Internal alkyne-to-vinylidene isomerization at cationic ruthenium and iron complexes

Article abstract of DOI:10.1246/cl.2009.534

Cationic ruthenium and iron complexes [CpM(PP)]⁺ (Cp=η⁵-C₅H₅; M=Ru and Fe; PP=Ph ₂PCH₂CH₂PPh₂, 2PPh₃) can affect vinylidene rearrangement of general interna

Full text of DOI:10.1246/cl.2009.534

534
Chemistry Letters Vol.38, No.6 (2009)
Internal Alkyne-to-vinylidene Isomerization at Cationic Ruthenium and Iron Complexes
Yuichiro Mutoh, Yousuke Ikeda, Yusuke Kimura, and Youichi Ishiiꢀ
Department of Applied Chemistry, Faculty of Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551
(Received March 12, 2009; CL-090258; E-mail: yo-ishii@kc.chuo-u.ac.jp)
Cp
BArF
Cationic ruthenium and iron complexes [CpM(PP)]þ
NaBArF
4
Cp
4
(Cp = ꢀ5-C5H5; M = Ru and Fe; PP = Ph2PCH2CH2PPh2,
2PPh3) can affect vinylidene rearrangement of general internal
alkynes via the 1,2-migration of aryl and alkyl groups. Judging
from the migratory aptitude of substituted aryl groups, the pres-
ent reaction is viewed as an uncommon electrophilic rearrange-
ment.
Ph
Ar
Ru
Ru
PPh2
2
Ph2P
Ph
Ph2P
•
Cl
C2H4Cl2, 70 °C
PPh2
Ar
Ar = C6H4OMe-p
Ar = C6H4Me-p
Ar = C6H5
Ar = C6H4Cl-p
Ar = C6H4CO2Et-p
88%
90%
85%
89%
71%
0.5 h 3a
1 h 3b
1 h 3c
12 h 3d
12 h 3e
NaBArF
4
Et
C2H4Cl2
70 °C, 1 h
Me
It is well known that terminal alkynes are readily converted
into the corresponding vinylidenes at transition-metal complexes
by several distinct mechanisms,1 and this rearrangement has
been utilized as the key step in many metal-promoted or -cata-
lyzed transformations of alkynes.2 In contrast, migration of car-
bon substituents of internal alkynes has been observed in very
few rearrangements of acylalkynes,3 though vinylidene rear-
rangement of heteroatom-substituted (–SiR3,4 –SnR3,5 –SR,6
and –I7) internal alkynes has recently been receiving considera-
ble attention. In the course of our studies on transition-metal
cyclophosphato complexes8 which are structurally related to hy-
droxyapatite-supported metal catalysts,9 we have revealed that a
ruthenium cyclotriphosphato (P3O93ꢁ) complex (PPN)[Ru-
(P3O9)(MeOH)(dppe)] (1; PPN = (Ph3P)2Nþ; dppe = Ph2-
PCH2CH2PPh2) can affect the vinylidene rearrangement of gen-
eral internal alkynes via the 1,2-migration of alkyl, aryl, and acyl
groups.8d The findings prompted us to examine whether more
commonly used CpRu and CpFe (Cp = ꢀ5-C5H5) complexes
can affect the internal alkyne-to-vinylidene isomerization.
Initially, we examined the reaction of [CpRuCl(dppe)] (2)
with PhCꢂCC6H4OMe-p which was found to be the most reac-
tive in the reaction with 1.8d When 2 was allowed to react with
BArF
BArF
Cp
4
Cp
4
Et
Ru
•
Ru
Ph2P
Ph2P
Et
C2H4Cl2
PPh2
70 °C, 10 d
PPh2
Me
Me
3f 68% (from 2)
4f 86%
Scheme 1.
