Synthesis and structure of novel dimethylcobalt(III) complexes containing trimethylphosphine and salicylaldiminato(N:O) ligands

Article abstract of DOI:10.1002/zaac.200500296

Dimethyl(salicylaldiminato[N: O])cobalt complexes [CoMe₂(2-O- C₆H₁R¹R² R³-CH=NR ⁴)L²] (L=PMe₃) (1-6) have been prepared through the reaction of [CoMe_3<

Full text of DOI:10.1002/zaac.200500296

Synthesis and Structure of Novel Dimethylcobalt(III) Complexes Containing
Trimethylphosphine and Salicylaldiminato(N:O) Ligands
Xiaoyan Li*, Liye Huang, Hongjian Sun, and Mu Li
Jinan / PR China, School of Chemistry and Chemical Engineering, Shandong University
Received May 30th, 2005.
Abstract.
Dimethyl(salicylaldiminato[N:O])cobalt
complexes
octahedral coordination of cobalt, with two equatorial cis-methyl
groups opposite to the planar N:O-chelate ring.
[CoMe2(2-O-C6H1R1R2 R3-CHϭNR4)L2] (LϭPMe3) (1 - 6) have
been prepared through the reaction of [CoMe3(PMe3)3] with the
corresponding substituted salicylaldimine. The complexes were
characterized with IR, 1H NMR, 13C NMR, 31P NMR and ele-
mental analyses. The X-ray crystal structure of complex 1 shows an
Keywords: Cobalt; Methyl complexes; Salicylaldimine; Trimethyl-
phosphine; Crystal structure
Introduction
Experimental Details
Methyl cobalt(III) complexes are important intermediates
for the cobalamin-dependent methionine synthase [1]. Some
alkyl cobalt(III) complexes undergo insertion reactions with
CO, an alkyne or an alkene to generate new C-C bonds [2].
If a complex bearing two alkyl groups reacts in this way,
two new C-C bonds can be formed. Insertion followed by
reduction elimination in the new acyl-alkyl, vinyl-alkyl, or
dialkyl complexes can generate a ketone, olefin or alkane,
respectively. Dimethyl cobalt(III) macrocycles can undergo
photodealkylation [3]. In environmental chemistry dimethyl
cobalt(III) complexes are used as methylation agents for
germanium, tin and lead compounds [4, 5].
General procedures and materials
Standard vacuum techniques were used in manipulations of volatile
and air-sensitive material. Microanalyses: Elemental analysis on C,
H and N was carried out at Shandong University using a vario
ELIII elemental analyzer, FRG. Melting points/decomposition
temperatures: Sealed capillaries, uncorrected values. Literature
methods were applied in the preparation of trimethyl-tris(trimethyl-
phosphine)cobalt [14], Salicylaldimine Schiff base [15]. IR: Nujol
mulls between KBr discs, Bruker Vector 22. 1H and 31P NMR spec-
tra and 13C NMR spectra (400 MHz, 162.0 MHz, and 100.6 MHz,
respectively) were recorded with a Brucker AV 400MHz spec-
trometer, 13C and 31P NMR resonances were obtained with broad-
band proton decoupling.
Schiff-base has many important applications in industrial
chemical production and scientific research as chelating ag-
ent, stabilizer, bio-activator and analytical reagent. Com-
plexes of transition metals with Schiff-bases can be widely
used as catalysts for olefin polymerization [6], olefin epoxid-
ation [7], olefin hydrogenation [8], C-H activation reaction
[9], and copolymerization of CO2/epoxides [10], as well as
lactone polymerization [11].
The reaction of [CoMe3(PMe3)3] with salicylaldhyde and
its derivatives affords us stable dimethyl phenolato co-
balt(III) complexes [12]. We have introduced the isoelec-
tronic Schiff base ligands under similar conditions and re-
port here on the synthesis and structural properties of some
novel mononuclear dimethyl cobalt(III) complexes.
Preparation of (N-methyl-salicylaldiminato-N:O)-cis-
dimethyl-trans-bis(trimethylphosphine)cobalt(III) (1)
0.36 g of n-methylsalicylaldimine (2.70 mmol) in 10 ml of pentane
at Ϫ80 °C were combined with 0.90 g [CoMe3(PMe3)3] (2.71 mmol)
in 50 ml of pentane. The mixture was warmed to 20 °C and stirred
for 18 h. During this period the reaction solution turned nacarat,
which was filtered and crystallization at Ϫ20 °C afforded red plate-
lets of 1. Yield 0.37 g (36 %); m. p. 139-141°C (dec.). Anal. Calc. for
C16H32NOP2Co (375.3): C 51.20, H 8.53, N 3.73; found C 51.34, H
8.65, N 3.81 %.
