Activation of terminal alkynes by frustrated lewis pairs

Article abstract of DOI:10.1021/om9008636

The reactions of frustrated Lewis pairs (FLPs) derived from B(C ₆F₅)₃ and the bulky Lewis bases 2,2,6,6-tetramethylpiperidine (TMP), tri-tert-butylphosphine, and lutidine (Lut) with terminal alkynes (acetylene, phenylacetylene, 3-ethynylthiophene) were investigated. The FLPs TMP ... B(C₆F₅)₃, t-Bu₃P ...B(C₆F₅)₃ and Lut ... (C₆F₅)3 reacted with acetylene (HC=CH) to yield the apparently thermodynamically more stable Eisomers [TMPH][(C ₆F₅)₂B-C(C₆F₅)=C(H) B(C₆F₅)₃] (1-E), t-Bu₃PC(H)-C(H) B(C₆F₅)₃ (2-E; 90%), and [t-Bu ₃PH][C₆F₅)₂B-C(C₆F ₅)=C(H)B(C₆F₅)₃] (3-E; 10%), and LutC(H)=C(H)B(C₆F₅)₃ (4-E), respectively. A mechanistic pathway for the reaction of acetylene is suggested to start with the formation of a weak B(C6F5)3/acetylene adduct followed by a deprotonation of this species with any mentioned Lewis bases (LB), yielding the acetylide salts [LBH][(C₆F₅)₃BC=CH]. Alternatively, nucleophilic addition of the LB to this adduct occurs to yield LBC(H)=C(H)B(C₆F₅)₃ compounds. Formation of 1 and 3-E is explained by the reactions of [LBH][B(C₆F ₅)₃C=CH] salts with a second equivalent of B(C ₆F₅)₃ to undergo electrophilic addition, forming the vinylidene adduct (C₆F₅)₃B ^-C⁺=C(H)B(C₆F₅)₃, which is subsequently stabilized by 1,2-migration of a C₆F₅ group to form [(C₆F₅)₂BC(C₆F ₅)=C(H)B(C₆F₅)₃]. The reaction between B(C₆F₅)₃ and phenylacetylene yielded a mixture of (Z)- and (E)-PhC(H)=C(C₆F₅)B(C ₆F₅)₂ (H-Z and 11-E), confirming that the reaction proceeds via an acetylene/vinylidene rearrangement and subsequent 1,2-shift of a C₆F₅ group to the carbenic center. The FLPs TMP ...B(C₆F₅)₃ and tBu ₃P... B(C₆F₅)₃ were converted with phenylacetylene or 3-ethynylthiophene to yield the acetylide products [TMPH][PhC=CB(C₆F₅)₃] (5), [TMPH][SC ₄H₃C=CB(C₆F₅)3] (6), [t-Bu ₃PH][PhC≡ CB(C₆F₅)₃] (7), and [t-Bu₃PH][SC₄H₃C≡CB(C₆F ₅)₃] (8), where TMP and t-Bu₃P acted as a base deprotonating the acetylenic proton. When the FLP Lut ... B(C ₆F₅)₃ was reacted with phenylacetylene or 3-ethynylthiophene, the deprotonated product [LutH][PhC=CB(C₆F ₅)₃] (9; 47%) and the 1,2-addition compound LutC(SC ₄H₃C)=C(H)B(C₆F₅)₃ (10; 55%) were obtained. Compounds 1-E, 2-E, 5, and 6 were characterized by X-ray diffraction studies.

Full text of DOI:10.1021/om9008636

Organometallics 2010, 29, 125–133 125
DOI: 10.1021/om9008636
Activation of Terminal Alkynes by Frustrated Lewis Pairs
Chunfang Jiang, Olivier Blacque, and Heinz Berke*
€
€
Anorganisch-chemisches Institut, Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich,
€
Switzerland
Received October 5, 2009
The reactions of frustrated Lewis pairs (FLPs) derived from B(C6F5)3 and the bulky Lewis bases
2,2,6,6-tetramethylpiperidine (TMP), tri-tert-butylphosphine, and lutidine (Lut) with terminal
alkynes (acetylene, phenylacetylene, 3-ethynylthiophene) were investigated. The FLPs TMP
B(C6F5)3, t-Bu3P B(C6F5)3 and Lut (C6F5)3 reacted with acetylene (HCtCH) to yield the
3 3 3
3 3 3
3 3 3
apparently thermodynamically more stable E isomers [TMPH][(C6F5)2B-C(C6F5)dC(H)B(C6F5)3]
(1-E), t-Bu3PC(H)dC(H)B(C6F5)3 (2-E; 90%), and [t-Bu3PH][(C6F5)2B-C(C6F5)dC(H)B(C6F5)3]
(3-E; 10%), and LutC(H)dC(H)B(C6F5)3 (4-E), respectively. A mechanistic pathway for the reaction
of acetylene is suggested to start with the formation of a weak B(C6F5)3/acetylene adduct followed by
a deprotonation of this species with any mentioned Lewis bases (LB), yielding the acetylide salts
[LBH][(C6F5)3BCtCH]. Alternatively, nucleophilic addition of the LB to this adduct occurs to yield
LBC(H)dC(H)B(C6F5)3 compounds. Formation of 1 and 3-E is explained by the reactions of
[LBH][B(C6F5)3CtCH] salts with a second equivalent of B(C6F5)3 to undergo electrophilic addition,
forming the vinylidene adduct (C6F5)3B-CþdC(H)B(C6F5)3, which is subsequently stabilized by
1,2-migration of a C6F5 group to form [(C6F5)2BC(C6F5)dC(H)B(C6F5)3]. The reaction between
B(C6F5)3 and phenylacetylene yielded a mixture of (Z)- and (E)-PhC(H)dC(C6F5)B(C6F5)2 (11-Z
and 11-E), confirming that the reaction proceeds via an acetylene/vinylidene rearrangement and
subsequent 1,2-shift of a C6F5 group to the carbenic center. The FLPs TMP B(C6F5)3 and
tBu3P B(C6F5)3 were converted with phenylacetylene or 3-ethynylthiophene to yield the acetylide
3 3 3
3 3 3
products [TMPH][PhCtCB(C6F5)3] (5), [TMPH][SC4H3CtCB(C6F5)3] (6), [t-Bu3PH][PhCt
CB(C6F5)3] (7), and [t-Bu3PH][SC4H3CtCB(C6F5)3] (8), where TMP and t-Bu3P acted as a base
deprotonating the acetylenic proton. When the FLP Lut B(C6F5)3 was reacted with phenylacety-
lene or 3-ethynylthiophene, the deprotonated product [LutH][PhCtCB(C6F5)3] (9; 47%) and the
1,2-addition compound LutC(SC4H3C)dC(H)B(C6F5)3 (10; 55%) were obtained. Compounds 1-E,
2-E, 5, and 6 were characterized by X-ray diffraction studies.
3 3 3
I. Introduction
of inducing novel transformations6,7 or was employed as a
stoichiometric reagent to generate new types of organo-
metallic and organic compounds.8-10 More recently, Stephan
et al. discovered that H2 can be activated reversibly with
heterolytic splitting by the “metal-free” internal Lewis pair
[(2,4,6-Me3C6H2)2PC6F4B(C6F5)2].11 On the basis of this
finding “metal-free” catalysts could be developed for the
hydrogenation of bulky imines with the Lewis acid
B(C6F5)3.12 This type of reactivity required the formation
of encounter complexes called frustrated Lewis pairs (FLPs),
consisting of sterically hindered Lewis bases in combina-
tion with sterically hindered Lewis acids and providing
“unquenched” reactivity and prevention of Lewis pair
The strong Lewis acid tris(pentafluorophenyl)boron is
capable of strongly polarizing hydrogen and preferential sp
and sp2 carbon centers, shaping them for further reactivities.
