The photochemistry of (CO)4Mn(μ-η3: η6-C3H4C6H5)Cr(CO) 3 in frozen gas matrices at ca. 12 K

Article abstract of DOI:10.1039/b206697a

We have investigated the photochemistry of [(CO)₄Mn(μ- η³:η⁶-C₃H₄C ₆H₅)Cr(CO)₃] in low temperature matrices. In an argon matrix we see CO loss from only the Mn end of the molecule and [(CO) ₃Mn(μ-η³:η⁶-C₃H ₄C₆H₅)Cr(CO)₃] is the only observed photoproduct. However, in a N₂ matrix photosubstitution is observed at both metal centres and we were able to identify [(CO)₄Mn(μ- η³:η⁶-C₃H₄C ₆H₅)Cr(CO)₂(N₂)], [(CO) ₃(N₂)Mn(μ-η³:η⁶-C ₃H₄C₆H₅)Cr(CO)₃] and [(CO)₂(N₂)₂Mn(μ-η³: η⁶-C₃H₄C₆H₅)Cr(CO) ₃]. In all these experiments, characterisation of photoproducts was aided by comparison with experiments using the mononuclear fragments [(η⁶-C₆H₅C₂H₅)Cr(CO) ₃] and [η³-C₃H₄C ₆H₅)Mn(CO)₄] where we were able to characterise [(η³-C₃H₄C₆H ₅)Mn(CO)₂], [(η⁶-C₆H ₅C₂H₅)Cr(CO)₂(N₂)], [(η³-C₃H₄C₆H₅)Mn(CO) ₃(N₂)] and [(η³-C₃H ₄C₆H₅)Mn(CO)₂(N₂) ₂]. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b206697a

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The photochemistry of (CO)4Mn(ꢀ-ꢁ3:ꢁ6-C3H4C6H5)Cr(CO)3 in
frozen gas matrices at ca. 12 K
Paul A. Hamley, Marina K. Kuimova, Alexander J. Blake, Catherine Hughes,
Simon B. L. Lyons, Martyn Poliakoff, Anthony H. Wright† and Michael W. George*
School of Chemistry, University of Nottingham, University Park, Nottingham, UK NG7 2RD.
E-mail: mike.george@nottingham.ac.uk
Received 10th October 2002, Accepted 29th October 2002
First published as an Advance Article on the web 7th March 2003
We have investigated the photochemistry of [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] in low temperature matrices. In
an argon matrix we see CO loss from only the Mn end of the molecule and [(CO)3Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] is
the only observed photoproduct. However, in a N2 matrix photosubstitution is observed at both metal centres and we
were able to identify [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)2(N2)], [(CO)3(N2)Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] and
[(CO)2(N2)2Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3]. In all these experiments, characterisation of photoproducts was aided
by comparison with experiments using the mononuclear fragments [(η6-C6H5C2H5)Cr(CO)3] and [(η3-C3H4C6H5)-
Mn(CO)4] where we were able to characterise [(η3-C3H4C6H5)Mn(CO)2], [(η6-C6H5C2H5)Cr(CO)2(N2)], [(η3-C3H4C6-
H5)Mn(CO)3(N2)] and [(η3-C3H4C6H5)Mn(CO)2(N2)2].
Introduction
There is continuing interest in the reaction mechanism of
photochemical substitution reactions of bimetallic or higher
nuclearity metal carbonyl compounds.1 The photochemistry of
homonuclear complexes, such as [CpM(CO)3]2 (M = Cr, Mo
and W)2–19 and [CpFe(CO)2]2,20–35 has been extensively stud-
ied.36 However, there have been comparatively few studies on
the photochemistry of heterodinuclear complexes. Wrighton
and co-workers found that irradiation of [(η5-C5R5)Fe(CO)2-
Mn(CO)5] (R = H, Me) produced both homolytic cleavage of
the Fe–Mn bond37,38 and CO loss.39 Irradiation of [(η5-C5-
R5)Fe(CO)2Mn(CO)5] in the presence of PR3 (R = Ph, OPh)
resulted in formation of [(η5-C5R5)Fe(CO)2Mn(CO)4(PR3)].39
Irradiation of MnRe(CO)10 in the presence of PPh3 led to the
Mn-substituted species [Mn(CO)4(PPh3)Re(CO)5].40 Firth et al.
