Low-valent chemistry of cobalt amide. Synthesis and structural characterization of cobalt(II) amido, aryloxide, and thiolate compounds

Article abstract of DOI:10.1021/ic0102945

The binuclear cobalt(II) amide complex [(CoL₂)₂·(TMEDA)] (1) [L = N(Si^tBuMe₂)(2-C₅H₃N-6-Me); TMEDA = Me₂NCH₂CH₂NMe₂] has been synthesized by the

Full text of DOI:10.1021/ic0102945

Inorg. Chem. 2001, 40, 4691-4695
4691
Low-Valent Chemistry of Cobalt Amide. Synthesis and Structural Characterization of
Cobalt(II) Amido, Aryloxide, and Thiolate Compounds
Hung Kay Lee,* Chung Hei Lam, Song-Lin Li, Ze-Ying Zhang, and Thomas C. W. Mak
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong SAR, People’s Republic of China
ReceiVed March 19, 2001
The binuclear cobalt(II) amide complex [(CoL2)2‚(TMEDA)] (1) [L ) N(SitBuMe2)(2-C5H3N-6-Me); TMEDA
) Me2NCH2CH2NMe2] has been synthesized by the reaction of anhydrous CoCl2 with 2 equiv of [Li(L)(TMEDA)].
X-ray crystallography revealed that complex 1 consists of two {CoL2} units linked by one TMEDA ligand molecule,
which binds in an unusual N,N′-bridging mode. Protolysis of 1 with the bulky phenol ArMeOH (ArMe ) 2,6-
tBu2-4-MeC6H2) and thiophenol ArSH (Ar ) 2,4,6-tBu3C6H2) gives the neutral monomeric cobalt(II) bis(aryloxide)
[Co(OArMe)2(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)] (3), respectively. Complexes 1-3 have been
characterized by mass spectrometry, microanalysis, magnetic moment, and melting-point measurements, in addition
to X-ray crystallography.
Introduction
for the lone-pair electron density of the amido moiety through
(drp) π-bonding interaction may also impose an unfavorable
The chemistry of transition metal amides has attracted much
interest over the past decade because of their important roles in
various industrial1-3 and biological processes.2,4 Although the
chemistry of amido complexes of the early transition metals
has been developed in detail, that of the low-valent late transition
metals remains relatively unexplored.5,6 One of the factors that
hinders the development of the chemistry of the latter complexes
may be ascribed to an unfavorable combination between the
“hard” anionic amido ligand and the “soft” low-valent late
transition metal center.5,6 Moreover, the “reluctance” of the low-
valent late transition metal center to function as a π-acceptor
effect on the stability of the M-N bond.5,7
Strategies for the synthesis of amido complexes of the low-
valent late transition metals usually involve the incorporation
of “soft” phosphine donors as supporting ligands3,6 or the
utilization of sterically hindering aryl- and alkylamido ligands.8-11
In recent years, the chemistry of the N-functionalized amido
ligands [N(R)(2-C5H4N)]- (R ) Ph,12,13 2-C5H4N,14,15 SiMe3,16
1-admantyl17), [N(R)(2-C5H3N-6-Me)]- (R ) SiMe3,18 1-ad-
mantyl17), [N(SiMe3)(2-C5H3N-4-Me)]-,19 and [N(SiMe3)(8-
C9H6N)]-20 has attracted much interest, and a number of main-
group and transition metal amido complexes with unusual
coordination geometry have been isolated. However, reports of
late transition metal amides derived from these ligands remain
scarce.15a,c,e-g,19a One of the current issues in our laboratory
focuses on the syntheses, structures, and reactivities of amido
metal complexes derived from sterically demanding aryl- and
* To whom correspondence should be addressed. Tel: +852-2609-6331.
Fax: +852-2603-5057. E-mail: hklee@cuhk.edu.hk.
(1) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163-1188.
(2) Roundhill, D. M. Chem. ReV. 1992, 92, 1-27.
(3) (a) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. J. Am. Chem.
Soc. 1988, 110, 6738-6744. (b) Cowan, R. L.; Trogler, W. C.
Organometallics 1987, 6, 2451-2453. (c) Cowan, R. L.; Trogler, W.
C. J. Am. Chem. Soc. 1989, 111, 4750-4761. (d) Seligson, A. L.;
Trogler, W. C. Organometallics 1993, 12, 744-751. (e) Klein, D. P.;
Hayes, J. C.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 3704-
3706. (f) Glueck, D. S.; Winslow, L. J.; Bergman, R. G. Organome-
tallics 1991, 10, 1462-1479. (g) Hartwig, J. F.; Bergman, R. G.;
Andersen, R. A. J. Am. Chem. Soc. 1991, 113, 6499-6508. (h)
Widenhoefer, R. A.; Buchwald, S. L. Organometallics 1996, 15,
2755-2763. (i) Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1997,
119, 6054-6058. (j) Villanueva, L. A.; Abboud, K. A.; Boncella, J.
