η2-Coordination of a phosphaalkyne to an amino olefin nickel complex and regioselective catalyzed cyclooligomerization to dewar 1,3,5-triphosphabenzene

Article abstract of DOI:10.1002/ejic.201301135

We report herein an efficient synthesis of a Dewar-triphosphabenzene derived from [2+2+2] cycloaddition of three phosphaalkyne molecules promoted by an amino olefin Ni⁰ complex as the catalyst. Amino diolefin Ni ^I complex 1 serves as a precursor complex that reacts with triphenylmethylphosphaethyne under reducing conditions at low temperature to give Ni⁰ complex 3 with a coordinated phosphaalkyne in a η²-mode. The structure of 3 was determined by X-ray diffraction methods and suggests a bonding situation for the phosphaalkyne that is between a side-on coordinated C≡P molecule and a metallaphosphacyclopropene structure. The reaction of 3 with a 10-fold excess of phosphaethylene under reducing conditions at room temperature resulted in the formation of 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphosphabenzene (4) in good yield. Copyright

Full text of DOI:10.1002/ejic.201301135

SHORT COMMUNICATION
DOI:10.1002/ejic.201301135
η2-Coordination of a Phosphaalkyne to an Amino Olefin
Nickel Complex and Regioselective Catalyzed
Cyclooligomerization to Dewar 1,3,5-Triphosphabenzene
CLUSTER
ISSUE
Mónica Trincado,*[a] Amos J. Rosenthal,[a] Matthias Vogt,[a][‡] and
and Hansjörg Grützmacher*[a,b]
Keywords: Nickel / Phosphaalkynes / Cyclooligomerization / Coordination modes / Alkene ligands
We report herein an efficient synthesis of a Dewar-tri-
phosphabenzene derived from [2+2+2] cycloaddition of three
phosphaalkyne molecules promoted by an amino olefin Ni0
complex as the catalyst. Amino diolefin NiI complex 1 serves
as a precursor complex that reacts with triphenylmethyl-
phosphaethyne under reducing conditions at low tempera-
ture to give Ni0 complex 3 with a coordinated phosphaalkyne
in a η2-mode. The structure of 3 was determined by X-ray
diffraction methods and suggests a bonding situation for the
phosphaalkyne that is between a side-on coordinated CϵP
molecule and a metallaphosphacyclopropene structure. The
reaction of 3 with a 10-fold excess of phosphaethylene under
reducing conditions at room temperature resulted in the for-
mation of 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphos-
phabenzene (4) in good yield.
in the coordination sphere of metals, because the phos-
phorus lone pair of electrons or the CϵP unit may be en-
gaged in bonding to the metal centers. Note that the
number of isolated examples of side-on coordination com-
plexes is rather limited owing to the tendency of phospha-
alkynes to oligomerize in the coordination sphere of a metal
center.[6,14] It has been proposed that species with η2-coor-
dinated CϵP units are key intermediates in the formation
of phosphaheterocycles.[7,8] In the coordination sphere of
electron-rich transition metals (M = Ni, Co, Rh, Fe), phos-
phaalkynes have shown the tendency to cyclodimerize to
1,3-diphosphete ligands.[7a,7b,7h,9] By analogy to alkynes,
which readily cyclotrimerize to benzene derivatives in a
large number of transition-metal-catalyzed processes,[10] it
is expected that phosphaalkynes readily form 1,3,5-triphos-
phabenzene derivatives or isomers thereof. This, however,
has been observed only in some cases. Scheme 1 displays
valence isomers of triphosphabenzene systems coordinated
to Hf[7f] and V[11] and an earlier example of a partially char-
acterized Mo0 complex derived from a triolefin metal pre-
cursor.[4a] The suggested structure of the latter species could
not be confirmed by independent studies.[12] A significant
example of cyclotrimerization to form the complexed De-
war 1,3,5-benzene, which was fully characterized by single-
