Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions

Article abstract of DOI:10.1039/b822054a

A straightforward Peterson olefination reaction between either [{(Me ₂PhSi)₃C}Li(THF)] or in situ-generated [(Me ₃Si)₂{Ph₂P(BH₃)}CLi(THF) _n] and paraformaldehyde gives the alkenes (Me₂PhSi) ₂C=CH₂ (1) and (Me₃Si){Ph₂P(BH ₃)}C=CH₂ (2), respectively, in good yield. Ultrasonic treatment of 1 with lithium in THF yields the lithium complex [{(Me ₂PhSi)₂C(CH₂)}Li(THF)_n]₂ (3), which reacts in situ with one equivalent of KOBu^t in diethyl ether to give the potassium salt [{(Me₂PhSi)₂C(CH ₂)}K(THF)]₂ (4). Similarly, ultrasonic treatment of 2 with lithium in THF yields the lithium complex [[{Ph₂P(BH ₃)}(Me₃Si)C(CH₂)]Li(THF)₃] ₂.2THF (5). The bis(phosphine-borane) [(Me₃Si){Me ₂(H₃B)P}CH(Me₂Si)(CH₂)]₂ (6) may be prepared by the reaction of [Me₂P(BH₃) CH(SiMe₃)]Li with half an equivalent of ClSiMe₂CH ₂CH₂SiMe₂Cl in refluxing THF. Metalation of 6 with two equivalents of MeLi in refluxing THF yields the lithium complex [[{Me₂P(BH₃)}(Me₃Si)C{(SiMe₂) (CH₂)}]Li(THF)₃]₂ (9), whereas metalation with two equivalents of MeK in cold diethyl ether yields the potassium complex [[{Me₂P(BH₃)}(Me₃Si)C{(SiMe₂) (CH₂)}]₂K₂(THF)₄]_∞ (10) after recrystallisation. X-Ray crystallography shows that, whereas the lithium complex 5 crystallises as a discrete molecular species, the potassium complexes 4 and 10 crystallise as sheet and chain polymers, respectively.

Full text of DOI:10.1039/b822054a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and structural characterisation of alkali metal complexes of
heteroatom-stabilised 1,4- and 1,6-dicarbanions†
Keith Izod,* Lyndsey J. Bowman, Corinne Wills, William Clegg and Ross W. Harrington
Received 9th December 2008, Accepted 16th February 2009
First published as an Advance Article on the web 12th March 2009
DOI: 10.1039/b822054a
A straightforward Peterson olefination reaction between either [{(Me2PhSi)3C}Li(THF)] or
in situ-generated [(Me3Si)2{Ph2P(BH3)}CLi(THF)n] and paraformaldehyde gives the alkenes
=
=
(Me2PhSi)2C CH2 (1) and (Me3Si){Ph2P(BH3)}C CH2 (2), respectively, in good yield. Ultrasonic
treatment of 1 with lithium in THF yields the lithium complex [{(Me2PhSi)2C(CH2)}Li(THF)n]2 (3),
which reacts in situ with one equivalent of KOBut in diethyl ether to give the potassium salt
[{(Me2PhSi)2C(CH2)}K(THF)]2 (4). Similarly, ultrasonic treatment of 2 with lithium in THF yields the
lithium complex [[{Ph2P(BH3)}(Me3Si)C(CH2)]Li(THF)3]2.2THF (5). The bis(phosphine-borane)
[(Me3Si){Me2(H3B)P}CH(Me2Si)(CH2)]2 (6) may be prepared by the reaction of [Me2P(BH3)CH-
(SiMe3)]Li with half an equivalent of ClSiMe2CH2CH2SiMe2Cl in refluxing THF. Metalation of 6 with
two equivalents of MeLi in refluxing THF yields the lithium complex [[{Me2P(BH3)}(Me3Si)C{(SiMe2)-
(CH2)}]Li(THF)3]2 (9), whereas metalation with two equivalents of MeK in cold diethyl ether yields the
potassium complex [[{Me2P(BH3)}(Me3Si)C{(SiMe2)(CH2)}]2K2(THF)4]• (10) after recrystallisation.
X-Ray crystallography shows that, whereas the lithium complex 5 crystallises as a discrete molecular
species, the potassium complexes 4 and 10 crystallise as sheet and chain polymers, respectively.
This paper extends further this set of functionalised ligands
Introduction
with the synthesis and structural characterisation of a series of
alkali metal complexes of three new dicarbanion ligands: a silicon-
stabilised 1,4-dicarbanion, a phosphine-borane-stabilised 1,4-
dicarbanion and a phosphine-borane-stabilised 1,6-dicarbanion.
Sterically demanding bis- and tris(triorganosilyl)methyl ligands
have been used extensively over the last three decades for
the synthesis of a wide range of highly unusual main group,
transition metal and lanthanide complexes.1 The range of such
ligands has recently been extended through the incorporation
of peripheral donor functionalities, enabling the formation of
chelate rings in their complexes. For example, ligands of the
type (Me3Si)2(Me2XSi)C- and (Me3Si)(Me2XSi)CH- [X = e.g.
OMe, NMe2, PPh2, CH2PPh2, 2-C5H4N] have been used for
the stabilisation of various novel complexes, such as (i) the
first samarium(II) dialkyl,2 (ii) rare homoleptic heavier group
2 dialkyls,3 (iii) an unusual Ni(I) alkyl4 and (iv) a number of
polynuclear alkali metal and lanthanide complexes.5
Results and discussion
=
The 1,1-disilyl-substituted alkene (Me2PhSi)2C CH2 (1) has pre-
viously been synthesised via a number of rather complex or
low-yielding routes, including (i) the Wittig reaction between
bis(dimethylphenylsilyl)ketone and methylenetriphenylphosphi-
rane,9 (ii) the dehydrobromination of 1-bromo-1,1-bis(dimethyl-
phenylsilyl)ethane,10 (iii) the photolytically induced, cobalt-
catalysed disproportionation of dimethylphenylsilylethene,11 and
(iv) the reaction between two equivalents of PhMgBr and 2,2,4,4-
tetramethyl-3-methylene-1,5-dioxa-2,4-disilacycloheptane.12 We
find that 1 may be accessed more simply via the Peterson
olefination of the known lithium alkyl [{(Me2PhSi)3C}Li(THF)]13
with paraformaldehyde (Scheme 1). A simple aqueous work-
up, followed by removal of the (Me2PhSi)2O side-product by
distillation at reduced pressure, gives 1 as a colourless oil in good
yield.
