Yttrium and scandium complexes of a bulky bis(phosphinimine)carbazole ligand

Article abstract of DOI:10.1016/j.ica.2014.05.045

The synthesis and reactivity of a bulky bis(phosphinimine)carbazole pincer ligand (HL) bearing mesityl N-aryl groups is described. Reaction of HL with Y(CH₂SiMe₃)₃(THF)₂ afforded a doubly cyclometalated organoyttrium complex, whereby the ligand was κ³N, κ²C coordinated to the metal via three nitrogen atoms and two ortho-metalated P-phenyl rings. Deprotonation of (HL) with ⁿBuLi liberated a monomeric and thermally stable lithium salt of the ligand (LLi). Salt metathesis reactions of LLi with ScCl₃(THF)₃ and YCl₃(THF)_3.5 generated the corresponding rare earth dichloro complexes, which were found to be monomeric and Lewis-base free.

Full text of DOI:10.1016/j.ica.2014.05.045

Inorganica Chimica Acta xxx (2014) xxx–xxx
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Inorganica Chimica Acta
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Yttrium and scandium complexes of a bulky bis(phosphinimine)carbazole
ligand
⇑
Kevin R.D. Johnson, Paul G. Hayes
Department of Chemistry and Biochemistry, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 3M4, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and reactivity of a bulky bis(phosphinimine)carbazole pincer ligand (HL) bearing mesityl
N-aryl groups is described. Reaction of HL with Y(CH2SiMe3)3(THF)2 afforded a doubly cyclometalated
organoyttrium complex, whereby the ligand was j3N, j2C coordinated to the metal via three nitrogen
atoms and two ortho-metalated P-phenyl rings. Deprotonation of (HL) with nBuLi liberated a monomeric
and thermally stable lithium salt of the ligand (LLi). Salt metathesis reactions of LLi with ScCl3(THF)3 and
YCl3(THF)3.5 generated the corresponding rare earth dichloro complexes, which were found to be mono-
meric and Lewis-base free.
Received 29 April 2014
Accepted 30 May 2014
Available online xxxx
Dedicated to Prof. T. Don Tilley on the
occasion of his 60th birthday.
Ó 2014 Published by Elsevier B.V.
Keywords:
Ligand design
Rare earth
Scandium
Yttrium
Phosphinimine
Cyclometalation
1. Introduction
and rare earth complexation of a bulky bis(phosphinimine)carba-
zole ligand bearing two mesityl N-aryl substituents. Insight gained
The incorporation of phosphinimine functionalities into ancil-
lary ligands for supporting main group [1], early [2] and late [3]
transition metal, actinide [4], and rare earth [5] complexes has
been the subject of increased attention in recent years. These phos-
phinimine complexes have been applied in a variety of catalytic
transformations including hydroamination [5h–k], as well as the
polymerization of olefins [2c,5q,r] and lactones [1f,g,5a–e]. Of par-
ticular interest to us is the use of phosphinimine ligands in the fun-
damental study of structure and reactivity of rare earth complexes;
notable examples include the use of phosphinimine ligands for the
development of rare earth complexes that exhibit metal–ligand
multiple bonds. For example, bis(phosphinimine)methane ligands
have been used to pave the development of rare earth carbene
complexes [6]. In addition, the synthesis of terminal scandium
imido complexes supported by a cyclopentadienyl-phosphinimine
ligand [7] and more recently, a phosphazene ligand have been
described [8]. These reports have largely fueled our interest in
the design and complexation of new phosphinimine pincer ligands
that can be used in stabilizing rare earth metal ions, with the intent
of developing a platform for obtaining unique bonding modes and
reaction behavior. Herein, we report the synthesis, characterization
from the fundamental studies of these complexes, including their
reaction behavior is described.
2. Results and discussion
2.1. Ligand synthesis
We have previously reported the synthesis of a variety of
bis(phosphinimine)carbazole pincers whereby the phosphinimine
functionality was comprised of two phenyl rings attached to
phosphorus, and an aryl group (phenyl, para-isopropylphenyl or
pyrimidine) bound to nitrogen (ligands 1–3, Chart 1) or
a
dioxaphospholane ring, and a para-isopropylphenyl moiety at the
nitrogen atom (ligand 4, Chart 1) [9]. Although these ligands pos-
sess a moderate degree of steric bulk, ancillary ligands that impose
very high degrees of steric protection can sometimes permit the
isolation of low-coordinate species that are not accessible when
less bulky ligands are utilized [10]. In addition, sterically demand-
ing complexes of the lanthanides have been instrumental in the
development of sterically induced reduction (SIR) chemistry by
Evans [11]. For these reasons, we were inclined to synthesize a
more sterically encompassing bis(phosphinimine)carbazole pincer
bearing two N-mesityl rings, with the intention of developing a
⇑
Corresponding author. Tel.: +1 403 329 2313; fax: +1 403 329 2057.
E-mail address: p.hayes@uleth.ca (P.G. Hayes).
http://dx.doi.org/10.1016/j.ica.2014.05.045
0020-1693/Ó 2014 Published by Elsevier B.V.
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K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
Table 1
then quenched with an excess of chlorodiphenylphosphine to
Selected bond distances/Å and angles/° for 7.
afford the compound 1,8,9N-tris(diphenylphosphino)-3,6-dimeth-
ylcarbazole 7 (Scheme 1). The formation of 7 via this route is
unsurprising as the reaction of a chlorophosphine with a silyla-
mide is facile and proceeds to form an aminophosphine with con-
comitant loss of chlorosilane. A similar approach is utilized in the
preparation of dichalcogenoimidodiphosphinates ((E = PR2)2NH,
E = O, S, Se), whereby a chlorophosphine (PR2Cl, R = Ph, iPr) is
reacted with hexamethyldisilazane to generate a (PR2)2NH prod-
uct, which is then oxidized to the corresponding dic-
halcogenoimidodiphosphinate [12]. Triphosphine 7 can be readily
prepared in good yield and purity via this method. The 31P{1H}
NMR spectrum of 7 (chloroform-d) exhibits a triplet at d 53.3
(1P, JPP = 69.5 Hz) and a doublet at d À17.2 (2P, JPP = 69.5 Hz) indi-
cating coupling between the 1,8-carbazole phosphines and the N-
bound phosphine. The 1H and 13C{1H} NMR spectra corroborated
the expected structure of 7 and suggest C2v symmetry in solution.
Single crystals of 7 were obtained from a concentrated toluene
solution at À35 °C and the solid-state structure was determined by
X-ray crystallography. The compound crystallized in the ortho-
rhombic space group Pna21 (#33) with one molecule of toluene
in the asymmetric unit. The molecular structure is depicted in
Fig. 1 as a thermal ellipsoid plot and selected metrical parameters
are listed in Table 1.