crystal X-ray diffraction, is depicted in Scheme 1. This re-
Introduction
Innovative materials with interesting reactivities and
properties that diverge from carbon-based chemistry can be
expected from studies of heteroatom-based π systems, in
which phosphorus centers with a low coordination number
substitute the CR groups. In comparison to the chemistry
of benzene, the chemistry of analogous aromatic phos-
phorus heterocycles is still poorly developed. This is espe-
cially true for heterocycles with more than one phosphorus
atom within the ring skeleton.[1] Several phospha-[2] and di-
phosphabenzene derivatives,[3]
a few 1,3,5-triphospha-
benzene valence isomers,[4] and hexaphosphabenzene are
known.[5]
The synthesis of sterically stabilized phosphaalkynes has
been developed over the past decades, and these molecules
show a remarkable versatility as useful building blocks in
organophosphorus chemistry. Frequently, they react like
their organic counterparts, alkynes, and undergo a wide
range of cycloadditions, but they may show dual behavior
[a] Department of Chemistry and Applied Biosciences, ETH
Zürich,
8093 Zürich, Switzerland
E-mail: trincado@inorg.chem.ethz.ch
hgruetzmacher@ethz.ch
www.gruetzmacher.ethz.ch
[b] Lehn Institute of Functional Materials (LIFM), Sun Yat-Sen port was followed by the only metal-promoted cyclo-
University,
trimerization of phosphaalkynes to give metal-free phos-
510275 Guangzhou, China
phaheterocycles under stoichiometric conditions.[4b]
[‡] Current address: The Weizmann Institute of Science,
Department for Organic Chemistry,
The Hf complex with a Dewar triphosphabenzene ligand
reacts readily with hexachloroethane and subsequent ther-
mal treatment to afford the two isomeric structures shown
76100 Rehovot, Israel
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301135.
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SHORT COMMUNICATION
Scheme 1. Known examples of triphosphaheterocycles derived from RCP oligomerization: 1,3,5-triphosphabenzene, Dewar benzene (two
coordination modes known), and spirocyclic betaine.
in Scheme 1.[7f,7j] The trimerization of phosphaalkynes pro- ing the reaction mixture to –30 °C for 12 h, complex 3 was
moted by AlCl3 has been reported by Regitz et al. In this isolated as orange crystals in 60% yield. A suitable single
reaction, the Lewis acid is incorporated in the phospha- crystal was used for X-ray diffraction analysis to elucidate
heterocycle to afford a cyclotetramer after an oxidative pro- the structure.
cess in which the not-isolated Dewar benzene is an interme-
diate.[13] To the best of our knowledge, a catalytic cyclo-
trimerization of phosphaalkynes to give metal-free products
has not been reported. Moreover, although Dewar triphos-
phabenzene species have been fully characterized by NMR
spectroscopy experiments,[7f] a detailed experimental struc-
ture determination of a non-coordinated molecule by X-ray
crystallography is lacking.
Results and Discussion
We synthesized the stable Ph3C–CP phosphaalkyne from
Ph3C–CH2–PCl2 through a simple elimination reaction and
investigated its coordination chemistry to group 8 transi-
Figure 1. (a) ORTEP diagram of complex 1 with 50% ellipsoid
probability. The second crystallographically independent molecule
tion-metal centers. The very robust η1-complexes
and hydrogen atoms are omitted for clarity. Selected bond lengths
[pm] and angles [°] with data for second molecule in brackets: Ni1–
N1 207.31(15) [205.87(15)], Ni1–Ct1 200.5 (201.2), Ni1–Ct2 198.4
(198.7), C4–C5 138.9(3) [138.9(3)], C19–C20 139.1(3) [139.5(3)],
Ni1–O1 214.07(13) [207.98(13)], Ni1–O2 224.64(13) [240.80(14)].
(b) ORTEP diagram of complex 3 with 50% ellipsoid probability.
Hydrogen atoms and two solvent molecules are omitted for clarity.
