Study of insertion of olefins and/or carbon monoxide into phosphine-imine palladium methyl complexes

Article abstract of DOI:10.1021/om000880q

Palladium methyl complexes with a phosphine-imine (P～N) bidentate ligand, [Pd(P～N)-MeCl] (1), [Pd(P～N)Me(CH₃CN)](BF₄) (2), and [Pd(P～N)Me(PPh₃)](BF₄) (3), are treated with CO to result in the corresponding Pd-acyl complexes 4-6. NMR studies indicate the formation of a sole isomer with the acyl group cis to the phosphine donor. The neutral complex 4 and the triphenylphosphine-substituted complex 6 cannot serve for the insertion of ethylene. However, the acetonitrile complex 5 appears to be active in the insertion reaction with various alkenes as well as ethylene/CO (E-CO) co-oligomerization, resulting in the products 7-14 and 16, which have been isolated and characterized by spectroscopic methods. X-ray structures of 1, 2, 3, 4, 7, 10, 11, and 13 are revealed.

Full text of DOI:10.1021/om000880q

1292
Organometallics 2001, 20, 1292-1299
Stu d y of In ser tion of Olefin s a n d /or Ca r bon Mon oxid e
in to P h osp h in e-Im in e P a lla d iu m Meth yl Com p lexes
K. Rajender Reddy, K. Surekha, Gene-Hsiang Lee, Shie-Ming Peng,
J wu-Ting Chen, and Shiuh-Tzung Liu*
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received October 16, 2000
Palladium methyl complexes with a phosphine-imine (P ∼N) bidentate ligand, [Pd(P ∼N)-
MeCl] (1), [Pd(P ∼N)Me(CH3CN)](BF4) (2), and [Pd(P ∼N)Me(PPh3)](BF4) (3), are treated with
CO to result in the corresponding Pd-acyl complexes 4-6. NMR studies indicate the
formation of a sole isomer with the acyl group cis to the phosphine donor. The neutral complex
4 and the triphenylphosphine-substituted complex 6 cannot serve for the insertion of ethylene.
However, the acetonitrile complex 5 appears to be active in the insertion reaction with various
alkenes as well as ethylene/CO (E-CO) co-oligomerization, resulting in the products 7-14
and 16, which have been isolated and characterized by spectroscopic methods. X-ray
structures of 1, 2, 3, 4, 7, 10, 11, and 13 are revealed.
In tr od u ction
tory insertion of CO and olefins into Pd-alkyl and Pd-
acyl bonds, respectively.5-7
Insertion of small unsaturated molecules into the
metal-carbon bond is an important step for the metal-
catalyzed reactions of C-C bond formation.1 Among
them, the alternating insertion of carbon monoxide and
olefins into metal-carbon bonds leading to the forma-
tion of polyketones by various palladium complexes has
received considerable interest.2 It is known that the
coordinating ability of the ligand and its steric environ-
ments generally control the efficiency of the catalyst.
In this regard, palladium-based catalysts with sym-
metrical bidentate phosphorus [P-P]3 or nitrogen [N-N]4
donor atoms are found to be very effective. A number
of stoichiometric and theoretical studies have provided
valuable information on mechanistic aspects of migra-
Recently, interest in searching for new catalysts with
unsymmetrical bidentate ligands has been increasing,8-11
particularly with P-N ligands.12,13 Although the pal-
ladium complexes with phosphino-oxazolines ligands in
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complexes with P-P ligands see: (a) Shultz, C. S.; Ledford, J .;
DeSimone, J . M.; Brookhart, M. J . Am. Chem. Soc. 2000, 122, 6351.
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W. N. M. Organometallics 1999, 18, 3394. (d) Zuideveld, M. A.; Kamer,
P. C. J .; van Leeuwen, P. W. N. M.; Klusener, P. A. A.; Stil, H. A.;
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A. J . Am. Chem. Soc. 1997, 119, 10028. (f) Toth, I.; Elsevier, C. J . J .
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P. S. J . Am. Chem. Soc. 1996, 118, 4746. (e) Markies, B. A.; Kruis, D.;
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* E-mail: stliu@ccms.ntu.edu.tw.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
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University Science Books: Mill Valley, CA, 1987. (b) Cornils, B.;
Herrmann, W. A. Applied Homogeneous Catalysis with Organometallic
Compounds; VCH: Weinheim, Germany, 1996; Vol. 1.
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M. Chem. Rev. 2000, 100, 1169. (b) Britovsek, G. J . P.; Gibson, V. C.;
Wass, D. Angew. Chem., Int. Ed. 2000, 38, 428. (c) Drent, E.; Budzelaar,
P. H. M. Chem. Rev. 1996, 96, 663. (d) Cavell, K. J . Coord. Chem. Rev.
1996, 155, 209. (e) Sen, A. Acc. Chem. Res. 1993, 26, 303.
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Organometallics 2000, 19, 3154. (b) Verspui, G.; Schanssema, F.;
Sheldon, R. A. Angew. Chem., Int. Ed. 2000, 39, 804. (c) Bianchini, C.;
Lee, H. M.; Meli, A.; Oberhauser, W.; Vizza, F.; Bruggeller, P.; Haid,
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G. R.; Tooze, R. P.; Scanlan, T. H.; Williams, D.; Elsegood, M. R. J .;
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van Breokhoven, J . A. M.; Doyle, M. J . J . Organomet. Chem. 1991,
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see: (a) Milani, B.; Alessio, G.; Zangrando, E.; Randaccio, L.; Consiglio,
G. J . Chem. Soc., Dalton Trans. 1996, 1021. (b) J iang, Z.; Adams, S.
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Svensson, M.; Matsubara, T.; Morokuma, K. Organometallics 1996,
15, 5568. (b) Margl, P.; Ziegler, T. Organometallics 1996, 15, 5519.
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Nozaki, K.; Hiyama, T.; Kacker, S.; Horvath, I. Organometallics 2000,
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(e) van Leeuwen, P. W. N. M.; Roobeek, C. F.; van der Heijden, H. J .
