Alkali metal complexes of sterically demanding amino-functionalised secondary phosphanide ligands

Article abstract of DOI:10.1039/b614373c

The reaction between {(Me₃Si)₂CH}PCl₂ (4) and one equivalent of either [C₆H₄-2-NMe₂]Li or [2-C₅H₄N]ZnCl, followed by in situ reduction with LiAlH₄ gives the

Full text of DOI:10.1039/b614373c

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www.rsc.org/dalton | Dalton Transactions
Alkali metal complexes of sterically demanding amino-functionalised
secondary phosphanide ligands
Keith Izod,* John C. Stewart, William Clegg and Ross W. Harrington
Received 3rd October 2006, Accepted 23rd October 2006
First published as an Advance Article on the web 1st November 2006
DOI: 10.1039/b614373c
The reaction between {(Me3Si)2CH}PCl2 (4) and one equivalent of either [C6H4-2-NMe2]Li or
[2-C5H4N]ZnCl, followed by in situ reduction with LiAlH4 gives the secondary phosphanes
{(Me3Si)2CH}(C6H4-2-NMe2)PH (5) and {(Me3Si)2CH}(2-C5H4N)PH (6) in good yields as colourless
oils. Metalation of 5 with BunLi in THF gives the lithium phosphanide
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]Li(THF)2] (7), which undergoes metathesis with either NaOBut or
KOBut to give the heavier alkali metal derivatives [[{(Me3Si)2CH}(C6H4-2-NMe2)P]Na(tmeda)] (8) and
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]K(pmdeta)] (9) after recrystallisation in the presence of the
corresponding amine co-ligand [tmeda = N,N,Nꢀ,Nꢀ-tetramethylethylenediamine, pmdeta =
N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine]. The pyridyl-functionalised phosphane 6 undergoes
deprotonation on treatment with BunLi to give a red oil corresponding to the lithium compound
[{(Me3Si)2CH}(2-C5H4N)P]Li (10) which could not be crystallised. Treatment of this oil with NaOBut
gives the sodium derivative [{[{(Me3Si)2CH}(2-C5H4N)P]Na}2·(Et2O)]2 (11), whilst treatment of 10
with KOBut, followed by recrystallisation in the presence of pmdeta gives the complex
[[{(Me3Si)2CH}(2-C5H4N)P]K(pmdeta)]2 (12). Compounds 5–12 have been characterised by 1H,
1
1
13C{ H} and 31P{ H} NMR spectroscopy and elemental analyses; compounds 7–9, 11 and 12 have
additionally been characterised by X-ray crystallography. Compounds 7–9 crystallise as discrete
monomers, whereas 11 crystallises as an unusual dimer of dimers and 12 crystallises as a dimer with
bridging pyridyl-phosphanide ligands.
aggregation state and reactivity there has been a growing interest
in the structural chemistry of these species.
Introduction
Alkali metal phosphanides are key starting materials for the
synthesis of transition metal and main group phosphanides,
phosphinidenes and organophosphorus compounds. By far the
most common alkali metal phosphanide reagents are the lithium
derivatives, (RRꢀP)Li, due to their ease of preparation and
widespread applicability.1 However, in some circumstances the
use of lithium reagents leads to unwanted incorporation of the
alkali metal cation in the product. This is particularly true in
lanthanide chemistry, where the formation of lithium-containing
ate complexes is a major concern.2 A typical strategy used to avoid
the formation of ate complexes is to employ heavier alkali metal
compounds, in particular potassium salts, as metathesis reagents.
The low charge/radius ratio of the heavier alkali metal cations
and the essentially ionic nature of the M–P bond typically result
in highly aggregated heavier alkali metal phosphanides which
have low solubilities in non-polar solvents; aggregation states
may be reduced and solubilities increased by the use of sterically
demanding phosphanide ligands and the judicious choice of co-
ligands. Crystallographic studies have revealed a wide array of
structural motifs for heavier alkali metal phosphanides, ranging
from monomers, dimers, trimers and tetramers to polymeric and
lattice structures.1 As a consequence of this structural diversity
and of the need to understand better the relationship between
We have previously shown that a suitable combination of
sterically demanding substituents, ligand donor functionality
and co-ligands enables the isolation of monomeric heavier al-
kali metal phosphanides which have excellent solubility, even
in hydrocarbon solvents. The complexes [[{(Me3Si)2CH}(C6H4-
2-CH2NMe2)P]ML] [ML
=
Li(THF)2 (1), Na(tmeda) (2),
K(pmdeta) (3)] crystallise as discrete monomers in which the
phosphanide ligands bind the metal centres via their P and
N atoms, generating puckered, six-membered chelate rings
[tmeda = N,N,Nꢀ,Nꢀ-tetramethylethylenediamine, pmdeta =
N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine].3 We have now
extended this study to include related dimethylaminophenyl-
and pyridyl-functionalised phosphanide ligands, [{(Me3Si)2CH}-
(C6H4-2-NMe2)P]− and [{(Me3Si)2CH}(2-C5H4N)P]−, in order to
determine the influence of the amine donor group and the size of
the potential chelate ring on the structures of their alkali metal
derivatives.
