Synthesis, characterization, and electrochemistry of compounds containing 1-diphenylphosphino-1 -(di-tert-butylphosphino)ferrocene (dppdtbpf)

Article abstract of DOI:10.1021/om800850c

The anodic electrochemistry of 1-di-tert-butylphosphino-l -diphenylphosphinoferrocene (dppdtbpf) was performed in methylene chloride with tetrabuflylammonium hexafluorophosphate as the supporting electrolyte. The electrochemistry is complicated by a chemi

Full text of DOI:10.1021/om800850c

Organometallics 2009, 28, 2119–2126
2119
Synthesis, Characterization, and Electrochemistry of Compounds
Containing 1-Diphenylphosphino-1′-(di-tert-butylphosphino)ferrocene
(dppdtbpf)
Sarah L. Kahn,† Meghan K. Breheney,† Sarah L. Martinak,† Stephanie M. Fosbenner,†
Ashley R. Seibert,† W. Scott Kassel,‡ William G. Dougherty,‡ and Chip Nataro*,†
Department of Chemistry, Hugel Science Center, Lafayette College, Easton, PennsylVania 18042, and
Department of Chemistry, VillanoVa UniVersity, VillanoVa, PennsylVania 19085
ReceiVed September 2, 2008
The anodic electrochemistry of 1-di-tert-butylphosphino-1′-diphenylphosphinoferrocene (dppdtbpf) was
performed in methylene chloride with tetrabutlylammonium hexafluorophosphate as the supporting
electrolyte. The electrochemistry is complicated by a chemical reaction after the oxidation. Three new
transition metal complexes of dppdtbpf ([NiCl2(dppdtbpf)], [PtCl2(dppdtbpf)], and [Au2Cl2(dppdtbpf)])
were prepared and characterized. The electrochemistry of the three new compounds and one previously
prepared compound ([PdCl2(dppdtbpf)]) was examined. In addition, the reaction of dppdtbpf with sulfur
and/or selenium afforded a series of compounds containing a phosphine sulfide (dppSdtbpSf or dppdtbpSf),
a phosphine selenide (dppSedtbpSef or dppdtbpSef), or both a phosphine sulfide and a phosphine selenide
(dppSedtbpSf or dppSdtbpSef). These compounds were characterized by NMR, and the structures of
three of the compounds were determined. Two of the structures are of the isomeric compounds,
dppSdtbpSef and dppSedtbpSf, in which the sulfur and selenium atoms are switched between the two
different phosphine groups. The anodic electrochemistry of these sulfur- and/or selenium-containing
compounds was examined in methylene chloride. The potentials at which oxidation occurs are more
positive than those of the free phosphine. Nearly all of the oxidations are complicated by at least one
chemical reaction.
and time for complete uptake of hydrogen. The only other study
to employ dppdtbpf examined the catalytic activity of [Ni(COD)-
dppdtbpf] in the isomerization of 2-methyl-3-butenenitrile using
either ZnCl2 or BEt3 as the co-catalyst.6 While not focused
exclusively on dppdtbpf, this study does suggest that the
Introduction
Bis(phosphino)ferrocenes are commonly used ligands in a
variety of catalytic applications.1 While the symmetrically
substituted 1,1′-bis(phosphino)ferrocenes such as 1,1′-bis(diphe-
nylphosphino)ferrocene (dppf)2 and 1,1′-bis(di-tert-butylphos-
phino)ferrocene (dtbpf)2j,3 (Chart 1) continue to be actively
investigated, closely related asymmetric compounds have not
been given equal consideration. Although Cullen first reported
1-diphenylphosphino-1′-di-tert-butylphosphinoferrocene (dpp-
dtbpf) in 1985,4 it has received surprisingly little attention.5 In
addition to the synthesis and characterization of dppdtbpf the
synthesis of [PdCl2(dppdtbpf)] has been reported.4a The catalytic
hydrogenation of a series of olefins using [Rh(NBD)(P-P)]ClO4
(P-P ) dppf, dtbpf, or dppdtbpf) as the catalyst precursor was
investigated.4b While no clear trends were observed, the dppf
and dppdtbpf complexes tended to give similar results, which
were superior to the dtbpf analogue in terms of induction time
(2) Recent examples include the following: (a) Csok, Z.; Vechorkin,
O.; Harkins, S. B.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc. 2008, 130,
8156. (b) Jamali, S.; Nabavizadeh, S. M.; Rashidi, M. Inorg. Chem. 2008,
47, 5441. (c) Serra-Muns, A.; Jutand, A.; Moreno-Manas, M.; Pleixats, R.
Organometallics 2008, 27, 2421. (d) Kuwano, R.; Kusano, H. Org. Lett.
2008, 10, 1979. (e) Vo, G. D.; Hartwig, J. F. Angew. Chem., Int. Ed. 2008,
47, 2127. (f) Kawatsura, M.; Hirakawa, T.; Tanaka, T.; Ikeda, D.; Hayase,
S.; Itoh, T. Tetrahedron Lett. 2008, 49, 2450. (g) Kawatsura, M.; Hirakawa,
T.; Tanaka, T.; Ikeda, D.; Hayase, S.; Itoh, T. Tetrahedron Lett. 2008, 49,
2450. (h) Shaw, A. P.; Guan, H.; Norton, J. R. J. Organomet. Chem. 2008,
693, 1382. (i) Song, L.-C.; Wang, H.-T.; Ge, J.-H.; Mei, S.-Z.; Gao, J.;
Wang, L.-X.; Gai, B.; Zhao, L.-Q.; Yan, J.; Wang, Y.-Z. Organometallics
2008, 27, 1409. (j) Fey, N.; Harvey, J. N.; Lloyd-Jones, G. C.; Murray, P.;
Orpen, A. G.; Osborne, R.; Purdie, M. Organometallics 2008, 27, 1372.
(k) Dahl, T.; Tornoee, C. W.; Bang-Andersen, B.; Nielsen, P.; Joergensen,
M. Angew. Chem., Int. Ed. 2008, 47, 1726. (l) Guan, B.-T.; Xiang, S.-K.;
Wang, B.-Q.; Sun, Z.-P.; Wang, Y.; Zhao, K.-Q.; Shi, Z.-J. J. Am. Chem.
Soc. 2008, 130, 3268. (m) Jensen, T.; Pedersen, H.; Bang-Andersen, B.;
Madsen, R.; Joergensen, M. Angew. Chem., Int. Ed. 2008, 47, 888. (n) Arias,
J.; Bardaji, M.; Espinet, P. Inorg. Chem. 2008, 47, 1597.
