Oxidative dehydrogenation of tris(o-isopropylphenyl)phosphines by platinum complexes

Article abstract of DOI:10.1021/om800382m

The binuclear cyclometalates [Pt₂Cl₂{2-CMe ₂C₆H₄P(C₆H₄(2- ⁱPr))₂}₂] (1a) and [Pt₂Cl ₂[2-CMe₂C₆H₃(4-OMe)P(C ₆H₃(2-ⁱPr)(4-OMe))₂}₂] (1b) react with CHCl₂CHCl₂ to give the corresponding mononuclear phosphine-alkene chelates [PtCl₂ {2-CH ₂=CMeC₆H₄P(C₆H₄(2- ⁱPr))₂}] (2a) and [PtCl₂ [2-CH ₂=CMeC₆H₃(4-OMe)P(C₆H ₃(2-ⁱPr)(4-OMe))₂}] (2b). The product 2a can also be formed directly from [PtCl₂(NC^tBu)₂] and L_a in CHCl₂CHCl₂ or by addition of SO ₂Cl₂ to 1a. Addition of an excess of SO₂Cl ₂ to 1b gave [PtCl₂ {2-CH₂=CMeC ₆H₃(4-OMe)P(C₆H₂(2- ⁱPr)(4-OMe)(5-Cl))₂}] (3b), a derivative of 2b featuring metachlorine substituents on the terminal P groups as a result of electrophilic aromatic substitution. A mechanism for the conversion of 1a,b to 2a,b is proposed involving an electrophilic alkyl C-H activation by a coordinatively unsaturated platinum(IV) species. The mechanism is supported by the isolation of the diplatinum(IV) cyclometalate [Pt₂Cl₂ {2-CH ₂C₆H₃(4-OMe)P(C₆H ₃(2-Me)(4-OMe))₂}] as a mixture of syn and anti isomers 5b and 5b′. The crystal structures of 2a and 3b have been determined.

Full text of DOI:10.1021/om800382m

5906
Organometallics 2008, 27, 5906–5910
Oxidative Dehydrogenation of Tris(o-isopropylphenyl)phosphines by
Platinum Complexes
Angharad Baber, Cheng Fan, David W. Norman, A. Guy Orpen, Paul G. Pringle,* and
Richard L. Wingad
School of Chemistry, UniVersity of Bristol, Cantock’s Close, Bristol, BS8 1TS, U.K.
ReceiVed May 1, 2008
The binuclear cyclometalates [Pt2Cl2{2-CMe2C6H4P(C6H4(2-iPr))2}2] (1a) and [Pt2Cl2{2-CMe2C6H3(4-
OMe)P(C6H3(2-iPr)(4-OMe))2}2] (1b) react with CHCl2CHCl2 to give the corresponding mononuclear
phosphine-alkene chelates [PtCl2{2-CH2dCMeC6H4P(C6H4(2-iPr))2}] (2a) and [PtCl2{2-CH2dCMeC6H3(4-
OMe)P(C6H3(2-iPr)(4-OMe))2}] (2b). The product 2a can also be formed directly from [PtCl2(NCtBu)2]
and La in CHCl2CHCl2 or by addition of SO2Cl2 to 1a. Addition of an excess of SO2Cl2 to 1b gave
[PtCl2{2-CH2dCMeC6H3(4-OMe)P(C6H2(2-iPr)(4-OMe)(5-Cl))2}] (3b), a derivative of 2b featuring meta-
chlorine substituents on the terminal P groups as a result of electrophilic aromatic substitution. A
mechanism for the conversion of 1a,b to 2a,b is proposed involving an electrophilic alkyl C-H activation
by a coordinatively unsaturated platinum(IV) species. The mechanism is supported by the isolation of
the diplatinum(IV) cyclometalate [Pt2Cl2{2-CH2C6H3(4-OMe)P(C6H3(2-Me)(4-OMe))2}] as a mixture of
syn and anti isomers 5b and 5b′. The crystal structures of 2a and 3b have been determined.
