N-phosphanylformamidines (phosfam) R2′N-C(H)=N-PR 2: One-pot synthesis and versatile protonation reaction

Article abstract of DOI:10.1002/ejic.200701299

A straightforward synthesis of unprecedented N-phosphanylformamidines (phosfam), 3a,b has been developed. The single-crystal X-ray study of 3a revealed an E-formamidine stereoisomer. The structural parameters show a strong localization of the C1-N1 double bond in the formamidine pattern. Versatile protonation reactions with HCl on 3a and 3b are reported, leading to P-N cleavage vs. prototropy. Experimental studies and DFT calculations have evidenced that the imino nitrogen atom is the basic center of phosfams 3a and 3b. DFT calculations show that the isomers and rotamers of the N- and P-protonated forms of 8a/9a and 8b/9b are energetically close, which prevents conclusions being drawn on the existence of thermodynamic and/or kinetic products. The accessibility of the anti bonding PN orbital (σ* _P1N1) is partly responsible for the cleavage of the PN bond in 8a; 8b possesses a less energetically accessible σ*_P1N1 orbital which is consistent with the preservation of the PN bond and the quantitative formation of the corresponding phosphonium compound 9b·Cl. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701299

FULL PAPER
DOI: 10.1002/ejic.200701299
N-Phosphanylformamidines (phosfam) R2ЈN–C(H)=N–PR2: One-Pot Synthesis
and Versatile Protonation Reaction
Thanh Dung Le,[a] Marie-Christine Weyland,[a] Yamna El-Harouch,[a] Damien Arquier,[a]
Laure Vendier,[a] Karinne Miqueu,[b] Jean-Marc Sotiropoulos,[b] Stéphanie Bastin,[a] and
Alain Igau*[a]
Keywords: Phosphanes / Formamidines / Protonation / Density functional calculations / Substituent effects
A straightforward synthesis of unprecedented N-phosphan-
ylformamidines (phosfam), 3a,b has been developed. The
single-crystal X-ray study of 3a revealed an E-formamidine
stereoisomer. The structural parameters show a strong local-
ization of the C1–N1 double bond in the formamidine
pattern. Versatile protonation reactions with HCl on 3a and
3b are reported, leading to P–N cleavage vs. prototropy. Ex-
perimental studies and DFT calculations have evidenced that
the imino nitrogen atom is the basic center of phosfams 3a
and 3b. DFT calculations show that the isomers and rotamers
of the N- and P-protonated forms of 8a/9a and 8b/9b are en-
ergetically close, which prevents conclusions being drawn on
the existence of thermodynamic and/or kinetic products. The
accessibility of the anti bonding PN orbital (σ*P1N1) is partly
responsible for the cleavage of the PN bond in 8a; 8b pos-
sesses a less energetically accessible σ*P1N1 orbital which is
consistent with the preservation of the PN bond and the
quantitative formation of the corresponding phosphonium
compound 9b·Cl.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
as P-protonated phosphoramidite salts[10] have been pre-
pared and characterized. To the best of our knowledge, an
N-protonated isomer of a PIII–N amide unit has never been
detected except when treating tetramethylguanidinyl PIII
amides with HCl.[11]
If we refer to the results described in the literature on the
protonation of aminophosphanes ϾP–NϽ[9–10] and (meth-
yleneamino)phosphanes ϾP–N=CϽ[11] it is not possible to
anticipate the privileged site of protonation of N-phosphan-
ylformamidines 3a,b and the thermodynamic stability of the
corresponding protonated compounds.
Herein, we report the straightforward high-yield synthe-
sis and the versatile protonation reaction of a new class of
PIII-functionalized phosphorus derivatives, the N-phos-
phanylformamidines (phosfam) iPr2N–C(H)=N–PR2 3a,b.
These studies were supported by quantum-chemical calcu-
lations.
Introduction
Formamidines are of special interest for general and syn-
thetic organic chemistry.[1] Since the isolation of the first N-
heterocyclic carbenes (NHC),[2] acyclic and cyclic com-
pounds containing the formamidine functionality have been
largely used as carbene precursors.[3] In the chemistry of
neutral organic bases, formamidines belong to one of the
most important families of strong bases.[4] Aiming at the
preparation of new classes of PIII-functionalized phospho-
rus ligands, we were interested in preparing unprecedented
N-phosphanylformamidine (phosfam) derivatives, R2ЈN–
C(H)=N–PR2.[5,6] The bond between phosphorus and
nitrogen in tervalent organophosphorus compounds is par-
ticularly susceptible to attack by Brönsted acids.[7] In
aminophosphane chemistry, protonation reactions on the
ϾP–NϽ unit take place under mild conditions with either
cleavage or preservation of the phosphorus–nitrogen link-
age.[8] Protonation reactions with preservation of the phos-
phorus–nitrogen linkage are believed to take place initially
at the P-center. P-protonated phosphorus amides[9] as well
Results and Discussion
[a] Laboratoire de Chimie de Coordination, CNRS,
205 route de Narbonne, 31077 Toulouse Cedex 4, France
Fax: +33-5-61553003
N-Phosphanylformamidines 3a,b were prepared in good
yields in a one-pot procedure as single E-stereoisomers after
treatment of the cyanamide derivative iPr2N–CN with suc-
cessive additions of 1 equiv. of the hydridozirconocene com-
plex 1[12] and the corresponding chlorophosphanes R2PCl
(2a,b) (Scheme 1).
E-mail: alain.igau@lcc-toulouse.fr
[b] IPREM CNRS 5254, Université de Pau & des Pays de l’Adour,
Avenue de l’Université, B. P. 1155, 64013 Pau cedex, France
E-mail: jean-marc.sotiro@univ-pau.fr
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2008, 2577–2583
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A. Igau et al.
