Abstract
Reduction of (Nacnac)DippCo(μ-Cl)2Li(THF)2 (Nacnac = HC(C(Me)NC6H3iPr2)2) by KC8 in toluene led to isolation of inverted-sandwich complex (μ-η2:η2-C7H8)[Co(Nacnac)Dipp]2 (1) in good yield. Then we found compound 1 able to activate small molecules and various organic functionalities, generating novel cobalt-containing complexes. Treatment of 1 with P4 afforded a P4-bridged compound (μ-η4:η4-P4)[Co(Nacnac)Dipp]2 (2), then we heat 2 for 4 days resulted in (μ-η3:η3-P3)[Co(Nacnac)Dipp]2 (3) with one phosphorus loss. Reaction with chalcogen elements furnished [Co(Nacnac)Dipp(μ-X)]2 (4: X = S; 5: X = Se) and [Co(Nacnac)Dipp(μ-TeH)]2 (6) respectively. While treatment of 1 with excess nitric oxide afforded diamagnetic compound Co(Nacnac)Dipp(NO)2 (7). Then we investigated the reactivity of 1 with organic functionalities. Reaction with p-TolN3 produced not only a five-membered-ring complex Co(Nacnac)Dipp(1,4-p-Tol2N4) (8), but a minor product [Co(Nacnac)Dipp(μ-N-p-Tol)]2 (9). Treatment of 1 with azobenzene led to isolation of (μ-κ1:κ1-PhNNPh)[Co(Nacnac)Dipp]2 (10), which had slightly activated N-N bond. Moreover, complex 1 can catalyze cyclotrimerization of alkynes and form C-C triple bond coordinated complexes while reaction with more steric hindered alkynes such as Me3SiCCH. The reaction of 1 with 1,3,5,7-cyclooctatetraene afforded novel compound C16H16Co2(Nacnac)Dipp2 (13), two COTs forming a new C16H16 skeleton containing 3 fused ring. While treatment with 1,3,5-cycloheptatiene produced (μ-η4:η4-C7H8)[Co(Nacnac)Dipp]2 (14) without dimerization of cycloheptatriene. Moreover, we used less hindered ligand to synthesize vanadium complex (Nacnac)ArVCl2 (Ar = Dmp or Dep). Then we reduced it by KC8 in THF under N2 afforded [(Nacnac)ArV]2 (15: Ar = Dmp; 16: Ar = Dep) without N2 fixation. Reaction of amidinate with anhydrous CoCl2 and NiI2 produced (DippNC(H)NDipp)Co(μ-Cl)2Li(THF)2 (18) and (η1-DippNC(H)NDipp)NiI3Li(THF)2(OEt2)2 (22) respectively. Reduction of 18 and 22 furnished unprecedented low-coordinate complex [M(μ-η2-DippNC(H)NDipp)]2 (20: M = Co; 24: M = Ni). Moreover, treatment of 22 with 1.5 equivalent KC8 produced mixed-valence (μ-I)[Ni(μ-η2-DippNC(H)NDipp)]2 (23).