Reactivity of Zn(ii), Mg(ii) and Al(iii) chlorides with a phosphinimine ligand: New tetrameric inverse crown ether structures

Article abstract of DOI:10.1039/b925580j

Reaction of [Me₃SiNPPh₂CH₃] 1 with ZnCl₂ yields the dimer [ClZn(μ-Cl)(Me₃SiNPPh ₂CH₃)]₂2 whereas treatment of 1 with AlCl ₃ in THF leads to the monomeric N

Full text of DOI:10.1039/b925580j

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Reactivity of Zn(II), Mg(II) and Al(III) chlorides with a phosphinimine ligand:
new tetrameric inverse crown ether structures†
´
Cintya Valerio Ca´rdenas, Miguel Angel Mun˜oz Herna´ndez* and Jean-Michel Gre´vy*
Received 4th December 2009, Accepted 7th May 2010
First published as an Advance Article on the web 9th June 2010
DOI: 10.1039/b925580j
Reaction of [Me3SiNPPh2CH3] 1 with ZnCl2 yields the dimer [ClZn(m-Cl)(Me3SiNPPh2CH3)]2 2
whereas treatment of 1 with AlCl3 in THF leads to the monomeric N adduct [Cl3Al(Me3SiNPPh2CH3)]
3. Compounds 2 and 3 were found to be thermally stable and were fully characterized by NMR
spectroscopy, X-ray diffraction, and elemental analysis. On the other hand, treatment of
phosphinimine 1 with nBuLi/ZnCl2 or (CH3)2CHMgCl yields the zinc and magnesium complexes
[M4(Me3SiNPPh2CH2)4(m4-O)(m2-Cl)2] 5 (M = Zn) and 6 (M = Mg), respectively. These compounds
can be considered as new examples of inverse crown ethers in which the oxygen atom is encapsulated by
polar organometallic complexes in a tetrameric arrangement. In contrast, reaction of 1 with
nBuLi/AlCl3 in Et2O under inert atmospheric conditions leads to the formation of the dimeric species
[Cl2Al(Me3SiNPPh2CH2O)]2 7, which displays oxygen insertion into the C–Al bond, while the same
reaction in the presence of air yields the compound [m-(AlCl2)(NPPh2CH3)]2 8 with loss of ClSiMe3
and without oxygen insertion into the C–Al bond.
Subsequently, two research groups simultaneously published the
use of a-lithiated phosphinimines in transmetallation reactions to
obtain new organometallic derivatives. Lappert et al. reported
the monometallic complex I [Pb(Me3SiNPPh2CHSiMe3)2]12 in
which two phosphinimine carbanions coordinate to one PbII
cation, forming two four-membered rings in a spiro arrangement.
Furthermore, Dehnicke et al. reported the bimetallic complexes
II and III (Scheme 2). In the heterobimetallic complex II, two
ligands in cis arrangement are coordinated to one CuI center
through their carbon atoms and to one Li center through their
N atoms, forming an eight-membered ring. In the homobimetallic
complex III, two ligands in trans arrangement coordinate to two
different ZnII centers, each to one C and one N atom, forming
an eight-membered ring.13 This complex obtains a higher degree
of organization in solid state through the formation of bridges
between Cl and Zn centers, which lead to a dodecameric structure
of six eight-membered rings.
1
Introduction
Since the first report of an organometallic complex stabilized
by a phosphinimine ligand in 1962,1 the subject has attracted
much interest and a wide variety of compounds and their
applications have been reported.2 The bis(phosphinimine)methane
=
ligand CH2(PR2 NR¢)2 (Scheme 1) has been one of the most
studied members of this family. It contains two N atoms that are
prompt to bind metal centers in high oxidation states with usual
coordination environments3,4 and few unusual geometries.5–7
Scheme 1 Structure of a bis(phosphinimine) ligand (left) and the
P-methyl phosphinimine ligand 1 (right).
However, published information on phosphinimine chemistry is
limited and in particular, only a few reports refer to the P-methyl
phosphinimine 1. Apart from its ability to undergo the common
N-coordination to Lewis acid metal halides,8 this compound can
endure a-metalation when reacted with simple organolithium
reagents.
Scheme 2 Structure of some a-metalated phosphinimine complexes.
For example the groups of Lo´pez-Ortiz and Elsevier have shown
that the Li complex [Li(PhNPPh2CH2)] is extremely reactive and
forms a four-membered LiCPN ring in solid state.9–11
Additionally, Muller et al. later demonstrated the high reactivity
of a-metallated phosphinimines when investigating the reaction
between [Me3SiNPMe3)] and the Grignard reagent EtMgI. They
found that byproduct IV (Scheme 3) resulted from the rupture
of a diethylether solvent molecule, followed by the insertion of
the CH3CHO fragment into the C–Mg bond. The X-ray structure
shows a three coordinated O atom encapsulated by two Mg centers
and one C atom.14,15
Centro de Investigaciones Qu´ımicas, Universidad Auto´noma del Estado de
Morelos, Av., Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos,
62209, Me´xico. E-mail: mamund2@uaem.mx, jeanmichelg@gmail.com;
Fax: +52 777 3297998; Tel: +52 777 3297997
† CCDC reference numbers 775390–775395. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b925580j
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◦
as colorless oil. Yield, 6.7 g, 90%. Bp 90–100 C/10-2 mm Hg.
