Tridentate assembling ligands based on oxazoline and phosphorus donors in dinuclear Pd(I)-Pd(I) complexes

Article abstract of DOI:10.1021/ic9018579

To examine the bonding preferences of potentially tridentate phosphorus, nitrogen donor ligands on a dinuclear metal core, we have studied the coordination of the oxazoline-based ligands bis(4,5-dihydro-2-oxazolylmethyl) phenylphosphine (NPN) and bis(4,4-dimethyl-2-oxazolyl dimethylmethoxy) phenylphosphine (NOPON^Me2) toward the dinuclear d⁹-d ⁹ Pd(I) complex [Pd₂(NCMe)₆][BF ₄]₂. In the dinuclear product [Pd₂(NPN-N,P,N) ₂](BF₄)₂ (1), in which the Pd-Pd bond length of 2.5489(7) A is rather short, the two interacting metal centers are P,N bridged by two molecules of the NPN ligand, forming two six-membered rings. The other oxazoline ring of each ligand further chelates a Pd center through its nitrogen atom, forming five-membered chelates, as in the mononuclear complex [PdCl₂(NPN-N,P)] (5). In contrast, the reaction between [Pd ₂(NCMe)₆](BF₄)₂ and NOPON ^Me2 in the presence of LiCl afforded the mononuclear cationic complex [Pd(NOPON^Me2-N,P,N)Cl](BF₄) (3), which is also obtained by halide abstraction from [Pd(NOPON^Me2-N,P)Cl₂] with NaBF₄. When this reaction was performed in the presence of 1 equiv of t-BuNC, the new dinuclear Pd(I)-Pd(I) complex [Pd₂Cl ₂(CNt-Bu)(NOPON^Me2-N,P,N)] (4) was isolated, which can also be obtained from a comproportionation reaction between Pd(II) and Pd(0) complexes. The oxazoline in the P,N bridge is involved in a seven-membered ring moiety, a situation rarely encountered in Pd(I)-Pd(I) chemistry. Its nitrogen atom is coordinated trans to the isonitrile ligand whereas that of the P,N chelate at Pd(1) is trans to Pd(2). The fluxional processes involving the oxazoline moieties of the NPN and NOPON^Me2 ligands in 1 and 4, respectively, were examined by variable-temperature NMR spectroscopy. The crystal structures of 1, 3 · 0.5CH₃CN, and 4 have been determined by X-ray diffraction. Prior to this work, relatively few complexes have been reported in the literature in which a potentially tridentate functional phosphorus ligand is simultaneously chelating and bridging a dinuclear Pd(I)-Pd(I) system.

Full text of DOI:10.1021/ic9018579

11954 Inorg. Chem. 2009, 48, 11954–11962
DOI: 10.1021/ic9018579
Tridentate Assembling Ligands Based on Oxazoline and Phosphorus Donors in
Dinuclear Pd(I)-Pd(I) Complexes
Jing Zhang, Roberto Pattacini, and Pierre Braunstein*
ꢀ
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Universite de Strasbourg,
4 rue Blaise Pascal, F-67081 Strasbourg Cedex, France
Received September 21, 2009
To examine the bonding preferences of potentially tridentate phosphorus, nitrogen donor ligands on a dinuclear metal
core, we have studied the coordination of the oxazoline-based ligands bis(4,5-dihydro-2-oxazolylmethyl)phenylpho-
sphine (NPN) and bis(4,4-dimethyl-2-oxazolyl dimethylmethoxy)phenylphosphine (NOPONMe2) toward the dinuclear
d9-d9 Pd(I) complex [Pd2(NCMe)6][BF4]2. In the dinuclear product [Pd2(NPN-N,P,N)2](BF4)2 (1), in which the
˚
Pd-Pd bond length of 2.5489(7) A is rather short, the two interacting metal centers are P,N bridged by two molecules
of the NPN ligand, forming two six-membered rings. The other oxazoline ring of each ligand further chelates a Pd
center through its nitrogen atom, forming five-membered chelates, as in the mononuclear complex [PdCl2(NPN-N,P)]
(5). In contrast, the reaction between [Pd2(NCMe)6](BF4)2 and NOPONMe2 in the presence of LiCl afforded the
mononuclear cationic complex [Pd(NOPONMe2-N,P,N)Cl](BF4) (3), which is also obtained by halide abstraction from
[Pd(NOPONMe2-N,P)Cl2] with NaBF4. When this reaction was performed in the presence of 1 equiv of t-BuNC, the new
dinuclear Pd(I)-Pd(I) complex [Pd2Cl2(CNt-Bu)(NOPONMe2-N,P,N)] (4) was isolated, which can also be obtained
from a comproportionation reaction between Pd(II) and Pd(0) complexes. The oxazoline in the P,N bridge is involved
in a seven-membered ring moiety, a situation rarely encountered in Pd(I)-Pd(I) chemistry. Its nitrogen atom is
coordinated trans to the isonitrile ligand whereas that of the P,N chelate at Pd(1) is trans to Pd(2). The fluxional
processes involving the oxazoline moieties of the NPN and NOPONMe2 ligands in 1 and 4, respectively, were examined
by variable-temperature NMR spectroscopy. The crystal structures of 1, 3 0.5CH3CN, and 4 have been determined by
X-ray diffraction. Prior to this work, relatively few complexes have been reported in the literature in which a potentially
3
tridentate functional phosphorus ligand is simultaneously chelating and bridging a dinuclear Pd(I)-Pd(I) system.
Introduction
increasing number of their applications in homogeneous
catalysis, in particular for asymmetric synthesis.1 When an
oxazoline moiety isassociatedwith one ormore donoratoms,
such as phosphorus, nitrogen, or oxygen, a range of bifunc-
tional ligands results which often lead to unique properties
for their metal complexes in stoichiometric or catalytic
reactions. We have previously reported the synthesis of
two new tridentate ligands which associate two oxazoline
moieties with a phosphine- or a phosphonite-type donor,
NPN2 and NOPONMe2,3 respectively:
Oxazoline-based ligands continue to be much investi-
gated in transition metal chemistry, largely because of the
*To whom correspondence should be addressed. E-mail: braunstein@
unistra.fr.
ꢀ
(1) (a) Gomez, M.; Muller, G.; Rocamora, M. Coord. Chem. Rev. 1999,
193-195, 769–835. (b) Helmchen, G. J. Organomet. Chem. 1999, 576, 203–
214. (c) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336–345. (d)
Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680–699. (e)
Braunstein, P. J. Organomet. Chem. 2004, 689, 3953–3967. (f) Speiser, F.;
Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005, 38, 784–793. (g) Braunstein,
P. Chem. Rev. 2005, 106, 134–159. (h) Desimoni, G.; Faita, G.; Jorgensen, K. A.
Chem. Rev. 2006, 106, 3561–3651. (i) Agostinho, M.; Braunstein, P. Chem.
Commun. 2007, 58–60. (j) Agostinho, M.; Braunstein, P.; Welter, R. Dalton
Trans. 2007, 759–770. (k) Agostinho, M.; Braunstein, P. C. R. Chim. 2007, 10,
666–676. (l) Gade, L. H.; Bellemin-Laponnaz, S. Coord. Chem. Rev. 2007, 251,
718–725. (m) Kermagoret, A.; Pattacini, R.; Chavez Vasquez, P.; Rogez, G.;
Welter; Braunstein, P. Angew. Chem., Int. Ed. 2007, 46, 6438–6441. (n)
McManus, H. A.; Cusack, D.; Guiry, P. J. Phosphorus Ligands Asymmetric
Catal. 2008, 2, 549–596. (o) Nishiyama, H.; Ito, J.-i.; Shiomi, T.; Hashimoto, T.;
Miyakawa, T.; Kitase, M. Pure Appl. Chem. 2008, 80, 743–749. (p) Fraile, J. M.;
Garcia, J. I.; Mayoral, J. A. Coord. Chem. Rev. 2008, 252, 624–646. (q)
Kermagoret, A.; Braunstein, P. Organometallics 2008, 27, 88–99. (r) Pattacini,
R.; Margraf, G.; Messaoudi, A.; Oberbeckmann-Winter, N.; Braunstein, P. Inorg.
