Pentacoordinate cobalt(III) thiolate and nitrosyl tropocoronand compounds

Article abstract of DOI:10.1021/ic010181l

Reaction of [Co(TC-n,m)]⁺ with (Me₄N)(SC₆F₅), where (TC-n,m) is a tropocoronand with n and m linker chain methylene groups, yielded the thiolate complexes [Co(SC₆F₅)(TC-3,3)] (1a), and [Co(SC₆F₅)(TC-4,4)] (2a), which were structurally characterized. Use of more electron-releasing thiolates afforded the [Co(TC-n,m)] reduction product and the corresponding disulfide. The bent nitrosyl complexes [Co(NO)(TC-3,3)] (1b) and [Co(NO)(TC-4,4)] (2b) were synthesized from [Co(TC-n,m)] and NO and their structures were also determined. Compounds 1a and 1b have square-pyramidal geometry like all other structurally characterized [MX(TC-3,3)] complexes. Compounds 2a and 2b have trigonal-bipyramidal stereochemistry, formerly rare for Co(III). Although 1a, 1b, and 2a are paramagnetic, 2b is diamagnetic due to the strong antibonding π-interaction between the metal and NO π* orbitals. In the presence of excess NO, [Co(TC-4,4)] exhibited novel reactivity in which a putative Co(N₂) adduct formed.

Full text of DOI:10.1021/ic010181l

3774
Inorg. Chem. 2001, 40, 3774-3780
Pentacoordinate Cobalt(III) Thiolate and Nitrosyl Tropocoronand Compounds
Katherine J. Franz, Linda H. Doerrer, Bernhard Spingler, and Stephen J. Lippard*
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
ReceiVed February 12, 2001
Reaction of [Co(TC-n,m)]+ with (Me4N)(SC6F5), where (TC-n,m) is a tropocoronand with n and m linker chain
methylene groups, yielded the thiolate complexes [Co(SC6F5)(TC-3,3)] (1a), and [Co(SC6F5)(TC-4,4)] (2a), which
were structurally characterized. Use of more electron-releasing thiolates afforded the [Co(TC-n,m)] reduction
product and the corresponding disulfide. The bent nitrosyl complexes [Co(NO)(TC-3,3)] (1b) and [Co(NO)(TC-
4,4)] (2b) were synthesized from [Co(TC-n,m)] and NO and their structures were also determined. Compounds
1a and 1b have square-pyramidal geometry like all other structurally characterized [MX(TC-3,3)] complexes.
Compounds 2a and 2b have trigonal-bipyramidal stereochemistry, formerly rare for Co(III). Although 1a, 1b,
and 2a are paramagnetic, 2b is diamagnetic due to the strong antibonding π-interaction between the metal and
NO π* orbitals. In the presence of excess NO, [Co(TC-4,4)] exhibited novel reactivity in which a putative Co(N2)
adduct formed.
Introduction
smallest tropocoronand ring size, TC-3,3, for which we were
unable to obtain Mn and Fe analogues.
The tropocoronand family of ligands (H2TC-n,m) has proved
valuable for studying how changes in macrocycle ring size and
flexibility can tune the physical and chemical properties of
transition metal ions.1-5 Such changes can also be manifest in
unusual reactivity exhibited by these compounds.6,7 Metal
Tropocoronand macrocycles afford a series of four-coordinate
Co(II) complexes, [Co(TC-n,m) where (n + m) ) 6, 7, 8, 9,
10, or 12, having a range of geometries from square planar to
tetrahedral.2 In the present article we report the synthesis,
molecular structures, and magnetic and electronic properties of
several new 5-coordinate Co(III) tropocoronand complexes,
[Co(SC6F5)(TC-n,m)] and [Co(NO)(TC-n,m)], where n ) m )
3 or 4. When n ) 3, the thiolato and nitrosyl compounds are
both square-pyramidal (SP); however, when n ) 4 the com-
plexes are constrained to be trigonal-bipyramidal (TBP).
The nitrosyl compounds especially demonstrate the physical
and chemical tuning achieved with tropocoronands. Whereas
[Co(NO)(TC-3,3)] is paramagnetic, [Co(NO)(TC-4,4)] is the
first reported diamagnetic TBP Co(III) complex. In the course
of studying the NO reactivity of this particular compound, we
obtained infrared spectroscopic evidence for a putative cobalt-
dinitrogen species produced from reaction with NO.
nitrosyl complexes [M(NO)(TC-n,m)] nicely illustrate these
characteristics. The unique properties of [Mn(NO)(TC-5,5)]8 and
[Fe(NO)(TC-5,5)]9 that distinguish them from other Mn and
Fe nitrosyl species derive from their constrained trigonal-
bipyramidal geometries and the strongly donating tetraaza
environment provided by the TC-5,5 N4 donor set. Unlike related
complexes of other ligands, these Mn and Fe nitrosyl complexes
readily promote the disproportionation of NO.8,9 Given this
precedent, it seemed likely that [Co(TC-n,m)] complexes would
similarly display interesting reactivity with NO. Moreover, by
using cobalt it was possible to access compounds with the
Experimental Section
General Information. All reactions were carried out in a dinitrogen-
filled glovebox or Schlenk line unless otherwise noted. The complexes
[Co(TC-3,3)] (1) and [Co(TC-4,4)] (2) were synthesized as described
previously.2 Pentane, toluene, diethyl ether, and tetrahydrofuran were
distilled from sodium benzophenone ketyl. Methylene chloride and
fluorobenzene were distilled from CaH2. Methanol was distilled from
magnesium and stored over 4 Å molecular sieves. All solvents were
distilled under dinitrogen. Cp2FePF6 was obtained commercially and
purified by removing Cp2Fe by sublimation. NO (Matheson, 99+%)
and 15NO (Aldrich, 99%) were purified of higher nitrogen oxides by
passage through a column of NaOH pellets and a mercury bubbler and
kept over mercury in gas storage bulbs.