1
Spectroscopic data of 1: H NMR (200 MHz, CDCl3): d 0.01
2
(s, 9H, Si(CH3)3), 1.90 (d, JP–H = 3.2 Hz, 3H, PCH3), 7.39–7.72
(m, 10H, 2 Ph). 13C NMR (50 MHz, CDCl3): d 4.30 (Si(CH3)3),
1
18.82 (d, JC–P = 72 Hz, PCH3), 128.37–137.55 (Ph). 31P NMR
(80.81 MHz, CDCl3): d -2.57; 31P NMR (80.81 MHz, THF):
d -2.5. 29Si NMR (39.74 MHz, CDCl3): d -11.81. 15N NMR
(40.52 MHz, C6D6): d 42.12. Anal. Calcd. for C16H22NPSi (287.13):
C 66.87, H 7.72, N 4.87. Found: C 66.29, H 7.71, N 4.87%.
Scheme 3 Structure ofIV showing the insertion of the CH3CHO fragment
into the C–Mg bond.
These results demonstrate potential uses of iminophosphoranes
in ethereal solvents for the synthesis of inverse crown ether (ICE)
complexes; a family of compounds which exhibit a topological
(anti) relationship to crown ether complexes, i.e. metal atoms that
act as a host, whereas the oxygen occupies the guest position.16,17
The interest in ICE complexes has continuously grown during
the last decade and recently, they have found new applications
in organometallic chemistry. The majority of the ligands that
have been used to synthesize such complexes are amidinates
and it has been shown that the combination of Na and Mg
into a heterobimetallic ICE provides hyperbasic properties, which
have been used to convert a metallocene into an unprecedented
polymetallated form.18
2.3 Synthesis of [ClZn(l-Cl)(Me3SiNPPh2CH3)]2 (2)
A solution of 1 (0.53 g, 2 mmol) in THF (5 mL) was added under
stirring and at room temperature to a suspension of ZnCl2 (0.27 g,
2 mmol) in THF and a white precipitate immediately formed.
After stirring overnight the reaction medium was filtered through
cannula and all volatile components eliminated under reduced
pressure. The resulting yellowish powder was dissolved in a small
volume of benzene and after several days at room temperature
pale yellow crystals which were suitable for X-ray diffraction
analysis formed. Yield, 0.2 g, 38%. Mp 85 ◦C. Spectroscopic data
of 2: 1H NMR (200 MHz, THF): d -0.30 (s, 9H, Si(CH3)3), 1.62
2
(d, JH–P = 12.8 Hz, 3H, PCH3), 7.12–7.44 (m, 10H, 2 Ph). 13C
1
In this report, we show our results on the reactivity be-
tween the ligand [Me3SiNPPh2CH3] 1 and its carbanionic form
[Me3SiNPPh2CH2]- 4 with MgCl2, ZnCl2, and AlCl3. The neutral
ligand 1, reacted with these Lewis acids, yielded complexes
[ClZn(m-Cl)(Me3SiNPPh2CH3)]2 2 and [Cl3Al(Me3SiNPPh2CH3)]
NMR (50 MHz, THF): d 2.25 (Si(CH3)3), 14.52 (d, JC–P
=
37.95 Hz, PCH3), 129.10–133.05 (Ph). 31P NMR (80.81 MHz,
THF): d 35.7. Anal. Calcd. for C32H44Cl4N2P2Si2Zn2 (847.42): C
45.36, H 5.23, N 3.31. Found: C 45.35, H 5.40, N 3.15%.
3
in THF, whereas 4 with different reaction conditions
2.4 Synthesis of [Cl3Al(Me3SiNPPh2CH3)] (3)
gave complexes [Cl2Al(Me3SiNPPh2CH2O)]2 7 and [m-(AlCl2)
(NPPh2CH3)]2 8. Interestingly, the reaction of 1 with tBuLi/ZnCl2
and iPrMgCl, yielded the novel “inverse crown ethers”
[M4(Me3SiNPPh2CH2)4(m4-O)(m2-Cl)2] 5 (M = Zn) and 6 (M =
Mg) by reaction with an unidentified source of chalcogen.
A solution of 1 (0.53 g, 2 mmol) in THF (5 mL) was added
at -78 ◦C to a stirred suspension of AlCl3 (0.26 g, 2 mmol) in
THF. After further stirring of the reaction overnight, a white
precipitate was formed in small quantity and filtered off by
means of a cannula. The resulting clear solution was stored
at -30 ◦C and after several days crystals suitable for X-ray
diffraction formed in substantial quantities. Yield, 0.175 g, 33%.
Mp 188 ◦C. Spectroscopic data of 3: 1H NMR (200 MHz,
2
Experimental
2.1 Materials and methods
2
CDCl3): d 0.15 (s, 9H, Si(CH3)3), 2.53 (d, J P–H= 12.6 Hz, 3H,
PCH3), 7.62–7.79 (m, 10H, 2 Ph). 13C NMR (50 MHz, CDCl3):
All manipulations of air and moisture-sensitive compounds were
performed under an atmosphere of argon or dry nitrogen gas
using standard high vacuum Schlenk and cannula techniques
or in an inert atmosphere glovebox. Solvents were dried over
sodium/benzophenone and freshly distilled prior to use. NMR
spectra were recorded on a Varian-Inova-400 MHz and a Varian-
Gemini-200 MHz instruments. Chemical shifts were referenced
1
d 5.36 (s, Si(CH3)3), 20.08 (d, JC–P = 69.7 Hz, PCH3), 129.60–
133.83 (Ph). 31P NMR (80.81 MHz, THF): d 38.2. Anal. Calcd.
for C16H22AlCl3NPSi (420.75) C 45.67, H 5.27, N 3.33. Found:
C 45.67, H 5.38, N 3.25%.
2.5 Synthesis of [Li(Me3SiNPPh2CH2]·2Et2O (4)
1
to TMS for H and 13C. 31P NMR spectra were referenced to
t
By means of a syringe, commercial BuLi 1.47 M in hexane
external 85% H3PO4, while 7Li was referenced to LiCl. Elemental
analyses (C, H, and N) were run on an Elemental microanalysis
instrument using the CHN mode. (CH3)3SiN3, ZnCl2, MgCl2,
AlCl3, tBuLi 1.47 M in hexane and iPrMgCl 2 M in Et2O solution
were purchased from the Aldrich Chemical Co.
