is in a p orbital, it spin-polarizes the electrons of the C—H a bond, thus producing a further mechanism for transferring spin density on the proton. The proton A/h value from this mechanism is proportional to the spin density on the carbon pz orbital, p , through a proportionality constant >ch ... 

The 1,4-addition of diethylzinc to a, )-unsaturated ketones is catalyzed by nickel (II) complexes. Bolm showed in 1991 that a chiral amino alcohol derived from pyridine and Ni(acac)2 catalyzed the addition of diethylzinc to chalcone with a moderate asymmetric amplification.42 ML -type species are assumed, with the meso complex being the less reactive. Other examples of this reaction are collected in Table 2. 

---