American Chemical Society
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A Binding Pocket for Coordinated Water Formed by the Metal Center and Two Heterocyclic Nitrogens in Chelating Bis-thioethers of the Complexes {Cp*M[Im‘S(CH2)2SIm‘](H2O)}2+ (M = Rh, Ir; Im‘ = 1-alkyl-4-tert-butylimidazol-2-yl)

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posted on 2005-11-07, 00:00 authored by Valentin Miranda-Soto, Miguel Parra-Hake, David Morales-Morales, Ruben A. Toscano, Grant Boldt, Anatol Koch, Douglas B. Grotjahn
Two new chelating bis-thioethers of the form Im‘S(CH2)2SIm‘ were made, where Im‘ = 1-methyl and 1-isopropyl-4-tert-butylimidazol-2-yl (4-Me and 4-iPr, respectively). When coordinated to Cp*Ir2+ and Cp*Rh2+ fragments in the presence of water, complexes 2 of the form {Cp*M[Im‘S(CH2)2SIm‘](H2O)}2+{OTf-}2 were isolated in high yields. In these species, hydrogen-bonding networks were formed between the O−H bonds of the coordinated water molecule and the imidazole nitrogens on each side, as revealed in X-ray diffraction structures of 2-Me-Ir and 2-Me-Rh. Proton NMR spectra of the complexes in the presence of varying amounts of D2O and H2O led to formation of the three possible isotopomers, of which the H2O and HOD isotopomers were detected by 1H NMR. Three of the complexes were evaluated as modestly active catalysts for transfer hydrogenation of acetophenone in the absence of added base. As a control, the Cp*Rh2+ complex from PhSCH2CH2SPh was made and shown to be an ineffective catalyst.