Carbon-carbon and carbon-chlorine bond formation on reaction of iodine(III) reagents with the bis(alkynyl)palladium(II) motif, and structural chemistry of trans-Pd(C≡C-o-Tol)2(PMe2Ph)2] and trans-[PdCl(C≡C-o-Tol)(PMe2Ph)2]

Article abstract of DOI:10.1016/j.jorganchem.2011.01.018

Trans-di(ortho-tolylethynyl)bis(dimethylphenylphosphine)palladium(II) reacts above -20 °C with the iodonium reagent IPhCl₂ to give predominantly o-Tol-CC-Cl, above 15 °C with IPh₂(OTf) (OTf = triflate) to give o-Tol-CC-Ph and (o-Tol-CC)₂ in ca. 3:1 ratio, and above 10 °C with IPh(CCR)(OTf) (R = Bu^t, SiMe₃) to give predominantly o-Tol-CC-CC-R and (o-Tol-CC)₂. ³¹P NMR spectra provide evidence for detection of intermediates. The complexes trans-[Pd(CC-o-Tol)₂(PMe₂Ph)₂] and trans-[PdCl(CC-o-Tol)(PMe₂Ph)₂] are obtained on reaction of trans-[PdCl₂(PMe₂Ph)₂] with Li(CC-o-Tol) and o-Tol-CCH/Et₃N, respectively, and have been characterised by X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2011.01.018

Journal of Organometallic Chemistry 696 (2011) 1441e1444
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Carbonecarbon and carbonechlorine bond formation on reaction of iodine(III)
reagents with the bis(alkynyl)palladium(II) motif, and structural chemistry of
trans-Pd(C^C-o-Tol)2(PMe2Ph)2] and trans-[PdCl(C^C-o-Tol)(PMe2Ph)2]
*
Manab Sharma, Allan J. Canty , Michael G. Gardiner, Roderick C. Jones
School of Chemistry, University of Tasmania, Hobart, Tasmania 7001, Australia
a r t i c l e i n f o
a b s t r a c t
Trans-di(ortho-tolylethynyl)bis(dimethylphenylphosphine)palladium(II) reacts above ꢀ20 ꢁC with the
iodonium reagent IPhCl2 to give predominantly o-ToleC^CeCl, above 15 ꢁC with IPh2(OTf) (OTf ¼ triflate)
to give o-ToleC^CePh and (o-ToleC^C)2 in ca. 3:1 ratio, and above 10 ꢁC with IPh(C^CR)(OTf)
(R ¼ But, SiMe3) to give predominantly o-ToleC^CeC^CeR and (o-ToleC^C)2. 31P NMR spectra provide
evidence for detection of intermediates. The complexes trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] and trans-[PdCl
(C^C-o-Tol)(PMe2Ph)2] are obtained on reaction of trans-[PdCl2(PMe2Ph)2] with Li(C^C-o-Tol) and o-Tol-
C^CH/Et3N, respectively, and have been characterised by X-ray crystallography.
Article history:
Received 19 November 2010
Received in revised form
18 December 2010
Accepted 11 January 2011
Keywords:
Palladium
Alkynyl
Ó 2011 Elsevier B.V. All rights reserved.
Alkynylpalladium
Oxidation
Reductive elimination
Carbonecarbon bond formation
1. Introduction
2. Results and discussion
Alkynylpalladium(IV) species have been proposed as intermediates
in stoichiometric [1] and catalytic [2e9] organic synthesis, but spec-
troscopic detection is limited to NMR studies of the formation of very
unstable PdIVIMe2(C^CSiMe3)(dmpe) (dmpe ¼ 1,2-bis(dimethyl-
phosphino)ethane) and PdIV(OTf)(O2CPh)(C^CSiMe3)(NCN) (OTf-
¼ triflate, NCN ¼ 2,6-(Me2NCH2)2C6H3 ‘pincer’) at ꢀ50 ꢁC and ꢀ80 ꢁC,
respectively [8]. These complexes were obtained using IPh(C^CSiMe3)
(OTf) as a strong oxidising agent via elimination of PhI and formal
transfer of ‘C^CSiMeþ3 ’ to PdII. Organopalladium(III) complexes have
also been well characterised by X-ray crystallography, including
mononuclear [9] and PdIIIePdIII bonded species [10,11]. In view of an
earlier report proposing undetected mono(alkynyl)palladium(IV) and
bis(alkynyl)palladium(IV) intermediates in complex reactions of trans-
[PdCl2(PBu3)2] with SnMe3(C^CR) (R ¼ Me, But) [12], we have
explored the interaction of a typical trans-[Pd(alkynyl)2(phosphine)2]
reagent with IPh(C^CR)(OTf)(R ¼ But, SiMe3) and other iodine(III)
reagents (IPh2(OTf), IPhCl2) to explore potential higher oxidation state
organopalladium chemistry.
