Synthesis, Structure, and Reactivity of Low-Spin Cobalt(II) Imido Complexes [(Me3P)3Co(NAr)]

Article abstract of DOI:10.1021/acs.inorgchem.7b00941

The reactions of [Co(PMe₃)₄] with the bulky organic azides, DippN₃ and DmpN₃ [Dipp, 2,6-diisopropylphenyl; Dmp, 2,6-di(2′,4′,6′-trimethylphenyl)phenyl], afforded the cobalt(II) terminal imido complexes [(Me₃P)₃Co(NAr)] (Ar = Dipp, 1; Dmp, 2). The cobalt imido complexes in their solid states show trigonal pyramidal coordination geometry and long Co-N(imido) separations (ca. 1.71 ?). Spectroscopic characterization and theoretical studies indicated their low-spin cobalt(II) nature. Reactivity studies on 1 revealed its nitrene-transfer reactions with PMe₃ and CO, the imido/oxo and imido/sulfido exchange reactions with PhCHO and CS₂, and the single-electron oxidation reaction by ferrocenium cation to form cobalt(III) imide.

Full text of DOI:10.1021/acs.inorgchem.7b00941

Article
pubs.acs.org/IC
Synthesis, Structure, and Reactivity of Low-Spin Cobalt(II) Imido
Complexes [(Me3P)3Co(NAr)]
Yang Liu, Jingzhen Du, and Liang Deng*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of
Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R. China
S
* Supporting Information
ABSTRACT: The reactions of [Co(PMe3)4] with the bulky organic
azides, DippN3 and DmpN3 [Dipp, 2,6-diisopropylphenyl; Dmp, 2,6-
di(2′,4′,6′-trimethylphenyl)phenyl], afforded the cobalt(II) terminal
imido complexes [(Me3P)3Co(NAr)] (Ar = Dipp, 1; Dmp, 2). The
cobalt imido complexes in their solid states show trigonal pyramidal
coordination geometry and long Co−N(imido) separations (ca. 1.71
Å). Spectroscopic characterization and theoretical studies indicated
their low-spin cobalt(II) nature. Reactivity studies on 1 revealed its
nitrene-transfer reactions with PMe3 and CO, the imido/oxo and
imido/sulfido exchange reactions with PhCHO and CS2, and the
single-electron oxidation reaction by ferrocenium cation to form cobalt(III) imide.
imides were synthesized from the reactions of cobalt(I)
precursors with organic azides, except D that was obtained
from hydrogen-atom abstraction of a cobalt(II) amide
precursor by phenoxy radical.3g It is noteworthy that the
reactivity of the cobalt(III) imides remains poorly understood.
Nitrene transfer to CO3a,e or carbene ligand3c to form
isocyanates and guanidinate, respectively, was known for A,
B, and C. C−H bond activation of ligand was observed on B
and H, in which thermal-induced decomposition of B rendered
nitrene-insertion into a C−H bond of the But groups to form
cobalt(I) product3e and the decomposition of H led to benzylic
C−H activation of the mesityl group, producing a cobalt(III)
cycloindoline.3i Both B and H have thermally accessible open-
shell states (S = 1 and 2, respectively). The other cobalt(III)
imides are low-spin and diamagnetic.
INTRODUCTION
■
Cobalt imides attract great interest for their role as key
intermediates in cobalt-catalyzed nitrene-transfer reactions.1,2
As is typical of late transition-metal species featuring metal−
ligand multiple bonds, the high 3d-electron counting of cobalt
could render the occupation of electrons on Co (3d)−N (2p)
π* orbitals.1 Consequently, cobalt imido complexes of the
terminal type are reactive, and the reported isolable cobalt
imides have to rely on the use of bulky ancillary ligands and
bulky substituents on imido to achieve kinetic stabilization.
Chart 1 summarizes the reported isolable examples.3,4 Among
them, cobalt(III) imides supported by tripodal and bidentate
ligands are dominating (A−H in Chart 1).3 These cobalt(III)
Chart 1. Examples of Isolable Cobalt Imido Complexes
The syntheses of the first cobalt(II),4a,b cobalt(IV),4c and
cobalt(V)4c imido complexes (I−K in Chart 1) were achieved
recently by using monodentate N-heterocyclic carbene (NHC)
as ancillary ligand. The cobalt(II) and cobalt(IV) imides were
prepared from the reactions of three-coordinate NHC-
cobalt(0)-bis(olefin) precursors with 1 and 2 equiv of organic
azides, respectively, and the cobalt(V) complex was obtained
from one-electron oxidation of cobalt(IV) bis(imide). The
formal cobalt(IV) and cobalt(V) complexes have low-spin
ground states (S = 1/2 and 0, respectively). Interestingly, the
cobalt(IV) imide undergoes intramolecular C−H bond
amination at 50 °C, whereas the cobalt(V) species is stable
under similar conditions.4c The two-coordinate cobalt(II)
imido complex has an S = 3/2 ground state and displays
slow magnetic relaxation behavior.4a,b It shows nitrene-transfer
Received: April 18, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
reactivity toward CO and ethylene and can also perform [2π +
2σ]-addition with C(sp)−H and H−Si bonds.4a In addition to
these studies, we wish to report herein the synthesis,
characterization, and reactivity of low-spin cobalt(II) terminal
imido complexes in the form of [(Me3P)3Co(NAr)]. These
four-coordinate complexes are the first examples of low-spin
cobalt(II) imides. They exhibit nitrene-transfer and imido/
oxo(sulfido) exchange reactivity toward CO, PMe3, CS2,
PhCHO, etc., as shown below.
days. Complexes 1 and 2 have been characterized by 1H NMR,
solution magnetic susceptibility measurements, absorption
spectroscopy, elemental analyses, X-band EPR spectroscopy,
and single-crystal X-ray diffraction studies. The solid-state
structures of 1 and 2 (Figure 1 and Figure S1, respectively)
RESULTS AND DISCUSSION
■
Preparation and Characterization of the Cobalt(II)
Imido Complexes. Inspired by the success of using NHC-
cobalt(0)-bis(olefin) as cobalt precursors in the synthesis of
cobalt imides,4 we examined the reactions of the cobalt(0)
phosphine complex [(Me3P)4Co] with organic azides, which
also proved to be an effective cobalt(0) precursor to access
cobalt imides. The reaction of [(Me3P)4Co] with DippN3
(Dipp: 2,6-diisopropylphenyl, 2 equiv) in Et2O took place at
room temperature, leading to the quick formation of dark green
solution and effervescence of dinitrogen. Further workup on
the reaction mixture upon recrystallization gave the cobalt(II)
imido complex [(Me3P)3Co(NDipp)] (1) in 74% isolated yield
as a black crystalline solid and the iminophosphine Me3PNDipp
in 71% yield as a light yellow crystalline solid (Scheme 1). The
Figure 1. Molecular structure of [(Me3P)3Co(NDipp)] (1) with 30%
probability ellipsoids. Selected distances (Å) and angles (deg): Co1−
N1 1.7089(15), Co1−P1 2.2445(6), Co1−P2 2.1814(6), Co1−P3
2.1543(6), N1−C1 1.348(2), Co1−N1−C1 177.85(14), P1−Co1−
N1 108.87(6), P2−Co1−N1 124.63(5), P3−Co1−N1 119.16(5), P1−
Co1−P2 101.60(2), P1−Co1−P3 101.83(2), P2−Co1−P3 97.38(2).
Scheme 1. Synthesis of Low-Spin Cobalt(II) Imides
feature unique distorted trigonal pyramidal CoP3N cores with
the corresponding τ4 values6 of 0.82 and 0.80, being close to
the τ4 values of 0.85 for a standard trigonal pyramidal.6 The
displacements of the cobalt centers toward the basal planes
(P2−P3−N1) in 1 and 2 are 0.491 and 0.436 Å, respectively.
