Benzyl ether-substituted phosphido-borane complexes of the alkali metals

Article abstract of DOI:10.1002/ejic.201101367

Reduction of {(Me₃Si)₂CH}PCl(C₆H ₄-2-CH₂OMe) withLiAlH₄, followed by reaction with BH₃·SMe₂, gives the phosphane-borane {(Me ₃Si)₂CH}PH(BH₃)(C₆H ₄-2-CH₂OMe) (2) in good yield. Compound 2 undergoes rapid deprotonation on treatment with nBuLi, PhCH₂Na or PhCH₂K to give the corresponding alkali metal phosphido-borane complexes [[{(Me ₃Si)₂CH}P(BH₃)(C₆H ₄-2-CH₂OMe)]ML]₂ [ML = Li(THF) (3), Na(tmeda) (4), K(pmdeta) (5)] after crystallization in the presence of the respective co-ligand L. The exact binding mode of the phosphido-borane ligand depends on the nature of the metal center in each case. However, all three alkali metal complexes crystallize as discrete dimers exhibiting M-P, M-O and M·BH₃ contacts. Copyright

Full text of DOI:10.1002/ejic.201101367

FULL PAPER
DOI: 10.1002/ejic.201101367
Benzyl Ether-Substituted Phosphido–Borane Complexes of the Alkali Metals
Keith Izod,*[a] James M. Watson,[a] William Clegg,[a] and Ross W. Harrington[a]
Keywords: Alkali metals / Phosphane ligands / Boranes / Main group elements
Reduction of {(Me3Si)2CH}PCl(C6H4-2-CH2OMe) with
LiAlH4, followed by reaction with BH3·SMe2, gives the phos-
phane–borane {(Me3Si)2CH}PH(BH3)(C6H4-2-CH2OMe) (2)
in good yield. Compound 2 undergoes rapid deprotonation
on treatment with nBuLi, PhCH2Na or PhCH2K to give the
corresponding alkali metal phosphido–borane complexes
(THF) (3), Na(tmeda) (4), K(pmdeta) (5)] after crystallization
in the presence of the respective co-ligand L. The exact bind-
ing mode of the phosphido–borane ligand depends on the
nature of the metal center in each case. However, all three
alkali metal complexes crystallize as discrete dimers exhibit-
ing M–P, M–O and M···BH3 contacts.
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]ML]2 [ML
=
Li-
Introduction
Phosphido–borane complexes (alternatively known as
phosphanylborohydride or mono(borane)phosphide com-
plexes) are key intermediates in the synthesis of (chiral)
phosphanes and in the catalytic dehydrocoupling of phos-
phane–boranes to generate polymeric materials.[1,2] None-
theless, despite their synthetic utility, alkali metal phos-
phido–borane complexes have rarely been isolated in the
solid state and are usually generated and used in situ; few
such complexes have been structurally characterized.[3–6]
The absence of well-characterized phosphido–borane com-
plexes is particularly notable given the isoelectronic rela-
tionship between phosphido–boranes [R2P(BH3)]– and
methyl-substituted silyl anions [R2SiMe]–, the latter of
which have a well-developed coordination chemistry; the
similarities between these two ligand systems have been
probed by Holthausen, Wagner and co-workers in a series
of iron complexes.[3g] In addition, it has recently been re-
ported that [Ph2P(BH3)]Li (1) exhibits temperature-depend-
ent reactivity in THF: at low temperatures 1 reacts with
aldehydes as a P-nucleophile, generating a phosphane–bor-
ane-substituted alcohol, whereas at higher temperatures the
borane group in 1 acts as a hydride transfer reagent, gener-
ating a phosphane-free alcohol (Scheme 1).[7] This dual re-
activity has been attributed to the ditopic nature of the li-
gand: when the lithium cation resides near the borane hy-
drogen atoms nucleophilic attack at the aldehyde by the
phosphorus center is favored, whereas association of the
lithium cation with the phosphorus center favors hydride
transfer reactivity.
Scheme 1.
Structurally-characterized phosphido–borane complexes
are limited to a small number of alkali metal derivatives
and a smattering of mid-to-late transition metal com-
pounds.[3–6] In general, these ambidentate ligands typically
bind to soft transition metal ions through their phosphorus
centers, whereas hard alkali metal cations are principally
bound through the borane hydrogen atoms of the ligand. A
deeper understanding of the factors which affect the bind-
ing modes of these ligands is clearly desirable in order better
to understand and control their reactivity patterns.
