Synthesis and structural characterization of phosphine-borane-stabilized dicarbanions with either rigid or flexible spacers

Article abstract of DOI:10.1021/om4011142

The reaction between 1,2-C₆H₄(CH₂Cl) ₂ and 2 equiv of in situ generated [R₂P(BH₃)]Li in THF gives the corresponding o-phenylene-bridged bis(phosphine-boranes) 1,2-C₆H₄{CH₂P(BH₃)R ₂}₂ (R = iPr (1a), Ph (2a), Cy (3a)). Treatment of 1a-3a with 2 equiv of nBuLi and 2 equiv of tmeda yields the corresponding phosphine-borane-stabilized carbanion (PBC) complexes [1,2-C₆H ₄{CHP(BH₃)R₂}₂][Li(tmeda)] ₂·nL (R = iPr, n = 0 (1b); R = Ph, nL = THF (2b); R = Cy, nL = 2PhCH₃ (3b)). In contrast, treatment of 1a with 2 equiv of MeK, followed by 2 equiv of pmdeta, yields the monodeprotonation product [1,2-C ₆H₄{CHP(BH₃)iPr₂}{CH ₂P(BH₃)iPr₂}][K(pmdeta)] (1c), due to a competing side reaction with the solvent. Treatment of 1a and 3a with the less aggressive metalating agent PhCH₂K gives the corresponding dipotassium salts, the latter of which was isolated as the adduct [1,2-C ₆H₄{CHP(BH₃)Cy₂}₂] [K(pmdeta)]₂ (3c). X-ray crystallography reveals that 1b-3b adopt similar structures in which the lithium ions are coordinated by the carbanion centers and the borane hydrogen atoms of the phosphine-borane-stabilized carbanions. The potassium ion in 1c is coordinated by the carbanion center and by B-H···K contacts with both borane groups, whereas the two potassium ions in 3c exhibit multihapto interactions with the aromatic ring of the PBC ligand, along with B-H···K contacts. The reaction between ClSiMe₂CH₂CH₂SiMe ₂Cl and 2 equiv of in situ generated [R₂P(BH ₃)CH₂]Li gives the bis(phosphine-boranes) [CH ₂SiMe₂CH₂P(BH₃)R₂] ₂ (R = Me (4a), Ph (5a)). Treatment of 4a or 5a with 2 equiv of nBuLi in THF readily yields the 1,6-dicarbanion complexes [CH₂SiMe ₂CHP(BH₃)R₂]₂[Li(THF) ₂]₂ (R = Me (4b), Ph (5b)). A similar reaction of 5a, 2 equiv of PhCH₂K, and 2 equiv of pmdeta in THF gives the potassium complex [CH₂SiMe₂CHP(BH₃)Ph₂] ₂[K(pmdeta)]₂ (5c). Complex 5b adopts a linear structure in the solid state, while 5c adopts an unusual polycyclic structure by virtue of bridging K···H-B-H···K contacts.

Full text of DOI:10.1021/om4011142

Article
pubs.acs.org/Organometallics
Synthesis and Structural Characterization of Phosphine−Borane-
Stabilized Dicarbanions with either Rigid or Flexible Spacers
Keith Izod,*,† Casey M. Dixon,† Emma McMeekin,† Lee Rodgers,† Ross W. Harrington,†
and Ulrich Baisch‡
†Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne NE1 7RU,
U.K.
‡Department of Chemistry, University of Malta, Msida MSD 2080, Malta
S
* Supporting Information
ABSTRACT: The reaction between 1,2-C6H4(CH2Cl)2 and 2 equiv of in situ generated
[R2P(BH3)]Li in THF gives the corresponding o-phenylene-bridged bis(phosphine−
boranes) 1,2-C6H4{CH2P(BH3)R2}2 (R = iPr (1a), Ph (2a), Cy (3a)). Treatment of 1a−3a
with 2 equiv of nBuLi and 2 equiv of tmeda yields the corresponding phosphine−borane-
stabilized carbanion (PBC) complexes [1,2-C6H4{CHP(BH3)R2}2][Li(tmeda)]2·nL (R =
iPr, n = 0 (1b); R = Ph, nL = THF (2b); R = Cy, nL = 2PhCH3 (3b)). In contrast,
treatment of 1a with 2 equiv of MeK, followed by 2 equiv of pmdeta, yields the
monodeprotonation product [1,2-C6H4{CHP(BH3)iPr2}{CH2P(BH3)iPr2}][K(pmdeta)]
(1c), due to a competing side reaction with the solvent. Treatment of 1a and 3a with the
less aggressive metalating agent PhCH2K gives the corresponding dipotassium salts, the
latter of which was isolated as the adduct [1,2-C6H4{CHP(BH3)Cy2}2][K(pmdeta)]2 (3c).
X-ray crystallography reveals that 1b−3b adopt similar structures in which the lithium ions
are coordinated by the carbanion centers and the borane hydrogen atoms of the
phosphine−borane-stabilized carbanions. The potassium ion in 1c is coordinated by the carbanion center and by B−H···K
contacts with both borane groups, whereas the two potassium ions in 3c exhibit multihapto interactions with the aromatic ring of
the PBC ligand, along with B−H···K contacts. The reaction between ClSiMe2CH2CH2SiMe2Cl and 2 equiv of in situ generated
[R2P(BH3)CH2]Li gives the bis(phosphine−boranes) [CH2SiMe2CH2P(BH3)R2]2 (R = Me (4a), Ph (5a)). Treatment of 4a or
5a with 2 equiv of nBuLi in THF readily yields the 1,6-dicarbanion complexes [CH2SiMe2CHP(BH3)R2]2[Li(THF)2]2 (R = Me
(4b), Ph (5b)). A similar reaction of 5a, 2 equiv of PhCH2K, and 2 equiv of pmdeta in THF gives the potassium complex
[CH2SiMe2CHP(BH3)Ph2]2[K(pmdeta)]2 (5c). Complex 5b adopts a linear structure in the solid state, while 5c adopts an
unusual polycyclic structure by virtue of bridging K···H−B−H···K contacts.
from the diversity of coordination modes adopted by PBC
ligands: although a terminal C-donor mode has been observed,
in the majority of cases B−H···M contacts are dominant,
leading to an array of chelating and bridging coordination
motifs.3−6 In addition, B−H···E contacts have been shown to
significantly stabilize electron-deficient metal centers: DFT
calculations suggest that the B−H···Sn and B−H···Pb contacts
observed in a series of phosphine−borane-substituted dialkyl-
stannylenes and -plumbylenes stabilize these compounds by
around 30 kcal mol−1.4 Furthermore, Me2P(BH3) substituents
stabilize an adjacent carbanion center to a greater degree in
comparison to SiMe3 groups by virtue of the more efficient
negative hyperconjugation in the former. This has the
consequence that C−H groups adjacent to a PMe2(BH3)
moiety are more acidic than those adjacent to a SiMe3 group.
