Infrared spectra of CX3-MnX and CX2=MnX2 (X = H, F, Cl) prepared in reactions of laser-ablated manganese atoms with halomethanes

Article abstract of DOI:10.1021/om100791h

Small manganese insertion (CX₃-MnX) and methylidene (CX ₂=MnX₂) complexes, carrying the highest multiplicities (sextet and quartet) among the analogous group 3-12 metal complexes, are produced in laser-ablated Mn atom reactions with halomethanes and identified in matrix infrared spectra with isotopic shifts and DFT frequency calculations. The linear C-M-X structure of the Mn insertion complexes resembles that of Grignard reagent molecules unlike those of other transition-metal analogues except Fe, and the Mn-C bond bears high s character, on the basis of DFT calculations. The Mn methylidenes have planar structures, common among early transition-metal analogues, revealing that Mn has borderline properties between the early and late transition metals. The computed C-Mn bond lengths of the carbene complexes in the quartet states (1.855-1.872 A) are considerably shorter than those of the insertion complexes in the sextet states (2.057-2.120 A), which is likely due to the one-half π-bond order and large ionic contribution to bonding in the carbene complexes. The tendency of increasing preference for higher oxidation-state products on going down in a family group is most dramatic among the group 7 metals Mn and Re.

Full text of DOI:10.1021/om100791h

Organometallics 2011, 30, 477–486 477
DOI: 10.1021/om100791h
Infrared Spectra of CX3-MnX and CX2dMnX2 (X = H, F, Cl) Prepared
in Reactions of Laser-Ablated Manganese Atoms with Halomethanes
Han-Gook Cho and Lester Andrews*
Department of Chemistry, University of Incheon, 177 Dohwa-dong, Nam-ku, Incheon, 402-749, South Korea, and
Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville, Virginia 22904-4319,
United States
Received August 13, 2010
Small manganese insertion (CX3-MnX) and methylidene (CX2dMnX2) complexes, carrying the
highest multiplicities (sextet and quartet) among the analogous group 3-12 metal complexes, are produced
in laser-ablated Mn atom reactions with halomethanes and identified in matrix infrared spectra with
isotopic shifts and DFT frequency calculations. The linear C-M-X structure of the Mn insertion
complexes resembles that of Grignard reagent molecules unlike those of other transition-metal analogues
except Fe, and the Mn-C bond bears high s character, on the basis of DFT calculations. The Mn
methylidenes have planar structures, common among early transition-metal analogues, revealing that Mn
has borderline properties between the early and late transition metals. The computed C-Mn bond lengths
˚
of the carbene complexes in the quartet states (1.855-1.872 A) are considerably shorter than those of the
˚
insertion complexes in the sextet states (2.057-2.120 A), which is likely due to the one-half π-bond order
and large ionic contribution to bonding in the carbene complexes. The tendency of increasing preference for
higher oxidation-state products on going down in a family group is most dramatic among the group 7
metals Mn and Re.
Introduction
Mn electronegativity (1.55) is similar to those for Mg and Zn
(1.55 and 1.65).5
Manganese is an essential element in daily food consumption
and has important industrial uses, such as in steel production for
strength, hardness, and durability.1 Manganese nodules, pro-
duced from the hot volcanic waters, are found in large quantity
on the deep ocean floor and provide an important future natural
resource.2 This group 7 metal is cheap and toxicologically
benign, and it is the 12th most abundant element in the Earth’s
crust, the next transition metal after iron.3 Organomanganese
reagents are generally more stable than most organometallics
from other transition metals, which is a favorable property for
manganese-mediated reactions and catalytic activities.4
Since synthesis of the first organomanganese complex in
1937 to form phenylmanganese iodide from phenyllithium and
manganese(II) iodide, reactions of manganese halides with
orgnanolithium or organomagnesium compounds (transmeta-
lation) still remain a primary route to provide these first-row
transition-metal compounds.3 Manganese carbonyl derivatives
such as [BrMn(CO)5] and [LiMn(CO)5] are also precursors
to generate alkyl, aryl, and acyl products. The reactivities of
organomanganese compounds are often compared to those of
organomagnesium and organozinc compounds. Note that the
Several simple neutral manganese-bearing species that are
relevant to the present work have been studied. The reaction of
atomic manganese with CH4 or H2O yields CH3-MnH or
HMnOH following photoexcitation, but thermal Mn atoms
react spontaneously with CH2N2 to form MnCH2 in matrix
isolation investigations.6 Dimethyl manganese, methyl manga-
nese chloride, and other alkyl manganese species have been
synthesized by metathesis of Grignard reagents with manganese
chloride, but they decompose rapidly.7
The first examples of manganocene-carbene complexes have
been prepared by reaction of the sterically demanding nucleo-
philic carbenes 1,3-bis(2,6-dimethyl-4-bromophenyl)imidazol-2-
ylidene and 1,3-dimesitylimidazol-2-ylidene with manganocene.8a
(5) Comprehensive Organometallic Chemistry III; Mingos, M. P.,
Crabtree, R. H., Eds.; Elservier Ltd.: Oxford, U.K., 2007; Vols. 10 and 11.
(6) (a) Billups, W. E.; Konarski, M. M.; Hauge, R. H.; Margrave,
J. L. J. Am. Chem. Soc. 1980, 102, 7394 Mn þ CH4. (b) Kauffman, J. W.;
Hauge, R. H.; Margrave, J. L. J. Phys. Chem. 1985, 89, 3541 Mn þ H2O. (c)
Billups, W. E.; Chang, S.-C.; Margrave, J. L.; Hauge, R. H. Organometallics
1999, 18, 3551 Mn þ CH2N2.
(7) (a) Riemschneider, R.; Kassahn, H. G.; Schneider, W. Z. Nat-
urforsch. B 1960, 15, 547. (b) Beermann, C.; Clauss, K. Angew. Chem.
1959, 71, 627. (c) Tamura, M.; Kochi, J. J. Organomet. Chem. 1971, 29, 111
Mn alkyl complexes.
*Author to whom correspondence should be addressed. E-mail:
lsa@virginia.edu.
(1) http://www.webelements.com/manganese.
(2) Cronan, D. S. In Encyclopedia of Ocean Sciences; Steele, J.; Turekian,
K.; Thorpe, S., Eds.; Academic Press: San Diego, 2001; pp 1526-1533.
(3) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley-
VCH: Weinheim, Germany, 2003; Vol. 20, p 497.
