Hydrophosphination of carbodiimides using protic heptaphosphide cages: A unique effect of the bimodal activity of protonated group 15 Zintl ions

Article abstract of DOI:10.1021/om300072z

Direct reaction of the hydrogen heptaphosphide dianion, [HP ₇]^2- (1), with carbodiimides RN=C=NR (R = Dipp (2,6-diisopropylphenyl), ⁱPr, Cy) afforded the amidine-functionalized Zintl ions [P₇C(NHR)(NR)]^2- (R = Dipp (2), ⁱPr (3), and Cy (4)). The bimodal activity of 1, which contains both negatively charged phosphide vertices alongside "electron-precise" phosphine-like nuclei allows for the direct hydrophosphination of the carbodiimides without need for an external proton source. Further reaction of the bis(2,6- diisopropylphenyl)amidine-functionalized cluster 2 with a proton source such as [NH₄][BPh₄] or [H(OEt₂)₂][BAr ^F₄] affords the protonated monoanionic species [HP ₇C(NHDipp)(NDipp)]^- (5). As with 1, species 5 also has bimodal character, and additional hydrophosphination reactions are possible by reacting 5 with RN=C=NR to yield the bis-functionalized monoanions {[P ₇[C(NHDipp)(NDipp)][C(NHR)(NR)]}^- (R = Dipp (6), ⁱPr (7), and Cy (8)). All species were characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition clusters 3, 5, and 6-8 were characterized by single-crystal X-ray diffraction in [K(18-crown-6)]₂[3], [K(2,2,2-crypt)][5], [K(2,2,2-crypt)][6] ?THF, [K(2,2,2-crypt)][7]?hex, and [K(2,2,2-crypt)][8]?0. 65THF?0.35hex, respectively. Density functional theory level calculations were conducted on all anionic species to probe their electronic structure.

Full text of DOI:10.1021/om300072z

Article
pubs.acs.org/Organometallics
Hydrophosphination of Carbodiimides Using Protic Heptaphosphide
Cages: A Unique Effect of the Bimodal Activity of Protonated Group
15 Zintl Ions
Robert S. P. Turbervill and Jose M. Goicoechea*
Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA U.K.
S
* Supporting Information
ABSTRACT: Direct reaction of the hydrogen heptaphosphide dianion,
[HP7]2− (1), with carbodiimides RNCNR (R = Dipp (2,6-
i
diisopropylphenyl), Pr, Cy) afforded the amidine-functionalized Zintl
i
ions [P7C(NHR)(NR)]2− (R = Dipp (2), Pr (3), and Cy (4)). The
bimodal activity of 1, which contains both negatively charged phosphide
vertices alongside “electron-precise” phosphine-like nuclei allows for the
direct hydrophosphination of the carbodiimides without need for an
external proton source. Further reaction of the bis(2,6-
diisopropylphenyl)amidine-functionalized cluster 2 with a proton source
such as [NH4][BPh4] or [H(OEt2)2][BArF ] affords the protonated
4
monoanionic species [HP7C(NHDipp)(NDipp)]− (5). As with 1,
species 5 also has bimodal character, and additional hydrophosphination
reactions are possible by reacting 5 with RNCNR to yield the bis-
functionalized monoanions {[P7[C(NHDipp)(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), iPr (7), and Cy (8)). All species were
characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition clusters 3, 5, and 6−8 were
characterized by single-crystal X-ray diffraction in [K(18-crown-6)]2[3], [K(2,2,2-crypt)][5], [K(2,2,2-crypt)][6]·THF,
[K(2,2,2-crypt)][7]·hex, and [K(2,2,2-crypt)][8]·0.65THF·0.35hex, respectively. Density functional theory level calculations
were conducted on all anionic species to probe their electronic structure.
center, two-electron bonds to exo-functionalities. The earliest
reactivity studies of group 15 Zintl anions found that [P7]3−
could be functionalized yielding neutral trisubstituted adducts
INTRODUCTION
■
The heptaphosphide trianion, [P7]3−, is an archetypal example
of the family of “naked” anionic main-group clusters typically
referred to as Zintl ions.1 This species and the heavier group 15
congeners ([As7]3− and [Sb7]3−) are “electron-precise” anions
exhibiting nortricyclane-like geometries. Four of the cluster
vertices of the cage (one apical and three basal) form three two-
center, two-electron bonds to adjacent atoms, whereas the
remaining three vertices form two bonds to neighboring atoms
and subsequently carry formal negative charges. These two
different types of vertices (neutral and anionic) are known to
interconvert with one another; the [P7]3− trianion has been
shown to exhibit fluxional behavior in solution and in the solid
state, with all of the phosphorus atoms appearing equivalent on
the NMR time-scale due to a degenerate Cope rearrangement
process.2,3
5−15
n
such as R3P7 (e.g., R = Bu, SiMe3, FeCp(CO)2).
Alkyl
exchange reactions between [P7]3− and R3P7 or reactions of the
heptaphosphide trianion with alkyl tosylates, tetraalkylammo-
nium salts, or N-methylated amino acid esters were also found
to give disubstituted monoanionic species, [R2P7]− (R = Me,
Et, nBu, Bz, iPr, iBu, (EtO)C(O)CH2, (EtO)C(O)-
CHMe).16−19
In addition to the aforementioned clusters, where the
heptaphosphide cages can be considered to act as lone pair
donors via individual cage atoms (in an η1-coordination mode),
several additional coordination modes have been observed for
the interaction of the [P7]3− anion with Lewis acidic species.
The cluster cage can coordinate to Lewis acidic metal centers
via two (η2-) cage atoms acting as a four-electron donor in an
analogous fashion to chelating bidentate phosphines such as
1,2-bis(diphenylphoshino)ethane (dppe).20,21 Alternatively, the
anion can undergo a mild activation of the nortricyclane cage,
giving rise to a norbornadiene-like geometry, which coordinates
to metal centers via four (η4-) atoms (donating six electrons) in
species such as [P7M(CO)3]3− (M = Cr, Mo, W)22,23 and
The anionic phosphide vertices available in [P7]3− give rise to
the unique reactivity exhibited by the cluster anion. The
strongly basic and nucleophilic character of the heptaphosphide
trianion is manifested in its ability to deprotonate relatively
weak Brønsted acids to generate mono- and diprotic anions
([HP7]2− and [H2P7]−) and the neutral hydrogen polyphos-
phane H3P7 (which is unstable with regard to disproportiona-
tion).2,4,5 The nucleophilicity of the cluster is manifested in the
ability of [P7]3− to undergo alkylation and metalation reactions,
yielding functionalized species where the cluster forms two-
Received: January 30, 2012
Published: March 8, 2012
© 2012 American Chemical Society
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Article
[P7Ni(CO)]3−.24 These species retain their basicity and can
deprotonate weak acids, yielding [HP7M(CO)3]2− (M = Cr,
W) and [HP7Ni(CO)]2−, respectively.24,25 Alternatively, they
may undergo further reactions with electrophiles, giving rise to
of both nucleophilic phosphide vertices and a protonated cage
atom). Isotopic labeling studies have shown that the proton is
transferred from the cage to the amidine functionality. When
[HP7]2− is reacted with carbodiimides in deuterated solvents
(such as d5-pyridine or d7-DMF), only the protio-amidine-
functionalized cages {P7[C(NHR)(NR)]}2− are obtained.
Conversely, when reacting [DP7]2− with a carbodiimide in a
protonated solvent, only the deuterated amidine-functionalized
cage [P7C(NDR)(NR)]2− is observed by NMR spectroscopy.30
This observation strongly suggests that the mechanism of
reaction is likely to be concerted and involve the nucleophilic
attack of a negatively charged phosphide vertex at the
C(NDipp)2 carbon atom. This would result in a bending of
the linear carbodiimide and a transfer of negative charge from
the phosphorus atom to one of the more electronegative imide
nitrogen atoms (yielding an amidinate). The amidinate can
rapidly abstract a proton from the heptaphosphide cage,
yielding an amidine-functionalized cage. An alternative
mechanism first involving protonation of the carbodiimide by
the [HP7]2− cage to yield a carbocation (in an analogous
fashion to the way carbodiimides are employed as dehydrating
agents in peptide bond formation) is also possible;31 however
this seems less likely considering the high basicity of the
[HP7]2− cage. The use of carbodiimides to cross-link carboxylic
acids with amines is known to proceed most effectively under
acidic conditions. In our experience in order to deprotonate the
hydrogen heptaphosphide cage, a strong base such as potassium
hexamethyldisilazide (KHMDS) is necessary (deprotonation
will not take place with weaker non-nucleophilic bases such as
potassium tert-butoxide). It warrants highlighting at this stage
n
[RP7W(CO)3]2− (R = Me, Et, Bu, CH2Ph, SiMe3, GeEt3, Sn
nBu3, PbPh3).25−27 Direct reaction of the protonated hydrogen
heptaphosphide dianion with transition metal reagents has also
recently been shown as an accessible route to [HP7]2− clusters
coordinated to metal centers in an η4-mode.28 More complex
coordination modes have also been shown to arise when two
metal atoms are bridged by cluster anions as in [M2(HP7)2]2−
(M = Ag, Au).29
Recently we have developed an interest in using anionic Zintl
clusters for the activation of small molecules. We are
particularly enthused by the possibility of exploiting the
bimodal activity of species such as the hydrogen heptaphos-
phide dianion, [HP7]2− (1), which contains both phosphine-
and phosphide-like vertices, for the hydrophosphination of
unsaturated molecules. In a recent report we noted that 1 reacts
with bis(2,6-diisopropylphenyl)carbodiimide (DippNC
NDipp) to yield the amidine-functionalized cluster [P7C-
(NHDipp)(NDipp)]2− (2).30 Herein we report a follow-up
study to that finding and show that reactions of [HP7]2− with
i
different carbodiimides (RNCNR; R = Pr, Cy) yield the
corresponding amidine-functionalized cages [P7C(NHR)-
(NR)]2− (R = iPr (3), Cy (4)). Protonation of the
functionalized cages seems to be dependent on the steric
bulk of the amidine substituent, and thus while it is possible to
protonate 2 to yield the protic monoanion [HP7C(NHDipp)-
(NDipp)]− (5), protonation of 2 and 3 gives rise to known
polyphosphides, [P16]2− and [P21]3−, and the corresponding
formamidines. The protic amidine-functionalized cluster anion
5 can be further reacted with an additional equivalent of a
carbodiimide to yield the bis-functionalized cages {P7[C-
3−
that reactions of the deprotonated parent anion P7 with
carbodiimides do not give rise to amidine-functionalized cages.