UV-vis data were recorded with a Hewlett-Packard 8452A diode
array or Cary 1E spectrophotometer. Magnetic moments were deter-
mined by the Evans method10,11 on a 250 MHz Bruker NMR
spectrometer by using (TMS)2O as an internal standard in CD2Cl2. 1H
NMR data were also collected on this instrument. Standard IR spectra
(1) Davis, W. M.; Roberts, M. M.; Zask, A.; Nakanishi, K.; Nozoe, T.;
Lippard, S. J. J. Am. Chem. Soc. 1985, 107, 3864-3870.
(2) Jaynes, B. S.; Doerrer, L. H.; Liu, S.; Lippard, S. J. Inorg. Chem.
1995, 34, 5735-5744.
(3) Jaynes, B. S.; Ren, T.; Liu, S.; Lippard, S. J. J. Am. Chem. Soc. 1992,
114, 9670-9671.
(4) Scott, M. J.; Lippard, S. J. Inorg. Chim. Acta 1997, 263, 287-299.
(5) Davis, W. M.; Zask, A.; Nakanishi, K.; Lippard, S. J. Inorg. Chem.
1985, 24, 3737-3743.
(6) Jaynes, B. S.; Ren, T.; Masschelein, A.; Lippard, S. J. J. Am. Chem.
Soc. 1993, 115, 5589-5599.
(7) Doerrer, L. H.; Bautista, M. T.; Lippard, S. J. Inorg. Chem. 1997, 36,
3578-3579.
(8) Franz, K. J.; Lippard, S. J. J. Am. Chem. Soc. 1998, 120, 9034-9040.
(9) Franz, K. J.; Lippard, S. J. J. Am. Chem. Soc. 1999, 121, 10504-
10512.
(10) Evans, D. F. J. Chem. Soc. 1959, 2003-2005.
(11) Sur, S. K. J. Magn. Reson. 1989, 82, 169-173.
10.1021/ic010181l CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/12/2001

Pentacoordinate Co(III) Tropocoronand Compounds
Inorganic Chemistry, Vol. 40, No. 15, 2001 3775
were recorded on a Bio Rad FTS-135 instrument; solid samples were
prepared as pressed KBr disks and solution samples were prepared in
an airtight Graseby-Specac solution cell with CaF2 windows. In situ
IR sample monitoring was performed with a ReactIR 1000 from ASI
Applied Systems equipped with a 1-in diameter, 30-reflection silicon
ATR (SiComp) probe optimized for maximum sensitivity. Reaction
protocols were described previously.9
Synthetic Procedures. (Me4N)(SC6F5). A 50-mL round-bottom flask
was charged with Me4NOH‚5H2O (4.53 g, 25.0 mmol) in 15 mL of
ethanol and purged with N2 for 5 min. One equivalent of C6F5SH (5.0
g, 25.0 mmol) was added via syringe, and the solution was allowed to
stir for another 5 min. The solvents were removed in vacuo and
triturated with 5 mL of MeOH to remove residual water. The crude
product was washed with 10 mL of DME and 5 mL of pentane and
dried in vacuo. A white powder was obtained (6.09 g, 89% yield) which
showed a single resonance in the 1H NMR spectrum at 3.22 ppm
(DMSO-d6).
[Co(SC6F5)(TC-3,3)] (1a). A portion of 1 (205.7 mg, 0.545 mmol)
was dissolved in 15 mL of CH2Cl2, and 1 equiv of Cp2FePF6 (180.4
mg, 0.545 mmol) was added with stirring. The dark-green color changed
to deep pink-purple. After 4 h, the solvent was removed in vacuo. The
dark purple powder was washed three times with 10 mL of pentane
until the golden color of Cp2Fe was no longer observed in the pentane
wash. The remaining solid was extracted into 15 mL of CH2Cl2 and
filtered through Celite. To the filtrate was added 1 equiv of (Me4N)-
(SC6F5) (149.1 mg, 0.545 mmol) which had been dissolved in 5 mL of
THF. The purple solution began to turn orange brown and was stirred
for 3 h until the solution was dark orange-brown, after which time the
solvents were removed in vacuo. The resultant brown powder was
dissolved in CH2Cl2, filtered through Celite to remove (Me4N)(PF6),
and concentrated in vacuo. The product was recrystallized from hot
fluorobenzene in 29% yield (92.1 mg). Fine brown needles suitable
for an X-ray diffraction study were grown from fluorobenzene solutions
layered with pentane. Evans method moment (CD2Cl2), µeff ) 3.1 µB.
UV-vis (CH2Cl2) [λmax, nm (ꢀM, M-1 cm-1)] 391 (12,900), 477
(15,300), 573 (7700). Anal. Calcd for CoN4C26H22SF5: C, 54.17; H,
3.85; N, 9.72. Found: C, 54.15; H, 4.18; N, 9.53.
4H, C-CH2-C), 1.76 (m, 4H, C-CH2-C), 3.52 (m, 4H, N-CH2-
C), 3.76 (m, 4H, N-CH2-C), 6.12 (2H, t, J ) 9 Hz, Hc), 6.62 (4H, d,
J ) 11 Hz, Ha), 6.85 (4H, t, J ) 11 Hz, Hb). IR (νNO, KBr) 1584 cm-1
.
UV-vis (CH2Cl2) [λmax, nm (ꢀM, M-1 cm-1)] 409 (20,300), 486 (9200),
796 (2400). Anal. Calcd for CoN5C22H26O: C, 60.69; H, 6.02; N, 16.08.
Found: C, 60.68; H, 6.25; N, 15.55.
X-ray Crystallography. Single crystal X-ray diffraction data were
collected on either an Enraf-Nonius CAD4 four-circle or a Bruker
(formerly Siemens) CCD diffractometer. The general procedures for
data collection and reduction with each instrument follow those reported
previously.12,13 Structures of 1a, 2a, and 2b were solved with the direct
methods package SIR-92, an updated version of SIR8814 and incorpo-
rated into the TEXSAN15 package of programs, which typically afforded
positions for the majority of the non-hydrogen atoms. The structure of
1b was solved with the program XS by using direct methods, and
refinements were carried out with XL, both part of the SHELXTL
program package.16 The structure was refined by full matrix least
squares and difference Fourier techniques. Empirical absorption cor-
rections were calculated and applied from the SADABS program.17
Correct space group assignments were confirmed by successful
refinement and checked with the program PLATON.18 The structure
of 1b was solved in the acentric space group Cmc21 and refinements
were performed with both enantiomorphs to determine the correct
absolute configuration. The Flack absolute structure parameter was
0.05(3), compared to expected values of 0.0 for the correct and +1.0
for the inverted structure.19 Non-hydrogen atoms were refined aniso-
tropically except as noted. Hydrogen atoms were assigned idealized
positions and given a thermal parameter 1.2 times that of the carbon
atom to which each was attached. One molecule of toluene was found
in the lattice of 2a and refined isotropically with appropriate constraints.