reported for transfer dehydrogenation4 and acceptorless dehy-
Introduction
drogenation of alkanes5 but not for the oxidative dehydroge-
Understanding the factors involved in the activation of alkyl
C-H bonds by transition metal complexes is a topic of
fundamental interest because of the prospect and importance
of selectively functionalizing alkanes.1,2 Ever since Shilov’s
pioneering work1 on alkane activation with platinum(II)/(IV)
systems in the 1970s, much effort has been directed at using
precious metal complexes for homogeneous functionaliza-
tion of alkanes.3-7 Efficient homogeneous catalysts have been
nation of alkanes,8 which is potentially a very attractive process.2
One of the most promising strategies for homogeneous, oxida-
tive, alkane dehydrogenation involves electrophilic C-H activa-
tion by late transition metal complexes and especially with
platinum(II)/(IV) systems, for which stoichiometric dehydro-
genations have been reported.6,7
Cyclometalation is a common form of intramolecular C-H
activation, and the reactivity of the resulting M-C bonds has
been well documented.9 We reported10 rare examples of tertiary
carbon-metal bonds formed upon cycloplatination of La and
Lb, and here we report that the C-H bonds of the methyl groups
in the isopropyl substituents are activated upon oxidation of
the complex, resulting in the formation of a coordinated alkene.
Overall the reaction constitutes an oxidative dehydrogenation
of a tertiary phosphine.
* To whom correspondence should be addressed. E-mail: paul.pringle@
bristol.ac.uk. Fax: +44 (0)117 929 0509. Tel: +44 (0)117 928 8114.
(1) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879.
(2) For reviews see: (a) Marks, T. J.; et al. Chem. ReV. 2001, 101, 953.
(b) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (c) Crabtree,
R. H. J. Chem. Soc., Dalton Trans. 2001, 2437. (d) Jia, C.; Kitamura, T.;
Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (e) Sen, A. Acc. Chem. Res.
1998, 31, 550. (f) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson,
T. H. Acc. Chem. Res. 1995, 28, 154.
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P. R.; Voss, G.; Masuda, T. Science 1993, 259, 340. (b) Periana, R. A.;
Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998,
280, 560. (c) Periana, R. A.; Mironov, O.; Taube, D. J.; Bhalla, G.; Jones,
C. J. Science 2003, 301, 814. (d) Sen, A.; Benvenuto, M. A.; Lin, M.;
Hutson, A. C.; Basickes, N. J. Am. Chem. Soc. 1994, 116, 998. (e) Lin,
M.; Shen, C.; Garcia-Zayas, E. A.; Sen, A. J. Am. Chem. Soc. 2001, 123,
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(4) (a) Jensen, C. M. Chem. Commun. 1999, 2443, and references therein.
(b) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am.
Chem. Soc. 1999, 121, 4086. (c) Baudry, D.; Ephritikhine, M.; Felkin, H.;
Holmes-Smith, R. J. Chem. Soc., Chem. Commun. 1983, 788. (d) Gupta,
M.; Hagen, C.; Flesher, R. J.; Kaska, W. C.; Jensen, C. M. Chem. Commun.
1996, 2083. (e) Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; Jensen,
C. M. J. Am. Chem. Soc. 1997, 119, 840. (f) Gupta, M.; Kaska, W. C.;
Jensen, C. M. Chem. Commun. 1997, 461. (g) Burk, M. J.; Crabtree, R. H.;
Parnell, C. P.; Uriarte, R. J. Organometallics 1984, 3, 816. (h) Felkin, H.;
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(j) Maguire, J. A.; Goldman, A. S. J. Am. Chem. Soc. 1991, 113, 6706. (k)
Wang, K.; Goldman, M. E.; Emge, T. J.; Goldman, A. S. J. Organomet.
Chem. 1996, 518, 55. (l) Renkema, K. B.; Kissin, Y. V.; Goldman, A. S.
J. Am. Chem. Soc. 2003, 125, 7770. (m) Gottker-Schnetmann, I.; White,
P. S.; Brookhart, M J. Am. Chem. Soc. 2004, 126, 1804, and references
therein.
