Palladium complexes of a P2C = Ligand containing a central carbene moiety

Article abstract of DOI:10.1021/om700414t

Palladium(II) complexes of the PCHP pincer ligand were prepared from PdCl₂, a "proto-pincer" P₂CH₂, and base. The resulting (PCHP)PdCl was converted to (PCHP)PdOTf. (PCHP)PdCl did not react with NaN(SiMe₃)₂ but produced (PCHP)PdR (R = Me, Et, Ph) upon reaction with the corresponding organolithium, Grignard, or organozinc reagent. Trityl cation abstracted a hydride from (PCHP)PdCl to yield cationic Pd carbene complex (P₂C=)PdCl. Analysis of the structural data points to minimal π-interaction between the carbene center and palladium.

Full text of DOI:10.1021/om700414t

Organometallics 2007, 26, 3315-3320
3315
Palladium Complexes of a P2Cd Ligand Containing a Central
Carbene Moiety
Wei Weng, Chun-Hsing Chen, Bruce M. Foxman, and Oleg V. Ozerov*
Department of Chemistry, Brandeis UniVersity, MS 015, 415 South Street, Waltham, Massachusetts 02454
ReceiVed April 29, 2007
Palladium(II) complexes of the PCHP pincer ligand were prepared from PdCl2, a “proto-pincer” P2-
CH2, and base. The resulting (PCHP)PdCl was converted to (PCHP)PdOTf. (PCHP)PdCl did not react
with NaN(SiMe3)2 but produced (PCHP)PdR (R ) Me, Et, Ph) upon reaction with the corresponding
organolithium, Grignard, or organozinc reagent. Trityl cation abstracted a hydride from (PCHP)PdCl to
yield cationic Pd carbene complex (P2Cd)PdCl. Analysis of the structural data points to minimal
π-interaction between the carbene center and palladium.
Chart 1
Introduction
We have recently reported the preparation of a new pincer
“proto-ligand” P2CH2 (1, Chart 1).1 Unlike the conventional PCP
ligands (C),2 P2CH2 can give rise to pincer complexes of both
a “phosphine-alkyl-phosphine” (PCHP, A) and a “phosphine-
carbene-phosphine” (P2Cd, B) types. In the sense of this duality,
the P2CH2 “proto-pincer” can be likened to bis(dialkylphosphi-
no)pentane.3 However, the framework of the P2Cd ligand is
much more rigid and more strongly prearranged for the
formation of pincer-type complexes. We have reported examples
* Corresponding author. E-mail: ozerov@brandeis.edu.
(1) Weng, W.; Parkin, S.; Ozerov, O. V. Organometallics 2006, 25, 5345.
(2) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759.
(3) (a) Crocker, C.; Errington, R. J.; McDonald, W. S.; Odell, K. J.;
Shaw, B. L.; Goodfellow, R. J. J. Chem. Soc., Chem. Commun. 1979, 498.
(b) Gusev, D. G.; Lough, A. J. Organometallics 2002, 21, 2601. (c) Gusev,
D. G.; Lough, A. J. Organometallics 2002, 21, 5091.
(4) Fan, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2004, 23,
326.
of both PCHP and P2Cd types of ruthenium complexes in an
earlier contribution.1 In the present report, we describe the
synthesis and structural characterization of both types of
complexes arising from 1 with palladium.
(5) Cross, R. J.; Kennedy, A. R.; Muir, K. W. J. Organomet. Chem.
1995, 487, 227.
(6) Fafard, C. M.; Ozerov, O. V. Inorg. Chim. Acta 2007, 360, 286.
(7) (a) Bahr, S. R.; Boudjouk, P. J. Org. Chem. 1992, 57, 5545. (b)
Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992, 11, 3920.
(8) Kiel, W. A.; Buhro, W. E.; Gladysz, J. A. Organometallics 1984, 3,
879.
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6580.
(10) (a) Viciu, M. S.; Germaneau, R. F.; Navarro-Fernandez, O.; Stevens,
E. D.; Nolan, S. P. Organometallics 2002, 21, 5470. (b) Viciu, M. S.; Kelly,
R. A., III; Stevens, E. D.; Naud, F.; Studer, M.; Nolan, S. P. Org. Lett.
2003, 5, 1479. (c) Waltman, A. W.; Grubbs, R. H. Organometallics 2004,
23, 3105.
(11) Schuster, O.; Raubeheimer, H. G. Inorg. Chem. 2006, 45, 7997.
(12) Persistence of Vision Ray Tracer (POV-Ray), available at http://
www.povray.org/.
(13) ORTEP plots were created using Ortep-3 for Windows. Farugia, L.
J. Appl. Crystallogr. 1997, 30, 565.
(14) Morales-Morales, D.; Grause, C.; Kasaoka, K.; Redon, R.; Cramer,
R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300-302, 958.
(15) Ozerov, O. V.; Guo, C.; Foxman, B. M. J. Organomet. Chem. 2006,
691, 4802.
(16) Lee, H. M.; Zeng, J. Y.; Hu, C.-H.; Lee, M.-T. Inorg. Chem. 2004,
43, 6822.
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Chem. 2003, 27, 1446.
Results and Discussion
Synthesis of (PCHP)PdCl. By analogy with the syntheses
of a number of Pd complexes with other PCP ligands,2 we
anticipated that the combination of PdCl2 and base will react
with P2CH2 via C-H activation and result in formation of a
(PCHP)PdCl complex, 2. One-pot reaction of P2CH2 with
(COD)PdCl2 and Et3N afforded 2 as the main product in a 65%
isolated yield (Scheme 1). Alternatively, allowing P2CH2 to react
with (COD)PdCl2 first, followed by removal of volatiles, and
subsequent thermolysis of the residue in toluene in the presence
of 2 equiv of 2,6-lutidine afforded (PCHP)PdCl (2) in a 72%
isolated yield.
