Structures, dynamic behaviour, and reactivity of P-cyclopentadienyl- substituted 1,3,2-diazaphospholenes

Article abstract of DOI:10.1039/b702720f

P-Cyclopentadienyl-substituted 1,3,2-diazaphospholenes were prepared by salt metathesis from NaCp or LiCp* and 2-chloro-1,3,2-diazaphospholenes. Comprehensive spectroscopic and X-ray diffraction studies revealed a significant lengthening of the phosphorus-carbon bonds as compared with typical P-C bond distances, and the presence of fluxional molecular structures in solution and solid state as a consequence of circumambulatory migration of the diazaphospholene moiety around the Cp-ring. The P-C bond lengthening is accompanied by the capability to react with transition metal complexes under P-C bond activation and cyclopentadienyl transfer. At the same time, 2-Cp-diazaphospholenes react with strong bases under deprotonation to afford a phosphinyl-cyclopentadienide anion that reacts further with FeCl₂ to a 1,1′-bisphosphinyl-ferrocene. The ambivalent behaviour of the diazaphospholenes offers interesting prospects to develop new synthetic methods for functional cyclopentadienyl complexes. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b702720f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Structures, dynamic behaviour, and reactivity of
P-cyclopentadienyl-substituted 1,3,2-diazaphospholenes
Sebastian Burck,a Dietrich Gudat,*a Martin Niegerb and Ju¨rgen Tirree´c
Received 21st February 2007, Accepted 16th March 2007
First published as an Advance Article on the web 2nd April 2007
DOI: 10.1039/b702720f
P-Cyclopentadienyl-substituted 1,3,2-diazaphospholenes were prepared by salt metathesis from NaCp
or LiCp* and 2-chloro-1,3,2-diazaphospholenes. Comprehensive spectroscopic and X-ray diffraction
studies revealed a significant lengthening of the phosphorus–carbon bonds as compared with typical
P–C bond distances, and the presence of fluxional molecular structures in solution and solid state as a
consequence of circumambulatory migration of the diazaphospholene moiety around the Cp-ring. The
P–C bond lengthening is accompanied by the capability to react with transition metal complexes under
P–C bond activation and cyclopentadienyl transfer. At the same time, 2-Cp-diazaphospholenes react
with strong bases under deprotonation to afford a phosphinyl–cyclopentadienide anion that reacts
further with FeCl2 to a 1,1ꢀ-bisphosphinyl–ferrocene. The ambivalent behaviour of the
diazaphospholenes offers interesting prospects to develop new synthetic methods for functional
cyclopentadienyl complexes.
In the course of the investigation of cyclopentadienyls of
Introduction
main-group elements, several r3,k3-phosphines (Scheme 1) were
synthesised and studies on their structure and dynamic behaviour
carried out. Derivatives with dialkyl or diaryl phosphinyl moieties
exist normally as vinylic isomers 2 and undergo no intramolecular
dynamic processes at normal temperature.3,4 Allylic structures 1
were observed for cyclopentadienyl phosphines with fluorine,5
hydrogen, chlorine6 or alkoxy substituents7 at phosphorus, al-
though most of these compounds exhibit very low thermal stability
and decompose either at room temperature to give undefined
products (R = H, F, Cl)5,6 or rearrange slowly to a vinylic isomer
2 (R2 = (OCH2)2CMe2).7 Still, a degenerate [1,5]-migration of
the phosphinyl group (interconversion between 1 and 1ꢀ) was
detected at room temperature for CpP(OCH2)2 and CpPF2.5,7 The
dioxophospholane CpP(OCH2)2 is sufficiently stable to be isolated
The cyclopentadienyl (Cp) group is a versatile spectator ligand
in complexes of transition metals, lanthanides, and actinides,
and was also successfully introduced as a substituent into the
chemistry of main-group elements.1 The resulting compounds
display a remarkable structural and electronic diversity as the
1
cyclopentadienyl can act as a pure r-donor (g -ligation mode) or a
2
3
5
1
combined r/p-donor (g -, g - or g -coordination). The g -bonded
Cp groups frequently display fluxional behaviour as a consequence
of degenerate intramolecular [1,5]-migration of the main-group
moiety around the Cp ring (“circumambulatory rearrangement”).
Alternatively, a non-degenerate [1,5]-shift of a hydrogen atom may
occur (Scheme 1).2
◦
as the allylic isomer but dimerises at 65 C in an intermolecular
Diels–Alder reaction rather than rearranging via hydrogen shift to
a vinylic isomer 2.7
The formal replacement of the cyclopentadienyl hydrogen
atoms by methyl groups leads to pentamethylcyclopentadienyl
(Cp*) r3,k3-phosphines. As these species lack a possibility to
undergo [1,5]-hydrogen-shifts and rearrange to isomer 2, the [1,5]-
sigmatropic shift of the phosphinyl group is the only observ-
able dynamic process.9 The activation barrier for this process
is determined by the substituents on the phosphorus atom:8
electronegative halides or five membered ring systems with two
directly attached oxygen, sulfur or nitrogen atoms which tend to
stabilise the migrating phosphenium cation decrease the activation
energy.
Scheme 1
We have recently shown that 2-hydrido- and 2-phosphinyl-
1,3,2-diazaphospholenes feature polarised P–H and P–P bonds,
respectively.11 The reasons for this effect are intimately related to
the high stability of the diazaphospholenium cation and have been
discussed elsewhere.12 Applying the same concept to 2-Cp-1,3,2-
diazaphospholenes leads to a description of the bonding in terms
of bond/no-bond resonance between the canonical structures 3, 3ꢀ
aInstitut fu¨r Anorganische Chemie, Universita¨t Stuttgart, Stuttgart, Ger-
many. E-mail: gudat@iac.uni-stuttgart.de; Fax: +49 711 685 64241;
Tel: +49 711 685 64186
bLaboratory of Inorganic Chemistry, University of Helsinki, A.I. Virtasen
aukio 1, Helsinki, Finland
cInstitut fu¨r Anorganische Chemie, Universita¨t Bonn, Bonn, Germany
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(Scheme 1). The high diazaphospholenium cation stability implies
then an energetic stabilization, and thus an increased weight, for
the ionic structure 3ꢀ. As a consequence, one would expect not only
a low activation barrier for circumambulatory migration of the
1,3,2-diazaphospholene fragment but also increased polarity of
the exocylic phosphorus–carbon bond as compared to a “normal”
PC-single bond which should in turn lead to enhanced chemical
reactivity.
