Synthesis, characterization, and reactivity of a versatile dinuclear palladium β-diiminate complex

Article abstract of DOI:10.1021/om701147k

The reaction of (Ph₂nacnac)H (Ph₂nacnac = [CH(C(CH₃)NPh)₂]^-) with [PdCl ₂(C₆H₅CN)₂] in the presence of a base (KO^tBu) yields [Pd(Ph₂nacnac)Cl]₂ (1) as an air- and moisture-stable solid. The dimeric structure in 1 has been confirmed by X-ray crystallographic analysis. This complex has proven to be a useful starting material for the rich and novel Pd-nacnac chemistry. Thus, treatment of 1 with neutral monodentate ligands N-methyl-4,5-diphenylimidazole (L1), 4-tert-butylaniline (L2), and CO results in the scission of the chloride bridge and the formation of mononuclear Pd species [Pd(Ph₂nacnac)Cl(L1)] (2), [Pd(Ph₂nacnac)Cl(L2)] (3), and [Pd(Ph₂nacnac)Cl(CO)] (4), respectively. The reaction of 1 with an oxidant PhI(OAc)₂ produces a novel homobimetallic complex [{Pd(Ph₂nacCl)] ₂(μ-OAc)₂] (5) (Ph₂nacCl = [ClC(C(CH ₃)NPh)₂]^-), resulting from the oxidation of coordinated nacnac ligand rather than the Pd(II) metal center. In the presence of 6 equiv of CuCl complex 1 reacts with 4 equiv of L1 to afford a novel heteromultinuclear complex {[Pd(Ph₂nacnac)(L1)₂] ₂(μ-Cu₆Cl₈)) (6).

Full text of DOI:10.1021/om701147k

1290
Organometallics 2008, 27, 1290–1298
Synthesis, Characterization, and Reactivity of a Versatile Dinuclear
Palladium ꢀ-Diiminate Complex
Alen Hadzovic and Datong Song*
DaVenport Chemical Research Laboratories, Department of Chemistry, UniVersity of Toronto,
80 St. George Street, Toronto, Ontario, Canada, M5S 3H6
ReceiVed NoVember 14, 2007
The reaction of (Ph2nacnac)H (Ph2nacnac ) [CH(C(CH3)NPh)2]-) with [PdCl2(C6H5CN)2] in the
presence of a base (KOtBu) yields [Pd(Ph2nacnac)Cl]2 (1) as an air- and moisture-stable solid. The dimeric
structure in 1 has been confirmed by X-ray crystallographic analysis. This complex has proven to be a
useful starting material for the rich and novel Pd-nacnac chemistry. Thus, treatment of 1 with neutral
monodentate ligands N-methyl-4,5-diphenylimidazole (L1), 4-tert-butylaniline (L2), and CO results in
the scission of the chloride bridge and the formation of mononuclear Pd species [Pd(Ph2nacnac)Cl(L1)]
(2), [Pd(Ph2nacnac)Cl(L2)] (3), and [Pd(Ph2nacnac)Cl(CO)] (4), respectively. The reaction of 1 with an
oxidant PhI(OAc)2 produces a novel homobimetallic complex [{Pd(Ph2nacCl)}2(µ-OAc)2] (5) (Ph2nacCl
) [ClC(C(CH3)NPh)2]-), resulting from the oxidation of coordinated nacnac ligand rather than the Pd(II)
metal center. In the presence of 6 equiv of CuCl complex 1 reacts with 4 equiv of L1 to afford a novel
heteromultinuclear complex {[Pd(Ph2nacnac)(L1)2]2(µ-Cu6Cl8)} (6).
coordinate Pt(IV) species [Pt(Ar2nacnac)Me3].11 Most of the
nacnac coordination chemistry reported to date is concentrated
Introduction
The ꢀ-diiminate ligands (I, Scheme 1) have gained particular
attention in coordination chemistry.1 Much of this interest stems
from the fact that their steric and electronic properties can be
easily tuned by choosing the appropriate substituents on the
nitrogen donor atoms. The most developed subgroup of this
ligand class contains the ꢀ-diiminates derived from acetylac-
etone. These have been popularly nicknamed nacnac (III) to
reflect the similarity with their isoelectronic parent acetylac-
etonate (acac, II) ligand.
on the first row transition metals. This trend is mostly due to
the discovery of the highly active Zn-nacnac catalysts for the
copolymerization of CO2 and epoxides12,13 and more recently
for epoxides and cyclic anhydrides,14 Cu-nacnac dioxygen
complexes,15–18 and models of the type 1 copper protein active
site7,19 as well as Fe-nacnac dinitrogen20,21 and sulfido22 complexes.
Also recently a unique Cr(II) phenyl hydride supported by nacnac
ligand [{(Ar2nacnac)Cr}2(µ-Ph)(µ-H)}]23 and [(Ar2nacnac)Zn-
Zn(Ar2nacnac)] complex containing the ZnI-ZnI bond24 have been
reported.
To date the nacnac complexes of many main group elements,
most transition metals, and several lanthanides and actinides
have been reported. This high popularity of nacnac ligands is
in part due to the ability of carefully designed ligands to stabilize
unusual oxidation states and geometries. Thus (ArNC(CH3)-
CHC(CH3)NAr)- (Ar ) 2,6-diisopropylphenyl) has recently
been used to isolate crystalline rare Al(I),2 Ge(I),3 and Cr(I)4
complexes. The same ligand enabled isolation and characteriza-
tion of three-coordinate Fe(II),5,6 Cu(II),7,8 and Zn(II)9,10 species
as well as the coordinatively and electronically unsaturated five-
However, while the first row transition metal nacnac chem-
istry is well developed, the second and third row counterpart is
(11) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc. 2001,
123, 6423.
(12) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J. Am.
Chem. Soc. 2003, 125, 11911.
(13) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738.
(14) Jeske, R. C.; DiCiccio, A. M.; Coates, G. W. J. Am. Chem. Soc.
2007, 129, 11330.
(15) Reynolds, A. M.; Gherman, B. F.; Cramer, C. J.; Tolman, W. B.
Inorg. Chem. 2005, 44, 6989.
* Corresponding author. E-mail: dsong@chem.utoronto.ca
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
(16) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P. Inorg.
Chem. 2003, 42, 7354.
(2) Cui, C. M.; Roesky, H. W.; Schmidt, H. G.; Noltemeyer, M.; Hao,
H. J.; Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274.
(3) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000,
1991.
(17) Heppner, D. E.; Gherman, B. F.; Tolman, W. B.; Cramer, C. J.
Dalton Trans. 2006, 4773.
(18) Hill, L. M. R.; Gherman, B. F.; Aboelella, N. W.; Cramer, C. J.;
Tolman, W. B. Dalton Trans. 2006, 4944.
