Alkali-metal- and alkaline-earth-metal-mediated C-O activation of an anisole-substituted phosphido-borane ligand

Article abstract of DOI:10.1021/acs.organomet.7b00262

The reaction between {(Me₃Si)₂CH}PH(C₆H₄-2-OMe) (4) and 1 equiv of BH₃·SMe₂ yields the phosphine-borane {(Me₃Si)₂CH}PH(BH₃)(C₆H₄-2-OMe) (5). Subsequent reaction between 5 and 1 equiv of n-BuLi in THF gives the phosphido-borane complex [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-OMe)]Li(THF) (6a), which was isolated as a colorless microcrystalline solid. Treatment of 5 with 1 equiv of PhCH₂M yields the corresponding complexes [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-OMe)]ML (ML = Na(THF) (6b), K(pmdeta) (6c); pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine), after crystallization in the presence of the corresponding coligand. While compounds 6b,c are stable toward heat, compound 6a decomposes on heating to 50 °C in toluene to give the cluster [[{(Me₃Si)₂CH}PH(C₆H₄-2-O)]Li]₆ (7) and the tertiary phosphine-borane {(Me₃Si)₂CH}P(BH₃)(Me)(C₆H₄-2-OMe) (8). Related C-O cleavage reactions are observed when MgI₂ is treated with 2 equiv of 6a and when CaI₂ is treated with 2 equiv of [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-OMe)]K in THF, giving [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-O)Mg(THF)₂]₂ (9) and [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-O)Ca(THF)]₄ (10), respectively, along with 1 equiv of 8 in each case. In contrast, the reaction between SrI₂ and 2 equiv of [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-OMe)]K in THF yields [{(Me₃Si)₂CH}P(BH₃)(C₆H₄-2-OMe)Sr(THF)₄] (11).

Full text of DOI:10.1021/acs.organomet.7b00262

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pubs.acs.org/Organometallics
Alkali-Metal- and Alkaline-Earth-Metal-Mediated C−O Activation of
an Anisole-Substituted Phosphido−Borane Ligand
Keith Izod,* James M. Watson, Salima M. El-Hamruni, Ross W. Harrington, and Paul G. Waddell
Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne NE1 7RU,
U.K.
S
* Supporting Information
ABSTRACT: The reaction between {(Me3Si)2CH}PH(C6H4-2-
OMe) (4) and 1 equiv of BH3·SMe2 yields the phosphine−borane
{(Me3Si)2CH}PH(BH3)(C6H4-2-OMe) (5). Subsequent reaction
between 5 and 1 equiv of n-BuLi in THF gives the phosphido−
borane complex [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]Li(THF)
(6a), which was isolated as a colorless microcrystalline solid.
Treatment of 5 with 1 equiv of PhCH2M yields the corresponding
complexes [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]ML (ML = Na-
(THF) (6b), K(pmdeta) (6c); pmdeta = N,N,N′,N″,N″-pentam-
ethyldiethylenetriamine), after crystallization in the presence of the
corresponding coligand. While compounds 6b,c are stable toward
heat, compound 6a decomposes on heating to 50 °C in toluene to
give the cluster [[{(Me3Si)2CH}PH(C6H4-2-O)]Li]6 (7) and the
tertiary phosphine−borane {(Me3Si)2CH}P(BH3)(Me)(C6H4-2-OMe) (8). Related C−O cleavage reactions are observed when
MgI2 is treated with 2 equiv of 6a and when CaI2 is treated with 2 equiv of [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]K in THF,
giving [{(Me3Si)2CH}P(BH3)(C6H4-2-O)Mg(THF)2]2 (9) and [{(Me3Si)2CH}P(BH3)(C6H4-2-O)Ca(THF)]4 (10), respec-
tively, along with 1 equiv of 8 in each case. In contrast, the reaction between SrI2 and 2 equiv of [{(Me3Si)2CH}P(BH3)(C6H4-2-
OMe)]K in THF yields [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)Sr(THF)4] (11).
polymeric species having been identified.7−9 Our own work in
this area has focused on the synthesis, structures, and dynamic
INTRODUCTION
■
Phosphine−borane adducts R3PBH3 (R = H, alkyl, aryl, etc.)
are of great current interest due to their potential applications
in the synthesis of polyfunctional and/or polydentate (chiral)
behavior of alkaline-earth-metal complexes of sterically
demanding, donor-functionalized phosphide ligands9 and their
relationship to the corresponding lanthanide(II) complexes.10
phosphines and as precursors to poly(phosphine−borane)
During the course of this work, we found that certain alkaline-
earth-metal complexes of anisole-functionalized phosphide
materials, the latter of which are (valence) isoelectronic
analogues of polyolefins.1 In many of these applications
ligands underwent an unexpected C−O cleavage reaction to
complexes of the corresponding phosphido−borane anions
generate the corresponding alkoxo−phosphides (Scheme 1).9a
[R2P(BH3)]− are either key intermediates or else have been
This reaction is highly dependent upon the identity of the
implicated as the active species in catalytic cycles. Nonetheless,
alkaline-earth-metal cation: whereas the putative compound
a surprisingly small number of such compounds have been
isolated and characterized in the solid state: structurally
[{(Me3Si)2CH}P(C6H4-2-OMe)]2Ca(THF)n (1a) undergoes
C−O cleavage rapidly at room temperature to give
characterized phosphido−borane complexes are limited to
alkali-metal derivatives,2 a small number of mid-to-late-
[[{(Me3Si)2CH}P(C6H4-2-O)]Ca(THF)]4 (1b) as the sole
transition-metal complexes,3 and a very few p-block deriva-
calcium-containing product, the corresponding strontium
tives.2e,4 There has been no previous report of an alkaline-earth-
metal complex of this class of ligand. This is perhaps surprising,
compound (1c) undergoes this decomposition only upon
extended heating, while the barium analogue (1d) is stable
toward C−O cleavage. We attributed this to the significant
given the well-established chemistry of the analogous amido−
boranes.5 These latter compounds have been investigated as
decrease in Lewis acidity of the metal centers with increasing
atomic number. Muller and Knapp have also reported a related
̈
potential hydrogen storage materials and as catalysts for the
dehydrocoupling of amine−boranes; complexes of amido−
boranes with both alkali-metal and alkaline-earth-metal centers
have been reported.6
C−O cleavage reaction of an anisole-substituted phosphino-
methanide ligand: the reaction between 2 equiv of [(4-
MeC6H4)2PCH(C6H4-2-OMe)]Li(OEt2) and CaI2 in THF
While alkaline-earth-metal phosphido−borane complexes are
as yet unknown, a rich structural chemistry has emerged for
their phosphide analogues, with mononuclear, polynuclear, and
Received: April 7, 2017
© XXXX American Chemical Society
A
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Scheme 1
yields the cluster [[(4-MeC6H4)2PCH(C6H4-2-O)]Ca-
(THF)]4; however, the side products from this reaction were
not identified and so the fate of the cleaved methyl group is
unknown.11
In related chemistry, we have also found that alkali-metal
complexes of thioanisole-functionalized phosphide ligands
[RP(C6H4-2-SR′)]M (2a; M = Li, Na, K; R = (Me3Si)2CH,
t-Bu, Ph, 2,4,6-Me3C6H2; R′ = Me, Ph, n-Pr) undergo a
complementary, photolytically induced intramolecular alkyl/aryl
migration to give the tertiary-phosphine-substituted thiolate
complex [RR′P(C6H4-2-S)]M (2b) (Scheme 2).12 We have
N,N,N′,N′-tetramethylethylenediamine, pmdeta =
N,N,N′,N″,N″-pentamethyldiethylenetriamine).13
The foregoing prompted us to investigate whether anisole-
substituted phosphido−borane complexes would undergo C−
O cleavage similar to 1, or whether this reactivity might be
suppressed by the borane group, as observed in 3a−c. We now
describe the synthesis of a series of alkali-metal and alkaline-
earth-metal complexes of the anisole-substituted phosphido−
borane ligand [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]− and
show the effect of the borane group and the metal center on
the activation of the OMe functionality.