In the realm of metallocene Ziegler-type polymerization
catalysis metal-carbon bonds were seen to be heterolytically
cleaved by B(C6F5)3, leaving vacant sites behind. In addition,
electrophilic carbon centers could be opened up by B(C6F5)3
addition to coordinated or noncoordinated π systems.1-5
Moreover, the Lewis acid B(C6F5)3 was shown to be capable
*To whom correspondence should be addressed. E-mail: hberke@
aci.unizh.ch.
(1) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,
3623.
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€
(2) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Ed. Engl. 1994, 33, 1480.
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Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(3) Karl, J.; Erker, G.; Frohlich, R. J. Am. Chem. Soc. 1997, 119,
11165.
(9) Erker, G.; Ahlers, W.; Frohlich, R. J. Am. Chem. Soc. 1995, 117,
5853.
(10) Erker, G.; Schmuck, S.; Bendix, M. Angew. Chem., Int. Ed. Engl.
€
(4) Coates, G. W. Chem. Rev. 2000, 100, 1223.
1994, 33, 1955.
(5) Piers, W. E. Adv. Organomet. Chem. 2005, 52, 1.
(6) Ishihara, K; Hananki, N.; Yamamoto, H. Synlett 1993, 577.
(7) Nagata, T.; Toshihiro, T.; Yamada, T.; Imagawa, K.; Mukaiyama,
T. Bull. Chem. Soc. Jpn. 1994, 67, 2614.
(11) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124.
(12) Chase, P. A.; Welch, G. C.; Jurca, T.; Stephan, D. W. Angew.
Chem., Int. Ed. 2007, 46, 8050.
r
2009 American Chemical Society
Published on Web 12/11/2009
pubs.acs.org/Organometallics

126 Organometallics, Vol. 29, No. 1, 2010
Jiang et al.
Scheme 1
formation. FLPs possess great potential in small-molecule
chemistry.13,14 B(C6F5)3, because of its strong Lewis acidity
and its bulkiness, was demonstrated to be an appropriate
constituent of FLPs, and in combination with sterically hindered
phosphines, amines, and carbenes, it allowed facile cleavage of
H2.15-23 In addition to this H2 splitting capability, ionic products
were shown to serve as efficient catalysts for the hydrogenation
of imines, nitriles, and aziridines, as well as enamine and silyl enol
CdC double bonds.24-26 In addition, FLPs with B(C6F5)3 can
undergo 1,2-addition to olefins together with the Lewis base,16,17
open the THF ring in a bifunctional manner,19,27 and activate
B-H28 and N-H bonds,18 but only little has been reported
about the reaction of such FLPs toward alkynes.29,30 Stephan et
al. have shown that FLPs can promote 1,2-addition reactions
with substituted terminal alkynes to yield donor/acceptor sub-
stituted alkenes of type A or undergo C-H deprotonation to
establish ionic products of type B.
II. Results and Discussion
IIa. Reactions of Acetylene with FLPs of B(C6F5)3 and
TMP, t-Bu3P, and Lut. When dried HCtCH was introduced
into the toluene solution of FLP TMP B(C6F5)3, the
3 3 3
reaction mixture turned orange and an oil separated at the
bottom of the Young NMR tube after 30 min. Hexane was
added to the oily residue to prompt precipitation of the
ionic compound [TMPH][(C6F5)2BC(C6F5)dC(H)B(C6F5)3]
(1-E) (Scheme 1), which was isolated as an off-white solid in
56% yield. Multinuclear NMR in CDCl3 showed that 1-E
exhibits a broad 1H NMR resonance at 5.32 ppm attributable
to the NH proton, as well as a resonance at 9.32 ppm assigned to
the unique dCH proton. The 19F NMR spectrum showed three
sets of o-, p-, and m-C6F5 signals. One set of resonances at
δ -140.60, -159.18, and -165.08 ppm was attributed to the
carbon-bound C6F5 unit; the other two sets were detected at
δ -132.14, -151.65, and -162.76 ppm and at δ -131.69,
-162.31, and -167.05 ppm, in agreement with C6F5 residues
bound to three-coordinate (Δδp,m = 11.11) and four-coordinate
boron centers (Δδp,m = 4.74).31,32 In the 11B NMR spectrum
one signal at -15.19 ppm was assigned to the four-coordinate
boron moiety, but no signal was observed for the three-coordi-
nate boron center of the anion. The X-ray crystallographic study
confirmed the spectroscopically derived (E)-vinylidene structure
of the anion of 1-E33 1,2-connected to the two different boron
fragments -B(C6F5)3 and -B(C6F5)2 possessing a CdC dis-
In this article we describe reactions between various FLPs
and acetylene or substituted terminal alkynes.
(13) Stephan, D. W. Org. Biomol. Chem. 2008, 6, 1535.
(14) Stephan, D. W. Dalton Trans. 2009, 3129.
(15) Welch, G. C.; Stephan, D. W. J. Am. Chem. Soc. 2007, 129, 1880.
(16) McCahill, J. S. J.; Welch, G. C.; Stephan, D. W. Angew. Chem.,
Int. Ed. 2007, 46, 4968.
(17) Ullrich, M.; Seto, K. S.-H.; Lough, A. J.; Stephan, D. W. Chem.
Commun. 2009, 2335.
(18) Chase, P. A.; Stephan, D. W. Angew. Chem., Int. Ed. 2008, 47,
7433.
(19) Holschunmacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.;
˚
tance of 1.363(3) A (Figure 1). The electron-deficient boron
center is in a trigonal arrangement deviating somewhat from
planarity, in which the three B-C bond distances (B2-C2 =
1.532(3), B2-C27 = 1.589(3), B2-C33 = 1.577(3) A) are
longer than those in the pseudotetrahedral geometry of the
˚
B(C6F5)3 substituent (B1-C1 = 1.634(3), B1-C3 = 1.674(3),
˚
B1-C9 = 1.648(3), B1-C15 = 1.650(3) A). A very important
Tamm, M. Angew. Chem., Int. Ed. 2008, 47, 7428.
(20) Sumerin, V.; Schulz, F.; Nieger, M.; Leskela, M.; Repo, T.;
structural feature of 1-Eis the parallel arrangement of the unique
C-bound C6F5 group with one of the B-C6F5 groups, which is
presumed to further stabilize the compound via π stacking of the
aryl substituents. The ions are connected through multiple weak
€
Rieger, B. Angew. Chem., Int. Ed. 2008, 47, 6001.
(21) Huber, D. P.; Kehr, G.; Bergander, K.; Frohlich, R.; Erker, G.;
€
Tanino, S.; Ohki, Y.; Tatsumi, K. Organometallics 2008, 27, 5279.
(22) Ramos, A.; Lough, A. J.; Stephan, D. W. Chem. Commun. 2009,
1118.
(23) Geier, S. J.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 3476.
€
(24) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
C-H F hydrogen-bonding contacts.
A possible reaction mechanism for the formation of 1-E
would start from the presumably weak terminal alkyne/
3 3 3
Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543.
(25) Sumerin, V.; Schulz, F.; Atsumi, M.; Wang, C.; Nieger, M.;
€
€
Leskela, M.; Repo, T.; Pyykko, P.; Rieger, B. J. Am. Chem. Soc. 2008,
130, 14117.
€
(31) Vagedes, D.; Erker, G.; Frohlich, R. Angew. Chem., Int. Ed.
€
(26) Wang, H.; Frohlich, R.; Kehr, G.; Erker, G. Chem. Commun.
1999, 38, 3362.
(32) Spies, P.; Frohlich, R.; Kehr, G.; Erker, G.; Grimme, S. Chem.
€
2008, 5966.
(27) Welch, G. C.; Masuda, J. D.; Stephan, D. W. Inorg. Chem. 2006,
45, 478.
(28) Dureen, M. A.; Lough, A; Gilbert, T. M.; Stephan, D. W. Chem.
Commun. 2008, 4303.
(29) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131,
Eur. J. 2008, 14, 779.
