Bi- and poly-metallic cyanide-bridged complexes of the redox-active cyanomanganese nitrosyl unit [Mn(CN)(PR3)(NO)(eta-C5H4Me)].

Article abstract of DOI:10.1039/b313654j

Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)(eta-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential, Eo', vs. nu(NO) or the Lever parameters, EL, for L1 and L2, allow Eo' to be estimated for unknown analogues. In the presence of TlPF6, [MnIL'(NO)(eta-C5H4Me)] reacts with [Mn(CN)L(NO)(eta-C5H4Me)] to give [(eta5-C5H4Me)(ON)LMn(mu-CN)MnL'(NO)(eta5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; DeltaE, the difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers. Novel pentametallic complexes such as [Mn[(mu-NC)Mn(CNBut)(NO)(eta5-C5H4Me)]4(OEt2)][PF6]2 and [Mn[(mu-NC)Mn(CNXyl)(NO)(eta5-C5H4Me)]4(NO3-O,O')][PF6], containing a trigonal bipyramidal and a distorted octahedral Mn(II) centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(eta5-C5H4Me)] in the presence of TlPF6.

Full text of DOI:10.1039/b313654j

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Bi- and poly-metallic cyanide-bridged complexes of the
redox-active cyanomanganese nitrosyl unit [Mn(CN)(PR3)(NO)-
(ꢀ-C5H4Me)]
Christopher J. Adams,a Kirsty M. Anderson,a Manuel Bardaji,a Neil G. Connelly,*a
Nicholas J. Goodwin,a Estefania Llamas-Rey,a A. Guy Orpena and Philip H. Riegerb
a School of Chemistry, University of Bristol, Bristol, UK BS8 1TS
b Department of Chemistry, Brown University, Rhode Island, RI 02912, USA
Received 29th October 2003, Accepted 17th December 2003
First published as an Advance Article on the web 22nd January 2004
Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)-
(η-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential,
EЊЈ, vs. ν(NO) or the Lever parameters, EL, for L1 and L2, allow EЊЈ to be estimated for unknown analogues.
In the presence of TlPF6, [MnILЈ(NO)(η-C5H4Me)] reacts with [Mn(CN)L(NO)(η-C5H4Me)] to give [(η5-C5H4Me)-
(ON)LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; ∆E, the
difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers.
Novel pentametallic complexes such as [Mn{(µ-NC)Mn(CNBut)(NO)(η5-C5H4Me)}4(OEt2)][PF6]2 and [Mn{(µ-NC)-
Mn(CNXyl)(NO)(η5-C5H4Me)}4(NO3-O,OЈ)][PF6], containing a trigonal bipyramidal and a distorted octahedral
Mn() centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from
the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(η5-C5H4Me)] in the presence of TlPF6.
In addition, the acetonitrile complexes [Mn(NCMe)L(NO)-
Introduction
(η5-C5H4Me)][PF6] were prepared in order to understand better
The octahedral redox-active cyanomanganese() complexes cis-
or trans-[Mn(CN)LЈ(CO)2(dppm)] {LЈ = P(OPh)3 or P(OEt)3,
the electrochemistry and IR spectra of the binuclear complexes.
Although methods are available for the synthesis of [MnI-
dppm = Ph2PCH2PPh2}1 have been used as N-donor ligands in
(PPh3)(NO)(η5-C5H4Me)] 16–8 a slightly modified route was
the synthesis of a wide variety of bi- and poly-nuclear com-
developed in order to gain access to other halide complexes. At
plexes of both transition2 and main group3 metals. When
room temperature the reaction of [Mn(CO)2(NO)(η5-C5H4-
N-bound, such ligands are useful probes for studying intra-
Me)][PF6] with KI in acetone gave a black solution of the highly
molecular metal-metal charge transfer in mixed-valence sys-
tems, including dimanganese complexes in which two such
octahedral units are linked, e.g. [(dppm)L(CO)2Mn(µ-CN)-
reactive complex [MnI(CO)(NO)(η5-C5H4Me)] {ν(CO) = 2027
cmϪ1, ν(NO) = 1776 cmϪ1}.8 Addition of a ligand, L, to this
solution then gave the green or brown complexes [MnIL(NO)-
Mn(CO)2LЈ(dppm)]ϩ.4 Here we report on the use of the tetra-
(η5-C5H4Me)] {L = PPh3 1,6,7 P(OPh)3 2, CNBut 3 or CNXyl 4}
hedral† ligands [Mn(CN)L(NO)(η5-C5H4Me)] {L = PPh3,
in good yield. One complex containing the η5-C5Me5 ligand,
P(OPh)3, CNBut or CNXyl} in the synthesis of related bi-
namely [MnI(CNBut)(NO)(η5-C5Me5)] 5, was similarly pre-
nuclear complexes of the general formula [(η5-C5H4Me)(ON)-
pared from [Mn(CO)2(NO)(η5-C5Me5)][PF6], and the bromide
LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6], and of structurally
[MnBr(PPh3)(NO)(η5-C5H4Me)] 6 was prepared by adding
characterised pentametallic species such as [Mn{(µ-NC)Mn-
PPh3 to a solution of [MnBr(CO)(NO)(η5-C5H4Me)], made by
(CNXyl)(NO)(η5-C5H4Me)}4(OH2)][PF6]2 and [Mn{(µ-NC)-
reacting [NBun ]Br with [Mn(CO)2(NO)(η5-C5H4Me)][PF6].
4
Mn(CNXyl)(NO)(η5-C5H4Me)}4(NO3-O,OЈ)][PF6] in which
The cationic nitrile complex [Mn(NCMe)(PPh3)(NO)(η5-C5-
four such ligands are coordinated to trigonal bipyramidal and
H4Me)][PF6] 7 was also prepared by an alternative to the
octahedral high spin Mn() centres. An analysis of the oxid-
published method.6 Thus, TlPF6 was added to a solution of
ation potentials of mononuclear complexes [MnL1L2(NO)-
[MnI(PPh3)(NO)(η5-C5H4Me)] 1 in MeCN and the mixture
(η-C5H4Me)]z in terms of the Lever parameters5 of the ligands
stirred for 10 min. The red solution was filtered through Celite,
L1 and L2 supports the deduction, from individual ligand effects
the mixture evaporated to dryness and the product purified by
on the oxidation potentials of [(η5-C5H4Me)(ON)LMn(µ-CN)-
dissolving the residue in CH2Cl2, adding n-hexane and reducing
MnLЈ(NO)(η5-C5H4Me)], that the N-bound manganese centres
of the binuclear species are oxidised first.
the volume of the mixture under vacuum. The purple com-
plexes [Mn(NCMe)L(NO)(η5-C5H4Me)][PF6] (L = CNBut 8,
CNXyl 9) were prepared in a similar manner, from 3 and 4,
respectively.
Results and discussion
The orange carbonyl complexes [Mn(CO)L(NO)(η5-C5H4-
Synthesis and characterisation of mononuclear complexes
Me)][PF6] {L = PPh3 10 or P(OPh)3 11} were prepared using the
literature method,9 and [Mn(CO)L(NO)(η5-C5H4Me)][PF6]
(L = CNBut 12 or CNXyl 13) were synthesised similarly, i.e.
from [Mn(CO)2(NO)(η5-C5H4Me)][PF6] and the appropriate
isocyanide. However, the use of two equivalents of CNBut or
CNXyl yielded the bis(isocyanide) complexes [MnL2(NO)-
(η5-C5H4Me)][PF6] (L = CNBut 14 or CNXyl 15), analogues of
[Mn(CNEt)2(NO)(η5-C5H4Me)][PF6].6
In order to synthesise the cyanide-bridged dimanganese
complexes described below, it was first necessary to prepare
mononuclear Mn() iodide, carbonyl and cyanide precursors
containing the Mn(NO)(η5-C5R4Me) fragment (R = H or Me).
† Complexes of the general formula [ML3(η5-C5R5)] can be regarded as
octahedral, if the cyclopentadienyl ring is assumed to occupy three
coordination sites, or tetrahedral, if occupying one. In this paper, the
geometry of an MnXL(NO)(η5-C5H4Me) unit is regarded as tetra-
hedral at manganese.
The orange or red cyanide complexes [Mn(CN)L(NO)-
(η5-C5H4Me)] {L = PPh3 16,6,10 P(OPh)3 17,10 CNBut 18 or
CNXyl 19} were prepared by heating a mixture of [Mn(CO)-
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 4
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
683

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L(NO)(η5-C5H4Me)][PF6] and [NEt4]CN under reflux in
CH2Cl2 for 18 h, and purified by column chromatography
followed by recrystallisation. The η5-C5Me5 analogue of 18,
namely [Mn(CN)(CNBut)(NO)(η5-C5Me5)] 20, was synthesised
by an alternative method because the reaction of [Mn(CO)-
(CNBut)(NO)(η5-C5Me5)][PF6] 12 with [NEt4]CN in CH2Cl2
gave a mixture of 20 and [Mn(CN)(CO)(NO)(η5-C5Me5)] 21,
i.e. the cyanide ion displaces either CO or CNBut from 12.
Thus, the dicarbonyl [Mn(CO)2(NO)(η5-C5Me5)][PF6] was
reacted with [NEt4]CN in CH2Cl2 at room temperature to give,
after extraction in toluene, the stable red crystalline complex
[Mn(CN)(CO)(NO)(η5-C5Me5)] 21 (unusual in containing the
three different π-acceptor ligands CN, CO and NO). Reaction
of 21 with CNBut then gave 20.
(PPh3)(NO)(η5-C5H4Me)]2ϩ has limited stability even on the CV
timescale. The CVs of [Mn(NCMe)(CNBut)(NO)(η5-C5H4-
Me)][PF6] 8 and [Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)][PF6]
9, in either CH2Cl2 or MeCN, are more complicated, each
showing both reduction (irreversible) and oxidation (partially
reversible) waves. Fig. 1 shows that the oxidation wave of 9, at
1.30 V, has an associated, apparently reversible, product wave
centred at 1.65 V, a potential similar to that of the oxidation
wave of [Mn(CNXyl)2(NO)(η5-C5H4Me)][PF6] 15. (The prod-
uct wave at ca. 0.6 V is unassigned but may be associated with
the second product of a disproportionation process). It is note-
worthy that 14 is also formed by the (much slower) thermal
decomposition of 8, as noted above.
