Group 4 metalloporphyrin diolato complexes and catalytic application of metalloporphyrins and related transition metal complexes

Abstract

<p>In this work, the first examples of group 4 metalloporphyrin 1,2-diolato complexes were synthesized through a number of strategies. In general, treatment of imido metalloporphyrin complexes, (TTP)M=NR, (M = Ti, Zr, Hf), with vicinal diols led to the formation of a series of diolato complexes. Alternatively, the chelating pinacolate complexes could be prepared by metathesis of (TTP)MCl 2 (M = Ti, Hf) with disodium pinacolate. These complexes were found to undergo C-C cleavage reactions to produce organic carbonyl compounds.;For titanium porphyrins, treatment of a titanium(II) alkyne adduct, (TTP)Ti(eta 2-PhC≡CPh), with aromatic aldehydes or aryl ketones resulted in reductive coupling of the carbonyl groups to produce the corresponding diolato complexes. Unreactive aliphatic aldehydes or ketones could be incorporated into a diolato complex on reaction with a reactive precursor, (TTP)Ti[O(Ph) 2C(Ph)2O] to provide unsymmetrical diolato complexes. In addition, an enediolato complex (TTP)Ti(OCPhCPhO) was obtained from the reaction of (TTP)Ti(eta2-PhC≡CPh) with benzoin.;Titanium porphyrin diolato complexes were found to be intermediates in the (TTP)Ti=O-catalyzed cleavage reactions of vicinal diols, in which atmospheric oxygen was the oxidant. Furthermore, (TTP)Ti=O was capable of catalyzing the oxidation of benzyl alcohol and a alpha-hydroxy ketones to benzaldehyde and alpha-diketones, respectively. Other high valent metalloporphyrin complexes also can catalyze the oxidative diol cleavage and the benzyl alcohol oxidation reactions with dioxygen.;A comparison of Ti(IV) and Sn(IV) porphyrin chemistry was undertaken. While chelated diolato complexes were invariably obtained for titanium porphyrins on treatment with 1,2-diols, the reaction of vicinal diols with tin porphyrins gave a number of products, including mono-, bis-alkoxo, and chelating diolato complexes, depending on the identity of diols and the stoichiometry employed. Tin porphyrin complexes also promoted the oxidative cleavage of vicinal diols and the oxidation of alpha-ketols to alpha-diketones with dioxygen.;In extending the chemistry of metalloporphyrins and analogous complexes, a series of chiral tetraaza macrocyclic ligands and metal complexes were synthesized. Examination of iron(II) complexes showed that they efficiently catalyzed the cyclopropanation of styrene by diazo reagents. Good yields and high diastereoselectivity were obtained with modest enantioselectivity. A rationalization of the stereoselectivity was presented on the basis of structural factors in a carbene intermediate.</p>