Trans-bis[1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene] dichlorinickel(II): Synthesis and structure

Article abstract of DOI:10.1135/cccc20070609

trans-Bis[1,3-bis(2,4/6-trimethylphenyl)imidazolidin-2-ylidene] dichloronickel(II), [NiCl₂(SIMes)₂], was synthesized in a one-pot reaction of fluorenyllithium with nickel(II) bromide followed by the addition of 1,3-bis(2,4,6-trimethylphenyl)imidazolidinium chloride. Labile difluorenyl-nickel, formed in the course of the reaction, behaves differently than nlckelocene and indenocene in analogous reactions. It exchanges both fluorenyl ligands giving the title compound. The crystal and molecular structure of this compound have been determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic crystal system with square-planar geometry around the central nickel atom.

Full text of DOI:10.1135/cccc20070609

trans-Bis[1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichloronickel(II)
609
tra n s-BIS[1,3-BIS(2,4,6-TRIMETHYLPHENYL)IMIDAZOLIDIN-
2-YLIDENE]DICHLORONICKEL(II): SYNTHESIS AND STRUCTURE
Andrzej KOZIOŁa1, Stanisław PASYNKIEWICZa2, Antoni PIETRZYKOWSKIa3,* and
b
Lucjan B. JERZYKIEWICZ
a
Faculty of Chemistry, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw,
1
2
3
Poland; e-mail: andrzej.koziol@interia.pl, pasyn@ch.pw.edu.pl, anpietr@ch.pw.edu.pl
Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-353 Wrocław, Poland;
e-mail: jerzyk@wchuwr.chem.uni.wroc.pl
b
Received March 7, 2007
Accepted April 18, 2007
Dedicated to Dr Karel Mach on the occasion of his 70th birthday in recognition of his outstanding
contributions to organometallic chemistry and homogeneous catalysis.
trans-Bis[1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin -2-yliden e]dich loron ickel(II), [NiCl2(SIMes)2],
was syn th esized in a on e-pot reaction of fluoren yllith ium with n ickel(II) brom ide followed
by th e addition of 1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin ium ch loride. Labile difluoren yl-
n ickel, form ed in th e course of th e reaction , beh aves differen tly th an n ickelocen e an d
in den ocen e in an alogous reaction s. It exch an ges both fluoren yl ligan ds givin g th e title com -
poun d. Th e crystal an d m olecular structure of th is com poun d h ave been determ in ed by
sin gle-crystal X-ray diffraction . Th e com poun d crystallizes in th e m on oclin ic crystal system
with square-plan ar geom etry aroun d th e cen tral n ickel atom .
Keyw ord s: Nickel; N-h eterocyclic carben es; Carben e com plexes; Im idazolium salts; Fluoren e;
Crystal structure determ in ation ; X-ray diffraction .
Alth ough m etal carben e com plexes h ave been kn own for over 40 years, an
in terest in th em h as rapidly grown wh en Arduen go et al.1 prepared a stable
crystallin e carben e. N-h eterocyclic carben es (NHC) h ave foun d m an y appli-
cation s as ligan ds in th e fields of organ om etallic ch em istry an d catalysis
(for recen t reviews, see refs2–5). Several papers dealin g with stable Ni(0) an d
Ni(II) com plexes with N-h eterocyclic carben es h ave been publish ed re-
cen tly6–11. Bis(carben e)n ickel com plexes of Ni(0) as well as of Ni(II) h ave
been also prepared. Th e first such com plex of Ni(0) was obtain ed by
Arduen go et al.12 in th e reaction of an NHC with [Ni(cod)2]. Th e first
bis(carben e) com plex of Ni(II) was syn th esized by Herrm an n et al.13 in th e
reaction of an NHC with [NiX2L2] (X = Cl, Br; L = PPh 3) in THF solution .
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 609–617
© 2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20070609

610
Kozioł, Pasynkiewicz, Pietrzykowski, Jerzykiewicz:
Th ey determ in ed also th e crystal an d m olecular structure of th is com plex.
Baird et al.14 used Herrm an n ’s m eth od to prepare bis(carben e) com plex
[NiCl2(IPr)2] (IPr = 1,3-bis(2,6-diisopropylph en yl)im idazolidin -2-yliden e).
