Synthesis and investigation of the metal-metal interactions in early/late heterobimetallic complexes linking group 5 imido fragments to Co(i)

Article abstract of DOI:10.1039/c2dt00034b

Phosphinoamide ligands have been utilized to link a Co^I center to a Nb or Ta imido fragment. The resulting heterobimetallic complexes, ICo(Ph₂PNⁱPr)₃MN^tBu, have weakened dative metal-metal interactions as a result of the strongly donating imido ligand. These complexes can be reduced by 2 electrons to generate dinitrogen-bound complexes.

Full text of DOI:10.1039/c2dt00034b

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PAPER
Synthesis and investigation of the metal–metal interactions in early/late
heterobimetallic complexes linking group 5 imido fragments to Co(I)†
Deirdra A. Evers, Alia H. Bluestein, Bruce M. Foxman and Christine M. Thomas*
Received 5th January 2012, Accepted 24th February 2012
DOI: 10.1039/c2dt00034b
Phosphinoamide ligands have been utilized to link a CoI center to a Nb or Ta imido fragment. The
resulting heterobimetallic complexes, ICo(Ph2PNiPr)3MvNtBu, have weakened dative metal–metal
interactions as a result of the strongly donating imido ligand. These complexes can be reduced by 2
electrons to generate dinitrogen-bound complexes.
Bimetallic complexes featuring interactions between an early
transition metal and a late transition metal center have re-
emerged as interesting targets with potential applications as
bifunctional catalysts for the activation of small molecule sub-
strates and organic transformations.1–4 With the overall goal of
cooperative reactivity in mind, our group has been exploring
early/late heterobimetallic complexes utilizing the hard/soft
donor combination provided by phosphinoamide ligands.5
Specifically, our primary focus thus far has been Zr–Co com-
heterobimetallic complexes in the literature, very few examples
of Group 5/Co heterobimetallic complexes have been reported.
These include a single example of a Nb–Co complex, Cp2CoNb-
(μ-CO)Co(CO)3,14 and two heterobimetallic Ta–Co complexes
reported by Bergman and coworkers.15,16
Unlike the previously reported Zr metalloligand, simple
addition of a lithiated phosphinoamide ligand to Ta or Nb halide
MX5 starting materials did not lead to the desired X2M
t
(iPrNPPh2)3 products. Instead, the Bu-imido starting materials
i
plexes of the type ClZr(R′NPR2)3CoI (R′ = Mes, Pr; R = Ph,
tBuNvMCl3(pyr)2 (pyr = pyridine) were treated with three
iPr). Among our more substantive findings are: (1) a dramatic
increase in Co reduction potential as a result of dative donation
to Zr,6 (2) the ability to stabilize unusual structural motifs via
formation of Co → Zr multiple bonds,7 and (3) the facile bi-
metallic activation of substrates such as alkyl halides, H2, and
CO2.8–10 The strength of the metal–metal interactions and the
reactivity of these compounds are affected not only by the iden-
tity of the phosphine and amido substituents, but also the ancil-
lary ligands on both the early and late transition metal.6–9,11
Thus far, however, our investigations have essentially been
limited to Zr–Co complexes, and the Hf–Co combination
revealed only minor differences from Zr analogues.12 Herein we
report Nb–Co and Ta–Co complexes, with the goal of evaluating
differences in structure and reactivity as a function of early metal
identity. For synthetic accessibility reasons, however, we have
also replaced the early metal halide with an electron-rich imido
fragment, somewhat complicating our comparison.
equivalents of LiNiPrPPh2 at low temperature to afford the tris
t
(phosphinoamide) metalloligands BuNvM(iPrNPPh2)3 (M =
Nb (1Nb), Ta (1Ta)), as shown in Scheme 1. A single 31P NMR
resonance is observed at room temperature for 1Nb and 1Ta at
11.4 and 8.7 ppm, respectively. However, the solid state structure
of 1Nb (Fig. 1) reveals that only one phosphine is bound to Nb in
the solid state (Nb–P2 = 2.6362(4) Å), while the other two Nb–P
distances are too long to signify a significant interaction (2.9431
(5) Å, 2.9550(4) Å). Since the planarity of the three phosphino-
amide nitrogen atoms signifies π-donation to Nb, a simple elec-
tron counting argument accounts for this phenomenon. In
solution, however, M-phosphine binding is sufficiently reversible
to allow coordination of these Group 5 metalloligands to Co.
