Balancing Steric and Electronic Effects in Carbonyl–Phosphine Molybdacarboranes

Article abstract of DOI:10.1002/ejic.201700492

Analysis of the literature structures [(CO)(PPh₃)₂MC₂B₉H₁₁] and [(CO)₂(PPh₃)MC₂B₉H₁₁] suggests that in [L₃MC₂B₉H₁₁] metallacarboranes the trans influence of CO is greater than that of PPh₃. Extending this study to the [L₄MC₂B₉H₁₁] system the new molybdacarboranes [3,3,3-(CO)₃-3-PPh₃-3,1,2-closo-MoC₂B₉H₁₁] (2), [1,2-Me₂-3,3,3-(CO)₃-3-PPh₃-3,1,2-closo-MoC₂B₉H₉] (3) and trans-[3,3-(CO)₂-3,3-(PPh₃)₂-3,1,2-closo-MoC₂B₉H₁₁] (4) were prepared and fully characterised. Consideration of the exopolyhedral ligand orientations (ELO) in 2 confirms that, in terms of trans influence, CO > PPh₃ in [L₄MC₂B₉H₁₁] also. The ELO is effectively reversed in 3 through intramolecular steric crowding between the cage CH₃ groups and the PPh₃ ligand. The dicarbonylbis(triphenylphosphine) compound 4 has effective C_s symmetry with one CO ligand trans and the other CO ligand cis to the cage C–C connectivity. Unexpectedly the Mo–CO bond lengths are equal. DFT calculations on 4 reproduce this unusual result, but suggest that in the less-crowded PH₃ analogue, the Mo–CO bond length trans to cage C would be about 0.2 ? shorter than that trans to cage B. To test this prediction, the analogous PEt₃ complex was prepared as cis and trans structural isomers 5 and 6. The cis isomer 5 is quantitatively converted into the trans isomer 6 when heated to reflux in THF. In 6 the Mo–CO bond more trans to cage C is about 0.2 ? shorter than that which is more trans to cage B, in line with the DFT prediction.

Full text of DOI:10.1002/ejic.201700492

A Journal of
Accepted Article
Title: Balancing Steric and Electronic Effects in Carbonyl-Phosphine
Molybdacarboranes
Authors: Alasdair Robertson, Alexander Reckziegel, John Jones,
Georgina Rosair, and Alan Welch
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700492
Link to VoR: http://dx.doi.org/10.1002/ejic.201700492

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
Balancing Steric and Electronic Effects in Carbonyl-Phosphine
Molybdacarboranes
Alasdair P. M. Robertson,[a] Alexander Reckziegel,[a] John J. Jones,[a] Georgina M. Rosair,[a] and Alan
J. Welch*[a]
Abstract: Analysis of the literature structures [(CO)(PPh3)2MC2B9H11]
and [(CO)2(PPh3)MC2B9H11] suggests that in [L3MC2B9H11]
metallacarboranes the trans influence of CO > PPh3. Extending this
study to the [L4MC2B9H11] system the new molybdacarboranes [3,3,3-
(CO)3-3-PPh3-3,1,2-closo-MoC2B9H11] (2), [1,2-Me2-3,3,3-(CO)3-3-
PPh3-3,1,2-closo-MoC2B9H9] (3) and trans-[3,3-(CO)2-3,3-(PPh3)2-
3,1,2-closo-MoC2B9H11] (4) were prepared and fully characterised.
Consideration of the Exopolyhedral Ligand Orientations (ELO) in 2
confirms that, in terms of trans influence, CO > PPh3 in [L4MC2B9H11]
also. The ELO is effectively reversed in 3 through intramolecular steric
crowding between the cage CH3 groups and the PPh3 ligand. The
set. Here the preferred molecular conformation will be that in
which the exopolyhedral ligand with the stronger or strongest
trans influence will tend to lie opposite the cage carbon atom(s),
with exopolyhedral ligands of weak trans influence tending to lie
opposite the cage boron atoms. We have previously named this
phenomenon Exopolyhedral Ligand Orientation (ELO).[4]
Amongst many examples of ELO are the preferred cisoid
conformations in indenyl and naphthalene metallacarboranes
and the motivation to redetermine the structure of [3,3-(2-NO2)-
3-PPh3-3,1,2-closo-RhC2B9H11].[4]
The origin of a preferred ELO is electronic and hence the
interpretation of a molecular structure in terms of ELO assumes
no significant competing steric effects. For this reason ELO
analysis is best done using carborane ligands with only H
substituents, e.g. [LxMC2B9H11] species. In this paper we explore,
through ELO considerations, the relative trans influences of CO
and PPh3, initially by analysis of [(CO)2(Ph3P)MC2B9H11] and
[(CO)(Ph3P)2MC2B9H11] and related structures in the literature,
and then by the synthesis and structural characterisation of
[(CO)3(Ph3P)MoC2B9] and [(CO)2(Ph3P)2MoC2B9] species, the
former both with and without methyl substituents on the cage C
atoms. Unexpected equal Mo−CO distances in trans-[3,3-(CO)2-
3,3-(PPh3)2-3,1,2-closo-MoC2B9H11] prompted us to study this
species by DFT calculation, as a consequence of which we also
prepared and studied the analogous PEt3 complex, which was
isolated in two isomeric forms.
[5]
dicarbonylbis(triphenylphosphine) compound
4 has effective Cs
symmetry with one CO ligand trans and the other CO ligand cis to the
cage C−C connectivity. Unexpectedly the Mo−CO bond lengths are
equal. DFT calculations on 4 reproduce this unusual result, but
suggest that in the less-crowded PH3 analogue the Mo−CO bond
length trans to cage C would be ca. 0.2 Å shorter than that trans to
cage B. To test this prediction the analogous PEt3 complex was
prepared as cis and trans structural isomers (5) and (6). The cis
isomer 5 is quantitatively converted to the trans isomer 6 when heated
to reflux in THF. In 6 the Mo−CO bond more trans to cage C is ca. 0.2
Å shorter than that which is more trans to cage B, in line with the DFT
prediction.
Introduction
In the vast majority of metallacarboranes the carborane ligand
face to which the metal is bonded contains either one or two
carbon atoms, and we have had a long-standing interest in the
consequences of this on the bonding of the exopolyhedral ligands.
