Nickel complexes incorporating an amido phosphine chelate with a pendant amine arm: Synthesis, structure, and catalytic Kumada coupling

Article abstract of DOI:10.1039/c1dt11338k

A series of organonickel(ii) complexes incorporating an amido phosphine ligand tethered with an amino pendant have been prepared and characterized. Deprotonation of N-(dimethylaminoethyl)-2-diphenylphosphinoaniline (H[PNN]) with one equivalent of n-BuLi in ethereal or hydrocarbon solutions at -35°C generates cleanly dimeric {Li[PNN]}₂ as yellow crystals. The reaction of NiCl₂(DME) with {Li[PNN]}₂ in THF at -35°C affords green crystalline [PNN]NiCl. Treating [PNN]NiCl with NaX in acetone solutions gives [PNN]NiX (X = Br, I). Alkylation or arylation of [PNN]NiCl with appropriate Grignard reagents in THF at -35°C produces red crystalline [PNN]NiR (R = Me, Et, i-Bu, n-hexyl, CH₂Ph, Ph). The chloride complex [PNN]NiCl was found to be an active catalyst precursor for Kumada coupling reactions of PhX (X = I, Br, Cl) with aryl or alkyl Grignard reagents, including those containing β-hydrogen atoms. The X-ray structures of {Li[PNN]} ₂ and [PNN]NiX (X = Cl, Br, Me, Et, n-hexyl) are reported.

Full text of DOI:10.1039/c1dt11338k

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PAPER
Nickel complexes incorporating an amido phosphine chelate with a pendant
amine arm: Synthesis, structure, and catalytic Kumada coupling†
Lan-Chang Liang,* Wei-Ying Lee, Yu-Ting Hung, Yi-Chen Hsiao, Liang-Chien Cheng and Wei-Chen Chen
Received 15th July 2011, Accepted 13th October 2011
DOI: 10.1039/c1dt11338k
A series of organonickel(II) complexes incorporating an amido phosphine ligand tethered with an
amino pendant have been prepared and characterized. Deprotonation of N-(dimethyl-
aminoethyl)-2-diphenylphosphinoaniline (H[PNN]) with one equivalent of n-BuLi in ethereal or
hydrocarbon solutions at -35 ◦C generates cleanly dimeric {Li[PNN]}2 as yellow crystals. The reaction
of NiCl2(DME) with {Li[PNN]}2 in THF at -35 ◦C affords green crystalline [PNN]NiCl. Treating
[PNN]NiCl with NaX in acetone solutions gives [PNN]NiX (X = Br, I). Alkylation or arylation of
[PNN]NiCl with appropriate Grignard reagents in THF at -35 ◦C produces red crystalline [PNN]NiR
(R = Me, Et, i-Bu, n-hexyl, CH2Ph, Ph). The chloride complex [PNN]NiCl was found to be an active
catalyst precursor for Kumada coupling reactions of PhX (X = I, Br, Cl) with aryl or alkyl Grignard
reagents, including those containing b-hydrogen atoms. The X-ray structures of {Li[PNN]}2 and
[PNN]NiX (X = Cl, Br, Me, Et, n-hexyl) are reported.
amido phosphine systems,17,20,21 we began to explore the reaction
chemistry of metal complexes containing a potentially hemil-
Introduction
Late transition metal alkyls that are resistant to b-hydrogen
elimination are of interest.1,2 Compounds of this type have
been found to be key intermediates for a number of important
chemical transformations such as catalytic olefin polymerization3–6
and cross-coupling reactions,7–14 etc. The search for appropriate
methods to effectively prohibit or diminish the propensity for
such a frequently observed decomposition pathway is particularly
attractive. We have recently demonstrated that organonickel(II)
abile amino donor that preserves the possibilities of stabilizing
and activating reactive species upon amine coordination and
dissociation, respectively.22–30 To this end, we have set out to
prepare a series of nickel complexes of N-(dimethylaminoethyl)-2-
diphenylphosphinoanilide ([PNN]-), aiming particularly to assess
the synthetic possibilities of organonickel(II) derivatives bearing b-
hydrogen atoms and survey the catalytic activities of [PNN]NiCl
with respect to Kumada coupling reactions.31–33 We describe herein
the preliminary results in these attempts. Scheme 1 summarizes
the synthesis of the [PNN]- derivatives in this study; the nickel
complexes are all square planar, similar to those of PNP15–17 and
other PNN-type34 analogues.
i
complexes of [N(o-C6H4PR2)2]- ([PNP]-; R = Ph, Pr, Cy) are
thermally stable, including those containing b-hydrogen atoms
◦
even at temperatures higher than 80 C.15,16 This unusual phe-
nomenon was found to be a consequence of the fact that [PNP]NiH
exists in higher energy than [PNP]NiCH2CH2X, due to the non-
dissociative nature of both phosphorus donors in [PNP]-, and
thus b-hydrogen elimination in this case is thermodynamically
uphill.17 Consistently, catalytic Kumada coupling of alkyl Grig-
nard reagents bearing b-hydrogen atoms with phenyl halides may
be viable in the presence of [PNP]NiCl as the catalyst precursors.16
Hu et al. have also reported an elegant system on Kumada
coupling catalysis based on a diaminoamido nickel complex18,19
constructed with an o-phenylene backbone similar to [PNP]NiCl.
As a part of our research program in unsymmetrical tridentate
Results and discussion
Synthesis and characterization of {Li[PNN]}2
Treatment of H[PNN]22 with one equivalent of n-BuLi in tetrahy-
drofuran, diethyl ether, or pentane solutions at -35 ◦C generates
1
cleanly the lithium complex of [PNN]- as indicated by the 31P{ H}
1
NMR spectra of the corresponding reaction solutions. The H
NMR spectra of the product isolated from these reactions are
all identical from one to another, suggesting that the lithium
complex does not incorporate any coordinating THF or OEt2.
This phenomenon is interesting as lithium complexes of [PNP]-
adopt either coordinated THF or OEt2.15,16 A THF adduct
was also reported for a lithium complex of an unsymmetrical
amido diphosphine35 whose ligand backbone is similar to that
of [PNN]-. This discrepancy thus underscores particularly the
Department of Chemistry and Center for Nanoscience & Nanotechnology,
National Sun Yat-sen University, Kaohsiung, 80424, Taiwan. E-mail:
lcliang@mail.nsysu.edu.tw
† Electronic supplementary information (ESI) available: X-ray crystallo-
graphic data for {Li[PNN]}2 and [PNN]NiX (X = Cl, Br, Me, Et, n-hexyl).