Clusters 2−4 can be considered as heptaphosphaguanidine
dianions. It is worth noting that, to date, all of the reported
synthetic routes to phosphaguanidines typically involve the in
situ generation of phosphides (via deprotonation of secondary
phosphines) prior to the reaction of such species with
carbodiimides. The resulting phosphaguanidinates are typically
protonated using an aqueous workup to generate the
corresponding phosphaguanidines.32 These three steps(1)
deprotonation to yield a phosphide; (2) nucleophilic attack of
the phosphide at the carbodiimide carbon; and (3) protonation
of the anionic -ate saltare not necessary when reacting
carbodiimides with [HP7]2−. The cluster cage contains both the
phosphide vertices necessary for reaction with the carbodii-
mides and a source of a proton (the protonated phosphine
vertex). As a result no workup is necessary for protonation. The
bimodal activity of 1 (which contains both phosphine- and
phosphide-like vertices) gives rise to a “self-catalyzed” hydro-
phosphination, which occurs quantitatively. Related trans-
formations involving the catalytic transformation of secondary
phosphines and carbodiimides to phosphaguanidines using s-
block metal alkyl complexes and amides have previously been
reported in the chemical literature.33
i
(NHDipp)(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), Pr
(7), Cy (8)).
RESULTS AND DISCUSSION
■
Synthesis of Monoamidine-Functionalized Dianions
[P7C(NHR)(NR)]2− (R = Dipp (2), Pr (3), Cy (4)). The
i
precursor reagents [K(18-crown-6)]2[1] and [K(2,2,2-
crypt)]2[1]·solv (solv = en, py) can be readily synthesized in
high yields by direct reaction of K3P7 with stoichiometric
amounts of water in the presence of the appropriate alkali metal
sequestering agent. We recently reported that 1 reacts with one
equivalent of bis(2,6-diisopropylphenyl)carbodiimide to yield
the amidine-functionalized Zintl ion [P7C(NHDipp)-
(NDipp)]2− (2).30 We have since found that the reaction of
1 toward carbodiimides is a relatively versatile procedure that
gives rise to quantitative transformation of the hydrogen
heptaphosphide dianion to amidine-functionalized Zintl ions
i
[P7C(NHR)(NR)]2− (R = Pr (3), Cy (4); Scheme 1). This
process is effectively a hydrophosphination of the unsaturated
carbodiimides by the [HP7]2− cage (facilitated by the presence
Species 3 and 4 were characterized by multielement NMR
spectroscopy and reveal very similar 31P NMR spectra to that of
2. At room temperature the spectra of 3 and 4 show three
resonances due to a fluxional process whereby nonfunctional-
ized cluster vertices interconvert with one another. These
resonances occur at −18.3, −87.6, and −118.8 ppm for 3 and at
−18.5, −87.5, and −111.7 ppm for 4. The lowest field
resonances correspond to the functionalized cluster vertex
(P3). Cooling the samples (−50 °C in d7-DMF) retards cluster
Scheme 1. Synthesis of Amidine-Functionalized Cluster
a
Anions [P7C(NHR)(NR)]2−
a
i
R = Dipp (2), Pr (3), Cy (4).
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Article
fluxionality, and seven distinct resonances can be observed in
the NMR spectra arising from each of the seven magnetically
inequivalent phosphorus nuclei of the amidine-functionalized
cages. The seven resonances and their assignments are listed in
Table 1.
The structure of 3 is very similar to that previously reported
for 2.30 The functionalized P3 position is chiral, and a racemic
mixture of enantiomers is observed by single-crystal X-ray
diffraction (a single cluster site is occupied by one of the two
enantiomers in the C2/c centrosymmetric space group). The
N-substituents of the cage have an Esyn configuration as in 3.34
The bond distances between C1 and the nitrogen atoms of the
amidine functionality, 1.356(3) and 1.287(3) Å (ΔCN = 0.06
Å), are consistent with that of 2 and other literature reported
phosphaguanidines32 and indicate that the C1−N1 and C1−N2
bonds have single- and double-bond character, respectively. It is
worth noting that no structural or spectroscopic evidence of
amidine-functional group tautomerism was observed,35 perhaps
due to intramolecular interactions between the amidine proton
and a cluster phosphide vertex. The P3−C1 bond distance,
1.891(2) Å, is also consistent with related complexes (1.895(3)
Å for 2). The P3 vertex has a distorted pyramidal geometry,
which precludes any significant π-interactions arising between
the phosphorus atom and the amidine functionality (as is
common in guanidines). Interatomic P−P distances within the
cluster are largely unremarkable and comparable to other
literature reported values (ranging between 2.139(1) and
2.264(1) Å).5−21,30 The exposed coordination spheres of the
[K(18-crown-6)]+ countercations allow for short interactions
that are electrostatic in nature to arise between the lone pairs of
the cluster vertices and the potassium ions (between 3.6 and
4.1 Å).
The cluster anions 3 and 4 were also characterized by
electrospray mass spectrometry, where the [P7C(NHR)(NR)]−
anions were observed as the molecular ions in the negative ion
mode spectra. These peaks occur at m/z values of 344.7 and
424.9 for 3 and 4, respectively. As is common with the ES-MS
spectra of related Zintl ions, the clusters were observed with
reduced charges as a result of the oxidation of the parent cluster
anions, presumably arising as a result of the electrical potential
difference applied to samples during the ionization process. In
the positive ion mode mass envelopes were observed for the
{[K(2,2,2-crypt)]2[P7C(NHR)(NR)]}+ and {[K(2,2,2-
crypt)]3[P7C(NHR)(NR)]}+ ion pairs at 1174.4 and 1588.3
for 3 and 1254.9 and 1668.7 for species 4.
a
Table 1. 31P NMR Chemical Shifts for Samples 2−4
b
resonance (ppm)
2
3
4
P3
P1
P5
P4
P2
P7
P6
−6.3
−28.3
−68.7
−17.7
−28.9
−73.0
−18.7
−28.2
−73.5
−91.6
−96.2
−95.7
−100.0
−134.1
−211.7
−105.0
−130.3
−225.0
−103.8
−130.3
−223.3
a
Data collected at −50 °C in d7-DMF. Phosphorus nuclei numbering
b
scheme as used in Figure 1. Data taken from ref 30.
The 1H and 13C{1H} NMR spectra of 3 and 4 were found to
be consistent with the formulation of such species as amidine-
functionalized cages. Of particular interest is the observation of
resonances in the 1H spectra arising from the amidine protons,
which were observed at 4.05 and 3.14 ppm for 3 and 4,
respectively (compared to 6.29 ppm for 2). The chemical shift
of this resonance is very sensitive to the chemical environment
of the amidine proton and shifts substantially depending on the
nature of the nitrogen R substituent. The wide range of
chemical shifts observed for the amidine proton in 2−4 is
consistent with values reported in the literature for such
resonances in related phosphaguanidine systems.32
Single-crystal X-ray data were collected for 3, which was
crystallographically characterized in [K(18-crown-6)]2[3]. The
unit cell contains a single crystallographically unique [P7C-
(NHiPr)(NiPr)]2− dianion (Figure 1) accompanied by two
[K(18-crown-6)]+ cations. Selected data collection and refine-
ment details for all single-crystal analyses reported in this article
can be found in Table 2.
The optimized cluster geometries for 3 and 4 were calculated
using density functional theory (DFT) methods. The
computed bond distances and angles obtained for 3 show
good correlation with crystallographically determined values,
and both computed structures are very closely related to that
previously reported for 2 (see Supporting Information for full
details). The computed P−P interatomic distances are slightly
longer than the crystallographically determined values, a
consequence of the simplistic method used to model the
crystal environment for the cluster anions, which was simulated
using a continuum dielectric. As would be expected, the
HOMO and HOMO−1 have significant lone pair character at
the two negatively charged phosphorus vertices, P2 and P4.
Mulliken and Hirshfeld charge analyses are consistent with the
greatest degree of negative charge being localized on these two
nuclei, confirming the phosphide character of these two
negatively charged vertices.
Figure 1. The single crystallographically unique anion present in
[K(18-crown-6)]2[3]. Anisotropic thermal ellipsoids pictured at 50%
probability level. Hydrogen atoms, except H1, have been omitted for
clarity. A minor disordered component (17%) of the isopropyl moiety
defined by C2 has also been omitted. Selected bond distances (Å):
P3−C1, 1.891(2); C1−N1, 1.356(3); C1−N2, 1.287(3), N1−C2,
1.452(3); N2−C5, 1.454(3); P1−P2, 2.168(1); P1−P3, 2.221(1);
P1−P4, 2.167(1); P2−P5, 2.164(1); P3−P6, 2.186(1); P4−P7,
2.139(1); P5−P6, 2.236(1); P5−P7, 2.264(1); P6−P7, 2.248(1).
