Synthesis of unsymmetrical 5,6-POCOP′-type pincer complexes of nickel(II): Impact of nickelacycle size on structures and spectroscopic properties

Article abstract of DOI:10.1039/c5nj00807g

This report describes the synthesis and characterization of a family of unsymmetrical pincer complexes of nickel(ii), featuring both 5- and 6-membered nickelacycles. The room temperature reaction of NiBr₂(NCCH₃)_x with bis(phosphinite) ligand, 1-(i-Pr₂PO),3-(i-Pr₂POCH₂)-C₆H₄ (POCHOP′), results in direct nickelation at the 2-position of the aromatic ring to give (5,6-POCOP′)NiBr (5,6-POCOP′ = κ^P,κ^C,κ^P′-2-(i-Pr₂PO),6-(i-Pr₂POCH₂)-C₆H₃). This complex undergoes salt metathesis reactions with M′X to give the corresponding charge neutral derivatives, (5,6-POCOP′)NiX (X = OSO₂CF₃, OSO₂(4-CH₃-C₆H₄), CH₃, and CCCH₃), whereas the abstraction of bromide by AgBPh₄ in acetonitrile gave the cationic derivative, [(5,6-POCOP′)Ni(NCCH₃)][BPh₄]. The new complexes have been characterized by multinuclear NMR spectroscopy and X-ray diffraction studies. The reactivities of the new complexes (5,6-POCOP′)NiX (X = Br, OSO₂CF₃) have been explored briefly to establish the nucleophilicity of the X ligand and the substitutional lability of the phosphinite moiety in the 6-membered cycle.

Full text of DOI:10.1039/c5nj00807g

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Graphic for Table of Contents and Abstract
For:
Synthesis of Unsymmetrical 5,6-POCOP´-Type Pincer Complexes of Nickel (II):
Impact of Nickelacycle Size on Structures and Spectroscopic Properties
Abderrahmen Salah, Martin Corpet, Najm ul-Hassan Khan, Davit Zargarian,* and
Denis Spasyuk†
* Département de chimie, Université de Montréal, Montréal (Québec), Canada H3C 3J7
† Current address: Department of Chemistry, University of Calgary,
2500 University Dr. NW, Calgary, Alberta, Canada, T2N1N4
Different structures and reactivities have been observed with the unsymmetrical pincer-
type complex (5,6-POCOP´)Ni(II)Br and its various derivatives compared to their
analogous symmetrical 5,5-POCOP systems, thus serving to establish the importance of
the size and degree of flexibility in the metallacycle rings.

New Journal of Chemistry
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Synthesis of Unsymmetrical 5,6-POCOP´-Type Pincer Complexes of Nickel (II):
Impact of Nickelacycle Size on Structures and Spectroscopic Properties
Abderrahmen Salah, Martin Corpet, Najm ul-Hassan Khan, Davit Zargarian,* and
Denis Spasyuk†
* Département de chimie, Université de Montréal, Montréal (Québec), Canada H3C 3J7
† Current address: Department of Chemistry, University of Calgary,
2500 University Dr. NW, Calgary, Alberta, Canada, T2N1N4

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Abstract
This report describes the synthesis and characterization of a family of unsymmetrical
pincer complexes of nickel(II) featuring both 5- and 6-membered nickelacycles. The
room temperature reaction of NiBr2(NCCH3)x with the bis(phosphinite) ligand 1-(i-
Pr2PO),3-(i-Pr2POCH2)-C6H4 (POCHOP´) results in direct nickelation at the 2-position of
the aromatic ring to give (5,6-POCOP´)NiBr (5,6-POCOP´ = {κP,κC,κP´-2-(i-Pr2PO),6-(i-
Pr2POCH2)-C6H3}). This complex undergoes salt metathesis reactions with M´X to give
the corresponding charge neutral derivatives (5,6-POCOP´)NiX (X = OSO2CF3, OSO2(4-
CH3-C6H4), CH3, and C≡CCH3), whereas abstraction of the bromide by AgBPh4 in
acetonitrile gave the cationic derivative [(5,6-POCOP´)Ni(NCCH3)][BPh4]. The new
complexes have been characterized by multinuclear NMR spectroscopy and X-ray
diffraction studies. The reactivities of the new complexes (5,6-POCOP´)NiX (X= Br,
OSO2CF3) have been explored briefly to establish the nucleophilicity of the X ligand and
the substitutional lability of the phosphinite moiety in the 6-membered cycle.
Keywords: unsymmetrical pincer complex, POCOP, 5,6-POCOP´

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Introduction
The term “pincer” was coined in 1989 by van Koten1 to refer to the then-growing
family of terdentate ligands and their complexes introduced in the late 1970’s and early
1980’s by Shaw,2 van Koten3 and Fryzuk.4 According to van Koten’s original definition,
pincer ligands were classified according to the donor atoms of their charge-neutral (E)
and monoanionic (X) donor moieties. Thus, the normally meridional ligation of metal
ions by EXE-type pincer ligands (terdentate, monoanionic) generated the corresponding
EXE-type pincer complexes that were, for the most part, robust and thermally stable
species displaying a variety of interesting reactivities and physical/material properties.5
Over the past two decades, pincer complexes have experienced substantial growth due,
primarily, to their versatility in catalysis6 and potential applications in functional
materials.7
Most pincer complexes reported to date are based on a symmetrical ligand
architecture featuring two fused, five-membered metallacycles. On the other hand, recent
reports have shown a growing interest in the structures and reactivities of nonsymmetrical
EXE´-type ligands based on both different donor moieties and differently-sized
metallacycles, including : 5,6-NCS;8 5,6-SCN;9 5,6-POCN;10 3,6-, 3,7-, and 4,5-PNP´;11
5,6-PCN;12 5,6-POCOP´.13,14 These new types of pincer ligands represent a number of
potential advantages over their more popular symmetrical analogues. For instance, the
presence of differently sized metallacycles allows a modulation of ligand bite angle and
binding pocket, thereby altering the lability of a donor moiety and influencing
reactivities. Moreover, different donor moieties based on hard-soft and large-small donor