We recently expanded this range of compounds with the syn-
thesis of two new oxygen-functionalised dicarbanions, [O(SiMe2)-
2-
C(SiMe3)2]2 and [CH2(SiMe2)C(SiMe3)(SiMe2OMe)]22-, as their
alkali metal salts.6 We subsequently demonstrated that these
salts are excellent ligand transfer reagents for the synthesis of
dialkyllanthanide(II) and -lanthanide(III) complexes.7 In related
chemistry, we have also shown that phosphine-borane-stabilised
dicarbanions are readily accessible and that the incorporation
of dialkylphosphine-borane groups adjacent to a carbanion
centre leads to new binding modes in which B–H ◊ ◊ ◊ M contacts
dominate.8
In related chemistry, we have previously shown that Pe-
terson olefination is favoured over Horner-type olefination in
mixed silyl- and phosphine-borane-substituted lithium alkyls
of the form [(R3Si){R2P(BH3)}nCR(2-n)]Li.14 In this regard,
Main Group Chemistry Laboratories, School of Chemistry, Bedson Building,
University of Newcastle, Newcastle upon Tyne, UK NE1 7RU. E-mail:
k.j.izod@ncl.ac.uk
† CCDC reference numbers 713037–713040. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b822054a
=
the vinylidene phosphine-borane (Me3Si){Ph2P(BH3)}C CH2
(2) may be prepared by a straightforward Peterson olefina-
tion protocol (Scheme 1): treatment of the phosphine-borane
(Me3Si)2CH{PPh2(BH3)} with BunLi in THF gives the lithium
3340 | Dalton Trans., 2009, 3340–3347
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Scheme 1
previously noted that P–C cleavage reactions are competitive with
Schlenk dimerisation when (i) the metal is sufficiently reducing,
and (ii) the phosphide produced by this side-reaction is sufficiently
salt [(Me3Si)2{Ph2P(BH3)}CLi(THF)n], which reacts in situ with
paraformaldehyde to give 2 in excellent yield.
Ultrasonic treatment of 1 with lithium in THF yields the
Schlenk dimerisation product [{(Me2PhSi)2C(CH2)}Li(THF)n]2
(3). Unfortunately, we were unable to isolate 3 in a suitable form for
analysis, attempts at crystallisation consistently yielding a viscous
oil; however, 3 undergoes an in situ metathesis reaction with one
equivalent of KOBut in diethyl ether to give the potassium salt
[{(Me2PhSi)2C(CH2)}K(THF)]2 (4) in good yield as an orange
powder (Scheme 2). Compound 4 may also be isolated directly
from the Schlenk dimerisation of 1 with elemental potassium in
DME, although yields from these reactions were consistently lower
than those from the metathesis route. Compound 4 is soluble in
ether solvents, but is insoluble in hydrocarbons; over a period
of several hours 4 reacts with toluene to give benzylpotassium
and the free ligand (Me2PhSi)2CH(CH2)2CH(SiPhMe2)2. Single
crystals of 4 suitable for X-ray crystallography were obtained by
crystallisation from cold diethyl ether/n-hexane.
Ultrasonic treatment of 2 with an excess of lithium shot
in THF yields the 1,4-dicarbanion complex [[{Ph2P(BH3)}-
(Me3Si)C(CH2)]Li(THF)3]2 as a reddish-brown oil (Scheme 2),
which is soluble in ether solvents, but only slightly soluble
in light petroleum. Crystallisation of this oil from methyl-
cyclohexane/THF gives single crystals of the THF solvate
[[{Ph2P(BH3)}(Me3Si)C(CH2)]Li(THF)3]2·2THF (5) suitable for
X-ray crystallography.
=
stabilised. For example, whereas (Ph2P)2C CH2 undergoes facile
Schlenk dimerisation on treatment with lithium,16 treatment of
this vinylidene phosphine with potassium yields KPPh2 as the
major phosphorus-containing product.17 In contrast, the closely
n
=
related vinylidene phosphine (Pr P)2C CH2 undergoes Schlenk
2
dimerisation exclusively when treated with any of the alkali
metals Li, Na or K, with no evidence for P–C cleavage.18 Thus,
charge-stabilising phenyl groups favour P–C cleavage over Schlenk
dimerisation, whereas the reverse is true for charge-destabilising
propyl groups. For 2, it would appear that the presence of
the borane group at phosphorus results in a sufficiently large
increase in charge-stabilisation that P–C cleavage is observed
even in the presence of lithium, the least reducing of the alkali
metals.
Compound 4 crystallises with a complex sheet polymer struc-
ture; the structure of 4 is shown in Fig. 1, along with selected bond
lengths and angles. The two crystallographically independent
potassium ions lie in almost identical, but subtly different, environ-
ments: each potassium ion is coordinated by one of the carbanion
3
centres, by a molecule of THF and, in an h -manner, by the phenyl
ring of an adjacent SiMe2Ph group. The coordination sphere of
6
each potassium ion is completed by an h -interaction with a phenyl
ring from a SiMe2Ph group in a symmetry-equivalent ligand. Thus,
the intermolecular K ◊ ◊ ◊ Ph contacts link the dicarbanion units
into an infinite sheet network. In addition, K(1) has short contacts
to two methylene carbon atoms, one in the ligand backbone and
one in the THF co-ligand [K(1) ◊ ◊ ◊ C(2) 3.251(2), K(1) ◊ ◊ ◊ C(22)
Unfortunately, the reaction between 2 and lithium is not clean
under these conditions due to competition between Schlenk
dimerisation of the alkene and cleavage of the P–C(alkene)
bond and so isolated yields of 5 are rather low. This competing
reaction presumably generates the lithium phosphino-borohydride
Li[PPh2(BH3)] and 1-lithio-vinyl silane, although this latter com-
pound was not identified; the phosphino-borohydride salt was
identified from its signal at -31.8 ppm (q, JPB = 31 Hz) in
˚
3.444(4) A]; in contrast, K(2) has a single short contact to the
methylene carbon atom in the ligand backbone [K(2) ◊ ◊ ◊ C(24)
˚
3.070(2) A].