Results and discussion
The reaction between {(Me3Si)2CH}PCl2 (4) and one equiva-
lent of [C6H4-2-NMe2]Li in THF yields the monochlorophos-
phane {(Me3Si)2CH}(C6H4-2-NMe2)PCl, which may be re-
duced in situ with LiAlH4 to give the secondary phosphane
{(Me3Si)2CH}(C6H4-2-NMe2)PH (5) as a colourless oil after
an aqueous work-up (Scheme 1). In contrast, the reaction
Main Group Chemistry Laboratories, Department of Chemistry, School of
Natural Sciences, Bedson Building, University of Newcastle, Newcastle upon
Tyne, UK NE1 7RU. E-mail: k.j.izod@ncl.ac.uk
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Scheme 1
between 4 and one equivalent of [2-C5H4N]Li under similar
conditions yields an inseparable mixture of products containing
unreacted 4, {(Me3Si)2CH}(2-C5H4N)PCl and {(Me3Si)2CH}(2-
C5H4N)2P. However, a metathesis reaction between [2-C5H4N]Li
and ZnCl2 gives the less nucleophilic zinc reagent [2-C5H4N]ZnCl,4
which reacts cleanly with 4 to give the monochlorophosphane
{(Me3Si)2CH}(2-C5H4N)PCl as the sole phosphorus-containing
product; reduction of this chlorophosphane with LiAlH4 gives
the secondary phosphane {(Me3Si)2CH}(2-C5H4N)PH (6) in
reasonable yield as a colourless oil after an aqueous work-up.
and toluene but is insoluble in light petroleum; compounds 8 and
9 are soluble in ether solvents but are insoluble in hydrocarbons.
X-Ray crystallography reveals that 7, 8, and 9 crystallise as
discrete monomers in which the phosphanide ligands bind the
metal ions via their P and N centres to give envelope-shaped,
five-membered chelate rings in each case with N–M–P bite angles
of 80.70(18) and 79.75(17)◦ (7), 70.53(3)◦ (8) and 59.79(5)◦ (9).
These angles are significantly smaller than the corresponding
angles in 1, 2 and 3 [93.8(3)/94.5(3), 81.40(4) and 75.53(3)◦,
respectively],3 consistent with the smaller chelate ring size in the
former compounds. The structures of 7, 8, and 9 are shown in
Fig. 1, 2 and 3, respectively, and details of selected bond lengths
and angles for these compounds are given in Tables 1, 2 and 3.
1
1
1
The H, 13C{ H} and 31P{ H} NMR spectra of 5 and 6 are as
1
expected; in the H NMR spectra the two diastereotopic Me3Si
groups give rise to a pair of singlets in each case and the PH
protons are observed as a doublet of doublets at 4.41 ppm (JPH
=
214.5 Hz, JHH = 6.1 Hz) and 4.38 ppm (JPH = 210.2 Hz, JHH
=
1
4.9 Hz) for 5 and 6, respectively. The 31P{ H} spectra of 5 and 6
exhibit singlets at −69.3 and −56.2 ppm, respectively.
Treatment of 5 with one equivalent of BunLi in THF yields
the lithium salt [[{(Me3Si)2CH}(C6H4-2-NMe2)P]Li(THF)2] (7) as
orange blocks after crystallisation from cold n-hexane containing
a few drops of THF. A metathesis reaction between 7 and one
equivalent of either NaOBut or KOBut in diethyl ether yields
the corresponding heavier alkali metal derivatives as highly air
and moisture sensitive orange powders which may be isolated as
the adducts [[{(Me3Si)2CH}(C6H4-2-NMe2)P]Na(tmeda)] (8) and
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]K(pmdeta)] (9) after crystallisa-
tion from methylcyclohexane in the presence of the corresponding
1
1
amine co-ligand (Scheme 2). The H and 13C{ H} NMR spectra
of 7, 8 and 9 are consistent with these formulations and exhibit
a single singlet for the two Me3Si groups in each case, suggesting
that P–M cleavage is rapid on the NMR time-scale; a similar
phenomenon has been observed for the closely related compounds
Fig. 1 Molecular structure of one of the two independent molecules of 7
with H atoms and minor disorder components omitted for clarity.
Compound 7 crystallises with two crystallographically distinct
molecules in the asymmetric unit which differ only trivially in
their bond lengths and angles. The lithium coordination sphere in
7 is completed by two molecules of THF, conferring a distorted
1
1–3.3 Metalation of the phosphane results in a shift in the 31P{ H}
signal from −69.3 ppm in 5 to −78.6, −73.1 and −61.3 ppm in
7, 8, and 9, respectively. Compound 7 is soluble in ether solvents
Scheme 2
258 | Dalton Trans., 2007, 257–264
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 7
Molecule 1
P(1)–Li(1)
O(2)–Li(1)
P(1)–C(8)
2.489(5)
1.933(6)
1.828(3)
N(1)–Li(1)
Li(1)–C(13)
2.154(6)
2.733(6)
O(1)–Li(1)
P(1)–C(1)
1.942(6)
1.897(3)
Si(1)–C(1)
Si(2)–C(1)
1.883(3)
1.885(3)
P(1)–Li(1)–O(1)
O(1)–Li(1)–N(1)
C(1)–P(1)–C(8)
Molecule 2
P(2)–Li(2)
O(4)–Li(2)
127.4(3)
111.7(3)
104.46(13)
P(1)–Li(1)–O(2)
O(2)–Li(1)–N(1)
120.1(3)
112.6(3)
P(1)–Li(1)–N(1)
Li(1)–P(1)–C(1)
80.70(18)
126.28(16)
O(1)–Li(1)–O(2)
Li(1)–P(1)–C(8)
102.3(3)
80.25(16)
2.505(5)
1.939(5)
N(2)–Li(2)
Li(2)–C(36)
2.159(6)
2.700(6)
O(3)–Li(2)
P(2)–C(24)
1.933(5)
1.896(3)
Si(3)–C(24)
Si(4)–C(24)
1.881(3)
1.880(3)
P(2)–C(31)
1.830(3)
117.9(2)
108.9(3)
103.37(13)
P(2)–Li(2)–O(3)
O(3)–Li(2)–N(2)
C(24)–P(2)–C(31)
P(2)–Li(2)–O(4)
O(4)–Li(2)–N(2)
124.6(2)
113.9(3)