Complexes 1–21 were characterised by elemental analysis
and by IR (Table 1) and NMR spectroscopy (Table 2). The
ν(CO), ν(NO) and ν(CN) stretching frequencies show the
1
expected dependence on L, R and the overall charge; the H
NMR spectra {though generally broad, possibly due to very
small amounts of high spin Mn() impurities, see below} show
the expected resonances for the various ligands.
The neutral iodide complexes 1–6 are soluble in MeCN, thf,
CH2Cl2 and toluene but insoluble in n-hexane and diethyl ether.
In air, 2–5 and the acetonitrile complexes 8 and 9 decom-
pose slowly in the solid state, and more readily in solution, to
give products identifiable by IR spectroscopy. Thus, for
example, solutions of [MnI(CNBut)(NO)(η5-C5H4Me)] 3 or
[Mn(NCMe)(CNBut)(NO)(η5-C5H4Me)][PF6]
8 in CH2Cl2
become orange after ca. 30 min, then showing two strong
ν(CNR) bands at 2192 and 2173 cmϪ1 and one ν(NO) band at
1786 cmϪ1, identical bands to those of [Mn(CNBut)2(NO)-
(η5-C5H4Me)][PF6] 14. Similarly, both [MnI(CNXyl)(NO)-
(η5-C5H4Me)] 4 and [Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)]-
[PF6] 9 disproportionate in solution, giving [Mn(CNXyl)2-
(NO)(η5-C5H4Me)][PF6] 15. No other products were identified.
In solution, [MnI{P(OPh)3}(NO)(η5-C5H4Me)] 2 shows a
single ν(NO) band at 1746 cmϪ1 which, after 15 min in air, is
replaced by a new band at 1798 cmϪ1, assigned to the bis(phos-
phite) cation [Mn{P(OPh)3}2(NO)(η5-C5H4Me)]ϩ {cf. ν(NO)
(CH2Cl2) = 1797 cmϪ1 for [Mn{P(OPh)3}2(NO)(η5-C5H5)]ϩ 9}.
In contrast, the PPh3 complexes [MnI(PPh3)(NO)(η5-C5H4Me)]
1 and [Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7 are air-
stable in the solid state for months. In CH2Cl2 they decompose
in air in ca. 3 h to unidentified products showing no IR absorp-
tions in the region 1600–1850 cmϪ1. These decomposition
products are therefore not analogous to [MnL2(NO)(η5-C5-
H4Me)]ϩ {L = P(OPh)3, CNBut or CNXyl}. Attempts have been
made previously to synthesise [Mn(PPh3)2(NO)(η5-C5H4R)]ϩ 9
by reacting [Mn(CO)2(NO)(η5-C5H4R)]ϩ (R = H or Me) with
two equivalents of PPh3 but only the monosubstituted product
[Mn(CO)(PPh3)(NO)(η5-C5H4R)]ϩ was observed.
Fig. 1 The CV in CH2Cl2 of [Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)]-
[PF6] 9 from 0.3 to 1.8 V at a scan rate of 200 mV sϪ1. The wave marked
with an asterisk, *, corresponds to the oxidation of [Mn(CNXyl)2(NO)-
(η5-C5H4Me)]ϩ.
The CVs of the carbonyl complexes [Mn(CO)L(NO)(η5-C5-
H4Me)][PF6] 10–13 differ from those of [Mn(NCMe)L(NO)-
(η5-C5H4Me)][PF6] 7–9 in that no oxidation waves were detected
in the potential range 0.0 to 1.8 V {cf. [Mn(CO)L(NO)-
(η5-C5H5)] (L = PPh3 or PMe2Ph) for which oxidation waves
were reported, at ca. 1.6 V vs. a calomel electrode 1.0 mol dmϪ3
in LiCl11}. However, each complex shows an irreversible reduc-
tion process, at a potential between Ϫ0.66 and Ϫ0.86 V (cf. ref.
12), accompanied by a small irreversible oxidation product
wave, between 0.18 and 0.49 V. In addition, 12 and 13 each
show a second irreversible reduction, at Ϫ1.38 and Ϫ1.05 V,
respectively.
The irreversible reduction of the bis(isocyanide) complex
[Mn(CNBut)2(NO)(η5-C5H4Me)][PF6] 14 (at Ϫ1.30 V, accom-
panied by a small reversible product wave centred at Ϫ0.44 V) is
shifted to a more negative potential (by ca. 0.5 V) than that of
[Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12. Both of the
waves are shifted to more positive potentials (by ca. 0.2 V) as
the alkyl isocyanides of [Mn(CNBut)2(NO)(η5-C5H4Me)][PF6]
14 are replaced by the aryl isocyanides of [Mn(CNXyl)2-
(NO)(η5-C5H4Me)][PF6] 15.
Each of the cyanomanganese complexes [Mn(CN)L(NO)-
(η5-C5R4Me)] 16–20 shows an oxidation wave, between 0.79 and
1.11 V, which is only reversible at scan rates above 500 mV sϪ1.
Two small, apparently reversible, product waves are observed,
e.g. at 0.44 and 1.32 V for [Mn(CN)(CNBut)(NO)(η5-C5H4Me)]
18 (Fig. 2). Though these products have not been identified, it is
noteworthy that the potential of the wave at 1.32 V is the same
as that of the second oxidation wave of the binuclear, cyanide-
bridged complex [(η5-C5H4Me)(ON)(ButNC)Mn(µ-CN)Mn-
(CNBut)(NO)(η5-C5H4Me)][PF6], described below. (The first
oxidation wave of this binuclear complex, if formed, would be
obscured by the oxidation wave of 18 itself; the source of the
product wave at 0.44 V remains unknown). Finally, [Mn(CN)-
(CO)(NO)(η5-C5Me5)] 21 shows an irreversible oxidation wave
at 1.33 V accompanied by a reversible product wave at 0.28 V.
Voltammetry of mononuclear complexes
Electrochemical studies of the oxidation of [Mn(CO)2ϪnLn(NO)-
(η5-C5H5)]ϩ {n = 1, L = PPh3 or PMe2Ph; n = 2, L = P(OPh)3 or
PMe2Ph},11 [MnI(PPh3)(NO)(η5-C5H4Me)]6 and [Mn(CN)-
6,10
L(NO)(η5-C5H4Me)] {L = PPh3
or P(OPh)3 10}, and of the
reduction of [Mn(CO)L(NO)(η5-C5H4Me)]ϩ {L = CO, PPh3 or
P(OPh)3} (including electron-transfer catalysed substitution)12
have been described previously. All of the complexes described
herein have been studied by cyclic voltammetry at a Pt disc
electrode, in CH2Cl2 unless otherwise stated (Table 3).
The neutral halide complexes [MnXL(NO)(η5-C5H4Me)] 1–6
undergo one-electron oxidations at potentials, EЊЈ, between
0.42 and 0.70 V, which are reversible in all cases except for 1 and
2 where the process is only so at scan rates above 200 mV sϪ1.
Theoxidationwaveof[Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)]-
[PF6] 7 in CH2Cl2 or MeCN is reversible at scan rates greater
than 500 mV sϪ1, indicating that the dication [Mn(NCMe)-
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
684

Table 1 Analytical and IR spectroscopic data for mononuclear cyclopentadienylmanganese nitrosyl complexes
Analysis (%)a
IRb/cmϪ1
Complex
Colour
Yield (%)
C
H
N
ν(CNR)
ν(CN)
ν(CO)
ν(NO)
[MnI(PPh3)(NO)(η5-C5H4Me)] 1
Brown
Green
Green
Green
Green
Brown
–
–
–
–
–
68
60
67
57
74
75
–
–
–
–
–
52.5 (52.1)
47.5 (47.9)
35.3 (35.6)
42.7 (42.7)
41.7 (41.9)
56.4 (56.9)
–
–
–
–
–
4.1 (4.0)
3.7 (3.7)
4.4 (4.3)
3.9 (3.8)
5.6 (5.6)
4.8 (4.4)
–
–
–
–
–
2.5 (2.5)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2038
2055
2065
2067
–
–
–
–
–
1719
1746
1740
1746
1715
1721
1801
1798
1797
1801
1806
1801
1753
1775
1778
1794
1813
1815
1818
1786
1793
1734
1758
1753
1758
1732
1768
[MnI{P(OPh)3}(NO)(η5-C5H4Me)] 2
[MnI(CNBut)(NO)(η5-C5H4Me)] 3
[MnI(CNXyl)(NO)(η5-C5H4Me)] 4
[MnI(CNBut)(NO)(η5-C5Me5)] 5
2.5 (2.3)
7.5 (7.5)
6.6 (6.6)
6.0 (6.5)
2.9 (2.8)
2158m
2131m
2144m
–
–
–
2238
2209
2217
–
–
2183
2157
–
–
2204
[MnBr(PPh3)(NO)(η5-C5H4Me)] 6
[MnI(PPh3)(NO)(η5-C5H4Me)]ϩ 1؉ c
[MnI{P(OPh)3}(NO)(η5-C5H4Me)]ϩ 2؉ c
[MnI(CNBut)(NO)(η5-C5H4Me)]ϩ 3؉ c
[MnI(CNXyl)(NO)(η5-C5H4Me)]ϩ 4؉ c
[MnI(CNBut)(NO)(η5-C5Me5)]ϩ 5؉ c
[MnBr(PPh3)(NO)(η5-C5H4Me)]ϩ 6؉ c
[Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7
[Mn(NCMe)(CNBut)(NO)(η5-C5H4Me)][PF6] 8
[Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)][PF6] 9
–
–
–
–
–
–
–
–
–
–
Brown
Purple
Purple
–
72
55
66
–
52.5 (52.1)
35.8 (36.0)
42.0 (42.4)
–
4.1 (4.0)
4.1 (4.4)
3.8 (4.0)
–
2.5 (2.5)
9.4 (9.7)
8.6 (8.7)
[Mn(CO)(PPh3)(NO)(η5-C5H4Me)][PF6] 10
–
–
d
[Mn(CO){P(OPh)3}(NO)(η5-C5H4Me)][PF6] 11
[Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12
[Mn(CO)(CNXyl)(NO)(η5-C5H4Me)][PF6] 13
[Mn(CNBut)2(NO)(η5-C5H4Me)][PF6] 14
[Mn(CNXyl)2(NO)(η5-C5H4Me)][PF6] 15
–
–
–
–
–
–
–
–
d
Orange
Orange
Orange
Orange
–
51
77
47
68
–
34.3 (34.3)
40.6 (41.0)
46.6 (46.1)
50.0 (50.4)
–
3.7 (3.8)
3.4 (3.4)
6.4 (6.0)
4.4 (4.4)
–
6.6 (6.7)
5.9 (6.0)
10.1 (10.1)
7.2 (7.4)
–
2179
2192, 2173
2171, 2148
–
–
[Mn(CN)(PPh3)(NO)(η5-C5H4Me)] 16
2099w
2107w
2107w
2109w
2100w
2115w
e
[Mn(CN){P(OPh)3}(CN)(NO)(η5-C5H4Me)] 17
[Mn(CN)(CNBut)(NO)(η5-C5H4Me)] 18
[Mn(CN)(CNXyl)(NO)(η5-C5H4Me)] 19
[Mn(CN)(CNBut)(NO)(η5-C5Me5)] 20
[Mn(CN)(CO)(NO)(η5-C5Me5)] 21
–
–
–
–
–
–
e
.