M. Organometallics 1992, 11, 2963-2965. (k) Boncella, J. M.;
Villanueva, L. A. J. Organomet. Chem. 1994, 465, 297-304. (l)
Villanueva, L. A.; Abboud, K. A.; Boncella, J. M. Organometallics
1994, 13, 3921-3931. (m) VanderLende, D. D.; Abboud, K. A.;
Boncella, J. M. Inorg. Chem. 1995, 34, 5319-5326. (n) Driver, M.
S.; Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 7217-7218. (o) Dorta,
R.; Egli, P.; Zu¨rcher, F.; Togni, A. J. Am. Chem. Soc. 1997, 119,
10857-10858.
(4) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. ReV. 1996, 96,
2239-2314.
(5) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal
and Metalloid Amides; Ellis Horwood: Chichester, 1980; pp 465-
544.
(6) (a) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. ReV. 1989, 95,
1-18. (b) Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. Soc. 1981,
103, 3592-3593. (c) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J.;
Secco, A. S.; Trotter, J. Organometallics 1982, 1, 918-930.
(7) Mayer, J. M. Comments Inorg. Chem. 1988, 8, 125-135.
(8) (a) Bu¨rger, H.; Wannagat, U. Monatsh. Chem. 1963, 94, 1007-1012.
(b) Bu¨rger, H.; Wannagat, U. Monatsh. Chem. 1964, 95, 1099-1102.
(c) Bradley, D. C.; Hursthouse, M. B.; Malik, K. M. A.; Mo¨seler, R.
Transition Met. Chem. 1978, 3, 253-254. (d) Murray, B. D.; Power,
P. P. Inorg. Chem. 1984, 23, 4584-4588. (e) Andersen, R. A.; Faegri,
K.; Green, J. C.; Haaland, A.; Lappert, M. F.; Leung, W.-P.; Rypdal,
K. Inorg. Chem. 1988, 27, 1782-1786.
(9) (a) Bartlett, R. A.; Power, P. P. J. Am. Chem. Soc. 1987, 109, 7563-
7564. (b) Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M. M.;
Power, P. P. J. Am. Chem. Soc. 1989, 111, 4338-4345.
(10) Hope, H.; Olmstead, M. M.; Murray, B. D.; Power, P. P. J. Am. Chem.
Soc. 1985, 107, 712-713.
(11) (a) Bartlett, R. A.; Feng, X.; Olmstead, M. M.; Power, P. P.; Weese,
K. J. J. Am. Chem. Soc. 1987, 109, 4851-4854. (b) Chen, H.; Bartlett,
R. A.; Olmstead, M. M.; Power, P. P.; Shoner, S. C. J. Am. Chem.
Soc. 1990, 112, 1048-1055.
(12) (a) Barr, D.; Clegg, W.; Mulvey, R. E.; Snaith, R. J. Chem. Soc.,
Chem. Commun. 1984, 700-701. (b) Barr, D.; Clegg, W.; Mulvey,
R. E.; Snaith, R. J. Chem. Soc., Chem. Commun. 1984, 469-470.
(13) (a) Polamo, M.; Leskela¨, M. J. Chem. Soc., Dalton Trans. 1996, 4345-
4349. (b) Polamo, M.; Leskela¨, M. Acta Chem. Scand. 1997, 51, 449-
454.
(14) Wu, L.-P.; Field, P.; Morrissey, T.; Murphy, C.; Nagle, P.; Hathaway,
B.; Simmons, C.; Thornton, P. J. Chem. Soc., Dalton Trans. 1990,
3835-3840.
10.1021/ic0102945 CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/28/2001

4692 Inorganic Chemistry, Vol. 40, No. 18, 2001
Lee et al.
spectra were obtained on a Hewlett-Packard 5989B Mass Engine
spectrometer. Magnetic moments were measured in benzene solutions
at 300 K by the Evans method.24 Elemental analyses were performed
by MEDAC Ltd., Brunel University, U.K.
alkylamido ligands. We reasoned that bulkiness of substituents
on the amido nitrogen does impose an important influence on
the structure of the corresponding amido metal complexes.
Accordingly, two sterically more encumbered N-functionalized
amido ligands [N(R)(2-C5H3N-6-Me)]- (R ) SitBuMe2,
SitBuPh2) have been developed in our laboratory.21,22a With these
sterically more demanding ligands, a number of main-group and
transition metal amido complexes with quite different structures
have been prepared and structurally characterized.21,22 Herein
we report the synthesis and crystal structure of a novel binuclear
cobalt(II) amide [(CoL2)2‚(TMEDA)] (1) [L ) N(SitBuMe2)-
(2-C5H3N-6-Me); TMEDA ) Me2NCH2CH2NMe2] in which
the TMEDA ligand binds two cobalt ions in an unusual N,N′-
bridging coordination mode. Subsequent reactions of 1 with the
bulky phenol ArMeOH (ArMe ) 2,6-tBu2-4-MeC6H2) and thio-
phenol ArSH (Ar ) 2,4,6-tBu3C6H2) gave the neutral mono-
nuclear cobalt(II) bis(aryloxide) [Co(OArMe)2(TMEDA)] (2) and
dithiolate [Co(SAr)2(TMEDA)] (3), respectively.
