Reactivity studies of group 15 Zintl ions towards homoleptic post-transition metal organometallics: A 'bottom-up' approach to bimetallic molecular clusters

Article abstract of DOI:10.1039/b911544g

Reactions between ethylenediamine (en) solutions of the intermetallic Zintl phases K₃E₇ (E = P, As) and a series of homoleptic post-transition metal organometallics such as Cu₅(Mes)₅, M(C₆H₅)₂ (M = Zn, Cd) and In(C ₆H₅)₃ have yielded a family of novel bimetallic cluster anions. These new species were isolated as [K(2, 2,2-crypt)] ⁺ salts in [K(2,2,2-crypt)]₄Cu₂E₁₄ (E = P (1), As (2)), [K(2,2,2-crypt)]₄ZnE₁₄ (E = P (3), As (4)), [K(2,2,2-crypt)]₄CdP₁₄·6py (5) and [K(2,2,2-crypt)]₂E₇InPh₂ (E = P (6), As (7)). Species 2, 3, 5 and 6 were crystallographically characterised by single-crystal X-ray diffraction. The stability of all of the cluster anions in solution was confirmed by electrospray mass-spectrometry and by ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopy when possible. The Royal Society of Chemistry.

Full text of DOI:10.1039/b911544g

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PAPER
www.rsc.org/dalton | Dalton Transactions
Reactivity studies of group 15 Zintl ions towards homoleptic post-transition
metal organometallics: a ‘bottom-up’ approach to bimetallic molecular
clusters†
Caroline Knapp, Binbin Zhou, Mark S. Denning, Nicholas H. Rees and Jose M. Goicoechea*
Received 15th June 2009, Accepted 11th September 2009
First published as an Advance Article on the web 1st October 2009
DOI: 10.1039/b911544g
Reactions between ethylenediamine (en) solutions of the intermetallic Zintl phases K3E7 (E = P, As)
and a series of homoleptic post-transition metal organometallics such as Cu5(Mes)5, M(C6H5)2 (M =
Zn, Cd) and In(C6H5)3 have yielded a family of novel bimetallic cluster anions. These new species were
isolated as [K(2, 2,2-crypt)]+ salts in [K(2,2,2-crypt)]4Cu2E14 (E = P (1), As (2)), [K(2,2,2-crypt)]4ZnE14
(E = P (3), As (4)), [K(2,2,2-crypt)]4CdP14·6py (5) and [K(2,2,2-crypt)]2E7InPh2 (E = P (6), As (7)).
Species 2, 3, 5 and 6 were crystallographically characterised by single-crystal X-ray diffraction. The
stability of all of the cluster anions in solution was confirmed by electrospray mass-spectrometry and by
1
1
1H, 13C{ H} and 31P{ H} NMR spectroscopy when possible.
single three-coordinate E atom at the apex (see Fig. 1). A formal
negative charge can be assigned to each bridging E atom and each
E–E bond can be considered a two-centre, two-electron covalent
bond.
1. Introduction
In recent years numerous studies on deltahedral group 14 Zintl
n-
anions, E9 (E = Si, Ge, Sn, Pb; n = 2–4), have greatly expanded
our understanding of the behaviour of these unique clusters in
solution, giving rise to a renaissance of this area of main group
chemistry.1,2 Interestingly, while the number of studies on the
solution reactivity of group 14 clusters has increased dramatically,
3-
research on related seven-atom group 15 analogues, E7 (E = P,
As, Sb), has generally slowed down despite the fact that some of
the earliest and most ground breaking reactivity studies reported
on Zintl ions were first carried out on these cluster anions.
As a matter of fact, many of the synthetic techniques and
strategies initially developed in relation to group 15 clusters have
been successfully transferred to the chemistry of their group 14
analogues contributing to the surge of research activity currently
devoted to the field.
There are several known homoatomic group 15 Zintl ions that
can be isolated from solution. These include the cluster-like species
3-
3-
3-
E73-, E11 E16 and E21 (E = P, As, Sb), first reported in seminal
3-
Fig. 1 Diagrammatic representation of the E7 cluster anion.
publications by von Schnering, Corbett and others,3,4 as well
2-
as negatively-charged molecular squares and dimers, E4 (E =
3-
Early reactivity studies on E7 (E = P, As) anions found
2-
Sb, Bi) and Bi2 isolated by Corbett and Sevov, respectively.5,6
3-
3-
that both P7 and As7 could systematically be functionalised
3-
Of these, this manuscript will focus on the E7 cluster anions,
giving rise to neutral trisubstituted adducts such as R3E7 (e.g.
which are available quantitatively from the congruent dissolution
of preformed precursor alloys of nominal composition A3E7 (A =
alkali metal; E = P, As, Sb) in ethylenediamine or liquid ammonia.
R = H, Bu, SnMe3).7–17 Similarly, alkyl exchange reactions or
n
reactions with tetraalkylammonium salts or alkyl tosylates (R4N+
and ROTs, respectively) can be used to give rise to the disubstituted
3-
The E7 cluster anions have a nortricyclane-like structure with
monoanions R2E7 (E = P, As; R = Me, Et, nBu, Bz, iPr, iBu).18–21
-
C3v point group symmetry, consisting of a three-membered ring
of basal E atoms, three two-coordinate bridging E atoms, and a
Functionalisation of the parent cluster anions is effectively a redox
process resulting in the chemical oxidation of the cluster core and
the reduction of the alkylating agent. This yields products with
reduced anionic charges and exo-bonds to substituents which can
be rationalised as two-centre, two-electron bonds.
Department of Chemistry, Chemistry Research Laboratory, University of
Oxford, Mansfield Road, Oxford, UK OX1 3TA
† Electronic supplementary information (ESI) available: Calculated and
More recently, comprehensive reactivity studies with transition
metal organometallic reagents carried out by Eichhorn and others
have also served to highlight the chemical versatility of the E7
(E = P, As, Sb) cluster anions. These main group clusters have
1
experimentally determined 31P{ H} NMR spectra and tables detailing
31P-31P coupling constants for samples 5 and 6. CCDC reference numbers
736076–736079. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b911544g
3-
426 | Dalton Trans., 2010, 39, 426–436
This journal is
The Royal Society of Chemistry 2010
©

been found to undergo multiple functionalisation reactions with
transition metal reagents. In many of the reactions studied, the
seven atom cluster cores remain largely intact yielding products
14 are electron-deficient species where bonding is best rationalized
employing a Wade-Mingos model (each group 14 element being
isolobal with a B–H fragment),47 the Zintl ions of the group 15
elements are electron-precise, and their bonding can be described
using a conventional two-centre, two-electron bonding model. As
such as E7M(CO)33- (E = P, As, Sb; M = Cr, W),22,23 HP7M(CO)3
2-
(M = Cr, W),24 RP7W(CO)3 (R = Me, Et, nBu, CH2Ph),19
2-
R3EP7W(CO)3 (e.g. R3E = Me3Si, Et3Ge, Bu3Sn, Ph3Pb),25–26
we mentioned previously, the E7 (E = P–Sb) clusters have four
2-
n
3-
P7[FeCp(CO)2]3,27 P7Ni(CO)3-,28 HP7Ni(CO)2-,28 E7PtH(PPh3)2-
vertices that have a formal oxidation state of zero (atoms E1, E5,
E6 and E7 in Fig. 1) each of which is bound to three neighbouring
cluster vertices, while the remaining three atoms (E2, E3 and
E4) each form two, two-centre, two-electron bonds to adjacent
atoms and therefore formally carry a negative charge. The clear
distinction between nuclei in the solid-state structures of these
nortricyclane-like anions is slightly blurred in solution.
(E = P, As),28,29 and Pd2As14
.
30 Furthermore, additional reactions
4-
where the cluster anions undergo extensive bond dissociation and
cluster core re-assembly are also possible resulting in more unusual
n-
intermetallic species such as ME8 ions (M = Nb, Cr, Mo; E =
3-
4-
4-
As, Sb; n = 2, 3),31–34 Sb7Ni3(CO)3
, , ,
35 Ni5Sb17 36 Pd7As16 30 and
the remarkable As@Ni12@As20 ion.37 Empirically it would seem
that the Zintl ions of the heavier elements of group 15 (such as
antimony) are more inclined to give rise to larger cluster geometries
than their lighter counterparts (such as phosphorus) which tend to
maintain their seven atom cluster cores. The As73- cluster exhibits
chemical traits somewhere between those of its phosphorus and
antimony neighbours. This behaviour may be attributed to the
need to cleave multiple bonds in the seven atom cluster cage
precursors in order to give rise to systems with higher nuclearities,
and E–E bond dissociation enthalpies are known to decrease down
group 15. The logical conclusion of this trend is perhaps most
visible in the entirely unique chemistry exhibited by the heaviest
of the group 15 Zintl ions. The chemistry of anionic bismuth
Zintl ions is distinct from that of the lighter group 15 analogues.
