Syntheses, Structures, Bonding and Photoelectron Spectra of "Push-Pull"-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-?2λ3-iminophosphanes

Article abstract of DOI:10.1002/ejic.200300823

?²λ³-"Push-pull" iminophosphanes Ar_f-P=N-R, bearing an electron-acceptor substituent at phosphorus [Ar_f = 2,6-bis(trifluoromethyl)phenyl] and a donor group at nitrogen (R = tBu, NMe2), have been synthesized and characterized by NMR spectroscopy and X-ray analysis. Density functional calculations [B3LYP/6-311G(d,p)] have been carried out on different iminophosphanes: HP=NH (1), Ar_fP=NH (2), Ar_fP=NSiMe3 (3), Ar_fP=NtBu (4), HP=NNMe2 (5) and Ar_fP=NNMe2 (6) in order to determine the electronic effect of the Ar_f substituent and the influence of the donor group R on the stability of the monomeric species. A comparison of the theoretical results and UV photoelectron spectroscopy data for the iminophosphanes 4 and 6 is presented. Theoretical and experimental data suggest that for all iminophosphanes under investigation the ?-system of the Ar_f group is almost orthogonal to the ?_P=N system, preventing any stabilizing interaction between the ?_P=N and ?*_b1(aryl) orbitals previously observed for the Ar_fPH^- anion. Here, the Ar_f substituent effect is mainly steric.

Full text of DOI:10.1002/ejic.200300823

FULL PAPER
Syntheses, Structures, Bonding and Photoelectron Spectra of ‘‘Push-Pull’’-
Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes[‡]
Karinne Miqueu,[a] Jean-Marc Sotiropoulos,[a] Genevieve Pfister-Guillouzo,*[a]
Valentyn L. Rudzevich,[b] Heinz Gornitzka,[c] Vincent Lavallo,[d] and Vadim D. Romanenko[e]
Keywords: Iminophosphanes / X-ray diffraction / Photoelectron spectroscopy / Density functional calculations /
Ionization potentials
σ2λ3-‘‘Push-pull’’ iminophosphanes Arf−P=N−R, bearing an
electron-acceptor substituent at phosphorus [Arf = 2,6-bis(tri-
and UV photoelectron spectroscopy data for the iminophos-
phanes 4 and 6 is presented. Theoretical and experimental
fluoromethyl)phenyl] and a donor group at nitrogen (R = tBu, data suggest that for all iminophosphanes under investi-
NMe2), have been synthesized and characterized by NMR
spectroscopy and X-ray analysis. Density functional calcula-
tions [B3LYP/6-311G(d,p)] have been carried out on different
iminophosphanes: HP=NH (1), ArfP=NH (2), ArfP=NSiMe3
gation the π-system of the Arf group is almost orthogonal to
the πP=N system, preventing any stabilizing interaction be-
tween the πP=N and the π*b1(aryl) orbitals previously observed
for the ArfPH− anion. Here, the Arf substituent effect is
(3), ArfP=NtBu (4), HP=NNMe2 (5) and ArfP=NNMe2 (6) in mainly steric.
order to determine the electronic effect of the Arf substituent
and the influence of the donor group R on the stability of the
monomeric species. A comparison of the theoretical results
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
because of the inherent ‘‘electronegativity’’ of the P-N
double bond, most of the known iminophosphanes feature
π-donors (R2N, RO, R2P) or electron-rich alkyl/aryl sub-
stituents (tBu, Mes, Mes*) at the dicoordinated phosphorus
atom.[3Ϫ5] Compared with the rich chemistry of iminophos-
phanes having electron-donating substituents, little is
known about iminophosphanes containing electron-ac-
cepting groups. Notable exceptions are the heteroatom-sub-
stituted iminophosphanes ClϪPϭNMes* and TfOϪPϭ
NMes*. In these examples the XϪP bond tends to become
ionic due to the large difference in electronegativity between
phosphorus, chlorine and oxygen. This large difference in
electronegativity promotes the formation of a close ion-pair
[X]Ϫ[PNMes*]؉.[6Ϫ9] Theoretical studies of iminophos-
phanes, using simple models, have demonstrated that re-
placement of the hydrogen atom at phosphorus in HPϭNH
by more electronegative substituents (π-acceptors) results in
an appreciable strengthening of the double bond. At the
same time the Z-configuration becomes more stable with
respect to the E-configuration. Exactly opposite effects have
been predicted for the influence of the corresponding sub-
stituents at nitrogen.[10,11] This concept is strongly operative
in P-halo- and P-oxy-iminophosphanes, but its application
to highly sterically crowded P-carbosubstituted species has
evident limitations. We expected iminophosphanes bearing
electron-acceptor carbon substituents at the phosphorus
σ2λ3-Iminophosphanes, XPϭNR, have been the subject
of enthusiastic study for the last two decades because they
constitute a bridge between the classical chemistry of C-C
unsaturated systems and unconventional pπ-bonded com-
pounds of heavy main group elements.[1] Consequently, a
plethora of structures have been reported and charac-
terized, including several short-lived species.[2,3] In general,
[‡]
Application of Photoelectron Spectroscopy to molecular
properties, 67. Part 68: K. Miqueu, J.-M. Sotiropoulos, P.
`
´
Baylere, S. Joanteguy, G. Pfister-Guillouzo, H. Ranaivonjatovo,
´
J. Escudie, M. Bouslikhane, J. Mol. Struct. 2004, 690, 53Ϫ61.
[a]
´
Laboratoire de Chimie Theorique et Physico-Chimie
´
´
Moleculaire, CNRS UMR 5624, Universite de Pau et des Pays
´
de lЈAdour Avenue de lЈUniversite,
BP 1155, 64013 Pau Cedex, France
Fax: (internat.) ϩ 33-5-59407588
E-mail: genevieve.pfister@univ-pau.fr
Institute of Organic Chemistry, National Academy of Sciences
of Ukraine,
[b]
[c]
Murmanskaya St. 5, Kiev, 02094, Ukraine
´ ´
´
Laboratoire d’Heterochimie Fondamentale et Appliquee du
CNRS (UMR, 5069), Universite Paul Sabatier 118,
´
Route de Narbonne, 31062 Toulouse Cedex 04, France
Department of Chemistry, University of California Riverside,
CA 92521-0403, USA
[d]
[e]
Institute of Bioorganic Chemistry and Petrochemistry, National
Academy of Sciences of Ukraine,
Murmanskaya St. 1, Kiev, 02094, Ukraine
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
DOI: 10.1002/ejic.200300823
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2289