Protonation of Amidine-Functionalized Cages: Syn-
thesis of [HP7C(NHDipp)(NDipp)]− (5). The aforementioned
synthesis of a family of monofunctionalized heptaphosphide
i
amidine complexes [P7C(NHR)(NR)]2− (R = Dipp (2), Pr
(3), Cy (4)) prompted us to carry out further reactivity studies
aimed at assessing the reactivity of the remaining “naked”
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Table 2. Selected X-ray Data Collection and Refinement Parameters for [K(18-crown-6)]2[3], [K(2,2,2-crypt)][5], [K(2,2,2-
crypt)][6]·THF, [K(2,2,2-crypt)][7]·hex, and [K(2,2,2-crypt)][8]·0.65THF·0.35hex
[K(18-crown-
6)]2[3]
[K(2,2,2-crypt)]
[K(2,2,2-crypt)]
[K(2,2,2-crypt)]
[K(2,2,2-crypt)]
[8]·0.65THF·0.35hex
[5]
[6]·THF
[7]·hex
formula
fw [g mol−1
cryst syst
space group
a (Å)
C31H63K2N2O12 P7
950.82
C43H72KN4O6 P7
996.94
C72H114KN6O7P7
1431.58
C56H100KN6O6P7
1209.31
C60.7H104.1KN6O6.65P7
1280.26
]
monoclinic
C2/c
orthorhombic
Pna21
monoclinic
P21
orthorhombic
P212121
monoclinic
P21n
49.6456(14)
9.7578(2)
20.2349(6)
20.5480(5)
16.9255(3)
15.8004(3)
15.6647(3)
15.1270(3)
17.1338(4)
15.9418(2)
16.7687(2)
26.4606(4)
16.0447(2)
26.4964(3)
16.9173(1)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
105.114(3)
91.220(2)
91.488(1)
9463.4(4)
8
5495.1(2)
4
4059.1(2)
2
7073.5(2)
4
7189.6(1)
4
radiation, λ (Å)
Cu Kα, 1.54184
150(2)
1.171
T (K)
150(3)
1.335
150(2)
1.205
150(2)
1.136
150(2)
1.183
ρcalc (g cm−3
μ (mm−1
)
)
4.462
3.129
2.280
2.518
2.512
reflns collected
indep reflns
params
24 236
9773
18 599
8402
23 963
25 827
14 024
729
45 894
14 987
983
12 512
549
614
973
R(int)
0.0388
4.45/11.41
5.27/12.29
1.035
0.0496
4.83/11.71
6.80/13.15
1.071
0.0355
0.0261
6.31/16.99
7.29/17.99
1.034
0.0341
4.04/10.37
4.98/11.11
1.023
a
R1/wR2, I ≥ 2σI (%)
R1/wR2, all data (%)
6.29/17.06
7.49/18.35
a
GOF
1.018
a
2
R1 = [∑||Fo| − |Fc||]/∑|Fo|; wR2 = {[∑w[(Fo) 2 − (Fc)2]2]/[∑w(Fo )2]}1/2; w = [σ2(Fo)2 + (AP)2 + BP]−1, where P = [(Fo)2 + 2(Fc)2]/3 and the
A and B values are 0.0686 and 6.91 for [K(18-crown-6)]2[3], 0.0629 and 1.19 for [K(2,2,2-crypt)][5], 0.1235 and 0.89 for [K(2,2,2-crypt)][6]·THF,
0.0985 and 3.37 for [K(2,2,2-crypt)][7]·hex, and 0.0547 and 2.25 for [K(2,2,2-crypt)][8]·0.65THF·0.35hex.
negatively charged cluster vertices. The presence of two
phosphide atoms on the monofunctionalized cages should
allow for additional protonation of these cluster cages. With this
in mind we set out to protonate 2−5 using Brønsted acidic
species such as ammonium tetraphenylborate, [NH4][B-
the second species is found at 14.6, 0.0, −50.8, −54.0, −112.2,
−152.9, and −170.6 ppm. We believe that these two sets of
seven resonances correspond to two of the four possible
isomers available upon protonation of 2 (see Figure 2). There
is no noticeable change to the relative intensities of these
resonances if a solution of [K(2,2,2-crypt)][5] is left to stand
for several weeks. DFT level calculations show that the four
(C6H5)4], or Brookhart’s acid, [H(OEt2)2][BArF ] (ArF
=
4
3,5-(CF3)2C6H3).36 In situ 31P NMR studies showed that while
2 is readily protonated to give the monoanionic species
[HP7C(NHDipp)(NDipp)]− (5), clusters 3 and 4 rapidly
decompose to the known higher nuclearity polyphosphides
[P16]2− and [P21]3−.37 The separation of [K(2,2,2-crypt)][5]
from the reaction side-product proved challenging when using
[NH4][B(C6H5)4] as a proton source; however protonation
using [H(OEt2)2][BArF ] allows for the resulting [K(2,2,2-
4
crypt)][BArF ] to be removed by washing the bulk sample with
4
diethyl ether ([K(2,2,2-crypt)][5] is only sparingly soluble in
Et2O). This allowed us to obtain compositionally pure samples
of [K(2,2,2-crypt)][5]; that is, no evidence of the [BArF ]−
4
1
anion was appreciable in the H and 19F NMR spectra after
washing, and an accurate elemental analysis could be obtained
for 5.
Species 5 has been characterized by multielement NMR
spectroscopy, single-crystal X-ray diffraction, electrospray mass-
spectrometry, and elemental analysis. Monitoring the reaction
of 2 with a proton source by 31P NMR spectroscopy shows that
there is quantitative conversion of the starting material to a
mixture of two species each displaying seven characteristic
NMR multiplet resonances (as confirmed by a 31P−31P 2D
COSY NMR experiment). The two products are generated in
roughly the same ratio with one of the species observed at 34.8,
−32.4, −75.6, −92.7, −95.0, −165.3, and −191.7 ppm, while
Figure 2. The four possible diastereomers of an asymmetrically
substituted bifunctionalized heptaphosphide cluster (their correspond-
ing enantiomers are not pictured). Pyramidal inversion at the
functionalized sites would allow interconversion of A with B and C
with D. Atoms highlighted in red carry a formal negative charge.
Tautomeric forms of amidine functionalities are not pictured.
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1
Figure 3. 1D H−31P HMQC NMR spectra of [K(2,2,2-crypt)][5] (1H observed) showing the results of (a) broadband {31P} decoupling, (b)
optimizing the experiment for a 1JH−P value of 116 Hz, (c) optimizing the experiment for a 1JH−P value of 250 Hz, (d) optimizing the experiment for
1
a JH−P value of 180 Hz.
possible isomers lie in a 25 kJ mol−1 range, making it difficult to
unequivocally identify the isomers present.
of the crystallographic disorder, the P−P interatomic distances
are poorly determined, and subsequently a significant analysis
of these data is not possible (a table comparing selected bond
distances and angles for both enantiomers is provided in the
Supporting Information). Despite the limitations of the single-
crystal X-ray data, the structure offers a good idea of the charge
and connectivity associated with the cluster anion (Figure 4).
There is a single [K(2,2,2-crypt)]+ cation accompanying the
cluster cage, consistent with the cage being protonated. The
An additional possibility is that we are observing the time-
averaged spectra for the two species resulting from protonation
at sites P2 and P4 (from Figure 1), respectively, and that there
is a rapid pyramidal inversion at the protonated phosphorus
atoms (this would allow interconversion of the isomer pairs A/
B and C/D). Facile pyramidal inversion has previously been
reported for related functionalized cluster anions by Eichhorn
and co-workers.17,25,27 It is worth noting, however, that in such
cases cluster fluxionality can be slowed on cooling and that we
see no significant change to the 31P NMR spectrum of 5 with
varying temperature. This indicates that if such an inversion
process is taking place, it is very rapid on the NMR time scale.
1H and 13C NMR experiments further support the hypothesis
that two different isomers of 5 are present in solution. The
1H{31P} NMR spectrum of [K(2,2,2-crypt)][5] exhibits two
resonances at 6.57 and 6.27 ppm corresponding to the amidine
protons of the two isomers and a single resonance at 0.95 ppm
corresponding to the proton attached to the cage. Integration
of the spectrum indicates that the cage protons of each of the
two isomers overlap and that this resonance integrates to twice
the intensity of the amidine proton singlets. This is further
1
supported by the fact that a one-dimensional H−31P HMQC
experiment exhibits two doublets with 1JH−P coupling constants
of 254 and 117 Hz, respectively. The relative intensities of the
1
doublets were found to be dependent on the JH−P coupling
constant value for which each experiment was optimized
(Figure 3).
Single crystals containing 5 were obtained by layering a THF
solution of [K(2,2,2-crypt)][5] with hexanes. The crystal
structure exhibits “up−down” disorder at the anion site, a
result of the two enantiomers of the [P7C(NHDipp)(NDipp)]
core occupying the single cluster site in a non-centrosymmetric
point group. The amidine functionalities of both enantiomers
occupy the same atomic positions, and subsequently only the
atoms of the heptaphosphide cages are disordered. On account
Figure 4. One of the two disordered components present at the
anionic site in [K(2,2,2-crypt)][5]. The anion exhibits “up−down”
disorder with the occupancy of the components refining to a 54% to
46% ratio. Anisotropic thermal ellipsoids pictured at the 50%
probability level. Hydrogen atoms, except H1 and H2A, have been
omitted for clarity. All hydrogen positions in the structure were fixed.