IR (Nujol): 1613 s ν(CϭN); 1144 m, 1133 m ν(Co-CH3) cmϪ1 1H NMR
.
(400 MHz, CDCl3, 300.2 K): δ ϭ Ϫ1.08 (t, 3J(PH) ϭ 8.6 Hz, 3H, Co-CH3),
Ϫ0.15 (t, 3J(PH) ϭ 9.5 Hz, 3H, Co-CH3), 1.11 (tЈ,Η2J(PH) ϩ 4J(PH)Η ϭ
6.1 Hz, 18H, PCH3), 3.13 (s, 3H, NCH3), 6.17 (t, 3J(HH) ϭ 7.2 Hz, 1H,
CH), 6.44 (d, 3J(HH) ϭ 7.6 Hz, 1H,CH), 6.80 (dd, 3J(HH) ϭ 7.4 Hz,
4J(HH) ϭ 1.2 Hz, 1H, CH), 6.98 (dt, 3J(HH) ϭ 7.6 Hz, 4J(HH) ϭ 1.6 Hz,
1H, CH), 7.90(s, 1H, CHϭN) ppm. 13C NMR (100.6 MHz, CDCl3,
300.2 K): 10.71 (tЈ,Η1J(PC) ϩ 3J(PC)Η ϭ 20.9 Hz, PCH3), 52.07 (s, NCH3),
109.9, 123.5, 132.2, 133.9 (CH), 119.4(C), 165.5 (s, CHϭN), 168.9(s, C-O)
ppm. 31P NMR (162.0 MHz, CDCl3, 300.2 K): 8.0 (s br) ppm.
* Dr. Xiaoyan Li
School of Chemistry and Chemical Engineering,
Shandong University
Shanda Nanlu 27
250100 Jinan / PR China
Fax: 0086-531-88564464
E-mail: xli63@sdu.edu.cn
Preparation of (N-methyl-3,5-di-tert-butyl-
salicylaldiminato-N:O)-cis-dimethyl-trans-
bis(trimethylphosphine)cobalt(III) (2)
Supporting information for this article is available on the
WWW under http://www.wiley-vch.de/home/zaac or from the
author
In a similar procedure starting from 0.49 g of n-methyl-3,5-di-tert-
butyl-salicylaldimine (1.98 mmol) and 0.66 g of [CoMe3(PMe3)3]
3096
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
DOI: 10.1002/zaac.200500296
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Novel Dimethylcobalt(III) Complexes
3J(HH) ϭ 7.0 Hz, 1H, CH), 7.27 (t, 3J(HH) ϭ 6.0 Hz, 1H, CH), 7.37 (d,
3J(HH) ϭ 9.1 Hz, 1H, CH), 7.47 (d, 3J(HH) ϭ 8.5 Hz, 1H, CH), 7.74 (d,
(1.99 mmol), 0.43 g dark red cubes of 2 (45 % yield) were obtained,
m.p. 129-130 °C (dec.). Anal. Calc. for C24H48NOP2Co (487.5):
calcd. C 59.13, H 9.85, N 2.87; found C 59.08, H 9.58, N 2.91 %.
3J(HH)
ϭ
8.5 Hz, 1H, CH) 8.80 (s, 1H, CHϭN) ppm. 13C NMR
(100.6 MHz, CDCl3, 300.2 K): δ ϭ 10.76(t, Η1J(PC)ϩ3J(PC)Η ϭ 21.0 Hz,
PCH3), 52.9 (s, NCH3), 116.6, 119.3, 126.0, 127.5, 128.2, 132.2 (CH), 108.0,
124.9, 135.1 (C), 159.6 (s, CHϭN), 169.4 (s, C-O) ppm.
IR (Nujol): 1610 s ν(CϭN); 1163 m, 1125 m ν(Co-CH3) cmϪ1 1H NMR
.
(400 MHz, CDCl3, 296 K): δ ϭ Ϫ1.02(t, 3J(PH) ϭ 7.8 Hz, 3H, CoCH3),
0.04(t, 3J(PH) ϭ 7.8 Hz, 3H, CoCH3), 1.22(s, 18H, PMe3), 1.35 (s, 9 H,
C(CH3)3, 1.37 (s, 9 H, C(CH3)3), 3.18 (s, 3H, NCH3), 6.66 (s, 1H,CH), 7.19
(s, 1H, CH), 7.93(s, 1H, CHϭN) ppm. 13C NMR (100.6 MHz, CDCl3,
Preparation of (N-phenyl-salicylaldiminato-N:O)-cis-
dimethyl-trans-bis(trimethylphosphine)cobalt(III)
(6)
300.2 K):
δ ϭ Ϫ19.8 (s br, CoCH3), Ϫ8.4 (s br, CoCH3), 11.92(tЈ,
Η1J(PC)ϩ3J(PC)Η ϭ 20.1 Hz, PCH3), 29.8 (s, C(CH3)3), 30.9 (s, C(CH3)3), 33.0
(s, C(CH3)3),34.7 (s, C(CH3)3), 51.2 (s, NCH3), 127.4, 127.7 (CH), 118.6,
130.6, 140.5(C), 167.1(s, CHϭN), 167.2(s, C-O) ppm..
