Stable N-phosphanyl acyclic diaminocarbenes

Article abstract of DOI:10.1002/ejic.201402166

The deprotonation of N-di-tert-butylphosphanyl-N-aryl-N′-diisopropylformamidinium salts led to a new type of stable acyclic N-phosphanyl-diaminocarbene (PADC). Carbenes 8a-8d were separated as single compounds. The molecular structure of 8c was determined by X-ray diffraction analysis. The PADC 8 possess an optimal substitution pattern at the nitrogen atoms, and the N-C_carbene-N bond angle is 120.7°. Structural changes near the carbenic carbon atom, such as substitution of phenyl with mesityl, phosphanyl with selenophosphoryl, or the diisopropylamino group with 2,2,6,6-tetramethylpiperidino, rendered them unstable. The PADCs underwent N,C-phosphorus shifts to afford new C-phosphanylformamidines. The deprotonation of P^III N-substituted formamidinium salts afforded a new type of stable acyclic N-phosphanyl-diaminocarbene. The carbenes possess an optimal substitution pattern, deviations from which make them unstable. They transform into C-phosphanylformamidines by a N,C-phosphorus shift, which was studied by quantum chemistry calculations.

Full text of DOI:10.1002/ejic.201402166

FULL PAPER
DOI:10.1002/ejic.201402166
Stable N-Phosphanyl Acyclic Diaminocarbenes
Anatoliy Marchenko,[a] Georgyi Koidan,[a] Anastasiya Hurieva,[a]
Olena Kurpiieva,[a] Yurii Vlasenko,[a] Alexander B. Rozhenko,[a,b]
and Aleksandr Kostyuk*[a]
Keywords: Carbenes / Carbene precursors / Phosphanes / Density functional calculations
The deprotonation of N-di-tert-butylphosphanyl-N-aryl-NЈ-
diisopropylformamidinium salts led to a new type of stable
acyclic N-phosphanyl-diaminocarbene (PADC). Carbenes
8a–8d were separated as single compounds. The molecular
structure of 8c was determined by X-ray diffraction analysis.
The PADC 8 possess an optimal substitution pattern at the
nitrogen atoms, and the N–Ccarbene–N bond angle is 120.7°.
Structural changes near the carbenic carbon atom, such as
substitution of phenyl with mesityl, phosphanyl with seleno-
phosphoryl, or the diisopropylamino group with 2,2,6,6-tet-
ramethylpiperidino, rendered them unstable. The PADCs
underwent N,C-phosphorus shifts to afford new C-phos-
phanylformamidines.
carbenes (ADCs), provide greater opportunity to fine-tune
their catalytic activities. The N–Ccarbene–N angles of ADCs
can be changed in a greater range and they offer an even
broader variety of reactivity through the placement of
bulky or chiral substituents near the catalytic substrate
binding sites.[10–13] The first ADC B was prepared by Alder
et al. and was claimed to have indefinite lifetime at room
temperature. Later, it was shown to be much more reac-
tive.[14]
Other thermodynamically and kinetically stabilized
acyclic carbenes, such as carbenes C, were isolated.[15–18]
Bertrand et al. prepared persistent aminohydrazinocarbenes
D, which bear an amino group instead of one diisopropyl
substituent. Carbenes D underwent spontaneous radical
fragmentation or N,C-intramolecular migration.[19,20] As
NHCPs A are quite stable owing to their bulky tert-butyl
groups, it was reasonable to assume that the analogous acy-
clic N-phosphanyl-diaminocarbenes (PADCs) E would also
be stable compounds. In our previous publication, we de-
scribed some convenient approaches to N-di-tert-butyl-
selenophosphorylformamidinium salts 3 (Scheme 1) and
phosphanylformamidinium salts 7 (Scheme 3).[21] The pro-
Introduction
Over the last two decades, N-heterocyclic carbenes
(NHCs) have been the focus of many investigations. Their
properties such as their σ-donor ability and oxidative and
thermal stabilities can be varied in a broad range, which
makes them suitable for many catalytic processes.[1,2] They
are in competition with ubiquitous phosphane ligands and
quite often surpass them. NHC-based hybrid ligands with
two different types of donors, NHC and phosphane moie-
ties, have attracted considerable interest.[3] Recently, we
have designed and introduced into synthetic practice N-
phosphanyl-substituted N-heterocyclic carbenes (NHCPs)
A (Figure 1). These ligands bearing a second P-based coor-
dination site are stable and have already found some appli-
cations.[4–9] Another type of carbene, the acyclic diamino-
Figure 1. NHCPs (A), acyclic carbenes (B–D), and PADCs (E).
[a] Institute of Organic Chemistry National Academy of Sciences
of Ukraine,
Murmanska 5, Kyiv-94 02660, Ukraine
www.ioch.kiev.ua
[b] Department of Chemistry, Bielefeld University,
P. O. Box 100131, 33501 Bielefeld, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402166.
Scheme 1. Synthesis of PV N-substituted formamidinium salts 3a–
3e.
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posed methods allowed the synthesis of differently substi-
tuted formamidinium salts, which are precursors to a new
type of acyclic N-phosphanyl-diaminocarbene. The current
study is devoted to the synthesis of PADCs.
Results and Discussion
Compounds 3a–3c were described in our previous pa-
per,[21] and 3d and 3e were prepared by the same method
(Scheme 1, see Exp. Sect. for details). Compounds 3a–3e
are hydrolytically stable crystalline solids, which are insolu-
ble in water and can be handled in open air without special
precautions.
Figure 2. Perspective view of phosphane selenide 6. Selected bond
lengths [Å] and angles [°]: Se(1)–P(1) 2.1179(6), P(1)–C(9) 1.847(2),
N(1)–C(18) 1.272(3), N(2)–C(18) 1.352(3); Se(1)P(1)C(9) 113.86(7),
C(15)N(1)C(18) 118.4(2), N(2)C(18)N(1) 124.4(2).
1. Deprotonation of PV N-Substituted Formamidinium Salts
The deprotonation of salts 3a–3d was performed with
lithium hexamethyldisilazide in tetrahydrofuran (THF) at
–90 °C. In all cases, a previously unknown phosphane selen-
ide was obtained in high yield (5a–5d, Scheme 2). We as-
sumed that deprotonation led to the intermediate carbenes
4a–4d. In the 31P NMR spectrum of the reaction mixture
of 3b and lithium hexamethyldisilazide recorded at –50 °C,
2. Deprotonation of PIII N-Substituted Formamidinium
Salts
Bulky substituents kinetically stabilize carbenes. At the
same time, they broaden the NCN carbene bond angle
towards linear geometry and destabilize the singlet carbene
ground state. The broadening of the NCN carbene bond
angle through internal repulsion between bulky tBu2P(Se)
and iPr groups might be one of the factors for the instability
of carbenes 4. As PV groups are more bulky than their PIII
homologues, one might expect that trivalent PADCs E
would be more stable. The reduction of 3 was performed
with hexamethylphosphorous triamide in dichloromethane
(DCM) at room temperature in 30 min (Scheme 3).
signals at δp = 116 (1JP,Se = 749 Hz) and 80 ppm (1JP,Se
=
696 Hz) in a 3:1 ratio were detected and assigned to 4b and
5b, respectively. At room temperature, only the δp = 80 ppm
signal of phosphane selenide 5b remained in the spectrum.
Scheme 2. Deprotonation of selenophosphorylformamidinium salts
3.
Scheme 3. Reduction of salts 3.
The deprotonation of salt 3e under the same conditions
afforded phosphane selenide 6, which was formed by depro-
tonation of a methyl group by lithium hexamethyldisilazide.
The formation of 5e via carbene 4e is discussed below (see
Compounds 7a–7c were described in our previous
Scheme 5). The structure of 6 was elucidated by an X-ray work.[21] The chemical characteristics of 7d and 7e are given
diffraction study, and the perspective view and selected geo- in the Exp. Sect. Unlike the PV salts 3, the PIII N-substi-
metrical parameters are given in Figure 2. In 6, the N(2) tuted formamidinium salts 7 are sensitive both to hydrolysis
atom has a trigonal-planar environment [the sum of the and oxidation; hence, they should be handled under a rigor-
bond angles is 359.9(6)°]. Although the N(1)–C(18) bond ously inert atmosphere.
length [1.272(3) Å] corresponds to the usual C=N double
The deprotonation of salts 7 was performed by applying
bond length, the N(2)–C(18) bond [1.352(3) Å] is shorter the same procedure that was used for the deprotonation of
than the usual length of a C(sp2)–N(sp2) single bond salts 3, that is, lithium hexamethyldisilazide in THF at
(1.45 Å).[22]
–90 °C. Unlike formamidinium salts 3, which feature a
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pentavalent phosphorus substituent, N-phosphanylform-
amidinium salts 7 bear a trivalent phosphorus substituent
and afforded stable carbenes 8, which are low-melting crys-
talline compounds or oils (Scheme 4). The lifetimes (t1/2) of
carbenes 8a–8d in solution at 20 °C are 14 d. The formation
of carbene 8e was observed only by 31P NMR spectroscopy
(δp = 110 ppm). It has a short lifetime (t1/2 = 8 h at 16 °C)
and, hence, was used for further transformations without
separation. Such a striking difference in the stability of 8e
compared with those of 8a–d can be attributed to the higher
bulkiness of the mesityl group compared to the other aryl
groups in 8a–d.