P1–C1
1.845(2)
1.836(2)
1.818(2)
1.844(2)
1.846(3)
3.111(1)
P1–C21
N1–P2
P2–C27
P3–C39
P1Á Á ÁP2
1.842(2)
1.742(2)
1.831(2)
1.829(3)
3.673(1)
P1–C15
P2–C33
P3–C8
P3–C45
P3Á Á ÁP2
C15–P1–C21
C15–P1–C1
C33–P2–N1
C39–P3–C45
C39–P3–C8
102.7(1)
C21–P1–C1
C27–P2–N1
C27–P2–C33
C45–P3–C8
102.1(1)
99.0(1)
105.9(1)
101.2(1)
105.3(1)
103.7(1)
106.8(1)
100.7(1)
The C–P bond lengths in 7 are unexceptional (average C–
P = 1.836 Å, range = 1.818(2)–1.846(3) Å). The N–P bond distance
of 1.742(2) Å also falls within the normal range. In the compound,
P1 resides within the plane defined by the carbazole backbone;
however, P2 sits below the same plane by 0.918 Å and P3 lies above
by 0.611 Å. This twisting of the diphenylphosphino moieties in and
out of the carbazole plane is likely due to steric crowding.
Compound 7 can be reacted with [Et3NH]I in refluxing methy-
lene chloride under an inert atmosphere to cleave the P–N bond
and liberate the known compound 1,8-bis(diphenylphosphino)-
3,6-dimethylcarbazole 5 (Scheme 1). Following recrystallization
from hot toluene, we found that samples of 5 prepared by this
method were consistently contaminated with the reaction byprod-
uct IPPh2 and required column chromatography for purification.
Due to the oxophillic nature of compound 5, rigorous exclusion
of oxygen was required as the diphosphine rapidly oxidizes to
the phosphine oxide under atmospheric oxygen at ambient tem-
perature. For this reason, we prefer our previously reported syn-
thesis of 5, which allows for the quick and effective removal of
reaction byproducts to afford pure product 5 without the need
for column chromatography.
As mentioned previously, the final step of the ligand synthesis
involves a Staudinger reaction of diphosphine 5 with an aryl azide
to generate the phosphinimine functionality. To this end, reaction
of 5 with two equivalents of mesityl azide in toluene at ambient
temperature afforded proteo ligand HL (8) in 68% yield after
recrystallization (Scheme 2). The compound exhibits a single reso-
nance in its 31P{1H} NMR spectrum at d À6.5 (benzene-d6) and its
1H and 13C{1H} NMR spectra indicate C2v symmetry in solution. The
proton NMR spectrum (benzene-d6) has a broad NH peak at d
12.18, an expectedly complicated aromatic region and three
methyl resonances at d 2.26, 2.22 and 1.95 corresponding to the
Chart 1. Bis(phosphinimine)carbazole proteo ligands 1–4.
ligand that imparts a larger degree of steric protection to a coordi-
nated metal than our previously reported derivatives 1–4.
Using a protocol similar to that previously described [9], our
new bulky bis(phosphinimine) pincer was prepared via the
Staudinger reaction of 1,8-bis(diphenylphosphino)-3,6-dimethyl-
carbazole 5 with two equivalents of mesityl azide. The synthesis
of reagent 5 has been previously reported by us [9a]; however,
during this study an alternate route to the same precursor was dis-
covered and is discussed below.
For this modified preparation, the compound 1,8-dibromo-
3,6-dimethylcarbazole 6 was reacted with one equivalent of
n-butyllithium followed by trimethylsilyl chloride to afford 1,8-
dibromo-3,6-dimethyl-9N-trimethylsilylcarbazole in situ. Subse-
quently, a lithium halogen exchange reaction was performed by
addition of tert-butyllithium. The resultant lithiated species was
Scheme 1. Synthesis of 1,8,9N-tris(diphenylphosphino)-3,6-dimethylcarbazole 7 and its reactivity to give 5.
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K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
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Fig. 1. Thermal ellipsoid plot (50% probability) of 7. Hydrogen atoms and toluene
solvent molecule are omitted for clarity.
Table 2
Selected bond distances/Å, angles/° and torsion angles/° for the crystallographically
independent molecules of compound 8.
P1–N1
P2–N3
N2Á Á ÁN3
1.549(3)
1.560(3)
2.805(4)
P1B–N1B
P2B–N3B
N2BÁ Á ÁN1B
1.551(3)
1.551(3)
2.835(4)
N1–P1–C1
N3–P2–C8
111.7(2)
110.1(2)
N1B–P1B–C1B
N3B–P2B–C8B
110.3(2)
112.5(2)
N1–P1–C1–C2
N3–P2–C8–C7
À154.4(3)
À173.4(3)
N1B–P1B–C1B–C2B
N3B–P2B–C8B–C7B
165.5(3)
153.2(3)
Fig. 2. Thermal ellipsoid plots (50% probability) depicting two crystallographically
independent molecules of HL (8). Hydrogen atoms (except H2A and H2B) and
toluene solvent molecules are omitted for clarity.
2.2. Protonolysis reactivity
In an effort to access an organolanthanide complex of the
bis(phosphinimine) ligand via alkane elimination, proteo ligand 8
was reacted with one equivalent of the rare earth precursor Y(CH2-
SiMe3)3(THF)2 at ambient temperature. When the reaction was fol-
lowed in situ by NMR spectroscopy in benzene-d6 solution, the
31P{1H} NMR spectrum revealed the formation of a doublet at d
24.1 (2JPY = 6.2 Hz) and unreacted proteo ligand at d À6.5 with rel-
ative integrations of 20:80 after 1 h. Continued reaction at ambient
temperature over the course of 24 h resulted in complete conver-
sion to product. The doublet at d 24.1, resulting from coupling
between 89Y (100% abundant, I = ½) and the phosphorus nuclei of
the ancillary ligand, is indicative of ligand coordination to yttrium.
Analysis of the product by 1H and 13C{1H} NMR spectroscopy
revealed that the expected dialkyl yttrium complex had not been
isolated, but rather, a doubly cyclometalated product. The complex
consisted of the ligand bound to the yttrium center in a j5 mode
through its three nitrogen atoms and two ortho-metalated P-phe-
nyl rings. The 1H and 13C{1H} NMR spectra suggested a molecule
with C2-symmetry; accordingly, the numerous signals in the aro-
matic regions corresponded to inequivalent phenyl rings bound
to phosphorus. A particularly diagnostic signal in the 13C{1H}
NMR spectrum was the metalated carbon directly bonded to
yttrium. This ipso carbon was highly deshielded and resonated as
Scheme 2. Synthesis of mesityl substituted bis(phosphinimine) ligand 8.
p-mesityl, 3,6-carbazole and o-mesityl methyl signals, respec-
tively. The high frequency of the NH resonance signifies that the
group is likely involved in a hydrogen bonding interaction.
