Unexpected formation of a π-coordinate Schiff base cobalt(0) complex

Article abstract of DOI:10.1002/zaac.200500456

Both tetrakis(trimethylphosphine)cobalt(0) and methyltetrakis (trimethylphosphine)cobalt(I) react with 2-(benzylidene-amino)pyridine (1) exclusively giving a complex of composition (η²(N,C)-2-Py-N=CH- C₆H₅)Co(PMe₃)₃ (2), which is shown by single-crystal X-ray diffraction to constitute the first π-coordinate imine cobalt(0) complex. The route of formation is proposed and discussed.

Full text of DOI:10.1002/zaac.200500456

DOI: 10.1002/zaac.200500456
Unexpected Formation of a π-Coordinate Schiff Base Cobalt(0) Complex
Fengli Yu, Xiaoyan Li*, and Hongjian Sun
Jinan / PR China, School of Chemistry and Chemical Engineering, Shandong University
Received November 2nd, 2005.
Abstract. Both tetrakis(trimethylphosphine)cobalt(0) and methyl-
tetrakis(trimethylphosphine)cobalt(I) react with 2-(benzylidene-
amino)pyridine (1) exclusively giving a complex of composition
(η2(N,C)-2-Py-NϭCH-C6H5)Co(PMe3)3 (2), which is shown by
single-crystal X-ray diffraction to constitute the first π-coordinate
imine cobalt(0) complex. The route of formation is proposed and
discussed.
Keywords: Cobalt; Imine; π-Coordinate; Crystal structure
Introduction
In 1997, Jun and co-workers reported a new kind of
highly active catalyst system for hydroacylation of olefins
by utilizing 2-aminopyridine derivatives as a chelation
auxiliary [15Ϫ17]. In the postulated mechanism, the C-H
bond of an aldimine formed by condensation of aldehyde
and 2-amino-3-picoline is cleaved by rhodium(I) complex
to give an (iminoacyl)rhodium(III) hydride (Eq. (3)). The
N-donor of the pyridine ring coordinates to the rhodium
center forming a five-membered rhodacycle. Facile catalytic
C-C bond activation of unstrained ketones and cleavage of
a CϵC bond of alkynes have also been successfully
achieved through chelation assistance of 2-amino-3-picoline
by a rhodium(I) complex [18, 19]. In these catalytic reac-
tions, metalated intermediates, for example (iminoacyl)-
rhodium(III) hydride in Eq. (3), could not be isolated by
experiment. It would be of great practical importance to
shed more light on the reaction mechanism.
Activation of a C-H bond by a transition metal center is
usually a key step for a wide variety of catalytic reactions
[1Ϫ5]. There has been an increasing interest in N-centered
chelating ligands forming metallacyclic compounds which
are utilized in organic synthesis [6Ϫ9]. New organometallic
intermediates containing (N, C)-metallacycles formed in
C-H activation by ruthenium and rhodium have been ef-
ficiently applied to C-C coupling reactions between aro-
matic imines and olefins [10]. However, a few examples of
C-H activations were reported also with the cheaper cobalt
complexes [11Ϫ14]. Recently, Klein recounted cyclometal-
ation reactions at a cobalt center by using imine and pyridyl
anchoring groups for the first time (Eq. (1) and Eq. (2)). N,
C-cobaltacyclic compounds are produced as the result of
C-H bond activation [14].
In our study using trimethylphosphine supported cobalt
complexes we have tried to activate the C-H bond of aldim-
ines in order to obtain cobaltacyclic complexes with poten-
tial application in organic synthesis. However, the exper-
imental results showed that an unexpected product was
formed, which was shown to be a π-coordinate imine
cobalt(0) complex.
