Consequence of Ligand Bite Angle on Bismuth Lewis Acidity

Communication pubs.acs.org/IC

Consequence of Ligand Bite Angle on Bismuth Lewis Acidity Ramkumar Kannan,† Sandeep Kumar,‡ Alex P. Andrews,† Eluvathingal D. Jemmis,*,‡ and Ajay Venugopal*,† †

School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura, Thiruvananthapuram 695551, India ‡ Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India S Supporting Information *

and [(Me2NC6H4)(mesityl)Bi]+ (cation B, Figure 1). Acceptor numbers calculated using the Gutmann−Beckett method10 and the reactivity of the cations vindicate this strategy.

ABSTRACT: Ligand bite angle, a common parameter to fine-tune reactivity in transition-metal chemistry, is used for the first time in main-group chemistry to control and tune the Lewis acidity in organobismuth cations bearing 2[(dimethylamino)methyl]phenyl (Me2NCH2C6H4) and 2(dimethylamino)phenyl (Me2NC6H4) ligands. The latter chelating ligand induces a shorter C−Bi−N bite angle, leading to a weaker Bi−N bond with a corresponding lower Bi−N σ*-acceptor orbital and hence exhibiting remarkably higher Lewis acidity. The Gutmann−Beckett method is successfully employed to quantify the Lewis acidity in organobismuth cations.

Figure 1. Reactive organanobismuth cations.

We initially considered neutral and cationic diarylbismuth compounds bearing mesityl and 2-[(dimethylamino)methyl]phenyl (Me2NCH2C6H4) ligands to quantify the Lewis acidity at bismuth. The reaction between (mesityl)BiCl 2 and Me2 NCH 2C6 H4Li gave the complex [(Me2 NCH2C 6H4)(mesityl)BiCl] (1a; Scheme 1). Treatment of 1a with AgOTf

L

ewis acidity has been a subject of interest in the pnictogen family. Lighter pnictogen halides, PnX3 (Pn = P, As, Sb), exhibit mild Lewis acidity1 in the 3+ oxidation state, while bismuth salts exhibit significant Lewis acidity.1,2 In recent years, several cationic organobismuth3−7 and amidobismuth8 compounds have been probed in this context. Efforts to prepare lowcoordinate reactive [BiR2]+ (Chart 1a) were not successful,3c

Scheme 1. Synthesis of 1a−4a

Chart 1. Representations of Cationic Compounds of the Type [BiR2]+ (a), [LBiR2]+ (b), and [L2BiR2]+ (c)

in CH2Cl2 led to the triflate derivative [(Me2NCH2C6H4)(mesityl)Bi(OTf)] (2a). The reaction between 1a and AgPF6 in tetrahydrofuran (THF) resulted in the cationic bismuth compound [(Me2NCH2C6H4)(mesityl)Bi(OC4H8)][PF6] (3a). Complexes 1a−3a possess a bisphenoidal coordination geometry around the bismuth atom (Figure 2). These reactions possibly involve a [LBiR2]+-type (Chart 1b) reactive intermediate cation A (Figure 1), which could not be isolated. The structures of 1a−3a were elucidated by single-crystal X-ray diffraction (XRD) studies and NMR spectroscopy. These studies provide insight into the extent of interaction of the NMe2 group with the bismuth center and the dependence on the nature of the ligand present in the trans position.

+

while [L2BiR2] (L is a neutral donor ligand; Chart 1c) has been obtained in a facile manner.3,4 The introduction of additional donor ligands to [BiR2]+ quenches the Lewis acidity at bismuth. Recently, a few examples of [LBiR2]+ have been reported (Chart 1b).5 The Lewis acidity in [LBiR2]+ (Chart 1b) must arise from the σ* molecular orbital (MO) located trans to L. However, the control, tuning, and quantification of Lewis acidity has not been achieved. Lewis acidity in cationic organobismuth compounds is an evolving area, and highly reactive cationic bismuth compounds remain elusive. Herein, we experimentally demonstrate that the ligand bite angle, a well-known parameter in transition-metal chemistry,9 can be used to control the Lewis acidity at bismuth by utilizing the inferences obtained from electronic structure studies of the cations [(Me2NCH2C6H4)(mesityl)Bi]+ (cation A, Figure 1) © 2017 American Chemical Society

