5 years ago

End-On Bridging Dinitrogen Complex of Scandium

End-On Bridging Dinitrogen Complex of Scandium
Filipp Furche, Timothy J. Boyle, Guo P. Chen, David H. Woen, William J. Evans, Joseph W. Ziller
The first (N═N)2– complex of a rare-earth metal with an end-on dinitrogen bridge, {K(crypt)}2{[(R2N)3Sc]2[μ-η11-N2]} (crypt = 2.2.2-cryptand, R = SiMe3), has been isolated from the reduction of Sc(NR2)3 under dinitrogen at −35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically characterized rare-earth metal (N═N)2– complexes of formula [A2Ln(THF)x]2[μ-η22-N2] (Ln = Sc, Y, and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide, and aryloxide). The 1.221(3) Å N—N distance and the 1644 cm–1 Raman stretch are consistent with the presence of an (N═N)2– bridge. The observed paramagnetism of the complex by Evans method measurements is consistent with DFT calculations that suggest a triplet (3A2) ground state in D3 symmetry involving two degenerate Sc—N2—Sc bonding orbitals. Upon brief exposure of the orange Sc3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc2+ complex, [K(crypt)][Sc(NR2)3], was observed. Conversion of the Sc2+ complex to the Sc3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)}2{[(R2N)3Sc]2[μ-η11-N2]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b08456

DOI: 10.1021/jacs.7b08456

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