Divergent carbonylation reactivity preferences of nickel complexes containing amido pincer ligands: Migratory insertion versus reductive elimination

Article abstract of DOI:10.1021/om201041z

The reactivity of a series of nickel(II) hydride, alkyl, and anilide complexes supported by amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2] (R = Ph (1a), iPr (1c), Cy (1d)) and unsymmetrical [N(o-C6H4PPh2)- (o-C₆H₄PiPr₂)] (1b), with carbon monoxide is described. Exposure of a benzene solution of [1ad]NiH to carbon monoxide under ambient conditions leads to reductive elimination of diarylamine to give quantitatively zerovalent nickel dicarbonyl complexes [H1ad]Ni(CO)₂ (2). Migratory insertion of CO into the Ni-R bonds of [1]NiR in benzene solutions affords Ni(II)-acyl derivatives [1]NiC(O)R (R = Me (3), Et (4), n-hexyl (5), 2-norbornyl (6)). Interestingly, further carbonylation of acyl 3a and 4a generates [RC(O)N(o-C₆H₄PPh ₂₎₂]Ni(CO)₂ (R = Me (7a), Et (8a)) as a result of CN bondforming reductive elimination whereas no reaction occurs for 3bc or 4bc under similar conditions. Carbonylation of the anilide complexes [1]NiNHPh produces carbamoyl [1]Ni[C(O)NHPh] (9) as the final product irrespective of the identity of the phosphorus substituents. The decisive factors on the generation of these divergent carbonylation products are discussed.

Full text of DOI:10.1021/om201041z

Article
pubs.acs.org/Organometallics
Divergent Carbonylation Reactivity Preferences of Nickel Complexes
Containing Amido Pincer Ligands: Migratory Insertion versus
Reductive Elimination
Lan-Chang Liang,* Yu-Ting Hung, Yu-Lun Huang, Pin-Shu Chien, Pei-Ying Lee, and Wei-Chen Chen
Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424,
Taiwan
S
* Supporting Information
ABSTRACT: The reactivity of a series of nickel(II) hydride,
alkyl, and anilide complexes supported by amido diphosphine
ligands, including symmetrical [N(o-C6H4PR2)2]− (R = Ph
(1a), iPr (1c), Cy (1d)) and unsymmetrical [N(o-C6H4PPh2)-
(o-C6H4PiPr2)]− (1b), with carbon monoxide is described.
Exposure of a benzene solution of [1a−d]NiH to carbon
monoxide under ambient conditions leads to reductive
elimination of diarylamine to give quantitatively zerovalent
nickel dicarbonyl complexes [H·1a−d]Ni(CO)2 (2). Migratory insertion of CO into the Ni-R bonds of [1]NiR in benzene
solutions affords Ni(II)-acyl derivatives [1]NiC(O)R (R = Me (3), Et (4), n-hexyl (5), 2-norbornyl (6)). Interestingly, further
carbonylation of acyl 3a and 4a generates [RC(O)N(o-C6H4PPh2)2]Ni(CO)2 (R = Me (7a), Et (8a)) as a result of C−N bond-
forming reductive elimination whereas no reaction occurs for 3b−c or 4b−c under similar conditions. Carbonylation of the
anilide complexes [1]NiNHPh produces carbamoyl [1]Ni[C(O)NHPh] (9) as the final product irrespective of the identity of
the phosphorus substituents. The decisive factors on the generation of these divergent carbonylation products are discussed.
[PNP]− nickel(II) complexes with respect to carbon monoxide.
Fryzuk et al. have previously demonstrated that
hydrocarbylnickel(II) complexes NiX[N(SiMe2CH2PR2)2] (R
= Ph, X = Me, vinyl, allyl, Ph; R = Me, X = Ph) react with CO
to give Ni(CO)2[R2PCH2SiMe2OC(X)NSiMe2CH2PR2]
after a sequence of successive transformations including
migratory insertion, reductive elimination, and N,O-silatropic
rearrangement (Scheme 1).50−52 Note that the formation of the
INTRODUCTION
Migratory insertion of carbon monoxide into a reactive
transition-metal−ligand bond is of fundamental and commer-
cial importance. These reactions are particularly relevant to
■
catalytic olefin hydroformylation,1 olefin/CO copolymeriza-
tion,2−5 Monsanto acetic acid process,6 water-gas shift
reactions,7 and thioester formation in Acetyl coenzyme A
synthase,8−10 etc. Application of CO insertion chemistry has
also proven essential in a variety of multiple-component
reactions for the construction of carbonyl containing molecules
such as amides,11 lactones,12,13 acid anhydrides,14 ketones,15,16
and thiocarbamates,17 etc. In addition to the carbonylation step,
oxidative addition and reductive elimination are often
accompanied in these catalytic transformations. Understanding
the decisive factors that control the efficacy of each of these
elementary steps under carbonylation conditions is thus vital.
We are currently investigating reaction chemistry employing
metal complexes of diarylamido phosphine ligands.18−28
Complexes of this type have recently received increasing
attention.29−46 In particular, a series of hydridonickel(II)
complexes of symmetrical [N(o-C6H4PR2)2]− (R = Ph (1a),
iPr (1c), Cy (1d)) and unsymmetrical [N(o-C6H4PPh2)(o-
C6H4PiPr2)]− (1b) are known to undergo olefin insertion
reactions,47 generating [PNP]− ligated organonickel(II) de-
rivatives that are markedly thermally stable and resistant to β-
elimination even at elevated temperatures.48,49 Given the
widespread applications of carbonylation to synthetic chem-
istry, we are also interested in the reactivity studies of these
Scheme 1
nickel(0) dicarbonyl products in these reactions is independent
of the identity of R or X incorporated. In this contribution, we
show that the carbonylation reactivity of analogous o-phenylene
derived [PNP]− complexes is, in contrast to that of
[N(SiMe2CH2PR2)2]− derivatives, a function of the character-
istics of the phosphorus substituents and the nickel-bound
hydro(carbyl) ligand. Without the incorporation of the N−Si
bonds in [PNP]−, the transformations reported herein thus
prohibit N,O-silatropic rearrangement. The possibilities of CO
Received: October 27, 2011
Published: December 30, 2011
© 2011 American Chemical Society
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insertion and/or CO induced reductive elimination involving
Ni−H, Ni−C, and Ni−N bonds are discussed.
relatively downfield as compared to those of the corresponding
H[1] (δNH ranging from 6.7 to 8.5 ppm; δP ranging from ca.
−13 to −22 ppm).47−49 The coordination of terminal carbonyl
ligands in 2 is confirmed by the observation of a diagnostic
signal at ∼200 ppm with 2JCP of 5 Hz in the 13C NMR and two
C−O stretching bands at ∼2000 and 1930 cm−1 in the infrared
spectra. The formation of the zerovalent nickel dicarbonyl
complexes 2 is obviously a consequence of reductive
elimination of diarylamine from [1]NiH upon carbonylation.
These results are intriguing as the divalent nickel hydride
complexes [1]NiH were readily produced (quantitatively less
than 10 min) by oxidative addition of Ni(COD)2 with
H[1].47,53 We note that [1c]NiH is thermally stable; no
RESULTS AND DISCUSSION
Scheme 2 summarizes the carbonylation of [1]NiX (X = H,
alkyl) under ambient conditions. Treating a benzene solution of
■
Scheme 2
1
decomposition was observed by H or 31P{1H} NMR when a
benzene solution of [1c]NiH (57 mmol) was heated at 100 °C
for 4 days. The N−H bond-forming reductive elimination from
[1]NiH is thus apparently triggered by prior CO coordination
rather than thermal decomposition. This result is ascribable to
an increase in electrophilicity of a metal due to the ligation of a
strong π acid. In comparison, no reductive elimination was
found for [1]NiH upon reactions with relatively weak π
acceptors, such as olefins.47
The solid-state structures of 2b and 2c were established
crystallographically. The molecular structure of 2b is depicted
in Figure 1. As illustrated, the nickel center is surrounded by
two phosphorus donors and two terminal carbonyl ligands with
the geometry being best described as distorted tetrahedral. The
core geometry of 2c (Supporting Information Figure S1)
resembles closely that of 2b. The Ni−P, Ni−C, and C−O
distances and the bond angles about nickel are all typical for a
Ni(0) dicarbonyl diphosphine complex.10,59,60 Selected bond
distances and angles are summarized in Tables 2 and 3.