As an illustration of this, SiMe4 undergoes slow metalation with
nBuLi only in the presence of activating tertiary amine donors
such as tmeda,7 whereas isoelectronic PMe3(BH3) reacts
INTRODUCTION
■
Phosphine−borane-stabilized carbanions (PBCs) have been
used widely for the synthesis of polyfunctional phosphines,
including chiral diphosphines such as DIPAMP, many of which
have applications as supporting ligands in catalysis.1 However,
these carbanions are typically generated and used in situ and,
until recently, little attention had been paid to their
composition and structures. This is particularly notable, given
that a PMe2(BH3) group is isoelectronic and isosteric with a
SiMe3 group and that the latter substituent has played a key
role in the development of main-group, transition-metal, and
lanthanide organometallic and coordination chemistry, espe-
cially in the stabilization of new classes of compounds with, for
example, unusually low coordination numbers or EM/EE
multiple bonds.2
Despite the isoelectronic nature of SiMe3 and PMe2(BH3)
groups, silicon-stabilized carbanions and PBCs exhibit some-
what different characteristics in their metal complexes. For
example, the residual hydridic character of the BH3 hydrogen
atoms in PBCs provides unique opportunities for the
interaction of these groups with metal centers. This is evident
Received: November 17, 2013
Published: December 19, 2013
© 2013 American Chemical Society
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Scheme 1
Scheme 2
rapidly with nBuLi in the absence of such activators to give the
corresponding phosphine−borane-stabilized carbanion complex
Me2P(BH3)CH2Li (tmeda = N,N,N′,N′-tetramethylethylene-
diamine).3e A corollary of this enhanced acidity is that the
corresponding PBCs are somewhat less nucleophilic than their
silicon-stabilized counterparts and so are less likely to induce
unwanted redox processes in their reactions with easily
reducible metal centers such as Pb(II).4
Over the past few years we, and others, have developed a
range of PBCs and have shown that these are excellent ligands
for s-, p-, d-, and f-block metal centers.3−6,8 With very few
exceptions, the PBCs reported previously fall into three
categories: (i) monodentate ligands stabilized by a single
phosphine−borane substituent [R2CP(BH3)R2]−,3b−g,l,4d,e,6 (ii)
monodentate ligands stabilized by two adjacent phosphine−
borane substituents [R2P(BH3)CHP(BH3)R2],3j,k,m,n,5 or (iii)
sterically demanding bidentate ligands in which each carbanion
center is stabilized by a single phosphine−borane substituent,
e.g. [R2P(BH3)CSiMe2(SiMe3)CH2CH2SiMe2(Me3Si)CP-
(BH3)R2]2−.3a,h,4a−c In each of these cases the monodentate
nature of the ligands and/or the flexibility of the linker group
allows the phosphine−borane groups to tilt toward the metal
centers where necessary, maximizing the B−H···M contacts;
this is of particular importance in compounds where these
contacts result in the significant stabilization of an electron-
poor metal center (e.g., Sn(II) or Pb(II)).4 We were interested
to observe the effect that a rigid backbone might have on these
contacts, since this should reduce the degree to which the
borane groups can tilt toward the metal and thus substantially
affect the nature of the B−H···M interactions, and so have
developed a new range of rigid o-phenylene-linked PBCs. In
this contribution we describe the synthesis of the phosphine−
borane precursors to these PBCs, their metalation, and the
structures of their alkali-metal derivatives. For comparison, we
also describe the synthesis of two new bis(phosphine−boranes)
linked by a flexible spacer group and the metalation of these
species to give the corresponding 1,6-dicarbanions.
RESULTS AND DISCUSSION
■
o-Phenylene-bridged bis(phosphine−boranes), 1,2-
C6H4{CH2P(BH3)R2}2, with a selection of substituents at
phosphorus have previously been prepared as intermediates in
the synthesis of o-xylyl-bridged diphosphines, ligands which
have been successfully exploited in transition-metal-mediated
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Figure 1. Molecular structures of (a) 1b, (b) 2b, and (c) 3b, with 40% probability ellipsoids and with C-bound H atoms (except those bound to
benzylic C atoms) omitted for clarity. Minor disorder components for 2b and solvent of crystallization for 2b and 3b are also omitted for clarity.
Selected bond lengths (Å) are as follows. 1b: Li(1)−C(1) 2.235(5), Li(1)···C(2) 2.636(5), Li(1)−N(3) 2.147(5), Li(1)−N(4) 2.124(5), Li(1)−
H(1C) 2.08(3), Li(1)···B(1) 2.763(6), Li(2)−C(8) 2.227(5), Li(2)···C(7) 2.626(5), Li(2)−N(1) 2.146(5), Li(2)−N(2) 2.110(5), Li(2)−H(2C)
2.03(2), Li(2)···B(2) 2.708(6), P(1)−B(1) 1.934(3), P(2)−B(2) 1.929(3). 2b: Li(1)−C(1) 2.241(4), Li(1)···C(2) 2.701(4), Li(1)−N(1) 2.041(6),
Li(1)−N(2) 2.094(5), Li(1)−H(1A) 2.05(2), Li(1)···B(1) 2.635(5), B(1)−P(1) 1.930(2). 3b: Li(1)−C(1) 2.254(6), Li(1)···C(2) 2.700(6), Li(1)−
N(1) 2.118(6), Li(1)−N(2) 2.047(6), Li(1)−H(1B) 2.09(3), Li(1)···B(1) 2.551(7), Li(2)−C(8) 2.271(6), Li(2)···C(7) 2.530(6), Li(2)−N(3)
2.123(6), Li(2)−N(4) 2.134(6), Li(2)−H(2A) 1.96(3), Li(2)···B(2) 2.695(7), P(1)−B(1) 1.937(4), P(2)−B(2) 1.951(4).
catalysis.9 However, until now the deprotonation of these
compounds to give PBCs has not been investigated. In the
current study, we have prepared the previously unreported
bis(phosphine boranes) 1,2-C6H4{CH2P(BH3)R2}2 (R = iPr
(1a), Ph (2a), Cy (3a)) according to the method used by
Imamoto and co-workers for the synthesis of related bis-
(phosphine−boranes) (e.g., R = tBu).9a The reactions between
1,2-C6H4(CH2Cl)2 and 2 equiv of in situ generated R2P(BH3)
Li in THF gave 1a−3a as air-stable, colorless solids after a
straightforward aqueous workup (Scheme 1). In contrast,
similar reactions between 1,2-C6H4(CH2Br)2 and R2P(BH3)Li
under the same conditions gave complex mixtures of products,
possibly arising from partial quaternization of the phosphorus
centers.1 0 The linear bis(phosphine−boranes)
[CH2SiMe2CH2P(BH3)R2]2 (R = Me (4a), Ph (5a)) were
prepared by the reaction between ClSiMe2CH2CH2SiMe2Cl
and 2 equiv of R2P(BH3)CH2Li and were isolated as colorless,
borane adducts.1,3−6 In order to enable comparison with the
metalated derivatives, compounds 1a and 4a were studied by X-
ray crystallography; details of the structures of 1a and 4a may
be found in the Supporting Information.
Treatment of THF solutions of 1a−3a with 2 equiv of nBuLi,
followed by 2 equiv of tmeda, gave the complexes [1,2-
C6H4{CHP(BH3)R2}2][Li(tmeda)]2·nL (R = iPr, n = 0 (1b); R
= Ph, nL = THF (2b); R = Cy, nL = 2PhCH3 (3b)) as yellow
to orange crystals in good yield (Scheme 1). The 1H, 13C{1H},
11B{1H}, 31P{1H}, and 7Li NMR spectra of 1b−3b are
consistent with deprotonation at both of the benzylic sites in
each case. The 31P{1H} NMR spectra of these compounds
consist of broad multiplets at 16.3 (1b), 6.2 (2b), and 12.3 ppm
(3b), respectively. We have previously noted that α-metalation
of phosphine−borane adducts leads to a significant increase in
the 31P−11B coupling constant of between 20 and 50 Hz. For
2b no coupling was resolved; however, for 1b and 3b the
31P−11B coupling constants are 78.4 and 105.3 Hz, respectively,
consistent with the formation of a phosphine−borane-stabilized
carbanion in each case.