Over the last few years we have explored the chemistry
of sterically-demanding, donor-functionalized phosphide li-
gands of type A with main group and lanthanide metal cen-
ters.[8] We have now begun to extend this investigation to
their phosphido–borane counterparts (B) and recently re-
ported the synthesis and structural characterization of a
series of thioether-functionalized phosphido–borane com-
plexes of the alkali metals.[9] We noted that the introduction
of a borane group at the phosphorus center quenched the
photolytic rearrangement observed for the analogous bor-
ane-free phosphide complexes. As part of this study we have
begun to explore the coordination chemistry of phosphido–
borane ligands with different peripheral functionalization,
with a view to gaining an insight into the influence that the
peripheral donor group exerts on the structures and reactiv-
ities of their complexes. In this contribution we describe
the synthesis and structural characterization of a new ether-
functionalized phosphane–borane and its lithium, sodium
and potassium derivatives.
[a] Main Group Chemistry Laboratories, School of Chemistry,
Bedson Building, Newcastle University,
Newcastle upon Tyne, NE1 7RU, UK
E-mail: k.j.izod@ncl.ac.uk
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Ether-Functionalized Phosphido–Borane Complexes
the corresponding tertiary amine [tmeda = N,N,NЈ,NЈ-tetra-
methylethylenediamine, pmdeta = N,N,NЈ,NЈЈ,NЈЈ-penta-
methyldiethylenetriamine].
Upon metalation, the 31P{1H} NMR signal for 2
(–16.2 ppm) moves significantly upfield, although there is
only a small difference between the 31P chemical shifts of
the alkali metal complexes (3 –66.6, 4 –65.3, 5 –64.2 ppm).
In contrast, the 11B-31P coupling constant decreases steadily
with decreasing electronegativity of the metal center [1JPB
= 49.0 (2), 37.2 (3), 29.4 (4), 19.6 Hz (5)]; we have pre-
viously noted a similar trend in the 1JPB coupling constants
for the thioether-functionalized analogue {(Me3Si)2CH}-
PH(BH3)(C6H4-2-SMe) and its alkali metal derivatives.[9]
This is consistent with the decreasing electronegativity of
the elements on descending group 1, which leads to an in-
crease in the s-character of the H/M–P bond and a conse-
quent increase in the p-character of the P–B and P–C
bonds.[13] This reduces the Fermi contact term for the 31P
and 11B nuclei and, therefore, the scalar coupling between
these nuclei.
Results and Discussion
The reaction between LiC6H4-2-CH2OMe (prepared in
situ by a low-temperature lithium-halogen exchange reac-
tion between nBuLi and 2-bromobenzyl methyl ether) and
[10]
one equivalent of {(Me3Si)2CH}PCl2
gives the corre-
sponding chlorophosphane {(Me3Si)2CH}PCl(C6H4-2-
CH2OMe) in essentially quantitative yield, as shown by
31P{1H} NMR spectroscopy (Scheme 2). Treatment of this
chlorophosphane with LiAlH4, followed by one equivalent
of BH3·SMe2 gives the air-stable, ether-functionalized sec-
ondary phosphane–borane {(Me3Si)2CH}PH(BH3)(C6H4-
2-CH2OMe) (2) as a colorless oil which was crystallized
from hot light petroleum as colorless blocks.
1
In the H NMR spectrum of 2 the PH proton gives rise
3
to a doublet of quartets of doublets [1JPH = 375.5, JHH
=
6.6, JHHЈ = 3.2 Hz], due to coupling to the 31P nucleus,
the three borane protons, and the methine proton of the
CH(SiMe3)2 substituent. Decoupling the 11B nucleus has no
observable effect on this signal, but collapses the broad
quartet at δ = 0.89 ppm due to the borane protons into a
3
Scheme 2.
sharp doublet of doublets [2JPH = 15.0, JHH = 6.6 Hz]. As
3
The reaction between 2 and one equivalent of nBuLi in
THF yields the phosphido–borane complex [[{(Me3Si)2-
CH}P(BH3)(C6H4-2-CH2OMe)]Li(THF)]2 (3), which was
isolated as colorless, air-sensitive crystals from cold methyl-
cyclohexane/THF (Scheme 3). A similar reaction between 2
and one equivalent of either benzylsodium[11] or benzyl-
potassium[12] in THF yields the corresponding phosphido–
borane salts, which were isolated as the adducts [[{(Me3Si)2-
expected, the diastereotopic SiMe3 groups give rise to a pair
1
of singlets in both the H and 13C{1H} NMR spectra of 2–
5.
