Encouraged by the high activity of the semihydrogenation of 1a, a series of aryl-aryl substituted alkynes were investigated as substrates (Table ). It turned out that in order to achieve high yields and good E/Z rations, for substrates other than 1a the catalyst loadings had to be increased from 0.5 to 1 or 2 mol% in the case of terminal alkynes (vide infra). Likewise, when the reactions were performed at 90 o C significantly higher yields and E/Z ratios could be achieved.