Synthesis, structures, and catalytic reactivity of bis(N-heterocyclic carbene) supported diphenyldiazomethane and 1-azidoadamantane complexes of nickel

Article abstract of DOI:10.1016/j.jorganchem.2016.03.031

Diphenyldiazomethane reacts with Ni(NHC)₂ (1, NHC = N-heterocyclic carbene) to afford complexes of the type (NHC)₂Ni(κ¹-N₂CPh₂) (3) in which the diazoalkane ligand is bound to the metal in an end-on κ

Full text of DOI:10.1016/j.jorganchem.2016.03.031

Accepted Manuscript
Synthesis, Structures, and Catalytic Reactivity of Bis(N-Heterocyclic Carbene)
Supported Diphenyldiazomethane and 1-Azidoadamantane Complexes of Nickel
Nicole D. Harrold, Amanda R. Corcos, Gregory L. Hillhouse
PII:
S0022-328X(16)30115-2
10.1016/j.jorganchem.2016.03.031
JOM 19456
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 25 January 2016
Revised Date: 28 March 2016
Accepted Date: 28 March 2016
Please cite this article as: N.D. Harrold, A.R. Corcos, G.L. Hillhouse, Synthesis, Structures, and
Catalytic Reactivity of Bis(N-Heterocyclic Carbene) Supported Diphenyldiazomethane and 1-
Azidoadamantane Complexes of Nickel, Journal of Organometallic Chemistry (2016), doi: 10.1016/
j.jorganchem.2016.03.031.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Synthesis, Structures, and Catalytic Reactivity of Bis(N-Heterocyclic Carbene) Supported
Diphenyldiazomethane and 1-Azidoadamantane Complexes of Nickel
Nicole D. Harrold,* Amanda R. Corcos,‡ and Gregory L. Hillhouse
Gordon Center for Integrative Science, Department of Chemistry, The University of Chicago,
929 East 57th Street, Chicago, Illinois, 60637, USA
* Email: nharrold@uchicago.edu
1

ACCEPTED MANUSCRIPT
HIGHLIGHTS.
1. Family of bis(N-heterocyclic carbene)-supported Ni complexes bind N2CPh2 and N3Ad
2. Unique binding modes for N2CPh2 and N3Ad have rarely been observed in group 10 metals
3. Catalytic cyclopropanation with Ni-N2CPh2 complexes is efficient and high yielding
4. The proposed catalytic cycle does not include formation of a metallacarbene
ABSTRACT.
Diphenyldiazomethane reacts with Ni(NHC)2 (1, NHC = N-heterocyclic carbene) to af-
ford complexes of the type (NHC)2Ni(κ1-N2CPh2) (3) in which the diazoalkane ligand is bound
to the metal in an end-on κ1 fashion. Additionally, 1-IMes (IMes = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene) reacts with 1-azidoadamantane (N3Ad) to produce
(IMes)2Ni(η2-N3Ad) (4) in which the azide ligand is bound to the metal in a side-bound η2-
fashion. While thermolysis of 3 and 4 does not induce N2 loss to form terminal carbenes and im-
idos, respectively, (IMes)2Ni(κ1-N2CPh2) (3-IMes) reacts with olefins at elevated temperatures
to give cyclopropane products in excellent yields. Either 3-IMes or 1-IMes can also perform this
reaction catalytically with a 1:1 ratio of diphenyldiazomethane to olefin. An olefin activation
mechanism is proposed to explain the cyclopropanation reaction.
GRAPHICAL ABSTRACT.
Complexes of type (NHC)2Ni(κ1-N2CPh2) (3), in which diphenyldiazomethane is bound
to an N-heterocyclic carbene-supported nickel center in an unusual κ1 end-on fashion, react with
olefins at elevated temperatures to give cyclopropane products in excellent yields. 3-IMes or 1-
IMes can also perform this reaction catalytically with an efficient 1:1 ratio of diphenyldiazome-
thane to olefin.
2

ACCEPTED MANUSCRIPT
K
EYWORDS.
1. Nickel
2. N-heterocyclic carbene (NHC)
3. Catalysis
4. Cyclopropanation
5. Diazoalkane
6. Organoazide
1. INTRODUCTION
.
Diazoalkanes are commonly used precursors for the synthesis of metallacarbenes,[1-3]
which in turn are versatile chemical moieties capable of olefin cyclopropanation, C–H activation,
and other reactions.[4-12] While N2 elimination from diazoalkanes is generally facile upon reac-
tion with metal complexes, the isolation and characterization of metal-bound diazoalkane ad-
ducts is possible and has yielded a plethora of complexes spanning multiple coordination
modes.[6, 7, 13, 14] Five coordination modes are possible for a diazoalkane moiety bound to a single
transition metal center (Chart 1): κ1-N end-on coordination involving the terminal N (type A),[15-
22]
η2-N,N side-on (type B),[23-28] η2-C,N side-on (type C), κ2-C,N metallacyclic (type D), and
κ1-C coordination (type E). Coordination of a diazoalkane to more than one metal atom is also
possible.[29]
Several limiting electronic configurations for the κ1-N binding configuration (A) are
shown in Chart 2. In configuration A1, the diazoalkane ligand serves as a neutral 2-electron do-
nor with a dative interaction between the terminal nitrogen and the metal center. The diazoalkane
ligands in configurations A2 (singly bent) and A3 (doubly bent) are bound to the metal center
through two covalent bonds (σ + π). Configuration A4 features two covalent bonds and one da-
tive bond.
Chart 1. Diazoalkane binding modes to a single metal center.
3

ACCEPTED MANUSCRIPT
Chart 2. Electronic configurations for a κ1-N end-on diazoalkane bound to a single metal center.
In a similar manner, organoazides are often used as imido precursors,[30-32] which can un-
dergo group transfer and C-H amination after reacting with a metal center to induce loss of
N2.[33-37] There are several possible coordination modes for organoazides to bind to a metal cen-
ter. In the few instances where these complexes are stable enough for isolation, the ligand is usu-
ally bound as a diazenylimido (RN32- as F, G, or H in Chart 3)[38-42] or as a neutral RN3 through
the
α or γ
N-atoms (I and J).[43-45]
Chart 3. Common organoazide binding modes to a metal center.
Herein we report the synthesis, structures, and reactivity of several new bis(N-
heterocyclic carbene) (NHC) supported diphenyldiazomethane complexes of Ni in which the di-
azo ligand is bound to the metal in a κ1 end-on fashion (A). These complexes mediate cyclopro-
pane formation in high yields from stoichiometric and catalytic 1:1 mixtures of diazoalkanes and
olefins, whereas typical cyclopropanation catalysis requires an excess of olefin for good selectiv-
ity and high yields. It is proposed that catalysis for this system occurs without the intermediacy
of a metallacarbene. The synthesis and reactivity of a new bis(NHC) supported organoazide
complex of Ni, in which the azide ligand is bound to the metal in an
and its reactivity discussed.
η
2-fashion, is also reported
4

