Reaction of [PPN][Re(CO)5] with [Mn(CO)5(C 2H4)][BF4], a rapid two-electron, ethylene transfer reaction, PPN=bis(triphenylphosphine)nitrogen(1+)

Article abstract of DOI:10.1016/S0020-1693(02)00793-4

Reaction of Re(CO)₅^- with Mn(CO)₅(C ₂H₄)⁺ produces initially, among other products, Re(CO)₅(C₂H₄)⁺ and Mn(CO) ₅^-. The ethylene transfer accompanied by a two-electron process provides another example of rapid two-electron reactions, more rapid than single electron transfer. The ultimate products are bimetallic from single electron reactions.

Full text of DOI:10.1016/S0020-1693(02)00793-4

Inorganica Chimica Acta 334 (2002) 71ꢃ76
/
www.elsevier.com/locate/ica
Reaction of [PPN][Re(CO)5] with [Mn(CO)5(C2H4)][BF4], a rapid
two-electron, ethylene transfer reaction, PPNꢀ
bis(triphenylphosphine)nitrogen(1ꢁ
/
/
)
David C. Hoth, Jim D. Atwood *
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260-3000, USA
Received 12 September 2001; accepted 21 January 2002
Abstract
Reaction of Re(CO)5ꢂ with Mn(CO)5(C2H4)ꢁ produces initially, among other products, Re(CO)5(C2H4)ꢁ and Mn(CO)5ꢂ. The
ethylene transfer accompanied by a two-electron process provides another example of rapid two-electron reactions, more rapid than
single electron transfer. The ultimate products are bimetallic from single electron reactions. # 2002 Elsevier Science B.V. All rights
reserved.
Re(CO)ꢂ ꢁMn(CO)5(C2H4)ꢁ0 Re(CO)5(C2H4)ꢁ
5
1. Introduction
ꢁMn(CO)ꢂ5
(2)
Group-transfer reactions are an important subset of
electron-transfer reactions. In inner sphere electron
transfer the bridging group remains with the more inert
center after electron transfer, frequently involving
transfer of the bridging group to a new metal center
The reaction has been examined by IR and NMR.
2. Experimental
[1ꢃ
carbonyl complexes we have shown that various atoms
[6] and groups [7ꢃ10] are transferred.
/
5]. In reactions of metal carbonyl anions with metal
2.1. General comments
/
All compounds were manipulated under inert atmo-
sphere using a glove-box, Schlenk-line techniques or
high vacuum-line techniques. Diethyl ether (Baxter) was
dried by refluxing over sodium/benzophenone and then
distilled under N2. Methylene chloride (Fisher Scientific)
was dried by refluxing over P2O5 and distillation under
N2. Acetonitrile (Fisher Scientific) was dried over CaH2
and distilled under N2. Acetonitrile-d3 (Aldrich Chemi-
cal Company, Inc.) was stirred overnight with CaH2,
MꢀXꢁM?ꢂ0 M?ꢀXꢁMꢂ
XꢀHꢁ; CH3ꢁ; Brꢁ; CO2ꢁ
M?ꢂ; Mꢂ ꢀmetal carbonyl anions
(1)
The X group transfer is only observed when M?ꢂ is
more nucleophilic than Mꢂ. The nucleophilicities of
Mꢂ and M?ꢂ are measured from rates of reaction with
MeI [11]. In many examples, the rapid group transfer
accompanied by two-electron transfer is followed by a
slower one-electron transfer that results in bimetallic
products [10].
freezeꢃthaw degassed and then vacuum distilled on the
/
high vacuum line. Acetone-d6 (Cambridge Isotope
Laboratories, Inc.) was used as received in a 1 g vial.
Ethylene (Matheson Gas Products), Ph3CBF4, NOBF4,
1,4-dimethoxybenzene (Aldrich Chemical Company,
Inc.) and Mn2(CO)10 (Strem) were used without further
purification. Solubility of the anions, cations and
bimetallic complexes limited the choice of solvent to
CH3CN. PPNRe(CO)5 was prepared as previously
described [12].
In this manuscript we report an example of a two-
electron process accompanied by C2H4 transfer between
two metal centers.
* Corresponding author. Tel.: ꢁ
/
1-716-645 6800; fax: ꢁ1-716-645
/
6963.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 7 9 3 - 4

