The zirconium and hafnium imido metalloporphyrin complexes (TTP)M=NAriPr (TP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; Ar-iPr, 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC('Bu)CHC('Bu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO](2) (4) is fanned upon reaction of (TTP)Zr=NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr](2)(mu-O)(mu-OH)(2) (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.