The two known homoatomic anions available from dissolution of
precursor alloys are Bi42- and Bi22-, both of which have been found
to give rise to large bimetallic cluster systems when reacted with
transition metal reagents.38–41
3-
The behaviour of ‘naked’ or substituent-free group 14 and group
15 Zintl ions in solution is governed by their geometric fluxionality.
In early solution NMR studies, Baudler and co-workers used 31
P
NMR spectroscopy to study the high degree of fluxionality of the
P73- systems.10 At room temperature the only observable feature in
3-
the 31P NMR spectrum of P7 is a non-specific broad resonance.
If the temperature is raised to 50 ◦C a singlet at d = -119 ppm is
observed as at this temperature all seven P atoms are equivalent
on the NMR timescale. However, below -35 ◦C, the 31P NMR
spectrum consists of three separate resonances at d = -57, -103
and -162 ppm with an intensity ratio of 1 : 3 : 3, corresponding
to the single P atom at the apex, the three negatively-charged
two coordinate bridging P atoms, and the three basal P atoms,
respectively. Similar behaviour in solution is observed for the
Sn94- cluster, which also shows a single 119/117Sn resonance at room
temperature.48
3-
In solution, the E7 (E = P, As) cluster anions act as strong
3-
The rich chemistry of the E7 (E = P, As, Sb) clusters and
reducing agents capable of the reductive bond activation of
relatively strong bonds such as the N–C single bonds in species
such as [NR4]+.18–20 Similar reductive bond cleavage has been
reported for the group 14 cluster anions E94- (E = Si–Pb) towards
a series of homoleptic organometallic reagents such as M(C6H5)2
(M = Zn, Cd, Hg) and Cu5(Mes)5.42–46 In an attempt to observe
whether analogous M–C bond activation could also be achieved
by the Zintl ions of group 15 we carried out a series of studies
the diverse nature of their reactivity towards transition metal and
main-group reagents prompted us to explore the reactivity of these
species towards several reagents at the transition metal/main-
group element divide. Building on recent research which has found
that group 14 Zintl ions are capable of reacting with homoleptic
organometallic reagents such as M(C6H5)2 (M = Zn, Cd, Hg) and
Cu5Mes5 (Mes = 2,4,6-Me3C6H2) to yield functionalized clusters
i
3-
such as E9ZnR3- (E = Si, Ge, Sn, Pb; R = C6H5, Pr, Mes),42,43
exploring the reactivity of E7 (E = P–Sb) towards a family of
10- 45
3-
E9Cd(C6H5)3- (E = Sn, Pb),44 Hg3(Ge9)4
,
and Cu@E9 (E =
organometallic reagents, the results of which we report herein.
Sn, Pb),46 we set out to explore the reactivity of group 15 Zintl
ions towards similar homoleptic organometallic reagents. The
results of these studies are reported herein and have resulted in
the synthesis, isolation and characterisation of a family of unique
cluster anions such as those found in [K(2,2,2-crypt)]4Cu2E14 (E =
P (1), As (2)), [K(2,2,2-crypt)]4ZnE14 (E = P (3), As(4)), [K(2,2,2-
crypt)]4CdP14·6py (5) and [K(2,2,2-crypt)]2E7InPh2 (E = P (6),
As (7)).
3-
Reactivity studies of E7 (E = P, As) towards Cu5(Mes)5
Reaction of ethylenediamine solutions of K3E7 (E
=
P,
As) and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-
[8.8.8]hexacosane) with mesitylcopper(I) (‘CuMes’) in a 1 : 1
stoichiometric ratio (K4E9–CuMes) yielded [K(2,2,2-crypt)]+ salts
of the novel copper-bridged clusters [Cu2(E7)2)]4- (E = P (1); As
(2)), the first examples of copper-functionalised group 15 Zintl
ions. These reactions are analogous to those observed for group 14
Zintl ions with M(C6H5)2 (M = Zn, Cd, Hg)42–45 and Cu5(Mes)5,46
and proceed via the reduction of the M–C bond of the post-
transition metal organometallic reagent. This reaction has been
previously found to yield an aryl (phenyl or mesityl) anion, which
can abstract a proton from the ethylenediamine solvent giving rise
to an amide and the corresponding protonated aryl substituent.
2. Results and discussion
The cluster anions of group 14 (EIV 4-; EIV = Si–Pb) and 15
9
(EV 3-; EV = P–Sb) are available by dissolution of stoichiometric
7
bimetallic alloys of alkali metals and main group elements (A4EIV
9
and A3EV7, respectively) in basic, polar, non-protic solvents such
as ammonia and ethylenediamine. Despite the many similarities
that exist between these two families of Zintl anions, there are
certain fundamental differences which set them apart. The most
notable of these is that while the nine-atom deltahedra of group
Compound
diffraction data as
2
was characterised by single-crystal X-ray
[K(2,2,2-crypt)]+ salt in [K(2,2,2-
a
crypt)]4[Cu2(As7)2]·2en (Fig. 2). Details of the crystallographic
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 426–436 | 427
©

Table 1 Selected X-ray data collection and refinement parameters for [K(2,2,2-crypt)]4Cu2As14 (2), [K(2,2,2-crypt)]4ZnP14·6py (3), [K(2,2,2-
crypt)]4CdP14·6py (5) and [K(2,2,2-crypt)]2P7InPh2 (6)
Compound
2
3
5
6
Chemical formula
FW
C76H160As14Cu2K4N12O24
2958.52
C102H174K4N14O24P14Zn
C102H174CdK4N14O24P14
C48H82InK2N4O12P7
1316.99
Monoclinic
P21/c
2635.90
Orthorhombic
Fdd2
2682.93
Orthorhombic
Fdd2
Crystal system
Space group
Z
Triclinic
¯
P1
1
8
8
4
˚
a/A
15.1540(2)
15.1810(2)
15.7640(2)
111.460(1)
90.070(1)
118.900(1)
2883.41(7)
1.704
0.71073
150
4.565
595
19 140
23.6766(2)
74.2498(6)
15.1492(2)
90
90
90
26632.0(5)
1.315
0.71073
150
0.545
718
23.5977(2)
75.1887(8)
15.1082(1)
90
90
90
26806.2(4)
1.330
0.71073
150
0.521
726
11.4911(1)
24.2435(2)
22.4105(2)
90
92.211(1)
90
6238.57(9)
1.402
0.71073
150
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
r
calcd/g cm-3
˚
l(MoKa)/A
T/K
m/mm-1
0.748
667
21 140
10 893 (0.062)
No. refined parameters
Reflections collected
Unique reflections
14 850
14 850 (0.084)
10 425
10 425 (0.046)
10 050 (0.035)
(Rint
)
R1/wR2,a I ≥ 2sI (%)
R1/wR2,a all data (%)
4.81/13.18
5.83/13.72
4.77/10.60
6.87/11.73
5.41/10.86
7.69/11.61
5.90/18.35
7.16/19.06
2
a R1 = [RꢀFo| - |Fcꢀ]/R|Fo|; wR2 = {[Rw[(Fo)2 - (Fc)2]2]/[Rw(Fo2)2]}1/2; w = [s (Fo)2 + (AP)2 + BP]-1, where P = [(Fo)2 + 2(Fc)2]/3 and the A and B
values are 0.0703 and 13.18 for 2, 0.0558 and 49.79 for 3, 0.0435 and 162.06 for 5 and 0.1071 and 28.36 for 6.
data collection are given in Table 1. The single-crystal X-ray
structure of 2 reveals two seven-atom arsenic clusters that are
bridged by a diatomic copper moiety giving rise to an anionic
dimer, [Cu2(As7)2]4- (Fig. 2). The [Cu2(As7)2]4- cluster has Ci point
symmetry with a crystallographic centre of inversion located at
the centre of the Cu–Cu bond. The geometry exhibited by the
cluster anion is highly unusual and to our knowledge there is only
one other literature-reported example in which a dimer of metal
atoms bridges two seven-atom clusters giving rise to a charged
‘molecular alloy’, c.f. [Pd2(As7)2]4-, however there are notable
structural differences between the two anions.30 The structure of
˚
Database (CSD) reveals a mean bond distance of 2.747 A for
the 1339 species that display copper–copper interactions.50 This
copper dimer bridges two crystallographically related seven atom
cluster anions. The two seven atom clusters maintain the general
nortricyclane structure of the As73- precursor without undergoing
major geometric distortions. There is a significant lengthening of
one of the bond distances of the triangular base of the cluster (As5–
As6) which exhibits a distance of 2.772(1) A. This is approximately
0.3 A longer than the other two analogous distances, 2.465(1)
and 2.456(1) A for As5–As7 and As6–As7, respectively, and is
a direct result of metal functionalisation (a selected list of bond
distances is given in Table 2). Cu1 sits above four arsenic atoms
of one of the seven-atom cages (atoms As2, As3, As5, As6) and
this causes some distortion to the structure of the cluster anion.
