Chromium(III) bis(diketiminate) complexes

Article abstract of DOI:10.1021/om100144y

Reaction of two equivalents of the lithium salt of N,N--dibenzyl-2-amino-4- iminopent-2-ene, nacnac^BnLi(THF), 1, with CrCl₃(THF) ₃ or CrCl₃ yielded nacnac^Bn₂CrCl as a putative intermediate, which could be trapped by addition of 2,6-xylyl isocyanide to give the isocyanide-coordinated, octahedral complex nacnac ^Bn₂CrCl(CNC₆Me₂H₃), 5. In the absence of isocyanide, ligand redistribution to the homoleptic tris(diketiminate) complex nacnac^Bn₃Cr, 3, occurred upon concentration, standing, or workup with apolar solvents. Workup with diethyl ether afforded the bimetallic-bridged complex nacnac^Bn ₂Cr(μ-Cl)₂Li(THF)₂, 6. Reaction of CrCl ₃(THF)₃ with one equivalent of 1 afforded the monodiketiminate complexes {nacnac^BnCrCl(THF)(μ-Cl)}₂ or {nacnac^BnCrCl(μ-Cl)}₂, depending on reaction conditions. Reaction of CrCl₂(THF)_x with two equivalents of 1 gave rise to nacnac^Bn₂Cr, 4. Complexes 3-6 were characterized by X-ray diffraction studies. All octahedral complexes display a cis geometry with two nacnac ligands in a distorted, boat-like conformation.

Full text of DOI:10.1021/om100144y

2180 Organometallics 2010, 29, 2180–2185
DOI: 10.1021/om100144y
Chromium(III) Bis(diketiminate) Complexes
Saıda Latreche and Frank Schaper*
ꢀ ꢀ ꢀ ꢀ ꢀ
Departement de Chimie, Universite de Montreal, Montreal, Quebec, H3C 3J7, Canada
Received February 24, 2010
Reaction of two equivalents of the lithium salt of N,N0-dibenzyl-2-amino-4-iminopent-2-ene, nacnacBnLi-
(THF), 1, with CrCl3(THF)3 or CrCl3 yielded nacnacBn2CrCl as a putative intermediate, which could be
trapped by addition of 2,6-xylyl isocyanide to give the isocyanide-coordinated, octahedral complex
nacnacBn2CrCl(CNC6Me2H3), 5. In the absence of isocyanide, ligand redistribution to the homoleptic
tris(diketiminate) complex nacnacBn3Cr, 3, occurred upon concentration, standing, or workup with apolar
solvents. Workup with diethyl ether afforded the bimetallic-bridged complex nacnacBn2Cr(μ-Cl)2Li(THF)2,
6. Reaction of CrCl3(THF)3 with one equivalent of 1 afforded the monodiketiminate complexes
{nacnacBnCrCl(THF)(μ-Cl)}2 or {nacnacBnCrCl(μ-Cl)}2, depending on reaction conditions. Reaction of
CrCl2(THF)x with two equivalents of 1 gave rise to nacnacBn2Cr, 4. Complexes 3-6 were characterized by
X-ray diffraction studies. All octahedral complexes display a cis geometry with two nacnac ligands in a
distorted, boat-like conformation.
Scheme 1
Introduction
Octahedral bis(diketiminate) complexes, nacnac2M(X/L)2,
seem to fulfill several requirements of a successful catalytic
system: a (reasonably) rigid ligand framework, a C2-symmetric
cis geometry, and an economical and easily modifiable specta-
tor ligand (nacnac).1 Recently, we have found that bis(dike-
timinate) zirconium complexes, nacnacR2ZrCl2, where R =
Coordination of more than one ligand to chromium is achieved
only if one N-Xyl or N-dipp group is replaced by less bulky
groups, such as oxygen (acnac) or pyrrolide.5-7 Alternatively,
nacnacdipp can be combined with a less encumbered ligand, such
as acetylacetonate (acac), to afford nacnacdipp(acac)CrCl.8 How-
ever, reduction of steric hindrance enables the planar coordina-
tion of both ligands, with the two ancillary ligands (or the
ancillary ligand and the open coordination site) trans to each
other.5,7-9 We have recently found that employing diketiminate
ligands with N-alkyl instead of N-aryl substituents allows the
coordination of two nacnac ligands in octahedral zirconium
complexes. Although the complexes undergo a Bailar-twist iso-
merization in solution, NMR spectroscopy showed that the trans
isomer was not accessible, even as a short-lived intermediate at
elevated temperatures.2 We present in the following our attempts
to prepare nacnacBn2CrCl(L) complexes (Bn = CH2Ph), which
shouldshowthesamepreferenceforcis geometries as observed in
the Zr complexes, but will hopefully enable easier exchange of the
chloride ligand.