(33) Crystal data for 1-E: C50H24B2F30N, Mr = 1230.32, triclinic, P1,
˚
˚
˚
a = 11.7619(4) A, b = 11.9617(4) A, c = 20.1408(7) A, R = 84.658(3)°,
3
˚
β = 75.635(3)°, γ = 60.642(4)°, V = 2391.16(17) A , Z = 2, Dc =
1.709 g cm-3, μ = 0.181 mm-1, λ = 0.710 73 A, T = 183(2) K, 30 688
˚
8396.
reflections collected, 9745 independent (Rint = 0.0567) and 5597 ob-
served reflections (I > 2σ(I)), 749 refined parameters, R1 = 0.0410,
wR2 = 0.08919. CCDC 748013.
€
€
€
(30) Momming, C. M.; Fromel, S.; Kehr, G.; Frohlich, R.; Grimme,
S.; Erker, G. J. Am. Chem. Soc. 2009, 131, 12280.

Article
Organometallics, Vol. 29, No. 1, 2010 127
constants (Figure 2). The 31P NMR signal for 2-E was found at
36.31 ppm and the 11B NMR resonance at -14.25 ppm. The 19
F
NMR spectrum of 2-E showed signals at δ -132.82 (o-C6F5),
-162.33 (p-C6F5), and -166.85 ppm (m-C6F5) originating from
the four-coordinate boron atom. A single-crystal X-ray analysis
confirms the formulation of 2-E as (E)-t-Bu3PC(H)dC(H)-
B(C6F5)3 (Figure 3).34 The distances of C1-C2 (1.333(3) A)
˚
˚
and C1-B (1.612(3) A) are quite comparable to those in 1-E.
˚
The C2-P bond length was found to be 1.787(2) A, which is
unexceptionally long.
It should be pointed out that TMP and t-Bu3P exhibit
similar basicities (pKa for t-Bu3P is 11.4 and for TMP is
11.07),35-37 so that the difference of the reaction paths of
FLPs TMP B(C6F5)3 and t-Bu3P B(C6F5)3 with acet-
3 3 3
3 3 3
ylene are thought to originate from the difference in sterics of
these Lewis bases. Enhanced steric congestion leads prefer-
entially to deprotonation; less steric hindrance provokes 1,2-
addition to the acetylenic moiety. In the case of compounds 2
and 3 there is apparently competition between deprotona-
tion and 1,2-addition. However, t-Bu3P may not be big
enough to prevent attacking one carbon atom of acetylene;
thus, the majority is 1,2-addition product, with only a small
amount of Csp-H deprotonated product in the mixture.
The reaction of lutidine (Lut) and B(C6F5)3 leads first of all
to a classical Lewis acid-base adduct, which was however
found to display FLP behavior in the activation of H2.23 In
toluene solution an equilibrium is established; in the 1H
NMR spectra at room temperature both the Lewis adduct
and the free Lewis acid and base are observed. When the
reaction mixture was purged with acetylene at 80 °C for
20 h, only the 1,2-addition product LutC(H)dC(H)B(C6F5)3
(4-E) could be isolated, which like 2-E could be envisaged to
form by nucleophilic addition of Lut to a weak σ or π
B(C6F5)3/acetylene adduct. 4-E was isolated in 34% yield.
4-E features 1H NMR resonances at 6.66 (d, J = 15 Hz) and
Figure 1. Molecular structure of 1-E with 30% probability
thermal ellipsoids. Hydrogen atoms, except for HN and the
˚
H
C1, are omitted for clarity. Selected bond lengths (A):
C1-H1 = 0.958(17), N1-H3 = 0.90(2), N1-H2 = 0.93(2),
N1-C39 = 1.537(3), N1-C43 = 1.540(3), B1-C1 = 1.634(3),
B1-C3 = 1.674(3), B1-C9 = 1.648(3), B1-C15 = 1.650(3),
B2-C2 = 1.532(3), B2-C27 = 1.589(3), B2-C33 = 1.577(3),
C1-C2=1.363(3). Selected bond angles (deg): C39-N1-C43=
121.27(15), C39-N1-H2=107.7(14), C43-N1-H2=103.5(13),
C39-N1-H3 = 110.2(13), C43-N1-H3 = 107.6(14), H2-
N1-H3=105.2(18), C1-B1-C9=109.92(15), C1-B1-C15=
108.24(16), C9-B1-C15=114.67(16), C1-B1-C3=106.86(15),
C9-B1-C3=104.96(15), C15-B1-C3=111.91(15), C2-B2-
C33=127.65(17), C2-B2-C27 = 119.33(17), C33-B2-C27 =
113.00(16).
6.18 ppm (d, J = 15 Hz) for Ha and Hb (Scheme 2). The 19
F
B(C6F5)3 adduct, which thus gets polarized with an increase
in the acidity of the acetylenic hydrogens. In the presence of
TMP the acidic C-H bond of the terminal alkyne was
deprotonated to form the σ-acetylide adduct [B(C6F5)3Ct
CH]-. This anion behaves as a nucleophile at the β-position,
adding B(C6F5)3 to afford the vinylidene adduct (C6F5)3-
B-CþdC(H)B(C6F5)3. This zwitterionic species possesses a
strongly electrophilic R-carbon center, triggering (similar to
a Wagner-Meerwein rearrangement) a 1,2-shift of a per-
fluorophenyl group to the more stable 1-E product. This per-
fluorophenyl group migration could also be found in the reaction
of B(C6F5)3 with phenylacetylene (vide infra, Scheme 5).
NMR signals are located at δ -133.11 (o-C6F5), -163.75
(p-C6F5), and -168.00 ppm (m-C6F5) and are quite similar to
those found for compound 4-E. This observation would
support the view that the less sterically hindered Lewis bases
favor the formation of 1,2-addition products in reactions of
their FLPs with acetylene.
The reaction of phenylacetylene (PhCtCH) or 3-ethy-
nylthiophene (SC4H3CtCH) with the TMP B(C6F5)3 or
t-Bu3P B(C6F5)3 FLPs proceeded exclusively along the
3 3 3
3 3 3
deprotonation pathway, forming the respective salts [TMPH]-
[PhCtCB(C6F5)3] (5), [TMPH][SC4H3CtCB(C6F5)3] (6),
[t-Bu3PH][PhCtCB(C6F5)3] (7), and [t-Bu3PH][SC4H3Ct
CB(C6F5)3] (8) (see Scheme 3).
The related reactions of the FLPs t-Bu3P B(C6F5)3 and
3 3 3
Lut B(C6F5)3 with acetylene were also investigated. Simi-
3 3 3
lar to the reaction to 1-E, after dried HCtCH was intro-
duced into the toluene solution of the t-Bu3P B(C6F5)3
(34) Crystal data for 2-E: C39H37BF15P, Mr = 832.47, monoclinic,
˚
3 3 3
˚
˚
P21/c, a = 12.3469(2) A, b = 18.0538(2) A, c = 17.8463(2) A, β =
3
104.935(2)°, V = 3843.71(9) A , Z = 4, Dc = 1.439 g cm-3, μ = 0.173
FLP an oil separated at the bottom of the Young NMR tube
after 30 min. The isolated off-white product was character-
ized as a mixture containing about 90% of (E)-t-Bu3PC-
(H)dC(H)B(C6F5)3 (2-E) and about 10% of [t-Bu3PH]-
[(E)-(C6F5)2BC(C6F5)dC(H)B(C6F5)3] (3-E). The 1H and
31P NMR of 3-E exhibit typical resonances for its cation,
and the 19F and 11B NMR spectra are similar to those
resonances seen for the [B(C6F5)2C(C6F5)dC(H)B(C6F5)3]-
anion of 1-E. In the 1H NMR spectrum 2-E features two triplet
resonances at 8.24 ppm (t, J = 21 Hz) and 5.60 ppm (t, J =
21 Hz) for Ha and Hb (Scheme 2). The triplet splitting pattern
is anticipated to be caused by similar H-H and H-P coupling
˚
mm-1, λ = 0.710 73 A, T = 183(2) K, 33 277 reflections collected, 7864
˚
independent (Rint = 0.026) and 5618 observed reflections (I > 2σ(I)),
523 refined parameters, R1 = 0.050, wR2 = 0.134. CCDC 748014.
