Frustrated lewis pairs and ring-opening of THF, dioxane, and thioxane

Article abstract of DOI:10.1021/om1003896

The reaction of tBu₂PH and B(p-C₆F₄H) ₃ in THF afforded tBu₂(H)P(CH₂) ₄OB(p-C₆F₄H)₃ (1). Similarly, reactions of N-bases with a THF solution of B(C₆F₅) ₃ led to the formation of the THF-ring-opening products C ₅H₃Me₂N(CH₂)₄OB(C ₆F₅)₃ (2), C₆H₅CH ₂NMe₂(CH₂)₄OB(C₆F ₅)₃ (3), and Me₂NC₆H ₄NMe₂(CH₂)₄OB(C₆F ₅)₃ (4). THF-ring-opening also occurs with aliphatic amines to form the compounds Me₃N(CH₂) ₄OB(C₆F₅)₃ (5), Et ₃N(CH₂)₄OB(C₆F₅) ₃ (6), Me₂N(CH₂)₂NMe ₂(CH₂)₄OB(C₆F₅) ₃ (7), and tBuHN(CH₂)₂NHtBu(CH ₂)₄OB(C₆F₅)₃ (8). In related chemistry, reactions of B(C₆F₅)₃, 1,4-dioxane, and the appropriate base yielded tBu₃P(CH ₂)₂O(CH₂)₂OB(C₆F ₅)₃ (10), C₆H₅CH₂NMe ₂(CH₂)₂O(CH₂)₂OB(C ₆F₅)₃ (11), ((tBuN)₂C ₃H₂)(CH₂)₂O(CH₂) ₂OB(C₆F₅)₃ (12), Me ₂NC₆H₄NMe₂(CH₂) ₂O(CH₂)₂OB(C₆F₅) ₃ (13), and C₅H₃Me₂N(CH ₂)₂O(CH₂)₂OB(C₆F ₅)₃ (14). In a related fashion, the thioxane adduct (C₆F₅)₃B(SC₄H₈O) (15) reacted with N,N-dimethylbenzylamine, N,N,N′,N′-tetramethyl-p- phenylenediamine, 2,6-lutidine, or tBu₃P to give the corresponding ring-opened products L(CH₂)₂S(CH₂) ₂OB(C₆F₅)₃ (L = tBu₃P (16), C₆H₅CH₂NMe₂ (17), Me ₂NC₆H₄NMe₂ (18), and C ₅H₃Me₂N (19)). The crystal structures of 1-7, 10-12, 14, 18, and 19 are reported.

Full text of DOI:10.1021/om1003896

5310 Organometallics 2010, 29, 5310–5319
DOI: 10.1021/om1003896
Frustrated Lewis Pairs and Ring-Opening of THF,
Dioxane, and Thioxane†
Birgit Birkmann,‡ Tanja Voss,‡,§ Stephen J. Geier,‡ Matthias Ullrich,‡ Gerald Kehr,§
Gerhard Erker,§ and Douglas W. Stephan*,‡
‡Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S
§
3H6, and Organisch-Chemisches Institut, Westfalische Wilhelms-Universitat, Corrensstrasse 40, 48149
€
Mu€nster, Germany
€
Received April 30, 2010
The reaction of tBu2PH and B(p-C6F4H)3 in THF afforded tBu2(H)P(CH2)4OB(p-C6F4H)3 (1).
Similarly, reactions of N-bases with a THF solution of B(C6F5)3 led to the formation of the THF-
ring-opening products C5H3Me2N(CH2)4OB(C6F5)3 (2), C6H5CH2NMe2(CH2)4OB(C6F5)3 (3), and
Me2NC6H4NMe2(CH2)4OB(C6F5)3 (4). THF-ring-opening also occurs with aliphatic amines to form
the compounds Me3N(CH2)4OB(C6F5)3 (5), Et3N(CH2)4OB(C6F5)3 (6), Me2N(CH2)2NMe2(CH2)4-
OB(C6F5)3 (7), and tBuHN(CH2)2NHtBu(CH2)4OB(C6F5)3 (8). In related chemistry, reactions of
B(C6F5)3, 1,4-dioxane, and the appropriate base yielded tBu3P(CH2)2O(CH2)2OB(C6F5)3 (10), C6H5-
CH2NMe2(CH2)2O(CH2)2OB(C6F5)3 (11), ((tBuN)2C3H2)(CH2)2O(CH2)2OB(C6F5)3 (12), Me2NC6-
H4NMe2(CH2)2O(CH2)2OB(C6F5)3 (13), and C5H3Me2N(CH2)2O(CH2)2OB(C6F5)3 (14). In a re-
lated fashion, the thioxane adduct (C6F5)3B(SC4H8O) (15) reacted with N,N-dimethylbenzylamine,
N,N,N0,N0-tetramethyl-p-phenylenediamine, 2,6-lutidine, or tBu3P to give the corresponding ring-
opened products L(CH2)2S(CH2)2OB(C6F5)3 (L= tBu3P (16), C6H5CH2NMe2 (17), Me2NC6H4NMe2
(18), and C5H3Me2N (19)). The crystal structures of 1-7, 10-12, 14, 18, and 19 are reported.
Introduction
including H2,4-9 olefins,10 dienes,11 alkynes,12 boranes,13 di-
sulfides,14 CO2,15,16 and N2O.17,18 While broadening impli-
cations of the chemistry of FLPs continue to develop, it is
interesting to note that our initial studies of these systems
were prompted by an earlier finding that phosphine/borane
combinations react with THF to effect ring opening, affording
zwitterionic phosphonium borates of the form R3P(CH2)4-
OB(C6F5)3.19 While this reactivity is understandable in the
In recent work, we have demonstrated that a combination
of sterically encumbered donors with Lewis acids results in
unique reactivity.1-3 Such systems, referred to as “frustrated
Lewis pairs” (FLPs), react with a variety of small molecules,
† Part of the Dietmar Seyferth Festschrift. Dedicated to Professor Dietmar
Seyferth on the occasion of his retirement as Editor of Organometallics.
*To whom correspondence should be addressed. E-mail: dstephan@
chem.utoronto.ca.
(1) Stephan, D. W. Org. Biomol. Chem. 2008, 6, 1535–1539.
(2) Stephan, D. W. Dalton Trans. 2009, 3129–3136.
(3) Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2010, 49, 46–76.
(4) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Frohlich, R.;
Grimme, S.; Stephan, D. W. Chem. Commun. 2007, 5072–5074.
€
(5) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
context of the reactivity of FLPs, this ring opening of THF is
20
€
not unprecedented. Indeed, in 1950, Wittig and Ruckert
described the reaction of [Ph3C]- with THF(BPh3), afford-
ing the borate anion [Ph3C(CH2)4OBPh3]-. Some 40 years
later we reported the related reaction of PCy3 with
ZrCl4(THF)2, which resulted in the formation of the dimeric
zwitterionic species (Cy3P(CH2)4OZrCl4)2 (Scheme 1).21 Sub-
sequently, other transition-metal Lewis acids, including
complexes derived from U,22,23 Sm,24 Ti,25 and Zr26,27 as well
€
Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543–7546.
(6) Sumerin, V.; Schulz, F.; Atsumi, M.; Wang, C.; Nieger, M.;
€
€
Leskela, M.; Repo, T.; Pyykko, P.; Rieger, B. J. Am. Chem. Soc. 2008,
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(7) Sumerin, V.; Schulz, F.; Nieger, M.; Leskela, M.; Repo, T.;
(15) Momming, C. M.; Otten, E.; Kehr, G.; Frohlich, R.; Grimme, S.;
Rieger, B. Angew. Chem., Int. Ed. 2008, 47, 6001–6003.
(8) Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124–1126.
(9) Welch, G. C.; Stephan, D. W. J. Am. Chem. Soc. 2007, 129, 1880–
1881.
(10) McCahill, J. S. J.; Welch, G. C.; Stephan, D. W. Angew. Chem.,
Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2009, 48, 6643–6646.
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1796–1797.
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2009, 48, 9709–9712.
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131, 9918–9919.
ꢀ
Int. Ed. 2007, 46, 4968–4971.
(11) Ullrich, M.; Seto, K. S.-H.; Lough, A. J.; Stephan, D. W. Chem.
Commun. 2009, 2335–2337.
(12) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131,
8396–8397.
(13) Dureen, M. A.; Lough, A.; Gilbert, T. M.; Stephan, D. W. Chem.
(19) Welch, G. C.; Masuda, J. D.; Stephan, D. W. Inorg. Chem. 2006,
45, 478–480.
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(20) Wittig, G.; Ruckert, A. Liebigs Ann. Chem. 1950, 566, 101–113.
(21) Breen, T. L.; Stephan, D. W. Inorg. Chem. 1992, 31, 4019–4022.
(22) Avens, L. R.; Barnhart, D. M.; Burns, C. J.; McKee, S. D. Inorg.
Chem. 1996, 35, 537–539.
Commun. 2008, 4303–4305.
(14) Dureen, M. A.; Welch, G. C.; Gilbert, T. M.; Stephan, D. W.
Inorg. Chem. 2009, 48, 9910–9917.
