Synthesis and reactivity of dialkyl lutetium complexes supported by a novel bis(phosphinimine)carbazole pincer ligand

Article abstract of DOI:10.1021/om900731x

The synthesis of a novel bis(phosphinimine) ancillary ligand based on a carbazole framework is described (HL^Ph, 4a; HL^Pipp, 4b; Ph = phenyl, Pipp = para-isopropylphenyl). Protonolysis with Lu(CH ₂SiMe₃)₃(THF)₂ afforded the corresponding lutetium dialkyl complexes (LuL^Ph(CH ₂SiMe₃)₂, 5a; LuL^Pipp(CH ₂SiMe₃)₂, 5b), which were thermally sensitive and rapidly underwent intramolecular metalative alkane elimination to generate LuL^Ph*(CH₂SiMe₃)(THF), 6a, and LuL ^Pipp*(CH₂SiMe₃)(THF), 6b, as highly reactive intermediates. Complexes 6a and 6b further decomposed, cleanly generating doubly metalated complexes LuL^Ph**(THF), 7a, and LuL^Pipp**(THF), 7b, respectively, as the thermodynamic products. Kinetic analysis of the decomposition of 5a revealed a first-order mechanism with activation parameters ΔH? = 19.2(1) kcal.mol^-1 and ΔS? = -8.2(2) Cal.K^-1.mol ^-1. Compounds 4a, 4b, 6b, and 7b were characterized by single-crystal X-ray diffraction studies.

Full text of DOI:10.1021/om900731x

6352 Organometallics 2009, 28, 6352–6361
DOI: 10.1021/om900731x
Synthesis and Reactivity of Dialkyl Lutetium Complexes Supported by a
Novel Bis(phosphinimine)carbazole Pincer Ligand
Kevin R. D. Johnson and Paul G. Hayes*
Department of Chemistry and Biochemistry, University of Lethbridge, 4401 University Drive, Lethbridge,
AB, Canada, T1K 3M4
Received August 20, 2009
The synthesis of a novel bis(phosphinimine) ancillary ligand based on a carbazole framework is
described (HLPh, 4a; HLPipp, 4b; Ph=phenyl, Pipp=para-isopropylphenyl). Protonolysis with Lu-
(CH2SiMe3)3(THF)2 afforded the corresponding lutetium dialkyl complexes (LuLPh(CH2SiMe3)2, 5a;
LuLPipp(CH2SiMe3)2, 5b), which were thermally sensitive and rapidly underwent intramolecular
metalative alkane elimination to generate LuLPh*(CH2SiMe3)(THF), 6a, and LuLPipp*(CH2SiMe3)-
(THF), 6b, as highly reactive intermediates. Complexes 6a and 6b further decomposed, cleanly
generating doubly metalated complexes LuLPh**(THF), 7a, and LuLPipp**(THF), 7b, respectively, as
the thermodynamic products. Kinetic analysis of the decomposition of 5a revealed a first-order
mechanism with activation parameters ΔHq=19.2(1) kcal mol-1 and ΔSq=-8.2(2) cal K-1 mol-1
.
3
3
3
Compounds 4a, 4b, 6b, and 7b were characterized by single-crystal X-ray diffraction studies.
Introduction
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Published on Web 10/13/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 21, 2009 6353
of organolanthanide chemistry,8 it is limited in the extent to
which it can be electronically or sterically tuned.9 Thus, the
development of more versatile ancillary ligands may provide
access to metal complexes with unique structure, reactivity,
and enhanced catalytic activity. Herein, we report the synth-
esis of a novel family of monoanionic carbazole-based pincer
ligands and their ability to support well-defined monomeric
organolutetium complexes.
blocking Lewis bases such as tetrahydrofuran (THF) from
binding to the metal center. The presence of sterically
demanding groups can also help to reduce the potential for
dimerization; however, the degree of incorporated bulk must
be carefully selected so as to not completely inhibit reactivity
at the metal center.
The high-yielding synthesis of the dmc-based ancillary is
outlined in Scheme 1. From 1,8-dibromo-3,6-dimethylcar-
bazole,13 N-protection with tert-butoxycarbonyl afforded 1,
which was lithiated and allowed to react with chlorodiphe-
nylphosphine to generate the corresponding diphosphine 2.
Removal of the protecting group was efficiently achieved
under thermal conditions14 (160 °C for 4.5 h), liberating
deprotected compound 3. The synthesis of the desired proteo
ligand (HLPh, 4a; HLPipp, 4b; Ph = phenyl; Pipp = para-
isopropylphenyl) was completed by reaction of 3 with an
appropriate aryl azide under standard Staudinger condi-
tions,15 installing the phosphinimine functionality with con-
comitant loss of N2. This four-step synthetic pathway is
highly efficient with overall yields of 73% (4a) and 53% (4b).
Single crystals of 4a suitable for an X-ray diffraction study
were readily obtained upon recrystallization from a benzene
solution layered with pentane at ambient temperature. The
molecular structure of 4a is illustrated in Figure 1 as a
thermal ellipsoid plot. Ligand 4a was designed to chelate
metals in a tridentate motif with N1, N2, and N3 occupying a
common plane with the aromatic dmc backbone. In the solid
state, N1 indeed lies approximately within the same plane as
the dmc backbone (N1-P1-C1-C12 torsion angle of
-11.1(4)°). However, N3 lies significantly out of this plane
with an N3-P2-C8-C9 torsion angle of 68.4(4)°. The
rotation of the P2-N3 arm out of the plane of the dmc
backbone is likely due to steric interactions between the two
N-phenyl groups on the phosphinimine moiety. It is possible
that in the solid state N1 lies within the plane of the dmc
backbone due to the hydrogen-bonding interaction that
exists between it and H2C. The distance between the donor
Results and Discussion
Ligand Synthesis and Characterization. A novel monoa-
nionic ligand has been prepared whereby two phosphinimine
donors have been installed at the 1 and 8 positions of a rigid
3,6-dimethylcarbazole (dmc) backbone. The presence of
polar phosphinimine subunits is desirable, as they have been
shown to provide ancillary ligands with enhanced capacity
for electronic donation.10-12 Furthermore, the phosphini-
mine functionality allows for a high degree of steric and
electronic tunability through adjustment of R groups at-
tached at the phosphorus and nitrogen atoms. In particular,
the incorporation of sufficient steric bulk may assist in
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and acceptor nitrogen atoms in the N2-H2C N1 inter-
3 3 3
˚
action in 4a is 2.789(5) A.
Similar to 4a, single crystals of 4b were obtained from a
concentrated benzene solution layered with pentane. The
molecular structure of 4b, as determined from an X-ray
diffraction experiment, is depicted in Figure 2. Analogous
to that described for 4a, ligand 4b has one nitrogen donor
(N1) lying in the same plane as the dmc backbone and one
(N3) out of the plane. The N1-P1-C1-C12 and
N3-P2-C8-C9 torsion angles of 7.8(2)° and -70.7(2)°,
respectively, correspond well with that observed for 4a. In
comparison to that of 4a, the N3 group in 4b is rotated about
2° further out of plane from the aromatic backbone, while
the N1 group is approximately 2° closer to the plane of the
dmc backbone. This small, but statistically relevant differ-
ence may be attributed to the presence of the isopropyl
groups in the para positions of the N-aryl rings of 4b, which
create slightly greater steric repulsion between the N-aryl
rings. It is notable that only minor differences in the geome-
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Synthesis 2000, 14, 2085–2091.