P(2)–Li(2)–N(2)
Li(2)–P(2)–C(24)
79.75(17)
126.37(15)
O(3)–Li(2)–O(4)
Li(2)–P(2)–C(31)
107.9(3)
79.76(15)
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 8
Na–P
Na–N(3)
P–C(1)
P–Na–N(3)
Na–P–C(1)
C(1)–P–C(8)
2.8189(8)
2.4900(14)
1.8967(13)
123.52(4)
126.06(5)
103.91(6)
Na–N(1)
Na–C(8)
P–C(8)
N(1)–Na–N(2)
Na–P–C(8)
2.4758(13)
3.0072(14)
1.8257(13)
128.96(5)
77.45(4)
Na–N(2)
Na–C(13)
2.4582(13)
2.8792(14)
Si(1)–C(1)
Si(2)–C(1)
1.8794(14)
1.8813(15)
P–Na–N(1)
N(1)–Na–N(3)
70.53(3)
109.32(4)
P–Na–N(2)
N(2)–Na–N(3)
148.88(4)
76.74(4)
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for 9
K–P
K–N(3)
K–C(8)
P–C(8)
N(1)–K–P
N(3)–K–N(1)
N(3)–K–P
C(8)–P–C(1)
3.2198(10)
2.866(3)
3.117(3)
1.812(3)
59.79(5)
116.39(8)
169.90(7)
103.70(12)
K–N(1)
K–N(4)
K–C(14)
Si(1)–C(1)
N(2)–K–N(1)
N(4)–K–N(1)
N(4)–K–P
2.869(3)
2.797(3)
3.371(4)
K–N(2)
K–C(13)
K–C(24)
Si(2)–C(1)
N(2)–K–N(3)
N(4)–K–N(3)
C(8)–P–K
2.830(3)
2.990(3)
3.277(6)
1.862(3)
64.43(9)
64.09(9)
70.29(9)
K–C(21)
K–C(23)
P–C(1)
3.324(6)
3.344(2)
1.899(3)
1.867(3)
138.62(8)
100.23(9)
106.59(7)
N(4)–K–N(2)
N(2)–K–P
C(1)–P–K
114.16(9)
125.05(7)
118.59(10)
Fig. 3 Molecular structure of 9 with H atoms and minor disorder
components omitted for clarity.
Fig. 2 Molecular structure of 8 with H atoms omitted for clarity.
tetrahedral geometry on the lithium ion. In addition, there is a
close contact between the lithium ion and the ipso-carbon atom di-
rectly bonded to nitrogen [Li(1) · · · C(13) 2.733(6), Li(2) · · · C(36)
The sodium ion in 8 is also formally four-coordinate with
a distorted tetrahedral geometry, its coordination sphere being
completed by the two nitrogen atoms of a chelating tmeda ligand.
Once again, the Na–P and Na–N(1) distances to the phosphanide
˚
˚
2.700(6) A]. The Li–P distances of 2.498(5) and 2.505(5) A
˚
are similar to the corresponding distances in 1 [2.535(8) and
ligand of 2.8189(8) and 2.4758(13) A, respectively, are similar
3
˚
2.535(7) A] and other lithium phosphanides; for example, the Li–
to the corresponding distances in 2 [Na–P 2.8396(9), Na–N
5
3
˚
˚
P distances in [(Ph2P)Li(DME)]∞ are 2.563(3) and 2.541(3) A,
2.4689(18) A]. The Na–P distance in 8 is at the shorter end of the
whereas the Li–P distances in [{([Me3Si]2CH)2P}Li]2 are 2.481(10)
typical range of such distances;1 for example, the Na–P distances in
[(CyPH)Na(tmeda)]2 are 2.884(8) and 2.936(7),8 whereas the Na–P
distances in [EtSi{P(Na)(SiPri3)}3]2·(PhMe)2 range from 2.778(2)
6
˚
and 2.473(9) A. The Li–N distances also fall in the range typically
exhibited by tertiary amine-complexed organolithiums.7
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9
˚
Although in the solid state there are two distinct sodium
environments and two distinct phosphanide ligand environments
to 3.357(2) A. In addition to these Na–P and Na–N contacts
the sodium atom has close contacts with both of the ipso-carbon
1
1
(see below), the room temperature 1H, 13C{ H} and 31P{ H} NMR
atoms of the aromatic ring [Na · · · C(8) 3.0072(14), Na · · · C(13)
2
˚
spectra of 11 all exhibit a single, rather broad, set of peaks for the
2.8792(14) A]; these distances are within the typical range of g -
1
1
10
˚
phosphanide ligands; the H and 13C{ H} NMR spectra exhibit
a single signal for the two SiMe3 groups, indicating that P–Na
cleavage is rapid on the NMR time-scale. The NMR spectra of
11 suggest either that the tetranuclear structure observed in the
solid state de-aggregates in solution or else that 11 is subject to
a dynamic exchange process which rapidly interconverts the two
ligand environments on the NMR time-scale. A variable tempera-
arene–sodium contacts [2.57–3.00 A].
The potassium compound 9 crystallises as a discrete monomer
in which the K–P and K–N contacts to the phosphanide
ligand are supplemented through coordination by the three
nitrogen atoms of a pmdeta ligand. The K–P distance of
˚
3.2198(10) A is similar to the corresponding distance in 3
and related potassium phosphanides;1,3 for example the K–P
1
˚
ture H NMR study of 11 was uninformative: the phosphanide
distances in [{(mes*)PH}K]∞ are 3.181(2), 3.271(2) and 3.357(2) A
[mes* = 2,4,6-But3-C6H2].11 The K–N distances in 9 [2.797(3)–
signals merely broaden as the temperature is reduced and de-
˚
coalescence was not observed even at −80 ◦C. In contrast, the
2.869(3) A] are also similar to the K–N distances in 3 [2.8008(16)–
1
3
˚
single, broad signal observed in the 31P{ H} NMR spectrum of
2.8725(17) A] and related tertiary amine-complexed organopotas-
sium complexes.12 Once again, the potassium ion has short
contacts to the two ipso-carbon atoms of the aromatic ring
11 de-coalesces as the temperature is reduced, until at −80 ◦C
the spectrum consists of numerous, broad, overlapping signals
in the range −40 to −75 ppm, suggesting that 11 is subject to
complex dynamic equilibria between several species in toluene
solution.
