Theoretical Investigation of Obtaining Compounds with Planar

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The Journal of Physical Chemistry

Theoretical Investigation of Obtaining Compounds with Planar Tetracoordinate Carbons by Frustrated Lewis Pairs

Shaoni Yang and Congjie Zhang*

Key Laboratory of Macromolecular Science of Shaanxi Province, School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xi’an, 710062, China

ABSTRACT: Ten derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene (1a-1j) with different degree of frustration have been investigated using density functional theory. Moreover, 1a-1j as Lewis bases were used to form Lewis adducts C3X2BYH/B(C6F5)3 (2a-2j) with Lewis acid B(C6F5)3. Optimized geometries and the thermodynamic properties of giving the Lewis adducts C3X2BYH/B(C6F5)3 reveal that 2a-2j are frustrated Lewis pairs (FLPs). Their reactivity of activating H2 and HF show that 2a-2j are unfavorable to heterolytically cleave H2, while 2c-2j can cleave HF to form [C3X2BYH]+[FB(C6F5)3]-. In addition, we found the structures of [C3X2BYH]+ in [C3X2BYH]+[FB(C6F5)3]- contained a planar tetracoordinate carbon (ptC). Therefore, a new method of obtaining main group element compounds with ptC by using FLPs was presented.

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INTRODUCTION In

2006,

Stephan

para-Mes2P(C6F4)B(C6F5)2

and

co-workers

obtained

the

compound

(Mes = 2,4,6-trimethylphenyl) and found it could

heterolytically cleave H2 rapidly at room temperature.1 Interestingly, the Lewis base from the lone pair electron on P atom and Lewis acid from the empty orbital on B atom in para-Mes2P(C6F4)B(C6F5)2 were prevented to form classic Lewis adduct due to the steric effect, thus, this compound was named as frustrated Lewis pair (FLP). Besides the intramolecular FLPs, many intermolecular FLPs arisen from the significant steric effect of the Lewis acid and base in different molecules have been observed, such as the Lewis adducts boranes and phosphines B(C6F5)3/PR3 (R = tBu, Mes). Moreover, B(C6F5)3/PR3 can also heterolytically cleave dihydrogen under facile conditions.2 From then on, FLPs have been attracting increasing attention both experimentally and theoretically due to their special reactivity in the activation and fixation of a few small molecules of H2,2-15 CO2,16-21 nitrogen oxides,21-24 alkenes,25-27 alkynes,28-30 and so on.31-38 According to the atoms situated at the Lewis acid and base sites in FLPs, FLPs can be classified into boron/phosphorus,2-7 boron/carbon,39-42 carbon/carbon,39,43 aluminum/carbon,44 boron/nitrogen,11-15 aluminum/phosphorus (or nitrogen)45-47 and transition metal/phosphorus.48,49 FLPs achieved by N-Heterocyclic carbene (NHC) and Lewis acid are very important species due to the special properties of NHC.8,39 For the sake of convenience, the FLPs formed by NHC and B(C6F5)3 are be described as NHC/B(C6F5)3. In general, the thermodynamic properties of NHC/B(C6F5)3 could be calculated with Density Functional Theory (DFT) 2 z


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method50 to confirm that Lewis acid and base form a classic Lewis adduct or FLP.39,51 Additionally, the reactivity of FLPs towards activating small molecules can be also predicted by DFT method.9,39 Recently, a new mechanism of the heterolytic cleavage of H2 by FLPs was proposed, in which H2 is put into the electric field created by the donor/acceptor atoms in FLPs, then activated via a transition state called a prepared Lewis pair (PLP).52 Besides the Lewis bases mentioned above, our previous studies indicated that the derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene53,54 are also Lewis bases. The HOMOs of the derivatives are similar to that of NHC; in addition, the lone pair electrons are situated at the carbon atoms. Moreover, the complexes of the derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene with AgCl and AuCl were theoretically found to be stable.54 Therefore, we have designed a family of novel FLPs formed by the derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene with B(C6F5)3 in this contribution. Theoretically, we have investigated the reactivity of the novel FLPs towards heterolytically cleaving a nonpolarized molecule (H2) and a polarized molecule (HF). We found that the cleavage of HF by the FLPs is thermodynamically favorable. Thus, a new kind of approach of obtaining main group element compounds with a planar tetracoordinate carbon (ptC) was given.

