Synthesis and electrochemistry of 1,1′-bis(phosphino)cobaltocenium compounds

Article abstract of DOI:10.1016/j.jorganchem.2011.09.004

The electrochemistry of 1,1′-bis(diphenylphosphino)cobaltocenium hexafluorophosphate ([dppc][PF₆]), 1,1′- bis(dicyclohexylphosphino)cobaltocenium hexafluorophosphate ([dcpc][PF ₆]), 1,1′-bis(di-iso-propylphosphino)cobaltocenium hexaf

Full text of DOI:10.1016/j.jorganchem.2011.09.004

Journal of Organometallic Chemistry 696 (2011) 3882e3894
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and electrochemistry of 1,10-bis(phosphino)cobaltocenium compounds
,
1
,
Kyle D. Reichla , Chelsea L. Mandella, Owen D. Henna 2, William G. Doughertyb, W. Scott Kasselb,
,
Chip Nataroa
*
a Department of Chemistry, Lafayette College, Easton, PA 18042, USA
b Department of Chemistry, Villanova University, Villanova, PA 19085, USA
a r t i c l e i n f o
a b s t r a c t
The electrochemistry of 1,10-bis(diphenylphosphino)cobaltocenium hexafluorophosphate ([dppc][PF6]),
1,10-bis(dicyclohexylphosphino)cobaltocenium hexafluorophosphate ([dcpc][PF6]), 1,10-bis(di-iso-propyl-
phosphino)cobaltocenium hexafluorophosphate ([dippc][PF6]), and 1-(di-tert-butylphosphino)cobaltoce-
nium hexafluorophosphate ([1-dtbpc][PF6])was examined in methylene chloridewith tetrabutylammonium
hexafluorophosphate as the supporting electrolyte. A reversible reductive wave followed by an irreversible
wave at more negative potentials was observed. Ten new phosphinothioyl ([dppcS2][PF6], [dcpcS2][PF6],
[dippcS2][PF6], [1-dtbpcS][PF6], and 1,10-bis(dicyclohexylphosphinothioyl)ferrocene) and phosphinoselenoyl
derivatives ([dppcSe2][PF6], [dcpcSe2][PF6], [dippcSe2][PF6], [1-dtbpcSe][PF6], and 1,10-bis(dicyclohex-
ylphosphinoselenoyl)ferrocene) were prepared and characterized, and the structures of eight of these
compounds were determined. The electrochemistry of these phosphinochalcogenyl cobaltocenium
compounds, as well as the previously prepared [dppcO2][PF6], displayed two reversible reductive waves at
potentials less negative than that of the free phosphines. A correlation was found to exist between the
Hammett substituent constant sp and the reduction potentials of these compounds. In addition, the phos-
phinoselenoyl [dppcSe2][PF6], [dcpcSe2][PF6], and [dippcSe2][PF6] displayed anelectrochemically irreversible
oxidative wave, potentially indicating an intramolecular SeeSe bonded trication. The electrochemistry of
three new and five previously reported transition metal complexes of the general formula [MnCl2(PXP)][PF6]
(M ¼ Pd or Pt, n ¼ 1, PXP ¼ dppc, dcpc or dippc; M ¼ Au, n ¼ 2, PXP ¼ dppc or dcpc)) was also examined
displaying at least two reductive waves at potentials less negative than that of the free phosphines.
Comparison of the electrochemical datawith that previously obtained foranalogous ferrocenes indicates that
a correlation exists between the reduction potentials of the cobaltocenium phosphines and the potentials at
which oxidation of the ferrocene phosphines occurs. In addition, the structure of [Au2Cl2(dppc)][PF6] was
determined.
Article history:
Received 18 August 2011
Received in revised form
30 August 2011
Accepted 2 September 2011
Keywords:
Electrochemistry
Cyclic voltammetry
Crystal structures
Cobaltocenium
Phosphine
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
[2e8]. Despite the success of these catalytic systems, the homo-
geneous nature of these catalysts has several drawbacks including
Bis(phosphino)metallocene ligands are of particular interest in
catalytic applications due to their relatively high rates of electron
transfer and unique stereochemical properties [1e7]. Undoubtedly
the most recognized and researched ligand of this type is 1,10-
bis(diphenylphosphino)ferrocene (dppf) which has been success-
fully employed in various catalytic reactions such as the palladium-
catalyzed Suzuki, Heck, and Buchwald-Hartwig coupling reactions
difficulty in the isolation of the desired product, recovery and
recycling of the catalyst, and the requirement of organic solvents
[9]. A variety of options have been considered to limit or eliminate
such drawbacks such as supporting Pd-catalysts on a polymer [10]
and using ionic liquids as solvents [9]. Coupled with their low
volatility and ability to readily dissolve transition metal complexes,
ionic liquids provide an excellent “green” option to sequester and
recycle valuable catalysts within a single liquid phase [11].
Recently, there have been several reports within the literature
successfully utilizing 1,10-bis(diphenylphosphino)cobaltocenium
cation (dppcþ), the isoelectronic analogue of dppf, as a ligand for
transition metal catalyzed reactions in ionic liquids. Ren has shown
that the catalytic system [PdCl2(dppc)][PF6]/[BMIM][PF6]
(BMIM ¼ 1-butyl-3-methyl imidazolium) was active in the Suzuki
* Corresponding author. Tel.: þ1 610 330 5216; fax: þ1 610 330 5714.
E-mail address: nataroc@lafayette.edu (C. Nataro).
Present address: Department of Chemistry, Pennsylvania State University,
1
University Park, PA 16802.
2
Present address: Church & Dwight Co., Inc., Princeton, NJ 08543.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.004

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3883
+
+
PR
PR
2
2
R = Ph (dppc+)
R = Cy (dcpc+)
R = iPr (dippc+)
Co
Co
R = tBu (1-dtbpc+)
PR
2
Fig. 1. Phosphinocobaltocenium cations.
coupling reaction between several aryl bromides and phenyl-
boronic acid giving the products in excellent yields [9]. The same
system was also applied to the Sonogashira coupling reaction
between aryl iodides and several aryl- and alkyl-acetylenes with
exceptional results [12]. In addition, dppcþ was utilized in the
biphasic rhodium-catalyzed hydroformylation of 1-octene in
[BMIM][PF6], giving high selectivity of n-nonanal [13]. In each
instance, no apparent leaching of the metal catalyst into the organic
phase was observed, and the catalytic solution was recovered and
recycled with minimal loss of activity. The [PdCl2(dppc)]][PF6]/
[BMIM][PF6] catalytic system did not exhibit significant loss of
activity in the Suzuki reaction after 140 uses, which was attributed
to tight complexation of the catalyst with the ionic liquid [9,12].
Repeating the Suzuki and hydroformylation reactions with the
analogous dppf catalyst resulted in significant leaching of the
catalyst into the organic phase, in addition to reduced activity of the
catalytic solution. Similar loss of catalytic activity was also observed
upon repeating the Sonogashira reaction with [PdCl2(PPh3)2]/
[BMIM][PF6] [14].
With such significant differences, it is surprising that relative to
dppf, little research into the properties of dppcþ and its derivatives
has been undertaken. Many of the reported studies of dppcþ and
the 19-electron 1,10-bis(diphenylphosphino)cobaltocene (dppc)
involve the ligand bound to molybdenum, ruthenium, and
rhenium carbonyl complexes and have examined the electro-
chemistry of these compounds [1,15e17]. Free dppcþ displays two
reductive waves, the less negative of which is reversible [1].
Complexation of dppcþ generally increased the reversibility of the
second reductive wave which was attributed to the bidentate
coordination of the ligand [1,16,17]. The electrochemical and
catalytic studies, in addition to the reduced reactivity of the
cyclopentadienyl rings imparted by the central cobalt atom [13],
suggest that dppcþ and its derivatives are potentially useful
ligands for transition metal catalysis in ionic liquids. These ligands
also provide a unique opportunity to study the reactivity and
electrochemical properties of charged, stable bis(phosphino)met-
allocenes, and compare these results to the well-characterized,
netural ferrocene analogues.
Since the effect of varying phosphine substituent effects has not
been investigated for derivatives of dppcþ, the electrochemistry of
1,10-bis(dicyclohexylphosphino)cobaltocenium (dcpcþ) and 1,10-
bis(di-iso-propylphosphino)cobaltocenium (dippcþ) cations was
performed (Fig. 1). Phosphinothioyls and phosphinoselenoyls, as
well as transition metal complexes of each ligand were synthesized
and characterized by NMR spectroscopy and electrochemistry. For
comparison, the previously unreported phosphinothioyl and
phosphinoselenoyl of 1,10-bis(dicyclohexylphosphino)ferrocene
were prepared and characterized. The electrochemistry of the
monophosphine 1-(di-tert-butylphosphino)cobaltocenium cation
(1-dtbpcþ), as well as the phosphinothioyl and phosphinoselenoyl,
was also analyzed. X-ray structures of eight of the phosphinothioyls
and phosphinoselenoyls as well as that of [Au2Cl2(dppc)][PF6] are
also reported. In addition, a new preparation of the previously
synthesized phosphine oxide [dppcO2][PF6] [18] is also described.
Table 1
Crystal data and structure refinement for phosphinothioyl X-ray structures.
[dcpcS2][PF6]
36H56Cl4CoF6P3S2
960.57
dcpfS2
[dppcS2][PF6]
[1-dtbpcS][PF6]
Formula
FW
C
C34H52FeP2S2
642.67
C17H14Co0.50F3P1.50
383.26
S
C18H27CoF6P2S
510.33
Crystal system
Space Group
a (Å)
b (Å)
c (Å)
Triclinic
P1
Monoclinic
P21/c
11.5769(11)
29.015(3)
10.3153(9)
90
106.322(3)
90
3325.3(6)
4
Monoclinic
C2/c
30.8091(10)
6.8241(2)
17.5448(7)
90
118.188(3)
90
3251.22(19)
8
Orthorohombic
Pbca
7.6368(8)
15.2489(19)
36.500(5)
90
90
90
4250.5(9)
8
12.7138(3)
13.3874(4)
15.2744(4)
83.588(1)
66.646(1)
65.582(1)
2169.06(10)
2
a
b
g
(Å)
(Å)
(Å)
V (Å3)
Z
Dcalc
1.471
1.284
1.566
1.595
Crystal size
Crystal color
Temperature (K)
Absorption coefficient
F(000)
0.14 ꢀ 0.11 ꢀ 0.11
0.19 ꢀ 0.16 ꢀ 0.10
0.18 ꢀ 0.12 ꢀ 0.02
0.16 ꢀ 0.15 ꢀ 0.12
Yellow
Orange
Yellow
Yellow
100(2)
0.901
996
2.80e33.47
100(2)
0.697
1376
1.96e33.18
100(2)
0.864
1560
2.34e33.20
135(2)
1.109
2096
2.23e33.31
q
Range (ꢁ)
Data collected
h
k
l
ꢂ19 to 19
ꢂ20 to 20
ꢂ23 to 21
SADABS
0.0396, 0.0870
0.0625, 0.0958
1.023
ꢂ17 to 17
ꢂ44 to 29
ꢂ15 to 15
SADABS
0.0321, 0.0727
0.0469, 0.0787
1.017
ꢂ47 to 46
ꢂ9 to 10
ꢂ11 to 10
ꢂ14 to 23
ꢂ40 to 56
SADABS
0.0482, 0.1025
0.0927, 0.1187
1.006
ꢂ27 to 26
Absorption correction
R, wR [I > 2s(I)]a
R, wR (all data)a
Goodness-of-fit on F2
SADABS
0.0406, 0.0750
0.0826, 0.0873
1.003
P
P
Quantity minimized ¼ RðwF2Þ ¼ ½wðF02 ꢂ Fc2Þ2ꢃ= ½ðwF20Þ2ꢃ0:5
;
D
R ¼ S =SðF0Þ;
D
¼ jðF0 ꢂ FcÞj; w ¼ 1=½s2ðF02Þ þ ðaPÞ2 þ bPꢃ; P ¼ ½2Fc2 þ MaxðF0; 0Þꢃ=3
a

