"β-cis-SAr effect" on decarbonylation from α,β-unsaturated acyl and aroyl complexes

Article abstract of DOI:10.1039/b515616e

Lone pair of heteroatom located at the β-cis position in α,β-unsaturated acyl and aroyl group 10 metal complexes dramatically facilitated the stoichiometric and catalytic decarbonylation reactions. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b515616e

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
‘‘b-cis-SAr effect’’ on decarbonylation from a,b-unsaturated acyl and
aroyl complexes{
Tomohiro Kato, Hitoshi Kuniyasu,* Takamichi Kajiura, Yasunori Minami, Atsushi Ohtaka,
Masanori Kinomoto, Jun Terao, Hideo Kurosawa and Nobuaki Kambe*
Received (in Cambridge, UK) 3rd November 2005, Accepted 12th December 2005
First published as an Advance Article on the web 18th January 2006
DOI: 10.1039/b515616e
The 1H NMR spectrum taken after 20 min indicated the
Lone pair of heteroatom located at the b-cis position in
formation of a platinum complex 6a by a couple of Me singlets at
d 1.72 and d 2.18 as well as a vinyl singlet at d 6.35 with JPt-H
a,b-unsaturated acyl and aroyl group 10 metal complexes
dramatically facilitated the stoichiometric and catalytic
decarbonylation reactions.
=
28.8 Hz in 93% yield and its 31P NMR spectrum showed the
formation of 2% of suspected CO-coordinated vinylplatinum
complex 7a (vide infra) and 5% of cis-Pt[(Z)-CHLC(Stol-p)-
(Ph)](Stol-p)(PPh3)2 (cis-4a).4 It must be noted that the signals of
2a, 3a and even 6a and free PPh3 were not detected by 31P NMR
under the present conditions. The yield of 4a increased to 35%
yield after 3 h and additional heating at 60 uC for 2 h resulted in
the formation of 4a and 49a (dimeric form of 4a) in good combined
yields (97%).5 In stark contrast, the reaction of (E)-
PhC(H)LCHC(O)(Stol-p) (1b) with 5 generated 2b and 3b as
major products3 and only a trace amount of the corresponding
vinylplatinum complex trans-Pt[(E)-C(H)LCH(Ph)](Stol-p)(PPh3)2
(trans-4b) (0.5%) was furnished after 3 h at 25 uC and heating the
solution at 60 uC for 5 h resulted in the formation of a complicated
mixture, which included 13% of trans-4b.6
Revealing how to activate organic compounds in collaboration
with metal complexes is one of the most fascinating topics in
current chemistry.1 Now it is well-acknowledged that the
coordination of a lone pair of heteroatoms to metals can direct
and facilitate various types of reactions represented by the
oxidative addition of inert bonds to low-valent transition-metal
complexes.2 Herein we wish to report on a novel type of activation
utilizing the coordination of a lone pair on sulfur to metals: the
decarbonylation from a,b-unsaturated acyl and aroyl complexes.
Recently, we have disclosed that substituent effects on the reac-
tions of a,b-unsaturated carbonyl compounds with low-valent
metals were clearly elicited by exploiting fine-tunable reactivity of the
C–S bond of thioester 1 having substituents at A and B toward
platinum(0)-complex to give p-complex 2 and acyl complex 3, which
can potentially lead to the formation of vinyl complex 4(Scheme 1).3
With respect to 6a, a good crystal suitable for X-ray crystal-
lographic analysis was gratifyingly obtained from chlorobenzene/
pentane solution, and its ORTEP diagram is shown in Fig. 1,
demonstrating that 6a was the acyl complex with b-cis-SAr
˚
coordination to Pt. The S–Pt distance was 2.32 A, much shorter
7
than the sum of van der Waals radii (3.55 A) and the five-
˚
membered ring lay almost coplanar with the Pt(II) square plane.8
The 31P NMR spectra of the crystal of 6a dissolved in C6D6
Scheme 1
showed two singlets at d 30.0 (JPt-P = 4571 Hz) and d 17.5 (JPt-P
=
During the course of further endeavors to understand the
substituent effects, the reaction of (Z)-(Ph)(p-tolS)CLCHC(O)-
(Stol-p) (1a) (0.022 mmol) with Pt(PPh3)2(C2H4) (5) (0.020 mmol)
was examined in C6D6 (0.5 mL) at 25 uC using SLP(C6H4OMe-p)3
as an internal standard (eqn (1)).
