Impact of backbone substituents on POCOP-Ni pincer complexes: A structural, spectroscopic, and electrochemical study

Article abstract of DOI:10.1021/om3009475

When treated at room temperature and in the presence of NEt₃ with {(i-PrCN)NiBr₂}_n, the pincer-type ligands R-POC ^HOPR^′ undergo direct C-H nickellation to give the pincer complexes (R-POCOPR^′)NiBr in 45-92% yields (R-POCOP = κ^P,κ^C,κ^P-{R _n-2,6-(R′₂PO)₂C₆H _3-n}; R_n = 4-OMe, 4-Me, 4-CO₂Me, 3-OMe, 3-CO₂Me, 3,5-t-Bu₂; R′ = i-Pr, t-Bu). These complexes have been characterized by multinuclear NMR and UV-vis spectroscopy as well as single-crystal X-ray diffraction studies to delineate the impact of R and R′ on Ni-ligand interactions. The solid-state structural data have revealed slightly shorter Ni-Br bonds in the complexes bearing a 4-CO ₂Me substituent, shorter Ni-P bonds in the complex bearing t-Bu substituents at the 3- and 5-positions, and longer Ni-P bonds in complexes featuring OP(t-Bu)₂ donor moieties. The UV-vis spectra indicate that a 4-CO₂Me substituent causes a red-shift in the frequency of the MLCT bands (330-365 nm), whereas the ligand field transitions appearing in the 380-420 nm region are influenced primarily by the P-substituents. Cyclic voltammetry measurements have shown that the oxidation potentials of the title complexes are affected by P- and ring-substituents, oxidation being somewhat easier with t-Bu₂PO (vs i-Pr₂PO), OMe and Me (vs CO ₂Me), and t-Bu (vs Cl). Moreover, oxidation potentials are affected more by the aromatic substituents at the 4-position vs those at the 3- and 5-positions.

Full text of DOI:10.1021/om3009475

Article
pubs.acs.org/Organometallics
Impact of Backbone Substituents on POCOP-Ni Pincer Complexes: A
Structural, Spectroscopic, and Electrochemical Study
Boris Vabre, Denis M. Spasyuk, and Davit Zargarian*
́ ́ ́ ́ ́
Departement de Chimie, Universite de Montreal, Montreal (Quebec), Canada H3C 3J7
S
* Supporting Information
ABSTRACT: When treated at room temperature and in the presence of NEt3 with {(i-
PrCN)NiBr2}n, the pincer-type ligands R-POCHOPR′ undergo direct C−H nickellation to give the
pincer complexes (R-POCOPR′)NiBr in 45−92% yields (R-POCOP = κP,κC,κP-{Rn-2,6-
(R′2PO)2C6H3−n}; Rn = 4-OMe, 4-Me, 4-CO2Me, 3-OMe, 3-CO2Me, 3,5-t-Bu2; R′ = i-Pr, t-
Bu). These complexes have been characterized by multinuclear NMR and UV−vis spectroscopy as
well as single-crystal X-ray diffraction studies to delineate the impact of R and R′ on Ni−ligand
interactions. The solid-state structural data have revealed slightly shorter Ni−Br bonds in the
complexes bearing a 4-CO2Me substituent, shorter Ni−P bonds in the complex bearing t-Bu
substituents at the 3- and 5-positions, and longer Ni−P bonds in complexes featuring OP(t-Bu)2
donor moieties. The UV−vis spectra indicate that a 4-CO2Me substituent causes a red-shift in the
frequency of the MLCT bands (330−365 nm), whereas the ligand field transitions appearing in
the 380−420 nm region are influenced primarily by the P-substituents. Cyclic voltammetry
measurements have shown that the oxidation potentials of the title complexes are affected by P- and ring-substituents, oxidation
being somewhat easier with t-Bu2PO (vs i-Pr2PO), OMe and Me (vs CO2Me), and t-Bu (vs Cl). Moreover, oxidation potentials
are affected more by the aromatic substituents at the 4-position vs those at the 3- and 5-positions.
Chart 1.
INTRODUCTION
■
Pincer complexes of nickel based on the 1,3-bis-
(phosphinomethyl)- and 1,3-bis(aminomethyl)phenyl ligands
were among the first pincer complexes reported by the groups
of Shaw1 and van Koten,2 respectively. The organonickel
chemistry of these so-called PCP- and NCN-type pincer ligands
has received increasing scrutiny over the past three decades and
led to the development of interesting applications based on
both divalent and trivalent systems.3 The past decade has also
witnessed exciting discoveries emerging from the chemistry of
nickel pincer complexes based on related new ligands such as
PCsp3P,4 POCOP5 and POCsp3OP,5b,c POCN,6 PNP,7 and
NNN8 (Chart 1). These developments have underlined the
possibility of fine-tuning the reactivities of nickel pincer
complexes through modifications in donor moieties and the
ligand backbone.
In this context, the groups of Guan, Goldberg, Peruzzini, and
Hazeri have reported on the reactivities of (POCOP)Ni(H)9
and (PCP)Ni(H)10 as a function of P-substituents, while our
group has reported on the structures and reactivities of charge-
neutral and cationic PCP- and POCOP-type complexes of
nickel as a function of different P-substituents and pincer
backbones (aromatic vs aliphatic).11 The impact of ring-
substituents on the structures and reactivities of aromatic PCP-
and POCOP-Ni complexes has not been examined in a
systematic manner, but this issue is beginning to attract interest.
For instance, Morales−Morales’ group has reported very
recently the synthesis of POCOP-type systems based on 4-n-
dodecylresorcinol12 and 1,3-dihydroxynaphthalene13 and exam-
ined the effectiveness of the latter complex in Suzuki coupling,
whereas Huang’s group has studied the homocoupling of
benzyl halides by (R-POCOPR′)NiX (X = Cl, Br, I) to ascertain
the influence of ring- and P-substituents R and R′ on this
reaction.14 Our group has also shown that in the cationic
complexes [(POCOP)Ni(NCMe)]+ the P-substituents have
greater influence on structures and reactivities relative to
chloride substituents at the 3- and 5-positions (with respect to
the metallated carbon).11a In contrast to these sporadic and
limited studies for POCOP-Ni systems, the impact of ring- and
P-substituents on the properties of POCOP-Ir complexes has
Received: October 9, 2012
Published: December 10, 2012
© 2012 American Chemical Society
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Chart 2.
been investigated in much more detail.15 Similar studies have
been reported on NCN-Ni and NCN-Pt complexes.16
As a continuation of our investigations on the chemistry of
POCOP-Ni complexes, we have set out to examine how the Ni
center is influecned by ring-substituents, in particular those at
the more sensitive 4-position (para with respect to the
metalated carbon). The present report describes the synthesis
and characterization of the complexes (R-POCOPR′)NiBr
where R and R′ represent, respectively, the substituents on
the resorcinol ring and the phosphinite moiety (Chart 2). The
impact of R and R′ on solid-state structures, electronic
transitions, and electrochemical properties of these compounds
will be discussed.
reported ligand POCHOPt‑Bu was also subjected to single-crystal
X-ray diffraction analysis (vide infra). All the ligands were then
treated with a small excess of {(i-PrCN)NiBr2}n in the presence
of NEt3 at ambient temperature to give the corresponding
pincer complexes via a direct nickellation step (Scheme 1).18
This straightforward methodology has allowed the preparation
of eight new complexes in 45−92% yields (Table 1). It is
interesting to note that the lowest yield is obtained from the
ligand bearing bulky t-Bu substituents at the 3- and 5-positions
on the ring (45% for complex 7′), whereas in the case of t-
Bu2P-based derivatives placing a COOMe substituent at the
para position appears to favor the yield (52% for complex 8′ vs
72% for complex 9′).19 The new complexes have been
characterized by combustion analysis, NMR and UV−vis
spectroscopy, and single -crystal diffraction studies (vide infra).
