Formation of hexacarbonylmanganese(I) salts, [Mn(CO)6] +X-, in anhydrous HP

Article abstract of DOI:10.1021/ic700798z

A convenient one-step synthesis for [Mn(CO)₆]⁺ salts has been developed. The method involves the one-electron oxidation of Mn ₂(CO)₁₀ by protons in solutions of Lewis acids (BF ₃, (CF₃)₃BCO) and anhydrous HF. The molecular structure of [Mn(CO)₆][BF₄]·SO₂ was determined by single-crystal X-ray diffraction. Crystal data: orthorhombic, space group Cmc2₁, a = 8.7001(2) A, b = 11.8497(3) A, and c = 11.7437(3) A; Z = 4; R1 = 0.0320 and wR2 = 0.1106. The structural, NMR, and vibrational spectroscopic properties of [Mn(CO)₆] ⁺ fit perfectly with those of the isoelectronic species (V(CO) ₆]^_, Cr(CO)₆, and [Fe(CO)₆] ²⁺.

Full text of DOI:10.1021/ic700798z

Inorg. Chem. 2007, 46, 7210−7214
+
-
Formation of Hexacarbonylmanganese(I) Salts, [Mn(CO) ] X , in
Anhydrous HF
6
|
Jens Geier,† Helge Willner,*,† Christian W. Lehmann,*,‡ and Friedhelm Aubke§
FB C, Anorganische Chemie, Bergische UniVersit a¨ t Wuppertal, Gauâstrasse 20,
D-42097 Wuppertal, Germany, Max Planck Institut f u¨ r Kohlenforschung,
Kaiser-Wilhelm-Platz 1, D-45470 M u¨ lheim an der Ruhr, Germany, and Department of Chemistry,
the UniVersity of British Columbia, VancouVer, British Columbia V6T 121, Canada
Received April 26, 2007
A convenient one-step synthesis for [Mn(CO)
oxidation of Mn (CO)10 by protons in solutions of Lewis acids (BF
structure of [Mn(CO) ][BF SO was determined by single-crystal X-ray diffraction. Crystal data: orthorhombic,
space group Cmc2 ; a 8.7001(2) Å, b
6
]+ salts has been developed. The method involves the one-electron
, (CF BCO) and anhydrous HF. The molecular
2
3
3 3
)
6
4
]
‚
2
1
)
)
11.8497(3) Å, and c
)
11.7437(3) Å; Z
)
6
4; R1
) 0.0320 and wR2
)
0.1106. The structural, NMR, and vibrational spectroscopic properties of [Mn(CO)
the isoelectronic species [V(CO)
]+ fit perfectly with those of
]-, Cr(CO) ]2+.
, and [Fe(CO)
6 6
6
Introduction
5
in the presence of SbF because of its oxidizing power.
Hence, other Lewis acids must be used.
Superacids1,2 have played an unique role as reaction media
5
Recently, we reported on the synthesis of [Co(CO) ]-
in the generation and stabilization of homoleptic metal-
[
(CF
3
)
3
BF] by the treatment of Co
BCO, whose proton acts as
a mild oxidizer. This new approach is extended in this study
2 8
(CO) with the new Lewis
3
-6
carbonyl cations in the form of thermally stable salts, as
Brønsted superacid HF-(CF )
3 3
reported by us.7 In particular, the use of SbF
conjugate Lewis Brønsted superacid HF-SbF has allowed
,8
and its
5
9
5
to the oxidative carbonylation of Mn
2
(CO)10 to form [Mn-
the formation of a substantial number of salts with homo-
+
(CO)
6
] in anhydrous hydrogen fluoride (aHF) solutions of
leptic σ-bonded metal-carbonyl cations containing metals
varying Brønsted acidity, i.e., neat aHF, aHF/BF
3
, and aHF/
6
,8
in the oxidation states +2 and +3 under mild conditions.
