Neutral N-O chelated palladium(II) complexes: Syntheses, characterization, and reactivity

Article abstract of DOI:10.1021/om050126a

A series of neutral salicylaldiminato Pd(II) complexes, Pd(Me)(Ph-CH=N-R′)[3-^tBu-2-(O)-C₆H ₃-CH=N-2,6-diⁱPr-C₆H₃] (R = CH ₃, n-Pr, tert-Bu, Ph, benzyl) (3a-3e) and Pd(Me)[2-(CH=N

Full text of DOI:10.1021/om050126a

3508
Organometallics 2005, 24, 3508-3515
Neutral N-O Chelated Palladium(II) Complexes:
Syntheses, Characterization, and Reactivity
Myeongsoon Kang and Ayusman Sen*
Department of Chemistry, The Pennsylvania State University,
University Park, Pennsylvania 16802
Received February 22, 2005
A series of neutral salicylaldiminato Pd(II) complexes, Pd(Me)(Ph-CHdN-R′)[3-tBu-2-(O)-
C6H3-CHdN-2,6-di-iPr-C6H3] (R ) CH3, n-Pr, tert-Bu, Ph, benzyl) (3a-3e) and Pd(Me)[2-
(CHdN-t-Bu)-Py][3-tBu-2-(O)C6H3-CHdN-2,6-di-iPr-C6H3] (4), have been synthesized and
characterized. The structures of complexes 3a, 3c-3e, and 4 have been confirmed by X-ray
analysis. NMR studies utilizing 3c indicate that the insertion of CO into the Pd-Me bond
occurs through a five-coordinate intermediate. The acyl compounds in turn undergo imine
insertion. The neutral complexes 3a-3e show moderate catalytic activity for the polymer-
ization of methyl acrylate at ambient temperature. However, a radical rather than vinyl
insertion mechanism appears to be operative.
Introduction
Grubbs,15,16 Brookhart,17-19 and others.20-22 However,
these cause little or no incorporation of acrylates in
polymerization reactions. Palladium-based neutral cata-
lysts have also been reported by Novak23 and Sen.24
Homopolymerization of methyl acrylate and its copo-
lymerization with 1-alkenes has been achieved. How-
ever, a radical rather than vinyl insertion mechanism
appears to be operative in these cases.
We report here the synthesis and structural charac-
terization of a series of neutral palladium complexes
based on an [N,O] chelating ligand. The reactivity of
the complexes toward CO and methyl acrylate is also
discussed.
Since the advent of metallocene-based catalysts for
ethene and 1-alkene polymerization,1,2 much effort has
been made to develop metallocene-3 and nonmetallocene-
based4-7 complexes for the successful homo- or copo-
lymerization of vinyl monomers through successive
coordination insertion mechanism. In recent years, the
emphasis has been on the development of systems
capable of polymerizing polar vinyl monomers, such as
acrylates. Because of their tolerance toward function-
alities, late transition metal complexes, such as those
of palladium and nickel, have been the particular focus
of the recent work.4-8 For the most part, the complexes
investigated have been cationic, and while several of
them are able to incorporate acrylates in copolymeri-
zation reactions, there is a significant attenuation of
activity due to coordination of the ester functionality to
the metal center.
Results and Discussion
Complex Synthesis. The salicylaldimine ligand was
prepared by condensation of 3-tert-butyl-2-hydroxy-
(10) Ostoja-Starzewski, K. A.; Witte, J. Angew. Chem., Int. Ed. Engl.
1987, 26, 63-64.
(11) Klabunde, U.; Ittel, S. D. J. Mol. Catal. 1987, 41, 123-134.
(12) Klabunde, U.; Mu¨lhaupt, R.; Herskovitz, T.; Janowicz, A. H.;
Calabrese, J.; Ittel, S. D. J. Polym. Sci., Part A: Polym. Chem. 1987,
25, 1989-2003.
(13) Kurtev, K.; Tomov, A. J. Mol. Catal. 1994, 88, 141-150.
(14) Johnson, L. K.; Bennett, A. M. A.; Ittel, S. D.; Wang, L.;
Parthasarathy, A.; Hauptman, E.; Simpson, R. D.; Feldman, J.;
Coughlin, E. B. WO 98/30609, 1998.
(15) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149-
3151.
(16) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460-462.
(17) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217-
3219.
In view of the observed inhibition of polymerization
by polar vinyl monomers for cationic palladium and
nickel complexes, attention has turned to the develop-
ment of less electrophilic, neutral complexes for polym-
erization of such monomers.6,7 Recently, several neutral
nickel catalysts with [N,O] chelating ligands, modeled
after the [P,O] ligands used with SHOP-type
catalysts,9-13 have been reported by DuPont,14
* To whom correspondence should be addressed. E-mail: asen@
psu.edu.
(1) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1996, 127, 143-187.
(2) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(3) Alt, H. G.; Koeppl, A. Chem. Rev. 2000, 100, 1205-1221.
(4) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169-1203.
(18) Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22, 250-
256.
(19) Hicks, F. A.; Jenkins, J. C.; Brookhart, M. Organometallics
2003, 22, 3533-3545.
(20) Rachita, M. J.; Huff, R. L.; Bennett, J. L.; Brookhart, M. J.
Polym. Sci., Part A: Polym. Chem. 2000, 38, 4627-4640.
(21) Dohler, T.; Gorls, H.; Walther, D. Chem. Commun. 2000, 945-
946.
(5) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428-447.
(6) Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534-540.
(7) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283-
315.
(8) Boffa, L. S.; Novak, B. M. Chem. Rev. 2000, 100, 1479-1493.
(9) Ostoja-Starzewski, K. A.; Witte, J. Angew. Chem., Int. Ed. Engl.
1985, 24, 599-601.
(22) Walther, D.; Dohler, T.; Theyssen, N.; Gorls, H. Eur. J. Inorg.
Chem. 2001, 2049-2060.
(23) Tian, G.; Boone, H. W.; Novak, B. M. Macromolecules 2001,
34, 7656-7663.
(24) Elia, C.; Elyashiv-Barad, S.; Sen, A.; Lopez-Fernandez, R.;
Albeniz, A. C.; Espinet, P. Organometallics 2002, 21, 4249-4256.
10.1021/om050126a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 06/04/2005

Neutral N-O Chelated Pd(II) Complexes
Organometallics, Vol. 24, No. 14, 2005 3509
Scheme 1
Scheme 2
Figure 1. ORTEP view of complex 3a. Hydrogen atoms
are omitted for clarity.
shown at -0.47 to -0.86 ppm, with corresponding 13C
NMR resonances at -4.1 to -6.1 ppm.