The Co−N−C alignment of the imido moiety in 1 is nearly
linear (177.9(1)°), and slightly bent in 2 (161.9(2)°). The Co−
N separations (1.709(2) Å and 1.717(2) Å for 1 and 2,
respectively) are longer than those of the cobalt(III) imides A−
E (1.609(3)−1.683(2) Å),3a−c,e−g,j consistent with their formal
cobalt(II) nature. Despite their distorted trigonal pyramidal
geometry in the solid state, the PMe3 ligands in 1 and 2 only
show one 1H NMR signal, implying the presence of a dynamic
process in the solution phase. The X-band EPR spectrum of 1
in toluene glass measured at 1.8 K is characterized by a nearly
isotropic g factor (gav = 2.03) with a complex superhyperfine
splitting pattern (Figure 2), probably caused by the 59Co (I =
7/2), 14N (I = 1), and 31P (I = 1/2) nuclei. The g value and
equimolar reaction of [(Me3P)4Co] with DippN3 gave a
mixture of [(Me3P)4Co], 1, and Me3PNDipp. In contrast, the
reaction of [(Me3P)4Co] with 1 equiv of DmpN3 [Dmp: 2,6-
di(2′,4′,6′-trimethylphenyl)phenyl] could furnish the imido
complex [(Me3P)3Co(NDmp)] (2) in high yield (81%)
without noticeable formation of Me3PNDmp (Scheme 1). As
control experiments showed that, while both DippN3 and
DmpN3 can react with Me3P at room temperature to produce
the corresponding iminophosphine (Figures S11 and S12),5 the
interaction of 1 with an excess amount of Me3P gives
Me3PNDipp (vide infra), whereas 2 is inert toward Me3P at
ambient conditions. We reason that the iminophosphine
Me3PNDipp formed in the equimolar reaction of
[(Me3P)4Co] with DippN3 should be formed via the
interaction of 1 with PMe3 with the five-coordinate species
(Me3P)4Co(NDipp) as a probable intermediate. In the case of
the reaction of [(Me3P)3Co(NDmp)] with Me3P, the steric
encumbrance of Dmp might make a similar five-coordinate
intermediate difficult to form.
Complexes 1 and 2 are air- and moisture-sensitive. In solid
states, they are stable at room temperature under a N2
atmosphere. In C6D6, the solution of 1 shows partial
decomposition in 1 week to give Me3PNDipp, [(Me3P)4Co],
and unidentified cobalt species, whereas no decomposition was
noticed when the solution of 2 stood at room temperature for
Figure 2. EPR spectrum of [(Me3P)3Co(NDipp)] (1) recorded in a
frozen toluene solution at 1.8 K. Instrumental parameters: ν = 9.387
GHz, modulation frequency = 100 kHz, modulation amplitude = 2 G,
microwave power = 0.0502 mW, conversion time = 40.00 ms, time
constant = 81.92 ms, sweep time = 240.0 s.
B
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
complex superhyperfine pattern are similar to those of Peters’
low-spin cobalt(II) complex [PhB(CH2PPh2)3CoI].7 The
measured solution magnetic moments of 1 and 2 (1.9(1) and
2.1(1) μB in C6D6 at room temperature)8 are also indicative of
their common S = 1/2 ground state.
Scheme 2. Reactions of 1 with PMe3, CO, and Olefin
In accordance with the low-spin ground state indicated by
the experimental data, spin-unrestricted DFT calculations at the
B3LYP level using TZVP/SVP basis sets5 based on the
structure of 1 suggested that the single-point energy of 1 at the
S = 1/2 state is lower in energy than that of the S = 3/2 state by
16.8 kcal/mol. Analyzing the composition of the frontier
m o l e c u l a r
o r b i t a l s
r e v e a l e d
a
2
2
2
2
2
1
0
(πxz)2(πxy)2(dx −y ) (dz ) (dyz) (π*xz) (π*xy) electronic config-
2
S2), and the structure was refined as a two-component
inversion twin giving a Flack parameter of 0.68(3). On the
other hand, 1 is inert toward the electron-richer olefins styrene
and 1-octene. The conversion of the cobalt(II) imido complex
to Me3PNDipp and the cobalt(0) species draws a parallel to
ligand-coordination-induced C−C bond-forming reductive
elimination reactions of organo-transition-metal compounds.9
Consequently, we propose that five-coordinate species
(Me3P)3(L)Co(NDipp) (L = PMe3, dimethyl fumarate)
might be the intermediates en route to the iminophosphine
and cobalt(0) species.
uration (Figure 3). The comparable Co 3d and N 2p
Complex 1 can readily undergo nitrene-transfer reaction with
CO at room temperature to give the carbodiimide DippNCN-
Dipp in high yield (86%, based on 1) (Scheme 2). This
reaction forms a sharp contrast to the slow reaction of Peters’
[PhB(CH2PPh2)3Co(N(tolyl))] with CO (70 °C, 14 days) that
produced isocyanate, rather than carbodiimide.3a The slow rate
of the latter reaction might be due to steric effect as the
cobalt(III) imido moiety is buried in the pocket of the tripodal
ligand. As late transition-metal imido complexes usually react
with CO to produce isocyanates,1,3a,e,4a,10 the formation of the
carbodiimide in the current system is unique. The reaction
might involve DippNCO, formed from the interaction of 1 with
CO (step 1 in Scheme 3), as an intermediate. Once formed, the
Figure 3. Qualitative frontier molecular orbital diagram of [(Me3P)3-
Co(NDipp)] (1) at its S = 1/2 state, based on its UHF natural
orbitals.
contributions in the in-plane π-interactions (πxy and π*xy)
indicate its high covalency. On the other hand, the relatively
high Co 3d orbital and imido orbital content in π*xz and πxz,
respectively, suggests the polarity of the out-of-plane π-
bonding. The difference between the two π-interactions should
be rooted in the delocalization of the out-of-plane N 2p lone
pair to the arene π*-orbital. In addition, the unique trigonal
pyramidal coordination geometry of the cobalt center might
also play a role. These Co 3d−N 2p π-interactions render the
Co−N multiple bond nature, which has the Mayer bond order
of 1.38, much larger than those of the Co−P bonds (0.67−
0.80).5
Scheme 3. Possible Routes for the Formation of
Carbodiimide from the Reaction of 1 with CO
Reactivity of the Cobalt(II) Imido Complexes. As
mentioned earlier, while plenty of isolable cobalt imido
complexes are known, their reactivity has remained poorly
understood. With the low-spin cobalt(II) imides in hand, we
then explored their reactivity.
The formation of Me3PNDipp in the preparation of 1 implies
the nitrene-transfer reactivity of the low-spin cobalt imido
complex toward Me3P. Indeed, the reactivity was confirmed by
an NMR-scale reaction of 1 with an excess amount of Me3P at
room temperature, which gave Me3PNDipp and the cobalt(0)
species [Co(PMe3)4] in high yields (Scheme 2). In addition to
PMe3, the interaction of the electron-deficient olefin dimethyl
fumarate with 1 could also trigger the formation of
Me3PNDipp, along with the cobalt(0) complex [(Me3P)3Co-
(η2-(E)-MeO2CCHCHCO2Me)] (3). Figure S10 shows the
1H NMR spectra. The molecular structure of 3 has been
established by a single-crystal X-ray diffraction study (Figure
isocyanate might then react with 1 equiv of 1 to form a urinate
intermediate (Me3P)3Co(κ2-N(Dipp)C(NDipp)O) (4) that
could further convert to DippNCNDipp via retro-[2π + 2π]-
addition (step 2a in Scheme 3).11 As the solution of 4, which
was synthesized from the reaction of 1 with DippNCO (vide
infra), does not show decomposition either by itself or under a
CO atmosphere, the proposed route (step 2a) seems less likely.
Alternatively, noting the capability of certain metal carbonyls in
catalyzing the conversion of isocyanates into carbodiimides and
CO2,12 we propose that the carbodiimide might be formed
C
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
from low-valent cobalt species-catalyzed disproportionation of
the isocyanate (step 2b in Scheme 3).
Examining the reactivity of 1 toward unsaturated polar
organic substrates revealed its imido/oxo and imido/sulfido
exchange reactions with benzaldehyde and CS2, respectively
(Scheme 4). Both reactions occurred readily at room
Mulliken atomic charges on the cobalt and nitrogen atoms of
1 are +0.19 and −0.66, respectively. In contrast, the interactions
of 2, which features the sterically encumbered aryl group Dmp,
with PhCHO and CS2 led to the formation of the
iminophosphine Me3PNDmp in 91% and 70% NMR yields
(Figure S13), respectively. While the exact causes for the
differentiated reactivity of 1 and 2 are unclear, we speculate that
the different steric nature of Dmp and Dipp in the two imido
complexes might play a role. The attempts to isolate the cobalt-
containing products in the reactions of 2 were unsuccessful.