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r
pubs.acs.org/Organometallics
Published on Web 07/08/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 21, 2010 5311
Scheme 1. Examples of Lewis Acid-Lewis Base Mediated
Ring-Opening Reactions
When intended to be used in the glovebox, all solvents were
transferred through the antechambers in bombs with evacuated
headspaces and refilled inside into brown glass bottles equipped
˚
with 4 A molecular sieves (small pieces of silver foil were further
added to CH2Cl2 and CD2Cl2). 1H, 11B, 13C, 19F, and 31P NMR
spectra were recorded at 25 °C on Varian 300 and 400 MHz
Bruker spectrometers. Chemical shifts are given relative to
SiMe4 and referenced to the residual solvent signal (1H, 13C)
or relative to an external standard (11B, (Et2O)BF3; 19F, CFCl3;
31P, 85% H3PO4). In some instances, signal and/or coupling
assignment was derived from two-dimensional NMR experi-
ments. Chemical shifts are reported in ppm and coupling con-
stants as scalar values in Hz. For more detailed assignments of
the NMR data, please see the Supporting Information. Combus-
tion analyses were performed in house by employing a Perkin-
Elmer CHN analyzer. tBu3P and 1,3-di-tert-butylimidazol-2-
ylidene were obtained from Strem Chemicals, Inc. (USA) and
used as received. B(C6F5)3 was doubly sublimed prior to use.
Dimethylbenzylamine, 2,6-lutidine, 1,4-dioxane, and 1,4-thio-
xane were obtained from Sigma-Aldrich and stored over mole-
cular sieves.
as Mn-carborane complexes,28 were also shown to induce
similar THF-ring-opening, while Campbell and Gladfelter29
showed that the main group species amine-alane adduct
reacts in THF to give a zwitterionic ammonium aluminate
(Scheme 1). Similarly, Te nucleophiles and Lewis acids have
resulted in related ring-openings:30,31 for example, Chivers
and Schatte30 described the ring-opening of THF by reaction
of a tellurium diimide dimer with B(C6F5)3 in THF (Scheme 1).
While these previous studies were not described as such, it is
clear that these ring-opening reactions are conceptually
related to the more recent FLP chemistry as each involves
attack of Lewis acid activated THF by a nucleophile. In this
paper, we undertake an effort to further generalize such FLP
ring-opening reactions. Herein we first probe the generality
of such THF-ring-opening reactions by FLPs, exploring ana-
logous reactions with combinations of phosphines, amines,
pyridines, and carbenes with electron-deficient boranes. In a
second aspect, we further probe the extension of such reacti-
vity in ring-opening reactions of dioxane and thioxane.
Synthesis of tBu2(H)P(CH2)4OB(p-C6F4H)3 (1), C5H3Me2N-
(CH2)4OB(C6F5)3 (2), C6H5CH2NMe2(CH2)4OB(C6F5)3 (3),
and Me2NC6H4NMe2(CH2)4OB(C6F5)3 (4). These compounds
were prepared in a similar fashion, and thus only the prepara-
tion of 3 is detailed: N,N-dimethylbenzylamine (30 mg, 0.223
mmol) in 0.5 mL of THF was added to a solution of B(C6F5)3
(114 mg, 0.223 mmol) in 0.5 mL of THF and the resulting
mixture stirred at room temperature for 4 h, before the solvent
was removed in vacuo. A 0.5 mL portion of dichloromethane
and 6 mL of pentane were added, so that a white powder started
to precipitate. The mixture was stored at -39 °C overnight and
the supernatant removed via syringe. After drying in vacuo, the
product 3 was obtained in 81% yield (130 mg, 0.181 mmol).
Crystals suitable for X-ray diffraction analysis were obtained by
layering a dichloromethane solution with hexane.
1: yield 74 mg (0.112 mmol, 87%). 1H NMR (CD2Cl2): 6.75
(tt, 3H, 3JHF = 9.8 Hz, 4JHF = 7.6 Hz, p-CH), 5.45 (dt, 1JHP
=
447 Hz, 3JHH = 4.6 Hz, 1H, PH), 3.27 (t, 3JHH = 5.1 Hz, 2H,
CH2), 2.57 (tdm, br, 3JHH = 7.8 Hz, 3JHH = 4.6 Hz, 2H, CH2),
1.97 (m, 2H, CH2), 1.68 (t, br, 3JHH = 5.1 Hz, 2H, CH2), 1.41 (d,
3JHP = 16.5 Hz, 27H, tBu). 13C{1H} NMR (CD2Cl2): 148.6
(dm, 1JCF ≈ 238 Hz, o-C6F4H), 145.8 (dm, 1JCF ≈ 247 Hz, m-
C6F4H), 132.3 (br, Cq), 102.0 (t, 2JCF ≈ 23 Hz, p-C6F4H), 64.0
(CH2), 33.4 (d, 1JCP = 34.5 Hz, tBu), 32.1 (d, br, 3JCP = 10.5 Hz;
Experimental Section
General Remarks. All manipulations were carried out under
an atmosphere of dry, O2-free N2 by employing an Innovative
Technology glovebox and a Schlenk vacuum line. Solvents were
purified with a Grubbs-type column system manufactured by
Innovative Technology and dispensed into thick-walled Schlenk
glass bombs equipped with Young-type Teflon valve stopcocks
(hexanes, toluene, CH2Cl2) or were dried over the appropriate
agents and distilled into the same kind of Young bombs
(C6H5Br). All solvents were thoroughly degassed after purifica-
tion (repeated freeze-pump-thaw cycles). Deuterated solvents
were dried over the appropriate agents, vacuum-transferred into
Young bombs, and degassed accordingly (C6D5Br, CD2Cl2).
CH2), 27.5 (tBu), 26.2 (d, 2JCP = 6.5 Hz, CH2), 15.4 (d, 1JCP
=
38.5 Hz, PCH2). 19F NMR (CD2Cl2): -134.4 (br, 6F, o-C6F4H),
-142.9 (m, 6F, m-C6F4H). 11B{1H} NMR (CD2Cl2): -2.8 (s).
31P NMR (CD2Cl2): 51.3 (dm, 1JPH = 447 Hz). Anal. Calcd for
C30H30BF12OP: C, 53.28; H, 4.47. Found: C, 52.92; H; 4.66.
2: yield 120 mg (89%). X-ray-quality crystals were grown
from CH2Cl2 at room temperature. 1H NMR (THF-d8): 8.09 (t,
3
3JHH = 8 Hz, CH), 7.65 (d, JHH = 8 Hz, CH), 4.68 (m, 2H,
CH2), 3.18 (t, 3JHH = 8 Hz, 2H, CH2), 2.74 (s, 6H, CH3), 1.90
(m, 2H, CH2), 1.62 (m, 2H, CH2). 13C{1H} NMR (THF-d8;
1
partial): 158.0, 150.1 (dm, JCF ≈ 241 Hz, C6F5), 145.7, 140.3
1
(dm, 1JCF ≈ 244 Hz, C6F5), 138.5 (dm, JCF ≈ 244 Hz, C6F5),
129.8, 65.4 (CH2), 55.5 (CH2), 30.2 (CH3), 28.7 (CH2), 22.0
(24) Evans, W. J.; Leman, J. T.; Ziller, J. W.; Khan, S. I. Inorg. Chem.
1996, 35, 4283–4291.
(25) Mommertz, A.; Leo, R.; Massa, W.; Harms, K.; Dehnicke, K. Z.
(CH2),n.o.(ipso-C6F5).19F NMR (THF-d8):-132.5 (d, 6F, 3JFF
=
21 Hz, o-C6F5), -163.3 (t, 3F, 3JFF= 21 Hz, p-C6F5), -166.6 (t,
6F, 3JFF = 19 Hz, m-C6F5). 11B NMR (THF-d8): -6.3 (s). Anal.
Calcd for C29H17BF15NO: C, 50.39; H, 2.48; N, 2.03. Found: C,
50.30; H, 2.66; N, 2.17.
Anorg. Allg. Chem. 1998, 624, 1647–1652.
(26) Guo, Z. Y.; Bradley, P. K.; Jordan, R. F. Organometallics 1992,
11, 2690–2693.
€
(27) Polamo, M.; Mutikainen, I.; Leskela, M. Acta Crystallogr., Sect.
C 1997, C53, 1036–1037.
(28) Gomez-Saso, M.; Mullica, D. F.; Sappenfield, E.; Stone,
F. G. A. Polyhedron 1996, 15, 793–801.
(29) Campbell, J. P.; Gladfelter, W. L. Inorg. Chem. 1997, 36, 4094–
4098.
(30) Chivers, T.; Schatte, G. Eur. J. Inorg. Chem. 2003, 3314–3317.
(31) Kunnari, S. M.; Oilunkaniemi, R.; Laitinen, R. S.; Ahlgren, M.
Dalton Trans. 2001, 3417–3418.
