New POCN-type pincer complexes of nickel(II) and nickel(III)

Article abstract of DOI:10.1021/om900751f

Unsymmetrical POC(H)N-type pincer ligands react with NiBr ₂(NCMe)_x to give the complexes (POCN)Ni^IIBr (POCN= k^p, k^c, kⁿ-{2-(i-Pr₂PO),6- (NR₂CH₂)-C₆

Full text of DOI:10.1021/om900751f

Organometallics 2009, 28, 6531–6540 6531
DOI: 10.1021/om900751f
New POCN-Type Pincer Complexes of Nickel(II) and Nickel(III)
Denis M. Spasyuk,† Davit Zargarian,*,† and Art van der Est‡
†
‡
Departement de Chimie, Universite de Montreal, Montreal, QC, Canada H3C 3J7, and Department of
ꢀ
ꢀ
Chemistry, Brock University, St. Catharines, ON, Canada L2S 3A1
ꢀ
ꢀ
Received August 27, 2009
Unsymmetrical POC(H)N-type pincer ligands react with NiBr2(NCMe)x to give the complexes
(POCN)NiIIBr (POCN= κP,κC,κN-{2-(i-Pr2PO),6-(NR2CH2)-C6H3}; NR2= 3-morpholino (3a),
NMe2 (3b), and NEt2 (3c)). The presence of an added base such as NEt3 in these metalation reactions
maximizes the yields of the target pincer complexes by suppressing the formation of side-products
arising from protonation of the ligand by the in situ-generated HBr. The cyclic voltammograms of 3
exhibit a quasi-reversible, one-electron oxidation at ca. þ1.0 V, in addition to an irreversible
oxidation at higher potentials likely due to ligand oxidation. Reaction of the 16-electron, yellow
complexes 3 with Br2, N-bromosuccinimide, or CBr4 gives black crystalline compounds identified as
the 17-electron complexes (POCN)NiIIIBr2 (5). Complexes 3 and 5 adopt square-planar and distorted
square-pyramidal geometries, respectively. The Ni-Br bond lengths in 5 are significantly longer for
˚
the Br atom occupying the axial position (2.43-2.46 vs 2.37 A), consistent with the repulsive
interactions expected between the bromide lone pair and the singly occupied dz2/dpz hybrid MO. In
agreement with this picture, the g-values obtained from the EPR spectrum of 5a are gxx ≈ gyy ≈ 2.2,
gzz ≈ 2.00, and strong Br hyperfine coupling is observed on the gzz component. Our preliminary
studies indicate that the thermal stabilities of 5, both in the solid state (as probed by differential
scanning calorimetry) and in solution (as probed by UV-vis spectroscopy), vary in the order 5a ≈ 5b
> 5c; this order of stability is consistent with the relative steric demands of the N-moiety. Complexes
5a (or 3a) and 5b (or 3b) promote the Kharasch addition of CX4 (X=Cl, Br) to styrene at 80 °C, giving
PhC(X)CH2CX3, the product of an anti-Markovnikov addition, in up to 50 catalytic turnovers.
Introduction
bis(phosphino)amides (PNP),4 bis(phosphinites) (POCOP),5
bis(phosphinidines) (PNCNP),6 bis(amino)amides (NNN),7
and bis(carbenes) (CCC),8 as well as nonsymmetrical
pincer ligands such as PCN9,10 and CNS.11 The relatively
facile access to such a diverse array of new ligands has
accelerated the exploration of the reactivities of their metal
complexes, which has led in turn to discovery of novel
reactivities.12
Since their initial introduction by Shaw’s group over 30
years ago,1 pincer-type complexes have been shown to
promote many interesting and useful reactivities.2 The
initial phase in the development of the chemistry of
pincer complexes was dominated by complexes featuring
monoanionic, terdentate ligands based on bis(phosphine)
(PCP)1 and bis(amine) (NCN)3 donor moieties. More re-
cent years have witnessed the introduction of com-
plexes based on a large variety of new ligands, including
ꢀ
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Chem. Commun. 2000, 1619. (b) Morales-Morales, D.; Grause, C.; Kasaoka,
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K.; Redon, R; Cramer, R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300,
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Organometallics 2001, 20, 1144. (d) Salem, H.; Ben-David, Y.; Shimon,
L. J. W.; Milstein, D. Organometallics 2006, 25, 2292. (e) Sykes, A. C.;
White, P.; Brookhart, M. Organometallics 2006, 25, 1664.
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*Corresponding author. E-mail: zargarian.davit@umontreal.ca. All
correspondence regarding the EPR data should be addressed to A.v.d.E.
(1) (a) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
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B. L.; Goodfellow, R. J. J. Chem. Soc., Chem. Commun. 1979, 498.
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Soc., Chem. Commun. 1978, 250. (b) Grove, D. M.; van Koten, G.; Ubbels,
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r
2009 American Chemical Society
Published on Web 10/26/2009
pubs.acs.org/Organometallics

6532 Organometallics, Vol. 28, No. 22, 2009
Spasyuk et al.
Scheme 1
Our long-standing interest in the chemistry of organo-
nickel complexes13 combined with van Koten’s landmark
reports on NCN-Ni complexes3b-d and the emerging chemi-
stry of PCP-Ni complexes14 inspired us to investigate the
synthesis and reactivities of Ni compounds with various
pincer-type ligands. In earlier reports, we have described
the chemistry of the PCsp2P-NiII species {1,3-(Ph2PCH2-
CH2)2-2-indenyl}NiCl15 and the PCsp3P-NiII complexes {(t-
Bu2PCH2CH2)2CH}-NiX (X = Cl, Br, I, Me, H) and [{(t-
Bu2PCH2CH2)2CH}NiL]þ (L = CH3CN, CH2dCHCN).16
Recently, we have described new POCsp2OP and POCsp3OP
complexes of NiII and NiIII as well as their catalytic activities
in hydroamination (Michael addition) and Kharasch addi-
tion.17,18 Our studies to date indicate that the nature of the
pincer ligand has a major influence on the metalation step as
well as the stabilities and reactivities of the ensuing pincer
complexes. For instance, metalation of the ligand’s central
C-H bond is more facile with POCOP versus PCP and with
ligands based on aromatic versus aliphatic linkers. Further-
more, stable and isolable trivalent species are accessible with
POCsp3OP-18 and PCsp3P-type16a,b ligands, whereas ligands
based on aromatic linkers (POCsp2OP- or PCsp2P-type
ligands) have not yielded high-valent nickel complexes.18
The latter observation, that PCP and POCOP ligands
based on an aromatic linker do not yield NiIII species, is in
direct contrast to the relatively facile preparation of trivalent
species based on aromatic NCN ligands, as reported by van
Koten’s group.3b-d The discrepancy between the chemistry
of PCP/POCOP versus NCN ligands featuring an aromatic
skeleton prompted us to investigate the preparation of high-
valent nickel complexes based on unsymmetrical PCN-type
ligands. Since bis(phosphinite) ligands have been found to
undergo metalation more readily than their bis(phopsphine)
counterparts, our initial studies have been focused on the
phosphinite-amine ligands R2PO-C6H4-CH2NR2 (POCN).
The present report describes the preparation of POCN-type
pincer ligands and their di- and trivalent complexes of nickel.
(12) (a) Gozin, M.; Aizenberg, M.; Liou, S.-Y.; Weisman, A.; Ben-
David, Y.; Milstein, D. Nature 1994, 370, 42. (b) Kanzelberger, M.; Singh,
B.; Czerw, M.; Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc.
2000, 122, 11017. (c) Gusev, D. G.; Fonatine, F.-G.; Lough, A. J.; Zargarian,
D. Angew. Chem., Int. Ed. 2003, 42, 216. (d) Zhao, J.; Goldman, A. S.;
Hartwig, J. F. Science 2005, 307, 1080. (e) Goldman, A. S.; Roy, A. H.;
Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M. Science 2006, 312, 257.
(f) Ingleson, M.; Fan, H.; Pink, M.; Tomaszewski, J.; Caulton, K. G. J. Am.