Am. Chem. Soc. 1994, 116, 12117.
10.1021/om000880q CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/27/2001

Study of Insertion of Olefins
Organometallics, Vol. 20, No. 7, 2001 1293
asymmetric catalysis have been reported,14 ligands with
phosphorus and π-accepting imine nitrogen donors in
palladium-catalyzed reactions show very promising
activity for homo- and copolymerization.13 Unlike the
symmetrical counterparts, the soft and hard nature of
phosphorus and nitrogen, combined with their trans
effecting nature, are expected to influence the binding
properties of the substrates as well as migratory inser-
tion with keen discerning ability. Isolation and charac-
terization of the insertion intermediates with P-N
ligands can contribute valuable information on the
reactivity of these catalysts.13 Some preliminary results
concerning the insertions of CO with various function-
alized alkenes and alkynes in cationic palladium com-
plexes [Pd(P ∼N)(Me)L]+ from our laboratory were re-
ported recently.15 Continuing this trend, we report the
synthesis and detailed structural characterization of
both neutral and cationic palladium complexes and their
reactivity toward CO and various olefins.
Ta ble 1. Selected IR a n d NMR Da ta of F r ee
Liga n d a n d Its P a lla d iu m Com p lexesa ,b
νCdN
,
ν(NtCMe)
,
IH NMR
Pd-CH3
cm-1
cm-1
-HCdN
31P NMR
P ∼N 1625
8.12
8.62
-14.5
1
2
3
1611
0.88 (d,
3J PH ) 2.9)
1609 2322, 2289 0.58 (d,
3J PH ) 1.6)
0.77 (dd,
3J PH ) 6.1)
35.4
9.26
8.61
38.6
1610
30.8 and 27.5
(2J PP ) 381 Hz)
In KBr. bIn CDCl3, ppm, J in Hz.
a
Resu lts
P r ep a r a tion of Liga n d a n d th e [P d (P ∼N)MeCl]]
Com p lex. The phosphine-imine ligand was prepared
by simple condensation of 2-(diphenylphosphino)-
aniline16 with excess benzaldehyde and characterized
by spectroscopic methods. Substitution reaction of Pd-
(COD)MeCl17 with the P ∼N ligand in a THF solution
provided the neutral methyl palladium complex [Pd-
(P ∼N)MeCl] (1) in excellent yield. Recrystallization
F igu r e 1. ORTEP plot of complex 1.
from dichloromethane and hexane gave the analytically
pure product. Spectroscopic analysis confirms the struc-
ture of the complex (Table 1). A downfield shift of ca.
50 ppm with respect to the free ligand reflects the
coordination of the phosphine to the palladium metal.18,19
Appearance of a single peak in the 31P NMR for the
complex suggests the formation of a single isomer. The
stereochemistry of the methyl group cis to the phospho-
rus was established from its 1H NMR spectra, where
the methyl group bound to the palladium appears as a
doublet with a coupling constant J P-H ≈ 3.0 Hz, which
is in the typical range for the cis-[PdMeCl(P-N)]
complexes.12a,20
Further confirmation of cis-geometry for 1 is obtained
from the X-ray structural analysis. The ORTEP diagram
for 1, as shown in the Figure 1, indicates the square
planar geometry around the palladium metal center
with the phosphine and methyl groups being cis to each
other. Selected bond lengths and angles are listed in
the Table 2, which are in agreement with the reported
[Pd(P-N)RX] complexes.12b,20
(9) For CO and/or olefin insertion and catalytic studies with unsym-
metrical (N-N*)Pd-complexes see: (a) Meneghetti, S. P.; Lutz, P. J .;
Kress, J . Organometallics 1999, 18, 2734. (b) Groen, J . H.; Vlaar, M.;
van Leeuwen, P. W. N. M.; Vrieze, K.; Kooijman, H.; Spek, A. L. J .
Organomet. Chem. 1998, 551, 67. (c) Ru¨lke, R. E.; Delis, J . G. P.; Groot,
A. M.; Elsevier: C. J .; van Leeuwen, P. W. N. M.; Vrieze, K.; Goubitz,
K.; Schenk, H. J . Organomet. Chem. 1996, 508, 109. (d) Delis, J . G.
P.; Rep, M.; Rulke, R. E.; van Leeuwen, P. W. N. M.; Vrieze, K.;
Fraanje, J .; Goubitz, K. Inorg. Chim. Acta 1996, 250, 87.
(10) For CO and/or olefin insertion and catalytic studies with
unsymmetrical (N-O)Pd-complexes see: (a) Green, M. J .; Britovsek,
G. J . P.; Cavell, K. J .; Gerhards, F.; Yates, B. F.; Frankcombe, K.;
Skelton, B. W.; White, A. H. J . Chem Soc., Dalton Trans. 1998, 1137.
(b) Gree, M. J .; Bristovsek. G. J . P.; Cavell, K. J .; Skelton, B. W.; White,
A. H. J . Chem. Soc., Chem. Commun. 1996, 1563. (c) Frankcombe, K.;
Cavell, K.; Yates, B. J . Chem. Soc., Chem. Commun. 1996, 781. (d)
Hoare, J . L.; Cavell, K. J .; Hecker, R.; Skelton, B. W.; White, A. H. J .
Chem Soc., Dalton Trans. 1996, 2197.
(11) For CO and/or olefin insertion and catalytic studies with
unsymmetrical (P-O)Pd-complexes see: (a) Braunstein, P.; Frison, C.;
Morise, X. Angew. Chem., Int. Ed. 2000, 39, 2867, and references
therein. (b) Bristovsek, G. J . P.; Keim, W.; Mecking, S.; Sainz, D.;
Wagner, T. J . Chem. Soc., Chem. Commun. 1993, 1632.
