Synthesis, characterization, and reactivity of group 4 metalloporphyrin diolate complexes

A number of group 4 metalloporphyrin diolate complexes were synthesized via various approaches. For example, treatment of imido complex (TTP)Hf=NAriPr with diols resulted in formation of the corresponding diolato complexes (TTP)Hf[OCR1R2CR1R2O] (R-1 = R-2 = Me, 1; R-1 = Me, R-2 = Ph, 2; R-1 = R-2 Ph, 3). Treatment of (TTP)Ti=(NPr)-Pr-i with diols generated (TTP)Ti[OCR1R2CR1R2O] (R-1 = R-2 Me, 5; R-1 = Me, R-2 = Ph, 6; R, = H, R-2 = Ph, 7; R-1 = H, R-2 = p-tolyl, 8). Alternatively hafnium and titanium pinacolates 1 and 5 were prepared through metathetical reactions of (TTP)MCl2 (M = Hf, Ti) with disodium pinacolate. The substitution chemistry of hafnium complexes correlated well with the basicity of the diolato ligands. Complexes 1-6 underwent oxidative cleavage reaction, producing carbonyl compounds and oxometalloporphyrin species. For less substituted diolates 7 and 8, an array of products including the enediolate complexes (TTP)Ti [OC(Ar)C(Ar)O] (Ar = Ph, 9; Ar = p-tolyl, 10) was observed. The possible cleavage reaction pathways are discussed.