˚
[K · · · C(8) 3.117(3), K · · · C(13) 2.990(3) A]. In addition to these
short K · · · C contacts the potassium atom has short, agostic-type
K · · · Me contacts to one NMe group on the phosphanide ligand
and three methyl groups on the triamine co-ligand [K · · · C(14)
3.371(4), K · · · C(21) 3.324(6), K · · · C(23) 3.344(2), K · · · C(24)
X-Ray crystallography shows that 11 crystallises as an unusual
“dimer of dimers” with a crystallographic inversion centre; the
molecular structure of 11 is shown in Fig. 4 and details of
˚
3.277(6) A]. The increasing tendency towards M · · · Me agostic
interactions and M · · · arene contacts for the heavier alkali metal
cations is consistent with the larger ionic radius of K+ compared
to Li+ and Na+. The K · · · C(aryl) distances are typical for this type
of contact, whereas the K · · · C(Me) distances in 9 are at the longer
10
˚
end of the range of typical K · · · C(Me) distances [3.20–3.30 A].
Treatment of a diethyl ether solution of the colourless, pyridyl-
functionalised secondary phosphane 6 with BunLi gives a deep
red solution, strongly suggesting conversion of the phosphane
to the lithium phosphanide [{(Me3Si)2CH}(2-C5H4N)P]Li (10).
However, attempts to isolate this material in a suitable state
for analysis were unsuccessful; this compound was consistently
isolated as a deep red oil. The successful formation of 10 was
confirmed by its conversion into the corresponding sodium and
potassium salts. A metathesis reaction between in situ prepared 10
and NaOBut in diethyl ether, followed by the removal of solvent
in vacuo and extraction of the LiOBut side-product into light
petroleum gives a sticky, deep red solid, which may be crystallised
from hot n-hexane as deep red blocks of the sodium derivative
[{[{(Me3Si)2CH}(2-C5H4N)P]Na}2.(Et2O)]2 (11) (Scheme 3).
Fig. 4 Molecular structure of 11 with C atoms of Me3Si groups and all
H atoms omitted for clarity.
Scheme 3 Reagents and conditions: (i) BunLi, Et2O; (ii) NaOBut, Et2O; (iii) KOBut, Et2O, pmdeta.
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◦
a
˚
Table 4 Selected bond lengths (A) and angles ( ) for 11
Na(1)–P(1)
Na(1)–P(2A)
Na(2)–O(1)
P(1)–C(1)
2.9638(13) Na(1)–N(1)
2.8701(13) Na(1)–N(2)
2.485(3)
2.425(2)
2.619(3)
1.786(3)
1.885(3)
96.59(6)
145.84(7)
96.94(6)
137.91(9)
Na(1)–N(2A)
Na(1)–C(8)
Na(2)–C(8)
Si(1)–C(1)
Si(3)–C(13)
N(1)–Na(1)–N(2A)
P(1)–Na(2)–P(2)
P(1)–Na(2)–N(1)
P(2)–Na(2)–N(1)
2.654(2)
2.944(3)
3.104(3)
1.868(3)
1.870(3)
92.56(8)
108.17(4)
57.90(5)
111.31(7)
Na(1)–C(20A)
Na(2)–P(1)
Na(2)–P(2)
Si(4)–C(13)
3.029(3)
2.8195(13)
2.9356(13)
1.880(3)
2.346(2)
1.870(2)
1.878(3)
150.01(4)
57.11(6)
122.46(7)
57.56(5)
Na(2)–N(1)
P(1)–C(8)
P(2)–C(13)
P(1)–Na(1)–N(2)
P(1)–Na(1)–N(2A)
P(2A)–Na(1)–N(2)
N(1)–Na(1)–N(2)
Si(2)–C(1)
P(1)–Na(1)–P(2A)
P(1)–Na(1)–N(1)
P(2A)–Na(1)–N(1)
P(2A)–Na(1)–N(2A)
N(2)–Na(1)–N(2A)
P(1)–Na(2)–O(1)
P(2)–Na(2)–O(1)
O(1)–Na(2)–N(1)
97.41(8)
121.72(7)
130.05(7)
97.72(8)
a Symmetry operation: (A) −x, −y, −z.
selected bond lengths and angles are given in Table 4. The solid
state structure of compound 11 contains two distinct sodium
environments and two distinct ligand environments; Na(2) is
coordinated by the phosphorus and nitrogen atoms of ligand 1
and by the phosphorus atom of ligand 2. In addition, Na(2) is
bound by the oxygen atom of a molecule of diethyl ether and
has a short contact with the ipso-carbon of ligand 1. In contrast,
Na(1) is coordinated by the nitrogen and phosphorus atoms of
ligand 1 and by the nitrogen atom of ligand 2. In addition, Na(1) is
coordinated by the nitrogen and phosphorus atoms of a symmetry
equivalent of ligand 2, and has short contacts with the ipso-carbon
atoms of both ligand 1 and ligand 2. Thus, ligand 1 bridges Na(1)
and Na(2) in a l2-P,l2-N mode; ligand 2 bridges Na(1) and a
symmetry equivalent of Na(2) in a l2-P mode and bridges Na(1)
and its symmetry equivalent in a l2-N mode. The Na–P distances
˚
are 2.8195(13), 2.8701(13), 2.9356(13) and 2.9638(13) A and are
similar to the corresponding distances in 2 and 8 (see above).3 The
Fig. 5 Molecular structure of 12 with minor disorder components and H
atoms omitted for clarity.
