Mechanism for Forming B,C,N,O Rings from NH3BH3 and CO2 via

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Mechanism for Forming B,C,N,O Rings from NHBH and CO via Reaction Discovery Computations 2

Maxwell Wei-Hao Li, Ian Matthew Pendleton, Alex J Nett, and Paul M. Zimmerman J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.5b11156 • Publication Date (Web): 04 Feb 2016 Downloaded from http://pubs.acs.org on February 7, 2016

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The Journal of Physical Chemistry

Mechanism for Forming B,C,N,O Rings from NH3BH3 and CO2 via Reaction Discovery Computations Maxwell W. Li, Ian M. Pendleton, Alex J. Nett, and Paul M. Zimmerman* Department of Chemistry, University of Michigan, Ann Arbor, Michigan, 48109 Ammonia-Borane, CO2 Reduction, ORR Electrocatalyst, BN Codoped Graphene Oxide, Automated Reaction Finding, Growing String Method

Abstract This study employs computational reaction finding tools to probe the unique biphilic reactivity between ammonia-borane (AB) and CO2. The results show that sequential reactions involving multiple equivalents of AB and CO2 can lead to the formation of stable non-planar B,C,N,O-heterocycles (Cy-BCN). Cy-BCN is shown to emerge through boron-oxygen bond formation, hydroboration, dative bond formation, and single- or double-hydrogen transfers. The most kinetically facile reactions (computed at the coupled cluster singles and doubles with perturbative triples (CCSD(T)) level of theory) result from polarized nitrogen-boron double bonds while thermodynamic stability results from formation of covalent boron-oxygen bonds. An important structure, HCOOBHNH2 (DHFAB), contains both of these features and is the key intermediate involved in generation of Cy-BCN. Crucially, it is shown that favorable boron-oxygen bond formation results in production of Cy-BCN species that are more stable than polyaminoboranes. These types of reaction intermediates could serve as building blocks in the formation of B,N-codoped graphene oxide (BCN). Introduction Detailed analysis of chemical reaction mechanisms can stimulate the development and refinement of new methods for materials synthesis. Especially in cases where a complex array of reaction intermediates are present, computational investigations are vital to uncover the atomistic details which dictate reaction selectivity.1 As an example of an interesting reaction in this area, BN co-doped graphene oxide (BCN, see end of paper for list of abbreviations)2-15 can be formed via the reaction of CO2 and ammonia-borane (AB) in a process shown in Figure 1. BCN has attracted interest as a viable alternative to expensive transition metal-containing catalysts16-19 for the oxygen reduction reaction (ORR).16-21 BCN and related materials22-29 have been shown to improve the efficiency of the oxygen reduction reaction ORR in fuel cells, motivating studies of their structure-activity relationships.16-19,22-29,30-32

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Figure 1. Two step synthesis of BCN.35-38

Synthetic strategies for formation of BCN typically modify graphene or graphene oxide by doping with nitrogen and/or boron sources.2,33,34 Although this approach offers control over elemental composition of the resulting material, alternative synthetic routes could lead to control over BCN structure as well as composition. In the case of CO2 reduction by AB, the material composition in the initial stages of chemical synthesis and the structure of the final BCN material remain unclear. Therefore computational exploration of elementary reactions involving AB and CO2 will aid in understanding the nature of the intermediates and stable chemical structures formed along the reaction sequence. Analysis of AB reactivity has shown simultaneous two-hydrogen transfers from AB to oxidizing agents39-50 and high reactivity of the resulting N=B double bond in NH2BH2. AB’s special reactivity can be attributed to its protic N-H hydrogen and hydridic B-H hydrogen. In NH2BH2 the biphilic N=B double bond results in facile B-H bond activation and cycloadditions.49-52 In contrast, CO2 reductions typically lead to formic acid, CO, or further reduced species such as methanol.46-48,53-55 While most CO2 reduction mechanisms involve sequential additions of hydrogen to CO2,53,56-57 concerted hydrogen transfer from AB43-44 provides an interesting contrast in which CO2’s amphoteric nature is matched by AB’s protic and hydridic N-H and B-H bonds. These reactive diversities suggest that a combination of known processes and unusual chemistries may all be kinetically relevant. The current investigation aims to provide insight into the mechanism of the carbon fixation step of process (1) in Figure 1.35-38 The most accessible paths leading from multiple equivalents of AB and CO2 to formation of two six-membered heterocycles (CyBCN) were determined to reveal reactive intermediates and reactive trends which are applicable beyond the scope of reactions shown here. These trends, summarized in Figure 2, include covalent B-O bond formation, dative bond formation, and hydrogen transfers. Analysis of these reactions through benchmark-level electronic structure theory shows that B-O bond formation is the critical thermodynamic driving force which provides an avenue to carbon incorporation into Cy-BCN. It is further shown that two hydrogen transfer events create the N=B double bonds responsible for much of the favored reactivity. Computational Details Geometries were optimized using the B3LYP density functional57-58 in a spin restricted formalism with the double-zeta, polarized 6-31G** basis set.60 The automated reaction finding program (ARF)61-64 used here invokes the combined reaction path and transition state finding search of the latest Growing String Method (GSM).65-68 GSM simultaneously finds the minimum energy path and exact transition state by an unconstrained saddle point search at the highest energy node within the string. ARF and GSM invoke Q-Chem 4.069 to provide quantum mechanical energies and gradients.

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The Journal of Physical Chemistry Reactions

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Figure 2. Key reaction types in the AB/CO2 system on paths leading to stable rings.

Electronic energies were computed as single point energies using the Molpro software package.70-73 These calculations utilize coupled-cluster singles and doubles with perturbative triples, CCSD(T),74 with the augmented triple-zeta aug-cc-pVTZ75 basis set for all atoms. Entropic and enthalpic corrections were applied at a temperature of 100 °C. Herein, energies are reported as gas phase free energies at the CCSD(T)/aug-cc-pVTZ level. All reported structures and their total energies can be found in the Supporting Information (Tables S1 and S2). Results and Discussion Due to the anticipated complexity and unknown nature of reactions involving CO2 and AB, our group’s automated reaction finding (ARF) tools were used to locate the key chemical transformations. These methods enable the discovery of reaction pathways from a given set of reactants by systematically applying changes to the reactants’ chemical structures.61-64 The procedure generates plausible elementary steps,76 which include reaction intermediates for thermodynamic evaluation, and transition states found using the Growing String Method.65-68 These data are then analyzed to determine the most favorable reaction pathways. Once the complete set of favorable elementary steps are found, additional reagents like AB or CO2 are added to the simulation and the process is repeated. An outline of the ARF procedure is shown in Figure 3.