CCDC reference numbers 834550–834555. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c1dt11338k
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˚
Table 1 Selected bond distances (A) and angles (deg) for {Li[PNN]}2
N(1)–Li(1)
N(2)–Li(1)
N(3)–Li(2)
N(3)–Li(1)
N(4)–Li(2)
P(1)–Li(2)
C(23)–Li(2)
P(1)–Li(1)
1.974(5)
2.061(5)
1.967(5)
2.166(5)
2.037(5)
2.694(4)
2.500(5)
2.884(4)
2.865(4)
2.856(4)
2.644(6)
88.2(2)
P(2)–Li(2)
P(2)–Li(1)
Li(1)–Li(2)
N(1)–Li(1)–N(2)
N(1)–Li(1)–N(3)
N(2)–Li(1)–N(3)
N(3)–Li(2)–N(4)
N(3)–Li(2)–C(23)
N(4)–Li(2)–C(23)
N(3)–Li(2)–P(1)
N(4)–Li(2)–P(1)
C(23)–Li(2)–P(1)
118.8(2)
117.5(2)
92.6(2)
92.7(2)
137.3(2)
118.4(2)
106.0(2)
108.4(2)
rationalized by close contacts for Li(1) with P(1) and P(2), though
˚
P(1)–Li(1) and P(2)–Li(1) distances of 2.884(4) and 2.856(4) A,
respectively, are significantly longer than P(1)–Li(2) of 2.694(4)
˚
A. A similar close contact is also found between P(2) and Li(2)
˚
(2.865(4) A). Though relatively long, these Li–P distances are
somewhat similar to those of Li[N(o-C6H4PPh2)2](THF)2 (2.779(5)
Scheme 1 Synthesis of the [PNN]- derivatives.
15
˚
and 2.824(5) A). Thus, both lithium atoms in {Li[PNN]}2
may alternatively be regarded as five-coordinate. Notably, one
inherent electronic properties between hard nitrogen and soft
phosphorus donors to bind to a hard lithium atom, making
the former complex apparently less electrophilic. Yellow crystals
of this lithium complex suitable for X-ray diffraction analysis
were grown by layering pentane on a concentrated diethyl ether
of the ipso carbons at P(2)-bound phenyl groups is weakly
coordinated to Li(2) (C(23)–Li(2) = 2.500(5) A). This phenomenon
˚
is unprecedented in lithium phosphine chemistry though sim-
ilar close contacts are known for lithium aniline or lithium
anilide complexes such as [Li(OEt2)]2[Zr(NMe2)2(2,4-di-tert-
◦
butyl-6-(tert-butylamido)phenolate)2] (2.406 A),36 Li2[CpCH(tert-
solution at -35 C. An X-ray study showed it to be {Li[PNN]}2
˚
37
(Fig. 1, Table 1), a dimer composed of two Li[PNN] units without
incorporating any coordinating ethereal molecules. At first glance,
this structure is unusual as Li(1) is three-coordinate, surrounded
by three nitrogen atoms in a trigonal pyramidal geometry that
is in principle only accessible for species having a lone electron
pair at the central atom. This abnormal result, however, may be
˚
butyl)N(p-anisyl)] (2.570(4) A), and {[(Me3Si)2CH](C6H4-2-
NMe2)P}Li(THF)2 (2.733(6) A),38 etc. In addition, the two lithium
˚
atoms are evidently bridged by the amido donor N(3) though
˚
the N(3)–Li(2) distance of 1.967(5) A is significantly shorter than
˚
N(3)–Li(1) of 2.166(5) A. Collectively, this dimeric molecule is
thus C1-symmetric in the solid state. In contrast, the solution
NMR data of {Li[PNN]}2 are suggestive of a dimer having C2
symmetry at the low temperature limit (-80 ◦C in toluene-d8)
but a structure having higher symmetry (possibly C2v) at room
temperature, indicating a fluxional exchange process occurring in
1
solution. A variable-temperature H NMR study in toluene-d8
revealed that the two methyl groups in the pendant amine arm
at room temperature are observed as a somewhat broad singlet
resonance that, upon cooling to temperatures lower than -10 ◦C,
resolves to become two singlet signals. A similar phenomenon is
also found for nitrogen bound methylene groups, which show two
signals in the 1H NMR at room temperature but four well-resolved
broad singlet resonances at temperatures lower than -10 ◦C,
a result that is reflective of the diastereotopic nature of these
NCH2 moieties in dimeric {Li[PNN]}2 at low temperature. The
coordination of the phosphorus donor to lithium is confirmed by
◦
1
1
31P{ H} and 7Li{ H} NMR spectra at -80 C wherein a 1 : 1 : 1 : 1
quartet resonance at -18.0 ppm and a doublet at 1.1 ppm (1JPLi
=
34 Hz) are observed, respectively. We propose that the solution
structure of {Li[PNN]}2 at low temperature limit is somewhat
similar to that in the solid state except that the two lithium atoms
Fig. 1 Molecular structure of {Li[PNN]}2 with thermal ellipsoids drawn
at the 35% probability level.
1382 | Dalton Trans., 2012, 41, 1381–1388
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Table 2 Selected NMR spectroscopic dataa
are bridged with two amido nitrogen donors as illustrated in
Scheme 1. The C2 axis coincides approximately with the vector
defined by the connection of central points between two amido
nitrogen donors and two lithium atoms. At room temperature,
phosphine dissociation from the lithium atoms likely takes place
Compound
dHa (3JPH
)
dCa (2JPC
)
dP
H[PNN]b
-19.3
-15.2
28.9
33.5
41.5
39.8
39.9
37.9
40.1
37.2
37.7
{Li[PNN]}2
1
1
and thus both 31P{ H} and 7Li{ H} signals are observed as broad
[PNN]NiCl
[PNN]NiBr
[PNN]NiI
singlet.
[PNN]NiMe
[PNN]NiEt
[PNN]Ni(i-Bu)
[PNN]Ni(n-hexyl)
[PNN]Ni(CH2Ph)
[PNN]NiPh
0.65 (4)
0.15c
-11.6 (35)
-1.3 (33)
17.2 (32)
7.7 (32)
9.8 (30)
161.0 (40)
Synthesis and characterization of nickel complexes of [PNN]-
0.17 (6)
0.07c
Salt metathesis of NiCl2(DME)39 with {Li[PNN]}2 in THF
at -35 ◦C produces cleanly diamagnetic, green crystalline
[PNN]NiCl. Alternatively, [PNN]NiCl may be prepared quan-
titatively by treating a THF solution of NiCl2(DME) with
H[PNN] in the presence of triethylamine at room temperature.