˚
Na–N distances range from 2.425(2) to 2.654(2) A and fall in the
range of Na–N distances observed in complexes where two sodium
ions are l2-bridged by a pyridyl ligand; for example, the Na–
In contrast to monomeric 9, which contains the same co-
ligand (pmdeta), compound 12 crystallises from n-hexane as a
centrosymmetric dimer. Each potassium ion is coordinated by the
three nitrogen atoms of a molecule of pmdeta, by the nitrogen
atom of a bridging phosphanide ligand and by the nitrogen and
phosphorus atoms of a second symmetry equivalent phosphanide
ligand. Thus, each phosphanide ligand chelates one potassium
ion, whilst simultaneously bridging the two potassium ions in
the dimer via its pyridyl nitrogen atom. These contacts are
supplemented by short K–C(aryl) contacts and short, agostic-
type interactions with one methyl group on each of the three
N distances in [{(2-C5H4N)N(SiMe3)}Na(THF)0.5]∞ range from
13
˚
2.494(4) to 2.624(5) A.
A metathesis reaction between 6 and KOBut in diethyl
ether gives the corresponding potassium phosphanide, which
may be crystallized as the pmdeta adduct [[{(Me3Si)2CH}(2-
C5H4N)P]K(pmdeta)]2 (12) as deep red blocks (Scheme 3); we
were unable to crystallise the potassium salt in the absence of
co-ligands. The molecular structure of 12 is shown in Fig. 5 and
details of selected bond lengths and angles are given in Table 5.
1
1
The 1H, 13C{ H} and 31P{ H} NMR spectra of 12 are as expected
and contain sharp resonances, suggesting that 12 is not subject to
the same dynamic behaviour in solution as 11; once again in the
1H NMR spectrum a single singlet is observed for the two SiMe3
groups.
˚
pmdeta nitrogen atoms. The K–P distance of 3.3605(7) A is
somewhat longer than the corresponding distance in 9, but falls
in the typical range of K–P distances in potassium phosphanide
complexes (see above). The K–N(pyridyl) distances of 2.8029(17)
◦
a
˚
Table 5 Selected bond lengths (A) and angles ( ) for 12
K–P
K–N(2)
K–C(8)
K–C(17)
N(1A)–K–N(4)
N(4)–K–N(1)
N(4)–K–N(2)
N(1A)–K–N(3)
N(1)–K–N(3)
3.3605(7)
2.9023(19)
3.4721(18)
3.371(3)
K–N(1)
K–N(3)
K–C(12A)
K–C(20)
N(1A)–K–N(1)
N(1A)–K–N(2)
N(1)–K–N(2)
N(4)–K–N(3)
N(2)–K–N(3)
2.8737(16)
2.9382(17)
3.324(2)
3.459(4)
93.79(4)
97.97(5)
139.34(5)
62.26(5)
K–N(1A)
K–N(4)
K–C(13)
P–C(1)
N(1A)–K–P
N(1)–K–P
N(3)–K–P
C(8)–P–K
2.8029(17)
2.8305(19)
3.392(4)
1.8858(19)
96.08(4)
49.75(3)
149.09(5)
78.39(6)
P–C(8)
Si(1)–C(1)
Si(2)–C(1)
1.7807(19)
1.872(2)
1.879(2)
128.79(5)
N(4)–K–P
N(2)–K–P
C(8)–P–C(1)
C(1)–P–K
125.73(4)
90.23(4)
103.13(9)
145.17(6)
93.17(5)
108.70(5)
97.92(5)
154.88(5)
60.63(5)
a Symmetry operation: (A) 1 − x, 1 − y, 1 − z.
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˚
in vacuo from the filtrate to give 5 as a colourless oil. Yield 4.11 g,
64.9%. dH (CDCl3): 0.01 (9H, s, SiMe3), 0.16 (9H, s, SiMe3), 0.45
[1H, dd, 3JHH = 6.1 Hz, JPH = 3.1 Hz, CHP], 2.72 (6H, s, NMe2),
4.41 [1H, dd, 3JHH = 6.1 Hz, JPH = 214.5 Hz, PH], 7.01–7.41 (4H,
m, ArH). dC (CDCl3): 0.88 (SiMe3), 5.70 [d, JPC = 41.7 Hz, CHP],
44.98 (NMe2), 119.44, 123.43, 128.40, 133.41 (ArH), 134.88 [d,
JPC = 21.9 Hz, Ar], 156.51 [d, JPC = 9.8 Hz, Ar]. dP (CDCl3):
−69.3 [d, JPH = 214.5 Hz].
and 2.8737(16) A are similar to the corresponding distances in
other pyridyl-bridged potassium complexes; for example, the K–N
distances in [{(2-C5H4N)N(SiMe3)}K(12-crown-4)]2·(PhMe)2 are
14
˚
2.853(2) and 2.858(2) A. The remaining K–N distances are as
expected.
In summary, amino-functionalised phosphanes 5 and 6 and
their alkali metal derivatives are readily accessible. The solid state
structures of the lithium, sodium and potassium phosphanides are
dependent upon the nature of the amine donor group, the size of
the alkali metal cation and the presence of co-ligands: whilst the
N,N-dimethylaminophenyl substituent in 5 favours monomeric
species, the pyridyl substituent in 6 favours the formation of dimers
or higher aggregates.