Scheme 4. Synthesis of carbenes 8.
The molecular structure of 8c was determined by single-
crystal X-ray diffraction (Figure 3). Two independent mo-
lecules are found in the unit cell. The N(1)C(1)N(2) angle
of 121.1(2)° is almost the same as that in ADC B (121.0°).
The N(1) and N(2) atoms both have a trigonal-planar bond angles [°]: P(1)–N(1) 1.746(2), N(1)–C(1) 1.380(3), N(2)–C(1)
configuration [the sums of the bond angles are 358.6(6)° for
Figure 3. Perspective view of 8c. Selected bond lengths [Å] and
1.325(3); P(1)N(1)C(1) 118.8(1), N(1)C(1)N(2) 121.1(2), P(1)N(1)
C(7) 112.3(1).
N(1) and 359.4(6)° for N(2)]. Although the N(1)–C(1) bond
lengths are almost identical in both carbenes [1.380(3) and
1.381(6) Å for 8c and B, respectively], the significantly
shorter N(2)–C(1) bond of 8c [1.325(3) Å] than that in B
[1.363(6) Å] indicates a higher double bond character. As a
result, the isopropyl groups of carbenes 8 are nonequivalent
and exhibit double sets of signals in their 1H and 13C NMR
spectra. The 13C NMR chemical shift of the carbenic center
lies at δ = 271 ppm, which is 15 ppm downfield of the chem-
ical shift of the methylidene carbon atom in B.
The distillation of carbenes 8 in vacuo resulted in a N,C-
phosphorus shift to afford the C-phosphanyl formamidines
9 (Scheme 5). As was shown previously,[4,5,7,23] NHCPs un-
dergo a N,C-phosphorus shift at 20–150 °C to give 2-phos-
phorylated imidazoles. The carbenes bearing an imino
Scheme 5. Reactivity of carbenes 8.
group as a wingtip substituent are also prone to N,C-mi-
gration if they are not kinetically stabilized. Thus, com-
pounds of the type 1-methylimidazolium-3-[C(Ph)=N(2,6- sterically protected N-dimethyl-NЈ-tolyl-NЈ-di(diisoprop-
R2C6H3)] chloride (R = H, Me, iPr) undergo N,C-re- ylamino)phosphanylformamidinium salt in the presence of
arrangement upon deprotonation with KH. At the same selenium to form
a
stable, distillable compound
time, the analogous carbene with a tert-butyl substituent Me2NC[SeP(NiPr2)2]=NC6H4Me.[27] We rationalized that
instead of a methyl group [1-tert-butylimidazolium-3- deprotonation led to the transient carbene, which reacted
C(Ph)=NPh] was isolated, and some metal complexes were with selenium at the carbenic atom followed by a phos-
prepared.[24,25]
phorus shift from nitrogen to selenium.[27] In contrast, carb-
Stable (amino)(phosphanyl)carbenes react with elemen- enes 8 with the more bulky substituents react with selenium
tal sulfur at the phosphorus atom to afford (amino)(thio- at the phosphorus atom. The intermediately formed carb-
phosphoranyl)carbenes.[26] Also, other group 16 elements enes 4 underwent N,C-phosphorus shift to give phosphane
form stable adducts with short-lived and persistent carb- selenides 5 in high yields (Scheme 5). It should be noted
enes. Previously, we described the deprotonation of the less that carbene 8e bearing a mesityl group reacted with selen-
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ium like the other carbenes 8. This corroborates the fact hydrogen shift from a methyl group bound to the piperidine
that deprotonation of 3e does not proceed via carbene 4e ring. Highly basic aminoalkyl and aminosilyl carbenes un-
(Scheme 2).
dergo analogous rearrangements.[16,17] The second pathway
Preliminary studies on the reactions of the carbenes 8 is a N,C-phosphorus shift to afford phosphane 17 analo-
with palladium salts showed that they readily afford chelate gously to the transformation of carbenes 8 to phosphanes
complexes. These results will be reported separately.
9 (Scheme 5). The third radical pathway resulted in the for-
mation of dimers 15 and 16 in almost equal quantities. An
analogous radical fragmentation was proposed for hydraz-
inoaminocarbenes.[19,20] It also might be assumed that some
amount of phosphane 17 formed by this pathway as well.
The structure of 15 was unambiguously confirmed by sin-
gle-crystal X-ray diffractometry. The perspective view of the
structure of 15 and selected geometrical parameters are
given in Figure 4. The N(1)–C(8) and N(2)–C(8) bonds in
3. Deprotonation of Formamidinium Salts Featuring a
2,2,6,6-Tetramethylpiperidino Group
The lifetimes of carbenes 8 (14 d, 20 °C) are much
shorter than that of carbene B. To further kinetically stabi-
lize these carbenes, we introduced a bulkier 2,2,6,6-tet-
ramethylpiperidino group instead of the diisopropylamino
one to check whether it made them more stable. The corre-
sponding Alder dimer 11 was prepared by the standard pro-
cedure by mixing amide 10 with triflic anhydride. Com-
pound 11 is stable in the solid state and can be stored in a
fridge, but it slowly decomposes in solution. The PV (12)
and PIII (13) N-substituted formamidinium salts were pre-
pared as described previously for analogous diisoprop-
ylamino salts 3 and 7 (Scheme 6).
Scheme 6. Synthesis of formamidinium salt 12.
The deprotonation of salt 13 was carried out in THF at
–90 °C. The 31P NMR spectrum of the reaction mixture at
–50 °C exhibited a signal at δp = 123.4 ppm, which might
be assigned to carbene 8f (Scheme 7, δp = 119 ppm for carb-
enes 8). Warming the reaction mixture to room temperature
led to the decomposition of carbene 8f and resulted in a set
of compounds 14–17, which were separated and charac-
terized. This set of compounds testifies that the decomposi-
tion of 8f proceeds by at least three pathways. The first
Figure 4. Perspective view of 15. Selected bond lengths [Å] and
angles [°]: N(1)–C(5) 1.411(2), N(1)–C(8) 1.281(2), N(2)–C(8)
1.424(2), C(8)–C(8Ј) 1.542(2); C(5)N(1)C(8) 129.4(1), N(2)C(8)
pathway is an intramolecular rearrangement to 14 by a N(1) 125.1(1), C(8)N(2)C(9) 117.7(1).
Scheme 7. Synthesis of carbene 8f and its decomposition products.
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15 are of usual lengths; the only exception is the C(8)–C(8Ј) mechanisms for their rearrangements or decompositions,
bond [1.542(2) Å], which is definitely longer than the typi- quantum chemistry calculation were performed at the DFT
cal single C(sp2)–C(sp2) bond length of 1.48 Å.[22]
level of approximation (RI-BP86/TZVP, level I). We have
Carbene 8f bearing a tetramethylpiperidino group ap- calculated the stable carbene structure 8a, piperidine deriva-
peared to be less stable than the other carbenes 8 with a tive 8f, and model structure 20, in which the substituents
diisopropylamino group. Thus, the introduction of the R1–R3 are replaced by methyl groups for comparison. The
bulkier substituent destabilized carbene 8f. The stability of latter makes it possible to model all the processes in a sim-
carbenes correlate to some extent with the difference in en- pler way. The most important factor for the instability of
ergies of the single and triple ground states (ΔEST).[28,29] the compounds of interest is the migration of the di-tert-
Increasingly bulky substituents at the carbenic center butylphosphanyl group to the carbenic carbon atom. The
broaden the N–Ccarbene–N angle and, therefore, favor the most significant distinction between B and carbenes 8 is
triplet state and decrease ΔEST (vide infra).
that the phosphanyl group attached to the nitrogen atom is
By analogy, we expected that the deprotonation of PV N- clearly more disposed towards migration than the isopropyl
substituted formamidinium salt 12 would result in phos- group of carbene B.
phane selenide 18. The deprotonation was monitored by 31
P
At first sight, the environments of the carbene centers of
NMR spectroscopy. In 2 h after the addition of lithium structures 8a and 8f seem to be very similar. However, the
hexamethyldisilazide, the reaction mixture exhibited a optimized (RI-BP86/TZVP) structures within the gas-phase
broadened signal of carbene 4f at δp = 116 ppm, which approximation differ significantly. In 8a and in 8f, the dialk-
upon warming to room temperature transformed into a sig- ylamino moieties are involved to a greater extent in the n,p-
1
nal (δp = 86 ppm, JP,Se = 706 Hz) assigned to phosphane electron delocalization than the phosphorylated amino moi-
selenide 18. Our attempts to isolate 18 led to an unidentifi- eties. This is well demonstrated by comparing the N1–C
able mixture. At the same time, it was possible to reduce 18 and N2–C bond lengths in 8a (1.342 and 1.377 Å, respec-
to phosphane 17 in good yield (Scheme 8).
tively). However, these two bonds in 8f are longer (the cor-
responding values are 1.355 and 1.391 Å). Therefore, the
amino groups in 8f donate less effectively into the formally
vacant p orbital at the methylidene carbon atom. The envi-
ronment of the N2 atom in 8f is less planar than that in 8a
(the sums of the bond angles are 351.8 and 358.4°, respec-
tively). The only visible reason for this is the more compact
conformation of the isopropyl groups in the iPr2N substitu-
ents in 8a, in which the hydrogen atoms point in the same
direction. Such a conformation is not possible for 8f, in
which the position of the CMe2 moieties in the cyclic struc-
ture are fixed and the structure suffers from the steric repul-
sion between the phenyl ring and methyl groups at the 2-
position of the piperidine ring. In the experiments (vide su-
pra), 8f undergoes the rearrangement of the phosphanyl
group more easily, and this can be clearly linked to the
lower thermodynamic stability of 8f compared to that of
8a. The less sterically crowded model structure 20
(Scheme 10, R1–R3 = Me) is probably the best suited for
the n,p-conjugation (the N1–C and N2–C bond lengths are
1.345 and 1.348 Å, respectively), but, similarly to bis(di-
methylamino)carbene, it will lose some steric protection.