COMPUTATIONAL METHODS Ten derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene (C3BH3) which were designed by replacing the H atoms of C3BH3 with Me, Et, tBu, P(Me)2 and P(tBu)2 groups were optimized using density functional theory M06 method in combination 3 z



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with 6-311G** basis sets. In addition, the geometries of Lewis adducts formed by the derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene and B(C6F5)3 were optimized at the same level of the theory. The vibrational frequencies of the derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene and Lewis adducts were calculated to confirm the true minima on the potential energy surfaces. The thermodynamic properties of formation of Lewis adducts were calculated to assess whether the Lewis adducts are FLPs. Moreover, the reactivity of the FLPs towards H2 and HF were studied by calculating the thermodynamic properties of the reactions. The natural bond orbital (NBO) analysis were performed in order to understand the chemical bonding better.55 All calculations were performed with the Gaussian09 program.56

RESULTS AND DISCUSSION Optimized geometries of ten derivatives of 2-Borabicyclo[1.1.0]but-1(3)-ene, C3X2BY (X = H, Me, Et and tBu, Y = Me, Et, tBu, P(Me)2 and P(tBu)2), were displayed in Figure 1 (1a-1j). As can be seen from Figure 1, the steric hindrance of 1a (C3H2BMe) is the smallest, while 1e (C3(tBu)2B(tBu)) has the greatest steric hindrance. The steric hindrance of 1b, 1c, 1d and 1e increases with the changing of groups X from H to Me, Et and tBu groups. The steric hindrance of 1f, 1g and 1e increases with the changing of groups Y from Me to Et and tBu groups. The order of the steric hindrance of 1h (C3(Et)2BP(Me)2), 1i (C3(Et)2BP(tBu)2) and 1j (C3(tBu)2BP(tBu)2) with P(Me)2 and P(tBu)2 groups on B atoms is 1h < 1i < 1j. The vibrational frequencies of 1a-1j are positive, showing they are the true minima on the 4 z


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potential energy surfaces. The lengths of horizontal C-C bond in 1a-1j are in the range of 1.440-1.450 Å, the distances of C-C(X2) and C-B(Y) bonds in 1a-1j are close to 1.475 Å and 1.458 Å, respectively. Therefore, the different groups bonded to C (top) and B have little influence on the geometrical structures. And the WBIs of C-C, C-C(X2) and C-B(Y) in 1a-1j are approximately 1.37, 1.00 and 1.15, respectively. Thus, the C-C bond is between single and double bond, while C-C(X2) and C-B(Y) have single bond characteristics. The HOMOs of 1a-1j were illustrated in Figure 2, in which the lone pair electrons are situated at the two sides of the carbon atoms and consistent with the previous results.52 Therefore, these molecules are Lewis bases. Calculated energy gaps between HOMO and LUMO, charge distributions and electron configurations of the horizontal C atoms in 1a-1j were listed in Table 1. The energy gaps in 1a-1g are in the range of 6.9-7.2eV and greater than that in 1h-1j by 1.0eV at least, which the difference results from the conjugate effect of B and P atoms in 1h-1j. The charges and electron configurations of the horizontal C atoms in 1a-1j are 0.17e and 2s1.22p2.9-3.0, respectively, indicating that the C atoms adopt approximately sp3 hybrid. Further, the isomers with possible configurations of the ten Lewis adducts which were formed by Lewis bases (1a-1j) and Lewis acid B(C6F5)3 were optimized. The geometries with the lowest energy were displayed in Figure 3 (2a-2j), and they are the minima on the potential energy surfaces because the calculated vibrational frequencies of the ten Lewis adducts are positive.

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The lengths of C-B(C6F5) bonds in 2a-2j are longer than that in NHC/B(C6F5)3 FLPs,49 so the C-B bonds between Lewis bases and acids are not formed. WBIs values of C-B(C6F5) bonds in 2a-2j are in the range of 0.55-0.70, indicating that the Lewis bases and acids have weak interaction via C atoms in 1a-1j and B atoms in B(C6F5)3. The variations of the electronic energies with zero-point energies (ZPEs) corrected, Gibbs free energies and enthalpies at 298 K of giving Lewis adducts 2a-2j were calculated and listed in Table 2. The variations of the electronic energies of forming 2a-2j are all negative, so the 1a-1j and B(C6F5)3 can form adducts. The variations of Gibbs free energies of obtaining 2a-2c and 2h are slightly negative (-2.91 to -0.63), which indicate that considerable amounts of free 1a-1c, 1h and B(C6F5)3 exist in the reaction system. However, the variations of Gibbs free energies of forming 2d-2g and 2i-2j are 1.14, 16.18, 10.42, 13.93, 0.64 and 16.04 kcal/mol, respectively. Thus, 2a-2j are FLPs, which are consistent with the bond lengths and WBIs. 2a-2j

were

further

used

to

cleave

H2

heterolytically

to

form

[C3X2BYH]+[HB(C6F5)3]- (3a-3j), respectively, which the cleavage process is C3X2BY+B(C6F5)3+H2=[C3X2BYH]+[HB(C6F5)3]-. Optimized geometries of 3a-3j were illustrated in Figure 4, the variations of the electronic energies with zero-point energies (ZPEs) corrected, Gibbs free energies and enthalpies at 298 K of obtaining 3a-3j were listed in Table 3. Table 3 shows that the variations of Gibbs free energies of forming 3a-3j are around 20.00 kcal/mol, indicating that the reactions are not thermodynamically favorable. According to the mechanism of dihydrogen activation 6 z