Complex 2 is soluble in ether and toluene and slightly soluble
in pentane. It has been fully characterized by multinuclear NMR
(21) (a) The lower π-basicity of Pd(II) vs Ru(II) is likely owing to the
increase in the effective nuclear charge left to right in the periodic table
and can be illustrated by the difference in the stretching frequencies of
coordinated CO in [Cl(Et3P)2Pd(CO)]+ (2130 cm-1
)
and in (iPr3P)2Ru-
21b
(H)(Cl)(CO) (1910 cm-1).21d These two examples are particularly relevant
to the discussion at hand since these are related to 9 and 15 by formal
replacement of the P2Cd ligand with two phosphines and a CO. Clearly,
the much lower νCO in a Ru(II) complex testifies to its greater back-donating
ability (i.e., π-basicity). (b) Clark, H. C.; Dixon, K. R. J. Am. Chem. Soc.
1969, 91, 596. (c) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986,
303, 221.
(19) Pincer complexes of a divalent group 10 metal with a near planar
backbone were reported for the bis(quinolyl)amido NNN ligand: Peters, J.
C.; Harkins, S. B.; Brown, S. D.; Day, M. W. Inorg. Chem. 2001, 40, 5083.
(20) Gusev, D. G.; Madott, M.; Dolgushin, F. M.; Lyssenko, K. A.;
Antipin, M. Yu. Organometallics 2000, 19, 1734.
10.1021/om700414t CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/12/2007

3316 Organometallics, Vol. 26, No. 14, 2007
Weng et al.
Scheme 1
Scheme 2
Figure 1. ORTEP drawing (50% thermal ellipsoids) of (PCHP)-
Pd(Cl) (2) showing selected atom labeling. Hydrogen atoms and
methyl groups are omitted for clarity. The Cl atom, Pd atom, and
the bridging carbon C5 between two pyrrole rings were found to
be disordered over two adjacent positions with refined occupancy
factors of 0.83 and 0.17, respectively. Only the molecular structure
with the higher occupancy factor is shown. Selected bond distances
(Å) and angles (deg): Pd1-Cl1 2.4011(11); Pd1-P1 2.2715(8);
Pd1-P2 2.3101(9); Pd1-C5 2.076(2); Cl1-Pd1-P1 94.62(5);
Cl1-Pd1-P2 97.82(4); P1-Pd1-P2 163.95(4); Cl1-Pd1-C5
175.41(10); P1-Pd1-C5 84.88(7); P2-Pd1-C5 83.52(7); Cl1-
Pd1-C51 155.0(3); P1-Pd1-C51 82.8(2); P2-Pd1-C51 81.7-
(3).
in solution and X-ray crystallography in the solid state (vide
infra). Two methine resonance and four methyl resonances were
1
observed for the Pri2P groups in the H NMR spectrum of 2,
indicating Cs symmetry in solution. The presence of a Pd-CH
moiety in 2 was evidenced by a singlet at δ 5.61 ppm in the 1H
NMR spectrum and a triplet at δ 32.8 ppm in the 13C{1H} NMR
spectrum. The 31P NMR chemical shift of 2 (δ 101.7),
considerably downfield from that of free ligand (δ 56.8), is
indicative of coordination of the phosphine arms to the metal
center.
Synthesis of (PCHP)Pd(OTf). (PCHP)PdOTf (3) was pre-
pared using Me3SiOTf as the Cl/OTf metathesis reagent. This
metathesis results in an observable equilibrium (Scheme 2).
Repeated application of Me3SiOTf followed by removal of
volatiles afforded clean conversion to 3. The OTf group is
directly coordinated to the metal center, which was deduced
from its characteristic 19F NMR resonance (δ -79.9 ppm in
C6D6), distinct from that of a free OTf anion (δ -80.6 ppm in
C6D6).22 Similarly to 2, (PCHP)PdOTf also displays Cs sym-
metry in solution.
Structures of 2 and 3. Solid-state X-ray diffraction studies
(Figures 1 and 2) confirmed the proposed identities of 2 and 3.
In both structures, the environment about the Pd center is close
to an idealized square-planar geometry, with the deviations
arising primarily from the chelate constraint. The “pincer bite”
angles (P-Pd-P) of ca. 164° and 168° in 2 and 3, respectively,
are roughly similar to those in related (PNP)PdCl (4)4 and
(PCP)PdCl (5)5 complexes (Chart 2). The Pd-Cl distance in 2
(ca. 2.40 Å) resembles that in 5 and is substantially longer than
its counterpart in 4. This difference can likely be traced to the
weaker trans influence of the amido ligand in 4. The Pd-P
distances in 2 and 3 are unremarkable.
Figure 2. ORTEP drawing (50% thermal ellipsoids) of (PCHP)-
Pd(OTf) (3) showing selected atom labeling. Hydrogen atoms and
methyl groups are omitted for clarity. P atoms and the Pd atom
and atoms C4, C5, C6, and N2 were found to be disordered over
two adjacent positions with refined occupancy factors of 0.92 and
0.08, respectively. Only the molecular structure with the higher
occupancy factor is shown. Selected bond distances (Å) and angles
(deg): Pd1-O3 2.1921(15); Pd1-P1 2.3072(8); Pd1-P2 2.2860-
(7); Pd1-C5 2.059(2); O3-Pd1-P1 96.45(5); O3-Pd1-P2 94.65-
(4); P1-Pd1-P2 167.76(3); O3-Pd1-C5 177.22(8); P1-Pd1-
C5 84.52(6); P2-Pd1-C5 84.63(6).