NMR Analyses. Assignments of NMR spectra for the new
ligands and complexes were facilitated by comparison to the
corresponding data obtained previously for fully characterized
analogues.5 Interestingly, the NMR data are only slightly
affected by the ring-substituents R, as reflected in the fairly
narrow ranges of 31P δ values observed for all ligands (ca. 147−
156 ppm) and complexes (ca. 188−192 ppm). In this regard,
31P δ values of the ligand signals are more strongly affected as a
result of nickellation, which causes a deshielding by ca. 40 ppm
on average; the nearly linear relationship between ligand/
RESULTS AND DISCUSSION
■
The synthesis of m-phenylene-based POCHOP ligands used in
this study involved treating the doubly deprotonated resorcinol
or its substituted derivatives Rn-POCHOP with ClPR′2 (Scheme
1)17 and vacuum distillation of the oily products where
Scheme 1.
complex 31P chemical shift values is apparent from a plot of 31
P
δ values provided as Supporting Information. In contrast, the
impact of nickellation on the 13C{1H} δ values appears to be
more complex: the aromatic carbon nucleus directly bonded to
the Ni center experiences a downfield shift of ca. 17−24 ppm,
whereas upfield shifts were noted for the remaining aromatic
possible; this methodology furnished six new ligands in 60−
94% yields (Table 1). The new ligands were characterized by
combustion analysis and NMR spectroscopy; the previously
Table 1. POCOP Ligands and Complexes Synthesized
ligands
complexes
b
R′
R
no.
yield (%)
31P δ†
149.0
no.
yield (%)
31P δ
a
a
i-Pr
1
1′
188.2
189.1
190.6
190.6
4-Me
2
3
4
5
6
85
70
89
60
94
148.9
2′
3′
4′
5′
6′
7′
8′
9′
76
74
92
90
86
45
57
72
4-OMe
4-CO2Me
3-OMe
3-CO2Me
3,5-t-Bu2
H
147.5
151.9
c
151.7, 157.2
151.2, 151.6
139.5
187.5 (d), 192.2 (d)
190.4 (d), 192.1 (d)
185.2
d
a
7
a
t-Bu
8
153.1
191.0
4-CO2Me
9
63
155.8
191.8
a
b
c
d
Previously reported ligands/complexes. Unless otherwise indicated, all signals are singlet resonances. AB signal, JPP ≈ 318 Hz. AB signal, JPP
≈
323 Hz.
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carbon nuclei (ca. 1−6 ppm) as well as most aromatic protons
(ca. 0.2−0.4 ppm).
the data was very good for all other products including complex
8′, which displayed disordered t-Bu substituents.22 The ORTEP
diagrams are shown in Figure 2 (8) and Figure 3 (3′, 4′, 7′, and
The 31P NMR spectra of the nonsymmetrical ligands 5 and 6
and their complexes 5′ and 6′ were particularly instructive. The
two inequivalent phosphinite moieties of these ligands showed
two singlets appearing at fairly different chemical shifts in 5
(151.7 and 157.2 ppm), but very close to each other in 6 (151.1
and 151.6 ppm). The spectrum for complex 5′ displayed a
“normal” AB pattern consisting of two doublets at 187.5 and
192.2 ppm (2JP−P = 318 Hz; Δν/JP−P ≈ 2.5), whereas the
spectrum for 6′ appeared to consist of two closely spaced
singlets (192.06 and 192.13 ppm) instead of the expected AB
doublets. The 31P{1H} NMR spectrum of a more concentrated
sample recorded on a higher field instrument (ca. 202.5 MHz)
showed a four-peak AB-type signal displaying very weak outer
peaks (∼1:20:20:1, Figure 1), which is presumably caused by
Figure 2. ORTEP diagram for ligand 8. Thermal ellipsoids are shown
at the 50% probability level. Hydrogen atoms are omitted for clarity.
8′), and the main structural parameters are listed in Table 2;
details of the diffraction studies are listed in Table 1S and Table
2S (Supporting Information).
The t-Bu2PO moieties in ligand 8 adopt positions that
minimize steric interactions, with one moiety being in the plane
of the aromatic ring, while the other phosphorus is out of plane
by 0.798 Å. Comparison of the P−O distances in 8 and 8′
reveals a significant shrinkage (by 0.024 Å) upon complexation
to nickel; this might arise from the P→Ni donation in the
complexes that would enhance the dipolar character of the P−
O bond. This is the first solid-state structure of a POCOP-type
ligand.
The nickel center in all complexes adopts a distorted square-
planar geometry due, primarily, to the small bite angle of the
POCOP ligands (P−Ni−P ∼164−165°). The Ni−C distances
are fairly similar in all cases (∼1.87−1.89 Å) as are Ni−Br
distances (∼2.31−2.34 Å), but the latter appear to be shortest
in complexes bearing a 4-CO2Me substituent. This point is best
illustrated by comparing the Ni−Br distances in unsubstituted
complexes 1′ (2.323(1) Å) and 8′ (2.338(2) Å) vs their 4-
CO2Me counterparts 4′ (2.312(1) Å) and 9′ (2.321(1) Å). The
shorter Ni−Br distances in the complexes bearing electron-
withdrawing substituents can be attributed to the weaker trans
influence of the electron-depleted aryl rings.23
The Ni−P distances were found to be fairly insensitive to the
ring-substituents R, but important variations were noted as a
function of P-substituents R′ (∼2.19 Å with t-Bu and ∼2.14−
2.16 with i-Pr). It is interesting to note that the shortest Ni−P
bond distances in the i-Pr2PO series are found in 7′, implying
that the presence of bulky t-Bu substituents on the 3- and 5-
positions of the aromatic ring reinforces the Ni−P interactions.