1
crystalline solids (Scheme 2). The H, 13C{1H}, 11B{1H}, and
31P{1H} NMR spectra of 1a−5a are as expected. The 31P
signals fall in a reasonably wide range (3.4−35.2 ppm),
depending on the nature of the substituents at phosphorus,
whereas the 11B{1H} signals fall in the narrow range −37.5 to
−44.3 ppm; where resolved, the 31P−11B coupling constants lie
in the range 49.0−69.5 Hz, as expected for neutral phosphine−
In contrast to the foregoing, treatment of 1a with 2 equiv of
MeK in cold (−10 °C) diethyl ether does not result in double
deprotonation of the bis(phosphine−borane); 31P{1H} NMR
spectra of the crude reaction solution clearly indicate
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monodeprotonation of 1a under these conditions (Scheme 1).
Addition of pmdeta to the reaction solution, removal of solvent,
and crystallization from n-hexane gave the monodeprotonated
compound 1,2-C6H4{CHP(BH3)iPr2}{CH2P(BH3)iPr2}][K-
(pmdeta)] (1c) as pale yellow crystals in reasonable yield
(pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine).
Since MeK is typically more reactive than nBuLi, we attribute
the formation of 1c to the competing reaction between MeK
and the diethyl ether solvent.11 This suggests that while the
initial deprotonation of 1a to give 1c is rapid, deprotonation of
the second benzylic site is rather sluggish, allowing the side
reaction between MeK and the solvent to compete. In this
regard, treatment of either 1a or 1c with 2 equiv of PhCH2K,
which does not react rapidly with the THF solvent, results in
clean double deprotonation of the bis(phosphine−boranes), as
judged by 31P{1H} NMR spectroscopy of the crude reaction
mixtures, to give the corresponding dipotassium salts, the latter
of which was isolated as the adduct [1,2-C6H4{CHP(BH3)-
Cy2}2][K(pmdeta)]2 (3c) as a yellow crystalline solid.
2.551(7), 2.695(7) Å) are consistent with an η1-BH3−Li
contact.
Compound 1c also crystallizes as a discrete molecular
species; the structure of 1c is shown in Figure 2, along with
Compounds 1b−3b crystallize as discrete monomers. These
compounds adopt similar structures in the solid state but are
not isostructural: while 1b has no solvent of crystallization, 2b
crystallizes with a molecule of THF and 3b crystallizes with two
molecules of toluene in the asymmetric unit. For both 2b and
3b the solvent of crystallization is only weakly held and is
rapidly lost under vacuum, such that samples of 2b and 3b
which had been exposed to vacuum for 15 min showed no
evidence of THF and toluene, respectively, in their NMR
spectra.
Figure 2. Molecular structure of 1c with 40% probability ellipsoids and
with C-bound H atoms omitted for clarity. Selected bond lengths (Å):
K(1)−C(8) 3.211(2), K(1)···C(7) 3.384(2), K(1)−N(1) 2.870(2),
K(1)−N(2) 2.946(2), K(1)−N(3) 3.019(2), K(1)−H(1A) 2.75(3),
K(1)−H(1C) 2.94(3), K(1)−H(2A) 3.05(3), K(1)−H(2C) 2.86(4),
K(1)···B(1) 3.319(3), K(1)···B(2) 3.371(3), K(1)···C(22) 3.535(3),
K(1)···C(25) 3.463(3), K(1)···C(28) 3.426(3), P(1)−B(1) 1.924(2),
P(2)···B(2) 1.935(3).
The structures of 1b−3b are shown in Figure 1, along with
selected bond lengths. In 1b each lithium ion is bound to one
carbanion center, the two nitrogen atoms of a chelating
molecule of tmeda, and one of the borane hydrogen atoms; in
addition, each lithium ion has short contacts to one of the two
ipso carbon atoms adjacent to a carbanion center of the PBC
ligand. The two lithium ions lie on opposite faces of an
essentially planar C6H4(CP)2 fragment. Compounds 2b and 3b
adopt structures similar to that of 1b; however, 2b possesses a
crystallographic C2 axis, which bisects the o-phenylene linker
group, and exhibits additional short contacts between each
lithium ion and one of the methyl carbon atoms of the tmeda
coligand (Li···C(22) 2.758(9) Å), while 3b exhibits an
additional short contact between one of the lithium ions and
one of the methylene carbon atoms of the tmeda coligand
(Li(1)···C(36) 2.751(5) Å).
selected bond lengths. The potassium ion is coordinated by the
carbanion center, by two η2-BH3 contacts to the PBC ligand,
and by the three nitrogen atoms of the pmdeta coligand. In
addition, there are short contacts between the potassium ion
and the ipso carbon of the aromatic ring adjacent to the
carbanion center and to three of the methyl groups of the
pmdeta coligand. The K−C(8) distance of 3.211(2) Å is at the
longer end of previously reported K−C distances involving a
benzylic carbanion center;12,15 for example, the K−C-
(carbanion) distance in [(PhCH2)K(pmdeta)]∞ is 3.171(2)
Å,16 while the K−C(carbanion) distance in [{(Me3Si)CH}-
C6H4-2-NMe2]K]∞ is 2.966(4) Å.17 However, the K−C(8)
distance in 1c is similar to the K−C distances in other
potassium complexes of PBCs; for example, the K−C distances
in [[(Me3 Si)2 {Me2 P(BH3 )}C]K(tmeda)]2 and
[[(Me3Si)2{Me2P(BH3)}C]K(pmdeta)]2 are 3.107(3) and
3.440(3) Å, respectively.3f
The Li−C(carbanion) distances in 3b (2.254(6) and
2.271(6) Å) are slightly longer than those in 1b and 2b
(2.235(5) and 2.227(5) Å, and 2.241(4) Å, respectively),
possibly due to the somewhat more sterically demanding
cyclohexyl substituents in the former compound. Overall, the
Li−C(carbanion) distances in 1b−3b are somewhat longer
than the corresponding distances in related benzyllithium
compounds12 but are similar to the Li−C distances in
previously reported PBC complexes.3 For example, the Li−C
distances in [Ph(Me2tBuSi)CH]Li(tmeda)13 and
While 31P{1H} NMR spectroscopy of the crude reaction
solutions clearly indicates that both 1a and 1c undergo double
deprotonation at the benzylic sites on treatment with
benzylpotassium to give the bis(phosphine−boranes)
C6H4{CHP(BH3)R2}2][K(pmdeta)]2 (R = iPr (1d), Cy
(3c)), only the latter of these compounds was isolated as
single crystals suitable for X-ray crystallography. The structure
of 3c is shown in Figure 3, along with selected bond lengths.