However, there are limitations to the use of SbF and HF-
SbF : (i) Many 3d metal cations are not carbonylated in these
+
(CF
3
)
3
BCO. The [Mn(CO)
6
] salts are thereby formed in a
5
very convenient manner. Furthermore, some previously
5
unknown thermal, spectroscopic, and structural properties
media but form fluoroantimonate salts instead; and (ii)
carbonyl cations in low oxidation states cannot be obtained
+
of the [Mn(CO)
6
] cation are investigated.
The salt [Mn(CO)
et al. in 1962 as the first example of a homoleptic metal-
carbonyl cation by the reaction of Mn(CO) Cl with AlCl at
100 °C and 300 bar CO pressure. The diamagnetic complex
reacts with moisture with the formation of Mn(CO) H and
6 4
][AlCl ] was prepared by E.O. Fischer
*
To whom correspondence should be addressed. E-mail: willner@
uni-wuppertal.de (H.W.), lehmann@mpi-muelheim.mpg.de (C.W.L.).
5
3
Phone: (49)202-439-2517. Fax: (+49)202-439-3053.
10
†
Bergische Universit a¨ t Wuppertal.
Max Planck Institut f u¨ r Kohlenforschung.
The University of British Columbia.
Dedicated to Professor Beck on the occasion of his 75th birthday.
‡
5
§
CO
2
and decomposes thermally into CO and Mn
2
(CO)10
.
|
-
(
1) Olah, G. A.; Prakash, G. K. S.; Sommer, J. Superacids; Wiley: New
York, 1985.
2) O’Donell, T. A. Superacids and Acidic Melts as Inorganic Reaction
Media; VCH: Weinheim, Germany, 1993.
Later, the [PF
using NH PF
other [Mn(CO)
6
] salt was prepared by a metathesis reaction
11
4
6
in THF. A more convenient synthesis of
(
+
6
] salts, which avoids the need for high CO
(
(
(
3) Beck, W.; S u¨ nkel, K. Chem. ReV. 1988, 88, 1405.
4) Abel, E. W.; Tyfield, S. P. AdV. Organomet. Chem. 1970, 8, 117.
5) Lupinetti, A. J.; Strauss, S. H.; Frenking, G. Prog. Inorg. Chem. 2001,
pressures, was found by T. Kruck and M. Noack, who have
49, 1-112.
(9) Bernhardt, E.; Finze, M.; Willner, H.; Lehmann, C. W.; Aubke, F.
Chem.sEur. J. 2006, 12, 8276.
(10) Fischer, E. O.; Fichtel, K.; O¨ fele, K. Chem. Ber. 1962, 95, 249.
(11) McLean, R. A. N. Can. J. Chem. 1974, 52, 213.
(
(
(
6) Xu, Q. Coord. Chem. ReV. 2002, 231, 83.
7) Willner, H.; Aubke, F. Angew. Chem. 1997, 109, 2506.
8) Willner, H.; Aubke, F. Organometallics 2003, 22, 3612.
7210 Inorganic Chemistry, Vol. 46, No. 17, 2007
10.1021/ic700798z CCC: $37.00
© 2007 American Chemical Society
Published on Web 07/07/2007

Formation of Hexacarbonylmanganese(I) Salts
used Mn(CO)
to eq 112
5
CO
2
C
H
2 5
as the starting material according
Vibrational Spectroscopy. Infrared spectra were recorded at
room temperature on a FTIR spectrometer IFS 66v (Bruker,
Karlsruhe, Germany) equipped with a DTGS detector and a KBr/
Ge or Mylar/Ge beam splitter operating in the regions of 4000-
Mn(CO) CO C H + HCl f [Mn(CO) ]Cl + C H OH (1)
5
2
2
5
6
2
5
-
1
400 or 700-100 cm , respectively. The solid powdered samples
This method allowed also the preparation of the [BF
Subsequently, the [Mn(CO)
4
]- salt.13
] cation has been characterized
were measured neat between AgCl disks or as Nujol mulls between
polyethylene disks. For each spectrum, 64 scans were added with
+
6
-
1
11 55
an apodized resolution of 2 cm . Raman spectra were recorded at
room temperature on a Bruker Equinox 55 FT Raman spectrometer
by a complete vibrational analysis,
Mn NMR spectra in
14 13
solution, C magic-angle spinning (MAS) NMR solid-state
-
1
(
(
Bruker, Karlsruhe, Germany) using the 9394.8 cm exciting line
500 mW) of a Nd:YAG laser. The solid samples were contained
15
16
studies, cyclic voltammetry, ligand and electron exchange
17
13
reactions with carbonyl metalates, UV-vis spectroscopy,
in glass capillaries. For each spectrum, 2000 scans were added with
and DFT calculations.18
-1
a resolution of 2 cm
.
