(β-diketiminato)palladium complexes

Article abstract of DOI:10.1021/om0606486

Reaction of Pd(acac)₂ with 1 equiv of the lithium β-diketiminate Li(ⁱPr₂-nacnac) (ⁱPr ₂-nacnac = CH{C(Me)NⁱPr}₂) affords the dark red mixed-ligand complex (acac)Pd(ⁱPr₂-nacnac) (1), while with 2 equiv of Li(ⁱPr₂-nacnac) the light red homoleptic Pd(ⁱPr₂-nacnac)₂ (2) is formed. A similar reaction of Pd(acac)₂ with the more bulky (THF)Li(Ar ₂-nacnac) (Ar₂-nacnac = CH{C(Me)N(C₆H ₃-2,6-ⁱPr₂)}₂) proceeds only to the stage of the mixed-ligand complex. While below 0 °C red (acac) Pd(κ²N,N-Ar₂-nacnac) (4) is isolated as the kinetically controlled product, which is stable in the solid state, this complex isomerizes in solution at ambient temperature to yield the lighter red and chiral (acac)Pd(κ²C,N-Ar₂-nacnac) (5), displaying a novel nacnac bonding mode. The reaction of [Pd(MeCN)₄](BF ₄)₂ and that of the Pd(I) complex [Pd₂(MeCN) ₆](BF₄)₂ with (THF)Li(Ar₂-nacnac) gives [κ²N,N-Ar₂-nacnac)Pd(MeCN)₂]- (BF₄) (6). The κ²N,N-Ar₂-nacnac ligand in 6 is sufficiently nucleophilic to displace acetonitrile from [Pd(MeCN) ₄](BF₄)₂ and produce the pure dinuclear [(MeCN)₃Pd{μ-CH(C(Me)NAr)₂}Pd(MeCN)₂] (BF₄)₃ (A), previously accessible only in a mixture. From the reactions of {(η³-C₃H₅)Pd(μ-Cl)} ₂ with Li(ⁱPr₂-nacnac) and (THF)Li(Ar ₂-nacnac) the mixed-ligand complexes (η³-C ₃H₅)Pd(ⁱPr₂-nacnac) (3a) and (η³-C₃H₅)Pd(κ²N,N-Ar ₂-nacnac) (3b) have been obtained. Reaction of (cod)PdMeCl with (THF)Li(Ar₂-nacnac) affords (Ar₂-nacnac)PdMe(MeCN) (7). An anisotropic effect of the Ar₂-nacnac ligand in the ¹H NMR spectra of 3b and 4 can be noted. The structures of 2, 3a, 4, and 5 have been determined by X-ray crystallography.

Full text of DOI:10.1021/om0606486

5854
Organometallics 2006, 25, 5854-5862
Articles
(â-Diketiminato)palladium Complexes
Xin Tian, Richard Goddard, and Klaus-Richard Po¨rschke*
Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany
ReceiVed July 18, 2006
Reaction of Pd(acac)2 with 1 equiv of the lithium â-diketiminate Li(iPr2-nacnac) (iPr2-nacnac )
CH{C(Me)NiPr}2) affords the dark red mixed-ligand complex (acac)Pd(iPr2-nacnac) (1), while with 2
equiv of Li(iPr2-nacnac) the light red homoleptic Pd(iPr2-nacnac)2 (2) is formed. A similar reaction of
Pd(acac)2 with the more bulky (THF)Li(Ar2-nacnac) (Ar2-nacnac ) CH{C(Me)N(C6H3-2,6-iPr2)}2)
proceeds only to the stage of the mixed-ligand complex. While below 0 °C red (acac)Pd(κ2N,N-Ar2-
nacnac) (4) is isolated as the kinetically controlled product, which is stable in the solid state, this complex
isomerizes in solution at ambient temperature to yield the lighter red and chiral (acac)Pd(κ2C,N-Ar2-
nacnac) (5), displaying a novel nacnac bonding mode. The reaction of [Pd(MeCN)4](BF4)2 and that of
the Pd(I) complex [Pd2(MeCN)6](BF4)2 with (THF)Li(Ar2-nacnac) gives [(κ2N,N-Ar2-nacnac)Pd(MeCN)2]-
(BF4) (6). The κ2N,N-Ar2-nacnac ligand in 6 is sufficiently nucleophilic to displace acetonitrile from
[Pd(MeCN)4](BF4)2 and produce the pure dinuclear [(MeCN)3Pd{µ-CH(C(Me)NAr)2}Pd(MeCN)2](BF4)3
(A), previously accessible only in a mixture. From the reactions of {(η3-C3H5)Pd(µ-Cl)}2 with Li(iPr2-
nacnac) and (THF)Li(Ar2-nacnac) the mixed-ligand complexes (η3-C3H5)Pd(iPr2-nacnac) (3a) and (η3-
C3H5)Pd(κ2N,N-Ar2-nacnac) (3b) have been obtained. Reaction of (cod)PdMeCl with (THF)Li(Ar2-nacnac)
1
affords (Ar2-nacnac)PdMe(MeCN) (7). An anisotropic effect of the Ar2-nacnac ligand in the H NMR
spectra of 3b and 4 can be noted. The structures of 2, 3a, 4, and 5 have been determined by X-ray
crystallography.
coined to account for the fact that the ligands represent nitrogen
derivatives of acac. Recent studies have revealed the ability of
â-diketiminate ligands to stabilize metals in unusual oxidation
states such as Al(I),6 Ga(I),7 Sc(I),8 Ni(I),9 and Ni(III)9c and to
invoke unusual coordination numbers such as three-coordinate
M(II) (M ) Fe, Co, Ni)9a,10 and five-coordinate Pt(IV).11
In view of these unusual properties and the fact that the
â-diketiminate ligand is monoanionic and bidentate like the
π-allyl ligand, we were intrigued to study what effect replacing
the π-allyl group by the â-diketiminate ligand would have on
our Pd-π-allyl chemistry.12 Although â-diketiminate complexes
Introduction
(â-Diketiminato)metal complexes have attracted much atten-
tion in recent years. Original interest focused on the study of the
classical coordination chemistry of homoleptic M(II) (M ) Co,
Ni, Cu) complexes,1 but soon it emerged that â-diketiminate
ligands are rather versatile with respect to possible substituents
and bonding modes.2 A major development came with the imple-
mentation3a of the twofold N-2,6-diisopropylphenyl-substituted
-
pentane-2,4-diiminate ligand HC{C(Me)NAr}2 (Ar ) C6H3-
2,6-iPr2), which due to the particular electronic properties of
the Schiff base donor N atoms and the large bulk of the aryl
substituents turned out to be especially suited to impose unusual
properties on its metal complexes. Pentane-2,4-diiminate ligands
with relatively bulky N-alkyl substituents such as isopropyl and
tert-butyl have also become accessible.4 The catchy acronym
R2-nacnac5 for the substituted pentane-2,4-diiminates has been
(5) Kim, W.-K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541.
(6) Cui, C.; Roesky, H. W.; Schmidt, H.-G,; Noltemeyer, M.; Hao, H.;
Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274.
(7) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000,
1991.
(8) Neculai, A. M.; Neculai, D.; Roesky, H. W.; Magull, J.; Baldus, M.;
Andronesi, O.; Jansen, M. Organometallics 2002, 21, 2590.
(9) (a) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416. (b) Puiu, S. C.;
Warren, T. H. Organometallics 2003, 22, 3974. (c) Kogut, E.; Wiencko,
H. L.; Zhang, L.; Cordeau, D. E.; Warren, T. H. J. Am. Chem. Soc. 2005,
127, 11248. (d) Zhang, D.; Jin, G.-X.; Weng, L.-H.; Wang, F. Organome-
tallics 2004, 23, 3270. (e) Bai, G.; Wei, P.; Stephan, D. W. Organometallics
2005, 24, 5901.
