First-row transition-metal chloride complexes of the wide bite-angle diphosphine iPrDPDBFphos and reactivity studies of monovalent nickel

Article abstract of DOI:10.1021/ic200589e

The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as ^iPrDPDBFphos) has been metalated with transition metal dichlorides of zinc, cobalt, and nickel to yield (^iPrDPDBFphos) MCl₂ complexes. Withi

Full text of DOI:10.1021/ic200589e

ARTICLE
pubs.acs.org/IC
First-Row Transition-Metal Chloride Complexes of the Wide
iPr
Bite-Angle Diphosphine DPDBFphos and Reactivity Studies of
Monovalent Nickel
Elodie E. Marlier, Stephen J. Tereniak, Keying Ding, Jenna E. Mulliken, and Connie C. Lu*
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States
S Supporting Information
b
ABSTRACT: The diphosphine 4,6-bis(3-diisopropylphosphi-
iPr
nophenyl)dibenzofuran (abbreviated as DPDBFphos) has
been metalated with transition metal dichlorides of zinc, cobalt,
iPr
and nickel to yield ( DPDBFphos)MCl complexes. Within
2
iPr
these compounds, the diphosphine DPDBFphos adapts a
wide range of bite angles (115 to 180ꢀ) as determined by
X-ray crystallography. A three-coordinate planar Ni(I) species
iPr
was isolated from the reduction of ( DPDBFphos)NiCl2
with KC . Low-temperature electron paramagnetic resonance
8
iPr
(
EPR) measurements of ( DPDBFphos)NiCl allow the determination of g values (2.09, 2.14, 2.37) and hyperfine coupling
31 ꢀ4 37 35
ꢀ1
ꢀ4
ꢀ1
constants to two P nuclei, A = 46 ꢁ 10 cm , and one Cl/ Cl nucleus, A = (12, 0.7, 35) ꢁ 10 cm . Density functional
iso
theory (DFT) studies reveal the nature of the magnetic orbital to be d , which has σ-antibonding and π -antibonding interactions
xy
with the phosphorus and chloride atoms, respectively. The monovalent nickel complex reacts with substrates containing CꢀX
iPr
bonds; and in the case of vinyl chloride, a Ni(II) vinyl species ( DPDBFphos)Ni(CHdCH )Cl is generated along with the Ni(II)
2
dichloride complex. The monovalent Ni(I) chloride is an active catalyst in the Kumada cross-coupling reaction of vinyl chloride and
phenyl Grignard reagent.
iPr
I. INTRODUCTION
Chart 1. Ligands DBFphos and DPDBFphos
In homogeneous transition-metal catalysis, the reactivity of
the metal center is often fine-tuned by modifications to the
supporting ligand(s). The development of ligand scaffolds
becomes invaluable when these scaffolds confer new reactivities
at the metal center that result in advances in catalysis. We have
iPr
reported a conformationallyflexiblediphosphine, DPDBFphos,
shown in Chart 1 and its cis- and trans-coordination complexes
1
iPr
of Rh(I) and Pd(II). The ligand DPDBFphos is analogous to
4
2,3
,6-bis(diphenylphosphino)dibenzofuran (DBFphos) but has
an aryl linker between the dibenzofuran backbone and the
phosphine donors. One effect is to distance the backbone from
the transition metal center, and hence, to prevent binding of the
O-atom to the metal. Another effect is to confer flexibility to
2
0
21
hydroformylation and cross-coupling; and nickel-mediated poly-
4,5
iPr
22ꢀ24
25,26
the ligand’s chelate properties. Specifically, DPDBFphos sup-
merization and oligomerization of olefins,
cross-coupling,
and cyclization reactions. More relevant to the complexes reported
here, P MX -type complexes of cobalt and zinc have been shown
to be effective catalysts for the polymerization of methyl acrylate
27
ports a wider range of bite angles within coordination complexes
6
,7
(
compared to DBFphos, whose bite angle is limited to 150ꢀ157ꢀ)
2
2
and can switch from the cis to trans coordination mode with a
1
28,29
calculated 3.5 kcal/mol driving force.
and CO /ethylene oxide, respectively.
2
iPr
iPr
Herein, we extend the coordination chemistry of DPDBF-
The ( DPDBFphos)MCl complexes are characterized by
2
phos to the first-row transition metals zinc, cobalt, and nickel. A long-
UVꢀvisible (UVꢀvis) spectroscopy, heteronuclear NMR spectro-
scopies, and single-crystal X-ray diffraction studies. A three-coordi-
nate nickel(I) chloride complex is presented with additional
standing goal in homogeneous catalysis is to replace precious
8,9
transition-metal catalysts with their earth-abundant counterparts.
Notable organometallic examples include iron-mediated cross-cou-
10
11ꢀ14
pling reactions, hydroxylation of aliphatic CꢀH bonds,
and
Received: March 23, 2011
Published: August 31, 2011
15ꢀ17
18,19
hydrogenation of alkenes
and ketones;
cobalt-mediated
r 2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
Scheme 1. SyntheticRoutes to Coordination Complexes 1 to 4
Figure 2. Electronic absorption spectra of Zn 1 (black solid line), Co 2
(blue dashed line), and Ni 3 (red solid line) in THF at ambient
temperature.
Information, Figure 1S), which are typical of d-d transitions
of a high-spin Co(II) center. The bright red nickel complex 3
has a prominent, intense transition with a maximum at 377 nm
ꢀ
1
ꢀ1
(
ε = 9,500 L mol cm , Supporting Information, Figure 2S)
and overlapping broad features from 420 to 600 nm (ε ∼
ꢀ
1
ꢀ1 32
3
00 L mol cm ). The broad features are likely d-d transi-
tions, while the intense peak is tentatively assigned as a ligand-to-
metal charge transfer band.
Compounds 1ꢀ3 have been characterized by NMR spectros-
copy. For the two diamagnetic complexes, Zn 1 and Ni 3, one
type of phosphorus nucleus is observed at 2.7 and 26.5 ppm,
Figure 1. Electronic absorption spectra of Zn 1 (black solid line), Co 2
iPr
1
(blue dashed line), Ni 3 (red solid line), and DPDBFphos (gray solid
respectively. In the corresponding H NMR spectrum of 1
line) in THF at ambient temperature.
(
Supporting Information, Figure 3S), half of the aryl protons
of the ligand are unique, consistent with the approximate 2-fold
symmetry observed in its solid-state structure (vide infra). For
the four isopropyl groups of the ligand, only one methine proton
and two methyl resonances are seen. This is an unexpected
observation since a 2-fold axis should result in two chemically
distinct methine types. Hence, their full equivalency must be
rationalized by another mechanism (vide infra).
characterization from electron paramagnetic resonance (EPR)
spectroscopy and density functional theory (DFT) calculations.
Preliminary reactivity studies of the nickel(I) chloride have
been conducted, and our results join recent studies in demon-
strating the relevance of isolated monovalent nickel species in
3
0,31
cross-coupling catalysis.
1
At room temperature, the H NMR spectrum of the nickel
compound 3 contains both sharp and broad resonances
II. RESULTS AND DISCUSSION
(
Figure 3). The sharp signals correspond to the dibenzofuran
iPr
Syntheses of ( DPDBFphos)MCl , where M = Zn, Co, Ni.
group, while those belonging to the isopropyl groups and the aryl
2
iPr
The diphosphine ligand DPDBFphos is cleanly metalated with
linkers are significantly broadened. Upon cooling to ꢀ45 ꢀC, the
1
the anhydrous transition metal dichlorides as shown in Scheme 1
to provide the zinc, cobalt, and nickel dichloride complexes,
H NMR spectrum of 3 sharpens completely, and exactly half of
the protons of the ligand are uniquely observed, consistent with
the approximate mirror-plane symmetry of its molecular struc-
ture. At low temperature, the isopropyl groups resolve into two
distinct methine and three methyl resonances. The presence of
the mirror plane means that the two chemically different methine
iPr
iPr
[
[
( DPDBFphos)ZnCl ] 1, [( DPDBFphos)CoCl ] 2, and
2 2
iPr
trans-( DPDBFphos)NiCl ] 3, respectively.