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atoms allow for greater control over electronic and steric tuning of the environment
around the metal center.15
Our laboratory’s studies in the area of pincer-Ni chemistry have been focused
primarily on the reactivities of symmetrical complexes featuring 5,5-PCP-16 and 5,5-
POCOP-type17 ligands, but more recently we have initiated new projects aimed at
studying the synthesis, structures, and reactivities of unsymmetrical systems. Thus, we
have reported Ni complexes featuring 5,5-POCN18 and 5,6-PimioCOP ligands,19 and the
promising results emerging from these projects have prompted us to explore the
reactivities of other closely related ligand systems. We have also been inspired by
literature reports on 5,6-POCOP´-Pd complexes13a to examine the structures and
reactivities of 5,6-POCOP´-Ni complexes.
This report describes the synthesis, characterization, and preliminary reactivity
studies on the unsymmetrical pincer complexes (5,6-POCOP´)NiX (κP,κC,κP−5,6-
POCOP´ = 2-(i-Pr2PO),6-(i-Pr2POCH2)-C6H3; X = Br, 1; OSO2ArCH3, 2; OSO2CF3, 3;
CCMe, 5; CH3, 6) and [(5,6-POCOP)Ni(NCMe)][Y] (Y = OSO2CF3, 4a; BPh4, 4b). All
complexes were characterized by NMR spectroscopy and single crystal X-ray diffraction
studies in an effort to determine the effect of metallacycle on the spectroscopic properties
and structures of the title complexes, as described below.
Results and Discussion
Synthesis of POCHOP´ and its nickelation. The previously reported13a synthesis of 1-
(i-Pr2PO),3-(i-Pr2POCH2)-C6H4 uses dimethylamino pyridine (DMAP) for phosphination
of the precursor diol, 3-hydroxybenzyl alcohol, which was obtained from commercial
sources. We have developed a slightly modified synthesis based on in-house prepared

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diol and use of NEt3 in the phosphination step, as illustrated in Scheme 1 and discussed
below.
HO
HO
NaBH4 MeOH
,
OH
O
r.t. h)
(3
0 °C h)
(1
79%
i-Pr
2PCl
NEt3 benzene
,
r.t., 1
58%
h,
P( -Pr)
i
2
Br
Ni
P( -Pr)
i
CN)X
2
Ni(Br)2(CH3
O
O
-Pr) P
i
(
P( -Pr)
i
2
2
Toluene, NEt3
r.t., N2
O
O
a
24 60%
h,
1
Scheme 1. Synthesis of (5,6-POCOP´)NiBr, 1.
Treating the commercially available 3-hydroxybenzaldehyde with excess NaBH4
in methanol at 0 °C and stirring the sample further at r.t. gave 3-hydroxybenzylalcohol,
which was obtained as colorless crystals in 79% yield by recrystallization from ethyl
acetate. Reaction of this diol with i-Pr2PCl in the presence of NEt3 gave the target
bis(phosphinite) a as an off-white oil in 58% yield. Finally, subsequent treatment of a
with Br2Ni(NCMe)x in toluene and in the presence of NEt3 gave the target bromo
derivative (5,6-POCOP´)NiBr, 1, as a yellow solid in 60 % yield (Scheme 1). Tests
established that POCHOP´ is readily oxidized in air and must, therefore, be protected
from ambient conditions, whereas complex 1 is much easier to handle. For example, solid
samples of 1 are indefinitely air-stable, and its r. t. solutions resist air oxidation and
hydrolysis for hours. Indeed, this compound can be purified under aerobic conditions by

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extraction into Et2O, or by column chromatography (silica gel, toluene). Finally,
solutions of 1 are thermally stable indefinitely under a nitrogen atmosphere.
The role of NEt3 in the synthesis of 1 deserves some comment. Previous reports20
have shown that the primary role of base in the synthesis of (POCOP)Ni and (POCN)Ni
complexes is to merely remove the HX generated during the C-H nickelation step. In
other words, the base does not facilitate the C-H nickelation step, serving instead to
ensure optimal yields by preventing protonation of the unreacted ligand by in-situ
generated HX. Thus, most tertiary amines should be equally effective for this purpose.
Consistent with this assertion, using DMAP as base instead of NEt3 gave similar yields of
1.
Synthesis of new 5,6-POCOP´ derivatives. Treatment of 1 with silver tosylate and
silver triflate in dry dichloromethane (DCM) gave the corresponding derivatives 2 and 3
(Scheme 2). Given the light-sensitivity of these silver salts, care was taken to minimize
exposing the reaction mixtures to ambient light. The cationic acetonitrile adducts 4 were
obtained by reacting the tosylate derivative 2 with excess acetonitrile in DCM, or by
treating 1 with AgBPh4 in a 1:1 mixture of DCM and acetonitrile (Scheme 2). The
tosylate derivative is stable in ambient atmosphere for days in the solid state and for ca.
24 h in solution, whereas its triflate analogue proved to be less robust, with solid samples
decomposing gradually (> 6 h) and solutions over 2-3 h. The cationic adducts were also
quite prone to hydrolysis, decomposing over 12 h in the solid and over 5-6 h in wet
solvents.

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DCM / CH3CN
1:1
NCCH3
R2P
O
Ni
PR2
O
4a
4b
OTs
(75%)
(70%)
or
r.t., N
min
2, 15
BPh4
OTf
Ni
OTs
Ni
R2P
O
PR2
O
R2P
O
PR2
O
N
AgBPh 60°C,
DCM/CH3CN
2
30
min
3
2
1:1
Br
Ni
DCM
min,
DCM
AgOTs,
r.t., N2
AgOTf,
R2P
O
PR2
O
r.t., N 12
30
85%
80%
h,
,
2,
MeLi, THF
THF toluene
/
R'MgBr,
r.t.
r.t., N2 12 h
,
or
60 °C,
N
2
1
=
R
=
-Pr
i
Me
R'
Ni
OTf OSO2CF3
3-C
PR2
O
R2P
Ni
PR2
O
R2P
=
OTs OSO2 -CH 6H4
p
(
)
O
O
R'=
5
CCMe
6
,
R'= Me
6
,
Scheme 2. Synthesis of 5,6-POCOP´ complexes 2-6.
The propynyl and methyl derivatives 5 and 6 were synthesized by treating 1 with
the corresponding Grignard reagents in mixtures of THF and toluene (Scheme 2). Both
reactions led to a color change from yellow to dark brown. The reaction with
(CH3C≡C)MgBr required heating at 60 °C for at least 1 h to complete the conversion of
the bromo precursor, but even then we obtained no more than a 30% crude yield of the
propynyl derivative 5. In the case of the MeMgBr reaction, the conversion could be
pushed to completion at room temperature, but the methyl derivative 6 was obtained with
low yields only (< 20%). Using excess MeLi (ca. 10 equiv) at room temperature gave
higher yields (ca. 40-45%), but the desired product was always contaminated with side-