Received: May 18, 2017 Published: August 9, 2017 9391

DOI: 10.1021/acs.inorgchem.7b01243 Inorg. Chem. 2017, 56, 9391−9395

Communication

Inorganic Chemistry

Hence, the acceptor number for cation A is 55 [see the Supporting Information (SI) for calculation of the acceptor number], which is similar to the value for BPh3.13,14 Having experimentally observed the Lewis acidity in cation A, we wanted to find ways of increasing the acidity further. At this stage, we resorted to computational methods before proceeding to experiments. Initially, the structures of 1a−4a were optimized by density functional theory methods, and later natural bond orbital analysis (see the SI for details) was carried out to understand the extent of lone-pair donation from the nitrogen atom in the NMe2 group to the bismuth atom in 1a−4a. The second-order perturbation energies E(2) (Table 2) and deletion Table 2. Second-Order Perturbation Energies E(2) (kcal mol−1) Calculated for lp(N)/lp(O) → σ*(Bi−Cl)/p(Bi) Interactions and the Energies (eV) of HOMO and LUMOa Figure 2. Solid-state structures of 1a−4a. Hydrogen atoms in all of the structures and noncoordinating anions in 3a and 4a are omitted for clarity.

lp(N) → p(Bi) 1a 2a 3a 4a A 1b 2b 3b 4b B

A single-crystal XRD study on 1a reveals that the Bi−N and Bi−Cl distances (Table 1) are within the range of those observed Table 1. Selected Bond Lengths (Å), the C−Bi−N Bite Angle (deg), and the Chemical Shift (δ ppm) Observed in 1H NMR Spectra for the N(CH3)2 Group

a b

compound

N−Bi

X−Bia

C−Bi−N

δ (ppm)

1a 2a 3a 4a 1b 2b 4b

2.582(4) 2.446(2) 2.426(7) 2.501(5) 2.796(3) 2.547(4)

2.636(2) 2.612(2) 2.576(6) 2.399(4) 2.560(2) 2.443(4)

89.6(2) 74.0(1) 75.4(2) 73.8(3) 55.4(1) 59.0(2)

2.21 and 2.36b 2.49 and 2.65b 2.65 and 2.83b 2.56 2.34 2.82 2.81

lp(O) → p(Bi)

13.84 32.71 54.26 41.68

87.51 33.98 72.47

9.20 23.84 44.79 31.90

92.70 37.57 78.62

LUMO

HOMO

−1.004 −1.399 −4.601 −3.982 −5.780 −1.181 −1.565 −4.868 −4.159 −6.215

−6.317 −6.622 −9.430 −9.084 −9.727 −6.404 −6.713 −9.447 −9.071 −9.804

a

Calculated at the B3PW91 level with the cc-pVTZ basis set for hydrogen, carbon, nitrogen, oxygen, fluorine, phosphorus, and sulfur atoms and Def2-TZVPP for the bismuth atom.

energies Edel (see the SI) corresponding to lp(N) → p(Bi) interactions in 1a−4a were calculated. The lp(N) → p(Bi) donation increases when the trans ligand becomes a weak donor, as is evident from 1a−3a. On the other hand, the lp(N) → p(Bi) donation decreases upon going from 3a to 4a, because OPEt3 is a better donor than THF. An understanding of the frontier MOs of the cationic intermediate A (Figure 3) helps to explain the

X = Cl (1a and 1b), OTf (2a and 2b), OC4H8 (3a), and OPEt3. 1a−3a are diastereomeric mixtures.4e

in the related bismuth compounds in the literature.4 The bite angle made by the Me2NCH2C6H4 ligand around bismuth is 89.6(2)°. Replacement of the chloride in 1a by a relatively weakly coordinating triflate anion (OTf−) leads to a shortening of the Bi−N distance in 2a. Compound 3a is a cationic bismuth(III) compound featuring a neutral oxygen donor ligand, THF, bound to the bismuth center trans to the NMe2 group. The Bi−N distance is further reduced in 3a compared to 2a (Table 1). NMR spectroscopic investigations were performed to explore the extent of electron donation from the NMe2 group. The trend in the chemical shifts of the protons in the NMe2 group in the 1H NMR spectra of 1a−3a recorded in CD2Cl2 indicates that the deshielding effect increases from the neutral to the cationic bismuth complexes, which, in turn, point out that the cationic bismuth is more Lewis acidic (Table 1). 3a is stable in THF and CH2Cl2 for several days at ambient temperature and inert conditions. The Gutmann−Beckett method is a traditional experimental method to estimate Lewis acidity.10 While the method has been successful in scaling the Lewis acidity of trivalent boron compounds,11 its applicability to heavier p-block Lewis acids is limited.12 This method was used to estimate the Lewis acidity of cation A. 3a was treated with 1 equiv of OPEt3 to obtain 4a. The 31 P NMR spectrum of 4a recorded in CD2Cl2 exhibits a single sharp peak at 66 ppm corresponding to the coordinated OPEt3.