Results and Discussion
It was previously reported10 that treatment of [PtCl2(NCBut)2]
with La or Lb in refluxing toluene gave the binuclear cyclom-
etalated complexes 1a and 1b, which contain tertiary C-Pt
(5) Liu, F.; Goldman, A. S. Chem. Commun. 1999, 655.
(6) (a) Fekl, U.; Kaminsky, W.; Goldberg, K. J. Am. Chem. Soc. 2003,
125, 15286. (b) Fekl, U.; Goldberg, K. J. Am. Chem. Soc. 2002, 124, 6804.
(c) Fekl, U.; Goldberg, K. J. Am. Chem. Soc. 2001, 123, 6423.
(7) (a) Vedernikov, A. N.; Huffman, J. C.; Caulton, K. G. New J. Chem.
2003, 27, 665. (b) Kostelansky, C. N.; MacDonald, M. G.; White, P. S.;
Templeton, J. L. Organometallics 2006, 25, 2993. (c) Khaskin, E.; Zavalij,
P. Y.; Vedernikov, A. N. J. Am. Chem. Soc. 2006, 128, 13054.
10.1021/om800382m CCC: $40.75
2008 American Chemical Society
Publication on Web 10/08/2008

OxidatiVe Dehydrogenation of Tris(o-isopropylphenyl)phosphines
Organometallics, Vol. 27, No. 22, 2008 5907
Scheme 1
Figure 2. Structure of 3b with hydrogen atoms removed for clarity
(except those on C8). Important geometric parameters include
Pt1-P1 2.242(3), Pt1-C7 2.199(13), Pt1-C8 2.114(13), Pt1-Cl1
2.369(3), Pt1-Cl2 2.310(3), C7-C8 1.404(18) Å.
bonds. We now find that when 1a or 1b is refluxed in
CHCl2CHCl2, a single P-containing complex was observed in
each case. The complex products are assigned the phosphine-
alkene chelate structures 2a and 2b on the basis of elemental
analysis, NMR spectroscopy, and the X-ray crystal structure of
is, there is no molecule with the same configuration at the
sterogenic carbon C7 and a g-g- diaryl conformation. The
chelating phosphino-alkene ligands in 2a,b are related to those
in complexes of (o-vinylphenyl)diphenylphosphine reported by
Bennett et al.11
1
2a (see below). The H and 13C NMR spectra of 2a and 2b
show peaks characteristic of a coordinated alkene (see Experi-
mental Section). Complex 2a was also formed by heating
[PtCl2(NCtBu)2] with La in CHCl2CHCl2 (Scheme 1).
Crystals of 2a were grown from its CDCl3 solution, and the
X-ray crystal structure of 2a, as a chloroform solvate, was
determined (see Figure 1). The molecular structure confirms
that assigned above, with a conventional square-planar Pt(II)
coordination geometry. The conformation of the diaryl portion
of the chelating ligand is of the g+g+ type,10 and only one pair
of (enantiomeric) diastereoisomers is seen in the unit cell; that
The transformation of 1a,b into 2a,b must involve reaction
with the solvent and, since the Cl:Pt ratio has increased from
1:1 to 1:2 (see Scheme 1), an abstraction of a Cl atom has taken
place. Two stoichiometries were considered plausible, where
CHCl2CHCl2 acts as the source of HCl (eq 1) or Cl2 (eq 2).12
The modest yields of 2a,b in the CHCl2CHCl2 reactions were
accompanied by significant decomposition to metallic platinum
and other brown insoluble products, and therefore a more
selective route to 2a,b was sought. To investigate the feasibility
of the reactions shown in eqs 1 and 2, more accessible sources
of HCl and Cl2 than CHCl2CHCl2 were investigated.