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products, even after repeated recrystallizations.21 As a result, neither of these hydrocarbyl
derivatives could be isolated in analytically pure forms, but small quantities of impurity-
free single crystals were obtained for both compounds, allowing analysis by X-ray
diffraction studies (vide infra). As described below, the reaction with excess MeLi was
investigated briefly in an attempt to shed some light on the side reaction(s) that
complicated the synthesis and isolation of pure products.
NMR monitoring the reaction of 1 with excess MeLi showed the emergence of
1
several upfield H signals (0.2 to -1 ppm) and an additional 31P peak at -15 ppm.
Comparison of the latter signal to the corresponding 31P signals for PMe3 (-60 ppm),
PMeEt2 (-34 ppm), PMe(i-Pr)2 (-10 ppm in C6D6), and P(i-Pr)3 (+20 ppm), suggested that
the phosphinite moiety in 1 or in the Ni-Me product might be reacting with MeLi to
generate P(Me)(i-Pr)2; such a side-reaction would then set into motion the dismantling of
the pincer backbone.17a
Spectroscopic characterization. Nickelation of POCHOP´ could be confirmed by the
absence of the 2-H signal in the 1H NMR spectrum of 1, as well as the appearance in its
31P{1H} NMR spectrum of AB doublets at δ 156 and 188 for the two inequivalent and
mutually coupled trans P nuclei (2JP-P= 283 Hz). Analogous AB doublets featuring large
2JP-P constants were also observed for the other derivatives (Table 1), as follows: ca. 148
and 189 ppm for the triflate (2JP-P= 285) and tosylate (2JP-P= 302) derivatives; ca. 152 and
194 ppm for the acetonitrile adduct (2JP-P= 260); ca. 160 and 187 ppm for the propynyl
derivative (2JP-P= 323), and 160 and 187 ppm for the methyl derivative (2JP-P= 323).

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Table 1. 31P{1H} NMR chemical shifts of POCHOP´ and complexes 1-6
Compound
d for ArO-P
d for ArCH2O-P
(multicplicity, 2Jpp in Hz) (multicplicity, 2Jpp in Hz)
POCHOP´
154 (s)
147 (s)
187 (d, 283)
189 (d, 302)
189 (d, 285)
194 (d, 260)
187 (d, 323)
187 (d, 323)
155 (d, 283)
148 (d, 302)
148 (d, 285)
152 (d, 260)
160 (d, 323)
160 (d, 323)
1
2
3
4b
5
6
Comparison of the 31P signals for the new derivatives 1-6 to the corresponding
singlets for the symmetrical POCOP complexes (POCOP)NiBr (ca. 186 ppm),
(POCOP)Ni(OTf) (184 ppm), and (POCOP)NiMe (ca. 192 ppm) has allowed us to assign
the more downfield of the doublets for 1-6 to the phosphinite moiety in the 5-membered
metalacycle. It is interesting to note that coordination to the nickel center results in
significant downfield shifts for the ArOP moiety, which changes from ca. 154 ppm in the
ligand to 187-194 ppm in the complexes, whereas the ArCH2OP moiety is much less
affected, going from ca. 147 ppm in the ligand to 148-160 ppm in the complexes
(Table1).
1
The H and 13C NMR spectra of the new complexes revealed useful information
about their symmetry properties in solution. Thus, in all but one case,22 the P-C-CH3
protons and P-C-CH3 carbons displayed four (not eight) distinct signals (doublets or
singlets), whereas the P-CH protons and P-C carbons displayed two (not four) doublets of

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10
doublets (when resolved). These observations imply the maintenance in the coordination
plane of a plane of symmetry that renders equivalent the nuclei above and below it. Given
the puckered conformation of the 6-membered metalacycle in the solid state (vide infra),
the effective planar symmetry inferred from the solution NMR data is likely the result of
a rapid “flipping” motion by this ring at ambient temperature.
The protons of the central aromatic moiety in the title complexes were readily
identified from their characteristic 1H resonances, doublets for H3/H5 and pseudo-triplets
for H4. The 13C{1H} NMR spectra showed singlets for C4/C5, doublets for C3, doublets
of doublets for C2/C6, and the following signals for C1: doublet of doublets in complexes
1 and 6; weak singlet for complexes 3 and 4b; doublet for 2. Interestingly, the Ni-CCCH3
carbon in 5 showed triplets, not doublets of doublets; this is presumably due to an
accidental equivalence of the two JP-C values.
Solid state characterization. Single crystals of all but the triflate derivatives were
obtained from various recrystallization experiments and subjected to crystallography in
order to study their solid state structures. All the structures were successfully refined to a
high degree of confidence. Crystal and data collection details for complexes 1, 2, 4b, 5
and 6 are presented in Table 1S, selected structural parameters are listed in Table 2, and
ORTEP diagrams are shown in Figure 1.
In all structures, the coordination geometry around the Ni atom is square planar, but
some distortions are evident because of the bite angle of the 5,6-POCOP´ ligand. For
example, the C1-Ni-P1 and P-Ni-P angles are tighter than ideal (ca. 82-84° and 168-170°,
respectively), whereas the remaining cis angles are closer to 90° (C1-Ni-P2~ 92-94°; P-
Ni-X~ 89-94°) and the C1-Ni-X angles are fairly linear (167-178°).

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11
Table 2. Selected Bond Distances (Å) and Angles (deg) for Complexes 1, 2, and 4b-6.
5†
1
2
4b
6
Ni-C(1)
Ni-P(1)
1.920(2)
2.1443(7)
2.1744(7)
2.3372(4)
169.26(3)
91.15(2)
92.24(2)
83.39(6)
93.06(6)
174.53(6)
21
1.916(2) 1.919(2)
2.1924(5) 2.1559(5)
2.1684(5) 2.1921(5)
1.937(1) 1.881(1)
169.19(2) 169.30(2)
94.39(4) 93.71(5)
88.55(4) 92.82(5)
83.95(5) 81.56(5)
92.92(5) 91.86(5)
178.26(6) 175.27(7)
1.936(3)
1.947(2)
2.1267(8) 2.1177(6)
2.1283(8) 2.1355(5)
Ni-P(2)
Ni-X/L
1.9100(3)
2.065(2)
P(1)-Ni-P(2)
P(1)-Ni-X
P(2)-Ni-X
P(1)-Ni-C(1)
P(2)-Ni-C(1)
C(1)-Ni-X
Twist angle‡
Tetrahedral
170.26(4) 168.14(3)
92.24(9)
91.28(9)
92.19(5)
91.89(5)
83.03(6)
92.78(6)
85.39(10)
93.76(10)
176.57(13) 175.22(8)
16
25
9
22
0.197
0.280
0.000
0.124
0.213
distortion*
†
All the values cited for this complex represent averages of the corresponding
values in two independent molecules.
‡ Twist angle is defined as the angle between the (mean) planes encompassing the
benzenic moiety of the 5,6-POCOP´ ligand (C(1)-C(6)) and the atoms P(1), C(1),
and P(2). See Chart 1 for a schematic representation.
* Distance of Ni from the plane defined by the atoms P(1), C(1), and P(2).

