Regiodivergent Hydrogermylation of Alkynes Enabled by Dinuclear Cobalt Catalysts Bearing Different Ligands

Abstract

ABSTRACT Transition‐metal‐catalyzed hydrogermylation of alkynes represents an ideal atom‐economical method to prepare vinylgermanes that are valuable reagents in medicinal chemistry, material science and organic synthesis. Nevertheless, its development―particularly in achieving high regioselectivity with earth‐abundant 3d metal catalysts―remains as a formidable challenge. Herein, we report regiodivergent hydrogermylation reactions of alkynes employing structure well‐defined dicobalt carbonyl complexes as catalysts: the reaction using [(IPent)Co 2 (CO) 7 ] (IPent = 1,3‐di(2,6‐di(pentan‐3‐yl)phenyl)imidazol‐2‐ylidene) affords selectively α ‐vinylgermanes, whereas that with [(Xantphos)Co 2 (CO) 6 ] (Xantphos = (9,9‐dimethyl‐9 H ‐xanthene‐4,5‐diyl)bis(diphenylphosphane) yields selectively β‐ ( E )‐vinylgermanes. Both cobalt catalysts effect the hydrogermylation of alkyl‐ and aryl‐substituted terminal alkynes with tertiary hydrogermanes with good functional group compatibility in good to high yields and selectivity. Mechanistic studies establish alkyne‐bridged dicobalt carbonyl species as the active intermediates in both catalytic systems and the distinct steric nature of the metalloligands LCo (L = IPent, Xantphos) governs the observed regiodivergent selectivity. The application of these dicobalt‐catalysts to alkyne hydroelementation reactions allows the selective preparation of different configurational isomers of vinylgermanes/silanes that can be further utilized for the stereoselective synthesis of alkene derivatives.