Single crystals of 8 suitable for an X-ray diffraction experiment
were grown from a concentrated toluene solution at À35 °C. The
ꢀ
ligand crystallized in the space group P1 with two crystallograph-
ically independent molecules in the asymmetric unit; both struc-
tures are depicted in Fig. 2 as thermal ellipsoid plots.
The solid-state structure of 8 corroborated its identity, as previ-
ously suggested by multinuclear NMR spectroscopy. In each inde-
pendent molecular unit of the structure, one phosphinimine
nitrogen donor interacts with the carbazole N–H through a hydro-
gen bond (d(N2Á Á ÁN3) = 2.805(4) Å, d(N2BÁ Á ÁN1B) = 2.835(4) Å).
The phosphinimine groups are rotated periplanar to the aromatic
carbazole backbone with N1–P1–C1–C2 and N3–P2–C8–C9 torsion
angles of À154.4(3)° and À173.4(3)° in one molecule, and
153.2(3)° and 165.5(3)° in the other. Finally, the phosphinimine
P–N bond lengths (ranging from 1.549(3) to 1.560(3) Å) correlate
well with others in the literature and are indicative of significant
P@N double bond character [9,13]. A survey of selected metrical
parameters from both independent molecules of 8 (Table 2) indi-
cated a high degree of agreement between the two structures.
1
2
a doublet of doublets at d 198.1 (dd, JCY = 42.5 Hz, JCP = 38.8 Hz).
It was also found that the 1H and 13C{1H} NMR spectra of the
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K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
product were consistent with a complex that possessed mesityl
rings incapable of free rotation on the NMR timescale at ambient
temperature. Thus, it is reasonable to conclude that the complex
is extremely sterically crowded.
Complex 10 can be obtained as a pure microcrystalline solid in
reasonable yield (69%) after recrystallization. Unfortunately, single
crystals suitable for an X-ray diffraction experiment could not be
isolated despite repeated attempts. Consequently, the solid-state
structure of 10 was not determined. In light of the fact that the
dialkyl yttrium complex of the carbazole pincer ligand was ther-
mally unstable and only spectroscopic data could be obtained for
its decomposition product, the alkane elimination reactivity of 8
with organorare earth reagents was not investigated further.
It is likely that formation of the observed yttrium complex
occurred as outlined in Scheme 3, in a manner similar to that pre-
viously documented for organolutetium complexes of the related
bis(phosphinimine)carbazole pincer ligands 1 and 2 [9a]. Presum-
ably, reaction of 8 with Y(CH2SiMe3)3(THF)2 liberated the dialkyl
yttrium complex 9 as a highly reactive species with loss of one
equivalent of tetramethylsilane. Subsequently, 9 likely rapidly
decomposed by two sequential intramolecular cyclometalative
alkane elimination reactions to afford doubly cyclometalated prod-
uct 10. Due to the fact that proteo ligand 8 reacted slowly with
Y(CH2SiMe3)3(THF)2, attempts to conduct this reaction at low tem-
peratures (i.e. À35 °C) in an effort to observe putative dialkyl com-
plex 9 prior to cyclometalation, were hampered by extremely slow
reaction rates. The apparent relative rates of formation and decom-
position contrast the alkane elimination reactivity of our previ-
2.3. Synthesis and characterization of LLnCl2 (Ln = Sc, Y)
Reaction of 8 with one equiv of n-butyllithium resulted in facile
and quantitative conversion to the expected lithiated derivative 11,
(L-j3N)Li, with loss of butane (Scheme 4). Compound 11 exhibited
a
31P{1H} NMR resonance at d 11.0 (benzene-d6), which was
17.5 ppm downfield from that observed for the proteo ligand. In
general, the chemical shift of the 31P{1H} phosphinimine resonance
was found to be highly sensitive to the coordination environment
ously
reported
less
bulky
bis(phosphinimine)carbazole
of the ligand with a downfield shift being indicative of strong
r-
derivatives 1–4; all of these ligands underwent rapid reaction
(<10 min) with the organolutetium reagent Lu(CH2SiMe3)3(THF)2
at ambient temperature to afford dialkyl complexes of generic
form LLu(CH2SiMe3)2. The retarded rate of formation of complex
9 is a testament to the high degree of steric bulk imparted by the
mesityl-substituted ancillary ligand.
Due to the fact that the ancillary ligand in putative complex 9
forms two six-membered chelate rings with yttrium, its subse-
quent double cyclometalation reactivity is facilitated by this tightly
enforced pincer chelation geometry. Specifically, the ortho carbon
atoms on the P-phenyl rings are situated with appropriate distance
and angle to the metal centre that they can readily undergo C–H
bond activation. This can be contrasted with an analogous
bis(phosphinimine)pyrrole NNN pincer ligand, which we have pre-
viously documented [13a,c], whereby upon tridentate coordination
with a metal, the ligand forms two five-membered chelate rings.
The more open chelation geometry enforced by the analogous
bis(phosphinimine)pyrrole framework has been demonstrated to
aid in reducing the propensity for rare earth dialkyl complexes to
undergo ligand cyclometalative reactivity.
donation from the phosphinimine functionalities to a metal center.
Like the proteo derivative, the 1H and 13C{1H} NMR spectra of 11
were suggestive of C2v symmetry in solution.
X-ray quality single crystals of 11 were readily obtained from a
concentrated toluene solution at À35 °C and its molecular struc-
ture was determined. Compound 11 crystallized in the space group
ꢀ
P1 with one disordered molecule of toluene in the asymmetric
unit. The solid-state structure of 11 is depicted in Fig. 3 as a ther-
mal ellipsoid plot and selected metrical parameters are listed in
Table 3.
Compound 11 exhibits a pseudotrigonal planar lithium cation
that is coordinated by the three nitrogen atoms. Notably, the ligand
has sufficient steric bulk to saturate the coordination sphere of the
cation; as such, lithio derivative 11 is both monomeric and solvent-
free. In the solid state, the complex exhibits three N–Li contacts
that are similar to one another (N1–Li1 = 2.008(5) Å, N3–
Li1 = 2.011(5) Å, N2–Li1 = 1.945(5) Å) and short P–N bonds (P1–
N1 = 1.585(2) Å, P2–N3 = 1.570(2) Å). The P–N bonds are slightly
elongated relative to those of proteo ligand 8, but remain consis-
tent with double bond character. In the ligand, there is rotation
Scheme 3. Synthesis and decomposition of organoyttrium complex 9.
Scheme 4. Synthesis of complexes 11–13.