Chem. Soc. 2006, 128, 1804. (g) Gunanathan, C.; Ben-David, Y.; Milstein,
D. Science 2007, 317, 790. (h) Kohl, S. W.; Weiner, L.; Schwartsburd, L.;
Konstantinovski, L.; Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein,
D. Science 2009, 324, 74.
(13) (a) Gareau, D.; Sui-Seng, C.; Groux, L. F.; Brisse, F.; Zargarian,
D. Organometallics 2005, 24, 4003. (b) Chen, Y.; Sui-Seng, C.; Zargarian,
D. Angew. Chem., Int. Ed. 2005, 44, 7721. (c) Boucher, S.; Zargarian, D.
Can. J. Chem. 2005, 84, 233. (d) Chen, Y.; Sui-Seng, C.; Boucher, S.;
Zargarian, D. Organometallics 2005, 24, 149. (e) Groux, L. F.; Zargarian, D.
Organometallics 2003, 22, 4759. (f) Fontaine, F.-G.; Nguyen, R.-V.; Zargar-
ian, D. Can. J. Chem. 2003, 81, 1299. (g) Groux, L. F.; Zargarian, D.; Simon,
L. C.; Soares, J. B. P. J. Mol. Catal. A 2003, 19, 51. (h) Rivera, E.; Wang, R.;
Zhu, X. X.; Zargarian, D.; Giasson, R. J. Mol. Catal. A 2003, 204-205, 325.
(i) Wang, R.; Groux, L. F.; Zargarian, D. J. Organomet. Chem. 2002, 660,
98. (j) Wang, R.; Groux, L. F.; Zargarian, D. Organometallics 2002, 21,
5531. (k) Fontaine, F.-G.; Dubois, M.-A.; Zargarian, D. Organometallics
2001, 20, 5156. (l) Groux, L. F.; Zargarian, D.; Simon, L. C.; Soares, J. B. P. J.
Mol. Catal. A 2003, 193, 51.
Results and Discussion
Synthesis of Complexes. The synthetic route leading to the
new complexes 3a-c is illustrated in Scheme 1. The amino-
phenol precursors for the POCN ligands 2 were prepared by
condensation of 3-hydroxybenzaldehyde with the corre-
sponding secondary amines, followed by reduction of the
in situ-formed imine with NaBH4 in methanol.19 Formation
of the amino phenols 1 is quite exothermic, requiring step-
wise addition of NaBH4 and cooling of the reaction mixture
to avoid forming side-products such as 3-(hydroxy-
methyl)phenol that complicate separation of pure 1. The
preligands 1 were isolated in good yields as white solids (1a
and 1b) or a pale yellow oil (1c); the identities of these
(14) (a) Kennedy, A. R.; Cross, R. J.; Muir, K. W. Inorg. Chim. Acta
1995, 231, 195. (b) Bachechi, F. Struct. Chem. 2003, 14 (3), 263. (c)
Kozhanov, K. A.; Bupnov, M. P.; Cherkasov, V. K.; Fukin, G. K.; Abakumov,
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Canejo, M. M.; Alvarez, E. Organometallics 2004, 23, 5653. (e) Campora, J.;
Palma, P.; del Río, D.; Alvarez, E. Organometallics 2004, 23, 1652. (f) Van
der Boom, M. E.; Liou, S.-Y.; Shimon, L. J.W.; Ben-David, Y.; Milstein, D.
Inorg. Chim. Acta 2004, 357, 4015.
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2005, 83, 634.
(16) (a) Castonguay, A.; Sui-Seng, C.; Zargarian, D.; Beauchamp,
A. L. Organometallics 2006, 25, 602. (b) Castonguay, A.; Beauchamp,
A. L.; Zargarian, D. Acta Crystallogr. 2007, E63, m196. (c) Sui-Seng, C.;
Castonguay, A.; Chen, Y.; Gareau, D.; Groux, L. F.; Zargarian, D. Top. Catal.
2006, 37, 81. (d) Castonguay, A.; Beauchamp, A. L.; Zargarian, D. Inorg.
Chem. 2009, 48, 3177. (e) Castonguay, A.; Beauchamp, A. L.; Zargarian, D.
Organometallics 2008, 27, 5723.
(17) Castonguay, A.; Spasyuk, D. M; Madern, N.; Beauchamp,
A. L.; Zargarian, D. Organometallics 2009, 28, 2134.
(18) (a) Pandarus, V.; Zargarian, D. Chem. Commun. 2007, 978. (b)
Pandarus, V.; Zargarian, D. Organometallics 2007, 26, 4321.
(19) Abdel-Magid, A. F.; Carson, K. G.; Harris, B. D.; Maryanoff,
C. A.; Shah, R. D. J. Org. Chem. 1996, 61, 3849.

Article
Organometallics, Vol. 28, No. 22, 2009 6533
Scheme 2
compounds were established by elemental analysis and
NMR spectroscopy. The phosphination of 1 with chlorodi-
isopropylphosphine and triethylamine gave the correspond-
ing POC(H)N-type pincer ligands 2, which were isolated in
high yields as colorless oils and characterized by NMR
spectroscopy and elemental analysis. All ligands proved to
be quite sensitive to residual moisture, but relatively inert to
oxygen. Heating 2 with NiBr2(MeCN)x20 in the presence of
triethylamine (benzene, 60 °C, 3-4 h) led to the metalation of
the ligands and gave the new complexes 3 in ∼86% yields as
yellow solids. Use of different precursors such as NiBr2-
(THF)x or NiBr2, or different bases such as N,N-dimethyl-
aminopyridine (DMAP), led to significantly lower yields of
the complexes (∼35%). Pd and Pt complexes based on
similar POCN ligands have been reported previously,21 but
complexes 3 are, to our knowledge, the first examples of
POCN-type complexes of nickel.
It is noteworthy that the use of a base was found to be
necessary in order to maximize the reaction yield of com-
plexes 3a-c. When the reaction of 2a was performed without
any added base, we obtained the desired pincer complex 3a in
poor yields (<50%) along with variable amounts of a
sparingly soluble, NMR-silent turquoise-green solid 4. In-
terestingly, the latter side-product generates the desired
pincer complex 3a when treated with 2 equiv of Et3N.
Unfortunately, we have not succeeded in growing suitable
single crystals of this compound due to its poor solubility in
common aprotic and noncoordinating solvents and its de-
composition in coordinating solvents. Nevertheless, the
above observations and the results of a combustion analysis
carried out on this solid allow us to propose the structure
shown in Scheme 2 (4). It should be noted that anionic,
tetrahedral species analogous to 4 have been detected pre-
viously during the preparation of PCsp3P-type pincer com-
plexes of Ni (Scheme 2).16a Such side-products likely arise
from the reaction of the HBr, liberated at the cyclometala-
tion stage of the synthesis, with the amino moiety of the
ligand, prior to or after the latter’s coordination to the metal
center.
Figure 1. Cyclic voltammograms of 1 mM solutions of com-
plexes 3a-c in dichloromethane containing 0.1 M tetrabuty-
lammonium hexafluorophosphate at 25 °C at a scan rate of 100
mV/s on a glassy carbon working electrode.
1.0 V; this redox process is assigned to oxidation of the Ni
center (NiII f NiIII).22 Comparison of the oxidation poten-
tials of these POCN complexes to that of the previously
reported complex (POCsp2OP)NiBr17,18 suggests that high-
valent compounds should be easier to prepare and isolate
with these POCN-based complexes. This is borne out by the
successful chemical oxidation of 3 and the isolation of NiIII
species (vide infra). We conclude, therefore, that POCN
ligands are more effective than their POCOP homologues in
stabilizing high-valent nickel species, which can be under-
stood in terms of both the greater nucleophilicity and
“hardness” of amine moieties relative to OPR2 moieties.
Chemical oxidation of 3 to their NiIII counterparts was
achieved by reaction with bromine in dry Et2O, which gave
The redox properties of complexes 3 were investigated by
cyclic voltammetry measurements in CH2Cl2. The voltammo-
grams (Figure 1) showed quasi-reversible redox waves at ca.
(22) It should be noted that these redox processes appear to be more
complex for 5a and 5b, as judged by the less symmetrical shapes of these
waves; changing the cutoff potential or varying the scan rates (100-300
mV/s) did not produce more symmetrical redox couples. Moreover,
complexes 3 undergo other (irreversible) oxidative processes at higher
potentials; comparison to the CV of the free ligands indicates that these
processes are ligand-based. See the Supporting Information for the full
CV plots of 3, the preligand 1a, and ligand 2a.