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Figure 3. Automated reaction finding (ARF) iterative logic.

Reactions of AB, CO2, and NH2BH2. Using the reactants AB and CO2 (1) as a starting point, ARF located the paths shown in Figure 4. TS I effects simultaneous two-hydrogen transfer from AB to CO2, forming formic acid (FA) and NH2BH2 (2) with a barrier of 27.8 kcal/mol above 1.43-44 This and all additional barriers are referenced to reactant complexes, not separated species. Notably, proton and hydride transfer through TS I is a concerted path for reduction of CO2 into FA. While FA is a common CO2 reduction product,42-44,53-55 most mechanisms of H transfer to CO2 are sequential.53,56-57 TS I results from AB’s protic and hydridic H being matched by CO2’s oxygen lone pairs and electron-deficient carbon, leading to a concerted 2H+-2e- event. Subsequent reactivity between FA and NH2BH2 (2) was found to proceed through B-O bond formation between NH2BH2 and FA with concomitant O-H proton transfer to NH2BH2’s nitrogen in reaction II. This process yields formoxy ammonia-borane (FAB, see species 3) with a transition state energy of 4.4 kcal/mol (compared to 1).

Figure 4. Free energy profile for reaction paths involving Ammonia-Borane, CO2, and NH2BH2.


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Due to production of NH2BH2 through TS I, reactions involving AB and NH2BH2 are potentially competitive with reaction II. For example, previously reported reactions related to AB/NH2BH2 oligomerization51-52 as well as AB dehydrogenation pathways77-82 may be relevant at this step. Since the dehydrogenation reactions lead to NH2BH2, they can be considered as sources of this important monomer. AB/NH2BH2 oligomerization competes with the herein reported ring formation pathways, and therefore is considered further. Relevant AB/NH2BH2 pathways are given in Figure 5 for comparison to analogous AB/CO2 paths. As previously described,51,52 two NH2BH2 molecules react to give the BN-analogue of cyclobutane (c-dimer, 5), or the hydroboration product (BH3-int, 6), the BN analogue of 1-butene, both with barriers of 15.8 kcal/mol. Reaction of NH2BH2 with AB gives the butane analogue (sp3-dimer, 7) at a barrier of 29.6 kcal/mol. The barrier for reaction II is 1.9 kcal/mol above 2, which is 27.7 kcal/mol lower than the barrier for sp3-dimer formation and 13.9 kcal/mol lower than the barriers for formation of BH3-int and c-dimer (Figure 5). Additionally, reaction II was calculated to be thermodynamically favorable with a free energy of -10.2 kcal/mol (from 2) compared to -5.3 kcal/mol and -0.5 kcal/mol for formation of c-dimer and BH3-int, respectively. These data suggest that reaction II is thermodynamically and kinetically favored over NH2BH2 oligomerization. Importantly, TS II initiates carbon incorporation into cy-BCN precursors.

Figure 5. Free energy profiles for vital AB/NH2BH2 oligomerization pathways.

51,52



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An ARF search from FAB alone did not generate any accessible elementary steps leading to stable products. The most favorable

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path was the uphill reverse reaction forming FA and NH2BH2, with a barrier of 12.1 kcal/mol and free energy of reaction of 10.2 kcal/mol above FAB. Unreacted FA and NH2BH2, and the same species generated by decomposition of FAB, were considered available for further reactions along with additional AB and CO2. Thus AB, CO2, FA, and NH2BH2 were each reacted pairwise with FAB in the following ARF iterations. Reaction of FAB and NH2BH2 in III was the most accessible with a barrier of 18.9 kcal/mol (compared to 3) and outcompetes reactions of FAB with CO2, FA, or AB, which were found to be high energy with barriers above 30 kcal/mol relative to FAB alone.83 TS III proceeds through concerted proton and hydride transfer to yield dehydrogenated formoxy ammonia-borane (DHFAB) and AB (4). At this step, the moderate barrier for reaction of FAB and NH2BH2 suggests that NH2BH2 oligomerization51,52 may be kinetically competitive. The energy profile for this reactivity (see Figure 4) highlights the favorable covalent B-O bond formation step (reaction II) compared to the higher barrier two-hydrogen transfer steps in reactions I and III. The comparatively large downhill free energy of reaction for II also emphasizes the stability of FAB and its derivative DHFAB, which is important due to the observed production of carbon-containing compounds under temperatures of around 100 C.35-38 These observations provide evidence that covalent B-O bond formation is a critical thermodynamic driving force associated with AB/CO2 reactivity. Comparatively, reactions from NH2BH2 oligomerization produce relatively unstable intermediates (see Figure 5).51,52 Therefore NH2BH2 oligomerization intermediates may break down at 100 C and be incorporated into species such as FAB and DHFAB through B-O bond formations, allowing BCN formation to outcompete polyaminoborane synthesis. Intermediates FAB and DHFAB are structurally related to AB and NH2BH2, respectively (see Figure 6). N-B bond lengths in FAB and AB are 1.65 and 1.66 Å compared to 1.39 and 1.40 Å in DHFAB and NH2BH2. Additionally, the N-B-H angle in AB is 104.8° compared to 108.7° in FAB. In contrast, N-B-H angles in DHFAB and NH2BH2 are 123.4° and 118.7°, respectively. This suggests the hybridization of nitrogen and boron atoms and bond order of the N-B bond in FAB are similar to AB, both containing sp3 hybridized N and B resulting in a single N-B bond. Similarly, in both DHFAB and NH2BH2, the hybridization of B and N is sp2 (see Table S6). These structural similarities suggest that the N-B bonds as well as N-H and B-H hydrogen in FAB and DHFAB may also react much like their counterparts in AB and NH2BH2. Having demonstrated the reactivity of AB and CO2 leading to NH2BH2, FA, FAB and DHFAB, further ARF runs examined the reaction mechanisms proceeding from these intermediates (see Figure 7). Application of ARF on the pairwise combinations of DHFAB with FA, NH2BH2, and AB generated favorable paths with barriers of 10.0 kcal/mol, 15.3 kcal/mol, and 22.4 kcal/mol, respectively. Comparatively, the most favorable path from FAB is reaction III, which forms DHFAB with a barrier of 18.9 kcal/mol. Since reactions between DHFAB and FA were found to be the most accessible, they are presented in the following section.