0.5 1a,b + HCl f 2a,b + H2
0.5 1a,b + Cl2 f 2a,b + HCl
(1)
(2)
No reaction was observed by 31P NMR spectroscopy upon
treatment of 1a in toluene with a large excess of HCl in diethyl
ether at ambient temperature or at reflux. However 1a reacted
(8) Cu systems that catalyze the oxidative dehydrogenation of cycloal-
kanes with turnover numbers of less than 10 have been described; see:
Vedernikov, A. N.; Caulton, K. G. Chem. Commun. 2004, 162.
(9) Omae, I. Organometallic Intramolecular Coordination Compounds;
Elsevier, Amsterdam, 1986.
(10) Baber, R. A.; Orpen, A. G.; Pringle, P. G.; Wilkinson, M. J.;
Wingad, R. L. Dalton Trans. 2005, 659.
(11) (a) Bennett, M. A.; Nyholm, R. S.; Saxby, J. D. J. Organomet.
Chem. 1967, 10, 301. (b) Bennett, M. A.; Chiraratvatana, C.; Robertson,
G. B.; Tooptakong, U. Organometallics 1988, 7, 1394. (c) Bennett, M. A.;
Chiraratvatana, C.; Robertson, G. B.; Tooptakong, U. Organometallics 1988,
7, 1403.
(12) The mechanism by which the CHCl2CHCl2 delivers the chlorine
to 1a,b is not clear but probably involves Cl radicals. If it were a sequence
of oxidative addition/reductive elimination, then the byproducts would be
CHCldCHCl or CHCldCCl2, but neither was detected by GC/MS analysis
of the final product solution of the reaction of 1a with CHCl2CHCl2. Instead,
several chlorocarbons (including significant amounts of C2Cl6) were
detected, consistent with radicals being involved in the reaction.
Figure 1. Structure of 2a with hydrogen atoms removed for clarity
(except those on C8). Important geometric parameters include
Pt1-P1 2.2426(14), Pt1-C7 2.207(5), Pt1-C8 2.135(5), Pt1-Cl1
2.3651(14), Pt1-Cl2 2.3201(15), C7-C8 1.402(7) Å.

5908 Organometallics, Vol. 27, No. 22, 2008
Baber et al.
Scheme 2
Scheme 3
rapidly with SO2Cl2 (as a source of Cl2) in CH2Cl2 at ambient
temperatures to give 2a, showing that the stoichiometry of eq
2 is viable.
The reaction between SO2Cl2 and 1a was monitored by 31P
NMR spectroscopy. At low conversions to 2a, the only
P-containing species observed were 1a and 2a; that is, no
intermediates were detected. At higher conversions, it was
noticed that a minor species (up to 10%) formed with 31P NMR
parameters (δP 19.0, 1JPtP 3202 Hz) similar to those for 2a (δP
1
17.5, JPtP 3279 Hz). The likely structure of this impurity (3a,
see eq 3) emerged only after the reaction of 1b with SO2Cl2
had been investigated.
Reaction of 1b with an excess of SO2Cl2 initially gave two
products in the ratio 1:1 with similar 31P NMR parameters.13
After 4 h, a single product was present, for which crystals were
grown from its CDCl3 solution and the X-ray crystal of 3b, as
a chloroform solvate, was determined (see Figure 2). The crystal
structure revealed that meta chlorination of the terminal aryl
substituents had occurred in the reaction of 1b with SO2Cl2.
The conformation of the diaryl portion of the chelating ligand
in 3b is again of the g+g+ type, and the configuration at C7 is
also as in 2a. The details of the molecular structure around the
metal in 3b are less precisely determined than for 2a but are
otherwise very similar.
