Synthesis and reactivity towards amines of benzisothiazolinate-bridged paddlewheel dimers [M2(μ-bit)4·2H2O] (M = Mn, Co, Ni, Cu)

Abstract

Addition of sodium benzisothiazolinate, Na(bit), to metal salts MX2·nH2O (M = Mn, Co, Ni, Cu) affords a simple high yielding route to benzisothiazolinate-bridged paddlewheel dimers [M2(μ-bit)4·2H2O]. Upon reaction with amines these serve as useful synthons to access benzisothiazolinate chemistry. Addition of 4-aminopyridine (4-ampy) in ethanol leads to cleavage of dimers and formation of all trans-[M(4-ampy)2(κ1-bit)2(EtOH)2] (M = Co, Ni), the bit ligand binding in a monodentate fashion through the amide-nitrogen. With a slight excess of ethylenediamine (en) a similar cleavage occurs to afford trans-[M(κ1-bit)2(κ2-en)2] (M = Co, Ni, Cu). For nickel and copper, the intermediate five-coordinate mono-diamine derivatives cis-[M(κ1-bit)2(κ2-en)(H2O)] (M = Ni, Cu) have also been isolated. It is not necessary to isolate the dimers to access this chemistry; direct reactions of MX2·nH2O with either 1,4-bipyridine (bipy) or 1,10-phenanthroline (phen) and Na(bit) lead to cis-[M(κ1-bit)2(κ2-bipy)(H2O)2] (M = Co, Cu) and cis-[M(κ1-bit)2(κ2-phen)(H2O)L] (M = Mn, Co, L = H2O; M = Cu, L = EtOH) respectively. Molecular structures of [Cu2(μ -bit)4.2dmf]·2dmf, trans-[Co(4-ampy)2(κ1-bit)2(EtOH)2] and [Cu(κ1-bit)2(en)(H2O)]·H2O have been determined. This work highlights the easy accessibility of under exploited transition metal benzisothiazolinate chemistry and shows that this flexible ligand can adopt monodentate and bridging bidentate coordination modes.