The molecular structures of the complexes 3a and
3c-3e were determined by single-crystal X-ray struc-
ture analysis. X-ray quality crystals of the complexes
were obtained either by slow diffusion of pentane into
a concentrated solution of 3e in methylene chloride at
room temperature or by cooling a concentrated solution
of a complex in pentane to room temperature (3a and
3d) or to -25 °C (3c). The ORTEP plots of 3a and 3c-
3e are shown in Figures 1-4 (for crystallographic data,
see Table 6 or the Supporting Information for detailed
data). The selected bond lengths and angles for 3a and
3c-3e are given in Tables 1-4. In the solid state they
adopt geometries best described as square planar about
each palladium center, having slight distortions from
idealized geometry. An imine is coordinated through the
nitrogen in the trans position to the nitrogen of the
[N,O] chelate ring. The C-N-C plane including pal-
ladium-bound nitrogen of the imine ligand is roughly
perpendicular to the square planes around each pal-
ladium. The cis N-Pd-O angles for the complexes 3a-e
exceed 90°, due to the formation of six-membered [N,O]
chelate rings. Conversely, the cis N-Pd-C angles,
containing the imine nitrogen and methyl group, are
smaller than 90°.
Complex 4 was prepared to compare the coordinating
ability of an imine to pyridine. The reaction of the
potassium salt 2 with (COD)PdMeCl in the presence of
tert-butylpyridin-2-ylmethylene-amine in toluene af-
forded the target compound 4 as a yellow solid in good
yield after removing the solvent under vacuo following
filtration. The CH imine protons of the monodentate
ligand and [N,O] chelate ring show resonances at 7.71
and 9.94 ppm, respectively. The palladium-bound meth-
yl proton resonates at -0.26 ppm. The molecular
structure of complex 4 was confirmed by single-crystal
X-ray structure analysis. Cooling a concentrated solu-
tion of 4 in pentane to room temperature produced a
yellow crystal that was suitable for analysis. Figure 5
displays the ORTEP diagram of compound 4. Selected
bond distances and bond angles are collected in Table
5 (see Table 6 for crystallographic data or the Support-
ing Information for detailed data). In the solid state it
shows square planar coordination geometry about pal-
ladium, with bond angles slightly deviated from 90° due
benzaldehyde with 2,6-di-isopropylaniline (Scheme 1).
In situ formation of the sodium salt from 1 upon
deprotonation with sodium hydride at room tempera-
ture, followed by reaction with the palladium precursor,
(1,5-cyclooctadiene)palladium(methyl)(chloride), (COD)-
Pd(Me)Cl,25 in toluene was not satisfactory in our case.15
Only starting ligand was recovered. However, by depro-
tonation of 1 with a slight excess of potassium hydride
in THF, potassium salt 2 as a THF adduct with 1 equiv
of THF coordinated was successfully isolated as a yellow
solid after triturating with pentane. The potassium salt
2 was relatively stable over the course of several months
under a dinitrogen atmosphere.
Neutral palladium complexes 3a-3e (Scheme 2) were
first synthesized by combining the potassium salt 2 with
(COD)PdMeCl in the presence of a slight excess of an
appropriate imine in toluene for ca. 12 h. Potassium
chloride was separated by filtration, and the product
was isolated by triturating with ether, followed by
washing with pentane. Complexes 3a-3e were obtained
as yellow solids in yields of ca. 90% upon recrystalliza-
tion from pentane or methylene chloride/pentane.
For all the complexes, coordination of an imine to the
palladium center appears to inhibit the rotation of the
2,6-di-isopropylphenyl group about the N-aryl bond on
the NMR time scale and thus renders the individual
methyl groups of an isopropyl unit inequivalent in the
1H NMR spectrum. Four doublets, each of which inte-
grates to three protons, are observed. For complex 3e,
two doublets, each of which integrates to one proton,
are observed at 5.61 and 5.10 ppm. Clearly, the two
methylene protons on the benzyl group (dN-CH2-Ph)
have different stereochemical environments, which
results in the above two sets of doublets. The resonances
attributed to the palladium-bound methyl groups are
(25) Rulke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, Piet W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769-5778.

3510 Organometallics, Vol. 24, No. 14, 2005
Kang and Sen
Figure 2. ORTEP view of complex 3c. Hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Distances (Å) and Angles
(deg) for 3a
Pd1-N2
Pd1-C12
Pd1-N1
Pd1-O2
Pd2-N3
Pd2-C52
Pd2-N4
Pd2-O1
O2-C1
1.989(10)
2.035(10)
2.038(9)
2.051(7)
1.978(10)
2.010(12)
2.060(9)
2.090(7)
1.275(13)
N4-C45
N4-C44
N1-C7
N1-C21
N2-C14
N2-C13
O1-C33
N3-C39
N3-C53
1.281(13)
1.397(14)
1.299(14)
1.414(14)
1.283(14)
1.525(12)
1.308(11)
1.307(14)
1.489(12)
N2-Pd1-C12
N2-Pd1-N1
C12-Pd1-N1
N2-Pd1-O2
C12-Pd1-O2
N1-Pd1-O2
N3-Pd2-C52
N3-Pd2-N4
C52-Pd2-N4
N3-Pd2-O1
C52-Pd2-O1
N4-Pd2-O1
C1-O2-Pd1
87.0(4)
178.6(5)
94.1(4)
87.4(3)
174.4(4)
91.4(3)
93.5(4)
178.4(5)
87.3(4)
91.4(3)
175.0(4)
87.8(3)
131.0(7)
C45-N4-C44
C45-N4-Pd2
C44-N4-Pd2
C7-N1-C21
C7-N1-Pd1
C21-N1-Pd1
C14-N2-C13
C14-N2-Pd1
C13-N2-Pd1
C33-O1-Pd2
C39-N3-C53
C39-N3-Pd2
C53-N3-Pd2
120.9(10)
127.4(8)
111.7(7)
119.6(9)
120.7(7)
119.6(7)
116.3(10)
129.7(8)
113.9(7)
125.8(6)
113.0(9)
125.0(7)
121.9(7)
Figure 3. ORTEP view of complex 3d. Hydrogen atoms
are omitted for clarity.
1
complexes 3a-3e with CO was monitored by H NMR
spectroscopy. Treatment of neutral palladium complexes
3a-3e with 13CO in CD2Cl2 or chlorobenzene-d5 at
ambient temperature or 60 °C cleanly generates the
corresponding palladium acyl species. The methyl group
of the acyl appears as a doublet resonance around 2.7
ppm (23 °C in CD2Cl2) in the 1H NMR spectrum due to
13C-1H splitting [J ) 6.4 Hz]. The formation of acyl
compounds was confirmed by the proton-coupled 13C
NMR, in which the labeled acyl carbon appears as a
quartet at ∼231 ppm (23 °C in CD2Cl2).
