A Dinitrogen Dicopper(I) Complex via a Mixed-Valence Dicopper Hydride

Article abstract of DOI:10.1002/anie.201603970

Low-temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide [^iPr2TpCu]₂(μ-OH)₂with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [^iPr2TpCu]₂(μ-1,2-N₂) (3). X-ray crystallography reveals an only slightly activated N₂ligand (N-N: 1.111(6) ?) that bridges between two monovalent^iPr2TpCu fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest weak π-backbonding between the d¹⁰Cu^Icenters and the N₂ligand, they reveal a degree of cooperativity in the dinuclear Cu-N₂-Cu interaction. Addition of MeCN, CNAr^2,6-Me, or O₂to 3 releases N₂with formation of^iPr2TpCu(L) (L=NCMe, CNAr^2,6-Me2) or [^iPr2TpCu]₂(μ-η²:η²-O₂) (1). Addition of triphenylsilane to [^iPr2TpCu]₂(μ-OH)₂in pentane allows isolation of a key intermediate [^iPr2TpCu]₂(μ-H) (5). Although 5 thermally decays under N₂to give 3, it reduces unsaturated substrates, such as CO and HC≡CPh to HC(O)H and H₂C=CHPh, respectively.

Full text of DOI:10.1002/anie.201603970

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International Edition: DOI: 10.1002/anie.201603970
German Edition: DOI: 10.1002/ange.201603970
Dinitrogen Complexes
Hot Paper
A Dinitrogen Dicopper(I) Complex via a Mixed-Valence Dicopper
Hydride
Shiyu Zhang, Hengameh Fallah, Evan J. Gardner, Subrata Kundu, Jeffery A. Bertke,
Thomas R. Cundari,* and Timothy H. Warren*
ꢁ
ꢁ
Abstract: Low-temperature reaction of the tris(pyrazolyl)bo-
rate copper(II) hydroxide [iPr2TpCu]2(m-OH)2 with triphenyl-
silane under a dinitrogen atmosphere gives the bridging
dinitrogen complex [iPr2TpCu]2(m-1,2-N2) (3). X-ray crystal-
lography reveals an only slightly activated N2 ligand (N-N:
1.111(6) ꢀ) that bridges between two monovalent iPr2TpCu
fragments. While DFT studies of mono- and dinuclear copper
dinitrogen complexes suggest weak p-backbonding between
the d10 CuI centers and the N2 ligand, they reveal a degree of
cooperativity in the dinuclear Cu-N2-Cu interaction. Addition
of MeCN, CNAr2,6-Me, or O2 to 3 releases N2 with formation of
iPr2TpCu(L) (L = NCMe, CNAr2,6-Me2) or [iPr2TpCu]2(m-h2:h2-
O2) (1). Addition of triphenylsilane to [iPr2TpCu]2(m-OH)2 in
pentane allows isolation of a key intermediate [iPr2TpCu]2(m-H)
(5). Although 5 thermally decays under N2 to give 3, it reduces
despite the specific electronic differences in M O2 and M N2
bonding.[2,5e,8,9] For instance, binding of both N2 (nN2
=
2331 cmꢁ1) and O2 have been observed at a sterically
demanding tris(pyrazolyl)borate Co complex (Fig-
ure 1a).[5e,10] Using b-diketiminate supporting ligands, both
ꢀ
unsaturated substrates, such as CO and HC CPh to HC(O)H
=
and H2C CHPh, respectively.
C
oordination of N2 and O2 to transition metals represents
a crucial step that precedes the multi-electron reduction of
these ligands involved in ammonia formation and the
oxidation of organic substrates.[1] While binding of O2 to
transition metals has a long history,[2] coordination of N2 to
transition metals was not observed until 1965, likely due to
the weak s-donating and poor p-accepting nature of N2.[3] In
particular, backbonding interactions from transition-metal
d orbitals to the degenerate dinitrogen p* antibonding
Figure 1. Selected late-transition-metal O2 and N2 complexes.
a
bridging dinitrogen complex [Ni]2(m-1,2-N2) (nN2 =
2164 cmꢁ1) and mononuclear superoxo [Ni](h2-O2) species
were isolated by Limberg[6a] and Driess.[8] (Figure 1b,c).
Further reduction with KC8 gives monoanionic and dianionic
species K{[Ni]2(m-N2)} and K2{[Ni]2(m-N2)} with lower N2
stretching frequencies (nN2 = 1825 and 1696 cmꢁ1, respec-
tively), mirroring the further reduction of the superoxo
complex [Ni](h2-O2) to form the corresponding side-on
peroxo species {[Ni](h2-O2)}K(18-C-6).[11]
orbitals represents a key interaction that leads to elongation
and activation of the N N bond.
