Reversible orthopalladation of phosphinimine-imine dichloropalladium(II) complexes

Article abstract of DOI:10.1021/om900194s

The synthesis and characterization of triphenylphosphinimine-arylimine bidentate ligands (aryl = 2,4,6-trimethylphenyl or 4-methylphenyl) along with their dichloropalladium(II) complexes are reported. These complexes form tridentate orthopalladated specie

Full text of DOI:10.1021/om900194s

Organometallics 2009, 28, 3889–3895 3889
DOI: 10.1021/om900194s
Reversible Orthopalladation of Phosphinimine-Imine
Dichloropalladium(II) Complexes
Christopher J. Wallis, Ira L. Kraft, Jeffrey N. Murphy, Brian O. Patrick, and
Parisa Mehrkhodavandi*
Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
Received March 13, 2009
The synthesis and characterization of triphenylphosphinimine-arylimine bidentate ligands (aryl =
2,4,6-trimethylphenyl or 4-methylphenyl) along with their dichloropalladium(II) complexes are reported.
These complexes form tridentate orthopalladated species upon heating in the presence of sodium acetate.
The reverse reaction occurs upon addition of HCl Et2O. The rate of orthopalladation and reprotonation is
3
highly dependent on the steric bulk of the ligand. Related cationic species were also synthesized and
characterized and found to be inert in the presence of 1-hexene and styrene.
Introduction
Urriolabeitia et al.4,5 To the best of our knowledge, orthopalla-
dation of a discrete complex bearing a bidentate phosphini-
mine-imine ligand has not been reported. We have explored a
family of palladium complexes bearing bidentate phosphini-
mine-imine ligands and have developed a controlled method
for their orthopalladation. We have also elucidated the direct
and controlled reverse reaction. Herein we report the results of
our findings.
In the past decade bidentate phosphinimine ligands have
received significant attention as versatile supports for late transi-
tion metals.1 There have been reports on bidentate phosphini-
mine systems incorporating pyridine, imidazole, and pyrazole
moieties, many of which have been used in catalytic reactions
with varying degrees of success.2,3 In most of these systems the
phosphinimine moiety plays only a structural role, either as a
bulky substituent or as part of the ligand backbone.
Results and Discussion
Orthopalladation of phosphinimines offers a facile route to
asymmetric pincer complexes and, in circumstances where the
orthopalladation can be controlled, allows the facile transforma-
tion of a bidentate to a tridentate ligand.4 These complexes are
usually obtained directly via reaction of a proligand with a
palladium salt; direct orthopalladation of phosphinimines upon
reaction with Pd(OAc)2 has recently been studied in detail by
Synthesis and Characterization of Proligands and Metal
Complexes. The triphenylphosphinimine-arylimine com-
pounds, LAr (Ar = Mes, 2,4,6-Me3C6H2; Tol, 4-MeC6H4),
were synthesized in four steps from 2-aminobenzophenone
(Scheme 1).6 The phosphinimine and imine moieties are
installed via sequential Staudinger and condensation reac-
tions, respectively. The 31P NMR spectra of LMes and LTol
show singlets at 1.2 and 0.87 ppm, and the IR spectra show
the ν(PN) stretches at 1358 and 1360 cm-1, respectively;
both are characteristic of phosphinimine compounds.2,3 The
1H NMR spectrum of LMes shows two broad signals for the
ortho mesityl CH3 groups at 2.03 and 2.24 ppm, indicating
hindered rotation in the compound. LTol had one character-
*Corresponding author. E-mail: mehr@chem.ubc.ca.
(1) For some recent examples see: (a) Reetz, M. T.; Bohres, E.;
Goddard, R. Chem. Commun. 1998, 935–936. (b) Tardif, O.; Donnadieu,
B.; Reau, R. C. R. Acad. Sci. Paris. 1998, 1, II, 661–666. (c) Sauthier, M.;
Fornies-Camer, J.; Toupet, L.; Reau, R. Organometallics 2000, 19,
553–562. (d) Sauthier, M.; Leca, F.; de Souza, R. F.; Bernardo-Gusmao,
K.; Queiroz, L. T. F.; Toupet, L.; Reau, R. New J. Chem. 2002, 26,
630–635. (e) Bernardo-Gusmao, K.; Queiroz, L. F. T.; de Souza, R. F.;
Leca, F.; Loup, C.; Reau, R. J. Catal. 2003, 219, 59–62. (f) Co, T. T.;
Shim, S. C.; Cho, C. S.; Kim, T.-J. Organometallics 2005, 24, 4824–4831.
(g) Metallinos, C.; Tremblay, D.; Barrett, F. B.; Taylor, N. J.
J. Organomet. Chem. 2006, 691, 2044–2047. (h) Al-Benna, S.; Sarsfield,
M. J.; Thorton-Pett, M.; Ormsby, D. L.; Maddox, P. J.; Bres, P.;
Bochmann, M. J. Chem. Soc., Dalton Trans. 2000, 4247–4257.
(i) Beaufort, L.; Demonceau, A.; Noels, A. F. Tetrahedron 2005, 61,
9025–9030. (j) Beaufort, L.; Benvenuti, F.; Delaude, L.; Noels, A. F.
J. Mol. Catal. A: Chem. 2008, 283, 77–82.
istic singlet at 2.21 ppm. The molecular structure of LMes
,
determined by single-crystal X-ray crystallography, illus-
trates the origin of the hindered rotation (Figure 1). In the
solid state streric hindrance directs the N-mesityl group
away from the phosphinimine moiety. The PNphosphinimine
and CNimine bond lengths are consistent with similar
compounds.4
Reaction of LMes and LTol with (PhCN)2PdCl2 in dichloro-
methane at room temperature forms the corresponding
air- and moisture-stable, orange dichloropalladium(II)
complexes, LMesPdCl2 (1) and LTolPdCl2 (2) (Scheme 2).
Complexes 1 and 2 show 31P NMR signals shifted signifi-
cantly downfield of the proligands (37 and 34 ppm) and
(2) Spencer, L. P.; Altwer, R.; Wei, P.; Gelmini, L.; Gauld, J.;
Stephan, D. W. Organometallics 2003, 22, 3841–3854.
(3) Wu, H.-R.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Eur. J. Inorg.
Chem. 2003, 3152–3159.
(4) Katti, K. V.; Santarsiero, B. D.; Pinkerton, A. A.; Cavell, R. G.