G. Pfister-Guillouzo et al.
FULL PAPER
atom would be interesting, since the presence of an elec- dichlorophosphane Mes*PCl2 with silylamides [LiN-
tron-acceptor substituent at the phosphorus atom should (SiMe3)R] leads exclusively to the diphosphene Mes*Pϭ
considerably increase the polarity of the PϭN double bond. PMes*.[3] We found that the interaction of ArfPCl2 with
Moreover, the combination of substituents with acceptor silylamides [LiN(SiMe3)R] proceeds by the ‘‘normal’’ way,
and donor properties at the PϭN bond (‘‘push-pull’’ substi- allowing the isolation of amino(chloro)phosphanes
tution) should lead to unusually stable XPϭNR species.
ArfP(Cl)N(SiMe3)R. Thus, treatment of ArfPCl2 with an
Recently, molecular design utilizing the highly electro- equimolar quantity of [LiN(SiMe3)2] in THF solution at
negative 2,6-bis(trifluoromethyl)phenyl group[12] allowed us Ϫ78 °C afforded the corresponding amino(chloro)phos-
to prepare the first phosphanide salt, [K([15]-crown- phane in virtually quantitative yield (Scheme 1). However,
5)2]ϩ[ArfPH]Ϫ, featuring a ‘‘naked’’ dicoordinated phos- elimination of Me3SiCl from ArfP(Cl)N(SiMe3)2 occurs
phorus anion.[13] Our observations indicate that the planar only at high temperatures (Ͼ180 °C) and leads to 1,3,2,4-
structure is a privileged form of the anion, due to a strong diazadiphosphetidine 3Ј instead of the expected monomeric
interaction between the pπ phosphorus lone-pair and the iminophosphane 3. The 19F NMR spectrum of 3Ј exhibits
π*b1(aryl) orbital (localized on the C1 and C4 atoms of the doublets at δ ϭ 23.0 ppm (4JF,P ϭ 72.3 Hz) and δ ϭ
aryl ring).Thus, the Arf group behaves like a π-electron ac- 27.4 ppm (4JF,P ϭ 134.7 Hz), corresponding to the reson-
ceptor and contributes considerably to the observed struc- ances of two magnetically non-equivalent ortho-CF3 groups
ture of the ArfPHϪ anion. Along these lines, desiring to on the Arf substituent. The 31P resonance is observed as a
study the P-carbosubstituted iminophosphanes bearing multiplet at δ ϭ 277.3 ppm.
electron-withdrawing substituents, we turned our atten-
tion to P-[2,6-bis(trifluoromethyl)phenyl-σ2λ3-iminophos-
phanes. Two different stabilizing interactions may be envi-
sioned in these compounds because of energetically closely
spaced π (PϭN) and σ (combination of lone-pair at P and
N) frontier orbitals: (i) nϩ (trans) or nϪ (cis) Ǟ π*b1(aryl) [π
system of Arf orthogonal to the πPϭN system, as observed
for the carbene (iPr2N)2PCArf][14] or (ii) πPϭN Ǟ π*b1(aryl)
(π system of Arf coplanar to πPϭN system, as previously
observed for ArfPHϪ).[13] The latter type of stabilizing in-
teraction is related to electronic effects previously observed
for the ArfPHϪ anion and would be especially pronounced
in the case of ‘‘push-pull’’ substitution.
This paper deals with the preparation and characteriz-
ation of a series of iminophosphanes ArfϪPϭNR. Along
with our exploration into the synthesis of new and highly
reactive PN multiple-bond systems, we performed a theo-
retical analysis of their structures to study the effect of the
Arf group and the variation of the donor group R. The
Scheme 1
following iminophosphanes were studied theoretically:
HPϭNH (1), ArfPϭNH (2), ArfPϭNSiMe3 (3), ArfPϭ
The molecular structure of 3Ј is presented in Figure 1.
NtBu (4), HPϭNNMe2 (5) and ArfPϭNNMe2 (6). Full The four-membered P2N2 cycle is planar, as observed in
characterization of the iminophosphanes 4 and 6 included most other trans-1,3,2,4-diazadiphosphetidines.[16] The Arf
an investigation by NMR spectroscopy and X-ray analysis. rings form a twist angle of 39.3°. The geometry around the
A comparison of the results of our theoretical calculations nitrogen atoms is trigonal planar. The average PϪN bond
˚
[B3LYP/6-311G(d,p)] and UV/PE studies is also reported.
length is about 1.722 A and the PNP and NPN bond angles
are 95.73° and 84.27°, respectively.
In contrast to N,N-disilyl analogues, thermolysis of
ArfP(Cl)N(SiMe3)tBu (120 °C, 80 h) afforded the mono-
meric iminophosphane 4. The latter was characterized by
Results and Discussion
Iminophosphanes containing a CPϭN skeleton are rare. mass spectrometry and NMR spectroscopy. The 31P NMR
These compounds are usually unstable due to their dimeriz- spectrum shows a septet at δ ϭ 412.4 ppm (4JF,P ϭ 28 Hz),
ation or oligomerization and can only be isolated in the in a region characteristic of the CPϭN backbone.[2] The X-
presence of bulky substituents. Very effective in this sense is ray crystal structure of 4 is shown in Figure 2. Molecules
the 2,4,6-tri-tert-butylphenyl group (Mes*), which provides of 4 adopt a trans geometry and the PϭN bond length of
˚
access to a series of stable RϪPϭNMes* compounds upon 1.537 A is consistent with a bond order of two; it is 0.019
[17]
˚
condensation of phosphorus chlorides RPCl2 with the silyl- A shorter than that in trans Mes*-PϭN-tBu.
The PϪC
˚
amide [LiN(SiMe3)Mes*] followed by a 1,2-elimination re- bond length (1.866 A) falls in the normal range for a single
action.[15] Iminophosphanes Mes*PϭNR are not accessible bond. The aromatic ring is in an orthogonal orientation to
by this route since the reaction of the sterically crowded the CPN plane (the corresponding dihedral angle is 99.8°).
2290
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300

“Push-Pull”-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes
FULL PAPER
(δP ϭ 478 ppm).[19] This property is without precedent in
iminophosphane chemistry and suggests that the PϭN
bond strength is dramatically reduced by ‘‘push-pull’’ sub-
stitution. Interestingly, the iminophosphane 7 (δP
ϭ
173.1 ppm), which can be obtained by a similar route start-
ing from iPr2NPCl2 and Me2NN(SiMe3)Li, undergoes di-
merization to form trans-[iPr2NPNNMe2]2 (δP ϭ 74.2 ppm)
instead of disproportionation. We found, however, that
chloroform as solvent promotes Me3SiCl elimination
reaction from P(Cl)ϪN(SiMe3)R moiety. Thus, when
ArfP(Cl)ϪN(SiMe3)2NMe2 was treated with anhydrous
CHCl3 (25 °C, 14 h), Me3SiCl elimination with formation
of 6 takes place quantitatively. In 6 the signal for the two-
coordinate phosphorus atom is shifted drastically up field
(δP ϭ 224.3 ppm) in comparison to that of 4 (δP
ϭ
412.4 ppm).
Figure 1. Crystal structure of (ArfPNSiMe3)2 (3Ј); hydrogen atoms
˚
are omitted for clarity; selected bond lengths (A) and bond angles
(deg): P1ϪN1(A) 1.713(2), P1(A)ϪN1(A) 1.714(2), P1ϪC1
1.935(2); P1ϪN1ϪP1(A) 95.73(1), N1ϪP1ϪN1(A) 84.27(1)
Scheme 2
Bright-yellow crystals of 6 were grown from a saturated
toluene solution. The molecular structure of the compound
is shown in Figure 3. Essentially, the molecule adopts a
trans-configuration and the aromatic ring system is almost
orthogonal to the CPN system (the corresponding dihedral
angle is 110°). The planar-coordinated N atoms of the hy-
Figure 2. Crystal structure of ArfPϭNtBu (4); hydrogen atoms are
˚
omitted for clarity; selected bond lengths (A) and bond angles
(deg): P1ϪN1 1.537(3), P1ϪC1 1.866(4), N1ϪC6 1.489(4);
C1ϪP1ϪN1 99.73(1), C6ϪN1ϪP1 123.82(0)
The C1P1N1 and C6N1P1 angles are 99.73° and 123.82°,
respectively. In the related iminophosphane RfPϭNRf [Rf ϭ
2,4,6-(CF3)3C6H2] the angle around the phosphorus is
99.81°, while the angle at nitrogen is more opened
(130.22°).[18]
The strategy for the preparation of 4 was successfully ex-
tended to the synthesis of iminophosphanes 6 containing
the π-donor NMe2 group at the nitrogen atom (Scheme 2).
Compared to ArfP(Cl)ϪN(SiMe3)R (R ϭ Me3Si, tBu), the
corresponding dimethylhydrazino derivative splits off Me3-
SiCl under considerably milder conditions (0.05 Torr, Ͻ 100
°C). However, attempts to isolate 6 in pure form by vacuum
distillation failed. In contrast to the quite thermally stable
compound 4, compound 6, which is stable for extended per-
iods of time in pure form and in solution, easily dispro-
Figure 3. Crystal structure of ArfPϭNNMe2 (6); hydrogen atoms
˚
are omitted for clarity; selected bond lengths (A) and bond angles
(deg): P1ϪN1 1.629(1), P1ϪC1 1.863(5), N1ϪN2 1.319(2);
portionates on heating to form the diphosphene ArfPϭPArf C1ϪP1ϪN1 95.31(7), P1ϪN1ϪN2 121.13 (1)
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2291

