Formation of Allenes by 1,4-Addition of Intermolecular Phosphane/Borane Frustrated Lewis Pairs to a Conjugated Enyne

Abstract

The t-Bu₃P/B(C₆F₅)₃ frustrated Lewis pair (6a) undergoes competing acetylene deprotonation (to give the phosphonium–alkenylborate salt 8) and 1,4-P/B FLP addition to the conjugated enyne 2-methylbutenyne to yield the zwitterionic allene derivative 9a. The less basic (o-tolyl)₃P/B(C₆F₅)₃ system (6b) avoids the acetylene deprotonation pathway. The zwitterionic allene derivative 9b formed by 1,4-P/B FLP addition to the enyne is again a prominent reaction product; here competing 1,2-addition is observed to give the olefinic product 10. The allene derivatives 9a and 9b and their competing products 8 and 10 were characterized by X-ray diffraction.

Frustrated Lewis pairs (FLPs) evade strong mutual adduct formation by steric bulk[1] (sometimes by electronic means).[2] The pair of, for example, coexistent phosphane and borane in solution can then undergo cooperative reactions with a variety of small molecules. Activation of ­dihydrogen by heterolytic dissociation to give a phosphonium–hydrido borate pair is a most prominent case.[3] [4] It has provided the basis for the development of a variety of metal-free catalytic hydrogenation processes.[5] FLPs were shown to react with CO₂,[6] SO₂,[7] nitrogen oxides,[8] CO,[9] isonitriles,[10] etc. Many FLPs add to alkenes or alkynes, with 1-alkynes sometimes competing deprotonation and formation of phosphonium–alkynyl borate salts was observed.[11]

We have previously shown that the reactive intramolecular ethylene-bridged FLP 1 often undergoes 1,4-addition reactions to unsaturated substrates. This was observed when 1 was treated with conjugated ynones,[12] but also upon exposure of 1 to a small series of conjugated diynes and to a conjugated enyne (Scheme [1]). In the latter case some competing acetylene deprotonation was also observed.[13] We had begun to investigate some analogous reactions of intermolecular FLPs. We had initially found that the t-Bu₃P/B(C₆F₅)₃ pair (6a) undergoes trans-1,4-addition to 4,6-decadiyne (to yield 7); with the less bulky 2,4-hexadiyne we observed the formation of a mixture of 1,2- (predominant) and 1,4-addition.[14]

We have now treated the intermolecular FLP t-Bu₃P/ B(C₆F₅)₃ (6a) and (o-tolyl)₃P/B(C₆F₅)₃ (6b) with the conjugated enyne 2-methylbutenyne and found some closely related behavior.

The t-Bu₃P/B(C₆F₅)₃ FLP (6a) was treated with a stoichiometric amount of 2-methylbutenyne in dichloromethane solution at ambient temperature (24 h). The NMR spectra of the crude mixture showed the formation of the deprotonation product 8 and the product of 1,4-FLP addition to the conjugated π-system to give the zwitterionic allene derivative 9a in a ca. 1:1 ratio (Scheme [2]). We noted that the mixture contained more than the expected quantity of the t-Bu₃PH⁺ cation without any additional detectable anion. We assume that some hydrolysis had taken place. The products 8 (33%) and 9a (21%) could be separated by column chromatography and isolated. Both products were characterized by spectroscopy and by X-ray diffraction.

The salt 8 shows a ¹¹B NMR resonance at δ = –21.0. It features ¹⁹F NMR signals at δ = –132.6 (o), –164.0 (p), and –167.4 (m of C₆F₅) with a small δ¹⁹F _m,p  = 3.4 ppm chemical shift difference that is typical for a RB(C₆F₅)₃ ^– borate situation. The anion of 8 shows ¹H NMR signals of the terminal C(CH₃)=CH₂ group at δ = 4.97/4.92, and 1.82 (CH₃) ppm. It shows ¹³C NMR signals of the conjugated enyne moiety at δ = 95.4 [≡C; δ(B¹³C≡) not observed], 130.8 and 116.8 (=CH₂) ppm.

The X-ray crystal structure analysis of compound 8 (Figure [1]) has confirmed that a proton had been abstracted by the phosphane and the enynyl group had become attached to the (C₆F₅)₃B unit. The central B1 to C3 framework is linear [B1–C1: 1.582(5) Å, C1–C2: 1.201(4) Å, C2–C3: 1.442(5) Å, angles B1–C1–C2: 174.9(3)°, C1–C2–C3: 175.7(4)°]. It features the –C(CH₃)=CH₂ moiety at its end [C3–C4: 1.351(5) Å, angle C2–C3–C4: 121.2(3)°].

The allene product 9a shows a typical =C= ¹³C NMR resonance[15] at δ = 207.1 ppm with a small ³ J _PC coupling constant of 6.7 Hz. The adjacent sp² carbon atoms of the allene unit give rise to ¹³C NMR signals at δ = 98.5 (=CHB) and 80.0 ppm, respectively, with corresponding ¹H NMR signals at δ = 5.94 (=CHB), 3.13/2.26 {CH₂[P]} and 1.66 (CH₃) ppm. The zwitterionic compound 9a shows heteronuclear magnetic resonance signals at δ = 49.2 (³¹P) and –15.6 (¹¹B) ppm, respectively.

The X-ray crystal structure analysis of 9a features the central allene unit that was formed by 1,4-addition of the P/B FLP to the conjugated enyne [C2–C3: 1.315(7) Å, C3–C4: 1.295(6) Å, angle C2–C3–C4: 174.9(5)°]. It shows the typical perpendicular arrangements of the substituent vectors at the allene termini [B1–C4: 1.628(7) Å, dihedral angle B1–C4···C2–C1: –85.4°] (Figure [2]). The P1–C1 bond length in compound 9a amounts to 1.818(6) Å.[16]

We then treated the 2-methylbutenyne reagent with the (o-tol)₃P/B(C₆F₅)₃ FLP. The bulky triarylphosphane is less basic than the previously used t-Bu₃P Lewis base. Therefore, we did not observe the formation of the acetylene deprotonation product any more. After 24 hours at room temperature the reaction was complete and we monitored the formation of a ca. 3:4 mixture of the 1,2- and 1,4-P/B FLP addition products 10 and 9b (Scheme [3]). The products were separated by chromatography and crystallization and isolated in 20% (10) and 33% (9b) yield, respectively. Both compounds were characterized by spectroscopy and by X-ray diffraction.