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12
1
2
5
4b
6
Figure 1. ORTEP diagrams for complexes 1, 2, 4b, 5, and 6. Thermal ellipsoids are set at
the 50% probability level for all complexes. The following have been omitted for clarity:
calculated H atoms and atom labels for i-Pr carbons in all diagrams; the BPh4 anion in
4b.

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13
Structural distortions similar to those noted above are also observed in all
symmetrical (5,5-POCOP)NiX complexes, but there are other structural differences
between the latter compounds and those studied here, the most important being the
varying degrees of co-planarity of the ligating atoms. Roddick23 has surveyed this co-
planarity feature for a large number of four-coordinate 5,5-pincer complexes, in the
process defining the so-called C2 twist involving the central aryl moiety and the “arms”
linking it to the pendant donor atoms. (See Chart 1 for a pictorial definition of the C2
twist angle θ.)
ring
H2
C
aryl
Ni
R
R
O
R
P2
P1
O
R
twist
angle
Chart 1. Schematic representation of “twist angle”
On the basis of this C2 twist, Roddick has concluded that the twisting is at a
minimum for 5,5-POCOP complexes, most of which generate nearly planar P-O-Ar-O-P-
M arrays (θ ~ 2°), and increasing for the analogous complexes based on the ligands 5,5-
PNCNP (θ ~ 4°) and 5,5-PCP (θ ~ 10°). By comparison to these values, the C2 twist is
generally greater in the title 5,6-POCOP´ systems (9-25°, Table 2), which is not
surprising given the greater degree of puckering possible in the 6-membered
metallacycle. On the other hand, the relatively large variation in the twist angles among
our complexes implies that the twisting is energetically “soft” and might not have
significant impact on the properties of these complexes; a similar observation has been
noted by Roddick for other pincer systems.23

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14
Another significant difference in the structures of 5,5-POCOP and 5,6-POCOP´
complexes pertains to the generally longer Ni-L distances found in the latter complex.
Thus, the following bond distances (all in Å) are longer in the 5,6-POCOP´analogues: Ni-
Br (2.3372(4) vs. 2.3231(5); Ni-C(1) in the bromo derivative (1.920(2) vs. 1.885(3)); Ni-
CH3 (2.065(2) vs. 1.996(2)). The Ni-P bond distances are also longer in the 6-membered
metalacycles in all compounds except 5: ∆(Ni-P) ~ 30-70 × (e.s.d.) in 1, 2, 4b, and 6. On
the other hand, the Ni-C1 distances are fairly similar in 1, 2, and 4 (ca. 1.92 Å), but much
longer in 5 (ca. 1.94 Å) and 6 (1.95 Å); these observations are consistent with the
respective trans influences of the various ligands X.
Reactivity tests. An important question about the potential reactivities of pincer
complexes touches on the substitutional lability of the donor moieties. This so-called
hemilabile character of a pincer system is particularly important in a catalytic setting
where strongly donor substrates might displace one or both donor moieties of a pincer
ligand, thus disrupting its terdentate binding and, consequently, altering the reactivities of
the metal center. In an effort to establish the binding lability of this ligand, we have tested
the lability of the two phosphinite moieties in the 5,6-POCOP´complex 1. Mixtures of 1
with different nucleophiles such as PPh3, imidazole and 2-methylimidazole, pyrazole,
31
N,N-dimethylpyridin-4-amine, and nicotinonitrile were heated at 60 °C for 18 h, and P
NMR spectroscopy was used to detect reactivity. The results of these experiments
showed that the terdentate binding in 1 is completely stable (Scheme 3).

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15
Br
Ni
Br
Br
Ni
L
+
R2P
O
PR2
O
X
R2P
O
Ni
L
L
L
60 °C
O
O
O
L
PR2
PR2
1
H
N
N
N
=
L
PPh3
HN
N HN
N
N
CN
NMe2
Scheme 3. Tests of the hemilabile character of complex 1.
Next, we tested the substitutional lability of the X ligand, using the triflate
derivative 3 as a model complex. Reaction of this species with various ligands led to
facile displacement of triflate to form the corresponding cationic species, as confirmed by
31P NMR spectroscopy (Scheme 4). The impact of the ligand substitution on the chemical
shifts of the phosphinite moieties varied considerably from one case to another. For
instance, coordination of morpholine caused significant upfield shifts for both the
phosphinite moiety of the 5-membered metallacycles (by 11 ppm) and that of the 6-
membered metalacycle (by 5 ppm), as well as a much larger coupling constant (2JP-P
=
343 Hz). By comparison, pyridine caused a 5 ppm shift upfield for both phosphinite
moieties (2JP-P = 271 Hz). Interestingly, the product obtained from the reaction of 2-N,N-
dimethylaminopyridine caused a dramatic color change from yellow to deep red and 13
ppm upfield shifts for both phosphinite moieties, in addition to a weaker P-P coupling;
we infer from these observations that a penta-coordinated species forms by the
coordination of both nitrogen moieties to the Ni(II) center.24 Finally, stirring a solution of
3 in an atmosphere of CO led to a gradual bleaching of the initial solution. To our
surprise, the 31P NMR spectrum of the very pale yellow final mixture showed no signals,

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16
not even those of the ligand. Exposing this sample to ambient air and re-examining its 31P
NMR spectrum showed two singlets at 62 and 50 ppm, a region characteristic of
phosphine oxides. We speculate that coordination of CO to the Ni center generates a
stereochemically labile penta-coordinated species featuring one or two CO ligands.24
OTf
OTf
pyridine
O
morpholine
N
Ni(5,6-POCOP')
N
Ni(5,6-POCOP')
H
2
d:
=
271
Hz
184 143, J
/
2
PP
d:
=
343
Hz
178 143, J
/
PP
3
,
(5,6-POCOP')Ni(OTf)
light yellow
red-orange
2
d:
=
Hz,
285
189 148, J
/
yellow
PP
Me2
OTf
N
?
n
(5,6-POCOP')Ni(CO) (OTf)
No 31P NMR
N
Ni(5,6-POCOP')
signal
NMe2
CO
2
very
d:
=
Hz
JPP 264
176
/135,
pale yellow
N
deep-red
Scheme 4. Substitution of triflate (OTf) in 3 by various ligands.
Another reactivity that was tested briefly was oxidation of the Ni(II) center.
Previous studies have shown that trivalent species are accessible by oxidation of certain
Ni(II) pincer complexes, including (POCsp3OP)NiX (POCsp3OP= (R2POCH2)2CH).17f, 17g
Symmetrical (POCOP)NiX complexes based on an aromatic backbone do not seem to
stabilize trivalent species; nevertheless, we conducted some tests to establish whether the
unsymmetrical (5,6-POCOP´)NiX derivatives might show different reactivities. Reacting
1 with NBS at room temperature converted the initial orange solution into dark green, a
color change we observe frequently when trivalent species are generated from
(pincer)Ni(II)Br. The green color of the reaction mixture is persistent at low
temperatures, indicating that the putative trivalent species is more stable than the