Syntheses. [(CoL2)2‚(TMEDA)] (1). A solution of 2-(tert-butyldi-
methylsilyl)amino-6-picoline (2.68 g, 12 mmol) and TMEDA (1.82 mL,
12 mmol) in ether (10 mL) at 0 °C was slowly treated with a solution
of nBuLi in hexane (1.6 M, 9.0 mL, 14.4 mmol). The reaction mixture
was stirred for 15 min at room temperature, and all volatiles in the
resulting solution were removed in vacuo. The solid residue was washed
twice with hexane and dried under vacuum. It was redissolved in ether
(20 mL) and added to a suspension of CoCl2 (0.78 g, 6.0 mmol) in the
same solvent (10 mL) at 0 °C. The reaction mixture was stirred for 24
h at room temperature and was filtered. The filtrate was concentrated
under reduced pressure to give complex 1 as a green crystalline solid.
Yield: 2.3 g (68%). Mp: 66-69 °C. EI-MS (70 eV): m/z 502 (11)
[CoL2]+, 445 (35) [CoL2 - tBu]+, 222 (3) [L]+. µeff ) 3.06 µB per Co
atom. Anal. Found: C, 57.23; H, 8.33; N, 12.70. Calcd for C54H100N10-
Co2Si4: C, 57.93; H, 9.00; N, 12.51.
[Co(OArMe)2(TMEDA)] (2). To a solution of ArMeOH (0.85 g, 3.86
mmol) in hexane (10 mL) was slowly added a solution of 1 (1.08 g,
0.97 mmol) in the same solvent (30 mL) at 0 °C. The resultant solution
was stirred at room temperature for a further 24 h. All volatiles were
then removed in vacuo to give a green residue, which was washed
twice with hexane and dried under vacuum. Toluene was added to
redissolve the residue, and the solution was filtered through Celite.
The filtrate was concentrated under reduced pressure. Crystals of
complex 2 was obtained after 1 day. Yield: 0.57 g (48%). Mp: 227-
230 °C (dec). EI-MS (70 eV): m/z 498 (12) [Co(OArMe)2]+, 220 (34)
[ArMeO]+, 205 (100) [ArMeO - Me]+. µeff ) 3.64 µB. Anal. Found: C,
70.55; H, 10.06; N, 4.68. Calcd for C36H62N2CoO2 (613.81): C, 70.33;
H, 10.33; N, 4.55.
Experimental Section
General Procedures. All experiments were performed under a
purified nitrogen atmosphere using modified Schlenk techniques or in
a Braun MB 150-M drybox. Solvents were dried over and distilled
from calcium hydride (hexane) or sodium benzophenone (ether, THF,
and toluene) and degassed twice before use. Anhydrous CoCl2 was
purchased from Fluka and was used as received. 2-(tert-Butyldimethyl-
silyl)amino-6-picoline was prepared as described.21 2,6-tBu2-4-MeC6H2-
OH (ArMeOH) was purchased from Aldrich and was recrystallized from
hexane before use. 2,4,6-tBu3C6H2SH (ArSH) was prepared according
to literature procedures.23
Physical Measurements. Melting points were recorded on an
Electrothermal melting point apparatus and were uncorrected. EI mass
[Co(SAr)2(TMEDA)] (3). A solution of 1 (1.32 g, 1.18 mmol) in
hexane (30 mL) was added to a solution of ArSH (1.32 g, 4.74 mmol)
in hexane (10 mL) at 0 °C. The reaction mixture was stirred at room
temperature for 24 h and filtered, and the filtrate was concentrated under
reduced pressure. Crystallization at -30 °C afforded complex 2 as
reddish-brown needles. Yield: 0.76 g (44%). Mp: 142-146 °C (dec).
EI-MS (70 eV): m/z 278 (26) [ArS]+, 263 (34) [ArS - Me]+, 221 (6)
(15) Representative examples include: (a) Cotton, F. A.; Daniels, L. M.;
Jordan, G. T., IV. Chem. Commun. 1997, 421-422. (b) Cotton, F.
A.; Daniels, L. M.; Murillo, C. A.; Pascual, I. J. Am. Chem. Soc. 1997,
119, 10223-10224. (c) Cotton, F. A.; Daniels, L. M.; Jordan, G. T.,
IV; Murillo, C. A. J. Am. Chem. Soc. 1997, 119, 10377-10381. (d)
Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Pascual, I. Inorg. Chem.