Red
Red
Red
Red
51
43
61
77
52.8 (52.7)
60.3 (59.8)
58.5 (58.4)
52.6 (52.6)
5.7 (5.9)
5.3 (5.0)
7.1 (7.4)
5.3 (5.5)
15.1 (15.4)
13.3 (13.1)
12.7 (12.8)
10.0 (10.2)
2164
2139
2150
–
–
–
2020
a Calculated values in parentheses. b Strong absorptions in CH2Cl2 unless stated otherwise; m = medium, w = weak. c Not isolated, see text. d Data from ref. 9. e Data from ref. 10.

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Table 2 Proton NMR data for mononuclear cyclopentadienylmanganese nitrosyl complexesa
Complex
Chemical shift/ppm
[MnI(PPh3)(NO)(η5-C5H4Me)] 1
[MnI{P(OPh)3}(NO)(η5-C5H4Me)] 2
[MnI(CNBut)(NO)(η5-C5H4Me)] 3
[MnI(CNXyl)(NO)(η5-C5H4Me)] 4
7.55–7.40 (15H, m, PPh3), 4.99 (2H, br s, C5H4Me), 4.40 (1H, br s, C5H4Me), 3.80 (1H, br s,
C5H4Me), 1.91 (3H, s, C5H4Me)
7.34–7.11 {15H, m, P(OPh)3}, 4.70 (2H, br s, C5H4Me), 4.33 (1H, br s, C5H4Me), 3.66 (1H, br
s, C5H4Me), 1.60 (3H, s, C5H4Me)
5.55 (1H, br s, C5H4Me), 5.51 (1H, br s, C5H4Me), 5.30 (1H, br s, C5H4Me), 5.24 (1H, br s,
C5H4Me), 2.49 (3H, s, C5H4Me), 2.05 (9H, s, CNBut)
7.11 (3H, br s, CNC6H3Me2), 5.15 (1H, br s, C5H4Me), 5.11 (1H, br s, C5H4Me), 4.94 (1H, br
s, C5H4Me), 4.86 (1H, br s, C5H4Me), 2.47 (6H, s, CNC6H3Me2), 2.02 (3H, s, C5H4Me)
1.78 (15H, C5Me5), 1.45 (9H, s, CNBut)
7.56–7.39 (15H, m, PPh3), 4.95 (2H, br s, C5H4Me), 4.47 (1H, br s, C5H4Me), 3.37 (1H, br s,
C5H4Me), 1.82 (3H, s, C5H4Me)
[MnI(CNBut)(NO)(η5-C5Me5)] 5
[MnBr(PPh3)(NO)(η5-C5H4Me)] 6
[Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7
[Mn(NCMe)(CNBut)(NO)(η5-C5H4Me)][PF6] 8
[Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)][PF6] 9
7.53 (15H, m, PPh3), 5.38 (1H, br s, C5H4Me), 5.24 (1H, br s, C5H4Me), 4.66 (1H, br s,
C5H4Me), 4.24 (1H, br s, C5H4Me), 2.04 (3H, s, C5H4Me), 1.85 (3H, s, NCMe)
5.24 (1H, br s, C5H4Me), 5.18 (1H, br s, C5H4Me), 4.97 (1H, br s, C5H4Me), 4.90 (1H, br s,
C5H4Me), 2.41 (3H, s, C5H4Me), 1.85 (3H, s, NCMe) 1.57 (9H, s, CNBut)
7.16 (3H, br s, CNC6H3Me2), 5.49 (1H, br s, C5H4Me), 5.40 (1H, br s, C5H4Me), 5.21 (1H, br
s, C5H4Me), 4.99 (1H, br s, C5H4Me), 2.44 (9H, br s, C5H4Me and CNC6H3Me2), 1.91 (3H, s,
NCMe)
[Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12
[Mn(CO)(CNXyl)(NO)(η5-C5H4Me)][PF6] 13
5.86–5.74 (4H, m, C5H4Me), 2.15 (3H, s, C5H4Me), 1.63 (9H, s, CNBut)
7.20–7.34 (3H, m, CNC6H3Me2), 5.66 (2H, br s, C5H4Me), 5.56 (2H, br s, C5H4Me), 2.46 (6H,
s, CNC6H3Me2), 2.16 (3H, s, C5H4Me)b
[Mn(CNBut)2(NO)(η5-C5H4Me)][PF6] 14
[Mn(CNXyl)2(NO)(η5-C5H4Me)][PF6] 15
5.29 (2H, br s, C5H4Me), 5.12 (2H, br s, C5H4Me), 1.98 (3H, s, C5H4Me), 1.58 (9H, s, CNBut)
7.15 (3H, br s, CNC6H3Me2), 5.56 (2H, br s, C5H4Me), 5.43 (2H, br s, C5H4Me), 2.45 (12H, s,
CNC6H3Me2), 2.11 (3H, s, C5H4Me)
[Mn(CN)(CNBut)(NO)(η5-C5H4Me)] 18
[Mn(CN)(CNXyl)(NO)(η5-C5H4Me)] 19
4.93 (2H, br s, C5H4Me), 4.83 (2H, br s, C5H4Me), 1.94 (3H, s, C5H4Me), 1.52 (9H, s, CNBut)
7.24–7.06 (3H, m, CNC6H3Me2), 5.11 (1H, br s, C5H4Me), 5.05 (1H, br s, C5H4Me), 4.99 (2H,
br s, C5H4Me), 2.46 (6H, s, CNC6H3Me2), 2.03 (3H, s, C5H4Me)
1.80 (15H, s, C5Me5), 1.52 (9H, s, CNBut)
[Mn(CN)(CNBut)(NO)(η5-C5Me5)] 20
[Mn(CN)(CO)(NO)(η5-C5Me5)] 21
1.92 (s, C5Me5)
a In CDCl3 unless otherwise stated. b In CD2Cl2.
Table 3 Electrochemical dataa for mononuclear cyclopentadienylmanganese nitrosyl complexes
EoЈ/V
Complex
Oxidation
Reductionb
[MnI(PPh3)(NO)(η5-C5H4Me)] 1
0.45c
–
–
–
–
–
–
–
[MnI{P(OPh)3}(NO)(η5-C5H4Me)] 2
[MnI(CNBut)(NO)(η5-C5H4Me)] 3
0.67c
0.66c
[MnI(CNXyl)(NO)(η5-C5H4Me)] 4
0.70c
[MnI(CNBut)(NO)(η5-C5Me5)] 5
0.42c
[MnBr(PPh3)(NO)(η5-C5H4Me)] 6
0.44c
[Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7
[Mn(NCMe)(CNBut)(NO)(η5-C5H4Me)][PF6] 8
[Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)][PF6] 9
[Mn(CO)(PPh3)(NO)(η5-C5H4Me)][PF6] 10
[Mn(CO){P(OPh)3}(NO)(η5-C5H4Me)][PF6] 11
[Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12
[Mn(CO)(CNXyl)(NO)(η5-C5H4Me)][PF6] 13
[Mn(CNBut)2(NO)(η5-C5H4Me)][PF6] 14
[Mn(CNXyl)2(NO)(η5-C5H4Me)][PF6] 15
[Mn(CN)(PPh3)(NO)(η5-C5H4Me)] 16
[Mn(CN){P(OPh)3}(NO)(η5-C5H4Me)] 17
[Mn(CN)(CNBut)(NO)(η5-C5H4Me)] 18
[Mn(CN)(CNXyl)(NO)(η5-C5H4Me)] 19
[Mn(CN)(CNBut)(NO)(η5-C5Me5)] 20
[Mn(CN)(CO)(NO)(η5-C5Me5)] 21
1.11,1.02d
1.23 (1.44), 1.14 (1.36)d
Ϫ1.23(I), Ϫ1.15(I)d
1.30 (1.65), 1.20 (1.51)d
Ϫ1.05(I), Ϫ0.89(I)d
–
–
–
–
1.45
1.61
0.85 (0.35, 1.24)
1.11 (0.49, 1.49)
1.00 (0.44, 1.32)
1.11 (0.51, 1.41)
0.79 (0.20, 1.18)
1.33(I) (0.28)
Ϫ0.86 (0.49)
Ϫ0.81 (0.47)
Ϫ0.79 (0.18)e
Ϫ0.66 (0.20)f
Ϫ1.30(I)
Ϫ1.06(I)
–
–
–
–
–
–
a At a Pt electrode in CH2Cl2, with potentials relative to the saturated calomel electrode, calibrated vs. the [Fe(η-C5H5)2]ϩ/[Fe(η-C5H5)2] couple (at
0.47 V) unless stated otherwise. The potentials of associated product waves are given in parentheses, at a scan rate of 200 mV sϪ1 b For an irreversible
(I) reduction process, the reduction peak potential, (Ep)red, is given at a scan rate of 200 mV sϪ1 c Potentials calibrated vs. the [Fe(η-C5Me5)2]ϩ/[Fe-
(η-C5Me5)2] couple (at Ϫ0.08 V). d In MeCN. e Second irreversible reduction wave at Ϫ1.38 V. f Second irreversible reduction wave at Ϫ1.05 V.
.
.
