Highly air-stable anionic mononuclear and neutral binuclear palladium(II) complexes for C-C and C-N bond-forming reactions

Article abstract of DOI:10.1021/ic701674x

The short-bite aminobis(phosphonite), PhN{P(-OC₁₀H ₆(μ-S)C₁₀H₆O-)}₂ (2), containing a mesocyclic thioether backbone is synthesized by either treating PhN(PCl ₂)₂ with 2 equiv of thiobis(2,2′-naphthol) or reacting chlorophosphite (-OC₁₀H₆(μ-S)C ₁₀H₆O-)PCl (1) with aniline in the presence of a base. Treatment of 2 with an equimolar amount of Pd(COD)Cl₂ in the presence of H₂O affords a P-N-P-bridged and P,S-metalated binuclear complex, [PhN(P(-OC₁₀H₆(μ-S)C₁₀H₆O-)- κP)₂Pd₂Cl₂{P(-OC₁₀H ₆(μ-S)C₁₀H₆O-)(O)-κP,κS} ₂] (3), whereas the same reaction with 2 equiv of Pd(COD)Cl ₂ in the presence of H₂O and Et₃N produces the mononuclear anionic complex [{(-OC₁₀H₆-(μ-S)C ₁₀H₆O-)P(O)-κP,κS}PdCl₂](Et ₃NH) (5). By contrast, reaction of 2 with 2 equiv of Pd(COD)Cl ₂ and H₂O in the absence of Et₃N gives the hydrogen phosphonate coordinated complex [{(-OC₁₀H ₆(μ-S)C₁₀H₆O-)P(OH)}-PdCl₂] (4) which converts to the anionic complex in solution or in the presence of a base. Compound 2 on treatment with Pt(COD)X₂ (X = Cl or I) afforded P-coordinated four-membered chelate complexes [PhN(P(-OC₁₀H ₆(μ-S)-C₁₀H₆O-)-κP) ₂PtX₂] (6 X = Cl, 7 X = I). The crystal structures of compounds 2, 3, 5, and 7 are reported. Compound 3 is the first example of a crystallographically characterized binuclear palladium complex containing a bidentate bridging ligand and its hydrolyzed fragments forming metallacycles containing a palladium-phosphorus σ bond. All palladium complexes proved to be very good catalysts for the Suzuki-Miyaura and Mizoroki-Heck cross-coupling and amination reactions with excellent turnover numbers (TON up to 1.46 × 10⁵ in the case of the Suzuki-Miyaura reaction).

Full text of DOI:10.1021/ic701674x

Inorg. Chem. 2007, 46, 11316−11327
Highly Air-Stable Anionic Mononuclear and Neutral Binuclear
Palladium(II) Complexes for C C and C N Bond-Forming Reactions
−
−
Benudhar Punji,† Joel T. Mague,‡ and Maravanji S. Balakrishna*,†
Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay,
Powai, Mumbai 400 076, India, and Department of Chemistry, Tulane UniVersity,
New Orleans, Louisiana 70118
Received August 25, 2007
The short-bite aminobis(phosphonite), PhN
backbone is synthesized by either treating PhN(PCl2)2 with 2 equiv of thiobis(2,2
OC10H6( -S)C10H6O )PCl (1) with aniline in the presence of a base. Treatment of 2 with an equimolar amount
of Pd(COD)Cl2 in the presence of H2O affords a P P-bridged and P,S-metalated binuclear complex, [PhN(P(
OC10H6( -S)C10H6O )- P)2Pd2Cl2 P( OC10H6( -S)C10H6O )(O)- P, 2] (3), whereas the same reaction with 2
equiv of Pd(COD)Cl2 in the presence of H2O and Et3N produces the mononuclear anionic complex [ OC10H6-
-S)C10H6O )P(O)- P, PdCl2](Et3NH) (5). By contrast, reaction of 2 with 2 equiv of Pd(COD)Cl2 and H2O in
the absence of Et3N gives the hydrogen phosphonate coordinated complex [ OC10H6( -S)C10H6O )P(OH)
PdCl2] (4) which converts to the anionic complex in solution or in the presence of a base. Compound 2 on treatment
with Pt(COD)X2 (X Cl or I) afforded P-coordinated four-membered chelate complexes [PhN(P( OC10H6( -S)-
C10H6O )- P)2PtX2] (6 X Cl, 7 X I). The crystal structures of compounds 2, 3, 5, and 7 are reported. Compound
3 is the first example of a crystallographically characterized binuclear palladium complex containing a bidentate
bridging ligand and its hydrolyzed fragments forming metallacycles containing a palladium phosphorus bond. All
palladium complexes proved to be very good catalysts for the Suzuki Miyaura and Mizoroki Heck cross-coupling
105 in the case of the Suzuki
Miyaura
{P(−OC10H6(µ-S)C10H6O−)} (2), containing a mesocyclic thioether
2
′
-naphthol) or reacting chlorophosphite
(
−
µ
−
−N−
−
µ
−
κ
{
−
µ
−
κ κS}
{(−
(
µ
−
κ κS}
{
(−
µ
−
}-
)
−
µ
−
κ
)
)
−
σ
−
−
and amination reactions with excellent turnover numbers (TON up to 1.46
reaction).
×
−
Introduction
ligands that can be handled under normal atmospheric
conditions. Complexes such as Pd(PPh3)4 are highly air and
moisture sensitive and often form phosphido-bridged dimers
which are catalytically inactive. Further, the dissociated
phosphines in solution can be readily oxidized to give Ph3Pd
O, which prevents regeneration of the catalyst, thereby
reducing the catalytic efficiency. In order to overcome these
challenges, the following strategies are considered: (i)
Protecting the P(III) center as a BH3 adduct until in situ
generation of the active catalytic species and (ii) stabilizing
the P(III) center in the form of a suitable P(V) species which
can undergo tautomerism in the presence of a transition metal
to give a phosphinous acid type derivative as pointed out by
Chatt and Heaton (Scheme 1).2 Since the R3P:BH3 adduct is
unstable toward the routinely used catalytic reaction condi-
Despite a plethora of phosphorus ligands available,1 the
enthusiasm to generate new ones is remarkable mainly due
to the demand from industry for economical and robust
* To whom correspondence should be addressed. Phone: + 91 22 2576
7181. Fax: + 91 22 2576 7152/2572 3480. E-mail:krishna@chem.iitb.ac.in.
† Indian Institute of Technology.
‡ Tulane University.
(1) For examples, see: (a) Homogeneous Catalysis with Metal Phosphine
Complexes; Pignolet, L. H., Ed.; Plenum Press: New York, 1983. (b)
Applied Homogeneous Catalysis with Organometallic Compounds;
Cornils, B., Herrmann, W. H., Eds.; VCH: Weinheim, 1996. (c) Bader,
A.; Lindner, E. Coord. Chem. ReV. 1991, 108, 27-110. (d) Bal-
akrishna, M. S.; Reddy, V. S.; Krishnamurthy, S. S.; Nixon, J. F.; St.
Laurent, J. C. T. R. B. Coord. Chem. ReV. 1994, 129, 1-90. (e)
Dilworth, J. R.; Wheatley, N. Coord. Chem. ReV. 2000, 199, 89-
158. (f) Appleby, T.; Woollins, J. D. Coord. Chem. ReV. 2002, 235,
121-140. (g) Le Floch, P. Coord. Chem. ReV. 2006, 250, 627-681.
(h) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-2483. (i)
Suzuki, A. In Metal Catalysed Cross Coupling Reactions; Diederich,
F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; pp 49-97 and
references therein. (j) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron
2002, 58, 9633-9695.
(2) (a) Chatt, J.; Heaton, B. T. J. Chem. Soc. A 1968, 2745-2757. See
also: (b) Dixon, K. R.; Rattray, A. D. Can. J. Chem. 1971, 49, 3997-
4004. (c) Lindner, E.; Schilling, B. Chem. Ber. 1977, 110, 3266-
3271.
11316 Inorganic Chemistry, Vol. 46, No. 26, 2007
10.1021/ic701674x CCC: $37.00
© 2007 American Chemical Society
Published on Web 11/15/2007

