Synthesis, structure, and stability of adducts between phosphide and amide anions and the lewis acids borane, tris(pentafluorophenyl)borane, and tris(pentafluorophenyl)alane

Article abstract of DOI:10.1021/ic901799q

The phosphinoborane adduct H₃P-B(C₆F ₅)₃ can be deprotonated using LiN(SiMe₃) ₂ to give the phosphidoborate salt Li[H₂PB(C ₆F₅)₃], which was converted to the phosphidodiborates Li[H₂P{B(C₆F₅) ₃}₂] and Li[H₂P(B(C₆F ₅)₃}{BH₃}] by treatment with an equivalent of B(C₆F₅)₃ or Me₂S-BH₃, respectively. A series of anions of the form [RR'P{M(C₆F ₅)₃}{BH₃}^-, where R=R' = Ph or R= ¹Bu, R'=H, and M = B or Al, were prepared (through treatment of salts Li[RR'P(BH₃)] with the corresponding Lewis acid) and characterized using multinuclear NMR, elemental analysis and X-ray crystallography. The solid state structures of [Li(Et₂O)_x][Ph₂P{M(C ₆F₅)₃}{BH₃}] exhibit η²-bonding of the BH₃ group to the cationic lithium center. The attempted preparation of an analogous series with amide cores of the form [R₂N{B(C₆F₅)₃}(BH ₃)]^- proved unsuccessful; among the competing reaction pathways hydride abstraction occurred preferentially to yield Li[HB(C ₆F₅)3] and dimers or higher oligomers with the composition (R₂NBH₂)_n.

Full text of DOI:10.1021/ic901799q

11474 Inorg. Chem. 2009, 48, 11474–11482
DOI: 10.1021/ic901799q
Synthesis, Structure, and Stability of Adducts between Phosphide and Amide
Anions and the Lewis Acids Borane, Tris(pentafluorophenyl)borane, and
Tris(pentafluorophenyl)alane
Anna-Marie Fuller,† Andrew J. Mountford,† Matthew L. Scott,† Simon J. Coles,‡ Peter N. Horton,‡
David L. Hughes,† Michael B. Hursthouse,‡ and Simon J. Lancaster*,†
†Wolfson Materials and Catalysis Centre, School of Chemistry, University of East Anglia, Norwich NR4 7TJ,
U.K., and ‡School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, U.K.
Received September 9, 2009
The phosphinoborane adduct H3P B(C6F5)3 can be deprotonated using LiN(SiMe3)2 to give the phosphidoborate salt
3
Li[H2PB(C6F5)3], which was converted to the phosphidodiborates Li[H2P{B(C6F5)3}2] and Li[H2P{B(C6F5)3}{BH3}] by
treatment with an equivalent of B(C6F5)3 or Me2S BH3, respectively. A series of anions of the form [RR0P{M-
3
t
(C6F5)3}{BH3}]-, where R =R0 =Ph or R= Bu, R0 =H, and M= B or Al, were prepared (through treatment of salts
Li[RR0P(BH3)] with the corresponding Lewis acid) and characterized using multinuclear NMR, elemental analysis and
X-ray crystallography. The solid state structures of [Li(Et2O)x][Ph2P{M(C6F5)3}{BH3}] exhibit η2-bonding of the BH3
group to the cationic lithium center. The attempted preparation of an analogous series with amide cores of the form
[R2N{B(C6F5)3}{BH3}]- proved unsuccessful; among the competing reaction pathways hydride abstraction occurred
preferentially to yield Li[HB(C6F5)3] and dimers or higher oligomers with the composition (R2NBH2)n.
Introduction
adduct formation, in which the compounds were further
stabilized by intramolecular hydrogen-bonding.7-9
The complexation reaction between small dibasic anions
and 2 equiv of perfluoroaryl-substituted group 13 Lewis acids
has been demonstrated to be a highly effective method for the
synthesis of large poorly coordinating anions.1-6 For exam-
ple, treatment of sodium amide with 2 equiv of tris-
(pentafluorophenyl)borane gives the sodium salt of the
amidodiborate anion, [H2N{B(C6F5)3}2]- (I).4 This simple
adduct formation reaction suggests that a family of anions of
the general formula [R2E{M(C6F5)3}2]- (where R is a hydro-
carbon substituent, E=N or P and M=B or Al) should be
readily accessible. On route to these anions the preparation
of protic amine adducts of tris(pentafluorophenyl)-borane
and -alane proved to be a relatively straightforward case of
The first indication that tris(pentafluorophenyl)borane
does not always form simple adducts came with the elegant
investigation of its interaction with the tertiary amines
dimethylaniline, diethylaniline, and triethylamine. Treat-
ment of tris(pentafluorophenyl)borane with dimethylaniline
yields a mixture of the adduct and the iminium salt
[PhCH3N=CH2][HB(C6F5)3]. In the case of diethylaniline
no adduct was observed but as well as unreacted starting
material the ionic [Ph(Et)2NH][HB(C6F5)3] and zwitterionic
PhEtNþ=CH-CH2B-(C6F5)3 were identified.10 The reac-
tion between triethylamine and tris(pentafluorophenyl)-
borane proceeds similarly but to completion giving an
equimolar mixture of [Et3NH][HB(C6F5)3] and Et2Nþ=
CH-CH2B-(C6F5)3.11
*To whom correspondence should be addressed. E-mail: s.lancaster@
uea.ac.uk. Fax: 44 1603 592003. Phone: 44 1603 592009.
(1) Lancaster, S. J.; Walker, D. A.; Thornton-Pett, M.; Bochmann, M.
Chem. Commun. 1999, 1533.
(8) For reviews of the chemistry of tris(pentafluorophenyl)borane see: (a)
Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345. (b) Chen, E. Y.-X.;
Marks, T. J. Chem. Rev. 2000, 100, 1391. (c) Erker, G. Dalton Trans. 2005,
1883. (d) Piers, W. E. Adv. Organomet. Chem. 2005, 52, 1.
(9) For a review of nitrogen adducts of tris(pentafluorophenyl)borane
see: Focante, F.; Mercandelli, P.; Sironi, A.; Resconi, L. Coord. Chem. Rev.
2006, 250, 170.
(2) LaPointe, R. E.; Roof, G. R.; Abboud, K. A.; Klosin, J. J. Am. Chem.
Soc. 2000, 122, 9560.
(3) Zhou, J.; Lancaster, S. J.; Walker, D. A.; Beck, S.; Thornton-Pett, M.;
Bochmann, M. J. Am. Chem. Soc. 2001, 123, 223.
(4) Lancaster, S. J.; Rodriguez, A.; Lara-Sanchez, A.; Hannant, M. D.;
Walker, D. A.; Hughes, D. L.; Bochmann, M. Organometallics 2002, 21, 451.
(5) Hannant, M. H.; Wright, J. A.; Lancaster, S. J.; Hughes, D. L.;
Horton, P. N.; Bochmann, M. Dalton Trans. 2006, 2415.
(10) Millot, N.; Santini, C. C.; Fenet, B.; Basset, J. M. Eur. J. Inorg. Chem.
2002, 3328.
€
(6) Bernsdorf, A.; Brand, H.; Hellmann, R.; Kockerling, M.; Schulz, A.;
(11) Di Saverio, A.; Focante, F.; Camurati, I.; Resconi, L.; Beringhelli, T.;
D’Alfonso, G.; Donghi, D.; Maggioni, D.; Mercandelli, P.; Sironi, A. Inorg.
Chem. 2005, 44, 5030.
Villinger, A.; Voss, K. J. Am. Chem. Soc. 2009, 131, 8958.