The reagent trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1) was used as
a palladium(II) substrate in order to provide convenient NMR probes
for the phosphine and alkynyl groups in both the aromatic and
aliphaticregions, and presence of an alkynyl group different from IPh
(C^CR)(OTf) (R ¼ But, SiMe3) in order to probe potential selectivity
in decomposition processes from intermediates. Complex 1 was
obtained on reaction of trans-[PdCl2(PMe2Ph)2] with Li(C^C-o-Tol).
In order to assist with NMR characterisation of some reaction
products (see below), trans-[PdCl(C^C-o-Tol)(PMe2Ph)2] (2) was
obtained on reactionof trans-[PdCl2(PMe2Ph)2] with o-ToleC^CH in
triethylamine/acetone.
Complexes 1 and 2 formed as crystalline solids suitable for X-ray
diffraction studies (Fig. 1) and have structural parameters similar to
the closely related complexes trans-[Pd(C^CPh)2(PEt3)2] [13] and
trans-[PdCl(C^CPh)(PPh3)2] [14].
Complex 1 contains one half of a centrosymmetric molecule in
the asymmetric unit, while 2 contains one molecule in the asym-
metric unit, and complex 2 has disorder involving rotation about the
Pd(1)eP(1) bond, modelled by two complementary refined occu-
pancies for a methyl group and the phenyl substituent. For the
phenyl ring, two orientations were noted that shared adjacent ortho
and meta carbon atoms.
* Corresponding author. Tel.: þ61 3 6226 2162; fax: þ61 3 6226 2858.
E-mail address: Allan.Canty@utas.edu.au (A.J. Canty).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.01.018

1442
M. Sharma et al. / Journal of Organometallic Chemistry 696 (2011) 1441e1444
Fig. 1. ORTEP representations of the structures of (a) trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1), and (b) trans-[PdCl(C^C-o-Tol)(PMe2Ph)2] (2). Displacement ellipsoids are drawn at the
50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) for 1: Pd(1)eC(1) 2.006(3); Pd(1)eP(1) 2.2976(8); C(1)eC(2) 1.215(5) Å;
C(1)ePd(1)eP(1) 88.65(9), 91.35(9)ꢁ; 2: Pd(1)eC(1) 1.955(5); Pd(1)eP(1,2) 2.2959(15), 2.3080(13); Pd(1)eCl(1) 2.3536(12); C(1)eC(2) 1.197(7) Å; C(1)ePd(1)eCl(1) 178.11(15);
ꢁ
C(1)ePd(1)eP(1,2) 86.04(14), 87.72(14); Cl(1)ePd(1)eP(1,2) 93.42(5), 92.96(5); P(1)ePd(1)eP(2) 172.20(6); Pd(1)eC(1)eC(2) 179.0(5); C(1)eC(2)eC(3) 178.6(5)
.
The reactivity of trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1) toward
iodonium reagents was monitored by 1H and 31P NMR spectroscopy,
and organic products characterised by GCMS (Scheme 1). Reactions
occurred with elimination of iodobenzene from iodonium reagents,
and was least facile for IPh2(OTf) (reaction above 15 ꢁC) and most
facile for IPhCl2 (reaction above ꢀ20 ꢁC). Colourless solutions of
reagents are dark brown on completion of reaction and, for IPhCl2 as
oxidant, an initial bright red colouration occurs at ꢀ20 ꢁC (visible
spectra exhibit a broad shoulder at ca. 460 nm) and disappears
during reaction as the dark brown colouration develops. 1H NMR
spectra during reactions were complex, showing low intensity
resonances that arose and disappeared for reaction with IPh2(OTf)
exchange reactions between PdII centres and reductive elimination
of biphenyl from ‘PdIIPh2’ species. Similarly, for reaction (ii) [1 þ IPh
(C^CSiMe3)(OTf)], (Me3SieC^C)2 may be formed from ‘(Me3Si-
C^C)2PdII’ species formed after alkynyl group exchange [14,15]
between ‘(Me3SieC^C)PdII’ decomposition product(s).
