Organonickel chemistry
Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds featuring nickel-carbon bonds. They are used as a catalyst, as a building block in organic chemistry and in chemical vapor deposition. Organonickel compounds are also short-lived intermediates in organic reactions. The first organonickel compound was nickel tetracarbonyl Ni(CO)4, reported in 1890 and quickly applied in the Mond process for nickel purification. Organonickel complexes are prominent in numerous industrial processes including carbonylations, hydrocyanation, and the Shell higher olefin process. A popular reagent is Ni(CH3)2(tetramethylethylenediamine). Many alkyl and aryl complexes are known with the formula NiR(X)L2. Examples include [(dppf)Ni(cinnamyl)Cl)], trans-(PCy2Ph)2Ni(o-tolyl)Cl]], (dppf)Ni(o-tolyl)Cl]], (TMEDA)Ni(o-tolyl)Cl, and (TMEDA)NiMe2. Nickel compounds of the type NiR2 also exist with just 12 valence electrons. In solution however solvent always interact with the metal atom increasing the electron count. One 12 VE compound is di(mesityl)nickel prepared from (allyl)2Ni2Br2 and the corresponding Grignard reagent. (allyl)2Ni2Br2 + 4 C6H2Me3MgBr → 2 (allyl)MgBr + 2 MgBr2 + 2 (C6H2Me3)2Ni Many complexes exist of nickel coordinated to an alkene. Practical applications of this theme include polymerization or oligomerization of alkenes, as in the Shell Higher Olefin Process. In these compounds nickel is formally zerovalent Ni0 and the bonding is described with the Dewar–Chatt–Duncanson model. One common representative is Bis(cyclooctadiene)nickel(0) (Ni(COD)2), which contains two cyclooctadiene ligands. It is a 18VE compound with 10 electrons provided by nickel itself and 4x2 electrons more by the double bonds. This solid, which melts at 60 °C, is used as a catalyst and as a precursor for many other nickel compounds. Nickel forms several simple allyl complexes. Allyl halides react with Ni(CO)4 to form pi-allyl complexes, (allyl)2Ni2Cl2. These compounds in turn are sources of allyl nucleophiles.
