Synthesis and structural studies of NCN diimine palladium pincer complexes bearing m-terphenyl scaffolds

Article abstract of DOI:10.1021/ic062476a

The reaction of 2,6-[2-{RN=C(H)}C₆H₄] ₂C₆H₃I [R = Ph (4), Cy (5), 2,6-Me ₂C₆H₃ (6), 2,4,6-Me₃C ₆H₂ (7), (S)-α-methylbenzyl (8)] with P

Full text of DOI:10.1021/ic062476a

Inorg. Chem. 2007, 46, 5220−5228
Synthesis and Structural Studies of NCN Diimine Palladium Pincer
Complexes Bearing m-Terphenyl Scaffolds
Liqing Ma,† Philip M. Imbesi,† James B. Updegraff III,† Allen D. Hunter,‡ and John D. Protasiewicz*,†
Department of Chemistry, Case Western ReserVe UniVersity, 10900 Euclid AVenue, CleVeland,
Ohio 44106, and Department of Chemistry, Youngstown State UniVersity, One UniVersity Plaza,
Youngstown, Ohio 44555
Received December 27, 2006
The reaction of 2,6-[2-
methylbenzyl (8)] with Pd2(dba)3 afforded the NCN diimine pincer palladium complexes [2,6-[2-
PdI] (9 13) by oxidative addition of the C I bonds of the ligand precursors. Single-crystal X-ray diffraction analyses
of complexes 9 13 reveal formal C2-symmetric environments. Variable-temperature NMR studies of complexes 11
and 12 show hindered rotation about the N Ar bonds and also suggest that atropisomers of complexes 9 13 do
{RNd
C(H)}C6H4]2C6H3I [R
)
Ph (4), Cy (5), 2,6-Me2C6H3 (6), 2,4,6-Me3C6H2 (7), (S)-
R-
{
RN C(H) C6H4]2C6H3-
d
}
−
−
−
−
−
not interconvert on the NMR time scale. Consistent with this proposal, isolation of the two possible isomers of 13
(13a and 13b) was possible, and their structures and NMR properties have been examined in detail.
Chart 1
Introduction
Transition-metal complexes containing pincer-type ligands
have attracted broad interest1 for a spectrum of applications
since the first report of these materials.2 Pincer complexes
have shown excellent applications in many catalytic reac-
tions, such as Heck reactions,3 transfer hydrogenation,4 and
catalytic dehydrogenation of alkanes.5 Among the many types
Chart 2
* To whom correspondence should be addressed. E-mail: protasiewicz@
case.edu.
† Case Western Reserve University.
‡ Youngstown State University.
(1) (a) Slagt, M. Q.; van Zwieten, D. A. P.; Moerkerk, A.; Gebbink, R.
J. M. K.; van Koten, G. Coord. Chem. ReV. 2004, 248, 2275. (b)
Crabtree, R. H. Pure Appl. Chem. 2003, 75, 435. (c) van der Boom,
M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759. (d) Albrecht, M.;
van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. (e) Rietveld,
M. H. P.; Grove, D. M.; van Koten, G. New J. Chem. 1997, 21, 751.
(2) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976, 1020.
(3) (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1997, 119, 11687. (b) Bergbreiter, D. E.; Osburn, P. L.;
Liu, Y. S. J. Am. Chem. Soc. 1999, 121, 9531. (c) Peris, E.; Loch, J.
A.; Mata, J.; Crabtree, R. H. Chem. Commun. 2001, 201. (d) Eberhard,
M. R. Org. Lett. 2004, 6, 2125. (e) Yoon, M. S.; Ryu, D.; Kim, J.;
Ahn, K. H. Organometallics 2006, 25, 2409.
of pincer complexes, those containing PCP, NCN, and SCS
donor sets are the most investigated. Common to many of
these pincer ligands is an anchoring ring housing the central
donor atom and upon which the two outer donor sets are
tethered. In particular, the m-xylyl framework ([2,6-
(DCH2)2C6H3]-, where D ) donor atoms or groups such as
NR2, PR2, SR, etc.; Chart 1) has proven to be both popular
and profitable for a variety of interesting applications. Related
(4) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, G. Angew.
Chem., Int. Ed. 2000, 39, 743.
(5) (a) Jensen, C. M. Chem. Commun. 1999, 2443. (b) Morales-Morales,
D.; Redo´n, R.; Yung, C.; Jensen, C. M. Chem. Commun. 2000, 1619.
(c) Krogh-Jespersen, K.; Czerw, M.; Summa, N.; Renkema, K. B.;
Achord, P. D.; Goldman, A. S. J. Am. Chem. Soc. 2002, 124, 11404.
(d) Go¨ttker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem.
Soc. 2004, 126, 1804. (e) Zhu, K. M.; Achord, P. D.; Zhang, X. W.;
Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2004, 126,
13044. (f) Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski,
W.; Brookhart, M. Science 2006, 312, 257.
5220 Inorganic Chemistry, Vol. 46, No. 13, 2007
10.1021/ic062476a CCC: $37.00
© 2007 American Chemical Society
Published on Web 06/01/2007

Studies of NCN Diimine Palladium Pincer Complexes
Chart 3
Scheme 3
Chart 4
Φ dictate that there will be two possible C2-symmetric
atropisomers that are possibly interconvertible by two mutual
ring inversions.
For many of the pincer complexes utilizing the m-xylyl
framework ([2,6-(DCH2)2C6H3]), small twist angles are
observed and/or rapid interconversion between atropisomers
is facile. The rates of interconversion, however, are sensitive
to the nature of the (a) anchoring ring, (b) tethers, and (c)
donor atoms and groups. For example, pincer-type complexes
having various anchoring rings and/or tether sizes, such as
A,6 B,7 and C8 (Chart 3), have been reported. Although
complex A displayed a relatively large twist angle of 49°,
facile interconversion between its two possible atropisomers,
however, yielded an effective planar geometry, even at very
low temperature.6 The interconversion of atropisomers of
Scheme 1
1
complex B was observed by H NMR spectroscopy when
Scheme 2
the complex was heated to 77 °C. Complex C, having been
modified at the methylene positions with relatively large alkyl
groups, is conformationally rigid to an impressive temper-
ature of 150 °C.8 Another interesting type of nonplanar
binding mode, D, has been reported as well.9
The study of the structural rigidity of these complexes is
motivated, in part, by their promise for asymmetric
catalysis.10-13 Pincer complexes have been modified by the
(6) Lee, H. M.; Zeng, J. Y.; Hu, C. H.; Lee, M. T. Inorg. Chem. 2004,
43, 6822.
(7) Gru¨ndemann, S.; Albrecht, M.; Loch, J. A.; Faller, J. W.; Crabtree,
R. H. Organometallics 2001, 20, 5485.
(8) D´ıez-Barra, E.; Guerra, J.; Lo´pez-Solera, I.; Merino, S.; Rodr´ıguez-
Lo´pez, J.; Sa´nehez-Verdu´, P.; Tejeda, J. Organometallics 2003, 22,
541.
