2,6-Bis(oxazolinyl)phenylnickel(II) bromide and 2,6-bis(ketimine) phenylnickel(II) bromide: Synthesis, structural features, and redox properties

Article abstract of DOI:10.1021/om061055y

2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R′-Phebox)] (2) were synthesized via two synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R′-PheboxBr], followed by a transmetalation reaction with [NiBr₂(PEt₃)₂], yielded not only complexes 2 with an η³-mer-N,C,N′-bonded Phebox ligand but also [NiBr(R,R′-Phebox)(PEt₃)₂], 7, where the nickel center is η¹-C bonded to the intra-annular C_ipso of the Phebox ligand. Coordination of two PEt₃ ligands completes the square-planar coordination sphere of the Ni center in 7. When R = t-Bu, R′ = H, only complex 7c was formed. Alternatively, when route B (oxidative addition with [Ni(cod)₂], cod = cyclooctadiene) was followed, selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries with a planar, η³- mer-N,C,N′ coordination of the terdentate ligand systems. Complexes 2 were found to be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate (MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl₄ to MMA. This is ascribed to the relatively high oxidation potential of Ni^II-Phebox complexes, which excludes the (reversible) formation of a d⁷-Ni ^III-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)₄NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)₄NBr as supporting electrode). Theoretical calculations showed that the energy (E_ox) needed for the oxidation reaction occurring during the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)-phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV).

Full text of DOI:10.1021/om061055y

Organometallics 2007, 26, 3985-3994
3985
2,6-Bis(oxazolinyl)phenylnickel(II) Bromide and
2,6-Bis(ketimine)phenylnickel(II) Bromide: Synthesis, Structural
Features, and Redox Propertiesg
Marianne Stol,†,‡ Dennis J. M. Snelders,† Meenal D. Godbole,§ Remco W. A. Havenith,|
David Haddleton, Guy Clarkson, Martin Lutz,4 Anthony L. Spek,4,#
Gerard P. M. van Klink,† and Gerard van Koten*,†
Organic Chemistry and Catalysis, Faculty of Science, Utrecht UniVersity, Padualaan 8, 3584 CH Utrecht,
The Netherlands, Dutch Polymer Institute, P.O. Box 902, 5600 AX EindhoVen, The Netherlands,
Leiden Institute of Chemistry, Gorleaus Laboratories, Leiden UniVersity, P.O. Box 9502, 2300 RA Leiden,
The Netherlands, Theoretical Chemistry Group, Faculty of Science, Utrecht UniVersity, Padualaan 8,
3584 CH Utrecht, The Netherlands, Department of Chemistry, Warwick UniVersity, CoVentry CV4 7Al,
United Kingdom, and Crystal and Structural Chemistry, Faculty of Science, Utrecht UniVersity,
Padualaan 8, 3584 CH Utrecht, The Netherlands
ReceiVed NoVember 16, 2006
2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R′-Phebox)] (2) were synthesized via two
synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R′-PheboxBr], followed by a
transmetalation reaction with [NiBr2(PEt3)2], yielded not only complexes 2 with an η3-mer-N,C,N′-bonded
Phebox ligand but also [NiBr(R,R′-Phebox)(PEt3)2], 7, where the nickel center is η1-C bonded to the
intra-annular Cipso of the Phebox ligand. Coordination of two PEt3 ligands completes the square-planar
coordination sphere of the Ni center in 7. When R ) t-Bu, R′ ) H, only complex 7c was formed.
Alternatively, when route B (oxidative addition with [Ni(cod)2], cod ) cyclooctadiene) was followed,
selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-
(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries
with a planar, η3-mer-N,C,N′ coordination of the terdentate ligand systems. Complexes 2 were found to
be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate
(MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl4 to MMA.
This is ascribed to the relatively high oxidation potential of NiII-Phebox complexes, which excludes the
(reversible) formation of a d7-NiIII-Phebox complex, a crucial condition for subsequent reactions.
Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical
waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode).
Theoretical calculations showed that the energy (Eox) needed for the oxidation reaction occurring during
the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)-
phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV).
Introduction
Chelating aryl ligands have become an important class of
ligands in homogeneous catalysis1 and materials chemistry.1b,2
We and others have extensively studied metal complexes derived
from the so-called ECE pincer ligand (ECE is [C6H3(CH2E)2-
2,6]- in which E is NR2 (A,1-3 Figure 1), PR2, SR, OMe). The
g Dedicated to Professor Miguel Yus on the occasion of his 60th birthday
in recognition of his skills and contribution to the field of organic chemistry.
* Author to whom correspondence should be addressed. E-mail:
Figure 1. N,C,N′-terdentate coordinating ligand systems applied
in organometallic complexes.
g.vankoten@uu.nl. Fax: +31-30-2523615. Tel: +31-30-2533120.
† Organic Chemistry and Catalysis, Utrecht University.
‡ Dutch Polymer Institute.
§ Leiden University.
ECE pincer ligands have a rich coordination chemistry origi-
nating from the conformational flexibility of the CH2E ortho
substituents. The bis(ortho-oxazolinyl)phenyl or Phebox ligand
(B,4,5,6,7 Figure 1) and the bis(aldimine)phenyl ligand (C,8 Figure
1) have ortho substituents with a pronounced restriction of
conformational freedom; that is, only rotation about Caryl-Cimine
is possible as well as syn/anti configurations (for C). The
| Theoretical Chemistry Group, Utrecht University.
Warwick University.
4 Crystal and Structural Chemistry, Utrecht University.
# Author to whom crystallographic inquiries may be directed. E-mail:
a.l.spek@chem.uu.nl.
(1) (a) Singleton, J. T. Tetrahedron 2003, 59, 1837. (b) Albrecht, M.;
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M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759.
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Org. Lett. 2000, 2, 3461. (b) Guillena, G.; Kruithof, C. A.; Casado, M. A.;
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10.1021/om061055y CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/30/2007

3986 Organometallics, Vol. 26, No. 16, 2007
Stol et al.
oxazolinyl CdN groupings in these ligands have the tendency
to be coplanar with the arene ring, thus creating a planar NCN-
terdentate ligand system. This has been observed in Rh-,4
Ni-,5 Pd-,4a,b,6 and Pt-Phebox4b,7 derivatives and in
Li-Phebox compounds in which Cipso is three-center two-
electron bonded to two lithium atoms in a dimeric structure.9
Nevertheless, the Phebox ligand can also be η1-C bonded to a
metal center, as has been found for [Au(Me,Me-Phebox)-
(PPh3)]10 and [Sn(Me,Me-Phebox)Me3].9
The Phebox ligand attracted much attention because of the
ample opportunities to introduce chirality in the oxazoline ring
by the use of readily available chiral amino alcohols in the
oxazolinyl substituent synthesis. In 1997, the Phebox ligand was
introduced in catalysis by Denmark (cyclopropanation with
Phebox-Pd complexes)6a and was studied extensively by
Nishiyama,4,7a who employed Phebox-Rh, -Pd, and -Pt
complexes in catalysis (asymmetric aldol-type condensation of
isocyanides and aldehydes,4b,c asymmetric Michael addition,4e
enantioselective allylation of aldehydes,4d,11 and asymmetric
alkylation of aldimines7a).
In the search for catalytic properties of E,C,E′-pincer metal
complexes, the unique atom-transfer radical addition (abbrevi-
ated as ATRA, 1:1 addition of CClX3 to MMA)12 and atom-
transfer radical polymerization (abbreviated as ATRP, polym-
erization of MMA)13 reactions catalyzed by [NiBr(C6H3-
(CH2NMe2)2-2,6)] (1, A (M ) NiBr, see Figure 1)) were
Figure 2. [NiBr(Phebox)] (2) and [NiBr(bis(ketimine)phenyl)] (3).
discovered. Extensive studies revealed that both the ATRP and
ATRA reactions are catalyzed by these Ni compounds because
of (i) the low and reversible NiII f NiIII oxidation potential
and (ii) the persistence of a d7 NiIII species [NiIIIX2(C6H3-
(CH2NMe2)2-2,6)]. So far, this catalytic reactivity was not found
for PCP- and SCS-nickel complexes and seems to be unique
for the NCN-nickel complexes. Accordingly, we set out to study
the synthesis and properties of other NiII complexes with N,C,N′-
terdentate coordinating ligands related to 1, i.e., the Ni-Phebox
(2) and Ni-ketimine (3) NCN complexes, both with re-
stricted conformational freedom as compared to [NiBr(C6H3-
(CH2NMe2)2-2,6)] (1, abbreviated as [NiBr(NCN)].
Here, the synthesis of [NiBr(R,R′-Phebox)] and [NiBr(bis-
(ketimine)phenyl)] complexes (Figure 2) and analysis of their
structural properties are described. The Ni-ketimine complex
3 is closely related to the 2,6-bis(aldimine)phenyl-Pd, -Pt, and
-Rh complexes, recently described by Elsevier et al. (C, Figure
1).8 In addition the catalytic activity of 2 in the radical
polymerization of methyl methacrylate (MMA) and the Khara-
sch addition of CCl4 to MMA has been tested. The redox
properties of [NiBr(R,R′-Phebox)] (2) and [NiBr(bis(ketimine)-
phenyl)] (3) are compared to those of [NiBr(NCN)] (1).
Theoretical calculations provide further insight into the redox
properties of 2 and 3, which have implications for their reactivity
in ATRA and ATRP.
(4) (a) Motoyama, Y.; Makihara, N.; Mikami, Y.; Aoki, K.; Nishiyama,
H. Chem. Lett. 1997, 951. (b) Motoyama, Y.; Kawakami, H.; Shimozono,
K.; Aoki, K.; Nishiyama, H. Organometallics 2002, 21, 3408. (c) Motoyama,
Y.; Shimozono, K.; Aoki, K.; Nishiyama, H. Organometallics 2002, 21,
1684. (d) Motoyama, Y.; Okano, M.; Narusawa, H.; Makihara, N.; Aoki,
K.; Nishiyama, H. Organometallics 2001, 20, 1580. (e) Motoyama, Y.;
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H. Organometallics 1999, 18, 3584. (b) Fossey, J. S.; Richards, C. J.