Attempts at Deprotonation of (PCHP)PdX Complexes and
Syntheses of (PCHP)PdR (R ) Me (6), Et (7), Ph (8)). We
were interested in exploring the possibility of accessing Pd
complexes of the carbenic P2Cd ligand. At first we sought to
prepare complexes containing the (P2Cd)Pd0 fragment; we
believed that such species might possess unusual reactivity. One
ostensible route to such derivatives is through elimination of
HX from the (PCHP)PdX complexes. However, attempts to
dehydrochlorinate 2 or dehydrotriflate 3 using NaN(SiMe3)2 as
a strong base were unsuccessful. No reaction was observed upon
mixing NaN(SiMe3)2 with 2 (NMR evidence). The reaction of
NaN(SiMe3)2 with 3 did not lead to dehydrotriflation either:
while new unidentified products were formed, no significant
amount of HN(SiMe3)2 was produced and the characteristic Pd-
1
CH signal was still detectable by H NMR.
We then resorted to using stronger, hydrocarbyl bases with
2. However, instead of dehydrochlorination, preparation of
(PCHP)PdR (6-8) was accomplished by the action of alkyl-
lithium, alkylzinc, or alkylmagnesium reagent on 2 (Scheme
3). The alkylating agents were used in excess with no detriment
to the yield of product. The Pd products 6-8 can be easily
separated from the excess of the alkylating agent by passing
the reaction mixture through silica gel. Complexes 6-8 were
fully characterized by solution NMR spectroscopic methods,
1
(22) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346.
and all displayed Cs symmetry in solution when probed by H

Palladium Complexes of a P2Cd Ligand
Organometallics, Vol. 26, No. 14, 2007 3317
Chart 2. Comparison of the Structural Features (bond
distances in Å and the P-Pd-P angle in deg) of Compounds
4 and 54,5
Scheme 3
Figure 3. ORTEP drawing (50% thermal ellipsoids) of 9-PF6
showing selected atom labeling. Hydrogen atoms, methyl groups,
and the counteranion (PF6) are omitted for clarity. Selected bond
distances (Å) and angles (deg): Pd1-P1A 2.2730(7); Pd1-P1
2.2730(7); Pd1-Cl1 2.3337(11); Pd1-C5 1.999(4); P1A-Pd1-
P1 171.30(4); P1A-Pd1-Cl1 94.35(2); P1-Pd1-Cl1 94.35(2);
P1A-Pd1-C5 85.65(2); P1-Pd1-C5 85.65(2); Cl1-Pd1-C5
179.99(4).
Scheme 4
Chart 3. “Remote” NHC Complexes of Pd
NMR and 13C NMR. The Pd-CH of the PCHP ligand in 6-8
resonates at ca. δ 4.7 ppm as a singlet in the 1H NMR spectrum
and at ca. δ 34.0 as a triplet (JC-P ) 2 Hz) in the 13C{1H}
NMR spectrum. The R-carbons of the Pd-bound R groups in
6-8 gave rise to characteristic triplet resonances in the 13C-
{1H} NMR spectra (6, d -17.3 (t, JCP ) 12 Hz, Pd-CH3); 7,
d -3.8 (t, JCP ) 10 Hz, Pd-CH2CH3); 8, d 151.8 (t, JCP ) 10
Hz, ipso-Ph); all in C6D6).
Complexes 6-8 are all stable in solution at ambient temper-
ature, which is particularly surprising for 7, where the obvious
decomposition pathway via â-hydrogen elimination (BHE) can
be envisioned. Remarkably robust Pd alkyls supported by a PNP
pincer system have recently been reported by our group
elsewhere.6 The stability of 7 toward BHE in the present work
can probably be explained using similar reasoning: the rigidity
of the PCHP pincer backbone prevents dissociation of the
phosphine arms and thus blocks the BHE pathway. We have
tested the stability of 6 at elevated temperature as well.
Thermolysis of C6D6 solutions of 6 at 100 °C for 2 days did
not result in any change observable by NMR spectroscopy. Thus,
it appears that P2Cd complexes of Pd0 are not readily syntheti-
cally available. It is likely that the stereoelectronic requirements
of a Pd0 center are incompatible with the geometry imposed by
the rigid P2Cd ligand.
a diarylcarbene of Ta(V) in a pincer-like context.9 Ph3CH was
observed in both reactions by H NMR spectroscopy. These
cationic Pd carbene complexes are not soluble in pentane, only
1
slightly soluble in toluene, but dissolve well in CH2Cl2. 9-PF6
F
1
and 9-BAr4 exhibit nearly identical H and 13C NMR spectra
for the C2V-symmetric cation 9 (CD2Cl2 solution). The ligated
carbene carbon resonates at δ 189.6 ppm in the 13C{1H} NMR
spectrum of 9. This chemical shift is comparable to those
observed for PdII complexes of N-heterocyclic carbenes (NHC).10
Schuster and Raubenheimer recently reported “remote NHC”
complexes of PdII (10 and 11, Chart 3) in which the carbon
attached to Pd resonates at δ 187.0 (10) and 180.7 ppm (11) in
the 13C{1H} NMR spectra.11
Analysis of the Structural Features of 9-PF6. An X-ray
diffraction study of a suitable crystal of 9-PF6 revealed an
approximately square-planar geometry about Pd with two
phosphine arms trans to each other and carbene trans to Cl
(Figure 3). The remarkable feature of the structure of 9-PF6 is
that the pyrrolyl rings are almost perfectly coplanar with the
coordination plane of the carbenic carbon and the coordination
plane of Pd. Figure 4 provides a convenient side view of the
cation of 9-PF6 in contrast to the puckered structure of 2. The
“pincer bite” P-Pd-P angle in 9-PF6 is greater than that in 2,
consistent with the flattening of the whole ligand framework.
