A critical component for the successful development of fuel cell applications is hydrogen storage. For back-up power applications, where long storage periods under extreme temperatures are expected, the thermal stability of the storage material is particularly important. Here, we describe the development of an unusually kinetically stable chemical hydrogen storage material with a H2 storage capacity of 4.7 wt%. The compound, which is the first reported parental BN isostere of cyclohexane featuring two BN units, is thermally stable up to 150 °C both in solution and as a neat material. Yet, it can be activated to rapidly desorb H2 at room temperature in the presence of a catalyst without releasing other detectable volatile contaminants. We also disclose the isolation and characterization of two cage compounds with S4 symmetry from the H2 desorption reactions.

Time-resolved reaction calorimetry provides a measure of the turnover frequency (TOF), ca. 1.1 min-1 , and enthalpic driving force, ca. −73 kJ/mol, for the metal-free catalytic reduction of an organic imine, tert-butylbenzaldimine, (tBu-IM) with a frustrated Lewis acid-base pair, [2-(dimesitylphosphino)ethyl] bis(pentafluorophenyl)borane (PBCat), at 298 K and 13.8 bar hydrogen (H 2) pressure. Lowering the H 2 pressure by a factor of two decreases the TOF (0.6 min-1), which is consistent with a pseudo first-order reaction in H 2. In the absence of imine, the heat flux measured in the calorimeter provides a measure of the enthalpy for heterolytic splitting of H 2 , PBcat + H 2-> PBCatH 2 , ΔH ca. −43(4) kJ/mol. Solution phase 19 F nuclear magnetic resonance spectroscopy was used to determine the rate of heterolytic splitting of H 2 by PBCat, k = 0.7(.3) M-1 s-1 and the equilibrium constant for PBCat + H 2(soln)  PBCatH 2 , K eq (295) = 2.2(.5) x 10 5 M, providing an estimate of the free energy for heterolytic splitting of H 2 , ΔG ca. −29.8(1.3) kJ/mol at 295 K in toluene. Deconvolution of the instrument time constant from the heat flux using the Tian equation shows the concentration of imine decreases linearly in time (i.e., the substrate imine is not involved in the rate limiting step, suggesting that H 2 activation by the Lewis acid-base pair is rate limiting).

In this work we demonstrate enhanced hydrogen storage capacities through increased solubility of sodium borate product species in aqueous media achieved by adjusting the sodium (NaOH) to boron (B(OH) 3) ratio, i.e., M/B, to obtain a distribution of polyborate anions. For a 1:1 mole ratio of NaOH to B(OH) 3 , M/B = 1, the ratio of the hydrolysis product formed from NaBH 4 hydrolysis, the sole borate species formed and observed by 11 B NMR is sodium metaborate, NaB(OH) 4. When the ratio is 1:3 NaOH to B(OH) 3 , M/B = 0.33, a mixture of borate anions is formed and observed as a broad peak in the 11 B NMR spectrum. The complex polyborate mixture yields a metastable solution that is difficult to crystallize. Given the enhanced solubility of the polyborate mixture formed when M/B = 0.33 it should follow that the hydrolysis of sodium octahydrotriborate, NaB 3 H 8 , can provide a greater storage capacity of hydrogen for fuel cell applications compared to sodium borohydride while maintaining a single phase. Accordingly, the hydrolysis of a 23 wt% NaB 3 H 8 solution in water yields a solution having the same complex polyborate mixture as formed by mixing a 1:3 molar ratio of NaOH and B(OH) 3 and releases >8 eq of H 2. By optimizing the M/B ratio a complex mixture of soluble products, including B 3 O 3 (OH) 5 2-, B 4 O 5 (OH) 4 2-, B 3 O 3 (OH) 4-, B 5 O 6 (OH) 4 and B(OH) 3 , can be maintained as a single liquid phase throughout the hydrogen release process. Consequently, hydrolysis of NaB 3 H 8 can provide a 40% increase in H 2 storage density compared to the hydrolysis of NaBH 4 given the decreased solubility of sodium metaborate.

Regio- and stereoselective alkane dehydrogenation is a difficult challenge in organometallic chemistry. Intermolecular reactions of this type typically produce numerous olefin stereo- and regioisomers. Herein, we report our initial investigations into the intramolecular dehydrogenation of a datively bound alkyl ligand, demonstrating the first example of a site-selective dehydrogenation of an unactivated acyclic alkyl group. The alkyl group is located on an acylphosphine ligand that is coordinated to a Cp*IrCl2 monomer. A mechanistic proposal, guided by the isolation of a dimeric iridium complex and supported by computational results, is also described.