2
UVꢀvis and NMR Spectroscopic Characterization of
iPr
(
DPDBFphos)MCl , where M = Zn, Co, Ni. The UVꢀvis
2
spectra of compounds 1ꢀ3 were collected at room temperature in
tetrahydrofuran (THF). All complexes have characteristic bands in
the UV region from 275 to 330 nm (Figure 1, Supporting Informa-
protons occur within the same phosphine group, that is,
0
P(CHMe
)(C HMe
). If PꢀCmethine bond rotation is fast, then
2
2
two methyl peaks would be expected; if slow, four. At ꢀ45 ꢀC,
4
ꢀ1
ꢀ1
tion, Table 1S). These bands are intense (ε ∼ 10 L mol cm )
and do not shift significantly for the different transition metal ions.
These excitations primarily originate from the dibenzofuran
only three methyl signals are apparent because of a coincidental
33
overlap of two of the four possible methyl peaks. At room
temperature, the H NMR spectrum of 3 shows one methine and
1
iPr
group since the ligand DPDBFphos has analogous absorbances
two methyl signals, akin to that of 1. Again, the higher symmetry
solution structure cannot be explained by a mirror plane alone.
Additional fluxional processes will be described in the next
section.
in this range. Between 330 and 800 nm, the colorless zinc
complex 1 has no absorbances, which is consistent with its d
electron count (Figure 2). The brilliant blue cobalt complex 2
1
0
has several bands between 550 and 800 nm with molar absorp-
tivity values between 320 and 530 L mol cm ( Supporting
The cobalt dichloride compound 2 is characterized by a
paramagnetic H NMR spectrum, which is consistent with a
ꢀ1
ꢀ1
1
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Inorganic Chemistry
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2
.2413(5) Å) are unremarkable compared to other trans-dipho-
sphine nickel dichloride complexes (average PꢀNi = 2.24 Å,
6,7
Cambridge Structural Database). An approximate mirror plane
bisects the solid-state structure of 3. The two chloride atoms in 3
reside in the mirror plane and are nonequivalent. One chloride is
near the dibenzofuran backbone while the other chloride is
sandwiched between the isopropyl substituents. At room tem-
1
perature, the H NMR peaks representing the isopropyl groups
coalesce into one methine and two methyl resonances. The
coalescence requires a combination of two dynamic motions
illustrated in Scheme 2: (1) canting of the aryl linkers, which flips
the relative bent orientation of the dibenzofuran group, and (2)
rotation of the PꢀNiꢀP vector, equalizing the two chlorides.
Similar fluxional behavior has been previously described for the
iPr
analogous square-planar complexes, [trans-( DPDBFphos)-
iPr
Rh(NCMe) ]BF and [trans-( DPDBFphos)Pd(NCMe) ]-
2
4
2
1
(
BF ) . We propose that canting of the aryl linkers would also
4 2
occur in tetrahedral 1 to rationalize the solution-structure
equivalency of all the methine protons of the ligand.
Synthesis and Characterization of ( DPDBFphos)Ni Cl.
iPr
I
The redox properties of compounds 1ꢀ3 were investigated by
n
cyclic voltammetry (0.1 M [ Bu N]PF in THF), but no
4
6
reversible redox events were found (Supporting Information,
Figure 4S). Interestingly, the nickel dichloride complex 3 ex-
hibited two irreversible events when scanning cathodically,
whereas only one reductive signal was seen for the zinc and
cobalt dichloride complexes, presumably a ligand-based reduc-
tion. Therefore, the chemical reduction of compound 3 was
investigated. Sodium-based reducing agents such as sodium
metal, sodium amalgam, and sodium naphthalide resulted in
3
1
decomposition of 3 and formation of the free ligand by P NMR
spectroscopy. Mixing potassium graphite with 3 in THF resulted
in an immediate color change from red to yellow (Figure 7). The
resulting product is paramagnetic, and a single-crystal X-ray
diffraction study reveals a three-coordinate, formally 15-electron
iPr
Ni(I) complex, [( DPDBFphos)]NiCl 4 as shown in Figure 8.
Three-coordinate nickel complexes constitute a rich area in
coordination chemistry. Supported by the bulky monophosphine
1
Figure 3. Variable-temperature H NMR spectra (300 MHz, CDCl )
3
iPr
of [trans-( DPDBFphos)NiCl
region at ꢀ45 ꢀC.
2
] 3. Inset is an expansion of the methyl
PCy , zerovalent nickel forms adducts with small-molecules, as
3
observed in the end-on dinitrogen dinickel compound {(PCy ) -
3
2
34
Co(II) oxidation state. Its solution magnetic moment of μeff
.01 μ is slightly greater than the spin-only magnetic moment
for an S = 3/2 state (μS.O. = 3.88 μ ), which leads to the expected
=
Ni}
dioxide complex, (PCy
neered the area of divalent NidE complexes featuring multiply
2
(μ-N
2
)
and the first structurally characterized carbon-
2 35
4
) Ni(η -CO ). Hillhouse has pio-
3 2 2
B
B
assignment of a high-spin Co(II) center.
Solid-State Structures of ( DPDBFphos)MCl , Where
bonded ligands (E = NR, PR, CR
1,2-bis(di-tert-butylphosphino)ethane.
2
) using the bulky diphosphine,
iPr
36ꢀ38
Other notable three-
2
M = Zn, Co, Ni. Crystallographic data are provided in Table 1,
and selected bond lengths and angles are collected in Table 2.
The geometry of the zinc and cobalt centers in 1 and 2, respec-
tively, are tetrahedral. The structures of 1 and 2 are highly homo-
logous as shown in Figures 4 and 5, and their unit cell dimensions
are nearly identical. Both structures contain an approximate 2-fold
rotation axis. The P-M-P bond angles are 115.27(3)ꢀ and 114.62(2)ꢀ
in the zinc and cobalt complexes, respectively. Previously, we
coordinate nickel complexes have been supported by nontradi-
tional phosphine ligands, including the Fryzuk-type tridentate
39
40ꢀ42
bis(phosphine)amides, diketiminates,
N-heterocyclic car-
43,44
45
benes,
and the unusual N-heterocyclic silenes. Typically,
the oxidation state of the nickel center is monovalent for the
anionic ligands, and zerovalent for the neutral carbenes/silenes.
The rare Ni(III) oxidation state has also been proposed in three-
coordinate Ni(III) imides, which can be remarkably reactive and
iPr
46,47
observed a more acute bite angle of 104.5ꢀ for DPDBFphos in
decompose via radical pathways.
iPr
iPr
the distorted square planar complex [cis-( DPDBFphos)-
Yellow crystals of [( DPDBFphos)]NiCl 4 were grown from
1
Rh(nbd)]BF . The CoꢀP and ZnꢀP bond distances in 1 and
a concentrated CD CN solution at room temperature. Two
4
3
2
, respectively, are comparable to other diphosphine dichloride
independent molecules of 4 are found in the unit cell. Both nickel
centers are three-coordinate and planar. The LꢀNiꢀL angles
sum to 359 and 360ꢀ. There are, however, significant variations in
the bond and angle metrics between these two molecules
(Table 2, A and B). For instance, the NiꢀL bond distances
within the two molecules differ from each other by 0.02 to 0.03 Å.
coordination complexes with the corresponding transition metal
centers.
