Cleavage of C-S and O-H bonds by platinum(O) complexes to give five-membered 1,2-oxaplatinacycles

Article abstract of DOI:10.1002/anie.201001937

chemical equation presented Spectacular platinum(0): 1,2-Oxaplatinacycles 2 were formed unexpectedly from 2-hydroxybenzyl sulfide derivatives 1 by bond cleavage mediated by platinum(O) (see scheme; nb = norbornene). The thermal reaction of 2 gave novel six-membered 1,2,3-oxaphosphaplatinacycles through ring expansion accompanied by the insertion of a phosphorus atom into the Pt-O bond and the 1,2-shift of a phenyl group.

Full text of DOI:10.1002/anie.201001937

Communications
DOI: 10.1002/anie.201001937
Oxaplatinacycles
À
À
Cleavage of C S and O H Bonds by Platinum(0) Complexes To Give
Five-Membered 1,2-Oxaplatinacycles**
Norio Nakata, Noriyuki Furukawa, Tomoyuki Toda, and Akihiko Ishii*
À
À
À
C S bonds are known to be efficiently activated by transition
reaction of 5a involving the unexpected P C/Pt O meta-
thesis.
À
metals and lead, through cleavage of C S bonds, to novel
sulfur compounds or sulfide complexes. This transformation
allows insight into the related processes that may occur during
heterogeneous catalytic processes.[1] The platinum(0)-medi-
We have examined the coordination ability of [OSSO]-
type diphenolate 6[11] as a chelate ligand toward transition-
metal complexes. When 6 was treated with 3 equivalents of
[Pt(h2-nb)(PPh3)2] in toluene,[12] the activation of both ben-
À
ated C S bond cleavage reactions have been well studied and
2
[2]
zylic C S and O H bonds[13] in 6 occurred unexpectedly and
gave novel 1,2-oxaplatinacycle 5b and cis-(dithiolato)PtII
complex 7[14] in 72% and 69% yields, respectively
(Scheme 1). On monitoring this reaction that was carried
out in a sealed NMR tube, the generation of H2 was observed
by 1H NMR spectroscopy (d = 4.21 ppm in C6D6).
À
À
À
are established for the C(sp ) S bonds of thiophene,
thioester,[3] and vinyl sulfide.[4] However, to the best of our
3
À
knowledge, a simple C(sp ) S bond activation with plati-
num(0) complexes has never been explored. Meanwhile,
oxametallacycles are of great interest because of their unique
structure and catalytic activity. Although there are several
reports on the preparation and application of oxametalla-
cycles containing nickel[5,6] or palladium,[7] the chemistry of
oxaplatinacycle is limited. Pregosin and co-workers have
reported
the
synthesis
of
five-membered
acyl-
(oxa)platinacycle 1 by the reaction of salicylaldehyde with
K2PtCl4 in the presence of PPh3.[8] Also, Sweigart and co-
À
workers have described that the platinum(0)-mediated C O
bond cleavage reaction of benzofuran afforded the six-
membered oxaplatinacycle 2.[9] As a four-membered ana-
logue, Sharp and co-workers have reported the formation and
unique reactivity of platinaoxetane 3 (cod = 1,5-cycloocta-
3
diene).[10] Herein, we report the cleavage of C(sp ) S and
À
À
Scheme 1. Reaction of [OSSO]-type diphenolate 6 with [Pt(h2-nb)-
(PPh3)2]. nb=norbornene.