Thus it appears that 2b readily undergoes electrophilic
aromatic substitution by chlorine to afford 3b. This was
confirmed by addition of 2 equiv of SO2Cl2 to 2b, which gave
3b quantitatively (eq 3). The activation by the ortho-directing
methoxy substituents would explain why the electrophilic
aromatic substitution occurs more readily with 2b than with 2a
(eq 3). Notably, it appears that the terminal aryl groups are more
activated to the chlorination than the aryl group that is part of
the chelate.
diplatinum(IV) intermediate A. Dissociation to give a five-
coordinate mononuclear species B would be promoted by the
bulky phosphine. Intermediate B may have an agostic C-H
interaction in the ground state (as depicted in Scheme 2) or in
the transition state of the ꢀ-hydrogen elimination step to give
C. Reductive elimination of HCl from C would give the
observed 2a. This mechanism is reminiscent of Shilov’s
proposal1 to explain the formation of hexene from hexane using
[PtCl6]2- in aqueous solution: ꢀ-hydrogen elimination from the
five-coordinate platinum(IV) species [RCH2CH2PtCl4]- to give
[(η-RCHdCH)Pt(H)Cl4]- followed by HCl loss to give [(η-
RCHdCH)PtCl3]-.
The previously reported10 complexes 4a,b are analogues of
1a,b but have ortho-methyl rather than ortho-isopropyl substit-
uents, and therefore do not have the potential to be dehydro-
genated in the same way as 1a,b. The lack of solubility of 4a
precluded a study of its reactions with SO2Cl2. However
treatment of 4b with SO2Cl2 smoothly gave a 1:1 mixture of
two species with closely similar 31P NMR parameters (δ 29.6,
JPtP 2870 Hz, 28.1, JPtP 2824 Hz). The diplatinum(IV) isomers
5b and 5b′ (eq 4) are assigned to the products on the basis of
1
elemental analysis, mass spectrometry, and H and 31P NMR
spectroscopy (see Experimental Section for the data). Complexes
5b/5b′ are close analogues of the proposed intermediate A, and
their formation supports the mechanism given in Scheme 2.
A mechanism for the conversion of 1a into 2a is proposed
in Scheme 2. Oxidative addition of Cl2 to 1a would give the

OxidatiVe Dehydrogenation of Tris(o-isopropylphenyl)phosphines
Organometallics, Vol. 27, No. 22, 2008 5909
Table 1. Crystallographic Data for 2a · 2CHCl3 and 3b
2a · 2CHCl3
3b
color, habit
size (mm)
formula
M
colorless, block
0.15 × 0.1 × 0.1
C29H33Cl8PPt
891.21
colorless, block
0.2 × 0.18 × 0.18
C30H35Cl4O3PPt
811.47
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P21/c
13.348(3)
15.743(3)
15.330(3)
90.00
109.57(3)
90.00
3035.4(11)
4
j
11.281(3)
12.104(2)
13.133(3)
89.331(15)
76.72(2)
75.780(19)
1689.8(7)
2
R (deg)
ꢀ (deg)
γ (deg)
V (Å-3
)
Z
µ (mm-1
T (K)
)
4.851
173(2)
5.059
100(2)
reflns: total/indep/Rint
final R1
18 174/7680/0.0574 34 003/6966/0.1058
0.0422
0.0951
largest peak, hole (e Å-3
)
1.256, -0.912
1.752
4.729, -4.792
1.776
Fcalc (g cm-3
)
NMR spectra were measured on a Jeol Eclipse 300, Jeol Eclipse
1
400, or Jeol GX 400. Unless otherwise stated, H, 13C, and 31P
NMR spectra were recorded at 300, 100, and 121 MHz, respec-
tively, at +23 °C. Mass spectra were recorded on a MD800.
Elemental analyses were carried out by the Microanalytical Labora-
tory of the School of Chemistry, University of Bristol.
Synthesis of [PtCl2{2-CH2dCMeC6H4P(C6H4(2-iPr))2}] (2a).
Method a. [Pt2Cl2{2-CMe2C6H4PAr2}2] (1a) (0.094 g, 0.076 mmol)
was suspended in CHCl2CHCl2 (5 cm3) and heated at reflux for
4 h to give a yellow solution and some metallic Pt deposit. The
solvent was removed under reduced pressure, and the resulting
residue was dissolved in CDCl3. The solution was filtered through
Florisil to remove the metallic deposit, and the solvent was removed
under reduced pressure to give an off-white solid, 2a (0.054 g,
55%). Colorless crystals were obtained by slowly evaporating the
CDCl3 solution in a NMR tube.
