Stimuli-Responsive Frustrated Lewis-Pair-Type Reactivity of a Tungsten Iminoazaphosphiridine Complex

Article abstract of DOI:10.1002/chem.201501628

Reactions of 3-imino-azaphosphiridine complexes 1 a,b with carbodiimides 2 a,b, isocyanates 3 a,b, and carbon dioxide are described. Whereas exchange of the carbodiimide unit occurs in the first case, an overall ring expansion takes place with phenyl isocyanate (3 a) and carbon dioxide to yield complexes 4 and 5 bearing novel 1,3,5-oxazaphospholane ligands; the isopropyl derivative 3 b did not react under these conditions. DFT calculations provide insight into the pathway of the reaction with carbon dioxide with model complex 1 c, revealing effects of initial non-covalent interactions with the substrate onto the ring bonding, thus triggering an initially masked frustrated Lewis-pair-type behavior.

Full text of DOI:10.1002/chem.201501628

DOI: 10.1002/chem.201501628
Communication
&
Azaphospiridine Complexes
Stimuli-Responsive Frustrated Lewis-Pair-Type Reactivity of
a Tungsten Iminoazaphosphiridine Complex
JosØ Manuel Villalba Franco,[a] Gregor Schnakenburg,[a] Takahiro Sasamori,[b]
Arturo Espinosa Ferao,*[c] and Rainer Streubel*[a]
Dedicated to Professor Manfred Scheer on the occasion of his 60th birthday
Abstract: Reactions of 3-imino-azaphosphiridine com-
plexes 1a,b with carbodiimides 2a,b, isocyanates 3a,b,
and carbon dioxide are described. Whereas exchange of
the carbodiimide unit occurs in the first case, an overall
ring expansion takes place with phenyl isocyanate (3a)
and carbon dioxide to yield complexes 4 and 5 bearing
novel 1,3,5-oxazaphospholane ligands; the isopropyl de-
Scheme 1. 1,1’-Vinyl-derived frustrated Lewis pairs I, closed isomers I’, and
rivative 3b did not react under these conditions. DFT cal-
neutral rings with polar bonds II and zwitterions thereof II’ (LB1 =CR2); 3-
culations provide insight into the pathway of the reaction
imino-aziridines III, 3-imino-azaphosphiridines IV and their complexes V, V’.
Lines denote organic substituents, [M] a transition-metal complex, LA=Le-
with carbon dioxide with model complex 1c, revealing ef-
fects of initial non-covalent interactions with the substrate
onto the ring bonding, thus triggering an initially masked
frustrated Lewis-pair-type behavior.
wis acid, and LB=Lewis base.
bered heterocycles having three different, strongly polarized
ring bonds,[5] high ring strain being combined with an exo nu-
cleophilic center LB1.[6] Since it is well known that implementa-
tion of an sp2-hybridized center increases ring strain in three-
membered P-heterocycles[7] and bond strain in the distal bond,
we started to study heterocycles of type II possessing a phos-
phorus unit in reactions with important heterocumulenes, that
is, RN=C=NR, RN=C=O, CO2. Until recently, only 3-iminoaziri-
dines III[8] were at hand, and IV remained unknown. On the
other hand, it has been recently shown that dinuclear phosphi-
nidene complexes react with carbodiimides to form a wealth
of interesting N,P,C-heterocycles,[9] but complexes of type V
have not been obtained by this route. Complexes V, which
have been described recently,[10] appear as particularly interest-
ing targets as they may feature a masked (crypto) FLP-type
character that is ready to be unveiled upon cleavage of a mark-
edly weakened endocyclic PÀN bond (V’).
Recently, the challenge was solved of building up an array of
three atoms in a molecular compound, two of which have no
bonding interactions and being opponents in terms of the
Lewis acid–base concept; this has been termed a frustrated
Lewis pair (FLP).[1] Due to this, a wide range of new chemical
structures such as I were discovered in recent years[2] (I,I’: LB1 =
CR2; Scheme 1); evidence for I’ was not obtained so far.