The π*-character of the singly occupied orbital of 1 hints at
the possibility of accessing analogue cobalt(III) imido
complexes upon the oxidation of the cobalt(II) species.
Electrochemistry study on 1 by cyclic voltammetry disclosed
the reversible one-electron redox event of [(Me3P)3Co-
(NDipp)]0/1+ with E1/2 = −1.0 V (vs SCE) (Figure S4).
Scheme 4. Reactions of 1 with PhCHO, CS2, and DippNCO,
and Their Probable Intermediates
Using [Cp2Fe][BArF ] (ArF = 3,5-di(trifluoromethyl)phenyl)
4
as oxidant, the cobalt(II) imido complexes 1 and 2 were readily
oxidized into the cobalt(III) imido complexes [(Me3P)3Co-
(NAr)][BArF ] (Ar = Dipp, 5; Dmp, 6) in high yields (Scheme
4
5).5 Similar to the other four-coordinate low-spin cobalt(III)
Scheme 5. One-Electron Oxidation of 1 and 2
temperature, and gave the imine DippNCHPh and isothiocya-
nate DippNCS in 72% and 90% yields, respectively. The imine
and isothiocyanate might result from retro-cycloaddition
reaction of four-membered metallacycles (L and N in Scheme
4) formed from the [2π + 2π] cycloaddition of 1 with
benzaldehyde and CS2, along with cobalt(II) oxide and
cobalt(II) sulfide as byproducts.13 While the attempts to isolate
the cobalt intermediates were unsuccessful, a five-coordinate
cobalt(II) complex bearing an N,O-urinate chelate,
[(Me3P)3Co(κ2-N(Dipp)C(NDipp)O)] (4), was obtained
from the reaction of 1 with 1 equiv of DippNCO (Scheme
4).5 The structure of 4 has been established by X-ray
crystallography (Figure 4). The occurrence of the cycloaddition
reactions reflects the nucleophilicity of the imido ligand in the
cobalt(II) complex, which should associate with the small
electronegativity of 3d metals (Pauling electronegativity: 1.36
to 1.90 for Sc−Cu, versus 3.04 for N) that renders charge
polarization in their metal−nitrogen bonds. Indeed, the
imido complexes (A, C, and D in Chart 1),3a,c,g 5 and 6 are
diamagnetic, and show well-resolved NMR spectra (1H, 13C,
and 31P NMR). A single-crystal X-ray diffraction study (Figure
5) indicated a distorted trigonal pyramidal geometry of the
Figure 5. Structure of the cation in [(Me3P)3Co(NDmp)][BArF ] (6)
4
with 30% probability ellipsoids. Selected distances (Å) and angles
(deg): Co1−N1 1.6540(17), N1−C1 1.373(3), Co1−P1 2.1871(6),
Co1−P2 2.1738(6), Co1−P3 2.1829(7), Co1−N1−C1 166.99(15),
P1−Co1−N1 121.93(6), P2−Co1−N1 105.61(6), P3−Co1−N1
123.47(6), P1−Co1−P2 104.30(3), P1−Co1−P3 98.33(2), P2−
Co1−P3 99.91(3).
cation [(Me3P)3Co(NAr)]+ (τ4 = 0.81)6 that was similar to
those of 1, 2, the ruthenium imido complex [(Me3P)3Ru-
(NDipp)],14 as well as the cobalt(III) imido complexes A and
C.3a,c The shorter Co−N distance (1.654(2) Å) in 6 as
compared with that in 2 (1.717(2) Å) is in accord with the
expectation that the loss of one electron from the antibonding
orbital enhances the multiple bond character of the Co−N
interaction.
Figure 4. Molecular structure of [(Me3P)3Co(κ2-(Dipp)C(NDipp)-
O)] (4) with 30% probability ellipsoids. Selected distances (Å) and
angles (deg): Co1−N1 1.9212(17), Co1−O1 1.9437(14), Co1−C1
2.391(2), Co1−P1 2.2711(7), Co1−P2 2.2501(7), Co1−P3
2.1683(7), N1−C2 1.414(3), N1−C1 1.362(2), C1−O1 1.328(2),
N2−C1 1.290(3), N2−C14 1.410(3), Co1−N1−C1 91.88(12), Co1−
O1−C1 91.96(11), N1−C1−O1 107.67(17), C1−N2−C14
119.54(17).
D
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Paratone-N oil and mounted on a Bruker APEX CCD based
diffractometer equipped with an Oxford low-temperature apparatus.
Cell parameters were retrieved with SMART software and refined
using SAINT software on all reflections. Data integration was
performed with SAINT, which corrects for Lorentz polarization and
decay. Absorption corrections were applied using SADABS.19 Space
groups were assigned unambiguously by analysis of symmetry and
systematic absences determined by XPREP. All structures were solved
and refined using SHELXTL.20 The metal and first coordination
sphere atoms were located from direct-methods E maps. Non-
hydrogen atoms were found in alternating difference Fourier synthesis
and least-squares refinement cycles and during the final cycles were
refined anisotropically. Final crystal parameters and agreement factors
are reported in Table S1.
CONCLUSIONS
■
The synthesis, structure, and reactivity studies of the first low-
spin cobalt(II) terminal imido complexes were achieved. The
reaction of the cobalt(0) precursor [(Me3P)4Co] with bulk
organic azides serves as a facile entry to the four-coordinate
cobalt(II) imido complexes [(Me3P)3Co(NAr)] (Ar = Dipp,
Dmp). X-ray diffraction studies disclosed a distorted trigonal
pyramidal geometry for the CoP3N core in the imido
complexes. Spectroscopic characterization, in combination
with DFT studies, indicates their low-spin nature. The
cobalt(II) imido complexes could perform nitrene-transfer
reaction with PMe3 and CO, producing Me3PNDipp and
DippNCNDipp, respectively. They could also undergo imido/
oxo and imido/sulfido exchange reactions with PhCHO and
CS2 to give PhCHNDipp and DippNCS, respectively. In
addition, the reversible one-electron redox conversion of
[(Me3P)3Co(NAr)]0/1+ has also been observed on the cobalt
imides. The diversified reactivity of the cobalt(II) imides shows
resemblance to nickel(II) imido complexes,10c,d,15 which might
be typical for late 3d transition-metal imido complexes with
high d-electron counting.
Computational Details. Density functional theory21 studies have
been performed with the ORCA 2.8 program22 using the B3LYP23
method. The SVP basis set24 was used for the N, C, and H atoms, and
the TZVP basis set25 was used for the Co and imido N atoms. The
RIJCOSX approximation26 with matching auxiliary basis sets24,27 was
employed to accelerate the calculations. The structure of 1 obtained
from X-ray diffration study was used, and only positions of the
hydrogen atoms are optimized. TIGHTSCF was used for SCF
calculations.28 The Mulliken spin population and Mayer bond orders
of selected bonds of [(Me3P)3Co(NDipp)] at its doublet state are
shown in Figures S7 and S8, respectively. Coordinates of the calculated
structure are included in the Supporting Information.
EXPERIMENTAL SECTION
■
Preparation of [(Me3P)3Co(NDipp)] (1). To a Et2O (8 mL) solution
of [Co(PMe3)4] (660 mg, 1.82 mmol) was added a Et2O (4 mL)
solution of DippN3 (739 mg, 3.64 mmol) slowly. The color of the
solution changed to dark green immediately, and bubbles were
released vigorously. The reaction mixture was stirred for 0.5 h at room
temperature and then subjected to vacuum to remove all the volatiles.
The resulting black solid was washed with n-pentane (2 mL × 3) and
dried under vacuum to leave 1 as a brown crystalline solid (620 mg,
74%). Single crystals of 1 suitable for X-ray diffraction studies were
General Considerations. All manipulations on air- and moisture-
sensitive materials were performed under an atmosphere of dry
dinitrogen with the rigid exclusion of air and moisture using standard
Schlenk or cannula techniques, or in a glovebox. Solvents were dried
with a solvent purification system (Innovative Technology) and
degassed prior to use. [(Me3P)4Co],16 DippN3,17a DmpN3,17b and
[Cp2Fe][BArF ]18 were synthesized according to literature procedures.