G. Pfister-Guillouzo et al.
FULL PAPER
˚
drazine moiety and the P atom of the double-bond system
Table 1. Bond angles (°) and bond lengths (A) for the minima
(mini: Arf almost orthogonal to the PNR moiety) and transition
states (ts: Arf coplanar to the PNR moiety) of HPϭNH (1), ArfPϭ
NH (2), ArfPϭNSiMe3 (3), ArfPϭNtBu (4), HPϭNNMe2 (5),
ArfPϭNNMe2 (6); corresponding energies in ua (Eelec for electronic
energy and Erep for repulsive energy)
are located in one plane (three-center, four π-electron sys-
˚
tem). The PϪN bond in 6 is the longest (1.629 A) ever
found for iminophosphanes.[20,21] The opposite effect is ob-
˚
served for the NϪN single bond (1.319 A). Thus, the tend-
ency of the iminophosphane 6 to disproportionate at high
temperatures can be inferred from the remarkably long
PϪN bond, which is evident in the X-ray structure analysis
of the molecule.
Parameter cis
HPϭNH (1)
trans (mini)
trans (ts)
/
/
/
PϭN
1.574 (1.539)[10] 1.588 (1.578)[a][10]
(1.611)[b][38]
(1.618)[b] [38]
Theoretical and PE Spectroscopic Studies
PNH
118.52 (120.0)[10] 109.79 (112.3)[10]
(113.7)[b] [37] (107.6)[b] [37]
105.95 (104.8)[10] 98.77 (99.9)[10]
HP؍NH (1), ArfP؍NH (2) and ArfP؍NSiMe3 (3)
HPN
Eelec
Erep
-446.929393
49.626276
-446.859285
49.555519
In order to estimate the effect of the Arf substituent on
the CPϭN part we compared the HPϭNH (1) and ArfPϭ
NH (2) model molecules. The geometrical parameters of
these species are summarized in Table 1. Two minima were
found on the potential-energy surface corresponding to the
cis and trans isomers. For 2, the π-system of the aryl sub-
stituent in both isomers is almost orthogonal to the πPϭN
ArfPϭNH (2)
PϭN
PϪCArf
PNH
1.562
1.576
1.571
1.893
105.59
1.920
1.890
120.91
110.66
system (the dihedral angles for cis and trans structures are CArfPN
108.23
-2624.280808
1321.595174
100.14
-2624.457073
1321.774013
110.53
-2618.133251
1315.457185
Eelec
116.6° and 115.6° respectively). The PϪN bond lengths in
Erep
cis- and trans-2 are slightly shorter than those in 1. The cis-
2 isomer is more stable than trans-2 by 1.42 kcal/mol. This
is in agreement with an opening of the P and N bond angles
ArfPϭNSiMe3 (3)
on passing from trans-2 to cis-2. Unlike 1 and 2 only the
PϭN
1.539
1.957
154.63
107.29
Ϫ3764.610290
2053.155544
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
cis-3 isomer was found on the potential energy surface, as
was previously observed for ClPϭNSiMe3 and ClAsϭ
NSiMe3.[22] The aromatic ring in 3 is almost orthogonal to
the plane of the CPN skeleton (dihedral angle is 89.6°).
Such a conformation excludes any interaction between the
π-system of the PϭN bond and the π*b1(aryl) orbital of the
PϪCArf
PNSi
CArfPN
Eelec
Erep
ArfPϭNtBu (4)
˚
aromatic ring. As a consequence, the PϪC (1.957 A) and
˚
PϪN (1.539 A) bond lengths correspond to a single and
PϭN
1.546
1.962
146.14
111.86
Ϫ3378.517746
1918.535908
1.576
1.895
99.34
124.68
Ϫ3347.618957
1887.636238
1.567
1.902
126.17
104.85
Ϫ3338.250879
1878.275201
double bond, respectively. The latter is longer than the ex-
P-CArf
PNCtBu
CArfPN
Eelec
perimental value for the PϪN bond of cis-ClPϭNMes*
[6]
˚
(1.495 A). The silyl group at the nitrogen atom leads to a
˚
˚
shortening of the PϭN bond [1.574 A (cis-1), 1.562 A (cis-
Erep
˚
2), 1.539 A (cis-3)] and an opening of the bond angle at
nitrogen, as was previously observed for FPϭNSiH3.[23]
Moreover, we observed a lengthening of the PϪC bond.
For the cis isomers of 1, 2 and 3 the energetic positions
of the nϩ, π and nϪ orbitals as well as the plot[24] of the
MO are displayed in Figure 4. For cis-2, the antibonding
combination of lone pairs (nϪ) is mixed with the σPC orbital
while the bonding combination of lone pairs (nϩ) is mixed
with the πb1(aryl) orbital of the Arf ring. For trans-2, the
bonding combination of lone pairs (nϩ) is mixed with the
σPC orbital while the antibonding combination of lone pairs
(nϪ) is mixed with the σPC and the πb1(aryl) orbitals (Fig-
ure 5).
Thus, in this case, the stabilizing effect of the CF3 groups
is attenuated or counterbalanced by destabilizing interac-
tions with the σPC orbital and the πb1(aryl) orbital, respec-
tively (see Figure 4 and Figure 5). For 2, the energetic posi-
tion of the nϪ orbital is weakly modified when going from
1 to 2. At the same time the nϩ orbital is destabilized.
HPϭNNMe2 (5)
PϭN
NϪN
PNN
HPN
Eelec
1.629
1.301
131.82
102.98
Ϫ758.689409
227.388860
1.655
1.303
122.58
93.38
Ϫ759.664804
228.363706
Ϫ
Ϫ
Ϫ
Ϫ
Erep
ArfPϭNNMe2 (6)
PϭN
PϪCArf
NϪN
PNN
CArfPN
Eelec
1.600
1.937
1.300
142.12
110.28
Ϫ3202.638297
1765.966288
1.637
1.878
1.304
123.93
96.70
Ϫ3173.831281
1737.156040
1.629
1.875
1.296
124.54
102.24
Ϫ3168.455747
1731.785927
Erep
[a]
[b]
SCF double zeta basis set. QCISD/LanL2DZdp.
www.eurjic.org Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
2292
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

“Push-Pull”-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes
FULL PAPER
We studied the rotation process of the aryl group theo-
retically. One transition state has been found on the poten-
tial energy surface. It corresponds to a structure where the
π-system of the aromatic ring is coplanar with the πPϭN
system (4ts). The latter is energetically very close to the
minimum (4.38 kcal/mol). Thus, taking into account this
weak energetic difference, a free rotation of the Arf group
can occur in the gas phase. The geometric parameters of
4mini and 4ts are summarized in Table 1. It is noteworthy
to mention that the geometric parameters for both rotamers
are similar in spite of the different positions of the aromatic
˚
˚
ring. Moreover, the PϭN (1.576 A for 4mini; 1.567 A for 4
˚
˚
ts) and PϪC (1.895 A for 4mini; 1.902 A for 4 ts) bonds
are slightly longer than the experimental ones (1.537 A and
1.866 A, correspondingly). In the same way, the calculated
˚
˚
KohnϪSham energies (Figure 5) are energetically close (nP
ϩ nN, σPC: Ϫ 6.44 eV for 4mini and Ϫ 6.33 eV for 4ts;
πPϭN: Ϫ7.64 eV for 4mini and Ϫ7.49 eV for 4ts). All these
observations show that the orientation of the aromatic ring
seems to have a negligible effect on the geometric and elec-
tronic structures of ArfPϭNtBu. In contrast to the co-
planar structure of the [ArfPH]Ϫ anion where only the in-
teraction between nπ Ǟ π*b1(aryl) occurs (9.4 kcal/mol),[13]
P
for 4ts the stabilizing πPϭN Ǟ π*b1(aryl) interaction [4.8 kcal/
mol (NBO calculation)] is added to the destabilizing inter-
action πPϭN Ǟ πb1(aryl) (the plot of the molecular orbital in
Figure 7 visualizes these interactions). On the contrary, for
4mini the stabilizing (nP Ǟ π*b1(aryl)) interaction is not ob-
served.
Considering the free PϪC rotation in the gas phase, the
UV-PE spectrum (Figure 6, a) corresponds to the super-
position of all the rotamers’ spectra close to 4mini and 4ts.
Thus, taking into account this observation as well as the
nature of the molecular orbital, the ∆SCF values for the
first ionic state (4 mini: nP ϩ nN ϩσPC: 8.25 eV; 4 ts: nP ϩ
nN ϩσPC: 8.10 eV) and the energetic position of the
KohnϪSham orbitals for 4mini and 4ts (Table 2), we as-
signed the first band in the PE spectrum (8.5 eV) to the
removal of an electron from the nP ϩ nN orbitals mixed
with the σPC orbital. The second band (centered at 10 eV),
which is more intense and broader than the first band, is
associated with the ionization of the πPϭN Ϫ πb1(aryl) and
Figure 4. KohnϪSham energies in eV and KohnϪSham orbitals
calculated with the B3LYP functional hybrid and the 6-311G(d,p)
basis set for the cis isomers of HPϭNH (1) and ArfPϭNR [R ϭ
H (2), SiMe3 (3); πCC(Arf) almost perpendicular to πPϭN
]
The H/SiMe3 substitution promotes destabilization of the
nϩ, nϪ and π orbitals. The destabilization of the nϪ orbital
is more important than that of the nϩ orbital because of
the strong p character of the nitrogen lone pair in the nϪ
orbital. In fact, for the previous system only the push effect
is observed.
π
PϭN ϩ πb1(aryl) orbitals as well as the πa2 ionizations of the
aromatic ring. Finally, the ionization at 11.0 eV was as-
signed to the removal of an electron from the nP Ϫ nN or-
bitals (in interaction with the σPC orbital).
ArfP؍NtBu (4)
In addition to X-ray analysis, compound 4 was studied
Surprisingly, the energetic positions of the nϩ and π ioni-
by coupling the Ultraviolet Photoelectron Spectroscopy in zations of 4 were found to be close to the spectroscopic
the gas phase (UV-PES) and calculations. The UV-PE spec- findings for tBuPϭNtBu. Indeed, the HeI PE spectrum of
trum of 4 presents a first ionization at 8.5 eV, a second band the latter presents two first ionizations at 8.11 and 9.70 eV,
at 10.0 eV with a broad shoulder at 9.8 eV and then a broad which have been assigned to the nϩ and πPN orbitals,
signal with different shoulders at 11.0 and 11.8 eV (Fig- respectively.[25] The close energetic position of the πPN or-
ure 6, a).
bital for 4 and tBuPϭNtBu (9.8 eV and 9.7 eV, respectively)
In contrast to 3, the trans isomer of 4 is slightly more means that the Arf group has a destabilizing effect on the
stable than the cis isomer (0.72 kcal/mol). The energetically π-system close to the tBu group.
privileged form trans-4mini features an aromatic ring al-
most perpendicular to the CPN plane (dihedral angle is gap between the nϩ orbitals of 4 (σ-attractor effect of Arf)
116.1°), in agreement with the X-ray structure. and tBuPϭNtBu (σ-donor effect of tBu), whereas the gap
As for the σ-bond system, one could expect an important
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2293

G. Pfister-Guillouzo et al.
FULL PAPER
Figure 5. KohnϪSham energies in eV and KohnϪSham orbitals calculated with the B3LYP functional hybrid and the 6-311G(d,p) basis
set for the trans isomers of HPϭNH (1), HPϭNNMe2 (5) and ArfPϭNR [R ϭ H 2mini; R ϭ tBu 4mini; R ϭ NMe2 6mini; Arf almost
orthogonal to the PNR moiety]; KohnϪSham energies in brackets for the transition state (Arf planar to the PNR moiety)
Figure 7. Plot of the πPϭN Ϫ πb1(aryl) (ϩ π*b1(aryl)) orbital for the
transition state (Arf coplanar to the PNR moiety) of ArfPϭNH (2
ts), ArfPϭNtBu (4 ts) and ArfPϭNNMe2 (6 ts); plot of the nP
Ϫ
π*b1(aryl) for the minimum of ArfPHϪ
Figure 6. HeI photoelectronic spectra of a) ArfPϭNtBu (4) and b)
ArfPϭNNMe2 (6)
anced by the destabilizing interaction between the bonding
or antibonding combination of lone pairs and the σPC or-
was actually found to be relatively weak (0.4 eV). This is bital. The expected stabilizing effect of the Arf group is not
consistent with the previous theoretical conclusion: the really observed either on the σ- or the π-systems. Indeed,
strong stabilizing effect of the fluorinated aryl group is bal- tBuPϭNtBu and ArfPϭNtBu present close electronic
2294
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300

