Imino-bridged bisphosphaalkenes (2,4-diphospha-3-azapentadienes)

Article abstract of DOI:10.1002/chem.200903166

Deprotonation of aminophosphaalkenes (RMe₂Si)₂C= PN(H)(R') (R = Me, iPr; R' = tBu, 1adamantyl (1-Ada), 2,4,6-tBu ₃C₆H₂ (Mes^*)) followed by reactions of the corresponding Li salts Li[(RMe₂Si)₂C= P(M)(R')] with one equivalent of the corresponding P-chlorophosphaalkenes (RMe₂Si)₂C=PCl provides bisphosphaalkenes (2,4-diphospha-3-azapentadienes) [(RMe₂Si)₂C=P] ₂NR'. The thermally unstable tert-butyliminobisphosphaalkene [(Me₃Si)₂C=P]₂NtBu (4a) undergoes isomerisation reactions by Me₃Si-group migration that lead to mixtures of four-membered heterocyles, but in the presence of an excess amount of (Me ₃Si)₂C=PCl, 4a furnishes an azatriphosphabicyclohexene C₃(SiMe₃)₅P₃NtBu (5) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P=C double bond and an exocyclic ylidic P⁽⁺⁾-C^(-),(SiMe₃) ₂unit. Using the bulkier tPrMe₂Si substituents at three-coordinated carbon leads to slightly enhanced thermal stability of 2,4-diphospha-3-azapentadienes [(tPrMe₂Si)₂C=P] ₂NR' (R' = tBu: 4b; R' = l-Ada: 8). According to a low-temperature crystal-structure determination, 8 adopts a non-planar structure with two distinctly differently oriented P=C sites, but ³¹P NMR spectra in solution exhibit singlet signals. ³¹P NMR spectra also reveal that bulky Mes^* groups (Mes^* = 2,4,6-tBu ₃C₆H₂) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P-N bonds in persistent compounds [(RMe₂Si) ₂C=P]₂NMes^* (11a, 11b). DFT calculations for the parent molecule [(H₃Si)₂C=P]₂NCH ₃ suggest that the non-planar distortion of compound 8 will have steric grounds.

Full text of DOI:10.1002/chem.200903166

FULL PAPER
DOI: 10.1002/chem.200903166
Imino-Bridged Bisphosphaalkenes (2,4-Diphospha-3-azapentadienes)
Roxana M. Bꢀrzoi,[a] Delia Bugnariu,[a] Rafael Guerrero Gimeno,[a] Daniela Lungu,[a]
Vera Zota,[b] Constantin Daniliuc,[a] Peter G. Jones,[a] Zoltꢁn Benkꢂ,[c] Lꢁszlꢃ Kçnczçl,[c]
Lꢁszlꢃ Nyulꢁszi,[c] Rainer Bartsch,[a] Wolf-W. du Mont,*[a] and Edgar Niecke[b]
Abstract: Deprotonation of amino-
phosphaalkenes (RMe2Si)2C=
PN(H)(R’) (R=Me, iPr; R’=tBu, 1-
adamantyl (1-Ada), 2,4,6-tBu3C6H2
(Mes*)) followed by reactions of the
an
azatriphosphabicyclohexene
Ada: 8). According to a low-tempera-
ture crystal-structure determination, 8
adopts a non-planar structure with two
distinctly differently oriented P=C
sites, but 31P NMR spectra in solution
exhibit singlet signals. 31P NMR spectra
also reveal that bulky Mes* groups
(Mes*=2,4,6-tBu3C6H2) at the central
imino function lead to mixtures of sym-
metric and unsymmetric rotamers, thus
implying hindered rotation around the
C3AHCTUNGTRNN(ENUG SiMe3)5P3NtBu (5) that gave red
single crystals. Compound 5 contains a
diphosphirane ring condensed with an
azatriphospholene system that exhibits
an endocylic P=C double bond and an
ꢀ
corresponding Li salts LiACTHNUTRGEN[UNG (RMe2Si)2C=
P(M)(R’)] with one equivalent of the
corresponding P-chlorophosphaalkenes
(RMe2Si)2C=PCl provides bisphos-
phaalkenes (2,4-diphospha-3-azapenta-
dienes) [(RMe2Si)2C=P]2NR’. The ther-
mally unstable tert-butyliminobisphos-
phaalkene [(Me3Si)2C=P]2NtBu (4a)
undergoes isomerisation reactions by
Me3Si-group migration that lead to
mixtures of four-membered hetero-
cyles, but in the presence of an excess
amount of (Me3Si)2C=PCl, 4a furnishes
exocyclic ylidic P(+) (ꢀ)(SiMe3)2 unit.
C ACHTUNTGNRUEGN
Using the bulkier iPrMe2Si substituents
at three-coordinated carbon leads to
slightly enhanced thermal stability of
2,4-diphospha-3-azapentadienes [(iPr-
Me2Si)2C=P]2NR’ (R’=tBu: 4b; R’=1-
ꢀ
P N bonds in persistent compounds
[(RMe2Si)2C=P]2NMes* (11a, 11b).
DFT calculations for the parent mole-
cule [(H3Si)2C=P]2NCH3 suggest that
the non-planar distortion of compound
8 will have steric grounds.
Keywords: bisphosphaalkenes
·
density functional calculations · het-
erocycles · PNP ligands · X-ray
diffraction
Introduction
Multiply unsaturated organophosphorus compounds are
useful tools in coordination chemistry and catalysis, but as
energy-rich compounds they are also excellent starting ma-
terials for cycloaddition reactions that lead to heterocyles,
cages and polymers.[1,2] The 2,3,4-triphosphapentadienide
anion [(Me3Si)2C=P]2Pꢀ (Scheme 1A; E=P),[3] which allows
electronic communication between the p systems (P=C
bonds) of two neighbouring phosphaalkene moieties, is a
precursor to P3C2 heterocycles and bicycles.[3] Its heavier 3-
[a] Dr. R. M. Bꢀrzoi, Dr. D. Bugnariu, Dr. R. G. Gimeno, D. Lungu,
Dr. C. Daniliuc, Prof. Dr. P. G. Jones, Dr. R. Bartsch,
Prof. Dr. W.-W. d. . Mont
Institut fꢁr Anorganische und Analytische Chemie
Technische Universitꢂt Braunschweig
Hagenring 30, 38106 Braunschweig (Germany)
Fax : (+49)531-3915387
E-mail: w.du-mont@tu-bs.de
[b] Dr. V. Zota, Prof. Dr. E. Niecke
Institut fꢁr Anorganische Chemie, Universitꢂt Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
[c] Dr. Z. Benkꢃ, L. Kçnczçl, Prof. Dr. L. Nyulꢄszi
Department of Inorganic and Analytical Chemistry
Budapest University of Technology and Economics
Szt Gellꢅrt tꢅr 4, 1521 Budapest (Hungary)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200903166.