1737 Hz) in a ratio of 92 : 8. The former was ascribed to 6a, in
(1)
Department of Applied Chemistry & Frontier Research Center, Graduate
School of Engineering, Osaka University, 2-1 Yamadaoka Suita, Osaka,
565-0871, Japan. E-mail: kuni@chem.eng.osaka-u.ac.jp;
kambe@chem.eng.osaka-u.ac.jp; Fax: +81 6 6879 7390;
Tel: +81 6 6879 7389
{ Electronic supplementary information (ESI) available: Reaction details,
NMR spectra and crystal structure. See DOI: 10.1039/b515616e
Fig. 1 ORTEP diagram of 6a (Ph on PPh3 omitted).
868 | Chem. Commun., 2006, 868–870
This journal is ß The Royal Society of Chemistry 2006

View Article Online
Table 2 The Pd-catalyzed decarbonylation of 9a
which weak intramolecular b-cis-SAr coordination induced a
significantly large JPt-P value. The latter signal can be tentatively
assigned to Pt[(Z)-C(H)LC(Stol-p)(Ph)](Stol-p)(PPh3)(CO) (7a)
judging from the JPt-P value9 and CO stretching (2065 cm21) of
IR spectrum in solution.10 Leaving the sample at 25 uC gradually
produced dimeric acyl platinum 39a3 in 46% after 6 h (eqn. (2)).
Entry
9
Ar
10
Yield (%)b
1
2
3
4
5
6
7
a
9a
9b
9c
9d
9e
9f
Ph
10a
10b
10c
10d
10e
10f
10g
10
97
10
71
13
92
3
o-PhSC6H4
p-PhSC6H4
o-ClC6H4
p-ClC6H4
o-MeOC6H4
p-MeOC6H4
ð2Þ
9g
9 (0.5 mmol) and Pd(PPh3)4 (5 mol%) under toluene (0.5 mL)
b
reflux for 1 h. Isolated yield.
On the other hand, when a catalytic amount of PPh3
(0.26 equiv.) was added into the solution of the crystal of 6a,
only the signals of 7a (4%) and cis-4a (5%) were detected at 25 uC,
while the signal of 6a (82%) was clearly detected by the 1H NMR
spectrum.
decarbonylation to produce the corresponding vinylsulfide 8a in
98% yield after 1 h (Entry 2). Similar results were also obtained
when n-C6H13 and SAr were introduced at A and C to form the
corresponding vinylsulfide 8c in 95% yield after 3 h (Entry 3), while
the decarbonylation hardly proceeded when 1d (A = Stol-p, C =
n-C6H13), the stereoisomer of 1c, was employed as a substrate (6%
of 8d) (Entry 4). Moreover, the generality of the present principle
was validated using decarbonylation of arylthioester ArC(O)Stol-p
(9) (Table 2).
Scheme 2
As expected, the dramatic facilitation of decarbonylation was
observed by introducing o-SPh (9b) to produce 10b in 97% yield,
although 9a (Ar = Ph) and 9c (Ar = p-SPh) underwent
decarbonylation only in 10% in both cases (90% of 9a and 9c
both recovered) (Entries 1–3). Intriguingly, the present prototype
was not confined to the b-cis-SAr group. Significant (Entry 4 vs.