Chem. 2008, 47, 9986–9997. (s) Hargaden, G. C.; Guiry, P. J. Chem. Rev. 2009,
109, 2505–2550. (t) Maggini, S. Coord. Chem. Rev. 2009, 253, 1793–1832. (u)
Pattacini, R.; Jie, S.; Braunstein, P. Chem. Commun. 2009, 890–892.
(2) Braunstein, P.; Fryzuk, M. D.; Naud, F.; Rettig, S. J. J. Chem. Soc.,
Dalton Trans. 1999, 589–594.
(3) Braunstein, P.; Naud, F.; Dedieu, A.; Rohmer, M.-M.; DeCian, A.;
Rettig, S. J. Organometallics 2001, 20, 2966–2981.
r
pubs.acs.org/IC
Published on Web 11/18/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 24, 2009 11955
in 2000 in Rh(I) chemistry,13 then in Pd(II) and Pt(II)
chemistry,14 and, more recently, also observed in Cu(I)15,16
and Ag(I)16,17 complexes. Particularlyrelevant toour systems
Whereas it was expected that these ligands would behave
either as P,N-bidentate or N,P,N-tridentate donors to-
ward a metal center, the recent finding that a ligand of the
NPN family could also act as a N,N-chelate to form an
eight-membered chelate, with no participation of the
phosphorus group, was surprising.4,5 Furthermore, these
ligands can display hemilabile behavior in their metal
complexes1d and lead to active catalysts in (asymmetric)
transfer hydrogenation of acetone in propan-2-ol,2,6 cy-
clopropanation of olefins,6 and oligomerization of ethy-
lene.5 Until now, only few studies have been concerned
with the reactivity of oxazoline-based heterotopic ligands
with metal-metal bonded complexes,7 the general focus
having been placed on mononuclear complexes or on non
metal-metal bonded polynuclear systems.1,8
ꢀ
are the results by Reau and co-workers with a 2,5-bis(2-
pyridyl)phosphole ligand which bridges a dipalladium unit in
a symmetrical μ2-manner via the phosphorus atom,14 and
those by Klausmeyer on phenylbis(pyrid-2-ylmethyl)pho-
sphine and bis(pyrid-2-ylmethyl) phenylphosphonite ligands
with symmetrically bridge dicopper and disilver units.16
As an extension of our previous work on the NPN and
NOPONMe2 ligands,2-5 we were interested in investigating
their behavior in metal-metal bonded complexes, and we
selected first the dinuclear Pd(I)-Pd(I) system, which has
often been used in short-bite ligand chemistry where
Ph2PCH2PPh2 (dppm) and 2-(diphenylphosphino)pyridine
(P-Py) belong to the most frequently used assembling li-
gands.9 The ligands NPN and NOPONMe2 would then lead
to six- and seven-membered ring systems, respectively, in
contrast to the five-membered rings commonly observed in
dinuclear dppm or P-Py chemistry. Considering that addi-
tional stabilization might be required, we have chosen as a
dinuclear template the metal-metal bonded d9-d9 complex
[Pd2(NCMe)6](BF4)2,10 with six labile acetonitrile ligands,
because in addition to the anticipated P-coordination and
bridge formation involving one oxazoline group, this di-
nuclear precursor should allow chelation of the other oxazo-
line and formation of a favorable five-membered (in the case
of NPN) or six-membered ring chelate (in the case of
NOPONMe2) in an arrangement of type A. In addition to
the molecular stabilization it provides, combined bridge and
chelate formation is attractive in the context of cooperative
bimetallic catalysis.11 A more unusual arrangement of type B
could not be ruled out.12 Indeed, examples of tertiary
phosphines bridging two metal centers were first reported
Open questions at the onset of the work include whether
on steric grounds one or two of our potentially tridendate
ligands can be accommodated by the dinuclear template,
and whether the ligand system will be static or display
fluxional behavior.
Results and Discussion
The reaction of [Pd2(NCMe)6](BF4)2 with 2 equiv of the
NPN ligand in CH2Cl2 afforded the yellow complex 1 in 80%
yield (eq 1). This compound is poorly soluble in most
common organic solvents (CH2Cl2, CHCl3, THF, etc.) but
can be dissolved in acetonitrile or nitromethane. Since the
coordinated phosphorus becomes a stereogenic center, a pair
of diastereoisomeric complexes is expected. However, we
have no evidence for the presence of the meso diastereoi-
somer, neither in solution nor in the solid-state (see below).
(4) Kermagoret, A.; Braunstein, P. Dalton Trans. 2008, 585–587.
(5) Kermagoret, A.; Tomicki, F.; Braunstein, P. Dalton Trans. 2008,
2945–2955.
(6) (a) Braunstein, P.; Naud, F.; Pfaltz, A.; Rettig, S. J. Organometallics
2000, 19, 2676–2683. (b) Braunstein, P.; Naud, F.; Rettig, S. J. New J. Chem.
2001, 25, 32–39.
(7) (a) Braunstein, P.; Clerc, G.; Morise, X.; Welter, R.; Mantovani, G.
Dalton Trans. 2003, 1601–1605. (b) Cabeza, J. A.; Da Silva, I.; Del Rio, I.;
Gossage, R. A.; Miguel, D.; Suarez, M. Dalton Trans. 2006, 2450–2455. (c)
Braunstein, P.; Clerc, G.; Morise, X. New J. Chem. 2003, 27, 68–72. (d) Jie, S.;
Pattacini, R.; Rogez, G.; Loose, C.; Kortus, J.; Braunstein, P. Dalton Trans. 2009,
97–105.
Its 31P{1H} NMR spectrum in CD3NO2 contains only a
singlet at δ 13.3 ppm, a value which is consistent with
coordination of the phosphorus atom.2 Surprisingly, the
1H NMR of 1 in CD3NO2 at room temperature contains
only a doublet for the PCH2 protons and two triplets for
the methylene protons of the oxazoline rings (see below).
1
This simplification of the H NMR and 31P{1H} NMR
spectra of 1 suggests a fluxional behavior at room tem-
perature. Therefore, low temperature NMR measure-
ments have been undertaken, and the results are
detailed below. The IR spectrum of 1 in KBr shows a
(8) Jie, S.; Agostinho, M.; Kermagoret, A.; Cazin, C. S. J.; Braunstein, P.
Dalton Trans. 2007, 4472–4482.
(9) (a) Murahashi, T; Kurosawa, H. Coord. Chem. Rev. 2002, 231, 207–
228. (b) Newkome, G. R. Chem. Rev. 1993, 93, 2067–2089. (c) Mague, J. T. J.
Cluster Sci. 1995, 6, 217–269. (d) Zhang, Z.-Z.; Cheng, H. Coord. Chem. Rev.
1996, 147, 1–39. (e) Espinet, P.; Soulantica, K. Coord. Chem. Rev. 1999,
193-195, 499–556. (f) Braunstein, P.; Knorr, M.; Stern, C. Coord. Chem. Rev.
1998, 178-180, 903–965.
(10) Murahashi, T.; Nagai, T.; Okuno, T.; Matsutani, T.; Kurosawa, T.