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K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
5
Fig. 3. Thermal ellipsoid plot (50% probability) of (L-j3N)Li (11). Hydrogen atoms
and toluene solvent molecule are omitted for clarity.
Fig. 4. Thermal ellipsoid plot (50% probability) of 13 (L-j3N)YCl2 with hydrogen
atoms and solvent molecules of crystallization omitted for clarity. The solid-state
structure of (L-j3N)ScCl2 (12) is isostructural to that of 13.
Table 3
Selected bond distances/Å, angles/° and torsion angles/° for compounds 11, 12 and 13.
11
12
13
a single resonance in its 31P{1H} NMR spectrum at d 26.4 while a
doublet at d 25.2 (2JPY = 2.3 Hz) is evident in the spectrum of 13.
Recrystallization of complexes 12 and 13 from concentrated tol-
uene solutions at À35 °C generated high quality yellow crystals
suitable for X-ray diffraction experiments. The two complexes
are isostructural and crystallized in the rhombohedral space group
P1–N1
P2–N3
N1–Ma
N3–Ma
N2–Ma
Cl1–Ma
Cl2–Ma
1.585(2)
1.570(2)
2.008(5)
2.011(5)
1.945(5)
1.619(4)
1.619(4)
2.221(3)
2.188(4)
2.200(4)
2.392(1)
2.434(1)
1.608(2)
1.615(2)
2.356(2)
2.317(2)
2.358(2)
2.532(1)
2.570(1)
–
–
ꢀ
R3 (#148). Complex 13 is depicted in Fig. 4 as a thermal ellipsoid
plot. The similar geometries of 12 and 13 are reflected in the highly
comparable metrical parameters listed in Table 3.
P1–N1–Ma
P2–N3–Ma
N2–M–N1a
N2–M–N3a
N1–M–Cl2a
N3–M–Cl2a
N2–M–Cl1a
Cl2–M–Cl1a
N1–M–Cl1a
Cl1–M–N3a
108.6(2)
121.0(2)
121.8(1)
107.7(2)
104.1(2)
103.6(2)
126.1(2)
85.3(1)
84.5(1)
88.7(1)
92.9(1)
96.9(1)
98.44(5)
111.3(1)
101.1(1)
126.3(1)
82.41(7)
81.92(8)
90.06(6)
95.93(6)
96.82(5)
99.82(3)
113.38(5)
100.52(6)
In the solid state, complexes 12 and 13 are THF-free, mono-
meric and adopt a distorted square pyramidal geometry at the
metal center defined by coordination of two chloride ligands and
the j3 bound pincer ligand. The nitrogen atoms of the ancillary
ligand (N1, N2 and N3) and one chloride (Cl2) make up the base
of the pyramid while Cl1 occupies the apical site. The bond angles
around the base of the pyramid are close to 90° (N2–Sc1–
–
–
–
–
–
–
N1–P1–C1–C2
N3–P2–C8–C7
134.6(2)
À129.4(3)
À139.1(4)
À137.6(2)
N1 = 85.3(1)°,
N2–Sc1–N3 = 84.5(1)°,
N1–Sc1–Cl2 = 88.7(1)°,
170.0(3)
168.0(2)
N3–Sc1–Cl2 = 92.9(1)°, 12; N2–Y1–N1 = 82.41(7)°, N2–Y1–N3 =
81.92(8)°, N1–Y1–Cl2 = 90.06(6)°, N3–Y1–Cl2 = 95.93(6)°, 13),
and the apical atom (Cl1) is situated close to perpendicular to this
base (average perpendicular angle = 101.9°, 12; 102.6°, 13). As
expected, the Y–Cl bond lengths (2.532(1) and 2.570(1) Å) are
slightly longer than the Sc–Cl distances (2.392(1) and
2.434(1) Å). The phosphinimine P–N contacts in 12 and 13 (ranging
a
M corresponds to the atom Li1 for compound 11, Sc1 for compound 12 and Y1
for compound 13.
of the pincer phosphinimine groups out of the plane defined by the
carbazole backbone (N1–P1–C1–C2 and N3–P2–C8–C7 torsion
angles of 134.6(2)° and À129.4(3)°, respectively). As a result of this
twisting, the lithium cation sits below the plane of the aromatic
backbone by 0.771 Å. An interesting feature in the solid-state
structure of 11 is a p-stacking interaction between the mesityl aro-
matic rings wherein they exhibit near parallel alignment with a
centroid–centroid distance of 4.156 Å.
Lithio ligand 11 was found to be thermally robust. A solution of
11 in benzene-d6 was heated to 140 °C for 48 h in a J-Young NMR
tube with no sign of decomposition. Such thermal stability is a
desirable feature because salt metathesis reactions involving bulky
ligands with rare earth metal halides often require forcing condi-
tions [14].
Lithio ligand 11 reacts readily with rare earth metal chlorides to
afford the corresponding dichloride complexes (Scheme 4). For
example, reaction of 11 with the THF adducts of scandium or
yttrium trichloride (ScCl3(THF)3 or YCl3(THF)3.5) in toluene solution
at 60 °C gave the anticipated base-free group 3 dichloride com-
plexes (L-j
3N)LnCl2 (Ln = Sc, 12; Y, 13) in good yield. The NMR
Fig. 5. Space-filling diagram of 13 (L-j3N)YCl2 with atoms drawn at their respective
van der Waals radii.
spectral properties of 12 and 13 are quite similar, with the excep-
tion of 89Y coupling observed in spectra of 13. Complex 12 exhibits
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K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
from 1.608(2) to 1.619(4) Å) are longer than those in 8 and 11
(ranging from 1.549(3) to 1.585(2) Å); this elongation is indicative
of strong electron donation of the phosphinimine functionality to
the scandium and yttrium metal centers, which is also reflected
in the downfield chemical shift of the 31P{1H} NMR resonances
(vide supra).
[16]. The reagents ScCl3(THF)3 [17], YCl3(THF)3.5 [18], Y(CH2
SiMe3)3(THF)2 [19], 1,8-dibromo-3,6-dimethylcarbazole [20],
1,8-bis(diphenylphosphino)-3,6-dimethyl-9H-carbazole [9a] and
mesityl azide [21] were prepared according to literature proce-
dures. All other reagents were obtained from commercial sources
and used as received.