For the purposes of comparison with the metalated de-
rivatives the X-ray crystal structure of the free phosphane–
borane 2 was determined; the structure of 2 is shown in
Figure 1, along with selected bond lengths and angles. The
CH}P(BH3)(C6H4-2-CH2OMe)]Na(tmeda)]2
(4)
and
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]K(pmdeta)]2 (5),
after recrystallization from cold toluene in the presence of
Figure 1. Molecular structure of 2 with 40% probability displace-
ment ellipsoids and with C-bound H atoms omitted for clarity. Se-
lected bond lengths [Å] and angles [°]: P–B 1.9232(18), P–C(1)
1.8101(13), P–C(8) 1.8135(14), C(1)–Si(1) 1.8954(14), C(1)–Si(2)
1.9059(13), B–H(1A) 1.14(2), B–H(1B) 1.103(18), B–H(1C)
1.117(17), B–P–C(1) 118.23(7), B–P–C(8) 112.53(8), C(1)–P–C(8)
108.88(6).
Scheme 3.
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K. Izod, J. M. Watson, W. Clegg, R. W. Harrington
FULL PAPER
structure of this compound is unexceptional; the P–B, P–
C(1), and P–C(8) distances [1.9232(18), 1.8101(13) and
1.8135(14) Å, respectively] are typical of such bonds.
Compound 3 crystallizes as discrete dimers with approxi-
mate, non-crystallographic C2 symmetry; the structure of 3
is shown in Figure 2, along with selected bond lengths and
angles. Each lithium ion is bound by the P and O centers
of a phosphido–borane ligand, generating a puckered six-
membered chelate ring [P–Li–O bite angles 84.8(2) and
89.5(2)°]. The coordination about each lithium ion is com-
pleted by the O atom of a molecule of THF and an η2-BH3
contact with the borane group of the second phosphido–
borane ligand in the dimer. Thus the borane groups bridge
the two units in the dimer to give a pseudo-six-membered
(Li–P–BH3)2 ring. Unexpectedly, the two phosphido–bor-
ane ligands adopt a syn configuration, positioning the two
sterically demanding CH(SiMe3)2 groups on the same side
of the molecule.
Figure 3. Molecular structure of 4 with 40% probability displace-
ment ellipsoids and with C-bound H atoms omitted for clarity.
Minor disorder components are not shown. Selected bond lengths
[Å] and angles [°]: Na–P 3.0520(18), Na–O 2.445(3), Na–N(1)
2.650(9), Na–N(2) 2.540(4), Na–H(1A) 2.45(4), Na–H(1A)Ј
2.34(5), Na···B 2.987(5), Na···BЈ 2.845(5), P–B 1.972(5), P–C(1)
1.880(4), P–C(8) 1.855(4), P–Na–O 76.38(8), P–Na–B 38.10(9),
N(1)–Na–N(2) 67.6(2), B–Na–BЈ 93.85(13), Na–B–NaЈ 86.15(13).
The prime denotes an inversion-related atom.
Each sodium ion is coordinated by the P and O atoms
of a phosphido–borane ligand, generating a puckered, six-
membered chelate ring [bite angle 76.38(8)°] and by the two
nitrogen atoms of a chelating molecule of tmeda. The two
halves of the dimer are linked by a μ2-η1:η1-BH3 group
from each phosphido–borane ligand, such that each sodium
ion has two η1-BH3 contacts, creating a central, planar
pseudo-four-membered (Na-BH3)2 ring. The Na–P distance
[3.0520(18) Å] is somewhat longer than the corresponding
distances [2.9661(17) and 2.9474(16) Å] in the closely re-
lated complex [[{(Me3Si)2CH}P(BH3)(C6H4-2-SMe)]Na-
(tmeda)]ϱ (7),[9] the only other crystallographically charac-
terized sodium complex of a phosphido–borane anion; in-
deed, the Na–P distance in 4 is at the longer end of the
range of previously reported Na–P distance in borane-free
sodium phosphide complexes.[14] The Na···B distances
[2.987(5) and 2.845(5) Å] are significantly longer than the
Figure 2. Molecular structure of 3 with 40% probability displace-
ment ellipsoids and with C-bound H atoms omitted for clarity. Se-
lected bond lengths [Å] and angles [°]: Li(1)–P(1) 2.611(6), Li(1)–
O(1) 1.988(6), Li(1)–O(2) 1.986(6), Li(1)–H(2A) 1.99(4), Li(1)–
H(2B) 2.05(4), Li(1)···B(2) 2.453(7), P(1)–B(1) 1.977(4), P(1)–C(1)
1.886(3), P(1)–C(8) 1.861(3), Li(2)–P(2) 2.657(6), Li(2)–O(3)
1.982(7), Li(2)–O(4) 1.958(7), Li(2)–H(1A) 1.98(4), Li(2)–H(1B)
1.97(4), Li(2)···B(1) 2.370(8), P(2)–B(2) 1.983(4), P(2)–C(20)
1.886(4), P(2)–C(27) 1.863(4), P(1)–Li(1)–O(1) 84.8(2), P(1)–Li(1)···
B(2) 125.0(3), P(2)–Li(2)–O(2) 89.5(2), P(2)–Li(2)···B(1) 121.8(3).