(9) Kossoy, E.; Iron, M. A.; Rybtchinski, B.; Ben-David, Y.; Shimon, L.
J. W.; Konstantinovski, L.; Martin, J. M. L.; Milstein, D. Chem.s
Eur. J. 2005, 11, 2319.
(10) (a) Xia, Y.-Q.; Tang, Y.-Y.; Liang, Z.-M.; Yu, C.-B.; Zhou, X.-G.;
Li, R.-X.; Li, X.-J. J. Mol. Catal. A: Chem. 2005, 240, 132. (b)
Motoyama, Y.; Nishiyama, H. Synlett 2003, 1883. (c) Medici, S.;
Gagliardo, M.; Williams, S. B.; Chase, P. A.; Gladiali, S.; Lutz, M.;
Spek, A. L.; van Klink, G. P. M.; van Koten, G. HelV. Chim. Acta
2005, 88, 694. (d) Takenaka, K.; Uozumi, Y. AdV. Synth. Catal. 2004,
346, 1693. (e) Baber, R. A.; Bedford, R. B.; Betham, M.; Blake, M.
E.; Coles, S. J.; Haddow, M. F.; Hursthouse, M. B.; Orpen, A. G.;
Pilarski, L. T.; Pringle, P. G.; Wingad, R. L. Chem. Commun. 2006,
3880.
(11) Takenaka, K.; Minakawa, M.; Uozumi, Y. J. Am. Chem. Soc. 2005,
127, 12273.
(12) Longmire, J. M.; Zhang, X. M.; Shang, M. Y. Organometallics 1998,
17, 4374.
ligands have also featured rings such as pyridine and
N-heterocyclic carbenes (Chart 1) as platforms for tridentate
ligands.
The rigidity and flexibility of these ligands have become
a matter of interest because ring conformations might have
a significant impact on the reactivity of the complexes.
Particular attention has been centered on the rigidity of the
two metallocyclic ring conformations and the orientation of
the donor atoms relative to the anchoring central ring. In
these systems, one can characterize the overall shape by
noting the orientation of two key planes. The first is the
coordination plane involving the metal and the three donor
atoms of the pincer ligand (b in Chart 2). The second plane
includes the anchoring ring and the metal atom (a in Chart
2). The deviation from coplanarity of the two planes can be
defined by a “twist angle” Φ (Chart 2). Nonzero values for
Inorganic Chemistry, Vol. 46, No. 13, 2007 5221

Ma et al.
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) for Complexes 9-13
complex
9
10
11
12
13a
13b
Pd1-C1
1.971(2)
2.025(2)
2.023(2)
2.7024(3)
173.56(7)
174.15(7)
87.19(9)
87.04(8)
64.90
1.980(3)
2.033(2)
2.034(2)
2.7139(3)
175.60(8)
173.94(9)
86.57(10)
86.72(10)
64.96
2.005(2)
2.055(2)
2.055(2)
2.7089(2)
179.24(5)
177.39(6)
88.48(7)
88.97(7)
62.74
2.010(2)
2.051(1)
2.055(1)
2.7163(1)
178.10(4)
177.89(4)
89.56(5)
88.49(5)
61.46
1.970(1)
2.029(1)
2.033(1)
2.7157(1)
171.61(4)
173.04(4)
87.30(6)
85.92(6)
65.07
1.963(8)
Pd1-N1
2.024(6)
2.028(7)
2.7059(8)
175.5(2)
174.7(3)
87.3(3)
Pd1-N2
Pd1-I1
C1-Pd1-I1
N1-Pd1-N2
N1-Pd1-C1
N2-Pd1-C1
twist angle
88.1(3)
63.05
introduction of appropriate substituents onto either the
methylene groups8,12 or donor atoms14 to generate chiral
complexes. Complexes having a C2-symmetric ligand back-
bone might allow resolution of the enantiomers of metal
complexes and could represent alternative strategies for the
development of new chiral complexes.
We have recently communicated on PCP pincer complexes
constructed upon m-terphenyl backbones that display highly
rigid structures and twist angles Φ of up to 76° (Chart 4).15
Interconversion of atropisomers of these complexes was not
detected even at elevated temperatures.
Since the success of the integration of m-terphenyl
scaffolds to the PCP pincer complexes, it was thus of
immediate concern to establish if NCN pincer ligands and
complexes containing m-terphenyl scaffolds could be pro-
duced. In this work, we report on the synthesis and structural
characterization of high-twist-angle NCN diimine pincer
complexes. Furthermore, we report on the successful com-
plete characterization of two diastereomerically pure NCN
pincer complexes that demonstrate independently of NMR
experiments that such complexes are both isolable and stable.
In anticipation of similar challenges for generating m-
terphenyl NCN ligands, we initially prepared ligand NC-
(Br)N precursor 4a from 3a.15,18 Compound 3a was previ-
ously utilized for the synthesis of PC(Br)P ligands.
Surprisingly, the reaction of 4a with Pd2(dba)3 yielded a
precipitate of palladium metal over time. NMR analysis of
the resulting mixture provided no evidence for discernible
complexes. Undaunted, we then prepared precursors having
C-I bonds that would be more susceptible to oxidative
addition. From iodoterphenyl 3b, a series of NC(I)N ligand
precursors, 4b-7b, were prepared and characterized by
standard synthetic methods (Scheme 1). As found for related
PC(Br)P precursors, the related NC(X)N precursors showed
evidence for both syn and anti isomers, as ascertained by
1H NMR spectroscopy.
Satisfyingly, the reaction of ligand precursors 4b-7b with
Pd2(dba)3 produces pincer complexes 9-12 in good yields
(Scheme 2). The new materials were isolated as air-stable
pale-yellow crystalline solids and fully characterized.
Related NCN ligand precursor 8 was prepared bearing the
chiral substituent R ) (S)-R-methylbenzyl from the reaction
of the readily available chiral amine and 3b (Scheme 3).
Compound 8 reacts with Pd2(dba)3 to afford a mixture of
complexes 13a and 13b (Scheme 3), which were separated
by flash column chromatography. Because the rigidity of
m-terphenyl PCP diphosphine pincer complexes was estab-
lished by variable-temperature 1H NMR spectroscopic studies
(no evidence of the interconversion of the atropisomers even
at temperatures up to 130 °C),15 the isolation of individual
complexes 13a and 13b should provide a more direct and
straightforward method to elucidate configuration stability.
X-ray Studies. Single-crystal structures of complexes
9-13 have been determined. A summary of the results are
presented in Tables 1 and 2. Single crystals of compound
9-12 suitable for analysis by X-ray diffraction were grown
by slow vapor diffusion of hexane into chloroform solutions.
The structures of complexes 9 and 10 are portrayed in Figure
1, and the structures of complexes 11 and 12 are portrayed
in Figure 2.