[4]
ꢁ
Dinitrogen complexes for Co,[5] Ni,[6] and especially Cu[7]
are less common than for the early to middle transition metals
a result of the weaker p-backbonding to N2 at Co, Ni, and Cu
centers. Much more easily reduced, dioxygen often binds at
metal fragments capable of stabilizing dinitrogen complexes
Despite the prevalence of O2 binding to copper(I) centers
in biology and related coordination complexes,[12] no molec-
ular mononuclear or dinuclear dinitrogen adducts [Cu]-N2 or
[Cu]2(m-N2) have been reported. For instance, the tris(pyr-
azolyl)borate complex [iPr2TpCu]2(m-h2:h2-O2) (1; Figure 2a)
serves as a model for the reversible binding of O2 at
hemocyanin that occurs at a binuclear His3CuI···ICuHis3
site.[13] Nonetheless, a related [iPr2TpCu]2(m-N2H2) (2; Fig-
ure 2c) complex has been isolated (nNN = 1358 cmꢁ1), illus-
trating the ability of this fragment to support reduced species
related to dinitrogen.[14]
Until very recently, no copper coordination compound
featuring a bound N2 ligand had been isolated,[7a] though
[(bpy)Cu-N2]+ had been detected by electrospray mass
spectrometry.[15] Coordination of N2 to copper in copper-
doped zeolites occurs,[16] with nN2 stretching frequencies only
slightly depressed from the free value of 2331 cmꢁ1, such as
[*] S. Zhang, E. J. Gardner, Dr. S. Kundu, Dr. J. A. Bertke,
Prof. T. H. Warren
Department of Chemistry
Georgetown University
Box 571227, Washington, DC 20057-1227 (USA)
E-mail: thw@georgetown.edu
H. Fallah, Prof. T. R. Cundari
Department of Chemistry, Center for Advanced Scientific Computing
and Modeling (CASCaM)
University of North Texas
Denton, TX 76203 (USA)
E-mail: t@unt.edu
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under http://dx.doi.org/10.
1002/anie.201603970.
occurs the in the copper-exchanged mordenite (nN2
=
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[
iPr2TpCu]2(m-N2) unit is completed by an inversion center
ꢁ
through the center of the N N bond. A single N2 molecule is
captured in between two CuI centers to give an end-on
ꢁ
binding mode (Molecule A: Cu N 1.829(3); Molecule B:
ꢁ
1.822(3) ꢀ) with a just slightly lengthened N N bond distance
(Molecule A: 1.112(5); Molecule B: 1.110(6) ꢀ) compared to
free dinitrogen (1.0975 ꢀ). Each unique copper center of 3
adopts a pseudo-tetrahedral environment (t = 0.774 and
0.770; idealized tetrahedral geometry t = 1)[18] with three
very similar Cu-NTp bond lengths (Molecule A: 2.026(3),
2.033(3), 2.046(3); Molecule B: 2.016(3), 2.025(3), 2.050-
(3) ꢀ). This pseudo C3 coordination environment at Cu
renders the highest energy Cu d orbitals essentially degener-
ate to maximize their interaction with the degenerate N2 p*
orbitals (Figure 4). This idealized C3 structure is in marked
contrast to many tris(pyrazolyl)borate copper(II) complexes
Figure 2. Tris(pyrazolyl)borate copper dioxygen (a and b) and diaze-
ne (c) adducts along with a tricopper dinitrogen complex (d).
2299 cmꢁ1).[16c] Copper coordination polymers contain parti-
ally reduced N2 supporting ligands (nN2 = 1607 cmꢁ1) have
been prepared recently.[7b] Murray reported a seminal copper
coordination complex featuring N2 as a ligand in 2014
(Figure 2d). It takes advantage of a strongly donating tris(b-
diketiminato) ligand which upon incorporation of three CuI
ions, binds N2 in an unusual trimetallic manner with a reason-
ably activated N2 ligand (nN2 = 1952 cmꢁ1) that is kinetically
stabilized by the cryptophane binding pocket formed by the
linked b-diketiminate ligands.[7a] Herein, we present the
isolation of the first example of an end-on, molecular
dicopper dinitrogen complex [Cu]2(m-1,2-N2) and its forma-
tion from a mixed valence, dicopper monohydride [Cu]2(m-
H).
that often feature two short and one long Cu NTp bonds.[19]
ꢁ
Although this dicopper dinitrogen complex 3 is stable in the
solid state at ꢁ408C for an extended period, it decays in
solution (CH2Cl2 or toluene) over minutes at room temper-
ature, converting to several untraceable products. Colorless
crystals of 3 slowly crack with gas evolution upon standing at
room temperature.