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Figure 6. Geometric comparison of FAB/AB and DHFAB/NH2BH2.

Figure 7. Comparison of paths leading from DHFAB and FAB showing rate-limiting activation barriers (kcal/mol) for each overall pathway.

Cycle for Formation of FAB from FA and NH2BH2. Application of ARF to DHFAB and FA yielded the steps shown in Figure 8. The initial reaction of DHFAB and FA (8) generated 8a through a change in H-bonding in step IV. 8a subsequently reacted to yield bi-formoxy ammonia-borane (BFAB, see 8b) through step V. Reaction V is similar to II, the concerted B-O bond formation and proton transfer between NH2BH2 and FA in Figure 4. The transition state energies of 4.4 kcal/mol for II (referenced to 1) and 5.9 kcal/mol for V (referenced to 8) suggest that concerted B-O bond formation and proton transfer steps are both facile. The low barriers can be understood by the fact that N=B double bonds are highly reactive in DHFAB as well as NH2BH2. TS structures for reactions V and II are compared in Figure S1. ARF searches from BFAB—which is chemically similar to FAB—did not result in any productive steps. The lowest energy path was found to be the reverse reaction to reform 8a with a barrier of 19.9 kcal/mol and a free energy of reaction of 13.2 kcal/mol above BFAB. BFAB was thus reacted pairwise with AB, FA, and NH2BH2. Reaction between NH2BH2 and BFAB (reaction VI) was found to have the lowest energy barrier of 19.0 kcal/mol above 8b.



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Figure 8. Free energy profile for the reaction cycle leading to the formation of FAB. In comparison, reactions of BFAB with FA and AB have barriers of 19.6 kcal/mol and over 30 kcal/mol, respectively. TS VI involves concerted proton and formate transfer to NH2BH2 to regenerate DHFAB and produce one equivalent of FAB (8c). Reaction of BFAB with FA was found to produce the highly oxidized boron species BH(OCHOH)3-NH4+ (9). There was no indication, however, that the oxidized boron would lead to nitrogen containing rings. Therefore, further reactions of this species were not considered and the reactivity of BFAB and NH2BH2 was focused on next (see Figure S2). Overall, Figures 4 and 8 show that the high reactivity of N=B double bonds (in NH2BH2 and DHFAB) in conjunction with FA result in generation of FAB. Furthermore, the only competitive path leading from FAB results from reaction with NH2BH2 to yield DHFAB through TS III (see Figure 7). Having established multiple pathways for FAB formation and recognizing that FAB leads primarily to DHFAB, reactions involving DHFAB and NH2BH2 are considered next. Cy-BCN Formation from DHFAB and NH2BH2. DHFAB and NH2BH2 (10) provided the starting materials for the following ARF iterations, which yielded competitive paths leading to heterocyclic rings (see Figure 9). Reaction of DHFAB and NH2BH2 through TS VII forms 11a with a barrier of 16.9 kcal/mol. Reaction VII proceeds through concerted N-B bond formation and hydride transfer, resembling the hydroboration step of Figure 4.49-53 2+2 cycloaddition was also observed (16), but with a significantly higher transition state energy of 21.0 kcal/mol above 10 (see Figure S3). Subsequent dative B-O bond formation from 11a (reaction VIII) generates 11b with a transition state energy of 4.6 kcal/mol (compared to 10). Reaction IX provides a concerted path for 11b formation equivalent to sequential reactions VII and VIII and has a barrier of 17.6 kcal/mol. Application of ARF to 11b yielded two favorable reactions: the reverse reaction to form 11a, or decomposition into DHFAB and NH2BH2 (10), both of which are uphill by 3.1 and 3.7 kcal/mol, respectively. The six-membered heterocycle 11b therefore is a weakly stable Cy-BCN species.


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Figure 9. Cy-BCN precursor formation from DHFAB and NH2BH2. The black and blue paths indicate the most favorable paths for 11b and 15b formation, respectively.

Formation of a more stable Cy-BCN structure (15b) was found to result from reactions X through XVI (Figure 9). First, reaction X produces 12 through formation of an N-B bond and a hydride bridge. Previous work has shown that molecules containing bridged hydrides are commonly observed in the process of forming NH2BH2 dimers and BN rings.51,52,84-86 The path through 12 is part of a stepwise mechanism for formation of 13, which completes with H transfer to B in reaction XI. The stepwise pathway from 10 to 13 has transition state energies of 15.3 and 8.2 kcal/mol (referenced to 10) for TS X and XI, respectively. The concerted path for formation of 13 from 10 has a transition state energy of 16.0 kcal/mol in TS XII, suggesting that concerted and stepwise paths are each relevant mechanisms for generation of 13. Intermediate 13 contains an N-B single bond, an N=B double bond, and a B-O bond, all of which are structural features that exist in AB, NH2BH2, FAB, and DHFAB. This suggested that there were many different possible reactions that could occur from 13. Previous work, for example, has shown that hydroboration events from this intermediate could be favorable51-52,78,80,87-88. ARF, however, indicated that hydroboration from 13 is comparatively unfavorable with a barrier of 21.0 kcal/mol and produces a c-dimer analogue that shows no further reactivity (Figure S3). Instead, the lowest barrier path actually proceeds through TS XIII, a reaction type that had not yet been observed. Reaction XIII yields 14 through transfer of BH3 to form a new B-O dative bond. This pathway has the relatively low transition state energy of 13.1 kcal/mol above 10, but is uphill by 10.4 kcal/mol compared to 13. Subsequent B-H hydrogen transfer to carbon through TS XIV yields 15a, which is more stable than either 13 or 14. 15a undergoes ring closure by N-B bond formation in XV to form 15b with a barrier of 5.5 kcal/mol above 15a. Simultaneous hydrogen transfer and ring closure in reaction XVI with a transition state energy of 19.1 kcal/mol (compared to 10) provides a concerted path for 15b formation from 14. Application of ARF to 15b yielded only the reverse reaction to form 15a, which is uphill by 1.8 kcal/mol. The