(12) For catalytic studies with (P-N)Pd-complexes see: (a) Braun-
stein, P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig, S. J .; Speiser,
F. J . Chem Soc., Dalton Trans. 2000, 1067. (b) van den Beuken, E. K.;
Smeets, W. J . J .; Spek, A. L.; Feringa, B. L. Chem. Commun. 1998,
223. (c) Aeby, A.; Gsponer, A.; Consiglio, G. J . Am. Chem. Soc. 1998,
120, 11000. (d) Aeby, A.; Bangerter, F.; Consiglio, G. Helv. Chim. Acta
1998, 81, 764. (e) Aeby, A.; Consiglio, G. Helv. Chim. Acta 1998, 81,
35. (f) Sperrle, M.; Consiglio, G. Helv. Chim. Acta 1996, 79, 1387.
(13) For insertion studies with (P-N)Pd-complexes see: (a) Brink-
mann, P. H. P.; Luinstra, G. A. J . Organomet. Chem. 1999, 572, 193
(b) Aeby, A.; Consiglio, G. J . Chem. Soc., Dalton Trans. 1999, 655. (c)
Luinstra, G. A.; Brinkmann, P. H. P. Organometallics 1998, 17, 5160.
(d) Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J .; Vrieze, K.; van
Leeuwen, P. W. N. M.; Smeets, W. J . J .; Spek, A. L.; Wang, Y. F.; Stam,
C. H. Organometallics 1992, 11, 1937.
P r ep a r a tion of th e Ca tion ic [P d (P ∼N)Me(L)]+ {L
) CH3CN or P P h 3} Com p lexes. The cationic complex
2 is prepared by the treatment of 1 with AgBF4 in a
mixture of dichloromethane and acetonitrile solution
(Scheme 1). After the removal of AgCl by filtration, the
solution was evaporated to a small volume and the
desired complex was precipitated upon the addition of
(14) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336, and
references therein.
(15) Reddy, K. R.; Chen, C.-L.; Liu, Y.-H.; Peng, S.-M.; Chen, J .-T.;
Liu, S.-T. Organometallics 1999, 18, 2574.
(18) Pelagatti, P.; Bacchi, A.; Carcelli, M.; Costa, M.; Fochi, A.;
Ghidini, P.; Leporati, E.; Masi, M.; Pelizzi, C.; Pelizzi, G. J . Organomet.
Chem. 1999, 583, 94.
(16) Cooper, M. K.; Downes, J . M.; Duckworth, P. A. Inorg. Synth.
1989, 25, 129.
(17) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier: C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(19) Bhattacharyya, P.; Parr, J .; Slawin, A. M. Z. J . Chem. Soc.,
Dalton Trans. 1998, 3609.
(20) Ankersmit, H. A.; Løken, B. H.; Kooijman, H.; Spek, A. L.;
Vrieze, K.; van Koten, G. Inorg. Chim. Acta 1996, 252, 141.

1294 Organometallics, Vol. 20, No. 7, 2001
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg) of P a lla d iu m Com p lexes
Reddy et al.
1
2
3
4
7
9
10
11
13
Pd-C1
2.029(6)
2.375(2)
2.224(4)
2.045(4)
2.075(7)
1.983(3)
2.3777(7)
2.284(2)
2.022(5)
2.003(9)
2.026(4)
2.059(3)
2.034(5)
Pd-Cl1
Pd-N1
2.198(3)
2.112(3)
2.2075(9)
2.183(5)
2.208(3)
2.180(1)
2.182(7)
2.186(2)
2.191(3)
2.186(9)
2.148(3)
2.212(1)
2.175(4)
2.189(1)
Pd-N2
Pd-P1
2.196(2)
2.312(2)
2.333(2)
2.2495(7)
Pd-P2
Pd-O1
2.143(3)
92.7(2)
82.98(9)
175.2(2)
2.127(4)
95.4(3)
81.6(2)
175.4(4)
2.148(3)
93.05(13)
83.36(8)
2.161(2)
95.89(12)
82.76(7)
2.112(3)
94.8 (2)
82.37(10)
175.6(2)
C1-Pd-P1
P1-Pd-N1
C1-Pd-N1
N1-Pd-Cl1
C1-Pd-Cl1
Cl1-Pd-P1
N1-Pd-N2
C1-Pd-N2
N2-Pd-P1
N1-Pd-P2
C1-Pd-P2
P2-Pd-P1
N1-Pd-O1
C1-Pd-O1
O1-Pd-P1
91.6(2)
90.38(13)
83.28(7)
173.61(14)
92.2(2)
79.49(14)
170.9(2)
97.48(9)
78.90(6)
176.18(11)
97.85(6)
85.92(9)
169.78(3)
81.37(11)
172.7(2)
98.56(11)
88.1(2)
176.03(14)
177.72(14)
170.96(7)
99.05(11)
87.3(2)
173.61(9)
101.29(13)
87.7(2)
163.97(7)
103.53(12)
80.9(2)
172.79(9)
101.8(3)
81.3(4)
176.5(3)
103.39(11)
80.0(2)
171.31(8)
99.27(10)
81.68(13)
168.34(8)
99.03(13)
83.5(2)
173.44(9)
Sch em e 1
ether. Selected IR and NMR data of the complexes are
also shown in Table 1.
The presence of two low-intensity bands at 2322 and
2289 cm-1 in the IR spectrum, which are assigned to
the coordinated acetonitrile, is comparable to the re-
ported palladium complexes.13a Phosphorus-31 NMR
again shows only one signal corresponding to the for-
mation of a single isomer. The peaks are slightly down-
field shifted (1-2 ppm) compared to the less electrophilic
neutral analogues. A slightly smaller hydrogen-phos-
phorus coupling (J P-H ≈ 1.6 Hz) for the methyl hydrogen
atoms is observed.13a X-ray structural analysis of 2
(Figure 2) also confirms the cis-arrangement of phos-
phine and methyl group and the coordination of aceto-
nitrile to palladium as well. Selected bond lengths and
angles are given in Table 2. The triphenylphosphine-
substituted complex 3 was prepared by substitution
reaction of 2 with PPh3 in dichloromethane solution, and
F igu r e 2. Molecular diagram of the cation [(P ∼N)Pd(Me)-
(NCCH3)]+.