ACCEPTED MANUSCRIPT
2. MATERIALS AND METHODS
.
2.1. General Considerations. Unless stated otherwise, all operations were performed in
an MBraun Lab Master dry box under an atmosphere of purified nitrogen. Anhydrous diethyl
ether (Et2O) and tetrahydrofuran (THF) were purchased from Fischer, stirred over sodium metal,
and filtered through activated alumina.[46] Pentane was purchased from Sigma Aldrich and dried
by passage through activated alumina and Q-5 columns. C6D6 was purchased from Cambridge
Isotope Laboratories, degassed by freeze-pump-thaw cycles, and dried over CaH2 or activated 4
Å molecular sieves. Celite, alumina, and 4 Å molecular sieves were activated by evacuation
[55]
overnight at 180 °C. N2CPh2,[47] N3Ad,[48-50] IMes,[51-53] SIMes,[51] IPr,[51, 52, 54] and Ni(IMes)2
were prepared according to the literature. All other chemicals were used as received. Please note:
caution should used when conducting photolytic and thermolytic experiments on diazoalkane
and organoazide species, for such species have the potential to be explosive. Due to the small
scale on which these reactions were performed and the low temperatures utilized, all reactions
performed here are deemed safe.
2.2. Instruments. Elemental analyses were performed by Midwest Microlab (Indianapolis,
IN). 1H NMR spectra were recorded on a Bruker 500 MHz NMR spectrometer and reported with
reference to solvent resonance (for example, residual C6D5H in C6D6 at 7.16 ppm). Infrared data
(Fluorolube or Nujol mulls, CaF2 or KBr plates, respectively) were measured using a Nicolet
Nexus 670 FT-IR.
2.3. Synthesis.
2.3.1. Preparation of (NHC)2Ni(κ 3). A typical procedure is given for the syn-
1-N2CPh2) (
thesis of 3-IMes. A cold (-35 °C) solution of 145 mg (750 mmol) N2CPh2 in 5 mL diethyl ether
was added to a cold stirring solution of 500 mg (750 mmol) Ni(IMes)2 (1-IMes) in 10 mL dieth-
yl ether. The reaction was stirred at room temperature for 1 hour after which the reaction mixture
was reduced to dryness. The resulting solids were then washed with cold hexanes (3 x 5 mL).
The resulting orange red solids were dried under vacuum for 2 hours. The characterization data
for 3-IMes, 3-SIMes, and 3-IPr are given below. All complexes are stable in the freezer (-35
°C) for up to 6 months but degrade if left at room temperature or exposed to light for more than
one week.
5

ACCEPTED MANUSCRIPT
1
2.3.1.1. (IMes)2Ni(κ
1-N2CPh2) (3-IMes). Yield: 620 mg (96%). H NMR (298 K, 500.13
MHz, C6D6): δ 7.68 (d, 4H, o-C6H6), 7.19 (t, 4H, m-C6H6), 6.86 (t, 2H, p-C6H6), 6.69 (s, 8H,
13
C6H2), 6.02 (s, 4H, NC2H2N), 2.28 (s, 12H, C6H2(CH3)3), 1.87 (s, 24H, C6H2(CH3)3); C{1H}
NMR (298 K, 125.76 MHz, C6D6): δ 199.8, 138.8, 138.4, 137.7, 136.4, 129.8, 128.3, 125.8,
123.6, 121.7, 21.9, 18.9. IR (Nujol, KBr): 3153 (m), 2915 (m), 2041 (s), 1703 (s), 1608 (s), 1560
(s), 1487 (s), 1447 (s), 1405 (s) cm-1. Anal. Calcd. for C55H58NiN6: C, 76.75; H, 6.78; N, 9.75.
Found: C, 74.71; H, 6.30; N, 9.06. Please note these values are not within the standard range due
to (unavoidable) decomposition of the complex during shipment to the EA facilities. All other
characterizations and catalytic reactions presented here were performed with freshly-made (non-
decomposed) materials.
1
2.3.1.2. (SIMes)2Ni(
κ
1-N2CPh2) (3-SIMes). Yield: 595 mg (92%). H NMR (298 K,
500.13 MHz, C6D6): δ 7.71 (d, 4H, o-C6H6), 7.33 (t, 4H, m-C6H6), 6.99 (t, 2H, p-C6H6), 6.89 (d,
8H, C6H3), 6.76 (t, 4H, C6H3), 3.15 (s, 8H, NC2H4N), 6.69 (s, 8H, C6H2), 2.27 (s, 12H,
13
C6H2(CH3)3), 1.98 (s, 24H, C6H2(CH3)3); C{1H} NMR (298 K, 125.76 MHz, C6D6): δ 138.9,
138.6, 137.2, 136.7, 130.3, 125.9, 121.8, 51.8, 21.9, 18.8. IR (Nujol, KBr): 2810 (m), 2043 (s),
1713 (s), 1606 (s), 1563 (s), 1487 (s), 1448 (s), 1410 (s) cm-1.
1
2.3.1.3. (IPr)2Ni(
κ
1-N2CPh2) (3-IPr). Yield: 631 mg (82%). H NMR (298 K, 500.13
MHz, C6D6): δ 7.65 (d, 4H, o-C6H6), 7.58 (t, 4H, m-C6H6), 7.22 (t, 2H, p-C6H6), 6.04 (s, 4H,
NC2H2N), 2.23 (m, 8H, CH(CH3)2), 1.31 (d, 24H, CH(CH3)2), 1.07 (d, 24H, CH(CH3)2); 13C{1H}
NMR (298 K, 125.76 MHz, C6D6): δ 204.8, 142.8, 137.4, 137.3, 134.3, 127.8, 126.4, 126.3,
125.8, 123.6, 121.7, 21.9, 18.9, 18.7. IR (Nujol, KBr): 2805 (m), 2042 (s), 1713 (s), 1605 (s),
1559 (s), 1484 (s), 1448 (s), 1410 (s) cm-1.
2.3.2. Stoichiometric Procedure for Formation of Cyclopropane. A typical procedure is
given for the formation of 1,2-diphenyl-2-butylcyclopropane. In a 25 mL glass bomb equipped
with a stir bar was loaded 3-IMes (100 mg, 0.116 mmol) and 10 mL toluene. To the solution was
added 1-hexene (9.8 mg, 0.116 mmol) dissolved in 1 mL of toluene at 22 °C. The solution re-
mained red in color upon addition. Upon heating (2 hours, 60 °C) the solution turned dark purple
in color. After completion the solution was exposed to air and filtered through celite. The filtrate
was then passed through a short SiO2 column (1:1 hexanes: diethyl ether). The yellow band was
collected and dried under reduced pressure for 2 hours to afford pure cyclopropane. The charac-
terization data for cyclopropane products are given below.
6