(3) Clapham, K. M.; Batsanov, A. S.; Greenwood, R. D. R.; Bryce,
M. R.; Smith, A. E.; Tarbit, B. J. Org. Chem. 2008, 73, 2176.
(4) (a) Cullen, W. R.; Kim, T. J.; Einstein, F. W. B.; Jones, T.
Organometallics 1985, 4, 346. (b) Butler, I. R.; Cullen, W. R.; Kim, T. J.;
Rettig, S. J.; Trotter, J. Organometallics 1985, 4, 972.
(5) The isomeric compound 1,1′-bis(phenyl-tert-butylphosphino)fer-
rocene has also been prepared and appears in ref 1b and the following. (a)
Kim, T.-J. Bull. Korean Chem. Soc. 1990, 11, 134. (b) Butler, I. R.; Coles,
S. J.; Hursthouse, M. B.; Roberts, D. J.; Fujimoto, N. Inorg. Chem. Commun.
2003, 6, 760.
* To whom correspondence should be addressed. E-mail: nataroc@
lafayette.edu.
† Lafayette College.
‡ Villanova University.
(1) (a) Gan, K.-S.; Hor, T. S. A. In Ferrocenes: Homogeneous Catalysis,
Organic Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; VCH:
New York, 1995; p 3. (b) Hayashi, T. In Ferrocenes: Homogeneous
Catalysis, Organic Synthesis, Materials Science; Togni, A., Hayashi, T.,
Eds.; VCH: New York, 1995; p 105. (c) Chien, A. W.; Hor, T. S. A. In
Ferrocenes: Ligands, Materials and Biomolecules; Ste`pnic`ka, P., Eds.; John
Wiley & Sons, Ltd.: West Sussex, 2008; p 33. (d) Colacot, T. J.; Parisel,
ˇ
ˇ
S. In Ferrocenes: Ligands, Materials and Biomolecules; Ste`pnic`ka, P., Ed.;
John Wiley & Sons, Ltd.: West Sussex, 2008; p 117.
(6) Acosta-Ramirez, A.; Munoz-Hernandez, M.; Jones, W. D.; Garcia,
J. J. Organometallics 2007, 26, 5766.
10.1021/om800850c CCC: $40.75
2009 American Chemical Society
Publication on Web 03/04/2009

2120 Organometallics, Vol. 28, No. 7, 2009
Chart 1. Bis(phosphino)ferrocenes and Bis(phosphinechalcogenide)ferrocenes Used in This Report
Kahn et al.
asymmetric steric and/or electronic properties of dppdtbpf can
have a significant impact on reactivity. When BH3 was used as
the co-catalyst, [Ni(COD)dppdtbpf] had a higher selectivity
for the formation of 3-pentenenitrile than either the dppf or 1,1′-
bis(diisopropylphosphino)ferrocene (dippf) analogues. In addi-
tion, the stoichiometric reaction of [Ni(COD)dppdtbpf], ZnCl2,
and 2-methyl-3-butenenitrile yields exclusively a compound in
which the -PtBu2 group is bound to Zn and the -PPh2 group
remains bound to Ni.
yield [R3P-S-S-PR3]2+ in which intermolecular S-S bond
formation has occurred. Similarly, oxidation of (Me2N)3PdSe
yields [(Me2N)3P-Se-Se-(NMe2)3]2+ 13 To date there are no
.
examples of the oxidation of a phosphine sulfide and a
phosphine selenide to yield
a Se-S bonded species,
[R3P-Se-S-PR3]2+. There are also no examples of the reaction
of two different phosphine sulfides or phosphine selenides to
yield either an S-S or Se-Se bonded species,
[R3P-E-E-PR′3]2+ (E ) S or Se; R * R′).
While previous studies have focused on the steric and
electronic properties of the phosphorus atoms in dppdtbpf, the
presumably redox-active iron center of the ferrocenyl backbone
has not been examined. Redox activity of the iron center can
play an important role in the catalytic activity of compounds
containing ferrocenyl phosphine ligands such as redox-switch
catalysis using CpRu(dppf)H.7 The closely related dtbpf un-
dergoes a chemically and electrochemically reversible one-
electron oxidation in methylene chloride (CH2Cl2).8 Under
similar conditions, the oxidation of dppf is complicated by a
follow-up reaction.9 Upon coordination to a transition metal
center, the oxidation of dppf and dtbpf occurs at a potential
more positive than that of the free phosphine and is typically
chemically and electrochemically reversible.8,9
In addition to the transition metal complexes, the anodic
electrochemistry of the phosphine sulfides and phosphine
selenides of dppf and dtbpf have been investigated (Chart 1).
Both dppfS2 and dtbpfS2 undergo chemically and electrochemi-
cally reversible oxidations, while dppfSe2 and dtbpfSe2 undergo
electrochemically irreversible oxidations.8,10 The oxidation of
dtbpfS2 is a one-electron oxidation that presumably occurs at
the iron center.8 However, dtbpfSe2 undergoes two one-electron
oxidations that result in the intramolecular formation of a Se-Se
bond, yielding [dtbpfSe2]2+ (eq 1).8 The reason for the difference
in oxidation products between dtbpfS2 and dtbpfSe2 is unclear.
Oxidation of Ph3PdS11 and (Me2N)3PdS12 has been shown to
The inherent asymmetry of dppdtbpf provides the opportunity
to study the electrochemistry of a dppSdtbpSf and dppSedtbpSef
in which the sulfur or selenium atoms are inequivalent. In
addition, by taking advantage of the different reactivity of the
two phosphines in dppdtbpf, the mixed phosphine sulfide-
phosphine selenide compounds can be prepared. Besides the
synthesis of these compounds, the anodic electrochemistry of
these compounds was investigated in CH2Cl2. In addition, the
anodic electrochemistry of dppdtbpf was examined in CH2Cl2.
Three new transition metal compounds containing dppdtbpf as
a ligand were synthesized and characterized. The anodic
electrochemistry of these three compounds as well as one
previously prepared compound4a was examined. Finally, the
mixed phosphine sulfide-phosphine selenide, dppfSSe, was
prepared, and the oxidative electrochemistry was studied.
Experimental Section
General Procedures. Reactions were carried out under an
atmosphere of argon using standard Schlenck techniques. Diacetyl-
(7) Hembre, R. T.; Moqueen, J. S.; Day, V. W. J. Am. Chem. Soc. 1996,
118, 798.
(8) Blanco, F. N.; Hagopian, L. E.; McNamara, W. R.; Golen, J. A.;
Rheingold, A. L.; Nataro, C. Organometallics 2006, 25, 4292.
(9) Nataro, C.; Campbell, A. N.; Ferguson, M. A.; Incarvito, C. D.;
Rheingold, A. L. J. Organomet. Chem. 2003, 673, 47.