Inorg. Chem. 1993, 32, 5919–5925.
(5) (a) Aguilar, D.; R.; Bielsa, R.; Contel, M.; Lledos, A.; Navarro,
R.; Soler, T.; Urriolabeitia, E. P. Organometallics 2008, 27, 2929–2936.
(b) Bielsa, R.; Navarro, R.; Soler, T.; Urriolabeitia, E. P. Dalton Trans.
2008, 1203–1214. (c) Bielsa, R.; Larrea, A.; Navarro, R.; Soler, T.;
Urriolabeitia, E. P. Eur. J. Inorg. Chem. 2005, 1724–1736.
(6) (a) Bielsa, R.; Navarro, R.; Urriolbeitia, E. P.; Lledos, A. Inorg.
Chem. 2007, 46, 10133–10142. (b) Aguilar, D.; Aragues, M. A.; Bielsa,
R.; Serrano, E.; Navarro, R.; Urriolabeitia, E. P. Organometallics 2007,
26, 3541–3551.
r
2009 American Chemical Society
Published on Web 05/14/2009
pubs.acs.org/Organometallics

3890 Organometallics, Vol. 28, No. 13, 2009
Wallis et al.
Scheme 1. Synthesis of Proligands LMes and LTol
IR stretches at significantly lower frequencies (ν(PN) =
1270 and 1251 cm-1), indicative of a decrease in the P-N
bond order and characteristic of bidentate phosphinimine-
1
based dichloropalladium(II) complexes.1,2,3 The H NMR
spectrum of 1 shows two sharp signals for the ortho mesityl
CH3 groups at 1.72 and 2.36 ppm, indicating that the
hindered rotation observed in LMes is conserved.
The molecular structures of 1and 2were determined by single-
crystal X-ray crystallography (Figures 2 and 3). Although
complex 1 has square-planar geometry around the palladium
atom, the molecule itself is not planar. The ligand bond lengths
and angles are similar to those of the proligand LMes; however,
there is a slight twist in the ligand and the backbone aryl group
tilts away from the plane of the molecule by 65°. This twist
creates a Pd1-N2-C7-C6 torsion angle of 0.42°, which is
smaller than the torsion angle of 4.3° reported by Stephan et al.
in an analogous phosphinimine-pyridine system.2 The
Pd-Cl bond lengths in 1 suggest a similar trans influence for
Figure 1. Molecular structure of LMes (depicted with 35% prob-
ability ellipsoids, H atoms are omitted for clarity). Selected
bond distances (A) and angles (deg): P(1)-N(1) = 1.5689(2),
P(1)-C(19) = 1.380(2); C(25)-N(2) = 1.282(2); C(32)-N(2) =
1.416(3); C(19)-N(1)-P(1) = 127.5(1); C(25)-N(2)-C(32) =
122.1(2); N(2)-C(25)-C(24) = 124.1(2); N(1)-C(19)-C(24) =
117.8(2).
˚
Scheme 2. Synthesis of LArPdCl2, Ar = Mes (1), Tol (2)
˚
the phosphinimine and imine donors (Pd-Cl(1) = 2.301(1) A,
2,3
˚
Pd-Cl(2) = 2.305(1) A).
There are two independent palladium complexes in the
molecular structure of LTolPdCl2: 2 and 20. Structural ana-
lysis of 2 and 20 indicates that the two structures may be a
result of a greater degree of freedom associated with the
Pd-Nimine bond compared to the more hindered analogue 1.
In 2 the Pd(1)-N(2)-C(7)-C(6) torsion angle is 0.90° (0.42°
in 1), whereas the analogous torsion angle in 20 is 3.82°. In
contrast the torsion angles at the phosphinimine nitrogen
atom are nearly identical for 2 and 20. Other bond distances
and angles are similar to 1.
substituent and indicates a relief of steric hindrance observed
for LMes and 1. The 13C{1H} NMR spectrum (CDCl3) shows a
characteristic doublet for the orthopalladated carbon atom at
157.6 ppm (JCP = 19.4 Hz).
A similar reaction with the less hindered LTolPdCl2
requires more forcing conditions. Orthopalladation of
2 under strictly thermal conditions is achieved after 8 days
in refluxing chlorobenzene; an orange solution of 2
becomes a yellow solution of the orthopalladated complex
L0TolPdCl (4) (L0Tol = (C6H4)(Ph)2PN(C6H4)C(Ph)(dNTol)).
Addition of 1.1 equiv of sodium acetate reduced the reaction
time to 2 days in refluxing chlorobenzene. The NMR and
IR spectra of 4 are similar to those of 3. Our findings are
consistent with ligand-induced orthopalladation due to
steric repulsion reported for other phosphinimine and
phosphorus ylide systems:6,9 increasing the steric bulk at
the imine moiety increases the susceptibility of the complexes
to undergo orthopalladation. A closer structural analysis of
1 and 2 supports this hypothesis: the distance between the
nearest ortho carbon atom on the phenyl ring and the
Reversible Orthopalladation of LMesPdCl2 and LTolPdCl2.
Orthopalladation of complexes 1 and 2 can be induced ther-
mally and catalyzed chemically by addition of base (Scheme 3).
When 1 is refluxed in chlorobenzene for 3 days, the
initially orange suspension is converted to a yellow solution
of the orthopalladated product L0MesPdCl, 3 (L0Mes
=
(C6H4)(Ph)2PN(C6H4)C(Ph)(dNMes)). The accepted mechan-
ism for this reaction is electrophilic substitution followed by
HCl formation and thus may be base-catalyzed.5a Accordingly,
addition of 1.1 equiv of sodium acetate reduces the reaction
time to 2 days in refluxing chloroform. The 31P NMR spectrum
of 3 shows a signal at 41 ppm, and the IR spectrum shows a
ν(PN) stretch at 1234 cm-1; both are characteristic of ortho-
palladated phosphinimines.5,8 The 1H NMR spectrum
(CD2Cl2) of 3 shows one sharp signal at 1.99 ppm correspond-
ing to six protons of the ortho-methyl groups of the mesityl
˚
˚
palladium center is 0.1 A shorter in 1 than it is in 2 (3.457 A
˚
for 2 and 3.510 A for 1) (Figures 2 and 3).