O H bonds of 2-hydroxybenzyl sulfide derivatives 4 medi-
ated by platinum(0). This process led to an unusual formation
of novel five-membered 1,2-oxaplatinacycles (5a, 5b; see
Scheme 2 for structures). We also describe the thermal
To elucidate the general validity of this platinum(0)-
À
À
mediated benzylic C S and phenolic O H bond activation,
we examined the reactions of alkyl or aryl 2-hydroxybenzyl
sulfides 4a–d, which have only half the framework of 6
(i.e. [Pt(h2-nb)(PPh3)2]). The reactions readily proceeded in
toluene at room temperature and gave the corresponding
1,2-oxaplatinacycles 5a or 5b in 55–84% yields, together with
polymeric thiolato PtII complexes [Pt(SR)2]n as insoluble
materials (Scheme 2). When 4b was allowed to react with
[Pt(h2-nb)(PPh3)2] in the presence of an excess amount of
PPh3 in toluene at room temperature, 5a and the bis(thiolato)
PtII complex cis-[Pt(SPh)2(PPh3)2] 8,[15] instead of polymeric
thiolato Pt complexes, were formed in 16% and 38% yields,
respectively. These results show that substrates having a set of
[*] Dr. N. Nakata, N. Furukawa, T. Toda, Prof. Dr. A. Ishii
Department of Chemistry, Graduate School of Science
and Engineering, Saitama University
255 Shimo-okubo, Sakura-ku, Saitama 338-8570 (Japan)
Fax: (+81)48-858-3700
E-mail: ishiiaki@chem.saitama-u.ac.jp
À
À
phenolic O H and the ortho benzylic C S bonds react with a
platinum(0) complex to yield five-membered oxaplatina-
cycles and thiolato PtII complexes, where 1.5 equivalents of
the platinum(0) complex are required for the stoichiometric
Homepage: http://www.chem.saitama-u.ac.jp/ishii-lab/
[**] This work was supported by a Grant-in-Aid for Scientific Research on
Priority Areas (nos. 19027014 and 20036013, Synergy of Elements)
from the Ministry of Education, Culture, Sports, Science and
Technology (Japan).
1
reaction. In the H NMR spectra, the characteristic benzylic
protons resonate at d = 2.75 ppm (3J(P,H) = 9, 3 Hz) for 5a
and 2.77 ppm (3J(P,H) = 9, 3 Hz) for 5b as a doublet of
doublets. The 31P{1H} NMR spectra showed two doublet
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201001937.
5784
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 5784 –5787

Angewandte
Chemie
À
of Pt1 P2 (2.232(2) ꢀ), thus suggesting the higher trans
influence of the benzylic carbon atom compared to the
oxo ligand.
We next investigated the thermal reaction of oxaplatina-
cycle 5a.[17] A solution of 5a in toluene at reflux for 24 hours
gave the novel six-membered 1,2,3-oxaphosphaplatinacycle 9
in 39% yield after column chromatography on silica gel
(Scheme 3). The thermal reaction of 5a in xylene at reflux
Scheme 2. Reactions of alkyl or aryl 2-hydroxybenzyl sulfides 4a–d with
[Pt(h2-nb)(PPh3)2]. Cy=cyclohexyl, Tol=tolyl.
signals with the 195Pt satellites at d = 16.3 (1J(Pt,P) = 3972 Hz)
and 27.8 ppm (1J(Pt,P) = 1788 Hz) for 5a and d = 17.4
(1J(Pt,P) = 3947 Hz) and 28.1 ppm (1J(Pt,P) = 1743 Hz) for
5b (see the Supporting Information). These resonances were
assigned to the signals resulting from the phosphorus atoms
lying trans with respect to the oxygen and benzylic carbon
atoms, respectively. The molecular structure of 5a was
confirmed by X-ray crystallography (Figure 1).[16] In the
crystalline state, the platinum core lies at the centre of a
slightly distorted square-planar coordination sphere consist-
ing of two PPh3 ligands as well as oxygen and carbon atoms.
The P1-Pt1-P2 angle of 98.33(10)8 deviates considerably from
Scheme 3. Thermal reactions of oxaplatinacycle 5a.