Organometallics 2004, 23, 367.
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Organometallics 2001, 20, 4437. (b) Hoogervorst, W. J.; Koster, A. L.;
Lutz, M.; Spek, A. L.; Elsevier, C. J. Organometallics 2004, 23, 1161. (c)
Hoogervorst, W. J.; Goubitz, K.; Fraanje, J.; Lutz, M.; Spek, A. L.; Ernsting,
J. M.; Elsevier, C. J. Organometallics 2004, 23, 4550. (d) Hoogervorst, W.
J. Isophthalaldimine Compounds of Palladium, Platinum and Rhodium.
Thesis, 2003, Universiteit van Amsterdam, Amsterdam, The Netherlands.
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J.; Ferna´ndez, A.; Ortigueira, J. M. J. Organomet. Chem. 1996, 506, 165.
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Kooijman, H.; Spek, A. L.; van Koten, G. Organometallics 2005, 24, 743.
(10) Stol, M.; Lutz, M.; Spek, A. L.; van Klink, G. P. M.; van Koten,
G. To be published.
(11) (a) Motoyama, Y.; Narusawa, H.; Nishiyama, H. Chem. Commun.
1999, 131. (b) Motoyama, Y.; Nishiyama, H. Synlett 2003, 12, 1883.
(12) (a) van de Kuil, L. A.; Veldhuizen, Y. S. J.; Grove, D. M.; Zwikker,
J. W.; Jenneskens, L. W.; Drenth, W.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. Recl. TraV. Chim. Pays-Bas 1994, 113, 267. (b) Knapen, J. W.
J.; van der Made, A.; de Wilde, J. C.; van Leeuwen, P. W. N. M.; Wijkens,
P.; Grove, D. M.; van Koten, G. Nature 1994, 372, 659. (c) 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. (d) Gossage,
R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem. Res. 1998, 31, 423.
(e) Grove, D. M.; van Koten, G.; Verschuuren, A. H. M. J. Mol. Catal.
1988, 45, 169. (f) Grove, D. M.; Verschuuren, A. H. M.; van Koten, G.;
van Beek, J. A. M. J. Organomet. Chem. 1989, 372, C1. (g) Kleij, A. W.;
Gossage, R. A.; Klein Gebbink, R. J. M.; Brinkmann, N.; Reijerse, E. J.;
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Gossage, R. A.; Jastrzebski, J. T. B. H.; van Ameijde, J.; Mulders, S. J. E.;
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Results and Discussion
Ligand Synthesis. Three different Phebox ligands (5) were
synthesized using modified literature procedures.14-16 One
achiral Phebox ligand (5a) was derived from 2-amino-2-methyl-
1-propanol, and the two chiral Phebox ligands (5b, 5c,
respectively, Scheme 1) were obtained from L-valinol and L-tert-
leucinol, respectively. Synthesis of 2,6-bis(4,4′-R,R′-2′-oxazoli-
nyl)phenyl bromide 5a (R ) R′ ) Me), 5b (R ) i-Pr, R′ ) H),
and 5c (R ) t-Bu, R′ ) H) (abbreviated as [R,R′-PheboxBr])
started with the oxidation of 1-bromo-2,6-dimethylbenzene with
KMnO4 to 2-bromoisophthalic acid.14 The latter acid was
chlorinated with SOCl2, followed by reaction of the resulting
2-bromoisophthaloyl chloride (4) with the appropriate amino
alcohol.15 The resulting amide was cyclized in situ via a
procedure of Vorbru¨ggen using a CCl4/PPh3 reagent.16
The synthesis of 2,6-bis[N,N′-(2′,6′-dimethylphenyl)ketimino]-
phenyl bromide (6, abbreviated as [bis(ketimine)phenylBr])
(13) (a) Granel, C.; Dubois, Ph.; Je´roˆme, R.; Teyssie´, Ph. Macromolecules
1996, 29, 8576. (b) Granel, C.; Teyssie´, Ph.; Je´roˆme, R.; Nicol, P. (Elf
Atochem S. A., France) Eur. Pat. Appl. EP796870, 1999. (c) Granel, C.;
Moineau, G.; Lecomte, Ph.; Dubois, Ph.; Je´roˆme, R.; Teyssie´, Ph. Polym.
Prepr. 1997, 38, 450.
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(16) Vorbru¨ggen, H.; Krolikiewicz, K. Tetrahedron 1993, 49, 9353.

2,6-Bis(oxazolinyl)phenylnickel(II) Bromide
Organometallics, Vol. 26, No. 16, 2007 3987
Scheme 1. Synthesis of [R,R′-PheboxBr] (5)
Scheme 2. Synthesis of [Bis(ketimine)phenylBr] (6)
lithiation of 5 via Br-Li exchange can be achieved with n-BuLi
in Et2O at -78 °C.9 Reaction of either [Me,Me-PheboxBr] (5a)
or [i-Pr,H-PheboxBr] (5b) with n-BuLi and subsequent reaction
with [NiBr2(PEt3)2] resulted in the formation of [NiBr(Me,Me-
Phebox)] (2a) and [NiBr(i-Pr,H-Phebox)] (2b), respectively,
which could be isolated as pure products. A disadvantage of
this route is that in addition to the desired η3-mer-N,C,N′-
Phebox-NiBr complexes 2, η1-C-Phebox-NiBr(PEt3)2 com-
plexes of type 7 are also formed. The amount of 7 seems to be
dependent on the nature of the oxazolinyl substituents R and
R′. In the reactions to 2a and 2b, 7a and 7b, respectively, were
formed as side products in relatively small amounts (max. 26%),
while 7c was formed exclusively in the transmetalation reaction
of 5c with [NiBr2(PEt3)2]. In the latter reaction, formation of
the desired product 2c was not even observed.
could not be accomplished via common condensation proce-
dures: precipitation of the product, as was used for the 2,6-
bis(ketimine)pyridine analogue,17 or via removal of the gener-
ated H2O by azeotropic distillation using a trap (Dean Stark).
The synthesis of 6 was successfully accomplished by reacting
2,6-diacetylphenyl bromide18 with 2.8 equiv of 2,6-dimethyl-
aniline, in the presence of Si(OEt)4, under removal of ethanol
at high temperature (Scheme 2).
This procedure was developed for the synthesis of sterically
hindered imines,19 and these forcing conditions are necessary
indeed to obtain the bis(ketimine)phenyl bromides such as 6.
Synthesis of Ni Complexes 2 and 3. Starting from [R,R′-
PheboxBr] 5, synthesis of the Phebox-Ni complexes was
accomplished via two different synthetic routes. Route A
involved selective bis-ortho lithiation followed by transmeta-
lation of the in situ formed Phebox-Li with, e.g., [NiBr2(PEt3)2].
In a previous paper we demonstrated that selective bis-ortho
Isolation of side products 7a and 7b was hampered because
of similar solubility properties to the starting complex [NiBr2-
(PEt3)2]. However, 7c could be isolated pure as a dark red solid.
31P{1H} spectra (singlet at δ 1.4 ppm) showed that the two PEt3
ligands are trans-coordinated. The [NiBr(t-Bu,H-Phebox)(PEt3)2]
1
stoichiometry was confirmed by H and 13C{1H} NMR spec-
troscopy of 7c in benzene-d6. Consequently the Phebox ligand
in 7c is η1-C bonded to the Ni center and has a structure as
proposed in Scheme 3. In this proposed structure, the plane of
the aryl ring of the t-Bu,H-Phebox ligand is perpendicular to
the square-planar coordination plane of the NiII center. The meta-
aryl protons show a diagnostic downfield shift from 6.96 in
square-planar complex 2c with an η3-mer-N,C,N′-coordinated
t-Bu,H-Phebox ligand (Vide infra) to 7.60 ppm in 7c. The latter
value corresponds to the chemical shift for the meta-aryl protons
found in the starting t-Bu,H-Phebox bromide 5c. Accordingly
the formation of 7a and 7b in the corresponding reactions could
be identified by the shifts of the respective meta-aryl protons
in these compounds from 6.98 (2a) to 7.87 ppm for 7a and
6.98 (2b) to 7.98 for 7b, respectively. In the course of the
formation of 2, the PEt3 ligands have to be replaced by bis-
ortho coordination with the imine-N ligands. This feature was
observed earlier in the transmetalation reaction of bis-ortho-
amine chelating aryllithium compounds [Li{C6H3(CH2NR1R2)-
2,6}] with [NiBr2(PEt3)2], yielding products with and without
the phosphine ligands coordinated to the NiII center, depending
on the R1 and R2 substituents of the ligand.20 It is not clear yet
why 2b is formed in high yield, whereas in the case of the
compound with a t-Bu instead of an i-Pr group the reaction
stops at the stage of the bisphosphine compound 7c.
(17) (a) Brookhart, M. S.; Small, B. L. (E. I. Du Pont de Nemours &
Co., U.S.A.) PCT Int. Appl. WO9830612, 1998. (b) Bennet, A. M. A. (E.
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The alternative route B (Scheme 4) consists of an oxidative
addition reaction of the Phebox bromides 5 with [Ni(cod)2].
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van Koten, G.; Ramp, M. J.; Coenjaarts, N. C.; Grove, D. M.; Goubitz, K.;
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3988 Organometallics, Vol. 26, No. 16, 2007
Scheme 3. Route A: Bis-ortho Lithiation/Transmetalation
Stol et al.