(4) Tsai, Y.-C.; Wang, P.-W.; Chen, S.-A.; Chen, J.-M. J. Am. Chem.
Soc. 2007, 129, 8066.
(19) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2000, 122, 6331.
(20) 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.
(5) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun. 2001,
1542.
(6) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.; Lachicotte,
R. J. J. Am. Chem. Soc. 2002, 124, 14416.
(21) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. J. Am. Chem. Soc.
2003, 125, 15752.
(7) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270.
(8) Jazdzewski, B. A.; Holland, P. L.; Pink, M.; Young, V. G.; Spencer,
D. J. E.; Tolman, W. B. Inorg. Chem. 2001, 40, 6097.
(9) Prust, J.; Stasch, A.; Zheng, W. J.; Roesky, H. W.; Alexopoulos,
E.; Uson, I.; Bohler, D.; Schuchardt, T. Organometallics 2001, 20, 3825.
(10) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem. 2002,
41, 2785.
(22) Vela, J.; Stoian, S.; Flaschenriem, C. J.; Mun¨ck, E.; Holland, P. L.
J. Am. Chem. Soc. 2004, 126, 4522.
(23) Monillas, W. H.; Yap, G. P. A.; Theopold, K. H. Angew. Chem.,
Int. Ed. 2007, 46, 6692.
(24) Wang, Y. Z.; Quillian, B.; Wei, P. R.; Wang, H. Y.; Yang, X. J.;
Xie, Y. M.; King, R. B.; Schleyer, P. v. R.; Schaefer, H. F.; Robinson,
G. H. J. Am. Chem. Soc. 2005, 127, 11944.
10.1021/om701147k CCC: $40.75
2008 American Chemical Society
Publication on Web 02/29/2008

A Versatile Dinuclear Palladium ꢀ-Diiminate Complex
Organometallics, Vol. 27, No. 6, 2008 1291
Scheme 1
Scheme 2. Synthesis of [Pd(Ph2nacnac)Cl]2 (1)
lagging behind. This is particularly true for late transition metals.
Good examples of this case are Group 10 metals. The nickel
nacnac chemistry is one of the earliest in this field25,26 and
includes catalysts for olefin polymerization27,28 and unusual low
coordinate Ni(I) complexes.5,29–32 For the heavier Group 10
metals the situation is different. For platinum, apart from the
above-mentioned [Pt(Ar2nacnac)Me3] (Ar ) 2,6-diisopropyl-
phenyl) complex and its noted relevance to the C-H bond
activation, the only recent examples of Pt-nacnac monomethyl
species have been reported as the responsible species for the
dehydrogenation of ethers and alkanes.33 Palladium nacnac
chemistry is also limited to a small number of well-characterized
species. These include the fully characterized complexes
[Pd(iPr2nacnac)2],34 [Pd(η3-C3H5)(iPr2nacnac)],34 the unstable
complex [Pd(acac)(Ar2nacnac)] (Ar ) 2,6-diisopropylphenyl)
that isomerizes into [Pd(acac)(κ2-C,N-Ar2nacnac)],34 [Pd(Ar2-
nacnac)ClMe],36 and the dinuclear complex [(CH3CN)3-
Pd-{µ-CH(C(Me)NAr)2}Pd(CH3CN)2](BF4)3.34,35 Compound
[Pd{CH(C(Ph)NSiMe3)2}2] has also been briefly mentioned in
a review.1 The underdeveloped Pd-nacnac chemistry could be
attributed at least in part to the lack of a good starting material
that would allow the entry to participate in more advanced
coordination chemistry.
with numbering schemes in crystal structures, the middle carbon
of the nacnac backbone will be called the ꢀ-carbon (ꢀ-C) for
the purposes of general discussion (Scheme 1).
Results and Discussion
Synthesis and Structure of [Pd(Ph2nacnac)Cl]2 (1). The
reaction of Ph2nacnacH, KOtBu, and Pd(PhCN)2Cl2 at a 1:1:1
molar ratio in methanol produces [Pd(Ph2nacnac)Cl]2 (1) as a
green precipitate in 65% yield (Scheme 2).
Other palladium compounds, such as Pd(MeCN)2Cl2 and
PdCl2, can also be used as starting materials. The use of
methanol as a solvent is particularly convenient since all the
starting materials are soluble in it while the product is not. The
synthesis of 1 can also be performed with acetone and
triethylamine in the place of methanol and KOtBu, respectively.
However, the yield is usually ∼50%, presumably due to the
instability of acetone under basic condition.
Complex 1 is an air- and moisture-stable compound and is
soluble in most common, nonpolar organic solvents (CHCl3,
CH2Cl2, toluene, benzene, etc.) but sparingly soluble to insoluble
in alcohols, acetone, and water. It appears to be stable in the
solution since no decomposition was observed visually or
spectroscopically (NMR and IR) over several days. Tian et al.
attempted to synthesize similar compounds by treating
(cod)2PdCl2 with Li(iPr2nacnac) at low temperature, but obtained
[Pd(iPr2nacnac)2] along with Pd black instead.34
Herein we report the synthesis, full characterization, and
reactivities of a versatile Pd-nacnac compound, [Pd(Ph2-
nacnac)Cl]2 (1) (Ph2nacnac ) [CH(C(CH3)NPh)2]-). Complex
1 is easily obtainable, air- and moisture-stable, and can easily
be transformed into novel Pd-nacnac species. To avoid confusion
The molecular structure of 1 is shown in Figure 1, while the
selected crystallographic data are presented in Table 1. The
dimeric complex 1 crystallized in the monoclinic space group
P21/n with a crystallographically imposed inversion center in
the middle. The Pd(II) center adopts a typical square-planar
coordination geometry, with two N and two bridging Cl atoms
occupying the four coordination sites and displaying typical
bond lengths and angles. The six-membered chelate ring adopts
a boat conformation, folding along N1 · · · N2 and C2 · · · C3 axes.
The dihedral angle between the planes defined by N1, Pd, N2
and C2, C3, C4 is ∼27°.
(25) McGeachin, S. G. Can. J. Chem. 1968, 46, 1903.
(26) Parks, J. E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408.
(27) Zhang, D.; Jin, G.-X.; Weng, L.-H.; Wang, F. Organometallics
2004, 23, 3270.
(28) Kroger, M.; Folli, C.; Walter, O.; Doring, M. AdV. Synth. Catal.
2006, 348, 1908.
(29) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005, 24, 5901.
(30) Puiu, S. C.; Warren, T. H. Organometallics 2003, 22, 3974.
(31) Eckert, N. A.; Bones, E. M.; Lachicotte, R. J.; Holland, P. L. Inorg.
Chem. 2003, 42, 1720.
(32) Eckert, N. A.; Dinescu, A.; Cundari, T. R.; Holland, P. L. Inorg.