ACCEPTED MANUSCRIPT
1
2.3.2.1. 1,2-diphenyl-2-butylcyclopropane. Yield: 26.1 mg (90%). H NMR (298 K,
500.13 MHz, CDCl3): δ 7.35 – 7.19 (m, 10H, Ph), 1.61 (m, 1H, C4H9), 1.43 (m, 2H, C4H9), 1.32
(m, 1H, C4H9), 1.25 (4 line, 1H, CH2, JHH = 8.8, 4.6 Hz), 1.19 (4 line, 1H, CH2, JHH = 4.6, 6.3
Hz), 0.85 (t, 3H, C4H9), 0.74 (m, 1H, C4H9); 13C{1H} NMR (298 K, 125.76 MHz, CDCl3): δ
130.8, 128.6, 126.2, 125.7, 35.4, 31.8, 29.9, 26.6, 22.7, 21.1, 11.7; GC/MS (m/z): 250 (M+), 193
(M-Bu), 165 (Ph2C+-H).
1
2.3.2.2. 1,1-diphenyl-2,2,3-trimethylcyclopropane. Yield: 24.7 mg (90%). H NMR (298
K, 500.13 MHz, CDCl3): δ 7.27 – 6.95 (m, 10H, Ph), 1.34 (s, 3H, CH3), 1.02 (s, 3H, CH3), 1.00
(s, 3H, CH3); 13C{1H} NMR (298 K, 125.76 MHz, CDCl3): δ 146.1, 129.2, 128.2, 128.1, 127.4,
126.2, 126.1, 46.0, 33.7, 26.4, 22.4, 15.2; GC/MS (m/z): 236 (M+), 221 (M+-Me), 143 (M+-Me-
Ph).
1
2.3.2.3. 7,7-diphenylbicyclo[4.1.0]heptane. Yield: 24.8 mg (86%). H NMR (298 K,
13
500.13 MHz, CDCl3): δ 7.35 – 7.01 (m, 10H, Ph), 2.30 – 0.62 (m, 10H, C4H8); C{1H} NMR
(298 K, 125.76 MHz, CDCl3): δ 149.7, 140.1, 131.6, 128.5, 127.8, 36.2, 25.2, 22.3, 21.4;
GC/MS (m/z): 250 (M+), 205 (M+ -C3H6), 165 (Ph2C+ -H).
1
2.3.2.4. 1,1-diphenyl-2-butyl-3-methylcyclopropane. Yield: 23.2 mg (80%). H NMR
(298 K, 500.13 MHz, CDCl3): δ 7.28 – 7.01 (m, 10H, Ph), 1.64 – 1.39 (m, 7H), 1.08 – 1.04 (m,
13
3H), 0.96 – 0.91 (m, 2H); C{1H} NMR (298 K, 125.76 MHz, CDCl3): δ 147.4, 147.3, 129.7,
129.5, 128.2, 128.1, 126.4, 126.1, 56.0, 35.1, 34.1, 24.6; GC/MS (m/z): 250 (M+), 207 (M-Pr).
2.3.3. Catalytic Procedure for 1,2-diphenyl-2-butylcyclopropane. In a 25 mL glass bomb
equipped with a stir bar was loaded Ni(IMes)2 (1-IMes) (205 mg, 0.238 mmol, 20 mol %) and 10
mL toluene. To the solution was added 1-hexene (100 mg, 1.19 mmol) and N2CPh2 (231 mg,
1.19 mmol) dissolved in 1 mL of toluene at 22 °C. The solution remained red in color upon addi-
tion. Upon heating (12 hours, 60 °C) the solution turned dark purple in color. After completion
the solution was exposed to air and filtered through celite. The filtrate was then passed through a
short SiO2 column (1:1 hexanes: diethyl ether). The yellow band was collected and dried under
reduced pressure for 2 hours to afford pure cyclopropane (250 mg, 84%).
2.3.4. Preparation of (IMes)2Ni(η 4). A cold, 5 mL THF solution of N3Ad (26.6
2-N3Ad) (
mg, 0.150 mmol) was added to a cold, 10 mL solution of 1-IMes (100 mg, 0.150 mmol). The
solution was stirred at room temperature for 1 hour. The resulting solution was reduced to dry-
ness under reduced pressure. The crude light brown solid was then washed with cold hexanes (2
7

ACCEPTED MANUSCRIPT
x 5 mL) resulting in a light tan solid, from which crystals were grown after concentration in cold
toluene and layering with hexanes (68 mg, 55%). This complex is stable in the freezer (-35 °C)
for up to 3 months but degrades if left at room temperature or exposed to light for more than one
1
week. H NMR (298 K, 500.13 MHz, C6D6): δ 6.69 (s, 8H, C6H2), 6.09 (s, 4H, NC2H2N), 2.29
(s, 12H, C6H2(CH3)3), 2.23 (s, 4H, Ad), 2.19 (s, 6H, C6H2(CH3)3), 2.03 (s, 12H, C6H2(CH3)3),
1.91 (d, 5H, Ad), 1.76 (d, 5H, Ad), 1.41 (s, 2H, Ad). 13C{1H} NMR (298 K, 125.76 MHz, C6D6):
δ 204.3, 137.7, 137.2, 137.1, 135.1, 132.7, 128.5, 126.4, 118.0, 51.0, 38.7, 36.5, 2.4, 21.9, 17.2,
17.1; IR (Nujol, KBr): 1349 (m), 1283 (w), 1181 (s), 1149 (s), 1116 (s), 1099 (s), 1078 (m), 1044
(w), 1022 (m), 938 (m), 898 (w), 845 (s), 813 (s), 783 (s), 724 (w), 686 (s), 657 (s), 582 (m), 496
(s) cm-1. Anal. Calcd for C52H63NiN7: C, 73.93; H, 7.52; N, 11.61. Found: C, 71.40; H, 7.37; N,
10.05. Please note these values are not within the standard range due to (unavoidable) decompo-
sition of the complex during shipment to the EA facilities. All other characterizations and cata-
lytic reactions presented here were performed with freshly-made (non-decomposed) materials.
2.3.5. Synthesis of (IMes)2Ni(η 5). A solution of 1-IMes (10.0 mg) was put in an
2-C6H12) (
NMR tube and dissolved in C6D6. To the NMR tube was added 1-hexene (28 mg, 0.33 mmol) via
syringe. Immediately the color changed from purple to red. The NMR was taken immediately.
The NMR tube was heated at 60 °C and no visible or spectroscopic change occurred even after
1
prolonged (12 h) in the oil bath. The H NMR (shown below) of complex 5 was obtained in a
C6D6 solution with excess (~ 40 equivalents) 1-hexene. Due to the large excess of 1-hexene the
13C shifts of 5 could not be obtained. Attempts to isolate complex 5 on a preparatory scale were
1
unsuccessful as 1-hexene dissociates from the metal upon solvent removal. H NMR (298 K,
500.13 MHz, C6D6): δ 6.72 (s, 8H, C6H2), 6.72 (m, 1H, 1-hex), 6.69 (m, 1H, 1-hex), 6.33 (m,
1H, 1-hex), 6.11 (s, 4H, NC2H2N), 2.26 (s, 24H, C6H2(CH3)3), 2.20-1.96 (m, 9H, 1-hex), 2.07 (s,
12H, C6H2(CH3)3).
2.4. Crystal Structure Determination. Data Collection and Structure Solution and Re-
finement. Suitable crystals of 3-Mes, 3-SIMes, 3-IPr, and 4 were selected under a stereomicro-
scope while they were immersed in mineral oil to minimize contact with air or water. The crystal
was removed from the oil using a tapered fiber, which also served to hold the crystal for data col-
lection, and was mounted in a stream of cold nitrogen at 100(2) K. X-ray diffraction data were
collected on a Bruker SMART APEX diffractometer with Mo Kα (λ = 0.71073 Å) radiation. A
Siemens Platform goniometer and a Charged Coupled Device (CCD) detector were used. The
8