Figure 3. Plot of the LUMOs (isovalue = 0.03) along with the optimized geometries of the cationic reactive intermediates A and B. The eigenvalues (eV) are given in parentheses.

orientation of the incoming nucleophile. The lowest unoccupied molecular orbital (LUMO) of cation A is a predominantly Bi−N σ* MO with the expected large contribution from the bismuth atom due to the electronegativity difference (Figure 3). This explains the preference for the incoming ligand to be trans to the Bi−N bond, as seen in 1a−4a. To increase the Lewis acidity at bismuth, an obvious strategy is to decrease the extent of donation of the lone pair from the nitrogen atom of the chelating agent. This can be achieved by decreasing the bite angle C−Bi−N. While the idea of controlling the molecular properties using variation of the bite angle is 9392


Communication

Inorganic Chemistry

the bismuth center. Replacement of the chloride in 1b by a triflate group reduces the Bi−N distance in 2b by 9% (Table 1 and see the SI for experimental details). Our attempts to prepare the computationally predicted 3b were not successful. When 1b was treated with 1 equiv of AgPF6 in THF at −30 °C, instantaneous precipitation of silver chloride was observed. Upon filtration warming to ambient temperature, the viscosity of the solvent increased, indicative of THF polymerization in the presence of a highly Lewis acidic bismuth species, cation B.15 To trap the reactive intermediate cation B, 1b was treated with 1 equiv each of OPEt3 and AgPF6 in THF at −35 °C. The triethylphosphine oxide adduct 4b was obtained and characterized by NMR spectroscopy and elemental analysis. A chemical shift of 72 ppm was observed in the 31P NMR spectrum of 4b for the coordinated OPEt3, and an acceptor number of 68.5 (see the SI for calculation of the acceptor number) was obtained. This value is very close to that observed in B(C6H3-2,6-F2)3,16 B(C6F5)((CH2)2Binaph),17 and [Sb(C6F5)4]+.12c The acceptor number (68.5), and, hence, the Lewis acidity of cation B, is appreciably higher than that of cation A (55). This observation underlines the importance of the ligand bite angle in tuning the Lewis acidity in organobismuth cations. We are exploring the applicability of cation B in Lewis acid mediated organic transformations. In summary, we have quantitatively investigated the Lewis acidity in two organobismuth cations. A decrease in the chelate ring size in cationic bismuth complexes leads to a notable increase in the Lewis acidity at bismuth, demonstrating that the bite angle is as important a ligand parameter in main-group chemistry as in transition-metal chemistry.

prevalent in transition-metal chemistry, this is not very common in main-group chemistry. A possibility is to replace the Me2NCH2C6H4 ligand with the 2-(dimethylamino)phenyl (Me2NC6H4) ligand, which will lead to a four-membered metallacycle with a smaller bite angle in place of a five-membered one. We investigated the electronic structures of 1b−4b [structurally similar to those of 1a−4a, except (Me2NCH2C6H4) was replaced by (Me2NC6H4)] and observed that the extent of lp(N) → p(Bi) donation decreases upon going from fivemembered ring structures (1a−4a) to constrained fourmembered ring structures (1b−4b; Table 2). This also increases the Bi−N distances in each of them (1b−4b). The bite angles made by the Me2NC6H4 ligand in 1b−4b are significantly smaller than those found with the Me2NCH2C6H4 ligand in 1a−4a. The effect of the constrained ring is directly seen in the reactive intermediate cation B (inset in Scheme 2) in comparison to Scheme 2. Synthesis and Reactivity of 1b