The Pd-Ccarbenic bond distance in 9-PF6 of 1.999(4) Å is only
ca. 0.08 Å shorter than the Pd-CH distance in 2 (2.076(2) Å).
The hybridization change from C(sp3) in 2 to C(sp2) in 9-PF6
probably accounts for a portion of this difference. Indeed, the
Pd-C(carbene) distance in 9-PF6 is very similar to the (presum-
ably single bond) Pd-C(aryl) distances in (PCP)PdCl complexes
(5,5 13,14 14,15 Chart 4). The observed Pd-C distance in 9-PF6
is also similar to the Pd-C distance in the NHC-containing
Preparation of Carbenic P2Cd Complexes of PdII. Since
removal of the R-H in the (PCHP)PdX complexes formally as
a proton was not at all successful, we conceived that it may be
amenable to abstraction as a formal hydride. Indeed, the reaction
of 2 (Scheme 4) with an archetypal hydride abstraction agent
F 7
[Ph3C][An] (An ) PF6, BAr4 ) afforded the cationic PdII
carbene/phosphine pincer complex [(P2Cd)PdCl][An] (9-An)
F
with the corresponding counterion (PF6 or BAr4 ). Abstraction
of a hydride form the R-C of a metal-bound alkyl has previously
been used by others to prepare carbene complexes,8 including

3318 Organometallics, Vol. 26, No. 14, 2007
Weng et al.
Figure 4. POV-Ray12 renditions of the Ortep drawings13 (50% probability ellipsoids) of 2 (left) and 9-PF6 (right) viewed along the P-Pd-P
i
-
axis. Omitted for clarity: H atoms, methyls of the Pr groups, PF6 group.
Chart 4. Data on the Metal-Carbon Distances (in Å) in Complexes 9 (this work), 5,5 12,16 13,14 14,15 15,1 16,18 and 1719
pincer complex 12.16 N-Heterocyclic carbenes are usually
thought of as only weakly π-acidic.17 The metric data thus
suggest little π-interaction in 9-PF6, indicating the dominant
σ-donor characteristics of the P2Cd carbene moiety in this
complex. This is consistent with the planarization of the pincer
system that presumably takes place to increase the overlap of
the pyrrolyl π-systems with what essentially is a carbocationic
center.19 A similar planarization of a diarylcarbene/bis(phenox-
ide) ligand attached to a Ta(V) center was observed by
Kawaguchi et al.9 In contrast, the reported Ru-carbene distance
in (P2Cd)Ru(H)(Cl) (15, Chart 4)1 is (a) noticeably smaller than
that in the structurally similar NHC complex 16,18 (b) much
shorter than the Pd-C distance in 9-PF6 despite the larger size
of Ru, and (c) much shorter than the Ru-C(aryl) distance in
the pincer complex 17.20 As well, the pyrrolyl rings in 15 are
significantly twisted out of coplanarity (and therefore conjuga-
tion) with the carbene center. Consistent with the lower degree
of conjugation in 15, the Cring-Ccarbene distance in 15 is ca. 1.45
Å, while it is ca. 1.41 Å in 2.
The above observations allow for tentative conclusions
regarding the electronic properties of the carbene donor in the
P2Cd ligand. The carbene ligand in P2Cd possesses variable
π-acidity that is moderated by the conjugation with the pyrrolyl
rings. With a weakly π-basic metal (PdII), it acts as a weak
π-acceptor at best. However, with a stronger π-base (RuII),21 it
behaves as a stronger π-acceptor. This variability is more
pronounced than for the NHC carbenes.
leads to the formation of Pd(II) complexes of the rigid carbene/
bis(phosphine) pincer ligand P2Cd. Analysis of the structural
data leads to the conclusion that the P2Cd ligand is only weakly
π-acidic toward Pd(II).
Experimental Section
General Considerations. Unless specified otherwise, all ma-
nipulations were performed under an argon atmosphere using
standard Schlenk line or glovebox techniques. Toluene, pentane,
Et2O, C6D6, C6H6, THF, and iso-octane were dried over NaK/Ph2-
CO/18-crown-6, distilled or vacuum transferred, and stored over
molecular sieves in an Ar-filled glovebox. CD2Cl2 was dried over
CaH2 and then vacuum transferred. Ligand P2CH2 was prepared
according to the published procedure,1 as was (COD)PdCl2.22 All
other chemicals were used as received from commercial vendors.
NMR spectra were recorded on a Varian iNova 400 (1H NMR,
399.755 MHz; 13C NMR, 100.518 MHz; 31P NMR, 161.822 MHz;
1
2H, 61.365 MHz) spectrometer. For H and 13C NMR spectra, the
residual solvent peak was used as an internal reference. 31P NMR
spectra were referenced externally using 85% H3PO4 at δ 0 ppm.