Air-Stable Palladium(II) Complexes
Scheme 1
activity in addition to catalysis. The P-O bonds present in
phosphonites derived from naphthyl derivatives are resistant
to hydrolytic cleavage but can readily form phosphonate
anion if they contain a P-N or P-halogen bond as they are
prone to hydrolysis. Further, the anionic complexes men-
tioned above have never been isolated and characterized. In
this context, we report the first examples of fully character-
ized, readily accessible, and air stable anionic mononuclear
as well as neutral binuclear PdII complexes and their catalytic
utility in C-C and C-N cross-coupling reactions.
Scheme 2
Scheme 3. Formation of Active Anionic Catalytic Complex
Experimental Section
All experimental manipulations were carried out under an
atmosphere of dry nitrogen or argon using Schlenk techniques
unless otherwise stated. Solvents were dried and distilled prior to
use by conventional methods. Bis(2-hydroxy-1-naphthyl)sulfide,6
chlorophosphite (1),7 PhN(PCl2)2,8 M(COD)Cl2 (M ) Pd, Pt),9 and
Pt(COD)I210 were prepared according to the published procedures.
Other reagents were obtained from commercial sources and used
1
after purification. The H and 31P{1H} NMR (δ in ppm) spectra
were obtained on a Varian VRX 400 spectrometer operating at
frequencies of 400 and 162 MHz, respectively. The spectra were
recorded in CDCl3 (or DMSO-d6) solutions with CDCl3 (or DMSO-
d6) as an internal lock; TMS and 85% H3PO4 were used as internal
and external standards for 1H and 31P{1H} NMR, respectively.
Positive shifts lie downfield of the standard in all cases. Infrared
spectra were recorded on a Nicolet Impact 400 FT IR instrument
as a KBr disk. Microanalyses were carried out on a Carlo Erba
(model 1106) elemental analyzer. Electrospray ionization (EI) mass
spectrometry experiments were carried out using Waters Q-Tof
micro(YA-105). Melting points of all compounds were determined
on a Veego melting point apparatus and are uncorrected. GC
analyses were performed on a Perkin-Elmer Clarus 500 GC fitted
with a FID detector and packed column.
Synthesis of PhN{P(-OC10H6(µ-S)C10H6O-)}2 (2). Method
I. A solution of PhN(PCl2)2 (0.69 g, 2.36 mmol) in THF (20 mL)
was added dropwise to a solution of bis(2-hydroxy-1-naphthyl)-
sulfide (1.5 g, 4.71 mmol), Et3N (1.37 mL, 9.89 mmol), and a
catalytic amount of DMAP (4-N,N-dimethylaminopyridine) in THF
(60 mL) at -15 °C. The reaction mixture was warmed to room
temperature and stirred for an additional 20 h. The solvent was
removed under reduced pressure, and the white residue obtained
was dissolved in 40 mL of toluene and filtered through celite to
remove the Et3N‚HCl salt. The filtrate obtained was concentrated
under reduced pressure and stored at -25 °C to give white
crystalline product of 2. Yield: 83% (1.54 g).
tions (especially toward acids and Lewis bases), the second
option looks reasonable and also is supported by the
following reaction of Pt(PPh3)4 with phosphinous acid
(Scheme 2).3
Li and others employed phosphinous acid complexes of
type I for palladium-catalyzed cross-coupling reactions
(Scheme 3).4 These dimers can be readily deprotonated in
the presence of a base to yield an electron-rich anionic
species (II) which was thought to be a catalyst for carbon-
carbon coupling reactions. It is speculated that the anionic
species facilitates the oxidative addition reaction and also
stabilizes the Pd0 species in the catalytic cycle.5 Although
this strategy has been explored in homogeneous catalysis of
these coupling reactions, the active species involved in the
catalytic process have not been fully identified and the
mechanistic details are not yet clear. Tertiary phosphines with
sterically bulky groups are often employed for cross-coupling
reactions in organic synthesis with excellent results. After
scanning several substituted aromatic derivatives we found
that biphenyl groups showed good activity and are easy to
make. The donor atoms such as sulfur can be readily
incorporated into the framework. Further, compounds with
biphenyl groups are known for their excellent photophysical
Method II. A mixture of aniline (0.24 mL, 2.63 mmol) and Et3N
(2.67 mL, 19.2 mmol) in toluene (30 mL) was added dropwise to
a solution of chlorophosphite (2 g, 5.26 mmol) also in toluene (50
mL) at -15 °C. The reaction mixture was warmed to room
temperature and stirred for an additional 12 h. The suspension
obtained was filtered through celite to remove amine hydrochloride;
the filtrate was concentrated to 20 mL under reduced pressure and
on storing at -25 °C gave product 2 as colorless crystals. Yield:
(3) Beaulieu, W. B.; Rauchfuss, T. B.; Roundhill, D. M. Inorg. Chem.
1975, 14, 1732-1734.
(4) (a) Li, G. Y. Angew. Chem., Int. Ed. 2001, 40, 1513-1516. (b) Li, G.
Y. J. Org. Chem. 2002, 67, 3643-3650. (c) Li, G. Y.; Zheng, G.;
Noonan, A. F. J. Org. Chem. 2001, 66, 8677-8681. (d) Arif, A. M.;
Bright, T. A.; Jones, R. A. J. Coord. Chem. 1987, 16, 45-50. (e)
Cobley, C. J.; van den Heuvel, M.; Abbadi, A.; de Vries, J. G.
Tetrahedron Lett. 2000, 41, 2467-2470. (f) Ghaffar, T.; Parkins, A.
W. Tetrahedron Lett. 1995, 36, 8657-8660. (g) Goerlich, J. R.;
Fischer, A.; Jones, P. G.; Schmutzler, R. Z. Z. Naturforsch. B 1994,
49, 801-811.
(6) Mercado, R. M. L.; Chandrasekaran, A.; Day, R. O.; Holmes, R. R.
Organometallics 1999, 18, 906-914.
(7) Punji, B.; Mague, J. T.; Balakrishna, M. S. Inorg. Chem. 2006, 45,
9454-9464.
(5) (a) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314-321. (b)
Grushin, V. V.; Alper, H. Chem. ReV. 1994, 94, 1047-1062. (c)
Grushin, V. V.; Alper, H. Topics in Organometallic Chemistry; Murai,
S., Ed.; Springer: New York, 1999; Vol. 3, pp 193-226 and references
there in.
(8) Davies, A. R.; Dronsfield, A. T.; Haszeldine, R. N.; Taylor, D. R. J.
Chem. Soc., Perkin Trans. 1973, 1, 379-385.
(9) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346-349.
(10) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-
428.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11317

