Thermal reaction of a (hydrido)(selenolato)platinum(ii) complex having a dibenzobarrelenyl group leading to three cyclometalations

Article abstract of DOI:10.1039/c0dt00483a

The thermal reaction of a (dibenzobarreleneselenolato)(hydrido)platinum(ii) complex gave two four-membered selenaplatinacycles, one of which is formed by hydroplatination of the Pt-H bond to the etheno bridge and the other is a vinylic C-H bond activation product, and a five-membered selenaplatinacycle formed by an aromatic C-H bond activation.

Full text of DOI:10.1039/c0dt00483a

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Thermal reaction of a (hydrido)(selenolato)platinum(II) complex having a
dibenzobarrelenyl group leading to three cyclometalations†
Akihiko Ishii,* Yuki Yamaguchi and Norio Nakata
Received 17th May 2010, Accepted 28th May 2010
First published as an Advance Article on the web 8th June 2010
DOI: 10.1039/c0dt00483a
The thermal reaction of a (dibenzobarreleneselenolato)-
(hydrido)platinum(II) complex gave two four-membered sele-
naplatinacycles, one of which is formed by hydroplatination
of the Pt–H bond to the etheno bridge and the other is a
vinylic C–H bond activation product, and a five-membered
selenaplatinacycle formed by an aromatic C–H bond
activation.
two types of C(sp2)-H bonds, aromatic and vinylic C–H bonds.
Cyclometalations by activation ofthese C–H bonds are expected to
give five- and/or four-membered selenaplatinacycles, respectively,
the latter of which is a hitherto unknown ring system.9 In addition,
one can anticipate a competitive hydroplatination to the etheno
bridge in Dbb, which is another common reaction for hydrido
transition-metal complexes.10,11
The reaction of DbbLi, prepared by treatment of DbbBr 412
with t-BuLi, with elemental selenium gave (Dbb)2Sen, reduction of
which with NaBH4 provided DbbSeH 5 in 78% from 4 (Scheme 2).
Activation of a C–H bond by transition metals accounts for a
major part of organometallic chemistry,1 and the C–H activation
occurring on a ligand leads to cyclometalation, which is known
before several decades.2 We recently reported the reaction of
selenoseleninate 1 having sterically demanding 9-triptycyl groups
2
(hereafter abbreviated as Trip) with [Pt(h -C2H4)(PPh3)2] to give
selenaplatinacycle 2 by a cyclometalation.3 In relation to this
reaction, we synthesised the first isolable (hydrido)(selenolato)PtII
2
complex 3 by the reaction of selenol TripSeH with [Pt(h -
Scheme 2 Reaction Conditions: (a) t-BuLi (2 equiv.), -78 ◦C, THF; (b)
Se, -78 ◦C, and then reflux; (c) NaBH4, THF, rt.
C2H4)(PPh3)2], which could lead to selenaplatinacycle 2 by heating
3
or treatment with HBF4 (Scheme 1). In the course of our
study on the generality of the above reactions, we have been
investigating the effects of transition metals,4 substituents on
selenium,5 and phosphine ligands6 in addition to the reactions
of 9-triptycenethiol7 and 9-triptycylgermane with Pt0 complexes.8
2
The reaction of selenol 5 with [Pt(h -nb)(PPh3)2] (nb = nor-
bornene) in toluene gave cis-[PtH(SeDbb)(PPh3)2] 6 in 83% yield.
In the 31P{ H} NMR spectrum, two doublets accompanying satel-
1
lites due to the 195Pt isotope were observed at d 20.2 (2JP–P 15, 1JPt–P
2
1
3265) and 29.9 (d, JP–P 15, JPt–P = 2086), which are assigned as
phosphorus atoms trans to the selenolato and the hydrido ligands,
respectively.3 The thermal reaction of (hydrido)(selenolato)PtII
complex 6 was carried out in refluxing toluene, and we isolated
three platinum(II) complexes 7–9. The major product is the four-
membered selenaplatinacycle 7, a hydroplatination product of
the Pt–H bond to the etheno bridge. The minor products are
another four-membered selenaplatinacycle 8 and five-membered
selenaplatinacycle 9, which are the products via vinylic and
aromatic C–H bonds activation, respectively (Scheme 3). The
Scheme 1 Formation of selenaplatinacycle 2.
One of our present interest is, when different types of
C(sp2)-H bonds exist in a substituent on the selenium of
(hydrido)(selenolato)PtII complexes, which C(sp2)-H bond is ac-
tivated intramolecularly. As such a substituent with adequate
steric demand, we chose 9,10-etheno-9,10-dihydroanthracen-9-yl
group (dibenzobarrelenyl, hereafter abbreviated as Dbb) that has
Department of Chemistry, Graduate School of Science and Engineering,
Saitama University, Shimo-okubo 255, Sakura-ku, Saitama, 338-8570,
Japan. E-mail: ishiiaki@chem.saitama-u.ac.jp; Fax: +81-48-858-3394
† Electronic supplementary information (ESI) available: Synthetic pro-
cedures and spectral characterization of 5–9. CCDC reference numbers
773881 (7) and 773882 (8). For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00483a
Scheme 3 Formation of three selenaplatinacycles 7, 8 and 9.
