Nickel complexes stoichiometry

Despite the incontrovertible evidence regarding the structure of copper and nickel complexes of o-hydroxydiarylazo compounds, confusion remained with regard to their cobalt complexes. Thus some workers13a b>14,16 reported the isolation of complexes having 2 1 stoichiometry whilst others5 17 reported 3 1 stoichiometry. The oxidation state of the cobalt was also in dispute. The situation was clarified18 when more modem techniques were employed to study the reaction of l-phenylazo-2-naphthol and related compounds with various cobalt salts and complexes. The results of this work are summarized in Scheme 1. 

Iron, copper and nickel complexes of the products obtained by the nitrosation of arylazore-sorcinols have been claimed139 to dye leather in brown shades having excellent fastness to light. The structures of these products is open to debate since the position in which the resorcinol moiety is nitrosated (205 or 206) has not been established with any degree of certainty. Further, dyestuffs of this type, particularly those (207) derived from o-aminophenols, contain two metallizable systems and no information appears to be available regarding the stoichiometry and structure of their iron complexes. 

As described before, nickel complexes react with aldehydes stoichiometri-cally. In view of the fact that aldehydes may undergo oxidative addition to palladium complexes, it is rather peculiar that ketones are not formed via oxidative addition. (This reaction will be discussed again in Chapt. V.)... 

A review has appeared on the synthesis and reactivity of (sUylamino) and (silyl-anilino)phosphines. The S5mthesis, derivatisation and coordination behaviour of the morpholine (69) and piperazine (70) derivatives have been described. They are formed from the appropriate amine with diphenylchlorophosphine, and both react with sulfur or selenium to give the chalcogenide, whilst reaction of (69) with paraformaldehyde leads to insertion of methylene into the P N bond to give the phosphine oxide. The reaction between ethylenediamine and diphenylchlorophosphine can lead to the bis-, tris- and tetrakis(diphenylphosphino)ethylene-diamines, depending upon the stoichiometry. The first two are oxidised in situ whist the latter, (71), is stable. A nickel complex of (71) has been shown to be active as a catalyst for ethylene pol5nnerisation. ... 

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

The cocondensation of nickel atoms and CS2 at 12 K resulted in the formation of three binary, mononuclear, nickel/CS complexes, NKCSjln, n = 1-3 (145). Mixed CS2/ CS2 isotopes were used to identify the lowest stoichiometry species. An interpretation of the IR and UV-visible spectra, as well as normal-coordinate analyses (144), suggested that these species are best considered as normal 7r-complexes, with the nickel atom coordinated to the C=S bond in a manner analogous to C=C bond coordination (123). 

With 2-formylpyridine S-methyldithiocarbazate, planar, diamagnetic nickel(II) complexes with stoichiometry [Ni(6-H)A], where A = Cl, Br, I, and NCS, have been isolated [126]. Also, paramagnetic, octahedral [Ni(6-H)2] has been prepared and spectrally characterized. These complexes have NNS coordination as does the related S-benzyldithiocarbazate, 24, in [Ni(31-H)A], A = Cl, Br [165]. 

Methyl-3-formylpyrazole A-phenylthiosemicarbazone, 45, coordinates as a deprotonated NNS tridentate ligand to form the diamagnetic, spin-paired [Ni(45-H)NCS] complex [200]. However, the complexes formed with other nickel(II) salts have stoichiometry [Ni(45)2]A2, where A = Cl, Br, NO3, CIO4, and BF4. These octahedral complexes NNS coordinated neutral hgands have Dq values between 1086 and 1150cm" ... 

Formylthiophene thiosemicarbazone, 26, as well as the N-methylfhio-semicarbazone, and N-phenylthiosemicarbazone, each yield complexes of stoichiometry [Ni(26-H)2] from heated aqueous alcohol solutions brought to above pH = 7 with ammonia [209]. All complexes are four-coordinate, diamagnetic and the thiophene sulfur does not bond to the nickel(II) center. 

---