* Dr. Xiaoyan Li
School of Chemistry and Chemical Engineering, Shandong University
Shanda Nanlu 27
Experimental Section
General Procedures and Materials
250100 Jinan / PR China
All air-sensitive and volatile materials were handled either in vacuo
or under argon by using standard Schlenk techniques. Melting
Fax: ϩ8653188564464
E-mail: xli63@sdu.edu.cn
Z. Anorg. Allg. Chem. 2006, 632, 501Ϫ504
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
501

F. Yu, X. Li, H. Sun
˚
Table 1 Crystal data and structure refinement for complex 2.
Table 3 Bond lengths /A and angles /° for 2.
Co(1)ϪN(1)
Co(1)ϪC(6)
Co(1)ϪP(2)
Co(1)ϪP(3)
Co(1)ϪP(1)
C(1)ϪN(2)
C(1)ϪC(2)
C(2)ϪC(3)
C(3)ϪC(4)
C(4)ϪC(5)
C(5)ϪN(2)
C(5)ϪN(1)
C(6)ϪN(1)
C(6)ϪC(7)
C(7)ϪC(8)
C(7)ϪC(12)
C(8)ϪC(9)
C(9)ϪC(10)
C(10)ϪC(11)
C(11)ϪC(12)
C(13)ϪP(2)
C(14)ϪP(2)
C(15)ϪP(2)
C(16)ϪP(1)
C(17)ϪP(1)
C(18)ϪP(1)
C(19)ϪP(3)
C(20)ϪP(3)
C(21)ϪP(3)
1.8948(14)
2.023(2)
2.1981(5)
2.2046(5)
2.2189(5)
1.335(3)
1.367(3)
1.367(3)
1.376(3)
1.401(2)
1.343(2)
1.368(2)
1.384(2)
1.468(2)
1.381(3)
1.398(3)
1.392(3)
1.387(4)
1.356(4)
1.380(3)
1.833(2)
1.825(2)
1.834(2)
1.821(2)
1.830(3)
1.829(3)
1.825(2)
1.835(2)
1.826(2)
N(2)ϪC(1)ϪC(2)
124.9(2)
117.6(2)
119.6(2)
119.4(2)
117.4(2)
120.8(2)
121.7(2)
120.3(2)
64.43(9)
118.82(12)
117.9(2)
122.1(2)
120.0(2)
120.8(2)
119.5(3)
120.6(2)
119.8(2)
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system, space group
Unit cell dimensions
C21 H37 Co N2 P3
469.37
C(3)ϪC(2)ϪC(1)
C(2)ϪC(3)ϪC(4)
C(3)ϪC(4)ϪC(5)
N(2)ϪC(5)ϪN(1)
N(2)ϪC(5)ϪC(4)
N(1)ϪC(5)ϪC(4)
N(1)ϪC(6)ϪC(7)
N(1)ϪC(6)ϪCo(1)
C(7)ϪC(6)ϪCo(1)
C(8)ϪC(7)ϪC(12)
C(8)ϪC(7)ϪC(6)
C(12)ϪC(7)ϪC(6)
C(7)ϪC(8)ϪC(9)
C(10)ϪC(9)ϪC(8)
C(11)ϪC(10)ϪC(9)
C(10)ϪC(11)ϪC(12)
C(11)ϪC(12)ϪC(7)
C(5)ϪN(1)ϪC(6)
C(5)ϪN(1)ϪCo(1)
C(6)ϪN(1)ϪCo(1)
C(1)ϪN(2)ϪC(5)
C(16)ϪP(1)ϪC(18)
C(16)ϪP(1)ϪC(17)
C(18)ϪP(1)ϪC(17)
C(16)ϪP(1)ϪCo(1)
C(18)ϪP(1)ϪCo(1)
C(17)ϪP(1)ϪCo(1)
C(14)ϪP(2)ϪC(13)
C(14)ϪP(2)ϪC(15)
C(13)ϪP(2)ϪC(15)
C(14)ϪP(2)ϪCo(1)
C(13)ϪP(2)ϪCo(1)
C(15)ϪP(2)ϪCo(1)
C(19)ϪP(3)ϪC(21)
C(19)ϪP(3)ϪC(20)
C(21)ϪP(3)ϪC(20)
C(19)ϪP(3)ϪCo(1)
C(21)ϪP(3)ϪCo(1)
C(20)ϪP(3)ϪCo(1)
293(2) K
˚
0.71073 A
triclinic,P-1
a ϭ 8.5108(6) A
˚
α ϭ 97.6760(10)°
β ϭ 101.8900(10)°
γ ϭ 101.1560(10)°
˚
b ϭ 10.1467(7) A
˚
c ϭ 15.8202(11) A
Volume
1290.02(16) A3
2, 1.208 Mg/m3
0.859 mmϪ1
Z, calculated density
Absorption coefficient
F(000)
498
Crystal size
0.98 x 0.50 x 0.30 mm
Theta range for data collection 2.08 to 25.25o deg.