There are two possible pathways for the formation of
the acyl species through CO insertion (Scheme 4). The
first pathway involves a four-coordinated species: for-
mation of a T-shaped three-coordinate species by dis-
sociation of the coordinated imine, followed by the coor-
dination of CO, migratory insertion, and the re-coor-
dination of the imine. The other possible pathway is
through a five-coordinated species: coordination of CO
forming the pyramidal structure, followed by migratory
insertion. To distinguish between these two mecha-
nisms, the kinetics of the reaction was monitored by
following the disappearance of the Pd-CH3 resonance
and/or the appearance of the corresponding Pd-C(O)-
Me resonance in the 1H NMR spectrum in CD2Cl2 over
time. The first-order rate constants and the correspond-
ing enthalpy and entropy of activation for carbon mon-
Figure 4. ORTEP view of complex 3e. Hydrogen atoms
are omitted for clarity.
to constraint of the chelate ring. The nitrogen of the
pyridine ring rather than that of the imine functionality
is bonded to the metal center. Since both nitrogens are
sp2 hybridized, their coordinating abilities might be
expected to be similar. On this basis, the observed
selectivity can be ascribed to the steric crowding around
the imine nitrogen due to the neighboring tert-butyl
group. Note, however, despite this crowding the nitrogen
atom can coordinate to the metal as seen in 3c.
Mechanistic Studies of CO Insertion into the
Pd-Me Bond in Complex 3c. The reaction of the

Neutral N-O Chelated Pd(II) Complexes
Organometallics, Vol. 24, No. 14, 2005 3511
Table 2. Selected bond distances (Å) and angles
(deg) for 3c
Pd1-C12
Pd1-N1
Pd1-N2
Pd1-O1
Pd2-N3
Pd2-C52
Pd2-N4
Pd2-O2
Pd3-N5
Pd3-C89
Pd3-N6
Pd3-O3
N1-C7
2.026(3)
2.0314(19)
2.059(2)
O1-C1
1.285(3)
1.302(3)
1.449(3)
1.277(3)
1.521(3)
1.284(3)
1.282(3)
1.517(3)
1.285(3)
1.280(3)
1.515(3)
1.299(3)
1.453(3)
N5-C67
N5-C71
N6-C82
N6-C102
O3-C61
N2-C25
N2-C92
O2-C32
N4-C53
N4-C60
N3-C38
N3-C43
2.0990(16)
2.0272(19)
2.023(2)
2.071(2)
2.0944(16)
2.0234(19)
2.028(2)
2.066(2)
2.0950(16)
1.294(3)
N1-C13
1.451(3)
C12-Pd1-N1
C12-Pd1-N2
N1-Pd1-N2
C12-Pd1-O1
N1-Pd1-O1
N2-Pd1-O1
N3-Pd2-C52
N3-Pd2-N4
C52-Pd2-N4
N3-Pd2-O2
C52-Pd2-O2
N4-Pd2-O2
N5-Pd3-C89
N5-Pd3-N6
C89-Pd3-N6
N5-Pd3-O3
C89-Pd3-O3
N6-Pd3-O3
C7-N1-C13
C7-N1-Pd1
93.36(9)
88.82(9)
177.68(8)
175.50(9)
91.08(7)
86.74(7)
92.45(9)
178.13(8)
89.28(9)
91.05(7)
176.50(9)
87.22(7)
92.45(9)
176.09(8)
89.05(9)
91.28(7)
176.08(9)
87.31(7)
114.01(19)
C13-N1-Pd1
C1-O1-Pd1
123.47(15)
128.26(15)
113.35(19)
122.30(16)
124.08(14)
116.6(2)
123.31(18)
120.04(15)
128.19(14)
117.3(2)
123.13(18)
119.58(15)
128.42(15)
116.1(2)
123.94(18)
119.98(15)
113.00(19)
122.37(16)
124.59(15)
Figure 5. ORTEP view of complex 4. Hydrogen atoms are
omitted for clarity.
C67-N5-C71
C67-N5-Pd3
C71-N5-Pd3
C82-N6-C102
C82-N6-Pd3
C102-N6-Pd3
C61-O3-Pd3
C25-N2-C92
C25-N2-Pd1
C92-N2-Pd1
C32-O2-Pd2
C53-N4-C60
C53-N4-Pd2
C60-N4-Pd2
C38-N3-C43
C38-N3-Pd2
C43-N3-Pd2
Table 4. Selected Bond Distances (Å) and Angles
(deg) for 3e
O1-C7
1.280(3)
N1-C1
1.296(3)
1.447(3)
1.280(3)
1.468(3)
O1-Pd1
Pd1-N1
Pd1-C24
Pd1-N2
2.0880(16)
2.0126(18)
2.020(3)
N1-C12
N2-C25
N2-C32
2.0386(19)
C7-O1-Pd1
N1-Pd1-C24
N1-Pd1-N2
C24-Pd1-N2
N1-Pd1-O1
C24-Pd1-O1
N2-Pd1-O1
128.02(14)
92.89(9)
178.87(7)
88.08(9)
91.64(7)
175.39(8)
87.40(7)
C1-N1-C12
C1-N1-Pd1
C12-N1-Pd1
C25-N2-C32
C25-N2-Pd1
C32-N2-Pd1
113.94(18)
122.46(15)
123.58(15)
117.1(2)
127.01(17)
115.89(15)
122.43(16)
Table 5. Selected Bond Distances (Å) and Angles
(deg) for 4
Table 3. Selected Bond Distances (Å) and Angles
(deg) for 3d
Pd1-N2
Pd1-C12
Pd1-N1
Pd1-O1
Pd2-N4
Pd2-C42
Pd2-N5
Pd2-O2
N2-C23
N2-C27
N5-C56
2.023(10)
2.029(17)
2.039(11)
2.069(12)
1.981(11)
2.017(19)
2.073(11)
2.084(12)
1.323(14)
1.364(16)
1.339(16)
N5-C52
N4-C36
N4-C41
N1-C7
N1-C13
O2-C30
O1-C1
N3-C28
N3-C29
N6-C57
N6-C58
1.368(18)
1.29(2)
1.433(19)
1.264(18)
1.46(2)
1.316(14)
1.23(2)
1.149(16)
1.500(18)
1.303(15)
1.485(15)
Pd1-C21
Pd1-N1
Pd1-N2
Pd1-O1
Pd2-N3
Pd2-O2
Pd2-C58
Pd2-N4
N1-C7
2.009(9)
2.024(8)
2.048(4)
2.105(6)
1.992(6)
2.048(7)
2.075(10)
2.096(5)
1.267(11)
N1-C12
N3-C48
N3-C49
O2-C38
O1-C1
N2-C28
N2-C22
C59-N4
C65-N4
1.405(11)
1.332(9)
1.499(10)
1.303(10)
1.275(11
1.289(6)
1.511(9)
1.567(10)
1.245(7)
C21-Pd1-N1
C21-Pd1-N2
N1-Pd1-N2
C21-Pd1-O1
N1-Pd1-O1
N2-Pd1-O1
N3-Pd2-O2
N3-Pd2-C58
O2-Pd2-C58
N3-Pd2-N4
O2-Pd2-N4
C58-Pd2-N4
C7-N1-C12
94.7(3)
85.7(3)
165.9(2)
173.3(3)
91.9(3)
87.7(2)
90.8(3)
93.3(4)
175.9(4)
170.0(2)
87.3(2)
88.7(3)
118.3(7)
C7-N1-Pd1
C12-N1-Pd1
C48-N3-C49
C48-N3-Pd2
C49-N3-Pd2
C38-O2-Pd2
C1-O1-Pd1
C28-N2-C22
C28-N2-Pd1
C22-N2-Pd1
C65-N4-C59
C65-N4-Pd2
C59-N4-Pd2
122.4(6)
119.0(6)
112.0(6)
124.0(5)
123.7(5)
132.7(5)
124.4(5)
114.4(5)
128.7(4)
116.9(4)
115.4(6)
119.1(5)
125.4(5)
N2-Pd1-C12
N2-Pd1-N1
C12-Pd1-N1
N2-Pd1-O1
C12-Pd1-O1
N1-Pd1-O1
N4-Pd2-C42
N4-Pd2-N5
C42-Pd2-N5
N4-Pd2-O2
C42-Pd2-O2
N5-Pd2-O2
C23-N2-C27
C23-N2-Pd1
89.2(5)
174.7(6)
95.3(6)
C27-N2-Pd1
C56-N5-C52
C56-N5-Pd2
C52-N5-Pd2
C36-N4-C41
C36-N4-Pd2
C41-N4-Pd2
C7-N1-C13
C7-N1-Pd1
C13-N1-Pd1
C30-O2-Pd2
C1-O1-Pd1
C28-N3-C29
C57-N6-C58
124.8(8)
119.0(12)
120.8(9)
85.2(5)
119.5(9)
174.2(6)
90.2(5)
91.3(6)
177.5(5)
89.4(6)
92.0(5)
176.6(6)
87.2(4)
117.3(11)
117.8(8)
115.2(13)
118.4(10)
126.4(12)
115.5(12)
126.9(11)
117.6(10)
128.6(9)
123.5(10)
127.0(13)
119.1(12)
oxide insertion into the Pd(II)-Me bond for 3c in the
absence or presence of benzylidene-tert-butylamine are
listed in Table 7. It is clear that the presence of an
excess imine has little effect on the rate of the reaction.