ACCEPTED MANUSCRIPT
data were collected using a routine to survey the reciprocal space to the extent of a full sphere to
a resolution of 0.75 Å and were indexed by the APEX program.[56] Rotation and still images
showed diffractions to be sharp. Frames separated in reciprocal space were obtained and provid-
ed an orientation matrix and the initial cell parameters. Final cell parameters were obtained from
the full data set. Integration of intensities and refinement of cell parameters were done using
SAINT. The structures were solved by direct methods refined by iterative cycles of least-squares
refinement on F2 followed by difference Fourier synthesis using the XS software.[57, 58] All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms were included in the final
structure factor calculation at idealized positions and were allowed to ride on the neighboring
atoms with relative isotropic displacement coefficients. Absorption corrections were based on a
fitted function to the empirical transmission surface as sampled by multiple equivalent measure-
ments.[59] Observation during and after data collection showed that the crystal was still clear,
suggesting no decomposition.
2.4.1. Crystal Structure of 3-IMes·2(C7H8). Red block crystals suitable for X-ray diffrac-
tion were obtained from a concentrated toluene solution left at -35 °C for 7 days. The systematic
absences in the diffraction data were uniquely consistent for the space group P21/c. Two mole-
cules of toluene are present in the unit cell.
2.4.2. Crystal Structure of 3-SIMes. Red block crystals suitable for X-ray diffraction
were obtained from a concentrated toluene solution layered with hexanes. The systematic ab-
sences in the diffraction data were uniquely consistent for the space group P21. The structure was
refined as an inversion twin, and the resulting Flack X parameter confirms we have the correct
handedness.
2.4.3. Crystal Structure of 3-IPr·Et2O. Red block crystals suitable for X-ray diffraction
were obtained from a concentrated diethyl ether solution at -35 °C. The systematic absences in
the diffraction data were uniquely consistent for the space group P-1. One diethyl ether molecule
is present in the unit cell.
2.4.4. Crystal Structure of 4. Yellow needle crystals suitable for X-ray diffraction were
obtained from a concentrated toluene solution layered with hexanes left at -35 °C for 7 days. The
systematic absences in the diffraction data were uniquely consistent for the space group P-1. The
unit cell contains 1.72 toluene molecules, which have been treated as a diffuse contribution to the
overall scattering without specific atom positions by SQUEEZE/PLATON.[60]
9

ACCEPTED MANUSCRIPT
3. RESULTS AND DISCUSSION
.
3.1. Reaction of Ni(NHC)2 with Diphenyldiazomethane. A series of biscarbene Ni(0)
complexes were synthesized using the carbenes IMes, SIMes and IPr (IMes = 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-ylidene, SIMes
=
1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-
ylidene and IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (Scheme 1).[61] The reac-
tions of these homoleptic complexes with diazoalkanes were investigated to study the possibility
of performing group transfer chemistry.
Scheme 1. NHC ligands utilized in this work.
Ni(IMes)2 (1-IMes) was first prepared in 1994 by Arduengo, who took advantage of the
bulky nature of IMes to prepare one of the first known two-coordinate homoleptic transition
metal complexes (Scheme 2).[55] This thermally stable, 14-electron Ni(0) complex is prepared as
dark purple crystals by reaction of Ni(cod)2 (cod = 1,5-cyclooctadiene) with 2 equivalents of the
IMes ligand in tetrahydrofuran (THF). We found that this route also provides the analogous new
complex Ni(SIMes)2 (1-SIMes) in 92% yield (Scheme 2).
10

ACCEPTED MANUSCRIPT
Scheme 2. Synthetic formation of 1-IMes and 1-SIMes.
In contrast, reaction of Ni(cod)2 and 2 equivalents of IPr ligand forms an equilibrium be-
tween Ni(cod)2 and Ni(IPr)2 (1-IPr).[62] Only a 30% yield of 1-IPr could be isolated from this
mixture in our hands. We therefore developed a new route to generate 1-IPr in good yield
(Scheme 3). The known complex (IPr)2NiCl2, 2, was prepared as a pale pink powder in 95%
yield from IPr and (PPh3)2NiCl2.[63] Further reaction of 2 with 2.1 equivalents of KC8 affords 1-
IPr as a purple-black powder. This method provides 1-IPr in better yield than NaH reduction
starting from Ni(acac)2[64] (acac = acetylacetonate) and in comparable yield to reductive elimina-
tion of ethane from (IPr)2NiMe2 without the necessity of isolating the sensitive Ni-alkyl interme-
diate.[65]
Scheme 3. Synthetic formation of 1-IPr.
11

ACCEPTED MANUSCRIPT
Treatment of Ni(NHC)2 (1-Mes, 1-SIMes, and 1-Pr) with 1 equivalent of diphenyldiaz-
omethane at -35 °C followed by stirring at room temperature for 1 hour in diethyl ether affords
(NHC)2Ni(κ1-N2CPh2) (3-IMes, 3-SIMes, and 3-IPr). Removal of the ether under vacuum fol-
lowed by washing with cold hexanes affords 3-IMes, 3-SIMes, and 3-IPr as red or orange-red
solids in high yields (Scheme 4).
3.2. Structural Analysis of (NHC)2Ni(κ1-N2CPh2) Complexes. The X-ray structures of
complexes 3-IMes, 3-SIMes, and 3-IPr were investigated to determine how the diazoalkane lig-
and interacts with the Ni center. Crystals suitable for X-ray analysis of 3-IMes (Figure 1) were
obtained from a concentrated toluene solution cooled to -35 °C while crystals of 3-SIMes (Fig-
ure 2) were obtained from a concentrated toluene solution layered with hexanes at room tempera-
ture. Crystals of 3-IPr (Figure 3) were obtained from a concentrated diethyl ether solution at -35
°C.
Scheme 4. Synthetic formation of 3-IMes, 3-SIMes, and 3-IPr from their respective Ni(NHC)2
precursors.
Figure 1. Thermal ellipsoid plot of (IMes)2Ni(κ1-N2CPh2)·2(C7H8) (3-IMes·2(C7H8)) drawn at
50% probability. H atoms and molecules of solvation omitted for clarity.
12

ACCEPTED MANUSCRIPT
Figure 2. Thermal ellipsoid plot of (SIMes)2Ni(κ1-N2CPh2) (3-SIMes) drawn at 50% probabil-
ity. H atoms omitted for clarity.
Figure 3. Thermal ellipsoid plot of (IPr)2Ni(κ1-N2CPh2)·Et2O (3-IPr·Et2O) drawn at 50% prob-
ability. H atoms and molecules of solvation omitted for clarity.
Table 1. Selected bond lengths (Å) and angles (°) for 3.
3-IMes
3-SIMes 3-IPr
Ni–N(1) (Å)
1.721(2) 1.728(4) 1.748(2)
1.231(3) 1.208(5) 1.219(2)
1.349(4) 1.338(5) 1.339(3)
1.942(3) 1.921(4) 1.984(2)
1.907(3) 1.910(4) 1.914(2)
161.5(2) 159.1(3) 147.2(2)
N(1)–N(2) (Å)
N(2)–C(1) (Å)
Ni–C(2) (Å)
Ni–C(3) (Å)
Ni–N(1)–N(2) (°)
N(1)–N(2)–C(1) (°) 137.7(3) 139.1(4) 139.8(2)
C(2)–Ni–C(3) (°) 114.7(1) 123.8(2) 142.80(9)
13