CH2Ph, Cy, or S-CH(Me)Ph,2 do not undergo chloride ex-
change with reagents such as LiR, MeMgBr, AlR3, or NaOEt,
unless one diketiminate ligand is partially dissociated. We
speculated that moving from a Zr(IV) to a Cr(III) metal center
will relieve the need for the second ancillary anionic ligand and
that the open coordination site on the metal center will render
the chloride ligand more susceptible to exchange (Scheme 1).
Evidence for bis(diketiminate) chromium complexes in the lite-
rature is limited to Theopold’s work on nacnacPh2Cr and nac-
nacPh2CrX (X = Cl, Ph).3 The crystal structure of the latter
complex (X = Ph) displayed the targeted structure (Scheme 1): a
square-pyramidal complex with an empty coordination site in cis
position to the ancillary ligand. Possible modifications of the
ligand in nacnacPh2CrX are limited, however. Substitution of the
N-phenyl substituents in ortho position prevents the coordination
of two diketiminate ligands, and consequently, reactions of the
commonly used nacnacdipp or nacnacXyl ligands (dipp = 2,6-
diisopropylphenyl, Xyl = 2,6-dimethylphenyl), for example, with
CrCl3(THF)3 or CrCl2(THF)x yielded only the monosubstituted
complexes {nacnacCrCl(μ-Cl)}2 or {nacnacCr(THF)(μ-Cl)}2.4,5
Results and Discussion
Reaction of 2 equiv of nacnacBnLi(THF), 1, with CrCl3-
(THF)3 in toluene/THF (20:1) at room temperature afforded,
after removal of LiCl by filtration, a green solution. Evaporation
*Corresponding author. E-mail: Frank.Schaper@umontreal.ca.
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
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DOI: 10.1021/om900852y.
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(6) Collman, J. P.; Kittleman, E. T. Inorg. Chem. 2002, 1, 499.
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J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2002, 4017.
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(4) Charbonneau, F. M.Sc. thesis, Universite de Montreal, 2009.
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pubs.acs.org/Organometallics
Published on Web 03/30/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 9, 2010 2181
Scheme 2
and extraction with hexane yielded a hexane-insoluble, apple-
green residue, 2a (vide infra). From the hexane solution olive-
green crystals were obtained. X-ray diffraction analysis identi-
fied the latter to be not the expected product nacnacBn2CrCl-
(THF)0-1, but the homoleptic complex nacnacBn3Cr 2THF, 3a
3
(Scheme 2). Complex 3a was also prepared independently from
3 equiv of 1 and CrCl3(THF)3 in 90% yield. Under modified
reaction conditions (co-evaporation with toluene), crystals of 3
incorporated co-crystallized toluene to give nacnacBn3Cr C7H8,
3
3b. Despite the multitude of trisacetylacetonate metal complexes,
only selected examples of homoleptic tris(diketiminate) com-
plexes are known. Thus, preparation of tris(nacnacAr)Ln has
been reported for several lanthanides, where increased M-N
bond lengths allow the coordination of three diketiminate
ligands.10 With aliphatic substituents on nitrogen, synthesis of
nacnacEt3M (M = Al, Ti, and Cr) has been reported in the
patent literature, although the compounds were not characte-
rized,11 while Kuhn et al. isolated nacnacMe3Al.12
The crystal structures of 3a and 3b differ only in the nature
of the co-crystallized solvent, which does not show any
interaction with the complex, and in that 3b crystallizes on
a crystallographic C2 axis. In the margin of errors, geome-
trical parameters of both structures were nearly identical. In
both 3a and 3b (Figure 1) two diketiminate ligands adopt the
typical boat-like distortion of κ2-coordinated diketiminates,
with the metal bent out of the mean ligand plane by 35° (3a)
and 37° (3b) and both phenyl groups in a syn orientation on
the same side of the ligand. The third diketiminate ligand has
both phenyl groups in an anti orientation, and the metal
center is situated in the mean ligand plane. Cr-N distances
are slightly longer and the N-Cr-N bite angle slightly larger
in the latter ligand. Out-of-plane coordination of the chro-
mium center with syn-oriented substituents seems thus pre-
ferable to in-plane coordination with the substituents in anti
position. The same coordination geometry, i.e., two ligands
Figure 1. Crystal structure of 3b. (The structure of 3a is nearly
identical and not shown.) Hydrogen atoms and disordered
solvent molecule were omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level.
with a boat-like distortion and one ligand with the metal in
the mean ligand plane, a slightly increased N-M-N bite
angle, and increased metal-nitrogen distances, was ob-
served in the crystal structure of nacnacMe3Al.12
We were unable to obtain single crystals of the hexane-
insoluble precipitate 2a, obtained in the reactions that
yielded 3. Its elemental analysis was in reasonable agreement
with an assignment as nacnacBnCrCl2(THF)2, 2a (Scheme 2).