In a similar procedure starting from 0.43 g of n-phenyl-salicylaldi-
mine (2.18 mmol) and 0.73 g of [CoMe3(PMe3)3] (2.20 mmol),
0.34 g red crystals of 6 (36 % yield) were obtained, m.p. 115-116 °C
(dec.). Anal. Calc. for C21H34NOP2Co (437.4): calcd. C57.66,
H7.83, N3.20; found C57.62, H7.55, N3.27 %.
IR (Nujol): 1600 s ν(CϭN); 1164 m, 1140 m ν(Co-CH3) cmϪ1 1H NMR
(400 MHz, CDCl3, 300.2 K): δ ϭ Ϫ1.27(s br, 3H, Co-CH3), 0.01(s, 3H,
CoCH3), 1.27(s br, 18H, PCH3), 6.21 (s, 1H,CH), 6.53 (d, 3J(HH) ϭ 7.3 Hz,
1H, CH), 6.87 (d, 3J(HH) ϭ 6.1 Hz, 1H, CH), 6.95 (s, 2H, CH), 7.06 (s, 1H,
CH), 7.18 (s, 1H, CH), 7.33 (s, 2H, CH), 8.0 (s, 1H, CHϭN) ppm. 13C NMR
(100.6 MHz, CDCl3, 300.2 K): δ ϭ 11.41(tЈ, Η1J(PC)ϩ3J(PC)Η ϭ 20.4 Hz,
PCH3), 110.7, 123.6, 124.5, 127.8, 133.1, 135.2 (CH), 124.2, 155.2 (C), 167.3
(s, CHϭN) ppm.
Preparation of (N-methyl-3-tert-butyl-5-methyl-
salicylaldiminato-N:O)-cis-dimethyl-trans-
bis(trimethylphosphine)cobalt(III) (3)
In a similar synthesis 0.29 g n-methyl-3-tert-butyl-5-methyl-salicyl-
aldimine (1.41 mmol) and 0.51 g CoL3Me3 (1.53 mmol) gave 0.31 g
of red needles (49 % yield), m.p. 159-160 °C (dec.). Anal. Calc. for
C21H42NOP2Co (445.4): C 56.63, H 9.50, N 3.14; found C 56.50,
H 9.49, N 3.24 %.
IR (Nujol): 1610 s ν(CϭN); 1163 m, 1133 m ν(Co-CH3) cmϪ1 1H NMR
.
(400 MHz, CDCl3, 300.2 K): δ ϭ Ϫ1.17 (t, 3J(PH) ϭ 7.7 Hz, 3H, Co-CH3),
Ϫ0.09 (t, 3J(PH) ϭ 9.1 Hz, 3H, Co-CH3), 1.06 (s, 18H, PCH3), 1.21 (s, 9 H,
C(CH3)3, 2.03 (s, 3 H, CH3), 3.03 (s, 3H, NCH3), 6.40 (s, 1H, CH), 6.80 (s,
1H, CH), 7.75 (s, 1H, CHϭN) ppm. 13C NMR (100.6 MHz, CDCl3,
300.2 K): δ ϭ Ϫ19.6 (s br, CoCH3), Ϫ8.3 (s br, CoCH3), 11.94 (tЈ,
Η1J(PC)ϩ3J(PC)Η ϭ 19.5 Hz, PCH3), 19.9 (s, CH3), 29.8 (s, C(CH3)3), 34.5 (s,
C(CH3)3), 51.4 (s, NCH3), 131.0, 131.9 (CH), 117.0, 119.3, 141.4 (C), 166.7(s,
CHϭN), 167.1(s, C-O) ppm.
