Nickel-carbon dioxide complex, coordination

Aresta s conqrlex, (PCy3)2Ni[T) -(C,0)-C02], has been well studied for its physical and chemical properties. The ti -(C,0) coordination of carbon dioxide to the nickel con lex, (I Cy3)2Ni[Ti -(C,0)-C02], is fivored as a starting con lex with the ylide due to the electrophilic carbon of the coordinated CO2. The complex was first reported in 1974 ° l The reaction between the Aresta s carbon dioxide complex and an ylide provides the first exanqile of a Wittig Reaction on a coordinated carbon dioxide complex. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

Some complexes are known in which carbon dioxide is bonded to a transition metal. Aresia era/. [19) isolated the nickel complex (1)in which the CO ligand is coordinated througli the carbon atom and one of the oxygen atoms. Fachinetti et al. [20] found the polymeric cobalt complex (2), in which carbon dioxide is C bonded to cobalt and 0-bonded to two different potassium ions. Lappert isolated tlie remarkably stable niobium complex (3). which was the first authentic CO complex of an early d-block metal [21 j. 

The reaction between 1,3-dienes and carbon dioxide leads to the formation of carboxylato (ri -allyl)nickel(II) complexes, which may equilibrate with seven-membered ring nickelacycles in which the metal coordinates the allyl in a Ti -fashion (Eq. 5). ... 

Representative work A Dedieu and F. Ingold, Angew. Chem., Int. Ed. Engl., 28, 1694 (1989). Monohapto Versus Dihapto Coordination of Carbon Dioxide in Bis(ammine) Nickel(O) Complexes. A CAS-SCF Investigation. C. Bo and A. Dedieu, Inorg. Chem., 28, 304 (1989). CO2 Interaction with HCr(CO)J Theoretical Study of the Thermodynamic Aspects. A. Dedieu and S. Nakamura, J. Organomet. Chem., 260, C63 (1984). lative Thermodynamic Stabilities of Acetyl and Formyl Complexes A Theoretical Determination. 

There is now a growing literature of nickel organometallic complexes that contain carbon dioxide or related cumulene ligands that result from reactions with carbon monoxide. The first structurally characterized complex of carbon dioxide was the nickel complex Ni(G02)(PCy3)2 reported in 1975. A more recent study of this complex provides the complete assignments of the vibrational spectra and theoretical calculations of different isomers in support of a mechanism for CO2 fluxionality that involves end-on coordination. The tridentate pincer ligand 2,6-bis((diiso-propylphosphino)methyl)phenyl (PGP) has been used to form the square-planar Ni(ii) hydroxide complex Ni(OH)(PGP). The complex Ni(OH)(PCP) reacts with CO to give a binuclear /X-GO2 complex (Equation (2)). 

Schindler et al. carried out a kinetic analysis for the reaction of isoprene (ip) with carbon dioxide and Ni(bpy)(cod) [103]. Ni(bpy)(cod) did not react directly with CO2 (see also Sect. 5.2), but reacted reversibly with isoprene to give Ni(bpy)(ip). The kinetic results support a mechanism where, in a fast preequilibrium step, one of the bonds between Ni and cod is cleaved and, in a following step, ip coordinates to the free coordination site (Scheme 5.23). At low temperatures Ni(bpy)(ip) can further react, through a consecutive equilibrium, with another ip molecule to give Ni(bpy)(ip)2. However, in the presence of CO2, the nickel-ip complex, Ni(bpy)(ip), reacts irreversibly with the heterocumulene to form the product complex (3-5-q )-3-methyl-3-pentenylato)nickel bipyridine (Scheme 5.23). The activation parameters for the latter step were calculated to be A// = 25 7 kJ/mol and = 184 24 J/(mol K). The large negative activation entropy indicates that the carboxylation reaction proceeds in an associative way, during which CO2... 

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