The 1,2-addition product 10 shows a ¹¹B NMR signal at δ = –16.2 ppm and a ³¹P NMR signal at δ = 23.4 ppm. The ¹⁹F NMR Δδ¹⁹F _m,p  = 4.4 ppm chemical shift difference is in the typical RB(C₆F₅)₃ ^– borate range. The ¹³C NMR spectrum (233 K) of compound 10 shows resonances of the central [B]–CH=C[P] unit at δ = 181.2 {[B]–CH= ¹H NMR signal at δ = 8.27 ppm} and 124.8 (¹ J _PC = 64.7 Hz) ppm, respectively. The adjacent –C(CH₃)=CH₂ substituent shows ¹H NMR signals at δ = 4.97/4.58 (with corresponding ¹³C NMR signals at δ = 139.3 and 122.6 ppm) and 0.88 (CH₃) ppm, respectively.

The X-ray crystal structure analysis has confirmed the trans-1,2-P/B FLP addition to the C≡C triple bond of the enyne to generate compound 10. It shows typical bonding features of the central E-configured trisubstituted C=C double bond [B1–C2: 1.646(3) Å, C2–C1: 1.344(3) Å, C1–P1: 1.828(2) Å, bond angles B1–C2–C1: 132.5(2)°, C2–C1–P1: 118.5(2)°]. Both, the boron atom B1 and the phosphorus atom P1 show pseudotetrahedral coordination geometries (Figure [3]). Carbon atom C1 bears the remaining –C(CH₃)=CH₂ substituent [C1–C3: 1.499(3) Å, C3–C4: 1.349(3) Å, C3–C5: 1.481(3) Å, angle C1–C3–C4: 118.1(2)°].

The X-ray crystal structure analysis of the 1,4-P/B FLP addition product 9b shows the typical allene core [C4–C3: 1.294(5) Å, C3–C2: 1.322(5) Å, angle C2–C3–C4: 175.9(3)°] to which the B(C₆F₅)₃ group [B1–C4: 1.641(6) Å] is bonded at the terminal carbon atom and the methyl substituent and the CH₂P(o-tolyl)₃ ⁺ group is found attached at the other allene terminus [C2–C5: 1.516(5) Å, C2–C1: 1.521(5) Å, C1–P1 1.820(3) Å, angle C1–C2–C5: 113.9(3)°, dihedral angle B1–C4···C2–C1: 98.1°]. Both, the boron atom B1 and the phosphorus atom P1 show pseudotetrahedral coordination geometries in the zwitterionic borate–phosphonium product 9b (Figure [4]).

In solution compound 9b shows ¹¹B and ³¹P NMR resonances at δ = –15.7 and 25.4 ppm, respectively. The compound shows a typical central =C= allene C(sp) ¹³C NMR signal at δ = 206.7 ppm (with ³ J _PC = 9.2 Hz coupling constant). The ¹³C NMR signal of the adjacent allene [B]–C(sp²)(H)= unit appears at δ = 99.2 ppm as a typical 1:1:1:1 intensity quartet (¹ J _BC = ca. 50 Hz). The corresponding allenic ¹H NMR resonance occurs at δ = 5.55 ppm. The ¹³C NMR signal of the remaining allene terminus was located at δ = 80.7 ppm.[17]

The intramolecular P/B FLP 1 has a pronounced tendency of undergoing 1,4-addition reactions to conjugated π systems. The cyclic allene 5 is actually the major product of the reaction of 1 with 2-methylbutenyne, although a minor product 4 was obtained originating from acetylene deprotonation. The intermolecular P/B FLPs 6a and 6b react similarly albeit with a slightly lower selectivity. In both cases there is a pronounced tendency of 1,4-P/B addition to the conjugated enyne 2-methylbutenyne. In both cases the corresponding allene (9a,b) is a prominent product. Not unexpectedly, the rather basic t-Bu₃P Lewis base gives rise to a competing formation of the phosphonium–alkynylborate salt by the deprotonation route. This type of product seems to be absent in the reaction involving the less basic (o-tolyl)₃P Lewis base. It seems that the bulkiness of the Lewis base is a determining feature of the 1,2- vs. 1,4-addition reaction. The less basic but also sterically less bulky (o-tolyl)₃P/(B(C₆F₅)₃ system avoids the deprotonation reaction but allows for the formation of some 1,2-P/B FLP addition product.[14]