NMR Spectroscopy. 13C NMR spectra were measured on a
Bruker Avance DRX-400 spectrometer operating at 100.6 MHz.
A glass NMR tube (5.0 mm o.d., 0.5 mm wall thickness) fitted
Experimental Section
Gaseous reagents were manipulated in glass or stainless steel
vacuum lines, and the amounts were determined by pressure-
volume-temperature techniques. Anhydrous hydrogen fluoride was
obtained from Solvay GmbH (Hannover, Germany) and stored over
20
with a rotational symmetric valve was charged with 20 mg of
[
Mn(CO)
added by vacuum transfer, and the solution was measured at room
temperature. Cr(CO) (100 mg) was measured in 0.4 mL of CDCl
6 4 3 2
][BF ] inside a drybox. About 0.4 mL of CD NO was
2 6
K [NiF ]. Carbon monoxide (99.97%), boron trifluoride (>99.6%),
6
3
and dimanganese decacarbonyl (>98%) were obtained from Messer-
Griesheim (Krefeld, Germany), Merck-Schuchard (Germany), and
Fluka (Buchs, Switzerland), respectively, and were used without
at 80 °C under an additional pressure of 1 bar of nitrogen. Chemical
shifts were measured relative to external TMS.
Differential Scanning Calorimetry. Thermoanalytical measure-
ments were performed with a Netzsch DSC 204 (Netzsch GmbH,
Selb, Germany) instrument. In the range of 20-600 °C, temperature
and sensitivity calibrations were carried out with naphthalene,
further purification. (CF
according to the published procedure.
Synthetic Reactions. 1. Hexacarbonylmanganese(I) Tetrafluo-
roborate. Mn (CO)10 (0.78 g, 2.0 mmol), boron trifluoride
6.0 mmol), carbon monoxide (6.0 mmol), and anhydrous hydrogen
fluoride (20 mL) were combined and stirred in a 250 mL PFA (PFA
tetrafluoroethylene-perfluorovinyl ether copolymer) flask at
room temperature. After 10 days, all volatile components were
3 3 3 4
) BCO was synthesized from K[B(CF ) ]
1
9
2
benzoic acid, KNO
3 3 3
, AgNO , LiNO , and CsCl. About 30 mg of
(
the solid sample, contained in a sealed aluminum crucible, was
-1
heated at a rate of 10 °C min under an atmosphere of dry nitrogen.
)
Theoretical Calculations. The structure was optimized with the
Gaussian 03W program (version 6.0, revision B.04)21 at the B3LYP/
-
3
removed in a dynamic vacuum (≈10 mbar), leaving a colorless,
air-sensitive powder (1.22 g, 99%), identified as [Mn(CO) ][BF ],
which is modestly soluble in hydrogen fluoride, but dissolves easily
in nitromethane. It is slightly soluble in SO , and single crystals of
the SO monosolvate can be grown by slow evaporation of the
solvent. The crystals lose SO rapidly at room temperature.
. Hexacarbonylmanganese(I) Fluorotris(trifluoromethyl)-
borate. Mn (CO)10 (0.98 g, 2.5 mmol), (CF BCO (1.41 g, 5.7
6
1
-311+G(2d) level using optimization convergence criteria of 2 ×
6
4
-6 -6
0
for maximum force and 6 × 10 for maximum displacement.