A space-filling diagram of 13, depicted in Fig. 5, illustrates the
substantial steric shielding that the bulky ligand provides the
metal center. In the diagram, the metal is largely obscured by the
chloride ligands; however, coordination of the nitrogen donor
atoms to the metal is evident. The combination of phenyl and
4.2. Synthesis of compounds
4.2.1. 1,8,9N-Tris(diphenylphosphino)-3,6-dimethylcarbazole (7)
A hexane solution (1.6 M) of n-BuLi (0.38 mL, 0.608 mmol) was
added dropwise to a solution of 1,8-dibromo-3,6-dimethylcarba-
zole (0.210 g, 0.595 mmol) in diethyl ether at 0 °C. The yellow reac-
tion mixture was stirred at 0 °C for 1 h, following which, an aliquot
mesityl groups on the ancillary ligand provides
a sterically
crowded coordination pocket for the metal, essentially sandwich-
ing the chloride ligands in place. In light of the solid state structure
of complex 13, it seems probable that the instability of the fleeting
dialkyl complex (L-j3N)Y(CH2SiMe3)2 9 (which contained two ste-
rically demanding –CH2SiMe3 ligands), and its resultant cyclo-
metalative C–H bond activation chemistry, is due to steric
pressure imparted by the ancillary ligand [15].
of trimethylsilyl chloride (83 lL, 0.652 mmol) was added by micro-
syringe. The solution was warmed to ambient temperature and
stirred for 1 h to give a cloudy yellow mixture. The flask was cooled
to À78 °C and a pentane solution (1.7 M) of t-BuLi (1.5 mL,
2.55 mmol) was added dropwise via syringe. The solution was stir-
red at À78 °C for 1 h, followed by 3 h at ambient temperature and
over this time, acquired a very cloudy yellow appearance with the
formation of a thick precipitate. The flask was cooled back to
À78 °C and chlorodiphenylphosphine (3.2 mL, 1.78 mmol) was
slowly added to generate an intense orange-red colored solution.
The reaction mixture was allowed to slowly warm to ambient tem-
perature as it stirred overnight for 12.5 h and over this time
acquired a cloudy yellow appearance. The solution was filtered
through a fine porosity frit to remove insoluble byproducts and
the frit was then washed with diethyl ether (2 Â 20 mL) until the
washings were colorless. All volatile components were removed
from the clear, dark yellow filtrate under reduced pressure to
afford a yellow residue. The residue was washed with heptane
(25 mL), collected on a fine porosity frit and dried thoroughly
under vacuum. Yield: 0.224 g (50.4%). 1H NMR (chloroform-d): d
7.96 (s, 2H, Cz 4,5-CH), 7.42–7.28 (ov m, 10H, aromatic CH),
7.24–7.10 (ov m, 12H, aromatic CH), 6.96–6.90 (ov m, 10H, aro-
matic CH), 2.43 (s, 6H, CH3). 13C{1H} NMR (chloroform-d): d 139.2
(d, JCP = 5.9 Hz, aromatic ipso-C), 139.0 (d, JCP = 5.9 Hz, aromatic
ipso-C), 137.0 (dd, JCP = 6.9 Hz, JCP = 6.9 Hz, aromatic ipso-C), 136.8
(dd, JCP = 6.9 Hz, JCP = 6.9 Hz, aromatic ipso-C), 136.6 (s, aromatic
CH), 133.2 (d, JCP = 18.7 Hz, aromatic CH), 131.2 (s, aromatic ipso-
C), 130.5 (dt, JCP = 18.7 Hz, JCP = 3.1 Hz, aromatic CH), 127.8 (s, aro-
matic CH), 127.7 (s, aromatic CH), 127.7 (d, JCP = 26.1 Hz, aromatic
CH), 127.3 (s, aromatic CH), 122.6 (dd, JCP = 20.1 Hz, JCP = 3.1 Hz,
aromatic ipso-C), 121.0 (s, Cz, 4,5-CH), 21.2 (s, CH3). 31P{1H} NMR
(chloroform-d): d 53.3 (t, JPP = 69.5 Hz, 1P), 17.2 (d, JPP = 69.5 Hz,
2P). Anal. Calc. (%) for C50H40NP3: 80.31; H, 5.39; N, 1.87. Found:
C, 80.36; H, 6.14; N, 1.83.
3. Conclusions
The design and synthesis of
a new mesityl-substituted
bis(phosphinimine)carbazole pincer ligand (HL, 8) has been
described and its ability to coordinate rare earth metals was dem-
onstrated. It was found that the presence of bulky mesityl rings
afforded a sterically demanding coordination pocket for rare earth
metals and as such, ligand coordination via alkane elimination
proved to be slow. Furthermore, the high degree of steric pressure
inflicted by the ligand caused a dialkyl yttrium complex to be
highly susceptible to a cyclometalative C–H bond activation pro-
cess resulting in a doubly ortho-metalated derivative. Ligand 8
proved to be suitable for salt metathesis reactivity; the deproto-
nated compound reacted readily with the THF adducts of rare earth
trichlorides to afford dichloride complexes of the ligand in high
yield. The developed complexes acted as useful models to study
the reactivity patterns of the ancillary ligand and its ability to sup-
port rare earth metal complexes.