The nickel halide complexes [PNN]NiBr and [PNN]NiI were
also prepared from reactions of [PNN]NiCl with NaBr and
NaI, respectively, in acetone solutions. Subsequent alkylation
or arylation of [PNN]NiCl with appropriate Grignard reagents
in THF at -35 ◦C generates the corresponding diamagnetic
hydrocarbyl complex [PNN]NiR (R = Me, Et, i-Bu, n-hexyl,
CH2Ph, Ph; Scheme 1) as a red crystalline solid in moderate to
high yield. Of particular note are those containing b-hydrogen
atoms. Interestingly, these complexes resist b-hydrogen elimination
even at elevated temperatures. For instance, [PNN]NiEt and
[PNN]Ni(i-Bu) remain intact (70 mM in C6D6) upon heating
1.59 (6)
a Unless otherwise noted, all spectra were recorded in C6D6 at room
temperature, chemical shifts in ppm, coupling constants in Hz. b Data
selected from reference 22. JPH not determined due to the presence of
3JHH arisen from b-hydrogen atoms.
c
3
at 70 ◦C for 20 h as evidenced by 1H and 31P{ H} NMR
1
studies. Similar to the known [PNP]- chemistry,15–17,40–44 the high
thermal stability of [PNN]NiCH2CHRR’ is ascribable to the
coordinative nature of the donor atoms involved in view of
the lack of analogous precedents derived from closely related
[N(SiMe2CH2PR2)2]-,45,46 [o-(2,6-Me2C6H3N)C6H4PPh2]-,47 and
[o-(2,6-iPr2C6H3N)C6H4PPh2]- ligands.47 It should also be noted
that analogous organonickel complexes of [NX(CH2CH2PR2)2]
(X = H, alkyl)48–50 or [(R1 PCH2CH2)NX(CH2CH2NR2 )] (X = H,
Fig. 2 Molecular structure of [PNN]NiCl with thermal ellipsoids drawn
at the 35% probability level.
2
2
alkyl) ligands24,51 constructed with a saturated, ethylene backbone
are not known though their corresponding halide derivatives have
been reported.51–54
Solution NMR data of [PNN]NiX (X = halide, hydrocarbyl) are
all consistent with Cs symmetry for these molecules, indicating that
the [PNN]- ligand is meridionally bound to a square planar nickel
center. The amine nitrogen bound methyl groups are chemically
equivalent in all cases. In general, the 31P chemical shifts of these
nickel complexes are all significantly downfield shifted from their
protio or lithium precursor (Table 2). The coordination of the
phosphorus donor in hydrocarbyl complexes is corroborated by
the observed multiplicity of resonances of a-hydrogen or a-carbon
1
atom in the 1H and 13C{ H} NMR spectra, respectively.
Several nickel complexes of [PNN]- were characterized crys-
tallographically. Fig. 2–6 depict the X-ray structures of these
molecules. Selected bond distances and angles are summarized
in Tables 3 and 4, respectively. Consistent with the solution NMR
studies, these complexes contain a square planar coordination
core with the [PNN]- ligand being meridionally bound. The Ni–
N(amide) distance in [PNN]NiCl is slightly shorter than those in
hydrocarbyl derivatives, in agreement with the anticipated trans
influence order of alkyl > chloride. Notably, the Ni–N distances
are substantially shorter for anionic amide than neutral amine.
Interestingly, though the Ni–X distances in [PNN]NiX (X =
Fig. 3 Molecular structure of [PNN]NiBr with thermal ellipsoids drawn
at the 35% probability level.
Cl, Br, alkyl) are all comparable to the corresponding values in
[PNP]NiX, the Ni–P and Ni–N(amide) lengths in the former
˚
are shorter than those in the latter, e.g., Ni–P = 2.178(1) A
16
˚
and Ni–N = 1.967(8) A in NiMe[N(o-C6H4PPh2)2]. We ascribe
this discrepancy to the incorporation of a more flexible ethylene
backbone in [PNN]-, contrasting to the rigidity enforced by the
two o-phenylene rings in the [PNP]- backbone.40 Consistently, the
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Table 3 Selected bond distances (A) for nickel complexes
Compound
Ni–P
Ni–N1
Ni–N2
Ni–Xa
[PNN]NiCl
[PNN]NiBr
[PNN]NiMe
[PNN]NiEtb
[PNN]Ni(n-hexyl)
2.138(3)
2.134(3)
2.113(1)
2.0996(8)
2.099(1)
1.826(7)
1.885(8)
1.893(5)
1.901(2)
1.892(4)
1.987(7)
2.018(7)
2.005(4)
2.006(2)
2.013(3)
2.164(2)
2.311(2)
1.979(5)
1.960(3)
1.951(5)
a X represents a halide or a-carbon atom. b The data summarized represent
one of the two independent molecules found in the asymmetric unit cell.
precursor for Kumada coupling reactions of Grignard reagents
with halogenated hydrocarbons35,55–61 as what was demonstrated
for nickel complexes of [PNP]-.16 Indeed, we found that both
alkyl and aryl Grignard reagents could be effectively coupled
with phenyl halides in the presence of 1 mol% of [PNN]NiCl
in THF at room temperature (Table 5). Of particular interest
are those involving alkyl building blocks bearing b-hydrogen
atoms, consistent with the thermal stability of these organonickel
complexes. The reaction conversion is nearly quantitative in 12
h for couplings involving phenyl iodide (entries 1–4) or phenyl
bromide (entries 5–8) but only about a half or less for those
employing phenyl chloride (entries 9–10). Attempts to assess the
substituent steric effect with 2- and 4-tolyl Grignard reagents
were not conclusive. Reactions employing n-butyl nucleophile,
however, appear to be more satisfactory than those involving ethyl.
Overall, [PNN]NiCl is comparatively more reactive and more
selective than [PNP]NiCl16 in view of milder reaction temperature,
higher conversion of phenyl halides, and lower yield of undesirable
homo-coupling products for the former. For instance, entries 11–
12 summarize the representative results of Kumada coup◦lings
catalyzed by 1 mol% of NiCl[N(o-C6H4PPh2)2] in THF at 60 C.16
These results highlight the discrepancy of these tridentate amido
phosphine ligands that are incorporated. Complexes [PNN]NiBr
and [PNN]NiI are also active (entries 13–14); their reactivity and
selectivity are virtually identical to those of [PNN]NiCl.
Fig. 4 Molecular structure of [PNN]NiMe with thermal ellipsoids drawn
at the 35% probability level.
Fig. 5 Molecular structure of [PNN]NiEt with thermal ellipsoids drawn
at the 35% probability level. The asymmetric unit cell contains two
independent molecules; only one is presented for clarity.
Mechanistically, the [PNN]NiCl catalyzed Kumada couplings
may proceed via [PNN]NiR intermediates, which in turn react
with PhX to give the cross-coupling products. Attempts to react
[PNN]NiEt with a stoichiometric amount of PhI or PhBr in THF
at room temperature, however, did not lead to [PNN]NiX (X =
1
I, Br; 31P{ H} NMR evidence, Table 2) or ethylbenzene (GC-
MS evidence) unless the reactions were heated to 60 ◦C for a
prolonged period of time (>2 days). Instead, addition of EtMgCl
to a THF solution containing [PNN]NiEt and PhBr at room
temperature gave ethylbenzene successfully. The cross-coupling of
EtMgCl with PhBr may also be satisfactorily achieved in THF at
room temperature in the presence of 1 mol% of [PNN]NiEt, whose
activity and selectivity are similar to what is found for [PNN]NiCl
(entry 7 in Table 5). Similar activity and selectivity were also found
for reactions conducted in the presence of typical radical inhibitors
such as 2,6-di-tert-butyl-4-hydroxytoluene or 2,2,6,6-tetramethyl-
1-piperidinyloxy (1 equivalent to [PNN]NiCl), suggesting that
radicals are unlikely to be involved. In comparison, no reaction
was found for EtMgCl with PhBr in the absence of [PNN]NiCl or
[PNN]NiEt under similar conditions, highlighting the involvement
of [PNN]NiR as a key intermediate in these coupling reactions.
