Conversion of CC to CO in alkynyl-metal complexes: Oxidation of carbon chains capped by carbon-tricobalt clusters

Article abstract of DOI:10.1039/c002997c

Treatment of Co₃(μ₃-CCCR)(μ-dppm)(CO) ₇ with O₂ (air) in the presence of [FcH]PF₆ afforded Co₃{μ₃-CC(O)R}(μ-dppm)(CO)₇ by the formal conversion -CC- + O-O → >C-O + CO.

Full text of DOI:10.1039/c002997c

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Conversion of C C to CO in alkynyl-metal complexes: oxidation of carbon
chains capped by carbon-tricobalt clusters†
Michael I. Bruce,*a Paul A. Humphrey,a Natasha N. Zaitseva,a Brian K. Nicholson,b Brian W. Skeltonc and
Allan H. Whitec
Received 11th February 2010, Accepted 11th June 2010
DOI: 10.1039/c002997c
Treatment of Co3(m3-CC CR)(m-dppm)(CO)7 with O2 (air) in the presence of [FcH]PF6 afforded
Co3{m3-CC(O)R}(m-dppm)(CO)7 by the formal conversion –C C– + O–O → >C–O + C O. In this
way, complexes with R = Ph, Fc, and W(CO)3Cp, bis-clusters {Co3(m-dppm)(CO)7}2{m3:m3-
[
C(O)(C C)C ]}, {Co3(m-dppm)(CO)7}2{m3:m3-[ C(O)(C C)xC(O)C ]} (x = 1, 2), and
{Co3(m-dppm)(CO)7} {m3:m3-[ CC(O)C CC6H4C CC(O)C ]}, and heterometallic bis-clusters
{Co3(m-dppm)(CO)7}{2 m3:m3-[ CC(O)C CC ]}{M3(m-H)3(CO)9} (M = Ru, Os) have been prepared.
Single-crystal XRD structure determinations of several products are reported together with that of
precursor {Co3(m-dppm)(CO)7}2{m3:m3-[ C(C C)2C6H4(C C)2C ]}.
ing attempts to obtain
a cationic complex by oxida-
Introduction
tion of {(OC)7(m-dppm)Co3}{m3:m3-[ C(C C)2C ]}{Ru3(m-
H)3(CO)9} with the 1-e oxidant [FcH]PF6 suggested that reaction
was occurring with dioxygen (traces of air). A more detailed
study of this reaction has revealed an efficient general method of
converting alkynylmethylidyne-Co3 clusters to the corresponding
acylmethylidyne-Co3 complexes, as described below.
Interest in transition metal complexes containing alkynyl or poly-
ynyl ligands continues as a result of their potential as models for
molecular wires, and the possibility of constructing molecular-
scale devices from them.1,2 A particular facet of their chemistry
relates to the various oxidation processes which have been ob-
served, in particular those in which facile oxidation of complexes
containing Cx chains end-capped by redox-active metal–ligand
fragments takes place.3 For some years, several groups have sought
to delineate the various transformations occurring in this type
of complex, using spectro-electrochemical and theoretical (DFT)
methods.4–7
Chemical oxidation of several of these complexes has also
been described. In the simplest case, preparation, isolation and
characterisation of the oxidised species has been successfully
accomplished, for example with {Cp¢(PP)M}(C C)x{M(PP)Cp¢}
derivatives, for which homometallic systems with Fe(dppe)Cp*
(x = 2),8 Fe(dippp)Cp* (x = 3),9 Ru(PP)Cp¢ [(PP)Cp¢ = (PPh3)2Cp,
(dppe)Cp*] (x = 2)10 have been described. Heterometallic examples
with Fe–Ru end-groups have also been made.11 At the same time,
extensive studies of the oxidation of monometallic systems such
as M(C CAr)(dppe)Cp* (M = Fe, Ru; Ar = C6H4R-4, R = NO2,
CN, CF3, Br, F, H, Me, But, OMe, NH2, NMe2) have shown
that monocationic derivatives can be readily obtained in the iron
series, when AgOTf is used as the oxidising agent,12 whereas for
ruthenium, the monocations are too reactive to be isolated.13
These results encouraged us to examine similar reac-
tions of other complexes containing carbon chains. The
serendipitous formation of the acyl derivative {(OC)7(m-
dppm)Co3}{m3:m3-[ CC(O)C CC ]}{Ru3(m-H)3(CO)9} dur-
Results
Treatment of a solution of Co3(m3-CC CPh)(m-dppm)(CO)7 with
[FcH]PF6 while passing a rapid stream of air or oxygen through
the solution results in formation of the analogous benzoyl cluster
Co3{m3-CC(O)Ph}(m-dppm)(CO)7 1 (Scheme 1). The product is
readily isolated by preparative t.l.c. of the reaction mixture and
characterised by the usual methods, including microanalysis and
IR, NMR and ES mass spectra. The IR spectrum contained
n(CO) bands at 2062, 2012 and 1971 cm-1 with the s-vs-w
pattern characteristic of the Co3(CO)7 cluster, together with
the acyl n(CO) band at 1726 cm-1. The various NMR spectra
contained characteristic resonances for the dppm (dH 3.45, 4.76;
dC 38.35; dP 34.6) and Ph groups (dH 7.05–7.57, dC 126.9–138.2),
together with signals for Co–CO and acyl CO at dC 201.58 and
211.15, respectively. The electrospray mass spectrum (ES-MS)
from solutions containing NaOMe contains an ion at m/z 1771,
corresponding to [2M + Na]+, moving to m/z 1787 ([2M + K]+)
if K+ is present. In addition, well defined ions corresponding
to [M - H - nCO]- (n = 0, 1) are observed in the negative ion
spectrum, the latter possibly corresponding to loss of a terminal
CO group. The molecular structure of this complex was also
aSchool of Chemistry & Physics, University of Adelaide, Adelaide, South
Australia 5005. E-mail: michael.bruce@adelaide.edu.au; Fax: + 61 8 8303
4358
bDepartment of Chemistry, University of Waikato, Hamilton, New Zealand
cChemistry, SBBSC, University of Western Australia, Crawley, Western
Australia 6009
† CCDC reference numbers 754937–754946, 766034. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/c002997c
Scheme 1
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Scheme 2
confirmed by a single-crystal XRD structure determination (see
below). Related reactions occur with other complexes containing
the Co3(m-dppm)(CO)7 cluster supporting m3-CC CR ligands,
to give Co3{m3-CC(O)R}(m-dppm)(CO)7 [R = Fc 2, W(CO)3Cp
3]. As detailed in the Experimental section, microanalytical and
spectroscopic data were all consistent with these compositions,
with Fc group resonances at dH 4.25 (Cp), 4.1, 4.84 (C5H4) for
2, and W(CO)3Cp resonances at dH 5.51, dC 91.86 (Cp), and dC
194.13 (W–CO) for 3. The IR n(CO) spectra contained bands at
2063 and 2015 cm-1, which can be assigned to the Co3(CO)7 moiety,
and at 2038 and 1954 cm-1, resulting from the W(CO)3Cp group.
