[23777-40-4] · C38H34NiP2 · Ethylenebis(triphenylphosphine)nickel(0) · (MW 611.34)
Physical Data: mp. 108-110 °C (dec); 1H NMR d (C6D6) 2.55 ppm (C2H4).
Solubility: very sol benzene, toluene; sparingly sol ether, pentane.
Form Supplied in: yellow crystalline solid; not commercially available.
Preparative Methods: most readily prepared in 75% yield from Nickel(II) Acetylacetonate, Diethylaluminum Ethoxide, and Triphenylphosphine. In the presence of Ethylene the yields can be raised to >95% (eq 1).8 Alternatively, Triethylaluminum may be employed in an ethylene saturated solution, yielding 85% of the complex.9
The reagent has also been prepared from Dichlorobis(triphenylphosphine)nickel(II), Zinc, and ethylene (eq 2) or Nickel(II) Chloride, zinc, PPh3, and ethylene in yields of 80% and 71%, respectively.10
Purification: can be recrystallized from methanol at reduced temperatures.
Handling, Storage, and Precautions: is very air sensitive and should be stored under inert atmosphere, preferably in a dry box.
The relatively weak nature of the ethylene-nickel interaction allows for the facile replacement with other coordinating ligands. Much of the chemistry of the catalyst is therefore attributed to this fact. In addition, a number of other related catalysts differ only by the nature of the phosphine ligands, thereby modifying some of its properties.1
Ethylenebis(triphenylphosphine)nickel(0) has been used as an isomerization catalyst for the ring expansion of vinylcyclobutenes to cyclohexadienes.2,11 It also promotes the dechlorination of 1,2-dichlorides to the corresponding cyclobutenes. The reactions can be carried out independently, or direct conversion of the dichloride to the cyclohexadiene is also possible (eq 3). Conditions under which these transformations are carried out include thermolysis followed by oxidation of the resulting Ni0 alkene complex to NiI and subsequent ring expansion, or preoxidation of the catalyst to NiI. Yields range from 40-50%. The presence of electron-withdrawing substituents on the cyclobutene system are required, whereas substitution on the vinyl group effectively lowers yields.
The reaction of halomethyl benzene derivatives with the catalyst results in oxidative addition to nickel, yielding the corresponding NiI or NiII benzyl complexes that have properties similar to nucleophilic Grignard species.12,13 Appropriately, use of di-, tri-, to oligosubstituted aromatics results in the production of a variety of [2
Other examples include the synthesis of (1,2,4,5)-cyclophane from 1,2,4,5-tetrabromomethylbenzene in 64% yield (eq 5).14
On a related note, the reaction of ethylenebis(triphenylphosphine)nickel(0) with 1,4-bis(chloromethyl)benzene in benzene at room temperature yields a variety of paracyclophanes including [2.2.2] (5%), [188.8.131.52] (20.3%), and [184.108.40.206.2] (8.1%).3 These mild and efficient one-step preparations offer attractive alternatives to conventional syntheses that often employ reactive and corrosive alkali metals (Wurtz coupling) and/or multistep routes.15
The catalyst can be utilized with a number of alkenes under either thermal or photochemical conditions to produce cyclobutane and other dimerized products. For example, irradiation of a toluene solution of 1,7-octadiene with ethylenebis(triphenylphosphine)nickel(0) followed by air oxidation yields stereospecifically trans-bicyclo[4.2.0]octane accompanied by oligomers (eq 6).4 The reaction also works intermolecularly with monosubstituted alkenes, yielding the corresponding 1,2-trans-cyclobutanes (eq 7).
It is also possible to induce such alkene dimerizations thermally via well known nickelacyclopentane intermediates.16 Treatment of such intermediates with a variety of reagents yields a number of useful organic products (eq 8).5,17 Other catalytic ethylene dimerization systems include (PPh3)2Ni(C2H4) embedded on an alumina surface.18 A variety of cyclopropene systems can be cyclodimerized to the corresponding cyclobutane derivatives via oxidation of the intermediate nickelacyclopentane intermediates as well.19,20
It has been found that a catalyst prepared from ethylenebis(triphenylphosphine)nickel(0) and Chloromethyl Methyl Sulfide acts as a cyclopropanation reagent for cyclooctene (eq 9).6
Another cationic complex which is active towards styrene oligomerization is derived from Benzyl Chloride. Treatment of the intermediate h3-coordinated cationic complex (0.09 mol %) with styrene at rt for 2 h forms oligomers with M
Isomerization and skeletal rearrangements22 of alkenes are also promoted by the catalyst. For example, allylbenzene is quantitatively converted into trans-1-phenylpropene by a catalyst derived from ethylenebis(triphenylphosphine)nickel(0) and HCl (eq 11).7
The catalyst (2.5 mol %) also reacts with allene at elevated temperatures to yield a mixture of the trimer, tetramer, pentamer, and higher oligomers (eq 12).23 The related complex Bis(1,5-cyclooctadiene)nickel(0) also promotes a similar reaction.
Ethylenebis(triphenylphosphine)nickel(0) reacts with alkenes (ethylene and propene) and isocyanates, producing isolable azanickelacyclopentanes which can be further converted into a variety of useful intermediates depending upon the conditions employed. Thus reaction with Phenyl Isocyanate and ethylene can yield amides or carbamides (eq 13).24 Reaction with propene yields a mixture of regiosiomers. Related catalysts that also induce the desired transformations include (TPP)Ni(CDT) and Ni(cod)2.24
Eugene I. Bzowej & Francis J. Montgomery
The Ohio State University, Columbus, OH, USA