Crystallographic data for 1
(C16H32CoNOP2, Mr ϭ 375.30): crystal size 0.37 ϫ 0.22 ϫ
0.17 mm3, monoclinic, space group P21/c, a ϭ 13.908(20), b ϭ
3
˚
˚
11.060(16), c ϭ 13.069(18) A, β ϭ 101.651(19)°, V ϭ 1969(5) A ,
Dc ϭ 1.266 g cmϪ3 for Z ϭ 4, F(000) ϭ 800, μ ϭ 1.033 mmϪ1
,
˚
Bruker AXS P4 diffractometer, λ ϭ 0.71073 A, T ϭ 293 K, ω-scans,
9965 reflections, Θmax ϭ 25.03°, 3467 independent reflections
[R (int) ϭ 0.0754], semi-empirical absorption correction, hydrogens
calculated, 190 refined parameters, R ϭ 0.0629 (observed data),
wR2 ϭ 0.1561 (independent data). Detailed data see “Supporting
information“.
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-270616 for 1. 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].
Preparation of (N-methyl-3-methoxy-
salicylaldiminato-N:O)-cis-dimethyl-trans-
bis(trimethyl- phosphine)cobalt(III) (4)
In a similar procedure starting from 0.26 g n-methyl-3-methoxy-
salicylaldimine (1.58 mmol) in 10 ml of ether and 0.53 g of [CoMe3-
(PMe3)3] (1.60 mmol) in 50 ml of ether, 0.39 g red-brown needles
of 4 (61 % yield) were obtained, m. p. 140-141 °C (dec.). Anal. Calc.
for C17H34NO2P2Co (405.3): C50.37, H8.45, N3.45; found C50.44,
H8.31, N3.55 %,
IR (Nujol): 1610 s ν(CϭN); 1148 m, 1099 m ν(Co-CH3) cmϪ1 1H NMR
.
(400 MHz, CDCl3, 300.2 K): δ ϭ Ϫ1.08 (t, 3J(PH) ϭ 8.4 Hz, 3H, Co-CH3),
Ϫ0.08 (t, 3J(PH) ϭ 9.3 Hz, 3H, Co-CH3), 1.12 (s, 18H, PCH3), 3.13 (s, 3H,
NCH3), 3.75 (s, 3 H, OCH3), 6.09 (t, 3J(HH) ϭ 7.3 Hz, 1H,CH), 6.52 (d,
3J(HH) ϭ 7.3 Hz, 1H,CH), 6.64 (d, 3J(HH) ϭ 7.0 Hz, 1H, CH) 7.91 (s,
1H, CHϭN) ppm. 13C NMR (100.6 MHz, CDCl3, 300.2 K): δ ϭ 10.73 (tЈ,
Η1J(PC)ϩ3J(PC)Η ϭ 20.9 Hz, PCH3),52.1 (s, NCH3), 57.4 (s, OCH3),108.5,
116.2, 127.0 (CH), 119.7, 153.4 (C), 161.1(s, C-O), 165.3(s, CHϭN) ppm.
Results and Discussion
Substituted salicylaldimines react with [CoMe3(PMe3)3]
(Eq. (1)) with the elimination of methane and subtraction
of trimethylphosphine as well as utilizing both the phe-
nolato-O and the imine-N atom to afford the six coordinate
cobalt(III) complexes 1 to 6 as red solids that are soluble
in pentane or diethyl ether.
Preparation of (N-methyl-naphtalaldiminato-N:O)-
cis-dimethyl-trans-bis(trimethylphosphine)cobalt(III)
(5)
In the infrared spectra, the characteristic bands for sym-
metric deformation vibration of (Co-Me)-bond can be
In a similar procedure starting from 0.31 g n-methyl-naphtalaldim-
ine (1.69 mmol) in 10 ml of ether and 0.56 g of [CoMe3(PMe3)3]
(1.69 mmol) in 50 ml of ether, 0.29 g nacarat powder of 5 (41 %
yield) were obtained, m. p. 159-160 °C (dec.). Anal. Calc. for
C24H48NOP2Co (487.5): calcd. C59.13, H9.92, N2.87; found
C59.08, H9.78, N2.91 %.
IR (Nujol): 1606 s ν(CϭN); 1186 m, 1164 m ν(Co-CH3) 1H NMR (400 MHz,
CDCl3, 300.2 K): δ ϭ Ϫ1.03(tЈ, 3J(PH) ϭ 8.7 Hz, 3H, Co-CH3), Ϫ0.18(tЈ,
3J(PH) ϭ 9.5 Hz, 3H, Co-CH3), 1.12 (tЈ, Η2J(PH)ϩ4J(PH)Η ϭ 6.6 Hz, 18H,
PCH3), 3.23 (s, 3H, NCH3), 6.65 (d, 3J(HH) ϭ 9.2 Hz, 1H, CH), 7.01 (t,
found in the region of 1140Ϫ1190 cmϪ1
.