FULL PAPER
over, the R substituents on the phosphorus atom in 3a,b
and 5 do not modify significantly the geometrical param-
eters of the formamidine skeleton iPr2N–C(H)=N- (Table 1
and see Supporting Information).
Table 1. Selected bond lengths [Å] and angles [°] for formamidine
4 and N-phosphanylformamidines 5, 3a,b. NPA charges (qX).
Scheme 1. Synthesis of N-phosphanylformamidines (phosfam)
3a,b.
X
4[a]
5[a]
3a[b]
3a[a]
3b[a]
C1–N1
C1–N2
P1–N1
1.286
1.369
/
1.292
1.360
1.741
124.05
114.77
288.5
–0.85
–0.46
0.45
1.289(3) 1.293
1.341(3) 1.358
1.697(2) 1.737
123.5(2) 124.48
115.7(2) 115.56
1.292
1.362
1.746
124.32
116.13
300.9
–0.89
–0.47
1.00
The composition and constitution of 3a,b follow from
mass analysis, IR, and 31P, 1H, 13C, 15N NMR spectra. The
2
3JHP [18.9 (3a) and 17.4 (3b) Hz] and JCP [52.7 (3a) and
N2–C1–N1 123.82
47.9 (3b) Hz] coupling constants values, and the 1JNP coup- C1–N1–P1
109.45
/
–0.77
–0.48
/
ΣP1
300.1
300.6
–0.89
–0.46
1.03
ling constant values of 44.6 (3a) and 39.4 (3b) Hz definitely
qN1
confirmed the presence of the phosphanyl group –PR2 at-
qN2
/
/
/
/
tached to the formamidine fragment. X-ray quality crystals
qP1
were obtained from a saturated pentane solution of 3a at
–5 °C, and the single-crystal X-ray study revealed an E-
formamidine stereoisomer. As depicted in Figure 1, the
compound exhibits pyramidal geometry at phosphorus with
a classical covalent P–N bond length [1.697(2) Å] and a
planar amino nitrogen atom iPr2N-. The structural param-
eters of 3a show a strong localization of the ϾC1=N1–
double bond in the formamidine pattern. The C1–N1 bond
length of 1.289(3) Å is in the range for carbon–nitrogen
double bonds and there is a significant difference of 0.052 Å
between the C1–N1 and C1–N2 bond lengths of the for-
mamidine NC(H)N moiety.[13]
qC
0.26
0.29
0.30
0.29
[a] Calculated, see Supporting Information for details. [b] Ob-
served, see Supporting Information for selected X-ray structure
analysis data.
With regard to the molecular orbitals (MO), the HOMO
and HOMO–1 in the NH-formamidine derivative 4 (Fig-
ure 2) are represented by the (πC1N1 – nN2) and nN1 orbitals,
respectively. For 3a (Figure 2), the HOMO corresponds to
the bonding combination of the phosphorus and nitrogen
lone pairs (nP1 + nN1) mixed with the σP1N1 bond (through-
bond interaction)[14] with an important weight on the phos-
phorus atom. Thus, the most striking changes between 4
and phosfam 3a appear in the MO: the HOMO in 4, is
energetically more accessible than in 3a but above all, the
order of the first two orbitals is reversed with a decrease of
the HOMO/HOMO–1 gap (1.1 eV for 4, 0.6 eV for 3a).
Figure 1. Molecular structure of 3a. Hydrogen atoms have been
omitted for clarity except for the formamidine hydrogen atom H1.
Selected bond lengths [Å] and angles [°]: C1–N1 1.289(3), C1–N2
1.341(3), P1–N1 1.697(2), N2–C1–N1 123.5(2), C1–N1–P1
115.7(2).
In order to have a better insight into the geometrical and
electronic structures of the phosfam derivatives, DFT calcu-
lations at the B3LYP/6-31G** level of theory were carried
out on different formamidine derivatives iPr2N–C(H)=NH
(4) and iPr2N–C(H)=N–PR2 with R = H (5), Ph (3a), and
iPr (3b). As expected, for the phosfams 3a,b and 5, the E
configuration corresponds to the most thermodynamically
Figure 2. Molekel plots and energy levels (Kohn–Sham energies in
eV) of the HOMO and HOMO–1 for 4 and 3a.
In summary, DFT calculations confirmed that the lone
stable structure in which the imino nitrogen and phospho- pairs of the imino nitrogen and of the phosphorus atoms in
rus lone pairs are in a trans position.
3a are the two privileged binding sites. The additional bind-
The calculated geometrical parameters for 3a are in good ing site, the phosphanyl fragment -PR2, in phosfam 3[15]
agreement with those recorded by X-ray crystallography induces a drastic decrease of the HOMO/HOMO–1 gap
(Table 1) and show that substitution of the proton on the and a change in the nature of the HOMO without mod-
imino nitrogen atom N1 of the formamidine 4 by a phos- ifying the structural parameters of the formamidine 4 to
phanyl fragment –PR2 leads only to weak changes. More- any great extent.