The latter band is broad and probably overlaps with the third band
expected from the Co3 cluster. The ES MS contained [M + Na]+
ions at m/z 1005 (2) or 1177, together with [M - W(CO)3Cp]+ at
m/z 821 for 3.
Fig. 1 Plot of a molecule of Co3{m3-CC(O)Ph}(m-dppm)(CO)7 1.
CC(O)C CC6H4C CC(O)C ]} 9 (Scheme 3) from {Co3(m-
Symmetrical bis-tricobalt clusters {Co3(m-dppm)(CO)7}2{m3:
m3-[ C(C C)xC ]} (x = 2–4) react in similar fashion (Scheme 2).
In the case of x = 2, only one CC triple bond is oxidised, the product
being {Co3(m-dppm)(CO)7}{m3:m3-[ CC(O)C CC ]}{Co3(m-
[
dppm)(CO)7}2{m3:m3-[ C(C C)2C6H4(C C)2C ]} 8 [obtained
from the Pd(0)/Cu(I)-catalysed reaction between Co3{m3-
CC C[Au(PPh3)]}(m-dppm)(CO)7 and 1,4-C6H4(C CI)2 in
60% yield and characterised by analysis, spectroscopically
and from its XRD-determined molecular structure (below)]
and the heterometallic clusters {Co3(m-dppm)(CO)7}{m3:m3-
dppm)(CO)7} 4. For
x
=
3, intermediate formation of
the
[
mono-acyl
derivative
{Co3(m-dppm)(CO)7}{m3:m3-
CC(O)(C C)2C ]}{Co3(m-dppm)(CO)7} 5 is accompanied
by formation of the diacyl {Co3(m-dppm)(CO)7}2{m3:m3-
[CC(O)C CC(O)C ]} 6. For x = 4, the diacyl {Co3(m-
dppm)(CO)7}2{m3:m3-[CC(O)(C C)2C(O)C ]} 7 was the only
product obtained. The same complex was also formed by
oxidation of trans-Pt{(C C)2-m3-C[Co3(m-dppm)(CO)7]}2(dppe),
deplatination occurring. Similar deplatination occurred
upon heating to give {Co3(m-dppm)(CO)7}2(m3:m3-C10).14
Related oxidation reactions gave {Co3(m-dppm)(CO)7}2{m3:m3-
[
CC(O)C CC ]}{M3(m-H)3(CO)9} (M = Ru 10, Os 11)
(Scheme 4).
These complexes were again characterised by the usual methods,
the IR spectra being notable for the presence of weak n(C C)
bands at ca. 2129–2112 cm-1 (if present) and n(CO) absorptions
between 2070–2062, 2017–2012 and 1980–1970 cm-1. For 10
and 11, additional n(CO) bands resulted from the other metal
8802 | Dalton Trans., 2010, 39, 8801–8811
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Scheme 3
carbonyl fragments present. The various NMR spectra contained
the resonances expected for the dppm and CO ligands, as detailed
in the Experimental section, together with characteristic acyl CO
signals between dC 207–211. Two dppm resonances are found for
the asymmetric bis-cluster complexes 4 and 5 at dP 38.5, 40.7 and
34.4, 35.2, respectively. For 10 and 11, the cluster-bonded H atoms
resonate at dH -17.86 and -19.09, respectively. Characteristic ions
in the ES-MS correspond to [M + Na]+ and [M + H]+ or [M - H]-,
with loss of up to six CO groups.
parameters are again normal and where present, alternate long-
short C–C bonds are consistent with the illustrated C–C single and
C
C triple bonds. In the acyl groups, the C(2)–O(2) separations
˚
are 1.195(7)–1.251(2) A. Angles at individual carbon atoms
range between 114.9(3)–122.1(6) [for C(1)–C(2)–C(3)], 114.7(5)–
148.7(5) [for Co(1–3)–C(1)–C(2)] and 166.8(2)–179.2(8)◦ [for C–
C
C fragments]. Parameters for the other substituents [Ph, Fc,
W(CO)3Cp] are similar to those observed on many previous
occasions for complexes containing these groups.
The molecular structures of 10 (Fig. 9) and 11 (which is
isostructural) are based upon the CM3(m-H)3 clusters which
have M–M [Ru–Ru 2.8448–2.8529(4), Os–Os 2.8826–2.8896(9) A]
Molecular structures
˚
and M–C separations [M–C 2.071–2.093(3) (Ru), 2.087–2.134(15)
The molecular structures of these complexes have been determined
by single-crystal XRD studies. Plots of single molecules of
each acyl complex described above are shown in Fig. 1–8, with
significant bond parameters collected in Table 1. The common
features include the Co3(m-dppm)(CO)7 clusters and the carbon
chains in which C(2), adjacent to the apical carbon C(1) of the Co3
cluster, bears an oxygen atom O(2). In 5 and the heterometallic
clusters 10 and 11, only one acyl CO group is present.