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]Li(THF)2] (7)
To a stirred solution of 5 (0.92 g, 2.94 mmol) in diethyl ether
(20 ml) was added BunLi (1.17 ml, 2.94 mmol) and this mixture
was stirred at room temperature for 1 h. The solvent was removed
in vacuo giving an orange, viscous oil which was crystallised from
cold (−30 ◦C) n-hexane containing a few drops of THF as yellow
blocks of 7 suitable for X-ray crystallography. Yield 0.68 g, 72.6%.
Found: C, 59.96; H, 9.86; N, 3.14%. C23H45LiNO2PSi2 requires
C, 59.87; H, 9.76; N, 3.04%. dH (C6D6): 0.49 (18H, s, SiMe3), 0.63
(1H, s, CHP), 1.28 (8H, m, THF), 2.61 (6H, s, NMe2), 3.36 (8H, m,
THF), 6.70–7.44 (4H, m, ArH). dC (C6D6): 2.40 (SiMe3), 4.95 [d,
JPC = 64.6 Hz, CHP], 26.06 (THF), 45.02 (NMe2), 69.12 (THF),
115.55, 116.19, 125.33, 127.72 (Ar), 148.14 [d, JPC = 21.1 Hz, Ar]
158.37 [d, JPC = 65.6 Hz, Ar]. dP (C6D6): −78.6.
Experimental
All manipulations were carried out using standard Schlenk
techniques under an atmosphere of dry nitrogen. Diethyl ether,
THF, n-hexane, methylcyclohexane and light petroleum (bp 40–
◦
60 C) were distilled under nitrogen from potassium or sodium–
potassium alloy; pyridine was distilled under nitrogen from CaH2.
THF and pyridine were stored over activated 4A molecular sieves;
light petroleum, methylcyclohexane, n-hexane and diethyl ether
were stored over a potassium film. Deuterated THF, toluene and
C6D6 were distilled from potassium and CDCl3 was distilled from
CaH2; all NMR solvents were deoxygenated by three freeze–
pump–thaw cycles and were stored over activated 4A molecular
sieves. tmeda and pmdeta were dried over CaH2 and purified by
distillation. n-Butyllithium was purchased from Aldrich as a 2.5 M
solution in hexanes and was used as supplied. ZnCl2 was treated
with Me3SiCl and dried in vacuo prior to use; NaOBut and KOBut
were dried in vacuo at 100 ◦C for 2 h prior to use. The compounds
{(Me3Si)2CH}PCl2,15 and [C6H4-2-NMe2]Li16 were prepared by
previously published procedures. All other compounds were used
as supplied by the manufacturer.
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]Na(tmeda)] (8)
To a solution of 5 (1.51 g, 3.29 mmol) in diethyl ether (20 ml) was
added BunLi (1.32 ml, 3.30 mmol) and this mixture was stirred for
1 h. The resulting solution was added to a slurry of NaOBut (0.31 g,
3.29 mmol) in diethyl ether (20 ml) and this mixture was stirred
at room temperature for 1 h. The solvent was removed in vacuo
giving a sticky yellow solid which was washed with light petroleum
(3 × 20 ml) and dried in vacuo, yielding a yellow, pyrophoric solid.
Crystals of 8 suitable for◦an X-ray crystallographic study were
obtained from cold (−30 C) methylcyclohexane containing one
equivalent of tmeda. Yield 0.56 g, 50.8%. Found: C, 55.91; H, 9.85;
N, 9.09%. C21H45NaN3PSi2 requires C, 56.03; H, 10.00; N, 9.34%.
dH (d8-THF): 0.07 (18H, s, SiMe3), 0.19 [1H, d, JPH = 2.2 Hz, CHP],
2.14 (12H, s, CH2NMe2), 2.30 (4H, s, CH2N), 2.74 (6H, s, NMe2),
1H and 13C{ H} NMR spectra were recorded on a JEOL
1
Lambda500 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{ H} NMR spectra were
1
6.14–6.85 (4H, m, ArH). dC (d8-THF): 1.63 (SiMe3), 4.57 [d, JPC
=
recorded on a JEOL Lambda500 spectrometer operating at
202.35 MHz and chemical shifts are quoted in ppm relative to
external 85% H3PO4. Elemental analyses were obtained by the
Elemental Analysis Service of London Metropolitan University.
67.85 Hz, CHP], 44.12 (NMe2), 46.16 (CH2NMe2), 58.88 (CH2N),
113.67, 115.08, 123.17, 126.65 (Ar), 148.78 [d, JPC = 21.2 Hz, Ar],
158.47 [d, JPC = 69.1 Hz, Ar]. dP (d8-THF): −73.1.
[[{(Me3Si)2CH}(C6H4-2-NMe2)P]K(pmdeta)] (9)
{(Me3Si)2CH}(C6H4-2-NMe2)PH (5)
To a solution of 5 (0.96 g, 3.07 mmol) in diethyl ether (20 ml) was
added BunLi (1.22 ml, 3.07 mmol) and this mixture was stirred at
room temperature for 1 h. The resulting solution was added to a
solution of KOBut (0.34 g, 3.07 mmol) in diethyl ether (20 ml) and
this mixture was stirred at room temperature for 1 h. Solvent was
removed in vacuo to give a sticky brown solid which was washed
with light petroleum (3 × 20 ml) and dried in vacuo, yielding a
yellow-orange, pyrophoric solid. Crystals of 9 suitable for an X-ray
crystallographic study were obtained from hot methylcyclohexane
containing one equivalent of pmdeta. Yield 0.64 g, 59.5%. Found:
C, 55.19; H, 10.00; N, 10.77%. C24H52KN4PSi2 requires C, 55.07;
H, 9.94; N, 10.71%. dH (d8-THF): 0.06 (18H, s, SiMe3), 0.15 [1H, d,
JPH = 3.0 Hz, CHP], 2.14 (12H, s, CH2NMe2), 2.20 (3H, s, NMe),
A solution of [C6H4-2-NMe2]Li (2.56 g, 20.2 mmol) in THF
(30 ml) was added, dropwise, to a cold (−78 ◦C) solution of
{(Me3Si)2CH}PCl2 (5.28 g, 20.2 mmol) in THF (20 ml). The
reaction mixture was allowed to warm to room temperature and
was stirred overnight. Solid LiAlH4 (0.76 g, 20.2 mmol) was
cautiously 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 quenched by the careful
addition of deoxygenated water (30 ml). The organic layer was
decanted and the aqueous layer was extracted into diethyl ether
˚
(3 × 20 ml). The combined organic extracts were dried over 4A
molecular sieves. The solution was filtered and the solvent removed
262 | Dalton Trans., 2007, 257–264
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2.31 (4H, m, CH2N), 2.40 (4H, m, CH2N), 2.73 (6H, s, NMe2),
6.03–6.77 (4H, m, ArH). dC (d8-THF): 1.47 (SiMe3), 5.17 [d, JPC
69.1 Hz, CHP], 43.13 (CH2NMe2), 43.46 (NMe), 46.03 (NMe2),
57.20 (CH2N), 58.67 (CH2N), 112.36, 115.15, 122.89, 125.96 (Ar),
148.62 [d, JPC = 23.9 Hz, Ar], 159.7 [d, JPC = 75.3 Hz, Ar]. dP
(d8-THF): −61.3.