The Li–P distances [2.611(6) and 2.657(6) Å] are similar corresponding distances in
7 [Na···B 2.694(4) and
to the corresponding distance in [{Me2P(BH3)}Li(tmeda)]ϱ 2.646(4) Å], consistent with the η2-BHn-Na and η3-BHn-Na
(6) [2.620(4) Å][4a] and are typical of Li–P distances in lith- interactions observed in the latter, compared to the μ2-
ium phosphide complexes.[14] The Li···B distances [2.370(8) η1:η1-BH3 binding mode observed in 4. However, the
and 2.453(7) Å] are rather dissimilar, but lie in the typical Na···B distances in 4 are similar to the corresponding dis-
range for such η2-BH3–Li contacts; for example, the Li···B tances in [(benzo-15-crown-5)Na{(BH3)2NMe2}] [Na···B
distance in 6 is 2.403(3) Å,[4a] while the corresponding dis- 2.944(5) and 3.110(6) Å],[16] which exhibits two η1-BH3–Na
tance in Li(η2-BH4)(py)3 is 2.401(7) Å.[15]
contacts, and in [(tmeda)Na(μ-HBEt3)]2 [Na···B 2.912 and
Compound 4 also crystallizes as discrete dimers, al- 3.236 Å], which exhibits a μ2-η1:η1-bridging interaction
though these have a crystallographic inversion center mid- similar to that observed in 4.[17]
way along the Na···Na vector; the molecular structure of 4
Compound 5 also crystallizes as discrete centrosymmet-
is shown in Figure 3, along with selected bond lengths and ric dimers; the molecular structure of 5 is shown in Fig-
angles.
1698
ure 4, along with selected bond lengths and angles.
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Ether-Functionalized Phosphido–Borane Complexes
alation of 2 also leads to a decrease in the sum of angles
about phosphorus in the PBC2 framework; for 2 the sum
of the B–P–C(1), B–P–C(8) and C(1)–P–C(8) angles is
339.64°, whereas for 3–5 the sums of the corresponding
angles lie in the narrow range 309.54–310.92°. The contrac-
tion of the angles about phosphorus on metalation is con-
sistent with Bent’s rule:[13] replacement of a hydrogen atom
by a more electropositive alkali metal cation leads to in-
creased s-orbital character in the P–M bond, and thus to
increased p-character in the remaining bonds about phos-
phorus, and a consequent decrease in the angles between
these bonds. The contraction in the angles about the phos-
phorus center may also, in part, be attributed to the in-
creased steric demands of the alkali metal fragments, with
all of their ligands, compared to the small hydrogen atom
bound to phosphorus in 2.
Figure 4. Molecular structure of 5 with 40% probability displace-
ment ellipsoids and with C-bound H atoms omitted for clarity. Se-
lected bond lengths [Å] and angles [°]: K–P 3.7619(10), K–O
2.8240(16), K–N(1) 3.0339(19), K–N(2) 2.9192(18), K–N(3)
2.9054(19), K–H(1A) 2.796(18), K–H(1AЈ) 2.816(18), K–H(1BЈ)
2.970(19), K–H(1CЈ) 3.06(2), K···B 3.322(3), K···BЈ 3.103(3),
K···C(16) 3.333(3), K···C(20) 3.501(3), P–B 1.987(3), P–C(1)
1.894(2), P–C(8) 1.861(2), P–K–O 60.74(3), P–K···B 31.82(4),
N(1)–K–N(2) 60.39(5), N(2)–K–N(3) 63.41(5), B–K–BЈ 92.79(6),
K–B–KЈ 87.21(6). The prime denotes an inversion-related atom.