Scheme 2
RESULTS AND DISCUSSION
■
Synthesis and Stability. Treatment of the secondary
phosphine {(Me3Si)2CH}PH(C6H4-2-OMe) (4)9a with 1 equiv
of BH3·SMe2 in THF gives the air-stable phosphine−borane
{(Me3Si)2CH}PH(BH3)(C6H4-2-OMe) (5) as a colorless solid
in good yield (Scheme 3). The reaction between 5 and 1 equiv
of n-BuLi in THF proceeds smoothly to give the phosphido−
borane complex [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]Li-
(THF) (6a), which was isolated as a colorless microcrystalline
solid. Similarly, treatment of 5 with 1 equiv of either PhCH2Na
or PhCH2K in THF yields the analogous complexes
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]ML (ML = Na(THF)
(6b), K(pmdeta) (6c)), after crystallization in the presence of
the corresponding coligand.
recently shown that this photolytic rearrangement is suppressed
in the corresponding phosphido−borane complexes
[{(Me3Si)2CH}P(BH3)(C6H4-2-SMe)]ML (ML = Li (THF)
(3a), Na(tmeda) (3b), K(pmdeta) (3c)), such that these latter
compounds are stable toward both heat and light (tmeda =
a
Scheme 3
a
R = CH(SiMe3)2.
B
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Scheme 4
a
Scheme 5
a
R = CH(SiMe3)2.
1
1
The H, 13C{1H}, 11B{1H}, and 31P{1H} NMR spectra of 5
amine−borane adduct was confirmed by H NMR spectrosco-
py and X-ray crystallography).
and 6a−c are as expected: in each case the diastereotopic SiMe3
groups give rise to a pair of signals in both the 1H and 13C{1H}
NMR spectra, while for 5 the PH proton gives rise to a complex
The nature of the decomposition reaction was finally
revealed when single crystals of a toluene solvate of the
unusual alkoxo−phosphine cluster [[{(Me3Si)2CH}PH(C6H4-
2-O)]Li]6 (7), from which the methyl group of the anisyl
substituent has been cleaved, were isolated in moderate yield
from the thermolysis reaction. The fate of the cleaved methyl
group was revealed by analysis of the mother liquor from which
7 was isolated: NMR spectroscopy indicates that the tertiary
phosphine−borane {(Me3Si)2CH}P(BH3)(Me)(C6H4-2-OMe)
(8) is the major side product in this reaction (the identity of 8
was confirmed by comparison with the NMR spectra of a
deliberately prepared sample). Thus, the observed decom-
position reaction involves P−B cleavage, along with proto-
nation of the phosphorus center, and migration of a methyl
group from the O atom of one ligand to the P atom of another
(Scheme 4).
doublet of quartets of doublets in its H{11B} NMR spectrum,
1
due to coupling to the adjacent phosphorus nucleus, the three
BH3 protons, and the methine proton of the CH(SiMe3)2
substituent. There is a significant upfield shift of the 31P{1H}
NMR signal on metalation of 5, although there is little
difference in the chemical shifts of the metalated species (δP
−22.3 (5), −62.5 (6a), −64.3 (6b) −63.0 ppm (6c)). We have
noted previously that the 11B−31P coupling constant in related
alkali-metal phosphido−borane complexes decreases with
increasing ionic character of the P−M bond;13,14 however,
although there is a substantial difference between the 11B−31P
coupling constants of the free phosphine−borane 5 and its
metalated derivatives, there is only a small decrease in coupling
constant among compounds 6a−c (JPB = 49.0 (5), 39.3 (6a),
37.3 (6b), 36.1 Hz (6c)), possibly as a consequence of these
compounds adopting structures different from each other in
solution.
Somewhat unexpectedly, we noted on several occasions that
toluene solutions of 6a appeared to decompose over a period of
several days at room temperature; this decomposition appears
to be accelerated at higher temperatures. In contrast, solutions
of 6b or 6c in either THF or toluene are stable, even after
prolonged periods at elevated temperatures. Monitoring the
decomposition of 6a by 31P NMR spectroscopy revealed that
the broad quartet at −62.5 ppm due to 5 was replaced by a
broad quartet at 11.7 ppm (JPB = 58.8 Hz) and a sharp doublet
at −72.7 ppm (JPH = 219.6 Hz) of approximately equal
intensity. The appearance of a sharp doublet clearly suggests
that the decomposition reaction involves cleavage of the P−B
bond in at least part of the sample. Consistent with this, when
the decomposition reaction was conducted in the presence of 1
equiv of tmeda, the known amine−borane adduct Me2N(BH3)-
CH2CH2N(BH3)Me2 was isolated,15 suggesting that free BH3 is
liberated during the thermolysis reaction (the identity of the
In order to identify the source of the PH proton in 7, we
have carried out a number of deuterium-labeling experiments.
Thermolysis of toluene solutions of the labeled compounds
[{(Me3 Si)2 CH}P(BD3 )(C6 H4 -2-OMe)]Li(THF),
[{(Me3Si)2CH}P(BH3)(C6H4-2-OCD3)]Li(THF), and
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]Li(d8-THF) led exclu-
sively to mixtures of 7 and 8; neither H nor 31P{1H} NMR
2
spectroscopy exhibited any evidence for the incorporation of
deuterium at the phosphorus atom in 7. Similarly, thermolysis
of 6a in d8-toluene showed no evidence for incorporation of
deuterium in 7. We are, therefore, unable to identify
unambiguously the source of this proton and can only conclude
that it is derived from the presence of adventitious moisture.
The loss of the borane group during the degradation of 6a is
unexpected. However, it has previously been observed that (S)-
(Ph)(Me)(C6H4-2-OMe)P(BH3) racemizes slowly when it is
heated under reflux in xylene.16 This was attributed to
abstraction of the borane group by the anisyl oxygen atom,
followed by inversion at phosphorus and subsequent re-
formation of the phosphine−borane adduct. A similar process
C
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may account for the loss of BH3 from the phosphorus center in
6a, i.e. formation of an intermediate of the form
[{(Me3Si)2CH}P{C6H4-2-O(BH3)Me}]Li(THF)n, from which
the borane group could easily be abstracted by tmeda to give
the isolated amine−borane.
Given the substantial effect of the borane group on the
chemistry of thioanisole-substituted phosphide ligands, we were
interested to see whether the presence of the borane group
would suppress the alkaline-earth-metal-induced interligand
methyl migration observed previously for the borane-free
anisole-substituted analogue (see above).9a This was found not
to be the case: the reaction between MgI2 and 2 equiv of 6a in
THF gives the alkoxo−phosphido−borane complex
[[{(Me3Si)2CH}P(BH3)(C6H4-2-O)]Mg(THF)2]2·THF (9)
as colorless crystals in reasonable yield, along with the tertiary
phosphine−borane 8 as the sole phosphorus-containing
products (Scheme 5). Once crystallized, compound 9 has
surprisingly low solubility in aromatic and ethereal solvents,
including THF, and so characterization by NMR spectroscopy
is limited; however, the 31P{1H} and 11B{1H} NMR spectra of
9 in THF consist of broad signals at −74.3 and −30.0 ppm,
respectively, consistent with a phosphido−borane complex.
Similarly, the reaction between CaI2 and 2 equiv of in situ
generated [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]K in THF
yields the alkoxo−phosphido−borane cluster complex
[[{(Me3Si)2CH}P(BH3)(C6H4-2-O)]Ca(THF)]4 (10), along
with 8 as the only phosphorus-containing species; these two
compounds possess very similar solubilities, even in the
extremely poor solvent hexamethyldisiloxane, and so are very
difficult to separate, but a few single crystals of 10, sufficient to
obtain a crystal structure and elemental analysis, were isolated
Figure 1. Molecular structure of 5 with 40% probability ellipsoids and
with C-bound H atoms omitted for clarity. Selected bond lengths (Å)
and angles (deg): P(1)−B(1) 1.925(2), P(1)−C(1) 1.8169(16),
P(1)−C(8) 1.8107(18), P(1)−H(1) 1.32(2); C(1)−P(1)−B(1)
117.59(10), C(8)−P(1)−B(1) 112.72(9), C(1)−P(1)−C(8)
109.37(8).
We were unable to isolate single crystals of either 6a or 6b
suitable for X-ray crystallography; however, single crystals of 6c
were obtained from cold toluene. Compound 6c crystallizes as
discrete centrosymmetric dimers in which the two potassium
ions are bridged by B−H···K contacts, such that each borane
group acts as a μ-η2:η1 bridge (Figure 2). Each potassium ion is
thus coordinated by the phosphorus and η1-borane groups of a
phosphido−borane ligand, by the three nitrogen atoms of a
molecule of pmdeta, and by an η2-BH3 contact. Somewhat
surprisingly, there is no short contact between the potassium
cation and the methoxy oxygen atom of the anisole substituent
of the ligand.
