Evaluating Metal Ion Identity on Catalytic Silylation of Dinitrogen Using a Series of Trimetallic Complexes

Article abstract of DOI:10.1002/ejic.201901335

We report catalytic silylation of dinitrogen to tris(trimethylsilyl)amine by a series of trinuclear first row transition metal complexes (M = Cr, Mn, Fe, Co, Ni) housed in our tris(β-diketiminate) cyclophane (L^3–). Yields are expectedly dependent on metal ion type ranging from 14 to 199 equiv. NH₄ ⁺/complex after protonolysis for the Mn to Co congeners, respectively. For the series of complexes, the observed trend for the number of turnovers as a function of metal ion type is Co > Fe > Cr > Ni > Mn, consistent with prior reports of greater efficacy of Co over Fe in other ligand systems for this reaction.

Full text of DOI:10.1002/ejic.201901335

DOI: 10.1002/ejic.201901335
Full Paper
Catalytic Dinitrogen Silylation
Evaluating Metal Ion Identity on Catalytic Silylation of
Dinitrogen Using a Series of Trimetallic Complexes
[a]
[a]
[b]
[a]
Mary C. Eaton, Brian J. Knight, Vincent J. Catalano, and Leslie J. Murray*
Abstract: We report catalytic silylation of dinitrogen to tris(tri- complex after protonolysis for the Mn to Co congeners, respec-
methylsilyl)amine by a series of trinuclear first row transition tively. For the series of complexes, the observed trend for the
metal complexes (M = Cr, Mn, Fe, Co, Ni) housed in our tris(ꢀ- number of turnovers as a function of metal ion type is Co > Fe
3
–
diketiminate) cyclophane (L ). Yields are expectedly depend- > Cr > Ni > Mn, consistent with prior reports of greater efficacy
+
ent on metal ion type ranging from 14 to 199 equiv. NH / of Co over Fe in other ligand systems for this reaction.
4
Introduction
Given that demetalation, hydrogen production, or both can
compete with N2 fixation by homogeneous catalysts in the
The industrial production of ammonia from N2 and H2 pio- presence of protons and chemical reductants, use of a silyl cat-
th
neered by Haber and commercialized by Bosch in the early 20
ion source as a proton surrogate provides a complementary
fixation by coordination compounds.
Notably, this process, which is vital The resultant silylamine products from such catalytic silylation
century represents one of the most important technological ad- approach to examine N
vances of that century.
to support current agricultural output and industrial chemical experiments can be readily decomposed to NH
2
[
1–4]
+
using a strong
4
processes, has remained largely unchanged since its implemen- mineral acid. Catalytic silylation has been demonstrated by
tation. Despite the high energy efficiency and yields of this complexes of Ti, V, Cr, Fe, Mo, W, Co, and Rh, with single run
process, significant interest has focused on addressing the yields as high as 195 equiv. N(SiMe
)
reported by Lu and co-
3
3
[
15–33]
drawbacks, such as the reliance on fossil fuels as the H source workers.
Two observations are notable for this series, how-
2
and the need for highly centralized and large scale production ever. First, the supporting ligands typically differ across these
facilities. The pursuit of novel catalytic systems for N fixation complexes; in some cases, Co and Fe congeners are evaluated,
2
methods to alleviate these issues remains an area of active re- but examples extending such series to include to Cr, Mn, or Ni
search. Significant advances have been made with respect to remain absent from the literature. The only systematic study is
[
5]
N conversion to NH and N H under ambient conditions.
that from Shiina wherein catalytic N
For homogeneous systems, the majority employ iron or molyb- chloride salts is examined and CrCl
denum centers and derive their inspiration from the iron- cious with 5.4 equiv. N(SiMe
molybdenum cofactor, which is the active site for nitrogen fixa- salt.[34] Other first row transition metal ions in that survey in-
2
fixation by various metal
noted as the most effica-
) per equivalent of the metal
3 3
2
3
2 4
3
II
II
II
II
tion in molybdenum-dependent nitrogenases. Notable exam- cluded chloride salts of Mn , Fe , Co , and Ni . Second, standard
ples in this regard are the first report of stepwise conversion of approaches have not been employed, and particularly with re-
N to NH for multiple cycles, catalytic N fixation by an iron spect to mol-% of catalyst or electron equivalents. The latter
2
3
2
complex in the presence of protons and reducing agents, and prevents a faithful comparison of the yields of fixed nitrogen as
the recent reports of Fe and Mo catalysts that effect N fixation a function of metal ion type.
2
[
6–13]
using PCET reagents.
lyst reported by Nishibayashi and co-workers generates up to
,350 equivalents of NH using SmI and alcohols or water. Ex-
Impressively, the molybdenum cata-
Previously, our group demonstrated that a family of triiron
3–
complexes housed in our tris(ꢀ-diketiminate) cyclophane (L )
4
3
2
is competent for the catalytic reduction of N to N(SiMe ) using
2
3 3
[
14]
amples have been reported for other metal centers; however,
a systematic approach to evaluating the role of metal ion type
KC8 and Me SiCl as the reductant and electrophile, respec-
3
[35]
tively.