Ru
P1
P2
C1
C2
P1
P2
Ru
C1
O
C2
Figure 1. ORTEP drawings of 3a (left) and 4f (right). Anionic
part and hydrogen atoms are omitted for clarity.
plex [CpRu(EtCꢂCMe)(dppe)][BArF4] (4f) in 86% isolated
yield as yellow needles (Scheme 1), which was characterized
by the 13C{1H} NMR signals at ꢁ 77.8 and 82.1 (coordinated
CꢂC) and the IR absorption at 1951 cmꢁ1 (ꢄCꢂC) as well as
by crystallographic study (Figure 1, right).10 The alkyne com-
plex 4f was further transformed into the corresponding vinyli-
dene complex 3f as the sole product by heating in C2H4Cl2 for
10 d. Unlike the P3O9–alkyne complexes (PPN)[Ru(P3O9)(RCꢂ
CR)(dppe)],8d 4f was not converted into 3f by UV irradiation.
Similar vinylidene formation took place at the PPh3 com-
plex [CpRuCl(PPh3)2] (5) to give [CpRu(=C=C(Ph)Ar)-
(PPh3)2][BArF4] (6) in high yields (Scheme 2).10 This result
indicates that the vinylidene rearrangement of internal alkynes
enjoys considerably high applicability as a synthetic method
for disubstituted vinylidenes.12
PhCꢂCC6H4OMe-p (4 equiv) in the presence of NaBArF (1.2
4
equiv; ArF = 3,5-(CF3)2C6H3) in 1,2-dichloroethane (C2H4Cl2)
at 70 ꢃC for 0.5 h, the vinylidene complex [CpRu(=C=C(Ph)-
C6H4OMe-p)(dppe)][BArF4] (3a) was obtained in 88% yield
as red crystals (Scheme 1).10 Use of NaBArF was essential
4
for the selective formation of 3a; either AgPF6 or NaBPh4 in-
stead of NaBArF4 resulted in the formation of a complex mixture
containing 3a. Complex 3a exhibits 13C{1H} NMR signals at ꢁ
2
350.4 (t, JPC ¼ 16 Hz) and 133.3 (s) characteristic of the ꢂ
and ꢃ carbons of a vinylidene ligand, respectively. The molecu-
lar structure of 3a has been established unambiguously by X-ray
analysis to confirm that migration of an aryl group took place to
form the disubstituted vinylidene ligand (Figure 1, left).10 The
metrical features including the Ru–C1 and C1–C2 bond dis-
BArF
NaBArF
Cp
Ru
˚
Cp
Ru
4
4
tances of 1.838(4) and 1.327(6) A, respectively, and the Ru–
C1–C2 bond angle of 173.3(2)ꢃ fall in the range of common
RuII–vinylidene complexes.11 Similar reactions were also ob-
served with other internal alkynes to give the corresponding
vinylidene complexes 3b–3e in high yields.
Ph
Ar
Ph3P
Ph3P
Ph
Ph3P
Ph3P
•
Cl
C2H4Cl2, 70 °C
Ar
5
Ar = C6H4OMe-p
Ar = C6H4Me-p
88%
83%
0.5 h 6a
2 h 6b
On the other hand, treatment of 2 with EtCꢂCMe (7 equiv)
at 70 ꢃC for 1 h resulted in the formation of the ꢀ2-alkyne com-
Scheme 2.
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.6 (2009)
535
Cp
BArF
4
isomerization and determined the migratory aptitude of aryl
groups in the reaction of 2. Detailed mechanisms and synthetic
applications of this reaction will be reported in due course.
NaBArF
Cp
4
Ph
Ar
Fe
Fe
Ph2P
Ph
Ph2P
•
Cl
C6H6
70 °C, 12 h
PPh2
PPh2
Ar
This work was supported by Grants-in-Aid for Scientific Re-
search (No. 20037060) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
7
Ar = C6H4OMe-p
Ar = C6H4Cl-p
84%
74%
8a
8b
Scheme 3.
References and Notes
NaBArF
4
1
a) M. I. Bruce, Chem. Rev. 1991, 91, 197. b) C. Bruneau, P. H. Dixneuf,
Acc. Chem. Res. 1999, 32, 311. c) Y. Wakatsuki, J. Organomet. Chem.
2004, 689, 4092.
*
Ph
Ph
Ar
Ph
Ar
*
*
•
+
[Ru]
•
[Ru]
2
C2H4Cl2
70 °C, 0.5 h–12 h
[Ru] = [CpRu(dppe)][BArF
Ar
2
3
Metal Vinylidenes and Allenylidenes in Catalysis, ed. by C. Bruneau, P. H.