(10) (a) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun.
2001, 1542. (b) Smith, J. M.; Lachicotte, R. J.; Pittard, K. A.; Cundari, T.
R.; Lukat-Rodgers, G.; Rodgers, K. R.; Holland, P. L. J. Am. Chem. Soc.
2001, 123, 9222. (c) Gregory, E. A.; Lachicotte, R. J.; Holland, P. L.
Organometallics 2005, 24, 1803.
(1) (a) Tsybina, N. M.; Vinokurov, V. G.; Protopopova, T. V.; Skoldinov,
A. P. J. Gen. Chem. USSR 1966, 36, 1383. (b) Honeybourne, C. L.; Webb,
G. A. Chem. Commun. 1968, 739. (c) McGeachin, S. G. Can. J. Chem.
1968, 46, 1903. (d) Parks, J. E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408.
(e) Holm, R. H.; O’Connor, M. J. Prog. Inorg. Chem. 1971, 14, 241. (f)
Truex, T. J.; Holm, R. H. J. Am. Chem. Soc. 1972, 94, 4529. (g) Knorr, R.;
Weiss, A. Chem. Ber. 1981, 114, 2104.
(2) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
(3) (a) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514. (b) Clegg,
W.; Cope, E. K.; Edwards, A. J.; Mair, F. S. Inorg. Chem. 1998, 37, 2317.
(c) Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.; Olmstead, M. M.;
Roesky, H. W.; Power, P. P. Dalton Trans. 2001, 3465.
(4) (a) Kuhn, N.; Fahl, J.; Fuchs, S.; Steimann, M.; Henkel, G.; Maulitz,
A. H. Z. Anorg. Allg. Chem. 1999, 625, 2108. (b) Kuhn, N.; Lanfermann,
H.; Schmitz, P. Liebigs Ann. Chem. 1987, 727.
(11) (a) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc.
2001, 123, 6423. (b) Fekl, U.; Goldberg, K. I. J. Am. Chem. Soc. 2002,
124, 6804. (c) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc.
2003, 125, 15286.
10.1021/om0606486 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/09/2006

(â-Diketiminato)palladium Complexes
Organometallics, Vol. 25, No. 25, 2006 5855
with nickel have been widely investigated,1,9,13 relatively little
is known about palladium. The reaction of [Pd(MeCN)4](BF4)2
with Ar2-nacnacH affords the dinuclear tricationic [(MeCN)3Pd-
{µ-CH(C(Me)NAr)2}Pd(MeCN)2](BF4)3 (A; Ar ) C6H3-2,6-
iPr2) as an impure product.3a (cod)PdCl2 reacts with LiCH-
(C(Ph)NSiMe3)2 to give the centrosymmetric square-planar
Pd{CH(C(Ph)NSiMe3)2}2 (B), mentioned in a review.2 The
reaction of (cod)PdMeCl with Tl(Ar2-nacnac) and a salicylal-
dimine gives (Ar2-nacnac)PdMe(κ1N-PhCHdNCH2Ph) (C) in
quantitative yield.14 Furthermore, addition of a â-diimine to
PdCl2 yields the adduct {Me2C(C(Me)NC6H4-2-iPr)2}PdCl2,15a
and oxidative addition of methallyloxyphosphonium salts to Pd-
(0) in the presence of various neutral â-iminoamines results in
the formation of cationic â-diimine complexes [(η3-C3H4Me)-
Pd{CH2(C(Me)NAr′)2}]Y (Y ) PF6, BArF).15b
Figure 1. Molecular structure of Pd(iPr2-nacnac)2 (2). Selected
bond distances (Å), bond angles (deg), and interplanar angles (deg):
Pd1-N1 ) 2.045(1), Pd1-N2 ) 2.042(1), N1-C2 ) 1.321(2),
N2-C4 ) 1.331(2), C2-C3 ) 1.412(2), C3-C4 ) 1.408(2); N1-
Pd1-N2 ) 82.85(5); Pd1,N1,N2/N1,N2,C2,C4 ) 49(1), N1,N2,-
C2,C4/C2,C3,C4 ) 23(1), Pd1,N1,N2/N1,N2,C6,C9 ) 103(1).
We now wish to report our findings on the reactions of
various Pd(I) and Pd(II) starting complexes with Li(iPr2-nacnac)
and Li(Ar2-nacnac), which afford Pd(iPr2-nacnac)2 (2), (η3-
C3H5)Pd(iPr2-nacnac) (3a), (acac)Pd(κ2N,N-Ar2-nacnac) (4), and
its isomer (acac)Pd(κ2C,N-Ar2-nacnac) (5) as structurally char-
acterized products.
both complexes the molecular ions are observed as intense peaks
(1, m/e 386, 53%; 2, m/e 468, 33%). While fragmentation of
1+ is initiated by cleavage of a methyl group (m/e 371, 48%)
to eventually give the unassigned m/e 165 as the base ion, 2+
Results and Discussion
i
fragments by eliminating Pr2-nacnac - H to afford the base
Pd(II)-iPr2-nacnac Complexes 1-3a. Reacting Pd(acac)2
with 2 equiv of Li(iPr2-nacnac) in diethyl ether by heating the
mixture from -78 °C to ambient temperature affords a red
solution, from which light red crystals of the homoleptic
complex 2 separate in 73% yield. When only 1 equiv of Li-
(iPr2-nacnac) is used, the dark red mixed-ligand intermediate 1
can be isolated in 28% yield, but some 2 is also formed. The
synthesis of 2 from Pd(acac)2 is thus likely to pass through 1
as an intermediate (eq 1). Complex 1 does not form by ligand
ion [(iPr2-nacnac)PdH]+ (m/e 288).
The 1H and 13C NMR spectra (Table 1) of 1 show enantiotopic
isopropyl methyl groups in agreement with an apparent C2V sym-
metry, indicating either a planar or a flexible envelope structure
of the Pd(iPr2-nacnac) chelate. In contrast, for 2 the isopropyl
methyl groups are diastereotopic, as expected for a rigid enve-
lope conformation of the Pd(iPr2-nacnac) chelate rings, giving
rise to C2h symmetry of the complex in solution. Both complexes
furnish the characteristic resonances for the central CH groups
i
of the acac and Pr2-nacnac ligands (1, δ(H) 5.27 and 4.33; 2,
4.77).
The molecular structure of 2 has been determined by X-ray
crystallography, and details of the structure refinement are given
in Table 2. Complex 2 crystallizes with two independent
molecules in the elementary cell. The structure of one molecule
is depicted in Figure 1; a similar structure was outlined for
complex B. The Pd(II) center in 2 is coordinated in an exact
i
plane by the four N atoms of the two Pr2-nacnac ligands, and
the geometry of the N atoms is trigonal planar, in accord with
sp2 hybridization (sum of the three angles at nitrogen is 359°).
i
The Pr substituents at N are bent to the same side out of the
coordination plane and away from Pd (plane angle Pd1,N1,-
N2/N1,N2,C6,C9 ) 103°), presumably as a consequence of their
bulk, and the N1-Pd1-N2 angle at 82.85(5)° is smaller than
the ideal 90° (cf. 3a and 4), so that the six-membered Pd(nacnac)
chelate rings adopt a pronounced boat conformation with folds
along N1‚‚‚N2 and C2‚‚‚C4 and interplanar angles Pd1,N1,-
N2/N1,N2,C2,C4 of 49° and N1,N2,C2,C4/C2,C3,C4 of 23°.
Apart from the inversion center the two independent molecules
exhibit no additional symmetry and adopt almost identical
conformations, despite different crystal environments (root-
mean-square deviation 0.04 Å), indicating that the 12 methyl
groups have little flexibility and are close-packed, completely
shielding the core of the complex.
