Rhodium mediated bond activation: from synthesis to catalysis

Abstract

Recently, our lab has developed monoanionic tridentate ligand, To{sup R}, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the To{sup R}-supported rhodium compounds. Tl[To{sup R}] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[To{sup M}] with [Rh({mu}-Cl)(CO)]{sub 2} and [Rh({mu}- Cl)(COE)]{sub 2} gives To{sup M}Rh(CO){sub 2} (2.2) and To{sup M}RhH({eta}{sup 3}-C{sub 8}H{sub 13}) (3.1) respectively while Tl[To{sup P}] with [Rh({mu}-Cl)(CO)]{sub 2} affords To{sup P}Rh(CO){sub 2} (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Bronsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex To{sup M}Rh(H){sub 2}CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary alcohols have been investigated as well. The proposed mechanism is based on the stochiometric reactions of the possible metal and organic intermediates. Primary amines, hypothesized to undergo a similar reaction pathway, have been verified to give dehydrogenative coupling product, imines. In the end, the well-developed neutral tridentate Tpm coordinates to the rhodium bis(ethylene) dimer in the presence of TlPF{sub 6} to give the cationic complex, [TpmRh(C{sub 2}H{sub 4}){sub 2}][PF{sub 6}] (5.1). 5.1 serves as the first example of explicit determination of the solid state hapticity, evidenced by X-ray structure, among all the cationic Tpm{sup R}M(C{sub 2}H{sub 4}){sub 2}{sup +} (Tpm{sup R} = Tpm, Tpm*, M = Rh, Ir) derivatives. The substitution chemistry of this compound has been studied by treating with soft and hard donors. The trimethylphosphine-sbustituted complex activates molecular hydrogen to give the dihydride compound.