ACCEPTED MANUSCRIPT
The crystal structures of all three complexes reveal planar, three-coordinate Ni centers in
which the N2CPh2 ligand is coordinated in an end-on κ1 fashion to the metal. The angle between
the NHC ligands [C(2)–Ni–C(3): 3-IMes 114.7(1)° < 3-SIMes 123.8(2)° < 3-IPr 142.80(9)°] lie
in the order consistent with the relative bulk of the three ligands as measured by percent buried
volume.[66, 67] The Ni–N(1) bond lengths of the complexes (1.721 – 1.7482 Å) fall between the
experimentally obtained value for a Ni–N single bond distance of 1.881(2) Å and the Ni=N dou-
ble bond distance of 1.702(2) Å as observed in (dtbpe)Ni–NH(2,6-iPrC6H3) and
(dtbpe)Ni=N(2,6-iPrC6H3) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane), respectively.[68] The
N(1)–N(2) bond lengths for the complexes (1.208 – 1.231 Å) are closer to typical N=N double
bonds (~1.24 Å) than typical N–N single bonds (~1.45 Å).[69] The N(2)–C(1) bond lengths for
the complexes (1.338 – 1.349 Å) are comparable to typical partial double bonds found in pyri-
dine (1.352 Å).[70] This lengthening (and weakening) of what would be expected for a C=N dou-
ble bond, is consistent with the observed reduction in ν(C=N) upon diazoalkane binding to a
[71]
metal center, from 2032 cm-1 for free N2CPh2 to 1560 cm-1 observed for each of these three
complexes. The Ni–N(1)–N(2) (147.2 – 161.5°) and N(1)–N(2)–C(1) (137.7 – 139.8°) bond an-
gles show significant deviations from linearity. Collectively, the metrical data for 3-IMes, 3-
SIMes, and 3-IPr are consistent with a bonding mode that is intermediate between A2 and A3.
The κ1 coordination of N2CPh2 observed for 3-IMes, 3-SIMes and 3-IPr contrasts with
that observed for L2Ni(N2CR2) complexes with smaller L ligands. Radius reported that when L is
iPr2Im (iPr2Im = 1,3-diisopropylimidazol-2-ylidene), then N2CPh2 forms an η2-N,N complex of
type B (Figure 1).[27] The smaller size of iPr2Im allows the C–Ni–C angle to contract to 104.8(2)°
(cf. 114.7 – 142.8° for 3), which affords room for the side-on binding of the diazoalkane. Otsuka
and Ibers have also crystallographically characterized a similar complex where Ni(CNtBu)2 binds
diazafluorene in a type-B η2-N,N fashion.[23] Here again the C–Ni–C angle of 100.4(2)° is signif-
icantly smaller than those seen in 3.
3.3. Reaction and structural analysis of Ni(IMes)2 with 1-Azidoadamantane. The obser-
vation that the (NHC)2Ni(κ1-N2CPh2) complexes 3-IMes, 3-SIMes, and 3-IPr are resistant to
elimination of N2 and thus do not form carbene complexes (vide infra) suggested that analogous
azide species could exhibit similar properties. 1-Azidoadamantane (N3Ad) was chosen because it
is capable of many of the same binding modes as diphenyldiazomethane yet possesses steric bulk
further from the terminal N=N moiety.
14

ACCEPTED MANUSCRIPT
The reaction of N3Ad with 1-IMes in tetrahydrofuran yields a yellow solution (Scheme
5). No gas evolution was observed. From this solution, after concentration and layering with
hexanes, crystals of 4 were isolated. An X-ray diffraction study of 4 revealed an η2-azide adduct
coordinated through the terminal N atoms (Figure 4). The C–Ni–C angle in 4 of 120.1(1)° is
1
even larger than that seen in 3-IMes (114.7(1)°). The H NMR spectrum reveals a diamagnetic
compound that is fluxional in solution.
Scheme 5. Synthetic formation of 4 from 1-IMes.
Figure 4. Thermal ellipsoid plot of (IMes)2Ni(η2-N3Ad) (4) drawn at 50% probability. H-atoms
omitted for clarity. Select bond lengths (Å) and angles (°): Ni(1)-N(1) = 1.926(3), Ni(1)-N(2) =
1.826(3), N(1)-N(2) = 1.234(4), N(2)-N(3) = 1.311(4), N(3)-C(1) = 1.487(5), Ni(1)-C(2) =
1.914(4), Ni(1)-C(3) = 1.918(4), C(2)-Ni(1)-C(3) = 120.1(1), N(1)-Ni(1)-N(2) = 38.3(1), N(1)-
N(2)-N(3) = 139.9(3), N(2)-N(3)-C(1) = 114.6(3).
3.4. Reactivity of (NHC)2Ni(κ1-N2CPh2) Complexes. The utility of 3-IMes, 3-SIMes and
3-IPr as precursors for Ni-carbene complexes was explored by studying their thermal and photo-
chemical stability. Complexes 3-IMes, 3-SIMes, and 3-IPr are remarkably robust under an inert
15

ACCEPTED MANUSCRIPT
atmosphere in benzene up to 60 °C and do not undergo N2 loss under thermal or photochemical
conditions. At 60 °C, however, the diazoalkane ligand dissociates from the metal center to re-
generate 1 cleanly.
Computational studies suggest that the formation of a carbene complex from a diazo-
alkane must involve the intermediacy of a κ2-C,N metallacycle (type D, Chart 1) or κ1-C diazo-
alkane intermediate (type E, Chart 1).[72] Such a binding motif is unlikely in these complexes be-
cause of steric constraints imposed by the bulky NHC ligands. Space-filling models of 3-IMes
and 3-IPr (Figure 5), where N2CPh2 is coordinated to the Ni center in the κ1-N binding mode,
show considerable steric interaction between the phenyl substituents of N2CPh2 and the aryl sub-
stituents of the NHC ligand . This interaction would only be further exacerbated in κ1-C or κ2-
C,N binding modes.
Figure 5. Space-filling models of (IMes)2Ni(κ1-N2CPh2) (3-IMes, left) and (IPr)2Ni(κ1-N2CPh2)
(3-IPr, right).
While the (NHC)2Ni(κ1-N2CPh2) complexes 3 do not eliminate N2 to form stable car-
benes, they do undergo stoichiometric and catalytic group transfer with alkenes to give cyclopro-
pane products (Table 2). Treatment of a toluene solution of 3-IMes with 1-hexene (1 equiv, 60
°C, 2 h) affords 1-IMes and 1,1-diphenyl-2-butylcyclopropane in 90% yield, while reaction with
1-methyl-2-butene, 2-hexene, or cyclohexene provides the corresponding cyclopropane products
in good yield.
Table 2. Stoichiometric group transfer reactions of (IMes)2Ni(κ1-N2CPh2) (3-IMes).
16

ACCEPTED MANUSCRIPT
The ability of Ni(NHC)2 to catalyze cyclopropanation was also tested (Scheme 6). Tolu-
ene solutions of 1-hexene react with N2CPh2 (1 equiv, 60 °C, 12 h) with 20 mol% 3-IMes or 1-
IMes to give the corresponding cyclopropane in 90% isolated yield. There is no distinguishable
difference between the catalytic rates of 3-IMes and 1-IMes, which is not surprising as 3-IMes
readily converts to 1-IMes at 60 °C. The high reactivity of metal-stabilized carbenoids usually
requires cyclopropanation reactions to be performed with excess olefin, by slow addition of di-
azoalkane, or both, to minimize the concentration of carbenes and thus avoid dimerization side
products.[9, 73-76] The ability of 1-IMes to give high yields of cyclopropanation with a 1:1 ratio of
diazoalkane to olefin is therefore particularly noteworthy.
Scheme 6. Synthetic formation of 1,1-diphenyl-2-butylcyclopropane mediated by catalytic
amounts of either 1-IMes or 3-IMes.
17