Dixneuf, Wiley-VCH, Weinheim, 2008.
Ar migration
Ph migration
]
4
a) P. J. King, S. A. R. Knox, M. S. Legge, A. G. Orpen, J. N. Wilkinson,
E. A. Hill, J. Chem. Soc., Dalton Trans. 2000, 1547. b) M. J. Shaw,
S. W. Bryant, N. Rath, Eur. J. Inorg. Chem. 2007, 3943.
Ar = C6H4OMe-p
Ar = C6H4Me-p
Ar = C6H4Cl-p
6
23
55
86
94
77
45
14
/
/
/
/
4
a) H. Werner, M. Baum, D. Schneider, B. Windmuller, Organometallics
¨
Ar = C6H4CO2Et-p
1994, 13, 1089. b) N. G. Connelly, W. E. Geiger, M. C. Lagunas, B. Metz,
A. L. Rieger, P. H. Rieger, M. J. Shaw, J. Am. Chem. Soc. 1995, 117, 12202.
c) H. Katayama, K. Onitsuka, F. Ozawa, Organometallics 1996, 15, 4642.
d) H. Werner, R. W. Lass, O. Gevert, J. Wolf, Organometallics 1997, 16,
Scheme 4. Migratory aptitude of alkyne substituents. The aster-
isks represent 13C-enriched carbon atoms.
´
4077. e) M. V. Jimenez, E. Sola, F. J. Lahoz, L. A. Oro, Organometallics
Unexpectedly, the disubstituted vinylidene formation was
also found to proceed with
´
2005, 24, 2722. f) K. Ilg, M. Paneque, M. L. Poveda, N. Rendon, L. L.
a CpFe system. Although
Santos, E. Carmona, K. Mereiter, Organometallics 2006, 25, 2230.
a) K. Venkatesan, O. Blacque, T. Fox, M. Alfonso, H. W. Schmalle,
S. Kheradmandan, H. Berke, Organometallics 2005, 24, 920. b) K.
Venkatesan, T. Fox, H. W. Schmalle, H. Berke, Eur. J. Inorg. Chem.
2005, 901.
[CpFeCl(dppe)] (7) failed to react with PhCꢂCAr in C2H4Cl2
in the presence of NaBArF4, the desired vinylidene complexes
[CpFe(=C=C(Ph)Ar)(dppe)][BArF4] (8) were obtained in high
yields by using benzene as the solvent (Scheme 3). Complexes
8 were fully characterized by spectroscopy as well as an X-ray
diffraction study of 8a (structure not shown).13 This reaction pro-
vides the first example of the internal alkyne-to-vinylidene iso-
merization at an iron complex. It should be noted that the reverse
process, that is, vinylidene-to-alkyne rearrangement was ob-
served with the carbonyl complex [CpFe(CO)2(=C=CR2)]-
(OTf) (Tf = SO2CF3).14
5
6
7
8
D. C. Miller, R. J. Angelici, Organometallics 1991, 10, 79.
T. Miura, N. Iwasawa, J. Am. Chem. Soc. 2002, 124, 518.
a) S. Kamimura, S. Kuwata, M. Iwasaki, Y. Ishii, Dalton Trans. 2003,
2666. b) S. Kamimura, T. Matsunaga, S. Kuwata, M. Iwasaki, Y. Ishii,
Inorg. Chem. 2004, 43, 6127. c) S. Kamimura, S. Kuwata, M. Iwasaki,
Y. Ishii, Inorg. Chem. 2004, 43, 399. d) Y. Ikeda, T. Yamaguchi, K. Kanao,
K. Kimura, S. Kamimura, Y. Mutoh, Y. Tanabe, Y. Ishii, J. Am. Chem. Soc.
2008, 130, 16856.
In order to shed light on the mechanistic aspects of the pres-
ent reaction, the migratory aptitude of aryl groups has been
9
K. Kaneda, K. Ebitani, T. Mizugaki, K. Mori, Bull. Chem. Soc. Jpn. 2006,
79, 981.