(10) Swartz, B. D.; Nataro, C. Organometallics 2005, 24, 2447.
(11) Blankespoor, R. L.; Doyle, M. P.; Smith, D. J.; Van Dyke, D. A.;
Waldyke, M. J. J. Org. Chem. 1983, 48, 1176.
(12) (a) Ainscough, E. W.; Brodie, A. M.; Brown, K. L. J. Chem. Soc.,
Dalton Trans. 1980, 1042. (b) Slinkard, W. E.; Meek, D. W. Inorg. Chem.
1969, 8, 1811. (c) Slinkard, W. E.; Meek, D. W. Chem. Commun. 1969,
361.
(13) Willey, G. R.; Barras, J. R.; Rudd, M. D.; Drew, M. G. B. J. Chem.
Soc., Dalton Trans. 1994, 3025.

Compounds Containing dppdtbpf
Organometallics, Vol. 28, No. 7, 2009 2121
ferrocene, decamethylferrocene (Fc*), ferrocene (FcH), dppf, dp-
pdtbpf, 2,2′-thiodiethanol, NiCl2 · 6H2O, and selenium were pur-
chased from Aldrich Chemical Co., Inc. Sulfur was purchased from
Fisher Chemicals, Inc. [PdCl2(MeCN)2], [PtCl2(C6H5CN)2],
HAuCl4 · H2O, and dtbpf were purchased from Strem Chemicals,
Inc. FcH was sublimed prior to use. Lithium tetratkis(pentafluo-
rophenyl)borate was purchased form Boulder Scientific, Inc. and
metathesized to the tetrabutylammonium salt ([NBu4][B(C6F5)4])
using the literature procedure.14 Diacetylferrocenium tetrafluoro-
borate,15 dppfS,16 [(AuCl)2dppf],17 and [PdCl2(dppdtbpf)]4a were
prepared according to the literature procedures. Hexanes, CH2Cl2,
and diethyl ether (Et2O) were purified under Ar using a Solv-tek
purification system similar to one previously described.18 Toluene,
methanol, 2-propanol, benzene, and chloroform were degassed prior
to use. A JEOL Eclipse 400 FT-NMR spectrometer was used to
obtain the 31P{1H } and 1H NMR spectra. The 31P{1H} spectra were
31P{1H} NMR (CDCl3): δ (ppm) 69.9 (s, -PtBu2), 27.6 (s, -PPh2).
1H NMR (CDCl3): δ (ppm) 7.54 (m, 10H, -C6H5), 4.87 (br s, 2H,
-C5H4), 4.68 (br s, 2H, -C5H4), 4.42 (br s, 4H, -C5H4), 1.30 (d,
3
18H, JH-P ) 15.4 Hz, -CH3).
Preparation of dppSdtbpSf. Chloroform (15.0 mL) was added
to a mixture of sulfur (0.125 g, 0.390 mmol) and dppdtbpf (0.1000
g, 0.194 mmol), and the resulting solution was refluxed overnight.
Heat was then removed from the reaction, and the solution was
filtered. The volume of the filtrate was reduced in Vacuo to
approximately 10 mL, methanol (20 mL) was added, and the
resulting solution was placed in a refrigerator overnight. The
solution was filtered, and the solid was washed with diethyl ether
(10 mL) and dried in Vacuo, yielding dppSdtbpSf (0.1015 g,
90.2%) as an orange-yellow solid. Anal. Calcd for C30H36FeP2S2:
C, 62.28; H, 6.27. Found: C, 62.06; H, 6.14. 31P NMR (CDCl3): δ
(ppm) 77.6 (s, -P(S)tBu2), 41.7 (s, -P(S)Ph2). 1H NMR (CDCl3):
δ (ppm) 7.69 (m, 4H, -C6H5), 7.45 (m, 6H, -C6H5), 4.82 (m, 2H,
-C5H4), 4.63 (m, 2H, -C5H4), 4.46 (m, 2H, -C5H4), 4.39 (m, 2H,
1
referenced to an external sample of 85% H3PO4, while the H
spectra were referenced to internal TMS. Quantitative Technologies,
Inc. performed the elemental analysis.
3
-C5H4), 1.23 (d, JH-P ) 15.4 Hz, 18H, -CH3).
Preparation of [NiCl2(dppdtbpf)]. NiCl2 · 6H2O (0.0663 g,
0.279 mmol) was dissolved in 3.5 mL of a mixture of 2-propanol/
methanol (5:2 v/v). In a separate flask, dtbpdppf (0.1485 g, 0.289
mmol) was dissolved in 4 mL of warm 2-propanol. The dtbpdppf
solution was added to the nickel solution, and the reaction was
stirred for 30 min at approximately 80 °C. During this time, a dark
green precipitate was noted. The solution cooled to room temper-
ature and was then filtered, giving a dark green solid. The solid
was washed with a minimal amount of cold methanol, yielding
[NiCl2(dtbpf)] (0.0315 g, 20%). Anal. Calcd for C30H36Cl2FeNiP2:
C, 55.95; H, 5.63. Found: C, 55.61; H, 5.55.
Preparation of dppSedtbpSef. Chloroform (20.0 mL) was added
to a mixture of selenium (0.0767 g, 0.9708 mmol) and dppdtbpf
(0.2497 g, 0.4854 mmol). The reaction was refluxed overnight, and
upon cooling, the solution was filtered and then the solvent was
reduced to approximately 10 mL. Methanol (20 mL) was added,
and the solution was placed in a refrigerator overnight. The solution
was filtered, leaving the product as a light orange solid. The solid
was washed with diethyl ether (10 mL) and dried in Vacuo, yielding
dppSedtbpSef (0.2752 g, 84.3%). Anal. Calcd for C30H36FeP2Se2:
C, 53.59; H, 5.40. Found: C, 53.25; H, 5.29. 31P NMR (CDCl3): δ
1
1
(ppm) 74.7 (s, JP-Se ) 700 Hz, -P(Se)tBu2), 31.9 (s, JP-Se
)
Preparation of [PdCl2(dppdtbpf)]. Elemental analysis and 1H
NMR data for this compound have been reported previously.4a
1
728 Hz, -P(Se)Ph2). H NMR (CDCl3): δ (ppm) 7.69 (m, 4H,
-C6H5), 7.44 (m, 6H, -C6H5), 4.90 (m, 2H, -C5H4), 4.68 (m, 2H,
-C5H4), 4.48 (m, 2H, -C5H4), 4.43 (m, 2H, -C5H4), 1.27 (d, 3JH-P
) 15.4 Hz, 18H, -CH3).
2
31P{1H} NMR (CDCl3): δ (ppm) 80.6 (d, JP-P ) 20.8 Hz), 38.8
2
(d, JP-P ) 20.8 Hz).