(7) (a) Hall, H. J.; Behr, F. E.; Reed, R. L. J. Am. Chem. Soc. 1972, 14,
4952–4958. (b) Adger, B. M.; Bradbury, S.; Keating, M.; Rees, C. W.;
Storr, R. C.; Williams, M. T. J. Chem. Soc., Perkin Trans. 1 1975, 1,
31–40.
The molecular structures of 3 and 4 show a slightly distorted
square-planar geometry around the palladium center similar to
the dichloropalladium(II) complexes (Figure 4). The Nimine-
Pd bond lengths in 3 and 4, 2.148(1) and 2.105(19) A, respec-
˚
(8) (a) Avis, M. W.; van der Boom, M. E.; Elsevier, C. J.; Smeets, W.
J. J.; Spek, A. L. J. Organomet. Chem. 1997, 527, 263–276. (b) Falvello,
L. R.; Fernandez, S.; Garcia, M. M.; Navarro, R.; Urriolbeitia, E. P. J.
Chem. Soc., Dalton Trans. 1998, 3745–3750. (c) Falvello, L. R.; Garcia,
M. M.; Lazaro, I.; Navarro, R.; Urriolabeitia, E. P. New J. Chem. 1999,
227–235. (d) Bielsa, R.; Navarro, R.; Soler, T.; Urriolabeitia, E. P.
Dalton Trans. 2008, 1787–1794.
˚
˚
tively, are longer than those for 1 (2.054(2) A) and 2 (2.016(5) A)
likely due to the trans influence of the newly formed Pd-Caryl
(9) Falvello, L. R.; Fernandez, S.; Navarro, R.; Rueda, A.; Urriolabeitia,
E. P. Organometallics 1998, 17, 5887–5900.

Article
Organometallics, Vol. 28, No. 13, 2009 3891
˚
Figure 2. Molecular structure of 1 (left) (depicted with 35% probability ellipsoids, H atoms are omitted for clarity). Selected bond distances (A)
and angles (deg): P(1)-N(1) = 1.6267(16), C(7)-N(2) = 1.293(2); Pd(1)-N(1) = 2.0504(15); Pd(1)-N(2) = 2.0543(15); Pd(1)-Cl(1) =
2.3009(6); Pd(1)-Cl(2) = 2.3047(5); N(1)-Pd(1)-N(2) = 85.67(6); N(1)-Pd(1)-Cl(1) = 178.15(4); N(2)-Pd(1)-Cl(2) = 175.18(4); Cl(1)-
Pd(1)-Cl(2) = 89.34(2).
Figure 3. Molecular structure of 2 and 20. There are two Pd complexes in the asymmetric unit, in addition to four solvent CH2Cl2 molecules
˚
(depicted with 35% probability ellipsoids, solvent molecules and H atoms are omitted for clarity). Selected bond distances (A) and angles (deg) for
2: P(1)-N(1) = 1.615(5); C(7)-N(2) = 1.296(8); Pd(1)-N(1) = 2.044(5); Pd(2)-N(2) = 2.016(5); Pd(1)-Cl(1) = 2.2933(17); Pd(1)-Cl(2) =
2.3003(19); N(1)-Pd(1)-N(2) = 83.80(2); N(1)-Pd(1)-Cl(2) = 170.34(15); N(2)-Pd(1)-Cl(1) = 175.77(16); Cl(1)-Pd(1)-Cl(2) = 90.32(7).

3892 Organometallics, Vol. 28, No. 13, 2009
Wallis et al.
Figure 4. Molecular structure of 3 (left) and 4 (right) (depicted with 35% probability ellipsoids, H atoms are omitted for clarity). Selected
˚
bond distances (A) and angles (deg): For 3 P(1)-N(1) = 1.6171(15); C(7)-N(2) = 1.293(2); Pd(1)-N(1) = 2.0483(14); Pd(1)-N(2) =
2.1481(14); Pd(1)-Cl(1) = 2.3083(5); Pd(1)-C(24) = 1.9911(17); N(1)-Pd(1)-N(2) = 89.66(5); N(1)-Pd(1)-Cl(1) = 172.19(4);
Cl(1)-Pd(1)-C(24) = 91.90(5); C(24)-Pd(1)-N(2) = 165.27(6). For 4 P(1)-N(1) = 1.6222(19); C(7)-N(2) = 1.295(3); Pd(1)-N(1) =
2.0433(17); Pd(1)-N(2) = 2.1053(19); Pd(1)-Cl(1) = 2.3027(6); Pd(1)-C(21) = 1.976(2); N(1)-Pd(1)-N(2) = 88.62(7); N(1)-Pd(1)-
Cl(1) = 175.01(5); Cl(1)-Pd(1)-C(21) = 90.34(6); C(21)-Pd(1)-N(2) = 173.00(8).
Scheme 3. Reversible Orthopalladation of LArPdCl2,
Ar = Mes (1), Tol (2)
Scheme 4. Formation of [L0ArPd(NCCH3)][BF4],
Ar = Mes (5), Tol (6)
complete after heating at 50 °C for 18 h. In a similar
reaction with 4, however, the 31P NMR spectrum of the
reaction mixture after 15 min shows ca. 70% reversion to
complex 2 and the conversion is complete after stirring at
room temperature for 18 h. Complexes 1 and 2 were
isolated in ca. 80% yield, and their identities were con-
firmed by spectroscopic means. Hence, increasing the steric
bulk at the imine moiety favors the tridentate orthopalla-
dated complex, whereas decreasing the steric bulk favors
the bidentate dichloropalladium complex.
bonds. A closer inspection of the structures illustrates a more
severe distortion for 3, demonstrated by the N2-Pd-C24 angle
of 165.2(6)° compared to 173.0(8)° for the analogous angle in 4.
The top hemispheres of the molecules are sterically protected
by one of the free P-bound phenyl groups; however, the
Pd-Cipso bond length is significantly longer for 3 than the less
Reactivity of the Orthopalladated Complexes. The chloride
ligand can be abstracted from 3 and 4 upon reaction with
NaBF4 in the presence of excess0 acetonitrile to generate
[L0MesPd(NCCH3)][BF4] (5) and [L TolPd(NCCH3)][BF4] (6),
respectively; both were isolated as an air-stable yellow solids
in 86% yield (Scheme 4). The 31P NMR spectra of 5 and
6 show signals at 51 and 50 ppm, respectively, while the
13C{1H} NMR spectra shows Pd-bound carbon atoms as
doublets at 155.4 ppm (JCP = 20.3 Hz) and 153.9 ppm
˚
bulky 4 (3.78 vs 3.40 A).