1
its characterization was performed by both H and 31P
NMR spectroscopy (Table 1).21 In addition, the X-ray
structure of 3 (Figure 3) was obtained.
NMR indicated the formation of the acyl product. The
resulting acyl complexes 4-6 were isolated in stable
solid form as described in Experimental Section. Se-
lected spectroscopic data for the acyl derivatives are
shown in Table 3.
Infrared absorption for the CdO stretching band
appears in the range 1688-1705 cm-1, which is typical
for the acyl complexes.13a 31P NMR signals for 4-6
suggest the formation of one inserted product in each
case. It is noticed that complex 5 exhibits relatively
CO a n d Eth ylen e In ser tion s in to Neu tr a l a n d
Ca tion ic P a lla d iu m Com p lexes. Insertion reactions
of CO into the Pd-C bond for complexes 1-3 were
monitored by 31P NMR. In a typical experiment, a CDCl3
solution of the respective complex (10-15 mg) was
1
bubbled with CO for 30 min, and the 31P NMR and H
(21) Crociani, L.; Bandoli, G.; Dolmella, A.; Basato, M.; Corain, B.
Eur. J . Inorg. Chem. 1998, 1811.

Study of Insertion of Olefins
Organometallics, Vol. 20, No. 7, 2001 1295
F igu r e 3. Structure of complex 3.
F igu r e 4. ORTEP plot of complex 7.
Ta ble 3. Selected IR a n d NMR Da ta of th e
In ser ted P r od u ctsa ,b
Further CO insertion into 7 in dichloromethane was
not successful, but could be done in acetonitrile or a
mixture of acetonitrile and dichloromethane. Appar-
ently, the coordinating solvent is necessary to stabilize
the resulting acyl product, as observed in prior cases.13d
The crystal structures of complex 8 and the subsequent
ethylene-inserted one 9 have been reported in our
preliminary communication, Scheme 2.15 The Pd-C1
bond distances in 7 [2.022(5) Å] and 9 [2.003(9) Å] are
comparable with those in the diimine analogues, and
the Pd-O1 bond distances in 7 [2.143(3) Å] and 9 [2.127-
(4) Å] are in agreement with those in the diphosphine
complexes.6e,22 The formation of a five-membered (C,O)
chelation product via olefin insertions into the Pd-acyl
bond is known.2c Nevertheless further insertion by CO
and the fact that it serves as a catalyst for CO/ethylene
copolymerization in complex 9 indicate that the phos-
phine-imine system may be promising for the use of
insertion processes.15
CdOc
ν (cm-1
)
1H NMR Pd-R
-HCdN
31P NMR
4
5
6
1688
1705
1694
2.23 (s, -COCH3) 8.55 (m)
1.76 (s, -COCH3) 9.11 (s)
14.8
18.4
1.79 (s)
8.62 (s)
16.5 and 12.5
(2J PP) 250)
7
1636
1.86 (t, J ) 7.0,
Pd-CH2)
9.15 (s)
36.7
8
9
2.72 (s, -COCH2) 9.07 (s)
19.9
36.8
1712 (f)
1629 (c)
1.89 (m, 5H,
CH2, CH3)
9.20 (s)
10 1630
0.93 (t, 3H) (10a )
1.33 (d, 3H) (10b) 9.18
2.51 (s, Pd-CH)
9.14
36.3
39.5
37.3
11 1708,
9.29 (s)
1686 (f)
1630 (c)
12 1610 (c)
13 1626 (c)
14 1713 (f)
1610 (c)
3.46 (m, Pd-CH)
1.32 (d, Pd-CH)
5.15 (s, Pd-CH)
9.11 (s)
9.19 (s)
9.15 (s)
31.2
35.3
35.7
15 1620 (c)
16
5.27 (s, Pd-CH)
1.83 (t, Pd-CH2)
9.30 (s)
9.26 (s)
34.7
37.7
In ser tion of F u n ction a lized Olefin s in to 5. Inser-
tion of propene with 5 leads to the formation of two
mixed species (10a and 10b) in 1:1 ratio according to
a
c
In KBr. bIn CDCl3, in ppm, J in Hz. (f) free carbonyl, (c)
the H and 31P NMR spectroscopic data. On the other
coordinated carbonyl.
1
hand, complex 5 undergoes regiospecific insertions (2,1-
insertion) with methyl acrylate or styrene to provide 11
and 12, respectively, as shown in Scheme 3. The
insertion of norbornene into 5 proceeds exclusively from
the exo-face to give the product 13. Such face-selective
insertion of norbornene into the Pd-acyl bond was also
observed with bidentate nitrogen and bis(phosphine)
complexes earlier.6e,22 The complexes 10-13 are isolated
in solid form and characterized by spectroscopic meth-
ods (Table 3) and by X-ray structural analysis. The
molecular structure of 13 is illustrated in Figure 5, and
selected bond distances and angles are summarized in
Table 2.
It is generally known that olefin insertion into a Pd-
acyl bond is faster than into the Pd-alkyl bond.
Experimental evidence also suggests that the formation
of the five-membered (C,O) chelation product provides
the extra stability to avoid competing â-hydride elimi-
nation. In all instances investigated in this work,
consecutive insertion of alkene molecules is not feasible,
i.e., no insertion of alkene into Pd-C(alkyl), except that
better stability and can be isolated at room temperature
and kept at 0 °C for several days.
Insertion of ethylene into the palladium-acyl bond
was achieved by bubbling ethylene through a solution
of dichloromethane containing the complex 5. The NMR
spectrum of the resulting reaction mixture was taken
immediately. Complete conversion of 5 into 7 was done
within 1 h. The 31P NMR spectrum shows a downfield
shift representing the palladium-alkyl bond formation.