Goldberg et al.6 have shown that one of the isopropyl groups
in the five-coordinate organoplatinum(IV) complex 6 is dehy-
drogenated at elevated temperatures to give 7 via three-
coordinate cycloplatinate(II) intermediate 8 (Scheme 3), which
was formed by elimination of ethane and methane. Complex 6
has some similarities to the organoplatinum(IV) intermediate
B proposed in Scheme 2, although the Pt in 6 is more electron-
rich, and therefore 6 would be less electrophilic than B. The
alkane dehydrogenation mechanisms in Schemes 2 and 3 differ
significantly in that the crucial step involves ꢀ-hydrogen
migration to platinum(IV) in Scheme 2 and to platinum(II) in
Scheme 3.
Method b. [Pt2Cl2{2-CMe2C6H4PAr2}2] (1a) (0.094 g, 0.076 mmol)
was suspended in CH2Cl2 (2 cm3), and an excess of SO2Cl2 (0.1 cm3)
was added. The mixture was stirred for 4 h. The volatiles were then
removed under reduced pressure. The resultant yellow solid was
washed with toluene (3 × 2 cm3) and hexane (3 × 1 cm3) and then
filtered off. The white solid 2a was then dried under reduced pressure
(0.091 g, 92%). Anal. Found (calc for C27H31Cl2PPt): C, 49.64 (49.70);
H, 4.71 (4.79). Mass spectrum (FAB): m/z 652 (M+). NMR (CDCl3):
Conclusion
The oxidative alkane dehydrogenation reported here is
stoichiometric and intramolecular and uses a source of Cl2 as
the oxidant with HCl as the byproduct. This is a long way from
the sought-after catalytic, intermolecular alkane dehydrogenation
using O2 as the oxidant with H2O as the byproduct.2 Neverthe-
less the great facility with which the putative platinum(IV)
activates the alkyl C-H bonds described here suggests that
functionalization of alkanes mediated by electrophilic transition
metal complexes has great potential.
1
31P{1H}, δ 17.5, JPtP 3279 Hz; H, δ 7.66-7.08 (m, 10H, C6H4),
6.79-6.73 (m, 2H, C6H4), 4.97 (s, JPtH 48 Hz, 1H, CCH2), 4.07 (m,
1H, CH(CH3)2), 3.89 (m, 1H, CH(CH3)2), 3.29 (s, JPtH 42 Hz, 1H,
CCH2), 2.49 (s, JPtH 36 Hz, 3H, CCH3), 1.36 (d, 6H, CH(CH3)2), 1.22
(d, 3H, CH(CH3)2), 0.22 (d, 3H, CH(CH3)2); 13C{1H}, δ 163.3 (d,
JPC 5 Hz) 163.0 (s), 162.9 (d, JPC 5 Hz), 156.4 (d, JPC 12 Hz) 156.2
(d, JPC 12 Hz), 154.0 (d, JPC 18 Hz), 135.9 (d, JPC 5 Hz), 135.3 (d, JPC
11 Hz), 134.8 (d, JPC 13 Hz), 122.1 (d, JPC 69 Hz), 115.8 (d, JPC 70
Hz), 115.0 (d, JPC 10 Hz), 114.5 (d, JPC 6 Hz), 114.3 (d, JPC 7 Hz),
112.5 (d, JPC 5 Hz), 112.1 (d, JPC 12 Hz), 111.4 (d, JPC 14 Hz), 110.6
(d, JPC 13 Hz), 74.2 (s), 70.4 (JPtC 151), 33.1 (d, JPC 6 Hz), 32.8 (d,
JPC 9 Hz), 27.8 (s), 24.7 (s), 24.1 (s), 23.6 (s), 22.8(s).