To unequivocally establish the identity of the trapped
diatomic molecule between the two copper centers in 3,
a solid state sample of 3 was subjected to Raman spectros-
copy. The assignment of the bound dinitrogen stretching
frequency was confirmed through the preparation of 15 N
labelled [iPr2TpCu]2(m-15N2) (3-15N2) under an 15N2 atmos-
phere. Raman difference spectra of 3 (Figure S1B in the
Supporting Information) clearly identify nN2 at 2130 cmꢁ1
(14N2) and 2060 cmꢁ1 (15N2), approximately 200 cmꢁ1 lower
than free 14N2 (2331 cmꢁ1). While the bound N2 ligand in 3 has
a higher nN2 stretching frequency than in Murrayꢁs tricopper
dinitrogen complex Cu3N2L (1952 cmꢁ1),[7a] it is significantly
lower than more weakly bound N2 ligands in copper-
exchanged zeolites such as Cu-ZSM-5 (2295, 2207 cmꢁ1).[16a,e,f]
Simple MO considerations supported by high-level DFT
calculations outline the nature of the [CuI]-N2-[CuI] inter-
action in [iPr2TpCu]2(m-N2) (3). The effective C3 coordination
of the tris(pyrazolyl)borate ligand renders the dyz and dxz
orbitals on the d10 TpCuI fragment degenerate (Figure S22).
This leads to degenerate p-backbonding interactions between
the filled Cu dyz and dxz orbitals and the empty p* levels of the
N2 ligand in the mononuclear TpCu-N2 complex (Figure 4 and
S22). Due to the low energies of the Cu d orbitals, weak p-
backbonding is expected. Interaction with an additional
TpCuI fragment allows for p-backbonding from two trigonal
d10 CuI centers, presumably enhancing the overall copper-
dinitrogen interaction.[4c,5a,6a,20] This simple MO analysis,
however, illustrates that the set of filled dyz/dxz orbitals
brought in by the additional TpCuI fragment is non-bonding
with respect to the N2 p* orbitals. Thus, only modest
enhancement in the copper-dinitrogen interaction is antici-
pated.
The previously reported, blue [iPr2TpCu]2(m-OH)2 was
prepared by mixing a 1m KOH aqueous solution with
iPr2TpCu(NO3) in toluene under an inert atmosphere.[17]
Reaction of [iPr2TpCu]2(m-OH)2 with two equiv Ph3SiH at
ꢁ208C in dichloromethane led to several color changes,
starting from a blue solution that transitioned through purple
and green before becoming colorless with precipitation of
colorless crystals. X-ray crystallography reveals that this
colorless product is [iPr2TpCu]2(m-1,2-N2) (3; Figure 3), iso-
lated in 38% yield. The asymmetric unit of 3 consists of two
crystallographically independent halves in which each
Figure 3. Crystal structure of [iPr2TpCu]2(m-N2) (3), selected bond
lengths [ꢀ] and angles [8] (Molecule A shown). Molecule A: N13-N13’
1.112(5), Cu1-N13 1.829(3), Cu1-N1 2.033(3), Cu1-N3 2.026 (3), Cu1-
N5 2.046(3); N13’-N13-Cu1 177.0(4); Molecule B: N14-N14’ 1.110(6),
Cu2-N14 1.822(3), Cu2-N7 2.050(3), Cu2-N9 2.025(3), Cu2-N11 2.016-
(3); N14’-N14-Cu2 174.7(4). Pink B, dark blue N, light blue Cu.
