Abstract
The reaction between [Mo(CO)~4~(NO)(ClAlCl~3~)] and the sterically hindered diphosphanes (P∩P) 1,3‐bis(diisopropylphosphanyl)propane (dippp, a), 1,2‐bis(diisopropylphosphanyl)ethane (dippe, b), 1,1′‐bis(diisopropylphosphanyl)ferrocene (dippf, c) and 1,2‐bis(dicyclohexylphosphanyl)ethane (dcype, d) produced the chlorides [Mo(P∩P)(CO)~2~(NO)Cl] (1a–1d), which were transformed into the corresponding hydrides [Mo(P∩P)(CO)~2~(NO)H] (2a–2d) by reaction with LiBH~4~ in Et~3~N at room temperature. The molybdenum–THF complex [Mo(dippp)(CO)~2~(NO)(THF)][BAr^F^~4~] [3a; Ar^F^ = 3,5‐(CF~3~)~2~C~6~H~3~], obtained by the reaction of 2a with [H(Et~2~O)~2~][BAr^F^~4~], was exemplarily tested in the hydrogenation of the imine PhCH=N(α‐naphthyl). Replacement of the [BAr^F^~4~]^–^ counterion by the more stable [B(C~6~F~5~)~4~]^–^ anion greatly increased the catalytic activity. The use of in situ mixtures of the hydrides 2a–2d and [H(Et~2~O)~2~][B(C~6~F~5~)~4~] improved the hydrogenation activity. The hydride 2b in combination with [H(Et~2~O)~2~][B(C~6~F~5~)~4~] exhibited the highest TOF value of 123 h^–1^ in the reduction of PhCH=N(α‐naphthyl). The hydrogenation of the imines PhCH=NPh, p‐ClC~6~H~4~CH=NPh, p‐ClC~6~H~4~CH=N‐p‐C~6~H~4~Cl, PhCH=NCH(Ph)~2~ and PhCH=NMes showed TOF values of 34, 74, 41, 18 and 84 h^–1^ at room temperatureand a H~2~ pressure of 30 bar. A mechanism for the ionic hydrogenation with “proton‐before‐hydride transfer” is anticipated.