Metal Node Control of Bronsted Acidity in Heterobimetallic Titanium-Organic Frameworks

Abstract

[EN] Compared to indirect framework modification, synthetic control of cluster composition can be used to gain direct access to catalytic activities exclusive of specific metal combinations. We demonstrate this concept by testing the aminolysis of epoxides with a family of isostructural mesoporous frameworks featuring five combinations of homometallic and heterobimetallic metal-oxo trimers (Fe3, Ti3, TiFe2, TiCo2, and TiNi2). Only TiFe2 nodes display activities comparable to benchmark catalysts based on grafting of strong acids, which here originate from the combination of Lewis Ti4+ and Bronsted Fe3+-OH acid sites. The applicability of MUV-101(Fe) to the synthesis of beta-amino alcohols is demonstrated with a scope that also includes the gram scale synthesis of propranolol, a natural beta-blocker listed as an essential medicine by the World Health Organization, with excellent yield and selectivity.