3884
K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
Table 2
Crystal data and structure refinement for phosphinoselenoyl X-ray structures.
[dcpcSe2][PF6]
dcpfSe2
[dppcSe2][PF6]
[1-dtbpcSe][PF6]
Formula
FW
Crystal system
Space Group
a (Å)
C
52.50H81Cl2.50Co1.50F9P4.50Se3
C34H52FeP2Se2
736.47
Triclinic
C52.50H81Cl2.50Co1.50F9P4.50Se3
860.32
C18H27CoF6P2Se
557.23
Monoclinic
P21/c
19.165(3)
7.8356(11)
15.012(2)
90
106.141(5)
90
1436.44
Monoclinic
P2/n
25.9240(6)
9.6293(2)
26.4985(6)
90
115.822(1)
90
5954.3(2)
4
Monoclinic
P21/c
17.968(5)
10.509(3)
18.884(5)
90
116.100(6)
90
3202.0(14)
4
P1
11.3523(11)
12.3513(12)
13.6862(17)
97.085(5)
110.003(5)
104.593(6)
1698.1(3)
2
b (Å)
c (Å)
a
b
g
(Å)
(Å)
(Å)
V (Å3)
2165.6(5)
4
Z
Dcalc
1.602
1.440
1.785
1.709
Crystal size
Crystal color
Temperature (K)
Absorption coefficient
F(000)
0.14 ꢀ 0.13 ꢀ 0.05
Orange
100(2)
6.337
2918
0.18 ꢀ 0.10 ꢀ 0.05
0.20 ꢀ 0.16 ꢀ 0.10
Orange
110(2)
3.020
1704
0.17 ꢀ 0.11 ꢀ 0.04
Orange
Yellow
100(2)
2.703
760
3.01e33.31
150(2)
2.673
1120
2.73e33.19
q
Range (ꢁ)
1.71e33.25
2.28e33.82
Data collected
h
k
l
ꢂ39 to 37
ꢂ14 to 10
ꢂ40 to 40
SADABS
0.0457, 0.0783
0.0872, 0.0860
1.011
ꢂ17 to 17
ꢂ19 to 19
ꢂ11 to 20
SADABS
0.0605, 0.1100
0.1691, 0.1387
1.018
ꢂ27 to 27
ꢂ14 to 16
ꢂ29 to 25
SADABS
0.0427, 0.1170
0.0666, 0.1290
1.028
ꢂ29 to 28
ꢂ12 to 12
ꢂ18 to 23
SADABS
0.0414, 0.0787
0.0840, 0.0906
1.005
Absorption correction
R, wR [I > 2s(I)]a
R, wR (all data)a
Goodness-of-fit on F2
P
P
Quantity minimized ¼ RðwF2Þ ¼ ½wðF02 ꢂ Fc2Þ2ꢃ= ½ðwF20Þ2ꢃ0:5
;
R ¼ S
D
=SðF0Þ;
D
¼ jðF0 ꢂ FcÞj; w ¼ 1=½s2ðF02Þ þ ðaPÞ2 þ bPꢃ; P ¼ ½2Fc2 þ MaxðF0; 0Þꢃ=3
a
2. Experimental
temperature for 1.5 h. After removing the solvent in vacuo, the
resulting yellow residue was dissolved in CH2Cl2 (5 mL), dried over
Na2SO4, and filtered via cannula. The solvent was removed in vacuo,
and the resulting residue was washed with Et2O (3 ꢀ 3 mL) and
dried in vacuo to yield 0.1278 g (87% yield) of [dppcO2][PF6] as a
2.1. General procedures
All reactions were carried out under an argon atmosphere using
standard Schlenk techniques. Dicyclopentadiene, ClPPh2, ClPtBu2,
n-BuLi (1.6 M in hexanes), C2Cl6, ammonium hexafluorophosphate,
[PdCl2(CH3CN)2], [PtCl2(CH3CN)2], and hydrogen peroxide were
purchased from Aldrich Chemical Co., Inc. Selenium, H[AuCl4]ꢄH2O,
ClPCy2, ClPiPr2, and dcpf were purchased from Strem Chemicals,
Inc. All reagents were used without further purification. Ferrocene
was purchased from Strem Chemicals, Inc. and sublimed prior to
use. CoCl2ꢄ6H2O and tetrabutylammonium hexafluorophosphate
([NBu4][PF6]) were purchased from Aldrich Chemical Co. and dried
at 100 ꢁC under vacuum. Methylene chloride (CH2Cl2), diethyl ether
(Et2O), hexanes, and THF were purified under argon using a Solv-
tek purification system [19]. Chloroform (CHCl3), water, nitro-
methane, 1,2-dichloroethane, di-iso-propyl ether and methanol
were degassed prior to use. Dimethylformamide (DMF) was puri-
fied according to literature procedure [20]. All column chroma-
tography was performed using silica gel as the stationary phase.
The compounds [dppc][PF6] [13], [dcpc][PF6] [21], [dippc][PF6] [21],
[1-dtbpc][PF6] [21], [Au2Cl2(dppc)][PF6] [22], [Au2Cl2(dcpc)][PF6]
[22], and [PtCl2(dppc)][PF6] [23] were synthesized according to the
literature procedures. 1H and 31P{1H} NMR spectra were obtained in
CDCl3 unless otherwise noted, using a JEOL Eclipse 400 FT-NMR
spectrometer. The 31P{1H} spectra were referenced to an external
sample of 85% H3PO4, and the 1H spectra were referenced to an
internal TMS standard.
yellow solid. 31P NMR:
d
(ppm) 20.7 (s), ꢂ143.8 (sept, 1JP-F ¼ 711 Hz).
Table 3
Crystal data and structure refinement for phosphinothioyl X-ray structures.
[Au2Cl2(dppc)][PF6]
Formula
FW
Crystal system
Space Group
a (Å)
C42H44Au2Cl10CoF6P3
1563.05
Monoclinic
P21/n
17.8836(8)
13.1421(6)
20.4629(9)
90
104.6250(10)
90
4653.5(4)
4
b (Å)
c (Å)
a
b
g
(Å)
(Å)
(Å)
V (Å3)
Z
Dcalc
2.231
Crystal size
Crystal color
Temperature (K)
Absorption coefficient
F(000)
0.16 ꢀ 0.12 ꢀ 0.03
Yellow
100(2)
7.378
3000
1.35e33.13
q
Range (ꢁ)
Data collected
h
k
l
ꢂ24 to 27
ꢂ19 to 20
ꢂ31 to 25
SADABS
0.0316, 0.0576
0.0528, 0.0611
1.023
Absorption correction
R, wR [I > 2s(I)]a
R, wR (all data)a
Goodness-of-fit on F2
2.2. Preparation of [dppcO2][PF6]
[dppc][PF6] (0.1406 g, 0.200 mmol) was dissolved in THF (70 mL)
P
P
and cooled to 0 ꢁC. Chilled H2O2 (48.1
mL, 0.471 mmol, 30 wt.% in
Quantity minimized ¼ RðwF2Þ ¼ ½wðF02 ꢂ Fc2Þ2ꢃ= ½ðwF20Þ2ꢃ0:5; R ¼ S
=SðF0Þ;
a
D
D
¼ jðF0 ꢂ FcÞj; w ¼ 1=½s2ðF02Þ þ ðaPÞ2 þ bPꢃ; P ¼ ½2Fc2 þ MaxðF0;0Þꢃ=3
H2O) was added, and the solution was allowed to stir at ambient