(1.25 mL, 2 mmol) was added dropwise under stirring conditions
to a solution of 1 (0.53 g, 2 mmol) in ether (5 mL) at room
temperature. The reaction medium, which immediately turned
yellow, was further stirred for two hours. The crude solution was
consistently of high enough purity to be used in the following
synthesis without additional purification. Furthermore, the
elimination of all volatile components of a sample under reduced
pressure led to a yellow powdery substance which could be
analyzed by NMR. Spectroscopic data of 4: 1H NMR (200 MHz,
2.2 Synthesis of [Me3SiNPPh2CH3] (1)
(CH3)3SiN3 (4.82 mL, 36.66 mmol) was added to Ph2PCH3
(7.34 g, 36.66 mmol) prepared in the laboratory using a reported
procedure.19 The mixture was heated to 110–120 ◦C for 4 h, until
no more N2 evolution could be observed. After distillation of the
crude reaction under reduced pressure compound 1 was obtained
2
C6D6): d 0.07 (s, 9H, Si(CH3)3), 2.89 (d, JH–P = 7.0 Hz, 2H,
PCH2), 7.05–7.67 (m, 10H, 2 Ph). 13C NMR (50 MHz, C6D6):
d 4.86 (Si(CH3)3), 6.59 (d, 1JC–P = 64.4 Hz, PCH2), 127.93–143.82
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(Ph). 31P NMR (80.81 MHz, C6D6): d 30.5. 29Si NMR (39.74 MHz,
C6D6): d 0.44. 7Li NMR (77.75 MHz, C6D6): d 0.88. Anal. Calcd.
for C24H41NLiO2PSi (441.59): C 65.28, H 9.36, N 3.17 Found: C
65.35, H 9.40, N 3.29%.
concentrated under reduced pressure to a small volume. After
storage at -30 ◦C for several weeks, a few crystals that were
suitable for X-ray diffraction analysis were obtained. Anal. Calcd.
for C26H26Al2Cl4N2P2 (624.23): C 50.03, H 4.20, N 4.49. Found: C
50.17, H 4.26, N 4.62%.
2.6 Synthesis of [Zn4(Me3SiNPPh2CH2)4(l4-O)(l2-Cl)2] (5)
2.10 X-Ray diffraction measurements
A freshly prepared solution of 4 (2 mmol) in Et2O was added
via cannula to a stirred suspension of ZnCl2 (0.27 g, 2 mmol) in
ether at room temperature. A white precipitate rapidly formed
and the mixture was left under stirring conditions overnight.
The solution was then filtered through cannula and stored at
-30 ◦C. Large hexagonal crystals suitable for X-ray crystallog-
raphy were formed after several days of storage. Yield, 0.22 g,
Crystals of 2, 3, and 5–8 were mounted directly from solution
under argon using inert oil to protect them from atmospheric
oxygen and moisture. X-Ray intensity data were collected using
the SMART20 program, on a Bruker APEX CCD diffractometer
˚
with monochromatized Mo-Ka radiation (l = 0.71073 A). Cell
refinement and data reduction were carried out with the use
of the SAINT program using intensity data up to 2q = 25◦.
The SADABS program was used to make incident beam, decay
and absorption corrections in the SAINT-Plus v. 6.0 suite.21
Subsequently, the structures were solved by direct methods with
the SHELXS program and refined by full-matrix least-squares
techniques with SHELXL in the SHELXTL v. 6.1 suite.22 Further
details of the structure analyses are given in Table 1. For 7, two
THF solvate molecules were positional disordered giving two split
positions of the rings. Refinement including restraints to obtained
satisfactory anisotropic displacement parameters for the C and
O atoms, gave an occupancy factor level of 0.63. In the case of
8, diethyl ether solvate was near an inversion center, refinement
including restraints and taking into account the special position
gave satisfactory anisotropic displacement parameters for the
C and O atoms. All hydrogen atoms were generated in calculated
positions for all complexes and constrained with the use of a
riding model. The final models involved anisotropic displacement
parameters for all non-hydrogen atoms.
◦
1
42%. Mp 103 C. Spectroscopic data of 5: H NMR (200 MHz,
CDCl3): d 0.28 (s, 9H, Si(CH3)3), 2.28 (d, 2JP–H = 13.6 Hz, PCH2),
6.93–8.19 (m, 10H, 2 Ph). 13C NMR (50 MHz, CDCl3): d 4.85
1
(Si(CH3)3), 13.01 (d, JP–C = 60.6 Hz, PCH2), 128.35–139.62
(Ph). 31P NMR (80.81 MHz, CDCl3): d 42.4. Anal. Calcd. for
C64H84Cl2N4OP4Si4Zn4 (1494.10): C 51.45, H 5.67, N 3.75. Found:
C 50.96, H 6.10, N 3.56%.
2.7 Synthesis of [Mg4(Me3SiNPPh2CH2)4(l4-O)(l2-Cl)2] (6)
A solution of 1 (0.53 g, 2 mmol) in ether (10 mL) was cooled
down to -78 ◦C and iPrMgCl (1 mL, 2 mmol) was added dropwise
by means of a syringe under stirring conditions. A substantial
quantity of white solid immediately precipitated and subsequently
disappeared after warming to room temperature. The solution was
reduced to a small volume under reduced pressure and stored at
-30 ◦C. After two days large hexagonal colorless crystals were
formed and were deemed suitable for X-ray diffraction analysis.
