Synthesis and characterization of two novel cobalt (II) phosphine complexes: Crystal structures of [CoCl3(Cy2PCH 2PCy2H)] and [Co(NO3)2(Cy 2PCH2PCy2O)]. Cy = cyclohexyl, C 6H11

Article abstract of DOI:10.1016/j.ica.2004.06.063

The complexes [(Cy₂PCH₂PCy₂H)CoCl ₃] (1) and [(Cy₂PCH₂PCy₂O)Co(NO ₃)₂] (2), Cy = cyclohexyl (C₆H₁₁), have been prepared and characterized by EPR, UV-Vis, microanalysis and X-ray crystallography. The reaction CoCl₂ ? 6H₂O and dcpm, dcpm = bis(dicyclohexylphosphino)methane, was found to form the thermochromic and paramagnetic complex [(Cy₂PCH₂PCy₂H) CoCl₃] (1). Of particular interest is the formation of a zwitterion, or inner salt. The reaction of Co(NO₃)₂ ? 6H ₂O and dcpm in a toluene/methanol/methylene chloride mixture yields the pseudo-octahedral complex [(Cy₂PCH₂PCy ₂O)Co(NO₃)₂] (2). The complexes [(Cy ₂PCH₂PCy₂H)CoCl₃] (1) and [(Cy ₂PCH₂PCy₂O)Co(NO₃)₂] (2), Cy = cyclohexyl (C₆H₁₁), have been prepared and characterized by EPR, UV-Vis, microanalysis and X-ray crystallography. The reaction CoCl₂ ? 6H₂O and dcpm, dcpm = bis(dicyclohexylphosphino)methane, was found to form the monomeric, four coordinate, thermochromic and paramagnetic complex [(Cy₂PCH ₂PCy₂H)CoCl₃] (1). Of particular interest is the formation of a zwitterion, or inner salt, in which the dangling phosphine adds a hydrogen atom, giving the phosphorus a +1 formal charge. The molecule adopts a pseudo-tetrahedral geometry around the central cobalt atom to which the cyclohexyl groups bind in an equatorial fashion to the phosphine. The reaction of Co(NO₃)₂ ? 6H₂O and dcpm in a toluene/methanol/methylene chloride mixture yields the pseudo-octahedral complex [(Cy₂PCH₂PCy₂O)Co(NO₃)₂] (2). The cobalt is in the +2 oxidation state with one of the phosphorus atoms again having a +1 formal charge. The complex adopts a pseudo-octahedral geometry around the central cobalt atom with the cyclohexyl groups binding in an equatorial fashion to the phosphine similar to [(Cy₂PCH ₂PCy₂H)CoCl₃].

Full text of DOI:10.1016/j.ica.2004.06.063

Inorganica Chimica Acta 358 (2005) 57–62
www.elsevier.com/locate/ica
Synthesis and characterization of two novel cobalt (II)
phosphine complexes: crystal structures of
[CoCl3(Cy2PCH2PCy2H)] and
[Co(NO3)2(Cy2PCH2PCy2O)]. Cy = cyclohexyl, C6H11
a,
a
a
a
Charles E. Kriley *, Max M. Majireck , Jake M. Tobolewski , Luke E. Kelvington ,
a
a
a
a
Stephen H. Cummings , Stefan J. Hershberger , Jason D. Link , Anthony L. Silverio ,
b
Phillip E. Fanwick , Ian P. Rothwell
b
a
Department of Chemistry, Grove City College, 100 Campus Drive, Grove City, PA 16127, USA
b
Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette, IN 47907- 1393, USA
Received 3 May 2004; accepted 8 June 2004
Available online 23 September 2004
Abstract
The complexes [(Cy2PCH2PCy2H)CoCl3] (1) and [(Cy2PCH2PCy2O)Co(NO3)2] (2), Cy = cyclohexyl (C6H11), have been prepared
and characterized by EPR, UV–Vis, microanalysis and X-ray crystallography. The reaction CoCl2 Æ 6H2O and dcpm,
dcpm = bis(dicyclohexylphosphino)methane, was found to form the monomeric, four coordinate, thermochromic and paramagnetic
complex [(Cy2PCH2PCy2H)CoCl3] (1). Of particular interest is the formation of a zwitterion, or inner salt, in which the dangling
phosphine adds a hydrogen atom, giving the phosphorus a +1 formal charge. The molecule adopts a pseudo-tetrahedral geometry
around the central cobalt atom to which the cyclohexyl groups bind in an equatorial fashion to the phosphine. The reaction of
Co(NO3)2 Æ 6H2O and dcpm in
a toluene/methanol/methylene chloride mixture yields the pseudo-octahedral complex
[(Cy2PCH2PCy2O)Co(NO3)2] (2). The cobalt is in the +2 oxidation state with one of the phosphorus atoms again having a +1 formal
charge. The complex adopts a pseudo-octahedral geometry around the central cobalt atom with the cyclohexyl groups binding in an
equatorial fashion to the phosphine similar to [(Cy2PCH2PCy2H)CoCl3].