There is insufficient evidence to conclude the potential
involvement of PdIII or PdIV species such as ‘PdIV(OTf)(C^C-o-Tol)2X
(PMe2Ph)2’ (X ¼ Ph, C^CR, Cl), followed by reductive elimination
processes. Although spectroscopic data are insufficient to conclude
that such intermediate(s) are present, they do indicate the forma-
tion of intermediates for reactions of IPh2(OTf), IPh(C^CSiMe3)
(OTf) and IPhCl2, although 31P NMR spectra exhibit resonances
close to that expected of PdII species. The distinctive red colouration
observed during reaction of IPhCl2 may be indicative of PdIIIePdIII
species, as reported complexes of this type are all red [10,11]. Well
documented mononuclear PdIII species are green and paramagnetic
[9], and we observed no indication of paramagnetic shifts in NMR
spectra.
The reactions reported here do appear to provide the first
examples of alkynylealkynyl and alkynyl-halogen coupling from
palladium centres in moderate to high yield in the presence of
strong oxidising agents that are known to transfer ‘ReC^Cþ’, ‘Phþ’
and ‘Clþ’ electrophiles to PdII centres in other systems. The detec-
tion of C(sp)-halogen coupling reported here is complementary to
earlier reports of C(sp2)-halogen coupling from isolated or detected
PdIII [11] and PdIV [27] complexes, and C(sp3)-halogen coupling
from isolated or detected PdIII [9] and PdIV complexes [28].
(7.64
m and 2.05 s ppm), IPh(C^CSiMe3)(OTf) (8.13 s and
8.14 s ppm), and IPhCl2 [8.25 and 8.26 ppm (singlets or doublet)]. 31
P
NMR spectra showed new resonances that arose and disappeared as
reaction concluded for reaction with IPh2(OTf) (two resonances
at ꢀ5.52 and ꢀ5.71 ppm, downfield from 1 (ꢀ6.58 ppm)), reaction
with IPh(C^CSiMe3)(OTf) (one resonance at ꢀ8.10 ppm), and
reaction with IPhCl2 showed only the formation of trans-[PdCl
(C^C-o-Tol)(PMe2Ph)2] (2) at ꢀ7.17 ppm. On completion, reactions
(i) and (ii) exhibit several 31P resonances, consistent with the
more complex decomposition pathways indicated by GCMS anal-
yses (see below).
The major organic products, as indicated in Scheme 1, involve
coupling of an o-ToleC^C group with a group anticipated to be
transferred to PdII from the iodonium reagent, together with
(o-ToleC^C)2 for reactions of IPh2(OTf) and IPh(C^CR)(OTf)
(R ¼ But, SiMe3). Based on the yield of ortho-tolylethynyl groups
these organic products, and anticipated complementary PdII
products, the overall yields are ca. 65% for reaction (i), ca. 35% for
reaction (ii), and ca. 70% for reaction (iii). Reaction (iii) [1 þ IPhCl2]
gave traces of PhePh and C6H4ICl; reaction (iii) [1 þ IPh(C^CSiMe3)
(OTf)] gave a small quantity of (Me3SieC^C)2 (5%). Forma-
tion of PhePh can be most likely attributed to oxidative addi-
tion of iodobenzene to Pd0 decomposition products followed by
3. Experimental
Air-sensitive materials were handled under an argon atmo-
sphere using standard Schlenk techniques. All solvents were dried
and distilled by conventional methods prior to use. The reagent
trans-[PdCl2(PMe2Ph)2] was obtained using PdCl2(SMe2)2 instead of
PdCl2 [16]; IPh(C^CR)(OTf) (R ¼ But, SiMe3) [17], IPh2(OTf) [18],
Scheme 1. Reactions of trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1) with iodonium reagents at 10 ꢁC in acetone-d6 (R ¼ But, SiMe3; OTf ¼ triflate) illustrating major organic products;
trans-[PdCl(C^C-o-Tol)(PMe2Ph)2] is isolated from reaction (iii).

M. Sharma et al. / Journal of Organometallic Chemistry 696 (2011) 1441e1444
1443
and IPhCl2 [19] were prepared as reported. NMR spectra were
recorded on a Varian Mercury Plus 300 MHz and Varian 400 Unity
Inova spectrometers. 1H NMR spectra were secondary-referenced
to residual solvent signals. 31P NMR spectra were externally refer-
enced to 85% H3PO4.GCMS analyses were carried out on a Varian
3800 GC coupled to Varian 1200 triple quadrupole mass spec-
trometer in single quadrupole mode. A Varian ‘Factor Four’ VF-5 ms
(30 m ꢂ 0.25 mm internal diameter and 0.25 micron film) column
(300 MHz, CD2Cl2)
7.10e6.99 (m, 4H, tolyl), 2.20 (s, 3H, PhCH3), 1.87 (bs, 12H, PCH3).