The geometry of the nickel center in 3 is square planar with a
iPr
trans-spanning DPDBFphos ligand (PꢀNiꢀP = 176.55(2)ꢀ)
as shown in Figure 6. The NiꢀP bond distances in 3 (2.2410(5),
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Inorganic Chemistry
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Table 1. Crystallographic Data for 1ꢀ4 and 6
1
2
3
4
6
chemical formula
formula weight
crystal system
space group
a (Å)
C
36
H
42Cl
2
ZnOP
2
C
36
H
42Cl
2
CoOP
2
C
36
H
42Cl
2
NiOP
2
C
36
H
42ClNiOP
2
38 2
C H45ClNiOP
688.98
triclinic
P1
682.50
triclinic
P1
682.27
monoclinic
P2 /c
646.81
673.84
monoclinic
triclinic
1
P2
1
/c
P1
9.772(3)
9.772(1)
19.181(3)
9.059(1)
21.040(3)
90
24.277(4)
17.431(3)
16.052(3)
90
11.952(3)
15.245(3)
20.695(5)
88.084(3)
73.958(2)
89.567(3)
3622(1)
4
b (Å)
10.024(3)
17.882(6)
80.286(5)
75.748(5)
85.834(5)
1672.6(9)
2
10.020(1)
17.939(2)
80.377(2)
76.006(1)
85.940(2)
1679.5(3)
2
c (Å)
α (deg)
β (deg)
115.196(2)
90
105.405(2)
90
γ (deg)
3
V (Å )
3308.0(8)
4
6549(2)
8
Z
ꢀ3
D
calcd (g cm
)
1.368
1.350
1.370
1.312
1.236
ꢀ1
λ (Å), μ (mm
T (K)
)
0.71073, 1.017
173(2)
0.71073, 0.793
173(2)
0.71073, 0.873
123(2)
0.71073, 0.799
173(2)
0.71073, 0.725
123(2)
θ range (deg)
1.19 to 26.37
16699
1.18 to 27.52
20155
1.17 to 27.49
31527
1.46 to 26.37
56856
1.71 to 26.51
26923
reflns collected
unique reflns
6815
7590
7531
13372
14614
data/restraint/parameters
, wR (I > 2σ(I))
6815/0/387
0.0428, 0.0959
7590/0/387
0.0372, 0.0830
7531/0/387
0.0295, 0.0669
13372/0/755
0.0540, 0.0904
14614/0/775
0.0563, 0.1406
R
1
2
Table 2. Experimental Bond Distances (Å) and Angles (deg)
for 1ꢀ4
a
4
, Ni(I)
1
, Zn(II) 2, Co(II) 3, Ni(II)
A
B
Bond Distances
MꢀP(1)
MꢀP(2)
MꢀCl(1)
MꢀCl(2)
2.420(1) 2.3920(7) 2.2410(5) 2.209(1) 2.233(1)
2.416(1) 2.3844(7) 2.2413(5) 2.217(1) 2.243(1)
2.255(1) 2.2331(7) 2.1748(5) 2.163(1) 2.180(1)
2.2641(9) 2.2435(7) 2.1609(5)
Bond Angles
P(1)ꢀMꢀP(2) 115.27(3) 114.62(2) 176.55(2) 115.53(4) 119.49(4)
Cl(1)ꢀMꢀCl(2) 117.38(3) 118.55(3) 175.10(2)
a
Two values are reported because two independent molecules (A, B) are
iPr
Figure 4. Solid-state structure of the [( DPDBFphos)ZnCl ] 1 at
2
present in the unit cell.
50% probability level. Hydrogen atoms were omitted for clarity.
One may normally expect to see a shortening of NiꢀP bonds
upon reduction of the Ni center (from 3 to 4) because of
increased π-back bonding into the phosphine ligands. However,
this is not necessarily the case here. While molecule A does
distortion is unclear. We looked for indications of crystal packing
forces, but the shortest nonbonded contact distances to the
chloride atom in the more distorted molecule (B) are too long
48
have significantly shorter NiꢀP bond lengths relative to
(>2.88 Å for Cl----H) to have much impact (Supporting
iPr
49
[
trans-( DPDBFphos)NiCl ] 3, molecule B has essentially
Information, Table 2S). Of relevance, the molecular structure
2
identical NiꢀP bond lengths to those in 3. The diphosphine
iPr
of Ni(PPh ) Cl is slightly distorted trigonal planar, and the
3
2
bite angle in molecule A, 115.53(4)ꢀ, is nearly identical to that in
observed asymmetry was attributed to a first-order JahnꢀTeller
50
the tetrahedral [( DPDBFphos)MCl ] compounds reported
effect. This rationale, however, is inherently flawed because no
2
here, but molecule B has a wider bite angle of 119.49(4)ꢀ.
Moreover, the NiA center is nearly trigonal planar with similar
P(1)ꢀNiAꢀCl and P(2)ꢀNiAꢀCl bond angles of 122.94(4)
and 121.53(4)ꢀ, respectively. The NiB center has a more
distorted trigonal geometry with the chloride ligand positioned
asymmetrically between the two phosphorus atoms. The P(1)ꢀ
NiBꢀCl and P(2)ꢀNiBꢀCl bond angles are quite different
at 104.61(4) and 135.00(4)ꢀ, respectively. The origin of the
degenerate d-orbitals can exist for NiP X species, even with
idealized D2h symmetry. Instead, we propose that the chloride
2
atom wiggles within the NiP -plane, and that these structural
2
perturbations cost little energy.
The X-band EPR spectrum of 4 in frozen toluene at 20 K
is shown in Figure 9. A slightly rhombic signal is observed with
g-values of 2.09, 2.14, and 2.37 (giso = 2.20), which are consistent
40,51,52
with the assignment of a S = 1/2 Ni(I) center.
EPR spectra
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ꢀ
4
ꢀ1
ꢀ4
ꢀ1
of three-coordinate Ni(I) complexes typically have rhombic
(43, 40, 55) ꢁ 10 cm (Aiso = 46 ꢁ 10 cm ) and to one
46,53
37
35
anisotropy with g ꢀ g > g ꢀ g .
The spectrum was fitted
Cl/ Cl nucleus (I = 3/2, abundance ratio = 0.3196) of (12,
3
2
2
1
31
ꢀ4
ꢀ1
using hyperfine coupling constants to two P (I = 1/2) nuclei of
0.7, 35) ꢁ 10 cm . Large hyperfine coupling constants to the
31
two P nuclei are observed for all three g-values, while the
37
35
hyperfine splitting caused by Cl/ Cl coupling is significant only
for g . The equivalence of the two phosphorus nuclei in the frozen
3
solution EPR of 4 stands in contrast to the classical work of Nilges
et al. on the single-crystal EPR study of Ni(I)-doped Cu-
(
PPh ) Cl, in which the hyperfine coupling constants of the two
3 2
31
phosphorus nuclei are remarkably inequivalent, A ( P) = 38 and
5
midway between these two values determined for Ni(PPh ) Cl.
iso
ꢀ4
ꢀ1 54
31
9 ꢁ 10 cm . Of note, our P hyperfine coupling constant is
3
2
iPr
I
Theoretical Studies of ( DPDBFphos)Ni Cl. DFT calcula-
tions were performed on the Ni(I) complex 4 using the BP86 and
M06-L functionals. The optimized geometries compare favor-
ably with the experimental structure (molecule A), whose
coordinates were used as the initial geometry (Supporting
Information, Table 3S). All calculated NiꢀL bond distances
are within 0.015 Å of their experimental values. The optimized
bite angles were also remarkably close to the experimental value,
differing at most by 2ꢀ.
iPr
Figure 5. Solid-state structure of the [( DPDBFphos)CoCl ] 2 at
5
2
0% probability level. Hydrogen atoms were omitted for clarity.
iPr
Figure 6. Solid-state structure of the [( DPDBFphos)NiCl ] 3 at 50%
Figure 7. Electronic absorption spectra of the nickel compounds 3
(red solid line) and 4 (black dotted line) in THF at ambient temperature.
