Research

Organometallic Chemistry, Bond Activation and Green Homogeneous Catalysis

The insertion of transition metal complexes into chemical bonds can activate them towards uncommon transformations and form the basis for the design of new catalytic reactions and new synthetic methodology. Our studies in this area include the selective activation and functionalization of strong C-X (X= C, H, F, Cl), O-H and N-H bonds by specifically designed late transition metal complexes, leading, for example, to the first demonstration and mechanistic evaluation of metal insertion into strong C-C bonds, and to catalytic C-F activation. Among the ligands utilized in these studies are pincer-type tridentate frameworks which can impart on metal centers unusual modes of reactivity, leading to the discovery of novel metal-based compounds, including the first metalla-quinone, and a Pt(IV) terminal oxo complex which exhibits diverse reactivity, providing new insight into oxidation catalysis.

The design of ”green” synthetic methodology and new approaches to sustainable energy are major goals of modern catalysis. In recent years we have developed a new approach to bond activation by metal complexes, involving metal-ligand cooperation by aromatization-de-aromatization processes of pincer-type complexes, and have designed several environmentally benign catalytic reactions based on it, including (a) ruthenium-catalyzed dehydrogenative coupling of alcohols to form esters and H₂ (b) hydrogenation of esters to alcohols under mild conditions (c) coupling of amines with alcohols to form amides with liberation of H₂ (d) selective synthesis of primary amines directly from alcohols and ammonia (e) direct formation of acetals by dehydrogenative coupling of alcohols (f) generation of imines and hydrogen by coupling of alcohols with amines (g) dehydrogenative amidation of esters (h) dehydrogenative acylation of alcohols with esters (i) hydrogenation of amides to amines and alcohols (j) mild iron-catalyzed hydrogenation of ketones to acohols (k) iron catalyzed CO₂ hydrogenation to formate salts (l) hydrogenation of CO₂-derived organic carbonates, carbamates, ureas and formates as alternative routes for the conversion of CO₂ to methanol (m) catalytic transformation of alcohols to carboxylic acid salts using water as the terminal oxidant.  These reactions are efficient, proceed under neutral conditions and produce no waste.

Metal-ligand cooperation by aromatization – dearomatization of the hetero-aromatic ligand core of a pincer ruthenium complex has led to a distinct stepwise approach towards water splitting, based on consecutive thermal H₂ generation and light-induced O₂ liberation, using no sacrificial oxidants or reductants, and involving a new O-O bond-forming step.