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by FLPs,50 we can conclude that the magnitude of the electric field of C3X2BY/B(C6F5)3 FLP is not enough to active H2. The energies of the highest occupied molecular orbitals (HOMOs) of 1a-1j are between -0.283 and -0.232 a.u., which are lower than that of 1,3-di-tert-butylimidazolin-2-ylidene by 0.40eV at least. Thus, the ability of donating electrons of 1a-1j is a little weaker than that of NHC. Therefore, the strength of Lewis base and acid in FLPs plays a key role in activating small molecules. Is it possible that a polarized molecule might be cleaved in the weak electronic field created by the FLPs? We have considered the cleavage of HF by 2a-2j, which the reaction equation is C3X2BY+B(C6F5)3+HF=[C3X2BYH]+[FB(C6F5)3]-. The variations of the electronic energies with ZPEs corrected, Gibbs free energies and enthalpies at 298K of obtaining 4a-4j by cleaving HF with 2a-2j were listed in Table 4. The variations of the electronic energies of forming 4a-4j are less than -30.00 kcal/mol. The variations of Gibbs free energies of giving 4c-4j range from -8.20 to -4.00 kcal/mol, while those of 4a and 4b are positive, thus, the reactions of cleavage of HF with 2c-2j are thermodynamically favorable. In addition, we displayed the optimized geometries of 4c-4j ([C3X2BYH]+[FB(C6F5)3]-) in Figure 5. According to the mechanism of activation of H2 by FLPs, the HF was put into the active cavity between the bases (1c-1j) and B(C6F5)3, electron transfer is more likely to be occurred among them than H2, then the cleavage of H-F bond results in the formation of stable compounds of [C3X2BYH]+[FB(C6F5)3]-. We further focus on the structures of C3X2BYH+ in [C3X2BYH]+[FB(C6F5)3]- in Figure 5. The lengths and WBIs of C-H 7 z



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bond in C3X2BYH+ in 4c-4j are about 1.124 Ǻ and 0.67, respectively, slightly longer than the distance of the usual C-H bond. The lengths of C-C(X2), C-C and C-B bonds in 4c-4g are in the range of 1.515-1.560 Ǻ, 1.400-1.410 Ǻ and 1.550-1.575 Ǻ, respectively. And the WBIs of C-C(X2), C-C and C-B bonds are in the range of 0.80-0.88, 1.32-1.35 and 0.70-0.78, respectively. Moreover, the sum of bond angles of H-C-C(X2), C(X2)-C-C, C-C-B and B-C-H are close to 360.0°. Therefore, the C atom in 4c-4g is a ptC. Different from 4c to 4g, the bond distances of C-C(X2) bonds in 4h-4j are 1.529, 1.558 and 1.568 Ǻ, respectively, slightly longer than the length of C-C single bond, while the WBIs of C-C(X2) bonds are 0.84, 0.80 and 0.81, indicating C-C(X2) is weaker than usual C-C single bond due to the electron-donating effect of P(Me)2 and P(tBu)2 groups. The lengths and WBIs of C-C, C-B and C-H have little influence by the P(Me)2 and P(tBu)2 groups. In addition, the sum of bond angles of H-C-C(X2), C(X2)-C-C, C-C-B and B-C-H are also close to 360.0°, showing that the C atom in 4h-4j is also a ptC. Therefore, a new class of molecules with ptC were obtained by FLPs.

CONCLUSIONS Theoretically, we have constructed ten derivatives (1a-1j, C3X2BY) of 2-Borabicyclo[1.1.0]but-1(3)-ene with different substitution patterns and found that 1a-1j are Lewis bases. The structures and thermodynamic properties of the Lewis adducts (2a-2j) forming by the ten Lewis bases 1a-1j with B(C6F5)3 were investigated and 2a-2j were confirmed to be frustrated Lewis pairs (FLPs). Their reactivity of 8 z


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2a-2j in activating H2 and HF showed that the 2a-2j are unfavorable to cleave H2, while 2c-2j are favorable to cleave HF to form [C3X2BYH]+[FB(C6F5)3]- (4c-4j). Moreover, the structures of [C3X2BYH]+ in [C3X2BYH]+[FB(C6F5)3]- were found to contain a planar tetracoordinate carbon (ptC). Therefore, we obtained a new method to design FLP and the compounds with ptC in this contribution.

AUTHOR INFORMATION Corresponding Author *[email protected]; 86-29-81530726 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by the National Science Foundation of China (21373133) and the Fundamental Research Funds for the Central Universities (No. GK201101004).