Selected bond lengths [pm] and angles [°]: Ni1–P1 221.88(13), Ni1–
N1 208.5(4), Ni1–Ct1 193.3, Ni1–C32 188.7(4), P1–C32 163.5(4),
C4–C5 140.2(6), N1–Ni1–P1 107.09(10), P1–C32–C33 145.29(10),
N1–Ni1–C4 93.60(15).
[MH(dppe)2(Ph3CCP)]OTf [M = Fe or Ru, dppe = 1,2-
bis(diphenylphosphino)ethane][14] are easily obtained.
Strong protic acids promote intramolecular electrophilic
aromatic substitution in coordinated Ph3C–CP, which leads
to benzophosphole compounds.[15] It is well established that
Ni0 complexes catalyze the [2+2+2] cycloaddition of alk-
ynes to give arene compounds.[10a,16] In this paper, we re-
port an analogous reaction by using the stabilized Ph3C–
CP phosphaalkyne that proceeds under reducing conditions
to give a Dewar triphosphabenzene. A NiI complex coordi-
nated by a tridentate ligand containing two potentially
Figure 1 (a, b) shows ORTEP plots of the structures of
hemilabile olefin ligands was used as the catalyst precursor. complexes 1 and 3. NiI complex 1 (Figure 1, a) has a struc-
The NiI complex [Ni(trop2NMe)(O2CCF3)] (1)[17] was ture that is very similar to its NH analogue [Ni(trop2-
prepared by the addition of the tridentate ligand trop2NMe NH)(O2CCF3)].[17] Notably, the coordinated olefinic units,
(trop = 5H-dibenzo[a,d]cyclohepten-5-yl) to NiII(O2CCF3)2 C=Ctrop, have a rather short interatomic distance (about
by using Zn powder as a reducing agent. The coordination 139 pm); this is indicative of rather weak metal-to-ligand
sphere of this 19-valence-electron-configured NiI center backbonding, which supports the assumption that the
consists of the trop2NMe ligand, which has a preorganized trop2NMe ligand may behave as a hemilabile ligand in 1.
concavely shaped binding site for transition-metal centers, Ni0 complex 3 adopts a planar geometry (see Figure 1) with
and a non-symmetrically κ2-binding trifluoroacetate (see N1, the centroid of the C=Ctrop unit (ct1), P1, and C32
Figure 1 for a structure plot). The reaction of NiI complex approximately in the same plane.
1 under reducing conditions with the use of phosphaalkyne
The trop2NMe ligand binds through the NMe moiety
2 as the ligand furnished complex 3 (Scheme 2). After cool- and only one η2-olefin unit in a bidentate fashion. The Ni–
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SHORT COMMUNICATION
Scheme 2. η2-Coordination of TrCP to Ni at low temperature and catalyzed regioselective oligomerization.
N bond in Ni0 complex 3 has the same length as that in NiI either complex 1 or 3 was stirred in THF in the presence of
complex 1 within experimental error, 208 vs. 207 pm. Likely a 10-fold excess of the tritylphosphaalkyne and an excess
because of the lower coordination number of the 16 val- amount of Zn powder for about 24 h at room temperature,
ence-electron-configured Ni0 center, the Ni–ct1 (ct1 = the reaction gave 4 as the major product with the minimal
centroid of the C4–C5 bond) distance (193 pm) is substan- presence of complex 3, as assayed by 31P{1H} NMR spec-
tially shorter than that in the monovalent diolefin NiI com- troscopy (Scheme 3). Compound 4 was obtained in good
plex (Ni–ct1 210 pm, Ni–ct2 212 pm). The length of the co- yield (70–75%) in this catalytic reaction.
ordinated C=Ctrop bond (C4–C5, 140 pm) is only slightly
longer than that in complex 1 (C4–C5 139 pm, C19–C20
139 pm) and indicates, likewise, a comparatively low degree
of metal-to-ligand backbonding from filled d orbitals at the
metal center into the π* orbital of the C=Ctrop unit. The
CϵP unit is coordinated to the Ni center in a side-on mode.