Chem. 2005, 44, 7702.
The 1H and 13C NMR spectra are consistent with the
symmetrical structure found in the solid state. Thus the methyl
groups of Ph2nacnac backbone appear as a sharp singlet at 1.56
(33) West, N. M.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc.
2007, 129, 12372.
(34) Tian, X.; Goddard, R.; Porschke, K.-R. Organometallics 2006, 25,
5854.
1
ppm in H NMR and 23.56 ppm in 13C NMR. The aromatic
(35) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(36) Kang, M.; Sen, A. Organometallics 2005, 24, 3508.
region of 1H NMR consists of three sets of multiplets with the
integration ratio of 1:2:2. UV–vis absorption measurements at

1292 Organometallics, Vol. 27, No. 6, 2008
HadzoVic and Song
1.29 ppm. Similarly the two methyl groups of the nacnac
backbone resonate at 23.86 and 24.39 ppm, respectively, in the
13C NMR spectrum. A broad singlet at 3.82 ppm in the 1H NMR
spectrum integrating to two protons is assigned to the -NH2
group. The IR spectrum exhibits two sharp, medium-intensity
bands at 3211 and 3304 cm-1 for the symmetric and asymmetric
NH2 stretches, respectively.
Bubbling CO through a solution of 1 produces a red complex
[Pd(Ph2nacnac)Cl(CO)] (4). The complex is stable only under
CO atmosphere. If CO gas is removed it slowly loses CO and
forms the characteristic green solution of 1 (as confirmed by
1
1H and 13C NMR and IR). In the H NMR spectrum of 4 all
characteristic resonances are shifted downfield compared to
those of 1, probably due to the electron-withdrawing effect of
the new CO ligand. Thus two signlets for -CH3 groups appear
at 1.79 and 1.84 ppm while H(ꢀC) appears at 4.98 ppm (4.66
ppm in 1). A similar trend is visible in the 13C NMR spectrum
in which the coordinated CO appears at 168.7 ppm, at a
significantly higher field than the free CO (184 ppm). The IR
spectrum of a freshly prepared solution of 4 in either CCl4 or
toluene exhibits a sharp band at 2130 cm-1 assigned to the CO
stretch, shifted by only 13 cm-1 compared to free CO (2143
cm-1). The small shift indicates that the Pd-CO bond involves
mostly the σ-donation with a relatively small contribution from
π-backbonding. This places the CO ligand in compound 4 at
the borderline between classical (ν(CO) > 2143 cm-1) and
nonclassical carbonyls (ν(CO) < 2143 cm-1).37
Addition of pentane saturated with CO to a concentrated
solution of 4 in toluene followed by cooling the resulting pale
red solution to -30 °C under 1 atm of CO produces single
crystals of 4 suitable for X-ray crystallographic analysis.
Interestingly, when wet crystals of 4 were left standing in air,
single crystals of 1 of high quality were obtained as confirmed
by X-ray crystallography.
Figure 1. The molecular structure of [Pd(Ph2nacnac)Cl]2 (1) with
thermal ellipsoids at 50% probability. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å): Pd1-N1 ) 2.001(3),
Pd1-N2 ) 2.003(3), Pd1-Cl1 ) 2.342(1), Pd1-Cl1A ) 2.356(1),
N1-C2 ) 1.330(5), N2-C4 ) 1.332(4). Selected angles (deg):
N1-Pd1-N2 ) 91.4(1), N1-Pd1-Cl1 ) 93.24(9), Cl1-Pd1-Cl1A
) 81.25(4).
different concentrations suggest that 1 does not dissociate in a
CH2Cl2 solution.
Reactions of 1 with Monodentate Neutral Ligands. Com-
plex 1 has proven to be an excellent starting material for the
entry to the novel Pd-nacnac chemistry. It exhibits reactivity at
both the Pd center (breaking the chloro-bridge) and the
coordinated Ph2nacnac ligand. The reactions involving the bridge
cleavage are outlined in Scheme 3.
The addition of a stoichiometric amount of N-methyl-4,5-
diphenylimidazole (L1) to a solution of 1 in CH2Cl2 within
minutes produces a red solution from which [Pd(Ph2-
nacnac)Cl(L1)] (2) can be isolated. The 1H and 13C NMR
spectra support the structure shown in Scheme 3. Due to the
introduction of L1, the two methyl groups of the nacnac
backbone of 2 are inequivalent, which display in the 1H NMR
spectrum as two sharp singlets at 1.55 and 1.69 ppm, indicating
a lower symmetry of complex 2 compared to 1. The same groups
resonate at 23.86 and 24.33 ppm in the 13C NMR spectrum.
The single-crystal X-ray diffraction analysis of 2 confirmed
the proposed structure. The molecular structure of complex 2
is shown in Figure 2 while the selected structural data are
summarized in Table 1. Complex 2 crystallized in the mono-
clinic space group C2/c. The geometry at the Pd center is square
planar with three N and one Cl donor atoms occupying the four
coordination sites. The six-membered chelate ring, unlike in 1,
is now almost planar with the dihedral angle between the Pd,
N1, N2 and C2, C3, C4 planes of ∼3.5°. The imidazole ring of
L1 and one of the nacnac phenyl rings are facing each other
probably due to the steric effects and the weak π-π stacking
interactions between the two rings. The chlorine atom is in close
contact with the hydrogen atom on the imidazole ring of an
adjacent molecule with the Cl · · · H distances of ∼2.77 Å (Figure
3), leading to the formation of molecule pairs in the crystal
lattice of 2.
¯
Compound 4 crystallized in the triclinic space group P1.
There are two independent molecules of 4 in the asymmetric
unit (Figure 4). The two molecules are held together by
intermolecular interactions between a chloride ligand in one
molecule and a carbonyl carbon in the other. The Cl1 · · · C36
and Cl2 · · · C18 contact distances are 3.359(7) and 3.192(7) Å,
respectively, and both are less than the sum of the van der Waals
radii. This type of intermolecular interaction is relatively scarce
in the literature. The notable example is the neutral complex
[Pd(CO)2(SO3F)2] that shows several C(CO) · · · O(SO3F) inter-
actions.38 Similarly, in the crystal lattice of Au(CO)Cl each
carbon atom interacts with four Cl ligands of neighboring
molecules.39 The steric bulk of phenyl rings in the structure of
4 probably prevents the formation of a more extensive network.