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(3) Neu, R. C.; Ouyang, E. Y.; Geier, S. J.; Zhao, X. X.; Ramos, A.; Stephan, D. W. Probing Substituent Effects on the Activation of H2 by Phosphorus and Boron Frustrated Lewis Pairs. Dalton Trans. 2010, 39, 4285-4294. (4) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Froehlich, R.; Grimme, S.; Stephan, D. W. Rapid Intramolecular Heterolytic Dihydrogen Activation by a Four-Membered Heterocyclic Phosphane-Borane Adduct. Chem. Commun. 2007, 47, 5072-5074. (5) Spies, P.; Kehr, G.; Bergander, K.; Wibbeling, B.; Froehlich, R.; Erker, G. Metal-free Dihydrogen Activation Chemistry: Structural and Dynamic Features of Intramolecular P/B Pairs. Dalton Trans. 2009, 9, 1534-1541. (6) Axenov, K. V.; Momming, C. M.; Kehr, G.; Froehlich, R.; Erker, G. Structure and Dynamic Features of an Intramolecular Frustrated Lewis Pair. Chem. Eur. J. 2010, 16, 14069-14073. (7) Geier, S. J.; Gilbert, T. M.; Stephan, D. W. Activation of H(2) by Phosphinoboranes R(2)PB(C(6)F(5))(2). J. Am. Chem. Soc. 2008, 130, 12632-12633. (8) Chase, P. A.; Stephan, D. W. Hydrogen and Amine Activation by a Frustrated Lewis Pair of a Bulky N-Heterocyclic Carbene and B(C6F5)3. Angew. Chem. Int. Ed. 2008, 47, 7433-7437. (9) Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones P. G.; Tamm, M. Heterolytic Dihydrogen Activation by a Frustrated Carbene-borane Lewis Pair Angew. Chem. Int. Ed. 2008, 39, 7428-7432. (10) Holschumacher, D.; Taouss, C.; Bannenberg, T.; Hrib, C. G.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Dehydrogenation Reactivity of a Frustrated Carbene-Borane 10 z


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Lewis Pair. Dalton Trans. 2009, 35, 6927-6929. (11) Jiang, C. F.; Blacque, O.; Fox, T.; Berke, H. Heterolytic Cleavage of H2 by Frustrated B/N Lewis Pairs. Organometallics 2011, 30, 2117-2124. (12) Geier S. J.; Stephan, D. W. Lutidine/B(C6F5)3: At the Boundary of Classical and Frustrated Lewis Pair Reactivity. J. Am. Chem. Soc. 2009, 131, 3476-3477. (13) Webb, J. D.; Laberge, V. S.; Geier, S. J.; Stephan, D. W.; Crudden, C. M. Borohydrides from Organic Hydrides: Reactions of Hantzsch’s Esters with B(C6F5)3. Chem. Eur. J. 2010, 16, 4895-4902. (14) Sumerin, V.; Schulz, F.; Nieger, M.; Leskelae, M.; Repo, T.; Rieger, B. Facile Heterolytic H2 Activation by Amines and B(C6F5)3. Angew. Chem. Int. Ed. 2008, 47, 6001-6003. (15) Jiang, C. F.; Blacque O.; Berke, H. Metal-free Hydrogen Activation and Hydrogenation of Imines by 1,8-bis(dipentaﬂuorophenylboryl)naphthalene. Chem. Commun. 2009, 37, 5518-5520. (16) Momming, C. M.; Otten, E.; Kehr, G.; Froehlich, R.; Grimme, S.; Stephan, D. W.; Erker, G. Reversible Metal-Free Carbon Dioxide Binding by Frustrated Lewis Pairs. Angew. Chem. Int. Ed. 2009, 48, 6643-6646. (17) Zhu, J.; An, K. Mechanistic Insight into the CO2 Capture by Amidophosphoranes: Interplay of the Ring Strain and the trans Influence Determines the Reactivity of the Frustrated Lewis Pairs. Chem. Asian J. 2013, 8, 3147-3151. (18) Peuser, I.; Neu, R. C.; Zhao X.; Ulrich M.; Schirmer B.; Tannert, J. A.; Kehr G.; Grimme S.; Erker G.; Stephan D. W.; et al. CO2 and Formate Complexes of 11 z



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Phosphine/Borane Frustrated Lewis Pairs. Chem. Eur. J. 2011, 17, 9640-9650. (19) Berkefeld, A.; Piers, W. E.; Parvez, M. Tandem Frustrated Lewis Pair/Tris (pentfluorophenyl) Borane-Catalyzed Deoxygenative Hydrosilylation of Carbon Dioxide. J. Am. Chem. Soc. 2010, 132, 10660-10661. (20) Wang, T.; Stephan, D. W. Carbene-9-BBN Ring Expansions as a Route to Intramolecular Frustrated Lewis Pairs for CO2 Reduction. Chem. Eur. J. 2014, 20, 3036-3039. (21) Theuergarten, E.; Bannenberg, T.; Walter M. D.; Holschumacher, D.; Freytag M.; Daniliuc C. G.; Jones P. G.; Tamm, M. Computational and Experimental Investigations of CO2 and N2O Fixation by Sterically Demanding N-Heterocyclic Carbenes(NHC) and NHC/Borane FLP Systems. Dalton Trans. 2014, 43, 1651-1662. (22) Otten, E.; Neu, R. C.; Stephan, D. W. Complexation of Nitrous Oxide by Frustrated Lewis Pairs. J. Am. Chem. Soc. 2009, 131, 9918-9919. (23) Thomas, M. G. Computational Studies of Complexation of Nitrous Oxide by Borane-Phosphine Frustrated Lewis Pairs. Dalton Trans. 2012, 41, 9046-9055. (24) Cardenas, A. J. P.; Culotta, B. J.; Warren, T. H.; Grimme, S.; Stute, A.; Froehlich, R.; Kehr G.; Erker, G. Capture of NO by a Frustrated Lewis Pair: A New Type of Persistent N-oxyl Radical. Angew. Chem. Int. Ed. 2011, 50, 7567-7571. (25) McCahill, J. S. J.; Welch G. C.; Stephan, D. W. Reactivity of “Frustrated Lewis Pairs”: Three-component Reactions of Phosphines, a Borane, and Olefins. Angew. Chem. Int. Ed. 2007, 46, 4968-4971. (26) Stirling, A.; Hamza, A.; Rokob T. A.; Pápai, I. Concerted Attack of Frustrated 12 z