Absorption Spectroscopy. UV−vis spectra were recorded
for ca. 10−4 M CH2Cl2 solutions of the ligands (pale yellow)
and complexes (yellow). The ligand spectra displayed multiple
intense bands in the UV region below 250 nm, in addition to
one or two bands of moderate intensity centered at higher
wavelengths. The energies of the latter bands appear to be
much more sensitive to the ring-substituents R than the P-
substituents R′. For instance, the ligands bearing electron-
releasing substituents or none absorb at 272−276 nm
regardless of R′ (e.g., ligands 3, 2, and 8), whereas those
bearing the electron-withdrawing substituent 4-CO2Me absorb
at 306 nm (ligand 4) or 308 nm (ligand 9). We conclude that
Figure 1. 31P{1H} NMR spectra of complexes 5′ (above) and 6′
(below).
the very similar chemical shifts of the two P nuclei and their
large coupling constant (Δν/JP−P ≈ 0.96).20 A similar “roof
effect” has already been observed in an asymmetric PCP
platinum pincer complex.21
Crystallographic Analyses. X-ray diffraction studies have
been conducted on single crystals of complexes 3′−7′ as well as
ligand 8. Reliable structural data could not be obtained for
compounds 5′ and 6′ due to the inferior quality of the single
crystals obtained for these complexes, but the overall quality of
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Figure 3. ORTEP diagrams for complexes 2′−4′ and 7′−9′. Thermal ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted
for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Ligand 7 and Complexes 1′−4′, 7′, 8′, and 9′ (molecule 1)
compound
Ni−C
Ni−Br
Ni−P1
Ni−P2
P1−Ni−P2
P1−O1
a
1′
1.885 (3)
1.885 (3)
1.877 (2)
1.872 (2)
1.892 (4)
1.887 (2)
2.323 (1)
2.330 (1)
2.319 (1)
2.312 (1)
2.320 (1)
2.338 (2)
2.153 (1)
2.158 (1)
2.155 (1)
2.157 (1)
2.139 (1)
2.193 (1)
2.142 (1)
164.92 (4)
164.21 (3)
164.65 (2)
165.26 (2)
165.06 (5)
164.13 (3)
1.663 (2)
1.655 (2)
1.663 (2)
1.656 (2)
1.650 (3)
1.654 (2)
1.678 (1)
1.652 (2)
2′
3′
4′
7′
8′
8
2.152 (1)
2.159 (1)
2.143 (1)
2.189 (1)
9′
1.877 (2)
2.321 (1)
2.189 (1)
2.194 (1)
164.58 (3)
a
The data for 1′ are taken from ref 5b.
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Figure 4. UV−vis spectra (CH2Cl2, rt) for complexes 2′−4′ and 7′−9′.
these bands involve π→π* transitions, and the difference
between the frequencies observed for ligands 4 and 9, on one
hand, and all other ligands (ca. 4000 cm−1) can be rationalized
by considering that such transitions should be lower in energy
when the buildup of charge in the excited state can be stabilized
more effectively. In other words, ligands bearing the most
effective electron-accepting ring-substituent should exhibit
lower energy π→π* transitions; a similar phenomenon is at
work for the MLCT transitions in the complexes (vide infra).
Similarly to the ligands, the complexes displayed multiple
high-intensity bands in the UV region, in addition to a few less
intense bands in the regions 330−365 nm and 380−420 nm
(Figure 4 and Table 3). Since the latter bands are absent in the
caused by 4-CO2Me, and this observation can be rationalized as
was discussed above for the π→π* transitions of the
unmetalated ligands. It is also worth noting that in some
cases the energy of the MLCT band is more sensitive to the
position of the ring-substituent R as opposed to its electronic
character. Thus, the MLCT band of complex 6′ appears ca.
1600 cm−1 higher than that of 4′, implying that the CO2Me
substituent exerts greater electronic influence at the 4- vs 3-
position. As will be discussed below, the cyclic voltammetry
measurements corroborate the greater impact of the 4-CO2Me
substituent on oxidation potentials of the complexes. The
electron-releasing substituents Me, t-Bu, and OMe also
influence the oxidation potentials of the complexes (vide
infra), but they show little or no impact on the energies of the
MLCT bands regardless of the substitution position. Thus,
complexes 3′ and 5′, bearing a OMe substituent at the 3- or 4-
position, show MLCT bands at virtually identical energies.
Cyclic Voltammetry Measurements. Figure 5 shows the
cyclic voltammograms of (R-POCOPR′)NiBr, and Table 4 lists
the potentials (vs ferrocene) in each case. Previous studies have
established that PCP-,4 POCOP-,5b−d and POCN-Ni6a−c
complexes undergo one-electron oxidation of the nickel center
that can be irreversible or reversible, depending on the specific
complex and the conditions under which the measurements are
made. The CV curves obtained for the complexes under
discussion here show that the oxidation process is reversible for
2′ and 7−9′, quasi-reversible for 3′ and 5′, and irreversible for
6′.
Table 3. Absorption Spectral Data for Complexes 1′−9′
R′
R
no.
λmax (nm) (ε, M−1 cm−1
)
i-Pr
H
1′
2′
3′
4′
5′
6′
7′
8′
9′
337(9409)
338(1063)
336(10109)
362(8552)
337(900)
389(1975)
396(164)
387(1753)
384(3863)
389(158)
397(157)
388(1631)
407(198)
413(228)
4-Me
4-OMe
4-CO2Me
3-OMe
3-CO2Me
3,5-t-Bu2
341(817)
337(9060)
334(916)
t-Bu
4-CO2Me
360(1043)
ligand spectra, they can be assigned to electronic transitions of
the complexes. Moreover, since the lowest energy bands are
fairly insensitive to ring-substituents R and more sensitive to P-
substituents R′, they can be attributed to spin-forbidden d−d
transitions involving the ligand fields. This is anticipated for
metal-centered transitions and most evident when we compare
the energies of these bands for complexes 4′ and 9′ (ca. 26 000
vs 24 000 cm−1). On the other hand, the more intense
transitions in the region 330−365 that show greater sensitivity
to the ring-substituents R are considered to be spin-allowed
charge transfer bands (MLCT).24
The frequencies of MLCT transitions range from ca. 30 000
cm−1 in the spectra of complexes bearing either electron-
releasing substituents (2′, 3′, 5′, and 7′) or none (1′ and 8′) to
ca. 28 000 cm−1 observed in the spectra of complexes 4′ and 9′,
bearing 4-CO2Me substituents. Evidently, the largest electronic
impact on MLCT transition frequencies (ca. 2000 cm−1) is
Comparison of the potentials for complexes 3′−7′ relative to
complex 1′ (Table 4) provides valuable insights into the impact
of ring- and P-substituents on one-electron oxidation in this
family of complexes. Thus, the oxidation process is much easier
for complexes containing electron-releasing substituents Me,
OMe, and t-Bu (complexes 3′, 2′, 5′, and 7′). The greatest
influence is exerted by the 4-OMe substituent, which lowers the
oxidation potential by nearly 200 mV, whereas the 3-OMe has
less influence.25 By comparison, P-substituents appear to have
less influence over the oxidation potential of these complexes,
as seen from the nearly equal potentials of 1′ and 8′. However,
it is worth noting that the Ph2PO analogue of these complexes
shows a somewhat higher oxidation potential,5d as anticipated
on account of the weaker donor aptitude of the Ph substituents.
Finally, oxidation is more difficult for complexes containing
electron-withdrawing ring-substituents (4′, 6′, and 9′), the
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Figure 5. Cyclic voltammograms of 3′, 2′, 6′, an equimolar mixture of 8′ and ferrocene, and 9′. The measurements were carried out at 298 K on
CH2Cl2 solutions containing the sample complexes (1 mM) and [Bu4N][PF6] as electrolyte (0.1 M). A scan rate of 100 mV s−1 was used, and the
potentials were referenced to the Cp2Fe/Cp2Fe+ redox couple.