found that photolysis of [MnRe(CO)10] led to the formation
of [(CO)4Mn(µ-CO)Re(CO)4] with CO being lost exclusively
from the Mn centre.41 By contrast, thermal substitution of
CO in [MnRe(CO)10] also occurs at the Re.42,43 More recently,
Stufkens and co-workers44 showed that photochemical
substitution of PPh3 into [(CO)5ReMn(CO)3(α-diimine)] led
exclusively to [(CO)5ReMn(CO)2(PPh3)(α-diimine)] through
photo-dissociation of CO from Mn.
In this paper, we investigate the photochemistry of the com-
pound [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (1). The syn-
thesis of 1 was recently reported by Lyons and Wright and is
documented in this paper for completeness.45a Unlike the com-
pounds listed above, this complex does not contain a metal–
metal bond. In the solid state the Mn and Cr carbonyl moieties
lie above and below the phenyl–allyl plane of the ligand,
Fig. 1.45b
Although the photochemistry of this dinuclear compound is
largely unexplored, the photochemistry of the constituent
mononuclear fragments is known. For instance, the photo-
chemistry of [(η3-C3H5)Mn(CO)4] has been examined in low
temperature matrices as part of elegant experiments by Rest
and co-workers46 on the precursor [(η1-C3H5)Mn(CO)5] species.
Photolysis of [(η1-C3H5)Mn(CO)5] isolated at high dilution in
Ar and CH4 matrices at 12 K resulted in ejection of a CO ligand
together with a σ–π rearrangement of the η1-allyl ligand to
Fig. 1 Ellipsoid plot drawing of 1 with 50% probability displacement
ellipsoids.
generate the complex [(η3-C3H5)Mn(CO)4]. Subsequent UV
photolysis led to loss of a second carbonyl ligand and form-
ation of the sixteen-electron species [(η3-C3H5)Mn(CO)3]. The
same initial photodecarbonylation and allyl rearrangement was
observed in a nitrogen matrix, with formation of the complex
[(η3-C3H5)Mn(CO)4]. Extended photolysis led to new ν(CO)
and ν(NN) bands, which were assigned to [(η3-C3H5)Mn-
(CO)3(N2)]. The photochemistry of (η6-C6H6)Cr(CO)3 in Ar
matrices has also been investigated by Rest and co-workers.47
The unsaturated species [(η6-C6H6)Cr(CO)2] was formed as
the primary photoproduct. In a nitrogen matrix, [(η6-C6H6)-
Cr(CO)2] was not observed but instead new ν(CO) and ν(NN)
bands were generated which were assigned to the nitrogen
substituted complex [(η6-C6H6)Cr(CO)2(N2)], which was sub-
sequently shown to be a stable isolable complex. More recently
the photochemistry of [(η6-C6H6)Cr(CO)3] has been studied in
alkane solution at room temperature by Creaven et al.48 who
observed [(η6-C6H6)Cr(CO)2(n-heptane)] in n-heptane solution
at room temperature.
In this paper, our strategy has been to use these mononuclear
compounds to investigate the photochemistry of the dinuclear
complex. We begin by showing that the two metal carbonyl
moieties are essentially vibrationally uncoupled. We then
analyse the spectra of the primary photoproducts as the super-
position of the spectra of two mononuclear fragments.
† Current address: Institute of Fundamental Sciences, Massey
University, Science Tower A 3.07, Turieta Site, Palmerston North
Campus, Private Bag 11222, Palmerston North 5301, New Zealand.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
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Results and discussion
Fig. 2 shows the infrared spectra of [(CO)4Mn(µ-η3:η6-
C3H4C6H5)Cr(CO)3] (1), [Mn(η3-C3H4C6H5)(CO)4] (2) and
[(η6-C6H5C2H5)Cr(CO)3] (3), all in n-heptane solution, at room
temperature. In the absence of vibrational coupling between the
metal centres, the coaddition of the carbonyl regions of the
infrared spectra of the mononuclear compounds should be very
similar to that of the dinuclear compound. It is clear from Fig.