“Push-Pull”-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes
FULL PAPER
Table 2. KohnϪSham energies in eV and KohnϪShan orbitals for the minimum (mini) and transition state (ts) of ArfPϭNSiMe3 (3),
ArfPϭNtBu (4) and ArfPϭNNMe2 (6); ∆SCF values (in eV) in brackets
3
4
6
Theor.
3mini
Theor.
4mini[a]
Exp.
Theor.
Exp.
6
4ts
4
6mini[a]
6ts
Ϫ6.49
nP Ϫ nN
Ϫ6.44 (8.25)
nP ϩ nN ϩ σPC
Ϫ6.33 (8.10)
nP ϩ nN ϩ σPC
band at 8.5 eV
Ϫ5.74 (7.51)
πPϭN Ϫ nNamino πPϭN Ϫ nNamino
Ϫ5.74 (7.44)
band at 7.8 eV
Ϫ7.80
Ϫ7.64
Ϫ7.49
πPϭN Ϫ πb1(aryl)
Ϫ6.67
nP ϩ nN ϩ σPC
Ϫ6.60
nP ϩ nN ϩ σPC
band at 8.8 eV
band at 9.5 eV
πb1(aryl) (Ϫnϩ) πPϭN (Ϫπb1(aryl)
)
Ϫ7.92
πPϭN Ϫ πSiC
Ϫ8.05
πa2
Ϫ8.09
πa2
band centred at
10.0 eV
Ϫ7.73
πb1(aryl)
Ϫ7.74
πa2(aryl)
[b]
[c]
Ϫ8.19
πa2
Ϫ8.11
πPϭN (ϩ πb1(aryl)
Ϫ8.58
πPϭN ϩ πb1(aryl)
Ϫ7.78
πa2(aryl)
Ϫ7.91
πb1(aryl)
)
Ϫ8.24
σSiC
Ϫ9.02
nP Ϫ nN ϩ σPC
Ϫ8.94
nP Ϫ nN ϩ σPC, σCC
band at 11.0 eV Ϫ9.27
nP Ϫ nN ϩ σPC
Ϫ9.20
nP Ϫ nN ϩ σPC
band at 11.0 eV
band at 11.6 eV
Ϫ9.13
πPϭN ϩ πSiC
Ϫ9.50
σCC
Ϫ9.49
nP Ϫ nN ϩ σNC, σCC
band at 11.8 eV Ϫ9.71
‘‘πNϭN’’
Ϫ9.92
‘‘πNϭN’’
[a]
[b]
[c]
πCC(Arf) almost orthogonal to the πPϭN system.
Symmetrical orbital against the C1C4 axis of the aryl group. Anti-symmetrical
orbital against the C1C4 axis of the aryl group.
properties [π: 9.7 eV (4) and 9.8 eV (tBuPϭNtBu); n: 8.5 eV
(4) and 8.11 eV (tBuPϭNtBu)]. Thus, Arf seems to exert a
kinetic rather than a stabilizing electronic effect on the
ϪPϭNtBu system bonds. In passing, we note that the 3 Ǟ
3Ј dimerization process cannot be explained either by the
nature of the energetic position of the π and π* orbitals or
the polarity of the PϭN bond. In fact, for 3 and 4, the gap
between the πPϭN and the πPϭN orbitals is relatively large
and more pronounced in the case of the silyl derivative
(5.64 eV vs. 5.39 eV: see Figure 4 and 5). Moreover, the po-
larity of the PϭN double bonds are also close, although
slightly higher for 3 (Figure 8). On this basis, it seems that
the reason for the higher stability of 4 in comparison with
3 is that SiMe3 is a less-bulky protecting group than tBu.
Indeed, the SiϪC bond is longer than the CϪC bond and
the bond angle at Si is more open than the bond angle at
C. Consequently the dimerization is easier with SiMe3.
Figure 8. NBO charges (total and π) for ArfPϭNSiMe3 (3) and
ArfPϭNtBu (4); polarity of the PN bond in brackets
ArfP؍NNMe2 (6)
ilizing interaction between the amino nitrogen lone-pair
In order to determine the role of the Arf group on the and the π*PϭN orbital [nNǞ π*PϭN ϭ 77 kcal/mol (cis);
ϪPϭNϪNMe2 moiety, a theoretical study of the model nNǞ π*PϭN ϭ 76.5 kcal/mol (trans)]. The trans form fea-
˚
molecule HPϭNNMe2 (5) was undertaken. The isomer tures a PϪN bond (1.653 A) that is significantly longer than
˚
trans-5 was found to be slightly more stable than the cis the corresponding distance in 1 (1.588 A). The NϪN bond
˚
˚
isomer (0.22 kcal/mol). This corresponds to the form where (1.302 A) is intermediate between a single (1.450 A) and
˚
the electronic energy is more important (see Table 1). The a double bond (1.250 A). As can be seen in Figure 5, the
geometrical parameters of the cis and trans forms are de- replacement of H by an NMe2 group at the nitrogen atom
scribed in Table 1. In contrast to the previously studied im- destabilizes the πPϭN orbital by 3.15 eV (Figure 5). The
inophosphanes Tmp-PϭNϪN(SiMe3)2,[26] (Tmp ϭ 2,2,6,6- NMe2 group also has an important influence on the ener-
tetramethylpiperidino) and tBu2PϪPϭNϪN(SiMe3)2,[20] getic position of the antibonding combination of lone pairs
the NMe2 group in 6 is coplanar with the CArf PN moiety. mainly localized on nitrogen. On the other hand, the bond-
This orientation involves the presence of an important stab- ing combination of lone pairs is less affected by this sub-
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2295

G. Pfister-Guillouzo et al.
FULL PAPER
stituent (the difference in the energies is 1.48 eV and
0.52 eV, respectively).
Next we carried out calculations on compound 6. Two
minima corresponding to the trans and cis isomers were
found on the potential energy surface. In both isomers, the
amino nitrogen atom is sp2 hybridized and the NMe2 group
is coplanar with the CPN moiety, thus establishing a three-
center, four-electron system. The trans form 6mini (energetic
minimum) is more stable than the cis form by 2.07 kcal/mol
because of less steric hindrance (see Table 1, Erep). For
6mini the dihedral angle between the Arf group and the
CPN system is 126.4°. The substitution of H by Arf in 5
has only a weak influence on the geometrical parameters of
˚
the CPN system (Table 1). The PϪC bond length (1.878 A)
remains characteristic of a single bond. These theoretical
results are in agreement with the RX structure (Figure 3).
As previously observed, the structure with the Arf group
coplanar with the PNN moiety (6ts) corresponds to a tran-
sition state. It is energetically very close to the minimum
(3.3 kcal/mol) and should involve a free rotation of the aro-
matic group in the gas phase. For 6ts, the PϪN, PϪC and
NϪN bond lengths are slightly shorter than in 6mini.
The calculated NBO charges of the ArfPϭNϪR (R: tBu
4, NMe2 6) system show that the phosphorus charge is
about 0.961 au for 4 and 0.638 au for 6. This modification
affects the 31P NMR chemical shift (4: δ ϭ 412.4 ppm; 6:
δ ϭ 224.2 ppm). The peak due to the NMe2-substituted
phosphorus atom appears at higher field than the tBu-sub-
stituted phosphorus atom. This result is in agreement with
those previously reported by Yoshifuji et al.[1b] on the ϪPϭ
PϪ part.
Figure 9. Plot of the molecular orbitals for the minimum of
ArfPϭNNMe2 (6mini)
The weak geometrical changes between the forms 5, interaction is counterbalanced by the stabilizing πPϭN
Ǟ
6mini and 6ts lead to negligible modifications of their elec- π*b1(aryl) interaction (see MO plots Figure 7). However,
tronic structure. Figure 9 summarizes the energetic posi- it should be noted that even when the aromatic group is
tions of the nϩ, nϪ and πPϭN orbitals for these compounds. coplanar with the PNN system the πPϭN Ǟ π*b1(aryl) inter-
The inductive σ-attractor effect of Arf exerts a weak stabili- action is not important enough to allow a strong delocaliza-
zing influence on the nϩ and nϪ orbitals (0.2Ϫ0.3 eV for tion of the πPϭN system. Perhaps, the presence of strong
nϩ and 0.37Ϫ0.44 eV for nϪ); this stabilization is more pro- σ-donor groups on the amino nitrogen would allow the sta-
nounced for the nϪ orbital since it is mainly localized on bilizing πPϭN Ǟ π*b1(aryl) interaction to be more important
phosphorus. The plots of the combination of lone pairs than the destabilizing πPϭN Ǟ πb1(aryl) interaction. In this
show a destabilizing interaction with the σPC orbital (as case a structure close to the ArfPHϪ anion structure would
previously observed for 3 and 4), which reduces the stabiliz- be observed.
ing inductive effect of the CF3 groups. This is the reason
We have recorded the HeI PE spectrum of 6 in order to
why the energetic positions of the nϩ and nϪ orbitals in 5 confirm the modifications of the electronic structure of the
and 6 are not strongly modified. In the same way, whatever CPϭN part on going from 4 to 7 (Figure 6b). It presents
the orientation of the fluorinated aromatic group, the sub- three first-ionization bands at 7.8, 8.8 and 9.5 eV which are
stitution on phosphorus by Arf group seems to have no ef- lower in energy than the first ionizations of ArfPϭNtBu
fect on the energetic position of the πPϭN orbital. Indeed, (8.5, 10.0 and 11.0 eV). The ∆SCF values (6mini: πPϭN
Ϫ
the KohnϪSham energies are similar for these three com- nNamino ϭ 7.51 eV; 6ts: πPϭN Ϫ nNamino ϭ 7.44 eV) as well
pounds [Ϫ5.68 (5), Ϫ5.74 (6mini), Ϫ5.74 eV (6ts)]. For 6ts, as the KohnϪSham energy orbitals allowed us to assign the
taking into account the orientation of the aryl group, we first band at 7.8 eV to the removal of an electron from the
might expect an interaction between the πb1(aryl) orbital of (πPϭN Ϫ nNamino Ϫ π*PϭN) orbital of all rotamers around
Arf and the πPϭN system. In fact, the presence of a planar 6mini and 6ts (see Figure 9); the second band at 8.8 eV was
amino group coplanar with the PNN moiety involves a de- assigned to the phosphorus and nitrogen bonding combi-
stabilization of the πPϭN orbital (interaction nN Ǟ πPϭN). nation of lone pairs (nP ϩ nN) for the different rotamers.
Consequently, the energy gaps πPϭN/π*b1(aryl) and πPϭN
/
The experimental gap (1 eV) between the first two orbitals
πb1(aryl) are decreased and increased, respectively. In the is theoretically well represented (0.86Ϫ0.93 eV). The third
particular case of 6ts, the strong destabilizing πPϭN Ǟ πb1(aryl) ionization at 9.5 eV corresponds to the removal of an elec-
2296
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300