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Eur. J. Inorg. Chem. 2008, 2577–2583

N-Phosphanylformamidines (phosfam) R2ЈN–C(H)=N–PR2
Natural Population Analysis coming from a NBO calcu- intermediate compound 8b·Cl (Scheme 4), which was iden-
lation shows that similar charges appear in 3 and 4, the tified by the 1H and 13C chemical shifts of the formamidine
3
3
most negative charge being on the imino nitrogen. Proton- skeleton ϾN–C(H)=N– at 7.51 (dd, JHH = 13.7 Hz, JHP
2
ation is a charge-controlled reaction, therefore, the imino = 6.1 Hz) and 156.6 (d; JCP = 45.1 Hz) ppm, respectively.
nitrogen atom can be considered as the basic center of The signal of the NH proton appeared at 11.24 (broad,
phosfams 3a and 3b. Consequently, as the first step of the 3JHH = 13.7 Hz) ppm. This assignment was confirmed by
protonation reaction with HCl, it seems reasonable to pos- 2D 15N NMR experiments which showed a chemical shift
tulate the formation of the corresponding N-protonated for the imino nitrogen atom at –258.4 ppm with N–H and
1
1
formamidinium intermediates.
N–P coupling constants of JNH 81.8 and JNP 56.5 Hz,
The protonation reaction of phosfam 3a was investigated respectively. At room temperature the N-protonated com-
upon addition of HCl in solution in Et2O. At 298 K in pound 8b·Cl totally isomerizes to the isolated P-protonated
CH2Cl2, in the 31P NMR spectrum of the reaction mixture, phosphonium compound 9b·Cl. The protonation reaction
the initial chemical shift at δ = 54.3 ppm (3a) is replaced of 3b with HCl occurs with preservation of the P–N bond
after addition of HCl by two broad signals at 31.7 and to give the final isomerized product 9b·Cl.
–17.6 ppm (6·Cl) (Scheme 2) which are resolved into two
sharp doublets by exchanging the chloride for tetrafluo-
roborate to give 6·BF4 (1JPP = 293 Hz).[16] The H and 13C
1
NMR spectra of the reaction mixture showed the character-
istic proton and carbon chemical shift of the formamidine
framework ϾN–C(H)=N– of compound 6·Cl and also evi-
denced the formation of the formamidinium product 7·Cl
in stoichiometric amount.
Scheme 4. Protonation reaction of phosfam 3b.
Depending on the nature of the substituents R on the
phosphorus atom, protonation reactions with HCl on phos-
fams 3 occur via either cleavage (R = Ph) or preservation (R
= iPr) of the P–N bond of the corresponding N-protonated
compounds 8·Cl, which has been observed and fully charac-
terized for 8b·Cl.
In order to obtain more insight on the protonation reac-
tions of phosfams 3a,b, DFT calculations were carried out.
They show that in the gas phase the isomers of the N- and
P-protonated forms of 8a/9a and 8b/9b are energetically
close. These energy differences (Ͻ5 kcal/mol) between the
isomers and rotamers are too weak to conclude on the exis-
tence of thermodynamic and/or kinetic products (see Sup-
porting Information Figures S2 and S3). Since solvation
can affect the relative stabilities of the isomeric structures,
we carried out calculations using the PCM model.[15] We
observed that the energy differences between the isomers
remain weak with a slightly more thermodynamically stable
structure corresponding to the N-protonated compounds,
in agreement with the first experimentally postulated step.
As previously observed for phosfams 3a,b, the geometrical
parameters of the formamidine skeleton iPr2N–C(H)=N–
in the N- and P-protonated forms are not influenced by the
substituents on the phosphorus atom (Table 2). The C1–N1
bond lengths for 8 and 9 are quasi similar. However, be-
cause of the presence of negative hyperconjugation between
Scheme 2. Protonation reaction of phosfam 3a.
In order to confirm the synthesis of 6·Cl resulting from
the in situ formation of Ph2PCl in the protonation reaction
of 3a with HCl, 3a was independently reacted with Ph2PCl.
Quantitative formation of 6·Cl is observed (Scheme 3).
Therefore, a protonation reaction on the methyleneami-
nophosphane 3a with HCl takes place with cleavage of the
=N–PϽ unit.
Scheme 3. Synthesis of the phosphanyl-phosphonium formamidine
6·Cl.
The protonation reaction with HCl was then conducted the imino nitrogen lone pair and the antiperiplanar σ*P1H
on phosfam 3b. After 4 h at room temperature, phosfam orbital (ca. 11 kcal/mol: NBO calculation), the P1N1 bond
3b gave quantitatively the formamidine PH-phosphonium lengths in the P-protonated forms 9 decreased drastically
9b·Cl as the product of the reaction (Scheme 4). In the 31P compared to the N-protonated forms 8 (Table 2).
NMR spectrum, a signal appeared at δ = 50.4 ppm with a
To gain more insight into the origin of the PN bond
P–H coupling constant value (1JPH = 459 Hz) characteristic splitting of 8a, we evaluated the nature and the energy level
of σ4-PH compounds. The 1H and 13C NMR spectra of of the molecular orbitals, more particularly the σ*PN one.
9b·Cl showed the presence of the proton at 9.06 (3JHP
=
We may notice that the LUMO and the LUMO+1 in 8a are
21.9 Hz) ppm and the carbon at 162.6 (2JCP = 2.5 Hz) ppm quasi of the same nature as in 8b (Figure 3); they corre-
of the formamidine framework ϾN–C(H)=N–. Low-tem- spond to the π*C1N1–nN2 and σ*P1N1 orbitals, respectively.
perature NMR allowed us to characterize the N-protonated However, their energy levels are substantially different. If
Eur. J. Inorg. Chem. 2008, 2577–2583
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. Igau et al.
FULL PAPER
Table 2. Selected calculated[a] bond lengths [Å] and angles [°] for model the barrier, this high value suggests that the isomer-
the N- and P-protonated forms 8a,b and 9a,b. NPA charges (qX).
ization process may involve an intermolecular rather than
an intramolecular pathway.