Unlike the hydride [1]NiH, the alkyl complexes [1]NiR
undergo CO migratory insertion involving the Ni-R bond to
produce the corresponding acyl derivatives [1]NiC(O)R (R =
Me (3), Et (4), n-hexyl (5), 2-norbornyl (6)). In general, these
reactions proceed cleanly to give the insertion products in few
hours under ambient conditions; no N−Csp3 bond-forming
reductive elimination occurs.61 It is likely that the more
[1a−d]NiH47,53 with an atmosphere of carbon monoxide at
room temperature led to the generation of diamagnetic,
colorless or pale yellow crystalline [H·1a−d]Ni(CO)2 (2a−
d) in high isolated yield. No CO insertion product, i.e., formyl
complexes,54−57 was detectable by 1H or 31P{1H} NMR
spectra. Upon carbonylation, the characteristic hydride
resonance of [1]NiH at −18 ppm disappears gradually in the
1H NMR spectra to give instead a new signal at 9−11 ppm with
JHP of ∼10 Hz because of the formation of an N−H bond
(Table 1). The observed NH and 31P chemical shifts of 2 are all
a
Table 1. Selected NMR and IR Spectroscopic Data
compound
δNH
δP
2JPP
δCα
2JPCα
v(CO)
v(CO)
2a
2b
2c
2d
3a
3b
3c
4a
4b
4c
5b
6b
7a
8a
9a
9b
9c
8.61
9.99
16.2
199.4
200.4
201.6
201.9
4.5
4.6
5.0
5.5
1993, 1924
2004, 1948
2000, 1942
1997, 1937
23.7, 13.7
19.3
10.65
10.63
9.8
18.8
c
37.8, 18.3
35.8
192
194
259.7
259.2
18.8
20.5
1621
1618
16.0
c
c
c
c
c
36.9, 17.6
35.6
261.2
259.3
260.8
264.1
197.2
197.9
194.5
195.7
196.1
19.2
20.6
18.8
18.3
4.5
1622
1618
1621
1621
1695
1693
36.9, 17.9
34.8, 18.2
23.4, 22.2
24.7, 23.5
22.3
193
194
c
5.6
2002, 1943
1994, 1927
5.5
6.0
c
c
6.77
6.89
7.19
31.0
1558 (1573)
1572 (1585)
1572
b
b
b
b
b
42.8, 21.1
40.9
222
27.0
27.4
a
Unless otherwise noted, all NMR spectra were recorded in C6D6 at room temperature, chemical shifts in ppm, coupling constants in Hz; all IR
b
c
spectra were recorded in Nujol at room temperature, stretching frequency in cm−1. Data selected from ref 58. Data recorded in THF.
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accompanied by either [1a]NiR or the final product [RC(O)-
N(o-C6H4PPh2)2]Ni(CO)2 (R = Me (7a), Et (8a)) throughout
the reaction. The 31P chemical shifts of 3a (δP 19) and 4a (δP
16) are comparable to those corresponding to the phenyl-
substituted phosphorus atom in 3b and 4b, respectively (Table
1). This phenomenon is reminiscent of the established
organonickel chemistry involving [1a]−, [1b]−, and [1c]−.47
Complexes 7a and 8a are zerovalent nickel dicarbonyls similar
to 2, though the diphosphine ligands in the former are amide
functionalized due to N−Csp2 bond-forming reductive elimi-
nation involving Ni−N and Ni-acyl bonds. This result is
interesting in view of the fact that neither N−Csp3 nor N−Csp2
bond-forming reductive elimination occurs for the hydrocarbyl
complexes [1a]NiR (R = Me, Et, Ph) under similar conditions,
highlighting the higher reactivity of the Ni−acyl bond to
undergo reductive elimination due to increased electrophilicity
induced by the high electronegative acyl oxygen atom. In
contrast to 3a and 4a, no reaction was found for 3b−c or 4b−c
upon carbonylation, even after a prolonged period of time (>4
days). The discrepancy in carbonylation reactivity of 3a and 4a
versus 3b−c and 4b−c thus underscores the phosphorus
substituent effect in the amido pincer ligands [1]− on N−
Csp2(acyl) bond-forming reductive elimination. In general, these
acyl complexes remain intact even at elevated temperatures on
the basis of 31P{1H} NMR studies; for instance, no
decomposition was found when a benzene solution of 4c (46
mM) was heated to 80 °C for 10 days. Though 3a and 4a were
not isolated, their thermal stability is presumably similar to that
of 3b−c and 4b−c. The reductive elimination reactivity found
for 3a and 4a in the presence of carbon monoxide should thus
be initiated by CO coordination to form five-coordinate64
intermediates 3a·CO and 4a·CO, respectively, taking into
account the nondissociative nature of [1]−.47−49 With the
incorporation of more electron-releasing phosphorus-bound
isopropyl substituents in [1b−c]−, the metal center in acyl 3b−
c and 4b−c is less electrophilic, even with the ligation of a
strong π acidic CO, and thus more reluctant to reductive
elimination. Interestingly, the reactivity similarity of [1b]−
complexes to [1c]− instead of [1a]− derivatives upon
carbonylation described herein is notably different from what
was found in the established olefin insertion chemistry, where
the reactivity of [1b]NiH resembles that of [1a]NiH instead of
[1c]NiH.47 On steric grounds, ligands with bulky substituents
should encourage reductive elimination. The fact that [1a]−
complexes rather than sterically more demanding [1b]− and
[1c]− derivatives undergo reductive elimination suggests
electronic factors predominate in these transformations. Note
that with the incorporation of a sterically demanding acyl
ligand, 6b does not undergo reductive elimination in the
presence of CO.
Figure 1. Molecular structure of 2b with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms (except NH) and one
benzene molecule present in the asymmetric unit cell are omitted for
clarity.
Table 2. Selected Bond Distances (Å) for 2b, 2c, and 8a
compound
Ni−P
Ni−C
CO
CO
2b
2.2425(19),
2.248(2)
1.756(10),
1.796(9)
1.139(10),
1.122(9)
a
2c
2.285(3),
2.286(3)
1.800(14),
1.833(17)
1.089(17),
1.104(16)
8a
2.2139(8),
2.2151(8)
1.768(4),
1.768(3)
1.149(3),
1.151(4)
1.210(3)
a
The data summarized represent one of two independent molecules
found in the asymmetric unit cell.
Table 3. Selected Bond Angles (deg) for 2b, 2c, and 8a
compound
P−Ni−P
C−Ni−C
P−Ni−C
Ni−CO
2b
118.41(7)
114.3(4)
106.3(3), 107.2(2),
103.8(3), 107.1(2)
177.2(9),
177.9(7)
a
2c
120.68(13)
110.01(3)
110.2(6)
100.3(4), 110.7(4),
109.3(4), 105.4(4)
177.0(14),
176.0(13)
8a
110.54(14) 105.49(11),
108.57(10),
171.4(3),
178.5(3)
104.17(11),
117.39(9)
a
The data summarized represent one of two independent molecules
found in the asymmetric unit cell.
electron-releasing nature of alkyl ligands makes [1]NiR more
reluctant to reductive elimination than [1]NiH. In contrast, no
reaction was observed for [1]NiPh48,49,53 under similar
conditions unless after a prolonged period of time as evidenced
by 31P{1H} NMR,62 indicating that migratory insertion of CO
into a Ni−Csp2 bond proceeds much slower than that involving
Ni−Csp3.