The numerical integration was performed with a pruned (99,590)
2
grid (INTEGRAL Keyword: GRID ) ULTRAFINE). SCF con-
2
-
8
vergence criteria of 1 × 10 for the density matrix (rms) and 1 ×
2
-
6
10
for the energy were applied. The validity of the single reference
2
22
calculation was checked by a stability analysis.
2
3 3
)
mmol), carbon monoxide (5.0 mmol), and anhydrous hydrogen
fluoride (10 mL) were combined and stirred in a 250 mL PFA flask
at room temperature for 1 day. All volatile components (including
Single-Crystal and Powder X-ray Diffraction. Single-crystal
diffraction data were collected at 100 K on a Kappa CCD
diffractometer (Bruker AXS) using Mo KR radiation (λ ) 0.71073
Å) and a graphite monochromator. The crystal structure of [Mn-
-3
unreacted Mn
mbar), leaving a colorless, air-sensitive powder (0.94 g, 41%). [Mn-
CO) ][(CF BF] is modestly soluble in hydrogen fluoride but
dissolves easily in SO
2
(CO)10) were removed in a dynamic vacuum (≈10
(CO)
6
][BF
4
2
]‚SO was solved by direct methods using SHELXS-
23
2
(
6
)
3 3
97, and full-matrix least-squares refinement on F was performed
2
.
3
. Hexacarbonylmanganese(I) Dihydrogentrifluoride. A mix-
(20) Gombler, W.; Willner, H. Int. Lab. 1984, 14, 84.
ture of Mn
2
(CO)10 (1.40 g, 3.6 mmol), carbon monoxide (10.5
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P.
Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J.
B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03W, version
6.0, Revision B04; Gaussian, Inc.: Pittsburgh, PA, 2003.
mmol), and anhydrous hydrogen fluoride (25 mL) was stirred in a
50 mL PFA flask at room temperature for 4 weeks. All volatile
components (including unreacted Mn (CO)10) were removed in a
dynamic vacuum (≈10 mbar), leaving a slightly yellow, air-
sensitive powder (0.42 g, ≈20%) of [Mn(CO) ][H ].
2
2
-
3
6
2 3
F
(
(
(
(
(
(
12) Kruck, T.; Noack, M. Chem. Ber. 1964, 97, 1693.
13) Beach, N. A.; Gray, H. B. J. Am. Chem. Soc. 1968, 90, 5713.
14) Nakano, T. Bull. Chem. Soc. Jpn. 1977, 50, 661.
15) Bach, C. Thesis, University of Hannover, Hannover, Germany, 1999.
16) Kuchynka, D. J.; Kochi, J. K. Inorg. Chem. 1989, 28, 855.
17) Zhen, Y.; Feighery, W. G.; Lai, C.-K.; Atwood, J. D. J. Am. Chem.
Soc. 1989, 111, 7832.
(
18) Ehlers, A. W.; Ruiz-Morales, Y.; Baerends, E. J.; Ziegler, T. Inorg.
Chem. 1997, 36, 5031.
(
19) Finze, M.; Bernhardt, E.; Terheiden, A.; Berkei, M.; Willner, H.;
Christen, D.; Oberhammer, H.; Aubke, F. J. Am. Chem. Soc. 2002,
(22) Bauernschmitt, R.; Ahlrichs, R. J. Chem. Phys. 1996, 104, 9047.
(23) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution;
University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
124, 15385.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7211

Geier et al.
Table 1. Crystallographic Data for [Mn(CO)6][BF4]‚SO2 at 100 K
formula
molecular weight 373.87
C6BF4MnO8S
V [Å3]
Z
1210.70(5)
4
-
1
[g mol
]
color
space group
a [Å]
b [Å]
c [Å]
colorless
Cmc21
8.7001(2)
11.8497(3)
11.7437(3)
Fcalcd [g cm-3]
Θ range [deg]
2.051
3.38-31.53
0.0320
0.1106
1.098
a
R1 (I > 2σ)
b
wR2 (all data)
2
GOF on F
a
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(Fo2 - Fc ) /∑w(Fo ) ]
b
2 2
2 2 1/2
.
with SHELXL-97.24 Diffracted intensities were corrected for absorp-
tion based on indexed crystal faces, Tmin ) 0.87 and Tmax ) 0.95.