Appearance of one 31P signal indicates the formation of
only one isomer. The IR spectrum shows a CdO
stretching band at 1636 cm-1, which is shifted about
70 cm-1 to lower wavenumber with respect to that of
5,5i,6e indicating the coordination of the acyl-oxygen to
the palladium center. Both 1H and 13C NMR support
the formation of the insertion products (Table 3). It is
noticed that the compound 7 is much more stable than
the acyl complex 5 presumably due to the chelation
effect. The detailed structure of 7 is confirmed by its
X-ray single-crystal structural analysis (Figure 4). No
insertion of the ethylene molecule into the Pd-acyl bond
of 4 and 6 was observed. Bubbling for a longer period
(∼24 h) resulted in the precipitation of palladium black.
(22) Brumbaugh, J . S.; Whittle, R. R.; Parvez, M.; Sen, A. Organo-
metallics 1990, 98, 1735.

1296 Organometallics, Vol. 20, No. 7, 2001
Reddy et al.
Sch em e 2
Sch em e 3
investigated. In an autoclave was placed the 27 mg of
catalyst in dichloromethane (70 mL), and 40 psi each
of CO and ethylene was stirred at room temperature
for 48 h. The resulting white solid was filtered and
washed with 5 N HCl, followed by water and acetone,
respectively. A small amount of polymer product (440
mg) was formed. It appears that complex 2 is not a very
efficient catalyst for E-CO copolymerization. However,
such reaction allows us to isolate the rare species of a
metal-capped E-CO copolymer. The reaction proceeds
at room temperature for 4 h, and an E-CO oligomeric
palladium complex 16 was acquired. It was character-
ized by spectroscopic methods. 1H NMR and mass spec-
tra are shown in Figures 6 and 7, which clearly evidence
the attached ethylene/CO oligomeric units to palladium
metal. By NMR integration, the average repeating units
of each chain have been estimated to be 14.
F igu r e 5. Structure of complex 13.
vinyl acetate can insert into 5 and 2 to yield 14 and 15,
respectively.15
Discu ssion
In this work, we demonstrate that the unsymmetric
P ∼N bidentate tends to allow single regioisomers in
each insertion process. Since the migratory insertion
could change the coordination site for the carbon-bound
ligand, one might expect to see the kinetic products with
the carbon ligand being trans or cis to phosphine.
Cop olym er iza tion . Taking advantage of the feasi-
bility of the stepwise insertion of CO/ethylene (E-CO)
in 2, the use of 2 as the catalyst for copolymerization is

Study of Insertion of Olefins
Organometallics, Vol. 20, No. 7, 2001 1297
The Pd-acyl complexes with weak coordinating ligands
such as acetonitrile can be subjected to decarbonylation,
which accounts for the unstable nature of some Pd-
acyl complexes.5d,6e,g,10a The deinsertion process can be
hindered by strongly coordinating or inert ligands such
as chloride or phosphines. Indeed, acyl complexes 4 and
6 are found to be stable at 25 °C. Curiously, the cationic
palladium acyl complex 5 with a weak coordinating
acetonitrile is stable and allows us to utilize it for
further studies of alkene and alkyne insertions.15 Lu-
instra and co-workers also demonstrated the isolation
of CO-inserted products with mixed bidentate P-N
ligands.13a Like compound 5, the stable Pd-acyl com-
plex 17 with an unsymmetric P-O ligand was reported
by Braunstein and co-workers recently.11a In fact, we
demonstrated that the metal-capped polymeric species
16 can be isolated under copolymerization conditions,
indicating that the P ∼N bidentate plays a role in
stabilization of the palladium-attached carbon ligand,
which also explains the lower catalytic activity in
copoylermization; that is, every metal center can carry
only one polymer chain.
Complex 5 shows reactivity toward insertion with
various alkenes. R-Olefins such as styrene, methyl
acrylate, or vinyl acetate undergo a regioselective inser-
tion (2,1-insertion). Norbornylene undergoes insertion
selectively at the exo-face. Only propene gives a mixture
of 1,2- and 2,1-inserted products. This selectivity is
consistent with most of the other insertion instances,
in which the coordinating orientation of the olefin would
determine the regio- or stereoproperties of the products.
Unlike the diimine-palladium complexes, neither 2
nor 5 can serve as a polymerization catalyst for olefins,
even for ethylene. Our previous study indicates that
complex 2 mediates the dimerization and trimerization
of ethylene,24 but shows no reactivity toward propene
or styrene. On the other hand, alternating insertion of
CO and olefins in 2 or 5 is facile, indicating the greater
activation barrier for olefin insertion than that of CO-
insertion reactions.5a,6d
F igu r e 6. (a) 1H NMR spectrum of complex 2. (b) 1H NMR
spectrum of complex 7. (c) H NMR spectrum of complex
16, the metal-capped oligomer.
1
The crystallographic results in this work confirm that
the ligands of the P,N chelates always have the carbon
ligand seated trans to the imine donors. The configura-
tions of the coordinating atoms in complexes are in
typical square planar geometry, as expected. The bond
distances and bond angles are in the normal range,
except the angles of N-Pd-P (Tables 2) are smaller,
due to o-phenylene linkage. Whether the angle of
N-Pd-P is related to the activity of insertion is
currently under investigation.
F igu r e 7. (a) FAB mass spectrum of complex 16 in the
range m/z 900-1300. (b) Expansion of m/z at 1102, which
is consistent with formula of [(P ∼N)Pd(CH2CH2CO)11CH3]+.
(c) Simulated pattern of the formula of [(P ∼N)Pd(CH2CH2-
CO)11CH3]+.
However, only one of that kind of intermediate with a
carbon ligand cis to phosphine is observed in our studies.
This is similar to the carbonylation of other known P-N
palladium complexes13a,d and suggests that a rapid
isomerization process must occur during the insertion
steps. This outcome is consistent with Pearson’s anti-
symbiotic effect.23
Con clu sion
The designed P∼N ligand in this work allows the
formation of a stable five-membered chelation product
(23) Pearson, R. G. Inorg. Chem. 1973, 12, 712.
(24) Chen, J .-T.; Liu, S.-T.; Zhao, K.-Q. J . Chin. Chem. Soc. 2000,
47, 279.

1298 Organometallics, Vol. 20, No. 7, 2001
Reddy et al.