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D.C. Hoth, J.D. Atwood / Inorganica Chimica Acta 334 (2002) 71ꢃ76
/
2.2. Syntheses
3. Results and discussion
2.2.1. [Mn(CO)5(C2H4)][BF4]
Beck and coworkers reported reactions of ethylene-
containing manganese and rhenium cations with metal
carbonyl anions to produce ethylene-bridged bimetallic
complexes that precipitated from mixed solvent systems
at low temperature [13].
The procedure outlined by Beck [13] was followed,
substituting a 500 ml round bottom flask adapted for
the high vacuum line and sealed with a Teflon stopper
for a Schlenk flask. In a typical synthesis, 0.75 g
Mn(CO)5(CH3) (3.6 mmol) was placed into the flask
along with 1.2 g Ph3CBF4 (3.7 mmol), 20 ml CH2Cl2
and a magnetic stir bar. The atmosphere was evacuated
from the flask and ethylene at 1000 Torr (28 mmol) was
added. The reaction mixture was stirred at ambient
temperature for 14 days, then filtered on a fine frit. The
yellow solid (60% yield) was washed with copious
amounts of CH2Cl2 and dried by vacuum on the frit.
Two bands were seen in the infrared spectrum, 2163
(vw) and 2067 (vs,br) cmꢂ1 in KBr and 2159 (w) and
2075 (vs,br) cmꢂ1 in CH3CN. These agree with the
M(CO)ꢂ ꢁM(CO)5(C2H4)ꢁ0 M2(CO)10(m-C2H4) (3)
5
MꢀMn or Re
When different metal cations and anions were used, the
bimetallic products differed, depending on the metal
carbonyl anion.
Mn(CO)ꢂ ꢁRe(CO)5(C2H4)ꢁ0 MnRe(CO)10
5
 (m-C2H4)
(4)
Re(CO)ꢂ ꢁMn(CO)5(C2H4)ꢁ0 Mn2(CO)10(m-C2H4)
5
infrared spectrum from Beck [12], 2163 (m) and 2065ꢃ70
/
ꢁRe2(CO)10(m-C2H4)
(5)
(s,br) in Nujol.
1H NMR spectra in CD3CN and acetone-d6 show a
singlet at 4.57 and 5.37 ppm, respectively. Beck reported
The nature of the bimetallic product depending on the
reactant anion mirrored our results where group transfer
with two electron change was more rapid than single
electron transfer [6,10]. Our reexamination of reactions
4 and 5 confirm Beck’s results and provide evidence of
C2H4 transfer.
Our syntheses, by standard procedures, produced
well-characterized products; the infrared data are in
Table 1 and 1H NMR data are in Table 2. The solubility
of the cationic complexes Mn(CO)5(C2H4)BF4 and
Re(CO)5(C2H4)BF4 dictates many of the choices. These
species have very low solubility, precluding low tem-
perature studies by IR or NMR. The lack of solubility in
THF and other polar organic solvents mandates use of
CH3CN. We found that Mn(CO)5(C2H4)ꢁ loses C2H4
in CH3CN.
a singlet at 4.59 ppm in CD3CN at ꢂ
/
40 8C [13].
2.2.2. [Mn(CO)5(CH3CN)][BF4]
A procedure adapted from Darensbourg [14] was
used. Into a 25 ml Erlenmeyer flask, 0.21 g Mn2(CO)10
(0.54 mmol), 0.36g NOBF4 (3.04 mmol), 6 ml CH3CN
and a magnetic stir bar were placed. Effervescence
occurred for approximately 6 min as the CH3CN was
added. To precipitate the product, 15 ml of Et2O was
added and the mixture was stirred for an additional 10
min. The mixture was filtered on a fine frit to give a
sticky, off-white solid in 51% yield.
The infrared spectrum of Mn(CO)5(CH3CN)BF4 was
found to have bands at 2163 (vw), 2075 (vs) and 2050
(m) cmꢂ1 in acetonitrile. This agrees with the literature
spectrum [14] with bands at 2162 (w), 2110 (vw,sh), 2073
(s) and 2049 (m) cmꢂ1 in acetone. The 1H NMR
spectrum has a singlet at 2.26 ppm in CD3CN.
Table 1
Infrared spectra in CH3CN
Compound
nCO (cmꢂ1
)
PPNRe(CO)5
PPNMn(CO)5
1914 (m), 1860 (s)
1902 (m), 1864 (s)
2172 (w), 2070 (vs)
2162 (w), 2075 (vs)
2.2.3. [Re(CO)5(C2H4)][BF4]
The procedure used was similar to that for the
Re(CO)5(C2H4)BF4
Mn(CO)5(C2H4)BF4
synthesis of [Mn(CO)5(C2H4)][BF4], using 1.08
g
Re(CO)5(CH3) (3.15 mmol), 1.09 g Ph3CBF4 (3.30
mmol), 20 ml CH2Cl2 and ethylene at 1000 Torr (28
mmol) to give a white solid in 75% yield.
The infrared spectrum in KBr had two bands, 2175
(w) and 2050 (vs,br) cmꢂ1. In acetonitrile, the bands
shifted to 2171 (w) and 2069 (vs) cmꢂ1. The reported
[13] infrared spectrum was similar with bands at 2174
(m) and 2055 (s,br) cmꢂ1 in Nujol.
An 1H NMR spectrum was obtained with a singlet at
5.13 ppm in acetone-d6 and 5.40 ppm in CD3CN, which
compares to that reported at 5.12 ppm in acetone-d6
[13].
Re(CO)5(CH3CN)BF4 2171 (w), 2062 (vs), 2033 (w)
Mn(CO)5(CH3CN)BF4 2163 (w), 2075 (vs), 2049 (m)
Re2(CO)10(m-C2H4)
Mn2(CO)10(m-C2H4)
MnRe(CO)10(m-
2113 (m), 2040 (vw), 2009 (vs), 1971 (m),
1941 (vw)
2110 (m), 2033 (vw), 2012 (vs), 1982 (s), 1943
(vw)
2123 (w), 2095 (m), 2040 (vw br), 2013 (vs),
1999 (m), 1984 (s), 1966 (vw), 1943 (w-vw)
2072 (m), 2012 (vs), 1968 (m)
2047 (m), 2012 (vs), 1981 (w)
2128 (vw), 2055 (m), 2017 (vs), 1972 (m),
1983 (vw)
a
C2H4)
Re2(CO)10
Mn2(CO)10
MnRe(CO)10
a
In cyclohexane [12].