6354 Organometallics, Vol. 28, No. 21, 2009
Johnson and Hayes
Scheme 1. Synthesis of (ArNdPPh2)2(dmc) Ancillary Ligand 4
Scheme 2. Synthesis of Organolutetium Complexes 5a and 5b
the identical reaction rates of ligand metalation observed for
complexes 5a and 5b (vide infra).
Proteo ligands 4a and 4b are both C2v symmetric on the
NMR time scale. Each ligand exhibits a sharp singlet (δ 5.41,
4a; δ 11.7, 4b) in its 31P{1H} NMR (CDCl3) spectrum. The
1H NMR spectrum of 4a (CDCl3) has a single methyl reso-
nance at δ 2.44, a broad NH peak at δ 11.8, and an expectedly
complicated aromatic region. Similarly, the 1H NMR spec-
trum of 4b (CDCl3) displays a singlet at δ 2.45 corresponding
to the symmetric methyls of the dmc backbone and a broad
NH signal at δ 11.7. The 1H NMR spectrum of 4b also fea-
tures isopropyl resonances at δ 2.74 (sp, CH) and δ 1.17 (d,
CH3) in addition to a well-defined AB spin pattern (δ 6.74, d;
δ 6.64, d) corresponding to protons on the N-aryl rings.
Organolutetium Reactivity. Complexation with lutetium
was readily achieved via the alkane elimination reaction of
Lu(CH2SiMe3)3(THF)2 with 4a or 4b (Scheme 2). When
equimolar quantities of 4 and Lu(CH2SiMe3)3(THF)2 were
reacted in cold (-78 °C) toluene-d8, the corresponding dial-
Figure 1. Thermal ellipsoid plot (50% probability) of HLPh (4a)
with hydrogen atoms (except H2A) and solvent molecules of
˚
crystallization omitted for clarity. Selected bond distances (A)
and angles (deg): P1-N1=1.581(4), P2-N3=1.570(4), N1-
P1-C1 = 107.2(2), N3-P2-C8 = 106.0(2), C27-N1-P1 =
126.7(3), C45-N3-P2 = 131.3(4).
kyl metal complexes LuLPh(CH2SiMe3)2, 5a, and LuLPipp
-
(CH2SiMe3)2, 5b, began to cleanly form as highly thermally
sensitive compounds. Upon warming the solution to 0 °C,
complete conversion to dialkyl 5 was achieved, as evidenced
by consumption of the sparingly soluble proteo ligand and
formation of a clear yellow solution. Accordingly, when the
reaction was monitored in situ, the generation of 1 equiv of
1
Figure 2. Thermal ellipsoid plot (50% probability) of HLPipp
(4b) with hydrogen atoms (except H2C) and solvent molecules
˚
of crystallization omitted for clarity. Selected bond distances (A)
and angles (deg): P1-N1=1.574(2), P2-N3=1.575(2), N1-
P1-C1 = 105.3(1), N3-P2-C8 = 106.8(1), C27-N1-P1 =
128.8(2), C48-N3-P2 = 127.0(2).
tetramethylsilane was observed by H NMR spectroscopy.
Due to the thermal sensitivity of dialkyl species 5a and 5b,
neither complex could be isolated as a pure solid. All
attempts to do so resulted in samples contaminated with
the thermodynamic decomposition product 7 (vide infra).
However, both complexes were quantitatively generated

Article
Organometallics, Vol. 28, No. 21, 2009 6355
Figure 3. Stacked plot of 31P{1H} NMR spectra (toluene-d8) depicting the decomposition of 5a to 7a (via intermediate 6a) at 293.5 K
from t = 1760 s to t = 15 500 s.
Scheme 3. Intramolecular Decomposition of Dialkyl Complex 5 to Doubly Metalated Complex 7
in situ at low temperature and used in this form to further
investigate reactivity. Complexes 5a and 5b were fully char-
acterized by multinuclear NMR spectroscopy at low tem-
perature with no sign of decomposition over the course of the
experiments.
a σ-bond metathesis pathway with the ortho C-H bonds of
the adjacent P-phenyl rings. Upon monitoring the decom-
1
position of 5 by H and 31P{1H} NMR spectroscopy, the
formation of an asymmetric intermediate with C1 symmetry
was observed (Scheme 3). This transient species, assigned as
monometalated complex 6, then undergoes a second intra-
molecular σ-bond metathesis process with a phenyl group
from the other phosphinimine phosphorus (vide infra), re-
leasing a second equivalent of tetramethylsilane. The final C2
symmetric products 7a and 7b are the result of a rare double-
metalation process. These κ5-bound lutetium diaryl species
consist of two six-membered metallacycles complete with
bridging phenyl rings.
The 1H NMR spectra of 5 in toluene-d8 exhibit diagnostic
methyl and methylene resonances upfield of 0 ppm for the
protons of the trimethylsilylmethyl groups (5a, 271.3 K: δ
-0.06 (CH3), -0.79 (CH2); 5b, 249.1 K: δ -0.01 (CH3),
-0.72 (CH2)). Upon cooling solutions of 5a or 5b below
-60 °C the two trimethylsilylmethyl moieties become in-
equivalent with splitting of the methylene resonances, in-
dicating a reduction in molecular symmetry from C2v to Cs.
In the 31P{1H} NMR spectra (toluene-d8), a significant
downfield shift of the phosphinimine resonance is observed
upon complexation with lutetium (5a, 271.3 K: δ 29.6; 5b,
249.1 K: δ 29.4). As the phosphinimine functionality is
highly sensitive to its coordination environment, the large
downfield shift is indicative of complexation with the elec-
tropositive lutetium center.10-12 In addition, the sharp single
resonance in the 31P{1H} NMR spectrum corroborates that
the ancillary is bound to lutetium in a κ3-coordination mode.
Although 2 equiv of THF are present in the in situ-generated
reaction mixture, it appears that the dialkyl lutetium com-
plex is five-coordinate with no THF donors bound to the
metal. Specifically, toluene-d8 solutions of 5 at temperatures
between -40 and 0 °C (the range in which 5 is relatively
thermally stable) exhibit resonances in the 1H and 13C{1H}
NMR spectra consistent with free THF.
The loss of symmetry in the final thermodynamic pro-
ducts, 7a and 7b, compared to the initial dialkyl complexes
1
(5a and 5b), was difficult to ascertain through H NMR
spectroscopy due to overlapping signals in the aromatic
region of the spectrum. However, 13C{1H} NMR spectros-
copy proved to be diagnostic in this regard. The metalated
ipso carbon attached directly to lutetium is highly deshielded
and resonates far downfield as a doublet of doublets at δ
204.6 (dd, 2JPC = 41.2 Hz, 4JPC = 1.1 Hz, 7a) and δ 204.7
(2JPC = 40.9 Hz, 4JPC = 1.2 Hz, 7b). Such values correspond
well with the shifts reported for other neutral lutetium aryl
species such as LuPh3(THF)2 (δ 198.7, benzene-d6),16 Lu(p-
tol)3(THF)2 (δ 195.2, benzene-d6),16 Lu(C6H4-p-Et)3(THF)2
(δ 194.2, benzene-d6),16 (Cp*)2LuPh (δ 198.5, cyclohexane-
d12),17 and Lu(o-C6H4CH2NMe2)3 (δ 196.7, benzene-d6).18
(16) Zeimentz, P. M.; Okuda, J. Organometallics 2007, 26, 6388–6396.
(17) Watson, P. L. J. Chem. Soc., Chem. Commun. 1983, 276–277.
(18) Wayda, A. L.; Atwood, J. L.; Hunter, W. E. Organometallics
1984, 3, 939–941.