(8) (a) Abernethy, C. D.; Cowley, A. H.; Jones, R. A.; Macdonald,
C. L. B.; Shukla, P.; Thompson, L. K. Organometallics 2001, 20, 3629.
(b) Braunschweig, H.; Burzler, M.; Radacki, K.; Seeler, F. Angew. Chem.,
Int. Ed. 2007, 46, 8071. (c) Ruiz, J.; Perandones, B. F.; Garc'a, G.; Mosquera,
M. E. G. Organometallics 2007, 26, 5687. (d) Swope, W. C.; Schaefer, H. F.,
III. Mol. Phys. 1977, 34, 1037. Xiang, H.; Yang, J.; Hou, J. G.; Zhu, Q. J.
Am. Chem. Soc. 2006, 128, 2310. Pandey, R.; Rao, B. K.; Jena, P.; Blanco,
M. A. J. Am. Chem. Soc. 2001, 123, 3799 Mn π-complexes.
(4) Cahiez, G.; Duplais, C.; Buendia, J. Chem. Rev. 2009, 109, 1434,
and references therein.
r
2011 American Chemical Society
Published on Web 01/12/2011
pubs.acs.org/Organometallics

478 Organometallics, Vol. 30, No. 3, 2011
Cho and Andrews
˚
This complex featured a C(1)-Mn(1) bond length of 2.227 A
from an X-ray crystal structure. Related derivative complexes
provided similar C-Mn bond lengths. The Mn carbene com-
plex [(η5-C5H5)(OC)2MndCPh2] has been formed through
borylene metathesis reactions.8b N-Heterocyclic carbene com-
plexes of Mn(I) have also been synthesized with a shorter
Table 1. Frequencies of Product Absorptions Observed from
Reactions of Mn with Fluoromethane Isotopomers in Excess
Argona
group
CH3F
CD3F
13CH3F
description
i
1157.6
918.4
1149.0
A1 CH3 deform
635.0, 628.8 628.3, 622.2 633.4, 627.4 A1 Mn-F stretch
576.0, 574.4 441.0, 436.6 572.5, 570.6 E CH3 rock
8c
˚
Mn-C bond length of 2.068 A. Simple manganese π-com-
plexes with C2H2, C2H4, and C6H6 have also been investigated
a All frequencies are in cm-1. The stronger matrix site split absorption
is bold. Description gives major vibrational coordinate. A1 and E denote
mode symmetry.
theoretically.8d
Recent reactions of laser-ablated transition metals with
small alkanes and halomethanes have introduced a variety of
small transition-metal complexes showing interesting structures
and photochemical reactions.9-15 Moreover, these transition-
metal reactions provide a very efficient means to form small
high-oxidation-state complexes with C-M multiple bonds.
While W, Re, and Os preferentially produce high-oxidation-
state complexes with C-M triple bonds,9,11,12 the higher-oxida-
tion-state complexes become less favored before and after them
in the transition-metal rows in the periodic table.9-14
In this study, reactions of manganese with halomethanes
have been investigated, and the products are identified in the
matrix infrared spectra through isotopic substitution and
with helpful predictions from DFT calculations for the
plausible products. These Mn complexes bear the highest
multiplicities among the group 3-12 metal complexes, and
they provide simple models for manganese carbene com-
plexes that can be explored theoretically. The insertion
complexes resemble those of the group 2 metal analogues,
the Grignard reagents.16
argon. The Nd:YAG laser fundamental (1064 nm, 10 Hz repetition
rate, 10 ns pulse width) was focused on a rotating metal target (Mn,
Johnson-Matthey) using 5-10 mJ/pulse. After initial reaction,
infrared spectra were recorded at 0.5 cm-1 resolution using a Nicolet
550 spectrometer with a Hg-Cd-Te range B detector. Then
samples were irradiated for 20 min periods by a mercury arc street
lamp (175 W) with the globe removed using a combination of
optical filters and annealed to allow further reagent diffusion.
To provide support for the assignment of new experimental
frequencies and to correlate with related works,9-15 density
functional theory (DFT) calculations were performed using
the Gaussian 03 program system,18 the B3LYP density func-
tional,19 and the 6-311þþG(3df,3pd) basis sets for H, C, F, Cl,
and Mn20 to provide vibrational frequencies for the reaction
products. Geometries were fully relaxed during optimization,
and the optimized geometry was confirmed by vibrational
analysis. The BPW91 functional21 was also employed to com-
plement the B3LYP results. The vibrational frequencies were
calculated analytically, and zero-point energy is included in the
calculation of binding and reaction energies. Previous investiga-
tions have shown that DFT-calculated harmonic frequencies are
usually slightly higher than observed frequencies,9-15,22,23 and
they provide useful predictions for infrared spectra of new
molecules.
Experimental and Computational Methods
Laser-ablated manganese atoms were reacted with CH3F
(Matheson), 13CH3F, CH2F2, CH2FCl, CH2Cl2, CD2Cl2,
13CH2Cl2 CHCl3, CDCl3, (MSD Isotopes), CFCl3, CF2Cl2
(Dupont), CCl4 (Fisher), 13CCl4 (90% enriched, MSD Isotopes),
CD3F, CD2FCl, and CD2F2 (synthesized17a) in excess argon during
condensation at 10 K using a closed-cycle refrigerator (Air Products
Displex). These methods have been described in detail in previous
publications.9,17b,c Reagent gas mixtures are typically 0.5% in
Results and Discussion
The matrix infrared spectra from reaction products of
laser-ablated manganese atoms with halomethanes have been
investigated, and the observed frequencies (Tables 1-4) and
their computed structures will be presented in turn. The DFT-
computed frequencies of the products are compared with the
observed values (Tables S1-S16), and parameters from natural
(9) (a) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and
references therein (review article, groups 4-6). (b) Lyon, J. T.; Cho, H.-G.;
Andrews, L. Organometallics 2007, 26, 2519 (Ti, Zr, Hf þ CHX3, CX4). (c)
Lyon, J. T.; Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 6373 (Cr,
Mo, W þ CHX3, CX4).
(18) 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.; Moroku-
ma, 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.; Challa-
combe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
(10) (a) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 2480.
(b) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633 (group 3).
(11) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 4098. (b)
Cho, H.-G.; Andrews, L. Inorg. Chem. 2008, 47, 1653 (Re).
(12) (a) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008,
27, 5241. (b) Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 2537.
(c) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 1786 (group 8).
(13) (a) Cho, H.-G.; Andrews, L. Organometallics 2009, 28, 5623 (Ni
þ CX4). (b) Cho, H.-G.; Andrews, L.; Vlaisavljevich, B; Gagliardi, L.
Organometallics 2009, 28, 6871 (Pd þ CX4). (c) Cho, H.-G.; Andrews, L.
J. Am. Chem. Soc. 2008, 130, 15836. (d) Cho, H.-G.; Andrews, L.
Organometallics 2009, 28, 1358. (e) Cho, H.-G.; Andrews, L. J. Phys.
Chem. A 2008, 112, 12293 (group 10).
(14) (a) Cho, H.-G.; Andrews, L. Organometallics 2010, 29, 2211 (Rh
þ CX4). (b) Cho, H.-G.; Andrews, L. Dalton Trans. 2010, 39, 5478 (Ir þ
CX4). (c) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2010, 114, ASAP (Co
þ CX4).
(15) (a) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796. (b)
Cho, H.-G.; Lyon, J. T.; Andrews, L. J. Phys. Chem. A 2008, 112, 6902. (c)
Lyon, J. T.; Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 1047
(actinides).
(19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
Y.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(20) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062.