A full description of the refinement details is available in the
Supporting Information.
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Scheme 2. Synthesis of the Protic Amidine-Functionalized Cluster Anion [HP7C(NHDipp)(NDipp)]2− (5) and of the
i
Disubstituted Bis-amidine Clusters {P7[C(NHDipp)(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), Pr (7), Cy (8))
proton position of the cluster cage could not be located by
studying the residual electron density after all atomic positions
had been refined anisotropically and the hydrogen positions of
the cryptand and amidine substituent were fixed. As a result, the
proton position of the cage was fixed (this prevents the
determination of which isomers of 5 are formed on
protonation). Location of the proton positions on the cluster
cages of group 15 Zintl ions can often prove challenging even in
nondisordered systems.26 Bond distances within the amidine
moiety are very similar to those previously observed for 2 and
3. The C1−N1 and C1−N2 bond distances are 1.366(5) and
1.273(5) Å, respectively (ΔCN = 0.09 Å).
The disubstituted cluster anion 6 exhibits five resonances in
its 31P NMR spectrum at 12.5, −29.0, −64.2, −113.8, and
−129.5 ppm. These chemical shift values are comparable to
other symmetrically disubstituted heptaphosphide monoan-
ions.16−19 The H NMR spectrum of 6 shows a resonance at
1
6.31 ppm corresponding to the two equivalent amidine
protons. No evidence of the cage proton could be observed
in the spectrum. Similarly, species 7 and 8 also appear to exhibit
only five resonances in their 31P NMR spectra; however when
trying to simulate the spectra, it becomes apparent that this is
the result of overlapping multiplets for the functionalized
positions P3 and P4 and the basal positions P6 and P7 (see
Figures 6 and 7 for numbering schemes). An optimal model
can be obtained by allowing the chemical shift values of these
two closely related resonances to refine individually. As a result,
seven chemical shift values can be determined for 7 and 8 at
6.5, 3.2, −34.0, −69.6, −112.2, −134.0, −136.3 and 7.3, 4.9,
−33.6, −69.6, −112.7, −135.7, −136.5 ppm, respectively. In
each instance the first and last two multiplets overlap
extensively. The 1H NMR spectrum of 7 displays two
resonances, each arising from the protons of the amidine
groups (6.22 and 3.87 ppm). In the case of 8 only one such
resonance was observed, at 6.20 ppm, although it is thought
that the other (NHCy) is obscured by one of the intense 2,2,2-
crypt resonances.
DFT calculations on the four isomers of 5 show that their
total bonding energies fall within a narrow window of 25 kJ
mol−1, with isomers A and B being the most energetically
favorable (within 4 kJ mol−1 of one another). Isomers C and D
are somewhat higher in energy (17 to 25 kJ mol−1 higher in
energy than A and B; within 5 kJ mol−1 of one another);
however these data are not significant enough to definitively
determine which isomers are present in solution. The HOMO
of each isomer is consistent with there being a significant
amount of lone-pair character on the remaining “naked” vertex.
Despite being unable to unequivocally identify the nature of the
isomers of 5 present in solution, spectroscopic and structural
data strongly indicate that protonation of 2 has taken place.
This is further confirmed by the reactivity of 5 toward
carbodiimides, which is discussed herein.
The bis-amidine-functionalized clusters 6−8 were charac-
terized by single-crystal X-ray diffraction in [K(2,2,2-crypt)]-
[6]·THF, [K(2,2,2-crypt)][7]·hex, and [K(2,2,2-crypt)]-
[8]·0.65THF·0.35hex, respectively. The crystal structures of
all three clusters show that only the “symmetrical” disubstituted
isomers are present in the solid state (isomer A, Figure 2; see
Figures 5, 6, and 7). In the case of 6, because both substituents
are identical, there is only one possible stereoisomer of the
Synthesis of {P7[C(NHDipp)(NDipp)][C(NHR)(NR)]}− (R
i
= Dipp (6), Pr (7), and Cy (8)). Direct reaction of 5 with
i
carbodiimides RNCNR (R = Dipp, Pr, Cy) was found to
yield the bis-functionalized cluster anions {P7[C(NHDipp)-
i
(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), Pr (7), and Cy
(8); see Scheme 2). As with the formation of 2−4 these
reactions proceed cleanly and can be considered as the
hydrophosphination of a second carbodiimide by the P−H
bond present in 5. In situ monitoring of the reaction mixtures
by multielement NMR spectroscopy shows quantitative
conversion of 5 to 6−8 at room temperature within 24 h of
the addition of one molar equivalent of the corresponding
carbodiimide. It is worth noting that no reaction is observed
when 2−4 are reacted directly with carbodiimides, highlighting
the importance of the protonated cage site.
Species 6−8 were characterized by single-crystal X-ray
diffraction, multielement NMR spectroscopy, electrospray
mass spectrometry, and elemental analysis. The 31P NMR
spectra of clusters 6−8 are closely related, and each show five
multiplet resonances arising from the presence of a single
disubstituted isomer (isomer A in Figure 2). The presence of a
single isomer was confirmed by single-crystal X-ray diffraction.
The large steric bulk of the amidine functionalities rules out the
possibility of obtaining other isomers as in the case of 5. In the
case of the unsymmetrically disubstituted species, 7 and 8, there
are only five apparent multiplets due to the fact that the
resonances arising from the functionalized cluster vertices
overlap, as do the resonances from the basal atoms to which
they are bonded.
Figure 5. The single crystallographically unique anion present in
[K(2,2,2-crypt)][6]·THF. Anisotropic thermal ellipsoids pictured at
50% probability level. Hydrogen atoms, except H1 and H3, have been
omitted for clarity. Selected bond distances (Å): P3−C1, 1.879(5);
C1−N1, 1.354(5); C1−N2, 1.292(6), N1−Dipp, 1.425(8); N2−Dipp,
1.414(6); P4−C26, 1.892(5); C26−N3, 1.342(6); C26−N4, 1.280(7);
N3−Dipp, 1.437(7); N4−Dipp, 1.417(7); P1−P2, 2.145(2); P1−P3,
2.217(2); P1−P4, 2.225(2); P2−P5, 2.139(3); P3−P6, 2.201(2); P4−
P7, 2.190(2); P5−P6, 2.223(3); P5−P7, 2.228(3); P6−P7, 2.230(2).
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cluster anion (there is no enantiomer). The two functionalized
positions P3 and P4 are chiral and have R- and S-symmetry,
respectively, according to Cahn−Ingold−Prelog priority rules.38
In the case of 7 and 8 there are two possible enantiomers: (1)
P3 is bonded to a bis(2,6-diisoproyplphenyl)amidine (R) and
P4 is bonded to the other amidine substituent (S), or (2) P3 is
i
bonded to C(NHR)(NR) (R = Pr, Cy) (R) and P4 is bonded
to the bis(2,6-diisoproyplphenyl)amidine (S). As with 2 and 3,
the N-substituents for each of the amidine substituents in 6, 7,
and 8 have Esyn configurations.34 As with species 2−5, no
evidence of amidine-group tautomerism was observed exper-
imentally.35
The structure of 6 has a single crystallographically unique
cluster anion in the asymmetric unit accompanied by a
[K(2,2,2-crypt)]+ cation and a THF molecule. There is some
rotational disorder of the cation/cryptand complex. The cluster
anion (pictured in Figure 5) exhibits two exo-functionalized
phosphorus positions, P3 and P4, and a single “naked”
phosphide vertex (P2). As with the monofunctionalized cluster
anions discussed earlier, the internuclear bond distances within
the heptaphosphide cage are largely unremarkable (2.139(3)−
2.230(2) Å) and comparable to other exo-functionalized
systems with nortricyclane-like geometries (2: 2.139(1)−
2.226(1) Å). The exo-bonds to the amidine substituents P3−
C1 and P4−C26 are 1.879(5) and 1.892(4) Å, respectively, and
very similar to those in 2, 3, and 5 (1.895(3) and 1.891(2) Å
for 2 and 3, respectively). Similarly it is also possible to
differentiate between the single and double bonds of the
amidine moieties by analysis of bond metric data. The C1−N1
and C26−N3 distances (1.354(6) and 1.342(6) Å, respectively)
are notably longer than the neighboring C1−N2 and C26−N4
bond distances (1.292(6) and 1.280(7) Å, respectively). The
planarity of the core of the amidine moieties (P3−C1−N1−N2
and P4−C26−N3−N4) is also consistent with the previously
discussed exo-functionalized systems and related phosphagua-
nidines.
Figure 6. The single crystallographically unique anion present in
[K(2,2,2-crypt)][7]·hex. Anisotropic thermal ellipsoids pictured at the
50% probability level. Hydrogen atoms, except H1 and H3, have been
omitted for clarity. The bis(isopropyl)amidine substituent defined by
C26 exhibits some rotational disorder, and only the major component
(78% occupancy) is pictured. Selected bond distances (Å): P3−C1,
1.874(3); C1−N1, 1.363(4); C1−N2, 1.277(5), N1−Dipp, 1.428(5);
N2−Dipp, 1.398(4); P4−C26, 1.893(6); C26−N3, 1.412(8); C26−
N4, 1.281(9); N3−iPr, 1.480(8); N4−iPr, 1.455(13); P1−P2,
2.139(2); P1−P3, 2.200(1); P1−P4, 2.213(2); P2−P5, 2.115(2);
P3−P6, 2.199(2); P4−P7, 2.171(3); P5−P6, 2.222(2); P5−P7,
2.225(3); P6−P7, 2.208(2).