Experimental Section
General: All manipulations were carried out using standard
Schlenk techniques under an atmosphere of dry nitrogen. Diethyl
ether, THF, light petroleum (b.p. 40–60 °C), toluene, and methylcy-
clohexane 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 sol-
vents were stored over a potassium film. Deuterated THF was dis-
tilled from potassium and CDCl3 was distilled from CaH2 under
nitrogen and both solvents were deoxygenated by three freeze-
pump-thaw cycles and were stored over activated 4-Å molecular
sieves. Benzylsodium,[11] benzylpotassium,[12] [(Me3Si)2CH]PCl2,[10]
and 2-BrC6H4CH2OMe[18] were prepared by previously published
procedures; n-butyllithium was purchased from Aldrich as a 2.5 m
solution in hexanes and BH3·SMe2 was purchased from Aldrich as
a 2.0 m solution in THF. 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 manufac-
turer.
Each potassium ion is coordinated by the P and O cen-
ters of a phosphido–borane ligand [P–K–O bite angle
60.74(3)°], by the three nitrogen atoms of a molecule of
pmdeta, and by an η1-BH3 contact with the phosphido–
borane ligand; in addition, each potassium ion has short
contacts to two of the methyl groups in the pmdeta ligand
[K···C(16) 3.333(3), K···C(20) 3.501(3) Å]. The two halves
of the dimer are connected by an η3-BH3-K contact, such
that each BH3 group acts as a μ2-η1:η3 bridge between the
two potassium cations, generating a planar pseudo-four-
membered (K-BH3)2 ring. The “tridentate” P,O,BH3 coor-
dination mode of the phosphido–borane ligand in 5 echoes
the P,S,BH3 coordination mode adopted by the phosphido–
borane ligand in the closely related potassium complex
[[{(Me3Si)2CH}P(BH3)(C6H4-2-SMe)]K(pmdeta)]2 (8).[9]
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 Li{1H} NMR spectra
7
were recorded on a JEOL ECS500 spectrometer operating at
The K–P distance in 5 [3.7619(10) Å] is similar to the 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. Elemental analyses were obtained by the
Elemental Analysis Service of London Metropolitan University.
corresponding distance in 8 [3.6617(6) Å], and lies in the
typical range for K–P distances in potassium phosphides.[14]
The K···B distance [3.322(3) Å] is substantially longer than
the intra-dimer K···BЈ distance [3.103(3) Å] and is longer
{(Me3Si)2CH}PH(BH3)(C6H4-2-CH2OMe) (2): To a cold (0 °C)
than the K···B distance in [{PPh2(BH3)}K(18-crown-6)] solution of 2-BrC6H4CH2OMe (2.39 g, 11.9 mmol) in diethyl ether
(20 mL) was added one equivalent of nBuLi (4.8 mL, 11.9 mmol).
The resulting solution was stirred for 2 h at 0 °C, then added, drop-
wise, to a cold (–78 °C) solution of {(Me3Si)2CH}PCl2 (2.85 g,
11.0 mmol) in THF (30 mL). The mixture was stirred for 16 h and
allowed to attain room temperature. Solid LiAlH4 (0.41 g,
11.0 mmol) was carefully added, and the reaction mixture was
heated under reflux for 2 h. The reaction mixture was allowed to
cool to room temperature, and excess LiAlH4 was destroyed by the
careful addition of deoxygenated water (30 mL). The organic layer
was decanted, and the aqueous layer was extracted into diethyl
K···B 3.162 Å], which exhibits a similar K,BH3 binding
mode.[4c]
Comparison of the structures of 3, 4, and 5 with that of
the free phosphane–borane 2 reveals that metalation results
in significant lengthening of the P–B bond from
1.9232(18) Å in 2 to a value between 1.972(5) and
1.987(3) Å for 3–5. Similarly, both the P–C(1) and P–C(8)
distances increase on metalation of the phosphane–borane
[P–C(1) 1.8101(13) (2), 1.880(4)–1.894(2) Å (for 3–5); P–
C(8) 1.8135(14) (for 2), 1.855(4)–1.863(4) Å (for 3–5)]. Met- ether (3ϫ20 mL). The combined organic extracts were dried with
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K. Izod, J. M. Watson, W. Clegg, R. W. Harrington
FULL PAPER
4-Å molecular sieves, the solution was filtered, and the solvent was
2
2
(m, 4 H, THF), 4.82 (d, JHH = 11.5 Hz, 1 H, CH2), 5.12 (d, JHH
removed in vacuo from the filtrate to give {(Me3Si)2CH}PH(C6H4- = 11.5 Hz, 1 H, CH2), 7.14 (m, 1 H, ArH), 7.20 (m, 1 H, ArH),
2-CH2OMe) as a colorless oil. Isolated yield: 2.62 g, 76%.