Yield, 0.22 g, 42%. Mp 208 ◦C. Spectroscopic data of 6: 1H NMR
(200 MHz, C6D6): d 0.39 (s, 9H, Si(CH3)3), 1.51 (d, 2JP–H = 12.8 Hz,
2H, PCH2), 7.08–7.56 (m, 10H, 2 Ph). 13C NMR (50 MHz, C6D6):
3. Results and discussion
1
d 4.98 (Si(CH3)3), 11.86 (d, JP–C = 62 Hz, PCH2), 130.5–133.65
3.1 Synthesis of 1
(Ph). 31P NMR (80.81 MHz, C6D6): d 42.1. Anal. Calcd. for
C64H84Cl2Mg4N4OP4Si4 (1329.76): C 57.81, H 6.37, N 4.21. Found:
C 57.96, H 6.45, N 4.56%.
Synthesis of compound 1 occurred by oxidation of the corre-
sponding methyl diphenylphosphine via Staudinger reaction with
trimethylsilylazide. After distillation under reduced pressure, the
expected phosphinimine was obtained as a colorless oily liquid
which was of very high purity and near quantitative yield. The
liquid was stored under inert atmosphere and low temperature for
months without any sign of decomposition. Before exploring the
s–C coordination ability of ligand 1, which is expected to involve
intramolecular coordination of the imino function, we decided
to first study its simple reaction with the chloride derivatives of
Zn(II), Mg(II) and Al(III).
2.8 Synthesis of [Cl2Al(Me3SiNPPh2CH2O)]2 (7)
A freshly prepared solution of 4 (2 mmol) in THF (10 mL) was
added at room temperature to a stirred suspension of AlCl3 (0.26 g,
2 mmol) in Et2O (10 mL). After the mixture was stirred for
30 min and a white precipitate formed, the solution was filtered
via cannula and concentrated under reduced pressure to a small
volume. After storage at -30 ◦C for two weeks, a few crystals that
were suitable for X-ray diffraction analysis were formed. Anal.
Calcd. for C32H42Al2Cl4N2O2P2Si2 (800.59): C 48.01, H 5.29, N
3.50. Found: C 48.26, H 5.43, N 3.58%.
3.2 Reaction of 1 with ZnCl2, MgCl2 and AlCl3
Phosphinimines usually react with Lewis acids to form the
corresponding donor–acceptor adducts. In our study the reaction
of 1 with ZnCl2 and AlCl3 in THF yielded the expected complexes
2 and 3, whereas the reaction with MgCl2 after workup resulted
in the isolation of unreacted 1 and MgCl2 (Scheme 4). Possible
reasons for this lack of reactivity may be the weaker Lewis acidity
and lower solubility in THF of MgCl2 compared to ZnCl2.
These reactions were monitored by 31P NMR in THF. On
time, the resonance due to 1 at d -2.5 ppm disappeared and
2.9 Synthesis of [l-(AlCl2)(NPPh2CH3)]2 (8)
A freshly prepared solution of 4 (2 mmol) in THF (10 mL) was
added at room temperature to a stirred suspension of AlCl3 (0.26 g,
2 mmol) in Et2O (10 mL). After the mixture was stirred for
30 min under inert atmosphere and a white precipitate formed,
the flask was left open for a short time in order to replace N2
atmosphere by air. The solution was filtered via cannula and
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Scheme 4 Formation of donor–acceptor adducts between 1 and Lewis
acids. Reagents and conditions: (i) ZnCl2, THF; (ii) MgCl2, THF; (iii) AlCl3,
THF.
was replaced by a new resonance at d 35.7 and d 38.2 ppm for
2 and 3, respectively. The resulting downfield shift in both cases is
typical for the coordination of the phosphinimine nitrogen atom to
Lewis acid centers and in addition, all others NMR spectroscopic
data are consistent with the formulation of the corresponding
complexes.
An X-ray crystallographic study of 2 (Fig. 1) shows a sym-
metrical dimeric structure in which m2-chloro bridges bind two
Zn atoms in a tetrahedral geometry and both iminophosphorane
groups and exocyclic Cl atoms are arranged trans to each other.
The four membered core is almost perfectly square and planar
with Zn–Cl–Zn and Cl–Zn–Cl bond angles of 89.98(4)◦ and
90.02(4)◦, respectively. The cyclic Zn–Cl bond lengths are slightly
˚
˚
different [2.3393(10) A and 2.3939(11) A], although longer than
˚
the exocyclic Zn–Cl bond lengths [2.2076(11) A]. Both N atoms
are in a trigonal planar environment around the Zn atom with
a P–N–Zn bond angle of 113.85(16)◦, thus they may be seen as
sp2 hybridized. In each monomeric unit, the Zn atom bound to N
arranges trans to one of the phenyl substituents on P, and both the
CH3 substituents and the exocyclic Cl atoms are oriented towards
˚
the same side of the dimer. The Zn–N bond lengths [2.005(3) A]
˚
as well as the P–N bond lengths [1.601(3) A] are similar to those
found in [Cl2Zn{Me3SiNP(C4H8)tBu}]2.23 The P–N bond length is
Fig.
1
Molecular
structure
of
dimeric
complex
˚
[ClZn(m-Cl)(Me3SiNPPh2CH3)]2 2. Selected bonds lengths (A) and
angles (◦): Zn(1)–Cl(1) 2.3393(10), Zn(1)–Cl(2) 2.2076(11), Zn(1)–N(1)
2.005(3), P(1)–N(1) 1.601(3), Si(1)–N(1) 1.755(3); Zn(1)–Cl(1)–Zn(1A)
89.98(4), Cl(1)–Zn(1)–Cl(1A) 90.02(4), Cl(1)–Zn(1)–Cl(2) 117.54(4),
Zn(1)–N(1)–P(1) 113.85(16), Zn(1)–N(1)–Si(1) 113.55(17). Symmetry
transformations used to generate equivalent atoms: -x + 1, -y + 1, -z + 1.