Here, the back donation of Ni0 of the Ni(trop2NMe) frag-
ment into the π* orbitals of the CϵP bond induces a sub-
stantial elongation of the interatomic distance (163 pm)
compared to that of free Ph3CϵP (153 pm).[5] The degree of
sp2 hybridization at C32 is also reflected in the considerable
bending of the P–C32–C33 bond angle (145°) versus the
almost-linear disposition of the phosphaalkyne (178°). This
type of bonding is similar to that in previously reported
structures of η2-ligated phosphaalkynes [RCϵP, R = tBu
or adamantyl (Ad)] and indicates an intermediate bonding
Scheme 3. Mechanistic hypothesis for Ni-catalyzed R–CϵP oligo-
situation that lies between a side-on coordinated CϵP bond
and a metallaphosphacyclopropene structure.[6d,18] Further-
more, in the 31P NMR spectrum, the resonance (δ =
merization.
The structure of 4 was investigated by single-crystal X-
194 ppm) is considerably shifted to higher frequencies with ray diffraction analysis, which confirmed a Dewar 1,3,5-tri-
respect to uncoordinated Ph3CCϵP (δ = –64 ppm), typi- phosphabenzene (Figure 2). The P=Csp2 distances in the bi-
cally observed for a η2-bonding mode.[19] In the 13C NMR cyclic structure show the archetypal interatomic distances
spectrum, the resonance for C32 (δ = 234.3 ppm) is con- (168 pm) also observed in phosphetes.[19] Species 4 is re-
siderably shifted to a lower field relative to the same reso- markably stable for prolonged periods of time. We would
nance of the starting material (δ = 177.6 ppm).
like to stress that trityl-substituted Dewar benzene does not
The 31P{1H} NMR spectroscopic data acquired for the thermally rearrange to the benzenoid isomer upon heating
mother liquor from the crystallization indicate the presence at 90 °C for 5 h, as was previously observed for the former
of phosphorus-containing product 4, which exhibits two tert-butyl-substituted compound, whereas photochemical
coupled resonances at δ = +346 ppm for two phosphorus conditions provoke the formation of multiple uncharac-
3
nuclei in chemically identical environments (d, JPP
=
terized products. This aspect is currently under further in-
3
36 Hz) and at δ = 86 ppm (t, JPP = 36 Hz) for one nucleus vestigation.
coupled to two 31P nuclei with identical coupling constants,
By monitoring the reaction of complex 3 with 2 by 31P
which give rise to a triplet. An early example of tert-butyl- NMR spectroscopy, no intermediates were observed. How-
substituted Dewar 1,3,5-triphosphabenzene was isolated ever, a plausible mechanism for the cyclotrimerization of
and characterized spectroscopically by Binger et al.,[7f] and phosphaalkynes to a Dewar triphosphabenzene can be pro-
it shows an almost-identical 31P{1H} NMR spectrum. If posed (Scheme 3). On the basis of the established mecha-
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SHORT COMMUNICATION
groups (R = FG). Such molecules are relevant for the devel-
opment of new materials based on phosphorus-containing
building blocks.
Experimental Section
General: All experiments were performed by using standard
Schlenk and vacuum-line techniques or were performed in a Braun
glove box under an inert atmosphere of Ar. All reagents were used
as received from commercial suppliers unless otherwise noted. All
solvents were distilled under an atmosphere of Ar from the appro-
priate drying agent and stored over 4 Å molecular sieves prior to
use. All NMR spectra were recorded with Bruker Avance 250, 300,
and 400 MHz spectrometers. Coupling constants J are given as ab-
solute values. IR spectra were recorded with a Perkin–Elmer-Spec-
trum 2000 FTIR Raman spectrometer with KBr beam splitter
(range 500–4000 cm–1). Mass spectra were recorded with a Waters
Micromass AutoSpec Ultima MassLynx 4.0 EI, a Bruker Daltonics
maxis ESI-QTOF, and a Varian HiResMALDI by ETH Zürich D-
CHAB/LOC MS Service. Melting points were determined with a
Büchi melting point apparatus. The compounds Ph3CCH2Cl,
Ph3CCH2PCl2, and Ph3CCP were synthesized according to pre-
viously reported procedures.[15]
Figure 2. ORTEP diagram of 4 with 50% ellipsoid probability. Hy-
drogen atoms and one solvent molecule are omitted for clarity. Se-
lected bond lengths [pm] and angles [°]: P1–P2 262.71(14), P2–P3
265.14(15), P1–C1 186.3(4), P1–C2 168.7(4), P2–C1 186.6(4), P2–
C2 182.6(4), P2–C3 184.6(4), P3–C1 187.6(4), P3–C3 168.8(4), C1–
P1–C2 88.42(18), C1–P3–C3 88.38(17), ΣC2 358.7(8), ΣC3 359.7(8).