(20) Hathaway, B. J.; Holah, D. G. J. Chem. Soc. 1964, 2400.
(21) (a) Motoyama, Y.; Shimozono, K.; Nishiyama, K. Inorg. Chim.
Acta 2006, 359, 1725. (b) Gong, J.-F.; Zhang, Y.-H.; Song, M.-P.; Xu, C.
Organometallics 2007, 26, 6487.

6534 Organometallics, Vol. 28, No. 22, 2009
Spasyuk et al.
the corresponding (POCN)NiIIIBr2 complexes (5a-c) as
black solids in greater than 90% yields (Scheme 1). The
relative thermal instability of 5c (vide infra) required that its
synthesis be performed at -78 °C (in dry solvents) over 10
min, followed by addition of cold hexane to precipitate the
product. N-Bromosuccinimide (NBS) and CBr4 were also
competent oxidants for generation of NiIII species, but these
reagents furnished lower yields of the products (50-70%).
The NBS reaction led to formation of succinimide that has
solubility properties similar to those of 5, which complicated
the isolation of pure products. Complexes 5 are soluble in
Et2O, THF, CH2Cl2, and CH3CN. Et2O or CH2Cl2 solutions
of complexes 5a and 5b were found to be fairly stable at room
temperature, whereas solutions of complex 5c were signifi-
cantly less stable and had to be handled rapidly and at
significantly lower temperatures (vide infra).
Characterization of 3a-c. The diamagnetic NiII complexes
3 were fully characterized by NMR spectroscopy, elemental
analysis, and single-crystal X-ray diffraction studies. The
31P{1H} NMR spectra of 3 were straightforward, each
consisting of a single resonance at about 200 ppm; this signal
is significantly downfield of the corresponding signal for the
free ligands (147 ppm) but close to the chemical shift region
where we find the 31P signal for the analogous (POCOP)NiBr
compounds (186 ppm).18 The 1H and 13C{1H} NMR spectra
were much more complex, but 1H-COSY and HMQC
correlation experiments allowed us to assign all 1H and 13
C
signals. Together, these spectra indicate that complexes 3
possess a plane of symmetry in solution, as reflected in the
equivalence of the two CHMe2 and the NCH2Ar protons in
3a-c, the two NCH2 and OCH2 carbons in 3a, and the two
signals for N(CH2CH3) (3c) and N(CH3) (3b). The plane of
symmetry, which coincides with the plane of coordination,
also renders the following nuclei (sitting above and below the
plane) pairwise equivalent: CH(CH3)2 in 3a-c; morpholine
protons in 3a; and NCH2CH3 signals in 3c.
Single-crystal X-ray diffraction studies of 3 showed that
these complexes adopt moderately distorted square-planar
geometries in the solid state (Figure 2), the greatest structural
distortions appearing in the angles P-Ni-N (162-167°) and
P-Ni-C (82°); these distortions away from ideal geometry
arise presumably from the terdentate nature of the pincer
ligand. The Ni center and the aromatic ring are only slightly
out of the coordination plane, which is consistent with the
existence in solution of a plane of symmetry. The Ni-P
distances in these POCN-type complexes are shorter than the
corresponding distances in the analogous (POCOP)Ni-X
Figure 2. ORTEP diagram for complexes 3a (a), 3b (b), and 3c
(c). Thermal ellipsoids are shown at the 50% probability level.
Hydrogen atoms are omitted for clarity.
18
˚
compounds (ca. 2.11 vs 2.15-2.16 A), implying a greater
trans influence for the OPR2 moieties versus the amine
ligands. Moreover, in comparison to their POCOP-type
counterparts, the POCN-type complexes 3 display somewhat
˚
3: for Ni-C, ca. 1.89-1.90 vs 1.85-1.86 A; for Ni-P, ca.
˚
˚
2.19-2.21 vs 2.11 A;and forNi-N, 2.05-2.07 vs 2.02-2.04 A.
The Ni-Br bond for the Br atom occupying the axial position
is also much longer than that involving the basal Br atom
˚
shorter Ni-C distances (ca. 1.85-1.86 vs 1.88 A) and longer
˚
Ni-Br (ca. 2.33-2.36 vs 2.32 A) distances.
Characterization of 5a-c. The identities of the NiIII com-
plexes 5a-c were established by elemental analyses and single-
crystal X-ray diffraction studies. As can be seen from their
ORTEP diagrams (Figure 3), these 17-electron compounds
adopt square-pyramidal structures displaying a slight pyrami-
dal distortion reflected in the out-of-plane displacement of the
Ni center from the basal plane defined by the atoms P1, C1, N1,
˚
(2.43-2.46 vs 2.37 A); this is consistent with the repulsive
interactions anticipated between the bromide lone pair and the
half-filled dz2/dpz hybrid MO. Unequal axial and basal Ni-X
bonds have been observed in POCOPNiIIIX218 and the closely
related (but divalent) complex PCP-NiII(catecholate)
14c
˚
˚
(Ni-O1= 1.92 A vs Ni-O2= 2.06 A), whereas the two
Ni-I bond distances in van Koten’s NCN-NiIII(I)2 complex
are fairly similar (2.61 and 2.63 A) and identical for
˚
23
˚
and Br1 (by ca. 0.31 (5a), 0.34 (5b), and 0.30 (5c) A). This
distortion results in trans angles of 158-162° and cis angles of
80-98°, in addition to significantly longer (>10 esd) Ni-X
bonds relative to the corresponding distances in the NiII species
(23) Grove, D. M.; van Koten, G.; Zoet, R. J. Am. Chem. Soc. 1983,
105, 1379.

Article
Organometallics, Vol. 28, No. 22, 2009 6535
Table 1. Crystal Data Collection and Refinement Parameters for
Complexes 3a-c
3a
3b
3c
chemical
formula
Ffw
C17H27NO2PNiBr C15H25NOPNiBr C17H29NOPNiBr
446.99
150(2)
wavelength (A) 1.54178
409.00
150(2)
433.00
150(2)
1.54178
Pna21
20.5409(5)
8.1439(2)
11.5377(3)
90
T (K)
˚
1.54178
P1
space group
˚
P21/n
a (A)
9.9289(2)
8.2128(2)
23.0832(4)
90
9.3512(2)
9.4406(2))
10.7745(2)
67.668(1)
79.819(2)
75.681(1)
2
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
Z
98.695(1)
90
90
90
4
4
3
˚
V (A )
F
1860.66(7)
1.596
48.94
847.19(2)
1.587
52.60
1930.06(8)
1.490
46.56
calcd (g cm-3)
μ (cm-1)
θ range (deg)
3.87-67.94
4.46 - 67.81
0.0296
0.0781
4.30 -68.13
0.0218
0.0576
0.0219
0.0576
1.102
R1a [I > 2σ(I)] 0.0293
wR2b [I > 2σ(I)] 0.0763
R1 [all data]
wR2 [all data]
GOF
0.0293
0.0763
1.143
0.0301
0.0784
1.060
P
P
P
P
a R1 = (||Fo| - |Fc||)/ |Fo|. b wR2 = { [w(Fo - Fc2)2]/ [w-
2
(Fo2)2]}1/2
.
˚
Table 2. Selected Bond Distances (A) and Angles (deg) for
Complexes 3a-c
3a
3b
3c
Ni-C(1)
1.853(2)
2.1107(6)
2.0428(18)
2.3319(4)
176.26(7)
162.20(6)
95.08(2)
99.65(5)
81.72(7)
83.85(9)
1.859(2)
2.1119(7)
2.0206(19)
2.3407(5)
177.16(8)
163.81(6)
95.56(2)
98.34(6)
81.99(9)
83.89(9)
1.8557(19)
2.1088(7)
2.025(2)
2.3615(4)
172.47(7)
166.63(5)
95.53(2)
97.82(5)
81.51(8)
85.15(9)
Ni-P(1)
Ni-N(1)
Ni-Br
C(1)-Ni-Br
P(1)-Ni-N(1)
P(1)-Ni-Br
N(1)-Ni-Br
P(1)-Ni-C(1)
N(1)-Ni-C(1)
III
24
˚
NCN-Ni (Cl)2 (2.30 A). Finally, close inspection of the
ORTEP diagrams for 5 reveals significant steric repulsions
between the axial Br and the N-alkyl substituents; this repul-
sion appears to be greatest in complex 5c, which displays the
longest Ni-Br2 bond and the least thermal stability (vide infra).
