Communication
1
in this sample. After 1 h, the H NMR spectrum of the reaction
mixture reveals a decrease in the amount of staring material.
In addition, the hydride signal at 2.13 ppm decreases in inten-
sity, while those at 3.47 ppm and 2.75 ppm increase. This
change occurs concomitantly with a color change to green
and formation of a dark precipitate. After 17 h, the signals at
1
2.13 and 2.75 ppm are no longer present in the H NMR spec-
trum, and the only hydride resonance observed in the dark
2
blue solution is that assignable to 1. An in situ H NMR spec-
trum of the reaction mixture was also recorded. This spectrum
features a broad singlet at 3.27 ppm, which we have assigned
to CD2HCl, the by-product of a CD2Cl2/CuH metathesis reac-
tion,[13] confirming that the ClÀ counterions in 1 are derived
from dichoromethane. This result also rationalizes the long re-
action times required to form 1 in high yield, as the hydride
metathesis step is likely slow and rate-determining.
Scheme 2. Reactivity of complex 1 with CO2 and CH2Cl2.
ing the reaction by NMR spectroscopy revealed the rapid con-
sumption of 1 and the formation of 4 in 37% yield (Scheme 2,
see the Supporting Information for full characterization details),
demonstrating that the hydride ligands in 1 are accessible to
incoming substrates. Complex 3 is also formed in this reaction.
In summary, we have isolated and structurally characterized
a novel Cu14 hydride cluster. This complex is the largest struc-
turally characterized CuH cluster supported by neutral donor li-
gands. As a consequence, it has a larger H:Cu ratio than other
reported high nuclearity clusters. Importantly, the capping hy-
dride ligands in this cluster are accessible to incoming sub-
strates, as demonstrated by its reaction with CO2. Moreover,
the synthesis of complex 1 demonstrates that [(Ph3P)CuH]6 is
a viable precursor for the generation of copper hydride clus-
ters with high nuclearity. We suggest that with the appropriate
choice of co-ligand, even larger Cu nanocrystals could be ac-
cessible by this route. We will continue to explore the synthe-
sis of new copper hydride complexes from [(Ph3P)CuH]6 and
we will probe their reactivity with CO2.
To further confirm the importance of the chloride counterion
in the formation of the Cu14 cluster, we performed the reaction
of phen with [(Ph3P)CuH]6, in the presence of a [OTf]À source.
Thus, addition of MeCN to a vial charged with 1 equiv of
[(Ph3P)CuH]6, 3 equiv of phen, and 1 equiv of [Cu(MeCN)4][OTf]
results in the formation of [Cu14H12(phen)6(PPh3)4][OTf]2 (2),
which can be isolated as a blue crystalline solid in 41% yield
(Scheme 1). Importantly, complex 2 forms immediately upon
mixing of the reagents, as revealed by the rapid color change
to blue. Interestingly, if [Cu(MeCN)4][OTf] is not added to the
reaction mixture, then a brown intractable suspension is
formed instead, demonstrating the required presence of
a counterion for the formation of 2. Complex 2 features similar
1H and 31P NMR spectral parameters as 1. It also features a sin-
glet at À79.33 ppm in its 19F{1H} NMR spectrum, which is as-
signable to the OTfÀ anion, consistent with our proposed for-
mulation. Complex 2 features a signal at m/z 1515.96 in its ESI
mass spectrum, which corresponds to the parent [M]2+ species
(calcd m/z 1515.94). Finally,
2
features
a
LM of
261.5 ohmÀ1 cm2 molÀ1, also consistent with its formulation as
a 2:1 electrolyte.[8]
Acknowledgements
Complex 1 is soluble in CH2Cl2 and MeCN, and insoluble in
THF, Et2O and non-polar solvents. It is stable in MeCN for at
least 72 h. However, it slowly reacts with CH2Cl2 to generate
a new species, [(phen)(Ph3P)CuCl] (3), along with H2, copper
metal, and other unidentified decomposition products
(Scheme 2, see the Supporting Information for full characteriza-
tion details). Presumably, 3 is formed through a hydride meta-
thesis with the CH2Cl2 solvent. Remarkably, though, in the pres-
ence of excess phen, 1 is indefinitely stable in CH2Cl2, suggest-
ing that the loss of the phen ligand is the first step in its de-
composition. Complex 1 is air sensitive, and rapidly decompos-
es upon exposure to air. However, it only slowly reacts with
water. Finally, we explored the reactivity of complex 1 with
CO2. Several research groups have previously described the re-
activity of discrete copper hydrides with CO2.[1i,4c,d,14] Of most
relevance to our study, Sneeden and co-workers reported that
reaction of [(Ph3P)CuH]6 with CO2, in the presence of 6 equiv
PPh3, resulted in the formation of the formate complex,
[(Ph3P)2Cu(k2-O2CH)] (4).[14a] Similarly, complex 1 was reacted
with CO2 in CD2Cl2, in the presence of excess PPh3.[15] Monitor-
This work was supported by the Center for Sustainable Use of
Renewable Feedstocks (CenSURF), a National Science Founda-
tion Center for Chemical Innovation (NSF CCI).
Keywords: cluster compounds · CO2 insertion · copper ·
density functional calculations · hydrides
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[2] M. S. Eberhart, J. R. Norton, A. Zuzek, W. Sattler, S. Ruccolo, J. Am. Chem.
[3] a) R. D. Kçhn, Z. Pan, M. F. Mahon, G. Kociok-Kohn, Chem. Commun.
2003, 1272–1273; b) P.-K. Liao, C.-S. Fang, A. J. Edwards, S. Kahlal, J.-Y.
Chem. Eur. J. 2015, 21, 1 – 5
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