This distortion has been previously reported for species such as
˚
˚
˚
2+
the anionic component of 2 exhibits a Cu2 dimer, which bridges
3-
two As7 anions. Clearly, the assignment of oxidation states in
species such as this is largely a formalism as the bonding in these
clusters is expected to be fundamentally covalent on account of the
negligible electronegativity difference between copper and arsenic.
˚
The Cu–Cu internuclear distance in the cluster anion is 2.445(2) A,
4-
˚
Table 2 Selected bond distances (A) for the [Cu2(As7)2] cluster anion
which is relatively short for a copper-copper bond (the atomic
radius of copper is 1.35 A).49 A survey of the Cambridge Structural
˚
˚
Bond distances/A
As1–As2
As1–As3
As1–As4
As2–As5
As3–As6
As4–As7
As5–As6
As5–As7
As6–As7
Cu1–Cu1A
Cu1–As2
Cu1–As3
Cu1–As5
Cu1–As6
Cu1–As2A
2.446(1)
2.423(1)
2.361(1)
2.400(1)
2.375(1)
2.365(1)
2.772(1)
2.465(1)
2.456(1)
2.445(2)
2.690(1)
2.490(1)
2.479(1)
2.435(1)
2.409(1)
Fig. 2 Thermal ellipsoid plot of the [Cu2(As7)2]4- cluster anion present in
sample 2. Anisotropic displacement ellipsoids pictured at 50% probability
level.
428 | Dalton Trans., 2010, 39, 426–436
This journal is
The Royal Society of Chemistry 2010
©

[Pd2(As7)2]4- and [As7M(CO)3]3- (M = Cr, Mo, W),22,23,30 and has
reveals no significant mass envelopes corresponding to any species
1
been rationalised as a nortricyclane to norbornadiene transition
other than the [Cu2(P7)2]4- cluster cage. Low temperature 31P{ H}
3-
of the E7 cluster core, resulting in the cleavage of one the
NMR experiments show seven well-resolved resonances arising
from seven magnetically inequivalent nuclei corresponding to a
cluster anion with a geometry analogous to that discussed above
for [Cu2(As7)2]4- (isomer 1, Fig. 4). Two of the observed resonances
overlap significantly giving rise to a multiplet which integrates
with twice the intensity of the other five resonances. The seven
multiplets occur at -25.5, -50.3, -77.9, -110.6, -111.1, -123.3
and -234.1 ppm. A second isomer, corresponding to an ‘activated’
Cu22+ bridged dimer of norbornadiene-like P73- clusters (isomer 2,
see Fig. 4), gives rise to three broader resonances which integrate
in a 2 : 1 : 4 ratio. The resonances corresponding to this second
isomer occur at -32.4, -42.5 and -82.2 ppm and correspond to
P1/P7, P4 and P2/P3/P5/P6, respectively. A diagram highlighting
the proposed mechanism for interconversion between the two
isomeric species is pictured in Fig. 4. We have tentatively assigned
the resonances arising from isomer 1 based on their multiplicity,
coupling constants and relative chemical shifts, however further
NMR experiments are necessary if we are to unambiguously assign
each of the multiplets to each of the magnetically inequivalent
phosphorus nuclei. 1H NMR and proton-coupled 31P NMR
spectra were also run on sample 1 in order to rule out the
possibility of the existence of cluster anions containing protonated
seven atom cluster cages (E7H2-), a phenomenon that has been
previously reported for related functionalised cluster anions.19,23,25
The 1H NMR spectrum revealed no protic resonances other that
those arising from the 2,2,2-crypt and the low temperature proton
coupled 31P NMR spectrum was found to be identical to that
obtained during the proton decoupled experiment.
E–E bonds of the triangular base of E73-. Interestingly, it is worth
noting that the degree of E–E bond weakening in the case of the
[Cu2(As7)2]4- cluster core is significantly less than that observed for
[Pd2(As7)2]4- and [As7M(CO)3]3- as the analogous As–As bonds are
˚
substantially longer (av. 3.084 A) for the latter two cluster anions.
Cu1 exhibits short bonding distances to atoms As3, As5 and As6
3-
from one of the As7 cages with values of 2.490(1), 2.479(1) and
˚
2.435(1) A, respectively. The interaction between Cu1 and As2 is
˚
˚
substantially longer (approx. 0.2 A) at 2.690(1) A, indicating a
weaker interaction with this particular atom of the cage. Another
interesting structural feature is the short Cu1–As2A bond distance
˚
of 2.409(1) A, which exists between Cu1 and an arsenic atom
from the second, more distant As73- cage (As2A). As a result each
copper atom (Cu1) has a coordination number of six, with bonds
to a neighbouring copper (Cu1A), and five arsenic atoms: four
from one seven-atom cluster anion (three short and one long),
and one from the more distant cage.
Our attempts to grow single-crystal X-ray diffraction quality
crystals of the analogous [Cu2(P7)2]4- anion proved unsuccessful,
however an elemental analysis of sample 1 and solution phase
experiments such as multielement NMR spectroscopy and electro-
spray mass-spectrometry indicate that such a species is available
via the reaction of K3P7 and mesityl-copper(I). The [Cu2(P7)2]4-
cluster anion was found to be highly fluxional in solution at
room temperature on the NMR timescale. A room temperature,
1
the 31P{ H} NMR spectrum of a d7-DMF solution of [K(2,2,2-
crypt)]4[Cu2(P7)2] revealed the existence of three broad resonances
at -24.3, -65.0 and -108.3 ppm, in addition to an extremely
broad resonance, spanning several hundred MHz, centred at
approximately -65 ppm. Upon cooling the sample to -50 ◦C, these
1
resonances resolve giving rise to a total of ten unique 31P{ H}
resonances (pictured in Fig. 3) which we believe arise from the
presence of two different structural isomers of the [Cu2(P7)2]4-
anion. This hypothesis is further corroborated by the fact that
positive and negative ion mode electrospray mass-spectrometry
Fig. 4 Schematic representation of the two possible isomers of the
[Cu2(P7)2]4- cluster in solution. Isomer 1 is isostructural with the cluster
anion characterized by single-crystal X-ray diffraction in sample 2. Isomer
2 arises as a result of the ‘activation’ of the bond present between P5 and
P6 to give rise to a norbornadiene-like structure.
◦
1
Fig. 3 Low temperature (-50 C) 31P{ H} NMR spectrum of a d7-DMF
solution of sample 1. Resonances are labelled as per Fig. 2. Resonances
highlighted in green correspond to the isomer present in the single-crystal
X-ray structure (isomer 1). The broader resonances highlighted in red arise
from the ‘activated’ norbornadiene-like isomer (isomer 2).
[Cu2(P7)2]4- and [Cu2(As7)2]4- were characterised in solution by
positive and negative ion mode electrospray mass-spectrometry of
DMF solutions of 1 and 2, respectively. Cluster peaks appear
as distinct mass envelopes, which allows for the unequivocal
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 426–436 | 429
©

assignment of cluster-based signals. In the negative ion mode
spectra, the clusters were observed with reduced charges as a
result of the oxidation of the parent cluster anions during the
ionization process. This has been previously reported for the
electrospray mass-spectra of other Zintl ions in the literature
and is a common phenomenon, presumably arising as a result
of the electrical potential difference applied to samples during
the ionisation process. Both positive and negative ion mode
spectra showed evidence of extensive ion pairing between anions
and charge-balancing cations such as K+ and [K(2,2,2-crypt)]+.