While Ta and Nb have considerably smaller covalent radii
and greater electronegativity than the Group IV elements,13 we
anticipated that the availability of multiple common oxidation
states may lead to enhanced redox activity in early/late hetero-
bimetallic combinations. Despite the abundance of early/late
Department of Chemistry, Brandeis University, 415 South Street, MS
015 Waltham, Massachusetts, USA. E-mail: thomasc@brandeis.edu;
Fax: +(781)736-2516; Tel: +(781)736-2576
†Electronic supplementary information (ESI) available: experimental
procedures, additional spectral data, and crystallographic details and data
in CIF format for 1–3. CCDC 862673–862677. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c2dt00034b
Scheme 1 Synthesis of heterobimetallic Co–MvNtBu complexes.
Dalton Trans., 2012, 41, 8111–8115 | 8111
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Fig. 1 Displacement ellipsoid (50%) representation of 1Nb. Hydrogen
atoms have been omitted for clarity. Relevant interatomic distances (Å):
Nb–N1, 2.0526(13); Nb–N2, 2.1028(13); Nb–N3, 2.0797(13); Nb–N4,
1.7659(14); Nb–P1, 2.9431(5); Nb–P2, 2.6362(4); Nb–P3, 2.9550(4).
Fig. 3 Cyclic voltammograms of 2Nb (red) and 2Ta (black) in 0.4 M
[nBu4N][PF6] in THF (scan rate: 100 mV s−1).
also relatively long. The strong donating ability of the tert-butyl
imido ligand likely attenuates the Lewis acidity of the MV
centers, eliminating the need for the early metal to datively
accept electron density from Co.
In the absence of direct metal → metal bonding, we were
curious to ascertain whether the proximity of the early metal
center would still affect the redox activity at the Co center. Inter-
estingly, the cyclic voltammograms (CVs) of both 2Nb and 2Ta
Fig. 2 Displacement ellipsoid (50%) representation of 2Nb and 2Ta
.
revealed reversible reductions at identical potentials (E1/2
=
Hydrogen atoms have been omitted for clarity. Relevant interatomic dis-
tances (Å) and angles (°): 2Nb: Nb–Co, 3.0319(4); Nb–N4, 1.775(2);
Co–I, 2.5316(4); Nb–N4–C46, 177.9(2). 2Ta: Ta–Co, 3.0388(3); Ta–N4,
1.788(2); Co–I, 2.5315(4); Ta–N4–C46, 178.04 (17).
−2.02 V, Fig. 3). A subsequent irreversible reduction was also
observed at −2.83 V for both species. Thus, both the reversibil-
ity and the reduction potentials of these heterobimetallic
complexes differ substantially from the monometallic
(Ph2PNHiPr)3CoI complex, whose CV features two subsequent
irreversible reductions at −2.49 and −2.66 V.6 It is also impor-
tant to note that the CV of the analogous Zr–Co complex ClZr
(iPrNPPh2)3CoI also features a reversible reduction followed by
an irreversible reduction, but the redox potentials in this case are
ca. 0.4 V more positive (−1.65 V and −2.45 V).6 Thus, we can
conclude that the presence of the proximal group 5 metal plays a
role in facilitating reduction of Co even in the absence of a direct
metal–metal dative bond, suggesting the importance of electronic
communication through the phosphinoamide ligand and/or
through space.