Acknowledgment

Financial support from the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

• References and Notes

• 1 Stephan DW, Erker G. Angew. Chem. Int. Ed. 2010; 49: 46
  CrossrefSearch in Google Scholar
• 2a Stute A, Kehr G, Daniliuc CG, Fröhlich R, Erker G. Dalton Trans. 2013; 42: 4487
  CrossrefSearch in Google Scholar
• 2b Rosorius C, Kehr G, Fröhlich R, Grimme S, Erker G. Organometallics 2011; 30: 4211
  CrossrefSearch in Google Scholar
• 3a Welch GC, San Juan RR, Masuda JD, Stephan DW. Science 2006; 314: 1124
  CrossrefPubMedSearch in Google Scholar
• 3b Geier SJ, Gilbert TM, Stephan DW. J. Am. Chem. Soc. 2008; 130: 12632
  CrossrefSearch in Google Scholar
• 4a Spies P, Erker G, Kehr G, Bergander K, Fröhlich R, Grimme S, Stephan DW. Chem. Commun. 2007; 5072
• 4b Spies P, Schwendemann S, Lange S, Kehr G, Fröhlich R, Erker G. Angew. Chem. Int. Ed. 2008; 47: 7543
  CrossrefPubMedSearch in Google Scholar
• 5 Stephan DW, Erker G. Topics Curr. Chem. 2013; 332: 85
  Search in Google Scholar
• 6a Mömming CM, Otten E, Kehr G, Fröhlich R, Grimme S, Stephan DW, Erker G. Angew. Chem. Int. Ed. 2009; 48: 6643
  CrossrefSearch in Google Scholar
• 6b Peuser I, Neu RC, Zhao X, Ulrich M, Schirmer B, Tannert JA, Kehr G, Fröhlich R, Grimme S, Erker G, Stephan DW. Chem. Eur. J. 2011; 17: 9640
  CrossrefSearch in Google Scholar
• 6c Zhao X, Stephan DW. Chem. Commun. 2011; 47: 1833
  CrossrefSearch in Google Scholar
• 6d Takeuchi K, Stephan DW. Chem. Commun. 2012; 48: 11304
  CrossrefSearch in Google Scholar
• 7a Sajid M, Klose A, Birkmann B, Liang L, Schirmer B, Wiegand T, Eckert H, Lough AJ, Fröhlich R, Daniliuc CG, Grimme S, Stephan DW, Kehr G, Erker G. Chem. Sci. 2013; 4: 213
  CrossrefSearch in Google Scholar
• 7b Sajid M, Kehr G, Wiegand T, Eckert H, Schwickert C, Pöttgen R, Cardenas AJ. P, Warren TH, Fröhlich R, Daniliuc CG, Erker G. J. Am. Chem. Soc. 2013; 135: 8882
  CrossrefSearch in Google Scholar
• 8a Otten E, Neu RC, Stephan DW. J. Am. Chem. Soc. 2009; 131: 9918
  CrossrefSearch in Google Scholar
• 8b Cardenas AJ. P, Culotta BJ, Warren TH, Grimme S, Stute A, Fröhlich R, Kehr G, Erker G. Angew. Chem. Int. Ed. 2011; 50: 7567
  CrossrefSearch in Google Scholar
• 8c Sajid M, Stute A, Cardenas AJ. P, Culotta BJ, Hepperle JA. M, Warren TH, Schirmer B, Grimme S, Studer A, Daniliuc CG, Fröhlich R, Petersen JL, Kehr G, Erker G. J. Am. Chem. Soc. 2012; 134: 10156
  CrossrefSearch in Google Scholar
• 8d Menard G, Hatnean JA, Cowley HJ, Lough AJ, Rawson JM, Stephan DW. J. Am. Chem. Soc. 2013; 135: 6446
  CrossrefSearch in Google Scholar
• 8e Pereira JC. M, Sajid M, Kehr G, Wright AM, Schirmer B, Qu Z.-W, Grimme S, Erker G, Ford PC. J. Am. Chem. Soc. 2014; 136: 513
  CrossrefSearch in Google Scholar
• 9a Dobrovetsky R, Stephan DW. J. Am. Chem. Soc. 2013; 135: 4974
  CrossrefSearch in Google Scholar
• 9b Sajid M, Elmer L.-M, Rosorius C, Daniliuc CG, Grimme S, Kehr G, Erker G. Angew. Chem. Int. Ed. 2013; 52: 2243
  CrossrefSearch in Google Scholar
• 9c Sajid M, Lawzer A, Dong W, Rosorius C, Sander W, Schirmer B, Grimme S, Daniliuc CG, Kehr G, Erker G. J. Am. Chem. Soc. 2013; 135: 18567
  CrossrefSearch in Google Scholar
• 9d Sajid M, Kehr G, Daniliuc CG, Erker G. Angew. Chem. Int. Ed. 2014; 53: 1118
  CrossrefSearch in Google Scholar
• 10 Ekkert O, Miera GG, Wiegand T, Eckert H, Schirmer B, Petersen JL, Daniliuc CG, Fröhlich R, Grimme S, Kehr G, Erker G. Chem. Sci. 2013; 4: 2657
  CrossrefSearch in Google Scholar
• 11a Ullrich M, Seto KS.-H, Lough AJ, Stephan DW. Chem. Commun. 2009; 2335
• 11b Dureen MA, Stephan DW. J. Am. Chem. Soc. 2009; 131: 8396
  CrossrefSearch in Google Scholar
• 11c Mömming CM, Frömel S, Kehr G, Fröhlich R, Grimme S, Erker G. J. Am. Chem. Soc. 2009; 131: 12280
  CrossrefSearch in Google Scholar
• 11d Chen C, Eweiner F, Wibbeling B, Fröhlich R, Senda S, Ohki Y, Tatsumi K, Grimme S, Kehr G, Erker G. Chem. Asian J. 2010; 5: 2199
  CrossrefPubMedSearch in Google Scholar
• 11e Dureen MA, Brown CC, Stephan DW. Organometallics 2010; 29: 6594
  CrossrefSearch in Google Scholar
• 11f Voss T, Chen C, Kehr G, Nauha E, Erker G, Stephan DW. Chem. Eur. J. 2010; 16: 3005
  CrossrefSearch in Google Scholar