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3885
Table 4
Comparison of the redox potentials and Hammett parameters (sp) for ferrocene and cobaltocenium derivatives. Potentials (V vs. FcH0/þ) were measured in CH2Cl2 with [NBu4]
[PF6] as the supporting electrolyte.
Substituent (X)
Fe(C5H4X)2
[Co(C5H4X)2-n(C5H5)n][PF6]
sp
Reference
E0
Reference
n
E0
Erped
Reference
ꢂH
0.00
0.19
[25]
[25]
[28]
[25]
[25]
0.00
0.24
0.02
0.05
0.06
[26]
[27]
[28]
[29]
[30]
0
0
0
0
1
ꢂ1.33
ꢂ1.14
ꢂ1.27
ꢂ1.25
ꢂ1.27
[20]
ꢂPPh2
ꢂPCy2
ꢂPiPr2
ꢂPtBu2
ꢂ2.32
ꢂ2.42
ꢂ2.37
this work
this work
this work
this work
ꢂ0.04
0.06
0.15
2.3.2. [dcpcS2][PF6]
A solution of [dcpc][PF6] (0.0991 g, 0.136 mmol) and sulfur
(0.0097 g, 0.302 mmol) in CH2Cl2 (20 mL) was refluxed overnight.
Upon cooling to room temperature the solution was filtered, and
the volume of solvent was reduced to approximately 5 mL in vacuo.
The addition of Et2O resulted in the formation of a yellow precip-
itate. The solution was filtered via cannula. The resulting yellow
solid was washed with Et2O (3 ꢀ 5 mL), and dried in vacuo to yield
0.0882 g (82% yield) of [dcpcS2][PF6]. 31P NMR:
d (ppm) 6.12 (s, 4H, C5H4),
5.96 (s, 4 H, C5H4), 2.20e1.12 (m, 44H, C6H11). Anal. Calcd for
d
(ppm) 53.9
(s), ꢂ143.7 (sept, 1JP-F ¼ 711 Hz). 1H NMR:
Fig. 2. CV scan for the reduction of 1.0 mM [dcpc][PF6] in CH2Cl2 with 0.1 M [NBu4]
[PF6] as the supporting electrolyte at 100 mV/s.
C34H52CoF6P3S2: C, 51.64; H, 6.63. Found: C, 51.33; H, 6.62.
2.3.3. dcpfS2
1H NMR:
d (ppm) 7.62 (m, 20H, C6H5), 5.96 (s, 4H, C5H4), 5.74 (s, 4 H,
A solution of dcpf (0.1579 g, 0.273 mmol) and sulfur (0.0179 g,
0.558 mmol) in 25 mL of chloroform was refluxed for 2 h. Upon
cooling the solution was filtered via cannula and the filtrate was
dried in vacuo. Column chromatography using 2:1 (v/v) hexanes:
CH2Cl2 as the eluent yielded 0.0754 g (43% yield) of pure dcpfS2 as
C5H4). Anal. Calcd for C34H28CoF6O2P.30.25 CH2Cl2: C, 54.44; H, 3.80.
Found: C, 54.23; H, 3.63.
2.3. Preparation of phosphinothioyls
an orange solid upon removal of the solvent. 31P NMR:
d (ppm) 57.3
(s). 1H NMR:
d (ppm) 4.74 (br s, 4H, eC5H4) 4.42 (br s, 4H, C5H4) 1.32
2.3.1. [dppcS2][PF6]
(m, 44H, C6H11). Anal. Calcd for C34H52FeP2S.2C6H14: C, 65.91; H,
A solution of [dppc][PF6] (0.0999 g, 0.142 mmol) and sulfur
(0.0094 g, 0.29 mmol) in CH2Cl2 (20 mL) was refluxed for 5 days.
Removal of solvent in vacuo, followed by column chromatography
using CH2Cl2 as the eluent, yielded 0.0283 g (26% yield) of [dppcS2]
9.13. Found: C, 66.13; H, 9.11.
2.3.4. [dippcS2][PF6]
[PF6] as a yellow solid upon removal of the solvent. 31P NMR:
d
(ppm)
A solution of [dippc][PF6] (0.0248 g, 0.0438 mmol) and sulfur
(0.0029 g, 0.090 mmol) in CH2Cl2 (15 mL) was refluxed overnight.
Upon cooling the solution was filtered, and the volume of solvent
was reduced to approximately 5 mL in vacuo. The addition of Et2O
34.5 (s), ꢂ143.9 (sept, 1JP-F ¼ 711 Hz). 1H NMR:
d (ppm) 7.64 (m, 20H,
C6H5), 5.99 (s, 4H, C5H4), 5.64 (s, 4 H, C5H4). Anal. Calcd for
C34H28CoF6P3S.20.25 CH2Cl2: C, 52.22; H, 3.65. Found: C, 51.94; H, 3.58.
Fig. 3. Perspective view of [dcpcS2][PF6] with 30% ellipsoids. H atoms and PF-6 omitted for clarity.