Table 4. Redox and Oxidation Potentials of (R-
a
POCOPR′)NiBr
R′
R
E1/2 (mV)
Eox (mV)
i-Pr
H (1′)
4-Me (2′)
810
800
620
940
761
900
750
735
565
4-OMe (3′)
4-CO2Me (4′)
3-OMe (5′)
3-CO2Me (6′)
3,5-t-Bu2 (7′)
3,5-Cl2
715
687
b
840
t-Bu
H (8′)
4-CO2Me (9′)
750
860
800
920
a
See captions of Figure 2 or 3, or the Experimental section, for
b
measurement details. Reported in ref 11a.
greatest influence (ca. 130 mV) being exerted by 4-CO2Me.
Thus, the electrochemical oxidation potential of (R-POCOP)-
NiBr can be modulated over a range of 300 mV (3′ vs 4′) by
judicious choice of the ring- substituents R.
The question arises as to how closely oxidation potentials
reflect the level of electron density at the Ni center in the
complexes under discussion. In the absence of reactivity data, it
is tempting to seek other correlations that might shed light on
this question. As discussed above, the energies of metal-
centered electronic transitions are influenced by P-substituents,
but they appear fairly insensitive to ring-substituents. We
sought to establish whether or not there is any correlation
between oxidation potentials obtained from CV measurements,
on one hand, and the 13C (δ C1) and 31P chemical shifts on the
other. Figure 6 shows plots of the 13C and 31P chemical shifts of
various complexes against the corresponding oxidation
potentials. These plots reveal a moderate degree of correlation
between Eox and δ C1 but a much more tenuous correlation
with 31P chemical shifts.
Figure 6. Plots of oxidation potentials vs NMR chemical shifts for the
C1 (above) and P (below) nuclei.
structural, and redox properties. Our findings point to a strong
correlation between the redox potential of a given complex (R-
POCOP)NiBr and the electronic nature of the ring-substituent
R placed at the para position with respect to the nickellated
carbon. An observable impact was also observed in the
electronic spectra of the complexes bearing electron-with-
drawing substituents COOMe at the 3- or 4-positions. On the
other hand, the electronic properties of ring-substituents appear
to have little or no impact on solid-state structures, but the
steric bulk of the t-Bu substituents at the 3- and 5-positions
appears to reinforce Ni−P interactions. The insights gleaned
from the present study will help us design future investigations
aimed at probing the impact of ring-substituents on the
reactivities of this family of complexes.
CONCLUSION
■
A previous study helped establish that substituents placed on
the aromatic ring of resorcinol-based POCOP-type ligands can
influence the nickellation step, leading to the formation of
pincer complexes.17 The present study is the first systematic
attempt to measure the influence of ring-substituents on the
electronics of the Ni center as manifested in its spectral,
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1,3-(i-Pr2PO)-5-Me-C6H3, 2. This ligand (a colorless oil) was
prepared in 85% yield (2.45 g) using the same procedure described for
the synthesis of 3. 1H NMR (300 MHz, CDCl3): δ 1.09 (d, JHH = 7.2,
EXPERIMENTAL SECTION
■
General Procedures. Unless otherwise indicated, all manipu-
lations were carried out under a nitrogen atmosphere using standard
Schlenk and glovebox techniques. Solvents were dried by passage over
activated alumina contained in MBRAUN systems. Triethylamine was
dried by distillation over CaH2. The reagents isobutyronitrile, nickel
powder, bromine, ClP(i-Pr)2, ClP(t-Bu)2, ClP(Ph)2, 5-methyl-1,3-
benzenediol, 4,6-dichloro-1,3-benzenediol, methyl 2,4-dihydroxyben-
zoate, methyl 3,5-dihydroxybenzoate, and NaH were purchased from
Sigma-Aldrich and used without further purification. 5-Methoxy-
resorcinol was purchased from Chemsavers. 4-Methoxyresorcinol has
been synthesized following a published procedure.26
CH(CH3)2, 6H), 1.13 (d, JHH = 7.2, CH(CH3)2, 6H), 1.17 (d, JHH
=
7.0, CH(CH3)2, 6H), 1.19 (d, JHH = 7.0, CH(CH3)2, 6H), 1.92 (dh,
JHP = 2.2, JHH = 7.1, 4H, PCH(CH3)2) 2.28 (s,CH3, 3H), 6.58 (m, Ar,
2H), 6.72 (m, Ar, 1H). 31P{1H} NMR (162 MHz, CDCl3): δ 148.9
(s). 13C{1H} NMR (101 MHz, CDCl3): δ 17.10 (d, JCP = 8.5, 4C,
CH3), 17.8 (d, JCP = 20.2, 4C, CH3), 21.6 (s, 1C, CH3), 28.35 (d, JCP
=
17.5, 4C, PCH(CH3)2), 106.3 (t, JPC = 10.36, 1C, 2-CAr), 112.7 (d, JPC
= 10.7, 2C, 4,6-CArH), 139.85 (s, 1C, CArMe), 160.1 (d, JPC = 8.7, 2C,
CArOP), Anal. Calcd for C19H34O2P2 (356.42): C, 64.03; H, 9.62.
Found: C, 63.83; H, 10.06.
Most NMR spectra were recorded at 400 (1H) and 161.9 MHz
(31P) using a Bruker AV400rg spectrometer or at 400 (1H) and 100.56
MHz (13C{1H}) using a Bruker ARX400 spectrometer. The 31P{1H}
NMR spectrum of complex 6′ was recorded at 202.5 MHz using a
Bruker AV500 spectrometer. Chemical shift values are reported in
ppm (δ) and referenced internally to the residual solvent signals (1H
and 13C: 7.26 and 77.16 ppm for CDCl3; 7.16 and 128.06 ppm for
C6D6) or externally (31P, H3PO4 in D2O, δ = 0). Coupling constants
are reported in Hz. UV/vis spectra were measured on a Varian Cary
500i. The IR spectra were recorded on a Bruker Alpha-P FTIR (4000−
1,3-(i-Pr2PO)2-5-COOMe-C6H3, 4. This ligand (a yellow oil) was
prepared in 89% yield (4.23 g) using the same procedure described for
the synthesis of 3. 1H NMR (400 MHz, CDCl3): δ 1.09 (dd, JHP = 16,
JHH = 7.2, 12H, CH(CH3)2), 1.16 (dd, JHP = 10.8, JHH = 7.0, 12H,
CH(CH3)2), 1.91 (dh, JHP = 2.4, JHH = 7.1, 4H, PCH(CH3)2), 3.88 (s,
3H, OCH3), 7.08 (m, JHP = 2.0, 1H, Ar), 7.38 (m, 2H, Ar). 31P{1H}
NMR (162 MHz, CDCl3): δ 151.9 (s). 13C{1H} NMR (101 MHz,
CDCl3): δ 17. 0 (d, JCP = 8.4, 4C, CH3), 17.7 (d, JCP = 20.1, 4C, CH3),
28.3 (d, JCP= 17.8, 4C, PCH(CH3)2), 52.1 (s, 1C, OCH3), 113.0 (d,
JPC = 10.8, 2C, 4,6-CAr), 113.4 (t, JPC = 11.0, 1C, 2-CAr), 131.7 (s, 1C,
CArCO), 160.2 (d, JPC = 9.1, 2C, CArOP), 166.5 (s, 1C, CO) Anal.