Limiting indices Ϫ10<ϭh<ϭ10, Ϫ11<ϭk<ϭ12, Ϫ18<ϭl<ϭ12
Reflections collected / unique 6927 / 4586 [R(int) ϭ 0.0150]
Completeness to theta ϭ 25.25 98.0 %
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints / parameters 4586 / 0 / 253
Goodness-of-fit on F∧2
1.017
Final R indices [I>2sigma(I)] R1 ϭ 0.0308, wR2 ϭ 0.0834
121.4(2)
122.35(14)
134.50(12)
74.36(9)
117.6(2)
100.20(14)
100.3(2)
Semi-empirical from equivalents
0.7825 and 0.4863
Full-matrix least-squares on F2
101.0(2)
117.62(9)
113.42(10)
121.05(10)
99.53(13)
98.21(12)
101.32(14)
119.76(8)
114.32(9)
120.07(9)
101.71(13)
98.94(13)
100.76(14)
119.42(9)
110.21(9)
122.51(9)
R indices (all data)
Largest diff. peak and hole
R1 ϭ 0.0331, wR2 ϭ 0.0847
0.513 and Ϫ0.297 e·AϪ3
N(1)ϪCo(1)ϪC(6)
N(1)ϪCo(1)ϪP(2)
C(6)ϪCo(1)ϪP(2)
N(1)ϪCo(1)ϪP(3)
C(6)ϪCo(1)ϪP(3)
P(2)ϪCo(1)ϪP(3)
N(1)ϪCo(1)ϪP(1)
C(6)ϪCo(1)ϪP(1)
P(2)ϪCo(1)ϪP(1)
P(3)ϪCo(1)ϪP(1)
41.21(6)
135.42(5)
105.95(5)
100.72(4)
141.74(5)
102.17(2)
111.21(5)
97.66(6)
Table 2 Atomic coordinates (x 104) and equivalent isotropic
displacement parameters (A x 10 ) for 2. U(eq) is defined as one
third of the trace of the orthogonalized Uij tensor.