The K(1)–C(1) and K(2)–C(23) distances of 3.016(2) and
1
the 31P{ H} NMR spectra of the crude reaction mixture [cf.
˚
3.047(2) A, respectively, are similar to the K–C distances in the
-28.8 for the potassium salt K[PPh2(BH3)] in THF].15 We have
related dicarbanion complex [[{(Me3Si)2C(SiMe2)}2O]K2(OEt2)]•
Scheme 2
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Fig. 1 (a) The two centrosymmetric ligands and two independent K+ ions of 4 with H atoms and minor disorder component omitted for clarity; a
◦
+
˚
symmetry-generated phenyl ring is also included to complete the K coordination. Selected bond lengths (A) and angles ( ): K(1)–C(1) 3.016(2), K(1)–O(1)
2.706(2), K(1)–C(5) 3.061(2), K(1)–C(6) 3.246(3), K(1)–C(10) 3.292(3), K(1)–C(27)a 3.537(2), K(1)–C(28)a 3.284(3), K(1)–C(29)a 3.111(3), K(1)–C(30)a
3.152(3), K(1)–C(31)a 3.352(3), K(1)–C(32)a 3.535(3), K(1) ◊ ◊ ◊ C(2) 3.251(2), K(1) ◊ ◊ ◊ C(22) 3.444(4), K(2)–C(23) 3.047(2), K(2)–C(35) 3.032(3),
K(2)–C(36) 3.272(3), K(2)–C(40) 3.187(3), K(2)–C(13) 3.542(3), K(2)–C(14) 3.298(3), K(2)–C(15) 3.123(3), K(2)–C(16) 3.137(3), K(2)–C(17) 3.319(3),
K(2)–C(18) 3.512(3), K(2) ◊ ◊ ◊ C(24) 3.370(2), Si(1)–C(1)–Si(2) 124.80(13), Si(1)–C(1)–C(2) 115.57(16), Si(2)–C(1)–C(2) 119.14(16), Si(3)–C(23)–Si(2)
124.95(13), Si(3)–C(23)–C(24) 118.18(16), Si(4)–C(23)–C(24) 116.05(16); symmetry operator a: x, y, z - 1. (b) The sheet structure of 4, viewed down the
crystallographic b axis.
˚
molecules of THF. The Li ◊ ◊ ◊ H distances of 2.13(3) and
[3.0132(18) and 3.2302(18) A] and in [{(Me3Si)2(Me2MeOSi)-
6
˚
˚
1.97(3) A are similar to those in the closely related propyl-
C}K]• [3.063(3) and 3.148(3) A]. The K ◊ ◊ ◊ Ph and K ◊ ◊ ◊ CH2
distances lie within the typical range for these types of contact.19
The lithium complex 5 crystallises, by contrast, as a dis-
crete, centrosymmetric molecular species with two molecules
of THF of crystallisation per molecular unit; the molecu-
lar structure of 5 is shown in Fig. 2, along with selected
bond lengths and angles. Each lithium ion is coordinated
substituted analogue [[{Pri2P(BH3)}(Me3Si)C(CH2)]Li(pmdeta)]2
8a
˚
[Li ◊ ◊ ◊ H 2.05(3) and 1.94(3) A] and in the ate complex
[(THF)3Li[(Me3Si)2C{PMe2(BH3)}]2Li]8b [Li ◊ ◊ ◊ H 2.03(8)–2.31(6)
˚
A] (pmdeta = N,N,N¢,N¢¢,N¢¢-pentamethyldiethylenetriamine).
There are no short contacts between the lithium ions and the
carbanion centres, which are essentially planar [sum of angles at
C(1) = 359.98◦].
2
in an h -manner by the borane hydrogens and by three
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˚
Fig. 2 Molecular structure of 5 with H atoms bonded to carbon and minor disorder components omitted for clarity. Selected bond lengths (A) and
angles (◦): Li–H(1A) 2.13(3), Li–H(1B) 1.97(3), Li ◊ ◊ ◊ B 2.480(5), Li–O(1) 1.989(5), Li–O(2) 1.940(5), Li–O(3) 1.927(5), P–B 1.952(3), P–C(1) 1.711(2),
P–C(6) 1.854(2), P–C(12) 1.860(2), Si–C(1) 1.824(2), P–C(1)–Si 122.77(13), P–C(1)–C(2) 118.55(16), Si–C(1)–C(2) 118.66(16).
structure of rac-6 is shown in Fig. 3, along with selected bond
The bis(phosphine-borane) [(Me3Si){Me2(H3B)P}CH(Me2Si)-
lengths and angles.
(CH2)]2 (6) was prepared via a two-step synthetic route (Scheme 3).
The reaction between in situ generated Me2P(BH3)CH2Li and one
equivalent of Me3SiCl cleanly gives the silicon-substituted species
Me2P(BH3)CH2SiMe3 (7). Treatment of 7 with BunLi gives the
complex [Me2P(BH3)CH(SiMe3)]Li, which reacts in situ with half
an equivalent of ClSiMe2CH2CH2SiMe2Cl in refluxing THF to
give 6 as an oily solid, which consists of an equimolar mixture
of the rac- and meso-diastereomers, along with a small amount
of phosphorus-containing impurities. Repeated crystallisation of
this oily solid from hot methylcyclohexane yields essentially pure
rac-6 as colourless blocks; however, we were unable to obtain a
clean sample of the meso diastereomer, either by crystallisation or
chromatographic methods, samples always containing rac-6, along
with other phosphorus-containing impurities. The configuration
of rac-6 was confirmed by X-ray crystallography; the molecular
Compound 6 may be considered a dimeric analogue of
the mono-basic phosphine-borane {(Me2P(BH3)}(Me3Si)2CH (8);
we previously reported that 8 undergoes deprotonation readily
on treatment with one equivalent of BunLi in THF at room
temperature.8b In contrast, treatment of rac-6 with two equiv-
alents of either BunLi or MeLi under the same conditions
leads only to incomplete deprotonation. However, complete
deprotonation at both sites may be achieved by the reaction
of rac-6 with two equivalents of MeLi in THF under re-
flux for 1 hour (Scheme 3). This yields the lithium complex
[[{Me2P(BH3)}(Me3Si)C{(SiMe2)(CH2)}]Li(THF)3]2 (9) as an oily
solid after removal of the solvent. Although we were unable
to grow single crystals of this compound suitable for X-ray
crystallography, the identity of 9 was confirmed by multi-element
1
Scheme 3 Reagents and conditions: (i) BunLi, THF; (ii) Me3SiCl, THF; (iii) ClSiMe2CH2CH2SiMe2Cl, THF, reflux; (iv) 2MeLi, THF, reflux;
2
(v) 2MeK, Et2O, 0 ◦C.