Calcd for C20H34O4P2 (400.43): C, 59.99; H, 8.56. Found: C, 59.45;
H, 8.66.
400 cm−1). The elemental analyses were performed by the Laboratoire
́
d’Analyse Elem
́
entaire, Dep
́
artement de Chimie, Universite
́
de
́
Montreal.
1,3-(i-Pr2PO)2-4-OMe-C6H3, 5. The standard procedure described
{(i-PrCN)NiBr2}n. To a suspension of nickel powder (1 g, 17.04
mmol) in isobutyronitrile (50 mL) at 0 °C was added bromine
dropwise (1.00 mL, 19.05 mmol), which caused a color change to
green after a few minutes. Stirring the reaction mixture overnight at
room temperature, followed by filtration, washing of the solid residue
with Et2O (2 × 25 mL), and drying under vacuum gave the desired
product as a beige powder (4.58 g, 98%). This compound must be
protected from ambient atmosphere, because it appears to be
hygroscopic: the beige powder turns green after overnight exposure
to air and becomes a green liquid after days. This compound has been
identified based on its IR spectrum and elemental analysis. Multiple
attempts to grow crystals of this compound have failed to produce
single crystals. IR (cm−1): 2974m, 2914m, 2864w, 2288vs, 1452vs,
1387w, 1367w, 1314w, 1278w, 1168w, 1103vs, 936w, 915w, 774w,
571w, 556s. Anal. Calcd for C4H7Br2NNi (287.61): N, 4.87 ; C, 16.70
; H, 2.45. Found: N, 4.85; C, 17.00; H, 2.42. UV−vis (iPrCN, 1.66 ×
10−3 M) [λmax, nm (ε, L mol−1 cm−1)]: 648 (103), 381(609),
313(1429), 284 (2001), 247 (1182), 223 (1885). Tdecomposition = 155
°C.
for the synthesis of 3 gave a yellow oil after vacuum distillation (1.5 g,
60%). H NMR (400 MHz, CDCl3): δ 1.07 (dd, JHP = 6.8, JHH = 7.0,
6H, CH(CH3)2), 1.11 (dd, JHP = 7.2, JHH = 7.0, 6H, CH(CH3)2), 1.16
1
(dd, JHP = 11.2, JHH = 7.1, 6H, CH(CH3)2), 1.21 (dd, JHP = 10.8, JHH
=
7.1, 6H, CH(CH3)2), 1.88 (dh, JHH = 7.1, JHP = 2.2, 2H, 3-
OPCH(CH3)2), 1.94 (dh, JHH = 7.1, JHP = 1.8, 2H, 1-OPCH(CH3)2),
3.77 (s,OCH3, 3H), 6.64 (dm(AB), JHH = 9.4, 1H, 6-HAr), 6.72
(d(AB), JHH = 8.8, 1H, 5-HAr), 6.98 (m, 1H, 2-HAr). 31P{1H} NMR
(162 MHz, CDCl3): δ 151.7 (s), 157.2 (s). 13C{1H} NMR (101 MHz,
CDCl3): δ 17.08 (d, JCP = 8.6, 2C, CH3), 17.17 (d, JCP = 9.0, 2C,
CH3), 17.73 (d, JCP = 8.4, 2C, CH3), 17.93 (d, JCP = 8.4, 2C, CH3),
28.3 (d, JCP = 17.9, 2C, PCH(CH3)2), 28.5 (d, JCP = 18.5, 2C,
PCH(CH3)2), 56.7 (s, 1C, OCH3), 111.1 (dd, JCP′ = 9.1, JCP″ = 8.8, 1C,
2-CAr), 111.2 (d, JPC = 10.7, 1C, 6-CAr), 113.3 (s, 1C, 5-CAr), 145.6 (s,
1C, CArOMe), 149.0 (d, JPC = 8.25, 1C, 1-CArOP or 3-CArOP), 153.4
(d, JPC = 9.1, 1C, 3-CArOP or 1-CArOP). Anal. Calcd for C19H34O2P2
(372.42): C, 61.28; H, 9.20. Found: C, 60.97; H, 9.72.
1,3-(i-Pr2PO)2,4-(COOMe)-C6H3, 6. This ligand (a yellow oil) was
prepared in 94% yield (4.5 g) using the same procedure described for
the synthesis of 3. 1H NMR (400 MHz, CDCl3): δ 1.03 (dd, JHP = 16,
JHH = 7.2, 6H, CH(CH3)2), 1.10 (dd, JHP = 15.6, JHH = 7.2, 6H,
CH(CH3)2), 1.17 (dd, JHP = 10.8, JHH = 7.0, 6H, CH(CH3)2), 1.31
General Procedure for Synthesis of Ligands. We have followed
previously published procedures for the synthesis of ligands 115b and
7.27 Ligand 9 was prepared using the same method as reported for
8,15c whereas the remaining ligands were prepared using slightly
modified versions of these procedures, as described below.
(dd, JHP = 10.8, JHH = 7.0, 6H, CH(CH3)2), 1.81 (dh, JHH = 7.1, JHP
=
2.8, 2H, 1-OPCH(CH3)2), 1.96 (dh, JHH = 7.0, JHP= 3.5, 2H, 3-
OPCH(CH3)2), 3.65 (s, 3H, OCH3), 6.92 (dm, JHH = 8.7, 1H, 6-HAr),
7.87 (m, 1H, 2-HAr), 8.05 (d, JHH = 8.7, 1H, 5-HAr). 31P{1H} NMR
(162 MHz, CDCl3): δ 151.1 (s), 151.6 (s). 13C{1H} NMR (75 MHz,
CDCl3): δ 16.88 (d, JCP = 8.5, 2C, CH3), 16.92 (d, JCP = 8.5, 2C,
CH3), 17.41 (d, JCP = 9.3, 2C, CH3), 17.7 (d, JCP = 10.1, 2C, CH3),
28.14 (d, JCP = 17.8, 2C, PCH(CH3)2), 28.2 (d, JCP = 18.1, 2C,
PCH(CH3)2), 51.36 (s, 1C, OCH3), 108.3 (dd, JCP′ = 12.7, JCP″ = 11.8,
1C, 2-CAr), 110.9 (d, JPC = 10.9, 1C, 6-CAr), 114.4 (s, 1C, 5-CAr), 132.9
(s, 1C, CArCOOMe), 160.7 (d, JPC = 9.2, 1C, 1-CArOP or 3-CArOP),
163.5 (d, JPC = 8.5, 1C, 3-CArOP or 1-CArOP), 166.2 (s, 1C, CO).
Anal. Calcd for C20H34O4P2 (400,43): C, 59.99; H, 8.56. Found: C,
60.06; H, 8.61.