63 Introduction of carbon monoxide (ca. 5 equiv) to a
benzene solution containing [1]NiH and an excess amount of
olefin (e.g., 5 equiv) also generates cleanly the corresponding
acyl complexes; no N−H bond-forming reductive elimination
product 2 was detectable by 31P{1H} NMR. This result implies
that olefin insertion into the Ni−H bond of [1]NiH proceeds
at a much faster rate than the N−H bond-forming reductive
elimination under carbonylation conditions. We note that 2
does not react with olefins, thus ruling out the possibility of
reversible reductive elimination/oxidative addition involving
[1]NiH and 2, respectively, followed by sequential olefin and
CO insertion. These reactions are particularly relevant to
catalytic olefin/CO copolymerization,2−5 though in the current
study olefins appear not to effectively insert into the Ni-acyl
bond. Interestingly, solution 31P{1H} NMR studies on
carbonylation of [1a]NiR (R = Me, Et) revealed that
[1a]NiC(O)R (3a/4a) is an intermediate that is always
The solution NMR and infrared spectroscopic data of 3−6
are all consistent with a constitution having a nickel-bound acyl
ligand in these molecules. The characteristic acyl carbonyl
carbon resonance is observed in the 13C NMR spectra at ca.
260 ppm, a value that is markedly downfield shifted as
compared to those of the terminal carbonyl ligands in 2. The
2JCP coupling constants of ∼20 Hz observed for 3−6 are
significantly larger than those of tetrahedral 2 but well within
the range expected for square planar organonickel(II)
complexes of [PNP]− ligands.47−49 The infrared spectra of
3−6 show a carbonyl band at ca. 1620 cm−1, diagnostic of an
acyl CO stretching frequency. Reminiscent of the established
[1]NiR,47−49 the amido diphosphine ligands of 3−6 are
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meridionally bound to nickel as evidenced by virtual triplet
resonances observed in the 13C{1H} NMR spectra for the o-
phenylene carbon atoms in [1c]− complexes and somewhat
2
large JPP values of ca. 193 Hz found in the 31P{1H} NMR
spectra for the unsymmetrically substituted phosphorus atoms
in [1b]− derivatives. The two phosphorus atoms in [1a]− and
[1c]− derived acyl complexes are chemically equivalent on the
NMR time scale.
The acyl complexes 3b, 3c, 5b, and 6b were also
characterized by X-ray diffraction analysis. As depicted in
Figures 2−5, these complexes are four-coordinate species with
Figure 5. Molecular structure of 6b with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms and one benzene
molecule present in the asymmetric unit cell are omitted for clarity.
complexes lies perfectly on the square planar coordination
plane. The geometry of the sp2-hybridized carbonyl carbon
atom is trigonal planar. The acyl ligand is oriented such that the
OCα-Cβ plane is roughly orthogonal to the mean
coordination plane, consistent with what is expected from the
steric standpoint. Selected bond distances and angles of these
acyl complexes are summarized in Tables 4 and 5. Though
Figure 2. Molecular structure of 3b with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms and one unbound THF
present in the asymmetric unit cell are omitted for clarity.
Table 4. Selected Bond Distances (Å) for 3b, 3c, 5b, 6b, 9a,
and 9c
compound
Ni−N
Ni−C
Ni−P
CO
3b
3c
1.982(11)
1.891(17) 2.159(4), 2.174(4)
1.184(17)
1.187(3)
1.9522(17)
1.890(2)
1.873(4)
1.886(4)
1.881(4)
1.89(2)
2.1718(6),
2.1772(6)
5b
6b
9a
1.967(3)
1.974(3)
1.934(3)
1.948(18)
2.1685(11),
2.1698(11)
1.211(5)
1.218(5)
1.223(4)
1.25(2)
2.1782(10),
2.1899(10)
2.1627(10),
2.1710(10)
a
9c
2.173(7), 2.200(7)
a
The data summarized represent one of two independent molecules
found in the asymmetric unit cell.
Figure 3. Molecular structure of 3c with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms are omitted for clarity.
these values are all well within the expected ranges, the Ni−C
distances reported herein are shorter by ∼0.05−0.11 Å than
those of their corresponding alkyl precursors,65 reflective of the
intrinsic differences in atomic sizes of sp2- versus sp3-hybridized
carbon atoms. Nevertheless, the acyl ligands exhibit approx-
imately the same trans influence as alkyls as evidenced by the
corresponding Ni−N distances. The Ni−CO angles are
decreased with increased steric sizes of the hydrocarbyl
substituent in the acyl ligands as indicated by a series of
[1b]− derivatives characterized.
Unlike acyl 3a and 4a, both 7a and 8a exhibit two doublet
resonances in the 31P{1H} NMR spectra for the phosphorus
atoms, indicating dissymmetrization of this diphosphine ligand
upon N−Csp2(acyl) bond-forming reductive elimination. In 8a,
the methylene protons in the amide group −NC(O)Et are
diastereotopic as indicated by two multiplet resonances
Figure 4. Molecular structure of 5b with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms and one benzene
molecule present in the asymmetric unit cell are omitted for clarity.
1
observed at 2.29 and 2.16 ppm in the H NMR spectrum.
Note that the two phosphorus atoms in 2a are chemically
equivalent on the NMR time scale. The lower symmetry
observed for 7a and 8a than for 2a is apparently a consequence
of larger N-substituents in the diphosphine ligands derived. The
the amido diphosphine ligands being meridionally bound to the
nickel center, consistent with the solution structure determined
by NMR studies. In general, the nickel atom in these acyl
2
low JPP values of ca. 6 Hz found for 7a and 8a are consistent
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Table 5. Selected Bond Angles (deg) for 3b, 3c, 5b, 6b, 9a, and 9c
compound
N−Ni−P
P−Ni−P
P−Ni−C
N−Ni−C
Ni−CO
3b
3c
5b
6b
9a
85.2(4), 86.1(3)
171.29(18)
167.61(2)
168.97(5)
167.98(4)
163.74(4)
165.7(3)
93.1(4), 95.7(4)
177.1(6)
126.4(13)
122.8(2)
123.1(4)
120.7(3)
124.4(3)
120.5(17)
85.17(5), 85.92(5)
85.28(10), 85.24(10)
83.55(9), 84.53(9)
82.90(9), 86.28(9)
85.1(6), 85.1(6)
94.24(7), 94.87(7)
93.90(12), 95.58(12)
94.46(11), 97.39(11)
95.77(12), 95.50(12)
92.7(7), 95.6(7)
178.48(9)
179.18(15)
177.08(15)
177.31(15)
172.3(9)
a
9c
a
The data summarized represent one of two independent molecules found in the asymmetric unit cell.
with two cis-disposed phosphorus atoms in these molecules. In
the 13C NMR spectra of 7a and 8a, the terminal carbonyl
carbon resonance is observed at 197 ppm whereas the amide
carbonyl is at 202 ppm. The infrared spectra of 7a and 8a show
CO stretching bands at ca. 2000 and 1930 cm−1 for the terminal
ligands and ca. 1693 cm−1 for the amide group. It is interesting
to note that the single 13C NMR signal found for the terminal
carbonyl carbon atoms in 2a−d, 7a, and 8a implies presumably
rapid inversion at the pyramidal diarylamino nitrogen, which is
somewhat unusual particularly for 7a and 8a that carry a
relatively large N-substituent.