nism for the trimerization of alkynes promoted by Ni0 com-
plexes,[10] the initial step could involve the coordination of
a second molecule of Ph3C–CP (eventually under displace-
ment of the last coordinated C=Ctrop unit in 3) followed
by oxidative coupling of both coordinated phosphaalkyne
molecules to give metallocyclodiphosphapentadiene com-
plex II as an intermediate. A third equivalent of Ph3C–CP
can then add (either directly or after previous coordination
to the NiII center in II) in a [4+2] cycloaddition process to
[Ni(trop2NMe)(O2CCF3)] (1): A 20 mL Schlenk tube was charged
with (trop2NMe) (200 mg, 0.48 mmol, 1.0 equiv.). The solid was
suspended in THF (3 mL) and [Ni(tfa)2] (138 mg, 0.48 mmol,
1.0 equiv.) was subsequently added. Zinc powder (327 mg,
5.00 mmol, 10 equiv.) was added to the pale-greenish solution. The
mixture was allowed to stir overnight. The zinc powder was filtered
afford metallobicyclotriphosphadiene complex III. Re- off the dark-green solution through a plug of Celite. Subsequently,
iPr2O (2 mL) was added to the filtrate. Layering the solution with
n-hexane (3 mL) resulted in the formation of colorless crystals after
12 h at –30 °C. The deep-green supernatant solution was decanted
from the colorless byproduct and layered with n-hexane (2 mL).
Large deep-green needles grew within 24 h at room temperature
(also suitable for single-crystal X-ray diffraction analysis). The
mother liquor was decanted, and the crystals were washed with
cold iPr2O (3ϫ 1 mL). The obtained air-sensitive crystals were
dried in a stream of argon (200 mg, 71% yield), m.p. 155–158 °C.
HRMS (ESI): calcd. for C31H25NNi [Ni(trop2NMe)]+ 469.1340;
ductive elimination would finally afford product 4. It is
likely that the aminobisolefin trop2NMe ligand plays the
role of a hemilabile ligand in this catalytic process. We be-
lieve that the C=Ctrop units help to stabilize the reduced
nickel species. However, it remains unclear how Zn as a
reducing agent intervenes in the reaction. Note that Ni0
complex 3 does not promote the trimerization to 4 in the
absence of Zn. Likewise, a reaction with the use of Zn alone
in the absence of nickel complex 1 or 3 does not give any
product.
found 469.1336. IR (ATR): ν = 1642 (s), 1483 (w), 1457 (w), 1276
˜
(w), 1189 (s), 1134 (s), 1037 (w), 981 (w), 901 (w), 912 (w), 875 (w),
We assume that the steric bulk of the trityl group on the
phosphaalkyne and its interaction with the coordination
sphere of the Ni complex are responsible for the regioselec-
tive formation of non-planar compound 4 resulting from
head-to-tail couplings of Ph3C–CP units.
846 (m), 704 (w), 767 (w), 741 (m), 726 (s) cm–1.