The C’O bond lengths (C18-O1 ) 1.107(8) Å and C36-O2
) 1.109(8) Å) are similar in the two molecules found in the
asymmetric unit. Both CtO bonds appear to be somewhat
shorter than the CtO bond in free CO (1.12822 Å).37
Reaction of 1 with PhI(OAc)2. Both Pt(IV) and Pd(IV)
species have been proposed as the responsible intermediates for
the catalytic functionalization of C-H bonds. Prompted by the
successful isolation of the five-coordinate Pt(IV)-nacnac com-
pound by Goldberg and co-workers,11 we attempted to oxidize
complex 1 to a Pd(IV) species using iodobenzene-diacetate
that has been used successfully in the catalytic systems to
The reaction of 1 with 4-tert-butylaniline (L2) similarly
produces a red complex [Pd(Ph2nacnac)Cl(L2)], 3 (Scheme 3).
1
On the basis of H and 13C NMR spectra it is expected that 3
(37) Lupinetti, A. J.; Strauss, S. H.; Frenking, G. Prog. Inorg. Chem.
2001, 49, 1.
has a similar structure to that of 2. Thus, the methyl groups of
the Ph2nacnac ligand give two sharp singlets at 1.70 and 1.71
ppm in 1H NMR along with a singlet for the tert-butyl group at
(38) Wang, C.; Willner, H.; Bodenbinder, M.; Batchelor, R.; Einstein,
F. B.; Aubke, F. Inorg. Chem. 1994, 33, 3521.
(39) Jones, P. G. Z. Z. Naturforsch. 1982, 37B, 823.

A Versatile Dinuclear Palladium ꢀ-Diiminate Complex
Organometallics, Vol. 27, No. 6, 2008 1293
Table 1. Crystallographic Data for 1, 2, 4, 5, and 6
1
2
4
5
6 · C6H6
formula
FW
T (K)
space group
a (Å)
b (Å)
C34 H34N4Cl2Pd2
782.36
150(2)
C33H31N4ClPd
625.47
150(2)
C18H17N2OClPd
419.19
C38H38N4O4Cl2Pd2
898.45
150(2)
C
104H96N12Cl8Cu6Pd2
2391.57
150(2)
P1
150(2)
¯
¯
P21/n
C2/c
P1
P21/n
7.4968(2)
9.9044(4)
21.6197(2)
90
97.241(2)
90
1592.59(9)
2
1.632
1.327
3.01 to 27.51
9521
3594
190
29.4540(10)
14.3066(6)
15.0385(5)
90
112.939(5)
90
5835.9(4)
8
1.424
0.756
2.94 to 27.57
18427
6678
355
9.3629(5)
10.1302(6)
20.1619(12)
97.107(4)
93.707(3)
114.448(3)
1713.21(17)
4
1.625
1.244
2.96 to 25.0
12874
5691
17.8544(4)
11.2625(2)
18.3314(4)
90
90.086(1)
90
3686.17(13)
4
1.620
1.167
2.91 to 27.50
28397
8399
457
12.6173(3)
19.6119(8)
20.1906(8)
86.249(1)
85.637(2)
87.367(2)
4966.8(2)
2
1.599
1.881
3.00 to 27.58
49342
22458
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
Dc (g · cm-3
)
µ (mm-1
)
θ range (deg)
no. of refln collected
no. of indept refln
no. of parameters
GOF on F2
417
1.076
1205
1.003
1.065
1.022
1.038
R [I > 2σ(I)]
R1 ) 0.0427
wR2 ) 0.1077
R1 ) 0.0520
wR2 ) 0.1155
R1 ) 0.0458
wR2 ) 0.1107
R1 ) 0.0669
wR2 ) 0.1243
R1 ) 0.0681
wR2 ) 0.1776
R1 ) 0.0813
wR2 ) 0.1906
R1 ) 0.0413
wR2 ) 0.0832
R1 ) 0.0733
wR2 ) 0.0961
R1 ) 0.0620
wR2 ) 0.1378
R1 ) 0.1262
wR2 ) 0.1676
R (all data)
Scheme 3. Reactivity of [Pd(Ph2nacnac)Cl]2 (1)
The methyl groups of the nacnac backbone show a sharp singlet
at 2.15 ppm, a significant downfield shift compared to those of
the complexes described in the previous sections and consistent
with the presence of an electron-withdrawing group on the
nacnac backbone. A similar trend is observed in the 13C NMR
spectrum. Thus, the ꢀ-carbon shows a signal at 105.1 ppm,
downfield shifted by ∼10 ppm compared with those of
compounds 1-4. The IR absorption bands at 1568 (asym) and
1430 (sym) cm-1 are consistent with the presence of bridging
acetates. The similar ligand [ClC(C(Me)NAr2]- (Ar ) 2,6-
diisopropylphenyl) has been reported previously.8
The proposed structure of 5 in Scheme 4 was confirmed by
X-ray crystallography (Figure 5). The new Ph2nacCl ligand
coordinates to the Pd(II) center in a bidentate fashion, producing
a six-membered chelate ring in a boat conformation folding
along the N1 · · · N2 and C2 · · · C4 and N3 · · · N4 and C19 · · · C21
axes. The dihedral angles between the N-Pd-N and nacnac
C-C-C planes are significantly different between the two six-
oxidize Pd(II) to Pd(IV).40–44 Oxidations with PhI(OAc)2 usually
produce two acetate anions. We reason that the two acetate
anions could serve as ligands to saturate the coordination sphere
of Pd(IV) with or without a coordinating solvent.
However, the reaction of compound 1 and PhI(OAc)2 did not
allow the access to Pd(IV) species. Instead, a homobimetallic
complex [(Ph2nacCl)Pd]2(µ-OAc)2 (5) was produced, which
contains a novel nacnac ligand ClC(C(CH3)NPh)2 (Ph2nacCl)
coordinated to Pd(II) centers (Scheme 4). The reaction is fast
and completed within minutes monitored by NMR spectroscopy.
The 1H NMR spectrum of 5 lacks the characteristic resonance
of the proton on the ꢀ-carbon usually found at about 4.7 ppm.
(40) Yoneyama, T.; Crabtree, R. H. J. Mol. Catal., A: Chem. 1996, 108,
35.
Figure 2. The molecular structure of [Pd(Ph2nacnac)Cl(L1)] (2)
with hydrogen atoms omitted for clarity. The thermal ellipsoids
are plotted at 50% probability. Selected bond lengths (Å): Pd1-Cl1
) 2.3419(9), Pd1-N1 ) 2.019(3), Pd1-N2 ) 2.008(3), Pd1-N3
) 2.049(3), N1-C2 ) 1.330(4), N2-C4 ) 1.322(4). Selected
angles (deg): N1-Pd1-N2 ) 91.2(1), N1-Pd1-N3 ) 91.9 (1),
N2-Pd1-Cl1 ) 93.82(8), N3-Pd1-Cl1 ) 83.15(8).
(41) Tong, X.; Beller, M.; Tse, M. K. J. Am. Chem. Soc. 2007, 129,
4906.
(42) Welbes, L. L.; Lyons, T. W.; Cychosz, K. A.; Sanford, M. S. J. Am.