Elemental analyses were performed by CALI Labs, Inc. (Parsip-
pany, NJ). GC/MS spectra were recorded on a Hewlett-Packard
G1800C GCD system (GCD Plus gas chromatograph electron
ionization detector) employing HP-5MS from Agilent Technologies
(30 m (column length) × 0.25 mm (i.d.)) and 1227032 from J &
W Scientific (30 m × 0.250 mm). Helium was used as a carrier
gas.
(PCHP)PdCl (2). Method 1. A mixture of PdCl2 (308 mg, 1.74
mmol Pd), P2CH2 (1, 658 mg, 1.74 mmol), and Et3N (731 µL, 5.22
mmol) in 15 mL of toluene was stirred for 18 h at 80 °C. (PCHP)-
PdCl (2) and 1 were observed in the resulting mixture by 31P NMR
in a ratio of 10:1. Then, the mixture was filtered and all volatiles
were removed under vacuum. The resulting dark red solid was
extracted with toluene, and the toluene solution was concentrated
Conclusion
In summary, we have been able to prepare Pd(II) complexes
of the previously reported PCHP ligand. The R-CH moiety in
the (PCHP)PdX complexes resists abstraction of H as a proton,
but permits abstraction of H as a hydride. Hydride abstraction

Palladium Complexes of a P2Cd Ligand
Organometallics, Vol. 26, No. 14, 2007 3319
to ∼5 mL. Pentane was added to further precipitate the product.
The yellowish solid was collected and dried under vacuum. Yield:
656 mg (65%).
was quenched with methanol. Then the volatiles were evaporated
under reduced pressure. The solid residue was extracted with ether
and then passed through a pad of silica gel. The filtrate was pumped
to dryness. The resulting residue was washed with a small quantity
of pentane and dried under vacuum. Yield: 75 mg (55%). 1H NMR
(C6D6): δ 6.64 (t, J ) 3 Hz, 2H, py-H), 6.49 (s, 2H, py-H), 6.28
(d, J ) 2 Hz, 2H, py-H), 4.72 (s, 1H, PdCH), 2.17 (m, 2H, CHMe2),
2.04 (m, 2H, CHMe2), 1.10 (dvt, app. quartet, JH-P ) 8 Hz, JH-H
) 8 Hz, 6H, CHMe2), 1.06 (dvt, app. quartet, JH-P ) 8 Hz, JH-H
) 8 Hz, 6H, CHMe2), 0.94 (m, 12H, two CHMe2 signals overlap),
0.18 (t, app. quartet, JH-P ) 6 Hz, 3H, PdMe). 13C{1H} NMR
(C6D6): δ 152.1 (t, J ) 10 Hz), 117.6 (s), 115.3 (s), 104.3 (t, J )
6 Hz), 36.0 (t, J ) 2 Hz, PdCH), 28.2 (m, two CHMe2 signals
overlap), 18.6 (t, J ) 4 Hz, CHMe2), 17.8 (s, CHMe2), 17.7 (s,
CHMe2), 17.4 (t, J ) 3 Hz, CHMe2), -17.3 (t, J ) 12 Hz, PdMe).
31P{1H} NMR (C6D6): δ 104.3 (s). Anal. Calcd for C22H38N2P2-
Pd: C, 52.96; H, 7.68. Found: C, 52.87; H, 7.82.
Method 2. To a solution of P2CH2 (1, 1.60 g, 4.233 mmol) in
toluene was added (COD)PdCl2 (1.183 g, 4.15 mmol). A yellow
precipitate was observed. The mixture was stirred for 20 min. 31P
NMR analysis showed the absence of NMR resonances of 1. The
immediate release of free COD was observed via GC/MS analysis
of an aliquot. The yellow solid was collected by filtration and
thoroughly washed with pentane and then toluene, followed by
drying under vacuum. This solid was then suspended in toluene,
2,6-lutidine (2 equiv) was added, and the mixture was heated at
80 °C. NMR analysis indicated the clean formation of 2 (>96%
by NMR). The mixture was filtered, and all volatiles were removed
under vacuum from the filtrate. The resulting dark red residue was
extracted with toluene, and the toluene solution was concentrated.
Pentane was then added to precipitate the product. The yellowish
solid was collected and dried under vacuum to give 1.55 g (72%)
of 2. Both method 1 and method 2 result in the formation of some
(PCHP)Pd(Et) (7). A screw-cap test tube was charged with 2
(100 mg, 0.193 mmol), EtMgBr in ether (100 µL, 0.30 mmol, 3
M), 60 µL of dioxane, and 15 mL of ether. After 3 days at ambient
temperature, 31P NMR in situ indicated quantitative formation of
7. The reaction was quenched with methanol. Then the volatiles
were evaporated under reduced pressure. The solid residue was
extracted with ether and then passed through a pad of silica gel.
The filtrate was pumped to dryness. The resulting residue was
washed with pentane and dried under vacuum. Yield: 49 mg (50%).
