Preparation, reaction, and catalysis of the new ruthenium carbamato complex Et2NCO2RuH(CO)(PCy3)2

Article abstract of DOI:10.1021/om990306i

CO₂ promoted the RuCl₃·3H₂O-catalyzed dimerization of phenylacetylene (2) in the presence of PR₃ (R = Bu, Cy) and Et₂NH to afford 1,4-diphenyl-1-buten-3-yne (3). Et₂NCO₂RuH(CO)(PCy₃)₂ (4) and (PhC≡C)₂Ru-(CO)(PCy₃)₂ (5) were isolated by the RuCl₃·3H₂O/PCy₃/ Et₂NH/CO₂ and 4/2 reactions, respectively, and catalyzed the dimerization of 2 to afford 3 with the concomitant formation of a poly(phenylacetylene).

Full text of DOI:10.1021/om990306i

Organometallics 1999, 18, 2741-2743
2741
P r ep a r a tion , Rea ction , a n d Ca ta lysis of th e New
Ru th en iu m Ca r ba m a to Com p lex
Et2NCO2Ru H(CO)(P Cy3)2
Tetsuo Tsuda*,† and Moto-o Shiro*,‡
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Kyoto 606-8501, J apan, and X-ray Research Institute, Rigaku Corporation,
Matsubara 3-9-12, Akishima, Tokyo 196-8666, J apan
Received April 26, 1999
Summary: CO2 promoted the RuCl3‚3H2O-catalyzed
dimerization of phenylacetylene (2) in the presence of PR3
(R ) Bu, Cy) and Et2NH to afford 1,4-diphenyl-1-buten-
3-yne (3). Et2NCO2RuH(CO)(PCy3)2 (4) and (PhCtC)2Ru-
(CO)(PCy3)2 (5) were isolated by the RuCl3‚3H2O/ PCy3/
Et2NH/ CO2 and 4/ 2 reactions, respectively, and catalyzed
the dimerization of 2 to afford 3 with the concomitant
formation of a poly(phenylacetylene).
pot RuCl3‚3H2O/PCy3/Et2NH/CO2 reaction, along with
the ruthenium bis(alkynyl) complex (PhCtC)2Ru(CO)-
(PCy3)2 (5) by the 4/2 reaction with CO2 evolution
(Scheme 1). The complexes 4 and 5 exhibited a dual
catalytic activity to effect the dimerization and poly-
merization of 2 concomitantly to afford 3 and poly-
(phenylacetylene) (6) (eq 3). These findings indicate that
One of us developed recently transition-metal-cata-
lyzed alkyne cycloaddition polymerization1 as a new and
useful method of polymer synthesis using the transition-
metal-catalyzed monoyne cycloaddition as a polymer-
forming elementary reaction. We are therefore inter-
ested in the monoyne reaction effected by an easily
accessible transition-metal catalyst. Synthesis of enol
carbamate 1 by the RuCl3‚3H2O-catalyzed phenylacetyl-
ene (2)/Et2NH/CO2 reaction was previously reported (eq
1).2 On the basis of a finding that addition of a PBu3
the role of CO2 in the CO2-promoted RuCl3‚3H2O-
catalyzed formation of 3 is the facile generation of the
catalytically active ruthenium bis(alkynyl) complex 5 via
the ruthenium carbamato complex 4.
The results of the RuCl3‚3H2O-catalyzed head-to-head
dimerization of 2 to form 3 under various conditions are
summarized in Table 1. The RuCl3‚3H2O/PBu3 system
was ineffective (entry 4), but addition of Et2NH pro-
duced 3 (entry 5). In contrast, the RuCl3‚3H2O/PCy3
system exhibited a considerable activity (entry 10), but
addition of Et2NH had no effect (entry 11). It is
noteworthy that further addition of CO2 increased the
catalytic activity of the RuCl3‚3H2O/PBu3 and PCy3/Et2-
NH systems (entries 7, 12) without significant formation
of the carboxylated product 1. Various ruthenium
catalysts are reported for the alkyne head-to-head
dimerization.3 All these ruthenium catalysts are the
preformed ruthenium hydrido complexes or their de-
rivatives. Thus, the composite RuCl3‚3H2O/PR3/Et2NH/
CO2 system (R ) Bu, Cy) is a new and unique catalyst,
although its efficiency is not high.