Scheme 3
terminal Ni−N bond in [1]NiNHPh is involved in these
reactions, indicating that a nickel-amide bond is indeed reactive
toward CO insertion but the lack of reactivity of that involving
[1]− is a consequence of chelate effect. In contrast to the acyl
3a and 4a, the carbamoyl complexes 9 do not undergo N−Csp2
bond-forming reductive elimination in the presence of CO. The
discrepancy in reactivity of 9a versus 3a and 4a is ascribed to
lower electrophilicity of the former due to the participation of a
nitrogen lone electron pair in carbamoyl −C(O)N− π
resonance. These carbamoyl complexes are thermally stable;
neither decarbonylation nor β-elimination was observed even at
elevated temperatures. For instance, [1c]Ni[C(O)NHPh] (40
mM in benzene) remains intact upon heating to 110 °C for 4
days as evidenced by 31P{1H} NMR spectroscopy.
Figure 6 depicts the X-ray structure of 8a. Similar to 2b and
2c derived from reductive elimination, 8a contains a
The NMR and infrared spectroscopic data of 9a−c are all
consistent with the formation of a carbamoyl ligand in these
molecules. Upon carbonylation, the characteristic NH reso-
nance of [1]NiNHPh at ca. −1.2 ppm moves downfield to ca.
7.0 ppm in the 1H NMR spectra. The carbonyl carbon
resonance is observed in the 13C NMR spectra at ∼196 ppm, a
value that is significantly upfield shifted as compared to those of
the acyl 3−6. The CO stretching frequencies of 9, as
determined by IR spectroscopy at ∼1570 cm−1, are lower than
those of 3−6, consistent with the occurrence of π resonance in
carbamoyl −C(O)N− moiety of the former complexes.
Compounds 9a and 9c were also characterized crystallo-
graphically. As illustrated in Figure 7, 9a contains a nickel-
bound carbamoyl ligand. The Ni−P, Ni−N, and Ni−Csp2
distances (Table 4) and the bond angles about nickel (Table
5) are all typical for a square planar nickel(II) derivatives.
Notably, the Ni−N distance of 9a is comparable to those of
[1]NiR and [1]NiC(O)R, indicating that the trans influence of
the carbamoyl ligand is nearly identical to those of alkyls and
acyls. The core geometry of 9c (Supporting Information Figure
S2) is similar to that of 9a, though 9c crystallizes as a dimer
linked with hydrogen bonds between carbamoyl groups
(Supporting Information Figure S3).
Figure 6. Molecular structure of 8a with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms and one benzene
molecule present in the asymmetric unit cell are omitted for clarity.
tetrahedral, zerovalent nickel core supported by two
phosphorus donors and two carbonyl ligands. The mono-
anionic [1a]− ligand in the precursor complex 4a has
transformed upon carbonylation to become a neutral
diphosphine chelate functionalized with one amide group. As
expected, the C−O distances in terminal carbonyls are shorter
than that in the amide group (Table 2). The amide −C(O)N−
group is nearly coplanar. The Ni−C1−O1 angle of 171.4(3)°
(Table 3) is markedly deviated from the ideal linearity due to
steric repulsion arisen from the amide group.
In principle, compounds 7a and 8a may be alternatively
produced by CO insertion into the Ni−N bond of [1a]NiR
followed by Csp2−Csp3 bond-forming reductive elimination.
Though this is not the case found in this study, we are
interested to evaluate the possibilities of CO insertion into a
nickel-amide bond. In this regard, the carbonylation reactivity
of [1]NiNHPh58,66 that contains an unsupported Ni−N bond
was examined. Though not unprecedented, CO insertion into a
late-transition-metal−amide bond is uncommon.67,68 Exposure
of a benzene solution of [1a−c]NiNHPh to an atmosphere of
CO at room temperature results in the formation of the
corresponding carbamoyl complexes [1a−c]Ni[C(O)NHPh]
(9a−c) in high isolated yield (Scheme 3). Notably, only the
CONCLUSIONS
■
We have demonstrated that the product constitution of
carbonylation of [PNP]NiX (X = hydride, alkyl, and amide)
is governed by the characteristics of the phosphorus
substituents and the identity of the nickel-bound X ligands.
These results are notably different from those derived from
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Article
and 9c were of poor quality but sufficient to establish the identity of
these molecules.
Synthesis of [1b]NiMe. To a THF solution (3 mL) of [1b]NiCl
(165 mg, 0.29 mmol) at −35 °C was added MeMgCl (0.1 mL, 3 M in
THF, 0.3 mmol) dropwise. The reaction solution was stirred at room
temperature for 2 h and evaporated to dryness in vacuo. The solid
residue thus obtained was triturated with pentane (2 mL × 2) and
benzene (6 mL) was added. The benzene solution was filtered through
a pad of Celite, which was further washed with benzene until the
washings became colorless. The combined filtrate was evaporated to
dryness in vacuo to afford the product as a red solid. Red crystals
suitable for X-ray diffraction analysis were grown by layering diethyl
ether on a concentrated THF solution at −35 °C; yield 130 mg (82%).
The X-ray structure is depicted in Supporting Information Figure S4.
1H NMR (C6D6, 500 MHz) δ 7.82 (dd, 1, Ar), 7.75 (m, 4, Ar), 7.12
(dt, 1, Ar), 7.07 (dt, 1, Ar), 7.03 (m, 7, Ar), 7.00 (q, 2, Ar), 6.52 (t, 1,
Ar), 6.41 (t, 1, Ar), 2.10 (m, 2, CHMe2), 1.22 (dd, 6, CHMe2), 1.06
(dd, 6, CHMe2), −0.09 (dd, 3, J = 8.5 and 9.5, NiMe). 31P{1H} NMR
Figure 7. Molecular structure of 9a with thermal ellipsoids drawn at
the 35% probability level. All hydrogen atoms (except NH) and one
unbound THF present in the asymmetric unit cell are omitted for
clarity.
2
2
(C6D6, 202 MHz) δ 37.73 (d, JPP = 282.2, PiPr2), 27.05 (d, JPP
=
=
282.2, PPh2). 13C{1H} NMR (C6D6, 125.7 MHz) δ 163.41 (dd, JCP
analogous [N(SiMe2CH2PR2)2]− complexes.50−52 In the
presence of carbon monoxide, the hydride complexes [1]NiH
undergo exclusively N−H bond-forming reductive elimination
to generate zerovalent nickel dicarbonyl 2 whereas the anilide
[1]NiNHPh prefer migratory insertion to give nickel(II)
carbamoyl derivatives 9. Interestingly, though all alkyl
complexes [1a−c]NiR react with CO to produce acyl [1a−
c]NiC(O)R, it is the phenyl substituted [1a]− derivatives that
undergo subsequent N−Csp2 bond-forming reductive elimi-
nation to afford 7 and 8, where the nickel-bound diphosphine
ligands are amide functionalized. These reactivity preferences
are clearly a function of the electrophilicity of the metal center
involved. These results are particularly relevant to the synthesis
of carbonyl containing organic molecules via successive
oxidative addition, CO migratory insertion, and reductive
elimination.
21.0 and 4.0, C), 163.18 (dd, JCP = 25.1 and 3.3, C), 134.85 (s, CH),
134.04 (d, JCP = 11.4, CH), 132.89 (dd, JCP = 40.8 and 1.4, C), 132.52
(s, CH), 132.30 (d, JCP = 1.4, CH), 131.59 (d, JCP = 1.8, CH), 130.36
(d, JCP = 2.4, CH), 129.19 (d, JCP = 9.7, CH), 125.19 (d, JCP = 45.7,
C), 122.23 (d, JCP = 36.5, C), 116.75 (d, JCP = 16.1, CH), 116.74 (s,
CH), 116.34 (d, JCP = 5.5, CH), 115.71 (d, JCP = 10.9, CH), 24.27 (dd,
JCP = 21.6 and 1.9, CHMe2), 19.32 (d, JCP = 5.0, CHMe2), 18.30 (s,
CHMe2), −20.45 (dd, JCP = 23.34 and 23.85, NiMe). Anal. Calcd. for
C31H35NNiP2: C, 68.65; H, 6.51; N, 2.58. Found: C, 68.27; H, 6.28;
N, 2.74.