3886
K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
washed with hexanes (3 ꢀ 5 mL), and dried in vacuo to yield
0.0206 g (54% yield) of [1-dtbpcS][PF6] as a yellow solid. 31P NMR:
d
(ppm) 74.3 (s), ꢂ143.6 (sept, 1JP-F ¼ 711 Hz). 1H NMR:
d (ppm) 6.11
(s, 2H, C5H4), 6.06 (s, 2H, C5H4), 5.89 (s, 5H, C5H5), 1.40 (d,
3JH-P ¼ 16.1 Hz, 18H, C(CH3)3). Anal. Calcd for C18H27CoF6P2S: C,
42.36; H, 5.33. Found: C, 42.08; H, 5.56.
2.4. Preparation of phosphinoselenoyls
2.4.1. [dppcSe2][PF6]
A solution of [dppc][PF6] (0.1500 g, 0.214 mmol) and selenium
(0.0379 g, 0.480 mmol) in CHCl3 (20 mL) was refluxed for 7 h. Upon
cooling the solution was filtered via cannula, and the addition of
Et2O resulted in the formation of an orange precipitate. The solu-
tion was filtered via cannula and the resulting solid was dried in
vacuo to yield 0.1252 g (68% yield) of [dppcSe2][PF6] as a red-orange
1
solid. 31P NMR:
d
(ppm) 53.9 (s, JP-Se ¼ 773 Hz), ꢂ143.9 (sept,
Fig. 4. Perspective view of dcpfS2 with 30% ellipsoids. H atoms omitted for clarity.
1JP-F ¼ 711 Hz). 1H NMR:
d (ppm) 7.62 (m, 20H, C6H5), 6.02 (s, 4H,
C5H4), 5.67 (s, 4 H, C5H4). Anal. Calcd for C34H28CoF6P3Se2: C, 47.47;
resulted in the formation of a yellow precipitate. The solution was
filtered via cannula, and the filtrate was washed with Et2O
(3 ꢀ 5 mL), and dried in vacuo to yield 0.0246 g (89% yield) of
H, 3.28. Found: C, 47.78; H, 3.16.
2.4.2. [dcpcSe2][PF6]
[dcpcSe2][PF6] was prepared in a similar fashion as [dcpcS2][PF6],
using [dcpc][PF6] (0.0999 g, 0.137 mmol) and selenium (0.0230 g,
yellow [dippcS2][PF6]. 31P NMR:
d
(ppm) 61.4 (s), ꢂ143.7 (sept,
1JP-F ¼ 711 Hz). 1H NMR:
d (ppm) 6.20 (s, 4H, C5H4), 6.05 (s, 4 H,
3
C5H4), 2.44 (m, 4H, CH(CH3)2), 1.27 (dd, JH-P
¼
18.5 Hz,
0.291 mmol). A total of 0.1091 g (90% yield) of the red-orange
3
3JH-H ¼ 6.78 Hz, 12H, CH(CH3)2), 1.22 (dd, JH-P ¼ 17.8 Hz,
3JH-H ¼ 6.04 Hz, 12H, CH(CH3)2). Anal. Calcd for C22H36CoF6P3S2: C,
41.91; H, 5.76. Found: C, 41.95; H, 5.36.
product was obtained. 31P NMR:
d
(ppm) 46.4 (s, JP-Se
¼
1
736 Hz), ꢂ143.7 (sept, 1JP-F ¼ 711 Hz). 1H NMR:
d (ppm) 6.22 (s, 4H,
C5H4), 6.01 (s, 4 H, C5H4), 2.25e1.10 (m, 44H, C6H11). Anal. Calcd for
C34H52CoF6P3Se2: C, 46.17; H, 5.93. Found: C, 46.03; H, 5.63.
2.3.5. [1-dtbpcS][PF6]
A solution of [1-dtbpc][PF6] (0.0357 g, 0.0746 mmol) and sulfur
(0.0050 g, 0.16 mmol) in CHCl3 (15 mL) was refluxed overnight.
Upon cooling the resulting solution was filtered via cannula. The
solvent volume was reduced to approximately 5 mL in vacuo, and
the addition of hexanes resulted in the formation of a precipitate.
The resulting solution was filtered via cannula, and the filtrate was
2.4.3. dcpfSe2
A solution of dcpf (0.1557 g, 0.269 mmol) and selenium
(0.0599 g, 0.632 mmol) in 25 mL of chloroform was refluxed for 2 h.
Upon cooling the solution was filtered via cannula and the filtrate
was dried in vacuo. Column chromatography using 4:1 (v/v)
hexanes: CH2Cl2 as the eluent yielded 0.0951 g (48% yield) dcpfSe2
Fig. 5. Perspective view of [dppcS2][PF6] with 30% ellipsoids. H atoms and PFL6 omitted for clarity.

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3887
(0.0074 g, 0.094 mmol). A total of 0.0277 g (86% yield) of the
redeorange product was obtained. 31P NMR:
d
(ppm) 54.9 (s,
(ppm) 6.23
1JP-Se ¼ 746 Hz), ꢂ143.7 (sept, 1JP-F ¼ 711 Hz). 1H NMR:
d
(s, 4H, C5H4), 6.05 (s, 4 H, C5H4), 2.48 (m, 4H, CH(CH3)2), 1.26 (dd,
3
3JH-P ¼ 14.2 Hz, JH-H ¼ 5.68 Hz, 12H, CH(CH3)2), 1.21 (dd,
3
3JH-P ¼ 15.2 Hz, JH-H ¼ 7.08 Hz, 12H, CH(CH3)2). Anal. Calcd for
C22H36CoF6P3Se2: C, 36.48; H, 5.01. Found: C, 36.21; H, 4.96.
2.4.5. [1-dtbpcSe][PF6]
A solution of [1-dtbpc][PF6] (0.0351 g, 0.0734 mmol) and sele-
nium (0.0092 g, 0.12 mmol) in CHCl3 (15 mL) was refluxed for
2.25 h. The solution was filtered via cannula and the volume of
solvent was reduced to approximately 5 mL in vacuo. The addition
of Et2O resulted in the formation of a precipitate. The resulting
solution was filtered via cannula, and the remaining solid was
washed with hexanes (3 ꢀ 5 mL), and dried in vacuo to yield 0.283
(69% yield) of [1-dtbpcSe][PF6] as a yellow-orange solid. 31P NMR:
1
d
(ppm) 70.8 (s, JP-Se ¼ 731 Hz), ꢂ143.6 (sept, 1JP-F ¼ 711 Hz). 1H
NMR:
1.43 (d, JH-P
d (ppm) 6.12 (s, 2H, C5H4), 6.10 (s, 2H, C5H4), 5.91 (s, 5H, C5H5),
3
¼
16.5 Hz, 18H, C(CH3)3). Anal. Calcd for
C18H27CoF6P2Se: C, 38.79; H, 4.88. Found: C, 38.40; H, 4.51.
2.5. Preparation of transition metal complexes
2.5.1. [PdCl2(dppc)][PF6]
A
solution of [dppc][PF6] (0.1194 g, 0.170 mmol) and
Fig. 6. Perspective view of [1-dtbpcS][PF6] with 30% ellipsoids. H atoms and PF6L
omitted for clarity.
[PdCl2(CH3CN)2] (0.0445 g, 0.172 mmol) in CH2Cl2 (25 mL) was
stirred overnight at ambient temperature, resulting in the forma-
tion of a yellow precipitate. The solution was filtered via cannula.
The solid was washed with Et2O (3 ꢀ 5 mL), and dried in vacuo
yielding 0.0108 g (72% yield) of the product as a yellow solid. 31P
as an orange solid upon removal of the solvent. 31P NMR:
d (ppm)
49.9 (s, 1JP-Se ¼ 710 Hz). 1H NMR:
d
(ppm) 4.80 (AA’BB0, 4H, C5H4)
(ppm) 28.6 (s), ꢂ144.1 (sept, 1JP-F ¼ 707 Hz). 1H
(ppm) 7.86 (m, 20H, C6H5), 5.93 (s, 4H, C5H4), 5.90
4.44 (AA’BB0, 4H, C5H4) 1.32 (m, 44H, C6H11). Anal. Calcd for
NMR (CD3NO2):
NMR (CD3NO2):
d
C34H52FeP2Se.20.5C6H14: C, 57.01; H, 7.63. Found: C, 57.11; H, 7.68.
d
(s, 4 H, C5H4). Anal. Calcd for C34H28Cl2CoF6P3Pd.0.5 CH2Cl2: C,
44.93; H, 3.17. Found: C, 45.11; H, 2.86.
2.4.4. [dippcSe2][PF6]
[dippcSe2][PF6] was prepared in a similar fashion as [dippcS2]
[PF6], using [dippc][PF6] (0.0252 g, 0.0445 mmol) and selenium
2.5.2. [PdCl2(dcpc)][PF6]
A
solution of [dcpc][PF6] (0.1000 g, 0.138 mmol) and
[PdCl2(CH3CN)2] (0.0371 g, 0.143 mmol) in CH2Cl2 (20 mL) was
stirred at ambient temperature overnight, resulting in the forma-
tion of a precipitate. The solution was filtered via cannula, and the
volume of solvent was reduced to approximately 5 mL in vacuo. The
addition of Et2O resulted in the formation of a precipitate. The
resulting solution was filtered via cannula, and the remaining solid
was washed with Et2O (3 ꢀ 5 mL), and dried in vacuo. A total of
0.0599 g (48% yield) of the yellow product was obtained. 31P NMR
(CD2Cl2):
(CD2Cl2):
d
(ppm) 48.6 (s), ꢂ1143.7 (sept, 1JP-F ¼ 711 Hz). 1H NMR
d
(ppm) 6.03 (s, 4H, C5H4), 5.98 (s, 4 H, C5H4), 2.79 (br, 4H,
C6H11), 2.36 (br, 4H, C6H11), 1.84 (m, 20H, C6H11), 1.38 (m, 16H,
C6H11). Anal. Calcd for C34H52Cl2CoF6P3Pd: C, 45.18; H, 5.80. Found:
C, 45.53; H, 5.99.
2.5.3. [PdCl2(dippc)][PF6]
A
solution of [dippc][PF6] (0.0268 g, 0.0473 mmol) and
[PdCl2(CH3CN)2] (0.0123 g, 0.0474 mmol) in CH2Cl2 (10 mL) was
stirred overnight at ambient temperature, resulting in the forma-
tion of a yellow precipitate. The solution was filtered via cannula,
and the remaining solid was washed with Et2O (3 ꢀ 5 mL), and
dried in vacuo. A total of 0.0151 g (43% yield) of the yellow product
was obtained. 31P NMR (CD3NO2):
d
(ppm) 58.1 (s), ꢂ144.1 (sept,
1JP-F ¼ 707 Hz). 1H NMR (CD3NO2):
d
(ppm) 6.24 (s, 4H, C5H4), 6.08
3
(s, 4 H, C5H4), 3.11 (m, 4H, CH(CH3)2), 1.62 (dd, JH-P ¼ 17.6 Hz,
3JH-H
¼
6.96 Hz, 12H, CH(CH3)2), 1.31 (dd, JH-P
¼
16.5Hz,
3
3JH-H ¼ 6.60 Hz, 12H, CH(CH3)2). Anal. Calcd for C22H36Cl2CoF6P3Pd:
Fig. 7. Perspective view of [dcpcSe2][PF6] with 30% ellipsoids.
H
atoms and PFL6
omitted for clarity.
C, 35.53; H, 4.88. Found: C, 35.50; H, 4.75.