Qualitatively, the potential, EЊЈ, for the oxidation of 1–9 and
14–21 is essentially independent of the halide X (in 1 and 6) but
depends on L in the order EЊЈ = CNXyl > P(OPh)3 ≈ CNBut >
PPh3; methylation of the cyclopentadienyl ring decreases the
oxidation potential by ca. 60 mV per methyl substituent, e.g. for
[MnI(CNBut)(NO)(η5-C5H4Me)] 3 and [MnI(CNBut)(NO)-
(η5-C5Me5)] 5 EЊЈ = 0.66 and 0.42 V, respectively. However, a
more quantitative comparison of the effects of the ligands on
potential can be made by comparing EЊЈ with ν(NO) or with
Lever ligand parameters.5
Based on the linear relationships between ν(CO) and EЊЈ for
the one-electron oxidations of [Cr(CO)2L(η6-C6Me6)]13 and
[Mn(CO)3ϪnLn(η5-C5H5ϪnMen)],14 measurements of carbonyl
stretching frequencies have been used to predict EЊЈ values of
unknown analogues in these series. A similar plot of EЊЈ for the
oxidation of 1–9 and 14–21 vs. ν(NO) (Fig. 3) is also linear
(correlation coefficient, R = 0.92) {cf. a similar plot for 18
complexes of the general formula [MnLLЈ(NO)(η-C5H4Me)]z
(L, LЈ = neutral Lewis base N- or P-donors or bidentate
S-donors11)},allowingEЊЈforthecarbonylcomplexes[Mn(CO)-
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
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addition of 0.2 to ΣEL for each isonitrile in the complex). The
constant 0.35 relates to contributions made to EЊЈ by the nature
of the Mn()/Mn() redox centre and to the effects of the NO
and η-C5H4Me ligands.
EЊЈ = 1.05(ΣEL) ϩ 0.35
(1)
With the aid of eqn. (1), and knowing the Lever parameters
for L1 and L2, EЊЈ can be estimated for other examples of
[MnL1L2(NO)(η-C5H4Me)]z. Thus, EЊЈ for the carbonyls 10–13
are again estimated to be >1.75 V, in agreement with the esti-
mate based on ν(NO) (see above). Estimates of Lever param-
eters for the cyanide complexes [Mn(CN)L(NO)(η5-C5R4Me)]
as N-donor ligands in binuclear cyanide-bridged complexes are
described below.
Fig. 2 The two-scan CV in CH2Cl2 of [Mn(CN)(CNBut)(NO)(η5-
C5H4Me)] 18 from 0.3 to 1.5 V at a scan rate of 200 mV sϪ1
.
Chemical oxidation of [MnXL(NO)(ꢀ5-C5R4Me)]
Attempts to oxidise [Mn(CN)L(NO)(η5-C5R4Me)] with the
strong oxidants [N(C6H4Br-p)3]ϩ or [NO]ϩ led to decomposition
even at low temperature and the monocations [Mn(CN)-
L(NO)(η5-C5R4Me)]ϩ could not be isolated. However, the
electrochemical studies noted above suggested that mono-
cations of the halide analogues, [MnXL(NO)(η5-C5R4Me)],
should be readily formed with milder oxidants. Accordingly,
addition of [Fe(η5-C5H5)(η5-C5H4COMe)][PF6] (EЊЈ = 0.74 V)
to 1–4 and 6, and of [Fe(η5-C5H5)2][PF6] (EЊЈ = 0.47 V) to
[MnI(CNBut)(NO)(η5-C5Me5)] 5, in CH2Cl2 at 0 ЊC, resulted in
shifts of the ν(NO) bands {and of the ν(CNR) bands of 3–5} to
higher energy (Table 1). Such shifts are in accord with one-
electron oxidation, giving [MnXL(NO)(η5-C5R4Me)]ϩ. How-
ever, the formation of such cations remains unproven given the
results of low temperature ESR spectroscopy.
In situ oxidation for ESR spectroscopy was carried out
by adding solid [Fe(η5-C5H5)2][PF6] or [Fe(η5-C5H5)(η5-C5H4-
COMe)][PF6] to a frozen CH2Cl2 solution of [MnXL(NO)-
(η5-C5R4Me)], warming the mixture to the lowest possible tem-
perature at which reaction occurred and then refreezing the
sample to record the anisotropic spectrum. The temperature
was then slowly raised until an isotropic spectrum was
observed.
Qualitative analyses of the spectra indicate that mixtures of
paramagnetic products are formed which do not include the
monocations [MnXL(NO)(η5-C5R4Me)]ϩ 1؉–6؉. A high field
spectrum (g = ca. 1.99) was common to all samples, consisting
of fifteen narrow lines, equally spaced with a separation of ca. 9
× 10Ϫ4 cmϪ1; Fig. 5 shows the best resolved isotropic spectrum,
obtained on oxidation of 2. This pattern might arise from coup-
ling of the unpaired electron to 55Mn (I = 5/2, 100%), with
A(55Mn) = ca. 18 × 10Ϫ4 cmϪ1, and to two equivalent 14N (I = 1,
100%) nuclei, with A(14N) = ca. 9 × 10Ϫ4 cmϪ1, i.e. from a
paramagnetic 17-electron species such as [Mn(NO)2(η5-C5R4-
Me)]ϩ (assuming that the η5-C5R4Me ligand is not lost).
No further analysis of these ESR spectra was possible but it
is interesting to note that a fragment corresponding to the ion
[Mn(NO)2(η5-C5H4Me)]ϩ was observed in the mass spectrum of
the binuclear complex [Mn2I(µ-NO)2(NO)(η5-C5H4Me)2].7
Fig. 3 Plot of EЊЈ vs. ν(NO) for [MnL1L2(NO)(η5-C5H4Me)]z 1–9, 14–
21.
L(NO)(η5-C5H4Me)][PF6] 10–13 to be predicted as >1.75 V on
the basis of ν(NO), i.e. outside the potential range accessible
under the experimental conditions used for cyclic voltammetry.
For compounds 1–9 and 14–19 with the general formula
[MnL1L2(NO)(η-C5H4Me)]z, a plot of the sum of the Lever
parameters, EL,5 for L1 and L2 (i.e. ΣEL) against experimental
redox potential, EЊЈ, (Fig. 4) is almost linear (R2 = 0.96; eqn. (1))
as expected5 if the Lever analysis holds. (Note that the Lever
parameter for CNPh is used for CNXyl for which there is no
published value. Moreover, isocyanide complexes have been
described by Lever as ‘less well-behaved systems’ and, as Lever
has noted,5 adherence to the linear relationship required the
Synthesis and characterisation of binuclear complexes
Treatment of equimolar quantities of the iodide complexes
[MnILЈ(NO)(η5-C5H4Me)] (LЈ = PPh3 1, CNBut 3 or CNXyl 4)
and the cyanide complexes [Mn(CN)L(NO)(η5-C5H4Me)] (L =
PPh3 16, CNBut 17 or CNXyl 18) in CH2Cl2 in the presence
of TlPF6 gave green or red-purple solutions from which the
binuclear species [(η5-C5H4Me)(ON)LMn(µ-CN)MnLЈ(NO)-
(η5-C5H4Me)][PF6] (L = PPh3, LЈ = PPh3 22, CNBut 23 or
CNXyl 24; L = CNBut, LЈ = PPh3 25, CNBut 26 or CNXyl 27;
L = CNXyl, LЈ = PPh3 28, CNBut 29 or CNXyl 30) were pre-
pared in 40–75% yield. Note that the choice of appropriate
Fig. 4 Plot of EЊЈ vs. the sum of Lever parameters, ΣEL, for the
ligands L1 and L2 in [MnL1L2(NO)(η-C5H4Me)]z.
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
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Fig. 5 The ESR spectrum of the product of the reaction of [MnI-
{P(OPh)3}(NO)(η5-C5H4Me)] 2 with [Fe(η5-C5H5)(η5-C5H4COMe)]-
[PF6].
pairs of mononuclear precursors leads to the isolation of stable
cyanide-bridged linkage isomers, e.g. 24 and 28.
The green or purple salts 22–30, characterised by elemental
analysis, IR spectroscopy (Table 4) and cyclic voltammetry (see
below), are soluble in polar solvents such as MeCN, thf and
CH2Cl2 but not in less polar solvents such as n-hexane, toluene
and diethyl ether. In the IR spectra, the ν(CN) band intensity
remains weak on N-coordination, indicating little change in the
dipole moment of the CN bond. However, ν(CN) is shifted to
higher energy by ca. 20–30 cmϪ1, as expected from the kine-
matic effect of restricting the CN motion by N-coordination.
The ν(CNR) and ν(NO) absorptions of the C-bound unit,
MnL(NO)(η5-C5H4Me), of the binuclear species [(η5-C5H4Me)-
(ON)LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)]ϩ are shifted by ca.
15 cmϪ1 to higher energy with respect to those of [Mn(CN)-
L(NO)(η5-C5H4Me)], and those corresponding to the N-bound
unit, MnLЈ(NO)(η5-C5H4Me), approximate to those of the
acetonitrile complexes [Mn(NCMe)LЈ(NO)(η5-C5H4Me)]ϩ.
For example, [(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)Mn(CNXyl)-
(NO)(η5-C5H4Me)][PF6] 24 shows bands at ν(NO) = 1747 cmϪ1
{cf. 1734 for [Mn(CN)(PPh3)(NO)(η5-C5H4Me)] 16} and at
ν(NO) = 1768 and ν(CNR) = 2149 cmϪ1 {cf. 1778 and 2157 cmϪ1
for the acetonitrile complex [Mn(NCMe)(CNXyl)(NO)(η5-C5-
H4Me)][PF6] 9}.
In binuclear complexes where L = LЈ, the IR spectra show a
single ν(NO) absorption and, for L = LЈ = CNBut 26 or CNXyl
30, only one strong ν(CNR) band. Coincidence of the energy
of the ν(NO) absorptions corresponding to the two metal
fragments has also been observed for [(η5-C5H5)(ON)(Ph3P)-
Re(µ-CN)Re(PPh3)(NO)(η5-C5H5)]ϩ.15
The crystal structure of complex 30
An X-ray structural analysis was carried out on [(η5-C5H4-
Me)(ON)(XylNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)]-
[PF6] 30 as a representative example of the binuclear species 22–
30. The structure of the cation of 30 is shown in Fig. 6 and
selected bond lengths and angles are given in Table 5.