◦
˚
A (Os)] and angles [M(n)–C(5)–C(4) [122.7(2)–134.4(2) (Ru),
122.4(11)–136.0(11)◦ (Os)] which fall within the ranges found
for several related M3(m-H)3(m3-CC CR)(CO)9 clusters found
on earlier occasions.15 The M–M bonds are elongated from
those found for M3(CO)12 [2.8512(4)–2.8595(4) (Ru),16 2.8737(5)–
17
˚
2.8824(5) A (Os) ]. The three H atoms in 10 are in refined positions
˚
with Ru–H distances of 1.66–1.86(6) A (the Os–H atoms in 11 were
refined based on H positions in 10). Atom C(5) caps the M3 face
[M(1–3)–C(5) 2.071–2.093(3) (Ru), 2.087–2.134(15) A (Os)], with
M(n)–C(5)–C(4) angles ranging between 122.7–134.4(2) (Ru) and
Bond lengths for the Co3 clusters fall within the normal ranges,
viz. Co–Co 2.460(1)–2.4985(6), Co–P 2.1850(5)–2.227(2), and
Co–C(1) 1.858(6)–1.981(8) A. Along the carbon chains, these
˚
˚
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Table 1 Selected bond parameters
Compound 2 (3 mols.)
1
3
5a
6
7
8
9a
10
11
˚
Bond distances/A
Co(1)–Co(2)
2.4665(3) 2.460(1);
2.466(1);
2.463(1)
2.4723(3) 2.473(1);
2.494(1);
2.453(1)
2.4901(3) 2.491(1);
2.480(1);
2.483(1)
2.1880(4) 2.189(2);
2.196(2);
2.484(1)
2.472(1)
2.485(2)
2.207(2)
2.193(2)
1.886(7)
1.891(7)
1.941(7)
2.4870(3)
[2.4767(3)]
2.4965(7)
2.4631(7)
2.4769(7)
2.191(1)
2.208(1)
1.879(4)
1.883(4)
1.924(4)
2.477(1);
2.480(1)
2.4756(6)
2.4985(6)
2.4799(6)
2.2029(9)
2.1939(9)
1.898(3)
1.896(3)
1.925(3)
2.472(1);
2.463(1)
2.4914(7) 2.495(3)
2.4705(6) 2.477(3)
2.4677(6) 2.477(3)
2.1999(8) 2.199(4)
2.1861(9) 2.185(5)
Co(1)–Co(3)
Co(2)–Co(3)
Co(1)–P(1)
Co(2)–P(2)
Co(1)–C(1)
Co(2)–C(1)
Co(3)–C(1)
2.4680(4)
[2.4894(3)]
2.479(1);
2.481(1)
2.484(2);
2.477(2)
2.4804(4)
[2.4783(4)]
2.483(1);
2.498(1)
2.481(1);
2.478(2)
2.1850(5)
[2.2091(5)]
2.187(2);
2.196(2)
2.208(2);
2.186(3)
2.196(2)
2.2118(4) 2.212(2);
2.198(2);
2.2104(5)
[2.2093(5)]
2.205(2);
2.227(2)
2.195(2);
2.195(3)
2.210(2)
1.898(1)
1.883(1)
1.936(1)
1.902(6);
1.884(6);
1.912(6)
1.920(6);
1.899(6);
1.900(6)
1.947(6);
1.900(2)
[1.905(2)]
1.879(6);
1.871(6)
1.874(7);
1.858(6)
1.873(3)
1.892(3)
1.916(2)
1.89(1)
1.89(2)
1.93(2)
1.885(2)
[1.907(2)]
1.881(6);
1.871(7)
1.867(6);
1.876(7)
1.933(2)
1.919(6);
1.981(8)
1.926(7);
1.933(7)
1.932(6);
1.931(6)
1.457(8);
1.485(8);
1.470(8)
1.226(8);
1.232(8);
1.234(8)
1.485(9);
1.473(9);
1.505(9)
[1.913(2)]
C(1)–C(2)
C(2)–O(2)
C(2)–C(3)
1.464(2)
1.230(2)
1.472(10) 1.457(3)
1.472(5)
1.223(4)
1.473(5)
1.478(9);
1.494(9)
1.390(4)
1.469(9);
1.460(9)
1.460(4)
1.235(3)
1.437(4)
1.48(2)
1.23(2)
1.44(2)
1.208(9)
1.251(2)
1.215(7);
1.195(7)
1.237(8);
1.219(9)
1.503(2)
[C(201)]
1.478(11) 1.440(3)
1.458(9);
1.436(10)
1.218(5)
1.442(9);
1.472(9)
C(3)–C(4)
C(4)–C(5)
1.171(11) 1.225(3)
1.199(7)
[C(3¢)]
1.203(9);
1.206(9)
1.357(10)
1.361(5)
1.198(5)
1.198(8);
1.177(8)
1.419(8);
1.445(8)
1.210(4)
1.401(4)
1.17(2)
1.42(2)
2.156(8)
[W]
1.400(3)
Bond angles (◦)
Co(1)–C(1)–C(2)
131.3(1)
140.2(1)
120.9(1)
122.3(1)
146.4(5);
144.1(5);
148.7(5)
123.3(5);
123.1(4);
122.1(5)
124.3(4);
124.8(4);
122.5(4)
120.4(6);
119.4(6);
121.0(6)
118.4(6);
118.4(6);
117.0(6)
[C(n01)]
121.1(6);
122.1(6);
122.0(6)
[C(n01)]
133.1(5)
133.0(5)
127.5(5)
122.7(7)
121.6(7)
131.4(1)
[129.8(1)]
133.6(3)
130.2(3)
128.9(3)
124.9(3)
120.2(3)
130.9(5);
134.7(5)
129.9(2)
135.4(3)
128.0(2)
133.2(5);
134.0(5)
130.6(2)
132.1(2)
130.0(2)
123.4(3)
120.2(3)
139.8(11)
133.7(11)
129.8(11)
121.8(13)
121.5(13)
Co(2)–C(1)–C(2)
Co(3)–C(1)–C(2)
C(1)–C(2)–O(2)
C(3)–C(2)–O(2)
134.0(1)
[133.0(1)]
138.1(5);
139.5(5)
134.7(5);
137.0(5)
128.4(1)
[131.2(1)]
122.4(4);
114.7(5)
123.5(6);
119.9(5)
123.0(2)
124.0(6);
123.8(6)
123.1(6);
124.5(6)
118.9(1)
[C(201)]
118.1(2)
120.9(6);
119.6(6)
120.1(6);
119.2(6)
C(1)–C(2)–C(3)
118.6(1)
[C(201)]
115.6(6)
177.9(9)
118.9(2)
114.9(3)
115.1(6);
116.1(6)
176.1(4)
116.7(6);
116.3(6)
116.5(2)
116.7(13)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
166.8(2)
174.1(2)
179.1(5)
[C(3¢)]
174.9(7);
174.3(8)
179.2(8);
178.9(9)
175.4(4)
179.1(4)
173.2(8);
175.3(8)
175.6(7);
177.2(8)
175.1(3)
174.8(3)
174.9(16)
174.9(17)
175.4(7)
[W]
a Unparenthesised data reads from the acyl end of the molecule; parenthesized data is◦for the other end. Data for 5.S is less precise and not given.
