Synthesis, Structure, Spectroscopy, and Reactivity of Azapentadienyl–Cobalt–Phosphine Complexes

We report the synthesis, structure, spectroscopy, and reactivity of the first examples of azapentadienyl–cobalt complexes. Treatment of (Cl)­Co­(PMe3)3 with potassium tert-butylazapentadienide produces ((1,2,3-η3)-5-tert-butylazapentadienyl)­Co­(PMe3)3 (1), a dark red solid. Compound 1 undergoes ligand substitution reactions with trimethyl phosphite and carbon monoxide, producing ((1,2,3-η3)-5-tert-butylazapentadienyl)­Co­(PMe3)2[P­(OMe)3] (2) and ((1,2,3-η3)-5-tert-butylazapentadienyl)­Co­(PMe3)2(CO) (3), respectively. Compounds 1–3 react with 1 equiv of triflic acid (HO3SCF3) at the azapentadienyl nitrogen, yielding the corresponding η4-(tert-butylamino)­butadiene–cobalt complexes (4–6). These cations have unusually long Co–C4 bond distances, indicating that η3 resonance structures are contributing to the overall bonding picture. Treatment of compound 4 with P­(OMe)3 or CO leads to displacement of (tert-butylamino)­butadiene (rather than PMe3 ligand exchange) and formation of Co­(PMe3)2[P­(OMe)3]3+O3SCF3– (7) or Co­(PMe3)3(CO)2+O3SCF3– (8), respectively. Compound 5 reacts readily with a another 1 equiv of triflic acid, again at the nitrogen center. The dicationic product, 9, possesses an η4-(tert-butylammonium)­butadiene ligand with a strong Co–C4 interaction. The X-ray crystal structures of compounds 1–4, 6, 7, and 9 have been obtained.