Entry 5) and quite remarkable (Entry 6 vs. Entry 7) facilitation was
also shown by o-Cl and o-MeO groups. A possible reaction route
of the present palladium-catalyzed decarbonylation is shown in
Scheme 3. After the oxidative addition of 1 (or 9) to the Pd(0)-
complex took place to form 11, the lone pair in C (C = SAr, Cl,
OMe) would spontaneously coordinate to the Pd-center to form
12. The decarbonylation, the rate-determining step of the whole
Pd-catalyzed decarbonylation, would be much faster from 12
than that from 11 to afford vinyl or aryl palladium 13, from which
Taking the foregoing facts into account, after the formation of
trans-3a, b-cis-SAr would promptly coordinate to Pt to generate 6a
overwhelmingly (Scheme 2). In the presence of free PPh3, there
would be fast interconversion between trans-3a and 6a, although,
probably due to the entropic factor, the equilibrium between trans-
3a and 6a strongly leaned to the side of 6a at 25 uC.11 This is why
the signals of 6a, free PPh3 and a trace amount of trans-3a were
submerged into the baseline of the 31P NMR chart, although the
1H NMR signals of Me and vinyl of 6a were hardly affected by
this exchange. The vinyl moiety of 6a would migrate onto Pt with
the assistance of b-cis-SAr coordination to generate 7a, which was
gradually trapped by PPh3 to afford vinylplatinum cis-4a as a
kinetic product.12,13,4 In the absence of free PPh3, 6a (or via trace
amount of 3a) would slowly produce dimeric 39a.
Furthermore, the utility of the present "b-cis-SAr effect" was
attested by catalytic decarbonylation of 1 (Table 1).14,15
In contrast to the fact that no decarbonylation of 1b (A = Ph,
C = H) took place in the presence of 5 mol% of Pd(PPh3)4 under
benzene reflux for 5 h (Entry 1), 1a successfully underwent
Table 1 The Pd-catalyzed decarbonylation of 1a
Entry
1
A
C
Time/h
8
Yield (%)b
1
2
3
4
a
1b
1a
1c
1d
Ph
Ph
n-C6H13
p-tolS
H
5
1
3
3
8b
8a
8c
8d
0
98
95
6
p-tolS
p-tolS
n-C6H13
1 (0.5 mmol) and Pd(PPh3)4 (5 mol%) under C6H6 (0.5 mL) reflux.
Isolated yield.
Scheme 3 Proposed mechanism of the Pd-catalyzed decarbonylation of
b
thioester.
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 868–870 | 869

View Article Online
reflections measured, 8619 unique, R(I > 2.0s (I)) = 0.059, and Rw(all
reflections) = 0.172. It is possible that methyl H atoms of two C6H4Me-p
groups are incorrectly oriented.
8 (or 10) was reductively eliminated with the regeneration of the
Pd(0)-complex.
In conclusion, this paper revealed that the lone pair of the
heteroatom located at the b-cis position in a,b-unsaturated acyl
and aroyl group 10 metal complexes can significantly promote the
decarbonylation process. Although the coordination of sulfur to
metal has often been considered to suppress catalytic reactions,16
the results described herein clearly substantiate that the sulfur
functionality present at pertinent positions can rather effectively
function as a powerful promoter.
8 It has been reported that stable metalacycles with similar fragments such
as CpM[(Z)-C(O)C(E)LC(E)(SR)](CO)n (M = Fe, Mo, W; E = CF3,
C(O)OMe) have been formed by cycloaddition reactions, see: (a)
M. M. Kubicki, R. Kergoat, H. Scordia, L. C. Gomes de Lima,
J. E. Guerchais and P. L’Haridon, J. Organomet. Chem., 1988, 340, 41;
(b) M. M. Kubicki, L. C. Gomes de Lima, H. Scordia, J. E. Guerchais
and P. L’Haridon, J. Organomet. Chem., 1989, 367, 143; (c) L. Carlton,
J. L. Davidson and M. Shiralian, J. Chem. Soc., Dalton Trans., 1986,
1577; (d) P. Veya, C. Floriani, A. Chiesi-Villa and C. Rizolli,
Organometallics, 1993, 12, 4646; (e) S. Lee, K. Cheung and W. Wong,
J. Organomet. Chem., 1995, 494, 273 and references therein.
9 It has been reported the JPt-P values of trans CO, SAr, and vinyl of
PPh3-ligated Pt(II)-complexes were ranging about >3500 Hz, 2700–
3100 Hz and 1500–1800 Hz, respectively. G. K. Anderson and
R. J. Cross, J. Chem. Soc., Dalton Trans., 1980, 1434. See also ref. 3
and 4.