4. Experimental
4.1. General
All reactions were carried out under an argon atmosphere with
the rigorous exclusion of oxygen and water using standard glove-
box (MBraun) or high vacuum line techniques. The solvents diethyl
ether, pentane, heptane and toluene were dried and purified using
a solvent purification system (MBraun) and distilled under vacuum
prior to use from sodium benzophenone ketyl (diethyl ether) or
‘‘titanocene’’ indicator (pentane, heptane and toluene). Deuterated
solvents were dried over sodium benzophenone ketyl (benzene-d6)
or CaH2 (chloroform-d), degassed via three freeze–pump–thaw
cycles, distilled under vacuum, and stored over 4 Å molecular
sieves under an argon atmosphere. Samples for NMR spectroscopy
were recorded on a 300 MHz Bruker Avance II (ultrashield)
spectrometer (1H 300.13 MHz, 13C{1H} 75.47 MHz, 31P{1H}
121.49 MHz) and referenced relative to either SiMe4 through the
residual solvent resonance(s) for 1H and 13C{1H}, or to external
85% H3PO4 for 31P{1H}. All NMR spectra were recorded at ambient
temperature (25 °C) unless specified otherwise. Elemental analyses
were performed using an Elementar Americas Vario MicroCube
instrument. Despite repeated attempts, several of the rare earth
complexes consistently gave values that were low in carbon. Such
problems are well known for rare earth complexes and are gener-
ally accepted to be the result of the formation of inert carbides
4.2.2. HL (8)
Toluene (40 mL) was added to a flask charged with 1,8-
bis(diphenylphosphino)-3,6-dimethyl-9H-carbazole
(1.324 g,
2.35 mmol) to give a yellow solution. An aliquot of mesityl azide
(0.798 g, 4.95 mmol) was added via syringe at ambient tempera-
ture. Upon addition, a reaction was evident by the evolution of
nitrogen gas. The reaction mixture was stirred for 22 h under an
argon atmosphere and the solvent was removed under vacuum
to afford a yellow solid. In a glovebox, the residue was reconsti-
tuted in hot toluene (5 mL), allowed to slowly cool to ambient tem-
perature and then left at À35 °C to crystallize. The mother liquor
was decanted to allow for collection of pale yellow crystals of 8,
which were washed with pentane (5 Â 1 mL) and dried thoroughly
under reduced pressure. Yield: 1.33 g (68.1%). 1H NMR (benzene-
d6): d 12.18 (s, 1H, NH), 7.78 (m, 10H, phenyl CH + Cz 4,5-CH),
7.29 (d, 3JHP = 13.9 Hz, 2H, Cz 2,7-CH), 6.95–6.85 (m, 12H, aromatic
CH), 6.81 (s, 4H, mesityl CH), 2.27 (d, JHP = 2.6 Hz, 6H, mesityl CH3),
Please cite this article in press as: K.R.D. Johnson, P.G. Hayes, Inorg. Chim. Acta (2014), http://dx.doi.org/10.1016/j.ica.2014.05.045

K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
7
2.22 (s, 6H, Cz CH3), 1.95 (d, JHP = 1.6 Hz, 12H, mesityl CH3). 13C{1H}
NMR (benzene-d6): d 145.3 (d, JCP = 3.2 Hz, aromatic ipso-C), 141.2
(d, JCP = 3.4 Hz, aromatic ipso-C), 132.8 (s, aromatic ipso-C), 132.5
(d, JCP = 9.6 Hz, aromatic CH), 131.5 (s, aromatic ipso-C), 131.2 (d,
JCP = 2.6 Hz, aromatic CH), 129.9 (d, JCP = 8.8 Hz, aromatic CH),
128.9 (d, JCP = 3.8 Hz, aromatic CH), 128.6 (d, JCP = 12.0 Hz, aromatic
CH), 127.6 (s, aromatic ipso-C), 127.4 (d, JCP = 4.1 Hz, aromatic ipso-
C), 124.0 (d, JCP = 2.2 Hz, aromatic CH), 123.9 (d, JCP = 8.4 Hz, aro-
matic ipso-C), 117.1 (d, JCP = 106.2 Hz, aromatic ipso-C), 21.4 (s,
CH3), 21.0 (ov s, CH3), 21.0 (ov s, CH3). 31P{1H} NMR (benzene-
d6): d À6.5. Anal. Calc. (%) for C56H53N3P2: C, 81.04; H, 6.44; N,
5.06. Found: C, 81.24; H, 6.30; N, 4.73.
NMR (benzene-d6):
d
153.7 (d, JCP = 4.2 Hz, aromatic ipso-C),
144.1 (d, JCP = 7.1 Hz, aromatic ipso-C), 133.9 (d, JCP = 7.4 Hz, aro-
matic ipso-C), 132.7 (d, JCP = 9.3 Hz, aromatic CH), 132.7 (s, aro-
matic ipso-C), 131.4 (d, JCP = 2.9 Hz, aromatic CH), 129.4 (d,
JCP = 2.6 Hz, aromatic CH), 129.3 (d, JCP = 4.0 Hz, aromatic ipso-C),
128.6 (s, obscured by solvent, aromatic CH), 128.4 (s, obscured
by solvent, aromatic CH), 127.2 (s, aromatic ipso-C), 125.4 (d,
JCP = 3.3 Hz, aromatic CH), 122.4 (d, JCP = 12.6 Hz, aromatic ipso-C),
115.2 (d, JCP = 99.3 Hz, aromatic ipso-C), 21.9 (s, CH3), 21.0 (s,
CH3), 20.9 (s, CH3). 31P{1H} NMR (benzene-d6): d 11.0. Anal. Calc.
(%) for C56H52LiN3P2: C, 80.46; H, 6.27; N, 5.03. Found: C, 80.39;
H, 6.76; N, 4.26.
4.2.3. (L-j j
3N, 2C)Y(THF) (10)
In a glovebox, toluene (2 mL) was added to a 25 mL Erlenmeyer
flask charged with 8 (0.134 g, 0.161 mmol) and Y(CH2SiMe3)3(-
THF)2 (0.0795 g, 0.161 mmol) to give a clear yellow solution. The
reaction mixture was stirred at ambient temperature for 17.5 h
and gradually acquired a red color. The solution was filtered
through a bed of Celite and the Celite was washed with a further
2 mL of toluene. The clear red filtrate was concentrated to 1 mL
under vacuum and then left at À35 °C to crystallize. The mother
liquor was decanted off, leaving a yellow microcrystalline solid
that was washed with cold pentane and dried under reduced pres-
sure. Yield: 0.110 g (69.4%). 1H NMR (benzene-d6): d 7.77 (br ov m,
4.2.5. (L-j
3N)ScCl2 (12)
Toluene (25 mL) was added to a bomb charged with 11 (0.389 g,
0.466 mmol) and ScCl3(THF)3 (0.183 g, 0.499 mmol) to give an
orange suspension. The reaction mixture was heated to 100 °C
for 17 h resulting in a light orange solution with a white precipi-
tate. The solution was brought into a glovebox where it was fil-
tered through a fine porosity frit to remove LiCl. The filtrate was
concentrated under reduced pressure and left at À35 °C to crystal-
lize. Yellow crystals of 12 were collected by filtration, washed with
pentane and dried under vacuum. Yield: 0.367 g (83.3%). 1H NMR
(chloroform-d): d 8.17 (s, 2H, Cz 4,5-CH), 7.47 (m, 20H, phenyl
3
3
3
6H, 4,5-Cz CH + phenyl CH), 7.71 (dd, JHP = 7.6 Hz, JHH = 8.7 Hz,
CH), 6.85 (d, JHP = 15.2 Hz, 2H, Cz 2,7-CH), 6.55 (s, 4H, mesityl
3
2H, phenyl CH), 7.56 (d, JHH = 6.7 Hz, 2H, phenyl CH), 7.38 (dd,
CH), 2.44 (s, 6H, CH3), 2.05 (s, 6H, CH3), 1.53 (s, 12H, CH3). 13C
NMR (chloroform-d): d 151.0 (d, JCP = 4.1 Hz, aromatic ipso-C),
141.4 (d, JCP = 9.1 Hz, aromatic ipso-C), 137.0 (d, JCP = 6.0 Hz, aro-
matic ipso-C), 134.4 (d, JCP = 9.7 Hz, aromatic CH), 133.2 (d,
JCP = 4.2 Hz, aromatic ipso-C), 132.4 (d, JCP = 2.6 Hz, aromatic CH),
131.2 (d, JCP = 10.5 Hz, aromatic CH), 129.2 (d, JCP = 3.5 Hz, aromatic
CH), 128.1 (d, JCP = 12.1 Hz, aromatic CH), 127.8 (d, JCP = 96.2 Hz,
aromatic ipso-C), 126.2 (d, JCP = 13.1 Hz, aromatic ipso-C), 125.8
(d, JCP = 9.0 Hz, aromatic ipso-C), 125.0 (s, aromatic CH), 109.3 (d,
JCP = 106.5 Hz, aromatic ipso-C), 21.3 (s, CH3), 20.8 (s, CH3), 20.3
(s, CH3). 31P{1H} NMR (benzene-d6): d 26.4. Anal. Calc. (%) for C56-
H52Cl2N3P2Sc: C, 71.19; H, 5.55; N, 4.45. Found: C, 69.21; H, 5.59;
N, 4.32.