The lack of inhibition by the addition of imine, together
with a significant negative activation entropy, suggests
that CO insertion proceeds through a five-coordinate
intermediate (route 2, Scheme 4).
Insertion of Imine into the Pd-Acyl Bond. Reac-
tion of the title complexes 3a-e with excess imine in
the presence of 13CO in chlorobenzene-d5 was monitored
by 1H, 13C{1H}, and proton-coupled 13C NMR spectros-
copy. The insertion of CO into the Pd-Me bond to form
the corresponding acyl compound was observed at
ambient temperature (compound 5, Scheme 4, carbonyl
resonance ∼231 ppm).
Warming the reaction mixture to 40 °C resulted in
the formation of a new species with a carbonyl reso-
nance at ∼214 ppm. The concentration of this species
is gradually increased at the expense of the acyl
compound. To rule out the possibility that the resonance
at 214 ppm was due to an isomeric acyl species, complex
6 incorporating the symmetrical bidentate ligand [2-[(2,6-

3512 Organometallics, Vol. 24, No. 14, 2005
Kang and Sen
Table 6. Crystallographic Data and Data Collection Parameters for Complexes 3a-e and 4
3a
3c
3d
3e
4
formula
mol wt
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
C
32H42N2OPd
C105H144N6O3Pd3
1857.46
98(2)
0.71073
monoclinic
P2(1)/c
11.4483(11)
19.4368(19)
43.765(4)
90
C74H88N4O2Pd2
1278.28
98(2)
0.71073
triclinic
P1h
C38H46N2OPd
653.17
C34H47N3OPd
620.18
98(2) K
0.71073 Å
triclinic
P1h
577.08
98(2)
218(2)
0.71073
triclinic
P1h
0.71073
triclinic
P1h
11.1653(17)
11.3688(17)
13.611(2)
105.623(2)
99.448(2)
113.062(2)
1458.3(4)
2
11.9939(16)
12.1298(16)
13.9255(18)
82.955(2)
69.190(2)
60.381(2)
1642.8(4)
2
9.6685(4)
13.0421(6)
14.8920(7)
71.6700(10)
81.2500(10)
71.0830(10)
1683.65(13)
2
10.895(2)
13.620(3)
13.959(3)
64.930(3)
71.179(3)
73.707(3)
1750.8(6)
2
b (Å)
c (Å)
R (deg)
â (deg)
90
90
γ (deg)
volume (Å3)
Z
9738.5(17)
4
3912
0.0384
0.0358
1.267
F(000)
604
668
684
694
R(F)
0.0207
0.0164
0.0364
0.0263
Rw(F)
0.0586
0.0532
0.0937
0.0849
Dcalcd(g/cm3)
1.314
1.292
1.288
1.245
Scheme 3
Table 7. Kinetic Data for Insertion of CO into
Pd(II)-Me Bond in Complex 3c
k
∆Hq
∆Sq
T (K)
(×104 s-1
)
(kcal/mol) (cal/K‚mol)
no imine
273.99
286.42
0.075
0.25
0.079
0.20
19.0
14.7
-12.5
-28.1
Figure 6. ORTEP view of complex 6. Hydrogen atoms are
omitted for clarity.
50 equiv imine 273.99
286.42
Table 9. Crystallographic Data and Data
Collection Parameters for Complexes 6
Table 8. Selected Bond Distances (Å) and Angles
(deg) for 6
formula
mol wt
C44H57N3Pd
734.33
Pd1-N1
Pd1-N3
Pd1-N2
Pd1-C44
N3-C30
2.0432(12)
2.0550(13)
2.1380(12)
2.0423(17)
1.4925(19))
N1-C1
N1-C6
N2-C3
N2-C18
N3-C37
1.335(2)
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
150(2)
1.4398(19)
1.3192(19)
1.4368(18)
1.281(2)
0.71073
monoclinic
P2(1)/c
8.8271(4)
19.8265(10)
22.4034(11)
90
b (Å)
C44-Pd1-N1
N2-Pd1-N1
N1-Pd1-N3
91.87(6)
91.83(5)
172.29(5)
C44-Pd1-N3
N3-Pd1-N2
C44-Pd1-N2
81.11(6)
95.33(5)
175.53(6)
c (Å)
R (deg)
â (deg)
94.9130(10)
90
γ (deg)
volume (Å3)
Z
3906.4(3)
4
diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imi-
no]pent-2-ene, (2,6-di-iPr-C6H3)-NdC(CH3)-CHdC(CH3)-
NH-(2,6-di-iPr-C6H3), and N-benzylbenzylideneimine,
Ph-CHdN-CH2-Ph, were prepared and utilized (Figure
6, for crystal data see Tables 8 and 9). Figure 7 shows
part of the proton-coupled 13C NMR (C6D5Cl) spectrum
observed in the reaction of 6 with 13CO and PhCHd
NCH2Ph at 50 °C. The quartet at the peak at 231.1 ppm
corresponds to the acyl carbon formed by CO insertion
into the Pd-Me bond. The simple quartet at 168.7 ppm
can be ascribed to the carbonyl resonance of the species
formed by imine insertion into the Pd-acyl bond, as has
been reported previously (species 7, Scheme 5).26,27
F(000)
1552
R(F)
0.0256
Rw(F)
0.0677
Dcalcd (g/cm3)
1.249
However, this reaction is not clean, as evidenced by the
other resonances including a ketone-like carbonyl reso-
nance at 214.4 ppm. Unfortunately, our inability to
isolate and characterize the formed products has sty-
mied further understanding of the reaction.