Scheme 8. Deprotonation of salt 12.
With phosphane 17 in hand, we verified the stability of
its pentavalent derivatives. The reaction of phosphane 17
with selenium led to a complex mixture, and no products
could be separated. Compound 18 appeared to be unstable.
At the same time, its oxygen congener 19 is a stable crystal-
line compound. Compound 19 was prepared in good yield
by oxidation of phosphane 17 with hydrogen peroxide
(Scheme 9).
Scheme 9. Oxidation of phosphane 17.
To summarize the data on the synthesized carbenes, it
can be stated that stable acyclic diaminocarbenes 8 have
an optimal substitution pattern with substituents such as
diisopropylamino and di-tert-butylphosphanyl(phenyl)-
amino groups. Increasing the volume of the substituents in
this substitution pattern destabilizes the carbenes.
Scheme 10. Intramolecular phosphanyl group N,C-rearrangement
in carbene structures 8, 8f, and 20.
As already mentioned above, the singlet–triplet energy
gap (ΔEST) correlates to some extent with the thermo-
dynamic stability of carbenes.[28,29] Our calculations predict
a significantly larger ΔEST value for 8a (37.5 kcal/mol) than
4. DFT Calculations
To estimate quantitatively the relative stabilities of PIII for 8f (22.8 kcal/mol; see the Supporting Information for a
and PV N-substituted carbenes and elucidate plausible detailed description of the triplet state structures).
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Conventional DFT methods are known to overestimate magnitudes derived for 8f (21.9 and 21.3 kcal/mol, respec-
unfavorable steric interactions. Under definite conditions, tively). These data are in the best agreement with the experi-
the repulsion can turn into attraction, owing to favored van mentally found lower stability of 8f towards the rearrange-
der Waals forces. To ensure that electron dispersion effects ment in Scheme 10. The migration should proceed even
and the lower thermodynamic stability of 8f compared to more easily for 20 (see Figure S1 in the Supporting Infor-
8a were taken into account, these structures were reopti- mation): the energy barrier ΔE is only 19.0 kcal/mol (ΔG =
mized by using the RI-B97 DFT functional with the newest 19.5 kcal/mol). Such simple structures are expected to be
generation of corrections on dispersion effects of Grimme even less stable than 8f, in particular towards to the N,C-
(D3)[30,31] and more-polarized def2-TZVP basis sets[32] rearrangement.
(level II). The corresponding equilibrium structures and the
The situation becomes more complicated for the addition
most important geometry parameters are shown in Fig- of selenium to 8a and 20 (Schemes 5 and 11). The two nu-
ure 5. All of the above-mentioned structural differences for cleophilic centers in the carbenes of interest allow the dif-
the structures optimized with the less accurate DFT func- ferent intermediate adducts 4 and 21 (R1–R3 = Me). The
tional are also observed for the reoptimized geometries.
DFT calculations (level I) indicate higher stability for the
products of C-addition of selenium (21) than for the P=Se
derivatives 4 (ΔG = –3.7 kcal/mol). Our calculations predict
that a stepwise energy decrease is expected for the suggested
transformation 21Ǟ22Ǟ23, as shown in Scheme 11 (ΔG
0.0, –2.7, and –5.8 kcal/mol, respectively), whereas for the
isomerization of the experimental structure 8a, the reaction
should end at the stage of 22b (ΔG 0.0, –12.9 and –6.2 kcal/
mol, respectively). However, the intrinsic reaction coordi-
nate (IRC) calculations for pathway I exhibit no transition
state corresponding to the migration from 21 to 22. The
reaction could only proceed by a two-step mechanism that
Figure 5. Jmol[33] presentation of the most-favored optimized (RI- includes the dissociation into a [PR3 ]+ phosphenium cation
B97-D3/def2-TZVP) structures 8a (left) and 8f (right). The most
2
and the remaining anionic structure with the subsequent
important calculated bond lengths [Å] and angles [°] for 8a and 8f,
formation of the C–P bond. Such a reaction is more prob-
respectively: C1–N1 1.335, 1.347; C1–N2 1.377, 1.390; P1–N2
able for the more-stable bis(amino)phosphenium cation, for
1.784, 1.797; N1C1N2 121.1, 121.8; C1N1C2 130.0, 128.8;
example, as in structure Me2NC[SeP(NiPr2)2]=NC6H4Me
(24), which was isolated recently as one of the two products
of the reaction of the carbene Me2NC(:)N(C6H4Me-p)-
P[N(iPr)2]2 with selenium.[27]
C1N1C3 114.3, 109.5; C2N1C3 115.2, 117.3; C1N2P1 118.2, 116.8;
C1N2C4 127.0, 124.8; P1N2C4 113.0, 112.4.
To put these qualitative considerations on firmer ground,
we have also located the transition-state structures that
correspond to the N,C-rearrangement of the phosphanyl
groups in 8a and 8f. The reaction proceeds in a concerted
mode via the three-membered cyclic structures 8a-TS and
8f-TS (Figure 6). Within the gas-phase approximation, the
calculated 8a activation energies (ΔE = 23.3 and ΔG =
23.6 kcal/mol) for the stable species are higher than the
Scheme 11. Two routes for the intramolecular N,C-rearrangement
in carbene structures 8, 20.
Product 24 did not isomerize to the corresponding C–P
derivative. Indeed, our DFT calculations predict no path-
ways for the direct 21Ǟ23 and 22Ǟ23 transformations (see
Supporting Information for details).
The transformation of 4 by pathway II is characterized
by the transition-state structure 4-TS (Figure 7) with a
three-membered cyclic geometry similar to that of 8a-TS.
The activation energy values (ΔE = 19.2, ΔG = 20.3 kcal/
mol) are significantly lower than the corresponding values
derived for the more-stable N-phosphanyl derivative 8a (ΔE
Figure 6. Jmol presentation of optimized (RI-BP86/TZVP) struc-
tures 8a-TS (left) and 8f-TS (right). The most important calculated
bond lengths [Å] and angles [°] for 8a-TS and 8f-TS, respectively:
C1–N1 1.359, 1.386; C1–N2 1.337, 1.328; P1–C1 2.237, 2.295; P1–
N2 2.006, 1.999; N1C1N2 125.1, 125.7; C1N1C2 123.8, 127.1;
C1N1C3 120.5, 115.0; C2N1C3 115.3, 117.3; C1N2P1 81.4, 84.7;
P1C1N2 62.4, 60.2; C1P1N2 36.2, 35.2; C1N2C4 143.0, 138.4;
P1N2C4 135.2, 136.1.
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= 23.3, ΔG = 23.6 kcal/mol), which agrees well with the ness of the substituents at the nitrogen atoms, an optimal
experimental findings discussed above.
substitution pattern that renders the carbenes stable was
found. N-Diisopropylamino-NЈ-di-tert-butylphosphanyl-
NЈ-(p-R-phenyl)aminocarbenes were separated and charac-
terized. On heating, the carbenes underwent N,C-phos-
phorus migration to afford C-phosphanyl-substituted for-
mamidines. The pentavalent N-phosphoroselenoyl-substi-
tuted diaminocarbenes appeared to be transient species,
which were identified only in solution by 31P NMR spec-
troscopy. They underwent spontaneous N,C-phosphorus
migration to afford C-phosphoroselenoyl-substituted for-
mamidines. Quantum chemical analyses of the reaction
mechanism predict that the intramolecular migration oc-
curs via a transition state with a three-membered ring. For
sterically crowded phosphanylcarbenes, a radial cleavage/re-
combination mechanism is also possible.
Figure 7. Jmol presentation of the optimized (RI-BP86/TZVP)
structures 4 (left) and 4-TS (right). The most important calculated
bond lengths [Å] and angles [°] for 4 and 4-TS, respectively: C1–
N1 1.338, 1.356; C1–N2 1.369, 1.332; P1–C1 –, 2.127; P1–N2
1.813, 1.983; N1C1N2 123.4, 126.7; C1N1C2 130.8, 122.4;
C1N1C3 115.0, 122.6; C2N1C3 114.2, 114.8; C1N2P1 112.1, 77.1;
P1C1N2 –, 65.3; C1P1N2 –, 37.6; C1N2C4 129.9, 136.9; P1N2C4
117.1, 142.6.