Punji et al.
90% (1.86 g). Mp: 168-170 °C. Anal. Calcd for C46H29NO4P2S2:
Synthesis of [PhN(P(-OC10H6(µ-S)C10H6O-)-κP)2PtI2] (7).
This was synthesized by a procedure similar to that of 6 using
aminobis(phosphonite) 2 (0.056 g, 0.072 mmol) and Pt(COD)I2
(0.04 g, 0.072 mmol). Yield: 78% (0.069 g). Mp: 250 °C (dec).
Anal. Calcd for C46H29I2NO4P2S2Pt: C, 44.75; H, 2.37; N, 1.13;
S, 5.19. Found: C, 44.71; H, 2.35; N, 1.09; S, 5.17. 1H NMR (400
MHz, DMSO-d6, δ): 8.65 (d, 4H, Ar, 3JHH ) 8.4 Hz), 7.21-8.17
(m, 20H, Ar, 5H, Ph). 31P{1H} NMR (162 MHz, DMSO-d6, δ):
C, 70.31; H, 3.72; N, 1.78; S, 8.16. Found: C, 70.29; H, 3.71; N,
1
1.75; S, 8.12. H NMR (400 MHz, CDCl3, δ): 8.76 (d, 4H, Ar,
3JHH ) 8.4 Hz), 7.65-7.79 (m, 8H, Ar, 5H, Ph), 7.61 (t, 4H, Ar,
3
3JHH ) 6.8 Hz), 7.59 (t, 4H, Ar, JHH ) 6.8 Hz), 7.30 (d, 4H, Ar,
3JHH ) 8.8 Hz). 31P{1H} NMR (162 MHz, CDCl3, δ): 127.5 (s).
MS (EI): M+, 786.2.
Synthesis of [PhN(P(-OC10H6(µ-S)C10H6O-)-κP)2Pd2Cl2-
{P(-OC10H6(µ-S)C10H6O-) (O)-κP,κS}2] (3). A solution of Pd-
(COD)Cl2 (0.05 g, 0.175 mmol) in dichloromethane (6 mL) was
added dropwise to a dichloromethane (10 mL) solution of 2 (0.137
g, 0.175 mmol) followed by addition of H2O (3.15 µL, 0.175 mmol).
The reaction mixture was stirred for 1 h at room temperature. The
solution was concentrated under vacuum, and diethyl ether was
added to precipitate a yellowish solid which was filtered off and
dried. Recrystallization from a CH2Cl2/diethyl ether mixture (1:1)
gave analytically pure crystals of 3. Yield: 68% (0.112 g). Mp:
220-222 °C. Anal. Calcd for C86H53NO10P4S4Pd2Cl2‚CH2Cl2: C,
55.55; H, 2.95; N, 0.74; S, 6.82. Found: C, 55.52; H, 2.93; N,
1
76.9 (s), JPtP ) 6334 Hz.
Catalysis. In a two-necked round-bottom flask under an atmo-
sphere of nitrogen were placed the appropriate amount of catalyst
solution and 5 mL of solvent (methanol or toluene). The correct
amount of catalyst was added as a methanol solution made up by
multiple volumetric dilutions of stock solutions. After stirring for
5 min, aryl bromide (0.5 mmol), phenylboronic acid (0.75 mmol),
and K2CO3 (0.138 g, 1 mmol) for Suzuki reaction, aryl bromide
(0.5 mmol), tert-butylacrylate (0.088 mL, 0.6 mmol), and K2CO3
(0.138 g, 1 mmol) for Heck coupling reaction, and aryl bromide
(0.5 mmol), morpholine (0.052 mL, 0.6 mmol), and NaOtBu (0.058
g, 0.6 mmol) for amination reaction were introduced into the
reaction flask. The mixture was heated at 60 or 80 or 100 °C for
the required time under an atmosphere of nitrogen (the course of
the reaction was monitored by GC analysis), and the solvent was
removed under reduced pressure. The residual mixture was diluted
with H2O (8 mL) and Et2O (8 mL) followed by extraction with
Et2O (2 × 6 mL). The combined organic fractions were dried
(MgSO4) and stripped of the solvent under vacuum, and the residue
obtained was redissolved in 5 mL of dichloromethane. An aliquot
was taken with a syringe and subjected to GC analysis. Yields were
calculated versus aryl bromides or dodecane as an internal standard.
1
0.72; S, 6.78. IR (KBr disk, cm-1): υ(PdO), 1212 s. H NMR
3
(400 MHz, CDCl3, δ): 8.64 (d, 4H, Ar, JHH ) 8.4 Hz), 7.07-
3
8.63 (m, 40H, Ar, 5H, Ph), 6.01 (d, 4H, Ar, JHH ) 8.8 Hz), 5.29
(s, 2H, CH2Cl2). 31P{1H} NMR (162 MHz, CDCl3, δ): 100.8 (d,
2
2P, N-P), 47.0 (d, 2P, P(O)), JPP ) 104 Hz.
Synthesis of [{(-OC10H6(µ-S)C10H6O-)P(OH)}PdCl2] (4).
A solution of Pd(COD)Cl2 (0.06 g, 0.21 mmol) in dichloro-
methane (8 mL) was added dropwise to a dichloromethane (8 mL)
solution of 2 (0.083 g, 0.105 mmol) followed by addition of H2O
(3.8 µL, 0.21 mmol). The reaction mixture was stirred for 1 h at
room temperature and filtered through celite. The filtrate was
concentrated under vacuum and diluted with diethyl ether (5 mL)
to give analytically pure product of 4 as yellow crystals. Yield:
82% (0.093 g). Mp: 216-218 °C. Anal. Calcd for C20H13Cl2O3-
PSPd: C, 44.35; H, 2.42; S, 5.92. Found: C, 44.52; H, 2.48; S,
5.81. 1H NMR (400 MHz, CDCl3, δ): 8.93 (d, 2H, Ar, 3JHH ) 8.4
X-ray Crystallography. Crystals of 2, 5, and 7 were mounted
in a Cryoloop with a drop of Paratone oil and placed in the cold
nitrogen stream of the Kryoflex attachment of the Bruker Smart
APEX CCD diffractometer. A full sphere of data was collected
for each using three sets of 400 scans in ω (0.5° per scan) at æ )
0°, 90°, and 180° plus two sets of 800 scans in æ (0.45° per scan)
at ω ) -30° and 210° using the SMART software package.11 The
raw data were reduced to F2 values using the SAINT+ software,12
and a global refinement of unit cell parameters using 6790-8770
reflections chosen from the full data sets was performed. Multiple
measurements of equivalent reflections provided the basis for an
empirical absorption correction as well as a correction for any
crystal deterioration during data collection (SADABS13). The
structures were solved by direct methods and refined by full-matrix
least-squares procedures using the SHELXTL program package.14
Hydrogen atoms were placed in calculated positions and included
as riding contributions with isotropic displacement parameters tied
to those of the attached non-hydrogen atoms with the exception of
5 where the hydrogen attached to nitrogen in the cation was refined.
The crystal of 3 was mounted on a, Oxford Diffraction XCALI-
BUR-S CCD system equipped with graphite-monochromated Mo
KR radiation (0.71073 Å). Data was collected by the ω-2θ scan
mode, and absorption correction was applied using multiscan. The
structure was solved by direct methods SHELXS 97 and refined
by full-matrix least-squares against F2 using SHELXL 97 software.14b
Non-hydrogen atoms were refined with anisotropic thermal param-
3
3
Hz), 8.04 (d, 2H, Ar, JHH ) 9.2 Hz), 7.88 (d, 2H, Ar, JHH ) 8.4
Hz), 7.28-7.85 (m, 6H, Ar). 31P{1H} NMR (162 MHz, CDCl3,
δ): 85.1 (s).
Synthesis of [{(-OC10H6(µ-S)C10H6O-)P(O)-κP,κS}PdCl2]
(Et3NH) (5). This was synthesized similar to that of 4 by reacting
2 (0.083 g, 0.105 mmol) with Pd(COD)Cl2 (0.06 g, 0.21 mmol),
H2O (3.8 µL, 0.21 mmol), and Et3N (29 µL, 0.21 mmol) in THF
(20 mL). Yield: 68% (0.092 g). Mp: 230 °C (dec). Anal. Calcd
for C26H28Cl2NO3PSPd: C, 48.57; H, 4.39; N, 2.18; S, 4.99.
Found: C, 48.51; H, 4.34; N, 2.15; S, 4.94. IR (KBr disk, cm-1):
1
υ(PdO), 1206 s. H NMR (400 MHz, CDCl3, δ): 9.98 (br s, 1H,
NH), 8.84 (d, 2H, Ar, 3JHH ) 8.8 Hz), 7.88 (d, 2H, Ar, 3JHH ) 9.2
3
3
Hz), 7.76 (d, 2H, Ar, JHH ) 8.0 Hz), 7.69 (t, 2H, Ar, JHH ) 7.6
3
3
Hz), 7.46 (t, 2H, Ar, JHH ) 7.6 Hz), 7.31 (d, 2H, Ar, JHH ) 8.8
3
Hz), 3.18 (quartet, 6H, CH2, JHH ) 5.2 Hz), 1.33 (t, 9H, CH3,
3JHH ) 7.2 Hz). 31P{1H} NMR (162 MHz, CDCl3, δ): 48.7 (s).
Synthesis of [PhN(P(-OC10H6(µ-S)C10H6O-)-κP)2PtCl2] (6).
A solution of Pt(COD)Cl2 (0.03 g, 0.08 mmol) in dichloromethane
(6 mL) was added dropwise to a solution of 2 (0.063 g, 0.08 mmol)
also in dichloromethane (8 mL) at room temperature, and the
reaction mixture was stirred for 6 h. The solution was concentrated
under vacuum and layered with petroleum ether to give crystalline
product 6. Yield: 87% (0.073 g). Mp: 260 °C (dec). Anal. Calcd
for C46H29Cl2NO4P2S2Pt: C, 52.53; H, 2.78; N, 1.33; S, 6.08.
(11) SMART, Version 5.625; Bruker-AXS: Madison, WI, 2000.
(12) SAINT+, Version 6.35A; Bruker-AXS: Madison, WI, 2002.
(13) Sheldrick, G. M. SADABS, Version 2.05; University of Go¨ttingen:
Go¨ttingen, Germany, 2002.
(14) (a) SHELXTL, Version 6.10; Bruker-AXS: Madison, WI, 2000. (b)
Sheldrick, G. M. SHELXS97 and SHELXL97; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997.
1
Found: C, 52.49; H, 2.76; N, 1.31; S, 6.05. H NMR (400 MHz,
3
CDCl3, δ): 8.62 (d, 4H, Ar, JHH ) 8.8 Hz), 7.23-7.69 (m, 20H,
1
Ar, 5H, Ph). 31P{1H} NMR (162 MHz, CDCl3, δ): 71.9 (s), JPtP
) 6525 Hz.
11318 Inorganic Chemistry, Vol. 46, No. 26, 2007