At temperatures above 0 °C, toluene solutions of 5 under-
go two sequential intramolecular metalative alkane elimina-
tions whereby both alkyl groups are liberated as RH through

6356 Organometallics, Vol. 28, No. 21, 2009
Johnson and Hayes
Figure 4. (a) First-order plots of the metalation of 5a at various
temperatures. (b) Eyring plot for the metalation of 5a.
Figure 6. (a) Thermal ellipsoid plot (50% probability) of
LuLPipp**(THF) (7b) with hydrogen atoms and solvent molecules
˚
of crystallization omitted for clarity. Selected bond distances (A)
and angles (deg): Lu1-N1=2.293(6), Lu1-N3=2.285(6), Lu1-
N2=2.343(6), Lu1-C26=2.472(8), Lu1-C47=2.431(8), Lu1-
O1=2.30(1), P1-N1=1.619(6), P2-N3=1.607(7), N1-Lu1-
N3=166.3(2), C26-Lu1-C47=176.4(3), N2-Lu1-O1=174.6(4).
(b) Thermal ellipsoid plot (50% probability) of LuLPipp**(THF)
(7b0) with hydrogen atoms and solvent molecules of crystallization
˚
omitted for clarity. Selected bond distances (A) and angles (deg):
Lu1A-N1A=2.291(6), Lu1A-N3A=2.298(6), Lu1A-N2A=
2.349(6), Lu1A-C26A=2.450(8), Lu1A-C47A=2.425(8), Lu1A-
O1A = 2.35(2), P1A-N1A = 1.606(6), P2A-N3A = 1.612(6),
N1A-Lu1A-N3A =167.3(2), C26A-Lu1A-C47A= 178.1(2),
N2A-Lu1A-O1A = 174.2(6).
Kinetic Analysis. The decomposition from derivative 5a to
6a was quantitatively monitored by 31P{1H} NMR spectro-
scopy and revealed to be first order in the dialkyl species. The
reaction progress at 293.5 K (from t = 1760 s to t = 15 500 s)
is depicted in Figure 3 as a stacked plot of 31P{1H} NMR
spectra. As can be seen from the plot, the decreasing con-
centration of 5a (δ 29.4) is accompanied by the growth of two
broad peaks resonating at δ 27.5 and 22.7 for asymmetric
intermediate 6a. Within 4 h at this temperature complex 6a
gradually converts exclusively to thermodynamic product 7a
(δ 25.6).
Figure 5. Thermal ellipsoid plot (50% probability) of LuLPipp*
(CH2SiMe3)(THF) (6b) with hydrogen atoms omitted for clarity.
-
Table 1. Observed Rate Constants for the Intramolecular Meta-
lation of Compounds 5a and 5b to 6a and 6b at Temperatures
Ranging from 282.4 to 326.9 K
compound
T/K
kobs/s-1
t1/2/s
5a
5a
5a
5a
5a
5a
5b
282.4
293.5
295.7
304.6
315.7
326.9
295.7
1.22 ꢀ 10-4
4.37 ꢀ 10-4
5.89 ꢀ 10-4
1.71 ꢀ 10-3
4.46 ꢀ 10-3
1.55 ꢀ 10-2
5.98 ꢀ 10-4
5690
1590
1180
405
155
44.7
1160
The reaction was followed over a broad range of tempera-
tures (282.4 to 326.9 K; Figure 4a), with observed t1/2 values
ranging from 5690 to 44.7 s (Table 1). Construction of
an Eyring plot (Figure 4b) allowed for extraction of the

Article
Organometallics, Vol. 28, No. 21, 2009 6357
Table 2. Summary of Crystallography Data Collection and Structure Refinement for Compounds 4a, 4b, 6b, and 7b
4aa
4bb
6b
7bc
formula
fw/g mol-1
cryst syst
C56H47N3P2
823.91
triclinic
P1
9.018(3)
14.813(4)
19.162(6)
103.236(4)
99.522(4)
106.150(4)
2320.5(12)
2
C68H65N3P2
986.17
triclinic
C64H70LuN3OP2Si
1162.23
monoclinic
P21/n
10.7680(13)
21.278(3)
26.917(3)
90
99.461(2)
90
6083.3(13)
4
1.269
1.736
2392
C138H134Lu2N6O2P4
2382.33
monoclinic
P21/n
10.9319(9)
44.979(4)
24.495(2)
90
99.5860(10)
90
11876.1(17)
4
1.332
1.761
4888
3
space group
˚
P1
a/A
8.9413(6)
16.6229(12)
19.4273(14)
77.5770(10)
80.3780(10)
78.8940(10)
2743.2(3)
2
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
volume/A
Z
Dcalc/mg m-3
1.179
0.134
868
1.194
0.124
1048
3
μ/mm-1
F000
cryst size /mm
cryst color
cryst habit
0.24 ꢀ 0.13 ꢀ 0.082
colorless
plate
0.25 ꢀ 0.14 ꢀ 0.055
pale green
plate
0.19 ꢀ 0.17 ꢀ 0.072
yellow-green
block
0.38 ꢀ 0.078 ꢀ 0.035
green-yellow
needle
θ range/deg
N
Nind
1.59-26.37
31 432
9473
1.82-25.03
33 540
9677
2.14-20.82
68 237
6349
1.69-26.37
158 092
24 286
completeness to θ = 27.10°
Tmax; Tmin
99.7%
99.8%
99.7%
99.9%
0.7456; 0.6744
9473/0/553
0.809
0.0763
0.1221
0.7456; 0.6894
9677/2/664
1.033
0.0518
0.1232
0.7456; 0.6019
6349/4/318
1.060
0.0994
0.2487
0.7456; 0.6455
24 286/7/1299
1.111
0.0790
0.1395
data/restraints/params
GoF on F2
R1d (I > 2σ(I))
wR2e (I > 2σ(I))
ΔFmax and ΔFmin/e A
-3
˚
0.259; -0.260
0.470; -0.411
5.600; -2.051
2.559; -2.021
3
a Crystallized with one molecule of benzene in the asymmetric unit. b Crystallized with two molecules of benzene in the asymmetric unit. c Crystallized
P
with two independent molecules of 7b, three molecules of benzene, and one disordered molecule of pentane in the asymmetric unit; d R1 =
Fo| - |Fc /
P
P
P
|Fo|. e wR2 = { [w(Fo2 - Fc2)2]/ [w(Fo2)2]1/2
.
activation parameters, ΔHq = 19.2(2) kcal mol-1 and
resonances for the N-aryl ring compared to that available for
5a. Furthermore, the solid state structures of proteo ligands,
4a and 4b, which were used to prepare 5a and 5b, were
essentially isostructural (vide supra).
3
ΔSq= -8.2(2) cal K-1 mol-1, for the metalation process.
3
3
These values correspond to that expected for a highly
ordered four-centered transition state16,19 and agree well
with others reported for intramolecular σ-bond metathesis
reactions.20
Solid State Structures. In order to unambiguously estab-
lish that the C-H bond activation of the ancillary ligand
occurred through the ortho carbon of the phenyl rings on
phosphorus, single-crystal X-ray diffraction studies were
performed. Crystals of 6b were serendipitously obtained
from an in situ-generated solution of 5b in a 4:1 mixture of
toluene and THF at -35 °C over the course of ∼1 week. As
5b slowly decomposed at this temperature, intermediate 6b
selectively crystallized out of solution. Under these dynamic
and highly variable conditions the single crystallinity of 6b
was of low quality, and repeated attempts to grow higher
quality crystals of this unstable intermediate were unsuccess-
ful. Despite the challenges encountered with crystal quality,
a reliable set of low-intensity single-crystal data was obtained
for complex 6b. Such data were sufficient for unambiguously
establishing the connectivity of the structure; however, no
meaningful comments on the metrical parameters can be
made at this time.