As a result, a negative ion mode spectrum of a solution of 1
showed signals at the following m/z values: 560.6, 600.5, 1016.8,
samples after several days. Attempts to grow crystals of the Zn/As
analogue, [K(2,2,2-crypt)]4[Zn(As7)2] (4), yielded copious amounts
of orange crystals, which appeared to be of good quality, however
single-crystal X-ray data reveal extensive crystallographic disorder
that could not be satisfactorily modelled. The crystalline material
is of sufficient quality to unquestionably reveal the presence of
the [Zn(As7)2]4- anion, but the disorder arising from one of the
[K(2,2,2-crypt)]+ cations makes it unsuitable for publication or for
the meaningful discussion of interatomic distances.51
Samples 3 and 5 are isostructural. The single-crystal X-ray
structure of each sample reveals the presence of a [M(P7)2]4-
cluster (M = Zn, Cd; Fig. 5 and 6, respectively) accompanied by
four charge-balancing [K(2,2,2-crypt)]+ cations and six pyridine
molecules. The cluster anions have C2 point group symmetry with a
two-fold rotational axis running through the bridging metal atoms
rendering the two seven-atom cluster cages crystallographically
equivalent. The central Zn and Cd atoms adopt distorted tetra-
hedral coordination environments in which two of the negatively-
charged phosphorus atoms from each of the two E73- cages (atoms
P2 and P3) coordinate to the metal. In purely ionic terms, the
clusters can be rationalised as consisting of a central metal cation
-
1393.1 and 1807.3, corresponding to [Cu2P14]-, {K[Cu2P14]} ,
-
-
{K[K(2,2,2-crypt)][Cu2P14]} , {[K(2,2,2-crypt)]2[Cu2P14]} , and
-
{[K(2,2,2-crypt)]3[Cu2P14]} , respectively. Similarly, the positive
ion mode revealed peaks at m/z values of 1809.2, 2223.5
and 2637.6 corresponding to the ion-paired species {[K(2,2,2-
+
+
crypt)]3[Cu2P14]} , {[K(2,2,2-crypt)]4[Cu2P14]} , and {[K(2,2,2-
+
crypt)]5[Cu2P14]} . Electrospray mass-spectrometry measurements
of sample 2 also revealed peaks corresponding to related clus-
ter anions. The negative ion mode spectrum showed mass-
envelopes with m/z values of 1176.0, 1216.0, 1592.4, 2008.5 and
3-
in the 2+ oxidation state and two P7 cages, giving rise to the
2422.4, corresponding to [Cu2As14]-, {K[Cu2As14]} , {[K(2,2,2-
overall 4- charge associated with the dimeric cluster units. The
seven-atom cluster cages in both [Zn(P7)2]4- and [Cd(P7)2]4- are
largely unperturbed by coordination to the post-transition metal
bridges. Each of the coordinated phosphorus atoms (P2, P3, P2A
and P3A) acts as a two electron donor (Lewis base) making the
total electron count of the central metal atom eighteen electrons.
-
-
-
crypt)][Cu2As14]} , {[K(2,2,2-crypt)]2[Cu2As14]} , and {[K(2,2,2-
-
crypt)]3[Cu2As14]} . Positive ion mode mass-spectrometry revealed
peaks at m/z values of 2839.0, 2877.0, and 3253.3 arising
+
from the ion-pairs {[K(2,2,2-crypt)]4[Cu2As14]} , {K[K(2,2,2-
+
+
crypt)]4[Cu2As14]} , and {[K(2,2,2-crypt)]5[Cu2As14]} , respec-
tively. These measurements in addition to the 31P NMR studies
carried out on sample 1 clearly show that the [Cu2(E7)2]4- (E = P,
As) cluster anions maintain their structural integrity in solution.
3-
As we mentioned previously, for each P7 cage there are three
phosphorus atoms, which formally carry a negative charge (P2,
P3 and P4) and each of these atoms has two lone-pairs associated
3-
Reactivity studies of E7 (E = P, As) towards M(C6H5)2
(M = Zn, Cd)
Ethylenediamine solutions of K3E7 (E = P, As) and 2,2,2-crypt
were also found to react with the diphenyl group 12 reagents
M(C6H5)2 (M = Zn, Cd). These reactions give rise to [K(2,2,2-
crypt]+ salts of the metal bridged dimers [M(E7)2)]4- (M = Zn:
E = P (3); As (4); M = Cd: E = P (5)). The reactions are
analogous to those discussed previously for Cu5(Mes)5, and
proceed via the reductive cleavage of both M–C bonds of the
homoleptic organometallic reagent, yielding novel functionalised
cluster anions where two seven-atom group 15 clusters are bridged
by a post-transition metal. Each of the [M(E7)2)]4- cluster anions
Fig. 5 Thermal ellipsoid plot of the [Zn(P7)2]4- cluster anion present in 3.
Anisotropic displacement ellipsoids pictured at 50% probability level.
3-
can be regarded as being composed of two E7 cluster cages
bridged by a 2+ cation, ultimately giving rise to the overall
4- charge associated with such species. Interestingly, attempts
to synthesise an analogous [Cd(As7)2]4- cluster proved entirely
unsuccessful as indicated by the mass-spectra of crude reaction
mixtures of K3As7 and Cd(C6H5)2, which did not show evidence
of any cadmium-containing cluster anions. Similarly, attempts to
3-
synthesise related clusters from the Sb7 precursor also proved
unfruitful according to electrospray mass-spectrometry.
Compounds 3 and 5 were characterised by single-crystal X-ray
diffraction as two isostructural phases [K(2,2,2-crypt)]4MP14·6py
(M = Zn (3), Cd (5)). Crystals suitable for X-ray diffraction
were grown from pyridine solutions, which were carefully layered
with anhydrous toluene yielding compositionally pure crystalline
Fig. 6 Thermal ellipsoid plot of the [Cd(P7)2]4- cluster anion present in
sample 5. Anisotropic displacement ellipsoids pictured at 50% probability
level.
430 | Dalton Trans., 2010, 39, 426–436
This journal is
The Royal Society of Chemistry 2010
©

◦
◦
4-
4-
˚
˚
Table 3 Selected bond distances (A) and angles ( ) for the [Zn(P7)2]
Table 4 Selected bond distances (A) and angles ( ) for the [Cd(P7)2]
cluster anion
cluster anion
˚
˚
Bond distances/A
Bond distances/A
P1–P2
P1–P3
P1–P4
P2–P5
P3–P6
P4–P7
P5–P6
P5–P7
P6–P7
Zn1–P2
Zn1–P3
2.204(1)
2.208(1)
2.163(1)
2.168(1)
2.166(1)
2.139(1)
2.241(1)
2.260(1)
2.250(1)
2.474(1)
2.498(1)
P1–P2
P1–P3
P1–P4
P2–P5
P3–P6
P4–P7
P5–P6
P5–P7
P6–P7
Cd1–P2
Cd1–P3
2.211(2)
2.203(2)
2.161(2)
2.165(2)
2.164(2)
2.137(2)
2.229(2)
2.247(2)
2.263(2)
2.675(2)
2.658(2)
Bond angles/◦
Bond angles/◦
P2–Zn1–P3
82.89(3)
P2–Cd1–P3
77.31(4)
P2–Zn1–P2A
P2–Zn1–P3A
P3–Zn1–P3A
127.04(5)
124.32(3)
120.86(5)
P2–Cd1–P2A
P2–Cd1–P3A
P3–Cd1–P3A
124.89(7)
126.63(5)
131.90(7)
3-
with them allowing them to act as nucleophiles. Each P7 cage
acts as a chelating ligand donating a total of four electrons to the
bridging metal centre. This chelating binding mode gives rise to
the distorted tetrahedral coordination geometry about the central
zinc atom as the bite angle of the seven atom cage is relatively
small, 82.89(3)◦. The Zn–P bonds in [Zn(P7)2]4- are 2.474(1) and
1
Table 5 31P-31P NMR coupling constants (Hz) taken from the 31P{ H}
NMR spectrum of the [Zn(P7)2]4- anion
-42.9 -14.8 -14.8 -56.2 -162.3 -162.3 -104.7
d/ppm
P1
P2
P3
P4
P5
P6
P7
˚
-42.9 P1
—
256
—
-161
12
412
6
10
256
-161 12
—
12
6
412
10
337
27
412
6
-5
—
-17
203
27
6
-42
10
10
420
203
203
—
2.498(1) A, for Zn1–P2 and Zn1–P3, respectively. These distances
-14.8 P2 256
-14.8 P3 256
-56.2 P4 337
-162.3 P5 27
-162.3 P6 27
-104.7 P7 -42
are substantially longer than the mean Zn–P bond distance of
2.405 A uncovered by a search of the Cambridge Structural
Database,50 however they are of comparable magnitude to the
12
—
-5
-5
420
412
-5
˚
-17
˚
—
values of 2.500 (av) and 2.505 (av) A reported for closely-related
203
molecular zinc-telluride clusters.52 A list of selected bond distances
and angles is given in Table 3. The bond distances of the seven atom
cluster cages are entirely unremarkable and a detailed inspection
of these values reveals that the cages experience very little deviation
away from the nortricyclane structure of the ‘naked’ cluster anions
upon complexation to zinc. Cadmium–phosphorus interatomic
distances in the [Cd(P7)2]4- anion present in sample 5 display values
in Fig. 7 (a table of coupling constants is provided in Table 5). A
similar 31P{ H} spectrum, albeit of lower resolution, was recorded
1
for the [Cd(P7)2]4- anion and also revealed five multiplet resonances
which occurred at -4.5, -36.0, -82.1, -134.7 and -161.0 ppm (see
ESI).† These values are in good agreement with those observed
for [Zn(P7)2]4-. Proton-coupled 31P NMR spectra were also run on
samples 3 and 5 and were found to be identical to those observed
for the proton decoupled experiments. 1H NMR spectroscopy on
samples 3 and 5 revealed no protic resonances other than those
arising from the [K(2,2,2-crypt)]+ cations.