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Crystal structure complexes; Cobalt complexes; Phosphine complexes
1. Introduction
it can be seen that the thermochromic nature of the co-
balt (II) phosphine complexes provides a visual means
of determining the position of the equilibrium at various
temperatures and molar concentrations. A classical
example of the thermochromic nature of some cobalt
(II) complexes is the equilibrium established between
The equilibria of the solvolytic displacement of phos-
phine, in cobalt (II) complexes, by coordinating solvents
has been of particular interest in both research and as an
academic exercise illustrating the effects of temperature
and concentration on equilibria [1]. With this in mind
2þ
2þ
2ꢀ
the CoðH2OÞ
and CoCl4 ions. In this equilibrium
2ꢀ
the CoðH2OÞ6 ion is pink in color, while the CoCl4
6
ion is blue [2], thus at lower temperatures the solution
turns pink and the equilibrium is shifted to the left
(Scheme 1).
*
Corresponding author. Tel.: +1 724 458 2976; fax: +1 724 458
3855.
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.06.063

58
C.E. Kriley et al. / Inorganica Chimica Acta 358 (2005) 57–62
fashion in which the cobalt is bound to the dcpm ligand
in [(Cy2PCH2PCy2H)CoCl3] [4a].
Scheme 1.
Only a few complexes similar to [(Cy2PCH2PCy2O)-
Co(NO3)2] (2) have been found in the literature [5]. Berti
et al. [5b] has synthesized [(H2(P(Ph)O2)2)Co(OH2)3]
from the reaction of Co(CH3CO2H)2 and P,P0-diph-
enylmethylenediphosphinic acid.
We report here the preparation and characterization
of a novel cobalt dcpm complexes [(Cy2PCH2PCy2H)-
CoCl3] and [(Cy2PCH2PCy2O)Co(NO3)2].
Our current system closely models a system discov-
ered by Sestili et al. (Scheme 2). Sestili et al. [1]
showed that [CoX2P2] and [CoX3P]ꢀ undergo practi-
cally complete solvolytic displacement of phosphine
in coordinating solvents such as acetonitirile while
remaining more stable in non-coordinating solvents
like dichloromethane establishing the successive
equilibria.
Crystal structures have been determined by Carlin
et al. [3] for [CoX2PPh2] in which X is either Cl or Br.
It has also been determined that both of these com-
plexes, [CoCl2PPh2] and [CoBr2Ph2], adopt a pseudo-
tetrahedral structure in which the Co–P bonds are
2. Experimental
2.1. General procedures
EPR measurements were obtained on a Bruker ESP
300E system with an ER 4121 VT liquid-nitrogen varia-
ble-temperature controller. The operating microwave
frequency was 9.32 GHz. UV spectra were obtained
on a Spectral Instruments CCD Array.
˚
2.384(1) and 2.349(2) A, respectively, similar to the
Co–P bond distance found in [(Cy2PCH2PCy2H)CoCl3]
˚
(1), Co–P equals 2.4069(8) A (Table 1).