Experimental details and crystal data are collected in Table 1.
The CCDC reference no. is 644834. Crystallographic data in CIF
format can be obtained free of charge on application to the CCDC,
Figure 1. Structure of [Mn(CO)6]+ in [Mn(CO)6][BF4] (thermal ellipsoids
for 50% probability).
1
2 Union Road, Cambridge, U.K. (fax, (+44)-1223-336-033;
Table 2. Selected Bond Distances (Å) and Angles (deg)
e-mail: deposit@ccdc.cam.ac.uk).
The identity of the single crystal with the bulk material was
verified by comparison of the calculated and experimental powder
diffractograms of [Mn(CO)
porting Information, Figures S1 and S2). The latter was measured
Mn1-C1
1.899(3)
1.900(2)
1.914(2)
1.906(2)
O1-C1
1.112(3)
1.130(2)
1.119(3)
1.124(2)
89.21(7)
89.83(7)
89.1(1)
178.91(8)
91.03(7)
91.2(1)
Mn1-C2
O2-C2
Mn1-C3
Mn1-C4
O3-C3
O4-C4
6
][BF
4
] and [Mn(CO)
6
][BF
4
]‚SO
2
(Sup-
O1-C1-Mn1
O2-C2-Mn1
O3-C3-Mn1
O4-C4-Mn1
C1-Mn1-C2
C1-Mn1-C3
C1-Mn1-C4
177.8(3)
C2-Mn1-C3
C2-Mn1-C4
C2-Mn1-C2*
C2-Mn1-C4*
C3-Mn1-C4
C4-Mn1-C4*
177.2(2)
177.9(2)
178.0(2)
90.51(8)
179.6(1)
89.25(8)
on a Stoe STADI P powder diffractometer at room temperature.
The samplessolid [Mn(CO)
synthesis in HFswas sealed with excess SO
0.5 mm i.d.). The experimental powder pattern was indexed using
6 4
][BF ] obtained directly from the
2
in a glass capillary
(
the unit cell information from the single-crystal low-temperature
experiment. The lattice parameters at room temperature are a )
*
Note: -x, y, z.
8
.863(6) Å, b ) 12.025(7) Å, c ) 11.963(6) Å, and V ) 1275.0-
3
(18) Å , retaining the crystal system as orthorhombic.
affect the reaction rates. Strong Brønsted acids like
H[RCB11
syntheses of additional [Mn(CO)
The [(CF ) BF] , [BF ] , and [H F
room temperature and start to decompose endothermic at 160,
45, and 115 °C, respectively (DSC). [Mn(CO) ][BF ] was
decomposed at a vacuum line of known volume, connected
to an IR cell. The observed amounts of CO and sublimed
2
5
11
F ]
are expected to be likewise suitable for the
Results and Discussion
+
6
] salts.
Synthetic Aspects. The known multistep syntheses of
-
-
]- salts are stable at
3 3 4 2 3
+
I
[
Mn(CO)
6
] salts are based on the anion abstraction of Mn -
10,12
carbonyl derivatives (vide supra).
The aim of this study
1
6
4
was the development of a one-step synthesis starting from
+
Mn
analogy to [Co(CO)
according to the equations
2
(CO)10. We found that [Mn(CO)
6
] salts are formed in
+
9
5
]
by oxidative carbonylation in aHF
Mn
2
(CO)10 correspond to the stoichiometric equation
1
70 °C
0
.5 bar CO
4[Mn(CO) ][BF ]
8 Mn (CO) + 2Mn[BF ] + 14CO
6
4
2 10 4 2
Mn (CO) + 2HF + 2(CF ) BCO
8 2[Mn(CO)6]
2
10
3 3
(5)
RT
[
(CF ) BF] + H (2)
3 3 2
A second endothermic thermal event at about 190 °C may
be due to the decomposition of Mn[BF
4
Structural and Spectroscopic Aspects. [Mn(CO) ][BF ]
0
.6 bar CO
4 2
] .