DFT
[BP86 + GD3BJ/6-311 ++ G(d,p)/SMD-CH2Cl2/
BP86/6-31 + G(d)/gas] calculations on the mono- and dicop-
per adducts iPr2TpCu-N2 (4) and [iPr2TpCu]2(m-N2) (3) support
ꢁ
these simple MO considerations. The calculated N N dis-
2
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binding at the iPr2TpCu fragment. At equal concentrations,
binding of N2 is comparable to that of MeCN, a commonly
employed ligand that often provides labile copper(I) com-
plexes. For instance, exchange of N2 at iPr2TpCu-NCMe to
form iPr2TpCu-N2 (4) with release of MeCN is predicted to be
essentially thermoneutral (DH = 0.3 kcalmolꢁ1
;
DG =
0.6 kcalmolꢁ1). DFT calculations reveal modest cooperativity
that exists in the binding of a second iPr2TpCu fragment to
iPr2TpCu-N2. While binding of N2 to the naked, tripodal
iPr2TpCu fragment is quite favorable (DH = ꢁ22.2 kcalmolꢁ1,
DG = ꢁ11.6 kcalmolꢁ1), addition of a second iPr2TpCu frag-
ment to iPr2TpCu-N2 is even more favorable (DH =
ꢁ29.8 kcalmolꢁ1, DG = ꢁ15.3 kcalmolꢁ1). This positive coop-
erativity is reflected in the reaction of iPr2TpCu-NCMe with
iPr2TpCu-N2 predicted to give [iPr2TpCu]2(m-N2) and MeCN
with DH = ꢁ7.3 kcalmolꢁ1 and DG = ꢁ3.1 kcalmolꢁ1. Under
experimental conditions, however, we do not see the displace-
ment of MeCN by N2, perhaps due to the low solubility of N2
in CH2Cl2 solution.[22] On the other hand, binding of O2 in the
experimentally observed [iPr2TpCu]2(m-h2:h2-O2) (1) is pre-
dicted to be considerably more favorable than N2 binding in 3
Figure 4. p-backbonding and non-bonding orbital interactions in
[TpCu]2(m-N2).
tance marginally increases from iPr2TpCu-N2 (4) (N N:
ꢁ
ꢁ
1.134 ꢀ) to
[
iPr2TpCu]2(m-N2) (3) (N N: 1.149 ꢀ) with
a modest decrease in nN2 (2309 to 2224 cmꢁ1); free N2 values
are 1.117 A and 2349 cmꢁ1 at this level of theory. For each
mono- and dicopper dinitrogen adduct 4 and 3, the degener-
ate sets of LUMOs for both mononuclear and dinuclear
dinitrogen complexes are largely N2 p* in character, with only
minor contributions from the corresponding Cu d orbitals
(Figures 4, S21, and S22).
(DH = ꢁ43.2 kcalmolꢁ1
and
DG = ꢁ38.9 kcalmolꢁ1
;
Scheme 1 and Scheme 2). Thus, such dicopper sites are
highly selective for O2 over N2.
Suggested by its modest thermal stability, the solution
behavior of [iPr2TpCuI]2(m-N2) (3) as monitored by 1H and 15
N
NMR spectroscopy indicated that the bound N2 is quite labile.
For instance, addition of 15N2 to [iPr2TpCuI]2(m-14N2) in
[D2]dichloromethane at ꢁ208C gives a broad 15N NMR
signal (d = 309.0 ppm vs. NH3), suggesting dynamic exchange
between free 15N2 (d = 309.7 ppm vs. NH3) and 3-15N2.
Addition of either excess MeCN or CNAr2,6-Me to a solution
of 3 in dichloromethane releases N2 with clean formation of
the corresponding CuI adducts iPr2TpCu(L) (L = MeCN or
Scheme 2. Calculated thermodynamic parameters for the formation of
[
at 298 K.
iPr2TpCu]2(m-N2) (3) and [iPr2TpCu]2(m-h2:h2-O2) (1). Values in kcalmolꢁ1
CNAr2,6-Me
)
complexes in essentially quantitative yield
Intrigued by the numerous color changes observed upon
(Scheme 1). In addition, 3 reacts readily with O2 at low
temperature to form [iPr2TpCu]2(m-h2:h2-O2) (1; 98% UV/Vis
yield; Scheme 1, X-ray structure in Figure S15). In the
absence of such added ligands, loss of N2 from 3 in dichloro-
methane leads to a mixture of products. [TpCu]2 dimers with
bridging pyrazole arms have been crystallographically iden-
tified for other Tp ligands.[21]
mixing of Ph3SiH and [iPr2TpCu]2(m-OH)2 that ultimately
leads to [iPr2TpCu]2(m-N2) (3), we set out to investigate
possible intermediates en route to N2 capture. Reaction
between
[
iPr2TpCu]2(m-OH)2 and two equiv HSiPh3 in
dichloromethane at ꢁ208C affords a purple complex over
an hour. Although the purple intermediate is reasonably
stable at ꢁ208C at low concentrations (e.g. 1 mm), crystal-
lization attempts are often frustrated by the formation of
colorless crystals of the dicopper dinitrogen species 3.
Given the lability of N2 under experimental conditions, we
employed DFT calculations to outline the strength of N2
Fortunately, reaction between
[
iPr2TpCu]2(m-OH)2 and
HSiPh3 in 1 mm pentane solution at ꢁ208C, followed by
crystallization at ꢁ408C affords purple crystals suitable for X-
ray crystallographic analysis. X-ray diffraction reveals that the
purple intermediate is the dicopper hydride [iPr2TpCu]2(m-H)
(5; Figure 5). Two Cu centers with nearly identical coordina-
tion environments are bridged by a single hydride ligand
found in the Fourier difference map (Cu1-H1 1.78(3), Cu2-H1
1.79(3) ꢀ) to give a short Cu–Cu distance (2.5117(4) ꢀ).