(7) Mountford, A. J.; Lancaster, S. J.; Coles, S. J.; Horton, P. N.; Hughes,
D. L.; Hursthouse, M. B.; Light, M. E. Inorg. Chem. 2005, 44, 5921.
r
pubs.acs.org/IC
Published on Web 10/28/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 23, 2009 11475
Scheme 1
There are somewhat fewer examples of isolated phosphine
compared to amine adducts of tris(pentafluorophenyl)borane.
the adducts between dialkyl amide anions and trihydridro-
borane are well-known. Lithium dimethylamidoborate, Li-
Me2NBH3, is available commercially as a reducing agent,19
and the sodium salt of the dimethylamidodiborate anion,
NaMe2N(BH3)2 was first reported in 1971.20,21 Primary and
secondary phosphine adducts of BH3 react with nBuLi to give
the corresponding salts, in which there is competing Li-P
and Li;H;B bonding.22
Herein the phosphidodiborate anion is reported and com-
pared to the amidodiborate anion (I). The formation and
stability of adducts between amido- and phosphido-trihy-
droborate anions and the Lewis acids tris(pentafluoro-
phenyl)-borane and -alane are investigated and contrasted.
The adduct H3P B(C6F5)3 was investigated by Bradley and
3
co-workers and, in contrast to the ammonia adduct, found to
be rather weakly bound, decomposing at approximately 50 °C
under vacuum and when dissolved in basic solvents such as
tetrahydrofuran (THF).12,13 If a trialkyl phosphine of modest
steric bulk is employed the complexes formed are unremark-
able.14 However, when sterically demanding phosphine ligands
were employed by Stephan and co-workers this led to the
landmark discovery of “frustrated Lewis pairs”.15 No adduct is
formed if 1 equiv of (tBu)3P or (C6H2Me3)3P is combined with
B(C6F5)3. However, these mixtures react with dihydrogen to
form the respective phosphonium hydridoborate salts.16 The
sterically hindered secondary phosphines (tBu)2PH and
(C6H2Me3)2PH react, not by adduct formation, but through
nucleophilic aromatic substitution at one of the para-carbons.
The liberated fluoride anion coordinates to boron, and zwitter-
ions of the form [R2PþH(C6F4)B-(C6F5)2F] are generated.17
Attempts to prepare examples of anions [R2E{M(C6-
F5)3}2]-, either through direct complexation of the anionic
core with 2 equiv of Lewis acid or by first deprotecting the
protic adduct and treating it with a second equivalent of
Lewis acid, employing anything other than R=H, lead only
to complex product mixtures.18 The presence of one or both
of the [B(C6F5)4]- and [B(C6F5)3H]- anions suggests that in
these systems abstraction reactions are successfully compet-
ing with adduct formation, but a detailed understanding of
the competing reaction pathways remains elusive.
Results and Discussion
n
The reaction between H3N B(C6F5)3 and BuLi in THF
3
solution proceeds cleanly giving the salt [Li(THF)2]-
[H2NB(C6F5)3] in essentially quantitative yield.23 However,
this deprotonation protocol is not viable for the more labile
H3P B(C6F5)3, even when THF was replaced with light
3
petroleum; spectroscopic characterization revealed a com-
plex mixture of products, suggesting competition between
substitution and deprotonation reactions. In contrast, the
reaction of the poorly nucleophilic base Li[N(SiMe3)2] with
H3P B(C6F5)3 proceeds cleanly in light petroleum solu-
3
tion precipitating Li[H2PB(C6F5)3] (1) as a colorless solid
(Scheme 1). Spectroscopic characterization was achieved by
dissolution in an equal volume mixture of 1,2-difluoroben-
zene and benzene-d6. The 1H NMR spectrum of 1 consisted
of a doublet at δ 2.25 ppm (JPH=247 Hz) versus δ 3.89 ppm
In contrast to the apparent instability of dialkylamido- and
dialkylphosphido-di(tris(pentafluorophenyl))borate anions,
(JPH=410 Hz) for H3P B(C6F5)3. In this instance coupling
3
to phosphorus was observed in the 11B spectrum with a
doublet at δ -18.0 ppm (JBP = 46 Hz), which is at some-
what lower frequency than that of the amidoborate salt
(12) Bradley, D. C.; Hursthouse, M. B.; Motevalli, M.; Dao-Hong, Z.
J. Chem. Soc., Chem Commun. 1991, 7.
(13) Bradley, D. C.; Harding, I. S.; Keefe, A. D.; Motevalli, M.;
Dao-Hong, Z. J. Chem. Soc., Dalton Trans. 1996, 3931.
(14) Chase, P. A.; Parvez, M.; Piers, W. E. Acta Crystallogr., Sect. E 2006,
62, o5181.
(19) Pasumansky, L.; Singaram, B. Aldrichimica Acta 2005, 38, 61.
(20) Keller, P. C. Inorg. Chem. 1971, 10, 2256.
(21) The article following reference 20 is the first report of sodium
phosphidoborate, NaH2P(BH3): Mayer, E. Inorg. Chem. 1971, 10, 2259.
(15) Stephan, D. W. Dalton Trans. 2009, 3129.
(16) Welch, G. C.; Stephan, D. W. J. Am. Chem. Soc. 2007, 129, 1880.
(17) Welch, G. C.; Cabrera, L.; Chase, P. A.; Hollink, E.; Masuda, J. D.;
Wei, P.; Stephan, D. W. Dalton Trans. 2007, 3407.
(18) Walker D. A.; Bochmann, M.; Fuller, A.; Mountford A. J.;
Lancaster, S. J. unpublished results.
€
(22) Muller, G.; Brand, J. Organometallics 2003, 22, 1463.
(23) Mountford, A. J.; Clegg, W.; Coles, S. J.; Harrington, R. W.;
Horton, P. N.; Humphrey, S. M.; Hursthouse, M. B.; Wright, J. A.;
Lancaster, S. J. Chem.;Eur. J. 2007, 13, 4535.

11476 Inorganic Chemistry, Vol. 48, No. 23, 2009
Fuller et al.
Figure 1. ORTEP of 2 with displacement ellipsoids drawn at the 30% probability level, hydrogen atoms on the 12-crown-4 ligand have been omitted for
˚
clarity. Selected bond lengths [A] and angles [deg] P(1);B(1) 2.056(6), P(1);B(2) 2.058(6), P(1);H(41) 1.22(4), P(1);H(42) 1.28(4), B(1);C(11)
1.640(7), B(1);C(21) 1.664(7), B(1);C(31) 1.647(7), B(2);C(51) 1.661(7), B(2);C(61) 1.637(7), B(2);C(71) 1.647(7), Li(1);O(81) 2.325(10), Li(1);
O(84) 1.975(9), Li(1);O(87) 2.022(10), Li(1);O(90) 2.011(9), Li(1);O(81)0 1.988(9). B(1);P(1);B(2) 129.8(2), P(1);B(1);C(11) 115.8(3), P(1);
0
B(1);C(21) 107.7(3), P(1);B(1);C(31) 99.5(3), P(1);B(2);C(51) 111.0(3), P(1);B(2);C(61) 111.7(3), P(1);B(2);C(71) 102.8(3). indicates
symmetry operation 1 - x, 2 - y, 1 - z.