Polymerization of Polar or Nonpolar Vinyl Mono-
mers. Polymerization of nonpolar vinyl monomers, such
as ethene, propene, or norbornene, using the complexes
3a-e or 4 was unsuccessful. Presumably this is due to
the failure of the coordinated imine to dissociate and
provide a vacant coordination site for the incoming
(26) Kacker, S.; Kim, J. S.; Sen, A. Angew. Chem., Int. Ed. 1998,
37, 1251-1253.
(27) Dghaym, R. D.; Yaccato, K. J.; Arndtsen, B. A. Organometallics
1998, 17, 4-6.

Neutral N-O Chelated Pd(II) Complexes
Organometallics, Vol. 24, No. 14, 2005 3513
Figure 7. Part of the proton-coupled 13C NMR (C6D5Cl) spectrum observed in the reaction of 6 with 13CO and PhCHd
NCH2Ph.
Scheme 4
Scheme 5. Proposed Imine Insertion Pathway
tant reason for high polydispersity is that the rapid
increase in solution viscosity prevented effective stir-
ring. Indeed, decreasing the monomer concentration by
increasing the amount of solvent from 6 mL to 30 mL
gave a higher polymer yield with a narrower polydis-
persity (entry 4 versus 5).
One focus of this study was the possible application
of the palladium-based neutral complexes as catalysts
for the vinyl insertion polymerization of polar or non-
polar vinyl monomers. Recently, Sen24 as well as Novak
and co-workers23 reported on the homopolymerization
of methyl acrylate using neutral palladium compounds
where a radical mechanism was invoked. Complexes
3a-e or 4 failed to initiate the polymerization of methyl
methacrylate or styrene, two other monomers that are
readily polymerized by a radical pathway. However, the
polymerization of methyl acrylate by 3a-e or 4 was
completely halted upon addition of the radical trap,
galvinoxyl, to the reaction mixture. Thus, a radical
(albeit “nontraditional”) pathway appears to be opera-
tive, although there has been “a warning on the use of
radical traps as a test for radical mechanisms”.28
In conclusion, we have synthesized a serious of
neutral salicylaldiminato Pd(II) complexes: Pd(Me)(Ph-
CHdN-R′)[3-tBu-2-(O)C6H3-CHdN-2,6-di-iPr-C6H3] (R
) CH3, n-Pr, tert-Bu, Ph, benzyl) (3a-3e) and Pd(Me)-
[2-(CHdN-t-Bu)-Py][3-tBu-2-(O)C6H3-CHdN-2,6-di-iPr-
C6H3] (4). These complexes have been isolated and
characterized spectroscopically, and the solid-state struc-
Table 10. Polymerization of Methyl Acrylate Using
Complexes 3a-e and 4a
c
c
entry catalyst time (h) yield (g) Mn (×10-3
)
Mw/Mn
1
2
3
4
5b
6
7
3a
3b
3c
3d
3d
3e
4
3
3
3
3
3
3
3
1.1
1.1
1.1
1.7
2.9
2.0
0.7
211
970
1584
1616
346
1.78
6.74
5.83
5.85
2.14
612
3.10
a Reaction conditions: Pd complex (3.1 × 10-5 mol), MA (8 g),
chlorobenzene (6 mL), ambient temperature. b In chlorobenzene
(30 mL). c Molecular weight determined by GPC versus polysty-
rene standards with chloroform as eluent.
monomer. The observation that CO insertion proceeds
without imine dissociation (Scheme 4, route 2) supports
this hypothesis.
Polymerization of methyl acrylate using catalysts
3a-e or 4 was carried out in chlorobenzene at ambient
temperature (Table 10). Low to moderate yields of poly-
(methyl acrylate) were obtained at the condition indi-
cated. The polymers produced have high (Mn > 211 000)
to ultrahigh (Mn > 1 600 000) molecular weight and
showed high polydispersity index in general. An impor-
(28) Albeniz, A. C.; Espinet, P.; Lopez-Fernandez, R.; Sen, A. J. Am.
Chem. Soc. 2002, 124, 11278-11279.

3514 Organometallics, Vol. 24, No. 14, 2005
Kang and Sen
solution was stirred at room temperature for 12 h. Removal
of solvent in vacuo yielded a yellow oil. Residual 2,6-diisopro-
pylaniline was further removed by vacuum distillation, giving
a yellow oily product that solidified upon cooling. 1H NMR
(CDCl3) (ppm): 13.65 (br, 1H, -OH), 8.35 (s, 1H, -CHdN-),
7.49-6.91 (m, 6H, Ar-H), 3.06 (sept, 2H, -CH(CH3)2), 1.52 (s,
9H, -C(CH3)3), 1.22 (d, 12H, -CH(CH3)2). 13C NMR (CDCl3)
(ppm): 167.96 (-CHdN-), 160.99, 146.72, 139.31, 137.95,
131.08, 130.78, 125.70, 123.57, 118.96, 118.60 (Ar), 35.22
(-CMe3), 29.51 (-C(CH3)3), 28.49 (-CH(CH3)2), 23.73 (-CH-
(CH3)2).
tures of the complexes have also been characterized by
X-ray single-crystal structure analysis. According to the
results of the NMR studies, the complexes react with
carbon monoxide to form corresponding acyl complexes
through a five-coordinated intermediate. The acyl com-
pounds in turn undergo imine insertion. The neutral
complexes show moderate catalytic activity for the
polymerization of methyl acrylate at ambient temper-
ature, producing polymers with a high molecular weight
but broad polydispersity index. The complexes are
unreactive toward insertion polymerization of alkenes
presumably because of the inability of the coordinate
imine (or pyridine) to undergo ready displacement by
an incoming substrate. Efforts to synthesize more
substitutionally labile complexes are underway.
[3-tBu-2-(OK)C6H3-CHdN-2,6-di-iPr-C6H3]‚THF (2). To
a stirred suspension of KH (0.19 g, 4.68 mmol) in THF (30
mL) was added ligand 1 (0.79 g, 2.34 mmol) in THF (20 mL)
at room temperature. The reaction mixture was stirred for 2
h and filtered to remove excess KH. After removing solvent
under vacuum, a small amount of pentane was added to
dissolve starting material. Upon filtering and washing with
pentane, the potassium salt THF adduct was obtained as a
yellow solid. Yield: 0.97 g, 92%.
Experimental Section
Generation Considerations. All syntheses and manipula-
tions of air- and moisture-sensitive compounds were carried
out in flame-dried Schlenk-type glassware on a dual-manifold
Schlenk line, on a high vacuum with argon line, or in a
nitrogen-filled glovebox.