Attempts to prepare 2a independently under similar condi-
tions yielded the corresponding compounds 2b and 2c, with
one or no coordinated THF molecule per metal center,
respectively (Scheme 1), which are probably present as
chloride-bridged dimers.5,8 Kim et al. obtained the related
compound nacnacPhCrCl2(THF)2 from crystallization in
THF and reported THF binding-dissociation equilibria
for this complex.13 Although the assignment of 2a remains
tentative, elemental analysis data and its magnetic moment
suggest the presence of a chromium(III) complex with one
coordinated diketiminate ligand.
(10) Drees, D.; Magull, J. Z. Anorg. Allg. Chem. 1994, 620, 814.
Barbier-Baudry, D.; Bouazza, A.; Brachais, C. H.; Dormond, A.; Visseaux,
M. Macromol. Rapid Commun. 2000, 21, 213. Bonnet, F.; Visseaux, M.;
Barbier-Baudry, D.; Vigier, E.; Kubicki, M. M. Chem. Eur. J. 2004, 10,
2428. Lazarov, B. B.; Hampel, F.; Hultzsch, K. C. Z. Anorg. Allg. Chem.
2007, 633, 2367.
(11) Kruck, T.; Blessmann, D.; Kurek, G. (Solvay Deutschland
GmbH) German Patent DE4202889, 1993.
(12) Kuhn, N.; Fuchs, S.; Steimann, M. Eur. J. Inorg. Chem. 2001,
2001, 359.
(13) Kim, W. K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold,
A. L.; Theopold, K. H. Organometallics 1998, 17, 4541.

2182 Organometallics, Vol. 29, No. 9, 2010
Latreche and Schaper
of 4 is similar to that observed for nacnaciPr2Pd,14 but notably
different from the only other reported bis(diketiminate) chromi-
um(II) complex, nacnacPh2Cr,3 which shows a severely distorted
planar geometry with a 57° angle between the (Cr/N/N) planes
of the two diketiminate ligands. As we have noted before for
other metal complexes,2,15 diketiminates with primary alkyl sub-
stituents on nitrogen provide significantly less congested coordi-
nation environments than ligands with N-aryl substituents.
During reactions of CrCl3(THF)3 with 1 described above,
changes observed in the solubility of compounds seemed to
indicate that a nacnacBn2CrCl species was indeed obtained at
some point of the reaction and underwent ligand redistribution
to 2 and 3 upon concentration or standing. Evidence for the
intermediate formation of nacnacBn2CrCl came from the treat-
ment of the reaction mixture of 1 and CrCl3(THF)3 with xylyl
isocyanide prior to concentration, which afforded the isocya-
nide-coordinated compound 5in 72% yield after crystallization
(Scheme 4). In its structure (Figure 3, Table 1), the chloride and
the isocyanide ligand replaced the diketiminate ligand found
with a trans orientation of the phenyl rings in 3a or 3b, in
agreement with its weaker coordination indicated in the struc-
tures of 3a and 3b (vide supra). The two remaining diketiminate
ligands again show a boat-like distortion with phenyl rings in a
syn orientation on one side of the mean ligand plane. The ligand
distortion places the benzylic carbon atoms (C20, C50,
Figure 3) between the chloride and the isocyanide ligand,
instead of being eclipsed with the Cr-Cl or Cr-C60 bond.
In this, the structure of 5 is very similar to the corresponding
nacnacBn2ZrCl2 complex.2 Due to the mediocre crystal quality
in the X-ray diffraction study of 5, we refrain from a more in-
depth analysis of the structure.
Figure 2. Crystal structure of 4. Hydrogen atoms were omitted
for clarity. Thermal ellipsoids are drawn at the 50% probability
level.
Scheme 3
Complex 5shows a stretching frequency of νCN = 2117 cm-1
in its IR spectra, practically unchanged from free isocyanide
(νCN = 2119 cm-1). The frequency is notably lower than in
(C6F5S)3Cr(CNXyl)3 (νCN=2183, 2330, and 2358 cm-1 16
) and
comparable to those observed in Shapiro’s ansa-chromo-
cene complexes ([Me4C2(C5H4)2CrIII(CNXyl)]þ: νCN = 2119
cm-1, Me4C2(C5H4)(C5H4B(C6F5)3)CrIII(CNXyl): νCN=2100
cm-1).17,18 In contrast to these pseudotetrahedral chromo-
cenes, for which coordination of isocyanide to a cationic,
high-spin chromocene resulted in a low-spin isocyanide ad-
duct,18 octahedral 5 remains, as expected, a high-spin complex
(μeff = 3.5(1) μB).