Results and Discussion
Synthesis of NCN Pincer Ligand Precursors and
Complexes. While the synthesis of pincer complexes can
be achieved by the reaction of metal salts with donor-
substituted hydrocarbons, it is found that the synthesis of
NCN pincer complexes often fails from the corresponding
NC(H)N ligand precursors.16 In our efforts to generate
m-terphenyl-based PCP pincer complexes from PC(H)P
precursors and palladium salts, only trans-spanning diphos-
phine complexes were obtained.17 Synthesis of the bona fide
pincer complexes required utilization of the more reactive
PC(Br)P precursors.
(13) Motoyama, Y.; Kawakami, H.; Shimozono, K.; Aoki, K.; Nishiyama,
H. Organometallics 2002, 21, 3408.
(14) Williams, B. S.; Dani, P.; Lutz, M.; Spek, A. L.; van Koten, G. HelV.
Chim. Acta 2001, 84, 3519.
(15) Ma, L.; Woloszynek, R. A.; Chen, W.; Ren, T.; Protasiewicz, J. D.
Organometallics 2006, 25, 3301.
The structures of 9-12 are somewhat similar and reveal
slightly distorted square-planar geometries for the palladium-
(II) centers. The Pd-C1, Pd-N1, Pd-N2, and Pd-I1 bond
lengths are comparable to values previously reported for
NCN palladium pincer complexes.8,13,19 The planes contain-
(16) (a) Steenwinkel, P.; Gossage, R. A.; van Koten, G. Chem.sEur. J.
1998, 4, 759. (b) Jung, I. G.; Son, S. U.; Park, K. H.; Chung, K. C.;
Lee, J. W.; Chung, Y. K. Organometallics 2003, 22, 4715. (c) van de
Kuil, L. A.; Luitjes, H.; Grove, D. M.; Zwikker, J. W.; van der Linden,
J. G. M.; Roelofsen, A. M.; Jenneskens, L. W.; Drenth, W.; van Koten,
G. Organometallics 1994, 13, 468.
(17) (a) Smith, R. C.; Protasiewicz, J. D. Organometallics 2004, 23, 4215.
(b) Smith, R. C.; Bodner, C. R.; Earl, M. J.; Sears, N. C.; Hill, N. E.;
Bishop, L. M.; Sizemore, N.; Hehemann, D. T.; Bohn, J. J.;
Protasiewicz, J. D. J. Organomet. Chem. 2005, 690, 477.
(18) (a) Saednya, A.; Hart, H. Synthesis 1996, 1455. (b) Vinod, T.; Hart,
H. J. Org. Chem. 1990, 55, 881.
5222 Inorganic Chemistry, Vol. 46, No. 13, 2007

Studies of NCN Diimine Palladium Pincer Complexes
Table 2. Crystal Data and Structure Refinement Details for 9-13
9‚CHCl3
10
11
empirical formula
fw
C33H24Cl3IN2Pd
788.19
100
0.71073
monoclinic
P2(1)/n
C32H35N2IPd
680.92
100
0.71073
triclinic
P1h
C36H31N2IPd
724.93
100
0.71073
monoclinic
P2(1)/c
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
12.110(1)
14.012(1)
18.952(2)
90.00
107.876(2)
90.00
3060.6(5)
4
1.711
9.7013(2)
10.4575(2)
14.4524(3)
88.357(1)
85.110(1)
73.893(1)
1403.51(5)
2
1.611
1.784
680
17.3546(4)
14.2975(4)
12.2046(3)
90.00
99.881(1)
90.00
2983.4 (1)
4
1.614
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
density (calcd, g/cm3)
abs coeff (mm-1
F(000)
)
1.903
1544
1.684
1440
cryst size (mm)
0.19 × 0.14 × 0.15
colorless block
1.78-28.28
-16 < h < 16
-18 < k < 18
-25 < l < 25
31328
0.20 × 0.15 × 0.15
colorless block
2.03-27.50
-12 < h < 12
-13 < k < 13
-18 < l < 18
22801
0.13 × 0.12 × 0.12
colorless block
1.19-27.50
-22 < h < 22
-18 < k < 18
-15 < l < 15
42236
cryst color and shape
θ range data collection
limiting indices
reflns collected
indep reflns
7604 (Rint ) 0.0205)
6411 (Rint ) 0.0174)
full-matrix least squares on F 2
6411/0/325
1.169
6849 (Rint ) 0.0309)
refinement method
data/restraint/ param
GOF on F 2
7604/0/361
1.118
R1 ) 0.0266
wR2 ) 0.0615
R1 ) 0.0276
wR2 ) 0.0621
6849/0/365
1.062
R1 ) 0.0212
wR2 ) 0.0540
R1 ) 0.0251
wR2 ) 0.0563
final R indices [I > 2σ(I)]a,b
R1 ) 0.0237
wR2 ) 0.0600
R1 ) 0.0251
wR2 ) 0.0607
R indices (all data)
12
13a
13b·1/3C6H6
empirical formula
fw
C38H35N2IPd
752.98
100
0.71073
monoclinic
C2/c
C36H31IN2Pd
724.93
100
0.71073
trigonal
P3(1)
C38H33IN2Pd
750.96
100
0.71073
monoclinic
P2(1)
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
27.4660(8)
13.7460(4)
19.5017(6)
90.00
121.316(1)
90.00
6290.2 (3)
8
1.590
15.7499(2)
15.7499(2)
10.5822(2)
90.00
90.00
120.00
2273.33(6)
3
1.589
1.658
1080
10.0764(3)
14.6621(4)
33.0584(10)
90.00
97.881(2)
90.00
4838.0(2)
6
1.547
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
density (calcd, g/cm3)
abs coeff (mm-1
F(000)
)
1.601
3008
1.561
2244
cryst size (mm)
0.35 × 0.25 × 0.20
colorless block
1.72-27.50
-34 < h < 35
-17 < k < 17
-25 < l < 25
31842
0.18 × 0.17 × 0.17
colorless block
2.44-27.99
-20< h <20
-20< k < 20
-13< l < 13
51541
0.24 × 0.21 × 0.01
colorless thin plate
1.24-30.67
-14< h <13
-20< k < 20
-47< l < 46
92517
cryst color and shape
θ range data collctn
limiting indices
reflns collected
indep reflns
7193 (Rint ) 0.0174)
7199 (Rint ) 0.0342)
full-matrix least squares on F 2
7199/1/363
1.019
29483 (Rint ) 0.1219)
refinement method
data/restraint/ param
GOF on F 2
7193/0/386
1.090
R1 ) 0.0165
wR2 ) 0.0459
R1 ) 0.0180
wR2 ) 0.0469
29483/1/1111
0.978
R1 ) 0.0669
wR2 ) 0.1141
R1 ) 0.1324
wR2 ) 0.1385
final R indices [I > 2σ(I)]a,b
R1 ) 0.0139
wR2 ) 0.0335
R1 ) 0.0143
wR2 ) 0.0336
R indices (all data)
2
2
2
2
2
2
a R(F) ) ∑||Fo| - |Fc||/∑|Fo|. b Rw(F2) ) [∑{w(Fo - Fc )2}/∑{w(Fo )2}]0.5; w-1 ) σ2(Fo ) + (aP)2 + bP, where P ) [Fo + 2Fc ]/3 and a and b are
constants adjusted by the program.
ing the directly attached phenyl ring and the Pd atom are
containing the Pd, C1, I1, N1, and N2 atoms. These twist
twisted by 61.5-65.1° from that of the coordination plane
angles (Chart 2) are 11° or so greater than the largest
Inorganic Chemistry, Vol. 46, No. 13, 2007 5223

Ma et al.