2
3
˚
100.65(2)
102.10(2)
x
y
z
U(eq)
Co(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
9486(1)
12818(3)
13721(3)
13941(3)
13253(2)
12312(2)
11264(2)
12106(2)
12984(2)
13767(3)
13671(3)
12830(3)
12054(3)
9231(4)
8443(3)
6133(3)
6962(4)
5635(3)
8368(4)
8697(3)
7354(4)
10808(3)
11640(2)
12119(2)
7631(1)
8343(1)
9024(1)
7628(1)
5609(2)
6407(3)
7791(2)
8325(2)
7439(2)
9189(2)
10241(2)
9934(2)
10954(3)
12294(3)
12619(2)
11606(2)
8219(3)
10292(2)
7848(3)
9227(3)
6419(3)
7373(3)
4174(2)
4610(3)
5073(3)
7918(1)
6081(2)
7645(1)
8462(1)
5440(1)
7416(1)
9494(1)
10273(2)
10340(1)
9635(1)
8864(1)
8191(1)
7780(1)
7166(2)
6786(2)
7033(2)
7642(2)
8017(1)
5337(2)
6406(2)
5782(2)
8445(2)
7880(2)
9335(2)
7558(2)
5889(2)
6479(2)
8138(1)
8796(1)
8216(1)
6292(1)
6856(1)
35(1)
61(1)
69(1)
64(1)
49(1)
38(1)
41(1)
44(1)
57(1)
77(1)
82(1)
74(1)
58(1)
82(1)
73(1)
83(1)
83(1)
96(1)
88(1)
73(1)
87(1)
76(1)
39(1)
48(1)
51(1)
48(1)
50(1)
(2-(benzylideneamino)pyridine)tris(trimethylphosphine)cobalt(0)
(2). Method a: An ether solution (10 ml) containing 1 (0.6 g,
3.30 mmol) was added to a stirred solution of Co(PMe3)4 (1.2 g,
3.30 mmol) in diethyl ether (50 ml) at room temperature. The yel-
low-brown mixture was kept stirring for 18 h and gradually turned
orange-red. A slight turbidity was filtered off, and after the solution
was kept at 4 °C yellow-brown crystals of 2 were obtained. At
Ϫ27 °C a second fraction of crystals was collected. Combined yield
810 mg (52 %). Method b: A THF solution (10 ml) containing 1
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
N(1)
N(2)
P(1)
(0.62 g, 3.41 mmol) was added to
a stirred solution of
Co(PMe3)4Me (1.3 g, 3.40 mmol) in THF (50 ml). The mixture was
kept at room temperature for 15 h, during which a brown turbid
solution formed. The volatiles was removed in vacuo, and the solid
residue was extracted with pentane. At 4 °C yellow-brown crystals
of 2 were obtained. Upon cooling to Ϫ27 °C, a second fraction of
crystal was collected. Combined yield 720 mg (45 %); m. p. 130 °C
(dec.). Anal. Calcd. for C21H37CoN2P3 (469.37 g/mol): C, 53.73; H,
7.94; N, 5.97. Found: C, 53.53; H, 7.96; N, 6.25 %. IR (Nujol):
P(2)
P(3)
1621 (CϭN); 1585, 1562, 1544 (CϭC) cmϪ1
.
points/decomposition temperatures: Sealed capillaries, uncorrected
values. 2-(benzylideneamino)pyridine (1) was obtained by conden-
sation of benzaldehyde with 2-aminopyridine. Tetrakis(trimethyl-
phosphine)cobalt(0) and methyltetrakis(trimethylphosphine)cobalt(I)
were prepared by published procedures [20]. Other chemicals were
used as purchased. All solvents were dehydrated and degassed be-
fore use. IR: Nujol mulls between KBr discs, Bruker spectrophoto-
meter type VECTOR 22. For C, H, N analyses an automatic
ELEMENTAR Vario ELIII analyzer was used. X-ray diffraction
analyses were carried out on a Bruker Smart 1000 diffractometer.
Crystallographic data for 2
C21H37CoN2P3: Mr ϭ 469.37, crystal size 0.98 x 0.50 x 0.30 mm3,
triclinic, space group P-1, a ϭ 8.5108(6), b ϭ 10.1467(7), c ϭ
˚
15.8202(11) A,
Ͱ
ϭ
97.6760(10),
β
ϭ
101.8900(10),
γ
ϭ
3
3
˚
101.1560(10)°, V ϭ 1290.02(16) A , Dc ϭ 1.208 Mg/m for Z ϭ 2,
F(000) ϭ 498, µ ϭ 0.859 mmϪ1, Bruker Smart 1000 diffractometer,
˚
λ ϭ 0.71073 A, T ϭ 293(2) K, ω-scans, 6927 reflections, Θmax
ϭ
25.25°, 4586 independent reflections [R (int) ϭ 0.0150], semi-em-
pirical absorption correction, hydrogen atoms were fixed in calcu-
502
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Z. Anorg. Allg. Chem. 2006, 501Ϫ504

Unexpected Formation of a π-Coordinate Schiff Base Cobalt(0) Complex
lated positions, 253 refined parameters, R ϭ 0.0331 (observed
data), wR2 ϭ 0.0834 (independent data).