Studies have shown that dcpm, [dcpm = bis(dic-
yclohexylphosphino-methanol)], acting as a ligand can
bind in a variety of fashions including bridging, mono-
dentate and bidentate [4]. Prior research by our group
has determined that the reaction of nickel (II) chloride
hexahydrate and dcpm, forms the complex (dcpm)NiCl2,
in which the phosphine is bound in a bidentate fashion to
the nickel metal center as opposed to the monodentate
2.1.1. Preparation of [(Cy2PCH2PCy2H)CoCl3] (1)
To 50 mL of a methanol solution of [CoCl2] Æ 6H2O
(0.264 g, 1.11 mmol) was added 50 mL of a toluene
solution of dcpm (0.50 g, 1.22 mmol). An immediate
color change of purple to dark blue was observed upon
the addition of the dcpm/toluene solution. The solution
was stirred for 12 h, stripped to dryness and dissolved
in degased methylenechloride. The resulting blue solu-
tion was then placed in a freezer, which resulted in
the formation of large blue blocks of pure product
(1) in high yield (0.5538 g, 99.2%). The complex was
found to be EPR active showing a g value of 2.028 g
Scheme 2.
at T = 100 K. Anal. Calc. for
C25.5H49Cl5CoP2,
[(dcpm-H)CoCl3] Æ 1/2CH2C12: C, 49.54; H, 7.84; Cl,
22.97; P, 10.02. Found: C, 50.67; H, 7.8; Cl, 22.48; P,
9.09%.
Table 1
Co–P and Co–O bond lengths for selected cobalt compounds
˚
d(Co–P) A d(Co–O) A
˚
Compound
Reference
[(Cy2PCH2PCy2H)CoCl3]
[CoBr2Ph2]
[CoCl2PPh2]
2.4069(8)
2.349(2)
2.384(1)
this work
[3]
2.1.2. Preparation of [(Cy2PCH2PCy2O)Co(NO3)2]
(2)
[3]
[11]
[CoCl2{CH3N-
(CH2CH2PPh2)2}]
2.3666(14)
To 50 mL of a methanol solution of [Co(NO3)2] Æ 6-
H2O (0.234 g, 0.80 mmol) was added 50 mL of a toluene
solution of dcpm (0.50 g, 1.22 mmol) 10.0 mL of deg-
ased methylene chloride was then added to the solution.
A gradual color change of the solution from light pink
to purple was observed upon stirring the solution over
a 12 h period in a dcpm/toluene/methylene chloride solu-
tion. The solution was then stripped to dryness and dis-
solved in degased methylenechloride. The resulting
purple solution was then allowed to slowly evaporate
resulting in the formation of small purple chunk of pure
product (2) in high yield (0.6024 g, 89.4%). Anal. Calc.
for C25H46CoN2O7P2, [(Cy2PCH2PCy2O)Co(NO3)2]:
C, 49.41; H, 7.64; N, 4.61; P, 10.2. Found: C, 50.35;
H, 7.63; N, 4.44; P, 8.45%.
2.3731(15)
[(Cy2PCH2PCy2O)Co(NO3)2] 2.6358(14) 1.982(3)
this work
NaCo2{NH3CH(PO3)-
(PO3H0.5)2}2(H2O)2 Æ xH2O
2.055(4) min. [5a]
2.181(4) max.
[Co2(PMIDA)(H2O)5] Æ H2O
2.053(2)
2.073(2)
2.079(2)
2.101(2)
2.075(2)
2.053(2)
[14]
[Co(C2H8O6NP2)2(H2O)2]
2.067(2)
2.132(2)
[15]
Cy = cyclohexane; Ph = phenyl; PMIDA = N-(phosphonomethyl)imi-
nodiacetic acid.

C.E. Kriley et al. / Inorganica Chimica Acta 358 (2005) 57–62
59
Fig. 1. Molecular structure of [(Cy2PCH2PCy2H)CoCl3] (1).
Fig. 2. Molecular structure of [(Cy2PCH2PCy2O)Co(NO3)2] (2).
2.2. X-ray crystallography
solved by direct methods using SIR-97 [6]. The space
group was determined to be P21/c(#14). The remain-
ing atoms were located in succeeding difference Fou-
rier synthesis. Hydrogen atoms were included in the
refinement but restrained to ride on the atom to which
they are bonded. Except as noted in the table of
Preliminary examination and data collection were
˚
performed with Mo Ka radiation (k = 0.71073 A) on
a Nonius KappaCCD (Figs. 1 and 2). The crystallo-
graphic structure [(Cy2PCH2PCy2H)CoCl3] (1) was

60
C.E. Kriley et al. / Inorganica Chimica Acta 358 (2005) 57–62
Table 3
positional parameters, hydrogen atoms were located
and added to the structure factor calculations but
˚
Selected bond distances (A) and angles (°) for [CoCl3(Cy2PCH2P-
Cy2H)] (1)
not
refined.