Syn th eses of several oth er n ickel com plexes bearin g two or th ree N-h etero-
cyclic carben e ligan ds h ave also been reported15–26. Th e m ost com m on
m eth od of preparation of bis(carben e)n ickel(II) com plexes is th e replace-
m en t of weaker don or ligan ds in [NiX2L2] com plexes (X = Cl, Br; L = PPh 3,
th f, cod, etc.) by a stable N-h eterocyclic carben e13. Herrm an n et al.13 de-
m on strated also preparation of bis(1,3-dim eth ylim idazolidin -2-yliden e)-
diiodon ickel(II) in th e reaction of n ickel(II) acetate with 1,3-dim eth yl-
im idazolium iodide. Th e deproton ation of th e im idazolium salt requires
quite drastic con dition s (150 °C, vacuum , n o solven t).
In th is paper we presen t a con ven ien t m eth od of preparation of
bis[1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin -2-yliden e]dich loron ickel(II)
in th e reaction of difluoren yln ickel with 1,3-bis(2,4,6-trim eth ylph en yl)-
im idazolidin ium ch loride. Th e reaction proceeds at room tem perature an d
sh ows th e un expected beh avior of difluoren yln ickel(II).
EXPERIMENTAL
Tech n iques an d Materials
All m an ipulation s were carried out un der an atm osph ere of purified argon usin g stan dard
Sch len k tech n iques. Solven ts were dried an d distilled un der argon em ployin g stan dard dry-
in g agen ts. Fluoren e (Aldrich ) was recrystallized from h exan e, butyllith ium as 2.5 M solution
in h exan e was purch ased from Aldrich . 1,3-Bis(2,4,6-trim eth ylph en yl)im idazolidin ium ch lo-
ride, [SIMesH]+Cl–, was prepared accordin g to th e literature m eth od27 1H NMR (400 MHz)
.
an d 13C NMR (100 MHz) spectra (δ, ppm ; J, Hz) were recorded on a Mercury-400BB spec-
trom eter in C6D6 or THF-d8 at am bien t tem perature. Mass spectra (EI, 70 eV) were m easured
on an AMD-604 m ass spectrom eter.
Syn th esis of Fluoren yllith ium [LiFlu]
A solution of butyllith ium in h exan e (2.7 cm 3, 6.8 m m ol) was added at on ce to a solution
of fluoren e (1.13 g, 6.8 m m ol) in 40 cm 3 of h exan e at room tem perature. Th e m ixture was
stirred for th ree days. Th e yellow solid was filtered off, wash ed four tim es with 30 cm 3 of
h exan e an d dried un der reduced pressure. Yield 1.12 g (6.4 m m ol, 96%). 1H NMR (THF-d8,
3
3
3
25 °C): 7.79 (d, 2 H, JHH = 7.6, H-4,5); 7.18 (d, 2 H, JHH = 7.6, H-1,8); 6.67 (t, 2 H, JHH
=
3
6.8, H-2,7); 6.29 (t, 2 H, JHH = 6.8, H-3,6); 5.81 (s, 1 H, H-9).
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trans-Bis[1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichloronickel(II)
611
Syn th esis of trans-Bis[1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin -2-yliden e]-
dich loron ickel(II) (1)
A solution of LiFlu in THF (1.2 cm 3, 1.22 m m ol) was added at on ce to a suspen sion of
[NiBr2(dm e)2] (0.188 g, 0.61 m m ol) in THF at –78 °C. Th e reaction m ixture was slowly
h eated to room tem perature. Th e resultin g brown solution was stirred for 30 m in an d th en
1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin ium ch loride [SIMesH]+Cl– (0.21 g, 0.61 m m ol)
was added in on e portion . Th e oran ge reaction m ixture was stirred for an oth er 24 h . Th e
solven t was rem oved un der reduced pressure. Th e crude product was extracted with toluen e
(3 × 20 cm 3). Th e extract was con cen trated an d left stan din g for crystallization at 0 °C, af-
fordin g 0.27 g (0.366 m m ol, 60%) of 1. 1H NMR (C6D6, 25 °C): 6.96 (s, 8 H, arom . H); 2.86
(s, 8 H, NCH2); 2.43 (s, 12 H, p-CH3); 2.26 (s, 24 H, o-CH3). 13C NMR: 19.48, o-CH; 21.3,
p-CH3; 50.39, NCH2; 129.76, C-3,5; 136.15, C-2,6; 137.09, C-4; 137.53, C-1; 200.12, NCN.