Crystallographic data (excluding structure factors) for the structure
described in this publication have been deposited as supplementary
material with the Cambridge Crystallographic Data Centre. Depo-
sition number is CCDC-279760 for 2. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK [Fax: ϩ44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
Results and Discussion
2-(benzylideneamino)pyridine (1) when combined with
Co(PMe3)4 in diethyl ether at room temperature reacts with
liberation of trimethylphosphine to afford the π-coordinate
imine cobalt(0) complex 2 (Scheme 1, route a).
˚
Fig. 1 Molecular structure of 2; selected distances /A and
angles /°:
Co(1)-N(1) 1.8948(14), Co(1)-C(6) 2.0226(17), Co(1)-P(2) 2.1981(5), Co(1)-
P(3) 2.2046(5), Co(1)-P(1) 2.2189(5), C(6)-N(1) 1.384(2); N(1)-Co(1)-C(6)
41.21(6); N(1)-Co(1)-P(2) 135.42(5), C(6)-Co(1)-P(2) 105.95(5), N(1)-Co(1)-
P(3) 100.72(4), C(6)-Co(1)-P(3) 141.74(5), P(2)-Co(1)-P(3) 102.17(2), N(1)-
Co(1)-P(1) 111.21(5), C(6)-Co(1)-P(1) 97.66(6), P(2)-Co(1)-P(1) 100.65(2),
P(3)-Co(1)-P(1) 102.10(2), N(1)-C(6)-C(7) 120.27(16), C(5)-N(1)-C(6)
122.35(14).
Owing to an iso-electronic relationship of 2-(benzylidene-
amino)pyridine with diphenylethene the structure of com-
plex 2 is very similar to that of stilbenetris(trimethylphos-
phine)cobalt(0) complex [26]. The difference is that stilbene
adopts a trans configuration, while 2-(benzylideneamino)-
pyridine in complex 2 is in a cis-orientation. Therefore there
is less repulsion of phenyl and pyridine rings with the
Co(PMe3)3 moiety than in the former. Furthermore, in
2-(benzylideneamino)pyridine the molecular plane of con-
jugation is retained after coordination, while the molecular
plane of trans-stilbene is lost upon coordination affecting
the conjugation of the CϭC bond with two phenyl rings.
It may be argued that the C-H bond of the imine group
cannot be activated and cleaved because of the coordination
of N atoms, and that the formation of Co-C and Co-H
bonds together with chelation cannot compensate the
energy required for an oxidative addition. It was suggested
that the N-donor function is coordinated first, followed by
activation and cleavage of the most suitable ligand C-H
bond [14]. The reverse conclusion would be, that without
cleavage of a C-H bond no coordination of a single N-do-
nor atom is likely. We prefer to consider the back-bonding
in the π-coordination of the imine group to cobalt(0) as
dominant contribution to the formation of complex 2.
As tetrakis(trimethylphosphine)cobalt(0) could not
cleave a C-H bond of 2-(benzylideneamino)pyridine we pro-
ceeded to utilize tetrakis(trimethylphosphine)methylcobalt(I)
for a C-H bond activation of the imine group in ligand 1.
The reaction of 2-(benzylideneamino)pyridine (1) with
tetrakis(trimethylphosphine)methylcobalt(I) was carried out
Scheme 1
Complex 2 forms a red solid that is soluble in pentane or
diethyl ether. The yellow-brown crystals of complex 2 under
ambient conditions are thermally stable and can be handled
in air for several days without any sign of decomposition,
while under argon decomposition begins above 130 °C.