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˚
Fig. 3 Molecular structure of rac-6. Selected bond lengths (A) and
angles (◦): P–B 1.9198(19), C(1)–P 1.8256(13), C(1)–Si(1) 1.9097(13),
C(1)–Si(2) 1.9045(13), Si(1)–C(1)–Si(2) 114.73(7), P–C(1)–Si(1) 115.19(6),
P–C(1)–Si(2) 112.23(6).
1
1
1
1
(1H, 13C{ H}, 7Li{ H}, 11B{ H} and 31P{ H}) NMR spectroscopy.
These spectra exhibit a single set of ligand resonances each
and indicate that the diastereotopic PMe2 and SiMe2 groups are
equivalent, consistent with rapid exchange between diastereomers
on the NMR time-scale in solution.
Treatment of a 1:1 mixture of rac- and meso-6 with an
excess of MeK in cold diethyl ether gives the di-potassium salt
[[{Me2P(BH3)}(Me3Si)C{(SiMe2)(CH2)}]2K2(THF)4]• (10) after
a simple work-up in good yield as a highly viscous colourless
oil (Scheme 3). The THF co-ligands in 10 are only weakly
held: 1H NMR spectroscopy shows that 10 slowly loses THF
Fig. 4 Structure of (a) the molecular unit of 10 with minor disorder
component and H atoms bonded to carbon omitted for clarity, and
1
1
under vacuum. Once again, multi-element (1H, 13C{ H}, 11B{ H}
˚
(b) the extended polymeric structure of 10. Selected bond lengths (A)
1
and 31P{ H}) NMR spectroscopy indicates rapid inter-conversion
and angles (◦): K–C(1) 3.0232(19), K–O(1) 2.701(2), K–O(2) 2.6481(16),
K ◊ ◊ ◊ H(1A)a 2.68(2), K ◊ ◊ ◊ H(1C)a 2.79(3), K ◊ ◊ ◊ Ba 3.215(2), K ◊ ◊ ◊ C(4)
3.3868(18), K ◊ ◊ ◊ C(10A) 3.457(13), P–B 1.930(2), C(1)–P 1.7371(18),
C(1)–Si(1) 1.8305(18), C(1)–Si(2) 1.8454(18), Si(1)–C(1)–Si(2) 117.02(10),
Si(1)–C(1)–P 119.52(10), Si(2)–C(1)–P 114.64(10); symmetry operator a:
1 - x, 1 - y, 2 - z.
of the diastereomers of 10 on the NMR time-scale in so-
lution. Despite several attempts, it was not possible to crys-
tallise 10 from solution; however, a small number of single
crystals of 10 suitable for X-ray crystallography were isolated
from a sample of the viscous oil that had been left to stand
at room temperature for several weeks. The structure of 10
is shown in Fig. 4, along with selected bond lengths and
angles.
Si-Me ◊ ◊ ◊ K contacts, forming [K-C-Si-Me]2 rings. The K–C
˚
The crystal of 10 studied by X-ray crystallography was
of the meso-diastereomer. Compound 10 crystallises with
a polymeric structure composed of centrosymmetric [{Me2-
P(BH3)}(Me3Si)C{(SiMe2)(CH2)}]2K2(THF)4 units, linked into
chains via BH3 ◊ ◊ ◊ K contacts. Each potassium cation is coor-
dinated by one of the carbanion centres, by two molecules of
distance in 10 of 3.0232(19) A is slightly longer than the
˚
K–C distance in 11 [2.937(3) A], but is similar to the K–C
distance in the closely related phosphine-borane-stabilised car-
8c
˚
banion complex [[(Me3Si)2{Me2P(BH3)}C]K]• [K–C 3.018(5) A].
˚
The K ◊ ◊ ◊ H distances [2.68(2) and 2.79(3) A] and the K ◊ ◊ ◊ B
˚
distance [3.215(2) A] are similar to the corresponding distances
2
THF, and by an h -BH3 group from an adjacent unit; in addition,
in related complexes;8 for example, the K ◊ ◊ ◊ H distances in poly-
meric [[(Me3Si)2{Me2P(BH3)}C]K(THF)0.5]• range from 2.73(3)
there is a short contact between the potassium ion and one of
˚
the methylene carbon atoms of the ligand backbone [K ◊ ◊ ◊ C(4)
to 2.95(3) A, while the K ◊ ◊ ◊ B distances in this compound range
8f
˚
˚
3.3868(18) A] and between the potassium ion and one of the
from 3.171(3) to 3.389(3) A.
methylene carbon atoms in the minor disorder component of a
Metalation of the free phosphine-borane 6 leads to a signifi-
cant shortening of the P–C(1) and Si–C(1) distances, consistent
with partial multiple bond character due to delocalisation of
the carbanion charge via negative hyperconjugation; for rac-6
the P–C(1), Si(1)–C(1) and Si(2)–C(1) distances are 1.8256(13),
˚
THF molecule [K ◊ ◊ ◊ C(10A) 3.457(13) A].
The monomer unit of 10 bears
a remarkable resem-
blance to that of the isoelectronic compound [[(Me3Si)2-
C{(SiMe2)(CH2)}]2K2(THF)4]• (11),20 which also crystallises with
a polymeric structure. Indeed, the method by which the monomer
units in 10 and 11 are linked into chains is rather similar:
˚
1.9097(13) and 1.9045(13) A, respectively, whereas in 10 the corre-
˚
sponding distances are 1.7371(18), 1.8305(18) and 1.8454(18) A,
2
in 10 the units are linked via h -P-BH3 ◊ ◊ ◊ K contacts, forming
respectively. At the same time the P–B distances increase slightly
˚
˚
[K-C-P-BH3]2 rings, whereas in 11 the units are linked via
from 1.9198(19) A in rac-6 to 1.930(2) A in 10.