(21) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Burke, K.;
Perdew, J. P.; Wang, Y. In Electronic Density Functional Theory: Recent
Progress and New Directions; Dobson, J. F., Vignale, G., Das, M. P., Eds.;
Plenum: New York, 1998.
(16) Bare, W. D.; Andrews, L. J. Am. Chem. Soc. 1998, 120, 7293.
(17) (a) Isotopic modifications synthesized: Andrews, L.; Willner,
H.; Prochaska, F. T. J. Fluorine Chem. 1979, 13, 273. (b) Andrews, L.;
Citra, A. Chem. Rev. 2002, 102, 885, and references therein. (c) Andrews, L.
Chem. Soc. Rev. 2004, 33, 123, and references therein.
(22) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.
(23) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937.

Article
Organometallics, Vol. 30, No. 3, 2011 479
Table 2. Frequencies of Product Absorptions Observed from Reactions of Mn with Dihalomethanes in Excess Argona
group
CH2F2
CD2F2
CH2FCl
CD2FCl
CH2Cl2
CD2Cl2
13CH2Cl2
description
i
921.1
642.5, 639.9 638.0, 636.2
558.6
910.3, 906.8, 546.3, 540.0
539.0
651.2, 650.0, 636.5 649.8, 642.0
564.3
545.3, 541.3 551.8
A00 C-X str.
A Mn-X str.
A00 CH2 rock
A0 C-M str.
526.9
542.1
536.7
459.7, 457.5, 455.3
736.6
589.2
600.9
539.0
525.1
510.8
577.0
507
m
746.1
740.7
626.9
589.2
736.4
584.1, 583.5
603.7
693.9
700.6
609.5
682.0
581.8
459.5, 457.4, 455.0 MnX2 as. str.
covered
563.9
CH2 wag
C-Mn str.
CH2 rock
a All frequencies are in cm-1. Stronger absorptions in a set are bold. Description gives major vibrational coordinate: str. = stretch; as. str. =
antisymmetric stretch.
0.972, 0.988, and 0.999 of the B3LYP-computed frequencies as
shown in Table S1, substantiating formation of this C-F bond
activation insertion complex. The Grignard-type primary pro-
duct is also the most stable among the plausible ones.
CH3-MnF (S for sextet, 6A1) and CH2dMnHF (Q for quartet)
are 58 and 8 kcal/mol lower energy than the ground-state
reactants (Mn(6S) þ CH3F), while CH2F-MnH (singlet) is
6 kcal/mol higher.
Table 3. Frequencies of Product Absorptions Observed from
Reactions of Mn with Trichloromethane Isotopomers in Excess
Argona
group
CHCl3
CDCl3
459.9
description
m
586.7
478.5
436.6
501.2, 491.5
C-H oop bend
C-Mn str.
MnCl2 as. str.
428
477.3, 468.1
h
higher order complex
The unobserved higher energy CH2dMnHF (Q) complex
shows no evidence of agostic distortion, as illustrated in Figure 2,
in contrast to the analogous group 4, 5, and 6 methylidenes, but
the H atom bonded to Mn is tilted back toward carbon, similar
to the case of the Fe analogue.12 Clearly, H migration from C to
Mn to form CH2dMnHF is not energetically favorable. Evi-
dently the stability of a small methylidene complex carrying an
Mn-H bond relative to the insertion complex decreases on
going to the right side of the periodic table in the first-row
transition metals. CH2dMHX is observed in the Sc, Ti, and V
matrix spectra along with CH3-MX during co-deposition with
methyl halides and on subsequent photolysis, whereas only the
insertion products are identified in later first-row transition-
metal experiments.6,9-14,27 It is also notable that Re, another
group 7 metal, exclusively produces methylidyne complexes via
H migration in reactions with small alkanes and halomethanes.11
Mn þ CH2X2. Product absorptions from reactions of Mn
with dihalomethane (CH2F2, CH2FCl, and CH2Cl2) isotopo-
mers are given in Table 2. Both methylidene (m) and insertion (i)
complex absorptions are observed unlike the fluoromethane
(CH3F) case. The CH2F2 isotopomer spectra in Figure 3 show
the i and m absorptions increase ∼35% and ∼25% on visible
irradiation, but they remain unchanged on subsequent UV
irradiation. They sharpen in the early stages of annealing but
decrease on higher annealings. The product absorption at
699.5 cm-1 observed in the spectra with difluoromethane does
not show intensity variation upon photolysis, unlike other Mn
product absorptions, and agrees with the 699.4 cm-1 band
identified as the antisymmetric stretching mode of the MnF2
molecule isolated in solid argon.28a Hence, Mn atoms clearly
activate the C-F bond in fluoromethanes.
a All frequencies are in cm-1. Description gives major coordinate.
bond order analysis for the Mn-C bond of the insertion
products are given (Table S17) as Supporting Information. A
number of bands are common to laser-ablated metal experi-
ments with each precursor, and these are due to precursor
photolysis products that have been identified previously.9-15
For each precursor the observed bands are grouped by photo-
lysis and annealing behavior, and the vibrational modes are
assigned on the basis of isotopic shifts and correlation with
DFT-calculated vibrational frequencies and intensities for a
particular new product molecule.
Mn þ CH3F. The product absorptions all marked “i” (for
insertion product) from reactions of Mn with CH3F isotopo-
mers are shown in Figure 1. They increase ∼5% and ∼20% on
visible and UV irradiations and gradually decrease on annealing.
This information shows that irradiation is required to initiate
further reaction and that cold reagents do not react on annealing
the matrix sample. The frequencies of the observed product
absorptions are listed in Table 1 and compared with calculated
frequencies for the anticipated CH3-MnF product in Table S1.
No Mn-H stretching absorptions expected near 1600 cm-1 are
observed in these Mn þ CH3F spectra nor in other Mn product
spectra reported here, indicating that products with Mn-H
bonds are not generated in the reactions with halomethanes.24
Deuteration and 13C substitution shift the i absorption at 1157.6
cm-1 to 918.4 and 1149.0 cm-1 (H/D and 12/13 ratios of 1.260
and 1.007), which are characteristic of a CH3 deformation mode
of the insertion complex (CH3-MnF). The strong i absorption
at 635.0 cm-1 with small isotopic shifts is assigned to the Mn-F
stretching mode, and another absorption at 574.4 cm-1 is
appropriate for the CH3 rocking mode. CH3-MnF has the
C3v structure shown in Figure 2, which is similar to that of
CH3-MgCl,25 but in contrast to the Cs structures for previously
reported transition-metal insertion complexes.9-15
The i absorption at 921.1 cm-1, with D counterpart at
906.8 cm-1, is assigned to the C-F stretching mode of CH2F-
MnF. The strongest iabsorption is observed at 639.9 cm-1 along
with its D counterpart at 636.2 cm-1, and it is assigned to the
Mn-F stretching mode. Mode analysis shows that the Mn-F
stretching mode coupled with the C-Mn stretching mode,
CH3-MnF, therefore, has four parallel (A1) and four per-
pendicular (E) bands. The observed bands are the strongest ones
computed for CH3-MnF, and the observed frequencies are
(26) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899, and references therein.