13C NMR (75 MHz, CD2Cl2)
131.8, 131.7, 131.4, 130.4, 129.2, 128.7,
125.8, 125.3 (aryl); 20.9 [CH3(Tolyl)], 8.7 (PCH3). 31P NMR (162 MHz,
CD2Cl2)
ꢀ7.17.
d 7.85e7.82 (m, 4H, PPh), 7.46e7.44 (m, 6H. PPh),
d
d
3.2. Studies of reactions of trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1)
with iodonium reagents
was used. Injections of 1 mL were made using a Varian CP-8400
autosampler and a Varian 1177 split/splitless injector at 220 ꢁC with
a split ratio of 30:1. The ion source was at 220 ꢁC, and theꢀt1ransfer
line at 290 ꢁC. The carrier gas was helium at 1.2 mL min using
constant flow mode. The column oven was held at 50 ꢁC for 2 min
then ramped to 290 ꢁC at 8 ꢁC minꢀ1. The range from m/z 35 to 550
was scanned 3 times per sec. GCFID was carried out on a Varian
450-GC with 1177 split/splitless injector using similar conditions to
the above, except that the carrier gas was nitrogen. The FID
response factor for n-heptadecane was determined from a solution
of known concentration and response factors for individual anal-
yses were taken from the literature where known, e.g. iodobenzene
[20]. For others the ‘effective carbon number’ concept and known
negative effects on FID response [21e23] was employed to estimate
corrections required for heteroatoms.
A solution of iodonium reagent (IPh(C^CSiMe3)(OTf), IPh
(C^CBut)(OTf), IPh2(OTf), or IPhCl2) (8.16 ꢂ 10ꢀ2 mmol) in dich-
loromethane-d2 (0.5 mL) was added to a solution of trans-[Pd(C^C-
o-Tol)2(PMe2Ph)2] (8.16 ꢂ 10ꢀ2 mmol) in dichloromethane-d2
(0.5 mL) at ꢀ40 ꢁC (slush bath). An aliquot was immediately
transferred to a pre-cooled NMR tube and quickly inserted into the
NMR probe which was pre-cooled - 40 ꢁC. The temperature was
raised slowly until reaction was evident, and this temperature
maintained until completion of reaction.
3.3. Structural determinations
Data for 1 and 2 were collected at ꢀ173 ꢁC for crystals mounted
on a Hampton Scientific cryoloop at the MX1 beamline of the
3.1. Synthesis of complexes
Australian Synchrotron (
l
¼ 0.77487, 0.77506 for 1 and 2, respec-
tively) using Blue Ice software [24] and data reduced using XDS. The
structures were solved by direct methods with SHELXS-97, refined
using full-matrix least-squares routines against F2 with SHELXL-97
[25], and visualised using X-SEED [26]. All non-hydrogen atoms
were refined anisotropically using a riding model with fixed CeH
distances of 0.95 Å (sp2 CeH), 0.99 Å (CH2), 0.98 Å (CH3). The
thermal parameters of all hydrogen atoms were estimated as
Uiso(H) ¼ 1.2Ueq(C) except for CH3 where Uiso(H) ¼ 1.5Ueq(C).
Phosphine ligand disorder in 2 is described in Section 2.