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17
corresponding species generated from (5,5-POCOP)NiBr. Unfortunately, we have not
succeeded in isolating a tractable product yet.
Finally, we have briefly investigated the stoichiometric reactions of complexes 2
and 3 to establish the nucleophilic character of the Ni-X moiety (toward aliphatic
halides)25 or its basicity (toward alcohols). In all cases, the reactions were conducted at
90 °C for 4 h and their progress was monitored by 31P NMR spectroscopy (Table 3); the
contents of the final reaction mixture were analyzed by GC/MS. Complex 2 proved
generally less reactive toward the substrates tested: no reaction was detected with
alcohols, and only partial conversion of 2 to the bromo precursor 1 was noted with 2-
bromopropane (22%) and 4-bromobutene (5%). On the other hand, complex 3 reacted
with all the haloalkanes tested, giving varying degrees of conversion to the corresponding
halo derivatives (Table 3). The tests with alcohols showed that complex 3 is inert toward
ethanol, trifluoroethanol, and 1-nonanol, but reacted with hexafluoroprapan-2-ol (~24%
conversion); the latter reaction gave a new product displaying a pair of 31P doublets at ca.
3 ppm downfield of the original signals for 3 (192/151 ppm; JPP = 258 Hz). We speculate
that this new species is the corresponding alkoxide derivative, but we have not succeeded
in isolating pure samples of this compound.

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Table 3. Reactivities of complexes 2 and 3 with R-Y and H-Y
or
R Y
H Y
or
R X
H X
(5,6-POCOP')Ni-X
(5,6-POCOP')Ni-Y
°
4
90
h
C,
% conversion*
2
3
Cl
Br
0
27
22
100
Br
R-Y
H-Y
5
0
54
20
Br
OH
0
24
F
3C
CF3
* Conversion is based on integration of 31P NMR signals for the Ni-X and Ni-Y
derivatives.
Conclusion
The present study has established a viable synthetic route to a new series of Ni(II)
species based on an unsymmetrical 5,6-POCOP´-type pincer ligand 1-(i-Pr2PO),3-(i-
Pr2POCH2)-C6H4. The ambient temperature nickelation at the C2 position of this ligand
has demonstrated that the facile C-H nickelation step characteristic of the symmetrical
5,5-POCOP ligands is preserved in their unsymmetrical counterpart. Indeed, the presence
of inequivalent, mutually trans phosphinite moieties in the title compounds renders their
31P NMR spectra very informative and provides a convenient diagnostic tool for
monitoring reactions and assessing the impact of X/L ligands on the two donor moieties.

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These practical aspects should facilitate the synthesis of (5,6-POCOP´)NiX and [(5,6-
POCOP´)NiL]+ and pave the way for systematic explorations of their reactivities.
The solid state structures presented in this report have allowed us to measure the
extent to which the 6-membered metallacycle disrupts the co-planarity of the ligating
atoms observed in the symmetrical (5,5-POCOP)Ni systems (“twist angles” = 9-25°).
Another impact of the differently-sized metallacycles is reflected in the generally longer
Ni-P distance in the 6-membered metallacycles. On the other hand, these structural
features do not appear to have significant consequences for the relative lability of the
phosphinite moieties in 5,6-POCOP´ vs. 5,5-POCOP compounds, at least not on the basis
of the preliminary reactivity probes presented here. Future investigations will seek to
confirm these findings and also identify potentially promising reactivities for further
developments.
Experimental Section
General. All manipulations were carried out using standard Schlenk and glove box
techniques under a nitrogen atmosphere. All solvents used for experiments were dried to
water contents of less than 10 ppm (determined using a Mettler Toledo C20 coulometric
Karl Fischer titrator) by passage through activated aluminum oxide columns (MBraun
SPS) and degassed prior to use. C6D6 was dried over 4 Å molecular sieves and then
freeze-thaw degassed. The nickel precursor Br2Ni(NCMe)x was prepared according to a
reported procedure.26 All used chemicals were purchased from Aldrich and, unless
otherwise noted, used without further purification.
The NMR spectra were recorded using the following Bruker spectrometers:
1
AV300, AV400RG and AVII400. H and 13C chemical shifts are reported in ppm

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downfield of TMS and referenced against the residual C6D6 signals (7.15 ppm for 1H and
31
128.02 ppm for 13C); P chemical shifts are reported in ppm and referenced against the
signal for 85% H3PO4 (external standard, 0 ppm). Coupling constants are reported in Hz.
Syntheses.
3-Hydroxybenzyl alcohol. NaBH4 (3.22 g, 85.0 mmol, 2.1 equiv.) was added portion-
wise and over 1 h to a 0 °C solution of 3-hydroxybenzaldehyde (5.01 g, 41.0 mmol, 1
equiv) in 15 mL of methanol. The resulting mixture was allowed to warm to room
temperature, stirred an additional 3 h, and evaporated. Aqueous HCl solution (3M) was
then added to bring the pH of the mixture to ~2, and the mixture extracted with ethyl
acetate (4 × 20 mL), the organic phase was dried over MgSO4, filtered, and evaporated
under vacuum to give an off-white solid. Recrystallization from ethyl acetate gave
1
3
colorless crystals (3.93 g, 79%). H NMR (300 MHz, C6D6) δ 7.00 (t, JHH = 8, 1H,
{Ar}H5), 6.70 (d, 3JHH = 8, 1H, {Ar}H4), 6.56 (s, 1H, {Ar}H2), 6.49 (dd, JHH = 8, 2; 1H,
13
{Ar}H6), 4.24 (s, 2H, CH2), 9.21 (s, 1H, Ph-OH), 5.53 (s, 1H, CH2-OH). C{1H}NMR
(76 MHz, C6D6) : d 115.62 (s, 1C, {Ar}C4), 113.52 (s, 1C,{Ar}C6), 128.84 (s, 1C,
{Ar}C5), 113.30 (s, 1C, {Ar}C2), 159.70 (s, 1C, {Ar}C1), 143.86 (s, 1C, {Ar}C3).
1-(i-Pr2PO),3-(i-Pr2POCH2)C6H4 , a. i-Pr2PCl (2.8 mL, 17 mmol, 2 equiv.) was added
to a mixture of 3-hydroxybenzyl alcohol (1.05 g, 8.50 mmol, 1 equiv.) and NEt3 (3.60
mL, 25.5 mmol, 3 equiv.) in 30 mL of benzene, and the resulting white suspension was
stirred at room temperature for 1 h. Evaporation under vacuum followed by extraction of
the solid residues with hexane (3 × 20 mL) and evaporation gave the product as an off-
white, air sensitive oil (1.75 g, 4.90 mmol, 58%). 1H NMR (400 MHz, C6D6) : δ 0.91 (dd,
JHP/HH = 7, 2; 6H, 2 × CH3), 1.00 (dd, JHP/HH = 7, 2; 6H, 2 × CH3), 1.10 (dd, JHP//HH = 7, 2;