Chem. Soc. 2007, 129, 5836.
(43) Wang, D.-H.; Hao, X.-S.; Wu, D.-F.; Yu, J.-Q. Org. Lett. 2006, 8,
3387.
(44) Alexanian, E. J.; Lee, C.; Sorensen, E. J. J. Am. Chem. Soc. 2005,
127, 7690.

1294 Organometallics, Vol. 27, No. 6, 2008
HadzoVic and Song
planes (31.3°). The reason for this difference probably lies in
the crystal packing effects. The two six-membered chelate rings
are in a staggered conformation with the twist angle of 28.3°.
Two acetate ligands bridge over two of the [Pd(Ph2nacCl)]+
motifs producing a dimeric species.
Coordination Chemistry of the ꢀ-Carbon of the Nacnac
Ligand. Reaction between 1 and 4 equiv of L1 in the presence
of 6 equiv of CuCl produces a novel complex 6 (Scheme 5).
The structure of 6 has been confirmed by X-ray crystal-
lography. The complex cocrystallized with benzene in the
¯
triclinic space group P1. The unit cell contains two different
molecules 6A and 6B (Figure 6). Both 6A and 6B have
crystallographically imposed inversion center symmetry. Each
molecule contains a unique [Cu6Cl8]2- cluster attached to the
nacnac ꢀ-carbon atoms of two [Pd(Ph2nacnac)(L1)2]+ fragments
through two Cu-C bonds. The geometry around the nacnac
ꢀ-C can be best described as distorted trigonal pyramidal (the
hydrogen atom on ꢀ-C was located from the difference Fourier
map) with the ꢀ-C of the nacnac ligand at the center of the
trigonal base and the Cu atom at the top of the pyramid. Within
the trigonal base, the sum of the bond angles around the ꢀ-C is
∼352° in 6A and ∼350° in 6B. Coordination of the ꢀ-carbon
of Pd-nacnac species has been reported previously in a dinuclear
complex [(CH3CN)3Pd-{µ-CH(C(Me)NAr)2}Pd(CH3CN)2]-
(BF4)3, in which the geometry around the ꢀ-C can be described
as a distorted tetrahedron.35
Figure 3. A diagram showing the Pd-Cl · · · H-C interactions
(Cl · · · H ) ∼2.77 Å) in the crystal lattice of 2, with thermal
ellipsoids at 50% probability. The methyl group of L1 and all phenyl
groups are omitted for clarity.
The structures of the [Pd(Ph2nacnac)(L1)2]+ fragments do
not differ significantly in 6A and 6B. The structure of such a
fragment in molecule 6A is shown in Figure 7. It consists of a
square-planar Pd(II) center coordinated by four nitrogen donor
atoms from a bidentate Ph2nacnac ligand and two N-methyl-
4,5-diphenylimidazole ligands (L1). The six-membered chelate
ring is once again in a boat conformation with a dihedral angle
between N1, Pd1, N2 and C2, C3, C4 planes of 47.5°. The two
L1 ligands are “antiparallel” with their methyl groups pointing
in opposite directions. The dinuclear complex [(CH3CN)3Pd-
{µ-CH(C(Me)NAr)2}Pd(CH3CN)2](BF4)3 reported by Feldman35
has been described as two localized CdN double bonds
(1.274(5) Å and 1.294(5) Å) and two CsC single bonds
(1.477(6) Å and 1.469(6) Å) and an sp3 hybridized ꢀ-C atom
within the six-membered chelate ring. However, the bond
lengths in the nacnac backbone of complex 6 (N1-C2 )
1.309(6) Å, N2-C4 ) 1.310(6) Å, C2-C3 ) 1.424(8) Å,
C3-C4 ) 1.408(8) Å) suggest a certain level of delocalization
over the two N, two R-C, and two ꢀ-C atoms.
Figure 4. The molecular structures of two independent molecules
of [Pd(Ph2nacnac)Cl(CO)] (4) as found in the asymmetric unit (all
hydrogen atoms are omitted for clarity, ellipsoids at 50% prob-
ability). Selected bond lengths (Å): Pd1-C18 ) 1.950(8), Pd1-N1
) 2.016(5), Pd1-N2 ) 2.018(6), Pd1-Cl1 ) 2.335(2), C18-
O1 ) 1.107(8), Pd2-C36 ) 1.928(7), Pd2-N3 ) 2.020(6),
Pd(2)-N4 ) 2.013(5), Pd2-Cl2 ) 2.323(2), C36-O2 ) 1.109(8).
Selected angles (deg): C18-Pd1-N1 ) 93.1(3), N1-Pd1-N2 )
91.6(2), N2-Pd1-Cl1 ) 95.0(2), Cl1-Pd1-C18 ) 80.5(2),
C36-Pd2-N3 ) 94.2(3), N3-Pd2-N4 ) 92.3(2), N4-Pd2-Cl2
) 93.5(2), Cl2-Pd2-C36 ) 79.9(2).
The [Cu6Cl8]2- clusters in 6A and 6B are both centrosym-
metric. The [Cu6Cl8]2- cluster in 6A (Figure 8, left) can be
viewed as two six-membered Cu3Cl3 rings in a chair conforma-
tion doubly linked together by two µ2-Cl ions. Each Cu(I) ion
is three-coordinate with an almost perfect trigonal-planar
geometry (average sum of angles around Cu: 357.5°). Each
chloride ion is two-coordinate with a bent local geometry. The
cluster in molecule 6B (Figure 8, right) can be viewed as a 12-
membered Cu6Cl6 ring capped by two µ4 chlorides (Cl7 and its
symmetry related counterpart). Each of the remaining chlorides
is two-coordinate with a bent local geometry. The Cu5 center
is bound to three chloride ions with pseudo-T-shaped coordina-
tion geometry. The Cu6 center is tetrahedrally coordinated by
four chloride ions, while the tetrahedral Cu4 center is bound to
three chloride ions and one C donor from the nacnac ligand.
The two [Cu6Cl8]2- clusters are, to the best of our knowledge,
the first of this kind that have been structurally characterized.