Scheme 4. Route B: Oxidative Addition with [Ni(cod)2]
complexes 2a, 2b, and 3 are stable as solids in air, whereas
2c decomposes rapidly. In solution all complexes (2a-c and
3) decompose upon exposure to air. Ultimately, the correspond-
ing protonated arene ligand is observed. However, upon addi-
tion of a small amount of water to a solution of the Phebox-
nickel complexes in benzene-d6 under exclusion of oxygen,
no decomposition through hydrolysis is observed. This sug-
gests that these nickel complexes are stable toward water but
react with oxygen in solution, subsequently followed by
hydrolysis.
Structural Features. Single crystals of 2b, suitable for X-ray
crystallography, were obtained by vapor diffusion of pentane
to a saturated solution in diethyl ether. The top and side-on views
of the molecular structure of 2b are depicted in Figure 3.
The X-ray crystal structure of 3 was determined from single
crystals, obtained from slow evaporation of a saturated solu-
tion in pentane. The molecular structure of 3 is depicted in
Figure 4.
The structure of 2b is directly related to the recently published
structure of [NiI(Me,Me-Phebox)]5 and the analogous Phebox-
Pd,4a,b,5-Pt,4b,7 and -Rh4 complexes. The square-planar NiII
centers in 2b and 3 are four-coordinate, being bonded to Cipso
of the aryl ring, the two trans-positioned oxazolinyl-N or
imine-N ligands, and a bromide ligand that occupies the fourth
coordination site.
Because of the absence of potentially coordinating phosphine
ligands, formation of complexes of type 7 is prevented. There-
fore, route B is a preferred route for the synthesis of 2a and
2b, and 2c in particular.
The ketimine-nickel complex 3 was prepared by the oxida-
tive addition of [Ni(cod)2] with aryl bromide 6. The nickel
Figure 3. Displacement ellipsoid plot (50% probability) of [NiBr(i-Pr,H-Phebox)] (2b) showing full numbering scheme and a side-on
view along the Ni(1)-C(1) bond. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ni(1)-
C(1) 1.8491(19), Ni(1)-Br(1) 2.3572(4), Ni(1)-N(1) 1.908(2), Ni(1)-N(2) 1.910(2), N(1)-C(7) 1.290(3), N(2)-C(13) 1.286(3), C(1)-
Ni(1)-Br(1) 178.10(6), N(1)-Ni(1)-N(2) 162.20(8), C(1)-Ni(1)-N(1) 81.08(13), C(1)-Ni(1)-N(2) 81.15(13), Br(1)-Ni(1)-N(1) 99.86(6),
Br(1)-Ni(1)-N(2) 97.93(6).

2,6-Bis(oxazolinyl)phenylnickel(II) Bromide
Organometallics, Vol. 26, No. 16, 2007 3989
Figure 4. Displacement ellipsoid plot (50% probability) of 3, showing full numbering scheme and a view onto the N-Ni-N moiety along
the Ni(1)-C(1) bond. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å), angles (deg), and torsion angles (deg):
Ni(1)-C(1) 1.819(2), Ni(1)-Br(1) 2.3419(3), Ni(1)-N(1) 1.9394(19), Ni(1)-N(2) 1.9318(19), N(1)-C(7) 1.307(3), N(1)-C(9) 1.435(3),
N(2)-C(17) 1.311(3), N(2)-C(19) 1.439(3), C(1)-Ni(1)-Br(1) 174.63(7), N(1)-Ni(1)-N(2) 162.06(8), C(1)-Ni(1)-N(1) 81.26(9), C(1)-
Ni(1)-N(2) 81.27(9), Br(1)-Ni(1)-N(1) 98.75(6), Br(1)-Ni(1)-N(2) 99.03(6), C(7)-N(1)-C(9) 120.4(2), C(17)-N(2)-C(19) 119.25-
(19), Ni(1)-N(1)-C(9)-C(10) -72.9(3), Ni(1)-N(2)-C(19)-C(20) 89.2(2), Br(1)-Ni(1)-N(1)-C(9) -7.96(18), Br(1)-Ni(1)-N(2)-
C(19) 13.54(18).
The overall geometry of 2b corresponds well to that of
[NiI(Me,Me-Phebox)].5
the η3-mer-N,C,N′ chelate amounts to 0.012(3) Å for 2b and
0.020(2) Å for 3. The angles between these two planes are 1.61-
(12)° and 3.45(10)°, respectively. In 3, the ortho-xylyl N
substituents bend slightly to one side of the planar ketiminearyl
skeleton, while the bromide is bending to the opposite side. This
structural feature is illustrated by the torsion angles of Br(1)-
Ni(1)-N(1)-C(9) and Br(1)-Ni(1)-N(2)-C(19) of -7.96-
(18)° and 13.54(18)°, respectively, and the C(1)-Ni(1)-Br(1)
angle of 174.63(7)°.
The bond lengths about the Ni centers in 2b and 3 follow
the general trend as expected (Ni < Pd ∼ Pt) when comparing
the Phebox-Pd and -Pt (B, Figure 1) and NCN-Ni, -Pd, and
-Pt (A, Figure 1) and bis(aldimine)phenyl-Pd and -Pt (C,
Figure 1) bond lengths (Table 1).
The N(1)-Ni(1)-N(2) angles of 2b and 3 are 162.20(8)°
and 162.06(8)°, respectively. This acute angle reflects the
distortion from the square-planar geometry around Ni, which
is a common structural feature found in η3-mer-N,C,N′ pincer
nickel(II) complexes (163.2-168.59°).12a,20b,21
The degree of planarity of the Phebox ligand skeleton
(CdN substituent and aryl ring) is illustrated by the side-on
views depicted in Figures 3 and 4. The largest deviation from
the least-squares planes of the two five-membered rings forming
(21) (a) Kleij, A. W.; Kleijn, H.; Jastrzebski, J. T. B. H.; Spek, A. L.;
van Koten, G. Organometallics 1999, 18, 277. (b) Kleijn, H.; Jastrzebski,
J. T. B. H.; Gossage, R. A.; Kooijman, H.; Spek, A. L.; van Koten, G.
Tetrahedron 1998, 54, 1145. (c) Schimmelpfennig, U.; Zimmering, R.;
Schleinitz, K. D.; Sto¨sser, R.; Wenschuh, E.; Baumeister, U.; Hartung, H.
Z. Anorg. Allg. Chem. 1993, 619, 1931. (d) Grove, D. M.; van Koten, G.;
Ubbels, H. J. C.; Zoet, R.; Spek, A. L. J. Organomet. Chem. 1984, 263,
C10.
(23) (a) Albrecht, M.; James, S. L.; Veldman, N.; Spek, A. L.; van Koten,
G. Can. J. Chem. 2001, 79, 709. (b) Terheijden, J.; van Koten, G.; Vinke,
I. C.; Spek, A. L. J. Am. Chem. Soc. 1985, 107, 2891. (c) Smeets, W. J. J.;
Spek, A. L.; Duisenberg, A. J. M.; van Beek, J. A. M.; van Koten, G. Acta
Crystallogr., Sect. C 1987, 43, 463. (d) Terheijden, J.; van Koten, G.; van
Beek, J. A. M.; Vriesema, B. K.; Kellogg, R. M.; Zoutberg, M. C.; Stam,
C. H. Organometallics 1987, 6, 89. (e) Steenwinkel, P.; Kooijman, H.;
Smeets, W. J. J.; Spek, A. L.; Grove, D. M.; van Koten, G. Organometallics
1998, 17, 5411. (f) Back, S.; Albrecht, M.; Spek, A. L.; Rheinwald, G.;
Lang, H.; van Koten, G. Organometallics 2001, 20, 1024. (g) Albrecht,
M.; Lutz, M.; Schreurs, A. M. M.; Lutz, E. T. H.; Spek, A. L.; van Koten,
G. J. Chem. Soc., Dalton Trans. 2000, 3797. (h) Dijkstra, H. P.;
Chuchuryukin, A.; Suijkerbuijk, B. M. J. M.; van Klink, G. P. M.; Mills,
A. M.; Spek, A. L.; van Koten, G. AdV. Synth. Catal. 2002, 344, 771. (i)
Suijkerbuijk, B. M. J. M.; Slagt, M. Q.; Klein Gebbink, R. J. M.; Lutz, M.;
Spek, A. L.; van Koten, G. Tetrahedron Lett. 2002, 43, 6565. (j) Albrecht,
M.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten, G. Chem.-Eur. J.
2000, 6, 1431. (k) Jude, H.; Bauer, J. A. K.; Connick, W. B. Inorg. Chem.
2002, 41, 2275. (l) Slagt, M. Q.; Klein Gebbink, R. J. M.; Lutz, M.; Spek,
A. L.; van Koten, G. J. Chem. Soc., Dalton Trans. 2002, 2591. (m) James,
S. I.; Verspui, G.; Spek, A. L.; van Koten, G. Chem. Commun. 1996, 1309.
(n) Davies, P. J.; Veldman, N.; Grove, D. M.; Spek, A. L.; Lutz, B. T. G.;
van Koten, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 1959. (o) Albrecht,
M.; Kocks, B. M.; Spek, A. L.; van Koten, G. J. Organomet. Chem. 2001,
624, 271. (p) van Beek, J. A. M.; van Koten, G.; Dekker, G. P. C. N.;
Wissing, E.; Zoutberg, M. C.; Stam, C. H. J. Organomet. Chem. 1990,
394, 659.
(22) (a) Mills, A. M.; van Beek, J. A. M.; van Koten, G.; Spek, A. L.