A thermal ellipsoid plot of 6b is depicted in Figure 5. The
solid state structure confirms that the ligand is bound to
lutetium in a κ4-fashion, binding through three nitrogen
atoms, as well as via an ortho carbon of one P-phenyl ring.
One trimethylsilylmethyl group remains attached to lutetium
as well as one THF donor, giving rise to a structure with
distorted octahedral geometry. This structural information
corroborates the postulated intermediate in the conversion
of dialkyl complex 5b to diaryl species 7b (Scheme 3). Due to
the very small (<10 mg) crop of crystals obtained from the
crystallization of 6b, insufficient material was available for
further characterization.
Kinetic data for the conversion of 6a to 7a was not
ascertained due to problems in accurately determining the
concentration of 6a over the course of decomposition. Such
difficulty stemmed from the broad peaks for 6a in the 31P-
{1H} NMR spectra, which could not be reproducibly inte-
grated due to the low signal-to-noise ratio. In addition,
certain temperature ranges gave rise to an overlap of reso-
nances for 6a and 7a. As such, the sum of the concentration
of 6a and 7a could be readily determined at those tempera-
tures; however, it was not always possible to establish the
concentration of each individual species without introducing
significant error.
At 295.7 K, metalation of 5a proceeds at a rate of 5.89 ꢀ
10-4 s-1, while that for 5b was found to be 5.98 ꢀ 10-4 s-1
(Table 1). The high degree of correlation between these two
rates suggests that the presence of the isopropyl groups in the
para positions of the N-aryl rings of 5b does not significantly
alter reactivity. This result was anticipated, as the incor-
poration of isopropyl groups on 5b was intended solely for
the purposes of (a) increasing solubility, (b) increasing
1
crystallinity, and (c) providing more diagnostic H NMR
(19) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am.
Chem. Soc. 1987, 109, 203–219.
(20) (a) Hayes, P. G.; Piers, W. E.; Parvez, M. Organometallics 2005,
24, 1173–1183. (b) Conroy, K. D.; Hayes, P. G.; Piers, W. E.; Parvez, M.
Organometallics 2007, 26, 4464–4470. (c) Hayes, P. G.; Piers, W. E.; Lee, L.
W. M.; Knight, L. K.; Parvez, M.; Elsegood, M. R. J.; Clegg, W. Organo-
metallics 2001, 20, 2533–2544.

6358 Organometallics, Vol. 28, No. 21, 2009
Johnson and Hayes
In contrast to the unstable nature of 6b, diaryl lutetium 7b
can easily be prepared on a multigram scale. Reaction of 4b
with Lu(CH2SiMe3)3(THF)2 in benzene for 18 h at ambient
temperature generated 7b, which was isolated as a pure
yellow crystalline solid. Recrystallization from a benzene
solution layered with pentane at ambient temperature af-
forded large needles of 7b, which were suitable for X-ray
diffraction. It was found that complex 7b crystallized with
two independent molecules in the asymmetric unit, in addi-
tion to a variety of solvent molecules. These independent
structures, 7b and 7b0, are enantiomers of one another and
are depicted as thermal ellipsoid plots in Figure 6a and b,
respectively.
Experimental Section
General Procedures. All reactions were carried out under an
argon atmosphere with the rigorous exclusion of oxygen and
water using standard glovebox (MBraun) or high vacuum line
techniques, unless specified otherwise. The solvents THF, di-
ethyl ether, dichloromethane (DCM), pentane, benzene, and
toluene were dried and purified using a solvent purification
system (MBraun) and stored in evacuated 500 mL bombs over
sodium benzophenone ketyl (THF and ether), CaH2 (DCM), or
“titanocene” (pentane, benzene, and toluene). Deuterated sol-
vents were dried over sodium benzophenone ketyl (benzene-d6
and toluene-d8) or CaH2 (CDCl3), degassed via three free-
ze-pump-thaw cycles, distilled under vacuum, and stored in
glass bombs under argon. Unless otherwise specified, all sol-
vents required for air-sensitive manipulations were introduced
directly into the reaction flasks by vacuum transfer with con-
densation at -78 °C. For air-stable manipulations, the solvents
THF, diethyl ether, DCM, and n-hexane were purchased from
EMD Chemicals and used without further purification. Samples
for NMR spectroscopy were recorded on a 300 MHz Bruker
Avance II (Ultrashield) spectrometer (1H 300.138 MHz, 13C-
{1H} 75.468 MHz, 31P{1H} 121.495 MHz) and referenced
relative to either SiMe4 through the residual solvent resonance-
(s) for 1H and 13C{1H} or external 85% H3PO4 for 31P{1H}. All
NMR spectra were recorded at ambient temperature (295 K)
unless specified otherwise. FT-IR spectra were recorded on a
Bruker ALPHA FT infrared spectrometer with Platinum ATR
sampling. Elemental analyses were performed using an Elemen-
tar Americas Vario MicroCube instrument. Phenyl azide,23
1,8-dibromo-3,6-dimethylcarbazole,13 and Lu(CH2SiMe3)3-
(THF)224 were prepared according to literature procedures. The
compound 4-isopropylphenyl azide was prepared according to a
modified literature procedure.25 Chlorodiphenylphosphine was
purchased from Strem Chemicals and used as received. All
deuterated solvents were purchased from Cambridge Isotope
Laboratories. All other reagents were obtained from Aldrich
Chemicals or Alfa Aesar and used as received.
0
˚
At ∼1.61 A, complexes 7b and 7b exhibit P-N bonds
that are elongated relative to that of the free ligand (average
˚
P-N = 1.575 A). Such lengthening is indicative of strong
donation from the phosphinimine functionality to the metal
center; however, such a distance is still consistent with a
formal phosphorus-nitrogen double bond.11c The Lu-Caryl
0
0
˚
contacts in 7b and 7b range from 2.425(8) A in 7b to 2.472(8)
˚
A in 7b. These values fall within the normal range for neutral
Lu-Caryl bonds.11a,b,18,21 Complexes 7b and 7b0 both exhibit
distorted octahedral geometry at the lutetium center, with
the ancillary ligand occupying five of the six coordination
sites. The sixth site composing the octahedron is occupied by
a THF donor. No attempt has yet been made to remove or
exchange the coordinated Lewis base. Future work will
explore such processes and investigate the exciting possibility
that 7b may serve as a low-valent (Lu(I)) synthon (via
metalation reversal promoted by reaction with reagents of
the form H2ER or H2SiR2 (E=N, P; R=sterically bulky
group)).22
Concluding Remarks
4-Isopropylphenyl Azide. Aqueous 5 M HCl (125 mL) was
added dropwise to a clear dark red solution of 4-isopropylani-
line (10.0 g, 74.2 mmol) in THF (100 mL) at 0 °C. The red-brown
solution was stirred for 15 min, following which a solution of
NaNO2 (5.63 g, 81.6 mmol) in H2O (65 mL) was added dropwise
over 20 min. Urea (0.708 g, 11.8 mmol) was added as a solid to
remove excess nitrous acid. A solution of NaN3 (5.65 g, 87.0
mmol) in H2O (50 mL) was added very slowly at 0 °C, after
which the solution was stirred at this temperature for a further 2
h. The product was extracted into Et2O (3 ꢀ 100 mL), and the
organic layer was washed with 1ꢀ100 mL of 1 M HCl, dried
over MgSO4, and concentrated in vacuo to give a dark red liquid.