Briefly, in a carborane ligand the frontier molecular orbitals of the
carborane are localised on the boron atoms in the open face,[1]
resulting in cage carbon having a weaker trans influence than
cage boron. In bis(phosphine) metallacarboranes this results in
longer M−P distances trans to boron,[2] and in [3,3,3-(CO)3-3,1,2-
closo-MC2B9H11] metallacarboranes to longer M−CO distances
trans to boron (see Table 2 of ref.[3]). The effects are also visible
in metallacarboranes with a heterogeneous exopolyhedral ligand
Results and Discussion
CO and PPh3 are two of the most common exopolyhedral ligands
encountered in metallacarborane chemistry and it is of interest to
use ELO considerations to probe their relative trans influences
(alternatively known as structural trans effects). Coe and
Glenwright classify both CO and PPh3 as “moderate trans
influence ligands”,[6] but go on to point out that analysis of the
structures of [M(CO)5PPh3] for relatively electron-rich metals (M =
Cr,[7] Mo,[8] W,[9] and V− [10]) suggests that, in terms of trans
influence, CO > PPh3 since in all cases the M−CO distance trans
to PPh3 is shorter than those cis to PPh3 (interestingly, for the
relatively electron-poor metal Tc+ there is no significant difference
between the M−CO distances,[11] perhaps indicating the
importance of  back-bonding on trans influence). On the other
hand, See and Kozina conclude, from analysis of square-planar
d8 and low-spin octahedral d6 complexes, that the relative trans
influence is CO < PPh3.[12]
[a]
Institute of Chemical Sciences,
Heriot-Watt University,
Edinburgh, EH14 4AS
UK
E-mail: a.j.welch@hw.ac.uk
Homepage: http://heteroborane.eps.hw.ac.uk
The relative trans influences of CO and PPh3 in
metallacarboranes can be assessed by considering
Supporting Information for this article is available on the WWW
under http://dx.doi.org./10.1002/ejic.2017xxxxx.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
Exopolyhedral Ligand Orientations of structurally characterised
literature compounds. Restricting the search to only {3,1,2-closo-
MC2B9H11} fragments to minimise the possible influence of
intramolecular steric crowding on conformation, there is only one
[(CO)(PPh3)2MC2B9H11] species, [3-CO-3-(PPh3)2-3,1,2-closo-
RuC2B9H11] (BIHQUE),[13] and one [(CO)2(PPh3)MC2B9H11]
species, [3-(CO)2-3-PPh3-3,1,2-closo-FeC2B9H11] (KISBIX),[14] in
the Cambridge Structural Database (CSD).[15] Key ELO data for
these, together with those of the closely related species [3--
(PPh2CH2PPh2)-{3-(CO)2-3,1,2-closo-RuC2B9H11}2] (HIZQUC),[16]
are presented in Tables 1 and 2.
has the greatest trans influence. The two PPh3 ligands have quite
different  values; that at intermediate ││ (less trans to B) has a
significantly shorter Ru−P bond than that at low ││ (more trans
to B), as expected. In KISBIX one of the two CO ligands is at
highest ││, the other is intermediate, and the unique PPh3 ligand
resides at lowest ││, and the same pattern is seen in both
crystallographically-independent cages in the related species
HIZQUC. Unfortunately the crystallographic study of neither
KISBIX nor HIZQUC is sufficiently precise for statistically-
significant differences in the M−CO distances to be observed.
Nevertheless, these data strongly indicate that in mixed CO/PPh3
compounds containing the {3,1,2-closo-MC2B9H11} fragment the
trans influence of CO is greater than that of PPh3.
In comparison to the number of known [L3MC2B9H11] species
(L = same or different ligands) there are relatively few
[L4MC2B9H11] compounds,[17] and atomic co-ordinates for only
four such species could be found in the CSD. Note that an
{ML2L′2} or {ML2L′L′′} fragment introduces the possibility of “cis” or
“trans” configurations of the L ligands.
Table 1. ELO data for [3-(CO)-3-(PPh3)2-3,1,2-closo-RuC2B9H11] (/°, /Å)
CSD code
M
CO
P, M−P
P, M−P
BIHQUE
Ru
131.52(16)
−118.33(13),
2.3873(7)
15.50(15),
2.4021(7)
ELO data for cis-[3,3-(CO)2-3,3-(Cl)2-3,1,2-closo-ReC2B9H11]−
(FINWIJ),[18] cis-[3,3-(CO)2-3,3-(SPh)2-3,1,2-closo-MoC2B9H11]2−
(TOJREP),[19]
trans-[3,3-(PPh3)2-3-H-3-Cl-3,1,2-closo-
Table 2. ELO data for [(CO)2(P)MC2B9H11] compounds (/°, /Å)
OsC2B9H11] (TEXYUQ),[20] and trans-[3,3-(PPh3)2-3-H-3-Cl-3,1,2-
CSD code
M
CO, M−CO
CO, M−CO
P
[21]
closo-RuC2B9H11] (QEXWAS)
are presented in Table 3. The
data for FINWIJ and TOJREP clearly demonstrate that CO has a
stronger trans influence than the ligands Cl and SPh, respectively,
since the cis-CO ligands adopt positions defined by high ││
values. In TEXYOQ and its analogue QEXWAS the ││ values
clearly indicate that H has the strongest, and Cl the weakest, trans
influence of the three types of ligand present (H, Cl, PPh3), as fully
expected.[6]
KISBIX
Fe
−133.5(6),
1,762(13)
113.1(6),
1.754(13)
−12.8(6)
−130.2(4),
1.881(7)
114.3(4),
1.886(8)
−11.5(4)
HIZQUC
Ru
127.4(3),
1.886(7)
−113.6(4),
1.889(6)
8.5(3)
Table 3. ELO data for [L2L′2MC2B9H11] and [L2L′L′′MC2B9H11] species
CSD code
FINWIJ
M
 values (/°)
Ru
Mo2−
Os
Ru
CO 133.4(4)
CO 133.5(6)
H 165.9(17)
H 166.9(11)




CO −137.1(4)
CO −141.0(7)
Cl −13.41(18)
Cl −13.62(11)




Cl 43.7(3)




Cl −48.1(3)
TOJREP
TEXYUQ
QEXWAS
SPh 32.3(4)
P 88.3(2)
SPh −49.6(5)
P −115.5(18)
P −122.26(0)
P 91.93(10)
Figure 1. The ELO of ligand L is described by the torsion angle , where  =
L−M−A−B, A is the centroid of the metal-bound C2B3 face (green dot) and B is
the centroid of the C−C connectivity (purple dot).