Acta Crystallogr., Sect. C 2002, 58, m304. (b) Grove, D. M.; van Koten,
G.; Ubbels, H. J. C.; Spek, A. L. J. Am. Chem. Soc. 1982, 104, 4285. (c)
Tsubomura, T.; Tanihata, T.; Yamakawa, T.; Ohmi, R.; Tamane, T.; Higuchi,
A.; Katoh, A.; Sakai, K. Organometallics 2001, 20, 3833. (d) Rodr´ıguez,
G.; Lutz, M.; Spek, A. L.; van Koten, G. Chem.-Eur. J. 2002, 8, 45. (e)
Alsters, P. L.; Baesjou, P. J.; Janssen, M. D.; Kooijman, H.; Sicherer-
Roetman, A.; Spek, A. L.; van Koten, G. Organometallics 1992, 11, 4124.
(f) Dijkstra, H. P.; Slagt, M. Q.; McDonald, A.; Kruithof, C. A.; Kreiter,
R.; Mills, A. M.; Lutz, M.; Spek, A. L.; Klopper, W.; van Klink, G. P. M.;
van Koten, G. Eur. J. Inorg. Chem. 2003, 830. (g) Steenwinkel, P.; James,
S. L.; Grove, D. M.; Kooijman, H.; Spek, A. L.; van Koten, G.
Organometallics 1997, 16, 513. (h) Lagunas, M.-C.; Gossage, R. A.; Spek,
A. L.; van Koten, G. Organometallics 1998, 17, 731. (i) Slagt, M. Q.;
Dijkstra, H. P.; McDonald, A.; Klein Gebbink, R. J. M.; Lutz, M.; Ellis, D.
D.; Mills, A. M.; Spek, A. L.; van Koten, G. Organometallics 2003, 22,
27. (j) Dijkstra, H. P.; Meijer, M. D.; Patel, J.; Kreiter, R.; van Klink, G.
P. M.; Lutz, M.; Spek, A. L.; Canty, A. J.; van Koten, G. Organometallics
2001, 20, 3159. (k) Hartshorn, C. M.; Steel, P. J. Organometallics 1998,
17, 3487. (l) Canty, A. J.; Patel, J.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 2000, 607, 194. (m) Diez-Barra, E.; Guerra, J.; Lopez-
Solera, I.; Merino, S.; Rodriguez-Lopez, J.; Sanchez-Verdu, P.; Tejeda, J.
Organometallics 2003, 22, 541.

3990 Organometallics, Vol. 26, No. 16, 2007
Stol et al.
Table 1. Comparison of Selected Crystallographic Data of
Phebox-MII, NCN-MII, and Bis(aldimine)phenyl-MII
Complexes
Catalysis and Redox Properties. The catalytic properties
of Phebox-Ni complexes 2a-c were investigated by testing
their catalytic activity in both the radical polymerization reaction
of MMA and the Kharasch addition reaction of CCl4 to MMA.
It appeared that all these nickel complexes were inactive as
catalysts in these types of reactions. This is in concert with the
observation that the complexes were stable in the presence of
oxidating agents such as CCl4, which excludes the possibility
that the persistent “radical” d7-NiIII compound was irreversibly
formed. This would block catalysis, as the occurrence of a fast
electron-transfer back step is a crucial condition for the
re-formation of the d8-NiII catalyst.12d
Cipso-M (Å)
N-M (Å)
bis(ketimine)Ph-Ni (3)
iPr,H-Phebox-Ni (2b)
Me,Me-Phebox-Ni5
R,R′-Phebox-Pd4a,b,5
R,R′-Phebox-Pt4b,7
bis(aldimine)Ph-Pt8a,c,e
bis(aldimine)Ph-Pd8d
NCN-Ni12a,20b,21
1.819(2)
1.8491(19)
1.9318(19), 1.9394(19)
1.908(2), 1.910(2)
1.968-1.977
1.857-1.859
1.845-1.956
1.892-1.963
1.889-1.945
1.905-1.918
1.788-1.899
1.900-2.017
1.901-2.025
2.056-2.072
2.026-2.066
2.036-2.097
2.087-2.143
1.971-2.208
NCN-Pd22
2.007-2.136
NCN-Pt14,22i,45,46
2.036-2.168
These observations prompted us to investigate the redox
properties of the Phebox- and ketimine-NiII complexes 2a-c
and 3 and compare them to [NiBr(NCN)] (1), which is a highly
effective catalyst.12,13 Cyclovoltammetric (CV) experiments with
2a, 2c, and 3 were performed in distilled acetone using
(n-Bu)4NBr as supporting electrolyte in the -1.00 to +1.50 V
region. The potentials are given against the Ag/AgCl reference
electrode. For comparison, CV experiments were also performed
on the [NiBr(NCN)] complex. The latter complex shows two
distinct electron-transfer processes, which are coupled to chemi-
cal reactions (transfer of bromide) in the specified experimental
region (eqs 1 and 2).25
Table 2. Calculated IP1’s for 1, 2a, and 3
2a
1
3
total energy (Eh) -760.6755751 -1063.5225188 -1298.9355291
IP1 (eV),a eq 3
IP1 (eV),b eq 4a
IP1 (eV),c eq 4b
IP1 (eV),d eq 5
6.95
1.45
2.19
5.69
7.33
1.87
2.52
6.13
6.92
1.90
2.53
6.01
a Ionization potential, calculated as E[NiBr] - E[NiBr]
‚
bIonization
+
potential, calculated as E[NiBr2] - {E[NiBr] + E[Br] }. c Ionization potential,
calculated as E[NiBr2] - E[NiBr2] . Ionization potential, calculated as
•
-
d
-
•
+•
E[NiBr(ac.)] - {E[NiBr] + E[ac.]}.
calculation. The calculated geometries of 1, 2a, and 3 are in
reasonable agreement with those obtained from X-ray crystal-
lography data.26-28 Only the Ni-Br bond length is systemati-
cally overestimated by about 0.1 Å in the calculations.
Equations 3, 4, and 5 schematically represent the processes
for which theoretical calculations were performed regarding the
ionization potential of the NiII complexes. The calculated
energies for the first ionization potential (IP1) for the depicted
processes starting from the three d8-NiII complexes [NiBr(NCN)]
(1), [NiBr(Me,Me-Phebox)] (2a), and [NiBr(bis(ketimine)-
phenyl)] (3) are depicted in Table 2.
Experiments with 2a, 2c, and 3 showed no electrochemical
waves in the region where chemical reversible transformations
of aryl-NiII to aryl-NiIII complexes usually occur. This
illustrates that Phebox-Ni and bis(ketimine)phenyl-Ni com-
plexes are much more difficult to oxidize as compared to the
[NiBr(NCN)] complex.
Theoretical calculations on existing nickel(II) complexes 1,
2a, and 3 were performed to gain insight in the electronic
structure of these complexes. All geometries were characterized
as real minima by means of a numerical force constant
(24) (a) Donkervoort, J. G.; Vicario, J. L.; Jastrzebski, J. T. B. H.; Smeets,
W. J. J.; Spek, A. L.; van Koten, G. J. Organomet. Chem. 1998, 551, 1. (b)
Maassarani, F.; Davidson, M. F.; Wehman-Ooyevaar, I. C. M.; Grove, D.
M.; van Koten, M. A.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. Inorg.
Chim. Acta 1995, 235, 327. (c) Schmulling, M.; Grove, D. M.; van Koten,
G.; van Eldik, R.; Veldman, N.; Spek, A. L. Organometallics 1996, 15,
1384. (d) van der Ploeg, A. F. M. J.; van Koten, G.; Vrieze, K.; Spek, A.
L.; Duisenberg, A. J. M. Organometallics 1982, 1, 1066. (e) Gossage, R.
A.; Ryabov, A. D.; Spek, A. L.; Stufkens, D. J.; van Beek, J. A. M.; van
Eldik, R.; van Koten, G. J. Am. Chem. Soc. 1999, 121, 2488. (f) Grove, D.
M.; van Koten, G.; Ubbels, H. J. C.; Vrieze, K.; Niemann, L. C.; Stam, C.
H. J. Chem. Soc., Dalton Trans. 1986, 717. (g) Terheijden, J.; van Koten,
G.; Mul, W. P.; Stufkens, D. J.; Muller, F.; Stam, C. H. Organometallics
1986, 5, 519. (h) van Beek, J. A. M.; van Koten, G.; Smeets, W. J. J.;
Spek, A. L. J. Am. Chem. Soc. 1986, 108, 5010. (i) Mayboroda, A.; Comba,
P.; Pritzkow, H.; Rheinwald, G.; Lang, H.; van Koten, G. Eur. J. Inorg.
Chem. 2003, 1703. (j) Canty, A. J.; Patel, J.; Skelton, B. W.; White, A. H.
J. Organomet. Chem. 2000, 599, 195. (k) Albrecht, M.; Gossage, R. A.;
Spek, A. L.; van Koten, G. Chem. Commun. 1998, 1003. (l) Chuchuryukin,
A. V.; Dijkstra, H. P.; Suijkerbuijk, B. M. J. M.; Klein Gebbink, R. J. M.;
van Klink, G. P. M.; Mills, A. M.; Spek, A. L.; van Koten, G. Angew.
Chem., Int. Ed. 2003, 42, 228.
The calculated ionization potentials for the electron-transfer
reactions of d8-NiII to d7-NiIII complexes (IP1, eq 3, Table 2)
show that for 2a a higher oxidation potential is expected
compared to 1 (7.33 vs 6.95 eV). However, according to these
(26) Comparison of the calculated geometrical features of [NiBr(NCN)]
and experimental21c geometrical features of [NiBr(C6H3(CH2NEt2)2-2,6)]
(distances in Å, angles in deg) calcd (expt): Ni(1)-Br(1) 2.501 (2.420-
(1)), Ni(1)-N(1) 2.028 (2.002(5)), Ni(1)-N(2) 2.028 (2.006(4)), C(1)-
Ni(1) 1.854 (1.825(5)), C(1)-Ni(1)-N(1) 83.67 (84.5(2)), C(1)-Ni(1)-
N(2) 83.61 (84.2(2)), C(1)-Ni(1)-Br(1) 179.99 (176.6(2)), N(1)-Ni(1)-
N(2) 167.27 (168.6(2)), N(1)-Ni(1)-Br(1) 96.33 (95.6(1)), N(2)-Ni(1)-
Br(1) 96.40 (95.8(1)).