The product was purified by filtration through a silica column
(20 cm), eluting with hexane. The hexane was removed from the
eluent by rotational evaporation, leaving PippN3 as a canary
yellow liquid. Yield: 10.4 g (86.7%). 1H NMR (CDCl3): δ 7.21
(d, 2H, J = 8.4 Hz, Ar-H), 6.96 (d, 2H, J = 8.4 Hz, Ar-H),
2.90 (sp, 1H, J = 6.9 Hz, CH), 1.24 (d, 6H, J = 6.9 Hz, CH3).
13C{1H} NMR (CDCl3): δ 145.9, 137.5, 127.9, 119.1 (Ar-Cs),
33.7 (CH), 24.2 (CH3). IR (neat): 2960 (m), 2128 (s), 2092 (s),
In summary, the synthesis and characterization of a
versatile family of pincer ligands, which represent a new
platform for stabilizing low-coordinate, electronically un-
saturated organometallic species, have been described. These
carbazole-based ligands have been utilized to prepare mon-
omeric base-free dialkyl lutetium complexes. Although these
highly electrophilic complexes are thermally sensitive and
undergo a rare double-metalative mechanism with the ortho
C-H bonds of the P-phenyl rings, it is likely that minor
structural modifications will yield complexes that are suffi-
ciently stable to allow full exploration of their organometal-
lic chemistry. As such, we are currently reducing the steric
bulk around the peripheral edge of the ligand. It is antici-
pated that replacement of the phenyl groups attached to
phosphorus with a less bulky moiety will dampen undesired
metalation pathways.
€
(21) (a) Rufanov, K. A.; Muller, B. H.; Spannenberg, A.; Rosenthal,
1506 (s), 1292 (s), 828 (s), 756 (m), 728 (m), 619 (m), 539 (s) cm-1
.
U. New J. Chem. 2006, 30, 29–31. (b) Wayda, A. L.; Rogers, R. D.
Organometallics 1985, 4, 1440–1444. (c) Protchenko, A. V.; Almazova,
O. G.; Zakharov, L. N.; Fukin, G. K.; Struchkov, Y. T.; Bochkarev, M. N. J.
Organomet. Chem. 1997, 536, 457–463. (d) Rabe, G. W.; Zhang-Presse, M.;
Riederer, F. A.; Incarvito, C. D.; Golen, J. A.; Rheingold, A. L. Acta
Crystallogr., Sect. E: Struct. Rep. Online 2004, 60, m1389–m1390. (e)
Hogerheide, M. P.; Grove, D. M.; Boersma, J.; Jastrzebski, J. T. B. H.;
Kooijman, H.; Spek, A. L.; van Koten, G. Chem.;Eur. J. 1995, 1, 343–350.
(f) Gao, W.; Cui, D. J. Am. Chem. Soc. 2008, 130, 4984–4991.
(22) (a) Roering, A. J.; Maddox, A. F.; Elrod, L. T.; Chan, S. M.;
Ghebreab, M. B.; Donovan, K. L.; Davidson, J. J.; Hughes, R. P.;
Shalumova, T.; MacMillan, S. N.; Tanski, J. M.; Waterman, R.
Organometallics 2009, 28, 573–581. (b) Mork, B. V.; Tilley, T. D. J. Am.
Chem. Soc. 2004, 126, 4375–4385.
(23) Cwiklicki, A.; Rehse, K. Arch. Pharm. Pharm. Med. Chem. 2004,
337, 156–163.
(24) (a) Masuda, J. D.; Jantunen, K. C.; Ozerov, O. V.; Noonan, K. J.
T.; Gates, D. P.; Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2008,
130, 2408–2409. (b) Estler, F.; Eickerling, G.; Herdtweck, E.; Anwander, R.
Organometallics 2003, 22, 1212–1222. (c) Arndt, S.; Voth, P.; Spaniol, T. P.;
Okuda, J. Organometallics 2000, 19, 4690–4700. (d) Schumann, H.;
Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem. 2002, 628,
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Article
Organometallics, Vol. 28, No. 21, 2009 6359
The spectroscopic analysis of this compound agrees with pre-
viously published data for the fully characterized product.26
1,8-Dibromo-3,6-dimethyl-9-tBOC-carbazole (1). An intimate
mixture of 1,8-dibromo-3,6-dimethylcarbazole (0.468 g, 1.33
mmol) and dimethylaminopyridine (0.171 g, 1.40 mmol) was
dissolved in 30 mL of dichloromethane to give a clear yellow
solution. An excess of di-tert-butoxycarbonyl (0.479 g, 2.19
mmol) was added via syringe at ambient temperature. The clear
red reaction mixture was stirred for 18 h, generating a yellow
solution. The reaction was quenched by addition of 50 mL of 1
M HCl. The layers were separated, and the acidic layer was
extracted with a further 2 ꢀ 50 mL of DCM. The combined
fractions were then washed with 3 ꢀ 50 mL of 1 M NaHCO3
followed by 2 ꢀ 50 mL of 3 M NaCl. The organic layer was dried
over MgSO4 and filtered, and the solvent was removed under
vacuum, giving the N-protected product as an off-white solid.
Yield: 0.506 g (84.2%). 1H NMR (CDCl3): δ 7.62 (s, 2H,
Ar-H), 7.43 (s, 2H, Ar-H), 2.44 (s, 6H, CH3), 1.68 (s, 9H,
OC(CH3)3). 13C{1H} NMR (CDCl3): δ 151.5 (CdO), 137.0,
133.3, 133.1, 127.5, 119.3, 106.2 (Ar-Cs), 86.5 (OC(CH3)3), 28.1
(OC(CH3)3), 20.9 (CH3). IR (neat): 2978 (w), 2922 (w), 2860 (w),
1749 (m, ν CdO), 1557 (w), 1478 (m), 1419 (w), 1368 (m), 1309
(m), 1230 (m), 1177 (m), 1127 (s), 1064 (m), 836 (s) cm-1. Anal.
Calcd (%) for C19H19Br2NO2: C, 50.36; H, 4.23; N, 3.09.
Found: C, 49.83; H, 4.17; N, 3.16.
140.8 (d, JCP = 12.9 Hz, Ar-C), 135.7 (d, JCP = 9.7 Hz, Ar-C),
133.3 (d, JCP=19.1 Hz, Ar-C), 133.2 (d, JCP=16.1 Hz, Ar-C),
129.0 (d, JCP = 6.2 Hz, Ar-C), 128.9-128.7 (ov m, 2 Ar-Cs),
122.9 (m, Ar-C), 121.8 (Ar-C), 117.0 (d, JCP=12.7 Hz, Ar-C),
21.5 (CH3). 31P{1H} NMR (benzene-d6): δ -15.4. Anal. Calcd
(%) for C38H31NP2: C, 80.98; H, 5.54; N, 2.49. Found: C, 81.19;
H, 5.60; N, 2.77.