Scheme 1. Heteroatom-bridged bisphosphaalkenes.
Chem. Eur. J. 2010, 16, 4843 – 4851
ꢆ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4843

arsenic congener [(Me3Si)2C=P]2Asꢀ (Scheme 1A; E=As)[4]
as well as isoelectronic uncharged species [(Me3Si)2C=P]2E
(E=O, S, Se; Scheme 1B)[5,6] are also known, but nitrogen-
bridged derivatives (2,4-diphospha-3-azapentadienes) are
(Mes*=2,4,6-tBu3C6H2).[14,16] Experimental results are de-
scribed in the following.
extremely rare. [Ph
A
C
Results and Discussion
alkyl-2,4-diphospha-3-azapentadiene already reported in the
literature, is thermally unstable, and only a particular 2-[6-
bis(trimethylsilyl)amino]pyridylimino-bridged bisphosphaal-
kene (Scheme 1C), which contains its P=C functions orien-
tated orthogonally out of the NP2 plane, was found to be a
stable compound.[8] Related 2,4-diphospha-1,3,5-triazapenta-
dienes (RN=P)2NR’, however, are well established.[9] In the
last decade, bifunctional phosphaalkene ligands have led to
remarkable applications in catalysis.[2,10,11] The recent obser-
vation that two-coordinated phosphorus atoms from “mono-
unsaturated” P-(phosphanylamino)phosphaalkene ligands
(Me3Si)2C=P-N(R)-PPh2 tend to undergo carbene-like inser-
Syntheses, reactions and structures: The numbering of start-
ing materials, their reactions and products is depicted in
Scheme 2.
New alkyl- and arylaminophosphaalkenes: The pathway to
the new chlorophosphaalkene 1b and to new aminophos-
phaalkenes 2b, 6, 9a and 9b is described in Equations (1)–
(3) (see Scheme 2).[5,16b,18,19]
tButylimino-bridged bisphosphaalkenes: Lithium salts Li-
ACHUTNGREN[NUG (RMe2Si)2C=PNCAHTUNGTNER(NUGN tBu)] [3a: R=Me; 3b: R=iPr; Eq. (3)]
ꢀ
ꢀ
tion reactions into Pd Cl and Pt Cl bonds that lead to
were generated by deprotonation of the parent aminophos-
phaalkenes 2a, 2b with lithium diisopropylamide (LDA) in
THF and subsequent removal of iPr2NH in vacuo.
unique metalla
ACHTUNGTRENNUNG
stable “bi-unsaturated” iminobisphosphaalkenes that may
also exhibit unusual behaviour as ligands in transition-metal
chemistry, and, because of the inductively electron-with-
drawing and p-conjugating properties of the central nitrogen
atom,[13,14] offer particular tunable p-acceptor properties.
The first attempts to prepare compounds related to the
Compounds 3a and 3b react with the corresponding P-
chlorophosphaalkenes[15,19] at temperatures below ꢀ408C in
a straightforward manner to furnish solutions of the desired
tert-butylimino-bridged bis-phosphaalkenes 4a, 4b, which
exhibit singlet signals in 31P NMR spectra. Raising the tem-
perature to 08C and above leads to decomposition reactions,
as indicated by the increasing intensity of one or more
31P NMR spectroscopic signals that appear as AX-type (d,d)
patterns.
unstable [Ph
ACHTUNGTRENNUNG(Me3Si)C=P]2NAHCUTNGTREN(NUGN nC3H7) according to Appelꢇs
protocol,[7] P-chlorophosphaalkene/primary amine, using
(Me3Si)2C=PCl (1a) in place of PhACHTNUTRGNEUNG(Me3Si)C=PCl as a start-
ing material,[15] were unsuccessful, and aminophosphaal-
kenes (Me3Si)2C=PNHR with bulkier substituents at nitro-
[13]
gen (R=tBu, SiMe3
) were
unreactive under amine-libera-
tion conditions.[16] Subsequently,
we turned to alkali metal chlo-
ride elimination procedures
based on the deprotonation of
the
aminophosphaalkene
fol-
(Me3Si)2C=PN(H)tBu[13]
lowed by coupling of the in situ
prepared anion [(Me3Si)2C=
PNtBu]ꢀ[16,17] with P-chloro-
phosphaalkene 1a. Since the in-
sufficient stability of the prod-
ucts precluded the isolation of
single-crystalline solids, we
chose bulkier silyl groups (iPr-
Me2Si) at carbon for reactions
of anions [(RMe2Si)2C=PNR’]ꢀ
with the related chlorophos-
phaalkenes
(RMe2Si)2C=PCl
(1)[17–19] To improve crystallisa-
tion properties of thermolabile
N-alkyl products, N-1-adaman-
tyl derivatives were also intro-
duced into our study. Addition-
al experiments were carried out
with
N-Mes*
derivatives Scheme 2. Numbering of starting materials, intermediates, and products DABCO=diazabicyclooctane.
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Chem. Eur. J. 2010, 16, 4843 – 4851

Bisphosphaalkenes
FULL PAPER
In the case of [(Me3Si)2C=P]2NACTHUNGTRNEUNG(tBu) (4a), one of the new
AX patterns (31P NMR: d=358.4, 55.1 ppm, J=9 Hz; spe-
cies I) indicates the presence of a phosphaalkene-type 31P
nucleus coupling with a tri- or tetra-coordinated phosphorus
atom. The second AX pattern (31P NMR: d=135, 7.5 ppm,
J=76 Hz; species II) involves two nuclei that do not belong
to phosphaalkene functions. In some cases, apparently fav-
oured by protic impurities, a third AX pattern appears
(31P NMR: d=351.9, 38.5 ppm, J=107 Hz; species III) that
has to be assigned to another 31P(=C) nucleus coupling with
another tri- or tetra-coordinated phosphorus atom that is
Figure 1. Molecular structure of 5. Selected bond lengths [ꢈ] and angle
ꢀ
ꢀ
ꢀ
ꢀ
[8]: P1 P2 2.1933(13), P1 C7 1.688(3), P1 C15 1.783(3), P1 C8 1.829(3),
part of a 31P-C-H function (2J
ACTHNUTRGNE(NUG P,H)=13 Hz). Possible struc-
ꢀ
ꢀ
ꢀ
ꢀ
P2 C8 1.915(3), P2 N 1.720(3), P3 N 1.694(3), P3 C15 1.679(3); P2-N-
P3 120.71(16). Hydrogen atoms are omitted for clarity. Atoms are drawn
as 50% thermal ellipsoids.
tures with the measured and computed (see below)
31P NMR spectroscopic chemical shifts are depicted in
Scheme 3. The calculated and measured values are in quali-
tative agreement (see also the Supporting Information).