Mn (CO) + 2HF + 2BF + 2CO
8 2[Mn(CO)6]
BF ] + H (3)
2
10
3
RT
6
[
crystallizes from sulfur dioxide solution as the monosolvate
4
2
+
[
Mn(CO)
6
][BF
4
]‚SO
2
. The [Mn(CO)
6
] cation (Figure 1) has
1
bar CO
RT
crystallographic C
angles are given in Table 2).
There are only slight deviations from octahedral symmetry.
The metal-carbon distances differ by up to 0.015(5) Å, while
the C-Mn-C angles deviate by up to 1.2(1)° from the ideal
s
symmetry (selected bond lengths and
Mn (CO) + 6HF + 2CO
8 2[Mn(CO) ][H F ] +
6 2 3
2
10
H (4)
2
While reactions 2 and 3 proceed within a few days, reaction
requires several weeks to achieve a 20% conversion. Pure
white products are easily obtained in the case of the
] salts after the removal of all volatile
materials in a dynamic vacuum, while the [H
slightly yellow due to the presence of remaining traces of
Mn (CO)10. The Lewis acids BF and (CF BCO increase
the concentration of the oxidizing species H
4
values of 90° and 180°, respectively. [Mn(CO)
6
][BF
4
]‚SO
2
is the first structurally characterized salt of the homoleptic
-
-
[
(CF
3
)
3
BF] and [BF
4
+
26
[
6 6 2
Mn(CO) ] cation and, after [Re(CO) ][Re F11], the second
-
F
2 3
] salt was
example of a structurally studied metal-carbonyl cation in
group 7.
2
3
3 3
)
+
2
F and therefore
(25) K u¨ ppers, T.; Bernhardt, E.; Eujen, R.; Lehmann, C. W.; Willner, H.
Angew. Chem., Int. Ed., in press.
(26) Bruce, D. M.; Holloway, J. H.; Russel, D. R. J. Chem. Soc., Dalton
Trans. 1978, 64.
(
24) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
7212 Inorganic Chemistry, Vol. 46, No. 17, 2007

Formation of Hexacarbonylmanganese(I) Salts
n
Table 3. Average M-C Bond Lengths, NMR Parameters, and Average νj (CO) and νj (MC) Wavenumbers of the Isoelectronic Species [M(CO)6] , M )
V, Cr, Mn, Fe and n ) -1, 0, 1, 2
[
V(CO)6]-
Cr(CO)6
[Mn(CO)6]+
[Fe(CO)6]2+
a,k
1.903(17)b,k
212
26.1
1.53
c,k
d(MC)/Å
δ C/ppm
1.947(16)
1.905(7)
200
126.7
1.909(5)
1
3
d
c,k
225
116
178
1
d
19.2c,k
J(CM)/Hz
g
21
K(CM) /10
1.46
1.70
1.97
-
2
-3
N A
m
h
-1
-1
e
f
f
f
c,k
νj (CO) /cm
1897
423
162
2029
414
118
2125
397
93
2209
369
41
i
e
e
c,k
c,k
νj (MC) /cm
j
-1
∆
ν(CO) /cm
a
DEZYUC, IYOPUH, TIRQAM, YATHAD. FOHCOU01, WOVHOE. c CEHHON, HOLMIE, HOLMOK. d Reference 35. Reference 36. f Reference
b
e
i
j
3
7. g Reduced coupling constants; magnetogyric ratios from ref 34. h (ν1 + 2ν3 + 3ν6)/6. (ν2 + 2ν4 + 3ν8)/6. (ν1 - ν6). k Average from CSD entries.