HLPh (4a). Benzene (150 mL) was added to a flask charged
with 3 (4.73 g, 8.39 mmol) to give a yellow solution. An aliquot
of phenyl azide (2.07 g, 17.4 mmol) was added via syringe at
ambient temperature. Upon addition, a red product rapidly
precipitated out of solution along with concurrent evolution of
nitrogen gas. The dark red suspension was stirred under an
argon atmosphere for 21 h, following which the solvent was
removed under vacuum and the residue brought into a glove-
box. The product was washed with 5 ꢀ 2 mL of pentane to
remove excess azide and dried thoroughly under reduced pres-
sure to afford crude HLPh as a pale red solid. Recrystallization
from a hot benzene solution (20 mL) layered with pentane (15
mL) at ambient temperature generated 4a as analytically pure
pale yellow prisms. Yield: 6.03 g (96.4%). 1H NMR (CDCl3): δ
11.8 (s, 1H, NH), 8.01 (s, 2H, Ar-H), 7.69 (m, 8H, PPh-H),
7.46 (t, 4H, J = 6.9 Hz, PPh-H), 7.34 (m, 8H, PPh-H), 7.20 (d,
2H, J = 14.5 Hz, Ar-H), 6.85 (t, 4H, NPh-H), 6.68 (d, 4H, J =
8.0 Hz, NPh-H), 6.58 (t, 2H, J = 14.5 Hz, NPh-H), 2.44 (s,
6H, CH3). 13C{1H} NMR (CDCl3): δ 151.0 (d, JCP = 3.5 Hz,
Ar-C), 140.6 (d, JCP = 2.9 Hz, Ar-C), 132.9 (d, JCP = 9.8 Hz,
Ar-C), 131.7 (d, JCP = 2.6 Hz, Ar-C), 131.3 (d, JCP = 10.5 Hz,
Ar-C), 130.8 (d, JCP = 89.5 Hz, Ar-C), 128.7 (d, JCP = 11.8
Hz, Ar-C), 128.3 (Ar-C), 128.0 (d, JCP = 12.7 Hz, Ar-C),
124.2 (d, JCP = 2.5 Hz, Ar-C), 123.8 (d, JCP = 18.0 Hz, Ar-C),
1,8-Bis(diphenylphosphino)-3,6-dimethyl-9-tBOC-carbazole
t
(2). A pentane solution of BuLi (1.40 mL, 2.38 mmol) was
added dropwise to a solution of 1 (0.506 g, 1.12 mmol) in 50 mL
of ether at -78 °C, resulting in a cloudy white suspension. The
reaction mixture was stirred at -78 °C for 3.5 h, after which an
aliquot of chlorodiphenylphosphine (0.425 mL, 2.37 mmol) was
slowly added at -78 °C, producing a red-orange color. The
solution was allowed to slowly warm to ambient temperature as
it was stirred for 16 h, generating a cloudy yellow suspension.
The reaction mixture was filtered through a fine-porosity frit to
remove insoluble byproducts, and the frit was then washed with
ether (2 ꢀ 20 mL) until the washings were colorless. The solvent
was removed from the filtrate under reduced pressure to yield a
gold-colored solid. Recrystallization from a toluene solution
layered with pentane at -35 °C gave 2 as an off-white solid.
Yield: 0.713 g (96.0%). 1H NMR (benzene-d6): δ 7.54 (m, 8H,
Ph-H), 7.46 (s, 2H, Ar-H), 7.70 (d, 2H, J = 4.4 Hz, Ar-H),
7.06 (ov m, 12H, Ph-H), 2.06 (s, 6H, CH3), 1.40 (s, 9H,
OC(CH3)3). 13C{1H} NMR (CDCl3): δ 152.6 (s, CdO), 144.2
(d, JCP = 20.9 Hz, Ar-C), 139.0 (d, JCP = 14.8 Hz, Ar-C),
135.3 (s, Ar-C), 133.8 (d, JCP = 20.4 Hz, Ar-C), 133.2 (s,
Ar-C), 128.3 (s, Ar-C), 128.2 (s, Ar-C), 127.8 (d, JCP = 5.5
Hz, Ar-C), 126.2 (d, JCP = 22.2 Hz, Ar-C), 120.5 (s, Ar-C),
85.5 (s, OC(CH3)3), 28.2 (t, JCP = 2.6 Hz, OC(CH3)3), 21.3, (s,
Ar-CH3). 31P{1H} NMR (benzene-d6): δ -12.0. IR (neat): 3060
(w), 2982 (w), 1724 (s, ν CdO), 1557 (w), 1474 (m), 1434 (m),
1388 (m), 1398 (m), 1277 (m), 1246 (m), 1139 (s), 1090 (m), 1023
(w), 856 (m), 829 (m), 741 (s), 694 (s) cm-1. Anal. Calcd (%) for
C43H39NO2P2: C, 77.81; H, 5.92; N, 2.11. Found: C, 78.24; H,
6.02; N, 2.39.
1,8-Bis(diphenylphosphino)-3,6-dimethyl-9H-carbazole (3).
Toluene (50 mL) was added to a 100 mL bomb charged with 2
(9.33 g, 14.1 mmol) to give a cloudy brown suspension. The
bomb was heated to 160 °C for 4.5 h under static vacuum,
generating a clear red solution. The product was cannula
transferred to a 100 mL round-bottom flask, where the solvent
was removed under vacuum to yield an orange solid. Recrys-
tallization from a toluene solution layered with pentane at -35
°C gave 3 as an analytically pure pale yellow solid. Yield: 7.43 g
(93.8%). 1H NMR (benzene-d6): δ 8.36 (s, 1H, NH), 7.81 (s, 2H,
Ar-H) 7.37-7.31 (ov m, 10H, Ar-H þ PPh-H), 6.98-6.96 (ov
m, 12H, PPh-H), 2.26 (s, 6H, CH3). 13C{1H} NMR (CDCl3): δ
123.6 (d, JCP = 8.5 Hz, Ar-C), 117.3 (Ar-C), 111.6 (d, JCP
=
118.8 Hz, Ar-C), 21.6 (CH3). 31P{1H} NMR (CDCl3): δ 5.4.
Anal. Calcd (%) for C50H41NP2: C, 80.52; H, 5.54; N, 5.63.
Found: C, 80.60; H, 5.93; N, 5.37.
HLPipp (4b). Benzene (75 mL) was added to a flask charged
with 3 (2.09 g, 3.71 mmol) to give a light yellow solution. An
aliquot of 4-isopropylphenyl azide (1.25 g, 7.72 mmol) was
added via syringe at ambient temperature. Upon addition, the
solution gradually became a red-orange color with concurrent
evolution of nitrogen gas. The solution was stirred under an
argon atmosphere for 20 h, following which the solvent was
removed under vacuum and the residue brought into a glove-
box. The product was recrystallized from hot benzene (15 mL)
layered with pentane (5 mL) at ambient temperature. Pale green
crystals of 4b formed over 24 h and were collected by filtration,
washed with 2 ꢀ 1 mL of pentane, and dried thoroughly under
1
reduced pressure. Yield: 2.17 g (70.4%). H NMR (CDCl3): δ
11.7 (s, 1H, NH), 8.00 (s, 2H, Ar-H), 7.71 (m, 8H, PPh-H),
7.46 (t, 4H, J = 7.4 Hz, PPh-H), 7.33 (m, 8H, PPh-H), 7.23 (d,
2H, J = 14.6 Hz, Ar-H), 6.74 (d, 4H, J = 8.2 Hz, Pipp-H),
6.64 (d, 4H, J = 8.3 Hz, Pipp-H), 2.74 (sp, 2H, J = 6.9 Hz,
CH(CH3)2), 2.45 (s, 6H, CH3), 1.17 (d, 12H, J = 6.9 Hz,
CH(CH3)2). 13C{1H} NMR (CDCl3): δ 148.3 (Ar-C), 140.5
(d, JCP = 2.9 Hz, Ar-C), 137.5 (Ar-C), 133.0 (d, JCP = 9.8 Hz,
Ar-C), 131.6 (d, JCP = 2.5 Hz, Ar-C), 131.3 (d, JCP = 10.9 Hz,
Ar-C), 130.9 (d, JCP = 87.2 Hz, Ar-C), 128.6 (d, JCP = 11.7
Hz, Ar-C), 127.9 (d, JCP = 12.8 Hz, Ar-C), 126.2 (Ar-C),
124.1 (d, JCP = 2.6 Hz, Ar-C), 123.5 (d, JCP = 17.6 Hz, Ar-C),
123.5 (d, JCP=9.0 Hz, Ar-C), 111.9 (d, JCP=120.2 Hz, Ar-
C), 33.2 (CH(CH3)2), 24.4 (CH(CH3)2), 21.6 (CH3). 31P{1H}
NMR (CDCl3): δ 4.57. Anal. Calcd (%) for C56H53N3P2: C,
81.04; H, 6.44; N, 5.06. Found: C, 80.21; H, 6.50; N, 4.98.
