N,N-Bis(Mercaptoethyl)-1,4-Diazacycloheptane (H2BME-DACH) and its Nickel Complex: A Model for Bioinorganic Chemistry
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2014 by John Wiley & Sons, Inc. All rights reserved. The impressive sulfur-based reactivity of square planar nickel complexes containing tetradentate N2S2 ligands has been known for many years. Interest has recently resurfaced because of the discovery of similar donor sites in metalloproteins that bind nickel, iron, and cobalt. The seven-membered ring analog diazacycloheptane (DACH) is commercially available and reacts with ethylene sulfide to produce the bis(mercaptoethyl) derivative, BME-DACH. This chapter describes the synthesis of the H2(BME-DACH) ligand and its nickel complex. Sulfur dioxide can bind to a metal center as a Lewis base in at least five different coordination modes, and can also act as a Lewis acid by interacting with an electron-rich metal or with available lone pairs such as those on a thiolate, SR-, ligand. Examples of complexes capable of forming ligand-based SO2 adducts are Ni(BME-diazacyclooctane (DACO)), Ni(Ph2PCH2CH2S)2, and Pd(BME-DACO). The chapter also describes another example of reactivity at sulfur: the acylation of Ni(BME-DACH).