Experimental Section
General: All procedures with air- and moisture-sensitive com-
pounds were performed under an atmosphere of dry argon in
flame-dried glassware. Solvents were purified and dried by standard
methods. Melting points were determined with an electrothermal
The presence of 15 and 16 within the reaction products
in the attempt to prepare carbene 8f gives evidence of the
radical decomposition of 8f. Our calculations predict a pos-
itive reaction energy for the homolytic cleavage of the P–N
bond in 8a (Scheme 10, ΔE = +12.4 kcal/mol; Ar = Ph) but
a negative energy value for 8f (ΔE = –4.4 kcal/mol). As the
theoretical estimation of activation energies for radical pro-
cesses is cumbersome within the single-determinant
approximation and this aspect is beyond the scope of the
current manuscript, we can only conclude that the radical
mechanism of the migration of the phosphanyl group in 8f
is also thermodynamically favored (Scheme 12).
1
capillary melting point apparatus. H NMR spectra were recorded
with a Bruker Avance DRX 500 (500.1 MHz) or Varian VXR-300
(299.9 MHz) spectrometer. 13C NMR spectra were recorded with a
Bruker Avance DRX 500 (125.7 MHz) spectrometer. 31P NMR
spectra were recorded with a Varian VXR-300 (121.4 MHz) spec-
trometer. Chemical shifts (δ) are reported in ppm relative to in-
1
ternal tetramethylsilane (TMS; for H and 13C) and external 85%
H3PO4 (for 31P). Chromatography was performed on silica gel
Gerudan SI60. Elemental analyses were performed at the analytical
laboratory of the Institute of the Organic Chemistry, National
Academy of Sciences of Ukraine.
Details of Calculations: All of the structures were first optimized
by using the TURBOMOLE set of programs (version 6.2 or
6.4)[34–36] without symmetry constrains. The resolution of the ident-
ity (RI) based BP86 approach[37,38] was used in combination with
the TZVP basis sets (basis sets of triple-zeta quality[32] plus one p
function set for hydrogen atoms or plus one d function set for all
other atoms). To increase agreement with the experimental results,
structures 8a, 8f, and 20 were reoptimized by using the Grimme
RI-B97 DFT functional corrected for dispersion effects (D3)[30,31]
and the more-polarized def2-TZVP basis sets.[32] The IRC calcula-
tions and the preliminary searches of the TS structures were per-
formed with the GAUSSIAN-03 program package at the BP86/6-
31G* level of theory. The located TS structures were then reopti-
mized by using the TURBOMOLE set of programs at the RI-
BP86/TZVP level of approximation with the standard parameters
for the transition-state optimization routine (itvc = 1, -trans option
by geometry optimization). The vibrational frequencies were calcu-
lated analytically or numerically (for the RI-B97-D3 functional).
All the stationary points are characterized by no imaginary fre-
quencies (local minima) or one imaginary frequency (TS struc-
tures). The equilibrium structures were plotted by using the Jmol
program.[33]
Scheme 12. The homolytic cleavage of the P–N bond in N-phos-
phanyl carbenes.
Thus, the quantum chemical calculations predict an in-
tramolecular concerted N,C-rearrangement for the studied
carbenes. However, lower activation energies were predicted
for the rearrangement of the selenophosphoryl group in
carbenes 4; they may not be isolable. In contrast, the larger
activation barriers calculated for the migration of the phos-
phanyl groups in phosphanylcarbenes 8 determine their
higher stability. For the more sterically crowded carbene 8f,
the homolytic cleavage of the P–N bond also seems to be
favored. This explains the presence of the radical recombi-
nation products within the experimentally isolated sub-
stances.
X-ray Crystal Structure Determination of 6, 8c, and 15: Crystal data
for 6: C24H43N2PSe, M = 469.55, monoclinic, space group P21/n,
a = 12.4773(2), b = 14.3874(3), c = 15.4889(3) Å, β = 106.538(1)°,
Conclusions
A new type of acyclic N-phosphanyl-substituted diami-
nocarbene was prepared. Through variation of the bulki- V = 2665.48(9) Å3, Z = 4, dc = 1.170 gcm–3, μ = 1.480 mm–1,
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F(000) = 1000, crystal size ca. 0.45ϫ 0.56ϫ 0.67 mm. 8c:
C22H39N2OP, M = 378.54, monoclinic, space group P21/n, a =
10.4148(5), b = 27.512(1), c = 16.3944(8) Å, β = 92.757(3)°, V =
(125.7 MHz, CDCl3): δ = 19.2 (s, CH3), 20.9 (s, CH3), 21.3 (s,
CH3), 24.7 (s, CH3), 29.3 (s, CH3), 46.6 (d, J = 26 Hz, C), 52.9 (s,
CH), 53.7 (s, CH), 131.4 (s, CH), 135.3 (d, J = 1 Hz, C), 136.6 (s,
4692.0(4) Å3, Z = 8, dc = 1.072 gcm–3, μ = 0.129 mm–1, F(000) = CH), 142.0 (s, C), 162.3 (d, J = 16 Hz, CH) ppm. 31P NMR
1664, crystal size ca. 0.34ϫ 0.36ϫ 0.49 mm. 15: C34H50N4O2, M ( 2 0 2 . 4 M H z , C D C l 3 ) : δ = 1 4 8 ( J P, S e = 7 9 8 H z ) p p m .
= 546.80, monoclinic, space group P21/c, a = 9.6872(2), b =
C25H44F3N2O3PSSe (619.64): calcd. C 48.46, H 7.16, N 4.52; found
20.0485(5), c = 7.8825(2) Å, β = 100.111(1)°, V = 1507.11(6) Å3, Z C 48.59, H 7.54, N 4.61.
= 2, dc = 1.205 gcm–3, μ = 0.075 mm–1, F(000) = 596, crystal size
General Procedure for the Deprotonation of Salts 3: To a suspension
ca. 0.26ϫ 0.31ϫ 0.36 mm. The intensities of 49130 (6), 110196
(8c), and 15550 (15) reflections were measured at 173(1) K (for 8c
and 15) with a Bruker Smart Apex II diffractometer operating in
the ω and φ scan mode. 5453 (6), 9713 (8c), and 3182 (15) unique
reflections [Rint = 0.059 (6), 0.072 (8c), 0.035 (15)] were used in
further refinements. The data were corrected for Lorentz and polar-
ization effects. The structures were solved by direct methods and
refined by the full-matrix least-squares technique in the anisotropic
approximation for non-hydrogen atoms by using the SHELXS97
and SHELXL97 programs[39,40] and the CRYSTALS program
package.[41] Hydrogen atoms were located in the difference Fourier
maps and refined with fixed positional and thermal parameters.
The Chebychev[42] weighting Scheme was used. SADABS absorp-
tion corrections were applied. For 6, the refinement converged to
R1 = 0.0304, Rw = 0.0318, GOF = 1.1299 for 3574 observed reflec-
tions with IϾ3σ(I) (253 parameters; observed/variable ratio 14.1);
for 8c, R1 = 0.0628, Rw = 0.0574, GOF = 1.1096 for 6405 observed
reflections with IϾ3σ(I) (469 parameters; observed/variable ratio
13.7); for 15, R1 = 0.0396, Rw = 0.0356, GOF = 1.0457 for 2451
observed reflections with IϾ3σ(I) (181 parameters; observed/vari-
able ratio 13.5).
of 3b (1 mmol) in THF (10 mL) cooled to –90 °C was added a
solution of lithium hexamethyldisilazide (1 mmol) in THF (5 mL)
over 5 min with stirring. The 31P NMR spectrum of the reaction
mixture taken at –50 °C exhibited a signal at δp = 116 ppm (JP,Se
=
749 Hz), assigned tentatively to the corresponding carbene 4b, and
a signal of 5b (δp = 80 ppm, JP,Se = 696 Hz) in a ratio 3:1. The
reaction mixture was warmed to room temperature over 1 h. The
31P NMR spectrum of the reaction mixture exhibited only the sig-
nal of 5b. The solvent was evaporated, and the residue was treated
with pentane (30 mL). The solid was removed by filtration and
washed with pentane (3ϫ 10 mL). The pentane was evaporated,
and the residue was kept in vacuo at 50 °C and 0.05 Torr until the
mass was constant. Pentane (10 mL) was added to the residue to
give a solution with some solid residue, which was removed by fil-
tration. The clear solution was evaporated to give pure target com-
pound 5b.
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(phenyl)phosphanylcarbox-
imidamide Selenide (5a): White crystals, yield 91 %, m.p. 140–
141 °C (pentane). 1H NMR (300 MHz, CDCl3): δ = 1.39 (d, J =
7.2 Hz, 12 H, CH3), 1.52 (d, J = 15.6 Hz, 18 H, CH3), 4.41 (m, 2
H, CH), 6.83 (d, J = 7.5 Hz, 2 H, CH), 7.03 (t, J = 7.2 Hz, 1 H,
CH), 7.32 (t, J = 8.1 Hz, 2 H, ArH) ppm. 13C NMR (125.7 MHz,
CDCl3): δ = 23.6 (s, CH3), 29.0 (s, CH3), 41.1 (d, J = 29 Hz, C),
51.6 (s, CH), 119.1 (s, CH), 123.0 (s, CH), 129.3 (s, CH), 149.0
(d, J = 18 Hz, ipso-C), 158.6 (d, J = 97 Hz, CH) ppm. 31P NMR
(202.4 MHz, CDCl3): δ = 80.6 (JP,Se = 698 Hz) ppm. MS: m/z =
427 [M]+. C21H37N2PSe (427.48): calcd. C 59.01, H 8.72, N 6.55;
found C 59.43, H 8.59, N 6.82.