m, ArH). dC (CDCl3): 0.79 (SiMe3), 3.82 [d, JPC = 40.1 Hz, CHP],
121.56, 127.85, 134.69, 149.93 (Ar), 163.96 [d, JPC = 9.80 Hz, Ar].
dP (CDCl3): −56.2 [d, JPH = 210.2 Hz].
=
[{[{(Me3Si)2CH}(2-C5H4N)P]Na}2.(Et2O)]2 (11)
To a solution of 6 (0.83 g, 3.08 mmol) in diethyl ether (20 ml)
was added BunLi (1.2 ml, 3.08 mmol) and this mixture was stirred
at room temperature for 1 h. The resulting deep red solution was
added to a solution of NaOBut (0.29 g, 3.08 mmol) in diethyl ether
(20 ml) and this mixture was stirred at room temperature for 1 h.
The solvent was removed in vacuo to give a sticky, deep red solid
which was washed with light petroleum (3 × 20 ml) and dried in
vacuo. The solid was recrystallised from hot n-hexane (10 ml) to
give 11 as red blocks. Yield 0.56 g, 62.4%. Found: C, 50.90; H,
8.41; N, 4.32%. C56H112Na4O2N4P4Si8 requires C, 51.14; H, 8.52;
{(Me3Si)2CH}(2-C5H4N)PH (6)
A solution of bromopyridine (2.2 ml, 22.08 mmol) in diethyl ether
(10 ml) was added to a cold (−40 C) solution of BunLi (8.8 ml,
◦
22.08 mmol) in diethyl ether (20 ml). The reaction mixture was
allowed to warm to −15 ◦C for 15 min and then re-cooled to
−40 ◦C. A slurry of freshly prepared anhydrous ZnCl2 (2.98 g,
22.08 mmol) in a mixture of THF–pyridine (40 ml : 10 ml) was
added to the reaction mixture. The reaction was allowed to warm
to room temperature whilst stirring overnight. The resulting white
precipitate was isolated by filtration and a mixture of THF–
pyridine (40 ml : 10 ml) was added to the resulting solid to form
a slurry. The slurry was cooled to −40 ◦C and added to a cold
N, 4.26%. dH (d8-toluene): 0.20 (18H, s, SiMe3), 0.23 [1H, d, JPH
=
3
4.0 Hz, CHP], 0.93 [3H, t, JHH = 7.1 Hz, Et2O], 3.08 [2H, q,
3JHH = 7.1 Hz, Et2O], 5.96–7.63 (4H, m, ArH). dC (d8-toluene):
2.32 (SiMe3), 5.07 [d, JPC = 59.9 Hz, CHP], 16.03 (Et2O), 66.83
(Et2O), 111.02, 122.24, 135.09 (Ar), 150.27 [d, JPC = 15.5 Hz, Ar],
192.94 [d, JPC = 43.9 Hz, Ar]. dP (d8-toluene): −45.6.
◦
(−40 C) solution of {(Me3Si)2CH}PCl2 (5.76 g, 22.08 mmol) in
pyridine (10 ml) and this mixture was allowed to warm to room
temperature overnight. The solution was filtered and the solvent
removed in vacuo from the filtrate to give a colourless oil. This oil
was dissolved in THF (30 ml), solid LiAlH4 (0.83 g, 22.08 mmol)
was added and the reaction mixture was heated under reflux for 2 h.
The mixture was cooled to room temperature and excess LiAlH4
was quenched by the careful addition of deoxygenated water. The
organic layer was decanted and the aqueous layer was extracted
into diethyl ether (3 × 20 ml). The combined organic extracts were
[[{(Me3Si)2CH}(2-C5H4N)P]K(pmdeta)]2 (12)
To a solution of 6 (1.03 g, 3.83 mmol) in diethyl ether (20 ml) was
added BunLi (1.5 ml, 3.83 mmol) and this mixture was stirred at
room temperature for 1 h. This solution was added to a solution
of KOBut (0.42 g, 3.83 mmol) in diethyl ether (20 ml) and the
mixture was stirred at room temperature for 1 h. The solvent
was removed in vacuo to give a sticky, deep red solid which was
washed with light petroleum (3 × 20 ml) and dried in vacuo,
yielding a red, pyrophoric solid. Crystals of 12 suitable for an
˚
dried over 4A molecular sieves, the solution was filtered and the
solvent removed in vacuo from the filtrate to give 6 as a colourless
oil. Yield 1.83 g, 30.8%. dH (CDCl3): 0.03 (9H, s, SiMe3), 0.09
(9H, s, SiMe3), 0.92 [1H, dd, 3JHH = 4.0 Hz, JPH = 8.9 Hz, CHP],
4.38 [1H, dd, 3JHH = 4.0 Hz, JPH = 210.2 Hz, PH], 7.07–8.60 (4H,
◦
X-ray crystallographic study were grown from cold (−30 C) n-
hexane containing one equivalent of pmdeta. Yield 0.67 g, 56.9%.