While 5 confirmed the intermediate formation of a bis-
(diketiminate) complex, the strong coordination of the isocya-
nide ligand prevents further modifications. Attempts to trap the
intermediate product with pyridine or triphenylphosphine
failed. Use of CrCl3(py)3 as starting material or reaction of
the putative intermediate with NaOtBu or BnMgBr, to replace
chloride with a less easily exchangeable ligand, likewise did not
yield any identifiable products. Reactions of 1 with CrCl3-
(THF)3 afforded in some cases batches whose elemental analysis
proposed a composition of nacnacBn2Cr(μ-Cl)2Li(THF)2, 6.
Yields of this compound were, however, unreliable, and in most
cases ligand redistribution to 2 and 3 occurred. Addition of
Variation of the reaction conditions (solvent, temperature)
or the starting material (CrCl3(THF)3 or CrCl3) did not
influence the outcome of the reaction, and we consistently
obtained insoluble precipitates and the hexane-soluble tris-
(diketiminate) adduct 3, in the form of either 3a or 3b
(identified in most cases by X-ray diffraction and/or ele-
mental analysis). Reactions of the diketimine nacnacBnH
with CrPh3 or CrBn3, prepared in situ, led to reduction of
the metal and afforded the homoleptic Cr(II) complex 4
(Scheme 3), which can also be prepared independently from
CrCl2(THF)x and 1. In contrast to nacnacPh2Cr,3 attempts to
oxidize 4 to nacnacBn2CrCl under a variety of conditions
(including addition of 2,6-xylyl isonitrile prior to crystal-
lization) did not yield any identifiable products.
The crystal structure of 4 shows the chromium center in a
square-planar coordination with the metal atom on a crystal-
lographic inversion center (Figure 2, Table 1). The bite angle of
the diketiminate ligand (86.30(5)°) is comparable to those ob-
served in 3a and 3b (84.63(5)-85.31(9)°) and causes the N-
Cr-N angle between the two diketiminate ligands to be slightly
larger than 90° (93.70(5)°). Both diketiminate ligands show a
boat-like distortion with the metal center bent by 36° out of the
mean ligand plane, which can be attributed to the unfavorable
in-plane interactions of the N-alkyl substituents. The structure
(15) Oguadinma, P. O.; Schaper, F. Organometallics 2009, 28, 6721.
(16) Danopoulos, A. A.; Wilkinson, G.; Sweet, T. K. N.; Hursthouse,
M. B. Polyhedron 1997, 16, 2631.
(17) Shapiro, P. J.; Zehnder, R.; Foo, D. M.; Perrotin, P.; Budzelaar,
P. H. M.; Leitch, S.; Twamley, B. Organometallics 2006, 25, 719. Shapiro,
P. J.; Sinnema, P.-J.; Perrotin, P.; Budzelaar, P. H. M.; Weihe, H.; Twamley, B.;
Zehnder, R. A.; Nairn, J. J. Chem. Eur. J. 2007, 13, 6212.
€
(14) Tian, X.; Goddard, R.; Porschke, K. R. Organometallics 2006,
25, 5854.
(18) Sinnema, P.-J.; Nairn, J.; Zehnder, R.; Shapiro, P. J.; Twamley,
B.; Blumenfeld, A. Chem. Commun. 2004, 110.

Article
Organometallics, Vol. 29, No. 9, 2010 2183
Table 1. Selected Bond Lengths [A] and Bond Angles [deg] for 3a, 3b, and 4-6
˚
3a
3b
4
5
6
Cr-Na
2.052(2)-2.083(2)
2.104(2), 2.112(2)
2.054(1), 2.110(1)
2.116(1)
2.060(1), 2.059(1)
2.013(8)-2.054(8)
2.356(3), 2.365(3)
2.132(12), 2.142(14)
85.6(3)-86.4(3)
2.016(3)-2.060(3)
2.422(1), 2.430(1)
Cr-Nb/Cr-Cl
Cr-C
N-Cr-Nc
N-Cr-Nd
N-Cr-Xe
Cl-Cr-Yf
bending angleg
85.20(8) 85.31(9)
89.91(9)
85.76(9)-97.16(8)
84.63(5)
88.24(8)
85.62(8)-96.75(5)
86.30(5)
93.70(5)
36
85.09(11), 85.30(11)
88.9(4)-94.0(2)
84.4(3), 85.0(3)
36-38
89.63(8)-93.84(8)
87.82(3)
39, 40
0, 35, 35
0, 37
a Diketiminate ligands with boat-like distortions (3a: N3-N6; 3b: N1, N2). b Diketiminate ligand with Cr in the mean ligand plane (3a: N1, N2; 3b:
N3). c Bite angle of diketiminate ligands with boat-like distortion. d Bite angle of diketiminate ligands with in-plane metal coordination. e X = 3a, 3b, 4: N
atoms of a different ligand. 5: N atoms of a different ligand, C60, C200, Cl1, Cl2. 6: N atoms of a different ligand, Cl1, Cl2. f Y = 5: C60, C200. 6: Cl2.
g Bending of the metal center out of the mean ligand plane, described by the angle between the (N1, N2, C2, C4) and the (Cr1, N1, N2) plane (numeration
according to Figure 1).