2
probability level. Hydrogen atoms were omitted for clarity.
Scheme 2. Proposed Fluxional Processes in 3
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iPr
Figure 8. Solid-state structures of [( DPDBFphos)NiCl] 4 at 50% probability level. Both independent molecules in the unit cell are shown (A, left; B,
right). Hydrogen atoms were omitted for clarity. Selected bond angles (deg): P1AꢀNiAꢀP2A 115.53(4), P1AꢀNiAꢀClA 122.94(9), P2AꢀNiAꢀClA
121.53(4), P1BꢀNiBꢀP2B 119.49(4), P1BꢀNiBꢀClB 104.61(4), P2BꢀNiBꢀClB 135.00(4).
0
0
Figure 9. X-band EPR spectrum (dX /dB) of Ni 4 in toluene glass
shown in black (1 mM, 20.0 K, frequency = 9.65 GHz, modulation to
10.0 G, power = 0.02 mW). The spectrum was simulated (shown in red)
by adopting the following values: g = (2.09, 2.14, 2.37); line widths,
3
1
ꢀ4
ꢀ1
W = (12, 21, 13.5) G; A(two P, I = 1/2) = (43, 40, 55) ꢁ 10 cm
;
37
35
ꢀ4
ꢀ1
A( Cl/ Cl, I = 3/2) = (12, 0.7, 35) ꢁ 10 cm
.
Figure 10 is the molecular-orbital (MO) diagram showing the
splitting of the d-orbital manifold. Because the MO diagrams
derived from the two functionals are very similar, only the results
from the BP86 optimization are shown. For the following
discussion, the molecular trigonal plane is defined as the xy-
plane with the NiꢀCl vector along the x-axis. The d-orbital
manifold comprises three energetically high-lying d-orbitals and
two low-lying d-orbitals. The singly occupied MO (SOMO) is
predominantly dxy in composition and is σ-antibonding with
respect to the phosphorus atoms and π -antibonding with the
chloride atom. This magnetic orbital description is consistent
with the EPR spectrum of 4, which is characterized by a large
hyperfine coupling constant to both phosphorus nuclei and a
smaller interaction with the chloride nucleus. The next two
55
Figure 10. Qualitative MO diagram of the d-orbital manifold derived
from a DFT-BP86 calculation of [( DPDBFphos)NiCl] 4.
iPr
electron density throughout the π-system of the dibenzofuran
MOs, which have dz
π^-antibonding interactions with the chloride. Significantly low-
2
and dxz parentage, are characterized by
backbone.
iPr
I
Reactivity Studies of ( DPDBFphos)Ni Cl. Preliminary re-
activity studies reveal that the Ni(I) complex 4 can cleave CꢀX
bonds. Benzyl bromide and 4 react instantly at room temperature
to yield bibenzyl ( H NMR). The product mixture is character-
ized by a singularly broad signal in the P NMR spectrum, which
er in energy are the d
2
2
and d orbitals. The former is slightly
x ꢀy
yz
σ-antibonding with respect to chloride, and the latter is formally
nonbonding. The calculated electronic structure is fully consis-
tent with monovalent nickel. The lowest unoccupied MO (LUMO,
not shown) is ligand-based and is characterized by delocalized
1
31
upon cooling to 0 ꢀC resolves into three distinct peaks at 26.5,
9
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Inorganic Chemistry
ARTICLE
Table 3. Kumada Cross-Coupling Reactions of Vinyl Chlor-
a
ide and PhMgBr
b
entry
Ni source (5 mol %)
avg. yield (%)
no. of runs
iPr
II
1
2
3
[( DPDBFphos)Ni Cl
2
] 3
66.4 ( 9.8
85.9 ( 7.8
5
4
4
iPr
I
[( DPDBFphos)Ni Cl] 4
no nickel, no ligand
8.7 ( 7.7
a
b
See Experimental Section for reaction conditions. The yield of styrene
is determined by GC-MS analysis.
comproportionation reactions with Ni(I). Though the assorted
products in the reaction of 4 and vinyl bromide hint at radical
processes, we cannot exclude the intermediacy of Ni(III) species.
Encouraged by the clean reactivity between 4 and vinyl
chloride, we decided to investigate the catalytic potential of
Ni(I) 4 in the original Kumada coupling reaction of vinyl
iPr
56
Figure 11. Solid-state structure of [( DPDBFphos)Ni(CHdCH
6
2
)Cl]
chloride and phenyl Grignard reagent. Using a loading of 5
mol % catalyst with excess vinyl chloride, both Ni(I) 4 and Ni(II)
at 50% probability level. Only one of the two independent molecules in
the unit cell is shown. Hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (deg): NiꢀP1 2.204(1), NiꢀP2 2.210(1),
NiꢀCl 2.241(1), NiꢀC37 1.919(4), C37ꢀC38 1.220(6), P1ꢀNiꢀP2
3
generated styrene as the product in good yields (∼65 to 85%,
Table 3, entries 1 and 2), with 4 slightly outperforming 3. The
control reaction (Table 3, entry 3) showed that no significant
amount of styrene is formed under the same conditions in the
absence of a catalyst.
1
8
74.39(4), P1ꢀNiꢀCl 93.35(4), P2ꢀNiꢀCl 92.19(4), P1ꢀNiꢀC37
7.6(1), P2ꢀNiꢀC37 86.8(1), NiꢀC37ꢀC38 136.9(3).
Monovalent nickel species had long been proposed by Tsou
2
9.0, and 31.2 ppm (Supporting Information, Figure 6S). The
iPr
and Kochi as intermediates in the nickel-catalyzed biaryl synthesis
former corresponds to [trans-( DPDBFphos)NiCl ] 3. The latter
two are assigned as the mixed halide [( DPDBFphos)NiClBr]
and dibromide [( DPDBFphos)NiBr ] compounds based on the
following evidence. Metalation of ( DPDBFphos) with NiBr
proceeds cleanly to [( DPDBFphos)NiBr ] 5. Complex 5 is
characterized by a single peak at 31.2 ppm in the P NMR
spectrum at 0 ꢀC, which matches well with that seen in the benzyl
bromide reaction mixture. The third peak in the P NMR
2
57
iPr
from aryl halides. Indeed, mechanistic proposals for Ni-cata-
lyzed cross-couplings commonly feature Ni(0), Ni(I), Ni(II), and
Ni(III) species, which undergo one- and/or two-electron redox
iPr
2
iPr
2
25,58,59
iPr
steps in the catalytic cycle.
Isolated monovalent nickel
2
31
compounds have been found to be catalytically competent in
3
0,31,60,61
various cross-coupling schemes.
