Synthesis and characterization of free and coordinated 1,2,3-tripnictolide anions

Article abstract of DOI:10.1021/om4001296

We have investigated the chemical reactivity of heptaatomic anionic clusters of the group 15 elements ([E₇]^3-/[HE ₇]^2-, E = P, As) toward the symmetric and asymmetrically substituted alkynes diphenylacetylene and phenylacetylene. The results reported herein, alongside a previous report on the reactivity of such clusters toward acetylene, describe a versatile route by which to access otherwise elusive 1,2,3-tripnictolide anions of the general formula [E₃C ₂RR′]^- (R = R′ = H, E = P (1), As (2); R = R′ = C₆H₅, E = P (3) As (4); R = H, R′ = C₆H₅, E = P (5), As (6)). These species can be isolated as [K(18-crown-6)]⁺ or [K(2,2,2-crypt)]⁺ salts. All anions were characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition, single-crystal X-ray diffraction structures of the novel species [K(18-crown-6)(THF)₂][3], [K(2,2,2-crypt)][4] ·xTHF (x = 0, 0.5), and [K(18-crown-6)THF][6] were also obtained. The chemical reactivity of these group 15 cyclopentadienyl analogues has been explored in a series of ligand displacement reactions with Mo(CO) ₃(L)₃ (L = CO, CH₃CN) to yield the complex anions [(η⁵-E₃C₂H₂)Mo(CO) ₃]^- (E = P (7), As (8)), [{η⁵-E ₃C₂(C₆H₅)₂}Mo(CO) ₃]^- (E = P (9), As (10)), and [{η⁵-E ₃C₂H(C₆H₅)}Mo(CO)₃] ^- (E = P (11), As (12)).

Full text of DOI:10.1021/om4001296

Article
pubs.acs.org/Organometallics
Synthesis and Characterization of Free and Coordinated 1,2,3-
Tripnictolide Anions
Robert S. P. Turbervill, Andrew R. Jupp, Phillip S. B. McCullough, Doruk Ergocm̧ en,
̈
and Jose M. Goicoechea*
Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, U.K.
S
* Supporting Information
ABSTRACT: We have investigated the chemical reactivity of
heptaatomic anionic clusters of the group 15 elements
([E7]3−/[HE7]2−, E = P, As) toward the symmetric and
asymmetrically substituted alkynes diphenylacetylene and
phenylacetylene. The results reported herein, alongside a
previous report on the reactivity of such clusters toward
acetylene, describe a versatile route by which to access
otherwise elusive 1,2,3-tripnictolide anions of the general
formula [E3C2RR′]− (R = R′ = H, E = P (1), As (2); R = R′ =
C6H5, E = P (3) As (4); R = H, R′ = C6H5, E = P (5), As (6)).
These species can be isolated as [K(18-crown-6)]+ or
[K(2,2,2-crypt)]+ salts. All anions were characterized by
multielement NMR spectroscopy and electrospray mass
spectrometry. In addition, single-crystal X-ray diffraction structures of the novel species [K(18-crown-6)(THF)2][3],
[K(2,2,2-crypt)][4]·xTHF (x = 0, 0.5), and [K(18-crown-6)THF][6] were also obtained. The chemical reactivity of these group
15 cyclopentadienyl analogues has been explored in a series of ligand displacement reactions with Mo(CO)3(L)3 (L = CO,
CH3CN) to yield the complex anions [(η5-E3C2H2)Mo(CO)3]− (E = P (7), As (8)), [{η5-E3C2(C6H5)2}Mo(CO)3]− (E = P (9),
As (10)), and [{η5-E3C2H(C6H5)}Mo(CO)3]− (E = P (11), As (12)).
are far more elusive.1,7 1,3-Diphospholide and 1,2,4-triphos-
pholide anions can be obtained by chemical reduction of
INTRODUCTION
■
The 6-π-electron phospholide (or phospholyl) anions
phospha-alkynes, and their coordination chemistry has been
extensively investigated.1,8 In contrast, the related isomers 1,2-
diphospholides and 1,2,3-triphospholides are much rarer, due
to the lack of versatile synthetic methods for their synthesis.9−13
The tetraphospholide anion is similarly uncommon,14 while the
pentaphospholide species, which has been observed in solution
but has yet to be isolated as a free ligand,15 has been isolated in
a number of transition-metal complexes typically as a result of
the metal-mediated activation of white phosphorus.5,16,17
The chemistry of aromatic arsolide anions, [Asn(CR)5−n]− (n
= 1−5), is much more poorly developed than that of their
phosphorus-containing analogues. Thus, while a handful of
examples of mono- and pentaarsolide anions have been
isolated,18,19 to date no examples of any di- or tetraarsolide
anions have been reported. The first triarsolide anion was
reported by our research group in 2012.20
−
[Pn(CH)5−n
] (n = 1−5) are a unique family of aromatic
phosphorus-containing molecules.1 The isolobal relationship
between methine (C−H) groups and phosphorus atoms makes
such species heavier analogues of the ubiquitous cyclo-
pentadienyl anion ([Cp]−). However, despite this cursory
similarity, the electronic structures of these “carbon-copy”
ligands reveal two notable differences in comparison to
cyclopentadienyl and derivatized cyclopentadienyl ligands.
First, they generally possess greater π-acceptor character than
[Cp]− ligands, allowing for the stabilization of complexes of
electron-rich metal centers.2,3 This allows for the isolation of
phospha-organometallic analogues of elusive complexes such as
3,4
titanocene: e.g., [Ti(η5-P3C2 Bu2)2] and [Ti(η5-P5)2]2−.
A
t
second contrast is the presence of Lewis basic sites on the
phospholide ring (energetically accessible phosphorus lone
pairs), which allow for multiple coordination modes and the
formation of multimetallic molecules and supramolecular
We recently detailed the synthesis of the protic 1,2,3-
tripnictolide anions [E3C2H2]− (E = P (1), As (2)) via the
reaction of acetylene with the Zintl phases K3E7 (E = P, As,
respectively).20 The ability to isolate these species as [K(18-
crown-6)]+ or [K(2,2,2-crypt)]+ salts has opened up the
systems.1,5
−
The number of known [Pn(CR)5−n
]
phospholide ligands
(and their respective metal complexes) varies dramatically
depending on the isomer in question.6 Thus, while the
synthesis of monophospholide ligands is relatively straightfor-
ward (following a method first reported by Braye and co-
workers involving the reduction of phospholes), other isomers
Received: February 14, 2013
© XXXX American Chemical Society
A
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opportunity of studying their coordination chemistry toward a
variety of metal reagents. This synthetic method may also be
employed to access asymmetrically derivatized 1,2,3-tripnicto-
lides such as 4-(2′-pyridyl)-1,2,3-triphospholide.21 Herein we
present a follow-up report to these preliminary studies where
we explore the synthetic versatility of this “Zintl ion route” to
1,2,3-tripnictolides. This has resulted in the isolation of
[E3C2(C6H5)2]− (E = P (3), As (4)) and [E3C2H(C6H5)]−
(E = P (5), As (6)) as [K(18-crown-6)]+ or [K(2,2,2-crypt)]+
salts. Furthermore, we also report coordination chemistry
studies on Mo(CO)3(L)3 reagents (L = CO, CH3CN) for 1−6,
which yielded the complexes [(η5-E3C2H2)Mo(CO)3]− (E = P
(7), As (8)), [{η5-E3C2(C6H5)2}Mo(CO)3]− (E = P (9), As
(10)), and [{η5-E3C2H(C6H5)}Mo(CO)3]− (E = P (11), As
(12)). This family of compounds allows for the direct
comparison of the electronic properties of these 1,2,3-
tripnictolide anions and the complexes they form.
Addition of 3 equiv of diphenylacetylene to a DMF solution
of [K(18-crown-6)]2[HP7] (or of K3P7 in the presence of an
alkali-metal sequestering agent) results in a rapid darkening of
the reaction mixture. A combined 31P{1H} NMR spectroscopic
and electrospray mass spectrometric analysis of the reaction
mixture shows the presence of 3, observed as two multiplet
resonances at 297.9 and 273.3 ppm (arising from a second-
order AB2 spin system) and a peak in the negative ion mode
ESI-MS spectrum at 270.7 Da. Small quantities of unidentified
phosphorus-containing products are also observed (see the
Supporting Information for spectra). The desired 4,5-diphenyl-
1,2,3-triphospholide anion can be extracted in moderate to
good yields by the purposeful introduction of air, which results
in the decomposition and precipitation of side products, while
the air-stable [P3C2(C6H5)2]− anion remains in solution.