• 11g Voss T, Sortais J.-B, Fröhlich R, Kehr G, Erker G. Organometallics 2011; 30: 584
  CrossrefSearch in Google Scholar
• 11h Zhao X, Stephan DW. Chem. Sci. 2012; 3: 2123
  CrossrefSearch in Google Scholar
• 12 Xu B, Kehr G, Fröhlich R, Wibbeling B, Schirmer B, Grimme S, Erker G. Angew. Chem. Int. Ed. 2011; 50: 7183
  CrossrefSearch in Google Scholar
• 13 Mömming CM, Kehr G, Wibbeling B, Fröhlich R, Schirmer B, Grimme S, Erker G. Angew. Chem. Int. Ed. 2010; 49: 2414
  CrossrefSearch in Google Scholar
• 14 Feldhaus P, Schirmer B, Wibbeling B, Daniliuc CG, Fröhlich R, Grimme S, Kehr G, Erker G. Dalton Trans. 2012; 41: 9135
  CrossrefSearch in Google Scholar
• 15 Kalinowski H.-O, Berger S, Braun S In ¹³C NMR-Spektroskopie . Thieme; Stuttgart: 1984
  Search in Google Scholar
• 16 Compounds 8 and 9a Tri-tert-butylphosphane (102 mg, 0.50 mmol) in CH₂Cl₂ (3 mL) was added to a solution of tris(pentafluorophenyl)-borane (256 mg, 0.50 mmol) in CH₂Cl₂ (10 mL). After addition of 2-methyl-1,3-butenyne (33 mg, 47.5 μL, 0.50 mmol) the reaction mixture was stirred for 24 h at r.t. Subsequently, all volatiles were removed under reduced pressure and the obtained residue was dried in vacuo to give a ca. 1:1 mixture of compounds 8 and 9a (302 mg). The both products were separated by column chromatography (silica gel; eluent: n-pentane–CH₂Cl₂, 3:5). Drying of the respective fraction in vacuo gave compound 8 (131.9 mg, 33%) and compound 9a (81.6 mg, 21%). Crystals suitable for the X-ray crystal structure analysis for both compound 8 and compound 9a were obtained from a solution of the respective compound in CH₂Cl₂ layered by n-pentane at –40 °C. Analytical Data of Compound 8 Anal. Calcd for C₃₅H₃₃BF₁₅P: C, 53.87; H, 4.26. Found: C, 53.04; H, 4.22. Mp 141 °C (DSC). ¹H NMR (600 MHz, 299 K, CD₂Cl₂): δ = 5.05 (d, ¹ J _PH = 428.6 Hz, 1 H, PH), 4.97 (dq, ² J _PH = 2.7 Hz, ⁴ J _HH = 1.0 Hz, 1 H, =CH₂ ^Z), 4.92 (dq, ² J _PH = 2.7 Hz, ⁴ J _HH = 1.5 Hz, 1 H, =CH₂ ^E), 1.82 (dd, ⁴ J _HH = 1.5 Hz, ⁴ J _HH = 1.0 Hz, 3 H, CH₃), 1.63 (d, ³ J _PH = 15.9 Hz, 27 H, t-Bu). ¹³C{¹H} NMR (151 MHz, 299 K, CD₂Cl₂): δ = 148.6 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 138.5 (dm, ¹ J _FC = ca. 250 Hz, C₆F₅), 136.9 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 130.8 (=C), 124.8 (br, ipso-C₆F₅), 116.8 (=CH₂), 95.4 (br, ≡C), 38.1 (d, ¹ J _PC = 26.8 Hz, t-Bu), 30.4 (t-Bu), 24.4 (CH₃); resonance for ≡CB was not observed. ³¹P NMR (243 MHz, 299 K, CD₂Cl₂): δ = 60.4 (dm, ¹ J _PH = 428.6 Hz). ¹¹B{¹H} NMR (192 MHz, 299 K, CD₂Cl₂): δ = –21.0 (ν_1/2 = ca. 25 Hz). ¹⁹F NMR (564 MHz, 299 K, CD₂Cl₂): δ = –132.6 (m, 2 F, o-C₆F₅), –164.0 (t, ³ J _FF = 20.3 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.4]. Analytical Data of Compound 9a HRMS: m/z calcd for C₃₅H₃₃BF₁₅PNa⁺: 803.2072; found: 803.2031. Decomposition: 247 °C (DSC). ¹H NMR (600 MHz, 298 K, CD₂Cl₂): δ = 5.94 (br m, 1 H, =CH), 3.13 (ddd, ² J _PH = 16.2 Hz, ² J _HH = 14.8 Hz, ⁵ J _HH = 3.1 Hz, 1 H, CH₂), 2.26 (ddd, ² J _PH = 15.5 Hz, ² J _HH = 14.8 Hz, ⁵ J _HH = 1.3 Hz, 1 H, CH₂), 1.66 (br d, ⁴ J _PH = 3.1 Hz, 3 H, CH₃), 1.57 (d, ³ J _PH = 13.9 Hz, 27 H, t-Bu). ¹³C{¹H} NMR (151 MHz, 298 K, CD₂Cl₂): δ = 207.1 (d, ³ J _PC = 6.7 Hz, =C=), 148.4 (dm, ¹ J _FC = ca. 238 Hz, C₆F₅), 138.4 (dm, ¹ J _FC = ca. 231 Hz, C₆F₅), 136.8 (dm, ¹ J _FC = ca. 233 Hz, C₆F₅), 125.1 (br, i-C₆F₅), 98.5 [br q (1:1:1:1), ¹ J _BC = ca. 50 Hz, =CH], 80.0 (br m, =C), 39.7 (d, ¹ J _PC = 27.4 Hz, t-Bu), 30.4 (t-Bu), 23.5 (d, ¹ J _PC = 31.4 Hz, CH₂), 23.1 (d, ³ J _PC = 3.2 Hz, CH₃). ³¹P{¹H} NMR (243 MHz, 298 K, CD₂Cl₂): δ = 49.2 (ν_1/2 = ca. 10 Hz). ¹¹B{¹H} NMR (192 MHz, 298 K, CD₂Cl₂): δ = –15.6 (ν_1/2 = ca. 15 Hz). ¹⁹F NMR (564 MHz, 298 K, CD₂Cl₂): δ = –132.2 (m, 2 F o-C₆F₅), –163.6 (t, ³ J _FF = 20.4 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.8].