In an attempt to synthesize {(iPr2-nacnac)Pd(µ-Cl)}2, the iPr2-
nacnac analogue of {(η3-C3H5)Pd(µ-Cl)}2, we reacted (cod)-
PdCl2 with 1 equiv of Li(iPr2-nacnac), but instead of the
expected product we isolated small amounts of 2. The reaction
of (cod)PdCl2 with 2 equiv of Li(iPr2-nacnac) similarly gave 2
in low yield (30%). Both reactions were carried out in diethyl
ether by starting at -78 °C, and some palladium black was
metathesis between Pd(acac)2 and 2. Complexes 1 and 2 dissolve
well in pentane and other solvents.
Complexes 1 and 2 have been characterized by their DSC,
MS, and NMR spectra and additionally, in the case of 2, by
single-crystal X-ray crystallography. Solid 1 is thermally stable
to about 120 °C and 2 to 153 °C (DSC), at which temperatures
melting occurs with decomposition. In the EI mass spectra of
(12) (a) Krause, J.; Goddard, R.; Mynott, R.; Po¨rschke, K.-R. Organo-
metallics 2001, 20, 1992. (b) Alberti, D.; Goddard, R.; Po¨rschke, K.-R.
Organometallics 2005, 24, 3907. (c) Ding, Y.; Goddard, R.; Po¨rschke, K.-
R. Organometallics 2005, 24, 439. (d) Chernyshova, E. S.; Goddard, R.;
Po¨rschke, K.-R. Manuscript in preparation.
(13) Recent (â-diketiminato)nickel(II) complexes: (a) Eckert, N. A.;
Bones, E. M.; Lachicotte, R. J.; Holland, P. L. Inorg. Chem. 2003, 42,
1720. (b) Wiencko, H. L.; Kogut, E.; Warren, T. H. Inorg. Chim. Acta
2003, 345, 199. (c) Kogut, E.; Zeller, A.; Warren, T. H.; Strassner, T. J.
Am. Chem. Soc. 2004, 126, 11984.
(14) Kang, M.; Sen, A. Organometallics 2005, 24, 3508.
(15) (a) Cope-Eatough, E. K.; Mair, F. S.; Pritchard, R. G.; Warren, J.
E.; Woods, R. J. Polyhedron 2003, 22, 1447. (b) Landolsi, K.; Richard, P.;
Bouachir, F. J. Organomet. Chem. 2005, 690, 513.

Table 1. 1H and 13C NMR Data of Complexes 1-7 and of Reference Compounds in CD2Cl2 at 25 °Ca
1H NMR Data
δ(H)
acac
nacnac
Me
iPr
CH
Me
CH
CH
Me
phenyl
other
iPr2-nacnacH
4.38 1.89
4.60 1.73
4.59 1.66
3.67
3.65
3.09
1.19
1.09, 1.08
1.20, 1.02
11.36 (NH)
Li(iPr2-nacnac)
(THF)Li(Ar2-nacnac)
Pd(acac)2
7.06, 6.95
7.13, 7.04
7.27, 7.16 deg, 7.08 deg,
6.99
7.26, 7.17
5.42 2.01
5.27 1.98
(acac)Pd(iPr2-nacnac) (1)
Pd(iPr2-nacnac)2 (2)
(acac)Pd(κ2N,N-Ar2-nacnac) (4)
(acac)Pd(κ2C,N-Ar2-nacnac) (5)
4.33 1.87
4.77 1.89
4.86 1.68
2.65 1.93, 1.83 3.66, 3.46,
3.26, 2.82
3.31
3.15
3.39
1.48
1.22, 1.07
1.23, 1.20
1.37, 1.29, 1.24, 1.19,
1.17, 1.15, 1.12, 1.09
1.49, 1.25
4.92 1.13
5.22 1.78, 1.75
[(Ar2-nacnac)Pd(MeCN)2](BF4) (6)
[(MeCN)3Pd{µ-CH(C(Me)NAr)2}-
Pd(MeCN)2](BF4)3 (A)
5.11 1.76
6.17 2.30
3.25
3.61, 3.00
1.72 (MeCN)
3.04, 2.42, 2.34,
1.86 (MeCN)
1.59, 1.55, 1.40, 1.24
7.47, 7.36, 7.31
(Ar2-nacnac)PdMe(MeCN) (7)
4.71 1.62, 1.59 3.40, 3.36
nacnac
1.36, 1.27, 1.20, 1.17
7.15-7.00 (4 signals expctd)
1.48 (MeCN), -0.47 (PdMe)
allyl
CH2
iPr
CH
CH
Me
CH
Me
phenyl
(η3-C3H5)Pd(iPr2-nacnac) (3a)b
(η3-C3H5)Pd(Ar2-nacnac) (3b)
4.75 3.53 (syn), 2.26 (anti)
5.24 2.16 (anti), 1.76 (syn)
4.47 1.96
4.79 1.67
3.61
3.49, 3.19
1.26, 1.15
1.28, 1.20, 1.19, 1.16
7.12-7.00 (3 signals expctd)
13C NMR Data
δ(C)
acac
nacnac
CH
iPr
CdO
CH
Me
CdN
158.2
163.3
163.3
Me
18.9
14.3
25.2
CH
Me
phenyl
other
iPr2-nacnacH
94.0
64.7
68.0
47.2
51.0
28.0
25.0
23.5, 23.5
24.2, 23.4
Li(iPr2-nacnac)
(THF)Li(Ar2-nacnac)
149.1, 140.9, 123.1, 122.7
Pd(acac)2
187.3 101.4 25.3
185.5 99.2 19.8
1
2
4
5
156.7
161.2
157.1
99.2
106.5 26.9
94.5 24.2
25.5
52.3
50.6
28.3
24.7
23.5, 19.7
24.0, 23.8
24.0, 23.9, 23.8,
23.7, 23.5, 23.1,
23.0, 22.9
23.8, 23.7
24.3, 24.3, 24.2,
24.2
186.0 99.6 24.4
145.0, 144.0, 125.7, 122.9
148.9, 141.7, 141.0, 137.5,
137.2, 136.6, 127.6, 124.1,
123.5, 123.0, 122.7, 122.5
148.0, 143.4, 128.2, 124.0
145.3, 141.4, 140.4,
188.0,
174.8
99.9 22.6, 21.7
210.0, 195.2 10.8
28.8, 28.6 28.4, 28.4,
27.6, 27.0
6
A
157.7
182.7
96.0
36.0
23.0
25.9
28.5
30.1, 29.6
120.1, 1.9 (MeCN)
4.9, 4.4, 3.1,
130.6, 126.0, 125.2
2.8 (MeCN)
7
158.8, 158.4 93.6
25.8, 23.8 28.1, 27.9
24.2 deg, 24.0, 23.5
149.7, 149.4, 142.2 deg, 124.6, 118.0, 2.2 (MeCN),
124.4, 123.2, 123.1
0.9 (PdMe)
allyl
CH2
nacnac
iPr
CH
CdN
157.2
159.1
CH Me
CH
Me
phenyl
3ab
3b
108.3 52.1
115.4 61.1
96.2
94.1
24.3
22.8
51.2
24.0, 20.0
24.4, 24.0, 23.8,
23.4
28.3,
27.9
154.3, 140.7,
139.5, 124.4, 123.5, 123.3
a deg ) degenerate. b Solvent C6D6.