“Push-Pull”-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes
FULL PAPER
tron from the πa2 orbitals of the aromatic ring. We can note into account the strong s character of the phosphorus lone
an inversion of the first two orbitals. Compared to 4 (nϩ, pair (phosphorus angle shrunk), this interaction is not ef-
πPϭN for 4 and πPϭN, nϩ for 6), the πPϭN orbital is being ficient. In fact, in these compounds the Arf group acts
destabilized because of the interaction with the nitrogen mainly as a sterically protective ligand. The stabilizing effect
lone pair of the amino group. The following bands at 11.0 of Arf is not efficient in the σ system because it is attenuated
and 11.6 eV are assigned to the ionization from the (nP Ϫ by a destabilizing interaction between the phosphorus and
nN) orbital and the (πPϭN ϩ nNamino ϩ π*PϭN) orbitals, nitrogen combination of lone pairs and the σPC orbital.
respectively. In fact, the plot of this latter looks like the plot Moreover, in spite of a different electronic effect between
of a πNϭN orbital, since the interaction between the πPϭN SiMe3 and tBu, the isolation of the monomer in the latter
and π*PϭN orbitals cancels the weight on the phosphorus case can only be explained by a smaller protecting effect of
atom (Figure 9).
the SiMe3 substituent compared to tBu.
In summary, previous works on the effect of the Arf
In addition, all these results show that the Arf group only
group on the stabilization of the reactive part of the mol- stabilizes a system which presents a weakly nucleophilic
ecule have shown that this latter could act as a spectator lone pair with a strong p character. In this case, it can be-
group or a π-acceptor group. For instance, for the two fol- have like an acceptor group with the π*b1(aryl) orbital. Thus,
[14]
lowing compounds: the carbene ArfCP(NiPr2)2
and the it seems interesting to use Arf in order to stabilize anionic
anion ArfPHϪ, [13] a delocalization of the carbene lone pair species with a heteroatom. This substituent could allow us
(carbene) or the π phosphorus lone pair (anion) in the Arf to stabilize the singlet state of phosphinidenes and homol-
˚
group was observed, respectively. The CcarbϪCaryl (1.390 A) ogues.
˚
or PϪCaryl (1.794 A) bonds are short and the
C
A(aryl)ϪCB(aryl) or CA(aryl)ϪCBЈ(aryl) bonds [CA(aryl): carbon
Experimental Section
linked to the carbon center or phosphorus, CB(aryl) and
C
are longer than the other bonds of the ring (1.43Ϫ1.44 A
compared to 1.37Ϫ1.39 A), indicating a delocalization of
BЈ(aryl): carbon in α position to CA(aryl)] of the Arf groups
General Remarks: All reactions and manipulations were carried out
under argon using standard Schlenk techniques. Solvents were
dried according to the appropriate method: dichloromethane and
chloroform with P4O10, pentane and hexane with calcium hydride,
toluene, xylene, tetrahydrofuran and diethyl ether with sodium/
benzophenone.
˚
˚
the carbene lone pair or the negative charge (phosphanide
anion) over the ring. In this case, the Arf group behaves
like a π-electron acceptor by the π*b1(aryl) orbitals of the
aryl group.
NMR spectra were recorded on Bruker AC200, and WM250 spec-
A recent publication[27] has shown that the potentially π-
acceptor Arf group can also act as a spectator group. In-
deed, for the amino(aryl)carbene ArfCN(Me)tBu, it has
1
trometers. H and 13C chemical shifts are reported in ppm relative
to tetramethylsilane as an external reference. 19F and 31P NMR
downfield chemical shifts are expressed with a positive sign relative
to external CF3COOH and 85% H3PO4, respectively. Mass spectra
were obtained on a Nermag R 10Ϫ10 instrument. The photoelec-
tron spectra were recorded on a Helectros 0078 instrument
equipped with a 127° cylindrical analyser and monitored by a
micro-computer supplemented with a digital analogic converter.
The spectra were calibrated with the known auto-ionization of he-
lium at 4.98 eV [HeII(He)] and nitrogen ionization at 15.59 eV.
˚
been shown that the CcarbϪCaryl bond is long (1.453 A), the
carbene bond angle acute and the CϪC bonds of the aryl
group quite similar (1.37Ϫ1.42 A), which indicates that the
Arf group does not interact with the carbene lone pair and
is therefore a spectator.
In our case [iminophosphanes ArfPϭNtBu (4) and
ArfPϭNNMe2 (6)], all the CϪC bonds of the aryl group
are almost similar (1.38Ϫ1.41 A) and the PϪCaryl bond
quite long (single bonds: 1.866 A for 4 and 1.863 A for 6).
We did not observe a shortening of the PϪCaryl bond or a
lengthening of the CA(aryl)ϪCB(aryl) or CA(aryl)ϪCBЈ(aryl)
bonds. These geometrical data can be compared to the pre-
vious ones and allow us to conclude that the Arf substituent
effect is mainly steric.
˚
˚
ArfP(Cl)؊N(SiMe3)2: A 1.6  solution of nBuLi in hexane
(6.92 mmol) was added to a solution of HN(SiMe3)2 (1.12 g,
6.92 mmol) in THF (8 mL) at Ϫ50 °C. The mixture was then
warmed to ambient temperature and stirred for 1 h. This solution
of LiN(SiMe3)2 was added dropwise to a solution of ArfPCl2
(2.18 g, 6.92 mmol) in THF (5 mL) at Ϫ80 °C. The reaction mix-
ture was slowly warmed to ambient temperature, stirred for 1 h and
the solvents evaporated. Pentane was added to the residue and the
precipitated LiCl was filtered off. Removal of solvent and volatiles
in vacuo yielded ArfP(Cl)N(SiMe3)2 as a yellow oil. Yield 86%
(95% pure by NMR). 1H NMR (CDCl3): δ ϭ 0.02 (s, 9 H, SiMe3),
˚
˚
Conclusion
3
3
6.59 (t, JH,H ϭ 7 Hz, 1 H, p-Harom), 7.82 (d, JH,H ϭ 7 Hz, 2 H,
m-Harom) ppm. 13C NMR (CDCl3): δ ϭ 4.1 (d, JP,C ϭ 7.4 Hz,
3
The experimental (NMR, X-rays and UV Photoelectron
Spectroscopy data) and theoretical studies on the imino-
phosphanes ArfϪPϭNR (R: tBu, NMe2) show that the Arf
group is orthogonal to the PNR moiety. This orientation
could have allowed an interaction between the phosphorus
lone pair and the π*b1(aryl) orbital of the Arf group, as pre-
viously observed for (iPr2N)2PCArf (p character of the car-
3
1
SiMe3), 124.1 (dq, JP,C ϭ 5.6, JP,C ϭ 275.6 Hz, CF3), 129.3 (d,
4JP,C ϭ 2.8 Hz, p-Carom), 130.7 (m, m-Carom), 134.7 (dq, JP,C
ϭ
2
2
1
11.1, JC,F ϭ 32.4 Hz, o-Carom), 149.0 (d, JP,C ϭ 110.9 Hz, ipso-
Carom) ppm. 19F NMR (CDCl3): δ ϭ 24.45 (d, 4JF,P ϭ 39 Hz) ppm.
31P{1H} NMR (CDCl3): δ ϭ 143.9 (sept, JF,P ϭ 39 Hz) ppm.
4
[ArfPNSiMe3]2 (3Ј): A solution of ArfP(Cl)N(SiMe3)2 (1.20 g,
bon σ lone pair, short CcarbϪCaryl bond). However, taking 2.73 mmol) in 1,2,4-trichlorobenzene (5 mL) was heated at 150 °C
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
www.eurjic.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2297