ligand to the reaction mixture suppressed almost com-
pletely the formation of 1 and, instead, effected the
dimerization of 2 to afford 1,4-diphenyl-1-buten-3-yne
(3), the RuCl3‚3H2O/PBu3 system was suggested to be
an efficient catalyst for the alkyne dimerization.2
We examined the dimerization of 2 by the RuCl3‚
3H2O/PR3 catalytic system together with related reac-
tions involving Et2NH and/or CO2. The RuCl3‚3H2O/
PBu3 system was ineffective, but the RuCl3‚3H2O/PCy3
system (PCy3 ) tricyclohexylphosphine) formed 3. CO2
promoted the RuCl3‚3H2O-catalyzed formation of 3 in
the presence of PR3 and Et2NH (eq 2). On the basis of
The RuCl3‚3H2O-catalyzed dimerization of 2 promoted
by Et2NH/CO2 suggests intermediacy of a ruthenium
carbamato complex. The new ruthenium carbamato
complex Et2NCO2RuH(CO)(PCy3)2 (4)4 was isolated in
(3) (a) Dahlenburg, L.; Frosin, K.-M.; Kerstan, S.; Werner, D. J .
Organomet. Chem. 1991, 407, 115. (b) Bianchini, C.; Peruzzini, M.;
Zanobini, F.; Frediani, P.; Albinati, A. J . Am. Chem. Soc. 1991, 113,
5453. (c) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.; Zanobini,
F. Organometallics 1994, 13, 4616 and references therein. (d) Rappert,
T.; Yamamoto, A. Organometallics 1994, 13, 4984. (e) Yi, C. S.; Liu,
N. Organometallics 1996, 15, 3968.
these findings, the new ruthenium carbamato complex
Et2NCO2RuH(CO)(PCy3)2 (4) was isolated by the one-
† Kyoto University.
(4) Characteristic spectral data of 4: IR (cm-1; Nujol) 2061 (RuH),
1897 (CO), 1521, 1497 (NCO2); 1H NMR (δ, ppm; C6D6) -17.1 (t, 2J (HP)
) 19.3 Hz, RuH); 13C NMR (δ, ppm; C6D6) 163.9 (NCO2), 208.0 (t,
2J (CP) ) 14.1 Hz, CO). Anal. Calcd for C42H77NO3P2Ru: C, 62.50; H,
9.62; N, 1.74. Found: C, 62.25; H, 9.54; N, 1.62. The PCy3 ligand plays
an important role in the formation of 4: preparation of the ruthenium
carbamato complex without PCy3 by the RuCl3‚3H2O/Et2NH/CO2
reaction was unsuccessful.
‡ Rigaku Corporation.
(1) (a) Tsuda, T. In The Polymeric Materials Encyclopedia; Salam-
one, J . C., Ed.; CRC: Boca Raton, FL, 1996; Vol. 3, p 1905, and Vol. 5,
p 3525. (b) Tsuda, T. In Recent Research Developments in Macromol-
ecules Research; Research Signpost: Trivandrum, 1997; Vol. 2, p 23.
(2) Mahe, R.; Sasaki, Y.; Bruneau, C.; Dixneuf, P. H. J . Org. Chem.
1989, 54, 1518.
10.1021/om990306i CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/29/1999

2742 Organometallics, Vol. 18, No. 15, 1999
Communications
Sch em e 1
Ta ble 1. Ru Cl3‚3H2O-Ca ta lyzed Dim er iza tion of
P h en yla cetylen e (2) To Affor d
1,4-Dip h en yl-1-bu ten -3-yn e (3) (Eq 2)a
amt
amt of
PR3,
PR3/
Rub
amt of amt of
Et2NH, CO2,
of 2, RuCl3‚3H2O,
yield of
entry mmol
mmol
mmol kg/cm2 (Z)-3, %c
1
2
3
4
5
6
7
8
9
10
11
12
13
1
1
1
1
1
2
1
1
2
1
1
1
1
0.05
0.05
0.05
0.05
0.05
0.1
0.05
0.05
0.1
0.05
0.05
0.05
0.05
0
0
0
0
2
2
0
2
4
2
2
4
0
2
2
2
0
0
50
0
1.2
5.2
4.3d
2.6
PBu3, 2
PBu3, 2
PBu3, 1
PBu3, 2
PBu3, 4
PBu3, 2
PCy3, 2
PCy3, 2
PCy3, 2
PPh3, 2
0
33
50
50
50
50
0
0
50
50
15e
43f
22
53
36
34
48g
37
F igu r e 1. ORTEP structure (50% thermal ellipsoid prob-
ability) of Et2NCO2RuH(CO)(PCy3)2 (4). H atoms are omit-
ted for clarity, except for Ru1-H.
