Nickel complex compounds, with structure

Ni3(2,2,2-tet)3(/u-N3)3](PF6)3 and its perchlorate analogue have been suggested as trinuclear complexes with an irregular triangle structure.2117 While a crystal structure is lacking, EXAFS and XANES spectra support the occurrence of azido-bridged trinuclear nickel(II) compounds with Ni- -Ni separations of 5.16 A and 5.12 A, respectively. Two J parameters had to be... 

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

There can be little doubt that the active species involved in most or even all of the various combinations described in Section II is HNi(L)Y (see below), because the different catalysts prepared by activating the nickel with Lewis acids have been shown to produce, under comparable conditions, dimers and codimers which have not only identical structures but identical compositions. On modification of these catalysts by phosphines, the composition of dimers and codimers changes in a characteristic manner independent of both the method of preparation and the nickel compound (2, 4, 7, 16, 17, 26, 29, 42, 47, 76). Similar catalysts are formed when organometallic or zero-valent nickel complexes are activated with strong Lewis acids other than aluminum halides or alkylaluminum halides, e.g., BFS. 

Kockerling, M. and Henkel, G. (2000) Synthesis and structure of [Ni4(S2C7Hio)4], the first tetranuclear cyclic nickel complex with bifunctional thiolate ligands and of the mononuclear precursor compound Na2[Ni(S2C7Hio)2]- 4MeOH. (PrOH)-Pr-i, Inorg. Chem. Commun., 3, 117-9. 

The number of theoretical investigations of transition metal complexes with carbodiphosphoranes and related divalent carbon(O) ligands is rather small. Quantum chemical calculations of the nickel complexes (CO) Ni-C(PPh3)2 with n = 2, 3 have been pubhshed together with experimental work which describes the S3mthesis and X-ray structure analyses of the compounds [107]. The first systematic... 

Table 6 collects the structures of transition metal dithiphosphate complexes along with comparative data for related compounds. As is readily noted, by far the most structural work is for nickel(II) complexes and their adducts. 

It is usual for a coordination compound to write the formula of a ligand with the donor atom first. The nickel complex represented above has both S and P bonded to the metal (as well as all the carbon atoms of the C5H5). The ring structure for chlorocyclohexane should be obvious. 

The borohydride reduction of nickel(II) compounds in protic solvents may result either in the formation of nickel(O) complexes66,71 or in the formation of hydrido complexes of nickel(II). Two easily interconvertible isomers, Ni(triphos)2, have been obtained in the reduction of Ni(N03)2 in the presence of the ligand triphos, but their structures are not known with certainty. 

---