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Lewis Acid-base Pairs on Olefinic Double Bonds: A Theoretical Study. Chem. Commun. 2008, 3148-3150. (27) Ullrich, M.; Seto, K. S. H.; Lough, A. J.; Stephan, D. W. 1,4-Addition Reactions of Frustrated Lewis Pairs to 1,3-dienes. Chem. Commun. 2009, 17, 2335-2337. (28) Dureen M. A.; Stephan, D. W. Terminal Alkyne Activation by Frustrated and Classical Lewis Acid/Phosphine Pairs. J. Am. Chem. Soc. 2009, 131, 8396-8397. (29) Jiang, C. F.; Blacque, O.; Berke, H. Activation of Terminal Alkynes by Frustrated Lewis Pairs. Organometallics 2010, 29, 125-133. (30) Dureen, M. A.; Brown C. C.; Stephan, D. W. Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes. Organometallics 2010, 29, 6594-6607. (31) Chase, P. A.; Gille, A. L.; Gilbert T. M.; Stephan, D. W. Frustrated Lewis Pairs Derived from N-heterocyclic Carbenes and Lewis Acids. Dalton Trans. 2009, 7179-7188. (32) Birkmann, B.; Voss, T.; Geier, S. J.; Ullrich, M.; Kehr, G.; Erker, G.; Stephan, D. W. Frustrated Lewis Pairs and Ring-Opening of THF, Dioxane, and Thioxane. Organometallics 2010, 29, 5310-5319. (33) Li, H. X.; Zhao, L. L.; Lu, G.; Mo, Y. R.; Wang, Z. X. Insight into the Relative Reactivity of “Frustrated Lewis Pairs” and Stable Carbenes in Activating H2 and CH4: A Comparative Computational Study. Phys. Chem. Chem. Phys. 2010, 12, 5268-5275. (34) Morton, J. G. M.; Dureen M. A.; Stephan, D. W. Ring-Opening of Cyclopropanes by “Frustrated Lewis Pairs”. Chem. Commun. 2010, 46, 8947-8949. 13 z



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(35) Dureen, M. A.; Welch, G. C.; Gilbert T. M.; Stephan, D. W. Heterolytic Cleavage of Disulfides by Frustrated Lewis Pairs. Inorg. Chem. 2009, 48, 9910-9917. (36) Holschumacher, D.; Bannenberg, T.; Ibrom, K.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Selective Heterolytic P-P Bond Cleavage of White Phosphorus by a Frustrated Carbene-borane Lewis Pair. Dalton Trans. 2010, 39, 10590-10592. (37) Momming, C. M.; Kehr, G.; Wibbeling, B.; Froehlich, R.; Erker, G. Addition Reactions to the Intramolecular Mesityl(2)P-CH2-CH2-B(C6F5)(2) Frustrated Lewis Pair. Dalton Trans. 2010, 39, 7556-7564. (38) Kolychev, E. L.; Bannenberg, T.; Freytag, M.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Reactivity of a frustrated Lewis Pair and Small-Molecule Activation by an Isolable Arduengo Carbene-B{3,5-(CF3)2C6H3}3 Complex. Chem. Eur. J. 2012, 18, 16938-16946. (39) Kolychev, E. L.; Theuergarten, E.; Tamm, M.; N-Heterocyclic Carbenes in FLP Chemistry. Top. Curr. Chem. 2013, 334, 121-155. (40) Alcarazo, M.; Gomez, C.; Holle, S.; Goddard, R. Exploring the Reactivity of Carbon(0)/Borane-based Frustrated Lewis Pairs. Angew. Chem. Int. Ed. 2010, 49, 5788-5791. (41) Dureen, M. A.; Brown, C. C.; Stephan, D. W. Addition of Enamines or Pyrroles and B(C6F5)3(3) “Frustrated Lewis Pairs” to Alkynes. Organometallics 2010, 29, 6422-6432. (42) Zhao X. X.; Stephan, D. W. Frustrated Lewis Pair Olefin Addition Reactions: P-, N-, C- and H-based Nucleophilic Additions to an Olefin-tethered Borane. Chem. Sci. 14 z