cation A (Table 1). The Bi−N interaction becomes weak, the Bi−N bonding MO goes up, and the corresponding Bi−N σ* MO (LUMO) comes down, making cation B a better Lewis acid (Figure 3 and Table 2). The energies for the formation of 1a−4a from cation A are calculated to be lower in energy than the corresponding values for 1b−4b from cation B (see the SI). This indicates that cation B with a constrained four-membered chelating ring binds with the incoming ligands more strongly than cation A with a five-membered chelating ring. Following computational analysis, [(Me2NC6H4)(mesityl)BiCl] (1b) was synthesized from [(mesityl)BiCl2] and [Me2NC6H4Li] (Scheme 2). 1b is the first bismuth complex bearing Me2NC6H4 ligand that chelates to bismuth as expected (Figure 4). The solid-state structure of 1b showed that the

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01243. Experimental details, characterization and crystallographic data, and computational methods and details (PDF) Accession Codes

CCDC 1537551−1537556 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Authors

Figure 4. Solid-state structures of 1b and 2b. Hydrogen atoms in the structures are omitted for clarity.

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

constrained four-membered ring in 1b led to a significantly smaller bite angle C1−Bi1−N1 [55.36(9)°], as compared to 1a [89.6(2)°]. Consequently, the Bi−N distance in 1b is longer by 8% than that in 1a (Table 1), indicating that access of the nitrogen atom to the bismuth center is restricted because of the smaller ring size in the former case. Accordingly, the Bi−Cl distance is shorter in 1b [2.560(2) Å] than in 1a [2.636(2) Å]. These observations reveal that the electronic environment at the coordination site trans to the NMe2 group can be tuned by controlling the accessibility of the nitrogen atom to coordinate to

Eluvathingal D. Jemmis: 0000-0001-8235-3413 Ajay Venugopal: 0000-0001-5875-9448 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank SERB, Govt. of India for generous funding (SB/FT/ CS-007/2012 to A.V. and J. C. Bose Fellowship to E.D.J.). 9393