Subsequent workup allows the isolation of this anion in
approximately 70% yield as the [K(18-crown-6)]+ salt. This
anion was previously reported by Mathey and co-workers but
has never been crystallographically authenticated as a free
ligand.12 Metal complexes of the triphospholide have been
isolated by the research groups of Scherer, Scheer, and Nixon.11
Extension of this synthetic methodology allowed for the
isolation of the novel arsenic analogue 4,5-diphenyl-1,2,3-
triarsolide, [As3C2(C6H5)2]− (4), staring from the K3As7 Zintl
phase.
RESULTS AND DISCUSSION
■
Synthesis of 1,2,3-Tripnictolide Anions from Hepta-
pnictide Trianion Precursors. We have previously reported
that solutions of the K3E7 (E = P, As) Zintl phases react with a
stoichiometric excess of acetylene in the presence of a suitable
cation sequestering agent (2,2,2-crypt or 18-crown-6) to yield
the 1,2,3-tripnictolide anions [1,2,3-E3C2H2]− (E = P (1), As
(2)) in moderate (∼20%) crystalline yields.20 Similarly,
reaction of the protonated hydrogenheptaphosphide dianion,22
[HP7]2−, with acetylene in DMF also yields the [P3C2H2]−
anion, albeit in a slightly higher isolable yield (∼30%). We
attribute this to the increased purity of the heptaphosphide
precursor relative to K3P7. Reactions with the as-synthesized
K3P7 Zintl phase typically exhibit a small quantity of insoluble,
unidentified black residue as a side product. The reaction of
acetylene with the isotopically labeled [DP7]2− cage shows that
there is no deuterium incorporation in the product; hence, it is
likely that both phospholide protons originate from the
acetylene. The yield of the heavier arsenic congener 2 is not
improved by the use of [HAs7]2−, perhaps due to the increased
purity of the K3As7 phase relative to K3P7.
The structures of 3 and 4 were determined by single-crystal
X-ray diffraction in [K(18-crown-6)(THF)2][3] and [K(2,2,2-
crypt)][4]·xTHF (x = 0, 0.5). Thermal ellipsoid representa-
tions of the anionic moieties are provided in Figure 1 (tables of
We have extended these studies to other alkynes, with the
aim of establishing the versatility of this synthetic method. The
reactions of [HP7]2− (as either the [K(2,2,2-crypt)]+ or [K(18-
crown-6)]+ salt) or K3As7 with a slight stoichiometric excess of
diphenyl- and phenylacetylene proceed rapidly at room
temperature to form the previously reported (but never
structurally authenticated) species [P3C2(C6H5)2]− (3)12 and
the novel anions [As3C2(C6H5)2]− (4) and [E3C2H(C6H5)]−
(E = P (5), As (6)), as depicted in Scheme 1. Analogous
reactions with the aliphatic internal alkynes RCCR′ (R = Me,
Figure 1. Thermal ellipsoid plots of the anionic moieties crystallo-
graphically characterized in (a) [K(18-crown-6)(THF)2][3] and (b)
[K(2,2,2-crypt)][4a]. Anisotropic thermal displacement ellipsoids are
pictured at the 50% probability level. Hydrogen positions were
assigned idealized coordinates and are pictured as spheres of arbitrary
radii. Selected bond distances (Å) and angles (deg) for 3: P1−P2,
2.098(1); P2−P3, 2.091(1); P3−C1, 1.762(1); C1−C2, 1.402(2);
C2−P1, 1.760(1); C1−C3, 1.490 (2); C2−C9, 1.492(2); P1−P2−P3,
98.95(2); P2−P3−C1, 100.15(5); P3−C1−C2, 120.43(11); C1−C2−
P1, 120.35(11); C2−P1−P2, 100.11(5); C3−C1−C2, 123.95(12);
C9−C2−C1, 122.84(13). Selected bond distances (Å) and angles
(deg) for 4a: As1−As2, 2.300(1); As2−As3, 2.306(1); As3−C1,
1.896(4); C1−C2, 1.377(5); C2−As1, 1.890(4); C1−C3, 1.495(6);
C2−C9, 1.495(5); As1−As2−As3, 96.66(2); As2−As3−C1,
98.45(13); As3−C1−C2, 123.0(3); C1−C2−As1, 123.1(3); C2−
As1−As2, 98.75(11); C3−C1−C2, 123.0(3); C9−C2−C1, 122.7(3).
n
R′ = Me, Pr; R = R′ = Et) require extended reaction times at
high temperatures for reaction to occur, which results in
multiple reaction products and extensive decomposition of the
Zintl phase (the results of this research will be reported
elsewhere).
Scheme 1. Synthesis of 1,2,3-[E3C2RR′]− Anions
selected refinement and data collection parameters for all of the
crystal structures reported herein are available in the
Supporting Information). Two solvates of 4 were found,
[K(2,2,2-crypt)][4a] and [K(2,2,2-crypt)][4b]·0.5THF, the
former of which is the predominant crystalline phase according
to a powder X-ray diffraction study (see the Supporting
B
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Article
Information for a PXRD diffractogram). All three crystal
structures reveal a planar geometry for the [E3C2R2]− rings, as
expected for aromatic systems. Bond metric data within the
phospholide ring for 3 (P−P = 2.095 Å (av); P−C = 1.761 Å
(av); C−C = 1.402(2) Å) are in good agreement with those for
other structurally authenticated 1,2,3-triphospholides, including
the parent protic species [K(2,2,2-crypt)][1] (P−P = 2.093 Å
(av); P−C = 1.754 Å (av); C−C = 1.393(3) Å) and the
recently reported 1,2,3-triphosphaindenyl anions.13,20 In
contrast to the two known structures of the protic 1,2,3-
triarsolide, [K(2,2,2-crypt)][2] and [K(18-crown-6)][2],20 the
crystallographically unique anions in 4a,b do not exhibit
positional disorder, which allows for a meaningful discussion of
bond metric parameters. A comparison of bond distances in
4a,b shows that they are very similar, and as a result, for clarity
purposes, only 4a will be discussed. The As−As bond distances
are 2.300(1) and 2.306(1) Å, while the As−C bonds are
identical within experimental error (1.896(4) and 1.890(4) Å).
Both sets of bonds are longer than the equivalent distances in 3,
as would be expected due to the different covalent radii of P
and As (Δrcov = 0.10 and 0.12 for single and double bonds,
respectively).23 In both 3 and 4, the phenyl rings lie tilted away
from the plane of the phospholide moiety in a propeller-like
arrangement (torsion angles of phenyl rings relative to
tripnictolide plane: 46.3 and 53.4° for 3 and 53.6 and 58.1°
for 4), due to the steric constraints of the system.
1.375(3) Å, respectively) are also closely related to those
observed for 4a (1.893 (av) and 1.377(5) Å, respectively). The
torsion angle between the 1,2,3-triarsolide ring and the phenyl
ring is 46.5°. Asymmetrically derivatized 1,2,3-tripnictolide
anions are extremely rare and have only been observed by
spectroscopic methods in reaction mixtures12 or as composi-
tionally pure samples in the immediate coordination sphere of a
transition metal.11b,c The ability to access compositionally pure
samples of the “free” (uncoordinated) ligands represents a
significant breakthrough in the field, as such species are
prochiral and may ultimately allow access to planar chiral metal
complexes.
Species 3−6 were all characterized by multielement NMR
spectroscopy. The 31P{1H} NMR spectrum of 3 reveals two
multiplet resonances (273.3 and 297.9 ppm; AB2 spin system),
while that of 5 displays three resonances (269.0, 275.5, and
289.2 ppm; ABC spin system), as expected for symmetrically
and asymmetrically derivatized 1,2,3-triphospholides, respec-
tively. These were observed between 260 and 290 ppm due to
the deshielding aromatic character of the phospholide ring and
compare well with those of the protic 1,2,3-triphospholide
anion, 1, which have been observed as two multiplet resonances
at 261.1 and 272.8 ppm. A comparison of the chemical shifts
observed for anions 1−6 is provided in Table 1, while details of
a
1
Table 1. 31P, 13C, and H NMR Chemical Shifts for 1−6
A reaction similar to that employed for the synthesis of 3 and
4 using phenylacetylene (as opposed to diphenylacetylene) was
found to yield the asymmetrically derivatized tripnictolide
anions [P3C2H(C6H5)]− (5) and [As3C2H(C6H5)]− (6). Of
these, only 6 could be structurally authenticated by means of
single-crystal X-ray diffraction, although multielement NMR
spectroscopy and electrospray mass spectrometry clearly
support the synthesis of 5. Species 6 was isolated as yellow
needlelike crystals in [K(18-crown-6)THF][6] (Figure 2).
resonance (ppm)
b
b
1
2
3
4
5
6
P1
272.8
261.1
272.8
155.2
155.2
9.03
297.9
273.3
297.9
174.9
174.9
275.5
289.2
269.0
178.5
157.7
8.97
P2
P3
C1
C2
H1/2
172.4
172.4
10.68
193.1
193.1
194.0
172.0
10.58
a
Data were collected at 20 °C in d8-THF or d5-pyridine. The
phosphorus nuclei numbering scheme is that used in Figures 1 and 2.
b
Data taken from ref 20.
the internuclear J coupling constants are provided in the
Experimental Section. A full analysis of the spin-systems for all
of the compounds discussed in this manuscript is provided in
the Supporting Information.