[Li(THF)2][H2NB(C6F5)3], δ -9.1 ppm. The increased elec-
tetrahedral coordination environments. The two boron
atoms are essentially equidistant from the phosphorus atom
at approximately 2.06 A. The obtuse B;P;B angle of 129.8°
minimizes the steric interactions between pentafluorophenyl
groups, but is nevertheless smaller than the B;N;B angle
of 134.3(2)° found in I, where the shorter B-N bonds would
lead to greater steric interactions between the two B(C6F5)3
tron density at phosphorus on anion formation induces a low
frequency shift of the 31P resonance from that in H3P B-
˚
3
(C6F5)3 (δ -99.6 ppm) to -155 ppm. Further evidence
for anion formation is provided by the small chemical
shift difference of the para- and meta-fluorine resonances
(Δδ = 4.0 ppm), which is characteristic of anionic tris-
(pentafluorophenyl)boron species.24,25 Compound 1 and
derivatives in which the lithium salt was treated with THF
or 12-crown-4 could not be induced to crystallize.
groups. There is only one intramolecular H F interaction
3 3 3
˚
with a separation less than 2.40 A in the structure of 2
˚
{(P(1);H(42) F(36) 2.39 A, 120.56°}, which can be
regarded as a weak hydrogen bond. There are three other
3 3 3
Treatment of 1 with a second equivalent of B(C6F5)3 in
THF solution gave a foam on removal of the solvents. A pure
sample was successfully isolated only after the addition of
12-crown-4 and cooling a concentrated THF solution to
-25 °C giving colorless crystals of [Li(12-crown-4)][H2P{B-
(C6F5)3}2] (2). The composition of 2 was confirmed by
elemental analysis and multinuclear NMR. The PH2 doublet
intramolecular H F contacts within the van der Waals
3 3 3
radii; however, they are all somewhat long (2.43, 2.44, and
˚
2.50 A) with rather acute angles (98, 111, and 100°,
respectively) and thus do not meet our interpretation of the
Dunitz criteria for designation as a hydrogen bond.7,26 This
contrasts with the structure of I, which has a number of short
in the 1H NMR spectrum of 2 was found at δ 5.08 ppm (JPH
=
N-H F-C contacts.4
3 3 3
354 Hz), significantly higher frequency than that of 1 reflect-
ing the decrease in electron density when coordinating the
second borane. Accordingly, the 31P chemical shift of 2
Treatment of 1 with Me2S BH3 in diethyl ether solution
3
followed by removal of the solvents under reduced pressure
yielded a colorless oil; recrystallization from dichloro-
methane/light petroleum in the presence of 2 equiv of
12-crown-4 provided the salt [Li(12-crown-4)2][H2P-
{B(C6F5)3}{BH3}] (3) as a colorless crystalline solid. The
quality of the X-ray analysis was suitable only for establish-
ing connectivity. The bulk composition was confirmed by
multinuclear NMR and elemental analysis. In the 1H NMR
spectrum the PH2 signal was observed as a doublet at δ 3.78
(JPH = 334 Hz), at higher frequency than 1 but lower
frequency than that observed for 2, reflecting the stronger
Lewis acidity of B(C6F5)3 versus BH3. The BH3 signal in the
1H NMR is broad and unresolved. The 31P resonance was
found as a broad peak at δ -92 ppm, similar to that observed
at δ -97 ppm is closer to that of the neutral adduct H3P
3
B(C6F5)3 than the monoborate 1. Here the 11B NMR con-
sisted of a broad peak at -12 ppm and the phosphorus-
boron coupling was not resolved.
The solid-state structure of 2 was elucidated by X-ray
crystallography (Figure 1). The lithium counterion is a
centrosymmetric dimer [Li2(12-crown-4)2] in which each
lithium binds to the four oxygen atoms of a molecule of
12-crown-4 and has a fifth close Li O contact to the
3 3 3
second, symmetry-related, Li(12-crown-4) fragment. In the
anion, the boron and phosphorus atoms have distorted
(24) Horton, A. D.; de With, J. Organometallics 1997, 16, 5424.
(25) Blackwell, J. M.; Piers, W. E.; Parvez, M. Org. Lett. 2000, 2, 695.
(26) Dunitz, J. D.; Taylor, R. Chem.;Eur. J. 1997, 3, 89.

Article
Inorganic Chemistry, Vol. 48, No. 23, 2009 11477
Scheme 2
Table 1. 11B, 19F, and 31P NMR data in Chloroform-d1
11B
11B
19F
19F
19F
31P
BH3
B(C6F5)3
o-F
p-F
m-F
1a
2
3
4
5
6
7
-18.0
-15.3
-18.0
-11.4
-133.9
-129.7
-130.2
-126.2
-120.0
-128.2
-120.8
-161.5
-159.8
-160.9
-160.2
-155.5
-160.7
-155.6
-165.5
-165.8
-165.7
-166.5
-163.3
-165.6
-162.9
-154.6
-96.8
-92.3
0.3
-39.2
-22.9
-54.9
-41.3
-32.3
-34.2
-40.5
-40.8
-15.8
a Run in benzene-d6/1,2-difluorobenzene.
117.06(7)° is significantly closer to the tetrahedral ideal than
the corresponding angle in 2 (129.8(2)°), which is possible
˚
because of the reduced size of the BH3 group. At 1.951(2) A
the P-BH3 bond length is comparable to those in the
previously reported phosphidoborate complexes [(PEt3)2Pt-
(H){P(Ph)(H)(BH3)}] and [CpFe(CO)2{PPh2(BH3)}] at
for 2. The 11B NMR spectrum revealed the expected pair of
signals, with the B(C6F5)3 boron at -18 ppm (1JBP=69 Hz)
and the 11B BH3 signal at δ -41 ppm, but the phosphorus-
boron coupling was unresolved.
27,28
˚
1.953(7) and 1.949(7) A, respectively.
greater steric requirement of the fragment, at 2.121(2) A the
Reflecting the
˚
In contrast to the [PH2]- chemistry, the reactions between
P-B(C6F5)3 bond is somewhat longer than the P-BH3 bond
and slightly longer than those found in H2(Ph)P B(C6F5)3
either LiPR2 and 1 or 2 equiv of B(C6F5)3 or RR0(H)P B-
3
3
29
˚
(C6F5)3 and nBuLi do not proceed cleanly, despite the
stability of the analogous BH3 adducts. The question there-
fore arose as to whether anions related to that in 3 utilizing 1
equiv of BH3 and 1 equiv of B(C6F5)3 would be accessible and
stable. The reactions of Li[RR0P(BH3)] with M(C6F5)3 in
diethyl ether resulted in the formation of [Li(OEt2)n]-
[RR0P{M(C6F5)3}{BH3}] (where R= R0 =Ph, M=B (4),
M=Al (5) and R=H, R0 =tBu, M=B (6), M=Al (7))
(Scheme 2). The diphenylphosphide complexes were isolated
as colorless solids, while the tert-butylphosphides were
obtained as colorless oils.
(2.039 A) and 2. Three molecules of diethyl ether are
coordinated to the lithium cation, which is closely associated
with the anion. There are two short B-H Li contacts of
3 3 3
2.02 and 2.17 A.30 The B(1) Li(1) distance of 2.477(3) A is
˚
˚
3 3 3
˚
similar to the value of 2.43 A found for Li[(Ph)(H)P(BH3)2],
in which the BH3 group also acts an η2-donor.31 There are
two short intramolecular contacts between aromatic hydro-
gens and organofluorines which are within the range for
˚
˚
designation as hydrogen bonds: H(42) F(12) 2.17 A,
3 3 3
3 3 3
C(42);H(42) F(12) 148° and H(52) F(22) 2.26 A,
3 3 3
3 3 3
C(52);H(52) F(22) 147°. However, while these para-
meters are reminiscent of the dimensions found in primary
and secondary amine adducts of B(C6F5)3,7 here they do not
complete the six-membered rings favored by Etter’s rules32,
and their strength and significance are not clear.