Scheme 4
Figure 3. Crystal structure of 5. Only one of two independent
molecules in the unit cell is shown. Hydrogen atoms and co-
crystallized diethyl ether were omitted for clarity. Thermal
ellipsoids are drawn at the 50% probability level.
excess LiCl did not improve the yields of 6or the reliability of the
synthetic protocol. Change of the workup procedure to extrac-
tion with diethyl ether finally afforded 6 in 70% crystallized
site. Complexes 5 and 6 show the targeted octahedral
yield (Scheme 4).
The crystal structure of 6 (Table 1, Figure 4) confirms a
ing the free coordination site cis to chloride. As envisioned,
chloride-bridged dinuclear complex, with chromium in an
octahedral environment and two additional THF ligands
complementing the coordination sphere of the lithium atom.
The steric influence of the coordinated THF molecules is
notable in a slightly greater boat-like distortion of the ligands
of the chloride ligands. This was resolved by switching the
central metal to Cr(III) and thus opening one coordination
nacnacBn2CrCl(L) geometry with isocyanide or μ-Cl occupy-
chloride exchange became easier with Cr, as shown by the
fast formation of homoleptic 3 from 1 and CrCl3(THF)3 at
room temperature.
The crystal structures of 3a, 3b, 5, and 6 displayed a common
structural motif for the obtained nacnacBn2CrX2 complexes,
(Table 1), i.e., an increased bending of the chromium center
consisting of two boat-like distorted, nearly coplanar diketimi-
out of the mean ligand plane, but otherwise the structure is
very similar to that of isocyanide-coordinated 5.
nate ligands. The N-alkyl substituents are found in a syn orien-
tation, pointing away from the metal center, and placed directly
It is notable that in contrast to nacnacBn2CrCl its analogue
above and below the cis-coordinated CrX2 fragment. The essen-
tially identical coordination of the diketiminate ligands ob-
with N-phenyl substituents, nacnacPh2CrCl,3 does not under-
go a comparable ligand exchange. Taking into account the
served in nacnacBn2ZrCl2, carrying the same ligand,2 as well as
in other nacnacR2MX2 complexes (R=alkyl, phenyl, tolyl; M=
strong distortions observed in the crystal structure of nac-
nacPh2Cr compared to the symmetrical nacnacBn2Cr, the
Al, Ti, Zr),2,12,19 appears to indicate that this geometry is a
general motif for octahedral bis(diketiminate) metal complexes.
stability of nacnacPh2CrCl might well be based on its inability
to form the corresponding tris(diketiminate) complex.
(19) Rahim, M.; Taylor, N. J.; Xin, S.; Collins, S. Organometallics
1998, 17, 1315. Kakaliou, L.; Scanlon, W. J.; Qian, B.; Baek, S. W.; Smith, M.
R.; Motry, D. H. Inorg. Chem. 1999, 38, 5964. Franceschini, P. L.; Morstein,
Conclusions
The presented study was motivated by the lack of reacti-
vity observed in nacnacR2ZrCl2 complexes toward exchange
Duan, Y.-Q.; Li, X.-F.; Li, Y.-S. J. Organomet. Chem. 2006, 691, 2023.
M.; Berke, H.; Schmalle, H. W. Inorg. Chem. 2003, 42, 7273. Tang, L.-M.;

2184 Organometallics, Vol. 29, No. 9, 2010
Latreche and Schaper
Attempted Synthesis of nacnacBn2CrCl(THF). A solution
nacnacBnLi(THF), 1 (1 g, 2.80 mmol), in toluene (20 mL) was
added to a suspension of CrCl3(THF)3 (0.5 g, 1.40 mmol) in
toluene (20 mL). After the mixture was stirred for 12 h at room
temperature, it was filtered to remove LiCl. The volatiles were
removed, and the residue extracted with hexane (100 mL).
Filtration yielded an apple-green powder, tentatively assigned
to nacnacBnCrCl2(THF)2, 2a (500 mg, 65%). Anal. Calcd for
C27H37N2O2CrCl2: C, 59.56; H, 6.85; N, 5.14. Found: C, 60.72;
H, 6.32; N, 5.19. μeff(298 K) = 4.2(1) μB.
Slow evaporation of the olive-green filtrate obtained above at
room temperature yielded olive-green crystals of nac-
nacBn3Cr 2THF, 3a, identified by X-ray diffraction analysis.