3: yield given above. 1H NMR (CD2Cl2): 7.55 (m, 3H, C6H5),
7.37 (m, 2H, C6H5), 4.26 (s, 2H, CH2), 3.84 (m, 2H, CH2), 3.24
(m, 2H, CH2), 2.90 (s, 6H, CH3), 2.04 (m, 2H, CH2), 1.64 (m, 2H,
CH2). 13C{1H} NMR (CD2Cl2; partial): 132.8, 131.9, 130.2
(C6H5), 126.4 (Cq), 69.2 (CH2), 66.9 (CH2), 63.9 (CH2), 50.2
(CH3), 28.2 (CH2), 22.2 (CH2). 19F NMR (CD2Cl2): -134.5 (m,
6F, o-C6F5), -162.8 (t, 3JFF = 20.1 Hz, 3F, p-C6F5), -166.8 (m,

5312 Organometallics, Vol. 29, No. 21, 2010
Birkmann et al.
6F, m-C6F5). 11B NMR (CD2Cl2): -3.0 (s, ν1/2 = 22 Hz). Anal.
Calcd for C31H21BF15NO: C, 51.76; H, 2.94; N, 1.95. Found: C,
51.38; H, 3.36; N, 2.14.
9: 1H NMR (toluene-d8): 3.17 (br, ν1/2 ≈ 3 Hz, CH2). 13C{1H}
NMR (toluene-d8): 147.9 (dm, 1JCF ≈ 245 Hz, C6F5), 141.3 (dm,
1JCF ≈ 255 Hz, C6F5), 137.7 (dm, 1JCF ≈ 248 Hz, C6F5), 114.3
(br m, i-C6F5), 70.2 (br, ν1/2 ≈ 28 Hz, CH2). 19F NMR (toluene-
d8): -133.1 (br, 2F, o-C6F5), -155.3 (m, 1F, p-C6F5), -163.6 (m,
2F, m-C6F5). 11B{1H} NMR (toluene-d8): 6.8 (ν1/2 ≈ 400 Hz).
4: yield 72 mg (0.096 mmol, 92%). 1H NMR (CD2Cl2): 7.34
(m, 2H, Ar H), 6.73 (m, 2H, Ar H), 4.28 (m, 2H, CH2), 3.42 (s,
6H, CH3), 3.19 (m, 2H, CH2), 3.04 (s, 6H, CH3), 1.63 (m, 2H,
CH2), 1.57 (m, 2H, CH2). 13C{1H} NMR (CD2Cl2; partial):
2
1H NMR (toluene-d8, 203 K): 3.28 (t, 3J ≈ J ≈ 12 Hz, OCH2),
150.9 (Cq), 147.9 (dm, 1JCF ≈ 238 Hz, C6F5), 138.3 (dm, 1JCF
≈
3.24 (d, 2J ≈ 12 Hz, BOCH2), 2.81 (d, 2J ≈ 12 Hz, OCH2), 2.63 (t,
1
2
246 Hz, C6F5), 136.5 (dm, JCH ≈ 242 Hz, C6F5), 131.5 (Cq),
120.4 (Ar C), 112.2 (Ar C), 70.5 (CH2), 63.9 (CH2), 54.9 (CH3),
39.8 (CH3), 27.9 (CH2), 23.0 (CH2), n.o. (i-C6F5). 19F NMR
(CD2Cl2): -134.4 (m, 2F, o-C6F5), -163.0 (t, 3JFF = 20.6 Hz,
1F, p-C6F5), -166.9 (m, 2F, m-C6F5). 11B NMR (CD2Cl2): -3.0
(s, ν1/2 = 20 Hz). Anal. Calcd for C32H24BF15N2O: C, 51.36; H,
3.23; N, 3.74. Found: C, 50.97; H, 3.23; N, 3.35.
3J ≈ J ≈ 12 Hz, BOCH2). 13C{1H} NMR (toluene-d8, 203 K):
75.5 (ν1/2 ≈ 12 Hz, BOCH2), 64.4 (ν1/2 ≈ 15 Hz, OCH2). n.a.
(C6F5). 19F NMR (toluene-d8, 203 K): -130.9 (o), -152.5 (t,
3JFF = 20.0 Hz, p), -163.2 (m) (C6F5A), -131.1 (o), -156.2 (p),
-163.0 (m) (C6F5B), -137.7 (o), -156.3 (p), -163.1 (m) (C6F5C).
1,4-dioxane/B(C6F5)3 (ca. 1:2): 1H NMR (toluene-d8): 3.17 (br,
ν1/2 ≈ 5 Hz, CH2). 13C{1H} NMR (toluene-d8): 148.1 (dm,
1JCF ≈ 247 Hz, C6F5), 142.6 (dm, 1JCF ≈ 261 Hz, C6F5), 137.9
Synthesis of Me3N(CH2)4OB(C6F5)3 (5), Et3N(CH2)4OB-
(C6F5)3 (6), Me2N(CH2)2NMe2(CH2)4OB(C6F5)3 (7), tBuHN-
(CH2)2NHtBu(CH2)4OB(C6F5)3 (8). The preparation of 5 is
detailed: 10 μL of thf was added to B(C6F5)3 (50 mg, 0.098 mmol)
dissolved in 0.5 mL of BrC6D5, and the mixture was stirred for
5 min. Tetramethylmethanediamine (9 mg, 0.102 mmol) was
added to the solution, and the reaction mixture was stirred for
4 h at room temperature. A 2 mL portion of pentane was added
to the solution to yield a white precipitate. Single crystals of 5
were obtained from a concentrated CH2Cl2 solution and diffu-
sion of pentane.
(dm, 1JCF ≈ 255 Hz, C6F5), 113.9 (br m, i-C6F5), 70.5 (br, ν1/2
≈
25 Hz, CH2). 19F NMR (toluene-d8): -133.8 (br, 2F, o-C6F5),
-150.3 (br, 1F, p-C6F5), -162.8 (m, 2F, m-C6F5). 11B{1H} NMR
(toluene-d8): 31 (ν1/2 ≈ 1400 Hz).
Synthesis of tBu3P(CH2)2O(CH2)2OB(C6F5)3 (10), C6H5CH2-
NMe2(CH2)2O(CH2)2OB(C6F5)3 (11), ((tBuN)2C3H2)(CH2)2-
O(CH2)2OB(C6F5)3 (12), and Me2NC6H4NMe2(CH2)2O(CH2)2-
OB(C6F5)3 (13). These compounds were prepared in a similar
fashion, and thus only the preparation of 11 is detailed: 10 μL of
1,4-dioxane was added to a solution of 10 mg (0.074 mmol) of
N,N-dimethylbenzylamine and 38 mg (0.074 mmol) of B(C6F5)3
in 1 mL of C6D5Br, and the mixture was heated to 50 °C until
NMR control showed full conversion (∼12 h). After layering
with5 mLofhexaneandstoring the solutionat -39 °C for several
days, 46 mg (0.063 mmol, 85%) of white powder precipitated.
Single crystals were grown from slow evaporation of a concen-
trated dichloromethane solution at room temperature.
5: yield 34 mg (0.053 mmol, 54%). 1H NMR (CD2Cl2): 3.88
(m, 2H, CH2), 3.25 (m, 2H, CH2), 3.08 (s, 9H, CH3), 1.97 (m, 2H,
CH2), 1.65 (m, 2H, CH2). 13C{1H} NMR (CD2Cl2; partial):
1
1
147.9 (dm, JCF ≈ 236 Hz, C6F5), 138.3 (dm, JCF ≈ 245 Hz,
C6F5), 136.5 (dm, 1JCF ≈ 248 Hz, C6F5), 68.0 (CH2), 63.6 (CH2),
53.5 (CH2), 27.6 (CH2), 22.2 (CH2), n.o. (ipso-C6F5). 19F NMR
(CD2Cl2): -134.6 (m, 2F, o-C6F5), -162.9 (t, 3JFF = 20.0 Hz,
1F, p-C6F5), -166.8 (m, 2F, m-C6F5). 11B{1H} NMR (CD2Cl2):
-3.0 (s, ν1/2 = 15 Hz).
10: yield 34 mg (0.042 mmol, 86%). 1H NMR (C6D5Br): 4.05
(m, 2H, CH2), 3.71 (br m, 2H, CH2), 3.47 (br m, 2H, CH2), 1.93
3
6:yield58 mg(0.085mmol,87%). 1H NMR(CD2Cl2): 3.59 (m,
2H, CH2), 3.23 (m, 2H, CH2), 3.16 (q, 3JHH = 7.4 Hz, 6H, CH3),
1.80 (m, 2H, CH2), 1.66 (m, 2H, CH2), 1.29 (t, 3JHH = 7.4Hz, 9H,
CH3). 13C{1H} NMR (CD2Cl2; partial): 148.0 (dm, 1JCF ≈ 240
(m, 2H, CH2), 0.87 (d, JPH = 14.2 Hz, 27H, tBu). 19F NMR
(C6D5Br): -133.1 (m, 6F, o-C6F5), -161.9 (t, 3JFF = 21.0 Hz,
3F, p-C6F5), -165.6 (m, 6F, m-C6F5). 11B NMR (C6D5Br): -2.9
(s, ν1/2 = 26 Hz). 31P{H} NMR (C6D5Br): 49.4 (s). Anal. Calcd
for C31H21BF15NO2: C, 50.89; H, 4.40. Found: C, 50.30; H, 4.51.
