Alternative Conceptual Approach to the Design of Bifunctional Catalysts: An Osmium Germylene System for the Dehydrogenation of Formic Acid

Abstract

The reaction of the hexahydride OsH 6 (P i Pr 3 ) 2 with a P,Ge,P-germylene-diphosphine affords an osmium tetrahydride derivative bearing a Ge,P-chelate, which arises from the hydrogenolysis of a P–C(sp 3 ) bond. This Os(IV)–Ge(II) compound is a pioneering example of a bifunctional catalyst based on the coordination of a σ-donor acid, which is active in the dehydrogenation of formic acid to H 2 and CO 2 . The kinetics of the dehydrogenation, the characterization of the resting state of the catalysis, and DFT calculations point out that the hydrogen formation (the fast stage) exclusively occurs on the coordination sphere of the basic metal center, whereas both the metal center and the σ-donor Lewis acid cooperatively participate in the CO 2 release (the rate-determining step). During the process, the formate group pivots around the germanium to approach its hydrogen atom to the osmium center, which allows its transfer to the metal and the CO 2 release.

Homogeneous catalysis with polyhydride complexes

“…The first of these polyhydrides is stabilized by the P , O , P -pincer ether-diphosphine 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(P i Pr 2 ) 2 ), 84 whereas the pincer positions in the tetrahydride are occupied by a mixed-system ligand formed by the monodentate triisopropylphosphine and a P ,Ge( ii )-chelate. 85 In both cases, the kinetic study of the catalysis revealed that the dehydrogenation rate is independent of the concentration of formic acid, while it is first order in osmium concentration. The Δ G ‡ 298K values lie within the range of those reported for such dehydrogenation promoted by other homogeneous systems (17–26 kcal mol −1 ).…”

“…In contrast to the latter, it is a pioneering example of a bifunctional catalyst alternative to the traditional ones. 85 Bifunctional catalysts are based on metal–ligand cooperation, which implies a distribution of roles between the metal and some coordinated ligand. 87 In most cases, the metal acts as a Lewis acid whereas the ligand is a Lewis base, 88 but there are also catalysts of this class formed by a basic metal and an acidic σ- and π-acceptor Z-type ligand.…”

Mechanistic Investigations on Hydrogenation, Isomerization and Hydrosilylation Reactions Mediated by a Germyl‐Rhodium System

“…This system circumvents the traditional Chalk‐Harrod type mechanisms and instead operates through the direct addition of a silylene Si–H bond to the olefin, with implications in other catalytic processes [8] . More recently, Esteruelas and Cabeza have described an osmium germylene complex that mediates the dehydrogenation of formic acid by an Os/Ge synergistic pathway [9] …”

“…[8] More recently, Esteruelas and Cabeza have described an osmium germylene complex that mediates the dehydrogenation of formic acid by an Os/Ge synergistic pathway. [9] Our group has recently capitalized on this capacity for transition metal-tetrel bimetallic cooperation to disclose an unusual dehydrogenative double CÀ H bond activation process. This transformation, which involves the formation of compound 3, is triggered by thermolysis of compound 2 (Figure 1).…”

Sn,P-Peri-Substituted Naphthalene as a Ligand for Transition Metals

“…Incorporation of additional donors into HTs thus provided diverse pincer systems of the E , C , E -, E , N , E -, N , E , N -, and P , E , P -type ( E = Si, Ge, or Sn). Their reactions with TMs, including some catalytic reactions, were also studied. , However, the main emphasis of this line of research is on lighter elements (Si or Ge), while studies based on stannylene ligands are less common. Hahn and co-workers reported N , Sn , N -type pincer ligands A , Deelman showed possible P , Sn , P -coordination in complexes B , while Castel’s group reported the isolation of a potential P , Sn , P ligand C (Figure ).…”