The bonding and electronic structure of 5a were investi-
gated further by EPR analysis. The EPR spectrum of this
compound (Figure 4) is typical of NiIII pincer compounds
with halogen ligands3d,23,25 and shows a nearly axial g-tensor
with strong hyperfine coupling to the halogen nucleus on the
gzz component. The splitting due to the spin 3/2 Br nucleus is
shown schematically above the spectrum. The z-component
of the g-tensor is close to the free electron g-value (2.0023),
while the x- and y-components are in the vicinity of g = 2.2.
The deviation of the g-tensor from axial symmetry is hard to
estimate accurately from the spectrum, because the Br
hyperfine coupling on the gzz component is of similar mag-
nitude to the g-anisotropy and a so-called “anomalous line”
Figure 3. ORTEP diagram for complexes 5a (a), 5b (b), and 5c
(c). Thermal ellipsoids are shown at the 50% probability level.
Hydrogen atoms are omitted for clarity.
similar to that found in many CuII spectra26 is expected.
Hence, it is not clear whether the low-field peak is due to the
gxx component or the anomalous line. In any case, this
combination of g-factors (gxx ≈ gyy > gzz =2.0023) is
expected for a low-spin d7 metal ion with tetragonally
elongated octahedral symmetry such that the unpaired elec-
tron resides in the dz2 orbital.3d,27 The strong Br hyperfine
splitting seen only on the gzz component indicates that the dz2
orbital is involved in bonding to Br and is consistent with a
bonding scheme in which the MOs involved in the axial Br
bond are derived from dz2 and pz orbitals of the NiIII and hold
three electrons. Closer inspection of the spectrum reveals a
large number of small, partially resolved hyperfine splittings
due to coupling to the phosphorus (spin 1/2), nitrogen
(spin 1), and/or in-plane Br (spin 3/2). In principle, these
(24) Kleij, A. W.; Gossage, R. A.; Gebbink, K.; Brinkmann, N.;
Reijerse, E. J.; Kragl, U.; Lutz, M.; Spek, A. L.; van Koten, G. J. Am.
Chem. Soc. 2000, 122, 12112.
(25) (a) Grove, D. M.; van Koten, G.; Mul, P.; Zoet, R.; van der
Linden, J. G. M.; Legters, J.; Schmitz, J. E. J.; Murrall, N. W.; Welch,
A. J. Inorg. Chem. 1988, 27, 2466–2473. (b) Kozhanov, K. A.; Bubnov,
M. P.; Cherkasov, V. K.; Fukin, G. K.; Vavilina, N. N.; Efremova, L. Y.;
Abakumov, G. A. J. Magn. Reson. 2009, 197, 36–39.
(26) Kivelson, D.; Neiman, R. J. Chem. Phys. 1961, 35, 156–161.
(27) (a) Maki, A. H.; Davison, A.; Edelstein, N.; Holm, R. H. J. Am.
Chem. Soc. 1964, 86, 4580–4587. (b) Lappin, A. G.; Murray, C. K.;
Margerum, D. W. Inorg. Chem. 1978, 17, 1630–1634. (c) Chmielewski,
P. J.; Latos-Grazynski, L. Inorg. Chem. 1997, 36, 840–845.

6536 Organometallics, Vol. 28, No. 22, 2009
Spasyuk et al.
Table 3. Crystal Data Collection and Refinement Parameters for
Complexes 5a-c
5a
5b
5c
chemical formula C17H27NO2PNiBr2 C15H25NOPNiBr2 C17H29NOPNiBr2
fw
T (K)
526.90
150(2)
wavelength (A) 1.54178
484.86
150(2)
1.54178
P21/n
512.91
150(2)
1.54178
P21/n
˚
space group
˚
Pna21
21.1300(16)
9.8048(8)
9.3608(9)
90
a (A)
9.3685(2)
11.2260(3)
18.1186(4)
90
8.1481(2)
19.8813(4)
12.9752(3)
90
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
Z
90
90
100.817(1)
90
104.770(1)
90
4
4
4
3
˚
V (A )
F
1939.30(30)
1.805
71.30
1871.69(8)
1.721
72.84
2032.46(8)
1.676
67.43
calcd (g cm-3)
μ (cm-1)
θ range (deg)
4.18-68.38
4.66-67.69
0.0229
0.0581
0.0259
0.0593
1.062
4.17-67.84
0.0220
0.0580
0.0221
0.0581
1.133
R1a [I > 2σ(I)] 0.0362
wR2b [I > 2σ(I)] 0.0869
R1 [all data]
wR2 [all data]
GOF
0.0358
0.0873
1.044
Figure 4. X-band (9 GHz) EPR spectrum of 5a in toluene at 120
K. Microwave frequency 9.405102 GHz, microwave power
2 mW, modulation amplitude 1.0 G.
P
P
P
P
a R1 = (||Fo| - |Fc||)/ |Fo|. b wR2 = { [w(Fo - Fc2)2]/ [w-
2
(Fo2)2]}1/2
.
˚
Table 4. Selected Bond Distances (A) and Angles (deg) for
Complexes 5a-c
5a
5b
5c
Ni-C(1)
1.883 (4)
2.2013 (11)
2.072(3)
2.3673(7)
2.4339(9)
161.21(13)
91.30(13)
159.92(10)
94.23(3)
1.897(2)
2.1905(6)
2.0508(18)
2.3710(4)
2.4350(4)
159.60(6)
95.24(6)
158.08(6)
92.43(2)
98.29(5)
79.92(7)
83.52(8)
1.8907(19)
2.2078(5)
2.0690(16)
2.3688(4)
2.4638(3)
162.27(6)
90.98(5)
159.42(5)
92.266(17)
98.09(4)
Ni-P(1)
Ni-N(1)
Ni-Br(1)
Ni-Br(2)
C(1)-Ni-Br(1)
C(1)-Ni-Br(2)
P-Ni-N
P-Ni-Br(1)
N-Ni-Br(2)
P-Ni-C(1)
N-Ni-C(1)
95.78(11)
80.09(12)
83.94(15)
80.31(6)
84.47(7)
couplings could provide a clearer picture of the spin density
distribution and, by extension, the bonding in the molecular
plane; without additional information, however, the large
number of unknown parameters precludes a meaningful
simulation of the spectrum.
Figure 5. DSC curve of complexes 5a-c: nitrogen flow of 20
mL/min, heating rate of 10 °C/min, ca. 8 mg samples weighed in
an alumina crucible.
We have also subjected the NiIII complexes 5 to cyclic
voltammetry measurements and compared the results to
those obtained with the divalent species 3. The voltammo-
grams (see Supporting Information) show a reduction wave
(NiIII f NiII) and an irreversible oxidation peak, which we
assign to a ligand-based oxidation process.
decomposition (exothermic) for these complexes appears to
coincide with an endothermic process at ca. 165-173 °C (5a)
and 160-165 °C (5b), which we attribute to the melting of 3a
(observed at 175-177 °C) and 3b (observed at 166-168 °C).
A second endothermic process is observed for 5b above
190 °C, which we attribute to the evaporation of the decom-
position product 3b. In constrast, 5c appears to be stable only
up to 60 °C, beginning to decompose significantly at ca.
80 °C; for this sample, too, there was an endothermic process
at 105-110 °C, which we attribute to the melting of the
decompostion product 3c (observed at 110-111 °C).
An examination of the thermal stabilities of complexes 5 in
solution was conducted by variable-temperature UV-vis
spectroscopy (Figure 6), and the results point to the same
order of thermal stability as in the solid state, namely, 5a ∼
5b > 5c. Thus, 5a and 5b display a t1/2 of about 4 and 3 h,
respectively, at 70 °C, whereas 5c begins to decompose upon
dissolution at room temperature and displays a t1/2 of about
Thermal Stabilities of 3 and 5. The thermal stability of NiII
complexes was examined by thermogravimetric analysis
(TGA). The results showed no decomposition of NiII com-
plexes 3 even above their melting points; the compounds
simply evaporated without leaving any significant amount of
residue (see TGA thermograms in the Supporting In-
formation). The thermal stabilities of the NiIII complexes
in the solid state were established by studying their thermal
profiles using differential scanning calorimetry (DSC). As
can be seen in Figure 5, complexes 5a and 5b appear to be
stable to well above 130 °C, showing exothermic decomposi-
tion only above 150 and 140 °C, respectively. The onset of

Article
Organometallics, Vol. 28, No. 22, 2009 6537
nonchain cycle wherein the carbon-based radical entities are
held within the solvent cage of the NiIII complex (NCN)-
NiX2, thereby favoring 1:1 additions over radical chain type
polymerization or telomerization reactions.