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6H, 2 × CH3), 1.14 (dd, JHP/HH = 7, 2; 6H, 2 × CH3), 1.76 (m, 4H, 4 × CH), 4.72 (d, 3JHP
=
8, 2H, CH2), 6.82 (d, 3JHH = 6, 1H,{Ar}H5), 6.90 (m, 2H, 2 × {Ar}H3,4), 7.10 (d, 3JHP = 2,
1H,{Ar}H2). 13C{1H}NMR (101 MHz, C6D6) : d 17.81 (d, JCP = 20, 2C, 2 × CH3), 17.53
(d, JCP = 20, 2C, CH3), 16.92 (d, JCP = 20, 2C, 2 × CH3), 16.82 (d, JCP= 20, 2C, 2xCH3),
28.13 (dd, JCP = 24, 3; 2C, 2 × CH), 28.31 (dd, JCP = 20, 3; 2C, 2 × CH), 74.03 (d, JCP
=
21, 1C, CH2), 114.66 (d, JCP = 6, 1C, {Ar}C4), 141.45 (s, 1C,{Ar}C6), 129.30 (s, 1C,
{Ar}C5), 120.52 (d, JCP = 2, 1C, {Ar}C2) 159.70 (d, JCP = 9, 1C,{Ar}C1), 141.45 (dd,
JCP = 8, 1C; {Ar}C3). 31P{1H} NMR (162 MHz, C6D6) : d 147 (s, 1P, CH2O-P-(i-Pr)2),
154 (s, 1P, OP-(i-Pr)2).
(POCOPiPr(5,6))NiBr, 1. A mixture of a (1.75 g, 4.90 mmol, 1equiv.), NEt3 (0.90 mL,
5.9 mmol, 1.2 equiv.) and (Ni(Br)2(MeCN)x (2.6 g, 8.5 mmol, 1.7 equiv.) in toluene (35
mL) was stirred at room temperature for 24 h, filtered through a short silica gel column,
and evaporated under vacuum to give the product as air stable yellow crystals (1.45 g, 60
1
%). H NMR (400 MHz, C6D6) : δ 1.09 (dd, JHP/HH = 13, 7; 6H, 2 × CH3), 1.16 (dd,
JHP/HH = 14, 7 ; 6H, 2 × CH3), 1.42 (dd, JHP//HH = 7, 2; 6H, 2 × CH3), 1.46 (dd, JHP/HH = 7,
3
2; 6H, 2 × CH3), 2.42 (m, 4H, 4 × CH), 4.60 (d, 3JHP = 17, 2H; CH2), 6.43 (d, JHH = 6,
13
1H,{Ar}H5), 6.88 (m, 2H, 2 × {Ar}H3,4). C{1H}NMR (101 MHz, C6D6) : d 17.10 (d,
JCP = 15, 4C, 4 × CH3), 18.34 (d, JCP = 4, 2C, 2 × CH3), 19.15 (d, JCP = 5, 2C, 2 × CH3),
28.06 (dd, JCP = 24, 3; 2C, 2 × CH), 28.47 (dd, JCP = 20, 3; 2C, 2×CH), 76.10 (s, 1C,
CH2), 111.63 (d, JCP = 13, 1C, {Ar}C3), 120.89 (s, 1C,{Ar}C5), 127.17 (s, 1C, {Ar}C4),
130.64 (dd, JCP = 19, 22, 1C, {Ar}C1Ni) 142.15 (d, JCP = 12, 1C,{Ar}C6), 170.07 (dd,
JCP = 17, 2; 1C, {Ar}C2). 31P{1H} NMR (162 MHz, C6D6) : d 155 (d, 2Jpp = 283, CH2O-

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2
P-(i-Pr)2 ), 187 (d, Jpp = 283, O-P-(i-Pr)2). Elemental Anal. for C19H33O2P2NiBr Calc.
(found) % : C, 46.19 (46.50); H, 6.73 (6.96).
(POCOPiPr(5,6))Ni(OTs), 2. A dry Schlenk flask was charged with complex 1 (49 mg,
0.099 mmol, 1 equiv.), silver tosylate (31 mg, 0.11 mmol, 1.1 equiv.), and dry CH2Cl2 (4
mL). The mixture was stirred for 30 min at room temperature and then filtered through a
pad of Celite. The clear orange yellow solution obtained was slowly evaporated under
inert atmosphere to afford complex 2 as a yellow solid (49 mg, 85%). Crystals for X-ray
analysis were obtained by recrystallization in CH2Cl2. 1H NMR (400 MHz, C6D6) : δ 0.96
(dd, JHP/HH = 13, 7; 6H, 2 × CH3), 1.21 (dd, JHP/HH = 12, 7; 6H, 2 × CH3), 1.37 (dd, JHP/HH
= 17, 7; 6H, 2 × CH3), 1.74 (dd, JHP/HH = 19, 7; 6H, 2 × CH3), 1.92 (s, 3H, TsCH3), 2.02
(m, 2H, 2 × CH), 2.90 (m, 2H, 2 × CH), 4.54 (d, JHP = 17, 2H, CH2), 6.35 (d, JHH = 7,
1H, Ar}H3), 6.74 (m, 2H, 2 × {Ar}H4,5), 6.84 (d, 3JHH = 8, 2H, 2 × {ArTs}H3,5), 7.96 (d,
3JHH = 8, 2H, 2 × {ArTs}H2,6).13C{1H}NMR (101 MHz, C6D6) : δ 16.69 (s, 2C, 2 ×
CH3), 17.30 (s, 2C, 2 × CH3), 18.15 (d, JCP = 6,2C, 2 × CH3), 19.83 (d, JCP = 7, 2C, 2 ×
CH3), 21.06 (s, 1C, TsCH3), 27.08 (d, JCP = 21, 2C, 2 × CH), 29.75 (dd, JCP = 16, 3; 1C,
2 × CH), 76.99 (s, 1C, CH2), 111.93 (d, JCP = 11, 1C,{Ar}C3), 121.30 (s, 1C, {Ar}C5),
126.54 (s, 2C, {TsAr}C3,5), 127.46 (s, 1C, {Ar}C4), 128.95 (s, 1C,{TsAr}C2,6), 140.42 (s,
1C, {TsAr}C4), 131.56 (d, JCP = 21, 1C, Ni{Ar}C1), 142.63 (d, JCP = 12, 1C, {Ar}C6),
170.24 (d, JCP = 15, 1C, {Ar}C2). 31P{1H} NMR (162 MHz, C6D6) : δ 148 (d, 2JPP = 302,
2
1P, CH2OP(i-Pr)2), 189 (d, JPP = 302, 1P, OP(i-Pr)2). Elemental Anal. for
C26H40O5P2SNi Calc. (found) % : C, 53.35 (53.22); H, 6.89 (7.16).
(POCOPiPr(5,6))Ni(OTf), 3. A dry Schlenk flask covered with aluminum foil was
charged with complex 1 (25 mg, 0.051 mmol), silver triflate (74 mg, 0.29 mmol, 5.8