X
8a
8b
9a
9b
C1–N1
C1–N2
P1–N1
N2–C1–N1
C1–N1–P1
ΣP1
qN1
qN2
qP1
qC
1.327
1.316
1.817
128.99
121.24
301.9
–0.85
–0.39
1.09
1.329
1.316
1.810
128.91
121.38
302.8
–0.86
–0.39
1.06
1.318
1.327
1.634
124.27
122.71
/
–0.97
–0.39
1.64
1.317
1.325
1.631
124.30
124.56
/
–0.98
–0.39
1.62
Conclusions
In conclusion, we have developed a straightforward and
high-yield synthesis of unprecedented N-phosphanylforma-
midine (phosfam) derivatives R2ЈN–C(H)=N–PR2. Experi-
mental studies demonstrate that protonation reactions take
place initially at the imino nitrogen center of the formamid-
ine pattern, in agreement with PCM model DFT calcula-
tions. Surprisingly, replacing the substituent on the phos-
phorus atom from R = Ph to R = iPr dramatically changes
the course of the protonation reaction. The energy level of
the molecular orbitals suggests that cleavage of the P–N
unit in the N-protonated compound 8a is induced by the
accessibility of the antibonding PN orbital (σ*P1N1). Preser-
vation of the phosphorus–nitrogen linkage upon proton-
ation of 3b is observed; the N-protonated compound 8b
isomerizes to form the corresponding PH phosphonium
compound. Considering the high energy barrier, this formal
prototropy process may involve a polymolecular rather than
an intramolecular pathway. Studies on the reactivity of
these new formamidines are underway. Since the electronic
and steric properties of the phosphane and the imino nitro-
gen centers can be finely and easily tuned, studies to evalu-
ate the potential uses of these ligands in catalysis are under
active investigation.
0.36
0.36
0.34
0.34
[a] See Supporting Information for details.
we specifically consider the two LUMO+1, their difference
(0.6 eV) is significant; the energies of the orbitals are
–3.23 eV for 8b and –3.98 eV for 8a, making the latter ener-
getically more accessible.[17] On this basis, it is reasonable
to propose that the accessibility of the anti bonding PN
orbital (σ*P1N1) is partly responsible for the cleavage of the
PN bond in 8a followed by the in situ formation of Ph2PCl.
In contrast, 8b possesses a less energetically accessible
σ*P1N1 orbital, which is consistent with the preservation of
the PN bond and the quantitative formation of the phos-
phonium compound 9b·Cl.
Experimental Section
General Information: All reactions were conducted under an inert
atmosphere of dry argon using standard Schlenk-line techniques.
Chemicals were treated as follows: pentane and CH2Cl2 distilled
from CaH2. CDCl3 distilled from P2O5; C6D6, CD2Cl2 (Euriso-top)
and other solvents stored on 4-Å molecular sieves. Solvents were
degassed by standard methods before use. Chlorodiphenylphos-
phane (97%) was obtained from ALFA AESAR and distilled prior
to use. All other commercial chemicals were from Aldrich (N,N-
diisopropylcyanamide, 97% and hydrochloric acid solution 1  in
diethyl ether), Acros (chlorodiisopropylphosphane, 96%), and
Strem [bis(cyclopentadienyl)zirconium dichloride, 99%] and were
used as received. [Cp2ZrHCl]n was prepared following the pro-
cedure reported by Buchwald et al.[12a]
NMR spectra were recorded with Bruker AV 500, AV 400, AV 300,
1
or AC200 spectrometers. Chemical shifts for H and 13C are refer-
enced to residual solvent resonances used as an internal standard
and reported relative to SiMe4. 31P and 15N NMR chemical shifts
are reported relative to external aqueous 85% H3PO4 (31P) and
CH3NO2 (15N), respectively. All the 1H and 13C signals were as-
signed on the basis of chemical shifts, spin-spin coupling constants,
splitting patterns and signal intensities, and by using 2D experi-
ments such as 1H–1H COSY45, 1H–13C HMQC, and 1H–13C
HMBC experiments. All spectra were recorded at ambient probe
temperature unless stated otherwise. Crude reaction mixtures were
controlled by NMR in CH2Cl2 with a sealed tube of [D8]toluene
as a reference. All compounds were then fully characterized in the
Figure 3. Molekel plots and energy levels (Kohn–Sham energies in
eV) of the HOMO, LUMO, and LUMO+1 for 8a and 8b. [a]: the
nP + πb1 orbital is at –10.64 eV.
Calculations in gas phase and in solution show that the
energy barrier between the N- and P-protonated forms in
the protonation reaction with phosfam 3b is found to be
high (Figure S4 in the Supporting Information: ca. 50–
60 kcal/mol). Even if DFT calculations do not accurately deuterated solvent stated in the experimental part. Infrared spectra
2580 Eur. J. Inorg. Chem. 2008, 2577–2583
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

N-Phosphanylformamidines (phosfam) R2ЈN–C(H)=N–PR2
were performed in solution (KBr windows) with a Perkin–Elmer
GX 2000 spectrometer. Mass spectra were recorded with a
TSQ7000 Thermo Electron (EI) and a Q Trap (ES–MS) mass spec-
trometer. Melting points were obtained using an Electrothermal
Digital Melting Point apparatus and are uncorrected. Elemental
analyses were carried out by the “Service d’Analyse du Laboratoire
de Chimie de Coordination” in Toulouse.