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=
indicative of a double bond character. Therefore, the P N bond
in 2 is not affected upon coordination to Zn.
slow decomposition on time, consequently they were used in the
following metathesis reactions immediately after their production.
Monitoring of the metathesis reaction between 4 and ZnCl2
by 31P NMR in diethyl ether revealed the complete conversion
of 4 into merely one compound (5) by the emergence of a single
resonance at d 42.4 ppm. After filtration of the precipitate and
storage of the resulting solution at -30 ◦C for several days,
crystals of quality suitable for an X-ray diffraction study were
obtained. The spectroscopic study of the crystals in CDCl3
solution displayed a single 31P NMR resonance at d 42.4 ppm
and a doublet signal with negative phase at 13.6 ppm in a DEPT
135 experiment, which confirmed the presence of a carbanionic
The crystal structure of compound 3 presented in Fig. 2 shows a
monomeric Lewis acid–base adduct in which the Al atom adopts
a pseudo tetrahedral geometry and arranges trans to the CH3
substituent on P. This situation contrasts with 2, in which the
Zn atom is located trans to a phenyl substituent. The Al–N
˚
bond length [1.875(3) A] and the average Al–Cl bond lengths
[2.1389(8) A], are in the range found for similar compounds.24 The
˚
geometry around N is approximately trigonal planar with P–N–
Si, P–N–Al and Si–N–Al bond angles of 121.66 (15)◦, 119.70(11)◦
and 118.56(12) , respectively. The P–N bond length [1.620(2) A]
is marginally longer than the one observed for the Zn adduct 2,
but still in the expected range for phosphinimine adducts with Al
◦
˚
CH2 bound to Zn (1JC–P = 61.8 Hz). The characterization was
-
1
completed with H and 13C NMR spectroscopy and elemental
8
˚
[Me3Al(Me3SiNPPh3), d(P–N) = 1.646(2) A].
analysis.
As seen in Fig. 3, complex
5
is
a
tetramer of
[Zn(Me3SiNPPh2CH2]+ organometallic units in which each Zn
atom coordinate a central O2- and one of two outer Cl- ions. It
shows the structure of an ICE that contains four six-membered
ZnNPCZnO rings in boat conformation and connected through
the central O atom. In the central Zn4O cluster, the four Zn2+ ions
span a tetrahedron around the central O2- ion. The Zn atom is
˚
in a usual tetracoordinated environment with Zn–O [1.9712(5) A],
˚
˚
Zn–C [2.047(4) A] and Zn–N [2.048(3) A] bond lengths close to the
26–28
˚
values reported for related compounds [Zn–O (1.9 to 2.02 A)].
The two outer Cl atoms bridge pairs of Zn centers and form two
four-membered perpendicular ZnOZnCl rings with normal Zn–Cl
˚
bond lengths [2.4803(5) A]. The phosphinimine P–N bond length
Fig.
2
Molecular structure of complex [Cl3Al(Me3SiNPPh2CH3)]
◦
˚
3. Selected bonds lengths (A) and angles ( ): Al(1)–N(1) 1.875(3),
Al(1)–Cl(1) 2.1389(8), Al(1)–Cl(2) 2.1381(12), Al(1)–Cl(3) 2.1296(12),
P(1)–N(1)
1.620(2),
Si(1)–N(1)
1.7863(19);
P(1)–N(1)–Al(1)
119.70(11), P(1)–N(1)–Si(1) 121.66(15), Si(1)–N(1)–Al(1) 118.56(12),
N(1)–Al(1)–Cl(1) 109.65(7), N(1)–Al(1)–Cl(2) 111.20(9), N(1)–
Al(1)–Cl(3) 111.22(8), Cl(3)–Al(1)–Cl(1) 109.21(4), Cl(2)–Al(1)–Cl(1)
104.83(4), Cl(3)–Al(1)–Cl(2) 110.52(5).
In contrast to the straightforward formation of the Lewis acid–
base complexes 2 and 3, all attempts to obtain the corresponding
adduct with MgCl2 resulted in no reaction under a variety of
conditions.
3.1 Reaction of 4 with ZnCl2
a-Lithiated phosphinimines are readily accessible by metalla-
tion with nBuLi and may be used as reagents in metathe-
sis reactions with metal halides.25 Thus, the reaction between
[Me3SiNPPh2CH3] 1 with nBuLi or tBuLi occurred rapidly
and was straightforward (monitored by 31P NMR), yielding
[Li(Me3SiNPPh2CH2)] 4 in near quantitative yield. Even though
the a-lithiation was fully established by elemental analysis and
NMR spectroscopy of the product, all attempts to obtain crystals
of sufficient quality for X-ray crystallography were unsuccessful.
The 31P NMR spectrum of 4 revealed a singlet at d 30.5 ppm
and a DEPT 135 experiment clearly demonstrated the presence
Fig. 3 Molecular structure of [Zn4(Me3SiNPPh2CH2)4(m4-O)(m2-Cl)2]
◦
˚
5. Selected bonds lengths (A) and angles ( ): Zn(2)–O(1) 1.9712(5),
Zn(2)–C(5) 2.047(4), Zn(2)–N(3) 2.048(3), Zn(2)–Cl(22) 2.4803(15),
P(4)–N(3) 1.600(3), Si(18)–N(3) 1.744(3); Zn(2)–Cl(22)–Zn(2A)
76.90(6), Zn(2)–O(1)–Zn(2A) 102.96(3), Zn(2C)–O(1)–Zn(2) 112.821
(17), C(5)–Zn(2)–Cl(22) 116.58(12), C(5)–Zn(2)–N(3) 119.10(14),
O(1)–Zn(2)–C(5) 109.48(12), O(1)–Zn(2)–N(3) 118.46(9), O(1)–Zn(2)–
Cl(22) 90.07(3). Symmetry transformations used to generate equivalent
atoms: #1 - x, -y, z #2 y, -x, -z #3 -y, x, -z.
