Functionalization of the nitrogen atoms in the hafnocene oxamidide complexes [Me2Si(eta Me-5(4))(eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2) and (eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2), prepared from CO-induced N-2 bond cleavage, was explored by cycloaddition and by formal 1,2-addition chemistry. The ansa-hafnocene variant, [Me2Si(eta Me-5(4))(eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2), undergoes facile cycloaddition with heterocumulenes such as tBuNCO and CO2 to form new N-C and Hf-O bonds. Both products were crystallographically characterized, and the latter reaction demonstrates that an organic ligand can be synthesized from three abundant and often inert small molecules: N-2, CO, and CO2. Treatment of [Me2Si(eta Me-5(4))(eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2) with 12 yielded the monomeric iodohafnocene isocyanate, [Me2Si(eta Me-5(4))(eta(5)-C5H3-3-Bu-t)Hf](2)(NCO) demonstrating that C-C bond formation is reversible. Alkylation of the oxamidide ligand in eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2) was explored due to the high symmetry of the complex. A host of sequential 1,2-addition reactions with various alkyl halides was discovered and both N- and N,N'-alkylated products were obtained. Treatment with Bronsted acids such as HCl or ethanol liberates the free oxamides, H(R-1)NC(O)C(O)N(R-2)H, which are useful precursors for N,N'-diamines, N-heterocyclic carbenes, and other heterocycles. Oxamidide functionalization in (eta(5)-C5H3-3-Bu-t)Hf](2)(N2C2O2) was also accomplished with silanes and terminal alkynes, resulting in additional N-Si and N-H bond formation, respectively.