The maximum yield reported under those conditions
on N fixation has yet to be reported.
2
was 83 equiv. N(SiMe ) per complex for Fe Br L, which was
3 3 3 3
1
determined by H-NMR spectroscopic quantification of the
+
NH4 generated after quenching the reaction with acid. Nota-
[
[
a] Center for Catalysis, Department of Chemistry, University of Florida,
Gainesville, FL 32611-7200, USA
E-mail: murray@chem.ufl.edu
https://murray.chem.ufl.edu
b] Department of Chemistry, University of Nevada,
Reno, NV 89557, USA
bly, this yield corresponds to conversion of 50 % of the added
electrons into fixed nitrogen species – the highest reported for
any catalyst of this reaction to date. For these triiron complexes,
a general trend is apparent in which complexes bearing π-basic
ligands (e.g., sulfide and bromide) afford higher number of turn-
overs of fixed nitrogen as compared to those with strong σ
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201901335.
Eur. J. Inorg. Chem. 0000, 0–0
1
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
donors and/or π-acidic donors (viz. hydride and carbonyl, re- Spectroscopic data on the trinickel(II) tri(bromide) congener
spectively). Indeed, changing one hydride in Fe H L to a for- agrees with the expected C2v symmetry and the proposed for-
3
3
mate in Fe H (O CH)L restores the number of turnovers to lev- mulation.
3
2
2
els comparable to that of the bromide complex. We speculate
that this trend results from more facile dissociation of the ancil-
lary ligands upon reduction by KC , which creates a vacant co-
8
ordination site for N binding and subsequent activation. Given
2
we can access isostructural complexes of L3– wherein metal ion
type is varied, our system provides a unique opportunity to
evaluate the effect of metal ion type on N fixation by polynu-
2
clear metal complexes. Herein, we report catalytic silylation of
N by a family of M X L complexes in which M = Cr, Mn, Fe, Co,
2
3 3
or Ni, and X = Cl or Br (Scheme 1). Our results highlight the
superiority of Co for this reaction, which has been previously
noted by others.
Figure 1. Side-view (left) and top-view (right) of solid-state structure of
Cr Cl L. Cr1 and Cr2 are best described as trigonal pyramidal, whereas Cr3 is
consistent with a trigonal planar Cr center with Cr3···Cl1 or Cl2 distances
being > 2.76Å. Cr, Cl, C, and N atoms are depicted as maroon, lime green,
grey, and blue ellipsoids at 70 % probability maps, respectively. Solvent mol-
ecules and H atoms are omitted for clarity.
3
3
II
Catalytic Silylation of Dinitrogen
With the series comprising the trinuclear chromium, manga-
nese, iron, cobalt, and nickel compounds in hand, we then
sought to evaluate the effect of metal ion type on the catalytic
silylation of dinitrogen. We intended to employ the conditions
reported in our prior study; however, Mn Cl L is poorly soluble
3 3
Scheme 1. Dinitrogen silylation catalysed by M X L complexes.
3
3
Results and Discussion
in toluene or toluene/ether mixtures. Consequently, we deter-
mined the turnover for catalytic silylation of dinitrogen by these
complexes, including Fe Br L, in a 9:1 mixture of Et O and THF
Synthesis of M X L (M/X = Cr/Cl, Ni/Br)
3
3
3
3
2
(
Scheme 2). Under these conditions, all complexes proved to be
Given our prior success at generating trimetallic complexes of
Mn, Fe, Co, Cu, and Zn, we extended a similar methodology to
the syntheses of the related chromium(II) and nickel(II) com-
plexes. The synthetic scheme bears resemblance to that previ-
competent precatalysts for the catalytic silylation of N . Includ-
2
ing mercury in the catalytic reaction did not result in a signifi-
cant effect on the number of turnovers, strongly suggesting
that trace heterogeneous species are not responsible for the
observed catalysis. In addition, experiments in which the pre-
catalyst is subjected to catalytic conditions and, following con-
sumption of KC8 and Me SiCl, the reaction is refreshed with
more equivalents to continue catalysis were performed for
Co Br L. This portion wise addition method gives a similar yield
to a single addition of reductant and electrophile. Taken to-
gether, these experiments demonstrate that the active species
is likely homogeneous and recyclable (Table S1). From these
results, the trend observed is that Co > Fe > Cr > Ni > Mn.
Insofar as our species are discrete trimetallic complexes, our
data are reported per complex rather than per metal ion and
our comparisons to prior articles based on number of turnovers
per complex.
[
36]
ously reported for Mn Br L
with the following exceptions.
3
3
[38]
First, the THF adducts of CrCl and NiBr were used as these
2
2
starting materials have improved solubility in THF as compared
to the desolvated anhydrous metal dihalides and react more
readily with the deprotonated ligand. Second, initial metalation
of the deprotonated ligand was conducted at –34 °C followed
by stirring at room temperature for an extended period. Yields
of the target tri-chromium(II) and -nickel(II) complexes at 35 %
and 34 %, respectively, are low in comparison to other conge-
ners.
