Tripodal ligands nickel complexes

By reducing hydrated nickel(II) nitrate with NaBHt, in the presence of the tetradentate tripodal ligand np3 (equation 80), the complex [Ni(np3)j (66) has been obtained.263 Complex (66) undergoes oxidative reaction with HC104 or HBF4 to afford the nickel(II) hydrido complex [NiH ps)]-1".264 It also reacts with CO to give the carbonyl derivative263 and with white... 

Most of the nickel(l) complexes are four-coordinate, either tetrahedral (phosphine and arsine complexes) or square planar (macrocyclic and dithiolene complexes), but five-coordinate complexes are also easily formed in the presence of tetradentate tripodal ligands. 

Selected nickel(I) complexes with phosphines and arsines, together with relevant properties and synthetic routes, are reported in Table 21. In general, these nickel(I) complexes are air-unstable, especially when dissolved in solution consequently their preparation and handling require the exclusion of oxygen and, often, of moisture. The synthetic routes which afford nickel(I) complexes are strictly dependent on the nature of the phosphines and arsines and are not of general application, except in the case of some tripodal ligands. Most of the nickel(I)... 

This subject has been extensively reviewed recently, 1348 139Z 1394 and therefore this section will include only the main aspects of the coordination chemistry of these peculiar ligands towards nickel(II). A list of the tripodal ligands which give complexes with nickel(II) is reported in Table 70. 

Table 74 Some Organometallic Complexes of Nickel(II) with Tripodal Ligands...

With the tripod ligand np3 an entire series of compounds with tbp structures Ni(np3)X (X = Cl, Br, I, CN, CO, and H) can be prepared by reaction of nickel halides with the np3 ligand in the presence of borohydride, followed, if necessary, by metathesis with other X groups. The comproportionation of the Ni complex Ni2(CO)2(/i.-CO)(/i.-dppm)2 with NiG2(dppm)2 (dppm = Ph2PCH2PPh2) gives the iluxional A-frame compound (17-G-XIX).18... 

A tripod-type Schiff-base ligand, (127), was prepared by a 3 1 condensation reaction of 2-phenyl-4-formylimidazole in methanol.204 In two nickel(II) complexes, the screw coordination arrangement of the tripod ligand (127) around the metal ion induces chirality, resulting in a A (clockwise) or a A (anticlockwise) enantiomer.204 A multifunctional tripodal ligand possessing two different functionalities, such as pyridine and cyano moieties, (128), has been prepared by the reaction of 2-aminomethylpyridine, excess acrylonitrile, and glacial acetic acid. 

The ligands tris(2-pyridylmethyl)amine (tpma), tris(3,5-dimethyl-l-pyrazolylmethyl)amine (metpyma) and tris(3,5-dimethyl-l-pyrazolylethyl)amine (metpyea) are examples of tetraden-tate tripod-shaped ligands containing three heterocyclic nitrogen donors connected to an apical tertiary nitrogn donor by.aliphatic chains. Selected nickel(II) complexes with these ligands are reported in Table 50. 

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