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stability of six-membered heterocycle 15b, which is -18.4 kcal/mol downhill from DHFAB and NH2BH2 (10), suggests that 15b is a more stable form of Cy-BCN than 11b. The competition between formation of 11b and 15b requires analysis of the rate-limiting steps for each path (see Figure 9). The rate-limiting step for 11b formation is reaction VII, the hydroboration step which has a transition state energy of 16.9 kcal/mol above 10. Comparatively, concomitant proton transfer to carbon and N-B dative bond formation in reaction XVI has a limiting transition state energy of 19.1 kcal/mol (referenced to 10) along the lowest energy path for 15b formation. The comparison between rate limiting barriers suggests that the less stable form of Cy-BCN, 11b, is kinetically favored despite being less thermodynamically stable. The transformation of 11b to 15b, however, is possible through decomposition of 11b followed by paths X through XVI. The structural properties of 11b and 15b were examined to gain a better understanding of which forms of Cy-BCN would be more favored. The six-membered heterocycle 15b is closely related in structure to 11b (see Figure 10, Table 1, Tables S5 and S6), but is more stable by 14.6 kcal/mol. This stability is related to the shorter B-O bonds in 15b, which are 1.46 and 1.35 Å in comparison to 1.55 and 1.63 Å in 11b. The shorter B-O bonds in 15b result from the additional reduction of carbon by one hydrogen, whereas the backbone carbon of 11b remains more oxidized. The electron density in 11b is therefore withdrawn from the B-O bonds, increasing the bond length and decreasing the overall stabilizing interaction with the adjoining B-N-B portion of the molecule. The more reduced O-CHn-O backbone of 15b compared to 11b strengthens B-O bonds, and provides additional evidence that B-O bond formation is a significant thermodynamic driving force in the formation of Cy-BCN structures.

Figure 10. Comparisons of B-O bond length in Cy-BCN rings.

NBO analysis yielded further insight about electronic differences between 11b and 15b (see Table 1, Tables S5 and S6). In both 11b and 15b, boron and oxygen atoms act as Lewis acids and bases, respectively, to form dative bonds. In 15b, however, oxygen atoms have the ability to donate more electrons due to charge donation from the reduced carbon (lower C-O bond order in 15b) compared to in 11b. Natural charges on the oxygen atoms confirm this increased electron available, where in 15b these are -0.758 and -0.744 for the left and right oxygen atoms, respectively, compared to -0.610 -0.607 in 11b. While boron atoms in 15b have higher natural charge compared to 11b (1.164 and 0.367 compared to 0.708 and 0.334 for 15b and 11b, respectively), a partial double-bond between the boron and oxygen in 15b (SI-Table 3 and Figure 9), results in a strong B-O bond with a short 1.35 Å bond length (orbital images may be found in Table S6).


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Table 1. Natural charge of B and O in 11b and 15b. Refer to Figure 10 for left and right designations.

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Atom Left B Right B Left O Right O

Natural Charge 11b 0.708 0.334 -0.610 -0.607

Natural Charge 15b 1.164 0.367 -0.758 -0.744

15b’s stability and kinetic favorability may be compared to cyclotriborazane (CTB, 18), a stable aminoborane ring formed from AB dehydrogenation and oligomerization reactions49-53,89-90 (see Figure 11). The rate limiting step for CTB formation from three NH2BH2 has a transition state energy of 31.9 kcal/mol (referenced to ECB, 17) compared to 19.1 kcal/mol for 15b formation (referenced to 10), indicating that 15b formation is more facile. Relative to starting materials, CTB is formed with a free energy of reaction -17.8 kcal/mol downhill from two units of NH2BH2. In comparison, 15b is formed only when CO2 is present. These results are in agreement with experimental demonstration that BCN formation increases under increased CO2 pressure.35

Figure 11. Free energy profiles comparing of Cy-BCN and CTB formation.

Lee and coworkers reported that polyaminoborane formation was observed at temperatures of under 60 C in process (1) of Figure 1. IR signals corresponding to BN compounds, however, “almost vanished at 80 C”.35 These observations may be a result of the higher 19.1 kcal/mol barrier for 15b formation compared to the 15.8 kcal/mol barrier for formation of polyaminoborane moieties like c-dimer (5). The less stable BN compounds, however, may undergo reverse reactions at temperatures above 80 C, while Cy-



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BCN is generated irreversibly. The formation of Cy-BCN structure 15b under higher temperatures is also in line with spectroscopic

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evidence, which reports features including B-O, C-O, B-H, N-H, and sp3 C-H bonding.35-38 Taken together, the mechanisms reported in Figures 4, 8, and 9 provide detailed insight into the early stages of BCN formation. Multiple ring growth may result from reactions at the N=B functionality in 15b, or from the ring opening the N-B dative bond to yield 15a, which may bond to DHFAB or other open rings. For example, CO2 addition to 15b could result in B-O bond formation between the sp2 boron of 15b and an oxygen. Subsequent addition of one or two NH2BH2 would allow for growth of a second ring on top of the first by N-B bond formation to the added CO2 along with additional B-O bond formation between the borons of added NH2BH2 to the oxygen atoms on the original ring. Alternatively N-B bond formation between added NH2BH2 and N or B on 15b would allow for multiple ring growth as well. Further additions by the same mechanism would allow for further ring growth, which could create graphene-like sheets. Hypothetical mechanisms for these processes can be found in Figure S5. Conclusions This study provides a mechanism for the formation of two specific, kinetically viable six-membered ring (Cy-BCN) structures from AB and CO235-38 by detailing key elementary reactions at the benchmark CCSD(T) level of theory. These reactions comprise the initiation of the AB/CO2 reaction network and form a foundation for the formation of BCN from AB and CO2. B-O bond formation, hydroboration, dative bond formation, and concerted two-hydrogen transfers (see Figure 2) are shown to be the most important reaction motifs. The most kinetically favorable steps originate from intermediates containing highly polarized N=B double bonds, as expected from previous studies of AB and NH2BH2 reactivity.51-52,77-82 The proposed mechanism (summarized in Figure 12) shows how Cy-BCN formation becomes favored over generation of polyaminoborane moieties: in the presence of CO2, covalent B-O bond formation provides a thermodynamic driving force for carbon incorporation. From the starting materials of AB and CO2, simultaneous proton and hydride transfer followed by concerted B-O bond formation/proton transfer results in FAB generation. FAB can be dehydrogenated by NH2BH2 (and likely other N=B double bonds) to yield DHFAB. From this key intermediate, which contains B-O bonds as well as N=B double bonds, Cy-BCN is formed. The combination of high reactivity from DHFAB’s N=B double bond and stability from its B-O bond is therefore vital to Cy-BCN formation.