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hyde (2.52 g, 83.9 mmol) was added and this mixture was stirred for
1 h. The reaction was quenched with water (30 ml) and the organic
layer was extracted into diethyl ether (3 ¥ 20 ml) and dried over
activated 4A molecular sieves. The solution was filtered and the
solvent was removed in vacuo from the filtrate. The colourless solid
obtained was dissolved in toluene and cooled (-30 ◦C) in order to
crystallise out unreacted (Me3Si)2CHPPh2(BH3). Removal of the
solvent in vacuo from the mother liquor yielded 2 as a colourless
solid. Isolated yield 4.80 g, 91%. Anal. Calcd for C17H24BPSi: C,
Experimental
All manipulations were carried out using standard Schlenk
techniques under an atmosphere of dry nitrogen or argon. Diethyl
ether, THF, n-hexane and light petroleum (b.p. 40–60 ◦C) were
dried prior to use by distillation under nitrogen from sodium,
potassium or sodium/potassium alloy. THF was stored over
activated 4A molecular sieves; diethyl ether, n-hexane and light
petroleum were stored over a potassium film. Deuterated benzene,
toluene and THF were distilled from potassium and CDCl3 was
distilled from CaH2; all deuterated solvents were deoxygenated by
three freeze–pump–thaw cycles and were stored over activated
4A molecular sieves. Potassium tert-butoxide was dried under
vacuum at 100 ◦C/10-2 mmHg for 3 h before use; paraformalde-
1
68.46; H, 8.11%. Found: C, 68.35; H, 8.20%. H NMR (CDCl3,
25◦C): d 0.00 (s, 9H, SiMe3), 5.85 (dd, JHH = 2.5 Hz, JPH
=
3
28.1 Hz, 1H, CH2), 6.37 (dd, JHH = 2.5 Hz, 3JPH = 42.7 Hz, 1H,
◦
1
CH2), 7.08–7.58 (m, 10H, Ph). 13C{ H} NMR (CDCl3, 25 C): d
0.29 (SiMe3), 129.0 (m-Ph), 131.5 (p-Ph), 132.5 ◦(ipso-Ph), 133.7
◦
hyde was dried under vacuum at 70 C/10-2 mmHg for 1 h
1
(o-Ph), 143.0 (CH2). 11B{ H} NMR (CDCl3, 25 C): d -36.3 (d,
before use. The compounds (Me2PhSi)3CH,13,21 Me3P(BH3),22
(Me3Si)2CHPPh2(BH3)8g and MeK23 were prepared by previously
published procedures. All other compounds were used as supplied
by the manufacturer; low halide content methyllithium was
supplied by Fluka as a 1.6 M solution in diethyl ether and
butyllithium was supplied by Aldrich as a 2.5 M solution in
hexanes.
JPB = 61 Hz). 31P{ H} NMR (CDCl3, 25 ◦C): d 23.6 (q, JPB
=
1
61 Hz).
Me2P(BH3)CH2SiMe3 (7)
To a cold (0 ◦C) solution of Me3P(BH3) (1.09 g, 12.1 mmol) in
THF (30 ml) was added n-BuLi (4.84 ml, 12.1 mmol). The resulting
solution was allowed to attain room temperature and was stirred
for 3 h, then added to a cold (-78 ◦C) solution of Me3SiCl (1.84 ml,
14.5 mmol) in THF (20 ml). After attaining room temperature this
solution was stirred for 3 h, then water (40 ml) was added. The
organic layer was decanted, the aqueous layer was extracted into
diethyl ether (3 ¥ 20 ml) and the combined organic extracts were
dried over activated 4A molecular sieves. The solvent was removed
in vacuo to yield 7 as a colourless solid. Isolated yield: 1.67 g, 85%.
Anal. Calcd for C6H20BPSi: C, 44.46; H, 12.44%. Found: C, 44.37;
1
1H and 13C{ H} NMR spectra were recorded on a JEOL
Lambda500 spectrometer operating at 500.16 and 125.65 MHz,
respectively, or a Bruker Avance 300 spectrometer operating at
300.15 and 75.47 MHz, respectively; chemical shifts are quoted in
ppm relative to tetramethylsilane. 31P{ H}, 11B{ H} and 7Li{ H}
NMR spectra were recorded on a JEOL Lambda500 spectrometer
operating at 202.35, 160.35 and 194.25 MHz, respectively, and
chemical shifts are quoted in ppm relative to external 85% H3PO4
(31P), BF3(OEt2) (11B) and 1.0 M LiCl (7Li). Elemental analyses
were obtained by the Elemental Analysis Service of London
Metropolitan University; we were unable to obtain satisfactory
elemental analyses for the oily solid 9 or the viscous oil 10, possibly
as a consequence of their air sensitivity.
1
1
1
H, 12.40%. H{ B} NMR (d8-toluene, 25 ◦C): d 0.05 (s, 9H,
1
11
SiMe3), 0.35 (d, JPH = 11.0 Hz, 2H, CH2), 0.82 (d, JPH = 10.1 Hz,
1
6H, PMe2), 1.13 (d, JPH = 15.0 Hz, 3H, BH3). 13C{ H} NMR (d8-
◦
toluene, 25 C): d 0.02 (SiMe3), 14.48 (d, JPC = 36.2 Hz, PMe2),
◦
1
14.60 (d, JPC = 22.2 Hz, CH2). 11B{ H} NMR (d8-toluene, 25 C):
=
◦
d -34.5 (d, JPB = 59 Hz). 31P{ H} NMR (d8-toluene, 25 C): d 3.3
1
(Me2PhSi)2C CH2 (1)
(q, JPB = 59 Hz).