ꢁ
These Cu H bonds are somewhat longer than a previously
reported triangular copper {[CuI2H]}+ core (Cu-Cu = 2.5331-
(15); Cu-H 1.45(2) ꢀ) supported by N-heterocyclic car-
Scheme 1. Synthesis and reactivity of [iPr2TpCuI]2(m-N2) (3).
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Scheme 3. Proposed mechanism for the formation of [iPr2TpCu]2(m-H)
(5) from [iPr2TpCu]2(m-OH)2. Free energies in kcalmolꢁ1 at 298 K.
Figure 5. Crystal structure of [iPr2TpCu]2(m-H) (5), selected bond lengths
[ꢀ] and angles [8]: Cu1-Cu2 2.5117(4), Cu1-H1 1.78(3), Cu2-H11.79(3),
Cu1-N1 2.114(2), Cu1-N3 1.9997(19), Cu1-N5 2.116(2), Cu2-N7 2.024-
(2), Cu2-N9 2.061(2), Cu2-N11 2.109(2); Cu1-H-Cu2 89(1).
strates. Given the challenges in the isolation of [iPr2TpCu]2(m-
H) (5), for reactivity studies we prepared 5 in situ via the
reaction of [iPr2TpCu]2(m-OH)2 and two equiv HSiPh3, mon-
itoring the formation and loss of 5 via its low energy optical
signature at l = 810 nm (e = 1060mꢁ1 cmꢁ1). [iPr2TpCu]2(m-H)
(5) reacts readily with both CO and phenylacetylene at
ꢁ158C in CH2Cl2 to produce formaldehyde (63%) and
styrene (96%) within 30 min. Reaction of [iPr2TpCu]2(m-H)
benes.[23] To our knowledge, 5 represents the first example of
a mixed-valence dicopper hydride.
Hyperfine coupling from two 63/65Cu nuclei observed in
the frozen glass EPR spectra of [iPr2TpCu]2(m-H) (5) at 80 K
suggests a single unpaired electron shared equally among the
two copper centers. The axial spectrum of 5 (gk = 2.250, g? =
2.060) possesses strong, axial hyperfine coupling (Ak(2Cu) =
260 MHz, A?(2Cu) = 35 MHz; Figure 6). IR spectra of 5/5-D
ꢀ
(5) with DC CPh gave a mixture of cis- and trans-styrene-D1
in 37% and 56% yield, respectively (Figure S8). Upon
standing at ꢁ408C in dichloromethane, purple solutions of
[
[
iPr2TpCu]2(m-H) slowly deposit colorless crystals of
iPr2TpCu]2(m-N2).
In light of Kitajimaꢁs seminal finding that TpCu com-
plexes such as [iPr2TpCu]2(m-O2) (1) may be used to model O2
binding and activation in dicopper enzymes hemocyanin and
tyrosinase,[13] it is surprising that the corresponding bridging
N2 species [iPr2TpCu]2(m-N2) (3) was isolated over 20 years
later. DFT studies reveal that N2 binding is competitive with
MeCN, a typical weakly bound ligand in isolable copper(I)
complexes, but is much weaker than O2 binding. Formation of
this dicopper dinitrogen complex involves the intermediacy of
Figure 6. X-band EPR spectrum of 5 in frozen toluene at 80 K.
[
iPr2TpCu]2(m-H) (5), a unique dicopper hydride capable of
ꢀ
reducing triply bound substrates such as CO and HC CPh.
This [Cu]2(m-H) bonding mode that “protects” a highly
reactive terminal [CuII]-H species via a coordinatively unsa-
turated [CuI] species is reminiscent of dicopper carbenes
show an isotope-sensitive Cu-H-Cu vibration at 1573 cmꢁ1 (5)
and 1265 cmꢁ1 (5-D). Nonetheless, no difference is observed
between EPR spectra of 5 and 5-D. DFT calculations predict
little unpaired electron density at the bridging H and indicate
that the Cu centers carry an overwhelming majority of the
spin density (Figure S29).
[Cu]2(m-CPh2)[24] and nitrenes [Cu]2(m-NR)[25] that dissociate
a copper(I) fragment [Cu ] to reveal reactive [Cu] CPh2 and
I
=
=
[Cu] NR species.