3
3
3
The solid-state structure of Cr Cl L reveals a comparable lad-
3
3
3+
der-like pseudo C2v arrangement of the [M X ] cluster as ob-
3
3
served for a number of other complexes of this ligand, includ-
ing the tri-manganese(II) and -iron(II) tri(chloride) complexes of
this ligand (Figure 1). The metal centers in Cr Cl L are most
3
3
consistent with Cr1 and Cr2 in trigonal pyramidal coordination
[
37]
(
τ4 = 0.74–0.81)
whereas the bond metrics around Cr3 indi-
cate a planar 3-coordinate metal center (Cr3–Cl1 or Cl2 = 2.76
or 2.87 Å). Other bond metrics, such as the N–M–N angles and
M–(μ -Cl) bond lengths, are comparable for Cr Cl L, Mn Cl L,
2
Scheme 2. Catalytic silylation of N .
Cr Cl L affords up to 41(5) N(SiMe ) per complex using KC
8
3
3
3
3
3
3
3
3 3
and Fe Cl L. Combustion analysis and other spectroscopic char- and Me SiCl as the electron and silyl cation sources, respectively
3
3
3
acterization are consistent with the formulation of Cr Cl L. (Table 1, Entry 1). This yield is comparable to that previously
3
3
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
2
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
reported by Mock and co-workers for a chromium complex of as ring-opening, polymerization, and demetalation, have been
[
17]
a macrocyclic tetraphosphine ligand (A, Table S2). Optimized documented by others and may compete with N reduction in
2
[
17,21,23,31]
conditions for the Mock system yield 10.6 equiv. N(SiMe ) in a THF-rich solutions.
3
3
single run and up to 34.1 equiv/complex when catalytic reac-
Co Br L is the best complex for effecting catalytic silylation
3 3
tions are recharged with additional equivalents of reductant of dinitrogen of the suite of complexes reported here with 77(9)
and Me SiCl. Yin, et al. reported N reduction to N(SiMe ) by equiv. N(SiMe ) /complex and a 46 % yield based on reducing
3
2
3 3
3 3
anionic chromium(0)-bis(dinitrogen) complexes using K and equivalents (Table 1, Entry 5). This result is strikingly similar to
Me SiCl, with yields of up to 26 equiv. N(SiMe ) /complex (B, prior reports from others, in which the cobalt complex outper-
3
3 3
[
18]
Table S2). In both prior examples of Cr catalysts, the support- forms the iron congener for this reaction (Figure 2). The greater
ing ligands disfavor metal ion dissociation during redox cycling, electronegativity of cobalt vs. iron balances the metal-nitrogen
likely improving catalyst lifetime and resulting in the observed σ-bonding interactions with the extent of π-donation to the N2
yields. Similarly, stabilization of the complex towards substitu- ligand. Specifically, traversing the catalytic cycle requires stabil-
tion and demetalation may be operative in our system as ity of the various multimetallic complexes across the sampled
[
39]
well.
oxidation states as well as the ability to activate N . We opine
2
that the extent of activation of the coordinated N is reflected
in the electronegativity of the metal ion wherein the energy
2
2
Table 1. Silylation of N catalyzed by a family of trimetallic cyclophanates.
Entry
Precatalyst
Cr Cl
Mn Cl
N(SiMe
3
)
3
/complex[a]
Yield [%][b]
difference between the metal dπ orbitals and N2 π* orbitals
influences the extent of charge accumulation on the N frag-
2
1
2
3
3
3
L
3
L
41 ± 5
14 ± 2
56 ± 6
57 ± 7
77 ± 9
97 ± 2
199
25
8
ment, which leads to the nucleophilic character needed for silyl-
ation (e.g., comparison of the N–N vibration for Ti N vs. isova-
3
Fe
Fe
3
Br
Br
3
L
L
34
34
46
58
40
14
0
2
2
[
c]
4
5
6
7
8
9
3
3
[42,43]
lent Fe N complexes).
In contrast, the metal-ligand bond
2
2
Co
3
Co
3
Co
3
Br
Br
Br
3
L
L
L
lability with respect to the cyclophane ꢀ-diketiminate donors,
[
[
c]
3
3
c,d]
which are weak field ligands, can be described by the Irving–
II
Ni
3
Br
3
L
24 ± 4
0
Williams series with Mn complexes being more kinetically la-
[
e]
II
[44]
No catalyst
bile as compared to the Ni congeners. Indeed, we speculate
that the deleterious effect noted when the reaction solvent is
rich in THF results from metal-ion dissociation and complex dis-
solution from the cyclophane ligand. We suggest then that the
metal-cyclophanate bond lability and extent of charge accumu-
[
a] Reaction conditions unless stated otherwise: 0.66 μmol precatalyst (in
THF), 330 μmol KC and Me SiCl, 9:1 Et O/THF, r.t., 24 h, and 1 atm N . Quanti-
fied after acid hydrolysis by H NMR and reported as mol N(SiMe /mol pre-
catalyst averaged over 3 trials. [b] Yield based on reducing equivalents (KC ).