CCDC-988039 (for 6), -988038 (for 8c), and -988040 (for 15) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
General Procedure for the Synthesis of Compounds 3: To the Alder
dimer 2 (5 mmol) cooled to 0 °C was added a solution of 1
(5 mmol) in DMC (30 mL). Over 15 min, the temperature was in-
creased to 20 °C, and the reaction mixture was stirred for 3 h. The
solvent was removed under reduced pressure. The residue was
washed with diethyl ether (3ϫ 20 mL). The crystalline residue was
collected by filtration, washed with water (3ϫ 20 mL), dried with
P2O5, and then washed with a small amount of THF.
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(4-methylphenyl)phosphanyl-
carboximidamide Selenide (5b): White crystals, yield 84 %, m.p.
123–124 °C (pentane). 1H NMR (300 MHz, CDCl3): δ = 1.16 (d,
J = 7.2 Hz, 12 H, CH3), 1.52 (d, J = 15.6 Hz, 18 H, CH3), 2.32 (s,
3 H, CH3), 4.41 (m, 2 H, CH), 6.74 (d, J = 8.4 Hz, 2 H, CH), 7.12
(d, J = 8.4 Hz, 2 H, CH) ppm. 13C NMR (125.7 MHz, CDCl3): δ
= 20.9 (s, CH3), 23.6 (s, CH3), 29.0 (s, CH3), 41.1 (d, J = 29 Hz,
C), 51.5 (s, CH), 119.0 (s, CH), 129.9 (s, CH), 132.5 (s, ipso-C),
146.4 (d, J = 18 Hz, ipso-C), 158.4 (d, J = 98 Hz, C=N) ppm. 31P
NMR (202.4 MHz, CDCl3): δ = 80.7 (JP,Se = 696 Hz) ppm.
C22H39N2PSe (441.50): calcd. C 59.85, H 8.90, N 6.35; found C
60.12, H 8.77, N 6.51.
[(Di-tert-butylphosphanylselenoyl)-4-trifluoromethylphenylmeth-
ylene]diisopropylaminoammonium Trifluoromethanesulfonate (3d):
White crystals, yield 96%, m.p. 164–165 °C (CH3CN). 1H NMR
(300 MHz, CDCl3): δ = 0.97 (d, J = 6.6 Hz, 6 H, CH3), 1.49 (d, J
= 20.1 Hz, 18 H, CH3), 1.52 (d, J = 6.6 Hz, 6 H, CH3), 3.54 (m, 1
H, CH), 4.06 (m, 1 H, CH), 7.77 (d, J = 9.0 Hz, 2 H, CH), 7.85
(d, J = 8.7 Hz, 2 H, CH), 9.14 (d, J = 4.8 Hz, 1 H, CH) ppm. 13C
NMR (125.7 MHz, CDCl3): δ = 18.8 (s, CH3), 24.4 (s, CH3), 29.2
(s, CH3), 45.1 (q, J = 28 Hz, C), 53.1 (s, CH), 53.5 (s, CH), 120.8
(q, J = 290 Hz, CF3), 127.7 (s, CH), 130.4 (s, CH), 132.9 (q, J =
33 Hz, C), 141.3 (s, C), 158.0 (d, J = 14 Hz, CH) ppm. 31P NMR
(202.4 MHz, CDCl3): δ = 146 (JP,Se = 828 Hz) ppm. MS: m/z = 496
[M]+. C23H37F6N2O3PSSe (645.55): calcd. C 42.79, H 5.78, N 4.34;
found C 43.11, H 5.94, N 4.21.
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(4-methoxyphenyl)phosphanyl-
carboximidamide Selenide (5c): White crystals, yield 77%, m.p. 95–
96 °C (CH3CN). 1H NMR (300 MHz, CDCl3): δ = 1.16 (d, J =
6.9 Hz, 12 H, CH3), 1.49 (d, J = 15.6 Hz, 18 H, CH3), 3.77 (s, 3
H, CH3O), 4.37 (m, 2 H, CH), 6.78 (d, J = 7.8 Hz, 2 H, CH), 6.87
(d, J = 7.8 Hz, 2 H, CH) ppm. 13C NMR (125.7 MHz, CDCl3): δ
= 23.7 (s, CH3), 29.0 (s, CH3), 41.1 (d, J = 29 Hz, C), 51.4 (s, CH),
55.6 (s, CH3O), 114.7 (s, CH), 120.1 (s, CH), 142.2 (d, C), 155.8 (s,
C), 158.5 (d, J = 99 Hz, CN) ppm. 31P NMR (202.4 MHz, CDCl3):
δ = 80.7 (JP,Se = 696 Hz) ppm. MS: m/z = 457. C22H39N2OPSe
(457.50): calcd. C 57.76, H 8.59, N 6.12; found C 57.42, H 8.26, N
5.83.
[(Di-tert-butylphosphanylselenoyl)-2,4,6-trimethylphenylmethylene]-
diisopropylaminoammonium Trifluoromethanesulfonate (3e): White
crystals, yield 49 %, m.p. 161–163 °C (CH3CN). 1H NMR
(300 MHz, CDCl3): δ = 1.01 (d, J = 3.5 Hz, 6 H, CH3), 1.47 (d, J
= 12.5 Hz, 18 H, CH3), 1.52 (d, J = 4.0 Hz, 6 H, CH3), 2.33 (s, 3
H, CH3), 2.44 (s, 6 H, CH3), 3.69 (m, 1 H, CH), 4.20 (m, 1 H, 1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(4-trifluoromethylphenyl)phos-
CH), 8.05 (s, 2 H, CH), 9.75 (br s, 1 H, CH) ppm. 13C NMR
phanylcarboximidamide Selenide (5d): White crystals, yield 72%,
Eur. J. Inorg. Chem. 2014, 3259–3270
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m.p. 127–128 °C (pentane). 1H NMR (300 MHz, CDCl3): δ = 1.17
(d, J = 7.2 Hz, 12 H, CH3), 1.52 (d, J = 15.6 Hz, 18 H, CH3), 4.45
(m, 2 H, CH), 6.91 (d, J = 8.1 Hz, 2 H, CH), 7.57 (d, J = 8.4 Hz,
General Procedure for the Synthesis of Carbenes 8: To a suspension
of 7 (1 mmol) in THF (10 mL) cooled to –90 °C was added a solu-
tion of lithium hexamethyldisilazide (1 mmol) in THF (5 mL) over
2 H, CH) ppm. 13C NMR (125.7 MHz, CDCl3): δ = 23.5 (s, CH3), 5 min with stirring. The reaction mixture was warmed to room tem-
28.9 (s, CH3), 41.3 (d, J = 29 Hz, C), 51.7 (s, CH), 119.2 (s, CH),
perature over 1 h. The solvent was evaporated, and the residue was
124.4 (q, J = 272 Hz, CF3), 125.1 (q, J = 40 Hz, C), 126.6 (q, J = treated with pentane (30 mL). The solid was removed by filtration
4 Hz, CH), 152.0 (d, J = 18 Hz, C), 159.4 (d, J = 93 Hz, C=N)
ppm. 31P NMR (CDCl3, 202.4 MHz): δ = 82 (JP,Se = 706 Hz) ppm.
and washed with pentane (3ϫ 10 mL). The pentane was evapo-
rated, and the residue was kept in vacuo at 50 °C and 0.05 Torr
C22H36F3N2PSe (495.47): calcd. C 53.33, H 7.32, N 5.65; found C until the mass was constant. Pentane (10 mL) was added to the
53.72, H 7.51, N 5.81.
residue to give a solution with some solid residue, which was re-
moved by filtration. The clear solution was evaporated to give pure
target compound 8.
NЈ-(2-{[Di-tert-butyl(selanylidene)-λ5-phosphanyl]methyl}-4,6-di-
methylphenyl)-N,N-bis(propan-2-yl)methanimidamide (6): White
crystals, yield 88 %, m.p. 148–149 °C (pentane). 1H NMR
(300 MHz, CDCl3): δ = 1.23 (d, J = 6.6 Hz, 12 H, CH3), 1.32 (d,
J = 14.7 Hz, 18 H, CH3), 2.09 (s, 3 H, CH3), 2.26 (s, 3 H, CH3),
3.54 (m, 1 H, CH), 3.56 (d, J = 12 Hz, 2 H, CH2), 4.84 (m, 1 H,
CH), 6.87 (s, 1 H, CH), 7.36 (s, 1 H, CH=N), 7.91 (s, 1 H, CH)
ppm. 13C NMR (125.7 MHz, CDCl3): δ = 19.5 (s, CH3), 20.1 (s,
CH3), 20.8 (s, CH3), 24.5 (s, CH3), 24.5 (d, JC,P = 35 Hz, CH2),
28.4 (s, CH3), 38.0 (d, J = 33 Hz, C), 44.8 (s, CH), 45.1 (s, CH),
126.0 (d, J = 6 Hz, ipso-C), 128.5 (s, ipso-C), 129.3 (d, J = 3 Hz,
C), 130.3 (s, CH), 147.9 (d, J = 6 Hz, C), 151.5 (s, C) ppm. 31P
NMR (202.4 MHz, CDCl3): δ = 78 (JP,Se = 692 Hz) ppm. MS: m/z
= 469 [M]+. C24H43N2PSe (469.56): calcd. C 61.39, H 9.23, N 5.97;
found C 61.24, H 9.11, N 6.27.