Chem. Commun. 2000, 1689–1690.
(11) Aubry, D. A.; Bridges, N. N.; Ezell, K.; Stanley, G. G. J. Am. Chem.
Soc. 2003, 125, 11180.
(14) (a) Sauthier, M.; Le Guennic, B.; Deborde, V.; Toupet, L.; Halet,
ꢀ
J.-F.Reau, R. Angew. Chem., Int. Ed. 2001, 40, 228–231. (b) Leca, F.; Sauthier,
ꢀ
M.; Deborde, V.; Toupet, L.; Reau, R. Chem.;Eur. J. 2003, 9, 3785–3795.
(15) (a) Leca, F.; Lescop, C.; Rodriguez-Sanz, E.; Costuas, K.; Halet,
ꢀ
J.-F.; Reau, R. Angew. Chem., Int. Ed. 2005, 44, 4362–4365. (b) Nohra, B.;
ꢀ
Rodriguez-Sanz, E.; Lescop, C.; Reau, R. Chem.;Eur. J. 2008, 14, 3391–3403.
(16) Hung-Low, F.; Renz, A.; Klausmeyer, K. K. Eur. J. Inorg. Chem.
2009, 2994–3002.
ꢀ
(17) (a) Welsch, S.; Lescop, C.; Scheer, M.; Reau, R. Inorg. Chem. 2008,
(12) Braunstein, P.; Boag, N. Angew. Chem., Int. Ed. 2001, 40, 2427–2433.
(13) (a) Pechman, T.; Brandt, C. D.; Werner, H. Angew. Chem., Int. Ed.
2000, 39, 3909–3911. (b) Werner, H. Angew. Chem., Int. Ed. 2004, 43, 938–954.
47, 8592–8594. (b) Welsch, S.; Nohra, B.; Peresypkina, E. V.; Lescop, C.; Scheer,
ꢀ
M.; Reau, R. Chem.;Eur. J. 2009, 15, 4685–4703.

11956 Inorganic Chemistry, Vol. 48, No. 24, 2009
Zhang et al.
Figure 1. ORTEP of the molecular structure of 1, hydrogen atoms and
anions omitted for clarity. Ellipsoids drawn at 50% probability level.
˚
Selected bond distances (A) and angles (deg): Pd1-Pd2 2.5489(7),
Pd1-P1 2.189(1), Pd2-P2 2.189(1), Pd1-N1 2.135(3), Pd1-N4
2.111(3), Pd2-N2 2.114(3), Pd2-N3 2.194(3), N1-C2 1.274(5),
N2-C6 1.281(5), N3-C16 1.276(5), N4-C20 1.270(5), P1-Pd1-Pd2
81.42(3), N1-Pd1-P1 84.83(9), N4-Pd1-N1 99.8(1), N4-Pd1-Pd2
94.79(8), P2-Pd2-Pd1 75.95(3), P2-Pd2-N3 83.42(9), N2-Pd2-N3
102.5(1), N2-Pd2-Pd1 97.86(9).
Figure 2. Approximately orthogonal views of the crystal structure of
the cation in 1. Oxazoline rings and phenyls omitted for clarity. Distances
strong absorption at 1640 cm-1 consistent with the
coordination of each oxazoline to palladium. Unfortu-
nately, it was not possible to measure its IR absorption in
solution owing to the low solubility of the complex in
usual solvents and the absorptions of nitromethane
and acetonitrile in this spectral region. The solid-state
structure of 1 was established by single crystal X-ray
diffraction (see Figure 1).
˚
are in A.
indicating that the Pd atoms exert a higher trans influence.19
˚
The Pd-P distances of 2.189(1) A are in the expected
˚
range. The non-bonding P2 Pd1 distance of 2.929(1) A
3 3 3
is significantly shorter than the P1 Pd2 distance of
3.102(1) A, which suggests a slight distortion toward a
3 3 3
˚
B-type structure for the P2 ligand, when compared to
P1. The angle between the two mean planes defined by
the atoms P1, Pd1, N1, N4 and P2, Pd2, N2, N3 is
49.60(5)°.
When [Pd2(NCMe)6](BF4)2 was reacted with 1 or 2 equiv
of NOPONMe2, a rapid color change occurred, but the
only palladium complex that could be isolated was the known
[Pd(NOPONMe2)(NCMe)](BF4)2 (2)3 and formation of
palladium metal was observed.
In the molecular structure of the dinuclear cation in 1, the
two interacting metal centers are P,N bridged by two
molecules of the NPN ligand, forming two six-membered
rings. The other oxazoline ring of each ligand further chelates
a Pd center through its nitrogen atom, forming five-membered
chelates. Overall, the tridentate ligand adopts a type A con-
figuration. The geometry around the metal centers can be
described as distorted square-planar, when the Pd-Pd bond is
considered. The cation has an approximate C2 symmetry, the
axis passing through the middle of the Pd-Pd bond (see
Figure 2).
˚
The Pd-Pd bond length of 2.5489(7) A is in the lower part
of the normal bond length range18 observed in metal-metal
bonded dinuclear palladium complexes and is shorter than
19
˚
that in [Pd{PhP(CH2CH2PPh2)2}]2[BF4]2 (2.617(1) A).
This relatively short Pd-Pd bond length can be related to
the weaker trans influence of the oxazoline nitrogen
compared to that of phosphorus in [Pd{PhP(CH2CH2-
PPh2)2}]2[BF4]2.19 The Pd-N bond trans to the metal-metal
bond are longer than those in trans position with respect
˚
to phosphorus (Pd1-N1 2.135(3) and Pd1-N4 2.111(3) A;
˚
Pd2-N3 2.194(3) and Pd2-N2 2.114(3) A, respectively),
Obviously, a redox reaction has occurred which cor-
responds to the disproportionation of the precursor
complex: Pd(I)-Pd(I) f Pd(0) þ Pd(II). Other ap-
proaches to obtain Pd(I) complexes with this ligand have
been explored, such as comproportionation reactions
(18) CCDC database, November 2008 update. Median of the Pd-Pd
˚
bond lengths on 77 tetracoordinate dinuclear complexes: 2.594 A, mean:
˚
2.583 A (σ = 0.055).
(19) DuBois, D. L.; Miedaner, A.; Haltiwanger, R. C. J. Am. Chem. Soc.
1991, 113, 8753–8764.

Article
Inorganic Chemistry, Vol. 48, No. 24, 2009 11957
where Pd(0) species ([Pd(dba)2] or [Pd2(dba)3]) and
NOPONMe2 were added to a solution of 2, unfortunately
without success. The lack of formation of the NOPONMe2
analogue of 1 could be related to the lower stability
of a seven-membered ring bridge compared to the
six-membered ring found in 1 and to a possible
steric hindrance generated by the oxazoline methyl
groups.
When the reaction between [Pd2(NCMe)6](BF4)2 and
NOPONMe2 was performed in the presence of LiCl, the
complex [Pd(NOPONMe2-N,P,N)Cl](BF4) (3) was isolated
and some decomposition to Pd(0) was also observed. A better
synthesis of this complex was achieved by halide abstrac-
tion from [Pd(NOPONMe2-N,P)Cl2] with NaBF4 (eq 2)
(see Experimental Section).