3
{nacnacBnCrCl2(THF)}2, 2b. A solution of 1 (0.20 g, 0.56
mmol) in toluene (20 mL) was added dropwise to a solution of
CrCl3(THF)3 (0.20 g, 0.53 mmol) in THF (5 mL) and toluene (20
mL). After stirring overnight at room temperature and filtration
to remove LiCl, all volatiles were removed under vacuum. The
residue was extracted with hexane, filtered, and, after evapora-
tion of the filtrate, redissolved in a mixture of THF (5 mL)
and hexane (10 mL). A final evaporation of the solvent yielded
0.20 g (79%) of an apple-green powder. Anal. Calcd for C46H58-
N4Cl4Cr2O2: C, 58.48; H, 6.19; N, 5.93. Found: C, 58.82; H,
6.29; N, 5.91. Mp: 146 °C.
{nacnacBnCrCl2}2, 2c. A solution of 1 (0.300 g, 0.84 mmol) in
toluene (20 mL) was added to a solution of CrCl3(THF)3 (0.200
g, 0.53 mmol) in toluene (30 mL), upon which the color of the
latter changed from purple to green. After stirring overnight at
room temperature and filtration to remove LiCl, the solvent was
removed under vacuum and the residue extracted with hexane
(20 mL). The olive-green powder isolated by filtration was
washed several times with hexane and dried under vacuum to
yield 0.200 g (93%) of 2c. Anal. Calcd for C19H21N2CrCl2: C,
57.01; H, 5.29; N, 7.00. Found: C, 56.36; H, 5.61; N, 6.56. Mp:
160 °C.
Figure 4. Crystal structure of 6. Hydrogen atoms and disor-
dered atoms omitted for clarity. Thermal ellipsoids are drawn at
the 30% probability level.
Bis(diketiminate) chromium complexes thus seem to be
promising candidates for metal-assisted transformations: the
two spectator ligands form a predictable, rigid, and easily
modified C2-symmetric coordination environment, and the
reactive coordination sites are accessible to substrates.20
Future efforts will concentrate on potential applications
and to prevent the ligand redistribution to nacnacBn3Cr,
e.g., by bridging of the diketiminate ligands.
nacnacBn3Cr 2THF, 3a. A solution of 1 (1.0 g, 2.81 mmol) in
3
toluene (20 mL) was added to a solution of CrCl3(THF)3 (0.35 g,
0.94 mmol) in toluene (30 mL), upon which the color of the
solution changed from purple to green. After stirring overnight
at room temperature and filtration to remove LiCl, the solvent
was removed under vacuum and the residue was extracted with
hexane (100 mL). Filtration and evaporation of the solvent
yielded 3a as an olive-green powder (0.89 g, 92%). Anal. Calcd
Experimental Section
All reactions, except ligand synthesis, were carried out under
an inert atmosphere using Schlenk and glovebox techniques un-
der a nitrogen atmosphere. nacnacBnLi(THF) (1),2 nacnacCyLi-
(THF),2 S,S-nacnacCH(Me)PhLi(THF),2 CrCl3(THF)3,21 and
for C57H63N6Cr 2C4H8O: C, 75.92; H, 7.74; N, 8.17. Found: C,
75.29; H, 7.56; N, 8.25. Mp: 180 °C. Presence of 2 ( 0.3 equiv of
THF was confirmed by NMR.
3
nacnacBn3Cr C7H8, 3b. A solution of 1 (0.41 g, 1.2 mmol) in
3
22
CrCl2(THF)x were prepared according to literature proce-
toluene (15 mL) was added to a suspension of CrCl3(THF)3
(0.21 g, 0.6 mmol) in toluene (10 mL). After the mixture was
stirred overnight at room temperature, it was filtered to remove
LiCl. All volatiles were removed under vacuum, and the remain-
ing residue was co-evaporated twice with toluene (2 ꢀ 25 mL)
and washed twice with hexane (2 ꢀ 20 mL). Crystallization from
toluene at -30 °C yielded olive-green needles of 3b (300 mg,
dures. Solvents were dried by passage through activated alumi-
num oxide (MBraun SPS) and deoxygenated by repeated
extraction with nitrogen. C6D6 was dried over sodium and
degassed by three freeze-pump-thaw cycles. All others chemi-
cals were purchased from common commercial suppliers and
used without further purification. 1H and 13C NMR spectra
were acquired on a Bruker AMX 300 or Bruker AV 400 spectro-
meter. Chemical shifts were referenced to the residual signals of
58%). Anal. Calcd for C57H63N6Cr C7H8: C, 78.74; H, 7.33; N,
3
8.61. Found: C, 77.70; H, 7.46; N, 8.46.23 μeff(298 K) = 3.9(1)
1
the deuterated solvents (C6D6: H: δ 7.16 ppm, 13C: δ 128.38
μB. UV/vis (toluene; λ, nm (ε, M-1 cm-1)): 368 (1300), 414
3
ppm). Magnetic susceptibility measurements were carried out at
room temperature in grease-sealed capillaries on a Johnson
Matthey magnetic susceptibility balance. Elemental analyses
(1300), 770 (550). Mp: 180 °C.
nacnacBn2Cr, 4. From Cr(II). CrCl2(THF)x (0.4 g, 1.68 mmol
for x = 2) was dissolved in THF (30 mL), and a solution of 1
ꢀ
ꢀ
were performed by the Laboratoire d’Analyse Elementaire
ꢀ
ꢀ
(Universite de Montreal). Absorption spectra were measured
in dry solvent in a sealed cell at room temperature on a Cary 500i
spectrophotometer.