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structures of 7 and 8 were unambiguously determined by X-ray
respectively, on the basis of the 1JPt–P values.3 Satellite signals due
to the 77Se isotope were observed only for the doublet at d 18.4,
which is another sign for the phosphorus atom being trans to the Se
atom. In the 1H NMR spectrum of 7, the bridgehead proton of the
Dbb resonated at d 3.79 (s) and the a-proton of the platinum atom
appeared at d 1.39–1.63 (m, JPt–H 90). Two methylene protons of
the ethano bridge were observed at d 0.45–0.51 (m) and 1.03–
1.23 (m), which were assigned as those cis and trans to the
a-proton, respectively, based on the C–H COSY and NOESY
measurements; in the NOESY spectrum the correlation between
the a-proton (d 1.39–1.63) and the multiplet at d 0.45–0.51 was
observed.
crystallography (Fig. 1 and 2).13
In the 1H NMR spectrum of 8, the bridgehead proton of
the Dbb and the vinylic proton were observed at d 4.46 (dd,
J 5.6 and 2.0) and 5.26 (t, J 5.0, JPt–H 57), respectively. In
1
the 31P{ H} NMR spectrum, the phosphorus atom trans to the
2
1
selenium atom resonated at d 17.0 (d, JP–P 13, JPt–P 3256) and
2
1
that trans to the sp2 carbon atom at d 25.0 (d, JP–P 13, JPt–P
2044), where 2JSe–P satellite signals were observed for the doublet at
d 17.0.
Five-membered selenaplatinacycle 9 exhibited in the 1H NMR
spectrum the characteristic signal due to the aromatic proton
neighboring the platinum atom at d 5.80–5.86 as similar as 2.
Fig. 1 ORTEP drawing of 7 at the 30% ellipsoidal probability. Hydrogen
atoms except those in the ethano bridge are omitted for clarity. Relevant
◦
˚
bond length (A) and bond angle ( ) data: Pt1–C2 2.113(4); Pt1–Se1
2.4491(5); Se1–C1 1.970(4); C1–C2 1.559(6); Pt1–P1 2.3012(11); Pt1–P2
2.2532(11); C2–Pt1–Se1 72.47(12); C1–Se1–Pt1 78.89(13); C2–C1–Se1
99.7(3); C1–C2–Pt1 99.8(3); C2–Pt1–P2 94.31(13); C2–Pt1–P1 164.96(13);
P2–Pt1–P1 99.87(4); P2–Pt1–Se1 166.18(3); P1–Pt1–Se1 93.67(3); sum of
four bond angles around Pt1 360.32.
1
The 31P{ H} NMR exhibited two doublets with satellites due to
2
1
2
the 195Pt at d 21.9 (d, JP–P 21, JPt–P 1831) and 24.2 (d, JP–P 21,
1JPt–P 3259), which are assigned to phosphorus atoms trans to the
sp2 carbon and the selenium atom, respectively, based on the 1JPt–P
values similarly to the cases of 7 and 8.
In the crystalline state, the four-membered rings in 7 and 8 are
puckered and the puckered angles along the Se1-C2 bonds are
31.79◦ and 9.25◦, respectively. Thus, the four-membered ring in 7
is more puckered than that in 8, which is due to the presence of an
sp3 carbon in the ring of 7. The Pt–Se and Se–C bond lenghts are
˚
˚
2.4491(5) and 1.970(4) A for 7 and 2.4393(4) and 1.980(3) A for 8,
which are slightly larger than the corresponding bond lenghts in
3
˚
five-membered ring in 2 [2.4097(4) and 1.956(4) A, respectively].
2
˚
The Pt1-C2(sp ) bond in 8 [2.046(3) A] is shorter than the Pt1-
C2(sp ) in 7 [2.113(4) A] and the corresponding Pt–C(Ar) bond
in 2 [2.099(4) A]. The sums of bond angles around Pt1 in 7 and 8
3
˚
˚
are 360.32◦ and 361.05◦, respectively, resulting from the distortion
from planarity due to the strained four-membered rings (the sum
for 2 is 359.99◦) and the steric repulsion of the neighbouring
PPh3 ligands. The torsion angles between plane P1–Pt1–P2 and
plane Se1–Pt1–C2 are 6.70◦ for 7 and 12.82◦ for 8 (1.62◦
for 2).
