Synthesis and reactivity of a new Fe(II) 5-(4-pyridyl)-tetrazolate complex and X-ray structure of its doubly protonated derivative.

Abstract

The synthesis of the new Fe(II) complex [CpFe(CO) 2(N 4C–C 5H 4N)] ( 2) is described. 1H- and 13C-NMR spectroscopy data of ( 2) indicate the presence of interannular conjugation in the pyridyl-tetrazolate ligand, implying coplanarity between the two rings. Addition of electrophiles to 2 resulted in the formation of cationic complexes such as [CpFe(CO) 2(4-MeN 4C–C 5H 4N)][O 3SCF 3] ( 3), [CpFe(CO) 2(4-HN 4C–C 5H 4N)][O 3SCF 3] ( 4) and of the doubly protonated complex [CpFe(CO) 2(4-HN 4C–C 5H 4N–H)][O 3SCF 3] 2 ( 5). In all cases, the out-of-plane rotation of the pyridyl ring occurred as a consequence of the quaternization of the N-4 of tetrazole ring. X-ray structure of complex 5 indicates a torsion angle of 20.9(2)° between the aromatic rings. Protonation reactions were found to be reversible and complexes 4– 5 were easily converted into the starting complex 2 by addition of a base.