As, to the best of our knowledge, no Cp-substituted diamino-
phosphines and only a few examples of Cp*-substituted derivatives
are known,9,10 we set out to synthesise Cp- and Cp*-functionalised
1,3,2-diazaphospholenes, and to obtain experimental verification
of the hypotheses outlined above from the results of spectroscopic,
structural, and chemical reactivity studies.
To gain deeper insight into the dynamic behaviour, variable
temperature NMR studies of 5a were carried out. However, 1H and
13C spectra recorded at the lowest accessible temperature (193 K)
revealed only minor temperature induced shifts of the signals of the
hydrogen and carbon atoms in the Cp group, and the lack of any
dynamically induced change of line shapes indicated clearly that
the slow exchange regime was not reached. Considering that the
activation barriers for intramolecular dynamic processes are often
higher in the solid state than in solution,13 we also studied the 13
C
CP-MAS NMR spectra of solid 5a. Even though the observation,
as in solution, of a single resonance for all five ring carbon atoms
over the accessible temperature range (Fig. 1a,b) proves that the
fluxional behaviour persists at low temperature in the solid state,
we were able to verify qualitatively the slowing down of this process
with decreasing temperature. This was feasible by recording a 13
C
CP-MAS spectrum with delayed acquisition which is normally
used to distinguish signals of quaternary and protonated carbon
atoms (“non-quaternary suppression”).
Results and discussion
Syntheses
Salt metathesis of the 2-chloro-1,3,2-diazaphospholenes 4a–c
with sodium cyclopentadienide (NaCp) or◦lithium pentamethyl
cyclopentadienide (LiCp*) in THF at −78 C gave the P-Cp- or
Cp*-diazaphospholenes 5a,b and 6b,c, respectively (Scheme 2).
The crude products were purified by evaporation of the solvent,
dissolving the residue in n-hexane, filtering off the insoluble part,
and crystallisation at low temperature. Pure compounds were
isolated as white to pale brown, air and moisture sensitive powders
in yields from 78 to 85%.
Fig. 1 Aromatic region of the CP-MAS 13C NMR spectra of solid 5a
recorded with a normal CP pulse sequence (a,b) and a pre-acquisition
delay to suppress non-quaternary carbons (c,d). The spectra on the left
side (a,b) were recorded at ambient temperature and those on the right side
(c,d) at 195 K. The signal attributable to the carbons in the Cp-substituent
is marked with an asterisk.
The experiment is based on the fact that magnetisation of nuclei
in CH and CH2 moieties dephases rapidly under the influence of
the large CH dipolar coupling and decays prior to acquisition
whereas the signals of quaternary and methyl carbons survive as
the dipolar interactions are smaller or are scaled by motional
averaging introduced by methyl group rotation. In the case of 5a,
the signal of the Cp ring carbon atoms remains visible when the
spectrum is recorded at ambient temperature (Fig. 1c) where rapid
rotation of the Cp-ring induces a sizeable scaling of the CH dipolar
interaction, and vanishes at low temperature where the fluxional
process slows down and the effective dipolar interaction increases
accordingly (Fig. 1d).
Scheme 2 Synthesis of Cp- and Cp*-substituted 1,3,2-diazaphospholenes
(4/5a: R = 2,6-iPr2-C6H3; 4–6b: R = Mes; 4/6c: R = 2,6-Me2C6H3, Dmp).
Spectroscopic studies
The room temperature 31P NMR spectra of 5a and 5b display
signals at 108.5 and 100.9 ppm whereas the signals of the Cp*-
derivatives 6b and 6c are shifted to lower field and appear at 128.5
1
and 127.9 ppm. All H- and 13C NMR spectra show a single set
of resonances for the hydrogen and carbon atoms of all CH and
CCH3 moieties in the Cp- and Cp*-substituents, indicating the
occurrence of rapid dynamic exchange on the NMR time scale.
The observation of a JPH coupling of 2 Hz for the signal of the
Cp-protons of 5a,b suggests further that this process is strictly
Room temperature solution NMR spectra of 6c display likewise
a single set of resonances for the methyl groups (d1H = 1.61, d13C =
11.8) and ring carbon atoms (d13C = 134.9) of the Cp* moiety.
Cooling to 233 K induces broadening of the 1H and likewise the 31P
NMR signals while the chemical shifts remain nearly unchanged.
2
intramolecular.
Further cooling to 193 K goes along with decoalescence of the 31
P
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NMR signal into an intense singlet at 128.9 ppm and a second,
slightly broadened one at 103.1 ppm. The H NMR spectrum
attributable to restricted rotation of the aryl rings around the C–
N bonds and the slowing down of the [1,5]-sigmatropic migration
of the phosphinyl group around the Cp* ring. Owing to the
complexity of the dynamic processes and incomplete knowledge
of spectral parameters in the slow-exchange regime (it remains
unclear if the failure to resolve signals of methyl groups in different
position of the Cp* ring depends on a failure to reach the slow-
exchange regime or to the accidental near-degeneracy of chemical
shifts) no quantitative assessment of activation parameters for the
individual motional processes was attempted.
1
displays likewise two sets of signals (Fig. 2) attributable to two
different species which can be assigned from examination of
1H EXSY and 1H,31P HMQC spectra. Integration of the well
separated signals in the olefinic region was used to determine the
molar ratio of both species as 2 : 5. The more abundant isomer
exhibits according to this analysis five different signals for methyl
groups in the Cp* and four for those in the aryl substituents, and
two signals of olefinic protons in the diazaphospholene unit. The
less abundant isomer displays one set of resonances each for the
methyls at the Cp* and aryl rings and one signal for the olefinic
protons.