Among the many interesting transformations enabled by I is
the activation of quite unreactive substrates such as H2 and
CO2 through interactions of LA/LB centers such as B/P[3] and
Al/P.[4]
To approach the FLP concept from a different angle, we con-
templated the necessities to enhance reactivity of three-mem-
Herein, an unusual exchange reaction of 3-iminoazaphos-
phiridine complexes is described in the case of carbodiimides,
whereas isocyanates and carbon dioxide lead to an overall ring
expansion, thus yielding novel five-membered N,P,C-heterocy-
clic ligands. DFT calculations provide insight into the latter
pathway.
[a] J. M. Villalba Franco, Dr. G. Schnakenburg, Prof. Dr. R. Streubel
Institut für Anorganische Chemie
Reinischen Friedrich-Wilhelms-Universität Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
Fax:(+49)228-739616
E-mail: r.streubel@uni-bonn.de
[b] Prof. Dr. T. Sasamori
When the 3-iminoazaphosphiridine complex 1a[10] was al-
lowed to react with 1 equiv of dicyclohexyl carbodiimide (2b)
in THF at ambient temperature, a mixture of 1a and 1b (ratio
1:1) was obtained after 3 h (Scheme 2); this ratio remained
constant over time. Apparently, an unusual substitution reac-
tion had occurred in which the diisopropyl carbodiimide
moiety in 1a was exchanged[11] by the dicyclohexyl carbodii-
mide to form 1b. Besides the evidence obtained from the
Institut for Chemical Research, Kyoto University
Gokasho Uji, Kyoto, 611-0011 (Japan)
[c] Prof. Dr. A. Espinosa Ferao
Departamento de Química Orgµnica, Universidad de Murcia
Campus de Espinardo, 30100 Murcia (Spain)
Fax:(+34)868-884149
E-mail: artuesp@um.es
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501628.
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Communication
Scheme 2. Carbodiimide exchange reaction of 3-iminoazaphosphiridine
complex 1a.
31P{1H} NMR spectra, the nature of the newly formed product
as 1b was further confirmed through formation of a 1:1 mix-
ture of their hydrolysis products upon reaction of 1a,b with
water.[10,12] To examine this exchange further, the alternative re-
action of 1b with carbodiimide 2a was performed, and again
a 1:1 mixture was formed.
Figure 1. Molecular structure of 1,3,5-oxazaphospholane complex 4 (ellip-
soids set at 50% probability, hydrogen atoms are omitted and CPh3 group
shown in gray for clarity). Selected structural parameters (distances [Š] and
angles [8]): PÀW 2.5011(6), PÀC2 1.885(2), PÀO1 1.6562(15), O1ÀC1 1.386(2)
C1ÀN1 1.370(3), N1ÀC2 1.406(3); C2-P-O1 89.98(9), O1-C1-N1 111.20(19), N1-
C2-P 105.21(15).
When 3-iminoazaphosphiridine complex 1a was treated
with 1 equiv of phenyl isocyanate (3a) in Et2O or THF at ambi-
ent temperature (Scheme 3), 1,3,5-oxazaphospholane complex
Scheme 3. Reactions of 3-iminoazaphosphiridine complex 1a with phenyl
isocyanate (3a) and CO2 to give complexes 4 and 5.
4 was obtained; interestingly, no reaction was observed when
isopropyl isocyanate (3b) was used under the same conditions.
Figure 2. Molecular structure of 1,3,5-oxazaphospholane complex 5 (ellip-
soids set at 50% probability, hydrogen atoms are omitted for clarity). Select-
ed structural parameters (distances [Š] and angles [8]): PÀW 2.4935(8), PÀC2
1.885(3), PÀO1 1.671(3), O1ÀC1 1.377(4), C1ÀN1 1.370(5), N1ÀC2 1.407(4); C2-
P-O1 89.82(14), O1-C1-N1 111.2(3), N1-C2-P 104.9(2).