Figure 3. ORTEP of the molecular structure of the cation in 3 1/
3
2MeCN, hydrogen atoms, solvent and anions omitted for clarity. Only
one of the two similar independent molecules is shown. Ellipsoids drawn
˚
at 50% probability level. Selected distances (A) and angles (deg): Mole-
cule A: Pd1-N1 2.044(2), Pd1-N2 2.055(2), Pd1-P1 2.1889(7),
Pd1-Cl1 2.3734(7), N1-Pd1-P1 82.68(6), N2-Pd1-P1 91.02(6),
N1-Pd1-Cl1 92.79(6), N2-Pd1-Cl1 94.73(6); Molecule B: Pd2-N3
2.043(2), Pd2-N4 2.051(2), Pd2-P2 2.1876(7), Pd2-Cl2 2.3729(7),
N3-Pd2-P2 83.01(6), N4-Pd2-P2 89.96(6), N3-Pd2-Cl2 92.42(6),
N4-Pd2-Cl2 95.87(6).
bond is consistent with the high trans influence of the P
donor.20 The NOPONMe2 ligand coordinates in a slightly
asymmetrical manner, with a distortion from the ideal Cv
symmetry. The N1-Pd1-P1-C17 dihedral angle [69.4(1)°]
is smaller than the N2-Pd1-P1-C17 one [75.2(1)°], resulting,
for example, in mutually non-equivalent orientations of the
methyl groups with respect to the metal coordination plane.
The oxazoline rings are not coplanar; the angle between the
mean planes formed by their atoms is 33.3(1)°.
The IR spectrum of 3 in CH2Cl2 shows only one ν(CdN)
band, at 1623 cm-1, consistent with the coordination of both
oxazolines to Pd. Phosphorus coordination leads to a
31P{1H} NMR signal at 114.5 ppm which corresponds to
an upfield shift of 36 ppm with respect to the free ligand, and
of 8 ppm compared to [Pd(NOPONMe2)(NCMe)](BF4)2 (2),
which reflects the coordination of the chloride in place
of acetonitrile. The 1H NMR spectrum of 3 contains
only one AB spin system for the methylene protons of the
oxazoline rings, consistent with the expected Cv symmetry
of the complex. Three singlets and a doublet correspond to
the eight methyl groups of the molecule. The doublet
When the reaction between [Pd2(NCMe)6](BF4)2 and
NOPONMe2 was performed in the presence of 2 equiv of
LiCl and 1 equiv of t-BuNC, the new dinuclear complex 4 was
isolated in about 20% yield (eq 3). It has been identified
by single crystal X-ray diffraction (Figure 4, see below). Its
1H NMR spectrum at room temperature shows only one
AB spin system for the four methylene protons of the
oxazoline rings and four singlet resonances corresponding
to the eight methyl group protons of the oxazoline rings.
This is consistent with the existence of a fluxional process
between the two oxazolines of the NOPONMe2 ligand which
4
arises from a JPH coupling of 2.0 Hz between the protons
of one methyl group of the OC(CH3)2 fragment and the P
atom, as observed in the complex [Pd(NO-
PONMe2)(NCMe)](BF4)2 (2).3 The detailed assignment of
the resonances (see Experimental Section) was made from
1
COSY H/1H experiments. To examine whether the charge
difference between 2 and 3 had any influence on the bonding
parameters, the crystal structure of 3 1/2MeCN was deter-
3
1
render them equivalent on the H NMR time scale. Thus
mined by single crystal X-ray diffraction (Figure 3). There
are two independent but almost identical molecules in the
unit cell.
low temperature NMR measurements have been under-
taken, and their results are detailed below. The 31P{1H}
NMR spectrum in CD2Cl2 contains a singlet at δ 127.8
ppm which is consistent with coordination of the phosphorus
atom.3 The IR spectrum of 4 in KBr shows a strong, broad
band at 1641 cm-1, corresponding to the coordination of
both oxazolines to Pd, but in CH2Cl2, the IR spectrum shows
two absorptions at 1642 cm-1 and 1654 cm-1, supporting
the presence of coordinated and uncoordinated oxazoline
rings.3
In the molecular structure of 3, the tridentate NOPONMe2
ligand acts as pincer through thephosphorus and the nitrogen
atoms. The metal center adopts a slightly distorted square-
planar geometry, similar to that found in 2.3 Slight elonga-
tions of the donor-Pd bonds are observed in 3 when com-
pared with 2, in agreement with the lower charge of the
cation, and the longer Pd-P distance is also consistent with a
higher trans influence of the chloride with respect to the
˚
acetonitrile ligand [Pd-P distance: 2.1889(1) A in 3 vs
˚
˚
2.174(1) A in 2; Pd-N bonds: 2.044(2) and 2.055(2) A in 3
(20) Appelton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
˚
vs 2.038(2) and 2.030(2) A in 2]. The length of the Pd1-Cl1

11958 Inorganic Chemistry, Vol. 48, No. 24, 2009
Zhang et al.
antisymbiotic effect.23 The angle between the two coordina-
tion planes defined by the atoms P1, Pd1, N1, Cl1 and Pd2,
N2, Cl2, C23 is relatively large [70.77(6)°] compared to that in
complex 1 [49.60(5)°], in [Pd2{PhP(CH2CH2PPh2)2}] [BF4]2
(67°),19 or in [Pd2{o-Ph2PC6H4CH2O(CH2)3-2-C5H4N}2]-
[BF4]2 4H2O (58°).22 This difference can be related to the
3
fact that 4 contains only one tridentate ligand, which results
in less steric strain in the complex.
Knowing the structure of the Pd(I)-Pd(I) complex 4, we
were able to devise an alternative, higher yield synthesis
(80%) for this complex which consisted in the compro-
portionation reaction shown in eq 4:
Figure 4. ORTEP ofthe molecularstructure ofthe cationin 4, hydrogen
atoms omitted for clarity. Ellipsoids drawn at 50% probability level.
˚
Selected bond distances (A) and angles (deg): Pd1-Pd2 2.5230(4),
Pd1-P1 2.1553(9), Pd1-N1 2.175(3), Pd1-Cl1 2.395(1), Pd2-Cl2
2.429(1), Pd2-C23 1.909(4), Pd2-N2 2.087(3); P1-Pd1-N1 89.04(8),
N1-Pd1-Cl1 99.74(8), P1-Pd1-Pd2 79.72(3), Cl1-Pd1-Pd2 91.60(3),
C23-Pd2-Cl2 95.3(1), N2-Pd2-Cl2 92.54(8), C23-Pd2-Pd1 83.6(1),
N2-Pd2-Pd1 88.44(8).
However, when [Pd(NOPONMe2-N,P,N)Cl](BF4) (3) was
reacted with 1 equiv each of [Pd(dba)2], t-BuNC, and LiCl
in CH2Cl2, 4 was obtained in only 65% yield and 22% of 3
was recovered. This slightly lower yield may be due to the
relatively poor solubility of the added LiCl. It also
appears that [Pd(NOPONMe2-P,N)Cl2] reacts faster with
the Pd(0) precursor than 3. It is therefore possible that
when the latter is used, it first reacts with LiCl to give
[Pd(NOPONMe2-P,N)Cl2] and then 4, rather than directly
with the Pd(0) complex to give a cationic dinuclear Pd(I)
complex which would then react with LiCl.