1H NMR (C6D6): δ 6.63 (t, J ) 3 Hz, 2H, py-H), 6.49 (s, 2H,
py-H), 6.29 (d, J ) 3 Hz, 2H, py-H), 4.65 (s, 1H, PdCH), 2.20 (m,
2H, CHMe2), 2.07 (m, 2H, CHMe2), 1.60 (t, J ) 8 Hz, 3H,
PdCH2CH3), 1.32 (q, J ) 8 Hz, 2H, PdCH2CH3), 1.13 (dvt, JH-P
) 9 Hz, JH-H ) 8 Hz, 6H, CHMe2), 1.04 (dvt, app. quartet, JH-P
) 8 Hz, JH-H ) 8 Hz, 6H, CHMe2), 0.96 (m, 12H, two CHMe2
signals overlap). 13C{1H} NMR (C6D6): δ 152.0 (t, J ) 7 Hz),
117.3 (s), 115.3 (s), 104.2 (t, J ) 6 Hz), 34.7 (t, J ) 2 Hz, PdCH),
28.2 (t, J ) 10 Hz, CHMe2), 27.7 (t, J ) 11 Hz, CHMe2), 18.6 (t,
J ) 4 Hz, CHMe2), 18.4 (t, J ) 2 Hz, PdCH2CH3), 17.8 (s, CHMe2),
17.6 (s, CHMe2), 17.3 (t, J ) 4 Hz, CHMe2), -3.8 (t, J ) 10 Hz,
PdCH2CH3). 31P{1H} NMR (C6D6): δ 102.7 (s). Anal. Calcd for
C23H40N2P2Pd: C, 53.85; H, 7.86. Found: C, 53.85; H, 7.73.
1
Pd black, but method 2 results in apparently much less of it. H
NMR (CD2Cl2): δ 6.49 (t, J ) 3 Hz, 2H, py-H), 6.39 (t, J ) 2 Hz,
2H, py-H), 6.18 (d, J ) 3 Hz, 2H, py-H), 5.61 (s, 1H, PdCH), 2.29
(m, 2H, CHMe2), 2.09 (m, 2H, CHMe2), 1.36 (dvt, JH-P ) 9 Hz,
JH-H ) 7 Hz, 6H, CHMe2), 1.22 (dvt, JH-P ) 9 Hz, JH-H ) 7 Hz,
6H, CHMe2), 0.99 (dvt, app. quartet, JH-P ) 8 Hz, JH-H ) 8 Hz,
6 H, CHMe2), 0.89 (dvt, app. quartet, JH-P ) 8 Hz, JH-H ) 8 Hz,
1
6 H, CHMe2). H NMR (C6D6): δ 6.49 (t, J ) 3 Hz, 2H, py-H),
6.39 (t, J ) 2 Hz, 2H, py-H), 6.18 (d, J ) 3 Hz, 2H, py-H), 5.61
(s, 1H, PdCH), 2.29 (m, 2H, CHMe2), 2.09 (m, 2H, CHMe2), 1.36
(dvt, JH-P ) 9 Hz, JH-H ) 7 Hz, 6H, CHMe2), 1.22 (dvt, JH-P
9 Hz, JH-H ) 7 Hz, 6H, CHMe2), 0.99 (dvt, app. quartet, JH-P
8 Hz, JH-H ) 8 Hz, 6H, CHMe2), 0.89 (dvt, app. quartet, JH-P
)
)
)
8 Hz, JH-H ) 8 Hz, 6H, CHMe2). 13C{1H} NMR (C6D6): δ 150.1
(t, J ) 10 Hz), 118.0 (s), 116.7 (s), 105.0 (t, J ) 7 Hz), 32.8 (t, J
) 2 Hz, PdCH), 28.3 (t, J ) 11 Hz, CHMe2), 27.9 (t, J ) 10 Hz,
CHMe2), 18.1 (t, J ) 4 Hz, CHMe2), 17.7 (s, CHMe2), 17.4 (s,
CHMe2, two signals overlap). 31P{1H} NMR (C6D6): δ 101.7 (s).
Anal. Calcd for C21H35ClN2P2Pd: C, 48.57; H, 6.79. Found: C,
48.68; H, 6.91.
(PCHP)Pd(OTf) (3). To a solution of 2 (230 mg, 0.444 mmol)
in 15 mL of toluene was added Me3SiOTf (104 µL, 0.577 mmol).
Then, the mixture was stirred for 10 min. All volatiles were removed
under vacuum. The resulting residue was dissolved in 10 mL of
toluene, and Me3SiOTf (104 µL, 0.577 mmol) was added again.
The mixture was stirred for another 10 min, and the solution was
pumped to dryness. The resulting residue was extracted with
toluene, and the toluene solution was concentrated under vacuum
to almost dryness. About 20 mL of pentane was added to precipitate
3. 3 was collected by filtration and dried under vacuum. Yield:
264 mg (94%). 1H NMR (C6D6): δ 6.37 (t, J ) 3 Hz, 2H, py-H),
6.33 (s, 2H, py-H), 6.11 (d, J ) 3 Hz, 2H, py-H), 5.90 (s, 1H,
PdCH), 2.56 (m, 2H, CHMe2), 1.98 (m, 2H, CHMe2), 1.25 (dvt,
JH-P ) 10 Hz, JH-H ) 8 Hz, 6H, CHMe2), 1.19 (dvt, app. quartet,
JH-P ) 9 Hz, JH-H ) 9 Hz, 6H, CHMe2), 0.87 (dvt, app. quartet,
JH-H ) 9 Hz, JH-P ) 9 Hz, 6H, CHMe2), 0.79 (dvt, app. quartet,
JH-H ) 7 Hz, JH-P ) 7 Hz, 6H, CHMe2). 13C{1H} NMR (C6D6):
δ 148.7 (t, J ) 10 Hz), 117.9 (s), 117.8 (s), 105.7 (t, J ) 7 Hz),
30.5 (t, J ) 2 Hz, PdCH), 28.2 (t, J ) 11 Hz, CHMe2), 27.7 (t, J
) 10 Hz, CHMe2), 18.5 (t, J ) 3 Hz, CHMe2), 17.9 (t, J ) 2 Hz,
CHMe2), 17.1 (s, CHMe2), 16.3 (t, J ) 4 Hz, CHMe2). 31P{1H}
NMR (C6D6): δ 103.1 (s). 19F NMR (C6D6): δ -79.9 (s). Anal.
