Reactivity of the Metal→BX₃ Dative σ-Bond:  1,2-Addition Reactions of the Fe→BX₃ Moiety of the Ferraboratrane Complex [κ⁴-B(mim^But)₃]Fe(CO)₂

The ferraboratrane [κ⁴-B(mim^But)₃]Fe(CO)₂ (mim^But = 2-mercapto-1-tert-butylimidazolyl), the first example of a complex which possesses a retrodative (i.e., metal-to-ligand) Fe→B bond, is obtained via reaction of the tris(2-mercapto-1-tert-butylimidazolyl)hydroborato complex [Tm^But]FeCl with LiCH₂SiMe₃ followed by treatment with CO. Significantly, [κ⁴-B(mim^But)₃]Fe(CO)₂ exhibits novel reactivity towards a variety of reagents that results in eradication of the Fe→B bond via a formal 1,2-addition process and the formation of B-functionalized tris(mercaptoimidazolyl)borate derivatives, [XTm^But]FeY.