Structure solution of 2b in P21/c revealed a disorder of the nitrosyl
oxygen atoms O1 and O1* over two positions, which were refined to
a 65:35 site occupancy ratio, respectively.
Important crystallographic information for each complex including
refinement residuals is given in Table 1. Final positional parameters
and all bond distances and angles are provided as Supporting Informa-
tion.
Reaction of [Co(TC-3,3)]+ with Pentafluorobenzenethiolate. A
2.56 mL aliquot of a 12.6 µM solution of [Co(TC-3,3)]PF6 in CH2Cl2
was placed in a UV-vis cell with a Teflon septum and cooled to -78
°C. One equivalent of a 5.87 mM solution (5.5 µL) of (Me4N)(SC6F5)
in THF was added by syringe. Spectra recorded at approximately 20 s
intervals (Figure S1) revealed the rapid formation of [Co(TC-3,3)].
Extended Hu1ckel MO Calculations. Extended Hu¨ckel calculations
were carried out on a Gateway 2000 Pentium PC computer with the
CACAO program.20 The model complexes [CoCl(NH2)4]-, [Co(SPh)-
(NH2)4]-, and [Co(NO)(NH2)4]- were investigated in idealized trigonal-
bipyramidal geometries with the fifth ligand in an equatorial position.
The following distances and angles were taken from the crystallo-
graphically determined parameters in [CoCl(TC-4,4)], 2a, and 2b: Co-
NTC ) 1.92 Å, Co-Cl ) 1.80 Å, Co-NO ) 1.80 Å, Co-N-O )
130°, Co-S ) 2.29 Å, Co-S-C) 107°. In the [Co(SPh)(NH2)4]- and
[Co(NO)(NH2)4]- models, the NO and PhS- groups were bent in the
plane containing the principal axis of the trigonal bipyramid, consistent
with the structures of 2a and 2b.
[Co(SC6F5)(TC-4,4)] (2a). A portion of 2 (101.2 mg, 0.249 mmol)
was dissolved in CH2Cl2 and oxidized with 1 equiv of Cp2FePF6 (82.4
mg, 0.249 mmol) to form the dark maroon cation [Co(TC-4,4)]+ in
situ, which was allowed to react with 1 equiv of (Me4N)(SC6F5) (68.1
mg, 0.249 mmol). Procedures and workup followed those reported for
1a. A dark orange-brown solution in CH2Cl2 was obtained, which was
concentrated to dryness, and the product was recrystallized from hot
fluorobenzene in 43% yield (64.8 mg). Crystals suitable for an X-ray
diffraction study were grown as dark brown plates from a toluene
solution layered with pentane. Evans method moment (CD2Cl2), µeff
)
3.2 µB. UV-vis (CH2Cl2) [λmax, nm (ꢀM, M-1 cm-1)] 371 (21,300),
456 (22,600), 561 (7100), 669 (3000), 742 (3600). Anal. Calcd for
CoN4C28H26SF5: C, 55.63; H, 4.34; N, 9.27. Found: C, 55.85; H, 4.57;
N, 9.13.
[Co(NO)(TC-3,3)] (1b). A portion of 1 (38.3 mg, 0.101 mmol) was
dissolved in 10 mL of THF in a Schlenk flask under N2. The flask was
sealed and purged with NO while stirring. Immediately upon addition
of NO the dark green solution turned brown. After 15 min, the solvent
was removed in vacuo to give a brown powder which was recrystallized
from hot fluorobenzene in 22% yield (9 mg). Long brown-black needles
suitable for X-ray diffraction were grown from slow vapor diffusion
of pentane into a THF solution of the compound at ambient temperature.
Evans method moment (CD2Cl2), µeff ) 3.1 µB. IR (νNO, KBr) 1656
cm-1. UV-vis (CH2Cl2) [λmax, nm (ꢀM, M-1 cm-1)] 342 (14,300), 417
(12,000), 547 (4350), 677 (2300). Due to difficulty in obtaining
sufficient quantities of 1b, elemental analysis was not performed.
[Co(NO)(TC-4,4)] (2b). A portion of 2 (161 mg, 0.397 mmol) was
dissolved in 15 mL of THF in a 25-mL Schlenk flask. The initially
dark green solution turned red-brown upon exposure to NO. After 10
min of purging the solution with NO, the solvent was removed in vacuo
to give a brown powder, which was recrystallized from hot fluoro-
benzene in 65% yield (110 mg). Small, dark brown plate crystals of
X-ray quality were grown by cooling a fluorobenzene solution of the
(12) Feig, A. L.; Bautista, M. T.; Lippard, S. J. Inorg. Chem. 1996, 35,
6892-6898.
(13) Carnahan, E. M.; Rardin, R. L.; Bott, S. G.; Lippard, S. J. Inorg. Chem.
1992, 31, 5193-5201.
(14) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.; Polidori,
G.; Spagna, R.; Viterbo, D. J. Appl. Crystallogr. 1989, 22, 389-
393.
(15) TEXSAN: Single-Crystal Analysis Software. 2.0; Molecular Structure
Corporation; Woodlands, TX, 1993.
(16) SHELXTL: Structure Analysis Program. 5.1; Bruker Analytical X-ray
Systems; Madison, WI, 1997.
(17) Sheldrick, G. M. SADABS: Area Detector Absorption Correction.
University of Go¨ttingen; Germany, 1996.
(18) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool. Utrecht
University; Utrecht, The Netherlands, 1998.
(19) Flack, H. D. Acta Crystallogr. 1983, A44, 499-506.
(20) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399-402.