Figure 1. ORTEP representation of the molecular structure of 9‚CHCl3
(left) and 10 (right). H atoms and the solvent molecule (CHCl3) are omitted
for clarity. Selected bond lengths (Å) and angles (deg) for 9: Pd-N1, 2.025-
(2); Pd-N2, 2.023(2); Pd-C1, 1.971(2); Pd-I1, 2.7024(3); N1-Pd-N2,
174.15(7); C1-Pd-I1, 173.56(7). Selected bond lengths (Å) and angles
(deg) for 10: Pd-N1, 2.051(1); Pd-N2, 2.055(12); Pd-C1, 2.010(2); Pd-
I1, 2.7163(1); N1-Pd-N2, 177.89(4); C1-Pd-I1, 178.10(4).
Figure 3. ORTEP representation of the molecular structure of 13a (left)
and 13b‚1/3C6H6 (right; only one of the three independent molecules in the
asymmetric unit is shown). H atoms and solvent molecules are omitted for
clarity. Selected bond lengths (Å) and angles (deg) for 13a: Pd-N1, 2.029-
(1); Pd-N2, 2.033(1); Pd-C1, 1.970(1); Pd-I1, 2.7157(1); N1-Pd-N2,
173.04(4); C1-Pd-I1, 171.61(4). Selected bond lengths (Å) and angles
(deg) for 13b: Pd-N1, 2.024(6); Pd-N2, 2.028(7); Pd-C1, 1.963(8); Pd-
I1, 2.7059(8); N1-Pd-N2, 174.7(3); C1-Pd-I1, 175.5(2).
Figure 2. ORTEP representation of the molecular structure of 11 (left)
and 12 (right). H atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg) for 11: Pd-N1, 2.055(2); Pd-N2, 2.055(2); Pd-C1,
2.005(2); Pd-I1, 2.7089(2); N1-Pd-N2, 177.39(6); C1-Pd-I1, 179.24-
(5). Selected bond lengths (Å) and angles (deg) for 12: Pd-N1, 2.051(1);
Pd-N2, 2.055(12); Pd-C1, 2.010(2); Pd-I1, 2.7163(1); N1-Pd-N2,
177.89(4); C1-Pd-I1, 178.10(4).
Figure 4. Further view of complex 13a emphasizing the proximity of
methine protons H19 and H20 with phenyl rings.
previously reported NCN pincer complexes7 but smaller than
the twist angles in the analogous m-terphenyl-based PCP
complexes (73.8 and 76.0°).15 Larger N1-Pd-N2 bond
angles (174-178°) are realized for 9-12 compared to those
of m-xylyl-based NCN pincer complexes (∼157-163°).11,13,19
The larger angles are presumably a result of the greater ring
size for the seven-membered rings compared to the five-
membered rings. Correspondingly, the N-Pd-C bond angles
in 9-12 are closer to the idealized value of 90° (∼86-89°),
which might indicate less ring strain in these pincer
complexes than for the m-xylyl diimine pincer complexes
(∼78-79°).11
Figure 5. Illustration showing how hindered rotation about the N-Ar
bond of complex 12 distinguishes methyl protons a and a′ (other H atoms
are omitted for clarity).
Single crystals of compounds 13a and 13b were grown
by slow vapor diffusion of hexane into a benzene solution.
Their molecule structures are depicted in Figure 3. For the
structure of 13b, there are three independent molecules in
the asymmetric unit of the unit cell, and only one of them is
shown in Figure 3. Most of the metrical parameters are in
agreement with those determined for 9-12, with perhaps
barely significant shorter Pd-I bond lengths as compared
to the shortest Pd-I values found in 9. Interestingly, the twist
angles for 13a and 13b differ by 2° despite having essentially
the same substituents.
As desired, introduction of the chiral groups onto the
m-terphenyl backbones of these two pincer complexes allows
isolation of both diastereomers and thus provides additional
evidence that such complexes are configurationally stable.
Comparison of the structures of 13a and 13b shows how
the different orientations of the terphenyl core influence the
(19) (a) Stark, M. A.; Jones, G.; Richards, C. J. Organometallics 2000,
19, 1282. (b) van den Broeke, J.; Heeringa, J. J. H.; Chuchuryukin,
A. V.; Kooijman, H.; Mills, A. M.; Spek, A. L.; van Lenthe, J. H.;
Ruttink, P. J. A.; Deelman, B. J.; van Koten, G. Organometallics 2004,
23, 2287. (c) Mills, A. M.; van Beek, J. A. M.; van Koten, G.; Spek,
A. L. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2002, 58,
m304.
5224 Inorganic Chemistry, Vol. 46, No. 13, 2007

Studies of NCN Diimine Palladium Pincer Complexes
1
1
Figure 6. Temperature-dependent H NMR (600 MHz, CDCl3) spectra of 12 (left) and simulated H NMR spectra (right) for resonances a and a′.
1
1
Figure 7. Temperature-dependent H NMR (600 MHz, CDCl3) spectra of 11 (left) and simulated H NMR spectra (right) for resonances a and a′.
1
NMR Spectroscopic Studies. The H NMR spectra of
compounds 9-12 and 13b show that the chemical shifts of
the methine proton (CHdNR) range from δ 8.1 to 8.4 ppm,
slightly downfield (ca. 0.2 ppm) from their corresponding
ligand precursors. A rather large upfield shift of the methine
proton is observed for 13a, however, which appears at δ
7.60 ppm. Careful analysis of the structures of 13a and 13b
provides a reasonable explanation. Specifically, the structure
of 13a reveals close contacts for the phenyl ring of the
methylphenyl group with the methine protons H19/H20
(Figure 4). The structure of 13b, by contrast, shows no
comparable short contacts.
Figure 8. Eyring plots of ln(k/T) vs 1/T for complexes 11 (9) and 12
(4).
These results suggest that the structures determined by
X-ray diffraction in the solid state are rigorously maintained
in solution. The degree of rigidity is also signified by the
observation of 11 distinguishable sets of resonances for the
11 protons in the cyclohexyl groups in the 1H NMR spectrum
of complex 10. Apparently, rotation about the dNsCy bonds
does not occur on the NMR time scale at room temperature.
This effect was more readily examined in detail with
compounds 11 and 12.
orientation of the methylbenzyl groups attached to the N
donor atoms. In compound 13a, the two phenyl rings of the
methylbenzyl groups are farther apart than those in 13b on
either side of the plane of the central benzene ring of the
m-terphenyl backbone. Such orientations are probably dic-
tated by the desire of the phenyl groups to orientate
themselves away from the large I atom, which hampers
rotation about the N1-C21 and N2-C29 bonds. These
orientations have a significant impact on the 1H NMR spectra
for these materials (vide infra).