Having established that in [L3MC2B9H11] species the trans
influence of CO is greater than that of PPh3 it was of interest to
determine the relative trans influences of these ligands in the
relatively unexplored class of [L4MC2B9H11] compounds. We
therefore targeted the complexes [3,3,3-(CO)3-3-PPh3-3,1,2-
Initially, the published cage C atom positions in each database
structure were checked by the Vertex-to-Centroid Distance (VCD)
method,[4] and were found to be correct in all three cases. Then,
for each ligand, the parameter  which defines the ligand
orientation was calculated, as described in Figure 1. In essence,
ligands with high ││ lie trans to the cage C atoms whilst ligands
with low ││ lie trans to cage B. In all cases one ligand (bold) lies
at ││ ca. 125-135°, one lies at ca. 110-120° and the remaining
ligand (italics) lies at ca. 5-15°. For BIHQUE the unique CO ligand
lies at highest ││ confirming that of the three ligands present it
closo-MoC2B9H11]
and
[3,3-(CO)2-3,3-(PPh3)2-3,1,2-closo-
MoC2B9H11] (the latter as either or both the cis- and trans-isomers)
for synthesis and structural study. Although these specific
compounds were previously unknown the related cage-C
methylated analogues [1,2-Me2-3,3,3-(CO)3-3-PPh3-3,1,2-closo-
MoC2B9H9] (I) and [1,2-Me2-3,3-(CO)2-3,3-(PPh3)2-3,1,2-closo-
MoC2B9H9] (II) were reported by Stone et al. in 1993.[22]
Interestingly, both I and II are afforded by the protonation of
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
[PNP][1,2-Me2-3,3-(CO)2-3-(-C3H5)-3,1,2-closo-MoC2B9H9]
(PNP = [N(PPh3)2]+) in the presence of excess PPh3. Whilst the
formation of II simply represents replacement of the 4-e donor
[C3H5]− ligand by two PPh3 ligands, the co-formation of I can only
be explained by “CO-stealing” by an electron-deficient [1,2-Me2-
12-vertex, 13-Skeletal Electron Pair closo species in accord with
Polyhedral Skeletal Electron Pair Theory.[24]
3,3-(CO)2-3-PPh3-3,1,2-hypercloso-MoC2B9H9] species.
CO-
stealing must also occur in the decomposition of [1,2-Me2-3-CO-
3-PPh3-3-(-PhC2Ph)-3,1,2-closo-MoC2B9H9] to give I amongst a
mixture of products, although interestingly the non cage-C
methylated analogue, [3-CO-3-PPh3-3-(-PhC2Ph)-3,1,2-closo-
MoC2B9H11], is reported as stable towards decomposition under
the same conditions.[23]
Figure 3. Molecular structure of 3 with thermal ellipsoids as in Figure 2.
Selected interatomic distances (Å): Mo−C1 2.386(5), Mo−C2 2.375(5), Mo−B7
2.369(5), Mo−B8 2.390(6), Mo−B4 2.374(6), Mo−C31 2.023(5), Mo−C32
2.003(4), Mo−C33 2.000(6), Mo−P1 2.5309(14), C31−O31 1.132(6), C32−O32
1.134(5), C33−O33 1.145(6), C1−C2 1.668(7), C1−C11 1.516(7), C2−C21
1.523(7).
Compounds 2, 3 and 4 were all isolated as moderately air-
sensitive yellow/orange solids and were initially characterised by
elemental analysis (except for 2 which proved to be too unstable
for reliable results) and multinuclear NMR spectroscopy (NMR
spectra of all new compounds reported in this paper are available
as Supporting Information). All three compounds have time-
averaged Cs molecular symmetry in solution at room temperature.
In the case of 2 this is evident from the 11B{1H} NMR spectrum,
showing a 2:2:2:2:1 pattern from high to low frequency (one
resonance of integral 2 must be a 1+1 co-incidence), for 3 it is
clear from the observation of only one resonance for the CH3
protons, and for 4 it is apparent from both the 1:1:2:2:2:1 pattern
in the 11B{1H} NMR spectrum and the presence of equivalent PPh3
ligands in the 31P{1H} NMR spectrum.
Figure 2. Molecular structure of 2 with thermal ellipsoids drawn at the 50%
probability level except for H atoms. Selected interatomic distances (Å): Mo−C1
2.3684(16), Mo−C2 2.3508(17), Mo−B7 2.3709(19), Mo−B8 2.3962(19), Mo−B4
2.4013(19), Mo−C31 2.0108(18), Mo−C32 2.0049(18), Mo−C33 1.9877(19),
Mo−P1 2.5601(4), C31−O31 1.139(2), C32−O32 1.144(2), C33−O33 1.144(2),
C1−C2 1.601(2).
Treatment of an equimolar mixture of [PNP][3,3-(CO)2-3-(-
C3H5)-3,1,2-closo-MoC2B9H11] (1, prepared analogously to the
[NEt4]+ salt [22]) and PPh3 in CH2Cl2 (DCM) with one equivalent of
HBF4·OEt2 afforded moderate yields of the carbonyl-phosphine
molybdacarboranes [3,3,3-(CO)3-3-PPh3-3,1,2-closo-MoC2B9H11]
Compounds 2, 3 and 4 were also studied crystallographically.
A perspective view of a single molecule of 2 is shown in Figure 2.
Table 4 hosts relevant ELO data and Figure 8 provides a pictorial
view of the orientation of the exopolyhedral ligands. One carbonyl
ligand, C33O33, has the greatest ││ and P1 the smallest ││,
as might have been anticipated from the established relative trans
influences of CO and PPh3 in [L3MC2B9H11] species. Moreover,
the Mo−C33 bond length is significantly the shortest of the three
Mo−CO distances, as expected for the carbonyl ligand “most
trans” to cage C. In compound 3 (Figure 3) the ELO is completely
different, with the {(CO)3PPh3} unit having been effectively rotated
(2,
27%)
and
trans-[3,3-(CO)2-3,3-(PPh3)2-3,1,2-closo-
MoC2B9H11] (4, 26%) following work-up involving column
chromatography on silica. Compound 4 is formed in much
improved yield (65%) if three equivalents of PPh3 are used. The
cage-C methylated analogue of 2, [1,2-Me2-3,3,3-(CO)3-3-PPh3-
3,1,2-closo-MoC2B9H9] (3) was also prepared, again in modest
yield (29%), by protonation of [PNP][1,2-Me2-3,3-(CO)2-3-(-
C3H5)-3,1,2-closo-MoC2B9H9] in the presence of one equivalent of
PPh3. Clearly the isolation of the tricarbonyl species 2 and 3 from
dicarbonyl precursors represents further evidence of carbonyl-
stealing, the driving force for which is presumably the formation of
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
ca. 180° about the metal-carborane axis such the P1 is now trans
to cage C. Since it now lies trans to cage carbon which has a
weaker trans influence than cage boron, the Mo−P distance in 3
is significantly shorter than that in 2, 2.5309(14) Å vs. 2.5601(4)
Å. Presumably steric crowding between the PPh3 ligand and the
upward pointing methyl groups on the cage C atoms is
responsible for the observed exopolyhedral ligand orientation in 3,
emphasising that it is necessary to use only unsubstituted (other
than H) carborane ligands (or those substituted only on atoms not
directly connected to the metal atom) when interpreting
metallacarborane structures in terms of a preferred ELO.