I)-terpyridine” catalyst was reformulated as a nickel(II) center
bound to a reduced ligand radical based on EPR and DFT
In one case, the “nickel-
3
1
(
spectrum at 29.0 ppm is presumably the mixed halide species
62
iPr
studies. The other Ni(I) cross-coupling catalysts mostly have
N-heterocyclic carbenes (NHCs) as ligands
[( DPDBFphos)NiClBr] because its chemical shift is exactly
30,31
and are consid-
halfway between that of the nickel dichloride 3 and of the nickel
dibromide 5 complexes.
ered to be bona fide Ni(I) species because metal-NHC complexes
are not known to undergo ligand-based reductions (although
Compound 4 reacts with excess vinyl chloride to cleanly
63
iPr
NHCs can partake in π-backbonding). To our knowledge, this
report is the first comparative study between an isolated Ni(I)-
phosphine complex and its Ni(II) analogue in a cross-coupling
reaction.
produce [( DPDBFphos)NiCl ] 3 and the vinyl complex,
2
iPr
[
( DPDBFphos)Ni(CHdCH )Cl] 6, as identified by combus-
2
1
tion analysis, H NMR spectroscopy, and a single-crystal X-ray
diffraction experiment (Figure 11, Table 1). The product ratio of
3
1
:6 is 1:1 based on their relative integration in the H NMR
spectrum (Supporting Information, Figure 7S) and is consistent
with the chemical equation,
III. CONCLUSIONS
iPr
The diphosphine DPDBFphos was successfully used as a
iPr
I
supporting ligand in tetrahedral Zn(II) and Co(II) complexes, as
well as in square-planar Ni(II) and distorted trigonal planar Ni(I)
compounds. The breadth of coordination geometries as exem-
plified by these complexes is enabled by the conformationally
2
½ð DPDBFphosÞNi Clꢂ þ CH2dCHCl f
iPr
II
½
ð DPDBFphosÞNi Cl ꢂ
2
iPr
II
þ ½ð DPDBFphosÞNi ðCHdCH2ÞClꢂ
iPr
flexible backbone in DPDBFphos. Compared to cis-chelating
Of interest, 4 also reacts with 1 equiv of vinyl bromide to generate
a mixture that contains the Ni(II) dihalide complexes, 6, and a
new species that is assigned as the bromide analogue of 6 because
of their similar spectroscopic data. Collectively, these results
demonstrate that Ni(I) 4 cleaves vinylꢀX bonds to ultimately
produce stable Ni(II) products.
diphosphines, nonrigid trans-spanning diphosphines may be
advantageous when a nonlabile ligand platform is required that
must also accommodate different coordination geometries, such
as during a catalytic cycle.
Given the limited evidence for Ni(I) in cross-coupling reac-
tions, our results are intriguing in that a Ni(I) complex reacts
constructively with vinylꢀX bonds and is catalytically competent
for the cross coupling of vinyl chloride and phenyl Grignard
reagent. Definitive experimental proof for the direct involvement
of monovalent nickel in cross-coupling catalysis is still lacking.
The current results warrant further study of this Ni(I) system,
especially to evaluate its scope in other cross-coupling schemes as
Two limiting mechanisms are proposed for the cleavage of
vinyl halide: (1) a radical chain process is initiated by an inner-
II
sphere electron transfer to form a Ni(II)-alkene adduct, Ni ꢀ
2
•ꢀ
•
(
η -CH CHX) , which subsequently eliminates X and/or
2
•
CH CH , or (2) vinyl halide oxidatively adds to Ni(I) to produce
a Ni(III) intermediate, Ni X(CHCH ), which then undergoes
2
III
2
9
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Inorganic Chemistry
ARTICLE
0
31
well as to scrutinize the role of Ni(I) through detailed mechan-
istic investigations.
PCH(CH
Calcd. for C36
3
)(C H
3
)). P NMR (121 MHz, CDCl
3
): δ 26.5 (br). Anal.
H
42Cl OP Ni: C, 63.37; H, 6.20; N, 0. Found: C, 63.16; H,
2 2
6.20; N, 0.0.
iPr
Synthesis of [( DPDBFphos)NiCl] (4). A THF solution of 3 (0.095 g,
.14 mmol) was added to KC (0.020 g, 0.15 mmol) and stirred
IV. EXPERIMENTAL SECTION
0
8
overnight. An immediate color change from red to yellow was observed.
The reaction solution was filtered, and the filtrate was evaporated to dryness
under reduced pressure. The resulting crude was dissolved in toluene,
filtered, and then stored at ꢀ35 ꢀC. The resulting yellow precipitate was
collected and dried under reduced pressure (0.080 g, 90%). Single crystals
suitable for X-ray diffraction analysis were obtained from a concentrated
Synthetic Considerations. Unless otherwise stated, all manip-
ulations were performed under a dinitrogen atmosphere in a MBraun
glovebox or using standard Schlenk techniques. Standard solvents were
deoxygenated by sparging with dinitrogen and dried by passing through
activated alumina columns of a SG Water solvent purification system.
Deuterated solvents were purchased from Cambridge Isotope Labora-
ꢀ
1
ꢀ1
3
CD CN solution. UV (THF) λmax, nm (ε, L mol cm ): 263 (37,000),
2
tories, Inc., dried over CaH , distilled, and stored over activated 4 Å
molecular sieves. Elemental analyses were performed by Atlantic Microlab.
The synthesis of 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran, re-
298 (16,000), 314 sh (12,000), 324 (11,000), 346 sh (5,200), 375 (4,500).
1
H NMR (300 MHz, d
Calcd. for C36 42ClOP Ni: C, 66.85; H, 6.54; N, 0. Found: C, 67.00;
H, 6.48; N, 0.0.
Synthesis of [( DPDBFphos)NiBr
8
-THF): δ 13.98, 9.03, 8.62, 7.97, 3.14. Anal.
iPr
1
ferred to as DPDBFphos, was previously reported. Other reagents were
H
2
purchased commercially and used without further purification.
iPr
iPr
Synthesis of [( DPDBFphos)ZnCl ] (1). A solution of zinc(II)
] (5). A suspension of nickel(II)
2
2
iPr
chloride (0.026 g, 0.19 mmol) in 10 mL of THF was added dropwise
bromide (0.134 g, 0.615 mmol) and DPDBFphos (0.353 g, 0.638
mmol) in 20 mL of THF was heated to 70 ꢀC with stirring for 9 h. Upon
cooling to room temperature, the crude mixture was concentrated to
8 mL under reduced pressure, filtered through Celite, layered with
12 mL of pentane, and stored at ꢀ35 ꢀC. Purple crystals formed
iPr
to a solution of DPDBFphos (0.102 g, 0.18 mmol) in 10 mL of THF.
The reaction solution was stirred overnight. After 12 h, the solvent was
removed under reduced pressure, and the resulting solids were washed
with Et O and then extracted into THF. The THF solution was layered
2
with hexane and stored at ꢀ35 ꢀC overnight to give a white precipitate,
which was collected and dried under reduced pressure (0.089 g, 70%).
Single crystals suitable for X-ray diffraction analysis were grown from
overnight, and they were collected and dried under reduced pressure
1
(0.297 g, 63%). H NMR (400 MHz, CD
2
Cl
2
, ꢀ60 ꢀC): δ 8.74 (2H, br,
CH), 8.07 (2H, d, J = 7.5 Hz, CH), 7.62 (2H, d, J = 7.5 Hz, CH), 7.49
ꢀ
1
ꢀ1
Et
6,400). H NMR (500 MHz, CDCl
d, J = 7.0 Hz, CH), 7.74 (2H, br. s, CH), 7.66 (2H, d, J = 6.5 Hz, CH),
.62 (4H, m, J = 6.5 Hz, CH), 7.50 (2H, t, J = 7.5 Hz, CH), 2.59 (4H, m,
PCH(CH ), 1.29 (12H, dd, JHH = 8.0 Hz, JHP = 15 Hz, PCH(CH )-
C H )), 1.19 (12H, dd, J = 8.0 Hz, JHP = 15 Hz, PCH(CH )(C H )).