Even if the precise energetics of the Cp migration in 5a,b remain
unknown, the lack of evidence for a non-degenerate isomerisation
to a vinylic isomer and the failure to freeze out the dynamics
at low temperature suggest that the energy of the allylic isomer
is much lower than that of the vinylic isomer, and that [1,5]-
PR2 shifts require significantly lower activation energy than [1,5]-
H shifts. This is in accord with the high cation stability of a
diazaphospholenium unit which should favour the circumam-
bulatory rearrangement.8 In this respect, 5a,b differ from the
5
7
thermally unstable species CpPF2 and CpP(OCH2)2 which are
the only phosphines showing a similar dynamic behaviour, and
resemble more closely the cyclopentadienyls of heavier main group
elements.2 The dynamic behaviour of 6a,c compares better with
that of other known Cp* substituted phosphines.2 The observation
of spectra in the slow exchange regime at low temperature suggests
that the [1,5]-PR2 shift occurs in this case less facile, presumably as
a consequence of steric interlocking of the bulky Cp* and N-aryl
substituents.
Crystal structures
Fig. 2 Expansions of 1H NMR spectra of 6c at 303 K (bottom, in C6D6),
233 K (middle, in d8-toluene) and at 193 K (top, in d8-toluene). Labelled
signals are due to solvents (s) or impurities (*).
Suitable crystals for single-crystal X-ray diffraction studies of 5a
and 6b were grown from n-hexane at −20 ◦C.
Crystalline 5a (Fig. 3) contains discrete molecules that show
no interaction with each other and the co-crystallised solvent
(one molecule THF per formula unit). The diazaphospholene
Based on the number of observable signals we assign the
abundant species as a rotational conformer with C1 symmetry
that displays a fixed gauche-orientation of the two five-membered
rings at the central P–C bond (Scheme 3). The second isomer is
attributed to a Cs symmetric conformer with a presumed transoid
arrangement of the five-membered rings. The occurrence of both
species can be ascribed to restriction of the free rotation of the
Cp* substituents around the P–C bond whereas the splitting of
the signals of the Cp* and Dmp groups in the major isomer is
Fig. 3 Molecular structure of 5a. Thermal ellipsoids are drawn at 50%
probability level and H atoms have been omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ). P1–N1 1.715(2), P1–N5 1.724(2),
P1–C30 1.949(2), N2–C3 1.413(2), N5–C4 1.414(2), C3–C4 1.332(3),
C30–C31 1.472(3), C30–C34 1.472(3), C31–C32 1.356(3), C32–C33
1.438(3), C33–C34 1.346(3); N2–P1–N5 88.8(1), N2–P1–C30 101.8(1),
N5–P1–C30 101.1(1).
Scheme 3 Two rotamers of 6c observed in solution at 193 K. The
labels denote anisochronic hydrogen atoms at the diazaphospholene ring
(Ha–Hb), and CH3 groups in Dmp (MeA–MeD) and Cp* (Me1–Me5)
substituents, respectively.
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ring exhibits a flat envelope conformation and adopts a transoid
orientation relative to the planar Cp ring. The P–N, N–C, and
C–C bond lengths compare with those in known P-hydrido- or
P-phosphinyl-1,3,2-diazaphospholenes.11 The C–C bonds in the
Cp ring display the typical alternating pattern of a 1,3-diene
system with similar distances as in solid cyclopentadiene.15 All
features together with the tetrahedral geometry at the C30 carbon
atom support the proposed ground state structure of 5a with an
although still shorter than in 5a. This trend can be explained
by considering that the additional methyl groups render the Cp*
ligand a better nucleophile and increase thereby its interaction
with the diazaphospholene fragment, leading to a concomitant
PC bond shortening.
Reactivity
The lengthening of the exocyclic phosphorus–carbon bonds in 5a
and 6b is in accord with the postulated bond polarisation and
weakening and leads to expect enhanced reactivity. In fact it was
found that 5b reacted with an equimolar amount of Mn(CO)5Br
at room temperature via P–C/Mn–Br metathesis to yield the 2-
bromo-diazaphospholene 7 and CpMn(CO)3. Likewise, reaction
with 1/2 equivalent of FeCl2 gave 4b and Cp2Fe (Scheme 4). All
1
g -bound Cp ring that carries the PR2 substituent in an allylic
position.
A particularly remarkable aspect is the long exocyclic P1–C30
˚
distance of 1.949(2) A which compares with an average PC bond
length in r3,k3-phosphines of 1.86 0.03 A and is even longer
14
˚
than the corresponding bond in the only other structurally char-
acterised cyclopentadienyl phosphine, CpP(OCH2)2 (PC 1.892(3)
1
products were identified by their H and 4b and 6b also by their
7
˚
A ). This effect is in accord with the prediction that the lower
31P NMR data.17,18
electrophilicity of a 1,3,2-diazaphospholenium as compared to a
dioxaphospholenium cation12 increases the weight of the ionic
resonance structure 3ꢀ in the bonding description outlined in
Scheme 1 and thereby implies a lengthening of the exocyclic
phosphorus–carbon bond.11
The crystal structure study of 6b (Fig. 4) was carried out at
293 K as the crystals were found to undergo a phase transition
upon cooling. This phenomenon was not studied in detail. The
crystals contain discrete molecules of 6b which differ from that
of 5a in showing a distinct gauche arrangement of the Cp and
diazaphospholene rings relative to the central P–C bond. This
distortion leads to a distinct pyramidalisation at N5 (sum of
angles 350.5◦) due to enhanced steric interaction between the
methyl group at C24 of the Cp*-ring and the mesityl substituent
at N5. The coordination geometry at the second nitrogen atom
N2 remains planar (sum of angles 359.9◦). The P–N, N–C,
and C–C bond lengths in the diazaphospholene and the C–
C single and double bond lengths in the Cp* ring resemble
those in 5a. Moreover, the latter are comparable to those in
other Cp*-substituted phosphines.16 The exocyclic P1–C24 bond
˚
(1.917(2) A) in 6b is still longer than a typical PC single bond
Scheme 4
In order to establish if 5b allows also the expected for-
mation of a phosphinyl-substituted cylopentadienide anion via
CH deprotonation21 we further studied its reactivity toward
methyllithium in DME at −78 ◦C. It was found that the reaction
proceeded selectively to yield a single product with a 31P NMR
signal at 85.7 ppm that was isolated as colourless crystals by
cooling a concentrated reaction mixture to 4 ◦C and identified
by spectroscopic data and an X-ray diffraction study as the
Fig. 4 Molecular structure of 6b. Thermal ellipsoids are drawn at 50%
probability level and H atoms have been omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ). P1–N2 1.738(2), P1–N5 1.720(2),
P1–C24 1.917(2), N2–C3 1.406(3), N5–C4 1.418(2), C3–C4 1.319(3),
C24–C25 1.497(3), C24–C28 1.512(3), C25–C26 1.346(3), C26–C27
1.458(3), C27–C28 1.339(3); N2–P1–N5 90.2(1), N2–P1–C24 105.1(1),
N5–P1–C24 107.3(1).