Although we have been unable to observe any intermedi-
ate in the formation of 5, we propose that it forms via
iPr2TpCuI capture of iPr2TpCuII-H produced by hydride
Despite the modest backbonding ability exhibited by
many CuI complexes, alongside Murrayꢁs report of a [Cu]3(m-
N2) complex,[7a] our experimental and computational results
suggest that there may be a larger family of synthetically
accessible Cu-N2 complexes. This may offer new opportuni-
ties for N2 reduction chemistry, especially since the iPr2TpCu
exchange between HSiPh3 and
[
iPr2TpCu]2(m-OH)2
(Scheme 3). DFT studies reveal that bimolecular coupling
of the putative copper(II) hydride iPr2TpCuII-H to generate H2
along with 2 equiv iPr2TpCu is quite thermodynamically
downhill (DH = ꢁ29.0 kcalmolꢁ1, DG = ꢁ37.5 kcalmolꢁ1).
Similarly, capture of iPr2TpCuII-H by iPr2TpCuI-NCMe to
stabilize the copper hydride as [iPr2TpCu]2(m-H) (5) with
formation of MeCN is also favorable (DH =-30.7 kcalmolꢁ1,
DG = ꢁ23.4 kcalmolꢁ1).
=
fragment supports both the N2 and HN NH ligands in
[
iPr2TpCu]2(m-N2) (3) and [iPr2TpCu]2(m-N2H2) (2) complexes
(Figure 2c).[14] Moreover, closely related tris(pyrazolyl)bo-
rate and tris(pyrazolyl)methane copper complexes support
reduced nitrogen species, such as isolable copper(I) hydrazine
adducts [CuI]-NH2NH2 and {[CuI]2(m-NH2NH2)}2+, respec-
tively.[26]
To provide further support for a reactive hydride inter-
mediate, we examined reactions with small molecule sub-
4
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[11] S. Yao, Y. Xiong, M. Vogt, H. Grꢂtzmacher, C. Herwig, C.
Acknowledgements
Limberg, M. Driess, Angew. Chem. Int. Ed. 2009, 48, 8107;
Angew. Chem. 2009, 121, 8251.
T.H.W. is grateful for support from the National Science
Foundation (CHE-1459090) and the Georgetown Environ-
ment Initiative. T.H.W. also acknowledges NSF for funds to
purchase an X-ray diffractometer (CHE-1337975). T.R.C.
thanks NSF for support of this research through grant CHE-
1464943.
[12] a) E. A. Lewis, W. B. Tolman, Chem. Rev. 2004, 104, 1047;
b) E. I. Solomon, D. E. Heppner, E. M. Johnston, J. W. Gins-
bach, J. Cirera, M. Qayyum, M. T. Kieber-Emmons, C. H.
Kjaergaard, R. G. Hadt, L. Tian, Chem. Rev. 2014, 114, 3659;
c) L. M. Mirica, X. Ottenwaelder, T. D. P. Stack, Chem. Rev.
2004, 104, 1013; d) E. E. Chufan, S. C. Puiu, K. D. Karlin, Acc.
Chem. Res. 2007, 40, 563.
[13] N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Morooka, S. Hashi-
moto, T. Kitagawa, K. Toriumi, K. Tatsumi, A. Nakamura, J. Am.
Chem. Soc. 1992, 114, 1277.
Keywords: copper · dinitrogen · hydride ·
mixed-valent compounds · reduction
[14] K. Fujisawa, N. Lehnert, Y. Ishikawa, K. Okamoto, Angew.
Chem. Int. Ed. 2004, 43, 4944; Angew. Chem. 2012, 124, 5052.
ˇ
[15] C. L. Gatlin, F. Turecek, T. Vaisar, J. Mass Spectrom. 1995, 30,
775.
[16] a) A. Itadani, H. Sugiyama, M. Tanaka, T. Mori, M. Nagao, Y.
Kuroda, J. Phys. Chem. C 2007, 111, 16701; b) Y. Kuroda, S.
Konno, K. Morimoto, Y. Yoshikawa, J. Chem. Soc. Chem.
Commun. 1993, 18; c) Y. Kuroda, Y. Yoshikawa, S.-i. Konno, H.
Hamano, H. Maeda, R. Kumashiro, M. Nagao, J. Phys. Chem.
1995, 99, 10621; d) Y. Kuroda, Y. Yoshikawa, S. Emura, R.
Kumashiro, M. Nagao, J. Phys. Chem. B 1999, 103, 2155; e) G.
Spoto, S. Bordiga, G. Ricchiardi, D. Scarano, A. Zecchina, F.
Geobaldo, J. Chem. Soc. Faraday Trans. 1995, 91, 3285; f) A. I.