LuLPh(CH2SiMe3)2 (5a). An NMR tube was charged with 4a
(0.0400 g, 0.0536 mmol) and Lu(CH2SiMe3)3(THF)2 (0.0312 g,
0.0537 mmol) and sealed with a rubber septum and parafilm.
The tube was cooled to -78 °C, and an aliquot of toluene-d8 (0.5
mL) was added via syringe. The tube was removed from the cold
bath, shaken briefly to mix the reagents, and then immediately
inserted into a precooled (271.3 K) NMR probe. The dialkyl
(26) (a) Das, J.; Patil, S. N.; Awasthi, R.; Prasad Narasimhulu, C.;
Trehan, S. Synthesis 2005, 11, 1801–1806.

6360 Organometallics, Vol. 28, No. 21, 2009
Johnson and Hayes
complex (5a) was characterized by multinuclear NMR spectro-
scopy in situ. No decomposition was observed over the course of
characterization (2 h). 1H NMR (toluene-d8, 271.3 K): 8.12 (s,
2H, Ar-H), 7.47 (m, 8H PPh-H), 6.93-6.75 (ov m, 24H,
Ar-H), 2.29 (s, 6H, CH3), -0.06 (s, 18H, CH3), -0.79 (s, 4H,
solution. The reaction mixture was stirred for 18 h, giving a dark
red solution and a small quantity of an orange solid. An aliquot
of THF (0.5 mL) was added to redissolve all material, and the
clear red solution was then layered with pentane (10 mL) and left
at ambient temperature to crystallize. Fine needles developed
over 48 h, which were collected by filtration, washed with
pentane (2 mL), and dried under vacuum. Yield: 0.252 g
CH2). 13C{1H} NMR (toluene-d8; 271.3 K): δ 152.5 (d, JCP
=
3.6 Hz, Ar-C), 147.4 (d, JCP = 7.4 Hz, Ar-C), 137.1 (Ar-C),
134.1 (d, JCP = 9.4 Hz, Ar-CH), 132.3 (d, JCP = 2.2 Hz, Ar-
CH), 130.9 (d, JCP=11.4 Hz, Ar-CH), 129.4 (d, JCP=7.9 Hz,
Ar-CH), 129.1 (d, JCP=2.4 Hz, Ar-CH), 128.6 (d, JCP=11.8
Hz, Ar-CH), 127.3 (d, JCP = 9.3 Hz, Ar-C), 126.0 (d,
1
(38.5%). H NMR (benzene-d6): δ 8.14 (s, 2H, Ar-H), 8.00
(m, 4H, PPh-H), 7.72 (m, 2H, PPh-H), 7.57 (d, 2H, J=13.4
Hz, Ar-H), 7.13 - 6.98 (ov m, 12H, PPh-H), 6.69 (dd, 4H, J=
8.4, J=2.2 Hz, Pipp-H), 6.60 (d, 4H, J=8.2 Hz, Pipp-H), 4.04
(s, 4H, OCH2CH2), 2.63 (sp, 2H, J = 6.8 Hz, CH(CH3)2), 2.37
(s, 6H, CH3), 1.20 (s, 4H, OCH2CH2), 1.14 (d, 6H, J = 6.9 Hz,
CH(CH3)(CH3)0), 1.12 (d, 6H, J = 6.9 Hz, CH(CH3)(CH3)0).
JCP=2.2 Hz, Ar-CH), 125.2 (Ar-C), 123.2 (d, JCP=2.8 Hz,
Ar-CH), 108.9 (d, JCP =111.2 Hz, Ar-C), 40.4 (CH2), 21.3
(CH3), 4.63 (Si(CH3)3). 31P{1H} NMR (toluene-d8; 271.3 K):
δ 29.6.
13C{1H} NMR (benzene-d6): δ 204.7 (dd, 2JCP = 40.9 Hz, 4JCP
1.2 Hz, Lu-Ar-C), 151.6 (d, JCP =5.7 Hz, Ar-C), 144.6 (d,
CP = 7.3 Hz, Ar-C), 142.8 (d, JCP=3.5 Hz, Ar-C), 140.0 (d,
=
LuLPipp(CH2SiMe3)2 (5b). An NMR tube was charged with
4b (0.0216 g, 0.0260 mmol) and Lu(CH2SiMe3)3(THF)2 (0.0152
g, 0.0262 mmol) and sealed with a rubber septum and parafilm.
The tube was cooled to -78 °C, and an aliquot of toluene-d8 (0.5
mL) was added via syringe. The tube was removed from the cold
bath, shaken briefly to mix the reagents, and then immediately
inserted into a precooled (249.1 K) NMR probe. The dialkyl
complex (5b) was characterized by multinuclear NMR spectros-
copy in situ. No decomposition was observed over the course of
characterization (3 h). 1H NMR (toluene-d8; 249.1 K): δ 8.11 (s,
2H, Ar-H), 7.49 (m, 8H PPh-H), 7.11-7.10 (ov m, 4H,
Ar-H), 6.96-6.79 (ov m, 18 H, Ar-H), 2.63 (sp, 2H, CH-
(CH3)2), 2.29 (s, 6H, CH3), 1.13 (d, J = 6.6 Hz, 12H, CH-
(CH3)2), -0.01 (s, 18H, Si(CH3)3), -0.72 (s, 4H, CH2). 13C{1H}
NMR (toluene-d8; 249.1 K): δ 152.5 (d, JCP = 3.5 Hz, Ar-C),
144.8 (d, JCP = 7.5 Hz, Ar-C), 143.4 (d, JCP = 3.6 Hz, Ar-C),
137.0 (Ar-C), 134.1 (d, JCP = 9.6 Hz, Ar-CH), 132.2 (Ar-
CH), 130.9 (d, JCP=11.6 Hz, Ar-CH), 129.2 (Ar-CH), 128.5
(d, JCP=11.7 Hz, Ar-CH), 127.3 (d, JCP=9.3 Hz, Ar-C), 127.0
(Ar-CH), 126.0 (Ar-CH), 125.0 (Ar-C), 108.9 (d, JCP=110.6
Hz, Ar-C), 40.0 (CH2), 33.9 (CH(CH3)2), 24.5 (CH(CH3)2),
21.3 (CH3), 4.71 (Si(CH3)3). 31P{1H} NMR (toluene-d8; 249.1
K): δ 29.4.