-
of the carbanionic CH2 group through the emergence of an
inverse doublet at 7.9 ppm. The characterization was completed
with 1H, 13C, and 7Li NMR spectra. Solutions of 4 showed
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˚
ions. It forms four six-membered MgNPCMgO rings in a boat
conformation and linked through the central O atom. In the
central Mg4O cluster the four Mg2+ ions span a tetrahedron
around the central O2- ion. The Mg atom is tetracoordinated,
which is the usual coordination mode for this atom, and the Mg–
[1.600(3) A] is typical for a double bond and then the N atom is
sp2 hybridized.
3.3 Reaction of 1 with iPrMgCl
All attempts to prepare the organomagnesium derivative by means
of a metathesis reaction between 4 and MgCl2 were unsuccessful.
However, we assumed that organomagnesium nucleophiles should
be sufficiently reactive to form the organomagnesium derivative
by direct abstraction of a proton from phosphinimine 1. In
our first attempt, we discovered that the EtMgCl was not basic
˚
˚
˚
O [1.9598(11) A], Mg–C [2.186(3) A] and Mg–N [2.073(3) A] bond
lengths are similar to the values reported for related compounds
29,30
˚
˚ ˚
Mg–C(2.191 A), Mg–N(2.073 A)]. The two
[Mg–O (1.95 A),
outer Cl atoms bridge pairs of Mg centers such that two four-
membered perpendicular MgOMgCl rings are formed. The Mg–
Cl bond length [2.4652(16) A]31,32 is typical for magnesium chloride
˚
derivatives with a tetracoordinated Mg center. As previously
observed in the former complexes, the coordination of the imine
N to the Mg center does not affect the phosphinimine P–N bond
enough, however, the reaction with PrMgCl in ether at -70 ◦C
i
instantaneously lead to the formation of copious amounts of
solid. The immediate monitoring of the solution by 31P NMR
spectroscopy showed the complete conversion of 1 into a new
compound (6) that exhibits a single resonance at d 42.1 ppm,
the expected chemical shift for the corresponding a-metallated
derivative. The solution was stored at -30 ◦C and after several days
crystals of quality suitable for X-ray crystallography were formed.
Compound 6 was fully characterized by multinuclear NMR
spectroscopy and elemental analysis. A DEPT 135 experiment
exhibited a doublet signal with a negative phase centered at d
11.9 ppm (1JC–P = 65.5 Hz) which was unambiguously assigned to
the methylene group bound to Mg.
˚
distance [1.611(3) A], which is a hallmark for double bonding and
the N atom is sp2 hybridized.
Interestingly for 5 and 6, the M–O, M–N and M–Cl bond
lengths and bond angles around O and the metal centers are almost
equivalent. The only noticeable difference is that the Mg–C bond
˚
length in 6 [2.191(3) A] is slightly longer than the Zn–C bond
˚
length in 5 [2.043(4) A].
The chalcogen source for the obtention of 5 and 6 could be
attributed to air contamination (O2 or H2O) of the reaction
medium, to the presence of traces of metal oxide or hydroxide
in the metallic starting material or finally, to cleavage of the
diethylether solvent used in the reaction. In these particular cases
the last supposition is not likely, due to the fact that the oxygen
in 5 and 6 is not inserted into the metal–carbon bond of the
ligand. However, we observed that the result is reproducible under
stringent inert atmosphere conditions using freshly and cautiously
distilled solvent, and always with good yields (> 40%).
The crystal structure of compound 6 shown in Fig. 4, dis-
plays an ICE isostructural to compound 5, i.e. a tetramer of
[Mg(Me3SiNPPh2CH2)]+ organometallic units in which each metal
center coordinates to a central O2- and one of two outer Cl-
3.4 Reaction of 4 with AlCl3
In an attempt to prepare the organoaluminium derivative of
phosphinimine 1 via a metathesis reaction, [Li(Me3SiNPPh2CH2)]
and AlCl3 were combined in THF. 31P NMR spectroscopy of the
reaction medium showed a unique signal at d 24.1 ppm which is in
the expected region for the anticipated compound. Nevertheless,
the 31P NMR spectroscopy monitoring of the reaction showed
rapid decomposition of the main product into several compounds,
yielding to various broad signals in the narrow region between
24 and 30 ppm. After two weeks of storage at -30 ◦C the 31P
analysis of the reaction remain unchanged and few crystals were
formed. The measurement of one of these by X-ray diffraction
showed the structure of compound [Cl2Al(Me3SiNPPh2CH2O)]2
(7), product of oxygen insertion into the Al–C bond (Fig. 5). In
addition, the X-ray crystal structure showed two molecules of
THF solvate.
As seen in Fig. 5, compound
7
is
a
dimer of
[Cl2Al(Me3SiNPPh2CH2O)]2 units with inversion symmetry. It
shows a tricycle structure consisting of two five-membered OAl-
NPC rings bridged through O–Al coordination which leads to the
formation of a central four-membered Al2O2 ring. The O atoms
are tricoordinated in a tetrahedral geometry and the angles and
bond lengths they formed with their substituents are comparable
to those found for tricoordinated O atoms.33 The Al centers are
pentacoordinated with distorted trigonal bipyramidal geometry.