Pd(Me)(Ph-CHdN-CH3)[3-tBu-2-(O)C6H3-CHdN-2,6-di-
iPr-C6H3] (3a). To a mixture of [3-tBu-2-(OK)C6H3-CHdN-2,6-
di-iPr-C6H3]‚THF (0.42 g, 0.94 mmol) and Ph-CHdN-CH3 (0.11
g, 0.94 mmol) in toluene (30 mL) was added (COD)PdMeCl
(0.25 g, 0.94 mmol) in toluene (10 mL). The reaction mixture
was stirred for 12 h and was filtered to remove a small
quantity of dark insoluble material. The solvent was removed
in vacuo to yield a yellow solid. Recrystallization from pentane
gave a yellow crystalline solid, which was suitable for X-ray
crystal structure analysis. Yield: 0.49 g, 91%. 1H NMR (CD2-
Cl2) (ppm): 8.36 (s, 1H, Pd-O-Ar-CHdN-), 7.74 (s, 1H, Ph-
CHdN-CH3), 8.98 (d), 7.58-7.49 (m), 7.28 (dd), 7.21-7.16 (dd),
7.00 (dd), 6.35 (t) (11H, Ar-H), 3.99 (s, 3H, Ph-CHdN-CH3)
3.55, 3.22 (hept each, 2H, Ar-CH(CH3)2), 1.29 (s, 9H, Ar-
C(CH3)3), 1.38, 1.24, 1.18, 1.16 (d each, 12H, Ar-CH(CH3)2),
-0.49 (s, 3H, Pd-CH3). 13C NMR (CD2Cl2) (ppm): 167.7 (Pd-
O-Ar-CHdN-), 166.1 (Ph-CHdN-CH3), 141.6, 141.5, 134.9,
132.4, 131.3, 130.7, 129.1, 128.9, 128.6, 128.5, 126.4, 123.5,
119.9, 112.0 (Ar), 53.4 (Ph-CHdN-CH3) 35.4 (Ar-C(CH3)3), 29.5
(Ar-C(CH3)3), 28.0 (Ar-CH(CH3)2), 25.2, 25.0, 23.0, 22.7 (Ar-
CH(CH3)2), -5.6 (Pd-CH3).
Nuclear magnetic resonance (NMR) spectra were recorded
on a Bruker DRX 400 NMR spectrometer, DPX 300 NMR
spectrometer, and CDPX 300 NMR spectrometer. Splitting
patterns are designated as follows: s, singlet; bs, broad singlet;
d, doublet; dd, doublet of doublets; t, triplet; td, triplet of
1
doublets; sept, septet; m, multiplet. All H NMR spectra are
reported in δ units, parts per million (ppm) downfield from
tetramethylsilane. All 13C NMR spectra are reported in ppm
relative to tetramethylsilane using CD2Cl2, toluene-d8, or
chlorobenzene-d5 as an internal standard. Variable-tempera-
1
ture H NMR experiments were performed on a Bruker DPX
300 NMR spectrometer, using CD2Cl2, toluene-d8, or chlo-
robenzene-d5 as solvent. Actual NMR probe temperatures were
measured using anhydrous methanol (with 0.03% concentrated
HCl) or ethylene glycol (neat) in a 5 mm NMR tube. NMR
analyses of polymers were performed on a Bruker DPX 300
NMR spectrometer at ambient or elevated temperature, using
CDCl3, chlorobenzene-d5, dichlorobenzene-d4, or tetrachloro-
ethane-d2 as solvent unless otherwise noted.
Size exclusion chromatography data were obtained on a
Shimadzu SEC System using a three-column bank (Styragel
7.8 × 300 mm columns, 100-5000 D, 500-30 000 D, 2000-
4 000 000 D), a Shimadzu RID-10A differential refractometer,
and a Shimadzu LC-10AT pump/controller. Size exclusion
chromatography was performed in chloroform at ambient
temperature and calibrated to polystyrene standards.
Chlorobenzene and dichloromethane was obtained from
Aldrich and dried via passage over a column of activated
alumina (LaRoche A-2).29 Toluene and diethyl ether were
deoxygenated and dried via passage over a column of activated
alumina (LaRoche A-2) and columns of Engelhard CU-0226S.29
Pentane and tetrahydrofuran were distilled under nitrogen
from sodium benzophenone ketyl. All solvents were degassed
by repeated freeze-pump-thaw cycles and stored over 4 Å
molecular sieves under nitrogen. Norbornene was purchased
from Acros Organics and used without further purification.
Methyl acrylate and methyl methacrylate were purchased from
Aldrich and used after repeated freeze-pump-thaw cycles
prior to use. (1,5-Cyclooctadien)palladium(methyl)(chloride),
[(COD)Pd(Me)(Cl)], was prepared as previously reported.25
3-tBu-2-(OH)C6H3-CHdN-2,6-di-iPr-C6H3 (1). To 3-tert-
butyl-2-hydroxybenzaldehyde (1 g, 5.6 mmol) in methanol (50
mL) was added 2,6-diisopropylaniline (1.5 g, 8.4 mmol),
followed a catalytic amount of formic acid (2 drops). The
Pd(Me)(Ph-CHdN-CH2-CH2-CH3)[3-tBu-2-(O)C6H3-CHd
N-2,6-di-iPr-C6H3] (3b). To a mixture of [3-tBu-2-(OK)C6H3-
CHdN-2,6-di-iPr-C6H3]‚THF (0.42 g, 0.94 mmol) and Ph-CHd
N-CH2-CH2-CH3 (0.14 g, 0.94 mmol) in toluene (30 mL) was
added (COD)PdMeCl (0.25 g, 0.94 mmol) in toluene (10 mL).
The reaction mixture was stirred for 12 h and then was filtered
to remove a small quantity of dark insoluble material. The
solvent was removed in vacuo to yield a yellow solid. Recrys-
tallization from pentane gave a yellow crystalline solid, which
was suitable for X-ray crystal structure analysis. Yield: 0.51
1
g, 89%. H NMR (CD2Cl2) (ppm): 8.38 (s, 1H, Pd-O-Ar-CHd
N-), 7.70 (s, 1H, Ph-CHdN-CH2-Ph), 8.93 (d), 7.54-7.43 (m),
7.24 (dd), 7.17-7.12 (m), 6.96 (dd), 6.31 (t) (11H, Ar-H), 4.33,
3.68 (m each, 2H, Ph-CHdN-CHH-CH2-CH3), 3.64, 3.39 (hept,
2H, Ar-CH(CH3)2), 2.31 (sext, 2H, N-CH2-CH2-CH3), 1.25 (s,
9H, Ar-C(CH3)3), 1.34, 1.21, 1.15, 1.12 (d each, 12H, Ar-CH-
(CH3)2), 1.02 (Ph-CHdN-CH2-CH2-CH3), -0.62 (s, 3H, Pd-
CH3). 13C NMR (CD2Cl2) (ppm): 167.0 (Pd-O-Ar-CHdN-),
166.0 (Ph-CHdN-CH2-CH2-CH3), 148.7, 141.5, 141.4, 135.0,
134.2, 132.3, 131.4, 130.7, 128.5, 126.3, 124.5, 123.5, 123.4,
120.0, 112.0 (Ar), 68.6 (Ph-CHdN-CH2-CH2-CH3), 35.3 (Ar-
C(CH3)3) 29.5 (Ar-C(CH3)3), 28.1, 28.0 (Ar-CH(CH3)2), 25.0 (Ph-
CHdN-CH2-CH2-CH3), 25.3, 25.1, 23.1, 22.6 (Ar-CH(CH3)2),
11.8 (Ph-CHdN-CH2-CH2-CH3), -5.0 (Pd-CH3).