1
compound layered with pentane. H NMR (δ, ppm, CD2Cl2) 1.59 (m,

3776 Inorganic Chemistry, Vol. 40, No. 15, 2001
Franz et al.
Table 1. X-ray Diffraction Studies of Neutral Cobalt(III) Tropocoronand Complexes.
1a
2a‚C7H8
1b
2b
formula
fw
cryst system
space group
a (Å)
b (Å)
c (Å)
CoSF5N4C26H22
576.47
orthorhombic
Pbca
12.2478(2)
9.0636(2)
41.9264(2)
CoSF5N4C35H34
696.65
triclinic
P1h
9.532(5)
13.290(5)
13.449(5)
71.055(5)
89.469(5)
77.928(5)
1572.6(1)
2
CoON5C20H22
407.36
orthorhombic
Cmc21
16.1983(8)
12.2557(7)
8.8952(5)
CoON5C22H26
435.41
monoclinic
P21/c
12.791(1)
16.138(2)
9.862(1)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
104.077(2)
4654.2(1)
8
1.645
155
1765.9(2)
4
1.532
188
1974.5(3)
4
1.466
155
F
calcd, g/cm3
temp (K)
1.471
193
µ(Mo KR), mm-1
total no. of data
no. of unique dataa
no. of parameters
no. of restraints
Rb
8.92
16258
3322
334
0
0.064
0.110
0.361
0.10, 0.20, 0.30
6.74
7291
6503
404
9.93
8.93
11864
4698
271
0
0.086
0.164
0.710
0.20, 0.10, 0.05
3513
1295
130
85
1
0.0714
0.194
0.0357
0.0746
0.595
0.1, 0.1, 0.4
wR2c
largest peak, e/Å3
crystal size, mm
1.19d
0.10, 0.18, 0.45
a Observation criterion: I > 2σ(I). bR ) Σ||Fo| - |Fc||/Σ|Fo|. cwR2 ) [Σw(Fo2 - Fc2)2/Σw(Fo )]1/2. dThis peak occurs in the vicinity of a disordered
2
toluene molecule.
Results
Cobalt(III) Tropocoronand Thiolate Complexes. Synthesis
and Spectroscopy. From [Co(TC-n,m)]PF6 generated in situ,
neutral five-coordinate [Co(SC6F5)(TC-n,m)] complexes were
obtained. Reaction of the four-coordinate Co(III) cations in
CH2Cl2 with (Me4N)(SC6F5) was accelerated by dissolving the
thiolate in THF. The previously characterized7 THF adduct
[Co(THF)(TC-3,3)]+ does not form under these conditions,
consistent with the greater affinity of C6F5S- versus THF for
cobalt(III). The choice of thiolate was critical because the
initially formed [Co(SR)(TC-n,m)] species decomposed by
internal electron transfer to form [Co(TC-n,m)] and the corre-
sponding disulfide when more electron-releasing thiolates RSH
(R ) Me, Et, i-Pr, t-Bu, or Ph) were used. At room temperature
the color of the pink or purple [Co(TC-n,m)]+ cation changed
during the time of mixing with (Me4N)(SR) to the dark green
color characteristic of [Co(TC-n,m)]. At -78 °C, a brown color
was observed briefly upon addition of (Me4N)(SR), which
changed to dark-green in less than 3 min. Spectral changes at
452 nm accompanying the reaction of [Co(TC-3,3)]+ with PhS-
at -78 °C are shown in Figure S1. Diphenyl sulfide was
detected in the reaction mixture by GC/MS. When R ) C6F5
the product was quite stable even in boiling fluorobenzene (84
°C). Electronic spectra characteristic of [Co(TC-n,m)]+ were
observed upon addition of one equivalent of MeOTf or
Me3OBF4 to 1a or 2a, the thiolate presumably being removed
Figure 1. ORTEP drawing for [Co(SC6F5)(TC-3,3)], 1a, and [Co(SC6F5)-
(TC-4,4)], 2a, showing 50% probability ellipsoids for all non-hydrogen
atoms.
as MeSC6F5.
Structures. Figure 1 depicts the structure of 1a, and selected
bond lengths and angles are given in Table 2. The geometry at
acterized Co-SC6F4X species, X ) H, F.21-23 The penta-
cobalt is square-pyramidal with the metal displaced from the
fluorobenzenethiolate ring is stacked above the C8-C14 ami-
best N4 plane by 0.29 Å. The average S-Co-N angle is 98(5)°
notroponeiminate ring, with a ring centroid-to-centroid distance
and the average trans N-Co-N angle is 163(6)°, indicating a
of 3.65 Å.
slightly distorted square pyramid. The Co-Navg distance of
1.89(1) Å is consistent with previously reported Co-Navg
distances in five-coordinate Co(III) complexes. The values for
the bend angle at sulfur of 105.6(2)°, the Co-S distance of
2.262(2) Å and the corresponding S-C distance of 1.769(6) Å
are unexceptional compared to other crystallographically char-
(21) Doppelt, P.; Fischer, J.; Weiss, R. J. Am. Chem. Soc. 1984, 106, 5188-
5193.
(22) Doppelt, P.; Fischer, J.; Ricard, L.; Weiss, R. New J. Chem. 1987,
11, 357-364.
(23) Thompson, J. S.; Sorrell, T.; Marks, T. J.; Ibers, J. A. J. Am. Chem.
Soc. 1979, 101, 4193-4200.