The diethyl ether was removed in vacuo from a solution of MeLi
(14.92 ml, 23.7 mmol). The resulting solid was dissolved in THF
(30 ml) and this solution was added to solid (Me2PhSi)3CH
(10.00 g, 23.9 mmol) and heated under reflux for 2 h. The
reaction mixture was allowed to cool to room temperature and
a suspension of paraformaldehyde (0.72 g, 23.9 mmol) in THF
(20 ml) was added. The resulting mixture was stirred for 12 h at
room temperature. The solution was washed with water (3 ¥ 50 ml)
and the organic fraction was dried over anhydrous MgSO4. The
solution was filtered and the solvent was removed in vacuo from the
filtrate. The by-product (Me2PhSi)2O was removed by distillation
(1 mmHg, 110◦C) to leave 1 as ◦a colourless oil. Isolated yield
4.66 g, 66%. 1H NMR (CDCl3, 25 C): d 0.40 (s, 12H, SiMe2), 6.58
[(Me3Si){Me2(H3B)P}CH(Me2Si)CH2]2 (6)
To a solution of 7 (2.08 g, 12.8 mmol) in THF (30 ml) was
added n-BuLi (5.13 ml, 12.8 mmol) and the resulting solution
was stirred for 4 h. This solution was added to a solution of
ClMe2SiCH2CH2SiMe2Cl (1.38 g, 6.4 mmol) in THF (20 ml)
and this mixture was heated under reflux for 16 h. Water
(30 ml) was added, followed by dichloromethane (40 ml) and
the organic layer was decanted. The aqueous layer was extracted
into dichloromethane (2 ¥ 20 ml), the combined organic extracts
were dried over MgSO4, filtered, and the solvent was removed
in vacuo from the filtrate to yield crude rac-/meso-6 as a colourless
oily solid. This solid was repeatedly crystallised from hot methyl-
cyclohexane to yield essentially pure rac-6 as colourless needles.
Combined yield of rac- and meso-6: 2.48 g, 83%. The following
analytical data refer to rac-6. Anal. Calcd for C18H54B2P2Si4: C,
(s, 2H, CH2), 7.38–7.56 (m, 10H, Ph). 13C{ H} NMR (CDCl3,
1
25 ◦C): d 0.59 (SiMe2), 128.24 (p-Ph), 129.13 (m-Ph), 134.38
(o-Ph), 139.16 (ipso-Ph), 145.70 (CH2).
=
(Me3Si){Ph2P(BH3)}C CH2 (2)
1
11
46.34; H, 11.67%. Found: C, 46.30; H, 11.59%. H{ B} NMR
(CDCl3, 20 ◦C): d 0.24 (s, 6H, SiMe2), 0.26 (s, 18H, SiMe3), 0.26
(s, 6H, SiMe2), 0.40 (d, JPH = 17.4 Hz, 2H, CH), 0.64 (s, 4H, CH2),
0.66 (d, JPH = 14.7 Hz, 6H, BH3), 1.39 (d, JPH = 9.6 Hz, 6H, PMe),
To a solution of (Me3Si)2CH{PPh2(BH3)} (6.31 g, 17.6 mmol) in
THF (40 ml) was added n-BuLi (7.04 ml, 17.6 mmol) and this
mixture was stirred for 2 h. A large excess of solid paraformalde-
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Dalton Trans., 2009, 3340–3347 | 3345
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◦
1
1.40 (d, JPH = 9.6 Hz, 6H, PMe). 13C{ H} NMR (CDCl3, 20 C):
d 0.09 (d, JPC = 2.9 Hz, SiMe2), 0.39 (d, JPC = 2.9 Hz, SiMe2),
3.23 (d, JPC = 2.9 Hz, SiMe3), 10.50 (CH2), 11.14 (d, JPC = 4.8 Hz,
containing a few drops of THF to give 5 as red blocks suitable
for X-Ray crystallography. Isolated yield 0.27 g, 40.6%. 1H NMR
(C6D6, 25◦C): d 0.12 (s, 18H, SiMe3), 1.41 (m, 24H, THF), 1.59 (m,
1
4H, CH2), 3.57 (m, 24H, THF), 6.92–7.71 (m, 20H, Ph). 13C{ H}
CH), 17.22 (d, JPC = 37.4 Hz, PMe), 17.77 (d, JPC = 37.4 Hz,
◦
◦
1
1
PMe). 11B{ H} (CDCl3, 20 C): d -35.5 (d, JPB = 49 Hz). 31P{ H}
NMR (C6D6, 25 C): d 1.75 (SiMe3), 26.13 (THF), 39.51 (CH◦ 2),
(CDCl3, 20 ◦C): d 6.9 (q, JPB = 49 Hz).
1
68.18 (THF), 128.67, 129.43, 131.17 (Ph). 7Li{ H} (C6D6, 25 C):
◦
1
1
d 1.07 (br). 11B{ H} NMR (C6D6, 25 C): d -38.7 (br). 31P{ H}
NMR (C6D6, 25◦C): d 18.6 (br).
[(THF)K(Me2PhSi)2C(CH2)]2 (4)
To lithium powder (0.15 g, 21.32 mmol) in THF (10 ml) under
argon was added neat 1 (1.11 g, 4.28 mmol). This mixture was
treated ultrasonically for 1 h. Excess lithium was removed by
filtration and the solvent was removed in vacuo from the filtrate.
The resulting oil (1.33 g, 2.19 mmol) was dissolved in diethyl
ether (20 ml) and added dropwise to a slurry of KOBut (0.25 g,
2.19 mmol) in diethyl ether (10 ml). The reaction mixture was
stirred for 1 h. The solution was filtered to yield a red solid, which
was washed with light petroleum (3 ¥ 10 ml) and recrystallised
from cold (-20 ◦C) diethyl ether/n-hexane (10:1) containing a few
drops of THF over a period of several weeks to yield 4 as large
red blocks suitable for X-ray crystallography. Isolated yield 1.23 g,
69%. Anal. Calcd. for C44H64O2Si4K2: C 64.80; H 7.91%. Found: C
64.94; H 7.84%. 1H NMR (d8-THF, 21◦C): d 0.23 (s, 24H, SiMe2),
1.80 (m, 12H, CH2 and THF), 3.65 (m, 8H, THF), 7.07–7.65 (m,
[[{Me2P(BH3)}(Me3Si)C{(SiMe2)(CH2)}]Li(THF)3]2 (9)