Pd(Me)(Ph-CHdN-t-Bu)[3-tBu-2-(O)C6H3-CHdN-2,6-di-
iPr-C6H3] (3c). To a mixture of [3-tBu-2-(OK)C6H3-CHdN-2,6-
di-iPr-C6H3]‚THF (0.42 g, 0.94 mmol) and Ph-CHdN-t-Bu (0.15
g, 0.94 mmol) in toluene (30 mL) was added (COD)PdMeCl
(0.25 g, 0.94 mmol) in toluene (10 mL). The reaction mixture
was stirred for 12 h and then filtered to remove a small
(29) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.

Neutral N-O Chelated Pd(II) Complexes
Organometallics, Vol. 24, No. 14, 2005 3515
quantity of dark insoluble material. The solvent was removed
in vacuo to yield a yellow solid. Recrystallization from pentane
at -25 °C gave a yellow crystalline solid, which was suitable
for X-ray crystal structure analysis. Yield: 0.52 g, 90%. 1H
NMR (CD2Cl2) (ppm): 8.51 (s, 1H, Pd-O-Ar-CHdN-), 7.69 (s,
1H, Ph-CHdN-t-Bu), 8.92 (d), 7.52-7.43 (m), 7.25 (dd), 7.15-
7.07 (m), 6.95 (dd), 6.31 (t) (11H, Ar-H), 3.69, 3.21 (hept each,
2H, Ar-CH(CH3)2), 1.76 (s, 9H, -N-C(CH3)3), 1.29 (s, 9H, Ar-
C(CH3)3), 1.24, 1.12, 1.10, 1.03 (d each, 12H, Ar-CH(CH3)2),
-0.66 (s, 3H, Pd-CH3). 13C NMR(CD2Cl2) (ppm): 169.1 (Pd-
O-Ar-CHdN-), 166.2 (Ph-CHdN-t-Bu), 148.8, 141.6, 141.5,
135.9, 135.1, 131.9, 131.4, 130.4, 128.3, 126.2, 123.5, 123.3,
120.0, 111.8(Ar), 64.7 (-N-C(CH3)3), 35.4 (Ar-C(CH3)3), 32.1
(-N-C(CH3)3), 29.7 (Ar-C(CH3)3), 28.0, 27.9 (Ar-CH(CH3)2),
25.3, 25.1, 23.0, 22.8 (Ar-CH(CH3)2), -6.01 (Pd-CH3).
1.02 (s, 9H, dN-C(CH3)3), 1.35, 1.16, 1.12 (d each, 12H, Ar-
CH(CH3)2), -0.26 (s, 3H, Pd-CH3). 13C NMR (CD2Cl2) (ppm):
166.4 (Ph-CHdN-t-Bu), 156.9 (Pd-O-Ar-CHdN-), 168.2, 155.9,
152.3, 141.5, 137.7, 134.7, 131.4, 129.4, 128.6, 126.5, 125.2,
123.7, 123.5, 123.1, 119.8, 112.1 (Ar), 58.7 (dN-CH(CH3)2), 35.1
(Ar-CH(CH3)2), 29.5 (Ar-C(CH3)3), 29.3 (dN-C(CH3)3), 28.3, 28.1
(Ar-CH(CH3)2), 25.0, 22.9 (Ar-CH(CH3)2), -4.0 (Pd-CH3).
Pd(Me)(Ph-CHdN-CH2-Ph)[2,6-di-iPr-C6H3-N-C(Me)-
CH-C(Me)-N-2,6-di-iPr-C6H3] (6). To a mixture of [2,6-di-
iPr-C6H3-NdC(Me)-CHdC(Me)-N(H)-2,6-di-iPr-C6H3]‚Tl (0.50
g, 0.8 mmol) and Ph-CHdN-CH2-Ph (0.15 g, 0.8 mmol) in
toluene (30 mL) was added (COD)PdMeCl (0.21 g, 0.8 mmol)
in toluene (10 mL). The reaction mixture was stirred for 12 h
and then was filtered to remove a small quantity of dark
insoluble material. The solvent was removed in vacuo to yield
a yellow solid. Recrystallization from methylene dichloride and
pentane gave a yellow crystalline solid, which was suitable
for X-ray crystal structure analysis. Yield: 0.57 g, 97%. 1H
NMR (CD2Cl2) (ppm): 7.30 (s, 1H, Ph-CHdN-), 9.05 (d), 7.46-
7.32 (m), 7.22-6.86 (m), 6.63 (d) (16H, Ar-H), 4.68 (s, N-C(CH3)-
CH-C(CH3)-N), 4.57, 3.29 (d each, 2H, Ph-CHH-N), 3.79, 3.66,
3.41, 2.86 (hept each, 4H, Ar-CH(CH3)2, Ar-CH(CH3)2, Ar-
CH(CH3)2, Ar-CH(CH3)2), 1.56, 1.53 (s each, 6H, N-C(CH3)-
CH-C(CH3)-N), 1.50, 1.24, 1.20, 1.15, 1.06, 0.84, 1.82, 0.33 (d
each, 24H, Ar-CH(CH3)2), -0.74 (s, 3H, Pd-CH3). 13C DEPT135
NMR (CD2Cl2): δ 166.3 (-CHdN-), 132.4, 131.5, 129.2, 128.5,
125.0, 124.6, 124.2, 123.4, 123.2 (Ar), 94.5 (-C(CH3)-CH-
C(CH3)-), 65.9 (Ph-CH2-N), 28.4, 28.1, 27.7, 27.4 (Ar-CH-
(CH3)2), 26.2 ((-C(CH3)-CH-C(CH3)-), 25.4, 25.1, 24.9, 24.8,
24.7, 24.2, 24.1, 23.8 (Ar-CH(CH3)2), 4.8 (Pd-CH3).
General Procedures for Polymerization Reactions. In
a drybox under a nitrogen atmosphere, a title complex (3.1 ×
10-5 mol) was dissolved in chlorobenzene (6 mL or 30 mL) in
a 100 mL Schlenk flask. A specified amount of methyl acrylate
was introduced to the flask. The reaction mixture was stirred
at the desired temperature. After the specified reaction time,
the reaction was quenched with methanol. The precipitated
polymer was filtered and washed with methanol. Volatiles
were removed from the polymer in vacuo, and the polymer was
dried under vacuum overnight.