All four compounds were soluble and stable in aromatic
and chlorinated solvents facilitating spectroscopic characteri-
zation in chloroform-d (Table 1). The composition and
number of diethyl ether molecules present were determined
by integration of the signals in the 1H NMR spectra and were
in good agreement with the elemental analyses. Coinciden-
tally the boron compounds 4 and 6 contained 3 equiv of
diethyl ether, whereas the aluminum compounds 5 and 7 had
2 equiv. The BH3 hydrogens in compounds 4-7 give very
broad signals at δ 0.53 (4), 0.55 (5), -0.04 (6), and 0.06 (7)
ppm, respectively. These chemical shift values suggest that
substitution of aluminum for boron in the M(C6F5)3 group
has a very small effect on the BH3 electron density. This is in
contrast to the considerable difference observed when vary-
ing the phosphide substituent. The 11B (BH3) resonances
δ -32.3, -34.2, -40.5, and -40.8 ppm for 4-7, respectively,
follow a similar trend. The 31P resonances proved to be
sensitive to both the alkyl and the Lewis acid substituents,
with highest frequency resonances belonging to the B(C6F5)3
complexes, suggesting that this group is more effectively
removing electron density from the phosphorus center
than Al(C6F5)3. The normal pattern of 19F resonances of
aluminum-bonded pentafluorophenyl groups being found at
higher frequency than the boron analogues was also found
for these complexes.
Crystals of compound 5, [Li(OEt2)2][Ph2P{Al(C6F5)3}-
{BH3}], suitable for study by X-ray diffraction, were obtained
following recrystallization from diethyl ether (Figure 3).
There are two diethyl ether molecules coordinated to the
lithium cation, which also associates with the anion through
two B-H Li interactions slightly shorter than those pre-
3 3 3
˚
sent in 4, B(2);H(2b) Li(1) 1.95 A (96.6°) and B(2);
3 3 3
˚
H(2c) Li(1) 1.96 A (94.4°) with a B(2) Li(1) distance of
3 3 3
3 3 3
33
˚
2.346(4) A. At 112.19(8)° the central Al(1);P(1);B(2)
angle is more acute than the central B(1);P(1);B(2) angles
observed in 2 and 4 (Table 2) because of the relief in steric
strain associated with the greater P;Al bond length. The
˚
H3B(2);P(1) bond length at 1.949(2) A is comparable to that
(27) Angerer, W.; Sheldrick, W. S.; Malisch, W. Chem. Ber. 1985, 118,
1261.
(28) Jaska, C. A.; Dorn, H.; Lough, A. J.; Manners, I. Chem.;Eur. J.
2003, 9, 1.
(29) Denis, J.-M.; Forintos, H.; Szelke, H.; Toupet, L.; Pham, T.-N.;
Madec, J.-M.; Gaumont, A.-C. Chem. Commun. 2004, 54.
˚
(30) In 4, the B(2);H(2A) 1.13(2) A bond length of the hydrogen atom
not interacting with the cation is marginally shorter than those for the
˚
interacting pair where B(2);H(2B) 1.15(2) and B(2);H(2C) 1.15(2) A.
(31) Rudzevich, V. L.; Gornitzka, H.; Romanenko, V. D.; Bertrand, G.
Crystals of compound 4 were obtained by concentrating
and cooling a diethyl ether solution, and the solid state
structure was elucidated by X-ray crystallography
(Figure 2). In the anion the B;P;B linkage is bent and at
Chem. Commun. 2001, 1634.
(32) Etter, M. J. Phys. Chem. 1991, 95, 4601.
(33) As in 4, the B;H bond length of the non-interacting hydrogen in 5 is
˚
marginally shorter than the other two, (1.08(3) versus 1.10(3) and 1.16(2) A).

11478 Inorganic Chemistry, Vol. 48, No. 23, 2009
Fuller et al.
Figure 2. ORTEP of 4 with displacement ellipsoids drawn at the 30% probability level; aromatic protons and those on the diethyl ether have been omitted
˚
for clarity. Selected distances [A] and angles [deg] P(1);B(1) 2.1206(15), P(1);B(2) 1.9509(16), P(1);C(41) 1.8375(14), P(1);C(51) 1.8329(14), B(1);
C(11) 1.6480(19), B(1);C(21) 1.646(2), B(1);C(31) 1.6381(19), Li(1);O(61) 1.992(3), Li(1);O(71) 1.977(3), Li(1);O(81) 1.983(3). B(1);P(1);B(2)
117.06(7), B(1);P(1);C(41) 108.58(6), B(1);P(1);C(51) 113.31(6), B(2);P(1);C(41) 106.82(7), B(2);P(1);C(51) 105.86(7), C(41);P(1);C(51)
104.30(6), C(11);B(1);P(1) 110.07(9), C(21);B(1);P(1) 106.67(9), C(31);B(1);P(1) 103.54(9), O(61);Li(1);O(71) 106.79(13), O(61);Li(1);
O(81) 109.18(13), O(71);Li(1);O(81) 112.38(13).
Figure 3. ORTEP of 5 with displacement ellipsoids drawn at the 30% probability level, aromatic hydrogen atoms and those of the diethyl ether
˚
have been omitted for clarity. Selected bond lengths [A] and angles [deg] P(1);Al(1) 2.4538(9), P(1);B(2) 1.949(2), P(1);C(41) 1.831(2), P(1);
C(51) 1.834(2), Al(1);C(11) 2.008(2), Al(1);C(21) 2.009(2), Al(1);C(31) 2.007(2), Li(1);O(61) 1.887(4), Li(1);O(71) 1.891(4). Al(1);P(1);
B(2) 112.19(8), Al(1);P(1);C(41) 110.55(7), Al(1);P(1);C(51) 109.31(7), B(2);P(1);C(41) 110.73(10), B(2);P(1);C(51) 109.00(10),
C(41);P(1);C(51) 104.78(9), C(11);Al(1);P(1) 109.11(6), C(21);Al(1);P(1) 110.77(6), C(31);Al(1);P(1) 103.01(6), O(61);Li(1);
O(71) 124.7(2).

Article
Inorganic Chemistry, Vol. 48, No. 23, 2009 11479
observed in 4. The pattern of C-H F contacts in com-
absent in the secondary phosphine adducts H(R)2P B(C6F5)3
3 3 3
3
(where R=phenyl and cyclohexyl).13,34,35
pound 5 resembles that in compound 4, but here there is one
intramolecular and one intermolecular interaction and, pre-
sumably because of the greater P;M separation, the0distances
Evidently there are close parallels between anion forma-
tion chemistry in the case of the [EH2]- cores, and, like phos-
phidoborates, there are many known examples of amidobo-
rates. It might therefore be expected that the chemistry and
stability of the [R2N{M(C6F5)3}{BH3}]- anions would re-
flect the pattern observed for the phosphorus analogues.
However, the reaction between LiNHtBu{BH3} and B(C6-
F5)3 does not proceed cleanly and when monitored by 19F
NMR at least two unidentified products are observed. In this
instance there is no indication for the formation of
[HB(C6F5)3]-. The isolation of the constituents by fractional
crystallization methods was attempted, including the addi-
tion of 12-crown-4, but was not successful. The analogous
reaction between Li[N(CH3)2(BH3)] and B(C6F5)3 yields two
fluorine-containing products, one of which was identified as
[HB(C6F5)3]-. Treatment of Li [(cyclo-NC5H10)(BH3)] with
B(C6F5)3 in THF solution gave a product mixture from
which (cyclo-NC5H10)2(μ-BH2)2 (8) and [Li(12-crown-4)2]-
[HB(C6F5)3] (9) were subsequently fractionally crystallized
(Scheme 3). The identity of both components was definitively
established by diffraction methods. Compound 8 has been
reported,36 while the data for the salt 9 was only of sufficient
quality to establish connectivity; the anion has been pre-
viously crystallographically characterized.16,37 The reaction
of Li[NH2(BH3)] with B(C6F5)3 proceeds similarly and
cleanly giving [HB(C6F5)3]-, which was identified by multi-
nuclear NMR; however the second component of this mix-
ture, presumed to be an oligomer of the form [(H2N)-
(μ-BH2)]n, could not be isolated. The crude 11B solution
NMR spectrum did not show the signals around -10 ppm
recently observed for such species,38,39 but this may be
because of precipitation from the reaction medium.