À
the ideal 908 of a square-planar geometry. The Pt1 O1 bond
length was 2.082(7) ꢀ, which is similar to those of related
produced 9 and its cis isomer 10 in 38% and 41% yield,
respectively (Scheme 3). A small amount of the starting
material, 5a, was recovered from these thermal reactions
(27% and 20% yield, respectively). It is interesting to
compare this ring expansion by the insertion of a ligated
oxaplatinacycles 1 (2.07(1) ꢀ)[8] and 2 (2.067(1) ꢀ).[9] The
Pt1 P1 bond length (2.329(3) ꢀ) was slightly longer than that
À
À
phosphorus atom into the Pt O bond. Van Leeuwen and
Roobeek reported the insertion of a ligated phosphorus atom
accompanied by a 1,2-shift of a phenyl group on the
phosphorus atom with the thermal ring contraction of 1,3,2-
oxaphosphaplatinacycle 11 that gave platinum(II) complex
12, which has a 3H-2,1-benzoxaphosphole ligand.[18,19] They
proposed a mechanism involving nucleophilic attack of the
oxygen atom bound at the platinum center at the phosphorus
atom in the ring and a 1,2-shift of a phenyl group on the
phosphorus atom (Scheme 4).[18b,19]
The molecular structures of 9 and 10 were characterized
1
by H, 13C{1H}, and 31P{1H} NMR spectroscopy, and finally
verified by X-ray crystallography. The 31P{1H} NMR spectrum
of 9 displays two nonequivalent doublet signals with 195Pt
satellites and 31P coupling at d = 29.9 (2J(P,P) = 475, 1J(Pt,P) =
1
2948 Hz) and 142.3 ppm (2J(P,P) = 475, J(Pt,P) = 3899 Hz).
In sharp contrast, the 31P{1H} NMR spectrum of 10 exhibits
two nonequivalent singlet signals at d = 22.8 and 137.3 ppm
with the 195Pt satellites of 2080 and 2300 Hz, respectively. The
lower-field signals of complexes 9 (d = 142.3 ppm) and 10
(d=137.3 ppm) are assigned to the phosphorus atoms of the
phosphinite ligands, and these chemical shift values are
Figure 1. ORTEP drawing of oxaplatinacycle 5a with thermal ellipsoids
drawn at the 30% probability level. Selected bond lengths [ꢀ] and
bond angles [8]: Pt1–O1 2.082(7), Pt1–C1 2.096(9), Pt1–P1 2.329(3),
Pt1–P2 2.232(2); O1-Pt1-C1 82.9(3), O1-Pt1-P1 85.1(2), C1-Pt1-P2
94.5(2), P1-Pt1-P2 98.33(10), Pt1-C1-C2 107.3(6), C1-C2-C3 117.5(10),
C2-C3-O1 121.9(11).
Angew. Chem. Int. Ed. 2010, 49, 5784 –5787
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5785

Communications
Scheme 4. Thermal reaction of 1,3,2-oxaphosphaplatinacycle 11.
similar to that reported by van Leeuwen and Roobeek for
complex 11 (d = 125.9 ppm (1J(Pt,P) = 2730 Hz)).[18] In the X-
ray structures (Figure 2 and 3),[16] the platinum atoms in each
oxaphosphaplatinacycle 9 and 10 formed a distorted square-
Figure 3. ORTEP drawing of 1,2,3-oxaphosphaplatinacycle 10 with
thermal ellipsoids drawn at the 30% probability level (a solvated
hexane molecule was omitted for clarity). Selected bond lengths (ꢀ)
and bond angles [8]: Pt1–C1 2.119(4), Pt1–C8 2.057(4), Pt1–P1
2.2618(10), Pt1–P2 2.2920(10), P1–O1 1.640(3); C1-Pt1-P1 81.44(12),
C1-Pt1-C8 87.70(16), C8-Pt1-P2 88.45(11), P1-Pt1-P2 102.35(4), Pt1-P1-
O1 111.21(11), P1-O1-C3 123.03, O1-C3-C2 120.5(4), C2-C1-Pt1
106.0(3).