˚
of 2.675(2) and 2.658(2) A (a selected list of bond distances is
provided in Table 4). Analogously to what we observed for the zinc
analogue, these distances are rather long compared to the mean
Cd–P distance revealed by a search of the structural database
(2.584 A), yet consistent with values observed for negatively-
50
˚
charged clusters such as the [Li(THF)4]2{[(Ph)2P]10Cd4} cluster
53
˚
cage, which has a mean Cd–P bond distance of 2.647 A.
Further corroboration of the existence of the cluster an-
ions in solution was obtained by means of electrospray mass-
spectrometry, which revealed the existence of the [M(E7)2]4-
clusters in samples 3, 4 and 5. As discussed earlier for samples
1 and 2, extensive ion pairing was observed between the cluster
anions and K+ and [K(2,2,2-crypt)]+ cations in both the negative
and positive ion mode spectra. As a result, the negative ion mode
spectra of 3–5 all reveal peaks corresponding to the [M(E7)2]-,
[KM(E7)2]- ions. Similarly, the positive ion mode spectra of all
three samples revealed peaks corresponding to the {[K(2,2,2-
31P{ H} solution NMR studies on samples 3 and 5 revealed
1
well-resolved spectra at room-temperature. The 31P{ H} NMR
1
spectrum of each sample exhibits five characteristic multiplets
corresponding to each of the five magnetically inequivalent
environments of phosphorus nuclei. The 31P{ H} NMR spectrum
1
of sample 3 reveals five resonances at -14.8, -42.9, -56.2, -104.7
and -162.3 ppm. The resonance at -14.8 ppm arises from the two
magnetically equivalent phosphorus atoms P2 and P3, while that at
-162.3 ppm corresponds to the P5 and P6 positions. Resonances
at -42.9, -56.2 and -104.7 ppm arise as a result of atoms P1,
P4 and P7, respectively. The spectrum was of sufficient quality
for it to be modelled and the calculated spectrum was found to
nicely match the experimentally determined results as highlighted
+
crypt)]4[M(E7)2]} cation. Multiple additional peaks, which were
unique to the spectra of individual samples were also observed as
a result of ion-pairing between [M(E7)2]4- and charge-balancing
cations (see Experimental).
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 426–436 | 431
©

◦
2-
˚
Table 6 Selected bond distances (A) and angles ( ) for the [P7In(C6H5)2]
cluster anion
˚
Bond distances/A
P1–P2
P1–P3
P1–P4
P2–P5
P3–P6
P4–P7
P5–P6
P5–P7
P6–P7
In1–P2
In1–P3
In1–C1
In1–C7
2.203(2)
2.214(2)
2.157(2)
2.184(2)
2.166(2)
2.142(2)
2.261(2)
2.246(2)
2.248(2)
2.604(1)
2.551(2)
2.238(6)
2.195(5)
Bond angles/◦
P2–In1–P3
P2–In1–C1
P2–In1–C7
P3–In1–C1
P3–In1–C7
C1–In1–C7
80.33(4)
114.0(2)
113.9(1)
114.0(1)
120.5(2)
111.0(2)
1
Fig. 7 (a) Calculated 31P{ H} NMR spectrum for the [Zn(P7)2]4- anion.
1
(b) Experimentally recorded 31P{ H} NMR spectrum for a d5-pyridine
solution of sample 3. Resonances are labelled with the same numbering
scheme employed in Fig. 5.
3-
Reactivity studies of E7 (E = P, As) towards In(C6H5)3
The last of the M–C bond activation experiments we carried
out over the course of these studies focused on the reactivity
3-
of E7 (E = P, As) cluster anions towards In(C6H5)3. Reaction
of ethylenediamine solutions of K3E7 (E = P, As) and 2,2,2-
crypt with triphenylindium in a 1 : 1 stoichiometric ratio yielded
[K(2,2,2-crypt)]+ salts of the diphenylindium functionalised cluster
anions [E7In(C6H5)2]2- (E = P (6); As (7)). Changes to the overall
stoichiometry did not result in significant changes to the outcome
of the reactions and the diphenylindium functionalised cluster
anions were repeatedly isolated as the sole crystalline reaction
3-
Fig. 8 Thermal ellipsoid plot of the [P7In(C6H5)2]2- cluster anion
present in sample 6. Anisotropic displacement ellipsoids pictured at 50%
probability level.
products. Attempts to synthesise analogous clusters with Sb7
proved entirely unsuccessful. In situ monitoring of reactions
between K3Sb7 and In(C6H5)3 failed to reveal the presence of any
In/Sb containing adducts.
Single-crystal X-ray diffraction quality crystals of [K(2,2,2-
crypt)]2P7In(C6H5)2 (6) were obtained by carefully layering a
pyridine solution of sample 6 with toluene. The asymmetric unit
of the crystal reveals the presence of a crystallographically unique
dianionic [P7In(C6H5)2]2- moiety (pictured in Fig. 8) which is
accompanied by two [K(2,2,2-crypt)]+ cations. Bonding between
coordination environment with an acute P2–In1–P3 bite angle of
80.33(4)◦. The In1–P2 and In1–P3 bond distances of 2.604(1) and
˚
2.551(2) A, respectively, are comparable to similar bond lengths
reported in the literature.54 The In–C bonds in [P7In(C6H5)2]2-
˚
(2.238(6) and 2.195(5) A) are also of similar dimensions to those
observed for other anionic indium organometallics. A list of
selected bond lengths and angles is provided in Table 6.
