Direct Access to Titanocene Imides via Bis(eta(5):eta(1)-pentafulvene)titanium Complexes and Primary Amines

The formation of the titanocene imido complexes 2b, 4, and 5 via double N-H bond activations at ambient temperature of sterically demanding amines (2,6-diisopropylaniline, tert-butylamine) by the use of the bis(eta(5):eta(1)-adamantylidenepentafulvene)titanium complex (1) has been investigated. and The titanium imido complex 2b exists in equilibrium with its corresponding titanium monoamide complex 2a. The equilibrium can be shifted to the side of the imide 2b by increasing the temperature. Starting from the equilibrium 2a/2b, or the titanium imido pyridine adduct 5, a broad range of [2 + 2] cycloaddition reactions are realized. In reactions with alkynes, the regioselective formation of the azacyclobutenes 6 and 7 are observed. By using carbodiimides, asymmetric (8 and 10a) and symmetric cycloaddition products (9 and lob) are formed. In the reaction with isocyanates, dependent on the substitution pattern of the Ti=NR imido unit, the C=O or the C=N [2 + 2] cycloaddition occurs, resulting in the N,O-bound ureato(2-) complex 11 or the N,N-bound ureato(2-) complex 13. In the presence of isocyanates and nitriles, the equilibrium 2a/2b results in ring enlargement reactions to six-membered rings (12, 14) by insertion of a second equivalent of the substrate into the Ti-N bonds.