EI-MS, m/z (rel.%) (58Ni): 740 (M+, 8), 341 ([Cl(NHC) – H]+, 91), 305 ([NHC]+, 22), 277
([C19H21N2]+, 1), 158 ([C10H10N2]+, 2), 146 ([C9H10N2]+, 5), 119 ([C9H11]+, 1), 91 ([C7H7]+, 1).
HRMS: calculated for C42H5235Cl2N458Ni: 740.29225; foun d: 740.29125. Crystals suitable for
X-ray diffraction m easurem en ts were grown from a toluen e solution at 0 °C.
Reaction of [Ni(Flu)2] with PPh 3 an d CCl4
Solution of LiFlu in THF (2 cm 3, 0.35 m m ol) was added at on ce to th e suspen sion of [NiBr2-
(dm e)2] (0.055 g, 0.178 m m ol) in 4 cm 3 THF at room tem perature. To a brown solution
form ed, triph en ylph osph in e (0.046 g, 0.178 m m ol) an d CCl4 (0.1 cm 3, 0.16 g, 1.04 m m ol)
were added after 5 m in . Th e reaction h as been carried out for 1 h an d th en th e solven t was
rem oved un der reduced pressure. Th e solid was wash ed with h exan e (3 × 20 cm 3) an d th en
extracted with toluen e. 0.07 g of [NiCl2(PPh 3)2] (5.6 m m ol, 53%) was obtain ed. M.p. 245–
246 °C (dec.); lit.28 gives 247–250 °C (dec.). Broad sign als appeared in 1H NMR spectrum
owin g to param agn etism of th e com poun d. Th e spectrum is in good agreem en t with th e lit-
erature data29 1H NMR (C6D6, 25 °C): 18.36 (broad s, 2 H, H-2,6); –0.88 (broad s, 2 H, H-3,5);
.
–6.12 (broad s, 1 H, H-4).
Crystal Structure Determ in ation of 1
Crystal data, data collection an d refin em en t param eters for trans-[NiCl2(SIMes)2] (1) are
given in Table I. Th e m olecular structure of th is com poun d is presen ted in Fig. 1. Selected
bon d len gth s an d an gles are sh own in th e figure.
CCDC 639131 (1) con tain s th e supplem en tary crystallograph ic data for th is paper. Th ese
data can be obtain ed free of ch arge via www.ccdc.cam .ac.uk/con ts/retrievin g.h tm l (or from
th e Cam bridge Crystallograph ic Data Cen tre, 12, Un ion Road, Cam bridge, CB2 1EZ, UK;
fax: +44 1223 336033; or deposit@ccdc.cam .ac.uk).
Th e crystal was m oun ted on to a glass fiber an d th en flash -frozen to 100 K (Oxford
Cryosystem –Cryostream Cooler). Prelim in ary exam in ation an d in ten sity data collection were
carried out on a Kum a KM4CCD κ-axis diffractom eter with graph ite-m on och rom atized
MoKα radiation . Th e data were corrected for Loren tz, polarization an d absorption effects.
Data reduction an d an alysis were carried out with th e Kum a diffraction (Wrocław, Poland)
program s30. Th e structures were solved by direct m eth ods an d refin ed by th e full-m atrix
least-squares m eth od on all F2 data usin g th e SHELXTL program 31. Th e carbon -bon ded
h ydrogen atom s were in cluded in th e calculated position s an d refin ed usin g a ridin g m odel.