1
from cold methylcyclohexane. The 31P{1H}, 11B{1H}, and H
NMR spectra of samples of 10 contaminated with a small
amount of 8 in d8-toluene are highly complex and difficult to
interpret. The low-temperature 31P{1H} NMR spectrum of this
mixture consists of broad and overlapping signals in the range
−64 to −77 ppm, which gradually broaden and coalesce as the
temperature is increased until, at 90 °C, the spectrum consists
of a very broad signal centered at −69.3 ppm, which we assign
to the cluster 10, and a broad multiplet at 11.7 ppm, due to 8.
This suggests the presence of numerous species in solution in
rapid dynamic equilibrium and therefore indicates that the
highly symmetrical tetrameric structure observed in the solid
state (see below) fragments in toluene solution. In contrast, the
1
31P{1H}, 11B{1H}, 13C{1H}, and H NMR spectra of 10 in d8-
THF exhibit a single set of signals for the ligands, suggesting
either that a single species is present, possibly a solvated
monomer, or else that any dynamic equilibria between
oligomers are fast on the NMR time scale.
In contrast to the O−Me cleavage reactions observed for Mg
and Ca, the reaction between SrI2 and 2 equiv of
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]K in THF cleanly
yields the straightforward phosphido−borane complex
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)Sr(THF)4] (11), which
shows no evidence of decomposition, even after several weeks.
The 31P{1H} and 11B{1H} NMR spectra of 11 in d8-THF
consist of a broad multiplet at −66.1 ppm and a broad doublet
(JPB = 41 Hz) at −29.3 ppm, respectively.
Solid-State Structures. In order that we might investigate
the impact of metalation on the skeletal structure of the
phosphine−borane, we have obtained the solid-state structure
of the neutral precursor 5. The molecular structure of 5 is
shown in Figure 1, along with selected bond lengths and angles.
Figure 2. Molecular structure of 6c with 40% probability ellipsoids and
with C-bound H atoms omitted for clarity. Selected bond lengths (Å):
K(1)−P(1) 3.2338(5), K(1)···B(1) 3.317(2), K(1)···H(1A) 2.77(2),
K(1)···H(1B′) 2.76(2), K(1)···H(1C′) 3.35(2), K(1)−N(1)
2..8320(13), K(1)−N(2) 2.9373(12), K(1)−N(3) 2.8555(13),
K(1)···C(15) 3.3512(17), K(1)···C(19) 3.3518(17), K(1)···C(22)
3.3373(18), P(1)−B(1) 1.9568(18), P(1)−C(1) 1.8772(15), P(1)−
C(8) 1.8375(15).
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The P−K distance of 3.2338(5) Å is similar to the
corresponding distance in [Ph2P(BH3)]K(18-crown-6)
(3.320(2) Å)2f and to the K−P distances in a range of
potassium phosphide complexes7 but is substantially shorter
than the P−K distances in the related complexes
13
[[{(Me3Si)2CH}P(BH3)(C6H4-2-SMe)]K(pmdeta)]2 and
[[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]K(pmdeta)]2
(3.6617(6) and 3.7619(10) Å, respectively),14 which exhibit
either K−S(Me) or K−O(Me) contacts. The K···H (2.77(2),
2.76(2) and 3.35(2) Å) and the K···B distances (3.317(2) and
3.1365(18) Å) are typical of such contacts.
Compound 7 crystallizes with two independent molecules in
the asymmetric unit and with solvent-accessible voids partially
occupied by toluene, which is disordered over multiple
positions; the molecular structure of 7 is shown in Figure 3,
along with selected bond lengths and angles. Each of the two
independent molecules of 7 contains a hexagonal-prismatic
core structure which lacks any crystallographic symmetry, such
that each ligand and each lithium ion in the cluster is unique.
The hexanuclear Li6O6 core of 7 has been observed in several
other species, including the phenoxide [{2,6-(MeO)2C6H2O}-
Li]6 (12),17 and its formation is in line with the ring-stacking
principles developed by Snaith et al.18
Each lithium ion is coordinated by three μ3-O atoms and one
phosphorus atom in a highly distorted tetrahedral geometry. In
addition, Li(2), Li(3), and Li(6) have a close contact with the
ipso-C(O) atom from an alkoxo−phosphide ligand in the
opposite face of the hexagonal prism. The alkoxo−phosphide
ligands chelate a single lithium ion in each face of the hexagonal
prism (P−Li−O bite angles 84.3(3)−85.3(3)°), with the
oxygen atom of the ligand bridging two lithium ions in one
hexagonal face and forming a link to a third lithium ion in the
second face. The Li−P distances in 7 range from 2.529(7) to
2.551(7) Å and are typical of such distances.7 Similarly, the Li−
O distances, which range from 1.854(9) to 2.067(9) Å, lie in
the typical range of distances for these bonds; for example, the
Li−O distances in 12 range from 1.908(4) to 2.058(4) Å.17
While phosphido−borane complexes of the alkali metals are
reasonably well known,2,13,14 and derivatives of the p-block2e,4
and transition metals3 have been reported, compounds 9−11
represent the first alkaline-earth-metal complexes of this ligand
type. Compound 9 crystallizes as centrosymmetric dimers with
a rhombus-shaped Mg2O2 core and with one molecule of THF
of crystallization in the asymmetric unit; the structure of 9 is
shown in Figure 4, along with selected bond lengths and angles.
Each magnesium ion is coordinated by a μ2-alkoxide oxygen
atom, the oxygen atoms of two molecules of THF, and an η2-
BH3 group in a pseudo-trigonal-bipyramidal geometry; there is
no contact between the magnesium ions and the pyramidal
phosphorus centers.
The binding mode of the alkoxo−phosphido−borane ligand
in 9 (O and BH3 chelation, but no P−Mg contacts) is in
contrast with the binding mode of the precursor anisole-
substituted phosphido−borane ligand in the potassium
complex 6c (P and BH3 chelation, but no O−K contacts),
and this is clearly related to the localization of charge on the
oxygen atom in the former and the weak donor strength of the
aryl ether in the latter. The Mg−O(alkoxo) distances of
1.961(3) and 2.017(3) Å are similar to previously reported
Mg−O distances; for example, the Mg−O distances within the
Mg2O2 core in [(Ph3SiO)Mg(μ-OSiPh3) (py)]2 are 1.965(2)
and 1.988(2) Å.19
Figure 3. (a) Molecular structure of one of the two independent
molecules of 7 with 40% probability ellipsoids and with H atoms
omitted for clarity. (b) Core of the cluster with all C, Si, and H atoms
omitted. Selected bond lengths for one of the two independent
molecules (Å): Li(1)−P(1) 2.541(6), Li(1)−O(1) 1.912(8), Li(1)−
O(3) 2.062(8), Li(1)−O(5) 2.062(8), Li(2)−P(2) 2.539(8), Li(2)−
O(1) 1.913(8), Li(2)−O(2) 1.923(7), Li(2)−O(4) 2.065(8), Li(3)−
P(3) 2.551(7), Li(3)−O(2) 1.887(9), Li(3)−O(3) 1.921(8), Li(3)−
O(6) 2.067(9), Li(4)−P(4) 2.534(8), Li(4)−O(2) 2.059(9), Li(4)−
O(4) 1.924(7), Li(4)−O(6) 1.854(9), Li(5)−P(5) 2.529(7), Li(5)−
O(1) 2.062(8), Li(5)−O(4) 1.885(8), Li(5)−O(5) 1.920(9), Li(6)−
P(6) 2.543(8), Li(6)−O(3) 2.040(9), Li(6)−O(5) 1.889(7), Li(6)−
O(4) 1.931(8).
Compound 10 crystallizes with an unusual tetranuclear
structure containing a crystallographic C2 axis which lies
perpendicular to the Ca4 plane, midway along the Ca(1)···
Ca(1A) vector; the molecular structure of 10 is shown in
Figure 5, along with selected bond lengths. There are two
distinct calcium environments: Ca(1) is coordinated by four
oxygen atoms from four alkoxo−phosphido−borane ligands,
which bridge to a second symmetry-equivalent calcium ion, two
phosphorus atoms, and two η1-BH3 groups. In contrast, Ca(2)
is coordinated by two alkoxo−phosphido−borane oxygen
atoms, two η2-BH3 groups, and two molecules of THF, along
with a short Ca···Cipso contact with one of the aromatic rings.
