Table 2 IR and NMR data for new complexes
Complex
νCO a cmϪ1
1H NMRb,c (δ)
13C-{1H} NMRb (δ)
2i
1999s, 1812m,
1752w, 1770w
7.34–7.11 (m, 5H), 5.41 (s, 5H), 5.12 (s, 5H), 3.51
(s, 3H).
233.7 (µ-CO), 216.0 (C᎐O), 199.5 (CO), 176.2
᎐
(CO2Me), 135.6 (µ-CCO2Me), 134.6 (Ph), 128.8,
127.9, 125.3 (all Ph), 9.19 (C5H5), 91.2 (C5H5), 52.1
(CO2Me), 43.4 (CPh).
2j
7.34–7.11 (m, 5H), 5.34 (s, 5H), 5.23 (s, 5H), 3.71
(s, 3H).
238.0 (µ-CO), 216.0 (C᎐O), 199.2 (CO), 170.1
᎐
(CO2Me), 160.0 (µ-CPh), 149.6 (Ph), 128.4, 126.7
(all Ph), 90.6 (C5H5), 90.0 (C5H5), 52.4 (CO2Me), 29.9
(CCO2Me).
2k
1982s, 1810m,
1754w, 1707w
5.26 (s, 5H), 5.21 (s, 5H), 3.92 (s, 3H), 1.69 (s, 3H)d
234.0 (µ-CO), 218.9 (C᎐O), 198.9 (CO), 176.0
᎐
(CO2Me), 160.8 (µ-CCO2Me), 90.1 (C5H5), 89.3
(C5H5), 52.1 (CO2Me), 39.1 (CMe), 17.4 (Me).d
91.2 (C5H5), 91.0 (C5H5).e
2l
5.33 (s, 5H), 5.30 (s, 5H), 3.74 (s, 3H), 2.81 (s, 3H)
7.19 (s, 1H), 5.32 (s, 5H), 5.22 (s, 5H), 3.65 (s, 3H).d
trans-4c
1967s, 1801s,
1703m
275.8 (µ-C), 241.3 (µ-CO), 197.4 (CO), 197.3 (CO),
164.6 (CO2Me), 129.6 (C(H)CO2Me), 92.7 (C5H5),
92.3 (C5H5), 50.6 (CO2Me).d
275.1 (µ-C), 242.2 (µ-CO), 197.8 (CO), 197.7 (CO),
164.6 (CO2Me), 129.1 (C(H)CO2Me), 90.8 (C5H5),
90.0 (C5H5), 50.6 (CO2Me).d
175.2 (CO2Me), 146.7 (µ-CPh), 144.1 (Ph), 128.7,
128.4, 128.2 (all Ph), 121.8 (µ-CCO2Me), 83.6
(2C5H4), 52.4 (CO2Me).
cis-4c
2004s, 1967s,
1801s, 1703m
7.13 (s, 1H), 5.28 (s, 5H), 5.20 (s, 5H), 3.64 (s, 3H).d
7.35 (m, 5H), 4.92 (s, 10H), 3.81 (s, 3H).
5
6
1759s, 1693m
1967s, 1936s,
1718m, 1626m
7.44–7.17 (m, 4H), 5.95 (s, 1H), 5.26 (s, 5H), 4.71
(s, 5H), 3.70 (s, 3H).
240.0 (C᎐O), 207.6 (CO), 204.5 (CO), 176.2 (µ-C),
᎐
175.1 (CO2Me), 164.9 (CC᎐O), 150.2 (CC᎐C(H)-
᎐ ᎐
CO2Me), 131.3, 128.6, 120.6, 117.3 (all CH), 90.6
(C5H5), 90.0 (C5H5), 51.6 (C(H)CO2Me), 51.3
229.1 (µ-CO), 224.5 (µ-CO), 201.0 (CO), 179.6 (µ-
CPH), (CO2Me).
7
8
1971s, 1839s,
1799m, 1697m
7.22–7.06 (m, 5H), 5.63 (m, 1H), 5.35 (m, 1H), 5.23 179.5 (µ-CCO2Me), 177.3 (CO2Me), 154.2 (Ph),
(m, 1H), 5.00 (s, 5H), 4.94 (s, 5H), 4.66 (m, 1H), 3.65
(s, 3H).