The orthopalladated complexes 3 and 4 can be converted
back to 1 and 2, respectively, by the dropwise addition of
1.1 equiv HCl Et2O at room temperature. The steric bulk
3
on the imine moiety effects the ability of the orthopalla-
dated complexes to convert back to the bidentate dichlor-
opalladium(II) complex. Upon addition of the acid, a
yellow solution of 3 immediately reverts to orange; the
31P NMR spectrum of the reaction mixture after 15 min
shows ca. 50% reversion to complex 1. The reaction is
1
(JCP = 20.2 Hz), respectively. The H NMR spectrum of
5 shows equivalent ortho-methyl groups for the mesityl
moiety, indicating free rotation of the group on the

Article
Organometallics, Vol. 28, No. 13, 2009 3893
Table 1. Selected Crystallographic Data for Compounds LMes, 1, 2 3, 4, and 5
LMes
1
2
3
4
5
empirical formula
fw
C40H35N2P
574.67
173
13.343(4)
15.022(4)
16.788(4)
90
107.07(1)
90
3217(2)
4
C41H37N2PCl4Pd C40H35N2PCl6Pd C40H34N2PClPd C38H30N2PClPd C42H37N3PBF4Pd
807.93
173
836.9
173
893.77
173
715.51
173
687.46
173
T (K)
˚
a (A)
11.759(2)
15.851(3)
20.681(4)
90
18.1562(12)
22.9851(17)
20.5796(17)
90
9.7151(8)
12.7851(11)
14.0233(11)
98.186(3)
99.256(3)
103.113(4)
1645.1(2)
2
12.2462(10)
21.9905(18)
12.1611(10)
90
9.4453(9)
12.2825(12)
16.3277(17)
73.756
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
volume (A )
Z
96.746(7)
90
3828.0(12)
4
111.516(3)
90
6848.2(2)
8
112.617(3)
90
3023.1(4)
4
8.209(5)
86.4117(6)
1808.1(3)
2
3
˚
cryst syst
space group
dcalc (g/cm3)
monoclinic
P21/n
1.167
1.16
56.8
0.836, 0.966 0.775, 0.889
41 185 35 421
7770 (0.056) 8813 (0.025)
monoclinic
P21/n
1.452
8.38
55.1
monoclinic
P21/c
1.486
9.37
45.1
0.810, 0.954
42 250
10498 (0.075)
0.098; 0.126
tirclinic
P1h
1.444
7.26
55
0.823, 0.890
28 275
7474 (0.028)
0.028; 0.059
monoclinic
P21/c
1.51
7.86
56.2
0.808, 0.882
36 270
7364 (0.041)
0.051; 0.069
triclinic
P1
1.484
6.14
56.5
0.865, 0.976
40 233
8817 (0.030)
0.043; 0.086
μ(Mo KR) (cm-1
2θmax (deg)
absorp corr (Tmin, Tmax
)
)
total no. of reflns
no. of indep reflns (Rint
)
residuals (refined on F2, all data): 0.050; 0.117 0.035; 0.066
b
R1a; wR2
GOF
no. observations [I > 2σ(I )]
residuals (refined on F): R1; wR2
1
4334
0.108; 0.143 0.026; 0.062
1.03
7429
1.01
6986
0.053; 0.109
1.03
6780
0.024; 0.057
1.02
5648
0.030; 0.061
1.05
7545
0.032; 0.079
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
(NCCH3)][BF4] (5) is also inert toward reactions with excess
amounts of 1-hexene or styrene at room temperature or in
refluxing acetonitrile for 48 h. If the abstraction of a chloride
ligand in 5 using NaBF4 is carried out in the presence of
1-hexene (instead of acetonitrile), no reaction is observed
and there is no evidence for a coordinated olefin. Reactions
of 5 and 6 with acid do not result in protonation of the
Pd-bound aryl group and reversion to 1 and 2, respectively.
Complex 5 does not revert to 1 upon addition of HCl Et2O
at elevated temperatures; instead it slowly degrades to uni-
3
dentified materials. Upon addition of HCl Et2O at room
3
temperature, the sterically accessible [L0TolPd(NCCH3)]-
[BF4] (6) decomposes to an insoluble orange powder, uni-
dentifiable by NMR spectroscopy.
Conclusions
We have synthesized bidentate triphenylphosphinimine-
arylimine proligands, LMes and LTol, and their dichloropalla-
dium(II) complexes LMesPdCl2 (1) and LMesPdCl2 (2). Com-
plexes 1 and 2 can undergo orthopalladation under thermal or
chemical conditions to form L0MesPdCl (3) and L0TolPdCl (4),
although more forcing conditions are required for the less
hindered tolyl analogue. This process is reversible via addi-
Figure 5. Molecular structure of 5 (depicted with 35% probabil-
ity ellipsoids, BF4 anion and H atoms are omitted for clarity).
Selected bond distances (A) and angles (deg): P(1)-N(1) =
1.6361(19), C(7)-N(2) = 1.287(3); Pd(1)-N(1) = 2.0058(18);
Pd(1)-N(2) = 2.1068(18); Pd(1)-N(3) = 2.042(2); Pd(1)-
C(25) = 1.985(2); N(1)-Pd(1)-N(2) = 90.54(7); N(1)-Pd(1)-
N(3) = 175.01(8); N(2)-Pd(1)-C(25) = 171.16(8); N(3)-Pd-
(1)-C(25) = 89.32(8).
˚
tion of HCl Et2O and is more facile for the less hindered
3
complex 4. Complexes 3 and 4 are readily converted0to the
cationic complexes [L0MesPd(NCCH3)][BF4] (5) and [L TolPd-
(NCCH3)][BF4] (6), which are inert toward olefins but de-
grade upon reaction with acid.