• 17 Compounds 10 and 9b A solution of tri-ortho-tolylphosphane (152 mg, 0.50 mmol) in CD₂Cl₂ (4 mL) was added to a solution of tris(pentafluoro-phenyl)borane (256 mg, 0.50 mmol) in CD₂Cl₂ (4 mL) at r.t. Then the reaction mixture was added to 2-methyl-1,3-butenyne (33 mg, 47.5 μL, 0.50 mmol), and the resulting mixture was stirred for 10 min. After one day, an aliquot of the reaction mixture was investigated by NMR experiments at low temperature. A mixture of compound 10 (1,2-addition), compound 9b (1,4-addition) and tri-ortho-tolylphosphane. [10/9b/phosphane = ca. 28:37:35 (¹H NMR at 248 K)] was characterized. Then the volume of the reaction mixture was reduced to one half followed by separation of the compounds by column chromatography (silica gel; eluent CH₂Cl₂–n-pentane = 2:3). The first fraction contained compound 10 admixed with tri-ortho-tolylphosphane, which subsequently was purified by crystallization from a solution of compound 10 in CH₂Cl₂ layered by n-pentane to give compound 10 (89 mg, 20%). The second fraction contained compound 9b (148.9 mg, 33%). Crystals suitable for the X-ray crystal structure analysis for both compounds 10 and 9b, respectively, were obtained from a solution of the respective compound in CH₂Cl₂ layered with n-pentane at –40 °C. Analytical Data of Compound 10 Anal. Calcd for C₄₄H₂₇BF₁₅P·CH₂Cl₂: C, 55.87; H, 3.02. Found: C, 55.50; H, 2.55. Mp 98 °C (DSC). ¹H NMR (500 MHz, 233 K, CD₂Cl₂): δ = 8.27 (br d, ³ J _PH = 37.0 Hz, 1 H, =CH), 7.86 (o), 7.63 (p), 7.51 (m), 7.33 (m′) (4 × m, 4 × 1 H, o-tol^a), 7.65 (p), 7.60 (o), 7.43 (m), 7.36 (m′) (4 × m, 4 × 1 H, o-tol^b), 7.65 (p), 7.52 (m′), 7.27 (m), 7.27 (o) (4 × m, 4 × 1 H, o-tol^c), 4.97 (s, 1 H, =CH₂ ^Z), 4.58 (s, 1 H, =CH₂ ^E), 2.63 (s, 3 H, CH₃ of o-tol^c), 1.63 (s, 6 H, CH₃ of o-tol^a,b), 0.88 (s, 3 H, CH₃). ¹³C{¹H} NMR (126 MHz, 233 K, CD₂Cl₂): δ = 181.2 (br, =CH), 147.7 (dm, ¹ J _FC = ca. 242 Hz, C₆F₅), 145.1 (d, ² J _PC = 8.0 Hz, ortho′), 134.8 (d, ² J _PC = 11.4 Hz, ortho), 134.7 (d, ⁴ J _PC = 2.1 Hz, para), 133.3 (d, ³ J _PC = 10.2 Hz, meta′), 126.8 (d, ³ J _PC = 12.2 Hz, meta), 116.0 (d, ¹ J _PC = 80.7 Hz, ipso) (of o-tol^c), 144.1 (d, ² J _PC = 7.7 Hz, ortho′), 134.5 (d, ² J _PC = 12.0 Hz, ortho), 134.2 (d, ⁴ J _PC = 2.6 Hz, para), 133.4 (d, ³ J _PC = 11.4 Hz, meta′), 126.9 (d, ³ J _PC = 12.8 Hz, meta), 118.1 (d, ¹ J _PC = 83.2 Hz, ipso) (of o-tol^o), 143.3 (d, ² J _PC = 6.8 Hz, ortho′), 136.2 (d, ² J _PC = 13.5 Hz, ortho), 134.1 (d, ⁴ J _PC = 2.4 Hz, para), 132.9 (d, ³ J _PC = 10.3 Hz, meta′), 126.9 (d, ³ J _PC = 12.8 Hz, meta), 120.7 (d, ¹ J _PC = 80.6 Hz, ipso) (of o-tol^a), 139.3 (d, ² J _PC = 14.6 Hz, =C), 138.1 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 136.3 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 124.0 (br, i-C₆F₅), 124.8 (d, ¹ J _PC = 64.7 Hz, =CP), 122.6 (d, ³ J _PC = 10.9 Hz, =CH₂), 23.1 (br, CH₃ of o-tol^c), 22.9 (CH₃), 22.7 (d, ³ J _PC = 1.8 Hz, CH₃ of o-tol^b), 22.5 (d, ³ J _PC = 3.7 Hz, CH₃ of o-tol^a). ³¹P{¹H} NMR (202 MHz, 233 K, CD₂Cl₂): δ = 23.4 (ν_1/2 = ca. 60 Hz). ¹¹B{¹H} NMR (160 MHz, 233 K, CD₂Cl₂): δ = –16.2 (ν_1/2 = ca. 60 Hz). ¹⁹F NMR (282 MHz, 295 K, CD₂Cl₂): δ = –131.6 (m, 2 F, o-C₆F₅), –162.2 (m, 1 F, p-C₆F₅), –166.6 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 4.4]. Analytical Data of Compound 9b HRMS: m/z calcd for C₄₄H₂₇BF₁₅PNa⁺: 905.1604; found: 905.1602. Mp 110 °C (DSC). ¹H NMR (500 MHz, 298 K, CD₂Cl₂): δ = 7.67 (p), 7.65 (o), 7.45 (m′), 7.37 (m) (4 × m, 4 × 3 H, o-tol), 5.55 (br m, 1 H, =CH), 4.12, 3.24 (2 × m, 2 × 1 H, CH₂), 2.15 (s, 9 H, CH₃ of o-tol), 1.27 (m, 3 H, CH₃). ¹³C{¹H} NMR (126 MHz, 298 K, CD₂Cl₂): δ = 206.7 (d, ³ J _PC = 9.2 Hz, =C=), 148.4 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 143.7 (d, ² J _PC = 8.6 Hz, o′ of o-tol), 138.4 (dm, ¹ J _FC = ca. 245 Hz, C₆F₅), 136.8 (dm, ¹ J _FC = ca. 250 Hz, C₆F₅), 135.9 (d, ² J _PC = 11.7 Hz, o of o-tol), 135.3 (d, ⁴ J _PC = 2.9 Hz, p of o-tol), 133.9 (d, ³ J _PC = 11.0 Hz, m′ of o-tol), 127.6 (d, ³ J _PC = 12.7 Hz, m of o-tol), 125.1 (br, i-C₆F₅), 117.5 (d, ¹ J _PC = 80.6 Hz, i of o-tol), 99.2 [br q (1:1:1:1), ¹ J _BC = ca. 51 Hz, =CH], 80.7 (br m, =C), 31.3 (d, ¹ J _PC = 47.8 Hz, CH₂), 23.1 (d, ³ J _PC = 3.8 Hz, CH₃ of o-tol), 20.4 (d, ³ J _PC = 4.6 Hz, CH₃). ³¹P{¹H} NMR (202 MHz, 298 K, CD₂Cl₂): δ = 25.4 (ν_1/2 = ca. 10 Hz). ¹¹B{¹H} NMR (160 MHz, 298 K, CD₂Cl₂): δ = –15.7 (ν_1/2 = ca. 20 Hz). ¹⁹F NMR (470 MHz, 298 K, CD₂Cl₂): δ = –132.2 (m, 2 F o-C₆F₅), –163.6 (t, ³ J _FF = 20.3 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.7].