ACCEPTED MANUSCRIPT
3.5. Proposed catalytic cycle for cyclopropanation. Most transition-metal mediated cy-
clopropanation reactions are proposed to proceed through a metallacarbene intermediate,[77-80]
but this is not always the case. Peace has proposed diazoalkane attack on a Cu-coordinated olefin
as one of the pathways by which cyclopropanes are formed with [(MeO)3P]2CuI or Cu(acac)2,[81]
and Maulide has proposed olefin activation for a series of Au-catalyzed intramolecular cyclopro-
panations where the putative metallacarbene complex is inactive for cyclopropanation.[82] A me-
tallocarbene intermediate is unlikely with 3-IMes because, at the elevated temperature required
for cyclopropanation, the diazoalkane ligand dissociates from the metal center rather than form a
carbene (vide supra). Therefore, another catalytic pathway is probably operative.
The ability of olefins to coordinate to a metal center has significant effects on the rate and
selectivity for cyclopropanations with such catalysts as CuOTf and Pd(OAc)2.[83] When excess 1-
hexene is added to C6D6 solutions of 1-IMes, a color change occurs from purple to red and com-
1
plete conversion to a new complex is observed. The H NMR spectrum of this complex is con-
sistent with an η2-coordination of 1-hexene to the metal with one alkene molecule for every two
IMes ligands, (IMes)2Ni(η2-C6H12) (5) (Scheme 7). A similar mono-alkene adduct was charac-
terized by Radius who isolated (iPr2Im)2Ni(C2H4) from reaction of (iPr2Im)4Ni2(cod) and eth-
ylene.[84] Solutions of 5 in C6D6 are stable up to 80 °C with no sign of degradation by 1H NMR.
Upon removal of the solvent under vacuum, 5 completely reverts to 1-IMes. In contrast,
(iPr2Im)2Ni(C2H4), with smaller NHC ligands, is stable under vacuum.[84]
Scheme 7. Synthetic formation of 5 upon coordination of 1-hexene to 1-IMes.
Under cyclopropanation reaction conditions at 60 °C, it is clear that the diazoalkane ad-
duct is not stable but that the olefin adduct is. Thus, we propose a catalytic cycle where 1-IMes
18

ACCEPTED MANUSCRIPT
(I) activates the olefin (II) for electrophilic attack by the diazoalkane (Scheme 8) in a similar
manner to that observed by Peace.[81] N2 elimination from the intermediate complex (III) would
likely proceed with little to no barrier, and dissociation of the cyclopropane or displacement by
olefin should be facile to turn over the catalytic cycle.
Scheme 8. Proposed catalytic cycle for formation of cyclopropanation products.
Alternatively, III could eliminate N2 to form a modified metallacyclobutane (IV).[85] It
seems unlikely a metallacyclobutane intermediate supported by two IMes ligands would be steri-
cally achievable (vide supra), but it is possible to envision one IMes ligand dissociating before
formation of the metallacyclobutane. After reductive elimination of the cyclopropane product
and re-association of IMes, the starting complex (I) could be regenerated to complete the catalyt-
ic cycle. An argument against this mechanism is that IMes is known to react with N2CPh2,[86] for
Clyburne has shown that these reagents form the corresponding azine in 48% yield after stirring
at room temperature overnight. While we did not perform this control ourselves, our elevated
reaction conditions (60 °C for 12 h) would likely increase the relative azine yield. Such a reac-
tion would decrease the amount of N2CPh2 available to react with our olefin, which should there-
fore give a poor overall yield for the cyclopropane product. Due to the high overall yield seen
here for these cyclopropane products, this alternative mechanism is inconsistent with experi-
mental results.
19

ACCEPTED MANUSCRIPT
3.6. Reactivity of (IMes)2Ni(η2-N3Ad) (
4
). Several related Ni complexes with η2-bound
azide ligands are known.[87, 88] N3Ad and N3Mes (Mes = 2,4,6-trimethylphenyl) both bind to Ni
in an η2 fashion when Ni is supported by the chelating dtbpe ligand.[87] This also occurs when Ni
is supported by the chelating NHC ligand TMTBM (TMTBM = 3,3’-methylenebis(1-tert-butyl-
4,5-dimethylimidazol-iylidene)) and reacts with N3(2,6-iPr2C6H3) and N3dmp (dmp = 2,6-
dimesitylphenyl) to form (TMTBM)Ni{η2-N3(2,6-iPr2C6H3)} and (TMTBM)Ni(η2-N3dmp), re-
spectively.[88] While 4 is structurally similar to these reported η2-azides, its reactivity is distinct.
4 is stable up to 60 °C, at which point dissociation of azide occurs to regenerate 1-IMes; for-
mation of the corresponding imido complex is not observed. Cooling the mixture of 1-IMes and
N3Ad to room temperature results in the reformation of 4 along with significant decomposition.
In contrast, heating (dtbpe)Ni(η2-N3Ad) or (dtbpe)Ni( 2-N3Mes) to 50 °C results in loss of N2
η
and formation of three-coordinate imido complexes.[87] In the case of (TMTBM)Ni{η2-N3(2,6-
iPr2C6H3)}, N2 extrusion could not be induced thermally, chemically, or photochemically.[88]
However, use of a bulkier azide complex (TMTBM)Ni(η2-N3dmb) yielded an imido complex.
This result does not appear to be general, however, as we found that reaction of 1-IMes with
N3dmp resulted in decomposition without any apparent formation of an imido complex.[88] Thus,
only for 4 is even partially reversible azide coordination observed.
A more direct comparison between 4 and (dtbpe)Ni(η2-N3Ad) is warranted because the
two complexes have a similar coordination mode of the identical organoazide to a Ni(0) center
but exhibit very different reactivity (vide supra). This difference is most likely due to the steric
and chelating effects of the NHC versus dtbpe ligands. Pörschke’s complex ({(dtbpe)Ni}2(η2
-ꢀ-
C6H6)) was used to synthesize (dtbpe)Ni(η2-N3Ad), and during coordination of N3Ad to the Ni
center the P–Ni–P bite angle hardly changes (from 93.88(1)° to 93.75(2)°).[87, 89] Upon loss of N2
to form the corresponding imido complex (dtbpe)Ni=NAd, this bite angle contracts slightly to
91.69(3)°. This reactivity is due to the stability imparted by the chelating dtbpe ligand: the coor-
dinating N3Ad ligand is not sterically encumbered and so has the necessary space to form the
proposed κ2-N,N metallacyclic intermediate required to induce loss of N2.[87] Thus, the geometry
of the Ni center in the dtbpe system is independent of the identity of the coordinated azide lig-
and. In our current system, the C–Ni–C bite angle changes from 180° in 1-IMes to 120.1(1)° up-
on coordination of N3Ad to form 4. If 4 were to form an imido complex, this would probably oc-
20