We assume that the motif of a (p–p)p P=C double bond
(ꢀ)
“in conjugation” with an exocyclic ylidic P(+)
from
ꢀ
C
compound 5 is also present in species I (Scheme 3), which is
a likely precursor to 5 (see below).
Compound 5 is derived from 1a by reaction with 4a or
with species I (Scheme 3) by elimination of one equivalent
of Me3SiCl. The formation of rearranged products I and II
from 4a involves trimethylsilyl-group migration, and III is
ꢀ
apparently a product of protolytic P Si bond cleavage, fol-
lowed by proton migration to the basic ylid carbon atom.
When in a “cross” experiment anion 3a reacted in an
NMR spectroscopy tube with the bulkier chlorophosphane
1b, or anion 3b reacted with 1a, the mixed-substituted
Scheme 3. Proposed structures of products from decomposition of 4a.
[a] Measured and [b] calculated at the B3LYP/cc-pVTZ//B3LYP/6-
31+G* level of theory (in ppm).
ꢀ
ꢀ
bisphosphaalkene
(Me3Si)2C=P NACHTNGUTRENNU(G tBu) P=CACHTUGNTRENNNUG
(AB pattern, 31P NMR: d=365.3, 361.8 ppm, 2J
ACHTUNGTRENNUNG
ꢁ18 Hz) was accompanied by only one rearranged species
II’ (AX pattern, 31P NMR: d=136.7, 7.3 ppm, J=78 Hz) re-
lated to the proposed species II from the “symmetric” ex-
periment. We conclude that one of the silyl-group migration
pathways (exocyclic ylid function) is closed when two bulki-
er iPrMe2Si groups are introduced at the carbon atom of
one of the P=C bonds (Schemes 3 and 4).
The addition of 1a to a reaction mixture containing de-
composing 4a leads to consumption of 4a and of rearranged
species I, with formation of a new compound 5 that exhibits
an AMX pattern in the 31P NMR spectrum (31P NMR: d=
331.2, ꢀ17.2, ꢀ24.0 ppm), involving one 31P=C phosphorus
atom coupling with two inequivalent “non-(P=C)” 31P nuclei
in a diphosphirane unit. B3LYP/cc-pVTZ//B3LYP/6-31+G*
gauge-including atomic orbital (GIAO) calculations predict
chemical shifts of d=356.9, ꢀ35.3 and ꢀ4.5 ppm for the
s2,l3, s3,l3 and s4,l5-phosphorus, respectively (for further
calculations, see the Supporting Information). Compound 5
is also sometimes observed as a trace impurity in the course
of 1:1 reactions of 1a with 3a, and it can be isolated from
the straightforward 2:1 reaction in fair crude yield [Eq. (5)].
An X-ray crystal-structure determination reveals that 5 is a
Scheme 4. Proposed structure of a major product from the cyclisation of
ꢀ
ꢀ
the
AHCTUNGTRENNUNG
unsymmetric
bisphosphaalkene
(Me3Si)2C=P NACTHNGUTERNNU(G tBu) P=C-
5-methylene-2-aza-1,3,5-triphosphabicycloACTHUNGTRNEUN[NG 3.1.0]hex-2-ene
that contains an endocyclic P=C bond (1.679(3) ꢈ) “in con-
jugation” with an exocyclic ylidic P(+)
(1.688(3) ꢈ) involving one of the two bridgehead phospho-
rus atoms that are part of a diphosphirane together with an-
C
G
In the case of tert-butyliminobisphosphaalkene 4b (with
ꢀ
only iPrMe2Si groups at carbon), decomposition is signifi-
cantly slower than that in the case of 4a, but isolation of
pure 4b was precluded by decomposition (see the Experi-
mental Section). Subsequently, single crystals could be ob-
tained at low temperatures by switching to the correspond-
ing N-1-adamantyliminophosphaalkene anion 7, thereby fur-
nishing N-1-adamantyliminobis-phosphaalkene 8, which was
other C
Steric crowding around the quaternary carbon atom C8,
including repulsion between the two C(SiMe3)2 groups
bridged by P1, correlates with exceptionally long bond
ACHTUNGTRENNUNG(SiMe3)2 group (see Scheme 2, Figure 1).
ꢀ
ꢀ
ꢀ
lengths for C8 Si3, C8 Si4 and C8 P2 (all >1.9 ꢈ).
Chem. Eur. J. 2010, 16, 4843 – 4851
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4845

W.-W. du Mont et al.
subjected to X-ray structure determination as a tetrahydro-
furan solvate. In solution, 8 exhibits a 31P NMR spectroscop-
ic singlet resonance signal, but in the solid the two P=C moi-
eties of each independent molecule are inequivalent
(Figure 2, top). The three independent molecules in solid 8
31P NMR spectroscopic study on N-Mes*-bridged bisphos-
phaalkenes: The reaction mixtures from metalation of 9a or
9b with LDA, followed by reactions of 10a with 1a and of
10b with 1b, each exhibit in the 31P NMR spectrum a singlet
signal accompanied by an AM pattern (11a: d=352 (s), 329
2
(d), 323 ppm (d), J
N
326 ppm (d), 2J (P,P)=13.5 Hz), and another small singlet
assignable to [(Me3Si)2C=P]2O (d=353 ppm) and [(iPr-
Me2Si)2C=P]2O (d=354 ppm).[5,18] Clearly, the bulky NMes*
groups enhance the rotational barrier(s) of rotameric inter-
conversion of symmetric sym-11a or sym-11b and unsym-
metric S-shaped asym-11a or asym-11b. Initially, the
31P NMR spectroscopic peak height of symmetric sym-11b is
larger than the total intensities of the AM pattern from
asym-11b (ratio of about 5:2), but after a slight relative in-
crease of the amount of asymmetric species within two days,
an approximately 5:3 ratio of the two species in solution re-
mains unchanged for an extended period. Enrichment of
one of these species from the oily crude products was not
achieved.
DFT calculations on 2,4-diphospha-3-azapentadienes (imi-
nobisphosphaalkenes): First we explored the potential-
energy surface of the parent [(H3Si)2C=P]2NCH3 system by
ꢀ ꢀ
optimising the S-shaped, W-shaped and V-shaped C=P N
P=C moieties (Scheme 5).