Commun. 1998, 1, 1-3. (e) Cle´rac, R.; Cotton, F. A.; Dunbar, K. R.;
Murillo, C. A.; Pascual, I.; Wang, X. Inorg. Chem. 1999, 38, 2655-
2657. (f) Cle´rac, R.; Cotton, F. A.; Dunbar, K. R.; Lu, T.; Murillo, C.
A.; Wang, X. Inorg. Chem. 2000, 39, 3065-3070. (g) Cle´rac, R.;
Cotton, F. A.; Daniels, L. M.; Dunbar, K. R.; Kirschbaum, K.; Murillo,
C. A.; Pinkerton, A. A.; Schultz, A. J.; Wang, X. J. Am. Chem. Soc.
2000, 122, 6226-6236.
t
[ArS - Bu]+. µeff ) 3.78 µB. Anal. Found: C, 68.56; H, 10.10; N,
3.77. Calcd for C42H74N2CoS2: C, 69.09; H, 10.22; N, 3.84.
X-ray Structure Analysis. Single-crystals of 1-3 suitable for
crystallographic studies were mounted in glass capillaries and sealed
under nitrogen. Details of crystal parameters, data collection, and
structural refinement are summarized in Table 1. Data were collected
on a Rigaku RAXIS-IIC diffractometer at 294 K using graphite-
monochromatized Mo KR radiation (λ ) 0.71073 Å) by taking
oscillation photos. The structures were solved by direct phase deter-
mination using the computer program SHELX-97 on a PC 486 computer
and refined by full-matrix least squares with anisotropic thermal
parameters for the non-hydrogen atoms.25 Hydrogen atoms were
introduced in their idealized positions and included in structure factor
calculations with assigned isotropic temperature factors.26
(16) Liddle, S. T.; Clegg, W. J. Chem. Soc., Dalton Trans. 2001, 402-
408.
(17) Morton, C.; O’Shaughnessy, P.; Scott, P. Chem. Commun. 2000,
2099-2100.
(18) (a) Engelhardt, L. M.; Jacobsen, G. E.; Junk, P. C.; Raston, C. L.;
Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1988,
1011-1020. (b) Engelhardt, L. M.; Jacobsen, G. E.; Junk, P. C.;
Raston, C. L.; White, A. H. J. Chem. Soc., Chem. Commun. 1990,
89-91. (c) Engelhardt, L. M.; Jacobsen, G. E.; Patalinghug, W. C.;
Skelton, B. W.; Raston, C. L.; White, A. H. J. Chem. Soc., Dalton
Trans. 1991, 2859-2868. (d) Engelhardt, L. M.; Gardiner, M. G.;
Jones, C.; Junk, P. C.; Raston, C. L.; White, A. H. J. Chem. Soc.,
Dalton Trans. 1996, 3053-3057. (e) Raston, C. L.; Skelton, B. W.;
Tolhurst, V.-A.; White, A. H. Polyhedron 1998, 17, 935-942. (f)
Raston, C. L.; Skelton, B. W.; Tolhurst, V.-A.; White, A. H. J. Chem.
Soc., Dalton Trans. 2000, 1279-1285.
Results and Discussion
Synthesis of [(CoL2)2‚(TMEDA)] (1). The lithium reagent
[Li(L)(TMEDA)]21 was readily prepared by lithiation of 2-(tert-
butyldimethylsilyl)amino-6-picoline (HL), in the presence of
TMEDA, with a solution of nBuLi in hexane at 0 °C. Complex
1 was synthesized by treating a suspension of CoCl2 in diethyl
ether with 2 equiv of [Li(L)(TMEDA)] at ambient temperature.
The resultant solution was filtered and concentrated to afford 1
as a green crystalline solid in a satisfactory yield (68%) (Scheme
1).
(19) (a) Spannenberg, A.; Arndt, P.; Kempe, R. Angew. Chem., Int. Ed.
1998, 37, 832-835. (b) Spannenberg, A.; Fuhrmann, H.; Arndt, P.;
Baumann, W.; Kempe, R. Angew. Chem., Int. Ed. 1998, 37, 3363-
3354. (c) Kempe, R. Angew. Chem., Int. Ed. 2000, 39, 468-493, and
references therein.
(20) Engelhardt, L. M.; Junk, P. C.; Patalinghug, W. C.; Sue, R. E.; Raston,
C. L.; Skelton, B. W.; White, A. H. J. Chem. Soc., Chem. Commun.
1991, 930-932.
(21) Peng, Y. M.Phil. Thesis, The Chinese University of Hong Kong, 1999.
(22) (a) Lee, H. K.; Wong, Y.-L.; Zhou, Z.-Y.; Zhang, Z.-Y.; Ng, D. K.