Serykh, M. D. Amiridis, Microporous Mesoporous Mater. 2006,
94, 320.
[1] P. L. Holland, Dalton Trans. 2010, 39, 5415.
[2] a) L. Vaska, Acc. Chem. Res. 1976, 9, 175; b) J. S. Valentine,
Chem. Rev. 1973, 73, 235; c) M. Momenteau, C. A. Reed, Chem.
Rev. 1994, 94, 659; d) R. D. Jones, D. A. Summerville, F. Basolo,
Chem. Rev. 1979, 79, 139.
[3] A. D. Allen, C. V. Senoff, Chem. Commun. 1965, 621.
[4] a) B. A. MacKay, M. D. Fryzuk, Chem. Rev. 2004, 104, 385;
b) M. D. Fryzuk, S. A. Johnson, Coord. Chem. Rev. 2000, 200 –
202, 379; c) S. F. McWilliams, P. L. Holland, Acc. Chem. Res.
2015, 48, 2059.
[5] a) K. Ding, A. W. Pierpont, W. W. Brennessel, G. Lukat-
Rodgers, K. R. Rodgers, T. R. Cundari, E. Bill, P. L. Holland,
J. Am. Chem. Soc. 2009, 131, 9471; b) T. A. Betley, J. C. Peters, J.
Am. Chem. Soc. 2003, 125, 10782; c) A. C. Bowman, C.
Milsmann, C. C. Hojilla Atienza, E. Lobkovsky, K. Wieghardt,
P. J. Chirik, J. Am. Chem. Soc. 2010, 132, 1676; d) A. E.
Carpenter, G. W. Margulieux, M. D. Millard, C. E. Moore, N.
Weidemann, A. L. Rheingold, J. S. Figueroa, Angew. Chem. Int.
Ed. 2012, 51, 9412; Angew. Chem. 2012, 124, 9546; e) J. W.
Egan, Jr., B. S. Haggerty, A. L. Rheingold, S. C. Sendlinger,
K. H. Theopold, J. Am. Chem. Soc. 1990, 112, 2445; f) A. R.
Fout, F. Basuli, H. Fan, J. Tomaszewski, J. C. Huffman, M.-H.
Baik, D. J. Mindiola, Angew. Chem. Int. Ed. 2006, 45, 3291;
Angew. Chem. 2006, 118, 3369; g) C. C. Hojilla Atienza, C.
Milsmann, S. P. Semproni, Z. R. Turner, P. J. Chirik, Inorg.
Chem. 2013, 52, 5403; h) S. L. Marquard, M. W. Bezpalko, B. M.
Foxman, C. M. Thomas, J. Am. Chem. Soc. 2013, 135, 6018; i) Y.
Miura, A. Yamamoto, Chem. Lett. 1978, 937; j) D. L. M. Suess,
C. Tsay, J. C. Peters, J. Am. Chem. Soc. 2012, 134, 14158; k) A.
Yamamoto, Y. Miura, T. Ito, H. L. Chen, K. Iri, F. Ozawa, K.
Miki, T. Sei, N. Tanaka, N. Kasai, Organometallics 1983, 2, 1429;
l) D. Zhu, P. H. M. Budzelaar, Organometallics 2010, 29, 5759.
[6] a) S. Pfirrmann, C. Limberg, C. Herwig, R. Stoesser, B. Ziemer,
Angew. Chem. Int. Ed. 2009, 48, 3357; Angew. Chem. 2009, 121,
3407; b) R. Beck, M. Shoshani, J. Krasinkiewicz, J. A. Hatnean,
S. A. Johnson, Dalton Trans. 2013, 42, 1461; c) S. J. Connelly,
A. C. Zimmerman, W. Kaminsky, D. M. Heinekey, Chem. Eur. J.
2012, 18, 15932; d) Y.-E. Kim, J. Kim, Y. Lee, Chem. Commun.
2014, 50, 11458; e) C. Tsay, J. C. Peters, Chem. Sci. 2012, 3, 1313;
f) R. Waterman, G. L. Hillhouse, Can. J. Chem. 2005, 83, 328.
[7] a) L. J. Murray, W. W. Weare, J. Shearer, A. D. Mitchell, K. A.
Abboud, J. Am. Chem. Soc. 2014, 136, 13502; b) W. Hsu, K. B.
Thapa, X.-K. Yang, K.-T. Chen, H.-Y. Chang, J.-D. Chen,
CrystEngComm 2016, 18, 390.
[17] K. Fujisawa, T. Kobayashi, K. Fujita, N. Kitajima, Y. Moro-oka,
Y. Miyashita, Y. Yamada, K.-i. Okamoto, Bull. Chem. Soc. Jpn.
2000, 73, 1797.