Preparation of [PtCl2(dppdtbpf)]. PtCl2(C6H5CN)2 (0.0502 g,
0.098 mmol) and dtbpdppf (0.0541 g, 0.115 mmol) were dissolved
in 10 mL of benzene and stirred for 1 h, during which time an
orange precipitate was noted. The reaction was then placed in a
refrigerator for 2 h, after which time the solution was filtered. The
solid residue was washed with 2 × 5 mL of Et2O and dried in
Vacuo, giving [PtCl2(dtbpdppf)] as an orange solid (0.0235 g, 31%).
Preparation of dppdtbpSf. Sulfur (0.0185 g, 0.577 mmol) and
dppdtbpf (0.2999 g, 0.583 mmol) were combined and cooled to 0
°C. Toluene (15.0 mL) was added, and the reaction was stirred for
4 h while maintaining the temperature at 0 °C. Solvent was removed
in Vacuo. The residue was purified by column chromatography on
silica gel using hexanes/toluene (1:1 v/v) as the eluent. The first
band off the column (yellow-orange) was unreacted dppdtbpf. The
second band (yellow-orange) gave the desired product (0.0489 g,
15.5% yield) as a yellow solid upon removal of the solvent. The
final band from the column (orange-yellow) was dppSdtbpSf. Anal.
Calcd for C30H36FeP2S: C, 65.94; H, 6.64. Found: C, 65.57; H,
6.64. 31P NMR (CDCl3): δ (ppm) 77.8 (s, -P(S)tBu2), -17.1 (s,
Anal. Calcd for C30H36Cl2FeP2Pt: C, 46.17; H, 4.65. Found: C,
2
46.37; H, 4.70. 31P{1H} NMR (CDCl3): δ (ppm) 47.2 (d, JP-P
)
6.94 Hz, JP-Pt ) 3790 Hz, -PtBu2), 14.5 (d, JP-P ) 6.94 Hz,
1
2
1JP-Pt ) 3950 Hz, -PPh2). H NMR (CDCl3): δ (ppm) 8.04 (m,
1
4H, -C6H5), 7.56 (m, 2H, -C6H5), 7.42 (m, 4H, -C6H5), 4.78 (br
s, 2H, -C5H4), 4.45 (br s, 2H, -C5H4), 4.23 (br s, 2H, -C5H4),
1
-PPh2). H NMR (CDCl3): δ (ppm) 7.67 (m, 2H, -C6H5), 7.45
2
3.89 (br s, 2H, -C5H4), 1.57 (d, 18 H, JH-P ) 14.3 Hz, -CH3).
(m, 8H, -C6H5), 4.86 (m, 2H, -C5H4), 4.66 (m, 2H, -C5H4), 4.48
(m, 2H, -C5H4), 4.40 (m, 2H, -C5H4), 1.23 (d, 3JH-P ) 15.2 Hz,
18H, -CH3).
Preparation of [(AuCl)2dppdtbpf]. HAuCl4 · H2O (0.200 g,
0.589 mmol) was dissolved in 8.0 mL of methanol and cooled to
0 °C. After cooling, 0.70 mL of 2,2′-thiodiethanol in 1.5 mL of
methanol was added. The resulting solution was stirred for 15 min
at 0 °C, after which dppdtbpf (0.1330 g, 0.2203 mmol) was added.
The solution was stirred for 21 h, during which time a precipitate
formed. The reaction solution was filtered, and the resulting yellow
solid was washed with 3 × 5 mL of methanol and dried in Vacuo,
giving (AuCl)2dppdtbpf (0.1003 g, 42.6%). Anal. Calcd for
C30H36Au2Cl2FeP2: C, 36.80; H, 3.71. Found: C, 36.74; H, 3.33.
Preparation of dppdtbpSef. A similar synthesis to that of
dppdtbpSf was employed using 0.3010 g (0.585 mmol) of dppdtbpf
and 0.0455 g (0.576 mmol) of selenium. Purification by column
chromatography gave three bands. The first (yellow-orange) was
unreacted dppdtbpf. The second (yellow-orange) gave 0.0714 g
(20.9% yield) of the product upon removing the solvent. The third
band (orange-yellow) was dppSedtbpSef. Anal. Calcd for
C30H36FeP2Se: C, 60.73; H, 6.12. Found: C, 60.34; H, 6.11. 31P
1
NMR (CDCl3): δ (ppm) 73.9 (s, JP-Se ) 728 Hz, -P(Se)tBu2),
-17.1 (s, -PPh2). 1H NMR (CDCl3): δ (ppm) 7.67 (m, 2H,
-C6H5), 7.44 (m, 8H, -C6H5), 4.67 (br s, 2H, -C5H4), 4.43 (br s,
2H, -C5H4), 4.37 (br s, 2H, -C5H4), 4.15 (br s, 2H, -C5H4), 1.30
(14) LeSuer, R.; Geiger, W. E. Angew. Chem., Int. Ed. 2000, 39, 248.
(15) Guillon, C.; Vierling, P. J. Organomet. Chem. 1994, 464, C42.
(16) Broussier, R.; Bentabet, E.; Laly, M.; Richard, P.; Kuz’mina, L. G.;
Serp, P.; Wheatley, N.; Kalck, P.; Gautheron, B. J. Organomet. Chem. 2000,
613, 77.
(17) Hill, D. T.; Girard, G. R.; McCabe, F. L.; Johnson, R. K.; Stupik,
P. D.; Zhang, J. H.; Reiff, W. M.; Egglestons, D. S. Inorg. Chem. 1989,
28, 3529.
3
(d, JH-P ) 15.8 Hz, 18H, -CH3).
Preparation of dppSedtbpSf. Selenium (0.0091 g, 0.12 mmol)
and dppdtbpSf (0.0587 g, 0.107 mmol) were combined, and
chloroform (10.0 mL) was added. The reaction was allowed to stir
overnight. The solution was filtered, and the filtrate was evaporated
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

2122 Organometallics, Vol. 28, No. 7, 2009
Kahn et al.
