Iridium(iii) hydrido complexes for the catalytic dehydrogenation of hydrazine borane

Abstract

The synthesis of 3,5-disubstituted cyclometalated iridium(iii) hydrido complexes of the type [3,5-R(POCOP)IrHX] (3,5-R(POCOP) = κ-CHR-2,6-(OPtBu) with R = t-Bu, COOMe; X = Cl, H) is described. All complexes were investigated in the catalytic dehydrogenation of hydrazine borane and compared with the unsubstituted compounds [(POCOP)IrHX] (X = Cl, H). All catalysts are highly active and recyclable, clearly maintaining hydrogen production activity. The dehydrogenation products were structurally characterised by solid state NMR and FTIR spectroscopy. Experimental observations were complemented by a dispersion-corrected DFT study to rationalise the mechanism of hydrazine borane dehydrogenation.

Amine–Borane Dehydropolymerization: Challenges and Opportunities

“…The iterative development of new generation catalysts based on specific performance parameters of the polymer they produce, such as molecular weight ( M n ), dispersity ( Đ ), degree of chain branching and compositional purity has not yet been widely applied in amine–borane dehydropolymerization. Surprisingly, despite the key role of the IrH 2 (POCOP) catalyst in the area no derivatives of this system have been investigated, although there is a note that 3,5‐COOMe substituted derivatives show enhanced activity for the dehydrogenation of hydrazine borane . This lack of data is in contrast to widely explored alkane dehydrogenation where ligand derivatization has been shown to strongly modify catalyst performance .…”

“…15 N NMR spectroscopy of polyaminoboranes has not been studied in detail, but Beweries has reported the 1 H‐ 15 N HMQC NMR spectrum of (H 2 BNMeH) n , which displays a cross‐peak at δ ( 15 N) −365 with J NH ≈65 Hz . Solid‐state 11 B NMR can also give information about B‐environments . Despite these observations, as there are only a few oligomeric systems synthesized that provide models for chain branching and different polymer chain stereochemistries, correlations between NMR chemical shifts and chain structure remain to be developed.…”

“…Surprisingly,d espite the key role of the IrH 2 (POCOP) catalyst in the area no derivatives of this system have been investigated, although there is an ote that 3,5-COOMe substituted derivatives show enhanced activity for the dehydrogenation of hydrazine borane. [50] This lack of data is in contrastt ow idely exploreda lkane dehydrogenation where ligand derivatization has been shown to strongly modify catalystp erformance. [19] However,c atalystv ariations have been studied in an umber of other systems, providing tentatives teps towards catalyst structure activity relationships.…”

“…[33] Solid-state 11 BNMR can also give information aboutB -environments. [27,35,50] Despite these observations, as there are only a few oligomeric systems synthesized that provide models for chain branching and different polymer chain stereochemistries, correlationsb etween NMR chemical shifts and chain structure remain to be developed.…”

The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst

“…A number of closely related pincer-based systems have since been used to catalyse amine-borane dehydrocoupling. 21,26,[32][33][34][35] However to date no σ-amine-borane complexes have been reported with such systems, despite their key role in catalysis. Related off-cycle products have been characterised.…”