The result of a crystal structure determination of com-
plex 2 reveals that the reaction of 2-(benzylideneamino)pyr-
idine with tetrakis(trimethylphosphine)cobalt(0) proceeds
in an unexpected way, as both N atoms fail to coordinate
with the metal center forming a chelate ring (Scheme 1,
route b) as observed in rhodium complexes [21]. No oxidat-
ive addition of C-H bond to form a hydrido cobalt species
3 was found as reported by Frey [22]. Instead, the NϭC
bond of 1 replaces one of the trimethylphosphine ligands
and coordinates to the cobalt center in complex 2 by side-
on π-interaction. To the best of our knowledge, no π-imine
cobalt(0) compound has been described so far.
In the molecular structure (Fig. 1) of complex 2 the
cobalt atom occupies the central position of a tetrahedral
geometry. The midpoint of the CϭN group and three phos-
phorus atoms of trimethylphosphine ligands are positioned
at the four apices of a tetrahedron. The distance of Co to
N1 (1.8948(14) A) is shorter than that of Co to C6
(2.0226(17) A). Both of them lie in the normal region of
Co-N and Co-C bond length [23]. Three Co-P distances,
Co1-P1 ϭ 2.2189(5) A; Co1-P2 ϭ 2.1981(5) A; Co1-P3 ϭ
˚
˚
˚
˚
˚
2.2046(5) A, are comparable with those of trimethylphos-
phine supported monoolefin cobalt(0) complexes [24, 25].
Z. Anorg. Allg. Chem. 2006, 501Ϫ504
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
zaac.wiley-vch.de
503

F. Yu, X. Li, H. Sun
at room temperature and in THF as solvent. After 15 h, a
brown-yellow solution formed. The color of this solution
matches that of the reaction according to Scheme 2 without
formation of cobalt(III) complex through a C-H bond acti-
vation of the imine group. From pentane at 4 °C yellow-
brown crystals were obtained.
A single-crystal X-ray diffraction analysis confirmed that
the product is identical with complex 2, as obtained
through the reaction of ligand 1 with Co(PMe3)4 (Scheme 1,
route a). The proposed mechanism for a transformation of
a methyl cobalt(I) complex into a π-coordinate imine-
cobalt(0) complex is illustrated in Scheme 2. The first step
is displacement of one trimethylphosphine by ligand 1
through π-coordination of the imine group to form inter-
mediate 4, which would not be stable in solution. The fol-
lowing intermolecular elimination of ethane gives rise to the
end product, complex 2. The homolytic cobalt-carbon bond
cleavage was reported in other ligand systems [27].
References
[1] A. E. Shilov, G. B. Shul’pin, Chem. Rev. 1997, 97, 2879Ϫ2932.
[2] G. Dyker, Angew. Chem. 1999, 111, 1808; Angew. Chem. Int.
Ed. 1999, 38, 1698Ϫ1712.
[3] D.-Y. Lee, I.-J. Kim, C.-H. Jun, Angew. Chem. 2002, 114, 3157;
Angew. Chem. Int. Ed. 2002, 41, 3031Ϫ3033.
[4] C.-H. Jun, C. W. Moon, S.-G. Lim, H. Lee, Org. Lett. 2002,
4(9), 1595Ϫ1597.
[5] C.-H. Jun, K.-Y. Chung, J.-B. Hong, Org. Lett. 2001, 3(5),
785Ϫ787.
[6] A. Togni, L. M. Venanzi, Angew. Chem. 1994, 106, 517; An-
gew. Chem. Int. Ed. Engl. 1994, 33, 497Ϫ526.
[7] C. M. Thomas, B. Therrien, A. Neels, H. Stoeckli-Evans, G.
Suss-Fink, J. Orgmet. Chem. 2002, 658, 251Ϫ258.
[8] Y. J. Park, B.-I. Kwon, J.-A. Ahn, H. Lee, C.-H. Jun, J. Am.
Chem. Soc. 2004, 126, 13892Ϫ13893.
[9] C.-H. Jun, D.-Y. Lee, Y.-H. Kim, H. Lee, Organometallics
2001, 20, 2928Ϫ2931.