1
lithium cyclopentadienide 8 (Scheme 4). The H and 13C NMR
1894 | Dalton Trans., 2007, 1891–1897
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spectra display separate signals for the individual carbon and
proton environments in the Cp substituent which indicate that
the molecular structure is no longer fluxional.
both reactions are more widely applicable and that combination
of both processes permits the development of a novel synthetic
methodology e.g. to access multiply substituted cyclopentadienyl
complexes.
The results of the X-ray diffraction study of 8 (Fig. 5) discloses
the presence of isolated molecules without any intermolecular
interactions. The lithium cation is coordinated by the carbon
Conclusions
5
atoms of the g -bound cyclopentadienide unit (Li–C 2.24 to 2.32
˚
We have shown that thermally highly stable P-cyclopentadienyl-
substituted 1,3,2-diazaphospholenes are easily accessible via
salt elimination from P-chloro diazaphospholenes and metal
cyclopentadienides. The products display fluxional molecular
structures in solution and solid state. The experimental data
suggest that the cyclopentadienyl migration proceeds preferably
via reversible [1,5]-PR2-shifts; no evidence for the occurrence
of [1,5]-H-shifts was obtained. These effects, which are in ac-
cord with the high cation stability of the PR2 fragment, are
accompanied by a weakening of the P–C bonds which is further
substantiated by the results of X-ray diffraction studies. The
hypothesis that these results imply an increased activity of Cp
diazaphospholenes in bond metathesis processes was proven by
cyclopentadienide transfer reactions with transition metal halides.
Moreover, deprotonation of a cyclopentadienyl diazaphospholene
to give a stable phosphinyl–cyclopentadienide anion and further
conversion of the latter to a bis-phosphinyl substituted ferrocene
was demonstrated. The purposeful synthesis of both ferrocene
and a 1,1ꢀ-bisphosphinyl ferrocene from the same starting material
proves that precise control of the reactivity of these compounds is
feasible and may offer interesting prospects for new developments
in the synthetic chemistry of cyclopentadienyl compounds.
A) and the oxygen atoms of one molecule of DME. The C–C bonds
˚
in the Cp ring (C–C 1.38 and 1.43 A) match those in other lithium
cyclopentadienides22 and display the typical bond equalisation of
an aromatic p-system. The P–N bonds in the diazaphospholene
ring are slightly longer than in 5a and the N–Cand C–C bonds have
almost the same values. Quite striking, however, is the shortening
˚
of the P1–C24 bond (1.787(2) A) in 8 by some 15 pm as compared
to the P1–C30 bond in 5a (1.949(2) A). The observed distance
compares well to a normal single bond (1.80
indicating that the loss of hyperconjugation interactions with the
˚
14
˚
0.03 A ), thus
p-system implies a substantial bond strengthening effect.
Experimental
General considerations
All manipulations were carried out under protective gas atmo-
sphere (Ar) and in flame dried glassware. Solvents were dried
prior to use by means of common procedures. 4a–c11b and LiCp*23
were synthesised according to literature procedures. All other
chemicals were purchased from commercial suppliers. NMR
Spectra (at 303 K if not specified otherwise): Bruker Avance 400
(1H: 400.13 MHz, 31P: 161.9 MHz, 13C: 100.4 MHz) at 30 ◦C;
chemical shifts referred to external TMS (1H, 13C), 85% H3PO4
(N = 40.480747 MHz, 31P); positive signs of chemical shifts
denote shifts to lower frequencies; coupling constants are given
as absolute values; prefixes i-, o-, m-, p- denote atoms of aryl-
substituents. CP-MAS NMR spectra of solids were recorded in
4 mm rotors using spinning speeds between 4 and 10 kHz. MS:
Varian MAT 711, EI, 70 eV. Elemental analysis: Perkin Elmer
2400CHSN/O Analyser. Melting points were determined in sealed
capillaries.
Fig. 5 Molecular structure of 8. Thermal ellipsoids are drawn at 50%
probability level and H atoms have been omitted for clarity. Selected bond
◦
˚
lengths (A) and angles ( ). P1–N2 1.747(2), P1–N5 1.733(2), P1–C24
1.787(2), N2–C3 1.402(3), N5–C4 1.412(3), C3–C4 1.330(3), C24–C25
1.432(3), C24–C28 1.421(3), C25–C26, 1.381(3), C26–C27 1.404(4),
C27–C28 1.392(3), C24–Li1 2.275(5), C25–Li1 2.302(5), C26–Li1 2.321(5),
C27–Li1 2.283(5), C28–Li1 2.244(5), Zcp–Li1 1.947(5); N2–P1–N5 87.6(1),
N2–P1–C24 105.4(1), N5–P1–C24 105.2(1).
Whereas treatment of 8 with triethylamine hydrochloride lead
1
to complete recovery of 5b which was identified by H and 31P
NMR data, reaction with half an equivalent of anhydrous iron
dichloride yielded a new product the 31P NMR signal of which
displayed a slight deshielding (d = 87.9) as compared to 8.
The product was isolated after work-up as a violet powder and
identified by analytical and spectroscopic data as the 1,1ꢀ-bis-
diazaphospholenyl ferrocene 9 (Scheme 4).