2
O. UV (THF) λmax, nm (ε, L mol cm ): 294 sh (13,000), 310 sh
(6H, m, J = 7.5 Hz, CH), 7.29 (2H, br, CH), 2.81 (2H, br, PCH(CH
3
)
2
),
1
0
(
3
): δ 8.33 (2H, br, CH), 8.03 (2H,
2.42 (2H, br, PC H(CH
3
)
2
), 1.61 (12H, m, PCH(CH
3
)
2
), 1.19 (6H, m,
0
0
0
0
31
PC H(CH
(162 MHz, CD
0 ꢀC): δ 31.2. Anal. Calcd. for C36
Found: C, 55.94; H, 5.59; N, 0.0.
)(C H
)), 0.63 (6H, m, PC H(CH
)(C H
)). P NMR
-THF,
Ni: C, 56.07; H, 5.49; N, 0.
3
3
3
3
3
1
7
2
Cl2, ꢀ60 ꢀC): δ 30.3. P NMR (162 MHz, d
8
3
)
2
3
H
42Br OP
2
2
0
0
(
3
HH
3
3
3
1
+
iPr
P NMR (121 MHz, CDCl ): δ 2.7. ESI-MS-TOF m/z: [M ꢀ Cl]
Synthesis of [( DPDBFphos)Ni(CHCH )Cl] (6). A d -THF solution
2 8
3
calc. for C36
42Cl OP
.0. Several different crystalline batches of 1 were tested, but no
H
42ClZnOP
2
, 651.1691; found, 651.3. Anal. Calcd. for
of 4 (0.017 g, 0.03 mmol) was added to a sealable NMR tube. The tube
was frozen, evacuated, and refilled with excess vinyl chloride. An
immediate color change was observed from yellow to orange red upon
warming to room temperature. After 4 days at room temperature, the
NMR spectra showed no starting material and two different products;
complexes 3 and 6, present in a 1:1 ratio. Complex 6 was synthesized
independently through the reaction of vinyl chloride and a nickel(0)
complex. Single crystals suitable for X-ray diffraction analysis were
grown from a THF/Pentane (1:2) solution. UVꢀvis (THF) λmax, nm
C
0
36
H
2
2
Zn: C, 62.76; H, 6.14; N, 0. Found: C, 60.82; H, 6.09; N,
satisfactory analyses were obtained.
iPr
2
Synthesis of [( DPDBFphos)CoCl ] (2). A suspension of cobalt(II)
chloride (0.026 g, 0.20 mmol) in 20 mL of THF was added dropwise to a
iPr
solution of DPDBFphos (0.109 g, 0.20 mmol) in 20 mL of THF. The
reaction solution was stirred overnight. After 12 h, the solvent was
removed under reduced pressure, and the resulting solids were washed
ꢀ
1
ꢀ1
with Et O and then extracted into THF. The THF solution was filtered
(ε, L mol cm ): 285 (32,000), 308 sh (19,000), 318 sh (15,000), 430
2
1
and then evaporated to dryness under reduced pressure to give a blue
powder (0.133 g, 99%). Single crystals suitable for X-ray diffraction
(700). H NMR (500 MHz, d -THF): δ 8.50 (2H, m, CH), 8.12 (2H,
8
dd, J = 1.5 and 8.0 Hz, CH), 7.62 (2H, d, J = 8.0 Hz, CH), 7.58 (2H, dd,
J = 1.5 and 8.0 Hz, CH), 7.50 (2H, t, J = 8.0 Hz, CH), 7.49 (2H, t, J =
8.0 Hz, CH), 7.36 (2H, m, CH), 5.91 (1H, ddt, JHH = 10.2 and 17.5 Hz,
analysis were grown from Et
2
O. UVꢀvis (THF) λmax, nm (ε, L
ꢀ
1
ꢀ1
mol cm ): 295 sh (16,000), 322 sh (7,600), 618 sh (500), 636 (530),
1
0
7
4
4
35 (320). H NMR (300 MHz, C
6
D
6
): δ 21.36, 13.54, 7.95, 7.64, 6.79,
/CHCl , 300 MHz): μeff
J
HP = 5.5 Hz, NiCH = CHH ), 4.42 (1H, dt, JHH = 17.5 Hz, JHP = 3.0 Hz,
0
.19, 1.83, ꢀ14.03. Evans’ method (CDCl
3
3
=
cis-NiCHdCHH ), 4.14 (1H, dt, JHH = 10.2 Hz, JHP = 4.5 Hz, trans-
NiCHdCHH ), 2.96 (2H, m, PCH(CH
1.64 (6H, dd, JHH = 7.0 Hz,JHP = 14.0 Hz, PC H(CH
dd, JHH = 7.5 Hz, JHP = 15.0 Hz, PC H(CH
0
0
.01 μ . Anal. Calcd. for C H Cl OP Co: C, 63.35; H, 6.20; N, 0.
3
)
2
), 2.73 (2H, m, PC H(CH
3
)
2
),
)), 1.62 (6H,
)), 1.36 (6H, dd, JHH
)), 0.71 (6H, dd, JHH = 6.0 Hz,
B
36 42
2
2
0
0
Found: C, 62.83; H, 6.05; N, 0.0.
Synthesis of [( DPDBFphos)NiCl
3
)(C H
3
iPr
0
0
2
] (3). A suspension of nickel(II)
3
)(C H
3
=
0
31
chloride (0.068 g, 0.52 mmol) in 20 mL of THF was added dropwise to a
7.5 Hz, JHP = 15.5 Hz, PCH(CH
3
)(C H
3
iPr
0
solution of DPDBFphos (0.250 g, 0.45 mmol) in 20 mL. The reaction
JHP = 12.0 Hz, PCH(CH
3
)(C H
3 8
)). P NMR (121 MHz, d -THF): δ
solution was heated at 70 ꢀC with stirring. After 12 h, the solvent was
removed under reduced pressure, and the resulting solids were washed
29.1. Anal. Calcd. for C38
67.97; H, 6.89; N, 0.0.
H45ClOP Ni: C, 67.73; H, 6.73; N, 0. Found: C,
2
with Et
2
O and then extracted into THF. The THF solution was filtered
General Procedure for Kumada Coupling Reactions.
A THF solution of the Ni catalyst (0.003 mmol, 2.14 mL) was added
to a sealable reaction flask equipped with a magnetic stir bar, and the
and then stored at ꢀ35 ꢀC overnight to give red crystals, which were
collected and dried under reduced pressure (0.202 g, 65%). Single crystals
suitable for X-ray diffraction analysis were grown from a CH
2
Cl
2
/Et
2
O
2
solution was frozen with a glovebox LN coldwell bath. Once frozen, a
ꢀ1
ꢀ1
(
1:3) solution. UVꢀvis (THF) λ , nm (ε, L mol cm ): 295 sh
solution of phenylmagnesium bromide (0.06 mmol, 0.02 mL, 3.0 M in
Et O) diluted with Et O (0.84 mL) was added on top and frozen as a
max
1
(18,000), 322 sh (9,300), 377 (9,500), 487 (280). H NMR (300 MHz,
2
2
CDCl
3
): δ 8.74 (2H, br, CH), 8.06 (2H, d, J = 7.5 Hz, CH), 7.57 (2H, d,
separate layer. The reaction flask was then evacuated and charged with
excess vinyl chloride. Reactions were allowed to thaw and stir for 22 h at
J = 7.5 Hz, CH), 7.50 (6H, m, J = 7.5 Hz, CH), 7.13 (2H, br, CH), 2.75
0
(4H, br, PCH(CH ) ), 1.67 (12H, br, PCH(CH )(C H )), 1.27 (12H, br,
room temperature. The reaction was quenched by adding 2 mL of Et O
3
2
3
3
2
9
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Inorganic Chemistry
ARTICLE
and 4 mL of 1.0 M HCl to the solution. The organic layer was extracted,
’ AUTHOR INFORMATION
dried over MgSO and filtered. The filtrate was analyzed on the GC-MS.