was stirred for 5 min. The solvent was removed by oil pump vac-
uum to give 6·Cl in quantitative yield as a white residue (0.256 g,
0.480 mmol). Compound 6·Cl was characterized by NMR without
any further treatment. 31P NMR (81.0 MHz, CDCl3, 25 °C): δ =
1
1
31.7 (d, JP,P = 282.5 Hz), –17.6 (d, JP,P = 282.5 Hz) ppm. 1H
NMR (200.1 MHz, CDCl3, 25 °C): δ = 7.58–7.03 (m, 21 H, HPh
and CH=N), 4.37 (sept, 3JH,H = 6.8 Hz, 1 H, NCHCH3), 3.54 (sept,
3
3JH,H = 6.7 Hz, 1 H, NCHCH3), 1.12 (d, JH,H = 6.8 Hz, 6 H,
Representative Experimental Procedure for the Preparation of N-
Phosphanylformamidines iPr2NC(H)=N–PR2 (3a,b): A solution of
iPr2NCN (0.986 g, 7.814 mmol) in CH2Cl2 (5 mL) was added to a
suspension of [Cp2Zr(H)Cl]n (1, 2.015 g, 7.814 mmol) in CH2Cl2
(15 mL) in a Schlenk flask under argon. The suspension was stirred
NCHCH3), 0.92 (d, 3JH,H = 6.7 Hz, 6 H, NCHCH3) ppm. 13C{1H}
2
NMR (50.3 MHz, CDCl3, 25 °C): δ = 156.5 (d, JC,P = 3.4 Hz,
1
1
CH=N), 135.1 (d, JC,P = 7.0 Hz, iCPh), 134.7 (d, JC,P = 10.4 Hz,
iCPh), 134.5 (s, CPh), 134.2 (s, CPh), 131.9 (d, JC,P = 8.8 Hz, CPh),
131.3 (s, CPh), 129.7 (d, J = 11.8 Hz, CPh), 129.3 (d, JC,P = 7.3 Hz,
for 1 h until
a pale yellow solution was obtained. R2PCl
C
Ph), 50.1 (s, NCHCH3), 47.8 (s, NCHCH3), 23.1 (s, NCHCH3),
(7.814 mmol) was then slowly added via syringe, resulting in a col-
orless solution. The solvent was removed by oil pump vacuum to
give a white residue that was extracted using pentane (3ϫ20 mL)
to give 3a in 91% yield (2.221 g, 7.111 mmol) and 3b in 85% yield
(1.622 g, 6.642 mmol).
19.3 (s, NCHCH3) ppm. 15N NMR (50.7 MHz, [D8]toluene,
25 °C): δ = –210.0 (NiPr2), –244.0 (1JN,P = 51.0 Hz, C=N–P) ppm.
Synthesis of the Formamidinium 7·Cl: A solution of iPr2NCN
(0.095 g, 0.750 mmol) in CH2Cl2 (5 mL) was added to a suspension
of [Cp2Zr(H)Cl]n (1, 0.193 g, 0.750 mmol) in CH2Cl2 (15 mL) in a
Schlenk flask under argon. The suspension was stirred for 1 h until
a pale yellow solution was obtained. A solution of hydrochloric
acid (1  in diethyl ether) (0.750 mL, 0.750 mmol) in 5 mL of
CH2Cl2 was then added at 0 °C. The reaction mixture was stirred
for 1 h at room temperature. The solvent was removed by oil pump
vacuum and the residue obtained was washed with THF
(3ϫ10 mL) to give 7·Cl as a white powder in 90% yield (0.111 g,
iPr NC(H)=N–PPh (3a): IR (KBr, THF): ν = 1612 cm–1 (C=N).
˜
2
2
31P{1H} NMR (121.5 MHz, CD2Cl2, 25 °C): δ = 54.3 ppm. 1H
3
NMR (300.1 MHz, CD2Cl2, 25 °C): δ = 8.14 (d, JH,P = 18.9 Hz,
1 H, CH=N), 7.60–7.34 (m, 10 H, HPh), 4.85 [sept, 3J(H,H) =
3
5.7 Hz, 1 H, CHCH3], 3.66 (sept, JH,H = 5.7 Hz, 1 H, CHCH3),
3
3
1.38 (d, JH,H = 5.7 Hz, 6 H, CHCH3), 1.31 (d, JH,H = 5.7 Hz, 6
H, CHCH3) ppm. 13C{1H} NMR (75.5 MHz, CD2Cl2, 25 °C): δ =
158.6 (d, 2JC,P = 52.7 Hz, CH=N), 145.0 (d, 1JC,P = 12.3 Hz, CPh),
130.7 (d, JC,P = 19.7 Hz, CHPh), 128.0 (s, CHPh), 127.9 (d, JC,P
= 1.8 Hz, CHPh), 47.0 (s, NCHCH3), 45.2 (s, NCHCH3), 23.6 (s,
NCHCH3), 19.9 (s, NCHCH3) ppm. 15N NMR (40.6 MHz, [D8]-
toluene, 25 °C): δ = –182.2 (1JN,P = 44.6 Hz, C=N–P), –243.9
0.675 mmol); m.p. 280 °C. IR (KBr, CHCl ): ν = 1695 cm–1 (C=N).
˜
3
1H NMR (400.1, CDCl3, 25 °C): δ = 10.25 (br. s, 1 H, NH2), 9.95
3
3
3
(d, JH,H = 14.1 Hz, 1 H, NH2), 7.56 (dd, JH,H = 14.1, JH,H
=
3
6.3 Hz, 1 H, CH=N), 4.78 (sept, JH,H = 6.8 Hz, 1 H, NCHCH3),
3.80 (sept, 3JH,H = 6.8 Hz, 1 H, NCHCH3), 1.35 (d, 3JH,H = 6.8 Hz,
(NiPr2) ppm. EI MS: m/z (%) = 312 (1) [M+], 220 (100) [M+
–
3
6 H, NCHCH3), 1.34 (d, JH,H = 6.8 Hz, 6 H, NCHCH3) ppm.
CH3 – Ph]. C19H25N2P (312.1755): calcd. C 73.05, H 8.07, N 8.97;
found C 73.16, H 8.15, N 8.85.
