title: A Bioinspired Dinickel(II) Hydrolase: Solvent Vapor-Induced Hydrolysis of Carboxyesters under Ambient Conditions.
abstract: From the perspective of synthetic metallohydrolases, a phenoxo-bridged dinickel(II) complex [NiII2(L)(H2O)2(CH3OH)][ClO4]·CH3OH (1) (H3L = 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N',N″-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol) has been synthesized and structurally characterized. The presence of a vacant coordination site and a weakly bound water molecule provides the scope for substrate binding to act as a metallohydrolase model. Ethyl acetate vapor diffusion at 298 K to a CH3CN/CH3OH solution of 1 results in the formation of a pentanuclear acetato-bridged complex [NiII5(H2L)2(μ3-OH)2(μ-O2CCH3)4][ClO4]2·CH3CO2C2H5(2), demonstrating for the first time the metal-coordinated water-promoted hydrolysis of a carboxyester at room temperature. When the crystals of 1, moistened with a few drops of ethyl acetate, were kept for ethyl acetate vapor diffusion, it transforms into a monoacetato-bridged complex [NiII2(HL)(μ-O2CCH3)(H2O)2][ClO4]·4H2O (3). This kind of solvent (vapor)-induced single-crystal-to-single-crystal structural transformation concomitant with the hydrolysis of external substrate (ethyl acetate) is unprecedented. Reaction of H3L with 2 equiv of NiII(O2CCH3)2·4H2O, followed by the usual workup, and recrystallization from CH2Cl2led to the isolation of [NiII2(H2L)(μ-O2CCH3)2][ClO4]·CH2Cl2·2H2O (4). Complex 4 is structurally different from 3, confirming that the reaction of NiII(O2CCH3)2·4H2O with H3L is a different phenomenon from the hydrolysis of ethyl acetate, promoted by NiII-coordinated water in 1. Complex 1 is also capable of hydrolyzing ethyl propionate to a propionato-bridged complex [NiII2(HL)(μ-O2CCH2CH3)(H2O)2][ClO4] (5). For the hydrolytic phenomena mentioned above, the coordinated ligand donor sites (phenolate and tertiary amine) provide a microenvironment around the dinickel(II) center to facilitate efficient stoichiometric hydrolysis of ethyl acetate and ethyl propionate under ambient conditions. Temperature-dependent magnetic studies of dimeric complexes 1, 4, and 5 reveal the presence of moderate antiferromagnetic coupling: J = -25.0(1) cm-1for 1, J = -20.0(1) cm-1for 4, and J = -18.80(8) cm-1for 5. For pentanuclear complex 2, three types of magnetic-exchange interactions, two ferromagnetic (Ja= +16.02 cm-1, and Jb= +9.02 cm-1) and an antiferromagnetic (Jc= -49.7 cm-1), have been identified.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Suman K
authors.initials: SK
authors.lastname: Barman
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMOL), Universitat de València , Polígono de la Coma, s/n, 46980 Paterna, València, Spain.
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.|Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741 246, India.
authors.forename: Rabindranath
authors.identifier: http://orcid.org/0000-0003-0739-5896
authors.initials: R
authors.lastname: Mukherjee
mesh_terms: D018360:Crystallography, X-Ray; D004952:Esters / Q000737:chemistry*; D006867:Hydrolases / Q000737:chemistry*; D006868:Hydrolysis; D009532:Nickel / Q000737:chemistry*; D011199:Potentiometry; D012997:Solvents / Q000737:chemistry*
chemical_list: D004952:Esters; D012997:Solvents; D009532:Nickel; D006867:Hydrolases