a
Conditions: solvent, toluene 2 mL; reaction temperature, 100
°C; reaction time, 20 h; CO2, initial pressure at room temperature
in a 50 mL stainless steel autoclave. Molar ratio. c Based on 2
b
and determined by GC using bibenzyl as an internal standard.
d
similar to those of the Me2NCO2 ligand of [Me2NCO2-
Ru(PMe2Ph)4]PF6.8
Et2NCO2CHdCHPh (1) ((Z)-1/(E)-1 ) 4.3) was concomitantly
formed in 37% yield. e Conditions: solvent, toluene 4 mL. 1 was
formed in 11% yield. f (Z)-3/(E)-3 ) 3.2. 1 was formed in 2.0% yield.
Interestingly, it was found that addition of 2 to 4 in
toluene at 50 °C evolved CO2 gas in 44 and 50% yields
after 0.5 and 4 h, respectively. The ruthenium bis-
(alkynyl) complex (PhCtC)2Ru(CO)(PCy3)2 (5)9 was
isolated in good yield as prismatic crystals containing
one THF solvent molecule per two ruthenium atoms by
the reaction of 4 with 2 (2/4 ) 6, PCy3/4 ) 2, toluene,
reflux) and subsequent recrystallization from a THF/
hexane solution (Scheme 1). The formation of a PhCt
C-Ru bond by the reaction of a R2NCO2-Ru bond with
2 is unprecedented.
The molecular structure of 5 determined by X-ray
diffraction analysis is shown in Figure 2.10 The geometry
around the ruthenium center is a distorted square
pyramid: the ruthenium atom deviates from the P1-
C37-P2-C45 plane by 0.237(1) Å toward the CO ligand.
Change of the bidentate carbamato ligand of 4 into the
monodentate alkynyl ligand of 5 with concomitant
generation of one vacant coordination site in the pres-
ence of an excess amount of PCy3 is noteworthy in
g
(Z)-3/(E)-3 ) 3.5. 1 was formed in 3.4% yield.
moderate yield as colorless prismatic crystals from an
ethanol-insoluble part of the reaction mixture formed
by the one-pot RuCl3‚3H2O/PCy3/Et2NH/CO2 reaction
without 2. The transition-metal carbamato complexes
represent a class of compounds of considerable interest.5
5a,d-f
Transition-metal amide/CO2
halide/R2NH/CO2
and transition-metal
5g,i
reactions are the two common
preparative methods of transition-metal carbamato
complexes (R2NCO2)nM. Thus, the formation of 4 con-
taining the CO and hydrido ligands generated concomi-
tantly by the one-pot RuCl3‚3H2O/PCy3/Et2NH/CO2
reaction is unique.6
The molecular structure of 4 determined by X-ray
diffraction analysis is shown in Figure 1.7 The ruthe-
nium atom has a distorted-octahedral geometry. The
bond lengths relevant to the bidentate carbamato ligand
along with the small O1-Ru1-O2 bond angle were
(5) (a) Chandra, G.; J enkins, A. D.; Lappert, M. F.; Srivastava, R.
C. J . Chem. Soc. A 1970, 2550. (b) La Monica, G.; Cenini, S.; Porta,
F.; Pizzotti, M. J . Chem. Soc., Dalton Trans. 1976, 1777. (c) Tsuda, T.;
Washita, H.; Watanabe, K.; Miwa, M.; Saegusa, T. J . Chem. Soc.,
Chem. Commun. 1978, 815. (d) Tsuda, T.; Watanabe, K.; Miyata, K.;
Yamamoto, H.; Saegusa, T. Inorg. Chem. 1981, 20, 2728. (e) Chetcuti,
M. J .; Chisholm, M. H.; Folting, K.; Haitoko, D. A.; Huffman, J . C. J .
Am. Chem. Soc. 1982, 104, 2138. (f) J oslin, F. L.; J ohnson, M. P.;
Mague, J . T.; Roundhill, D. M. Organometallics 1991, 10, 2781. (g)
Bacchi, A.; Dell’Amico, D. B.; Calderazzo, F.; Giurlani, U.; Pelizzi, G.;
Rocchi, L. Gazz. Chim. Ital. 1992, 122, 429 and references therein. (h)
Srivastava, R. S.; Singh, G.; Nakano. M.; Osakada, K.; Ozawa, F.;
Yamamoto, A. J . Organomet. Chem. 1993, 451, 221. (i) Dell’Amico, D.
B.; Calderazzo, F.; Gingl, F.; Labella, L.; Strahle, J . Gazz. Chim. Ital.
1994, 124, 375.
