[Co1 (CN)2(CO)3] -, a new discovery from an 80-year-old reaction

Article abstract of DOI:10.1039/c3cc43269f

A systematic study of the 80-year-old simple and fundamental reaction of cobalt(ii) salt with cyanide under one atmosphere CO was carried out and two novel Co(i) complexes were isolated in the absence of hydroxide. These complexes are the first structurally characterized mixed cobalt CO-CN^- compounds.

Full text of DOI:10.1039/c3cc43269f

Chemical Communications
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Volume 49 | Number 67 | 28 August 2013 | Pages 7363–7462
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Chunhua Hu, Jianfeng Jiang et al.
[CoI(CN)2(CO)3]−, a new discovery from an 80-year-old reaction

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[CoI(CN)2(CO)3]ꢀ, a new discovery from an 80-year-old
reaction†
Cite this: Chem. Commun., 2013,
49, 7382
Wenfeng Lo,a Chunhua Hu,*b Marck Lumeij,c Richard Dronskowski,c
Michael Lovihayeem,a Oren Ishala and Jianfeng Jiang*a
Received 2nd May 2013,
Accepted 22nd May 2013
DOI: 10.1039/c3cc43269f
www.rsc.org/chemcomm
A systematic study of the 80-year-old simple and fundamental
The reactions were carried out on a millimolar scale. In the
reaction of cobalt(II) salt with cyanide under one atmosphere CO absence of hydroxide, the addition of four equivalents of
was carried out and two novel Co(I) complexes were isolated in the sodium cyanide to an aqueous cobalt(II) chloride solution
absence of hydroxide. These complexes are the first structurally under one atmosphere carbon monoxide gave a light yellow
characterized mixed cobalt CO–CNꢀ compounds.
solution in 24 hours. By treating the reaction mixture with a
solution of PPh4Cl in CH2Cl2, we separated two major products:
In the early 1930s, the addition of cyanide to a basic aqueous (PPh4)[CoI(CN)2(CO)3] from the organic phase and Na3[CoIII(CN)6]
solution of a Co2+ salt under one atmosphere CO was studied, from the aqueous phase.5 Both products were isolated in
and the cobalt carbonyl compound [Co(CO)4]ꢀ was isolated.1 around 50% yield. Even though other Co–CN–CO complexes
Protonation of [Co(CO)4]ꢀ yields [CoI(H)(CO)4], which is a major have been previously described by Stuhl and Foxman et al.,6
catalyst for the hydroformylation reaction and one of the first (PPh4)[CoI(CN)2(CO)3] represents the first example of a cobalt
homogeneous catalysts.2 Both [Co(CO)4]ꢀ and [CoI(H)(CO)4] complex with mixed cyanide–carbonyl ligands determined
have been extensively studied over the last 80 years. The using single crystal X-ray diffraction.‡
reaction leading to [Co(CO)4]ꢀ is shown in eqn (1). However,
The crystals of (PPh4)[CoI(CN)2(CO)3] were grown by diffusing
cyanide, a very strong ligand, was surprisingly not found in any hexane into the CH2Cl2 solution, and its crystal structure
of the cobalt complexes isolated from the reaction system. was established using single crystal X-ray diffraction. The
Cyanide is believed to serve only as a promoting agent according [CoI(CN)2(CO)3]ꢀ anion was analyzed by dispersion-corrected
to previous publications.3
density-functional calculations.5,7 In the structure CoI takes a
trigonal bipyramidal geometry with both CN ligands in the axial
position and three CO groups in the equatorial position. The
Co–CCO bond distances are around 1.8 Å, which are signifi-
cantly shorter than the Co–CCN bond distances (ca. 1.9 Å). This
observation agrees with the data in other metal cyanide carbonyl
complexes.4 The molecular drawing of the anion [CoI(CN)2(CO)3]ꢀ
is depicted in Fig. 1, and selected bond distances and angles
2ꢀ
2Co2+ + 12OHꢀ + 11CO - 2[Co(CO)4]ꢀ + 3CO3 + 6H2O
(1)
Driven by the recent discovery of other mixed metal cyanide
carbonyl complexes [M(CN)x(CO)y]nꢀ4 and our curiosity regarding
what really happens in such a simple and fundamental reaction
system, we decided to systematically study the reactions of
aqueous Co2+ solution with varying amounts of cyanide and
hydroxide under one atmosphere CO, just like initially investi-
gated 80 years ago. Astonishingly, we have discovered new
cyanide carbonyl compounds of cobalt(I).