(27) Comparison of the calculated geometrical features of [NiBr-
(Me,Me-Phebox)] (2a) and experimental5 geometrical features of [NiI-
(Me,Me-Phebox)] (distances in Å, angles in deg) calcd (expt): Ni(1)-
Br(1) 2.472 (Ni(1)-I(1) 2.5804(5)), Ni(1)-N(1) 1.978 (1.972(3)), Ni(1)-
N(2) 1.978 (1.977(3)), C(1)-Ni(1) 1.874 (1.859(4)), C(1)-Ni(1)-N(1)
81.06 (80.53(15)), C(1)-Ni(1)-N(2) 81.05 (80.73(15)), C(1)-Ni(1)-
Br(1) 179.95 (C(1)-Ni(1)-I(1) 172.61(11)), N(1)-Ni(1)-N(2) 162.12
(161.04(13)).
(25) 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.

2,6-Bis(oxazolinyl)phenylnickel(II) Bromide
Organometallics, Vol. 26, No. 16, 2007 3991
between the total energies of, for example, 8 and the sum of 1
and Br-. The ionization potentials thus calculated (1.45, 1.87,
and 1.90 eV, respectively, Table 2) show that for 2a and 3 a
similar oxidation potential is expected, while for 1 a significantly
lower energy is calculated, rationalizing the observed wave in
the CV experiments for 1 and the absence of a wave for 2a and
3 (in the region between -1.00 and +1.50 V).33 However, in
this calculation we assume that the Br- anion is not associated
with the Ni complex. Assuming that prior to the oxidation reac-
tion the bromide anion interacts with the neutral nickel complex
(eq 4b), theoretical calculations confirm that for 1 and 2a this
is indeed a plausible mechanism for the oxidation reactions.
For 1 and 2a, a [Ni-Br2]- complex could be located with a
Ni-Br- distance of 3.283 and 2.998 Å, respectively, but for
3-Br- the Ni-Br- distance is already 3.696 Å, indicating a
very weak interaction with the Ni atom. The IP1’s calculated
for these processes (eq 4b) lead to similar conclusions to those
for the model reactions with Br- at infinite distance (eq 4a).
Figure 5. Displacement ellipsoid plot (50% probability) of 8,
showing full numbering scheme. Hydrogen atoms have been omitted
for clarity. Selected bond distances (Å) and angles (deg): Ni(1)-
C(10) 1.894(3), Ni(1)-Br(1) 2.4373(6), Ni(1)-Br(2) 2.4272(6), Ni-
(1)-N(12) 2.041(2), Ni(1)-N(2) 2.036(3), C(10)-Ni(1)-Br(1)
166.19(9), C(10)-Ni(1)-Br(2) 90.85(9), N(12)-Ni(1)-N(2) 152.58-
(10), C(10)-Ni(1)-N(12) 82.15(11), C(10)-Ni(1)-N(2) 81.50-
(11), Br(1)-Ni(1)-N(12) 95.37(7), Br(2)-Ni(1)-N(12) 100.25(8),
Br(1)-Ni(1)-N(2) 95.29(8), Br(2)-Ni(1)-N(2) 101.85(8), Br(1)-
Ni(1)-Br(2) 102.96(2).
If instead of a complexing bromide ion, coordination by a
solvent molecule (acetone) is taken into account (eq 5), similar
results to those for the process described in eq 4a are obtained
(Table 2). This further corroborates the experimental result that
the counterion or the solvent is involved in the charge-transfer
process25 as well as the absence of an electrochemical wave
between -1.00 and +1.50 V in the cyclovoltammetric experi-
ments with 2a and 3.
In conclusion, synthesis of the Phebox-Ni complexes was
accomplished via two different synthetic routes. One route
involves the selective bis-ortho lithiation of the corresponding
Phebox-Br followed by transmetalation of the in situ formed
Phebox-Li with, for example, [NiBr2(PEt3)2] (route A). Fol-
lowing route A, a side product, characterized as [NiBr(R,R′-
Phebox)(PEt3)2] (7), was formed. In the case of reaction with
the most sterically hindered Phebox ligand 5c (R ) t-Bu, R′ )
H) 7c was formed exclusively. The second route, B, makes use
of an oxidative addition reaction of the aryl bromide with
[Ni(cod)2]. This route leads to the exclusive formation of 2 and
is also used for the synthesis of [NiBr(bis(ketimine)phenyl)]
(3). The molecular structures of 2b and 3 were determined by
X-ray crystal structure determination. The Phebox and bis-
(ketimine)phenyl ligands are η3-mer-N,C,N′ bonded in these
complexes. The terdentate N,C,N′ ligands in these complexes
have planar arrangements of the CdN and aryl plane. However,
even these rigid ligands can bind in the monodentate η1-C
bonding mode, as was demonstrated for [NiBr(t-Bu,H-Phebox)-
(PEt3)2] (7c). Complexes 2 are inactive in ATRP and ATRA,
which is ascribed to the relatively high oxidation potential of
NiII-Phebox complexes, which excludes the (reversible) forma-
tion of a d7-NiIII complex, a crucial condition for ATRP and
ATRA. This was confirmed by cyclic voltammetry measure-
ments with complexes 2a, 2c, and 3 using (n-Bu)4NBr as
electrolyte. Theoretical calculations showed that the energy (IP1)
needed for the oxidation reaction occurring during the CV
experiments is considerably higher for [NiBr(Me,Me-Phebox)]
(1.87 eV) and [NiBr(bis(ketimine)phenyl)] (1.90 eV) than for
[Ni(NCN)Br] (1.45 eV).
calculations, complex 3 should be as easy to oxidize as 1 (6.92
vs 6.95 eV), which is not in accordance with the cyclovolta-
mmetric experiments. As stipulated in ref 25, the counterion
(Br-) plays an essential role in the cyclic voltammetric
experiments (eqs 1, 2). In this process (eq 4a) [NiBr2(NCN)]
(8) is formed. Therefore, the reaction energies for reaction 4a
are better measures for the ionization potential observed in the
CV experiments than the IP1’s calculated for eq 3. Hence, the
energies (IP1) for the electron transfer and subsequent reaction
with Br- (eq 4a) were calculated for 1, 2a, and 3. The calculated
geometry of 8 is in reasonable agreement with the geometry
obtained from an X-ray crystal structure determination.29 The
molecular structure of 8 (depicted in Figure 5; single crystals
were obtained from slow evaporation of a saturated solution of
8 in xylene, RT25) is directly related to the molecular structure
of [NiI2(NCN)]30 and shows the same geometrical features: a
square-pyramidal geometry with the Ni atom displaced ca. 0.34
Å out of the basal plane31 toward the apical atom Br(2) and a
distortion from an ideal square-pyramidal geometry toward
trigonal bipyramidal (C(10) and Br(1) axial). A very similar
crystal structure was also found for the corresponding iron(III)
complex [FeCl2(NCN)].32
The energies (IP1) for this electron transfer and subsequent
reaction with Br- (eq 4a) were calculated as the difference
(28) Comparison of the calculated and experimental geometrical features
of [NiBr(bis(ketimine)phenyl)] (3) (distances in Å, angles in deg) calcd
(expt): Ni(1)-Br(1) 2.429 (2.3419(3)), Ni(1)-N(1) 1.985 (1.9394(19)),
Ni(1)-N(2) 1.985 (1.9318(19)), C(1)-Ni(1) 1.838 (1.819(2)), C(1)-Ni-
(1)-N(1) 81.40 (81.26(9)), C(1)-Ni(1)-N(2) 81.40 (81.27(9)), C(1)-Ni-
(1)-Br 180.00 (174.63(7)), N(1)-Ni-N(2) 162.80 (162.06(8)), N(1)-Ni-
Br 98.60 (98.75(6)), N(2)-Ni-Br 98.60 (99.03(6)).
(29) Comparison of the calculated and experimental geometrical features
of [NiBr2(NCN)] (8) (distances in Å, angles in deg) calc (expt): Ni(1)-
Br(1) 2.516 (2.4373(6)), Ni(1)-Br(2) 2.526 (2.4272(6)), Ni(1)-N(12) 2.087
(2.041(2)), C(10)-Ni(1) 1.893 (1.894(3)), C(10)-Ni(1)-N(12) 82.79
(82.15(11)), C(10)-Ni(1)-N(2) 82.86 (81.50(11)), C(10)-Ni(1)-Br(1)
162.00 (166.19(9)), C(10)-Ni(1)-Br(2) 87.99 (90.85(9)), N(12)-Ni(1)-
N(2) 157.50 (152.58(10)), N(12)-Ni(1)-Br(1) 94.16 (95.37(7)), N(12)-
Ni(1)-Br(2) 98.35 (100.25(8)), Br(1)-Ni(1)-Br(2) 110.02 (102.96(2)).
(30) Grove, D. M.; van Koten, G.; Zoet, R. J. Am. Chem. Soc. 1983,
105, 1379.
(31) Defined by the atoms C(10), N(12), N(2), and Br(1).
(32) De Koster, A.; Kanters, J. A.; Spek, A. L.; van der Zeijden, A. A.
H.; van Koten, G.; Vrieze, K. Acta Crystallogr. 1985, C41, 893.
(33) On the basis of the theoretical calculations, the experimental
oxidation wave for [NiBr(Me,Me-Phebox)] can be approximately expected
at about IP1([NiBr(Me,Me-Phebox)]) - IP1([NiBr(NCN)]) ) 0.42 V higher
than Eox for [NiBr(NCN)].

3992 Organometallics, Vol. 26, No. 16, 2007
Stol et al.