(35) Streuli, C. A. Anal. Chem. 1960, 32, 985.
(36) Bush, R. C.; Angelici, R. J. Inorg. Chem. 1988, 27, 681.
(37) Graton, J.; Berthelot, M.; Laurence, C. J. Chem. Soc., Perkin
Trans. 2001, 2130.
(38) Crystal data for 5: C35H25BF15N, Mr = 755.37, triclinic, P1, a =
˚
˚
˚
10.2056(11) A, b = 12.2576(8) A, c = 14.6323(8) A, R = 70.676(3)°, β =
3
˚
87.904(3)°, γ = 68.808(4)°, V = 1603.3(2) A , Z = 2, Dc = 1.565 g
cm-3, μ = 0.152 mm-1, λ = 0.710 73 A, T = 183(2) K, 20 184 reflections
˚
collected, 7943 independent (Rint = 0.0320) and 5663 observed reflec-
tions (I > 2σ(I)), 481 refined parameters, R1 = 0.0388, wR2 = 0.0904.
CCDC 748015.

128 Organometallics, Vol. 29, No. 1, 2010
Jiang et al.
Figure 2. 1H NMR spectrum of the mixture of 2-E and 3-E in CDCl3.
Scheme 2
Scheme 3
in 5 and 6. Also, the cations of 7 and 8 show the typical
resonances in the 1H and 31P NMR spectra. The X-ray
structural analysis of 5 shows that the boron atom adopts
a pseudotetrahedral geometry with a B-C(sp) bond distance
2
˚
of 1.5934(19) A, much shorter than the other three B-C(sp )
bond distances (B1-C9 = 1.653(2); B1-C15 = 1.644(2);
38
˚
B1-C21 = 1.6676(19) A) (Figure 4). The ions are con-
nected through a weak N-H F hydrogen bond; the
Figure 3. Molecular structure of 2-E with 30% probability
thermal ellipsoids. Hydrogen atoms, except for HC1 and HC2
3 3 3
˚
separation between H1 and F15 is 2.21 A. A crystallographic
,
˚
are omitted for clarity. Selected bond lengths (A): C1-C2 =
1.333(3), C1-B1 = 1.612(3), C1-H1 = 0.90(2), C2-P1 =
1.787(2), C2-H2 = 1.01(3), C3-P1 = 1.887(3), C7-P1 =
1.888(2), C11-P1 = 1.887(2), C15-B1 = 1.659(3), C21-B1 =
1.654(3), C27-B1 = 1.656(3). Selected bond angles (deg):
C2-P1-C11 = 105.77(10), C2-P1-C3 = 104.61(11), C11-
P1-C3 = 112.35(13), C2-P1-C7 = 109.97(11), C11-P1-
C7 = 112.23(11), C3-P1-C7 = 111.45(12), C1-B1-C21 =
113.90(17), C1-B1-C27 = 100.92(16), C21-B1-C27 =
112.81(17), C1-B1-C15 = 110.86(17), C21-B1-C15 =
105.02(16), C27-B1-C15 = 113.61(17).
study of 6 (Figure 5) revealed a structure related to 5 with the
counterions also connected through weak N-H F hydro-
3 3 3
39
˚
gen bonding of H1-F11 at a distance of 2.22 A. The
B-C(sp) and N-H bond lengths of 1.5969 (17) and 0.864
A are comparable to those in 5.
˚
We suppose that at higher temperatures the Lut-B(C6F5)3
adduct dissociates with formation of a Lut B(C6F5)3 FLP
3 3 3
in concentrations sufficient for subsequent reactivity. In-
deed, phenylacetylene (PhCtCH) and 3-ethynylthiophene
(SC4H3CtCH) were sought to be transformed in the pre-
sence of Lut and B(C6F5)3. We reckoned that the lower
basicity of Lut in comparison with TMP or t-Bu3P would
cause the deprotonation pathway to be less preferred and
In the 1H NMR spectra of 5 and 6 broad HN resonances
appear at δ 4.04 and 4.13 ppm, evidencing the presence of
ammonium cations. The 19F and 11B NMR spectra are quite
similar for 5 (19F NMR δ -133.89, -164.13, -168.20 ppm;
11B NMR δ -18.57 ppm) and 6 (19F NMR δ -133.92,
-164.15, -168.21; 11B NMR δ -18.53 ppm), pointing to the
structural similarities of these compounds. Compounds 7
and 8 exhibit the same 19F and 11B NMR resonances as those
(39) Crystal data for 6: C33H23BF15NS, Mr = 761.40, triclinic, P1,
˚
˚
˚
a = 11.0873(2) A, b = 12.1753(2) A, c = 12.7089(2) A, R = 100.776(2)°,
3
˚
β = 101.541(2)°, γ = 103.953(2)°, V = 1580.61(5) A , Z = 2, Dc =
1.600 g cm-3, μ = 0.218 mm-1, λ = 0.710 73 A, T = 183(2) K, 39 687
˚
reflections collected, 9654 independent (Rint = 0.0241) and 7111 ob-
served reflections (I > 2σ(I)), 473 refined parameters, R1 = 0.0401,
wR2 = 0.1114. CCDC 748016.

Article
Organometallics, Vol. 29, No. 1, 2010 129
Figure 5. Molecular structure of 6 with 30% probability ther-
mal ellipsoids. Hydrogen atoms, except for the HN atom, are
˚
omitted for clarity. Selected bond lengths (A): N1-H1 =
0.874(16), N1-H2 = 0.852(17), N1-C25 = 1.5398(16), N1-
C29 = 1.5394(15), B1-C1 = 1.6479(18), B1-C7 = 1.6440(18),
B1-C13 = 1.6609(17), B1-C19 = 1.5969(17). Selected bond
angles (deg): H1-N1-H2 = 108.9(14), H1-N1-C29 =
Figure 4. Molecular structure of 5 with 30% probability ther-
mal ellipsoids. Hydrogen atoms, except for the HN atom, are
omitted for clarity. Selected bond lengths (A): N1-H1 =
˚
0.881(16), N1-H2 = 0.914(17), N1-C27 = 1.5387(17), N1-
C31 = 1.5371(18), B1-C9 = 1.653(2), B1-C15 = 1.644(2),
B1-C21 = 1.6676(19), B1-C1 = 1.5934(19). Selected bond angles
(deg): H1-N1-H2 = 103.5(14), H1-N1-C27 = 105.6(10),
H1-N1-C31 = 106.1(10), H2-N1-C27 = 108.5(10), H2-
N1-C31 = 110.2(10), C31-N1-C27 = 121.37(10), C1-B-
C15 = 112.78(10), C1-B1-C9 = 102.93(11), C15-B1-C9 =
114.36(11), C1-B1-C21 = 109.37(11), C15-B1-C21 =
106.67(10), C9-B1-C21 = 110.71(10).
108.1(9), H1-N1-C25
107.0(11), H2-N1-C25
=
107.2(10), H2-N1-C29
104.4(11), C29-N1-C25
=
=
=
120.84(9), C1-B1-C7 = 112.76(9), C1-B1-C13 = 113.41(9),
C19-B1-C7 113.22(10), C1-B1-C19 102.86(9),
=
=
C19-B1-C13 = 109.23(9), C7-B1-C13 = 105.53(9).
Scheme 4
that Lut would mainly react as a Lewis base. The reaction
between SC4H3CtCH proceeded sluggishly, producing
[LutH][PhCtCB(C6F5)3] (9) (47%) and LutC(SC4H3C)d
1
C(H)B(C6F5)3 (10; 55%) (Scheme 4). The H NMR spec-
trum of 9 showed a broad signal attributable to the HN
nucleus at 12.30 ppm. The 19F and 11B NMR spectrum of 9
1
were found to be quite similar to those of 5 or 6. The H
NMR signal for the vinyl proton of 10 is located at 6.74 ppm.