Thus, each alkoxo oxygen atom acts as a μ3 bridge between two
Ca(1) and one Ca(2) ion, while each BH3 group acts as a μ2-
E
DOI: 10.1021/acs.organomet.7b00262
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Organometallics
Article
η1:η2 bridge between Ca(1) and Ca(2). The alkoxo−
phosphido−borane ligands chelate Ca(1) through the P and
O atoms (P−Ca(1)−O bite angles 67.53(6) and 67.04(6)°),
while also formally chelating Ca(2) through the O and BH3
hydrogen atoms (O−Ca(2)···B angles 72.92(11) and
74.55(12)°). The core structure of 10 may be considered as
an O4 square with one Ca ion lying over the center of each face
and two calcium ions bridging two of its opposing edges. This
structural motif is completely different from the heterocubane
structure adopted by the borane-free cluster [[{(Me3Si)2CH}-
P(C6H4-2-O)]Ca(THF)]4 (1b),9a clearly illustrating the
structural influence of the borane groups.
The Ca−P distances (2.8778(11) and 2.8454(12) Å) are at
the shorter end of the typical range for Ca−P distances (2.90−
3.10 Å) but are similar to the corresponding distances in
[(Me3Si)2N}Ca(THF){μ2-P(SitBu3)2}2]2Ca,20 which range
from 2.866(3) to 2.951(2) Å. The Ca(1)−Oalkoxo distances in
10 (2.369(2), 2.385(2), 2.518(2) and 2.524(2) Å) are
significantly longer than the Ca(2)−Oalkoxo distances
(2.297(2) and 2.299(2) Å) but lie in the typical range for
such distances.
In contrast to the multinuclear structure adopted by 10,
compound 11 crystallizes as discrete molecules with a single
pseudo-octahedral Sr ion. The structure of 11 is shown in
Figure 6, along with selected bond lengths and angles. The
Figure 4. Molecular structure of 9 with 40% probability ellipsoids.
Disorder components, solvent of crystallization, and C-bound H atoms
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Mg(1)−O(1) 1.961(3), Mg(1)-O(1A) 2.017(3), Mg(1)−O(2)
2.049(3), Mg(1)−O(3) 2.068(3), Mg(1)···B(1A) 2.428(4), Mg(1)···
H(1A) 1.98(4), Mg(1)···H(1B) 1.99(4), P(1)−C(1) 1.872(4), P(1)−
C(8) 1.835(4), P(1)−B(1) 1.972(4); O(1)−Mg(1)−O(1A)
80.44(11), Mg(1)−O(1)−Mg(1A) 99.56(11).
Figure 6. Molecular structure of 11 with 40% probability ellipsoids.
Solvent of crystallization and C-bound H atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Sr(1)−O(3) 2.5069(14),
Sr(1)−O(4) 2.5383(13), Sr(1)−O(5) 2.5556(13), Sr(1)−O(6)
2.5490(14), Sr(1)···H(1A) 2.59(2), Sr(1)···H(1B) 2.75(2), Sr(1)···
H(1C) 2.63(2), Sr(1)···H(2A) 2.59(2), Sr(1)···H(2B) 2.74(2),
Sr(1)···H(2C) 2.64(2), Sr(1)···B(1) 2.844(2), Sr(1)···B(2) 2.847(2),
P(1)−C(1) 1.840(2), P(1)−C(8) 1.8898(19), P(1)−B(1) 1.952(2),
P(2)−C(15) 1.8386(19), P(2)−C(22) 1.8882(19), P(2)−B(2)
1.952(2); B(1)···Sr···B(2) 174.68(7).
Figure 5. Molecular structure of 10 with 40% probability ellipsoids.
Disorder components and C-bound H atoms are omitted for clarity.
Selected bond lengths (Å): Ca(1)−O(1) 2.369(2), Ca(1)-O(2A)
2.387(2), Ca(1)−O(2) 2.517(2), Ca(1)-O(1A) 2.525(2), Ca(1)-
P(2A) 2.8449(10), Ca(1)−P(1) 2.8783(9), Ca(1)···B(2) 3.223(4),
Ca(1)···B(1A) 3.281(4), Ca(1)-H(1B) 2.64(1), Ca(2)−O(1)
2.295(2), Ca(2)−O(2) 2.298(2), Ca(2)−O(3) 2.350(2), Ca(2)−
O(4) 2.370(2), Ca(2)···B(1) 2.872(4), Ca(2)···B(2) 2.901(4),
Ca(2)···C(13) 3.1254(1), Ca(2)···C(26) 3.1333(1), Ca(2)···H(1A)
2.35(1), Ca(2)···H(1B) 2.39(1), Ca(2)···H(2F) 2.42(1), Ca(2)···
H(2E) 2.52(1), P(1)−C(1) 1.865(3), P(1)−C(8) 1.823(3), P(1)−
B(2) 1.966(4), P(2)−B(1) 1.984(4), P(2)−C(14) 1.867(5), P(2)−
C(21) 1.825(4).
strontium ion is coordinated in a trans configuration by two η3-
BH3 groups and by the oxygen atoms of four molecules of
THF. Somewhat surprisingly, given the potentially chelating
nature of the phosphido−borane ligand (which may act as a
P,O- or BH3,O-donor; see above), there is no contact between
the strontium ions and either the phosphorus or oxygen centers
of the ligand. We have previously observed a related preference
for BH3 donation (over C donation) in the phosphine−borane-
stabilized carbanion complex [(Me3Si)2{Me2(H3B)P}C]2Sr-
(THF)5.21 In the present case, this preference for borane
coordination may be attributed to the hard nature of the
strontium cation and the better donor properties of THF in
comparison to aryl ethers. The Sr···B distances in 11 (2.844(2)
and 2.847(2) Å) are similar to previously reported Sr···B
F
DOI: 10.1021/acs.organomet.7b00262
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Article
cold (−30 °C) mixture of n-hexane (20 mL) and THF (1 mL).
distances; for example, the Sr···B distance in Sr[HC{C(Me)-
N(2,6-iPr2C6H3)}2](BH4) (THF)2 is 2.8206(18) Å.22
Comparison of the structure of 5 with those of 6c and 9−11
reveals that metalation of the phosphine−borane precursor
results in a significant lengthening of the P(1)−C(1), P(1)−
C(8), and P(1)−B(1) distances by 0.02−0.07 Å.
1
Isolated yield: 5.00 g, 73%. H{11B} NMR (CDCl3): δ −0.01 (s, 9H,
SiMe3), 0.29 (s, 9H, SiMe3), 0.89 (dd, JPH = 14.9, JHH = 6.6 Hz, 3H,
BH3), 1.08 (d, JPH = 20.2 Hz, 1H, CHP), 3.90 (s, 3H OMe), 5.86
(dqd, JPH = 384.0, JHH = 6.6, JHH = 1.4 Hz, 1H, PH), 6.90 (m, 1H,
ArH), 7.06 (m, 1H, ArH), 7.48 (m, 1H, ArH), 7.92 (m, 1H, ArH).
13C{1H} NMR (CDCl3): δ 1.25 (d, JPC = 3.8 Hz, SiMe3), 2.11 (d, JPC
= 2.8 Hz, SiMe3), 6.51 (d, JPC = 4.8 Hz, CHP), 55.54 (OMe), 110.28
(d, JPC = 3.8 Hz, ArC), 116.87 (d, JPC = 50.8 Hz, ArC), 121.05 (d, JPC
= 12.5 Hz, ArC), 133.49 (ArC), 136.19 (d, JPC = 15.3 Hz, ArC),
160.78 (d, JPC = 2.0 Hz, ArC). 11B{1H} NMR (CDCl3): δ −40.6 (d,
br, JPB = 49.0 Hz). 31P{1H} NMR (CDCl3): δ −22.3 (q, br, JPB = 49.0
Hz).