◦
˚
For 8: C(5)–C(6) 1.426(5) A; C(4)–C(5)–C(6) 177.6(4), C(5)–C(6)–C(7,8) 120.1, 121.1(3) . For 9: C(13)–C(14) 1.460(9) . For 10: Ru(1)–Ru(2,3) 2.8451,
2.8448(4), Ru(2)–Ru(3) 2.8529(4), Ru(1)–H(2,3) 1.79(4), 1.86(6), Ru(2)–H(1,3) 1.77(4), 1.66(6), Ru(3)–H(1,2) 1.74(4), 1.76(4), Ru(1,2,3)–C 2.071, 2.093,
2.085(3) A; Ru(1,2,3)–C–C 134.4, 122.7, 126.0(2) . For 11: Os(1)–Os(2,3) 2.8841(9), 2.8826(10), Os(2)–Os(3) 2.8896(9), Os(1,2,3)–C 2.087(15), 2.134(14),
◦
˚
◦
˚
2.122(15) A; Os(1,2,3)–C–C 136.0(11), 122.4(11), 125.0(11) .
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Fig.
dppm)(CO)7 3.
3
Plot of
a
molecule of Co3{m3-CC(O)C C[W(CO)3Cp]}(m-
Scheme 4
Fig. 4 Plot of a molecule of {Co3(m-dppm)(CO)7}2{ CC(O)C CC
}
5.
Fig.
5
Plot of
a
(centrosymmetric) molecule of {Co3(mdppm)-
(CO)7}2{ CC(O)C CC(O)C } 6.
those discussed above, with the exception that the C5 chains are
approximately linear [angles at individual atoms C(1–5) range
between 175.4–179.1(4)◦], with the carbon chains having the
expected alternating long-short-long separations consistent with
the C–C C–C C–C formulation.
Fig. 2 Plots of (a) molecule 1 of Co3{m3-CC(O)Fc}(m-dppm)(CO)7 2;
(b) unit cell contents, projected down a.
122.4–136.0(11)◦ (Os), also similar to those found before. Each M
atom bears three CO groups, which occupy one axial and two
equatorial sites: there are no significant differences between the
two types of M–C–O group. The structure of 11 closely resembles
that of 10, as expected from the close similarity in size of these two
Group 8 atoms.
The structure of bis(cluster) 1,4-{Co3(m-dppm)(CO)7(m3-
C(C C)2}2C6H4 8 (Fig. 9, Table 1) was also determined during
this work. The CCo3 clusters are linked via diynyl bridges to
the 1,4-C6H4 fragment. Bond lengths and angles are similar to
Discussion
This paper describes a novel reaction whereby a C C unit of
an alkynyl or poly-ynyl chain attached to the apical carbon of
a CCo3 cluster is replaced by a carbonyl group. The reaction
appears to have wide applicability, examples with substituents
as disparate as Ph, Fc, W(CO)3Cp or M3(m-H)3(CO)9 (M =
Ru, Os) being found. Equally, if two CCo3 clusters end-cap
a carbon chain, then stepwise conversion to the mono- and
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Fig. 6 Plot of a molecule of {Co3(m-dppm)(CO)7}2{ CC(O)(C C)2-
C(O)C } 7.
Fig. 9 Plot of a (centrosymmetric) molecule of 1,4-{Co3(m-dppm)-
(CO)7[m3-C(C C)2]}2C6H4 8.
In the present cases, we suggest that formal dismutation
(metathesis) of O O with the –C C– unit takes place to give,
initially, the a-diketone –C(O)C(O)–. Considering the apical
carbon as a cluster atom, migration of the acyl group to C(1)
with concomitant formation of a CO ligand may then occur.
The latter can be temporarily accommodated on the cluster
by opening of a Co–Co bond. Subsequent elimination of this
CO with reformation of the Co–Co bond would produce the
observed products (Scheme 5). Migration of ligands from api-
cal carbon atoms to cluster metal atoms has been described
earlier.22 At this stage, the precise roles of the two oxidants await
further study, but oxidation of the alkynyl-CCo3 system to an
intermediate radical cation cannot be ruled out. Although the
complex (OC)9Co3CC(O)CCo3(CO)9 has been described,18,23,24 the
analogous a-diketone was not obtained here, even after extensive
oxidation of the C6 precursor.
Fig.
C
7
Plot of
a
molecule of {Co3(m-dppm)(CO)7}2{ CC(O)-
CC6H4C CC(O)C } 9.
A reaction that is possibly related to those described above is
the oxidative decarbonation of alkynylmetal-bridged complexes
of Co2(CO)6 that was first described over twenty years ago.25
Dioxygen reacts with Co2{m-PhC2[M(CO)2Cp]}(CO)6 (12, M =
Fe, Ru) to give heterometallic clusters Co2M(m3-CPh)(CO)7Cp 13
in good yield (Scheme 6). In these reactions, a net loss of C + CO
has occurred, labelling studies showing that oxidation converts Ca
to CO before elimination of another (cluster-bonded) CO occurs.
More recently, Gladysz and coworkers26 have commented
upon crystallographic evidence for species with R(C O)CCR–
CR(C O)R fragments [R = (C C)xPt moiety] being obtained
for air-oxidised samples of tetranuclear poly-ynyl-platinum(II)
complexes such as 14. However, the structures could not be fully
refined.