(â-Diketiminato)palladium Complexes
Organometallics, Vol. 25, No. 25, 2006 5857
Table 2. Crystal Data for Pd(iPr2-nacnac)2 (2), (η3-C3H5)Pd(iPr2-nacnac) (3a), (acac)Pd(K2N,N-Ar2-nacnac) (4), and
(acac)Pd(K2C,N-Ar2-nacnac) (5)
2
3a
4
5
empirical formula
color
C22H42N4Pd
orange-red
469.00
100
0.710 73
triclinic
C14H26N2Pd
yellow
328.77
C34H48N2O2Pd
orange
623.14
C34H48N2O2Pd
yellow
623.14
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
100
100
100
0.710 73
monoclinic
P21/n (No. 14)
0.710 73
monoclinic
C2/c (No. 15)
0.710 73
monoclinic
P21/c (No. 14)
P1h (No. 2)
8.1121(2)
9.6711(3)
16.6998(4)
78.659(1)
82.887(1)
65.204(1)
1164.88(5)
2
582.4
1.337
0.810
496
0.19 × 0.18 × 0.12
3.14-31.48
-11 e h e 11
-14 e k e 14
-24 e l e 24
26 528
9.0662(3)
17.4148(7)
9.6064(4)
90.0
101.143(2)
90.0
1488.1(1)
4
372.0
35.0185(5)
10.6251(1)
20.5768(3)
90.0
121.351(1)
90.0
6538.29(15)
8
817.3
1.266
0.598
2624
0.20 × 0.14 × 0.08
3.24-31.48
-51 e h e 51
-15 e k e 15
-30 e l e 29
89 328
18.0221(5)
10.6425(2)
17.2769(4)
90.0
107.205(1)
90.0
3165.43(13)
4
791.4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
V/Z (Å3)
calcd density (Mg m-3
)
1.467
1.230
680
1.308
0.617
1312
abs coeff (mm-1
F(000) (e)
)
cryst size (mm3)
0.06 × 0.06 × 0.05
0.130 × 0.090 × 0.024
3.45-31.52
-26 e h e 26
-14 e k e 15
-25 e l e 25
49 431
θ range for data collecn (deg)
index ranges
3.06-31.57
-13 e h e 13
-25 e k e 25
-14 e l e 14
13 710
no. of rflns collected
no. of indep rflns
no. of rflns with I > 2σ(I)
completeness (%)
abs cor
7540 (Rint ) 0.0352)
7091
4709 (Rint ) 0.1158)
3991
94.4 (θ ) 31.57°)
Gaussian
10 856 (Rint ) 0.0507)
9510
10 524 (Rint ) 0.0577)
7985
97.6 (θ ) 31.48°)
semiempirical from
equivalents
1.00/0.75
F2
99.8 (θ ) 31.48°)
semiempirical from
equivalents
1.00/0.94
F2
99.7 (θ ) 31.52°)
semiempirical from
equivalents
1.00/0.86
max/min transmissn
full-matrix least squares
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R1
0.955/0.902
F2
4709/0/155
1.067
F2
7540/0/247
1.115
10 856/0/356
1.080
10 524/0/375
1.045
0.0285
0.0759
0.0691
0.2031
0.0302
0.0714
0.0394
0.0799
wR2
R indices (all data)
R1
0.0300
0.0876
0.0379
0.0649
wR2
0.0769
0.783/-0.808
0.2454
0.0748
0.511/-0.986
0.0880
0.501/-0.729
largest diff peak/hole (e Å-3
)
3.21/-2.21 (1.1/0.69 Å from Pd1)
formed, even at about -50 °C. Workup of the reaction mixtures
led to isolation of an elusive colorless compound which has
been tentatively assigned as the neutral ligand dimer (iPr2-
nacnac)2. It seems likely that the intermediate {(iPr2-nacnac)-
Pd(µ-Cl)}2 is not stable and reacts partly with further Li(iPr2-
nacnac) to give 2, while the rest decomposes with reduction of
palladium and oxidation of the ligand (eq 2). The formation of
precipitated, as observed previously with (cod)PdCl2, and
complex 2 was isolated from the solution in about 30% of the
theoretical yield. The formation of these products can be
conceived as a disproportion reaction of Pd(I) into Pd(0) and
Pd(II) passing via a hypothetical dimer (eq 3). Workup of the
mother liquor also gave some ligand dimer (iPr2-nacnac)2.
Warming a mixture of {(η3-C3H5)Pd(µ-Cl)2}2 with Li(iPr2-
nacnac) in diethyl ether from -78 to 0 °C leads to isolation of
the light yellow mixed-ligand complex 3a (eq 4a). The solid
compound (mp 153 °C dec, DSC) is stable at ambient temper-
ature for a short period but is best stored cold. Whereas 3a
decomposes quickly in THF and CH2Cl2, even at low temper-
atures, it is more stable in diethyl ether and, in particular, in
benzene. In the EI mass spectrum (55 °C) the molecular ion of
3a appears with high intensity (44%). M+ fragments by cleavage
of an isopropyl substituent, whereas, quite unexpectedly, the
(iPr2-nacnac)2 appears analogous to that of (Ar2-nacnac)2 (Ar
) C6H3-2,6-iPr2), which was obtained when Ar2-nacnacH was
treated with AgPF6 in the presence of triethylamine.16
We also attempted to synthesize the dimeric Pd(I) complex
{(iPr2-nacnac)Pd}2, a pendent to the various Ni(I) complexes,
by reacting [Pd2(MeCN)6](BF4)2 with 2 equiv of Li(iPr2-nacnac)
in diethyl ether, but at around -50 °C some palladium black
(16) Shimokawa, C.; Itoh, S. Inorg. Chem. 2005, 44, 3010.

5858 Organometallics, Vol. 25, No. 25, 2006
Tian et al.
of 1) as the kinetically controlled product (eq 5). No Pd(Ar2-
nacnac)2 is formed (as a possible analogue of 2), even when an
excess of (THF)Li(Ar2-nacnac) is used.
allyl group remains attached. In the ambient-temperature 1H and
i
13C NMR spectra of 3a in C6D6 both the allyl and the Pr2-
nacnac resonances are sharply resolved with diastereotopic
methyl groups at the isopropyl substituents, indicating structural
rigidity of the π-allyl group.
In the crystal structure of 3a (Table 2 and Figure 2) the Pd-
(II) center is coordinated in a square-planar fashion by the
â-diketiminate and the π-allyl ligand, with the meso carbon of
the latter tilted away from the Pd center in the usual manner
(plane angle C12,C13,C14/C12,C14,Pd1 ) 109°). As for 2, the
geometry of the sp2 N atoms in 3a is trigonal planar (the sum
of the angles at N is 359°). The six-membered Pd(nacnac)
chelate ring also displays a boat conformation, but with plane
angles Pd1,N1,N2/N1,N2,C2,C4 of 30° and N1,N2,C2,C4/C2,-
C3,C4 of 16° it is less folded than in 2 (angles of 49 and 23°,
respectively), and the N1-Pd1-N2 angle at 88.9° is close to
the expected 90°. This is presumably a consequence of the
reduced steric repulsion in 3a, since the iPr substituents attached
to N are bent toward the Pd atom (plane angle Pd1,N1,N2/N1,-
N2,C6,C9 of 72°) instead of away as in the case of 2 (103°).
Pd(II)-Ar2-nacnac Complexes 3b-7. The reaction of {(η3-
C3H5)Pd(µ-Cl)2}2 with (THF)Li(Ar2-nacnac) affords yellow
crystals of 3b (eq 4b). As for 3a, in the EI mass spectrum of
the neutral 3b the molecular ion is observed with high intensity.
It breaks down by elimination of the allyl ligand (unlike 3a,
which cleaves off an iPr substituent) to give [(Ar2-nacnac)Pd]+
Isolated 4 is stable at ambient temperature. The melting point
of 4 determined by DSC is 227 °C, and no phase change is
indicated below this temperature. In the EI mass spectrum (120
°C) the molecular ion (m/e 622) is observed as the base ion. It
fragments by cleaving off acetylacetonate to afford the intense
[Pd(Ar2-nacnac)]+ (m/e 523, 40%).