The crystal structure of 7 is very similar to that of 6 and, as a
result, does not warrant extensive discussion. The sample
crystallizes in the non-centrosymmetric space group P212121
with only one crystallographically unique cluster anion in the
asymmetric unit (see Figure 6); however upon refinement, it is
apparent that the structure is an inversion twin (BASF
parameter 0.501). As with 6 there are two exo-functionalized
cluster positions, P3 (bonded to C(NHDipp)(NDipp)) and P4
(bonded to C(NHiPr)(NiPr), and a phosphide vertex P2.
Interatomic distances in the heptaphosphide cage range
between 2.115(2) and 2.225(3) Å, consistent with related
species. Bonds to the exo-substituents are identical within
experimental error to those observed in 6 (1.874(3) and
1.893(6) Å). There is some rotational disorder of the
bis(isopropyl)amidine substituent that is bonded to P4, which
can be modeled as two components in a 78% to 22% ratio. As a
result, the bond metric data for this amidine substituent should
be interpreted with caution.
Figure 7. One of the two disordered components present at the
anionic site in [K(2,2,2-crypt)][8]·0.65THF·0.35hex. The anion
exhibits “up−down” disorder, with the occupancy of the components
refining to a 65% to 35% ratio. Anisotropic thermal ellipsoids pictured
at the 50% probability level. Hydrogen atoms, except H1 and H3, have
been omitted for clarity.
diisopropylphenyl)amidine functionalities of each component
occupying the same atomic positions (similar crystallographic
disorder was observed for 5). In effect, this is a result of the two
possible enantiomers of the cluster occupying the same
crystallographic site. At the same time there are two solvent
molecules that fill the vacancies that are left in the asymmetric
unit as a result of the disordered cluster. A tetrahydrofuran
molecule accompanies one of the disordered components and
sits on the site of a Cy group in the amidine functionality of the
second component. Similarly, there is also a hexane molecule
that accompanies the second component, located at the site of a
Crystals of 8 (Figure 7) could also be grown from a THF/
hexane mixture, and while they proved adequate to determine
the composition and geometry of the cluster anion, there is
crystallographic disorder at the cluster site, which will have an
effect on the accuracy of the bond metric data despite the high
quality of the diffraction data that were collected.
The asymmetric unit contains a [K(2,2,2-crypt)]+ cation
accompanied by a cluster anion. The anion site exhibits “up−
down” disorder of two components with the bis(2,6-
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Cy group in the bis(cyclohexyl)amidine functionality of the
first. The bond metric data in the amidine components are
similar to those observed for 6. The C1−N1 and C26−N3
distances (1.361(2) and 1.366(av) Å, respectively) are longer
than those observed for the C1−N2 and C26−N4 distances
(1.281(2) and 1.278(av) Å, respectively). A full analysis of
bond metric data for 6−8 and their optimized computed
structures is available in the Supporting Information.
Clusters 6−8 were further characterized in solution by
negative and positive ion mode electrospray mass spectrometry.
The negative ion mode spectra of DMF solutions of the
clusters show mass envelopes corresponding to the {P7[C-
(NHDipp)(NDipp)][C(NHR)(NR)]}− anions at m/z values
of 943.8, 707.4, and 788.4 for 6, 7, and 8, respectively. Similarly,
the positive ion mode spectra show peaks arising from the ion-
paired species {[K(2,2,2-crypt)]2{P7[C(NHDipp)(NDipp)]-
[C(NHR)(NR)]}}− at m/z values of 1776.3, 1538.1, and
1617.4 for 6, 7, and 8, respectively.
DFT level calculations were also conducted on 6−8. As with
the cluster anions described previously, the optimized
computed geometries show a good correlation with the
crystallographically determined structures. Full tables compar-
ing bond metric data are available in the Supporting
Information. Interatomic P−P distances are slightly longer in
the computed structures (up to 0.04 Å), as previously observed
for related Zintl ions, a result of the continuum dielectric field
used to model the presence of the cations in the lattice. The
HOMO orbitals for all three cluster anions are predominantly
composed of lone-pair character on the phosphide vertices (P2
according to the numbering scheme employed in Figures 5−7).
EXPERIMENTAL SECTION
■
General Synthetic Methods. All reactions and product
manipulations were carried out under an inert atmosphere of argon
or dinitrogen using standard Schlenk-line or glovebox techniques
(MBraun UNIlab glovebox maintained at <0.1 ppm H2O and <0.1
ppm O2). The Zintl phase precursor K3P7 was synthesized according
to a previously reported synthetic procedure from a mixture of the
elements (K: 99.95%, Strem; P: 99.99%, Aldrich).39 Bis(2,6-
diisopropylphenyl)carbodiimide was synthesized according to the
method reported by Cowley and co-workers.40 Brookhart’s acid,
[H(OEt2)2][BArF ], was prepared according to a modified procedure
4
reported by Brookhart et al. and stored in a glovebox freezer at −25
°C.36 2,2,2-Crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8,8,8]-
hexacosane; VWR, 99%), 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooc-
tadecane; 99%, Alfa Aesar), and bis(cyclohexyl)carbodiimide (99%,
Sigma Aldrich) were used as received after careful drying under
vacuum. Bis(isopropyl)carbodiimide (99%, Sigma Aldrich) and HCl
(2.0 M in diethyl ether, Sigma Aldrich) were used as received. Hexanes
(hex; 99+%, Rathburn), diethyl ether (Et2O; pesticide residue grade,
Fisher), and dimethylformamide (DMF; 99.9%, Rathburn) were
purified using an MBraun SPS-800 solvent system. Tetrahydrofuran
(THF; 99.9%, Rathburn) and pyridine (py; 99%, Alfa Aesar) were
distilled over a sodium metal/benzophenone mixture and CaH2,
respectively. d5-Pyridine (99.5%, Cambridge Isotope Laboratories,
Inc.) and d7-DMF (99.5%, Cambridge Isotope Laboratories, Inc.) were
dried over CaH2 and vacuum distilled. All dry solvents were stored
under argon in gastight ampules. Additionally hexanes, Et2O, and THF
were stored over activated 3 Å molecular sieves.
[K(2,2,2-crypt)]2[1]·py (1: [HP7]2−). A slurry of K3P7 (887 mg,
2.65 mmol) in approximately 50 mL of pyridine was reacted with
degassed and deionized H2O (96 μL, 5.30 mmol), and the resulting
mixture stirred under argon for one hour. 2,2,2-Crypt (2.00 g, 5.30
mmol) was added, and the mixture stirred for an additional 5 min and
subsequently filtered. The bright orange-yellow filtrate was concen-
trated under dynamic vacuum to the point of saturation, after which
500 mL of toluene was added to precipitate the product as an orange
microcrystalline solid. The resultant product was isolated by filtration
and dried under vacuum for 2 h. Yield: 2.112 g (76%). Over time the
product very slowly changes to a yellow color with no discernible
change in the NMR spectra, possibly due to loss of pyridine from the
lattice. Anal. Calcd for C41H78K2N5O12P7: C, 43.65; H, 6.97; N, 6.21.
CONCLUSIONS
■
We have shown that the reactions of the heptaphosphide
dianion, [HP7]2−, with a range of bulky carbodiiimides give rise
to the exo-functionalized cluster anions [P7C(NHR)(NR)]2−
i
(R = Dipp (2), Pr (3), and Cy (4)). These 1:1 reactions take
1
Found: C, 43.39; H, 6.60; N, 5.99. H NMR (500 MHz, d7-DMF, 20
place due to the bimodal reactivity of protonated heptaphos-
phide cages that contain both “naked” anionic phosphide
vertices and protic phosphine-like atoms. Sequential hydro-
phosphination reactions are possible by protonating the
monofunctionalized cluster anions and reacting them with a
further equivalent of a carbodiimide. Attempts to protonate
species 2−4 proved that while 2 could be readily protonated to
yield a disubstituted cage [HP7C(NHDipp)(NDipp)]− (5),
similar reactions with 3 and 4 resulted in decomposition of the
amidine-functionalized clusters to polyphosphides of increased
nuclearities such as [P16]2− and [P21]3−. Reaction of 5 with a
further equivalent of a carbodiimide yielded both the
disubstituted clusters {P7[C(NHDipp)(NDipp)][C(NHR)-
3
°C): δ (ppm) 3.77 (s, 24H, 2,2,2-crypt), 3.74 (t, 24H, JH−H = 5 Hz,
3
2,2,2-crypt), 2.73 (t, 24H, JH−H = 5 Hz, 2,2,2-crypt), 0.46 (br s, 1H,
HP7). 31P NMR (202.4 MHz, d7-DMF, 20 °C): δ (ppm) −23.7 (br
m), −111.4 (br m). 1H NMR (500 MHz, d7-DMF, −50 °C): δ (ppm)
3
3
3.77 (s, 24H), 3.74 (t, 24H JH−H = 5 Hz), 2.73 (t, 24H, JH−H = 5
1
Hz), 0.49 (d, 1H, JP−H = 159 Hz). 31P NMR (202.4 MHz, d7-DMF,
−50 °C): δ (ppm) −22.7 (m, 1P), −48.8 (m, 1P), −76.8 (m, 1P),
−110.8 (m, 1P, overlapping resonance), −111.6 (m, 1P, overlapping
resonance), −123.6 (m, 1P), −235.8 (m, 1P). ESI−-MS (DMF): m/z
216.0 [HP7]− (there is extensive decomposition of the HP7 dianion
2−
during the ionization process, resulting in a complex spectrum that
shows evidence of higher nuclearity oxidized polyphosphides).