˚
are greater H(56) F(26) 2.39 and H(53) F(36) 2.39 A.
3 3 3
3 3 3
Crystals of [Li(OEt2)2][H(tBu)P{Al(C6F5)3}{BH3}] (7) suit-
able for X-ray diffraction could not be obtained despite
repeated attempts, including the addition of 12-crown-4
(7a); however, X-ray diffraction quality crystals of the
B(C6F5)3 analogue [Li(OEt2)3][H(tBu)P{B(C6F5)3}{BH3}]
(6) as [Li(12-crown-4)2][H(tBu)P{B(C6F5)3}{BH3}] (6a) could
be obtained through the addition of 2 equiv of 12-crown-4 to a
diethyl ether solution and cooling to -25 °C (Figure 4). The
phosphorus centers in 6a are bonded to four different substi-
tuents in an approximately tetrahedral geometry and are
therefore chiral, but crystallize as a racemic mixture. The
˚
H3B(2);P(1) (1.946(3) A) and (C6F5)3B(1);P(1) (2.040-
(3) A) distances are comparable to those found for 4. The
˚
B;P;B angle of 116.00(12)° suggests that the tert-butyl and
hydrogen combination presents a similar requirement to the
two phenyl substituents in 4, where the corresponding angle is
117.06(7)°. Since the Li cation is coordinated to two 12-crown-
4 molecules, effectively encapsulating the ion, there are no
close interactions with the BH3 hydrogen atoms and all three
B-H distances are comparable. The P-H bond length was
˚
experimentally determined to be 1.32(2) A, and the hydrogen
is engaged in hydrogen bonding to an o-F of one of the C6F5
˚
rings (H(51) F(12) 2.30(2) A, P-H F 114.4(14)°). Re-
3 3 3
3 3 3
lated H F interactions have been observed in the pri-
3 3 3
mary phosphine adduct H2(tBu)P B(C6F5)3, but were notably
3
˚
Table 2. Selected Bond Lengths (A) and Angles (deg)
While, where R=R0 =Me or R=H, R0 =tBu, one of the
sets of signals we observe may indicate the competing
formation of an anion of the type [RR0N{B(C6F5)3}-
{BH3}]-, the predominant fluorine-containing product in
this series is the hydridoborate anion. Where RR0 completes
M(1);P(1)
P(1);B(2)
M(1);P(1);B(2)
2
4
5
6a
2.056(6)
2.121(2)
2.4538(9)
2.040(3)
2.058(6)
1.951(2)
1.949(2)
1.946(3)
129.8(2)
117.06(7)
112.19(8)
116.00(12)
Figure 4. ORTEP of 6a with displacement ellipsoids drawn at the 30% probabilitylevel; tert-butyl hydrogenatoms and those of the crown ether have been
˚
omitted for clarity. Selected bond lengths [A] and angles [deg] P(1);B(1) 2.040(3), P(1);B(2) 1.946(3), P(1);C(41) 1.871(2), P(1);H(51) 1.32(2), B(1);
C(11) 1.650(3), B(1);C(21) 1.649(3), B(1);C(31) 1.653(3), Li(1);O(61) 2.382(5), Li(1);O(64) 2.268(5), Li(1);O(67) 2.363(5), Li(1);O(70) 2.359(5),
Li(1);O(81) 2.291(5), Li(1);O(84) 2.345(5), Li(1);O(87) 2.445(5), Li(1);O(90) 2.353(5). B(1);P(1);B(2) 116.00(12), B(1);P(1); C(41) 115.87(11),
B(2);P(1);C(41) 110.61(13), P(1);B(1);C(11) 116.37(16), P(1);B(1);C(21) 107.36(15), P(1);B(1);C(31) 101.43(15).

11480 Inorganic Chemistry, Vol. 48, No. 23, 2009
Fuller et al.
Scheme 3
Scheme 4
Conclusion
The chemistry of the phosphidodiborate anion [H2P{B(C6-
F5)3}2]- closely resembles that of the amidodiborate ana-
logue. Whether this anion will prove to be as useful in
polymerization catalysis and the isolation of reactive electro-
philes as the amidodiborate remains to be established.1-5 The
seemingly straightforward extension of this anion complexa-
tion chemistry to derivatives with alkyl-amide and -phos-
phide cores is frustrated by the existence of competing
reaction pathways and their apparent lack of stability.
Although anions of the form [RR0P{B(C6F5)3}2]- have
proven elusive, the analogous species in which the phosphide
core is complexed by a combination of BH3 and either
B(C6F5)3 or Al(C6F5)3 are both stable and isolable. These
[RR0P{M(C6F5)3}{BH3}]- anions are conveniently prepared
from Li[RR0P(BH3)] and the corresponding Lewis acid.
However, in the special (stable) case of the Li[H2P{B(C6-
F5)3}] precursor, the [H2P{B(C6F5)3}{BH3}]- anion can be
prepared by addition of BH3. In the solid state structures of
the salts [Li(OEt2)n][RR0P{M(C6F5)3}{BH3}] (M=B, n=3
and M=Al, n=2) the lithium counterion is η2-coordinated to
the BH3 group. The coordination chemistry of these species
awaits further investigation.
The analogous anions built on amide cores could not be
prepared. Despite the stability of the [H2N{B(C6F5)3}2]- and
[R2N(BH3)]- salts all attempts, regardless of the order of
reagent addition, at the isolation of salts of the form
[Li(OEt2)n][RR0N{B(C6F5)3}{BH3}] proved unsatisfactory.
In several instances Li[HB(C6F5)3] was observed, which
coupled with the isolation of an example of an aminoborane
dimer is strongly consistent with the supposition that these
anions are unstable with respect to hydride abstraction by
tris(pentafluorophenyl)borane. This is essentially the same
pathway that accounts for the instability of tertiary amine
adducts of tris(pentafluorophenyl)borane; however, in this
instance the more hydridic B-H is preferentially abstracted.
the piperidinyl ring, the reaction proceeds fairly selectively
giving almost exclusively the hydridoborate anion and the
concomitant isolation of [(cyclo-NC5H10)(μ-BH2)]2 (8) indi-
cates that the hydridoborate anion is formed by abstraction
of hydride from the BH3 group of the amidoborate anion,
giving a neutral aminoborane which subsequently dimerizes.