c] Stock solution of precatalyst in PhMe and the final solution is 9:1 Et O/
PhMe. [d] KC and Me SiCl increased to 990 μmol and the time increased to
4 h. [e] Standard reaction conditions. An equal volume of neat THF was
8
3
2
2
1
3 3
)
8
[
2
lation on the dinitrogen ligand (i.e., formally anionic N species)
2
8
3
5
are competing factors across the series explored here, with the
best compromise at Fe and Co. Such an analysis, however, pos-
its a mechanism wherein silyl-radicals are not catalytically rele-
vant. Future studies, such as DFT calculations or freeze–quench
experiments, will be necessary to provide further insight into
the mechanism of this reaction. Although few isostructural ex-
used instead of a THF solution of catalyst.
To the best of our knowledge, this report is only the second
example of dinitrogen reduction and functionalization by a
molecular manganese species, with the first being from Sell-
mann and co-workers. Our trimanganese(II) cyclophanate af-
fords 14(2) equiv. N(SiMe ) /complex, which is the lowest of our
reported systems (Table 1, Entry 2). The fact that this yield is
the lowest of all other metals tested, however, is consistent with
lack of substantial precedent for dinitrogen coordination and
[
19]
amples are known, comparison of Co and Fe towards N reduc-
2
3
3
tion to ammonia may follow the reverse trend of catalytic
silylation. This change in order as a function of electrophile
[
40]
activation at Mn centers.
of the d Mn ion results in ligand substitution reactivity and
bonding interactions analogous to s-block metal ions.
The spherical electron distribution
5
II
[
41]
We
postulate that the enhanced stability towards redox cycling af-
forded by our ligand is integral to the presumed N binding
2
and reduction to tristrimethylsilylamine by Mn Cl L.
3
3
Use of Fe Br L as the precatalyst affords yields of N(SiMe )
3
3
3 3
[
35]
which are within error from our prior reported values, imply-
ing minimal effect of the solvent composition change wherein
PhMe is replaced with THF (Table 1, Entries 3 and 4). However,
a solvent dependence has been observed under catalytic silyl-
ation conditions in our system and others; in particular, solu-
tions in which THF is the major solvent component (e.g., 1:9
mixture of PhMe/THF) results in a 3-fold decrease in the yield
of N(SiMe ) when Fe Br L is employed as precatalyst. The rea-
3
3
3
3
son for this solvent effect on catalysis is unclear; however, com-
peting reactions involving THF under reducing conditions, such
Figure 2. Relationship between Pauling electronegativity of the metal in the
+
precatalyst employed and the yield of NH
4
from catalytic silylation.
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
3
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
likely reflects the relative strengths of the Me Si/H–N and ular Ni complex. The ability to execute catalytic silylation of
3
Me Si/H–M (M = Fe or Co) bonds.
dinitrogen using our trinickel complex – albeit in low yield and
number of turnovers–may arise from metal–metal cooperative
effects. Specifically, the additive effect of multiple Ni centers
3
The tricobalt precatalyst yields fewer turnovers when THF is
used as the cosolvent instead of PhMe, contrasting the insensi-
tivity for this solvent change noted above for the triiron ana-
logs. For a single addition of reductant and silyl electrophile,
yields of tris(trimethylsilyl)amine per complex dramatically in-
crease from 77(9) equiv. for the THF-containing reaction to 97(2)
allows for sufficiently strong interactions with N to allow for
2
charge transfer and N–N bond scission, whereas such activation
is absent in isolated or aggregated monometallic species. Our
prior report of a tricopper-dinitrogen species reinforces this hy-
[
48]
pothesis.
equiv. for reactions performed in 9:1 Et O/toluene (Table 1, En-
2
try 6). Moreover, increasing the reaction time and decreasing
the mol-% of Co Br L (but not the catalyst concentration) in the
3
3
Et O/PhMe solvent system results in an impressive yield of 199 Conclusions
2
equivalents of the amine per complex (Table 1, Entry 7). These
In summary, a family of homotrimetallic cyclophanates were
demonstrated to be competent for catalyzing dinitrogen reduc-
tion under ambient conditions using KC and Me SiCl as the
yields are comparable to other molecular cobalt catalysts in the
literature, which have emerged as some of the most effective
I
catalysts for this reaction. For example, Fryzuk and Masuda's Co
8
3
electron and electrophile sources, respectively. The number of
complex binds N at –40 °C with minimal activation and is an
2
turnovers range from 14 to 199 equiv. N(SiMe ) /complex with
effective catalyst at this temperature for N2 silylation with
3 3
some of the highest reported yields based on electrons added
2
00 ± 20 equiv. N(SiMe ) /complex after 10 d (D, Table S2). A
3 3
(
58 % for Co Br L). These results include seminal examples of
more appropriate comparison, however, is of their catalyst at
3 3
a molecular manganese and molecular nickel catalyst for N2
room temperature; their reported yield of 100 equiv. NH Cl
4
reduction as well as the most turnovers in a single run by a
(
post hydrolysis of the tris-silylamine) after 24 h is comparable
chromium catalyst to date. The yield of fixed N correlate with
differences in the electronegativities of the metals utilized in
each complex, which balances the σ and π metal-dinitrogen
covalency. In addition, our trinucleating cyclophane ligand
likely serves to stabilize the catalyst to metal ion dissociation
during redox cycling.