90) in diethyl ether (Rf 0.25), resulting in a white solid (6.95 g,
81%). IR (neat, cm-1): νmax 2966, 1663, 1643, 1423, 1351, 1192,
Experimental Section
Experiments were carried out under a dry, oxygen-free, nitrogen
atmosphere, using standard Schlenk techniques. Solvents were dried
and distilled from sodium (pentane, toluene), Na/benzophenone
(diethyl ether, tetrahydrofuran), CaH2 (CH2Cl2, CH3CN), and KOH
(Et3N) prior to use. n-BuLi (1.6 M in hexanes) was ordered from
1
998, 952, 807, 736. H NMR (300 MHz, acetone-d6): δ 1.35 (s,
12H, CMe2), 4.14 (s, 4H, CH2), 7.52 (t, 1H, 3JH-H ) 7.7 Hz, ArH),
3
7.67 (d, 2H, JH-H ) 7.5 Hz, ArH). 13C{1H} NMR (75 MHz,
acetone-d6): δ 28.4 (CMe2), 69.1 (CMe2), 79.9 (OCH2), 121.7
(ArC), 128.1 (ArC), 133.2 (ArC), 133.7 (ArC), 161.7 (OCN). Anal.
Calcd for C16H19BrN2O2: C, 54.71; H, 5.45; N, 7.98. Found: C,
54.63; H, 5.38; N, 7.96.
Synthesis of [(S,S) i-Pr,H-PheboxBr] (5b).4d An analogous
procedure to the synthesis of 5a was employed with 2-bromoiso-
phthalic acid (5.05 g, 21 mmol) and L-valinol (4.91 g, 48 mmol):
1
Acros and used as received. H and 13C{1H} NMR spectra were
recorded on a Varian Inova 300 spectrometer; 31P{1H} NMR
experiments, on a Varian Mercury 200 spectrometer. Benzene-d6
was purchased from Cambridge Isotope Laboratories, distilled from
sodium, and stored in a nitrogen-filled M-Braun glovebox. Other
NMR solvents (acetone-d6, CDCl3) were used as received. 1H and
13C{1H} chemical shifts (δ) are given in ppm relative to the solvent
residual signal as an internal standard. 31P{1H} NMR chemical shifts
are referenced externally to H3PO4. Electrochemical experiments
were performed with an Autolab PGSTAT 10 cyclic voltammeter
under an argon atmosphere. Acetone, used for cyclovoltammetry
experiments, was distilled from CaCl2 under an argon atmosphere
prior to use. 2-Bromoisophthalic acid,14 L-valinol, and L-tert-
leucinol34 were synthesized according to literature procedures. [R,R′-
PheboxBr] was synthesized according to a combination of literature
procedures.15,16 All other chemicals were purchased from either
Acros or Aldrich and used as received. Elemental analyses were
performed by Kolbe, Mikroanalytisches Laboratorium, Mu¨lheim
a.d. Ruhr, Germany. Theoretical calculations were performed at
the (U)B3LYP/LANL2-DZ level,35 using GAMESS-UK.36
20
light yellow oil (5.16 g, 67%), Rf value (diethyl ether) 0.28, [R]D
-63.2 (c 0.10 g/mL, CH2Cl2). IR (neat, cm-1): νmax 2958, 1660,
1362, 1123, 1069, 965, 728. 1H NMR (300 MHz, CDCl3): δ 0.98
3
3
(d, 6H, JH-H ) 6.6 Hz, CHMe2), 1.04 (d, 6H, JH-H ) 6.6 Hz,
CHMe2), 1.91 (septet, 2H, 3JH-H ) 6.6 Hz, CHMe2), 4.18 (m, 4H,
3
OCH2), 4.45 (m, 2H, CHN), 7.37 (t, 1H, JH-H ) 7.7 Hz, ArH),
7.65 (d, 2H, JH-H ) 7.8 Hz, ArH). 13C{1H} NMR (CDCl3, 75
3
MHz): δ 32.3 (CMe2), 60.0 (CMe2), 70.2 (CHN), 72.6 (OCH2),
121.0 (ArC), 126.6 (ArC), 132.0 (ArC), 132.2 (ArC), 162.6 (OCN).
Anal. Calcd for C18H23BrN2O2: C, 57.00; H, 6.11; N, 7.39.
Found: C, 56.88; H, 6.07; N, 7.26.
Synthesis of [(S,S)-t-Bu,H-PheboxBr] (5c).6a An analogous
procedure to the synthesis of 5a was employed with 2-bromoiso-
phthalic acid (4.08 g, 15 mmol) and L-tert-leucinol (3.52 g, 30
mmol): colorless oil (4.31 g, 73%), Rf value (1:1 diethyl ether/
Synthesis of [Me,Me-PheboxBr] (5a). Thionyl chloride (12 mL,
164 mmol) was added to 2-bromoisophthalic acid (9.8 g, 40.1
mmol). The mixture was refluxed overnight, and the residual SOCl2
was removed in Vacuo. Of the resulting 2-bromoisophthalic acid
chloride, 6.9 g (24.5 mmol) was weighed in a 500 mL one-necked
round-bottom flask, equipped with a nitrogen inlet, and dissolved
in CH2Cl2 (25 mL). The temperature was cooled to 0 °C. In a
separate Schlenk vessel, 2-amino-2-methylpropanol (5.07 g, 56.3
mmol) and triethylamine (14 mL, 100 mmol) were dissolved in
CH2Cl2 (35 mL) and slowly added to the cooled 2-bromoisophthalic
acid chloride solution. The reaction mixture was warmed to room
temperature overnight, after which the solvent was removed in
Vacuo. Acetonitrile (200 mL), PPh3 (23.7 g, 90.6 mmol), and
triethylamine (15 mL, 108 mmol) were added to the residue. The
temperature was reduced to 0 °C, after which CCl4 (21 mL, 215
mmol) was slowly added via syringe. The reaction mixture was
warmed to room temperature overnight, after which the mixture
was quenched with H2O (10 mL) and the volatiles were removed
in Vacuo. The residue was dissolved in H2O (200 mL) and ethyl
acetate (200 mL). After separation of the layers, the organic layer
was washed with H2O (100 mL). The combined aqueous layers
were extracted with ethyl acetate (3 × 100 mL). The combined
organic layers were dried on MgSO4 and filtered. After the solvent
was removed in Vacuo, the residue was stirred for 3 h in diethyl
ether (250 mL). The suspension was filtered, the residue was washed
with diethyl ether (200 mL), and the filtrate was concentrated in
Vacuo. The crude product was filtered over alumina (neutral Merck
20
ethyl acetate) 0.71, [R]D -60.2 (c 0.11 g/mL, EtOH). IR (neat,
cm-1): νmax 2954, 1663, 1362, 970. 1H NMR (300 MHz, CDCl3):
3
2
δ 0.96 (s, 18H, CMe3), 4.06 (dd, 2H, JH-H ) 10.1 Hz, JH-H
)
8.3 Hz, OCH2), 4.22 (t, 2H, 3JH-H ) 8.7 Hz, CHN), 4.37 (dd, 2H,
3JH-H ) 10.1 Hz, JH-H ) 8.9 Hz, OCH2), 7.33 (t, 1H, JH-H
)
2
3
7.7 Hz, ArH), 7.60 (d, 2H, JH-H ) 7.2 Hz, ArH). 13C{1H} NMR
(75 MHz, CDCl3): δ 26.1 (CMe3), 34.0 (CMe3), 69.2 (CHN), 76.7
(OCH2), 121.4 (ArC), 127.0 (ArC), 132.4 (ArC), 132.6 (ArC), 163.0
(CN). Anal. Calcd for C20H27BrN2O2: C, 58.97; H, 6.68; N, 6.88.
Found: C, 59.10; H, 6.74; N, 6.76.
3
Synthesis of 2,6-Bis[N-(2′,6′-dimethylphenyl)ketimino]phenyl
Bromide (6). 2,6-Diacetylphenyl bromide (3.6 g, 15 mmol), 2,6-
dimethylaniline (4.5 mL, 36 mmol), and Si(OEt)4 (8 mL, 36 mmol)
were combined in a Schlenk vessel equipped with a still head and
treated with 20 drops of H2SO4 (95%). The solution was heated at
160 °C for 24 h. The distillate (EtOH) was discarded. 2,6-
Dimethylaniline (1.2 mL, 5.4 mmol) and 10 drops of H2SO4 (95%)
were added, and the mixture was heated for another 24 h at 160
°C. Ethanol (80 mL) and KOHaq (10 mL, 2 M solution in H2O)
were added to the reaction mixture at room temperature and stirred
for 4 h. The resulting suspension was concentrated in Vacuo, diethyl
ether was added, and the slurry was filtered. The filtrate was washed
with brine and with water, dried on MgSO4, and filtered. The filtrate
was dried in Vacuo. The residue was submitted to a Kugelrohr
distillation at 160 °C for 30 min. The residue was purified by
column chromatography (silica, hexane/EtOAc, 4:1, Rf 0.33): white
solid (5.9 g, 78%). IR (neat, cm-1): νmax 1664, 1646, 1467, 1199,
793, 758. 1H NMR (300 MHz, C6D6): δ 1.84 (s, 6H, NCMe), 2.28
(34) McKennon, M. J.; Meyers, A. I. J. Org. Chem. 1993, 58, 3568.
(35) Basis sets were obtained from the Extensible Computational
Chemistry Environment Basis Set Database, Version 02/25/04, as developed
and distributed by the Molecular Science Computing Facility, Environmental
and Molecular Sciences Laboratory, which is part of the Pacific Northwest
Laboratory, P.O. Box 999, Richland, WA 99352, and funded by the U.S.