4
All other chemicals were purchased from chemical vendors and used as
received unless otherwise noted. H, 13C, 31P, and 19F NMR spectra
1
1
grown by evaporation of its Et2O solution at room temperature. H
were recorded with VARIAN 400 MHz or Agilent 400 MHz
spectrometer at 400, 100, 162, and 376 MHz, respectively. All
chemical shifts were reported in units of ppm with reference to the
residual protons of the deuterated solvents for proton chemical shifts,
the 13C of deuterated solvents for carbon chemical shifts, the 19F of
CFCl3 (external standard) for fluorine chemical shifts, and the 31P of
85% phosphorous acid (external standard) for phosphine chemical
shifts. HRMS-ESI spectra were recorded with an Agilent Technologies
6224 TOF LC−MS instrument. GC−MS analyses were performed on
an Agilent Technologies spectrometer. Elemental analysis was
performed by the Analytical Laboratory of Shanghai Institute of
Organic Chemistry (CAS). Solution magnetic moments were
measured at 21 °C by the method originally described by Evans
with stock and experimental solutions containing a known amount of a
(CH3)3SiOSi(CH3)3 standard.8 Absorption spectra were recorded with
a Shimadzu UV-3600 UV−vis−NIR spectrophotometer. IR spectra
were recorded with Nicolet Avatar 330 FT-IR spectrophotometer or
Bruker TENSOR 27 ART-FT-IR spectrophotometer. The X-band
CW-EPR experiments were performed on a Bruker EMX plus
spectrometer (microwave (mw) frequency 8.75−9.65 GHz) equipped
with a He temperature control cryostat system (for complex 1) or a
JEOL spectrometer JES-FA2000 with a liquid nitrogen cryostat system
(for 2 and 4).
Caution! Organic azides are presumed to be potentially explosive.
Manipulations should be handled carefully in a hood with protective
equipment.
Electrochemistry. Electrochemical measurements were carried out
in a glovebox under an argon atmosphere with a CHI 600D
potentiostation. A glassy carbon was used as working electrode; a
platinum wire was used as the auxiliary electrode, and an SCE was used
as reference electrode. 0.1 M [(n-Bu)4N][PF6] in THF was used as
supporting electrolyte and was prepared in the glovebox. Under these
conditions, E1/2 = 0.55 V for the [Cp2Fe]0,+ couple.
NMR (400 MHz, C6D6, 294 K): δ (ppm) 53.34 (s, Δν1/2 = 1520 Hz),
40.31 (s, Δν1/2 = 1200 Hz), 22.92 (s, Δν1/2 = 580 Hz), 4.41 (s, Δν1/2
= 130 Hz). Anal. Calcd for C21H44CoNP3: C 54.54, H 9.59, N 3.03.
Found: C 54.44, H 9.65, N 3.16. Magnetic susceptibility (C6D6, 294
K): μeff = 1.9(1) μB. Absorption spectrum (in THF): λmax, nm (ε, M−1
cm−1) 300 (12 000), 320 (15 600), 380 (4900), 530 (750), 710
(1250), 960 (440). IR (KBr, cm−1): ν = 2958 (m), 2896 (m), 2864
(w), 1576 (m), 1458 (m), 1433 (m), 1418 (m), 1400 (m), 1363 (m),
1300 (s), 1283 (s), 1258 (m), 1164 (s), 1132 (m), 946 (s), 871 (m),
862 (m), 741 (m), 714 (m), 656 (w). After the black solid of 1 was
separated, the mother liquor of the n-pentane solution was collected.
Slow evaporation of the n-pentane solution at room temperature
afforded light yellow crystals that were collected and washed with
drops of n-hexane, giving the iminophosphine Me3PNDipp as light
1
yellow crystals (324 mg, 71%). H NMR (400 MHz, C6D6, 294 K): δ
(ppm) 7.27−7.20 (m, 2H), 7.07 (td, J = 7.6, 2.5 Hz, 1H), 3.59 (septet,
J = 6.9 Hz, 2H), 1.34 (d, J = 6.9 Hz, 12H), 0.93 (d, JP−H = 12.0 Hz,
9H). 13C NMR (100 MHz, C6D6, 294 K): δ (ppm) 145.8 (d, JP−C
=
2.9 Hz), 142.4 (d, JP−C = 7.3 Hz), 122.9 (d, JP−C = 3.2 Hz), 119.6 (d,
JP−C = 4.0 Hz), 28.7, 24.2, 17.7 (d, JP−C = 69 Hz). 31P NMR (162
MHz, C6D6, 294 K): δ (ppm) −8.23. HRMS (ESI) calcd for
C15H27NP [M + H]+: 252.1881. Found [M + H]+: 252.1875. IR
(powder, cm−1): ν = 3057 (w), 2956 (s), 2872 (w), 1441 (s), 1358
(s), 1292 (m), 1069 (w), 933 (s), 849 (w), 768 (w), 732 (w).
Preparation of [(Me3P)3Co(NDmp)] (2). To a Et2O (5 mL) solution
of [Co(PMe3)4] (182 mg, 0.50 mmol) was slowly added DmpN3 (180
mg, 0.50 mmol). The color of the solution changed to brown
immediately, and bubbles were released vigorously. The reaction
mixture was stirred for 2 h at room temperature and then subjected to
vacuum to remove all the volatiles. The resulting black solid was
washed with n-pentane (2 mL × 3) and dried under vacuum to leave 2
as a brown solid (250 mg, 81%). Single crystals of 2 suitable for X-ray
diffraction studies were grown by evaporation of its Et2O solution at
room temperature. 1H NMR (400 MHz, C6D6, 294 K): δ (ppm) 24.88
X-ray Structure Determination. The structures of five
compounds in Table S1 were determined. Crystals were coated with
E
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(s, Δν1/2 = 1940 Hz), 14.82 (s, Δν1/2 = 260 Hz), 6.33 (s, Δν1/2 = 120
Hz), 5.72 (s, Δν1/2 = 190 Hz). Anal. Calcd for C33H52CoNP3: C 64.49,
H 8.53, N 2.28. Found: C 64.43, H 8.42, N 2.23. Magnetic
susceptibility (C6D6, 294 K): μeff = 2.1(1) μB. Absorption spectrum (in
THF): λmax, nm (ε, M−1 cm−1) 300 (13 500), 330 (17 300), 380
(6400), 440 (2700), 540 (1240), 710 (1000), 990 (330). IR (KBr,
cm−1): ν = 2956 (s), 2912 (s), 2854 (m), 1609 (w), 1569 (w), 1451
(s), 1339 (m), 1297 (m), 1167 (s), 1104 (m), 937 (s), 851 (s), 751
(m).
Reaction of 1 with Me3P. To a C6D6 (0.4 mL) solution of
[(Me3P)3Co(NDipp)] (1, 14 mg, 0.03 mmol) in a J. Young NMR
tube was added excess Me3P (23 mg, 0.30 mmol), and 1,3,5-
trimethoxybenzene (5.5 mg, 0.033 mmol, as internal standard). The
reaction mixture was standing at room temperature and monitored by
1H NMR spectroscopy; during the course of the reaction, the color of
the solution changed to brown gradually. After 2 h, 1H NMR spectrum
analysis indicated the clean formation of [(Me3P)4Co] and the
formation of the iminophosphine Me3PNDipp in 80% NMR yield
(Figure S9). For [(Me3P)4Co], 1H NMR (400 MHz, C6D6, 294 K): δ
(ppm) 33.72 (s, Δν1/2 = 170 Hz). The 1H NMR spectrum is identical
to that reported in the literature.16
based on cobalt). 1H NMR (400 MHz, C6D6, 294 K): δ (ppm) 35.84
(s, Δν1/2 = 2390 Hz), −1.15 (s, Δν1/2 = 130 Hz). Anal. Calcd for
C15H35CoO4P3: C 41.77, H 8.18. Found: C 41.79, H 8.36. Magnetic
susceptibility (C6D6, 294 K): μeff = 2.1(1) μB. Absorption spectrum (in
THF): λmax, nm (ε, M−1 cm−1) 300 (14 300), 400 (1830), 920 (80),
1160 (100). IR (KBr, cm−1): ν = 2963 (m), 2981 (m), 2908 (m), 2807
(w), 1723 (s), 1671 (s), 1659 (s), 1591 (s), 1440 (s), 1302 (s), 1283
(s), 1253 (m), 1233 (m), 1170 (s), 1043 (m), 1013 (w), 991 (m), 946
(s), 871 (m), 862 (m), 745 (m), 673 (w), 660 (w).