To determine whether the failure to isolate [R2N{B(C6-
F5)3}{BH3}]- anions was a consequence of inherent instabil-
ity or the favorable competition of the abstraction reaction
resulting from the synthetic procedure being employed,
reactions between Li[R2N{B(C6F5)3}] and Me2S BH3 were
3
considered. However, the NH2 and N(Ph)H derivatives are
the only two known examples of isolable [R2N{B(C6F5)3}]-
anions.18,23 The imidazolium salt [tBu2N2C3H3][(Ph)HN{B-
(C6F5)3}] was recently reported by Stephan and co-work-
ers.37 Treatment of tris(pentafluorophenyl)borane with 1
equiv of aniline yields the Lewis adduct (Ph)H2N B(C6F5)3
3
(10) (Scheme 4). The lithium salt [Li(12-crown-4)2][(Ph)HN-
{B(C6F5)3}] (11) was prepared by the deprotonation of 10
followed by precipitation with 12-crown-4, and characterized
by X-ray diffraction methods.40 Treatment of this amido-
borate anion with 1 equiv of Me2S BH3 yielded only in-
3
tractable mixtures with multiple 11B resonances, none of
which had the characteristic quartet coupling expected for
the BH3 group of a [R2N{B(C6F5)3}{BH3}]- anion. The
failure to isolate examples of [R2N{B(C6F5)3}{BH3}]- ani-
ons despite utilizing two distinct synthetic approaches sug-
gests an intrinsic instability at odds with that of the analogous
phosphido anions and particularly surprising in the case of
the [NH2]- core where anion I has been demonstrated to
show excellent stability. However, it is consistent with earlier
observations on the instability of the Li[NH2(BH3)2] anion,
which was shown to be unstable with respect to the formation
of Li[BH4] and (BH2NH2)n.41
Experimental Section
All reactions were carried out under a dry nitrogen atmo-
sphere using standard Schlenk techniques in pre-dried glass-
ware. Solvents were dried using an appropriate drying agent
and distilled under nitrogen prior to use: dichloromethane
(CaH2), light petroleum (Na/K alloy or sodium/dyglyme/
benzophenone), diethylether and THF (sodium/benzophe-
none) and toluene (sodium). Samples for NMR analysis were
prepared using degassed deuterated solvents dried over acti-
(34) Lancaster, S. J.; Mountford, A. J.; Hughes, D. L.; Schormann, M.;
Bochmann, M. J. Organomet. Chem. 2003, 680, 193.
(35) In 6a, there is also a close interaction between one of the tBu
hydrogen atoms and an o-F of a second C6F5 ring (C(44);H(44a) F(36)
3 3 3
˚
2.31 A).
(36) Maringgele, W. Main Group Met. Chem. 2000, 23, 735.
(37) (a) Chase, P. A.; Stephan, D. W. Angew. Chem., Int. Ed. 2008, 47,
7433. (b) Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Commun. 2008, 1701.
(38) Dietrich, B. L.; Goldberg, K. I.; Heinekey, D. M.; Autrey, T.;
Linehan, J. C. Inorg. Chem. 2008, 47, 8583.
(39) Staubitz, A.; Presa Soto, A.; Manners, I. J. Angew. Chem., Int. Ed.
2008, 47, 6212.
(40) The anionic part of 11 is essentially the same as that reported in
reference 37; our results are reported in the Electronic Supporting Informa-
tion.
˚
vated 4 A molecular sieves. NMR spectra were obtained
using a Bruker Avance DPX300 spectrometer at 23 °C.
Chemical shifts are reported in parts per million and refer-
enced to residual solvent resonances (1H, 13C{1H}); 19F is
relative to CFCl3; 11B is relative to Et2O BF3; 31P{1H} is
3
relative to an 85% solution of H3PO4. Elemental analyses
were carried out at Medac Ltd. and at the Department of
(41) Schaeffer, G. W.; Basile, L. J. J. Am. Chem. Soc. 1955, 77, 331.

Article
Inorganic Chemistry, Vol. 48, No. 23, 2009 11481
1
C42H43B2F15LiO3P: C, 53.65 (53.72); H, 4.61 (4.32). H NMR
Health and Human Sciences, London Metropolitan Univer-
sity. The syntheses of B(C6F5)3 and Al(C6F5)3 toluene were
(CDCl3): δ 7.28 (10H, m, C6H5), 3.47 (12H, q, JHH =7.1 Hz,
3
conducted according to the literature procedures.42,43
Li[H2PB(C6F5)3] (1). A suspension of H3P B(C6F5)3 (0.72 g,
CH2), 1.15 (18H, t, JHH=7.1 Hz, CH3), 0.53 (3H, br, BH3). 13
C
NMR (CDCl3): δ 66.4 (CH2), 15.0 (CH3). 11B NMR (CDCl3): δ
3
-11.4 (1B, br, B(C6F5)3), -32.3 (1B, br, BH3). 19F NMR
1.3 mmol) in light petroleum (10 mL) was treated with a solution
of Li[N(SiMe3)2] (0.22 g, 1.3 mmol) in light petroleum (10 mL) at
-78 °C. The resulting suspension was warmed to room tem-
perature and stirred for a further 30 min before the solid was
isolated by filtration (0.67 g, 1.2 mmol, 93%). Elem. Anal. Calcd
(found) for C18H2BF15LiP: C, 39.17 (39.90); H, 0.37 (0.96). The
slightly elevated C and H values are due to the presence of
persistent traces of solvent, which were not removed on drying.
1H NMR (C6D6/C6H4F2 50:50): δ 2.25 (2H, d, 1JPH=250 Hz,
PH2). 11B NMR (96.3 MHz; C6D6/C6H4F2 50:50): δ -18.0 (d,
1JBP=46 Hz). 19F NMR (C6D6/C6H4F2 50:50): δ -133.9 (6F, m,
3
(CDCl3): δ -126.2 (6F, d, JFF =20 Hz, o-F), -160.2 (3F, t,
3JFF=20 Hz, p-F), -166.5 (6F, t, 3JFF=20 Hz, m-F). 31P NMR
(CDCl3): δ 0.3.
[Li(OEt2)2][Ph2P{Al(C6F5)3}{BH3}] (5). A solution of freshly
prepared Li[Ph2P(BH3)] (0.46 g, 2.2 mmol) in diethyl ether
(15 mL) was cooled to -78 °C and treated with Al(C6F5)3
3
toluene (1.38 g, 2.2 mmol). The resulting solution was stirred at
room temperature for 30 min before the solvent was removed
under vacuum affording a sticky colorless solid. The product
was washed with light petroleum to give a fine powder, which
was recrystallized by diffusion of light petroleum through a
diethyl ether solution at -25 °C affording needle-shaped crys-
tals (0.93 g, 1.1 mmol, 48%). Elem. Anal. Calcd (found) for
C38H33AlBF15LiO2P: C, 51.73 (51.64); H, 3.77 (3.69). 1H NMR
(CDCl3): δ 7.30 (10H, m, C6H5), 3.53 (8H, q, JHH =7.1 Hz,
o-F), -161.5 (3F, t, 3JFF=20 Hz, p-F), -165.5 (6F, m, m-F). 31
NMR (C6D6/C6H4F2 50:50): δ -154.6 (br).
P
[Li2(12-crown-4)2][H2P{B(C6F5)3}2]2 (2). A suspension of Li-
[H2PB(C6F5)3] (0.32 g, 0.6 mmol) in toluene (10 mL) was cooled
(-78 °C) and treated with B(C6F5)3 (0.30 g, 0.6 mmol). The
reaction mixture became homogeneous momentarily but pro-
ceeded to precipitate a colorless oil. The emulsion was stirred at
room temperature for 30 min before the solvent was removed
under vacuum yielding a foam which was washed with light
petroleum affording a fine powder (0.24 g, 0.2 mmol, 33%). 1H
NMR (C6D6/C6H4F2 50:50): δ 5.08 (2H, d, 1JPH=350 Hz, PH2).
11B NMR (C6D6/C6H4F2 50:50): δ -15.3. 19F NMR (C6D6/
C6H4F2 50:50): δ -129.7 (12F, m, o-F), -159.8 (6F, m, p-F),
-165.8 (12F, m, m-F). 31P NMR (C6D6/C6H4F2 50:50): δ -96.8
(br). The crude solid was treated with a THF (10 mL) solution of
12-crown-4 (0.1 mL, 0.6 mmol), concentration afforded block-
CH2), 1.17 (12H, t, JHH=7.1 Hz, CH3), 0.55 (3H, br, BH3). 11
B
NMR (CDCl3): δ -34.2 (br). 19F NMR (CDCl3): δ -120.0 (6F,
m, o-F), -155.5 (3F, t, 3JFF=20 Hz, p-F), -163.3 (6F, m, m-F).
31P NMR (CDCl3): δ -39.2 (br).