D.C. Hoth, J.D. Atwood / Inorganica Chimica Acta 334 (2002) 71ꢃ
/76
73
Re(CO)ꢂ ꢁMn(CO)5(C2H4)ꢁ0 Mn2(CO)10(m-C2H4)
Table 2
1H NMR data (d in ppm) for the complexes
5
ꢁRe(CO)5(C2H4)ꢁ ꢁRe2(CO)10(m-C2H4)
ꢁMn2(CO)10 ꢁRe2(CO)10 ꢁMn(CO)5(CH3CN)ꢁ
Compound
CD3CN
Acetone-d6
ꢁMn(CO)ꢂ5
(7)
C2H4
Mn(CO)5(C2H4)ꢁ
Re(CO)5(C2H4)ꢁ
5.408
4.573
5.400
5.367
5.365
5.124
ꢂ
The Re(CO)5 was consumed at rates more rapid than
can be measured on our stopped-flow system (k ꢀ
103
/
Mꢂ1 sꢂ1). As shown in Table 1, there is much overlap
of IR spectra. Fig. 1 shows an infrared spectrum taken
CH3CN
Mn(CO)5(C2H4)ꢁ 0 Mn(CO)5(CH3CN)ꢁ
ꢁC2H4
ꢂ
ꢂ
(6)
at 5 min. The anions Mn(CO)5 and Re(CO)5 over-
lap, but the location of the higher frequency absorption
(1914 cmꢂ1 for Re and 1902 cmꢂ1 for Mn) allows
ꢂ
The marked similarity of the infrared spectra precludes
study of the decomposition by IR, but in CD3CN the
distinction. The presence of Mn(CO)5 is shown clearly
in Fig. 1. Because of extensive overlap, the strongest
absorption bands (2070, 2050 and 2010 cmꢂ1) do not
define the products, but the weak bands are distinct.
Because of the weakness of the high frequency bands for
the cations, Fig. 1 does not show Re(CO)5(C2H4)ꢁ. Fig.
2 uses a fivefold excess of Mn(CO)5(C2H4)ꢁ over
Re(CO)5ꢂ to maximize the amount of Re(CO)5(C2H4)ꢁ
formed; the absorption at 2171 (w) cmꢂ1 clearly
identifies the rhenium ethylene complex, distinct from
Mn(CO)5(C2H4)ꢁ and Mn(CO)5(CH3CN)ꢁ overlap-
ping at 2161 cmꢂ1. Note that in both spectra after 5
min the full range of products (reaction 7) is present.
The neutral products are better defined in Fig. 3, which
1
free and coordinated C2H4 can be distinguished by H
NMR (C2H4, 5.4 (s) ppm; Mn(CO)5(C2H4)ꢁ, 4.6 (s)
ppm). Using an internal standard (1,4 dimethoxyben-
zene) the relative integrations of free C2H4 and
Mn(CO)5(C2H4)ꢁ gave a rate constant of 2.09
10ꢂ3 sꢂ1 for the decomposition (reaction 6) at 25 8C.
To minimize the effects of the decomposition on
/
0.2ꢄ
/
with Mn(CO)5(C2H4)ꢁ in
ꢂ
reaction of Re(CO)5
CH3CN the solids (PPNRe(CO)5 and Mn(CO)5-
(C2H4)BF4) were mixed and CH3CN added. After 5
min at room temperature IR analysis showed many
products.
Fig. 1. An infrared spectrum of Re(CO)5 and Mn(CO)5(C2H4)ꢁ (1:1) after 5 min in CH3CN.
ꢂ