The 1H and 13C{1H} NMR spectra of anions 3−6 are
unremarkable and are consistent with their formulation as
1,2,3-tripnictolide anions. The observation of three and five
Figure 2. Thermal ellipsoid plots of the anionic moiety crystallo-
graphically characterized in [K(18-crown-6)THF][6]. Anisotropic
thermal displacement ellipsoids are pictured at the 50% probability
level. Hydrogen positions were assigned idealized coordinates and are
pictured as spheres of arbitrary radii. Selected bond distances (Å) and
angles (deg) for 6: As1−As2, 2.311(1); As2−As3, 2.303(1); As3−C1,
1.894(2); C1−C2, 1.375(3); C2−As1, 1.870(2); C1−C3, 1.485(3);
As1−As2−As3, 97.18(1); As2−As3−C1, 98.08(6); As3−C1−C2,
122.16(14); C1−C2−As1, 125.17(14); C2−As1−As2, 97.39(6);
C3−C1−C2, 120.72(16). Torsion angle (Φ) between arsolide and
the phenyl ring: 46.5°.
1
resonances, respectively, in the H and 13C{1H} spectra of 3
and 4 suggests that there is free rotation around the C1−C3
and C2−C9 bonds to the phenyl substituents and that the
propeller-like arrangement observed in the solid state is not
1
retained in solution. The H NMR spectra of 5 and 6 are
consistent with asymmetrically derivatized 1,2,3-tripnictolide
anions. These spectra reveal a single resonance for the proton
of the pnictolide backbone at 8.97 and 10.58 ppm for 5 and 6,
respectively, with that of 5 appearing as a ddd multiplet due to
coupling with the phosphorus nuclei (2JH−P = 45 Hz, 3JH−P = 9
3
Hz, JH−P = 6 Hz). In addition, the proton spectra of these
The interatomic distances and angles in 6 are closely related
to those observed for 4a (vide supra). As−As bond distances
are 2.311(1) and 2.303(1) Å in 6 (cf. 2.300(1) and 2.306(1) Å
in 4a), lying between the sum of covalent radii for compounds
exhibiting single (2.42 Å) and double (2.28 Å) As−As bonds.23
The As−C and interannular C−C bonds (1.882 (av) and
compounds also reveal three additional resonances from the
phenyl substituents. The 13C NMR spectra of 5 and 6 reveal
two distinct resonances for the carbon atoms of the
tripnictolide anion backbones, due to the presence of two
different functionalities. These could be assigned by compar-
ison with the 13C NMR spectra of the symmetrical species 1−4.
C
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Electrospray mass spectrometry was also used to characterize
the 1,2,3-tripnictolide anions 3−6 in solution. The [E3C2RR′]−
anions were observed as the molecular ions in the negative ion
mode spectra, with peaks occurring at m/z values of 270.7,
402.7, 195.1, and 327.0 for 3−6, respectively. In the positive ion
mode, mass envelopes for the cation-paired species {[K(18-
crown-6)]2[E3C2RR′]}+ were recorded at 877.8, 801.4, and
933.7 Da for the [K(18-crown-6)]+ salts of 3, 5, and 6,
respectively. A related mass envelope arising from {[K(2,2,2-
crypt)]2[As3C2(C6H5)2]}+ was observed at 1233.5 Da for anion
4.
tripnictolide ligands 1−6 will be closely related (as will the
physical and chemical properties of the complexes formed). We
sought to corroborate these observations by synthesizing a
family of homologous metal complexes with which to further
probe the metal−ligand interactions arising from complexes
with these unique tripnictolide ligands.
Formation of Transition-Metal Complexes. The iso-
lation of a family of salts of 1,2,3-tripnictolide anions 1,2,3-
[E3C2RR′]− (R = R′ = H, E = P (1), As (2); R = R′ = C6H5, E
= P (3), As (4); R = H, R′ = C6H5, E = P (5), As (6))
prompted us to explore their reactivity toward metal complexes
with labile substituents. These highly elusive isomers of
tripnictolide anions have rarely been isolated as free ligands,
and what little is known about their coordination chemistry
stems from complexes that have been isolated by reaction of
metal compounds with highly reactive molecules such as
phospha-alkynes or white phosphorus (P4).10−13 This is in stark
contrast with the case for 1,2,4-triphospholide anions, for which
a wealth of literature is available, describing their coordination
toward main-group and d- and f-block elements.24−26 Isolation
of a family of 1,2,3-tripnictolide anions such as 1−6 provides a
unique opportunity to study the coordination chemistry of
these anions and compare structure and bonding within a
homologous series of compounds.
Monitoring the direct reaction of [K(18-crown-6)][1] with
Mo(CO)6 in refluxing d8-THF by 31P NMR spectroscopy
reveals the disappearance of resonances attributable to 1
(observed at 272.8 and 261.1 ppm) with the concomitant
growth of two new resonances significantly shifted to higher
field at 67.3 and 34.5 ppm. These two resonances integrate in a
2:1 intensity ratio and correspond to P1/P3 and P2,
respectively. The 1H NMR spectrum similarly shows an upfield
shift of the multiplet resonance attributable to the phospholide
protons to 5.83 ppm (from 9.03 ppm in 1). This is consistent
with the [P3C2H2]− anion acting as a six-electron donor to the
Mo(CO)3 fragment by displacement of three CO ligands,
resulting in the formation of the anionic “piano-stool” complex
[(η5-P3C2H2)Mo(CO)3]− (7). Optimization of the reaction
conditions revealed that the more labile acetonitrile ligands in
Mo(CO)3(MeCN)3 are rapidly displaced with gentle heating in
THF, and subsequent reactions were performed using this
more reactive source of the Mo(CO)3 moiety. Analogous
reactions using [K(18-crown-6)][2] as a starting material result
in the synthesis of [(η5-As3C2H2)Mo(CO)3]− (8). As with 7,
the formation of 8 can be monitored by NMR spectroscopy,
which shows a significant shift of the triarsolide proton
resonance on complexation to Mo(CO)3 from 10.68 ppm in
2 to 7.04 ppm in 8. Crystals of [K(18-crown-6)][7] and [K(18-
crown-6)][8] were grown from THF/hexane mixtures and are
isostructural (Figure 3).
Geometry optimizations at the density functional theory
(DFT) level were performed on all of the novel tripnictolide
anions 3−6. Similar calculations on the protic parent species 1
and 2 have been previously reported by our research group.20
The optimized computed geometries are in good agreement
with the geometries determined by single-crystal X-ray
diffraction for 3, 4, and 6 (see the Supporting Information
for a comparison of bond metric data). There is a moderate
lengthening of some distances in the tripnictolide rings
(particularly the E−E and E−C bonds), but this is never
greater than 1.6% of the crystallographically determined bond
distance and presumably arises due to the continuum dielectric
model employed to simulate the presence of charge-balancing
cations in the lattice. Generally speaking, the principal features
of the electronic structure for all of the tripnictolide anions are
very similar. The effect of varying the substituents on the rings
seems to have little bearing on the HOMO−LUMO gaps of the
anions or on the absolute energies of important frontier
orbitals. In all cases the HOMO and HOMO-1 orbitals have
pnictolide ring π-orbital character and exhibit a single angular
node as might be expected. An additional occupied π-manifold
orbital (the in-phase combination of the pz orbitals of the
pnictolide ring atoms) is located at lower energies for all
systems (HOMO-6 for 1 and 2, HOMO-4 for 3−6). Both the
energy and composition of this particular orbital seem to be the
most affected by the nature of the substituents on the ring.
Thus, it appears that while protons lower this orbital in energy
and increase the relative contribution of the tripnictolide
carbon atom pz orbitals, phenyl substituents have the opposite
effect, raising its energy and reducing carbon atom
participation. This effectively localizes electron density on the
pnictogen atoms of the ring for this specific orbital. Thus, it can
be argued that (on coordination) [P3C2H2]− has increased
cyclopentadienyl character relative to [P3C2(C6H5)2]−, which is
more triphosphaallylic in nature. This effect is also observed for
the analogous triarsolides.
