LAUSR

The bench-stable cationic bis(σ-B-H) aminoborane complex [Fe(PNPNMe-iPr)(H)(η2-H2B=NMe2)]+ (2) efficiently catalyzes the semi-hydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes. Moreover, selective incorporation of deuterium was achieved in the case of 1,3-diynes and 1,3-enynes. The catalytic reaction takes place under mild conditions (25oC, 4-5 bar H2 or D2) in 1 h and alkenes were obtained with high Z-selectivity for a broad scope of substrates. Mechanistic insight into the catalytic reaction, explaining also the stereo- and chemoselectivi-ty, is provided by means of DFT calculations. Intermediates featuring a bis-dihydrogen moiety [Fe(PNPNMe-iPr)(η2-H2)2]+ are found to play a key role. Experimental support for such species was unequivocally provided by the fact that [Fe(PNPNMe-iPr)(H)(η2-H2)2]+ (3) exhibited the same catalytic activity than 2. The novel cationic bis-dihydrogen complex 3 was obtained by protonolysis of [Fe(PNPNMe-iPr)(H)(η2-AlH4)]2 (1) with an excess of nonafluoro-tert-butyl alcohol.