Compound 3c crystallizes as discrete monomers but adopts a
structure somewhat different from those of 1b−3b and 1c. As
expected, the larger, more polarizable potassium ions in 3c
engender significantly increased multihapto interactions with
the ligand. The two potassium ions lie in slightly different
coordination environments: both potassium ions are coordi-
nated by the three nitrogen atoms of a molecule of pmdeta;
K(1) has short contacts to one of the carbanion centers and five
14
[Ph2(Me2PhSi)C]Li(THF)2 are 2.141(4) and 2.124(3) Å,
respectively, whereas the Li−C distances in [[(Me3Si)2{Me2P-
(BH3)}C]2Li]Li(THF)33b and (THF)2Li{(Me3SiCH)2P(BH3)-
Ph}Li(THF)33i are 2.249(8) and 2.252(8) Å, and 2.218(3) and
2.234(3) Å, respectively. The Li−H distances (1b, 2.03(2),
2.08(3) Å; 2b, 2.05(2) Å; 3b, 1.96(3), 2.09(3) Å) and the Li···
B distances (1b, 2.763(6), 2.708(6) Å; 2b, 2.635(5) Å; 3b,
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Hz; 5c, 113.8 Hz). This is consistent with our previous
observation that α-metalation of phosphine−borane adducts
leads to an increase in the 11B−31P coupling constant of
between 20 and 50 Hz.3
We have thus far been unable to isolate crystals of 4b suitable
for X-ray crystallography; however, 5b,c were isolated as
colorless blocks and their solid-state structures were obtained.
Compounds 5b,c both crystallize as discrete molecular species,
although they adopt quite distinct structures in the solid state;
the molecular structures of 5b,c are shown in Figure 4, along
with selected bond lengths. Compound 5b crystallizes with a
center of inversion midway along the C(2)−C(2′) vector; the
C(2) atoms and their symmetry equivalents are disordered over
two positions with equal occupancy. The lithium ions in 5b are
coordinated by the carbanion centers, by an η1-BH3 group, and
by the oxygen atoms of two molecules of THF, affording a
Figure 3. Molecular structure of 3c with 40% probability ellipsoids.
Minor disorder components and C-bound H atoms are omitted for
clarity. Selected bond lengths (Å): K(1)−H(14C) 2.81(3), K(1)−
C(5) 3.1588(18), K(1)···C(6) 2.8186(16), K(1)···C(7) 3.2770(18),
K(1)···C(11) 3.0078(16), K(1)···C(12) 3.5132(19), K(1)−N(61)
2.8642(19), K(1)−N(65) 2.926(5), K(1)−N(69) 2.8168(18), K(1)···
C(62) 3.412(4), K(1)···C(70) 3.382(3), K(2)−H(13C) 2.71(3),
K(2)···C(6) 3.0262(17), K(2)···C(7) 3.3935(18), K(2)···C(9)
3.5176(19), K(2)···C(10) 3.1475(17), K(2)···C(11) 2.8807(16),
K(2)−C(12) 3.446(2), K(2)−N(41) 2.8206(17), K(2)−N(45)
2.8913(17), K(2)−N(49) 2.9092(16), K(2)···C(42) 3.466(3),
K(2)···C(51) 3.346(2), P(3)−B(13) 1.943(2), P(4)−B(14) 1.943(2).
of the carbon atoms in the aromatic ring of the ligand, whereas
K(2) is coordinated by both carbanion centers and three of the
carbon atoms of the aromatic ring. In addition, each potassium
ion is coordinated by one H atom of an adjacent BH3 group
and the coordination of each potassium is completed by
agostic-type K···Me−N contacts with the pmdeta coligand. The
K(1)−C(5) distance of 3.1588(18) Å is similar to the K−
C(carbanion) distance in 1c; however, the K−C distances to
the bridging carbanion center (K(1)−C(12) 3.5132(19),
K(2)−C(12) 3.446(2) Å) are somewhat longer, as expected.
Indeed, these latter distances are significantly longer than some
of the K···C contacts to carbon atoms in the aromatic ring of
the ligand (the K···C(aromatic) distances range from
2.8186(16) to 3.5176(19) Å).
The linear bis(phosphine−boranes) 4a and 5a readily
undergo double deprotonation on treatment with 2 equiv of
nBuLi in THF to give the complexes [CH2SiMe2CHP(BH3)-
R2]2[Li(THF)2]2 (R = Me (4b), Ph (5b)) (Scheme 2).
Similarly, the reaction between 5a and 2 equiv of PhCH2K
yields the potassium complex [CH2SiMe2CHP(BH3)Ph2]2[K-
(pmdeta)]2 (5c) after crystallization in the presence of the
tertiary amine coligand.
Metalation of 4a with nBuLi leads to a small upfield shift of
the 31P NMR signal (4a, 3.4 ppm; 4b, −4.8 ppm) and a small
downfield shift of the 11B NMR signal (4a, −37.5 ppm; 4b,
−33.0 ppm); metalation also leads to a significant increase in
the 11B−31P coupling constant (4a, 58.8 Hz; 4b, 88.3 Hz).
Upon metalation the 31P NMR signal of 5a moves to higher
field with decreasing electronegativity of the metal (5a, 13.5
ppm; 5b, 12.5 ppm; 5c, 11.7 ppm), while the 11B NMR signal
moves to slightly lower field with decreasing electronegativity of
the metal (5a, −38.9 ppm; 5b, −35.7 ppm; 5c, −34.7 ppm).
The 11B−31P coupling constant increases significantly on
metalation of 5a and shows a slight increase with decreasing
electronegativity of the metal center (5a, 69.5 Hz; 5b, 107.9
Figure 4. Molecular structures of (a) 5b and (b) 5c with 40%
probability ellipsoids and with C-bound H atoms and disorder
components omitted for clarity. Selected bond lengths (Å) are as
follows. 5b: Li−C(1) 2.194(6), Li−O(1) 1.900(6), Li−O(2) 1.928(6),
Li−H(1B) 2.22(3), Li···B(1) 2.888(9), P(1)−B(1) 1.924(3). 5c: K−
C(1) 3.173(4), K−N(1) 2.883(4), K−N(2) 2.966(4), K−N(3)
2.906(4), K−H(1A) 2.82(6), K−H(B) 2.78(6), K···B 3.587(6), K···
B′ 3.524(7), K···C(18) 3.506(6), K···C(24) 3.392(5), K···C(21)
3.508(5), P−B 1.921(5).
382
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1H and 13C{1H} NMR spectra were recorded on a JEOL ECS500
spectrometer operating at 500.16 and 125.65 MHz, respectively, or a
Bruker Avance300 spectrometer operating at 300.15 and 75.47 MHz,
respectively; chemical shifts are quoted in ppm relative to
tetramethylsilane. 31P{1H}, 11B{1H}, and 7Li NMR spectra were
recorded on a JEOL ECS500 spectrometer operating at 202.35,
160.16, and 194.38 MHz, respectively; chemical shifts are quoted in
ppm relative to external 85% H3PO4, BF3·Et2O, and 0.1 M LiCl,
respectively. All NMR spectra were recorded at 295 K. Elemental
analyses were obtained by the Elemental Analysis Service of London
Metropolitan University.
distorted-tetrahedral geometry. The Li−C distance of 2.194(6)
Å is somewhat shorter than the corresponding distances in 1b−
3b but lies in the typical range of Li−C distances in alkyllithium
compounds (see above).
Compound 5c crystallizes with an unusual cyclic structure
with a crystallographic C2 axis perpendicular to the C(2)−
C(2A) bond. Each potassium ion is coordinated by the
carbanion center and by an H atom of the borane group at one
end of the PBC ligand. In addition, each potassium ion is
coordinated by the three nitrogen atoms of a molecule of
pmdeta and by one H atom of the second BH3 group in the
molecule. Thus, each BH3 group bridges between the two
potassium ions in a μ2-η1:η1 fashion to generate a (K−H−B−
H)2 cycle. The K−C distance of 3.173(4) Å lies in the typical
range for K−C σ bonds (see above). The K−H distances of
2.78(6) and 2.82(6) Å are also typical of such contacts; for
example, the K−H distances in [[(Me3Si)2{Me2P(BH3)}C]-
K]∞ range from 2.74(5) to 2.92(5) Å.3c
While compounds 1b−3b, 1c, and 3c possess planar
carbanion centers due to extensive delocalization of charge
into both the aromatic ring and the P−C σ* orbitals,
compounds 5b,c crystallize with pyramidal carbanion centers.