Pentacoordinate Co(III) Tropocoronand Compounds
Inorganic Chemistry, Vol. 40, No. 15, 2001 3777
Table 2. Selected Bond Distances and Angles for Cobalt Thiolate
Tropocoronandsa
distances (Å)
angles (deg)
[Co(SC6F5)(TC-3,3)] Co-N1 1.880(4) N1-Co-N2 81.7(2)
1a
Co-N2 1.891(4) N1-Co-N3 158.1(2)
Co-N3 1.899(4) N1-Co-N4 96.6(2)
Co-N4 1.902(4) N2-Co-N3 95.8(2)
Co-Navg 1.89(1) N2-Co-N4 167.4(2)
Co-S
2.262(2) N3-Co-N4 81.0(2)
S-C21
1.769(6) S-Co-N1
S-Co-N2
95.6(1)
95.3(1)
106.4(1)
97.3(1)
S-Co-N3
S-Co-N4
Co-S-C21 105.6(2)
[Co(SC6F5)(TC-4,4)] Co-N1 1.892(4) N1-Co-N2 81.9(2)
2a
Co-N2 1.895(4) N1-Co-N3 120.3(2)
Co-N3 1.898(4) N1-Co-N4 97.0(2)
Co-N4 1.906(4) N2-Co-N3 97.7(2)
Co-Navg 1.898(6) N2-Co-N4 178.5(2)
Co-S
S-C23
2.293(1) N3-Co-N4 81.9(2)
1.758(4) S-Co-N1
S-Co-N2
122.8(1)
96.0(1)
116.7(1)
85.4(1)
S-Co-N3
S-Co-N4
Co-S-C23 107.3(2)
a Numbers in parentheses are estimated standard deviations of the
last significant figure. Atoms are labeled as indicated in Figure 1.
Figure 2. ORTEP drawing for [Co(NO)(TC-3,3)], 1b, and [Co(NO)-
(TC-4,4)], 2b, showing 50% probability ellipsoids for all non-hydrogen
atoms. In 2b, only one of the disordered nitrosyl oxygen atoms is
depicted.
The structure of 2a, also given in Figure 1, is trigonal
bipyramidal with the thiolate ligand in an equatorial position.
The atoms N2 and N4 define the principal axis of the trigonal
bipyramid. The N-Co-N angle is 178.5(2)° and the angles in
the equatorial plane defined by S, N1, and N3 are 122.7(1)°,
116.7(1)°, and 120.3(2)°. The pentafluorobenzenethiolate ring
is bent along the principal axis toward N1, with a Co-S-C
angle of 107.3(2)°. The Co-S and S-C distances of 2.293(1)
and 1.758(4) Å are similar to those in 1a. Additional structural
details are provided in Table 2.
Co(III) Tropocoronand Nitrosyl Complexes. Synthesis and
Spectroscopy. Immediately upon exposure to NO, dark green
solutions of [Co(TC-n,m)] turned brown. This color change
suggested oxidation of Co(II) to Co(III), since all known five-
coordinate Co(III) tropocoronands are brown in solution, with
the exception of blue-green [Co{C(O)CH3}(TC-4,4)].6 Longer
exposure times of 2 to NO resulted in further reactivity and
decomposition of the nitrosyl species, as described below.
Although similar behavior was not expressly observed for 1, it
was difficult to isolate large enough quantities of 1b suitable
for elemental analysis. Once isolated, however, 1b could be
recrystallized in the presence of air. Solutions of 2b, on the
other hand, rapidly decomposed in air. The formation of 1b
and 2b was irreversible. Under vacuum, NO was not lost from
the solid or solutions, and the compounds were stable in boiling
fluorobenzene (84 °C).
Table 3. Selected Bond Distances and Angles for Cobalt Nitrosyl
Tropocoronands.a
distances (Å)
[Co(NO)(TC-3,3)] Co-N1 1.916(4) N1-Co-N1A 94.4(2)
1b Co-N2 1.900(4) N1-Co-N2 81.2(2)
angles (deg)
Co-NTC(avg) 1.90(1) N1-Co-N2A 159.7(2)
Co-N3
O1-N3
1.785(6) N2-Co-N2A 96.0(2)
1.137(7) N1-Co-N3 101.8(2)
N2-Co-N3
98.4(2)
Co-N3-O1 127.3(6)
[Co(NO)(TC-4,4)] Co-N1
1.906(6) N1-Co-N2
1.926(5) N1-Co-N3
81.0(2)
97.0(2)
2b
Co-N2
Co-N3
Co-N4
1.916(5) N1-Co-N4 129.3(2)
1.899(6) N1-Co-N5 114.1(3)
Co-NTC(avg) 1.91(1) N2-Co-N3 176.4(2)
Co-N5
O1A-N5
O1B-N5
1.779(6) N2-Co-N4
1.151(9) N2-Co-N5
1.18(2) N3-Co-N4
N3-Co-N5
97.5(2)
90.9(3)
81.4(2)
92.7(3)
N4-Co-N5 116.6(3)
Co-N5-O1A 128.9(6)
Co-N5-O1B 134.9(9)
a Numbers in parentheses are estimated standard deviations of the
last significant figure. Atoms are labeled as indicated in Figure 2.
netic [Zn(TC-n,m)],25 [Cd(TC-n,m)],25 and [Ni(TC-n,m)] com-
plexes (n + m ) 6, 8, 9).1 Extended Hu¨ckel calculations explain
this novel feature, as discussed below.
In the infrared spectra, νNdO bands at 1656 and 1584 cm-1
for 1b and 2b, respectively, are consistent with data for other
bent Co nitrosyls, although these values vary widely and do
not correlate with any other property of Co nitrosyls.24
Magnetic Properties. Compound 1b is paramagnetic at room
temperature with a µeff of 3.1 µB in solution, whereas 2b is
diamagnetic. The latter is the first example of a diamagnetic
trigonal-bipyramidal Co(III) complex. All ligand protons were
clearly resolved in the 1H NMR spectrum and showed the same
characteristic shifts and multiplicities observed in the diamag-
Structures. An ORTEP diagram of 1b is illustrated in Figure
2, and selected bond lengths and angles are reported in Table
3. The cobalt atom sits on a crystallographically required mirror
plane that relates the two halves of the molecule. The two central
methylene carbon atoms and the nitrosyl group lie on this mirror
plane. The linker chains adopt different conformations; one six-
membered chelate ring has a chair conformation whereas the
other has a boat conformation. As in compound 1a, the structure
of 1b is square-pyramidal with cobalt displaced out of the best
N4 plane by 0.54 Å and an average NTC-Co-NNO angle of
104(14)°. The average Co-NTC distance of 1.91(1) Å is similar
(24) Feltham, R. D.; Enemark, J. H. Topics Stereochem. 1981, 12, 155-
215.
(25) Doerrer, L. H.; Lippard, S. J. Inorg. Chem. 1997, 36, 2554-2563.