1,3-(i-Pr2PO)2-5-OMe-C6H3, 3. Dropwise addition of ClP(i-Pr)2
(2.56 mL, 16.13 mmol) to a solution of 5-methoxyresorcinol (1.13 g,
8.06 mmol) and NEt3 (2.47 mL, 17.7 mmol) in THF (50 mL) led to
the formation of a white precipitate. The reaction mixture was stirred
at room temperature for 1 h, followed by removal of the volatiles and
extraction of the solid residues with hexane (3 × 25 mL) to give the
crude product as a pale yellow oil (0.93 g, 70%). This material, which
was shown by NMR spectroscopy to be greater than 98% pure, was
used for the synthesis of the target complexes without further
purification. 1H NMR (400 MHz, C6D6): δ 0.97 (dd, JHP = 19.6, JHH
=
7.2, 12H, CH(CH3)2), 1.13 (dd, JHP = 10.4, JHH = 7.0, 12H,
CH(CH3)2), 1.74 (dh, JHP = 2.5, JHH = 7.0, 4H, PCH(CH3)2) 3.30 (s,
3H, OCH3), 6.70 (m, 2H, Ar), 7.13 (m, 1H, Ar). 31P{1H} NMR (162
MHz, C6D6): δ 147.5 (s). 13C{1H} NMR (101 MHz, C6D6): δ 17.15
1,3-(t-Bu2PO)-5-COOMe-C6H3, 9. This ligand was obtained as a
colorless oil in 63% yield (1.7 g) using the same method as reported
for ligand 8.15c 1H NMR (400 MHz, C6D6): δ 1.17 (d, JHP = 11.7,
C(CH3)3, 36H), 3.56 (s,OCH3, 3H), 7.72 (m, Ar, 1H), 7.97 (m, Ar,
2H). 31P{1H} NMR (162 MHz, C6D6): δ 155.8 (s). 13C{1H} NMR
(d, JCP = 8.6, 4C, CH3), 17.9 (d, JCP = 20.6, 4C, CH3), 28.6 (d, JCP
=
18.5, 4C, PCH(CH3)2), 54.9 (s, 1C, OCH3), 98.8 (d, JPC = 11.0, 2C,
4,6-CAr), 101.9 (t, JPC = 12.0, 1C, 2-CAr), 161.7 (d, JPC = 9.4, 2C,
CArOP), 162.0 (s, 1C, CArOMe). Anal. Calcd for C19H34O2P2
(372.42): C, 61.28 ; H, 9.20. Found: C, 60.73; H, 9.30.
(101 MHz, CDCl3): δ 27.5 (d, JCP = 15.6, 12C, CH3), 35.8 (d, JCP
=
26.7, 4C, CCH3), 51.8 (s, 1C, OMe), 113.1 (t, JPC = 11.9, 1C, 2-CAr),
8567
dx.doi.org/10.1021/om3009475 | Organometallics 2012, 31, 8561−8570

Organometallics
Article
113.2 (d, JPC = 10.8, 2C, 4,6-CAr), 133.0 (s, 1C, CArCO), 161.4 (d, JPC
= 10.1, 2C, CArOP), 166.3 (s, 1C, CO) Anal. Calcd for C24H42O4P2
(456.54): C, 63.14; H, 9.27. Found: C, 63.75; H, 9.87.
Synthesis of the Complexes. Previously published reports have
described the synthesis and characterization of complex 1′15b and the
chloro analogue of complex 8′.20 Slightly modified versions of these
procedures were used to prepare all other complexes, as described
below.
{2,6-(i-Pr2PO)2-3-COOMe-C6H2}NiBr, 6′. The standard procedure
described above for 3′ gave the desired product as a yellow solid (0.81
g, 86%). 1H NMR (300 MHz, C6D6): δ 1.11 (dtv, JHH = 7.63, 7.03, 6H,
CH(CH3)2), 1.21 (dtv, JHH = 7.8, JHP = 6.8, 6H, CH(CH3)2), 1.33 (dtv,
JHH = 7.4, JHP = 7.4, 6H, CH(CH3)2), 1.36 (dtv, JHH = 7.5, JHP = 7.5,
6H, CH(CH3)2), 2.20 (dh, JHH = 5.3, JHP = 1.6, 2H, 6-OPCH(CH3)2),
2.29 (dh, JHH = 5.1, JHP = 1.7, 2H, 2-OPCH(CH3)2), 3.53 (s, 3H,
OCH3), 6.52 (d JHH = 8.5, 1H, 5-HAr), 7.88 (d, JHH = 8.4, 1H, 4-CArH).
31P{1H} NMR (202 MHz, C6D6): δ 190.4 (d, (AB) JPP = 323, 1P),
192.1 (d, (AB) JPP = 323, 1P). 13C{1H} NMR (75 MHz, C6D6): δ
16.66 (s, 2C, CH3), 16.81 (s, 2C, CH3), 17.73 (t, JCP = 2.4, 2C, CH3),
17.83 (t, JCP = 2.4, 2C, CH3), 28.27 (vt, JCP = 12.4, 2C, PCH(CH3)2),
28.41 (vt, JCP= 13.4, 2C, PCH(CH3)2), 51.27 (s, 1C, OCH3), 106.1
(dd, JP′C = 5.3, JP″C = 5.1, 1C, 5-CAr), 110.62 (dd, JP′C = 5.3, JP″C = 5.5,
1C, CArCO), 131.33 (vt, JPC = 20.1, 1C, Ni-CAr), 132.77 (s, 1C, 4-
CAr), 165.37 (s, 1C, CO), 168.71 (t, JCP = 10.5, 1C, 6-CArOP), 172.0
{2,6-(i-Pr2PO)2-4-OMe-C6H2}NiBr, 3′. To the solution of ligand 3
(1.05 g, 2.81 mmol) and NEt3 (469 μL, 3.37 mmol) in THF (30 mL)
was added {(i-PrCN)NiBr2}n (807 mg, 2.81 mmol), and the mixture
was stirred at room temperature for one hour, during which it turned
brown initially and then yellow, and a white precipitate appeared.
Filtration of the final mixture and evaporation of the filtrate followed
by extraction of the residual solids with hexane (3 × 25 mL) gave a
solution that yielded yellow crystals by slow evaporation. Washing the
crystals with a small quantity of cold hexane gave the desired product
(t, JCP = 10.2, 1C, 2-CArOP). UV−vis (CH2Cl2, 6.88 × 10−4 M) [λmax
,
1
(0.81 g, 74%). H NMR (400 MHz, C6D6): δ 1.18 (dtv, JHH = 4.3,
nm (ε, L mol−1 cm−1)]: 397(157), 360(201), 343(776). Anal. Calcd
for C20H33O4P2NiBr (538.02): C, 44.65; H, 6.18. Found: C, 44.56; H,
6.15.