The cation of 30 contains two manganese centres linked by a
slightly bent cyanide bridge, with Mn–C–N and C–N–Mn
angles of 175.1(3) and 175.7(4)Њ, respectively. The torsion angle,
τ, defined by the centroids of the two cyclopentadienyl rings
and the two manganese atoms of the Mn–CN–Mn linkage is
104Њ, smaller than those found in [(η5-C5H5)(OC)2Mn(µ-CN)-
Mn(CO)2(η5-C5H5)]Ϫ (180.0Њ),16 [(η5-C5H5)(ON)(Ph3P)Re-
(µ-CN)Re(PPh3)(NO)(η5-C5H5)]ϩ (141.0Њ)15 and [(η5-C5H5)-
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
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Table 5 Selected bond lengths (Å) and angles (Њ) for [(η5-C5H4Me)-
(ON)(XylNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6] 30
Mn(2)–C(1)
Mn(1)–N(1)
C(1)–N(1)
Mn(1)–Cring (av)
Mn(2)–Cring (av)
N(3)–O(2)
1.926(4)
1.970(4)
1.156(4)
2.142(4)
2.134(4)
1.186(4)
1.191(4)
1.886(5)
1.905(4)
1.165(5)
1.150(4)
Mn(2)–C(1)–N(1)
Mn(1)–N(1)–C(1)
N(3)–Mn(2)–C(23)
N(3)–Mn(2)–C(1)
C(1)–Mn(2)–C(23)
N(2)–Mn(1)–C(8)
N(2)–Mn(1)–N(1)
N(1)–Mn(1)–C(8)
Mn(2)–N(3)–O(2)
Mn(1)–N(2)–O(1)
175.7(4)
175.1(3)
97.7(2)
97.5(2)
90.3(2)
99.3(2)
99.4(2)
88.3(2)
172.6(4)
173.2(3)
Fig. 7 Newman projections, down the M–CN–M axis, showing
the torsion angles, τ, for (a) [(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)-
Mn(CNXyl)(NO)(η5-C5H4Me)]ϩ (the cation of 30), (b) [(η5-C5H5)-
(OC)2Mn(µ-CN)Mn(CO)2(η5-C5H5)]Ϫ, and (c) [(η5-C5H5)(ON)-
(Ph3P)Re(µ-CN)Re(PPh3)(NO)(η5-C5H5)]ϩ.
N(2)–O(1)
Mn(2)–C(23)
Mn(1)–C(8)
C(23)–N(5)
C(8)–N(4)
0.33–0.61 V, in the potential range 0.0 to 1.6 V (Table 6), indi-
cating that both the di- and tri-cations [(η5-C5H4Me)(NO)-
LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)]zϩ (z = 2 and 3) are stable
on the cyclic voltammetry timescale. (No redox processes were
observed between 0.0 and Ϫ1.8 V). A comparison of the data in
Table 6 allows assignment of the order in which the two Mn()
centres are oxidised. For example, for [(η5-C5H4Me)(ON)-
(XylNC)Mn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6] (LЈ = PPh3
28, CNBut 29 or CNXyl 30) the first oxidation potential is low-
ered in the order CNXyl > CNBut > PPh3 while the potential
for the second oxidation is relatively unchanged. The first pro-
cess therefore corresponds to the reversible oxidation of the
N-bound manganese centre (where the ligand LЈ is varied). The
same trend is found for complexes 22–24 and 25–27. More
important, however, is the effect of linkage isomerism on ∆E,
the difference between the potentials for the two sequential one-
electron oxidation processes. Thus, for the linkage isomers 23
and 25, for example, ∆E = 0.36 and 0.56 V, respectively.
Surprisingly, the linkage isomers [(η5-C5H5)(ON)(Ph3P)Re-
(µ-CN)Re(PPh3)(NO)(η5-C5Me5)]ϩ and [(η5-C5Me5)(ON)-
(Ph3P)Re(µ-CN)Re(PPh3)(NO)(η5-C5H5)]ϩ each showed only
one oxidation wave, at 0.90 and 0.93 V, respectively. However, it
seems possible that a second oxidation wave for each of these
species might be obscured by the oxidation wave for the base
electrolyte salt. The more readily oxidised complex [(η5-
C5Me5)(ON)(Ph3P)Re(µ-CN)Re(PPh3)(NO)(η5-C5Me5)]ϩ does
show two such waves, at 0.75 and 0.88 V (i.e. separated by only
0.13 V).15
The binuclear complexes 22–30 may be regarded as further
members of the series [MnL1L2(NO)(η-C5H4Me)]ϩ, where L2 =
(NC)MnLЈ(NO)(η5-C5H4Me). The electrochemical data in
Table 6 can therefore be used to deduce a Lever parameter (EL)
for each of (NC)MnLЈ(NO)(η5-C5H4Me) (Table 7). Thus, by
using eqn. (1), and EЊЈ for the first oxidation of 22–30, and
noting that ΣEL is the sum of the Lever parameters for only two
ligands {i.e. LЈ and (NC)MnLЈ(NO)(η5-C5H4Me}, EL can be
computed, in each case from three different compounds. For
example, ELfor (NC)Mn(PPh3)(NO)(η5-C5H4Me) (i.e. 16 acting
as a ligand), calculated from the EЊЈ values for 22–24 is 0.02 V.
The first oxidation wave for 22–30, when scanned alone, is
also reversible in MeCN (at scan rates between 50 and 1000 mV
sϪ1) indicating that the mixed-valence dications [(η5-C5H4Me)-
Fig. 6 The molecular structure of the cation of [(η5-C5H4Me)-
(ON)(XylNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6]
30.
Hydrogen atoms have been omitted for clarity.
(Ph3P)2Ru(µ-CN)Ru(dppm)(η5-C5H5)]ϩ (114.0Њ).17 Newman
projections down the M–CN–M axis for 30, [(η5-C5H5)(OC)2-
Mn(µ-CN)Mn(CO)2(η5-C5H5)]Ϫ and [(η5-C5H5)(ON)(Ph3P)-
Re(µ-CN)Re(PPh3)(NO)(η5-C5H5)]ϩ (Fig. 7) illustrate the rel-
atively small torsion angle in 30, perhaps arising from a π–π
interaction between the xylyl groups of the two isocyanide
ligands, across a Mn(µ-CN)Mn distance of ca. 5.1 Å.
Cyclic voltammetric studies
At a platinum disc electrode in CH2Cl2 complexes 22–30
undergo two reversible one-electron oxidations, separated by
Table 6 Electrochemical dataa for the oxidation of binuclear cyclopentadienylmanganese nitrosyl complexes
EoЈ/V
Complex
CH2Cl2
MeCN
[(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 22
[(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)][PF6] 23
[(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6] 24
[(η5-C5H4Me)(ON)(ButNC)Mn(µ-CN)Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 25
[(η5-C5H4Me)(ON)(ButNC)Mn(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)][PF6] 26
[(η5-C5H4Me)(ON)(ButNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6] 27
[(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 28
[(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)][PF6] 29
[(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6] 30
0.83, 1.39
0.94, 1.30
0.99, 1.34
0.82, 1.38
0.97, 1.32
1.01, 1.34
0.85, 1.46
1.00, 1.45
1.06, 1.42
0.75, 1.36(I)
0.84, 1.29(I)
0.89, 1.29(I)
0.78, 1.38(I)
0.89, 1.32(I)
0.93, 1.32(I)
0.75, 1.42(I)
0.90, 1.41(I)
0.96, 1.38(I)
a At a Pt electrode in CH2Cl2, with potentials relative to the saturated calomel electrode, calibrated vs. the [Fe(η-C5H5)2]ϩ/[Fe(η-C5H5)2] couple
(at 0.47 V). For an irreversible (I) oxidation process, the oxidation peak potential, (Ep)ox, is given at a scan rate of 200 mV sϪ1
.
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Table 7 Calculated values of EL for fragments of compounds 22–30
Table 8 Selected bond lengths (Å) and angles (Њ) for [Mn{(µ-NC)Mn-
(CNBut)(NO)(η5-C5H4Me)}4(OEt2)][PF6]2 31
Fragment
In compounds
EL/V
Mn(1)–N(2)
Mn(1)–N(5)
Mn(1)–N(3)
Mn(1)–N(4)
Mn(1)–O(1)
Ceq–Neq (av)a
C(4)–N(4)
2.112(5)
2.098(5)
2.106(6)
2.173(5)
2.324(4)
1.142
N(2)–Mn(1)–N(3)
N(5)–Mn(1)–N(3)
N(5)–Mn(1)–N(2)
Neq–Mn(1)–N(4) (av)a
N(4)–Mn(1)–O(1)
Neq a–Mn(1)–O(1) (av)
MnI–Ceq–Neq (av)a
C(2)–N(2)–Mn(1)
C(5)–N(5)–Mn(1)
C(3)–N(3)–Mn(1)
C(4)–N(4)–Mn(1)
115.2(2)
114.5(2)
128.5(2)
94.5
176.5(2)
85.3
(NC)MnI(PPh3)(NO)(η-C5H4Me)
(NC)MnI(CNBut)(NO)(η-C5H4Me)
(NC)MnI(CNXyl)(NO)(η-C5H4Me)
22–24
25–27
28–30
0.02
0.04
0.07
(ON)LMnI(µ-CN)MnIILЈ(NO)(η5-C5H4Me)]2ϩ are also stable
in that solvent (on the time scale of cyclic voltammetry). How-
ever, the second oxidation process is irreversible, unlike in
CH2Cl2. Moreover, the irreversible wave has an associated
reduction product wave similar in potential to that of the
oxidation wave for [Mn(NCMe)LЈ(NO)(η5-C5H4Me)][PF6].
Fig. 8 shows the CV of [(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)-
Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 22 with the oxidation wave
of [Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7 superimposed.
The formation of [Mn(NCMe)LЈ(NO)(η5-C5H4Me)]ϩ sug-
gests Mn(µ-CN)Mn bridge cleavage by MeCN in the trications
[(η5-C5H4Me)(ON)LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)]3ϩ, at
the N-bound manganese centre.
1.153(7)
1.938
177.3
MnI–Ceq (av)a
174.0(6)
166.4(5)
171.5(5)
168.2(5)
a eq Refers to the equatorial positions for the trigonal bipyramidal
Mn() ion.
decomposition during crystallisation led to the unexpected
formation of novel polynuclear complexes in which four tetra-
hedral cyanomanganese() ligands are N-bound to either
trigonal bipyramidal or octahedral manganese() centres.
Layering a CH2Cl2 solution of 26 with a 1 : 1 toluene–diethyl
ether mixture at Ϫ20 ЊC gave, after two weeks, a mixture con-
taining easily separable orange and red crystals. The orange
product was identified as [Mn(CNBut)2(NO)(η5-C5H4Me)][PF6]
14 by its IR spectrum (bands at 2192, 2173 and 1785 cmϪ1;
Table 1). However, the red product showed absorptions (at
2173, 2117 and 1768 cmϪ1) which did not correspond to
those of any known mono- or bi-nuclear complex. A molecular
structure determination showed this red complex to be the
pentametallic salt [Mn{(µ-NC)Mn(CNBut)(NO)(η5-C5H4-
Me)}4(OEt2)][PF6]2 31.