ACCEPTED MANUSCRIPT
cur via a metallacyclic intermediate analogous to that proposed for formation of (dtbpe)Ni=NAd
from (dtbpe)Ni(η2-N3Ad).[87] This transformation would require further contraction of the C–Ni–
C bite angle, which is unfavorable, and place the large Ad group in proximity to the mesityl
t
groups of the NHC. This is not a problem with (dtbpe)Ni(η2-N3Ad) because the Bu groups are
pulled back from the Ni center by the chelating phosphine. Therefore, at the elevated tempera-
tures required to induce N2 loss and transform (dtbpe)Ni(η2-N3Ad) to (dtbpe)Ni=NAd, it is more
favorable for N3Ad to dissociate from 4 to generate the stable, linear 1-IMes precursor, before
reforming 4 upon cooling.
Complex 4 was also examined for stoichiometric alkane aziridination with 1-hexene in
the same manner that 3-IMes was studied (vide supra) so as to allow for direct comparison be-
tween these systems. Upon exposure of 4 to 1-hexene and heating to 60 °C, the corresponding
aziridination product was not generated. This lack of reactivity is likely due to dissociation and
partial decomposition of the N3Ad unit from the Ni center at 60 °C without loss of N2 or for-
mation of the coordinated imido for reasons described previously. Additionally, since 1-hexene
coordinates to the Ni center in 1-IMes to form 5, which is stable up to 80 °C, it is likely that, at
60 °C, the alkene displaces N3Ad without reacting. Thus, while 1-IMes has the capacity to bind
both diazoalkanes and organoazides to form coordinated Ni(0) species, only the bound diazo-
alkane adducts are useful for group transfer reactivity under the conditions tested here.
4. CONCLUSIONS
.
In conclusion, we have prepared and characterized the complexes (IMes)2Ni(κ1-N2CPh2)
(3-IMes), (SIMes)2Ni(κ1-N2CPh2) (3-SIMes), and (IPr)2Ni(κ1-N2CPh2) (3-IPr), all of which
possess a κ1-N end-on coordination mode to the Ni center through the terminal nitrogen atom of
the diazoalkane ligand. All three complexes display Ni–N–N and N–N–C angles that significant-
ly depart from linearity and have extensive delocalization of the π-bonds in the diazoalkane. We
have also prepared and characterized the organoazide complex (IMes)2Ni(η
2-N3Ad) (4) which
possesses an η2 coordination of the azide ligand to the Ni center. While elimination of N2 from
these complexes to create a new family of terminal Ni carbene and terminal imido complexes
does not occur, 3-IMes was successfully utilized in stoichiometric and catalytic olefin cyclopro-
panation reactions by producing cyclopropane products in good yields from 1:1 mixtures of di-
azoalkanes and olefins. 3-IMes mediates cyclopropanation with remarkable efficiency, and so
21

ACCEPTED MANUSCRIPT
these complexes are a promising starting point for the development of a new class of cyclopro-
panation catalysts.
ACKNOWLEDGEMENTS.
This paper is dedicated to the memory of Prof. Gregory L. Hillhouse who was a terrific advisor
and mentor. This work was supported by National Science Foundation through grants CHE-
0957816, CHE-1266281, CHE-0615274 (to G.L.H.). We thank Prof. Michael Hopkins and Prof.
Richard Jordan for their comments on and assistance with the manuscript.
APPENDIX A. SUPPLEMENTARY DATA.
CIF files contain the supplementary crystallographic data for this paper. Crystallographic data
tables, 1H/13C NMR, and mass spectra files for the structures of compounds 3-IMes, 3-SIMes, 3-
IPr, and 4, as well as alternative syntheses for 1-IMes, 1-IPr, and 2, can be found in the sup-
plementary data for this article.
CORRESPONDING AUTHOR
* E-mail: nharrold@uchicago.edu
PRESENT ADDRESS
‡ Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706, USA.
NOTES
The authors declare no competing financial interest.
Deceased March 6, 2014.
R
EFERENCES
.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
D. Seyferth, Chem. Rev. 1955, 55, 1155-1177.
W. R. Roper, J. Organomet. Chem. 1986, 300, 167-190.
H. Werner, J. Organomet. Chem. 1995, 500, 331-336.
W. A. Herrmann, Angew. Chem. Int. Ed. 1978, 17, 800-812.
M. P. Doyle, Chem. Rev. 1986, 86, 919-939.
D. A. Lemenovskii, M. Putala, Russ. Chem. Rev. 1994, 63, 197-216.
Y. Mizobe, Y. Ishii, M. Hidai, Coord. Chem. Rev. 1995, 139, 281-311.
A. Padwa, M. D. Weingarten, Chem. Rev. 1996, 96, 223-270.
M. P. Doyle, D. C. Forbes, Chem. Rev. 1998, 98, 911-936.
[10] H. M. L. Davies, S. A. Panaro, Tetrahedron 2000, 56, 4871-4880.
22

ACCEPTED MANUSCRIPT
[11] H. M. L. Davies, E. G. Antoulinakis, J. Organomet. Chem. 2001, 617-618, 47-55.
[12] R. Beckhaus, C. Santamaría, J. Organomet. Chem. 2001, 617-618, 81-97.
[13] D. Sutton, Chem. Rev. 1993, 93, 995-1022.
[14] M. Dartiguenave, M. J. Menu, E. Deydier, D. Yves, H. Siebald, Coord. Chem. Rev. 1998,
178-180, 623-663.
[15] N. P. Mankad, J. C. Peters, Chem. Commun. 2008, 1061-1063.
[16] J. J. Curley, T. Murahashi, C. C. Cummins, Inorg. Chem. 2009, 48, 7181-7193.
[17] K. Kromm, F. Hampel, J. A. Gladysz, Organometallics 2002, 21, 4264-4274.
[18] O. L. Sydora, D. S. Kuiper, P. T. Wolczanski, E. B. Lobkovsky, A. Dinescu, T. R.
Cundari, Inorg. Chem. 2006, 45, 2008-2021.
[19] M. E. García, D. García-Vivó, M. A. Ruiz, P. Herson, Organometallics 2008, 27, 3879-
3891.
[20] U. J. Kilgore, C. A. Sengelaub, M. Pink, A. R. Fout, D. J. Mindiola, Angew. Chem. Int.
Ed. 2008, 47, 3769-3772.
[21] A. I. Nguyen, K. J. Blackmore, S. M. Carter, R. A. Zarkesh, A. F. Heyduk, J. Am. Chem.
Soc. 2009, 131, 3307-3316.
[22] D. E. Herbert, N. C. Lara, T. Agapie, Chem. Eur. J. 2013, 19, 16453-16460.
[23] A. Nakamura, T. Yoshida, M. Cowie, S. Otsuka, J. A. Ibers, J. Am. Chem. Soc. 1977, 99,
2108-2117.
[24] S. Gambarotta, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Am. Chem. Soc. 1982, 104,
1918-1924.
[25] J. L. Polse, A. W. Kaplan, R. A. Andersen, R. G. Bergman, J. Am. Chem. Soc. 1998, 120,
6316-6328.
[26] A. W. Kaplan, J. L. Polse, G. E. Ball, R. A. Andersen, R. G. Bergman, J. Am. Chem. Soc.
1998, 120, 11649-11662.
[27] T. Schaub, U. Radius, Z. Anorg. Allg. Chem. 2007, 633, 2168-2172.
[28] V. M. Iluc, G. L. Hillhouse, J. Am. Chem. Soc. 2014, 136, 6479-6488.
[29] For a more complete discussion of diazoalkane binding motifs, see: G. L. Hillhouse, B. L.
Haymore, J. Am. Chem. Soc. 1982, 104, 1537-1548.
[30] W. A. Nugent, J. M. Mayer, Metal-Ligand Multiple Bonds, John Wiley & Sons, New
York, 1988.
[31] D. E. Wigley, Prog. Inorg. Chem. 1994, 42, 239-482.
[32] S. Cenini, E. Gallo, A. Caselli, F. Ragaini, S. Fantauzzi, C. Piangiolino, Coord. Chem.
Rev. 2006, 250, 1234-1253.
[33] R. Waterman, G. L. Hillhouse, J. Am. Chem. Soc. 2003, 125, 13350-13351.
[34] P. Müller, C. Fruit, Chem. Rev. 2003, 103, 2905-2920.
[35] 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, 9961-9964.
[36] N. D. Harrold, R. Waterman, G. L. Hillhouse, T. R. Cundari, J. Am. Chem. Soc. 2009,
131, 12872-12873.
[37] E. R. King, E. T. Hennessy, T. A. Betley, J. Am. Chem. Soc. 2011, 133, 4917-4923.
[38] M. G. Fickes, W. M. Davis, C. C. Cummins, J. Am. Chem. Soc. 1995, 117, 6384-6385.
[39] G. Proulx, R. G. Bergman, J. Am. Chem. Soc. 1995, 117, 6382-6383.
[40] G. Proulx, R. G. Bergman, Organometallics 1996, 15, 684-692.
[41] T. A. Hanna, A. M. Baranger, R. G. Bergman, Angew. Chem. Int. Ed. 1996, 35, 653-655.
[42] G. Guillemot, E. Solari, C. Floriani, C. Rizzoli, Organometallics 2001, 20, 607-615.
23

ACCEPTED MANUSCRIPT
[43] M. Barz, E. Herdtweck, W. R. Thiel, Angew. Chem. Int. Ed. 1998, 37, 2262-2265.
[44] H. V. R. Dias, S. A. Polach, S.-K. Goh, E. F. Archibong, D. S. Marynick, Inorg. Chem.
2000, 39, 3894-3901.
[45] G. Albertin, S. Antoniutti, D. Baldan, J. s. Castro, S. García-Fontán, Inorg. Chem. 2008,
47, 742-748.
[46] A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen, F. J. Timmers,
Organometallics 1996, 15, 1518-1520.
[47] J. Miller, J. Org. Chem. 1959, 24, 560-561.
[48] P. A. S. Smith, C. D. Rowe, L. B. Bruner, J. Org. Chem. 1969, 34, 3430-3433.
[49] J. A. Miller, Tetrahedron Lett. 1975, 16, 2959-2960.
[50] B. C. Ranu, A. Sarkar, R. Chakraborty, J. Org. Chem. 1994, 59, 4114-4116.
[51] A. J. Arduengo III, R. Krafczyk, R. Schmutzler, H. A. Craig, J. R. Goerlich, W. J.
Marshall, M. Unverzagt, Tetrahedron 1999, 55, 14523-14534.
[52] S. P. Nolan. U.S. Patent 7109348, 2006.
[53] V. Ritleng, E. Brenner, M. J. Chetcuti, J. Chem. Educ. 2008, 85, 1646.
[54] L. Jafarpour, E. D. Stevens, S. P. Nolan, J. Organomet. Chem. 2000, 606, 49-54.
[55] A. J. Arduengo III, S. F. Gamper, J. C. Calabrese, F. Davidson, J. Am. Chem. Soc. 1994,
116, 4391-4394.
[56] SMART; Bruker-AXS: Madison, WI, 2009.
[57] G. M. Sheldrick, Acta Cryst. 2008, A64, 112-122.
[58] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Puschmann, J. Appl.
Cryst. 2009, 42, 339-341.
[59] SADABS; Bruker-AXS: Madison, WI, 2012.
[60] http://www.cryst.chem.uu.nl/platon/.
[61] T. Dröge, F. Glorius, Angew. Chem. Int. Ed. 2010, 49, 6940-6952.
[62] J. Louie, J. E. Gibby, M. V. Farnworth, T. N. Tekavec, J. Am. Chem. Soc. 2002, 124,
15188-15189.
[63] K. Matsubara, K. Ueno, Y. Shibata, Organometallics 2006, 25, 3422-3427.
[64] K. Matsubara, S. Miyazaki, Y. Koga, Y. Nibu, T. Hashimura, T. Matsumoto,
Organometallics 2008, 27, 6020-6024.
[65] A. A. Danopoulos, D. Pugh, Dalton Trans. 2008, 30-31.
[66] A. C. Hillier, W. J. Sommer, B. S. Yong, J. L. Petersen, L. Cavallo, S. P. Nolan,
Organometallics 2003, 22, 4322-4326.
[67] H. Clavier, S. P. Nolan, Chem. Commun. 2010, 46, 841-861.
[68] D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2001, 123, 4623-4624.
[69] A. Hammerl, T. Klapotke, in Encyclopedia of Inorganic Chemistry, 2nd ed. (Ed.: R.
King), Wiley & Sons, Chichester, 2005.
[70] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen, R. Taylor, J. Chem.
Soc., Perkin Trans. 2 1987, S1-S19.
[71] M. I. Javed, M. Brewer, Org. Synth. 2008, 85, 189.
[72] R. Cohen, B. Rybtchinski, M. Gandelman, H. Rozenberg, J. M. L. Martin, D. Milstein, J.
Am. Chem. Soc. 2003, 125, 6532-6546.
[73] V. K. Singh, A. DattaGupta, G. Sekar, Synthesis 1997, 1997, 137-149.
[74] X. Dai, T. H. Warren, J. Am. Chem. Soc. 2004, 126, 10085-10094.
[75] H. Pellissier, Tetrahedron 2008, 64, 7041-7095.
[76] D. Intrieri, A. Caselli, E. Gallo, Eur. J. Inorg. Chem. 2011, 2011, 5071-5081.
24

ACCEPTED MANUSCRIPT
[77] K. H. Dötz, Angew. Chem. Int. Ed. 1984, 23, 587-608.
[78] M. P. Doyle, in Comprehensive Organometallic Chemistry II (Ed.: E. W. A. G. A. S.
Wilkinson), Elsevier, Oxford, 1995, pp. 387-420.
[79] W. D. Wulff, in Comprehensive Organometallic Chemistry II (Ed.: E. W. A. G. A. S.
Wilkinson), Elsevier, Oxford, 1995, pp. 469-547.
[80] D. F. Harvey, D. M. Sigano, Chem. Rev. 1996, 96, 271-288.
[81] D. S. Wulfman, R. S. McDaniel Jr, B. W. Peace, Tetrahedron 1976, 32, 1241-1249.
[82] X. Huang, S. Klimczyk, L. F. Veiros, N. Maulide, Chem. Sci. 2013, 4, 1105-1110.
[83] A. J. Anciaux, A. J. Hubert, A. F. Noels, N. Petiniot, P. Teyssie, J. Org. Chem. 1980, 45,
695-702.
[84] T. Schaub, U. Radius, Chem. Eur. J. 2005, 11, 5024-5030.
[85] C. Rodríguez-García, A. Oliva, R. M. Ortuño, V. Branchadell, J. Am. Chem. Soc. 2001,
123, 6157-6163.
[86] J. M. Hopkins, M. Bowdridge, K. N. Robertson, T. S. Cameron, H. A. Jenkins, J. A. C.
Clyburne, J. Org. Chem. 2001, 66, 5713-5716.
[87] R. Waterman, G. L. Hillhouse, J. Am. Chem. Soc. 2008, 130, 12628-12629.
[88] N. D. Harrold, G. L. Hillhouse, Chem. Sci. 2013, 4, 4011-4015.
[89] I. Bach, K.-R. Pörschke, R. Goddard, C. Kopiske, C. Krüger, A. Rufinska, K. Seevogel,
Organometallics 1996, 15, 4959-4966.
25