The room-temperature spectra of complexes 11 and 12
show broadened resonances attributable to the N-Ar reso-
nances. A series of variable-temperature NMR experiments
for complex 12 were thus conducted to examine this
Inorganic Chemistry, Vol. 46, No. 13, 2007 5225

Ma et al.
peroxide (50 mg, 0.20 mmol). The solution was heated to reflux
under nitrogen for 6 h, and another portion of N-bromosuccinimide
(3.14 g, 17.6 mmol) and benzoyl peroxide (50 mg, 0.20 mmol)
was added. After an additional 18 h of reflux, the mixture was
cooled and filtered. The filtrate was then washed with 5% Na2SO3
(100 mL × 3) and dried with anhydrous MgSO4. After filtration,
the solvent was evaporated and the remaining solid was washed
with n-pentane and then dried in vacuo to yield 4.98 g (91.2%) of
2b as a white solid. (Chemical shifts of two isomers are reported
for all ligand precursors without specific assignment to syn- or
anti-.) 1H NMR (CDCl3, 400 MHz): δ 6.35 (s, CHBr2), 6.41
(s, CHBr2), 7.09-7.17 (m, 2H), 7.33-7.35 (m, 2H), 7.38-7.44
(m, 2H), 7.53-7.58 (m, 3H), 8.08-8.10 (m, 2H). 13C {1H} NMR
(CDCl3, 100 MHz): δ 38.9 (CHBr2), 39.0 (CHBr2), 104.9
(Ar(C)-I), 105.8 (Ar(C)-I), 128.4, 128.5, 129.2, 129.4, 129.5,
129.7, 129.76, 129.79, 130.1, 139.3, 139.4, 140.5, 140.7, 145.3,
145.4. Anal. Calcd for C20H13Br4I: C, 34.32; H, 1.87. Found: C,
34.15; H, 1.52.
phenomenon in greater detail (Figure 6, left). At low
temperature (e.g., -25 °C), three sharp resonances are
discerned for three mesityl methyl groups. As the temperature
is raised, two of the three signals (a and a′) begin to broaden
and approach coalescence at 55 °C. Similar behavior is
observed for compound 11 (Figure 7, left). These NMR
spectra were simulated by using line-shape analysis software
WINDNMR-Pro20 (Figure 6, right; Figure 7, right). An Eyring
plot and the resulting activation parameters are presented in
Figure 8.
The data are consistent with hindered rotation about the
N-Ar bond of 11 and 12 (Figure 5), caused by the fact that
the m-terphenyl framework places the N-Ar methyl groups
in close proximity to the halogen atom. Hindered P-C bond
rotation was also discovered in the related pincer complex
[2,6-(2-tBu2PCH2C6H4)2C6H3PdBr],15 of which the rotation
barrier is 10.0 kcal/mol. Relatively larger values are found
for complexes 11 and 12, which are 15.2 and 15.7 kcal/mol,
respectively. These studies suggest that the present diimine
pincer complexes are somewhat more sterically demanding
than analogous pincer complexes having m-xylyl backbones.
2,6-(2-CH(O)C6H4)2C6H3I (3b). A mixture of 2b (4.00 g, 5.72
mmol), silver nitrate (4.00 g, 23.5 mmol), and sodium acetate (2.11
g, 25.7 mmol) in a 250 mL round-bottomed flask containing a
solvent mixture of 125 mL of EtOH and 25 mL of THF was heated
to reflux under nitrogen for 16 h. After removal of solids by
filtration, the solvent was evaporated to yield a sticky compound.
This sticky compound was dissolved in CH2Cl2 (150 mL), and 5
mL of hydrochloric acid (10%) was added. The reaction mixture
was stirred at room temperature for 6 h, then washed with water
(100 mL × 3), and dried with anhydrous MgSO4. The solvent was
evaporated, and the crude product was washed with diethyl ether
Conclusion
In summary, new diimine NCN pincer ligands based upon
the m-terphenyl scaffold have been synthesized, and their
palladium complexes have been prepared by an oxidative
addition route. Structural analyses of 9-13 reveal similar
structures and high twist angles. Variable-temperature NMR
spectroscopic studies of 11 and 12 indicated hindered rotation
about the N-Ar bond. Introduction of chiral imine groups
allowed resolution and complete structural characterization
of chiral pincer complexes 13a and 13b having a high degree
of nonfluxionality. This work firmly establishes that m-
terphenyls can be employed to construct rigid C2-symmetric
pincer complexes. Efforts are underway to develop related
pincers having other donor groups so that a better under-
standing of the relationship between donor groups and the
twist angles can be gained.
1
and then dried in vacuo to yield 1.98 g (84.0%) of 3b. H NMR
(CDCl3, 400 MHz): δ 9.88 (CHO), 9.87 (CHO), 8.02-8.04 (m,
2H), 7.66-7.70 (m, 2H), 7.55-7.59 (m, 2H), 7.50-7.54 (m, 1H),
7.31-7.36 (m, 4H). 13C {1H} NMR (CDCl3, 100 MHz): δ 191.3
(CHO), 191.6 (CHO), 106.0 (Ar(C)-I), 127.9, 128.07, 128.15,
128.4, 128.99, 129.03, 129.9, 130.0, 130.9, 131.1, 133.6, 133.7,
133.9, 134.1, 144.58, 144.61, 148.0, 148.3. Anal. Calcd for
C20H13O2I: C, 58.27; H, 3.18. Found: C, 58.09; H, 2.88.
2,6-{2-PhNdC(H)C6H4}2C6H3Br (4a). To a benzene (40 mL)
solution of 3a (1.00 g, 2.74 mmol) and aniline (0.60 g, 6.4 mmol)
in a 100 mL round-bottomed flask were added several pieces of
crystalline p-toluenesulfonic acid. The resultant mixture was heated
to reflux under nitrogen for 16 h. Water generated by this reaction
was collected by a Dean-Stark receiver. After being cooled to room
temperature, the solvent was removed under vacuum. The resultant
material was recrystallized from a MeOH/CH2Cl2 solvent mixture
Experimental Section
General Procedures and Materials. Experiments involving
reactions of Pd2(dba)3 and ligands were carried out in a glovebox
under nitrogen in anhydrous benzene. Certified ACS-grade solvents
[tetrahydrofuran (THF), CCl4, CHCl3, CH2Cl2, benzene, hexanes,
n-pentane, methanol (MeOH), and ethanol (EtOH)] and anhydrous
benzene from Fisher were used as received. Aniline, 2,6-dimethy-
laniline, and 2,4,6-trimethylaniline were distilled prior to use. The
NMR spectroscopy measurements were recorded on a Varian Inova
400 or 600 MHz spectrometer. Chemical shifts were referenced to
residual solvent signals (1H and 13C NMR). Elemental analyses were
performed by Quantitative Technologies, Inc., Whitehouse, NJ. 2,6-
(2-CH3C6H4)2C6H3I (1b) and 2,6-(2-CH(O)C6H4)2C6H3Br (3a) were
synthesized according to literature methods.15,18
1
to yield 1.13 g (80%) of a pale-yellow crystalline solid of 4a. H
NMR (CDCl3, 400 MHz): δ 8.22 (CHdNPh), 8.25 (CHdNPh),
6.94 (m), 7.06-7.10 (m), 7.21-7.38 (m), 7.45 (t, JHH ) 7 Hz),
7.53-7.58 (m, 4H), 8.35-8.37 (m, 2H). Anal. Calcd for C32H23N2-
Br: C, 74.57; H, 4.50; N, 5.43. Found: C, 74.01; H, 4.29; N,
5.31.