The effect of varying the substituents on the 1,2,3-
tripnictolide rings naturally has an effect on the net antibonding
frontier orbitals as well; thus, for 1 the LUMO and LUMO+1
orbitals are π-antibonding with two angular nodes, while in 3
the LUMO is generally located on the phosphorus atoms while
the LUMO+6 is effectively C−C π-antibonding. The effects on
the asymmetrically derivatized tripnictolides 5 and 6 lie
somewhere between the two extremes defined by [E3C2H2]−
and [E3C2(C6H5)2]−. The picture in this case is somewhat
perturbed, however, due to mixing of orbitals with pnictolide
and phenyl ring character, as the optimized torsion angles for
these species are somewhat small (29.5 and 35.6° for 5 and 6,
respectively).
Both crystal structures reveal a 1,2,3-tripnictolide anion
coordinated in an η5 fashion to a molybdenum center. There is
rotational disorder of the 1,2,3-tripnictolide anion around the
Mo1−centroid axis in both structures. The disorder in the
ligand was modeled as two discrete positions, with the major
component refining to 65% and 58% in 7 and 8, respectively.
On account of this disorder, interatomic bond distances within
the ligand moieties should be interpreted with caution,
although it suffices to say that they generally compare well
with those of the free ligands. The average Mo−E/Mo−C
bonds between the metal center and the tripnictolide ligands
are 2.607/2.349 and 2.719/2.385 Å for 7 and 8, respectively
(due to the aforementioned disorder, these values are also
Generally our findings show that the electronic properties of
1−6 are very similar. As a result, it is expected that the bonding
interactions arising between a specific metal center and the
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6)]+ or [K(2,2,2-crypt)]+ salts of these anions with Mo(CO)3L3
(L = CO, CH3CN) reagents afford the metal complexes [{η5-
E3C2(C6H5)2}Mo(CO)3]− (E = P (9), As (10)) and [{η5-
E3C2H(C6H5)}Mo(CO)3]− (E = P (11), As (12)) in high
yields, as determined by multielement NMR spectroscopy (vide
infra). The ESI-MS spectra for these additional ligand
displacement reactions reveal the molecular ions as the
predominant species in the negative ion mode spectra.
Molecular ion peaks were observed at m/z values of 452.5,
584.8, 376.9, and 508.8 for compounds 8−12, respectively. In
addition, the positive ion mode spectra also reveal ion-paired
mass envelopes at m/z 1058.1, 1415.5, and 1115.1 for {[K(18-
crown-6)]2[9]}+, {[K(2,2,2-crypt)]2[10]}+ and {[K(18-crown-
6)]2[12]}+, respectively.
Single-crystal X-ray structures could be obtained for the
complex of the 4,5-diphenyl-1,2,3-tripnictolide anions [K(18-
crown-6)THF][9] and [K(2,2,2-crypt)][10] and of the 4-
phenyl-1,2,3-triarsolide [K(18-crown-6)THF][12]. We will
first discuss the single-crystal X-ray structures of complexes 9
and 10 (Figure 4).
The crystal structures of [K(18-crown-6)THF][9] and
[K(2,2,2-crypt)][10] contain anionic metal complexes com-
parable to those of 7 and 8 (albeit without the rotational
disorder observed in the tripnictolide rings for the latter). The
structure of 10 contains two crystallographically unique anions
with comparable bond metrics (for clarity, only one of the two
complexes will be discussed). The E−E, E−C, and C−C bond
distances in the tripnictolide rings in 9 and 10 compare well
with those of the free ligands 3 and 4. The P−P, P−C, and C−
C distances in 9 are 2.142 (av), 1.780 (av) and 1.419(2) Å,
respectively (cf. 2.095 (av), 1.761 (av) and 1.402(2) Å in 3).
These values show that there is a moderate lengthening of the
P−P bonds (Δd = 0.05 Å) on coordination of the ligand to an
electron-rich metal center, as might be expected for a π-
acceptor type ligand. Similarly in 10 the As−As, As−C, and C−
C distances 2.354 (av), 1.912 (av) and 1.403 (3) Å,
respectively, also compare well with those of the free ligand
(2.306 (av), 1.895 (av) and 1.384 Å (av), respectively). The
As−As bonds also show a moderate lengthening in the complex
relative to the free ligand (Δd = 0.05 Å). The Mo−P, Mo−C,
and Mo−CO interatomic distances in 9, 2.624 (av), 2.401 (av)
and 1.954 Å (av), respectively, generally compare well with
those observed in 7 (2.607, 2.349, and 1.951 Å, respectively),
although there is a moderate lengthening of distances between
the molybdenum center and the triphospholide carbon atoms
in 9 relative to 7 (Δd = 0.05 Å). While this may be a result of
the increased bulk of the phenyl substituents, it could also arise
due to the decreased contribution of carbon atom pz orbitals to
the totally in-phase π orbital of the pnictolide ring in 3 relative
to 1 (vide supra). It is worth noting, however, that due to the
rotational disorder of the triphospholide moiety in 7 a
distortive effect on the distances between the metal and
triphospholide ring atoms in complex 7 cannot be ruled out.
The same effect was observed when comparing complexes 10
and 8: Mo−As, Mo−C, and Mo−CO distances in 10 are 2.721
(av), 2.423 (av), and 1.943 Å (av) (cf. 2.719 (av), 2.395 (av),
and 1.951 Å (av) in 8, respectively). The Mo−CO distances in
9 and 10 are very similar to one another. This observation is
consistent with the comparable carbonyl stretching vibrations
observed in the IR spectra of the complexes. Three bands were
observed in the spectra of each complex at 1921, 1842, and
1821 cm−1 for 9 and 1910, 1836, and 1818 cm−1 for 10 (cf.
Figure 3. Thermal ellipsoid plots of the anionic moieties crystallo-
graphically characterized in (a) [K(18-crown-6)][7] and (b) [K(18-
crown-6)][8]. Anisotropic thermal displacement ellipsoids are
pictured at the 50% probability level. Hydrogen positions were
assigned idealized coordinates and are pictured as spheres of arbitrary
radii. The 1,2,3-tripnictolide moieties in 7 and 8 exhibit discrete
positional disorder; only the major component is pictured. Selected
bond distances (Å) for 7: P1−P2, 2.119(7); P2−P3, 2.131(7); P3−
C1, 1.763(9); C1−C2, 1.400(8); C2−P1, 1.734(6); Mo1−P1,
2.576(5); Mo1−P2, 2.694(9); Mo1−P3, 2.551(5); Mo1−C1,
2.311(11); Mo1−C2, 2.386(7); Mo1−C3, 1.945(2); Mo1−C4,
1.953(2); Mo1−C5, 1.954(2); C3−O1, 1.168(3); C4−O2, 1.160(3);
C5−O3, 1.165(3); Mo1−centroid of triphospholide, 1.970. Selected
bond distances (Å) for 8: As1−As2, 2.325(5); As2−As3, 2.329(7);
As3−C1:, 1.996(10); C1−C2, 1.375(8); C2−As1, 1.822(8); Mo1−
As1, 2.679(3); Mo1−As2, 2.800(5); Mo1−As3, 2.677(4); Mo1−C1,
2.369(7); Mo1−C2, 2.400(7); Mo1−C3, 1.950(3); Mo1−C4,
1.946(3); Mo1−C5, 1.956(3); C3−O1, 1.163(4); C4−O2, 1.164(3);
C5−O3, 1.162(3). Mo1−centroid of triarsolide, 1.983.
inherently inaccurate). The distance between the molybdenum
center and the tripnictolide ligand centroid is only moderately
longer for the arsenic-containing system 8, 1.983 Å, relative to
1.970 Å in 7. Mo−CO and C−O distances are identical within
experimental error for 7 and 8. The latter distances are
consistent with the near-identical CO stretching bands
observed in the IR spectra of 7 and 8, which show three
peaks at 1916, 1834, and 1814 cm−1 for 7 and 1910, 1830, and
1817 cm−1 for 8. These values indicate that if there are any
significant differences in the π-acceptor properties of 1 and 2,
these are not manifested in the electronic properties of the
carbonyl ligands of the Mo(CO)3 moiety on complexation. It is
worth noting, however, that these frequencies are at wave-
numbers notably higher than those observed for the all-carbon
analogue [(η5-Cp)Mo(CO)3]− (1884 and 1760 cm−1 for the A1
and E modes, respectively),27 indicating that while the 1,2,3-
triphospholide ligand 1 and its arsenic analogue 2 may have
comparable π-acceptor properties, they are notably greater than
those of the cyclopentadienyl ligand.
[K(18-crown-6)][7] and [K(18-crown-6)][8] were also
characterized by ESI-MS and elemental analysis. The ESI-MS
spectra of DMF solutions of [K(18-crown-6)][7] and [K(18-
crown-6)][8] exhibit molecular ion peaks at 300.8 and 432.7
Da, respectively. Similarly, the positive ion mode spectrum of 8
shows evidence of the ion-coupled species {[K(18-crown-
6)]2[8]}+ at an m/z value of 1039.1. All of the aforementioned
mass envelopes occur with characteristic isotopic distributions
due to the seven naturally occurring molybdenum isotopes (92,
94, 95, 96, 97, 98, and 100).