13C{1H} NMR (100.6, CDCl3): δ = 151.4 (s, CH=N), 50.0 (s,
CHCH3), 48.5 (s, CHCH3), 24.3 (s, CHCH3), 19.9 (s, CH
CH3) ppm. ESI MS: m/z (%) = 129 [M – Cl]+.
iPr NC(H)=N–PiPr (3b): IR (KBr, THF): ν = 1606 cm–1 (C=N).
˜
2
2
31P{1H} NMR (161.9 MHz, CD2Cl2, 25 °C): δ = 90.0 ppm. 1H
3
NMR (400.1 MHz, CD2Cl2, 25 °C): δ = 7.88 (d, JH,P = 17.4 Hz,
Protonation Reaction on iPr2NC(H)=N–PiPr2 (3b). Synthesis of N-
Phosphonioformamidine Chloride [iPr2NC(H)=N–P(H)iPr2]Cl
(9b·Cl): To a solution of N-phosphanylformamidine 3b (0.122 g,
0.500 mmol) in CH2Cl2 (8 mL) hydrochloric acid (0.500 mL, 1  in
diethyl ether) was added dropwise at –78 °C. The reaction mixture
was warmed to room temperature and stirred for 10 min. The sol-
vent was removed by oil pump vacuum to give a white residue that
was washed using pentane (3ϫ20 mL) to give 9b·Cl. Yield: 75%
1 H, CH=N), 4.43 (br. m, 1 H, NCHCH3), 3.52 (br. m, 1 H,
3
NCHCH3), 1.66 (sept, JH,H = 6.9 Hz, 2 H, PCHCH3), 1.21 (d,
3
3JH,H = 6.9 Hz, 6 H, NCHCH3), 1.19 (d, JH,H = 6.9 Hz, 6 H,
3
3
NCHCH3), 0.97 (dd, JH,P = 11.9, JH,H = 6.9 Hz, 12 H,
PCHCH3) ppm. 13C{1H} NMR (100.6 MHz, CD2Cl2, 25 °C): δ =
2
158.2 (d, JC,P = 47.9 Hz, CH=N), 47.2 (s, NCHCH3), 45.1 (s,
NCHCH3), 26.6 (d, 1JC,P = 9.9 Hz, PCHCH3), 23.7 (s, NCHCH3),
2
(0.105 g, 0.375 mmol). IR (KBr, THF): ν = 1603 cm–1 (C=N). 31P
20.1 (s, NCHCH3), 18.9 (d, JC,P = 19.8 Hz, PCHCH3), 17.6 (d,
˜
2JC,P = 7.8 Hz, PCHCH3) ppm. 15N NMR (40.6 MHz, [D8]tolu-
ene): δ = –177.8 (1JN,P = 39.4 Hz, C=N–P), –240.1 (NiPr2) ppm.
EI MS: m/z (%) = 244 (1) [M+], 201 (47) [M+ – iPr]. C13H29N2P
(244.2068): calcd. C 63.90, H 11.96, N 11.46; found C 64.12, H
12.08, N 11.22.
1
NMR (161.9 MHz, CDCl3, 25 °C): δ = 50.4 (d; JH,P = 458.8 Hz,
PH) ppm. 1H NMR (400.1 MHz, CDCl3, 25 °C): δ = 9.06 (d; 3JH,P
= 21.9 Hz, 1 H, CH=N), 7.75 (d; 1JH,P = 458.8 Hz, 1 H, PH), 4.24
3
3
(sept, JH,H = 6.8 Hz, 1 H, NCHCH3), 3.65 (sept, JH,H = 6.8 Hz,
1 H, NCHCH3), 2.43 (br. m, 1 H, PCHCH3), 2.31 (br. m, 1 H,
PCHCH3), 1.22 (d, 3JH,H = 6.8 Hz, 6 H, NCHCH3), 1.14 (dd, 3JH,H
Protonation Reaction on iPr2NC(H)=N–PPh2 (3a): To a solution
of N-phosphanylformamidine 3a (0.156 g, 0.500 mmol) in CH2Cl2
(8 mL) hydrochloric acid (0.500 mL, 1  in diethyl ether) was
added dropwise at –78 °C. The reaction mixture was warmed to
room temperature and stirred for 10 min. The solvent was removed
by oil pump vacuum to give a white residue constituted of a mix-
ture of 6·Cl and 7·Cl as the sole products of the reaction according
to NMR analysis. These compounds were not isolated, they were
independently prepared as described below in order to confirm
their composition and constitution.
3
3
= 6.4, JH,P = 2.0 Hz, 12 H, PCHCH3), 1.11 (d, JH,H = 6.8 Hz, 6
H, NCHCH3) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ
2
= 162.6 (d; JC,P = 2.5 Hz, HC=N), 50.6 (s; NCHCH3), 46.8 (s;
NCHCH3), 23.4 (s; NCHCH3), 22.8 (d; 1JC,P = 63.2 Hz, PCHCH3),
2
19.8 (s; NCHCH3), 16.5 (d; JC,P = 2.0 Hz, PCHCH3), 15.6 (d;
2JC,P = 3.7 Hz, PCHCH3) ppm. 15N NMR (40.6 MHz, [D8]tolu-
ene): δ = –219.0 (N iPr2), –248.1 (1JN,P = 38.8 Hz, C=N–P) ppm.