For 5c the two carbanion centers adopt an R,S configuration,
while for 5c they adopt an S,S configuration; however, in
solution the C−Li/K contacts are likely to be highly labile and
racemization of these centers will be rapid.
Comparison of the structure of the free phosphine−borane
1a with that of the corresponding lithium complex 1b reveals
that metalation results in contraction of the C(carbanion)−P
distances (C(1)−P(1) 1.8392(11) (1a), 1.748(3) Å (1b);
C(8)−P(2) 1.8372(11) (1a), 1.755(3) Å (1b)), consistent with
extensive delocalization of charge from the carbanion centers
into the P−C σ* orbitals. Similarly, comparison of the
structures of 5b,c with that of the closely related precursor
bis(phosphine−borane) 4a reveals a comparable shortening of
the C(carbanion)−P and C(carbanion)−Si distances (C-
(carbanion)−P 1.8000(19) (4a), 1.729(3) (5b), 1.716(5) Å
(5c); C(carbanion)−Si 1.892(2) (4a), 1.830(3) (5b), 1.805(6)
Å (5c)).
Compounds 1b−5b, 5c, 1d, and 3c are potentially excellent
ligand transfer reagents for the synthesis of main-group and
transition-metal dialkyls. We are currently investigating this
chemistry, with a particular focus on the effect of the rigid
aromatic backbone in the o-phenylene-bridged systems on the
structures and stabilities of their main-group-element deriva-
tives.
1,2-C6H4{CH2P(BH3)iPr2}2 (1a). To a solution of iPr2PH(BH3)
(1.61 g, 12.39 mmol) in THF (20 mL) was added nBuLi (4.9 mL,
12.39 mmol), and this mixture was stirred for 1 h. To this solution was
added a solution of α,α′-dichloro-o-xylene (1.05 g, 6.19 mmol) in THF
(20 mL), and this mixture was stirred at room temperature for 16 h.
Water (30 mL) was added, and the organic phase was extracted into
dichloromethane (3 × 20 mL). The combined extracts were dried over
MgSO4, and the solvent was removed under vacuum to give 1a as a
colorless solid. Single crystals suitable for X-ray crystallography were
1
obtained from cold (−30 °C) toluene. Yield: 1.45 g, 67%. H{11B}
3
NMR (CDCl3): δ 0.33 (d, JPH = 14.5 Hz, 6H, BH3), 1.13 (dd, JPH
=
3
3
3
13.8, JHH = 7.1 Hz, 6H, CHMeMe), 1.20 (dd, JPH = 14.1, JHH = 7.3
2
Hz, 6H, CHMeMe), 2.00 (m, 4H, CHMe2), 3.32 (d, JPH = 11.6 Hz,
CH2P), 7.15 (m, 4H, ArH). 13C{1H} NMR (CDCl3): δ 17.2, 17.3
(CHMe2), 22.0 (d, JPC = 32.5 Hz, CHMe2), 25.9 (d, JPC = 26.3 Hz,
CH2P), 127.0, 131.5, 133.4 (Ar). 11B{1H} NMR (CDCl3): δ −44.3 (d,
JPB = 49.0 Hz). 31P{1H} NMR (CDCl3): δ 35.2 (m).
1,2-C6H4{CH2P(BH3)Ph2}2 (2a). To a solution of Ph2PH(BH3)
(1.64 g, 8.2 mmol) in THF (20 mL) was added nBuLi (3.3 mL, 8.2
mmol), and this mixture was stirred at room temperature for 1 h. To
this solution was added a solution of α,α′-dichloro-o-xylene (0.68 g,
4.1 mmol) in THF (20 mL), and this mixture was stirred for 16 h.
Water (20 mL) was added, and the organic phase was extracted into
dichloromethane (3 × 20 mL). The combined organic extracts were
dried over MgSO4, and solvent was removed under vacuum to give 2a
as a colorless solid. Yield: 1.61 g, 82%. 1H{11B} NMR (CDCl3): δ 0.90
(d, JPH = 15.5 Hz, 6H, BH3), 3.54 (d, JPH = 11.7 Hz, 4H, CH2P),
6.51−7.62 (m, 24H, ArH). 13C{1H} NMR (CDCl3): δ 30.9 (d, JPC
=
30.8 Hz, CH2P), 126.7, 128.8, 128.9, 129.3, 131.4, 131.6 (Ar), 132.7
(d, JPC = 8.6 Hz, Ar). 11B{1H} NMR (CDCl3): δ −40.1 (br). 31P{1H}
NMR (CDCl3) δ 18.3 (br m).
1,2-C6H4{CH2P(BH3)Cy2}2 (3a). To a solution of Cy2PH(BH3)
(1.58 g, 7.45 mmol) in THF (20 mL) was added nBuLi (3.0 mL, 7.50
mmol), and this mixture was stirred for 1 h. To this mixture was added
a solution of α,α′-dichloro-o-xylene (0.61 g, 3.73 mmol) in THF (20
mL), and this mixture was stirred at room temperature for 16 h. Water
(30 mL) was added, and the organic phase was extracted into
dichloromethane (3 × 20 mL). The combined organic extracts were
dried over MgSO4 and solvent was removed under vacuum to give 3a
as a colorless solid. Yield: 1.42 g, 77%. 1H{11B} NMR (CDCl3): δ 0.29
(d, JPH = 15.1 Hz, 6H, BH3), 1.16−1.93 (m, 44H, Cy), 3.29 (d, JPH
=
11.5 Hz, 4H, CH2P), 7.09−7.35 (m, 4H, ArH). 13C{1H} NMR
(CDCl3): δ 25.8 (d, JPC = 27.8 Hz, Cy), 26.1 (Cy), 27.0 (d, JPC = 7.7
Hz, CH2P), 27.1 (Cy), 32.0 (d, JPC = 30.7 Hz, Cy), 126.8, 131.5, 133.7
(Ar). 11B{1H} NMR (CDCl3): δ −43.6 (br m). 31P{1H} NMR
(CDCl3): δ 27.8 (br m).
EXPERIMENTAL SECTION
■
All manipulations were carried out using standard Schlenk techniques
under an atmosphere of dry nitrogen. THF, light petroleum (bp 40−
60 °C), diethyl ether, toluene, and n-hexane were dried prior to use by
distillation under nitrogen from sodium, potassium, or sodium/
potassium alloy, as appropriate. THF was stored over activated 4 Å
molecular sieves; all other solvents were stored over a potassium film.
Deuterated THF and benzene were distilled from potassium, and
CDCl3 was distilled from CaH2 under nitrogen; all NMR solvents
were deoxygenated by three freeze−pump−thaw cycles and were
stored over activated 4 Å molecular sieves. Benzylpotassium,18
MeK,11b,19 iPr2PH(BH3),20 Ph2PH(BH3),21 Cy2PH(BH3),22 Me3P-
(BH3),23 and Ph2MeP(BH3)21 were prepared by previously published
procedures; n-butyllithium was purchased from Aldrich as a 2.5 M
solution in hexanes. tmeda and pmdeta were distilled from CaH2
under nitrogen and were stored over activated 4 Å molecular sieves.