Mo−CO  back-bonding in 4, as evidenced by the Mo−CO and
C−O distances in 4 being significantly shorter and longer,
respectively, than those in 2 and 3. What is surprising, however,
is the apparent equivalence of the carbonyl ligands in 4. In spite
of the fact that C31O31 lies trans to cage C and C32O32 lies trans
to cage B the Mo−CO distances (and the C−O distances) are
exactly the same.Seeking to understand this unusual result
compound
4
has been studied by DFT calculations.[25]
Optimisation of the full molecule, starting from the crystallographic
model, resulted in no significant change in the structure and
afforded only slightly different Mo−CO distances, Mo−C31 1.969
Å, Mo−C32 1.980 Å. However, following replacement of PPh3 by
the smaller, less electron-withdrawing analogue PH3, re-
optimisation resulted in a much greater difference in Mo−CO
lengths, Mo−C31 1.975 Å, Mo−C32 1.997 Å. This perhaps
suggests that the unexpected equivalence of the Mo−CO lengths
in the crystallographic study of 4 might at least in part be a
consequence of intramolecular steric crowding. Figure 5 is a
space-filling representation of the structure of 4 looking towards
(left) C32O32 and (right) C31O31, and shows that each carbonyl
ligand appears to be tightly surrounded by four adjacent Ph
groups.
Table 4. ELO and bond length data for compounds 2-6 (/°, /Å)
2
3
4
5
6
C31O31
Mo−C31 2.0108(18) 2.023(5)
C31−O31 1.139(2) 1.132(6)
117.25(12) −80.7(3)
179.26(10) 139.65(4) 143.87(7)
1.9728(17) 1.9605(8) 1.9805(13)
1.152(2)
1.1587(10) 1.1697(15)
C32O32
Mo−C32 2.0049(18) 2.003(4)
C32−O32 1.144(2) 1.134(5)
−69.49(13) 99.1(3)
−0.04(12)
−138.12(4) −39.33(8)
1.9725(16) 1.9643(8) 1.9977(13)
1.156(2) 1.1611(10) 1.1694(16)
C33O33
Mo−C33 1.9877(19) 2.000(6)
C33−O33 1.144(2) 1.145(6)
−155.21(11) 9.5(3)
P1
25.03(11)
2.5601(4)
−170.85(18) 88.64(9)
52.26(4)
52.34(6)
Mo−P1
2.5309(14) 2.5301(5)
2.5675(2) 2.5417(4)
P2
−91.70(9)
−49.67(4) −124.79(6)
Figure 4. Molecular structure of 4 with thermal ellipsoids as in Figure 2.
Selected interatomic distances (Å): Mo−C1 2.3701(17), Mo−C2 2.3743(16),
Mo−B7 2.4065(18), Mo−B8 2.4690(18), Mo−B4 2.3932(19), Mo−C31
1.9728(17), Mo−C32 1.9725(16), Mo−P1 2.5301(5), Mo−P2 2.5267(5),
C31−O31 1.152(2), C32−O32 1.156(2), C1−C2 1.588(2).
Mo−P2
2.5267(5)
2.5743(2) 2.5190(4)
The dicarbonylbis(triphenylphosphine) species 4 is only
afforded as the trans-isomer – presumably the cis-isomer would
be too sterically crowded. As shown in Figures 4 and 8 the
{(CO)2P2MoC2B9H11} fragment of the molecule has almost exact
Cs symmetry in the solid state about a plane passing through the
CO ligands and Mo3. Thus the two PPh3 ligands have  values
which are effectively equal but opposite in sign, and effectively
equivalent Mo−P bond lengths. The two CO ligands lie on the
molecular mirror plane, one trans to the cage C-C connectivity
and the other trans to B8. With only two as opposed to three
carbonyl ligands it is not surprising that there is greater individual
This prompted us to target less-crowded analogues of 4.
Treatment of 1 with one equivalent of HBF4∙OEt2 at -78 °C
followed by addition of three equivalents of PEt3 afforded,
following work-up involving column chromatography, both cis-
[3,3-(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (5, 23%) and
trans-[3,3-(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (6, 6%) as
yellow/orange and bright yellow slightly air-sensitive solids,
respectively. We assume that, in contrast to the analogous
reaction with PPh3, the cis-isomer is accessible because of
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
Figure 5. Space-filling representations of compound 4 looking (left) towards C32O32 and (right) towards C31O31.
reduced steric crowding. In further contrast to the PPh3 reaction
there was no evidence of the formation of a tricarbonyl mono-
phosphine derivative. Although the trans-isomer 6 is afforded as
only a minor product, substantial amounts of 6 are easily prepared
by the clean, quantitative conversion of cis-5 to trans-6 in refluxing
THF.
ppm, although with individual resonances at measurably different
chemical shifts. The greatest difference, not surprisingly, is seen
in the 31P{1H} spectra, with singlet resonances at ca. 22 ppm for
the cis-isomer and ca. 40 ppm for the trans-isomer.
Compounds 5 and 6 were also studied crystallographically. A
perspective view of a single molecule of 5 is given in Figure 6 and
the orientation of the metal-ligand set with respect to the
carborane face is shown in Figure 8. The cis-isomer 5 has
effective Cs symmetry with the carbonyl and phosphine ligands
related pairwise across the effective mirror plane. Consequently,
in terms of ELO the  values for the CO ligands are essentially
equal but opposite in sign, as are the  values for the PEt3 ligands.
Moreover the Mo−CO bond lengths are barely statistically
different and this is equally true of the Mo−P bond lengths [the
small variations in distance reflect the high precision (low e.s.d.s)
of the determination rather than chemically-meaningful
differences].
Figure 6. Molecular structure of 5 with thermal ellipsoids as in Figure 2.
Selected interatomic distances (Å): Mo−C1 2.4148(7), Mo−C2 2.4162(8),
Mo−B7 2.3900(9), Mo−B8 2.3864(9), Mo−B4 2.3792(9), Mo−C31 1.9605(8),
Mo−C32 1.9643(8), Mo−P1 2.5675(2), Mo−P2 2.5743(2), C31−O31 1.1587(10),
C32−O32 1.1611(10), C1−C2 1.5971(11).
Compounds 5 and 6 were initially characterised by elemental
analysis (satisfactory in both cases) and multinuclear NMR
spectroscopy. The 1H NMR spectra of the two isomers differ
mainly in respect of the resonances assigned to the ethyl protons,
these appearing as three multiplets (6H, -CH2-; 6H, -CH2-; 18H, -
CH3) for 5 and two apparent pentets (12H, -CH2-; 18H, -CH3) for
6. The 11B spectra of the isomers are fairly similar, both having a
1:1:2:2:2:1 integral pattern of resonances between ca. -2 and +20
Figure 7. Molecular structure of 6 with thermal ellipsoids as in Figure 2.
Selected interatomic distances (Å): Mo−C1 2.3930(13), Mo−C2 2.4309(13),
Mo−B7 2.4305(16), Mo−B8 2.4467(15), Mo−B4 2.4176(16), Mo−C31
1.9805(13), Mo−C32 1.9977(13), Mo−P1 2.5417(4), Mo−P2 2.5190(4),
C31−O31 1.1697(15), C32−O32 1.1694(16), C1−C2 1.6101(19).