Calcd for C22H35F3N2O3P2SPd: C, 41.75; H, 5.57. Found: C, 41.95;
H, 5.71.
(PCHP)Pd(Ph) (8). A screw-cap tube was charged with 2 (110
mg, 0.212 mmol), PhLi in ether (160 µL, 0.32 mmol, 2 M), and 10
mL of ether. 31P NMR in situ indicated quantitative formation of
8 less than 10 min after mixing. A few drops of methanol were
added to the reaction mixture, and then all volatiles were evaporated
under reduced pressure. The solid residue was extracted with toluene
and then passed through a pad of silica gel. The filtrate was pumped
to dryness. The resulting residue was washed with a pentane and
1
dried under vacuum. Yield: 60 mg (50%). H NMR (C6D6): δ
7.66 (d, J ) 7 Hz, 2H, Ph-H), 7.24 (t, J ) 8 Hz, Ph-H), 7.06 (t, J
) 7 Hz, 1H, Ph-H), 6.62 (d, J ) 3 Hz, 2H, py-H), 6.52 (s, 2H,
py-H), 6.24 (d, J ) 2 Hz, 2H, py-H), 4.87 (s, 1H, PdCH), 2.14 (m,
2H, CHMe2), 1.94 (m, 2H, CHMe2), 0.93 (m, 18H, three CHMe2
signals overlap), 0.77 (dvt, app. quartet, JH-P ) 8 Hz, JH-H ) 8
Hz, 6H, CHMe2). 13C{1H} NMR (C6D6): δ 160.0 (t, J ) 15 Hz),
151.8 (t, J ) 10 Hz, ipso-Ph), 139.8 (s), 127.2 (s), 122.6 (s), 117.5
(s), 115.5 (s), 104.6 (t, J ) 6 Hz), 33.1 (t, J ) 2 Hz, PdCH), 27.5
(t, J ) 11 Hz, CHMe2), 26.6 (t, J ) 12 Hz, CHMe2), 18.2 (t, J )
4 Hz, CHMe2), 17.6 (s, CHMe2), 17.1 (s, CHMe2), 16.9 (t, J ) 3
Hz, CHMe2). 31P{1H} NMR (C6D6): δ 102.1 (s). Anal. Calcd for
C27H40N2P2Pd: C, 57.81; H, 7.19. Found: C, 57.98; H, 7.21.
-
[(P2Cd)PdCl]+PF6 (9-PF6). 2 (147 mg, 0.283 mmol) was
dissolved in ca. 10 mL of CH2Cl2. To the stirred solution was added
109 mg (0.281 mmol) of Ph3C+PF6-. The reaction mixture was
stirred at room temperature for 30 min. Formation of a yellow
precipitate was observed. The yellow solid was collected by
filtration, washed with toluene, and dried over vacuum. Yield: 123
mg (66%). Triphenylmethane was observed in the filtrate by NMR
(PCHP)Pd(Me) (6). 2 (143 mg, 0.276 mmol) was dissolved in
ether. To the stirred solution was added 260 µL (0.422 mmol) of
MeLi in hexane. The reaction mixture was stirred over 2 h. 31P
NMR in situ indicated quantitative formation of 6. The solution

3320 Organometallics, Vol. 26, No. 14, 2007
Weng et al.
1
and GC/MS. H NMR (CD2Cl2): δ 7.84 (s, 2H, py-H), 7.62 (d, J
solved using SIR-9224 and refined (full-matrix least-squares) using
the Oxford University Crystals for Windows program.25 All ordered
non-hydrogen atoms were refined using anisotropic displacement
parameters; hydrogen atoms were fixed at calculated geometric
positions and allowed to ride on the corresponding carbon atoms.
Each structure contained significant disorder, which was resolved
successfully for atoms separated significantly. In all cases the two-
component disorder was described with a constraint that the
occupancies of the major and minor components sum to 1.0. Major
component atoms were refined by using anisotropic displacement
parameters, while minor component atoms were refined by using
isotropic displacement parameters. For compound 2, the Pd and
Cl atoms, as well as atom C(5), were disordered, with the occupancy
of the major component at 0.827(5). If the two components were
present in equal amounts, the resultant image would be nearly C2-
symmetric about an axis passing through the midpoints of the
disordered Pd, Cl, and C atoms. The final least-squares refinement
converged to R1 ) 0.0275 (I > 2σ(I), 5166 data) and wR2 ) 0.0559
(F2, 6897 data, 257 parameters). For compound 3, the disorder of
the Pd and P atoms, as well as atoms C(4), C(5), C(6), and N(2),
could be resolved, with the occupancy of the major component at
0.918(2). If the two components were present in equal amounts,
the resultant image would be nearly Cs-symmetric, with the mirror
plane normal to the square plane and containing the Pd atom and
atom C(5). The final least-squares refinement converged to R1 )
0.0255 (I > 2σ(I), 5755 data) and wR2 ) 0.0559 (F2, 8190 data,
336 parameters). For compound 9-PF6, the Pd complex occupies a
site of crystallographic 2 symmetry containing Pd(1), Cl(1), and
) 4 Hz, 2H, py-H), 7.18 (dd, J ) 4 Hz, J ) 2 Hz, 2H, py-H), 2.91
(septet, J ) 7 Hz, 4H, CHMe2), 1.46 (dvt, JH-P ) 10 Hz, JH-H
)
7 Hz, 12H, CHMe2), 1.34 (dvt, JH-P ) 8 Hz, JH-H ) 7 Hz, 12H,
CHMe2). 13C{1H} NMR (CD2Cl2): δ 189.6 (s, PddC), 153.8 (t, J
) 11 Hz), 141.2 (s), 127.8 (s), 125.1 (t, J ) 4 Hz), 28.7 (t, J ) 10
Hz, CHMe2), 17.9 (s, two CHMe2 signals overlap). 31P{1H} NMR
(CD2Cl2): δ 125.5 (s), -143.9 (septet, JP-F ) 711 Hz). 19F NMR
(CD2Cl2): δ -76.0 (d, JP-F ) 711 Hz). Anal. Calcd for C21H34-
ClF6N2P3Pd: C, 38.03; H, 5.17. Found: C, 37.96; H, 5.03.