3778 Inorganic Chemistry, Vol. 40, No. 15, 2001
Franz et al.
Figure 3. In situ IR spectra of [Co(TC-4,4)] (2) in THF at -78 °C as
NO is introduced into the headspace above the solution. The increase
in intensity at 1590 cm-1 depicts the formation of [Co(NO)(TC-4,4)]
(2b), the NO stretch of which overlaps with a band present in the
starting complex. The band at 1640 cm-1 may represent the nitrosyl
stretch of a {Co(NO)(NO2)} species, whereas the band at 2108 cm-1
suggests a Co(N2) complex.
Figure 4. IR spectrum taken in THF solution 2 h after 5 equiv each
of 15NO and 14NO were added to a solution of [Co(TC-4,4)] (2) under
Ar. The bands at 2223 and 2153 cm-1 correspond to 14N2O and 15N2O,
respectively. The broad band centered at 2065 cm-1 is attributed to
overlapping ν(14N14N), ν(14N15N), and ν(15N15N) stretching modes.
to Co(III)-Navg distances in [CoEt(TC-3,3)]6 and [CoCl(TC-
3,3)]3 cited above. The Co-N-O angle of 127.3(6)° is in the
122-128° range of other axially coordinated nitrosyls of square-
pyramidal Co complexes, such as a variety of porphyrins.26-29
The N-O bond length of 1.137(7) Å in 1a is slightly shorter
than the 1.16-1.18 Å distances found in those same examples.
The structure of 2b is given in Figure 2 and selected distances
and angles in Table 3. Here the geometry is trigonal bipyramidal,
with the equatorial plane containing the nitrosyl group and atoms
N1 and N4, which form angles at Co of 129.3(2)°, 116.6(3)°,
and 114.1(3)°. The N2-Co-N3 angle is 176.4(2)°, and the bent
nitrosyl group lies in the plane of the axial ligands. The oxygen
atom of the nitrosyl group is disordered over two positions in
the N2-Co-N1 plane, which refined to a 65:35 site occupancy
ratio for O1A and O1B, respectively. The average Co-NTC
distance of 1.91(1) Å is essentially the same as that in 1b. The
average N-O distance is 1.17(2) Å and the Co-N-O angle is
132(4)°. Both nitrosyl complexes have the {CoNO}8 configu-
ration.30
Reactivity. Figure 3 contains the IR spectra recorded when
a THF solution of [Co(TC-4,4)] (2) at -78 °C and under an Ar
atmosphere was exposed to a stream of NO gas. The initial dark
green Co(II) complex rapidly turned red-brown in the presence
of NO. The first step in the reaction was formation of 2b,
identified by the characteristic NO stretch at 1590 cm-1 in
solution, which happens to overlap a band present in the starting
Co(II) complex. At about the same time, N2O appeared at 2223
cm-1 and a shoulder developed around 1640 cm-1. Within 20
min, a band developed at 2108 cm-1 and the N2O signal at 2223
cm-1 appeared to decay. A blackish precipitate began to form.
The reaction continued without noticeable spectral changes for
3 h, after which time the cold bath was removed and the reaction
was monitored, without any noticeable changes, for an additional
1 h at room temperature. The bands at 2108 and 1590 and the
shoulder around 1640 cm-1 did not shift during this time course.
We wondered whether the feature at 2108 cm-1 might be
signaling formation of a cobalt-dinitrogen species.31 Isotope-
labeling experiments should be diagnostic of such a unit.
Assuming a classic diatomic oscillator model, ν(15N15N) should
shift by 70 cm-1 compared with the corresponding ν(14N14N)
stretch, whereas the difference between ν(15NO) and ν(14NO)
should be 30 cm-1. Indeed, when the reaction was performed
with 15NO, bands appeared at 2031 cm-1 and 1612 cm-1
,
suggesting the 15N-shifted versions of the 2108 (ν14N14N) and
1640 cm-1(ν14NO) bands that are seen in Figure 3. In addition,
a band at 2153 cm-1 signaled the formation of 15N2O. When a
mixture of 14NO and 15NO was introduced to a THF solution
of 2 under Ar, one broad band spanning from 2130 to 1966
cm-1 appeared, centered at 2065 cm-1. The IR spectrum is
shown in Figure 4. We attribute this band to overlapping
contributions from ν(14N14N), ν(14N15N), and ν(15N15N) in a
1:2:1 ratio. For an observed ν(14N14N) band at 2108 cm-1, the
calculated, isotopically shifted frequencies are 2072 cm-1 for
ν(14N15N) and 2036 cm-1 for ν(15N15N). The 165 cm-1 width
(measured from baseline to baseline) of the 2065 cm-1 peak is
considerably broader than the 110 cm-1 peak width of the 2108
cm-1 band in Figure 3.
Because reduced metal centers react with N2O, we tested for
the formation of “Co(N2)” by exposing the known Co(I)
compound6 [Co(TC-4,4)]- both to N2 and N2O, but saw no
evidence for a dinitrogen adduct. Likewise, we saw no evidence
for reaction of 2 with N2O.
Discussion
Structural Properties of Cobalt(III) Tropocoronand Thi-
olate and Nitrosyl Complexes. Cobalt thiolate complexes in
which the mercaptide donor is monodentate and not a part of a
chelate ring are rare. The proclivity for RS- to reduce metal
atoms or to bridge them is well-known. Most structurally
characterized examples32 have either strongly electron-with-
drawing R groups, R ) C6F4H21,22,33 or C6F5,23 or low oxidation
states, Co(II)23,34-37 or Co(I),36,38,39 the latter being unlikely to
undergo further reduction. The requirement of a strongly
(26) Richter-Addo, G. B.; Hodge, S. J.; Yi, G.-B.; Khan, M. A.; Ma, T.;
Van Caemelbecke, E.; Guo, N.; Kadish, K. M. Inorg. Chem. 1996,
35, 6530-6538.
(27) Richter-Addo, G. B.; Hodge, S. J.; Yi, G.-B.; Khan, M. A.; Ma, T.;
Van Caemelbecke, E.; Guo, N.; Kadish, K. M. Inorg. Chem. 1997,
36, 2696.