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 609–617

612
Kozioł, Pasynkiewicz, Pietrzykowski, Jerzykiewicz:
TABLE I
Crystal data an d structure refin em en t for trans-[NiCl2(SIMes)2] (1)
Em pirical form ula
C42H52Cl2N4Ni C6H5CH3
0.23 × 0.10 × 0.04
m on oclin ic
Crystal size, m m
Crystal system
Space group
P21/n (No. 14)
Un it cell dim en sion s:
a, Å
10.612(5)
b, Å
16.201(5)
c, Å
26.710(5)
β, °
99.30(1)
V, Å3
4532(3)
Z
4
M, g m ol–1
834.62
D
calc, g cm –3
1.223
Tem perature, K
Absorption coefficien t, m m –1
F(000)
100(2)
0.583
1776
Radiation
MoKα (λ = 0.71073 Å, graph ite m on och rom ator)
θ ran ge, °
2.64–25.00
Scan type
ω
Absorption correction :
T
m in , Tm ax
0.851, 0.953
In dex ran ges
–7 ≤ h ≤ 12; –19 ≤ k ≤ 19; –31 ≤ l ≤ 31
26279
Reflection s collected
Un ique data
7971, Rin t = 0.0660
full-m atrix least-squares on F2
4524/0/518
Refin em en t m eth od
Data/restrain ts/param eters
GOFa on F2
0.811
Fin al R in dices [I > 2σ(I)]b
R1 = 0.0397
wR2 = 0.0701
R in dices (all data)
R1 = 0.0844
wR2 = 0.0747
Largest diff. peak an d h ole, e Å–3
Weigh tin g sch em e
0.354/–0.279
w = 1/[σ2(Fo2) + (0.0325P)2],
wh ere P = [2Fc + m ax(Fo2,0)]/3
2
GOF = S = {∑[w(Fo – Fc2)2]/(n – p)}1/ 2
.
b R1 = ∑||Fo| – |Fc||/∑|Fo|, wR2 = {∑[w(Fo
–
a
2
2
Fc2)2]/∑[w(Fo2)2]}
.
1/2
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trans-Bis[1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichloronickel(II)
613
FIG. 1
ORTEP drawin g of th e m olecular structure of trans-[NiCl2(SIMes)2] (1) with th e atom n um ber-
in g sch em e. Hydrogen atom s an d toluen e m olecule h ave been om itted for clarity. Th erm al el-
lipsoids are drawn at th e 50% probability level. Selected bon d len gth s (in Å) an d an gles (in °):
Ni1–Cl1 2.180(1), Ni1–Cl2 2.191(1), Ni1–C11 1.910(3), Ni1–C41 1.920(3), N1–C11 1.348(3),
N1–C12 1.486(3), N1–C23 1.440(3), N2–C11 1.348(3), N2–C13 1.478(3), N2–C14 1.437(3),
N3–C41 1.343(3), N3–C42 1.484(3), N3–C53 1.442(3), N4–C41 1.357(3), N4–C43 1.484(3),
N4–C44 1.436(3), C12–C13 1.515(3), C42–C43 1.525(3); C11–Ni1–C41 179.13(11),
Cl1–Ni1–Cl2 177.21(3), C11–Ni1–Cl1 88.42(8), C41–Ni1–Cl1 91.04(8), C11–Ni1–Cl2 90.50(8),
C41–Ni1–Cl2 90.06(8), N1–C11–Ni1 126.82(18), N2–C11–Ni1 126.18(19), N3–C41–Ni1
127.70(19), N4–C41–Ni1 125.11(19), C11–N1–C23 125.8(2), C11–N2–C14 128.3(2),
C11–N1–C12 112.8(2), C11–N2–C13 112.9(2), C41–N3–C53 127.4(2), C41–N4–C44 125.6(2),
C41–N3–C42 113.3(2), C41–N4–C43 112.8(2), N2–C11–N1 107.0(2), N3–C41–N4 107.2(2)
RESULTS AND DISCUSSION
1,2-Dim eth oxyeth an e com plex of n ickel(II) brom ide, [NiBr2(dm e)2], reacts
with fluoren yllith ium in THF form in g labile [Ni(Flu)2]. A on e-pot reaction
of [Ni(Flu)2] with 1,3-bis(2,4,6-trim eth ylph en yl)im idazolidin ium ch loride
at room tem perature affords dark oran ge crystals of 1 in 60% yield (Eq. (1)).
(1)
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 609–617

614
Kozioł, Pasynkiewicz, Pietrzykowski, Jerzykiewicz:
Th e m olecular structure of difluoren yln ickel(II) h as n ot been determ in ed
so far, but our curren t studies in dicate th at th e two fluoren yl ligan ds are
bon ded η5-Flu an d η1-Flu, form in g 16VE com plex [(η5-Flu)Ni(η1-Flu)] (Fig. 2).
We presum e th at lability of difluoren yln ickel is caused by h igh stability of
fluoren yl an ion or radical.