Figure 2. Top) Molecular structure of 8, molecule #1. Selected bond
ꢀ
ꢀ
ꢀ
lengths [ꢈ] and angles [8]: P1 C11 1.6670(3), P2 C22 1.6606(3), P1 N
ꢀ
ꢀ
1.712(2), P2 N 1.737(2), C23 N 1.524(13); P1-N-P2 126.77(13). P1-N-
C23 119.36(18), P2-N-C23 113.72(17), C11-P1-N-P2 ꢀ40.9(2), C22-P2-N-
P1 55.6(2). Hydrogen atoms are omitted for clarity. Atoms are drawn as
50% thermal ellipsoids. Bottom) Arrangement of the three independent
molecules of 8.
Scheme 5.
structures.
ACHTUNGNERT[NGNU (H3Si)2C=P]2NCH3 rotamers and their connecting transition
(Figure 2. bottom) exhibit different adamantyl-group orien-
tations relative to the common “helically distorted” CPNPC
skeleton and undergo different contacts to the solvating
THF molecules. The conformations of the non-planar C-P1-
N(R)-P’-C’ backbones (in molecule #1: torsion angles C11-
P1-N-P2 and C22-P2-N-P1) of the three independent mole-
cules are similar (molecule #1: ꢀ40.9(2) and ꢀ55.6(2)8; mol-
ecule #2: ꢀ41.1(2) and ꢀ54.2(2)8; molecule #3: ꢀ48.4(2)
and ꢀ48.5(2)8), with the P=C moieties being directed out of
the NP2 planes about halfway between orthogonal[8] and
planar. Within the non-planar CPNPC moieties, P=C
Whereas
for
the
parent
iminobisphosphaalkene
[(H3Si)2C=P]2NCH3 a small activation barrier and energeti-
cally close-lying rotamers were obtained at each investigated
level of the theory (Table 1), with bulkier groups no W-
shaped rotamers could be found on the B3LYP/6-31+G* po-
tential-energy hypersurface, and the energy difference be-
tween the S- and V-shaped rotamers is much larger than in
the case of the parent molecule. In the case of [(Me3Si)2C=
P]2NMes*, the unsymmetric S-shaped form is more stable
by 8–9 kcalmolꢀ1 than the quasi-symmetric V-shaped form
at different levels of theory (see the Supporting Informa-
tion). Clearly, the large Mes* substituent hinders the rota-
tion of the phosphaalkene units, and both the V- and S-
shaped rotamers can be present in solution, in good agree-
ment with the 31P NMR spectroscopic investigations. For the
compounds [(Me3Si)2C=P]2NR with R=1-Ada and tBu, nei-
ther S- nor W-shaped rotamers form, but the quasi-symmet-
ric V-shaped rotamer (in agreement with the X-ray struc-
ꢀ
(166.4–167.0 ꢈ) and P N bonds (171.2–173.7 ꢈ) appear es-
sentially undisturbed by conjugative effects. In this respect,
8 is comparable to the 2-[6-bis(trimethylsilyl)amino]pyridyl-
ACHTUNGTRENNUNG
imino-bridged bisphosphaalkene C (Scheme 1).[8] The latter
compound, which exhibits a 31P NMR spectroscopic AM
pattern in solution at ꢀ608C, shows sterically hindered PN
bond rotation at this temperature, but equilibration of the
two phosphorus nuclei on the 31P NMR spectroscopic time
scale occurs at room temperature.[8]
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Bisphosphaalkenes
FULL PAPER
Table 1. Relative energies (in kcalmolꢀ1) of the [(H3Si)2C=P]2NCH3 rotamers and activation barriers at differ-
ent levels of theory on geometries obtained at the B3LYP/6-311+G** level.
reasonably small activation bar-
riers, which are predicted to be
significantly lower at MP2 than
at the B3LYP level. It is worth
noting that the stabilities of
compounds I and II are compa-
rable; furthermore, the activa-
tion barriers to them are also
very similar. Thus the forma-
W-shaped
TSN
S-shaped
TS
G
V-shaped
B3LYP/6-31+G*
B3LYP/6-311+G**
MPW1K/6-311+G**
MP2/6-311+G**
0.5
0.4
0.5
1.0
3.8
3.5
3.8
3.4
0.0
0.0
0.0
0.3
3.6
3.5
3.7
3.3
2.3
2.2
2.1
0.0
ture) was found, thereby providing (as observed) a singlet
signal in the 31P NMR spectra.
To understand the formation of four-membered-ring inter-
mediates (I–III, Scheme 3) and thus the silyl-group migra-
tion, the reaction (Scheme 6) was calculated for model com-
tion of both isomers is feasible, which is in good agreement
with their experimental observation. To investigate the for-
mation of 5 from I and chlorophosphaalkene (Me3Si)2C=PCl
(3a), the reactions shown in Scheme 7 were calculated. It is
important to note that several attempts were made to ex-
plore possible transition structures (attack of 3a from differ-
ent directions), however, only TS
(Ij14), which corresponds
4
5
ꢀ
to an insertion into the s ,l -P N bond of I (Scheme 7),
turned out to be a first-order saddle point. Intermediate 14,
which is formed from TS
N
tion coordinate (IRC) calculations, can be stabilised
(Table 3) by Me3SiCl elimination that leads to 15. To check
the reliability of the results, further calculations were carried
out using the MPW1K functional as well as the MP2
method. Since for the SiH3-substituted systems the relative
energies obtained from single-point calculations at the
B3LYP-optimised geometries differ only slightly from the
values obtained at their optimised structures (see the Sup-
porting Information), for the SiMe3-substituted systems we
have used the energies obtained from single-point calcula-
tions (Table 3). The wavefunctions of intermediates 14 and
15 and transition structures TS
G
E
Scheme 6. Cyclisation
[(Me3Si)2C=P]2NtBu (methyl groups omitted for clarity).
pathway
of
alkyliminobisphosphaalkene
stable at the DFT levels, however, the Hartree–Fock wave-
function shows unrestricted Hartree–Fock (UHF) instability.