[Li(OEt2)3][H(tBu)P{B(C6F5)3}{BH3}] (6). Li[H(tBu)P(B-
H3)] (0.18 g, 1.6 mmol) in diethyl ether (20 mL) was treated
with B(C6F5)3 (0.83 g, 1.6 mmol) at -78 °C. The homogeneous
reaction mixture was allowed to warm to room temperature
where it was stirred for 30 min before all solvents were removed
1
under reduced pressure affording an oily material. H NMR
=
(CDCl3): δ 4.78 (1H, d, 1JPH=360 Hz, PH), 3.59 (12H, q, J HH
7.1 Hz, CH2), 1.19 (18H, t, JHH =7.1 Hz, CH3), 0.94 (9H, d,
shaped crystals. Elem. Anal. Calcd (found) for C36H2B2F30P
O4C8H16Li: C, 42.62 (43.27); H, 1.46 (1.44). H NMR (C6D6/
3
1
3JPH = 13 Hz, C(CH3)3), -0.04 (3H, br, BH3). 11B NMR
C6H4F2 50:50): δ 5.08 (2H, d, 1JPH=354 Hz, PH2), 3.07 (32H, s,
CH2). 11B NMR (C6D6/C6H4F2 50:50): δ -15.8. 19F NMR
(C6D6/C6H4F2 50:50): δ -129.1 (6F, br, o-F), -159.6 (3F, m,
p-F), -165.4 (6F, m, m-F). 31P (C6D6/C6H4F2 50:50): δ -100.8.
[Li(12-crown-4)2][H2P{B(C6F5)3}{BH3}] (3). Borane-dimethyl
sulfide (0.1 mL, 1 mmol) was added to a solution of Li[H2PB(C6-
F5)3] (0.56 g, 1.0 mmol) in diethyl ether (10 mL) at -78 °C. The
solution was then allowed to warm to room temperature before the
addition of 12-crown-4 (0.3 mL, 2 mmol) resulting in the precipita-
tion of impurities, which were separated by filtration. The filtrate
was reduced to dryness, and the pure product precipitated from
dichloromethane/light petroleum solution at -25 °C. Elem. Anal.
Calcd (found) for C34H37B2F15LiO8P: C, 44.48 (44.28); H, 4.06
(4.15). 1H NMR (CDCl3): δ 3.78 (2H, d, 1JPH=334 Hz, PH2), 3.65
(32H, s, CH2), 0.20 (3H, br, BH3). 13C NMR (CDCl3): δ 66.52
(CH2).11BNMR(CDCl3):δ-18.0 (1B, d, 1JBP=69 Hz, B(C6F5)3),
-41.3 (1B, br, BH3). 19F NMR (CDCl3): δ -130.2 (6F, br, o-F),
-160.9 (3F, t, 3JFF=21 Hz, p-F), -165.7 (6F, m, m-F). 31P NMR
(CDCl3): δ -92.33.
1
(CDCl3): δ -15.8 (1B, d, JBP=76 Hz, B(C6F5)3), -40.5 (1B,
br, BH3). 19F NMR (CDCl3): δ -128.2 (6F, br, o-F), -160.7
(3F, br, p-F), -165.6 (6F, br, m-F). 31P NMR (CDCl3): δ -22.9.
Needle shaped crystals of [Li(12-crown-4)] [H(tBu)P{B(C6-
F5)3}{BH3}] 6a were grown by dissolving the product in a
minimum volume of diethyl ether and adding 2 equiv of 12-
crown-4 before cooling the solution to -25 °C for several hours
(0.73 g, 0.9 mmol, 54%). Elem. Anal. Calcd (found) for
C22H13B2F15P C16H32O8Li: C, 46.85 (46.72); H, 4.66 (4.90).
3
1H NMR (CDCl3): δ 4.60 (1H, d, 1JPH=356 Hz, PH), 3.55 (32H,
s, CH2), 0.84 (9H, d, 3JPH=12 Hz, C(CH3)), 0.28 (3H, br, BH3).
13C NMR (CDCl3): δ 66.3 (CH2), 29.2 (CH3). 11B NMR
1
(CDCl3): δ -16.0 (1B, d, JBP = 75 Hz, B(C6F5)3), -41.0
(1B, br, BH3). 19F NMR (CDCl3): δ -127.5 (6F, v br, o-F),
-161.5 (3F, m, p-F), -166.0 (6F, m, m-F). 31P NMR (CDCl3):
δ -18.7 (br).
[Li(OEt2)2][H(tBu)P{Al(C6F5)3}{H3B}] (7). A solution of Al-
(C6F5)3 toluene (0.58 g, 0.9 mmol) in diethyl ether was treated
3
with freshly prepared Li[PH(tBu)(BH3)] (0.10 g, 0.93 mmol) at
-78 °C. The reaction mixture was allowed to warm to room
temperature and was then stirred for 30 min before the solvent
was removed under vacuum affording a colorless oil. 1H NMR
[Li(OEt2)3][Ph2P{B(C6F5)3}{BH3}] (4). Li[Ph2P(BH3)] (0.27g,
1.3 mmol), freshly prepared by the treatment of H(Ph)2PBH3
with nBuLi, was treated with a solution of B(C6F5)3 (0.68 g, 1.3
mmol) in diethyl ether (15 mL) at -78 °C. The reaction mixture
dissolved at 0 °C, before precipitating a colorless solid approa-
ching room temperature, which in turn redissolved after further
stirring for several minutes. After stirring for 30 min, all volatiles
were removed under vacuum. The product was purified by slow
evaporation of a concentrated diethyl ether solution, which was
cooled to -25 °C at the first sign of nucleation yielding crystals
of 4 (0.73 g, 0.8 mmol, 60%). Elem. Anal. Calcd (found) for
(CDCl3): δ 3.68 (1H, d, 1JPH=320 Hz, PH), 3.61 (8H, q, JHH
=
7.1 Hz, CH2), 1.21 (12H, t, JHH =7.1 Hz, CH3), 1.08 (9H, d,
3JPH=23 Hz, C(CH3)3), 0.06 (3H, br, BH3). 11B NMR (CDCl3):
δ -40.8. 19F NMR (CDCl3): δ -120.8 (6F, m, o-F), -155.6 (3F,
m, p-F), -162.9 (6F, m, m-F). 31P NMR (CDCl3): δ -54.9.
Light petroleum was layered over a dichloromethane solution
containing 12-crown-4 and cooled to -25 °C overnight afford-
ing small block-shaped crystals of [Li(12-crown-4)][H(tBu)-
P{Al(C6F5)3}{BH3}] 7a (0.42 g, 0.5 mmol, 57%). Elem. Anal.
Calcd (found) for C22H13AlBF15P C16H32O8Li: C, 46.08
3
(42) (a) Lancaster, S. J. http://www.syntheticpages.org/pages/215; (b)
Pohlmann, J. L. W.; Brinckman, F. E. Z. Naturforsch. 1965, 20b, 5.
(43) Chakraborty, D.; Chen, E. Y-X. Inorg. Chem. Commun. 2002, 5, 698.
(44) Fisher, G. B.; Fuller, J. C.; Harrison, J.; Alvarez, S. G.; Burkhardt,
E. R.; Goralski, C. T.; Singaram, B. J. Org. Chem. 1994, 59, 6378.
(45.43); H, 4.58 (4.96). The discrepancy in the elemental analyses
results for 7a is presumably due to the highly sensitive nature of
this compound and the resulting difficulties with its manipula-
tion. 1H NMR (CDCl3): δ 3.59 (1H, d, 1JPH=315 Hz, PH), 3.64

11482 Inorganic Chemistry, Vol. 48, No. 23, 2009
Fuller et al.