General Procedures for the Carbonylation of [1]NiX (X = H,
Me, Et, n-hexyl, 2-norbornyl, NHPh). In a Teflon-capped reaction
vessel (100 mL), a solution of [1]NiX (typically 0.2−0.5 mmol) in
benzene (5 mL) was degassed with freeze−pump−thaw cycles (three
times) and CO (1 atm) was introduced at room temperature. The
reaction solution was stirred at room temperature for 4−24 h and
evaporated to dryness under reduced pressure. The solid residue thus
obtained was triturated with pentane (2 mL × 2) and dried in vacuo.
Synthesis of [H·1a]Ni(CO)2 (2a). Isolated as a colorless crystalline
1
EXPERIMENTAL SECTION
solid; yield 94%. H NMR (C6D6, 500 MHz) δ 8.61 (t, 1, JHP = 7.0,
■
NH), 7.53 (m, 8, Ar), 7.07 (m, 2, Ar), 6.98 (m, 12, Ar), 6.92 (td, 2,
General Procedures. 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. The NMR spectra were recorded on Varian Unity
or Bruker AV instruments. Chemical shifts (δ) are listed as parts per
million downfield from tetramethylsilane. Coupling constants (J) are
listed in hertz. 1H NMR spectra are referenced using the residual
solvent peak at δ 7.16 for C6D6. 13C NMR spectra are referenced using
the internal solvent peak at δ 128.39 for C6D6. The assignment of the
carbon atoms for all new compounds is based on the DEPT 13C NMR
spectroscopy. 31P NMR spectra are referenced externally using 85%
H3PO4 at δ 0. Routine coupling constants are not listed. All NMR
spectra were recorded at room temperature in specified solvents unless
otherwise noted. The infrared spectra were recorded in Nujol mulls or
THF solutions between KBr plates on Varian 640-IR FT-IR
spectrometer. Elemental analysis was performed on a Heraeus
CHN-O Rapid analyzer.
Ar), 6.82 (td, 2, Ar), 6.56 (t, 2, Ar). 31P{1H} NMR (C6D6, 202 MHz)
2
δ 16.16. 13C{1H} NMR (C6D6, 125.7 MHz) δ 199.43 (t, JCP = 4.5,
NiCO), 149.98 (m, C), 136.77 (m, C), 134.26 (s, CH), 133.96 (m,
CH), 131.04 (s, CH), 129.80 (s, CH), 128.90 (m, CH), 126.43 (m,
C), 123.93 (t, JCP = 2.4, CH), 123.46 (t, JCP = 2.3, CH). Anal. Calcd
for C38H29NNiO2P2: C, 69.95; H, 4.48; N, 2.15. Found: C, 69.80; H,
4.60; N, 2.04.
Synthesis of [H·1b]Ni(CO)2 (2b). Isolated as pale yellow crystals
suitable for X-ray diffraction analysis by slow evaporation of a
1
concentrated benzene solution at room temperature; yield 70%. H
NMR (C6D6, 500 MHz) δ 9.99 (vt, 1, JHP = 9.8, NH), 7.60 (dd, 4, Ar),
7.26 (m, 2, Ar), 7.02 (m, 10, Ar), 6.80 (dd, 1, Ar), 6.65 (dd, 1, Ar),
2.02 (m, 2, CHMe2), 1.05 (dd, 6, CHMe2), 0.81 (dd, 6, CHMe2).
31P{1H} NMR (C6D6, 202 MHz) δ 23.67 (s, PiPr2), 13.65 (s, PPh2).
2
13C{1H} NMR (C6D6, 125.7 MHz) δ 200.38 (vt, JCP = 4.6, NiCO),
151.19 (d, JCP = 11.4, C), 150.66 (d, JCP = 13.2, C), 137.13 (dd, JCP
=
Materials. Compounds [1a−d]NiH,47,53 [1a]NiMe,48,49 [1c]-
NiMe,49 [1a−c]NiEt,47,49 [1b]Ni(n-hexyl),47 [1b]Ni(2-norbornyl),47
[1b]NiCl,58 and 9b58 were prepared according to the procedures
reported previously. All other chemicals were obtained from
commercial vendors and used as received.
X-ray Crystallography. Supporting Information Table S1
summarizes the crystallographic data for all structurally characterized
compounds. Data were collected on a Bruker-Nonius Kappa CCD
diffractometer with graphite monochromated Mo−Kα radiation (λ =
0.7107 Å). Structures were solved by direct methods and refined by
full matrix least-squares procedures against F2 using SHELXL-97.69 All
full-weight non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were placed in calculated positions. The crystals of 2c, 8a,
33.8 and 4.5, C), 134.46 (s, CH), 133.87 (d, JCP = 13.3, CH), 132.59
(s, CH), 131.41 (s, CH), 130.44 (s, CH), 129.76 (s, CH), 128.92 (s,
CH), 128.88 (d, JCP = 3.8, CH), 123.30 (d, JCP = 30.6, C), 123.25 (d,
JCP = 2.8, CH), 122.43 (dd, JCP = 55.4 and 4.6, CH), 121.43 (d, JCP
=
21.0, C), 120.45 (d, JCP = 3.3, CH), 26.82 (dd, JCP = 18.2 and 4.0,
CHMe2), 18.92 (d, JCP = 7.3, CHMe2), 18.41 (d, JCP = 2.3, CHMe2).
Anal. Calcd for C32H33NNiO2P2: C, 65.77; H, 5.69; N, 2.40. Found: C,
65.53; H, 5.30; N, 2.24.
Synthesis of [H·1c]Ni(CO)2 (2c). Isolated as pale yellow crystals
suitable for X-ray diffraction analysis by slow evaporation of a
concentrated benzene/THF solution at room temperature; yield 97%.
1H NMR (C6D6, 500 MHz) δ 10.65 (t, 1, JHP = 11.5, NH), 7.29 (dd, 2,
Ar), 7.14 (ddd, 2, Ar), 7.10 (t, 2, Ar), 6.84 (t, 2, Ar), 2.12 (m, 4,
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CHMe2), 1.05 (dd, 12, CHMe2), 0.93 (dd, 12, CHMe2). 31P{1H}
NMR (C6D6, 202 MHz) δ 19.25. 13C{1H} NMR (C6D6, 125.7 MHz)
δ 201.65 (t, JCP = 5.0, NiCO), 150.86 (t, JCP = 5.0, C), 132.81 (s,
(br m, 2, PCHMe2), 2.05 (br m, 2, PCHMe2), 1.23 (dd, 12, PCHMe2),
1.09 (m, 9, CH2Me and PCHMe2), 0.99 (br m, 6, PCHMe2). 31P{1H}
NMR (C6D6, 202 MHz) δ 35.56. 13C{1H} NMR (C6D6, 125.7 MHz)
δ 259.26 (t, JCP = 20.6, NiC(O)), 163.00 (t, JCP = 11.7, C), 132.63 (s,
CH), 131.88 (s, CH), 120.04 (t, JCP = 19.9, CH), 116.04 (t, JCP = 3.5,
CH), 115.89 (t, JCP = 4.9, C), 51.29 (t, JCP = 4.8, CH2), 23.26 (br m,
PCHMe2), 18.90 (s, Me), 18.00 (s, Me), 17.53 (s, Me), 17.28 (s, Me),
8.16 (s, Me). Anal. Calcd for C27H41NNiOP2: C, 62.80; H, 8.01; N,
2.71. Found: C, 62.73; H, 7.86; N, 2.65.
2
CH), 130.73 (s, CH), 121.10 (t, JCP = 1.4, CH), 119.54 (t, JCP = 1.8,
CH), 117.32 (dt, JCP = 19.2, C), 26.84 (dd, CHMe2), 18.96 (t, JCP
=
5.4, CHMe2), 17.74 (s, CHMe2). Anal. Calcd for C26H37NNiO2P2: C,
60.47; H, 7.23; N, 2.71. Found: C, 60.48; H, 6.96; N, 2.66.