(23) Elemental analyses for some compounds in this article showed
low carbon values up to ΔC = 1%, despite the use of crystalline material
suitable for single-crystal diffraction studies. Recrystallization did not
improve on these values. Although we cannot explain this behavior and
cannot exclude the presence of small amounts of impurities, slight
variations toward low carbon values might indicate oxidation/hydro-
lysis during the measurement, which is performed under ambient con-
ditions with samples prepared in a glovebox. We noted that MacAdams
et al. reported similar deviations for nacnacPh chromium complexes (see
ref 3).
(20) In very preliminary attempts, we added methyl Grignard to
reaction mixtures containing 6 and styrene. Small amounts (2-4%) of
isopropylbenzene were found in the organic phase after aqueous work-
up.
(21) Shamir, J. Inorg. Chim. Acta 1989, 156, 163.
(22) Kohler, F. H.; Prossdorf, W. Z. Naturforsch., B 1977, 32B, 1026.
€
€

Article
Organometallics, Vol. 29, No. 9, 2010 2185
Table 2. Details of X-ray Diffraction Studies
3aa
3b
4
5
6
a
formula
C
57H63CrN6
C57H63CrN6 C7H8
C38H42CrN4
606.76; 322
150; 1.54178
triclinic
C47H51ClCrN5 (C4H10O)0.25
C46H58Cl2CrLiN4O2
828.80
150; 1.54178
monoclinic
P21/c
13.928(2)
29.976(4)
11.357(1)
3
3
Mw (g/mol); F(000)
T (K); wavelength
cryst syst
space group
unit cell: a (A)
˚
b (A)
˚
c (A)
884.13; 1884 a
150; 1.54178
monoclinic
P21/c
976.27; 2084
150; 1.54178
monoclinic
C2/c
11.0133(3)
18.4416(5)
26.4697(6)
791.91; 1678
150; 1.54178
triclinic
P1
P1
˚
11.0625(6)
23.6978(13)
21.5716(11)
9.2442(4)
9.3053(4)
9.8732(4)
103.695(2)
98.265(2)
101.495(2)
792.17(6); 1
1.272
11.289(1)
17.818(2)
22.393(2)
86.836(4)
80.564(5)
81.874(4)
4396.6(7); 4
1.196
R (deg)
β (deg)
γ (deg)
92.399(2)
97.403(1)
110.141(6)
3
˚
V (A ); Z
5650.2(5); 4
1.039 a
5331.3(2); 4
1.216
4451.6(9); 4
1.237
dcalcd. (g/cm3)
θ range (deg); completeness
collected reflns; Rσ
unique reflns; Rint
2.8-55.6; 0.98
69 584; 0.084
7129; 0.091
1.947; multiscan
0.040; 0.078
0.073; 0.084
0.85
3.4-67.8; 0.98
42 914; 0.045
4732; 0.062
2.111; multiscan
0.034; 0.083
0.051; 0.087
0.95
4.7-67.7; 0.98
11 177; 0.028
2812; 0.041
3.211; multiscan
0.035; 0.101
0.035; 0.101
1.02
2.0-60.2; 0.89
67 699; 0.180
11673; 0.199
2.987; multiscan
0.089; 0.232
0.209; 0.303
0.954
3.0-67.6; 0994
61 562; 0.025
7990; 0.052
3.528; multiscan
0.060; 0.173
0.069; 0.181
1.02
μ (mm-1); abs corr
R1(F); wR(F2) (I > 2σ(I))
R1(F); wR(F2) (all data)
GoF(F2)
residual electron density
0.15
0.20
0.35
1.05
0.62
a Co-crystallized solvent removed with SQUEEZE.
(1.2 g, 3.37 mmol) in THF (20 mL) was added. The reaction
mixture was stirred overnight at room temperature. After
evaporation of the solvent, the residue was extracted with
diethyl ether (120 mL). The extract was filtered to remove LiCl,
concentrated, and cooled to -30 °C to yield red crystals of
nacnacBn2Cr (0.90 g, 90% yield). Anal. Calcd for C38H42N4Cr:
C, 75.22; H, 6.98; N, 9.23. Found: C, 73.66; H, 7.14; N, 8.96.23
solution was placed at -30 °C, and brown crystals of 6 were
obtained after several days (462 mg, 70% yield). Anal. Calcd for
C46H58N4O2LiCrCl2: C, 66.66; H, 7.05; N, 6.76. Found: C, 66.96;
H, 6.90; N, 7.22. UV/vis (toluene; λ, nm (ε, M-1 cm-1)): 308
3
(14000),392(6500),761(1900).μeff(298K) =3.4(1) μB.Mp:158°C.