The same methodology employed for the synthesis of 7 and
8 can be used to access “piano stool” complexes of the novel
tripnictolide anions 3−6. Thus, reactions of the [K(18-crown-
E
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Figure 5. Thermal ellipsoid plots of the anionic moiety crystallo-
graphically characterized in [K(18-crown-6)][12]. Anisotropic thermal
displacement ellipsoids are pictured at the 50% probability level.
Hydrogen positions were assigned idealized coordinates and are
pictured as spheres of arbitrary radii. The 4-phenyl-1,2,3-triarsolide
moieties in 12 exhibit discrete positional disorder; only the major
component is pictured. Selected bond distances (Å): As1−As2,
2.351(2); As2−As3, 2.346(1); As3−C1, 1.936(3); C1−C2, 1.384(6);
C2−As1, 1.876(8); C1−C3, 1.488(5); Mo1−As1, 2.725(3); Mo1−
As2, 2.795(1); Mo1−As3, 2.672(1); Mo1−C1, 2.416(3); Mo1−C2,
2.351(6); Mo1−C9, 1.957(4); Mo1−C10, 1.965(3); Mo1−C11,
1.953(4); C9−O1, 1.155(5); C10−O2, 1.150(4); C11−O3,
1.165(4). Mo1−centroid of triarsolide, 1.986.
arsenic atoms of the triarsolide ring are 2.725(3), 2.795(1), and
2.672(1) Å and compare well with those of the other 1,2,3-
triarsolide complexes discussed earlier (cf. 8 at 2.679(3),
2.800(5) and 2.677(4) Å and 10 at 2.706(1), 2.790(1), and
2.667(1) Å). The same is also true for the Mo1 distances to the
carbon atoms of the 1,2,3-triarsolide ring, which are 2.416(3)
and 2.351(6) Å in 12, in comparison to 2.369(7)/2.400(7) Å
and 2.431(2)/ 2.414(2) Å for 8 and 10, respectively. Mo−CO
distances range between 1.953(4) and 1.965(3) Å and are very
similar to those observed for 8 (1.943 Å (av)) and 10 (1.951 Å
(av)).
Figure 4. Thermal ellipsoid plots of the anionic moieties crystallo-
graphically characterized in (a) [K(18-crown-6)THF][9] and (b)
[K(2,2,2-crypt)][10]. Anisotropic thermal displacement ellipsoids are
pictured at the 50% probability level. Hydrogen positions were
assigned idealized coordinates and are pictured as spheres of arbitrary
radii. Selected bond distances (Å) for 9: P1−P2, 2.146(1); P2−P3,
2.138(1); P3−C1, 1.776(2); C1−C2, 1.419(2); C2−P1, 1.784(2);
C1−C3, 1.495(2); C2−C9, 1.497(2); Mo1−P1, 2.594(1); Mo1−P2,
2.699(1); Mo1−P3, 2.579(1); Mo1−C1, 2.413(2); Mo1−C2,
2.389(2); Mo1−C15, 1.957(2); Mo1−C16, 1.945(2); Mo1−C17,
1.960(2); C15−O1, 1.158(2); C16−O2, 1.167(2); C17−O3,
1.162(2); Mo1−centroid of triphospholide, 1.992. Selected bond
distances (Å) for one of the two crystallographically unique anions in
[K(2,2,2-crypt)][10]: As1−As2, 2.365(1); As2−As3, 2.343(1); As3−
C1, 1.910(2); C1−C2, 1.403(3); C2−As1, 1.914(2); C1−C3,
1.498(3); C2−C9, 1.502(3); Mo1−As1, 2.706(1); Mo1−As2, 2.790
(1); Mo1−As3, 2.667(1); Mo1−C1, 2.431(2); Mo1−C2, 2.414(2);
Mo1−C15, 1.938(3); Mo1−C16, 1.955(3); Mo1−C17, 1.937(3);
C15−O1, 1.154(4); C16−O2, 1.155(3); C17−O3, 1.164(4); Mo1−
centroid of triarsolide, 1.989.
IR data for complexes [{η5-E3C2H(C6H5)}Mo(CO)3]− (E =
P (11), As (12)) indicate that the 4-phenyl-1,2,3-tripnictolide
anions have π-acceptor properties comparable to those of the
protic and diphenyl functionalized anions. Bands arising due to
carbonyl stretching vibrational modes were observed at 1925,
1842, and 1828 cm−1 for 11 and 1911, 1828, and 1818 cm−1 for
12 (cf. 1921, 1842, and 1821 cm−1 for 9 and 1910, 1836, and
1818 cm−1 for 10).
NMR data for all of the “piano-stool” complexes 7−12 are
provided in Table 2. The 31P NMR spectra of complexes 7 and
9 each reveal two multiplet resonances in a 2:1 ratio for the P1/
1916, 1834, and 1814 cm−1 for 7 and 1910, 1830, and 1817
cm−1 for 8).
a
1
Table 2. 31P, 13C, and H NMR Chemical Shifts for 7−12
[K(18-crown-6)THF][12] crystallizes in the space group P1,
̅
resonance (ppm)
and the crystal structure determination confirms the “piano-
stool” geometry of the complex anion (Figure 5). There is a
single [{η5-As3C2H(C6H5)}Mo(CO)3]− anion in the asym-
metric unit, which exhibits discrete crystallographic disorder of
the 1,2,3-triarsolide moiety (two components of the triarsolide
can be refined in a 68:32 ratio). The disorder is such that the
Mo(CO)3 and phenyl ring moieties are in fixed positions but
the 1,2,3-triarsolide adopts two possible orientations (resulting
in both enantiomers of the anion occupying the same site). On
account of this disorder, bond metric data within the triarsolide
ring are unreliable. The bond distances between Mo1 and the
7
8
9
10
11
12
P1
67.3
34.5
97.6
20.8
70.6
40.5
P2
P3
67.3
97.6
77.0
C1
C2
H1/2
111.5
111.5
5.82
124.1
124.1
7.04
140.5
140.5
142.3
142.3
139.9
113.8
6.16
145.6
113.9
7.29
a
Data were collected at 20 °C in d8-THF or d5-pyridine. The
phosphorus nuclei numbering scheme is that used in Figure 1.
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Figure 6. Kohn−Sham molecular orbital representations (contour values 0.03 au) for (a) HOMO-2 and (b) LUMO in 7.
P3 and P2 sets of nuclei, as expected for η5 compounds of
symmetrically derivatized 1,2,3-triphospholides (67.3 and 34.5
ppm for 7; 97.6 and 20.8 ppm for 9). In both instances these
resonances are significantly upfield from those observed for the
free ligands (272.8 and 261.1 ppm for 1; 297.9 and 273.3 ppm
for 3). In each case the magnitude of the shift is larger for the
P2 nuclei (Δδ = −226.6 and −252.5 ppm for 7/1 and 9/3,
respectively) than for P1/P3 (Δδ = −205.5 and −200.3 ppm
for 7/1 and 9/3). The 31P NMR spectrum of complex 11,
which contains the asymmetrically functionalized 4-phenyl-
1,2,3-triphospholide, reveals three resonances of equal intensity
at 77.0, 70.6, and 40.5 ppm attributable to P3, P1, and P2,
respectively. As with 7 and 9, the largest chemical shift on
complexation of the free ligand is for the P2 nucleus (Δδ =
−248.7 ppm).
notable δ-type interaction with a ligand-based π orbital with a
single angular node (Figure 6a). The relative π-donor abilities
of aromatic cyclopentadienyl analogues will strongly influence
the magnitudes of these types of interactions. A similar effect
has been noted for 1,2,3-triphospholide systems previously.3
The LUMO in all cases is a net antibonding ligand based π
orbital with two angular nodes (Figure 6b).
CONCLUSIONS
■
We have shown that Zintl ion cages of phosphorus and arsenic
may be employed as precursors to access several symmetrically
and asymmetrically derivatized 1,2,3-tripnictolide anions of the
general formula [E3C2RR′]− (R = R′ = H, E = P (1), As (2); R
= R′ = C6H5, E = P (3) As (4); R = H, R′ = C6H5, E = P (5),
As (6)). These findings demonstrate that such reactions may be
used as a versatile protocol for the synthesis of these otherwise
elusive compounds. Density functional theory calculations and
the coordination chemistry studies we have carried out on these
ligands and Mo(CO)3L3 reagents show that 1−6 generally have
very similar π-acceptor properties and that the functional
groups studied do not significantly alter these properties. This
was probed by synthesizing a family of homologous η5
molybdenum tricarbonyl complexes, all of which exhibited
similar IR stretching frequencies regardless of the ligand in
question. All ligands 1−6 were found to have significantly
greater π-acceptor properties than the isolobal cyclopentadienyl
anion.