12H, CH(CH3)2), 1.40 (dtv, JHH = 6.1, 12H, CH(CH3)2), 2.26 (m,
4H, PCH(CH3)2), 3.25 (s, 3H,OCH3), 6.33 (s, 2H, Ar). 31P{1H}
NMR (162 MHz, C6D6): δ 190.63 (s). 13C{1H} NMR (101 MHz,
{2,6-(i-Pr2PO)2-3,5-t-Bu2-C6H}NiBr, 7′. The standard procedure
CDCl3): δ 16.79 (s, 4C, CH3), 17.89 (s, 4C, CH3), 28.29 (vt, JCP
=
described above for 3′ gave the desired product as a yellow solid (577
1
11.2, 4C, PCH(CH3)2), 55.5 (s, 1C, OCH3), 92.9 (vt, JPC = 6.1, 2C,
CHAr), 118.7 (t, JPC = 21.4, 1C, Ni-CAr), 162.65 (s, 1C, CArOMe),
169.5 (vt, JPC = 10.4, 2C, CArOP). UV−vis (CH2Cl2, 1.19 × 10−4 M)
[λmax, nm (ε, L mol−1 cm−1)]: 389(1748), 338(9895), 320(4876).
Anal. Calcd for C19H33O3P2NiBr (510.01): C, 44.75; H, 6.52. Found:
C, 44.82; H, 6.46.
{2,6-(i-Pr2PO)2-4-Me-C6H2}NiBr, 2′. The standard procedure
described above for 3′ gave the desired product as a yellow solid
(1.05 g, 76%). 1H NMR (300 MHz, CDCl3): δ 1.33 (dtv, JHH = 7.0, JHP
= 6.7, CH(CH3)2, 12H), 1.43 (dtv, JHH = 8.3, JHP = 8.0, (CH(CH3)2)2,
12H), 2.20 (s,CH3, 3H), 2.45 (m, JHH = 6.8, 4H, PCH(CH3)2), 6.28
(s, Ar, 2H). 31P{1H} NMR (162 MHz, CDCl3): δ 189.11 (s). 13C{1H}
NMR (101 MHz, CDCl3): δ 16.82 (s, 4C, CH3), 17.88 (s, 4C, CH3),
21.6 (s, 1C, CH3), 28.07 (vt, JCP = 11.3, 4C, PCH(CH3)2), 106.1 (vt,
JPC = 6.0, 2C, 3,5-CAr), 123.7 (t, JPC = 21.5, 1C, Ni-CAr), 139.65 (s, 1C,
CArMe) 168.6 (vt, JPC = 10.0, 2C, CArOP). UV−vis (CH2Cl2, 13.56 ×
10−4 M) [λmax, nm (ε, L mol−1 cm−1)]: 396(164), 355(237),
338(1063), 324(517). Anal. Calcd for C19H33O2P2NiBr (494.01): C,
46.19; H, 6.73. Found: C, 46.17; H, 6.66.
mg, 45%). H NMR (400 MHz, C6D6): δ 1.33 (s, 18H, C(CH3)3),
v
1.36 (dtv, JH−H = 10.8, JH−P = 7.3, 12H, CH3), 1.44 (dtv, JH−H = 8.3,
vJH−P = 7.6, 12H, CH3), 2.48 (m, 4H, PCH(CH3)2), 6.92 (s, 1H, HAr).
31P{1H} NMR (162 MHz, C6D6): δ 185.15 (s). 13C{1H} NMR (101
MHz, CDCl3): δ 17.08 (s, 4C, CH3), 18.01 (tv, JCP = 2.48, 4C, CH3),
28.18 (tv, JCP = 11.8, 4C, PCH(CH3)2), 30.06 (s, 6C, C(CH3)3), 34.41
(s, 2C, C(CH3)3), 123.89 (s, 1C, CHAr), 126.52 (tv, JCP = 5.17, 2C,
CAr(tBu)), 131.28 (t, JPC=19.8, 1C, Ni-CAr), 164.15 (tv, JPC = 9.55, 2C,
CArOP). UV−vis (CH2Cl2, 3.68 × 10−4 M) [λmax, nm (ε, L mol−1
cm−1)]: 389(1622), 355(1987), 338(8923), 325(5378), 307 (3445)
Anal. Calcd for C26H47O2P2NiBr (592.20): C, 52.73; H, 8.00. Found:
C, 53.06; H, 8.08.
{2,6-(t-Bu2PO)2-C6H3}NiBr, 8′. The standard procedure described
above for 3′ gave the desired product as a yellow solid (0.4 g, 57%).
1H NMR (400 MHz, C6D6): δ 1.46 (vt, JHP = 6.6, 36H, CH3), 6.6 (d,
J
HH = 7.8, 2H, HAr), 6.88 (t, JHH = 7.6, 1H, HAr). 31P{1H} NMR (162
MHz, C6D6): δ 191.00 (s). 13C{1H} NMR (101 MHz, CDCl3): δ
27.39 (s, 12C, CH3), 38.75 (vt, JCP = 7.1, 4C, PC), 103.84 (vt, JCP
=
5.6, 2C, 3,5-CAr), 126.14 (t, JCP = 20.0, 1C, Ni-CAr), 127.37 (s, 1C, 4-
CAr) 168.38 (vt, JPC = 9.4, 1C, CArOP). UV−vis (CH2Cl2, 4.51 × 10−4
M) [λmax, nm (ε, L mol−1 cm−1)]: 407(198), 352(138), 334(916).
Anal. Calcd for C20H33O4P2NiBr (536.09): C, 49.29; H, 7.33. Found:
C, 49.28; H, 7.39.
{2,6-(t-Bu2PO)2-4-COOMe-C6H2}NiBr, 9′. The standard proce-
dure described above for 3′ gave the desired product as a yellow solid
(0.94 g, 72%). 1H NMR (400 MHz, C6D6): δ 1.41 (vt, JHP = 6.1, CH3,
36H), 3.50 (s, 3H, OCH3), 7.45 (s, 2H, HAr). 31P{1H} NMR (162
MHz, C6D6): δ 191.81 (s). 13C{1H} NMR (101 MHz, CDCl3): δ
28.27 (s, 12C, CH3), 39.94 (vt, JCP = 6.9, 4C, PC(CH3)3), 52.06 (s,
1C, OCH3), 105.86 (vt, JCP = 5.3, 2C, 3,5-CAr), 130.48 (s, 1C,
CArCOOMe), 135.91 (t, JPC = 19.0, 1C, Ni-CAr), 167.04 (s, 1C, C
O), 169.0 (vt, JPC = 8.9, 2C, CArOP). UV−vis (CH2Cl2, 10.6 × 10−4
M) [λmax, nm (ε, L mol−1 cm−1)]: 413(228), 360(1043), 326(378).
Anal. Calcd for C20H33O4P2NiBr (594.12): C, 48.52; H, 6.96. Found:
C, 48.64; H, 7.16.
Cyclic Voltammetry Experiments. Cyclic voltammetry measure-
ments were performed using a SP50 BioLogic Science Instrument
potentiostat. A typical three-electrode system consisting of a graphite
working electrode, a Pt auxiliary electrode, and a Ag/AgCl reference
electrode was employed. The experiments were carried out at room
temperature on analyte solutions prepared in dry CH2Cl2 containing
[n-Bu4N][PF6] as electrolyte (0.1 M). The samples were bubbled with
nitrogen before each experiment. Under the experimental conditions
of our studies, the redox potential (E1/2) for the Cp2Fe+/Cp2Fe couple
was +0.43 V.