3.1.1. Trans-di(ortho-tolylethynyl)bis(dimethylphenylphosphine)
palladium(II), trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1)
A suspension of PdCl2(PMe2Ph)2 (0.512 g, 1.13 mmol) in dry
diethyl ether (15 mL) was cooled to ꢀ70 ꢁC for 15 min, and a freshly
prepared cold solution of LieC^C-o-Tol (2.26 mmol) in diethyl
ether (5 mL) in a Schlenk vessel was added dropwise over a period
of 15 min with constant stirring. The reaction mixture was then
allowed to rise slowly to 0 ꢁC over w2 h, during which the colour of
the suspension changed from light brown to milky white. The
suspension was stirred at 10 ꢁC for 5 min, cold water (1 mL) injected
and the diethyl ether layer was collected. The water layer was
further extracted with dichloromethane and, collected together
with the diethyl ether layer, was dried over MgSO4, filtered through
Celite and dried under vacuum to obtain a white product which was
further purified by recrystallisation from dichloromethane (0.54 g,
78%). Analysis (calc., C, 66.62; H, 5.92%): C, 66.41; H, 6.77. LSIMS m/z
612 [M-Xl]þ, [12C34H36 31P2106Pd]. 1H NMR (400 MHz, CD2Cl2)
3.3.1. Crystal data
trans-[Pd(C^C-o-Tol)2(PMe2Ph)2] (1): C34H36P2Pd, M ¼ 612.97,
space group P-1, triclinic, a ¼ 7.5170(8), b ¼ 9.6070(4), c ¼ 10.8760
(5) Å,
a
¼ 94.052(4),
b
¼ 99.588(9),
g
¼ 108.341(4) ꢁ, V ¼ 728.72
(9) Å3, Z ¼ 1, Dc ¼ 1.397 g cmꢀ3, specimen pale yellow prism,
0.05 mm ꢂ 0.02 mm ꢂ 0.02 mm, 7092 measured reflections,
Rint ¼ 0.0309, R ¼ 0.0491 for 1879 observed data ((I) ¼ 2
s(I)),
wR ¼ 0.0824, and GOOF ¼ 1.098 for all 1896 unique data.
d
7.92e7.90 (m, 4H PPh), 7.45e7.43 (m, 6H PPh), 7.16e6.98 (m, 8H, H
(3e6)Tolyl), 2.26 (s, 6H, CH3(Tolyl)), 1.98 (s, 12H, PCH3). 13C NMR
(75 MHz, CD2Cl2) 138.9, 131.9, 131.4, 130.2, 129.2, 128.6, 125.4,
125.3 (aryl); 115.8, 110.0 (C^C); 21.2 [CH3(Tolyl)], 1.4 (PCH3). 31P NMR
(162 MHz, CD2Cl2)
ꢀ6.58.
trans-[PdCl(C^C-o-Tol)(PMe2Ph)2] (2): C25H29ClP2Pd, M ¼ 533.27,
space group P-1, triclinic, a ¼ 9.270(2), b ¼ 9.2950(19), c ¼ 14.540
d
(3) Å,
a
¼ 80.454(4),
b
¼ 83.402(15),
g
¼ 86.165(2) ꢁ, V ¼ 1225.8
(5) Å3, Z ¼ 2, Dc ¼ 1.445 g cmꢀ3, specimen yellow prism,
0.10 mm ꢂ 0.03 mm ꢂ 0.02 mm, 12681 measured reflections,
d
Rint ¼ 0.0650, R ¼ 0.0479 for 3311 observed data [(I) ¼ 2
s(I)],
3.1.2. Trans-chloro(ortho-tolylethynyl)bis
(dimethylphenylphosphine)palladium(II), trans-[PdCl(C^C-o-Tol)
(PMe2Ph)2] (2)
wR ¼ 0.1176, and GOOF ¼ 1.036 for all 3409 unique data.
Acknowledgements
In a Schlenk vessel under argon, ortho-tolylethyne (0.23 mL,
1.83 mmol) was added to a mixture of triethylamine (3 mL) and
acetone (5 mL); after stirring for w5 min; to PdCl2(PMe2Ph)2
(0.45 g, 1.014 mmol) was added. The reaction mixture was stirred at
room temperature for 38 h, during which time the colour of the
reaction mixture changed from brown to yellowish white. The
solvent was evaporated under vacuum to obtain a sticky light
yellow mass, which was dissolved in dichloromethane and filtered
through Celite, and dichloromethane evaporated to dryness under
vacuum. The product was washed with hexane followed by diethyl
ether, dried overnight under vacuum, and collected as a white
powder (0.37 g, 70%). Analysis (calc. C, 56.30; H, 5.48%): C, 57.32; H,
6.47. LSIMS m/z 532 [M-Xl]þ, [12C25H29 35Cl31P2106Pd ]. 1H NMR
We thank the Australian Research Council for financial support,
and Dr Noel Davies of the Central Science Laboratory for assistance
with analysis of organic products. Aspects of this research were
undertaken on the MX1 beamline at the Australian Synchrotron,
Victoria, Australia.
Appendix A. Supplementary material
CCDC numbers 800027 and 800028 contain the supplementary
crystallographic data for this paper. This data can be obtained free
of charge via http://ww.ccdc.cam.ac.uk/data_request/cif.

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M. Sharma et al. / Journal of Organometallic Chemistry 696 (2011) 1441e1444
[14] M. Weigelt, D. Becher, E. Poetsch, C. Bruhn, D. Steinborn, Z. Anorg. Allg. Chem.
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