2 this is indeed the case; the superimposed IR spectra of the
mononuclear complexes gives a band pattern very similar to the
spectrum of the dinuclear compound. It also clear from Fig. 2
that the superimposition of their individual spectra yielded a
set of ν(CO) bands with relative intensities which match very
closely the pattern of ν(CO) bands in the spectrum of 1. We
concluded therefore that there is no appreciable vibrational
coupling between the two metal centres. Thus, the manganese
and chromium mononuclear compounds can be used as a
model of the dinuclear compound to aid interpretation of
spectra. Therefore, each of the ν(CO) bands of the dinuclear
complex can be assigned to the vibrations of the carbonyl
ligands on the two metal centres.
Fig. 3 FTIR spectra of 2 isolated in an argon matrix at 12 K (a) before
photolysis and (b) 30 minutes after photolysis (λ > 300 nm). (c) This
spectrum was generated by subtraction of (a) from (b). The negative
ν(C–O) bands show depletion of parent and the positive absorptions
show the growth of three new product bands assigned to [(η3-C3-
H4C6H5)Mn(CO)3] (4).
experiment and indicate the formation of a single species. An
additional band at 2138 cmϪ1 is readily assigned to the presence
of free carbon monoxide. The three new ν(C–O) bands are
shifted to lower wavenumbers than the parent molecule bands
and are assigned to [(η3-C3H4C6H5)Mn(CO)3] (4) by com-
parison with Rest’s data for [(η3-C3H5)Mn(CO)3], see Table 1.
Irradiation of the matrix with visible light (λ > 450 nm) caused
the intensity of the bands due to 4 to decrease and the parent
bands to be regenerated. This reversal could also be initiated by
annealing the matrix to ca. 38 K, for five minutes.
The bands for 4 are on average 4 cmϪ1 lower than those for
[(η3-C3H5)Mn(CO)3], a shift which can be rationalised by the
increase in electron donation onto the metal from the phenyl
ring thus weakening the C–O bonding. There was no evidence
for ejection of a second carbonyl ligand; 4 was the only photo-
product seen during the course of the experiment.
Fig. 2 FTIR spectra of (a) 3 (b) 2 and (c) 1 in n-heptane solution at
room temperature.
As explained above, the photochemistry of [(η3-C3H5)-
Mn(CO)4] and [(η6-C6H6)Cr(CO)3] have been examined in low
temperature matrices by Rest and co-workers. We now extend
this work to 2 and 3 which we then use as models to unravel the
photochemistry of 1.
(b) Photolysis of [(ꢁ3-C3H4C6H5)Mn(CO)4] (2) in nitrogen
matrices
The spectrum of 2, isolated in a nitrogen matrix, was very simi-
lar to that observed in an argon matrix, Table 1. UV irradiation
(λ > 300 nm) resulted in the formation of a photoproduct with
two new ν(C–O) absorptions, at 2032 and 1960 cmϪ1 (broad),
Fig. 4(a). At the same time, two bands grew in at higher wave-
numbers, a band at 2138 cmϪ1 due to free CO, and a weak band
at 2249 cmϪ1 which was assigned to a ν(N–N) vibration. The
growth of these suggests that the photoproduct is most likely to
be [(η3-C3H4C6H5)Mn(CO)3(N2)] (5).
