Reversible fixation of carbon dioxide at nickel(0) centers: a route for large organometallic rings, dimers, and tetramers.
The reaction between bis(cycloocta-1,5-diene)nickel(0), carbon dioxide and benzaldehyde-N-furfurylideneimine (A) in 1,4-dioxane or THF results in the formation of the 24-membered organometallic macrocycles of the type [(A)Ni(-CH(R1)-N(R2)-COO-)]6(solv)n (R1: phenyl, R2: furfurylidene, solv: 1,4-dioxane in 1a, THF in 1b). According to the X-ray analyses, six monomeric nickelacyclic units are connected through six Ni-mu2-OCO-Ni bridges in these macrocycles. The cavities of the metallomacrocycles (diameter: 9.410(1) A in 1a, 9.250(1) A in 1b) each contain one solvent molecule. Reaction of 1b with Me3P results in the displacement of the peripheral ligands A by the phosphine to form the 24-membered organometallic macrocycle 1c. Both 1a and 1b isomerize in benzene to form the dimeric complex [(A)Ni(-CH(R1)-N(R2)-COO-)]2(solv)n (2). The X-ray crystal structure reveals that 2 consists of the same monomeric units as found in 1a and 1b. However two Ni-mu2-O-Ni bonds link the carboxylato groups. The solvent-dependent isomerization of 1b yielding 2 is a reversible reaction. Furthermore, the macrocycle 1b partially eliminates carbon dioxide above 20 degrees C, followed by elimination of half of the monodentately coordinated Schiff base ligands to form the planar tetrameric complex 6. This is also a reversible process.
Walther
D
D
Institut für Anorganische und Analytische Chemie der Friedrich-Schiller-Universität Jena, Germany. cdw@rz.uni-jena.de
Fugger
C
C
Schreer
H
H
Kilian
R
R
Görls
H
H
D002245:Carbon Dioxide / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006576:Heterocyclic Compounds, 4 or More Rings; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D014510:Urease
D006576:Heterocyclic Compounds, 4 or More Rings; D008024:Ligands; D009942:Organometallic Compounds; D002245:Carbon Dioxide; D009532:Nickel; D014510:Urease