NMR time scale. The 1H NMR spectra of both 5 and
6 show the methyl signal for the coordinated acetonitrile
at 1.80 and 1.87 ppm, respectively. The molecular structure
of 5 shows a slightly distorted square-planar geometry at the
Synthesis of the proligands is facile and allows the
possibility of a family of ligands with varied steric and
electronic properties by varying the substituents on the
imine moiety. The controlled reversibility of the orthopal-
ladation may be promising for developing a system where a
switch from a bidentate to a tridentate ligand system (LMes
to L0Mes) can be triggered cleanly without decomposition of
compounds or formation of Pd black. In particular, the
inertness of the Pd-C bond in the cationic species to olefins
makes the compounds promising as catalysts for coupling
˚
Pd center. The Pd-N bonds in 5 are ca. 0.04 A shorter than
the analogous bonds in 3, which is indicative of the positive
charge now associated at the palladium center. Other bond
lengths and bond angles of 5 are similar to those of the parent
complex 3 and similar literature compounds.3,5
The Pd-C bonds in the cationic complexes are inert
toward insertion of olefins. The bond in [L0MesPd

3894 Organometallics, Vol. 28, No. 13, 2009
Wallis et al.
and insertion reactions. We are currently expanding this
work to include a family of ligands and other late tran-
sition metal centers, and we also intend to explore the
versatility of this ligand system with Lewis acidic metals
such as zinc.
and toluene (50 mL). A standard Dean-Stark apparatus topped
with a Dryrite drying column was assembled, and the reaction
mixture was refluxed for 48 h. Ether was added to the resulting
dark yellow solution to precipitate a bright yellow solid.
The solid was filtered and then dried in vacuo, yielding LMes as
a pale yellow solid, which was recrystallized from CH2Cl2
1
(2.15 g, 86%). H NMR (300.1 MHz; CD2Cl2): δ 2.03 (s, 3H,
Experimental Section
Mes ortho-CH3); 2.19 (s, 3H, Mes para-CH3); 2.24 (s, 3H,
Mes-ortho-CH3); 6.42 (qd, 4JH-H = 6.6 Hz, 4JH-H = 1.2 Hz,
2H, Mes m-CH); 6.83-6.64 (m, 4H, Ar-H); 7.53-7.26 (m, 18H,
Ar-H); 7.89-7.86 (m, 2H, Ar-H). 13C NMR (100.6 MHz;
CD2Cl2): δ 18.74 (s, σ CH3); 19.04 (s, σ CH3); 20.98
(s, p-CH3); 116.50 (s, CH); 122.26 (d, JC-P = 11.4 Hz, CH);
128.35 (s, CH); 128.92 (s, CH); 128.98 (s, CH); 129.04 (s, CH);
129.49 (s, CH); 129.75 (s, CH); 130.56 (s, C); 131.39 (s, C); 131.56
(s, C); 131.92 (s, C), 132.16 (d, JC-P = 2.8 Hz, CH); 132.92
(s, CH); 133.02 (s, CH); 141.47 (s, C); 147.86 (s, C); 149.91 (s, C);
170.37 (s, C). 31P NMR (121.5 MHz; CDCl3): δ 1.16 (s). IR
(Nujol, cm-1): 1595 (νCN), 1339 (νNP). Anal. Calcd for
C40H35N2P (574.69): C, 83.60; H, 6.14; N, 4.87. Found:
C, 83.43; H, 6.12; N, 4.92. MS (ESI, m/z): calcd mass
575.2615; obsd mass 575.2600 (M+).
(Ph)3NC(C6H4)C(Ph)(dN(4-MeC6H5)), LTol. The proligand
LTol was synthesized in an identical manner to LMes, except
p-methylaniline (0.541 mL, 4.6 mmol) was used instead of
2,4,6-trimethylaniline, and the reaction was refluxed for 24 h.
The reaction yielded LTol as a pale yellow solid (2.15 g, 86%).
1H NMR (300.1 MHz; CDCl3): δ 2.21 (s, 3H, CH3); 6.36
(dt, JH-H= 8.4, 0.9 Hz, 1H, Ar-H); 6.50 (td, JH-H= 8.7,
1.2 Hz, 1H, Ar-H); 6.85-6.77 (m, 6H, Ar-H); 7.61-7.31
(m, 18H, Ar-H); 7.85-7.82 (m, 2H, Ar-H). 13C NMR
(100.6 MHz; CD2Cl2): δ 21.15 (s, CH3); 116.87 (s, CH); 121.00
(s, CH); 121.19 (d, JC-P = 10.4 Hz, CH); 128.36 (s, CH); 128.87
(s, CH); 129.01 (s, CH); 129.13 (s, CH); 129.18 (s, CH); 129.24
(s, CH); 130.18 (s, CH); 130.86 (s, C); 131.85 (s, C); 132.21
(d, JC-P= 2.8 Hz, CH); 132.60 (s, C); 132.90 (s, CH); 133.00
(s, CH); 141.00 (s, C); 150.46 (s, C); 150.57 (s, C); 170.95 (s, C).
31P NMR (121.5 MHz; CDCl3): δ 0.87 (s). IR (Nujol, cm-1):
1624 (νCN), 1360 (νNP). Anal. Calcd for C38H31N2P (546.64):
C, 83.49; H, 5.72; N, 5.12. Found: C, 83.09; H, 5.67; N, 5.06.
MS (ESI, m/z): calcd mass 547.2307; obsd mass 547.2303 (M+).
General Procedures. Unless otherwise specified, all proce-
dures were carried out using standard Schlenk techniques. A
Bruker Avance 300 MHz spectrometer and Bruker Avance
1
400dir MHz spectrometer were used to record the H NMR,
13C{1H} NMR, and 31P{1H} NMR spectra. 1H NMR chemical
shifts are given in ppm versus residual protons in deuterated
solvents as follows: δ 5.32 for CD2Cl2, and δ 7.27 for CDCl3.
13C{1H} NMR chemical shifts are given in ppm versus residual
13C in solvents as follows: δ 54.00 for CD2Cl2, and δ 77.23 for
CDCl3. 31P{1H} NMR chemical shifts are given in ppm versus
85% H3PO4 set at 0.00 ppm. A Waters/Micromass LCT mass
spectrometer equipped with an electrospray (ESI) ion source
and a Kratos-50 mass spectrometer equipped with an electron
impact ionization (EI) source were used to record low-resolution
and high-resolution spectra. A Nicolet 4700 FT-IR spectro-
meter was used to record infrared spectra. All solvents were
˚
degassed and dried using 3 A molecular sieves in an mBraun
solvent purification system. The THF was further dried over
Na/benzophenone and distilled under N2. CD2Cl2 and CDCl3
were dried over CaH2 and degassed through a series of freeze-
pump-thaw cycles. (PhCN)2PdCl2 was purchased from Strem
Chemicals and used without further purification. All other
chemicals were obtained from Aldrich and used without further
purification.