Experimental Section
General Considerations. Unless otherwise stated, all work was
carried out under a dry nitrogen atmosphere, using standard Schlenk
line techniques. Dry N2-saturated solvents were collected from a
Grubbs system14 in flame- and vaccuum-dried glassware. Com-
plexes 1a,b and 4b were made by the previously reported method.10
Synthesis of [PtCl2{2-CH2dCMeC6H3(4-OMe)P(C6H3(2-iPr)(4-
OMe))2}] (2b). [Pt2Cl2{2-CMe2C6H3(4-OMe)PAr2}2] (1b) (0.100
g, 0.070 mmol) was suspended in CHCl2CHCl2 (5 cm3) and heated
at reflux for 4 h to give a yellow solution and some metallic Pt
deposit. The solvent was removed under reduced pressure, and the
resulting residue was dissolved in CDCl3. The solution was filtered
through Florisil to remove the metallic deposit, and the solvent was
removed under reduced pressure to give an off-white solid, 2b
(0.047 g, 45%). Anal. Found (calc for C30H37Cl2O3PPt): C, 47.90
(48.52); H, 5.38 (5.02). Mass spectrum (ESI): m/z 742 (M+). NMR
(CDCl3): 31P{1H}, δ 12.0, JPtP 3249; 1H, δ 7.27-6.65 (m, 9H,
(13) Presumably the monochloroaryl complex [PtCl2{2-CH2dCMeC6H3(4-
OMe)P(C6H2(2-iPr)(4-OMe)(5-Cl))(C6H2(2-iPr)(4-OMe))}] intermediate must
also be formed, but this was not detected in the 31P NMR spectrum either
because it is formed in only small quantities or its signals are masked by
those for 3b.
(14) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

5910 Organometallics, Vol. 27, No. 22, 2008
Baber et al.
C6H3), 4.99 (t, JPtH 48 Hz, 1H, CCH2), 4.13 (t, 3.74, 2H, CH(CH3)2),
3.89 (s, 3H, OCH3), 3.87 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 3.35
(s, JPtH 72 Hz, 1H, CCH2), 2.51 (s, JPtH 42 Hz, 3H, CCH3), 1.42
(d, 6H, CH(CH3)2), 1.30 (d, 3H, CH(CH3)2), 0.38 (d, 3H,
CH(CH3)2); 13C{1H} (CD2Cl2), δ 163.6 (s), 163.4 (d, JPC 2 Hz),
163.3 (d, JPC 2 Hz), 158.5 (d, JPC 10 Hz), 156.2 (d, JPC 13 Hz),
155.2 (d, JPC 9 Hz), 154.9 (d, JPC 10 Hz), 154.2 (d, JPC 12 Hz),
153.9 (d, JPC 11 Hz), 135.9 (s), 135.2 (d, JPC 11 Hz), 134.5 (d, JPC
11 Hz), 121.4 (d, JPC 38 Hz) 119.4 (d, JPC 14 Hz), 115.5 (d, JPC 10
Hz), 115.3 (d, JPC 11 Hz), 112.4 (d, JPC 12 Hz), 111.6 (d, JPC 12
Hz), 74.3 (s), 70.6 (JPtC 102 Hz), 33.3 (d, JPC 9 Hz), 32.8 (d, JPC
8 Hz), 27.4 (s), 24.5 (s), 23.6 (s), 23.2 (s), 22.3 (s).
1.82 (s, 3H, CH3); 13C{1H}, δ 163.1 (s), 162.8 (d, JPC 4 Hz), 155.8
(d, JPC 12 Hz), 144.6 (br m), 131.4 (t, JPC 7.5 Hz), 121.1 (s), 120.0
(s), 117.8 (br m), 113.3 (m), 111.4 (m), 55.7 (s), 55.5 (s), 55.4 (s),
41.7 (br m), 23.3 (s).
