Extreme N⋮N Bond Elongation and Facile N-Atom Functionalization Reactions within Two Structurally Versatile New Families of Group 4 Bimetallic “Side-on-Bridged” Dinitrogen Complexes for Zirconium and Hafnium

Chemical reduction of (η5-C5Me4R)M[N(R‘)C(X)N(R‘)]Cl2 (M = Zr or Hf, X = NMe2 or Me, R = H or Me, R‘ = i-Pr, Et) with 3 equiv of potassium graphite (KC8) in tetrahydrofuran (THF) provides modest isolated yields of the corresponding “side-on-bridged” dinitrogen complexes, {(η5-C5Me4R)M[N(R‘)C(X)N(R‘)]}2(μ-η2:η2-N2) (1−6). Single-crystal X-ray analyses of these compounds provide d(N−N) bond length values of 1.518(2), 1.581(4), 1.600(6), 1.611(4), 1.630(4), and 1.635(5) Å for 1−6, respectively, that correlate with an increasing fold angle of the M2N2 core for an increase in d(N−N). Compounds 1−6 all undergo hydrosilylation and hydrogenation with PhSiH3 and H2 to provide the corresponding N-functionalized products, 7 and 8, resulting from single addition of these reagents at 25 °C. Compounds 5 and 6 reacted with ethylbromide at 25 °C to provide the N-alkylated products 9a and 9b, respectively, while reaction of 5 with 1 equiv of Br2 provided a near quantitative yield of the diazene dibromide 10 which was obtained as a minor co-product in the N-alkylation of 5.