127.6, 127.4, 125.6 (all Ph), 118.5 (C5H4), 109.5
(C5H4), 95.4 (C5H4), 92.0 (C4H4), 90.4 (C5H5), 88.6
(C5H5), 84.1 (C5H4), 51.2 (CO2Me).
238.2 (µ-CO), 203.7 (CO), 179.7 (CO2Me), 156.1
(µ-C), 89.4 (C5H5), 85.1 (C5H5), 80.7 (CH), 51.9
(CO2Me), 40.6 (CH2).
1952s, 1786s,
1699m
5.18 (s, 5H), 4.96 (s, 5H), 4.87 (dd, J 7, 9, 1Ha), 3.81
(s, 3H), 2.65 (dd, J 3, 7, 1Hb), Ϫ0.11 (dd, J 3, 9, 1Hc).
a Dichloromethane solution. b CD2Cl2 solution unless otherwise stated. c Coupling constant, J, in Hz. d CDCl3 solution. e Minor isomer, other peaks
not observed.
decomposition over several hours and again no dimetalla-
cyclobutene complex was detected. It is evident, therefore, that
the formation of a dimetallacyclobutene in this system requires
the presence of two strongly electron withdrawing groups on
the alkyne: a CO2Me and a phenyl group are insufficient.
Heating a toluene solution of 1 with an excess of methyl
propiolate for 4 h, followed by chromatography, led to the
isolation of the yellow µ-vinylidene complex [Ru2(CO)2-
as A, the negative charge of which would be stabilised by the
CO2Me group.
(µ-CO){µ-C᎐C(H)CO Me}(η-C H ) ] (4c) as cis and trans
᎐
2
5
5 2
isomers in yields of 48 and 8% respectively. Characterisation
of these complexes proved straightforward, by comparing their
spectroscopic data with those of the isomers of the known
complexes [Ru (CO) (µ-CO){µ-C᎐C(H)R}(η-C H ) ] (4a,b).2
᎐
2
2
5
5 2
Fluxionality
The cis and trans isomers can be distinguished by their IR
spectra, that of the cis isomer showing two terminal carbonyl
stretches at 2004 and 1967 cmϪ1, whereas the more symmetric
trans isomer displays just one terminal carbonyl band at 1967
We have previously shown1 that dimetallacyclopentenone com-
plexes undergo the fluxional process shown in Fig. 1, involving
cleavage of the bond between C2 and Cb with simultaneous
formation of a new bond between C1 and Ca. In effect the
alkyne ‘slides’ back and forth between the CaO and CbO
cmϪ1
.
It has previously been observed that prolonged heating of
the dimetallacyclopentenone species [Ru2(CO)(µ-CO){µ-C(O)-
C(H)C(R)}(η-C5H5)2] (2a, R = H; 2e,f, R = Ph) leads to form-
ation of the corresponding vinylidene complexes 4a and 4b.2 It
is therefore likely that the reaction of 1 with methyl propiolate
initially produces a dimetallacyclopentenone complex [Ru2-
(CO)(µ-CO){µ-C(O)C(H)C(CO2Me)}(η-C5H5)2] which, under
the reaction conditions, rapidly isomerises to the µ-vinylidene
species 4c. This is clear evidence that a strongly electron with-
drawing substituent such as CO2Me promotes the proton
shift rearrangement of a dimetallacyclopentenone to give a
vinylidene, a conclusion supported by the failure of the
species 2c,d, which have an electron donating methyl substitu-
ent, to undergo the rearrangement. This in turn suggests that
the process may involve a charge-separated intermediate such
1
carbonyls. The H NMR spectra of 2i,j and 2k,l reveal that
these compexes are similarly fluxional. Thus, at room temper-
ature the 1H NMR spectrum of 2k,l shows the four cyclopenta-
dienyl signals and two methyl carboxylate signals expected of
two static isomers, but as the temperature is raised the signals
broaden and collapse, until coalescence occurs: at ca. 55 ЊC for
the cyclopentadienyl signals and ca. 65 ЊC for the CO2Me
signals. On further warming the signals sharpen and at 80 ЊC
two signals are observed for the cyclopentadienyl ligands and
one for the CO2Me groups, indicating rapid interconversion
of the two isomers on the NMR timescale. Similar behaviour is
seen for 2i,j with the four cyclopentadienyl signals at room
temperature undergoing coalescence at 60 ЊC and appearing as
two signals at higher temperature.
J. Chem. Soc., Dalton Trans., 2000, 2975–2982
2977