(24) Andrews, L.; Wang, X. J. Phys. Chem. A 2003, 107, 4081 Mn þ
H2.
(25) (a) Kauffmann, T.; Bisling, M. Tetrahedron Lett. 1984, 25, 293.
(b) Cahiez, G.; Alami, M. Tetrahedron Lett. 1986, 27, 569 Grignard reagent.
(27) Chang, S.-C.; Hauge, R. H.; Kafafi, Z. H.; Margrave, J. L.;
Billups, W. E. J. Chem. Soc., Chem. Commun. 1987, 1682.
(28) (a) Van Leirsburg, D. A.; DeKock, C. W. J. Phys. Chem. 1974,
78, 134. (b) Vogt, N. J. Mol. Struct. 2001, 570, 189 MnF2.

480 Organometallics, Vol. 30, No. 3, 2011
Cho and Andrews
Table 4. Frequencies of Product Absorptions Observed from Reactions of Mn with Tetrahalomethanes in Excess Argona
group
CF4
CF3Cl
13CF3Cl
CCl4
13CCl4
description
i
1078.4 (CF3-MnCl)
covered (CF3-MnCl)
1050.5 (13CF3-MnCl)
covered (13CF3-MnCl)
CX3 str.
CX3 str.
947.0
674.9
covered
CF3 deform
Mn-F str.
CX2 s. str.
CX2 as. str.
MnX2 as. str.
CX2 s. str.
CX2 as. str.
MnX2 str.
415 (CF3-MnCl)
415 (13CF3-MnCl)
m
1299.6 (CF2dMnFCl)
covered (CF2dMnFCl)
649.9 (CF2dMnFCl)
1226.4 (CF2-MnFCl)
covered (CF2-MnFCl)
622.6 (CF2-MnFCl)
1267.3 (13CF2dMnFCl)
covered (13CF2dMnFCl)
649.9 (13CF2dMnFCl)
1195.5 (13CF2-MnFCl)
covered (13CF2-MnFCl)
622.5 (13CF2-MnFCl)
860.9
460.8, 458.3
834.3
460.8, 458.2
720.7
m0
a All frequencies are in cm-1. Stronger absorptions in a set are bold. Description gives major vibrational coordinate: str. = stretch; s. = symmetric,
a. = antisymmetric. The m and m0 labels denote methylidene isomers.
Figure 1. Infrared spectra in the 1200-800 and 700-500 cm-1 regions for the reaction products of laser-ablated manganese atoms
with methyl fluoride isotopomers (0.5% in argon) at 10 K. (a) Mn and CH3F co-deposited for 1 h, (b) after visible (λ > 420 nm)
irradiation, and (c) after UV (240-380 nm) irradiation. (d) Mn and CD3F co-deposited for 1 h. (e, f) Spectra taken after visible and UV
irradiations. (g) Mn and 13CH3F co-deposited for 1 h and (h) after UV irradiation. i stands for the product absorption. HCF is
produced in CH3F reactions due to the ablation plume irradiation. P and c designate the precursor and common absorptions.
making it the C-Mn-F antisymmetric stretching mode. The
C-Mn-F symmetric stretching mode expected near 470 cm-1
is, however, not observed due to low intensity. Another i
absorption at 558.6 cm-1 is designated as the CH2 rocking
mode. The observed absorptions are the strongest bands pre-
dicted for the C-F insertion complex as shown in Table S2, and
the observed frequencies correlate with the B3LYP values of
923.4, 643.3, and 562.0 cm-1, substantiating the generation of
CH2F-MnF.
The identified CH2F-MnF(S) and CH2dMnF2(Q) are 43
and 48 kcal/mol more stable than the ground-state reactants
(Mn(6S) þ CH2F2), and we find a sextet transition state CH2-
(F)-MnF 25 kcal/mol lower than reactants but 18 kcal/mol
higher than the sextet insertion product and 6 kcal/mol higher
than the excited CH2-MnF2(sextet), which ultimately relaxes
to the CH2dMnF2(Q) ground state. In contrast, the excited
CH2F-MnF(Q), CH2dMnF2(doublet), and CH2-MnF2-
(sextet) are only 8, 11, and 31 kcal/mol more stable, respectively,
than reactants. The sextet ground state of CH2F-MnF and its
almost linear C-Mn-F moiety shown in Figure 2 resemble the
structure of CH3-MnF. Moreover, our computed structures
show that the Mn insertion products all carry linear or near linear
C-Mn-X moieties, and they all have the sextet ground states.
In the Mn þ CH2FCl spectra, Figure S1, both the i and m
absorptions remain unchanged on visible irradiation, but the i
absorptions double on UV irradiation and the m absorptions
increase ∼30%. The strongest i absorption is observed at
650.0 cm-1 along with its D counterpart at 546.3 cm-1 and is
assigned to the Mn-F stretching mode of CH2Cl-MnF. Ano-
ther iabsorption at 546.3 cm-1 with D counterpart at 539.0 cm-1
is designated to the C-Cl stretching mode, and the absorption at
526.9 cm-1 is assigned to the CH2 rocking mode.
The strongest m absorption observed at 746.1 cm-1 with D
counterpart at 736.4 cm-1 is assigned to the antisymmetric
MnF2 stretching mode of CH2dMnF2. The second m
absorption is observed at 740.7 cm-1, and deuteration
shifts it to 583.5 cm-1 (H/D ratio of 1.269) for the CH2
wagging mode. The m absorption at 626.9 cm-1 has a D
counterpart at 603.7 cm-1, and it is assigned to the C-Mn
stretching mode, which is coupled with the symmetric
MnF2 stretching mode. These three m absorptions sup-
port the formation of CH2dMnF2. Note that the B3LYP
and BPW91 functional antisymmetric MnF2 stretching
mode calculations bracket the observed value (Table S3),
which is in satisfactory agreement for this high-multi-
plicity transition-metal species.