More importantly, the catalysis is likely triggered by “alkylation”
of [PNN]NiR with Grignard reagents. Accordingly, we found
Fig. 6 Molecular structure of [PNN]Ni(n-hexyl) with thermal ellipsoids
drawn at the 35% probability level.
o-phenylene ring in [PNN]- is much less deviated from the mean
coordination plane than those in [PNP]-, e.g., 4.29◦ for [PNN]NiCl
versus 21.07◦ and 24.10◦ for NiCl[N(o-C6H4PPh2)2].16
Kumada coupling catalysis
Reminiscent of nickel hydrocarbyl complexes of [PNP]-,16
[PNN]NiMe shows no reactivity at room temperature with protic
molecules such as benzyl alcohol or piperidine, etc. Instead, it
reacts with dichloromethane cleanly to give [PNN]NiCl. This
result suggests that [PNN]NiCl is likely a potential catalyst
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Table 4 Selected bond angles (deg) for nickel complexes
Compound
P–Ni–N1
N1–Ni–N2
N2–Ni–Xa
P–Ni–Xa
P–Ni–N2
N1–Ni–Xa
[PNN]NiCl
[PNN]NiBr
[PNN]NiMe
[PNN]NiEtb
[PNN]Ni(n-hexyl)
86.2(3)
86.3(2)
86.0(1)
86.28(7)
85.9(1)
85.5(3)
85.7(3)
84.1(2)
84.3(1)
85.0(2)
96.6(2)
96.6(2)
95.8(2)
98.4(1)
97.5(2)
93.2(1)
91.41(8)
94.0(2)
91.24(9)
91.9(1)
164.1(3)
169.0(2)
169.8(2)
167.23(8)
167.6(1)
173.1(3)
177.6(2)
176.3(2)
176.9(1)
176.9(2)
a X represents a halide or a-carbon atom. b The data summarized represent one of the two independent molecules found in the asymmetric unit cell.
Table 5 Catalytic Kumada reactions of Grignard reagents with phenyl halidesa
Yield (%)b
Entry
R
X
Conversion (%)b
R–Ph
Ph–Ph
R–R
1
2
3
4
5
6
7
8
4-tolylc
2-tolyl
Et
n-Bu
4-tolylc
2-tolyl
Et
n-Bu
4-tolylc
2-tolyl
Et
I
I
I
I
Br
Br
Br
Br
Cl
Cl
I
Br
I
I
100
98
100
98
100
100
100
100
48
2
89
97
86
82
84
79
90
63
98
73
87
66
61
59
44
80
75
17
1
21
10
5
1
15
0
0
32
2
0
0
26
39
0
0
27
13
8
9
10
11d
12d
13e
14f
0
41
56
20
25
n-Bu
Et
Et
0
0
0
100
a Reaction conditions: 1.0 equiv of phenyl halide, 1.1 equiv of Grignard reagent, 2 mL THF, 25 ◦C, 12 h. b Determined by GC, based on phenyl halides;
average of two runs. c 4-Tolylmagnesium bromide was used. d 1 mol% NiCl[N(o-C6H4PPh2)2] was employed in the place of [PNN]NiCl, 60 ◦C; data
selected from reference 16 e 1 mol% [PNN]NiBr was employed in the place of [PNN]NiCl. f 1 mol% [PNN]NiI was employed in the place of [PNN]NiCl.
that addition of one equivalent of n-BuMgCl to a THF solution
of [PNN]NiCl than [PNP]NiCl highlight the identity of the
tridentate ligands employed.
of [PNN]NiEt produced cleanly a new species as evidenced by
1
31P{ H} NMR (d 60 ppm). More detailed mechanistic studies are
currently underway.
Experimental section
General procedures
Conclusions
Unless otherwise specified, all experiments were performed under
nitrogen using standard Schlenk or glovebox techniques. All
solvents were reagent grade or better and purified by standard
methods. Compounds H[PNN]22 and NiCl2(DME)39 were pre-
pared according to the literature procedures. All other chemicals
were obtained from commercial vendors and used as received.
The NMR spectra were recorded on Varian Unity or Bruker AV
instruments. Chemical shifts (d) are listed as parts per million
downfield from tetramethylsilane and coupling constants (J) and
In summary, we have prepared and characterized a series of
lithium and nickel(II) complexes of an amido phosphine ligand
tethered with an amino pendant. The lithium complex {Li[PNN]}2
exists as a dimer in the solid state without incorporating any
coordinating solvent molecules. The nickel halide and hydrocarbyl
complexes are all diamagnetic, square planar species with the
[PNN]- ligand being meridionally bound to the nickel center.
Among the organonickel derivatives prepared, alkyl complexes
that contain b-hydrogen atoms are of particular interest in view
of their thermal stability toward b-elimination, even at elevated
temperatures. The chloride complex [PNN]NiCl is an active
catalyst precursor for Kumada coupling reactions of both alkyl
and aryl Grignard reagents with phenyl halides under mild
conditions. Of particular note are those employing alkyls bearing
b-hydrogen atoms. Preliminary mechanistic studies showed that
alkylation of [PNN]NiR intermediates plays an important role in
this cross-coupling catalysis. The higher reactivity and selectivity
1
peak widths at half-height (Dv1/2) are in hertz. H NMR spectra
are referenced using the residual solvent peak at d 7.16 for C6D6
or d 7.24 for CDCl3. 13C NMR spectra are referenced using the
internal solvent peak at d 128.39 for C6D6. The assignment of
the carbon atoms for all new compounds is based on the DEPT
13C NMR spectroscopy. 31P and 7Li NMR spectra are referenced
externally using 85% H3PO4 at d 0 and LiCl in D2O at d 0,
respectively. Routine coupling constants are not listed. All NMR
spectra were recorded at room temperature in specified solvents
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Dalton Trans., 2012, 41, 1381–1388 | 1385
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unless otherwise noted. Elemental analysis was performed on a
Heraeus CHN-O Rapid analyzer. Attempts to obtain satisfactory
analysis data for some complexes were not successful due likely
to solvent contamination. The Kumada coupling reactions were
analyzed on a Varian 450-GC/240-MS instrument equipped with
a Restek MXT-5 column.
passed through a pad of Celite and evaporated to dryness under
reduced pressure to afford the product as a green solid; yield 608
mg (96%). Green crystals suitable for X-ray diffraction analysis
were grown from a concentrated diethyl ether solution at -35 ◦C.
1H NMR (C6D6, 500 MHz) d 8.13 (br s, 4, Ar), 7.05 (br s, 4, Ar),
6.33 (br s, 2, Ar), 2.47(br s, 2, NCH2), 2.18 (br s, 6, NMe2), 1.89 (br
s, 2, NCH2). 31P{ H} NMR (C6D6, 202.3 MHz) d 28.94. 13C{ H}
NMR (C6D6, 125.5 MHz) d 166.40 (d, JCP = 24.5, C), 134.17 (br
s, CH), 131.83 (d, JCP = 49.9, C), 130.91 (s, CH), 129.00 (s, CH),
117.21 (d, JCP = 52.7, C), 113.20 (br s, CH), 111.19 (br s, CH),
64.61 (s, NCH2), 47.37 (s, NMe2), 46.90 (s, NCH2). Anal. Calcd
for C22H24ClN2NiP: C, 59.82; H, 5.48; N, 6.35. Found: C, 61.15;
H, 5.66; N, 6.24.