Fig. 8 Plot of a molecule of {Co3(m-dppm)(CO)7}{ CC(O)C CC }-
{Ru3(m-H)3(CO)9} 10. Complex 11 is isostructural.
di-acyl derivatives has been found. At this time, the reaction is
limited to the CCo3 clusters mentioned herein. The formation
of an alkynyl-carboxamide complex in the reaction between
Co3(m3-CBr)(CO)9 and Co3{m3-CC2H[Co2(CO)6]}(CO)9 under
Cadiot–Chodkiewicz conditions [Cu(I)/NHEt2] was shown not
to require the bromo cluster, the conversion being suggested
to proceed via intramolecular insertion of CO into an NR2–
C bond.18 More recently, reactions between Co3(m3-CBr)(CO)9
and Ru(C CH)(PP)Cp¢ [(PP)Cp¢ = (PPh3)2Cp, (dppe)Cp*) have
been found to give the ethynyl-carbonyl derivatives Co3{m3-
CC(O)C C[Ru(PP)Cp¢]}(CO)8(PPh3).19 Alternatively, involve-
ment of a ketenylidene (CCO) ligand, which is then attacked by a
nucleophile to give the observed products, has been suggested.20
This type of reaction was first found for the reactions between
Co3(m3-CBr)(CO)9 and various amines, alcohols and phenols, inter
alia.21
8806 | Dalton Trans., 2010, 39, 8801–8811
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Scheme 5
Scheme 6
solution cell with NaCl windows. Nujol mull spectra were obtained
from samples mounted between NaCl discs. NMR spectra were
recorded on a Varian 2000 instrument (1H at 300.13 MHz, 13C
at 75.47 MHz, 31P at 121.503 MHz). Unless otherwise stated,
samples were dissolved in CDCl3 contained in 5 mm sample
tubes. Chemical shifts are given in ppm relative to internal
tetramethylsilane for 1H and 13C NMR spectra and external
H3PO4 for 31P NMR spectra. Electrospray mass spectra (ES
MS) were obtained from samples dissolved in MeOH unless
otherwise indicated. Solutions were injected into a VG Platform
II spectrometer via a 10 ml injection loop. Nitrogen was used as
the drying and nebulising gas. Chemical aids to ionisation were
used as required.27 HR ES-MS was on a Bruker MicrOTOF
instrument. Elemental analyses were by CMAS, Belmont, Vic.,
Australia.
Conclusions
We have described a novel reaction whereby a C C triple bond
attached to the apical carbon of a CCo3 cluster is converted into
an acyl group with elimination of CO. This reaction appears to be
of wide application, accommodating a wide range of substituents
at the other end of the carbon chain. Poly-ynyl chains end-capped
by two Co3 clusters also enter into this reaction, which can occur
in a stepwise manner. A possible mechanism involves metathesis
of O O with C C to give an a-diketone, which fragments by
loss of CO, possibly via migration to the CCo3 cluster followed by
elimination of a cluster-bound CO ligand.
Experimental
General
Common solvents were dried, distilled under nitrogen and de-
gassed before use. Separations were carried out by preparative
thin-layer chromatography on glass plates (20 ¥ 20 cm2) coated
with silica gel (Merck, 0.5 mm thick).
Reagents
The complexes Co3{m3-C(C C)xR}(m-dppm)(CO)7 (x = 1, R =
Ph, Fc;28 x = 2, R = W(CO)3Cp19], {Co3(m-dppm)(CO)7}2-
{m3:m3-C(C C)xC} (x = 2,29 3, 430), trans-Pt{(C C)2C[Co3(m-
dppm)(CO)7]}2(dppe),14 {(OC)7(m-dppm)Co3}{m3:m3-C(C C)2-
Instruments
C}{M3(m-H)3(CO)9} (M = Ru, Os)15 and [FcH]PF6 were ob-
31
IR spectra were obtained on a Bruker IFS28 FT-IR spectrometer.
Spectra in CH2Cl2 were obtained using a 0.5 mm path-length
tained as previously described.
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1
n(acyl CO) 1727 m (br). H NMR (CDCl3): d 3.35, 4.36 (2 ¥ m,
2H, dppm), 4.25 (s, 5H, Cp), 4.31, 4.84 (2 ¥ br s, 4H, C5H4), 7.03–
7.28 (m, 20H, Ph). 31P NMR (CDCl3): d 34.4 (br s, dppm). ES MS
(positive ion, MeOH/NaOMe, m/z): 1005, [M + Na]+; 983, [M +
H]+; 954, [M - CO]+; (negative ion, MeOH, m/z): 981, [M - H]-.
If Cl- is present in the system, an ion at m/z 1017, [M + Cl]-, is
formed. Considerable decomposition accompanies this reaction.
The product yield does not increase if more [FcH]PF6 is added.
(b) Co3{m3-C(C C)2[W(CO)3Cp]}(m-dppm)(CO)7 (40 mg,
0.035 mmol) and [FcH]PF6 (11.5 mg, 0.035 mmol) in CH2Cl2 (25
ml) for 5 h gave Co3{m3-CC(O)C C[W(CO)3Cp]}(m-dppm)(CO)7
3 (16.6 mg, 42%) (green-brown, Rf 0.30) as very dark green
crystals (CH2Cl2–EtOH). Anal. Found: C, 46.03; H, 2.55.
Calcd (C44H27Co3O11P2W): C, 45.78; H, 2.36; M, 1154. IR
(CH2Cl2, cm-1): n(C C) 2126w; n(CO) 2063 s, 2038 m, 2015vs,
1995 (sh), 1954 m (br); n(acyl CO) 1722w (br). 1H NMR (CDCl3):
d 3.32, 4.61 (2 ¥ m, 2H, dppm), 5.51 (s, 5H, Cp), 7.02–7.56 (m,
20H, Ph). 13C NMR (CDCl3): d 39.65 (br s, dppm), 86.34, 92.86
(2 ¥ s, carbon chain), 91.86 (s, Cp), 128.29–138.13 (m, Ph), 194.13,
202.44 (2 ¥ br s, W–CO, Co–CO), 210.55 (br s, acyl CO). 31P
NMR (CDCl3): d 35.4 (br s, dppm). ES MS (positive ion, MeOH
+ NaOMe, m/z): 1177, [M + Na]+; 1149–1093, [M + Na - nCO]+
(n = 1–3); (negative ion, MeOH, m/z): 1153, [M - H]-; 821, [M
- W(CO)3Cp]-. Addition of NaOMe increases the [M - H]- peak
intensity and an ion at m/z 1185, [M + OMe]-, is formed. If Cl- is
present in the system, an ion at m/z 1189, [M + Cl]-, is formed.