13
investigated using 13C-enriched alkynes PhCꢂ CAr (ca. 26%
10 Supporting Information is available electronically on the CSJ-Journal Web
site, http://www.csj.jp/journals/chem-lett/index.html.
13C). Migration of the Ar group gives rise to the ꢂ-13C-labeled
vinylidene complex (Ar migration), whereas the Ph group
migration leads to the ꢃ-13C-labeled product (Ph migration)
(Scheme 4). Detailed 13C{1H} NMR analysis10 of the reaction
products with a series of 13C-labeled alkynes disclosed that the
migratory aptitude of alkyne substituents is in the order C6H4-
CO2Et-p > C6H4Cl-p > C6H5 > C6H4Me-p > C6H4OMe-p.
Hammett analysis of the relative migratory aptitude indicates
a linear correlation between ꢅp and log[(Ar migration)/(Ph
migration)], where the ꢆ value is estimated to be 2.53 (R2 ¼
0:97).
A similar tendency was observed in the vinylidene rear-
rangement with 1,8d and the order of the migratory aptitude is op-
posite to that of common nucleophilic rearrangements in organic
chemistry.15 Obviously the electron-withdrawing group on an
alkyne substituent increases the migratory aptitude through the
stabilization of the negative charge on the migrating Ar group
in the transition state; therefore, the results shown above suggest
that an present rearrangement proceeds through the uncommon
electrophilic 1,2-shift of the carbon substituents.16
11 a) J. R. Lomprey, J. P. Selegue, J. Am. Chem. Soc. 1992, 114, 5518. b) M. I.
Bruce, B. G. Ellis, P. J. Low, B. W. Skelton, A. H. White, Organometallics
´
2003, 22, 3184. c) E. Bustelo, J. J. Carbo, A. Lledos, K. Mereiter, M. C.
´
Puerta, P. Valerga, J. Am. Chem. Soc. 2003, 125, 3311.
12 It was noted that the reaction of [{CpRu(PPh3)2}2(ꢇ-N2)][BArF
PhCꢂCPh failed to give vinylidene complex.3b
] with
2
4
13 8a: 1H NMR: ꢁ 3.01 (br, 2H, CH2 of dppe), 3.23 (br, 2H, CH2 of dppe), 3.69
(s, 3H, OCH3), 5.22 (s, 5H, C5H5), 6.44–7.72 (m, 41H, Ar). 13C{1H} NMR:
ꢁ 360.8 (t, J ¼ 33 Hz, Fe=C), 144.2 (Fe=C=C) 31P{1H} NMR: ꢁ 94.5
(s, dppe). IR (cmꢁ1): 1621 (m, ꢄC=C). Anal. Calcd for C78H53BF24FeOP2:
C, 58.89; H, 3.36%. Found: C, 58.63; H, 3.19%.
14 R. S. Bly, Z. Zhong, C. Kane, R. K. Bly, Organometallics 1994, 13, 899.
15 M. B. Smith, J. March, in March’s Advanced Organic Chemistry, Reac-
tions, Mechanisms, and Structure, 5th ed., John Wiley & Sons, Inc., New
York, 2001, pp. 1384–1386.
16 Theoretical calculation on the terminal alkyne–vinylidene isomerization
suggested that 1,2-hydrogen shift is most likely and that the migrating
hydrogen behaves as a proton.16a a) Y. Wakatsuki, N. Koga, H. Yamazaki,
K. Morokuma, J. Am. Chem. Soc. 1994, 116, 8105. b) M. Tokunaga, T.
Suzuki, N. Koga, T. Fukushima, A. Horiuchi, Y. Wakatsuki, J. Am. Chem.
Soc. 2001, 123, 11917. c) V. Cadierno, M. P. Gamasa, J. Gimeno, C.
´
´
´
Gonzalez-Bernardo, E. Perez-Carren˜o, S. Garcıa-Granda, Organometallics
2001, 20, 5177. d) F. De Angelis, A. Sgamellotti, N. Re, Organometallics
2002, 21, 5944.
In summary, we have revealed that commonly used CpRu
and CpFe complexes can affect the internal alkyne-to-vinylidene
Published on the web (Advance View) April 25, 2009; doi:10.1246/cl.2009.534