4
3JHP = 14.2 Hz, JHH = 1.3 Hz, 2H, 2,7-Cz CH), 7.18 (m, obscured by
solvent, 2H, phenyl CH), 7.11–6.90 (ov m, 8H, phenyl CH), 6.72 (s,
2H, mesityl m-CH), 6.65 (s, 2H, mesityl m-CH), 4.23 (m, 2H, OCH2-
CH2), 3.88 (m, 2H, OCH2CH2), 2.32 (s, 6H, Cz CH3), 2.10 (s, 6H, mesi-
tyl CH3), 1.97 (s, 6H, mesityl CH3), 1.74 (s, 6H, mesityl CH3), 1.22
(m, 4H, OCH2CH2). 13C{1H} NMR (benzene-d6):
d 198.1 (dd,
2
1JCY = 42.5 Hz, JCP = 38.8 Hz, C–Y), 150.6 (d, JCP = 4.9 Hz, aromatic
ipso-C), 142.3 (d, JCP = 8.0 Hz, aromatic ipso-C), 139.9 (d,
JCP = 123.4 Hz, aromatic ipso-C), 139.1 (d, JCP = 25.9 Hz, phenyl
CH), 137.7 (d, JCP = 5.6 Hz, aromatic ipso-C), 134.8 (d, JCP = 5.8 Hz,
aromatic ipso-C), 134.3 (d, JCP = 8.6 Hz, phenyl CH), 132.2 (d,
JCP = 2.0 Hz, phenyl CH), 131.4 (d, JCP = 3.9 Hz, aromatic ipso-C),
129.7 (s, Mes m-CH), 129.6 (d, JCP = 2.9 Hz, phenyl CH), 128.2 (s,
mesityl m-CH), 128.1 (d, JCP = 6.2 Hz, phenyl CH), 127.4 (d,
JCP = 3.5 Hz, phenyl CH), 127.3 (d, JCP = 10.0 Hz, Cz 2,7-CH), 126.6
(d, JCP = 9.2 Hz, aromatic ipso-C), 125.9 (d, JCP = 0.8 Hz, aromatic
ipso-C), 124.8 (d, JCP = 14.5 Hz, phenyl CH), 124.2 (d, JCP = 12.0 Hz,
aromatic ipso-C), 123.8 (d, JCP = 1.5 Hz, Cz 4,5-CH), 118.1 (d,
JCP = 94.0 Hz, aromatic ipso-C), 71.8 (s, OCH2CH2), 25.9 (s, OCH2-
CH2), 21.5 (s, Cz CH3), 21.0 (s, Mes CH3), 20.4 (s, Mes CH3), 20.3
(d, JCP = 1.2 Hz, Mes CH3). 31P{1H} NMR (benzene-d6): d 24.1 (d,
2JPY = 6.2 Hz). Anal. Calc. (%) for C60H58N3OP2Y: C, 72.94; H, 5.92;
N, 4.25. Found: C, 67.82; H, 6.39; N, 4.32.
4.2.6. (L-j
3N)YCl2 (13)
Toluene (50 mL) was added to a bomb charged with 11
(0.401 g, 0.481 mmol) and YCl3(THF)3.5 (0.226 g, 0.504 mmol) to
give a red-orange suspension. The reaction mixture was heated
to 60 °C for 95 h resulting in a light orange solution with a white
precipitate. The solution was brought into a glovebox where it
was filtered through a fine porosity frit to remove LiCl. The fil-
trate was concentrated under reduced pressure and left at
À35 °C to crystallize. Yellow crystals of 13 were collected by fil-
tration, washed with pentane and dried under vacuum. Yield:
0.343 g (72.1%). 1H NMR (chloroform-d): d 8.26 (s, 2H, Cz 4,5-
4.2.4. (L-
A hexane solution of n-BuLi (15.2 mL, 24.4 mmol) was added
dropwise over 10 min to vigorously stirred solution of
j
3N)Li (11)
3
CH), 7.42 (m, 20H, phenyl CH), 6.80 (d, JHP = 15.0 Hz, 2H, Cz
a
8
2,7-CH), 6.49 (s, 4H, mesityl CH), 2.41 (s, 6H, CH3), 2.10 (s, 6H,
CH3), 1.48 (s, 12H, CH3). 13C NMR (chloroform-d): d 151.1 (s, aro-
matic ipso-C), 138.7 (d, JCP = 8.4 Hz, aromatic ipso-C), 136.9 (d,
JCP = 6.5 Hz, aromatic ipso-C), 134.0 (d, JCP = 9.5 Hz, aromatic CH),
133.4 (d, JCP = 4.0 Hz, aromatic ipso-C), 132.5 (s, aromatic CH),
132.0 (d, JCP = 11.1 Hz, aromatic CH), 129.4 (s, aromatic CH),
128.3 (d, JCP = 12.0 Hz, aromatic CH), 128.0 (d, JCP = 96.1 Hz, aro-
matic ipso-C), 126.4 (d, JCP = 8.8 Hz, aromatic ipso-C), 125.7 (d,
JCP = 12.6 Hz, aromatic ipso-C), 125.2 (s, aromatic CH), 109.3 (d,
JCP = 107.7 Hz, aromatic ipso-C), 21.2 (s, CH3), 20.8 (s, CH3), 20.0
(10.2 g, 24.4 mmol) in heptane (200 mL) at À78 °C. The cloudy
white suspension was stirred at À78 °C for 2.5 h and then allowed
to gradually warm to 0 °C where it was stirred for a further 40 min
with the formation of a clear yellow solution and the evolution of
butane gas. The reaction mixture was allowed to warm to ambient
temperature where it was stirred for 1 h to ensure complete reac-
tion. The solvent was removed in vacuo leaving pure lithiated
ligand as an orange solid in nearly quantitative yield (10.2 g,
98.3%). 1H NMR (benzene-d6): d 8.19 (s, 2H, Cz 4,5-CH), 7.64 (m,
8H, phenyl CH), 7.13 (d, partially obscured by solvent, 2H, Cz 2,7-
CH), 6.97–6.81 (ov m, 12H, phenyl CH), 6.63 (s, 4H, mesityl CH),
2.42 (s, 6H, CH3), 2.15 (s, 6H, CH3), 2.01 (s, 12H, CH3). 13C{1H}
(s, CH3). 31P{1H} NMR (benzene-d6): d 25.2 (d, JPY = 2.3 Hz). Anal.