One set of 19F NMR signals for the aryl substituents
(δ -132.84, -163.72, -168.08 ppm) and one 11B NMR signal
(δ-16.39 ppm) are in agreement with a four-coordinate boron.
IIb. Reactions of Phenylacetylene (PhCtCH) and 3-Ethynyl-
thiophene (SC4H3CtCH) with B(C6F5)3. Further studies
were carried out in the absence of a Lewis base, which caused
another reaction pathway to become prevalent. A 1:1 mix-
ture of B(C6F5)3 and PhCtCH turned deep red in toluene
Scheme 5
1
solution, and according to the H and 19F NMR spectra
two products were identified as the isomers (Z)- and
(E)-PhC(H)dC(C6F5)B(C6F5)2 (11-Z and 11-E; near 1:1 in
ratio) (Scheme 5). The 1H NMR spectra exhibited reso-
nances at 7.73 and 7.59 ppm, respectively. The 19F NMR
spectra revealed several sets of signals attributable to both a
carbon-bound -C6F5 unit (11-E -144.43, -156.19, -162.59
ppm; 11-Z -140.78, -156.61, -162.59 ppm) and two boron-
bound -C6F5 units (11-E -130.63, -147.35, -163.79 ppm;
11-Z -131.88, -148.46, -163.79 ppm). It is reasonable to
assume that an acetylene/vinylidene rearrangement had
taken place and that related to a Wagner-Meerwein rear-
rangement40,41 the highly electrophilic R-carbon center of the
Scheme 6
(40) Hanson, J. R. Comp. Org. Syn. 1991, 3, 705.
(41) Olah, G. A. Accts.Chem. Res. 1976, 9, 41.

130 Organometallics, Vol. 29, No. 1, 2010
Jiang et al.
˚
Figure 6. Optimized geometries and selected bond distances (A) and angles (deg) of 11-E (bottom left), 11-Z (bottom right), and a
possible σ-type intermediate (top) during the reaction of B(C6F5)3 with phenylacetylene, calculated at the B3PW91/6-31þg(d) level.
formed vinylidene intermediate [(C6F5)3B-CþdC(H)Ph] be-
came saturated by a boron to carbon C6F5-1,2-shift. The
reaction between B(C6F5)3 and PhCtCH was very fast,
which made it impossible to trace intermediates.42,43
Furthermore, the Z and E isomers of PhC(H)dC(C6F5)-
B(C6F5)2 were found to be inert toward bulky Lewis bases so
that products other than 11-E and 11-Z could not be found.
Unlike the reaction between B(C6F5)3 and PhCtCH, the
reaction of a 1:1 mixture of SC4H3CtCH and B(C6F5)3
could not be driven to completion and most of the B(C6F5)3
Lewis acid remained unreacted, even after prolonged reac-
tion times at room temperatures. Only a trace amount of
however, for a deprotonation with strong Lewis base or for
1,2-addition with weak Lewis base so that compounds 6, 8,
and 10 could be formed.
IIc. DFT Calculations. It became evident from Schemes 1-5
that the activation of acetylenes by B(C6F5)3 could be envisaged
by primary weak interactions of both reaction partners, which
couldbeestablishedintheformofaσor a πcomplex (Scheme 6).
In the additional presence of a base (Lewis base) we could
envisage stepwise activation with initial formation of the σ or π
adducts and their subsequent deprotonation. Alternatively,
bifunctional activation through a four-centered FLP type
arrangement could occur, transferring the acetylide unit to
the Lewis acid B(C6F5)3 and the proton to the base (Lewis
base) in a more or less concerted fashion (Scheme 6).
The acetylene/vinylidene rearrangement is anticipated to
be base-mediated, proceeding with a deprotonation/proton-
ation sequence, or could simply operate on the basis of a
proton shift, preferably via a σ adduct.
The calculations revealed no stabilized form of interaction
with acetylene of the kinds sketched in Scheme 6, since no
prominent local minima were found on the energy hypersur-
face during the optimization process. This might be due to
deficiencies to the DFT calculational procedures not repre-
senting well polar structures with considerable charge sepa-
ration of the σ or π type. For the interaction of B(C6F5)3
with phenylacetylene, however, a local minimum could be
SC4H3CHdCþB-(C6F5)3 was formed, exhibiting a set of 19
F
NMR signals at δ -129.79, -160.68, and -165.67 ppm. On
the basis of a signal at 8.07 ppm in the 1H NMR spectrum a
S
H hydrogen-bonding contact seemed to be present.
3 3 3
Presumably the Sthiophene atom acts as a Lewis base and
prevents proper contact between the Lewis acid and the
acetylenic π-bond of the SC4H3CtCH molecule. The
very low concentration of this complex seemed sufficient,
€
(42) Dierker, G.; Ugolotti, J.; Kehr, G.; Frohlich, R.; Erker, G. Adv.
Synth. Catal. 2009, 351, 1080.
(43) (a) Wrackmeyer, B. Coord. Chem. Rew. 1995, 145, 125.
(b) Venkatesan, K.; Blacque, O.; Fox, T.; Alfonso, M.; Schmalle, H. W.;
Berke, H. Organometallics 2004, 23, 1183. (c) Selegue, J. P. J. Am. Chem.
Soc. 1983, 105, 5921.

Article
Organometallics, Vol. 29, No. 1, 2010 131
localized for the σ adduct I (Figure 6). The formation of this
σ-type adduct is slightly endothermic (7.1 kcal/mol) with
respect to the starting materials. Its potential energy would
still be in a range to be easily reached by thermal activation.
The isomeric σ adduct II was calculated to be unstable, and it
was not possible to find a local minimum for it.
In both cases of R = H, Ph the DFT optimization
processes to establish vinylidene adducts did not converge
to a definite local minimum structure, but still we have to
assume its transient existence, since it would ascribe the only
topological alternative to eventually reach 11-E and 11-Z
with a consecutive 1,2-C6F5 shift. 11-E and 11-Z were
calculated to possess high thermodynamic driving forces in
their formations (-42.5 vs -41.1 kcal/mol, respectively)
with respect to the energetic level of free B(C6F5)3 and
acetylene. The slight energetic preference for 11-E agrees
with the observation that this isomer is prevailing under
experimental circumstances.
techniques or in a glovebox (M. Braun 150B-G-II) filled with
dry nitrogen. Solvents were freshly distilled under N2 by em-
ploying standard procedures and were degassed by freeze-thaw
cycles prior to use. B(C6F5)3 was synthesized according to the
literature.44 All other organic reagents were purchased from
1
Aldrich and used without further purification. H NMR, 19F
NMR, 31P{1H} NMR, and 11B{1H} NMR data were recorded
on a Varian Gemini-200 or 300 spectrometer. Chemical shifts
are expressed in parts per million (ppm) referenced to deuterated
solvent used. 19F, 11B, and 31P NMR were referenced to CFCl3,
BF3 OEt2, and 85% H3PO4, respectively. Microanalyses were
carried out at Anorganisch-Chemisches Institut of the Univer-
3
€
sity of Zurich.
Crystallographic data were collected at 183(2) K on an
Oxford Xcalibur diffractometer (four-circle κ platform, Ruby
CCD detector, and a single-wavelength Enhance X-ray source
with Mo KR radiation, λ = 0.710 73 A).45 The selected suitable
˚
single crystals were mounted using polybutene oil on the top of a
glass fiber fixed on a goniometer head and immediately trans-
ferred to the diffractometer. Pre-experiment, data collection,
face-indexing analytical absorption correction,46 and data re-
duction were performed with the Oxford program suite CrysA-
lisPro.47 The structures were solved with direct methods and
were refined by full-matrix least-squares methods on F2 with
SHELXL-97.48 All programs used during the crystal structure
determination process are included in the WINGX software.49
The program PLATON50 was used to check the results of the
X-ray studies and to analyze the hydrogen-bonding systems.