The exact structure of 5 is not known, since the N2 group
could be in either an axial or equatorial position. Both axially
or equatorially substituted products would have Cs symmetry
and should display three ν(CO) bands, 2aЈ ϩ aЉ. However, only
two ν(CO) bands were observed but this is could due to failure
(a) Photolysis of (ꢁ3-C3H4C6H5)Mn(CO)4 (2) isolated in an Ar
matrix
Fig. 3(a) shows the IR spectrum of 2 in an Ar matrix at high
dilution at 12 K. Four ν(C–O) bands are observed, 3aЈ ϩ aЉ,
consistent with the complex having Cs symmetry. These bands
were much narrower than those in solution spectra but they are
split by matrix effects. UV irradiation (λ > 300 nm) resulted in
depletion of the parent bands and growth of three new bands at
2032, 1956 and 1930 cmϪ1, see Fig. 3(b). These changes can be
seen more clearly in the subtraction spectrum, Fig. 3(c). Fur-
ther UV irradiation caused more depletion of the parent
together with large increases in the intensity of these new bands
which all grew in at the same rate during the course of the
D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
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Table
1
IR frequencies (cmϪ1
low-temperature matrices
)
of Mn complexes observed in
Matrix
Table
2
IR frequencies (cmϪ1
) of Cr complexes observed in
low-temperature matrices
Matrix
Complex
Ar
N2
Assignment
Complex
Ar
N2
Assignment
[(η3-C3H4C6H5)Mn(CO)4] (2)
2072
2001
2073
ν(CO)
ν(CO)
[(η6-C6H6)Cr(CO)3]
1990
1923
1984
1914
ν(CO)
ν(CO)
2003}a
1998}a
1982
1981
1971
ν(CO)
ν(CO)
[(η6-C6H5C2H5)Cr(CO)3] (3)
[(η6-C6H6)Cr(CO)2]
1983
1915
ν(CO)
ν(CO)
1975
[(η3-C3H5)Mn(CO)4]b
2083
ν(CO)
ν(CO)
1938
1885
ν(CO)
ν(CO)
2004}a
2002}a
1986
ν(CO)
ν(CO)
[(η6-C6H5C2H5)Cr(CO)3] (7)
[(η6-C6H6)Cr(CO)3(N2)]
1930
1876
ν(CO)
ν(CO)
1972
[(η3-C3H4C6H5)Mn(CO)3] (4)
[(η3-C3H5)Mn(CO)3]b
2032
1956
1930
ν(CO)
ν(CO)
ν(CO)
2148
1940
1896
ν(NN)
ν(CO)
ν(CO)
2041
2060
1933
ν(CO)
ν(CO)
ν(CO)
shoulder to decrease as the main band increased in intensity.
This shift could either be due to the product changing its site in
the matrix or less probably to thermal interconversion of the
two isomers of 5.
[(η3-C3H4C6H5)Mn(CO)3(N2)] (5)
[(η3-C3H5)Mn(CO)3(N2)]b
2251
1960
2257
2019
1960
ν(NN)
ν(CO)
ν(NN)
ν(CO)
ν(CO)
Extended UV photolysis (λ = 254 nm) of 2 in the N2 matrix
caused an increase in the intensity of the bands of 5 and more
depletion of the parent molecule. During this photolysis the
production of free CO increased, indicating that further
decarbonylation was occurring, see Fig. 3(a). The ν(N–N) band
at 2250 cmϪ1 increased in intensity and ν(C–O) bands at 2212
and 2180 cmϪ1 grew in at an equal rate. This allows us to assign
these bands to a single photoproduct [(η3-C3H4C6H5)Mn(CO)2-
(N2)2] (6) with two carbonyl ligands substituted for N2 mole-
cules. The ν(N–N) bands at 2212 and 2180 cmϪ1 grew in at the
same rate and are assigned to a single photoproduct, see
Fig. 4(b). From these results the new photoproduct bands were
tentatively assigned to the disubstituted product [(η3-C3H4-
C6H5)Mn(CO)2(N2)2] (6). These results should be compared
with an experiment carried out by Rest and co-workers on
[(η3-C3H5)Mn(CO)4] in a N2 matrix. Their results were
similar to those above; however, UV photolysis produced
only the mono-N2 substituted species, [(η3-C3H5)Mn(CO)3-
(N2)], whereas we have evidence for the formation of the
disubstituted compound [(η3-C3H4C6H5)Mn(CO)2(N2)2] (6).
[(η3-C3H4C6H5)Mn(CO)2(N2)2] (6)
2212
2180
1949
ν(NN)
ν(NN)
ν(CO)
a Matrix split. b Ref. 7.