[(Di-tert-butylphosphanyl)phenylamino]diisopropylaminocarbene
(8a): Yield 97%, m.p. 28–30 °C (not crystallized), t1/2 = 14 d at
1
20 °C. H NMR (500 MHz, C6D6): δ = 0.62 (d, J = 6.5 Hz, 6 H,
CH3), 1.40 (d, J = 6.5 Hz, 6 H, CH3), 1.42 (d, J = 12.0 Hz, 18 H,
CH3), 3.42 (m, 1 H, CH), 3.84 (m, 1 H, CH), 6.83 (t, J = 7.5 Hz,
1 H, CH), 7.01 (t, J = 8.0 Hz, 2 H, CH), 7.14 (d, J = 8.5 Hz, 2 H,
CH) ppm. 13C NMR (125.7 MHz, C6D6): δ = 19.4 (s, CH3), 25.6
(s, CH3), 29.7 (d, J = 4.0 Hz, CH3), 36.6 (d, J = 31 Hz, C), 48.3 (s,
CH), 123.7 (d, J = 1 Hz, CH), 126.4 (d, J = 8 Hz, CH), 128.9 (s,
CH), 154.1 (d, J = 24 Hz, ipso-C), 273.7 (s, C:) ppm. 31P NMR
(202.4 MHz, C6D6): δ = 119 ppm.
[(Di-tert-butylphosphanyl)-4-methylphenylamino]diisopropylamino-
1
carbene (8b): Yellow oil, yield 96%, t1/2 = 14 d at 20 °C. H NMR
General Procedure for the Synthesis of Compounds 7: To a solution
of 3 (5 mmol) in DCM (15 mL) at 20 °C, hexamethylphosphorous
triamide (5.5 mmol) was added dropwise with stirring. After
30 min, the solvent was evaporated to dryness. Dry diethyl ether
(40 mL) was added to the residue. The flask was shaken till a crys-
talline solid formed. The solid was collected by filtration, washed
with diethyl ether, and dried to constant weight in vacuo
(0.05 Torr). If necessary, these compounds can be recrystallized
from dry THF.
(500 MHz): δ = 0.65 (d, J = 7 Hz, 6 H, CH3), 1.41 (d, J = 7 Hz, 6
H, CH3), 1.43 (d, J = 12.0 Hz, 18 H, CH3), 2.06 (s, 3 H, CH3),
3.44 (m, 1 H, CH), 3.93 (m, 1 H, CH), 6.86 (d, J = 8.0 Hz, 2 H,
CH), 7.06 (d, J = 8.0 Hz, 2 H, CH) ppm. 13C NMR (500 MHz,
C6D6): δ = 19.5 (s, CH3), 20.5 (s, CH3), 25.7 (s, CH3), 29.8 (d, J =
17 Hz, CH3), 36.5 (d, J = 30 Hz, C), 48.3 (s, CH), 48.5 (s, CH),
126.4 (d, J = 8 Hz, CN), 129.1 (s, CH), 133.1 (s, ipso-C), 151.5 (d,
J = 24 Hz, ipso-C), 272.4 (s, C:) ppm. 31P NMR (202.4 MHz,
C6D6): δ = 119 ppm.
[(Di-tert-butylphosphanyl)trifluoromethylphenylamino]methylenedi-
isopropylammonium Trifluoromethanesulfonate (7d): White crystals,
yield 98%, m.p. 169–170 °C. 1H NMR (300 MHz, CD3CN): δ =
1.04 (d, J = 6.6 Hz, 6 H, CH3), 1.38 (d, J = 13.2 Hz, 18 H, CH3),
1.52 (d, J = 6.6 Hz, 6 H, CH3), 3.66 (m, 1 H, CH), 4.12 (m, 1 H,
CH), 7.63 (d, J = 8.4 Hz, 2 H, CH), 7.87 (d, J = 8.4 Hz, 2 H, CH)
ppm. 13C NMR (125.7 MHz, CD3CN): δ = 17.6 (s, CH3), 23.3 (s,
CH3), 28.6 (d, J = 16 Hz, CH3), 36.8 (q, J = 38 Hz, C), 51.3 (s,
CH), 52.7 (s, CH), 121.2 (q, J = 322 Hz, CF3SO3), 123.7 (q, J =
272 Hz, CF3), 127.1 (q, J = 4 Hz, CH), 127.6 (q, J = 4 Hz, CH),
130.2 (q, J = 29 Hz, ipso-C), 147.9 (br s, C), 155.9 (br s, C) ppm.
31P NMR (CD3CN, 81 MHz): δ = 140 ppm. C23H37F6N2O3PS
(566.59): calcd. C 48.76, H 6.58, N 4.94; found C 48.28, H 6.72, N
5.31.
[(Di-tert-butylphosphanyl)-4-methoxyphenylamino]diisopropyl-
aminocarbene (8c): White crystals, yield 94%, m.p. 63–65 °C (pent-
ane), t1/2 = 14 d at 20 °C. H NMR (300 MHz, C6D6): δ = 0.67 (d,
1
J = 6.6 Hz, 6 H, CH3), 1.43 (d, J = 6.3 Hz, 6 H, CH3), 1.47 (d, J
= 12.0 Hz, 18 H, CH3), 3.28 (s, 3 H, CH3O), 3.44 (m, 1 H, CH),
3.94 (m, 1 H, CH), 6.64 (d, J = 9.3 Hz, 2 H, CH), 6.89 (d, J =
7.2 Hz, 2 H, CH) ppm. 13C NMR (125.7 MHz, C6D6): δ = 19.7 (s,
CH3), 25.7 (s, CH3), 29.8 (d, J = 16 Hz, CH3), 36.5 (d, J = 32 Hz,
C), 48.3 (s, CH), 48.4 (s, CH), 54.6 (s, CH3O), 113.8 (s, CH), 127.5
(s, CH), 147.0 (d, J = 25 Hz, ipso-C), 156.4 (s, ipso-C), 271 (s, C:)
ppm. 31P NMR (202.4 MHz, C6D6): δ = 119 ppm.
[(Di-tert-butylphosphanyl)-4-trifluoromethylphenylamino]diisoprop-
ylaminocarbene (8d): White crystals, yield 89%, m.p. 50–52 °C
(pentane), t1/2 = 14 d at 20 °C. 1H NMR (300 MHz, C6D6): δ =
0.53 (d, J = 6.6 Hz, 6 H, CH3), 1.35 (d, J = 6.6 Hz, 6 H, CH3),
1.36 (d, J = 12.3 Hz, 18 H, CH3), 3.39 (m, 1 H, CH), 3.72 (m, 1
H, CH), 7.03 (d, J = 8.7 Hz, 2 H, CH), 7.24 (d, J = 8.4 Hz, 2 H,
CH) ppm. 13C NMR (125.7 MHz, C6D6): δ = 18.7 (s, CH3), 25.4
(s, CH3), 29.5 (d, J = 18 Hz, CH3), 36.7 (d, J = 30 Hz, C), 48.6 (s,
CH), 49.5 (s, CH), 120.1 (q, J = 244 Hz, CF3), 125.5 (q, J = 4 Hz,
CH), 125.7 (d, J = 10 Hz, CH), 157.0 (d, J = 24 Hz, C), 278.3 (s,
C:) ppm. 31P NMR (81 MHz, C6D6): δ = 119 ppm. Carbene 8e:
31P NMR (81 MHz, reaction mixture): δ = 109.6 ppm. t1/2 = 8 h at
16 °C.
[(Di-tert-butylphosphanyl)-2,4,6-trimethylphenylamino]methylene-
diisopropylammonium Trifluoromethanesulfonate (7e): White crys-
tals, yield 99%, m.p. 169–170 °C, 1H NMR (300 MHz, CD3CN): δ
= 0.99 (d, J = 6.6 Hz, 6 H, CH3), 1.36 (d, J = 12.9 Hz, 18 H, CH3),
1.49 (d, J = 6.6 Hz, 6 H, CH3), 2.28 (s, 3 H, CH3), 2.39 (s, 6 H,
CH3), 3.69 (m, 1 H, CH), 4.09 (m, 1 H, CH), 7.07 (s, 2 H, CH),
7.70 (s, 1 H, CH) ppm. 13C NMR (125.7 MHz, CD3CN): δ = 18.5
(s, CH3), 19.9 (s, Ar CH3), 20.9 (s, Ar CH3), 21.0 (s, Ar CH3), 23.7
(s, CH3), 28.8 (d, J = 15 Hz, CH3), 37.2 (d, J = 40 Hz, C), 50.8 (s,
CH), 51.4 (s, CH), 131.6 (s, CH), 133.1 (d, J = 3 Hz, C), 138.6 (d,
J = 14 Hz, C), 139.7 (d, J = 1 Hz, C), 156.2 (d, J = 5 Hz, CH)
ppm. 31P NMR (CD3CN, 81 MHz): δ = 134 ppm. MS: m/z = 391
[M]+. C25H44F3N2O3PS (540.68): calcd. C 55.54, H 8.20, N 5.18;
found C 55.73, H 8.02, N 5.31.