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Figure 12. Summary of Cy-BCN formation pathways.

NH2BH2 oligomerization may compete with all of these pathways for Cy-BCN formation.51-52,77-82 While oligomerization of NH2BH2 is kinetically possible, many of these steps are reversible under the reaction conditions of 100 °C. In contrast, covalent BO bond formation is slightly less kinetically favored, but results in formation of the more stable species such as Cy-BCN. This evidence suggests that the reversibility of aminoborane oligomer formation is less relevant at lower temperatures while Cy-BCN formation is more prominent at high temperature. In summary, a wide variety of elementary reactions were identified by ARF, of which the low barrier paths leading to Cy-BCN are outlined in Figure 12. These newly uncovered reactions detail the mechanism for formation of BCN precursors, species 11b and 15b. Future analysis will target pathways leading to the formation of fused rings and subsequent materials products. In sum, the elementary reactions of Figure 2 show that the unique combination of AB and CO2 leads to a variety of interesting reaction paths, which may inspire new synthetic routes for novel materials.

ASSOCIATED CONTENT XYZ structures for all compounds, electronic energies and free energy corrections for all compounds, side reaction pathways, hypothetical mechanisms leading from 15b, and further characterization of compounds AB, FAB, NH2BH2, DHFAB, 11b, and 15b, This material is available free of charge via the Internet at (Insert link here)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Tel: 734 615-0191

ACKNOWLEDGMENT The authors would like to thank the University of Michigan Energy Institute for a summer fellowship (MWL). We thank David Braun for continued support in computer administration and Alan Chien for helpful insight in CCSD(T) calculations. This material is based in part



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upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1256260 and the NSF

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CAREER award No. 1551994. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

ABBREVIATIONS BCN, boron nitrogen codoped graphene oxide; Cy-BCN, cyclohexyl boron nitrogen codoped graphene oxide; AB, ammonia-borane; ORR, oxygen reduction reaction; FAB, formoxy ammonia-borane; DHFAB, dehydrogenated formoxy ammonia-borane; BFAB, bi-formoxy ammonia-borane; CTB, cyclotriborazane; FA, formic acid

REFERENCES (1) Page, A. J.; Ding, F.; Irle, S.; Morokuma, K. Insights Into Carbon Nanotube And Graphene Formation Mechanisms From Molecular Simulations: A Review. Reports Prog. Phys. 2015, 78, 036501. (2) Wang, S.; Zhang, L.; Xia, Z.; Roy, A.; Chang, D. W.; Baek, J. B.; Dai, L. BCN Graphene As Efficient Metal-Free Electrocatalyst For The Oxygen Reduction Reaction Angew. Chem. Int. Ed. 2012, 51, 4209-4212 (3) Choi, C. H.; Park, S. H.; Woo, S. I. Binary And Ternary Doping Of Nitrogen, Boron, And Phosphorus Into Carbon For Enhancing Electrochemical Oxygen Reduction Activity ACS Nano 2012, 6, 7084-7091 (4) Yang, L.; Jiang, S.; Zhao, Y.; Zhu, L.; Chen, S.; Wang, X.; Wu, Q.; Ma, J.; Ma, Y.; Hu, Z. Boron-Doped Carbon Nanotubes As Metal-Free Electrocatalysts For The Oxygen Reduction Reaction Angew. Chem. Int. Ed. 2011, 50, 7132-7135 (5) Sheng, Z. H.; Gao, H. L.; Bao, W. J.; Wang, F. B.; Xia, X. H. Synthesis Of Boron Doped Graphene For Oxygen Reduction In Fuel Cells J. Mater. Chem. 2012, 22, 390-395 (6) Yang, S.; Feng, X.; Wang, X.; Mϋllen, K. Graphene-Based Carbon Nanosheets As Efficient Metal-Free Electrocatalysts For Oxygen Reduction Reactions Angew. Chem. Int. Ed. 2011, 50, 5339-5343 (7) Unni, S. M.; Devulapally, S.; Karjule, N.; Kurungot, S. Graphene Enriched With Pyrrolic Coordination Of The Doped Nitrogen As An Efficient Metal-Free Electrocatalyst For Oxygen Reduction J. Mater. Chem. 2012, 22, 23506-23513 (8) Liu, R.; Wu, D.; Feng, X.; Mϋllen, K. Nitrogen-Doped Ordered Mesoporous Graphitic Arrays With High Electrocatalytic Activity For Oxygen Reduction Angew. Chem. 2010, 122, 2619-2623 (9) Ozaki, J. I.; Kimura, N.; Anahara, T.; Oya, A. Preparation And Oxygen Reduction Activity Of BN-Doped Carbons Carbon 2007, 45, 18471853 (10) Li, Y.; Zhou, W.; Wang, H.; Xie, L.; Liang, Y.; Wei, F.; Idrobo, J. C.; Pennycook, S. L.; Dai, H. An Oxygen Reduction Electrocatalyst Based On Carbon Nanotube-Graphene Complexes Nat. Nanotechnol. 2012, 7, 394-400 (11) Lin, Z.; Waller, G.; Liu, Y.; Liu, M.; Wong, C. P. Facile Synthesis Of Nitrogen-Doped Graphene Via Pyrolysis Of Graphene Oxide And Urea, And Its Electrocatalytic Activity Toward The Oxygen Reduction Reaction Adv. Energy Mater. 2012, 2, 884-888 (12) Lai, L.; Potts, J. R.; Zhan, D.; Wang, L.; Poh, C. K.; Tang, C.; Gong, H.; Shen, Z.; Lin, J.; Ruoff, R. S. Exploration Of The Active Center Structure Of Nitrogen-Doped Graphene-Based Catalysts For Oxygen Reduction Reaction Energy Environ. Sci. 2012, 5, 7936-7942 (13) Zheng, Y.; Jiao, Y.; Jaroniec, M.; Jin, Y.; Qiao, S. Z. Nanostructured Metal-Free Electrochemical Catalysts For Highly Efficient Oxygen Reduction. Small 2012, 8, 3550–3566.