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2012, 3, 2123-2132. (43) Palomas, D.; Holle, S.; Ines, B.; Bruns, H.; Goddard, R.; Alcarazo, M. Synthesis and Reactivity of Eelectron Poor Allenes: Formation of Completely Organic Frustrated Lewis Pairs. Dalton Trans. 2012, 41, 9073-9082. (44) Zhang, Y. T.; Miyake, G. M.; Chen, E.Y. X. Alane-Based Classical and Frustrated Lewis Pairs in Polymer Synthesis: Rapid Polymerization of MMA and Naturally Renewable Methylene Butyrolactones into High-Molecular-Weight Polymers. Angew. Chem. Int. Ed. 2010, 49, 10158-10162. (45) Appelt, C.; Westenberg, H.; Bertini, F.; Ehlers, A. W.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Geminal Phosphorus/Aluminium-Based Frustrated Lewis Pairs: C-H Versus C Equivalent to C Activation and CO2 Fixation. Angew. Chem. Int. Ed. 2011, 50, 3925-3928. (46) Roters, S.; Appelt, C.; Westenberg, H.; Hepp, A.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Dimeric Aluminum-Phosphorus Compounds as Masked Frustrated Lewis Pairs for Small Molecule Activation. Dalton Trans. 2012, 41, 9033-9045. (47) Zheng, W. J.; Pi, C. F.; Wu, H. S. An Alkynylaminomethylaluminium Species with a Six-Membered Chair Conformation Al2C2N2 Framework: A New Path to Geminal N/Al Frustrated Lewis Pairs. Organometallics 2012, 31, 4072-4075. (48) Chapman, A. M.; Haddow, M. F.; Wass, D. F. Frustrated Lewis Pairs Beyond the Main Group: Synthesis, Reactivity, and Small Molecule Activation with Cationic Zirconocene–Phosphinoaryloxide Complexes. J. Am. Chem. Soc. 2011, 133, 18463-18478. 15 z



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(49) Chapman, A. M.; Wass, D. F. Cationic Ti(IV) and Neutral Ti(III) Titanocene–phosphinoaryloxide Frustrated Lewis Pairs: Hydrogen Activation and Catalytic Amine-Borane Dehydrogenation. Dalton Trans. 2012, 41, 9067-9072. (50) Zhao Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157-167. (51) Kronig, S.; Theuergarten, E.; Holschumacher, D.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Dihydrogen Activation by Frustrated Carbene-Borane Lewis Pairs Experimental and Theoretical Study of Carbene Variation. Inorg. Chem. 2011, 50, 7344-7359. (52) Grimme, S.; Kruse, H. Erker, G. The Mechanism of Dihydrogen Activation by Frustrated Lewis Pairs Revisited. Angew. Chem. Int. Ed. 2010, 49, 1402-1405. (53) Zhang, C. J.; Jia, W. H.; Cao, Z. X. Stability Rules of Main-Group Element Compounds with Planar Tetracoordinate Carbons. J. Phys. Chem. A. 2010, 114, 7960-7966. (54) Zhang, C. J.; Lei, F.F. Toward Design of Ag(I) and Au(I) Complexes with Planar Tetracoordinate Carbon Using Novel Ligands. J. Phys. Chem. A. 2012, 116, 9123-9130. (55) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Interactions from a Natural Bond Orbital, Donor-Acceptor Viewpoint. Chem. Rev. 1998, 88, 899-926. (56) Frish, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb M. A.; Cheeseman J. R.; Scalmani G.; Barone V.; Mennucci B.; Petersson G. A.; et al. Gaussian 09, Revision C.01; Gaussian: Wallingford, CT, USA, 2009. 16 z


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H

Me

H C

1.466 1.03 1.443 1.38

C 1.451 1.37

1.458 1.457 1.16 B 1.16

H 1.465 1.03 1.443 1.37

C 1.458 1.15

B

C

1.458 1.15

tBu

1b

1d

But

tBu

1.477 0.99 1.444 1.36

C 1.458 1.16

Figure

1.

Optimized

1.450 1.36

1.456 1.460 1.15 B 1.13

1.477 0.99 C

1.477 0.99 C

1.456 1.15

1.457 B 1.14

Et

tBu

1f

1g

1e

Et

Et

But

Et C

C 1.474 0.99

1.478 0.99 C

C

tBu C

Me

Et

1.446 1.37

But

tBu C

1.477 0.99 C

C

1a

C

1.458 1.458 1.16 B 1.16

tBu

1.458 1.458 1.14 B 1.14

Me

1.474 0.99 C

1c

1.477 0.99 1.444 1.35

1.476 0.98 1.450 1.37

1.457 1.457 1.16 B 1.16

C 1.465 1.03 C

1.475 0.98 C

tBu

But

H C

Et C

1.475 0.98

1.465 1.03 C

C

Et

Me

1.476 0.98 C

1.443 1.39

1.458 B 1.16

tBu C

1.474 0.99 C

1.476 0.98 C

1.460 1.14

1.462 B 1.14

1.439 1.38

1.477 0.99

1.479 0.99 C

C 1.459 1.13

1.461 B 1.13

P(Me)2

P(tBu)2

P(tBu)2

1h

1i

1j

geometries

of

ten

derivatives

(C3X2BY)

of

2-Borabicyclo[1.1.0]but-1(3)-ene. Bond distances (in plain, in Ǻ) and WBIs (in bold).