P.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 2000, 539-544. (b)
Lee, H. K.; Peng, Y.; Kui, S. C. F.; Zhang, Z.-Y.; Zhou, Z.-Y.; Mak,
T. C. W. Eur. J. Inorg. Chem. 2000, 2159-2162.
(24) Evans, D. F. J. Chem. Soc. 1959, 2003-2005.
(25) Sheldrick, G. M. SHELX-97; Package for Crystal Structure Solution
and Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(26) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974.
(23) Rundel, W. Chem. Ber. 1968, 101, 2956-2962.

Low-Valent Chemistry of Cobalt Amide
Inorganic Chemistry, Vol. 40, No. 18, 2001 4693
Table 1. Crystal Data for Complexes 1-3
1
2
3
mol formula
mol wt
C54H100Co2N10Si4
1119.66
C36H62CoN2O2
613.81
0.30 × 0.25 × 0.22
monoclinic
P21/c
18.196(4)
14.902(3)
13.428(3)
90.00(3)
4
3641.1(13)
1.120
C42H74CoN2S2
730.08
0.40 × 0.25 × 0.20
orthorhombic
Pna2(1)
23.177(5)
11.056(2)
17.263(4)
90
cryst size, mm3
cryst syst
0.40 × 0.40 × 0.30
triclinic
space group
a, Å
b, Å
P1h
12.046(2)
12.286(3)
12.291(3)
72.65(3)
1
c, Å
â, deg
Z
4
V, Å3
1660.8(6)
1.119
0.610
4809
4809
4242
317
R1 ) 0.0643
wR2 ) 0.1779
R1 ) 0.0733
wR2 ) 0.1875
4423.6(15)
1.096
0.510
10495
3857
3222
401
R1 ) 0.0876
wR2 ) 0.2217
R1 ) 0.1077
wR2 ) 0.2372
density, g cm-3
abs coeff, mm-1
no. of reflns collected
unique data measd
obsd data with I g 2σ(I)
no. of variable
final R indices [I g 2σ(I)]a
0.502
8169
5129
3838
371
R1 ) 0.0784
wR2 ) 0.1683
R1 ) 0.1202
wR2 ) 0.1892
R indices (all data)a
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo )2]}1/2
.
2
2
Scheme 1
34%) were observed. The mass spectrum of 3 showed only
peaks due to [ArS]+ (m/z ) 278, 26%) and its fragments.
The protolysis of transition metal amides by bulky phenols
and thiols has proven to be a versatile route to the corresponding
aryloxide and thiolate complexes. It is well-documented that
transition metal aryloxides and thiolates usually have a high
tendency to associate and form insoluble polymers.27 This
renders their characterization difficult to carry out. However,
the degree of association can be reduced by introduction of bulky
aryl or alkyl substituents on the aryloxide or thiolate ligands.
Accordingly, a number of homoleptic and heteroleptic cobalt-
(II) alkoxide and thiolate complexes with low degrees of
association have been isolated by utilizing sterically demanding
alkoxy and thiolato ligands. On the other hand, neutral mono-
meric transition metal aryloxide and thiolate complexes with a
N2O2 and N2S2 coordination environment remain elusive.
Complexes 2 and 3 represent rare examples of complexes with
these types of coordination environment.
Scheme 2
X-ray Structural Studies. The molecular structure of
complex 1 with the atom numbering scheme is depicted in
Figure 1. Selected bond distances and angles are shown in Table
2. The X-ray structure of 1 features an unusual binuclear
complex which consists of two bis(amido)cobalt(II) {CoL2}
units bridged by one TMEDA molecule. Each amido ligand L
binds to the cobalt(II) center in a N,N′-chelating fashion, forming
a {CoN4} moiety. Coordination from one dimethylamino unit
of the TMEDA ligand completes a distorted trigonal bipyramidal
coordination geometry around each cobalt center. The two amido
nitrogens N(1) and N(3) and the amino nitrogen N(5) from
TMEDA define the trigonal plane (sum of bond angles )
359.8°). The remaining two axial sites are occupied by the
pyridyl nitrogens N(2) and N(4): N(2)-Co-N(4) ) 172.6-
(1)°. Deformation of the N(2)-Co-N(4) angle away from
linearity may be a consequence of the highly strained four-
membered metallacycle rings, the Namido-Co-Npyridyl bite angles
being 62.7(1)-63.8(1)°. A noteworthy feature of complex 1 is
the unusual N,N′-bridging coordination mode of the TMEDA
Protolysis of 1. Reactions of 1 toward protic reagents such
as the phenol ArMeOH and thiophenol ArSH, which bear bulky
ortho substituents, have been studied. Complex 1 reacted
smoothly with 4 equiv of ArMeOH or ArSH in hexane to give
the corresponding neutral monomeric cobalt(II) bis(aryloxide)
[Co(OArMe)2(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)]
(3), respectively (Scheme 2).