[K(18-crown-6)]2[1] (1: [HP7]2−). A similar procedure to that
detailed above can be used to synthesize [K(18-crown-6)]2[HP7]
using 18-crown-6 instead of 2,2,2-crypt. Anal. Calcd for
C24H49K2O12P7: C, 34.94; H, 5.99. Found: C, 34.49; H, 5.43. NMR
spectroscopic data are very similar to the [K(2,2,2-crypt)]+ salt and
have been reported previously by our research group.30 ESI−-MS
(DMF): m/z 216.0 [HP7]−. ESI+-MS (DMF): m/z 1129.1 {[K(18-
crown-6)]3[HP7]}+. As above, extensive decomposition of the starting
material is observed in the ESI-MS spectra.
i
(NR)]}− (R = Dipp (6), Pr (7), and Cy (8)). Species 7 and
8 are the first examples of heptaphosphide cages bearing two
different exo-functionalities and show that sequential mod-
ifications of Zintl cluster anions are possible to give rise to
macromolecular structures based on group 15 cluster core
backbones.
The research described shows that protonated heptaphos-
phide cages are highly reactive toward unsaturated adducts. We
are currently in the process of extending this work to other
unsaturated reagents such as isocyanates, alkenes, alkynes, and
other small-molecule substrates.
[K(2,2,2-crypt)]2[3] (3: [P7C(NHiPr)(NiPr)]2−). In an inert
atmosphere glovebox [K(2,2,2-crypt)]2[HP7] (50 mg, 47.6 μmol)
was weighed into a J. Young’s NMR tube equipped with an airtight
valve. The contents of the tube were dissolved in d7-DMF, and
bis(isopropyl)carbodiimide (7.4 μL, 47.6 μmol) was added with a
microsyringe. The reaction was then monitored by H and 31P NMR
1
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3
3JH−H = 4 Hz, 2,2,2-crypt), 2.31 (t, 24H, JH−H = 4 Hz), 1.86 (d, 3H,
spectroscopy, which showed immediate quantitative conversion to 2.
The contents of the tube were filtered into a Schlenk tube under
argon, and volatiles removed under dynamic vacuum, yielding an
orange oil. Sonication of the sample in 10 mL of diethyl ether
generated a yellow powder, which was isolated by filtration and dried
under dynamic vacuum. Isolated yield: 29.8 mg (52%). Anal. Calcd for
C43H87K2N6O112P7: C, 43.95; H, 7.46; N, 7.15. Found: C, 43.82; H,
7.53; N, 6.83. H NMR (500 MHz, d7-DMF, 20 °C): δ (ppm) 4.50
(sep, 1H, 3JH−H = 6 Hz, CH(CH3)2), 4.05 (s, 1H, NH), 3.60 (s, 24H,
3JH−H = 7 Hz, CH3), 1.81 (d, 3H, JH−H = 7 Hz, CH3), 1.73 (d, 3H,
3
3JH−H = 7 Hz, CH3), 1.65 (d, 3H, JH−H = 7 Hz, CH3), 1.61 (d, 3H,
3
3JH−H = 7 Hz, CH3), 1.52 (d, 3H, JH−H = 7 Hz, CH3), 1.38
3
3
3
(overlapping d, 6H, JH−H = 7 Hz, CH3), 1.36 (d, 3H, JH−H = 7 Hz,
3
CH3), 1.34 (d, 3H, JH−H = 7 Hz, CH3), 1.32 (overlapping d, 6H,
3JH−H = 7 Hz, CH3), 1.15 (d, 3H, JH−H = 7 Hz, CH3), 1.11 (d, 3H,
3
3JH−H = 7 Hz, CH3), 1.08 (d, 3H, JH−H = 7 Hz, CH3), 1.03 (d, 3H,
3
3
3JH−H = 7 Hz, CH3), 0.95 (s, 2H, PH). 1H{31P}−31P 1D-HMQC NMR
2,2,2-crypt), 3.57 (t, 24H, JH−H = 5 Hz, 2,2,2-crypt), 3.32 (sep, 1H,
(500 MHz, d5-pyridine, 20 °C): δ (ppm) 0.95 (s, PH). H−31P 1D-
1
3
3JH−H = 6 Hz, CH(CH3)2), 2.55 (t, 24H, JH−H = 5 Hz, 2,2,2-crypt),
HMQC NMR (500 MHz, d5-pyridine, 20 °C): δ (ppm) 0.95 (d, 1JH−P
0.92 (d, 6H, 3JH−H = 6 Hz, CH3), 0.72 (d, 6H, 3JH−H = 6 Hz, CH3). 31
P
= 254 Hz, PH), 0.95 (d, JH−P = 117 Hz, PH). 31P{1H} NMR (202.4
1
NMR (202.4 MHz, d7-DMF, 20 °C): δ (ppm) −18.3 (m, P3), −87.6
(br), −111.8 (br). 31P{1H} NMR (202.4 MHz, d7-DMF, −50 °C): δ
(ppm) −17.7 (m, 1P, 1JP−P = 355 Hz, 1JP−P = 401 Hz, P3), −28.9 (m,
1P, 1JP−P =366 Hz, 1JP−P = 381 Hz, P1), −73.0 (m, 1P, 1JP−P = 423 Hz,
MHz, d5-pyridine, 20 °C): δ (ppm) isomer 1, 34.8 (m, 1P, P3), −32.4
(m, 1P, P2), −75.6 (m, 1P, P1), −92.7 and −95.0 (overlapping
multiplets, 2P, P4 and P5), −165.3 (m, 1P, P7), −191.7 (m, 1P, P6);
isomer 2: 14.6 (m, 1P, P3), 0.0 (m, 1P, P2), −50.8 and −54.0
(overlapping multiplets, 2P, P1 and P4), −112.2 (m, 1P, P5), −152.9
(m, 1P, P7), −170.6 (m, 1P, P6). 13C{1H} NMR (125.8 MHz, d5-
1
1
1JP−P = 184 Hz, JP−P = 228 Hz, P5), −96.2 (1P, m, JP−P = 437 Hz,
P4), −105.0 (m, 1P, P2), −130.3 (m, 1P, 1JP−P = 184 Hz, P7), −225.0
(m, 1P, P6). 13C {1H} NMR (125.8 MHz, d7-DMF, 20 °C): δ (ppm)
1
3
pyridine, 20 °C): δ (ppm) 156.2 (d, JP−C = 63 Hz, PCN2, other
161.8 (d obscured by solvent, PCN2), 48.9 (d, JP−C = 31 Hz, NCH),
resonance not observed), 150.7, 148.7, 148.6, 148.2, 140.9, 140.6,
140.0, 139.9, 129.9, 129.2, 128.0, 126.3, 123.7, 123.6, 123.4, 123.2
(ArC), 71.0, 68.2, 54.4 (2,2,2-crypt), 29.9, 29.7, 29.6, 29.5 (CH-
(CH3)2), 29.0, 28.9, 28.8, 28.5, 27.8, 27.7, 27.6, 24.9, 24.9, 24.8, 24.7,
23.5, 23.4, 22.6, 22.5 (CH3). ESI−-MS (DMF): m/z 581.3 [HP7(C-
(NHDipp)(NDipp))]−. ESI+-MS (DMF): m/z 1414.0 {[K(2,2,2-
crypt)]2[HP7(C(NHDipp)(NDipp))]}+.
41.9 (NHCH), 25.8 (CH3), 22.1 (CH3). ESI−-MS (DMF): m/z 344.7
[P7C(NHiPr)(NiPr)]−. ESI+-MS (DMF): m/z 1174.4 {[K(2,2,2-
crypt)]2[P7C(NHiPr)(NiPr)]}+, 1588.3 {[K(2,2,2-crypt)]3[P7C-
(NHiPr)(NiPr)]}+. Single-crystal X-ray diffraction quality crystals of
[K(2,2,2-crypt)]2[P7C(NHiPr)(NiPr)] were unattainable; however the
use of 18-crown-6 as a sequestering agent allowed crystals of [K(18-
crown-6)]2[3] to be grown from a 1:1 mixture of THF and pyridine
that was layered with hexanes.
[K(2,2,2-crypt)][6] (6: {P7[(C(NHDipp)(NDipp)]2}−). In a glove-
box, [K(2,2,2-crypt)]2[HP7] (60 mg, 57.1 μmol) and bis(2,6-
diisopropylphenyl)carbodiimide (20.8 mg, 57.1 μmol) were weighed
into a glass vial and dissolved in DMF (2 mL) to give an orange
solution of the hydrophosphination product [K(2,2,2-crypt)]2[2]. To
[K(2,2,2-crypt)]2[4] (4: [P7C(NHCy)(NCy)]2−). A similar method
to that detailed for the synthesis of [K(2,2,2-crypt)]2[P7C(NHiPr)-
(NiPr)] was employed. [K(2,2,2-crypt)]2[HP7] (50 mg, 47.6 μmol)
was reacted with bis(cyclohexyl)carbodiimide (9.8 mg, 47.6 μmol).