Distillation of Carbenes (8): Carbenes 8a and 8c (1 g) were distilled
in vacuo at 0.05 Torr to give 9a and 9c. Compound 8e was trans-
formed into compound 9e at 20 °C.
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1
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(phenyl)phosphanylcarbox-
imidamide (9a): Yellow oil, yield 90%, b.p. 150–152 °C/0.05 Torr.
1H NMR (300 MHz, C6D6): δ = 1.03 (d, J = 6.9 Hz, 12 H, CH3),
1.40 (d, J = 11.7 Hz, 18 H, CH3), 4.1 (m, 2 H, CH), 6.7–6.9 (m, 2
Salt 12: White crystals, yield 97%, m.p. 131–132 °C (CH3CN). H
NMR (300 MHz, CD3CN): δ = 0.94 (s, 6 H, CH3), 1.45 (d, J =
18 Hz, 18 H, CH3), 1.66 (s, 6 H, CH3),1.80 (m, 4 H, CH2), 1.94
(m, 2 H, CH2),3.85 (s, 3 H, CH3), 7.07 (d, J = 9.3 Hz, 2 H, CH),
H, CH), 7.17 (m, 3 H, CH) ppm. 13C NMR (125.7 MHz, C6D6): δ 7.47 (d, J = 8.0 Hz, 2 H, CH), 9.99 (br s, 1 H, CH) ppm. 13C NMR
= 22.9 (d, J = 3 Hz, CH3), 30.5 (d, J = 14 Hz, CH3), 33.6 (d, J = (125.7 MHz, CD3CN): δ = 12.5 (s, CH2), 26.1 (s, CH3), 28.6 (s,
25 Hz, C), 49.4 (s, CH), 49.5 (s, CH), 118.8 (s, CH), 120.4 (s, CH), CH3), 31.3 (s, CH3), 31.2 (s, CH2), 35.5 (s, CH2), 45.9 (d, J = 29 Hz,
128.9 (s, CH), 152.4 (s, C), 163.3 (d, J = 19 Hz, CN) ppm. 31P C), 55.8 (s, CH3O), 65.1 (s, C), 68.6 (s, C), 115.5 (s, CH), 132.4 (s,
NMR (81 MHz, C6D6): δ = 39 ppm. C21H37N2P (348.52): calcd. N
8.04, P 8.89; found N 7.83, P 9.21.
CH), 161.4 (s, CO) ppm. 31P NMR (CD3CN, 81 MHz): δ = 149
ppm. MS: m/z = 498 [M]+. C26H44F3N2O4PSSe (647.65): calcd. C
48.22, H 6.85, N 4.33; found C 47.83, H 6.41, N 4.61.
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(4-methoxyphenyl)phosphanyl-
carboximidamide (9c): White crystals, yield 89 %, m.p. 63–64 °C
Salt 13: The general procedure for the synthesis of 7 was used.
1
1
(pentane). H NMR (300 MHz, C6D6): δ = 1.07 (d, J = 6.9 Hz, 12
White crystals, yield 97%, m.p. 111–112 °C. H NMR (300 MHz,
H, CH3), 1.42 (d, J = 11.7 Hz, 18 H, CH3), 3.39 (s, 3 H, CH3O),
4.16 (m, 2 H, CH), 6.74 (d, J = 9.0 Hz, 2 H, CH), 6.82 (d, J =
9.0 Hz, 2 H, CH) ppm. 13C NMR (125.7 MHz, C6D6): δ = 23.0 (d,
J = 3 Hz, CH3), 30.5 (d, J = 14 Hz, CH3), 33.6 (d, J = 25 Hz, C),
49.5 (d, J = 11 Hz, CH), 54.8 (s, CH3O), 114.5 (s, CH), 119.6 (s,
CH), 146.0 (s, C), 154.5 (s, C), 164.0 (d, J = 17 Hz, CN) ppm. 31P
NMR (81 MHz, C6D6): δ = 39 ppm. C22H39N2OP (378.54): calcd.
N 7.40, P 8.18; found N 7.74, P 8.41.
CDCl3): δ = 1.07 (s, 6 H, CH3), 1.33 (d, J = 12.9 Hz, 18 H, CH3),
1.66 (s, 6 H, CH3), 1.78 (m, 4 H, CH2), 1.99 (m, 2 H, CH2), 3.80
(s, 3 H, CH3O), 6.98 (d, J = 8.7 Hz, 2 H, CH), 7.18 (d, J = 8.7 Hz,
2 H, CH), 8.05 (s, 1 H, CH) ppm. 13C NMR (125.7 MHz, CDCl3):
δ = 13.1 (s, CH2), 27.3 (s, CH3), 29.4 (d, J = 16 Hz, CH3), 31.6 (s,
CH2), 31.8 (s, CH3), 36.9 (s, CH2), 37.3 (d, J = 39 Hz, C), 55.8 (s,
CH3O), 64.7 (s, C), 65.3 (s, C), 115.4 (s, CH), 128.8 (d, J = 6 Hz,
CH3), 139.8 (d, J = 18 Hz, C), 159.7 (s, C), 162.4 (d, J = 8 Hz, CH)
ppm. 31P NMR (CDCl3, 81 MHz): δ = 140 ppm. C26H44F3N2O4PS
(568.69): calcd. C 54.91, H 7.80, N 4.93; found C 55.13, H 7.91, N
5.07.
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(2,4,6-trimethylphenyl)phos-
phanylcarboximidamide (9e): White crystals, yield 76%, m.p. 114–
115 °C (pentane). 1H NMR (300 MHz, C6D6): δ = 1.11 (d, J =
6.9 Hz, 12 H, CH3), 1.46 (d, J = 11.7 Hz, 18 H, CH3), 2.23 (s, 3
H, CH3), 2.32 (s, 6 H, CH3), 4.10 (m, 2 H, CH), 6.82 (s, 2 H, CH)
ppm. 13C NMR (500 MHz, C6D6): δ = 20.8 (s, CH3), 20.9 (s, CH3),
24.0 (s, CH3), 31.1 (d, J = 15 Hz, CH3), 34.6 (d, J = 26 Hz, C),
49.5 (d, J = 11 Hz, CH), 125.3 (s, C), 129.2 (s, C), 129.4 (s, CH),
147.8 (s, C), 161.6 (d, J = 24 Hz, CN) ppm. 31P NMR (81 MHz,
C6D6): δ = 39 ppm. C24H43N2P (390.60): calcd. N 7.17, P 7.93;
found N 7.02, P 8.11.
Deprotonation of Salt 13: To a solution of 13 (2.43 g, 4.3 mmol) in
THF (15 mL) cooled to –90 °C was added a solution of lithium
hexamethyldisilazide (0.72 g, 4.3 mmol) in THF (15 mL) over
10 min with stirring. After 30 min, the 31P NMR spectrum of the
reaction mixture at –50 °C exhibited a signal at δp = 123.4 ppm,
which was tentatively assigned to the carbene 8f. The reaction mix-
ture was warmed to room temperature and left for 20 h. The sol-
vent was evaporated; the residue was extracted with pentane (2ϫ
20 mL). In 20 h, red crystals of 15 precipitated from the pentane
solution and were collected by filtration. The filtrate was placed in
a freezer at –18 °C, and after 72 h the precipitated 17 (0.74 g, 42%)
was collected by filtration. The filtrate was evaporated to dryness.
The residue was treated by silica gel chromatography (eluent:
dichloromethane) to give 14 (Rf = 0.05–0.35, oil, 0.8 g, 45%) and
16 (Rf = 0.6–0.8, 30 mg, 5%, δp = 40.6 ppm).
Reactions of Carbenes 8 with Selenium: To a solution of 8 (1 mmol)
in THF (5 mL) cooled to 0 °C was added finely ground selenium
(1.2 mmol). The reaction mixture was stirred for 1 h. The solvent
was evaporated, and the solid residue was extracted with pentane
(3ϫ 5 mL). The volume of the solution was reduced to 2 mL and
it was left in a freezer at –18 °C. The precipitated solid was col-
lected by filtration. 5c: yield 76%. 5d: yield 69%.