Accordingly, the perturbation treatment of the unstable
wavefunction can be in significant and unpredictable error,
thereby rendering the corresponding Møller–Plesset second-
order perturbation theory (MP2) results dubious. Apparent-
ly, for a highly accurate description of the electronic struc-
ture of 14 and 15, multireference methods would be the best
choice; unfortunately, the size of the investigated system ex-
cludes this possibility. Bicycle 5, however, can properly be
described by the closed-shell determinant at each level and
it is far more stable (considering the energy of SiMe3Cl)
than the starting materials. (It should be noted that at the
B3LYP/6-31+G* level 15 is somewhat more stable than 5,
which is in contrast with the observed formation of 5. Using
a larger basis set, the energy difference is reduced, whereas
with the MPW1K functional and at the MP2/6-31+G* level,
5 is the thermodynamical sink
pounds. The bulky SiMe3 and tBu groups have a significant
effect on the relative energies of the intermediates and tran-
sition structures (data for the smallest model systems with
SiH3/CH3 groups are given in the Supporting Information
for comparison). From 4a a four-membered intermediate
(12) can directly be obtained. Both observed decomposition
products (I and II) can be formed from 12 by 1,2-shifts. In-
termediate 13, which can be converted to intermediate II,
was also considered; its high energy (Table 2), however, ex-
cludes the possibility of this reaction pathway.
The formation of the energy-rich four-membered-ring in-
termediate 12 is kinetically feasible (16–22 kcalmolꢀ1 activa-
tion barriers at different levels), and from this species the
more stable products I and II can be formed by means of
in agreement with the experi-
mental results. Nevertheless,
the B3LYP/6-31+G*-optimised
structure of 5 (see the Support-
ing Information) is similar to
that obtained from the X-ray
investigation.
Table 2. Relative energies and activation barriers (compared to 4a) for the [(Me3Si)2C=P]2NtBu system at dif-
ferent levels of theory on geometries obtained at the B3LYP/6-31+G* level.
4a
TS
G
12
TS
U
I
TS
N
II
TS
G
13
B3LYP/6-31+G*
B3LYP/6-311+G**
MPW1K/6-311+G**
MP2/6-31+G*
0.0
0.0
0.0
0.0
21.5
20.9
19.6
16.9
14.9
15.4
10.7
5.3
29.4
30.2
23.1
18.4
6.0
7.2
29.6
30.4
24.8
19.4
5.6
6.5
47.0
47.7
50.6
56.3
35.4
36.5
38.4
41.3
ꢀ0.7
ꢀ0.1
5.3
6.1
Chem. Eur. J. 2010, 16, 4843 – 4851
ꢆ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4847

W.-W. du Mont et al.
Table 3. Relative energies of transition structures (TS) and intermediates for the formation of azatriphosphabicyclohexene 5 from I and (Me3Si)2C=PCl
at different levels of theory on geometries obtained at the B3LYP/6-31+G* level.
I+(Me3Si)2C=PCl
TS (Ij14)
14
TS (14j15)
15+Me3SiCl
TS
G
5+Me3SiCl
B3LYP/6-31+G*
B3LYP/6-311+G**
MPW1K/6-311+G**
MP2/6-31+G*
0.0
0.0
0.0
0.0
32.9
32.0
31.9
26.1
25.4
17.3
34.9
34.1
35.5
ꢀ21.6
ꢀ19.8
ꢀ14.3
1.7
2.1
ꢀ19.3
ꢀ19.3
ꢀ30.8
ꢀ49.0
ꢀ0.8
A
E
A
G
ꢀ17.8
[a] The HF wavefunction showed UHF instability; the perturbation treatment is likely to be in significant error.
corded using Bruker AC 200, Avance
200, Avance 400 and AMX 300 spec-
trometers, with 85% H3PO4 and SiMe4
as external or internal standards.
Aminophosphaalkenes
ACHUTNRGENN(UG iPrMe2Si)2C=PNAHCTUNGTREN(NUGN tBu)H (2b): tert-Bu-
tylamine (1.30 g, 17.86 mmol) was
added dropwise to a solution that con-
tained 1b (5.02 g, 17.86 mmol), trie-
thylamine (2.58 mL, 18.56 mmol) and
pentane (100 mL) at ꢀ408C. The mix-
ture was allowed to warm up slowly to
room temperature and stirring was
continued for 12 h. After removal of
the solid triethylammonium salt and
the solvent, vacuum distillation fur-
nished at 708C (0.2 mbar) 2b as
a
yellow oil (4.30 g, 76%). 1H NMR
Scheme 7. Probable formation of bicyclic product 5 from the four-membered-ring I and phosphaalkene
(Me3Si)2C=PCl (3a) (methyl groups omitted for clarity).
(300.1 MHz, C6D6, 258C): d=5.01 (d,
ACHTUNGTRENNUNG
2J
4J
A
ACHTUNGTRENNUNG
0.86–0.83 (m, 13H; CH
(s, 9H; NC
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Conclusion
A
ACHTUNGTRENNUNG
tert-Butyliminobisphosphaalkenes
[(RMe2Si)2C=P]2NtBu
N
G
G
ACHTUNGTRENNUNG
G
E
ACHTUNGTRENNUNG
(4a, 4b; R=Me, iPr), synthetically available from 1:1 reac-
tions of N-metalated P-alkylaminophosphaalkenes with P-
chlorophosphaalkenes, tend to isomerise by cyclisation with
silyl-group migration. Related rearrangements explain the
formation of an azatriphosphabicyclohexene tBuNC3P3-
E
N
G
ACHTUNGTRENNUNG
2
2
N
(Si,P)=8.7 Hz); 31P NMR
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(SiMe3)5 (5) from the reaction of LiAHCTUNGTRNE[NUGN (Me3Si)2C=PNtBu] with
two equivalents of (Me3Si)2C=PCl. C-Isopropyldimethylsilyl
groups slow down silyl migration reactions, allowing the
low-temperature crystal-structure determination of [(iPr-
Me2Si)2C=P]2NACHTUNGTRENNUNG(1-Ada) (8), which exists in a helically dis-
torted S-shaped conformation. 31P NMR spectra reveal that,
in solution, the 31P nuclei of the P=C functions of 8 are
equivalent (rapid interconversion of rotamers on the NMR
spectroscopic timescale), whereas mixtures of rotamers are
observed in solutions of iminobisphosphaalkenes with ex-
tremely bulky (2,4,6-tBu3C6H2) N-aryl groups. DFT calcula-
tions on less strained iminobisphosphaalkenes suggest that
the non-planar configuration of compound 8 will have steric
grounds and provide a likely mechanistic explanation for re-
arrangements by silyl-group migration.
ACHTUNGTREN(NUGN H,P)=12.5 Hz, 1H;
AHCTUNGTRENNUNG
4
AHCTUNGTREN(GNUN CH3)2), 0.01 (d, J-
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
R
G
ACHTUNGTRENNUNG
E
N
ACHTUNGTRENNUNG
G
2
Experimental Section
General methods: All experiments were carried out under oxygen-free
T
ACHTUNGTERN(NUGN Mes*)H (9a): A solution of 2,4,6-tri-tert-butylaniline
nitrogen by using standard Schlenk techniques. NMR spectra were re-
4848
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ꢆ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 4843 – 4851

Bisphosphaalkenes
FULL PAPER
under a nitrogen atmosphere. nBuLi (2.1 mL of a 2.5m hexane solution,
5.15 mmol) was slowly added to the stirred solution and the reaction mix-
ture was warmed to room temperature with magnetic stirring over 1 h.