Isolated yield: 32.1 mg (55%). Anal. Calcd for C49H95K2N6O12P7: C,
this stirring solution, [H(OEt2)2][BArF ] (57.8 mg, 57.1 μmol) was
4
1
added portionwise over approximately 2 min. The solution was stirred
for 1 h, after which a further equivalent of bis(2,6-diisopropylphenyl)-
carbodiimide (20.8 mg, 57.1 μmol) was added and the mixture stirred
for 20 h. The solution was then filtered through Celite, and the solvent
removed under dynamic vacuum to give a yellow oil, which was
washed with Et2O (5 × 2 mL) and dried in vacuo to yield a pale yellow
powder. Isolated yield: 52.5 mg (67%). Crystals suitable for single-
crystal X-ray diffraction were obtained by layering a THF solution (5
mL) of the compound with hexanes (20 mL) and leaving it to diffuse
at 5 °C. Anal. Calcd for C68H106KN6O6P7: C, 60.06; H, 7.86; N, 6.18.
46.88; H, 7.63; N, 6.69. Found: C, 46.66; H, 7.91; N, 6.62. H NMR
(500 MHz, d7-DMF, 20 °C): δ (ppm) 4.11 (m, 2H, NCH of Cy), 3.60
(s, 24H, 2,2,2-crypt), 3.57 (t, 24H, 3JH−H = 5 Hz, 2,2,2-crypt), 3.14 (s,
3
1H, NH), 2.56 (t, 24H, JH−H = 5 Hz, 2,2,2-crypt), 1.84 to 0.94 (m,
20H, Cy). 31P{1H} NMR (202.4 MHz, d7-DMF, 20 °C): δ (ppm)
−18.5 (m, P3), −87.5 (br), −111.7 (br). 31P{1H} NMR (202.4 MHz,
d7-DMF, −50 °C): δ (ppm) −18.7 (m, 1P, 1JP−P = 338 Hz, 1JP−P = 401
1
1
Hz, P3), −28.2 (m, 1P, JP−P = 378 Hz, JP−P = 379 Hz, P1), −73.5
1
1
1
(m, 1P, JP−P = 423 Hz, JP−P = 176 Hz, JP−P = 223 Hz, P5), −95.7
(m, 1P, 1JP−P = 439 Hz, P4), −103.8 (m, 1P, P2), −130.3 (m, 1P, 1JP−P
= 181 Hz, P7), −222.3 (m, 1P, P6). 13C{1H} NMR (125.8 MHz, d7-
DMF, 20 °C): δ (ppm) 161.3 (d obscured by solvent, PCN2), 57.3 (d,
3JC−P = 31.9 Hz, NCH), 48.5 (NHCH), 36.3 (Cy), 32.0 (Cy), 26.7
(Cy), 26.6 (Cy), 25.4 (Cy), 24.8 (Cy). ESI−-MS (DMF): m/z 424.9
{[P7C(NHCy)(NCy)]}−. ESI+-MS (DMF): m/z 1254.9 {[K(2,2,2-
crypt)]2[P7C(NHCy)(NCy)]}+, 1668.7 {[K(2,2,2-crypt)]3[P7C-
(NHCy)(NCy)]}+.
1
Found: C, 60.12; H, 8.76; N, 5.57. H NMR (500 MHz, d5-pyridine,
20 °C): δ (ppm) 7.26 (m, 2H, ArH), 7.19 (overlapping multiplets, 8H,
ArH), 7.11 (m, 2H, ArH), 6.31 (br s, 2H, NH), 3.72 (sept, 2H, JH−H
3
3
= 7 Hz, CH(CH3)2), 3.66 (sept, 2H, JH−H = 7 Hz, CH(CH3)2), 3.41
3
(sept, partially obscured by 2,2,2-crypt, JH−H = 7 Hz, CH(CH3)2),
remaining CH(CH3)2 obscured by 2,2,2-crypt, 3.40 (s, 12H, 2,2,2-
crypt), 3.35 (t, 12H, 3JH−H = 5 Hz, 2,2,2-crypt), 2.34 (t, 12H, 3JH−H = 5
Hz, 2,2,2-crypt), 1.81 (d, 6H, 3JH−H = 7 Hz, CH3), 1.57 (d, 6H, 3JH−H
= 7 Hz, CH3), 1.55 (d, 6H, 3JH−H = 7 Hz, CH3), 1.35 (d, 6H, 3JH−H = 7
[K(2,2,2-crypt)][5] (5: [HP7C(NHDipp)(NDipp)]−). In an inert
atmosphere glovebox, [K(2,2,2-crypt)]2[HP7] (60 mg, 57.1 μmol) and
bis(2,6-diisopropylphenyl)carbodiimide (20.8 mg, 57.1 μmol) were
weighed into a glass vial and dissolved in DMF (2 mL) to give an
orange solution of the hydrophosphination product [K(2,2,2-
3
3
Hz, CH3), 1.27 (d, 6H, JH−H = 7 Hz, CH3), 1.26 (d, 6H, JH−H = 7
3
3
Hz, CH3), 1.11 (d, 6H, JH−H = 7 Hz, CH3), 0.97 (d, 6H, JH−H = 7
Hz, CH31). 31P NMR (202.4 MHz, d5-pyridine, 20 °C): δ (ppm) 12.5
1
2
crypt)]2[2]. To this stirring solution, [H(OEt2)2][BArF ] (57.8 mg,
(m, 2P, JP−P = 292 Hz, JP−P = 347 Hz, JP−P = −270 Hz, P3/P4),
4
1
2
−29.0 (m, 1P, JP−P = 349 Hz, JP−P = −87 Hz, P1), −64.2 (m, 1P,
57.1 μmol) was added in small aliquots over approximately 2 min, and
the resulting solution was stirred for one hour. The reaction mixture
was filtered through Celite, and the solvent removed under dynamic
vacuum to afford a yellow-brown oil. This was washed with Et2O (5 ×
1JP−P = 357 Hz, P2), −113.8 (m, 1P, JP−P = 216 Hz, JP−P = 216 Hz,
1
1
P7), −129.5 (m, 2P, JP−P = 194 Hz, P6/P7). 13C {1H} NMR (125.8
1
MHz, d5-pyridine, 20 °C): δ (ppm) PCN2 not observed, 149.4, 149.3,
148.3, 147.8, 143.0, 141.6, 140.7, 139.6, 131.0, 130.3, 129.2, 127.4,
124.9, 124.5, 124.4, 124.2 (ArC), 72.1, 69.3, 55.6 (2,2,2-crypt), 30.9,
30.7, 29.9, 29.0 (C(CH3)2), 28.7, 26.5, 26.4, 26.3, 25.6, 24.7, 23.5, 23.0
(CH3). ESI−-MS (DMF): m/z 943.8 [P7[C(NHDipp)(NDipp)]2]−.
ESI+-MS (DMF): m/z 1776.3 {[K(2,2,2-crypt)]2{P7[C(NHDipp)-
(NDipp)]2}}+.
2 mL) to remove the [K(2,2,2-crypt)][BArF ] side-product and dried
4
in vacuo to yield a pale yellow powder. Isolated yield: 32.4 mg (57%).
Crystals of [K(2,2,2-crypt)][5] suitable for single-crystal X-ray
diffraction were obtained by layering a THF solution (5 mL) of the
compound with hexanes (20 mL) and leaving it to diffuse at 5 °C.
Anal. Calcd for C43H72KN4O6P7: C, 51.80; H, 7.28; N, 5.62. Found: C,
1
51.58; H, 7.15; N, 5.50. H{31P} NMR (500 MHz, d5-pyridine, 20
[K(2,2,2-crypt)][7] (7: {P7[C(NHDipp)(NDipp)][C(NHiPr)-
(NiPr)]}−). The procedure was the same as described above for
[K(2,2,2-crypt)]{P7[(C(NHDipp)(NDipp)]2}, with the exception
that bis(isopropyl)carbodiimide (8.9 μL, 57.1 μmol) was added after
°C): δ (ppm) 7.30−7.10 (overlapping multiplets, 12H, ArH), 6.57 (s,
1H, NH), 6.27 (s, 1H, NH), 3.82−3.49 (overlapping septets, 8H,
3JH−H = 7 Hz, CH(CH3)2), 3.36 (s, 24H, 2,2,2-crypt), 3.31 (t, 24H,
2460
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Organometallics
Article
1
addition of [H(OEt2)2][BArF ]. Isolated yield: 36.4 mg (57%). H
CrysAlisPro suite. Structures were subsequently solved using direct
methods and refined on F2 using the SHELXL 97-2 package.43
Other Characterization Techniques. Positive and negative ion
mode electrospray mass spectra were recorded on DMF solutions of
the compounds (10−20 mM) on a Masslynx LCT time of flight mass
spectrometer with a Z-spray source (150 °C source temperature, 200
°C desolvation temperature, 2.4 kV capillary voltage, and 25 V cone
voltage). The samples were made up inside a glovebox under an inert
atmosphere and rapidly transferred to the spectrometer in an airtight
syringe. Samples were introduced directly with a 1 mL SGE syringe
and a syringe pump at 0.6 mL h−1.
Transmission powder X-ray patterns were recorded using a Siemens
D5000 diffractometer in modified Debye−Scherrer geometry
equipped with an MBraun position sensitive detector. The instrument
produced Cu Kα1 radiation (λ = 1.54056 Å) using a germanium
monochromator and a standard Cu source. Data were recorded on
samples in flame-sealed capillaries under dinitrogen. The capillaries
were mounted on a goniometer head and aligned so that rotation
occurred along the long central axis of the capillary. During a
measurement the capillary was rotated at 60 rpm to minimize any
preferred orientation effects that might occur.