Article
Organometallics, Vol. 30, No. 3, 2011 481
Figure 2. B3LYP structures of the Mn insertion and methylidene products from reactions with mono- and dihalomethanes. The
˚
6-311þþG(3df,3pd) basis sets are used for H, C, F, Cl, and Mn. Bond distances and angles are in A and deg.
stretching frequency originates from the Cl-bridged struc-
ture of CH2Cl-MnF (Figure 2), leading to a weaker C-Cl
bond. The Cl-bridged structure is in fact common for late
transition-metal insertion complexes, particularly with
C-Cl bonds.12-14
While CH2Cl-MnF is clearly observed in the Mn þ
CH2FCl spectra, CH2F-MnCl is not identified. The strong
C-F stretching absorption for CH2F-MnCl expected at
∼900 cm-1 is not observed, and the product frequencies do
not agree with the predicted values for CH2F-MnCl. The
complexes with an M-Cl bond are normally favored over
the conformers with an M-F bond, due to the stronger C-F
bond than the C-Cl bond.9-15 Evidently the preference is
reversed in this Mn case. CH2Cl-MnF is favored over
CH2F-MnCl in preference for the structure with bridging
Cl (Figure 2), which is also consistent with the computations
showing that CH2F-MnCl and CH2Cl-MnF are 52 and
56 kcal/mol more stable than the reactants (Mn (6S) þ
Figure 3. Infrared spectra in the 1000-500 cm-1 region for the
CH2FCl).
reaction products of laser-ablated manganese atoms with
The strongest m absorption in the CH2FCl spectra at
CH2F2 and CD2F2 (0.5% in argon) at 10 K. (a) Mn and
693.9 cm-1 with D counterpart at 682.0 cm-1 is assigned to
CH2F2 co-deposited for 1 h, (b) after visible (λ > 420 nm)
the Mn-F stretching mode of CH2dMnFCl. Another m
irradiation, and (c) after UV (240-380 nm) irradiation. (d) Mn
and CD2F2 co-deposited for 1 h, (e) after visible (λ > 420 nm)
irradiation, and (f) after UV (240-380 nm) irradiation. i and m
stand for the product absorption groups, while P and c designate
the precursor and common absorptions.
absorption on the blue side at 700.6 cm-1 shifts to 581.8 cm-1
on deuteration, which is appropriate for the CH2 wagging
mode. On the low-frequency side, the m absorption at
609.5 cm-1 is assigned to the C-Mn stretching mode. The
observed m frequencies are in good agreement with the DFT
values for planar CH2dMnFCl (55 kcal/mol more stable
than the reactants), as shown in Table S6, which is also
energetically comparable with CH2Cl-MnF.
The three observed absorptions are in fact the three
strongest bands of CH2Cl-MnF (Table S5), substantiating
formation of the insertion complex. The relatively low C-Cl

482 Organometallics, Vol. 30, No. 3, 2011
Cho and Andrews
On the other hand, the m absorptions decrease slightly on
visible and UV irradiations, respectively. The strongest m
absorption is observed at 736.6 cm-1 in an area congested
with precursor absorptions (not shown), with D counterpart
at 577.0 cm-1 (H/D ratio of 1.277). It is designated as the
CH2 wagging mode of CH2dMnCl2. The m absorption at
600.9 cm-1 with its D counterpart at 507 cm-1 (H/D ratio of
1.185) is assigned to the CH2 rocking mode. The m absorp-
tion at 589.2 cm-1 is assigned to the C-Mn stretching mode.
A triplet of m absorptions at 459.7, 457.5, and 455.3 cm-1
with an intensity ratio of 9:6:1 again for the vibration of two
equivalent chlorine atoms falls just below that for isolated
MnCl2 and shows negligible 13C shifts. These bands are
assigned to the MnCl2 antisymmetric stretching mode of
CH2dMnCl2. The observed frequencies are in good correla-
tion with the B3LYP values (Table S8), which substantiates
the formation of CH2dMnCl2.
Mn þ CHCl3. Shown in Figure S2 are the product
absorptions in the infrared spectra from reactions of Mn with
CHCl3 and CDCl3. The relatively weak product absorptions (all
marked with “m”) halve on visible irradiation and recover on
UV and full arc irradiations. No insertion product absorptions
are identified, but their computed frequencies are listed in
Table S9. Another group of product absorptions marked “h”
increase gradually during photolysis and significantly in the
early stage of annealing. They probably originate from a higher-
order or aggregate product. The m absorptions are tentatively
assigned to CHCldMnCl2(Q) (Table S10). The m absorptions
at 586.7 and 436.6 cm-1 along with their D counterparts at 459.9
and 428 cm-1 are assigned to the C-H out-of-plane bending
and MnCl2 antisymmetric stretching modes of CHCldMnCl2.
CHCldMnCl2(Q) is also slightly more stable than CHCl2-
MnCl(S) (68 and 66 kcal/mol more stable than the reactants),
but the insertion product is not observed here.
Figure 4. Infrared spectra in the 620-420 cm-1 region for the
reaction products of the laser-ablated manganese atom with
CH2Cl2 isotopomers (0.5% in argon) at 10 K. (a) Mn and
CH2Cl2 co-deposited for 1 h, (b) after visible (λ > 420 nm)
irradiation, and (c) after UV (240-380 nm) irradiation. (d) Mn
and CD2Cl2 co-deposited for 1 h, (e) after visible (λ > 420 nm)
irradiation, and (f) after UV (240-380 nm) irradiation. (g) Mn
and 13CH2Cl2 co-deposited for 1 h, (h) after visible (λ > 420 nm)
irradiation, and (i) after UV (240-380 nm) irradiation. i and m
designate the product absorption groups. The absorptions as-
signed to MnCl2 are also shown.
Figure 4 shows product absorptions from reactions of Mn
with CH2Cl2 isotopomers, where both i and m absorptions
are observed. The i absorptions increase 15% and 30% on
visible and UV irradiations, respectively, and decrease on
annealing. The strongest i absorption is observed at 564.3
cm-1, and deuteration and 13C substitution shift it to 545.3
and 551.8 cm-1 (H/D and 12/13 ratios of 1.034 and 1.023). It
is assigned to the C-Cl stretching mode of CH2Cl-MnCl.
The insertion complex also has a bridged structure, resulting
in the relatively low C-Cl stretching frequency. The i ab-
sorption at 542.1 cm-1 has its 13C counterpart at 539.0 cm-1
for the CH2 rocking mode. On the red side, another i absorp-
tion is observed at 536.7 cm-1, with D and 13C counterparts
at 510.8 and 525.1 cm-1, and is assigned to the C-Mn
stretching mode. The observed i absorptions are the stron-
gest bands for CH2Cl-MnCl (Table S7).
Mn þ CX4. Figure S3 compares infrared spectra from
reactions of Mn atoms with CF4, CF3Cl, and 13CF3Cl. In the
CF4 spectra, the product absorptions show essentially no
change in the process of photolysis. The i absorption ob-
served at 947.0 cm-1 is assigned to the antisymmetric CF3
stretching mode of CF3-MnF. This insertion complex bears
a C3v structure, as shown in Figure 5, and the strongest
infrared absorption is the above mode computed at 998.2
cm-1 (Table S11). The weaker symmetric counterpart com-
puted at 1145.7 cm-1 is probably masked by the CF2
photolysis product band at 1102 cm-1 30
In the low-fre-
.
quency region a weaker i absorption is observed at 674.9
cm-1 for the CF3 deformation mode. The Mn-F stretching
absorption expected at ∼620 cm-1 is probably covered by
the CF4 precursor absorption at this position. These two
observed absorptions support the formation of CF3-MnF.