Air-Stable Palladium(II) Complexes
Table 1. Crystallographic Data for Compounds 2, 3, 5, and 7
2
3
5
7
formula
mol wt
cryst syst
cryst size (mm)
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C46H29NO4P2S2.CH2Cl2
870.71
C87H55Cl4NO11P4Pd2S4
1897.04
triclinic
C26H28Cl2NO3PSPd‚CH2Cl2
727.75
triclinic
C46H29I2NO4P2PtS2
1234.7
monoclinic
0.07 × 0.09 × 0.22
P21/n (No. 14)
10.105(1)
20.162(1)
20.186(1)
90
102.732(1)
90
4011.5(4)
4
monoclinic
0.11 × 0.15 × 0.16
P2/n (No. 13)
18.068(2)
11.882(1)
23.402(2)
90
111.127(1)
90
4686.3(8)
2
0.25 × 0.20 × 0.15
P1h (No. 2)
13.854(1)
17.168(2)
21.344(3)
80.239(1)
72.418(1)
74.730(1)
4646.1(1)
2
0.13 × 0.25 × 0.29
P1h (No. 2)
8.207(7)
12.610(1)
15.004(1)
101.169(1)
101.788(1)
97.862(1)
1465.9(2)
2
Z
F
calcd‚g cm-3
1.442
0.394
1792
1.356
0.714
1912
1.649
1.154
736
1.773
4.512
2392
µ (Mo KR), mm-1
F (000)
temp. (K)
100(2)
293(2)
100(2)
100(2)
θ (min, max) (deg)
2.1, 28.3
1.03
0.0563
2.97, 25.00
0.889
0.0747
2.4, 28.3
1.04
0.0278
2.1, 28.3
1.14
0.0414
GOF (F2)
a
R1
b
wR2
0.1451
0.1842
0.0694
0.0957
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) {∑w[(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
2
2
2
Scheme 4a
a (i) PhN(PCl2)2, Et3N, DMAP, THF, -15 °C; (ii) PhNH2, Et3N, toluene, -15 °C.
31P NMR spectrum of 2 shows a single resonance at 127.5
ppm. In the mass spectrum a peak is observed at m/z 786.2
for the molecular ion. The structure and molecular composi-
tion of the ligand 2 were further confirmed by 1H NMR data,
elemental analysis, and single-crystal X-ray structure deter-
mination.
Metal Complexes. Aminophosphines containing P-N
bond(s) are known to undergo hydrolytic cleavage when they
are exposed to moisture, acid, or base impurities during the
complexation reactions.16 This type of P-N bond cleavage
resulted in air-stable phosphine oxides (RR′P(O)H) which
in the presence transition metals can undergo tautomerization
to the less stable phosphinous acid (RR′POH) and subse-
quently coordinate to the metal centers to form metal
eters. All hydrogen atoms were geometrically fixed and allowed
to refine using a riding model. Crystallographic data are summarized
in Table 1.
Results and Discussion
Ligand Synthesis. Recently we reported the synthesis of
a novel 10-membered heterocycle PhN(PCl)2{(-OC6H2(t-
Bu)2)(µ-S)((tBu)2C6H2O-)} by reacting phenylaminobis-
(dichlorophosphine), PhN(PCl2)2, with 2,2′-thiobis(4,6-di-
tert-butylphenol) in a 1:1 ratio.15 A similar reaction between
thiobis(2,2′-naphthol) and PhN(PCl2)2 resulted in formation
of a mixture of the 10-membered heterocycle PhN(PCl)2{-
OC10H6(µ-S)C10H6O-} and the aminobis(phosphonite) PhN-
{P(-OC10H6(µ-S)C10H6O-)}2 (2) as indicated by 31P NMR
data. Attempts to separate them from the reaction mixture
have been unsuccessful; however, 2 was synthesized in good
yield by treatment of PhN(PCl2)2 with 2 equiv of thiobis-
(2,2′-naphthol) in the presence of Et3N and a catalytic amount
of DMAP (4-N,N-dimethylaminopyridine) (Scheme 4). In
another straightforward method reaction of aniline with 2
equiv of chlorophosphite (-OC10H6(µ-S)C10H6O-)PCl (1)
in the presence of an excess of Et3N at -15 °C also afforded
2 in good yield. The second method is more convenient as
it gives comparatively pure product in excellent yield. The
(16) (a) Balakrishna, M. S.; Krishnamurthy, S. S. Ind. J. Chem. 1991, 30A,
536-537. (b) Burrows, A. D.; Mahon, M. F.; Palmer, M. T.; Varrone,
M. Inorg. Chem. 2002, 41, 1695-1697. (c) Priya, S.; Balakrishna,
M. S.; Mague, J. T. J. Organomet. Chem. 2003, 679, 116-124.
(17) (a) Dubrovina, N. V.; Borner, A. Angew. Chem., Int. Ed. 2004, 43,
5883-5886. (b) Han, L.-B.; Mirzaei, F.; Zhao, C.-Q.; Tanaka, M. J.
Am. Chem. Soc. 2000, 122, 5407-5408. (c) Han, L.-B.; Tanaka, M.
J. Am. Chem. Soc. 1996, 118, 1571-1572. (d) Zhao, C.-Q.; Han, L.-
B.; Tanaka, M. Organometallics 2000, 19, 4196-4198. (e) Acker-
mann, L.; Born, R.; Spatz, J. H.; Meyer, D. Angew. Chem., Int. Ed.
2005, 44, 7216-7219. (f) Levine, A. M.; Stockland, R. A.; Clark, R.;
Guzei, I. Organometallics 2002, 21, 3278-3284. (g) Stockland, R.
A.; Levine, A. M.; Giovine, M. T.; Guzei, I. A.; Cannistra, J. C.
Organometallics 2004, 23, 647-656. (h) Pryjomska, I.; Bartosz-
Bechowski, H.; Ciunik, Z.; Trzeciak, A. M.; Zio`lkowski, J. J. Dalton
Trans. 2006, 213-220.
(15) Balakrishna, M. S.; Panda, R.; Mague, J. T. Inorg. Chem. 2001, 40,
5620-5625.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11319

