Super‐Bulky Penta‐arylcyclopentadienyl Ligands: Isolation of the Full Range of Half‐Sandwich Heavy Alkaline‐Earth Metal Hydrides

Hydrogenolysis of the half‐sandwich penta‐arylcyclopentadienyl‐supported heavy alkaline‐earth‐metal alkyl complexes (Cp^Ar)AeCH(SiMe₃)₂](S) (Cp^Ar=C₅Ar₅, Ar=3,5‐ⁱPr₂‐C₆H_3; S=THF or DABCO) in hexane afforded the calcium, strontium, and barium metal–hydride complexes as the same dimers (Cp^Ar)Ae(μ‐H)(S)]₂ (Ae=Ca, S=THF, 2‐Ca ; Ae=Sr, Ba, S=DABCO, 4‐Ae ), which were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. 2‐Ca , 4‐Sr , and 4‐Ba catalyzed alkene hydrogenation under mild conditions (30 °C, 6 atm, 5 mol % cat.), with the activity increasing with the metal size. A variety of activated alkenes including tri‐ and tetra‐substituted olefins, semi‐activated alkene (Me₃SiCH=CH₂), and unactivated terminal alkene (1‐hexene) were evaluated.