2052
Organometallics 1999, 18, 2052-2054
Syn th esis a n d Rea ction s of
[Co(RCN){P P h (OEt)2}3{η2-C6H5P O(OEt)2}]BP h 4
Der iva tives: Str on g Evid en ce for η2-Coor d in a tion of th e
P h en yl Rin g of th e C6H5P O(OEt)2 Liga n d
Gabriele Albertin,* Stefano Antoniutti, Emilio Bordignon, and Michela Carlon
Dipartimento di Chimica, Universita` Ca’ Foscari di Venezia, Dorsoduro 2137,
30123 Venezia, Italy
Received December 28, 1998
Sch em e 1a
Summary: Cobalt(I) complexes [Co(RCN)P3{η2-C6H5PO-
(OEt)2}]BPh4 (1; R ) Me, Ph; P ) PPh(OEt)2) were
prepared by allowing [CoClP4]BPh4 compound to react
with zinc dust in a cosolvent mixture of nitrile and
ethanol. η2-Coordination of the arene ring of the C6H5-
a
Legend: P ) PPh(OEt)2; R ) Me (a ), Ph (b).
1
PO(OEt)2 ligand was confirmed by H and 13C NMR
spectra and decoupling experiments. Substitution reac-
tions with CO or isocyanide gave free C6H5PO(OEt)2,
RCN, and [Co(CO)2P3]+ or [Co(RNC)2P3]+ cations. Treat-
ment of 1 with H2 (1 atm), in either the presence or
absence of a heterogeneous catalyst, gave the unstable
cobalt(III) dihydride derivative [CoH2P3{η2-C6H5PO-
(OEt)2}]+.
zinc dust gives a dark red solution from which, after
workup, a red solid6 characterized7 as [Co(RCN){PPh-
(OEt)2}3{η2-C6H5PO(OEt)2}]BPh4 (1) was obtained in
about 45% yield8 (Scheme 1).
The IR spectra show one weak band at 2278 cm-1 (1a )
and one at 2239 cm-1 (1b), due to the coordinated
nitrile, and a strong band at 1240 cm-1 attributed to
the νPdO of the C6H5PO(OEt)2 ligand. At room temper-
ature, the 31P{1H} NMR spectra of 1 in CD2Cl2 display
The coordination of aromatic molecules to transition
metals in an η2-fashion is rather uncommon,1 although
these complexes are suspected to be intermediates in
C-H activation and other catalytic processes.1,2 Recent
papers3 have in fact shown how η2-coordination acti-
vates the arene molecule toward selective hydrogenation
to alkene. The involvement of η2-species in C-H activa-
tion of aromatic molecules has also been the subject of
some studies.1c,2a
(6) All synthetic work was carried out under an inert atmosphere
using Schlenk techniques; solvents used were degassed and purified
by standard methods. Compounds 1 were prepared as follows. In a
50-mL three-necked round-bottomed flask 4 g (3.3 mmol) of [CoCl-
5
(PPh(OEt)2}4]BPh4 was dissolved in a cosolvent mixture of 10 mL of
ethanol and 15 mL of acetonitrile for 1a or in benzonitrile for 1b, and
the solution was treated at room temperature with an excess of zinc
dust (15 mmol, 1 g). The reaction mixture was stirred for 2 h, filtered
through silica gel, and then evaporated to dryness under reduced
pressure. During evaporation, the temperature of the solution must
be kept below 30 °C. The resulting oil was dissolved in ethanol (8 mL)
and treated with an excess of NaBPh4 (10 mmol, 3.4 g) dissolved in 5
mL of ethanol. A red solid separated out, which was filtered and
crystallized from CH2Cl2 (5 mL) and ethanol (15 mL); yield 45%. Note
that, to avoid the formation of oil, crystallization should be carried
out at 0 °C using ethanol containing a small amount of MeCN or PhCN
as precipitating agent. Furthermore, compounds 1 are air-sensitive
and must be handled under an inert atmosphere.
We now report a new example of η2-coordination of
an arene molecule involving the phenyl ring of the C6H5-
PO(OEt)2 ligand, bound to a cobalt4 central atom in an
η2-fashion.
Treatment of the complex5 [CoCl{PPh(OEt)2}4]BPh4
in an ethanol-nitrile (MeCN or PhCN) solution with
(7) The NMR spectra were recorded on a Bruker AC200 instrument.
1H and 13C NMR chemical shifts are referenced to internal SiMe4, 31P
shifts are referenced to 85% H3PO4 with downfield shifts considered
positive. Anal. Calcd for C66H83NBO9P4Co (1a ): C, 64.55; H, 6.81; N,
1.14. Found: C, 64.40; H, 6.73; N, 1.10. ΛM (CH3NO2, 25 °C): 53.6
Ω-1 mol-1 cm2. IR (KBr): 2278 w νCN cm-1; 1240 s νPdO cm-1. 1H NMR
(CD2Cl2, 25 °C): δ 7.75-6.60 (m, 38H, Ph), 5.63 (d, 1H, Ha), 5.01 (m,
1H, Hb), 4.01, 3.64, 3.39 (m, 16H, CH2), 1.25, 1.13, 1.04 (t, 24H, CH3).