Punji et al.
Scheme 5a
a (i) Pd(COD)Cl2, H2O, CH2Cl2; (ii) 2Pd(COD)Cl2, H2O, CH2Cl2; (iii) Et3N, THF; (iv) 2Pd(COD)Cl2, H2O, Et3N, THF.
Scheme 6. Probable Pathway for Formation of Complex 3
phosphinous acid complexes (Scheme 3). These phosphinous
acid metal complexes can produce neutral or anionic
complexes via HCl elimination which are excellent sources
of catalyst precursors.4c,17 With this in mind, the aminobis-
(phosphonite) 2 was treated with 1 equiv of Pd(COD)Cl2 in
the presence of H2O at room temperature which resulted in
formation of a P-N-P (ligand 2) bridged and thioether-
phosphonate-cyclometalated binuclear complex [PhN(P(-
OC10H6(µ-S)C10H6O-)-κP)2Pd2Cl2{P(-OC10H6(µ-S)C10H6O-
)(O)-κP,κ S}2] (3). However, the 1:2 reaction of 2 with
Pd(COD)Cl2 in the presence of H2O and Et3N gave the
anionic mononuclear complex [{(-OC10H6(µ-S)C10H6O-)P-
(O)-κP,κS}PdCl2] (Et3NH) (5) in moderate yield. The bi-
nuclear complex 3 formed as a result of the fission of the
P-N bond followed by oxidation of the P center on 0.5 equiv
of 2, whereas the remaining 0.5 equiv of the ligand 2 anchors
the two cyclometalated PdII centers in a bridged bidentate
mode of coordination (Scheme 5). Similarly, P-N bond
fission of the whole aminobis(phosphonite) resulted in the
hydrogen phosphonate which subsequently forms the anionic
complex 5. The complex [{(-OC10H6(µ-S)C10H6O-)P-
(OH)}PdCl2] (4) was obtained in the reaction of 2 with 2
equiv of Pd(COD)Cl2 and H2O in the absence of Et3N.
Complex 4 can be readily converted into the anionic complex
5 by treating it with Et3N. Complex 4 can be either in the
cyclometalated monomeric [{(-OC10H6(µ-S)C10H6O-)P-
11320 Inorganic Chemistry, Vol. 46, No. 26, 2007

Air-Stable Palladium(II) Complexes
Scheme 7. Probable Pathway for Formation of Complexes 4 and 5
Scheme 8
(OH)-κP,κS}PdCl2 (4a) or in the chloro-bridged dimeric form
[{(-OC10H6(µ-S)C10H6O-)P(OH)-κP}Pd(µ-Cl)Cl]2 (4b). Al-
though palladium complexes of simple monodentate phos-
phonate ligands such as HP(O)(OR)2 (R ) alkyl, aryl) are
known, only a few of them are well characterized.17f-h
Palladium complexes 3 and 5 are unique as similar types of
palladium complexes containing metalated thioether-phos-
phonates do not appear in the literature.
The phosphorus-31 NMR spectrum of complex 3 shows
two doublets centered at 100.8 and 47.0 ppm for the PIII and
P(O) phosphorus centers, respectively, with a 2JPP coupling
of 104 Hz, while for complex 4 a sharp singlet is observed
at 85.1 ppm. In the IR spectrum of 3 υ(PdO) appears at
1212 cm-1. The 31P NMR spectrum of complex 5 consists
of a singlet at 48.7 ppm, and the IR spectrum shows υ(Pd
O) at 1206 cm-1. The 1H NMR spectrum of complex 5 shows
a broad singlet at 9.98 ppm for the NH proton, a quartet
(3.18 ppm) and triplet (1.33 ppm) for the Et3NH+ cation.
The structures of 3 and 5 were determined by single-crystal
X-ray diffraction studies.
A plausible pathway for formation of complex 3 is given
in Scheme 6. The aminobis(phosphonite) reacts with Pd-
(COD)Cl2 to form a binuclear complex A, which on reaction
with H2O cleaves the P-N bonds of one of the ligands to
form B with elimination of aniline. Complex B then
eliminates 2 mol of HCl to form the chloro-bridged complex
C, which on further rearrangement involves sulfur coordina-
tion to form complex 3. Further addition of an excess of
water to 3 did not give complexes of the type 4 or 5.
However, addition of another mole of Pd(COD)Cl2 to
complex 3 in the presence of Et3N resulted in formation of
complex 5 as ascertained from phosphorus-31 NMR data.
The most plausible pathways for formation of complexes 4
and 5 are depicted in Scheme 7 (Path I). Formation of these
Inorganic Chemistry, Vol. 46, No. 26, 2007 11321