Accordingly, treatment of 1Nb and 1Ta with one equiv CoI2
leads to clean formation of the blue/green heterobimetallic com-
t
plexes BuNvM(iPrNPPh2)CoI (M = Nb (2Nb), Ta (2Ta)) in
46.6% and 40.4% yield (Scheme 1). While the exact mechanism
of Co reduction from CoII to CoI in these products is unclear,
this reduction is consistent with that observed in the synthesis of
similar M–Co complexes (M = Zr, Hf).6,12 Both 2Nb and 2Ta are
1
S = 1 complexes with broadened and shifted H NMR spectra,
but the expected number of resonances are observed. Of interest
in these compounds are the M–Co distances as an indication of
metal–metal interactions. Thus, the solid state structures of 2Nb
and 2Ta were obtained and are presented in Fig. 2. The isostruc-
tural Nb–Co and Ta–Co compounds feature M–Co distances
(3.03194 (4) Å and 3.0338(3) Å, respectively) larger than the
sum of the covalent radii of Ta/Nb and Co (2.50 Å)13 and longer
than those in the corresponding Zr–Co (2.7315(5) Å)6 and
Hf–Co (2.7548(5) Å)12 complexes. Nonetheless, the metal–
metal distances in previously reported bimetallic Nb–Co (2.986
(1) Å)14 and Ta–Co (2.708 Å, 2.8005(8) Å)15,16 complexes are
Another interesting feature observed in the CV of 2Nb and 2Ta
is a quasi-reversible one-electron oxidation at 0.00 and 0.05 V,
respectively (Fig. 3). The previously studied Zr–Co heterobime-
tallic complex ClZr(iPrNPPh2)3CoI was found to undergo com-
pletely irreversible oxidation processes at 0.32 and 0.53 V.6
Since the oxidation potentials are shifted cathodically and the
oxidative processes become more reversible in the case of the
Nb–Co and Ta–Co bimetallic complexes, it can be concluded
that the absence of a Co → M interaction in the group 5 metal
8112 | Dalton Trans., 2012, 41, 8111–8115
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In summary, tantalum and niobium imido fragments have
been linked to a CoI center through a C3-symmetric phosphino-
amide ligand framework. The metal–metal interactions in these
complexes are far less pronounced than those in similar Zr–Co
and Hf–Co complexes, as evidenced by longer metal–metal dis-
tances, less dramatic effects on the CoI/−I reduction potential,
and stronger backbonding of Co to N2 in reduced complexes.
These differences are more likely attributed to the strong π-donor
imido ligand bound to the early metal than to differences
between the electronic properties of Group IV and Group V
metals. Future investigations will target similar Nb or Ta-con-
taining heterobimetallic species with more labile, less electron-
donating ancillary ligands on the early metal fragment.
Scheme 2 Reduction of M–Co complexes to form anionic N2
complexes.
Experimental
General considerations
All syntheses reported were carried out using standard glovebox
and Schlenk techniques in the absence of water and dioxygen,
unless otherwise noted. Benzene, pentane, diethyl ether, tetra-
hydrofuran, and toluene were degassed and dried by sparging
with N2 gas followed by passage through an activated alumina
column. All solvents were stored over 3 Å molecular sieves.
Deuterated benzene was purchased from Cambridge Isotope
Laboratories, Inc., degassed via repeated freeze–pump–thaw
cycles, and dried over 3 Å molecular sieves. Solvents were fre-
quently tested using a standard solution of sodium benzophe-
none ketyl in tetrahydrofuran to confirm the absence of oxygen
and moisture. LiNiPrPPh2 was synthesized using a modification
Fig. 4 Displacement ellipsoid (50%) representation of 3Nb. Hydrogen
atoms have been omitted for clarity. Relevant interatomic distances (Å)
and angles (°): Nb–Co, 2.8492(4); Co–N4, 1.768(3); N4–N5, 1.115(4);
N5–Na, 2.489(3); Nb–N6, 1.810(3); Nb–N6–C46, 179.1(3).
of
a
literature procedure.17,18 tBuNvNbCl3(pyr)2 and
tBuNvTaCl3(pyr)2 were synthesized via a literature procedure.19
All other chemicals were purchased from commercial vendors
and used without further purification. NMR spectra were
recorded at ambient temperature on a Varian Inova 400 MHz
complexes facilitates oxidation of CoI to CoII. This can be
justified by the more electron rich nature of the Co center and
the anticipated higher energy of the highest doubly-occupied
orbital (dz2) in 2Nb and 2Ta in the absence of dative electron
donation to an early metal center.