3-
the seven atom P7 cluster cage and the [In(C6H5)2]+ fragment is
similar to what we have discussed earlier for the [M(P7)2]4- (M =
Attempts to grow single-crystal X-ray quality crystals of the
arsenic analogue, compound 7, proved unsuccessful and we were
only able to isolate the product as a non-crystalline solid. However,
3-
Zn, Cd) clusters. The P7 cage acts as a chelating four electron
donor to the indium metal centre via two of the negatively charged
atoms (P2 and P3). As a result, In1 adopts a distorted tetrahedral
1
elemental analysis of the solid sample, H NMR spectroscopy
432 | Dalton Trans., 2010, 39, 426–436
This journal is
The Royal Society of Chemistry 2010
©

and electrospray mass-spectrometry provide strong evidence of
the availability of the [As7In(C6H5)2]2- cluster anion.
synthesised from CuCl (97+%, Strem) and MesMgBr (1.0 M THF,
Aldrich) in THF according to a previously reported synthetic
procedure.56 Cd(C6H5)2 was synthesised from CdCl2 (99+%,
Strem) and (C6H5)MgCl (2.0 M THF, Aldrich) in THF according
to a modified literature-reported synthesis.57 Similarly, In(C6H5)3
was also synthesised according to a modified literature report from
InCl3 (99.999%, Strem) and Li(C6H5) (1.8 M in nBu2O, Aldrich) in
THF.58 Zn(C6H5)2 (99%, Strem) was used as received. 2,2,2-crypt
(99+%, Merck) was used as received after careful drying under
vacuum. Toluene (99.9%, Rathburn), THF (99.9%, Rathburn)
and DMF (99.9%, Rathburn) were purified through an MBraun
MB SPS-800 solvent system. Ethylenediamine (99%, Aldrich)
and pyridine (99.9%, Rathburn) were distilled over sodium metal
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 solvents were stored under argon in gas-tight ampoules. In
1
The room temperature 31P{ H} solution NMR spectrum of
sample 6 exhibits five multiplet resonances corresponding to each
of the five magnetically inequivalent phosphorus nuclei of the
[P7In(C6H5)2]2- cluster core. These occur at 3.6, -50.7, -67.8, -76.8
and -170.1 ppm. The multiplets at 3.6 and -170.1 integrate at twice
the intensity of the remaining three resonances and correspond to
the P2/P3 and P5/P6 pairs, respectively. The resonances at -50.7,
-67.8 and -76.8 ppm arise as a result of atoms P1, P4 and P7, re-
spectively. This room temperature spectrum is exceptionally well-
resolved and can be modelled giving rise to a calculated spectrum
that is in excellent agreement with the experimentally determined
spectrum. A figure comparing experimental and calculated spectra
and a table of 31P-31P coupling constants is provided in the ESI.†
1
The H NMR spectra for samples 6 and 7 reveal that the two
phenyl rings of the [E7In(C6H5)2]2- cluster anions are magnetically
inequivalent. There are two distinct families of resonances arising
from the ortho-, meta- and para-proton positions of the two phenyl
˚
addition toluene was stored over activated 3 A molecular sieves
(Acros).
1
ring systems in the aromatic region of the H NMR spectrum.
This indicates that there is no interconversion between the two
aromatic rings on the NMR timescale and that in solution the
cluster geometry pictured in Fig. 6 is maintained. 2D COSY
spectra were run in order to determine which groups of resonances
arose from each of the phenyl rings. As a result, we were able to
ascertain that a d5-pyridine solution of 6 reveals three resonances
at 8.85, 7.46 and 7.29 ppm arising from one phenyl ring system,
and a second group of aromatic proton resonances at 8.20, 7.18
and 7.12 ppm corresponding to the second phenyl ring. Similarly,
the 1H NMR spectrum of a d5-pyridine solution of 7 reveals one
group of aromatic proton resonances at 8.86, 7.47 and 7.29 ppm,
and a second set of resonances at 8.23, 7.20 and 7.09 ppm. The
inequivalence of the aromatic rings was further corroborated
[K(2,2,2-crypt)]4Cu2P14 (1)
K3P7 (94 mg, 0.282 mmol), Cu5(Mes)5 (69 mg, 0.075 mmol)
and 2, 2, 2-crypt (339 mg, 0.902 mmol) were dissolved in
approximately 2 mL of ethylenediamine in a Schlenk tube
yielding a brown solution that was stirred under argon for
approximately one hour. The resulting brown solution was filtered
into a crystallisation ampoule, layered with toluene and left to
crystallise. After several days red plate-like crystals of [K(2,2,2-
crypt)]4Cu2P14 were obtained in 36% yield (113 mg). These
crystals proved unsuitable for single-crystal X-ray diffraction
due to their small size and extensive twinning. Anal. calcd
for C72H144Cu2K4N8O24P14: C 38.88, H 6.53, N 5.04. Found:
C 38.72, H 6.42, N 5.00. ES- MS: m/z: 560.6 [Cu2P14]-,
1
by 13C{ H} NMR spectroscopy, which revealed a total of eight
-
-
resonances corresponding to two sets of inequivalent ipso-, ortho-,
meta- and para-carbon atoms.
600.5 {K[Cu2P14]} , 1016.8 {K[K(2,2,2-crypt)][Cu2P14]} , 1393.1
-
-
{[K(2,2,2-crypt)]2[Cu2P14]} , 1807.3 {[K(2,2,2-crypt)]3[Cu2P14]} .
+
Finally, compounds 6 and 7 were also characterised by negative
and positive ion mode electrospray mass-spectrometry. The nega-
tive ion mode electrospray spectra of 6 and 7 each revealed mass
ES+ MS: m/z: 1809.2 {[K(2,2,2-crypt)]3[Cu2P14]} , 2223.5
+
+
{[K(2,2,2-crypt)]4[Cu2P14]} , 2637.6 {[K(2,2,2-crypt)]5[Cu2P14]} .
1H NMR (300.2 MHz, d5-pyridine) d/ppm: 3.44 (48 H, s, 2,2,2-
-
3
envelopes arising from the [E7In(C6H5)2]-, {K[E7In(C6H5)2]} ,
crypt), 3.37 (48 H, t, JH-H = 5 Hz, 2,2,2-crypt), 2.35 (48 H, t,
-
1
and {[K(2,2,2-crypt)][E7In(C6H5)2]} ions. Similarly, the posi-
3JH-H = 5 Hz, 2,2,2-crypt). RT 31P{ H} NMR (202.4 MHz, d5-
tive ion mode of each sample also revealed mass-envelopes
pyridine) d/ppm:◦-24.3 (2 P, m), -65.0 (8 P, very broad), -108.3 (4
1
corresponding to the extensively ion paired species {[K(2,2,2-
P, broad m). -50 C 31P { H} NMR (202.4 MHz, DMF) d/ppm:
+
1
1
1
crypt)]3[E7In(C6H5)2]} .
-25.6 (1 P, Isomer 1, P3 ddd, JP-P = 364, JP-P = 287, JP-P =
158 Hz), -31.8 (2 P, Isomer 2, P1/P7 bm), -42.4 (1 P, Isomer 2,
P4, dd, 1JP-P = 378, 1JP-P = 370 Hz), -50.4 (1 P, Isomer 1, P1, m,
3. Experimental
1
1
2
1JP-P = 361, JP-P = 287, JP-P = 286, JP-P = 48 Hz), -77.9 (1 P,
Isomer 1, P4, ddd, 1JP-P = 445,1JP-P = 361, 2JP-P = 13 Hz), -82.1 (4
P, Isomer 2, P2/P3/P5/P6, bm), -110.8 (2 P, Isomer 1, P5/P6, m),
-123.2 (1 P, Isomer 1, P7, m, 1JP-P = 445, 1JP-P = 174, 1JP-P = 174,
Due to the highly air- and moisture-sensitive nature of the
products, all reactions and product manipulations were carried
out under an inert atmosphere using standard Schlenk-line or
glovebox techniques (MBraun UNIlab glovebox maintained at
< 0.1 ppm H2O and < 0.1 ppm O2). The intermetallic precursors,
K3E7 (E = P, As), were synthesised according to previously
reported synthetic procedures from stoichiometric mixtures of the
elements (K: 99.95%, Aldrich; P: 99.99%, Aldrich; As: 99%, Alfa
Aesar) heated between 550–900 ◦C for 72 h in sealed niobium
containers.55 In order to avoid the oxidation of the niobium vessels
at such high temperatures they were jacketed in flame-sealed
silica ampoules under vacuum prior to heating. Cu5(Mes)5 was
2JP-P = 48 Hz), -234.0 (1 P, Isomer 1, P2, m, 1JP-P = 362, 1JP-P
174, 1JP-P = 174 Hz).