{2,6-(i-Pr2PO)2,4-(COOMe)C6H2}NiBr, 4′. The standard proce-
dure described above for 3′ gave the desired product as a yellow solid
1
(0.87 g, 92%). H NMR (400 MHz, CDCl3): δ 1.20 (dtv, JHH = 7.26
JHP = 7.1, 12H, CH(CH3)2), 1.43 (dtv, JHH = 8.64 JHP = 8.02, 12H,
CH(CH3)2), 2.30 (m, 4H, PCH(CH3)2), 3.54 (s, 3H,OCH3), 7.66 (s,
2H, Ar). 31P{1H} NMR (162 MHz, C6D6): δ 190.56 (s). 13C{1H}
NMR (101 MHz, C6D6): δ 16.68 (s, 4C, CH3), 17.75 (s, 4C, CH3),
28.34 (vt, JCP = 11.24, 4C, PCH(CH3)2), 51.7 (s, 1C, OCH3), 106.8
(vt, 2C, CHAr), 131.9 (s, 1C, CArCOOMe), 137.19 (t, JPC = 20.8, 1C,
Ni-CAr), 166.6 (s, 1C, CO), 169.0 (vt, JPC = 10.0, 2C, CArOP). UV−
vis (CH2Cl2, 2.68 × 10−4 M) [λmax, nm (ε, L mol−1 cm−1)]:
384(3863), 362(8552), 326(3118). Anal. Calcd for C20H33O4P2NiBr
(538.02): C, 44.65; H, 6.18. Found: C, 44.66; H, 6.49.
{2,6-(i-Pr2PO)2-3-OMe-C6H2}NiBr, 5′. The standard procedure
described above for 3′ gave the desired product as a yellow solid (0.86
g, 90%). 1H NMR (400 MHz, CDCl3): δ 1.33−1.45 (m, 24H,
CH(CH3)2), 2.45 (m, 2H, 3-OPCH(CH3)2), 2.51 (m, 2H, 1-
OPCH(CH3)2), 3.77 (s, 3H, OCH3), 6.35 (d (AB) JHH = 7.25, 1H,
4-HAr), 6.61 (d (AB), JHH = 7.18, 1H, 5-HAr). 31P{1H} NMR (162
MHz, CDCl3): δ 187.5 (d, (AB) JPP = 317.8, 1P), 192.2 (d, (AB) JPP
=
317.8, 1P). 13C{1H} NMR (101 MHz, CDCl3): δ 16.79 (s, 2C, CH3),
16.93 (s, 2C, CH3), 17.86 (s, 2C, CH3), 17.90 (s, 2C, CH3), 28.16 (vt,
JCP = 19.1, 2C, PCH(CH3)2), 28.19 (vt, JCP = 18.9, 2C, PCH(CH3)2),
57.2 (s, 1C, OCH3), 103.9 (d, JPC = 12.6, 1C, 5-CAr), 113.2 (s, 1C, 4-
CAr), 129.7 (vt, JPC = 20.4, 1C, Ni-CAr), 140.6 (d, JPC = 13.9, 1C,
MeOCAr), 156.9 (m, 1C, 2-CArOP), 162.6 (dd, 1C, 6-CArOP). UV−vis
(CH2Cl2, 6.47 × 10−4 M) [λmax, nm (ε, L mol−1 cm−1)]: 394(153),
358(170), 339(852). Anal. Calcd for C19H33O3P2NiBr (510.01): C,
44.75; H, 6.52. Found: C, 45.11; H, 6.59.
Crystal Structure Determinations. The crystallographic data for
compounds 2′, 4′, and 8′ were collected on a Bruker Microstar
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Organometallics
Article
generator (Microsource) equipped with a Helios optics, a Kappa
Nonius goniometer, and a Platinum135 detector. The crystallographic
data for complexes 3′, 8, and 9′ were collected on a Nonius FR591
generator (rotating anode) equipped with a Montel 200, a D8
goniometer, and a Bruker Smart 6000 area detector. The crystallo-
graphic data for complexes 7′ were collected on a a Bruker APEX II
equipped with an Incoatec I\muS Microsource and a Quazar MX
monochromator. Cell refinement and data reduction were done using
SAINT.28 An empirical absorption correction, based on the multiple
measurements of equivalent reflections, was applied using the program
SADABS.29 The space group was confirmed by XPREP routine30 in
the program SHELXTL.31 The structures were solved by direct
methods and refined by full-matrix least-squares and difference Fourier
techniques with SHELX-97.32 All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms were set in
calculated positions and refined as riding atoms with a common
thermal parameter.
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A. B.; Offenstein, C.; Zargarian, D. Organometallics 2011, 30, 5352.
(f) Lefevre, X.; Durieux, G.; Lesturgez, S.; Zargarian, D. J. Mol. Catal.
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A: Chem. 2011, 335, 1. (g) Xu, G.; Li, X.; Sun, H. J. Organomet. Chem.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Tables of NMR data (1H and 13C{1H}) for ligands and
complexes, a plot correlating 31P chemical shifts for ligands and
complexes, tables of crystal data and collection/refinement
parameters, and a table of absorption spectral data for ligands
and complexes. This material is available free of charge via the
Internet at http://pubs.acs.org. Complete details of the X-ray
analyses reported herein have been deposited at The
Cambridge Crystallographic Data Centre (CCDC 895773
(8), 895779 (2′), 895774 (3′), 895778 (4′), 895776 (7′),
895777 (8′), 895775 (9′)). This data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by e-
mailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zargarian.davit@umontreal.ca.
(10) (a) Boro, B. J.; Duesler, E. N.; Goldberg, K. I.; Kemp, R. A. Inor.
Chem. 2009, 48, 5081. (b) Schmeier, T. J.; Hazari, N.; Incarvitoa, C.
D.; Raskatovb, J. A. Chem. Commun. 2011, 47, 1824. (c) Rossin, A.;
Peruzzini, M.; Zanobini, F. Dalton Trans. 2011, 40, 4447.
(11) (a) Castonguay, A.; Spasyuk, D. M.; Madern, N.; Beauchamp, A.
L.; Zargarian, D. Organometallics 2009, 28, 2134. (b) Castonguay, A.;
Beauchamp, A. L.; Zargarian, D. Inorg. Chem. 2009, 48, 3177.
(12) Solano-Prado, M. A.; Estudiante-Negrete, F.; Morales-Morales,
D. Polyhedron 2010, 29, 592.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to NSERC of Canada for a Discovery
Grant to D.Z., Universite
́
de Montrea
́
l and Centre in Green
Chemistry and Catalysis for graduate fellowships to B.V., Dr.
Laure Benhamou for valuable discussions, Mr. Olivier Marcadet
for technical assistance with some of the experiments, and Dr.
Michel Simard and Ms. Francine Belanger-Gariepy for their
́ ́
valuable assistance with crystallography.
(13) Estudiante-Negrete, F.; Hernan
D. Inorg. Chim. Acta 2012, 387, 58.
̀
dez-Ortega, S.; Morales-Morales,
(14) Chen, T.; Yang, L.; Li, L.; Huang, K.-W. Tetrahedron 2012, 68,
6152.
(15) (a) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.;
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