Scheme 4
membered chelate rings in 5. The dihedral angle between the
N1-Pd1-N2 and C2-C3-C4 planes (54.8°) is significantly
larger than that between the N3-Pd2-N4 and C19-C20-C21
The Cu-C bonds (Cu1-C3 ) 2.123(7) Å and Cu4-C52 )
2.197(6) Å) in complex 6 are significantly longer than a typical

A Versatile Dinuclear Palladium ꢀ-Diiminate Complex
Organometallics, Vol. 27, No. 6, 2008 1295
Figure 5. The molecular structure of complex 5 with thermal ellipsoids at 50% probability (left: side view; right: view along the Pd1-Pd2
axis with Pd2 on top). All hydrogen atoms are omitted for clarity. Selected bond lengths (Å): Pd1-N1 ) 1.989(3), Pd1-N2 ) 1.979(3),
Pd1-O1 ) 2.050(2), Pd1-O3 ) 2.049(2), Pd2-N3 ) 1.983(3), Pd2-N4 ) 1.995(3), Pd2-O2 ) 2.042(2), Pd2-O4 ) 2.049(2). Selected
angles (deg): N1-Pd1-N2 ) 87.4(1), N1-Pd1-O3 ) 90.8(1), N2-Pd1-O1 ) 93.6(1), O1-Pd1-O3 ) 88.1(1), N3-Pd2-N4 ) 90.7(1),
N4-Pd2-O2 ) 91.1(1), N3-Pd2-O4 ) 92.0(1), O2-Pd2-O4 ) 85.7(1).
Scheme 5
Cu-C bond (∼1.9 Å),46 indicating weak interactions between
the [Cu6Cl8]2- cluster and the ꢀ-C of the nacnac backbone. The
metal–carbon bond in complex 6 could be interpreted as weak,
π-type interactions rather than a typical σ bond as found in
[(CH3CN)3Pd-{µ-CH(C(Me)NAr)2}Pd(CH3CN)2](BF4)3. Al-
though 6A and 6B found in the crystal lattice show different
structural features, the solution NMR spectra show only one
The conformations of six-membered Pd-Ph2nacnac rings
warrant a short mention. Whether the ring will adopt a boat or
planar structure seems dependent on the nature of other ligands
around the Pd(II) center. In complexes 2 and 4 the rings are
almost planar, while in 1, 5, and 6 the rings are in a boat
conformation. The terminal chloride ligand in 2 and 4 might
play a role due to its π-donating capability. The chloride ligands
in 1 are in bridging mode and thus their π-donating capability
is reduced. However, it is hard to make a clearer picture because
palladium nacnac complexes remain scarce in the literature.
1
set of sharp H and 13C signals for the [Pd(Ph2nacnac)(L1)2]+
motif, possibly due to the dissociation of the [Cu6Cl8]2- clusters
or a fast equilibrium between 6A and 6B in solution. Because
of the net +1 charge on the [Pd(Ph2nacnac)(L1)2]+ fragment,
the proton on the ꢀ-C displays a signal at 5.21 ppm, downfield
shifted compared to all compounds in the above sections. The
proton on the imidazole ring of the L1 ligand is situated in the
shielding region of two phenyl rings in a sandwich manner.
Thus, it resonates at 5.53 ppm, upfield shifted by 1.73 ppm
compared to that in compound 2.
Conclusions
We have prepared and fully characterized a novel Pd-nacnac
complex [Pd(Ph2nacnac)Cl]2(1), which is air- and moisture-
stable in the solid state and in solution. It can serve as a very
versatile and useful starting material for rich and novel Pd-
nacnac chemistry. Complex 1 shows several places of reactivity
which can be targeted separately or in combination: cleavage
of the Cl bridge, full substitution of chloride ligands, and
reactivity on the coordinated Ph2nacnac ligand. Thus, the
chloride bridge can easily be broken with monodentate, neutral
ligands such as amines (in 3), imines (in 2), and CO (in 4) to
produce the mononuclear Pd-nacnac species. The reactions
complete within minutes at ambient conditions. The reaction
of 1 with PhI(OAc)2 produces a homobimetallic complex
[Pd(Ph2nacCl)2(µ-OAc)2] (5), a product of the oxidation of
The Cu-ꢀC bond has been reported in [Li(Et2O)(Ar2nacnac)]2-
µ2(Cu2I2) (Ar ) 2,6-diisopropylphenyl).45 It is worth pointing
out that complex 6 is the first one in which the ꢀ-C carbon
from a positively charged fragment exhibits a nucleophilic
character toward a negatively charged species [Cu6Cl8]2-
.
(45) Prust, J.; Hohmeister, H.; Stasch, A.; Roesky, H. W.; Magull, J.;
Alexopoulos, E.; Usoìn, I.; Schmidt, H.-G.; Noltemeyer, M. Eur. J. Inorg.
Chem. 2002, 2156.
(46) Davies, R. P.; Hornauer, S.; Hitchcock, P. B. Angew. Chem., Int.
Ed. 2007, 46, 5191.

1296 Organometallics, Vol. 27, No. 6, 2008
HadzoVic and Song
Figure 6. Two independent molecules of [Pd(Ph2nacnac)(L1)2]2-µ-(Cu6Cl8) (6) and their partial numbering scheme: molecule 6A (left) and
molecule 6B (right). Phenyl groups and protons of the methyl groups of the nacnac ligands and all carbon and hydrogen atoms of L1 are
omitted for clarity; the thermal ellipsoids are drawn at 50% probability. Selected bond lengths (Å): Cu1-C3 ) 2.123(7), Cu4-C52 )
2.197(6).
Pd(PhCN)2Cl247 and Ph2nacnacH48 were prepared according to the
literature procedures. 4-tert-Butylaniline (99%) was purchased from
Alfa Aesar. Copper(I) chloride (99%), triethylamine (reagent grade),
and PhI(OAc)2 (98%) were obtained from Aldrich Chemical Co.
N-Methyl-4,5-diphenylimidazole (L1) was prepared from com-
mercially available reagent grade 4,5-diphenylimidazole (Aldrich)
and NaH/MeI in dry THF. CD2Cl2 and C6D6 were purchased from
Cambridge Isotope Laboratories, Inc. CO gas was supplied by BOC
Canada.
NMR spectra were recorded on Varian 400 or a Mercury 400
1
instruments both working at 400 MHz for H and 100 MHz for
13C. Both 1H and 13C NMR spectra were referenced relative to the
solvent’s residual signals but are reported relative to Me4Si. IR
spectra were measured on a Perkin-Elmer SpectrumOne instrument,
using KBr plates. UV–vis spectra were recorded on a Perkin-Elmer
UV–vis/NIR Lambda 900 spectrometer, using a 1 cm cuvette.
Elemental analyses were performed at our Chemistry Department
with a PE 2400 C/H/N/S analyzer.