[(P2Cd)PdCl]+BAr4 (9-BArF ). 2 (60 mg, 0.115 mmol) was
dissolved in ca. 10 mL of CH2Cl2. To the stirred solution was added
116 mg (0.115 mmol) of Ph3C+BAr4 . The reaction mixture was
stirred at room temperature for 30 min. The volatiles were removed
under vacuum, and the residue was extracted with CH2Cl2. The
CH2Cl2 was pumped to dryness, and the resulting solid was washed
with 1 mL of pentane three times to afford the crude product. Pure
form of the title complex was obtained from recrystallization of
the crude solid out of a CH2Cl2/pentane mixture. Yield: 50 mg
F
4
F
1
F
(35%). H NMR (CD2Cl2): δ 7.72 (s, 8H, BAr4 ), 7.70 (s, 2H,
py-H), 7.56 (s, 4H, BAr4 ), 7.51 (br, s, 2H, py-H), 7.08 (dd, J ) 4
F
Hz, J ) 2 Hz, 2H, py-H), 2.91 (septet, J ) 7 Hz, 4H, CHMe2),
1.44 (dvt, JH-P ) 10 Hz, JH-H ) 7 Hz, 12H, CHMe2), 1.31 (dvt,
JH-P ) 8 Hz, JH-H ) 7 Hz, 12H, CHMe2). 13C{1H} NMR (CD2-
F
Cl2): δ 190.5 (s, PddC), 162.1 (q, JC-B ) 50 Hz, BAr4 ), 153.7
F
2
(t, J ) 11 Hz), 140.3 (s), 135.1 (s, BAr4 ), 129.2 (q, JC-F ) 31
F
1
F
Hz, BAr4 ), 127.3 (s), 123.9 (s, JC-F ) 272 Hz, CF3 of BAr4 ),
F
124.7 (t, J ) 4 Hz), 117.8 (s, BAr4 ), 28.6 (t, J ) 10 Hz, CHMe2),
-
17.6 (t, J ) 2 Hz, CHMe2), 17.5 (s, CHMe2). 31P{1H} NMR (CD2-
C(5), with no apparent disorder, while the PF6 anion occupies a
F
Cl2): δ 125.7 (s). 19F NMR (CD2Cl2): δ -65.8 (s, BAr4 ).
site of crystallographic -1 symmetry. The anion is disordered, with
the two components (atoms F(2) and F(3) and their minor
counterparts F(21) and F(31)) related approximately by a rotation
of 45° about the F(1)-P(2)-F(1)′ direction, with the occupancy
of the major component at 0.760(6). The final least-squares
refinement converged to R1 ) 0.0348 (I > 2σ(I), 3085 data) and
wR2 ) 0.0828 (F2, 3979 data, 170 parameters).
X-ray Data Collection, Solution, and Refinement for 2, 3, and
9-PF6. All operations were performed on a Bruker-Nonius Kappa
Apex2 diffractometer, using graphite-monochromated Mo KR
radiation. All diffractometer manipulations, including data collec-
tion, integration, scaling, and absorption corrections, were carried
out using the Bruker Apex2 software.23 Preliminary cell constants
were obtained from three sets of 12 frames. Data collection was
carried out at 120 K, using a frame time of 10 s (5 s for 68) and
a detector distance of 60 mm. The optimized strategy used for data
collection consisted of (four, three, and eight, respectively) phi and
omega scan sets, with 0.5° steps in phi or omega; completeness
for each structure was high (99.9%, 99.8%, and 98.8%, respec-
tively). A total of 443, 1128, and 1391, respectively, frames were
collected. Final cell constants were obtained from the xyz centroids
of 6889, 6110, and 2901, respectively, reflections after integration.
From the lack of systematic absences, the observed metric
constants, and intensity statistics, space groups P21/n, Pbca, and
C2/c were chosen initially; subsequent solution and refinement
confirmed the correctness of the initial choices. The structures were
Acknowledgment. Support of this research by the NSF
(CHE-0517798), Alfred P. Sloan Foundation (Research Fel-
lowship to O.V.O.), and Brandeis University is gratefully
acknowledged. We also thank the National Science Foundation
for the partial support of this work through grant CHE-0521047
for the purchase of a new X-ray diffractometer.
Supporting Information Available: Crystallographic informa-
tion in the form of CIF files. This material is available via the
Internet free of charge at http://pubs.acs.org.
OM700414T
(24) Altomare, A; Cascarano, G; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(25) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
(23) Apex2, Version 2 User Manual, M86-E01078; Bruker Analytical
X-ray Systems: Madison, WI, June 2006.