Table 3. Crystallographic Data
2
4
5
6a
chemical formula
[Li2(12-crown-4)2]
[H2P{B(C6F5)3}2]2
1240.11
triclinic
P1
[Li(OEt2)3][{H3B}P-
Ph2{B(C6F5)3}]
940.29
triclinic
P1
12.9559(9)
13.0944(7)
14.6714(6)
79.742(4)
80.895(5)
61.807(4)
2150.7(2)
120(2)
[Li(OEt2)2][{H3B}P-
Ph2{Al(C6F5)3}]
882.34
triclinic
P1
12.277(2)
12.334(2)
14.628(3)
84.969(12)
71.244(13)
73.580(14)
2011.8(6)
120(2)
[Li(12-crown-4)]
[{H3B}PHtBu{B(C6F5)3}]
974.27
triclinic
P1
8.545(2)
15.851(5)
16.004(3)
99.750(17)
96.41(2)
91.167(17)
2121.4(9)
120(2)
M
crystal system
space group
˚
a/A
12.465(13)
14.37(3)
˚
b/A
˚
c/A
14.461(14)
62.10(13)
84.68(10)
89.27(10)
2279(5)
120(2)
1
42972
R/deg
β/deg
γ/deg
3
˚
V/A
T/K
Z
2
46149
9827, 0.0279
8260
2
41196
9117, 0.0603
7606
2
48265
9718, 0.0649
6586
reflections measured
unique reflections, Rint
observed data
10370, 0.1233
5853
wR2, R1 (observed data)
wR2, R1 (all data)
Largest difference peak
0.1373, 0.0919
0.1620, 0.1821
0.630
0.0955, 0.0381
0.1016, 0.0481
0.808
0.1422, 0.0573
0.1501, 0.0684
0.780
0.1117, 0.0577
0.1270, 0.1019
0.725
(32H, s, CH2), 1.06 (9H, d, 3JPH=14 Hz, C(CH3)), 0.39 (3H, br,
BH3). 13C NMR (CDCl3): δ 66.1 (CH2), 28.1 (CH3). 11B NMR
(CDCl3): δ -40.9. 19F NMR (CDCl3): δ -119.7 (6F, d, JFF=20
Hz, o-F), -156.4 (3F, t, JFF=20 Hz, p-F), -163.2 (6F, m, m-F).
31P NMR (CDCl3): δ -50.5 (br).
[(cyclo-NC5H10)2(μ-BH2)2] and [Li(12-crown-4)2][HB(C6F5)3]
(8 and 9). To a solution of [Li(THF)n][cyclo-NC5H10(BH3)]
(prepared according to the literature method44) (5 mmol) in
THF (2 mL) was added B(C6F5)3 (2.56 g, 5 mmol) at room
temperature. The resultant solution was cooled to -25 °C,
affording colorless X-ray quality plates of [(cyclo-NC5H10)2-
(μ-BH2)2], which were separated by filtration. 1H NMR (C6D6):
δ 3.33 (8H, d, 3JHH=4.7 Hz, CH2), 1.38 (8H, m, CH2), 1.12 (4H,
m, CH2). 13C NMR (C6D6): δ 68.2, 23.7, 23.5. 11B NMR (C6D6):
δ 2.5 (t, 1JBH=112 Hz, BH2).
C40H38BF15LiNO8: C, 49.87 (49.80); H, 3.98 (3.85); N, 1.45
1
(1.45). H NMR (CDCl3): δ 3.60 (s, 32H, CH2), 3.78 (s, 1H,
NH), 6.25 (t, 1H, JHH=7.2 Hz, p-H), 6.30 (d, 2H, JHH=7.8 Hz,
o-H), 6.82 (m, 2H, m-H). 11B NMR (CDCl3): δ -9.9. 19F NMR
3
(CDCl3): δ -134.0 (m, 6F, o-F), -162.6 (t, 3F, JFF=20 Hz,
p-F), -166.4 (m, 6F, m-F).
Crystal Structure Analyses. Diffraction data for 2, 4, 5, and 6
were collected by the EPSRC Crystallography Service at the
University of Southampton on a Bruker-Nonius KappaCCD
diffractometer, and the data were processed using the DENZO/
SCALEPACK programs.45 Diffraction data for 3, 8, 9, and 11
werecollected atUEA on anOxfordDiffraction Xcalibur-3 CCD
diffractometer, and processed using the CrysAlis-CCD and RED
programs.46 Compound 8 has been reported previously.36 The
anion of 11 has been described,37 and the structural data for 11
are in the Supporting Information. Crystals of 3 and 9 gave poor
quality intensity data; the identities of these compounds were
established, but full analyses were not feasible. In each case, the
structure was determined by direct method routines in the
SHELXS program and refined by full-matrix least-squares meth-
ods on F2 in SHELXL47 within the WinGX program suite.48 The
results are collated in Table3. Scattering factors for neutral atoms
were taken from literature values.49
To the filtrate was added 12-crown-4 (0.2 mL, 1.2 mmol) at
room temperature before being cooled to -25 °C to afford small
colorless crystals of [Li(12-crown-4)2][(C6F5)3BH]; X-ray ana-
lysis of these crystals produced a poor quality result suitable
only to establish connectivity. 1H NMR (CDCl3): δ 3.66 (32H, s,
CH2), 1.88 (1H, br, BH). 13C NMR (CDCl3): δ 66.2. 11B NMR
1
(CDCl3): δ -25.3 (d, JBH = 88 Hz). 19F NMR (CDCl3): δ
-134.0 (6F, m, o-F), -146.4 (3F, t, 3JFF=20 Hz, p-F), -167.5
(6F, m, m-F).
H2PhNB(C6F5)3 (10). A solution of (C6F5)3B OEt2 (2.75 g,
Acknowledgment. The authors would like to thank the En-
gineering and Physical Sciences Research Council and the Uni-
versity of East Anglia for financial support. The help of Professor
Paul Pringle and co-workers at the University of Bristol with the
3
4.7 mmol) in toluene (50 mL) was treated with aniline (0.43 mL,
4.7 mmol). Addition of light petroleum (150 mL) followed by
cooling to -25 °C afforded a colorless solid. Elem. Anal. Calcd
(found): C, 47.64 (47.76); H, 1.17 (1.16); N, 2.31 (2.30). 1H NMR
(CDCl3): δ 7.28 (4H, m, CH), 7.02 (1H, m, CH), 6.79 (2H, br,
NH). 13C NMR (CDCl3): δ 134.0 (i-C), 130.0 (CH), 129.2 (CH),
122.3 (CH). 11B NMR (CDCl3): δ -5.3. 19F NMR (CDCl3): δ
-133.3 (6F, m, o-F), -155.1 (3F, t, 3JFF=20 Hz, p-F), -162.1
(6F, m, m-F).
preparation of H3P B(C6F5)3 is gratefully acknowledged.
3
Supporting Information Available: Additional information as
noted in the text. This material is available free of charge via the
Internet at http://pubs.acs.org.
[Li(12-crown-4)2][HPhNB(C6F5)3] (11). A solution of H2Ph-
NB(C6F5)3 (1.15 g, 1.9 mmol) in diethyl ether (10 mL)
was cooled to 0 °C before the addition of BuLi (1.9 mmol).
After warming to room temperature 12-crown-4 (0.6 mL, 3.8
mmol) was added, resulting in the precipitation of the pure
product as a colorless solid which was separated by filtration.
Colorless crystals suitable for X-ray analysis were obtained by
cooling the filtrate to 0 °C. Elem. Anal. Calcd (found) for
(45) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(46) Programs CrysAlis-CCD and -RED; Oxford Diffraction Ltd: Abing-
don, U.K., 2008.
(47) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008,
64, 112.
(48) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(49) International Tables for X-Ray Crystallography; Wilson, A. J. C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992, Vol. C, pp 193,
219, and 500.
n