1
1
X-ray crystallography
Crystallographic data are summarized in Tables S1–S6 (ESI†).
Data were collected on a Bruker-Nonius Kappa CCD diffractome-
ter with graphite monochromated Mo-Ka radiation (l = 0.7107
˚
A). Structures were solved by direct methods and refined by full
matrix least squares procedures against F2 using SHELXL-97.62
All full-weight non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed in calculated positions. CCDC
reference numbers 834550–834555.
General procedures for the synthesis of [PNN]NiR (R = Me, Et,
i-Bu, n-hexyl, CH2Ph, Ph)
The Grignard reagent RMgCl (1 equiv) was added dropwise to a
pre-chilled THF solution containing [PNN]NiCl and 1,4-dioxane
(1 equiv) at -35 ◦C. After being stirred at room temperature for 2
h, the reaction mixture was evaporated to dryness under reduced
pressure, extracted with benzene, and filtered through a pad of
Celite. All volatiles were removed in vacuo to afford the desired
product. The hydrocarbyl complexes are typically brownish red in
color.
Synthesis of {Li[PNN]}2
To a solution of H[PNN] (600 mg, 1.72 mmol) in THF (6 mL) at
-35 ◦C was added n-BuLi (1.08 mL, 1.6 M in hexane, 1.72 mmol).
The reaction mixture was naturally warmed to room temperature
and stirred for 3 h. All volatiles were removed in vacuo. The
red viscous residue was triturated with pentane (10 mL) to yield
a yellow solid. The yellow solid was isolated from the orange
solution, washed with pentane (5 mL ¥ 2), and dried in vacuo;
yield 447.9 mg (74%). Recrystallization of the yellow solid from
a mixture of ether and pentane solution at -35 ◦C gave yellow
Synthesis of [PNN]NiMe
Yield 90%. Layering pentane on a concentrated diethyl ether
1
crystals suitable for X-ray diffraction analysis. H NMR (C6D6,
solution at -35 ◦C afforded red crystals suitable for X-ray
500 MHz) d 7.46 (br s, 6, Ar), 7.41 (dt, 4, Ar), 7.10 (m, 4, Ar),
7.05 (m, 8, Ar), 6.70 (d, 2, Ar), 6.58 (d, 2, Ar), 6.39 (t, 2, Ar), 3.07
(t, 4, CH2), 2.50 (br s, 4, CH2), 1.53 (br s, 12, NMe2). 13C{1H}
NMR (C6D6, 125.5 MHz) d 163.53 (s, C), 137.62 (br s, C), 133.26
(s, CH), 132.64 (s, CH), 129.54 (s, CH), 129.08 (s, CH), 115.76
(s, C), 110.27 (s, CH), 109.86 (s, CH), 47.63 (s, CH2), 44.79 (br
1
diffraction analysis. H NMR (C6D6, 500 MHz) d 7.87 (m, 4,
Ar), 7.25 (tt, 1, Ar), 7.10 (m, 1, Ar), 7.04 (m, 6, Ar), 6.39 (dd, 1,
Ar), 6.35 (td, 1, Ar), 2.79 (t, 2, NCH2), 2.16 (t, 2, NCH2), 1.96 (s,
3
1
6, NMe2), 0.65 (d, 3, JHP = 4.0, NiCH3). 31P{ H} NMR (C6D6,
202.3 MHz) d 39.79. 13C{ H} NMR (C6D6, 125.5 MHz) d 165.37
1
(d, JCP = 25.6, C), 134.27 (d, JCP = 47.3, C), 133.89 (d, JCP = 10.9,
CH), 133.72 (s, CH), 130.23 (d, JCP = 2.6, CH), 128.91(d, JCP = 9.9,
CH), 128.69 (s, CH), 119.77 (d, JCP = 50.0, C), 111.19 (d, JCP = 7.3,
CH), 109.59 (d, JCP = 11.8, CH), 66.83 (s, NCH2), 46.84 (s, NMe2),
45.29 (s, NCH2), -11.56 (d, 2JCP = 34.6, NiCH3). Anal. Calcd for
C23H27N2NiP: C, 65.58; H, 6.47; N, 6.65. Found: C, 66.39; H, 6.13;
N, 6.02.
7
1
1
s, Me). Li{ H} NMR (C6D6, 194 MHz) d 1.78 (br s). 31P{ H}
NMR (C6D6, 202.3 MHz) d -15.20 (br s, Dv1/2 = 72). Anal. Calcd
for C44H48Li2N4P2: C, 74.57; H, 6.83; N, 7.91. Found: C, 74.95; H,
6.93; N, 7.85.
Synthesis of [PNN]NiCl
Method 1: Solid NiCl2(DME) (310 mg, 1.41 mmol) was suspended
in THF (6 mL) and cooled to -35 ◦C. To this was added dropwise
a solution of {Li[PNN]}2 (500 mg, 0.70 mmol) in THF (6 mL)
Synthesis of [PNN]NiEt
◦
at -35 C. Upon addition, the reaction mixture became green in
Yield 99%. Layering pentane on a concentrated diethyl ether
color and the suspended NiCl2(DME) dissolved. The solution was
stirred at room temperature for 2 d. All volatiles were removed in
vacuo. The product was extracted from the resulting residue with
benzene (3 mL ¥ 3). The benzene solution was filtered through a
pad of Celite and evaporated to dryness under reduced pressure to
give the product as a green solid; yield 405 mg (80%). Method 2: To
a suspension of NiCl2(DME) (316 mg, 1.44 mmol) in THF (8 mL)
at room temperature was added a THF solution (7 mL) of H[PNN]
(500 mg, 1.44 mmol) followed by neat NEt3 (218 mg, 2.15 mmol).
After being stirred at room temperature for 1 h, the reaction
mixture was evaporated to dryness under reduced pressure. The
residue was triturated with pentane (2 mL ¥ 2) and the product
was extracted with benzene (15 mL). The benzene solution was
solution at -35 ◦C afforded red crystals suitable for X-ray
1
diffraction analysis. H NMR (C6D6, 500 MHz) d 7.90 (m, 4,
Ar), 7.24 (t, 1, Ar), 7.14 (m, 1, Ar), 7.06 (m, 6, Ar), 6.37 (m, 1, Ar),
6.31 (m, 1, Ar), 2.77 (t, 2, NCH2), 2.22 (t, 2, NCH2), 2.06 (s, 6,
NMe2), 0.79 (t, 3, NiCH2CH3), 0.15 (dq, 2, NiCH2CH3). 31P{ H}
1
NMR (C6D6, 202.3 MHz) d 39.90. 13C{ H} NMR (C6D6, 125.5
1
MHz) d 165.25 (d, JCP = 23.6, C), 139.18 (s, CH), 134.65 (d, JCP
=
10.1, C), 134.06 (d, JCP = 10.9, CH), 133.49 (d, JCP = 30.9, CH),
130.20 (s, CH), 128.84 (d, JCP = 9.9, CH), 120.06 (d, JCP = 49.9,
C), 111.13 (d, JCP = 6.4, CH), 109.56 (d, JCP = 11.8, CH), 66.91 (s,
NCH2), 46.75 (s, NMe2), 45.02 (s, NCH2), 13.57 (s, NiCH2CH3),
-1.27 (d, 2JCP = 32.7, NiCH2CH3). Anal. Calcd for C24H29N2NiP:
C, 66.22; H, 6.72; N, 6.44. Found: C, 66.49; H, 6.80; N, 6.39.