Synthesis of [H·1d]Ni(CO)2 (2d). Isolated as a pale yellow
crystalline solid; yield 89%. 1H NMR (C6D6, 500 MHz) δ 10.63 (t, 1,
JHP = 12.0, NH), 7.36 (d, 2, Ar), 7.35 (d, 2, Ar), 7.13 (t, 2, Ar), 6.89 (t,
2, Ar), 2.13 (m, 4, Cy), 1.93 (d, 4, Cy), 1.73 (d, 4, Cy), 1.63 (d, 8, Cy),
1.45 (m, 12, Cy), 1.19 (m, 8, Cy), 1.03 (m, 4, Cy). 31P{1H} NMR
(C6D6, 202 MHz) δ 9.77. 13C{1H} NMR (C6D6, 125.7 MHz) δ 201.86
(t, 2JCP = 5.5, NiCO), 151.11 (m, C), 132.64 (s, CH), 130.66 (s, CH),
121.14 (s, CH), 119.85 (s, CH), 117.81 (m, C), 36.86 (m, PCH),
29.04 (t, JCP = 3.1, CH2), 27.87 (m, CH2), 27.65 (s, CH2), 27.59 (m,
CH2), 26.84 (s, CH2). Anal. Calcd for C38H53NNiO2P2: C, 67.45; H,
7.90; N, 2.07. Found: C, 67.50; H, 7.94; N, 1.86.
Synthesis of [1b]NiC(O)hexyl (5b). Isolated as yellow crystals
suitable for X-ray diffraction analysis by slow evaporation from a
1
concentrated benzene solution at room temperature; yield 96%. H
NMR (C6D6, 500 MHz) δ 7.85 (br s, 4, Ar), 7.75 (dd, 1, Ar), 7.59 (dd,
1, Ar), 7.11 (t, 1, Ar), 7.02 (m, 7, Ar), 6.94 (t, 2, Ar), 6.48 (t, 1, Ar),
6.45 (t, 1, Ar), 2.64 (t, 2, NiC(O)CH2(CH2)4Me), 2.13 (m, 2,
CHMe2), 1.28 (m, 8, CHMe2 and NiC(O)CH2(CH2)4Me), 1.16 (m,
2, NiC(O)CH2(CH2)4Me), 1.10 (m, 8, CHMe2 and NiC(O)-
CH2(CH2)4Me), 0.96 (m, 2, NiC(O)CH2(CH2)4Me), 0.83 (t, 3,
NiC(O)CH2(CH2)4Me). 31P{1H} NMR (C6D6, 202 MHz) δ 36.89 (d,
Synthesis of [1b]NiC(O)Me (3b). Isolated as yellow crystals
2
suitable for X-ray diffraction analysis by layering diethyl ether on a
2JPP = 193.4, PiPr2), 17.86 (d, JPP = 193.4, PPh2). 13C{1H} NMR
1
(C6D6, 125.7 MHz) δ 260.81 (vt, 2JCP = 18.8, NiC(O)), 162.48 (vt, JCP
= 3.9, C), 162.31 (d, JCP = 3.6, C), 134.86 (s, CH), 134.08 (s, C),
134.04 (s, C), 132.65 (d, JCP = 1.9, CH), 132.61 (s, CH), 131.93 (d,
JCP = 1.9, CH), 130.56 (s, CH), 129.24 (d, JCP = 10.0, CH), 128.92 (s,
CH), 124.12 (d, JCP = 48.9, C), 120.08 (d, JCP = 39.8, C), 116.62 (d,
JCP = 6.9, CH), 116.42 (d, JCP = 9.1, CH), 116.29 (d, JCP = 5.9, CH),
115.78 (d, JCP = 10.0, CH), 55.50 (t, JCP = 5.7, NiC(O)CH2), 32.33 (s,
CH2), 29.91 (s, CH2), 24.30 (s, CH2), 23.76 (d, JCP = 20.0, CHMe2),
23.30 (s, CH2), 18.92 (d, JCP = 7.2, CHMe2), 17.39 (s, CHMe2), 14.66
(s, NiC(O)CH2(CH2)4Me). Anal. Calcd for C37H45NNiOP2: C, 69.38;
H, 7.09; N, 2.19. Found: C, 69.37; H, 7.05; N, 1.96.
concentrated THF solution at −35 °C; yield 92%. H NMR (C6D6,
500 MHz) δ 7.84 (br m, 4, Ar), 7.77 (dd, 1, Ar), 7.62 (dd, 1, Ar), 7.12
(dt, 1, Ar), 7.01 (m, 7, Ar), 6.96 (dt, 1, Ar), 6.93 (dt, 1, Ar), 6.49 (tt, 1,
Ar), 6.44 (tt, 1, Ar), 2.07 (m, 2, CHMe2), 2.06 (s, 3, NiC(O)Me), 1.23
(dd, 6, CHMe2), 1.05 (dd, 6, CHMe2). 31P{1H} NMR (C6D6, 202
2
2
MHz) δ 37.84 (d, JPP = 192.4, PiPr2), 18.25 (d, JPP = 192.4, PPh2).
13C{1H} NMR (C6D6, 125.7 MHz) δ 259.69 (vt, JCP = 18.8, NiC(O)),
162.51 (d, JCP = 4.3, C), 162.34 (vt, JCP = 3.6, C), 134.89 (s, CH),
134.07 (d, JCP = 11.5, CH), 132.65 (d, JCP = 12.4, CH), 132.58 (s,
CH), 131.95 (d, JCP = 1.9, CH), 130.61 (s, CH), 129.25 (d, JCP = 9.8,
CH), 128.92 (s, C), 123.78 (d, JCP = 48.7, C), 120.03 (d, JCP = 39.7,
C), 116.68 (d, JCP = 7.3, CH), 116.61 (d, JCP = 9.8, CH), 116.42 (d,
JCP = 6.1, CH), 115.67 (d, JCP = 10.4, CH), 40.49 (t, JCP = 6.2,
NiC(O)Me), 23.60 (br d, JCP = 25.0, CHMe2), 18.88 (br s, CHMe2),
17.40 (s, CHMe2). Anal. Calcd for C32H35NNiOP2: C, 67.38; H, 6.19;
N, 2.46. Found: C, 67.08; H, 6.43; N, 2.31.
Synthesis of [1b]NiC(O)(2-norbornyl) (6b). Isolated as reddish
brown crystals suitable for X-ray diffraction analysis by layering
benzene on a concentrated THF solution at room temperature; yield
1
81%. H NMR (C6D6, 500 MHz) δ 7.89 (br s, 2, Ar), 7.77 (br s, 2,
Ar), 7.70 (dd, 1, Ar), 7.56 (dd, 1, Ar), 7.06 (m, 2, Ar), 6.99 (m, 7, Ar),
6.89 (t, 1, Ar), 6.45 (q, 2, Ar), 2.14 (m, 2, CHMe2), 2.01 (s, 1,
norbornyl), 1.71 (s, 1, norbornyl), 1.31−1.44 (m, 8, norbornyl and
CHMe2), 1.11−1.16 (m, 8, norbornyl and CHMe2), 1.01 (m, 2,
norbornyl), 0.87 (m, 2, norbornyl), 0.80 (d, 1, norbornyl). 31P{1H}
NMR (C6D6, 202 MHz) δ 34.79 (d, 2JPP = 194.2, PiPr2), 18.21 (d, 2JPP
Synthesis of [1c]NiC(O)Me (3c). Isolated as yellowish green
crystals suitable for X-ray diffraction analysis by slow evaporation of a
1
concentrated benzene solution at room temperature; yield 73%. H
NMR (C6D6, 500 MHz) δ 7.69 (d, 2, Ar), 7.00 (dt, 2, Ar), 6.92 (m, 2,
Ar), 6.48 (t, 2, Ar), 2.41 (s, 3, C(O)Me), 2.19 (br m, 2, PCHMe2),
2.02 (br m, 2, PCHMe2), 1.23 (dd, 12, PCHMe2), 1.06 (br m, 6,
PCHMe2), 0.98 (br m, 6, PCHMe2). 31P{1H} NMR (C6D6, 202 MHz)
δ 35.81. 13C{1H} NMR (C6D6, 125.7 MHz) δ 259.15 (t, JCP = 20.5,
NiC(O)Me), 162.99 (t, JCP = 11.9, C), 132.63 (s, CH), 131.93 (s,
CH), 119.93 (t, JCP = 19.7, C), 116.07 (t, JCP = 2.8, CH), 115.86 (t, JCP
= 4.2, CH), 44.17 (t, JCP = 5.7, NiC(O)Me), 23.36 (m, CHMe2), 18.90
(m, CHMe2), 17.60 (m, CHMe2), 17.27 (m, CHMe2). Anal. Calcd for
C26H39NNiOP2: C, 62.16; H, 7.83; N, 2.79. Found: C, 62.30; H, 7.60;
N, 2.78.