Page 15 of 19


(14) Qu, L.; Liu, Y.; Baek, J.; Dai, L. Nitrogen-Doped Graphene As Efficient Metal-Free Electrocatalyst For Oxygen Reduction In Fuel Cells. ACS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano 2010, 4, 1321–1326. (15) Zhang, C.; Hao, R.; Liao, H.; Hou, Y. Synthesis Of Amino-Functionalized Graphene As Metal-Free Catalyst And Exploration Of The Roles Of Various Nitrogen States In Oxygen Reduction Reaction. Nano Energy 2013, 2, 88–97. (16) Pollet, B. G.; Staffel, I.; Shang, J. L. Current Status Of Hybrid, Battery And Fuel Cell Electric Vehicles: From Electrochemistry To Market Prospects Electrochim. Acta 2012, 84, 235-249 (17) Debe, M. K. Electrocatalyst Approaches And Challenges For Automotive Fuel Cells. Nature 2012, 486, 43–51. (18) Peighambardoust, S. J.; Rowshanzamir, S.; Amjadi, M. Review Of The Proton Exchange Membranes For Fuel Cell Applications Elsevier Ltd, 2010, 35, 9349–9384. (19) Wang, Y.; Chen, K. S.; Mishler, J.; Cho, S. C.; Adroher, X. C. A Review Of Polymer Electrolyte Membrane Fuel Cells: Technology, Applications, And Needs On Fundamental Research. Appl. Energy 2011, 88, 981–1007. (20) Aricò, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J. M.; Van Schalkwijk, W. Nanostructed Materials For Advanced Energy Conversion And Storage Devices Nat. Mater. 2005, 4, 366-377 (21) Schlapbach, L.; Zϋttel, A. Hydrogen-Storage Materials For Mobile Applications Nature 2001, 414, 353-358 (22) Zhang, C.; Mahmood, N.; Yin, H.; Liu, F.; Hou, Y. Synthesis Of Phosphorus-Doped Graphene And Its Multifunctional Applications For Oxygen Reduction Reaction And Lithium Ion Batteries. Adv. Mater. 2013, 25, 4932–4937. (23) Zhang, J.; Byeon, A.; Lee, J. W. Boron-Doped Carbon-Iron Nanocomposites As Efficient Oxygen Reduction Electrocatalysts Derived From Carbon Dioxide. Chem. Commun. (Camb). 2014, 50, 6349–6352. (24) Huang, X.; Qi, X.; Boey, F.; Zhang, H. Graphene-Based Composites Chem. Soc. Rev. 2012, 41, 666-686 (25) Wu, G.; More, K.; Johnston, C.; Zelenay, P. High-Performance Electrocatalysts For Oxygen Reduction Derived From Polyaniline, Iron, And Cobalt. Science 2011, 443–448. (26) Yin, H.; Zhang, C.; Liu, F.; Hou, Y. Hybrid Of Iron Nitride And Nitrogen-Doped Graphene Aerogel As Synergistic Catalyst For Oxygen Reduction Reaction. Adv. Funct. Mater. 2014, 24, 2930–2937. (27) Chen, Z.; Higgins, D.; Yu, A.; Zhang, L.; Zhang, J. A Review On Non-Precious Metal Electrocatalysts For PEM Fuel Cells. Energy Environ. Sci. 2011, 4, 3167. (28) Poh, H. L.; Sofer, Z.; Luxa, J.; Pumera, M. Transition Metal-Depleted Graphenes For Electrochemical Applications Via Reduction Of CO2 By Lithium. Small 2014, 10, 1529–1535. (29) Zhang, J.; Lee, J. W. Production Of Boron-Doped Porous Carbon By The Reaction Of Carbon Dioxide With Sodium Borohydride At Atmospheric Pressure. Carbon N. Y. 2013, 53, 216–221. (30) Dreyer, D. R.; Park, S.; Bielawski, C. W.; Ruoff, R. S. The Chemistry Of Graphene Oxide. Chem. Soc. Rev. 2010, 39, 228–240. (31) Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Design Of Electrocatalysts For Oxygen- And Hydrogen-Involving Energy Conversion Reactions. Chem. Soc. Rev. 2015, 44, 2060–2086. (32) Wu, G.; Zelenay, P. Nanostructured Nonprecious Metal Catalysts For Oxygen Reduction Reaction. Acc. Chem. Res. 2013, 46, 1878–1889. (33) Tai, J.; Hu, J.; Chen, Z.; Lu, H. Two-Step Synthesis Of Boron And Nitrogen Co-Doped Graphene As A Synergistically Enhanced Catalyst For The Oxygen Reduction Reaction. RSC Adv. 2014, 4, 61437–61443.