Yields were calculated using GC-MS peak integrations and a styrene-
standard calibration curve.
4
Corresponding Author
*
E-mail: clu@umn.edu.
X-ray Crystallographic Data Collection and Refinement of
the Structures. A colorless plate of 1, a blue block of 2, a red plate of 3,
a yellow plate of 4, and a yellow block of 6 were placed onto the tip of a
’
ACKNOWLEDGMENT
E.E.M. thanks Professor Kris McNeill (ETH Z €u rich) and the
0.1 mm diameter glass capillary and mounted on a Bruker or a Siemens
NSF (CHE-0809575 and 0952054) for support. S.J.T. thanks 3M
for a graduate fellowship. The Lando-NSF Summer Research
Program is gratefully acknowledged for giving J.E.M. financial
support. Dr. Victor Young, Jr. (X-ray Crystallographic Laboratory)
and Dr. Yuming Zhou provided assistance with X-ray crystal-
lography and acquiring EPR spectra, respectively. We thank Pro-
fessors William Tolman and John Lipscomb for the generous use of
their GC/MS and EPR instruments, respectively. Computing
support and resources were provided by the Minnesota Super-
computing Institute, and partial funding for this work was given by
the Initiative for Renewable Energy and the Environment (U of M).
SMART Platform CCD diffractometer for data collection at 173(2) K
for complexes 1, 2, and 4, or 123(2) K for complexs 3 and 6. The data
collection was carried out using Mo Kα radiation (graphite mono-
chromator). The data intensity was corrected for absorption and decay
(SADABS). Final cell constants were obtained from least-squares fits of
all measured reflections. The structure was solved using SHELXS-97 and
refined using SHELXL-97. A direct-methods solution was calculated
which provided most non-hydrogen atoms from the E-map. Full-matrix
least-squares/difference Fourier cycles were performed to locate the
remaining non-hydrogen atoms. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms were placed
in ideal positions and refined as riding atoms with relative isotropic
displacement parameters. For 6, a highly disordered THF molecule
could not be modeled appropriately and was removed using the
’ REFERENCES
(1) Ding, K.; Miller, D. L.; Young, V. G., Jr.; Lu, C. C. Inorg. Chem.
64
PLATON program, SQUEEZE function. A total of 46 electrons in a
3
2011, 50, 2545–2552.
2) Haenel, M. W.; Jakubik, D.; Rothenberger, E.; Schroth, G. Chem.
Ber. 1991, 124, 1705–1710.
3) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995,
4, 3081–3089.
4) Jim ꢀe nez-Rodríguez, C.; Roca, F. X.; Bo, C.; Benet-Buchholz, J.;
volume of 353 Å located at (0.5, 1, 0) in the unit cell were determined.
(
Crystallographic data for 1ꢀ4 and 6 are summarized in Table 1.
1
31
Physical Measurements. H and P NMR spectra were acquired
on Varian Inova 300 and 500 MHz spectrometers at ambient tempera-
ture unless otherwise stated. Chemical shifts were referenced to residual
(
1
1
31
solvent in H NMR spectra, while P NMR spectra were referenced to
an external reference of 85% H PO set to 0 ppm. For 6, proton
(
3
4
Escudero-Ad ꢀa n, E. C.; Freixa, Z.; van Leeuwen, P. W. N. M. Dalton
Trans. 2006, 268–278.
assignments were based on a COSY NMR experiment. Solution
6
5,66
magnetic susceptibilities were determined by the Evans method
and
(5) Fairlamb, I. J. S.; Tommasi, S.; Moulton, B. E.; Zheng, W.; Lin,
Z.; Whitwood, A. C. Eur. J. Inorg. Chem. 2007, 2007, 3173–3178.
(6) Allen, F. Acta Crystallogr., Sect. B 2002, 58, 380–388.
(7) Orpen, A. G. Acta Crystallogr., Sect. B 2002, 58, 398–406.
(8) Kulkarni, A. A.; Daugulis, O. Synthesis 2009, 2009, 4087–4109.
were corrected for underlying diamagnetism using tabulated Pascal’s
67
constants. Electronic spectra of complexes were recorded on a Cary
3
00 Bio UVꢀvisible spectrophotometer. Perpendicular-mode X-band
EPR spectra were recorded on a Bruker EPP 300 spectrometer equipped
with an Oxford ESR 910 liquid helium cryostat and an Oxford tempera-
ture controller. X-band EPR spectra were simulated using EPR program
(
9) Bullock, R. M., Ed.; Catalysis Without Precious Metals; Wiley-
VCH: Weinheim, Germany, 2010.
10) F €u rstner, A.; Leitner, A.; M ꢀe ndez, M.; Krause, H. J. Am. Chem.
Soc. 2002, 124, 13856–13863.
11) Traylor, T. G.; Hill, K. W.; Fann, W.-P.; Tsuchiya, S.; Dunlap,
B. E. J. Am. Chem. Soc. 1992, 114, 1308–1312.
(
(version W95) written by Professor Frank Neese (University of Bonn,
Germany). Cyclic voltammetry experiments were performed inside a
glovebox with a CHInstruments Model 600D potentiostat/galvanostat.
A single-chamber cell was set up with a glassy carbon working electrode
(
(
(
12) Costas, M.;Que, L., Jr. Angew. Chem., Int. Ed. 2002, 41, 2179–2181.
13) Britovsek, G. J. P.; England, J.; White, A. J. P. Dalton Trans.
(3 mm diameter), a Pt wire as the auxiliary electrode, and a reference
electrode consisting of a silver wire in 10 mM AgNO solution (0.1 M
3
2
006, 1399–1408.
n
[
Bu N]PF6 in CH CN). All measurements were calibrated to an
4 3
(14) Chen, M. S.; White, M. C. Science 2007, 318, 783–787.
internal ferrocene standard. Mass spectrometry (MS) data were acquired
on a Bruker BioTOF ESI-MS under positive mode.
(15) Bianchini, C.; Meli, A.; Peruzzini, M.; Frediani, P.; Bohanna, C.;
Esteruelas, M. A.; Oro, L. A. Organometallics 1992, 11, 138–145.
(16) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 13794–13807.
(17) Daida, E. J.; Peters, J. C. Inorg. Chem. 2004, 43, 7474–7485.
(18) Morris, R. H. Chem. Soc. Rev. 2009, 38, 2282–2291.
6
8,69
70,71
Theoretical Calculations. DFT calculations (BP86,
M-06 L
)
72
were performed with the Gaussian09 program. The all-electron Gaussian
7
3
basis sets used were those reported by the Ahlrichs group. For nickel,
chloride, and phosphorus atoms, the triple-ζ-quality basis sets with one set
of polarization functions was used (def2-TZVP). The carbon, oxygen, and
hydrogen atoms were described by smaller polarized split-valence def2-
SV(P) basis sets.
(19) Bullock, R. M. Angew. Chem., Int. Ed. 2007, 46, 7360–7363.
(20) Hebrard, F.; Kalck, P. Chem. Rev. 2009, 109, 4272–4282.
(21) Gosmini, C.; Moncomble, A. Isr. J. Chem. 2010, 50, 568–576.
(22) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235–244.
(23) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460–462.
24) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
00, 1169–1204.
25) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2010, 111, 1346–1416.
(26) Negishi, E. Bull. Chem. Soc. Jpn. 2007, 80, 233–257.