We have reported recently that the (POCsp3OP)-
NiIIX/(POCsp3OP)NiIIIX2 systems promote the Kharasch
addition of CCl4 to a number of olefins, but the catalytic
efficacy of these systems are inferior to the reactivities
displayed by van Koten’s (NCN)NiIIX system. For example,
the latter catalyzes the addition of CCl4 to styrene and
methyl methacrylate with catalytic turnover numbers
(TON) of up to 1700 and an initial turnover frequency
(TOF) of 400 h-1 at room temperature, compared to a
TON of 1000 over 24 h displayed by our POCsp3OP systems
in refluxing acetonitrile.18 Access to isolable samples of the
(POCN)NiIIIX2 complexes via the relatively facile oxidation
of (POCN)NiIIBr complexes 3 with CCl4 prompted us to
screen the reactivities of these complexes for the Kharasch
addition reaction. The results of a preliminary study on the
addition of CCl4 to styrene are described below.
The catalytic runs were conducted over 18 h in acetonitrile
at 80 °C with a Ni:styrene:CCl4 ratio of 1:50:250. We
obtained 95% yields of the anti-Markovnikov addition
product when using 3a/5a or 3b/5b as precursors (TON =
45, TOF ≈ 2.5/h), but no conversion was noted when using
3c/5c as precursor. Analysis of the reaction mixture by NMR
spectroscopy and GC-MS showed nearly total conversion to
the expected product and no side-products arising from
telomerization or oligomerization of styrene. In contrast to
what was observed in van Koten’s NCN system and our
POCsp3OP system, we found that virtually identical catalytic
results are obtained whether the catalysis is carried out in air
or in an inert atmosphere.
The progress of the catalytic reactions can be monitored
by the colors of the catalytic mixtures: depending on whether
divalent or trivalent Ni precursors were used, the initial
colors of the catalytic mixtures are yellow (when using 3a
or 3b) or dark brown (5a or 5b), but all mixtures become
yellow-green as the catalysis progresses. No color change is
observed and no conversion takes place over days when
reaction mixtures are kept at room temperature. NMR
monitoring of the catalytic reactions in which 3a or 3b was
the Ni precursor revealed that the 31P signals of these species
disappeared ca. 10 min after the start of the reaction, whereas
reaction mixtures in which 3c or 5c was used as the Ni
precursor displayed the 31P signal expected for 3c through-
out the reaction. These observations indicate that promotion
of the Kharasch addition requires relatively stable and long-
lived NiIII intermediates, which is consistent with the gene-
rally accepted mechanism for this type of reaction.29
Figure 6. UV-vis spectra of 0.001 M toluene solutions of 5a (70
°C), 5b ( 70 °C), and 5c (30 °C) as a function of time.
20 min at 30 °C. It is noteworthy that the solution decom-
position is faster in more concentrated solutions, implying a
bimolecular pathway.
Kharasch Additions. A wide variety of paramagnetic metal
complexes are known to promote the Kharasch addition of
CCl4 to various olefins.28 Of relevance to our studies, van
Koten’s group has shown that Ni complexes based on NCN-
type pincer ligands are efficient promoters of the addition
of polyhalogenated alkanes to olefins, giving the anti-
Markovnikov product (eq 1). Mechanistic studies by this
group have concluded that this reaction proceeds through a
Conclusions
The current study has shown that POCN-type pincer
ligands serve as very attractive templates for preparing
organonickel complexes: they undergo relatively facile
nickelation and form thermally robust (POCN)NiII(Br)
(28) For recent reviews on metal-catalyzed Kharasch additions see:
(a) Severin, K. Curr. Org. Chem. 2006, 10, 217–224. (b) Delaude, L.;
Demonceau, A.; Noels, A. F. Top. Organomet. Chem. 2004, 11, 155–171.
(29) van de Kuil, L. A.; Grove, D. M.; Gossage, R. A.; Zwikker,
J. W.; Jenneskens, L. W.; Drenth, W.; van Koten, G. Organometallics
1997, 16, 4985.

6538 Organometallics, Vol. 28, No. 22, 2009
Spasyuk et al.
deriatives that can, in turn, furnish the high-valent species
(POCN)NiIII(Br)2. Two of the latter, 5a and 5b, are ther-
mally stable yet fairly reactive in the promotion of the
Kharasch addition of CCl4 to styrene
complexes 3a, 3b, and 3c were determined using a Mel-TEMP
1010 melting point apparatus equipped with a digital thermo-
meter. Thermal gravimetric analysis (TGA) was performed
using a 2950 TGA HR V5.4A system with nitrogen as purge
gas and a heating rate of 20 °C/min; a platinum crucible was
used in the TGA measurements, and samples were prepared by
using standard techniques.
It is instructive to review the factors affecting the catalytic
efficacy for the Kharasch additions catalyzed by pincer-
nickel complexes. van Koten has established that the cata-
lytic activities of (NCN)NiX complexes for the Kharasch
addition correlate reasonably well with the redox potential
for the one-electron oxidation of these complexes, the more
easily oxidizable systems being more effective catalysts. This
correlation appears to hold across the series NCN, POCOP,
and POCN as the ease of oxidation (NiII f NiIII) and
catalytic efficacy in the Kharasch addition follow the order
NCN > POCsp3OP > POCN, whereas (POCsp2OP)NiBr
does not form isolable high-valent species and does not
promote the Kharasch addition. Another important factor
is the steric bulk of the donor moieties in these systems, the
highest catalytic activities in the NCN systems being ob-
served with the NMe2 analogue. A similar phenomenon is in
effect in the POCN systems, with the more bulky NEt2
analogue 5c displaying the lowest thermal stability and being
inactive in the Kharasch addition. By extension, we speculate
that the greater steric bulk of the i-Pr2P moiety in our
POCsp3OP and POCN systems might be an important factor
contributing to their lower levels of catalytic activities and
the lower stabilities of the high-valent species LNiIIIX2 in
comparison to van Koten’s NCN systems. These considera-
tions might serve as guiding principles for the design of a new
generation of catalysts for the Kharasch addition based on
systems with less bulky donor moieties or larger and more
flexible metallacycle rings.
Synthesis of Preligands. [3-((Morpholino)methyl)phenol], 1a.
To a solution of 3-hydroxybenzaldehyde (0.500 g, 4.10 mmol) in
10 mL of methanol at rt was added a solution of morpholine
(0.714 g, 8.20 mmol) in 6 mL of methanol. The resulting mixture
was stirred for 1 h to obtain a yellow solution. The latter was
then cooled to -5 °C, and NaBH4 (0.200 g, 5.26 mmol) was
added portionwise during 1 h. The preligand was purified in one
of two ways. Purification Method A: The reaction mixture was
concentrated under reduced pressure and then treated with 10%
HCl until pH = 1, washed with a 1:1 mixture of EtOAc and
Et2O (3 ꢀ 10 mL), and finally treated with a concentrated
aqueous ammonia solution until pH = 10. This mixture was
then extracted with a 1:1 mixture of EtOAc and Et2O (5 ꢀ 10
mL), and the extracts were combined and dried over MgSO4,
filtered through a glass frit, and evaporated to give a colorless
oil, which crystallized over time to give a white powder (0.664 g,
84%). Purification Method B: The reaction mixture was eva-
porated, and the residue was resolubilized in 20 mL of benzene,
filtered through a short column of silica gel, and evaporated
under dynamic vacuum to give a white powder. (0.736 g, 93%).