(CdN). 1H NMR (CDCl3): δ 0.77 (t, 3 H, J ) 6.1 Hz), 7.0-
7.82 (m, 32 H), 8.05 (d, 2 H, J ) 6.8 Hz), 8.61 (s, 1 H). 13C
NMR (CDCl3): δ -0.16 (Pd-Me), 172.1 (CdN). 31P NMR
with palladium complexes. The mixed soft and hard
donors of phosphorus and nitrogen in the palladium
complexes influence the binding stability of the sub-
strates and ligand migration and results in the isolation
of various new inserted intermediates, including a rare
palladium-capped oligomer. This result allows the op-
portunity to build block polymerizations.
2
(CDCl3): δ 30.8 and 27.5 (d, J PP ) 381 Hz). Anal. Calcd for
C
44H38NP2BF4Pd: C, 63.20; H, 4.58; N, 1.67. Found: C, 62.98;
H, 4.70; N, 1.60. FABMS: 749.1 (M+).
Gen er a l P r oced u r e for P r ep a r a tion of Com p lexes 4-6.
To a solution of 1-3 (0.25 mmol) in 10 mL of CH2Cl2,
continuous bubbling of carbon monoxide for 2-4 h resulted in
the formation of the corresponding CO-inserted product. The
resulting solution was cooled and filtered through silica gel
(small amount of Pd black formation was observed in all these
reactions), and the filtrate was evaporated to a small volume.
The desired complex was precipitated by addition of diethyl
ether.
Exp er im en ta l Section
Gen er a l In for m a tion . All reactions, manipulations, and
purifications steps were performed under a dry nitrogen
atmosphere. Tetrahydrofuran was distilled under nitrogen
from sodium benzophenone ketyl. Dichloromethane and ace-
tonitrile were dried with CaH2 and distilled under nitrogen.
Other chemicals and solvents were of analytical grade and
were used as received unless otherwise stated. 2-(Diphen-
ylphosphino)aniline and Pd(COD)MeCl were prepared accord-
ing to literature procedures.16,17
Nuclear magnetic resonance spectra were recorded in CDCl3
on either a Bruker AC-E 200 or AM-300 spectrometer. Chemi-
cal shifts are given in parts per million relative to Me4S for
1H and relative to 85% H3PO4 for 31P NMR. Infrared spectra
were measured on a Nicolet Magna-IR 550 spectrometer
(Series II) as KBr pallets, unless otherwise noted.
Com p lex 4. (80%) IR (KBr): 1688 (CdO), 1610 s (CdN).
1H NMR (CDCl3): δ 2.23 (s, 3 H), 7.23-7.64 (m, 17 H), 8.44
(m, 1 H), 8.55 (m, 1 H). 31P NMR (CDCl3): δ 14.8. Anal. Calcd
for C27H23NOPClPd: C, 58.9; H, 4.21; 2.54. Found: C, 58.35;
H, 4.41; N, 2.34.
1
Com p lex 5. (75%) IR (KBr): 1705 (CdO), 1610 (CdN). H
NMR (CDCl3): δ 1.76 (s, 3 H), 1.99 (s, 3 H), 7.18-7.70 (m, 16
H), 8.28 (s, 1 H), 8.46 (s, 2 H), 9.11 (s, 1 H). 13C NMR (CDCl3):
δ 2.0 (Pd-NCCH3), 37.3 (COCH3), 169.4 (CdN), 226.8
(Pd-COMe). 31P NMR (CDCl3): δ 18.4. FABMS: 514 (M+
-
CH3CN).
1
Syn th esis of P ∼N Liga n d . To freshly distilled benzalde-
hyde (16 mL, 0.15 mol) was added 2-(diphenylphosphino)-
aniline (6.0 g, 0.02 mol) under nitrogen, and the mixture was
stirred at room temperature under vacuum. Completion of the
reaction was monitored by 31P NMR, which took 6-7 h. The
reaction mixture was poured into cold methanol and kept at
low temperature overnight. The desired ligand P ∼N was
crystallized as a white solid (5.2 g, 65%). IR (KBr): 1625 cm
Com p lex 6. (80%) IR (KBr): 1694 (CdO), 1608 (CdN). H
NMR (CDCl3): δ 1.79 (s, 3 H), 7.14-7.83 (m, 32 H), 8.18 (d, 2
H, J ) 6.7 Hz), 8.62 (s, 1 H). 31P NMR (CDCl3): δ 16.5 and
12.5 (d, trans, J PP ) 250 Hz). Anal. Calcd for C45H38NOP2-
BF4Pd: C, 62.5; H, 4.43; N, 1.62. Found: C, 61.6; H, 4.47; N,
2
1.57. FABMS: 777.1(M+).
Com p lex 7. To a solution of 5 (100 mg) in 5 mL of CH2Cl2
was bubbled ethylene for 1 h. The resulting solution was
filtered through silica gel and evaporated to a small volume.
The desired product was precipitated by addition of Et2O (74
mg, 72%). IR (KBr): 1636 (CdO), 1609 (CdN). 1H NMR
(CDCl3): δ 1.86 (t, 2 H, J ) 7.0 Hz, Pd-CH2), 2.18 (s, 3 H,
COCH3), 3.10 (t, 2 H, J ) 7.0, -CH2CO), 7.23-7.69 (m, 17
H), 8.29 (m, 2 H), 9.15 (s, 1 H). 13C NMR (CDCl3): δ 21.6
(Pd-CH2), 27.5 (COCH3), 50.4 (CH2-CO), 232.9 (CH3COCH2).
31P NMR (CDCl3): δ 36.7. Anal. Calcd for C30H29NOPBF4Pd:
C, 56.49; H, 4.58; N, 2.19. Found: C, 55.54; H, 4.37; N, 2.21.
FABMS: 550.9 (M+).