to our value here. A notable difference is the substantially
higher yield based on KC at 58 % for our complex as compared
8
to their value, which we calculate as 20 % based on their re-
ported conditions.
The final comparison is to the dicobalt catalyst reported by
Lu, which affords 195 equiv. N(SiMe ) /complex and a 30 %
3
3
yield relative to KC in a single run at room temperature after
8
[
21]
only 12 h (C, Table S2). This value is one of the highest num-
ber of turnovers reported for any catalyst of this reaction to
date. Interestingly the second cobalt, although potentially
Experimental Section
General Considerations: All manipulations were performed in an
Ar filled Vigor Tech glovebox or an N filled Innovative Technologies
glovebox. Solvents were purchased from Sigma-Aldrich, dried using
redox active, is presumed not to participate directly in N bind-
2
2
ing and reduction but rather acts as a ligand for the catalytically
active Co center. The importance of metal–metal interactions an Innovative Technologies solvent purification system, and stored
or cooperative metal-ligand effects (e.g., bridging ligands) to over 3 Å molecular sieves in the gloveboxes. Dimethyl sulfoxide-d
6
(
[D ]DMSO) was purchased from Cambridge Isotope Laboratories,
effect dinitrogen fixation are a developing theme from the as-
sembled data. Specifically, we surmise that multiple metal cen-
6
degassed, dried by stirring over activated basic alumina under an
Ar atmosphere, filtered, and stored over 3 Å molecular sieves in
ters improve electron efficiency for N reduction potentially by
2
the glovebox. [D ]Benzene was purchased from Cambridge Isotope
6
providing a means of storing reducing equivalents and reduc-
ing deleterious side reactions. Our system demonstrates the
ability of three metal centers, regardless of metal ion identity
Laboratories, dried by refluxing over CaH , distilled and degassed,
2
and then stored over 3 Å molecular sieves in the glovebox. H L,
3
Mn Cl L, Fe Br L, and Co Br L were synthesized using published
3
3
3
3
3
3
or type, to facilitate N binding and functionalization.
[36,53,54]
2
literature procedures.
Me SiCl was purchased from Sigma-
3
Aldrich and stored in the gloveboxes. KC was prepared under Ar
For Ni Br L, we observe fewer turnovers with only 24(4)
8
3
3
by the solid state reaction of K metal and graphite at 150 °C under
vacuum with vigorous mechanical stirring until a golden-brown
powder was obtained. BnK was synthesized as reported by
equiv. N(SiMe ) /complex and a 14 % yield based on reducing
3
3
equivalents (Table 1, Entry 8). Dinitrogen complexes of Group
[
45–47]
[48,49]
10
and 11
metals are relatively rare, although a grow-
[
55]
Schlosser.
THF adducts of metal halide salts were prepared via
ing number of nickel(I) and nickel(0) dinitrogen adducts are be-
ing reported. In general, however, the extent of activation of
the bound N2 is significantly less than that of the Fe or Co
1
Soxhlet extraction of the anhydrous material under N . H Nuclear
Magnetic Resonance ( H NMR) spectra were recorded on a Varian
2
1
Inova 500 MHz spectrometer or a Mercury operating at 300 MHz
congeners, in agreement with the expected weaker π-backdo- equipped with a three-channel 5 mm indirect detection probe with
nation from Ni to N as compared to Fe or Co if formal oxidation z-axis gradients. Chemical shifts were reported in δ (ppm) and were
2
state is held constant. Expectedly then, no examples of N2 referenced to solvent resonances δH = 7.16 ppm and 2.50 ppm for
[
D ]benzene and [D ]dimethyl sulfoxide, respectively.
cleavage on a nickel complex have been reported, with
dinitrogen dissociation typically preferred over functionaliza-
tion.
6 6
CCDC 1972558 (for Cr Cl L) contains the supplementary crystallo-
To the best of our knowledge, Ni Br L represents graphic data for this paper. These data can be obtained free of
3 3
3
3
[
47,50–52]
the first example of catalytic dinitrogen reduction by a molec- charge from The Cambridge Crystallographic Data Centre.