Calculations were carried out at the DFT level of theory with
the Gaussian03 program package51 using the hybrid functional
B3PW9152,53 and the standard Pople 6-31Gþ(d) basis set.54
Geometry optimizations were carried out without any symme-
try restrictions, and the nature of the optimized minima was
evaluated by computations of harmonic vibrational frequencies
at the same theory level. The relative energies were calculated by
correcting the B3LYP/6-31þG(d) total energies for zero-point
vibrational energies (ZPE).
III. Conclusion
In summary, we have applied the frustrated Lewis pairs
LB LA (TMP B(C6F5)3 t-Bu3P B(C6F5)3, and Lut-
3 3 3
3 3 3
3 3 3
B(C6F5)3) for the activation of terminal alkynes, which
furnished two different initial pathways: (a) a deprotonation
pathway and (b) a 1,2-addition pathway.
The deprotonation pathway (a) proceeded with deproto-
nation of any of the initial (C6F5)3B(σ-,π-HCtCR) com-
plexes with the Lewis base acting as a base or with
“bifunctional” heterolysis of the tC-H bond (Scheme 6).
This bifunctional heterolysis would involve a four-centered
transition state of the tC-H bond and the FLP encounter
complex. For any of these mechanistic alternatives the
primary products are the [B(C6F5)3CtCR][LBH] ion pairs
(R = H, Ar). However, neither the experimental nor the
theoretical studies provided definite clues on the type of
intermediate appearing in the reactions of Schemes 1-5.
Along pathway (b) the Lewis pairs could be envisaged to
undergo 1,2-additions to the alkynes to generate LBC-
(R)dC(H)B(C6F5)3 structures. Initially, we anticipate for
this case again a primary interaction of the Lewis acid
B(C6F5)3 with the acetylenes via σ and π complexes
(Scheme 6). The final step of nucleophilic addition of the
LB should naturally depend on the nucleophilic character of
the base, as seen for t-Bu3P and LUT. The regioselectivity of
LUT addition to the higher substituted end of the B(C6F5)3
adduct with SC4H3CtCH points to the involvement of the σ
complex of type I or of the π complex (Scheme 6).
Boron to carbon C6F5-1,2-migrations were also seen to be an
important feature of this chemistry. They appeared as follow-
up reactions of initially formed [B(C6F5)3CtCH]- anions of
1-E and 3-E, which then underwent B(C6F5)3 addition. Sub-
sequently this anion was transformed via C6F5 migration to an
(E)-[(C6F5)2BC(C6F5)dC(H)-B(C6F5)3]- product. The reac-
tion of phenylacetylene with B(C6F5)3 could be viewed as a
related 1,2-carboboration case42 where the electrophilic carbon
of the initially formed (C6F5)3B-CþdC(H)R vinylidene spe-
cies became saturated by the same migrational step to yield
(E)- and (Z)-RC(H)dC(C6F5)B(C6F5)2 compounds.43
IVb. [TMPH][(C6F5)2BC(C6F5)dC(H)B(C6F5)3] (1-E). In a
Young NMR tube, B(C6F5)3 (0.0768 g, 0.15 mmol) and 2,2,6,6-
tetramethylpiperidine (TMP; 0.0212 g, 0.15 mmol) were dis-
solved in 1 mL of toluene. Dried HCtCH (1000 mbar, ca. 0.15
(44) Lancaster, S. SyntheticPage 2003, 215.
(45) Xcalibur CCD System; Oxford Diffraction Ltd, Abingdon,
Oxfordshire, England, 2007.
(46) Clark, R. C.; Reid, J. S. Acta Crystallogr. 1995, A51, 887–897.
(47) CrysAlisPro (Versions 1.171.32/33), Oxford Diffraction Ltd,
Abingdon, Oxfordshire, England.
(48) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(49) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(50) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
(51) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.01; Gaussian, Inc.,
Wallingford, CT, 2004.
(52) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
IV. Experimental Section
(53) Burke, K., Perdew, J. P. Yang, W. Electronic Density Functional
Theory: Recent Progress and New Directions; Dobson, J. F., Vignale, G.,
Das, M. P., Eds.; Plenum: New York, 1998.
IVa. General Considerations. All manipulations were carried
out under an atmosphere of dry nitrogen using standard Schlenk
(54) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.

132 Organometallics, Vol. 29, No. 1, 2010
Jiang et al.
mmol) was then filled into the NMR tube and shaken. A brown
oil formed at the bottom of the NMR tube 30 min later at room
temperature. Hexane was then added to the oil to induce
precipitation. The mixture was filtered, washed with hexane,
and dried in vacuo. The product was collected as an off-white
solid. Yield: 56%. Crystals were obtained from a mixture of
benzene and hexane at 25 °C. Anal. Calcd for C47H21B2F30N: C,
dissolved in 2 mL of toluene, and the orange solution was stirred
at room temperature for 30 min. The reaction mixture was then
concentrated to half of its original volume, and hexane (5 mL)
was added to promote precipitation. The mixture was filtered,
washed with hexane, and dried in vacuo. The product was
collected as a white solid. Yield: 87%. Crystals were obtained
from a mixture of toluene and hexane at 25 °C. Anal. Calcd for
C35H25BF15N: C, 55.65; H, 3.34; N, 1.85. Found: C, 55.54; H,
3.41; N, 1.83. 1H NMR (toluene-d8, 300 MHz, 293 K): δ 0.41 (s,
12H, -CH3), 0.55 (m, 4H, CH2), 0.59 (m, 2H, CH2), 4.04 (br,
1
47.39; H, 1.78; N, 1.18. Found: C, 47.20; H, 1.53; N, 1.43. H
NMR (CDCl3, 300 MHz, 293 K): δ 1.49 (s, 12H, -CH3), 1.82
(m, 4H, CH2), 1.89 (m, 2H, CH2), 5.32 (br, 2H, NH2), 9.36 ppm
(s, 1H, CH). 11B{1H} NMR (CDCl3, 96 MHz, 293 K): δ -15.19
ppm (s). 19F NMR (CDCl3, 282 MHz, 293 K): δ -131.69 (d, 6F,
3JFF = 23 Hz, o-C6F5), -132.14 (d, 4F, 3JFF = 23 Hz, o-C6F5),
3
2H, NH2), 6.80 (d, 2H, JHH = 1.8 Hz, Ph H), 6.82 (d, 1H,
3JHH = 2.1 Hz, Ph H), 7.14 ppm (m, 2H, Ph H). 11B{1H} NMR
(toluene-d8, 96 MHz, 293 K): δ -18.57 ppm (s). 19F NMR
(toluene-d8, 282 MHz, 293 K): δ -133.89 (d, 6F, 3JFF = 25 Hz,
o-C6F5), -164.13 (t, 3F, 3JFF = 21 Hz, p-C6F5), -168.20 ppm
-140.60 (d, 2F, 3JFF = 23 Hz, o-C6F5), -151.65 (t, 2F, 3JFF
=
20 Hz, p-C6F5), -159.18 (t, 1F, 3JFF = 20 Hz, p-C6F5), -162.31
3
3
3
(t, 6F, JFF = 20 Hz, m-C6F5). 13C{1H} NMR (toluene-d8,
(t, 3F, JFF = 20 Hz, p-C6F5), -162.76 (t, 4F, JFF = 23 Hz,
m-C6F5), -165.08 (t, 2F, 3JFF = 23 Hz, m-C6F5), -167.05 ppm
(t, 6F, 3JFF = 23 Hz, m-C6F5). The solubility of 1 was too low to
permit C6F5 resonances of low intensity to be observed in the
13C NMR spectrum.
75 MHz, 293 K): δ 149.45 (dm, 1JC-F = 240 Hz, o-C6F5), 139.65
1
1
(dm, JC-F = 227 Hz, p-C6F5), 137.70 (dm, JC-F = 256 Hz,
m-C6F5), 132.67 (o-Ph), 132.26 (p-Ph), 127.37 (m-Ph), 84.02
(Ph-CCB), 77.67 (Ph-CCB), 54.16 (o-C5H7N), 36.50 (m-
C5H7N), 29.51 (CH3), 16.88 ppm (p-C5H7N).