Reaction of 1 with CO. The toluene (5 mL) solution of
[(Me3P)3Co(NDipp)] (1, 93 mg, 0.20 mmol) in a 25 mL flask was
quickly frozen with liquid N2 and subjected to vacuum to remove the
N2 atmosphere in the flask. Then CO was introduced to the mixture
via a CO balloon (1 atm). The reaction mixture was allowed to warm
to room temperature. The color of the solution changed from green to
orange immediately. After 10 min, the volatiles were removed under
vacuum to yield brown solid that was then extracted with n-pentane (3
mL × 2) and filtered. Then the filtrate was exposed to air and wet n-
hexane (2 mL) was added to quench the cobalt species. After flash
column chromatography separation (silica gel, n-hexane as elute),
1
DippNCNDipp was obtained as a light yellow oil (47 mg, 86%). H
NMR (400 MHz, C6D6, 294 K): δ (ppm) 7.05 (s, 6H), 3.66 (septet, J
Reaction of DippN3 with Me3P. To a C6D6 (0.4 mL) solution of
DippN3 (10 mg, 0.05 mmol) in a J. Young NMR tube was added Me3P
(5.8 mg, 0.08 mmol) at room temperature. The color of the solution
remained light yellow, and bubbles were released slowly. After 20 min
1
= 6.9 Hz, 4H), 1.24 (d, J = 6.9 Hz, 24H). The H NMR spectrum is
identical to that reported in the literature.11c
Reaction of 1 with PhCHO. To a toluene (2 mL) solution of
[(Me3P)3Co(NDipp)] (1, 92 mg, 0.20 mmol) was added PhCHO (24
mg, 0.23 mmol). The reaction mixture was stirred for 2 h at room
temperature; during the course of the reaction the color of the solution
changed to brown gradually. Then the solution was exposed to air and
wet n-hexane (2 mL) was added to quench the cobalt species. After
column chromatography separation (silica gel, 20:1 n-hexane/
CH2Cl2), DippNCHPh was obtained as a yellow oil (38 mg, 72%).
1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 8.24 (s, 1H), 8.01−
7.89 (m, 2H), 7.62−7.49 (m, 3H), 7.24−7.11 (m, 3H), 3.02 (septet, J
= 6.9 Hz, 2H), 1.21 (d, J = 6.9 Hz, 12H). GC−MS: m/z = 265.1
1
at room temperature, H NMR spectrum analysis indicated the clean
formation of iminophosphine Me3PNDipp (Figure S11). Scaled-up
reaction in toluene (8 mL) by using DippN3 (407 mg, 2.0 mmol) and
Me3P (228 mg, 3.0 mmol) at room temperature for 0.5 h gave the
iminophosphine Me3PNDipp (483 mg, 96% yield) as a light yellow
solid.
Reaction of DmpN3 with Me3P. To a C6D6 (0.4 mL) solution of
DmpN3 (18 mg, 0.05 mmol) in a J. Young NMR tube was added
Me3P (5.8 mg, 0.08 mmol) at room temperature. The color of the
solution remained light yellow, and bubbles were released slowly. After
20 min at room temperature, 1H NMR spectrum analysis indicated the
clean formation of iminophosphine Me3PNDmp (Figure S12). Scaled-
up reaction in toluene (5 mL) solution by using DmpN3 (142 mg, 0.4
mmol) and Me3P (46 mg, 0.6 mmol) at room temperature for 0.5 h
gave the iminophosphine Me3PNDmp as a light yellow solid (152 mg,
1
([M]+). The H NMR spectrum is identical to that reported in the
literature.29
Reaction of 1 with CS2. To a Et2O (2 mL) solution of CS2 (23 mg,
0.30 mmol) was slowly added a Et2O (2 mL) solution of
[(Me3P)3Co(NDipp)] (1, 46 mg, 0.10 mmol). The reaction mixture
was stirred for 30 min at room temperature; during the course of the
reaction the color of the solution changed to brown gradually. The
volatiles were removed under vacuum to yield a brown solid that was
then extracted with n-hexane (3 mL × 2) and filtered through Celite.
The filtrate was exposed to air and wet n-hexane (2 mL) was added to
quench the cobalt species, and then the reaction mixture was filtered
through Celite again. Removal of the volatiles under vacuum afforded
1
94%). H NMR (400 MHz, C6D6, 294 K): δ (ppm) 7.14 (m, 2H),
6.98 (td, J = 7.2, 2.4 Hz, 1H), 6.92 (s, 4H), 2.32 (s, 12H), 2.26 (s, 6H),
0.40 (d, JP−H = 12.5 Hz, 9H). 13C NMR (100 MHz, C6D6, 294 K): δ
(ppm) 146.8, 140.8, 137.1, 136.6 (d, JP−C = 6.9 Hz), 135.2, 129.2,
128.1, 118.6 (d, JP−C = 3.0 Hz), 21.3, 21.1, 17.5 (d, JP−C = 69 Hz). 31
P
NMR (162 MHz, C6D6, 294 K): δ (ppm) −9.34. HRMS (ESI) calcd
for C27H36NP [M + H]+: 404.2507. Found [M + H]+: 404.2503. IR
(powder, cm−1): ν = 2986 (w), 2945 (w), 2912 (w), 2852 (w), 1429
(s), 1335 (m), 1283 (w), 1100 (m), 933 (s), 847 (m), 762 (m), 731
(w).
1
DippNCS as a light yellow solid (20 mg, 90%). H NMR (400 MHz,
CDCl3, 294 K): δ (ppm) 7.24 (t, J = 7.9 Hz 1H), 7.14 (d, J = 7.6 Hz,
2H), 3.26 (septet, J = 6.9 Hz, 2H), 1.28 (d, J = 6.9 Hz, 12H). GC−
1
Reaction of 1 with (E)-MeO2CCHCHCO2Me. To a C6D6 (0.4
mL) solution of [(Me3P)Co(NDipp)] (1, 14 mg, 0.03 mmol) in a J.
Young NMR tube was added (E)-MeO2CCHCHCO2Me (4.3 mg,
0.03 mmol). The reaction mixture was monitored by 1H NMR
spectroscopy at room temperature; during the course of the reaction
the color of the solution changed to brown gradually. After 1 h, 1 was
consumed completely, and then 1,3,5-trimethoxybenzene (4.7 mg,
MS: m/z = 219.1 ([M]+). The H NMR spectrum is identical to that
reported in the literature.30
Reaction of 1 with DippNCO. To a toluene (8 mL) solution of
[(Me3P)3Co(NDipp)] (1, 159 mg, 0.34 mmol) was added DippNCO
(77 mg, 0.38 mmol). The reaction mixture was stirred for 3 h at room
temperature; during the course of the reaction the color of the solution
changed to brown gradually. The volatiles were removed under
vacuum to yield a brown solid that was washed with n-hexane (3 mL ×
3) first, then extracted with THF (3 mL), and filtered. Slow
evaporation of the THF solution at room temperature gave
[(Me3P)3Co(κ2-N(Dipp)C(NDipp)O)] (4) as brown crystals (114
1
0.028 mmol) was added as the internal standard. H NMR spectrum
analysis indicated the formation of the iminophosphine Me3PNDipp
(88% NMR yield) and [(Me3P)3Co(η2-(E)-MeCO2CH
CHCO2Me)] (3).
Isolation of [(Me3P)3Co(η2-(E)-MeCO2CHCHCO2Me)] (3). To a
toluene (8 mL) solution of [(Me3P)3Co(NDipp)] (1, 139 mg, 0.30
mmol) was added (E)-MeO2CCHCHCO2Me (43 mg, 0.30 mmol).
