title: Acetonitrile hydration and ethyl acetate hydrolysis by pyrazolate-bridged cobalt(II) dimers containing hydrogen-bond donors.
abstract: The preparation of new CoII-mu-OH-CoII dimers with the binucleating ligands 3,5-bis{bis[(N'-R-ureaylato)-N-ethyl]aminomethyl}-1H-pyrazolate ([H4PRbuam]5-, R=tBu, iPr) 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) A. Structural and spectroscopic studies show that there are four hydrogen-bond (H-bond) donors near the CoII-micro-OH-CoII moiety; however, they are too far away to be form intramolecular H-bonds with the bridging hydroxo ligand. Treating [CoII2H4PRbuam(micro-OH)]2- with acetonitrile led to the formation of bridging acetamidato complexes, [CoII2H4PRbuam(micro-1,3-OC(NH)CH3)]2-; in addition, these CoII-micro-OH-CoII dimers hydrolyze ethyl acetate to form CoII complexes with bridging acetato ligands. The CoII-1,3-micro-X'-CoII complexes (X'=OAc-, [OC(NH)CH3]-) were prepared independently by reacting [CoII2H3PRbuam]2- with acetamide or [CoII2H4PRbuam]- 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-tert-butyl-1H-pyrazolato ([H2PtBuuam]3-) was also developed and its CoII-OH complex prepared. In the crystalline state, [CoIIH2PtBuuam(OH)]2- contains two intramolecular H-bonds between the urea groups of [H2PtBuuam]3- and the terminal hydroxo ligand. [nPr4N]2[CoIIH2PtBuuam(OH)] does not hydrate acetonitrile or hydrolyze ethyl acetate. In contrast, K2[CoIIH2PtBuuam(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[CoIIH2PtBuuam(OH)] was still unable to hydrate acetonitrile.
authors.affiliation: Department of Chemistry, University of Kansas, 2010 Malott Hall, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Zinn
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Sorrell
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Powell
authors.forename: Victor W
authors.initials: VW
authors.lastname: Day
authors.forename: A S
authors.initials: AS
authors.lastname: Borovik
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000097:Acetonitriles / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D006860:Hydrogen Bonding; D006868:Hydrolysis; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*
chemical_list: D000085:Acetates; D000097:Acetonitriles; D009942:Organometallic Compounds; D011720:Pyrazoles; D003035:Cobalt; C007650:ethyl acetate; C032159:acetonitrile