(c) {Co3(m-dppm)(CO)7}2(m-C6) (30 mg, 0.019 mmol) and
[FcH]PF6 (6.3 mg, 0.019 mmol) in CH2Cl2 (20 ml) for 3 h afforded
recovered {Co3(m-dppm)(CO)7}2(m-C6) (0.6 mg, 2%) (brown-red,
Rf 0.70; CH2Cl2–hexane, 1/1) and {Co3(m-dppm)(CO)7}2{m3:m3-
Synthesis of {Co3(l-dppm)(CO)7}2{l3:l3-
C(C C)2C6H4(C C)2C ]} 8
[
A solution of Co3{m3-CC C[Au(PPh3)]}(m-dppm)(CO)7 (100 mg,
0.08 mmol) in thf (10 ml) was treated with IC CC6H4C CI
(15.1 mg, 0.04 mmol), followed by Pd(PPh3)4 (5 mg, 0.004
mmol) and CuI (1 mg, 0.04 mmol). After stirring at r.t.
for 2 h, the solution had turned red-brown. Purification by
preparative t.l.c. (acetone-hexane, 1/3) afforded one major
band (Rf 0.19) which contained {Co3(m-dppm)(CO)7}2{m3:m3-
[
C(C C)2C6H4(C C)2C ]} 8 (41.4 mg, 60%), obtained as
very dark red crystals (CH2Cl2–hexane). Anal. Found: C, 56.45;
H, 3.11. Calcd (C80H48Co6O14P4): C, 56.17; H, 2.83; M, 1710.
IR (CH2Cl2, cm-1): n(C C) 2151w; n(CO) 2058 s, 2013vs, 1972
(sh), n(acyl CO) 1726w (br). 1H NMR (CDCl3): d 3.49, 4.38
(2 ¥ m, 4H, dppm), 7.26–7.60 (m, 44H, Ph + C6H4). 13C NMR
(CDCl3): d 43.10 (br s, dppm), 72.12, 87.46, 94.36, 107.26 (4 ¥ s,
carbon chain), 128.7–134.3 (m, Ph + C6H4), 201.49 (br s, Co–
CO). 31P NMR (CDCl3): d 35.0 (br s, dppm). ES MS (positive
ion, MeOH/NaOMe, m/z): 1733–1593, [M + Na - nCO]+ (n
= 0–5); (negative ion, MeOH/NaOMe, m/z): 1709, [M = H]-;
1596, [M - H - 4CO]-; 941, [M - H - CCo3(dppm)(CO)7]-;
769, [C2C6H4C2CCo3(dppm)(CO)3]-. High resolution: [M + Na]+:
calcd 1732.788, found 1732.789; [M - H]-: calcd 1708.791, found
1708.795.
Oxidation of carbon chains end-capped by carbon-tricobalt clusters
The reaction is exemplified by the oxidation of Co3(m3-
CC CPh)(m-dppm)(CO)7. A solution of Co3(m3-CC CPh)(m-
dppm)(CO)7 (50 mg, 0.06 mmol) in CH2Cl2 (20 ml) was saturated
with dioxygen (ca. 1 h) and [FcH]PF6 (20 mg, 0.06 mmol) was
added. The reaction was continued under oxygen for 4 h. After
removal of solvent, purification by preparative t.l.c. (CH2Cl2–
hexane, 2/1) gave recovered Co3(m3-CC CPh)(m-dppm)(CO)7
(1.5 mg, 3%) (brown-green, Rf 0.8) and Co3{m3-CC(O)Ph}(m-
dppm)(CO)7 1 (27.1 mg, 54%) (Rf 0.3) as very dark green
crystals (CH2Cl2–EtOH). Anal. Found: C, 54.83; H, 3.09. Calcd
(C40H27Co3O8P2): C, 54.95; H, 3.11; M, 874. IR (CH2Cl2, cm-1):
n(CO) 2062 s, 2012vs, 1971 (sh), n(acyl CO) 1726w (br). 1H NMR
(CDCl3): d 3.45, 4.76 (2 ¥ m, 2H, dppm), 7.05–7.57 (m, 25H,
Ph). 13C NMR (CDCl3): d 38.35 [t, J(CP) = 23.7 Hz, dppm],
126.9–138.2 (m, Ph), 201.58 (br s, Co–CO), 211.15 (br s, acyl CO).
31P NMR (CDCl3): d 34.6 (br s, dppm). ES MS (positive ion,
MeOH/NaOMe, m/z): 1771, [2M + Na]+; if K+ is present in the
system, an ion at m/z 1787, [2M + K]+ is formed. (Negative ion,
MeOH/NaOMe, m/z): 873, [M - H]-; 845, [M - H - CO]-.
Under different conditions, such as the use of thf in place of
CH2Cl2 as reaction solvent, or of only a catalytic amount of
[FcH]PF6, poor yields of oxidized products were obtained. In all
such reactions some decomposition occurs.
[
CC(O)C CC ]} 4 (11.4 mg, 38%) (brown, Rf 0.63), which
formed very dark brown crystals (CH2Cl2–MeOH). Anal. Found:
C, 52.07; H, 2.93. Calcd (C69H44Co6O15P4): C, 52.10; H, 2.79; M,
1590. IR (CH2Cl2, cm-1): n(C C) 2119vw; n(CO) 2068 s, 2054
1
m, 2027 m, 2008vs, 1970 (sh), n(acyl CO) 1727w (br). H NMR
(CDCl3): d 3.47–3.61 (m, 2H, dppm), 4.58, 4.97 (2 ¥ m, 2H, dppm),
6.86–7.73 (m, 40H, Ph). 13C NMR (CDCl3): d 38.48, 40.70 (2 ¥
br s, dppm), 112.04, 114.72 (2 ¥ s, carbon chain), 128.3–137.75
(m, Ph), 201.87 (br s, Co–CO), 210.86 (br s, acyl CO). 31P NMR
(CDCl3): d 32.4, 35.0 (2 ¥ br s, 2 ¥ 1P, dppm). ES MS (positive
ion, MeOH/NaOMe, m/z): 1613, [M + Na]+; 1591, [M + H]+;
1613–1445, [M + Na - nCO]+ (n = 1–6); 1591–1395, [M + H -
nCO]+ (n = 1–7). If K+ is present in the system, an ion at m/z 1629,
[M + K]+, is formed.