X-ray Crystal Structure Analyses. X-ray diffraction experi-
ments on 2a as its chloroform solvate were carried out at 173 K
on a Bruker SMART diffractometer and on 3b at 100 K on a Bruker
SMART APEX diffractometer, using Mo KR X-radiation (λ )
0.71073 Å) and a CCD area detector, on single crystals coated
in paraffin oil and mounted on a glass fiber. Intensities were
integrated15 from several series of exposures, each exposure
covering 0.3° in ω. Absorption corrections were based on equivalent
reflections using SADABS V2.10,16 and structures were refined
Synthesis of [PtCl2{2-CH2dCMeC6H3(4-OMe)P(C6H2(2-iPr)(4-
OMe)(5-Cl))2}] (3b). [Pt2Cl2{2-CMe2C6H3(4-OMe)PAr2}2] (1b)
(0.100 g, 0.070 mmol) was suspended in toluene (10 cm3), and an
excess of SO2Cl2 (0.2 cm3) was added. The mixture was stirred
for 4 h. The volatiles were removed under reduced pressure. The
resulting off-white solid was washed with hexane (3 × 10 cm3) to
give 3b (0.076 g, 67%). Colorless crystals of 3b were obtained
from a toluene solution layered by hexane. Anal. Found (calc for
C30H35Cl4O3PPt): C, 45.61 (44.77); H, 4.75 (4.35). Mass spectrum
(ESI): m/z 811 (M+). NMR (CDCl3): 31P{1H}, δ 11.29, JPtP 3278
2
against all Fo data with hydrogen atoms riding in calculated
positions using SHELXTL17 Crystal and refinement data are given
in Table 1. Data for 3b were of low intensity and poor quality,
leading to high Rint and R1 values and a final difference map with
large electron density features within 1 Å of the platinum atom
but otherwise reasonable refinement characteristics.
Acknowledgment. We thank ORSAS and EPSRC for
support, Johnson Matthey for a loan of K2[PtCl4], The
Leverhulme Trust for a Research Fellowship (to P.G.P.), and
Claire McMullin for help with the presentation of the X-ray
material. D.W.N. thanks the Natural Sciences and Engineer-
ing Research Council of Canada (NSERC) and The Royal
Society for Postdoctoral Fellowships.
1
Hz; H, δ 7.27-6.79 (m, 7H, C6H3, C6H2), 5.03 (s, 1H, JPtH 54
Hz, CCH2), 4.04 (s, 3H, OCH3), 3.94 (s, 3H, OCH3), 3.92 (s, 3H,
OCH3), 3.87 (br, 3.74, 2H, CH(CH3)2), 3.36 (s, 1H, JPtH 66 Hz,
CCH2), 2.52 (s, 3H, JPtH 42 Hz, CCH3), 1.42 (d, 6H, CH(CH3)2),
1.31 (d, 3H, CH(CH3)2), 0.38 (d, 3H, CH(CH3)2).
Synthesis of the Diplatinum(IV) Complexes 5b/5b′. [Pt2Cl2{2-
CH2C6H3(4-OMe)PAr2}2] (4b) (0.25 g, 0.20 mmol) was dissolved
in CH2Cl2 (3 cm3), and SO2Cl2 (0.064 cm3, 0.8 mmol) added
dropwise to give a dark orange solution. Et2O (12 cm3) was added
after 20 min, and the resulting precipitate collected on a frit and
dried under reduced pressure to give a bright yellow powder, 5b/
5b′ (0.24 g, 86%). Anal. Found (calc for C48H52Cl6O6P2Pt2): C,
41.46 (41.48); H, 3.92 (3.77). High-resolution ESI mass spectrum
(calc for M+): m/z 1386.06603 (1386.06660). NMR (CD2Cl2):
31P{1H} (1:1 mixture of isomers), δ 29.6, JPtP 2870 Hz, 28.1, JPtP
Supporting Information Available: X-ray crystal data, atomic
coordinates, bond lengths and angles, and thermal displacement
parameters for compounds 2a · 2CHCl3 and 3b. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM800382M
(15) SAINT integration software; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1994.
(16) Sheldrick, G. M. SADABS V2.10; University of Go¨ttingen, 2003.
(17) SHELXTL program system Version 5.1; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.
1
2824 Hz; H (recorded at -80 °C), δ 7.25-6.48 (m, 18H, C6H3),
3.79 (br s, 18H, OCH3), 1.98 (br m, 2H, CH2), 1.85 (s, 3H, CH3),