The reaction mixture was stirred for 1 h at room temperature; during
the course of the reaction the color of the solution changed to brown
gradually. Then the volatiles were removed under vacuum to yield a
brown solid that was then washed with n-hexane (3 mL × 3) first, then
extracted with toluene (3 mL), and filtered. Standing the toluene
solution at −30 °C overnight gave 3 as brown crystals (52 mg, 40%,
mg, 50%). H NMR (400 MHz, C6D6, 294 K): δ (ppm) 14.74 (s,
1
Δν1/2 = 430 Hz), 13.64 (s, Δν1/2 = 400 Hz), 8.06 (s, Δν1/2 = 40 Hz),
5.95 (s, Δν1/2 = 35 Hz), 4.16 (s, Δν1/2 = 380 Hz), 1.87 (s, Δν1/2 = 60
Hz), 1.00 (s, Δν1/2 = 150 Hz). Anal. Calcd for C34H61CoN2OP3: C
61.34, H 9.24, N 4.21. Found: C 61.34, H 8.92, N 3.73. Magnetic
susceptibility (C6D6, 294 K): μeff = 2.0(1) μB. Absorption spectrum (in
THF): λmax, nm (ε, M−1 cm−1) 280 (10 000), 450 (2050), 650 (120),
840 (350), 1100 (130). IR (KBr, cm−1): ν = 2961 (m), 2900 (m),
2866 (m), 1683 (m), 1594 (w), 1549 (s), 1466 (w), 1433 (m), 1337
F
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(w), 1307 (w), 1294 (m), 1246 (w), 1152 (m), 940 (s), 907 (w), 776
(w), 749 (w).
Accession Codes
CCDC 1555942−1555946 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Reactions of [(Me3P)Co(NDmp)] (2) with PhCHO and CS2. To
C6D6 (0.4 mL) solutions of [(Me3P)3Co(NDmp)] (2) (12.3 mg, 0.02
mmol) in J. Young NMR tube were added equimolar amounts of
PhCHO and CS2, respectively. Then, 1,3,5-trimethoxybenzene was
1
added as internal standard, and the reactions were monitored by H
NMR spectroscopy at room temperature until there was complete
consumption of 2. 1H NMR spectrum analyses (Figure S13) show the
clean formation of the iminophosphine Me3PNDmp in 91% and 70%
NMR yields, respectively.
AUTHOR INFORMATION
Corresponding Author
*E-mail: deng@sioc.ac.cn.
■
Preparation of [(Me3P)3Co(NDipp)][BArF ] (5). To a Et2O (8 mL)
4
solution of [(Me3P)3Co(NDipp)] (1, 153 mg, 0.33 mmol) was slowly
added [Cp2Fe][BArF ] (346 mg, 0.33 mmol). The color of the
ORCID
4
solution changed to brownish red immediately. The reaction mixture
was stirred for 3 h at room temperature and then subjected to vacuum
to remove all the volatiles. The resulting red solid was washed with n-
hexane (3 mL × 3) first, then extracted with Et2O (5 mL), and filtered.
The dark red crystalline solid of 5 (350 mg, 87%) was obtained by
slow diffusion of n-hexane (10 mL) to its Et2O solution at −30 °C. 1H
NMR (400 MHz, d8-THF, 294 K): δ (ppm) 7.80 (br, 8H), 7.71 (t, J =
7.7 Hz, 1H), 7.58 (br, 4H), 6.79 (d, J = 7.8 Hz, 2H), 3.40 (septet, J =
6.9 Hz, 2H), 1.74 (d, JP−H = 8.9 Hz, 27H), 1.16 (d, J = 6.9 Hz, 12H).
13C NMR (100 MHz, d8-THF, 294 K): δ (ppm) 162.6 (q, J = 49.6 Hz,
C-B), 141.0 (d, J = 5.1 Hz), 135.4, 129.8 (q, J = 31.9 Hz, C-CF3),
127.6, 125.7, 125.3 (q, J = 270.8 Hz, CF3), 118.01, 29.1, 22.6, 20.0 (d, J
= 27.0 Hz). 19F NMR (376 MHz, d8-THF, 294 K): δ (ppm) −61.47
(s). 31P NMR (162 MHz, d8-THF, 294 K): δ (ppm) 12.04 (br). Anal.
Calcd for C53H56BCoF24NP3: C 48.02, H 4.26, N 1.06. Found: C
47.58, H 4.31, N 0.86. Absorption spectrum (in THF): λmax, nm (ε,
M−1 cm−1) 310 (10 500), 420 (3000), 550 (1800), 660 (470), 950
(72). IR (KBr, cm−1): ν = 2971 (w), 1611 (w), 1464 (w), 1427 (w),
1355 (s), 1278 (s), 1166 (s), 1128 (s), 940 (m), 888 (m), 839 (m),
716 (m), 682 (m), 669 (m).
Yang Liu: 0000-0002-2486-8520
Jingzhen Du: 0000-0003-4037-9281
Liang Deng: 0000-0002-0964-9426
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work was supported by the National Key Research and
Development Program (2016YFA0202900), the National
Natural Science Foundation of China (21690062, 21421091,
and 21432001), and the Strategic Priority Research Program of
the Chinese Academy of Sciences (XDB20000000). The EPR
study was performed at the Steady High Magnetic Field
Facilities, High Magnetic Field Laboratory, CAS.
REFERENCES
■
(1) (a) Berry, J. F. Terminal nitrido and imido complexes of the late
transition metals. Comments Inorg. Chem. 2009, 30, 28−66.
(b) Saouma, C. T.; Peters, J. C. ME and M = E complexes of
iron and cobalt that emphasize three-fold symmetry (EO, N, NR).
Coord. Chem. Rev. 2011, 255, 920−937. (c) Ray, K.; Heims, F.; Pfaff, F.
F. Terminal oxo and imido transition-metal complexes of groups 9−
11. Eur. J. Inorg. Chem. 2013, 2013, 3784−3807. (d) Shin, K.; Kim, H.;
Chang, S. Transition-metal-catalyzed C−N bond forming reactions
using organic azides as the nitrogen source: a Journey for the mild and
versatile C−H amination. Acc. Chem. Res. 2015, 48, 1040−1052.
(e) Cundari, T. R. Computational studies of transition metal-main
group multiple bonding. Chem. Rev. 2000, 100, 807−818.
Preparation of [(Me3P)3Co(NDmp)][BArF ] (6). To a Et2O (8 mL)
4
solution of [(Me3P)3Co(NDmp)] (2, 123 mg, 0.20 mmol) was slowly
added [Cp2Fe][BArF ] (210 mg, 0.20 mmol). The color of the
4
solution changed to brownish red immediately. The reaction mixture
was stirred for 3 h at room temperature and then subjected to vacuum
to remove all the volatiles. The resulting red solid was washed with n-
hexane (3 mL × 3) first, then extracted with Et2O (5 mL), and filtered.
Dark red crystals of 6 (183 mg, 62%) were obtained by slow
1
evaporation of its Et2O solution at room temperature. H NMR (400
MHz, d8-THF, 294 K): δ (ppm) 7.79 (br, 8H), 7.58 (br, 4H), 6.96 (s,
4H), 6.59 (d, J = 7.6 Hz, 2H), 2.32 (s, 6H), 2.03 (s, 12H), 1.30 (d, J =
10.1 Hz, 27H). 13C NMR (100 MHz, d8-THF, 294 K): δ (ppm) 162.6
(q, J = 48.8 Hz, C-B), 139.6, 138.0, 135.4 (two peaks included), 133.5
(d, J = 6.3 Hz), 133.2, 129.9 (q, J = 28.4 Hz, C-CF3), 129.6, 127.0,
125.3 (q, J = 270.9 Hz, CF3), 118.0, 21.2, 20.9, 20.3 (d, J = 27.5 Hz)
(one peak was not observed due to overlapping). 19F NMR (376 MHz,
d8-THF, 294 K): δ (ppm) −63.39 (s). 31P NMR (162 MHz, d8-THF,
294 K): δ (ppm) 16.09 (br). Anal. Calcd for C63H58BCoF24NP3: C
52.83, H 4.37, N 0.95. Found: C 52.87, H 4.27, N 0.71. Absorption
spectrum (in THF): λmax, nm (ε, M−1 cm−1) 310 (18 800), 420
(7100), 550 (4100), 680 (790). IR (KBr, cm−1): ν = 2976 (w), 1611
(w), 1425 (w), 1355 (s), 1285 (s), 1170 (s), 1126 (s), 961 (m),
940(w), 888(m), 839 (w), 715(w), 682 (m), 669 (m).
(2) (a) Lyaskovskyy, V.; Suarez, A. I. O.; Lu, H.; Jiang, H.; Zhang, X.