= 194.2, PPh2). 13C{1H} NMR (C6D6, 125.7 MHz) δ 264.11 (t, JCP
=
18.3, NiCO), 162.42 (dd, JCP = 3.6 and 14.0, C), 162.25 (dd, JCP = 3.0
and 9.7, C), 134.52 (s, CH), 134.21 (dd, JCP = 10.9 and 26.2, C),
132.80 (s, CH), 132.45 (s, CH), 131.93 (s, CH), 130.45 (d, JCP = 22.5,
CH), 129.20 (d, JCP = 7.4, CH), 129.12 (d, JCP = 7.4, CH), 125.05 (d,
JCP = 49.5, C), 120.24 (d, JCP = 40.1, C), 116.90 (d, JCP = 9.7, CH),
116.84 (d, JCP = 7.2, CH), 115.79 (d, JCP = 6.1, CH), 115.36 (d, JCP
=
9.1, CH), 65.17 (dd, JCP = 3.6 and 7.2, CH), 40.06 (s, CH), 36.83 (s,
CH2), 36.73 (s, CH), 34.89 (s, CH2), 30.65 (s, CH2), 29.76 (s, CH2),
24.44 (br m, CHMe2), 19.15 (br m, CHMe2), 17.44 (d, JCP = 18.3,
CHMe2). Anal. Calcd. for C38H43NNiOP2: C, 70.16; H, 6.67; N, 2.15.
Found: C, 69.82; H, 6.78; N, 1.78.
Synthesis of [1b]NiC(O)Et (4b). Isolated as a yellow solid; yield
82%. 1H NMR (C6D6, 500 MHz) δ 7.85 (br s, 4, Ar), 7.75 (dd, 1, Ar),
7.59 (dd, 1, Ar), 7.12 (t, 1, Ar), 7.01 (m, 7, Ar), 6.93 (t, 2, Ar), 6.48 (t,
1, Ar), 6.44 (t, 1, Ar), 2.52 (q, 2, NiC(O)CH2Me), 2.07 (m, 2,
CHMe2), 1.24 (dd, 6, CHMe2), 1.07 (dd, 6, CHMe2), 0.68 (t, 3,
Synthesis of [MeC(O)N(o-C6H4PPh2)2]Ni(CO)2 (7a). Isolated as a
pale yellow solid; yield 75%. 1H NMR (C6D6, 300 MHz) δ 8.08 (dd, 2,
Ar), 7.93 (dd, 2, Ar), 7.42 (br s, 2, Ar), 7.10 (m, 4, Ar), 6.79−6.93 (m,
12, Ar), 6.68 (m, 4, Ar), 6.55 (t, 2, Ar), 2.22 (s, 3, C(O)Me). 31P{1H}
NMR (C6D6, 121.5 MHz) δ 23.37 (d, 2JPP = 5.6), 22.16 (d, 2JPP = 5.6).
13C{1H} NMR (C6D6, 75.5 MHz) δ 202.11 (s, NC(O)Me), 197.24
(vt, JCP = 4.45, NiCO), 180.81 (s, C), 147.43 (d, JCP = 16, C), 140.33
(d, JCP = 34.43, C), 137.05 (s, C), 136.89 (d, JCP = 23.25, CH), 135.43
(d, JCP = 15.18, CH), 134.90 (d, JCP = 16.38, CH), 134.66 (s, CH),
133.13 (d, JCP = 4.83, CH), 132.33 (m, CH), 130.68 (s, CH), 130.22
(s, CH), 129.21 (m, CH), 26.72 (s, CH3). Anal. Calcd for
C40H31NNiO3P2: C, 69.18; H, 4.50; N, 2.02. Found: C, 69.01; H,
4.24; N, 2.21.
NiC(O)CH2Me). 31P{1H} NMR (C6D6, 202 MHz) δ 36.94 (d, 2JPP
=
2
194, PiPr2), 17.57 (d, JPP = 194, PPh2). 13C{1H} NMR (C6D6, 125.7
2
MHz) δ 261.24 (vt, JCP = 19.2, NiC(O)), 162.49 (dd, JCP = 1.6 and
3.4, C), 162.32 (dd, JCP = 2.3 and 4.0, C), 134.82 (s, CH), 134.04 (d,
JCP = 10.2, CH), 132.64 (d, JCP = 1.6, CH), 132.62 (s, CH), 131.94 (d,
JCP = 1.8, CH), 130.58 (s, CH), 129.24 (d, JCP = 10.2, CH), 128.62 (s,
C), 124.03 (d, JCP = 49.1, C), 120.11 (d, JCP = 39.4, C), 116.63 (d, JCP
= 7.3, CH), 116.46 (d, JCP = 9.0, CH), 116.32 (d, JCP = 5.7, CH),
115.75 (d, JCP = 9.7, CH), 47.79 (vt, JCP = 5.7, NiC(O)CH2Me), 23.68
(br d, JCP = 23.5, CHMe2), 18.92 (br s, CHMe2), 17.35 (s, CHMe2),
8.40 (s, NiC(O)CH2Me). Anal. Calcd for C33H37NNiOP2: C, 67.82;
H, 6.39; N, 2.40. Found: C, 67.60; H, 6.55; N, 2.06.
Synthesis of [EtC(O)N(o-C6H4PPh2)2]Ni(CO)2 (8a). Isolated as
pale yellow crystals suitable for X-ray diffraction analysis by slow
evaporation of a concentrated benzene solution at room temperature;
Synthesis of [1c]NiC(O)Et (4c). Isolated as a yellowish green
1
solid; yield 54%. H NMR (C6D6, 500 MHz) δ 7.68 (d, 2, Ar), 7.00
1
(dt, 2, Ar), 6.92 (m, 2, Ar), 6.48 (t, 2, Ar), 2.88 (q, 2, CH2Me), 2.18
yield 69%. H NMR (C6D6, 500 MHz) δ 8.05 (dd, 2, Ar), 7.93 (t, 2,
706
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Ar), 7.25 (t, 2, Ar), 7.18 (t, 2, Ar), 7.09 (t, 2, Ar), 7.03 (t, 2, Ar), 6.92−
6.98 (m, 6, Ar), 6.81−6.88 (m, 6, Ar), 6.71 (m, 4, Ar), 2.29 (qd, 1,
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118, 4746−4764.