Table 1. Crystal Data and Structure Analysis Results
dppdtbpSf
dppSdtbpSef
dppSedtbpSf
formula
fw
C30H36FeP2S
546.44
C30H36FeP2SSe
625.40
C30H36FeP2SSe
625.40
cryst syst
space group
monoclinic
P21/c
monoclinic
P21/n
orthorhombic
Pbca
a, Å
b, Å
c, Å
13.1591(5)
13.9408(6)
14.7454(6)
90
94.767(2)
90
13.2042(7)
12.4223(6)
17.7166(10)
90
102.650(2)
90
14.0210(2)
15.7391(2)
25.8400(3)
90
90
90
R, deg
ꢀ, deg
γ, deg
V, Å3
2695.66(19)
4
2835.5(3)
4
5702.32(13)
8
Z
cryst size, mm
cryst color
0.20 × 0.20 × 0.05
0.26 × 0.18 × 0.10
0.25 × 0.13 × 0.03
orange
yellow
yellow
radiation; λ, Å
temp, K
1.54178
100(2)
1.54178
100(2)
1.54178
100(2)
θ range, deg
data collected
3.37-68.23
4.38-68.18
3.42-68.02
h
k
l
-15 to 13
-15 to 16
-17 to 16
10 814
4658
SADABS
-15 to +15
-14 to +14
-21 to +8
14 384
4985
SADABS
-16 to 16
-18 to 11
-30 to 31
20 071
5124
SADABS
no. of data collected
no. of unique data
absorp corr
final R indices (obs. data)
R1
wR2
0.0363
0.0891
1.026
0.0553
0.1857
1.077
0.0531
0.1392
1.032
goodness of fit
to dryness, yielding 0.0369 g (55.1% yield) of dppSedtbpSf as an
orange-yellow solid. Anal. Calcd for C30H36FeP2SSe: C, 57.61; H,
5.80. Found: C, 57.41; H, 6.02. 31P NMR (CDCl3): δ (ppm) 77.6
M [NBu4][B(C6F5)4] as the supporting electrolyte. For all experi-
ments the working electrode was glassy carbon (1.5 mm diameter
disk), which was polished with two diamond pastes, first 1.0 µm
and then 0.25 µm, and rinsed with CH2Cl2 prior to use. The counter
electrode was a platinum wire, while the experimental reference
electrode was Ag/AgCl, separated from the solution by a fine frit.
FcH or Fc* was used as an internal standard depending on the
analyte.19 Cyclic voltammograms were recorded using PowerSuite
software and were performed at scan rates of 10, 25, 50, 75, and
from 100 to 1000 mV/s in 100 mV/s increments.
Bulk electrolysis experiments were performed under argon using
a CH Instruments model 630B electrochemical analyzer. The
working and auxiliary electrodes were platinum mesh baskets that
were in compartments separated by a fine glass frit. The Ag/AgCl
reference electrode was in the same compartment as the working
electrode, but was also separated by a fine glass frit. A 1.5 mm
glassy carbon electrode was used to obtain the cyclic voltammogram
after the bulk electrolysis, while a 10 µm glassy carbon electrode
was used for linear sweep voltammograms. The solvent was CH2Cl2
and the supporting electrolyte was 0.1 M [NBu4][PF6]. The analyte
concentration was 5.0 mM and the temperature was 22 ( 1 °C.
X-ray Crystal Structures. Crystals of dppdtbpSf, dppSdtbpSef,
and dppSedtbpSf were mounted using Paratone oil onto a glass
fiber and cooled to the data collection temperature of 100 K. Data
were collected on a Bru¨ker-AXS Kappa APEX II CCD diffracto-
meter (Table 1). Unit cell parameters were obtained from 90 data
frames. The systematic absences in the diffraction data were
consistent with space groups presented in Table 1. The data sets
were treated with SADABS absorption corrections based on
redundant multiscan data (Sheldrick, G., Bruker-AXS, 2001). All
non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were treated as idealized contribution.
1
1
(s, -P(S)tBu2), 31.9 (s, JP-Se ) 728 Hz, -P(Se)Ph2). H NMR
(CDCl3): δ (ppm) 7.68 (m, 4H, -C6H5), 7.44 (m, 6H, -C6H5),
4.86 (m, 2H, -C5H4), 4.66 (m, 2H, -C5H4), 4.48 (m, 2H, -C5H4),
3
4.40 (m, 2H, -C5H4), 1.23 (d, JH-P ) 15.0 Hz, 18H, -CH3).
Preparation of dppSdtbpSef. Sulfur (0.0048 g, 0.15 mmol) and
dppdtbpSef (0.0792 g, 0.133 mmol) were combined, and chloroform
(10.0 mL) was added. The reaction was stirred overnight and was
filtered, and the filtrate was evaporated to dryness, yielding 0.0382
g (45.9% yield) of the product as an orange-yellow solid. Anal.
Calcd for C30H36FeP2SSe: C, 57.61; H, 5.80. Found: C, 57.69; H,
1
5.35. 31P NMR (CDCl3): δ (ppm) 74.7 (s, JP-Se ) 723 Hz,
-P(Se)tBu2), 41.6 (s, -P(S)Ph2). 1H NMR (CDCl3): δ (ppm) 7.69
(m, 4H, -C6H5), 7.44 (m, 6H, -C6H5), 4.87 (m, 2H, -C5H4), 4.66
(m, 2H, -C5H4), 4.47 (m, 2H, -C5H4), 4.43 (m, 2H, -C5H4), 1.27
3
(d, JH-P ) 15.4 Hz, 18H, -CH3).
Preparation of dppfSSe. Chloroform (10.0 mL) was added to
a mixture of selenium (0.0091 g, 0.12 mmol) and dppfS (0.0654 g,
0.112 mmol). The reaction was allowed to stir overnight. The
solution was filtered, and the filtrate was evaporated to dryness,
yielding 0.0180 g (24.2% yield) of dppfSSe as an orange-yellow
solid. 31P NMR (CDCl3): δ (ppm) 41.3 (s, -P(S)Ph2, 31.6 (s, 1JP-Se
1
) 723 Hz, -P(Se)Ph2). H NMR (CDCl3): δ (ppm) 7.68 (m, 8H,
-C6H5), 7.43 (m, 12H, -C6H5), 4.88 (m, 2H, -C5H4), 4.67 (m,
2H, -C5H4), 4.46 (m, 2H, -C5H4), 4.41 (m, 2H, -C5H4), 1.27 (d,
3JH-P ) 15.4 Hz, 18H, -CH3). Anal. Calcd for C34H28FeP2SSe: C,
61.37; H, 4.24. Found: C, 61.23; H, 4.08.
Electrochemical Procedures. Cyclic voltammetric experiments
were conducted at ambient temperature (22 ( 1 °C) using a PAR
model 263A potentiostat/galvanostat. Scans were performed under
an argon atmosphere using 1.0 mM solutions of the analyte in
CH2Cl2 with 0.1 M tetrabutylammonium hexafluorophosphate
([NBu4][PF6]) as the supporting electrolyte. Background subtraction
of [NBu4][PF6] in CH2Cl2 was performed for all experiments. In
addition, cyclic voltammetric experiments were performed at 20.0,
10.0, 0.0, and -10.0 °C ((0.1 °C) for dppdtbpf with analyte
concentrations of 0.5, 1.0, 5.0, and 10 mM. The oxidative
electrochemistry of dppdtbpSef was also investigated using 0.05
Results and Discussion
The anodic electrochemistry of dppdtbpf displays a single
wave at 0.11 V vs FcH0/+ (Figure 1). The potential at which
(19) When Fc* was added as the standard, the potentials were referenced
to FcH by subtracting 0.548 V. Barrie`re, F.; Geiger, W. E. J. Am. Chem.