74
D.C. Hoth, J.D. Atwood / Inorganica Chimica Acta 334 (2002) 71ꢃ76
/
Fig. 2. An infrared spectrum of Re(CO)5 and Mn(CO)5(C2H4)ꢁ (1:5) after 3 min in CH3CN.
ꢂ
is a hexane spectrum of the products of the 1:1 reaction.
Mn2(CO)10 is defined by the 2046 cmꢂ1 absorption,
Re2(CO)10 by the 2070 cmꢂ1 absorption and the 2112
cmꢂ1 is either Mn2(CO)10(m-C2H4) or Re2(CO)10(m-
C2H4), probably the latter based on mass balance. The
absence of the heterobimetallics, MnRe(CO)10 at 2128
Fig. 3. An infrared spectrum of the hexane extract from reaction of Re(CO)5 with Mn(CO)5(C2H4)ꢁ in CH3CN.
ꢂ

D.C. Hoth, J.D. Atwood / Inorganica Chimica Acta 334 (2002) 71ꢃ
/76
75
The reactions of Re(CO)5 with Mn(CO)5(C2H4)ꢁ
ꢂ
are
complicated
by
the
decomposition
of
Mn(CO)5(C2H4)ꢁ. The decomposition product,
Mn(CO)5(CH3CN)ꢁ, reacts with Mn(CO)5 to give
ꢂ
Mn2(CO)10. The number of products is also a compli-
ꢂ
cating feature; however, clear formation of Mn(CO)5
and Re(CO)5(C2H4)ꢁ indicated a mechanistic compo-
nent,
Re(CO)ꢂ ꢁMn(CO)5(C2H4)ꢁ0 Re(CO)5(C2H4)ꢁ
5
ꢁMn(CO)ꢂ5
(8)
of ethylene transfer accompanied by a two electron
transfer. Given the large amount of CH3CN and small
amount of C2H4 present in solution, the transfer must
occur through an inner sphere, ethylene-bridged com-
plex, adding C2H4 to the X groups possible for the two-
electron processes represented by reaction 1.
The observations of Beck [13] and those reported in
this manuscript are consistent with the reactions shown
in Scheme 1. Attack of the nucleophile Re(CO)5ꢂ on the
coordinated ethylene produces MnRe(CO)10(m-C2H4)
which is in equilibrium with Re(CO)5(C2H4)ꢁ and
Mn(CO)5ꢂ. This equilibrium is the key to understand-
ing the reactions. Beck and coworkers synthesized
MnRe(CO)10(m-C2H4) from 3:1 CH3CN:THF solution
Scheme 1.
or 2055 cmꢂ1 and MnRe(CO)10(m-C2H4) at 2123 or
2095 cmꢂ1 is clear.
Confirmation of Re(CO)5C2H4 by 1H NMR cannot
ꢁ
be accomplished in CD3CN because of direct overlap of
Re(CO)5(C2H4)ꢁ and free C2H4 but in acetone-d6 the
resonances are distinguishable (C2H4, 5.4 (s) ppm;
Re(CO)5(C2H4)ꢁ, 5.1 (s) ppm) and confirm formation
of the rhenium ethylene complex.
ꢁ
after a few minutes reaction of Re(CO)5C2H4 and
ꢂ
Mn(CO)5 at ꢂ45 8C [13]. Our observations (Fig. 4) in
/
CH3CN show Mn(CO)5 and Re(CO)5(CH3CN)ꢁ are
dominant in solution after 1 day at room temperature.
ꢂ
Fig. 4. An infrared spectrum of Mn(CO)5 and Re(CO)5(C2H4)ꢁ (1:1) after 24 h in CH3CN.
ꢂ