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
Figure 8. The orientations of the {Mo(CO)3P} and {Mo(CO)2P2} fragments of compounds 2-6 projected onto the C2B3 carborane ligand faces.
sodium/benzophenone, petroleum ether (40-60 °C, petrol) from sodium,
The trans-isomer 6 is shown in Figure 7, and in this structure
the two carbonyl ligands and the two phosphine ligands are
distinct. C31O31 lies at high ││, being sited nearly opposite C2,
whereas C32O32 has a relatively low ││, lying trans to a B−B
connectivity. Consequently the Mo−CO bond lengths are quite
different, with Mo−C31 the shorter by ca. 0.02 Å. Recall that a
difference in Mo−CO bond lengths of this magnitude (again with
Mo−C31 the shorter) was predicted by the DFT calculation on
trans-[3,3-(CO)2-3,3-(PH3)2-3,1,2-closo-MoC2B9H11]. A similar
difference (for the same reasons) exists between the two Mo−P
bond lengths; P2 lies at high ││ and is ca. 0.02 Å closer to Mo
than P1, which lies at low ││.
with DCM and MeCN were distilled from CaH2. All solvents were freeze-
pump-thawed three times prior to use. CDCl3 and CD2Cl2 were dried over
4 Å molecular sieves. Column chromatography was conducted on 60 Å
silica supplied by Fisher and used as received. 1,2-closo-C2B10H12 was
purchased from Katchem Ltd. and Mo(CO)6 from Fluorochem, and both
were used without further purification. All other reagents were purchased
from Sigma Aldrich Ltd. and also used without further purification. [1,2-
Me2-1,2-closo-C2B10H10],[26] [HNMe3][7,8-R2-7,8-nido-C2B9H10] (R = H or
Me),[27] [Mo(CO)2(-C3H5)(MeCN)2Br] [28] and [PNP][1,2-Me2-3,3-(CO)2-3-
(-C3H5)-3,1,2-closo-MoC2B9H9] [22] were prepared by literature methods.
NMR spectra were recorded using a Bruker DPX-400 spectrometer, with
chemical shifts reported relative to residual protonated solvent peaks (1H,
13C), or to external standards (11B: BF3∙OEt2, 31P: H3PO4). All spectra were
recorded at 298 K and can be seen as Figures S1-S29 (Supporting
Information). Elemental analyses (EA) were carried out using an Exeter
CE-440 elemental analyser.
Conclusions
[PNP][3,3-(CO)2-3-(-C3H5)-3,1,2-closo-MoC2B9H11] (1): The synthesis
of this salt is closely related to that of the analogous [NEt4]+ salt reported
by Stone et al.[22] Thus, to a solution of [HNMe3][7,8-nido-C2B9H12] (0.75
g, 3.86 mmol) in THF (18 mL) at -78 °C was added a 2.5 M solution of
nBuLi in hexanes (3.10 mL, 7.72 mmol), and the resulting mixture warmed
to ambient temperature and stirred for 1 h. The mixture was then frozen
in liquid N2 and solid [Mo(CO)2(-C3H5)(MeCN)2Br] (1.38 g, 3.86 mmol)
added, before warming to ambient temperature and stirring for a further 30
mins. The mixture was re-frozen, and solid [PNP][Cl] (2.22 g, 3.86 mmol)
added, before warming once again to ambient temperature and stirring for
a further 30 mins. All volatiles were then removed under high vacuum to
yield a dark yellow/brown solid, which were purified by cold column
chromatography (MeCN/dry ice jacket), furnishing the product [PNP][3,3-
(CO)2-3-(-C3H5)-3,1,2-closo-MoC2B9H11] (1) as a bright-yellow solid,
which slowly decomposes in air. Yield: 1.86 g, 56%;[29] 1H NMR (400 MHz,
CD2Cl2): δH 7.70-7.63 (6H, m, Ph), 7.55-7.44 (24H, m, Ph), 3.32 (1H, tt,
JHH = 10.7 Hz, JHH = 7.1 Hz, CH2CHCH2), 2.92 (2H, d, JHH = 7.1 Hz,
CH2CHCH2), 1.83 (2H, s, CH), 1.10 (2H, d, JHH = 10.7 Hz, CH2CHCH2);
1H{11B} NMR (400 MHz, CD2Cl2): δH 7.70-7.63 (6H, m, Ph), 7.55-7.44 (24H,
Analysis of literature structures suggests that in mixed CO/PPh3
metallacarboranes the trans influence of CO is greater than that
of PPh3, and this is generally confirmed by consideration of the
Exopolyhedral Ligand Orientations in new carbonyl-phosphine
molybdacarboranes. However, intramolecular steric crowding
can compromise these orientations (noted in comparison of the
structures of 2 and 3) or can lead to unexpected bond distances
within the metal-ligand fragment (comparison of the structures of
4 and 6).
Experimental Section
Materials and General Procedures: All experiments were performed,
unless otherwise stated, under an atmosphere of nitrogen using standard
Schlenk techniques, with subsequent manipulations and purifications
carried out in air.
Tetrahydrofuran (THF) was distilled from
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
m, Ph), 3.32 (1H, tt (unresolved), CH2CHCH2), 2.92 (2H, d, JHH = 7.1 Hz,
CH2CHCH2), 2.27 (1H, s, BH), 2.09 (1H, s, BH), 1.88 (1H, v. br. s, BH),
(CO)2-3,3-(PPh3)2-3,1,2-closo-MoC2B9H11] (4), a moderately air-sensitive,
yellow/orange solid. Yield: 309 mg, 65%; 1H NMR (400 MHz, CD2Cl2): δH
7.72-7.60 (8H, m, Ph), 7.54-7.35 (18H, m, Ph), 7.27-7.15 (4H, m, Ph), 2.15
1.83 (2H, s, CH), 1.64 (2H, s, BH), 1.34 (4H, s, BH), 1.10 (2H, d, JHH
=
10.7 Hz, CH2CHCH2); 11B{1H} NMR (128 MHz, CD2Cl2): δB -4.2 (1B,
s), -7.3 (2B, s), -12.2 (1B, s), -13.9 (2B, s), -19.3 (3B, s); 11B NMR (128
(2H, s, CH); H{11B} NMR (400 MHz, CD2Cl2): δH 7.72-7.60 (8H, m, Ph),
1
7.54-7.35 (18H, m, Ph), 7.27-7.15 (4H, m, Ph), 2.72 (1H, s, BH), 2.41 (1H,
s, BH), 2.15 (2H, s, CH), 1.78 (2H, s, BH), 1.23 (3H, s, BH), 1.07 (2H, s,
BH); 11B{1H} NMR (128 MHz, CD2Cl2): δB 0.2 (1B, s), -2.5 (1B, s), -7.1 (2B,
s), -11.6 (2B, s), -15.8 (2B, s), -22.1 (1B, s); 11B NMR (128 MHz, CD2Cl2):
δB 0.2 (1B, d, 1JBH = 113 Hz), -2.5 (1B, d, 1JBH = 112 Hz), -7.1 (2B, d, 1JBH
= 129 Hz), -11.6 (2B, br. s), -15.8 (2B, br. s), -22.1 (1B, br. s); 31P{1H} NMR
(162 MHz, CD2Cl2): δP 62.6 (s). EA: C40H41B9MoO2P2 requires C 59.4, H
5.11; found C 58.7, H 5.06 %. Single crystals grown from CDCl3 at 20 °C
(crystals contain two molecules of CDCl3 per molecule of
metallacarborane).