(6) Some routes are possible for the ruthenium-mediated conversion
of CO2 into CO; see: Fu, P-f.; Khan, M. A.; Nicholas, K. M. J .
Organomet. Chem. 1996, 506, 49, and references therein. Gas chro-
matographic analysis of the reaction mixture formed by the RuCl3‚
3H2O/PCy3/Et2NH/CO2 reaction indicated the insignificant formation
of OdPCy3, which excludes the deoxygenation of CO2 by PCy3.
(7) Crystal structure data for 4: C42H77NO3P2Ru, colorless, mono-
clinic, P21/c (No. 14), a ) 20.398(6) Å, b ) 9.588(3) Å, c ) 24.566(5) Å,
â ) 113.75(2)°, Z ) 4, R ) 0.041, GOF ) 1.30. One of the N-ethyl
groups, C38 and C39 in Figure 1, is disordered at the two locations
close to each other with an occupancy ratio of 4:6 (the location shown
in Figure 1).
(8) Ashworth, T. V.; Nolte, M.; Singleton, E. J . Organomet. Chem.
1976, 121, C57.
(9) Characteristic spectral data of 5‚0.5THF: IR (cm-1; Nujol) 2074
(CtC), 1920 (CO), 1594 (Ph); 1H NMR (δ, ppm; C6D6) 7.04 (t, J ) 7.4
Hz, 1 H, Ph), 7.27 (t, J ) 7.6 Hz, 2 H, Ph), 7.76 (d, J ) 8.3 Hz, 2 H,
Ph); 13C NMR (δ, ppm; THF-d8): 122.8, 125.1, 128.6, 129.9, 130.0 (t,
2J (CP) ) 14.1 Hz), 130.2, 130.4, 130.8, 207.1 (t, 2J (CP) ) 12.6 Hz).
Anal. Calcd for C55H80O1.5P2Ru: C, 71.17; H, 8.69. Found: C, 70.90;
H, 8.69.
(10) Crystal structure data for 5‚0.5THF: C55H80O1.5P2Ru, yellow,
monoclinic, P21/n (No. 14), a ) 20.907(3) Å, b ) 22.683(4) Å, c ) 10.522-
(1) Å, â ) 90.32(1)°, Z ) 4, R ) 0.050, GOF ) 1.35. One of the
cyclohexyl rings, C31-C36 in Figure 2, is disordered at the two
locations close to each other with an equal probability.

Communications
Organometallics, Vol. 18, No. 15, 1999 2743
reaction in THF-d8 exhibited only the signals of 3 and
5, except for a broad signal centered at δ 7.1. The latter
signal was found to be due to a phenyl group of poly-
(phenylacetylene) (6):13a poly(phenylacetylene)s (6) with
GPC molecular weights of 3000-6000 were isolated in
15-20% yield14 in the 4- and 5-catalyzed reactions of 2
together with the formation of 3, and their phenyl
1
groups showed the H NMR broad signal at δ 7.1. Thus,
the dual catalysis of 4 and 5 with different natures, i.e.,
the dimerization and polymerization activities, is note-
worthy and the ruthenium catalysis is not usual in the
transition-metal-catalyzed acetylene polymerization.13b,c
To the best of our knowledge, the alkyne dimerization
and polymerization catalyzed by 4 is the first example
of catalysis of a transition-metal carbamato complex,
although stoichiometric reactions15 of its carbamato
group are well-known.
The isolation of 4 by the RuCl3‚3H2O/PCy3/Et2NH/
CO2 reaction, its conversion to 5 by 2 with CO2 evolu-
tion, and the catalysis of 4 and 5 for the dimerization
of 2 indicate that the role of CO2 in the CO2-promoted
RuCl3‚3H2O-catalyzed formation of the noncarboxylated
product 3 is the facile generation of the catalytically
active ruthenium bis(alkynyl) complex 53c via the ru-
thenium carbamato complex 4. CO2 is previously re-
ported to increase the efficiency and chemoselectivity
of the platinum-catalyzed dimerization of butadiene16a
and the palladium-catalyzed reaction of butadiene with
water,16b in which the role of CO2, however, is not
clarified. Thus, the present CO2-promoted ruthenium-
catalyzed alkyne dimerization is a good example eluci-
dating the function of CO2 in a CO2-promoted transition-
metal-catalyzed organicreaction without CO2 incorporation
into a product by the isolation of participating transi-
tion-metal species.
F igu r e 2. ORTEP structure (50% thermal ellipsoid prob-
ability) of (PhCtC)2Ru(CO)(PCy3)2‚0.5THF (5‚0.5THF). H
atoms and free solvent are omitted for clarity.