2-(Triphenylphosphinimine)benzophenone. HCl(100mL, 12M)
was added to a stirred suspension of 2-aminobenzophenone
(23.19 g, 100 mmol) in 95% ethanol (500 mL) at 0 °C. Potassium
nitrite (12.75 g, 150 mmol) in distilled water (150 mL) was added
dropwise to the suspension. The reaction mixture was warmed
to room temperature over 1 h while stirring. Over 15 min, a
cooled solution of sodium azide (13.66 g, 210 mmol, 150 mL of
H2O) was added to the reaction mixture at room temperature.
The reaction mixture was stirred for 45 min, then extracted with
ether (3 ꢀ 125 mL), the organic phase was washed with water
(125 mL) and dried over magnesium sulfate, and the solvent was
removed to yield a viscous, yellow-orange oil of 2-azidobenzo-
phenone, which was used without further purification. (Note:
Azidobenzophenone is a possible explosive hazard and should not
be isolated/stored.) Triphenylphosphine (7.5 g, 33 mmol) was
added to 2-azidobenzophenone (6.96 g, 30 mmol) in toluene
(500 mL) at 0 °C. The reaction mixture was stirred for 1.5 h, after
which ether (20 mL) was added to precipitate out a light yellow
solid. The solid was filtered and dried in vacuo to yield
2-(triphenylphosphinimine)benzophenone as a milky, yellow
LMesPdCl2 (1). A solution of LMes (0.28 g, 0.52 mmol) in
CH2Cl2 (10 mL) was added to a solution of (PhCN)2PdCl2
(0.22 g, 0.57 mmol) in CH2Cl2 (10 mL) and stirred for 22 h at
room temperature. The resulting reddish solution was concen-
trated, and diethyl ether (10 mL) was added to precipitate an
orange-red solid. Filtration and drying in vacuo yielded an
orange solid, LMesPdCl2 (1), which was recrystallized from
CH2Cl2 (0.30 g, 76%). A single crystal of 1 suitable for X-ray
crystallography was obtained by recrystallization from CH2Cl2
and hexane. 1H NMR (300.1 MHz; CD2Cl2): δ 1.72 (s, 3H,
CH3); 2.11 (s, 3H, CH3); 2.36 (s, 3H, CH3); 6.48 (s, 1H, Ar);
6.74-6.67 (m, 3H, Ar); 6.97-6.89 (m, 5H, Ar); 7.29-7.17
(m, 3H, Ar); 7.97-7.38 (m, 14H, Ar). 13C NMR (100.6 MHz;
CD2Cl2): δ 18.88 (s, o-CH3); 20.92 (s, p-CH3); 120.10 (s, CH);
125.33 (d, JC-P = 6.0 Hz, CH); 126.97 (s, CH); 127.64 (s, CH);
127.93 (s, CH); 128.03 (s, CH); 129.41 (s, CH); 129.69 (s, CH);
131.67 (s, CH); 133.11 (s, CH); 133.71 (CH); 134.27 (s, C);
135.19 (s, C); 135.87 (s, C); 137.59 (s, C); 137.72 (s, C); 144.48
(s, C); 146.78 (s, C); 171.77 (s, C). 31P NMR (121.5 MHz;
CDCl3): δ 37.91 (s). IR (Nujol, cm-1): 1549 (νCN), 1245 (νNP).
Anal. Calcd for C40H35N2PCl2Pd (752.02): C, 63.89; H, 4.69; N,
3.73. Found: C, 64.12; H, 4.78; N, 3.72. MS (EI, m/z): calcd mass
712.11918; obsd mass 711.11884 ((M - HCl)+).
1
solid (11.25 g, 82%). H NMR (300.1 MHz; CDCl3): δ 6.45
(d, JH-H = 8.1 Hz, 1H, Ar-H); 6.72 (td, JH-H= 6.9, 0.6 Hz, 1H,
Ar-H); 6.99 (td, JH-H = 7.5, 1.8 Hz, 1H, Ar-H); 7.53-7.26
(m, 19H, Ar-H); 7.90-7.86 (m, 2H, Ar-H). 13C NMR
(100.6 MHz; CD2Cl2): δ 117.46 (s, CH); 122.25 (d, JC-P
=
10.8 Hz, CH); 128.49 (s, CH); 129.01 (s, CH); 129.13 (s, CH);
130.34 (s, CH); 130.47 (s, C); 131.16 (s, CH); 131.47 (s, C); 132.27
(d, JC-P = 2.8 Hz, CH); 132.86 (s, CH); 132.95 (s, CH); 139.73
(s, C); 150.51 (s, C); 200.91 (s, C). 31P NMR (121.5 MHz;
CDCl3): δ 2.60 (s). IR (Nujol, cm-1): 1650 (νCO), 1325 (νNP).
Anal. Calcd for C31H24NOP (457.50): C, 81.38; H, 5.29; N, 3.06.
Found: C, 81.06; H, 5.24; N, 3.38. MS (ESI, m/z): calcd mass
458.1660; obsd mass 458.1674 (M+).
(Ph)3NC(C6H4)C(Ph)(dN(2,4,6-Me3C6H2)), LMes. A round-
bottom flask was charged with a spatula head of p-toluidine
sulfonic acid (0.1-0.2 g), 2-(triphenylphosphinimine)benzophe-
none (2.0 g, 4.6 mmol), 2,4,6-trimethylaniline (0.62 g, 4.6 mmol),
LTolPdCl2 (2). Complex 2 was synthesized in an identical
manner to 1, except using proligand LTol (0.30 g, 0.52 mmol)
instead. Complex 2 was isolated as a yellow solid and recrys-
tallized from dichloromethane and hexane (0.33 g, 81%).
1H NMR (300.1 MHz; CD2Cl2): δ 2.20 (s, 3H, pTol-CH3);
6.87-6.75 (m, 7H, Ar-H); 6.95 (dt, JH-H= 9.0, 1.8 Hz, 2H,

Article
Organometallics, Vol. 28, No. 13, 2009 3895
Ar-H); 7.27-7.06 (m, 4H, Ar-H); 7.60-7.53 (m, 6H, Ar-H);
7.64-7.68 (m, 3H, Ar-H); 7.98 (t, JH-H= 9.0 Hz, 6H, Ar-H).