Communication

Inorganic Chemistry

■

3,5-di-tert-butyl-4-hydroxybenzoic acid via the oxyarylcarboxy dianion, (O2CC6H2tBu2O)2−. Dalton Trans. 2014, 43, 3052−3054. (d) Kindra, D. R.; Casely, I. J.; Fieser, M. E.; Ziller, J. W.; Furche, F.; Evans, W. J. Insertion of CO2 and COS into Bi−C Bonds: Reactivity of a Bismuth NCN Pincer Complex of an Oxyaryl Dianionic Ligand, [2,6(Me2NCH2)2C6H3]Bi(C6H2tBu2O). J. Am. Chem. Soc. 2013, 135, 7777−7787. (e) Casely, I. J.; Ziller, J. W.; Fang, M.; Furche, F.; Evans, W. J. Facile Bismuth-Oxygen Bond Cleavage, C-H Activation, and Formation of a Monodentate Carbon-Bound Oxyaryl Dianion, (C6H2tBu2-3,5-O-4)2‑. J. Am. Chem. Soc. 2011, 133, 5244−5247. (f) Casely, I. J.; Ziller, J. W.; Mincher, B. J.; Evans, W. J. Bismuth Coordination Chemistry with Allyl, Alkoxide, Aryloxide, and Tetraphenylborate Ligands and the {[2,6-(Me2NCH2)2C6H3]2Bi}+ Cation. Inorg. Chem. 2011, 50, 1513−1520. (g) Soran, A. P.; Silvestru, C.; Breunig, H. J.; Balázs, G.; Green, J. C. Organobismuth(III) Dihalides with T-Shaped Geometry Stabilized by Intramolecular N→Bi Interactions and Related Diorganobismuth(III) Halides. Organometallics 2007, 26, 1196−1203. (7) (a) Qiu, R.; Yin, S.; Song, X.; Meng, Z.; Qiu, Y.; Tan, N.; Xu, X.; Luo, S.; Dai, F.-R.; Au, C.-T.; Wong, W.-Y. Effect of butterfly-shaped sulfur-bridged ligand and counter anions on the catalytic activity and diastereoselectivity of organobismuth complexes. Dalton Trans. 2011, 40, 9482−9489. (b) Qiu, R.; Yin, S.; Zhang, X.; Xia, J.; Xu, X.; Luo, S. Synthesis and structure of an air-stable cationic organobismuth complex and its use as a highly efficient catalyst for the direct diastereoselective Mannich reaction in water. Chem. Commun. 2009, 4759−4761. (c) Dostál, L.; Novák, P.; Jambor, R.; Růzǐ čka, A.; Císařová, I.; Jirásko, R.; Holeček, J. Synthesis and Structural Study of Organoantimony(III) and Organobismuth(III) Triflates and Cations Containing O,C,OPincer Type Ligands. Organometallics 2007, 26, 2911−2917. (8) (a) Dengel, H.; Lichtenberg, C. Cationic Bismuth Amides: Accessibility, Structure, and Reactivity. Chem. - Eur. J. 2016, 22, 18465− 18475. (b) Schwamm, R. J.; Day, B. M.; Coles, M. P.; Fitchett, C. M. Low-Coordinate Bismuth Cations. Inorg. Chem. 2014, 53, 3778−3787. (c) Lehmann, M.; Schulz, A.; Villinger, A. Cyclic Distiba- and Dibismadiazenium Cations. Angew. Chem., Int. Ed. 2012, 51, 8087− 8091. (d) Baumann, W.; Schulz, A.; Villinger, A. A Blue Homoleptic Bismuth-Nitrogen Cation. Angew. Chem. 2008, 120, 9672−9675. (e) Veith, M.; Bertsch, B.; Huch, V. Z. Zur Element-StickstoffDoppelbindung in Kationen cyclischer Bis(amino)-phospha-, -arsa-, -stiba- und − bismutane. Z. Anorg. Allg. Chem. 1988, 559, 73−88. (9) Selected references: (a) Ligand Design in Metal Chemistry: Reactivity and Catalysis; Stradiotto, M., Lundgren, R. J., Eds.; John Wiley and Sons, Ltd.: London, 2016. (b) Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Wide Bite Angle Diphosphines: Xantphos Ligands in Transition Metal Complexes and Catalysis. Acc. Chem. Res. 2001, 34, 895−904. (c) Dierkes, P.; van Leeuwen, P. W. N. M. J. Chem. Soc., The bite angle makes the difference: a practical ligand parameter for diphosphine ligands. J. Chem. Soc., Dalton Trans. 1999, 1519−1530. (d) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H. The bite angle makes the catalyst. Pure Appl. Chem. 1999, 71, 1443−1452. (10) (a) Beckett, M. A.; Strickland, G. C.; Holland, J. R.; Sukumar Varma, K. A convenient n.m.r. method for the measurement of Lewis acidity at boron centres: correlation of reaction rates of Lewis acid initiated epoxide polymerizations with Lewis acidity. Polymer 1996, 37, 4629−4631. (b) Mayer, U.; Gutmann, V.; Gerger, W. The acceptor number  A quantitative empirical parameter for the electrophilic properties of solvents. Monatsh. Chem. 1975, 106, 1235−1257. (11) (a) Körte, L. A.; Schwabedissen, J.; Soffner, M.; Blomeyer, S.; Reuter, C. G.; Vishnevskiy, Y. V.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Tris(perfluorotolyl)boraneA Boron Lewis Superacid. Angew. Chem., Int. Ed. 2017, 56, 8578. (b) Coffie, S.; Hogg, J. M.; Cailler, L.; Ferrer-Ugalde, A.; Murphy, R. W.; Holbrey, J. D.; Coleman, F.; Swadźba-Kwaśny, M. Lewis Superacidic Ionic Liquids with Tricoordinate Borenium Cations. Angew. Chem., Int. Ed. 2015, 54, 14970−14973. (c) Sivaev, I. B.; Bregadze, V. I. Lewis acidity of boron compounds. Coord. Chem. Rev. 2014, 270−271, 75−88. (12) The Gutmann−Beckett method has been used successfully in some cases for example (a) Tsao, F. A.; Waked, A. E.; Cao, L.; Hofmann,