the crude reaction mixture. In addition, the conversion of 10
into 9 and/or 5a was also observed when 10 was heated under
the same reaction conditions (the ratio of 9/5a/10 was
35:20:45 based on the integral ratio of the 31P{1H} NMR
spectrum of the crude reaction mixture). These results
indicate that the rearrangement is governed by the thermal
equilibrium among five-membered oxaplatinacycle 5a and
six-membered oxaphosphaplatinacycles 9 and 10. As shown in
Scheme 5, the rearrangement of 5a into 9 and 10 can be
explained by the initial nucleophilic attack of the phenoxido
ligand in 5a at the coordinated cis phosphorus center to give a
betaine intermediate 13, and subsequent migration of a
Figure 2. ORTEP drawing of 1,2,3-oxaphosphaplatinacycle 9 with ther-
mal ellipsoids drawn at the 30% probability level (the solvated CH2Cl2
molecules were omitted for clarity). Selected bond lengths (ꢀ) and
bond angles [8]: Pt1–C1 2.153(6), Pt1–C8 2.088(6), Pt1–P1 2.2240(16),
Pt1–P2 2.2968(15), P1–O1 1.635(4); C1-Pt1-P1 87.55(17), C1-Pt1-P2
91.96(18), C8-Pt1-P1 89.92(17), C8-Pt1-P2 91.25(17), Pt1-P1-O1
113.81(17), P1-O1-C3 117.2(4), O1-C3-C2 121.6(6), C2-C1-Pt1 114.4(4).
planar coordination sphere with phenyl, PPh3, phosphinite,
and benzylic carbon ligands. In both complexes 9 and 10, the
À
Pt1 P1 bond lengths (9: 2.2240(16), 10: 2.2618(10) ꢀ) were
À
somewhat shorter than those of the Pt1 P2 (9: 2.2968(15), 10:
2.2920(10) ꢀ), thus indicating weaker coordination of the
PPh3 ligand to the central platinum atom than that of the
cyclic phosphinite ligand , and results from the lower s-donor
À
ability of PPh3. The Pt1 C1 bond lengths were 2.153(6) ꢀ for
9 and 2.119(4) ꢀ for 10, which are longer than those of five-
membered oxaplatinacycles 5a (2.066(9) ꢀ) and
1
(1.96(2) ꢀ).[8]
To gain insight into the mechanism of formation for
oxaphosphaplatinacycles 9 and 10, we studied the thermolyses
of 9 and 10. Heating of trans complex 9 in xylene at reflux for
15 hours resulted in the formation of a mixture of cis complex
10, 5a, and the starting material 9 in the ratio of 13:24:63
based on the integral ratio of the 31P{1H} NMR spectrum of
Scheme 5. A plausible mechanism for the formation of oxaphospha-
platinacycles 9 and 10.
5786
www.angewandte.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 5784 –5787

Angewandte
Chemie
1351; b) S. Ogoshi, T. Arai, M. Ohashi, H. Kurosawa, Chem.
phenyl group from the anionic phosphorus atom to the
cationic platinum center.[18b,19]
Commun. 2008, 1347 – 1349; c) J. Langer, R. Fischer, H. Gꢄrls, D.
Walther, Eur. J. Inorg. Chem. 2007, 2257 – 2264; d) S. Ogoshi, K.
Tonomori, M. Oka, H. Kurosawa, J. Am. Chem. Soc. 2006, 128,
7077 – 7086; e) R. Fischer, J. Langer, A. Malassa, D. Walther, H.
Gꢄrls, G, Vaughan, Chem. Commun. 2006, 2510 – 2512; f) S.
Ogoshi, M. Ueta, T. Arai, H. Kurosawa, J. Am. Chem. Soc. 2005,
127, 12810 – 12811; g) S. Ogoshi, M. Oka, H. Kurosawa, J. Am.
Chem. Soc. 2004, 126, 11802 – 11803.
3
À
À
In summary, we have found unusual C(sp ) S and O H
bond cleavage in the reactions of a series of 2-hydroxybenzyl
sulfide derivatives 4 or 6 with [Pt(h2-nb)(PPh3)2] to form 1,2-
oxaplatinacycles 5a and 5b. The thermal isomerization of 5a
afforded novel six-membered 1,2,3-oxaphosphaplatinacycles
9 and 10 as trans and cis isomers, respectively. In addition, 5a,
9, and 10 are in equilibrium under the experimental reaction
conditions. Studies on the intrinsic reactivity of 5 are currently
in progress.