The weak m absorption observed in the MnF2 region at
720.7 cm-1 is tentatively assigned to the MnF2 antisym-
metric stretching mode of CF2dMnF2 on the basis of good
agreement with the DFT value (e.g., B3LYP frequency 748.9
cm-1 in Table S12) and its appearance just above MnF2 at
699.5 cm-1, while the CF2 stretching absorptions are not
observed, likely due to masking by strong C-F stretching
absorptions common to the CF4 experiments with laser-
ablated metals. Importantly CF3-MnF and CF2dMnF2 in
their sextet and quartet ground states are 43 and 38 kcal/mol
more stable than the reactants.
The absorptions at 476.4, 473.4, and 471.1 cm-1 observed
in the CH2Cl2 isotopomer spectra with an intensity ratio of
9:6:1 (the statistical ratio for 2 ꢀ 35Cl, 35Cl þ 37Cl, and 2 ꢀ
37Cl in natural abundance for the vibration of two equivalent
chlorine atoms) are appropriate for the MnCl2 product of the
reaction of Mn with halomethanes containing at least two Cl
atoms: this chlorine isotopic triplet for MnCl2 agrees (within
0.5 cm-1) with previous argon matrix spectra.29a The for-
mation of MnCl2 confirms activation of the C-Cl bond by
Mn in these experiments.
(29) (a) Thompson, K. R.; Carlson, K. D. J. Chem. Phys. 1968, 49,
4379. (b) Hargittai, M.; Subbotina, N. Y.; Kolonits, M.; Gershikov, A. G.
J. Chem. Phys. 1991, 94, 7278 MnCl2.
(30) Jacox, M. E. J. Phys. Chem. Ref. Data 1994, Monograph 3; 1998,
27 (2), 115, Supplement B, 2003, 32, 1.

Article
Organometallics, Vol. 30, No. 3, 2011 483
Figure 5. B3LYP structures of the Mn insertion and methylidene products from reactions with tri- and tetrahalomethanes. The
˚
6-311þþG(3df,3pd) basis sets are used for C, F, Cl, and Mn. Bond distances and angles are in A and deg. The Cl-C-Mn-Cl dihedral
angles for CHCldMnCl2 and CCl2dMnCl2 are also shown.
In the CF3Cl and 13CF3Cl spectra, new absorptions are
observed, marked “i, m, and m0 (for m structural isomer)”,
respectively, and they are assigned to CF3-MnCl(sextet),
CF2dMnFCl(quartet), and CF2-MnFCl(sextet). The i ab-
sorptions increase ∼0%, ∼10%, and ∼20% on visible, UV,
and full arc photolysis and gradually decrease on annealing.
The m absorptions increase together ∼0%, ∼10%, and ∼10%
on visible, UV, and full arc photolysis and gradually decrease on
annealing. The m0 absorptions increase ∼10%, ∼50%, and
∼40% on visible, UV, and full arc photolysis, respectively, and
sharpen in the early stage of annealing.
The i absorptions observed at 1078.4 (shoulder) cm-1 and
the 13C counterparts at 1050.5 (shoulder) and 975.0 cm-1 are
assigned to the CF3 stretching mode of CF3-MnCl (Table S14).
Another i absorption is observed at 415 cm-1 (not shown), with
no 13C shift, and it is assigned to the Mn-Cl stretching mode.
These are the strongest observable bands for the insertion
complex with a C3v structure shown in Figure 5 (Table S13).
The m absorption at 1299.6 cm-1 carries a 13C counterpart
at 1267.3 cm-1, and its relatively high frequency suggests a
higher-oxidation-state complex, leading to an assignment to the
CF2 symmetric stretching mode of CF2dMnFCl in the quartet
state. The weak m absorption at 649.9 cm-1 shows a negligible
13C shift, and therefore, it is assigned to the Mn-F stretching
mode. The m0 absorption at 1226.3 cm-1 has its 13C counterpart
at 1195.5 cm-1 and is tentatively assigned to the CF2 symmetric
stretching mode of the distorted CF2-MnFCl molecule in the
sextet state as shown in Table S15. The CF2 antisymmetric
stretching absorption expected near 1165 cm-1 is most prob-
ably covered by precursor absorption in this congested area. A
strong m0 absorption is observed at 622.5 cm-1 in the relatively
clean region and shows negligible 13C shift. It is assigned to
the Mn-F stretching mode. These conformers (CF3-MnCl,
CF2dMnFCl, and CF2-MnFCl) are energetically comparable
(60, 51, and 57 kcal/mol more stable than the reactants,
respectively), and trapping of both of the last two is reasonable
owing to their different structures.
Figure 6 shows the product spectra from reactions of Mn
with CCl4 and 13CCl4, where only m absorptions are ob-
mediate species common to experiments with CCl4.12-14,30 The
m absorptions increase approximately 30% and 70% on visible
and UV photolysis and decrease on annealing. The broad m
absorption at 860.9 cm-1 shifts to 834.3 cm-1 on 13C substitu-
tion (12/13 ratio of 1.032). In the low-frequency region, another
m absorption is observed at 460.9 cm-1 (with a shoulder at
458.3 cm-1), and it shows a negligible 13C shift. This band is just
below that for MnCl2 and CH2dMnCl2 assigned above, and
the shoulder is appropriate for the mixed chlorine-35,37 com-
ponent in the triplet for two equivalent chlorine atoms. They are
assigned to the CCl2 and MnCl2 antisymmetric stretching
modes of CCl2dMnCl2 on the basis of the frequencies and
appropriate 13C shifts for these modes.
These are the strongest bands for the Mn tetrachloro
methylidene, and the observed frequencies are in reasonable
agreement with the DFT values shown in Table S16. The
observed CCl2 stretching frequencies higher than the DFT

484 Organometallics, Vol. 30, No. 3, 2011
Cho and Andrews
Figure 6. Infrared spectra in the 1000-800 and 600-400 cm-1 regions for the reaction products of the laser-ablated manganese atom
with CCl4 and 13CCl4 (0.5% in argon) at 10 K. (a) Mn and CCl4 co-deposited for 1 h, (b) after visible (λ > 420 nm) irradiation, and (c)
after UV (240-380 nm) irradiation. (d) Mn and 13CCl4 co-deposited for 1 h, (e) after visible (λ > 420 nm) irradiation, and (f) after UV
(240-380 nm) irradiation. m designates the methylidene product absorption. The CCl3 and Cl2-CCl-Cl absorptions are produced
from the precursor by ablation plume radiation.
values are not unusual for the tetrahalo transition-metal
carbenes and carbynes probably due to underestimation of
the stretching frequencies by the DFT methods.12-14 The
CCl2dMnCl2 carbene and the unidentified CCl3-MnCl in
the quartet and sextet ground states are energetically com-
parable (78 and 74 kcal/mol more stable than the reactants).
However, CCl3-MnCl would show a strong CCl3 antisym-
metric stretching band near 640-620 cm-1, based on DFT
calculations, which is not observed in this study.
Structure and Bonding in Small Mn Complexes. The struc-
tures of the Mn insertion and carbene complexes investigated
here are illustrated in Figures 2 and 5. These Mn insertion
and carbene complexes are computed to have sextet and
quartet ground states in line with the quintet and triplet
grounds states for the previously studied Cr and Fe insertion
and carbene products.9,12 The Re carbyne complexes, which
are exclusively produced in reactions with small alkanes and
halomethanes, have doublet ground states.11 These Mn
insertion and methylidene complexes, therefore, have the
highest multiplicities among the group 3-12 metal com-
plexes produced from reactions with small alkanes and
halomethanes.