1
instrument. H and 13C NMR chemical shifts were referenced to
residual solvent. 31P NMR chemical shifts were referenced to
85% H3PO4. IR spectra were recorded on a Varian 640-IR spec-
trometer controlled by Resolutions Pro software. UV-vis spectra
were recorded on a Cary 50 UV-vis spectrophotometer using
Cary WinUV software. Elemental microanalyses were performed
by Complete Analysis Laboratories, Inc., Parsippany, NJ.
In light of the reversible reductive events in the CVs of 2Nb
and 2Ta, their bulk chemical reduction was investigated. Similar
to the Co–Zr complexes, treatment of 2Nb and 2Ta with excess
Na/Hg in a dinitrogen-filled glovebox affords deep red N2-bound
two-electron reduction products [tBuNvM(iPrNPPh2)3CoN2]-
[Na(THF)5] (M = Nb (3Nb), Ta (3Ta), Scheme 2). Both 3Nb and
3Ta are diamagnetic with infrared N2 vibrations at 1940 cm−1
.
These stretching frequencies are significantly lower in energy
compared to the analogous reduced Co–N2 complex tethered to
Zr–X fragments (2016 cm−1).8 In the absence of strong dative
Co → M donation, the Co center has more electron density avail-
able for backbonding with the π acidic N2 unit, substantially
lowering the energy of ν(N2) in 3Nb and 3Ta. Consistent with the
spectroscopic data, the solid state structures of 3Nb and 3Ta
(Fig. 4 and S5†) reveal M–Co distances that are contracted from
those in 2Nb and 2Ta but still well outside the range expected for
strong metal–metal interactions (2.8492(4) Å (3Nb); 2.8538(5) Å
(3Ta)). It is also interesting to note that upon reduction of Co in
3Nb and 3Ta, the M–Nimido distance lengthens noticeably (1.775
(2) Å/1.788(2) Å to 1.810(3) Å/1.811(3) Å), perhaps a result of
the reduced Co center and the imido fragment competing to
donate π electron density into the empty dxz and dyz orbitals on
the Group 5 metal center.
Synthesis of (Ph2PNiPr)3NbvNtBu (1Nb
)
LiNiPrPPh2 (2.039 g, 8.188 mmol) was suspended in a small
amount of Et2O and cooled to −78 °C. BuNvNbCl3(pyr)2
t
(1.179 g, 2.729 mmol) was added to the stirring solution as a
solid. The reaction mixture, which immediately became cloudy
and blue/gray, was allowed to come to room temperature and stir
overnight. The mixture was brought to dryness under vacuum
and re-dissolved in dichloromethane. The resulting solution was
filtered through Celite to remove LiCl and again dried in vacuo.
The remaining solids were washed with pentane until they were
white and dried in vacuo (1.357, 55.9% yield). 1H NMR
(400 MHz, CDCl3): δ 7.37 (m, 12H, o-Ph), 7.16 (m, 6H, p-Ph),
7.09 (m, 12H, m-Ph), 3.84 (m, 3H, CH(CH3)2), 1.36 (s, 9H,
tBu), 1.21 (d, J = 8.0 Hz, 18H, CH(CH3)2). 31P{1H} NMR
(161.8 MHz, CDCl3): δ 11.4 (s). 13C{1H} NMR (100.5 MHz,
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Dalton Trans., 2012, 41, 8111–8115 | 8113

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C6D6) δ 139.3 (ipso-Ph), 134.2 (Ph), 128.3–127.8 (Ph, overlap-