7.33 (m, 1 H, ArH), 8.08 (m, 1 H, ArH) ppm. 13C{1H} NMR ([D8]-
THF, 25 °C): δ = 1.98 (SiMe3), 3.23 (SiMe3), 25.44 (THF), 57.08
(OMe), 67.28 (THF), 72.80 (CH2), 125.84 (Ar), 127.83 (Ar), 129.02
(d, JPC = 5.8 Hz, Ar), 133.74 (d, JPC = 17.3 Hz, Ar), 139.54 (Ar),
145.90 (d, JPC = 37.4 Hz, Ar) ppm. 11B{1H} NMR ([D8]THF,
25 °C): δ = –31.4 (br. d, 1JBP = 37.2 Hz) ppm. 31P{1H} NMR ([D8]-
THF, 25 °C): δ = –66.6 (q, br., 1JPB = 37.2 Hz) ppm. 7Li{1H} NMR
([D8]THF, 25 °C): δ = –0.7 ppm.
To stirred solution of {(Me3Si)2CH}PH(C6H4-2-CH2OMe)
a
(4.62 g, 14.88 mmol) in THF (20 mL) was added BH3·SMe2
(7.4 mL, 14.80 mmol). After 1 h the solvent was removed in vacuo
to yield 2 as a colorless solid. The solid was dissolved in hot light
petroleum (10 mL) and crystallized upon cooling to room tempera-
ture. Isolated crystalline yield: 2.91 g, 60%. 1H NMR (CDCl3,
25 °C): δ = –0.04 (s, 9 H, SiMe3), 0.29 (s, 9 H, SiMe3), 0.89 (q,
1JBH = 6.6 Hz, 3 H, BH3), 1.14 (dd, 2JPH = 20.2 Hz, 3JHH = 3.2 Hz, [[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]Na(tmeda)]2 (4): To a
2
1 H, CHP), 3.41 (s, 3 H, OMe), 4.48 (d, JHH = 11.9 Hz, 1 H,
stirred solution of 2 (0.37 g, 1.14 mmol) in THF (15 mL) was added
a solution of benzylsodium (0.13 g, 1.14 mmol) in THF (15 mL).
After 1 h the solvent was removed in vacuo to yield an off-white
2
1
CH2), 4.65 (d, JHH = 11.5 Hz, 1 H, CH2), 5.97 (dqd, JPH
=
3
3
375.5 Hz, JHH = 6.6 Hz, JHHЈ = 3.2 Hz, 1 H, PH), 7.41 (m, 2 H,
ArH), 7.46 (m, 1 H, ArH), 8.05 (m, 1 H, ArH) ppm. 13C{1H} solid. The solid was slurried in toluene, tmeda (0.2 mL, 1.14 mmol)
3
NMR (CDCl3, 25 °C): δ = 1.52 (d, JPC = 2.9 Hz, SiMe3), 2.29 (d, was added, and solvent was removed in vacuo until incipient
3JPC = 2.9 Hz, SiMe3), 8.85 (d, 1JPC = 1.9 Hz, CHP), 58.22 (OMe),
crystallization was observed. Upon cooling to –30 °C colorless
crystals of 4 suitable for X-ray crystallography deposited. Isolated
crystalline yield: 0.46 g, 43%; m.p. 132 °C (dec.). [[{(Me3Si)2CH}-
P(BH3)(C6H4-2-CH2OMe)]Na(tmeda)]2: calcd. C 54.29, H 10.20,
N 6.03; found C 54.14, H 10.16, N 5.93. 1H{11B} NMR ([D8]THF,
73.47 (CH2), 128.43 (d, JPC = 13.4 Hz, Ar), 128.97 (d, JPC
=
47.0 Hz, Ar), 130.37 (d, JPC = 6.7 Hz, Ar), 131.58 (d, JPC = 1.9 Hz,
Ar), 135.83 (d, JPC = 18.2 Hz, Ar), 140.37 (Ar) ppm. 11B{1H}
NMR (CDCl3, 25 °C): δ = –39.8 (br. d, JPB = 49.0 Hz) ppm.