3888
K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
Fig. 8. Perspective view of dcpfSe2 with 30% ellipsoids. H atoms omitted for clarity.
2.5.4. [PtCl2(dppc)][PF6]
NMR:
d
(ppm) 20.5 (s, 1JP-Pt ¼ 3711 Hz), ꢂ143.6 (sept, 1JP-F ¼ 711 Hz).
[PtCl2(dppc)][PF6] was prepared according to the literature
procedure; however the only characterization of the compound
1H NMR:
d (ppm) 6.15 (s, 4H, C5H4), 5.92 (s, 4 H, C5H4), 2.81 (br, 4H,
C6H11), 2.37 (br, 4H, C6H11), 1.84 (m, 20H, C6H11), 1.38 (m, 16H,
C6H11). Anal. Calcd for C34H52Cl2CoF6P3Pd: C, 41.14; H, 5.28. Found:
C, 40.98; H, 5.05.
was the crystal structure [23]. 31P NMR (CD3NO2):
d (ppm) 9.3 (s,
1JP-Pt ¼ 3742 Hz), ꢂ144.1 (sept, 1JP-F ¼ 707 Hz). 1H NMR (CD3NO2):
d
(ppm) 7.80 (m, 20H, C6H5), 5.92 (s, 4H, C5H4), 5.84 (s, 4 H, C5H4).
Anal. Calcd for C34H28Cl2CoF6P3Pt: C, 42.17; H, 2.91. Found: C, 42.02;
H, 2.54.
2.5.6. [PtCl2(dippc)][PF6]
[PtCl2(dippc)][PF6] was prepared in
a similar fashion as
[PdCl2(dippc)][PF6], using [dippc][PF6] (0.0260 g, 0.0459 mmol) and
[PtCl2(CH3CN)2] (0.0160 g, 0.0460 mmol). A total of 0.0115 g (30%
yield) of the yellow product was collected. 31P NMR (CD3NO2):
2.5.5. [PtCl2(dcpc)][PF6]
A
solution of [dcpc][PF6] (0.1001 g, 0.138 mmol) and
[PtCl2(CH3CN)2] (0.0493 g, 0.142 mmol) in CH2Cl2 (20 mL) was
stirred at ambient temperature overnight, resulting in a yellow
solution. The volume of solvent was reduced to approximately 5 mL
in vacuo, and the addition of Et2O resulted in the formation of
a precipitate. The solution was filtered via cannula, and the
resulting solid was washed with Et2O (3 ꢀ 5 mL), and dried in vacuo.
The yellow product was collected giving 0.1151 g (84% yield). 31P
d
(ppm) 29.0 (s, 1JP-Pt ¼ 3731 Hz), ꢂ144.0 (sept, 1JP-F ¼ 707 Hz). 1H
NMR (CD3NO2):
d (ppm) 6.15 (s, 4H, C5H4), 6.07 (s, 4 H, C5H4), 3.13
3
3
(m, 4H, CH(CH3)2), 1.56 (dd, JH-P ¼ 17.8 Hz, JH-H ¼ 7.14 Hz, 12H,
CH(CH3)2), 1.27 (dd, 3JH-P ¼ 17.2 Hz, 3JH-H ¼ 6.96 Hz, 12H, CH(CH3)2).
Anal. Calcd for C22H36Cl2CoF6P3Pd: C, 31.75; H, 4.36. Found: C,
31.84; H, 4.57.
Fig. 9. CV Perspective view of [dppcSe2][PF6] with 30% ellipsoids. H atoms and PF-6 omitted for clarity.

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3889
2.7. Crystallographic procedures
Crystals of the phosphinothioyls and phosphinoselenoyls, with
the exception of [dppcSe2][PF6], suitable for X-ray analysis were
obtained by slow diffusion of hexanes into a solution of the desired
compound in CH2Cl2 in a freezer. Slow diffusion of Et2O into a solu-
tion of [dppcSe2][PF6] in CH2Cl2 in a freezer was utilized for growing
crystals of this compound. Crystals of [Au2Cl2(dppc)][PF6] were
obtained by slow diffusion of di-iso-propyl ether into a solution of
[Au2Cl2(dppc)][PF6] in 1,2-dichloroethane in a refrigerator. The
crystals were mounted using NVH immersion oil onto a nylon fiber
and cooled to the data collection temperature. Data were collected
on a Brüker-AXS Kappa APEX II CCD diffractometer with 0.71073 Å
Mo-Ka radiation for the phosphinothioyls (Table 1), phosphinose-
lenoyls (Table 2) and [Au2Cl2(dppc)][PF6] (Table 3). Unit cell
parameters were obtained from 90 data frames, 0.3ꢁ
F, from three
different sections of the Ewald sphere. Using SHELXS-97, direct
methods were employed to solve the structures and refinement was
performed by full-matrix least-square procedures on F2 [24]. The
diffraction data were consistent with the assigned space groups. The
data-sets were treated with SADABS absorption corrections based
on redundant multi-scan data [25]. All non-hydrogen atoms were
refined with anisotropic displacement parameters. All hydrogen
atoms were treated as idealized contributions.
For [dcpcS2][PF6] the asymmetric unit contains one [CoL]þ
cation, one [PF6]ꢂ anion and two molecules of CH2Cl2 solvent all
located on general positions yielding Z ¼ 2, and Z0 ¼ 1. For [dcpcSe2]
[PF6] the asymmetric unit contains 1.5 [dcpcSe2]þ cations, 1.5 [PF6]ꢂ
anions and 1.5 molecules of CH2Cl2 solvent yielding Z ¼ 4, and
Z0 ¼ 1.5. The CH2Cl2 solvent molecules were both disordered. The
full molecule was modeled over two positions but the half molecule
was disordered over a symmetry element and was SQUEEZED out
of the refinement [26]. The SQUEEZE results were consistent with
this model [26]. For [Au2Cl2(dppc)][PF6] the asymmetric unit
contains one [Au2Cl2(dppc)]þ cation, one [PF6]ꢂ anion, and four
molecules of dichloroethane solvent all located on general posi-
tions yielding Z ¼ 4, and Z0 ¼ 1. Three out of the four solvent
molecules were disordered, so the solvent was removed with
SQUEEZE [26]. The SQUEEZE results were consistent with this
model [26].
Fig. 10. Perspective view of [1-dtbpcSe][PF6] with 30% ellipsoids. H atoms and PF6-
omitted for clarity.
2.6. Electrochemical procedures
For all cyclic voltammetry experiments, scans were conducted at
ambient temperature (22 ꢅ 1 ꢁC) using a PAR 263A potentiostat/
galvanostat under an argon atmosphere. Solutions of analyte
(1.0 mM) in CH2Cl2 (10.0 mL) were examined, with [NBu4][PF6]
(0.1 M) serving as the supporting electrolyte. Voltammograms of
[PdCl2(dippc)][PF6] and [PtCl2(dippc)][PF6] were recorded under
similar conditions in nitromethane (10.0 mL). Scan rates were
conducted at 50 and 100e1000 mV/s, in 100 mV/s increments, and
recorded via PowerSuite software. Background scans of [NBu4][PF6]
were subtracted for the 100 mV/s scan rate. A 1.5 mm glassy carbon
3. Results and discussion
The phosphinocobaltocenium compounds employed in this
study were prepared according to the literature preparations
[13,21]. However, using the literature synthesis we were unable to
prepare 1,10-bis(di-tert-butylphosphino)cobaltocenium and thus it
is not included in this report [21]. In the course of preparing [dppc]
[PF6] X-ray quality crystals were obtained. As the structures of
[dppc][BF4] [27] and [dppc][NO3] [14] have previously been re-
ported, this structure is included in the supporting information.
disc, which was polished with 1.0 mm then 0.25 mm diamond pastes
and rinsed with CH2Cl2 prior to use, served as the working elec-
trode. A platinum wire served as the counter electrode, and Ag/
AgCl, separated from solution by an E-porosity glass frit, served as
the reference electrode. Ferrocene (1.0 mM) was added as a refer-
ence at the end of all experiments.
Table 5
Selected bond lengths (Å) and angles (ꢁ) for phosphinochalcogenyl cobaltocenium and phosphinochalcogenyl ferrocene compounds.
[dppcO2]
[PF6]
dppfO2
[dppcS2]
[PF6]
dppfS2
[dppcSe2]
[PF6]
dppfSe2
[dcpcS2]
[PF6]
dcpfS2
[dcpcSe2]
[PF6]
dcpfSe2
[1-dtbpcS]
[PF6]
[1-dtbpcSe]
[PF6]
P-E (avg.)
1.464
2.032
177.69
0.22
0.076
[18]
1.493
2.046
180.00
0.00
1.9425
2.0346
180.00
0.00
1.938
2.039
180.00
0.00
2.0679
2.017
84.50
4.09
ꢂ0.075
2.103
2.044
180.00
0.00
1.9528
2.0426
88.14
5.83
ꢂ0.118
1.9608
2.0508
151.85
2.04
ꢂ0.159
2.1076
2.040
145.02
5.88
2.1195
1.9503(8)
2.027
2.1089(6)
2.030
M-C (avg.)
2.048
150.07
1.09
ꢂ0.242
sa
qb
c
dP (avg.)
ꢂ0.011
ꢂ0.105
ꢂ0.035
ꢂ0.148
ꢂ0.160
Reference
[35]
[36]
[37]
a
The torsion angle CA-XA-XB-CB where C is the carbon atom bonded to phosphorus and X is the centroid of the C5 ring.
The dihedral angle between the two C5 rings.
Average deviation of the P atoms from the C5 planes; a positive value indicates P is closer to Co/Fe.
b
c