Complex 4 showed a 31P{1H} resonance at 131.7 ppm (1JW,P
=
277.7 Hz); this was accompanied by the formation of a complex
1
(ca. 4%; 31P{1H}=103.4 ppm, JW,P = 288.0 Hz) that could not be
identified. The 13C{1H} NMR spectra of 4 revealed resonances
for the imino carbon atoms at 143.5 ppm (2+3JP,C = 12.4 Hz) and
150.7 ppm (1+4
J
P,C = 10.2 Hz). In the case of 4, a formal insertion
respectively. The 1,3,5-oxazaphospholane rings in 4 and 5 are
planar, and the sum of bond angles at both N1 atoms (4:
359.98; 5: 360.08) shows a planar environment.
of the carbonyl group of the phenyl isocyanate into the PÀN
bond of complex 1a had occurred, whereby 4 was isolated in
65% yield and its molecular structure was confirmed by X-ray
analysis (Figure 1).
To understand the formal PÀN bond-selective ring expansion
process, quantum chemical calculations (COSMOtoluene/DLPNO-
CCSD(T)/def2-TZVPPecp//COSMOtoluene/B3LYP-D3/def2-TZVP
ecp)[13] were performed to elucidate the reaction pathway.
Here, the calculated reaction with carbon dioxide (for details of
the computations, see the Experimental Section and the Sup-
porting Information) of model complex 1c was explored
(methyl groups at both P and N atoms were used for the sake
of computational efficiency). Initially, the basic exocyclic N
atom of the most stable Z-configured initial model complex
1c[10] interacts with the electrophilic center of carbon dioxide
leading to 1c·CO2 that undergoes rotation of the weakened
exocyclic CÀN bond to afford the van der Waals complex
To test its reactivity, 1a was reacted with carbon dioxide first
in THF (1 bar, RT) to give readily 1,3,5-oxazaphospholane com-
plex 5 via ring expansion (Scheme 3). Under these conditions
about 15% of an unknown complex was observed (d 31P{1H}=
1
71.6, JW,P = 288.0 Hz, 1JP,H = 358.5 Hz) that could not be isolated.
This by-product formation was suppressed if the reaction was
carried out in Et2O at 20 bar and ambient temperature. Product
1
5 (d 31P{1H}=128.0, JW,P = 272.4 Hz) was fully characterized in-
cluding X-ray structure analysis (Figure 2) and showed 13C{1H}
NMR resonances of 151.0 ppm (1+4
J
P,C = 8.1 Hz) and 149.5
(
2+3JP,C = 12.1 Hz) for the imino and carbonylic carbon atoms,
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Figure 4. Computed (COSMOtoluene/DLPNO-CCSD(T)/def2-TZVPPecp) mini-
mum energy path for the transformation 1c+CO2!5c.
Scheme 4. Proposed mechanism for the formation of 5c.
Table 1. Ring strain and parameters related to PÀN bond strength for se-
lected computed species.
1cE·CO2 bound by weak non-covalent interactions (NCIs;
Scheme 4).
The van der Waals complex 1cE·CO2 is easily visualized by
the NCIplot technique of color-coded reduced density gradient
(RDG) isosurfaces (Figure 3).[17] The most significant NCIs are
those linking the exocyclic N atom with the CO2 carbon (d=
[a]
[b]
[c]
Entry
G(r)RCP
dPÀN
WBIPÀN
1(r)PÀN
1c
0.1362
0.1483
0.1621
1.747
1.750
1.768
0.748
0.739
0.673
0.1507
0.1493
0.1389
1cE·CO2
6c
3
[a] In au. [b] In Š. [c] In e/ao
.
moving from 1c to 1cE·CO2 and to 6c (Table 1), which parallels
a weakening of the PÀN bond. This situation approaches
a bonding described by formula II’ (or more specifically V’) as
result of an external substrate stimulus. Some commonly used
bond-strength-related parameters support this view (Table 1).
In conclusion, evidence was presented that the 3-iminoaza-
phosphiridine ring in 1 allows for an unusual carbodiimide ex-
change, but also displays a masked FLP-type reactivity which
comes to the fore upon interaction with a substrate, as illus-
trated by the reactions with phenyl isocyanate and carbon di-
oxide. Interestingly, use of isopropyl isocyanate led to no reac-
tion, that is, substrate discrimination. Quantum chemical calcu-
lations unveiled that the initial non-covalent interaction of the
exo nitrogen center with the substrate enhances ring strain
and hence triggers cleavage of the weakened distal PÀN bond,
thus increasing the electrophilicity of the P center and provok-
ing its reaction with the O atom of the carbonyl unit.