N-(Di-tert-butylphosphanyl)-NЈ-(2,6-dimethylhept-6-en-2-yl)-N-(4-
methoxyphenyl)methanimidamide (14): Yield 42%, oil. H NMR
1,1-Di-tert-butyl-N,N-diisopropyl-NЈ-(2,4,6-trimethylphenyl)phos-
phanylcarboximidamide Selenide (5e): White crystals, yield 81 %,
m.p. 158–160 °C (CH3CN). 1H NMR (300 MHz, CDCl3): δ = 1.20
(d, J = 6.5 Hz, 12 H, CH3), 1.63 (d, J = 16.0 Hz, 18 H, CH3), 2.25
(s, 9 H, CH3), 4.80 (m, 2 H, CH), 6.85 (s, 2 H, CH) ppm. 13C NMR
(125.7 MHz, CDCl3): δ = 20.5 (s, CH3), 20.7 (s, CH3), 24.8 (s,
CH3), 29.3 (s, CH3), 41.9 (d, J = 29 Hz, C), 51.3 (s, CH), 125.5 (s,
C), 129.6 (s, CH), 131.4 (s, C), 144.9 (d, J = 18 Hz, C), 156.2 (d, J
1
(500 MHz, C6D6): δ = 1.16 (s, 6 H, CH3), 1.26 (d, J = 12.0 Hz, 18
H, CH3), 1.44–1.52 (m, 4 H, CH2), 1.66 (s, 6 H, CH3), 1.95 (m, 2
H, CH2), 3.26 (s, 3 H, CH3O), 4.80 (m, 2 H, CH2), 6.75 (d, J =
8.0 Hz, 2 H, CH), 7.34 (d, J = 8.0 Hz, 2 H, CH), 7.97 (s, 1 H, CH)
ppm. 13C NMR (125.7 MHz, C6D6): δ = 22.2 (s, CH3), 22.5 (s,
CH2), 28.3 (s, CH3), 29.9 (d, J = 16 Hz, CH3), 35.9 (d, J = 33 Hz,
C), 38.3 (s, CH2), 44.0 (s, CH2), 54.5 (s, CH3O), 56.2 (s, CH2), 109.9
(s, CH2), 113.4 (s, CH) 129.2 (d, J = 5 Hz, CH), 145.7 (s, C), 150.3
(br s, CH=N), 156.7 (s, ipso-C) ppm. 31P NMR (C6D6, 81 MHz):
δ = 97 ppm. C25H43N2OP (418.61): calcd. N 6.69, P 7.40; found N
6.81, P 7.73.
= 97 Hz, CN) ppm. 31P NMR (81 MHz, CDCl3): δ = 81 (JP,Se
=
778 Hz) ppm. C24H43N2PSe (469.56): calcd. C 61.39, H 9.23, N
5.97, P 6.60; found C 61.07, H 9.55, N 6.27, P 6.92.
Alder Dimer 11: To a cooled –78 °C solution of trifluoromethane-
sulfonic anhydride (0.02 mol) in dichloromethane (30 mL), a solu-
tion of formamide 10 (0.044 mol) in dichloromethane (30 mL) was
added. The reaction mixture was stirred until the temperature rose
to 20 °C, and then for 2 h. The precipitate was collected by fil-
tration under argon, washed with dichloromethane (3ϫ 20 mL),
and dried to give pure compound 11, yield 72%, white crystals,
m.p. 180–184. 1H NMR (300 MHz, CD3CN): δ = 1.72 (s, 12 H,
1
Compound 15: Red crystals, yield 5%, m.p. 158–159 °C. H NMR
(300 MHz, C6D6): δ = 1.14 (s, 6 H, CH3), 1.47 (m, 2 H, CH), 1.53
(s, 6 H, CH3), 1.75 (m, 2 H, CH2), 1.85 (m, 2 H, CH2), 3.34 (s, 3
H, CH3), 6.90 (d, J = 9.0 Hz, 2 H, CH), 7.39 (d, J = 9.0 Hz, 2 H,
CH) ppm. 13C NMR (125.7 MHz, C6D6): δ = 18.7 (s, CH2), 30.1
(s, CH3), 31.6 (s, CH3), 39.4 (s, CH2), 54.6 (s, CH3O), 55.1 (s, C),
CH3), 1.77 (s, 12 H, CH3), 1.80–2.15 (m, 12 H, CH2), 8.96 (s, 1 H, 113.8 (s, CH), 123.5 (s, CH), 143.3 (s, C), 157.1 (s, C), 161.8 (s,
CH) ppm. C22H38F6N2O7S2 (620.68): calcd. C 42.57, H 6.17, N CH=N) ppm. C34H50N4O2 (546.80): calcd. C 74.68, H 9.22, N
4.51; found C 42.82, H 6.59, N 4.81.
10.25; found C 74.51, H 8.91, N 10.51.
Eur. J. Inorg. Chem. 2014, 3259–3270
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N-[(Di-tert-butylphosphanyl)(2,2,6,6-tetramethylpiperidin-1-yl)meth-
ylidene]-4-methoxyaniline (17): White crystals, m.p. 128–129 °C
(pentane), yield 42%. 1H NMR (500 MHz, C6D6): δ = 1.13 (s, 6
H, CH3), 1.43 (m, 24 H, CH3), 1.59 (m, 6 H, CH2), 3.36 (s, 3 H,
CH3O), 6.82 (m, 4 H, CH2) ppm. 13C NMR (125.7 MHz, C6D6):
δ = 14.7 (s, CH2), 30.9 (d, J = 13 Hz, CH3), 31.6 (d, J = 10 Hz,
CH3), 34.7 (d, J = 26 Hz, CH), 37.6 (s, CH2), 54.7 (s, CH3O), 56.9
(s, C), 114.5 (s, C), 120.8 (br s, CH), 146.8 (s, ipso-C), 155.2 (s, C),
166.9 (d, J = 30 Hz, C=N) ppm. 31P NMR (C6D6, 81 MHz): δ =
51 ppm. C25H43N2OP (418.61): calcd. C 71.73, H 10.35, N 6.69;
found C 71.51, H 10.03, N 6.78.
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Deprotonation of Salt 12: To a suspension of salt 12 (2.46 g,
3.8 mmol) in THF (40 mL) cooled to –78 °C was added a solution
of lithium hexamethyldisilazide (0.64 g, 3.8 mmol) in THF (25 mL)
with stirring. After 2 h, the 31P NMR spectrum of the reaction
mixture at –20 °C exhibited a broad signal at δp = 116.3 ppm, which
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room temperature, and in 20 min the 31P NMR spectrum of the
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reaction mixture exhibited a signal at δp = 85.7 ppm (JP,Se
=
706 Hz), which was assigned to the phosphane selenide 18. The
reaction mixture was cooled to –10 °C and added a solution of
(Me2N)3P (0.83 g, 5 mmol) in THF (5 mL). The temperature was
increased to 20 °C, and after 30 min the reaction mixture was evap-
orated to dryness. Pentane (25 mL) was added to the residue; solid
lithium triflate was removed by filtration and washed with pentane
(3ϫ 5 mL). The pentane was evaporated, and then (Me2N)3PSe
was removed by distillation at 120 °C and 0.05 Torr. The residue
was dissolved in pentane (5 mL) and treated with activated carbon.
The mixture was filtered; the activated carbon was washed with
pentane (3ϫ 5 mL). The pentane was evaporated to dryness. The
residue was dissolved in pentane (4 mL) and left in a freezer at
–30 °C. The precipitated phosphane 17 was collected by filtration,
yield 1.03 g, 65%.
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Compound 19: To a solution of 17 (0.27 g, 0.6 mmol) in benzene
cooled to 0–5 °C, hydrogen peroxide (0.3 mL, 30%) was added. The
reaction mixture was stirred for 10 min at 20 °C, the benzene was
evaporated, and the solid was washed with water (3ϫ 5 mL). The
remaining solid was purified by plate chromatography (eluent
EtOAc, Rf = 0.6–0.7) to give pure phosphane oxide 19, yield 86%,
white crystals, m.p. 117–118 °C (hexane). 1H NMR (500 MHz,
CDCl3): δ = 1.25 (s, 6 H, CH3), 1.37 (d, J = 13.5 Hz, 18 H, CH3),
1.4–1.8 (m, 6 H, CH2), 1.57 (s, 6 H, CH3), 3.80 (s, 3 H, CH3O),
6.85 (d, J = 9.3 Hz, CH), 6.97 (d, J = 8.7 Hz, 2 H, CH) ppm. 13C
NMR (125.7 MHz, CDCl3): δ = 16.2 (s, CH2), 28.6 (s, CH3), 29.8
(s, CH3), 32.3 (s, CH3), 38.7 (s, CH2), 39.6 (d, J = 55 Hz, C), 55.5
(s, CH3O), 58.2 (s, C), 114.2 (s, C), 122.3 (s, CH), 142.8 (d, J =
23 Hz, C), 156.4 (s, C), 160.7 (d, J = 127 Hz, C=N) ppm. 31P NMR
(CDCl3, 81 MHz): δ = 54 ppm. C25H43N2O2P (434.61): calcd. C
69.09, H 9.97, N 6.45; found C 69.31, H 10.17, N 6.34.
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Acknowledgments
The generous financial support from the German Alexander von
Humboldt Foundation to purchase computers and the license for
the TURBOMOLE set of programs is gratefully acknowledged.
The authors thank Prof. Uwe Manthe and Dr. Thorsten Tönsing,
University of Bielefeld (Germany), for access to the computer clus-
ter and the GAUSSIAN03 set of programs and the SKIT super-
computer team at the Institute of Cybernetic, NAS of Ukraine for
providing access to the SKIT computer cluster for A. B. R.
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Received: March 14, 2014
Published Online: June 12, 2014
Eur. J. Inorg. Chem. 2014, 3259–3270
3270
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim