Carbene Formation and Transfer at a Dinickel Active Site

Article abstract of DOI:10.1021/acs.organomet.8b00261

The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [^i-PrNDI]Ni₂(C₆H₆) complex (NDI = naphthyridine-diimine) reacts with Ph₂CN₂ to generate a metastable diazoalkane adduct, which eliminates N₂ at 60 °C to yield a paramagnetic Ni₂(μ-CPh₂) complex. The Ni₂(μ-CPh₂) complex undergoes carbene transfer to t-BuNC via an initial isonitrile adduct, which upon heating releases free t-BuNCCPh₂. On the basis of this sequence of stoichiometric reactions, a catalytic carbene transfer reaction is demonstrated.

Full text of DOI:10.1021/acs.organomet.8b00261

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Carbene Formation and Transfer at a Dinickel Active Site
Arnab K. Maity, Matthias Zeller, and Christopher Uyeda*
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
S
* Supporting Information
ABSTRACT: The synthesis and reactivity of a dinickel bridging
carbene is described. The previously reported [i‑PrNDI]Ni2(C6H6)
complex (NDI = naphthyridine−diimine) reacts with Ph2CN2 to
generate a metastable diazoalkane adduct, which eliminates N2 at 60
°C to yield a paramagnetic Ni2(μ-CPh2) complex. The Ni2(μ-CPh2)
complex undergoes carbene transfer to t-BuNC via an initial
isonitrile adduct, which upon heating releases free t-BuNCCPh2.
On the basis of this sequence of stoichiometric reactions, a catalytic
carbene transfer reaction is demonstrated.
INTRODUCTION
■
Transition metal carbene complexes are implicated as key
intermediates in catalytic cyclopropanation and bond insertion
reactions.1 Synthetic studies targeting isolable carbene
complexes have largely focused on accessing terminally
coordinated MCR2 species because of their potential to
exhibit high reactivity.2 It is well-established, however, that
carbene ligands can induce the spontaneous formation of
dinuclear M2(μ-CR2) assemblies, particularly when supporting
ligands lack sufficient steric protection.3 Because many
catalytically relevant systems may exhibit such monomer−
dimer equilibria, it is of interest to examine whether dinuclear
bridging carbenes are capable of participating in carbene
transfer reactions and whether they might access unique
pathways that involve the direct participation of two metals.
Dinuclear M2(μ-CR2) complexes are known to function as
Figure 1. (a) Examples of M2(μ-CR2) complexes. (b) A constrained
carbene transfer reagents, but they generally do so through an
initial dissociation to form a more reactive mononuclear
M(CR2) species (Figure 1a). For example, Warren reported
that a β-diketiminate Cu(I) precursor reacts with Ph2CN2 to
generate a Cu2(μ-CR2) dimer, which exists in solution
equilibrium with a mononuclear Cu(CR2) species.3a,b This
mixture is capable of effecting the cyclopropanation of alkenes,
and mechanistic studies indicated that the carbene transfer
occurs through the minority mononuclear species. In a related
study, the [(IPr)NiCl]2 dimer (IPr = 1,3-(2,6-(i-
Pr)2C6H3)2imidazolin-2-ylidene) was shown by Hillhouse to
undergo a reaction with Ph2CN2 in the presence of NaB(ArF)4
to generate a cationic {[(IPr)Ni]2(Cl)(μ-CR2)}+ complex.4
This dinuclear carbene reacts with t-BuNC to yield the
corresponding ketenimine product. However, it remains
unclear whether the dinuclear species is a kinetically
competent carbene transfer reagent or whether a pre-
dinuclear carbene complex using the [NDI]Ni2 platform.
equilibrium dissociation forms a more reactive terminal
(IPr)NiCR2 species.
Recently, our group described a redox-active naphthyr-
idine−diimine (NDI) pincer ligand that enables the synthesis
of well-defined dinickel complexes featuring metal−metal
single bonds.5 We hypothesized that the constrained environ-
ment of the [NDI]Ni2 system might suppress monomer−
dimer equilibria in group transfer processes, allowing the
reactivity of bridging carbene ligands to be studied in
isolation.6 Here we describe the synthesis of a Ni2(μ-CR2)
complex from its R2CN2 precursor and a prototypical carbene
transfer reaction to t-BuNC (Figure 1b).
Received: April 24, 2018
© XXXX American Chemical Society
A
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(SOMOs) correspond to a predominantly ligand-centered
SOMO and a SOMO−1 that has Ni2 character (Figure 3a).
RESULTS AND DISCUSSION
■
Synthesis of a Dinickel Carbene Complex. We initiated
our studies by pursuing the characterization of a stable carbene
complex using the [NDI]Ni2 platform. Addition of Ph2CN2
(1.0 equiv) to a THF solution of the complex [i‑PrNDI]-
Ni2(C6H6) (1) (1.0 equiv) yielded a dark-brown product 2
1
featuring paramagnetically shifted H NMR signals spanning a
range of −74 to 76 ppm. The identity of 2 was established by
X-ray diffraction (XRD) analysis and features an intact Ph2CN2
ligand bridging the two Ni centers in a μ-η2:η1 fashion (Figure
2b). The N−N bond of the diazo ligand is significantly
Figure 3. DFT (M06L/6-311G(d,p))-calculated (a) SOMO and
SOMO−1 and (b) spin-density plot for the S = 1 state of
[
i‑PrNDI]Ni2(CPh2) (3). Fractions of the total spin density for the
two Ni atoms and the NDI ligand are shown. The i-Pr groups have
been truncated to Me groups in the model.
Redox Chemistry of Dinickel Diphenyl Carbene. We
next carried out a series of experiments to probe the redox
behavior of carbene complex 3. In THF solution (0.4 M
[nBu4N][PF6] electrolyte), 3 exhibits two reduction and two
oxidation events spanning a potential range of −2.63 to −0.51
V vs Cp2Fe/Cp2Fe+ (Figure 4a). The first reduction at −1.80
V is accessible by treatment of 3 with KC8 (1.0 equiv) in the
presence of 18-crown-6 (Figure 4b). The resulting anionic
complex 4 is isostructural to 3 in the solid state and features an
Figure 2. (a) Thermal conversion of [i‑PrNDI]Ni2(N2CPh2) (2) to
[
3.135(1) Å. (c) Solid-state structure of 3. Ni1−Ni2: 2.372(1) Å.
i‑PrNDI]Ni2(CPh2) (3). (b) Solid-state structure of 2. Ni1−Ni2:
elongated (1.296(6) Å) relative to the characteristic distance
for a free diazoalkane (e.g., 1.146(2) Å for bis(4-
dibromophenyl)diazomethane),7 indicating a high degree of
back-bonding from the Ni2 fragment.
Gaseous N2 is liberated from the Ph2CN2 adduct 2 upon
heating in THF at 60 °C for 12 h (Figure 2a). The resulting
dark-purple carbene complex 3 possesses C2v symmetry on the
1H NMR chemical shift time scale (11 resolved signals ranging
from −46 to 54 ppm) and exhibits a solution magnetic
moment of 2.82μB (Evans method, 298 K), consistent with an
S = 1 ground state. In the solid state (Figure 2c), the symmetry
observed in solution is broken by a weak interaction between
one of the Ni centers and an ipso carbon of the carbene Ph
substituent (Ni1−C10 = 2.487(6) Å). The two Ni−C
distances are nonequivalent as a result of this interaction
(Ni1−C9 = 1.874(7) Å vs Ni2−C9 = 1.983(6) Å). A similar
fluxional arene interaction was observed in Hillhouse’s
{[(IPr)Ni]2(Cl)(μ-CR2)}+ complex.4
Given the redox-active nature of the NDI ligand, it was of
interest to further examine the electronic structure of μ-CPh2
complex 3. In comparison with the metrical parameters for free
i‑PrNDI, complex 3 exhibits contracted C(imine)−C(ipso)
distances and elongated C(imine)−N and C(ipso)−N
distances, which are bond distortions characteristic of ligand-
centered reduction.2j,5 By density functional theory (DFT)
(M06L/6-311G(d,p)), the spin density in 3 is highly
delocalized between the NDI π system and the Ni−Ni bond
(Figure 3b). The two singly occupied molecular orbitals
Figure 4. (a) Cyclic voltammogram for [i‑PrNDI]Ni2(CPh2) (3) (0.4
M [nBu4N][PF6] supporting electrolyte in THF, glassy carbon
working electrode, 100 mV/s scan rate). The open-circuit potential
and direction of the scan are indicated by the arrow. (b) Synthesis and
(c) solid-state structure of [K(18-crown-6)(THF)2][(i‑PrNDI)-
Ni2(CPh2)] (4). [K(18-crown-6)(THF)2] has been omitted for
clarity. Ni1−Ni2: 2.382(1) Å.
B
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outer-sphere K+ encapsulated by 18-crown-6 and two
molecules of THF (Figure 4c). Relative to the metrical
parameters for the neutral carbene complex 3, anion 4 displays
an NDI ligand that is further reduced, suggesting that the
electron being added to the system is located in a
predominantly ligand-centered orbital (Table 1). By contrast,
the Ni−Ni distance changes by only 0.01 Å upon reduction.
complexes when dissolved in THF. In accordance with this
observation, 5 is EPR-active and exhibits a sharp signal at g =
2.01 (2-MeTHF, 77 K) (Figure 5c). The minimal anisotropy
and narrow line width of the frozen-solution EPR spectrum are
characteristic features of an organic radical.10
Carbene Transfer with Isonitrile. Having isolated a well-
defined μ-CPh2 complex (3), we next sought to explore its
carbene transfer reactivity. In this context, we recently found
that [NDI]Ni2 complexes function as alkene cyclopropanation
catalysts using methylene equivalents derived from CH2Cl2/
Zn.11 The isolated Ni2(CPh2) complex 3, however, does not
react with alkenes such as styrene, 1-octene, or ethylene,
perhaps because of its higher degree of steric hindrance.
When t-BuNC (strictly 1.0 equiv) is added to a THF
solution of 3, the isonitrile adduct 6 is generated (Figure 6a).
a
Table 1. Selected Bond Distances (in Å) for 3 and 4
b
3
4
Ni1−Ni2
2.372(1)
2.382(1)
Ni1−C9, Ni2−C9
C1−N1, C8−N4
C1−C2, C7−C8
C2−N2, C7−N3
1.877(4), 1.984(5)
1.319(9), 1.305(9)
1.434(9), 1.450(6)
1.902(5), 1.975(5)
1.342(7), 1.329(7)
1.415(7), 1.432(7)
1.411(7), 1.384(6)
1.374(9), 1.369(8)
a
b
See Figures 2c and 4c for atom labels. Average of two independent
molecules in the asymmetric unit.
The reaction of carbene complex 3 with (Cp2Fe)PF6 (1.0
equiv) in MeCN yields an oxidized product 5 that crystallizes
as a homodimeric species in 91% isolated yield (Figure 5a).
Figure 6. (a) Stoichiometric Ph2C transfer to t-BuNC and solid-state
structure of 6. Ni−Ni: 3.0846(8) Å. (b) Catalytic Ph2C transfer to t-
BuNC using 10 mol % 1.
The μ-CPh2 fragment is retained in this structure, and one of
the Ni atoms bears the additional t-BuNC ligand. The
dinuclear structure of the complex remains intact, but the
Ni−Ni distance increases to 3.0846(8) Å, which is longer than
the sum of the van der Waals radii12 and suggests that there is
no significant metal−metal bonding. The bound t-BuNC
exhibits a C−N distance of 1.167(7) Å and a C−N stretching
frequency of 2156 cm−1, which is moderately red-shifted from
that of free t-BuNC (2146 cm−1).13 The Ni center not bearing
the isonitrile ligand forms a significant η2-arene interaction,
and the Ni−C(ipso) distance decreases from 2.487(6) Å in
carbene complex 3 to 2.072(8) Å in isonitrile adduct 6. When
isolated Ni2(μ-CPh2)(CNt-Bu) complex 5 is dissolved in C6H6
and gently heated at 80 °C for 1 h, Ni2(C6H6) complex 1 is
regenerated, and free t-BuNCCPh2 is formed in >99%
yield.
Figure 5. (a) Synthesis and (b) solid-state structure of 5. Ni−Ni:
2.9843(5) Å. C4−C4′: 1.588(3) Å. (c) Solution EPR spectrum of 5
(2-MeTHF, 77 K).
The solid-state structure of 5 reveals the formation of a new
C−C bond through the 4-position of the naphthyridine ring
(Figure 5b). The C4−C4′ distance of 1.588(3) Å is modestly
elongated relative to the typical length of a C−C single bond.
By comparison, a similar dimer generated from an iron
pyridine−diimine complex, [LMeFe(Py)]2(μ-C10H10N2) (LMe
=
2,4-bis(2,6-diisopropylimino)pentyl), features a C4−C4′ dis-
tance of 1.563(6) Å.8,9 The oxidized carbene complex 5 is
NMR-silent at room temperature and possesses a solution
magnetic moment of 2.0μB (Evans method, 298 K), suggesting
The sequence of diazoalkane binding, N2 extrusion, isonitrile
binding, and carbene transfer constitutes a complete set of
elementary transformations required to carry out a catalytic
group transfer reaction. Accordingly, slow addition of a t-
BuNC (1.0 equiv) and Ph2CN2 (1.0 equiv) solution to
1
that the solid-state dimer dissociates into monomeric S = /2
C
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Calcd for 3 (C49H54N4Ni2): C 72.09, H 6.67, N 6.86. Found: C 71.63,
H 6.64, N 6.44.
Ni2(C6H6) complex 1 (10 mol %), heated at 80 °C in C6H6,
provided t-BuNCCPh2 in 65% yield (Figure 6b). Slow
addition of both reaction partners is critical for the catalytic
process to be viable. When catalyst 1 is treated with excess t-
BuNC, demetalation occurs to generate free i‑PrNDI and
Ni(CNt-Bu)4. Furthermore, exposure of 1 to excess Ph2CN2
leads to catalytic consumption of the diazoalkane reagent to
form azine dimers.
In conclusion, the naphthyridine−diimine (NDI) ligand
framework enabled the synthesis of a well-defined dinickel
bridging carbene complex. The complex [i‑PrNDI]Ni2(CPh2)
(3) adopts an unusual paramagnetic ground state as a result of
the presence of low-lying π orbitals associated with the redox-
active NDI ligand. Complex 3 engages in carbene transfer to t-
BuNC by a mechanism in which the isonitrile initially
coordinates to one Ni center, cleaving the Ni−Ni bond. The
Ni−Ni bond is restored upon release of the ketenimine
product. Together, these studies highlight a unique mechanism
for carbene transfer from dinuclear M2(μ-CR2) species that
involves the direct participation of both metals.
Complex 4. To a 20 mL vial containing a stir bar were added
complex 3 (49 mg, 0.060 mmol, 1.0 equiv), 18-crown-6 (16 mg, 0.060
mmol, 1.0 equiv), and THF (5 mL). KC8 (8 mg, 0.060 mmol, 1.0
equiv) was added with vigorous stirring. An immediate color change
from dark purple to dark green was observed. The reaction mixture
was stirred at ambient temperature for an additional 15 min and then
filtered through a glass fiber pad to remove black graphite. The dark-
green filtrate was quickly concentrated to a final volume of
approximately 2 mL. The solution was stored at −30 °C overnight
to yield dark-green crystals of complex 4. The solvent was decanted,
and the crystals were washed with Et2O (3 × 1 mL) and dried under
1
reduced pressure. Yield: 75 mg, 88%. H NMR (400 MHz, 298 K,
THF-d8): δ −64.1, −24.0, −19.7, −18.0, 0.7, 0.8, 2.5, 3.9, 5.6, 11.1,
12.6, 15.6. UV−vis (THF, nm {M−1 cm−1}): 540 {6000}, 665
{5000}, 860 {5000}. Anal. Calcd for 4·2THF (C77H110KN4Ni2O10):
C 65.67, H 7.87, N 3.98. Found: C 65.66, H 7.68, N 4.03. Note: when
crystalline 4 was redissolved in THF, rapid decomposition to form red
impurities was observed.
Complex 5. To a 20 mL vial containing a stir bar were added
complex 3 (49 mg, 0.060 mmol, 1.0 equiv) and THF (5 mL).
(Cp2Fe)PF6 (19.5 mg, 0.060 mmol, 1.0 equiv) dissolved in MeCN
(0.5 mL) was added dropwise. An immediate color change from dark
purple to brown was observed. The reaction mixture was stirred at
ambient temperature for 1 h and then concentrated to dryness under
reduced pressure. Pentane (3 mL) was added to the residue, and the
resulting suspension was stirred for 30 min. The pale-yellow solution
was decanted from the crude solid material. The brown solid was
dissolved in THF (8 mL) and filtered through a glass fiber pad.
Diffusion of Et2O vapor into the concentrated THF solution at
ambient temperature yielded dark-brown crystalline material. The
solvent was decanted, and the crystals were washed with Et2O (3 × 1
mL) and dried under reduced pressure. Yield: 55 mg, 91%. Single
crystals suitable for XRD were grown from a concentrated DME
EXPERIMENTAL SECTION
■
General Information. All of the manipulations were carried out
using standard Schlenk or glovebox techniques under an atmosphere
of N2. Solvents were dried and degassed by passage through a column
of activated alumina and sparging with Ar gas. Deuterated solvents
were purchased from Cambridge Isotope Laboratories, Inc., degassed,
and stored over activated 3 Å molecular sieves prior to use. All of the
other reagents and starting materials were purchased from commercial
vendors and used without further purification unless otherwise noted.
Ph2CN2 was synthesized and purified by crystallization from cold
pentane.14 18-Crown-6 was dried according to reported procedures
solution stored at −30 °C overnight. EPR (77 K, 2-MeTHF): giso
=
prior to use.15 i‑PrNDI]Ni2(C6H6) (1) was prepared according to
[
2.01. UV−vis (THF, nm {M−1 cm−1}): 335 {28 000}, 470 {10 000}.
μeff = 2.0μB (Evans method, 298 K, THF-d8). Anal. Calcd for 5
(C102H112F12N10Ni4P2): C 61.17, H 5.64, N 6.99. Found: C 60.79, H
5.74, N 6.81.
previously reported procedures.5 Elemental analyses were performed
by Midwest Microlab (Indianapolis, IN).
Complex 2. To a 20 mL vial containing a stir bar were added
complex 1 (95 mg, 0.13 mmol, 1.0 equiv), THF (1 mL), and pentane
(10 mL). The mixture was stirred for 30 min to generate a red-brown
solution. To this stirring solution, Ph2CN2 (25 mg, 0.13 mmol, 1.0
equiv) dissolved in pentane (2 mL) was added dropwise. An
immediate color change to dark brown was observed. The stir bar was
removed, and the reaction mixture was stored at −30 °C overnight to
afford a microcrystalline solid. The mother liquor was decanted, and
the solid was washed with cold pentane (3 × 1 mL) and dried under
reduced pressure. Yield: 100 mg, 92%. Single crystals suitable for XRD
were obtained from a saturated pentane solution cooled at −30 °C
Complex 6. To a 20 mL vial containing a stir bar were added
complex 3 (82 mg, 0.10 mmol, 1.0 equiv) and THF (2 mL). t-BuNC
(11.4 μL, 0.10 mmol, 1.0 equiv) dissolved in hexane (1 mL) was
added dropwise with stirring. An immediate color change from dark
purple to dark brown was observed. The reaction mixture was
concentrated to dryness under reduced pressure. The dark-brown
solid was dissolved in hexane (5 mL) and stored at −30 °C overnight
to yield a dark-brown microcrystalline solid. The solvent was
decanted, and the crystals were washed with pentane (3 × 1 mL)
and dried under reduced pressure. Yield: 80 mg, 89%. Single crystals
suitable for XRD were grown from a concentrated Et2O solution
1
overnight. H NMR (400 MHz, 298 K, THF-d8): δ −73.6, −20.3,
1
−14.0, −13.8, −0.5, 2.9, 7.9, 12.4, 20.3, 22.1, 29.6, 63.9, 66.4, 76.1.
UV−vis (THF, nm {M−1 cm−1}): 358 {30 000}, 505 {9000}, 548
{sh}, 750 {8000}. μeff = 2.86μB (Evans method, 298 K, THF-d8).
Anal. Calcd for 2 (C49H54N6Ni2): C 69.70, H 6.45, N 9.95. Found: C
69.28, H 6.63, N 9.94.
stored at −30 °C for 24 h. H NMR (800 MHz, 298 K, THF-d8): δ
0.51 (s, 9H, −C(CH3)3), 0.70 (d, J = 8 Hz, 3H, −CH(CH3)2), 0.84
(d, J = 8 Hz, 3H, −CH(CH3)2), 1.09 (d, J = 8 Hz, 3H, −CH(CH3)2),
1.12 (d, J = 8 Hz, 3H, −CH(CH3)2), 1.14 (d, J = 8 Hz, 3H,
−CH(CH3)2), 1.32 (br s, 3H, −CH3), 1.34 (d, J = 8 Hz, 3H,
−CH(CH3)2), 1.40 (br s, 3H, −CH3), 1.45 (d, J = 8 Hz, 3H,
−CH(CH3)2), 1.57 (d, J = 8 Hz, 3H, −CH(CH3)2), 2.35 (sept, J = 8
Hz, 1H, −CH(CH3)2), 3.28 (sept, J = 8 Hz, 1H, −CH(CH3)2), 3.45
(sept, J = 8 Hz, 1H, −CH(CH3)2), 3.61 (sept, J = 8 Hz, 1H,
−CH(CH3)2), 4.82 (br s, 2H, Ar H), 5.77 (br s, 1H, Ar H), 6.00 (br s,
2H, Ar H), 6.08 (d, J = 8 Hz, 1H, Ar H), 6.31 (t, J = 8 Hz, 1H, Ar H),
6.54 (t, J = 8 Hz, 1H, Ar H), 6.57 (t, J = 8 Hz, 1H, Ar H), 6.79 (d, J =
8 Hz, 1H, Ar H), 6.83 (d, J = 8 Hz, 1H, Ar H), 6.94 (m, 2H, Ar H),
7.00 (m, 2H, Ar H), 7.09 (d, J = 8 Hz, 1H, Ar H), 7.23 (m, 1H, Ar
H), 7.28 (t, J = 8 Hz, 2H, Ar H), 8.11 (d, J = 8 Hz, 2H, Ar H). 13C
NMR (200 MHz, 298 K, THF-d8): δ 15.3, 23.4, 24.0, 24.1, 24.2, 24.3,
24.4, 28.2, 28.3, 28.5, 28.7, 56.6, 91.5, 122.3, 122.6, 123.1, 123.3,
123.5, 124.8, 125.0, 125.4, 126.2, 127.9, 128.1, 129.1, 129.4, 130.2,
135.4, 140.6, 148.4. UV−vis (THF, nm {M−1 cm−1}): 333 {21 000},
Complex 3. To a 50 mL Schlenk flask containing a stir bar were
added complex 2 (100 mg, 0.12 mmol) and THF (20 mL). The
reaction mixture was stirred at 60 °C for 12 h, during which time the
color of the solution turned from dark brown to dark purple. The
volatiles were removed under reduced pressure to afford a dark-purple
sticky solid. Hexane (5 mL) was added to the residue, and the mixture
was scraped with a spatula to obtain a uniform suspension. The
volatiles were removed under reduced pressure to afford complex 3.
Yield: 95 mg, 98%. Single crystals suitable for XRD were obtained
1
from a saturated pentane solution cooled at −30 °C overnight. H
NMR (500 MHz, 298 K, THF-d8): δ −45.5 (2H), −40.1 (4H), −3.0
(2H), 2.4 (12H), 2.5 (12H), 10.5 (4H), 20.5 (4H), 24.9 (4H), 37.4
(6H), 54.8 (2H). UV−vis (THF, nm {M−1 cm−1}): 350 {30 000},
542 {9000}. μeff = 2.82μB (Evans method, 298 K, THF-d8). Anal.
D
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1125 {14000}. Anal. Calcd for 5 (C54H63N5Ni2): C 72.10, H 7.06, N
7.79. Found: C 72.07, H 7.19, N 7.66.
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Catalytic Carbene Transfer Reaction with t-BuNC. To a 50 mL
Schlenk flask containing a stir bar were added complex 1 (9 mg,
0.0125 mmol, 10 mol %) and C6H6 (3 mL). The Schlenk flask was
placed in an oil bath heated at 80 °C. The catalyst solution was
stirred, and a mixture of Ph2CN2 (24 mg, 0.125 mmol) and t-BuNC
(14 μL, 0.125 mmol) dissolved in C6H6 (4 mL) was added dropwise
over a period of 12 h using a syringe pump. Following the addition,
the reaction mixture was stirred for an additional 3 h at 80 °C. The
solvent was removed under reduced pressure. Pentane (5 mL) was
added to the residue, and the mixture was filtered through a glass fiber
pad. The filtrate was concentrated to dryness under reduced pressure.
The crude product was redissolved in C6D6, and mesitylene was
added as a standard to determine the yield of t-BuNCCPh2.4
NMR Yield: 65%.
(6) Related studies of Ni2(μ-NR) species: (a) Powers, I. G.;
Kiattisewee, C.; Mullane, K. C.; Schelter, E. J.; Uyeda, C. Chem. - Eur.
J. 2017, 23, 7694−7697. (b) Powers, I. G.; Andjaba, J. M.; Luo, X.;
Mei, J.; Uyeda, C. J. Am. Chem. Soc. 2018, 140, 4110−4118.
(7) (a) Iikubo, T.; Itoh, T.; Hirai, K.; Takahashi, Y.; Kawano, M.;
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00261.
(9) Nocton, G.; Lukens, W. W.; Booth, C. H.; Rozenel, S. S.;
Medling, S. A.; Maron, L.; Andersen, R. A. J. Am. Chem. Soc. 2014,
136, 8626−8641.
Cartesian coordinates for calculated structures (XYZ)
Experimental details and characterization data (PDF)
Accession Codes
(10) (a) McMillan, J. A. J. Chem. Educ. 1961, 38, 438. (b) Symons,
M. C. R. Adv. Phys. Org. Chem. 1963, 1, 283−363.
CCDC 1839064−1839068 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
e-mailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.
(11) Zhou, Y.-Y.; Uyeda, C. Angew. Chem., Int. Ed. 2016, 55, 3171−
3175.
(12) Pauling, L. J. Am. Chem. Soc. 1947, 69, 542−553.
(13) Lukens, W. W.; Speldrich, M.; Yang, P.; Duignan, T. J.;
Autschbach, J.; Kogerler, P. Dalton Trans. 2016, 45, 11508−11521.
(14) Zhan, M.; Zhang, S.; Zhang, W.-X.; Xi, Z. Org. Lett. 2013, 15,
4182−4185.
(15) Gokel, G. W.; Cram, D. J.; Liotta, C. L.; Harris, H. P.; Cook, F.
L. J. Org. Chem. 1974, 39, 2445−2446.
AUTHOR INFORMATION
Corresponding Author
*E-mail: cuyeda@purdue.edu.
■
ORCID
Matthias Zeller: 0000-0002-3305-852X
Christopher Uyeda: 0000-0001-9396-915X
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Institutes of Health
(R35 GM124791). XRD data were collected using an
instrument funded by the NSF (CHE-1625543). C.U. is an
Alfred P. Sloan Foundation Research Fellow.
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DOI: 10.1021/acs.organomet.8b00261
Organometallics XXXX, XXX, XXX−XXX