The molecular structure of 4 is shown in Figure 3. The
complex consists of almost planar (acac)Pd (rms deviation 0.029
Å) and Pd(κ2N,N-Ar2-nacnac) units (rms deviation 0.028 Å),
which are tilted by 7° to each other at the formally square planar
Pd(II) center. While the O1-Pd1-O2 angle of the (acac)Pd
chelate at 90.51(5)° is normal, the N1-Pd1-N2 angle of the
Pd(κ2N,N-Ar2-nacnac) chelate at 92.61(5)° is much larger than
the corresponding angle in 2 (83°) and slightly larger than that
in 3a (89°). The ipso C atoms of the phenyl rings also lie in the
Pd(κ2N,N-Ar2-nacnac) plane (the sum of the angles at trigonal-
planar N is 360°), with the planes of the phenyl rings
approximately lying perpendicular to this (plane angles of 84
and 90°).
1
The solution H and 13C NMR spectra of 4 (Table 1) are
1
(m/e 523) as the base ion. The H and 13C NMR spectra of 3b
consistent with point symmetry C2V, which is almost that found
for the molecule in the crystal (but less so for its environment).
Thus, for the Ar2-nacnac ligand there are 4 phenyl ring 13C
resonances, and the 4 isopropyl groups are equivalent, but as
they have diastereotopic Me groups, a total of 10 13C resonances
occur for this ligand. Due to diastereotopy of the Me groups a
(Table 1) are in agreement with CS symmetry of the complex.
The occurrence of 15 13C signals for the Ar2-nacnac ligand
confirms the rigid coordination of the ligands at Pd and the
nonrotating nature of the N-C6H3-2,6-iPr2 substituents, with their
phenyl ring planes orientated perpendicular to the coordination
1
plane. In the H NMR spectrum the allyl syn protons (δ(H)
1.76) unexpectedly resonate upfield from the anti protons (δ(H)
2.16), which is attributed to an anisotropic effect of the nacnac
phenyl rings.
Warming a mixture of Pd(acac)2 and (THF)Li(Ar2-nacnac)
(Ar ) C6H3-2,6-iPr2) in pentane from -78 to 0 °C results in
the formation of the red mixed-ligand complex 4 (an analogue
Figure 3. Molecular structure of (acac)Pd(κ2N,N-Ar2-nacnac) (4).
Details of the structure refinement are given in Table 2. Selected
bond distances (Å), bond angles (deg), and interplanar angles
(deg): Pd1-N1 ) 1.993(1), Pd1-N2 ) 1.992(1), N1-C2 ) 1.326-
(2), N2-C4 ) 1.328(2), C2-C3 ) 1.403(2), C3-C4 ) 1.398(2),
Pd1-O1 ) 2.020(1), Pd1-O2 ) 2.009(1); O1-Pd1-O2 ) 90.51-
(5), N1-Pd1-N2 ) 92.61(5); Pd1,N1,N2,C2,C3,C4/Pd1,O1,O2,-
C31,C32,C33 ) 7(1).
Figure 2. Molecular structure of (η3-C3H5)Pd(iPr2-nacnac) (3a).
Selected bond distances (Å), bond angles (deg), and interplanar
angles (deg): Pd1-N1 ) 2.088(4), Pd1-N2 ) 2.088(4), N1-C2
) 1.323(6), N2-C4 ) 1.322(6), C2-C3 ) 1.406(5), C3-C4 )
1.415(6), Pd1-C12 ) 2.147(5), Pd1-C14 ) 2.170(6); N1-Pd1-
N2 ) 88.9(1); Pd1,N1,N2/N1,N2,C2,C4 ) 30(1), N1,N2,C2,C4/
C2,C3,C4 ) 16(2), Pd1,N1,N2/N1,N2,C6,C9 ) 72.

(â-Diketiminato)palladium Complexes
Organometallics, Vol. 25, No. 25, 2006 5859
possible rotation of the phenyl substituents about the N-C bond
1
can be excluded. The acac Me groups of 4 give rise to an H
NMR high-field signal at δ(H) 1.13 (cf. Pd(acac)2 and 1: δ(H)
≈ 2.0), which is also attributed to an anisotropic effect of the
adjacent phenyl rings.
When a solution of 4 in pentane or diethyl ether is kept at
ambient temperature for 2 h, the complex isomerizes into the
thermodynamically more stable 5. Complex 5 is also obtained
directly from Pd(acac)2 and (THF)Li(Ar2-nacnac) by performing
the reaction of eq 5 at 20 °C. The crystals of 5 are red like
those of 4, but slightly lighter. Both isomers show very similar
melting points (5; 229 °C, DSC) and give rise to practically
the same EI mass spectra.
In the solution 1H and 13C NMR spectra of 5 all carbon atoms
of the acac ligand (5 signals) and Ar2-nacnac ligand (29 signals)
are inequivalent, so that the spectra must be attributed to an
asymmetric structure with nonrotating C6H3-2,6-iPr2 substi-
tutents. The central methine group of the nacnac ligand furnishes
the resonances δ(H) 2.65 and δ(C) 10.8, which are shifted
substantially upfield compared with 4 (δ(H) 4.86 and δ(C) 94.5)
and which are in agreement with its carbanionic character. The
coordination of this ligand in 5 is reminiscent of that of the
κ1C-acac ligand in (κ2O,O-acac)Pd(PPh3)(κ1C-acac) (D; δ(H)
3.54).17a,b Since one of the imine groups is additionally
coordinated to Pd, the isomerization of 4 to 5 results in the
formation of a chiral center at the coordinated C atom. The
spectra rule out a possible exchange of the coordinated and
noncoordinated C(Me)dNAr imine moieties.
The results of the X-ray crystal structure analysis of 5 are
shown in Figure 4. The Pd ion is coordinated in a square-planar
fashion by anionic acac and κ2C,N-nacnac ligands. The latter
represents a formal azaallyl ligand,18 in which the electrons are
localized in an enyl structure and which coordinates to Pd(II)
via the methine carbon and one imine nitrogen atom through
σ-type bonds (and not a σ and a π bond), forming an almost
planar four-membered chelate ring (plane angle Pd,N1,C3/N1,-
C2,C3 ) 8°). Within the ring the N1-Pd1-C3 angle at 66.5-
(1)° is the smallest, while the other three angles range from
88.9 to 106.6°. While the Pd1-C3 length at 2.057(2) Å lies in
the typical range for Pd-C single bonds (2.00-2.11 Å), it is
shorter than in the closely related D (2.11 Å)17a and derivatives
(2.07-2.11 Å).17c-g The Pd1-N1 bond at 2.015(2) Å is only
slightly longer than in 4 (1.99 Å, mean). For the κ2C,N-Ar2-
nacnac backbone in 5 the N1-C2 and N2-C4 bonds have the
same short bond length of 1.281(3) Å (4, 1.33 Å, mean), as
expected for an imine, whereas C2-C3 at 1.500(3) Å inside
the ring and C3-C4 at 1.478(3) Å outside the ring are in agree-
ment with C(sp2)-C(sp3) single bonds (both bonds are signifi-
cantly longer than in 4: 1.40 Å, mean). It is worth noting that
the Pd1-O1 bond (2.084(2) Å), located trans to Pd1-C3, is
significantly longer than Pd1-O2 (2.013(2) Å), located trans to
Pd1-N1. The κ2C,N-Ar2-nacnac coordination is thus best ex-
plained by a strong coordination of the central carbanionic C3
Figure 4. Molecular structure of (acac)Pd(κ2C,N-Ar2-nacnac) (5).