The
crystallographic
structure
Co–Cl(3)
Co–Cl(2)
2.2371(10) Co–Cl(1)
2.2735(9)
2.4069(8)
1.846(3)
1.32(3)
[(Cy2PCH2-PCy2O)Co(NO3)2] (2) was solved by direct
methods using SIR-2002 [7] at a temperature of 150 K.
The space group was determined to be P21/n(#14).
The remaining atoms were located in succeeding dif-
ference Fourier synthesis. Hydrogen atoms were in-
cluded in the refinement but restrained to ride on
the atom to which they are bonded. Except as noted
in the table of positional parameters, hydrogen atoms
were located and added to the structure factor calcu-
lations but not refined.
2.2488(9)
1.839(3)
1.852(3)
1.786(3)
1.811(3)
Co–P(1)
P(1)–C(121)
P(2)–H(2)
P(1)–C(111)
P(1)–C(1B)
P(2)–C(1B)
P(2)–C(221)
P(2)–C(211)
Cl(3)–Co–Cl(2)
1.806(3)
115.65(4)
Cl(2)–Co–Cl(1)
Cl(3)–Co–P(1)
Cl(1)–Co–P(1)
112.56(4)
112.98(3)
105.97(3)
Cl(3)–Co–Cl(1)
Cl(2)–Co–P(1)
H(2)–P(2)–C(1B)
110.96(4)
97.68(3)
109.4(13)
H(2)–P(2)–C(211) 105.9(13)
H(2)–P(2)–C(221) 108.1(12)
All calculations were performed on a VAX computer.
Refinements for structures 1 and 2 were performed on
an AlphaServer 2100 using SHELX-97 [8]. Crystallo-
graphic drawings were done using programs ORTEP [9]
and PLUTON [10]. Lorentz and polarizaiton corrections
were applied to the data. A summary of the experimen-
tal data and parameters are shown in Table 2; the bond
distances and angles of [(Cy2PCH2PCy2H)CoCl3] (1)
and [(Cy2PCH2PCy2O)Co(NO3)2] (2) can be found in
Tables 1 and 2, respectively.
Table 4
˚
Selected bond distances (A) and angles (°) for [(cy2PCH2Pcy2O)-
Co(NO3)2] (2)
Co–P(2)
2.6358(14)
2.165(4)
2.225(3)
1.516(3)
1.840(4)
Co–O(1)
Co–O(12)
1.982(3)
2.154(3)
2.075(3)
Co–O(11)
Co–O(21)
P(1)–O(1)
P(2)–C(1B)
Co–O(22)
P(1)–C(1B)
O(1)–Co–O(11)
1.816(4)
159.27(13)
O(1)–Co–O(12)
O(1)–Co–O(22)
O(11)–Co–O(21)
O(12)–Co–O(21)
O(21)–Co–O(22)
O(11)–Co–P(2)
O(21)–Co–P(2)
C(1B)–P(2)–Co
146.77(13)
103.68(12)
89.84(16)
96.91(12)
60.01(12)
100.45(14)
162.61(9)
98.81(13)
O(1)–Co–O(21)
O(11)–Co–O(12)
O(11)–Co–O(22)
O(12)–Co–O(22)
O(1)–Co–P(2)
90.66(11)
59.53(12)
94.48(13)
146.77(13)
84.64(8)
2.2.1. [(Cy2PCH2PCy2H)CoCl3] (1)
The molecule can be seen to adopt a pseudo-tetrahe-
dal geometry for the central CoCl3P core (Fig. 1). Crys-
tal data and data collection parameters are given in
Table 2. A listing of important bond distances and an-
gles is found in Table 3. The Co–P distance (2.4069(8)
O(12)–Co–P(2)
O(22)–Co–P(2)
P(1)–O(1)–Co
100.38(10)
104.84(9)
123.32(15)
˚
A) is typical for those found in related Co–P complexes
2.2.2. [(Cy2PCH2PCy2O)Co(NO3)2] (2)
[10], and as seen in Table 1. The complex prepared in
this study is pseudo-tetrahedral and was found to con-
tain phosphines resting in a tetrahedral environment,
with all the cyclohexanes being bound in an equitorial
manner. A unique feature of this molecule is the coordi-
nation of a H atom to the dangling phosphine of the
dcpm.
The ligands are seen to adopt a pseudo-octahedral
arrangement around the central Co atom, CoO5P (Fig.
2). A listing of important bond distances and angles is
found in Table 4. The coordination around the phospho-
rus atoms is again distorted tetrahedral while all cyclo-
hexyl groups are bound in an equitorial manner to the
phosphorus atoms. The Co–P distance of (2.6358(14)
˚
A) is much larger than typical Co–P distances found in
other complexes (Table 1). An extensive search of the lit-
erature found only two similar cobalt complexes of this
type. The complex Co(CH2(P(Ph)O2)2)(OH2)3 was pre-
pared by Berti et al. [5b] by the reaction of Co(OAc)2,
water and CH2(P(PH)O(OH))2. However, in the case of
Berti et al. the complexes formed have neutral H2O mol-
ecules as coordinating ligands giving rise to the Co metal
center.
Table 2
Crystal and data collection parameters
Formula
Formula weight
C26H49Cl5CoP2
659.83
C25H46CoN2O7P2
607.54
Space group
˚
P21/c (No. 14)
10.8381(3)
19.7016(7)
15.2046(5)
90
P21/n (No. 14)
10.6234(3)
14.6139(5)
19.3986(5)
90
a (A)
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
95.287(2)
90
102.6466(16)
90
3
˚
V (A )
3232.8(3)
4
1.356
2938.55(15)
4
1.37
3. Results and discussion
Z
qcalc (g cmꢀ3
T (K)
Radiation (wavelength, A)
)
3.1. Spectroscopic studies
273
150
˚
Mo Ka (0.71073)
0.042
0.090
Mo Ka (0.71073)
0.069
0.166
R
Rw
The ligand, dcpm, was found to react with [Co-
Cl2] Æ 6H2O to form the corresponding Co(II) complex

C.E. Kriley et al. / Inorganica Chimica Acta 358 (2005) 57–62
61
(Fig. 1). [(Cy2PCH2PCy2H)CoCl3] (1), was formed in
high yield, giving a paramagnetic, thermochromic com-
pound with a pseudo-tetrahedral geometry, around the
CoPCl3 core (Scheme 3). The structure is indicative of
a cobalt d7, +2 oxidation state with Cs symmetry. A
search of the literature yields supports the opinion that
the quarternization reaction of phosphine and dichloro-
methane provides the additional chloride ion necessary
for the cobalt center. Examples of [CoX3P]ꢀ found in
the literature are representative of what would be ex-
pected under the present reaction conditions. The fact
that it is a bidentate phosphine that is involved in the
reaction allows for the phosphine and methylene chlo-
ride quarternization reaction to act as both the source
of the chloride ion as well as providing the counter ion
making the complex a zwitterion.
UV–Vis studies of [(Cy2PCH2PCy2H)CoCl3] (1) show
the concentration and thermal dependence of the com-
plex in relation to the solutions absorbance (Fig. 3).
UV–Vis temperature experiments of a 1:5 ratio of meth-
anol to methylene chloride solution of [(Cy2-
PCH2PCy2H)CoCl3] shows a reversible hypochromic/
hyperchromic system. The relevant absorption occurs
in the 500–750 run range where the spectral pattern is
characteristic of that for a pseudo-tetrahedral Co(II)
complex (13). This absorption pattern is due to the
4
[4A2 ! T2(F)] transition in the near-ir region, as well
4
as a transition of low energy, 4A2 ! T1 which is seldom
seen (1000–2000 nm) and is orbitally forbidden [12], as
interpreted from the Tanabe-Sugano diagram for a co-
balt (II) d7 pseudo-tetrahedral molecule.