(c) Photolysis of [(ꢁ6-C6H5C2H5)Cr(CO)3] (3) isolated in an Ar
matrix
The photolysis of 3 produced results very similar to those
obtained by Rest and co-workers for [(η6-C6H6)Cr(CO)3]. The
IR spectrum of 3 in an Ar matrix shows two strong bands
consistent with a1 (1983 cmϪ1) and e (1914 cmϪ1) vibrational
modes of a Cr(CO)3 fragment, having local C3v symmetry. UV
photolysis of 3 in an Ar matrix, (λ > 300 nm) resulted in
depletion of the parent band, appearance of free CO and the
production of a complex with two new ν(CO) bands at 1930
and 1876 cmϪ1 which were readily assigned to [(η6-C6H5C2H5)-
Cr(CO)2] (7) by analogy with (η6-C6H6)Cr(CO)2 formed in a
similar matrix, see Table 2.
(d) Photolysis of [(CO)4Mn(ꢀ-ꢁ3:ꢁ6-C3H4C6H5)Cr(CO)3] (1)
in an Ar matrix
Fig. 4 (a) A series of FTIR spectra obtained following photolysis of
[(η3-C3H4C6H5)Mn(CO)4] in a N2 matrix at 12 K. The spectra were
initially obtained after photolysis at λ > 300 nm and then after
photolysis at λ > 254 nm. The bands marked # are due to the generation
of [(η3-C3H4C6H5)Mn(CO)3(N2)] (5) and those marked ¶ are assigned to
[(η3C3H4C6H5)Mn(CO)2(N2)2] (6).
The IR spectrum of 1 in an Ar matrix showed five prominent
bands in the carbonyl stretching region of the spectrum, see
Fig. 5(a). As in solution, the pattern of these bands is very
similar to that obtained by coaddition of the spectra of 2 and 3.
UV photolysis (λ > 254 nm) of the matrix resulted in the
appearance of four new bands at 2037, 1963, 1934 and 2138
cmϪ1, Fig. 5 (b). The first three bands all grew in at the same
to resolve the low aЈ and aЉ vibrations, as occurs50 in
[(η5-C5H5)V(CO)3(N2)]. The ν(N–N) band at 2249 cmϪ1 has a
shoulder at ca. 2242 cmϪ1. Annealing of the matrix caused this
D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
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Fig.
5
FTIR spectrum of [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3]
Fig. 6 Subtraction spectra showing the photoproducts generated by
photolysis of (a) [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (b) [(η3-C3H4-
C6H5)Mn(CO)4] and (c) [(η6-C6H5C2H5)Cr(CO)3] in argon matrices at
12 K.
isolated in an argon matrix (a) before photolysis, the bands marked
᭛ and ᭝ are due to the Mn(CO)4 and Cr(CO)3 groups respectively,
(b) after 5.5 hours photolysis (λ > 254 nm). (c) This is (b) with the
ν(C–O) bands of the parent subtracted from the spectrum to show only
the product bands. The bands marked ‡ and ᭝ are due to the Mn(CO)3
and Cr(CO)3 moieties in [(CO)3Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3].
positions, and a slightly different matrix splitting pattern.
Photolysis with visible radiation (λ > 400 nm) generated a small
ν(CO) band at 1937 cmϪ1, together with weaker bands at 2037
and 1895 cmϪ1, Fig. 7. In the ν(NN) region of the spectrum, a
new band grew in at 2147 cmϪ1 alongside the band due to free
CO (2138 cmϪ1). This new photoproduct was assigned to
[(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)2(N2)] (10) by comparison
with the bands of 8 and [(η6-C6H6)Cr(CO)2(N2)], Tables 1 and
2. The formation of 10 means that the CO loss from the Cr
centre does occur. The results obtained in an Ar matrix indicate
that in a weakly coordinating matrix CO loss is reversible,
maybe due to a photoinduced back reaction.