Table 6 Crystallographic data for 7, 8, 9, 11 and 12
Compound
7
8
9
11
12
Formula
M
C23H45LiNO2PSi2
461.7
Triclinic
¯
P1
11.358(2)
14.476(3)
17.519(3)
86.512(12)
89.130(12)
82.367(17)
2849.6(9)
4
C21H45N3NaPSi2
449.7
Triclinic
¯
P1
9.8078(15)
11.4689(16)
13.6466(9)
90.930(9)
103.882(9)
103.782(15)
1442.9(3)
2
C24H52KN4PSi2
523.0
Monoclinic
C56H112N4Na4O2P4Si8
1314.1
Triclinic
¯
P1
11.1503(15)
13.5201(18)
15.406(2)
109.582(2)
97.502(2)
110.175(2)
1972.7(5)
1
C42H92K2N8P2Si4
961.7
Monoclinic
Crystal system
Space group
P21/c
P21/c
˚
a/A
14.4291(19)
11.2424(15)
19.576(3)
14.603(2)
10.0903(14)
23.551(3)
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
93.555(2)
122.270(6)
3
˚
V/A
3198.5(7)
4
0.308
22885
5630
2934.2(7)
2
0.331
25376
7075
Z
l/mm−1
0.198
62419
9984
0.204
31788
6595
0.276
14338
6865
Data collected
Unique data
Rint
0.056
7887
605
0.055
0.154
1.197
0.36, −0.38
0.036
5236
265
0.034
0.094
1.072
0.26, −0.27
0.031
4544
311
0.053
0.149
1.094
1.29, −0.54
0.025
5944
366
0.054
0.112
1.257
0.38, −0.27
0.028
5611
302
0.047
0.118
1.107
0.45, −0.33
Data with F2 > 2r
Refined parameters
R (on F, F2 > 2r)
Rw (on F2, all data)
Goodness of fit on F2
min, max electron
density/e A
−3
˚
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©

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Found: C, 52.36; H, 9.56; N, 11.58%. C42H92K2N8P2Si4 requires C,
52.45; H, 9.64; N, 11.65%. dH (d8-THF): 0.12 (18H, s, SiMe3),
0.16 (1H, s, CHP), 2.19 (12H, s, NMe2), 2.23 (3H, s, NMe),
2.35 (4H, m, CH2N), 2.45 (4H, m, CH2N), 5.74–7.74 (4H, m,
ArH). dC (d8-THF): 0.63 (SiMe3), 4.94 [d, JPC = 65.3 Hz, CHP],
42.33 (NMe), 45.30 (NMe2), 56.49 (CH2N), 57.89 (CH2N), 105.76,
Acknowledgements
The authors thank the Royal Society for support.
References
1 For a recent review of alkali metal phosphanide chemistry see: K. Izod,
Adv. Inorg. Chem., 2000, 50, 33.
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=
49.9 Hz, Ar]. dP (d8-THF): −31.9.
Crystal structure determinations of 7–9, 11 and 12
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Measurements were made at 150 K on Bruker AXS SMART
CCD and Nonius KappaCCD diffractometers using graphite-
˚
monochromated Mo-Ka radiation (k = 0.71073 A). For all
compounds cell parameters were refined from the observed
positions of all strong reflections in each data set. Intensities were
corrected semi-empirically for absorption, based on symmetry-
equivalent and repeated reflections. The structures were solved
by direct methods or Patterson synthesis and were refined on F2
values for all unique data; Table 6 gives further details. All non-
hydrogen atoms were refined anisotropically, and H atoms were
constrained with a riding model; U(H) was set at 1.2 (1.5 for methyl
groups) times Ueq for the parent atom. Disorder was resolved and
successfully modeled for one THF ligand in 7, for one of the
NMe groups of the pmdeta ligand in 9, and for one of the NMe
groups and two of the backbone carbons of the pmdeta ligand in
12. Programs were Bruker AXS SMART (control) and SAINT
(integration), Nonius COLLECT and associated programmes,
and SIR97 and SHELXTL for structure solution, refinement, and
molecular graphics.17
12 C. Schade and P. von R. Schleyer, Adv. Organomet. Chem., 1987, 27,
169.
13 M. L. Cole and P. C. Junk, New J. Chem., 2003, 27, 1032.
14 S. T. Liddle and W. Clegg, J. Chem. Soc., Dalton Trans., 2001, 402.
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16 E. B. Pederson, J. Chem. Soc., Perkin Trans. 2, 1977, 473.
17 (a) SMART and SAINT software for CCD diffractometers, Bruker
AXS Inc., Madison, WI, 2004 and 1997; (b) G. M. Sheldrick,
SHELXTL, user manual, version 6, Bruker AXS Inc., Madison, WI,
2001; (c) COLLECT software, Nonius BV, Delft, The Netherlands,
2000; (d) A. Altmore, M. C. Burla, M. Camalli, G. L. Cascarano,
C. Giacovazzo, A. Guiliardi, A. G. G. Moliterni, G. Polidori and R.
Spagna, SIR97, J. Appl. Crystallogr., 1999, 32, 115.
CCDC reference numbers 622825–622829.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b614373c
264 | Dalton Trans., 2007, 257–264
This journal is
The Royal Society of Chemistry 2007
©