[Ni(trop2NMe)(η2-TrCP)]·2DME (3): A 20 mL vial was charged
with Ph3C–CϵP (2; 23 mg, 0.08 mmol, 1.0 equiv.) and THF
(3 mL). [Ni(trop2NMe)(O2CCF3)] (61 mg, 0.08 mmol, 1.0 equiv.)
was added, and the mixture was stirred until a clear dark-green
solution formed. Zinc powder (52 mg, 0.80 mmol, 10 equiv.) was
added to the solution, and the mixture was stirred vigorously for
1 h at room temperature. The reaction mixture was cooled down
Conclusions
In this paper we have shown that side-on coordinated to –30 °C for 12 h. The color of the solution turned to red. The
phosphaalkyne 16e Ni0 complex 3 is easily obtained under
remaining zinc powder was filtered off by using syringe filters and
dimethoxyethane (2 mL) was added to the filtrate. The mixture was
reducing conditions from a 19e NiI precursor complex.
layered with n-hexane (3 mL). The product was allowed to crys-
Complex 3 promotes the cyclotrimerization of a phospha-
tallize for 24 h at –30 °C. The supernatant solution was decanted,
alkyne under reducing conditions, which allows the success-
and the orange crystals were washed with n-hexane (1 mL) and
ful synthesis of free Dewar 1,3,5-triphosphabenzene 4. In
dried under vacuum (45 mg, 60% yield), m.p. 210–212 °C (de-
this catalytic reaction, we obtained, for the first time, an
indication that trop-type molecules may behave as hemi-
labile ligands. We hope that this catalytic approach opens
the possibility for the related synthesis of new phospha-
comp.). 1H NMR (400.13 MHz, [D8]THF): δ = 7.90–7.88 (m, 3 H,
CHar), 7.57–7.40 (m, 5 H, CHar), 7.38–6.39 (m, 23 H, CHar), 5.40
3
3
(d, JHH = 9.4 Hz, 1 H, CHolef), 5.12 (d, JHH = 9.9 Hz, 1 H,
3
3
CHolef), 4.92 (d, JHH = 9.7 Hz, 1 H, CHolef), 4.82 (d, JHH
=
heterocycles including those that carry diverse functional 9.4 Hz, 1 H, CHolef), 3.84 (s, 1 H, CHbzl), 3.76 (s, 1 H, CHbzl), 1.78
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SHORT COMMUNICATION
(br. s, 3 H, NCH3) ppm. 13C{1H} NMR (100.6 MHz, [D8]THF): δ was included in the refinement by using a riding model. For details
= 234.3 (CP confirmed by correlation with CH3 in H13C HMBC,
J = 22.9 Hz), 151.2 (Cquart) 138.2 (Cquart), 137.9 (Cquart), 137.6
(Cquart), 137.3 (Cquart), 136.8 (CHar), 136.5 (CHar), 136.3 (CHar),
135.8 (CHar), 135.7 (CHar), 135.4 (CHar), 135.1 (CHar), 134.8
(CHar), 134.6, (CHar), 133.4 (CHar), 130.8 (CHar), 129.9 (CHar),
129.5 (CHar), 129.2 (CHar), 128.9 (CHar), 128.5 (CHar), 128.1
(CHar), 127.5 (CHar), 127.1 (CHar), 126.9 (CHar),125.3 (CHar),
124.7 (CHar), 92.8 (CHolef), 82.1 (CHolef), 79.6 (CHbnzl), 74.5
(CHolef), 72.3 (CHolef), 52.4 (CH3) ppm. 31P{1H} NMR
see the crystallographic data for each compound below.
1
CCDC-958684 (for 1), -954392 (for 3), and -954394 (for 4) contain
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.