• References and Notes

• 1 Stephan DW, Erker G. Angew. Chem. Int. Ed. 2010; 49: 46
  CrossrefSearch in Google Scholar
• 2a Stute A, Kehr G, Daniliuc CG, Fröhlich R, Erker G. Dalton Trans. 2013; 42: 4487
  CrossrefSearch in Google Scholar
• 2b Rosorius C, Kehr G, Fröhlich R, Grimme S, Erker G. Organometallics 2011; 30: 4211
  CrossrefSearch in Google Scholar
• 3a Welch GC, San Juan RR, Masuda JD, Stephan DW. Science 2006; 314: 1124
  CrossrefPubMedSearch in Google Scholar
• 3b Geier SJ, Gilbert TM, Stephan DW. J. Am. Chem. Soc. 2008; 130: 12632
  CrossrefSearch in Google Scholar
• 4a Spies P, Erker G, Kehr G, Bergander K, Fröhlich R, Grimme S, Stephan DW. Chem. Commun. 2007; 5072
• 4b Spies P, Schwendemann S, Lange S, Kehr G, Fröhlich R, Erker G. Angew. Chem. Int. Ed. 2008; 47: 7543
  CrossrefPubMedSearch in Google Scholar
• 5 Stephan DW, Erker G. Topics Curr. Chem. 2013; 332: 85
  Search in Google Scholar
• 6a Mömming CM, Otten E, Kehr G, Fröhlich R, Grimme S, Stephan DW, Erker G. Angew. Chem. Int. Ed. 2009; 48: 6643
  CrossrefSearch in Google Scholar
• 6b Peuser I, Neu RC, Zhao X, Ulrich M, Schirmer B, Tannert JA, Kehr G, Fröhlich R, Grimme S, Erker G, Stephan DW. Chem. Eur. J. 2011; 17: 9640
  CrossrefSearch in Google Scholar
• 6c Zhao X, Stephan DW. Chem. Commun. 2011; 47: 1833
  CrossrefSearch in Google Scholar
• 6d Takeuchi K, Stephan DW. Chem. Commun. 2012; 48: 11304
  CrossrefSearch in Google Scholar
• 7a Sajid M, Klose A, Birkmann B, Liang L, Schirmer B, Wiegand T, Eckert H, Lough AJ, Fröhlich R, Daniliuc CG, Grimme S, Stephan DW, Kehr G, Erker G. Chem. Sci. 2013; 4: 213
  CrossrefSearch in Google Scholar
• 7b Sajid M, Kehr G, Wiegand T, Eckert H, Schwickert C, Pöttgen R, Cardenas AJ. P, Warren TH, Fröhlich R, Daniliuc CG, Erker G. J. Am. Chem. Soc. 2013; 135: 8882
  CrossrefSearch in Google Scholar
• 8a Otten E, Neu RC, Stephan DW. J. Am. Chem. Soc. 2009; 131: 9918
  CrossrefSearch in Google Scholar
• 8b Cardenas AJ. P, Culotta BJ, Warren TH, Grimme S, Stute A, Fröhlich R, Kehr G, Erker G. Angew. Chem. Int. Ed. 2011; 50: 7567
  CrossrefSearch in Google Scholar
• 8c Sajid M, Stute A, Cardenas AJ. P, Culotta BJ, Hepperle JA. M, Warren TH, Schirmer B, Grimme S, Studer A, Daniliuc CG, Fröhlich R, Petersen JL, Kehr G, Erker G. J. Am. Chem. Soc. 2012; 134: 10156
  CrossrefSearch in Google Scholar
• 8d Menard G, Hatnean JA, Cowley HJ, Lough AJ, Rawson JM, Stephan DW. J. Am. Chem. Soc. 2013; 135: 6446
  CrossrefSearch in Google Scholar
• 8e Pereira JC. M, Sajid M, Kehr G, Wright AM, Schirmer B, Qu Z.-W, Grimme S, Erker G, Ford PC. J. Am. Chem. Soc. 2014; 136: 513
  CrossrefSearch in Google Scholar
• 9a Dobrovetsky R, Stephan DW. J. Am. Chem. Soc. 2013; 135: 4974
  CrossrefSearch in Google Scholar
• 9b Sajid M, Elmer L.-M, Rosorius C, Daniliuc CG, Grimme S, Kehr G, Erker G. Angew. Chem. Int. Ed. 2013; 52: 2243
  CrossrefSearch in Google Scholar
• 9c Sajid M, Lawzer A, Dong W, Rosorius C, Sander W, Schirmer B, Grimme S, Daniliuc CG, Kehr G, Erker G. J. Am. Chem. Soc. 2013; 135: 18567
  CrossrefSearch in Google Scholar
• 9d Sajid M, Kehr G, Daniliuc CG, Erker G. Angew. Chem. Int. Ed. 2014; 53: 1118
  CrossrefSearch in Google Scholar
• 10 Ekkert O, Miera GG, Wiegand T, Eckert H, Schirmer B, Petersen JL, Daniliuc CG, Fröhlich R, Grimme S, Kehr G, Erker G. Chem. Sci. 2013; 4: 2657
  CrossrefSearch in Google Scholar
• 11a Ullrich M, Seto KS.-H, Lough AJ, Stephan DW. Chem. Commun. 2009; 2335
• 11b Dureen MA, Stephan DW. J. Am. Chem. Soc. 2009; 131: 8396
  CrossrefSearch in Google Scholar
• 11c Mömming CM, Frömel S, Kehr G, Fröhlich R, Grimme S, Erker G. J. Am. Chem. Soc. 2009; 131: 12280
  CrossrefSearch in Google Scholar
• 11d Chen C, Eweiner F, Wibbeling B, Fröhlich R, Senda S, Ohki Y, Tatsumi K, Grimme S, Kehr G, Erker G. Chem. Asian J. 2010; 5: 2199
  CrossrefPubMedSearch in Google Scholar
• 11e Dureen MA, Brown CC, Stephan DW. Organometallics 2010; 29: 6594
  CrossrefSearch in Google Scholar
• 11f Voss T, Chen C, Kehr G, Nauha E, Erker G, Stephan DW. Chem. Eur. J. 2010; 16: 3005
  CrossrefSearch in Google Scholar
• 11g Voss T, Sortais J.-B, Fröhlich R, Kehr G, Erker G. Organometallics 2011; 30: 584