(28) Godbout, N.; Sanders, L. K.; Salzmann, R.; Havlin, R. H.; Wojdelski,
M.; Oldfield, E. J. Am. Chem. Soc. 1999, 121, 3829-3844.
(29) Ellison, M. K.; Scheidt, W. R. Inorg. Chem. 1998, 37, 382-383.
(30) Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV. 1974, 13, 339-
406.
(31) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. ReV. 1978, 78, 589-
625.
(32) Inouye, Y.; Kambe, T.; Tada, M. Acta Crystallogr. 1998, C54, 945-
947.
(33) Dance, I. G. Polyhedron 1986, 5, 1037-1104.

Pentacoordinate Co(III) Tropocoronand Compounds
Inorganic Chemistry, Vol. 40, No. 15, 2001 3779
electron-withdrawing thiolate in [Co(SR)(TC-n,m)] complexes
in order to avoid electron transfer from sulfur to Co(III) is
therefore not surprising.
The geometries of the 5-coordinate Co(III) complexes
presented here reflect the tendencies of the particular TC-n,m
ligand used in each case. The limited flexibility of the TC-3,3
ligand imposes a square-pyramidal configuration on 1a and 1b;
no other stereochemistry has been observed for any [MX(TC-
3,3)] complex.
Trigonal-bipyramidal geometry is much less common for
Co(III), but has been observed previously in the tropocoronand
complex [CoCl(TC-4,4)];3 a few [CoX3(PR3)2]40-43 complexes
also share this stereochemistry. Compounds 2a and 2b offer
two new examples of this formerly rare geometry for Co(III),
which is now routinely accessible because of the tuning
properties of the TC-4,4 ligand. From the torsional angles in
the linker chains of [CoCl(TC-4,4)]3 it was apparent that the
trigonal bipyramid was less strained than square pyramid for
5-coordinate TC-4,4 complexes, although one example, [Co(Me)-
(TC-4,4)], does exhibit the latter configuration.6 Because the
methyl group is a σ-donor with no ability to serve as a π-donor
or acceptor, it does not coordinate in the equatorial plane of a
2
2
trigonal bipyramid where it would have to share to the dx -y
orbital with two other ligands. Rather, it coordinates in the axial
2
position of a square pyramid, binding to the dz orbital, which
is not similarly shared. The nitrosyl is both a σ-donor and a
π-acceptor and can bind in the equatorial position of the trigonal
bipyramid, like chloride ion, which is both a σ- and π-donor.
The nitrosyl complexes 1b and 2b exemplify the two types
of geometries known for pentacoordinate {CoNO}8 systems,
square-pyramidal and trigonal-bipyramidal, and further delineate
the control of stereochemistry by ligand twist. Many other
square-pyramidal {CoNO}8 complexes with bent nitrosyl groups
have been structurally characterized, including [Co(dmgH)2-
(NO)],44 a substituted tmtaa complex [Co(NO)(Me2(COOEt)2-
taa)],45 salicylideneiminate derivatives,46 a variety of por-
phyrins26-28,30,47,48 and others.49,50 The bond distances and angles
Figure 5. Energies of frontier molecular orbitals for [CoCl(NH2)4]-,
[Co(SPh)(NH2)4]-, and [Co(NO)(NH2)4]- from EHMO calculations.
in 1b are unexceptional compared to the ones in these other
cobalt nitrosyls.
Among the structurally characterized five-coordinate {CoNO}8
complexes, bent nitrosyl groups occur almost exclusively in the
axial positions of square-pyramidal structures, like 1b, whereas
linear nitrosyls occupy an equatorial position of a trigonal
biypramid.51 Compound 2b is only the second structurally
characterized example of a {CoNO}8 system with a bent nitrosyl
in the equatorial position of a trigonal bipyramid. The other
example is [Co(NO)Cl2(PMe3)2],52 in which the nitrosyl is
clearly bent, but disorder of the NO moiety and a chlorine atom
over two sites prevented accurate determination of the nitrosyl
bond distances and angles. The disorder in 2b has been
successfully modeled.
(34) Corwin Jr., D. T.; Fikar, R.; Koch, S. A. Inorg. Chem. 1987, 26, 3079-
3082.
(35) Jiang, F.; Wei, G.; Huang, Z.; Lei, X.; Hong, M.; Kang, B.; Liu, H.
J. Coord. Chem. 1992, 25, 183-191.
(36) Wei, G.; Hong, M.; Huang, Z.; Liu, H. J. Chem. Soc., Dalton Trans.
1991, 3145-3148.
(37) Okamura, T.; Takamizawa, S.; Ueyama, N.; Nakamura, A. Inorg.
Chem. 1998, 37, 18-28.
The compounds [Co(NO)I2(PMe3)2]52 and [Co(NO)Cl2-
(PMePh2)2]53 also have trigonal-bipyramidal geometry, but their
symmetry is C2V and the nitrosyl groups are linear. The bending
of NO in [Co(NO)Cl2(PMe3)2] has been attributed to mixing
of the dz2 and NO π* orbitals.52 Consistent with this argument
is the bent nitrosyl group in [Co(NO)Cl2(PMe3)2], which has
stronger phosphine donors than [Co(NO)Cl2(PMePh2)2] bearing
a linear nitrosyl. Finally, the MO calculations described
elsewhere revealed that the tropocoronand ligand is a strong
π-donor,2,54 consistent with the bent NO groups in 1b and 2b.
Compound 2b is distinct from all other trigonal-bipyramidal
cobalt nitrosyls and all other trigonal-bipyramidal Co(III)
tropocoronand complexes because it is diamagnetic. This
(38) Vastag, S.; Markoj, L.; Rheingold, A. L. J. Organomet. Chem. 1990,
397, 231-238.
(39) Aubart, M. A.; Bergman, R. G. J. Am. Chem. Soc. 1996, 118, 1793-
1794.
(40) McAuliffe, C. A.; Godfrey, S. M.; Mackie, A. G.; Pritchard, R. G.
Angew. Chem., Int. Ed. Engl. 1992, 31, 919-921.
(41) Levason, W.; Ogden, J. S.; Spicer, M. D. Inorg. Chem. 1989, 28,
2128-2131.