10 M. Gerisch, F. W. Heinemann, C. Bruhn, J. Scholz and D. Steinborn,
Organometallics, 1999, 18, 564.
11 The 31P NMR spectrum of a solution of 6a and PPh3 (1.5 equiv.)
taken at 270 uC and 250 uC detected mixtures of trans-3a/6a in the
ratios of 56 : 44 and 8 : 92, respectively. See the ESI for more
details.
12 There can be two possible mechanisms. One is the migration of the vinyl
moiety to a vacant coordination site of Pt(II)-complex 6a and the other
is a coplanar slippage of vinyl carbon to the b-cis-SAr coordination site
with the C–S bond gradually cleaved.
Notes and references
1 (a) M. C. Whisler, S. MacNeil, V. Snieckus and P. Beak, Angew. Chem.,
Int. Ed., 2004, 43, 2206; (b) P. Beak, A. Basu, D. J. Gallagher, Y. S. Park
and S. Thayumanavan, Acc. Chem. Res., 1996, 29, 552; (c) V. Snieckus,
Chem. Rev., 1990, 90, 879; (d) P. Beak and A. I. Meyers, Acc. Chem.
Res., 1986, 19, 356; (e) A. H. Hoveyda, D. A. Evans and G. C. Fu,
Chem. Rev., 1993, 93, 1307.
2 For reviews of oxidative addition, see: (a) M. Albrecht and G. van
Koten, Angew. Chem., Int. Ed., 2001, 40, 3750; (b) M. E. van der Boom
and D. Milstein, Chem. Rev., 2003, 103, 1759; (c) V. Ritleng, C. Sirlin
and M. Pfeffer, Chem. Rev., 2002, 102, 1731; (d) F. Kakiuchi and
N. Chatani, Adv. Synth. Catal., 2003, 345, 1077.
3 H. Kuniyasu, T. Kato, Y. Minami, J. Terao and N. Kambe,
Organometallics, submitted.
13 Meyer et al. have recently proposed that a similar coordination by SeAr
to Pd promoted the carbonylation of vinylpalladium. (a) D. J. Knapton
and T. Y. Meyer, J. Org. Chem., 2005, 70, 785; (b) D. J. Knapton and
T. Y. Meyer, Org. Lett., 2004, 6, 687.
14 K. Osakada, T. Yamamoto and A. Yamamoto, Tetrahedron Lett., 1987,
28, 6321.
15 H. Kuniyasu and H. Kurosawa, Chem.–Eur. J., 2002, 8, 2669.
16 L. L. Hegedus and R. W. McCabe, Catalyst Poisoning, Marcel Dekker,
New York, 1984.
4 H. Kuniyasu, A. Ohtaka, M. Kinomoto and H. Kurosawa, J. Am.
Chem. Soc., 2000, 122, 2375.
5 Instead of heating, N2 gas bubbling was also efficient for decarbonyla-
tion to yield 4a selectively in good yield.
6 S. P. Dent, C. Eaborn and A. Pidcock, J. Organomet. Chem., 1975, 97,
307.
7 Crystal data of 6a: space group triclinic P-1 (No. 2) with a = 9.5969(5) A,
˚
˚
˚
b = 11.1578(3) A, c = 19.2187(6) A, a = 83.794(2)u, b = 89.248(5)u, c =
68.512(3)u, Z = 2, r = 1.455 g cm23, m(MoKa) = 38.53 cm21, 18020
870 | Chem. Commun., 2006, 868–870
This journal is ß The Royal Society of Chemistry 2006