UV photolysis (λ > 300 nm), of the matrix caused the bands
assigned to 10 and free CO to grow in further. New ν(CO)
bands grew in at 2036 and 1964 cmϪ1 (Table 3); they were gener-
ated at the same rate as a new ν(NN) band at 2255 cmϪ1. The
appearance of these new bands indicated that a second nitrogen
substituted product had been generated; the similarity in posi-
tions and relative intensities, compared with the spectrum of 5,
suggested that the photoproduct was [(CO)3(N2)Mn(µ-η3:η6-
C3H4C6H5)Cr(CO)3] (11). Only after extensive UV photolysis
(λ > 254 nm), did the bands due to 11 become more intense
than those of 10. This prolonged photolysis also caused the
production of more new ν(CO) and ν(NN) bands, Fig. 6. A new
ν(NN) band grew in at 2181 cmϪ1 with a weaker band at 2218
cmϪ1. In the carbonyl stretching region of the spectrum, the
broad band at ca. 1964 cmϪ1 split into two, as a new band at
1954 cmϪ1 increased in intensity. These new ν(CO) and ν(NN)
bands were assigned to the bis-substituted nitrogen product
[(CO)2(N2)2Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (12) by com-
parison with the results obtained from photolysis of 2 in a N2
matrix (see above).
rate as the band due to free carbon monoxide (2138 cmϪ1).
These bands were therefore attributed to the generation of a
single photoproduct which occurs by loss of a CO ligand.
There are two possible structures for the product, either
[(CO)3Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] or [(CO)4Mn(µ-η3:η6-
C3H4C6H5)Cr(CO)2]. In the case of [(CO)3Mn(µ-η3:η6-C3H4-
C6H5)Cr(CO)3], three new bands, 2aЈ ϩ aЉ, due to vibrations of
the Mn(CO)3 group would be expected. If, however, CO was
lost from the chromium centre, only two new ν(C–O) bands
would be expected. The three bands that grew in were all
approximately 40 cmϪ1 lower than the manganese parent bands;
a shift characteristic of loss of one carbonyl ligand from a
metal centre. The positions of the ν(CO) bands and their
relative intensities were similar to those observed during the
photolysis of 4 in an argon matrix. Fig. 6 compares the subtrac-
tion spectrum for the photoproduct of [(CO)3Mn(µ-η3:η6-
C3H4C6H5)Cr(CO)3], with the respective spectra of the
photoproducts of 4 and 7 in argon matrices. The close resem-
blance of the spectra in Fig. 6(a) to Fig. 6(b) strongly suggests
that the product was [(CO)3Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3]
(9). No new ν(CO) bands were observed which could be
assigned to a Cr(CO)2 moiety in the dinuclear complex, suggest-
ing that there was no loss of CO from the Cr centre. Further-
more, the parent absorptions of the Cr(CO)3 moiety decreased
only slightly during photolysis, whereas those due to Mn(CO)4
were greatly reduced in intensity. The absence of a Cr(CO)2
species could have been either due to the lowest energy excited
state not being labile with respect to CO loss from the Cr centre
or to the Cr(CO)2 undergoing photoreversible CO loss.
Overall, these results bear a close resemblance to those for
the photolysis of the mononuclear manganese and chromium
compounds in nitrogen matrices. CO was photoejected from
either end of the parent molecule and nitrogen substituted
products were formed; these were identified by their ν(CO) and
(e) Photoreactions of [(CO)4Mn(ꢀ-ꢁ3:ꢁ6-C3H4C6H5)Cr(CO)3]
(1) in a N2 matrix
The IR spectrum of 1 in a N2 matrix at 12 K, is similar to
that recorded in an Ar matrix, with only small shifts in band
D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
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Table 3 IR frequencies (cmϪ1) of Mn/Cr complexes observed in
C6H5)Cr(CO)2(N2)],
[(CO)3(N2)Mn(µ-η3:η6-C3H4C6H5)Cr-
(CO)3] and [(CO)2(N2)2Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] by
comparison with the mononuclear complexes [(η6-C6H5C2H5)-
Cr(CO)2(N2)], [(η3-C3H4C6H5)Mn(CO)3(N2)] and [(η3-C3H4-
C6H5)Mn(CO)2(N2)2] formed following photolysis of either
[(η6-C6H5C2H5)Cr(CO)3] or [(η3-C3H4C6H5)Mn(CO)4] in a N2
matrix at 12 K. Irradiation of [(CO)4Mn(µ-η3:η6-C3H4C6H-
5)Cr(CO)3] in an Ar matrix produced only [(CO)3Mn(µ-η3:η6-
C3H4C6H5)Cr(CO)3]. However, [(η6-C6H5C2H5)Cr(CO)2] could
be generated from [(η6-C6H5C2H5)Cr(CO)3] in an Ar matrix.
