Certain titanium and zirconium complexes catalyze intermolecular hydroamination of alkynes and allenes. Both stoichiometric and catalytic variants were initially examined with zirconocene bis(amido) complexes. Titanocene amido and sulfonamido complexes catalyze the intra-molecular hydroamination of aminoalkenes via a [[2+2 Photocycloaddition|[2+2] cycloaddition]] that forms the corresponding azametallacyclobutane, as illustrated in the figure below. Subsequent protonolysis by incoming substrate gives the α-vinyl-pyrrolidine (1) or tetrahydropyridine (2) product. Experimental and theoretical evidence support the proposed imido intermediate and mechanism with neutral group IV catalysts.