The suspension was added dropwise to a solution of 1a formed of
(Me3Si)2C=PCl (1.16 g, 5.15 mmol) in THF (15 mL) at ꢀ408C. Precipita-
tion of the lithium salt with pentane, removal of the salt by filtration and
removal of the solvent in vacuo gave 9a as a yellow solid (2.15 g, 93%).
1H NMR (200 MHz, C6D6, 258C): d=7.25 (brs, 2H; Ph), 6.13 (d,
formed iPr2NH and the solvent were removed in vacuo and the residue
was dissolved in THF (10 mL). The solution of 3b in THF was added
slowly to a solution of 1b (0.55 g, 1.96 mmol) in THF (10 mL) at ꢀ408C.
The reaction mixture was allowed to warm slowly to room temperature.
After 30 min, 31P NMR spectroscopic analysis (81 MHz, C6D6) showed
the formation of the desired product 4b (d=365.8 ppm). After removal
of the lithium salt by filtration and the solvent in vacuo, 31P NMR spec-
troscopic analysis showed, apart from 4b, very small signals appearing as
2J
0.15 (brs, 9H; CH3), 0.07 ppm (d, 4J
(50.32 MHz, C6D6, 258C): d=149.06 (d, 2J
148.03 (d, 5J(C,P)=1.2 Hz; C-p-Ph), 140.29 (d, 1J
137.34 (d, 3J
(C,P)=13.9 Hz; C-o-Ph), 123.24 (s; C-m-Ph), 36.87 (brs; o-
(CH3)3), 35.10 (brs; p-C (C,P)=4.2 Hz; o-C(CH3)3),
(CH3)3), 33.72 (d, 5J
31.04 (s; p-C (C,P)=2.3 Hz; CH3), 3.62 ppm (d,
(CH3)3), 4.01 (d, 3J
3J(C,P)=15.0 Hz; CH3); 31P NMR (81.02 MHz, C6D6, 258C): d=
318.1 ppm.
(iPrMe2Si)2C=PN
ACHTUNGTRENNUNG
AX patterns (31P NMR (81 MHz, C6D6): d=323.3 and 50.1 ppm, J
167 Hz (0.5); d=136.4 and 9.1 ppm, J(P,P)=77 Hz (0.4)). Over a period
ACHTUNGTRENNUNG(P,P)=
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
of 12 h, the sample was kept at room temperature and afterwards the
31P NMR spectrum showed that 4b (dP =365.8 ppm) is accompanied by
some rearranged species that show AX patterns: dP =323.3 and 50.1 ppm,
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
C
G
E
N
ACHTUNGTRENNUNG
J
N
JACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(2.3), which relates with species II. After 9 d, 4b and the compound relat-
ed to species II are completely consumed.
A
ACHTUNGTRENNUNG(Mes*)H (9b): A solution of 2,4,6-tri-tert-butylaniline
Reaction of 3b with 1a: LDA (0.8 mL of a 2m THF/heptane/ethylben-
zene solution, 1 equiv) was added to a solution of (iPrMe2Si)2CPN(H)tBu
(0.5 g, 1.6 mmol) in THF (8 mL) at ꢀ408C under a nitrogen atmosphere.
The reaction mixture was then warmed to room temperature and was
stirred for 1 h. 31P NMR spectroscopic analysis of the solution showed
quantitative formation of 3b (31P NMR (81 MHz, C6D6): d=404.3 ppm).
The formed iPr2NH and the solvent were removed in vacuo and the resi-
due was dissolved in THF (10 mL). The solution of 3b in THF was
added slowly to a solution of 1a (0.36 g, 1.6 mmol) in THF (5 mL) at
ꢀ408C. The reaction mixture was allowed to warm slowly to room tem-
perature. After 20 min, 31P NMR spectroscopic analysis showed the for-
mation of the desired mixed bisphosphaalkene (31P NMR (81 MHz,
(1.32 g, 5.03 mmol) in tetrahydrofuran (10 mL) was cooled at ꢀ408C
under a nitrogen atmosphere. nBuLi (2.02 mL of a 2.5m hexane solution,
1 equiv) was slowly added to the stirred solution and the reaction mixture
was warmed to room temperature with magnetic stirring over 1 h. The
suspension was added dropwise to a solution of 1b formed from (iPr-
Me2Si)2C=PCl (1.42 g, 5.03 mmol) in THF (15 mL) at ꢀ408C. Precipita-
tion of the lithium salt with pentane, its removal by filtration and the re-
moval of the solvent in vacuo gave 9b as a cherry-red solid (2.16 g,
85%). Single crystals suitable for X-ray analyses were obtained from
hexane. M.p. 97–988C; 1H NMR (300.1 MHz, C6D6, 258C): d=7.36 (s,
2H; Ph), 6.37 (d, 2J
4J
(H,P)=8 Hz, 1H; CH
CHACHTUNGTRENNUNG CATHGNUTREN(NUGN H,P)=3 Hz, 6H; CH3);
(CH3)2), 0.28 (s, 6H; CH3), 0.21 ppm (d, 4J
ACHTUNGTRENNUNG
C6D6): d=365.3 and 361.7 ppm, 2J
ACTHNUTRGNEU(GN P,P)=18 Hz). The lithium salt was re-
A
ACHTUNGTRENNUNG
moved by filtration and the solution was concentrated in vacuo followed
by 31P NMR spectroscopic analysis: the signals of the mixed bisphos-
phaalkene were accompanied by further AX patterns, among them one
(31P NMR (81 MHz, C6D6): d=136.32 and 7.25 ppm, J=78 Hz) closely
related to species II in Scheme 3 (see also Scheme 4). After 2 d at room
temperature, the species that represents the main product appeared in
the 31P NMR spectroscopy data at d=325.4 and 49.4 ppm, J=163 Hz.