Similar shifts are also observed for the tripnictolide ring
1
protons in the H spectra of 1, 2, 4, and 5 on complexation to
the Mo(CO)3 moiety. The proton resonances shift from 9.03,
10.68, 8.97, and 10.58 ppm for 1, 2, 4, and 5, respectively, to
5.83, 7.04, 6.16, and 7.29 ppm for 7, 8, 11, and 12, respectively.
The optimized computed geometries for [(η5-E3C2H2)Mo-
(CO)3]− (E = P (7), As (8)), [{η5-E3C2(C6H5)2}Mo(CO)3]−
(E = P (9), As (10)), and [{η5-E3C2H(C6H5)}Mo(CO)3]− (E
= P (11), As (12)) compare well with those of the structurally
authenticated anions 7−10 and 12 (see the Supporting
Information for further details). The electronic structures of
the complexes are similar to what would be expected for the all-
carbon analogue [(C5H5)Mo(CO)3]. All compounds have
comparable HOMO−LUMO gaps, and the energies and
relative ordering of important frontier orbitals are comparable.
The principal differences are a significant mixing of pnictogen
atom lone-pair character into important frontier orbitals and an
increased degree of δ bonding arising between the in-plane dxy
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 of H2O and <0.1
ppm of O2). The Zintl phase precursors K3P7 and K3As7 were
synthesized according to previously reported synthetic procedures
from a mixture of the elements (K, 99.95%, Strem; P, 99.99%, Sigma-
Aldrich; As, 99.99%, Alfa-Aesar).28 [K(18-crown-6)][P3C2H2] and
[K(18-crown-6)][As3C2H2] were prepared according to a literature
procedure recently reported by our group.20 Mo(CO)3(MeCN)3 was
prepared according to a literature procedure from freshly sublimed
Mo(CO)6 (Fluka, 90%).29 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-
diazabicyclo[8,8,8]-hexacosane; VWR, 99%), 18-crown-6
2
2
and dx −y orbitals and ligand π orbitals (the principal axis z is
defined as running through the molybdenum metal center and
the tripnictolide centroid with x oriented toward the E2 atom).
The top three occupied orbitals are the same for all of the
2
2
2
complexes and are of d orbital parentage (dxy, dz and dx −y for
HOMO, HOMO-1, and HOMO-2, respectively). It is worth
2
2
noting that the dx −y orbital is lower in energy relative to
[(C5H5)Mo(CO)3] (where it is the HOMO-1) due to a
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(1,4,7,10,13,16-hexaoxacyclooctadecane; 99%, Alfa Aesar), and
diphenylacetylene (99%, Sigma Aldrich) were used as received after
careful drying under vacuum. Hexanes (hex; 99+%, Rathburn), diethyl
ether (Et2O; pesticide residue grade, Fisher), acetonitrile (MeCN;
99.9%, Rathburn), and dimethylformamide (DMF; 99.9%, Rathburn)
were purified using an MBraun SPS-800 solvent system. Tetrahy-
drofuran (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%, Fluorochem) and d8-THF (99.5%,
Fluorochem) were dried over CaH2 and vacuum-distilled. All dry
solvents were stored under argon in gastight ampules. Additionally
hexanes, Et2O, MeCN, and THF were stored over activated 3 Å
molecular sieves.
phenyl), 7.05 (m, 2H, m-phenyl), 6.85 (m, 1H, p-phenyl), 3.45 (s,
24H, 18-crown-6). 31P{1H} NMR (202.4 MHz, d8-THF, 20 °C): δ
(ppm) 289.2 (dd, 1P, P2), 275.5 (dd, 1P, P1), 269.0 (dd, 1P, P2).
13C{1H} NMR (125.8 MHz, d8-THF, 20 °C): δ (ppm) 178.5
(C(C6H5)), 157.7 (CH) 146.3, 132.4, 128.2, 124.1, 71.3 (18-crown-6).
ESI-MS (negative ion mode, DMF): m/z 195.1 [P3C2H(C6H5)]−.
ESI-MS (positive ion mode, DMF): m/z 801.4 {[K(18-crown-
6)]2[P3C2H(C6H5)]}+.
Synthesis of [K(18-crown-6)][6] (6 = [As3C2H(C6H5)]−). The
same procedure used for the synthesis of [K(18-crown-6)][5] was
employed. K3As7 (100 mg, 0.156 mmol), 18-crown-6 (123 mg, 0.468
mmol), and phenylacetylene (51 μL, 0.390 mmol) were reacted in
DMF. It was not necessary to stir the THF solution in air. Yield: 152
Synthesis of [K(18-crown-6)(THF)2][3] (3 = [P3C2(C6H5)2]−).
[K(18-crown-6)]2[HP7] (400 mg, 0.49 mmol) and diphenylacetylene
(258 mg, 1.45 mmol) were stirred overnight in DMF (5 mL), yielding
a deep purple solution. The solvent was then removed under dynamic
vacuum and the resulting dark residue extracted with THF (5 mL). Air
was bubbled through the solution for 5 min, and the dark red-brown
solution was filtered. Volatiles were removed from the filtrate under
reduced pressure, and the dark residue was washed with diethyl ether
(10 mL) to yield the product as a pale red-brown powder (463 mg,
70% yield based on phosphorus). Crystals suitable for single-crystal X-
ray diffraction were grown by slow diffusion of hexanes (20 mL) into a
THF solution (5 mL) of the product. Anal. Calcd for C28H45KO8P3:
1
mg (66% based on arsenic). H NMR (500 MHz, d8-THF, 20 °C): δ
(ppm) 10.58 (s, 1H, CH phospholide), 7.80 (m, 2H), 7.14 (m, 2H),
6.97 (m, 1H), 3.52 (s, 24H). 13C NMR (125.8 MHz, d8-THF, 20 °C):
δ (ppm) 194.0 (C(C6H5)), 172.0 (CH), 146.4, 139.8, 126.0, 121.1
68.33. ESI-MS (negative ion mode, DMF): m/z 327.0 [P3C2H-
(C6H5)]−. ESI-MS (positive ion mode, DMF): m/z 933.7 {[K(18-
crown-6)]2[P3C2H(C6H5)]}+.
Synthesis of [K(18-crown-6)][7] (7 = [(P3C2H2)Mo(CO)3]−).
Mo(CO)3(MeCN)3 (72 mg, 0.238 mmol) and [K(18-crown-6)][1]
(100 mg, 0.238 mmol) were dissolved in THF (5 mL) and stirred
overnight under argon to give a dark red solution. The solution was
filtered into an ampule and layered with hexanes (20 mL). After
several days yellow crystals suitable for single-crystal X-ray diffraction
had formed. NMR spectroscopy shows that the yield for this reaction
is nearly quantitative. Isolated crystalline yield: 18 mg (13%). Anal.
Calcd for MoC17H26O9KP3: C, 33.90; H, 4.35. Found: C, 32.76; H,
1
C, 56.80; H, 7.01. Found: C, 56.66; H, 6.81. H NMR (500 MHz, d8-
THF, 20 °C): δ (ppm) 7.20 (m, 4H, o-phenyl), 6.92 (m, 4H, m-
phenyl), 6.83 (m, 2H, p-phenyl), 3.54 (m, THF), 3.49 (s, 24H, 18-
crown-6), 1.68 (m, THF). 31P{1H} NMR (202.4 MHz, d8-THF, 20
1
1
°C): δ (ppm) 297.9 (m, 2P, JP−P = −492 Hz, P1/P3), 273.3 (m, 1P,
4.28. H NMR (500 MHz, d8-THF, 20 °C): δ (ppm) 5.82 (m, 2H,
P2). 13C{1H} NMR (125.8 MHz, d8-THF, 20 °C): δ (ppm) 174.9
(P3C2), 146.7, 131.5, 127.2, 123.9, 71.3 (18-crown-6), 67.5 (THF),
25.5 (THF). ESI-MS (negative ion mode, DMF): m/z 270.7
[P3C2(C6H5)2]−. ESI-MS (positive ion mode, DMF): m/z 877.8
{[K(18-crown-6)]2[P3C2(C6H5)2]}+.