General Procedure for NMR Experiments. In a drybox
under a nitrogen atmosphere, 3c (1.7 × 10-5 mol) with or
without Ph-CdN-n-Pr (8.3 × 10-4 mol) was weighed into a
high-pressure NMR tube. CD2Cl2 (1 mL) was added to the
NMR tube. The tube was then capped, removed from the
drybox, and cooled to ca. -90 °C. After applying vacuum
briefly, the mixture are allowed to reach ambient temperature.
The NMR tube was then charged with 13C-labeled carbon
monoxide (50 psi) and cooled again to ca. -90 °C using a liquid
nitrogen/acetone slurry. The tube was shaken very briefly and
transferred to the NMR probe, which was at preset temper-
ature. NMR spectra were acquired every 10 min at the desired
temperature.
Pd(Me)(Ph-CHdN-Ph)[3-tBu-2-(O)C6H3-CHdN-2,6-di-
iPr-C6H3] (3d). To a mixture of [3-tBu-2-(OK)C6H3-CHdN-2,6-
di-iPr-C6H3]‚THF (0.42 g, 0.94 mmol) and Ph-CHdN-Ph (0.17
g, 0.94 mmol) in toluene (30 mL) was added (COD)PdMeCl
(0.25 g, 0.94 mmol) in toluene (10 mL). The reaction mixture
was stirred for 12 h and then was filtered to remove a small
quantity of dark insoluble material. The solvent was removed
in vacuo to yield a yellow solid. Recrystallization from pentane
gave a yellow crystalline solid, which was suitable for X-ray
crystal structure analysis. Yield: 0.55 g, 92%. 1H NMR (CD2-
Cl2) (ppm): 8.56 (s, 1H, Pd-O-Ar-CHdN-), 7.70 (s, 1H, Ph-
CHdN-Ph), 9.17 (d), 7.81 (d), 7.61-7.15 (m), 6.95 (d), 6.30 (t)
(16H, Ar-H), 3.54, 3.47 (hept each, 2H, Ar-CH(CH3)2), 1.13 (s,
9H, Ar-C(CH3)3), 1.25, 1.24, 1.16, 1.10 (d each, 12H, Ar-CH-
(CH3)2), -0.47 (s, 3H, Pd-CH3). 13C NMR (CD2Cl2) (ppm): 168.1
(Pd-O-Ar-CHdN-), 166.1 (Ph-CHdN-CH2-Ph), 153.0, 148.7,
141.6, 141.4, 134.8, 133.3, 131.4, 131.3, 129.2, 128.7, 128.0,
126.4, 124.1, 123.6, 119.8, 112.0 (Ar), 35.3 (Ar-C(CH3)3) 29.4
(Ar-C(CH3)3), 28.0 (Ar-CH(CH3)2), 25.3, 25.0, 23.0, 22.6 (Ar-
CH(CH3)2), -4.1 (Pd-CH3).
Pd(Me)(Ph-CHdN-CH2-Ph)[3-tBu-2-(O)C6H3-CHdN-2,6-
di-iPr-C6H3] (3e). To a mixture of [3-tBu-2-(OK)C6H3-CHdN-
2,6-di-iPr-C6H3]‚THF (0.23 g, 0.52 mmol) and Ph-CHdN-CH2-
Ph (0.11 g, 0.56 mmol) in toluene (30 mL) was added
(COD)PdMeCl (0.15 g, 0.57 mmol) in toluene (10 mL). The
reaction mixture was stirred for 12 h and then was filtered to
remove a small quantity of dark insoluble material. The
solvent was removed in vacuo to yield a yellow solid. Recrys-
tallization from methylene dichloride and pentane gave a
yellow crystalline solid, which was suitable for X-ray crystal
structure analysis. Yield: 0.31 g, 92%. 1H NMR (CD2Cl2)
(ppm): 8.49 (s, 1H, Pd-O-Ar-CHdN-), 7.71 (s, 1H, Ph-CHd
N-CH2-Ph), 5.61 (d, 1H, Ph-CHdN-CHH′-Ph), 5.10 (d, 1H, Ph-
CHdN-CHH′-Ph), 8.94 (d), 7.65-6.98 (m), 6.37 (t) (16H, Ar-
H), 3.42 (hept, 2H, Ar-CH(CH3)2), 1.38 (s, 9H, Ar-C(CH3)3),
1.22, 1.19, 1.16, 1.11 (d each, 12H, Ar-CH(CH3)2), -0.86 (s,
3H, Pd-CH3). 13C NMR (CD2Cl2) (ppm): 166.9 (Pd-O-Ar-CHd
N-), 166.3 (Ph-CHdN-CH2-Ph), 148.6, 141.6, 136.4, 135.0,
132.5, 131.5, 130.7, 129.1, 129.0, 128.7, 128.5, 126.3, 123.4,
112.1 (Ar), 69.45 (dN-CH2-Ph), 35.4 (Ar-C(CH3)3) 29.7 (Ar-
C(CH3)3), 27.9 (Ar-CH(CH3)2), 25.2, 23.2 (Ar-CH(CH3)2), -4.4
(Pd-CH3).
Acknowledgment. We thank the Department of
Energy, Office of Basic Energy Sciences, for funding. We
thank NSF (CHE-0131112) for funding the X-ray dif-
fractometer and Dr. Hemant Yennawar for assistance
with the X-ray structure determination.
Note Added after ASAP Publication. The com-
pounds 3a, 3d, and 4 have been refined in the higher
symmetry space group P1h. The updated CIF files now
appear in the Supporting Information.
Pd(Me)[2-(CHdN-t-Bu)-Py][3-tBu-2-(O)C6H3-CHdN-2,6-
di-iPr-C6H3] (4). To a mixture of [3-tBu-2-(OK)C6H3-CHdN-
2,6-di-iPr-C6H3]‚THF (0.42 g, 0.94 mmol) and 3-(CHdN-t-Bu)-
Py (0.15 g, 0.94 mmol) in toluene (30 mL) was added
(COD)PdMeCl (0.25 g, 0.94 mmol) in toluene (10 mL). The
reaction mixture was stirred for 12 h and then was filtered to
remove a small quantity of dark insoluble material. The
solvent was removed in vacuo to yield a yellow solid. Recrys-
tallization from pentane gave a yellow crystalline solid, which
was suitable for X-ray crystal structure analysis. Yield: 0.56
Supporting Information Available: Details of crystal
structure determinations, tables of positional parameters for
atoms, bond distances and angles, and anisotropic thermal
parameters, and CIF files for the crystal structures. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
g, 93%. H NMR (CD2Cl2) (ppm): 9.94 (s, 1H, Pd-O-Ar-CHd
N-), 7.71 (s, 1H, Py-CHdN-t-Bu), 8.97 (d), 8.24 (s), 7.87 (t),
7.36 (dt), 7.26-7.14 (m), 6.95 (dd), 6.30 (t) (10H, Ar-H), 3.69,
3.50 (hept each, 2H, Ar-CH(CH3)2), 1.33 (s, 9H, Ar-C(CH3)3),
OM050126A