a Department of Chemistry, Yeshiva University, 2495 Amsterdam Avenue, New York,
NY 10033, USA. E-mail: jiang@yu.edu; Fax: +1 212-9600035;
Tel: +1 212-9605400 ext. 5225
b Department of Chemistry, New York University, 100 Washington Square East,
New York, NY 10003, USA. E-mail: chunhua.hu@nyu.edu; Fax: +1 212-9954895;
Tel: +1 212-9988769
c Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1,
D-52056 Aachen, Germany
† Electronic supplementary information (ESI) available. CCDC 927721 and
927722. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3cc43269f
Fig. 1 ORTEP drawing of [CoI(CN)2(CO)3]ꢀ and [CoI(CN)3(CO)2]2ꢀ at the 50%
ellipsoid level.
c
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Table 1 Structural, IR and NMR data for [CoI(CN)2(CO)3]ꢀ and [CoI(CN)3(CO)2]2ꢀ
of the DFT calculations. These charges are listed in Table S1 in
the ESI,† and they do reflect our expectations on the oxidation
of cobalt as +1 and the whole [CoI(CN)2(CO)3]ꢀ anion as
ꢀ1 charged.
Anion
[CoI(CN)2(CO)3]ꢀ
[CoI(CN)3(CO)2]2ꢀ
Selected bond
distance (Å)
Co1–C1 1.896(2)
Co1–C2 1.789(3)
Co1–C3 1.801(4)
Co1–C1 1.9499(17)
Co1–C2 1.8912(19)
Co1–C3 1.8978(18)
Co1–C4 1.7781(19)
Co1–C5 1.7586(18)
C2–Co1–C1 91.59(7)
C2–Co1–C4 91.47(8)
During the preparation of [CoI(CN)2(CO)3]ꢀ, the reaction
mixtures were continuously monitored using IR spectroscopy.
There were additional peaks observed between 1900 and
2000 cmꢀ1 upon reaction, suggesting that other cobalt carbonyl
complexes might exist as reaction intermediates. It could be
Selected bond
angle (1)
C1–Co1–C2 89.35(12)
C1–Co1–C3 90.53(11)
C1–Co1–C20 90.10(12)a C2–Co1–C5 87.48(8)
C1–Co1–C10 178.9(2)
C2–Co1–C3 120.97(10)
C2–Co1–C3 175.58(7)
C1–Co1–C4 115.25(7)
[CoI(CN)3(CO)2]2ꢀ in accord with Halpern and Pribanic’s
´
findings.13a However, we were unable to separate the pure
product from the reaction mixtures. Varying the amount of
cyanide to the reaction system did not help either. We then
decided to treat the purified (PPh4)[CoI(CN)2(CO)3] with more
CNꢀ to test the former hypothesis. Indeed, the addition of
one equivalent CNꢀ to [CoI(CN)2(CO)3]ꢀ in CH2Cl2 resulted in
C2–Co1–C20 118.05(19) C1–Co1–C5 118.49(7)
C4–Co1–C5 126.25(8)
IR frequency in
nCO 2004
nCO 1917
1980
CH2Cl2 (cmꢀ1
)
nCN 2112
nCN 2074
2088
2114
dCO 195.1
dCN 131.0, 123.6
NMR 13C shift (ppm) dCO 195.0
dCN 126.0
+
[CoI(CN)3(CO)2]2ꢀ. Successfully we crystallized its PPh4 salt
and then determined the structure using single-crystal
X-ray diffraction.5 [CoI(CN)3(CO)2]2ꢀ prepared in this manner
is still trigonal bipyramidal, and in its structure two CO
ligands remain in the equatorial plane. The bond angle
a
The primed atoms are generated by the symmetry operation of ꢀx + 1,
y, ꢀz + 1.
are presented in Table 1. In CH2Cl2 solution [CoI(CN)2(CO)3]ꢀ between two CO ligands is 126.25(8)1. Two apical and one
has a D3h symmetry since only one CN and one CO peak were equatorial CN ligands form a T shape. An ORTEP drawing of
detected by the solution infrared spectrum (IR) at 2112 and [CoI(CN)3(CO)2]2ꢀ is depicted in Fig. 1, and selected bond
2004 cmꢀ1. To assign these peaks, the IR spectrum of the distances and angles are also listed in Table 1 for comparison
13C-labeled cyanide complex was measured. The peak at with [CoI(CN)2(CO)3]ꢀ.
2112 cmꢀ1 shifted to 2067 cmꢀ1 in the labeled complex, which
In CH2Cl2 solution [CoI(CN)3(CO)2]2ꢀ has C2v symmetry. All
was assigned to the asymmetric CN stretch; the peak at of its CO and CN vibration modes are IR active. The IR peaks
2004 cmꢀ1 remained at the same frequency and was assigned observed in CH2Cl2 solution at 1917(vs) and 1980(s) cmꢀ1 were
to the CO stretch. Density-functional theory calculations fully assigned to the C–O stretches, and peaks at 2074(w), 2088(w)
support the assignment. Compared to the isostructural and and 2114(w) were assigned to the C–N stretches. The IR
isoelectric iron analog, [Fe0(CN)2(CO)3]2ꢀ (nCO = 1844 cmꢀ1),4b frequencies of both [CoI(CN)2(CO)3]ꢀ and [CoI(CN)3(CO)2]2ꢀ
the CO vibration frequency has a blue shift of 160 cmꢀ1. The are also listed in Table 1. IR spectra of both compounds in
shift is from the different strength of the metal-to-CO p-back CH2Cl2 solution are shown in Fig. S2 in the ESI.† There are
donation bonding caused by the charge and/or electronegativity significant shifts in CO stretching frequencies in aqueous
on the center metal atom. Similar results were recorded for the solution observed at 1960 and 2004 cmꢀ1. These shifts caused
series of complexes such as [Mn(CO)6]+ (2100 cmꢀ1), [Cr(CO)6] by the solvent effect have also been observed in many other
(2000 cmꢀ1) and [V(CO)6]ꢀ (1859 cmꢀ1), which were well mixed CN–CO complexes and have been explained by theore-
documented in a textbook contribution.8
tical calculations.4,14
[CoI(CN)2(CO)3]ꢀ is oxygen-sensitive. A cyclic voltammetry
[CoI(CN)3(CO)2]2ꢀ is also oxygen-sensitive. A cyclic voltam-
experiment conducted in CH2Cl2 solution showed that the metry experiment conducted in CH2Cl2 solution indicates that
irreversible oxidation of CoII/CoI occurred at +206 mV vs. Ag/AgCl. the irreversible oxidation of CoII/CoI occurs at +49 mV vs.
Addition of the mild oxidant I2 led to the dissociation of all CO Ag/AgCl. The negative shift of 157 mV due to the substitu-
ligands, which was monitored by conducting an infrared study.
Dispersion-corrected density-functional calculations9 on the observed in [[Fe0(CN)(CO)4]ꢀ/Fe0(CN)2(CO)3]2ꢀ 4b
crystal structure of (PPh4)[CoI(CN)2(CO)3] were carried out in that [CoI(CN)3(CO)2]2ꢀ is just marginally more electron-rich
order to elucidate the relative structural stability, which is than [CoI(CN)2(CO)3]1ꢀ
evaluated by calculating the phonon density of states using
Both [CoI(CN)2(CO)3]ꢀ and [CoI(CN)3(CO)2]2ꢀ are diamagnetic
the quasi-harmonic approximation,10,11 as depicted in Fig. S1 as observed in NMR experiments. Not too surprisingly, spin-
(ESI†).
polarized DFT calculations of [CoI(CN)2(CO)3]ꢀ also arrive
tion of one CO by one CN is far less than the ꢀ550 mV shift
,
suggesting
.
Indeed, there are no imaginary phonon frequencies hence at full spin pairing and yield a diamagnetic ground state.
this very compound must be a relative minimum on the No paramagnetic NMR shift is observed in either complex.
energy hypersurface. We find the CRN peak in the range of The 13C chemical shifts of CN and CO for both complexes are
2160–2180 cmꢀ1 and the CRO peak at 1982–2060 cmꢀ1, which shown in Table 1.
is in good agreement with the experimental results.
While [CoI(CN)2(CO)3]ꢀ has been discovered for the first time
The electronic structure and its associated charge distribu- ever, [CoI(CN)3(CO)2]2ꢀ was previously reported by the carbonyl-
tion are easily mirrored from the Bader charges,12 a byproduct ation of [CoII(CN)5]3ꢀ in aqueous solution.13 Halpern and
c
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13a
suggested that the formation of [CoI(CN)3(CO)2]2ꢀ
M. Orchin, J. Am. Chem. Soc., 1958, 80, 4428; (g) L. Kirch and
M. Orchin, J. Am. Chem. Soc., 1959, 81, 3597; (h) R. F. Heck and
D. S. Breslow, J. Am. Chem. Soc., 1960, 82, 4438; (i) R. F.
Heck and D. S. Breslow, J. Am. Chem. Soc., 1961, 83, 4023.
3 A. A. Blanchard and P. Gilmont, J. Am. Chem. Soc., 1940, 62,
1192–1193.
´
Pribanic
was from the disproportionation of CoII. In fact, the dispropor-
tionation of CoII to CoIII and CoI is not rare, as some CoI
vitamin B12 model compounds were prepared by such dispro-
portionation.15 Based on the observation of close to 50% yield
of both CoIII hexacyanide and CoI dicyanide tricarbonyl in our
preparation and the disproportionation of CoII pentacyanide
under CO, we assume that the formation of [CoI(CN)2(CO)3]ꢀ is
from the disproportionation of CoII under one atmosphere CO
through the reaction shown in eqn (2):
4 (a) J. Jiang and S. A. Koch, Angew. Chem., Int. Ed., 2001, 40,
2629–2631; (b) A. Kayal and T. B. Rauchfuss, Inorg. Chem., 2003,
42, 5046–5048; (c) J. Jiang and S. A. Koch, J. Am. Chem. Soc., 2001,
123, 12109–12110; (d) J. Jiang and S. A. Koch, Inorg. Chem., 2002,
41, 158; (e) H. I. Karunadasa and J. R. Long, Angew. Chem., Int. Ed.,
2009, 48, 738; ( f ) P. Kurz, B. Spingler, T. Fox and R. Alberto, Inorg.
Chem., 2004, 43, 3789; (g) T. B. Rauchfuss, S. M. Contakes,
S. C. N. Hsu, M. A. Reynolds and S. R. Wilson, J. Am. Chem. Soc.,
2001, 123, 6933; (h) S. M. Contakes and T. B. Rauchfuss, Angew.
Chem., Int. Ed., 2000, 39, 1984; (i) S. M. Contakes, S. C. N. Hsu,
T. B. Rauchfuss and S. R. Wilson, Inorg. Chem., 2002, 41,
1670; ( j) S. A. Goldfield and K. N. Raymond, Inorg. Chem., 1974,
13, 770–775.
2Co2+ + 8CNꢀ + 3CO - [CoIII(CN)6]3ꢀ + [CoI(CN)2(CO)3]ꢀ
(2)
In summary, [CoI(CN)2(CO)3]ꢀ and [CoI(CN)3(CO)2]2ꢀ not
only represent the first examples of cobalt cyanide carbonyl
complexes characterized using single crystal X-ray diffraction,
their formation also suggests a comprehensive reaction mecha-
nism for the preparation of [Co(CO)4]ꢀ. These two anions may
be the reaction intermediates and might further react with OHꢀ
to form [Co(CO)4]ꢀ. More work is in progress in order to prove
this hypothesis.
We thank the National Science Foundation for financial sup-
port through CHE-1213241 and the support of the CRIF Program
(CHE-0840277) and the NSF MRSEC Program (DMR-0820341) for
the purchase of a Bruker GADDS microdiffractometer.
5 X-ray data for (PPh4)[CoI(CN)2(CO)3], M = 534.37, monoclinic, space
group I2, a = 13.042(4), b = 7.3431(13), c = 13.093(2) Å, b = 91.215(2)1,
V = 1253.6(5) Å3, T = 100(2) K, Z = 2, 8266 reflections measured, 2586
independent reflections (Rint = 0.0566); R1 = 0.0359 (I > 2s(I)) and
wR(F2)
= 0.0556 (all data); CCDC 927721. X-ray data for
(PPh4)2[CoI(CN)3(CO)2]ꢁ(H2O), M = 889.77, triclinic, space group
%
P1, a = 9.7538(3), b = 11.1003(3), c = 21.8916(6) Å, a = 96.4350(10),
b = 95.4790(10)1, g = 108.4320(10)1, V = 2212.80(11) Å3, T = 100(2) K,
Z = 2, 40 694 reflections measured, 8418 independent reflections
(Rint = 0.0382); R1 = 0.0308 (I > 2s(I)) and wR(F2) = 0.0737 (all data);
CCDC 927722†.
6 (a) S. J. Carter, B. M. Foxman and L. S. Stuhl, J. Am. Chem. Soc., 1984,
106, 4265–4266; (b) S. J. Carter and L. S. Stuhl, Organometallics, 1985,
4, 197–198; (c) S. J. Carter and L. S. Stuhl, Organometallics, 1988, 7,
1909–1918.
7 Crystal data obtained from structural optimization by DFT calcula-
tions for (PPh4)[CoI(CN)2(CO)3], space group I2, arrive at a = 12.911,
b = 7.121, c = 13.071 Å, b = 90.701, V = 1201.68 Å3.
8 G. L. Miessler and D. A. Tarr, Inorganic Chemistry, Prentice Hall,
3rd edn, 2004, p. 469.
9 The density-functional calculations were performed using the plane-
wave code VASPa–d with PAWe potentials and dispersion correction.f
Contributions of electronic exchange and correlation to the total
energy were treated using the PBE-GGA approximationg,h
(a) G. Kresse and J. Hafner, Phys. Rev. B, 1993, 47, 558–561;
(b) G. Kresse and J. Furthmu¨ller, Phys. Rev. B, 1996, 54,
11169–11186; (c) G. Kresse and D. Joubert, Phys. Rev. B, 1999, 59,
1758–1775; (d) G. Kresse and J. Furthmu¨ller, Comput. Mater. Sci.,
Notes and references
‡ Preparation of PPh4[CoI(CN)2(CO)3]: to a pink solution of CoCl2ꢁ6H2O
(238 mg, 1.00 mmol) in 20 mL H2O under 1 atm CO, a solution of NaCN
(196 mg, 4.00 mmol) in 10 mL H2O was added dropwise resulting in a
light green cloudy mixture. The mixture was stirred under CO for
24 hours to give a clear light yellow solution. A solution of PPh4Cl
(188 mg, 0.50 mmol) in 30 mL CH2Cl2 was added to the light yellow
aqueous solution and stirred under 1 atm CO for another hour. The
CH2Cl2 layer was collected under 1 atm CO, and CH2Cl2 was removed by a
constant flow of CO gas to afford 251 mg (47% yield) PPh4[CoI(CN)2(CO)3]
as an off-white solid. Absorption (l (nm), e (Lmolꢀ1cmꢀ1)): (262 nm,
7700; 269 nm, 7500; 276 nm, 6800). 13C NMR: dCO 195.0 ppm,
¨
1996, 6, 15–50; (e) P. E. Blochl, Phys. Rev. B, 1994, 50, 17953–17979;
d
CN 126.0 ppm. IR (CH2Cl2): nCO 2004 cmꢀ1, nCN 2112 cmꢀ1. Elementary
ˇ
( f ) J. Klimes, D. R. Bowler and A. Michaelides, Phys. Rev. B, 2011,
83, 195131; (g) J. P. Perdew, J. Chevary, S. H. Vosko, K. A. Jackson,
M. R. Pederson and D. J. Sing, Phys. Rev. B, 1992, 46, 6671–6687;
(h) J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77,
3865–3868.
analysis data are inconclusive since this compound is air and light
sensitive and only stable under 1 atm CO gas even in the solid state. The
49% yield of Na3Co(CN)6 was measured by a quantitative UV-visible
absorption experiment.
Preparation of (PPh4)2[CoI(CN)3(CO)2]: all operations were performed
under the protection of a flow of nitrogen gas. To a light yellow solution
of PPh4[CoI(CN)2(CO)3] (99 mg, 0.19 mmol) in 5 mL CH2Cl2, a solution
of PPh4CN16 (68 mg, 0.19 mmol) in 2 mL CH2Cl2 was added and the
resulting solution was stirred for 2 hours. 20 mL hexane was added to
the reaction mixture and a light green crystalline material was pre-
cipitated. The light green crystalline material was filtered and rinsed
three times using 3 mL hexane and dried in vacuo to afford 122 mg
(76% yield) (PPh4)2[CoI(CN)3(CO)2]ꢁH2O as a light green powder.
10 (a) A. Togo, Fropho: A Tool to Compute Phonon Band Structures and
Thermal Properties of Solids, RWTH Aachen University, 2007–2008.
Available at http://fropho.sourceforge.net; (b) A. Togo, F. Oba and
I. Tanaka, Phys. Rev. B, 2008, 78, 134106.
11 R. Stoffel, C. Wessel, M.-W. Lumey and R. Dronskowski, Angew.
Chem., Int. Ed., 2010, 49, 5242–5266.
12 (a) W. Tang, E. Sanville and G. Henkelman, J. Phys.: Condens. Matter,
2009, 21, 084204; (b) E. Sanville, S. D. Kenny, R. Smith and
G. Henkelman, J. Comput. Chem., 2007, 28, 899–908;
´
(c) G. Henkelman, A. Arnaldsson and H. Jonsson, Comput. Mater.
1 (a) A. A. Blanchard, J. R. Rafter and W. B. Adams Jr, J. Am. Chem. Soc.,
1934, 56, 16–17; (b) A. A. Blanchard and G. W. Coleman, J. Am. Chem. 13 (a) J. Halpern and M. Pribanic, J. Am. Chem. Soc., 1971, 93, 96–98;
Sci., 2006, 36, 254–360.
´
Soc., 1936, 58, 2160; (c) A. A. Blanchard, Chem. Rev., 1937, 21, 3;
(d) P. Gilmont and A. A. Blanchard, Inorganic Syntheses, McGraw-Hill,
New York, 1946, vol. 2, p. 238.
(b) J. Halpern, G. Guastalla and J. Bercaw, Coord. Chem. Rev., 1972, 8,
167–173; (c) A. Farcas and D. Lupu, J. Inorg. Nucl. Chem., 1975, 37,
837–838.
2 (a) F. Hebrard and P. Kalck, Chem. Rev., 2009, 109, 4272–4282; 14 R. Viswanathan, A. M. Etra and J. Jiang, Inorg. Chim. Acta, 2009, 362,
(b) I. Wender, H. W. Sternberg and M. Orchin, J. Am. Chem. Soc., 2728–2734.
1953, 75, 3041; (c) H. Aldkins and G. Krsek, J. Am. Chem. Soc., 1949, 15 T. M. Brown, A. T. Dronsfield, C. J. Cooksey and D. Crich, J. Chem.
71, 3051; (d) M. Orchin, L. Kirch and I. Goldfarb, J. Am. Chem. Soc., Educ., 1990, 67, 973–974.
1956, 78, 5450; (e) I. Wender, S. Metlin, S. Ergun, H. W. Sternberg 16 S. Andreades and E. W. Zahnow, J. Am. Chem. Soc., 1969, 91,
and H. Greenfirld, J. Am. Chem. Soc., 1956, 78, 5401; ( f ) L. Kirch and
4181–4190.
c
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