Calc. (%) for C56H52Cl2N3P2Y: C, 68.02; H, 5.30; N, 4.25. Found: C,
65.60; H, 5.28; N, 4.24.
2
Please cite this article in press as: K.R.D. Johnson, P.G. Hayes, Inorg. Chim. Acta (2014), http://dx.doi.org/10.1016/j.ica.2014.05.045

8
K.R.D. Johnson, P.G. Hayes / Inorganica Chimica Acta xxx (2014) xxx–xxx
Table 4
Summary of crystallography data collection and structure refinement for compounds 7, 8, 11, 12 and 13.
7
8
11
12a
13a
Formula
C50H40NP3ÁC7H8
839.87
orthorhombic
Pna21
17.4632(10)
23.0658(13)
11.4011(6)
90
90
90
4592.4(4)
4
1.215
C56H53N3P2ÁC7H8
922.09
C56H52LiN3P2ÁC7H8
928.02
C56H52Cl2N3P2ScÁ2C7H8
1036.94
C56H52Cl2N3P2YÁ2C7H8
1080.89
Formula weight (g molÀ1
Crystal system
Space group
a (Å)
)
triclinic
triclinic
rhombohedral
rhombohedral
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
R3
R3
13.702(2)
18.851(3)
20.642(3)
81.694(2)
79.290(2)
83.504(2)
5163.5(13)
4
1.186
0.127
0.24 Â 0.12 Â 0.07
1.52–27.10
74246
13.695(3)
14.183(3)
14.978(3)
113.836(2)
102.657(2)
92.431(2)
2568.4(8)
2
1.200
0.128
0.40 Â 0.22 Â 0.19
1.59–26.45
27644
23.6675(10)
23.6675(10)
23.6675(10)
107.38
107.38
107.38
10923.1(8)
6
0.946
23.7063(8)
23.7063(8)
23.7063(8)
107.28
107.28
107.28
11008.1(6)
6
0.978
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
Dcalc (g cmÀ3
)
l
(mmÀ1
)
0.169
0.250
0.943
Crystal size (mm3)
0.29 Â 0.19 Â 0.17
1.77–27.10
50663
0.32 Â 0.23 Â 0.07
1.68–27.10
122009
0.39 Â 0.35 Â 0.23
1.85–27.10
123788
h range (°)
N
Nind
10146
22697
10519
16076
16199
Data/restraints/parameters
10146/1/553
1.036
0.0433
0.1067
0.0559
0.1149
0.427 and À0.282
22697/0/1213
0.973
0.0753
0.1360
0.1915
0.1754
1.064 and À0.396
10519/232/684
1.003
0.0592
0.1449
0.1065
0.1706
1.153 and À0.432
16076/44/637
0.876
0.0728
0.1646
0.2047
0.2012
0.887 and À0.495
16199/0/649
1.074
0.0479
0.1455
0.0738
0.1561
0.547 and À0.411
Goodness-of-fit (GoF) on F2
R1 (I > 2
r
(I))b
r
wR2 (I > 2
(I))c
R1 (all data)b
wR2 (all data)c
D
qmax and
D
qmin (e ÅÀ3
)
a
The structure contained two toluene molecules in the asymmetric unit, one of which was severely disordered. In addition, a void existed in the unit cell that contained
highly disordered and unidentifiable solvent. The electron density associated with the disordered solvent regions was removed from the reflection file using the SQUEEZE
subroutine of PLATON
.
P
P
b
R1
=
||Fo| À |Fc||/ |Fo|.
P
P
c
wR2 = { [w(F2o À F2c)2]/ [w(F2o)2]}1/2
.
4.3. X-ray crystallography
both unit cells of 12 and 13 that contained highly disordered sol-
vent. The electron density associated with the disordered regions
was removed using the SQUEEZE subroutine of PLATON [26].
4.3.1. General crystallographic details for 7, 8, 11, 12 and 13
Recrystallization of compounds 7, 8, 11, 12 and 13 from concen-
trated toluene solutions at À35 °C afforded single crystals suitable
for X-ray diffraction. Crystals were coated in dry Paratone oil under
an argon atmosphere and mounted onto a glass fiber. Data were
collected at À100 °C using a Bruker SMART APEX II diffractometer
Acknowledgements
This research was financially supported by the Natural Sciences
and Engineering Research Council (NSERC) of Canada and the Can-
ada Foundation for Innovation (CFI). Prof. Jun Okuda and RWTH
Aachen University are thanked for hosting PGH during the prepa-
ration of this manuscript.
(Mo K
a radiation, k = 0.71073 Å) outfitted with a CCD area-detec-
tor and a KRYO-FLEX liquid nitrogen vapor cooling device. A data
collection strategy using and scans at 0.5° steps yielded full
x
u
hemispherical data with excellent intensity statistics. Unit cell
parameters were determined and refined on all observed reflec-
tions using APEX2 software [22]. Data reduction and correction for
Lorentz polarization were performed using SAINT-Plus software
[23]. Absorption corrections were applied using SADABS [24]. The
structures were solved by direct methods and refined by the least
squares method on F2 using the SHELXTL software suite [25]. All non-
hydrogen atoms were refined anisotropically, except for a certain
case of disorder in 8 (discussed vide infra). Hydrogen atom posi-
tions were calculated and isotropically refined as riding models
to their parent atoms. Details of the data collection and refinement
are given in Table 4. Special considerations were required in the
refinement of disordered moieties in the structures of 8, 11, 12
and 13. In the structure of 8, a toluene solvent molecule was disor-
dered over two positions (C1c, 54%/C1d, 46%) and held isotropic.
The disordered phenyl ring of this solvent was constrained to a reg-
ular hexagon with CÀC bond lengths of 1.39 Å. In the refinement of
11, a toluene solvent molecule was disordered over two positions
(C1s, 73%/C1r, 27%) and both components were modeled aniso-
tropically. Some geometric and displacement restraints were
applied in order to obtain reasonable bond distances and angles.
The structures of 12 and 13 both contained a severely disordered
toluene molecule in the asymmetric unit, for which no suitable
model could be found. Additionally, a solvent channel existed in
Appendix A. Supplementary materials
CCDC 998405–998409 contains the supplementary crystallo-
graphic data for compounds 7, 8, 11, 12 and 13, respectively. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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