Details

Autor(en) / Beteiligte

• Zinn, Paul J
• Sorrell, Thomas N
• Powell, Douglas R
• Day, Victor W
• Borovik, A. S

Titel

Acetonitrile Hydration and Ethyl Acetate Hydrolysis by Pyrazolate-Bridged Cobalt(II) Dimers Containing Hydrogen-Bond Donors

Ist Teil von

• Inorganic chemistry, 2007-11, Vol.46 (24), p.10120-10132

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2007

Quelle

MEDLINE

Beschreibungen/Notizen

• The preparation of new CoII−μ-OH−CoII dimers with the binucleating ligands 3,5-bis{bis[(N‘-R-ureaylato)-N-ethyl]aminomethyl}-1H-pyrazolate ([H4 P R buam]5-, R = t Bu, i Pr) is described. The molecular structure of the isopropyl derivative reveals that each CoII center has a trigonal-bipyramidial coordination geometry, with a Co···Co separation of 3.5857(5) Å. Structural and spectroscopic studies show that there are four hydrogen-bond (H-bond) donors near the CoII−μ-OH−CoII moiety; however, they are too far away to be form intramolecular H-bonds with the bridging hydroxo ligand. Treating [CoII 2H4 P R buam(μ-OH)]2- with acetonitrile led to the formation of bridging acetamidato complexes, [CoII 2H4 P R buam(μ-1,3-OC(NH)CH3)]2-; in addition, these CoII−μ-OH−CoII dimers hydrolyze ethyl acetate to form CoII complexes with bridging acetato ligands. The CoII−1,3-μ-X‘−CoII complexes (X‘ = OAc-, [OC(NH)CH3]-) were prepared independently by reacting [CoII 2H3 P R buam]2- with acetamide or [CoII 2H4 P R buam]- with acetate. X-ray diffraction studies show that the orientation of the acetate ligand within the H-bonding cavity depends on the size of the R substituent appended from the urea groups. The tetradentate ligand 3-{bis[(N‘-tert-butylureaylato)-N-ethyl]aminomethyl}-5-t ert-butyl-1H-pyrazolato ([H2 P t Bu uam]3-) was also developed and its CoII−OH complex prepared. In the crystalline state, [CoIIH2 P t Bu uam(OH)]2- contains two intramolecular H-bonds between the urea groups of [H2 P t Bu uam]3- and the terminal hydroxo ligand. [ n Pr4N]2[CoIIH2 P t Bu uam(OH)] does not hydrate acetonitrile or hydrolyze ethyl acetate. In contrast, K2[CoIIH2 P t Bu uam(OH)] does react with ethyl acetate to produce KOAc; this enhanced reactivity is attributed to the presence of the K+ ions, which can possibly interact with the CoII−OH unit and ester substrate to assist in hydrolysis. However, K2[CoIIH2 P t Bu uam(OH)] was still unable to hydrate acetonitrile.