In the molecular structure of the dinuclear complex 4, the
two metal-metal bonded palladium atoms are P,N-bridged
by a NOPONMe2 ligand to form a seven-membered ring, a
situation rarely encountered in Pd(I)-Pd(I) chemistry
(Figure 4). The nitrogen atom of the second oxazoline is
bound to Pd1, which leads to a six-membered chelate. Over-
all, the NOPONMe2 ligand gives rise to a chelating-bridging
coordination mode of type A, similar to that observed for the
PNP ligand in 1. Both metals are further coordinated by a
terminal chloride and show a distorted square planar co-
ordination geometry. The coordination sphere around Pd2 is
completed by a t-BuNC ligand. The Pd-Pd bond length of
To examine whether an NPN analogue of 4 could be
obtained, we first synthesized [Pd(NPN-P,N)Cl2] (5) by reac-
tion of [PdCl2(COD)] with 1 equiv of the NPN ligand. Its
31P{1H} NMR spectrum in CD2Cl2 contains only a singlet at
21.4 ppm which is consistent with coordination of the phos-
phorus atom. Its 1H NMR spectrum is quite intricate as there is
no symmetry element in the molecule. Therefore a detailed peak
assignment has been made using H/1H COSY and H/13C
HMBC experiments at room temperature (see Experimental
Section). Complex 5 was then reacted with [Pd2(dba)3] (or
[Pd(dba)2]) in the presence of 1 equiv of t-BuNC under the same
conditions as 4. The solution turned dark orange within a few
hours, and its 31P NMR spectrum revealed the formation of
several products but none of them has been successfully isolated.
1
1
˚
˚
2.5230(4) A is shorter than that in 1 (2.549(1) A) and in
[Pd2X2(μ-dppm)2] (X = anionic ligand),21 but longer than in
[Pd2{o-Ph2PC6H4CH2O(CH2)3-2-C5H4N}2][BF4]2 4H2O
3
(2.500(1) A).22 This relatively short Pd-Pd bond distance in
˚
complex 4 may be due to the moderate trans influences of the
oxazoline nitrogen and of the chloride donors. The terminal
chlorides Cl1 and Cl2 are in cis and trans positions with
respect to the Pd-Pd bond, respectively. The isonitrile
ligand is trans to the nitrogen donor, which is consistent
with the relative trans influences of these ligands and the
ꢀ
ꢀ
ꢀ
(21) Besenyei, G.; Parkanyi, L.; Gacs-Baitz, E.; James, B. R. Inorg. Chim.
Acta 2002, 327, 179–187.
(22) Tani, K.; Nakamura, S.; Yamagata, T; Kataoka, Y. Inorg. Chem.
1993, 32, 5398–5401.
(23) Pearson, R. G. Inorg. Chem. 1973, 12, 712–713.
Dynamic Behavior of Complexes 1 and 4. As mentioned
above, NMR and IR data of 4 indicate the existence of a

Article
Inorganic Chemistry, Vol. 48, No. 24, 2009 11959
Figure 5. Variable temperature 1H NMR spectra of 4 in CD2Cl2.
fluxional process involving the oxazoline moieties of the
NOPONMe2 ligand which make them become equivalent
Figure 6. Variable temperature 1H NMR spectra of 1 in CD3NO2/
CD2Cl2 (2:1).
1
on the H NMR time-scale. We thus examined the low
temperature behavior of 4. At 197 K, the 1H and 13C{1H}
NMR spectra show two sets of signals for the two chemi-
cally non-equivalent oxazoline moieties. The detailed as-
HMQC experiments, at 500.13 and 125.7 MHz, respec-
tively, have allowed here a detailed assignment. At this
temperature, a 31P{1H} NMR singlet at 9.6 ppm indicates
the presence of only one diastereoisomer. The PCH2
groups give rise to two different 1H spin systems: a
doublet at 3.58 and a multiplet at 3.13 ppm which has
an important upfield shift of 0.32 ppm with respect to the
room temperature PCH2 signal. The multiplet has been
identified as an ABX spin system and coupling constants
have been obtained by simulation. The 13C{1H} NMR
spectrum showed also the appearance of two broad
singlets which can each be assigned to a different
PCH2 group (JPC in both cases has not been resolved).
The 1H/1H COSY experiment also revealed a 5J coupling
between the PCH2 and NCH2 protons. The 1H/13C
HMQC and 1H/1H COSY experiments revealed the
presence of two different but overlapping NCH2 multi-
plets at 4.09 and 3.98 ppm. The OCH2 peaks overlapped
and appeared as an intricate multiplet at 4.61 ppm.
Upon further warming, the peaks broaden, the PCH2
resonances coalesce at 253 K and sharpen at room
temperature (see Figure 6).
1
1
signments resulted from H/1H and H/ 13C COSY and
HMQC experiments. Seven 1H NMR singlets correspond
to the eight methyl groups because 2 methyl groups
accidentally resonate at δ 1.47 ppm (see Figure 5).
In the 13C{1H} spectrum, eight resonances are indeed
observed for the methyl groups. The OCH2 protons give
rise to two AB spin systems which partly overlap and two
singlets are observed in the 13C{1H} spectrum for the
OCH2 carbons. The COP carbons gives rise to a singlet
and a doublet (with 2JPC = 9.8 Hz). When the tempera-
ture is increased to 207 K, the resonances of the OCH2
protons broaden, and the methyl resonances at 1.44 and
1.46 coalesce. Upon further warming, general broadening
occurs around 217 K, and the resonances progressively
sharpen until both oxazoline arms have become equiva-
lent. The dynamic behavior of the molecule may be
explained by an opening/closing movement of the
6-membered ring followed by that of the 7-membered
ring, or vice versa, and complete exchange of the oxazo-
lines by ligand rotation about the P-Pd bond. Opening of
the N(1)-Pd(1) bond trans to the metal-metal bond
could be easier than that trans to the RNC ligand, owing
to the trans effect of the former. Given a coalescence
temperature of 225(5) K for the OCH2 protons, the
estimated ΔGq of the overall process is 45(1) KJ/mol.
To know whether the NMR signals at low temperature
are those of the diastereoisomer identified by single crystal
X-ray diffraction, NMR spectra of a solution prepared by
dissolution of the crystals below 218 K were recorded. These
1
1H, H/1H, and 31P{1H} experiments afforded the same
spectra as the solution prepared at room temperature from a
powder sample. Overall, the spectrum observed at 218 K is
consistent with the solid state structure, in which the two
oxazoline arms within one ligand are not equivalent while
the two ligands can be related by the aforementioned C2
pseudosymmetry. As expected, all the CH2 groups appear
diastereotopic, with the exception of a PCH2 group, whose
ABX spin system is not fully resolved. To explain the
oversimplification of the spectrum at room temperature,
inversion of the P configuration is required, and this may
occur via an intermediate structure of type B (Scheme 1),
which would be related to situations described with the
2,5-bis(2-pyridyl)phosphole N,P,N ligand.14 From structural
and strain considerations, it should be also easier to envisage
first the uncoordination of the oxazoline arms to enable the
Berry pseudorotation mechanism.24 Given the coalescence
temperature of 253(5) K for the PCH2 system and a Δν =
129 Hz at low temperatures for these two signals, the
estimated global ΔGq of the process is 49(1) KJ/mol.
1
The H NMR spectrum of 1 in CD3NO2 at room
temperature contains only one AA0X spin system for
the PCH2 protons (which appears as a deceptively simple
A2X system) and two AA0MM0 spin systems (which
appear in the form of two triplets as deceptively simple
A2M2 systems) for the methylene groups of the oxazoline
rings, unlike the 1H NMR pattern of the free ligand where
one ABX spin system and two ABMN spin systems have
been observed.2 These data indicate intricate fluxional
behavior for complex 1. An opening/closing mechanism
of the chelate arm of the ligand and the decoordination/
rotation process described for 4 are not sufficient to
explain the oversimplification of the NMR pattern. At
variance with the case described above, the protons of
each CH2 group appear magnetically equivalent in the
spectrum of 1 recorded at 298 K. This can be only
explained by an inversion of the configuration at P.
Consequently, low temperature NMR experiments have
been undertaken in CD3NO2/CD2Cl2 (2:1). At 218 K, the
1H NMR spectrum shows the presence of two chemically
1
1
inequivalent oxazoline arms. H/1H COSY and H/13C
(24) Berry, R. S. J. Chem. Phys. 1960, 32, 933–938.