CONCLUSIONS
■
While alkali-metal complexes of the anisole-substituted
phosphide [{(Me3Si)2CH}P(C6H4-2-OMe)]M(THF)n (M =
Li, K) are stable at room temperature, the presence of the
borane group in the lithium complex 6a appears to be sufficient
to activate the C−O bond; C−O cleavage is not observed for
the corresponding sodium and potassium complexes 6b,c.
Similarly, while an analogous C−O cleavage reaction is
observed in the magnesium and calcium complexes 9 and 10,
this reaction is not seen for the strontium complex 11. This
suggests that the rate of the C−O cleavage reaction depends on
the Lewis acidity of the alkali-metal or alkaline-earth-metal
cation, paralleling the behavior of the borane-free derivatives.
The presence of the borane group additionally affects the
solid-state structures of the resulting complexes, leading to a
variety of ligand coordination modes, including (i) P,BH3
chelation/bridging (6c), (ii) O,BH3 chelation/bridging (9),
(iii) P,BH3,O chelation/bridging (10), and (iv) BH3-donor-
only (11) coordination modes.
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]Li(THF) (6a). To a solution of
5 (0.20 g, 0.64 mmol) in diethyl ether (20 mL) was added n-BuLi (0.4
mL, 0.76 mmol). This mixture was stirred for 1 h, and the solvent was
removed in vacuo. The yellow solid was dissolved in THF (2 mL), and
light petroleum (20 mL) was added, precipitating the product as a
colorless powder, which was isolated by filtration and washed with
1
cold (−10 °C) light petroleum (5 mL). Yield: 0.13 g, 54%. H{11B}
NMR (d8-THF): δ −0.11 (s, 9H, SiMe3), 0.15 (s, 9H, SiMe3), 0.62 (d,
JPH = 3.2 Hz, 3H, BH3), 0.73 (d, JPH = 6.9 Hz, 1H, CHP), 1.76 (m,
4H, THF), 3.65 (m, 4H, THF), 3.75 (s, 3H, OMe), 6.61 (m, 1H,
ArH), 6.65 (m, 1H, ArH), 6.90 (m, 1H, ArH), 7.69 (m, 1H, ArH).
13C{1H} NMR (d8-THF): δ 2.45 (d, JPC = 9.2 Hz, SiMe3), 3.79
(SiMe3), 7.15 (d, JPC = 43.2 Hz, CHP), 26.43 (THF), 55.52 (OMe),
68.37 (THF), 110.22, 120.41, 125.62, 134.73 (ArC), 141.25 (d, JPC
=
36.2 Hz, ArC), 162.35 (d, JPC = 11.1 Hz, ArC). 11B{1H} NMR (d8-
THF, 25 °C): δ −34.3 (d, JPB = 39.3 Hz). 31P{1H} NMR (d8-THF): δ
7
−62.5 (d, JPB = 39.3 Hz). Li NMR (d8-THF): δ −0.58.
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)Na](THF) (6b). To a solution
of 5 (0.21 g, 0.67 mmol) in diethyl ether (10 mL) was added a
solution of PhCH2Na (0.08 g, 0.67 mmol) in diethyl ether (10 mL),
and this mixture was stirred for 1 h. The solvent was removed in vacuo
to yield a yellow solid. This solid was dissolved in the minimum
amount of THF, and upon addition of light petroleum the product
precipitated from solution as a colorless powder, which was isolated by
filtration and washed with cold (−10 °C) light petroleum. Yield: 0.25
g, 96%. Anal. Calcd for [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]Na-
EXPERIMENTAL SECTION
■
General Considerations. 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;
hexamethyldisiloxane was dried by distillation from CaH2. THF and
hexamethyldisiloxane were stored over activated 4A molecular sieves;
all other solvents were stored over a potassium film. Deuterated THF,
toluene, 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 4A molecular sieves. Benzylsodium, benzylpotassium,23
and {(Me3Si)2CH}PH(C6H4-2-OMe) (4)9a 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 4A
molecular sieves. All other compounds were used as supplied by the
manufacturer.
1
(THF): C 53.19, H 9.18%. Found: C 53.06, H 9.31%. H{11B} NMR
(d8-THF): δ −0.07 (s, 9H, SiMe3), 0.15 (s, 9H, SiMe3), 0.66 (d, JPH
=
7.3 Hz, 1H, CHP), 0.72 (d, JPH = 6.9 Hz, 3H, BH3), 1.79 (m, 4H,
THF), 3.63 (m, 4H, THF), 3.77 (s, 3H, OMe), 6.66 (m, 2H, ArH),
6.92 (m, 1H, ArH), 7.72 (m, 1H, ArH). 13C{1H} NMR (d8-THF): δ
2.38 (d, JPC = 8.6 Hz, SiMe3), 3.76 (SiMe3), 7.07 (d, JPC = 40.2 Hz,
CHP), 26.43 (THF), 55.55 (OMe), 68.31 (THF), 110.14, 120.58,
125.89, 134.92 (ArC), 140.41 (d, JPC = 30.16 Hz ArC), 162.06 (d, JPC
= 11.1 Hz). 11B{1H} NMR (d8-THF,): δ −34.5 (d, br, JBP = 37.3 Hz).
31P{1H} NMR (d8-THF): δ −64.3 (q, br, JPB = 37.3 Hz).
[{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]K(pmdeta) (6c). To a sol-
ution of 5 (0.88 g, 2.82 mmol) in THF (20 mL) was added a solution
of PhCH2K (0.37 g, 2.82 mmol) in THF (20 mL). This mixture was
stirred for 1 h, and then the solvent was removed in vacuo to yield a
yellow solid. The product was dissolved in the minimum amount of
toluene, and pmdeta (0.6 mL, 2.87 mmol) was added. The solvent was
then carefully reduced in vacuo until incipient crystallization. The
solution was warmed to room temperature, dissolving the product, and
upon cooling (5 °C) colorless crystals of 6c suitable for X-ray
crystallography were deposited. Isolated crystalline yield: 0.54 g, 37%.
Anal. Calcd for [{(Me3Si)2CH}P(BH3)(C6H4-2-OMe)]K(pmdeta):
C, 52.75; H, 10.01; N, 8.02. Found: C, 52.69; H, 9.92; N, 7.87.
1H{11B} NMR (C6D6): δ −0.27 (s, 9H, SiMe3), 0.45 (s, 9H, SiMe3),
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}, Li, and H NMR spectra were
recorded on a JEOL ECS500 spectrometer operating at 202.35,
160.16, 194.38, and 76.78 MHz, respectively; chemical shifts are
quoted in ppm relative to external 85% H3PO4, BF3·Et2O, and 0.1 M
LiCl, respectively.
7
2
Where possible, compounds were subjected to combustion analysis
to assess bulk purity; where this was not possible, the purity of
compounds has been established by multielement NMR spectroscopy.
Elemental analyses were obtained by the Elemental Analysis Service of
London Metropolitan University.
{(Me3Si)2CH}PH(BH3)(C6H4-2-OMe) (5). To a solution of
{(Me3Si)2CH}PH(C6H4-2-OMe) (4; 6.55 g, 21.94 mmol) in THF
(20 mL) was added BH3·SMe2 (11.0 mL, 22.00 mmol). This mixture
was stirred at room temperature for 1 h, and then the solvent was
removed in vacuo to yield a colorless solid. This was crystallized from a
2
1.05 (d, JPH = 5.5 Hz, 3H, BH3), 1.07 (d, JPH = 7.8 Hz, 1H, CHP),
2.01 (s, 8H, NCH2), 2.05 (s, 3H, NMe), 2.11 (s, 12H, NMe2), 3.53 (s,
3H, OMe), 6.54 (m, 1H, ArH), 6.94 (m, 1H, ArH), 7.06 (m, 1H,
ArH), 8.04 (m, 1H, ArH). 13C{1H} NMR (C6D6): δ 2.42 (d, JPC = 8.6
Hz, SiMe3), 3.76 (SiMe3), 7.04 (d, JPC = 42.9 Hz, CHP), 43.23
(NMe), 46.22 (NMe2), 55.35 (OMe), 57.34 (NCH2), 58.79 (NCH2),
109.93, 120.44, 125.75, 134.77 (ArC), 140.84 (d, JPC = 31.4 Hz, ArC),
G
DOI: 10.1021/acs.organomet.7b00262
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Article
162.04 (d, JPC = 10.1 Hz, ArC). 11B{1H} NMR (C6D6): δ −32.3 (d, br,
JBP = 36.1 Hz). 31P{1H} NMR (C6D6): δ −63.0 (q, br, JPB = 36.1 Hz).