low-temperature matrices
Matrix
Complex
Ar
N2
[(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (1)
2076
2005
1981
1975
1918
2076
2006
1978
1970
1916}a
1914}a
1910}a
Experimental
[(CO)3Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (9)
2037
1963
1934
Matrix isolation
The matrix isolation apparatus (Air Products Displex CS202)
used in these experiments has been described previously.49 The
principal photolysis source was a Philips HPK 125 W medium
pressure Hg arc lamp, the output of which was controlled using
a variety of filters with cut off wavelengths as outlined in
the main text. All IR spectra were obtained using a Nicolet
MX-3600 FTIR interferometer. Matrices were prepared using
the “slow spray-on” technique in which a mixture of evaporat-
ing solid and matrix gas are co-condensed at low temperatures.
[(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)2(N2)] (10)
2149
1937
1895
[(CO)3(N2)Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] (11)
2036
1964
a Matrix splitting.
Synthesis
[Mn(CO)5(ꢁ1-C3H4C6H5)]. A solution of Mn2(CO)10 (2.0
g, 5.1 mmol) in THF (50 ml) was added to a sodium amalgam
(0.5 cm3 in 10 ml Hg) and stirred vigorously for 30 minutes. The
resulting solution of [Mn(CO)5]ϪNaϩ was cannula-filtered
into a solution of cinnamyl chloride (1.56 g, 10.2 mmol) in
THF (10 ml). After 30 min stirring the suspension yielded an
orange–yellow oil [Mn(CO)5(η1-C3H4C6H5)] which was used
directly in the preparation of [Mn(CO)4(η3-C3H4C6H5)] (2).
[(ꢁ3-C3H4C6H5)Mn(CO)4] (2). A solution of freshly sublimed
trimethylamine oxide (1.4 g, 18.7 mmol) in CH2Cl2 (50 ml) was
added dropwise to a solution of [Mn(CO)5(η1-C3H4C6H5)] in
CH2CH2 (20 ml). Stiring for 30 minutes gave a dark yellow
solution. Removal of the solvent (in vacuo), extraction with
diethyl ether followed by filtering through Kieselguhr yielded a
yellow oil. Sublimation (70 ЊC, 0.3 mmHg) gave [Mn(CO)4-
(η3-C3H4C6H5)] (1.9 g, 65%) as a yellow solid. 1H NMR
(CDCl3) δ 7.08–7.41 (m, 5H, C6H5), 5.43 (td, 1H, CH2CH-
CHC6H5, J = 14, 9 Hz), 3.60 (d, 1H, CH2CHCHC6H5, J =
14 Hz), 2.63 (dd, 1H, syn-CH2CHCHC6H5, J = 9, 1 Hz), 1.72
(dd, 1H, anti-CH2CHCHC6H5, J = 14, 1 Hz). 13C NMR
(deuteroaceetone) δ 221.5, 219.8, 217.0, 216.0 (4CO), 141.2
(quaternary of –C6H5), 129.7, 125.8 (ortho and meta of –C6H5),
127.1 (para of –C6H5), 91.02, 67.0 (CH2CHCHC6H5), 37.8
(CH2CHCHC6H5). m/z 284 (M=), 256 (M= Ϫ CO), 228
(M= Ϫ 2CO), 200 (M= Ϫ 3CO), 172 (M= Ϫ 4CO). Found: C,
55.2; H, 3.2. Calculated: C, 54.9; H, 3.2%.