=
[K(2,2,2-crypt)]4Cu2As14·2en (2)
K3As7 (96 mg, 0.150 mmol), Cu5(Mes)5 (27 mg, 0.030 mmol)
and 2,2,2-crypt (187 mg, 0.497 mmol) were dissolved in
approximately 2 mL ethylenediamine yielding a brown solution
that was stirred under argon for one hour. The resulting
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 426–436 | 433
©

reaction mixture was filtered into a crystallisation ampoule,
layered with toluene and left to crystallise. After several days
red/black block-like crystals of [K(2,2,2-crypt)]4Cu2As14·2en
suitable for X-ray diffraction were obtained in 61% yield
(134 mg). Anal. calcd for C76H160K4N12O24As14Cu2: C 30.84,
H 5.45, N 5.68. Found: C 30.73, H 5.30, N 5.78. ES- MS:
[K(2,2,2-crypt)]4CdP14·6py (5)
K3P7 (95 mg, 0.284 mmol), Cd(C6H5)2 (38 mg, 0.141 mmol) and
2,2,2-crypt (222 mg, 0.590 mmol) were dissolved in approximately
2 mL ethylenediamine giving rise to a brown solution that was
stirred under argon for one hour. The ethylenediamine solvent
was removed in vacuo yielding a brown solid, which was re-
dissolved in approximately 2 mL of pyridine. The resulting
brown solution was filtered into a crystallisation ampoule, layered
with toluene and left to crystallise. After 1 week red/orange
plate-like crystals of [K(2,2,2-crypt)]4CdP14·6py suitable for
X-ray diffraction were obtained in 43% yield (163 mg). Anal.
calcd for C102H174K4N14O24P14Cd: C 45.64, H 6.54, N 7.31.
Found: C 45.57, H 6.47, N 7.25. ES- MS: m/z 548.6 [CdP14]-,
-
m/z 1176.0 [Cu2As14]-, 1216.0 {K[Cu2As14]} , 1592.4 {[K(2,2,2-
-
-
crypt)][Cu2As14]} , 2008.5 {[K(2,2,2-crypt)]2[Cu2As14]} , 2422.4
-
{[K(2,2,2-crypt)]3[Cu2As14]} . ES+ MS: m/z 2839.0 {[K(2,2,2-
+
+
crypt)]4[Cu2As14]} ,
2877.0
{K[K(2,2,2-crypt)]4[Cu2As14]} ,
+
3253.3 {[K(2,2,2-crypt)]5[Cu2As14]} .
[K(2,2,2-crypt)]4ZnP14·6py (3)
-
-
588.6 {K[CdP14]} , 962.9 {[K(2,2,2-crypt)][CdP14]} , 1379.1
K3P7 (96 mg, 0.288 mmol), Zn(C6H5)2 (64 mg, 0.293 mmol)
and 2,2,2-crypt (338 mg, 0.898 mmol) were dissolved in ap-
proximately 2 mL of ethylenediamine giving rise to a yellow-
brown solution and was left to stir under argon for one hour.
The reaction mixture was subsequently reduced to dryness under
a dynamic vacuum yielding a yellow-brown solid which was
re-dissolved in approximately 2 mL pyridine (py) to give a
reddish-brown solution. The solution was filtered into a crys-
tallisation ampoule, layered with toluene and left to crystallise.
After several days red crystals of [K(2,2,2-crypt)]4ZnP14·6py
suitable for X-ray diffraction were obtained in 36% yield
(138 mg). Anal. calcd for C102H174K4N14O24P14Zn: C 46.46, H
6.66, N 7.44. Found: C 46.29, H 6.55, N 7.32. ES- MS:
-
-
{[K(2,2,2-crypt)]2[CdP14]} , 1793.4 {[K(2,2,2-crypt)]3[CdP14]} .
+
ES+ MS: m/z 2209.6 {[K(2,2,2-crypt)]4[CdP14]} , 2623.9
+
{[K(2,2,2-crypt)]5[CdP14]} . 1H NMR data (300.2 MHz, d5-
pyridine) d/ppm: 3.50 (48 H, s, 2,2,2-crypt), 3.43 (48 H, t, 3JH-H
=
5 Hz, 2,2,2-crypt), 2.41 (48 H, t, JH-H = 5 Hz, 2,2,2-crypt). 31P
NMR (121.4 MHz, d5-pyridine) d/ppm: -4.5 (4 P, m, P2/P3,
3
1
2
2
1JP-P = 377 Hz, JP-P = 273 Hz, JP-P = -60 Hz, JP-P = -47 Hz,
2JP-P = 42 Hz), -36.0 (2 P, m, P1, 1JP-P = 337 Hz, 1JP-P = 273 Hz,
2JP-P = -31 Hz, 2JP-P = 27 Hz), -82.1 (2 P, m, P4, 1JP-P = 425 Hz,
1JP-P = 337 Hz, 2JP-P = -60 Hz, 2JP-P = -5 Hz), -134.7 (2 P, m, P7,
1
2
2
1JP-P = 425 Hz, JP-P = 203 Hz, JP-P = -47 Hz, JP-P = -31 Hz),
1
1
2
-161.0 (4 P, m, P5/P6, JP-P = 377 Hz, JP-P = 203 Hz, JP-P
42 Hz, 2JP-P = 27 Hz, 2JP-P = -5 Hz).
=
-
m/z 498.5 [ZnP14]-, 536.3 {K[ZnP14]} , 911.1 {[K(2,2,2-
-
-
crypt)][ZnP14]} , 948.9 {K[K(2,2,2-crypt)][ZnP14]} . ES+ MS:
+
m/z 1746.7 {[K(2,2,2-crypt)]3[ZnP14]} , 1784.7 {K[K(2,2,2-
[K(2,2,2-crypt)]2P7In(C6H5)2 (6)
crypt)]3[ZnP14]} , 2160.8 {[K(2,2,2-crypt)]4[ZnP14]} . 1H NMR
+
+
(300.2 MHz, d5-pyridine) d/ppm: 3.50 (48 H, s, 2,2,2-crypt), 3.42
K3P7 (96 mg, 0.288 mmol), In(C6H5)3 (53 mg, 0.152 mmol) and
2,2,2-crypt (226 mg, 0.601 mmol) were dissolved in approximately
2 mL of ethylenediamine giving rise to an orange/brown solution
that was stirred under argon for one hour. The ethylenediamine
solvent was then removed under a dynamic vacuum yielding a
red solid, which was redissolved in approximately 2 mL pyridine
to give a dark red/brown solution. The pyridine solution was
filtered into a crystallisation ampoule, layered with toluene and
left to crystallise. After 2 weeks yellow crystals of [K(2,2,2-
crypt)]2P7In(C6H5)2 suitable for single-crystal X-ray diffraction
formed in 63% yield (126 mg). Anal. calcd for K2C48H82N4O12P7In:
C 43.75, H 6.28, N 4.25. Found: C 43.79, H 6.28, N 4.29.
3
3
(48 H, t, JH-H = 5 Hz, 2,2,2-crypt), 2.39 (48 H, t, JH-H = 5 Hz,
2,2,2-crypt). 31P NMR (121.4 MHz, d5-pyridine) d/ppm: -14.8 (4
P, m, P2/P3, 1JP-P = 412 Hz, 1JP-P = 256 Hz, 2JP-P = 12 Hz, 2JP-P
=
=
=
2
1
1
10 Hz, JP-P = 6 Hz), -42.9 (2 P, m, P1, JP-P = 337 Hz, JP-P
256 Hz, 2JP-P = -42 Hz, 2JP-P = 27 Hz), -56.2 (2 P, m, P4, 1JP-P
1
2
2
420 Hz, JP-P = 337 Hz, JP-P = 12 Hz, JP-P = -5 Hz), -104.7 (2
P, m, P7, 1JP-P = 420 Hz, 1JP-P = 203 Hz, 2JP-P = -42 Hz, 2JP-P
=
1
1
10 Hz), -162.3 (4 P, m, P5/P6, JP-P = 412 Hz, JP-P = 203 Hz,
2JP-P = 27 Hz, 2JP-P = 6 Hz, 2JP-P = -5 Hz).