Hz, C6F5), 138.3 (dm, 1JCF ≈ 245 Hz, C6F5), 136.5 (dm, 1JCF
≈
1
248 Hz, C6F5), 63.6 (CH2), 58.1 (CH2), 52.7 (CH3), 28.0 (CH2),
20.5 (CH2),7.0(CH2), n.o. (ipso-C6F5).19FNMR(CD2Cl2):-133.5
(m, 2F, o-C6F5), -162.2 (t, 3JFF = 20.5 Hz, 1F, p-C6F5), -166.1
(m, 2F, m-C6F5). 11B NMR (CD2Cl2): -3.0 (s, ν1/2 = 20 Hz).
7: yield 56 mg (0.080 mmol, 82%). 1H NMR (CD2Cl2): 3.80
(m, 2H, CH2), 3.26 (m, 4H, CH2), 3.11 (s, 6H, CH3), 2.71 (m, 2H,
CH2), 2.27 (s, 6H, CH3), 1.94 (m, 2H, CH2), 1.65 (m, 2H, CH2).
11: yield given above. H NMR (CD2Cl2): 7.58 (m, 1H, p-
C6H5), 7.50 (m, 2H, o-C6H5), 7.35 (m, 2H, m-C6H5), 4.40 (s, 2H,
CH2), 4.25 (br, 2H, CH2), 3.68 (m, 2H, CH2), 3.42 (m, 2H, CH2),
3.29 (m, 2H, CH2), 3.02 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2;
partial): 133.1 (m-C6H5), 131.8 (p-C6H5), 130.0 (o-C6H5), 126.6
(Cq), 73.9 (CH2), 70.8 (CH2), 65.3 (CH2), 65.1 (CH2), 65.0
(CH2), 51.9 (CH3). 19F NMR (CD2Cl2): -134.5 (m, 6F, o-C6F5),
-162.7 (t, 3JFF = 21.0 Hz, 3F, p-C6F5), -166.4 (m, 6F, m-C6F5).
11B NMR (CD2Cl2): -2.9 (s, ν1/2 = 22 Hz). Anal. Calcd for
C31H21BF15NO2: C, 50.64; H, 2.80; N, 1.90. Found: C, 50.38; H,
2.87; N, 1.92.
1
13C{1H} NMR (CD2Cl2; partial): 147.9 (dm, JCF ≈ 239 Hz,
C6F5), 138.3 (dm, 1JCF ≈ 245 Hz, C6F5), 136.5 (dm, 1JCF ≈ 247
Hz, C6F5), 67.0 (CH2), 63.5 (CH2), 60.9 (CH2), 53.4 (CH2), 51.3
(CH3), 44.7 (CH3), 27.8 (CH2), 21.6 (CH2), n.o. (i-C6F5). 19F
NMR (CD2Cl2): -134.5 (m, 2F, o-C6F5), -163.0 (t, 3JFF = 20.6
Hz, 1F, p-C6F5), -166.8 (m, 2F, m-C6F5). 11B NMR (CD2Cl2):
-3.0 (s, ν1/2 = 20 Hz).
12: yield 26 mg (0.033 mmol, 68%). 1H NMR (CD2Cl2): 7.34
(s, 2H, dCH), 4.05 (t, 3JHH = 6.8 Hz, 2H, CH2), 3.64 (t, 3JHH
6.8 Hz, 2H, CH2), 3.60 (br, 2H, CH2), 3.25 (br, 2H, CH2), 1.74 (s,
=
8: yield 56 mg (0.074 mmol, 76%). 1H NMR (CD2Cl2): 4.42
(br s, 2H, N-H), 3.39 (br, 2H, CH2), 3.26 (m, 2H, CH2), 3.11
(br, 2H, CH2), 2.96 (br, 2H, CH2), 1.95 (m, 2H, CH2), 1.60 (m,
2H, CH2), 1.40 (s, 9H, CH3), 1.16 (s, 9H, CH3). 13C{1H} NMR
(CD2Cl2; partial): 147.9 (dm, 1JCF ≈ 237 Hz, C6F5), 138.4 (dm,
18H, tBu). 13C{1H} NMR (CD2Cl2; partial): 147.9 (dm, 1JCF
≈
1
235 Hz, C6F5), 138.2 (dm, JCF ≈ 236 Hz, C6F5), 136.4 (dm,
1JCF ≈ 245 Hz, C6F5), 145.2 (Cq), 119.2 (dCH), 73.5 (CH2), 67.9
(CH2), 64.4 (CH2), 63.5 (Cq-tBu), 30.2 (tBu), 27.6 (CH2), n.o.
(i-C6F5). 19F NMR (CD2Cl2): -134.0 (m, 6F, o-C6F5), -163.5
1JCF ≈ 243 Hz, C6F5), 138.4 (dm, JCF ≈ 243 Hz, C6F5), 64.1
(t, JFF = 20.8 Hz, 3F, p-C6F5), -167.1 (m, 6F, m-C6F5). 11B
1
3
(Cq), 63.1 (CH2), 52.9 (CH2), 52.0 (Cq), 50.6 (CH2), 37.7 (CH2),
28.5 (CH2), 28.4 (CH3), 25.8 (CH2), 25.4 (CH3), n.o. (i-C6F5).
NMR (CD2Cl2): -3.0 (s, ν1/2 = 18 Hz). Anal. Calcd for C31H21-
BF15NO2: C, 50.72; H, 3.74; N, 3.59. Found: C, 50.47; H, 3.51;
N, 3.61.
19F NMR (CD2Cl2): -134.0 (m, 2F, o-C6F5), -162.9 (t, 3JFF
=
13: yield 49 mg (0.065 mmol, 66%). 1H NMR (CD2Cl2): 7.22
(m, 2H, C6H4), 6.62 (m, 2H, C6H4), 3.79 (m, 2H, CH2), 3.70 (m,
2H, CH2), 3.49 (m, 2H, CH2), 3.42 (s, 6H, CH3), 3.18 (m, 2H,
CH2), 2.93 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2; partial): 151.4
(Cq), 148.4 (dm, 1JCF ≈ 235 Hz, C6F5), 138.9 (dm, 1JCF ≈ 235
Hz, C6F5), 137.0 (dm, 1JCF ≈ 247 Hz, C6F5), 132.9 (Cq), 120.9
(C6H4), 112.5 (C6H4), 74.9 (CH2), 71.2 (CH2), 66.2 (CH2), 64.6
20.5 Hz, 1F, p-C6F5), -166.7 (m, 2F, m-C6F5). 11B NMR (CD2-
Cl2): -2.9 (s, ν1/2 = 20 Hz). Anal. Calcd for C32H32BF15N2O: C,
50.81; H, 4.26; N, 3.70. Found: C, 50.67; H, 4.33; N, 3.49.
Generation of (O((CH2)2)2O)B(C6F5)3 (9). 1,4-Dioxane (11
mg, 0.124 mmol, 1.1 equiv) and B(C6F5)3 (58 mg, 0.113 mmol)
were mixed in toluene-d8, and the product was characterized via
NMR spectroscopy.

Article
Organometallics, Vol. 29, No. 21, 2010 5313
(CH2), 55.9 (CH3), 40.2 (CH3), n.o. (ipso-C6F5). 19F NMR
(CD2Cl2): -133.4 (m, 6F, o-C6F5), -162.0 (t, 3JFF = 20.7 Hz,
3F, p-C6F5), -165.9 (m, 6F, m-C6F5). 11B NMR (CD2Cl2): -2.9
(s, ν1/2 = 19 Hz). Anal. Calcd for C32H24BF15N2O2: C, 50.28; H,
3.16; N, 3.67. Found: C, 49.77; H, 3.20; N, 3.61.
tBu3P(CH2)2S(CH2)2OB(C6F5)3 (16). A 10 μL portion of 1,4-
thioxane was added to a solution of 10 mg (0.049 mmol) of tri-
tert-butylphosphine and 25 mg (0.049 mmol) of B(C6F5)3 in
0.7 mL of C6D5Br, and the mixture was heated to 50 °C until
NMR control showed full conversion (∼12 h). After it was
layered with 1 mL of hexane, the solution was stored at -39 °C
for several days to yield a white solid (15 mg, 0.018 mmol, 37%) .