3
2
2JHAHB = 17, JHAMe = 7, C(O)CHAHBMe), 2.16 (qd, 1, JHAHB = 17,
3JHBMe = 7, C(O)CHAHBMe), 0.93 (t, 3, CH2Me). 31P{1H} NMR
(5) Nakamura, A.; Munakata, K.; Ito, S.; Kochi, T.; Chung, L. W.;
Morokuma, K.; Nozaki, K. J. Am. Chem. Soc. 2011, 133, 6761−6779.
2
2
(C6D6, 202 MHz) δ 24.72 (d, JPP = 5.5), 23.54 (d, JPP = 5.5).
13C{1H} NMR (C6D6, 125.7 MHz) 202.50 (s, NC(O)Et), 197.93 (vt,
JCP = 6.0, NiCO), 175.32 (s, C), 148.43 (dd, JCP = 90.6 and 16.4, C),
141.65 (d, JCP = 16.5, C), 139.73 (dd, JCP = 30.8 and 12.9, C), 137.57
(d, JCP = 31.6, C), 137.22 (s, CH), 136.25 (dd, JCP = 27.1 and 2.7, C),
135.97 (s, CH), 135.47 (d, JCP = 15.0, CH), 134.68 (d, JCP = 16.0,
CH), 134.58 (d, JCP = 25.2, C), 134.38 (t, JCP = 5.9, CH), 133.79 (d,
JCP = 22.5, C), 133.10 (d, JCP = 12.8, CH), 132.50 (d, JCP = 12.3, CH),
132.13 (d, JCP = 5.0, CH), 130.99 (s, CH), 130.33 (s, CH), 130.16 (s,
CH), 129.98 (d, JCP = 5.5, CH), 129.29 (vt, JCP = 5.0, CH), 129.05 (d,
JCP = 9.1, CH), 128.92 (s, CH), 128.69 (s, CH), 128.53 (m, CH),
128.33 (d, JCP = 8.3,CH), 128.18 (m, CH), 126.14 (d, JCP = 3.6, CH),
31.09 (s, CH2), 10.04 (s, CH3). Anal. Calcd for C41H33NNiO3P2: C,
69.50; H, 4.70; N, 1.98. Found: C, 69.76; H, 4.40; N, 2.16.
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Synthesis of [1a]Ni[C(O)NHPh] (9a). Isolated as red crystals
suitable for X-ray diffraction analysis by cooling a concentrated THF
solution to −35 °C; yield 92%. 1H NMR (C6D6, 500 MHz) δ 7.79 (d,
8, Ar), 7.10 (m, 1, Ar), 6.96 (m, 20, Ar), 6.77 (s, 1, NH), 6.71 (t, 2,
Ar), 6.44 (t, 2, Ar). 31P{1H} NMR (C6D6, 202 MHz) δ 22.25. 13C{1H}
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878−879.
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ez, G.; Moreto, J. M. J. Am. Chem. Soc. 1999, 121,
NMR (C6D6, 125.7 MHz) δ 194.48 (t, JCP = 31.0, NiC(O)NHPh)
162.30 (t, JCP = 13.8, C), 139.92 (s, C), 135.05 (s, CH), 134.28 (t, JCP
= 6.5, CH), 132.64 (s, CH), 131.71 (t, JCP = 23.8, C), 130.72 (s, CH),
129.30 (t, JCP = 4.6, CH), 128.99 (s, CH), 123.78 (t, JCP = 23.7, C),
122.43 (s, CH), 118.43 (s, CH), 117.57 (t, JCP = 3.6, CH), 116.49 (t,
JCP = 4.5, CH). Anal. Calcd for C43H34N2NiOP2: C, 72.18; H, 4.79; N,
3.92. Found: C, 71.98; H, 4.68; N, 3.95.
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R. R. Organometallics 2001, 20, 1028−1031.
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suitable for X-ray diffraction analysis by slow evaporation of a
1
concentrated benzene solution at room temperature; yield 78%. H
(21) Liang, L.-C.; Lee, W.-Y.; Tsai, T.-L.; Hsu, Y.-L.; Lee, T.-Y.
Dalton Trans. 2010, 39, 8748−8758.
NMR (C6D6, 500 MHz) δ 7.73 (d, 2, Ar), 7.59 (d, 2, Ar), 7.19 (s, 1,
NH), 7.15 (m, 2, Ar), 7.01 (t, 2, Ar), 6.97 (m, 2, Ar), 6.85 (t, 1, Ar),
6.50 (t, 2, Ar), 2.29 (m, 2, PCHMe2), 2.13 (m, 2, PCHMe2), 1.31 (m,
6, PCHMe2), 1.21 (m, 6, PCHMe2), 1.09 (m, 6, PCHMe2), 1.02 (m, 6,
PCHMe2). 31P{1H} NMR (C6D6, 202 MHz) δ 40.87. 13C{1H} NMR
(C6D6, 125.7 MHz) δ 196.13 (t, JCP = 27.4, NiC(O)NHPh), 163.46 (t,
JCP = 11.9, C), 139.49 (s, ipso-NHPh), 132.83 (s, CH), 132.01 (s,
CH), 129.76 (s, CH), 122.70 (s, CH), 120.58 (t, JCP = 18.7, C),
118.37 (s, CH), 116.45 (t, JCP = 3.2, CH), 115.96 (t, JCP = 4.6, CH),
23.70 (m, CHMe2), 18.74 (s, CHMe2), 18.00 (br s, CHMe2), 17.26 (br
s, CHMe2). Anal. Calcd for C31H42N2NiOP2: C, 64.25; H, 7.31; N,
4.84. Found: C, 63.96; H, 7.44; N, 4.46.
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2166−2174.
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2816.
(28) Liang, L.-C.; Lee, W.-Y.; Hung, C.-H. Inorg. Chem. 2003, 42,
5471−5473.
ASSOCIATED CONTENT
* Supporting Information
X-ray crystallographic data for 2b, 2c, 3b, 3c, 5b, 6b, 8a, 9a, 9c,
and [1b]NiMe; molecular structures of 2c, 9c, and [1b]NiMe.
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
(29) Winter, A. M.; Eichele, K.; Mack, H. G.; Potuznik, S.; Mayer, H.
A.; Kaska, W. C. J. Organomet. Chem. 2003, 682, 149−154.
(30) Menard, G.; Jong, H.; Fryzuk, M. D. Organometallics 2009, 28,
5253−5260.
S
(31) MacLachlan, E. A.; Hess, F. M.; Patrick, B. O.; Fryzuk, M. D. J.
Am. Chem. Soc. 2007, 129, 10895−10905.
(32) MacLachlan, E. A.; Fryzuk, M. D. Organometallics 2005, 24,
1112−1118.
AUTHOR INFORMATION
Corresponding Author
*E-mail: lcliang@mail.nsysu.edu.tw.
■
(33) Yurkerwich, K.; Parkin, G. Inorg. Chim. Acta 2010, 364, 157−
161.
(34) Ozerov, O. V. In The Chemistry of Pincer Compounds; Morales-
Morales, D., Jensen, C. M., Eds.; Elsevier: Amsterdam, 2007, p 287−
309.
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Ozerov, O. V. J. Am. Chem. Soc. 2007, 129, 10318−10319.
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H.; Baik, M. H.; Mindiola, D. J. J. Am. Chem. Soc. 2011, 133, 10700−
10703.
ACKNOWLEDGMENTS
■
We thank the National Science Council of Taiwan for financial
support (NSC 99-2113-M-110-003-MY3 and 99-2119-M-110-
002), Mr. Ting-Shen Kuo (NTNU) for assistance with X-ray
crystallography, and the National Center for High-performance
Computing (NCHC) for the access to chemical databases.
(37) Andino, J. G.; Kilgore, U. J.; Pink, M.; Ozarowski, A.; Krzystek,
J.; Telser, J.; Baik, M. H.; Mindiola, D. J. Chem. Sci. 2010, 1, 351−356.
(38) Adhikari, D.; Pink, M.; Mindiola, D. J. Organometallics 2009, 28,
2072−2077.
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