J
JCP = 25.3 Hz, Ar-CH), 138.5 (d, JCP=127.3 Hz, Ar-C), 134.2
(d, JCP =8.5 Hz, Ar-CH), 132.0 (d, JCP =2.2 Hz, Ar-CH),
129.7 (d, JCP=8.6 Hz, Ar-CH), 128.8 (d, JCP=24.7 Hz, Ar-
CH), 128.3 (d, JCP=4.8 Hz, Ar-CH), 128.1 (Ar-CH), 127.6 (d,
J
CP=3.9 Hz, Ar-CH), 127.1 (d, JCP=2.5 Hz, Ar-CH), 126.9
(d, JCP=0.96 Hz, Ar-C), 126.7 (d, JCP=81.3 Hz, Ar-C), 124.9
(d, JCP =11.3 Hz, Ar-C), 124.5 (d, JCP =14.8 Hz, Ar-CH),
124.1 (d, JCP=2.0 Hz, Ar-CH), 115.4 (d, JCP=86.2 Hz, Ar-C),
71.2 (OCH2CH2), 33.9 (CH(CH3)2), 25.4 (OCH2CH2), 24.5
(CH(CH3)(CH3)0), 24.5 (CH(CH3)(CH3)0), 21.5 (CH3). 31P{1H}
NMR (benzene-d6): δ 25.0. Anal. Calcd (%) for C60H58Lu-
N3OP2: C, 67.10; H, 5.44; N, 3.91. Found: C, 67.07; H, 6.02;
N, 3.64.
NMR Kinetics. All rate constants were determined by mon-
itoring the 31P{1H} NMR resonance(s) over the course of the
reaction (to at least 3 half-lives) at a given temperature. In a
typical experiment, proteo ligand 4a (0.0400 g, 0.0536 mmol) and
Lu(CH2SiMe3)3(THF)2 (0.0312 g, 0.0537 mmol) were added to a
Wilmad NMR tube, which was then sealed with a rubber septum
(Sigma-Aldrich) and parafilm. The tube was cooled to -78 °C
and 0.5 mL of toluene-d8 was injected via syringe. The tube was
removed from the cold bath and shaken briefly, generating
LuLPh(CH2SiMe3)2, 5a, in situ. The tube was then immediately
inserted into the NMR probe, which was pre-equilibrated to the
appropriate temperature. The sample was allowed to equilibrate
at the set temperature over the course of shimming the tube in the
magnet. 31P{1H} NMR spectra (16 scans) were recorded at preset
time intervals until the reaction had progressed to at least 3 half-
lives. The extent of reaction at each time interval was determined
by integration of the peak intensity of the starting material
relative to that of the intermediate and product. An appropriately
long delay between scans was utilized to ensure that integration
was quantitative and not affected bythe T1 relaxation times of the
reacting species. A summary of the observed rate constants and
half-lives is listed in Table 1.
LuLPh**(THF) (7a). In a glovebox, a small Erlenmeyer flask
was charged with 4a (0.193 g, 0.259 mmol) and Lu(CH2SiMe3)3-
(THF)2 (0.147 g, 0.252 mmol). Benzene (5 mL) was added to this
solid mixture at ambient temperature to give a clear dark red
solution. The reaction mixture was stirred for 18 h, following
which the volatiles were removed to afford a yellow powder. The
product was recrystallized from a 9:1 benzene/THF solution (10
mL) layered with pentane (10 mL). The crystals were collected
by filtration, washed with pentane (2 mL), and dried under
vacuum. Yield: 0.201 g (80.5%). 1H NMR (benzene-d6): δ 8.08
(s, 2H, Ar-H), 7.97 (m, 4H, PPh-H), 7.71 (m, 2H, PPh-H),
7.56 (d, 2H, J=13.4 Hz, Ar-H), 7.11 - 6.97 (ov m, 12H, PPh-
H), 6.77 (ov m, 10 H, NPh-H), 4.00 (s, 4H, OCH2CH2), 2.34 (s,
6H, CH3), 1.15 (s, 4H, OCH2CH2). 13C{1H} NMR (benzene-d6):
δ 204.6 (dd, 2JCP = 41.2 Hz, 4JCP=1.1 Hz, Lu-Ar-C), 151.5
(d, JCP=5.7 Hz, Ar-C), 147.5 (d, JCP=7.3 Hz, Ar-C), 140.0 (d,
X-ray Crystallography. Suitable crystals of 4a, 4b, 6b, or 7b
were selected, coated in dry Paratone oil, and mounted on a glass
fiber. Data were collected at 173 K using a Bruker SMART
JCP = 25.6 Hz, Ar-CH), 138.5 (d, JCP=126.7 Hz, Ar-C), 134.2
˚
APEX II instrument (Mo KR radiation, λ = 0.71073 A) equip-
(d, JCP=8.5 Hz, Ar-CH), 132.2 (d, JCP = 1.7 Hz, Ar-CH),
129.6 (d, JCP=8.7 Hz, Ar-CH), 129.1 (d, JCP=2.1 Hz, Ar-
CH), 128.7 (s, Ar-CH), 128.6 (d, JCP=7.2 Hz, Ar-CH), 128.2
ped with a CCD area detector and a KRYO-FLEX liquid
nitrogen vapor cooling device. Unit cell parameters were deter-
mined and refined on all observed reflections using APEX2
software.27 Data reduction and correction for Lorentz polariza-
tion were performed using the SAINT-Plus software.28 Absorp-
tion corrections were applied using SADABS.29 The structure
was solved by Patterson (4a) or direct (4b, 6b, and 7b) methods
and refined by the least-squares method on F2 using the
(Ar-CH), 127.8 (d, JCP =3.7 Hz, Ar-CH), 127.0 (d, JCP
=
9.8 Hz, Ar-C), 126.3 (d, JCP=81.5 Hz, Ar-C), 124.9 (d, JCP
=
11.3 Hz, Ar-C), 124.6 (d, JCP=14.7 Hz, Ar-CH), 124.2 (d,
JCP=2.3 Hz, Ar-CH), 122.6 (d, JCP = 3.2 Hz, Ar-CH), 115.0
(d, JCP=87.0 Hz, Ar-C), 71.3 (OCH2CH2), 25.3 (OCH2CH2),
21.5 (CH3). 31P{1H} NMR (benzene-d6): δ 25.9. Anal. Calcd
(%) for C54H46LuN3OP2: C, 65.52; H, 4.68; N, 4.24. Found: C,
64.47; H, 5.02; N, 3.99.
LuLPipp**(THF) (7b). In a glovebox, a small Erlenmeyer flask
was charged with 4b (0.506 g, 0.609 mmol) and Lu(CH2SiMe3)3-
(THF)2 (0.354 g, 0.0610 mmol). Benzene (5 mL) was added to
this solid mixture at ambient temperature to give a clear dark red
(27) APEX2, version 2.1-4; Data Collection and Refinement Program;
Bruker AXS: Madison, WI, 2006.
(28) SAINT-Plus, version 7.23a; Data Reduction and Correction
Program; Bruker AXS: Madison, WI, 2004.
(29) Sheldrick, G. M. SADABS, version 2004/1; Program for Em-
pirical Absorption Correction; Bruker AXS: Madison, WI, 2004.

Article
Organometallics, Vol. 28, No. 21, 2009 6361
SHELXTL program package.30 Details of the data collection
and refinement are given in Table 2 and the Supporting In-
formation.
Foundation for Innovation for a Leaders Opportunity
Grant, and the University of Lethbridge for a start-up
^ ꢀ
fund. The authors also wish to thank Dr. Adrien Cote
(Xerox Canada) for expert assistance with X-ray crystal-
lography and Mr. Craig Wheaton of this department for
performing elemental analyses.
Acknowledgment. P.G.H. acknowledges financial sup-
port from the Natural Sciences and Engineering Research
Council of Canada for a Discovery Grant, the Canada
Supporting Information Available: X-ray crystallographic
data in PDF format and CIF files are available free of charge
via the Internet at http://pubs.acs.org.
(30) (a) Sheldrick, G. M. SHELXTL, version 6.14; Structure Deter-
mination SoftwareSuite; Bruker AXS: Madison, WI, 2003. (b) Sheldrick, G.
M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112–122.