31P{1H} NMR (CD2Cl2, -80 °C): spin system AB2, δA 173.2, δB 158.4,
J AB ) 98 Hz (PPh(OEt)2), 19.58 (s, 1P, C6H5PO(OEt)2). 13C NMR (CD2-
Cl2 at 25 °C): δ 165-120 (m, Ph), 97.8 (d of d, Ca, 1J CH ) 170 Hz, 2J CP
(1) (a) Muetterties, E. L.; Blecke, J . R.; Wucherer, E. J .; Albright,
T. A. Chem. Rev. 1982, 82, 499. (b) Sweet, J . R.; Graham, A. G. J . Am.
Chem. Soc. 1983, 105, 305; Organometallics 1983, 2, 135. (c) J ones,
W. D.; Feher, F. J . J . Am. Chem. Soc. 1984, 106, 1650. (d) van der
Heijden, H.; Orpen, A. G.; Pasman, P. J . Chem. Soc., Chem. Commun.
1985, 1576. (e) Harman, W. D.; Taube, H. J . Am. Chem. Soc. 1987,
109, 1883. (f) Harman, W. D.; Sekine, M.; Taube, H. J . Am. Chem.
Soc. 1988, 110, 5725. (g) Chordia, M. D.; Harman, W. D. J . Am. Chem.
Soc. 1998, 120, 5637.
(2) (a) Parshall, G. W.; Ittel, S. D. In Homogeneous Catalysis. The
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes, 2nd ed.; Wiley: New York, 1992. (b) Chatt, J .; Davidson,
J . M. J . Chem. Soc. 1965, 843.
(3) (a) Harman, W. D.; Taube, H. J . Am. Chem. Soc. 1988, 110, 7906.
(b) Harman, W. D.; Schaefer, W. P.; Taube, H. J . Am. Chem. Soc. 1990,
112, 2682. (c) Chin, R. M.; Dong, L.; Duckett, S. B.; J ones, W. D.
Organometallics 1992, 11, 871. (d) Chin, R. M.; Dong, L.; Duckett, S.
B.; Partridge, M. G.; J ones, W. D.; Perutz, R. N. J . Am. Chem. Soc.
1993, 115, 7685.
(4) For our previous papers on cobalt(I) complexes, see: (a) Albertin,
G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Pelizzi, G. Organometallics
1995, 14, 4126. (b) Albertin, G.; Antoniutti, S.; Bordignon, E. Orga-
nometallics 1990, 9, 2177. (c) Albertin, G.; Amendola, P.; Antoniutti,
S.; Bordignon, E. J . Chem. Soc., Dalton Trans. 1990, 2979. (d) Albertin,
G.; Bordignon, E. J . Chem. Soc., Dalton Trans. 1986, 2551.
(5) Bertacco, A.; Mazzi, U.; Orio, A. A. Inorg. Chem. 1972, 11, 2547.
1
) 10 Hz), 91.3 (d, Cb, J CH ) 170 Hz), 62.7, 62.2 (m, CH2), 15.9 (m,
CH3). 13C NMR (CD3CN at 25 °C): δ 165-120 (m, Ph), 98.3 (d of d, Ca,
2
1
1J CH ) 170 Hz, J CP ) 10 Hz), 91.8 (d, Cb, J CH ) 170 Hz), 65 (m, br,
CH2), 16.5, 16.1 (q, CH3). Anal. Calcd for C71H85NBO9P4Co (1b): C,
66.10; H, 6.64; N, 1.09. Found: C, 65.91; H, 6.60; N, 1.08. ΛM (CH3-
NO2, 25 °C): 54.2 Ω-1 mol-1 cm2. IR (KBr): 2239 w νCN cm-1; 1240 s
νPdO cm-1 1H NMR (CD2Cl2, 25 °C): δ 8.00-6.60 (m, 43H, Ph), 5.65
.
(d, 1H, Ha), 5.02 (m, 1H, Hb), 3.70 (m, 16H, CH2), 1.14 (m, 24H, CH3).
1H NMR (CD3CN, 25 °C): δ 7.85-6.80 (m, 43H, Ph), 5.60 (d, 1H, Ha),
5.17 (m, 1H, Hb), 4.00-3.50 (m, 16H, CH2), 1.37, 1.10 (t, 24H, CH3).
31P{1H} NMR (CD2Cl2, -80 °C): δ 170, 158 (br, 3P, PPh(OEt)2), 19.64
(s, 1P, C6H5PO(OEt)2). 13C NMR (CD2Cl2, 25 °C): δ 165-122 (m, Ph),
98.0 (d of d, Ca, 1J CH ) 170, 1J CP ) 10 Hz), 91.5 (d, Cb, 1J CH ) 170 Hz),
62.7 (m, CH2), 16.4, 16.1 (q, CH3). 13C NMR (CD3CN, 25 °C): δ 160-
1
1
120 (m, Ph), 98.7 (d of d, Ca, J CH ) 170, J CP ) 10 Hz), 92.0 (d, Cb,
1J CH ) 170 Hz), 63.3 (m, CH2), 16.6 (m, CH3).
10.1021/om981046s CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/07/1999