2
3
3
1
3JH−H = 6 Hz, JP−H = 44 Hz, JP−H = 13 Hz, JP−H = 4 Hz, JP−P
=
2
−422 Hz, JP−P = 8 Hz, CH of phospholide; for a full analysis of the
spin system see the Supporting Information), 3.64 (s, 24H, 18-crown-
6). H{31P} NMR (500 MHz, d8-THF, 20 °C): δ (ppm) 5.83 (s, 2H,
1
CH of phospholide). 31P NMR (202.4 MHz, d8-THF, 20 °C): δ
(ppm) 67.3 (m, 2P, P1/P3), 34.5 (m, 1P, P2). 13C{1H} NMR (125.8
MHz, d8-THF, 20 °C): δ (ppm) 227.8 (CO), 111.5 (m, CH of
phospholide), 70.3 (18-crown-6). ESI-MS (negative ion mode, DMF):
m/z 300.8 [Mo(CO)3(P3C2H2)]−. ESI-MS (positive ion mode,
DMF): nothing observed. IR (νCO, cm−1): 1916, 1834, 1814.
Synthesis of [K(2,2,2-crypt)][4] (4 = [As3C2(C6H5)2]−). K3As7
(970 mg, 1.51 mmol), diphenylacetylene (672 mg, 4.53 mmol), and
2,2,2-crypt (1.705 g, 3.71 mmol) were dissolved in DMF (20 mL) and
stirred overnight under argon. The solvent was then removed under
dynamic vacuum and the resulting dark residue extracted with THF
(50 mL). The filtrate was reduced to half its original volume, and
hexanes (100 mL) were added to precipitate the product as a yellow-
green solid. This was isolated by filtration and washed with hexanes (3
× 15 mL) and then dried under dynamic vacuum for 3 h. Yield: 1.161
g (39% based on arsenic). Crystals suitable for single-crystal X-ray
diffraction were grown by slow diffusion of hexanes into a THF
solution of the compound. Anal. Calcd for C32H46N2O6KAs3: C,
[K(18-crown-6)][8] (8 = [(As3C2H2)Mo(CO)3]−). The reaction was
carried out as for 7, using Mo(CO)3(MeCN)3 (72 mg, 0.238 mmol)
and [K(18-crown-6)][2] (132 mg, 0.238 mmol). NMR spectroscopy
shows that the yield for this reaction is nearly quantitative. Isolated
crystalline yield: 26 mg (15%). Anal. Calcd for MoC17H26O9KAs3: C,
1
27.81; H, 3.57. Found: C, 28.79; H, 3.72. H NMR (500 MHz, d8-
THF, 20 °C): δ (ppm) 7.04 (s, 2H, CH of arsolide), 3.67 (s, 24H, 18-
crown-6). 13C{1H} NMR (125.8 MHz, d8-THF, 20 °C): δ (ppm)
228.1 (CO), 124.1 (CH of arsolide), 70.2 (18-crown-6). ESI-MS
(negative ion mode, DMF): m/z 432.7 [Mo(CO)3(As3C2H2)]−. ESI-
MS (positive ion mode, DMF): 1039.1 {[K(18-crown-6)]2[Mo-
(CO)3(As3C2Ph2)]}+. IR (νCO, cm−1): 1910, 1830, 1817.
1
46.93; H, 5.67; N, 3.42. Found: C, 47.18; H, 5.72; N, 3.52. H NMR
(500 MHz, d5-pyridine, 20 °C): δ (ppm) 7.90 (m, 4H, o-phenyl), 7.20
(m, 4H, m-phenyl), 7.08 (m, 2H, p-phenyl), 3.40 (s, 12H, 2,2,2-crypt),
3
3.35 (t, 12H, JH−H = 5 Hz, 2,2,2-crypt), 2.35 (t, 12H, 2,2,2-crypt).
13C{1H} NMR (125.8 MHz, d5-pyridine, 20 °C): δ (ppm) 193.1
(As3C2), 148.4, 131.2, 127.7, 124.5, 70.8 (2,2,2-crypt), 68.1 (2,2,2-
crypt), 54.3 (2,2,2-crypt). ESI-MS (negative ion mode, DMF): m/z
402.7 [As3C2Ph2]−. ESI-MS (positive ion mode, DMF)): m/z 1233.5
{[K(2,2,2-crypt)]2[As3C2Ph2]}+.
[K(18-crown-6)][9] (9 = [{P3C2(C6H5)2}Mo(CO)3]−). [K(18-
crown-6)][3] (100 mg, 0.174 mmol) and Mo(CO)6 (45.9 mg,
0.174 mmol) were dissolved in THF (5 mL) and heated at 50 °C for
36 h. The reaction mixture was filtered into a clean Schlenk tube, and
hexanes (20 mL) was added in order to precipitate out an orange solid.
The solution was filtered off and the solid dried under vacuum.
Isolated yield: 61 mg (46%). Crystals of [K(18-crown-6)THF][9]
could be grown from slow diffusion of hexanes into a THF solution of
the solid product. 1H NMR (500 MHz, d8-THF, 20 °C): δ (ppm) 7.13
(m, 2H, C6H5), 6.89 (m, 2H, C6H5), 6.86 (m, 1H, C6H5), 3.62 (s,
24H, 18-crown-6). 31P NMR (202.4 MHz, d8-THF, 20 °C): δ (ppm)
Synthesis of [K(18-crown-6)][5] (5 = [P3C2H(C6H5)]−). [K(18-
crown-6)2][HP]7 (0.200 g, 0.242 mmol) was weighed into a small
Schlenk flask and dissolved in DMF (5 mL). Phenylacetylene (79 μL,
0.715 mmol) was added using a micro syringe. Addition of
phenylacetylene gave rise to a dark purple solution, which was stirred
overnight under argon. The solvent was removed under dynamic
vacuum, yielding a dark purple oil, which was redissolved in THF (5
mL). The solution was stirred in air for 15 min, resulting in an orange-
brown solution which was filtered, and the product was precipitated by
addition of hexane (20 mL). Yield: 173 mg (61% based on
1
100.8 (m, 2P, JP−P = −415 Hz, P1/P3), 24.2 (m, 1P, P2). 13C{1H}
NMR (125.8 MHz, d8-THF, 20 °C): δ (ppm) 228.5 (s, CO), 140.6
(m, P3C2(C6H5)2), 132.5 (s, C6H5), 126.7 (s, C6H5), 125.8 (s, C6H5),
ipso C6H5 not observed. ESI-MS (negative ion mode, DMF): m/z
452.5 [Mo(CO)3{P3C2(C6H5)2}]−. ESI-MS (positive ion mode,
DMF): m/z 1058.1 {[K(18-crown-6)]2[Mo(CO)3{P3C2(C6H5)2}]}+.
IR (νCO, cm−1): 1921, 1842, 1821.
1
phosphorus). H NMR (500 MHz, d8-THF, 20 °C): δ (ppm) 8.97
(m, 1H, 2JH−P = 45 Hz, 3JH−P = 9 Hz, 3JH−P = 6 Hz, 1JP−P = −499 Hz,
1JP−P = −467 Hz, 2JP−P = 14 Hz, CH phospholide; for a full analysis of
the spin system see the Supporting Information), 7.75 (m, 2H, o-
H
dx.doi.org/10.1021/om4001296 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
[K(2,2,2-crypt)][10] (10 = [{As3C2(C6H5)2}Mo(CO)3]−). [K(2,2,2-
crypt)][4] (50 mg, 0.0611 mmol) and Mo(CO)3(MeCN)3 (18.5 mg,
0.0611 mmol) were dissolved in THF (5 mL) and stirred at 60 °C
overnight to give a dark red solution. The reaction mixture was filtered
into an airtight ampule and layered with hexanes. Orange blocklike
crystals suitable for single-crystal X-ray diffraction were obtained after
several days. Isolated yield: 30 mg (49%). Anal. Calcd for
C35H46KMoN2O9As3: C, 42.08; H, 4.64; N, 2.81. Found: C, 42.95;
Other Characterization Techniques. Positive and negative ion
mode electrospray mass spectra were recorded on DMF solutions of
the compounds (10−20 μM) on a Waters 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.
1
H, 4.58; N, 2.88. H NMR (500 MHz, d5-pyridine, 20 °C): δ (ppm)
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.
7.69 (m, 2H, C6H5), 7.05 (m, 2H, C6H5) 7.00 (m, 1H, C6H5), 3.42 (s,
3
12H, 2,2,2-crypt), 3.37 (t, JH−H = 5 Hz, 12H, 2,2,2-crypt), 2.37 (t,
12H, 2,2,2-crypt). 13C{1H} NMR (125.8 MHz, d8-THF, 20 °C): δ
(ppm) 229.8 (s, CO), 156.4 (s, C6H5), 142.3 (m, As3C2(C6H5)2),
132.4 (s, C6H5), 127.1 (s, C6H5), 126.0 (s, C6H5). ESI-MS (negative
ion mode, DMF): m/z 584.8 [Mo(CO)3{As3C2(C6H5)2}]−. ESI-MS
(positive ion mode, DMF): m/z 1415.5 {[K(2,2,2-crypt)]2[Mo-
(CO)3{As3C2(C6H5)2}]}+. IR (νCO, cm−1): 1910, 1836, 1818.