The paramagnetic structure gives an EPR signal with
a g value of 2.028 g at T = 100 K. [(dcpm-H)CoCl3] (1)
has been found to react with various reducing agents,
but at this point no products have been isolated. Initial
reactions CoCl2 Æ 6H2O with dppm, dppm = bis(diph-
enylphosphino)methane, at room temperature were
found to produce mainly unreacted phosphine and the
cobalt (II) chloride hexahydrate.
The IR spectrum of [(Cy2PCH2PCy2H)CoCl3] (1)
shows two strong bands at 736.1 and 1112.7 cmꢀ1, indic-
ative of a tetracoordinated phosphine [13].
Scheme 3.
Fig. 3. Spectrum of methylene chloride solutions prepared from 0.01 M [(Cy2PCH2PCy2H)CoCl3] (1) and varying solution temperatures —— at 269
K, –Æ–Æ– at 290.5 K, and —— at 303 K.

62
C.E. Kriley et al. / Inorganica Chimica Acta 358 (2005) 57–62
ated with this article can be found, in the online version,
at doi:10.1016/j.ica.2004.06.063.
References
[1] (a) L. Sestili, C. Furlani, G. Festuccia, Inorg. Chim. Acta 4 (4)
(1970) 542, and reference therein;
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Advanced Inorganic Chemistry, sixth ed., Wiley, New York,
1999, p. 821.
Scheme 4.
The reaction of [Co(NO3)2] Æ 6H2O and dcpm[bis(dic-
[3] R.L. Carlin, R.D. Chirico, Ekk Sinn, G. Mennenga, L.J.
DeJongh, Inorg. Chem. 21 (6) (1982) 2218.
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PCH2PCy2O)Co(NO3)2] (Fig. 2). [(Cy2PCH2PCy2O)-
Co(NO3)2] (2) (Fig. 2), was formed in high yield, giving
a paramagnetic compound with a pseudo-octahedral
geometry, around the CoO5P core (Scheme 4). The co-
balt is a d7 with a +2 oxidation state and Cs symmetry.
No evidence of [(Cy2PCH2PCy2)Co(NO3)2] was seen in
the final mixture.
The IR spectrum of [(Cy2PCH2PCy2O)Co(NO3)2] (2)
shows two strong bands at 723.9 and 1038.1 cmꢀ1, indic-
ative of a tetracoordinated phosphine [13]. A lower wave
number is expected for the P@O stretching vibration due
to the coordination of the oxygen atom to the cobalt
atom and is seen at 1149.4 cmꢀ1 [13]. Two bands are
seen due to the N@O stretching vibrations consisting
of a broad band at 1322.6 and 1622.7 cmꢀ1. Further
reactivity of the above complexes has yet to be
investigated.
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I dedicate this paper to the memory of Dr. Ian P.
Rothwell. The many hours spent advising his graduate
students, both past and present, will not be forgotten.
[8] G.M. Sheldrick, SHELXS-97: A Program for Crystal Structure
Refinement, University of Go¨ttingen, Go¨ttingen, Germany,
1997.
[9] C.K. Johnson, ORTEPII: Report ORNL-5138, Oak Ridge
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[10] A.L Spek, PLUTON: Molecular Graphics Program, University of
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Appendix A. Supplementary material
[11] Mei Wang, Xiaomin Yu, Zhan Shi, Mingxing Qian, Kun Jin,
Jiesheng Chen, Ren He, J. Organomet. Chem. 645 (1–2) (2002)
127.
Crystal data and data collection parameters are con-
tained in Table 2. Crystallographic data for the struc-
tural analyses has been deposited with the Cambridge
Crystallographic Data Center, CCDC numbers 239475
(1) and 239474 (2). Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44
1223 336 033) or e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk. Supplementary data associ-
[12] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fifth
ed., 1988, p. 730.
[13] M. Van Den Akker, R. Olthof, F. Van Bolhuis, F. Jellinek,
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[14] Jiang-Gao, A. Clearfield, Inorg. Chem. 41 (2002) 2319.
[15] H. Jankovics, M. Daskalakis, C.P. Raptopoulou, A. Terzis, V.
Tangoulis, J. Giapintzakis, T. Kiss, A. Salifoglou, Inorg. Chem.
41 (2002) 3366.