The compound was purified through crystallizations. Single
crystals were grown from slow evaporation of a concentrated
dichloromethane solution at -39 °C. 1H NMR (CD2Cl2): 3.48
Synthesis of (C5H3Me2N)(CH2)2O(CH2)2OB(C6F5)3 (14). A 5
mg portion (0.049 mmol) of 2,6-lutidine was added to a solution
of 25 mg (0.049 mmol) of B(C6F5)3 in 0.7 mL of BrC6D5 in a
J. Young NMR tube. The solution was stirred for 10 min, and
then 5 μL of 1,4-dioxane was added and the mixture was heated
to 50 °C for 2 days. The reaction was monitored by NMR
spectroscopy and showed formation of the Lewis 2,6-lutidine-
borane adduct and ring-opening product in a ratio of approxi-
mately 5:2. The product was purified by repetitive recrystalliza-
tion and was isolated as a white powder in 24% yield (8 mg,
0.012 mmol). Single crystals were obtained from a concentrated
(t, 3JHH = 5.7 Hz, 2H, CH2), 3.33 (m, 2H, CH2), 2.77 (t, 3JHH
=
5.7 Hz, 2H, CH2), 2.47 (m, 2H, CH2), 1.59 (d, 3JPH = 14.1 Hz,
2H, tBu). 13C{1H} NMR (CD2Cl2; partial): 148.0 (dm, 1JCF
≈
1
237 Hz, C6F5), 138.3 (dm, JCF ≈ 237 Hz, C6F5), 136.5, (dm,
1JCF ≈ 246 Hz, C6F5), 66.8 (CH2), 39.4 (d, 1JPC = 28.4 Hz, Cq-
tBu), 34.6 (CH2), 29.5 (br, tBu), 26.4 (d, 2JPC = 6.4 Hz, CH2),
1
1
dichloromethane solution layered with hexane at -39 °C. H
20.4 (d, JPC = 29.0 Hz, PCH2), n.o. (i-C6F5) . 19F NMR
3
NMR (CD2Cl2): 8.15 (t, JHH = 7.9 Hz, 1H, p-CH), 7.65 (d,
(CD2Cl2): -134.0 (m, 6F, o-C6F5), -163.3 (t, 3JFF = 20.4 Hz,
3F, p-C6F5), -166.8 (m, 6F, m-C6F5). 11B NMR (CD2Cl2):
-2.90 (s, ν1/2 = 17.3 Hz). 13P{1H} NMR (CD2Cl2): 50.2 (s).
Anal. Calcd for C32H33BF15OPS*1/2CH2Cl2: C, 48.13; H, 4.21.
Found: C, 48.72; H, 4.40.
3JHH = 7.9 Hz, 2H, m-CH), 4.72 (t, 3JHH = 5.2 Hz, 2H, CH2),
4.32 (t, 3JHH = 4.7 Hz, 2H, CH2), 3.57 (m, 2H, CH2), 3.16 (br m,
2H, CH2), 2.93 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2; partial):
156.4 (Cq-lutidine), 144.2, 128.0 (Ar C-lutidine), 73.2 (CH2),
68.4 (CH2), 64.6 (CH2), 53.8 (CH2), 22.0 (CH3-lutidine), n.o.
(C6F5). 19F NMR (CH2Cl2): -134.2 (m, 6F, o-C6F5), -163.2 (t,
3JFF = 20.7 Hz, 3F, p-C6F5), -166.9 (m, 6F, m-C6F5). 11B
NMR (CH2Cl2): -3.0 (s, ν1/2 = 20 Hz). Anal. Calcd for C31H21-
BF15NO2: C, 49.25; H, 2.42; N, 1.98. Found: C, 48.75; H, 2.49;
N, 2.13.
Synthesis of C6H5CH2NMe2(CH2)2S(CH2)2OB(C6F5)3 (17)
and Me2NC6H4NMe2(CH2)2S(CH2)2OB(C6F5)3 (18). These two
compounds were prepared in a similar fashion and thus only the
preparation of 17 is detailed: after a solution of 50 mg (0.370 mmol)
of N,N-dimethylbenzylamine, 190 mg (0.370 mmol) of B(C6F5)3
and 50 μL of 1,4-thioxane in 5 mL of bromobenzene was stirred
at 80 °C overnight, all volatiles were removed in vacuo. The
remaining oil was dissolved in 1 mL of dichloromethane, before
∼50 mL of hexanes was added to yield a white powder. This was
filtered off and dried in vacuo (165 mg, 0.220 mmol, 60%).
Synthesis of (C6F5)3B(SC4H8O) (15). A 5.0 μL portion of 1,4-
thioxane was added to a solution of 51 mg (0.1 mmol) of
B(C6F5)3 in 0.7 mL of BrC6H5, and the mixture was stirred at
room temperature for 30 min. All volatile materials were
removed, and the residue was dissolved in CD2Cl2 and analyzed
by NMR spectroscopy. The solution was transferred into a vial,
layered with hexane, and stored at -39 °C overnight to give
colorless crystals in 92% yield (57 mg, 0.092 mmol). 1H NMR
(CD2Cl2): 4.09 (m, 2H, CH2), 2.67 (m, 2H, CH2). 13C{1H} NMR
(CD2Cl2; partial): 148.1 (dm, 1JCF ≈ 234 Hz, C6F5), 141.2 (dm,
1
17: H NMR (CD2Cl2): 7.52 (m, 2H, C6H5), 7.28 (m, 3H,
C6H5), 4.17 (s, 2H, CH2), 3.73 (m, 2H, CH2), 3.53 (m, 2H, CH2),
3.26 (m, 2H, CH2), 2.82 (s, 6H, CH3), 2.75 (m, 2H, CH2).
1
13C{1H} NMR (CD2Cl2; partial): 148.3 (dm, JCF ≈ 245 Hz,
1
C6F5), 136.9 (dm, JCF ≈ 248 Hz, C6F5), 132.7, 131.8, 130.1
(C6H5), 125.8 (Cq), 69.2 (CH2), 68.3 (CH2), 66.9 (CH2), 50.2
(CH3), 35.6 (CH2), 25.2 (CH2). 19F NMR (CD2Cl2): -134.1 (m,
6F, o-C6F5), -162.3 (t, 3JFF = 20.0 Hz, 3F, p-C6F5), -166.2 (m,
6F, m-C6F5). 11B NMR (CD2Cl2): -2.9 (s, ν1/2 = 29 Hz). Anal.
Calcd for C31H21BF15NOS: C, 49.55; H, 2.82; N, 1.86; Found C,
49.26; H, 2.97; N, 2.01.
1
1JCF ≈ 236 Hz, C6F5), 137.5 (dm, JCF ≈ 243 Hz, C6F5), 67.8
(CH2), 30.6 (CH2), n.o. (i-C6F5). 19F NMR (CD2Cl2): -130.0
(d, 3JFF = 21.0 Hz, 6F, o-C6F5), -154.2 (t, 3JFF = 21.0 Hz, 3F,
=
p-C6F5),-162.8 (m, 6F, m-C6F5).11BNMR(CD2Cl2):4.0(s,ν1/2
245 Hz). Anal. Calcd for C31H21BF15NO2: C, 42.88; H, 1.31.
Found: C, 42.56; H, 1.02. Additional NMR experiments: 1,4-
thioxane (10 mg, 0.096 mmol) and B(C6F5)3 (49 mg, 0.096 mmol)
were mixed in toluene-d8 and characterized via NMR spectros-
copy.
18: yield 55 mg (0.070 mmol, 72%). 1H NMR (CD2Cl2): 7.26
(m, 2H, C6H4), 6.75 (m, 2H, C6H4), 4.20 (m, 2H, CH2), 3.47 (m,
2H, CH2), 3.32 (s, 6H, CH3), 3.04 (s, 6H, CH3), 2.75 (m, 2H,
CH2), 2.70 (m, 2H, CH2). 13C{1H} NMR (CD2Cl2; partial):
15: 1H NMR (toluene-d8): 3.18 (m, OCH2), 1.85 (m, SCH2).
13C{1H} NMR (toluene-d8): 148.6 (dm, 1JCF ≈ 254 Hz, C6F5),
151.0 (Cq, C6H4), 147.9 (dm, 1JCF ≈ 237 Hz), 138.4 (dm, 1JFC
≈
1
249 Hz), 136.6 (dm, JCF ≈ 247 Hz), 130.9 (Cq, C6H4), 120.2
(C6H4), 112.2 (C6H4), 70.6 (CH2), 67.2 (CH2), 54.8 (CH3), 39.8
(CH3), 35.9 (CH2), 25.9 (CH2), n.o. (ipso-C6F5). 19F NMR
(CD2Cl2): -134.1 (m, 6F, o-C6F5), -162.5 (t, 3JFF = 20.6 Hz,
3F, p-C6F5), -166.4 (m, 6F, m-C6F5). 11B NMR (CD2Cl2): -2.9
(s, ν1/2 = 22 Hz). Anal. Calcd for C32H24BF15N2OS: C, 49.25;
H, 3.10; N, 3.59. Found: C, 48.87; H, 2.97; N, 3.59.
1
1
141.3 (dm, JCF ≈ 254 Hz, C6F5), 137.8 (dm, JCF ≈ 255 Hz,
C6F5), 113.9 (br m, i-C6F5), 67.8 (br, ν1/2 ≈ 11 Hz, OCH2), 30.0
(br, ν1/2 ≈ 6 Hz, SCH2). 19F NMR (toluene-d8): -131.4 (m, 2F,
o-C6F5), -154.3 (m, 1F, p-C6F5), -163.4 (m, 2F, m-C6F5). 11
B
NMR (toluene-d8): 2.4 (ν1/2 ≈ 330 Hz).