Complexes 1-3 are very sensitive to oxygen and moisture.
They are very soluble in common organic solvents, such as
diethyl ether, THF, hexanes, and toluene. They were character-
ized by mass spectrometry, microanalysis, magnetic moment,
and melting-point measurements, as well as single-crystal X-ray
diffraction studies. The mass spectrum of complex 1 showed
only signals due to the mononuclear species [CoL2]+ (m/z )
502, 11%), indicating loss of the TMEDA ligand in the vapor
phase. Molecular ion peaks were not observed in the mass
spectra of complexes 2 and 3. For 2, fragmentation peaks such
as [Co(OArMe)2]+ (m/z ) 498, 12%) and [ArMeO]+ (m/z ) 220,
(27) (a) Dance, I. G. Polyhedron 1986, 5, 1037-1104. (b) Krebs, B.; Henkel
G. In Rings Cluster and Polymers of Main Group and Transition
Elements; Roesky, H., Eds.; Elsevier: Amsterdam, 1989; pp 439-
502. (c) Dilworth, J. R.; Hu, J. AdV. Inorg. Chem. 1994, 40, 411-
414.

4694 Inorganic Chemistry, Vol. 40, No. 18, 2001
Lee et al.
Figure 2. Molecular structure of [Co(OArMe)2(TMEDA)] (2) (30%
thermal ellipsoids) with the atomic labeling scheme.
Figure 1. Molecular structure of [(CoL2)2‚(TMEDA)] (1) (30% thermal
ellipsoids) with the atomic labeling scheme.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
[(CoL2)2‚(TMEDA)] (1)
Figure 3. Molecular structure of [Co(SAr)2(TMEDA)] (3) (30%
thermal ellipsoids) with the atomic labeling scheme.
Co(1)-N(1)
Co(1)-N(2)
Co(1)-N(5)
C(5)-N(2)
C(17)-N(4)
N(3)-Si(2)
2.007(4)
2.258(4)
2.176(4)
1.354(6)
1.369(5)
1.735(3)
Co(1)-N(3)
Co(1)-N(4)
C(5)-N(1)
C(17)-N(3)
N(1)-Si(1)
1.998(3)
2.355(3)
1.359(5)
1.362(5)
1.725(4)
Table 3. Selected Bond Distances (Å) and Angles (deg) for
[Co(OArMe)2(TMEDA)] (2)
Co(1)-O(1)
Co(1)-N(1)
C(1)-O(1)
1.907(3)
2.223(4)
1.341(5)
Co(1)-O(2)
Co(1)-N(2)
C(19)-O(2)
1.893(3)
2.183(4)
1.349(5)
N(2)-Co(1)-N(1)
N(3)-Co(1)-N(1)
N(2)-Co(1)-N(5)
C(5)-N(2)-Si(1)
Si(1)-N(2)-Co(1)
C(17)-N(4)-Co(1)
63.8(1)
N(4)-Co(1)-N(3)
N(4)-Co(1)-N(2)
N(4)-Co(1)-N(5)
C(5)-N(2)-Co(1)
C(17)-N(4)-Si(2)
Si(2)-N(4)-Co(1)
62.7(1)
120.5(1)
112.6(1)
127.8(3)
135.0(1)
99.6(2)
172.6(1)
126.7(1)
96.8(3)
125.8(3)
133.0(1)
O(1)-Co(1)-O(2)
N(1)-Co(1)-O(1)
N(2)-Co(1)-O(1)
C(1)-O(1)-Co(1)
108.1(1)
134.2(1)
104.6(1)
133.1(3)
N(1)-Co(1)-N(2)
N(1)-Co(1)-O(2)
N(2)-Co(1)-O(2)
C(19)-O(2)-Co(1)
83.0(1)
104.5(1)
122.8(1)
138.1(3)
ligand. Examples of this type of unusual coordination mode for
TMEDA have been reported for certain main-group metal alkyls
and hydrides,28 but are rarely observed in transition metal
complexes.29,30 The TMEDA molecule might be expected to
bind in a bidentate manner to the same cobalt atom, forming a
six-coordinate mononuclear complex. Presumably, the large
steric bulk of ligand L prevents the TMEDA molecule from
ligating in a bidentate fashion in the present complex.