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
4
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Cr Cl L: A 20 mL scintillation vial was charged with H L (200 mg,
3
3
3
Keywords: Nitrogen fixation · Dinitrogen silylation ·
Dinitrogen activation · Redox chemistry · Multimetallic
0
.289 mmol) and THF (10 mL). The suspension was cooled to –34 °C
for 30 min. To the cold suspension was added BnK (118 mg,
0
0
–
.906 mmol) and, upon dissolution, CrCl ·2THF (242 mg, catalysis
.906 mmol). The viscous, blood red suspension was stirred at
34 °C for 30 min followed by 3 h of stirring at room temperature.
2
THF was removed under reduced pressure and replaced with benz-
ene (15 mL). The mixture was stirred overnight at 80 °C and then
vacuum filtered through a pad of Celite to yield a brick red solution.
The filtrate immediately precipitated the product as an analytically
pure, brick red microcrystalline powder (96 mg, 35 %). Single crys-
[
[
[
1] A. Mittasch, W. Frankenburg, in Adv. Catal. (Eds.: W. G. Frankenburg, V. I.
Komarewsky, E. K. Rideal), Academic Press, 1950, pp. 81–104.
2] “The Nobel Prize in Chemistry 1918 ,” can be found under https://
www.nobelprize.org/prizes/chemistry/1918/haber/lecture/.
3] G. Prieto, F. Schüth, Angew. Chem. Int. Ed. 2015, 54, 3222–3239; Angew.
Chem. 2015, 127, 3268.
tals suitable for X-ray diffraction were grown by slow cooling of a
1
saturated benzene solution. H NMR (500 MHz, C D ): δ = –57.4,
6
6
[4] V. Smil, Nature 1999, 400, 415–415.
–
1
–
1
6
28.1, –20.4, 82.1, 88.2 ppm. ATR-IR (cm ): 2947, 1521, 1461, 1431,
395, 1371, 1325, 1066, 1013, 724. C H N Cr Cl ·2C H : calcd. C
1.867, H 6.831, N 7.594; found C 61.388, H 6.834, N 7.736.
[5] Y. Nishibayashi, Inorg. Chem. 2015, 54, 9234–9247.
[6] K. Arashiba, Y. Miyake, Y. Nishibayashi, Nat. Chem. 2011, 3, 120–125.
[7] J. S. Anderson, J. Rittle, J. C. Peters, Nature 2013, 501, 84–87.
4
5
63
6
3
3
6 6
[
[
8] D. V. Yandulov, R. R. Schrock, Science 2003, 301, 76–78.
9] S. Kuriyama, K. Arashiba, K. Nakajima, Y. Matsuo, H. Tanaka, K. Ishii, K.
Yoshizawa, Y. Nishibayashi, Nat. Commun. 2016, 7, 1–9.
Ni Br L: A 20 mL scintillation vial was charged with H L (200 mg,
3
3
3
0
.289 mmol) and THF (10 mL). The suspension was cooled to –34 °C
for 30 min. To the cold mixture was added BnK (118 mg,
.906 mmol) followed by NiBr ·2THF (329 mg, 0.906 mmol) upon
[
10] M. M. Rodriguez, E. Bill, W. W. Brennessel, P. L. Holland, Science 2011,
334, 780–783.
0
2
dissolution. The suspension was stirred at –34 °C for 30 min and
then 3 h at room temperature during which time the reaction grad-
ually turned dark green. The THF was removed under reduced pres-
sure and replaced with benzene (15 mL). The suspension was stirred
overnight at 80 °C and then vacuum filtered through a pad of Celite
to yield a dark green filtrate. The solvent was removed under re-
duced pressure to yield analytically pure material (110 mg, 34 %).
[11] Y. Lee, F. T. Sloane, G. Blondin, K. A. Abboud, R. García-Serres, L. J. Murray,
Angew. Chem. Int. Ed. 2015, 54, 1499–1503; Angew. Chem. 2015, 127,
1
519.
[
[
[
12] P. J. Hill, L. R. Doyle, A. D. Crawford, W. K. Myers, A. E. Ashley, J. Am. Chem.
Soc. 2016, 138, 13521–13524.
13] T. D. Lohrey, R. G. Bergman, J. Arnold, Dalton Trans. 2019, 48, 17936–
1
7944.
14] Z.-J. Lv, Z. Huang, W.-X. Zhang, Z. Xi, J. Am. Chem. Soc. 2019, 141, 8773–
1
–1
H NMR (500 MHz, C D ): δ = –65.6, 9.5, 19.5 ppm. ATR-IR (cm ):
6
6
8777.
2
948, 2921, 1526, 1429, 1392, 1370, 1275, 1216, 1009, 728.
[15] P. Ghana, F. D. van Krüchten, T. P. Spaniol, J. van Leusen, P. Kögerler, J.
Okuda, Chem. Commun. 2019, 55, 3231–3234.
[16] R. Imayoshi, K. Nakajima, Y. Nishibayashi, Chem. Lett. 2017, 46, 466–468.
C H Ni Br ·0.5C H O: calcd. C 49.524, H 5.925, N 7.373; found C
45
63
3
3
4 8
4
9.204, H 5.897, N 6.844.