Figure 3. Computed (B3LYP-D3/def2-TZVPecp) most stable structure for van
der Waals complex 1Ec·CO2 with NCIplot highlighting key stabilizing NCIs.
The RDG s=0.28 au isosurface is colored over the range À0.05<
sign(l2)·1<0.05 au: blue denotes strong attraction, green stands for moder-
ate interaction, and red indicates strong repulsion.
3
2.858 Š; WBI=0.010; 1(r)=1.15”10À2 e/ao ) and one CO2
oxygen atom with the P atom (d=3.330 Š; WBI=0.003; 1(r)=
Experimental Section
3
0.68”10À2 e/ao ) and a carbonyl ligand (d=3.205 Š; WBI=
0.002; 1(r)=0.51”10À2 e/ao ).
3
Preparative methods
Strengthening of the N···C interaction in the van der Waals
complex leads to zwitterionic intermediate 6c that undergoes
ring opening by attack of the negatively charged O atom to
phosphorus thus forming a new five-membered 1,3,5-oxaza-
phospholane ring 5cE in a highly exergonic low-barrier process
(Figure 4). Finally the exocyclic E-configured C=N bond rotates
to give the most stable Z-configuration of the final product 5c.
The driving force for the overall transformation 1c+CO2!
5c must be mainly related to the release of the remarkably
high ring strain (50.58 kcalmolÀ1 was reported for the parent
complex).[10,18] In line with this, the computationally inexpen-
sive G(r) (Lagrangian of the kinetic energy density at ring criti-
cal points)[19] values reveal a dramatic increase of ring strain on
All reactions and manipulations were carried out under an atmos-
phere of dry argon, using Schlenk and vacuum-line techniques or
glove-box. Argon was cleaned over a BTS catalyst; Ar gas was
dried using silica gel and P2O5. Solvents were dried according to
standard procedures using sodium or sodium/benzophenone and
stored under inert gas atmosphere.
General procedure for the synthesis of 1a,b: tert-Butyllithium
(1.6m in n-hexane, 1.1 equiv) was slowly added to a THF solution
of triphenylmethyl dichlorophosphane tungsten(0) complex and
12-crown-4 (1 equiv) at À788C. After 15 min, N,N’-dialkyl carbodi-
imide 2a,b (1 equiv) was slowly added at À788C. The reaction so-
lution was stirred and warmed up slowly to +48C and then kept
at 48C for 15 h. Afterwards, the solvent was removed in vacuo (ca.
10À2 mbar) and LiCl filtered from an n-pentane solution.
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Communication
1a: Yellow solid, yield: 900 mg (1.24 mmol, 87%), m.p. 120–1218C,
6.5–7.7 ppm (m, 15H, 3”C6H5); 13C NMR (CDCl3): d=17.5 (s, C-N-
CH-CH3), 18.5 (s, C-N-CH-CH3), 23.4 (s, C=N-CH-CH3), 24.7 (s, C=N-