Details of the structure refinement are given in Table 2. Selected
bond distances (Å) and angles (deg): Pd1-N1 ) 2.015(2), Pd1-
C3 ) 2.057(2), N1-C2 ) 1.281(3), N2-C4 ) 1.281(3), C2-C3
) 1.500(3), C3-C4 ) 1.478(3), Pd1-O1 ) 2.084(2), Pd1-O2 )
2.013(1); O1-Pd1-O2 ) 92.64(6), N1-Pd1-C3 ) 66.5(1), Pd1-
C3-C2 ) 88.9(1), C3-C2-N1 ) 106.6(2), C2-N1-Pd1 ) 97.4-
(1); Pd1,N1,C3/N1,C2,C3 ) 8(2), Pd1,N1,C3/Pd1,O1,O2 ) 3(1),
Pd1,O1,O2/O1,O2,C31,C32,C33 ) 8(2).
at the Pd center in the form of a Pd-C single bond and relatively
weak coordination of one imine nitrogen atom to complete the
fourfold coordination around the Pd(II) center, with the forma-
tion of the four-membered chelate ring. This coordination mode
of a nacnac ligand appears to be new, and only two other reports
of crystal structures of azaallyl-type (didehydrometallaazetane-
type) complexes, one of them involving palladium, are currently
listed in the Cambridge Structural Database.19
Treating [Pd(MeCN)4](BF4)2 with 1 equiv or an excess of
(THF)Li(Ar2-nacnac) in diethyl ether affords the red mixed-
ligand complex 6 (eq 6a) and, again, no Pd(Ar2-nacnac)2.
Complex 6 is likewise formed when the Pd(I) complex [Pd2-
(MeCN)6](BF4)2 is reacted with (THF)Li(Ar2-nacnac) at -78 °C
(eq 6b); the reaction also affords Pd black and some ligand dimer
(Ar2-nacnac)2.16 Reaction 6a is remarkable, since it was reported
that equal amounts of [Pd(MeCN)4](BF4)2 and Ar2-nacnacH
react to give dinuclear A (characterized by X-ray) and [Ar2-
nacnacH2]BF4, half of the Ar2-nacnacH thereby functioning as
a base to neutralize HBF4.3a While complex 6 has been
inaccessible in that study and A has only been isolated as a
mixture, we found that 6 prepared by us can be combined with
1 equiv of [Pd(MeCN)4](BF4)2 in acetonitrile to afford the
dinuclear A in a pure state (eq 7). Obviously, the central methine
group of the κ2N,N-Ar2-nacnac ligand in 6 has retained sufficient
nucleophilicity so that it is able to displace one acetonitrile
ligand in [Pd(MeCN)4](BF4)2 and undergo a bridging coordina-
tion to another Pd(II) center. The electron distribution of the
(17) (a) Baba, S.; Ogura, T.; Kawaguchi, S. Bull. Chem. Soc. Jpn 1974,
47, 665. Horike, M.; Kai, Y.; Yasuoka, N.; Kasai, N. J. Organomet. Chem.
1974, 72, 441. (b) Werner, H.; Kraus, H.-J. Chem. Ber. 1980, 113, 1072.
(c) Siedle, A. R.; Pignolet, L. H. Inorg. Chem. 1981, 20, 1849. (d)
Kurokawa, T.; Miki, K.; Tanaka, N.; Kasai, N. Bull. Chem. Soc. Jpn. 1982,
55, 45. (e) Xu, C.; Hampden-Smith, M. J.; Kodas, T. T.; Duesler, E. N.;
Rheingold, A. L.; Yap, G. Inorg. Chem. 1995, 34, 4767. (f) Cheng, J.-K.;
Li, Z.-J.; Chen, Y.-B.; Qin, Y.-Y.; Kang, Y.; Wen, Y.-H.; Yao, Y.-G. Chin.
J. Struct. Chem. 2003, 22, 43. (g) Navarro, O.; Marion, N.; Stevens, E. D.;
Scott, N. M.; Gonzalez, J.; Amoroso, D.; Bell, A.; Nolan, S. P. Tetrahedron
2005, 61, 9716.
(18) For a Pd-thiaallyl complex, see: Tamaru, Y.; Kagotani, M.;
Yoshida, Z. J. Org. Chem. 1979, 44, 2816. Miki, K.; Tanaka, N.; Kasai, N.
J. Organomet. Chem. 1981, 208, 407.

5860 Organometallics, Vol. 25, No. 25, 2006
Tian et al.
complex 7 (eq 8), which represents a parent complex of C (see
the Introduction).
Complex 7 has Cs symmetry due to its square-planar structure.
The “halves” of the Ar2-nacnac ligand are inequivalent with
the planes of the N-C6H3-2,6-iPr2 substituents perpendicular to
the coordinate plane, so that a total of 19 13C signals results for
this ligand. The MeCN and PdMe resonances are inconspicuous
(Table 1). The exchange of the MeCN ligand with free MeCN
is relatively slow and does not affect the symmetry of the
complex.
Finally, it is worth emphasizing that, with the exception of
the MeCN-ligated complexes, all other isolated Pd-nacnac com-
plexes have only a limited stability in solution at ambient tem-
perature, so that over the course of several hours some Pd black
is precipitated. Clearly, the ease with which these complexes
undergo degradation with reduction of Pd(II) to Pd(0) poses a
major obstacle to a substantial expansion of Pd-nacnac chemistry.
κ2N,N-nacnac-dienyl system thereby becomes localized in a
2,4-diimin-3-yl structure. While A crystallizes from MeCN with
three molecules of solute MeCN, it is depleted from the solute
MeCN by drying at ambient temperature under vacuum.
The ESIpos mass spectrum of the ionic 6 affords the cascade
of ions [(Ar2-nacnac)Pd(MeCN)2]+, [(Ar2-nacnac)Pd(MeCN)]+,
and [(Ar2-nacnac)Pd]+, with the last as the base ion. The
spectrum of A is very similar to that of 6. In the 13C NMR
spectrum of 6 in CD2Cl2 (Table 1) only 10 13C signals are found
for the Ar2-nacnac ligand, corresponding to C2V symmetry and
a planar or fluttering Pd(Ar2-nacnac) ring having nonrotating
C6H3-2,6-iPr2 substituents (as in the case of 4). The central
methine group of the nacnac ligand in 6 (CD2Cl2) gives rise to
signals at δ(H) 5.11 and δ(C) 96.0 (in CD3CN: δ(H) 5.25 and
δ(C) 96.5).
Conclusions
Having the pure dinuclear A in our hands, we reinvestigated
its NMR spectra (Table 1). It should be recalled that A displays
an approximate Cs-symmetrical structure with the (MeCN)3Pd
moiety lying in the symmetry plane.3a Thus, there are four
different types of MeCN ligands a-d. In fact, for A, which has
been depleted under vacuum from the solute MeCN, in CD2-
Cl2 solution at ambient temperature three separate MeCN signals
a-c at δ(H) 3.04, 2.42, and 2.34 (each 3 H) and δ(C) 4.9, 4.4,
and 3.1 are found for the (MeCN)3Pd moiety and further sharp
signals d at δ(H) 1.86 (6 H) and δ(C) 2.8 for the two equivalent
MeCN ligands of the diimine-Pd moiety. When the spectrum
of A containing three MeCN solute molecules is observed, the
signals c (originally at δ(H) 2.34 and δ(C) 3.1) are coalesced
with the solute signals, and with an increasing concentration of
MeCN the signals b and a also coalesce. Eventually, with a
larger amount of MeCN only the signal of the free MeCN in
rapid exchange with all MeCN ligands a-d is found. The spectra
show that (a) the (MeCN)3Pd moiety with three inequivalent
MeCN ligands is nonrotating in solution, (b) each of the three
MeCN ligands has an individual rate of exchange with free
MeCN, and (c) the exchange rates of ligands a-c are markedly
higher than that of d. Feldman et al.3a have given 1H NMR data
for the impure A in neat CD3CN. Here, due to the exchange of
all acetonitrile ligands with the solvent, merely one signal for
uncoordinated MeCN is observed. In addition to Cs symmetry,
We have reported the synthesis and properties of a series of
Pd(II)-nacnac complexes 1-7, containing the iPr2-nacnac and
Ar2-nacnac (Ar ) C6H3-2,6-iPr2) ligands. While the isolated
complexes are quite stable at ambient temperature, the MeCN-
free complexes slowly decompose in solution with the formation
of elementary palladium, presumably due to an internal redox
reaction between Pd(II) and the nacnac ligand. Particularly
interesting aspects of this work are (i) the unprecedented
isomerization of a κ2N,N-nacnac ligand into a κ2C,N-nacnac
ligand (4 f 5) with the creation of a chiral center, (ii) the high
nucleophilicity of the methine carbon in the κ2N,N-nacnac ligand
in 6, undergoing coordination to another Pd(II) center, and (iii)
the anisotropic effect of the C6H3-2,6-iPr2 substituents in the
1H NMR spectra of 3b and 4.