Preparations
The observed reaction pattern suggests that 5b behaves as
a versatile reagent which permits, depending on the reaction
conditions, either the transfer of a cyclopentadienyl fragment
under similar conditions as metal cyclopentadienides19 or stannyl
cyclopentadienes20 or, alternatively, of a phosphine-substituted
cyclopentadienyl unit. This process allows the accomplishment,
in one step, of the synthesis of novel metal cyclopentadienides
with functional phosphine substituents. It can be expected that
Synthesis of 5a. NaCp (1 mL of a 2 M solution in THF,
2 mmol) was added at −78 ◦C to a stirred solution of 4a (0.88 g,
2 mmol) in THF (30 ml). The reaction mixture was slowly
warmed to room temperature and stirred for 1 h. The solvent was
evaporated in vacuum, the residue dissolved in n-hexane (20 ml),
and filtered. Storage of the filtrate at −20 ◦C produced pale yellow
◦
1
crystals of 5a. Yield: 0.77 g (82%), mp 121 C. H NMR (C6D6)
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d = 7.20 to 7.10 (m, 6H, CH), 6.10 (s, 2H, N–CH), 6.06 (d, 5H,
mp 125 ◦C. 1H NMR (C6D6) d = 6.95 (m, 6H, m/p-CH), 5.67 (d,
2H, 3JPH = 0.6 Hz, N–CH), 2.46 (d, 12H, 5JPH = 1.3 Hz, o-CH3),
3
5
2JPH = 2.2 Hz, C5H5), 3.76 (dsep, 4H, JHH = 6.8 Hz, JPH
=
1.7 Hz, CH(CH3)2), 1.36 (d, 12, 3JHH = 6.8 Hz, CH3), 1.20 (d, 12,
1.61 (d, 15H, JPH = 2.6 Hz, CH3). 13C{ H} NMR (C6D6) d =
3
1
1
2
3
3JHH = 6.8 Hz, CH3). H NMR (C7D8, 193 K) d = 6.97 to 6.89
142.9 (d, JPC = 13.4 Hz, i-C), 137.6 (d, JPC = 15.9 Hz, o-C),
1
4
(m, 6H, CH), 6.06 (s, 2H, N–CH), 5.99 (d, 5H, C5H5), 3.73 (sep,
4H, 3JHH = 6.3 Hz, CH(CH3)2), 1.31 (d, 12, 3JHH = 6.0 Hz, CH3),
134.9 (d, JPC = 1.6 Hz, C5Me5), 129.6 (d, JPC = 1.0 Hz, m-C),
125.3 (d, 5JPC = 1.7 Hz, p-C), 119.5 (d, 2JPC = 6.9 Hz, N–CH), 20.8
1
1
1.15 (d, 12, 3JHH = 5.7 Hz, CH3). 13C{ H} NMR (C6D6) d = 145.6
(d, 4JPC = 9.4 Hz, o-CH3), 11.8 (d, 2JPC = 6,3 Hz, CH3). 31P{ H}
3
2
1
(d, JPC = 2.2 Hz, o-C), 135.6 (d, JPC = 9.5 Hz, i-C), 126.0 (d,
5JPC = 1.9 Hz, m-CH), 123.1 (d, 4JPC = 1.1 Hz, p-CH), 118.8 (d,
NMR (C6D6) d = 127.9. 31P{ H} NMR (C7D8, 193 K) d = 129.8,
103.1. 1H NMR (C7D8, 193 K): minor rotamer: d = 6.97 to 6.66
(m, 6H, m/p-CH), 5.30 (s, broad, 2 H, N–CH), 2.49 (s, broad, 12
H, o-CH3), 1.61 (s, broad, 15 H, CH3); major rotamer: d = 6.97 to
6.66 (m, 6 H, m/p-CH), 5.68 (s, 1 H, N–CH), 5.00 (s, 1 H, N–CH),
2.59 (s, 3 H, o-CH3), 2.49 (s, 3 H, o-CH3), 2.37 (s, 3 H, o-CH3),
2.28 (s, 3 H, CH3), 2.11 (s, 3 H, o-CH3), 1.86 (s, 3 H, CH3), 1.68 (s,
3 H, CH3), 1.27 (s, 3 H, CH3), 0.94 (d, 3 H, 3JPH = 15.5 Hz, CH3).
1
2JPC = 8.3 Hz, N–CH), 116.2 (d, JPC = 5.8 Hz, C5H5), 27.2 (d,
1
4JPC = 4.7 Hz, CH(CH3)2), 24.2 (s, CH3), 23.9 (s, CH3). 31P{ H}
1
NMR (C6D6) d = 108.5. 31P{ H} NMR (C7D8, 193 K) d = 99.6.
MS (EI, 70 eV, 375 K) m/z (%) = 472.3 ([M]+, <1%), 407.3 ([M −
C5H5]+, 100%). Anal. Calcd for C31H41N2P: C, 78.78, H, 8.74, N,
5.93. Found: C, 78.06, H, 8.67, N, 5.82%.
Reaction of 5b with FeCl2. 5b (39 mg, 1 mmol) and FeCl2 (7 mg,
Synthesis of 5b. NaCp (1 mL of a 2 M solution in THF,
2 mmol) was added at −78 ◦C to a stirred solution of 4b (0.72 g,
2 mmol) in THF (30 ml). The reaction mixture was slowly
warmed to room temperature and stirred for 1 h. The solvent was
evaporated in vacuum, the residue dissolved in n-hexane (20 ml),
1
0.5 mmol) were dissolved in C6D6 (0.5 ml). H and 31P NMR
spectra revealed the quantitative formation of 4b and ferrocene.
4b: 1H NMR (C6D6) d = 6.71 (s, 4H, m-CH), 5.82 (s, 2H, N–CH),
1
2.37 (s, 12H, o-CH3), 2.07 (s, 6H, p-CH3). 31P{ H} NMR (C6D6)
d = 144.0. FeCp2: 1H NMR (C6D6) d = 3.99 (s, 10 H).