Com p lex 8. To a solution of 7 (50 mg) in 2 mL of CH3CN
was bubbled carbon monoxide for 1 h, and the resulting
solution was filtered through silica gel and evaporated to a
small amount at low temperature and precipitated by adding
to an Et2O solution. The resulting pale yellow solid was filtered
and dried under vacuum. 1H NMR (CDCl3): δ 1.77 (s, 3 H,
Pd-NCCH3), 1.94 (s, 3 H, COCH3), 2.26 (br, 2 H, PdCOCH2),
2.72 (br, 2 H, COCH2CH2), 7.19-7.69 (m, 16 H), 7.89 (s, 1 H),
8.26 (s, 2 H), 9.07 (s, 1 H). 13C NMR (CDCl3): δ 29.3 (COCH3),
37.4 (CH2CO), 44.5 (PdCOCH2), 206.6 (COCH3), 223.1 (PdCO).
31P NMR (CDCl3): δ 19.9.
Com p lex 9. To a CH2Cl2 solution of the above complex 8
was bubbled ethylene gas for 2 h. The solution was filtered
through silica gel, concentrated to a small amount, and
precipitated by adding to an Et2O solution. The solid was
filtered and dried under vacuum. IR (KBr): 1712 (CdO, free),
1629 (CdO, coordinated), 1609 (CdN). 1H NMR (CDCl3): δ
1.89 (m, 5 H, COCH3 + PdCOCH2), 2.32 (t, 2 H, J ) 7 Hz),
2.77 (t, 2 H, J ) 7 Hz), 3.03 (t, 2 H, J ) 7.0 Hz), 7.18-7.95 (m,
17 H), 8.30 (m, 2 H), 9.20 (s, 1 H). 13C NMR (CDCl3): δ 20.7,
29.1, 33.7, 36.7, 48.9, 206.3, 231.3. 31P NMR (CDCl3): δ 36.8.
Gen er a l P r oced u r e for P r ep a r a tion of 10-14. To a
solution of 5 (100 mg, 0.15 mmol) in 5 mL of CH2Cl2 was added
the corresponding olefin in excess (5-10 mmol), and the reac-
tion mixture was stirred for 1-3 h. The resulting solution was
filtered through silica gel and evaporated to a small volume.
The desired complex was precipitated by addition of ether.
1
-1(CdN). H NMR (CDCl3): δ 6.84-7.31 (m, 17 H), 7.63 (m, 2
H), 8.12 (s, 1 H). 31P NMR (CDCl3): δ -14.5. Anal. Calcd for
C
25H20NP: C 82.17; H, 5.52; N, 3.83. Found: C, 81.84; H, 5.79;
N, 3.67. FABMS: 366 (M+).
Com p lex 1. To a colorless solution of Pd(COD)MeCl (265
mg, 1 mmol) in THF (5 mL) was added an equal molar amount
of the ligand in a THF solution (5 mL). The mixture was stirred
under N2 at room temperature. After 15 min a white solid
began to precipitate, and the solution was stirred for another
30 min. The resulting mixture was cooled, and the white solid
was filtered and washed with ether and dried under vacuum
(470 mg, 90%). IR (KBr): 1611 (CdN). 1H NMR (CDCl3): δ
0.88 (d, 3 H, J ) 2.9 Hz), 7.13-7.60 (m, 17 H), 8.53 (m, 2 H),
8.62 (s, 1 H). 13C NMR (CDCl3): δ 0.87 (Pd-Me), 168.9 (CdN).
31P NMR (CDCl3): δ 35.4. Anal. Calcd for C26H23NPClPd: C,
59.8, H, 4.43, N, 2.68. Found: C, 59.9; H, 4.78; N, 2.28.
Com p lex 2. To a solution of the neutral complexes 1 (0.5
mmol) in 20 mL of CH2Cl2 was added a stoichiometric amount
of AgBF4 in 5 mL of CH3CN under nitrogen, and the reaction
mixture was stirred at room temperature for 1 h. The resulting
white AgCl precipitate was filtered through silica gel, and the
solvent was evaporated to a small amount. Upon addition to
Et2O, a precipitate was deposited, which was filtered and dried
under vacuum, resulting in 262 mg (85%) of pure product. IR
1
(KBr): 1609 (CdN), 2322 and 2289 (CtN). H NMR (CDCl3):
δ 0.58 (d, 3 H, J ) 1.60 Hz), 1.80 (s, 3 H), 7.09-8.04 (m, 17
H), 8.23 (d, 2 H, J ) 7.0 Hz), 9.26 (s, 1 H). 13C NMR (CDCl3):
δ -2.09 (Pd-Me), 1.81 (Pd-NCMe), 169.6 (CdN). 31P NMR
(CDCl3): δ 38.6. Anal. Calcd for C28H26N2PBF4Pd: C, 54.70;
H, 4.26; N, 4.55. Found: C, 54.66; H, 4.17; N, 4.36. FABMS:
486.1 (M+ - CH3CN).
Com p lex 3. To a solution of the cationic complexes 2 (0.5
mmol) in 20 mL of THF was added a stoichiometric amount
of PPh3 under nitrogen, and the reaction mixture was stirred
for 1 h. The solvent was removed under vacuum, and the
residue was washed with Et2O and dried under vacuum,
resulting in 355 mg (85%) of pure product. IR (KBr): 1610

Study of Insertion of Olefins
Organometallics, Vol. 20, No. 7, 2001 1299
Com p lex 10. (80%) IR (KBr): 1630 (CdO, coordinated). 1H
NMR (CDCl3): δ 0.93 (t, 3 H, 50%, 7.6 Hz), 1.33 (d, 3 H, 50%,
7.3 Hz), 1.66 (m, 1 H, 50%), 2.03 (m, 1 H, 50%), 2.15 (s, 3 H,
50%), 2.21 (s, 3 H, 50%), 2.33 (m, 1 H, 50%), 2.69 (m, 1 H,
50%), 2.97 (m, 1 H, 50%), 3.17 (m, 1 H, 50%), 7.29-8.38 (m,
19 H), 9.16 (s, 1 H, 50%), 9.21 (s, 1 H, 50%). 31P NMR
(CDCl3): δ 36.3, 39.5. Anal. Calcd for C30H29NOPBF4Pd: C,
55.9; H, 4.54; N, 2.17. Found: C, 56.34; H, 4.53; N, 2.13.