G. Pfister-Guillouzo et al.
FULL PAPER
for 40 h. The solvent was evaporated in vacuo (60 °C, 0.1 Torr) and
275.6 Hz, F3C), 130.8 (s, p-Carom), 130.9 (br. m, m-Carom), 135.6
2
2
1
the crude 3Ј was purified by washing with hexane (5 mL). This (dq, JP,C ϭ 19.4, JC,F ϭ 31.4 Hz, o-Carom), 138.2 (d, JP,C
ϭ
procedure gave 0.81 g (90% yield) of pure product. 1H NMR
83.23 Hz, ipso-Carom) ppm. 19F NMR (C6D6): δ ϭ 22.50 (d, 4JF,P ϭ
3
(CD2Cl2): δ ϭ Ϫ0.28 (s, 18 H, SiMe3), 7.73 (t, JH,H ϭ 8 Hz, 2 H, 46 Hz) ppm. 31P{1H} NMR (C6D6): δ ϭ 122.5 (sept, 4JF,P ϭ 46 Hz)
p-Harom), 8.11 (two d, 3JH,H ϭ 8 Hz, 4 H, m-Harom) ppm. 13C NMR ppm. MS (70 eV): m/z (%)
ϭ 375 (100) [M Ϫ
Cl]ϩ.
1
(CD2Cl2): δ ϭ Ϫ1.1 (s, SiMe3), 124.1 (q, JF,C ϭ 275.3 Hz, CF3), C13H18ClF6N2PSi (410.80): calcd. C 38.01, H 4.42; found C 38.19,
1
124.6 (q, JF,C ϭ 276.7 Hz, CF3), 130.7 (s, p-Carom), 131.3 (q,
H 4.22.
3JF,C ϭ 32.1 Hz, m-Carom), 139.6 (dq, 2JC,P ϭ 36.1, 2JF,C ϭ 29.4 Hz,
ArfP؍N؊NMe2 (6):
A solution of ArfP(Cl)N(SiMe3)NMe2
1
o-Carom), 151.4 (d, JC,P ϭ 132.3 Hz, ipso-Carom) ppm. 19F NMR
(1.96 g, 4.78 mmol) in xylene (4 mL) was heated at 120 °C for 2 h,
then the solvent was evaporated. Distillation in vacuo (60Ϫ70 °C,
0.05 Torr) afforded 6 in ca. 50% yield and, according to the NMR
spectra, ArfPϭPArf (δP ϭ 478 ppm) as a side product (ca. 10%).
Pure 6 was isolated after stirring a solution of the amido(chloro)-
phosphane (1.52 g, 3.70 mmol) in CHCl3 (2 mL) at 25 °C for 14 h.
4
4
(CD2Cl2): δ ϭ 23.04 (d, JF,P ϭ 72.3 Hz) and 27.39 (d, JF,P
ϭ
134.7 Hz) ppm. 31P{1H} NMR (CD2Cl2): δ ϭ 277.3 (m) ppm.
C22H24F12N2P2Si2 (662.54): calcd. C 39.88, H 3.65; found C 39.65,
H 3.89.
ArfP(Cl)؊N(SiMe3)tBu: A solution of [LiN(SiMe3)tBu] in THF
(12 mL), prepared from HNtBu(SiMe3) (1.44 g, 9.89 mmol) and an Yield 95%; b.p. 65Ϫ70 °C at 0.5 Torr. 1H NMR (CDCl3): δ ϭ 3.34
4
3
equimolar amount of a 1.6  solution of nBuLi in hexane at Ϫ30
°C, was added dropwise to solution of ArfPCl2 (3.12 g,
(d, JH,P ϭ 7.4 Hz, 6 H, Me2N), 7.55 (t, JH,H ϭ 8 Hz, 1 H, p-
3
a
H
arom), 7.89 (d, JH,H ϭ 8 Hz, 2 H, m-Harom) ppm. 13C NMR
(CDCl3): δ ϭ 47.9 (d, JC,P ϭ 12.95 Hz, Me2N), 124.1 (q, JF,C ϭ
275.6 Hz, CF3), 128.6 (s, p-Carom), 129.6 (q, JF,C ϭ 5.5 Hz, m-
Carom), 135.3 (dq, JC,P ϭ 4.6, JF,C ϭ 29.6 Hz, o-Carom), 144.0 (d,
3
1
9.89 mmol) in THF (7 mL) at Ϫ80 °C. The reaction mixture was
slowly warmed to ambient temperature, stirred for 1 h and the sol-
vents evaporated. Pentane was added to the residue and the precipi-
3
2
2
tated LiCl was filtered off. Removal of the solvent and volatiles in 1JC,P ϭ 71.2 Hz, ipso-Carom) ppm. 19F NMR (CDCl3): δ ϭ 20.92
1
4
vacuo yielded 3.4 g (81%) of product. H NMR (CDCl3): δ ϭ 0.03
(d, JF,P ϭ 23.5 Hz) ppm. 31P NMR (CDCl3): δ ϭ 224.3 (br.s)
3
(s, 9 H, SiMe3), 1.54 (s, 9 H, tBu), 7.56 (t, JH,H ϭ 7.4 Hz, 1 H, p-
ppm. C10H9F6N2P (302.16): calcd. C 39.75, H 3.00; found C 40.10,
3
Harom), 7.79 (d, JH,H ϭ 7.4 Hz, 2 H, m-Harom) ppm. 13C NMR H 3.38.
3
(CDCl3): δ ϭ 6.4 (s, Me3Si), 32.7 (d, JP,C ϭ 13.9 Hz, CMe3), 61.5
iPr2NP(Cl)؊N(SiMe3)NMe2: A 1.6  solution of nBuLi in hexane
(6.36 mmol) was added to a solution of HN(SiMe3)(NMe2) (0.84 g,
6.36 mmol) in THF (10 mL) at Ϫ30 °C. This solution of lithium
hydrazide was added dropwise to a solution of iPr2NPCl2 (1.27 g,
6.36 mmol) in THF (5 mL) at Ϫ80 °C. The reaction mixture was
slowly warmed to ambient temperature, stirred for 1 h and the sol-
vents evaporated. Pentane (20 mL) was added to the residue and
2
1
4
(d, JC,P ϭ 29.6 Hz, CMe3), 123.9 (dq, JF,C ϭ 242.3, JC,P
ϭ
4
5.5 Hz, CF3), 129.0 (d, JC,P ϭ 3.7 Hz, p-Carom), 129.9 and 131.6
1
(m, m-Carom), 134.9 (m, o-Carom), 148.4 (d, JP,C ϭ 98.0 Hz, ipso-
Carom) ppm. 19F NMR (CDCl3): δ ϭ 24.89 (pseudo t, JF,P
ϭ
4
37 Hz) ppm. 31P{1H} NMR (CDCl3): δ ϭ 145.0 (sept, JF,P
ϭ
4
36 Hz) ppm.
ArfP؍NtBu (4): A solution of ArfP(Cl)N(SiMe3)tBu (1.95 g, the precipitated LiCl was filtered off. The solution was evaporated
4.61 mmol) in xylene (4 mL) was heated at 120 °C for 80 h, then
to yield colorless crystals of the product (89%). M.p. 32Ϫ34 °C. 1H
NMR (C6D6): δ ϭ 0.39 (s, 9 H, SiMe3), 1.08 and 1.28 (d, JH,H
3
the solvent was evaporated. Distillation in vacuo afforded 0.80 g
ϭ
(55%) of 4; b.p. 56Ϫ60 °C at 0.05 Torr. 1H NMR (CDCl3): δ ϭ 6.8 Hz, 12 H, CH(CH3)2], 2.52 and 2.61 (s, 6 H, NMe2), 3.71 [m,
3
3
1.49 (d, 4JH,P ϭ 1.8 Hz, 9 H, tBu), 7.63 (t, JH,H ϭ 7.8 Hz, 1 H, p-
2 H, CH(CH3)2] ppm. 13C NMR: δ ϭ 3.2 (d, JP,C ϭ 3.7 Hz,
3
3
3
Harom), 7.89 (d, JH,H ϭ 7.8 Hz, 2 H, m-Harom) ppm. 13C NMR
Me3Si), 23.2 [d, JP,C ϭ 12.95 Hz, CH(CH3)2], 23.9 [d, JP,C ϭ
3
2
3
(CDCl3): δ ϭ 32.5 (d, JC,P ϭ 15.7 Hz, CMe3), 64.6 (d, JC,P
ϭ
4.62 Hz, CH(CH3)2], 46.7 [d, JP,C ϭ 10.2 Hz, N(CH3)2], 47.4 [d,
10.2 Hz, CMe3), 124.1 (dq, JF,C ϭ 275.6, JC,P ϭ 1.9 Hz, CF3), 2JP,C ϭ 44.4 Hz, CH(CH3)2], 47, 6 [d, JP,C ϭ 39.8 Hz, CH(CH3)2]
1
3
2
3
129.8 (s, p-Carom), 129.9 (q, JF,C ϭ 5.6 Hz, m-Carom), 133.2 (dq,
ppm. 31P NMR (CDCl3): δ ϭ 129.3 (s) ppm. C13H18ClF6N2PSi
2JC,P ϭ 4.6, JF,C ϭ 31.5 Hz, o-Carom), 147.0 (d, JC,P ϭ 84.2 Hz, (410.80): calcd. C 38.01, H 4.42; found C 38.19, H 4.22.
2
1
ipso-Carom) ppm. 19F NMR (CDCl3): δ ϭ 21.65 (d, JF,P ϭ 28 Hz)
4
iPr2NP؍NNMe2 (7): A solution of iPr2NP(Cl)N(SiMe3)NMe2
ppm. 31P{1H} NMR (CDCl3): δ ϭ 412.4 (sept, 4JF,P ϭ 28 Hz) ppm.
(1.43 g, 4.80 mmol) in toluene (10 mL) was heated at 100 °C for
10 h. Solvent was removed in vacuo to afford iminophosphane 7
C12H12F6NP (315.19): calcd. C 45.73, H 3.84; found C 45.40, H
3.55.
contaminated by
a small amount (Ͻ10%) of the dimer
ArfP(Cl)؊N(SiMe3)NMe2: A 1.6  solution of nBuLi in hexane
(10.38 mmol) was added to a solution of HN(SiMe3)(NMe2)
(1.37 g, 10.38 mmol) in THF (15 mL) at Ϫ30 °C. The mixture was
then warmed to ambient temperature and stirred for 1 h. This solu-
tion of lithium hydrazide was added dropwise to a solution of
ArfPCl2 (3.27 g, 10.38 mmol) in THF (7 mL) at Ϫ80 °C. The reac-
[iPr2NPNNMe2]2.
7: 1H NMR (C6D6): δ ϭ 1.19 and 1.44 [br. s, 12 H, CH(CH3)2],
2.58 (s, 6 H, NMe2), 3.32 and 4.10 [br. s, 2 H, CH(CH3)2] ppm.
13C NMR (C6D6): δ ϭ 22.2 and 27.6 [br. s, CH(CH3)2], 44.8 [s,
N(CH3)2], 49.3 [pseudo t, JP,C ϭ 5.55 Hz, CH(CH3)2] ppm. 31P
NMR (C6D6): δ ϭ 173.13 (s) ppm. MS (70 eV): m/z (%) ϭ 189 (15)
2
tion mixture was slowly warmed to ambient temperature, stirred [Mϩ]. C8H20N3P (189.24).
for 1 h and the solvents evaporated. Pentane was added to the resi-
due and the precipitated LiCl was filtered off. Solvent and volatile
compounds were removed in vacuo. The resulting solid contained
the chlorophosphane ArfP(Cl)N(SiMe3)NMe2 and about 20% of
the diphosphene ArfPϭPArf. Recrystallization from diethyl ether
Iminophosphane 7 slowly dimerizes at room temperature to give
1,3,2,4-diazadiphosphetidine [iPr2NPNNMe2]2 according to X-ray
3
analysis. 1H NMR (CDCl3): δ ϭ 1.24 [d, JH,H ϭ 6.8 Hz, 12 H,
CH(CH3)2], 2.69 (s, 6 H, NMe2), 3.84 [br. s, 2 H, CH(CH3)2]; ppm.
3
13C NMR (CDCl3): δ ϭ 24.6 [br. s, NCH(CH3)2], 43.6 (t, JP,C
ϭ
afforded the pure product as dark yellow crystals. Yield 2.1 g 4.6 Hz, NMe2), 49.1 (t, 2JP,C ϭ 5.6 Hz, CH(CH3)2] ppm. 31P NMR
(49%). 1H NMR (C6D6): δ ϭ 0.02 (s, 9 H, SiMe3), 2.51 (br. s, 6 H,
(CDCl3): δ ϭ 74.2 (s) ppm. MS (70 eV): m/z (%) ϭ 378 (17) [Mϩ].
C8H20N3P (189.24): calcd. C 50.77, H 10.65, N 22.20; found C
50.86, H 10.84, N 22. 08. C16H40N6P2 (378.48): calcd. C 50.77, H
3
3
Me2N), 6.71 (t, JH,H ϭ 7.8 Hz, 1 H, p-Harom), 7.38 (d, JH,H
ϭ
7.8 Hz, 2 H, m-Harom) ppm.13C NMR (C6D6): δ ϭ 1.9 (d, JP,C
ϭ
3
2.8 Hz, Me3Si), 47.1 (d, 3JP,C ϭ 103.6 Hz, Me2N), 124.6 (q, 1JF,C ϭ 10.65, N 22.20; found C 50.55, H 10.49, N 22.13.
2298
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300