CH-CH3) 48.7 (s, C-N-CH), 56.2 (d, 3JP,C = 12.5 Hz C=N-CH), 71.2 (d,
1H NMR (CDCl3): d=0.80 (d, 3H, P-N-CH-CH3, 3JH,H =6.5 Hz), 0.80 (d,
3
3H, C=N-CH-CH3, 3JH,H =6.2 Hz), 1.17 (d, 3H, P-N-CH-CH3, JH,H
=
1
6.5 Hz), 1.29 (d, 3H, C=N-CH-CH3, 3JH,H =6.3 Hz), 3.35 (dsept, 1H, N-
CH(CH3)2), 3JH,H =6.5 Hz, 3JP,H = 3.8 Hz), 3.44 ppm (sept, 1H, N-
CH(CH3)2, 3JH,H =6.3 Hz); 13C NMR (CDCl3): d=19.6 (d, P-N-CH-CH3,
CPh3, JP,C = 4.1 Hz), 122.8 (s, C-CPh), 122.9 (s, C-CPh), 128.0 (s, C-CPh),
128.1(d, JP,C = 1.7 Hz C-CPh), 128.4(d, JP,C = 1.5 Hz C-CPh), 128.4 (s, C-
CPh), 128.7 (s, C-CPh), 130.9 (d, JP,C = 2.3 Hz C-CPh), 131.2 (d, JP,C
=
3
2
3JP,C = 2.7 Hz), 20.3 (d, P-N-C-CH3, JP,C = 1.7 Hz), 23.1 (s, C=N-C-CH3),
8.6 Hz C-CPh), 131.7 (d, JP,C = 6.3 Hz C-CPh), 137.6 (d, JP,C = 6.5 Hz C-
3
24.1(s, C=N-C-CH3), 50.6 (s, P-N-CH-CH3), 56.9 (d, N-CH-CH3, JP,C
=
Cipso–Ph), 138.9 (d, 2JP,C = 6.7 Hz C-Cipso–Ph), 141.9 (d, 2JP,C = 8.1 Hz C-
1
2
14.3 Hz), 65.6 (d, P-C-Ph3, JP,C = 15.8 Hz), 125.1 (s, Ph), 127.2 (s, Ph),
C
ipso–Ph), 143.5 (d, JP,C = 12.4 Hz, C=N-Ph), 145.6 (s, N-Cipso--Ph), 150.7
1
128.5 (s, Ph) 130.0 (d, ipsoPh, 2JP,C = 9.8 Hz), 137.0 (d, N=C, JP,C
=
=
(d, 1JP,C = 10.2 Hz, iPr-N=C), 195.2 (dSat, 2JP,C = 6.2 Hz, 1JW,C = 127.1,
cis-CO), 197.5 ppm (d, 2JP,C = 34.1 Hz, trans-CO); 31P NMR (CDCl3):
d=125.06 ppm, 1JW,P = 273.8 Hz. MS (EI, 184W) : m/z (%):843.1,
[M] +, (0.12); 787.2, [M]+À2”CO (0.1); 759.2, [M]+À3”CO, (0.1);
559.0, [M]+ÀCPh3À3”CO, (0.1); 488.9, [M]+ÀCPh3À3”CO, (0.12);
243.1 [CPh3]+; IR (ATR): n˜ =2971 (b, n-CH2), 2928 (b, n-CH2), 2077 (s,
n-CO), 1997 (s, n-CO), 1933 (s, n-CO), 1697 (s, n-CO), 1630 (b,
n-C=N), 1594 cmÀ1 (b, n-C=N); elemental analysis calcd (%) for
C38H34N3O6PW: C 54.11, H 4.06, N 4.98; found: C 53.97, H 4.11,
N 4.98.
2
7.2 Hz), 140.4 (d, Ph, JP,C = 3.0 Hz), 143.0 (s, Ph), 194.6 (dSat, JP,C
6.5 Hz, 1JW,C = 126.3 Hz, cis-CO), 196.1 ppm (d, 2JP,C = 35.9 Hz, trans-
CO); 31P NMR (CDCl3): d=2.1 ppm, 1JW,P = 257.4 Hz; MS (EI, 184W):
m/z (%): 724.1, [M]+, (0.3); 598.0, [M]+ÀiPrN=C=NiPr (0.3); 570.0,
[M]+ÀiPrN=C=NiPr ÀCO, (0.03); 542.0, [M]+-iPrN=C=NiPr À2xCO,
(0.1); 514.0,[M]+ÀiPrN=C=NiPr 3”CO, (0.5); 483.0, [M]+ÀiPrN=C=
NiPr À4”CO,(0.03); 458.0, [M]+ÀiPrN=C=NiPr À5”CO (1.2), 243.1,
[CPh3]+ (70), 69.1, [M]+ÀiPrN=C (100); IR (ATR): n˜ =2969 (b, n-CH2),
2072 (s, n-CO), 1980 (s, n-CO), 1917 (s, n-CO), 1740 (s, n-CO),
1597 cmÀ1 (b, n-C=N); elemental analysis (%) calcd for
C31H29N2O5PW: C 51.40, H 4.04, N 3.87; found: C 53.21, H 4.63,
N 3.59.