It is also interesting that the Mn insertion complexes have
a linear or near linear C-M-X moiety, parallel to that of the
Grignard reagent,16,25 and high Mn s character in the C-Mn
single bond based on NBO calculations (Table S17). Among
the previously studied small transition-metal insertion com-
plexes, only the Fe products have the linear C-M-X
moiety.9-14 The CH3-MnF, CF3-MnF, and CF3-MnCl
complexes have C3v structures as illustrated in Figures 2 and
5, similar to the Fe counterparts.12a However, the Mn
insertion complexes with a C-Cl bond all have bridged
structures. No Mn product with bridging F, similar to
CH2F-NiCl, is observed, reconfirming that the larger more
polarizable Cl is more effective than F to form a bridged
structure between C and Mn. The sextet ground state along
with the C3v structure of CH3-MnF indicate promotion of a
4s electron, and NBO26 calculations show a contribution of s
(65.7%) and d (33.7%) from Mn in the Mn-C bond. In
comparison, the Mg-C bond of CH3-MgCl has mostly s
character (97.9%) from Mg.
In order to supplement the DFT-based NBO calculations,
a complete active-space self-consistent-field (CASSCF) (9,9)
calculation was done for CH3-MnF. The nine orbitals are
1 from C and 1 from Mn forming σ and σ* C-M bonds, 5 3d-
orbitals from Mn, 1 p-orbital from F (2pz), and 1 p-orbital
from Mn (4pz) mixed with other orbitals forming a C, Mn, F
molecular orbital. The 9 electrons (1 from C, 7 from Mn,
1 from F) occupy the 9 CAS orbitals illustrated in Figure 7,
and the given occupation numbers are consistent with the
NBO results. The C-Mn bond order [bonding minus anti-
bonding electron occupancies divided by 2] is 0.97. In addi-
tion, these calculations show that one electron essentially
moves from Mn toward F, occupying the 2pz-orbital of F
(the two other 2p-orbitals of F, not shown, are also doubly
filled). This result demonstrates that CH3-MnF is basically
a single-configuration problem.
The Mn methylidene complexes identified here are mostly
planar like the previously studied early transition-metal
methylidene complexes through Cr.9,10 In contrast the late
transition-metal methylidene complexes including Fe have
instead staggered allene-type structures.12-14 The unidenti-
fied Re methylidene complexes would also have staggered
structures, suggesting that these small group 7 complexes
show borderline characteristics between the early and late
transition-metal compounds. CHCldMnCl2, on the other
hand, has a near planar structure (Φ(ClCMnCl) = 12.0°),
probably due to repulsion between large Cl atoms bonded to C

Article
Organometallics, Vol. 30, No. 3, 2011 485
Figure 7. CASSCF orbitals using a (9,9) active space for
CH3-MnF calculated at the B3LYP minimum and plotted with
isodensity 0.02 e/A . The occupation numbers are given in
3
˚
parentheses: the C-Mn bond order is 0.97. The z axis is the
molecular axis, the molecular plane is the yz plane, and the x axis
is perpendicular to the molecular plane.
and to Mn, leading to distortion along the C-Mn bond. More
distortion along the C-Mn bond is observed in CCl2dMnCl2,
with a C2 structure and Cl-C-Mn-Cl dihedral angle of 53.4°.
The computed C-Mn bond lengths of the carbene com-
˚
plexes in the quartet states (1.855-1.872 A) are considerably
shorter than those of the insertion complexes in the sextet states
˚
(2.057-2.120 A) and bond lengths measured for ligated man-
8a,c
˚
ganese carbene complexes (2.068 and 2.227 A).
NBO cal-
Figure 8. CASSCF orbitals using an (11,12) active space involved
in the carbon-manganese bond for CH2dMnF2 calculated at the
B3LYP minimum and plotted with isodensity 0.02 e/A . The
occupation numbers are given in parentheses: the C-Mn bond
order is 0.86 for sigma and 0.55 for pi. The z-axis is perpendicular to
the molecular plane, the C-Mn bond is on the y-axis, and xy is the
molecular plane.
culations26 for the methylidenes produced ionic fluoride struc-
tures and natural bond orders for the C-Mn bonds in CH2d
MnF2, CH2dMnCl2, and CCl2dMnCl2 of 1.42, 1.37, and 1.30,
respectively. In order to explore bonding in these carbene
complexes more extensively, CASSCF calculations18 were done
for the C-Mn bonds in CH2dMnF2, CH2dMnCl2, and
3
˚
14c
CCl2dMnCl2 like those recently reported for CCl2dCoCl2
but adding two more d-orbitals. This active space employed
7 electrons (2 from C and 5 from Mn, the 2 other electrons from
Mn ultimately go into F orbitals) in 8 orbitals (2 from C and
6 from Mn) (CAS(7,8)). The resulting molecular orbitals and
their occupancies are given below: On the basis of the CAS
orbital shapes and energies, the six MOs from Mn are mostly 4s-
and five 3d-orbitals. The 2s- and 2p-orbitals from C and the 4s-
and two 3d-orbitals from Mn constitute the active space along
with the remaining three 3d-orbitals of Mn, each of which
contains one electron in the quartet state. These form the given
σ, π, σ*, π*, 3dxy, 3dxz, 3dz2 and Mn,C,H,F molecular orbitals
(very small electron density shared over these atoms in the
latter). The CAS(7,8) molecular orbitals are illustrated in
Figure S5 for CH2dMnF2.
In order to be more complete and also to investigate the
Mn-F bonding, the CAS for CH2dMnF2 was expanded to
(9,10) by adding two more electrons and one unoccupied
low-energy MO as well as one MO from a fluorine p-orbital.
The energy decreased 2.7 kcal/mol, but the C-Mn bond
order was virtually the same, 1.39. Next, the CAS was
expanded to (11,12) by adding two more electrons and one
more unoccupied low-energy MO as well as one more MO
from fluorine p-orbitals. The choice of which two p-orbitals
to include on the F atoms affects the orbital energy ordering
but not the C-Mn bond order. For one choice of the two F
p-orbitals, the energy decreased another 3.2 kcal/mol, and
the C-Mn bond order is 1.40: these orbitals include two
Mn-F2 orbitals and are shown in Figure S6. For another
choice, the energy decreased a total of 7.3 kcal/mol. These
CAS (11,12) molecular orbitals are shown for CH2dMnF2 in
Figure 8, and the net C-Mn bond order is 1.41, essentially
the same as for the smaller (7,8) active space. These results all
demonstrate that inclusion of extra fluorine p-orbitals and
unoccupied orbitals causes only negligible changes in the
occupation numbers of the molecular orbitals involved in the
C-Mn bond. There are six MOs from the F 2p-orbitals, and
HF and B3LYP calculations show that they are all doubly
occupied, indicating even in the single configuration calcula-
tions that two electrons indeed move from Mn toward the
CH2dMnF2
σ (1.854), π (1.527), 3dxy (0.996), 3dxz (1.001)
σ* (0.145), π* (0.472), Mn,C,H,F (0.005), 3dz2 (1.000)
CH2dMnCl2
σ (1.803), π (1.515), 3dxy (0.996), 3dxz (1.000)
σ* (0.198), π* (0.485), Mn,C,H,Cl (0.005), 3dz2 (1.000)
CCl2dMnCl2
σ (1.822), π (1.547), 3dxy (0.995), 3dxz (1.000)
σ* (0.178), π* (0.452), Mn,C,H,Cl (0.005), 3dz2 (1.000)
The net C-Mn bond orders are 1.39, 1.32, and 1.37, which
reveal substantial π-character for these C-Mn bonds.