The axial positions are occupied by one of the O and the N atoms,
Fig. 4 Molecular structure of [Mg4(Me3Si◦NPPh2CH2)4(m4-O)(m2-Cl)2]
˚
6. Selected bonds lengths (A) and angles ( ): Mg(2)–O(1) 1.9598(11),
Mg(2)–C(5) 2.186(3), Mg(2)–N(3) 2.073(3), Mg(2)–Cl(22) 2.4652(16),
P(4)–N(3) 1.611(3), Si(18)–N(3) 1.731(1); Mg(2)–Cl(22)–Mg(2A)
76.48(6),
Mg(2)–O(1)–Mg(2A)
102.26(7),
Mg(2C)–O(1)–Mg(2)
113.19(4), C(5)–Mg(2)–Cl(22) 115.00(11), C(5)–Mg(2)–N(3) 118.35(12),
O(1)–Mg(2)–C(5) 105.68(11), O(1)–Mg(2)–N(3) 122.90(9), O(1)–Mg(2)–
Cl(22) 90.63(4). Symmetry transformations used to generate equivalent
atoms: #1 -x + 2, -y + 2, z #2 -y + 2, x, -z + 2 #3 y, -x + 2, -z + 2.
6446 | Dalton Trans., 2010, 39, 6441–6448
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to air for a short time. The monitoring of the solution by 31P
NMR showed a set of broad signals in the region between 25
and 30 ppm, very similar to the results obtain in the previous
reaction. However, the mixture was stored at -30 ◦C and after
several weeks few crystals were grown while the 31P NMR
spectroscopy study of the solution remained unchanged. An X-ray
diffraction measurement of one crystal of suitable quality showed
the structure of compound [m-(AlCl2)(NPPh2CH3)]2 (8) resulting
from SiMe3 substitution by AlCl2.
In Fig. 6, the solid state structure of compound 8 deter-
mined by X-ray crystallography shows a dimer of [m-(AlCl2)
(NPPh2CH3)] units in which two Al centers bridge two phos-
phinimine ligands by coordination to the N atom. The geometry
around Al is significantly distorted from tetrahedral with average
Fig.
5
Molecular
structure
of
[Cl2Al(Me3SiNPPh2CH2O)]2
7. Selected bonds lengths (A) and angles (◦): Al(1)–O(1)
1.869(17), O(1)–C(1) 1.411(3), O(1)–Al(1A) 1.9205(18), Al(1)–N(1)
1.969(2), Al(1)–Cl(1) 2.1720 (9), Al(1)–Cl(2) 2.1698(9), P(1)–N(1)
˚
˚
˚
bond lengths [Al–N 1.852(2) A and Al–Cl 2.1340(10) A] and bond
angles [Cl–Al–Cl 108.32(4)◦ and N–Al–N 88.39(9)◦] which are in
agreement with those reported for similar compounds.36 The four-
membered Al2N2 ring is almost perfectly square with angles close
to 90◦ [N–Al–N 88.39(9)◦ and Al–N–Al 91.61(9)◦] and generates
1.601(2),
O(1)–Al(1)–O(1A) 72.92(8), P(1)–N(1)–Si(1) 123.18(12), Al(1)–N(1)–Si(1)
124.85(11), O(1A)–Al(1)–N(1) 160.34(9), C(1)–O(1)–Al(1)
124.57(15), C(1)–O(1)–Al(1A) 127.95(14), O(1)–Al(1)–N(1) 88.25(8),
O(1)–Al(1)–O(1A) 72.92(8). Symmetry transformations used to generate
equivalent atoms: -x + 2, -y, -z + 1.
Si(1)–N(1)
1.764(2);
Al(1)–O(1)–Al(1A)
107.08(8),
˚
an Al–Al separation of 2.656(14) A. The P–N bond distance
˚
[1.5853(19) A] agrees with double bonding and the N atom is
sp2 hybridized.
while the second O and the two Cl atoms occupy the equatorial
˚
˚
positions. The Al–Oaxial [1.9205(18) A], Al–Oequat [1.8269(17) A]
˚
and Al–N [1.969(2) A] bond lengths and the N–Al–Oaxial bond
angle [160.34(9)◦◦] are in close agreement with the values reported
(range 158–162 ) for comparable compounds.34 The geometry
around N is approximately trigonal planar with a P–N–Si angle of
123.18(12)◦ (normal range 121.8–126.6) and a P–N bond distance
˚
[1.601(2) A] characteristic for a multiple bond.
Although the composition of 7 could be confirmed by elemental
analysis, no interpretable NMR data could be obtained from the
few crystals isolated from this reaction. As seen by the complexity
of the spectra in deuterated THF, this compound likely engages in
complicated equilibrium processes and decomposes in solution.
Compound 7 has a structure very similar to the one reported
by Schumann et al.35 for the organoaluminium chloride [Cl2Al(m-
OCH2CH2NMe2)]2 from which the diallyl derivative was synthe-
sized and found to be a useful reagent for the transfer of one
allyl group to aldehydes, imines, and enones. Similarly, 7 might
also posses such properties which lead us to further improve its
synthesis and complete its characterization by NMR methods.
As the insertion of an O atom into the C–Al bond suggested
inconspicuous exposure to air, it seemed reasonable to reproduce
the synthesis by deliberated exposure of the reaction medium
Fig. 6 Molecular structure of [m-Al(Cl)2(NPPh2CH3)]2 8. Selected bonds
◦
˚
lengths (A) and angles ( ): Al(1)–N(1) 1.852(2), Al(1)–N(1A) 1.8526(2),
Al(1)–Cl(1) 2.1349(9), Al(1)–Cl(2) 2.1340(10), P(1)–N(1) 1.5853(19),
N(1)–Al(1A) 1.852(2), Al(1)–Al(1A) 2.6560(14); N(1)–Al(1)–N(1A)
88.39(9), Al(1)–N(1)–Al(1A) 91.61(9), N(1)–Al(1)–Cl(1) 114.83(7),
N(1)–Al(1)–Cl(2) 113.35(7), Cl(1)–Al(1)–Cl(2) 108.28(4), P(1)–N(1)–Al(1)
133.97(13), P(1)–N(1)–Al(1A) 134.30(11). Symmetry transformations
used to generate equivalent atoms: #1 -x + 1, -y + 1, -z + 1 #2 -x +
2, -y, -z.