Figure 7. The structure of [Pd(Ph2nacnac)(L1)2]+ fragment from
X-ray Crystallographic Analysis. Single crystals suitable for
molecule 6A with thermal ellipsoids at 30% probability and the
X-ray crystallographic analysis of 1, 2, 4, 5, and 6 were obtained
partial labeling scheme. All hydrogen atoms are omitted for clarity.
as described for each complex below. The single-crystal X-ray
Selected bond lengths (Å): Pd1-N1)2.029(4), Pd1-N2 ) 2.016(4),
diffraction data were collected at 150 K on a Nonius Kappa-CCD
Pd1-N3 ) 2.051(4), Pd1-N5 ) 2.050(4), N1-C2 ) 1.309(6),
diffractometer with Mo KR radiation (λ ) 0.71073 Å). The data
N2-C4 ) 1.310(6), C2-C3 ) 1.424(8), C3-C4 ) 1.408(8).
were processed with the Denso-SMN package.49 The structures
Selected angles (deg): N2-Pd1-N1 ) 90.00(17), N1-Pd1-N5
were solved and refined with SHELXTL V6.10.50 All non-hydrogen
)
93.45(16), N2-Pd1-N3 ) 91.84(17), N5-Pd1-N3 )
atoms were refined anisotropically. The positions for hydrogen
atoms were either calculated or directly located from a difference
Fourier map and their contributions were included in the structure
factor calculations. The crystallographic data are summarized in
Table 1.
Synthesis of [Pd(Ph2nacnac)Cl]2 (1). A clear, yellow solution
of [Ph2nacnac]H (50 mg, 0.2 mmol) and KOtBu (22 mg, 0.2 mmol)
in methanol (2 mL) was added dropwise to a stirred solution of
Pd(C6H5CN)2Cl2 (76 mg, 0.2 mmol) in methanol (4 mL). A red
precipitate formed halfway through the addition. The mixture was
stirred overnight (∼20 h) and the precipitate changed color from
red to brown and finally to green. The precipitated product was
filtered off and washed with a small amount of methanol. The crude
material was dissolved in a minimum amount of toluene. Pentanes
were added to the green solution (about 20 times the volume of
used toluene) and the solution was placed in the freezer (-30 °C)
85.15(16).
coordinated nacnac along with the replacement of the bridging
chloride ligands. The ꢀ-carbon of the nacnac backbone shows
significant nucleophilicity as can be seen from the formation
of complex 6 in which two different, overall negatively charged
[Cu6Cl8]2- clusters bind to [Pd(Ph2nacnac)(L1)2]+ fragments.
These fragments are in turn products of complete substitution
of the chloride ligands from the starting complex 1.
The X-ray crystal structures of complexes 1, 2, 4, 5, and 6
have been determined. Each complex contains a typical square-
planar Pd(II) center. The six-membered Pd-Ph2nacnac ring
adopts either boat (in 1, 5, and 6) or planar conformation (in 2
and 4). The reason for this difference is unclear at the moment.
Further reactivity including the possible catalytic activity of
1 and its derivatives and a mechanistic study on various reactions
of 1 are currently under investigation in our group.
(47) Anderson, G. K.; Lin, M.; Sen, A.; Gretz, E. Inorg. Synth. 1990,
28, 61.
(48) Tang, L. M.; Duan, Y. Q.; Li, X. F.; Li, Y. S. J. Organomet. Chem.
2006, 691, 2023.
Experimental Section
(49) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(50) Sheldrick, G. M. SHELXTL/PC, Version 6.1 Windows NT Version;
Bruker AXS Inc.: Madison, WI, 2001.
General. Unless otherwise stated, all preparations and manipula-
tions were performed in air. All solvents used were of reagent grade.

A Versatile Dinuclear Palladium ꢀ-Diiminate Complex
Organometallics, Vol. 27, No. 6, 2008 1297
Figure 8. The structures of two Cu-Cl clusters: from molecule 6A (left) and from molecule 6B (right). The [Pd(Ph2nacnac)(L1)2]+ fragments
have been reduced to a connecting ꢀ-C atom.
overnight. The clear, colorless liquid was decanted leaving dark
green needle crystals that were dried in air to give 1 in 65% yield
(51 mg). The crystals obtained were suitable for X-ray crystal-
solution of 1 for 15–20 min. To obtain the NMR spectra, CO was
bubbled through a green solution of 1 (28 mg) in CD2Cl2 in a J.
Young NMR tube. After 15 min the tube was closed and the
collected spectra confirmed a full conversion of 1. For the IR
measurements, CO was bubbled through a solution of 1 in either
CCl4 or toluene for 20 min. The crystals suitable for X-ray
crystallographic analysis were obtained by adding pentane
saturated with CO to a solution of 4 in toluene in a vial under
a blanket of CO. The pale red solution was then cooled in the
freezer (-30 °C) to produce the crystalline 4 within a few hours.
1H NMR (CD2Cl2) δ 1.79 (s, 3H, CH3), 1.84 (s, 3H, CH3), 4.98
(s, 1H, CH), 6.95–6.98 (m, 2H, phenyl), 7.16–7.20 (m, 1H,
phenyl), 7.23–7.40 (m, 7H, phenyl). 13C NMR (CD2Cl2) δ 22.50
(CH3), 25.09 (CH3), 96.64 (CH), 125.8, 127.2, 128.0, 128.4,
129.7 (phenyl C), 150.9, 157.8, 159.7, 160.3 (CdN and ipso-
CPhsN), 168.7 (CO). IR (CCl4 solution, cm-1) 2130 (νCO), 1593
(νC)N), (PhCH3 solution, cm-1) 2130 (νCO). The instability of 2
did not allow for elemental analysis.
1
lographic analysis. H NMR (CD2Cl2) δ 1.56 (s, 6H, CH3), 4.66
(s, 1H, CH), 6.74–6.76 (m, 4 H, Ph), 7.00–7.04 (m, 2H, Ph),
7.08–7.13 (m, 4H, Ph). 13C NMR (CD2Cl2) δ 23.56 (CH3), 96.38
(CH), 125.9, 127.8, 128.5 (phenyl), 150.7 (CPh-N), 156.6 (CdN).
IR (Nujol, cm-1): 1560 (νC)N). UV–vis (CH2Cl2) 582 nm; 400 (
3 L · mol-1 · cm-1. Anal. Calcd for C34H34Cl2N4Pd2: C, 52.19; H,
4.38; N, 7.16. Found: C, 52.54; H, 4.54; N, 7.21.
Synthesis of [Pd(Ph2nacnac)Cl(L1)] (2). A solution of N-meth-
yl-4,5-diphenylimidazole (L1; 23 mg, 0.1 mmol) in CH2Cl2 (0.5
mL) was added to a dark green solution of 1 (39 mg, 0.05 mmol)
in CH2Cl2 (2 mL). The solution turned red within minutes. The
reaction was stirred for 30 min and the solvent was removed in
vacuo to leave a red residue. The crude product was dissolved in
a minimum amount of ether, filtered through a pad of Celite.