1386 | Dalton Trans., 2012, 41, 1381–1388
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Synthesis of [PNN]Ni(i-Bu)
109.97 (d, JCP = 11.8, CH), 66.70 (s, NCH2), 47.65 (s, NMe2), 45.93
(s, NCH2). Anal. Calcd for (C28H29N2NiP)(C4H8O)0.5(C4H8O2)0.5:
C, 68.21; H, 6.62; N, 4.97. Found: C, 68.26; H, 6.93; N, 5.25. The
amount of THF and 1,4-dioxane incorporated was estimated by
the signal integrals in the 1H NMR spectrum.
Yield 54%. 1H NMR (C6D6, 500 MHz) d 7.91 (m, 4, Ar), 7.24 (tq,
1, Ar), 7.14 (m, 1, Ar), 7.06 (m, 6, Ar), 6.35 (m, 2, Ar), 2.73 (t, 2,
NCH2), 2.25 (t, 2, NCH2), 2.08 (s, 6, NMe2), 1.50 (m, 1, CHMe2),
3
3
0.93 (d, 6, CHMe2), 0.17 (dd, 2, JHP = 5.5, JHH = 7.5, NiCH2).
1
1
31P{ H} NMR (C6D6, 202.3 MHz) d 37.91. 13C{ H} NMR (C6D6,
125.5 MHz) d 165.08 (d, JCP = 22.9, C), 134.60 (s, C), 134.27 (d,
JCP = 10.6, CH), 133.65 (d, JCP = 1.4, CH), 133.24 (d, JCP = 1.8,
CH), 130.27 (d, JCP = 2.3, CH), 128.78 (d, JCP = 10.1, CH), 120.31
(d, JCP = 50.9, C), 111.20 (d, JCP = 7.4, CH), 109.54 (d, JCP = 11.4,
CH), 67.31 (s, NCH2), 47.30 (s, NCH3), 45.14 (d, JCP = 2.3, NCH2),
30.56 (s, CHMe2), 27.54 (s, CHMe2), 17.23 (d, JCP = 32.4, NiCH2).
General procedures for the synthesis of [PNN]NiX (X = Br, I)
Method 1: A THF solution (1 mL) containing [PNN]NiEt (10 mg,
0.023 mmol) and PhX (1 equiv) in a J. Young NMR tube was
immersed into an oil bath at 60 ◦C. The reaction was monitored
1
by 31P{ H} NMR spectroscopy which indicated clean formation
of [PNN]NiX in 4 d. Method 2: This experiment was conducted
under aerobic conditions. Solid NaX (2.6 equiv) was suspended in
distilled acetone and added to a green solution of [PNN]NiCl
in acetone at room temperature. After being stirred at room
temperature for 20 h, the reaction mixture was evaporated to
dryness in vacuo. The residue was extracted with THF and filtered
through a pad of Celite. Solvent was removed in vacuo to yield
[PNN]NiBr as a green solid (95% yield) or [PNN]NiI as a brown
solid (48% yield).
Synthesis of [PNN]Ni(n-hexyl)
1
Yield 55%. H NMR (C6D6, 500 MHz) d 7.90 (m, 4, Ar), 7.24
(t, 1, Ar), 7.14 (m, 1, Ar), 7.07 (m, 6, Ar), 6.36 (m, 2, Ar), 2.78
(t, 2, NCH2), 2.23 (t, 2, NCH2), 2.10 (s, 6, NMe2), 1.23 (m, 6,
NiCH2(CH2)4CH3), 1,11 (m, 2, NiCH2(CH2)4CH3), 0.89 (t, 3,
3JHH = 7, Ni(CH2)5CH3), 0.07 (m, 2, NiCH2(CH2)4CH3). 31P{ H}
1
NMR (C6D6, 202.31 MHz) d 40.06. 13C{ H} NMR (C6D6, 125.70
1
MHz) d 165.40 (d, JCP = 23.38, C), 134.26 (d, JCP = 46.26, C),
134.25 (d, JCP = 10.56, CH), 133.81 (d, JCP = 1.38, CH), 133.50 (d,
JCP = 1.38, CH), 130.41 (d, JCP = 2.26, CH), 129.00 (d, JCP = 9.68,
CH), 120.26 (d, JCP = 50.41, C), 111.31 (d, JCP = 7.42, CH), 109.74
(d, JCP = 11.44, CH), 67.12 (s, NCH2), 46.99 (s, N(CH3)2), 45.23
(d, JCP = 1.89, NCH2), 36.04 (d, JCP = 1.38, NiCH2(CH2)4CH3),
32.85 (s, NiCH2(CH2)4CH3), 29.91 (s, NiCH2(CH2)4CH3), 23.78 (s,
NiCH2(CH2)4CH3), 15.05 (s, Ni(CH2)5CH3), 7.70 (d, JCP = 32.05,
Synthesis of [PNN]NiBr
Green crystals suitable for X-ray diffraction analys◦is were grown
1
from a concentrated diethyl ether solution at -35 C. H NMR
(C6D6, 500 MHz) d 8.08 (m, 4, Ar), 7.13 (td, 1, Ar), 7.04 (m, 6, Ar),
6.93 (td, 1, Ar), 6.33 (t, 2, Ar), 2.49 (t, 2, NCH2), 2.21 (s, 6, NMe2),
1.87 (t, 2, NCH2). 1H NMR (CDCl3, 300 MHz) d 7.90 (dd, 4, Ar),
7.44 (m, 6, Ar), 7.05 (t, 1, Ar), 6.85 (dd, 1, Ar), 6.25 (m, 2, Ar),
2.90 (t, 2, NCH2), 2.72 (s, 6, NMe2), 2.32 (t, 2, NCH2). 31P{ H}
1
NiCH2(CH2)4CH3). Anal. Calcd for (C28H37N2NiP)(C4H8O2)0.25
:
NMR (C6D6, 202.5 MHz) d 33.48. 31P{ H} NMR (CDCl3, 121.5
1
C, 67.84; H, 7.66; N, 5.46. Found: C, 67.75; H, 7.58; N, 5.45. The
amount of 1,4-dioxane incorporated was estimated by the signal
integrals in the 1H NMR spectrum.