REFERENCES

(1) (a) Atkins, P. W.; Overton, T.; Rourke, J. P.; Weller, M.; Armstrong, F. A. Shriver & Atkins’ Inorganic Chemistry; Oxford University Press, 2010. (b) Wiberg, N.; Holleman, A. F.; Wiberg, E. Inorganic Chemistry; Academic Press, 2001. (c) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry, 6th ed.; Wiley-Interscience: New York, 1999. (2) (a) Chitnis, S. S.; Vos, K. A.; Burford, N.; McDonald, R.; Ferguson, M. J. Distinction between coordination and phosphine ligand oxidation: interactions of di- and triphosphines with Pn3+ (Pn = P, As, Sb, Bi). Chem. Commun. 2016, 52, 685−688. (b) Chitnis, S. S.; Robertson, A. P. M; Burford, N.; Patrick, B. O.; McDonald, R.; Ferguson, M. J. Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and EV cations. Chem. Sci. 2015, 6, 6545− 6555. (c) Robertson, A. P. M.; Burford, N.; Gray, P. A. Interpnictogen cations: exploring new vistas in coordination chemistry. Angew. Chem., Int. Ed. 2014, 53, 6050−6069. (d) Chitnis, S. S.; Burford, N.; Decken, A.; Ferguson, M. J. Coordination Complexes of Bismuth Triflates with Tetrahydrofuran and Diphosphine Ligands. Inorg. Chem. 2013, 52, 7242−7248. (3) (a) Lichtenberg, C.; Pan, F.; Spaniol, T. P.; Englert, U.; Okuda, J. The bis(allyl)bismuth cation: a reagent for direct allyl transfer by Lewis acid activation and controlled radical polymerization. Angew. Chem., Int. Ed. 2012, 51, 13011−13015. (b) Kilah, N. L.; Petrie, S.; Stranger, R.; Wielandt, J. W.; Willis, A. C.; Wild, S. B. Triphenylphosphine-Stabilized Diphenyl-Arsenium, -Stibenium, and -Bismuthenium Salts. Organometallics 2007, 26, 6106−6113. (c) Carmalt, C. J.; Farrugia, L. J.; Norman, N. C. Cationic, arylbismuth(III) complexes of the form [BiR2L2]+ and [BiRL4]2+ where L is a neutral two-electron donor ligand. J. Chem. Soc., Dalton Trans. 1996, 443−454. (d) Carmalt, C. J.; Norman, N. C.; Orpen, A. G.; Stratford, S. E. A cationic, four-coordinate, tenelectron bismuth(III) complex: Synthesis and structure of [BiPh2(HMPA)2][BF4] (HMPA = hexamethylphosphoramide). J. Organomet. Chem. 1993, 460, C22−C24. (4) (a) Raţ, C. I.; Silvestru, C.; Breunig, H. Hypervalent organoantimony and -bismuth compounds with pendant arm ligands. Coord. Chem. Rev. 2013, 257, 818−879. (b) Murafuji, T.; Satoh, K.; Sugihara, Y.; Azuma, N. The First X-ray Structure Determination of an Optically Pure Bismuthane. Organometallics 1998, 17, 1711−1715. (c) Carmalt, C. J.; Cowley, A. H.; Culp, R. D.; Jones, R. A.; Kamepalli, S.; Norman, N. C. Synthesis and Structures of Intramolecularly Base-Coordinated Group 15 Aryl Halides. Inorg. Chem. 1997, 36, 2770−2776. (d) Carmalt, C. J.; Walsh, D.; Cowley, A. H.; Norman, N. C. Cationic Complexes of Antimony(III) and Bismuth(III) Stabilized by Intra- or Intermolecular Coordination. Organometallics 1997, 16, 3597−3600. (e) Suzuki, H.; Murafuji, T.; Matano, Y.; Azuma, N. Chiral chlorobismuthines stabilized by the intramolecular coordination of an N,N-dimethylamino group: Xray structure analysis, asymmetric induction at the bismuth centre, and dynamic behaviour in solution. J. Chem. Soc., Perkin Trans. 1 1993, 1, 2969−2973. (5) (a) Yin, S. F.; Maruyama, J.; Yamashita, T.; Shimada, S. Efficient Fixation of Carbon Dioxide by Hypervalent Organobismuth Oxide, Hydroxide, and Alkoxide. Angew. Chem., Int. Ed. 2008, 47, 6590−6593. (b) Bao, M.; Hayashi, T.; Shimada, S. Cationic Organobismuth Complex with 5,6,7,12-Tetrahydrodibenz[c,f][1,5]azabismocine Framework and Its Coordination Complexes with Neutral Molecules. Organometallics 2007, 26, 1816−1822. (c) Shimada, S.; Yamazaki, O.; Tanaka, T.; Suzuki, Y.; Tanaka, M. Synthesis and structure of 5,6,7,12tetrahydrodibenz[c,f][1,5]azabismocines. J. Organomet. Chem. 2004, 689, 3012−3023. (6) (a) Vránová, I.; Erben, M.; Jambor, R.; Růzǐ čka, A.; Jirásko, R.; Dostál , L. Z. Synthesis and Structure of (N,)C,N-chelated Organoantimony(III) and Bismuth(III) Cations and Isolation of Their Adducts with Ag[CB11H12. Z. Anorg. Allg. Chem. 2016, 642, 1212−1217. (b) Kindra, D. R.; Casely, I. J.; Ziller, J. W.; Evans, W. J. Nitric Oxide Insertion Reactivity with the Bismuth−Carbon Bond: Formation of the Oximate Anion, [ON = (C6H2tB2uO)]−, from the Oxyaryl Dianion, (C6H2tBu2O)2−. Chem. - Eur. J. 2014, 20, 15242− 15247. (c) Kindra, D. R.; Evans, W. J. Bismuth-based cyclic synthesis of 9394