1
15-O: H NMR (toluene-d83, 183 K): 3.98 (m, 1H, BOCH2),
3
0
2.90 (m, 1H, BOCH2 ), 2.72 (t, J ≈ J ≈ 11 Hz, 1H, SCH2), 1.21
Synthesis of C5H3Me2N(CH2)2S(CH2)2OB(C6F5)3 (19). A 5
mg (0.049 mmol) portion of 2,6-lutidine was added to a solution
of 25 mg (0.049 mmol) of B(C6F5)3 in 0.7 mL of BrC6D5 in a J.
Young NMR tube. The solution was stirred for 10 min, and then
5 μL of 1,4-thioxane was added and the mixture was heated to
80 °C for 2 days. The reaction was monitored by NMR spectros-
copy and showed formation of the FLP adduct and ring-open-
ing product in a ratio of approximately 3:1. The product was
purified through crystallization and was isolated as a colorless
solid powder in 20% yield (7 mg, 0.010 mmol). Single crystals
were obtained from a concentrated bromobenzene solution layered
with pentane at -39 °C. 1H NMR (CD2Cl2): 8.19 (t, 3JHH = 7.6
Hz, 1H, p-CH), 7.65 (d, 3JHH = 7.6 Hz, 2H, m-CH), 4.77 (m, 2H,
CH2), 3.52 (m, 2H, CH2), 3.44 (br m, 2H, CH2), 2.92 (s, 6H,
CH3 lutidine), 2.74 (br m, 2H, CH2). 13C{1H} NMR (CD2Cl2;
(m, 1H, SCH2 ). 13C{1H} NMR (from ghsqc experiment; to-
0
luene-d8, 183 K): 78.3 (BOCH2), 26.1 (SCH2).
3
15-S: 3.09 (d, 3J ≈ 11 Hz, 3H, OCH2), 2.44 (t, 3J ≈ J ≈ 11 Hz,
3H, OCH2 ), 1.61 (m, 3H, BSCH2), 1.12 (m, 3H, BSCH2 ). 13C-
0
0
{1H} NMR (from ghsqc experiment; toluene-d8, 183 K): 64.7
(OCH2), 30.8 (SCH2). 1,4-thioxane/B(C6F5)3 (1: 2): H NMR
1
(toluene-d8): 3.11 (m, OCH2), 1.80 (m, SCH2). 13C{1H} NMR
(toluene-d8): 148.3 (dm, 1JCF ≈ 254 Hz, C6F5), 144.0 (dm, 1JCF
≈
1
254 Hz, C6F5), 137.7 (dm, JCF ≈ 240 Hz, C6F5), 113.9 (br m,
i-C6F5), 67.7 (br, ν1/2 ≈ 5 Hz, OCH2), 30.6 (br, ν1/2 ≈ 4 Hz, SCH2).
19F NMR (toluene-d8): -130.7 (m, 2F, o-C6F5), -147.4 (br, 1F,
p-C6F5), -162.4 (m, 2F, m-C6F5). 11B NMR (toluene-d8): 39.4
(ν1/2 ≈1000 Hz). 1H NMR (toluene-d8,203K):3.45(br,1H,OCH2),
0
0
2.46 (br, 1H, OCH2 ), 2.09 (br, 1H, SCH2), 1.14 (br, 1H, SCH2 ).

5314 Organometallics, Vol. 29, No. 21, 2010
Birkmann et al.
Table 1. Crystallographic Data
1
2
3
4
5
6
7
formula
C30H30BF12OP C29H17BF15NO C31H21BF15NO C32H24BF15N2O C25H17BF15NO C62H50B2F30N2O2 C28H24BF15N2O
formula wt
cryst syst
space group
676.32
691.25
orthorhombic
Pna21
17.4334(9)
10.6793(6)
14.4679(8)
90.00
90.00
90.00
2693.6(3)
4
150(2)
1.705
0.0205
0.175
35 400
13 352
424
719.30
monoclinic
P21/c
10.3639(9)
18.5069(15)
15.0807(10)
90.00
92.054(4)
90.00
2890.7(4)
4
150(2)
1.653
0.0516
0.166
25 095
6612
444
748.34
triclinic
P1
643.21
triclinic
P1
1526.57
triclinic
P1
700.30
monoclinic
P21/c
11.0576(6)
12.6641(6)
20.5009(9)
90.00
94.936(2)
90.00
2860.2(2)
4
150(2)
1.626
0.0406
0.166
23 948
6521
428
orthorhombic
P212121
9.1959(6)
15.6009(10)
20.3479(11)
90.00
90.00
90.00
2919.2(3)
4
296(2)
˚
a (A)
10.4026(12)
11.8821(13)
13.3039(16)
93.177(5)
108.859(6)
97.387(5)
1535.0(3)
2
149(2)
1.619
0.0272
0.161
25 998
10.1478(10)
11.5115(12)
13.3066(15)
93.857(7)
106.083(7)
107.488(6)
1405.2(2)
2
150(2)
1.520
0.0567
0.161
35 230
10.0758(6)
13.0173(8)
13.2239(7)
67.466(3)
80.503(3)
83.416(3)
1577.55(16)
1
150(2)
1.607
0.0315
0.786
35 031
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
T (K)
D (g/cm3)
R(int)
1.539
0.0397
0.196
μ (cm-1
)
total no. of data 58 263
no. of obsd data 8006
no. of variables 416
7031
486
9777
391
9534
454
R (>2σ)
Rw
GOF
0.0301
0.0730
1.021
0.0389
0.1146
1.046
0.0436
0.0988
1.011
0.0459
0.1211
1.039
0.0574
0.1493
0.957
0.0497
0.1408
1.046
0.0403
0.1044
1.019
10 0.5C6H5Br
3
11 0.5CH2Cl2
3
12
14
15
18
19 C6H5Br
3
formula
C
37H34.5BBr0.5
F15O2P
-
C
31.5H22-
BClF15NO2
C33H28BF15
N2O2
780.38
monoclinic
Cc
20.136(3)
18.474(3)
9.9822(15)
90.00
112.825(4)
90.00
3422.5(9)
4
150(2)
1.514
0.0503
0.150
10 623
5735
475
-
C29H17BF15
NO2
707.25
monoclinic
P21/n
10.7712(6)
17.1693(10)
15.3473(9)
90.00
101.361(3)
90.00
-
C22H8-
BF15OS
616.15
monoclinic
P21/n
11.3535(9)
9.8755(8)
19.2199(15)
90.00
94.300(4)
90.00
2148.9(3)
4
150(2)
1.905
0.0375
0.298
18 297
4913
361
C
32H24BF15
N2OS
-
C
35H22-
BBrF15NOS
formula wt
cryst syst
space group
880.90
monoclinic
P21/n
15.6780(6)
13.9752(5)
18.5333(7)
90.00
110.439(2)
90.00
3805.1(2)
4
150(2)
1.538
0.0782
0.705
58 814
8758
523
0.0769
0.2348
1.019
777.76
triclinic
P1
780.40
triclinic
P1
880.32
monoclinic
P21/c
12.5351(3)
28.6052(6)
10.0729(2)
90.00
106.3280(10)
90.00
3466.16(13)
4
150(2)
˚
a (A)
10.8022(11)
12.5626(12)
12.7031(12)
72.288(5)
89.924(5)
74.042(4)
1572.5(3)
2
150(2)
1.643
0.0375
0.244
35 421
10.385(9)
11.969(9)
13.687(11)
92.10(4)
108.09(4)
95.89(3)
1604(2)
2
150(2)
1.615
0.0757
0.220
24 565
7218
473
0.0498
0.1742
0.899
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
2782.6(3)
4
150(2)
T (K)
D (g/cm3)
R(int)
1.688
1.687
0.0527
0.174
24 428
6282
435
0.0439
0.1071
1.007
0.0477
1.359
35 796
8946
498
0.0449
0.1044
1.023
μ (cm-1
)
total no. of data
no. of obsd data
no. of variables
R (>2σ)
Rw
GOF
9501
498
0.0586
0.2037
0.951
0.0628
0.1596
1.008
0.0360
0.0874
1.021
partial): 155.9 (ipso-C lutidine), 147.0 (dm, 1JCF ≈ 235 Hz, C6F5),
144.5 (C Ar lutidine), 138.3 (dm, 1JCF ≈ 237 Hz, C6F5), 136.0,
(dm, 1JCF ≈ 244 Hz, C6F5), 128.3 (C Ar lutidine), 67.0 (CH2),
54.1 (CH2), 34.9 (CH2), 30.1 (CH2), 21.7 (CH3 lutidine). 19F
NMR (CD2Cl2): -134.2 (m, 6F, o-C6F5), -162.9 (t, 3JFF = 20.4
Hz, 3F, p-C6F5), -166.8 (m, 6F, m-C6F5). 11B NMR (CD2Cl2):
-3.0 (s, ν1/2 = 20 Hz). Anal. Calcd for C31H21BF15NOS*
1/2C6H5Br: C, 47.93; H, 2.45; N, 1.75. Found: C, 47.49; H,
2.53; N, 1.92.