486 Organometallics, Vol. 30, No. 3, 2011
Cho and Andrews
fluorine p-orbitals, resulting in ionic Mn-F bonding. How-
ever, the CAS optimization changes the order of the molec-
ular orbital energies. While the original 8 MOs for CAS(7,8)
remain essentially unchanged, the σ (C-H2) orbital gets into
the active space, replacing an F 2p-orbital. In addition, the σ
(Mn-F2) molecular orbital shows that the Mn-F bonding is
not completely ionic (Figure 8).
with groups 6 and 8 metals.9,11,12 Reaction 1 summarizes the
Mn reactions described here. The evidence suggests that
excited Mn* forms an energized insertion complex, CX3-
MnX*, which can relax in the matrix to the ground sextet state,
as observed in many cases, or rearrange through a halogen-
bridged transition state (Figure S4) to an excited sextet state
CX2-MnX2. Thislatterintermediateisrelaxedby thematrixto
the ground quartet state methylidene final product.
The CH2F-MnF bond order from NBO analysis
(Table S17) is 0.93, and the bond is considerably longer
˚
(2.081 compared to 1.856 A). The higher-oxidation-state
carbene complex also has more ionic character, as the
Mulliken charges on C and Mn (Table S18, C 0.20,
H -0.02, F (on C) -0.41, Mn 0.82, and F (on Mn) -0.58)
indicate. So the multiple bond character in the methylidene
complexes arises in part from ionic bonding as well as the
π-character. (We have retained the double-bond notation for
the Mn methylidenes where the second bond is ionic as well
as pi, based on our calculations.)
The observed primary products are essentially in line with the
product stabilities as described above. The methylidene product
becomes relatively more stable than the insertion complex with
increasing number of halogen atoms, particularly Cl, and as a
result, only the insertion product is observed in the CH3F reac-
tions and only the methylidene complex in the CCl4 system.
Conclusions
For comparison, previous CASSCF calculations deter-
mine a 1.67 effective bond order for the CCl2dCoCl2
complex in the doublet state,14c where there is more
π-contribution to the bonding than in the Mn analogue
CCl2dMnCl2.
Reactions of laser-ablated Mn atoms with halomethanes
have been carried out, and the products are identified from
the matrix IR spectra on the basis of frequencies, isotopic
shifts, and correlation with the DFT-computed frequencies.
In contrast to the Re case,11 no Mn carbynes are identified.
Instead, only the insertion complex is observed in the CH3F
spectra, whereas both the insertion and carbene products are
identified in most other reactions, except for the CHCl3 and
CCl4 cases, where only the carbenes are observed. The ob-
served products have the lowest computed energies.
Finally, it is interesting to note that CF2-MnFCl in the
sextet state with a bridged structure has the longest the
˚
C-Mn bond (2.265 A) among the investigated Mn com-
plexes (Figure 5), and therefore, it is a single bond and this
Mn carbene with a bridged structure is in fact an extreme
case of Mn insertion complexes.
Reactions. The new Mn-bearing reaction products are
formed on reactions of laser-ablated Mn atoms on sample
depositions and on subsequent photolysis, which suggest
that these reactions require excited Mn atoms, a fact con-
sistent with the failure to observe product growth on anneal-
ing of cold reagents. This is also in line with the earlier
observation that thermal Mn atoms failed to react with pure
solid methane nor water in excess argon, but CH3-MnH or
HMnOH was formed on UV (300-340 nm) photolysis.6
Previous laser ablation investigations reveal the presence of
Mn* (8P, 4s3d54p) metastable states 53 kcal/mol above the
ground state (6S, 4s23d5), which are probably responsible for
our reactions during sample deposition.31 Clearly, photolysis
of the cold sample leads to reaction most likely through
photoexcitation of Mn. Parallel to the previously studied
transition-metal reactions with halomethanes, the Mn reac-
tion is also believed to undergo C-X bond insertion to
produce the insertion complex followed by X migration from
C to M to generate the higher-oxidation-state complexes
during sample co-deposition and on subsequent photolysis.9
The methylidyne complexes (CXtMnX3) are energetically
much higher (e.g., FCtMnF3 in the doublet ground state is 8
kcal/mol higher than the total ground-state reactant energy),
and as a result, no Mn carbynes are observed from the Mn
reactions investigated. This is in contrast to the exclusive
formation of Re methylidyne complexes.11 These results
reveal that the tendency of the increasing preference for the
higher-oxidation-state complexes on descending in the fa-
mily group is most dramatic among group 7 metals along
The Mn insertion complexes have either a linear or near
linear C-Mn-X moiety, similar to the Grignard reagents
and the Fe analogues, and NBO analysis shows that Mn has
a high s character (56-66%) in the single C-Mn bonds. The
small Mn methylidene complexes mostly have planar struc-
tures, like the early transition-metal methylidenes,9,10 which
is in contrast with the late transition-metal (including Fe and
Re) methylidenes with staggered allene-type structures.12-14
The computed C-Mn bond lengths for the methylidenes are
shorter than for the insertion complexes, which is explained
by a one-half π-bond order and increased ionic bonding in
the higher-oxidation-state species to augment the σ-bond
based on CASSCF calculations.
The linear C-Mn-X moiety of the Mn insertion com-
plexes and the high s character in the Mn-X bond resemble
those for group 2 metal analogues, such as the Grignard
reagents. The present results reveal that these small Mn
insertion and methylidene complexes carry the borderline
characteristics between the early and late transition metals
and also bear the highest multiplicities among the group
3-12 products. The tendency of the increasing preference for
higher-oxidation-state complexes is also most dramatic
among the group 7 metals (Mn and Re).
Acknowledgment. We gratefully acknowledge finan-
cial support from National Science Foundation (U.S.)
Grant CHE 03-52487 to L.A. and support from the
Korea Research Foundation (KRF) grant funded by
the Korean government (MEST) (No 2010-0016527).
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
(31) (a) Levy, M. R. J. Phys. Chem. 1989, 93, 5195. (b) Chertihin, G. V.;
Andrews, L. J. Phys. Chem. A 1996, 101, 8547.