Punji et al.
Scheme 9. Plausible Catalytic Cycle for the Cross-Coupling
Reactions
Figure 1. Molecular structure of 2. For clarity, solvent (CH2Cl2) and all
hydrogen atoms have been omitted. Thermal ellipsoids are drawn at the
50% probability level.
and 6334 Hz, respectively. These coupling constants are
significantly larger than in platinum complexes of similar
ligands reported in the literature7,18 and indicate a strong
σ-donor capability for the aminobis(phosphonite) which may
arise due to the coordinative tendencies of sulfur toward the
phosphorus atoms (vide infra).
Crystal and Molecular Structures of Compounds 2, 3,
5, and 7. The molecular structures of compounds 2, 3, 5,
and 7 with atom numbering schemes are depicted in Figures
1-4, and selected bond parameters are summarized in
Table 2.
complexes follows a pathway similar to that described above
until generation of B, which can liberate another molecule
of aniline via P-N bond cleavage and undergo a dispro-
portionation reaction with the unreacted Pd(COD)Cl2 present
in solution. Deprotonation of complex 4 in the presence of
a base can form the metallacyclic complex 5. Formation of
complex 5 can also follow path II (Scheme 7) by initial
formation of a P,S-chelated binuclear complex (D) followed
by hydrolysis and abstraction of a proton. However, recent
investigations have shown that compound 2 does not form
a P,S-chelate complex with palladium unless it undergoes
P-N bond hydrolysis.7 Hence, path II can be ruled out for
formation of anionic complex 5. The 1:1 reaction between
2 and Pd(COD)Cl2 produces complex 3, whereas the 1:2
reaction affords either 4 or 5. Hence, from both reaction
profiles it is concluded that the palladium precursor plays a
major role in the P-N bond cleavage to form complexes 3
or 5, although an H2O molecule evidently assists in the P-N
bond cleavage. Attempts to isolate the binuclear complex
[PhN(P(-OC10H6(µ-S)C10H6O-)-κP)2PdCl2]2 (A) was un-
successful as it readily cleaves one of the bridging ligands
and rearranges to give complex 3. In contrast, platinum forms
(complexes 6 and 7) moderately stable four-membered
chelate complexes with ligand 2 which are resistant to
hydrolytic cleavage of P-N bonds. Generally, palladium-
(II) complexes are more reactive in terms of both thermo-
dynamic and kinetic aspects, whereas the platinum(II)
analogues show kinetic inertness.
Compound 2 has approximate 2-fold rotation symmetry
following the classification of similar PNP compounds.19
Similar to the P-S containing eight-membered cyclic mono-
phosphite structures reported by Holmes and co-workers,20
the aminobis(phosphonite) 2 contains two such cyclic phos-
phite units in which the geometries around the phosphorus
atoms can be considered as pseudo trigonal bipyramidal
(TBP). Both eight-membered rings contain phosphorus and
sulfur atoms in a boat-like syn conformation. The sulfur atom
in the ring shows coordinative tendencies toward phosphorus
so that the geometry about the latter departs from pyramidal
toward a pseudo TBP. The P-S distances 2.993(1) and
2.967(1) Å are comparable with those in similar structures
(see Table 3) and considerably less than the sum of the van
der Waals’ radii for phosphorus and sulfur (3.65 Å)21 but
noticeably longer than the sum of their covalent radii (2.12
Å).22 Following the procedure of Day et al., the percent of
displacement from pyramidal toward TBP is found to be
42.9% and 44.7% for the P1 and P2 centers, respectively.23
The axial S-P-N angles are 166.46° and 167.99° for S1-
(18) (a) Slawin, A. M. Z.; Wainwright, M.; Woollins, J. D. J. Chem. Soc.,
Dalton Trans. 2002, 513-519. (b) Calabro`, G.; Drommi, D.; Graiff,
C.; Faraone, F.; Tiripicchio, A. Eur. J. Inorg. Chem. 2004, 1447-
1453. (c) Balakrishna, M. S.; George, P. P.; Mague, J. T. J. Organomet.
Chem. 2004, 689, 3388-3394.
(19) Calabro`, G.; Drommi, D.; Bruno, G.; Faraone, F. Dalton Trans. 2004,
81-89.
(20) (a) Sherlock, D. J.; Chandrasekaran, A.; Day, R. O.; Holmes, R. R.
Inorg. Chem. 1997, 36, 5082-5089. (b) Sherlock, D. J.; Chandraseka-
ran, A.; Day, R. O.; Holmes, R. R. J. Am. Chem. Soc. 1997, 119,
1317-1322.
(21) Bondi, A. J. Phys. Chem. 1964, 68, 441-451.
(22) Sutton, L. Tables of Interatomic Distances and Configuration in
Molecules and Ions; Special Publication Nos. 11 and 18; The Chemical
Society: London, 1958 and 1965.
Treatment of aminobis(phosphonite) 2 with Pt(COD)X2
(X ) Cl and I) in dichloromethane produces the four-
membered chelate complexes [PhN(P(-OC10H6(µ-S)C10H6O-
)-κP)2PtX2], (6, X ) Cl; 7, X ) I) in good yield (Scheme
8). The 31P NMR spectra of complexes 6 and 7 show single
resonances at 71.9 and 76.9 ppm with 1JPtP couplings of 6525
(23) Day, R. O.; Prakasha, T. K.; Holmes, R. R.; Eckert, H. Organometallics
1994, 13, 1285-1293.
11322 Inorganic Chemistry, Vol. 46, No. 26, 2007