(42) van Enckevort, W. J. P.; Hendriks, H. M.; Beurskens, P. T. Cryst.
Struct. Commun. 1977, 6, 531-536.
(43) Jensen, K. A.; Nygaard, B.; Pedersen, C. T. Acta Chem. Scand. 1963,
17, 1126-1132.
(44) Englert, U.; Stra¨hle, J. Gazz. Chim. Ital. 1988, 118, 845-855.
(45) Go¨rls, H.; Reck, G.; Ja¨ger, E.-G.; Mu¨ller, K.; Seidel, D. Cryst. Res.
Technol. 1990, 25, 1277-1286.
(46) Groombridge, C. J.; Larkworthy, L. F.; Mare´caux, A.; Povey, D. C.;
Smith, G. W.; Mason, J. J. Chem. Soc., Dalton Trans. 1992, 3125-
3131.
(47) van der Put, P. J.; Schilperoord, A. A. Inorg. Chem. 1974, 13, 2476-
(51) Enemark, J. H.; Feltham, R. D.; Riker-Nappier, J.; Bizot, K. F. Inorg.
Chem. 1975, 14, 624-632.
(52) Alnaji, O.; Peres, Y.; Dartiguenave, M.; Dahan, F.; Dartiguenave, Y.
Inorg. Chim. Acta 1986, 114, 151-158.
2481.
(48) Scheidt, W. R.; Hoard, J. L. J. Am. Chem. Soc. 1973, 95, 8281-
8288.
(49) Larkworthy, L. F.; Povey, D. C.; Smith, G. W.; Tucker, B. J. J.
Crystallogr. Spectrosc. Res. 1989, 19, 439-450.
(50) Enemark, J. H.; Feltham, R. D. J. Chem. Soc., Dalton Trans. 1971,
718-722.
(53) Brock, C. P.; Collman, J. P.; Dolcetti, G.; Farnham, P. H.; Ibers, J.
A.; Lester, J. E.; Reed, C. A. Inorg. Chem. 1973, 12, 1304-1313.
(54) Doerrer, L. H. Ph. D. dissertation, Massachusetts Institute of Technol-
ogy, 1996.

3780 Inorganic Chemistry, Vol. 40, No. 15, 2001
Franz et al.
property can be explained by the results of extended Hu¨ckel
MO calculations presented in Figure 5, which plot the rel-
ative d-orbital energies of three trigonal-bipyramidal models,
[CoCl(NH2)4]-, [Co(SPh)(NH2)4]-, and [Co(NO)(NH2)4]-, based
on the compounds [CoCl(TC-4,4)], 2a and 2b. The energy of
the dxy orbital greatly increases when NO is the fifth ligand,
compared to the thiolate and chloride cases, owing to interaction
with the NO π* orbitals. Neither chloride nor sulfur has π*
acceptor orbitals to interact with the dxy orbital. This difference
in orbital energies readily explains the observed diamagnetism
of 2b compared to [CoCl(TC-4,4)] and 2a, which are both
paramagnetic. The dxy orbital in 2b is sufficiently raised in
energy that the gap between the dxy orbital and the dx -y orbital
is greater than the pairing energy, resulting in an S ) 0 complex.
Reactivity. Difficulties in obtaining sufficient quantities of
1b limited detailed studies of the reactivity of [Co(TC-3,3)] with
NO. Some important differences between 1b and 2b are
apparent, however. No N2O was observed in the reactions
between 1 and excess NO, either by IR spectroscopy or gas
chromatography. Nor did we observe a stretch around 2100
cm-1 in the IR spectrum after 1 had been exposed to NO for
several hours. We were able, however, to recrystallize 1b in
air, indicating that this nitrosyl compound is not air sensitive.
The lack of reactivity of 1b, both in the presence of excess
NO and in air, contrasts sharply with the reactivity previously
reported for [Mn(NO)(TC-5,5)]8 and [Fe(NO)(TC-5,5)],9 as well
as the new results presented here for [Co(NO)(TC-4,4)]. In these
cases, the nitrosyl adducts rapidly decayed in the presence of
air. In the presence of excess NO, the Mn and Fe compounds
reacted further to disproportionate NO, affording N2O and NO2.
The latter was either metal-bound, as in [Mn(NO2)(TC-5,5)],8
or it nitrated the aromatic rings of the ligand to give [Fe(NO)-
(TC-5,5-NO2)].9 When supported by the TC-4,4 ligand however,
cobalt further reduced NO to give some fraction of what we
propose to be a dinitrogen adduct. Although the reaction was
not clean and an insoluble precipitate formed, the infrared data
strongly suggest the presence of a “Co(N2)” species. When 15NO
or a mixture of 14NO/15NO was used, the IR stretch of this
postulated functionality shifted by the expected amount for Co-
15N15N or Co-15N14N, respectively. The 14N2 and labeled 15N2
bands at 2108 and 2031 cm-1 correspond closely to the reported
values of a well characterized cobalt dinitrogen complex,
[CoH(N2)(PPh3)3], for which ν(14N14N) ) 2092 cm-1 and
ν(15N15N) ) 2026 cm-1 55
. We have not yet, however, been able
to isolate and characterize the molecular structure of this alleged
dinitrogen-containing species. No other metal-bound dinitrogen
adduct has to our knowledge arisen from the reaction of a metal
complex with NO, although free N2 has been produced via such
reactions.56,57
2
2
Acknowledgment. This work was supported by a grant from
the National Science Foundation. Dr. B. Spingler thanks the
Swiss Scientific National Foundation for postdoctoral fellowship
support.
Supporting Information Available: Figure S1, showing the
absorbance changes of [Co(TC-3,3)]+ upon reaction with PhS- at -78
°C and X-ray crystallographic files in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC010181L
(55) Yamamoto, A.; Kitazume, S.; Pu, L. S.; Ikeda, S. J. Am. Chem. Soc.
1971, 93, 371-380.
(56) McNeill, K.; Bergman, R. G. J. Am. Chem. Soc. 1999, 121, 8260-
8269.
(57) Bottomley, F.; Brintzinger, H. H. J. Chem. Soc., Chem. Commun. 1978,
234-234.