1
From H-NMR spectroscopy we know that both of the
cis-methyl groups have two triplet signals between Ϫ0.0 and
Ϫ1.0 ppm with coupling constant 3J(PH) ϭ 8 Ϫ 10 Hz,
which are created by coupling of two trans-phosphoratome
at an angle of approximate 90°. A pseudo-triplet between
1,1 and 1,3 ppm with coupling constant Η2J(PH) ϩ
Z. Anorg. Allg. Chem. 2005, 631, 3096Ϫ3099
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© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
3097

X. Li, L. Huang, H. Sun, M. Li
4J(PH)Η ϭ 6Ϫ7 Hz is recorded for two trans-PMe3. The sal-
icylaldimines protons are found in the range of 7.7 Ϫ
8.8 ppm as singlet signals. In the 13C NMR Spektra a res-
onance at 160 Ϫ 170 ppm is generated by the salicylaldim-
ine carbon atom. This value lies in the region of resonance
for phenolato carbon nucleus. This result tells us that the
salicylaldimine carbon atom and the phenolato carbon
atom have the similar electronic properties, which is caused
through the conjugation of the chelate ring. The resonances
of the two cobalt-methyl carbon atoms in compound 2 and
compound 3 are recorded at Ϫ19.8, Ϫ19.6 and Ϫ8.4,
Ϫ8.3 ppm, respectively. In the 31P NMR Spectra we got a
singlet for complex 1 at ca. 8 ppm for two trans-PMe3 at
room temperature.
All of the spectroscopic data suggest an octahedral coor-
dination with two trans-trimethylphosphine ligands, two
cis-methyl groups and the conjugated chelating imine phe-
nolato ligand at the cobalt atom. This conjecture is verified
through X-ray single crystal diffraction.
By re-crystallization from pentane at 4 °C suitable crys-
tals of 1 as red prism for X-ray diffraction analysis were
obtained. The molecular geometry is shown in Figure 1
with selected bond distances and angles. The cobalt atom
attains an octahedral coordination with two equatorial cis-
methyl groups (C9-Co-C10ϭ91.3(2)°) opposite to the
planar N:O-chelate ring of a salicylaldiminato anion with
the usual bite-angle (O1-Co-N1ϭ90.6 (2)°) and by two axial
trimethylphosphine which are slightly bent (P1-Co-P2ϭ
174.0(5)°) towards the Co-Me groups. This structure is re-
lated to that of (2-acetyl-4-methyl-6-tert-butyl-phenolato-
O:O)-cis-dimethyl-trans-bis(trimethyl-
˚
Fig. 1. Molecular structure of 1; selected bond distances /A and
angles /deg:
Co1-O1 1.984(4), Co1-C10 1.998(5), Co1-C9 2.001(5), Co1-N1 2.026(4),
Co1-P2 2.208(3), Co1-P1 2.215(3), C1-N1 1.276(6), N1-C8 1.468(6), O1-C3
1.288(5), C1-C2 1.436(6); C2-C3 1.409(6); O1-Co1-C10 83.4(2), O1-Co1-C9
174.6(2), C10-Co1-C9 91.3(2), O1-Co1-N1 90.6(2), C10-Co1-N1 173.9(2),
C9-Co1-N1 94.8(2), O1-Co1-P2 91.27(9), C10-Co1-P2 87.1(2), C9-Co1-P2
88.8(2), N1-Co1-P2 93.1(1), O1-Co1-P1 91.2(1), C10-Co1-P1 87.8(2), C9-
Co1-P1 88.3(2), N1-Co1-P1 92.3(1), P2-Co-P1 174.02(5), C1-N1-Co1
124.4(3), C3-O1-Co1 128.8(3), N1-C1-C2 128.6 (4), C1-C1-C3 122.5(4), C2-
C3-O1 124.8(4).
They are very reactive to CO. We will report the results in
the near future.
phosphane)cobalt(III)] [13]. Conjugational effects upon co-
˚
ordination shorten the original bond C1-C2 to 1.436(6) A,
˚
there is no great difference between C1-C2 1.436(6) A and
Acknowledgements. Financial supports of this work by the Excellent
Young Teachers Program of MOE, People’s Republic of China and
by the Scientific Research Foundation for the Returned Overseas
Chinese Scholars/State Education Ministry, Natural Science Foun-
dation of Shandong University for Young Scientists, are grate-
fully acknowledged.
˚
C2-C3 1.409 (6) A. The sum of internal angles of this chel-
ating ring with 719.7° indicates the chelating with weak
ring strain.
The complexes (1-6) are stable and can be handled in air
for several months without any sign of decomposition.
3098
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Novel Dimethylcobalt(III) Complexes
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