1
1
MHz, CD2Cl2): δB -4.2 (1B, d, JBH = 131 Hz), -7.3 (2B, d, JBH = 136
Hz), -12.2 (1B, d, unresolved due to overlap with peak at -13.9 ppm), -13.9
(2B, d, 1JBH = 141 Hz), -19.3 (3B, d, 1JBH = 150 Hz).
[3,3,3-(CO)3-3-PPh3-3,1,2-closo-MoC2B9H11] (2): To a solution of 1 (0.50
g, 0.58 mmol) [29] and Ph3P (152 mg, 0.58 mmol) in DCM (20 mL) at 0 °C
was added neat HBF4∙OEt2 (0.08 mL, 0.58 mmol), producing a dark red-
brown solution. The mixture was then warmed to ambient temperature
and stirred for 1 h before removing all volatiles under high vacuum. The
resulting brown solids were eluted with 30:70 DCM:petrol on a silica
column, with two well-separated yellow/orange bands moving down the
column. The higher Rf band was collected and identified as [3,3,3-(CO)3-
3-PPh3-3,1,2-closo-MoC2B9H11] (2), isolated as a moderately air-sensitive
yellow/orange solid. Yield: 92 mg, 27%; 1H NMR (400 MHz, CD2Cl2): δH
7.62-7.56 (3H, m, Ph), 7.54-7.48 (6H, m, Ph), 7.33-7.24 (6H, m, Ph), 2.53
cis-[3,3-(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (5) and trans-[3,3-
(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (6): To a solution of 1 (0.31 g,
[29]
0.36 mmol)
in CH2Cl2 (12 mL) at -78 °C was added neat HBF4∙OEt2
(0.05 mL, 0.36 mmol) and the mixture stirred for 30 mins to yield a dark
red-brown solution. Neat PEt3 (0.16 mL, 1.08 mmol) was then added, and
the mixture warmed to ambient temperature and stirred for 4 h. All volatiles
were then removed under high vacuum to furnish an oily red solid, which
was eluted onto a silica column with 50:50 DCM:petrol, yielding two, well-
separated, yellow bands.
1
(2H, s, CH); H{11B} NMR (400 MHz, CD2Cl2): δH 7.62-7.56 (3H, m, Ph),
7.54-7.48 (6H, m, Ph), 7.33-7.24 (6H, m, Ph), 3.09 (1H, s, BH), 2.53 (2H,
s, CH), 2.18 (1H, s, BH), 2.13 (2H, s, BH), 1.77 (3H, s, BH), 1.67 (2H, s,
BH); 11B{1H} NMR (128 MHz, CD2Cl2): δB -0.2 (2B, s), -3.2 (2B, s), -11.3
(2B, s), -14.9 (2B, s), -17.9 (1B, s); 11B NMR (128 MHz, CD2Cl2): δB -0.2
(2B, d, 1JBH = 126 Hz), -3.2 (2B, d, 1JBH = 141 Hz), -11.3 (2B, d, 1JBH = 136
Hz), -14.9 (2B, d, 1JBH = 150 Hz), -17.9 (1B, d, unresolved due to overlap
with peak at -14.9); 31P{1H} NMR (162 MHz, CD2Cl2): δP 47.4 (s). Single
crystals were grown from DCM at -20 °C and crystals contain one molecule
of DCM of solvation per molecule of 2. The second, lower Rf, band was
also collected and identified as [3,3-(CO)3-3,3-(PPh3)2-3,1,2-closo-
MoC2B9H11] (4) (yield 125 mg, 26%), subsequently prepared in
significantly higher yield via targeted independent synthesis, as described
below.
The major, slower moving band was collected and all volatiles removed to
furnish a yellow/orange solid, which slowly darkened in air, and was
identified as cis-[3,3-(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (5). Yield:
44 mg, 23%; 1H NMR (400 MHz, CDCl3): δH 2.87 (2H, br. s, CH), 2.10-2.00
(6H, m, -CH2-), 1.99-1.88 (6H, m, -CH2-), 1.24-1.15 (18H, m, -CH3);
1H{11B} NMR (400 MHz, CDCl3): δH 3.12 (1H, br. s, BH), 2.87 (2H, br. s,
CH), 2.10-2.00 (6H, m, -CH2-), 1.99-1.88 (6H, m, -CH2-), 1.82 (2H, br. s,
BH), 1.48 (2H, br. s, BH), 1.24-1.15 (18H, m, -CH3) [analysis of the relative
integrals suggest that at least 3 further BH resonances lie beneath the
phosphinic CH2 resonance at 2.10-2.00 (2×BH), and CH3 resonance at
1.24-1.15 ppm (1×BH), respectively]; 11B{1H} NMR (128 MHz, CDCl3):
δB -0.2 (1B, s), -3.0 (1B, s), -4.6 (2B, s), -12.5 (2B, s), -15.9 (2B, s), -19.4
(1B, s); 11B NMR (128 MHz, CDCl3): δB -0.2 (1B, d, JBH = 131 Hz), -3.0 (1B,
d, coupling not resolved due to overlap with peak at -4.6 ppm), -4.6 (2B, d,
JBH = 145 Hz), -12.5 (2B, d, JBH = 137 Hz), -15.9 (2B, d, JBH = 149 Hz), -19.4
(1B, d, JBH = 152 Hz); 31P{1H} NMR (162 MHz, CDCl3): δP 22.1 (s). EA:
C16H41B9MoO2P2 requires C 36.9, H 7.94; found C 36.9, H 8.07 %. Single
crystals grown from CDCl3/petrol at 5 °C.
[1,2-Me2-3,3,3-(CO)3-3-PPh3-3,1,2-closo-MoC2B9H9] (3): To a solution of
[PNP][1,2-Me2-3,3-(CO)2-3-(C3H5)-3,1,2-closo-MoC2B9H9] (0.47 g, 0.53
mmol) and PPh3 (0.14 g, 0.53 mmol) in DCM (25 mL) at 0 °C, was added
neat HBF4∙OEt2 (0.08 g, 0.53 mmol) and the mixture warmed to ambient
temperature before stirring for 1 h. All volatiles were then removed and
the resulting dark solids purified by column chromatography, eluting with
35:65 DCM:petrol, furnishing the product, [1,2-Me2-3,3,3-(CO)3-3-PPh3-
3,1,2-closo-MoC2B9H9] (3), as an orange/yellow, slightly air-sensitive solid.