P.; de Bruin, B. Mechanism of cobalt(II) porphyrin-catalyzed C-H
amination with organic azides: radical nature and H-atom abstraction
ability of the key cobalt(III)nitrene intermediates. J. Am. Chem. Soc.
2011, 133, 12264−12273. (b) Jin, L.-M.; Xu, X.; Lu, H.; Cui, X.;
Wojtas, L.; Zhang, X. P. Effective synthesis of chiral N-fluoroaryl
aziridines through enantioselective aziridination of alkenes with
fluoroaryl azides. Angew. Chem., Int. Ed. 2013, 52, 5309−5313.
(c) Goswami, M.; Lyaskovskyy, V.; Domingos, S. R.; Buma, W. J.;
́ ́
Woutersen, S.; Troeppner, O.; Ivanovic-Burmazovic, I.; Lu, H.; Cui,
X.; Zhang, X. P.; Reijerse, E. J.; DeBeer, S.; van Schooneveld, M. M.;
Pfaff, F. F.; Ray, K.; de Bruin, B. Characterization of porphyrin-
Co(III)-‘nitrene radical’ species relevant in catalytic nitrene transfer
reactions. J. Am. Chem. Soc. 2015, 137, 5468−5479. (d) Cundari, T. R.
Transition metal imido complexes. J. Am. Chem. Soc. 1992, 114, 7879−
7888. (e) Wasbotten, I. H.; Ghosh, A. Spin-state energetics and spin-
crossover behavior of pseudotetrahedral cobalt(III)-imido complexes.
The role of the tripodal supporting ligand. Inorg. Chem. 2007, 46,
7890−7898. (f) Conradie, J.; Ghosh, A. Electronic structure of
trigonal-planar transition-metal-imido complexes: spin-state energetics,
spin-density profiles, and the remarkable performance of the OLYP
functional. J. Chem. Theory Comput. 2007, 3, 689−702. (g) Hu, L.;
Chen, H. What factors control the reactivity of cobalt−imido
complexes in C−H bond activation via hydrogen abstraction? ACS
Catal. 2017, 7, 285−292.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00941.
Table of crystal data, molecular structures, absorption
spectra, NMR spectra, EPR spectra, cyclic voltammo-
gram, Mulliken spin populations and bond orders of the
calculated structure, and Cartesian coordinates of the
optimized structure (PDF)
G
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(3) (a) Jenkins, D. M.; Betley, T. A.; Peters, J. C. Oxidative group
transfer to Co(I) affords a terminal Co(III) imido complex. J. Am.
Chem. Soc. 2002, 124, 11238−11239. (b) Betley, T. A.; Peters, J. C.
Dinitrogen chemistry from trigonally coordinated iron and cobalt
platforms. J. Am. Chem. Soc. 2003, 125, 10782−10783. (c) Hu, X.;
Meyer, K. Terminal cobalt(III) imido complexes supported by
tris(carbene) ligands: imido insertion into the cobalt-carbene bond.
J. Am. Chem. Soc. 2004, 126, 16322−16323. (d) Dai, X.; Kapoor, P.;
Warren, T. H. [Me2NN]Co(η6-toluene): OO, NN, and ON
bond cleavage provides β-diketiminato cobalt μ-oxo and imido
complexes. J. Am. Chem. Soc. 2004, 126, 4798−4799. (e) Shay, D.
T.; Yap, G. P. A.; Zakharov, L. N.; Rheingold, A. L.; Theopold, K. H.
Angew. Chem., Int. Ed. 2005, 44, 1508−1510. (f) Mehn, M. P.; Brown,
S. D.; Jenkins, D. M.; Peters, J. C.; Que, L., Jr. Vibrational spectroscopy
and analysis of pseudo-tetrahedral complexes with metal imido bonds.
Inorg. Chem. 2006, 45, 7417−7427. (g) Cowley, R. E.; Bontchev, R. P.;
Sorrell, J.; Sarracino, O.; Feng, Y.; Wang, H.; Smith, J. M. Formation of
a cobalt(III) imido from a cobalt(II) amido complex. Evidence for
proton-coupled electron transfer. J. Am. Chem. Soc. 2007, 129, 2424−
2425. (h) Jones, C.; Schulten, C.; Rose, R. P.; Stasch, A.; Aldridge, S.;
Woodul, W. D.; Murray, K. S.; Moubaraki, B.; Brynda, M.; Macchia, G.
L.; Gagliardi, L. Amidinato- and guanidinato-cobalt(I) complexes:
characterization of exceptionally short Co-Co interactions. Angew.
Chem., Int. Ed. 2009, 48, 7406−7410. (i) King, E. R.; Sazama, G. T.;
Betley, T. A. Co(III) imidos exhibiting spin crossover and C-H bond
activation. J. Am. Chem. Soc. 2012, 134, 17858−17861. (j) Wu, B.;
1840−1841. (d) Kogut, E.; Wiencko, H. L.; Zhang, L.; Cordeau, D. E.;
Warren, T. H. A Terminal Ni(III)-imide with diverse reactivity
pathways. J. Am. Chem. Soc. 2005, 127, 11248−11249. (e) Cowley, R.
E.; Eckert, N. A.; Elhaïk, J.; Holland, P. L. Catalytic nitrene transfer
from an imidoiron(III) complex to form carbodiimides and
isocyanates. Chem. Commun. 2009, 1760−1762. (f) Geer, A. M.;
́
Tejel, C.; Lopez, J. A.; Ciriano, M. A. Terminal imido Rhodium
complexes. Angew. Chem., Int. Ed. 2014, 53, 5614−5618. (g) Wang, L.;
Hu, L.; Zhang, H.; Chen, H.; Deng, L. Three-coordinate iron(IV)
bisimido complexes with aminocarbene ligation: synthesis, structure,
and reactivity. J. Am. Chem. Soc. 2015, 137, 14196−14207.
(11) For examples of formation carbodiimide via [2π + 2π] and
retro-[2π + 2π]-addition of early transition-metal imido complexes
with isocyanates, please see: (a) Walsh, P. J.; Hollander, F. J.;
Bergman, R. G. Monomeric and dimeric zirconocene imido
compounds: synthesis, structure, and reactivity. Organometallics
1993, 12, 3705−3723. (b) Birdwhistell, K. R.; Boucher, T.;
Ensminger, M.; Harris, S.; Johnson, M.; Toporek, S. Catalysis of
phenyl isocyanate condensation to N,N′-diphenylcarbodiimide via
vanadium oxo and imido complexes. Organometallics 1993, 12, 1023−
1025. (c) Kilgore, U. J.; Basuli, F.; Huffman, J. C.; Mindiola, D. J. Aryl
isocyanate, carbodiimide, and isocyanide prepared from carbon
dioxide. A metathetical group-transfer tale involving a titanium-imide
zwitterion. Inorg. Chem. 2006, 45, 487−489. (d) Dunn, S. C.; Hazari,
N.; Cowley, A. R.; Green, J. C.; Mountford, P. Synthesis and reactions
of group 4 imido complexes supported by cyclooctatetraene ligands.
Organometallics 2006, 25, 1755−1700. (e) Darwish, W.; Seikel, E.;
́ ́
Hernandez Sanchez, R.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C.
M. Formation of heterobimetallic zirconium/cobalt diimido complexes
via a four-electron transformation. Inorg. Chem. 2014, 53, 10021−
10023.
Kasmarker, R.; Harms, K.; Sundermeyer, J. Synthesis and X-ray crystal
̈
structures of imido and ureato derivatives of titanium(IV)
phthalocyanine and their application in the catalytic formation of
carbodiimides by metathesis from isocyanates. Dalton Trans. 2011, 40,
1787−1794.
(4) (a) Du, J.; Wang, L.; Xie, M.; Deng, L. A two-coordinate
cobalt(II) imido complex with NHC ligation: synthesis, structure, and
reactivity. Angew. Chem., Int. Ed. 2015, 54, 12640−12644. (b) Yao, X.-
N.; Du, J.-Z.; Zhang, Y.-Q.; Leng, X.-B.; Yang, M.-W.; Jiang, S.-D.;
Wang, Z.-X.; Ouyang, Z.-W.; Deng, L.; Wang, B.-W.; Gao, S. Two-
coordinate Co(II) imido complexes as outstanding single-molecule
magnets. J. Am. Chem. Soc. 2017, 139, 373−380. (c) Zhang, L.; Liu, Y.-
S.; Deng, L. Three coordinate cobalt(IV) and cobalt(V) imido
complexes with N-heterocyclic carbene ligation: synthesis, structure,
and their distinct reactivity in C-H bond amination. J. Am. Chem. Soc.