Air-Stable Palladium(II) Complexes
Figure 4. Molecular structure of 7. For clarity, solvent (THF) and all
hydrogen atoms have been omitted. Thermal ellipsoids are drawn at the
50% probability level.
is coordinated to P, S, and one chloride ligand with the fourth
coordination site being occupied by the phosphonate phos-
phorus via a σ bond. Each sulfur atom is syn to the nearest
palladium atom with S‚‚‚Pd distances of 3.464(3) (Pd2‚‚‚
S3) and 3.688(3) Å (Pd1‚‚‚S2) which are too long for there
to be any significant interaction. The Pd-P bond distances
are 2.221(3) (P1-Pd1) and 2.224(2) Å (P4-Pd2). The two
palladium atoms are separated by 3.253(1) Å, which is
essentially the same as the sum of their van der Waals’ radii
(3.26 Å) and is therefore not considered to indicate a bonding
interaction. The P-N-P angle (P(2)-N(1)-P(3) ) 117.5-
(4)°) in the aminobis(phosphonite) ligand in complex 3 has
increased upon complexation approximately 5° compared to
that in the free ligand (P1-N-P2 ) 113.66(1)°).
Figure 2. (a) Molecular structure of 3. For clarity, solvent (CH2Cl2) and
all hydrogen atoms have been omitted. (b) Core view of complex 3. Thermal
ellipsoids are drawn at the 30% probability level.
In the structure of complex 5 the palladium center is
slightly distorted from the expected square-planar geometry.
The PdO (1.478(2) Å) and P-O (1.629(1) and 1.641(2) Å)
bond lengths are typical of those in similar metal complexes
containing phosphonate groups.17f,24 The Pd-Cl2 bond length
of 2.395(6) Å (trans to phosphorus) is slightly longer than
Pd-Cl1 (2.308(6) Å). This reflects the difference between
the σ-donor strengths of phosphorus and sulfur (trans
influence). The S-Pd-P bite angle is 85.48(2)°.
In the molecular structure of 7 the platinum atom adopts
a distorted square-planar geometry with the corners occupied
by two iodide ligands and two phosphorus atoms. There is
a large variation in the cis angles from 71.35(4)° (P1-Pt-
P2) to 100.52(3)° (I2-Pt-P2), primarily because of the small
“bite angle” of the bis(phosphonite) ligand. The Pt-P1 and
Pt-P2 bond lengths are 2.219(1) and 2.230(1) Å, respec-
tively, while the mean P-N bond length is 1.674(4) Å. The
P1-N-P2 bond angle (101.6(3) Å) is considerably smaller
than either tetrahedral or trigonal angles, but the sum of
angles around nitrogen is 359.8(1)°, which clearly indicates
that the geometry around the nitrogen is planar. In the crystal
packing the molecules show a π-π stacking interaction
between naphthyl rings with a mean interplanar separation
of 3.752 Å, which is within the range of π-π stacking
interactions (3.80 Å).25
Figure 3. Molecular structure of complex 5. For clarity, solvent (CH2-
Cl2) and all hydrogen atoms have been omitted. Thermal ellipsoids are drawn
at the 50% probability level.
P1-N and S2-P2-N, respectively. The P-N-P bond angle
is 113.66(1)°, and the geometry around the nitrogen center
is planar with the sum of the angles around nitrogen close
to 360°. The four donor atoms (two P and two S) are oriented
in the same direction with a S-P-P-S torsion angle of
8.49°.
In the structure of 3 two palladium atoms are bridged by
the aminobis(phosphonite) ligand to form a binuclear com-
plex. The thioether-phosphonate groups are in approxi-
mately eclipsed conformations and facing in opposite
directions. Both palladium centers are slightly distorted from
the expected square-planar geometry. Each palladium center
(24) Chang, C.; Lin, Y.; Lee, G.; Wang, Y. J. Chem. Soc., Dalton Trans.
1999, 4223-4230.
(25) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885-3896.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11323

Punji et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Compounds 2, 3, 5, and 7
2
3
5
7
S1-C12
S1-C2
P1-O2
P1-O1
P1-N
S2-C22
S2-C32
P2-O3
P2-O4
P2-N
1.769(2)
1.779(2)
1.658(2)
1.655(2)
1.701(2)
1.770(2)
1.776(2)
1.659(2)
1.659(2)
1.695(2)
Pd1-P1
2.221(3)
2.235(2)
2.358(2)
2.382(3)
2.224(2)
2.229(2)
2.342(2)
2.394(2)
1.446(7)
1.624(7)
1.637(7)
1.673(7)
1.690(7)
3.253(1)
90.86(9)
84.75(1)
168.64(8)
172.37(1)
88.05(9)
108.8(4)
105.6(4)
103.2(4)
102.9(4)
117.4(4)
Pd-Cl1
Pd-Cl2
Pd-S
2.308(6)
2.395(6)
2.261(6)
2.189(5)
1.784(2)
1.784 (2)
1.478(2)
1.628(1)
1.641(2)
1.675(4)
1.592(4)
1.593(4)
Pt-I1
2.636(1)
2.626(1)
2.219(1)
2.230(1)
1.767(5)
1.770(6)
1.583(4)
1.594(4)
1.673(4)
Pd1-P2
Pt-I2
Pd1-S1
Pt-P1
Pt-P2
S1-C2
S1-C12
P1-O1
P1-O2
P1-N
Pd1-Cl1
Pd-P
Pd2-P4
S-C11
S-C10
P-O3
P-O1
P-O2
P2-N
P2-O3
P2-O4
Pd2-P3
Pd2-S4
Pd2-Cl2
P1-O3
P1-O2
P1-O1
P2-N1
P3-N1
Pd1‚‚‚Pd2
P1-Pd1-P2
P1-Pd1-S1
P2-Pd1-S1
P1-Pd1-Cl1
S1-Pd1-Cl1
O3-P1-O2
O3-P1-O1
C12-S1-C10
C32-S2-C30
P2-N1-P3
C2-S1-C12
C22-S2-C32
O1-P1-O2
O1-P1-N
O2-P1-N
O3-P2-O4
O3-P2-N
O4-P2-N
P1-N-P2
104.21(1)
103.29(1)
98.86(9)
96.59(9)
96.86(9)
98.26(9)
96.84(9)
97.35(9)
113.66(1)
123.63(2)
122.69(2)
Cl1-Pd-Cl2
Cl1-Pd-S
Cl1-Pd-P
Cl2-Pd-S
Cl2-Pd-P
S-Pd-P
Pd-S-C10
Pd-P-O1
Pd-P-O2
Pd-P-O3
P2-N-C41
92.96(2)
176.43(2)
93.09(2)
88.37(2)
173.69(2)
85.48(2)
114.16(7)
108.14(6)
109.65(5)
123.92(6)
128.5(3)
I1-Pt-I2
89.73(1)
98.36(3)
169.22(3)
71.35(4)
104.2(2)
101.7(2)
119.02(1)
105.24(2)
101.6(3)
129.7(3)
I1-Pt-P1
I1-Pt-P2
P1-Pt-P2
C2-S1-C12
C22-S2-C32
Pt-P1-O1
O1-P1-O2
P1-N-P2
P1-N-C41
P1-N-C41
P2-N-C41
Suzuki-Miyaura, Mizoroki-Heck Cross-Coupling,
and Amination Reactions. The heterodifunctionl ligands
containing O, N, or S donors along with P are found to be
excellent for cross-coupling reactions. The anionic complexes
generated with such ligand systems with flexible coordination
modes are even better as they enhance the rate of oxidative
addition, a vital step in homogeneous catalysis. As a result,
the palladium complexes (3, 4, and 5) were employed for
C-C (Suzuki-Miyaura, Mizoroki-Heck cross-coupling)
and C-N bond-forming reactions of aryl bromides with the
coupling partners such as phenylboronic acid, tert-butylacry-
late, or morpholine, respectively. The catalytic reactions were
carried out in either methanol or toluene using inexpensive
inorganic bases (K2CO3, NaOtBu). Since the palladium
complex 4 transforms into complex 5 in the presence of a
base, catalytic activities of both the complexes are found to
be the same.
The palladium complexes 3 and 5 catalyze the cross-
coupling reactions of aryl bromides and phenylboronic acid
to yield the desired biaryls in high yields at 60 °C using
methanol as solvent (Table 4, entries 1-7). Using these
catalysts, high yields are obtained from catalyst loads from
0.05 to 0.005 mol %. A moderate yield (73%) is achieved
at a catalyst loading as low as 0.0005 mol % with a TON of
1.46 × 105 (Table 4, entry 5). Entries 3 and 6 illustrate that
the deactivated electron-rich 4-bromoanisole could be coupled
with phenylboronic acid in good yield. The activity of
catalysts 3 and 5 is found to be superior to that of the most
commonly used catalysts PdCl2(dppf) and Pd2(dba)3/(dppf)
which catalyze reactions between 4-bromoacetophenone and
phenylboronic acid in toluene at 70 °C in 94% and 86%
yield, respectively.26 In comparison with other P,S-chelated
palladium catalysts, the catalytic activity of 3 and 5 is similar
to the monomeric PdII complexes of the 1-phosphabarrelene
phosphine sulfide system whose reactions were carried out
in toluene at 110 °C.27
Although very high turnover numbers (TONs) and yields
are observed for both catalysts, complex 5 exhibits high
turnover rates in Suzuki-Miyaura cross-coupling reactions.
Hence, most of the experiments were performed with
complex 5. Entries 8 and 9 reveal that catalyst 5 is also
effective in the Mizoroki-Heck cross-coupling reactions of
aryl bromides with tert-butylacrylate under mild conditions.
Also noteworthy is the efficient catalytic activity even at 0.05
mol % of the catalyst (entry 8) in Heck reactions. Entries
10 and 11 show that aryl bromides can couple with
morpholine in the amination reaction at 100 °C in excellent
yield. Reports on efficient universal catalysts which can be
employed for both C-C and C-N bond-forming reactions
are limited. Buchwald’s28 and Fu’s29 groups used electron-
rich phosphine/palladium systems such as Pd(OAc)2/(o-
biphenyl)P(tBu)2 and Pd2(dba)3/P(tBu)3, respectively, to
promote cross-coupling reactions. However, the present
catalyst system is found to be very air stable and catalyzes
those reactions under mild reaction conditions.
Recently, Li and co-workers employed binuclear phos-
phinous acid (RR′POH) metal complexes for a variety of
C-C, C-N, and C-S bond-forming process.4a-c They
demonstrated that the binuclear complex [RR′P(OH)PdCl-
(µ-Cl)]2 is subjected to cleavage and deprotonation in the
presence of bases and thought to form an electron-
rich phosphane-containing mononuclear tricoordinated an-
(27) Piechaczyk, O.; Doux, M.; Ricard, L.; Le Floch, P. Organometallics
2005, 24, 1204-1213.
(28) (a) Wolfe, J. P.; Buchwald, S. L. Angew. Chem., Int. Ed. Engl. 1999,
38, 2413-2416. (b) Huang, X.; Anderson, K. W.; Zim, D.; Jiang, L.;
Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125, 6653-
6655. (c) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi,
J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369-4378.
(29) (a) Littke, A. F.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 6989-7000.
(b) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176-
4211.
(26) Colacot, T. J.; Qian, H.; Cea-Olivares, R.; Hernandez-Ortega, S. J.
Organomet. Chem. 2001, 637-639, 691-697.
11324 Inorganic Chemistry, Vol. 46, No. 26, 2007