[7] For recent examples of oxapalladacycles, see: a) T. Miura, T.
Toyoshima, Y. Takahashi, M. Murakami, Org. Lett. 2008, 10,
4887 – 4889; b) J. C. Hershberger, L. Zhang, G. Lu, H. C.
Malinakova, J. Org. Chem. 2006, 71, 231 – 235; c) G. Lu, J. L.
Portscheller, H. C. Malinakova, Organometallics 2005, 24, 945 –
961; d) G. Lu, H. C. Malinakova, J. Org. Chem. 2004, 69, 8266 –
8279; e) J. L. Portscheller, S. E. Lilley, H. C. Malinakova,
Organometallics 2003, 22, 2961 – 2971; f) C. Bianchini, A. Meli,
W. Oberhauser, P. W. N. M. van Leeuwen, M. A. Zuideveld, Z.
Freixa, P. C. J. Kamer, A. L. Spek, O. V. Gusev, A. M. Kalꢅsin,
Organometallics 2003, 22, 2409 – 2421; g) J. L. Portscheller, H. C.
Malinakova, Org. Lett. 2002, 4, 3679 – 3681; h) C. Fernꢂndez-
Rivas, D. J. Cꢂrdenas, B. Martꢁn-Matute, A. Monge, E. Gutiꢃr-
rez-Puebla, A. M. Echavarren, Organometallics 2001, 20, 2998 –
3006.
Received: April 1, 2010
Revised: May 20, 2010
Published online: July 7, 2010
Keywords: cleavage reactions · oxaphosphaplatinacycles ·
.
oxaplatinacycles · platinum · thermal rearrangements
À
[1] For recent studies on cleavage of C S bond by transition metals,
see: a) T. Schaub, M. Backes, O. Plietzsch, H. Radius, Dalton
Trans. 2009, 7071 – 7079; b) M. R. Grochowski, W. W. Brennes-
sel, W. D. Jones, Organometallics 2009, 28, 2661 – 2667; c) J.
Torres-Nieto, W. W. Brennessel, W. D. Jones, J. J. Garcꢁa, J. Am.
Chem. Soc. 2009, 131, 4120 – 4126; d) T. A. Atesin, W. D. Jones,
Inorg. Chem. 2008, 47, 10889 – 10894; e) K. Iwasa, H. Seino, Y.
Mizobe, J. Organomet. Chem. 2008, 693, 3197 – 3200; f) M.
Shibue, M. Hirotsu, T. Nishioka, I. Kinoshita, Organometallics
2008, 27, 4475 – 4483; g) T. Schaub, M. Backes, H. Radius, Chem.
Commun. 2007, 2037 – 2039; h) D. Shimizu, N. Takeda, N.
Tokitoh, J. Organomet. Chem. 2007, 692, 2716 – 2728; i) L. A.
Goj, M. Lail, K. A. Pittard, K. C. Riley, T. B. Gunnoe, J. L.
Petersen, Chem. Commun. 2006, 982; j) D. Shimizu, N. Takeda,
N. Tokitoh, Chem. Commun. 2006, 177 – 179; k) J. A. Cabeza, I.
del Rꢁo, I. M. G. Sꢂnchez-Vega, M. Suꢂrez, Organometallics
2006, 25, 1831 – 1834.
[8] C. Anklin, P. S. Pregosin, F. Bachechi, P. Mura, Z. Zamonelli, J.
Organomet. Chem. 1981, 222, 175 – 185.
[9] X. Zhang, E. J. Dullaghan, S. M. Gorun, D. A. Sweigart, Angew.
Chem. 1999, 111, 2343 – 2346; Angew. Chem. Int. Ed. 1999, 38,
2206 – 2208.
[10] E. Szuromi, S. Hui, P. P. Sharp, J. Am. Chem. Soc. 2003, 125,
10522 – 10523.