Standard Procedure for the Catalytic Conversion of N2 to
N(SiMe ) : KC (45.0 mg, 330 μmol) was suspended in Et O
[
17] A. J. Kendall, S. I. Johnson, R. M. Bullock, M. T. Mock, J. Am. Chem. Soc.
018, 140, 2528–2536.
2
3
3
8
2
[18] J. Yin, J. Li, G.-X. Wang, Z.-B. Yin, W.-X. Zhang, Z. Xi, J. Am. Chem. Soc.
2019, 141, 4241–4247.
[19] D. Sellmann, W. Weiss, Angew. Chem. Int. Ed. Engl. 1977, 16, 880–881;
Angew. Chem. 1977, 89, 918.
(
1.80 mL) in a 20 mL scintillation vial equipped with a glass stir bar.
Chlorotrimethylsilane (42.0 μL, 330 μmol) was added, followed by
the respective precatalyst as a solution in THF (200 μL, 3.3 m
.66 μmol). The reactions were stirred at room temperature for 24 h
after which they were filtered through a plug of Celite into a vial
containing HCl as a 2 solution in Et O (200 μL). The Celite plug
M,
[
[
20] Y. Ohki, Y. Araki, M. Tada, Y. Sakai, Chem. Eur. J. 2017, 23, 13240–13248.
21] R. B. Siedschlag, V. Bernales, K. D. Vogiatzis, N. Planas, L. J. Clouston, E.
Bill, L. Gagliardi, C. C. Lu, J. Am. Chem. Soc. 2015, 137, 4638–4641.
22] Y. Gao, G. Li, L. Deng, J. Am. Chem. Soc. 2018, 140, 2239–2250.
23] R. Imayoshi, H. Tanaka, Y. Matsuo, M. Yuki, K. Nakajima, K. Yoshizawa, Y.
Nishibayashi, Chem. Eur. J. 2015, 21, 8905–8909.
0
M
2
[
[
and reaction vial were rinsed with 2 mL of Et O. The resulting filtrate
was allowed to react for a minimum of 10 min before removing the
solvent under reduced pressure. The resulting white solids were
dissolved in dry [D ]DMSO with 1,3,5-trimethoxybenzene as an in-
ternal standard. The ammonium was quantified using H NMR. The
2
[
24] T. Suzuki, K. Fujimoto, Y. Takemoto, Y. Wasada-Tsutsui, T. Ozawa, T. Ino-
mata, M. D. Fryzuk, H. Masuda, ACS Catal. 2018, 8, 3011–3015.
6
1
[25] R. Kawakami, S. Kuriyama, H. Tanaka, K. Arashiba, A. Konomi, K. Nakajima,
experiments were performed in triplicate.
K. Yoshizawa, Y. Nishibayashi, Chem. Commun. 2019, https://doi.org/
1
0.1039.C9CC06896A.
Mercury Poisoning Test: To a 20 mL scintillation vial containing
[
26] D. E. Prokopchuk, E. S. Wiedner, E. D. Walter, C. V. Popescu, N. A. Piro,
KC (45.0 mg, 330 μmol) was added Et O (1.8 mL) followed by chlo-
8
2
W. S. Kassel, R. M. Bullock, M. T. Mock, J. Am. Chem. Soc. 2017, 139, 9291–
rotrimethylsilane (42.0 μL, 330 μmol) and a solution of precatalyst
in THF (200 μL, 3.3 m , 0.66 μmol). To the suspension was added
9
301.
M
[27] A. D. Piascik, R. Li, H. J. Wilkinson, J. C. Green, A. E. Ashley, J. Am. Chem.
Soc. 2018, 140, 10691–10694.
[28] G. Ung, J. C. Peters, Angew. Chem. Int. Ed. 2015, 54, 532–535; Angew.
Chem. 2015, 127, 542.
mercury (50.0 mg, 0.249 mmol). The reaction was allowed to stir at
room temperature for 24 h followed by filtration through a Celite
plug and quenching with 2
M HCl in Et O (200 μL). N(SiMe ) was
2 3 3
[
[
[
29] R. Araake, K. Sakadani, M. Tada, Y. Sakai, Y. Ohki, J. Am. Chem. Soc. 2017,
quantified as described above.
1
39, 5596–5606.
30] A. Cavaillé, B. Joyeux, N. Saffon-Merceron, N. Nebra, M. Fustier-Bouti-
gnon, N. Mézailles, Chem. Commun. 2018, 54, 11953–11956.
31] H. Tanaka, A. Sasada, T. Kouno, M. Yuki, Y. Miyake, H. Nakanishi, Y. Nishi-
bayashi, K. Yoshizawa, J. Am. Chem. Soc. 2011, 133, 3498–3506.
Acknowledgments
Support for L. J. M., B. J. K., and M. C. E. has been provided by
the National Institute of General Medical Sciences (NIGMS)
within the National Institutes of Health (NIH) through award
R01-GM123241. The content is solely the responsibility of the
authors and does not necessarily represent the official views of
the National Institutes of Health.