IVc. t-Bu3PC(H)dC(H)B(C6F5)3 (2-E) and [t-Bu3PH][-
(C6F5)2BC(C6F5)dC(H)B(C6F5)3] (3-E). In a Young NMR
tube, B(C6F5)3 (0.0768 g, 0.15 mmol) and tri-tert-butylpho-
sphine (0.03 g, 0.15 mmol) were dissolved in 1 mL of toluene.
Dried HCtCH (1000 mbar, ca. 0.15 mmol) was then filled into
the NMR tube and shaken. A brown oil formed at the bottom of
the NMR tube 30 min later at room temperature. Hexane was
then added to the oil to induce precipitation. The mixture was
filtered, washed with hexane, and dried in vacuo. The product
was collected as an off-white solid which contained about 90%
of 2-E and 10% of 3-E. Yield: 56%. Crystals of 2-E were
obtained from a mixture of toluene and hexane at 25 °C. Data
IVf. [TMPH][C4H3SCtCB(C6F5)3] (6). B(C6F5)3 (0.1024 g,
0.2 mmol), 2,2,6,6-tetramethylpiperidine (TMP; 0.0283 g,
0.2 mmol), and 3-ethynylthiophene (0.022 g, 0.2 mmol) were
dissolved in 2 mL of toluene, forming a deep red solution that
was stirred at room temperature for 30 min. The reaction
mixture was then concentrated to half of its original volume,
and hexane (5 mL) was added to prompt precipitation. The
mixture was filtered, washed with hexane, and dried in vacuo.
The product was collected as a light brown solid. Yield: 86%.
Crystals were obtained from a mixture of toluene and hexane at
25 °C. Anal. Calcd for C33H23BF15NS: C, 52.06; H, 3.04; N,
1.84. Found: C, 52.21; H, 3.08; N, 1.82. 1H NMR (toluene-d8,
300 MHz, 293 K): δ 0.47 (s, 12H, CH3), 0.64 (m, 4H, -CH2),
0.71 (m, 2H, CH2), 4.13 (br, 2H, NH2), 6.60 (m, 1H, C4H3S),
1
for 2-E are as follows. H NMR (CDCl3, 300 MHz, 293 K): δ
3
1.55 (d, 27H, JH-P = 12 Hz, P{C(CH3)3}3), 5.60 (t, overlap,
J = 21 Hz, dCH), 8.24 ppm (t, overlap, J = 21 Hz, dCH).
11B{1H} NMR (CDCl3, 96 MHz, 293 K): δ -14.25 ppm (s).
6.66 (m, 1H, C4H3S), 6.69 ppm (dd, 1H, 3JHH = 6 Hz, 4JHH
=
31P{1H} NMR (CDCl3, 121 MHz, 293 K): δ 36.31 ppm (s). 19
F
2 Hz, C4H3S). 11B{1H} NMR (toluene-d8, 96 MHz, 293 K):
δ -18.53 ppm (s). 19F NMR (toluene-d8, 282 MHz, 293 K):
=
3
NMR (CDCl3, 282 MHz, 293 K): δ -132.82 (d, 6F, JFF
=
23 Hz, o-C6F5), -162.33 (t, 3F, 3JFF = 20 Hz, p-C6F5), -166.85
ppm (t, 6F, 3JFF = 20 Hz, m-C6F5). 13C{1H} NMR (CDCl3, 282
MHz, 293 K): δ 147.91 (dm, 1JC-F = 238 Hz, o-C6F5), 138.62
(dm, 1JC-F = 230 Hz, p-C6F5), 136.51 (dm, 1JC-F = 238 Hz, m-
δ -133.92 (d, 6F, 3JFF = 25 Hz, o-C6F5), -164.15 (t, 3F, 3JFF
3
20 Hz, p-C6F5), -168.21 ppm (t, 6F, JFF = 20 Hz, m-C6F5).
13C{1H} NMR (toluene-d8, 75 MHz, 293 K): δ 149.47 (dm,
1
1JC-F = 238 Hz, o-C6F5), 139.83 (dm, JC-F = 230 Hz,
1
C6F5), 101.85, 101.08 (dCH), 39.62 (d, JC-P = 32 Hz, P{C-
(CH3)3}31), 30.02 ppm (s, P{C(CH3)3}3). Data for 3-E are as
follows. H NMR (CDCl3, 300 MHz, 293 K): δ 1.67 (d, 27H,
p-C6F5), 137.69 (dm, 1JC-F = 245 Hz, m-C6F5), 131.13 (C4H3S),
130.42 (C4H3S), 126.31 (C4H3S), 77.35 (CCB), 53.94 (o-C5H7N),
36.52 (m-C5H7N), 29.48 (CH3), 16.91 (p-C5H7N).
1
3JH-P = 15 Hz, P{C(CH3)3}3), 5.4 (d, 1H, JH-P = 440 Hz,
PH), 9.41 ppm (s, 1H, dCH). 11B{1H} NMR (CDCl3, 96 MHz,
293 K): δ -15.14 ppm (s). 31P{1H} NMR (CDCl3, 121 MHz, 293
K): δ 58.11 ppm (s).
IVg. [t-Bu3PH][C4H3SCtCB(C6F5)3] (8). B(C6F5)3 (0.1024 g,
0.2 mmol), tri-tert-butylphosphine (0.0405 g, 0.2 mmol), and
3-ethynylthiophene (0.022 g, 0.2 mmol) were dissolved in 2 mL
of toluene, forming a brown solution that was stirred at room
temperature for 30 min. The reaction mixture was then concen-
trated to half of its original volume, and hexane (5 mL) was
added to prompt precipitation. The mixture was filtered,
washed with hexane, and dried in vacuo. The product was
collected as a light brown solid. Yield: 82%. Anal. Calcd for
IVd. LutC(H)dC(H)B(C6F5)3 (4). In a Young NMR tube,
B(C6F5)3 (0.0768 g, 0.15 mmol) and Lutidine (Lut) (0.016 g,
0.15 mmol) were dissolved in 1 mL of toluene. Dried HCtCH
(1000 mbar, ca. 0.15 mmol) was filled into the NMR tube, and
the NMR tube was kept at 80 °C for 20 h. Hexane was then
added to the mixture solution to induce precipitation. The
mixture was filtered, washed with hexane and ethyl ether, and
dried in vacuo. The product was collected as a white solid. Yield:
34%. Anal. Calcd for C27H11BF15N: C, 50.26; H, 1.72; N, 2.17.