All other compounds were used as supplied by the manufacturer.
[CH2SiMe2CH2P(BH3)Me2]2 (4a). To a solution of Me3P(BH3)
(6.31 g, 70.17 mmol) in THF (30 mL) was added nBuLi (28.1 mL,
70.17 mmol), and this mixture was stirred for 1 h at room temperature.
This solution was added, dropwise, to a solution of 1,2-bis-
(chlorodimethylsilyl)ethane (7.55 g, 35.09 mmol) in THF (30 mL),
and the resulting mixture was stirred for 1 h at room temperature.
Water (30 mL) was added, and the organic phase was extracted into
dichloromethane (3 × 30 mL). The combined organic extracts were
dried over MgSO4 and filtered and the solvent was removed in vacuo
from the filtrate to give a colorless solid, which was crystallized from
hot methylcyclohexane (15 mL) to give colorless crystals of 4a.
1
Isolated yield: 6.97 g, 60%. H{11B} NMR (CDCl3): δ 0.13 (s, 12H,
SiMe2), 0.50 (m, 10H, CH2CH2 + BH3), 0.90 (d, JPH = 15.1 Hz, 4H,
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PCH2), 1.29 (d, JPH = 10.1 Hz, 12H, PMe2). 13C{1H} NMR (CDCl3):
δ −1.5 (SiMe2), 9.0 (CH2CH2), 13.5 (d, JPC = 24.0 Hz, PCH2), 15.6
C44H64B2Li2N4P2 (746.56): C, 70.80; H, 8.64; N, 7.51. Found: C,
70.61; H, 8.49; N, 7.80. 1H{11B} NMR (d8-THF) δ 0.99 (d, JPH = 14.6
Hz, 6H, BH3), 2.12 (s, 16H, NMe2), 2.20 (d, JPH = 14.4 Hz, 2H,
CHLi), 2.27 (s, 8H, CH2N), 5.74 (m, 2H, ArH), 6.41 (m, 2H, ArH),
7.13 (m, 12H, Ph), 7.72 (m, 8H, Ph). 13C{1H} NMR (d8-THF): δ
27.4 (d, JPC = 66.0 Hz, CHLi), 45.3 (NMe2), 57.9 (CH2N), 113.9
(Ar), 126.4 (d, JPC = 8.6 Hz, Ar), 126.9, 128.0, 128.7 (Ar), 132.8 (d,
JPC = 8.6 Hz, Ar), 140.2 (d, JPC = 47.7 Hz, Ar). 7Li NMR (d8-THF): δ
−0.9. 11B{1H} NMR (d8-THF): δ −34.4 (br m). 31P{1H} NMR (d8-
THF): δ 6.2 (br m). N.B.: solvent of crystallization is readily lost
under vacuum and was not observed in either the elemental analysis or
NMR spectra.
(d, JPC = 38.3 Hz, PMe2). 11B{1H} NMR (CDCl3): δ −37.5 (d, JPB
58.8 Hz). 31P{1H} NMR (CDCl3): δ 3.4 (q, JPB = 58.8 Hz).
=
[CH2SiMe2CH2P(BH3)Ph2]2 (5a). To a cold (0 °C) solution of
Ph2P(BH3)Me (4.76 g, 22.24 mmol) in THF (40 mL) was added
nBuLi (8.9 mL, 22.24 mmol), and this mixture was stirred for 1 h at
room temperature. This solution was added, dropwise, to a solution of
1,2-bis(chlorodimethylsilyl)ethane (2.39 g, 11.12 mmol) in THF (30
mL), and the resulting mixture was stirred for 1 h at room
temperature. Water (40 mL) was added, and the organic phase was
extracted into dichloromethane (3 × 30 mL). The combined organic
extracts were dried over MgSO4 and filtered, and the solvent was
removed in vacuo from the filtrate to give a colorless solid, which was
crystallized from hot methylcyclohexane/THF (15/5 mL) to give
[1,2-C6H4{CHP(BH3)Cy2}2][Li(tmeda)]2.2PhMe (3b). To a sol-
ution of 3a (1.00 g, 1.90 mmol) in THF (30 mL) was added nBuLi
(1.52 mL, 3.79 mmol), and this mixture was stirred for 30 min at room
temperature. The solvent was removed in vacuo to yield a dark orange
oil. This oil was dissolved in toluene (30 mL), and tmeda (0.57 mL,
3.79 mmol) was added. The solution was stirred for 5 min, the solvent
was reduced in vacuo to 20 mL, and the solution was cooled to −20
°C for 24 h to give 3b as yellow crystals, which were washed with a
small amount of cold (0 °C) light petroleum. Yield: 1.04 g, 57%. Anal.
Calcd for C44H88B2Li2N4P2 (770.65): C, 68.57; H, 11.51; N, 7.27.
1
colorless crystals of 5a. Isolated yield: 4.00 g, 64%. H{11B} NMR
(CDCl3): δ −0.11 (s, 12H, SiMe2), 0.29 (s, 4H, CH2CH2), 1.04 (s,
3H, BH3), 1.52 (d, JPH = 15.0 Hz, 4H, PCH2), 7.39 (m, 10H, PPh2),
7.69 (m, 10H, PPh2). 13C{1H} NMR (CDCl3): δ −2.2 (SiMe2), 8.5
(CH2CH2), 11.0 (d, JPC = 25.1 Hz, PCH2), 128.6 (d, JPC = 10.1 Hz,
Ph), 130.9 (Ar), 131.6 (d, JPC = 9.1 Hz, Ph), 132.6 (d, JPC = 55.2 Hz,
Ar). 11B{1H} NMR (CDCl3): δ −38.9 (br). 31P{1H} NMR (CDCl3):
δ 13.5 (q, JPB = 69.5 Hz).
1
Found: C, 68.53; H, 12.23; N, 7.04. H{11B} NMR (d8-THF): δ 0.33
[1,2-C6H4{CHP(BH3)iPr2}2][Li(tmeda)]2 (1b). To a solution of 1a
(0.87 g, 2.38 mmol) in THF (30 mL) were added nBuLi (2.0 mL, 5.00
mmol) and tmeda (0.77 mL, 5.10 mmol). This mixture was stirred at
room temperature for 2 h, and then solvent was removed in vacuo to
give a bright yellow solid. This was crystallized from diethyl ether at
room temperature to give a large crop of yellow crystals of 1b. Yield:
1.11 g, 76%. Anal. Calcd for C32H72B2Li2N4P2 (610.39): C, 62.97; H,
11.89; N, 9.18. Found: C, 62.83; H, 11.79; N, 9.08. 1H{11B} NMR (d8-
THF): δ 0.32 (d, JPH = 14.2 Hz, 6H, BH3), 1.10−1.17 (m, 24H,
CHMe2), 1.45 (d, JPH = 9.7 Hz, 2H, CHLi), 2.13 (s, 24H, NMe2), 2.25
(m, 4H, CHMe2), 2.31 (s, 8H, CH2N), 5.85 (m, 2H, ArH), 6.61 (m,
2H, ArH). 13C{1H} NMR (d8-THF): δ 18.3 (CHMe2), 18.5 (CHMe2),
23.7 (d, JPC = 59.5 Hz, CHLi), 24.3 (d, JPC = 34.5 Hz, CHMe2), 45.4
(NMe2), 57.9 (CH2N), 115.5, 116.7 (Ar), 139.2 (d, JPC = 13.4 Hz, Ar).