  CrossrefSearch in Google Scholar
• 11h Zhao X, Stephan DW. Chem. Sci. 2012; 3: 2123
  CrossrefSearch in Google Scholar
• 12 Xu B, Kehr G, Fröhlich R, Wibbeling B, Schirmer B, Grimme S, Erker G. Angew. Chem. Int. Ed. 2011; 50: 7183
  CrossrefSearch in Google Scholar
• 13 Mömming CM, Kehr G, Wibbeling B, Fröhlich R, Schirmer B, Grimme S, Erker G. Angew. Chem. Int. Ed. 2010; 49: 2414
  CrossrefSearch in Google Scholar
• 14 Feldhaus P, Schirmer B, Wibbeling B, Daniliuc CG, Fröhlich R, Grimme S, Kehr G, Erker G. Dalton Trans. 2012; 41: 9135
  CrossrefSearch in Google Scholar
• 15 Kalinowski H.-O, Berger S, Braun S In ¹³C NMR-Spektroskopie . Thieme; Stuttgart: 1984
  Search in Google Scholar
• 16 Compounds 8 and 9a Tri-tert-butylphosphane (102 mg, 0.50 mmol) in CH₂Cl₂ (3 mL) was added to a solution of tris(pentafluorophenyl)-borane (256 mg, 0.50 mmol) in CH₂Cl₂ (10 mL). After addition of 2-methyl-1,3-butenyne (33 mg, 47.5 μL, 0.50 mmol) the reaction mixture was stirred for 24 h at r.t. Subsequently, all volatiles were removed under reduced pressure and the obtained residue was dried in vacuo to give a ca. 1:1 mixture of compounds 8 and 9a (302 mg). The both products were separated by column chromatography (silica gel; eluent: n-pentane–CH₂Cl₂, 3:5). Drying of the respective fraction in vacuo gave compound 8 (131.9 mg, 33%) and compound 9a (81.6 mg, 21%). Crystals suitable for the X-ray crystal structure analysis for both compound 8 and compound 9a were obtained from a solution of the respective compound in CH₂Cl₂ layered by n-pentane at –40 °C. Analytical Data of Compound 8 Anal. Calcd for C₃₅H₃₃BF₁₅P: C, 53.87; H, 4.26. Found: C, 53.04; H, 4.22. Mp 141 °C (DSC). ¹H NMR (600 MHz, 299 K, CD₂Cl₂): δ = 5.05 (d, ¹ J _PH = 428.6 Hz, 1 H, PH), 4.97 (dq, ² J _PH = 2.7 Hz, ⁴ J _HH = 1.0 Hz, 1 H, =CH₂ ^Z), 4.92 (dq, ² J _PH = 2.7 Hz, ⁴ J _HH = 1.5 Hz, 1 H, =CH₂ ^E), 1.82 (dd, ⁴ J _HH = 1.5 Hz, ⁴ J _HH = 1.0 Hz, 3 H, CH₃), 1.63 (d, ³ J _PH = 15.9 Hz, 27 H, t-Bu). ¹³C{¹H} NMR (151 MHz, 299 K, CD₂Cl₂): δ = 148.6 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 138.5 (dm, ¹ J _FC = ca. 250 Hz, C₆F₅), 136.9 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 130.8 (=C), 124.8 (br, ipso-C₆F₅), 116.8 (=CH₂), 95.4 (br, ≡C), 38.1 (d, ¹ J _PC = 26.8 Hz, t-Bu), 30.4 (t-Bu), 24.4 (CH₃); resonance for ≡CB was not observed. ³¹P NMR (243 MHz, 299 K, CD₂Cl₂): δ = 60.4 (dm, ¹ J _PH = 428.6 Hz). ¹¹B{¹H} NMR (192 MHz, 299 K, CD₂Cl₂): δ = –21.0 (ν_1/2 = ca. 25 Hz). ¹⁹F NMR (564 MHz, 299 K, CD₂Cl₂): δ = –132.6 (m, 2 F, o-C₆F₅), –164.0 (t, ³ J _FF = 20.3 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.4]. Analytical Data of Compound 9a HRMS: m/z calcd for C₃₅H₃₃BF₁₅PNa⁺: 803.2072; found: 803.2031. Decomposition: 247 °C (DSC). ¹H NMR (600 MHz, 298 K, CD₂Cl₂): δ = 5.94 (br m, 1 H, =CH), 3.13 (ddd, ² J _PH = 16.2 Hz, ² J _HH = 14.8 Hz, ⁵ J _HH = 3.1 Hz, 1 H, CH₂), 2.26 (ddd, ² J _PH = 15.5 Hz, ² J _HH = 14.8 Hz, ⁵ J _HH = 1.3 Hz, 1 H, CH₂), 1.66 (br d, ⁴ J _PH = 3.1 Hz, 3 H, CH₃), 1.57 (d, ³ J _PH = 13.9 Hz, 27 H, t-Bu). ¹³C{¹H} NMR (151 MHz, 298 K, CD₂Cl₂): δ = 207.1 (d, ³ J _PC = 6.7 Hz, =C=), 148.4 (dm, ¹ J _FC = ca. 238 Hz, C₆F₅), 138.4 (dm, ¹ J _FC = ca. 231 Hz, C₆F₅), 136.8 (dm, ¹ J _FC = ca. 233 Hz, C₆F₅), 125.1 (br, i-C₆F₅), 98.5 [br q (1:1:1:1), ¹ J _BC = ca. 50 Hz, =CH], 80.0 (br m, =C), 39.7 (d, ¹ J _PC = 27.4 Hz, t-Bu), 30.4 (t-Bu), 23.5 (d, ¹ J _PC = 31.4 Hz, CH₂), 23.1 (d, ³ J _PC = 3.2 Hz, CH₃). ³¹P{¹H} NMR (243 MHz, 298 K, CD₂Cl₂): δ = 49.2 (ν_1/2 = ca. 10 Hz). ¹¹B{¹H} NMR (192 MHz, 298 K, CD₂Cl₂): δ = –15.6 (ν_1/2 = ca. 15 Hz). ¹⁹F NMR (564 MHz, 298 K, CD₂Cl₂): δ = –132.2 (m, 2 F o-C₆F₅), –163.6 (t, ³ J _FF = 20.4 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.8].