Experimental Section
All manipulations were carried out under argon with Schlenk-
type glassware. Solvents were dried prior to use by distillation from
NaAlEt4. Li(iPr2-nacnac) was synthesized in a modified literature
procedure,1c,4a so that a new protocol is given below. (THF)Li-
(Ar2-nacnac),20 [Pd(MeCN)4](BF4)2,21a [Pd2(MeCN)6](BF4)2,21b (cod)-
PdCl2,22 (cod)PdMeCl,23 and {(η3-C3H5)PdCl}224 were prepared as
published. Pd(acac)2 (Aldrich; 99% pure) was commercially avail-
able. Microanalyses were performed by the local Mikroanalytisches
Labor Kolbe. EI mass spectra were recorded at 70 eV and refer to
106Pd. For the ESI mass spectra an ESQ3000 instrument was used.
1
the ambient-temperature H and 13C spectra of A in CD2Cl2
and CD3CN evidence nonrotating C6H3-2,6-iPr2 substituents of
the 2,4-diimin-3-yl ligand. The PdCH group of A in CD2Cl2
furnishes resonances at δ(H) 6.17 and δ(C) 36.0 (CD3CN: δ(H)
5.45 and δ(C) 37.5), of which, as compared to the corresponding
nacnac methine resonances in 6, the 13C resonance is shifted
(19) (a) Henderson, W.; Fawcett, J.; Kemmitt, R. D. W.; Proctor, C.;
Russell, D. R. J. Chem. Soc., Dalton Trans. 1994, 3085. (b) Scholz, J.;
Scholz, A.; Weimann, R.; Janiak, C.; Schumann, H. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1171.
(20) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.
(21) (a) Wayland, B. B.; Schramm, R. F. Inorg. Chem. 1969, 8, 971. (b)
Murahashi, T.; Nagai, T.; Okuno, T.; Matsutani, T.; Kurosawa, H. Chem.
Commun. 2000, 1689.
(22) Chatt, J.; Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957, 3413.
(23) (a) Rudler-Chauvin, M.; Rudler, H. J. Organomet. Chem. 1977, 134,
115. (b) Ru¨lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(24) (a) Dent, W. T.; Long, R.; Wilkinson, A. J. J. Chem. Soc. 1964,
1585. (b) Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg. Synth. 1979, 19, 220.
1
upfield as expected for an sp3-C-Pd moiety, but for the H
resonance an unexpected deshielding is noted (cf. PdCH of 5:
δ(H) 2.65 and δ(C) 10.8), which is explained by anisotropy
exerted here by the 2,4-diimin-3-yl ligand.
While the reaction of (cod)PdCl2 with (THF)Li(Ar2-nacnac)
in pentane or diethyl ether did not yield a defined product (in
particular, no Pd(Ar2-nacnac)2), the reaction of (cod)PdMeCl
with (THF)Li(Ar2-nacnac) in acetonitrile afforded the PdMe

(â-Diketiminato)palladium Complexes
Organometallics, Vol. 25, No. 25, 2006 5861
1H NMR spectra were measured at 300 MHz and 13C NMR spectra
at 75.5 MHz (both relative to TMS) on Bruker AMX-300 and DPX-
300 instruments. If not given otherwise, the NMR data of the
products are listed in Table 1. DSC spectra at a 5 K min-1 heating
rate were recorded with the Mettler-Toledo TA8000 thermal
analysis system having a DSC820 measuring module.
MeC(NiPr)CHdC(OH)Me. An equimolar mixture of acetyl-
acetone (100.1 g, 1.00 mol) and isopropylamine (59.1 g, 1.00 mol)
in 400 mL of CH2Cl2 was kept at ambient temperature for 2 days,
whereupon a thin water layer was formed. The organic phase was
separated and dried over Na2SO4. The product was distilled under
vacuum to give a colorless liquid (bp 64 °C at 0.01 mmHg): yield
105 g (74%); C8H15NO (141.2). 1H NMR (CDCl3, 25 °C): δ 1.16
(d, 6H, NCHMe2), 1.88 (s, 3H, NdCMe), 1.90 (s, 3H, OCMe),
3.70 (sept, 1H, NCH), 4.86 (s, 1H, dCH-), 10.75 (s, 1H, OH).
iPr2-nacnacH. MeC(NiPr)CHdC(OH)Me (28.24 g, 200 mmol)
dissolved in 150 mL of CH2Cl2 was treated with 200 mL of a 1 M
solution of triethyloxonium tetrafluoroborate (200 mmol) in CH2-
Cl2 at 0 °C. The mixture was stirred at ambient temperature for 30
min, and 2 equiv of isopropyl amine (23.64 g, 400 mmol) in 100
mL of CH2Cl2 was added. (Excess iPrNH2 seems necessary because
of the formation of some iPrNH3BF4.) After 1 h the volatiles were
removed under vacuum and the remaining dark brown solid was
dissolved in a mixture of 300 mL of water, KOH (11.22 g, 200
mmol), and 200 mL of pentane. The water phase was washed twice
with 100 mL of pentane, and the combined organic phase was dried
over Na2SO4. Vacuum distillation gave a colorless liquid (bp 84
°C at 0.01 mmHg): yield 29.0 g (80%); C11H22N2 (182.3).
410 mg (62%); mp 95 °C dec (DSC). Crystals suitable for X-ray
analysis were recrystallized from diethyl ether. EI-MS (55 °C): m/e
(%) 328 ([M]+, 44), 285 ([M - iPr]+, 41), 165 (100). Anal. Calcd
for C14H26N2Pd (328.8): C, 51.14; H, 7.97; N, 8.52; Pd, 32.37.
Found: C, 51.03; H, 8.04; N, 8.46; Pd, 32.54.
(η3-C3H5)Pd(Ar2-nacnac) (3b). Synthesis was as for 3a, but
{(η3-C3H5)Pd(µ-Cl)}2 (364 mg, 1.00 mmol) was reacted with
(THF)Li(Ar2-nacnac) (993 mg, 2.00 mmol): yellow crystals; yield
800 mg (71%); mp 170 °C dec (DSC). EI-MS (120 °C): m/e (%)
564 ([M]+, 74), 523 ([Pd(Ar2-nacnac)]+, 100). Anal. Calcd for
C32H46N2Pd (565.2): C, 68.01; H, 8.20; N, 4.96; Pd, 18.83.
Found: C, 68.17; H, 8.15; N, 4.82; Pd, 18.69.