Page 16 of 19

(34) Pham, V. H.; Hur, S. H.; Kim, E. J.; Kim, B. S.; Chung, J. S. Highly Efficient Reduction Of Graphene Oxide Using Ammonia Borane. Chem.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Commun. 2013, 49, 6665. (35) Byeon, A.; Lee, J. W. Electrocatalytic Activity Of BN Codoped Graphene Oxide Derived From Carbon Dioxide J. Phys. Chem. C 2013, 117, 24167-24173 (36) Zhang, J.; Zhao, Y.; Guan, X.; Stark, R. E.; Akins, D. L.; Lee, J. W. Formation Of Graphene Oxide Nanocomposites From Carbon Dioxide Using Ammonia Borane J. Phys. Chem. C 2012, 115, 2639-2644 (37) Xiong, R.; Li, X.; Byeon, A.; Lee, J. W. Production Of Nitrogen-Doped Graphite From Carbon Dioxide Using Polyaminoborane RSC Adv. 2013, 3, 25752-25757 (38) Zhang, J.; Byeon, A.; Lee, J. W. Boron-Doped Electrocatalysts Derived From Carbon Dioxide J. Mater. Chem. A 2013, 1, 8665-8671 (39) Leitao, E.; Stubbs, N. Mechanism Of Metal-Free Hydrogen Transfer Between Amine–Boranes And Aminoboranes. J. Am. Chem. Soc. 2012, 54, 16805-16816 (40) Zimmerman, P. M.; Zhang, Z.; Musgrave, C. B. Dynamic Mechanisms For Ammonia Borane Thermolysis In Solvent: Deviation From GasPhase Minimum-Energy Pathways. J. Phys. Chem. Lett. 2011, 2, 276–281. (41) Al-Kukhun, A.; Hwang, H. T.; Varma, A. Mechanistic Studies Of Ammonia Borane Dehydrogenation. Int. J. Hydrogen Energy 2013, 38, 169–179. (42) Lim, C.; Holder, A.; Hynes, J. T.; Musgrave, C. B. Roles Of The Lewis Acid And Base In The Chemical Reduction Of CO2 Catalyzed By Frustrated Lewis Pairs. Inorg. Chem. 2013, 1–5. (43) Zimmerman, P. M.; Zhang, Z.; Musgrave, C. B. Simultaneous Two-Hydrogen Transfer As A Mechanism For Efficient CO2 Reduction Inorg. Chem. 2010, 49, 8724-8728 (44) Roy, L.; Zimmerman, P. M.; Paul, A. Changing Lanes From Concerted To Stepwise Hydrogenation: The Reduction Mechanism Of Frustrated Lewis Acid-Base Pair Trapped CO2 To Methanol By Ammonia-Borane. Chem. Eur. J. 2011, 17, 435–439. (45) Ai, D.; Guo, Y.; Liu, W.; Wang, Y. DFT Studies On Catalytic Dehydrogenation Of Ammonia Borane By Ni(NHC)2. J. Phys. Org. Chem. 2014, 27, 597–603. (46) Pal, A.; Vanka, K. A DFT Investigation Of The Potential Of Porous Cages For The Catalysis Of Ammonia Borane Dehydrogenation. Chem. Commun. (Camb). 2011, 47, 11417–11419. (47) Lee, T. B.; McKee, M. L. Mechanistic Study Of Linh(2)BH(3) Formation From (Lih)(4) + NH(3)BH(3) And Subsequent Dehydrogenation. Inorg. Chem. 2009, 48, 7564–7575. (48) Kalviri, H. a.; Gärtner, F.; Ye, G.; Korobkov, I.; Baker, R. T. Probing The Second Dehydrogenation Step In Ammonia-Borane Dehydrocoupling: Characterization And Reactivity Of The Key Intermediate, B-(Cyclotriborazanyl)Amine-Borane. Chem. Sci. 2014, 6, 618–624. (49) Malakar, T.; Bhunya, S.; Paul, A. Theoretical Investigation On The Chemistry Of Entrapment Of The Elusive Aminoborane (H2N=BH2) Molecule. Chem. Eur. J. 2015, 21, 6340–6345. (50) Bhunya, S.; Zimmerman, P. M.; Paul, A. Unraveling The Crucial Role Of Metal-Free Catalysis In Borazine And Polyborazylene Formation In Transition-Metal-Catalyzed Ammonia–Borane Dehydrogenation. ACS Catal. 2015, 5, 3478–3493. (51) Zimmerman, P. M.; Paul, A.; Zhang, Z.; Musgrave, C. B. Oligomerization And Autocatalysis Of NH2BH2 With Ammonia-Borane Inorg. Chem. 2009, 48, 1069-1081


Page 17 of 19


(52) Malakar, T.; Roy, L.; Paul, A. The Role Of Solvent And Of Species Generated In Situ On The Kinetic Acceleration Of Aminoborane

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Oligomerization Chem. Eur. J. 2013, 19, 5812-5817 (53) Ganesh, I. Conversion Of Carbon Dioxide Into Methanol – A Potential Liquid Fuel: Fundamental Challenges And Opportunities (A Review). Renew. Sustain. Energy Rev. 2014, 31, 221–257. (54) Lim, C.; Holder, A.; Hynes, J. T.; Musgrave, C. B. Reduction Of CO2 To Methanol Catalyzed By A Biomimetic Organo-Hydride Produced From Pyridine. J. Am. Chem. Soc. 2014, 136, 16081-16095 (55) Lim, C.; Holder, A.; Musgrave, C. B. Mechanism Of Homogeneous Reduction Of CO2 By Pyridine: Proton Relay In Aqueous Solvent And Aromatic Stabilization. J. Am. Chem. Soc. 2013, 135, 142-154 (56) Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Electrocatalytic And Homogeneous Approaches To Conversion Of CO2 To Liquid Fuels Chem. Soc. Rev. 2009, 38, 89-99 (57) Mikkelsen, M.; Jørgensen, M.; Krebs, F. C. The Teraton Challenge. A Review Of Fixation And Transformation Of Carbon Dioxide. Energy Environ. Sci. 2010, 3, 43-81 (58) Becke, A. D. J. Chem. Phys. Densityfunctional Thermochemistry. III. The Role Of Exact Exchange. 1993, 98, 5648-5652 (59) Lee, C.; Yang, W.; Parr, R. G. Development Of The Colle-Salvetti Correlation-Energy Formula Into A Functional Of The Electron Density. Phys. Rev. B 1988, 37, 785-789 (60) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. Selfconsistent Molecular Orbital Methods. Xx. A Basis Set For Correlated Wave Functions. J. Chem. Phys. 1980, 72, 650-654. (61) Zimmerman, P. M. Automated Discovery Of Chemically Reasonable Elementary Reaction Steps J. Comput. Chem. 2013, 34, 1385-1392 (62) Zimmerman, P. M. Growing String Method With Interpolation And Optimization In Internal Coordinates: Method And Examples J. Chem. Phys. 2013, 138, 184102(1-10) (63) Zimmerman, P. M. Reliable Transition State Searches Integrated With The Growing String Method J. Chem. Theory. Comput. 2013, 9, 30433050 (64) Zimmerman, P. M. Single-Ended Transition State Finding With The Growing String Method. J. Comput. Chem. 2015, N/A–N/A. (65) Zimmerman, P. M. Navigating Molecular Space For Reaction Mechanisms: An Efficient, Automated Procedure Mol. Si. 2014 (66) Sharada, S. M.; Zimmerman, P. M.; Bell, A. T.; Head-Gordon, M. Automated Transition State Searches Without Evaluating The Hessian J. Chem. Theory Comput. 2012. (67) Behn, A.; Zimmerman, P. M.; Bell, A. T.; Head-Gordon, M. Efficient Exploration Of Reaction Paths Via A Freezing String Method J. Chem. Phys. 2011, 135, 224108. (68) Behn, A.; Zimmerman, P.; Bell, A. T.; Head-Gordon, M. Incorporating Linear Synchronous Transit Interpolation Into The Growing String Method: Algorithm And Applications. J. Chem. Theory Comput. 2011, 4019–4025. (69) Shao, Y.; Molnar, L. F.; Jung, Y.; Kussmann, J.; Ochsenfeld, C.; Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V; Levchenko, S. V; O’Neill, D. P. Et Al. Advances In Methods And Algorithms In A Modern Quantum Chemistry Program Package Phys. Chem. Chem. Phys. 2006, 8, 3172– 3191. (70) MOLPRO, Version 2012.1, A Package Of Ab Initio Programs, H.-J. Werner, P. J. Knowles, G. Knizia, F. R. Manby, M. Schutz, P. Celani, T. Korona, R. Lindh, A. Mitrushenkov, G. Rauhut Et Al.