Scheme 5 Formation of 7 and 8 in reactions between a-lithiated phosphinimine 4 and AlCl3.
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It is worth noting that compound 8, formed as a side product in
this last reaction, could not be obtained by thermolysis of ClSiMe3
from 3. Additionally, the production of 8 can only be explained by
reaction of the organometallic species with moisture. In contrast,
the insertion of oxygen into the metal carbon bond of 7 suggests in
this case that the chalcogen source is more likely a contamination
of the reaction medium by traces of molecular oxygen or eventually
solvent activation (Scheme 5).
9 F. Lo´pez-Ortiz, E. Pelae´z-Arango, B. Tejerina, E. Pe´rez-Carren˜o and
S. Garc´ıa-Granda, J. Am. Chem. Soc., 1995, 117, 9972.
10 P. Imhoff, S. C. A. Nefkens and C. J. Elsevier, Organometallics, 1991,
10, 1421.
11 M. W. Avis, K. Vrieze, J. M. Ernsting and C. J. Elsevier, Organometallics,
1996, 15, 2376.
12 P. B. Hitchcock, M. F. Lappert and Z. Wang, Chem. Commun., 1997,
1113.
13 A. Mu¨ller, B. Neumu¨ller and K. Dehnicke, Angew. Chem., Int. Ed.
Engl., 1997, 36, 2350.
14 A. Mu¨ller, M. Krieger, B. Neumu¨ller and K. Dehnicke, Z. Anorg. Allg.
Chem., 1997, 623, 1081.
15 P. B. Hitchcock, M. F. Lappert, P. G. H. Uiterweerd and Z. Wang,
J. Chem. Soc., Dalton Trans., 1999, 3413.
Conclusions
The formation of N-donor adducts thermally stable from phos-
phinimines 1 and 4 with metallic halides and the reactivity of
organometallic phosphinimine compounds towards oxygen is
demonstrated in this study. The solid state structures of 5 and 6
showed oxygen encapsulation with tetrahedral coordination of the
chalcogenide center, opening the way to new ICE chemistry. The
deliberate and controlled exposure to air of the reaction medium
with aluminium chloride and 4 leads to hydrolysis and no oxygen
insertion was observed.
16 A. R. Kennedy, R. E. Mulvey, C. L. F. Raston, B. A. Roberts and R. B.
Rowlings, Chem. Commun., 1999, 353.
17 R. E. Mulvey, Organometallics, 2006, 25, 1060.
18 A. E. H. Wheatley, Chem. Soc. Rev., 2001, 30, 265; W. Clegg, K. H.
Henderson, A. R. Kennedy, R. E. Mulvey, C. T. O’Hara, R. B. Rowlings
and D. M. Tooke, Angew. Chem., Int. Ed., 2001, 40, 3902.
19 P. B. Hitchcock, M. F. Lappert and Z. Wang, J. Chem. Soc., Dalton
Trans., 1997, 1953.
20 G. M. Sheldrick, SMART Bruker AXS, Inc., Madison, WI, USA, 2000.
21 G. M. Sheldrick, SAINT-Plus 6.0 Bruker AXS, Inc., Madison, WI,
USA, 2000.
22 G. M. Sheldrick, SHELXTL 6.10 Bruker AXS, Inc., Madison, WI,
USA, 2000.
23 M. Krieger, K. Haims, J. Magull and K. Dehnicke, Z. Naturforsch.,B:
Chem. Sci., 1997, 52, 243.
Acknowledgements
24 P. R. Schonberg, R. T. Paine and C. F. Campana, J. Am. Chem. Soc.,
1979, 101, 7726.
25 C. M. Ong and D. W. Stephan, J. Am. Chem. Soc., 1999, 121, 2939.
26 N. Nimitsiriwat, V. C. Gibson, E. L. Marshall, P. Takolpuckdee, A. K.
Tomov, A. J. P. White, D. J. Williams, M. R. Elsegood and S. H. Dale,
Inorg. Chem., 2007, 46, 9988.
27 G. C. Forbes, A. R. Kennedy, R. E. Mulvey, R. B. Rowlings, W. Clegg,
S. T. Liddle and C. C. Wilson, Chem. Commun., 2000, 1759.
28 W. Clegg, S. H. Dale, D. Graham, R. W. Harrington, E. Hevia, L. H.
Hogg, A. R. Kennedy and R. E. Mulvey, Chem. Commun., 2007, 1641.
29 R. E. Mulvey, Chem. Commun., 2001, 1049–1056.
30 A. R. Kennedy, R. E. Mulvey and R. B. Rowlings, Angew. Chem., Int.
Ed., 1998, 37, 3180.
31 G. C. Forbes, F. R. Kenley, A. R. Kennedy, R. E. Mulvey, C. T. O’Hara
and J. A. Parkinson, Chem. Commun., 2003, 1140.
32 D. V. Graham, E. Hevia, A. R. Kennedy, R. E. Mulvey, C. T. O’Hara
and C. Talmard, Chem. Commun., 2006, 417.
We thank CONACYT-Me´xico (Grant 61003) for generously
sponsoring this research and Perla Roman Bravo Ph.D., for
determining the X-Ray crystal structure of 2. C. V. C thanks
CONACYT for a graduate scholarship (174139) and an under-
graduate studentship to H. O. C.
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