Standard uncertainties based on variance of sample. (CSD version 5.28, including Jan 2007 update).
a
Table 4. Observed and Calculated Band Positions and Band
Intensities of [Mn(CO)6][BF4]
Ramanb,d
IRc,d
νcalcd Icalcd(Raman) Icalcd(IR)
assignment
2
2
191 s
133 vs
2256
2198
098 vs 2184
204.8
290.0
0.0
0.0
0.0
984.3
ν1 A1g νs(CO)
ν3 Eg νs(CO)
ν6 T1u νas(CO)
2
1
1
1
1
0
1
-
103 sh
063 s
BF4 (ν3 T2)
-
BF4 (ν3 T2)
-
7
5
68 w
BF4 (ν1 A1)
ν7 T1u
6
34 s
639
26
0.0
0.0
141.6
0.0
5
ν10 T2g
-
21 vw
524w
BF4 (ν4 T2)
4
4
3
99 w
10 s
58 vw
507
393
0.0
0.0
0.0
27.2
ν12 T2u
ν8 T1u νas(MC)
-
BF4 (ν2 E)
3
3
86 sh
77 m
355
352
0.1
12.9
0.0
0.0
6.7
0.0
0.0
0.0
1.8
0.0
0.0
ν4 Eg νs(MC)
ν2 A1g νs(MC)
ν5 T1g
Figure 2. Correlation between C-O and Mn-C bond lengths in
manganese carbonyls. The regression line (rCO ) -0.37(4)rMnC + 1.83(7)
Å) is based on 63 values (indicated by small squares) with a correlation
coefficient of 0.62. The four values from [Mn(CO)6][BF4] are drawn as
triangles.
3
1
41
09
94
ν9 T1u
1
37 m-s
ν11 T2g
71
0.0
ν13 T2u
a
B3LYP/6-311+G(2d). Solid sample. c Neat powder between AgCl
b
The average lengths for terminal V-C, Cr-C, Mn-C,
and Fe-C bonds in metal carbonyls are 1.946, 1.866, 1.808,
-
1
d
disks, below 500 cm as Nujol mull between polyethylene disks. Key: s
strong, m ) medium, w ) weak, v ) very, sh ) shoulder.
)
27
and 1.782 Å, respectively. As expected, these lengths
decrease with increasing atomic number of the metal.
However, the M-C bond lengths in the series of the
+
[
Fe(CO)
6
]2 is clearly reflected in their vibrational spectra.
These show an increase in the averaged wavenumbers (IR,
Raman data) of the C-O stretching vibrations νj (CO), with
a concomitant decrease for the averaged M-C stretching
vibrations νj (MC) (Table 3). The diminishing electron delo-
calization between metal and ligands with increasing positive
charge is also indicated by the decrease of the separation
between the symmetric and asymmetric C-O stretching
vibrations (∆ν(CO)).
The anion bands of the three [Mn(CO)
identified by comparison to the published spectra of
[BF
can be observed in the Raman spectrum. The IR bands at
516 (m), 2337 (s), 1800 (vs), 1160 (s), and 1062 (vs) cm
agree quite well with those observed for the [H
-
+
isoelectronic carbonyls [V(CO)
and [Fe(CO) ]
6
6
] , Cr(CO)
6 6
, [Mn(CO) ] ,
2+
are in the rather narrow range between 1.95
and 1.90 Å (Table 3), thus pointing to the existence of two
opposing trends: (i) Metal atom radii diminish upon going
-
2+
from [V(CO)
6
]
6
to [Fe(CO) ] , and (ii) metal-ligand
backbonding decreases in the same direction, leading to
weaker metal-carbon bonding.
]+ salts are
6
The elongated Mn-C bonds in [Mn(CO)
6
][BF
4
2
]‚SO are
accompanied by correspondingly short C-O bonds. Perusal
-
30
- 9
- 31
-
of the CSD database28 shows a linear relation between the
4 3 3 2 3 2 3
] , [(CF ) BF] , and [H F ] . No bands of [H F ]
Mn-C and C-O distances in manganese carbonyls
-
1
2
(Figure 2).
-
2 3
F
] anion,
The values for [Mn(CO)
6 4 2
][BF ]‚SO , while lying at the
but the presence of higher poly(hydrogen) fluorides cannot
be excluded on grounds of the spectrum. However, such
species are known to be thermally unstable at room tem-
perature, and any excess of HF is removed during isolation.