Department of Energy. The Pacific Northwest Laboratory is a multiprogram
laboratory operated by Battelle Memorial Institute for the U.S. Department
of Energy under contract DE-AC06-76RLO 1830. Contact David Feller or
Karen Schuchardt for further information. Dunning, T. H., Jr.; Hay, P. J.
Methods of Electronic Structure Theory, 2nd ed.; Schaefer, H. F., III, Ed.;
Plenum Press: New York, 1977. Hay, P. J.; Wadt, W. R. J. Chem. Phys.
1985, 82, 284. Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(36) Guest, M. F.; Bush, L. J.; van Dam, H. J.; Sherwood, P.; Thomas,
M. J. H.; van Lenthe, J.; Haventih, R. W. A.; Kendrick, J. J. Mol. Phys.
2005, 103, 719.
3
(s, 12H, ArMe), 7.08-7.11 (m, 3H, ArH), 7.13 (d, 4H, JH,H
)
15.3 Hz, ArH), 7.40 (d, 2H, 7.5 Hz, ArH). 13C{1H} NMR (75 MHz,
C6D6): δ 18.5 (ArMe), 21.4 (NCMe), 117.9 (ArC), 123.6 (ArC),
125.7 (ArC), 128.6 (ArC), 129.4 (ArC), 145.0 (ArC), 148.7 (ArC),
169.2 (NCMe). Anal. Calcd for C26H27BrN2: C, 69.80; H, 6.08;
N, 6.26. Found: C,69.74; H, 6.07; N, 6.24.
Synthesis of [NiBr(Me,Me-Phebox)] (2a) via Route A. n-BuLi
(1.2 mL, 1.92 mmol, 1.6 M solution in hexanes) was added to a
solution of 5a (0.60 g, 1.71 mmol) in toluene (30 mL) at -78 °C.
After stirring for 3.5 h, the deep purple solution was added cold to
a solution of [NiBr2(PEt3)2] (0.73 g, 1.61 mmol) in toluene (30
mL). After stirring for 16 h, the dark brown reaction mixture

2,6-Bis(oxazolinyl)phenylnickel(II) Bromide
Organometallics, Vol. 26, No. 16, 2007 3993
containing a light precipitate was centrifugated and the supernatant
was separated. The precipitate was extracted with toluene (20 mL).
The toluene layers were dried in Vacuo and washed with hex-
anes (2 × 20 mL), which yielded a bright orange solid (0.49 g,
74%). IR (neat, cm-1): νmax 2964, 1644, 1645, 1490, 1405, 1131,
981, 796, 783. 1H NMR (C6D6, 300 MHz): δ 1.49 (s, 12H, CMe2),
13C{1H} NMR (C6D6, 75 MHz): δ 13.8 (CHMe2), 18.6 (CHMe2),
29.5 (CHMe2), 66.1 (CHN), 72.4 (OCH2), 124.0 (ArC), 124.4
(ArC), 129.9 (ArC), 173.1 (ArC), 173.3 (OCN). Anal. Calcd for
C18H23BrN2NiO2: C, 49.36; H, 5.29; N, 6.40. Found: C, 49.38;
H, 5.36; N, 6.33.
Synthesis of (S,S)-[NiBr(t-Bu,H-Phebox)] (2c) via Route B.
An analogous procedure to the synthesis of 2a was employed with
5c (250 mg, 0.61 mmol) and [Ni(cod)2] (160 mg, 0.58 mmol):
yellow-orange powder (0.162 g, 60%). 1H NMR (C6D6, 300
MHz): δ 0.93 (s, 18H, CMe3), 3.58 (t, 2H, 3JH-H ) 7.8 Hz, CHN),
3.83 (d, 2H, 3JH-H ) 7.5 Hz, OCH2), 4.04 (d, 2H, 3JH-H ) 7.5 Hz,
3
3.59 (s, 4H, OCH2), 6.69 (t, 1H, JH-H ) 7.5 Hz, ArH), 6.98 (d,
3
2H, JH-H ) 7.2 Hz, ArH). 13C{1H} NMR (C6D6, 75 MHz): δ
28.2 (CMe2), 65.6 (CMe2), 84.4 (OCH2), 124.0 (ArC), 124.5 (ArC),
130.5 (ArC), 168.7 (ArC), 172.0 (OCN). Anal. Calcd for
C16H19BrN2NiO2: C, 46.88; H, 4.67; N, 6.83. Found: C, 47.03;
H, 4.73; N, 6.75.
3
3
OCH2), 6.63 (t, 1H, JH-H ) 7.1 Hz, ArH), 6.96 (d, 2H, JH-H
)
6.6 Hz, ArH). 13C{1H} NMR (C6D6, 75 MHz): δ 26.9 (CMe3),
35.6 (CMe3), 68.5 (CHN), 75.1 (OCH2), 124.1 (ArC), 124.2 (ArC),
130.1 (ArC), 170.6 (ArC), 173.9 (OCN). Anal. Calcd for
C20H27BrN2NiO2: C, 51.54; H, 5.84; N, 6.01. Found: C, 51.28;
H, 5.97; N, 5.84.
Synthesis of (S,S)-[NiBr(i-Pr,H-Phebox)] (2b) via Route A.
An analogous procedure to the synthesis of 2a was employed with
5b (0.60 g, 1.58 mmol), n-BuLi (1.1 mL, 1.76 mmol, 1.6 M in
hexane), and [NiBr2(PEt3)2] (0.68 g, 1.45 mmol): orange powder
(0.58 g, 91%). IR (neat, cm-1): νmax 2960, 1607, 1586, 1489, 1404,
1387, 1146, 953, 726. 1H NMR (C6D6, 200 MHz): δ 0.54 (d, 6H,
Synthesis of 2,6-Bis[N-2′,6′-dimethylphenyl)ketimino]phe-
nylnickel(II) Bromide (3) via Route B. A solution of 6 (171 mg,
0.38 mmol) in THF (10 mL) was added to a solution of [Ni(cod)2]
in THF (15 mL) at -60 °C. The reaction mixture was stirred for
3 days (at room temperature), after which it was centrifuged, the
supernatant removed, and the residue extracted with THF (25 mL).
The THF was removed in Vacuo. The residue was washed with
pentane (2 × 7 mL), yielding a bright orange solid, which was
characterized as pure 3 (128 mg, 72%). IR (neat, cm-1): νmax 2965,
3
3JH-H ) 7.0 Hz, CHMe2), 0.65 (d, 6H, JH-H ) 7.0 Hz, CHMe2),
3
3.23 (sp d, 2H, JH-H ) 7.2 Hz, 2.8 Hz, CHMe2), 3.63 (m, 2H,
3
NCH), 3.95 (m, 4H, OCH2), 6.63 (t, 1H, JH-H ) 7.0 Hz, ArH),
3
6.98 (d, 2H, JH-H ) 7.4 Hz, ArH). 13C{1H} NMR (C6D6, 75
MHz): δ 13.8 (CMe2), 18.6 (CMe2), 29.5 (CMe2), 66.1 (NCH),
72.4 (OCH2), 124.0 (ArC), 124.4 (ArC), 129.9 (ArC), 173.1 (ArC),
173.3 (OCN).
Synthesis of (S,S)-[NiBr(t-Bu,H-Phebox)(PEt3)2] (7c) via
Route A. n-BuLi (1.3 mL, 2.08 mmol, 1.6 M solution in hexanes)
was added to a solution of 5c (0.74 g, 1.82 mmol) in THF (25 mL)
at -78 °C. After stirring for 10 min, the deep red solution was
added dropwise to a solution of [NiBr2(PEt3)2] (0.83 g, 1.82 mmol)
in diethyl ether (30 mL) at -78 °C. The reaction mixture was
warmed to room temperature. After stirring for 16 h, the dark brown
reaction mixture was dried in Vacuo and dissolved in toluene (50
mL). After centrifugation, the supernatant was separated. The
precipitate was extracted with toluene (20 mL). The mixture was
dried in Vacuo and centrifugated after addition of pentane (50 mL).
The supernatant was separated and dried in Vacuo, which afforded
a brown oil (0.99 g, 77%). A small quantity was further puri-
fied by crystallization from pentane at -20 °C, which yielded
1
1576, 1534, 1465, 1333, 1261, 1092, 1017, 786, 766. H NMR
(300 MHz, C6D6): δ 1.32 (s, 6H, NCMe), 2.27 (s, 12H, ArMe),
6.82 (m, 3H, ArH), 6.92 (m, 6H, ArH). 13C{1H} NMR (75 MHz,
C6D6): δ 15.9 (NCMe), 19.33 (ArMe), 123.0 (ArC), 125.7 (ArC),
126.5 (ArC), 128.2 (ArC), 128.4 (ArC), 130.5 (ArC), 145.5 (ArC),
147.3 (ArC), 180.3 (ArC), 185.3 (NCMe). Anal. Calcd for
C26H27BrN2Ni: C, 61.70; H, 5.38; N, 5.54. Found: C, 61.61; H,
5.33; N, 5.42.
Typical Polymerization Experiment. Ethyl-2-bromoisobutyrate
(11.5 µL, 0.078 mmol) was added to a mixture of 2a (32 mg, 0.077
mmol) and degassed MMA (2.0 mL, 19 mmol) in toluene (7.5 mL)
at 90 °C. The mixture was stirred for 16 h and then analyzed by
1H NMR spectroscopy. No color change was observed (orange).
Polymerization: 0%.
1
the product as a dark red powder. H NMR (C6D6, 300 MHz): δ
Kharasch Addition. CCl4 (10 mL, 104 mmol) was added to a
mixture of 2a (32 mg, 0.077 mmol) and degassed methyl meth-
acrylate (3.0 mL, 28 mmol) in CH2Cl2 (10 mL) at room temperature.