11960 Inorganic Chemistry, Vol. 48, No. 24, 2009
Zhang et al.
Scheme 1. Proposed Dynamic Behavior Based on Variable-Temperature NMR Experimentsa
a For symmetry reasons, we consider only one of the two N,P,N ligands bound to the dinuclear unit.
Conclusion
chemoselective manner,1t offer the possibility of undergoing
hemilabile1d or more complex dynamic behavior which may in
turn facilitate the fixation and activation of small organic
molecules.26
It appears clearly from this study that coordination of the
trifunctional NPN and NOPONMe2 ligands to a d9-d9 dipal-
ladium unit requires specific conditions. Whereas NPN was
better suited than NOPONMe2 for the synthesis of complexes
of type 1 in which two ligands simultaneously bridge and
chelate the dinuclear unit, and this may be due to steric
reasons, the reverse is true for complex 4 which contains only
one trifunctional bridging-chelating ligand and has no coun-
terpart with theNPN ligand. This may have electronic origins
since NPN is perfectly suited from a steric point of view to
bridge-chelate the Pd2 unit. Furthermore, the presence of the
methyl groups in NOPONMe2 may stabilize the structure of 4
through multiple non-classical H-bonding interactions be-
tween methyl protons and proximal chlorides. We have also
demonstrated that bothcomplexes display fluxionalbehavior
at room temperature and, for each of them, low temperature
NMR measurements have been carried out and a mechanism
has been proposed to account for their dynamic behavior.
Whereas an uncoordination/rotation process has been sug-
gested for 4, a Berry pseudorotation mechanism has been
proposed for 1, involving a pentacoordinated phosphorus in
a type B structure.
Experimental Section
All reactions wereperformed undernitrogen;solventswere
purified and dried under nitrogen by conventional methods.
The 1H, 31P{1H}, and 13C{1H} NMR spectra were recorded
at room temperature at 300.13, 121.5, and 75.4 MHz, respec-
tively, unless otherwise stated. IR spectra in the 4000-
400cm-1 rangewererecordedonaBrukerIFS66FTSpectro-
meter. The ligands NPN2 and NOPONMe2 3
and the
,
complexes [Pd2(NCMe)6][BF4]2,10 [Pd2(dba)3] CHCl3,27
3
and [Pd(dba)2]28 were prepared according to the literature.
[Pd2(NPN-N,P,N)2](BF4)2 (1). In a 100 mL Schlenk tube were
placed NPN (0.315 g, 1.14 mmol) and [Pd2(NCMe)6][BF4]2
(0.360 g, 0.57 mmol) in CH2Cl2 (30 mL) at -78 °C. The solution
turned yellow orange within 1 h, and a yellow precipitate
formed. The precipitation was completed by addition of Et2O
(50 mL), the solid was collected by filtration and washed twice
with Et2O (2 ꢀ 50 mL). Yield: 0.430 g (80%). This yellow solid
can be recrystallized from CH3CN/Et2O (1:3) or CH3NO2/Et2O
(1:3) affording yellow orange parallepipedic crystals. Selected
IR data (KBr): 1640 (s, ν(CdN) cm-1. 1H NMR (CD3NO2, 298
K) δ: 3.45 (d, 2JPH = 10.8 Hz, 8H, PCH2), 4.07 (t, 3JHH = 9.6
Hz, 8H, NCH2), 4.71 (t, 3JHH = 9.6 Hz, 8H, OCH2), 7.34-7.58
(m, 10H, aromatic). 13C{1H} (CD3NO2, 298 K) δ: 32.8 (d, 1JPC
= 34 Hz, PCH2), 55.7 (s, NCH2), 72.8 (s, OCH2), 130.7 (d, JPC
= 11.9 Hz, aryl), 131.4 (d, JPC = 12.5 Hz, aryl), 132.6 (s, p-aryl),
To the best of our knowledge, relatively few complexes have
been reported in the literature in which a potentially tridentate
functional phosphine ligand is simultaneously chelating and
bridging a dinuclear Pd(I)-Pd(I) system.1t,19,22,25 Multi-
dentate ligands displaying different types of donor functions,
such as phosphorus and nitrogen in this study, and able to
simultaneously bridge and chelate a dinuclear metal core in a
132.7
(d,
1JPC
=
24.1
Hz,
ipso-aryl),
2
174.7 (d, JPC = 12.5 Hz, CdN). 31P{1H} (CD3NO2, 298 K)
(26) See, for example, Jones, N. D.; Foo, S. J. L.; Patrick, B. O.; James,
B. R. Inorg. Chem. 2004, 43, 4056–4063.
(27) Milani, B.; Anzilutti, A.; Vicentini, L.; Sessanta, A.; Zangrando, E.;
Silvano, G.; Meastroni, G. Organometallics 1997, 16, 5064.
(28) Ukai, T.; Kawazura, H.; Ishii, H.; Bonnet, J. J.; Ibers, J. A.
J. Organomet. Chem. 1974, 65, 253–266.
(25) Wachtler, H.; Schuh, W.; Ongania, K.-H.; Kopacka, H.; Wurst, K.;
Peringer, P. J. Chem. Soc., Dalton Trans. 2002, 2532–2535. Song, H.-B.;
Zhang, Z.-Z.; Mak, T. C. W. Inorg. Chem. Commun. 2002, 5, 442–445.
Nuricumbo Escobar, J. J.; Campos-Alvarado, C.; Rios-Moreno, G.; Morales-
Morales, D.; Walsh, P. J.; Parra-Hake, M. Inorg. Chem. 2007, 46, 6182–6189.

Article
Inorganic Chemistry, Vol. 48, No. 24, 2009 11961
δ: 13.3 (s). In the low temperature spectra, the two different
oxazoline arms of the ligands are identified by primed and
(s, 6H, OC(CH3)(CH3)), AB spin system: δA 4.09 (d, 2H,
2JHH = 8.5 Hz, OCHH), δB 4.20 (d, 2JHH = 8.5 Hz, OCHH),
7.46-7.51 (m, 3H, aromatic H), 7.86-7.90 (m, 2H, aromatic H).
31C{1H} (125.7 MHz, CD2Cl2) δ: 27.8 (s, NC(CH3)(CH3)),
28.2 (br, OC(CH3)(CH3)), 29.0 (overlapping s and br, NC-
(CH3)(CH3) and OC(CH3)(CH3)), 30.1 (s, CNC(CH3)3), 57.7
1
unprimed labels as a result of 2D H-1H and 1H-13C experi-
ments. 1H NMR (300 MHz, CD3NO2/CD2Cl2 (2:1), 218 K)
δ: ABX spin system simulated by g-NMR (X = P), δA = 3.16
(q, 2JAB = 18.6 Hz, 2JPA = 5.2 Hz, 2H, PCH0AH0B), δB = 3.08
2
2
2
(q, JAB= 18.6 Hz, JPB = 10.2 Hz, 2H, PCH0AH0B), 3.58
(d, 2JPH = 11.5 Hz, 4H, PCH2), 3.94 (m, part of a ABMN spin
system, partly masked by the following signal), 4.09 (center of
m, 6H, NCH0AH0B and NCH2), 4.6 (overlapping m, 8H, OCH2
and OCH02), 7.14-7.18 (m, 4H, aromatic), 7.45-7.57 (m, 6H,
aromatic). 31P{1H} (CD3NO2/CD2Cl2 (2:1), 218 K) δ: 9.6 (s).