• 17 Compounds 10 and 9b A solution of tri-ortho-tolylphosphane (152 mg, 0.50 mmol) in CD₂Cl₂ (4 mL) was added to a solution of tris(pentafluoro-phenyl)borane (256 mg, 0.50 mmol) in CD₂Cl₂ (4 mL) at r.t. Then the reaction mixture was added to 2-methyl-1,3-butenyne (33 mg, 47.5 μL, 0.50 mmol), and the resulting mixture was stirred for 10 min. After one day, an aliquot of the reaction mixture was investigated by NMR experiments at low temperature. A mixture of compound 10 (1,2-addition), compound 9b (1,4-addition) and tri-ortho-tolylphosphane. [10/9b/phosphane = ca. 28:37:35 (¹H NMR at 248 K)] was characterized. Then the volume of the reaction mixture was reduced to one half followed by separation of the compounds by column chromatography (silica gel; eluent CH₂Cl₂–n-pentane = 2:3). The first fraction contained compound 10 admixed with tri-ortho-tolylphosphane, which subsequently was purified by crystallization from a solution of compound 10 in CH₂Cl₂ layered by n-pentane to give compound 10 (89 mg, 20%). The second fraction contained compound 9b (148.9 mg, 33%). Crystals suitable for the X-ray crystal structure analysis for both compounds 10 and 9b, respectively, were obtained from a solution of the respective compound in CH₂Cl₂ layered with n-pentane at –40 °C. Analytical Data of Compound 10 Anal. Calcd for C₄₄H₂₇BF₁₅P·CH₂Cl₂: C, 55.87; H, 3.02. Found: C, 55.50; H, 2.55. Mp 98 °C (DSC). ¹H NMR (500 MHz, 233 K, CD₂Cl₂): δ = 8.27 (br d, ³ J _PH = 37.0 Hz, 1 H, =CH), 7.86 (o), 7.63 (p), 7.51 (m), 7.33 (m′) (4 × m, 4 × 1 H, o-tol^a), 7.65 (p), 7.60 (o), 7.43 (m), 7.36 (m′) (4 × m, 4 × 1 H, o-tol^b), 7.65 (p), 7.52 (m′), 7.27 (m), 7.27 (o) (4 × m, 4 × 1 H, o-tol^c), 4.97 (s, 1 H, =CH₂ ^Z), 4.58 (s, 1 H, =CH₂ ^E), 2.63 (s, 3 H, CH₃ of o-tol^c), 1.63 (s, 6 H, CH₃ of o-tol^a,b), 0.88 (s, 3 H, CH₃). ¹³C{¹H} NMR (126 MHz, 233 K, CD₂Cl₂): δ = 181.2 (br, =CH), 147.7 (dm, ¹ J _FC = ca. 242 Hz, C₆F₅), 145.1 (d, ² J _PC = 8.0 Hz, ortho′), 134.8 (d, ² J _PC = 11.4 Hz, ortho), 134.7 (d, ⁴ J _PC = 2.1 Hz, para), 133.3 (d, ³ J _PC = 10.2 Hz, meta′), 126.8 (d, ³ J _PC = 12.2 Hz, meta), 116.0 (d, ¹ J _PC = 80.7 Hz, ipso) (of o-tol^c), 144.1 (d, ² J _PC = 7.7 Hz, ortho′), 134.5 (d, ² J _PC = 12.0 Hz, ortho), 134.2 (d, ⁴ J _PC = 2.6 Hz, para), 133.4 (d, ³ J _PC = 11.4 Hz, meta′), 126.9 (d, ³ J _PC = 12.8 Hz, meta), 118.1 (d, ¹ J _PC = 83.2 Hz, ipso) (of o-tol^o), 143.3 (d, ² J _PC = 6.8 Hz, ortho′), 136.2 (d, ² J _PC = 13.5 Hz, ortho), 134.1 (d, ⁴ J _PC = 2.4 Hz, para), 132.9 (d, ³ J _PC = 10.3 Hz, meta′), 126.9 (d, ³ J _PC = 12.8 Hz, meta), 120.7 (d, ¹ J _PC = 80.6 Hz, ipso) (of o-tol^a), 139.3 (d, ² J _PC = 14.6 Hz, =C), 138.1 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 136.3 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 124.0 (br, i-C₆F₅), 124.8 (d, ¹ J _PC = 64.7 Hz, =CP), 122.6 (d, ³ J _PC = 10.9 Hz, =CH₂), 23.1 (br, CH₃ of o-tol^c), 22.9 (CH₃), 22.7 (d, ³ J _PC = 1.8 Hz, CH₃ of o-tol^b), 22.5 (d, ³ J _PC = 3.7 Hz, CH₃ of o-tol^a). ³¹P{¹H} NMR (202 MHz, 233 K, CD₂Cl₂): δ = 23.4 (ν_1/2 = ca. 60 Hz). ¹¹B{¹H} NMR (160 MHz, 233 K, CD₂Cl₂): δ = –16.2 (ν_1/2 = ca. 60 Hz). ¹⁹F NMR (282 MHz, 295 K, CD₂Cl₂): δ = –131.6 (m, 2 F, o-C₆F₅), –162.2 (m, 1 F, p-C₆F₅), –166.6 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 4.4]. Analytical Data of Compound 9b HRMS: m/z calcd for C₄₄H₂₇BF₁₅PNa⁺: 905.1604; found: 905.1602. Mp 110 °C (DSC). ¹H NMR (500 MHz, 298 K, CD₂Cl₂): δ = 7.67 (p), 7.65 (o), 7.45 (m′), 7.37 (m) (4 × m, 4 × 3 H, o-tol), 5.55 (br m, 1 H, =CH), 4.12, 3.24 (2 × m, 2 × 1 H, CH₂), 2.15 (s, 9 H, CH₃ of o-tol), 1.27 (m, 3 H, CH₃). ¹³C{¹H} NMR (126 MHz, 298 K, CD₂Cl₂): δ = 206.7 (d, ³ J _PC = 9.2 Hz, =C=), 148.4 (dm, ¹ J _FC = ca. 240 Hz, C₆F₅), 143.7 (d, ² J _PC = 8.6 Hz, o′ of o-tol), 138.4 (dm, ¹ J _FC = ca. 245 Hz, C₆F₅), 136.8 (dm, ¹ J _FC = ca. 250 Hz, C₆F₅), 135.9 (d, ² J _PC = 11.7 Hz, o of o-tol), 135.3 (d, ⁴ J _PC = 2.9 Hz, p of o-tol), 133.9 (d, ³ J _PC = 11.0 Hz, m′ of o-tol), 127.6 (d, ³ J _PC = 12.7 Hz, m of o-tol), 125.1 (br, i-C₆F₅), 117.5 (d, ¹ J _PC = 80.6 Hz, i of o-tol), 99.2 [br q (1:1:1:1), ¹ J _BC = ca. 51 Hz, =CH], 80.7 (br m, =C), 31.3 (d, ¹ J _PC = 47.8 Hz, CH₂), 23.1 (d, ³ J _PC = 3.8 Hz, CH₃ of o-tol), 20.4 (d, ³ J _PC = 4.6 Hz, CH₃). ³¹P{¹H} NMR (202 MHz, 298 K, CD₂Cl₂): δ = 25.4 (ν_1/2 = ca. 10 Hz). ¹¹B{¹H} NMR (160 MHz, 298 K, CD₂Cl₂): δ = –15.7 (ν_1/2 = ca. 20 Hz). ¹⁹F NMR (470 MHz, 298 K, CD₂Cl₂): δ = –132.2 (m, 2 F o-C₆F₅), –163.6 (t, ³ J _FF = 20.3 Hz, 1 F, p-C₆F₅), –167.4 (m, 2 F, m-C₆F₅), [Δδ¹⁹F _m,p  = 3.7].

• Supplementary Material