[32] K. Komori, H. Oshita, Y. Mizobe, M. Hidai, J. Am. Chem. Soc. 1989, 111,
939–1940.
1
[
[
[
33] Y. Tanabe, Y. Nishibayashi, Coord. Chem. Rev. 2019, 389, 73–93.
34] K. Shiina, J. Am. Chem. Soc. 1972, 94, 9266–9267.
35] R. B. Ferreira, B. J. Cook, B. J. Knight, V. J. Catalano, R. García-Serres, L. J.
Murray, ACS Catal. 2018, 8, 7208–7212.
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
5
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[
[
36] G. L. Guillet, F. T. Sloane, D. M. Ermert, M. W. Calkins, M. K. Peprah, E. S.
Knowles, E. Čižmár, K. A. Abboud, M. W. Meisel, L. J. Murray, Chem. Com-
mun. 2013, 49, 6635–6637.
37] A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Verschoor, J. Chem.
Soc., Dalton. Trans. 1984, 1349–1356.
[48] L. J. Murray, W. W. Weare, J. Shearer, A. D. Mitchell, K. A. Abboud, J. Am.
Chem. Soc. 2014, 136, 13502–13505.
[49] S. Zhang, H. Fallah, E. J. Gardner, S. Kundu, J. A. Bertke, T. R. Cundari,
T. H. Warren, Angew. Chem. Int. Ed. 2016, 55, 9927–9931; Angew. Chem.
2016, 128, 10081–10085.
[
[
[
38] R. H. Crabtree, Chem. Rev. 2012, 112, 1536–1554.
39] R. B. Ferreira, L. J. Murray, Acc. Chem. Res. 2019, 52, 447–455.
40] E. A. Ison, in Transit. Met.-Dinitrogen Complexes, John Wiley & Sons, Ltd,
[50] P. Holze, B. Horn, C. Limberg, C. Matlachowski, S. Mebs, Angew. Chem.
Int. Ed. 2014, 53, 2750–2753; Angew. Chem. 2014, 126, 2788.
[51] B. Horn, C. Limberg, C. Herwig, B. Braun, Chem. Commun. 2013, 49,
10923–10925.
2019, pp. 271–284.
[
[
41] R. A. Layfield, Chem. Soc. Rev. 2008, 37, 1098–1107.
42] H. Seino, Y. Kajita, in Transit. Met.-Dinitrogen Complexes, John Wiley &
Sons, Ltd, 2019, pp. 79–158.
[52] R. C. Cammarota, J. Xie, S. A. Burgess, M. V. Vollmer, K. D. Vogiatzis, J. Ye,
J. C. Linehan, A. M. Appel, C. Hoffmann, X. Wang, et al.,, Chem. Sci. 2019,
10, 7029–7042.
[
43] A. D. Piascik, A. E. Ashley, in Transit. Met.-Dinitrogen Complexes, John
Wiley & Sons, Ltd, 2019, pp. 285–335.
[53] K. J. Anderton, D. M. Ermert, P. A. Quintero, M. W. Turvey, M. S. Fataftah,
K. A. Abboud, M. W. Meisel, E. Čižmár, L. J. Murray, Inorg. Chem. 2017,
56, 12012–12022.
[54] Y. Lee, K. J. Anderton, F. T. Sloane, D. M. Ermert, K. A. Abboud, R. García-
Serres, L. J. Murray, J. Am. Chem. Soc. 2015, 137, 10610–10617.
[55] M. Schlosser, J. Hartmann, Angew. Chem. Int. Ed. Engl. 1973, 12, 508–509;
Angew. Chem. 1973, 85, 544.
[
[
44] H. Irving, R. J. P. Williams, J. Chem. Soc., Resumed 1953, 3192–3210.
45] R. B. Ferreira, L. J. Murray, in Transit. Met.-Dinitrogen Complexes, John
Wiley & Sons, Ltd, 2019, pp. 403–439.
[
46] S. Pfirrmann, C. Limberg, C. Herwig, R. Stößer, B. Ziemer, Angew. Chem.
Int. Ed. 2009, 48, 3357–3361; Angew. Chem. 2009, 121, 3407.
47] S. Pfirrmann, S. Yao, B. Ziemer, R. Stösser, M. Driess, C. Limberg, Organo-
metallics 2009, 28, 6855–6860.
[
Received: December 17, 2019
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
6
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Catalytic Dinitrogen Silylation
M. C. Eaton, B. J. Knight,
V. J. Catalano, L. J. Murray* ............ 1–7
Evaluating Metal Ion Identity on
Catalytic Silylation of Dinitrogen Us-
ing a Series of Trimetallic Com-
plexes
Catalytic silylation of dinitrogen to reported. Yields depend on metal ion
tris(trimethylsilyl)amine by a series of type ranging from 14 to 199 equiv.
+
trinuclear first row transition metal NH /complex after protonolysis for
4
complexes (M = Cr, Mn, Fe, Co, Ni) is the Mn to Co congeners, respectively.
DOI: 10.1002/ejic.201901335
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
7
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim