Cobalt induced tandem C-H activation/decarbonylation of various aromatic aldehydes and related benzylic alcohols forming mononuclear aryl monocarbonyl complexes

Article abstract of DOI:10.1021/ic801673h

Reactions between Co(CH₃)(PMe₃)₄ and various ortho-substituted aromatic aldehydes (Ar(R₁,R ₂)CHO) and related benzylic alcohols (Ar(R₁,R ₂)CH₂OH) proceed with high sel

Full text of DOI:10.1021/ic801673h

Inorg. Chem. 2009, 48, 1416-1422
Cobalt Induced Tandem C-H Activation/Decarbonylation of Various
Aromatic Aldehydes and Related Benzylic Alcohols Forming
Mononuclear Aryl Monocarbonyl Complexes
Robert Beck,*,†,‡ Ulrich Flo¨rke,§ and Hans-Friedrich Klein†
Eduard-Zintl-Institut fu¨r Anorganische and Physikalische Chemie, Technische UniVersita¨t
Darmstadt, Petersenstrasse 18, D-64287 Darmstadt, Germany, and Anorganische and Analytische
Chemie, UniVersita¨t Paderborn, Warburger Strasse 100, D-33098 Paderborn, Germany
Received September 1, 2008
Reactions between Co(CH3)(PMe3)4 and various ortho-substituted aromatic aldehydes (Ar(R1,R2)CHO) and related
benzylic alcohols (Ar(R1,R2)CH2OH) proceed with high selectivity to give the mono carbonyl complexes
Aryl(R1,R2)(PMe3)3Co(CO): R1 ) H, R2 ) CH3 (1), R1) H, R2 ) ethyl (2), R1 ) CH3, R2 ) CH3 (3), R1 ) H, R2
) NH2 (4), R1 ) F, R2 ) F (5), R1 ) H, R2 ) CF3 (6), and R1 ) H, R2 ) benzo (7). This tandem C-H bond
activation/decarbonylation reaction provides easy and rapid access under mild conditions (-70 °C) to the first
isolated trimethylphosphine stabilized aryl-monocarbonyl complexes of cobalt. X-ray diffraction studies were performed
on ortho-amino substituted complex 4, ortho-trifluormethyl 6, and naphthyl derivative 7.
Introduction
a reaction of great interest due to its connection with the
catalytic decarbonylation of these substrates and its impor-
tance in organometallic and organic synthesis.
The activation of aldehyde C-H bonds has been inves-
tigated by other research groups with iron(0),5 ruthe-
nium(0),6,7 ruthenium(II),8 osmium(VI, IV, 0),9-11 rhod-
ium(I),12-18 rhodium(III),19 iridium(I),18,20-25 iridium(III),19
Stoichiometric and catalytic transformations involving
C-H activation are of present interest due to the synthetic
utility that the facile functionalization of unreactive C-H
bonds would provide.1 The relatively low cost of cobalt
complexes, as compared to their more expensive 4d and 5d
congeners, provides an impetus for their utilization in
catalytic or stoichiometric transformations that proceed
through C-H bond activation.2
Recently, we studied the activation of aromatic, vinylic,
and aliphatic C-H bonds and its high selectivity with
CoCH3(PMe3)4 assisted by nitrogen3 and phosphorus4 donor
functions. The activation of the C-H bond of aldehydes is
(6) Ozawa, F.; Yamagami, I.; Yamamoto, A. J. Organomet. Chem. 1994,
473, 265–272.
(7) Kondo, T.; Akazome, M.; Tsuji, Y.; Watanabe, Y. J. Org. Chem. 1990,
55, 1286–1291.
(8) Lehmkuhl, H.; Schwickardi, R.; Mehler, G.; Kru¨ger, C.; Goddard, R.
Z. Anorg. Allg. Chem. 1991, 606, 141–155.
(9) Barrio, P.; Esteruelas, M. A.; Onate, E. Organometallics 2004, 23,
1340–1348. Esteruelas, M. A.; Herna´ndez, Y. A.; Lo´pez, A. M.;
Oliva´n, M.; Rubio, L. Organometallics 2008, 23, 799–802. Arce, A. J.;
De Sanctis, Y.; Deeming, A. J. J. Organomet. Chem. 1986, 311, 371–
378.
(10) Hardcastle, K. I.; Minassiam, H.; Arce, A. J.; De Sanctis, Y.; Deeming,
A. J. J. Organomet. Chem. 1989, 368, 119–130.
(11) Brown, K. L.; Clark, G. R.; Headford, C. E. L.; Marsden, K.; Roper,
W. R. J. Am. Chem. Soc. 1979, 101, 503–505.
(12) Bianchini, C.; Meli, A.; Peruzzini, M.; Vacca, A.; Zanobini, F.
Organometallics 1987, 6, 2453–2455.
* To whom correspondence should be addressed. E-mail: metallacycle@
gmail.com.
†
Technische Universita¨t Darmstadt.
Present Address: School of Chemistry and Chemical Engineering,
‡
Shandong University, Shanda Nanlu 27, 250100 Jinan, People’s Republic
of China.
§
Universita¨t Paderborn.
(1) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879–2932.
(2) Omae, I. Appl. Organomet. Chem. 2007, 21, 318–344.
(3) (a) Klein, H.-F.; Camadanli, S.; Beck, R.; Leukel, D.; Flo¨rke, U.
Angew. Chem., Int. Ed. 2005, 44, 975–977. (b) Klein, H.-F.; Ca-
madanli, S.; Beck, R.; Flo¨rke, U. Chem. Commun. 2005, 381–382.
(4) Klein, H.-F.; Beck, R.; Flo¨rke, U.; Haupt, H.-J. Eur. J. Inorg. Chem.
2003, 853–862.
(13) Bianchini, C.; Meli, A.; Peruzzini, M.; Ramirez, J. A.; Vacca, A.;
Vizza, F.; Zanobini, F. Organometallics 1989, 8, 337–345.
(14) Marder, T. B.; Roe, D. C.; Milstein, D. Organometallics 1988, 7, 1451–
1453.
(15) Milstein, D. Organometallics 1982, 1, 1549–1551.
(16) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Bachechi, F.
Organometallics 1991, 10, 820–823.
(5) Tolman, C. A.; Ittel, S. D.; English, A. D.; Jesson, J. P. J. Am. Chem.
Soc. 1979, 101, 1742–1751.
(17) Milstein, D. Chem. Commun. 1982, 1357–1358.
(18) Ko, J.; Joo, W.-C. Bull. Korean Chem. Soc. 1987, 8, 372–376.
1416 Inorganic Chemistry, Vol. 48, No. 4, 2009
10.1021/ic801673h CCC: $40.75  2009 American Chemical Society
Published on Web 01/21/2009

Cobalt Induced Tandem C-H ActiWation/Decarbonylation
Scheme 1. Five-Membered Nickel and Cobalt Acyl Metallacycles
activation/carbonyl migration deinsertion pathway. The same
reaction products are observed with related benzylic alcohols
in fair yields.
Results and Discussion
The reaction of aromatic aldehydes with CoCH3(PMe3)4
proceeds at -70 °C through C-H activation followed by a
decarbonylation step according to eq 1. During warm up,
the evolution of gas (CH4) is detected, and the color changes
from dark red to orange-yellow.
and platinum(0).26 In some cases, the C-H activation step
is followed by decarbonylation which results in a R-M-CO
derivative,7,8,19-22,26 while in other examples, a stable
acyl-metal-hydride is formed.9,10,18,26
The majority of research studies centering on aldehyde
decarbonylation have utilized Rh(I) complexes, which have
been found to be the most efficient catalysts.27-35 Activity
has also been reported for cobalt(I) systems36 and for a
cobalt-protoporphyrin complex,37 but no information has
been given for intermediates. In a related study of aldehydic
C-H bond activation with a pentamethylcyclopentadiene
supported Co(I) center, Brookhart et al. described the
intermolecular hydroacylation of vinylsilanes with a variety
of alkyl aldehydes.38
We have previously reported on the activation of OC(R)-H
bonds of salicylaldehyde derivatives (A),39,40 2-diphe-
nylphosphinobenzaldehyde (B),41 with trimethylphosphine
supported methyl nickel, and methyl cobalt complexes, where
thermally stable acyl complexes were observed with five-
membered metallacycles (Scheme 1).
In this report, we describe the synthesis of stable ortho-
aryl-substituted cobalt complexes with one terminal carbonyl
group. With various aromatic aldehydes, the reaction of
CoCH3(PMe3)4 follows, regioselectively, a tandem C-H
This method provides high yields and appears to be widely
applicable by tolerating different functional groups in ortho
positions of the starting aldehydes, with the formation of
aryl carbonyl complexes [Aryl(R1,R2)(PMe3)3Co(CO)]: R1
) H, R2 ) CH3 (1), R1 ) H, R2 ) ethyl (2), R1 ) CH3, R2
) CH3 (3), R1 ) H, R2 ) NH2 (4), R1 ) F, R2 ) F (5), R1
) H, R2 ) CF3 (6), and R1 ) H, R2 ) benzo (7) (eq 1). All
products crystallize from pentane or diethyl ether as orange
rhombic crystals in 58-79% yield.
When the reactions were all carried out in pentane, without
crystallization of a product, just by filtering and washing with
ice-cold pentane, a light yellow powder was obtained in
almost quantitative yields, according NMR data.
(19) Gomez, M.; Kisenyi, J. M.; Sunley, G. J.; Maitlis, P. M. J. Organomet.
Chem. 1985, 296, 197–207.
(20) Gutierrez-Puebla, E.; Monge, A.; Paneque, M.; Poveda, M. L.; Salazar,
V.; Carmona, E. J. Am. Chem. Soc. 1999, 121, 248–249.
(21) Bernard, K. A.; Atwood, J. D. Organometallics 1988, 7, 235–236.
(22) Bernard, K. A.; Atwood, J. D. Organometallics 1989, 8, 795–800.
(23) Landvatter, E. F.; Rauchfuss, T. B. Organometallics 1982, 1, 506–
513.
(24) Rauchfuss, T. B. J. Am. Chem. Soc. 1979, 101, 1045–1047.
(25) Thorn, D. L. J. Mol. Catal. 1982, 17, 279–288.
(26) Koh, J. J.; Lee, W.-H.; Willard, P. G.; Risen, W. M. J. Organomet.
Chem. 1985, 284, 409–419.
(27) Tsuji, J.; Ohno, K. Tetrahedron Lett. 1967, 23, 2173–2176.
(28) Ohno, K.; Tsuji, J. J. Am. Chem. Soc. 1968, 90, 99–107.
(29) Walborsky, H. M.; Allen, L. E. Tetrahedron Lett. 1970, 11, 823–824.
(30) Walborsky, H. M.; Allen, L. E. J. Am. Chem. Soc. 1971, 93, 5465–
5468.
(31) Suggs, J. W. J. Am. Chem. Soc. 1978, 100, 640–641.
(32) Doughty, D. H.; Pignolet, L. H. J. Am. Chem. Soc. 1978, 100, 7083–
7085.
(33) Baldwin, J. E.; Barden, T. C.; Pugh, R. L.; Widdison, W. C. J. Org.
Chem. 1987, 52, 3303–3307.
(34) Abu-Hasanayn, F.; Goldman, M. E.; Goldman, A. S. J. Am. Chem.
Soc. 1992, 114, 2520–2524.
(35) O’Connor, J. M.; Ma, J. J. Org. Chem. 1992, 57, 5075–5077.
(36) Kovacs, I.; Szalontai, G.; Ungvary, F. J. Organomet. Chem. 1996,
524, 115–123.
(37) Dennis, M.; Kolattukudy, P. E. Proc. Natl. Acad. Sci. U.S.A. 1992,
89, 5306–5310.
The complexes (1-7) show similar 1H, 13C(1H), and
31P(1H) NMR spectra and absorption regions in the infrared
(IR) for the ν(C≡O) stretching frequencies. In the 1H NMR
spectra of 1-7, the resonances for the trimethylphosphine
ligands appear at 1.18-1.30 ppm as broad singlets, except
for 1, which appears at 1.23 ppm as a doublet (2JP,H ) 6.1
Hz). The metallated carbon resonances (Co-C) in the
13C(1H) NMR are observed as expected with a low field shift
for complexes 1-7 from 166 to 180 ppm as broad multiplets
(cobalt: I ) 7/2). The 31P(1H) NMR resonances of complexes
1-7 exhibit at δ ) 8.2-10.3 ppm broad singlets, which are
assigned for a trigonal bipyramidal coordination sphere with
dynamic ligand behavior (Berry type pseudorotation and
ligand dissociation). In addition, when cooling down the
NMR samples to -80 °C, no P,P-coupling of the different
phosphorus nuclei was observed. In the IR, these complexes
absorb at 1850-1886 cm-1 ν(CtO) in their IR spectra,
which are typical stretching frequencies for terminal carbon
monoxide ligands.42 To the best of our knowledge, 1-7
represent the first examples of simple aryl monocarbonyl
cobalt complexes.
(38) Lenges, C. P.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 1998,
120, 6965–6979.
(39) Klein, H.-F.; Bickelhaupt, A.; Hammmerschmitt, B.; Flo¨rke, U.; Haupt,
H.-J. Organometallics 1994, 13, 2944–2950.
(40) Klein, H.-F.; Haller, S.; Sun, H.; Li, X.; Jung, T.; Ro¨hr, C.; Flo¨rke,
U.; Haupt, H.-J. Z. Naturforsch. 1998, 53b, 587–598.
Inorganic Chemistry, Vol. 48, No. 4, 2009 1417

Beck et al.
for agostic or anagostic interactions, which was reported by
Brammer et al.,44 for a cobaltate anion containing a metal
contact (N-H · · · Co ) 2.613 Å).
In a reverse reaction pathway, a stable five-membered
2-aminoacyl palladium metallacycle was reported when
carbon monoxide inserts into the palladium aryl bond.45 In
the cobalt case, the balance of the hard NH2-donor and the
remaining soft trimethylphosphine ligands is not suitable for
stabilizing such a five-membered aminoacyl cobaltacycle.
Only when a soft donor atom in the ortho position of
2-diphenylphosphinobenzaldehyde is present does the reac-
tion with CoCH3(PMe3)4 afford stable acyl complexes as
aforementioned, by the insertion of carbon monoxide ob-
served with a phenyltris((tert-butylthio)methyl)borate cobalt
complex,46 or by hydrolysis of a CF2-group in a [Cp]
stabilized cobalt complex.47
The well-established and related nucleophilic reaction
pathway is observed when the carbonyl-metalate complex
reacts with the corresponding benzoylchloride derivatives
forming stable acyl complexes,48 which can readily decar-
bonylate.49 This is also reported for the anion [Co(CO)4]-.50
Typically, these complexes have a central equatorial tris-
carbonyl motif [Co(CO)3] in common.51 To the best of our
knowledge, an initial aldehyde-C-H activation reaction at
cobalt centers has not been reported before. We were able
to extend its scope with aryl aldehyde derivatives. The
reaction pathway allows the synthesis of aryl-cobalt (mono-
carbonyl) complexes, which cannot be prepared easily by
other routes. So far, only when π-acceptor substituents are
present (e.g., allyl- or diphenylphosphino chelating substit-
uents) were mononuclear complexes with an [Ar-Co-CO]
monocarbonyl unit described.52,53
Under similar reaction conditions, complex 6 was syn-
thesized (eq 1). Its spectroscopic data are very similar to
that of complex 4 (see Experimental Method section). The
molecular structure of 6 (Figure 2)shows a distorted trigonal
bipyramidal coordination environment of cobalt(I), with two
trimethylphosphine ligands in apical positions. The aryl
ligand that lies in a plane containing the carbonyl group and
Figure 1. Molecular structure of 4; selected bond lengths [Å] and angles
[deg]: Co1-C1 2.016(1), Co1-C7 1.709(1), Co1-P1 2.1709(4), Co1-P2
2.1620(4), Co1-P3 2.2369(5), C7-O1 1.158(2), C1-C6 1.425(2),
N1-H· · ·Co 2.76(2), C6-N1 1.379(2), C7-Co1-C1 137.37(6), P1-Co1-P2
164.57(2), C1-Co1-P3 110.89(4), C7-Co1-P3 111.74(4), P1-Co1-P3
97.27(2), P2-Co1-P3 97.57(2), C6-C1-Co1 123.99(10), N1-C6-C1
120.66(12).
A single-crystal X-ray diffraction study was performed on
the ortho-amino-substituted complex 4. Dark orange rhombic
crystals were grown through the cooling of ether solutions
of 4 to -27 °C.
The molecular structure of 4 is shown in Figure 1. The
cobalt atom resides in the center of a trigonal bipyramid of
donor atoms, where the carbon atom of the phenyl group, a
trimethylphosphine ligand, and the carbonyl group occupy
equatorial positions. The two remaining PMe3 ligands reside
in axial positions. The main axis connecting apical positions
(P2-Co1-P1 ) 164.57(2)°) is slightly bent from idealized
geometry (180°) and the angles from the equatorial (P3) to
the axial phosphorus atoms are similar to 97.57(2)° for P2
and 97.27(2)° for P1, respectively. The sum of inner ligand
angles in the equatorial plane (358°) is in accord with a cobalt
atom centered in the trigonal plane. The Co-P bond lengths
(2.1709(4) Å and 2.1620(4) Å) fall in a range also observed
for other cobalt complexes containing aryl and carbonyl
groups.43 The Co1-P3 distance (2.2369(5) Å) is elongated
due to the trans influence of the C1 atom of the phenyl group.
The complex contains two different Co-C bonds: a shorter
one connected to the carbonyl ligand (Co1-C7 ) 1.709(1)
Å) and a longer one connected to the phenyl group (Co1-C1
) 2.016(1) Å), which is typical for (sp, sp2) hybridized
carbon atoms.43
(44) Brammer, L.; McCann, M. C.; Bullock, R. M.; McMullan, R. K.;
Sherwood, P. Organometallics 1992, 12, 2339–2341.
(45) Vicente, J.; Abad, J.-A.; Frankland, A. D.; Ram´ırez de Arellano, M. C.
Chem. Eur. J. 1999, 5, 3066–3075. Vicente, J.; Abad, J.-A.; Frankland,
A. D.; Ram´ırez de Arellano, M. C. Chem. Commun. 1997, 959–960.
(46) DuPont, J. A.; Coxey, M. B.; Schebler, P. J.; Incarvito, C. D.;
Dougherty, W. G.; Yap, G. P. A.; Rheingold, A. L.; Riordan, C. G.
Organometallics 2007, 26, 971–979.
(47) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A.
Organometallics 1996, 15, 5678–5686.
(48) Heck, R. F.; Breslow, D. S. J. Am. Chem. Soc. 1962, 84, 2499–2502.
(49) Halle, L. F.; Crowe, W. E.; Armentrout, P. B.; Beauchamp, J. L.
Organometallics 1984, 10, 1694–1706.
(50) Gipson, S. L.; Bryson, L. A.; Klausmeyer, K. K. Inorg. Chim. Acta
2002, 340, 221–224.
The bond distance between the protons of the ortho amino
group and the cobalt atom is relatively short (N-H· · · Co )
2.76(2) Å). However, no spectroscopic evidence was found
(51) (a) Galamb, V.; Pa´lyi, G.; Cser, F.; Furmanova, M. G.; Struchkov,
Y. T. J. Organomet. Chem. 1981, 209, 183–195. (b) Galamb, V.; Pa´lyi,
G.; Boese, R.; Schmid, G. Organometallics 1987, 6, 861–867. (c)
Ungva´ry, F.; Kova´cs, I.; Hammerschmitt, B.; Cordier, G. Organome-
tallics 1993, 12, 2849–2852. (d) Zucchi, C.; Boese, R.; Alberts, K.;
Herbrich, T.; To´th, G.; Bencze, L.; Pa´lyi, G. Eur. J. Inorg. Chem.
2001, 2297–2304.
(41) Klein, H.-F.; Lemke, U.; Lemke, M.; Brand, A. Organometallics 1998,
17, 4196–4201.
(42) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Applications
of Organotransition Metal Chemistry; University Science Books: Mill
Valley, CA, 1987.
(52) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Pelizzi, G.
Organometallics 1995, 14, 4126–4131.
(43) Klein, H.-F.; Beck, R.; Flo¨rke, U.; Haupt, H.-J. Eur. J. Inorg. Chem.
2003, 1380–1387.
(53) Giesbrecht, G. R.; Gordon, J. C.; Clark, D. L.; Hijar, C. A.; Scott,
B. L.; Watkin, J. G. Polyhedron 2003, 22, 153–163.
1418 Inorganic Chemistry, Vol. 48, No. 4, 2009

Cobalt Induced Tandem C-H ActiWation/Decarbonylation
CoH(PMe3)4 is formed, identified by IR spectra ν(Co-H)
) 1935 cm-1. Ostensibly, in a prevailing side reaction, the
hydrido-cobalt side product (Scheme 3) attacks the benzene
1
system, observed in a raw product H NMR spectrum of 7,
which exhibits proton resonances in typical olefinic area
range between 5.3-5.8 ppm and other resonances of
unidentified byproducts. Unfortunately, we have not been
able to isolate those olefinic products.
However, again, the complexes (1, 4, and 7) crystallize
as orange-yellow rhombic crystals from pentane and diethyl
ether solutions. The predicted structure of 7 (similar to that
of 4 and 6) derived from NMR data in solution was
confirmed by X-ray diffraction (Figure 3). The Co-P and
P-C bond lengths are close to the average reported mean
values of bond lengths.54 In complex 7, the orientation of
the carbonyl ligand exhibits a syn orientation to the con-
densed aryl-ring in the ortho position. The distance between
the cobalt atom and the neighboring hydrogen atom in the
8-position of the naphthyl ring (H1 · · · Co1 ) 2.888 Å) is
relatively short, similar to that in complex 4, but, again,
without spectroscopic evidence for agostic or anagostic
interactions.55
Figure 2. Molecular structure of 6; selected bond lengths [Å] and angles
[deg]: Co1-C1 2.048(6), Co1-C8 1.733(6), Co1-P1 2.2465(15), Co1-P2
2.1793(19), Co1-P3 2.1783(18), C8-O1 1.178(7), C1-C6 1.416(8),
C6-C7 1.511(8), C7-F1 1.285(8), C7-F2 1.354(9), C7-F3 1.356(9),
C8-Co1-C1 118.4(2), P3-Co1-P2 168.88(6), C1-Co1-P3 85.49(17),
C8-Co1-P3 88.5(2), P1-Co1-P2 95.38(7), P1-Co1-P3 95.58(6),
C6-C1-Co1 134.9(4).
Scheme 2. Syn- and Anti-Conformation of the Ar(R)-Co-CO Unit in
4, 6, and 7 in Solid State
All spectral data obtained from solutions are consistent
with the results of the three X-ray diffraction experiments.
Selected structural and NMR data for 4 and 7 are summarized
in Table 1.
Proposed Reaction Mechanism. The proposed reaction
mechanism for the formation of complexes 1-7 is initiated
by dissociation of a trimethylphosphine ligand from the
starting complex [Co(CH3)(PMe3)4] (18 VE). The tetraco-
ordinated [Co(CH3)(PMe3)3] intermediate (16 VE) proceeds
in reaction with the aromatic aldehyde by an aldehydic C-H
bond activation when the hexacoordinated acyl cobalt
complex is formed (Scheme 1). A stable acyl cobalt complex
has been isolated in a previous study, when a diphenylphos-
phino group was introduced into the ortho position of the
aldehyde.41 Without a phosphorus donor atom in the ortho
position, the hydrido-methyl-Co(III) intermediate is un-
stable (release of CH4) and a decarbonylation step occurs
by insertion of the cobalt fragment into the aryl-acyl bond,
generating a terminal carbonyl Co(I) complex. A similar
tandem C-H activation/decarbonylation reaction of highly
hindered tertiary aliphatic aldehydes with iridium complexes
has been previously described by Alaimo et al.56
the third trimethylphosphine ligand occupy the equatorial
positions.
The Co-C and Co-P bond distances and angles closely
resemble those for the related complex 4. The most interest-
ing feature in the molecular structure is the anti-conformation
of the carbonyl ligand and the trifluoromethyl group in the
ortho position of 6 in a solid state (Scheme 2). Geometrical
parameters as well as the unresolved disorder of the CF3
group suffer from rather bad data quality and should be
understood as proof of connectivity only.
Interestingly, in 6, the steric demand of the trimethylphos-
phine ligand is oriented toward the trifluoromethyl substitu-
ent, and the smaller carbonyl group is pointing away. An
opposite arrangement would be expected with the bulky CF3-
substituent.
Alternative Reaction Pathway. An alternative reaction
pathway occurs with benzylic alcohols (2-methylbenzylal-
cohol, 2-aminobenzylacohol, and 1-naphthalenemethanol).
When combining CoCH3(PMe3)4 with the related alcohol in
diethyl ether, a slow color change from red to yellow is
observed after between 24 and 48 h has passed (eq 2).
With a reaction yield of 29-44%, the same products as
aforementioned (eq 1) for selected benzaldehydes were
achieved with the related benzylic alcohols, and additionally,
An alternative route starts from the related alcohol, which
proceeds through elimination of methane, producing an
(54) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.;
Taylor, R. J. Chem. Soc., Dalton. Trans. 1989, S1–S83.
(55) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci.
U.S.A. 2007, 104, 6908–6914.
(56) Alaimo, P. J.; Arndtsen, B. A.; Bergman, R. G. Organometallics 2000,
19, 2130–2143.
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Beck et al.
Scheme 3. Proposed Reaction Pathway of Co(CH3)(PMe3)4 with Aromatic Aldehydes and Benzylic Alcohol Derivatives
alcoholate cobalt complex (Scheme 3). ꢀ-Hydrogen elimina-
tion releases the in situ generated aldehyde and a stable
hydrido-cobalt(I) complex (NMR). Afterward, still present
CoCH3(PMe3)4 in solution reacts with the new formed
aldehyde, which might also explain the rather low yield
(<50%). Half of the initial complex [Co(CH3)(PMe3)4] is
used to generate the aldehyde, and the other half is used to
take the aldehyde to the final product. After the elimination
of methane from the hydrido-methyl d6-cobalt(III) species,
the d8-cobalt(I) acyl complex is formed, and the reaction
sequence ends up in the same pathway as described with
the related aldehydes.
Conclusion
The cobalt-induced tandem C-H activation/carbonyl
migratory deinsertion reaction described in this work has
provided easy and rapid access to mononuclear complexes,
with an Ar-Co-CO fragment as the general constituent.
The reaction pathway allows the preparation of monocar-
bonyl cobalt complexes, which cannot be easily prepared
by other routes. All new complexes (1-7) could be
synthesized under mild conditions (-70 °C) in high yield
starting from the benzaldehyde derivative or in fair yield from
the corresponding alcohol. The reaction proceeds regiose-
lectively with the aldehydic or alcoholic functional group,
with spectroscopic evidence for neither activation nor
interaction with the other substituents in the ortho position
(N-H/C-H/C-F bonds) of the aromatic backbone or even
other available aromatic C-H bonds.
Experimental Section
General Procedures and Materials. All air-sensitive and volatile
materials were handled using standard vacuum techniques and were
kept under argon. Microanalyses: Kolbe Microanalytical Laboratory,
Mu¨lheim/Ruhr, Germany. Melting points/decomposition tempera-
Table 1. Selected Structural and Spectroscopic Data of
Aryl-Co(I)-CO Complexes 4 and 7
4
7
aryl(C)-Co [Å]
Co-P [Å]
2.016(1)
2.16-2.23
1.709
1.158
2.762
164.57
137.37
1.28 s(br)
180.3 m
9.5 m
2.0170(17)
2.17-2.24
1.726
1.179
2.888
163.82
140.22
1.18 s(br)
171.5 m
7.8 m
Co-CO [Å]
C≡O [Å]
ortho H · · ·Co [Å]
P(ax)-Co-P(ax) [deg]
Caryl-Co-CO [deg]
1H NMR δ PMe3
13C(1H) NMR δ C-Co
31P(1H) NMR δ PMe3
IR ν (C≡O) cm-1
Figure 3. Molecular structure of 7; selected bond lengths [Å] and angles
[deg]: Co1-C1 2.0170(17), Co1-C11 1.7261(18), Co1-P1 2.1842(6),
Co1-P2 2.1745(5), Co1-P3 2.2436(6), C11-O1 1.179(2), C1-C10
1.454(2), C9-C10 1.430(2), H1 · · ·Co1 2.888(1), C1-Co1-C11 140.22(8),
P2-Co1-P1 163.82(2), C1-Co1-P3 109.45(5), C11-Co1-P3 110.33(6),
P1-Co1-P3 97.44(2), P2-Co1-P3 98.22(2), C10-C1-Co1
124.32(12).
1850
1872
1420 Inorganic Chemistry, Vol. 48, No. 4, 2009

Cobalt Induced Tandem C-H ActiWation/Decarbonylation
Table 2. Crystal Data and Refinement Details for Compounds 4, 6, and 7
4
6
7
empirical formula
molecular mass
crystal size [mm]
crystal system
space group
a [Å]
C16H33CoNOP3
407.3
C17H31CoF3OP3
460.3
0.35 × 0.31 × 0.23
monoclinic
P21/c
8.6290(12)
9.7981(14)
26.151(4)
90.0
91.910(12)
90.0
2209.8(5)
4
1.383
1.021
150(2)
2.22 - 27.88
-11 e h e 11
-12 e k e 12
-34 e l e 34
15396
4503 [Rint ) 0.105]
236/0
semiempirical
0.8141 and 0.7163
1.245
C20H34CoOP3
442.3
0.44 × 0.35 × 0.22
monoclinic
P21/n
12.9194(12)
13.3931(12)
13.7459(14)
90.0
100.45(2)
90.0
2339.0(4)
4
1.256
0.945
150(2)
1.99 - 26.94
-16 e h e 16
-16 e k e 17
-17 e l e 17
34196
5013 [Rint ) 0.056]
236/0
semiempirical
0.8191 and 0.6813
1.081
0.45 × 0.40 × 0.25
triclinic
j
P1
8.6624(12)
9.0674(13)
14.291(2)
80.705(11)
76.995(11)
69.557(10)
1020.6(2)
b [Å]
c [Å]
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
Z
2
Dcalcd [g/cm3]
µ(Mo KR) [mm-1
temperature [K]
Θ - limits [deg]
h
1.325
1.077
150(2)
1.47 - 26.37
-10 e h e 10
-11 e k e 11
-17 e l e 17
14959
4107 [Rint ) 0.090]
216/2
semiempirical
0.7745 and 0.6428
1.052
]
k
l
reflns measured
unique data
parameters/restraints
absorption corr.
max and min transmn.