17 z



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Page 18 of 29

1a

1b

1c

1d

1e

1f

1g

1h

1i

1j

Figure 2. HOMOs of ten derivatives (C3X2BY) of 2-Borabicyclo[1.1.0]but-1(3)-ene. H

Me

H

1.417 C

1.544

1.430

1.723 C B(C6F5)3 0.68 1.558

1.415

H

C

1.415

1.522 C

1.718 B(C6F5)3 0.69

1.563

C

1.601 1.432

1.754 B(C6F5)3 0.67

C

1.562

1.413 B

tBu

tBu

tBu

2b (26)

2c (25)

2d (27)

But

1.617 1.920 C B(C6F5)3 0.58

1.434

1.405

But

tBu C

1.420 C

1.421

1.740 C 0.67 B(C6F5)3

1.550

C

1.427

1.408

1.591 1.431

B

tBu

C 1.428

1.420 C

Et C

B

But

H

Et

Me C

C

1.570

1.411

1.650

1.409

1.411

1.835 C 0.64 B(C6F5)3

1.428

C

tBu C

1.583

C

1.652 1.430

C

1.831 B(C6F5)3 0.64

1.577

1.413

B

B

B

B

Me

Me

Et

tBu

2a (27)

2f (21)

2g (24)

2e (22)

Et

Et

Et

1.424 C

C 1.596

1.429

1.753 C 0.67 B(C6F5)3

1.562

1.411

But

Et

C 1.421

1.601 1.437

C

C

1.417

1.763 B(C6F5)3 0.67

1.570

1.412

tBu C

C

1.659 1.433

C

1.945 B(C6F5)3 0.57

1.578

1.413

B

B

B

P(Me)2

P(tBu)2

P(tBu)2

2h (28)

2i (25)

2j (16)

Figure 3. Optimized geometries of Lewis adducts C3X2BY/B(C6F5)3. Bond distances (in plain, in Ǻ), WBIs (in bold) and the smallest vibrational frequencies (in italic, in cm-1). 18 z


Page 19 of 29

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H

H

H

1.451 C

Me

H

1.494 1.405

C

1.411

1.442

1.132 H

H

C

B(C6F5)3

1.508 1.408

C

H

B(C6F5)3

C

1.413

1.426

B

B

B

tBu

Me

3b But

Et

But

1.409

C

1.418

H

H

B(C6F5)3

1.540 1.405

C

C

H

H

1.527

1.461

1.117 B(C6F5)3

C

1.403

1.414

1.577

1.417

1.569

B

B

tBu

tBu

Me

3d

3e Et

tBu

1.407

C

H

H

B(C6F5)3

1.410

C

B(C6F5)3

Et

C

H

H

1.582

1.432

1.121 B(C6F5)3

1.558

1.423

C

1.412

C

B

B

Et

P(Me)2

P(tBu)2

3g

3h

1.121 H

H

B(C6F5)3

1.546

1.434

B

But

H

C 1.551

1.446

1.119

1.570

1.416

Et

C 1.555

1.117 H

3f

Et

C 1.446

C 1.585

B

But

B(C6F5)3

C

1.454

1.122

H

tBu

C 1.531

1.122 H

3c

tBu

C 1.454

C 1.547

Me

Et

C

H

1.568

1.436

1.132

1.579

1.415

1.595

C

3a

C

Me

C

C

3i

tBu C 1.588

1.435 C

1.408

1.114

C

H

H

B(C6F5)3

1.560

1.432 B

P(tBu)2

3j

Figure 4. Optimized geometries of [C3X2BYH]+[HBC6F5)3]-. Bond distances (in Ǻ).