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equiv.), and CH2Cl2 (5 mL), and the resulting brown mixture stirred overnight at room
temperature. The final mixture was passed through a column of Celite to remove excess
of silver salt, and the resulting clear orange-yellow solution was evaporated slowly under
inert atmosphere to give the yellow product as a crystalline solid. (Yield 45 mg, 80%). 1H
NMR (400 MHz, C6D6) : δ 0.92 (dd, JHP/HH = 13, 7; 6H, 2×CH3), 1.05 (dd, JHP/HH = 12, 7;
6H, 2 × CH3), 1.36 (dd, JHP/HH = 18, 7; 6H, 2 × CH3),, 1.55 (dd, 3JHP/HH = 19, 7; 6H, 2 ×
CH3), 2.09 (m, 2H, 2 × CH), ), 2.58 (m, 2H, 2 × CH), 4.44 (d, 3JHP = 17, 2H, CH2), 6.28
3
3
3
(d, JHH = 7, 1H,{Ar}H5), 6.61 (d, JHH = 7 , 1H, 2 × {Ar}H3). 6.70 (dt, JHH = 7, 1;
13
1H,{Ar}H4). C{1H}NMR (101 MHz, C6D6) : d 16.29 (s, 2C, 2 × CH3), 16.69 (s, 2C, 2
× CH3), 17.63 (s, 2C, 2 × CH3), 17.69 (s, 2C, 2 × CH3), 27.28 (br, 2C, 2 × CH), 28.47
(br, 2C, 2 × CH), 76.53 (s, 1C, CH2), 112.00 (d, JCP = 13, 1C, {Ar}C3), 121.39 (s,
1C,{Ar}C5), 128.80 (s, 1C, {Ar}C4), 136.47 (s, 1C, {Ar}C1Ni) 141.51 (d, JCP = 12,
31
1C,{Ar}C6), 169.65 (dd, JCP = 17, 2; 1C, {Ar}C2). P{1H} NMR (162 MHz, C6D6) : d
2
189 (d, Jpp = 285, CH2O-P-(i-Pr)2), 148 (d, 2Jpp = 285, O-P-(i-Pr)2). IR (solid state, cm-
1): ν(C=CAr)= 1420, 1468, 1592, ν(SO3)= 1021, 1235, ν(CF3)= 1100.
[(POCOPiPr(5,6))Ni(CH3CN)][BPh4], 4b. A dry Schlenk flask was charged with
complex 1 (25 mg, 0.051 mmol, 1 equiv.), silver tetraphenylborate (25 mg, 0.057 mmol,
1.1 equiv.), and a 1:1 mixture of dry CH2Cl2/MeCN (6 mL). The reaction mixture was
stirred for 3 h at room temperature, then for 30 min at 60 °C, and finally filtered through
a pad of Celite. The resulting clear, light yellow solution was slowly evaporated under
inert atmosphere to afford complex 4b as a yellow solid (29 mg, 70%). Crystals for X-ray
1
analysis were obtained by recrystallization from CH2Cl2. H NMR (400 MHz, C6D6): δ
1.11 (dd, JHP/HH = 14, 7; 6H, 2 × CH3), 1.30 (dd, JHP/HH =14, 7; 6H, 2 × CH3), 1.38 (dd,

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JHP/HH = 7, 6; 6H, 2 × CH3), 1.43 (t, JHP/HH = 7, 6H, 2 × CH3), 1.97 (m, 2H, 2 × CH), 2.30
3
3
(m, 2H, 2 × CH), 2.57 (s, 3H, CH3CN), 4.89 (d, JHP = 17, 2H, CH2), 6.79 (d, JHH = 7,
3
1H, {Ar}H3,5), 6.87 (d, JHH = 7, 1H, {Ar}H3,5), 7.02 (t, JHH = 7, 1H, {Ar}H4), 7.12 (m,
8H, o-B{Ph}H), 7.30 (m, 12H, m+p-B{Ph}H3,5). 13C{1H}NMR (101 MHz, C6D6) : δ
17.54 (s, 2C, 2 × CH3), 18.39 (s, 2C, 2 × CH3), 19.06 (d, JCP = 7, 2C, 2 × CH3), 20.68 (d,
JCP = 8, 2C, 2 × CH3), 27.93 (d, JCP = 23, 2C, 2 × CH), 30.60 (dd, JCP = 18, 3; 1C, 2 ×
CH), 77.48 (s, 1C, CH2), 112.78 (d, JCP = 10, 1C,{Ar}C3), 122.15 (s, 1C, {Ar}C5),
128.31 (s, 1C, {Ar}C4), 133.96 (s, 1C, {Ar}C1), 143.49 (d, JCP = 14, 1C, {Ar}C6),
169.39 (d, JCP = 17, 1C, {Ar}C2), 30.94 (s, 1C, CH3CN), 137.42 (s, 8C, o-B{Ar}C),
124.78 (s, 12C, p+m-B{Ar}C). 31P{1H} NMR (162 MHz, CD3CN) : δ 152 (d, 2JPP = 260,
2
1P, CH2OP(i-Pr)2), 194 (d, JPP = 260, 1P, OP(i-Pr)2). IR (solid state, cm-1): ν(C=CAr)=
1430, 1585, ν(C≡N)= 2288. Elemental Anal. for C45H56BNNiO2P2 Calc. (found) % : C,
69.80 (68.99); H, 7.29 (7.47); N, 1.81 (1.66).
Synthesis of (POCOPiPr(5,6))Ni(CCCH3), 5. A dry Schlenk flask was charged with
complex 1 (128 mg, 0.259 mmol, 1 equiv.), MeCCMgBr (1.00 mL of a 0.50 M stock
solution in THF, 0.50 mmol, 1.9 equiv.), dry THF (6 mL), and toluene (12 mL). The
mixture was stirred at 60 °C until the original orange-yellow colour changed to brown.
Evaporation of the resulting mixture and extraction of the residues by hexane, followed
by filtration through a short column of Celite gave a yellow solution, which was slowly
evaporated under inert atmosphere to afford complex 5 as yellow crystals that appeared
to be covered with an oily residue (32 mg, crude yield: 27%). 1H NMR (400 MHz, C6D6):
δ 1.21 (m, 12H, 4 × CH3), 1.40 (dd, JHP/HH = 16, 7; 6H, 2 × CH3), 1.48 (dd, JHP/HH =16, 7;

