Small molecule activation with bimetallic systems: a landscape of cooperative reactivity

Abstract

There is growing interest in the design of bimetallic cooperative complexes, which have emerged due to their potential for bond activation and catalysis, a feature widely exploited by nature in metalloenzymes, and also in the field of heterogeneous catalysis. Herein, we discuss the widespread opportunities derived from combining two metals in close proximity, ranging from systems containing multiple M-M bonds to others in which bimetallic cooperation occurs even in the absence of M⋯M interactions. The choice of metal pairs is crucial for the reactivity of the resulting complexes. In this context, we describe the prospects of combining not only transition metals but also those of the main group series, which offer additional avenues for cooperative pathways and reaction discovery. Emphasis is given to mechanisms by which bond activation occurs across bimetallic structures, which is ascribed to the precise synergy between the two metal atoms. The results discussed herein indicate a future landscape full of possibilities within our reach, where we anticipate that bimetallic synergism will have an important impact in the design of more efficient catalytic processes and the discovery of new catalytic transformations.

Fig. 1. Tunable features of bimetallic complexes and some examples of representative pathways for single vs. multi-site bond activation.

Fig. 2. Selected examples of bimetallic systems that exhibit remarkable cooperative reactivity.

Fig. 3. (a) Seminal discovery of reversible dihydrogen activation at a phosphino–borane pair. (b) Representative examples of the first transition metal FLPs developed based on Zr(iv) and first example of a bimetallic FLP based on the Pt(0)/Al(iii) pair.

Scheme 1. Lewis adduct formation equilibrium and FLP-type bimetallic activation of dihydrogen and acetylene by Au(i)/Pt(0) system.

Fig. 4. Solvent-dependent thermodynamics of the FLP equilibrium.

Fig. 5. Representation of the key transition states for the most relevant modelled mechanistic pathways and their associated overall energy barriers for H₂ splitting.

Fig. 6. Selectivity during acetylene activation by Au(i)/Pt(0) TMOFLPs.

Scheme 2. Reactivity of Au(i)/Pt(0) TMOFLP towards tetrylene dihalides.

Scheme 3. Bimetallic FLPs based on Au(i)/Rh(i) combinations. Intramolecular reactivity and N–H bond activation.

Scheme 4. Representative examples of MOLPs for the activation of small molecules.

Scheme 5. Activation of dihydrogen, alkynes, water and ammonia by a metal-only Lewis pair based on Pt and Ag.

Scheme 6. (a) Reaction of Pt(P^tBu₃)₂ with Lewis acidic organozinc compounds. (b) Activation of polar O–H bonds by Pt(0)/Zn(ii) and Pt(0)/Cu(i) cooperative bimetallic species.

Scheme 7. Synthesis of Rh(i) MOLPs with s-, p- and d-block Lewis acids.

Scheme 8. (a) Representative examples of quadruple (Cotton) and quintuple (Power) bonds in bimetallic complexes. (b) [2+2+2] alkyne cyclotrimerization mediated by a quintuply bonded Cr₂ complex (Tsai).

Scheme 9. Bimetallic elementary reactions for the trans-[H–MoMo–H] fragment.

Scheme 10. Incorporation of Zn–C and Zn–H bonds in the coordination sphere of quadruple metal–metal bonds.

Scheme 11. Coordination of Li–H (a) and Li–C (b) bonds to a bimetallic dimolybdenum fragment. Dinickel complex with C₆H₄ bridging ligand from the reactivity of Ni(COD)₂ and LiPh (c).

Scheme 12. Synthesis and reactivity of germyl-rhodium complexes.

Scheme 13. Cis-semi-hydrogenation of alkynes followed by the trans-isomerisation of alkenes of the overall Rh/Ge-catalysed trans-semi-hydrogenation of alkynes.

Scheme 14. Synthesis of a cationic gold germylene compound stabilized by a Ge-based π-interaction.

Miquel Navarro

Juan José Moreno

Marina Pérez-Jiménez

Jesús Campos