7Li NMR (d8-THF): δ −1.0. 11B{1H} NMR (d8-THF): δ −39.3 (d, JPB
= 78.4 Hz). 31P{1H} NMR (d8-THF): δ 16.3 (q, JPB = 78.4 Hz).
[1,2-C6H4{CHP(BH3)iPr2}{CH2P(BH3)iPr2][K(pmdeta)] (1c). To a
slurry of MeK (0.70 g, 15.05 mmol) in cold (−10 °C) diethyl ether
(20 mL) was added a solution of 1a (2.43 g, 6.64 mmol) in cold (−10
°C) diethyl ether (20 mL), and this mixture was stirred for 16 h. The
solution was filtered, pmdeta (2.77 mL, 13.27 mmol) was added to the
filtrate, and this mixture was stirred for 5 min. Solvent was removed in
vacuo, and the resulting pale brown solid was crystallized from cold
(−30 °C) n-hexane (20 mL). The pale yellow crystals of 1c were
isolated by filtration and washed with a small amount of cold light
petroleum. Yield 2.69 g, 70%. Anal. Calcd for C29H64B2KN3P2
(577.51): C, 60.31; H, 11.17; N, 7.28. Found: C, 61.03; H, 11.43;
(d, JPH = 15.0 Hz, 6H, BH3), 1.12−2.02 (m, 46H, PCy2 + CHLi), 2.16
(s, 24H, NMe2), 2.31 (s, 8H, NCH2), 5.86 (br m, 2H, ArH), 6.59 (br
m, 2H, ArH). 13C{1H} NMR (d8-THF): δ 23.3 (d, JPC = 61.3 Hz,
CHLi), 26.9, 27.7 (PCy2), 27.8 (d, JPC = 10.1 Hz, PCy2), 28.1 (d, JPC
=
10.1 Hz, PCy2), 28.5 (PCy2), 34.8 (d, JPC = 34.2 Hz, PCy2), 45.4
(NMe2), 57.9 (CH2N), 112.5 (Ar), 116.3 (d, JPC = 6.0 Hz, Ar), 139.2
7
(d, JPC = 15.1 Hz, Ar). Li NMR (d8-THF): δ −1.0. 11B{1H} NMR
(d8-THF): δ −39.8 (br). 31P{1H} NMR (d8-THF): δ 12.3 (br q, JPB
=
105.3 Hz). N.B.: solvent of crystallization is readily lost under vacuum
and was not observed in either the elemental analysis or NMR spectra.
[1,2-C6H4{CHP(BH3)Cy2}2][K(pmdeta)]2 (3c). To a solution of 3a
(0.50 g, 0.95 mmol) in THF (30 mL) were added, dropwise, a solution
of benzylpotassium (0.30 g, 2.30 mmol) in THF (30 mL), followed by
pmdeta (0.39 mL, 1.90 mmol); this solution was stirred for 1 h at
room temperature. The solvent was removed in vacuo, the sticky
orange solid was dissolved in diethyl ether (10 mL), and the solution
was filtered and left to stand at room temperature for 24 h to yield
yellow crystals of 3c. Isolated yield: 0.37 g, 41%. Anal. Calcd for
C50H102B2K2N6P2 (949.15): C, 63.27; H, 10.83; N, 8.85. Found: C,
63.11; H, 11.01; N, 8.76. 1H{11B} NMR (d8-toluene): δ 0.98 (d, JPH
=
12.0 Hz, 6H, BH3), 1.09−2.23 (m, 67H, PCy2 + CH2N + NMe +
NMe2), 6.18 (s, 2H, ArH), 9.96 (s, 2H, ArH). 13C{1H} NMR (d8-
toluene): δ 27.2 (PCy2), 27.6 (PCy2), 27.8 (d, JPC = 10.1 Hz, PCy2),
28.0 (d, JPC = 10.1 Hz, PCy2), 28.5, 33.3 (d, JPC = 30.1 Hz, PCy2), 37.8
(d, JPC = 36.5 Hz, CHK), 41.8 (NMe), 45.0 (NMe2), 55.1, 57.0
(NCH2), 111.2, 113.7 (Ar), 141.9 (d, JPC = 3.9 Hz, Ar). 11B{1H} NMR
(d8-toluene): δ −40.3 (br). 31P{1H} NMR (d8-toluene): δ 12.7 (br).
[CH2SiMe2CHP(BH3)Me2]2[Li(tmeda)]2 (4b). To a solution of 4a
(0.51 g, 1.55 mmol) in THF (30 mL) were added nBuLi (1.24 mL,
3.10 mmol) and tmeda (0.46 mL, 3.10 mmol), and this mixture was
stirred for 1 h at room temperature. The solvent was removed in vacuo
to yield a colorless oil, which was crystallized from cold (−20 °C)
methylcyclohexane (10 mL) to give 4b as colorless crystals that were
isolated by filtration and washed with cold (0 °C) light petroleum (3 ×
5 mL). Yield: 0.39 g, 74%. Anal. Calcd for C24H68B2Li2N4P2Si2
(566.50): C, 50.89; H, 12.10; N, 9.89. Found: C, 50.68; H, 12.15;
1
N, 7.11. H NMR (d8-THF): δ 0.31 (br m, 6H, BH3), 1.04−1.81 (m,
24H, CHMe2), 1.75 (d, JPH = 4.4 Hz, 1H, CHK), 1.84 (m, 2H,
CHMe2), 2.12 (s, 12H, NMe2), 2.16 (s, 3H, NMe), 2.25 (m, 2H,
CHMe2), 2.27 (m, 4H, CH2N), 2.38 (m, 4H, CH2N), 2.83 (d, JPH
=
10.8 Hz, 2H, CH2P), 5.67 (m, 1H, ArH), 6.43 (m, 1H, ArH), 6.53 (m,
1H, ArH), 7.01 (m, 1H, ArH). 13C{1H} NMR (d8-THF): δ 16.7, 16.8,
17.8, 17.6 (CHMe2), 22.2 (d, JPC = 29.8 Hz, CHMe2), 25.3 (d, JPC
=
30.6 Hz, CH2P), 25.8 (d, JPC = 36.6 Hz, CHMe2), 34.8 (d, JPC = 76.5
Hz, CHK), 42.4 (NMe), 45.3 (NMe2), 56.4, 57.9 (CH2N), 106.4 (Ar),
115.9 (d, JPC = 5.9 Hz, Ar), 117.7 (dd, JPC = 15.0, JP′C = 6.6 Hz, Ar),
126.1, 130.4 (Ar), 151.7 (d, JPC = 9.5 Hz, Ar). 11B{1H} NMR (d8-
THF): δ −43.5 (d, JPB = 41.7 Hz, H3B-P-CH2), −40.6 (d, JPB = 83.3
Hz, H3B-P-CHK). 31P{1H} NMR (d8-THF): δ 16.7 (br q, JPB = 83.3
Hz, H3B-P-CHK), 34.2 (br q, JPB = 41.7 Hz, H3B-P-CH2).