31P{1H} NMR (CDCl3, 25 °C): δ = –16.2 (q, br., JPB = 49.0 Hz) 25 °C): δ = –0.02 (s, 9 H, SiMe3), 0.06 (s, 9 H, SiMe3), 0.40 (s, 1
2
ppm.
H, CHP), 0.62 (d, JPH = 5.5 Hz, 3 H, BH3), 3.31 (s, 3 H, OMe),
2
2
4.61 (d, JHH = 12.4 Hz, 1 H, CH2), 4.92 (d, JHH = 12.4 Hz, 1 H,
CH2), 6.90 (m, 1 H, ArH), 6.95 (m, 1 H, ArH), 7.18 (m, 1 H, ArH),
7.68 (m, 1 H, ArH) ppm. 13C{1H} NMR ([D8]THF, 25 °C): δ =
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]Li(THF)]2 (3): To
a
stirred solution of 2 (0.41 g, 1.26 mmol) in THF (15 mL) was added
nBuLi (0.5 mL, 1.25 mmol). After 1 h the solvent was removed in
vacuo to yield an off-white solid. The solid was slurried in methyl-
cyclohexane and sufficient THF was added to just dissolve it. Upon
cooling to –30 °C colorless crystals of 3 suitable for X-ray crystal-
lography deposited. Isolated crystalline yield: 0.36 g, 54%; m.p.
3
1
1.27 (d, JPC = 6.7 Hz, SiMe3), 2.88 (SiMe3), 8.01 (d, JPC
=
47.9 Hz, CHP), 42.29 (NMe2), 56.86 (OMe), 57.95 (NCH2), 73.52
2
(d, 3J = 32.6 Hz, CH2), 123.34 (Ar), 125.19 (Ar), 125.81 (d, JPC
=
3.8 Hz, Ar), 132.30 (Ar), 139.88 (d, 2JPC = 18.2 Hz, Ar), 151.69 (d,
1JPC = 32.6 Hz, Ar) ppm. 11B{1H} NMR ([D8]THF, 25 °C): δ =
147 °C
(dec.).
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]Li-
–31.9 (br. d, JBP = 29.4 Hz). 31P{1H} NMR ([D8]THF, 25 °C): δ
1
1
(THF)]2: calcd. C 56.43, H 9.72; found C 56.29, H 9.62. H{11B}
1
–65.3 (br. d, JPB = 29.4 Hz) ppm.
NMR ([D8]THF, 25 °C): δ = 0.05 (s, 9 H, SiMe3), 0.25 (s, 9 H,
2
2
SiMe3), 0.75 (d, JPH = 16.0 Hz, 1 H, CHP), 0.83 (d, JPH
=
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]K(pmdeta)]2 (5): To a
14.7 Hz, 3 H, BH3), 1.69 (m, 4 H, THF), 3.38 (s, 3 H, OMe), 3.54 stirred solution of 2 (0.39 g, 1.20 mmol) in THF (15 mL) was added
Table 1. Crystallographic data for 2, 3, 4, and 5.
2
3
4
5
Formula
Mw
C15H32BOPSi2
326.4
C38H78B2Li2O4P2Si4
808.8
C42H94B2N4Na2O2P2Si4 C48H108B2K2N6O2P2Si4
929.1
1075.5
Crystal size [mm]
Crystal system
Space group
0.55ϫ0.50ϫ0.40
orthorhombic
Pbca
0.28ϫ0.24ϫ0.24
triclinic
P1
0.20ϫ0.20ϫ0.15
triclinic
P1
0.24ϫ0.20ϫ0.20
monoclinic
P21/n
¯
¯
a [Å]
b [Å]
c [Å]
α [°]
15.9960(6)
12.5192(4)
19.8889(6)
11.7973(9)
13.885(5)
16.598(4)
82.37(3)
84.544(12)
69.843(11)
2526.2(11)
2
10.9716(8)
11.4084(9)
13.8139(10)
95.601(6)
110.887(7)
112.955(7)
1430.13(19)
1
12.089(3)
13.379(3)
21.091(3)
β [°]
101.544(19)
γ [°]
V [Å3]
3982.9(2)
8
0.253
3342.2(12)
2
0.298
Z
μ [mm–1]
0.213
0.209
Transmission coefficient range
Measured reflections
Unique reflections
Rint
0.873–0.905
17115
4860
0.030
3478
204
0.033
0.086
0.981
0.943–0.951
34707
8817
0.041
6729
507
0.059
0.143
1.176
0.960–0.970
12343
6042
0.035
4161
348
0.070
0.213
1.026
0.932–0.943
29613
5865
0.045
4322
322
0.038
0.081
1.049
Reflections with F2 Ͼ 2σ
Refined parameters
R (on F, F2 Ͼ 2σ)[a]
Rw (on F2, all data)[a]
Goodness of fit[a]
Max., min. e– density (eÅ–3)
0.31, –0.26
0.67, –0.51
0.71, –0.80
0.31, –0.22
[a] R = Σ||Fo| – |Fc||/Σ|Fo|; Rw = [Σw(Fo – Fc )2/Σw(Fo2)2]1/2; S = [Σw(Fo2 – Fc ) /(number of data – number of parameters)]1/2 for all data.