13C NMR (75.4 MHz, C6D6, 258C): d=148.78 (d, 2J
G
3
ipso-Ph), 147.76 (s; C-p-Ph), 137.24 (d, J
G
1
(d, J
(s; p-C
(CH3)3), 17.92 (s; CH
15.39 (d, 3J
(C,P)=2.3 Hz; CH
3J
G
A
U
ACHTUNGTRENNUNG
A
U
G
N
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
Compound 5: Compound 1a (0.9 g, 4 mmol) was added to a solution of
3a [formed from 2a (0.5 g, 2 mmol) and LDA (1 mL of a 2m THF/hep-
tane/ethylbenzene solution, 1 equiv) in tetraglyme (20 mL)] in tetraglyme
(20 mL) at ꢀ408C under a nitrogen atmosphere. The reaction mixture
was stirred for 2 h followed by NMR spectroscopic analysis. Removal of
the solvent in vacuo furnished a red oil; in one experiment, red crystals
(0.28 g, 25%) suitable for an X-ray structure determination were ob-
tained from the solution. 31P NMR (81.02 MHz, C6D6, 258C): d=331.2
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
2J(Si,P)=9.86 Hz); 31P NMR (121.5 MHz, C6D6, 258C): d=325.0 ppm;
MS (EI): m/z (%): 505 (16) [M]+, 406 (98) [MꢀtBuiPr+H]+, 318 (11)
[MꢀtBu3MeꢀH]+, 290 (31) [Mꢀ
ACHTUNGTRENNUNG
[MꢀNMes*]+; elemental analysis calcd (%) for C29H56NPSi2 (505.91): C
68.85, H 11.16, N 2.77; found: C 67.59, H 11.09, N 2.71.
Reactions of metalated aminophosphaalkenes with P-chlorophosphaal-
kenes
(“t”, line separation 28.8 Hz), ꢀ24.0 (dd, 1J
G
ACHTUNGTRENNUNG(P,P)=
31.6 Hz), ꢀ17.2 ppm (dd, 1J
(P,P)=175.7 Hz, 2J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
ACHTUNGTRENNUNG[(Me3Si)2C=P]2NtBu (4a): LDA (1 mL of a 2m THF/heptane/ethylben-
(75 MHz), C6D6): d=150.1 (ddd, 1J
N
R
zene solution, 1 equiv) was added to a solution of 2a (0.5 g, 2 mmol) in
diethyl ether (30 mL) at ꢀ408C under a nitrogen atmosphere. The mix-
ture was warmed to room temperature and stirred for 12 h. 31P NMR
spectroscopic analysis of the solution showed quantitative formation of
3a (31P NMR (81 MHz, C6D6): d=425.5 ppm). The formed iPr2NH and
the solvent were removed in vacuo and the residue was dissolved in di-
ethyl ether (30 mL). Compound 1a (0.45 g, 2 mmol) was added slowly to
this solution at ꢀ408C. The cooling bath was removed and the reaction
mixture was allowed to warm slowly to room temperature. After 12 h,
the lithium salt was removed by filtration and the solution was concen-
trated in vacuo followed by 31P NMR spectroscopic analysis (81 MHz,
C6D6): the singlet signal assigned to 4a (d=361.6 ppm) is accompanied
by AX patterns: d=358.4 and 55.1 ppm, J=9 Hz (species I); d=135.2
and 7.5 ppm, J=76 Hz (species II); d=351.9 and 38.5 ppm, J=107 Hz
(species III).
2
3J
(P,C)=2.0 Hz), 60.5 (dd, J
N
tion=10.2 Hz), 16.65 (ddd, 1J
2.9 Hz), 12.5 (dd, 1J(P,C)=22.6 Hz, 2J
(P,C)=5.5 Hz, 4J
(P,C)=1.3 Hz), 4.0 ppm (dd, 3J
(P,C)=4.0 Hz); elemental analysis calcd (%) for C22H54NP3Si5 (566.02):
N
(P,C)=19.6 Hz, 3J
ACHUTGTNRENNUG ACHTUNGTRENNUNG
A
U
ACHTUNGTRENNUNG
5.1 Hz), 5.6 (brs), 4.9 (dd, 3J
G
ACHTUNGTRENNUNG
3J
3J
A
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
C 46.48, H 9.62, N 2.47; found: Cꢂ45.5, Hꢂ9.4, N 2.46–2.60.
[(iPrMe2Si)2C=P]2N(1-Ada) (8): LDA (1.24 mL of a 2m THF/heptane/
A
ACHTUNGTRENNUNG
ethylbenzene solution, 1 equiv) was added to a solution of 6 (0.98 g,
2.48 mmol) in THF (5 mL) at ꢀ408C. The reaction mixture was warmed
to room temperature with magnetic stirring over 1 h. 31P NMR spectro-
scopic analysis of the solution showed quantitative formation of
7
(31P NMR (81 MHz, C6D6): d=405.8 ppm). The resulting iPr2NH and the
solvent were removed in vacuo and the residue was dissolved in THF
(5 mL). The solution of 7 in THF was added slowly to a solution of 1b
(0.7 g, 2.48 mmol) in THF (5 mL) at ꢀ408C. After 15 min, the 31P NMR
ACHTUNGTRENNUNG
a
1.96 mmol) in THF (7 mL) at ꢀ408C under a nitrogen atmosphere. The
reaction mixture was allowed to warm to room temperature and stirred
for 1 h. 31P NMR spectroscopic analysis of the solution showed quantita-
tive formation of 3b (31P NMR (81 MHz, C6D6): d=404.3 ppm). The
spectra showed the formation of the desired bisphosphaalkene 8
(31P NMR (81 MHz, C6D6): d=365.5 ppm).The solution was kept for 24 h
at ꢀ208C and yellow crystals were isolated (0.50 g, 32%).1H NMR
(400 MHz, [D8]toluene, ꢀ148C): d=2.09–2.07 (pseudo-q, outer line dis-
Chem. Eur. J. 2010, 16, 4843 – 4851
ꢆ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4849

W.-W. du Mont et al.
ꢀ
tance=8.9 Hz, 3H; CH-Ada), 1.89–1.87 (m, 1H; CH
(m, 12H; CH2-Ada), 1.28–1.05 (m, 13H; CH
N
(C H=0.98 ꢈ, H-C-H=109.58) allowed to rotate but not tip, or a riding
3
3
ꢀ
ꢀ
G
model for other H (C H=0.99 ꢈ; sp CH2 and C H=1.0 ꢈ; sp CH).
Structure 8 contains three formula units 8·THF per asymmetric unit.
CCDC-754788 (5) and 754789 (8) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Ada), 30.80 (s; CH-Ada), 18.15 (brs) and 15.61 (s; CH
ACHTUGNTRNEN(UNG CH3)2), 14.78
(brs, CH(CH3)2), 12.59 (pseudo-t, outer line distance=14.2 Hz; CH-
ACHTUNGTRENNUNG
A
Compound 5: C22H54NP3Si5; Mr =566.02; monoclinic; space group: P21/n;
a=11.1309(10), b=16.9649(15), c=18.4626(16) ꢈ; b=104.454(2)8; V=
3376.0(5) ꢈ3; Z=4; 1calcd =1.114 mgmꢀ3; T=133(2) K; orange prism. Of
39724 reflections measured, 10280 were independent (Rint =0.1464). The
final wR2 was 0.1613 (all data).