1
MHz) d 33.09. 13C{ H} NMR (C6D6, 125.5 MHz) d 165.43 (d,
JCP = 24.7, C), 134.4 (d, JCP = 10.2, CH), 134.11 (s, CH), 134.08 (s,
CH), 131.41 (d, JCP = 53.3, C), 131.04 (d, JCP = 2.8, CH), 128.97
(d, JCP = 10.2, CH), 118.83 (d, JCP = 52.2, C), 114.06 (d, JCP = 6.4,
CH), 111.39 (d, JCP = 12.8, CH), 64.52 (s, CH2), 48.12 (s, NMe2),
47.25 (s, CH2).
Synthesis of [PNN]Ni(CH2Ph)
Yield 85%. 1H NMR (C6D6, 500 MHz) d 7.88 (m, 4, Ar), 7.25 (t,
1, Ar), 7.13 (t, 2, Ar), 6.97–7.08 (m, 9, Ar), 6.92 (t, 1, Ar), 6.36 (m,
2, Ar), 2.65 (t, 2, NCH2), 2.13 (t, 2, NCH2), 1.86 (s, 6, NMe2), 1.59
Synthesis of [PNN]NiI
1
(d, 2, 3JHP = 6.0, NiCH2Ph). 31P{ H} NMR (C6D6, 202.3 MHz) d
1
37.24. 13C{ H} NMR (C6D6, 125.5 MHz) d 165.80 (d, JCP = 23.8,
1H NMR (C6D6, 300 MHz) d 8.08 (m, 4, Ar), 7.14 (m, 1, Ar), 7.02
(m, 6, Ar), 6.85 (td, 1, Ar), 6.32 (t, 2, Ar), 2.58 (t, 2, NCH2), 2.33
(s, 6, NMe2), 1.91 (t, 2, NCH2). H NMR (CDCl3, 300 MHz) d
7.90 (dd, 4, Ar), 7.42 (m, 6, Ar), 7.06 (t, 1, Ar), 6.76 (dd, 1, Ar),
C), 150.79, 134.06 (d, JCP = 10.9, CH), 133.64 (d, JCP = 41.1, CH),
130.45 (s, CH), 129.81 (s, CH), 129.07 (d, JCP = 10.1, CH), 126.55
1
(s, C), 122.86 (s, CH), 111.45 (d, JCP = 7.3, CH), 109.94 (d, JCP
=
11.8, CH), 67.72 (s, NCH2), 47.23 (s, NMe2), 45.26 (s, NCH2),
9.78 (d, 2JCP = 29.9, NiCH2Ph). Anal. Calcd for C29H31N2NiP: C,
70.03; H, 6.29; N, 5.64. Found: C, 70.60; H, 6.29; N, 5.43.
6.28 (m, 2, Ar), 2.98 (t, 2, NCH2), 2.84 (s, 6, NMe2), 2.74 (t, 2,
1
1
NCH2). 31P{ H} NMR (C6D6, 121.5 MHz) d 41.54. 31P{ H} NMR
1
(CDCl3, 121.5 MHz) d 40.77. 13C{ H} NMR (C6D6, 75.5 MHz)
d 164.84 (d, JCP = 22.1, C), 134.16 (d, JCP = 10.2, CH), 134.44 (d,
JCP = 4.6, CH), 132.06 (d, JCP = 52.5, C), 132.00 (s, CH), 131.14
(s, CH), 130.40 (s, CH), 113.03 (br s, CH), 109.86 (d, JCP = 11.1,
CH), 63.92 (s, CH2), 49.21 (s, NMe2), 47.14 (s, CH2).
Synthesis of [PNN]NiPh
Yield 97%. 1H NMR (C6D6, 500 MHz) d 7.62 (dd, 4, Ar), 7.49 (d,
2, Ar), 7.46 (m, 1, Ar), 7.25 (t, 1, Ar), 7.21 (t, 1, Ar), 6.91–7.04 (m,
8, Ar), 6.44 (dd, 1, Ar), 6.34 (t, 1, Ar), 2.87 (t, 2, NCH2), 2.22 (t,
General procedures for catalytic Kumada couplings outlined in
Table 5
1
2, NCH2), 1.82 (s, 6, NMe2). 31P{ H} NMR (C6D6, 202.3 MHz)
1
d 37.67. 13C{ H} NMR (C6D6, 125.5 MHz) d 165.58 (d, JCP
=
25.8, C), 161.00 (d, JCP = 39.9, C), 139.18 (s, CH), 134.09 (s, CH),
133.81 (d, JCP = 10.1, CH), 132.38 (d, JCP = 50.0, C), 130.26 (s,
CH), 129.39 (s, CH), 127.83 (d, JCP = 5.4, CH), 126.30 (s, CH),
122.53 (s, CH), 119.34 (d, JCP = 50.0, C), 111.73 (d, JCP = 8.2, CH),
A vial was charged with phenyl halide (1.0 equiv), Grignard
reagent (1.1 equiv), [PNN]NiX (X = Cl, Br, I; 1.0 mg for each
single experiment), THF (2 mL), and a magnetic stir bar. The
solution was stirred at room temperature for 12 h and quenched
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with deionized water. The products were extracted with diethyl
ether. The diethyl ether solution was separated from the aqueous
layer, driedover MgSO4, and filtered through a short Al2O3 column
prior to GC-MS analysis.
27 D. G. H. Hetterscheid, J. I. van der Vlugt, B. de Bruin and J. N. H.
Reek, Angew. Chem., Int. Ed., 2009, 48, 8178–8181.
28 D. M. Spasyuk, D. Zargarian and A. van der Est, Organometallics,
2009, 28, 6531–6540.
29 D. M. Spasyuk and D. Zargarian, Inorg. Chem., 2010, 49, 6203–
6213.
30 D. M. Spasyuk, S. I. Gorelsky, A. van der Est and D. Zargarian, Inorg.
Chem., 2011, 50, 2661–2674.
Acknowledgements
31 K. Tamao, K. Sumitani and M. Kumada, J. Am. Chem. Soc., 1972, 94,
We thank the National Science Council of Taiwan for financial
support (NSC 99-2113-M-110-003-MY3 and 99-2119-M-110-
002), Prof. Hon Man Lee (NCUE) and Mr. Ting-Shen Kuo
(NTNU) for assistance with X-ray crystallography, and the
National Center for High-performance Computing (NCHC) for
accesses to chemical databases.
4374–4376.
32 R. J. P. Corriu and J. P. Masse, J. Chem. Soc., Chem. Commun., 1972,
144a–144a.
33 J. Terao and N. Kambe, Acc. Chem. Res., 2008, 41, 1545–1554.
34 R. Lindner, B. van den Bosch, M. Lutz, J. N. H. Reek and J. I. van der
Vlugt, Organometallics, 2011, 30, 499–510.
35 K. Sun, L. Wang and Z.-X. Wang, Organometallics, 2008, 27, 5649–
5656.
36 K. J. Blackmore, J. W. Ziller and A. F. Heyduk, Inorg. Chem., 2008, 47,
265–273.