[K(2,2,2-crypt)]4ZnAs14 (4)
ES- MS: m/z 485.8 [P7In(C6H5)2]-, 524.8 {K[P7In(C6H5)2]} ,
-
-
K3As7 (96 mg, 0.149 mmol), Zn(C6H5)2 (32 mg, 0.146 mmol) and
2,2,2-crypt (178 mg, 0.473 mmol) were dissolved in approximately
2 mL of ethylenediamine yielding a red solution which was stirred
under argon for 1 h. The resulting red/brown reaction mixture was
filtered into a crystallisation ampoule, layered with toluene and
left to crystallise. After several days orange crystals of [K(2,2,2-
crypt)]4ZnAs14 were obtained in 41% yield (86 mg). The crystals
obtained for [K(2,2,2-crypt)]4ZnAs14 exhibit extensive disorder of
one of the [K(2,2,2-crypt)]+ cations and only a partial solution
was possible. Anal. calcd for C72H144K4N8O24As14Zn: C 31.13,
H 5.23, N 4.04. Found: C 30.02, H 5.18, N 4.06. ES- MS:
900.9 {[K(2,2,2-crypt)][P7In(C6H5)2]} . ES+ MS: m/z 1731.5
{[K(2,2,2-crypt)]3[P7In(C6H5)2]} . 1H NMR (300.2 MHz, d5-
+
3
pyridine) d/ppm: 8.85 (2 H, d, oA-CH, Jortho-meta = 7 Hz), 8.20
(2 H, d, oB-CH, 3Jortho-meta = 7 Hz), 7.46 (2 H, t, mA-CH, 3Jmeta-para
=
3
7 Hz), 7.29 (1 H, t, pA-CH, Jmeta-para = 7 Hz), 7.18 (2 H, t, mB-
CH, 3Jmeta-para = 7 Hz), 7.12 (1 H, t, pB-CH, 3Jmeta-para = 7 Hz), 3.41
(s, 2,2,2-crypt), 3.35 (t, 3JH-H = 5 Hz, 2,2,2-crypt), 2.34 (t, 3JH-H
=
5 Hz, 2,2,2-crypt). 31P NMR (121.4 MHz, d5-pyridine) d/ppm: 3.6
(2 P, m, P2/P3, 1JP-P = 387 Hz, 1JP-P = 234 Hz, 2JP-P= -162, 2JP-P
=
2
2
1
-14 Hz, JP-P = 14 Hz, JP-P = 0 Hz), -50.7 (1 P, m, P1 JP-P
=
1
2
2
339 Hz, JP-P = 234 Hz, JP-P = -61 Hz, JP-P = 28 Hz), -67.8 (1
-
1
1
2
2
m/z 1114.3 [ZnAs14]-, 1152.3 {K[ZnAs14]} , 1570.6 {K[K(2,2,2-
P, m, P4 JP-P = 405 Hz, JP-P = 339 Hz, JP-P = -14 Hz, JP-P
-5 Hz), -76.8 (1 P, m, P7, 1JP-P = 405 Hz, 1JP-P = 210 Hz, 2JP-P
=
=
-
-
crypt)][ZnAs14]} , 1606.6 {K2[K(2,2,2-crypt)][ZnAs14]} , 1983.0
-
2
1
{K[K(2,2,2-crypt)]2[ZnAs14]} . ES+ MS: m/z 2776.9 {[K(2,2,2-
-61 Hz, JP-P = 14 Hz), -170.1 (2 P, m, P5/P6, JP-P = 387 Hz,
+
+
2
2
2
crypt)]4[ZnAs14]} , 3191.0 {[K(2,2,2-crypt)]5[ZnAs14]} .
434 | Dalton Trans., 2010, 39, 426–436
1JP-P = 210 Hz, JP-P = 28 Hz, JP-P = -26 Hz, JP-P = -5 Hz,
This journal is
The Royal Society of Chemistry 2010
©

2JP-P = 0 Hz). 13C NMR (75.4 MHz, d5-pyridine) d/ppm: 165.2
(i-C), 160.2 (i-C), 140.5 (o-C), 140.2 (o-C), 127.9 (m-C), 127.3 (m-
C), 126.3 (p-C), 126.3 (p-C), 71.0 (2,2,2-crypt), 68.3 (2,2,2-crypt),
54.5 (2,2,2-crypt).
residual protic solvent resonance (pyridine d 7.22). 31P spectra
were externally referenced to H3PO4 (d 0). Variable temperature
31P experiments on compound 1 were carried out in protic DMF
with a d6-acetone capillary for the field frequency lock. Spectral
simulations were carried out using the program gNMR.61
[K(2,2,2-crypt)]2As7InPh2 (7)
Elemental analyses
K3As7 (98 mg, 0.152 mmol), In(C6H5)3 (37.1 mg, 0.107 mmol)
and 2,2,2-crypt (115 mg, 0.306 mmol) were dissolved in ap-
proximately 2 mL of ethylenediamine giving rise to a deep
red solution which was stirred under argon for one hour. The
resulting red solution was filtered into a crystallisation ampoule,
layered with toluene and left to crystallise. After several days
[K(2,2,2-crypt)]2As7In(C6H5)2 formed as a brown feathery solid
in 56% yield (139 mg). Anal. calcd for C48H82As7InK2N4O12:
C 35.47, H 5.09, N 3.45. Found: C 35.35, H 4.96, N 3.38.
Elemental analyses were carried out by Stephen Boyer of the
London Metropolitan University. Samples (approx. 5 mg) were
submitted in sealed Pyrex ampoules.
4. Conclusions
The seven cluster anions reported in this manuscript provide
evidence that the reductive bond activation of weak metal–carbon
bonds by group 15 Zintl ions can be used as an efficient route
toward the synthesis of interesting bimetallic clusters. As our
understanding of the solution reactivity of anionic Zintl ions devel-
ops we advance towards the possibility of being able to specifically
target alloys of a given composition and nuclearity. This goal,
which would potentially allow us to access interesting ‘molecular
nanoparticles’, would permit us to access well-defined cluster
species with interesting chemical and physical properties. The
isolation of clusters such as the diphenylindium-functionalised
anions [E7In(C6H5)2]2- (E = P, As) is the first step en route towards
the synthesis of molecular alloys of semiconducting III/V alloys.
We are currently involved in a series of studies exploring the
reactivity of the cluster anions reported towards a series of small
molecule adducts with the aim of understanding their chemical
behaviour in solution and exploiting this reactivity as we advance
towards larger molecular clusters.
-
ES- MS: m/z 794.6 [As7In(C6H5)2]-, 832.6 {K[As7In(C6H5)2]} ,
-
1208.9 {[K(2,2,2-crypt)][As7In(C6H5)2]} . ES+ MS: m/z 2039.4
+
{[K(2,2,2-crypt)]3[As7In(C6H5)2]} . 1H NMR (300.2 MHz, d5-
3
pyridine) d/ppm: 8.86 (2 H, d, oA-CH, Jortho-meta = 7 Hz), 8.23
(2 H, d, oB-CH, 3Jortho-meta = 7 Hz), 7.47 (2 H, t, mA-CH, 3Jmeta-para
=
7 Hz), 7.29 (1 H, t, pA-CH, 3Jmeta-para = 7 Hz), 7.20 (2 H, t, mB-CH,
3Jmeta-para = 7 Hz), 7.09 (1 H, t, pB-CH, 3Jmeta-para = 7 Hz), 3.42 (24 H, s,
2,2,2-crypt), 3.36 (24 H, t, 3JH-H = 5 Hz, 2,2,2-crypt), 2.35 (24 H,
3
t, JH-H = 5 Hz, 2,2,2-crypt). 13C NMR (75.4 MHz, d5-pyridine)
d/ppm: 168.1 (i-C), 161.5 (i-C), 140.1 (o-C), 139.8 (o-C), 127.8
(m-C), 127.2 (m-C), 126.1 (p-C), 126.1 (p-C), 71.1 (2,2,2-crypt),
68.3 (2,2,2-crypt), 54.5 (2,2,2-crypt).
Single-crystal X-ray structure determination
Single-crystal X-ray diffraction data were collected on an Enraf-
Nonius Kappa CCD diffractometer equipped with an Oxford
Cryosystems low-temperature device. The crystals were selected
under Paratone-N oil, mounted on micromount loops and posi-
tioned in the cold stream of the diffractometer. Data were collected
at 150 K using graphite monochromated Mo Ka radiation;
equivalent reflections were merged, and the images were processed
with the DENZO and SCALEPACK programs.59 Corrections for
Lorentz-polarization effects and absorption were performed, and
the structures were solved by direct methods and refined on F2
using the SHELX-97 package.60
Acknowledgements
We thank the EPSRC (EP/F00186X/1, PDRA MSD) and the
University of Oxford (studentship BZ) for financial support of this
research. We also thank the Oxford Crystallographic Service for
access to instrumentation and Steve Boyer (London Metropolitan
University) for the elemental analyses.
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