◦
and the precipitate filtered off. Storage of the filtrate at −20 C
produced a pre◦cipitate of 5b as a pale brown solid. Yield: 0.61 g
(78%), mp 159 C. 1H NMR (C6D6) d = 6.80 (s, 4H, m-CH), 6.04
(d, 5H, 2JPh = 2.1 Hz, C5H5), 5.78 (d, 2H, 3JPH = 0.6 Hz, N–CH),
Reaction of 5b with Mn(CO)5Br. 5b (39 mg, 1 mmol) and
Mn(CO)5Br (55 mg, 1 mmol) were dissolved in C6D6 (0.5 ml).
1H and 31P NMR spectra revealed the quantitative formation of
7 and CpMn(CO)3. 7: 1H NMR (C6D6) d = 6.79 (s, 4H, m-CH),
5.78 (s, 2H, N–CH), 2.40 (s, 12H, o-CH3), 2.12 (s, 6H, p-CH3).
1
2.41(s, 12H, o-CH3), 2.13 (s, 6H, p-CH3). 13C{ H} NMR (C6D6)
d = 137.3 (d, 2JPC = 10.0 Hz, i-C), 135.8 (d, 3JPC = 2.5 Hz, o-C),
135.6 (d, 4JPC = 2.4 Hz, m-C), 130.3 (d, 5JPC = 1.5 Hz, p-C), 128.3
(s, C5H5), 118.1 (d, 3JPC = 8.1 Hz, N–CH), 20.8 (d, 6JPC = 0.9 Hz,
1
1
31P{ H} NMR (C6D6) d = 175.2. CpMn(CO)3: H NMR (C6D6)
d = 6.01 (s, 5H).
4
1
m-CH3), 19.5 (d, JPC = 5.3 Hz, o-CH3). 31P{ H} NMR (C6D6)
d = 99.7. MS: (EI, 70 eV, 370 K) m/z (%) = 388.2 ([M]+, 2%),
323.1 ([M − C5H5]+, 100%). Anal. Calcd for C25H29N2P: C, 77.29,
H, 7.52, N, 7.21. Found C, 77.61, H, 7.63, N, 7.13%.
Synthesis of 8. A solution of 5b (0.72 g, 2 mmol) in DME
(30 ml) was cooled to −78 ◦C and methyllithium (1.4 mL of a
1.4 M solution in THF, 2 mmol) added slowly while stirring. The
reaction mixture was brought to room temperature and stirred
for 1 h. The solvents were evaporated in vacuo and the residue
dissolved in dimethoxyethane (10 ml). Crystallisation at 4 ◦C
Synthesis of 6b. LiCp* (0.29 g, 2 mmol) dissolved in THF
(10 ml) was slowly added to a stirred solution of 4b (0.72 g,
2 mmol) in THF (30 ml) at −78 ◦C. The stirring was continued for
1 h. The mixture was then allowed to warm to room temperature
and evaporated to dryness. The residue was dissolved in n-hexane
(20 ml) and the precipitate removed by filtration. Crystallisation
at −20 ◦C produced colourless crystals of 6b. Yield: 0.57 g (62%),
produced colourless crystals of 8. Yield: 0.90 g (93%), mp 185 ◦C.
3/4
1H NMR (C6D6) d = 6.78 (s, 4H, m-CH), 6.71 (dt, 2H,
J
=
HH
2.7 Hz, 3JPH = 3.8 Hz, 2-CH), 6.26 (dt, 2H, 3JHH = 2.7 Hz, 4JPH
=
2
1.6 Hz, 3-CH), 5.94 (d, 2H, JPH = 1.7 Hz, N–CH), 2.96 (s, 4H,
DME), 2.93 (s, 6H, DME), 2.55 (s, broad, 12H, o-CH3), 2.13 (s,
◦
1
6H, p-CH3). 13C{ H} NMR (C6D6) d = 140.4 (d, 2JPC = 14.3 Hz,
1
mp 133 C. H NMR (C6D6) d = 6.77 (s, 4H, m-CH), 5.73 (s,
2H, N–CH), 2.48 (s, 12H, o-CH3), 2.13 (s, 6H, m-CH3), 1.66 (d,
i-C), 137.5 (s, broad, o-C), 133.7 (d, 5JPC = 2.0 Hz, p-C), 129.3 (d,
3
1
15H, JPH = 2.3 Hz, CH3). 13C{ H} NMR (C6D6) d = 140.8 (d,
4JPC = 1.0 Hz, m-CH), 122.9 (d, 1JPC = 44.8 Hz, C), 116.8 (d, 2JPC
6.0 Hz, N–CH), 111.3 (d, 2JPC = 24.6 Hz, CH), 107.0 (d, 3JPC
=
=
2JPC = 13.5 Hz, i-C), 135.0 (d, JPC = 1.3 Hz, m-C), 134.7 (d,
4
3JPC = 1.8 Hz, o-C), 130.6 (d, 5JPC = 1.0 Hz, p-C), 129.5 (s, broad,
7.5 Hz, CH), 69.1 (s, broad, CH2DME), 58.7 (s, broad, CH3DME),
2
4
20.7 (s, broad, o-CH3), 19.7 (s, broad, p-CH3). 31P{ H} NMR
1
C5Me5), 120.1 (d, JPC = 7.1 Hz, CH), 21.1 (d, JPC = 9.4 Hz,
6
2
(C6D6) d = 85.7. MS: (EI, 70 eV, 370 K) m/z (%) = 484.2 ([M]+,
0.1), 323.2 ([M − C9H14O2Li]+, 11.6), 45.0 ([M − C27H33N2PLiO]+,
100.0). Anal. Calcd for C29H38N2PLiO2: C, 71.89, H, 7.91, N, 5.78,
found: C, 70.82, H, 7.68, N, 5.82%.
o-CH3), 21.1 (d, JPC = 0.5 Hz, p-CH3), 12.2 (d, JPC = 6.1 Hz,
CH3). 31P{ H} NMR (C6D6) d = 128.5. MS: (EI, 70 eV, 390 K)
1
m/z (%) = 458.0 ([M]+, 0.1), 323.1 ([M − C10H15]+, 100.0), 135.2
([M − C20H24N2P]+, 8.0). Anal. Calcd for C30H39N2P: C, 78.57, H,
8.57, N, 6.11, Found: C, 77.95, H, 8.60, N, 6.04%.