Addition of hexanes precipitated 2 as a red powder, which was
filtered, washed with a small amount of hexanes, and vaccuum-
dried. Yield 87% (55 mg). The crystals suitable for X-ray
crystallographic analysis were grown by slow diffusion of
hexanes into a concentrated solution of 2 in THF. 1H NMR
(CD2Cl2) δ 1.55 (s, 3H, CH3 nacnac), 1.69 (s, 3H, CH3 nacnac),
3.20 (s, 3H, CH3-N imidazole), 4.70 (s, 1H, CH nacnac),
6.91–6.63 (m, 2H, Ph), 7.00–7.16 (m, 8H, Ph), 7.26 (s, 1H,
N-CH-N imidazole), 7.29–7.39 (m, 8H, Ph), 7.97–8.00 (m,
2H, Ph). 13C NMR (CD2Cl2) δ 23.86 (CH3 nacnac), 24.33 (CH3
nacnac), 33.47 (N-CH3 imidazole), 97.09 (CH nacnac), 124.5,
124.8, 127.3, 127.9, 128.0, 128.1, 128.4, 129.0, 129.3, 129.4,
129.8, 130.6, 130.9, 132.6 (phenyl), 137.0, 139.0 (CdC,
imidazole), 139.0 (NCN, imidazole), 151.6, 153.3, 157.2, 158.2
(ipso-CPhsN and CdN). IR (Nujol, cm-1) 1557 (νC)N). Anal.
Calcd for C33H31ClN4Pd: C, 63.37; H, 5.00; N, 8.96. Found: C,
62.96; H, 5.09; N, 8.74.
Synthesis of [Pd(Ph2nacnac)Cl(L2)] (3). A solution of 4-tert-
butylaniline (L2, 14 mg, 0.1 mmol) in CH2Cl2 (0.5 mL) was
added to a green solution of 1 (39 mg, 0.05 mmol) in CH2Cl2 (2
mL). The solution turned red within minutes. Stirring was
continued for 20 min and the solvents were removed in vacuo
leaving a red solid residue. The crude product was washed with
hexanes and vaccuum-dried to yield 48 mg (90%) of complex
3. 1H NMR (CD2Cl2) δ 1.29 (s, 9H, (CH3)C-), 1.70 (s, 3H,
CH3), 1.71 (s, 3H, CH3), 3.82 (s, br, 2H, NH2), 4.81 (s, 1H,
CH), 6.95–7.00 (m, 2H, phenyl), 7.03–7.07 (m, 4H, Ph),
7.10–7.23 (m, 4H, Ph), 7.25–7.31 (m, 4H, Ph). 13C NMR
(CD2Cl2) δ 23.86 (CH3), 24.39 (CH3), 31.60 (CH3, tert-butyl),
97.59 (CH nacnac), 124.2, 125.0, 125.9, 126.3, 126,5, 127.7,
127.8, 128.0, 128.1, 129.8 (Ph), 137.0, 149.7, 150.4, 153.4,
157.1, 158.6 (ipso-CPhsN and CdN). IR (Nujol, cm-1) 3211,
3304 (νNH). Anal. Calcd for C27H32ClN3Pd: C, 60.01; H, 5.97;
N, 7.78. Found: C, 60.42; H, 6.14; N, 7.71.
Oxidation of 1: Synthesis of [Pd(Ph2nacCl)]2-(µ-OAc)2 (5).
Iodobenzene diacetate (16 mg, 0.05 mmol) in THF (1 mL) was
added dropwise to a solution of 1 (19 mg, 0.025 mmol) in THF
(0.3 mL). The resulting solution was stirred overnight. Hexanes
(4 mL) were added to the red solution producing a small amount
of brown solid, which was removed by filtration through a pad
of Celite. The filtrate was placed in the freezer (-30 °C). The
solvent was decanted from the precipitated product, which was
dried in air to give 5 in 75% yield. The crystals suitable for
X-ray crystallographic analysis were grown by slow diffusion
1
of hexanes into a concentrated solution of 5 in THF. H NMR
(CD2Cl2) δ 0.96 (s, 6H, CH3COO), 2.15 (s, 12H, CH3 nacnac),
7.15–7.17 (m, 8H, aromatic), 7.19–7.23 (m, 4H, aromatic),
7.30–7.34 (m, 8H, aromatic). 13C NMR (CD2Cl2) δ 22.36, 23.30
(nacnac and OAc CH3), 105.1 (CCl), 125.7, 127.9, 128.7
(aromatic), 149.8, 157.3 (ipso-CPhsN and CdN), 182.2 (OCO
acetate). IR (Nujol, cm-1) 1568, 1430 (νOAc). Anal. Calcd for
C38H38Cl2N4O4Pd2: C, 50.80; H, 4.26; N, 6.24. Found: C, 50.79;
H, 4.14; N, 6.18.
Synthesis of [Pd(Ph2nacnac)(L1)2]2-µ-(Cu6Cl8) (6). N-Methyl-
4,5-diphenylimidazole (L1, 46 mg, 0.2 mmol) was added to a stirred
green solution of 1 (39 mg, 0.05 mmol) in dry C6H6 (4 mL) in an
N2-filled glovebox. Within minutes the color of the reaction
mixture changed to red. After 30 min of stirring, CuCl (30 mg,
3mmol) was added and stirring was continued for 4 h. The
slightly cloudy red solution was filtered through a small pad of
Celite. Slow evaporation of the solvent from the filtrate gave
large red crystals of 6 · C6H6 in 45% yield. 1H NMR (CD2Cl2) δ
1.99 (s, 12H, nacnac-CH3), 2.93 (s, 12H, L1-CH3), 5.21 (s, 2H,
ꢀ-CH), 5.53 (s, 4H, imidazole-CH), 6.99–7.04 (m, 8H, aromatic),
7.05–7.14 (m, 12H, aromatic), 7.19 (t, broad, J ) 7.4 Hz, 12H,
aromatic), 7.38–7.50 (m, 14H, aromatic), 7.54–7.62 (m, 12H,
aromatic), 7.80–7.88 (m, 8H, aromatic). 13C NMR (CD2Cl2) δ
24.49, 33.70, 98.55, 125.71, 127.44, 128.20, 128.44, 128.68,
128.75, 128.84, 128.97, 129.64, 129.86, 129.93, 130.86, 132.88,
Synthesis of [Pd(Ph2nacnac)Cl(CO)] (4). The red solutions of
complex 4 can generally be prepared by bubbling CO through a

1298 Organometallics, Vol. 27, No. 6, 2008
HadzoVic and Song
136.36, 139.47, 151.35, 159.34. Anal. Calcd for C98H90-
N12Cl8Cu6Pd2 · C6H6: C, 52.22; H, 4.05; N, 7.03. Found: C, 52.35;
H, 3.99, N, 6.93.
Innovation, the Ontario Research Fund (ORF), and the
University of Toronto (Connaught Foundation).
Supporting Information Available: Crystallographic data for
1, 2, 4, 5, and 6 in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. This research is supported by grants
to D.S. from the Natural Science and Engineering Research
Council (NSERC) of Canada, the Canadian Foundation for
OM701147K