Soc. 2006, 128, 9103.

Compounds Containing dppdtbpf
Organometallics, Vol. 28, No. 7, 2009 2123
Table 2. Formal Potentials (V vs FcH0/+),a Potential Difference, ∆E
(defined as E0
- E0phosphine), and Reversibility for dppdtbpf and
cmpd
Transition Metal Compounds Containing a dppdtbpf Ligand (all
data reported at a scan rate of 100 mV/s)
red
E0
∆E
ipox/ip
dppfb
0.23
0.06
0.11
0.25
0.51
0.51
0.64
0.56
0.59
0.64
0.97
0.88
0.57
1.00
1.00
0.96
0.98
1.00
dtbpfc
dppdtbpf
[NiCl2(dppdtbpf)]
[PdCl2(dppdtbpf)]
[PtCl2(dppdtbpf)]
[(AuCl)2dppf]
[(AuCl)2dtbpf]c
[(AuCl)2dppdtbpf]
0.14
0.40
0.40
0.41
0.50
0.48
a
ox
red
.
b Ref 9. c Ref 8.
Determined from the midpoint of Ep and Ep
Figure 1. CV scans for the oxidation of 1.0 mM dppdtbpf in CH2Cl2
at 10.0 °C with 0.1 M [NBu4][PF6] as the supporting electrolyte at
two different scan rates: (top) 25 mV/s; (bottom) 400 mV/s.
oxidation of dppdtbpf occurs is approximately the average of
the potentials at which oxidation of dppf (0.23 V)9 and dtbpf
(0.06 V)8 occur. The reversibility of the oxidation of dppdtbpf
is dependent on the analyte concentration, scan rate, and
temperature (Figures S.1-S.5). At scan rates greater than 200
mV/s, a reversible couple is observed, while at lower scan rates
the oxidation of dtbpdppf is complicated by a follow-up reaction,
suggesting an EC mechanism.20 In addition, the oxidation is
more reversible at lower concentration and temperatures. This
behavior is similar to the oxidation of dippf,21 1,1′-bis(dicy-
clohexylphosphino)ferrocene (dcpf),22 and dppf.9 The exact
nature of this follow-up reaction requires further investigation.
The coordination of dppdtbpf to transition metal centers was
also examined. In addition to the previously reported
[PdCl2(dppdtbpf)],4a the remaining group 10 complexes,
[MCl2(dppdtbpf)] (M ) Ni or Pt) and [(AuCl)2dppdtbpf)], were
prepared. As with the dippf, dcpf, dppf, and dtbpf analogues,
the nickel complex is paramagnetic. Using the Evans method,
the magnetic moment was determined to be 3.3 µB (S ) 1, 2
unpaired electrons, high-spin Ni(II) in a tetrahedral environ-
ment), which is similar to the related nickel complexes of
dippf,21 dcpf,22 dppf,23 and dtbpf.8 Due to the inherent asym-
metry of dppdtbpf, the remaining transition metal compounds
gave two resonances in the 31P NMR spectra. The -PtBu2 and
-PPh2 were assigned by comparison to the dppf23 and dtbpf8
analogues.
Figure 2. CV scan for the oxidation of 1.0 mM [(AuCl)2dppdtbpf]
in CH2Cl2 with 0.1 M [NBu4][PF6] as the supporting electrolyte at
100 mV/s.
following oxidation of dppdtbpf is likely to involve the lone
pair on at least one of the phosphorus atoms. By coordinating
dppdtbpf to a transition metal, the anodic electrochemistry
generally simplifies (Figure 2). The oxidation of [PdCl2-
(dppdtbpf)] (Figure S.6), [PtCl2(dppdtbpf)] (Figure S.7), and
[(AuCl)2dppdtbpf] is chemically and electrochemically revers-
ible. The potential at which oxidation of these compounds occurs
is approximately 0.4 V more positive than that of dppdtbpf,
and the potentials are between those for the related dppf23 and
dtbpf8 compounds. A previous report of the electrochemistry
of [(AuCl)2dppf] suggested that the compound was electro-
chemically inert in methylene chloride and dimethylforma-
mide;24 however this was not the case using the conditions in
this study. The oxidation of [NiCl2(dppdtbpf)] displays a
chemically irreversible wave at a potential that is more positive
than that of free dppdtbpf (Figure S.8). This behavior is similar
to the dppf9 and dtbpf8 analogues. The lack of reversibility in
the nickel system has been attributed to weakening of the P-Ni
bond upon oxidation of the compound.25
In addition to coordinating to a transition metal, the phos-
phorus atoms of dppdtbpf react with chalcogenides to form the
corresponding phosphine chalcogenides. The disulfide (dppS-
dtbpSf) and diselenide (dppSedtbpSef) were prepared by reaction
of dppdtbpf with 2 equiv of either sulfur or selenium. There
are two signals in the 31P NMR for each compound. In
dppSdtbpSf the chemical shift for the -P(dS)Ph2 phosphorus
The anodic electrochemistry of the transition metal complexes
of dppdtbpf was examined in CH2Cl2 (Table 2). The reaction
(20) Geiger, W. E. In Laboratory Techniques in Electroanalytical
Chemistry, 2nd ed.; Kissinger, P. T., Heineman, W. R., Eds.; Marcel Dekker,
Inc.: New York, 1996; p 683.
(21) Ong, J. H. L.; Nataro, C.; Golen, J. A.; Rheingold, A. L.
Organometallics 2003, 22, 5027.
(22) Hagopian, L. E.; Campbell, A. N.; Golen, J. A.; Rheingold, A. L.;
Nataro, C. J. Organomet. Chem. 2006, 691, 4890.
(24) Houlton, A.; Roberts, R. M. G.; Silver, J.; Parish, R. V. J.
Organomet. Chem. 1991, 418, 269.
(23) Corain, B.; Longato, B.; Favero, G.; Ajo`, D.; Pilloni, G.; Russo,
U.; Kreissl, F. R. Inorg. Chim. Acta 1989, 157, 259.
(25) Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.;
Merrill, R. E.; Smart, J. C. J. Organomet. Chem. 1971, 27, 241.

2124 Organometallics, Vol. 28, No. 7, 2009
Kahn et al.
Figure 4. Perspective view of dppSdtbpSef with 30% ellipsoids.