(acac)Pd(κ2N,N-Ar2-nacnac) (4). A suspension of Pd(acac)2
(304 mg, 1.00 mmol) in 15 mL of pentane was combined with a
solution of (THF)Li(Ar2-nacnac) (496 mg, 1.00 mmol) in 15 mL
of pentane at -78 °C. The stirred reaction mixture was slowly
warmed to 0 °C, at which temperature it was kept for 7 h. Insoluble
materials were removed by filtration, and the clear orange filtrate
was concentrated under vacuum (0 °C) to a volume of 8 mL. Slow
cooling of the solution to -40 °C gave red crystals, which were
freed from the mother liquor and dried under vacuum (0 °C): yield
410 mg (66%); mp 227 °C (DSC). EI-MS (120 °C): m/e (%) 622
([M]+, 100), 523 ([Pd(Ar2-nacnac)]+, 40). ESIpos-MS (CH2Cl2):
m/e (%) 622 ([M]+, 100). Anal. Calcd for C34H48N2O2Pd (623.2):
C, 65.53; H, 7.76; N, 4.50; Pd, 17.08. Found: C, 64.56; H, 7.77;
N, 4.45; Pd, 17.06.
(acac)Pd(κ2C,N-Ar2-nacnac) (5). Synthesis and workup were as
for 4, but the reaction mixture was stirred at ambient temperature
overnight: red crystals; yield 330 mg (53%); mp 229 °C (DSC).
EI-MS (135 °C): m/e (%) 622 ([M]+, 100), 523 ([Pd(Ar2-nacnac)]+,
64). ESIpos-MS (CH2Cl2): m/e (%) 623 ([M + H]+, 100), 418
([Ar2-nacnacH]+, 96). Anal. Calcd for C34H48N2O2Pd (623.2): C,
65.53; H, 7.76; N, 4.50; Pd, 17.08. Found: C, 64.58; H, 7.78; N,
4.43; Pd, 17.06.
[(Ar2-nacnac)Pd(MeCN)2](BF4) (6). Route a. A solution of [Pd-
(MeCN)4](BF4)2 (444 mg, 1.00 mmol) in 15 mL of acetonitrile was
combined with a solution of (THF)Li(Ar2-nacnac) (496 mg, 1.00
mmol) in an equal volume of acetonitrile at -40 °C. The mixture
was strirred while the temperature was raised to ambient. The
resulting burgundy red solution was filtered and concentrated to
about 10 mL. Cooling the solution to -40 °C afforded dark red
crystals, which were isolated and dried under vacuum (20 °C): yield
510 mg (74%).
Route b. Synthesis was as for route a, but with [Pd2(MeCN)6]-
(BF4)2 (632 mg, 1.00 mmol) as the starting material. After separation
of some Pd black by filtration, the concentrated solution was cooled
to -40 °C to afford dark red crystals: yield 510 mg (37%
referenced to Pd). ESIpos-MS (CH2Cl2): m/e (%) 605 ([(Ar2-
nacnac)Pd(MeCN)2]+, 20), 564 ([(Ar2-nacnac)Pd(MeCN)]+, 15),
523 ([Pd(Ar2-nacnac)]+, 100). Anal. Calcd for C33H47BF4N4Pd
(693.0): C, 57.20; H, 6.84; N, 8.08; B, 1.56; Pd, 15.36. Found: C,
57.08; H, 6.74; N, 7.97; Pd, 15.46. For recording the NMR spectra,
the complex was recrystallized from CH2Cl2 to eliminate traces of
adherent MeCN.
(Ar2-nacnac)PdMe(MeCN) (7). Solutions of (cod)PdMeCl (265
mg, 1.00 mmol) and (THF)Li(Ar2-nacnac) (496 mg, 1.00 mmol),
each in 10 mL of acetonitrile, were combined at -20 °C. While
the mixture was stirred, the temperature was increased to ambient.
The mixture was filtered to remove the precipitated LiCl and
concentrated under vacuum to a volume of 10 mL. Cooling the
solution to -40 °C afforded brown crystals: yield 440 mg (76%).
Anal. Calcd for C32H47N3Pd (580.2): C, 66.25; H, 8.17; N, 7.24;
Pd, 18.34. Found: C, 66.18; H, 8.20; N, 7.20; Pd, 18.27.
[(MeCN)3Pd{µ-CH(C(Me)NAr)2}Pd(MeCN)2](BF4)3 (A). Com-
plexes 6 (693 mg, 1.00 mmol) and [Pd(MeCN)4](BF4)2 (444 mg,
1.00 mmol) were dissolved in 15 mL of acetonitrile at ambient
temperature. Cooling the solution to -40 °C gave large yellow
i
Li(iPr2-nacnac). Pr2-nacnacH (9.11 g, 50 mmol) dissolved in
150 mL of pentane was mixed with 20 mL of a 2.5 M solution of
tBuLi (50 mmol) in pentane at -78 °C. The reaction mixture was
slowly warmed to ambient temperature and kept overnight. The
precipitated colorless Li(iPr2-nacnac) was separated from the mother
liquor, washed with pentane, and dried under vacuum: yield 7.5 g
(80%); C11H21LiN2 (188.2).
(acac)Pd(iPr2-nacnac) (1). A suspension of Pd(acac)2 (304 mg,
1.00 mmol) in 15 mL of diethyl ether was stirred with a solution
of Li(iPr2-nacnac) (188 mg, 1.00 mmol) also in 15 mL of diethyl
ether, thereby slowly warming the mixture from -78 to 0 °C (4 h).
Insoluble materials were removed by filtration, and the clear red
filtrate was concentrated to a volume of about 5 mL. Cooling to
-40 °C gave red crystals: yield 110 mg (28%). EI-MS (85 °C):
m/e (%) 386 ([M]+, 53), 371 ([M - CH3]+, 48), 165 (100). ESIpos-
MS (CH2Cl2): m/e (%) 387 ([M + H]+, 100). Anal. Calcd for
C16H28N2O2Pd (386.8): C, 49.68; H, 7.30; N, 7.24; Pd, 27.51.
Found: C, 49.54; H, 7.18; N, 7.16; Pd, 27.42.
Pd(iPr2-nacnac)2 (2). A suspension of Pd(acac)2 (304 mg, 1.00
mmol) in 15 mL of diethyl ether was combined with a solution of
Li(iPr2-nacnac) (376 mg, 2.00 mmol) in 10 mL of ether at -78 °C.
The stirred reaction mixture was warmed to ambient temperature
overnight. Insoluble materials were removed by filtration, and the
clear red filtrate was concentrated to a volume of about 5 mL. Slow
cooling of the solution to -40 °C gave light red crystals, which
were freed from the mother liquor by means of a capillary, washed
with a small volume of cold pentane, and dried under vacuum (25
°C): yield 340 mg (73%); mp 153 °C dec (DSC). EI-MS (75 °C):
m/e (%) 468 ([M]+, 33), 288 ([(iPr2-nacnac)PdH]+, 100). Anal.
Calcd for C22H42N4Pd (469.0): C, 56.34; H, 9.03; N, 11.95; Pd,
22.69. Found: C, 56.15; H, 8.86; N, 11.87; Pd, 22.58.
(η3-C3H5)Pd(iPr2-nacnac) (3a). A suspension of {(η3-C3H5)Pd-
(µ-Cl)}2 (364 mg, 1.00 mmol) in 20 mL of pentane was combined
with a solution of Li(iPr2-nacnac) (376 mg, 2.00 mmol) in 15 mL
of pentane at -78 °C. The stirred mixture was slowly warmed to
0 °C, and the precipitated LiCl was removed by filtration. After
the solution was concentrated under vacuum to a volume of 10
mL, it was slowly cooled to -40 °C to obtain yellow crystals: yield

5862 Organometallics, Vol. 25, No. 25, 2006
Tian et al.
crystals, which contained three molecules of solute MeCN. Drying
under vacuum at ambient temperature depleted the product from
the solute MeCN: yield 750 mg (68%). Anal. Calcd for
C39H56B3F12N7Pd2 (1096.2): C, 42.73; H, 5.15; N, 8.49; Pd, 19.42.
Found: C, 42.47; H, 5.22; N, 9.01; Pd, 19.40.
Supporting Information Available: CIF files, giving X-ray
crystallographic data for 2, 3a, 4, and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0606486