Borane-Protected Cyanides as Surrogates of H-Bonded Cyanides in [FeFe]-Hydrogenase Active Site Models

摘要: Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN)2]2– [1]2– (pdt2– = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN)2]2– [3]2– (adt2– 1,3-azadithiolate, HN(CH2S–)2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3)2]2–. Attempts prepare 1:1 [1(BAr3)]2– (Ar Ph, C6F5) were unsuccessful, but related obtained using bulky borane B(C6F4-o-C6F5)3 (BArF*3). By virtue of N-protection by borane, salts [Fe2(pdt)(CO)4(CNBAr3)2]2– sustain protonation hydrides that are stable (in contrast [H1]−). The [H1(BAr3)2]− 2.5–5 pKa units more acidic than parent [H1]−. [1(BAr3)2]2– oxidize quasi-reversibly around −0.3 V versus Fc0/+ in ca. −0.8 observed for [1]2–/– couple. A simplified synthesis [1]2–, [3]2–, [Fe2(pdt)(CO)5(CN)]− ([2]−) was developed, entailing reaction diiron hexacarbonyl complexes with KCN MeCN.