“Push-Pull”-Substituted P-[2,6-Bis(trifluoromethyl)phenyl]-σ2λ3-iminophosphanes
Table 3. Crystallographic data for 3Ј, 4 and 6
FULL PAPER
3Ј
4
6
Empirical formula
Molecular mass
Temp. (K)
C11H12F6NPSi
331.28
223(2)
0.71073
monoclinic
P21/c
10.378(2)
17.730(3)
15.790(4)
Ϫ
93.75(2)
Ϫ
2899.3(9)
8
C12H12F6NP
315.20
193(2)
0.71073
orthorhombic
Pnma
7.031(1)
13.348(1)
15.263(2)
Ϫ
Ϫ
Ϫ
1432.4(3)
4
C10H9F6N2P
302.16
193(2)
˚
Wavelength (A)
0.71073
triclinic
Crystal system
Space group
¯
P1
˚
a (A)
7.160(1)
9.245(1)
10.565(1)
67.164(2)
78.394(2)
85.958(2)
631.4(1)
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
3
˚
V (A )
Z
2
θ range for data collection (°)
No. of rflns collected
No. of indep rflns.
No. of parameters
Goodness of fit on F2
R1 [I Ͼ 2σ(I)]
1.73 to 28.28
21424
7171 [R(int) ϭ 0.0246]
385
1.021
0.0504
2.03 to 24.71
6955
1278 [R(int) ϭ 0.0452]
102
1.043
0.0537
0.1471
0.357 and Ϫ0.311
2.13 to 29.46
4296
3074 [R(int) ϭ 0.0231]
174
1.026
0.0476
wR2 (all data)
0.1572
1.158 and Ϫ0.283
0.1387
0.342 and Ϫ0.297
Ϫ3
˚
Largest diff peak, hole (e·A
)
Computational Details: Calculations were performed with the
Gaussian 98 program[28,29] using the Density Functional theory
method.[30] The various structures were fully optimized at the
B3LYP level.[31] This functional is built with Becke’s three-param-
eter exchange functional[31a] and the LeeϪYangϪParr correlation
then one must take the absolute constant and linear orbital energy
shift into account by applying a suitable (ax ϩ b) scaling. In the
case of large molecules, the ordering of levels found by using the
DFT calculations seems to be qualitatively as well translated as by
using HF methods. This fact, despite the evident limits of corre-
functional.[31c] The 6-311G(d,p) basis set was used. All atoms were lation, gives a good basis for discussion about the ionizations as-
augmented with a single set of polarization functions. The second
derivatives were calculated in order to determine if a minimum or
a transition state (one negative eigenvalue) existed for the re-
sulting geometry.
signments which cannot be reached by a direct calculation.
X-ray Crystallographic Study: Crystal data for 3Ј, 4 and 6 are pre-
sented in Table 3. All data were collected at low temperature (Ϫ50
°C for 3Ј and Ϫ80 °C for 4 and 6) on a Bruker-AXS CCD 1000
˚
diffractometer with Mo-Kα radiation (λ ϭ 0.71073 A). The struc-
All total energies have been zero-point energy (ZPE) and tempera-
ture corrected using unscaled density functional frequencies.
tures were solved by direct methods by means of SHELXS-97[36]
and refined with all data on F2 by means of SHELXL-97.[37] All
non-hydrogen atoms were refined anisotropically.
NBO analysis population[32] was performed in order to determine
the presence of stabilizing interactions between a filled orbital and
an empty orbital. Ionization energies were determined as the differ-
ence between the cation and the neutral molecule energies (IE ϭ
Ecation Ϫ Emolecule; ∆SCF method). For the large molecules, an as-
sociation between the ionization potential and KohnϪSham (KS)
energies calculated with common functionals (Koopmans’ the-
orem-like) has been discussed in depth. Arduengo and co-work-
ers[33] first used DFT calculations at the nonlocal level to assign
their photoelectron spectra. They applied a uniform shift to the
orbital energies considering the difference between the calculated
and experimental molecular ionization potentials. The aim was to
directly compare the KS energies to the experimental energies.
Moreover, Werstiuk and Rademacher[34] have developed and suc-
cessfully applied a routine for the interpretation of PE spectra
based on B3LYP theory. This routine requires the calculation of the
molecule’s first vertical ionization potential IPv. Calculated orbital
energies Ϫε are then shifted uniformly so that the HOMO energy
equals that of the IPv, giving the higher IPs. More recently,
Hoffmann[35] has underlined that the KS orbitals are a good basis
for qualitative interpretation of molecular orbital. He concluded
that if one wants to go a step beyond a qualitative interpretation
and look at orbital energies as rough ionization potentials, and if
the DFT calculations are done with commonly used potentials,
CCDC 223052Ϫ223054 (for 3Ј, 4 and 6 respectively) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html
[or from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (internat.) ϩ44-1223/336-
033; E-mail: deposit@ccdc.cam.ac.uk].
Acknowledgments
Financial support of this work by the CNRS (France) is gratefully
acknowledged. We also thank the Institut du Developpement de
Ressources en Informatique Scientifique (IDRIS, Orsay, France),
administered by the CNRS, for the calculation facilities, and Dr.
Gijs Schaftenaar for allowing us to use his graphic program.[24]
[1] [1a]
E. Niecke, in Multiple Bonding and Low Coordination in
Phosphorus Chemistry (Eds.: M. Regitz, O. J. Scherer), Thieme
Verlag, Stuttgart, 1990, 293Ϫ320. See also the following refer-
ences for captodative or push-pull diphosphenes: [1b]M. Abe,
K. Toyota, M. Yoshifuji, Chem. Lett. 1992, 2349Ϫ2352; M.
Abe, K. Toyota, M. Yoshifuji, Bull. Chem. Soc. Jpn. 1993, 66,
3831Ϫ3833.
[2]
E. Niecke, D. Gudat, Angew. Chem. 1991, 103, 251Ϫ270; An-
gew. Chem. Int. Ed. Engl. 1991, 30, 217Ϫ236.
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2299