X-ray Diffraction Studies. Crystals suitable for X-ray diffrac-
tion studies were obtained directly from the synthetic recrystal-
lizations described above. Diffraction data were recorded on a
Bruker Proteum X8/Microstar (Cu radiation), using the APEX2
software package.24 Data reduction was performed with
SAINT;25 absorption corrections with SADABS.26 Structures
were solved with direct methods (SHELXS97).27 All non-
hydrogen atoms were refined anisotropically using full-matrix
least-squares on F2 and hydrogen atoms refined with fixed
isotropic U using a riding model (SHELXL97).27 For 3a, the
co-crystallized solvent was identified as disordered THF and
suppressed by application of SQUEEZE.28 Co-crystallized sol-
vent in 3b (toluene) and 5 (ether) and disorders of one isocyanide
ligand in 5 and of the THF and two phenyl groups in 6 were
modeled using appropriate restraints and refined isotropically
in most cases. For further details see Table 2 and the Supporting
Information.
μ
eff(298 K) = 4.1(1) μB. Mp: 152-155 °C.
From Cr(III). CrCl3 (0.50 g, 3.2 mmol) was suspended in THF
(40 mL) and cooled to -78 °C. A solution of PhLi in dibutyl ether
(2.0 M, 5.0 mL, 10 mmol) was added dropwise, which caused an
immediate color change to brown-red. After stirring for 5 h at -78
°C, a solution of nacnacBnH (2.1 g, 0.75 mmol) in THF (20 mL)
was added. The reaction was allowed to warm to room tempera-
ture overnight. The solvent was removed in vacuo, and the residue
was extracted with diethyl ether (100 mL). The extract was then
filtered to remove LiCl, concentrated, and kept at -30 °C to yield
red-purple crystals of nacnacBn2Cr (0.51 g, 26%), identified by X-
ray diffraction. Anal. Calcd for C38H42N4Cr: C, 75.22; H, 6.98; N,
9.23. Found: C, 74.48; H, 7.00; N, 9.30.23
nacnacBn2CrCl(CNC6Me2H3), 5. A solution of 1 (0.70 g, 2.0
mmol) in toluene (30 mL) was added to a suspension of CrCl3-
(THF)3 (0.34 g, 0.89 mmol) in toluene (40 mL). After stirring for
12 h at room temperature and filtration to remove LiCl, 2,6-
dimethylphenyl isocyanide (0.175 g, 1.3 mmol) was added. The
solution was stirred for additional 12 h and concentrated to 7
mL. Hexane (10 mL) was added and the solution left to stand
overnight. The precipitate formed was eliminated by filtration,
the volatiles were removed under vacuum, and the remaining
solid was recrystallized from diethyl ether (10 mL) at -30 °C to
yield 5 as green crystals (0.59 g, 72%). Anal. Calcd for
Acknowledgment. Funding for this research was pro-
vided by the Natural Sciences and Engineering Research
ꢀ
Council of Canada and the Universite de Montreal. We
thank Francine Belanger for her support with the crystal
ꢀ
ꢀ
structure determinations.
Supporting Information Available: Details of X-ray diffrac-
tion studies (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
C47H51N5ClCr (C4H10O)0.25: C, 72.80; H, 6.81; N, 8.84. Found:
C, 72.89; H, 7.78; N, 8.31. IR (toluene): νCN = 2117 cm-1
3
.
μ
eff(298 K) = 3.5(1) μB. Mp: 149 °C.
nacnacBn2Cr(μ-Cl)2Li(THF)2, 6. A solution of 1 (0.60 g, 1.7
(24) APEX2, Release 2.1-0; Bruker AXS Inc.: Madison, WI, 2006.
(25) SAINT, Release 7.34A; Bruker AXS Inc.: Madison, WI, 2006.
(26) Sheldrick, G. M. SADABS; Bruker AXS Inc.: Madison, WI, 1996
and 2004.
(27) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(28) Spek, A. L. PLATON; Utrecht University: Utrecht, The Nether-
lands, 2008.
mmol) in THF (20 mL) was added to a suspension of CrCl3-
(THF)3 (0.30 g, 0.80 mmol) in THF (20 mL). The reaction
mixture was stirred overnight at room temperature, the solvent
was evaporated, and the residue was extracted with diethyl ether
(60 mL). After filtration to remove LiCl and concentration, the