(d) {Co3(m-dppm)(CO)7}2(m-C8) (35 mg, 0.022 mmol) and
[FcH]PF6 (7.2 mg, 0.022 mmol) in CH2Cl2 (20 ml) for 3 h
afforded recovered {Co3(m-dppm)(CO)7}2(m-C6) (orange-brown,
Rf 0.55; 4 mg, 11%). A major brown band (Rf 0.21) contained
{Co3(m-dppm)(CO)7}2{m3:m3-[ CC(O)(C C)2C ]} 5 (10.7 mg,
31%), which formed a brown solid. Anal. Found: C, 52.89; H,
2.79. Calcd (C71H44Co6O15P4): C, 52.82; H, 2.75; M, 1614. IR
(CH2Cl2, cm-1): n(C C) 2129vw; n(CO) 2066 s, 2016vs, 1975
The following reactions were carried out in similar fashion:
(a) Co3(m3-CC CFc)(m-dppm)(CO)7 (30 mg, 0.03 mmol) with
[FcH]PF6 (10 mg, 0.03 mmol) in CH2Cl2 (20 ml) for 4 h gave
recovered Co3(m3-CC CFc)(m-dppm)(CO)7 (2.1 mg, 7%) (brown,
Rf 0.78) and Co3{m3-CC(O)Fc}(m-dppm)(CO)7 2 (3.5 mg, 12%)
(black, Rf 0.56) as dark red-brown crystals (CH2Cl2–EtOH). Anal.
Found: C, 54.46; H, 3.32. Calcd (C44H31Co3FeO8P2): C, 53.80; H,
3.18; M, 982. IR (CH2Cl2, cm-1): n(CO) 2062 s, 2015vs, 1979 (sh),
1
m, n(acyl CO) 1724w (br). H NMR (CDCl3): d 3.43 (m, 2H,
dppm), 4.21, 4.37 (2 ¥ m, 2H, dppm), 6.86–7.56 (m, 40H, Ph). 13
C
NMR (CDCl3): d 128.95–132.9 (m, Ph), 201.06 (br s, Co–CO).
31P NMR (CDCl3): d 34.4, 35.2 (2 ¥ br s, 2 ¥ 1P, dppm). ES MS
(negative ion, MeOH/NaOMe, m/z): 1613, [M - H]-; 1585, [M
- H - CO]-. The third, brown-green band (Rf 0.15) gave {Co3(m-
dppm)(CO)7}2{CC(O)(C C)C(O)C} 6 (1.2 mg, 3.4%) as brown
8808 | Dalton Trans., 2010, 39, 8801–8811
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crystals (CH2Cl2–EtOH). IR (CH2Cl2, cm-1): n(C C) 2127w;
1
n(CO) 2070 s, 2015vs, 1979 m (br), n(acyl CO) 1713w (br). H
NMR (CDCl3): d 3.38, 4.33 (2 ¥ m, 4H, dppm), 6.38–7.51 (m,
40H, Ph). 31P NMR (CDCl3): d 35.3 (br s, dppm). ES MS (positive
ion, MeOH/NaOMe, m/z): 1641, [M + Na]+; 1641–1473, [M +
Na - nCO]+ (n = 1–6).
(e) {Co3(m-dppm)(CO)7}2(m-C10) (25 mg, 0.015 mmol) and
[FcH]PF6 (10 mg, 0.03 mmol) in CH2Cl2 (20 ml) for 3 h afforded
{Co3(m-dppm)(CO)7}2{m3:m3-[ CC(O)(C C)2C(O)C ]}
7
(6.5 mg, 26%) (green-brown band; acetone-hexane, 3/7, followed
by CH2Cl2–hexane, 1/1) which formed very dark brown crystals
(CH2Cl2–hexane). Anal. Found: C, 52.68; H, 3.14. Calcd
(C72H44Co6O16P4): C, 52.63; H, 2.70; M, 1642. IR (CH2Cl2, cm-1):
n(C C) 2114vw; n(CO) 2068 s, 2017vs, 1979 m, 1958 (sh),
n(acyl CO) 1704w (br). 1H NMR (CDCl3): d 3.35, 4.25 (2 ¥
m, 4H, dppm), 7.07–7.46 (m, 40H, Ph). 13C NMR (CDCl3): d
39.84, [t, J(CP) = 23 Hz, dppm], 73.45, 85.11 (2 ¥ s, carbon
chain), 128.4–137.0 (m, Ph), 200.74 (br s, Co–CO), 207.63 (br s,
acyl CO). 31P NMR (CDCl3): d 34.7 (br s, dppm). ES MS
(positive ion, MeOH/NaOMe, m/z): 1665, [M + Na]+; 1643,
[M + H]+; 1643–1587, [M + H - nCO]+ (n = 1–2); (negative ion,
MeOH/NaOMe, m/z): 1641, [M - H]-.
(f) trans-Pt{(C C)2C[Co3(m-dppm)(CO)7]}2(dppe) (28 mg,
0.013 mmol) and [FcH]PF6 (8.2 mg, 0.025 mmol) in CH2Cl2
(20 ml) for 2 h afforded a green-brown band (acetone-hexane,
3/7; Rf 0.26) containing dark brown {Co3(m-dppm)(CO)7}2{m3:m3-
[
CC(O)(C C)2C(O)C ]} 7 (4.2 mg, 20%), identical with the
above complex (31P NMR, d 34.7).
(g)
{Co3(m-dppm)(CO)7}2{m3:m3-[ C(C C)2C6H4(C C)2-
C
]} (20 mg, 0.012 mmol) and [FcH]PF6 (8 mg, 0.024 mmol)
in CH2Cl2 (20 ml) for 3 h gave a green-brown band (acetone-
hexane, 3/7; Rf 0.25) containing {Co3(m-dppm)(CO)7}2{m3:m3-
[
CC(O)C CC6H4C CC(O)C ]} 9 (12 mg, 60%) as dark
brown crystals (CHCl3–MeOH). Anal. Found: C, 54.93; H,
2.83. Calcd (C78H48Co6O16P4): C, 54.51; H, 2.81; M, 1718. IR
(CH2Cl2, cm-1): n(C C) 2185w; n(CO) 2065 s, 2018vs, 1975 (sh),
1
n(acyl CO) 1711w (br). H NMR (CDCl3): d 3.40, 4.27 (2 ¥ m,
4H, dppm), 7.05–7.54 (m, 44H, Ph + C6H4). 13C NMR (CDCl3): d
39.21 br s, dppm), 75.27, 89.38 (2 ¥ s, carbon chain), 128.2–135.9
(m, Ph + C6H4), 201.08 (br s, Co–CO), 210.47 (br s, acyl CO).
