Barium‐Catalyzed Dehydrocoupling of Terminal Alkynes and Hydrosilanes

The dehydrocoupling of terminal alkynes and hydrosilanes catalyzed by alkaline‐earth complexes: calcium, strontium and, most prominently, barium, is reported. [Ba{N(SiMe 3 ) 2 } 2 .(thf) 2 ] ( 1 ) is a convenient precatalyst, affording conversions in the range 75–95+% and good chemoselectivity for substrates bearing aromatic substituents, e.g., with the benchmark phenylacetylene and phenyldimethylhydrosilane. Over 20 different combinations of substrates were coupled, typically over 12–24 h at 90 °C with a 5 mol‐% loading of 1 . Reaction rates increase upon descending group 2, according to Ca < Sr < Ba. Kinetic analysis performed for the coupling of our benchmark substrates catalyzed by 1 in pyridine‐ d 5 allows for the determination of the rate law r = k .[barium] 1 .[PhMe 2 SiH] 1 , with Δ H ‡ = 12.7(1) kcal mol –1 and Δ S ‡ = –42.8(1) cal mol –1 K –1 consistent with a kinetically affordable, albeit relatively slow, reaction. DFT calculations conducted on the system 1 /pyridine indicate the mono‐solvated [Ba{N(SiMe 3 ) 2 } 2 .pyridine] to be the prevailing catalyst, with a rate‐determining step consisting of the protonolysis between a [Ba]‐hydride intermediate and floating HN(SiMe 3 ) 2 . Compared to Ca and Sr, the greater efficiency of Ba precatalysts stems from the greater ability of barium to lose precoordinated pyridine and, thus, to generate the catalytically competent mono‐solvated species.