2014, 136, 15525−15528.
(12) (a) Ulrich, H.; Tucker, B.; Sayigh, A. A. R. Metal carbonyls as
catalysts in the conversion of isocyanates to carbodiimides.
Tetrahedron Lett. 1967, 8, 1731−1733. (b) Rahman, A. K. F.;
Nicholas, K. M. Catalytic conversion of isocyanates to carbodiimides
by cyclopentadienyl manganese tricarbonyl and cyclopentadienyl iron
dicarbonyl dimer. Tetrahedron Lett. 2007, 48, 6002−6004.
(13) For examples of formation imine and isothiocyanate via [2π +
2π] and retro-[2π + 2π]-addition of early transition-metal imido
complexes with carbonyl compounds and CS2, please see ref 11d and:
(a) Lee, S. Y.; Bergman, R. G. Generation of oxozirconocene
complexes from the reaction of Cp2(THF)ZrN-t-Bu with organic
and metal carbonyl functionalities: apparently divergent behavior of
transient [Cp2ZrO]. J. Am. Chem. Soc. 1996, 118, 6396−6406.
(b) Zuckerman, R. L.; Bergman, R. G. Structural factors that influence
the course of overall [2 + 2] cycloaddition reactions between
imidozirconocene complexes and heterocumulenes. Organometallics
2000, 19, 4795−4809.
(14) Singh, A. K.; Levine, B. G.; Staples, R. J.; Odom, A. L. A 4-
coordinate Ru(II) imido: unusual geometry, synthesis, and reactivity.
Chem. Commun. 2013, 49, 10799−10801.
(15) For examples, see: (a) Mindiola, D. J.; Hillhouse, G. L. Terminal
amido and imido complexes of three-coordinate nickel. J. Am. Chem.
Soc. 2001, 123, 4623−4624. (b) Mindiola, D. J.; Waterman, R.; Iluc, V.
M.; Cundari, T. R.; Hillhouse, G. L. Carbon−Hydrogen bond
activation, C−N bond coupling, and cycloaddition reactivity of a
three-coordinate nickel complex featuring a terminal imido ligand.
Inorg. Chem. 2014, 53, 13227−13238.
(16) Klein, H.-F.; Karsch, H. H. Methyltetrakis(trimethy1phosphin)-
kobalt und seine derivate. Chem. Ber. 1975, 108, 944−955.
(17) (a) Guisado-Barrios, G.; Bouffard, J.; Donnadieu, B.; Bertrand,
G. Crystalline 1H-1,2,3-triazol-5-ylidenes: new stable mesoionic
carbenes (MICs). Angew. Chem., Int. Ed. 2010, 49, 4759−4762.
(b) Gavenonis, J.; Tilley, T. D. Tantalum alkyl and silyl complexes of
the bulky (terphenyl)imido ligand [2,6-(2,4,6-Me3C6H2)2C6H3N =
]2‑([Ar*N = ]2‑). Generation and reactivity of [(Ar*N = )(Ar*NH)-
Ta(H)(OSO2CF3)], which reversibly transfers hydride to an aromatic
ring of the arylamide ligand. Organometallics 2002, 21, 5549−5563.
(5) Please see the Experimental Section and Supporting Information
for detailed information.
(6) Yang, L.; Powell, D. R.; Houser, R. P. Structural variation in
copper(I) complexes with pyridylmethylamide ligands: structural
analysis with a new four-coordinate geometry index, τ4. Dalton
Trans. 2007, 955−964.
(7) Jenkins, D. M.; Di Bilio, A. J.; Allen, M. J.; Betley, T. A.; Peters, J.
C. Elucidation of a low spin cobalt(II) system in a distorted tetrahedral
geometry. J. Am. Chem. Soc. 2002, 124, 15336−15350.
(8) (a) Evans, D. F. The determination of the paramagnetic
susceptibility of substances in solution by nuclear magnetic resonance.
J. Chem. Soc. 1959, 2003−2005. (b) Sur, S. K. Measurement of
magnetic susceptibility and magnetic moment of paramagnetic
molecules in solution by high-field fourier transform NMR spectros-
copy. J. Magn. Reson. 1989, 82, 169−173.
(9) For examples, see: (a) Johnson, J. B.; Rovis, T. More than
bystanders: the effect of olefins on transition-metal-catalyzed cross-
coupling reactions. Angew. Chem., Int. Ed. 2008, 47, 840−871. (b) Liu,
Y.; Xiao, J.; Wang, L.; Song, Y.; Deng, L. Carbon−Carbon bond
formation reactivity of a four-coordinate NHC-supported iron(II)
phenyl compound. Organometallics 2015, 34, 599−605.
(10) (a) Nugent, W. A.; Mayer, J. M. Metal−Ligand Multiple Bonds:
The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido,
Imido, Alkylidyne Ligands; Wiley: New York, 1988. (b) Eikey, R. A.;
Abu-Omar, M. M. Nitrido and imido transition metal complexes of
Groups 6−8. Coord. Chem. Rev. 2003, 243, 83−124. (c) Mindiola, D.
J.; Hillhouse, G. L. Isocyanate and carbodiimide synthesis by nitrene-
group-transfer from a nickel(II) imido complex. Chem. Commun. 2002,
H
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
́
(18) Chavez, I.; Alvarez-Carena, A.; Molins, E.; Roig, A.;
Maniukiewicz, W.; Arancibia, A.; Arancibia, V.; Brand, H.;
Manríquez, J. M. Selective oxidants for organometallic compounds
containing a stabilising anion of highly reactive cations: (3,5-
(CF3)2C6H3)4B−)Cp2Fe+ and (3,5(CF3)2C6H3)4B−)Cp*2Fe+. J. Orga-
nomet. Chem. 2000, 601, 126−132.
(19) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen: Germany,
̈
1996.
(20) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1997.
(21) (a) Hohenberg, P.; Kohn, W. Inhomogeneous electron gas.
Phys. Rev. 1964, 136, B864−B871. (b) Kohn, W.; Sham, L. J. Self-
consistent equations including exchange and correlation effects. Phys.
Rev. 1965, 140, A1133−A1138.
(22) Neese, F. ORCA: An ab Initio, Density Functional and
Semiempirical Program Package (v. 2.8); Universitat Bonn, 2011.
̈
(23) (a) Becke, A. D. Density-functional thermochemistry. III. The
role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (b) Lee,
C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti
correlation-energy formula into a functional of the electron density.
Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(24) Schafer, A.; Horn, H.; Ahlrichs, R. Fully optimized contracted
̈
Gaussian basis sets for atoms Li to Kr. J. Chem. Phys. 1992, 97, 2571−
2577.
(25) Schafer, A.; Huber, C.; Ahlrichs, R. Fully optimized contracted
̈
Gaussian basis sets of triple zeta valence quality for atoms Li to Kr. J.
Chem. Phys. 1994, 100, 5829−5835.
(26) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient,
approximate and parallel Hartree−Fock and hybrid DFT calculations.
A ‘chain-of-spheres’ algorithm for the Hartree−Fock exchange. Chem.
Phys. 2009, 356, 98−109.
(27) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence,
triple zeta valence and quadruple zeta valence quality for H to Rn:
design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7,
3297−3305.
(28) Manual for ORCA, Version 2.8; Institut fur Physikalische und
̈
Theoretische Chemie, Universitat Bonn: Bonn, 2010; p 453.
̈
(29) Mungwe, N.; Swarts, A. J.; Mapolie, S. F.; Westman, G. Cationic
palladacycles as catalyst precursors for phenyl acetylene polymer-
ization. J. Organomet. Chem. 2011, 696, 3527−3535.
(30) Shan, W. G.; Bian, G. F.; Su, W. K.; Liang, X. R. A facile one-pot
preparation of isothiocyanates from N-formamides and sulfur powder
with bis(trichloromethyl) carbonate. Org. Prep. Proced. Int. 2004, 36,
283−286.
I
DOI: 10.1021/acs.inorgchem.7b00941
Inorg. Chem. XXXX, XXX, XXX−XXX