Communication

Inorganic Chemistry J.; Liu, L.; Grimme, S.; Stephan, D. W. S(VI) Lewis acids: fluorosulfoxonium cations. Chem. Commun. 2016, 52, 12418−12421. (b) Großekappenberg, H.; Reißmann, M.; Schmidtmann, M.; Müller, T. Quantitative Assessment of the Lewis Acidity of Silylium Ions. Organometallics 2015, 34, 4952−4958. (c) Pan, B.; Gabbaï, F. P. [Sb(C6F5)4][B(C6F5)4]: An Air Stable, Lewis Acidic Stibonium Salt That Activates Strong Element-Fluorine Bonds. J. Am. Chem. Soc. 2014, 136, 9564−9567. (d) Caputo, C. B.; Hounjet, L. J.; Dobrovetsky, R.; Stephan, D. W. Lewis Acidity of Organofluorophosphonium Salts: Hydrodefluorination by a Saturated Acceptor. Science 2013, 341, 1374− 1377. In few cases, oxygenation of organophosphonium Lewis acids has been observed upon treatment with Et3PO. (e) Holthausen, M. H.; Hiranandani, R. R.; Stephan, D. W. Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines. Chem. Sci. 2015, 6, 2016−2021. (f) Holthausen, M. H.; Mehta, M.; Stephan, D. W. The Highly Lewis Acidic Dicationic Phosphonium Salt: [(SIMes)PFPh2][B(C6F5)4]2. Angew. Chem., Int. Ed. 2014, 53, 6538−6541. (13) Britovsek, G. J. P.; Ugolotti, J.; White, A. J. P. From B(C6F5)3 to B(OC6F5)3: Synthesis of (C6F5)2BOC6F5 and C6F5B(OC6F5)2 and Their Relative Lewis Acidity. Organometallics 2005, 24, 1685−1691. (14) The Gutmann−Beckett method was used to evaluate the Lewis acidity of the tricationic [(Bipy)2Bi][OTf]3. When [(Bipy)2Bi][OTf]3 was treated with 1 equiv of Et3PO, a peak at 66.9 ppm was observed in the 31P NMR spectrum. However, the resulting product has not been isolated and characterized.2b (15) THF polymerization has been observed by Burford and coworkers during their efforts to isolate cationic bismuth salts.2b,d (16) Greb, L.; Daniliuc, C.-G.; Bergander, K.; Paradies, J. FunctionalGroup Tolerance in Frustrated Lewis Pairs: Hydrogenation of Nitroolefins and Acrylates. Angew. Chem., Int. Ed. 2013, 52, 5876−5879. (17) Mewald, M.; Fröhlich, R.; Oestreich, M. An Axially Chiral, Electron-Deficient Borane: Synthesis, Coordination Chemistry, Lewis Acidity, and Reactivity. Chem. - Eur. J. 2011, 17, 9406−9414.

9395


Consequence of Ligand Bite Angle on Bismuth Lewis Acidity

Recommend Documents