The positions and relative intensities of the IR and Raman
end of the range of previously observed Mn-C distances,
still fit to this relation. Very recently, a comprehensive
database analysis of all transition metal-carbonyl bond
lengths has been published.29
32
The decrease in metal-ligand backbonding on going from
+
bands of the [Mn(CO)
6
] cation in the three salts are almost
-
+
6 6 6
V to Fe in the series [V(CO) ] , Cr(CO) , [Mn(CO) ] , and
(
30) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W.; Aubke, F.
(27) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
Inorg. Chem. 2005, 44, 4206.
G. J. Chem. Soc., Dalton Trans. 1989, S1.
28) Allen, F. H. Acta Crystallogr. 2002, B58, 380.
(31) Gennick, I.; Harmon, K. M.; Potvin, M. M. Inorg. Chem. 1977, 16,
2033.
(
(29) Hocking, R. K.; Hambley, T. W. Organometallics 2007, 26, 2815.
(32) Mootz, D.; Boenigk, D. Z. Anorg. Allg. Chem. 1987, 544, 159.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7213

Geier et al.
The distorted intensity pattern is due to quadrupole
relaxation and has been theoretically explained by Pople.33
Comparison of the reduced coupling constants K (Table 3)
shows an increase in spin-spin coupling upon going from
-
2+
[
V(CO)
6 6
] to [Fe(CO) ] . In the same direction, the chemi-
cal shift of the carbonyl atoms decreases, in line with a
34
reduction of the paramagnetic shielding term σpara
.
Figure 3. 13C NMR spectrum of [Mn(CO)6][BF4] in CD3NO2 solution at
room temperature.
Acknowledgment. Financial support by the Deutsche
Forschungsgemeinschaft (DFG) and the Fonds der Chemis-
chen Industrie is acknowledged.
identical. Ten of the 13 expected fundamentals have been
-
detected in the [BF
4
] salt. They are listed together with the
Supporting Information Available: Experimental and theoreti-
theoretical values from DFT calculations [B3LYP/6-311+G-
2d)] in Table 4. The three CO stretches are overestimated
cal X-ray powder pattern of [Mn(CO)
BF ]; IR and Raman spectra of [Mn(CO)
BF], and [Mn(CO) ][H F ]. This material is available free of charge
6
][BF
4
]‚SO
2
and [Mn(CO)
6
]-
(
[
4
6
][BF
4
], [Mn(CO)
6
][(CF ) -
3 3
by theory, but all other bands agree within a few wavenum-
bers. There is also excellent agreement with an earlier
6
2 3
via the Internet at http://pubs.acs.org.
1
1
complete vibrational analysis of [Mn(CO)
6
][PF
]+ as a fluoroantimonate
salt has been measured in the solid state at 195 ppm by the
6
].
IC700798Z
13
The C NMR signal of [Mn(CO)
6
(
33) Pople, J. A. Mol. Phys. 1958, 1, 168.
(34) Harris, R. K. NMR and the Periodic Table; Academic Press: London,
978.
35) Hoch, M.; Rehder, D. Inorg. Chim. Acta 1986, 111, L13.
15
55
MAS method, but spin-spin coupling to the Mn nucleus
1
5
(
I ) /
2
, 100%) could not be observed. In contrast, [Mn-
(
(
CO) ][BF
6
4
] dissolved in CD NO shows the fully resolved
3
2
13
(36) Abel, E. W.; McLean, R. A. N.; Tyfield, S. P.; Braterman, P. S.;
1
Walker, A. P.; Hendra, P. J. J. Mol. Spectrosc. 1969, 30, 29.
37) Jones, L. H.; McDowell, R. S.; Goldblatt, M. Inorg. Chem. 1969, 8,
sextet ( J ) 126.7 Hz) of the C resonance at 200 ppm
Figure 3).
(
(
2349.
7214 Inorganic Chemistry, Vol. 46, No. 17, 2007