FIG. 2
Presum ed bon din g m ode in difluoren yln ickel(II)
Th e proposed course of th e reaction is depicted in Sch em e 1. An attack of
th e ch loride an ion on th e n ickel atom of difluoren yln ickel(II) leads to th e
form ation of a Ni–Cl bon d with sim ultan eous dissociation of th e fluoren yl
an ion . Th is an ion reacts with im idazolidin ium cation to form fluoren e an d
th e stable carben e. Th e carben e form s a com plex with fluoren yln ickel ch lo-
ride. A rearran gem en t of th e fluoren yl ligan d η5-fluoren yl → η1-fluoren yl is
followed by th e reaction with th e secon d m olecule of 1,3-bis(2,4,6-tri-
m eth ylph en yl)im idazolidin ium ch loride leadin g to th e form ation of 1 an d
fluoren e.
In con trary to difluoren yln ickel(II), n ickelocen e an d n ickel in den ocen e
react differen tly with im idazolium salt. Th e reaction stops after substitution
of on e cyclopen tadien yl or in den yl group32 (Eq. (2)) form in g com plex 2.
(2)
Th e secon d cyclopen tadien yl or in den yl groups are n ot substituted owin g
to h igh stability of th eir η5 bon ds with n ickel atom ; th erefore η5 → η1 rear-
ran gem en t, sh own in Sch em e 1, is n ot possible, wh ich preven ts furth er re-
action s.
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trans-Bis[1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichloronickel(II)
615
SCHEME 1
Th e sam e differen ces in beh avior of fluoren yl an d cyclopen tadien yl lig-
an ds were observed in th e reaction s of difluoren yln ickel(II) an d n ickelocen e
with CCl4 an d triph en ylph osph in e. In th e case of difluoren yln ickel(II),
both th e fluoren yl ligan ds are substituted an d th e kn own com plex [NiCl2-
(PPh 3)2] is form ed (Eq. (3)).
(3)
Nickelocen e, on th e oth er h an d, exch an ges on ly on e cyclopen tadien yl
ligan d form in g [NiCl(η5-Cp)(PPh 3)] 33
.
Collect. Czech. Chem. Commun. 2007, Vol. 72, Nos. 5–6, pp. 609–617

616
Kozioł, Pasynkiewicz, Pietrzykowski, Jerzykiewicz:
Crystals of 1 suitable for X-ray diffraction structure determ in ation were
obtain ed by slow crystallization from a toluen e solution at 0 °C. On e m ole-
cule of toluen e per on e m olecule of 1 was in cluded in th e crystal an d it was
successfully refin ed. Th e com poun d crystallizes in th e m on oclin ic crystal
system with square-plan ar coordin ation sph ere of th e cen tral n ickel atom .
Th e carben e ligan ds are situated tran s to each oth er an d at an gles close to
90° to th e ch loride ligan ds wh ich is a com m on feature of bis(im idazolin -
2-ylidene)m etal com plexes13,14,24. Carbene–nickel bond lengths in 1 (1.910(3)
an d 1.920(3) Å) are very close to th ose exh ibited by trans-[NiCl2(1,3-di-
cycloh exylim idazolidin -2-yliden e)2] 13 an d by trans-[NiCl2(1,3-bis(2,6-diiso-
propylph en yl)im idazolidin -2-yliden e)2] 14,24. On th e oth er h an d, carben e–
n ickel distan ces in 1 are about 0.05 Å lon ger th an th ose exh ibited by oth er
n ickel(II) com plexes with im idazolidin -2-yliden es, reported by Sellm an n et
al.34,35. Th ese observation s in dicate th at C–C saturation h as n ot a substan -
tial in fluen ce on carben e σ don or abilities. Sh orter Ni–C distan ces reported
in refs34,35 can probably be explain ed by th e ch elatin g ch aracter of th e
carben e ligan ds used. Th e carben e rin gs in 1 are twisted again st th e square-
plan ar coordin ation sph ere by 70.1(1) an d 66.7(1)°. Th ese values are lower
by about 7° th an reported in refs13,14, wh ich is probably due to steric re-
quirem en ts of bulky substituen ts on n itrogen atom s.
The authors thank the Ministry of Education and Science, Poland, for financial support of this work
(grant No. PBZ-KBN-118/T09/03).
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