Reaction of 8 with Et3NHCl. 8 (48 mg, 0.1 mmol) and
Et3NHCl (12 mg, 0.1 mmol) were dissolved in C6D6 (0.5 ml).
1H and 31P NMR spectra revealed the quantitative formation of
Synthesis of 6c. LiCp* (0.29 g, 2 mmol) dissolved in THF
(10 ml) was slowly added at −78 ◦C to a stirred solution of 4c
(0.66 g, 2 mmol) in THF (30 ml). The stirring was continued for
1 h, the mixture warmed to room temperature, and evaporated
to dryness. The residue was dissolved in n-hexane (20 ml) and
the precipitate removed by filtration. Storage of the filtrate at
−20 ◦C produced 6c as a colourless powder. Yield: 0.60 g (69%),
1
Et3N and 5b. 5b: H NMR (C6D6) d = 6.80 (s, 4H, m-CH), 6.04
(d, 2 H, 3JPH = 1.6 Hz, N–CH), 3.11 (s, 5H, C5H5), 2.41 (s, 12H,
1
o-CH3), 2.13 (s, 6H, p-CH3). 31P{ H} NMR (C6D6) d = 99.7. Et3N:
3
1H NMR (C6D6) d = 2.40 (q, 6H, JHH = 7.0 Hz, CH2), 0.96 (t,
9H, 3JHH = 7.0 Hz, CH3).
1896 | Dalton Trans., 2007, 1891–1897
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The Royal Society of Chemistry 2007
©

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Synthesis of 9. 8 (0.97 g, 2 mmol) and FeCl2 (0.13 g, 1 mmol)
were dissolved in DME (30 ml) and stirred for 1 h. The solvents
were evaporated in vacuo, the residue dissolved in n-hexane (30 ml)
and the precipitate filtered off. The◦filtrated was concentrated to
a volume of 5 mL and stored at 4 C to produce violet crystals
Acknowledgements
We thank Dr G. Althoff from Bruker Biospin GmbH for recording
low temperature 13C CP-MAS NMR spectra of 5a.
◦
1
of 9. Yield: 0.56 g (68%), mp 172 C. H NMR (C6D6) d = 6.76
References
3
(s, broad, 8H, m-CH), 5.62 (t, 4H, JPH = 12 Hz, N–CH), 4.02
1 (a) P. Jutzi, Chem. Rev., 1999, 99, 969; (b) V. N. Sapunov, K. Kirchner
and R. Schmid, Coord. Chem. Rev., 2001, 214, 143; (c) P. H. Budzelaar,
J. J. Engelberts and J. H. von Lenthe, Organometallics, 2002, 22, 1562;
(d) T. P. Hanusa, Organometallics, 2002, 21, 2559.
3
3
(t, 4H, JHH = 0.8 Hz, CH), 3.96 (t, 4H, JHH = 1.7 Hz, CH),
2.62 (s, broad, 24H, o-CH3), 2.10 (s, 12H, p-CH3). 13C{ H} NMR
1
(C6D6) d = 139.0 (s, i-C), 136.5 (s, broad, o-C), 134.9 (s, p-C),
2 P. Jutzi, Chem. Rev., 1986, 86, 983.
130.1 (s, m-CH), 118.0 (t, 2JPC = 3.0 Hz, N–CH), 83.9 (dd, 1JPC
=
3 O. I. Kolodyazhni, Russ. J. Gen. Chem., 1981, 51, 2125.
4 F. Mathey and J. P. Lampin, Tetrahedron, 1975, 31, 2685.
5 J. Bentham, E. A. V. Ebsworth, H. Moretto and D. W. Rankin, Angew.
Chem., Int. Ed. Engl., 1972, 11, 640.
62.0 Hz, 3JPC = 1.7 Hz, CH), 71.8 (t, 2/3JPC = 13.5 Hz, CH), 71.2
(t, 3/4JPC = 2.4 Hz, CH), 20.9 (s, m-CH3), 19.9 (s, broad, o-CH3).
31P{ H} NMR (C6D6) d = 87.9. MS: (EI, 70 eV, 430 K) m/z (%) =
1
6 S. El Chaouch, J.-C. Guillemin, T. Karpati and T. Veszpremi,
Organometallics, 2001, 20, 5405.
7 I. E. Nifant’ev, V. A. Roznyatovskii, Yu. A. Ustynyuk, M. Yu. Antipin,
Yu. T. Struchkov, L. F. Manzhukova and E. E. Nifant’ev, Phosphorus,
Sulfur Silicon Relat. Elem., 1992, 69, 283.
830.3 ([M]+, 2.0), 508.2 ([M − C20H23N2P]+, 24.0), 323.2 ([M −
C30H32N2PFe]+, 100.0). Anal. Calcd for C50H56N4P2Fe: C, 72.28,
H, 6.79, N, 6.74, found: C, 72.08, H, 6.88, N, 6.51%.
8 (a) W. W. Schoeller, Z. Naturforsch., B: Anorg. Chem., Org. Chem.,
1983, 38, 1635; (b) W. W. Schoeller, Z. Naturforsch., B: Anorg. Chem.,
Org. Chem., 1984, 39, 1767.
Crystal structure studies
9 P. Jutzi and H. Saleske, Chem. Ber., 1984, 117, 222.
All single-crystal X-ray diffraction studies were carried out on a
Nonius Kappa-CCD diffractometer at 123(2) K (5a, 8) or 293(2)
10 T. Bauer, S. Schulz and M. Nieger, Z. Anorg. Allg. Chem., 2001, 627,
266.
˚
K (6b) using MoKa radiation (k = 0.71073 A). Direct methods
11 (a) D. Gudat, A. Haghverdi and M. Nieger, Angew. Chem., 2000, 112,
3211; (b) S. Burck, D. Gudat, M. Nieger and W.-W. du Mont, J. Am.
Chem. Soc., 2006, 128, 3946; (c) S. Burck, D. Gudat and M. Nieger,
Angew. Chem., 2004, 116, 4905.