The structure of 31 (Fig. 9, Table 8) includes four [Mn-
(CN)(CNBut)(NO)(η5-C5H4Me)] units N-bonded to a central
trigonal bipyramidal Mn() atom, with a diethyl ether molecule
occupying an axial position. The equatorial N–Mn()–N angles
range from 115 to 130Њ and the Naxial–Mn–N and N–Mn–O
angles are approximately 90Њ. The angles at the bridging
cyanides are nearly linear at carbon, but differ significantly
from linearity at nitrogen. The bond lengths and angles around
each Mn() ion are nearly identical to those of the C-bound
Mn(CNXyl)(NO)(η5-C5H4Me) unit in [(η5-C5H4Me)(ON)-
Fig.
8
The CV of (a) [(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)-
Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 22 with (b) the oxidation wave of
[Mn(NCMe)(PPh3)(NO)(η5-C5H4Me)][PF6] 7 superimposed.
(XylNC)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6]
30
(Table 5).
A second unusual polynuclear complex was formed on
Chemical oxidation reactions
attempted crystallisation of [(η5-C5H4Me)(ON)(XylNC)Mn-
In most cases, attempts to isolate the mixed valence dications
[(η5-C5H4Me)(ON)LMnI(µ-CN)MnIILЈ(NO)(η5-C5H4Me)]2ϩ,
from the oxidation of [(η5-C5H4Me)(ON)LMnI(µ-CN)MnII-
LЈ(NO)(η5-C5H4Me)]ϩ with NOϩ or [N(C6H4Br-p)3]ϩ, led to
decomposition even at low temperature. However, treatment of
[(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4-
Me)][PF6] 24 with one equivalent of [N(C6H4Br-p)3][PF6] in
CH2Cl2 gave a purple solution showing one ν(CNR) band at
2172 cmϪ1, one ν(CN) band at 2045 cmϪ1, and two ν(NO) bands
at 1814 and 1753 cmϪ1, consistent with one-electron oxidation
at the N-bound Mn() centre. The ν(NO) band corresponding
to the C-bound Mn(NO)(η5-C5H4Me) fragment shifts by ca. 8
cmϪ1 to higher wavenumber whereas that of the N-bound unit
shifts, in the same sense, by ca. 50 cmϪ1; ν(CNR) moves to
higher wavenumbers by 30 cmϪ1; and ν(CN) shifts to lower
wavenumbers by 80 cmϪ1.
The formation and structures of polynuclear cyanide-bridged
complexes of Mn(II)
In order to study the structural effects of varying the ligands
L and LЈ in the binuclear cyanide-bridged compounds
(cf. the structure of 30, see above), attempts were made to
crystallise [(η5-C5H4Me)(ON)(ButNC)Mn(µ-CN)Mn(CNBut)-
(NO)(η5-C5H4Me)][PF6] 26 and [(η5-C5H4Me)(ON)(XylNC)-
Mn(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)][PF6] 29. However,
Fig. 9 The molecular structure of the dication of [Mn{(µ-NC)-
Mn(CNBut)(NO)(η5-C5H4Me)}4(OEt2)][PF6]2 31. Hydrogen atoms
have been omitted for clarity.
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Table 9 Selected bond lengths (Å) and angles (Њ) for [Mn{(µ-NC)Mn-
(CNXyl)(NO)(η5-C5H4Me)}4(NO3-O,OЈ)][PF6]ؒ2Me2CO 32ؒ2Me2CO
Table 10 Selected bond lengths (Å) and angles (Њ) for [Mn{(µ-NC)-
Mn(CNXyl)(NO)(η5-C5H4Me)}4(OH2)][PF6]2 35
Mn(1)–O(3)
Mn(1)–N(1)
Mn(1)–N(2)
C(1)–N(1)
2.315(3)
2.164(4)
2.174(4)
1.147(6)
1.143(6)
1.945(5)
1.945(5)
1.256(4)
1.230(8)
O(3)–Mn(1)–O(3A)a
O(3)–Mn(1)–N(1)
N(1)–Mn(1)–O(3)
N(1)–Mn(1)–N(1A)a
N(2)–Mn(1)–N(2A)a
O(4)–N(1)–O(3)
55.3(2)
158.8(1)
103.5(1)
97.7(2)
176.2(2)
121.2(3)
117.6(6)
178.4(5)
164.5(4)
178.7(4)
162.2(4)
Mn(1)–N(3)
Mn(1)–N(4)
Mn(1)–N(2)
Mn(1)–N(6)
Mn(1)–O(1)
Ceq–Neq (av)a
C(5)–N(6)
2.099(10)
2.096(10)
2.111(9)
2.176(12)
2.293(8)
1.145
N(3)–Mn(1)–N(2)
N(4)–Mn(1)–N(2)
N(4)–Mn(1)–N(3)
Neq–Mn(1)–N(6) (av)a
N(6)–Mn(1)–O(1)
Neq–Mn(1)–O (av)a
Mn–Ceq–Neq (av)a
C(3)–N(3)–Mn(1)
C(4)–N(4)–Mn(1)
C(2)–N(2)–Mn(1)
C(5)–N(6)–Mn(1)
128.6(4)
113.1(4)
116.4(4)
94.9
172.6(4)
85.5
C(2)–N(2)
Mn(2)–C(2)
Mn(3)–C(1)
N(7)–O(3)
N(7)–O(4)
O(3)–N(1)–O(3A)a
Mn(3)–C(1)–N(1)
C(1)–N(1)–Mn(1)
Mn(2)–C(2)–N(2)
C(2)–N(2)–Mn(1)
1.146(15)
1.954
177.6
Mn–Ceq (av)
168.0(10)
157.2(10)
173.8(10)
160.9(13)
a The angle involves symmetry-equivalent pairs of atoms, e.g. O(3) and
O(3A).
a Eq refers to the equatorial positions for the trigonal bipyramidal
Mn() ion.
(µ-CN)Mn(CNBut)(NO)(η5-C5H4Me)][PF6] 29 from acetone–
n-hexane at Ϫ20 ЊC. In this case, a single crystal structural
determination of the red crystalline solid (IR absorptions at
2150, 2119 and 1771 cmϪ1 in CH2Cl2) revealed the formation
of pentametallic [Mn{(µ-NC)Mn(CNXyl)(NO)(η5-C5H4Me)}4-
(NO3-O,OЈ)][PF6] 32.
Complex 32 (Fig. 10, Table 9) contains four tetrahedral
cyanomanganese() units and a bidentate nitrate anion bound
to the central Mn() atom. The geometry around the Mn() ion
is distorted octahedral, with the bite angle of the chelating
nitrate ion only 55.3 Њ. The reduction of the octahedral angle
from the ideal 90Њ is shared approximately equally between the
other cis angles in the plane of the two O atoms. As observed
for 31, the Mn()–C–N angles are very close to 180Њ in the
Mn()–C–N–Mn() links, but the C–N–Mn() angles deviate
significantly from linearity.
(Ph3P)Mn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6] (LЈ = PPh3 22,
CNBut 23 or CNXyl 24) and [(η5-C5H4Me)(ON)(XylNC)-
Mn(µ-CN)Mn(CNXyl)(NO)(η5-C5H4Me)][PF6] 30 showed no
changes in their IR spectra over several hours in CH2Cl2
solution.
Given the formation of polynuclear complexes in the decom-
position of some of the binuclear cations [(η5-C5H4Me)(ON)-
LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)]ϩ, an attempt was made
to find a more rational synthetic route to [Mn{(µ-NC)-
MnL(NO)(η5-C5H4Me)}4][PF6]2 (L
=
PPh3, CNBut and
CNXyl), i.e. by reacting anhydrous MnI2 with two equivalents
of TlPF6 in thf for 15 min and then adding four equivalents of
[Mn(CN)L(NO)(η5-C5H4Me)]. In the case of L = PPh3 no reac-
tion was observed, but when L = CNBut or CNXyl, penta-
metallic [Mn{(µ-NC)MnL(NO)(η5-C5H4Me)}4][PF6]2 (L
=
CNBut 33 and CNXyl 34) were isolated and characterised by
elemental analysis and IR spectroscopy (Table 4).
Confirmation of the structures of 33 and 34 was sought by
X-ray crystallography but slow diffusion of a concentrated
CH2Cl2 solution of 34 into n-hexane at Ϫ20 ЊC gave deep red
crystals of [Mn{(µ-NC)MnL(NO)(η5-C5H4Me)}4(OH2)][PF6]2
35. The molecular structure (Fig. 11, Table 10) includes not
only four N-bound cyanomanganese() ligands [Mn(CN)-
(CNXyl)(NO)(η5-C5H4Me)] but also an axial water molecule,
giving a structure analogous to that of [Mn{(µ-NC)Mn-
(CNBut)(NO)(η5-C5H4Me)}4(OEt2)][PF6]2 31.
Interestingly, a CH2Cl2 solution of [Mn{(µ-NC)Mn(CNXyl)-
(NO)(η5-C5H4Me)}4(OH2)][PF6]2 35 shows identical IR absorp-
tions to solutions of [Mn{(µ-NC)Mn(CNXyl)(NO)(η5-C5H4-
Fig. 10 The molecular structure of the cation of [Mn{(µ-NC)-
Mn(CNXyl)(NO)(η5-C5H4Me)}4(NO3-O,OЈ)][PF6]ؒ2Me2CO 32ؒ2Me2-
CO. Hydrogen atoms have been omitted for clarity.
After 2 h in solution the complexes [(η5-C5H4Me)(ON)(But-
NC)Mn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6] (LЈ = PPh3 25,
CNBut 26 or CNXyl 27) showed new IR absorptions which do
not depend on LЈ but which are identical to those of 31. Simi-
larly, decomposition of [(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)-
Mn(PPh3)(NO)(η5-C5H4Me)][PF6] 28 gave a complex showing
bands at the same energy as those found in the decomposition
of
[(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)Mn(CNBut)(NO)-
Fig. 11 The molecular structure of the dication of [Mn{(µ-NC)-
Mn(CNXyl)(NO)(η5-C5H4Me)}4(OH2)][PF6]2 35. Hydrogen atoms have
been omitted for clarity.
(η5-C5H4Me)][PF6] 29, suggesting that the same pentametallic
complex, 32, is formed. By contrast, [(η5-C5H4Me)(ON)-
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Me)}4][PF6]2 34 and [Mn{(µ-NC)Mn(CNXyl)(NO)(η5-C5H4-
Me)}4(NO3-O,OЈ)][PF6] 32. Significant differences were
expected in the IR spectra due to the different coordination
geometries at Mn() and the overall charges of the complexes.