The Co-Npyridyl distances [Co(1)-N(2), Co(1)-N(4)] of
2.258(4) and 2.355(3) Å in 1 are somewhat longer than the Co-
Namine distance [Co(1)-N(5)] of 2.176(4) Å. This is probably
due to the presence of the highly strained four-membered
metallacycle rings in 1. The observed Co-Namido bond distances
in complex 1 [Co(1)-N(1) 2.007(4) Å, Co(1)-N(3) 1.998(3)
Å] are much longer than those of 1.84(2) and 1.898(3)-1.904(3)
Å in the monomeric Co[N(SiMe3)2]28e and [Co{N(SiMePh2)2}2],9
respectively. They are also longer than the Co-Namido distances
of 1.910(5)-1.922(5) Å for terminal ligands in the dimeric [Co-
{N(SiMe3)2}2]28d and 1.89 Å (av) in [Co(NPh2)2]2.10 The longer
Co-Namido distances in our current complex may be ascribed
to a more crowded five-coordinate environment around the metal
centers.
The amido nitrogen centers [N(1) and N(3)] exhibit a nearly
trigonal planar geometry [sum of bond angles: 359.02° (av)],
which is consistent with sp2-hybridized nitrogen atoms. The
observed Si-N bond distances in 1 [1.725(4)-1.735(3) Å] are
similar to the Si-N distances found in other silylamido
complexes.5,8,10,18-22 Moreover, delocalization of the lone-pair
electrons onto the pyridyl ring is evidenced by the short Cpyridyl
-
Namido bond distances of 1.359(5)-1.362(5) Å in 1. They are
close to the observed Caromatic-Namido distances in other metal
arylamido complexes, in which delocalization of electron density
onto the aromatic substituents have been suggested.3l,m,6,20,31
Apparently, ligand L behaves as a weak π-acceptor in complex
1, and this may account for the stability of the complex.
The molecular structures of complexes 2 and 3 are shown in
Figures 2 and 3, respectively. Selected bond distances and angles
are listed in Tables 3 and 4. The metal center of the neutral
monomeric bis(aryloxide) complex 2 is bound by two mono-
dentate ArMeO ligands and a bidentate TMEDA ligand, resulting
in a distorted tetrahedral N2O2 coordination geometry. The
(28) Some examples are: (a) Byers, J. J.; Pennington, W. T.; Robinson,
G. H. Acta Crystallogr. Sect. C 1992, 48, 2023-2024. (b) O’Hara,
D.; Foord, J. S.; Page, T. C. M.; Whitaker, T. J. J. Chem. Soc., Chem.
Commun. 1991, 1445-1447. (c) Atwood, J. L.; Bott, S. G.; Elms, F.
M.; Jones, C.; Raston, C. L. Inorg, Chem. 1991, 30, 3792-3793. (d)
Hallock, R. B.; Hunter, W. E.; Atwood, J. L.; Beachley, O. T., Jr.
Organometallics 1985, 4, 547-549.
(29) Kerby, M. C.; Eichhorn, B. W.; Creighton, J. A.; Vollhardt, K. P. C.
Inorg. Chem. 1990, 29, 1319-1323.
(30) Interestingly, an analogous iron(II) amido complex [(FeL2)2‚(TMEDA)],
which contains a TMEDA ligand ligating in a similar bridging
coordination mode, has recently been prepared and structurally
characterized in our laboratory and will be reported in a future article.
(31) (a) VanderLende, D. D.; Boncella, J. M.; Abboud, K. A. Acta
Crystallogr. 1995, C51, 591-593. (b) Penney, J.; VanderLende, D.
D.; Boncella, J. M.; Abboud, K. A. Acta Crystallogr. 1995, C51,
2269-2271.

Low-Valent Chemistry of Cobalt Amide
Inorganic Chemistry, Vol. 40, No. 18, 2001 4695
Table 4. Selected Bond Distances (Å) and Angles (deg) for
[Co(SAr)2(TMEDA)] (3)
slightly longer than the terminal Co-S bond distances of 2.222-
t
(2) Å in the neutral binuclear complex [Co(SC6H2 Bu3-
i
2,4,6)2]235a and 2.191(5)-2.215(5) Å in the anionic [Co2(SC6H2 -
Co(1)-S(1)
Co(1)-N(1)
C(1)-S(1)
2.277(4)
2.138(8)
1.832(5)
Co(1)-S(2)
Co(1)-N(2)
C(19)-S(2)
2.276(3)
2.148(9)
1.826(5)
Pr3-2,4,6)5]-.36
Magnetic Properties. The magnetic moments of 1-3 in
benzene, viz., 3.06 µB per Co for 1, 3.64 µB for 2, 3.78 µB for
3, have been measured by the Evans method. The reason for
the relatively low value for 1 is unclear at this moment. We
surmise that this may be ascribed to a mononuclear-to-binuclear
type equilibrium for complex 1 in solution. The magnetic
moments of complexes 2 and 3 are consistent with a high-spin
d7 electronic configuration with three unpaired electrons.