ping with C6D6), 55.16 (NCH(CH3)2), 34.3 (tBu), 28.4 (s, NCH
(CH3)2). Anal. Calcd for C49H60N4P3Nb: C, 66.06; H, 6.79; N,
6.29. Found: C, 66.09; H, 6.79; N, 6.41.
via vapor diffusion of pentane into a concentrated toluene sol-
1
ution of 2Ta at room temp. H NMR (400 MHz, C6D6): δ 15.3
t
(br s, Ph), 8.8 (br, CH(CH3)2), 1.4 (br s, Bu), 0.8 (br s, CH
(CH3)2), −7.0 (br s, Ph), −7.7 (br s, Ph). UV-vis: (λ, nm (ε,
cm−1 M−1)): 309 (11 000), 360 (5100), 611 (80), 750 (50), 875
(230). Evans’ method (C6D6): 2.88 μB. Anal. Calcd for
C49H60N4P3TaCoI: C, 50.53; H, 5.19; N, 4.81. Found: C, 50.37;
H, 5.17; N, 4.65.
Synthesis of (Ph2PNiPr)3TavNtBu (1Ta
)
A suspension of LiNiPrPPh2 (5.7462 g, 23.077 mmol) in Et2O
was cooled to −78 °C. To this stirring solution was added
tBuNvTaCl3(pyr)2 (3.9724 g, 7.692 mmol) in Et2O. The sol-
ution, which immediately became cloudy, was allowed to warm
to room temperature and stir for 2 hours. The resulting solution
was filtered through Celite to remove LiCl and the solvent was
removed from the filtrate in vacuo. The remaining solids were
washed twice with pentane and dried in vacuo to yield analyti-
Synthesis of [(THF)5Na][N2Co(Ph2PNiPr)3NbvNtBu] (3Nb
)
A 0.5% Na/Hg amalgam was prepared from 3.0 mg of Na
(0.13 mmol) and 595 mg of Hg. The amalgam was vigorously
stirred in a small amount of THF. To this mixture was added 2Nb
(56 mg, 0.052 mmol) in a small amount of THF. The reaction
mixture was stirred for 4 hours at room temperature as the color
changed from blue/green to red. The mixture was then decanted
away from the amalgam and filtered through glass microfiber
filter paper. The volume of the filtrate was reduced in vacuo, and
pentane was layered onto the remaining solution. Storage at
−35 °C for 12 hours resulted in spectroscopically pure product
as red crystals (40 mg, 71% yield). Crystals suitable for X-ray
diffraction were grown via vapor diffusion of pentane into a con-
1
cally pure product as a white solid (4.155 g, 44.77% yield). H
NMR (400 MHz, C6D6): δ 7.63 (m, 12H, o-Ph), 7.01 (m, 18H,
m,p-Ph), 4.25 (m, 3H, CH(CH3)2), 1.57 (s, 9H, tBu), 1.41 (d, J =
6.0 Hz, 18H, CH(CH3)2). 31P{1H} NMR (161.8 MHz, C6D6): δ
8.7 (s). 13C{1H} NMR (100.5 MHz, C6D6): δ 134.3 (s, Ph),
128.3–127.8 (Ph, overlapping with C6D6), 55.0 (s, NCH(CH3)2),
t
35.4 (s, s, Bu), 28.2 (s, NCH(CH3)2), ipso-Ph not observed.
Anal. Calcd for C49H60N4P3Ta: C, 60.12; H, 6.18; N, 5.72.
Found: C, 59.63; H, 6.19; N, 5.51.