Protonation Reaction on iPr2NC(H)=N–PiPr2 (3b): Identification
of [iPr2NC(H)=N(H)–PiPr2]Cl, 8b·Cl by low-temperature NMR
Addition of Ph2PCl on iPr2NC(H)=N–PPh2 (3a): A Schlenk flask
was charged with iPr2NC(H)=NPPh2 (3a, 0.151 g, 0.480 mmol),
Ph2PCl (2a, 0.106 g, 0.480 mmol), and CH2Cl2 (5 mL). The mixture
spectroscopy: 31P NMR (161.9 MHz, CD2Cl2, 0 °C): δ = 98.9 ppm.
3
1H NMR (400.1 MHz, CD2Cl2, 0 °C): δ = 11.24 (br. d, JH,H
=
3
3
13.7 Hz, 1 H, NH), 7.51 (dd, JH,H = 13.7, JH,P = 6.1 Hz, 1 H,
Eur. J. Inorg. Chem. 2008, 2577–2583
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2581

A. Igau et al.
FULL PAPER
3
CH=N), 3.79 (sept, JH,H = 6.8 Hz, 1 H, NCHCH3), 3.15 (sept, The transition state was calculated using the STQN method im-
3JH,H = 6.5 Hz, 1 H, NCHCH3), 2.48 (br. m, 1 H, PCHCH3), 2.39 plemented in Gaussian (opt = QST3). The connection between the
3
(br. m, 1 H, PCHCH3), 1.24 (d, JH,H = 6.8 Hz, 6 H, NCHCH3), transition state and the corresponding minima was confirmed by
3
3
1.17 (d, JH,H = 6.5 Hz, 6 H, NCHCH3), 1.00 (dd, JH,H = 7.1,
IRC calculations.
3JH,P = 17.3 Hz, 12 H, PCHCH3) ppm. 13C{1H} NMR (100.6,
Supporting Information (see also the footnote on the first page of
this article): Selected crystallographic data for 3a and detailed cal-
culated data for all compounds.
2
CD2Cl2, 0 °C): δ = 156.6 (d, JC,P = 45.1 Hz, HC=N), 51.9 (s,
NCHCH3), 48.2 (s, NCHCH3), 25.8 (d, 1JC,P = 11.2 Hz, PCHCH3),
2
24.3 (s, NCHCH3), 21.6 (s, NCHCH3), 18.9 (d, JCP = 7.2 Hz,
2
PCHCH3), 18.6 (d, JCP = 20.6 Hz, PCHCH3) ppm. 15N NMR
([D8]toluene, 40.6 MHz, 0 °C): δ = –220.0 (NiPr2), –258.4 [JN,H
81.8, JNP = 56.5 Hz, C=N(H)–P] ppm.
=
Acknowledgments
We thank the Institut du Developpement de Ressources en In-
formatique Scientifique administered by the CNRS, for the calcula-
tion facilities. Y. E.-H. is grateful to the Ministère de la Recherche
for a doctoral fellowship. D. A. thanks the European Community
for a post-doctoral fellowship (FSE).
X-ray Crystal Structure Determination of Compound 3a: Crystallo-
graphic data were collected at low temperature (180 K) with a Xcal-
ibur Oxford-Diffraction diffractometer using graphite-monochro-
mated Mo-Kα radiation (λ = 0.71073 Å) and equipped with an Ox-
ford Cryosystems Cryostream Cooler Device. The final unit cell
parameters were obtained by means of least-squares refinement
performed on a set of 2310 well-measured reflections. The structure
was solved by Direct Methods using SIR92,[18] and refined by me-
ans of least-squares procedures on F2 with the aid of the program
SHELXL97[19] included in the software package WinGX version
1.63.[20] The Atomic Scattering Factors were taken from Inter-
national tables for X-ray crystallography.[21] All hydrogen atoms
were geometrically placed and refined by using a riding model.
[1] T. M. Krygowski, K. Wozniak, in The Chemistry of Amidines
and Imidates (Eds.: S. Patai, Z. Rappoport), John Wiley &
Sons, Chichester, 1991.
[2] A. J. Arduengo III, R. L. Harlow, M. Kline, J. Am. Chem. Soc.
1991, 113, 361–363.
[3] a) Y. Ishida, B. Donnadieu, G. Bertrand, PNAS 2006, 103,
13585–13588; b) K. E. Krahulic, G. D. Enright, M. Parvez, R.
Roesler, J. Am. Chem. Soc. 2005, 127, 4142–4143; c) E. Despag-
net-Ayoub, R. H. Grubbs, J. Am. Chem. Soc. 2004, 126, 10198–
10199.
Crystallographic
Data
for
3a:
Colorless
platelet
(0.17ϫ0.17ϫ0.05 mm), C19H25N2P, M = 312.38, triclinic, a =
7.4702(14) Å, b = 9.915(3) Å, c = 13.169(4) Å, α = 104.57(2)°, β =
102.56 (2)°, γ = 97.098(18) , V = 904.9(4) Å3, T = 180 K, space
group P-1 (no. 2), Z = 2, µ(Mo-Kα) = 0.151 mm–1, 6498 reflections
measured, 3425 unique (Rint = 0.0565) which were used in all cal-
culations, R = 0.0578 (wR = 0.1259) for 3425 reflections with
[I Ͼ 2σ(I)], GOF = 1.088. Semi-empirical absorption corrections
were performed.[22] All non-hydrogen atoms were anisotropically
refined, and in the last cycles of refinement a weighting scheme was
used, where weights were calculated from the following formula: w
[4] E. D. Raczynska, P.-C. Maria, J.-F. Gal, M. Decouzon, J. Org.
Chem. 1992, 27, 5730–5735.