S(1)-Co(1)-S(2)
N(1)-Co(1)-S(1)
N(2)-Co(1)-S(1)
C(1)-S(1)-Co(1)
119.5(1)
112.5(2)
116.0(3)
117.0(2)
N(1)-Co(1)-N(2)
N(1)-Co(1)-S(2)
N(2)-Co(1)-S(2)
C(19)-S(2)-Co(1)
85.9(4)
106.7(2)
110.9(3)
116.7(2)
average Co-O distance of 1.90 Å in 2 is somewhat longer than
those of 1.84 Å (av) and 1.85 Å (av) in the ionic cobalt(II)
complexes [Co(Cl)(OCtBu3)2‚Li(THF)3]32a (4) and [Li(THF)4.5]-
[Co(Cl)(OCtBu3)2]32a (5), respectively. In comparison with other
neutral cobalt(II) aryloxide complexes, the Co-O distances in
2 are much longer than the terminal Co-O distances of 1.78 Å
(av) in the binuclear complex [Co{OC(C6H11)3}2]232b (6), 1.81
Conclusions
The novel binuclear cobalt(II) amido complexes [(CoL2)2‚
(TMEDA)] (1) are readily prepared by treating anhydrous CoCl2
with the lithium reagent [Li(L)(TMEDA)]. The solid-state
structure of 1 contains two {CoL2} moieties bridged by one
TMEDA ligand. The latter binds in an unusual N,N′-bridging
coordination mode, which is rarely observed in transition metal
complexes. Each Co(II) center in 1 is bound by a pair of N,N′-
chelating ligands L and an amino moiety of TMEDA, resulting
in a trigonal bipyramidal coordination geometry around the
metal center. Protolysis of 1 with ArMeOH and ArSH gave the
neutral mononuclear cobalt(II) bis(aryloxide) [Co(OArMe)2-
(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)] (3), respec-
tively. The metal center in the latter two complexes adopts a
distorted tetrahedral geometry. Studies on other late transition
metal amido complexes derived from ligand L are currently
under investigation in our laboratory.
Å (av) in [Co(OCPh3)2]232b (7), and 1.85 Å (av) in [Co(OSiPh3)2-
32b
(THF)]2
(8), where the metal centers in complexes 4-8
exhibit a nearly trigonal planar geometry. The Co-O distance
in 2 is slightly longer than that of 1.872(2) Å in the mononuclear
four-coordinate complex [Co(OCPh3)2(THF)2]32b (9). The Co-
O-C angles in 2, viz., 133.1(3)-138.1(3)°, are large. Such large
angles have been observed in a number of metal alkoxides and
aryloxides, which may be attributed to a (drp) π-interaction
between the oxygen atom and the metal center.32
The mononuclear dithiolate complex 3 exhibits a distorted
tetrahedral geometry around the metal center. The Co-S bond
distances of 2.276(3) and 2.277(4) Å in 3 are slightly shorter
than that of 2.33(1) Å (av) for the anionic [Co(SPh)4]2- 33
. The
small discrepancy in the bond lengths may be a consequence
of the anionic charge on the latter complex. The Co-S bond
distance in 3 is marginally longer than those of 2.228(1) (av)
and 2.260(2) Å (av) in the mononuclear four-coordinate [Co-
(dppp)(SPh)2] and [Co(bdpp)(SPh)2], respectively.34 It is also
Acknowledgment. This research work was supported by a
Direct Grant (A/C 2060157) of The Chinese University of Hong
Kong.
Supporting Information Available: Listings of X-ray crystal-
lographic data, atomic coordinates, thermal parameters, and complete
bond distances and angles for complexes 1-3. This material is available
free of charge via the Internet at http://pubs.acs.org.
(32) (a) Olmstead, M. M.; Power, P. P.; Sigel, G. Inorg. Chem. 1986, 25,
1027-1033. (b) Sigel, G. A.; Barlett, R. A.; Decker, D.; Olmstead,
M. M.; Power, P. P. Inorg. Chem. 1987, 26, 1773-1780, and
references therein.
IC0102945
(33) (a) Swenson, D.; Baenziger, N. C.; Coucouvanis, D. J. Am. Chem.
Soc. 1978, 100, 1932-1934. (b) Coucouvanis, D.; Swenson, D.;
Baenziger, N. C.; Murphy, C.; Holah, D. G.; Sfarnas, N.; Simopoulos,
A.; Kostikas, A. J. Am. Chem. Soc. 1981, 103, 3350-3362.
(34) Wei, G.; Hong, M.; Huang, Z.; Liu, H. J. Chem. Soc., Dalton Trans.
1991, 3145-3148.
(35) (a) Shoner, S. C.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1991,
30, 330-332. (b) MacDonnell, F. M.; Ruhlandt-Senge, K.; Ellison, J.
J.; Holm, R. H.; Power, P. P. Inorg. Chem. 1995, 34, 1815-1822.
(36) Ruhlandt-Senge, K.; Power, P. P. J. Chem. Soc., Dalton Trans. 1993,
649-650.