0.91 (m, 18H, P(CH2CH3)3), 1.01 (s, 18H, CMe3), 1.55 (m, 12H,
3
P(CH2CH3)3), 4.17 (m, 4H, OCH2), 4.45 (t, 2H, JH-H ) 9.2 Hz,
3
3
CHN), 6.77 (t, 1H, JH-H ) 7.7 Hz, ArH), 8.18 (d, 2H, JH-H
)
1
The mixture was stirred for 16 h and then analyzed by H NMR
7.5 Hz, ArH). 13C{1H} NMR (C6D6, 75 MHz): δ 8.4 (P(CH2CH3)3),
16.1 (t, 1JC-P ) 11.3 Hz, P(CH2CH3)3), 26.4 (CMe3), 34.2 (CMe3),
68.9 (CHN), 76.4 (OCH2), 122.0 (ArC), 132.1 (ArC), 137.0 (ArC),
162.8 (ArC), 166.8 (CN). 31P{1H} NMR (C6D6, 81 MHz): δ 1.4.
Anal. Calcd for C32H57BrN2NiO2P2: C, 54.72; H, 8.18; N, 3.99.
Found: C, 54.63; H, 8.07; N, 4.06.
spectroscopy. No change of color was observed (orange). Conver-
sion: 0%.
Cyclic Voltammetry. Cyclic voltammetry measurements were
performed with an Autolab PGSTAT 10 cyclic voltammeter, using
a Pt working electrode and a Ag/AgCl reference electrode in acetone
with tetrabutylammonium bromide (0.1 M) as supporting electrolyte,
at scan rates ranging from 0.025 to 1 V/s. Under these conditions
the ferrocene/ferrocenium (Fc/Fc+) couple was located at +0.44
V with a peak separation of 80 mV.
X-ray Crystal Structure Determination of (S,S)-[NiBr(i-Pr,H-
Phebox)] (2b). C18H23BrN2NiO2, fw ) 438.00, yellow plate, 0.18
× 0.12 × 0.03 mm3, monoclinic, P21 (no. 4), a ) 6.2846(7) Å, b
) 12.0673(5) Å, c ) 12.0639(13) Å, â ) 100.695(8)°, V ) 899.01-
(14) Å3, Z ) 2, F ) 1.618 g/cm3; 36 365 reflections up to a
resolution of (sin θ/λ)max ) 0.51 Å-1 were measured on a Nonius
KappaCCD diffractometer with rotating anode and graphite mono-
chromator (λ ) 0.71073 Å) at a temperature of 150(2) K. The
crystal appeared to be nonmerohedrally twinned with a 2-fold
rotation about hkl (102h) as twin operation. This direction is
approximately parallel to the Ni-Br bond. The intensity data were
evaluated with EvalCCD,37 taking the twin relation into account.
Synthesis of [NiBr(Me,Me-Phebox)] (2a) via Route B. To a
stirred suspension of Ni(cod)2 (258 mg, 0.94 mmol) in THF (30
mL) at -78 °C was added [Me,Me-PheboxBr] (5a) (363 mg, 1.0
mmol) in THF (10 mL). The mixture was warmed to room
temperature overnight. The mixture was centrifuged and separated.
The supernatant was dried in Vacuo and washed with pentane. The
1
solid orange residue was characterized by H NMR spectroscopy
as pure 2a (318 mg, 83%). 1H NMR (C6D6, 300 MHz): δ 1.49 (s,
3
12H, CMe2), 3.59 (s, 4H, OCH2), 6.69 (t, 1H, JH-H ) 7.5 Hz,
3
ArH), 6.98 (d, 2H, JH-H ) 7.2 Hz, ArH).
Synthesis of (S,S)-[NiBr(i-Pr,H-Phebox)] (2b) via Route B.
An analogous procedure to the synthesis of 2a was employed with
5b (623 mg, 1.64 mmol) and [Ni(cod)2] (432 mg, 1.57 mmol):
yellow-orange powder (697 mg, quant.). 1H NMR (C6D6, 300
MHz): δ 0.54 (d, 6H, 3JH-H ) 7.2 Hz, CHMe2), 0.65 (d, 6H, 3JH-H
3
) 7.2 Hz, CHMe2), 3.22 (septet d, 2H, JH-H ) 7.0 Hz, 2.7 Hz,
CHMe2), 3.64 (m, 2H, CHN), 3.95 (m, 4H, OCH2), 6.63 (t,
(37) Duisenberg, A. J. M.; Kroon-Batenburg, L. M. J.; Schreurs, A. M.
M. J. Appl. Crystallogr. 2003, 36, 220.
3
3
1H, JH-H ) 7.0 Hz, ArH), 6.98 (d, 2H, JH-H ) 7.2 Hz, ArH).

3994 Organometallics, Vol. 26, No. 16, 2007
Stol et al.
An analytical absorption correction was applied (µ ) 3.314 mm-1
,
reflection positions), T ) 220(2) K, λ ) 0.71073 Å, Z ) 4, D(calcd)
) 1.856 Mg/m3, F(000) ) 812, µ(Mo KR) ) 6.751 mm-1. Crystal
character: dark block. Crystal dimensions: 0.50 × 0.28 × 0.12
mm. Data collection and processing: Siemens SMART43 three-
circle system with CCD area detector. The crystal was held at 220-
(2) K with the Oxford Cryosystem cryostream cooler.44 Maximum
theta was 28.88°. The hkl ranges were -18/12, -10/10, -16/19;
8704 reflections measured, 3539 unique [Rint ) 0.0325]. Semiem-
pirical absorption correction from equivalents; maximum and
minimum correction factors: 0.54; 0.89. No crystal decay. Structure
analysis and refinement: Systematic absences indicated P21/c and
were shown to be correct by successful refinement. The structure
was solved by direct methods using SHELXS-9745 (TREF) with
additional light atoms found by Fourier methods. Hydrogen atoms
were added at calculated positions and refined using a riding model
with freely rotating methyl groups. Anisotropic displacement
parameters were used for all non-H atoms; H atoms were given
isotropic displacement parameters equal to 1.2 (or 1.5 for methyl
hydrogen atoms) times the equivalent isotropic displacement
parameter of the atom to which the H atom is attached. The
0.55-0.89 correction range), and the reflections were merged
according to the twin law, resulting in 7979 unique reflections (Rint
) 0.0637). The structure was solved with automated Patterson
methods (DIRDIFF-9938) based on the nonoverlapping reflections
of the first twin domain. The structure was then refined as a HKLF-
539 twin with SHELXL-9740 on F2 of all reflections, resulting in a
twin fraction of 0.5141(4); 222 parameters were refined with one
restraint for the origin shift in the polar space group. R1/wR2 [I >
2σ(I)]: 0.0328/0.0611. R1/wR2 [all reflns]: 0.0492/0.0656. S )
1.022. Flack x parameter:41 -0.008(6). Residual electron density
was between -0.36 and 0.64 e/Å3. Structure calculations, drawings,
and checking for higher symmetry were performed with the
PLATON42 package.
X-ray Crystal Structure Determination of [NiBr(bis(ketimi-
ne)phenyl)] (3). C26H27BrN2Ni, fw ) 506.12, red needle, 0.42 ×
0.09 × 0.09 mm3, monoclinic, P21/c (no. 14), a ) 11.7638(1) Å,
b ) 10.9956(1) Å, c ) 18.2973(1) Å, â ) 101.7010(3)°, V )
2317.57(3) Å3, Z ) 4, F ) 1.451 g/cm3; 55626 reflections up to a
resolution of (sin θ/λ)max ) 0.65 Å-1 were measured on a Nonius
KappaCCD diffractometer with rotating anode and graphite mono-
chromator (λ ) 0.71073 Å) at a temperature of 150(2) K. An
absorption correction based on multiple measured reflections was
applied (µ ) 2.576 mm-1, 0.58-0.79 correction range); 5318
reflections were unique (Rint ) 0.0468). The structure was solved
with automated Patterson methods (DIRDIF-9938) and refined with
SHELXL-9740 on F2 of all reflections. Non-hydrogen atoms were
refined freely with anisotropic displacement parameters. All
hydrogen atoms were located in the difference Fourier map and
refined as rigid groups; 277 parameters were refined without
restraints. R1/wR2 [I > 2σ(I)]: 0.0321/0.0736. R1/wR2 [all reflns]:
0.0461/0.0793. S ) 1.036. Residual electron density was between
-0.91 and 0.80 e/Å3. Structure calculations, drawings, and checking
for higher symmetry were performed with the PLATON42 package.
X-ray Crystal Structure Determination of [NiBr2(NCN)] (8).
C12H19Br2N2Ni, fw ) 409.82, monoclinic, space group P21/c, a )
13.7870(16) Å, b ) 7.6995(9) Å, c ) 14.7377(17) Å, â ) 110.337-
(3)°, V ) 1466.9(3) Å3 (by least-squares refinement on 6099
2
weighting scheme was w ) 1/[σ2(Fo ) + (0.0339P)2] where P )
2
(Fo + 2Fc2)/3. Goodness-of-fit on F2 was 0.927, R1[for 2681
reflections with I >2σ(I)] ) 0.0322, wR2 ) 0.0711. Data/restraints/
parameters: 3539/0/159. Extinction coefficient: 0.0004(2). Largest
difference Fourier peak and hole: 0.65 and -0.50 e/Å3. Refinement
used SHELXTL.46
Acknowledgment. We thank Prof. Dr. B. Hessen and Dr.
P. Chase for their suggestions and stimulating discussions. Prof.
Dr. J. Reedijk and Dr. E. Bouwman are acknowledged for their
hospitality at Leiden University. R.W.A.H. acknowledges
financial support from the Netherlands Organization for Sci-
entific Research (NWO), grant 700.53.401, and NWO/NCF for
use of supercomputer time on TERAS/ASTER, SARA (The
Netherlands, project number SG-032). G.C. thanks EPSRC and
Siemens Analytical Instruments for grants in support of the
diffractometer.
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