1
centrated THF solution of 3Nb. H NMR (400 MHz, THF-d8): δ
7.23 (s, 12H, o-Ph), 6.72 (m, 18H, m/p-Ph), 4.05 (s, 3H, CH
t
(CH3)2), 3.58 (m, THF), 1.74 (br s, THF), 1.58 (s, 9H, Bu),
Synthesis of ICo(Ph2PNiPr)3NbvNtBu (2Nb
)
1.23 (br s, 18H, CH(CH3)2). 31P{1H} NMR (161.8 MHz, THF-
d8): δ 70.4 (br s). 13C{1H} NMR (100.5 MHz, THF-d8): δ 145.6
(s, ipso-Ph), 134.1 (s, Ph) 126.0 (s, Ph) 125.4 (s, Ph), 52.0 (s,
CH(CH3)2), 34.0 (s, tBu), 27.4 (s, CH(CH3)2). IR: (KBr solution
cell, THF): 1940 cm−1. UV-vis: (λ, nm (δ, cm−1 M−1)): 360
(10 000), 465 (8000), 792 (210), 903 (150). Satisfactory com-
bustion analysis data could not be obtained. This is likely a
result of the extreme sensitivity of the complex to air and moist-
ure and the lability of the bound N2 unit.
Solid 1Nb (1.499 g, 1.685 mmol) and CoI2 (0.527 g,
1.685 mmol) were combined in THF and stirred overnight at
room temperature. The resulting dark green mixture was filtered
through a frit leaving light blue/green solids and a dark green
mother liquor. The solids were washed with toluene to yield 2Nb
as a light blue solid. The solvent was removed from the mother
liquor in vacuo and the remaining dark green residue was
washed with toluene and a second crop of light blue/green solids
were collected via filtration. This process was repeated with the
toluene washings to precipitate a third crop of 2Nb (0.838 g,
46.6% yield). Blue crystals suitable for X-ray diffraction were
grown from concentrated toluene at −35 °C. 1H NMR
Synthesis of [(THF)5Na][N2 Co(Ph2PNiPr)3TavNtBu] (3Ta
)
A 0.5% Na/Hg amalgam was prepared from 3.6 mg of Na
(0.16 mmol) and 716 mg of Hg. The amalgam was vigorously
stirred in a small amount of THF. To this mixture was added 2Ta
(73 mg, 0.063 mmol) in a small amount of THF. The reaction
mixture was stirred for 4 hours at room temperature as the color
changed from blue/green to red. The mixture was then decanted
away from the amalgam and filtered through glass microfiber
filter paper. The volume of the filtrate was reduced in vacuo, and
pentane was layered onto the remaining solution. Storage at
−35 °C for 12 hours resulted in spectroscopically pure product
as red crystals (72 mg, 98% yield). Crystals suitable for X-ray
diffraction were grown via vapor diffusion of pentane into a con-
t
(400 MHz, C6D6): δ 15.2 (br s, Ph), 1.2 (br s, Bu), 0.9 (br s,
Ph), −7.6 (br s, Ph). UV-vis: (λ, nm (ε, cm−1 M−1)): 311 (8900),
360 (4400), 585 (60), 877 (200). Evans’ method (C6D6):
2.82 μB. Anal. Calcd for C49H60N4P3NbCoI: C, 54.66; H, 5.62;
N, 5.20. Found: C, 54.19; H, 5.75; N, 4.88.