[(CO)4Mn(ꢀ-ꢁ3:ꢁ6-C3H4C6H5)Cr(CO)3] (1). [(η3-C3H4C6H5)-
Mn(CO)4] (1.0 g, 3.5 mmol) and chromium hexacarbonyl (2.0 g,
9 mmol) were heated to relux in THF–n-butyl ether (v/v 1 : 8)
for 16 hours under an inert atmosphere. The reaction mixture
was cooled and the solvent and excess chromium hexacarbonyl
were removed in vacuo. The green–yellow residue was extracted
into diethyl ether and filtered through Kieselguhr followed by
recrystallisation from diisopropyl yielding [(CO)4Mn(µ-η3:η6-
Fig. 7 FTIR spectra recorded after 60 minutes photolysis (λ > 240
nm) of [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] in a N2matrix at 12 K
and (b) subtraction spectrum showing the ν(C–O) bands of (᭜)
[(CO)3(N2)Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3], (ᮀ) [(CO)2(N2)2Mn(µ-
η3:η6-C3H4C6H5)Cr(CO)3] and (᭿) [(CO)4Mn(µ-η3:η6-C3H4C6H5)-
Cr(CO)2(N2)].
1
ν(NN) bands, which were very similar to the bands of the
photoproducts of the mononuclear complexes.
C3H4C6H5)Cr(CO)3] (1.5 g, 25%) as a bright yellow solid. H
MNR (deuteroacetone) δ 5.68–5.92 (m, 5H, C6H5), 5.48 (m,
1H, CH2CHCHC6H5), 3.48 (d, 1H, CH2CHCHC6H5, J =
14 Hz), 2.97 (dd, 1H, syn-CH2CHCHC6H5, J = 10, 2 Hz),
2.18 (dd, 1H, anti-CH2CHCHC6H5, J = 12, 2 Hz). 13C MNR
(deuteroacetone) δ 235.1 (Cr(CO3)), 113.1 (quaternary of
–C6H5), 96.2, 96.0, 93.6, 92.1, 91.2, 87.7 (ortho, meta and para
of C6H5 and CH2CHCHC6H5 or CH2CHCHC6H5), 60.7
Conclusions
Photolysis of [(CO)4Mn(µ-η3:η6-C3H4C6H5)Cr(CO)3] in N2
matrices at 12 K resulted in photosubstitution at both the
Mn and Cr centres. We have identified [(CO)4Mn(µ-η3:η6-C3H4-
D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
1549

View Article Online
25 A. J. Dixon, S. J. Gravelle, L. J. Burgt, M. Poliakoff, J. J. Turner and
E. Weitz, J. Chem. Soc., Chem. Commun., 1987, 1023.
26 J. N. Moore, P. A. Hansen and R. M. Hochstrasser, J. Am. Chem.
Soc., 1989, 111, 4563.
27 P. A. Anfinrud, C.-H. Han, T. Lian and R. M. Hochstrasser, J. Phys.
Chem., 1991, 95, 574.
(CH2CHCHC6H5 or CH2CHCHC6H5), 40.9 (CH2CHCHC6-
H5). m/z 420 (M= Ϫ CO), 392 (M= Ϫ 2CO), 363 (M= Ϫ 3CO),
336 (M= Ϫ 4CO), 284 (M= Ϫ Cr(CO)3). Found: C, 45.8; H, 2.2.
Calculated: C, 45.7; H, 2.1%.
28 A. J. Dixon, M. W. George, C. Hughes, M. Poliakoff and J. J. Turner,
J. Am. Chem. Soc., 1992, 114, 1719.
Acknowledgements
We thank the EPSRC, University of Notingham, BP (C. H.),
for financial support. M. W. G. wishes to acknowledge the
support of the Sir Edward Frankland Fellowship. We are also
grateful to Mr J. Yang for helpful advice.
29 S. Zhang and T. L. Brown, J. Am. Chem. Soc., 1992, 114, 2723.
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D a l t o n T r a n s . , 2 0 0 3 , 1 5 4 5 – 1 5 5 0
1550