{(Me3Si)2CH}PMe(BH3)(C6H4-2-OMe) (8). To a solution of 5
(0.31 g, 0.99 mmol) in THF (15 mL) was added n-BuLi (0.4 mL, 1.00
mmol). This mixture was stirred for 1/2 h, and then MeI (0.07 mL,
1.12 mmol) was added. The mixture was stirred for a further 1/2 h,
and the solvent was removed in vacuo to give 8 as a colorless solid.
of diethyl ether. Yield: 0.35 g, 74% (based on MgI2). Anal. Calcd for
[{(Me3Si)2CH}P(BH3)(C6H4-2-O)]Mg(THF)2]2: C, 50.00; H, 8.41.
Found: C, 49.84; H, 8.32. 31P{1H} NMR (THF): δ −74.3 (br),
11B{1H} NMR (THF): δ −30.0 (br)
[{(Me3Si)2CH}P(C6H4-2-O)(BH3)Ca(THF)]4 (10). To a solution of
5 (0.98 g, 3.14 mmol) in THF (15 mL) was added a solution of
PhCH2K (0.47 g, 3.30 mmol) in THF (20 mL), and this mixture was
stirred for 1 h. This solution was added to a slurry of CaI2 (0.48 g, 1.63
mmol) in THF (20 mL), and this mixture was stirred for 16 h. The
solvent was removed in vacuo, and the resulting sticky, colorless solid
was extracted into hexamethyldisiloxane (30 mL) and filtered. The
solvent was removed in vacuo from the filtrate to give a sticky solid,
which was washed with hexamethyldisiloxane. A small number of
single crystals of 10 suitable for X-ray crystallography were obtained
from cold (5 °C) methylcyclohexane. Isolated yield: 0.48 g, 69%
(based on CaI2). Anal. Calcd for [[{(Me3Si)2CH}P(C6H4-2-O)-
1
Isolated yield: 0.32 g, 99%. H{11B} NMR (CDCl3): δ −0.08 (s, 9H,
SiMe3), 0.31 (s, 9H, SiMe3), 0.88 (d, JPH = 14.7 Hz, 3H, BH3), 1.46 (d,
JPH = 20.2 Hz, 1H, CHP), 1.66 (d, JPH = 10.1 Hz, 3H, PMe), 3.91 (s,
3H, OMe), 6.88 (m, 1H, ArH), 7.06 (m, 1H, ArH), 7.48 (m, 1H,
ArH), 7.92 (m, 1H, ArH). 13C{1H} NMR (CDCl3): δ 2.43 (d, JPC
=
2.9 Hz, SiMe3), 3.52 (d, JPC = 1.9 Hz, SiMe3), 10.39 (d, JPC = 4.8 Hz,
CHP), 16.71 (d, JPC = 39.3 Hz, PMe), 55.22 (OMe), 110.68 (d, JPC
=
3.83 Hz, ArC), 120.82, 120.94, 132.90 (ArC), 135.71 (d, JPC = 15.3
Hz, ArC), 161.35 (ArC). 11B{1H} NMR (CDCl3): δ −37.5 (d, br, JPB
= 58.8 Hz). 31P{1H} NMR (CDCl3): δ 11.7 (q, br, JPB = 58.8 Hz).
{(Me3Si)2CH}PH(BD3)(C6H4-2-OMe). To a solution of 4 (0.37 g,
1.24 mmol) in THF (5 mL) was added BD3·THF (1.2 mL of a 1.0 M
solution in THF, 1.20 mmol). This mixture was stirred for 1 h, and the
solvent was removed in vacuo to give a colorless solid. Yield: 0.33 g,
1
(BH3)]Ca(THF)]4: C, 51.67; H, 8.79. Found: C, 51.56; H, 8.64. H
NMR (d8-THF): δ 0.15 (s, 9H, SiMe3), 0.19 (s, 9H, SiMe3), 1.06 (br
s, 3H, BH3), 1.78, (m, 4H, THF), 3.64 (m, 4H, THF), 6.48 (m, 1H,
ArH), 6.75 (m, 1H, ArH), 7.03 (m, 2H, ArH). 13C{1H} NMR (d8-
THF): δ 2.25 (SiMe3), 4.35 (SiMe3), 5.74 (d, JPC = 35.5 Hz, CHP),
26.44, 68.47 (THF), 116.16, 117.77, 124.89, 129.88 (Ar), 141.60 (d,
JPC = 18.1 Hz, Ar), 164.66 (d, JPC = 16.6 Hz, Ar). 31P{1H} NMR (d8-
THF): δ −69.8 (br). 11B{1H} NMR (d8-THF): −26.6 (br).
1
88%. H NMR (CDCl3): δ 0.00 (s, 9H, SiMe3), 0.28 (s, 9H, SiMe3),
1.08 (d, JPH = 20.9 Hz, 1H, CHP), 3.90 (s, 3H, OMe), 5.83 (d, JPH
=
380.6 Hz, 1H, PH), 6.90 (m, 1H, ArH), 7.04 (m, 1H, ArH), 7.48 (m,
2
1H, ArH), 7.90 (m, 1H, ArH). H NMR (CHCl3): δ 0.95 (br s).
11B{1H} NMR (CDCl3, 25 °C): δ −40.8 (br, s). 31P{1H} NMR
(CDCl3): δ −22.3 (br m).
[{(Me3Si)2CH}P(C6H4-2-OMe)(BH3)Sr(THF)4]·THF (11). To a
solution of 5 (0.78 g, 2.50 mmol) in THF (15 mL) was added a
solution of PhCH2K (0.31 g, 2.4 mmol), and this mixture was stirred
for 1/2 h. This solution was added to a suspension of SrI2 (0.43 g, 1.25
mmol) in THF, and this mixture was stirred for 24 h. The solution was
filtered, and the filtrate was reduced in volume to ca. 5 mL and cooled
to 6 °C for 16 h. The colorless crystals of 11 were isolated by filtration
and washed with a small amount of cold diethyl ether. The THF of
crystallization is held only weakly and is rapidly lost under vacuum.
Yield: 0.79 g, 63%. Anal. Calcd for [[{(Me3Si)2CH}P(C6H4-2-OMe)
{(Me3Si)2CH}PH(BH3)(C6H4-2-OCD3). To a cold (0 °C) solution
of KOH (0.63 g, 12.00 mmol) in acetonitrile (10 mL) was added 2-
bromophenol (2.0 mL of a 5.0 M solution in acetonitrile, 10.00
mmol). This mixture was stirred for 1/2 h at 0 °C, and then CD3I
(0.75 mL, 12 mmol) was added. The reaction mixture was stirred for
40 h. The solvent was removed in vacuo, and the residue was extracted
into light petroleum (3 × 20 mL) and filtered. The solvent was
removed in vacuo from the filtrate to yield 2-bromo-d3-anisole as a
colorless oil. To a cold (0 °C) solution of 2-bromo-d3-anisole (1.19 g,
6.23 mmol) in diethyl ether (10 mL) was added n-BuLi (2.5 mL, 6.25
mmol). The solution was stirred for 2 h at 0 °C and then added,
dropwise, to a cold (−78 °C) solution of {(Me3Si)2CH}PCl2 (1.70 g,
6.51 mmol) in diethyl ether (20 mL). The reaction mixture was stirred
for 16 h and warmed to room temperature. Solid LiAlH4 (0.28 g, 7.3
mmol) was carefully added to the solution, and this mixture was
heated under reflux for 2 h. The solution was cooled, BH3·SMe2 (3.2
mL, 6.4 mmol) was added, and the solution was stirred for 1 h at room
temperature. Water (40 mL) was carefully added, the organic phase
was extracted into diethyl ether (3 × 20 mL), and the combined
extracts were washed with brine (30 mL). The organic phase was dried
over MgSO4 and filtered, and the solvent was removed in vacuo. The
crude product was dissolved in hot n-hexane, and crystals were
deposited upon cooling to −30 °C. Isolated crystalline yield: 0.83 g,
1
(BH3)]2Sr(THF)4]: C, 52.92; H, 9.08. Found: C, 52.75; H, 8.95. H
NMR (d8-THF) δ −0.06 (s, 18H, SiMe3), 0.11 (s, 18H, SiMe3), 0.70
(d, JPH = 6.0 Hz, 2H, CHP), 0.90 (br q, JBH = 83.8 Hz, 6H, BH3), 1.79
(m, 16H, THF), 3.62 (m, 16H, THF), 3.76 (s, 6H, OMe), 6.65 (m,
4H, ArH), 6.95 (m, 2H, ArH), 7.65 (m, 2H, ArH). 13C{1H} NMR (d8-
THF): δ 2.31 (d, JPC = 9.0 Hz, SiMe3), 3.58 (SiMe3), 7.23 (d, JPC
=
44.2 Hz, CHP), 26.52 (THF), 55.50 (OMe), 68.39 (THF), 110.39,
120.31, 134.43, 134.71 (Ar), 162.50 (d, JPC = 11.5 Hz, Ar). 31P{1H}
NMR (d8-THF): δ −66.1 (m, br). 11B{1H} NMR (d8-THF): δ −29.3
(d, JPB = 41.4 Hz).