3890
K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
Table 6
%Vbur values for phosphinochalcogenyls with cobaltocenium and ferrocene back-
bones. Values in parentheses are the average deviation from the mean for the two
values.
Cobaltocenium
Compound
Ferrocene
%Vbur
Reference Compound %Vbur
Reference
[dppcO2][PF6]
[dppcS2][PF6]
[dppcSe2][PF6]
[dcpcS2][PF6]
[dcpcSe2][PF6]
[dippcO2][PF6]
[dippcS2][PF6]
[dippcSe2][PF6]
[1-dtbpcS][PF6]
[35]a
dppfO2
51.7(0.0) [36]b
40.5(0.0) [41]
37.3(0.0) [41]
42.4(0.2) this work
39.2(0.2) this work
51.9(0.9) [42]b
41.4(0.1) [42]b
39.6(1.2) [42]b
38.9(0.0)
45.8(5.4)
48.2(5.8)
this work dppfS2
this work dppfSe2
this work dcpfS2
40.2(1.1)c this work dcpfSe2
dippfO2
d
d
dippfS2
d
dippfSe2
this work dtbpfSe
this work dtbpfSee
dtbpfSe2
45.3
[1-dtbpcSe][PF6] 42.8
[dtbpcSe2][PF6]
e
42.6(0.4) [41]
a
While the structure of this compound has been published, the R-factor was
greater than 7% which has been suggested as the cutoff [39].
Fig. 11. CV scan for the reduction of 1.0 mM [dcpcSe2][PF6] in CH2Cl2 with 0.1 M [NBu4]
[PF6] as the supporting electrolyte at 100 mV/s.
b
Reference to the published structure; the %Vbur was calculated in this work.
c
The average deviation from the mean is for four values as there are two crys-
tallographically independent [dcpcSe2]þ in the unit cell.
d
dippf ¼ 1,10-bis(di-iso-propylphosphino)ferrocene.
Using methods adapted from the analogous bis(phosphino)
ferrocenes [34], eight new phosphinothioyls ([dppcS2][PF6],
[dcpcS2][PF6], [dippcS2][PF6], [1-dtbpcS][PF6]) and phosphinosele-
noyls ([dppcSe2][PF6], [dcpcSe2][PF6], [dippcSe2][PF6], [1-dtbpcSe]
[PF6]) were prepared in moderate to high yield. The compounds
were characterized by 1H and 31P{1H} NMR. The signals in the 31P
spectra showed the anticipated downfield shift upon addition of
the chalcogen. In order to compare these cobalt complexes to their
iron analogues, dcpfS2 and dcpfSe2 were prepared and character-
ized by 1H and 31P{1H} NMR. Crystals suitable for X-ray analysis
were obtained for eight of these compounds. The structures of
[dcpcS2][PF6] (Fig. 3), dcpfS2 (Fig. 4), [dppcS2][PF6] (Fig. 5), [1-
dtbpcS][PF6] (Fig. 6), [dcpcSe2][PF6] (Fig. 7), dcpfSe2 (Fig. 8),
[dppcSe2][PF6] (Fig. 9) and [1-dtbpcSe][PF6] (Fig. 10) are reported
herein. Selected bond lengths and angles are presented in Table 5.
The P ¼ E bond lengths are generally shorter in the cobalt
compounds as compared to the iron analogues. In addition, the
P ¼ E bonds are slightly longer when comparing cyclohexyl
substituted compounds to their phenyl substituted analogs.
e
dtbpf ¼ 1,10-bis(di-tert-butylphosphino)ferrocene.
The electrochemistry of the phosphinocobaltocenium
compounds was examined in CH2Cl2 using [NBu4][PF6] as the
supporting electrolyte. Each compound exhibited a reversible
reductive wave at potentials significantly more negative than that
of ferrocene (Table 4). The phosphine substituents have been found
to be less electron donating than a hydrogen in the oxidative
electrochemistry of the analogous bis(phosphino)ferrocene
compounds. Therefore the reduction potentials for the phosphi-
nocobaltocenium compounds are more positive than that of
cobaltocenium. In addition, the bis(phosphino)cobaltocenium
compounds exhibited an irreversible reductive wave at more
negative potentials (Fig. 2). This is likely due to the Co(I)/Co(II)
couple which is prone to dissociation of a cyclopentadienyl ring
[1,16,17].
The phosphine oxide, [dppcO2][PF6], was prepared in high yield
using a new procedure. This method circumvents the previous
requirement of freshly prepared peracetic acid and organic
extractions, and allows for faster isolation of the product as an
overnight recrystallization was eliminated [18]. Pure [dppcO2][PF6]
was isolated as a yellow solid using this new procedure despite
being previously reported as a black crystalline solid [18].
Recently, the percent buried volume (%Vbur) has been proposed
as an effective means of describing the overall steric parameters of
ligands [38]. Defined as the percent of the total volume of a sphere
occupied by a ligand around a central atom, %Vbur relies on crys-
tallographic data and has been shown to correlate well with the
Tolman cone angle of free tertiary phosphine ligands and linear
[(R3P)AuCl] complexes [39]. Calculations with bidentate phosphine
Table 7
Potentials (V vs. FcH0/þ in CH2Cl2 with [NBu4][PF6] as the supporting electrolyte) and
potential
phosphinochalcogenyl.
differences
(
D
E
¼
EphosphinochalcogenylꢂEphosphine
)
of
the
0
-0.05
-0.1
EOpx 1
ERped
ꢁ
ꢁ
ꢁ
EFe
Compound
E1
D
E1
E2
D
E2
[dppcO2][PF6]
[dppcS2][PF6]
[dcpcS2][PF6]
dcpfS2
[dippcS2][PF6]
[1-dtbpcS][PF6]
[dppcSe2][PF6]
dppfSe2
[dcpcSe2][PF6]
dcpfSe2
[dippcSe2][PF6]
dippfSe2
ꢂ0.85
ꢂ0.82
ꢂ0.90
0.28
0.31
0.37
ꢂ1.92
ꢂ1.90
ꢂ1.99
0.40
0.42
0.42
-0.15
-0.2
0.37
ꢂ0.89
ꢂ1.11
ꢂ0.80
0.36
0.17
0.34
ꢂ2.01
ꢂ2.20
ꢂ1.89
0.37
0.43
0.45
0.42
-0.25
-0.3
0.84
0.32
0.79
0.27
0.71
0.21
ꢂ0.14
ꢂ0.09
ꢂ0.04
0.05
1.10a
1.03a
1.00a
1.06a
ꢂ0.87
ꢂ0.85
ꢂ1.10
0.40
0.40
0.18
ꢂ1.96
ꢂ1.96
ꢂ2.18
-0.35
-0.1
0.1
0.3
0.5
0.7
ꢂ0.24
p
[1-dtbpcSe][PF6]
dtbpfSe2
0.24
ꢂ0.07
Fig. 12. Relationship between the EL values of 1,10-bis(substituted)cobaltocenium
complexes obtained in CH2Cl2 with the Hammett parameter (sp) of the substituents.
EL ¼ 0.4902(sp) - 0.3100, R2 ¼ 0.9645.
a
The reduction wave has a significantly larger peak current than the oxidative
wave suggesting deposition of the electrochemically generated trication.