Ta ble 2. F or m a tion of 1,4-Dip h en yl-1-bu ten -3-yn e
(3) by th e P h en yla cetylen e (2) Dim er iza tion
Ca ta lyzed by Ru th en iu m Ca r ba m a to Com p lex 4
a n d Bis(a lk yn yl) Com p lex 5a
4 or 5
2
8
PhCtCH
PhCtCCHdCHPh
catalyst
2
3
yield of 3, %b
amt of 4 or 5, amt of PCy3,
mmol
mmol
solvent
Z
E
3, Z/E
4, 0.024
4, 0.024
4, 0.024
4, 0.048
5, 0.030c
5, 0.024
0
0
0.1
0.2
0
toluene
THF
toluene
THF
THF
toluene
32
37
52
57
33
49
1.7
1.6
5.6
4.9
2.0
5.2
19
23
9.3
12
16
9.2
0.1
a
Conditions: 4 or 5/2 ) 0.048; solvent, 0.33 mL; temperature,
b
100 °C; reaction time, 20 h. Yields of (Z)- and (E)-3 were
determined by GC using bibenzyl as an internal standard. Another
product is poly(phenylacetylene) (6). c 5/2 ) 0.06.
Ack n ow led gm en t. This work was partly supported
bya Grant-in-Aid for ExploratoryResearch (No.08875176)
from the Ministry of Education, Science, Sports, and
Culture of J apan.
comparison to the octahedral ruthenium bis(alkynyl)
complexes such as trans-(Et3P)2Ru(CtCPh)2(CO)211 and
cis-(i-Pr3P)2Ru(CtCPh)2(CO)212 and may be ascribed to
steric congestion of the PCy3 ligand on the basis of a
face-to-face arrangement of its two C13-C18 and C25-
C30 cyclohexyl rings. The bond lengths relevant to the
phenylethynyl ligand were similar to those of trans-
(Et3P)2Ru(CtCPh)2(CO)2.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and spectroscopic data of 3-6 together with X-ray
structural information on 4 and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM990306I
The complexes 4 and 5 catalyzed the dimerization of
2 to afford 3 (Table 2). It may be concluded, therefore,
that 4 and 5 are important catalytic species in the
dimerization of 2 by the RuCl3‚3H2O/PCy3/Et2NH/CO2
system. The yield of 3 was not high, although almost
complete consumption of the starting 2 was confirmed
(13) (a) Simionescu, C. I.; Percec, V. J . Polym. Sci., Polym. Symp.
1980, 67, 43. (b) Masuda, T. In The Polymeric Materials Encyclopedia;
Salamone, J . C., Ed.; CRC: Boca Raton, FL, 1996; Vol. 1, p 32. For
the poly(phenylacetylene) formation by the Ru3{µ-H}{µ-C6H5N-
(C5H4N)}(CO)9/Et3SiH catalytic system, see: (c) Nombel, P.; Lugan,
N.; Mulla, F.; Lavigne, G. Organometallics 1994, 13, 4673.
(14) The low polymer yield may be due to the loss of oligomers and
6 with low molecular weights during the isolation of 6 with higher
molecular weights by toluene/ethyl alcohol and toluene/hexane.
(15) (a) Belforte, A.; Dell’Amico, D. B.; Calderazzo, F.; Giurlani, U.;
Labella, L. Gazz. Chim. Ital. 1993, 123, 119. (b) Dell’Amico, D. B.;
Calderazzo, F.; Marchetti, F.; Pampaloni, G. In Aqueous Organome-
tallic Chemistry and Catalysis; Horvath, I. T., J oo, F., Eds.; Kluwer
Academic: Dordrecht, The Netherlands, 1995; p 199.
1
by H NMR and gas chromatographic analyses of the
2/5 reaction mixture. The 1H NMR spectrum of the
resulting reaction mixture formed by the 5/2 PCy3/2
(11) Sun, Y.; Taylor, N. J .; Carty, A. J . J . Organomet. Chem. 1992,
423, C43.
(12) Werner, H.; Meyer, U.; Esteruelas, M. A.; Sola, E.; Oro, L. A.
J . Organomet. Chem. 1989, 366, 187.
(16) (a) Kohnle, J . F.; Slaugh, L. H.; Nakamaev, K. I. J . Am. Chem.
Soc. 1969, 91, 5904. (b) Atkins, K. E.; Walker, W. E.; Manyik, R. M. J .
Chem. Soc., Chem. Commun. 1971, 330.