¯
Crystal Data for 1: Triclinic P1, unit cell a = 1319.51(12) pm, b =
1446.68(12) pm, c = 1471.19(12) pm, α = 96.027(2)°, β = 91.983(2)°,
γ = 111.330(2)°, volume 2.5935(4) nm3, Z = 4, density (calculated)
= 1.494 gcm–3, absorption coefficient = 0.803 mm–1, coefficient
F(000) = 1204, crystal size 0.23ϫ0.12ϫ0.09 mm3, Θ range for data
collection 1.52 to 28.33°, index ranges –17 Յ h Յ 17, –19 Յ k Յ
19, –19 Յ l Յ 19, reflections collected 27093, independent reflec-
tions 12789 [R(int) = 0.0257], completeness to Θ (28.33°) = 99.0%,
absorption correction empirical, refinement method full-matrix
least-squares on F2, data/restraints/parameters 12789/0/723, good-
ness-of-fit on F2 1.053, final R indices [IϾ2σ(I)] R1 = 0.0403, wR2
= 0.1003, R indices (all data) R1 = 0.0487, wR2 = 0.1052, largest
diff. peak and hole 1.119 and –0.328 eÅ–3.
(161.9 MHz, [D ]THF): δ = 194.3 ppm. IR (ATR): ν = 2774 (w),
˜
8
2463 (w), 2358 (w), 2168 (w), 1597 (w), 1478 (s), 1456 (w), 1423
(w), 1360 (w), 1304 (w), 1273 (w), 1260 (w), 1187 (w), 1163 (w),
1136 (w), 1102 (w), 1044 (m), 957 (w), 948 (w), 914 (w), 878 (w),
819 (w), 776 (w), 740 (m), 725 (m), 654 (w) cm–1. HRMS (MALDI-
TOF): calcd. for C51H40NNiP 755.2252; found 755.2261.
2,4,6-Tris(trityl)-Dewar-1,3,5-triphosphabenzene (4)
Method A: Ph3CCϵP (2; 29 mg, 0.1 mmol, 10.0 equiv.) was added
to a solution of complex 3 (7.5 mg, 0.01 mmol, 1.0 equiv.) in THF
(3 mL). Zn powder (6.5 mg, 0.1 mmol, 10.0 equiv.) was added to
the red solution, and the mixture was vigorously stirred at room
temperature in a glove box for 24 h. The excess of zinc powder
was filtered off by using syringe filters. The volatile materials were
removed under reduced pressure to afford an orange residue.
Analysis of the residue by 31P NMR spectroscopy denoted the pres-
ence of 4 as the main phosphorus-containing compound. The resi-
due was extracted in toluene (5 mL) and filtered through a pad of
Celite. The solution was layered with n-hexane and cooled to
–30 °C for 48 h to afford pale-yellow crystals (20 mg, 69%).
¯
Crystal Data for 3: Triclinic P1, unit cell a = 1314.6(2) pm, b =
1339.3(2) pm, c = 1286.5(3) pm, α = 83.456(4)°, β = 76.260(4)°, γ
= 70.568(4)°, volume = 2.2346(7) nm3, Z = 2, density (calculated)
= 1.325 gcm–3, absorption coefficient = 0.518 mm–1, coefficient
F(000) = 942, crystal size 0.25ϫ0.21ϫ0.20 mm3, Θ range for data
collection 1.61 to 26.37°, index ranges –16 Յ h Յ 16, –16 Յ k Յ
16, –17 Յ l Յ 17, reflections collected 19791, independent reflec-
tions 9079 [R(int) = 0.0524], completeness to Θ (26.37°) = 0.993,
absorption correction empirical, absorption correction T min and
max 0.8814 and 0.90, 35 refinement method full-matrix least-
squares on F2, data/restraints/parameters 9079/0/572, goodness-of-
fit on F2 1.083, final R indices [IϾ2σ(I)] R1 = 0.0778, wR2 =
0.1849, R indices (all data) R1 = 0.1032, wR2 = 0.1974, largest diff.
peak and hole 1.360 and –1.010 eÅ–3.