However, CH2Cl2 solutions of [Mn{(µ-NC)Mn(CNBut)(NO)-
(η5-C5H4Me)}4(OEt2)][PF6]2 31 {five-coordinate Mn()} and
[Mn{(µ-NC)Mn(CNBut)(NO)(η5-C5H4Me)}4][PF6]2 33 {four-
coordinate Mn()} also show the same IR absorptions in the
region 2250–1650 cmϪ1.
A common feature in the molecular structures of the penta-
metallic complexes 31, 32 and 35 is the presence of an O-donor
ligand. The Mn()–O bond distances, 2.324, 2.315 and 2.293 Å,
respectively, are significantly longer than the average Mn-O dis-
tance [2.187(45) Å] found for 407 structures containing a MnII–
OH2 bond.18 Thus, the weakly coordinated diethyl ether (in 31),
nitrate (in 32) and water (in 35) ligands might be lost in CH2Cl2
to give four-coordinate Mn() complexes [Mn{(µ-NC)MnL-
(NO)(η5-C5H4Me)}4]2ϩ in solution. Other pentametallic com-
plexes with four cyanomanganese() complexes N-bound to
four-coordinate metal centres have been structurally character-
ised, namely [M{(µ-NC)MnLx}4][PF6]2 {Lx = trans-(CO)2-
{P(OEt)3}(dppm), M = Co19,20 (tetrahedral) and Pd19,21 (square
planar)}.
pared by published methods or variations thereof. The com-
pounds CNXyl and CNBut were purchased from Aldrich and
TlPF6 was purchased from Strem Chemicals. IR spectra
1
were recorded on a Nicolet 5ZDX FT spectrometer. H NMR
spectra were recorded on a JEOL GX270 spectrometer with
SiMe4 as an internal standard. X-band ESR spectra were
recorded on a Bruker ESP300 spectrometer equipped with a
Bruker variable temperature accessory and a Hewlett-Packard
5350B microwave frequency counter. The field calibration was
checked by measuring the resonance of the diphenylpicryl-
hydrazyl (dpph) radical before each series of spectra. Electro-
chemical studies were carried out using an EG&G model 273A
potentiostat linked to a computer using EG&G Model 270
Research Electrochemistry software in conjunction with a
three-electrode cell. The auxiliary electrode was a platinum wire
and the working electrode a platinum disc (1.6 mm diameter).
The reference was an aqueous saturated calomel electrode
separated from the test solution by a fine porosity frit and an
agar bridge saturated with KCl. Solutions were 5.0 × 10Ϫ4 or
1.0 × 10Ϫ3 mol dmϪ3 in the test compound and 0.1 mol dmϪ3 in
[NBun ][PF6] as the supporting electrolyte. The solvents used
4
were CH2Cl2 or MeCN. Under the conditions used, EЊЈ for the
one-electron oxidation of [Fe(η5-C5H5)2] or [Fe(η5-C5Me5)2],
added to the test solutions as internal calibrants, is 0.47 and
Ϫ0.08 V, respectively. in CH2Cl2; the EЊЈ value for [Fe(η5-
C5H5)2] in MeCN is 0.39 V.
Conclusions
Cyclic voltammetric studies on the mononuclear complexes
[MnXL(NO)(η5-C5H4Me)] (X = halide or cyanide), [Mn-
(NCMe)L(NO)(η5-C5H4Me)][PF6] and [Mn(CO)L(NO)(η5-C5-
H4Me)][PF6] show a linear relationship between oxidation
potential, EЊЈ, and ν(NO), and between experimental oxidation
potentials and those calculated using Lever parameters. Both
linear relationships can be used to estimate EЊЈ for complexes
where such information is otherwise unavailable.
Microanalyses were carried out by the staff of the Micro-
analytical Service of the School of Chemistry, University of
Bristol.
Syntheses
[MnI(PPh3)(NO)(ꢀ5-C5H4Me)] 1. A mixture of [Mn(CO)2-
(NO)(η5-C5H4Me)][PF6] (2.0 g, 6.51 mmol) and KI (1.08 g,
6.51 mmol) was stirred in acetone (100 cm3). After 16 h, PPh3
(1.71 g, 6.51 mmol) was added to the black solution and the
mixture stirred for a further 10 min. The solvent was removed
in vacuo and the brown solid extracted into toluene (3 × 20
cm3). The solution was filtered through Celite and the solvent
evaporated to low volume (ca. 20 cm3), n-hexane (20 cm3) was
added slowly and the mixture cooled to Ϫ20 ЊC to give the
product as a brown crystalline solid, yield 2.45 g (68%).
The complexes [MnI{P(OPh)3}(NO)(η5-C5H4Me)] 2, [MnI-
(CNBut)(NO)(η5-C5H4Me)] 3 and [MnI(CNXyl)(NO)(η5-C5-
H4Me)] 4 were prepared similarly.
The reaction of [Mn(CN)L(NO)(η5-C5H4Me)] with [MnILЈ-
(NO)(η5-C5H4Me)] in CH2Cl2 in the presence of TlPF6 gives
cyanide-bridged binuclear complexes of the general formula
[(η5-C5H4Me)(ON)LMn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6]
(L or LЈ = PPh3, CNBut or CNXyl) which undergo two sequen-
tial one-electron oxidations with the N-bound manganese
centre the site of first oxidation. The oxidation potentials and
IR spectra depend not only on L and LЈ but on the orientation
of the cyanide bridge in linkage isomers such as 23 and 25.
Some binuclear species decompose during attempted
crystallisation, giving the structurally characterised penta-
metallic species [Mn{(µ-NC)Mn(CNXyl)(NO)(η5-C5H4Me)}4-
[MnI(CNBut)(NO)(ꢀ5-C5Me5)] 5. To a stirred solution of
[Mn(CO)2(NO)(η5-C5Me5)][PF6] (700 mg, 1.66 mmol) in acet-
one (50 cm3) was added KI (275 mg, 1.66 mmol). After 16 h,
CNBut (0.19 cm3, 1.66 mmol) was added to the dark green
solution and after a further 10 min the solution was evaporated
to dryness in vacuo. The green residue was extracted into tolu-
ene (40 cm3) and the solution filtered through Celite. Addition
of n-hexane (40 cm3) induced precipitation of a green solid
which was dried in vacuo, yield 530 mg (74%).
(OH2)][PF6]2,
(NO3-O,OЈ)][PF6]
[Mn{(µ-NC)Mn(CNXyl)(NO)(η5-C5H4Me)}4-
and
[Mn{(µ-NC)Mn(CNBut)(NO)(η5-
C5H4Me)}4(OEt2)][PF6]2. Related pentametallic complexes
[Mn{(µ-NC)Mn(CNR)(NO)(η5-C5H4Me)}4][PF6]2 have been
synthesised from the reaction of MnI2 and [Mn(CN)L(NO)-
(η5-C5H4Me)] in thf in the presence of TlPF6.
Experimental
The preparation, purification and reactions of the complexes
described were carried out under an atmosphere of dry nitrogen
using dried and deoxygenated solvents purified either by distil-
lation or by using Anhydrous Engineering double alumina or
alumina/copper catalyst drying columns. Reactions were moni-
tored by IR spectroscopy where necessary. Unless stated other-
wise, complexes were purified using a mixture of two solvents.
The impure solid was dissolved in the more polar solvent, the
resulting solution was filtered and then treated with the second
solvent, and the mixture was reduced in volume in vacuo to
induce precipitation. The compounds [Mn(CO)2(NO)(η5-C5-
R4Me)][PF6] (R = H22 or Me23), [Mn(CO)(PPh3)(NO)(η5-C5-
H4Me)][PF6],9 [MnI(PPh3)(NO)(η5-C5H4Me)],6–8 [Mn(CN)-
(PR3)(NO)(η5-C5H4Me)] (R = Ph6,10 and OPh10), [Fe(η5-C5-
H5)2][PF6] and [Fe(η5-C5H5)(η5-C5H4COMe)][PF6]24 were pre-
[MnBr(PPh3)(NO)(ꢀ5-C5H4Me)] 6. To a stirred solution of
[Mn(CO)2(NO)(η5-C5H4Me)][PF6] (250 mg, 0.815 mmol) in
acetone (30 cm3) at 0 ЊC was added [NBun ]Br (263 mg, 0.815
4
mmol). After 30 min, PPh3 (214 mg, 0.815 mmol) was added to
the black solution and after a further 10 min the solution was
evaporated to dryness in vacuo. The brown residue was
extracted into toluene (3 × 10 cm3) and the solution filtered
through Celite. Addition of n-hexane (30 cm3) to the solution
induced precipitation of a brown solid which was thoroughly
washed with n-hexane and dried in vacuo, yield 180 mg (75%).
[Mn(NCMe)(PPh3)(NO)(ꢀ5-C5H4Me)][PF6] 7. Solid TlPF6
(260 mg, 0.72 mmol) was added to a stirred solution of
[MnI(PPh3)(NO)(η5-C5H4Me)] (400 mg, 0.72 mmol) in MeCN
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(25 cm3). After 30 min the brown solution was filtered through
Celite and the filtrate evaporated to dryness in vacuo. The
brown residue was dissolved in CH2Cl2 (20 cm3) and the
solution filtered through Celite. n-Hexane (20 cm3) was added
to the filtrate and the mixture reduced in volume in vacuo to
induce precipitation of a brown solid, yield 317 mg (72%).
The complexes [Mn(NCMe)(CNBut)(NO)(η5-C5H4Me)]-
[PF6] 8 and [Mn(NCMe)(CNXyl)(NO)(η5-C5H4Me)][PF6] 9
were prepared similarly.
[(ꢀ5-C5H4Me)(ON)(XylNC)Mn(ꢁ-CN)Mn(PPh3)(NO)(ꢀ5-C5-
H4Me)][PF6] 28. To a stirred solution of [Mn(CN)(CNXyl)-
(NO)(η5-C5H4Me)] 19 (58 mg, 0.18 mmol) and [MnI-
(PPh3)(NO)(η5-C5H4Me)] 1 (100 mg, 0.18 mmol) in CH2Cl2
(20 cm3) was added TlPF6 (96 mg, 0.19 mmol). After 20 min the
resulting red solution was filtered through Celite and evapor-
ated to dryness in vacuo. The oily brown residue was thoroughly
washed with toluene (2 × 10 cm3). The remaining solid was
purified using CH2Cl2–n-hexane, giving a red solid, yield 129
mg (63%).