Found: C, 50.17; H, 1.68; N, 2.19. 1H NMR (CD3CN, 300 MHz,
293 K): δ 2.52 (s, 6H, -CH3), 6.18 (d, 1H, 3JH-H = 18 Hz, dCH),
6.66 (d, 1H, 3JH-H = 18 Hz, dCH), 7.62 (d, 2H, 3JH-H = 6 Hz,
m-C5H3N), 8.10 ppm (t, 1H, 3JH-H = 6 Hz, p-C5H3N). 11B{1H}
NMR (CD3CN, 96 MHz, 293 K): δ -15.88 ppm (s). 19F NMR
C36H31BF15PS: C, 52.57; H, 3.80. Found: C, 52.32; H, 3.72. 1H
3
NMR (CD3CN, 300 MHz, 293 K): δ 1.6 (d, 27H, JH-P
=
15 Hz, P{C(CH3)3}3), 5.36 (d, 1H, 1JH-P = 444 Hz, PH), 1H,
C4H3S), 6.90 (dd, 1H, J = 6 Hz, 2 Hz, C4H3S), 7.25 (d, 1H, J =
6 Hz, C4H3S), 7.28 (d, 1H, J = 6 Hz, C4H3S). 11B{1H} NMR
(CD3CN, 96 MHz, 293 K): δ -21.11 ppm (s). 31P{1H} NMR
(CD3CN, 121 MHz, 293 K): δ 56.97 ppm (s). 19F NMR
(CD3CN, 282 MHz, 293 K): δ -133.91 (d, 6F, 3JFF = 23 Hz,
o-C6F5), -164.49 (t, 3F, 3JFF = 20 Hz, p-C6F5), -168.62 ppm
3
(CD3CN, 282 MHz, 293 K): δ -133.11 (d, 6F, JFF = 23 Hz,
3
(t, 6F, JFF = 20 Hz, m-C6F5). 13C{1H} NMR (CD3CN,
3
o-C6F5), -163.75 (t, 3F, JFF = 20 Hz, p-C6F5), -168.00 ppm
1
(t, 2F, 3JFF = 20 Hz, m-C6F5). 13C{1H} NMR (CD3CN, 75 MHz,
293 K) (partial): 157.20, 144.89, 127.17, 21.86 ppm.
75 MHz, 293 K; partial): δ 149.02 (dm, JC-F = 240 Hz,
1
o-C6F5), 139.52 (dm, JC-F = 230 Hz, p-C6F5), 137.77 (dm,
1JC-F = 242 Hz, m-C6F5), 130.82 (C4H3S), 130.60 (C4H3S),
125.92 (C4H3S), 38.16 (d, 1JC-P = 28 Hz, P{C(CH3)3}3), 30.07
ppm (s, P{C(CH3)3}3).
IVe. [TMPH][PhCtCB(C6F5)3] (5). B(C6F5)3 (0.1024 g,
0.2 mmol), 2,2,6,6-tetramethylpiperidine (TMP; 0.0283 g,
0.2 mmol), and phenylacetylene (0.021 g, 0.2 mmol) were

Article
IVh. [LutH][PhCtCB(C6F5)3] (9). B(C6F5)3 (0.1024 g,
Organometallics, Vol. 29, No. 1, 2010 133
ppm (s). 19F NMR (CD3CN, 282 MHz, 293 K): δ -132.84
(d, 6F, 3JFF = 23 Hz, o-C6F5), -163.72 (t, 3F, 3JFF = 20 Hz,
p-C6F5), -168.08 ppm (t, 2F, 3JFF = 23 Hz, m-C6F5). 13C{1H}
NMR (CD3CN, 75 MHz, 293 K; partial): δ 157.12, 149.25 (dm,
1JC-F = 240 Hz, o-C6F5), 145.39, 139.36 (dm, 1JC-F = 243 Hz,
p-C6F5), 137.40 (dm, 1JC-F = 245 Hz, m-C6F5), 129.12, 128.33,
126.92, 124.33, 21.44 ppm.
0.2 mmol), Lutidine (Lut; 0.021 g, 0.2 mmol), and phenylacetylene
(0.021 g, 0.2 mmol) were dissolved in 2 mL of toluene, and the
yellow solution was stirred at 80 °C for 8 h. The reaction mixture
was then concentrated to half of its original volume, and hexane
(5 mL) was added to promote precipitation. The mixture was
filtered, washed with hexane, and dried in vacuo. The product was
collected as a yellow solid. Yield: 37%. Anal. Calcd for
C33H15BF15N: C, 54.95; H, 2.10; N, 1.94. Found: C, 54.71; H,
2.08; N, 1.82. 1H NMR (CD3CN, 300 MHz, 293 K): δ 2.58 (s, 6H,
IVj. (Z)- and (E)-PhC(H)dC(C6F5)B(C6F5)2 (11-Z and 11-E).
B(C6F5)3 (0.0128 g, 0.025 mmol) and PhCtCH (0.0026 g,
0.025 mmol) were dissolved in 0.5 mL of benzene-d6 in a
3
1
-CH3), 7.22 (m, 5H, Ph H), 7.44 (d, 2H, JH-H = 6 Hz, m-
NMR tube, and the solution turned red. H NMR (benzene-
d6, 300 MHz, 293 K): δ 7.73 (s, 1H, dCH, 10-Z), 7.59 (s, 1H,
C5H3N), 8.02 (t, 1H, 3JH-H =6Hz, p-C5H3N), 12.30 ppm (br, 1H,
NH). 11B{1H} NMR (CD3CN, 96 MHz, 293 K): δ -20.89 ppm (s).
=
dCH, 11-E), 6.87-6.72 (m, 10H, Ph H, 10-Z and 11-E). 19F
19F NMR (CD3CN, 282 MHz, 293 K): δ -133.93 (d, 6F, 3JFF
NMR (benzene-d6, 282 MHz, 293 K): δ -130.63 (d, 4F, 3JFF
=
23 Hz, o-C6F5),-164.50 (t, 3F, 3JFF =20Hz,p-C6F5),-168.63 ppm
23 Hz, o-C6F5, 11-E B(C6F5)2), -131.88 (d, 4F, 3JFF = 23 Hz,
o-C6F5, 11-Z B(C6F5)2), -140.78 (d, 2F, 3JFF = 21 Hz, o-C6F5,
11-Z C6F5), -144.43 (d, 2F, 3JFF = 21 Hz, o-C6F5, 11-E C6F5),
-147.35 (t, 2F, 3JFF = 23 Hz, p-C6F5, 11-E B(C6F5)2), -148.46
(t, 2F, 3JFF = 23 Hz, m-C6F5). 13C{1H} NMR (CD3CN, 75 MHz,
293 K) (partial): 155.43, 149.41 (dm, JC-F = 246 Hz, o-C6F5),
=
1
144.21, 139.17 (dm, 1JC-F = 243 Hz, p-C6F5), 137.42 (dm, 1JC-F
245 Hz, m-C6F5), 131.55, 129.03, 127.02, 124.33, 20.74 ppm.
(t, 2F, 3JFF = 23 Hz, p-C6F5, 11-Z B(C6F5)2), -156.19 (t, 1F,
3
IVi. [Lut(C4H3S)CdC(H)B(C6F5)3] (10). B(C6F5)3 (0.1024 g,
0.2 mmol), Lutidine (Lut; 0.021 g, 0.2 mmol), and 3-ethynylthio-
phene (0.022 g, 0.2 mmol) were dissolved in 2 mL of toluene, and
the orange solution was stirred at 80 °C for 8 h. The reaction
mixture was then concentrated to half of its original volume, and
hexane (5 mL) was added to promote precipitation. The mixture
was filtered, washed with hexane, and dried in vacuo. The
product was collected as a brown solid. Yield: 45%. Anal. Calcd
for C31H13BF15NS: C, 51.19; H, 1.80; N, 1.93. Found: C, 51.15;
H, 1.85; N, 1.98. 1H NMR (CD3CN, 300 MHz, 293 K): δ 2.59
(s, 6H, -CH3), 6.74 (s, 1H, dCH), 6.82 (m, 1H, C4H3S), 7.16
(d, 1H, J = 6 Hz, C4H3S), 7.19 (d, 1H, J = 6 Hz, C4H3S), 7.70
(d, 2H, 3JH-H = 6 Hz, m-C5H3N), 8.19 (t, 1H, 3JH-H = 6 Hz,
p-C5H3N). 11B{1H} NMR (CD3CN, 96 MHz, 293 K): δ -16.39
3JFF = 21 Hz, p-C6F5, 11-E C6F5), -156.61 (t, 1F, JFF
=
21 Hz, p-C6F5, 11-Z C6F5), 162.59 (m, 4F, m-C6F5, 11-Z and
11-E C6F5), 163.79 (m, 8F, m-C6F5, 11-Z and 11-E B(C6F5)2).
Acknowledgment. Support from the Swiss National
Science Foundation and the Funds of the University of
Zurich are gratefully acknowledged.
Supporting Information Available: CIF files giving details of
the X-ray crystal structure analyses for 1-E, 2-E, 5, and 6 and
tables giving the energies and Cartesian coordinates of the DFT
optimized molecules. This material is available free of charge via
the Internet at http://pubs.acs.org.