[D8]toluene, ꢀ148C): d=364.7 ppm; MS (EI): m/z (%): 639 (10) [M]+,
538 (80) [MꢀiPrMe2Si]+, 504 (100) [MꢀAda]+; elemental analysis calcd
(%) for C32H67NP2Si4 (640.17): C 60.04, H 10.55, N 2.19; found: C 58.86,
H 10.29, N 2.27.
Compound 8 is unstable at room temperature. The reaction was repeated
and after filtration of the lithium salt and removal of the solvent the
31P NMR spectrum showed, apart from 8, some decomposition species: a
compound analogous to species II (31P NMR (81 MHz, C6D6): d=134.7
Compound 8: C36H75NOP2Si4; Mr =712.27; monoclinic; space group:
P21/c; a=10.7496(2), b=34.0778(8), c=35.1768(8) ꢈ; b=95.5588(18)8;
V=12825.5(5) ꢈ3; Z=12; 1calcd =1.107 mgmꢀ3
; T=100(2) K; yellow
tablet. Of 334611 reflections measured, 26186 were independent (Rint
0.0749). The final wR2 was 0.1640 (all data).
=
and 7.6 ppm, J
spectroscopic pattern: 31P NMR (81 MHz, C6D6) d=320.6 and 46.7 ppm,
(P,P)=173 Hz in small quantities. After one week at room temperature,
8 was completely consumed and the remaining species were as follows:
31P NMR (81 MHz, C6D6): d=320.6 and 46.7 ppm, J
(P,P)=173 Hz (main
product), d=354.3 and 35.3 ppm, J(P,P)=112 Hz (analogue to species
(P,P)=127 Hz, the last two species with
ACHTUNGTRENNUNG(P,P)=81 Hz) and a compound characterized by the NMR
Computations: The computations were carried out with the Gaussian 03
program package.[21] All structures were optimised with two different
basis sets (3-21G(*) for pre-optimisation and 6-31+G*) using the B3LYP
functional. Vibrational analysis was performed on each of the optimised
structures to check whether the stationary point located is a minimum of
the potential energy hypersurface or a first-order saddle point (in the
case of transition states). For the optimised structures, the stability of the
wavefunction was tested; no instability was found. At the saddle points
located, IRC calculations were performed to locate the minima connect-
ed by the transition structure. To investigate the convergence of the basis
set, calculations have been performed on the optimised geometries single
point with the larger 6-311+G** basis set using the B3LYP functional,
and the difference was found to be negligible. Further single-point calcu-
lations have been carried out at the MPW1K/6-311+G** and MP2/6-
311+G** or MP2/6-31+G* levels depending on the size of the molecules.
NMR spectroscopic chemical shifts were computed with the gauge-inde-
pendent atomic orbital (GIAO) method at the B3LYP/cc-pVTZ and
B3LYP/IGLO-III[22] levels (see the Supporting Information). The 31P
shifts were determined following the method in ref. [23]. For visualisation
of the molecules, the Molden program was used.[24]
JACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
III), d=331.3 and 34.2 ppm, JACHTGNUTRENNUNG
small intensities.
ACHTUNGTRENNUNG[(Me3Si)2C=P]2NACHTUNGTRENNUNG(Mes*) (11a): LDA (0.94 mL of a 2m THF/heptane/eth-
ylbenzene solution, 1 equiv) was added to a solution of 9a (0.84 g,
1.87 mmol) in THF (10 mL) at ꢀ408C under a nitrogen atmosphere. The
reaction mixture was allowed to warm to room temperature and stirred
for 1 h. 31P NMR spectroscopic analysis of the solution showed quantita-
tive formation of 10a (31P NMR (81 MHz, C6D6): d=355.9 ppm). The
formed iPr2NH and the solvent were removed in vacuo and the residue
was dissolved in THF (10 mL). The solution of 10a in THF was added
slowly to a solution of 1a (0.42 g, 1.87 mmol) in THF (5 mL) at ꢀ408C,
after which the reaction mixture was stirred for 20 min at room tempera-
ture. After removal of the lithium salt by filtration and the solvent in
vacuo, 31P NMR spectroscopic analysis of the oily residue showed the for-
mation of the sym-11a species (31P NMR (81.02 MHz, C6D6, 258C): d=
352.8 ppm) and species asym-11a (31P NMR (81.02 MHz, C6D6, 258C):
d=329.2 and 323.1 ppm 2J
ACTHNUGRTENUNG(P,P)=7.4 Hz) and small quantities of 9a and
[(Me3Si)2C=P]2O. Isolation of pure 11a was not achieved except in one
single experiment. After one week at room temperature, a decrease of
the amount of sym-11a in the mixture can be observed, whereas the
amount of asym-11a increases.
Acknowledgements
The COST action CM0802 “PhosSciNet” and Deutsche Forschungsge-
meinschaft (MO290/28-1) are acknowledged for support.
ACHTUNGTRENNUNG[(iPrMe2Si)2C=P]2NACHTUNGTRENNUNG(Mes*) (11b): LDA (0.6 mL of a 2m THF/heptane/
ethylbenzene solution, 1 equiv) was added with a syringe to a solution of
9b (0.60 g, 1.19 mmol) in THF (10 mL) at ꢀ408C. The reaction mixture
was warmed to room temperature with magnetic stirring over 1 h.
31P NMR spectroscopic analysis of the solution showed quantitative for-
mation of 10b (31P NMR (81 MHz, C6D6): d=364.3 ppm). The resulting
iPr2NH and the solvent were removed in vacuo and the residue was dis-
solved in THF (10 mL). The solution of 10b in THF was added dropwise
to a solution of 1b (0.33 g, 1.19 mmol) in THF (5 mL) at ꢀ408C. The so-
lution was allowed to warm slowly to room temperature and after 50 min
the 31P NMR spectra showed the formation of sym-11b (31P NMR
(81 MHz, C6D6): d=352.4 ppm) and asym-11b (31P NMR (81 MHz,
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ACTHNUTRGNEU(GN P,P)=13.5 Hz), with a ratio of about
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assigned to the oxide [(iPrMe2Si)2C=P]2O. Within 2 d, a slight increase of
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Received: November 18, 2009
Published online: March 16, 2010
Chem. Eur. J. 2010, 16, 4843 – 4851
ꢆ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4851