[K(18-crown-6)][11] (11 = [{P3C2H(C6H5)}Mo(CO)3]−). The
reaction was carried out as for 9, using [K(18-crown-6)][5] (100
mg, 0.200 mmol) and Mo(CO)6 (52.8 mg, 0.200 mmol). An orange
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
and δC 150.2 ppm; d8-THF, δH 3.58 ppm and δC 67.2 ppm). 31P
spectra were externally referenced to 85% H3PO4 (δP 0 ppm). Spectral
simulations were carried out using the program gNMR.34
IR data were recorded on solid samples in Nujol mulls. The mulls
were made up inside an inert-atmosphere glovebox and the KBr plates
placed in an airtight sample holder prior to data collection. Spectra
were recorded on a Thermo Scientific Nicolet iS5 FT-IR spectrometer
in absorbance mode.
All geometry optimizations described in this paper were performed
using the Amsterdam Density Functional package (ADF2012.01).35 A
triple-ζ Slater-type basis set, extended with a double polarization
function (TZ2P), was used to describe all atoms. The local density
approximation was employed for the optimizations,36 along with the
local exchange-correlation potential of Vosko, Wilk, and Nusair37 and
the gradient corrections to exchange and correlation proposed by
Becke and Perdew (BP86).38 Relativistic effects were incorporated
using the zeroth order relativistic approximation (ZORA).39 The
presence of cations in the crystal lattice was modeled by surrounding
the anion with a continuum dielectric using COSMO.40 The chosen
dielectric constant ε = 7.58 corresponds to that of tetrahydrofuran,
although structural parameters are not strongly dependent on this
choice. All structures were optimized using the gradient algorithm of
Versluis and Ziegler.41
The signs associated with the spin−spin coupling constants (J) for
1, 3, 5, 7, 9, and 12 were determined by computing the Fermi contacts
using the Gaussian09 program package revision A02.42 The B3PW91
functional43 was employed along with the 6-311++G (2d,2p) basis set
for all of the light atoms (H, C, O, and P).44 The 3-21G basis set was
used to describe the molybdenum atoms in 7, 9, and 12.45 Initial
atomic coordinates were taken from single-crystal X-ray diffraction
experiments for 1, 3, 7, 9, and 12. The coordinates for 5 were taken
from the optimized computed geometry.
1
precipitate was isolated: yield 99 mg (74%). H NMR (500 MHz, d5-
py, 20 °C): δ (ppm) 7.49 (m, 2H, C6H5), 7.08 (m, 2H, C6H5), 7.01
(m, 1H, C6H5), 6.16 (m, 1H, 2JH−P = 42 Hz, 3JH−P = 10 Hz, 3JH−P = 4
1
1
2
Hz, JP−P = −435 Hz, JP−P = −404 Hz, JP−P = 42 Hz, CH
phospholide; for a full analysis of the spin system see the Supporting
Information), 3.55 (s, 24H, 18-crown-6). H{31P} NMR (500 MHz,
1
d5-py, 20 °C): δ (ppm) 6.16 (s, 1H, P3C2H(C6H5)). 31P{1H} NMR
(202.4 MHz, d5-py, 20 °C): δ (ppm) 77.0 (dd, 1P, P3), 70.7 (dd, 1P,
P1), 40.6 (dd, 1P, P2). 13C{1H} NMR (125.8 MHz, d5-py, 20 °C): δ
(ppm) 228.9 (s, CO), 142.8 (C(C6H5)), 129.7 (C6H5), 128.3 (C6H5),
126.4 (C6H5), 115.0 (CH of phospholide) 71.2 (s, 12C, 18-crown-6),
ipso C6H5 not observed. ESI-MS (negative ion mode, DMF): m/z
376.9 [Mo(CO)3{P3C2H(C6H5)}]−. ESI-MS (positive ion mode,
DMF): nothing observed. IR (νCO, cm−1): 1925, 1842, 1828.
[K(18-crown-6)][12] (12 = [{As3C2H(C6H5)}Mo(CO)3]−). The
reactions was carried out as for 9, using [K(18-crown-6)][6] (100 mg,
0.159 mmol) and Mo(CO)6 (42.0 mg, 0.159 mmol). NMR
spectroscopy shows that the yield for this reaction is nearly
quantitative. A bright orange solid was isolated: yield 25.7 mg
(20%). Anal. Calcd for C23H30KMoO9As3: C, 34.09; H, 3.73. Found:
1
C, 34.07; H, 3.60. H NMR (500 MHz, d5-py, 20 °C): δ (ppm) 7.48
(m, 2H, C6H5), 7.29 (m, 1H, As3C2H(C6H5)) 7.09 (m, 2H, C6H5),
7.04 (m, 1H, C6H5), 3.61 (s, 24H, 18-crown-6). 13C{1H} NMR (125.8
MHz, d5-py, 20 °C): δ (ppm) 229.2 (CO), 153.6 (C6H5), 145.6
(C(C6H5)), 130.6 (C6H5), 128.2 (C6H5), 126.4 (C6H5), 113.9 (CH of
arsolide), 71.4 (s, 12C, 18-crown-6). ESI-MS (negative ion mode,
DMF): m/z 508.8 [Mo(CO)3{As3C2H(C6H5)}]−. ESI-MS (positive
ion mode, DMF): m/z 1115.1 {[K(18-crown-6)]2[Mo-
(CO)3{As3C2H(C6H5)}]}+. IR (νCO, cm−1): 1911, 1828, 1818.
Single-Crystal X-ray Structure Determination. Single-crystal
X-ray diffraction data were collected using either an Oxford Diffraction
Supernova dual-source diffractometer equipped with a 135 mm Atlas
CCD area detector or an Enraf-Nonius kappa-CCD diffractometer
equipped with a 95 mm 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.30
Data were collected at 150 K using mirror-monochromated Cu Kα
radiation (λ = 1.5418 Å; Oxford Diffraction Supernova) or graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å; Enraf-Nonius
kappa-CCD). Data collected on the Oxford Diffraction Supernova
diffractometer were processed using the CrysAlisPro package,
including unit cell parameter refinement and interframe scaling
(which was carried out using SCALE3 ABSPACK within CrysA-
lisPro).31 Equivalent reflections were merged and diffraction patterns
processed with the CrysAlisPro suite. For data collected on the Enraf-
Nonius kappa-CCD diffractometer equivalent reflections were merged
and the diffraction patterns processed with the DENZO and
SCALEPACK programs.32 Structures were subsequently solved using
direct methods and refined on F2 using the SHELXL 97-2 package.33
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, tables, and CIF files giving X-ray crystallographic
data, full experimental and computational details, NMR and
ESI-MS spectra, and the full ref 42. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for J.M.G.: jose.goicoechea@chem.ox.ac.uk.
I
dx.doi.org/10.1021/om4001296 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(12) Maigrot, N.; Sierra, M.; Charrier, C.; Mathey, F. Bull. Soc. Chim.
Fr. 1994, 131, 397.
Notes
The authors declare no competing financial interest.
́
(13) (a) Garcıa, F.; Less, R. J.; Naseri, V.; McPartlin, M.; Rawson, J.
M.; Sancho Tomas, M.; Wright, D. S. Chem. Commun. 2008, 859.
(b) Butts, C. P.; Green, M.; Hooper, T. N.; Kilby, R. J.; McGrady, J. E.;
Pantazis, D. A.; Russell, C. A. Chem. Commun. 2008, 856.
(14) (a) Scheer, M.; Deng, S.; Scherer, O. J.; Sierka, M. Angew.
Chem., Int. Ed. 2005, 44, 3755. (b) Ionkin, A. S.; Marshall, W. J.; Fish,
B. M.; Marchione, A. A.; Howe, L. A.; Davidson, F.; McEwen, C. N.
Eur. J. Inorg. Chem. 2008, 2386.
ACKNOWLEDGMENTS
■
We thank the EPSRC and the University of Oxford for financial
support of this research (DTA studentships for R.S.P.T. and
A.R.J.) and the University of Oxford for access to Chemical
Crystallography and Oxford Supercomputing Centre facilities.
We also thank Elemental Microanalysis Ltd. (Devon) for
performing the elemental analyses. The ERASMUS Student
Mobility for Placements programme is also acknowledged
(D.E. placement in Oxford).
(15) (a) Baudler, M.; Duster, D.; Ouzounis, D. Z. Anorg. Allg. Chem.
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1987, 544, 87. (b) Baudler, M.; Akpapoglou, S.; Ouzounis, D.;
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Chem., Int. Ed. Engl. 1988, 27, 280. (c) Baudler, M.; Ouzounis, D. Z.
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