[5] It is important to note that N-phosphanyl amidines (RЈ2N)
RЈЈC=N–PR2 (RЈЈ ϶ H) have been already described in the
literature[6] but their method of preparation can not be ex-
tended to the synthesis of the corresponding formamidine de-
rivatives.
[6] a) U. Scholz, M. Noltemeyer, H. W. Roesky, Z. Naturforsch.,
Teil B 1988, 43, 937–940; b) V. Chandrasekhar, T. Chivers, S. S.
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Manners, Inorg. Chem. 2004, 43, 802–811.
[7] O. Dahl in The Chemistry of Organophosphorus Compounds
(Ed.: F. R. Hartley), John Wiley & Sons, Chichester, 1996, vol.
4, pp. 1–45 and references cited therein.
= 1/[σ2(Fo2) + (aP)2 + bP] where P = (Fo + 2Fc )/3. The drawing
of the molecule was performed with the program ORTEP32[23] with
30% probability displacement ellipsoids for non-hydrogen atoms.
2
2
CCDC-614899 contains the supplementary crystallographic data
for his paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
data_request/cif.
[8] a) O. Dahl, Tetrahedron Lett. 1982, 23, 1493–1496; G. S. Har-
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Computational Details: Calculations were performed with the
Gaussian 98 and 03 programs,[24,25] using the density functional
method.[26] The hybrid exchange functional B3LYP in conjunction
with the 6-31G** basis set was used. B3LYP[27] is a three-parameter
functional developed by Becke which combines the Becke gradient-
corrected exchange functional and the Lee–Yang–Parr and Vosko–
Wilk–Nusair correlation functionals with part of the exact HF ex-
change energy. The optimized structures were confirmed as true
minima on the potential energy through vibrational analysis. The
frequencies were calculated with analytical second derivatives. All
total energies were zero-point energy (ZPE) and temperature-cor-
rected using unscaled density functional frequencies. Natural bond
orbital (NBO) analysis was used to calculate the natural charges.[28]
Molecular orbitals have been plotted with the Molekel package.[29]
Solvent effect calculations were performed with the PCM[30] model
implemented in Gaussian 03. The total energy and total free energy
were evaluated from single-point PCM calculations on the gas
phase optimized geometries at the same level of theory. CH2Cl2
was used as the solvent as in the experimental work.
[9] a) E. E. Nifant’ev, M. K. Gratchev, S. Yu. Burmistrov, Chem.
Rev. 2000, 100, 3755–3799; b) E. E. Nifant’ev, M. K. Gratchev,
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Struchkov, Tetrahedron 1991, 47, 9839–9860.
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[13] C–N bonds in organic formamidine derivatives have only a
partial double bond, see: a) T. M. Krygowski, K. Wozniak, in
The Chemistry of Amidines and Imidates (Eds.: S. Patai, Z. Rap-
poport), John Wiley & Sons, Chichester, 1991, p. 101–147; b)
A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Wat-
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Dunitz), VCH, Weinheim, 1994, vol. 2, pp. 770–774.
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2582
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Eur. J. Inorg. Chem. 2008, 2577–2583

N-Phosphanylformamidines (phosfam) R2ЈN–C(H)=N–PR2
[15] For DFT calculations on 3b see Supporting Information.
Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pom-
elli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y.
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K. 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. Johnson, W. Chen, M. W.
Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle, J. A. Po-
ple, Gaussian 98, Revision A.7, Gaussian, Inc., Pittsburgh PA,
2001 (A.11.1) or 2003 (A.11.3).
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Molecular Orbital Theory, John Wiley & Sons, New York,
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R. G. Parr, W. Yang, Functional Theory of Atoms and Molecules
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102, 7211–7218.
a) P. Flükiger, H. P. Lüthi, S. Portmann, J. Weber, Molekel 4.3,
Swiss Center for Scientific Computing, Manno, Switzerland,
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active Molecular Graphics Tool, Chimia 2000, 54, 766–770.
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1
[16] For JPP range values in phosphanyl-phosphonium derivatives
see for example: a) N. Burford, C. A. Dyker, A. Decken, An-
gew. Chem. Int. Ed. 2005, 44, 2364–2367; b) N. Burford, D. E.
Herbert, P. Ragogna, R. McDonald, M. J. Ferguson, J. Am.
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org. Chem. 1998, 1087–1094 and references cited therein.
[17] DFT calculations with the Cl– counterion (optimization of the
geometry of 8 in the presence of Cl–: 8·Cl) have also been car-
ried out. The geometrical parameters are quasi unchanged and
the energy difference between the σ*P1N1 orbitals in 8a·Cl and
8b·Cl is intensified (0.05 eV for 8b·Cl and –1.05 eV for 8a·Cl,
energy difference: 1.1 eV): see Figure S1 in SI.
[25]
[26]
[27]
[28]
[29]
[18] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
SIR92, A Program for Crystal Structure Solution, J. Appl.
Crystallogr. 1993, 26, 343–350.
[19] G. M.
Sheldrick,
SHELX97
(includes
SHELXS97,
SHELXL97, CIFTAB), Programs for Crystal Structure Analy-
sis (release 97-2), Universität Göttingen, Göttingen, Germany,
1998.
[20] L. J. Farrugia, WINGX-1.63, Integrated System of Windows
Programs for the Solution, Refinement and Analysis of Single
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837–838.
[21] International Tables for X-ray Crystallography, Kynoch Press,
Birmingham, England, 1974, vol. 4.
[22] R. H. Blessing, Acta Crystallogr., Sect. A 1995, 51, 33–58.
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[24] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
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[30]
Received: December 3, 2007
Published Online: April 21, 2008
Eur. J. Inorg. Chem. 2008, 2577–2583
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2583