4
NMR (500 MHz, d5-pyridine, 20 °C): δ (ppm) 7.30−7.10
(overlapping multiplets, 6H, ArH), 6.22 (s, 1H, NHDipp), 4.75
(sept, 1H, 3JH−H = 6 Hz, CH(CH3)2 of iPr), 3.87 (s, 1H, NHiPr) 3.72
3
i
(sept, 1H, JH−H = 6 Hz, CH(CH3)2 of Pr), 3.60 (overlapping sept,
3
2H, JH−H = 7 Hz, 2 × CH(CH3)2 of Dipp), 3.56 (overlapping sept,
2H, 3JH−H = 7 Hz, 2 × CH(CH3)2 of Dipp), 3.40 (s, 12H, 2,2,2-crypt),
3
3
3.35 (t, 12H, JH−H = 4 Hz, 2,2,2-crypt), 2.34 (t, 12H, JH−H = 4 Hz,
3
2,2,2-crypt), 1.82 (d, 3H, JH−H = 7 Hz, CH3 of Dipp), 1.63 (d, 3H,
3JH−H = 7 Hz, CH3 of Dipp), 1.58 (d, 3H, 3JH−H = 7 Hz, CH3 of Dipp),
3
1.38 (d, 3H, JH−H = 7 Hz, CH3 of Dipp), 1.30−1.25 (overlapping d,
i
3
12H, CH3 of Pr), 1.08 and 1.07 (overlapping d, 6H, JH−H = 7 Hz,
CH3 of Dipp), 1.02 (d, 3H, 3JH−H = 7 Hz, CH3 of Dipp), 0.92 (d, 3H,
3JH−H = 7 Hz, CH3 of Dipp). 31P NMR (202.4 MHz, d5-pyridine, 20
°C): δ (ppm) 6.5 (overlapping m, 1P, 1JP−P = 295 Hz, 1JP−P = 348 Hz,
2JP−P = −295 Hz, P3), 3.2 (overlapping m, 1P, 1JP−P = 295 Hz, 1JP−P
=
1
2
356 Hz), −34.0 (m, 1P, JP−P = 351 Hz, JP−P = −87 Hz, P1), −69.6
1
1
1
(m, 1P, JP−P = 368 Hz, P2), −112.2 (m, 1P, JP−P = 216 Hz, JP−P
=
216 Hz, P5), −134.0 (m, 1P, 1JP−P = 194 Hz, P6), −136.3 (m, 1P, P7).
13C{1H} NMR (125.8 MHz, d5-pyridine, 20 °C): δ (ppm) PCN2 not
observed, 149.6, 149.2, 141.7, 141.0, 124.7, 124.5, 124.4, 124.3 (ArC),
1H and 31P NMR spectra were acquired at 500 and 202.4 MHz,
respectively, on a Varian Unity 500 MHz NMR spectrometer. 13C
NMR spectra were acquired at 125.8 MHz on a Bruker AVII 500
NMR spectrometer equipped with a dedicated 13C cryoprobe. 1H and
13C spectra are reported relative to TMS and were referenced to the
most downfield residual solvent resonance (d5-pyridine: δH 8.74 ppm,
δC 150.2 ppm; d7-DMF: δH 8.04 ppm, δC 163.2 ppm). 31P spectra were
externally referenced to 85% H3PO4 (δP 0 ppm). Spectral simulations
were carried out using the program gNMR.44 All coupling constant
data provided in this article are for the fitted simulated spectra starting
from experimentally and computationally determined J values. Full
tables of NMR data for all of the compounds described are provided in
the Supporting Information.
3
53.6 (d, JC−P = 37 Hz, NCH), 45.0 (NHCH), 30.9, 30.7, 30.1, 28.9,
27.6, 27.4, 26.8, 26.0, 25.9, 24.6, 24.3, 24.1, 23.6. ESI−-MS (DMF): m/
z 707.4 {P7[C(NHDipp)(NDipp)][C(NHiPr)(NiPr)]}−. ESI+-MS
(DMF): m/z 1538.1 {[K(2,2,2-crypt)]2{P7[C(NHDipp)(NDipp)][C-
(NHiPr)(NiPr)]}}+.
[K(2,2,2-crypt)][8] (8: {P7[C(NHDipp)(NDipp)][C(NHCy)-
(NCy)]}−). The procedure was the same as described above for
[K(2,2,2-crypt)]{P7[(C(NHDipp)(NDipp)]2}, with the exception
that bis(cyclohexyl)carbodiimide (11.8 mg, 57.1 μmol) was added
after the addition of [H(OEt2)2][BArF ]. Isolated yield: 46.6 mg
4
(68%). Crystals suitable for single-crystal X-ray diffraction were
obtained by layering a THF solution (5 mL) of the compound with
hexanes (20 mL) and leaving it to diffuse at 5 °C. H NMR (500
1
All calculations described in this paper were performed using the
Amsterdam Density Functional package (ADF2007.01).45 A triple-ζ
Slater-type basis set, extended with a single polarization function, was
used to describe all atoms. The local density approximation was
employed for the optimizations,46 along with the local exchange−
correlation potential of Vosko, Wilk, and Nusair47 and the gradient
corrections to exchange and correlation proposed by Becke and
Perdew (BP86).48 Relativistic effects were incorporated using the
zeroth-order relativistic approximation.49 The presence of cations in
the crystal lattice was modeled by surrounding the anion with a
continuum dielectric using COSMO.50 The chosen dielectric constant
ε = 16.9 corresponds to that of ammonia, although structural
parameters are not strongly dependent on this choice. All structures
were optimized using the gradient algorithm of Versluis and Ziegler.51
MHz, d5-pyridine, 20 °C): δ (ppm) 7.28−7.10 (overlapping m, 6H,
ArH), 6.20 (s, NHDipp), 4.41 (br m, 1H, NCH of Cy), 4.00 (br m,
3
1H, NCH of Cy), 3.71 (sept, 2H, JH−H = 7 Hz, CH(CH3)2), 3.64
3
(sept, 2H, JH−H = 7 Hz, CH(CH3)2), NH of NHCy is obscured by
3
2,2,2-crypt, 3.37 (s, 12H, 2,2,2-crypt), 3.32 (t, 12H, JH−H = 5 Hz,
3
2,2,2-crypt), 2.32 (t, 12H, JH−H = 5 Hz, 2,2,2-crypt), 2.03−1.04
3
(overlapping m, 20H, Cy), 1.83 (d, 3H, JH−H = 7 Hz, CH3), 1.61 (d,
3
3
3H, JH−H = 7 Hz, CH3), 1.59 (d, 3H, JH−H = 7 Hz, CH3), 1.38 (d,
3H, 3JH−H = 7 Hz, CH3), 1.30 (overlapping d, 6H, 3JH−H = 7 Hz, CH3),
1.10 (d, 3H, 3JH−H = 7 Hz, CH3), 1.02 (d, 3H, 3JH−H = 7 Hz, CH3). 31
P
NMR (202.4 MHz, d5-pyridine, 20 °C): δ (ppm) 7.3 (overlapping m,
1
1
2
1P JP−P = 387 Hz, JP−P = 350 Hz, JP−P = −294 Hz, P3), 4.9
1
1
(overlapping m, JP−P = 305 Hz, JP−P = 356 Hz, P4), −33.6 (m, 1P,
1JP−P = 353 Hz, JP−P = −87 Hz, P1), −69.6 (m, 1P, JP−P = 368 Hz,
2
1
1
1
P2), −112.7 (m, 1P, JP−P = 216 Hz, JP−P = 216 Hz, P5), −135.7
ASSOCIATED CONTENT
* Supporting Information
■
1
(overlapping m, 1P, JP−P = 194 Hz, P6), −136.5 (overlapping m, 1P,
S
P7). 13C{1H} NMR (125.8 MHz, d5-pyridine, 20 °C): δ (ppm) PCN2
not observed, 149.6, 149.2, 141.7, 141.0, 129.1, 124.5, 124.4, 124.2
(ArC), 61.7 (d, 3JC−P = 37 Hz, NCH of Cy), 51.6 (NCH of Cy), 38.03,
37.7, 34.3, 34.0, 30.9, 30.7, 30.0, 29.9, 28.9, 28.0, 27.5, 26.9, 26.8,
26.45, 26.4, 26.1, 25.8, 24.7, 23.6. ESI−-MS (DMF): m/z 788.4
{P7[C(NHDipp)(NDipp)][C(NHCy)(NCy)]}−. ESI+-MS (DMF):
m/z 1617.4 {[K(2,2,2-crypt)]2{P7[C(NHDipp)(NDipp)][C(NHCy)-
(NCy)]}}+.
X-ray crystallographic files in CIF format. Full experimental and
computational details as well as NMR and ES-MS spectra are
available. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jose.goicoechea@chem.ox.ac.uk.
■
Single-Crystal X-ray Structure Determination. Single-crystal
X-ray diffraction data were collected using an Oxford Diffraction
Supernova dual-source diffractometer equipped with a 135 mm Atlas
CCD area detector. Crystals were selected under Paratone-N oil,
mounted on micromount loops, and quench-cooled using an Oxford
Cryosystems open flow N2 cooling device.41 Data were collected at
150 K using mirror monochromated Cu Kα radiation (λ = 1.5418 Å)
and processed using the CrysAlisPro package, including unit cell
parameter refinement and interframe scaling (which was carried out
using SCALE3 ABSPACK within CrysAlisPro).42 Equivalent reflec-
tions were merged, and diffraction patterns processed with the
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the EPSRC and the University of Oxford for financial
support of this research (DTA studentship R.S.P.T.) and the
University of Oxford for access to Chemical Crystallography
and Oxford Supercomputing Centre facilities. We also thank
2461
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Organometallics
Article
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