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3891
ligands were also found to agree well with Tolman’s prior work
[39]. We have shown that a correlation exists between and %Vbur
q
for simple monodentate phosphinochalcogenyls and have per-
formed %Vbur calculations on 1,10-bis(phosphinochalcogenyl)ferro-
cene compounds [40]. The %Vbur values have been calculated for the
cobaltocenium species and compared to the ferrocene analogues
(Table 6).
However, meaningful comparisons between the ferrocene and
cobaltocenium compounds cannot be made due to the large
differences in %Vbur for each phosphorus atom in the same mole-
cule. These large differences, in particular in the cobaltocenium
compounds, can be seen as the average deviation from the mean.
The general trend for the phosphinochalcogenyl ferrocene
compounds is that the %Vbur values decrease substantially on going
from O to S and slightly from S to Se. In addition, the size of the R
groups on the phosphorus are important as the %Vbur values are
i
t
Ph < Cy z Pr < Bu for the ferrocene compounds. The trends are
not as straightforward in the cobaltocenium analogues.
Fig. 13. CV for the oxidation of 1.0 mM [dcpcSe2][PF6] in CH2Cl2 with 0.1 M [NBu4][PF6]
as the supporting electrolyte at 100 mV/s.
The electrochemistry of each of the cobaltocenium phosphi-
nochalcogenyls was also examined (Table 7). Two reversible
reductive waves were observed for each cobaltocenium compound
at all scan rates (Fig. 11). The first wave, E1ꢁ, can be attributed to the
Co(II/III) couple while the secoꢁnd, E2ꢁ, is likely due to the Co(I/II)
couple. The reversibility of E2 suggests that the chalcogenides
stabilize the formation of an anionic cobaltocene species on the CV
timescale. Similar reversibility of the Co(I/II) couple was noted for
several metal carbonyl complexes containing dppcþ and was
attributed to a stabilizing template effect where bidentate coordi-
nation of dppcþ to a metal center prevented reactions of the elec-
trochemically generated Co(I) species [1,16,17]. The reversibility of
may also be occurring for the phosphinoselenoyl cobaltocenium
species which would result in the formation of a trication. Inter-
estingly, a reductive wave was not observed following the oxidation
of [dppcSe2][PF6], which may be attributable to the limited solu-
bility exhibited by many [dppc][PF6] compounds (vide infra). The
ferrocene derivatives also display an oxidation at approximately 1 V
vs. FcH0/þ which can be attributed to oxidation of the iron center.
In addition to the phosphinochalcogenyls, several transition
metal complexes with 1,10-bis(phosphino)cobaltocenium ligands
were prepared in moderate yields using methods previously
established for 1,10-bis(phosphino)ferrocenes [30e33]. Unlike
ꢁ
E2 for the phosphinochalcogenyls is interesting. Similar to the
instability of the electrochemically generated dppfþ [30], it would
seem that the presence of lone pair on the phosphorus of phos-
phine cobaltocenium compounds destabilized the Co(I) species.
The electrochemical parameter (EL) has been defined for
disubstituted sandwhich compoundsꢁas 1/2Eꢁ vs. SHE [43]. A
correlation exists between EL for the E1 reduction potentials of the
1,10-bis(substituted)cobaltocenium complexes and the known
Hammett substituent constants
(sp) for the corresponding
substituents (Fig. 12) [28,31,34]. This correlation suggests that the
electronic nature of the substituents is directly proportꢁional to the
reduction potential, allowing for the prediction of E1 reduction
potentials of 1,10-bis(substituted)cobaltocenium complexes based
on sp values. Previous estimates of the Hammett parameters for the
eP(Se)Ph2 and eP(Se)iPr2 functional groups [34] using the redox
potential of the 1,10-bis(substituted)ferrocene compounds were
based on the incorrect assumption that the oxidation occurred at
the iron center and thus the correlation between sp and the iron
redox potential held [33]. Using the data for the 1,10-bis(sub-
stituted)cobaltocenium complexes, estimates for the sp values for
the eP(Se)Ph2, eP(Se)Cy2, and eP(Se)iPr2 functional groups are
0.49, 0.42, and 0.44 respectively.
Oxidative sweeps of [dppcSe2][PF6], [dcpcSe2][PF6], and
[dippcSe2][PF6] exhibited an electrochemically irreversible oxida-
tion, followed by the reduction of an electrochemically generated
product (Fig. 13). Previous electrochemical experiments with
dppfSe2 and dippfSe2 produced similar results [34], although
oxidation occurred at potentials approximately 0.5 V less positive
than the cobaltocenium analogues. As the cobaltocenium
compounds are initially cationic, the difference in the potentials at
which oxidation occurs is anticipated. The same trend is observed
in the oxidation of [dcpcSe2][PF6] as compared to dcpfSe2. Oxida-
tion of dtbpfSe2 was shown to be a two-electron process that
resulted in the formation of [dtbpfSe2][BF4]2 in which there had
been intramolecular SeeSe bond formation [33]. A similar process
Fig. 14. Perspective view of [Au2Cl2(dppc)][PF6] with 30% ellipsoids. H atoms and PF6-
omitted for clarity.