To a solution of 6 (0.54 g, 1.16 mmol) in THF (20 ml) was added
a solution of MeLi (1.45 ml, 2.32 mmol). The resulting solution
was heated under reflux for 1 h. The solvent was removed in vacuo
to yield 9 as an oily solid. Attempts to obtain single crystals of
1
11
9 were unsuccessful. Isolated yield 0.67 g, 83%. H{ B} NMR
(d8-toluene, 25 ◦C): d 0.44 (s, 12H, SiMe2), 0.46 (s, 18H, SiMe3),
0.81 (d, JBH = 14.0 Hz, 6H, BH3), 0.91 (s, 4H, CH2), 1.48 (d, JPH
=
6.9 Hz, 12H, PMe2), 1.49 (m,◦16H, THF), 3.58 (m, 16H, THF).
1
13C{ H} NMR (d8-toluene, 25 C): d 5.09 (d, JPC = 2.9 Hz, SiMe2),
7.26 (d, JPC = 4.8 Hz, SiMe3), 13.76 (CH2), 21.24 (d, JPC = 35.5 Hz,
1
PMe), 25.26 (THF), 68.10 (THF). 7Li{ H} NMR (d8-toluene,
◦
◦
1
25 C): d 3.2. 11B{ H} NMR (d8-toluene, 25 C): d -31.6 (d, JPB
=
◦
94 Hz). 31P{ H} NMR (d8-toluene, 25 C): d -3.7 (q, JPB = 94 Hz).
1
◦
1
20H, Ph). 13C{ H} NMR (d8-THF, 25 C): d 3.51 (SiMe2), 24.58
(THF), 45.15 (CH2), 66.50 (THF), 125.08 (p-Ph), 126.42 (m-Ph),
127.46 (o-Ph), 128.43 (ipso-Ph).
[(Me3Si){Me2(H3B)P}C(Me2Si)CH2]2K2(THF)4 (10)
A solution of 6 (1.62 g, 3.4 mmol) in cold (0 ◦C) diethyl ether
(20 ml) was added to solid MeK (0.54 g, 10.2 mmol). The
resulting solution was stirred overnight and allowed to attain
room temperature. The solution was filtered and solvent was
removed in vacuo from the filtrate to yield an off-white highly
viscous oil. This oil was dissolved in methylcyclohexane (5 ml)
and treated with a few drops of THF. Removal of solvent in vacuo
gave 10 as a colourless, highly viscous oil; on standing for several
weeks this oil began to crystallise, yielding a small number of
[[{Ph2P(BH3)}(Me3Si)C(CH2)]Li(THF)3]2.2THF (5)
To a solution of 2 (0.76 g, 2.55 mmol) in THF (20 ml) under argon
was added lithium shot (0.07 g, 10.09 mmol). This mixture was
treated ultrasonically for 30 mins, the excess lithium was removed
by filtration and the solvent was removed in vacuo from the filtrate.
The resulting brown oily solid was washed with light petroleum (3 ¥
10 ml) and was crystallised from cold (-30 ◦C) methylcyclohexane
Table 1 Crystallographic data for 4, 5, rac-6, and 10
Compound
4
5
rac-6
10
Formula
M
C44H64K2O2Si4
815.5
triclinic
¯
P1
9.9778(8)
14.082(2)
16.708(2)
93.837(15)
90.063(8)
100.382(5)
2303.8(5)
2
C58H96B2Li2O6P2Si2.-2C4H8O
1187.2
triclinic
¯
P1
10.3298(12)
13.2276(13)
15.0800(15)
106.405(8)
108.263(7)
99.787(9)
1799.9(3)
1
C18H54B2P2Si4
466.5
triclinic
¯
P1
6.6106(1)
8.7160(2)
13.3995(4)
81.709(2)
86.352(2)
77.554(2)
745.61(3)
1
C34H84B2K2O4P2Si4
831.1
triclinic
¯
P1
9.3401(9)
11.3130(11)
13.0533(13)
78.290(2)
76.748(2)
71.916(1)
1263.2(2)
1
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
m/mm-1
0.343
65195
10520
0.141
39378
6322
0.310
6863
3477
0.376
9090
4402
Data collected
Unique data
Rint
0.051
7891
497
0.054
0.165
1.104
1.23, -0.38
0.051
4956
371
0.068
0.199
1.100
0.47, -0.48
0.022
2720
137
0.029
0.075
1.003
0.38, -0.19
0.013
4011
255
0.037
0.104
1.045
0.63, -0.46
Data with F2>2s
Refined parameters
R (on F, F2>2s)
Rw (on F2, all data)
Goodness of fit on F2
-3
˚
min, max electron density/e A
3346 | Dalton Trans., 2009, 3340–3347
This journal is
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©

View Article Online
single crystals suitable for X-ray crystallography. Isolated yield
2.16 g, 75%.
4 C. Eaborn, M. S. Hill, P. B. Hitchcock and J. D. Smith, J. Chem. Soc.
Chem. Commun., 2000, 691.
5 (a) P. B. Hitchcock, Q. G. Huang, M. F. Lappert and M. S. Zhou,
Dalton Trans., 2005, 2988; (b) P. B. Hitchcock, M. F. Lappert and X.
H. Wei, J. Organomet. Chem., 2004, 689, 1342; (c) F. Antolini, P. B.
Hitchcock, M. F. Lappert and X. H. Wei, Organometallics, 2003, 22,
2505.
6 L. J. Bowman, K. Izod, W. Clegg, R. W. Harrington, J. D. Smith and
C. Eaborn, Dalton Trans., 2006, 502.
7 (a) L. J. Bowman, K. Izod, W. Clegg and R. W. Harrington,
Organometallics, 2006, 25, 2999; (b) L. J. Bowman, K. Izod, W. Clegg
and R. W. Harrington, J. Organomet. Chem., 2007, 692, 806; (c) L. J.
Bowman, K. Izod, W. Clegg and R. W. Harrington, Organometallics,
2007, 26, 2646.