2
2
2 2
1700 Eur. J. Inorg. Chem. 2012, 1696–1701
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Ether-Functionalized Phosphido–Borane Complexes
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(0.3 mL, 1.44 mmol) was added, and solvent was removed in vacuo
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–30 °C colorless crystals of 5 suitable for X-ray crystallography
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(dec.).
[[{(Me3Si)2CH}P(C6H4-2-CH2OMe)(BH3)]K(pmdeta)]2:
calcd. C 53.60, H 10.12, N 7.81; found C 53.48, H 10.24, N 7.81.
1H{11B} NMR ([D8]THF, 25 °C): δ = –0.07 (s, 9 H, SiMe3), 0.09
2
(s, 9 H, SiMe3), 0.43 (s, 1 H, CHP), 0.68 (d, JPH = 5.0 Hz, 3 H,
BH3), 2.15 (s, 12 H, NMe2), 2.19 (s, 3 H, NMe), 2.31 (m, 4 H,
2
CH2N), 2.41 (m, 4 H, CH2N), 3.29 (s, 3 H, OMe), 4.53 (d, JHH
=
2
11.9 Hz, 1 H, CH2), 5.00 (d, JHH = 11.9 Hz, 1 H, CH2), 6.92 (m,
1 H, ArH), 6.98 (m, 1 H, ArH), 7.17 (m, 1 H, ArH), 7.71 (m, 1 H,
ArH) ppm. 13C{1H} NMR ([D8]THF, 25 °C): δ = 2.86 (SiMe3),
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1
8.26 (d, JPC = 49.8 Hz, CHP), 42.32 (NMe), 45.27 (NMe2), 56.40
(NCH2), 56.69 (OMe), 57.86 (NCH2), 73.48 (d, JPC = 24.0 Hz, [6] A. M. Fuller, A. J. Mountford, M. L. Scott, S. J. Coles, P. N.
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132.41 (Ar), 139.78 (d, JPC = 18.2 Hz, Ar), 152.93 (d, JPC
=
32.6 Hz, Ar) ppm. 11B{1H} NMR ([D8]THF, 25 °C): δ –29.2 (br.
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1
d, JBP = 19.6 Hz) ppm. 31P{1H} NMR ([D8]THF, 25 °C): δ –64.2
1
(br. d, JPB = 19.6 Hz) ppm.
Crystal Structure Determinations of 2, 3, 4 and 5: Measurements
were made at 150 K on an Oxford Diffraction (Agilent Technol-
ogies) Gemini A Ultra diffractometer or a Nonius KappaCCD dif-
fractometer, using Mo-Kα radiation (λ = 0.71073 Å). Cell param-
eters were refined from the observed positions of all strong reflec-
tions. Intensities were corrected semi-empirically for absorption,
based on symmetry-equivalent and repeated reflections. The struc-
tures were solved by direct methods and refined on F2 values for
all unique data. Table 1 gives 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 were
freely refined; U(H) was set at 1.2 (1.5 for methyl groups) times
Ueq for the parent C atom. Disorder in one of the trimethylsilyl
groups and the pmdeta co-ligand in 4 was successfully modeled
with the aid of restraints on geometry and displacement param-
eters. Programs were Oxford Diffraction CrysAlisPro and Nonius
COLLECT/EvalCCD for data collection and processing, and
SHELXTL for structure solution, refinement, and molecular
graphics.[19]
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CCDC-856685 (for 2), -856686 (for 3), -856687 (for 4),
-856688 (for 5) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[14] K. Izod, Adv. Inorg. Chem. 2000, 50, 33.
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Acknowledgments
The authors are grateful to the Engineering and Physical Sciences
Research Council (EPSRC) and Newcastle University for financial
support.
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Received: December 7, 2011
Published Online: February 21, 2012
Eur. J. Inorg. Chem. 2012, 1696–1701
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1701