2,6-{2-PhNdC(H)C6H4}2C6H3I (4b). A procedure similar to
that above was used for preparing NCN ligand precursor 4a. Starting
materials of 3b (0.50 g, 1.2 mmol) and aniline (0.30 g, 3.2 mmol)
were used, and 0.53 g of pale-yellow crystalline 4b (78%) was
obtained. (Chemical shifts of two isomers are reported without
1
specific assignment to syn or anti.) H NMR (CDCl3, 400 MHz):
2,6-(2-CHBr2C6H4)2C6H3I (2b). To a solution of 1b (3.00 g,
7.81 mmol) in 200 mL of CCl4 in a 500 mL round-bottomed flask
were added N-bromosuccinimide (2.79 g, 15.7 mmol) and benzoyl
δ 8.21 (CHdNPh), 8.22 (CHdNPh), 6.94-6.96 (m), 7.06-7.11
(m), 7.19-7.38 (m), 7.47 (t, JHH ) 7 Hz, 1H), 7.49-7.57 (m, 4H),
8.35-8.38 (m, 2H). 13C {1H} NMR (CDCl3, 100 MHz): δ 158.0
(CHdNPh), 159.0 (CHdNPh), 106.2 (Ar(C)-I), 106.5 (Ar(C)-
I), 120.9, 121.1, 126.1, 126.2, 127.0, 127.1, 127.9, 128.1, 128.8,
(20) Reich, H. J. WINDNMR, version 7.1.11; University of Wisconsins
Madison: Madison, WI, 2005.
5226 Inorganic Chemistry, Vol. 46, No. 13, 2007

Studies of NCN Diimine Palladium Pincer Complexes
129.4, 129.9, 130.2, 130.4, 130.7, 130.9, 131.1, 133.8, 145.7, 145.8,
146.8, 146.9, 152.0, 152.7. Anal. Calcd for C32H23N2I: C, 68.34;
H, 4.12; N, 4.98. Found: C, 68.30; H, 3.75; N, 4.83.
(m, 5H), 8.11-8.25 (m, 4H). 13C NMR (CDCl3, 100 MHz): δ 24.8,
25.1, 25.2, 69.7, 70.0, 70.2, 70.5, 106.5 (Ar(C)-I), 126.7, 126.8,
126.9, 127.0, 127.08, 127.13, 127.4, 127.7, 127.8, 128.0, 128.6,
128.7, 129.5, 129.6, 129.8, 129.9, 130.1, 130.16, 130.22, 130.4,
133.8, 133.9, 134.1, 134.2, 145.0, 145.4, 145.8, 146.0, 146.1, 157.6,
157.7, 157.9, 158.1. Anal. Calcd for C36H31N2I: C, 69.89; H, 5.05;
N, 4.53. Found: C, 69.76; H, 4.97; N, 4.22.
[2,6-{2-PhNdC(H)C6H4}2C6H3PdI] (9). A mixture of 4b (0.10
g, 0.18 mmol) and Pd2(dba)3 (0.10 g, 0.11 mmol) was dissolved in
15 mL of anhydrous benzene in a 20 mL vial and stirred under
nitrogen for 16 h. The precipitate that formed was filtered and
washed with 5 mL of benzene. The solids were extracted with 30
mL of CHCl3. Upon removal of CHCl3, 0.069 g of pale-yellow
crystalline 9 was obtained (45%). 1H NMR (CDCl3, 400 MHz): δ
8.44 (s, 2H, CHdNPh), 7.13-7.16 (m, 6H), 7.19-7.23 (m, 1H),
7.27-7.29 (m, 2H), 7.33-7.26 (m, 4H), 7.56-7.60 (m, 4H), 7.71-
7.72 (m, 4H). 13C {1H} NMR (CDCl3, 100 MHz): δ 165.5 (CHd
NPh), 150.8 (Ar(C)-Pd), 123.2, 125.6, 127.6, 128.5, 128.7, 128.8,
130.2, 131.1, 131.4, 132.7, 141.1, 141.8, 150.2. Anal. Calcd for
C32H23N2IPd‚CHCl3: C, 50.28; H, 3.07; N, 3.55. Found: C, 50.24;
H, 2.58; N, 3.40.
2,6-{2-CyNdC(H)C6H4}2C6H3I (5b; Cy ) cyclohexyl). To a
benzene (40 mL) solution of 3b (2.00 g, 4.85 mmol) and
cyclohexylamine (1.01 g, 10.2 mmol) in a 100 mL round-bottomed
flask were added several pieces of crystalline p-toluenesulfonic acid.
The resultant mixture was heated to reflux under nitrogen for 16
h. Water generated by this reaction was collected by a Dean-Stark
receiver. After being cooled to room temperature, the solvent was
removed under vacuum. The resultant material (2.72 g, 97%) was
1
of good quality, as indicated by H NMR spectroscopy, and was
1
used as received. H NMR (CDCl3, 400 MHz): δ 1.21-1.36 (m,
6H), 1.51-1.70 (m, 10H), 1.79 (br, 4H), 2.94-3.04 (m, 2H), 7.19-
7.22 (m, 2H), 7.25-7.27 (m, 2H), 7.43-7.48 (m, 5H), 8.03 (s,
1H, ArCHdN), 8.05 (s, 1H, ArCHdN), 8.10-8.14 (m, 2H). 13C
NMR (CDCl3, 100 MHz): δ 24.8, 24.9, 25.0, 25.9, 34.5, 34.6, 70.1,
70.3, 106.38 (Ar(C)-I), 106.43 (Ar(C)-I), 126.8, 126.9, 127.7,
127.8, 129.6, 129.8, 129.9, 130.0, 130.1, 134.2, 134.4, 145.75,
145.80, 145.82, 146.0, 156.7 (CHdN), 157.0 (CHdN). Anal. Calcd
for C32H35N2I: C, 66.90; H, 6.14; N, 4.88. Found: C, 66.48; H,
6.25; N, 4.82.
2,6-{2-XylNdC(H)C6H4}2C6H3I [6b; Xyl ) 2,6-(CH3)2C6H3].