G. Pfister-Guillouzo et al.
FULL PAPER
[3] [3a]
[24]
[25]
[26]
[27]
[28]
L. N. Markovskii, V. D. Romanenko, A. V. Ruban, The
G. Schaftenaar, J. H. Noordik, J. Comput. -Aided Mol. Des.
2000, 14, 123Ϫ134.
S. Elbel, A. Ellis, E. Niecke, H. Egsgaard, L. Carlsen, J. Chem.
Soc., Dalton Trans. 1985, 879Ϫ884.
U. Dressler, E. Niecke, S. Pohl, W. Saak, W. W. Schoeller, H.
G. Schäfer, J. Chem. Soc., Chem. Commun. 1986, 1086Ϫ1087.
S. Sole, H. Gornitzka, W. W. Schoeller, D. Bourissou, G. Ber-
Chemistry of Acyclic Twofold Coordinated Phosphorus Com-
pounds, Naukova Dumka, Kiev, 1988, 123Ϫ198. [3b]M. Yoshi-
fuji, N. Inamoto, K. Hirotsu, J. Am. Chem. Soc. 1981, 103,
4587Ϫ4589; M. Yoshifuji, N. Inamoto, K. Hirotsu, J. Am.
Chem. Soc. 1982, 104, 6167.
E. Niecke, M. Nieger, C. Gaertner-Winkhaus, B. Kramer,
Chem. Ber. 1990, 123, 477Ϫ479.
L. N. Markovskii, V. D. Romanenko, A. V. Ruban, A. B. Dra-
pailo, G. V. Reitel, A. N. Chernega, M. I. Povolotskii, Zh.
Obshch. Khim. 1990, 60, 2453Ϫ2462.
E. Niecke, M. Nieger, F. Reichert, Angew. Chem. 1988, 100,
1781Ϫ1784; Angew. Chem. Int. Ed. Engl. 1988, 27, 1715Ϫ1718.
A. N. Chernega, A. A. Korkin, N. E. Aksinenko, A. V. Ruban,
V. D. Romanenko, Zh. Obshch. Khim. 1990, 60, 2462Ϫ2469.
V. D. Romanenko, G. Reitel, A. N. Chernega, O. V. Kirichenko,
A. V. Ruban, M. Sanchez, R. Wolf, M. R. Mazieres, Het-
eroatom Chem. 1992, 3, 453Ϫ458.
E. Niecke, R. Detsch, M. Nieger, F. Reichert, W. W. Schoeller,
Bull. Chem. Soc. Fr. 1993, 130, 25Ϫ31.
W. W. Schoeller, T. Busch, E. Niecke, Chem. Ber. 1990, 123,
1653Ϫ1654.
G. David, V. von der Gonna, E. Niecke, T. Busch, W. W. Scho-
eller, P. Rademacher, J. Chem. Soc., Faraday Trans. 1994, 90,
2611Ϫ2616.
The electronic and steric properties of the related 2,4,6-tris(tri-
fluoromethylphenyl) group have been reviewed: F. T. Edelman,
Comments Inorg. Chem. 1992, 12, 259Ϫ284.
[4]
[5]
´
trand, Science 2001, 292, 1901Ϫ1903.
Gaussian 98, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J.
A. Montgomery, R. E. Stratman J. C. Burant S. Dapprich, J.
M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O.
Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Men-
nucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A.
Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick,
A. D. K. Rabuck, Raghavachari, J. B. Foresman, J. Cioslowswi,
J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. Jonhson, W.
Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S. Re-
plogle, J. A. Pople, Gaussian 98, Revision A.7, Gaussian Inc.,
Pittsburgh PA, 1998.
[6]
[7]
[8]
[9]
[10]
[11]
[29]
[30]
W. J. Hehre, L. Radom, P. v. R. Schleyer, J. A. Pople, Ab Initio
Molecular Orbital Theory, John Wiley & Sons: New York,
1986.
[12]
[13]
R. G. Parr, W. Yang, Functional Theory of Atoms and Molecules
(Eds.: R. Breslow, J. B. Goodenough), Oxford University Press:
New York, 1989.
V.-L. Rudzevich, H. Gornitzka, K. Miqueu, J.-M. Sotiro-
poulos, G. Pfister-Guillouzo, V.-D. Romanenko, G. Bertrand,
Angew. Chem. Int. Ed. 2002, 114, 1241Ϫ1243; Angew. Chem.
Int. Ed. 2002, 41, 1193Ϫ1195.
[31] [31a]
[31b]
A. D. Becke, Phys. Rev. 1988, A38, 3098Ϫ3100.
Becke, J. Chem. Phys. 1993, 98, 5648Ϫ5652.
Yang, R. G. Parr, Phys. Rev. 1988, B37, 785Ϫ789.
[32] [32a]
A. D.
[31c]
C. Lee, W.
[14]
[15]
[16]
[17]
[18]
C. Buron, H. Gornitzka, V.-D. Romanenko, G. Bertrand, Sci-
ence 2000, 288, 834Ϫ836.
A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988,
[32b]
88, 899Ϫ926.
1980, 102, 7211Ϫ7218.
J. P. Foster, F. Weinhold, J. Am. Chem. Soc.
L. N. Markovskii, V. D. Romanenko, A. B. Drapailo, A. V.
Ruban, Zh. Obshch. Khim. 1986, 56, 2231Ϫ2242.
T. Lübben, H. W. Roesky, H. Gornitzka, A. Steiner, D. Stalke,
Eur. J. Solid State Inorg. Chem. 1995, 32, 121Ϫ130.
A. N. Chernega, M. Yu. Antipin, Yu. T. Struchkov, A. V. Ru-
ban, V. D. Romanenko, Zh. Struct. Khim. 1987, 28, 105Ϫ110.
J.-T. Ahlemann, H. W. Roesky, R. Murugavel, E. Parisini, M.
Noltemeyer, H.-G. Schmidt, O. Müller, R. Herbst-Irmer, L. N.
Markovskii, Y. G. Shermolovich, Chem. Ber./Recueil 1997,
130, 1113Ϫ1121.
[33]
A. J. Arduengo III, H. Bock, H. Chen, M. Denk, D. A. Dixon,
J. C. Green, W. A. Hermann, N. L. Jones, M. Wagner, R. West,
J. Am. Chem. Soc. 1994, 116, 6641Ϫ6649.
[34] [34a]
H. M. Muchall, P. Rademacher, J. Mol. Struct. 1997, 435,
[34b]
157Ϫ167.
1998, 471, 189Ϫ194.
H. M. Muchall, P. Rademacher, J. Mol. Struct.
[34c]
H. M. Muchall, N. H. Werstiuk, B.
Choudhurry, Can. J. Chem. 1998, 76, 221Ϫ227. [34d] H. M. Mu-
chall, N. H. Werstiuk, B. Choudhurry, J. Ma, J. Warkentin, J.
P. Pezacki, Can. J. Chem. 1998, 76, 238Ϫ240.
R. Stowasser, R. Hoffmann, J. Am. Chem. Soc. 1999, 121,
3414Ϫ3420.
[19]
[20]
[21]
[22]
[23]
[35]
J. Escudie, C. Couret, H. Ranaivonjatovo, M. Lazraq, J. Satge,
Phosphorus, Sulfur Rel. Elem. 1987, 31, 27Ϫ31.
[36]
[37]
U. Dressler, E. Niecke, S. Pohl, W. Saak, W. W. Schoeller, H.-
G. Schaefer, J. Chem. Soc., Chem. Commun. 1986, 1086Ϫ1087.
O. Altmeyer, E. Niecke, M. Nieger, T. Busch, W. W. Schoeller,
D. Stalke, Heteroatom Chem. 1990, 1, 191Ϫ194.
K. Miqueu, J.-M. Sotiropoulos, G. Pfister-Guillouzo, V.-D. Ro-
manenko, New J. Chem. 2001, 930Ϫ938.
G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467Ϫ473.
G. M. Sheldrick SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, Germany, 1997.
C.-H. Lai, M.-D. Su, S.-Y. Chu, J. Phys. Chem. A. 2003, 107,
2700Ϫ2710.
[38]
Received November 5, 2003
Early View Article
Published Online April 7, 2004
W. W. Schoeller, T. Busch, E. Niecke, Chem. Ber. 1990,
1653Ϫ1654.
2300
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2289Ϫ2300