5: Route a: A solution of 1a was freshly prepared: tert-butyllithium
(1.6m in n-hexane, 0.30 mL, 1.1 equiv) was slowly added at À788C
to triphenylmethyl(dichloro)phosphane tungsten complex (295 mg,
0.44 mmol) and 12-crown-4 (69.4 mL, 1 equiv). N,N’-Diisopropyl car-
bodiimide 2a (69.5 mL, 1 equiv) was then slowly added at À788C
for 15 min. The reaction solution was stirred and warmed up
slowly to +48C and then kept at 48C for 15 h. Afterwards, CO2 was
bubbled through the solution during 30 min and then LiCl was fil-
tered off (Al2O3) from a 1:1 mixture of petroleum ether (40:60) and
Et2O at 258C, and the main impurity was extracted with n-pentane
at room temperature. The product was then crystallized from Et2O
at À208C and obtained as light yellow solid; yield: 100 mg
(0.14 mmol, 30%).
General procedure for the synthesis of hydrolysis products of
1a,b: Water (1 equiv) was added to a THF solution of 1a,b at room
temperature. The reaction mixture was stirred for 5 min. The sol-
vent was removed in vacuo (ca. 10À2 mbar) and a yellow oil was
obtained. The compound was then crystallized from pure Et2O at
À208C.
Hydrolysis product of 1a: White
solid, yield=250 mg (0.34 mmol,
70%), m.p. 162–1638C, 1H NMR
(CDCl3): d=1.0–1.4 (m, 12H, iPrCH3),
3.9 (bs, 2H, iPrCH), 6.7–7.7 ppm (m,
3”Ph), N-H are in coalescence pro-
cess at room temperature; 13C NMR
(CDCl3): d=22.8 (s, iPr-CH3), 22.9 (s,
iPr-CH3), 47.0 (s, 2 x iPrCH), 69.0 (d,
Route b:
A solution of 3-imino-azaphosphiridine complex 1a
(100 mg, 0.14 mmol) in Et2O (5 mL) was stirred under a CO2 atmos-
phere (20 bar) for 15 h. The solvent was removed in vacuo (ca.
10À2 mbar) and a yellow oil was obtained. The product was then
crystallized from Et2O at À208C and obtained as a white solid;
yield: 75 mg (0.98 mmol, 70%); m.p. 155–1568C, 1H NMR (C6D6):
d=0.27 (d, 3H, C=N-CH-CH3, 3JH,H =5.8 Hz), 0.94 (d, 3H, C=N-CH-
1JC,P =2.6 Hz, P-CPh3), 126.0 (d, JC,P
=
1.0 Hz, C-Ph), 127.0 (d, JC,P =1.7 Hz, C-
CH3, 3JH,H =5.8 Hz), 1.04 (d, 3H, C-N-CH-CH3, 3JH,H =7.0 Hz), 1.11 (d,
3
Ph), 127.1 (d, JC,P =1.0 Hz, C-Ph), 127.4 (d, JC,P =2.3 Hz, C-Ph), 128.0
3H, C-N-CH-CH3, 3JH,H =7.0 Hz), 3.48 (sept, 1H, C=N-CH(CH3)2, JH,H
=
(s, C-Ph), 128.5 (s, C-Ph), 130.0 (d, JC,P =6.4 Hz, C-Ph), 130.5 (d, JC,P
=
5.8 Hz), 4.52 (sept, 1H, C-N-CH(CH3)2, 3JH,H =7.0 Hz), 6.8–7.8 ppm (m,
15H, 3”C6H5); 13C NMR (C6D6): d=18.2 (s, C-N-CH-CH3), 18.5 (s, C-
N-CH-CH3), 23.4 (s, C=N-CH-CH3), 24.8 (s, C=N-CH-CH3), 48.0 (s, C-N-
CH), 55.6 (d, 1JP,C = 11.7 Hz, C=N-CH), 71.2 (d, CPh3, 1JP,C = 2.2 Hz),
128.5 (d, JP,C = 2.0 Hz C-CPh), 128.6 (d, JP,C = 2.7, Hz C-CPh), 128.9 (s, C-
CPh), 129.2 (s, C-CPh), 129.8 (s, C-CPh), 131.1 (d, JP,C = 2.7, Hz C-CPh),