’
ASSOCIATED CONTENT
(
1
S
Supporting Information. Additional spectroscopic and
b
(
1
theoretical data, including Beer’s Law plots for 1ꢀ3, the H
iPr
NMR spectrum of [( DPDBFphos)ZnCl ] 1, cyclic voltammo-
2
grams of 1ꢀ 4, the xyz file for the geometry optimized structure
(27) Montgomery, J. Angew. Chem., Int. Ed. 2004, 43, 3890–3908.
1
of 4, the H NMR and UVꢀvis spectra of 6. This material is
(28) Castro, P. M.; Lankinen, M. P.; Leskel €a , M.; Repo, T. Macromol.
Chem. Phys. 2005, 206, 1090–1097.
available free of charge via the Internet at http://pubs.acs.org.
9
298
dx.doi.org/10.1021/ic200589e |Inorg. Chem. 2011, 50, 9290–9299

Inorganic Chemistry
ARTICLE
(
29) Kim, H. S.; Bae, J. Y.; Lee, J. S.; Kwon, O.-S.; Jelliarko, P.; Lee,
S. D.; Lee, S.-H. J. Catal. 2005, 232, 80–84.
30) Miyazaki, S.; Koga, Y.; Matsumoto, T.; Matsubara, K. Chem.
Commun. 2010, 46, 1932–1934.
31) Zhang, K.; Conda-Sheridan, M.; Cooke, S. R.; Louie, J.
Organometallics 2011, 30, 2546–2552.
32) Chadwell, S. J.; Coles, S. J.; Edwards, P. G.; Hursthouse, M. B.;
Imran, A. Polyhedron 1995, 14, 1057–1065.
33) The methyl group protons appear as three multiplets with
(57) Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979, 101,
7547–7560.
(58) G ꢀo mez-Benítez, V.; Baldovino-Pantale ꢀo n, O.; Herrera-Alvarez,
C.; Toscano, R. A.; Morales-Morales, D. Tetrahedron Lett. 2006,
47, 5059–5062.
(59) Amatore, C.; Jutand, A. Organometallics 1988, 7, 2203–2214.
(60) Jones, G. D.; McFarland, C.; Anderson, T. J.; Vicic, D. A. Chem.
Commun. 2005, 4211–4213.
(61) Phapale, V. B.; Bu ~n uel, E.; García-Iglesias, M.; C ꢀa rdenas, D. J.
Angew. Chem., Int. Ed. 2007, 46, 8790–8795.
(62) Jones, G. D.; Martin, J. L.; McFarland, C.; Allen, O. R.; Hall,
R. E.; Haley, A. D.; Brandon, R. J.; Konovalova, T.; Desrochers, P. J.;
Pulay, P.; Vicic, D. A. J. Am. Chem. Soc. 2006, 128, 13175–13183.
(63) Hu, X.; Castro-Rodriguez, I.; Olsen, K.; Meyer, K. Organome-
tallics 2004, 23, 755–764.
ꢀ
(
(
(
(
relative integrations of 2:1:1. Upon close inspection, the splitting pattern
of the two smaller signals are pseudo quartets (1:2:2:1), while for the
larger signal, a pseudo quintet is seen. The pseudo quintet is rationalized
as a coincident overlap of two pseudo quartets, which could potentially
give rise to a more complicated 1:4:6:4:1 splitting pattern (see Figure 3,
inset).
(
34) Jolly, P. W.; Jonas, K.; Kr €u ger, C.; Tsay, Y.-H. J. Organomet.
Chem. 1971, 33, 109–122.
35) Aresta, M.; Nobile, C. F.; Albano, V. G.; Forni, E.; Manassero,
M. J. Chem. Soc., Chem. Commun. 1975, 636–637.
36) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2002, 124,
976–9977.
37) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2001, 123,
623–4624.
38) Melenkivitz, R.; Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem.
Soc. 2002, 124, 3846–3847.
39) Ingleson, M. J.; Fullmer, B. C.; Buschhorn, D. T.; Fan, H.; Pink,
M.; Huffman, J. C.; Caulton, K. G. Inorg. Chem. 2007, 47, 407–409.
40) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005,
4, 5901–5908.
41) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416–14424.
(64) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(65) Schubert, E. M. J. Chem. Educ. 1992, 69, 62.
(66) Evans, D. F.; Fazakerley, G. V.; Phillips, R. F. J. Chem. Soc. A
1971, 1931–1934.
(67) Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532–536.
(68) Becke, A. D. Phys. Rev. A 1988, 38, 3098–3100.
(69) Perdew, J. P. Phys. Rev. B 1986, 33, 8822–8824.
(70) Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157–167.
(71) Zhao, Y.; Truhlar, D. G. J. Chem. Phys. 2006, 125, 194101–
194118.
(72) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;
Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;
Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; J. A. Montgomery,
J.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; N.Staroverov, V.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma,
K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian, Inc.:
Wallingford, CT, 2009.
(
(
9
4
(
(
(
(
2
(
(
(
42) Puiu, S. C.; Warren, T. H. Organometallics 2003, 22, 3974–3976.
43) Hu, X.; Castro-Rodriguez, I.; Meyer, K. Chem. Commun.
2
004, 2164–2165.
44) Schaub, T.; Backes, M.; Radius, U. Organometallics 2006,
5, 4196–4206.
45) Schmedake, T. A.; Haaf, M.; Paradise, B. J.; Powell, D.; West, R.
Organometallics 2000, 19, 3263–3265.
46) Kogut, E.; Wiencko, H. L.; Zhang, L.; Cordeau, D. E.; Warren,
T. H. J. Am. Chem. Soc. 2005, 127, 11248–11249.
47) (a) Bai, G.; Stephan, D. W. Angew. Chem., Int. Ed. 2007, 46,
856–1859. (b) Iluc, V. M.; Miller, A. J. M.; Anderson, J. S.; Monreal,
M. J.; Mehn, M. P.; Hillhouse, G. L. J. Am. Chem. Soc. 2011, 133,
3055–13063.
(
2
(
(
(
1
(73) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7,
3297–3305.
1
(
(
48) Rowland, R. S.; Taylor, R. J. Phys. Chem. 1996, 100, 7384–7391.
49) To find short non-bonded contacts, the C-H bonds in both
independent molecules were first normalized to 1.083 Å. For the
distorted molecule B, no short bond contact near the Cl atom was
found below the 2.88 Å benchmark. Unexpectedly, the Cl atom in the
undistorted molecule A had three contacts within 2.88 Å (Supporting
Information, Table 2S). We draw the conclusion that short-bonded
contacts near the chloride atom are not responsible for its asymmetric
position between the two P atoms.
(
50) Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Whittell, G. R. Acta
Crystallogr., Sect. C 2002, 58, m160–m161.
51) Langer, J.; Fischer, R.; G €o rls, H.; Theyssen, N.; Walther, D. Z.
Anorg. Allg. Chem. 2007, 633, 557–562.
52) Eckert, N. A.; Dinescu, A.; Cundari, T. R.; Holland, P. L. Inorg.
Chem. 2005, 44, 7702–7704.
53) (a) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005, 24,
901–5908. (b) Saraev, V. V.; Kraikivskii, P. B.; Svoboda, I.; Kuzakov,
A. S.; Jordan, R. F. J. Phys. Chem. A 2008, 112, 12449–12455.
54) Nilges, M. J.; Barefield, E. K.; Belford, R. L.; Davis, P. H. J. Am.
Chem. Soc. 1977, 99, 755–760.
55) Kahn, O.; Prins, R.; Reedijk, J.; Thompson, J. S. Inorg. Chem.
987, 26, 3557–3561.
56) Tamao, K.; Sumitani, K.; Kumada, M. J. Am. Chem. Soc. 1972,
4, 4374–4376.
(
(
(
5
(
(
1
(
9
9
299
dx.doi.org/10.1021/ic200589e |Inorg. Chem. 2011, 50, 9290–9299