13C NMR (100.6 MHz; CD2Cl2): δ 21.00 (s, CH3); 121.74
(s, CH); 125.31 (s, CH); 126.12 (s, C); 127.14 (s, C); 128.87
(s, CH); 128.34 (s, CH); 128.89 (s, CH); 129.02 (s, CH); 129.59
(10 mL) at room temperature. The yellow solution immediately
turned orange. The orange solution was heated at 50 °C for 18 h.
Hexane (10 mL) was added to this solution to precipitate
complex 1 as an orange solid, which was isolated by filtration
and dried in vacuo (12.5 mg, 79%).
(s, CH); 129.88 (s, CH); 132.15 (s, CH); 133.39 (d, JC-P=
4.0 Hz, CH); 134.35 (s, C); 134.73 (s, CH); 136.00 (s, CH);
Conversion of 4 into 2. Dilute HCl Et2O (1.50 M, 11 μL,
3
0.023 mmol) was added dropwise via syringe to a solution of
4 (10 mg, 0.021 mmol) in CHCl3 (10 mL) at room temperature.
The yellow solution immediately turned orange. The orange
solution was stirred at room temperature for 18 h. Hexane
(10 mL) was added to this solution to precipitate complex 2 as
an orange solid, which was isolated by filtration and dried in
vacuo (9.0 mg, 85%).
146.59 (s, C); 146.81 (s, C); 154.21 (s, C); 175.26 (s, C). 31P NMR
(121.5 MHz; CD2Cl2):
δ
34.28 (s). IR (Nujol, cm-1):
1551 (νCN), 1251 (νNP). Anal. Calcd for C38H31N2PCl2Pd
(723.97): C, 63.04; H, 4.32; N, 3.87. Found: C, 61.94; H, 4.35;
N, 3.78. MS (EI, m/z): calcd mass 684.08864; obsd mass
684.08754 ((M - HCl)+).
L0MesPdCl (3). A round-bottomed flask was loaded with
1 (100 mg, 0.13 mmol) and NaOAc (16 mg, 1.5 equiv, 0.2 mmol).
Chloroform (25 mL) was added, and the orange suspension was
refluxed vigorously for 48 h. The resulting yellow solution was
filtered through Celite, and hexane was (∼5 mL) added until a
yellow solid began to precipitate. The mixture was then stirred
for 18 h at room temperature and filtered, and the resulting
yellow solid dried under vacuum, to yield complex 3 (70 mg,
74%). A single crystal suitable for X-ray crystallography
was grown by slow diffusion of ether into a solution of 3 in
[L0MesPd(NCCH3)][BF4] (5). A Schlenk flask was loaded with
3 (100 mg, 0.14 mmol) and NaBF4 (150 mg, 1.4 mmol).
Dichloromethane (10 mL) and acetonitrile (1 mL) were added,
and the reaction was stirred at room temperature for 18 h.
Addition of hexane (2 mL) produced a yellow precipitate, which
was filtered and dried in vacuo to yield 5 (97 mg, 86%). A single
crystal of 5 suitable for X-ray crystallography was grown from
slow evaporation from CH2Cl2 at room temperature 1H NMR
(300.1 MHz; CD2Cl2): δ 1.80 (s, 3H, CH3CN); 1.99 (s, 6H, Mes σ
CH3); 2.13 (s, 3H, Mes p-CH3); 6.69-6.77 (m, 4H, Ar-H); 6.96
(t, J = 9.9 Hz, 2H, Ar-H); 7.05 (d, J = 6.9 Hz, 2H, Ar-H); 7.15
(t, J = 8.4 Hz, 1H, Ar-H); 7.24-7.34 (m, 6H, Ar-H); 7.62-7.82
(m, 10H, Ar-H). 13C NMR (100.6 MHz; CD2Cl2): δ 3.19
(s, NCCH3); 19.76 (s, σ CH3); 21.54 (s, p-CH3); 120.21
(s, NCCH3); 121.90 (s, CH); 127.42 (s, CH); 128.31 (s, CH);
128.75 (s, CH); 129.43 (s, CH); 129.59 (s, CH); 129.61 (s, C);
129.86 (s, C); 130.58 (s, CH); 130.70 (s, CH); 130.76 (s, CH);
130.88 (s, CH); 131.30 (s, CH); 131.90 (d, JC-P = 10.4 Hz, CH);
135.26 (d, JC-P = 2.6 Hz, CH); 136.57 (s, C); 137.71 (s, CH);
1
CH2Cl2. H NMR (300.1 MHz; CD2Cl2): δ 1.99 (s, 6H, Mes
σ CH3); 2.13 (s, 3H, Mes p-CH3); 6.55-6.63 (m, 4H, Ar-H); 6.82
(m, 2H, Ar-H); 7.02 (m, 3H, Ar-H); 7.10 (t, J = 5.1 Hz, 1H,
d
t
Ar-H); 7.12-7.25 (m, 4H, Ar-H); 7.60 (dt, J = 2.1 Hz, J =
5.7 Hz, 4H, Ar-H); 7.71-7.79 (m, 6H, Ar-H); 8.08 (d, J =
6.0 Hz, 1H, Ar-H). 13C NMR (100.6 MHz; CDCl3): δ 20.40 (s,
σ CH3); 21.82 (s, p-CH3); 120.50 (s, CH); 128.16 (s, CH); 128.45
(s, CH); 128.61 (s, CH); 128.64 (s, CH); 129. 52 (s, CH); 130.00
(s, C); 130.17 (s, CH); 130.29 (S, CH); 130.67 (s, C); 130.69
(s, CH); 131.52 (s, C); 131.60 (d, JC-P = 3.2 Hz, CH); 132.24
(s, CH); 133.63 (d, JC-P= 11.3 Hz, CH); 134.14 (s, CH); 134.20
(s, CH); 134.23 (s, CH); 134.78 (s, C); 136.88 (s, CH); 137.36
(s, C); 139.66 (s, C); 147.12 (s, CH); 148.05 (d, JC-P= 3.6 Hz, C);
137.96 (s, C); 138.15 (s, C); 146.60 (s, C); 146.79 (d, JC-P
=
3.3 Hz, C); 155.39 (d, JC-P = 20.3 Hz, C-Pd); 173.46 (s, C).
31PNMR(121.5MHz;CD2Cl2): δ51.16 (s). 11B NMR (128.4 MHz,
CD2Cl2): δ 1.22 (s). IR (Nujol, cm-1): 1545 (νCN), 1228 (νNP).