131.6 (d, JP,C = 9.2, Hz C-CPh), 132.0 (d, JP,C = 7.0, Hz C-CPh), 136.9 (d,
2JP,C = 6.4 Hz C-Cipso–Ph), 139.3 (d, 2JP,C = 6.4 Hz, C-Cipso–Ph), 141.9 (d,
2.3 Hz, C-Ph), 131.1 (d, JC,P =7.4 Hz, C-Ph), 140.3 (d, 2JC,P =5.13 Hz,
C
ipso-Ph), 141.4 (d, 2JC,P =2.3 Hz, Cipso-Ph), 144.7 (d, 2JC,P =10.7 Hz,
Cipso-Ph), 172.5 (d, N-C-N, 1JP,C = 32.5 Hz), 197.7 (dSat, 2JP,C = 8.4 Hz,
1JW,C = 127.5, cis-CO), 200.4 ppm (d, 2JP,C = 27.5 Hz, trans-CO, JW,C
144.2, trans-CO); 31P NMR (CDCl3): d=92.4 ppm, qSat, JW,P
=
=
1
1
285.6 Hz, JP,H = 16. Hz; MS (EI, 184W): m/z (%): 743.1, [M]+, (1);
658.1, [M]+À3”CO, (2); 630, [M]+À4”CO,(1); 243.1, [CPh3]+ (100);
IR (ATR): n˜ =3347 (b, N-H), 2967 (b, n-CH2), 2068 (s, n-CO), 1986 (s,
n-CO), 1933 (s, n-CO), 1915 (s, n-CO), 1899 (s, n-CO), 1607 cmÀ1 (b,
n-C=N); elemental analysis calcd (%) for C31H31N2O6PW: C 50.15,
H 4.21, N 3.77; found: C 49.99, H 4.37, N 3.79.
2
2JP,C = 8.5 Hz C-Cipso–Ph), 149.5 (d, O-C=O, JP,C = 12.1 Hz), 151.0 (d, P-
C=N, 1JP,C = 8.1 Hz), 195.6 (dSat, 2JP,C = 6.2 Hz, 1JW,C =126.8, cis-CO),
197.4 ppm (d, 2JP,C = 34.1 Hz, trans-CO); 31P NMR (C6D6): d=
1
128.07 ppm, JW,P = 274.6 Hz. MS (EI, 184W): m/z (%):768.1, [M]+ (5);
740.1, [M]+ÀCO (2); 712.1, [M]+À2”CO (10); 684.1, [M]+À3”CO
(1); 712.1, [M]+À2”CO (10); 684.1, [M]+À3”CO (2); 640.1, [M]+
ÀCO2À3”CO, (10); 584.1, [M]+ÀCO2À5”CO, (25); 243, [CPh3]+
(100); IR (ATR): n˜ =2929 (b, n-CH2), 2076 (s, n-CO), 1992 (s, n-CO),
1930 (s, n-CO), 1774 (s, n-CO), 1723 (s, n-C=O), 1640 cmÀ1 (b, n-C=
N); elemental analysis calcd (%) for C32H29N2O7PW: C 50.02, H 3.80,
N 3.65; found: C 49.80, H 4.17, N 3.50.
4: Phenyl isocyanate 3a (82.2 mg, 1 equiv) was added to a solution
of iminoazaphosphiridine complex 1a (500 mg, 0.69 mmol) in Et2O
at room temperature and stirred for 5 h. The solvent was removed
in vacuo (ca. 10À2 mbar) and a dark yellow oil was obtained. The
product was then crystallized from Et2O at À208C and obtained as
white solid; yield: 380 mg (0.45 mmol, 65%), m.p. 148–1498C;
1H NMR (CDCl3): d=0.46 (d, 3H, C=N-CH-CH3, 3JH,H =5.9 Hz), 1.12 (d,
3
3H, C=N-CH-CH3, 3JH,H =5.8 Hz), 1.46 (d, 3H, C-N-CH-CH3, JH,H
=
CCDC 1056188 (1a), 1056102 (hydrolysis product of 1a), 1056103
(4), and 1056104 (5) contain the supplementary crystallographic
data for this paper. These data can be obtained free of
6.9 Hz), 1.56 (d, 3H, C-N-CH-CH3, 3JH,H =7.0 Hz), 3.48 (sept, 1H, C=N-
CH(CH3)2, 3JH,H =5.8 Hz), 4.89 (sept, 1H, C-N-CH(CH3)2, 3JH,H =6.9 Hz),
Chem. Eur. J. 2015, 21, 9650 – 9655
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Communication
Angew. Chem. 2011, 123, 4011–4014; b) G. MØnard, L. Tran, J. S. J. McCa-
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2015, DOI: 10.1021/om501206p.