Page 18 of 19

(71) Werner, H.-J.; Knowles, P. J.; Knizia, G.; Manby, F. R.; Schutz, M. MOLPRO: A General-Purpose Quantum Chemistry Program Package

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Wires Comput Mol Sci 2012, 2, 242–253 (72) Hampel, C.; Peterson, K.; Werner, H.-J. A Comparison Of The Efficiency And Accuracy Of The Quadratic Configuration Interaction (QCISD), Coupled Cluster (CCSD), And Brueckner Coupled Cluster (BCCD) Methods Chem. Phys. Lett. 1992, 190, 1-12 (73) Deegan, M. J. O.; Knowles, P. J. Perturbative Corrections To Account For Triple Excitations In Closed And Open Shell Coupled Cluster Theories Chem. Phys. Lett. 1994, 227, 321-326 (74) Bartlett, R. J.; Musial, M. Coupled-Cluster Theory In Quantum Chemistry. Rev. Mod. Phys. 2007, 79, 291-352 (75) Dunning, T. H. Jr.; Gaussian Basis Sets For Use In Correlated Molecular Calculations. I. The Atoms Boron Through Neon And Hydrogen. J. Chem. Phys. 1989, 90, 1007-1023. (76) Nett, A. J.; Zhao, W.; Zimmerman, P. M.; Montgomery, J. Highly Active Nickel Catalysts For C–H Functionalization Identified Through Analysis Of Off-Cycle Intermediates. J. Am. Chem. Soc. 2015, 137, 7636–7639. (77) Nguyen, V. S.; Matus, M. H.; Grant, D. J.; Nguyen, M. T.; Dixon, D. A. Computational Study Of The Release Of H2 From Ammonia Borane Dimer (BH3NH3)2 And Its Ion Pair Isomers. J. Phys. Chem. A 2007, 111, 8844–8856. (78) Pons, V.; Baker, R. T.; Szymczak, N. K.; Heldebrant, D. J.; Linehan, J. C.; Matus, M. H.; Grant, D. J.; Dixon, D. A. Coordination Of Aminoborane, NH2BH2, Dictates Selectivity And Extent Of H2 Release In Metal-Catalysed Ammonia Borane Dehydrogenation. Chem. Commun. (Camb). 2008, 6597–6599. (79) Nguyen, V. S.; Matus, M. H.; Nguyen, M. T.; Dixon, D. A. Reactions Of Diborane With Ammonia And Ammonia Borane: Catalytic Effects For Multiple Pathways For Hydrogen Release. J. Phys. Chem. A 2008, 112, 9946–9954. (80) Matus, M. H.; Anderson, K. D.; Camaioni, D. M.; Autrey, S. T.; Dixon, D. A. Reliable Predictions Of The Thermochemistry Of BoronNitrogen Hydrogen Storage Compounds: Bxnxhy, X = 2, 3. J. Phys. Chem. A 2007, 111, 4411–4421. (81) Grant, D. J.; Matus, M. H.; Anderson, K. D.; Camaioni, D. M.; Neufeldt, S. R.; Lane, C. F.; Dixon, D. A. Thermochemistry For The Dehydrogenation Of Methyl-Substituted Ammonia Borane Compounds. J. Phys. Chem. A 2009, 113, 6121–6132. (82) Grant, D. J.; Dixon, D. A. Thermodynamic Properties Of Molecular Borane Phosphines, Alane Amines, And Phosphine Alanes And The [BH(4)(-)][PH(4)(+)], [Alh(4)(-)][NH(4)(+)], And [Alh(4)(-)][PH(4)(+)] Salts For Chemical Hydrogen Storage Systems From Ab Initio Electronic Structure Theory. J. Phys. Chem. A 2005, 109, 10138–10147. (83) Reaction of FAB and CO2 involves concerted 2H transfer to CO2, yielding DHFAB and FA. Reaction of FAB and FA resulted in a concerted dehydrogenation step, yielding DHFAB and H2 along with regeneration of FA. Reaction of FAB and AB resulted in 2H transfer to FAB, reducing the C=O double bond and producing a reduced FAB structure along with NH2BH2. (84) Malcolm, A.; Sabourin, K. Donor–Acceptor Complexation And Dehydrogenation Chemistry Of Aminoboranes. Inorg. Chem. 2012. (85) Chen, X.; Zhao, J.; Shore, S. Facile Synthesis Of Aminodiborane And Inorganic Butane Analogue NH3BH2NH2BH3. J. Am. Chem. Soc. 2010, 10658–10659. (86) Chen, X.; Zhao, J.; Shore, S. The Roles Of Dihydrogen Bonds In Amine Borane Chemistry. Acc. Chem. Res. 2013, 46. 2666-2675 (87) Scheideman, M.; Shapland, P.; Vedejs, E. A Mechanistic Alternative For The Intramolecular Hydroboration Of Homoallylic Amine And Phosphine Borane Complexes. J. Am. Chem. Soc. 2003, 125, 10502–10503. (88) Luo, W.; Zakharov, L. N.; Liu, S. Y. 1,2-BN Cyclohexane: Synthesis, Structure, Dynamics, And Reactivity. J. Am. Chem. Soc. 2011, 133, 13006–13009.


Page 19 of 19


(89) Staubitz, A.; Robertson, A. P. M.; Manners, I. Ammonia-Borane And Related Compounds As Dihydrogen Sources. Chem. Rev. 2010, 110,

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4079–4124. (90) Hamilton, C. W.; Baker, R. T.; Staubitz, A.; Manners, I. B-N Compounds For Chemical Hydrogen Storage Chem. Soc. Rev. 2008, 38, 279-293

Synopsis: Quantum chemical reaction discovery tools unveil the mechanism of boron nitrogen codoped graphene oxide (BCN) formation from multiple equivalents of ammonia borane and CO2. These simulations show that the key intermediate, HCOOBHNH2, contains a highly reactive N=B double bond which leads to stable heterocyclic ring formation.

For Table of Contents Entry:


Mechanism for Forming B,C,N,O Rings from NH3BH3 and CO2 via

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