FABMS: 556.2 (M+).
Com p lex 11. (78%) IR (KBr): 1708, 1686 (CdO, free), 1630
(CdO, coordinated). 1H NMR (CDCl3): δ 2.20 (s, 3 H), 2.51 (s,
1 H), 2.93 (m, 2 H), 3.50 (s, 3 H), 7.21-7.67 (m, 16 H), 8.04
(m, 1 H), 8.44 (d, 2 H, J ) 7.5 Hz), 9.29 (s 1 H). 31P NMR
(CDCl3): δ 37.3. Anal. Calcd for C31H29NO3PBF4Pd: C, 54.13;
H, 4.25; N, 2.03. Found: C, 53.49; H, 4.32; N, 1.89. FABMS:
600.2 (M+).
Com p lex 15. To a solution of 2 (100 mg, 0.16 mmol) in
CH2Cl2 was added excess vinyl acetate, and the reaction
mixture was refluxed at 80 °C for about 24 h. The resulting
solution was filtered through silica gel, evaporated to a small
amount, and precipitated into ether. The pale white solid was
filtered and dried under vacuum (75 mg, 70%). IR (KBr): 1620
1
(CdO, coordinated). H NMR (CDCl3): δ 1.04 (t, 3 H, J ) 7.1
Hz), 1.59 (m, 2 H), 2.0 (s, 3 H), 5.27 (m, 1 H), 7.24-8.10 (m,
17 H), 8.41 (d, 2 H, J ) 7.5 Hz), 9.3 (s, 1 H). 31P NMR (CDCl3):
δ 34.7. Anal. Calcd for C30H29NO2PBF4Pd: C, 54.61; H, 4.43;
N, 2.12. Found: C, 54.12; H, 4.49; N, 1.91.
Com p lex 16. To an autoclave (100 mL) were loaded the
palladium complex 2 (60 mg) in CH2Cl2(10 mL), CO (50 psi),
and ethylene (50 psi), and the mixture was stirred at room
temperature. Reaction stopped after 4 h, and the resulting
clear solution was filtered through silica gel and evaporated,
which provided a transparent polymeric material (120 mg).
1H NMR (CDCl3): δ 1.83 (t, 2 H), 2.13 (s, 4 H), 2.28 (m, 6 H),
2.66 (br, ∼48 H), 3.0 (t, 2 H), 7.24-8.10 (m, 17 H), 8.28 (d, 2
H, J ) 6.3 Hz), 9.26 (s, 1 H). 31P NMR (CDCl3): δ 37.7.
Cr ysta llogr a p h y. Crystals suitable for X-ray determina-
tion were obtained for 1, 2, 3, 4, 7, 10, 11, and 13 by slow
diffusion of hexane into a dichloromethane solution at room
temperature. Cell parameters were determined by a Siemens
Com p lex 12. (75%) IR (KBr): 1610 (CdO, coordinated). 1H
NMR (CDCl3): δ 2.28 (s, 3 H), 2.95 (d, 1 H, J ) 2.0 Hz), 3.17
(s, 2 H), 3.46 (m, 1 H), 6.69-7.58 (m, 21 H), 7.86 (s, 1 H), 8.40
(s, 2 H), 9.11 (s, 1 H). 13C NMR (CDCl3): δ 27.7 (COCH3), 44.8
(CHCH2), 55.8 (CHCH2), 168.5 (CdN), 232.5 (COCH3). 31P
NMR (CDCl3): δ 31.2. Anal. Calcd for C35H31NOPBF4Pd: C,
59.56; H, 4.43; N, 1.98. Found: C, 58.96; H, 4.63; N, 1.79.
FABMS: 618.2 (M+).
Com p lex 13. (78%) IR (KBr): 1626 (CdO, coordinated). 1H
NMR (CDCl3): δ 0.49 (s, 1 H), 1.15 (m, 2 H), 1.32 (d, 1 H, J )
9.7 Hz), 1.49 (m, 1 H), 1.81 (d, 1 H, J ) 9.9 Hz), 1.91 (m, 1 H),
2.04 (s, 1 H), 2.10 (s, 3 H), 2.48 (s, 1 H), 2.77 (d, 1 H, J )
6.5 Hz), 7.40-7.93 (m, 17 H), 8.40 (m, 2 H), 9.19 (s, 1 H).
13C NMR (CDCl3): δ 27.0 (COCH3), 29.3, 30.2, 36.8, 43.1,
53.5, 71.2, 169.1 (CdN), 234.7 (COCH3). 31P NMR (CDCl3):
35.3. Anal. Calcd for C34H33NOPBF4Pd: C, 58.69; H, 4.78; N,
2.01. Found: C, 57.58; H, 4.83; N, 1.89. FABMS: 608.2 (M+).
Com p lex 14. (75%) IR (KBr): 1713 (CdO, free), 1610
(CdO, coordinated). 1H NMR (CDCl3): δ 1.92 (s, 3 H), 2.12 (s,
3 H), 2.78 (s, 2 H), 5.12 (s, 1 H), 7.19-7.93 (m, 17 H), 8.60 (s,
2 H), 9.15 (s, 1 H). 31P NMR (CDCl3): 35.7. Anal. Calcd for
SMART CCD or a CAD-4 diffractometer. Selected bond
distances and bond angles are collected in Table 2. Other
crystallographic data are deposited as Supporting Information.
Ack n ow led gm en t. We thank the National Science
Council for financial support (NSC89-2113-M002-07).
Su p p or tin g In for m a tion Ava ila ble: Complete descrip-
tion of the X-ray crystallographic structure determination of
1, 2, 3, 4, 7, 10, 11, and 13 including figures of ORTEP plots
and tables of crystal data, atomic coordinates, isotropic and
anisotropic thermal parameters, and bond distances and
angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
C
31H29NO3PBF4Pd: C, 54.13; H, 4.25; N, 2.03. Found: C,
53.68; H, 4.41; N, 1.78. FABMS: 600.2 (M+).
OM000880Q