19 z



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

H

H

H

C

C

1.133 0.67 H F

B

C 1.507 0.91

1.442 B(C6F5)3

1.406 1.36

1.592 0.68

1.413

C

B

But

C

C

1.122 0.67 H F

B

B(C6F5)3

1.404 1.35

C

4c tBu

1.123 0.67 H F

1.465 B(C6F5)3

1.403 1.34

B

C

C

B

4e

C

Et

C

C

B(C6F5)3

1.565 0.74

1.408 1.34

1.122 0.68 H F

C

1.421 B

Et

B(C6F5)3

1.569 0.74

1.440

1.558 0.80

C

C

1.410 1.34

1.430 B

P(Me)2

4g

1.125 0.67 H F

B(C6F5)3

1.557 0.78

P(tBu)2

4h But

Et C

1.529 0.84

C

B(C6F5)3

1.577 0.70

4f

Et

1.455

1.125 0.67 H F

Me

4d

1.125 0.67 H F

1.515 0.88

1.416

1.575 0.70

tBu

1.538 0.85

1.550 0.78

B

But

C

Et

B(C6F5)3

C

1.417

tBu

1.124 0.68 H F

tBu

1.527 0.87

tBu

B

C

1.423

tBu

1.458

1.573 0.72

1.418

C

C

C 1.528 0.85

1.418

B(C6F5)3

4b

C 1.455

1.33

1.411 1.34

tBu

Et

1.452

1.560 0.80

1.438

1.576 0.71

1.415

4a

But

1.132 0.66 H F

C

Me

1.35

Me

C 1.497 0.93

Et

Me

H

C 1.448 1.37

Page 20 of 29

4i

tBu C 1.568 0.81

1.441 1.407 1.34

C

1.120 0.68 H F

C

1.428 B

B(C6F5)3

1.565 0.76

P(tBu)2

4j

Figure 5. Optimized geometries of [C3X2BYH]+[FBC6F5)3]-. Bond distances (in plain, in Ǻ) and WBIs (in bold).

20 z


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Table 1. Energies of HOMO (EHOMO, in a.u.), LUMO (ELUMO, in a.u.) and energy gaps (Egap, in eV), charges (qC) and electron configurations of the horizontal C atoms in 1a-1j Species 1a 1b 1c 1d 1e 1f 1g 1h 1i 1j

EHOMO -0.28291 -0.28277 -0.27721 -0.27697 -0.27533 -0.27516 -0.27523 -0.24088 -0.23236 -0.23200

ELUMO -0.01966 -0.02310 -0.02138 -0.02205 -0.01957 -0.01610 -0.01698 -0.02376 -0.02594 -0.02223

Egap 7.16 7.07 6.96 6.94 6.96 7.05 7.03 5.91 5.62 5.71

qC -0.15 -0.15 -0.16 -0.17 -0.18 -0.17 -0.18 -0.17 -0.18 -0.19

electron configuration [core]2s1.212p2.92 [core]2s1.202p2.93 [core]2s1.192p2.95 [core]2s1.182p2.96 [core]2s1.172p2.98 [core]2s1.182p2.97 [core]2s1.182p2.97 [core]2s1.182p2.96 [core]2s1.172p2.98 [core]2s1.162p3.01

Table 2. Distances (in Ǻ) between C atom in C3X2BY and B atom in B(C6F5)3, electronic energies with ZPEs corrected (∆E, in kcal/mol), Gibbs free energies (∆G, in kcal/mol) and enthalpies (∆H, in kcal/mol) at 298K of obtaining 2a-2j by 1a-1j and B(C6F5)3 Species

dC-B

∆E

∆G

∆H

2a 2b 2c 2d 2e 2f 2g 2h 2i 2j

1.718 1.723 1.740 1.754 1.831 1.920 1.835 1.753 1.763 1.945

-17.02 -17.71 -17.17 -15.71 -0.97 -5.53 -1.98 -17.77 -16.47 -0.13

-2.91 -0.88 -1.87 1.14 16.18 10.42 13.93 -0.63 0.64 16.04

-17.62 -18.25 -17.54 -16.41 -1.38 -5.84 -2.07 -18.54 -17.05 -0.24

21 z



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Table 3. Electronic energies with ZPEs corrected (∆E, in kcal/mol), Gibbs free energies (∆G, in kcal/mol) and enthalpies (∆H, in kcal/mol) at 298K of giving 3a-3j by heterolytically cleaving H2 with 2a-2j Species

∆E

∆G

∆H

3a 3b 3c 3d 3e 3f 3g 3h 3i 3j

9.34 5.57 0.48 -3.79 -5.68 -3.53 -3.73 -2.21 -4.50 -3.73

28.25 25.44 21.22 18.45 14.13 16.58 17.04 20.79 17.29 18.07

7.53 4.04 -1.28 -5.86 -6.75 -4.79 -5.31 -4.68 -6.53 -5.36

Table 4. Electronic energies with ZPEs corrected (∆E, in kcal/mol), Gibbs free energies (∆G, in kcal/mol) and enthalpies (∆H, in kcal/mol) at 298K of obtaining 4a-4j by cleaving HF with 2a-2j Species

∆E

∆G

∆H

4a 4b 4c 4d 4e 4f 4g 4h 4i 4j

-19.67 -22.21 -28.30 -30.90 -32.29 -30.32 -31.85 -29.89 -30.87 -31.90

2.55 2.33 -3.97 -5.78 -8.23 -6.41 -7.50 -4.86 -4.50 -7.44

-21.08 -23.34 -29.71 -32.47 -33.26 -31.49 -33.05 -31.50 -32.65 -32.98

22 z


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TOC But

tBu C

C

C B

H F

tBu

But

∆G 0

B(C6F5)3

(C6F5)3B

H H

Planar tetracoordinate carbon

tBu

C C

C

B tBu

23 z



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Figure 1 169x187mm (300 x 300 DPI)


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Figure 2 169x99mm (300 x 300 DPI)



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

Figure 3 227x223mm (300 x 300 DPI)


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Figure 4 156x214mm (300 x 300 DPI)



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

216x272mm (300 x 300 DPI)


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Table of Content 109x49mm (300 x 300 DPI)


Theoretical Investigation of Obtaining Compounds with Planar

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