31P NMR (CDCl3): d 34.6 (br s, dppm). ES MS (positive ion,
MeOH/NaOMe, m/z): 1741, [M + Na]+; 1719, [M + H]+.
Syntheses of {Co3(l-dppm)(CO)7}{l3:l3-
[
CC(O)C CC }{M3(l-H)3(CO)9} (M = Ru 10,
Os 11)
(a) M = Ru. [FcH]PF6 (9 mg, 0.027 mmol) was added to a solution
of
{Co3(m-dppm)(CO)7}{m3:m3-[ CC CC CC ]}{Ru3(m-
H)3(CO)9} (36 mg, 0.026 mmol) in CH2Cl2 (7 ml). After stirring
at r.t. for 2 h, solvent was removed and a dichloromethane
extract of the residue was separated by preparative t.l.c. (acetone-
hexane, 3/7). The major brown band (Rf 0.60) contained
{Co3(m-dppm)(CO)7}{m3:m3-[ CC(O)C CC ]}{Ru3(m-H)3-
(CO)9} 10 (7 mg, 19%), which was isolated as black crystals
(CH2Cl2–MeOH). Anal. Found: C, 39.74; H, 1.94. Calcd
(C46H25Co3O17P2Ru3): C, 39.59; H, 1.79; M, 1393. IR
(CH2Cl2, cm-1): n(C C) 2120w; n(CO) 2095 (sh), 2088vs,
2063 m, 2039 m, 2012 s, 2000 (sh), 1974w; n(acyl CO) 1604w (br).
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1H NMR (CDCl3): d -17.86 (s, 3H, RuH), 3.36, 4.83 (2 ¥ m, 2 ¥
1H, dppm), 7.01–7.53 (m, 20H, Ph). ES-MS (positive ion, MeOH
+ NaOMe, m/z): 1416, [M + Na]+; 1393, M+.
10. One Ph ring was modelled as disordered over two sets of sites,
major component site occupancy 0.716(10). Cluster hydrogen
atoms were refined in (x, y, z, Uiso).
(b) M = Os. Similarly, a mixture of {Co3(m-dppm)(CO)7}{m3:m3-
11. Diffraction data were very weak as a result of small
crystal size, supporting refinement of anisotropic displacement
parameters for Os, Co, P atoms only (no disorder). Cluster H atom
positions were based on those of the isomorphous Ru analogue 10
and refined with Os–H bond lengths restrained to ideal values.
[
CC CC CC ]}{Os3(m-H)3(CO)9} (30 mg, 0.018 mmol)
and [FcH]PF6 (7 mg, 0.021 mmol) in CH2Cl2 (9 ml) was
stirred at r.t. for 1 h to give {Co3(m-dppm)(CO)7}{m3:m3-
[
CC(O)C CC ]}{Os3(m-H)3(CO)9} 11 (7 mg, 23%) con-
tained in a green-brown band (Rf 0.72) and obtained as black
crystals (CH2Cl2–MeOH). Anal. Found: C, 33.28; H, 1.56.
Calcd (C46H25Co3O17Os3P2): C, 33.29; H, 1.50; M, 1658. IR
(CH2Cl2, cm-1): n(C C) 2126w; n(CO) 2103w, 2088vs, 2061 m,
2025 m, 2009 s, 1973 (sh); n(acyl CO) 1606w (br). 1H NMR
(CDCl3): d -19.09 (s, 3H, OsH), 3.35, 4.83 (2 ¥ m, 2 ¥ 1H, dppm),
7.01–7.53 (m, 20H, Ph). ES-MS (positive ion, MeOH + NaOMe,
m/z): 1681, [M + Na]+; 1658, M+.
Acknowledgements
We thank the Australian Research Council for support of this
work and Johnson Matthey plc, Reading, UK, for generous loans
of RuCl3·nH2O and OsO4.
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˚
merged to N unique (Rint cited) after “empirical”/multiscan
absorption correction (proprietary software) and used in the full
matrix least squares refinements on F2, No with F > 4s(F)
being considered “observed”. Anisotropic displacement param-
eter forms were refined for the non-hydrogen atoms, hydrogen
atom treatment following a riding model. Neutral atom complex
scattering factors were used within the SHELXL 97 program
system.32 Pertinent results are given in the figures (which show non-
hydrogen atoms with 50% probability amplitude displacement
˚
envelopes and hydrogen atoms with arbitrary radii of 0.1 A) and
in Tables 1 and 2.
Variata
2. Crystals diffracted weakly and data were acquired using a
monochromatic Cu-Ka source (l = 1.54178 A). There are three
˚
molecules in the asymmetric unit, mol. 1 of opposed chirality
to the other two (# 2, 3), the molecules being disposed at z =
1/6, 1/3, 1/2 resulting in a pseudo-sub-cell c/3 [Fig. 2(b)]. Within
two of the molecules (# 1, 2), the outer ferrocenyl Cp rings are
rotationally disordered [major component occupancies 0.638(10),
0.586(11) (major and minor component displacement parameter
forms isotropic in refinement)]. Displacement envelope amplitudes
in Fig. 2 are at the 30% probability level. xabs was 0.27(4).
5. The structures of two forms are recorded, 5 (blocks) and 5.S
(rods) from the same crystallization (from CH2Cl2–MeOH). Data
acquired from the solvated form were poor in quality, consistent
with loss of solvent which was unsusceptible to satisfactory
modeling in the refinement and suppressed using SQUEEZE.33
A face-indexed analytical absorption correction was applied.
6. Unsuccessful attempts were made to model the solvent
molecule in terms of disorder.
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9. Data were of poor quality. Two of the solvent molecules (#
1, 3) were modeled as disordered, C and one Cl being common
to both components in each case; major component occupancies
were 0.751(4), 0.593(4), also one Ph ring (0.5).
8810 | Dalton Trans., 2010, 39, 8801–8811
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