Air-Stable Palladium(II) Complexes
Table 3. Comparison of P-S Bond Parameters, Ring Conformations, and 31P Chemical Shifts for Cyclic Phosphites (in increasing order of % TBP)
a Percent geometrical displacement from a pyramid toward a TBP. b With reference to a TBP with sulfur in an axial position and both ring oxygen atoms
in equatorial positions.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11325

Punji et al.
Table 4. Palladium Complex-Catalyzed Cross-Coupling of Aryl Bromides with PhB(OH)2, tert-Butylacrylate, and Morpholinea
a Reaction conditions: aryl bromide (1.0 equiv), boronic acid (or tert-butylacrylate, morpholine) (1.2-1.5 equiv), K2CO3 (or NaOtBu) (1.2-2 equiv),
methanol (or toluene) (5 mL). b Conversion to coupled product determined by GC, based on aryl halides (or dodecane); average of two runs.
ionic complex which is responsible for the high activity of
the catalyst (Scheme 3). However, in the present study
the isolated and fully characterized anionic palladium
complex 5 was employed for C-C and C-N cross-coupling
reactions. With regard to the involvement of anionic species
in catalysis,5a a plausible catalytic cycle for the cross-coupling
reactions of aryl halides is given in Scheme 9. During
catalysis the anionic complex 5 can exchange cation
with the base (i.e., K2CO3) to form [Pd]-[K]+ (I) as the
oxidative addition is faster in the presence of metal cations.30
The metal cation interacts with the halide anions ligated to
palladium by ion pairing to afford more reactive Pd(0)
complex (III). In this complex the sulfur coordination
provides a temporary platform for the active catalytic species
during an oxidative addition step and also extra stability to
the catalyst precursor. Although several hemilabile phos-
phorus ligands containing thioether sulfur have been used
in catalysis, well-characterized palladium complexes contain-
ing a hemilabile motif of this type are rare in catalytic
reactions. In the case of complex 3, the catalytic cycle would
be similar to any other palladium(II) complex which in the
presence of a base gives the catalytically active palladium-
(0) species.1
The homogeneous nature of the catalysis was checked
by the classical mercury test. Addition of a drop of mercury
to the reaction mixtures did not affect the activity of the
catalyst, thus showing them to be truly homogeneous
systems.31
Conclusion
Catalytically active PdII complexes 3 and 5 are synthesized
by oxidizing the phosphorus centers with an appropriate
amount of water from the 1:1 and 1:2 reactions of aminobis-
(31) (a) Widegren, J. A.; Bennett, M. A.; Finke, R. G. J. Am. Chem. Soc.
2003, 125, 10301-10310. (b) Widegren, J. A.; Finke, R. G. J. Mol.
Catal. A: Chem. 2003, 198, 317-341.
(30) Amatore, C.; Azzabi, M.; Jutand, A. J. Am. Chem. Soc. 1991, 113,
8375-8384.
11326 Inorganic Chemistry, Vol. 46, No. 26, 2007

Air-Stable Palladium(II) Complexes
(phosphonite) and palladium precursor, respectively,
where the thioether-phosphonate moiety forms a metalla-
cycle containing a metal-phosphorus σ bond. These are
the first examples of any thioether-based phosphorus ligands
which form anionic mononuclear and neutral binuclear
complexes. The bridged binuclear PdII complex of aminobis-
(phosphonite) is highly unstable essentially due to the
steric bulk of the ligand. However, PtII forms moderately
stable chelate complexes which are found to be resistant to
moisture-induced P-N bond cleavage reactions. The
sulfur atom present in the eight-membered aminobis(phos-
phonite) ring shows coordinative interaction toward phos-
phorus; as a result, the tricoordinated geometry around
phosphorus is displaced toward TBP. The anionic and neutral
binuclear palladium complexes show excellent catalytic
activity toward Suzuki-Miyaura cross-coupling (TON
up to 1.46 × 105) and Mizoroki-Heck coupling reactions
as well as amination reactions under mild conditions.
Interestingly, P-O bonds in phosphonites are quite stable
toward aerial oxidation and hydrolytic cleavage. They also
survive rigorous conditions employed during catalytic reac-
tions. Further studies on the utilization of these complexes
toward cross coupling of unactivated aryl chlorides with
arylboronic acids, amines, and thiols are currently under
investigation.
Acknowledgment. We are grateful to the Department of
Science and Technology (DST), New Delhi for funding. B.P.
thanks CSIR for Research Fellowship (JRF & SRF). We also
thank the Department of Chemistry Instrumentation Facili-
ties, Bombay, for spectral and analytical data and the
Louisiana Board of Regents through grant LEQSF(2002-03)-
ENH-TR-67 for purchase of the CCD diffractometer and the
Chemistry Department of Tulane University for support of
the X-ray laboratory. Mr. S. M. Mobin, National X-ray
facility center, I.I.T. Bombay, is gratefully acknowledged
for solving one of the crystal structures.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of 2, 3, 5, and 7.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC701674X
Inorganic Chemistry, Vol. 46, No. 26, 2007 11327