[11] A. Ishii, T. Toda, N. Nakata, T. Matsuo, J. Am. Chem. Soc. 2009,
131, 13566 – 13567.
[12] H. Petzold, H. Gꢄrls, W. Weigand, J. Organomet. Chem. 2007,
692, 2736 – 2742.
À
[13] O H activation of alcohols or phenols by low-valent metals
including platinum(0) have been less studied; a) D. B. Grotjahn,
Y. Gong, A. G. DisPasquale, L. N. Zakharov, A. L. Rheingold,
Organometallics 2006, 25, 5693 – 5695; b) R. S. Paonessa, A. L.
Prignano, W. C. Trogler, Organometallics 1985, 4, 647 – 657.
[14] N. Nakata, M. Sakashita, C. Komatsubara, A. Ishii, Eur. J. Inorg.
Chem. 2010, 447 – 453.
[2] a) A. Nova, F. Novio, P. Gonzalꢃs-Duarte, A. Lledos, R. Mas-
Ballestꢃ, Eur. J. Inorg. Chem. 2007, 5707 – 5719; b) K. Yu, H. Li,
E. J. Watson, K. L. Virkaitis, G. B. Carpenter, D. A. Sweigart,
Organometallics 2001, 20, 3550 – 3559; c) H. Li, G. B. Carpenter,
D. A. Sweigart, Organometallics 2000, 19, 1823 – 1825; d) A.
Arꢃvalo, S. Bernꢃs, J. J. Garcia, P. M. Maitlis, Organometallics
1999, 18, 1680 – 1685; e) C. A. Dullaghan, X. Zhang, D. L.
Greene, G. B. Carpenter, D. A. Sweigart, C. Camiletti, E.
Rajaseelan, Organometallics 1998, 17, 3316 – 3322; f) J. J.
Garcia, B. E. Mann, H. Adams, N. A. Bailey, P. M. Maitlis, J.
Am. Chem. Soc. 1995, 117, 2179 – 2186; g) J. J. Garcia, P. M.
Maitlis, J. Am. Chem. Soc. 1993, 115, 12200 – 12201.
[3] a) T. Kato, H. Kuniyasu, T. Kajiura, Y. Minami, A. Ohtake, M.
Kinomoto, J. Terao, H. Kurosawa, N. Kambe, Chem. Commun.
2006, 868 – 870; b) Y. Minami, T. Kato, H. Kuniyasu, J. Terao, N.
Kambe, Organometallics 2006, 25, 2949 – 2959.
[4] H. Kuniyasu, A. Ohtake, T. Nakazono, M. Kinomoto, H.
Kurosawa, J. Am. Chem. Soc. 2000, 122, 2375 – 2376.
[15] F. Yamashita, H. Kuniyasu, J. Terao, N. Kambe, Inorg. Chem.
2006, 45, 1399 – 1404.
[16] CCDC 771775 (5a), 771776 (5b), 771777 (9), and 771778 (10)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[17] We examined the thermal reaction of 5b in xylene at reflux, but
the reaction did not occur. This failure is probably a result of
À
steric hindrance from the tBu group ortho to the Pt O group in
the formation of the intermediate corresponding to 13.
À
[18] For reviews on cleavage of C P bonds mediated by transition
metals, see: a) T. J. Geldbach, P. S. Pregosin, Eur. J. Inorg. Chem.
2002, 1907 – 1918; b) S. A. Macgregor, Chem. Soc. Rev. 2007, 36,
67 – 76.
[19] P. W. N. M. van Leeuwen, C. F. Roobeek, Organometallics 1990,
9, 2179 – 2181.
[5] For a recent review on the application of oxanickelacycles, see:
M. Mori, Eur. J. Org. Chem. 2007, 4981 – 4993.
[6] For recent examples of oxanikelacycles, see: a) I. Koyama, T.
Kurahashi, S. Matsubara, J. Am. Chem. Soc. 2009, 131, 1350 –
Angew. Chem. Int. Ed. 2010, 49, 5784 –5787
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5787