12 (a) D. Gudat, Eur. J. Inorg. Chem., 1998, 1087; (b) D. Gudat, A.
Haghverdi, H. Hupfer and M. Nieger, Chem.–Eur. J., 2000, 6, 3414.
13 R. Benn, H. Grondey, G. Erker, R. Aul and R. Nolte, Organometallics,
1990, 9, 2493 and references cited therein.
14 Average and standard deviation of the result of a query in the CSD data
base for P–C distances in three coordinate phosphorus compounds
featuring formal sp2 or sp3 hybridisation at the carbon atom.
15 T. Haumann, J. Benet-Buchholz and R. Boesse, J. Mol. Struct., 1996,
374, 299.
16 (a) H. Schuhman, F. H. Go¨rlitz and M. Schaefers, Acta Crystallogr.,
Sect. C, 1993, 49, 688; (b) R. Pietschnig, J. Ebels, M. Nieger, N. Zoche,
M. Jansen and E. Niecke, Bull. Soc. Chim. Fr., 1997, 134, 1039; (c) H.
Voelker, D. Labahn, F. M. Bohnen, R. Herbst-Irmer, H. W. Roesky, D.
Stalke and F. T. Edelmann, New J. Chem., 1999, 23, 905; (d) J. Ebels,
R. Pietschnig, S. Kotila, A. Dombrowski, E. Niecke, M. Nieger and
H. M. Schiffner, Eur. J. Inorg. Chem., 1998, 331.
(SHELXS-9724) were used for structure solution; full-matrix least-
squares on F2 (SHELXL-97,25) for refinement. No absorption
corrections were applied, and H atoms were refined using a riding
model.
5a. Yellow crystals, C35H49N2OP (C31H41N2P·thf), M = 544.7,
crystal size 0.60 × 0.50 × 0.40 mm, monoclinic, space group P21/n
˚
˚
˚
(No. 14): a = 9.9003(2) A, b = 18.4544(4) A, c = 17.5559(4) A,
◦
3
˚
b = 98.506(1) , V = 3172.2(1) A , Z = 4, q(calcd) = 1.141 Mg
m−3, F(000) = 1184, l = 0.115 mm−1, 17886 reflexes (2 hmax = 55◦),
7035 unique [Rint = 0.028], 352 parameters, 36 restraints, R1 (I >
2r(I)) = 0.056, wR2 (all data) = 0.180, largest diff. peak and hole
−3
˚
0.660 and −0.680 e A .
6b. Colourless crystals, C30H39N2P, M = 458.6, crystal size
¯
0.50 × 0.35 × 0.20 mm, triclinic, space group P1 (No. 2): a =
17 C. H. Holm and J. A. Ibers, J. Chem. Phys., 1959, 30, 885.
18 E. A. Chermyshev, M. D. Reshetova and A. D. Volynskikh, Zh. Obshch.
Khim., 1980, 50, 952–953.
◦
˚
˚
˚
9.9703(2) A, b = 10.6255(3) A, c = 13.7990(4) A, a = 75.585(1) ,
◦
◦
3
˚
b = 85.812(1) , c = 69.263(1) , V = 1323.9(1) A , Z = 2, q(calcd) =
1.150 Mg m−3, F(000) = 496, l = 0.124 mm−1, 6707 reflexes (2
hmax = 50◦), 4456 unique [Rint = 0.023], 308 parameters, R1 (I >
2r(I)) = 0.044, wR2 (all data) = 0.122, largest diff. peak and hole
19 E. W. Abel, F. G. A. Stone and G. Wilkinson, Comprehensive
Organometallic Chemisty II, Pergamon Press, Oxford, 1995.
20 (a) G. R. Willey, T. J. Woodman and M. G. B. Drew, J. Organomet.
Chem., 1996, 510, 213; (b) X. Cheng, C. Slebodnick, P. A. Deck, D. R.
Billodeaux and F. R. Fronczek, Inorg. Chem., 2000, 39, 4921; (c) S. J.
Lancaster and D. L. Hughes, Dalton Trans., 2003, 1779; (d) P. J. Chirik,
D. L. Zubris, L. J. Ackerman, L. M. Henling, M. W. Day and J.E
Bercaw, Organometallics, 2003, 22, 172.
21 (a) M. D. Rausch, B. H. Edwards, R. D. Rogers and J. L. Atwood,
J. Am. Chem. Soc., 1983, 105, 3882; (b) C. Cornelissen, G. Erker, G.
Kehr and R. Fro¨hlich, Organometallics, 2005, 24, 214.
22 (a) M. F. Lappert, S. Singh, A. Engelhardt and A. H. White,
J. Organomet. Chem., 1984, 262, 271; (b) W.-P. Leung, F. Q. Song,
F. Xue and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1997, 4307;
(c) U. J. Bildmann, M. Winkler and G. Mu¨ller, Z. Naturforsch., B:
Chem. Sci., 2000, 55, 1005.
−3
˚
0.199 and −0.217 e A .
8. Colourless crystals, C29H38LiN2O2P, M = 484.5, crystal size
0.20 × 0.10 × 0.05 mm, monoclinic, space group P21/n (No.
˚
˚
˚
14): a = 8.5950(3) A, b = 21.7213(8) A, c = 14.6049(6) A, b =
◦
3
−3
˚
92.711(2) , V = 2723.6(2) A , Z = 4, q(calcd) = 1.182 Mg m ,
F(000) = 1040, l = 0.128 mm−1, 12355 reflexes (2 hmax = 56.5◦),
4776 unique [Rint = 0.041], 322 parameters, R1 (I > 2r(I)) = 0.050,
−3
˚
wR2 = 0.114, largest diff. peak and hole 0.632 and −0.275 e A .
CCDC reference numbers 631100–631302.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b702720f
23 F. X. Kohl and P. Jutzi, Chem. Ber., 1987, 120, 1539.
24 G. M. Sheldrick, Acta Crystallogr., Sect A, 1990, 46, 467.
25 G. M. Sheldrick, University of Go¨ttingen, Germany, 1997.
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 1891–1897 | 1897
©