Synthesis of ICo(Ph2PNiPr)3TavNtBu (2Ta
)
Solid 1Ta (205 mg, 0.209 mmol) and CoI2 (65.5 mg,
0.209 mmol) were combined in THF and stirred overnight at
room temperature. The resulting dark green mixture was filtered
through a frit leaving light blue/green solids and a dark green
mother liquor. The solids were washed with toluene to yield 2Ta
as a light blue solid. The solvent was removed from the mother
liquor in vacuo and the remaining dark green residue was
washed with toluene and a second crop of light blue/green solids
were collected via filtration. This process was repeated with the
toluene washings to precipitate a third crop of 2Ta (98.2 mg,
40.4%). Blue crystals suitable for X-ray diffraction were grown
centrated THF solution of 3Ta. H NMR (400 MHz, THF-d8): δ
7.31 (s, 12H, o-Ph), 6.75 (m, 18H, m/p-Ph), 4.38 (s, 3H, CH
1
t
(CH3)2), 3.62 (m, THF), 1.77 (m, THF), 1.59 (s, 9H, Bu), 1.26
(m, 18H, CH(CH3)2). 31P{1H} NMR (161.8 MHz, THF-d8): δ
69.8 (br s). 13C{1H} NMR (100.5 MHz, THF-d8): δ 145.5 (s,
ipso-Ph), 134.4 (s, Ph) 126.4 (s, p-Ph) 125.8 (s, m-Ph), 51.9 (s,
t
CH(CH3)2), 35.5 (s, Bu), 27.8 (s, CH(CH3)2). IR (KBr solution
cell, THF): 1940 cm−1. UV-vis: (λ, nm (ε, cm−1 M−1)): 313
8114 | Dalton Trans., 2012, 41, 8111–8115
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Table 1 X-Ray diffraction experimental details for 1Nb, 2Nb, 2Ta, 3Nb and 3Ta
1Nb
2Nb
2Ta
3Nb
3Ta
Chemical formula
Fw
C49H60N4NbP3
890.87
120
C63H76CoIN4NbP3
1260.99
120
0.71073
13.1155(4)
18.2831(6)
25.2678(8)
90
95.274(2)
90
6033.4(3)
P21/c
C63H76CoIN4P3Ta
1349.03
120
0.71073
13.1400(6)
18.2564(7)
25.2782(11)
90
95.270(2)
90
6038.3(4)
P21/c
C69H100CoN6NaNbO5P3
1361.34
120
C69H100CoN6NaO5P3Ta
1449.38
120
T (K)
λ (Å)
a (Å)
b (Å)
c (Å)
α (°)
0.71073
0.71073
0.71073
11.5194(7)
12.7582(8)
16.2521(10)
85.882(3)
84.414(3)
76.135(3)
2305.0(2)
12.8515(4)
12.9728(5)
13.2306(4)
91.900(2)
117.275(2)
112.938(2)
1744.07(12)
P1
12.8488(3)
12.9768(3)
13.2265(3)
91.961(1)
117.278(1)
112.849(1)
1744.62(8)
P1
β (°)
γ (°)
V (Å3)
Space group
Z
ˉ
P1
2
4
4
1
1
Dcalc (g cm−3
)
1.283
4.03
0.0317, 0.0733
0.037
1.388
10.97
0.0398, 0.0992
0.046
1.484
27.17
0.0248, 0.0635
0.020
1.296
5.29
0.0347, 0.0884
0.043
1.379
19.31
0.0324, 0.0723
0.031
μ (cm−1
)
R1 (I > 2σ(I)), wR2a(all)
Rint
Nref (all), Nref((I > 2σ(I))
13 461, 10 666
17 598, 13 273
17 465, 14 745
13 788, 12 445
19 327, 18 844
2 2
2 2
a R1 = Σ||Fo| − |Fc||/Σ|Fo|, wR2 = {Σ[w(Fo2 − Fc ) ]/Σ[w(Fo ) ]}1/2
.
(14 000), 455 (700), 792 (110), 904 (80). Satisfactory combus-
tion analysis data could not be obtained. This is likely a result of
the extreme sensitivity of the complex to air and moisture and
the lability of the bound N2 unit.
Brandeis University for initially funding this project and Mark
W. Bezpalko for assistance with X-ray crystallography.
Notes and references
Electrochemistry
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using a CH Instruments electrochemical analyzer. A glassy
carbon electrode and platinum wire were used as the working
and auxiliary electrodes, respectively. The reference electrode
was Ag/AgNO3 in THF. Solutions (THF) of electrolyte (0.40 M
[nBu4N][PF6]) and analyte (2 mM) were also prepared in the
glovebox.
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additional details and fully labeled ellipsoid diagrams are
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found in the accompanying CIF files.
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Acknowledgements
This material is based upon work supported by the Department
of Energy under Award No. DE-SC0004019. C.M.T. is grateful
for a 2011 Sloan Research Fellowship. The authors also thank
20 Apex 2: Version 2 User Manual, M86-E01078, Bruker Analytical X-ray
Systems, Madison, WI, 2006.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 8111–8115 | 8115