A procedure similar to that above was used for preparing NCN
ligand precursor 5b. Starting materials of 3b (1.00 g, 2.40 mmol)
and 2,6-dimethylaniline (0.88 g, 7.3 mmol) were used, and 1.35 g
of pale-yellow crystalline 5b (90%) was obtained. 1H NMR (CDCl3,
400 MHz): δ 7.96 (CHdNXyl), 8.00 (CHdNXyl), 1.95 (CH3-),
2.13 (CH3-), 6.88-7.07 (m, 6H), 7.22-7.30 (m, 4H), 7.38-7.41
(m, 1H), 7.55-7.58 (m, 4H), 8.40-8.42 (m, 2H). 13C {1H} NMR
(CDCl3, 100 MHz): δ 160.5 (CHdNXyl), 161.0 (CHdNXyl), 18.6
(CH3-), 18.8 (CH3-), 106.4 (Ar(C)-I), 123.9, 126.7, 126.9, 127.1,
127.6, 127.5, 127.7, 128.3, 128.4, 128.8, 129.6, 129.8, 130.4, 131.0,
130.9, 131.1, 133.8, 133.9, 145.7, 145.8, 146.6, 146.8, 159.9, 151.4.
Anal. Calcd for C36H31N2I: C, 69.90; H, 5.05; N, 4.53. Found: C,
69.60; H, 4.80; N, 4.42.
2,6-{2-MesNdC(H)C6H4}2C6H3I [7b; Mes ) 2,4,6-(CH3)3C6H2].
A procedure similar to that above was used for preparing NCN
ligand precursor 6b. Starting materials of 3b (1.00 g, 2.40 mmol)
and 2,4,6-trimethylaniline (0.86 g, 6.4 mmol) were used, and 1.44
g of pale-yellow crystalline 6b (92%) was obtained. 1H NMR
(CDCl3, 400 MHz): δ 7.95 (HdNMes), 7.97 (HdNMes), 1.92
(CH3-), 2.08 (CH3-), 2.27 (CH3-), 6.70 (s), 6.87 (s), 7.20-7.27
(m, 4H), 7.34-7.38 (m, 1H), 7.52-7.56 (m, 4H), 8.37-8.40 (m,
2H). 13C {1H} NMR (CDCl3, 100 MHz): δ 160.5 (CHdNMes),
161.1 (CHdNMes), 18.6, 18.8, 20.9, 21.1, 106.4 (Ar(C)-I), 126.6,
126.7, 127.2, 127.4, 127.7, 128.7, 128.9, 129.0, 129.6, 129.8, 130.4,
130.7, 130.9, 133.0, 133.6, 133.9, 134.0, 145.7, 145.8, 146.5, 146.7,
148.4, 149.0. Anal. Calcd for C38H35N2I: C, 70.59; H, 5.46; N,
4.33. Found: C, 70.37; H, 5.23; N, 4.18.
[2,6-{2-CyNdC(H)C6H4}2C6H3PdI] (10). A mixture of 5b (0.31
g, 0.54 mmol) and Pd2(dba)3 (0.30 g, 0.33 mmol) was dissolved in
15 mL of anhydrous benzene in a 20 mL vial and stirred under
nitrogen for 16 h. The precipitate that formed was filtered and
washed with 5 mL of benzene. The solids were extracted with 20
mL of CH2Cl2. Upon removal of CH2Cl2, 0.21 g of pale-yellow
1
crystalline 10 was obtained (59%). H NMR (CDCl3, 400 MHz):
δ 0.80-0.95 (m, 4H), 1.07-1.30 (m, 6H), 1.42-1.50 (m, 4H),
1.61-1.65 (m, 2H), 1.84 (d, JHH ) 11.6 Hz, 2H), 3.29 (d, JHH
12.8 Hz, 2H), 3.91-3.97 (m, 2H), 7.14-7.15 (m, 3H), 7.39-7.41
(m, 2H), 7.45-7.49 (m, 4H), 7.52-7.56 (m, 2H), 8.16 (d, JHH
)
)
1.6 Hz, 2H, CHdN). 13C {1H} NMR (CDCl3, 100 MHz): δ 24.9,
25.3, 25.6, 32.1, 36.2, 69.7 (Cy(C)-N), 125.0, 127.1, 127.8, 129.6,
131.3, 133.0, 141.1, 141.7, 151.3 (Ar(C)-I), 162.4 (CHdN).
[2,6-{2-XylNdC(H)C6H4}2C6H3PdI] (11). A mixture of 6b
(0.20 g, 0.32 mmol) and Pd2(dba)3 (0.18 g, 0.19 mmol) was
dissolved in 15 mL of anhydrous benzene in a 20 mL vial and
stirred at room temperature under nitrogen for 16 h. Using the same
procedure as that used to isolate 9, 0.15 g of pale-yellow crystalline
1
product 11 was obtained (65%). H NMR (CDCl3, 600 MHz): δ
8.13 (s, 2H, CHdNPh), 2.05 (br, 6H, CH3), 2.46 (br, 6H, CH3),
6.82 (br, 2H), 6.95 (t, JHH ) 8 Hz, 2H), 7.00 (br, 2H), 7.24-7.26
(m, 3H), 7.44 (d, JHH ) 8 Hz, 2H), 7.54-7.56 (m, 2H), 7.65 (d,
JHH ) 8 Hz, 2H), 7.68-7.7 (m, 2H). 13C {1H} NMR (CDCl3, 150
MHz): δ 172.1 (s, CHdNXly), 149.4 (Ar(C)-Pd), 21.6 (br, CH3),
22.0 (br, CH3), 125.3, 127.1, 127.2, 128.2 (br), 128.7, 128.8, 130.2,
131.1, 131.4, 132.7, 141.1, 141.8, 150.2. Anal. Calcd for C36H31N2-
IPd: C, 59.64; H, 4.31; N, 3.86. Found: C, 59.40; H, 4.00; N,
3.58.
[2,6-{2-(S)-PhCH(CH3)NdC(H)C6H4}2C6H3I] (8). To a ben-
zene (40 mL) solution of 3b (1.00 g, 2.43 mmol) and (S)-R-
methylbenzylamine (0.62 g, 5.1 mmol) in a 100 mL round-bottomed
flask were added several pieces of crystalline p-toluenesulfonic acid.