1H NMR (δ, CDCl3): 2.49 (m, 4H, 2 ꢀ NCH2), 3.46 (s, 2H,
ArCH2N), 3.72 (t, 3J = 5, 4H, 2 ꢀ CH2O), 6.70 (dd, 3J = 8, J =
3, 1H, {Ar}H6), 6.75 (s, 1H, {Ar}H2), 6.84 (d, 3J = 8, 1H,
3
{Ar}H4), 7.15 (t, J = 8, 1H, {Ar}H5), 7.84 (br s, 1H, OH).
13C{1H} NMR (δ, CDCl3): 53.48 (s, 2C, 2 ꢀ NCH2), 63.22 (s,
1C, ArCH2N), 66.68 (s, 2C, 2 ꢀ OCH2), 114.64 (s, 1C, {Ar}C6),
116.38 (s, 1C, {Ar}C2), 121.48 (s, 1C, {Ar}C4), 129.45 (s, 1C,
{Ar}C5), 138.70 (s, 1C, {Ar}C3), 156.03 (s, 1C, {Ar}C1). Anal.
Calcd for C11H15NO2: C, 68.44; H, 7.96; N, 7.18. Found: C,
68.37; H, 7.82; N, 7.25.
Experimental Section
[3-((N,N-Dimethylamino)methyl)phenol], 1b. The procedure
described above for the preparation of preligand 1a
(purification method B) was used with dimethylamonium chlor-
ide (1.174 g, 12.3 mmol) and triethylamine (1.71 mL, 12.3 mmol)
to prepare 3-((N,N-dimethylamino)methyl)phenol (1b), which
General Procedures. All manipulations were carried out using
standard Schlenk and glovebox techniques under a nitrogen
atmosphere. Solvents were degassed and dried using standard
procedures. The following were purchased from Aldrich and
used without further purification: Ni (metal), chlorodiisopro-
pylphosphine, 3-hydroxybenzaldehyde, triethylamine, and
C6D6. A Bruker AV 400 spectrometer was used for recording
1H, 13C{1H} (101 MHz), and 31P{1H} (162 MHz) NMR spectra.
1H and 13C chemical shifts are reported in ppm downfield of
TMS and referenced against the residual C6D6 signals (7.15 ppm
for 1H and 128.02 ppm for 13C); 31P chemical shifts are reported
in ppm and referenced against the signal for 85% H3PO4
(external standard, 0 ppm). Coupling constants are reported
1
was isolated as a white powder (0.390 g, 63%). H NMR (δ,
C6D6): 2.26 (s, 6H, 2 ꢀ CH3), 3.41 (s, 2H, ArCH2N), 6.74-6.67
(m, 2H, {Ar}H2,6), 6.76 (d, 3J = 8, 1H, {Ar}H4), 7.13 (t, 3J = 8,
1H, {Ar}H5), 8.42 (br s, 1H, OH). 13C{1H} NMR (δ, C6D6):
44.72 (s, 2C, 2 ꢀ CH3), 63.78 (s, 1C, ArCH2N), 115.44 (s,
1C,{Ar}C6), 117.19 (s, 1C, {Ar}C2), 121.24 (s, 1C, {Ar}C4),
129.36 (s, 1C, {Ar}C5), 138.15 (s, 1C,{Ar}C3), 157.09 (s, 1C,
{Ar}C1). Anal. Calcd for C9H13NO: C, 71.49; H, 8.67; N, 9.26.
Found: C, 71.55; H, 8.75; N, 9.13.
1
in Hz. The correlation and assignment of H and 13C NMR
[3-((N,N-Diethylamino)methyl)phenol], 1c. The procedure de-
scribed above for the preparation of preligand 1a (purification
method A) was used with diethyl amine to prepare 3-((N,N-
diethylamino)methyl)phenol, 1c, which was isolated as an off-
white oil (0.594 g, 81%). 1H NMR (δ, C6D6): 1.01 (t, 3J = 7, 6H,
2 ꢀ CH3), 2.50 (q, 3J = 7, 4H, 2 ꢀ NCH2), 3.49 (s, 2H,
resonances were aided by 2D COSY, HMQC, HMBC, DEPT,
and 1H{31P} experiments when necessary. GC/MS measure-
ments were made on an Agilent 6890N spectrometer. UV/vis
spectra were recorded on a Varian Bio 300 equipped with a
temperature-controlling system using standard sampling cells (1
cm optical path length). The EPR spectra of 5a were collected on
a Bruker Elexsys E580 spectrometer operating in CW mode. A
solution of 5a in toluene (∼1 mM) was prepared, filtered, and
placed in a 4 mm o.d. EPR tube. The solution was then degassed
by repeated freeze-pump-thaw cycles, and the tube was sealed
under vacuum. The sample was frozen to 120 K in the spectro-
meter resonator. DSC curves were obtained using a PerkinEl-
mer Jade Thermoanalyser system with a nitrogen flow of 20 mL/
min, a heating rate of 10 °C/min, and samples weighing about 8
mg; an alumina crucible was used in the DSC measurements,
and samples were prepared by using standard techniques. The
elemental analyses were performed by the Laboratoire d’Ana-
3
3
ArCH2N), 6.83 (dd, J = 8, J = 2, 1H, {Ar}H6), 6.96 (d,
J = 8, 1H, {Ar}H4), 7.03 (br s, 1H, OH), 7.06 (s, 1H, {Ar}H2),
7.17 (t, 3J = 8, 1H, {Ar}H5). 13C{1H} NMR (δ, C6D6): 11.29 (s,
2C, 2 ꢀ CH3), 46.61 (s, 2C, 2 ꢀ NCH2), 57.69 (s, 1C, ArCH2N),
115.03 (s, 1C, {Ar}C6), 116.93 (s, 1C, {Ar}C2), 121.15 (s, 1C,
{Ar}C4), 129.59 (s, 1C, {Ar}C5), 140.79 (s, 1C, {Ar}C3), 157.36
(s, 1C, {Ar}C1). Anal. Calcd for C11H17NO: C, 73.70; H, 9.56;
N,7.81. Found: C, 73.3; H, 9.62 ; N, 7.38.
Synthesis of POCN Ligands. [3-((Morpholino)methyl)pho-
sphinitobenzene], 2a. A solution of chlorodiisopropyl phosphine
(0.427 mL, 2.59 mmol, 96%) in THF (15 mL) was added to a
solution of 1a (0.500 g, 2.59 mmol) and triethylamine (0.400 mL,
2.85 mmol) in THF (35 mL), stirring at 0-5 °C. The resulting
ꢀ
ꢀ
lyse Elementaire (Universite de Montreal). Melting points for
ꢀ
ꢀ

Article
Organometallics, Vol. 28, No. 22, 2009 6539
2
mixture was allowed to warm to room temperature and stirred
for an additional 1 h. Evaporation of the solvent and extraction
of the residue with Et2O (3 ꢀ 25 mL) followed by filtration of the
combined extracts and evaporation gave the desired product as
{Ar}C5), 115.92 (s, 1C, {Ar}C4), 142.15 (d, JCP = 35, 1C,
{Ar}C1-Ni), 150.75 (s, 1C, {Ar}C6), 165.96 (d, JCP = 9, 1C,
2
{Ar}C2). 31P{1H} NMR (δ, C6D6): 201.48 (s). Anal. Calcd for
C17H27P1O2NiBr: C, 45.68; H, 6.09; N, 3.13. Found: C, 45.69;
H, 6.04; N, 3.04.