To verify that the intramolecular hydroplatination of 6 giving
7 occurs in the syn stereochemistry, deuterated selenol DbbSeD
5-d was allowed to react with [Pt(h -nb)(PPh3)2] to give the
Fig.
2
ORTEP drawing of 8 at the 30% ellipsoidal probability.
2
Hydrogen atoms and
a
solvated molecule (CH2Cl2) are ◦omitted
˚
for clarity. Relevant bond lengths (A) and bond angles ( ) data:
Pt1–C2 2.046(3); Pt1–Se1 2.4393(4); Se1–C1 1.980(3); C1–C2 1.543(5);
Pt1–P1 2.3083(9); Pt1–P2 2.2596(9); C2–Pt1–Se1 73.45(10); C1–Se1–Pt1
80.62(10); C2–C1–Se1 99.3(2); C1–C2–Pt1 105.9(2); C2–Pt1–P2 92.17(10);
C2–Pt1–P1 167.39(10); P2–Pt1–P1 99.70(3); P2–Pt1–Se1 161.42(3);
P1–Pt1–Se1 95.73(2); sum of four bond angles around Pt1 361.05.
deuterido complex cis-[PtD(SeDbb)(PPh3)2] 6-d. The thermal
reaction of 6-d gave 7-d as the main product, and only the
proton (d 1.03–1.23) cis to the platinum atom was deuterated.
However, the deuterium content was only 30%, which is probably
due to fast D-H exchange with a trace amount of residual H2O
through reductive elimination of 6-d giving 5-d and [Pt(PPh3)2]
on heating. When 6 or 6-d was heated in toluene in the presence
of D2O, quantitatively-deuterated 7-d was formed (eqn (1)). H-D
exchange of 7 did not take place at all under similar conditions.
Thus, the intramolecular syn-hydroplatination of 6 was evidenced
experimentally.
In the 31P{ H} NMR spectrum of 7, two doublets accompanying
1
195Pt satellites appeared at d 18.4 (d, 2JP–P 9.7, 1JPt–P 3530) and 26.4
2
1
(d, JP–P 9.7, JPt–P 1920), which are assigned as the phosphorus
atoms trans to the selenium atom and the sp3 carbon atom,
6182 | Dalton Trans., 2010, 39, 6181–6183
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from the Ministry of Education, Science, Sports, and Culture of
Japan.
Notes and references
(1)
1 Activation and Functionalization of C-H Bonds, ed. K. I.
Goldberg, and A. S. Goldman, ACS Symposium Series 885,
American Chemical Society, Washington, DC, 2004; K. Godula and
D. Sames, Science, 2006, 312, 67–72; A. R. Dick and M. S. Sanford,
Tetrahedron, 2006, 62, 2439–2463; R. Jazzar, J. Hitce, A. Renaudat,
J. Sofack-Kreutzer and O. Baudoin, Chem.–Eur. J., 2010, 16, 2654–
2672.
2 For examples of cyclometalation: (Rh) W. Keim, J. Organomet. Chem.,
1968, 14, 179–184(Ru, Rh); K. C. Dewhirst, W. Keim and C. A. Reilly,
Inorg. Chem., 1968, 7, 546–551(Ir); M. A. Bennett and D. L. Milner,
Chem. Commun., 1967, 581–582 (Ir, Rh); G. W. Parshall, Acc. Chem.
Res., 1970, 3, 139–144.
3 A. Ishii, N. Nakata, R. Uchiumi and K. Murakami, Angew. Chem., Int.
Ed., 2008, 47, 2661–2664.
4 N. Nakata, R. Uchiumi, T. Yoshino, T. Ikeda, H. Kamon and A. Ishii,
Organometallics, 2009, 28, 1981–1984.
5 N. Nakata, Y. Yamaguchi and A. Ishii, J. Organomet. Chem., 2010, 695,
970–973.
The thermal reaction of hydrido complex 6 was carried out in the
presence of 10 molar equivs of PPh3 as the additive. Interestingly,
hydroplatination product 7 was not formed and 8 was obtained
in 67% yield together with 9 in 13% yield (eqn (2)). This result
suggests that the equilibrium between 6 and {[PtH(SeDbb)(PPh3)]
(10) + PPh3} (Scheme 4) was inclined largely to the left side by
the addition of PPh3 to inhibit the formation of 7, that is, the
dissociation of a PPh3 ligand from 6 is necessary to form 7. It is
reasonable to consider that the coordination-unsaturated platinum
center in 10 coordinates on the etheno bridge intramolecularly
followed by the syn-hydroplatination and re-ligation of a PPh3 to
give 7, and that 8 and 9 are formed directly from 6 involving an
evolution of H2.
6 N. Nakata, T. Yoshino and A. Ishii, Phosphorus, Sulfur Silicon Relat.
Elem., 2010, 185, 992–999.