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6H, 2 × CH3), 1.94 (s, 3H, CCCH3), 2.56-2.30 (m, 1H), 4.75 (d, 3JHP= 15, 2H, CH2), 6.53
13
(d, JHH = 7, 1H), 6.97 (t, JHH = 7, 1H, ), 7.07 (d, JHH = 8, 1H, ). C NMR (101 MHz,
C
6
D ): δ 4.26 (s, 1C, CC-CH3), 14.47 (s, 2C, 2 × CH3), 15.49 (d, JCP = 5, 2C, 2 × CH3),
6
16.68 (d, JCP = 5, 2C, 2 × CH3), 25.68 (dd, JCP = 22, 3, 2C, 2 × CH), 26.67 (dd, JCP = 26,
3, 2C, 2 × CH), 72.59 (s, 1C, CH2), 86.90 (pseudo triplet, 2JCP = 40, 1C, CCMe), 108.15
(d, JCP = 13, 1C,{Ar}C3), 117.16 (s, 1C, CCMe), 117.61 (s, 1C, {Ar}C5), 124.10 (s, 1C,
2
{Ar}C4), 136.21 (t, JCP = 19, 1C, {Ar}C1), 139.74 (d, JCP = 12, 1C, {Ar}C6), 167.71
(dd, JCP = 18, 3, 1C, {Ar}C2). 31P{1H} NMR (162 MHz, C
CH2OP(i-Pr)2), 187 (d, 2JPP = 323, 1P, OP(i-Pr)2).
6
D
) : δ 160 (d, 2JPP = 323, 1P,
6
(POCOPiPr(5,6))Ni(CH3), 6. A dry Schlenk flask was charged with complex 1 (200 mg,
0.405 mmol), MeLi (92 mg, 4.2 mmol, 10 equiv.), dry THF (6 mL). The mixture was
stirred at room temperature until the original orange-yellow color changed to dark brown
after 24 h. Evaporation of the resulting mixture and extraction of the residues by hexane,
followed by filtration through a column of Celite gave a dark red solution, which was
slowly evaporated under inert atmosphere to afford complex 6 as yellow-reddish crystals
1
that appeared to be covered with an oily residue (75 mg, crude yield: 43%). H NMR
3
3
(400 MHz, C6D6): δ -0.38 (t, JHP = 10, 3H, NiCH3), 1.11 (dd, JHP/HH = 13, 7; 6H, 2 ×
3
3
CH3), 1.16 (dd, JHP/HH = 13, 7; 6H, 2 × CH3), 1.20 (dd, JHP/HH = 19, 7; 6H, 2 × CH3),
3
3
1.25 (dd, JHP/HH = 19, 7; 6H, 2 × CH3), 2.15 (brm, 4H, 4 × CH), ), 4.76 (d, JHP = 16,
2H, CH2), 6.59 (d, 3JHH = 8, 1H,{Ar}H3), 7.13 (d, 3JHH = 8 , 1H, {Ar}H5). 7.00 (dt, 3JHH
2
= 7, 2; 1H,{Ar}H4). 13C{1H}NMR (101 MHz, C6D6) : d -16.70 (t, JCP = 23, 1C, Ni-
CH3), 16.87 (s, 2C, 2 × CH3), 17.01 (s, 2C, 2 × CH3), 17.78 (d, JCP = 6, 2C, 2 × CH3),
18.83 (d, JCP = 6, 2C, 2 × CH3), 27.44 (dd, JCP = 12, 3; 2C, 2 × CH), 27.65 (dd, JCP
=

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26
12, 3; 2C, 2 × CH), 75.12 (s, 1C, CH2), 110.47 (d, JCP = 13, 1C, {Ar}C3), 119.56 (s,
1C,{Ar}C5), 125.74 (s, 1C, {Ar}C4), 142.40 (pseudo-triplet, 2JCP = 20.4, 1C, {Ar}C1Ni),
31
143.05 (d, JCP = 10, 1C,{Ar}C6), 169.20 (dd, JCP =18, 6; 1C, {Ar}C2). P{1H} NMR
(162 MHz, C6D6) : d 187 (d, 2Jpp =323, CH2O-P-(i-Pr)2), 160 (d, 2Jpp = 323, O-P-(i-Pr)2).
Crystal Structure Determinations. Single crystals of complexes 1, 5 and 6 were grown
by slow evaporation of hexane from their respective saturated solutions. The cationic
complex 4b was crystallized from a 9:1 mixture of dichloromethane and acetonitrile.
Crystals of complex 2 were obtained by slow evaporation of dichloromethane. The
crystallographic data for complexes 1, 2 and 4b-6 were collected on a Bruker Microstar
generator (micro source) equipped with a Helios optics, a Kappa Nonius goniometer and
a Platinum135 detector.
Cell refinement and data reduction were done using SAINT.27 An empirical
absorption correction, based on the multiple measurements of equivalent reflections, was
applied using the program SADABS.28 The space group was confirmed by XPREP
routine29 in the SHELXTL program.30 The structures were solved by direct-methods and
refined by full-matrix least squares and difference Fourier techniques with SHELX-97.31
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.
Acknowledgements. The authors gratefully acknowledge financial support received
from NSERC of Canada (Research Tools and Instruments and Discovery grants to D.Z.),
Universities Mission of Tunisia in Montreal (MUT, fellowships to A.B.S.), and
Université de Montréal.

New Journal of Chemistry
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DOI: 10.1039/C5NJ00807G
27
Supporting Information. Tables of 1H, 13C, 31P{1H}NMRs, details of data collection for
the X-ray analyses of complexes 1, 2, 4b, 5, and 6, and solid state bond distances and
angles. All crystallographic data have been deposited at The Cambridge Crystallographic
Data Centre (CCDC) and can be retrieved with the reference numbers 1052508 (1),
1052509 (2), 1052511 (4b), 1052510 (5) and 1052512 (6). These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
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.
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