13C{1H} (125.7 MHz, CD3NO2/CD2Cl2 (2:1), 218 K) δ: 31.2 (br
s, PCH2), 32.8 (br s, PC0H2), 54.1 (masked by CH2Cl2 but
(s, CNC(CH3)3), 70.3 (s, NC(CH3)2), 78.1 (d, JPC = 6.0 Hz,
OC(CH3)2), 81.9 (s, OCH2), 127.0 (br, CNC(CH3)3)), 128.5 (d,
3JPC = 12.5 Hz, m-aryl), 130.3 (d, 2JPC = 16.9 Hz, o-aryl), 131.5
(d, 4JPC = 1.9 Hz, p-aryl), 140.8 (d, 1JPC = 81.9 Hz, ipso-aryl),
167.4 (br s, CdN). 31P{1H} (CD2Cl2) δ: 127.8(s). 1H NMR (300
MHz, CD2Cl2, 197 K) δ: 1.22 (s, 9H, C(CH3)3), 1.44 (s, 3H,
NC(CH3)(CH3)), 1.46 (s, 3H, NC(CH3)(CH3)), 1.47 (s, 6H,
OC(CH3)(CH3) and NC(CH3)(CH3)), 1.68 (s, 3H, OC(CH3)-
(CH3)), 1.83 (s, 3H, OC(CH3)(CH3)), 1.86 (s, 3H, NC(CH3)-
(CH3), 2.16 (s, 3H, OC(CH3)(CH3)), 3.99 (d, 1H, 2JHH = 8.5 Hz,
OCHH), 4.16-4.21 (overlapping quart. and d, 3H, 2JHH = 8.5
Hz, 2 ꢀ OCHH and OCHH), 7.44-7.51 (m, 3H, aromatic H),
7.79-7.83 (m, 2H, aromatic H). 13C{1H} (125.7 MHz, CD2Cl2,
197 K) δ: 25.3 (s, OC(CH3)(CH3)), 25.4 (s, OC(CH3)(CH3)),
26.4 (s, NC(CH3)(CH3)), 27.2 (s, OC(CH3)(CH3)), 28.0 (s, NC-
(CH3)(CH3)), 29.1 (s, CNC(CH3)3 and OC(CH3)(CH3)), 29.3 (s,
NC(CH3)(CH3)), 30.5 (s, OC(CH3)(CH3)), 57.0 (s, CNC-
(CH3)3), 69.0 (s, NC(CH3)2), 69.2 (s, NC(CH3)2), 76.9 (s, OC-
1
determined from H-13C COSY NMR, s, NC0H2), 55.3
(masked by CH2Cl2 but determined from 1H-13C COSY
NMR, s, NCH2), 71.2 (s, OC0H2), 73.2 (s, OCH2), 129.9 (d,
JPC = 11.2 Hz, aryl), 131.4 (d, JPC = 12.8 Hz, aryl), 132.6 (s, p-C
1
of aryl), 132.7 (d, JPC = 24.1 Hz, ipso-C of aryl), 174.7 (br s,
CdN and C0dN). Anal. Calcd. for C28H34B2F8N4O4P2Pd2: C,
35.82; H, 3.65; N, 5.97. Found C, 35.64; H, 3.43; N, 6.03.
[Pd(NOPONMe2-N,P,N)Cl](BF4) (3). In a 100 mL Schlenk
tube were placed together NOPONMe2 (0.63 g, 1.50 mmol) and
[PdCl2(COD)] (0.44 g, 1.50 mmol) in CH2Cl2 (30 mL). The
yellow solution was stirred at room temperature for 1 h, then
NaBF4 (0.16 g, 1.50 mmol) was added, and the mixture solution
was stirred for another 24 h at room temperature and filtered.
The filtrate was taken to dryness under vacuum, the yellow solid
thus obtained was washed with a mixture of diethyl ether/
pentane (1/3) (3ꢀ 20 mL), then pentane (2 ꢀ 20 mL), dried
under vacuum to obtain 3 as a yellow solid: 0.83 g (87%).
2
(CH3)2), 77.6 (d, JPC = 9.8 Hz, OC(CH3)2), 80.4 (s, OCH2),
81.1 (s, OCH2), 124.6 (s, CNC(CH3)3)), 127.9 (d, JPC = 12.6
3
Hz, m-aryl), 129.5 (d, 2JPC = 17.5 Hz, o-aryl), 131.3 (s, p-aryl),
138.5 (d, JPC = 84.8 Hz, ipso-aryl), 163.6 (s, CdN), 168.9 (s,
1
CdN). Anal. Calcd for C28H44Cl4N3O4PPd2 (4 CH2Cl2)
3
(sample recrystallized from CH2Cl2/pentane): C, 38.55; H,
5.08; N, 4.82. Found C, 38.62; H, 5.04; N, 4.70.
Selected IR data (KBr): 1620 (s, ν(CdN)) cm-1 1H NMR
;
[PdCl2(NPN-N,P)] (5). In a 100 mL Schlenk tube were placed
together NPN (0.215 g, 0.78 mmol) and [PdCl2(COD)] (0.220 g,
0.78mmol)inCH2Cl2 (50mL) at roomtemperature. The solution
turned light yellow within 1 h, it was concentrated, and the
product was precipitated and washed twice by addition of Et2O
(3 ꢀ 50 mL). Yield: 0.430 g (80%). Selected IR data (KBr): 1660
(s, ν(CdN)), 1640 (s, ν(CdN)) cm-1. The resonances for the
bound and pendant oxazoline arms are identified by primed and
unprimed labels, respectively, as a result of 2D 1H-1H and
1H-13C NMR experiments. 1H NMR (CD2Cl2) δ: 3.31 (part of
anABX spinsystem (X = P), q, 2JAB = 18.3 Hz, 2JAX = 13.2Hz,
1H, PCH0BH0A), 3.49 (part of an ABX spin system (X = P),
(CD2Cl2) δ: 1.50 (s, 6H, NC(CH3)(CH3)), 1.78 (s, 6H, NC-
(CH3)(CH3)), 1.84 (d, 6H, 4JPH = 2.0 Hz, OC(CH3)(CH3)), 2.39
(s, 6H, OC(CH3)(CH3)), AB spin system: δB 4.38 (d, 2JHH = 9.0
Hz, OCHH), δA 4.50 (d, 2JHH = 9.0 Hz, OCHH), 7.55-8.07 (m,
5H, aromatic H). 31C{1H} (CD2Cl2) δ: 24.9 (d, 3JPC = 7.4 Hz,
OC(CH3)(CH3)), 26.6 (s, NC(CH3)(CH3)), 28.1 (s, NC(CH3)-
3
(CH3)), 29.2 (d, JPC = 3.4 Hz, OC(CH3)(CH3)), 72.5 (s, NC-
2
(CH3)2), 83.4 (d, JPC = 5.1 Hz, OC(CH3)2), 83.7 (s, OCH2),
128.1-135.2 (m, aryl), 172.1 (d, 3JPC = 10.2 Hz, CdN). 31P{1H}
δ: 114.5 (s). Anal. Calcd for C22H33BClF4N2O4PPd: C, 40.70;
H, 5.12; N, 4.32. Found C, 40.95; H, 5.20; 4.60.
2
apparent t, 2JAB ≈ JAX = 14.5 Hz, 1H, PCHBHA), 3.73-3.84
[Pd2Cl2(CNt-Bu)(NOPONMe2-N,P,N)] (4). Method (a).
