Tandem catalysis is a growing field that is beginning to yield important scientific and technological advances toward new and more efficient catalytic processes. 'One-pot' tandem reactions, where multiple catalysts and reagents, combined in a single reaction vessel undergo a sequence of precisely staged catalytic steps, are highly attractive from the standpoint of reducing both waste and time. Orthogonal tandem catalysis is a subset of one-pot reactions in which more than one catalyst is used to promote two or more mechanistically distinct reaction steps. This Perspective summarizes and analyses some of the recent developments and successes in orthogonal tandem catalysis, with particular focus on recent strategies to address catalyst incompatibility. We also highlight the concept of thermodynamic leveraging by coupling multiple catalyst cycles to effect challenging transformations not observed in single-step processes, and to encourage application of this technique to energetically unfavourable or demanding reactions.

Wet chemical screening reveals the very high reactivity of Mo(NMe ) with H S for the low-temperature synthesis of MoS . This observation motivated an investigation of Mo(NMe ) as a volatile precursor for the atomic layer deposition (ALD) of MoS thin films. Herein we report that Mo(NMe ) enables MoS film growth at record low temperatures-as low as 60 °C. The as-deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforward fabrication of diverse device structures.

Rapid, clean hydroboration of ketones and aldehydes with HBpin is achieved using the homoleptic rare-earth catalyst La­[N­(SiMe3)2]3 (LaNTMS). The reaction employs low catalyst loadings (0.01–1 mol % LaNTMS), proceeds rapidly (>99% in 5 min) at 25 °C, and is moderately air-tolerant. Additionally, this hydroboration has good functional group compatibility, including halides, nitro groups, and nitriles, and is exclusively carbonyl-selective in the presence of alkenes and alkynes.

Tris­[N,N-bis­(trimethylsilyl)­amido]­lanthanum (LaNTMS) is an efficient, highly active, and selective homogeneous catalyst for ester reduction with pinacolborane (HBpin). Alkyl and aryl esters are cleaved to the corresponding alkoxy- and aryloxy-boronic esters which can then be straightforwardly hydrolyzed to alcohols. Ester reduction is achieved with 1 mol % catalyst loading at 25–60 °C, and most substrates are quantitatively reduced in 1 h. Nitro, halide, and amino functional groups are well tolerated, and ester reduction is completely chemoselective over potentially competing intra- or intermolecular alkene or alkyne hydroboration. Kinetic studies, isotopic labeling, and density functional theory calculations with energetic span analysis argue that ester reduction proceeds through a rate-determining hydride-transfer step that is ligand-centered (hydride is transferred directly from bound HBpin to bound ester) and not through a metal hydride-based intermediate that is often observed in organolanthanide catalysis. The active catalyst is proposed to be a La-hemiacetal, [(Me3Si)2N]2La-OCHR­(OR)­[HBpin], generated in situ from LaNTMS via hydroboronolysis of a single La–N­(SiMe3)2 bond. These results add to the growing compendium of selective oxygenate transformations that LaNTMS is competent to catalyze, further underscoring the value and versatility of homoleptic lanthanide complexes in homogeneous catalytic organic synthesis.

Selective ether/ester C–O bond hydrogenolysis of an acetylated lignin model is achieved using a thermodynamically leveraged tandem catalytic strategy. Acetylation serves to (1) solubilize both lignin and lignin models and to (2) modify the reactivity of pendant hydroxy groups to promote more selective C–O cleavage.