7 N. Nakata, S. Yamamoto, W. Hashima and A. Ishii, Chem. Lett., 2009,
38, 400–401.
8 N. Nakata, S. Fukazawa and A. Ishii, Organometallics, 2009, 28, 534–
538.
(2)
9 Four-membered oxa- and thiaplatinacycles are known: J. Wu and
P. R. Sharp, Organometallics, 2008, 27, 1234–1241; J. Wu and
P. R. Sharp, Organometallics, 2008, 27, 4810–4816; J. Wu and P. R.
Sharp, Organometallics, 2009, 28, 6935–6943; F.-Y. Tsai, H.-W. Chen,
J.-T. Chen, G.-H. Lee and Y. Wang, Organometallics, 1997, 16, 822–
823.
10 C. Elschenbroich, in Organometallics, Wiley-VCH Verlag GmbH &
Co. KGaA, Weinheim, 2006, p. 635; J. A. Labinger, in Comprehensive
Organic Synthesis, ed. B. M. Trost, and I. Fleming, Pergamon Press,
Oxford, 1991, vol. 8, pp. 667-702; J. S. Hallock, A. S. Galiano-Roth
and D. B. Collum, Organometallics, 1988, 7, 2486–2494; N. Fujii, F.
Kakiuchi, A. Yamada, N. Chatani and S. Murai, Bull. Chem. Soc.
Jpn., 1998, 71, 285–298; A. Ohtaka, H. Kuniyasu, M. Kinomoto and
H. Kurosawa, J. Am. Chem. Soc., 2002, 124, 14324–14325; C.-H. Jun,
C. W. Moon, Y.-M. Kim, H. Lee and J. H. Lee, Tetrahedron Lett.,
2002, 43, 4233–4236; M. Shiotsuki, P. S. White, M. Brookhart and J. L.
Templeton, J. Am. Chem. Soc., 2007, 129, 4058–4067; L. Zhang, L.
Dang, T. B. Wen, H. H.-Y. Sung, I. D. Williams, Z. Lin and G. Jia,
Organometallics, 2007, 26, 2849–2860.
Scheme 4 A plausible formation pathway for selenaplatinacycles 7, 8
and 9.
11 Recently, Rourke and co-workers reported a balance between sp2
and sp3 C–H bond activation in a PtII complex with a dual agostic
interaction. S. H. Crosby, G. J. Clarkson and J. P. Rourke, J. Am. Chem.
Soc., 2009, 131, 14142–14143.
In conclusion, cyclometalation to the Dbb group in
(hydrido)(DbbSe)PtII complex 6 takes place in three ways to
give two, novel four-membered selenaplatinacycles 7 and 8 and
a five-membered one 9. The hydroplatination of the Pt–H to
the etheno bridge to give 7 occurs in the syn manner, which
is precedented by the dissociation of a PPh3 ligand. Although
the ring sizes are different, the vinylic C–H bond activation to
give 8 is preferred over the aromatic C–H bond activation to
give 9. Efforts are currently directed towards carboselenation of
7–9 with alkynes14 to synthesise functional selenium-containing
heterocycles incorporated in the Dbb skeleton.
12 M. Brynda, M. Geoffroy and G. Bernardinelli, Chem. Commun., 1999,
961–962.
13 Crystallographic data for 7 and 8. 7: (C52H42P2PtSe·CH2Cl2); colourless
prism, Mo-Ka radiation (l = 0.71073), 103 K, Mr = 1087.77, triclinic,
¯
˚
˚
P1, a = 10.5381(8), b = 12.8984(◦10), c = 17.2005(14) A, a = 84.159(2),
3
b = 87.716(2), g = 78.702(2) , V = 2256.7(3) A , Z = 2, m =
4.141 mm-1, dc = 1.601 g cm-3, R1 (I > 2s(I)) = 0.0340, wR2
=
0.0801 (all data) for 8294 reflections, 532 parameters, GOF 1.001.
8: (C52H40P2PtSe·CH2Cl2); colourless prism, Mo-Ka radiation (l =
¯
0.71073), 103 K, Mr = 1085.76, triclinic, P1, a = 12.9249(5), b =
˚
13.1578(5), c = 15.7079(6) A, a = 74.7340(10), b = 69.4590(10), g =
◦
3
-1
˚
61.9440(10) , V = 2191.88(15) A , Z = 2, m = 4.263 mm , dc
=
Acknowledgements
1.645 g cm-3, R1 (I > 2s(I)) = 0.0286, wR2 = 0.0706 (all data) for 8123
reflections, 560 parameters, GOF = 1.050.
We are grateful for the financial support of this work by a Grant-
in-Aid for Scientific Research (Nos. 19027014 and 20036013)
14 A. Ishii, H. Kamon, K. Murakami and N. Nakata, Eur. J. Org. Chem.,
2010, 1653–1659.
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6181–6183 | 6183
©