Anal. Calcd for C42H37N3PBF4Pd (807.96): C, 62.43; H, 4.62;
N, 5.20. Found: C, 61.96; H, 4.60; N, 5.20. MS (ESI, m/z):
calcd mass 677.1500; obsd mass 677.1515 [(M - MeCN, - BF4)].
[L0TolPd(NCCH3)][BF4] (6). Complex 6 was made in an
identical manner to 5, using 4 (100 mg, 0.14 mmol) instead.
The reaction yielded a dark yellow solid of 6 (97 mg, 86%).
1H NMR (300.1 MHz; CD2Cl2): δ 1.87 (s, 3H, CH3CN); 2.22
(s, 3H, pTol-CH3); 6.61 (d, J = 8.4 Hz, 1H, Ar-H); 6.72 (t, J =
8.0 Hz, 1H, Ar-H); 6.92 (t, J = 6.8 Hz, 1H, Ar-H); 6.99 (d, J =
8.4 Hz, 2H, Ar-H); 7.09 (m, 4H, Ar-H); 7.29 (m, 8H, Ar-H), 7.68
(m, 4H, Ar-H); 7,84 (m, 6H, Ar-H). 13C NMR (100.6 MHz;
CD2Cl2): δ 2.71 (s, NCCH3); 20.84 (s, p-CH3); 120.20 (s, NCCH3);
120.77 (s, CH); 123.26 (s, CH); 127.49 (s, C); 128.21 (s, CH); 128.35
(s, C); 128.60 (s, CH); 128.73 (s, CH); 129.06 (s, CH); 129.84
(s, CH); 129.88 (s, CH); 130.01 (s, CH); 132.50 (s, CH); 132.71
2
157.62 (d, JC-P= 20 Hz, C-Pd); 171. 68 (s, C). 31P NMR
(121.5 MHz; CD2Cl2): δ 41.62 (s). IR (Nujol, cm-1): 1546 (νCN),
1234 (νNP). Anal. Calcd for C40H34N2PClPd (715.57): C, 67.12;
H, 4.79; N, 3.91. Found: C, 66.94; H, 4.81; N, 3.86. MS (EI, m/z):
calcd mass 712.1186; obsd mass 712.1188 (M).
L0TolPdCl (4). A round-bottemed flask was loaded with
complex 2 (100 mg, 0.13 mmol) and NaOAc (16 mg, 0.2 mmol).
Chlorobenzene (25 mL) was added, and the orange suspension
was refluxed vigorously for 24 h. The resulting yellow solution
was filtered through Celite, and hexane was added until a yellow
solid began to precipitate. The mixture was then stirred for 18 h
at room temperature and filtered, and the resulting yellow solid
dried in vacuo to yield complex 4 (70 mg, 74%). 1H NMR (300.1
MHz; CD2Cl2): δ 1.99 (s, 3H, pTol-CH3); 6.38 (d, J = 8.4 Hz,
1H, Ar-H); 6.60 (t, J = 7.8 Hz, 1H, Ar-H); 6.68 (m, 2H, Ar-H);
6.84 (m, 4H, Ar-H); 7.17 (m, 8H, Ar-H); 7.63 (m, 4H, Ar-H);
7.74 (m, 2H, Ar-H); 7.87 (m, 4H, Ar-H); 7.99 (d, J = 7.5 Hz, 1H,
Ar-H). 13C NMR (100.6 MHz; CDCl3): δ 21.51 (s, p-CH3);
120.50 (s, CH); 123.26 (d, JC-P = 7.6 Hz, CH); 124.87 (s, CH);
125.01 (s, CH); 128.59 (d, JC-P = 10.1 Hz, CH); 129.22 (s, CH);
(s, CH); 133.17 (d, JC-P = 10.3 Hz, CH); 134.43 (d, JC-P
=
10.3 Hz, CH); 135.36 (s, C); 136.90 (s, CH); 137.11 (s, CH);
137.15 (s, C); 138.05 (s, C); 145.57 (s, C); 147.92 (s, C); 153.87
(d, JC-P = 20.2 Hz, C-Pd); 173.69 (s, C). 31P NMR (121.5 MHz;
CD2Cl2): δ 49.71 (s). 11B NMR (128.4 MHz, CD2Cl2): δ -1.04 (s).
IR (Nujol, cm-1): 1545 (νCN), 1221 (νNP). Anal. Calcd for
C40H33N3PBF4Pd (779.91): C, 61.60; H, 4.26; N, 5.39. Found: C,
61.63; H, 4.81; N, 4.96. MS (ESI, m/z): calcd mass 677.1500; obsd
mass 677.1515 [(M - MeCN, - BF4)].
129.92 (s, CH); 130.23 (s, CH); 130.35 (s, CH); 131.20 (d, JC-P
=
3.7 Hz, CH); 132.65 (s, CH); 133.24 (d, JC-P = 11.7 Hz, C);
134.13 (d, JC-P = 10.3 Hz, CH); 134.46 (d, JC-P = 2.7 Hz, CH);
134.81 (s, C); 136.69 (s, CH); 137.93 (s, C); 139.31 (s, C); 139.55
(s, CH); 139.60 (s, C); 139.70 (s, CH); 147.82 (s, C); 148.68 (s, C);
2
157.59 (d, JC-P = 19.4 Hz, C-Pd); 173.18 (s, C). 31P NMR
Acknowledgment. The authors thank UBC, NSERC,
CFI, and BCKDF for funding. We also thank Prof. Peter
Legzdins for valuable discussions.
(121.5 MHz; CD2Cl2): δ 36.16 (s). IR (Nujol, cm-1): 1543 (νCN),
1241 (νNP). Anal. Calcd. for C38H30N2PClPd CH2Cl2 (772.44):
3
C, 60.59; H, 4.18; N, 3.63. Found: C, 60.10; H, 3.82; N, 3.50. MS
(EI, m/z): calcd mass 712.1186; obsd mass 712.1188 (M).
Reversible Orthopalladation: Conversion of 3 into 1. Dilute
Supporting Information Available: Crystallographic informa-
tion files (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
HCl Et2O (1.68M, 12 μL, 0.020) was added dropwise via
syringe to a solution of 3 (15 mg, 0.021 mmol) in CHCl3
3