Stereoselective alkyne semihydrogenations with an air-stable copper(i) catalyst. 
An air-stable and preactivated copper(i) hydroxide/N-heteroyclic carbene (NHC) complex for alkyne semihydrogenations is reported.  Next to an enhanced practicability of the process, the resulting alkenes are obtained with high Z-selectivities and no overreduction to the corresponding alkanes.