[18] L. Yang, D. R. Powell, R. P. Houser, Dalton Trans. 2007, 955.
[19] a) J. S. Thompson, T. J. Marks, J. A. Ibers, J. Am. Chem. Soc.
1979, 101, 4180; b) J. S. Thompson, T. J. Marks, J. A. Ibers, Proc.
Natl. Acad. Sci. USA 1977, 74, 3114; c) N. Kitajima, K. Fujisawa,
M. Tanaka, Y. Morooka, J. Am. Chem. Soc. 1992, 114, 9232; d) N.
Kitajima, K. Fujisawa, Y. Morooka, J. Am. Chem. Soc. 1990, 112,
3210; e) D. Qiu, L. Kilpatrick, N. Kitajima, T. G. Spiro, J. Am.
Chem. Soc. 1994, 116, 2585.
[20] J. M. Smith, A. R. Sadique, T. R. Cundari, K. R. Rodgers, G.
Lukat-Rodgers, R. J. Lachicotte, C. J. Flaschenriem, J. Vela, P. L.
Holland, J. Am. Chem. Soc. 2006, 128, 756.
[21] a) C. Mealli, C. S. Arcus, J. L. Wilkinson, T. J. Marks, J. A. Ibers,
J. Am. Chem. Soc. 1976, 98, 711; b) S. M. Carter, C. E. Ruggiero,
R. P. Houser, W. B. Tolman, Inorg. Chem. 1993, 32, 4889; c) Z.
Hu, R. D. Williams, D. Tran, T. G. Spiro, S. M. Gorun, J. Am.
Chem. Soc. 2000, 122, 3556; d) T. Augenstein, F. Dorner, K.
Reiter, H. E. Wagner, D. Garnier, W. Klopper, F. Breher, Chem.
Eur. J. 2016, 22, 7935.
[22] K. Shirono, T. Morimatsu, F. Takemura, J. Chem. Eng. Data
2008, 53, 1867.
[23] C. M. Wyss, B. K. Tate, J. Bacsa, T. G. Gray, J. P. Sadighi, Angew.
Chem. Int. Ed. 2013, 52, 12920; Angew. Chem. 2013, 125, 13158.
[24] X. Dai, T. H. Warren, J. Am. Chem. Soc. 2004, 126, 10085.
[25] a) Y. M. Badiei, A. Krishnaswamy, M. M. Melzer, T. H. Warren,
J. Am. Chem. Soc. 2006, 128, 15056; b) Y. M. Badiei, A. Dinescu,
X. Dai, R. M. Palomino, F. W. Heinemann, T. R. Cundari, T. H.
Warren, Angew. Chem. Int. Ed. 2008, 47, 9961; Angew. Chem.
2008, 120, 10109; c) M. J. B. Aguila, Y. M. Badiei, T. H. Warren,
J. Am. Chem. Soc. 2013, 135, 9399.
[26] F. Paulat, N. Lehnert, Y. Ishikawa, K.-I. Okamoto, K. Fujisawa,
Inorg. Chim. Acta 2008, 361, 901.
[8] S. Yao, E. Bill, C. Milsmann, K. Wieghardt, M. Driess, Angew.
Chem. Int. Ed. 2008, 47, 7110; Angew. Chem. 2008, 120, 7218.
[9] W. H. Monillas, G. P. A. Yap, L. A. MacAdams, K. H. Theopold,
J. Am. Chem. Soc. 2007, 129, 8090.
Received: April 24, 2016
[10] D. C. Cummins, G. P. A. Yap, K. H. Theopold, Eur. J. Inorg.
Chem. 2016, DOI: 10.1002/ejic.201501326.
Revised: June 14, 2016
Published online: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Dinitrogen Complexes
S. Zhang, H. Fallah, E. J. Gardner,
S. Kundu, J. A. Bertke, T. R. Cundari,*
T. H. Warren*
&&&& — &&&&
A Dinitrogen Dicopper(I) Complex via
a Mixed-Valence Dicopper Hydride
Caught between two coppers: A tris(pyr-
azolyl)borate (Tp) dicopper N2 complex
[CuI]2(m-N2) forms through the interme-
diacy of a mixed-valence dicopper hydride
[Cu1·5]2(m-H). Besides allowing a direct
comparison between N2 and O2 binding
at copper(I), this [CuI]2(m-N2) complex
represents a key member in a family of
I
=
TpCu complexes [Cu ]2(m-NH NH) and
[CuI](NH2NH2) featuring reduced N2
ligands.
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!