3892
K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
Table 8
[36]. The %Vbur for the dppf ligand is 40.6 (average deviation from
the mean of 0.9) at a distance of 2.00 Å and 35.3 (average deviation
from the mean of 0.9) at 2.28 Å when all of the reported structures
of [Au2Cl2(dppf)] are considered. The %Vbur for the dppc ligand is
similar, 38.5 (average deviation from the mean 3.1) at a distance of
2.00 Å and 33.6 (average deviation from the mean 3.2) at 2.28 Å.
Similar to the chalcogenides, a large average deviation from the
mean for the %Vbur of the cobaltocenium compounds was observed.
Even in the structures of [Au2Cl2(dppf)] that are not symmetric
about the iron atoms [41,47], the average deviation from the mean
for the %Vbur values is only 0.8. The reason for the differences in the
cobalt compounds is unclear, but these results reinforce the
warning of caveat emptor in regard to %Vbur calculations [39].
The only [MCl2(PXP)][PF6] structure containing a 1,10-bis(phos-
phino)cobaltocenium ligand reported is [PtCl2(dppc)][PF6] [23].
The %Vbur calculation for a bidentate ligand does not treat the
phosphorus atoms separately [39]. The calculated %Vbur for the
dppc ligand in this compound is 54.9. This is slightly less than the %
Vbur for dppf in [PtCl2(dppf)] which was calculated to be 55.8 [40].
The electrochemistry of several 1,10-bis(phosphino)cobaltoce-
nium metal complexes was also examined (Table 9). Several
unsuccessful attempts were made to examine the electrochemistry
of [PdCl2(dppc)][PF6] and [PtCl2(dppc)][PF6]. In DMF significant
color changes of the solutions occurred and the experiments gave
Selected bond lengths (Å) and angles (ꢁ) for [Au2Cl2(dppc)][PF6] and [Au2Cl2(dppf)].
[Au2Cl2(dppc)][PF6]
[Au2Cl2(dppf)]a
Space group
PeAu
P21/n
P1
2.2404b
2.3076b
2.052
2.239(3), 2.229b
2.300(3), 2.226b
2.04, 2.06
AueCl
MeC (avg.)
AueAu
PeAueCl
sc
3.0873(2)
178.91b
74.44
3.083(1)
176.0(1), 174.4b
180.00, 124.18
0.00, 3.17
qd
4.93
e
dP (avg.)
0.059
4C2H4Cl2
0.061, ꢂ0.038
Solvent
Reference
2/3 CHCl3
[39]
a
The structure has two crystallographically independent molecules in the unit
cell.
b
Average value.
c
The torsion angle CA-XA-XB-CB where C is the carbon atom bonded to phos-
phorus and X is the centroid of the C5 ring.
d
The dihedral angle between the two C5 rings.
Average deviation of the P atoms from the C5 planes; a positive value indicates P
e
is closer to Co/Fe.
analogous ferrocene complexes, [MCl2(dppc)][PF6] (M ¼ Pd or Pt)
precipitated from solution, and were found to be insoluble in all but
very polar organic solvents such as DMF and nitromethane. Simi-
larly, [MCl2(dippc)][PF6] (M ¼ Pd or Pt) is sparingly soluble in
CH2Cl2 while [MCl2(dcpc)][PF6] (M ¼ Pd or Pt) is quite soluble in
CH2Cl2. Clearly the phosphine substituents contribute significantly
to the solubility of these transition metal complexes in organic
solvents. Alkyl groups appear to impart increased solubility over
phenyl groups. These observations may provide insight into the
observation that recycling a [PdCl2(PXP)][PF6] (PXP ¼ dcpc, dippc
or dtbpc) catalytic system in [BMIM][PF6] after extracting the
products with an organic solvent resulted in significant loss of
activity after the second trial [21].
The structure of [Au2Cl2(dppc)][PF6] was determined (Fig. 14).
Selected structural parameters for [Au2Cl2(dppc)][PF6] are presented
in Table 8. The solid-state structure is a long chain of cations, linked
through 3.0873 Å AueAu interactions, which follow the screw axis.
Six structures of the analogous [Au2Cl2(dppf)] have been deter-
mined: three different polymorphs of [Au2Cl2(dppf)] [44e46] as well
as [Au2Cl2(dppf)].2/3 CHCl3 [47], [Au2Cl2(dppf)].2 CH2Cl2 [48] and
[Au2Cl2(dppf)].CHCl3.1/2C6H14 [41]. Only the [Au2Cl2(dppf)].2/3 CHCl3
structure exhibits an intermolecular AueAu distance similar to that
found for [Au2Cl2(dppc)][PF6]. The synclinical eclipsed [2,49] geom-
etry found in [Au2Cl2(dppc)][PF6] allows for a short intramolecular
AueAu distance of 3.666 Å. The AueP and AueCl bond lengths are
slightly longer and the PeAueCl angle is closer to 180ꢁ in
[Au2Cl2(dppc)][PF6] as compared to [Au2Cl2(dppf)].
indiscernible
electrochemistry.
The
electrochemistry
of
[PdCl2(dippc)][PF6] and [PtCl2(dippc)][PF6] had to be performed in
nitromethane which gave only one reductive wave in the solvent
window. The reductive wave of [PdCl2(dippc)][PF6] was irreversible
at lower scan rates and chemically reversible at higher scan rates.
Cyclic voltammograms of [PdCl2(dcpc)][PF6] and [PtCl2(dcpc)][PF6]
displayed three reductive waves, the first of which is chemically
and electrochemically reversible and likely due to the Co(II/III)
couple (Fig. 15). Two irreversible waves were also common to both
complexes, one of which is likely due to the Co(I/II) couple. The final
wave is likely due to reduction of the Pd or Pt center. An irreversible
two electron reduction of the Pd in [PdCl2(dppf)] has been
observed at ꢂ1.59 V vs. FcH0/þ [50]. The bisphosphine complexes
[PtCl2(PPh3)2] and [PtCl2(PEt3)2] also undergo irreversible two
electron reductions of the Pt metal at ꢂ2.10 V and ꢂ2.56 V vs.
FcH0/þ, respectively [51]. Comparing the E1 and E2 values of
[MCl2(dcpc)][PF6] to the phosphinochalcogenyls, [PtCl2(dcpc)][PF6]
displayed very similar reduction potentials to [dcpcS2][PF6], sug-
gesting that these are likely reductions of the cobalt center.
Although the first reductive wave of [PdCl2(dcpc)][PF6] is similar to
that of the phosphinochalcogenyls the second reductive wave is
significantly less positive suggesting that Pd is reduced at ꢂ1.64 V
ꢁ
ꢁ
vs. FcH0/þ
.
The [(AuCl)2dppc][PF6] and [(AuCl)2dcpc][PF6]
complexes exhibited electrochemistry (Fig. 16) resembling that of
The %Vbur can be calculated to structurally compare 1,10-
bis(phosphino)cobaltocenium ligands with the iron analogues. The
%Vbur for the dppf ligand in one structure of [Au2Cl2(dppf)] [45] has
been calculated as 38.7 at a distance of 2.00 Å and 33.5 at 2.28 Å
Table 9
Potentials (V vs. FcH0/þ in CH2Cl2 with [NBu4][PF6] as the supporting electrolyte) and
potential differences (
D
E ¼ Ecmpd-Ephos) for the transition metal complexes.
Compound
Eꢁ
D
E1
Eꢁ
D
E2
Erped
1
2
[Au2Cl2dppc][PF6]
[Au2Cl2dcpc][PF6]
[PdCl2(dcpc)][PF6]
[PtCl2(dcpc)][PF6]
[PdCl2(dippc)][PF6]
[PtCl2(dippc)][PF6]
ꢂ0.66
ꢂ0.76
ꢂ0.88
ꢂ0.92
ꢂ0.87a,b
ꢂ0.89b
0.48
0.51
0.39
0.35
0.36c
0.34c
L1.83a
ꢂ1.86
0.49
0.56
ꢂ1.64a
ꢂ1.99a
ꢂ2.32
ꢂ2.25
Only Erped observed at 100 mV/s.
a
b
c
Experiments were performed in nitromethane.
Referenced to [dippc][PF6] examined in nitromethane.
Fig. 15. CV scan for the reduction of 1.0 mM [PtCl2(dcpc)][PF6] in CH2Cl2 with 0.1 M
[NBu4][PF6] as the supporting electrolyte at 100 mV/s.

K.D. Reichl et al. / Journal of Organometallic Chemistry 696 (2011) 3882e3894
3893
4. Summary
Free 1,10-bis(phosphino)cobaltocenium ligands display two
reductive waves, the first of which is reversible followed by an
irreversible reduction at more negative potentials. Ten new phos-
phinothioyls and phosphinoselenoyls were synthesized, and the X-
ray structures of eight of these compounds were determined.
Unlike the parent phosphines, each 1,10-bis(phosphinochalcogenyl)
cobaltocenium displays two reversible reductive waves. The elec-
tron withdrawing nature of the chalcogenides likely stabilizes the
anionic complex generated upon undergoing the second reduction.
The electron donating ability of the phosphine substituents appears
to correlate well with the reduction potentials of 1,10-bis(phos-
phino)cobaltocenium species, as evidenced by the linear relation-
ship between sp and the corresponding reduction potentials. In
addition, electrochemical oxidation of the phosphinoselenoyl
species displays an electrochemically irreversible oxidative wave,
potentially due to the formation of a SeeSe bonded trication
species. The %Vbur for the phosphinochalcogenyls decrease as the
size of the chalcogen increases. The %Vbur for the cobaltocenium
compounds is generally smaller than that of ferrocene analogues;
however, there are potential complications with these calculations
due to the asymmetry of the cobaltocenium compounds. The
synthesis of several transition metal complexes bearing 1,10-
bis(phosphino)cobaltocenium ligands was also performed, with
the solubility of such complexes depending substantially on the
phosphine substituents. The X-ray structure of [Au2Cl2(dppc)][PF6]
was determined and shows significant AueAu interactions. The %
Vbur for dppc is similar to that of dppf in analogous compounds.
Electrochemistry of these complexes displayed at least two
reductive waves, the first of which was reversible followed gener-
ally by at least one irreversible reductive wave. A correlation exists
between the reduction potentials of cobaltocenium species and the
potentials at which oxidation of analogous ferrocene species occur.
Fig. 16. CV scan for the reduction of 1.0 mM [(AuCl)2dcpc][PF6] in CH2Cl2 with 0.1 M
[NBu4][PF6] as the supporting electrolyte at 100 mV/s.
the phosphinothioyls. The first reductive wave for each complex
was reversible, while only [(AuCl)2dcpc][PF6] exhibited a degree of
reversibility for the second reductive wave.
ꢁ
With the correlation between the E1 values of several phos-
phinochalcogenyls and sp, the question arose as to a correlation
existing between the reduction potentials of cobaltocenium
compounds (ECo) and the potentials at which oxidation of related
ferrocene compounds (EFe) occur. There are few reports of reduc-
tion potentials for 1,10-bis(substituted)cobaltocenium compounds.
Plotting the reduction potentials of the 1,10-bis(substituted)cobal-
tocenium compounds versus the potential at which oxidation of
the analogous ferrocene compounds occurs resulted in a linear
relationship when both potentials were in CH2Cl2 (Fig. 17). It is
worth noting that the phosphinoselenoyl species were not included
as the selenium undergoes oxidation prior to the iron center. The y-
intercept value correlates very well with the ꢂ1.33 V difference
observed between the cobaltocene and ferrocene redox couples
[29]. In addition, the slope suggests that the substituent effects are
identical for both the 1,10-bis(substituted) iron and cobalt species.
This suggests that the redox potential of one of these species can be
reasonably predicted if the potential of the analogous complex is
known.
Acknowledgments
K.D.R., C.L.M., O.D.H. and C.N. thank the donors of the Petroleum
Research Fund, administered by the American Chemical Society, for
partial funding of this research, the Kresge Foundation for the
purchase of the JEOL NMR, and the Academic Research Committee
at Lafayette College for funding EXCEL scholars.
Appendix
-0.6
-0.7
-0.8
-0.9
-1
CCDC No. 839626 for [Au2Cl2(dppc)][PF6], CCDC No. 839627 for
[1-dtbpcS][PF6], CCDC No. 839628 for [1-dtbpcSe][PF6], CCDC No.
839629 for [dcpcS2][PF6], CCDC No. 839630 for [dcpcSe2][PF6],
CCDC No. 839631 for dcpfS2, CCDC No. 839632 for [dppc][PF6],
CCDC No. 839633 for [dppcS2][PF6], CCDC No. 839634 for [dppcSe2]
[PF6] and CCDC No. 840136 for dcpfSe2; contains the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
-1.1
-1.2
-1.3
-1.4
Appendix. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2011.09.
004
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
EFe (V vs. FcH0/+
)
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species (EFe) occurs. ECo ¼ 1.0244(EFe) e 1.3171, R2 ¼ 0.967.
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