Method B: Ph3CCϵP (2; 29 mg, 0.1 mmol, 10.0 equiv.) was added
to a solution of complex 1 (5.7 mg, 0.01 mmol, 1.0 equiv.) in THF
(3 mL). Zn powder (6.5 mg, 0.1 mmol, 10.0 equiv.) was added to
the green solution, and the mixture was vigorously stirred at room
temperature in a glove box for 24 h. The excess of zinc powder
was filtered off by using syringe filters. The volatile materials were
removed under reduced pressure to afford a reddish residue. The
same protocol as that in method A was followed to afford pale-
yellow crystals (21.5 mg, 75%), m.p. 180–182 °C. 1H NMR
(400.13 MHz, C6D6): δ = 7.71 (br. s, 3 H, CHar), 7.26–7.20 (m, 5
H, CHar), 7.12–7.10 (m, 2 H, CHar), 7.04–6.97 (m, 5 H, CHar)
ppm. 13C{1H} NMR (100.6 MHz, C6D6): δ = 262.1 (P–C=P), 147.4
(Cquart), 137.7 (Cquart), 129.8 (CHar), 129.1 (CHar), 128.2 (CHar),
127.8 (CHar), 127.6 (CHar), 126.5 (CHar), 72.1 (CP3), 61.0 (CPh3),
57.6 (CPh3) ppm. Note: Owing to the low relative intensity of the
quaternary carbon atoms attached to P, the following acquisition
parameters were used to record the 13C NMR spectrum: d1 = 30 s
and p1 = 0.2 μs and processing parameter lb = 10 Hz; nonetheless
the multiplicity of these signals were not resolved. 31P{1H} NMR
(161.9 MHz, C6D6): δ = 346.2 (d, 3JPP = 36.0 Hz, 2 P), 86.5 (t, 3JPP
Crystal Data for 4: Monoclinic P21/c, unit cell a = 962.16(17) pm,
b = 1833.2(3) pm, c = 2842.7(5) pm, β = 94.057(3)°, volume =
5001.6(15) nm3, Z = 4, density (calculated) = 1.263 gcm–3, absorp-
tion coefficient = 0.163 mm–1, coefficient F(000) = 2000, crystal
size 0.74ϫ0.04ϫ0.02 mm3, Θ range for data collection 1.32 to
25.06°, index ranges –11 Յ h Յ 11, –21 Յ k Յ 21, –33 Յ l Յ 33,
reflections collected 39775, independent reflections 8851 [R(int) =
0.1520], completeness to Θ (25.06°) = 0.997, absorption correction
empirical, absorption correction T min and max 0.7496 and 0.9280,
refinement method full-matrix least-squares on F2, data/restraints/
parameters 8851/0/632, goodness-of-fit on F2 1.012, final R indices
[IϾ2σ(I)] R1 = 0.0672, wR2 = 0.1335, R indices (all data) R1 =
0.1280, wR2 = 0.1581, largest diff. peak and hole 0.629 and
–0.403 eÅ–3.
Supporting Information (see footnote on the first page of this arti-
cle): Selected NMR spectra for 3 and 4.
= 36.0 Hz, 1 P) ppm. IR (ATR): ν = 3058 (w), 2964 (w), 1490 (m),
˜
1445 (s), 1263 (s), 1076 (s), 1023 (s), 798 (s), 760 (s), 747 (s), 699
(s) cm–1. HRMS (EI): calcd. for C60H45P3 858.2734, found
858.2769. C60H45P3 (858.92): calcd. C 83.90, H 5.28; found C 82.95,
H 5.75.
Acknowledgments
The authors are grateful to the ETH Zürich, the Swiss National
Science Foundation (SNF), and the Marie Curie Network Program
SusPhos for financial support. The authors thank Dr. R. Verel for
assistance with the NMR spectroscopic investigations.
Crystallographic Analysis: The crystals were measured with a
Bruker APEX’ platform diffractometer with CCD area detector;
Mo-Kα radiation (0.71073 Å). The refinement against full-matrix
(vs. F2) was done with SHELXTL (ver. 6.12) and SHELXL-97.
Empirical absorption correction was done with SADABS (ver.
2.03). All non-hydrogen atoms were refined anisotropically. The
contribution of the hydrogen atoms, in their calculated positions,
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Received: September 2, 2013
Published Online: October 14, 2013
Eur. J. Inorg. Chem. 2014, 1599–1604
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