Insertion of NH into the rheniumcarbon bonds of a Fischer-type rhenacyclobutadiene. Preparation and characterization of azarhenacyclic complexes

The rhenacyclobutadiene complex (CO)4ReC(CH3)C(CO2CH3)C(OEt) (1) reacts with 2,4-dinitrophenylhydrazine, tosylhydrazine or hydrazine hydrochloride to afford a new five-membered azarhenacyclic complex, (CO)4ReNHC(CH3)C(CO2CH3)C(OEt) (4), as a stable yellow solid. 4 was characterized by elemental analysis, EI mass spectrometry and IR and 1H and 13C NMR spectroscopy, and its structure was elucidated by X-ray diffraction techniques. The complex crystallizes in the triclinic system, space group P1, with a=8.721(1), b=12.172(2), c=15.013(2) A, α=86.42(1), β=88.83(1), γ=79.48(1)°, and four molecules per unit cell. The five-membered azarhenacycle is essentially planar, and the bond distances in the ring indicate strong electron delocalization, similar to that of the reported [1] analogous oxarhenacyclic complex (CO)4ReOC(CH3)C(CO2CH3)C(OEt) (2). Reaction between 1 and hydrazine monohydrate yields a mixture of 4 (minor product) and isomeric (CO)4ReC(CH3)C(CO2CH3)C(OEt)NH (major product, 5). The structure of 5 was assigned from spectroscopic evidence. 4 and 5 may be considered as organometallic analogues of pyrrole, i.e. rhenapyrrole complexes. Reaction of 4 with LDA followed by quenching with DCl in D20 at c. −78 °C results in hydrogen-deuterium exchange at the nitrogen atom.