a colorless oil (0.768 g, 96%). 1H NMR (δ, C6D6): 0.72 (dd, 3JHP
=
KP,KC,KN-{2,6-(i-Pr2PO)(C6H3)(CH2NMe2)}NiBr, 3b. The
procedure described above for the preparation of 3a was used
to prepare this complex, which was isolated as a yellow pow-
9, JHH = 7, 3H, CH3), 0.73 (dd, 3JHP = 8, JHH = 7, 3H, CHCH3),
0.93-0.85 (m, 6H, 2 ꢀ CHCH3), 1.57-1.47 (m, 2H, CH),
1.90-1.92 (m, 4H, 2 ꢀ NCH2), 2.95 (s, 2H, NCH2), 3.28-
3.30 (m, 4H, 2 ꢀ OCH2), 6.67 (d, 3JHH = 7, 1H,{Ar}H6), 6.85 (t,
3JHH = 8, 1H,{Ar}H5), 6.89 (s, 1H, {Ar}H2), 6.95 (d, 3JHH = 8,
1H, {Ar}H4). 13C{1H} NMR (δ, C6D6):17.17(d, 2JCP = 8, 2C, 2 ꢀ
1
3
der (0.583 g, 77%). H NMR (δ, C6D6): 1.17 (dd, JHP = 15,
3JHH = 7, 6H, 2 ꢀ CH3), 1.47 (dd, 3JHP = 18, 3JHH = 7, 6H, 2 ꢀ
CH3), 2.19 (m, 2H), 2.44 (d, 3JHH = 2, 6H, 2 ꢀ NCH3), 3.25 (s,
2H, NCH2), 6.40 (d, 3JHH = 7, 1H, {Ar}H5), 6.62 (d, JHH = 8,
1H, {Ar}H3), 6.93-6.87 (m, 1H, {Ar}H4). 13C{1H} NMR (δ,
C6D6): 16.87 (s, 2C, 2 ꢀ CH3), 18.26 (d, 2JCP = 4, 2C, 2 ꢀ CH3),
28.49 (d, 1JCP = 24, 2C, 2 ꢀ CH), 49.11 (s, 2C, 2 ꢀ NCH3), 71.84
(s, 1C, CH2), 108.38 (d, 3JCP = 13, 1C, {Ar}C3), 115.67 (s, 1C,
CHCH3) 17.89 (d, 2JCP = 20, 2C, 2 ꢀ CHCH3), 28.64 (d, 1JCP
=
19, 2C, 2 ꢀ CH), 53.99 (s, 2C, 2 ꢀ NCH2), 63.42 (s, 1C, ArCH2N),
67.10 (s, 2C, 2 ꢀ OCH2), 117.56 (d, 3JCP= 11, 1C, {Ar}C6), 119.41
(d, JCP = 10, 1C, {Ar}C2), 122.56 (s, 1C, {Ar}C4), 129.48
3
(s, 1C, {Ar}C5), 140.58 (s, 1C, {Ar}C3), 160.11 (d, 2JCP = 9,1C,
{Ar}C1). 31P{1H} NMR (δ, C6D6): 147.5 (s). Anal. Calcd for
C17H28NO2P: C, 66.00; H, 9.12; N, 4.53. Found: C, 66.18; H,
9.36; N, 4.32.
2
{Ar}C5), 127.04 (s, 1C, {Ar}C4), 143.11 (d, JCP = 33, 1C,
{Ar}C1-Ni), 151.09 (s, 1C, {Ar}C6), 166.16 (d, 2JCP = 11, 1C,
{Ar}C2). 31P{1H} NMR (δ, C6D6): 199.16 (s, P). Anal. Calcd for
C15H27P1O2NiBr: C, 44.50; H, 6.22; N, 3.46. Found: C, 44.56;
H, 6.41; N, 3.53.
[3-((N,N-Dimethylamino)methyl)phosphinitobenzene], 2b. The
procedure described above for the preparation of 2a was used to
prepare 3-((N,N-diethylamino)methyl)phosphinitobenzene, 2b,
which was isolated as a colorless oil (0.799 g, 91%). 1H NMR (δ,
C6D6): 0.68 (dd, JHP = 15, JHH = 7, 6H, 2 ꢀ CHCH3), 0.84 (dd,
KP,KC,KN-{2,6-(i-Pr2PO)(C6H3)(CH2NEt2)}NiBr, 3c. The
procedure described above for the preparation of 3a was used
to prepare this complex, which was isolated as a yellow powder
(0.616 g, 84%). 1H NMR (δ, C6D6): 1.12 (dd, 3JHP= 14, 3JHH
=
J
HP= 10, JHH = 7, 6H, 2 ꢀ CHCH3), 1.46 (m, 2H, 2 ꢀ CH), 1.76
7, 6H, 2 ꢀ CHCH3) 1.51-1.37 (m, 12H, 2 ꢀ CH2CH3 and 2 ꢀ
CHCH3), 2.08-1.96 (m, 2H, 2 ꢀ CH), 2.17 (m, 2H, CH2CH3),
3.41-3.28 (m, 2H, CH2CH3), 3.43 (s, 2H, ArCH2N), 6.35 (d,
3JHH = 8, 1H, {Ar}H5), 6.56 (d, 3JHH = 8, 1H, {Ar}H3), 6.85 (t,
3JHH = 8, 1H, {Ar}H4). 13C{1H} NMR (δ, C6D6): 13.34 (s, 2C,
(s, 6H, 2 ꢀ NCH3), 2.94 (s, 2H, ArCH2), 6.68 (d, JHH = 7, 1H,
{Ar}H6), 6.81 (t, JHH= 8, 1H, {Ar}H5), 6.85 (s, 1H, {Ar}H2),
6.89 (d, JHH= 8, 1H, {Ar}H4). 13C{1H} NMR (δ, C6D6): 17.17
(d, 2JCP = 9, 2C, 2 ꢀ CH3), 17.87 (d, 2JCP = 21, 2C, 2 ꢀ CH3),
28.64 (d, 1JCP= 19, 2C, 2 ꢀ CH), 45.34 (s, 2C, 2 ꢀ CH3N), 64.29
(s, 1C, ArCH2N), 117.48 (d, 3JCP= 11, 1C, {Ar}C6), 119.29 (d,
3JCP = 10, 1C, {Ar}C2), 122.43 (s, 1C, {Ar}C4), 129.44 (s, 1C,
2 ꢀ CH2CH3) 16.85 (d, 2JCP = 2, 2C, 2 ꢀ CH3), 18.19 (d, 2JCP
=
=
4, 2C, 2 ꢀ CH3), 28.6 (d, 1JCP = 24, 2C, 2 ꢀ CH), 56.3 (d, 3JCP
2, 2C, 2 ꢀ CH2CH3), 64.7 (d, 3JCP = 2, 1C, ArCH2N), 107.96 (d,
3JCP = 13, 1C, {Ar}C3), 114.3 (d, 4JCP = 2, C, {Ar}C5), 126.8 (s,
1C, {Ar}C4), 142.1 (d, 2JCP = 33, 1C, {Ar}C1-Ni), 154.1 (s, 1C,
{Ar}C5), 160.08 (d, JCP = 9, 1C, {Ar}C6). 31P{1H} NMR (δ,
2
C6D6): 147.4 (s). Anal. Calcd for C15H26NOP: C, 67.39; H, 9.80;
N, 5.24. Found: C, 66.97; H, 9.96; N, 4.91.
[3-((N,N-Diethylamino)methyl)phosphinitobenzene], 2c. The
procedure described above for the preparation of 2a was used
to prepare 3-((N,N-diethylamino)methyl)phosphinitobenzene,
2c, which was isolated as a colorless oil (0.730 g, 89%). 1H NMR
{Ar}C6), 165.8 (d, JCP = 11, 1C, {Ar}C2). 31P{1H} NMR (δ,
2
C6D6): 197.92 (s). Anal. Calcd for C17H29OPNNiBr: C, 47.16;
H, 6.75; N, 3.23. Found: C, 47.71; H, 6.68; N, 3.26.
KP-[1,3-{(i-Pr2PO)(C6H4)(CH2[c-NH(CH2)4O])}]NiBr3, 4. A
solution of 2a (0.500 g, 1.618 mmol) in benzene (15 mL) was
added to NiBr2(CH3CN)x (0.486 g, 1.62 mmol). The resulting
brown mixture was stirred at 60 °C for 3 h, which resulted in the
precipitation of a blue-green solid. Filtration through a glass frit
(under inert atmosphere) and washing the solid on a filter with
benzene followed by drying under vacuum gave a turquoise-
green solid (0.423 g, 43%). The filtrate was passed through a pad
of silica gel followed by removal of solvent to give 3a as a yellow
powder (0.333 g, 46%). Anal. Calcd for C17H29O2P1NiBr3: C,
33.54; H, 4.80; N, 2.30. Found: C, 33.58; H, 4.81; N, 2.39.