[1,2-C6H4{CHP(BH3)Ph2}2][Li(tmeda)]2.THF (2b). To a solution
of 2a (0.48 g, 0.96 mmol) in THF (20 mL) were added nBuLi (0.77
mL, 1.92 mmol) and tmeda (0.29 mL, 1.92 mmol), and this mixture
was stirred at room temperature for 1 h. The solvent was removed in
vacuo, and the sticky orange solid was crystallized from cold (−30 °C)
toluene as deep orange plates of 2b. Yield: 0.45 g, 63%. Anal. Calcd for
N, 9.78. H{11B} NMR (d6-benzene): δ −1.05 (d, JPH = 6.4 Hz, 2H,
1
LiCH), 0.30 (s, 12H, SiMe2), 0.76 (s, 4H, SiCH2CH2Si), 1.43 (d, JPH
=
10.1 Hz, 12H, PMe2), 1.78 (s, 8H, CH2N), 2.05 (s, 24H, NMe2).
13C{1H} NMR (d6-benzene): δ 2.5 (SiMe2), 3.2 (d, JPC = 17.1 Hz,
LiCH), 14.8 (SiCH2CH2Si), 19.7 (d, JPC = 33.2 Hz, PMe2), 45.8
7
(NMe2), 56.3 (CH2N). Li NMR (d6-benzene): δ 1.0. 11B{1H} NMR
(d6-benzene): δ −33.0 (d, JPB = 88.3 Hz). 31P{1H} NMR (d6-
benzene): δ −4.8 (q, JPB = 88.3 Hz).
[CH2SiMe2CHP(BH3)Ph2]2[Li(THF)2]2 (5b). To a solution of 5a
(0.50 g, 0.88 mmol) in THF (40 mL) was added nBuLi (0.70 mL, 1.75
mmol), and this mixture was stirred for 1 h at room temperature. The
384
dx.doi.org/10.1021/om4011142 | Organometallics 2014, 33, 378−386

Organometallics
Article
solvent was removed in vacuo to yield a yellow oil, which was
crystallized from cold (−20 °C) diethyl ether (10 mL) to give 5b as
yellow crystals. Yield: 0.41 g, 80%. Anal. Calcd for C48H26B2Li2O4P2Si2
(870.74): C, 66.21; H, 8.80. Found: C, 66.11; H, 8.70. 1H{11B} NMR
(d6-benzene): δ −0.10 (d, JPH = 25.0 Hz, 2H, LiCH), 0.29 (s, 12H,
SiMe2), 0.86 (s, 4H, SiCH2CH2Si), 1.33 (m, 16H, THF), 3.52 (m,
16H, THF), 7.00−8.10 (m, 20H, PPh2). 13C{1H} NMR (d6-benzene):
δ −1.2 (d, JPC = 16.1 Hz, LiCH), 2.0 (d, JPC = 6.0 Hz, SiMe2), 15.2
(SiCH2CH2Si), 25.2 (THF), 68.0 (THF), 127.6, 128.4 (Ph), 131.4 (d,
AUTHOR INFORMATION
Corresponding Author
*E-mail for K.I.: k.j.izod@ncl.ac.uk.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
7
The authors are grateful to Newcastle University for financial
support.
JPC = 9.1 Hz, Ph), 141.9 (d, JPC = 50.5 Hz, ipso-Ph). Li NMR (d6-
benzene): δ 1.2. 11B{1H} NMR (d6-benzene): δ −35.7 (d, JPB = 88.2
Hz). 31P{1H} NMR (d6-benzene): δ 12.5 (q, JPB = 88.2 Hz).
REFERENCES
[CH2SiMe2CHP(BH3)Ph2]2[K(pmdeta)]2 (5c). To a solution of 5a
(0.50 g, 0.88 mmol) in THF (20 mL) were added, dropwise, a solution
of benzylpotassium (0.26 g, 2.00 mmol) in THF (10 mL) followed by
pmdeta (0.37 mL, 1.75 mmol), and this mixture was stirred for 16 h at
room temperature. Solvent was removed in vacuo from the resulting
orange solution to yield a sticky yellow solid, which was crystallized
from hot toluene (20 mL) as yellow blocks. Yield: 0.53 g, 61%. Anal.
Calcd for C50H90B2K2N6P2Si2 (993.22): C, 60.46; H, 9.13; N, 8.46.
Found: C, 60.34; H, 9.06; N, 8.31. 1H{11B} NMR (d8-THF): δ −0.53
(d, JPH = 25.0 Hz, 2H, KCH), −0.15 (s, 12H, SiMe2), 0.43 (s, 4H,
SiCH2CH2Si), 0.95 (d, JPH = 15.0 Hz, 3H, BH3), 2.16 (s, 12H, NMe2),
2.19 (s, 3H, NMe), 2.32 (m, 4H, CH2N), 2.43 (m, 4H, CH2N), 7.00−
8.10 (m, 20H, Ph). 13C{1H} NMR (d8-THF): δ −2.2 (d, JPC = 38.2
Hz, KCH), −0.1 (SiMe2), 12.1 (d, JPC = 5.0 Hz, SiCH2CH2Si), 40.5
(NMe), 43.5 (NMe2), 54.6 (NCH2), 56.0 (NCH2), 124.9 (d, JPC = 9.1
Hz, Ph), 125.0 (Ph), 129.3 (d, JPC = 9.1 Hz, Ph), 129.9 (d, JPC = 9.1
Hz, Ph). 11B{1H} NMR (d8-THF): δ −34.7 (d, JPB = 78.3 Hz).
31P{1H} NMR (d8-THF): δ 11.7 (q, JPB = 78.3 Hz).
Crystal Structure Determinations of 1a−c, 2b, 3b,c, 4a, and
5b,c. Measurements were made at 150 K on an Oxford Diffraction
(Agilent Technologies) Gemini A Ultra diffractometer or a Nonius
KappaCCD diffractometer, using Cu Kα radiation (λ = 1.54178 Å; 4a)
or Mo Kα radiation (λ = 0.71073 Å; 1a−c, 2b, 3b,c, and 5b,c). Cell
parameters were refined from the observed positions of all strong
reflections. Intensities were corrected semiempirically for absorption,
on the basis of symmetry-equivalent and repeated reflections using
SADABS,24 except for 3d, where analytical numeric absorption
correction using a multifaceted crystal model based on expressions
derived by Clark and Reid25 was applied on the basis of symmetry-
equivalent and repeated reflections. The structures were solved by
direct methods and refined on F2 values for all unique data; see Table
S1 in the Supporting Information for further details. All non-hydrogen
atoms were refined anisotropically, and C-bound H atoms were
constrained with a riding model, while B-bound H atoms, having been
found directly in a Fourier difference synthesis, were freely refined;
U(H) was set at 1.2 (1.5 for methyl groups) times Ueq for the parent C
atom. Disorder in the pmdeta ligand of 1c, the tmeda ligands and
solvent molecules of 2b, one of the pmdeta ligands of 3d, and the two
backbone carbon atoms of 5b,c was successfully modeled with the aid
of restraints on geometry and displacement parameters. Programs used
were CrysAlisPro and Nonius COLLECT/EvalCC for data
collection,24 integration, and absorption corrections, and OLEX2,26
SHELXS/SHELXL, and SHELXTL for structure solution, refinement,
and graphics.24
■
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ASSOCIATED CONTENT
■
S
* Supporting Information
1
For 1a−5a figures giving H, 13C{1H}, 11B{1H} and 31P{1H}
NMR spectra and for 1a−c, 2b, 3b,c, 4a, and 5b,c tables,
figures, and CIF files giving details of structure determination,
atomic coordinates, bond lengths and angles, and displacement
parameters and details of the molecular structures of 1a and 4a.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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