1H NMR (d8-THF, 25 ◦C): d -0.01 (s, 12H, SiMe2), 0.02 (s, 18H,
SiMe3), 0.44 (s, 4H, CH2), 1.16 (d, JPH = 9.2 Hz, 12H, PMe2),
1
1.77 (m, 6H, THF), 3.61 (m, 6H, THF). 13C{ H} NMR (d8-THF,
25 ◦C): d 4.1 (d, JPC = 3.8 Hz, SiMe2), 7.1 (d, JPC = 3.8 Hz,
SiMe3), 16.4 (CH2), 22.9 (d, JPC = 34.5 Hz, PMe2), 25.5 (THF),
67.3 (THF). 11B{ H} NMR (d8-THF, 25 ◦C): d -30.4 (d, JPB
=
1
◦
93 Hz). 31P{ H} NMR (d8-toluene, 25 C): d -5.2 (q, JPB = 93 Hz).
1
Crystal structure determinations of 4, 5, rac-6 and 10
8 (a) K. Izod, W. McFarlane, B. V. Tyson, W. Clegg and R. W. Harrington,
Chem. Commun., 2004, 570; (b) K. Izod, C. Wills, W. Clegg and R. W.
Harrington, Organometallics, 2006, 25, 38; (c) K. Izod, C. Wills, W.
Clegg and R. W. Harrington, Organometallics, 2006, 25, 5326; (d) K.
Izod, C. Wills, W. Clegg and R. W. Harrington, Inorg. Chem., 2007,
46, 4320; (e) K. Izod, C. Wills, W. Clegg and R. W. Harrington,
Organometallics, 2007, 26, 2861; (f) K. Izod, C. Wills, W. Clegg and
R. W. Harrington, Dalton Trans., 2007, 3669; (g) K. Izod, C. Wills, W.
Clegg and R. W. Harrington, J. Organomet. Chem., 2007, 692, 5060.
9 K. Narasaka, N. Saito, Y. Hayashi and H. Ichida, Chem. Lett., 1990,
8, 1411.
10 A. Inoue, J. Kondo, H. Shinokubo and K. Oshima, Chem. Eur. J., 2002,
8, 1370.
11 (a) B. Mariniec, E. Walczuk-Gus´ciora and C. Pietraszuk, Catal. Lett.,
1998, 55, 125; (b) B. Mariniec, I. Kownacki and D. Chadyniak, Inorg.
Chem. Comm., 1999, 2, 581.
12 P. Pawluc, B. Mariniec, G. Hreczycho, B. Gaczewska and Y. Itami, J.
Org. Chem., 2005, 70, 370.
13 C. Eaborn, P. B. Hitchcock, J. D. Smith and A. C. Sullivan, J. Chem.
Soc. Chem. Commun., 1983, 1390.
14 K. Izod, W. McFarlane and B. V. Tyson, Eur. J. Org. Chem., 2004, 1043.
15 F. Dornhaus, M. Bolte, H.-W. Lerner and M. Wagner, Eur. J. Inorg.
Chem., 2006, 5138.
16 W. Clegg, K. Izod, W. McFarlane and P. O’Shaughnessy,
Organometallics, 1998, 17, 5231.
Measurements were made at 180 K (4 and 5) or 150 K (rac-6
and 10) on Nonius KappaCCD (4 and 5), Oxford Diffraction
Gemini A Ultra (rac-6), and Bruker SMART diffractometers (10)
using graphite-monochromated MoKa radiation (l = 0.71073 A).
˚
Cell parameters were refined from the observed positions of
all strong reflections. Intensities were corrected semi-empirically
for absorption, based on symmetry-equivalent and repeated
reflections. The structures 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 was
resolved and successfully modelled for the THF molecule in 4, two
of the three THF molecules in 5 and one of the two THF molecules
in 10. Programs were Nonius COLLECT and EvalCCD, Oxford
Diffraction CrysAlisPro, Bruker SMART and SAINT for data
collection and processing, and SHELXTL for structure solution,
refinement, and molecular graphics.24
17 K. Izod, W. McFarlane, B. V. Tyson, W. Clegg, R. W. Harrington and
S. T. Liddle, Organometallics, 2003, 22, 3684.
18 K. Izod, W. McFarlane, B. V. Tyson, W. Clegg and R. W. Harrington,
J. Chem. Soc. Dalton Trans., 2004, 4074.
Acknowledgements
19 J. D. Smith, Adv. Organomet. Chem., 1998, 43, 267.
20 C. Eaborn, M. S. Hill, P. B. Hitchcock, J. D. Smith, S. Zhang and T.
Ganicz, Organometallics, 1999, 18, 2342.
The authors are grateful to the Royal Society and the EPSRC for
support.
21 C. Eaborn, P. B. Hitchcock and P. D. Lickiss, J. Organomet. Chem.,
1984, 269, 235.
22 H. Schmidbaur, E. Weiss and G. Mu¨ller, Synth. React. Inorg. Met.-Org.
Chem., 1985, 15, 401.
23 (a) E. Weiss and G. Sauermann, Angew. Chem. Int. Ed. Engl., 1968,
7, 133; (b) E. Weiss and G. Sauermann, Chem. Ber., 1970, 103, 265;
(c) C. Eaborn, P. B. Hitchcock, K. Izod, A. J. Jaggar and J. D. Smith,
Organometallics, 1994, 13, 753.
24 (a) COLLECT, Nonius BV, Delft, The Netherlands, 1998; (b) CrysAl-
isPro, Oxford Diffraction, Abingdon, UK; (c) SMART and SAINT,
Bruker AXS Inc., Madison, Wisconsin, USA, 2004 and 1997; (d) G.
M. Sheldrick, Acta Crystallogr. Sect. A, 2008, 64, 112.
References
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Trans., 2001, 1541; (b) C. Eaborn, K. Izod and J. D. Smith, J.
Organomet. Chem., 1995, 500, 89; (c) C. Eaborn and J. D. Smith, Coord.
Chem. Rev., 1996, 154, 125.
2 W. Clegg, C. Eaborn, K. Izod, P. O’Shaughnessy and J. D. Smith,
Angew. Chem. Int. Ed. Engl., 1997, 36, 2815.
3 K. Izod, S. T. Liddle and W. Clegg, J. Am. Chem. Soc., 2003, 125,
7534.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3340–3347 | 3347
©