Yield: 89 mg, 29%; 1H NMR (400 MHz, CD2Cl2): δH 7.61-7.40 (15H, m,
Ph), 2.08 (6H, s, Me); 1H{11B} NMR (400 MHz, CD2Cl2): δH 7.61-7.40 (15H,
m, Ph), 3.01 (1H, br. s, BH), 2.17 (2H, br. s, BH), 2.11 (2H, br. s, BH), 2.08
(6H, s, Me), 1.98 (2H, br. s, BH), 1.81 (1H, br. s, BH), 1.76 (1H, br. s, BH);
11B{1H} NMR (128 MHz, CD2Cl2): δB 0.0 (2B, s), -3.1 to -8.8 (7B,
overlapping resonances, maxima at -4.5, -5.7, -7.1); 11B NMR (128 MHz,
The minor, faster moving band was collected and furnished a bright yellow
solid which also slowly darkened in air and was identified as trans-[3,3-
(CO)2-3,3-(PEt3)2-3,1,2-closo-MoC2B9H11] (6). Yield: 12 mg, 6%; 1H NMR
(400 MHz, CDCl3): δH 2.59 (2H, br. s, CH), 2.16 (12H, apparent pentet, -
CH2-), 1.23 (18H, apparent pentet, -CH3); 1H{11B} NMR (400 MHz, CDCl3):
δH 2.98 (1H, br. s, BH), 2.59 (2H, br. s, CH), 2.16 (12H, apparent pentet, -
CH2-), 1.96 (3H, br. s, BH), 1.76 (3H, br. s, BH), 1.35 (2H, br. s, BH), 1.23
(18H, apparent pentet, -CH3); 11B{1H} NMR (128 MHz, CDCl3): δB -1.4 (1B,
1
CD2Cl2): δB 0.0 (2B, d, JBH = 131 Hz), -3.1 to -8.8 (7B, overlapping
resonances, maxima at -3.9, -5.1, -6.3, -7.6); 31P{1H} NMR (162 MHz,
CD2Cl2): δP 51.3 (s); EA: C25H30B9MoO3 requires C 49.8, H 5.02; found C
49.7, H 5.12 %. Single crystals were grown from DCM/petrol at -20 °C.
s), -4.6 (1B, s), -6.5 (2B, s), -12.5 (2B, s), -16.9 (2B, s), -20.2 (1B, s); 11
B
NMR (128 MHz, CDCl3): δB -1.4 (1B, d, JBH = 122 Hz), -4.6 (1B, d, coupling
not resolved due to overlap with peak at -6.5 ppm), -6.5 (2B, d, JBH = 142
Hz), -12.5 (2B, d, JBH = 131 Hz), -16.9 (2B, d, JBH = 150 Hz), -20.2 (1B, d,
JBH = 160 Hz); 31P{1H} NMR (162 MHz, CDCl3): δP 40.6 (s). EA:
C16H41B9MoO2P2 requires C 36.9, H 7.94; found C 36.8, H 8.12 %. Single
crystals grown from CDCl3/petrol at 5 °C.
trans-[3,3-(CO)2-3,3-(PPh3)2-3,1,2-closo-MoC2B9H11] (4): To a solution
[29]
of 1 (0.50 g, 0.58 mmol)
and Ph3P (455 mg, 1.73 mmol) in DCM (20
mL) at 0 °C was added neat HBF4∙OEt2 (0.08 mL, 0.58 mmol), producing
a dark red-brown solution. The mixture was then warmed to ambient
temperature and stirred for 1 h before removing all volatiles under high
vacuum. The resulting brown solids were eluted with 30:70 DCM:petrol on
a silica column, with a well-defined bright orange band moving down the
column, preceded by a small amount of a very faint yellow band. The faint
yellow band was collected and identified as mono-phosphine complex (2),
whilst the major orange band was collected and identified as trans-[3,3-
Thermolysis of 5 to 6: An orange solution of 5(20 mg, 0.04 mmol) in THF
(20 mL) was heated to reflux for 18 h. After cooling to ambient temperature
all volatiles were removed under high vacuum to furnish a yellow solid,
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
analysis (by 11B and 1H NMR spectroscopies) of which indicated a clean
and quantitative conversion of cis-isomer 5 to trans-isomer 6.
Organomet. Chem., 2012, 721-722, 78-84; d) A. McAnaw, M. E. Lopez,
D. Ellis, G. M. Rosair, A. J. Welch, Dalton Trans., 2013, 42, 671-679.
B. J. Coe, S. J. Glenwright, Coord. Chem. Rev., 2000, 203, 5-80.
a) H. J. Plastas, J. M. Stewart, S. O. Grim, Inorg. Chem., 1973, 12, 265-
272; b) B. Ndiaye, S. Bhat, A. Jouaiti, T. Berclaz, G. Bernardinelli, M.
Geoffroy, J. Phys. Chem. A, 2006, 110, 9736-9742.
[6]
[7]
Crystallographic Studies: Diffraction data from compounds 2 and 4 were
collected at 120
K on a Rigaku Oxford Diffraction SuperNova
diffractometer at the University of Edinburgh, whilst data from 3 were
collected at 100 K on a Rigaku FR-E+ diffractometer by the UK National
Crystallography Service at the University of Southampton. Data from 5
and 6 were collected at 100 K on a Bruker X8 APEXII diffractometer at
Heriot-Watt University. In all cases Mo-K X-radiation was used with
[8]
[9]
F. A. Cotton, D. J. Darensbourg, W. H. Ilsley, Inorg. Chem., 1981, 20,
578-583.
M. J. Aroney, I. E. Buys, M. S. Davies, T. W. Hambley, J. Chem. Soc.,
Dalton Trans., 1994, 2827-2834.
[10] D. Rodewald, F. Sussmilch, D. Rehder, An. Quim., 1996, 92, 269-274.
[11] A. E. Miroslavov, A. A. Lumpov, G. V. Sidorenko, E. M. Levitskaya, N. I.
Gorshkov, D. N. Suglobov, R. Alberto, H. Braband, V. V. Gurzhiy, S. V.
Krivovichev, I. G. Tananaev, J. Organomet. Chem., 2008, 693, 4-10.
[12] R. F. See, D. Kozina, J. Coord. Chem., 2013, 66, 490-500.
[13] D. D. Ellis, S. M. Couchman, J. C. Jeffery, J. M. Malget, F. G. A. Sone,
Inorg. Chem., 1999, 38, 2981-2988.
crystals mounted in inert oil on a cryloop and cooled in a stream of cold N2.
[30]
Using OLEX2
structures were solved by direct methods using the
[31]
[32]
SHELXS
or SHELXT
programme and refined by full-matrix least-
squares (SHELXL).[31] There was no evidence for twinning and all the
metallacarborane cages were fully-ordered. Compound 2 crystallises with
one molecule of DCM per metallacarborane, 4 with two molecules of
CHCl3 per metallacarborane, and 5 with one molecule of CHCl3 per
metallacarborane, the last partially disordered. Cage C atoms bearing only
H substituents were distinguished from B atoms by the VCD [4] and BHD
[33] methods. H atoms bound to cage B or cage C atoms were allowed to
refine positionally whilst H atoms bound to other C atoms were constrained
[14] S. S. Lee, C. B. Knobler, M. F. Hawthorne, Organometallics, 1991, 10,
670-677.