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/
Wherland, Inorg. Chem. 31 (1992) 2605;
(d) M.T. James, R.N. McDonald, P.L. Schell, M.H. Ali, J. Am.
Chem. Soc. 111 (1989) 5983.
Slow reaction at room temperature and rapid reaction
with precipitation at ꢂ
an equilibrium. When Re(CO)5C2H4 and Re(CO)5
/
45 8C are most consistent with
ꢁ
ꢂ
[3] (a) T.Y. Cheng, R.M. Bullock, Organometallics 14 (1995) 4031;
(b) R.M. Bullock, J.S. Song, J. Am. Chem. Soc. 116 (1994) 8602;
(c) R.M. Bullock, E.G. Samsel, J. Am. Chem. Soc. 112 (1990)
6886;
are present, the stable Re2(CO)10(m-C2H4) is rapidly
formed consuming all of the Re(CO)5ꢂ. Mn2(CO)10(m-
C2H4) may be formed in solution but is unstable toward
loss of C2H4 (probably through heterolytic dissociation
and replacement of C2H4 from Mn(CO)5(C2H4)ꢁ by
CH3CN) to form Mn2(CO)10.
(d) R.M. Bullock, E.G. Samsel, J. Am. Chem. Soc. 109 (1987)
6542;
(e) R.M. Bullock, J. Am. Chem. Soc. 109 (1987) 8087;
(f) R.D. Simpson, R.G. Bergmann, Organometallics 12 (1993)
781;
Scheme 1 provides a simple explanation of the
ꢂ
observation of Beck et al. [13] that Re(CO)5 readily
ꢂ
(g) D.C. Eisenberg, C.J.C. Lawrie, A.E. Moody, J.R. Norton, J.
Am. Chem. Soc. 113 (1991) 4888;
replaces Mn(CO)5 from MnRe(CO)10(m-C2H4) in a ꢂ
/
(h) T.-Y. Cheng, R.M. Bullock, J. Am. Chem. Soc. 121 (1999)
3150;
40 8C suspension of CH3CN and THF forming
Re2(CO)10(m-C2H4).
(i) T.-Y. Cheng, B.S. Brunschwig, R.M. Bullock, J. Am. Chem.
Soc. 120 (1998) 13121.
Observation of groups as disparate as CO, C2H4, Br,
H and CH3 being transferred between metal carbonyl
moieties indicates a generality to the two electron, group
transfer reaction. Explanation for the rapidity of the
two-electron process is lacking.
[4] L.K. Woo, J.G. Goll, D.J. Czapla, J.A. Hays, J. Am. Chem. Soc.
113 (1991) 8478.
[5] G.J. Leigh, M. Jimanez-Tenorio, J. Am. Chem. Soc. 113 (1991)
5862.
[6] (a) W.S. Striejewske, J.D. Atwood, J. Coord. Chem. 38 (1996)
145;
(b) W.S. Striejewske, R.F. See, M.R. Churchill, J.D. Atwood,
Organometallics 12 (1993) 4413.
Acknowledgements
[7] (a) P. Wang, J.D. Atwood, J. Am. Chem. Soc. 114 (1992) 6424;
(b) P. Wang, J.D. Atwood, Organometallics 12 (1993) 4247.
[8] P. Wang, W.S. Striejewske, D. Cameron, J.D. Atwood, J. Coord.
Chem. 37 (1996) 141.
The support of the Department of Energy, Basic
Energy Sciences, ER 13775 is gratefully acknowledged.
[9] P. Wang, J.D. Atwood, J. Coord. Chem. 30 (1993) 393.
[10] (a) Y. Zhen, W.G. Feighery, C.-K. Lai, J.D. Atwood, J. Am.
Chem. Soc. 111 (1989) 7832;
References
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[11] C.-K. Lai, W.G. Feighery, Y. Zhen, J.D. Atwood, Inorg. Chem.
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[1] See for example: J.D. Atwood, Inorganic and Organometallic
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[2] (a) J.-S. Song, R.M. Bullock, C. Creutz, J. Am. Chem. Soc. 113
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[12] Y. Zhen, J.D. Atwood, J. Am. Chem. Soc. 111 (1989) 1506.
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