Crystal Structure Determinations of 5, 6c, 7, and 9−11.
Measurements were made at 150 K on an Oxford Diffraction (Agilent
Technologies) Gemini A Ultra diffractometer using Mo Kα radiation
(λ = 0.71073 Å), except for the structure of 9, which was collected
using Cu Kα radiation (λ = 1.54178 Å). 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. The structures were solved by
direct methods and refined on F2 values for all unique data; Table S1
in the Supporting Information gives further details. All non-hydrogen
atoms were refined anisotropically, and C-bound H atoms were
positioned with idealized geometry, while B-bound H atoms were
located using peaks in the Fourier difference map. The displacement
parameters for all hydrogen atoms were constrained with a riding
model; U(H) was set at 1.2 (1.5 for methyl groups) times Ueq for the
parent C atom. The structure of 10 contains large solvent-accessible
voids along the crystallographic [001] direction. These voids contain
multiple, partially occupied diethyl ether sites, disordered about a
center of symmetry. No sensible model for this disorder was
forthcoming; therefore, the electron density in the void space was
treated using PLATON/SQUEEZE. Programs were Oxford Diffrac-
tion CrysAlisPro for data collection and processing and SHELXTL for
structure solution, refinement, and molecular graphics.24
1
42%. H{11B} NMR (CDCl3): δ −0.01 (s, 9H, SiMe3), 0.28 (s, 9H,
SiMe3), 0.89 (dd, JHH = 6.6, JPH = 14.9 Hz, 3H, BH3), 1.07 (d, JPH
=
20.2 Hz, 1H, CHP), 5.84 (dq, JPH = 384.0, JHH = 12.9 Hz, 1H, PH),
6.89 (m, 1H, ArH), 7.04 (m, 1H, ArH), 7.47 (m, 1H, ArH), 7.91 (m,
1H, ArH). 13C{1H} NMR (CDCl3): δ 1.28 (d, JPC = 2.9 Hz, SiMe3),
2.14 (d, JPC = 2.9 Hz, SiMe3), 6.52 (d, JPC = 3.8 Hz, CHP), 110.23 (d,
JPC = 3.8 Hz, ArC), 116.91 (d, J = 50.8 Hz, ArC), 121.09 (d, JPC = 12.5
Hz, ArC), 133.49 (ArC), 136.28 (d, JPC = 15.3 Hz, ArC), 160.79
(ArC) [OCD3 signal not observed]. 11B{1H} NMR (CDCl3): δ −40.4
(d, br, JPB = 49.0 Hz). 31P{1H} NMR (CDCl3): δ −22.3 (q, br, JPB
49.0 Hz).
=
[{(Me3Si)2CH}P(C6H4-2-O)(BH3)Mg(THF)2]2 (9). To a solution of
5 (0.73 g, 2.34 mmol) in THF (10 mL) was added nBuLi (0.93 mL,
2.33 mmol) in THF (10 mL), and this mixture was stirred for 1 h.
This solution was added to a suspension of MgI2 (0.33 g, 1.19 mmol)
in THF (15 mL), and this mixture was stirred at room temperature for
48 h. The solution was filtered, and the filtrate was concentrated to ca.
10 mL. The colorless precipitate was redissolved by heating, and the
solution was cooled to 5 °C for 5 days, after which time colorless
crystals of 9 were isolated by filtration and washed with a small amount
H
DOI: 10.1021/acs.organomet.7b00262
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Vance, J. R.; Lee, K.; Du, V. A.; Haddow, M. F.; Whittel, G. R.;
Manners, I. Angew. Chem., Int. Ed. 2015, 54, 4836−4841.
(4) (a) Fernandez-Millan, M.; Allen, L. K.; Garcia-Rodriguez, R.;
Bond, A. D.; Mosquera, M. E. G.; Wright, D. S. Chem. Commun. 2016,
52, 5993−5996. (b) Fuller, A.-M.; Mountford, A. J.; Scott, M. L.;
Coles, S. J.; Horton, P. N.; Hughes, D. L.; Hursthouse, M. B.;
Lancaster, S. J. Inorg. Chem. 2009, 48, 11474−11482.
(5) For recent reviews see: (a) Crimmin, M.; Hill, M. S. Top.
Organomet. Chem. 2013, 45, 191−241. (b) Hill, M. S.; Liptrot, D. J.;
Weetman, C. Chem. Soc. Rev. 2016, 45, 972−988. (c) Stennett, T. E.;
Harder, S. Chem. Soc. Rev. 2016, 45, 1112−1128.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00262.
■
S
1H, 13C{1H}, 31P{1H}, and 11B{1H} NMR spectra for all
7
compounds, Li NMR spectrum for 6a, and crystal data
for 5, 6c, 7, and 9−11 (PDF)
Accession Codes
(6) For selected examples see: (a) Spielmann, J.; Piesik, D. F.-J.;
Harder, S. Chem. - Eur. J. 2010, 16, 8307−8318. (b) Liptrot, D. J.; Hill,
M. S.; Mahon, M. F.; MacDougall, D. J. Chem. - Eur. J. 2010, 16,
8508−8515. (c) Wolstenholme, D. J.; Fiogeras, J.; Che, F. N.; Decken,
A.; Sean McGrady, G. J. Am. Chem. Soc. 2013, 135, 2439−2442.
(d) Jones, C.; Bonyhandy, S. J.; Nembenna, S.; Stasch, A. Eur. J. Inorg.
Chem. 2012, 2012, 2596−2601. (e) Spielmann, J.; Harder, S. J. Am.
CCDC 1548771−1548776 contains the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Chem. Soc. 2009, 131, 5064−5065. (f) Noth, H.; Thomas, S.; Schmidt,
̈
AUTHOR INFORMATION
Corresponding Author
*E-mail for K.I.: keith.izod@ncl.ac.uk.
M. Chem. Ber. 1996, 129, 451−458. (g) Harder, S.; Spielmann, J.;
Tobey, B. Chem. - Eur. J. 2012, 18, 1984−1991. (h) Bellham, P.; Hill,
M. S.; Kociok-Kohn, G. Organometallics 2014, 33, 5716−5721.
(7) Izod, K. Adv. Inorg. Chem. 2000, 50, 33−108.
■
ORCID
(8) For selected examples see: (a) Reuter, K.; von Hanisch, C. Chem.
Commun. 2014, 50, 7709−7711. (b) Kopecky, P.; von Hanisch, C.;
Weigend, F.; Kracke, A. Eur. J. Inorg. Chem. 2010, 2010, 258−265.
(c) Westerhausen, M.; Digiser, M. H.; Krofta, M.; Wiberg, N.; Noth,
H.; Knizek, J.; Ponikwar, W.; Seifert, T. Eur. J. Inorg. Chem. 1999,
1999, 743−750. (d) Hey, E.; Engelhardt, L. M.; Raston, C. L.; White,
A. H. Angew. Chem., Int. Ed. Engl. 1987, 26, 81−82. (e) Crimmin, M.
R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A.
Inorg. Chem. 2007, 46, 10410−10415. (f) Gartner, M.; Gorls, H.;
Westerhausen, M. Z. Anorg. Allg. Chem. 2007, 633, 2025−2031.
(g) Westerhausen, M.; Digiser, M. H.; Weineke, B.; Noth, H. Eur. J.