XS and refined by full-matrix least squares on F2 using XL as
implemented in the SHELXTL suite of programs.32 All non-
hydrogen atoms were refined anisotropically. Carbon-bound
hydrogen atoms were placed in calculated positions using an
appropriate riding model and coupled isotropic temperature
factors. Crystal data for compounds 1-7, 10 0.5C6H5Br, 11
3
3
0.5CH2Cl2, 12, 14, 15, 18, and 19 C6H5Br are given in Table 1.
3
Results and Discussion
X-ray Data Collection, Reduction, Solution, and Refinement.
Single crystals were mounted in thin-walled capillaries either
placed under an atmosphere of dry N2 in a glovebox and flame-
sealed or coated in Paratone-N oil. The data were collected using
the SMART software package on a Siemens SMART System
CCD diffractometer using a graphite monochromator with Mo
Noting that sterically hindered phosphines in combination
with B(C6F5)3 have been previously19 shown to effect THF
ring-opening, we probed the corresponding reaction of the
34
borane B(p-C6F4H)3 with tBu2PH in THF. The species
tBu2(H)P(CH2)4OB(p-C6F4H)3 (1) was obtained in 87%
yield. The 31P NMR signal at 51.3 ppm exhibited P-H
coupling of about 447 Hz, consistent with the formation of
a phosphonium center. The 19F NMR data showed signals at
˚
KR radiation (λ = 0.710 73 A). A hemisphere of data was
collected in 1448 frames with 10 s exposure times unless other-
wise noted. Data reduction was performed using the SAINT
software package and an absorption correction applied using
SADABS. The structures were solved by direct methods using
(33) Geier, S. J.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 3476–
3477.
(32) Sheldrick, G. M. SHELXTL; Bruker AXS Inc., Madison, WI,
(34) Ullrich, M.; Lough, A. J.; Stephan, D. W. J. Am. Chem. Soc.
2009, 131, 52–53.
2000.

Article
Organometallics, Vol. 29, No. 21, 2010 5315
Figure 1. POV-ray depiction of 1. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
Scheme 2. Synthesis of 1-8a
Figure 2. POV-ray depiction of 2. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
a Note: the base used in the formation of 5 was CH2(NMe2)2.
-134.4 and -142.9 ppm, while the 11B{1H} resonance was
observed at -2.8 ppm, as expected for the borate fragment.
Crystallographic data (Figure 1) confirmed this interpreta-
tion. It is noted that, in the absence of THF, the combination
of B(C6F5)3 and tBu2PH has been previously shown to give
tBu2(H)P(C6F4)BF(C6F5)2 from nucleophilic attack by the
phosphine at the para position of one of the fluoroarene
rings.35 Thus, the inclusion of protons in the para positions
of the borane precludes such substitution.
Figure 3. POV-ray depiction of 3. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; P, orange.
To broaden the scope of such ring-opening reactions, we
considered related reactions of sterically encumbered N-bases.
In this regard, we previously communicated that the reaction
of 2,6-lutidine with a THF solution of B(C6F5)3 led to the
formation of the THF-ring-opening product (C5H3Me2N)-
(CH2)4OB(C6F5)3 (2), as evidenced by NMR and X-ray
crystallographic data (Scheme 2, Figure 2).33 The reactions
of N,N-dimethylbenzylamine with a THF solution of B(C6F5)3
were performed. Following workup the new species 3 was
isolated in 81% yield. 1H NMR data showed five methylene
resonances at 4.26, 3.84, 3.24, 2.04, and 1.64 ppm consistent
with the incorporation of the amine and ring-opening of a
THF molecule. 19F and 11B NMR spectral data were con-
sistent with the formation of a borate moiety, and thus 3 was
formulated as C6H5CH2NMe2(CH2)4OB(C6F5)3. Crystals
suitable for X-ray diffraction analysis were obtained from
CH2Cl2/hexane. The subsequent analysis confirmed the pro-
posed formulation of 3 (Figure 3). The B-O bond distance of
Figure 4. POV-ray depiction of 4. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
The corresponding reaction of N,N,N0,N0-tetramethyl-p-
phenylenediamine with B(C6F5)3 and THF gave Me2NC6-
H4NMe2(CH2)4OB(C6F5)3 (4) in 92% yield (Scheme 2). 19
F
and 11B NMR spectra were consistent with the formation of
a borate moiety. Four methylene resonances at 4.28, 3.19,
1.63, and 1.57 ppm were detected in the 1H NMR data and
are consistent with the ring-opening of a THF molecule.
Single crystals suitable for X-ray diffraction analysis (Figure 4)
confirmed the proposed formulation. The corresponding
reactions of B(C6F5)3(THF) with N,N,N0,N0-tetramethyl-
methanediamine, triethylamine, N,N,N0,N0-tetramethyletha-
nediamine, and N,N0-di-tert-butylethanediamine in C6D5Br
at 25 °C gave the corresponding ring-opened products 5-8
in 54, 87, 82, and 76% yields, respectively (Scheme 2). The
˚
1.462(3) A was similar to that seen in the phosphine THF-
ring-opened product 1 and in 2. The N-C distances were
unexceptional.
(35) Welch, G. C.; Cabrera, L.; Chase, P. A.; Hollink, E.; Masuda,
J. D.; Wei, P.; Stephan, D. W. Dalton Trans. 2007, 3407–3414.

5316 Organometallics, Vol. 29, No. 21, 2010
Birkmann et al.
Figure 7. POV-ray depiction of 7, Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
Figure 5. POV-ray depiction of 5. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
The combination of 1,4-dioxane and B(C6F5)3 in a ca. 1.1:1
ratio afforded formation of the (O(CH2CH2)2O)B(C6F5)3
adduct 9. At 25 °C only one broad methylene resonance was
observed (δ(1H) 3.17, δ(13C) 70.2), consistent with a fast
exchange of the borane, involving both oxygen atoms of the
1,4-dioxane. When the temperature was lowered to -70 °C,
two different CH2 groups, each with diastereotopic protons,
were detected (δ(1H) 3.28/2.81 (δ(13C) 64.4) (OCH2); 3.24/2.63
(δ(13C) 75.5) (BOCH2)). The 19F NMR spectrum at -70 °C
shows three sets of signals for three different C6F5 groups, -130.9
(o), -152.5 (p), -163.2 (m) (C6F5A), -131.1 (o), -156.2 (p),
-163.0 (m) (C6F5B), and -137.7 (o), -156.3 (p), -163.1 (m)
(C6F5C), due to hindered rotation around the B-O vector.
Similar NMR experiments were also carried out with a 1:2
mixture of 1,4-dioxane and B(C6F5)3. At 25 °C the 19F and
11B NMR spectra (δ(19F) -133.8 (o), -150.3 (p), -162.8 (m);
δ(11B) 31 (ν1/2 ≈ 1400 Hz)) clearly show an equilibrium
between the adduct 9 and free borane. At -70 °C the sample
became heterogeneous duetoprecipitation of B(C6F5)3, although
the very broad 1H and 19F resonances were consistent with
the presence of 9 and free B(C6F5)3.
The phosphine tBu3P, B(C6F5)3, and 1,4-dioxane were
mixed and heated to 50 °C for 2 days. This resulted in the
formation of the new species 10 in 86% yield. The 1H NMR
spectrum revealed resonances consistent with four inequi-
valent methylene groups in addition to resonances arising
from the tert-butyl groups. 19F and 11B NMR data were
consistent with the formation of a borate anion with reso-
nances very similar to those seen for 2. The 13P{1H} NMR
signal was clearly consistent with the quaternization of P,
with a resonance at 49.4 ppm. This suggested the formulation
of 10 as tBu3P(CH2)2O(CH2)2OB(C6F5)3, a formulation that
was subsequently confirmed crystallographically (Figure 8).
In a similar fashion, reaction of B(C6F5)3-1,4-dioxane
with N,N-dimethylbenzylamine, the carbene (tBuN)2C3H2,
N,N,N0,N0-tetramethyl-p-phenylenediamine, and 2,6-lutidine
afforded C6H5CH2NMe2(CH2)2O(CH2)2OB(C6F5)3 (11),
((tBuN)2C3H2)(CH2)2O(CH2)2OB(C6F5)3 (12), Me2NC6H4-
NMe2(CH2)2O(CH2)2OB(C6F5)3 (13), andC5H3Me2N(CH2)2-
O(CH2)2OB(C6F5)3 (14) in 85, 68, 66, and 24% isolated yields,
respectively (Scheme 3). The observation of a 13C resonance
for 12 at 145.2 ppm was consistent with the participation of
the carbene C in C-C bond formation. The formulation of
these zwitterionic salts was confirmed crystallographically
Figure 6. POV-ray depiction of 6. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
resonances of the 19F and 11B NMR data showed signals
expected for the borate fragment. 1H NMR data of 5 showed
an unexpected intensity ratio of 9:2 for the methyl and methylene
groups, respectively, suggesting the formulation of 5 as Me3-
N(CH2)4OB(C6F5)3, a formulation that was subsequently
confirmed crystallographically (Figure 5). This product pre-
sumably arises from the instability of transient ammonium
aminomethane with respect to methyl migration and elimi-
nation of MeNdCH2.