[10] F. Kakiuchi, S. Murai, Acc. Chem. Res. 2002, 35, 826Ϫ834.
[11] H.-F. Klein, S. Haller, H. Sun, X. Li, T. Jung, C. Roehr, U.
Floerke, H.-J. Haupt, Z. Naturforsch. 1998, 53b, 587Ϫ598.
[12] H.-F. Klein, R. Beck, U. Floerke, H.-J. Haupt, Eur. J. Inorg.
Chem. 2003, 853Ϫ862.
[13] H.-F. Klein, R. Beck, U. Floerke, H.-J. Haupt, Eur. J. Inorg.
Chem. 2002, 3305Ϫ3312.
[14] H.-F. Klein, S. Camadanli, R. Beck, D. Leukel, U. Floerke,
Angew. Chem. 2005, 117, 997Ϫ999; Angew. Chem. Int. Ed.
2005, 44, 975Ϫ977.
[15] C.-H. Jun, H. Lee, J.-B. Hong, J. Org. Chem. 1997, 62,
1200Ϫ1201.
[16] C.-H. Jun, C.-W. Huh, S.-J. Na, Angew. Chem. 1998, 110, 150;
Angew. Chem. Int. Ed. 1998, 37, 145Ϫ147.
[17] C.-H. Jun, D.-Y. Lee, H. Lee, J.-B. Hong, Angew. Chem. 2000,
112, 3214; Angew. Chem. Int. Ed. 2000, 39, 3070Ϫ3072.
[18] C.-H. Jun, H. Lee, J. Am. Chem. Soc. 1999, 121, 880Ϫ881.
[19] C.-H. Jun, H. Lee, C. W. Moon, H.-S. Hong, J. Am. Chem.
Soc. 2001, 123, 8600Ϫ8601.
[20] H.-F. Klein, H. H. Karsch, Chem. Ber. 1975, 108, 944Ϫ955.
[21] C.-H. Jun, C. W. Moon, D.-Y. Lee, Chem. Eur. J. 2002, 8,
2422Ϫ2428.
Scheme 2
[22] M. Frey, Doctoral Thesis, Darmstadt University of Technol-
ogy, Germany, 2005, 47.
[23] International Tables for Crystallography, Vol. C, Edited by A.
J. C. Wilson, 1992.
[24] H.-F. Klein, K. Ellrich, S. Lamac, G. Lull, L. Zsolnai, G.
Huttner, Z. Naturforsch. 1985, 40b, 1377.
[25] H.-F. Klein, G. Lull, B. Rodenhaeuser, G. Cordier, H. Paulus,
Z. Naturforsch. 1988, 43b, 1256.
In conclusion, both tetrakis(trimethylphosphine)cobalt(0)
and tetrakis(trimethylphosphine)methylcobalt(I) react with
2-(benzylideneamino)pyridine 1 giving an unexpected (Nϭ
C)π-coordinate cobalt(0) complex 2, which was confirmed
through single crystal X-ray diffraction studies. Two differ-
ent reaction routes result in the formation of the first Schiff
base π-complex of cobalt(0).
[26] Ch. Elschenbroich, A. Salzer, Organometallics, p. 229, second
Ed. VCH, 1992.
[27] (a) M. W. Witman, J. H. Weber, Inorg. Nucl. Chem. Letters
1975, 11, 591Ϫ594. (b) J. Y. Kim, T. Ukita, T. Kwan, Tetra-
hedron Letters 1972, 30, 3079Ϫ3082. (c) Ch. Elschenbroich, A.
Salzer, Organometallics, A Concise Introduction, VCH, 1992,
2.Ed. Page 202Ϫ203.
Acknowledgment. We gratefully acknowledge support by the Excel-
lent Young Teachers Program of MOE, the Scientific Research
Foundation for the Returned Overseas Chinese Scholars, SEM.
504
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Z. Anorg. Allg. Chem. 2006, 501Ϫ504