H atoms are omitted for clarity.
Figure 3. Perspective view of dppdtbpSf with 30% ellipsoids. H
atoms are omitted for clarity.
is similar to that of dppfS2,26 while the chemical shift of the
-P(dS)tBu2 phosphorus is similar to that of dtbpfS2.8 The same
is true for the chemical shifts and the 31P-77Se coupling
constants in dppSedtbpSef.8,26
The inherent asymmetry of dppdtbpf provided the opportunity
to prepare the mixed chalcogenide species, dppSdtbpSef and
dppSedtbpSf. On the basis of the synthesis of dppfS,16 dppdtbpf
and 1 equiv of either S or Se were combined and stirred for 4 h
at 0 °C. Column chromatography on silica gel using a 1:1 v/v
mixture of hexanes and toluene as the eluent gave in order of
elution dppdtbpf, either dppdtbpSf or dppdtbpSef, and either
dppSdtbpSf or dppSedtbpSef. Monosubstitution of dppdtbpf
occurred exclusively at the more electron-rich -PtBu2 phos-
phorus. Selective reactivity of dppdtbpf has been noted in the
reaction of [Ni(COD)dppdtbpf] with ZnCl2 and 2-methyl-3-
butenenitrile.7 The product of this reaction is (η3-C4H7)Ni(µ-
CN)(µ-dppdtbpf)ZnCl2, in which the -PtBu2 is bonded to Zn
and the -PPh2 group to Ni. It is unclear if this is due to steric
Figure 5. Perspective view of dppSedtbpSf with 30% ellipsoids.
H atoms are omitted for clarity.
Table 3. Select Bond Lengths (Å) and Angles (deg) for dppdtbpSf,
dppSdtbpSef, and dppSedtbpSf
dppdtbpSf
dppSdtbpSef
dppSedtbpSf
Bond Lengths
P(1)-S
P(1)-Se
P(2)-S
1.9701(7)
1.9867(11)
1
and/or electronic factors. Assignment of the H and 31P NMR
2.1167(11)
1.9687(13)
spectra of dppdtbpSf and dppdtbpSef was made by comparison
to dppdtbpf, dppSdtbpSf, and dppSedtbpSef. Upon isolation of
the monosubstituted compounds, dppfSSe, dppSdtbpSef, and
dppSedtbpSf were prepared by adding 1 equiv of the desired
chalcogen.
The X-ray structures of dppdtbpSf (Figure 3), dppSdtbpSef
(Figure 4), and dppSedtbpSf (Figure 5) were determined, and
select bond lengths and angles are presented in Table 3. The
PdS bond length in dppdtbpSf is similar to the PdS length in
dippfS2.27 As measured by δ, the phosphorus atom bonded to
sulfur sits significantly out of the plane of the C5 ring and away
from the iron center, whereas the phosphorus of the -PPh2
group is only slightly out of the plane of the ring and away
from the iron. This is similar to the δ value for the phosphorus
atoms in dppf, which is -0.066 Å.28 The PdSe bond length in
dppSdtbpSef is similar to that found in dtbpfSe2 (av 2.1197 Å),8
while the PdS bond length is similar to that for dppfS2 (av
P(2)-Se
P(1)-C(1)
P(2)-C(6)
Fe-CCp (av)
2.1083(9)
1.811(3)
1.795(3)
2.046
1.8113(19)
1.813(2)
2.047
-0.251
-0.020
1.809(4)
1.797(4)
2.044
a
δPdS
-0.218
a
δP
-0.052
-0.271
a
δPdSe
-0.095
Bond Angles
b
XA-Fe-XB
P-Fe-P
179.20
134.03
133.24
1.64
177.74
155.17
152.98
3.29
178.56
145.07
144.40
2.88
τc
θd
C(1)-P(1)-S
C(1)-P(1)-Se
C(6)-P(2)-S
C(6)-P(2)-Se
112.42(7)
111.85(16)
111.36(13)
112.94(13)
115.24(11)
a Deviation of the P atom from the C5 plane; a positive value means
the P is closer to the Fe. b Centroid-Fe-centroid. c The torsion angle
CA-XA-XB-CB where C is the carbon atom bonded to phosphorus and
X is the centroid. d The dihedral angle between the two C5 rings.
(26) Pilloni, G.; Longato, B.; Bandoli, G.; Corain, B. J. Chem. Soc.,
Dalton Trans. 1997, 819. Note: The space group for dppfS2 was initially
reported as Cc but later corrected to C2/c by: Clemente, D. A.; Marzotto,
A. Acta Crystallogr. Sect. B 2004, 60, 287.
(27) Necas, M.; Beran, M.; Woollins, J. D.; Novosad, J. Polyhedron
2001, 20, 741.
1.941 Å).26,29 In addition, the δ for the phosphorus atom of the
-P(Se)tBu2 group is similar to dtbpfSe2 (-0.268 Å),8 and the
δ for the phosphorus of the -P(S)Ph2 group is similar to dppfS2
(28) Casellato, U.; Ajo, D.; Valle, G.; Corain, B.; Longato, B.; Graziani,
R. J. Crystallogr. Spectrosc. Res. 1988, 18, 583.
(29) Fang, Z.-G.; Hor, T. S. A.; Wen, Y.-S.; Liu, L.-K.; Mak, T. C. W.
Polyhedron 1995, 14, 2403.

Compounds Containing dppdtbpf
Organometallics, Vol. 28, No. 7, 2009 2125
Table 4. Formal Potentials (V vs FcH0/+),a Potential Difference, ∆E
(defined as E0
- E0dppdtbpf), and Reversibility for dppdtbpf and
cmpd
Transition Metal Compounds Containing a dppdtbpf Ligand (all
data reported at a scan rate of 100 mV/s)
ox1
ox2
ox3
ox4
red1
red2
red3
Ep
Ep
Ep
Ep
Ep
Ep
Ep
Monosulfides
dppfS
dppdtbpSf
Disulfides
dppfS2
0.27a
0.40 0.67 0.72
0.14e
0.60
0.48b c
,
0.36b d
,
dtbpfS2
dppSdtbpSf
Monoselenide
dppdtbpSef
Diselenides
dppfSe2
0.40b
0.14a
0.40 0.68 0.95
0.77
0.32c
0.24d
0.27
-0.14
-0.07
0.78 0.55 -0.16
dtbpfSe2
dppSedtbpSef
Sulfide-selenides
dppfSSe
dppSdtbpSef
dppSedtbpSf
1.10
Figure 7. CV scan for the oxidation of 1.0 mM dppSedtbpSef in
CH2Cl2 with 0.1 M tetrabutylammonium hexafluorophosphate as
the supporting electrolyte at 100 mV/s. Scanning both waves (black)
and scanning just the first wave (gray).