In a 100 mL Schlenk tube were placed together NOPONMe2
(0.116 g, 0.28 mmol) and [Pd2(NCMe)6][BF4]2 (0.175 g, 0.28
mmol) in a mixture of MeCN (30 mL) and CH2Cl2 (15 mL). The
orange-brown solution was immediately cooled to -30 °C, then
t-BuNC (0.023 g, 0.28 mmol) and LiCl (0.024 g, 0.56 mmol) were
added sequentially. The solution was stirred at -30 °C for 24 h
and then filtered, the filtrate was taken to dryness under
vacuum, and the residue (brown oil) was dissolved in a mixture
of diethyl ether (20 mL) and MeCN (3 mL). The solution was
kept at -30 °C for several days, which yielded yellow parallel-
epipedic crystals. Yield: 0.044 g (20%).
(overlapping q and m, 3H, PCHBHA and NCH2), 3.95-4.31
(overlapping, 5H, NCH0BH0A, PCH0AH0B, NCH0BH0A and
OCH2), ABMN spin system simulated using g-NMR: δB
=
4.66 (2JAB = 8.6, JBM = 10.6, JBN = 8.7 Hz), δA = 4.76
(2JAB = 8.6, 3JAN = 10.6, 3JAM = 8.7 Hz), 7.51-7.65 (m, 3H,
aromatic), 7.97-8.04 (m, 2H, aromatic). 13C{1H} (CD2Cl2) δ:
25.7 (d, 1JPC = 33 Hz, PCH2), 28.3 (d, 1JPC = 36 Hz, PC0H2),
52.9 (masked by CH2Cl2 but determined from 1H/13C NMR
correlations, s, NC0H2), 54.8 (masked by CH2Cl2 but determined
from 1H/13C NMR, s, NCH2), 68.1 (s, OCH2), 72.9 (s, OC0H2),
3
3
129.3 (d, JPC = 10Hz, aryl), 132.3 (s, p-Cof aryl), 132.6 (d, JPC
=
14.3 Hz, aryl), 133.5 (d, 1JPC = 26.1 Hz, ipso-C of aryl), 165.1 (d,
2JPC = 6.8 Hz, CdN), 168.0 (d, 2JPC = 6.5 Hz, C0dN). 31P{1H}
(CD2Cl2) δ: 21.4 (s). Anal. Calcd for C14H17Cl2N2O2PPd: C,
37.07; H, 3.78; N, 6.18. Found C, 37.24; H, 3.90; N, 6.25.
X-ray Crystallography. Suitable crystals for the X-ray analysis
of all compounds were obtained as described above. The intensity
datawerecollectedat173(2) K ona Kappa CCD diffractometer29
Method (b). In a 100 mL Schlenk tube were placed together
[PdCl2NOPONMe2-P,N) (0.116 g, 0.45 mmol) and [Pd(dba)2]
(0.258 g, 0.45 mmol) in CH2Cl2 (30 mL). The red-brown
solution was cooled to 0 °C, then t-BuNC (0.037 g, 0.45 mmol)
in CH2Cl2 (3 mL) was added dropwise to the solution. The
solution was stirred at 0 °C for 3 h, the yellow solution was
filtered, and the filtrate was taken to dryness, the residue solid
was washed with a mixture of 1:1 diethyl ether and pentane (3 ꢀ
20 mL), and dried overnight under vacuum. Yield: 0.283 g
(80%). Selected IR data (KBr): 2174 (s, ν(CꢁN)), 1641 (s,
˚
(graphite monochromated Mo KR radiation, λ = 0.71073 A).
Crystallographic and experimental details for the structures are
summarized in Table 1. The structures were solved by direct
methods (SHELXS-97) and refined by full-matrix least-squares
ν(CdN)) cm-1
;
(CH2Cl2): 2185 (s, ν(CꢁN)), 1654 (m,
ν(CdN)), 1642 (s, ν(CdN)) cm-1. 1H NMR (300 MHz, CD2Cl2,
298 K) δ: 1.30 (s, 9H, C(CH3)3), 1.55 (s, 6H, NC(CH3)(CH3)),
1.73 (s, 6H, OC(CH3)(CH3)), 1.76 (s, 6H, NC(CH3)(CH3), 1.94
(29) Bruker-Nonius Kappa CCD Reference Manual; Nonius BV: The
Netherlands, 1998.

11962 Inorganic Chemistry, Vol. 48, No. 24, 2009
Zhang et al.
Table 1. Crystallographic data for 1, 3 0.5CH3CN, and 4
3
1
3 0.5CH3CN
3
4
chemical formula
Mr
C
938.95
28H34N4O4P2Pd2 2(BF4)
C22H33ClN2O4PPd 0.5(C2H3N) BF4
669.66
C27H42Cl2N3O4PPd2
787.31
3
3
3
cell setting, space group
temperature (K)
monoclinic, P21/c
173(2)
17.672(4)
11.911(3)
17.193(4)
90.00
110.980(10)
90.00
3379.1(14)
4
1.846
triclinic, P1
173(2)
orthorhombic, Pbca
173(2)
11.330(1)
17.826(2)
31.961(3)
90.00
90.00
90.00
6455.1(11)
8
1.620
˚
a (A)
11.580(1)
16.228(2)
16.892(2)
97.809(4)
109.390(4)
97.814(6)
2910.3(6)
4
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dx (g cm-3
radiation type
)
1.528
Mo-KR
0.84
Mo-KR
1.25
Mo-KR
1.37
μ (mm-1
)
crystal size (mm)
no. of measd, indep.
and obsvd. refl.
Rint
0.20 ꢀ 0.15 ꢀ 0.15
0.22 ꢀ 0.17 ꢀ 0.10
0.17 ꢀ 0.15 ꢀ 0.13
16689, 7350, 5766
34106, 12691, 10988
42849, 7040, 5406
0.038
27.0
0.038
0.090, 1.06
451
0.001
0.039
27.0
0.031
0.097, 1.14
723
0.002
0.069
27.0
0.034
0.100, 1.14
394
0.001
θ
max (deg)
R[F2 > 2σ(F2)]
wR(F2), S
no. of parameters
(Δ/σ)max
ΔFmax, ΔFmin (e A
-3
˚
)
1.12, -0.91
1.24, -0.96
0.71, -0.86
procedures (based on F2, SHELXL-97)30 with anisotropic ther-
mal parameters for all the non-hydrogen atoms, except those
mentioned below. The hydrogen atoms were introduced into the
geometrically calculated positions (SHELXL-97 procedures) and
refined riding on the corresponding parent atoms.
carbon in common. The methyl carbon atoms were refined with
restrained anisotropic thermal parameters and C-C bond distances.
CCDC 746987 (1), 746988 (3 0.5CH3CN), 746989 (4) contain
3
the supplementary crystallographic data for this paper that can
be obtained free of charge from the Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cif.
For 3 0.5CH3CN, one of the two BF4 anions was disordered
3
in two positions, sharing the B atom, with equal occupancy
factors. The fluorine atoms were refined with restrained aniso-
tropic parameters. The acetonitrile molecule was found disor-
dered in two positions with unequal occupancy factors and with
no atom in common. These atoms were refined with constrained
isotropic parameters and restrained C-C and C-N distances.
For 4, the t-Bu group was found disordered in two posi-
tions, with equal occupancy factors and having the quaternary
ꢁ
Acknowledgment. We are grateful to the Ministere de la
Recherche for a postdoctoral grant to J.Z., the Centre National
de la Recherche Scientifique for financial support, and to N.
Auvray for experimental help, Dr. A. DeCian and Prof.
R. Welter for the X-ray diffraction analyses, and R. Graff and
J. D. Sauer for NMR measurements.
Supporting Information Available: Crystallographic data in
CIF file format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(30) Sheldrick, M.; SHELXL-97, Program for crystal structure refinement;
€
€
University of Gottingen: Gottingen, Germany, 1997.