[15] C. R. Groom, F. H. Allen, Angew. Chem. Int. Ed., 2014, 53, 662-671. For
this search we used ConQuest version 1.19.
[16] J. C. Jeffery, P. A. Jelliss, E. Psillakis, G. E. A. Rudd, F. G. A. Stone, J.
to idealised geometries; Cphenyl–H = 0.95 Å, Cprimary–H = 0.98 Å, Csecondary
–
Organomet. Chem., 1998, 562, 17-27.
H = 0.99 Å, Ctertiary–H = 1.00 Å. All H displacement parameters, Uiso, were
constrained to be 1.2×Ueq (bound B or C) except Me H atoms [Uiso(H) =
1.5×Ueq C(Me)]. Table S1 (Supporting Information) contains further
experimental details. CCDC 1543882 (compound 2·CH2Cl2), 1543883
(compound 3), 1543884 (compound 4·2CHCl3), 1543885 (compound
5·CHCl3) and 1543886 (compound 6) contain the crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
[17] R. N. Grimes, Carboranes, 3rd ed., Academic Press, 2016.
[18] M. J. Fischer, P. A. Jelliss, L. M. Phifer, N. P. Rath, Inorg. Chim. Acta,
2005, 358, 1531-1544.
[19] J.-H. Kim, E. Hong, J. Kim, Y. Do, Inorg. Chem., 1996, 35, 5112-5113.
[20] I. T. Chizhevsky, P. V. Petrovskii, P. V. Sorokin, V. I. Bregadze, F. M.
Dolgushin, A. I. Yanovsky, Yu. T. Struchkov, Organometallics, 1996, 15,
2619-2623.
[21] D. N. Cheredilin, F. M. Dolgushin, I. D. Grishin, E. V. Kolyakina, A. S.
Nikiforov, S. P. Solodovnikov, M. M. Il’in, V. A. Davankov, I. T Chizhevsky,
D. F. Grishin, Russ. Chem. Bull., 2006, 55, 1163-1170.
[22] S. J. Dossett, S. Li, F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1993,
1585-1591.
Acknowledgements
[23] S. J. Dossett, S. Li, D. F. Mullica, E. L. Sappenfield, F. G. A. Stone, J.
Chem. Soc., Dalton Trans., 1993, 3551-3557.
We thank the Leverhulme Trust for support of A.P.M.R. and J.J.J.
(project RPG-2014-286). We are grateful to Prof. S. A. Macgregor
for the DFT calculations on compound 4 and its PH3 analogue,
and for helpful discussions. We also thank the UK National
Crystallography Service for data collection of compound 3. A.R.
is an Erasmus exchange student from the Phillips-Universität
Marburg, Germany.
[24] a) K. Wade, J. Chem. Soc. D, 1971, 792-793; b) D. M. P. Mingos, Nature
(London) Phys. Sci., 1972, 236, 99-102.
[25] Full details of the DFT calculations will be published subsequently: S. A.
Macgregor, to be published.
[26] H. D. Smith, T. A. Knowles, H. Schroeder, Inorg Chem., 1965, 4, 107-
111.
[27] M. F. Hawthorne, D. C. Young, P. M. Garrett, D. A. Owen, S. G. Schwerin,
F. N. Tebbe, P. A. Wegner, J. Am. Chem. Soc., 1968, 90, 862-868.
[28] R. G. Hayter, J. Organomet. Chem., 1968, 13, P1-P3.
[29] The requisite purification of this compound via column chromatography
Keywords: metallacarborane • steric effects • electronic effects •
carbonyl • phosphine
to remove
a dark red/brown material led, unavoidably, to some
[1]
[2]
a) D. M. P. Mingos, J. Chem. Soc., Dalton Trans., 1977, 602-610; b) D.
M. P. Mingos, M. I. Forsyth, A. J. Welch, J. Chem. Soc., Dalton Trans.,
1978, 1363-1374.
decomposition to yield a mixture of salt 1 and [PNP][7,8-nido-C2B9H12] in
a 2:1 ratio based on analysis by 11B NMR spectroscopy. This yield is,
therefore, calculated from an overall yield of solid of 2.58 g, factoring in
the presence of [PNP][7,8-nido-C2B9H12]. Purification of the compound
on a small scale via recrystallization from DCM/petrol at -20 °C produced
a small number of well-formed crystals suitable for the full spectroscopic
characterisation but, due to low yields in the recrystallization, the bulk
material was employed without further purification in subsequent
reactions (in which [PNP][7,8-nido-C2B9H12] should be a spectator
species).
a) A. J. Welch, J. Chem. Soc., Dalton Trans., 1975, 1473-1478; b) G. K.
Barker, M. Green, F. G. A. Stone, A. J. Welch, J. C. S. Dalton, 1980,
1186-1199; c) G. K. Barker, M. P. Garcia, M. Green, G. N. Pain, F. G. A.
Stone, S. K. R. Jones, A. J. Welch, J. C. S. Chem. Comm., 1981, 652-
653.
[3]
[4]
[5]
S. L. Powley, G. M. Rosair, A. J. Welch, Dalton Trans., 2016, 45, 11742-
11752.
A. McAnaw, G. Scott, L. Elrick, G. M. Rosair, A. J. Welch, Dalton Trans.,
2013, 42, 645-664.
[30] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.
Puschmann, J. Appl. Cryst., 2009, 42, 339-341.
a) D. E. Smith, A. J. Welch, Organometallics, 1986, 5, 760-766; b) G.
Scott, A. McAnaw, D. McKay, A. S. F. Boyd, D. Ellis, G. M. Rosair, S. A.
Macgregor, A. J. Welch, F. Laschi, F. Rossi, P. Zanello, Dalton Trans.,
2010, 39, 5286-5300; c) G. Scott, G. M. Rosair, A. J. Welch, J.
[31] G. M. Sheldrick, Acta Cryst., 2008, A64, 112-122.
[32] G. M. Sheldrick, Acta Cryst., 2015, A71, 3-8.
[33] A. McAnaw, M. E. Lopez, D. Ellis, G. M. Rosair, A. J. Welch, Dalton
Trans., 2014, 43, 5095-5105.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
This article is protected by copyright. All rights reserved.

10.1002/ejic.201700492
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
FULL PAPER
The balance between steric and
electronic preferences for the
exopolyhedral ligand orientation in
molybdacarboranes is explored by
synthetic and structural studies
Metallacarboranes
Alasdair P. M. Robertson, Alexander
Reckziegel, John J. Jones, Georgina M.
Rosair and Alan J. Welch*
xxxx – xxxx
((Insert TOC Graphic here: max.
width: 5.5 cm; max. height: 5.0 cm;
NOTE: the final letter height should
not be less than 2 mm.))
Balancing Steric and Electronic
Effects in Carbonyl-Phosphine
Molybdacarboranes
This article is protected by copyright. All rights reserved.