Inorg. Chem. 1998, 1998, 517−521. (h) Westerhausen, M.; Lang, G.;
Schwarz, W. Chem. Ber. 1996, 129, 1035−1040. (i) Gartner, M.; Gorls,
H.; Westerhausen, M. Inorg. Chem. 2008, 47, 1397−1405. (j) West-
erhausen, M.; Krofta, M.; Mayer, P. Z. Anorg. Allg. Chem. 2000, 626,
2307−2312.
(9) (a) Izod, K.; Clegg, W.; Liddle, S. T. Organometallics 2000, 19,
3640−3643. (b) Blair, S.; Izod, K.; Clegg, W. Inorg. Chem. 2002, 41,
3886−3893. (c) Blair, S.; Izod, K.; Clegg, W.; Harrington, R. W. Eur. J.
Inorg. Chem. 2003, 2003, 3319−3324. (d) Blair, S.; Izod, K.; Clegg, W.;
Harrington, R. W. Inorg. Chem. 2004, 43, 8526−8531.
(10) (a) Izod, K.; Liddle, S. T.; Clegg, W. Chem. Commun. 2004,
1748−1749. (b) Izod, K.; Liddle, S. T.; McFarlane, W.; Clegg, W.
Organometallics 2004, 23, 2734−2743. (c) Blair, S.; Izod, K.; Clegg, W.
J. Organomet. Chem. 2003, 688, 92−99. (d) Clegg, W.; Izod, K.; Liddle,
S. T. J. Organomet. Chem. 2000, 613, 128−131. (e) Izod, K.;
O’Shaughnessy, P.; Sheffield, J. M.; Clegg, W.; Liddle, S. T. Inorg.
Chem. 2000, 39, 4741−4748. (f) Clegg, W.; Izod, K.; Liddle, S. T.;
O’Shaughnessy, P.; Sheffield, J. M. Organometallics 2000, 19, 2090−
2096.
Keith Izod: 0000-0003-3882-9343
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors are grateful to Newcastle University and the
Libyan government for support.
■
REFERENCES
■
(1) For reviews see: (a) Staubitz, A.; Robertson, A. P. M.; Sloan, M.
E.; Manners, I. Chem. Rev. 2010, 110, 4023−4078. (b) Gaumont, A.-
C.; Carboni, B. Science of Synthesis 2004, 6, 485−512. (c) Carboni, B.;
Monnier, L. Tetrahedron 1999, 55, 1197−1248. (d) Paine, R. T.; Noth,
̈
H. Chem. Rev. 1995, 95, 343−379. (e) Ohff, M.; Holz, J.; Quirmbach,
M.; Borner, A. Synthesis 1998, 1998, 1391−1415.
(2) (a) Kuckmann, T. I.; Dornhaus, F.; Bolte, M.; Lerner, H.-W.;
̈
Holthausen, M. C.; Wagner, M. Eur. J. Inorg. Chem. 2007, 2007, 1989−
2003. (b) Fuller, A.-M.; Mountford, A. J.; Scott, M. L.; Coles, S. J.;
Horton, P. N.; Hughes, D. L.; Hursthouse, M. B.; Lancaster, S. J. Inorg.
Chem. 2009, 48, 11474−11482. (c) Dornhaus, F.; Bolte, M.; Lerner,
H.-W.; Wagner, M. Eur. J. Inorg. Chem. 2006, 2006, 1777−1785.
(d) Dornhaus, F.; Bolte, M. Acta Crystallogr., Sect. E: Struct. Rep. Online
2006, 62, m3573−m3575. (e) Muller, G.; Brand, J. Organometallics
̈
2003, 22, 1463−1467. (f) Dornhaus, F.; Bolte, M.; Lerner, H.-W.;
Wagner, M. Eur. J. Inorg. Chem. 2006, 2006, 5138−5147. (g) Izod, K.;
Watson, J. M.; Clegg, W.; Harrington, R. W. Inorg. Chem. 2013, 52,
1466−1475.
(3) (a) Amor, I.; Garcia-Vivo, D.; Garcia, M. E.; Ruiz, M. A.; Sae
Hamidov, H.; Jeffery, J. C. Organometallics 2007, 26, 466−468.
(b) McNamara, W. F.; Duesier, E. N.; Paine, R. T.; Ortiz, J. V.; Kolle,
́
z, D.;
(11) Knapp, V.; Muller, G. Angew. Chem., Int. Ed. 2001, 40, 183−186.
(12) Izod, K.; Clark, E. R.; Foster, P.; Percival, R. J.; Riddlestone, I.
M.; Clegg, W.; Harrington, R. W. Chem. - Eur. J. 2013, 19, 6094−6107.
(13) Izod, K.; Watson, J.; Harrington, R. W.; Clegg, W. Dalton Trans.
2011, 40, 11712−11781.
̈
P.; Noth, H. Organometallics 1986, 5, 380−383. (c) Hooper, T. N.;
̈
Weller, A. S.; Beattie, N. A.; MacGregor, S. A. Chem. Sci. 2016, 7,
2414−2426. (d) Abdellah, I.; Bernoud, E.; Lohier, J.-F.; Alayrac, C.;
Toupet, L.; Lepetit, C.; Gaumont, A.-C. Chem. Commun. 2012, 48,
4088−4090. (e) Dorn, H.; Singh, R. A.; Massey, J. A.; Nelson, J. M.;
Jaska, C. A.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2000, 122,
6669−6678. (f) Gaumont, A.-C.; Hursthouse, M. B.; Coles, S. J.;
Brown, J. M. Chem. Commun. 1999, 63−64. (g) Dornhaus, F.; Bolte,
M.; Lerner, H.-W.; Wagner, M. J. Organomet. Chem. 2007, 692, 2949−
2955. (h) Jaska, C. A.; Dorn, H.; Lough, A. J.; Manners, I. Chem. - Eur.
J. 2003, 9, 271−281. (i) Lee, K.; Clark, T. J.; Lough, A. J.; Manners, I.
Dalton Trans. 2008, 2732−2740. (j) Jaska, C. A.; lough, A. J.; Manners,
I. Dalton Trans. 2005, 326−331. (k) Pican, S.; Gaumont, A.-C. Chem.
Commun. 2005, 2393−2395. (l) Schafer, A.; Jurca, T.; Turner, J.;
(14) Izod, K.; Watson, J.; Harrington, R. W.; Clegg, W. Eur. J. Inorg.
Chem. 2012, 2012, 1696−1701.
(15) Chitsaz, S.; Breyhan, T.; Pauls, J.; Neumuller, B. Z. Anorg. Allg.
̈
Chem. 2002, 628, 956−964.
(16) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K. J.
Am. Chem. Soc. 1990, 112, 5244−5252.
(17) Munoz, M. T.; Urbajena, C.; Temprado, M.; Mosquera, M. E.
̃
G.; Cuenca, T. Chem. Commun. 2011, 47, 11757−11759.
(18) (a) Barr, D.; Clegg, W.; Mulvey, R. E.; Snaith, R.; Wade, K. J.
Chem. Soc., Chem. Commun. 1986, 295−297. (b) Mulvey, R. E. Chem.
Soc. Rev. 1998, 27, 339−346.
I
DOI: 10.1021/acs.organomet.7b00262
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(19) Zechmann, C. A.; Boyle, T. J.; Rodriguez, M. A.; Kemp, R. A.
Inorg. Chim. Acta 2001, 319, 137−146.
(20) Westerhausen, M.; Krofta, M.; Mayer, P. Z. Anorg. Allg. Chem.
2000, 626, 2307−2312.
(21) Izod, K.; Wills, C.; Clegg, W.; Harrington, R. W. Inorg. Chem.
2007, 46, 4320−4325.
(22) Collins, R. A.; Unruangsri, J.; Mountford, P. Dalton Trans. 2013,
42, 759−769.
(23) (a) Izod, K.; Rayner, D. G.; El-Hamruni, S. M.; Harrington, R.
W.; Baisch, U. Angew. Chem., Int. Ed. 2014, 53, 3636−3640.
(b) Lochmann, L.; Trekoval, J. J. Organomet. Chem. 1987, 326, 1−7.
(24) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015,
71, 3−8. (b) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found.
Crystallogr. 2008, 64, 112−122. (c) Dolomanov, O. V.; Bourhis, L. J.;
Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr.
2009, 42, 339−341.
J
DOI: 10.1021/acs.organomet.7b00262
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