The resultant mixture was heated to reflux under nitrogen for 16
h. Water generated by this reaction was collected by a Dean-Stark
receiver. After being cooled to room temperature, the solvent was
removed under vacuum. The resultant material (1.50 g, 99%) was
pure according to NMR spectroscopy and elemental analysis and
was used as received without further purification. 1H NMR (CDCl3,
400 MHz): δ 1.33 (d, JHH ) 6.4 Hz, -CH3), 1.52 (dd, JHH ) 6.4
and 1.0 Hz, -CH3), 4.19 (quartet, JHH ) 6.4 Hz, -CH-), 4.37
(sextet, JHH ) 6.4 Hz, -CH-), 7.16-7.42 (m, 14H), 7.43-7.50
[2,6-{2-MesNdC(H)C6H4}2C6H3PdI] (12). A mixture of 7b
(0.20 g, 0.31 mmol) and Pd2(dba)3 (0.17 g, 0.18 mmol) was
dissolved in 15 mL of anhydrous benzene in a 20 mL vial and
stirred at room temperature under nitrogen for 16 h. Using the same
workup procedure as that used for 9, 0.16 g of yellow crystalline
product 12 was obtained (69%). H NMR (CDCl3, 600 MHz): δ
8.10 (s, 2H, CHdNPh), 2.01 (br, 6H, CH3), 2.15 (s, 6H, CH3),
2.41 (br, 6H, CH3), 6.62 (br, 2H), 6.81 (br, 2H), 7.23-7.26 (m,
1
3H), 7.42 (d, JHH ) 8 Hz, 2H), 7.52-7.55 (m, 2H), 7.63 (d, JHH
)
7 Hz, 2H), 7.67 (t, JHH ) 7 Hz, 2H). 13C {1H} NMR (CDCl3, 150
MHz): δ 171.7 (s, CHdNMes), 149.60 (Ar(C)-Pd), 20.8 (s, CH3),
21.5 (br, CH3), 21.8 (br, CH3), 125.2, 127.1, 128.9 (br), 129.8, 130.1
(br), 130.4, 130.7 (br), 131.0 (br), 131.1, 131.6, 133.2, 136.5, 141.2,
Inorganic Chemistry, Vol. 46, No. 13, 2007 5227

Ma et al.
143.3, 149.63. Anal. Calcd for C38H35N2IPd: C, 60.61; H, 4.68;
N, 3.72. Found: C, 60.26; H, 4.41; N, 3.62.
distance of 5.02 cm from the crystal. Data were measured using ω
scans of 0.3° per frame for 10 s such that a hemisphere was
collected. The frames were integrated with the Bruker SAINT
software package using a narrow-frame integration algorithm, which
also corrects for the Lorentz and polarization effects. Absorption
corrections were applied using SADABS. The structure was solved
and refined using the Bruker SHELXTL (version 5.1) software. The
positions of all of the non-H atoms were derived from the direct
methods (TREF) solution. With all of the non-H atoms being
anisotropic, the structure was refined to convergence by a
least-squares method on F 2, SHELXL-93, incorporated in
SHELXTL.PC V 5.03.
Compounds 10-13. The X-ray intensity data were measured
at 100 K on a Bruker SMART Apex II CCD-based X-ray
diffractometer system equipped with a Mo-target X-ray tube (λ )
0.71073 Å) operated at 1500 W power (at Case Western Reserve
University). The crystals were mounted on a MiTeGen micromount
using paratone-N, which was then frozen. The detector was placed
at a distance of 6.00 cm from the crystal. Data were measured using
ω scans of 0.5° per frame for 10 s. The frames were integrated
with the Bruker SAINT build in the APEX II software package using
a narrow-frame integration algorithm, which also corrects for the
Lorentz and polarization effects. Absorption corrections were
applied using AXScale. The structure was solved and refined using
the Bruker SHELXTL (version 6.14) software. The positions of all
of the non-H atoms were derived from the direct methods (TREF)
solution. With all of the non-H atoms being anisotropic and all of
the H atoms being isotropic, the structure was refined to conver-
gence by a least-squares method on F 2, XSHELL (version 6.3.1),
incorporated in SHELXTL (version 6.14).
[2,6-{2-(S)-PhCH(CH3)NdC(H)C6H4}2C6H3PdI] (13). A mix-
ture of 8 (0.30 g, 0.49 mmol) and Pd2(dba)3 (0.23 g, 0.25 mmol)
was dissolved in 15 mL of anhydrous benzene in a 20 mL vial and
stirred under nitrogen for 16 h. The reaction mixture was filtered,
and the solvent was removed in vacuo. The resulting material was
purified by flash column chromatography using silica gel and 20%
(v/v) of ethyl acetate in hexanes as the eluent. The two diastere-
omers were thus separated. The first component that eluted was
assigned as 13a, and the second one was assigned as 13b. The
absolute configurations were determined by X-ray crystallography.
1
13a. H NMR (CDCl3, 400 MHz): δ 1.38 (d, JHH ) 6.8 Hz,
6H, -CH3), 5.60-5.65 (m, 2H, -CH-), 7.14-7.17 (m, 6H), 7.21
(s, 3H), 7.27-7.33 (m, 6H), 7.37-7.41 (m, 2H), 7.50-7.56 (m,
4H), 7.60 (d, JHH ) 2.0 Hz, 2H, -CHdN-). 13C NMR (CDCl3,
100 MHz): δ 22.8 (-CH3), 70.0 (-CH-), 125.2, 127.1, 128.4,
128.6, 129.1, 129.2, 130.0, 130.7, 131.5, 132.6, 139.3, 141.0, 141.8,
150.7 (Ar(C)-Pd), 165.0 (-CHdN-). Anal. Calcd for C36H31N2-
IPd: C, 59.64; H, 4.31; N, 3.86. Found: C, 59.57; H, 4.19; N,
3.66.
1
13b. H NMR (CDCl3, 400 MHz): δ 1.50 (d, JHH ) 6.8 Hz,
6H, -CH3), 5.69 (q, JHH ) 6.8 Hz, 2H, -CH-), 6.60 (d, JHH
)
7.6 Hz, 4H), 6.65 (d, JHH ) 7.6 Hz, 2H), 6.90 (d, JHH ) 7.2 Hz,
2H), 6.99-7.03 (m, 5H), 7.17 (t, JHH ) 7.6 Hz, 2H), 7.28-7.32
(m, 2H), 7.34-7.40 (m, 4H), 8.25 (s, 2H, -CHdN-). 13C NMR
(CDCl3, 100 MHz): δ 23.1 (-CH3), 70.3 (-CH-), 124.8, 126.7,
127.2, 128.1, 128.5, 129.9, 130.5, 131.7, 132.1, 140.2, 141.38,
141.43, 150.1 (Ar(C)-Pd), 164.9 (-CHdN-). Anal. Calcd for
C36H31N2IPd: C, 59.64; H, 4.31; N, 3.86. Found: C, 59.80; H,
4.21; N, 3.39.
Experimental Procedure for X-ray Crystallography. X-ray-
quality crystals were grown by slow vapor diffusion of hexane into
chloroform solutions of 9-12. Crystals of 13a and 13b were grown
by slow vapor diffusion of hexane into benzene solutions. 9‚CHCl3.
The X-ray intensity data for 9 were measured at 100 K on a
Bruker SMART Apex CCD-based X-ray diffractometer system
equipped with a Mo-target X-ray tube (λ ) 0.71073 Å) operated
at 2000 W power (at Youngstown State University). The crystal
was mounted on a glass fiber (pulled from a capillary tube) using
mineral oil, which was then frozen. The detector was placed at a
Acknowledgment. The authors acknowledge support
from the ACS-PRF (PRF 44644-AC3) and from the National
Science Foundation (Grant CHE 0541766) for funds to
purchase the X-ray diffractometer.
Supporting Information Available: Crystallographic informa-
tion files (CIF) for complexes 9-13 and 1H and 13C NMR spectra.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC062476A
5228 Inorganic Chemistry, Vol. 46, No. 13, 2007