GOF on F2
R1 [I g 2σ(I)]
0.0242
0.0794
0.0344
wR2 (all data)
0.0637
0.1820
0.0856
largest diff. peak/hole
0.369 and -0.275 e ·Å-3
0.632 and -0.798 e ·Å-3
0.705 and -0.588 e ·Å-3
tures: sealed capillaries, uncorrected values. Chemicals (Acros/
Merck) were used as purchased. Literature methods were followed
in the preparation of CoCH3(PMe3)457 and 2-aminobenzaldehyde.58
IR: Nujol mulls between KBR discs, Bruker spectrophotometer type
FRA 106. 1H, 13C(1H) NMR and 31P(1H) NMR spectra were
recorded with a Bruker DRX-500 spectrometer.
Experimental Method. Solutions of the cobalt complex in
tetrahydrofuran (THF) on a scale of about 1-4 mmol were
combined with equimolar amounts of the aldehyde (Method A) in
the same solvent or in diethyl ether for the related benzylic alcohol
derivatives (Method B) and stirred at -70 °C. The reaction mixture
was allowed to warm to 20 °C and stirred for maximum 3 h at 20
°C (Method B: 24 h). The volatiles were removed in vacuo, and
the residue was extracted with fresh pentane and/or diethyl ether
and filtered over a glass-sinter disk (G3). When the solution was
cooled, crystals formed. The solution was decanted off, and the
crystals were washed with cold pentane and dried in vacuo to afford
analytically pure materials 1-7.
PCH3); 28.2 (s, CH3); 120.4 (s, CH); 120.6 (s, CH); 125.6 (s, CH);
146.3 (s, CH); 147.4 (s, C); 166.9 (m, Co-C). 31P(1H) NMR (202
MHz, [D8]THF, 293 K, ppm): δ ) 8.8 (m(br), 3P, PCH3) ppm.
Anal. Calcd for C17H34CoOP3 (406.3): C, 50.25; H, 8.43; P, 22.87.
Found: C, 49.82; H, 8.93; P, 22.62.
Carbonyl[2-(ethylphenyl)-C]tris(trimethylphosphine)cobalt(I) (2).
Method A: 2-Ethylbenzaldehyde (338 mg, 2.51 mmol) was
combined at -70 °C with a solution of CoMe(PMe3)4 (952 mg,
2.51 mmol) to afford orange-yellow crystals. Yield 762 mg (72%).
Mp 103-105 °C (dec). IR (Nujol): ν˜ ) 1882 s (ν CdO); 1575 m
(ν CdC) cm-1. 1H NMR (500 MHz, [D8]THF, 293 K, ppm): δ )
3
6
0.91 (dt, JH,H ) 7.5 Hz, JP,H ) 5.7 Hz, 1H, CH3); 1.24 (s(br),
3
3
27H, PCH3); 2.63 (q, JH,H ) 7.5 Hz, 2H, CH2); 6.57 (dt, JH,H
)
7.2 Hz, 4JH,H ) 1.5 Hz, 1H, Ar-H); 6.74 (dt, 3JH,H ) 7.4 Hz, 4JH,H
3
4
) 1.5 Hz, 1H, Ar-H); 6.89 (dd, JH,H ) 7.5 Hz, JH,H ) 1.3 Hz,
1H, Ar-H); 7.40 (dd, 3JH,H ) 7.4 Hz, 4JH,H ) 1.5 Hz, 1H, Ar-H).
13C(1H) NMR (125 MHz, [D8]THF, 293 K, ppm): δ ) 10.9 (dt,
5JP,C ) 28.8 Hz, JP,C ) 14.7 Hz, CH3); 19.3 (m, PCH3); 32.4 (s,
5
Carbonyl[2-(methylphenyl)-C]tris(trimethylphosphine)co-
balt(I) (1). Method A: 2-Methylbenzaldehyde (695 mg, 5.78 mmol)
was combined at -70 °C with CoMe(PMe3)4 (2.18 g, 5.78 mmol)
to afford an orange, waxy solid of 1. Yield 1.52 g (65%). Method
B: 2-Methylbenzylalcohol (210 mg, 1.71 mmol) was combined at
20 °C with CoMe(PMe3)4 (650 mg, 1.71 mmol) to afford yellow
crystals. Yield 307 mg (44%). Mp 104-106 °C (dec). IR (Nujol):
ν˜ ) 1881 s (ν CdO); 1574 m (ν CdC) cm-1. 1H NMR (500 MHz,
[D8]THF, 293 K, ppm): δ ) 1.23 (d, 2JP,H ) 6.1 Hz, 27H, PCH3);
CH2); 120.1 (s, CH); 120.6 (s, CH); 123.1 (s, CH); 146.6 (s, CH);
153.4 (s, C); 166.8 (m, C). 31P(1H) NMR (202 MHz, [D8]THF,
293 K, ppm): δ ) 10.3 (s(br), 3P, PCH3) ppm. Anal. Calcd for
C18H36CoOP3 (420.3): C, 51.43; H, 8.63; P, 22.11. Found: C, 50.95;
H, 8.94; P, 21.88.
Carbonyl[2,6-(dimethylphenyl)-C]tris(trimethylphosphine)co-
balt(I) (3). Method A: 2,6-Dimethylbenzaldehyde (230 mg, 1.71
mmol) was combined with CoMe(PMe3)4 (648 mg, 1.71 mmol) at
-70 °C to afford a yellow powder of 3. Yield 482 mg (67%). Mp
114-116 °C (dec). IR (Nujol): ν˜ ) 1886 s (ν CdO); 1574 m (ν
3
2.34 (s, 3H, CH3); 6.56 (t, JH,H ) 6.9 Hz, 1H, Ar-H); 6.66 (dd,
4
3
3JH,H ) 6.3 Hz, JH,H ) 0.8 Hz, 1H, Ar-H); 6.85 (d, JH,H ) 7.1
Hz, 1H, Ar-H); 7.29 (d, 3JH,H ) 7.2 Hz, 1H, Ar-H). 13C(1H) NMR
(125 MHz, [D8]THF, 293 K, ppm): δ ) 19.5 (d, JP,C ) 21.0 Hz,
1
1
CdC) cm-1. H NMR (500 MHz, [D8]THF, 293 K, ppm): δ )
1.30 (s(br), 27H, PCH3); 2.14 (s, 6H, CH3); 6.46-6.55 (m, 3H,
Ar-H). 13C(1H) NMR (125 MHz, [D8]THF, 293 K, ppm): δ )
15.6 (m, PCH3); 23.7 (s, CH3); 121.2 (s, CH); 122.7 (s, CH); 140.2
(s, CH); 143.1 (s, C); 166.3 (m, Co-C). 31P(1H) NMR (202 MHz,
(57) Klein, H.-F.; Karsch, H. H. Chem. Ber. 1975, 108, 944–955.
(58) Becker, H. G. O.; Beckert, R.; Domschke, G.; Fangha¨nel, E.; Habicher,
W. D.; Metz, P.; Pavel, D.; Schwetlick, K. Organikum-Organisch-
chemisches Grundpraktikum, 21st ed.; Wiley-VCH: Weinheim, 2001.
Inorganic Chemistry, Vol. 48, No. 4, 2009 1421

Beck et al.
[D8]THF, 293 K, ppm): δ ) 9.0 (m(br), 3P, PCH3) ppm. Anal.
Calcd for C18H36CoOP3 (420.3): C, 51.43; H, 8.63. Found: C, 51.22;
H, 8.63.
6.91 (t, 3JH,H ) 7.1 Hz, 1H, Ar-H); 7.17 (s(br), 2H, Ar-H); 7.24
(d, 3JH,H ) 7.7 Hz, 1H, Ar-H); 7.34 (d, 3JH,H ) 6.5 Hz, 1H, Ar-H);
3
3
7.53 (d, JH,H ) 8.2 Hz, 1H, Ar-H); 8.56 (d, JH,H ) 7.1 Hz, 1H,
Ar-H). 13C(1H) NMR (125 MHz, [D8]THF, 293 K, ppm): δ )
Carbonyl[2-(aminophenyl)-C]tris(trimethylphosphine)co-
balt(I) (4). Method A: CoMe(PMe3)4 (850 mg, 2.24 mmol) was
combined with 2-aminobenzaldehyde (272 mg, 2.24 mmol) at -70
°C to afford after cooling to 4 °C orange crystals of 4 suitable for
X-ray diffraction. Yield 650 mg (71%). Method B: 2-Aminoben-
zylalcohol (340 mg, 2.76 mmol) in diethyl ether was combined at
20 °C with CoMe(PMe3)4 (1.04 g, 2.76 mmol) to afford yellow
crystals. Yield 425 mg (38%). Mp 123-127 °C (dec). IR (Nujol):
ν˜ ) 1850 s (ν CdO); 1577 m (ν CdC) cm-1. 1H NMR (500 MHz,
[D8]THF, 293 K, ppm): δ ) 1.28 (s(br), 27H, PCH3); 4.29 (s(br),
2H, NH2); 6.25 (m, 2H, Ar-H); 6.56 (m, 1H, Ar-H); 6.82 (m,
1H, Ar-H). 13C(1H) NMR (125 MHz, [D8]THF, 293 K, ppm): δ
) 20.0 (m, PCH3); 108.8 (s, CH); 115.7 (s, CH); 121.5 (s, CH);
144.7 (s, CH); 156.7 (s, C); 180.3 (m, Co-C); 207.6 (m, Co-CO).
31P(1H) NMR (202 MHz, [D8]THF, 293 K, ppm): δ ) 9.5 (m(br),
3P, PCH3) ppm. Anal. Calcd for C16H33CoNOP3 (407.3): C, 47.42;
H, 7.71; N, 3.46; P, 22.93. Found: C, 47.11; H, 8.49; N, 3.40; P,
22.75.
1
22.3 (d, JP,C ) 18.8 Hz, PCH3); 117.9 (s, CH); 118.0 (s, CH);
120.4 (s, CH); 120.5 (s, CH); 124.7 (s, CH); 130.6 (s, C); 135.9 (s,
CH); 138.8 (s, CH); 140.6 (s, C); 171.5 (m, C); 201.1 (m, Co-C).
31P(1H) NMR (202 MHz, [D8]THF, 293 K, ppm): δ ) 7.8 (m(br),
3P, PCH3) ppm. Anal. Calcd for C20H34CoOP3 (442.3): C, 54.31;
H, 7.75; P, 21.01. Found: C, 54.38; H, 7.85; P, 21.10.
In Situ Observation of Aldehydes/Co-hydride. In an NMR
Schlenk tube, CoCH3(PMe3)4 (7.52 mg, 0.0198 mmol) was com-
bined with 1-naphthalenemethanol (2.65 mg, 0.0198 mmol) in 0.8
mL THF-d8 condensed to the starting materials. Under vacuum,
the solution was frozen to -196 °C, and the reaction tube was
sealed. The reaction was immediately monitored at room temper-
1
ature by H NMR spectroscopy. Within 30 min, resonances were
observed for free 1-naphthaldehyde (δ ) 10.41 ppm, s(br),
Ar-CHO), and these resonances continued to increase for about
2 h. Other resonances were observed for CH4, and in the high-field
region (-23.9 ppm) it was indicated that the Co-hydride species
[CoH(PMe3)4]59 was the byproduct. Finally, after 4 h, a 13C(1H)
NMR spectrum of the reaction mixture was recorded and the CHO-
carbon resonance of 1-naphthaldehyde identified at 193.3 ppm.
Other resonances were also observed in the spectra including
multiplets at δ ) 5.80, 5.57, and 5.32, and resonances for
carbonyl[1-(naphthyl)-C]tris(trimethylphosphine)cobalt(I) (7) are
present in low intensity. For the in situ experiment with equimolar
amounts of 2-methylbenzylalcohol (5.23 mg, 0.0428 mmol) with
CoCH3(PMe3)4 (16.1 mg, 0.0428 mmol) under same conditions,
2-methylbenzylaldehyde was identified: (-1H NMR, 500 MHz, 296
K): δ ) 10.28 ppm (s(br) Ar-CHO); (13C(1H) NMR, 125 MHz,
296 K): δ ) 192.12 ppm (s, Ar-CHO).
X-ray Structure Determinations. Data collection was performed
on a STOE IPDSII image plate detector using Mo KR radiation (λ
) 0.71019 Å). Details of the crystal structure are given in Table 2.
Data collection: Stoe XAREA.60 Cell refinement: Stoe X-AREA.60
Data reduction: Stoe X-RED.60 The structure was solved by direct
methods using SHELXS-97,61 and anisotropic displacement pa-
rameters were applied to non-hydrogen atoms in a full-matrix least-
squares refinement based on F2 using SHELXL-97.61 The hydrogen
atoms were observed or calculated and refined riding on the bonded
carbon atoms. For 6: It was not possible to model the apparent
disorder of the C(7)F3 group accordingly, so the large a.d.p.’s
(anisotropic displacement parameters) of F1-F3 have no physical
relevance. The structure is of marginal quality and should be
understood as proof of connectivity only [R1 ) 0.0794 (I g 2σ(I))].
Carbonyl[2,6-(difluorophenyl)-C]tris(trimethylphosphine)co-
balt(I) (5). Method A: 2,6-Difluorbenzaldehyde (220 mg, 1.54
mmol) was combined at -70 °C with CoMe(PMe3)4 (585 mg, 1.54
mmol) to afford yellow crystals. Yield 437 mg (66%). Mp 108-110
°C (dec). IR (Nujol): ν˜ ) 1878 s (ν CdO); 1577 m (ν CdC) cm-1
.
1H NMR (500 MHz, [D8]THF, 293 K, ppm): δ ) 1.24 (s(br), 27H,
PCH3); 6.51 (dd, 3JH,H ) 6.6 Hz,3JH,H ) 6.0 Hz, 2H, Ar-H); 6.79
3
(dd, JH,H ) 7.4 Hz,3JH,H ) 6.9 Hz, 1H, Ar-H). 13C(1H) NMR
(125 MHz, [D8]THF, 293 K, ppm): δ ) 19.5 (m, PCH3); 107.4
(d,2JC,F ) 35.0 Hz, CH); 122.8 (t,3JC,F ) 9.0 Hz, CH); 169.1 (m,
CoC); 172.4 (dd,1JC,F ) 222.0 Hz,3JC,F ) 21.0 Hz, CF). 31P(1H)
NMR (202 MHz, [D8]THF, 293 K, ppm): δ ) 8.2 (m(br), 3P, PCH3)
ppm. Anal. Calcd for C16H30CoF2OP3 (428.3): C, 44.87; H, 7.06.
Found: C, 44.95; H, 7.37.
Carbonyl[2-(trifluoromethylphenyl)-C]tris(trimethylphosphi-
ne)cobalt(I) (6). Method A: 2-Trifluoromethylbenzaldehyde (720
mg, 4.13 mmol) was combined at -70 °C with CoMe(PMe3)4
(1.560 mg, 4.13 mmol) to afford deep red octahedral crystals of 6,
which were suitable for X-ray diffraction. Yield 1.10 g (58%). Mp
115-118 °C (dec). IR (Nujol): ν˜ ) 1866 s (ν CdO); 1578 m (ν
1
CdC) cm-1. H NMR (500 MHz, [D8]THF, 293 K, ppm): δ )
1.21 (s(br), 27H, PCH3); 6.84 (s, 2H, Ar-H); 7.28 (s, 1H, Ar-H);
7.57 (s, 1H, Ar-H). 13C(1H) NMR (125 MHz, [D8]THF, 300 K,
ppm): δ ) 19.7-20.1 (m, PCH3); 122.5 (s, CH); 126.9 (s, CH);
127.0 (s, CH); 129.1 (m, CF3); 146.2 (m, CH); 174.3 (m, Co-C);
204.6 (m, Co-CO). 31P(1H) NMR (202 MHz, [D8]THF, 293 K,
ppm): δ ) 10.3 (m(br), 3P, PCH3) ppm. Anal. Calcd for
C17H31CoF3OP3 (460.3): C, 44.36; H, 6.79; P, 20.19. Found: C,
44.29; H, 6.70; P, 20.20.
Acknowledgment. Financial support of this work by
Fonds der Chemischen Industrie is gratefully acknowledged.
Carbonyl[1-(naphthyl)-C]tris(trimethylphosphine)cobalt(I) (7).
Method A: 1-Naphthaldehyde (338 mg, 2.16 mmol) was combined
at -70 °C with a solution of CoMe(PMe3)4 (820 mg, 2.16 mmol)
to afford orange rhombic crystals, which were suitable for X-ray
diffraction. Yield 757 mg (79%). Method B: 1-Naphthalenemetha-
nol (270 mg, 1.71 mmol) was combined at 20 °C with CoMe-
(PMe3)4 (645 mg, 1.71 mmol) in diethyl ether to afford yellow
crystals at -27 °C. Yield 219 mg (29%). Mp 122-124 °C (dec).
IR (Nujol): ν˜ ) 1872 s (ν CdO); 1578 m (ν CdC) cm-1. 1H NMR
(500 MHz, [D8]THF, 293 K, ppm): δ ) 1.18 (s(br), 27H, PCH3);
Supporting Information Available: Tables containing full
X-ray crystallographic data for 4, 6 and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC801673H
(59) Klein, H.-F.; Hammer, R. Z. Naturforsch. 1977, 32b, 138–143.
(60) Stoe & Cie. X-AREA (Version 1.18) and X-RED32 (Version 1.04);
Stoe & Cie: Darmstadt, Germany, 2002.
(61) Sheldrick, G. M. SHELXS-97 and SHELXL-97; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997.
1422 Inorganic Chemistry, Vol. 48, No. 4, 2009