0.52
0.47
0.44
1.15
1.11
1.14
a These waves are likely due to adsorption. b These waves are
chemically and electrochemically reversible, so these values are E°.
c Ref 10. d Ref 8.
adsorption process. The cyclic voltammetry of dppdtbpSef was
performed in CH2Cl2 solvent using a less reactive supporting
electrolyte, [NBu4][B(C6F5)4].30 Under those conditions, three
anodic waves (0.28, 0.92, and 1.22 V vs FcH0/+) and one
cathodic wave (0.71 V vs FcH0/+) were observed. This suggests
that at least one wave in the oxidation of dppdtbpSf and
dppdtbpSef with [NBu4][PF6] is due to a species generated by
reaction with the supporting electrolyte.
Similar to the dppf10 and dtbpf8 analogues, the oxidation of
dppSdtbpSf displays one chemically and electrochemically
reversible wave. Bulk electrolysis confirms that the process is
one-electron (napp ) 0.99 e-, Eapp ) 1.15 V vs Ag/AgCl based
on a cyclic voltammogram of the bulk solution, T ) 22 ( 1
°C). Presumably oxidation of this compound occurs at the iron
center.
Oxidation of dppSedtbpSef displays two anodic waves and
three cathodic waves (Figure 7). If the sweep is switched just
positive of the first anodic wave, there is no change in the
reverse scan. In addition, when the potential is swept from 0.1
to -1.0 V, there is no cathodic wave. The two-electron oxidation
of dtbpfSe2 occurs at Se, as opposed to Fe, and results in the
formation of an intramolecular Se-Se bond (eq 1).8 The
similarity of the oxidation of dppSedtbpSef to dtbpfSe2 suggests
that the initial oxidation occurs at the selenium of the -P(Se)t-
Bu2 group. The fate of this selenium radical is unclear. The
similarity to the oxidation of dtbpfSe2 suggests interaction with
another selenium, either intermolecular with another -P(Se)tBu2
group or intramolecular with the -P(Se)Ph2 group. However,
additional reactions, e.g., with the solvent or supporting
electrolyte, cannot be ruled out. Initial attempts to perform
chemical oxidation of dppSedtbpSef using diacetylferrocenium
(E° 0.49 V vs FcH in CH2Cl2)31 did not yield any identifiable
products. Additional experimental and computational studies are
currently underway in order to gain a better understanding of
this process.
Figure 6. CV scan for the oxidation of 1.0 mM dppdtbpSef in
CH2Cl2 with 0.1 M tetrabutylammonium hexafluorophosphate as
the supporting electrolyte at 100 mV/s.
(-0.035 Å).26,29 It would seem that the greater steric bulk of
the tert-butyl groups seems to require a larger δ value. This
phenomenon is also observed in dppSedtbpSf, in which the value
of δ for the phosphorus of the -P(S)tBu2 group is significantly
larger than that of the phosphorus of the -P(Se)Ph2 group. In
addition, the PdSe bond length in dppSedtbpSf is similar to
that found in dppfSe2,26 while the PdE bond lengths and the
values for δ seem to indicate that the -P(E)tBu2 and -P(E)Ph2
groups do not significantly impact the structure of each other.
However, many of the remaining structural parameters are
intermediate between dppfS2, dppfSe2, and dtbpfSe2; for dppfS2
and dppfSe2 the angles XA-Fe-XB, P-Fe-P, and τ are all
180° and the angle θ is 0°.26,29 The same angles for dtbpfSe2
are 174.92°, 152.47°, 138.08°, and 6.29°, respectively.8
Oxidation of the mixed chalcogenide compounds, dppfSSe,
dppSdtbpSef, and dppSedtbpSf, all exhibited two chemically
irreversible anodic waves (Figure 8). The wave at less positive
potential is likely due to oxidation of the selenium, while the
other wave could be due to oxidation of the iron.
The anodic electrochemistry of these new compounds was
examined in CH2Cl2 (Table 4). The monosubstituted compounds,
dppdtbpSf and dppdtbpSef, displayed multiple anodic waves
and a single cathodic wave (Figure 6). The potentials at which
ox1
the first and last anodic waves occur, Ep
and Epox4, are
somewhat different, while the middle two waves, Epox2 and Ep
,
ox3
(30) Ghent, B. L.; Martinak, S. L.; Sites, L. A.; Golen, J. A.; Rheingold,
A. L.; Nataro, C. J. Organomet. Chem. 2007, 692, 2365.
(31) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.
are similar. The sharpness of the waves at 0.27 V (dppdtbpSf)
and 0.14 V (dppdtbpSef) suggest that these are due to an

2126 Organometallics, Vol. 28, No. 7, 2009
Kahn et al.
irreversible wave. The potentials at which the transition metal
compounds undergo oxidation are more positive than that of
dppdtbpf. The reaction of dppdtbpf with either sulfur or selenium
results in a series of phosphine chalcogenide compounds
depending on the reaction stoichiometry that is employed. The
disulfide, dppSdtbpSf, undergoes a chemically and electro-
chemically reversible oxidation. The diselenide, dppSedtbpSef,
undergoes two electrochemically irreversible oxidations steps,
possibly leading to the formation of Se-Se bonds. Oxidation
of the monosulfide, monoselenide, and mixed sulfide-selenides
displays multiple irreversible waves.
Acknowledgment. S.L.K., M.K.B., S.L.M., S.M.F., A.R.S.,
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, the Academic Research
Committee at Lafayette College for funding EXCEL scholars,
and Prof. Tina Huang of Lafayette College for use of the
CH Instruments electrochemical analyzer. M.K.B. thanks the
donors to the Joseph A. Sherma Chemistry Summer Research
Fund.
Figure 8. CV scan for the oxidation of 1.0 mM dppSdtbpSef in
CH2Cl2 with 0.1 M tetrabutylammonium hexafluorophosphate as
the supporting electrolyte at 100 mV/s.
Conclusion
Oxidation of dppdtbpf follows an EC mechanism and occurs
at a potential between that of dppf and dtbpf. The reversibility
of the oxidation is significantly influenced by the presence of
tert-butyl groups on the phosphorus atoms. The synthesis of
three different transition metal compounds containing dppdtbpf
is straightforward and occurs in reasonable yields. The oxidative
electrochemistry of dppdtbpf simplifies to a chemically and
electrochemically reversible wave upon coordination with the
exception of [NiCl2(dppdtbpf)], which displays a chemically
Supporting Information Available: cif files for the structures
of dpptbpSf, dppSdtbpSef, and dppSedtbpSf, additional cyclic
voltammograms, and a table of 31P NMR data. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM800850C