[Mn(CO)(CNXyl)(NO)(ꢀ5-C5H4Me)][PF6] 13. To a stirred
solution of [Mn(CO)2(NO)(η5-C5H4Me)][PF6] (500 mg, 1.36
mmol) and CNXyl (180 mg, 1.36 mmol) in acetone (20 cm3)
was added two drops of NEt3. After 15 min the orange solution
was evaporated to dryness in vacuo. The orange residue was
dissolved in CH2Cl2 (20 cm3) and the solution filtered through
Celite. n-Hexane (20 cm3) was added to the filtrate and the mix-
ture cooled to Ϫ20 ЊC to give the product as an orange crystal-
line solid which was removed by filtration and dried in vacuo,
yield 498 mg (77%).
The complexes [(η5-C5H4Me)(ON)(Ph3P)Mn(µ-CN)MnLЈ-
(NO)(η5-C5H4Me)][PF6] (LЈ = PPh3 22, CNBut 23), [(η5-C5-
H4Me)(ON)(ButNC)Mn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6]
(LЈ = PPh3 25, CNBut 26, CNXyl 27) and [(η5-C5H4Me)-
(ON)(XylNC)Mn(µ-CN)MnLЈ(NO)(η5-C5H4Me)][PF6] (LЈ =
CNBut 29) were prepared similarly.
[(ꢀ5-C5H4Me)(ON)(PPh3)Mn(ꢁ-CN)Mn(CNXyl)(NO)-
(ꢀ5-C5H4Me)][PF6] 24. To a stirred solution of [Mn(CN)-
(PPh3)(NO)(η5-C5H4Me)] 16 (113 mg, 0.25 mmol) and
[MnI(CNXyl)(NO)(η5-C5H4Me)] 4 (100 mg, 0.25 mmol) in
CH2Cl2 (20 cm3) was added TlPF6 (96 mg, 0.28 mmol). After
20 min the resulting red solution was filtered through Celite
and the volume of the solution reduced to ca. 5 cm3. Diethyl
ether (5 cm3) was added dropwise and the mixture stored at
Ϫ20 ЊC, giving the product as a dark red solid, yield 110 mg
(49%).
The complex [Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12
was prepared similarly.
[Mn(CNXyl)2(NO)(ꢀ5-C5H4Me)][PF6] 15. To a stirred solu-
tion of [Mn(CO)(CNXyl)(NO)(η5-C5H4Me)][PF6] 13 (146 mg,
0.31 mmol) and CNXyl (41 mg, 0.31 mmol) in acetone (15 cm3)
was added two drops of NEt3. After 5 min the orange solution
was evaporated to dryness in vacuo. The resulting solid was
dissolved in CH2Cl2 (15 cm3) and filtered through Celite.
n-Hexane (15 cm3) was added and the mixture cooled to Ϫ20 ЊC
to give the product as an orange crystalline solid, yield 120 mg
(68%).
The complex [(η5-C5H4Me)(ON)(XylNC)Mn(µ-CN)Mn-
(CNXyl)(NO)(η5-C5H4Me)][PF6] 30 was prepared similarly as a
dark purple solid in 73% yield.
[Mn{(ꢁ-NC)Mn(CNBut)(NO)(ꢀ5-C5H4Me)}4][PF6]2 33. Solid
MnI2 (40 mg, 0.13 mmol) and TlPF6 (90 mg, 0.26 mmol) were
stirred in acetone (20 cm3). After 15 min [Mn(CN)(CNBut)-
(NO)(η5-C5H4Me)] 18 (141 mg, 0.52 mmol) was added to
the mixture, and after a further 15 min the red solution was
filtered through Celite and the filtrate evaporated to dryness in
vacuo. The red oily residue was thoroughly washed with toluene
(2 × 10 cm3) and then stirred with n-hexane for 2 h to give the
product as a red solid, yield 86 mg (47%).
The complex [Mn(CNBut)2(NO)(η5-C5H4Me)][PF6] 14 was
prepared similarly.
[Mn(CN)(CNBut)(NO)(ꢀ5-C5H4Me)] 18.
A mixture of
[Mn(CO)(CNBut)(NO)(η5-C5H4Me)][PF6] 12 (2.4 g, 6.63
mmol) and [NEt4]CN (1.6 g, 7.3 mmol) in CH2Cl2 (100 cm3)
was heated under reflux for 18 h. The solution was evaporated
to dryness in vacuo and the resulting solid was extracted into
toluene (3 × 20 cm3). The extract was then reduced to low
volume (ca. 5 cm3) and added to an alumina/n-hexane chrom-
atography column. Elution with CH2Cl2 gave a yellow band
which was discarded. Elution with CH2Cl2–thf (1 : 1) gave a red
solution which was treated with n-hexane and then reduced in
volume in vacuo to give a red precipitate. The solid was purified
using CH2Cl2–n-hexane, yield 0.93 g (51%).
[Mn{(ꢁ-NC)Mn(CNXyl)(NO)(ꢀ5-C5H4Me)}4][PF6]2 34. Solid
MnI2 (35 mg, 0.11 mmol) and TlPF6 (79 mg, 0.23 mmol) were
stirred in thf (20 cm3). After 20 min, [Mn(CN)(CNXyl)-
(NO)(η5-C5H4Me)] 19 (145 mg, 0.45 mmol) was added to the
mixture, and after a further 10 min the red solution was filtered
through Celite and the solution evaporated to dryness in vacuo.
The red oily residue was thoroughly washed with diethyl ether
(3 × 10 cm3) and then stirred with n-hexane for 2 h to give the
product as a red solid, yield 99 mg (54%).
Complex [Mn(CN)(CNXyl)(NO)(η5-C5H4Me)] 19 was pre-
pared similarly but the first (yellow) band was eluted using
CH2Cl2–thf (4 : 1).
Crystal structure determinations of 30, 31, 32ؒ2Me2CO and
35. Crystals suitable for X-ray diffraction study were grown as
follows: 30, slow diffusion of n-hexane into a concentrated
CH2Cl2 solution of the complex at Ϫ10 ЊC; 31, layering a
CH2Cl2 solution of 26 with a 1 : 1 toluene–diethyl ether mixture
at Ϫ20 ЊC for two weeks; 32, slow diffusion of n-hexane into a
concentrated acetone solution of 29 at Ϫ20 ЊC; 35, slow diffu-
sion of n-hexane into a concentrated CH2Cl2 solution of 34
at Ϫ20 ЊC. All X-ray diffraction measurements were made at
173 K. Many of the other details of the structure analyses are
presented in Table 11.
The orientation of the cyanide bridge in complex 30 was
assigned, on the basis of the best agreement for the thermal
parameters and occupancy factors for the C and N atoms, after
refinement in two alternative models in which the C and N
atoms were exchanged. Complex 32 crystallises with the central
Mn atom lying on a site of crystallographic C2 symmetry. There
are thus half of a cation of 32, half of a [PF6]Ϫ anion, and one
molecule of acetone in the asymmetric unit. No protons were
assigned to the coordinated water in complex 35.
[Mn(CN)(CO)(NO)(ꢀ5-C5Me5)] 21. A mixture of [Mn-
(CO)2(NO)(η5-C5Me5)][PF6] (0.48 g, 1.13 mmol) and [NEt4]CN
(0.18 g, 1.13 mmol) was stirred for 10 min to give a red solution
which was filtered through Celite and then evaporated to dry-
ness in vacuo. The residue was dissolved in the minimum
volume of toluene, filtered through Celite and then evaporated
to dryness in vacuo. The resulting red solid was washed with
n-hexane (2 × 10 cm3) and dried in vacuo, yield 0.23 g (77%).
[Mn(CN)(CNBut)(NO)(ꢀ5-C5Me5)] 20.
A
mixture of
[Mn(CN)(CO)(NO)(η5-C5Me5)] 21 (0.7 g, 2.55 mmol) and
CNBut (0.29 cm3, 2.55 mmol) in CH2Cl2 (20 cm3) was heated
under reflux for 18 h. The solution was cooled to room temper-
ature, filtered through Celite and then evaporated to dryness
in vacuo. The resulting solid was dissolved in toluene (20 cm3)
and the solution filtered through Celite and concentrated in
vacuo before n-hexane (20 cm3) was slowly added. The mixture
was cooled to Ϫ20 ЊC to give the product as a red crystalline
solid, yield 0.51 g (61%).
D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
693

View Article Online
Table 11 Crystal and refinement data for cyanide-bridged manganese complexes
Compound
30
31
32ؒ2Me2CO
35
Formula
M
C31H32F6Mn2N5O2P
761.47
C52H74F12Mn5N12O5P2
1511.87
C70H76F6Mn5N13O9P
1663.11
C64H64F12Mn5N12O5P2
1645.91
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/Њ
β/Њ
Monoclinic
P21/c (14)
12.926(1)
16.551(2)
16.509(2)
90
105.172(2)
90
3408.8(6)
4
Triclinic
P1 (2)
Monoclinic
C2/c (15)
26.525(2)
12.159(1)
24.814(2)
90
108.690(2)
90
7580.8(11)
4
Triclinic
P1 (2)
¯
¯
9.422(1)
14.596(1)
25.831(1)
86.970(1)
82.885(1)
76.298(1)
3423.5(2)
2
15.268(6)
16.101(7)
17.677(9)
65.32(2)
87.48(5)
67.70(3)
3619(3)
γ/Њ
U/ÅϪ3
Z
2
µ/mmϪ1
0.856
1.027
0.909
0.979
Reflections collected
Independent reflections (Rint
Final R indices [I > 2σ(I )]: R1, wR2
21775
7813 (0.1097)
0.0535, 0.0853
29916
12028 (0.0479)
0.0681, 0.1754
19944
6669 (0.0533)
0.0577, 0.1364
31606
16259 (0.1434)
0.1118, 0.2786
)
Moreno, A. G. Orpen and A. J. Wood, J. Chem. Soc., Dalton Trans.,
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18 Cambridge Structural Database, version 5.21, CCDC, April 2002.
19 O. M. Hicks, Ph. D. Thesis, University of Bristol, 1997.
20 N. G. Connelly, O. M. Hicks, G. R. Lewis and A. G. Orpen,
unpublished results.
CCDC reference numbers 223106–223109.
See http://www.rsc.org/suppdata/dt/b3/b313654j/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the University of Bristol for Postgraduate Scholar-
ships (to K. M. A. and E. L-R) and the New Zealand Found-
ation for Research, Science and Technology for a Postdoctoral
Fellowship (to N. J. G.).
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D a l t o n T r a n s . , 2 0 0 4 , 6 8 3 – 6 9 4
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