Bis(η 5 :η 1 -(di-para-tolyl)pentafulvene)niobium chloride (1) reacts with methyl lithium via salt metathesis to the methylated bis(pentafulvene)niobium complex 2, and with lithium 2,6diisopropylanilide addition and subsequent NÀ H bond activation to the imido mono(pentafulvene)niobium complex 3. Avoiding the competing protonation of the chloride, bis(pentafulvene)niobium complex 2 reacts with primary aromatic and aliphatic amines to form terminal niobocene imido complexes, and with water to form the analog terminal oxo complex. Secondary methyl amines undergo a simultaneous NÀ H and CÀ H activation to form niobaaziridines under mild conditions. In contrast to other reported examples, 3 can be employed to investigate the uncontested reactivity of mono(pentafulvene)niobium complexes. Reaction with 4-tertbutylphenol selectively yields a niobocene phenolate complex. Unprecedented for mono(pentafulvene)niobium complexes, treating 3 with multiple-bond-containing substrates (nitriles, isocyanates) smoothly results the insertion into the Nb-C exo σbond, forming the corresponding alkylidene amido and imidato complexes.

Addition of the parent allene H2CCCH2 to the bis(pentafulvene)titanium complexes Ti1a,b results in the formal nucleophilic attack of one of the exocyclic quaternary carbon atoms (Cq,exo) of one pentafulvene ligand at the central propa-1,2-diene carbon atom to form the titanium complexes Ti2a,b bearing both one intact pentafulvene ligand and a bidentate cyclopentadienyl-/allyl-based ligand, whose functionalities are spaced by a C1 linker. Investigations into the nature of the Ti–allyl interaction is established by multinuclear NMR spectroscopy, single crystal X-ray diffraction, and combined computational studies. A first glimpse of the reactivity of Ti2a,b is demonstrated showing that both the intact pentafulvene ligand and the allyl unit can be modified.

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