KP,KC,KN-{2,6-(i-Pr2PO)(C6H3)(CH2[c-N(CH2)4O])}NiBr2,
5a. A solution of Br2 (6.5 μL, 0.123 mmol) in E2O (5 mL) was
cooled to -15 °C and then added to a solution of 3a (0.100 g, 0.224
mmol) in 10 mL of a 5:1 mixture of Et2O and CH2Cl2. The
resulting mixture was stirred for 20 min and then concentrated
under reduced pressure to ∼3-5 mL. The final mixture was
layered with cold hexane (5 mL) and placed in a -15 °C freezer
to obtain black crystals, which were collected by filtration (112 mg,
95%). Anal. Calcd for C17H27O2PNNiBr2: C, 38.75; H, 5.17; N,
2.66. Found: C, 38.47; H, 5.05; N, 2.57.
(δ, C6D6): 0.56 (t, 3JHH= 7, 6H, 2 ꢀ CH2CH3), 0.63 (dd, 3JHP
=
16, JHH = 7, 6H, 2 ꢀ CHCH3), 0.79 (dd, 3JHP = 11, JHH = 7,
6H, 2 ꢀ CHCH3), 1.51-1.26 (m, 2H, 2 ꢀ CH), 2.03 (q, 3JHH= 7,
3
4H, 2 ꢀ CH2), 3.06 (s, 2H, ArCH2N), 6.67 (d, JHH = 8, 1H,
{Ar}H6), 7.03-6.92 (m, 3H, {Ar}H4,2,5). 13C{1H} NMR (δ,
C6D6): 12.00 (s, 2C, 2 ꢀ CH2CH3), 14.76 (d, 2JCP = 3, 2C, 2 ꢀ
CHCH3), 15.85 (d, 2JCP = 2, 2C, 2 ꢀ CHCH3), 24.82 (d, 1JCP
=
64, 2C, 2 ꢀ CH), 46.96 (s, 2C, 2 ꢀ CH2CH3), 58.15 (s, 1C,
ArCH2N), 114.73 (s, 1C, {Ar}C6), 116.67 (s, 1C, {Ar}C2),
119.93 (s, 1C, {Ar}C4),129.44 (s, 1C, {Ar}C5), 158.86 (s, 1C,
{Ar}C1). 31P{1H} NMR (δ, C6D6): 147.1 (s). Anal. Calcd for
C17H30NOP: C, 69.12; H, 10.24; N, 4.74. Found: C, 69.32; H,
10.37; N, 4.48.
Synthesis of Complexes 3-5. KP,KC,KN-{2,6-(i-Pr2PO)-
(C6H3)(CH2[c-N(CH2)4O])}NiBr, 3a. Slow addition of a solu-
tion of 2a (0.500 g, 1.62 mmol) and NEt3 (0.23 mL, 1.62 mmol)
in 20 mL of benzene to the suspension of NiBr2(CH3CN)x (0.485
g, 1.618 mmol) in benzene (10 mL) resulted in a dark brown
mixture, which was heated for 3 h at 60 °C. Filtration of the final
mixture through a pad of silica gel followed by evaporation of
the volatiles gave the desired product as a yellow powder (0.659
g, 91%). 1H NMR (δ, C6D6): 1.16 (dd, 3JHP = 15, 3JHH = 7, 6H,
CH3) 1.47 (dd, 3JHP = 18, 3JHH = 7, 6H, CH3), 2.27-2.12 (m,
KP,KC,KN-{2,6-(i-Pr2PO)(C6H3)(CH2NMe2)}NiBr2, 5b. The
procedure described above for the preparation of 5a was used to
prepare this complex, which was isolated as black crystals (114
mg, 96%). Anal. Calcd for C15H25OPNNiBr2: C, 37.16; H, 5.20;
N, 2.89. Found: C, 37.13; H, 5.23; N, 2.97
2H, CH), 2.31 (d, 3JHH = 13, 2H, NCH2CH2), 3.14 (dd, 3JHH
=
3
12 and 3, 2H, NCH2CH2), 3.20 (td, JHH = 12 and 2, 2H,
OCH2), 3.62 (s, 2H, ArCH2N), 4.18 (m, 2H, OCH2), 6.44 (d,
3JHH = 8, 1H, {Ar}H5), 6.61 (d, 3JHH = 8, 1H, {Ar}H3), 6.92 (t,
3JHH = 8, 1H, {Ar}H4). 13C{1H} NMR (δ, C6D6): 16.90 (s, 2C, 2
ꢀ CH3) 18.34 (d, 2JCP = 4, 2C, 2 ꢀ ꢀ CH3), 28.61 (s, 2C, 2 ꢀ
CH), 54.13 (s, 2C, 2 ꢀ NCH2), 60.98 (s, 2C, 2 ꢀ OCH2), 62.99 (s,
1C, ArCH2N), 108.29 (d, 3JCP = 12, 1C, {Ar}C3), 108.42 (s, 1C,
KP,KC,KN-{2,6-(i-Pr2PO)(C6H3)(CH2NMe2)}NiBr2, 5b.
A
modified version of the procedure described above for the
preparation of 5a (reaction temperature -78 °C) was used to
prepare this complex, which was isolated as black crystals (93
mg, 80%). Anal. Calcd for C17H29OPNNiBr2: C, 39.81; H, 5.70;
N, 2.73. Found: C, 39.34; H, 5.86; N, 2.73.

6540 Organometallics, Vol. 28, No. 22, 2009
Spasyuk et al.
Cyclic Voltammetry. Cyclic voltammetry measurements were
performed using a BAS Epsilon potentiostat. The electroche-
mical properties of these compounds were measured at room
temperature in dichloromethane using a standard three-elec-
trode system consisting of a glassy carbon working electrode, a
Pt auxiliary electrode, and a Ag/AgCl reference electrode.
Bu4NPF6 was used as electrolyte (0.1 mol/L), and the solutions
were bubbled with nitrogen before each experiment. Reversible
redox waves of the ferrocenyl moieties were observed under
these conditions (E1/2{FeCp2þ/FeCp2} = þ0.47 V).
structures were solved by direct methods and refined by full-
matrix least-squares and difference Fourier techniques with
SHELX-97.34 All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. Hydrogen atoms were set in
calculated positions and refined as riding atoms with a common
thermal parameter.
Acknowledgment. The authors gratefully acknowledge
ꢀ
ꢀ
financial support received from Universite de Montreal
(fellowships to D.M.S.) and NSERC of Canada
(Research Tools and Instruments grants to D.Z.
and Discovery grants to D.Z. and A.v.d.E.). Profs. D.
Rochefort and M. S. Workentin are thanked for their
valuable help with electrochemical studies.
Crystal Structure Determinations. Single crystals of 3a-c were
grown by slow diffusion of hexanes into saturated benzene
solutions of the complexes. Single crystals of 5a-c were grown
from dichloromethane-hexane mixtures at -20 °C. The crys-
tallographic data for complexes 3a-c and 5a-c 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.30 An empirical absorption correction, based on the
multiple measurements of equivalent reflections, was applied
using the program SADABS.31 The space group was con-
firmed by XPREP routine32 in the program SHELXTL.33 The
Supporting Information Available: TGA for 3a-c and cyclic
voltammograms for complexes 3, ligand 2a, and preligand 1a.
This material is available free of charge via the Internet at http://
pubs.acs.org. Complete details of the X-ray analyses for com-
plexes 3a-c and 5a-c have been deposited at The Cambridge
Crystallographic Data Centre (CCDC 713853 (3a), 713858 (3b),
713854 (3c), 713856 (5a), 713855 (5b), 713857 (5c)). These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data_
request/cif, 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: þ44 1223 336033.
(30) SAINT, Release 6.06; Integration Software for Single Crystal
Data; Bruker AXS Inc.: Madison, WI, 1999.
(31) Sheldrick, G. M. SADABS, Bruker Area Detector Absorption
Corrections; Bruker AXS Inc., Madison, WI, 1999.
(32) XPREP, Release 5.10; X-ray Data Preparation and Reciprocal
Space Exploration Program; Bruker AXS Inc.: Madison, WI, 1997.
(33) SHELXTL, Release 5.10; The Complete Software Package for
Single Crystal Structure Determination; Bruker AXS Inc.: Madison, WI,
1997.
(34) (a) Sheldrick, G. M. SHELXS97, Program for the Solution of
Crystal Structures; Univ. of Gottingen: Germany, 1997. (b) Sheldrick, G. M.
SHELXL97, Program for the Refinement of Crystal Structures; Univer-
sity of Gottingen: Germany, 1997.