References
37 V. V. Kotov, C. Wang, G. Kehr, R. Fro¨hlich and G. Erker,
Organometallics, 2007, 26, 6258–6262.
38 K. Izod, J. C. Stewart, W. Clegg and R. W. Harrington, Dalton Trans.,
2007, 257–264.
39 H. Masotti, J. C. Wallet, G. Peiffer, F. Petit, A. Mortreux and G. Buono,
J. Organomet. Chem., 1986, 308, 241–252.
1 R. H. Crabtree, The Organometallic Chemistry of the Transition Metals,
5th edn, John Wiley & Sons, Inc., Hoboken, New Jersey, 2009.
2 J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles
and Applications of Organotransition Metal Chemistry, University
Science Books, Mill Valley, 1987.
3 S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000, 100,
1169–1203.
4 G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.,
1999, 38, 429–447.
5 J. C. Jenkins and M. Brookhart, J. Am. Chem. Soc., 2004, 126, 5827–
5842.
40 L.-C. Liang, Coord. Chem. Rev., 2006, 250, 1152–1177.
41 L.-C. Liang, P.-S. Chien and Y.-L. Huang, J. Am. Chem. Soc., 2006,
128, 15562–15563.
42 M.-H. Huang and L.-C. Liang, Organometallics, 2004, 23, 2813–
2816.
43 L.-C. Liang, J.-M. Lin and W.-Y. Lee, Chem. Commun., 2005, 2462–
2464.
44 O. V. Ozerov, in The Chemistry of Pincer Compounds, ed. D. Morales-
Morales and C. M. Jensen, Elsevier, Amsterdam, Editon edn, 2007, pp.
287–309.
6 F. A. Hicks, J. C. Jenkins and M. Brookhart, Organometallics, 2003,
22, 3533–3545.
7 M. R. Netherton and G. C. Fu, Adv. Synth. Catal., 2004, 346, 1525–
1532.
8 J. R. Zhou and G. C. Fu, J. Am. Chem. Soc., 2003, 125, 12527–12530.
9 T.-Y. Luh, M.-K. Leung and K.-T. Wong, Chem. Rev., 2000, 100, 3187–
3204.
10 D. J. Cardenas, Angew. Chem., Int. Ed., 1999, 38, 3018–3020.
11 M. R. Netherton, C. Y. Dai, K. Neuschutz and G. C. Fu, J. Am. Chem.
Soc., 2001, 123, 10099–10100.
12 A. E. Jensen and P. Knochel, J. Org. Chem., 2002, 67, 79–85.
13 J. Terao, H. Watanabe, A. Ikumi, H. Kuniyasu and N. Kambe, J. Am.
Chem. Soc., 2002, 124, 4222–4223.
45 M. D. Fryzuk, P. A. Macneil, S. J. Rettig, A. S. Secco and J. Trotter,
Organometallics, 1982, 1, 918–930.
46 M. D. Fryzuk, Can. J. Chem., 1992, 70, 2839–2845.
47 L.-C. Liang, W.-Y. Lee and C.-C. Yin, Organometallics, 2004, 23, 3538–
3547.
48 A. Choualeb, A. J. Lough and D. G. Gusev, Organometallics, 2007, 26,
3509–3515.
49 Z. E. Clarke, P. T. Maragh, T. P. Dasgupta, D. G. Gusev, A. J. Lough
and K. Abdur-Rashid, Organometallics, 2006, 25, 4113–4117.
50 C. Bianchini, E. Farnetti, M. Graziani, G. Nardin, A. Vacca and F.
Zanobin, J. Am. Chem. Soc., 1990, 112, 9190–9197.
51 D. Walther, T. Do¨hler, K. Heubach, O. Klobes, B. Schweder and H.
Go¨rls, Z. Anorg. Allg. Chem., 1999, 625, 923–932.
52 P. L. Orioli and C. A. ghiardi, J. Chem. Soc. A, 1970, 1511–1516.
53 C. Bianchini, C. Mealli, A. Meli and L. Sacconi, Inorg. Chim. Acta,
1980, 43, 223–228.
54 A. Bianchi, P. Dapporto, G. Fallani, C. A. Ghilardi and L. Sacconi, J.
Chem. Soc., Dalton Trans., 1973, 641–646.
55 R. Jothibasu, K.-W. Huang and H. V. Huynh, Organometallics, 2010,
29, 3746–3752.
14 J. Terao, A. Ikumi, H. Kuniyasu and N. Kambe, J. Am. Chem. Soc.,
2003, 125, 5646–5647.
15 L.-C. Liang, J.-M. Lin and C.-H. Hung, Organometallics, 2003, 22,
3007–3009.
16 L.-C. Liang, P.-S. Chien, J.-M. Lin, M.-H. Huang, Y.-L. Huang and
J.-H. Liao, Organometallics, 2006, 25, 1399–1411.
17 L.-C. Liang, P.-S. Chien and P.-Y. Lee, Organometallics, 2008, 27, 3082–
3093.
18 O. Vechorkin, V. Proust and X. Hu, J. Am. Chem. Soc., 2009, 131,
9756–9766.
19 O. Vechorkin and X. Hu, Angew. Chem., Int. Ed., 2009, 48, 2937–2940.
20 L.-C. Liang, C.-W. Li, P.-Y. Lee, C.-H. Chang and H. M. Lee, Dalton
Trans., 2011, 40, 9004–9011.
56 A. Castonguay, A. L. Beauchamp and D. Zargarian, Organometallics,
2008, 27, 5723–5732.
21 P.-Y. Lee and L.-C. Liang, Inorg. Chem., 2009, 48, 5480–5487.
22 W.-Y. Lee and L.-C. Liang, Dalton Trans., 2005, 1952–1956.
23 W.-Y. Lee and L.-C. Liang, Inorg. Chem., 2008, 47, 3298–3306.
24 A. Choualeb, A. J. Lough and D. G. Gusev, Organometallics, 2007, 26,
5224–5229.
57 K. Zhang, M. Conda-Sheridan, S. R. Cooke and J. Louie,
Organometallics, 2011, 30, 2546–2552.
58 S. Gu and W. Chen, Organometallics, 2009, 28, 909–914.
59 Y. Zhang, G. Song, G. Ma, J. Zhao, C.-L. Pan and X. Li,
Organometallics, 2009, 28, 3233–3238.
25 S. W. Kohl, L. Weiner, L. Schwartsburd, L. Konstantinovski, L. J. W.
Shimon, Y. Ben-David, M. A. Iron and D. Milstein, Science, 2009, 324,
74–77.
60 A. Liu, X. Zhang and W. Chen, Organometallics, 2009, 28, 4868–4871.
61 J. Berding, M. Lutz, A. L. Spek and E. Bouwman, Organometallics,
2009, 28, 1845–1854.
62 G. M. Sheldrick, SHELXTL, Version 5.1, Bruker AXA Inc., Madison,
WI, 1998.
26 C. Gunanathan, Y. Ben-David and D. Milstein, Science, 2007, 317,
790–792.
1388 | Dalton Trans., 2012, 41, 1381–1388
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