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Computational details
[5] For some recent examples, see: a) C. Murcia-García, A. Bauza, G. Schna-
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submitted.
DFT calculations were performed with the ORCA program.[20] All ge-
ometry optimizations were run in redundant internal coordinates
with tight convergence criteria, using the B3LYP functional[21] to-
gether with the def2-TZVP basis set.[22] For
W atoms the
[SD(60,MWB)] effective core potential[23] (ECP) was used. The latest
Grimme’s semiempirical atom-pair-wise London dispersion correc-
tion (DFT-D3) was included in all calculations.[24] Solvent effects (tol-
uene) were taken into account via the COSMO solvation model.[25]
Harmonic frequency calculations verified the nature of ground
states or transition states (TS) having all positive frequencies or
only one imaginary frequency, respectively. From these optimized
geometries all reported data were obtained by means of single-
point (SP) calculations using the more polarized def2-TZVPP basis
set.[26] Reported energies were corrected for the zero-point vibra-
tional term at the optimization level. Final energies were obtained
by means of the recently developed near-linear scaling domain-
based local pair natural orbital (DLPNO) method[14] to achieve cou-
pled cluster theory with single-double and perturbative triple exci-
tations (CCSD(T)). For the sake of comparison, energy values were
also obtained with local correlation schemes of type LPNO (local
pair natural orbital) for high-level single-reference methods, such
as CEPA (coupled electron-pair approximation),[16b,c] here the slight-
ly modified NCEPA/1 version implemented in ORCA was used,[16a]
the spin component scaled (SCS) Moeller-Plesset MP2 level[27] and
Grimme’s Double-hybrid-meta-GGA functional PWPB95[15] together
with D3 correction (PWPB95-D3). Energy values were corrected for
the BSSE (basis set superposition error) using the counterpoise
method[28] at the 1cE·CO2 stage. Wiberg bond indices (WBI) were
obtained from the natural bond orbital (NBO) population analy-
sis.[29] Bader’s AIM-derived topological analysis of the electron den-
sity was conducted with AIM2000.[30] The NCIplot in Figure 3 of the
main text was obtained using the wave function (electron density)
at the B3LYP/def2-TZVPPecp level and drawn with VMD.[31]
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[12] The hydrolysis products possess 31P{1H} resonances (THF) at 91.2 ppm
(1JWP =284.2 Hz; from 1a) and 90.7 ppm (1JWP =283.7 Hz; from 1b); the
corresponding N-isopropyl derivative was isolated and completely char-
acterized (see the Supporting Information).
[13] Besides the reference DLNPO-CCSD(T)/def2-TZVPP high computational
level,[14] some other levels were checked (see the Supporting Informa-
tion); according to their root-mean-square deviation (rmsd), a remark-
able agreement was obtained, particularly in case of LNPO-NCEPA/1[15]
(rmsd 0.17 kcalmolÀ1) and PWPB95-D3[16] (rmsd 0.60 kcalmolÀ1) with the
same basis set.
Acknowledgements
[14] C. Riplinger, B. Sandhoefer, A. Hansen, F. Neese, J. Chem. Phys. 2013,
139, 134101.
We are grateful to the Deutsche Forschungsgemeinschaft for
financial support (SFB 813 “Chemistry at Spin Centers”), the
Cost Action cm1302 “Smart Inorganic Polymers” (SIPs), and the
Alexander von Humboldt Foundation (Bessel Award for T.S.).
G.S. thanks Prof. A. C. Filippou for support.
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Keywords: azaphosphiridines
dioxide · frustrated Lewis pairs · phosphorus
·
carbodiimides
·
carbon
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Received: April 27, 2015
Published online on June 1, 2015
Chem. Eur. J. 2015, 21, 9650 – 9655
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