In the case of compound 8, upon ring-opening, the resulting
chiral N atom generates diastereotopic methylene groups, as
evidenced by low-temperature NMR data in dichloromethane
at -75 °C. While preliminary X-ray data confirmed the
formulation of 8, poor crystal quality precluded publishable
data. Nonetheless, crystallographic data were also obtained
for 6 and 7 (Figures 6 and 7).
In further extending this chemistry, we investigated the
possibility that such Lewis acid/Lewis base combinations
might also induce the ring-opening of other cyclic ethers.
While derivatization of cyclic oxonium derivatives has been
reported for polyhedral boron hydrides,36 it has not been
demonstrated for combinations of Lewis acids and bases.
(36) Semioshkin, A. A.; Sivaev, I. B.; Bregadze, V. I. Dalton Trans.
2008, 977–992.

Article
Organometallics, Vol. 29, No. 21, 2010 5317
Figure 9. POV-ray depiction of 11. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; P, orange.
Figure 8. POV-ray depiction of 10. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine.
Scheme 3. Synthesis of 9-19
Figure 10. POV-ray depiction of 12. Legend for atoms: C,
black; B, yellow-green; F, pink; O, red; N, aquamarine.
(Figures 9-11). The new N-C bond distance was unexcep-
tional and was similar to that seen in the previously reported
THF-ring-opened analogues. For compound 13 19F and 11
B
NMR spectral data were consistent with the formation of a
borate moiety. In the case of 14, the low yield resulted from
the simultaneous formation of the 2,6-lutidine-B(C6F5)3
adduct. The ratio of adduct 14 was approximately 5:2.
A further extension of this chemistry targeted 1,4-thioxane
ring-opening. To this end, the borane complex of thioxane
(C6F5)3B(SC4H8O) (15-S) was isolated in 92% yield. The 1H
NMR spectrum showed resonances at 4.09 and 2.67 ppm,
while the 19F NMR signals were observed at -130.0, -154.2,
and -162.8 ppm. The 11B NMR signal at 4.0 ppm was quite
broad, suggesting the possibility of an equilibrium governing a
donor-acceptor interaction. The X-ray structure of 15-S
(Figure 12) was determined, and it revealed that in the solid
state the thioxane is S-bound to B with a S-B distance of
Figure 11. POV-ray depiction of 14. Legend for atoms: C,
black; B, yellow-green; F, pink; O, red; N, aquamarine.
To examine the nature of species present in solution,
B(C6F5)3 and 1,4-thioxane were mixed in a 1:1 ratio and
characterized via variable-temperature NMR spectroscopy.
At 25 °C two methylene resonances attributable to an
AA0BB0 spin system (δ(1H) 3.18 (δ(13C) 67.8) (OCH2);
δ(1H) 1.85 (δ(13C) 30.0) (SCH2)) were detected, which in-
dicates fast exchange of the borane taking place under these
conditions. At -90 °C, the NMR spectra show two main
species in a 1:3 ratio, each exhibiting two different CH2
groups with diastereotopic protons. In combination with 2D
NMR experiments, these were assigned to be most likely the
sulfur-bonded adduct (15-S) (major compound δ(1H) 3.09/
2.44 (δ(13C) 64.7) (OCH2); δ(1H) 1.61/1.12 (δ(13C) 30.8)
ꢀ
˚
2.111(2) A. This bond length is considerably longer than that
seen for ether adducts and thus is consistent with the suggestion
of facile exchange in solution. The observation of S binding in
the solid state is perhaps surprising, given the oxophilicity of B.
37,38
However, S-bonded thioxane adducts are known with BH3
and BXnHn-1,
39 whereas BF3 and BCl3 prefer O binding.40
(37) Brown, H. C.; Mandal, A. K. J. Org. Chem. 1992, 18, 4970–4976.
(38) Brown, H. C.; Mandal, A. K. Synthesis 1980, 2, 153–155.
(39) Zaidlewicz, M.; Kanth, J. V. B.; Brown, H. C. J. Org. Chem.
2000, 20, 6697–6702.
(40) Baker, K. L.; Fowles, G. W. A. J. Chem. Soc. A 1968, 4, 801–804.

5318 Organometallics, Vol. 29, No. 21, 2010
Birkmann et al.
Figure 14. POV-ray depiction of 19. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; P, orange; S, yellow.
Reactions of B(C6F5)3 and thioxane with tBu3P, N,N-
dimethylbenzylamine, N,N,N0,N0-tetramethyl-p-phenylene-
diamine, and 2,6-lutidine in C6D5Br at 80 °C proceed to give
the corresponding ring-opened products 16-19 in 37, 60, 72,
and 20% yields, respectively (Scheme 3). NMR data were
consistent with ring-opening, as each product exhibited four
methylene resonances in the 1H NMR spectrum. In addition,
the products 16-19 exhibited similar 19Fand11B NMR spectra,
suggesting the formulations L(CH2)2S(CH2)2OB(C6F5)3
(L = tBu3P (16), C6H5CH2NMe2 (17), Me2NC6H4NMe2-
(CH2)2S(CH2)2OB(C6F5)3 (18), C5H3Me2N (19)). These for-
mulations were confirmed with crystallographic data. While
preliminary data confirmed the formulations of 16 and 17,
poor crystal quality precluded publishable data. Nonethe-
less, crystallographic data were also obtained for 18 (Figure 13)
and 19 (Figure 14). In these cases, the formation of the B-O
bond was confirmed, as the B-O distances were typical of
those described for the species above. The formation of these
ring-opening products where a C-O bond is cleaved is
seemingly in contradiction to isolation of the S-bound iso-
mer (15-S). However, the detection of the rapid interconver-
sion of O- and S-coordinated isomers of 15 in solution,
together with the shorter bond length of B-O versus B-S,
suggests that greater steric congestion in the O-bound adduct
may activate the ether linkages to attack by the nucleophilic
base. Apparently, 1,4-thioxane/B(C6F5)3 is a case where the
isolated crystalline product (15-S) does not completely re-
present the situation encountered in solution.
Figure 12. POV-ray depiction of 15. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; S, yellow.
Figure 13. POV-ray depiction of 18. Legend for atoms: C, black;
B, yellow-green; F, pink; O, red; N, aquamarine; S, yellow.
Scheme 4. Equilibria involving Thioxane and B(C6F5)3
Conclusions
The present results demonstrate the generality of ring-opening
of THF, dioxane, and thioxane with a variety of sterically
hindered combinations of boranes and bases, including
amines, phosphines, carbenes, and pyridines. Such reactivity
appears to be generally typical of FLPs. Moreover, the mecha-
nistic similarities to previously reported THF ring-openings by
transition-metal and main-group systems suggest that these
systems can also be described as FLPs. While this notion opens
the door to a broader exploration of FLP reactivity, the
present results suggest that ring-opening products may provide
a unique synthetic strategy to new mixed-donor ether or
thioether ligands. Both of these avenues of research are under
examination and will be described in due course.
(SCH2)) and the O-bonded adduct (15-O) (minor compound
δ(1H) 3.98/2.90 (δ(13C) 78.3) (OCH2); δ(1H) 2.72/1.21 (δ(13C)
26.1) (SCH2)). Similar to the 1,4-dioxane case, a 1:2 mixture of
1,4-thioxane and B(C6F5)3 shows fast exchange at 25 °C and
thus two methylene resonances in the NMR spectra (δ(1H)
3.11 (δ(13C) 67.7) (OCH2); δ(1H) 1.80 (δ(13C) 30.6) (SCH2))
were observed. However, whereas the 1:1 mixture forms two
different monoadducts at lower temperatures (Scheme 4), the
1:2 mixture apparently yields the bis-B(C6F5)3 adduct 15-O,S,
giving rise to the observation of four different 1H NMR
methylene signals in a 1:1:1:1 ratio (δ(1H) 3.45/2.46 (OCH2),
2.09/1.14 (SCH2) (all broad)). These data affirm the presence
of rapidly interconverting S- and O-bound adducts of B-
(C6F5)3 in solution despite the isolation of crystalline 15-S.
Acknowledgment. G.E. gratefully acknowledges the finan-
cial support of the Deutsche Forschungsgemeinschaft

Article
Organometallics, Vol. 29, No. 21, 2010 5319
and the Fonds der Chemischen Industrie. D.W.S.
gratefully acknowledges the financial support of the
NSERC of Canada, the award of a Canada Research
Chair, and a Killam Research Fellowship. B.B. is grate-
ful that this work was supported by a fellowship within the
postdoctoral program of the German Academic Exchange
Service (DAAD). T.V. is grateful for the Ph.D. fellowship of
the Fonds der Chemischen Industrie. S.J.G. is grateful
for the support of an NSERC postgraduate scholarship.
M.U. is grateful for the award of a Feodor-Lynen Post-
doctoral Fellowship by the Alexander-von-Humboldt
Foundation.
Supporting Information Available: Text and figures giving
additional characterization data for compounds 1-19 and CIF
files giving crystallographic data for 1-7, 10 0.5C6H5Br, 11
3
3
0.5CH2Cl2, 12, 14, 15, 18, and 19 C6H5Br. This material is
available free of charge via the Internet at http://pubs.acs.org.
3