1′-(diphenylphosphino)ferrocenecarboxylic acid and its P-oxide and methyl ester: Synthesis, characterization, crystal structure, and electrochemistry

Article abstract of DOI:10.1021/om950528q

The ferrocene derivative (η⁵-C₅H₄PPh₂)Fe(η ⁵-C₅H₄COOH) (3), a potential hybrid phosphine ligand with heteroannular soft and hard donor groups, was synthesized in 71% yield from 1-phenyl-1-phospha[1]ferrocenophane by ring opening with phenyllithium, followed by reaction with carbon dioxide and acidification. Oxidation of 3 with hydrogen peroxide and its esterification with diazomethane provided the derivatives, phosphine oxide 4 and methyl ester 5, respectively. The new compounds were characterized by IR, UV/vis, MS, and NMR spectroscopy, the degenerate ¹H NMR spectra being assigned with the aid of selective ¹H-{¹H} decoupling, ¹H¹H-COSY, ¹³C HMQC, and ⁿJ(P,C) from APT. The solid-state structures of 3-5 were determined by single-crystal X-ray diffraction. Voltammetric measurements of 3-5 and related monosubstituted derivatives in acetonitrile revealed that the phosphines are first oxidized to the corresponding ferrocenium derivatives which are then the subject of the intramolecular electron transfer from the phosphine group to iron, the resulting species being immediately stabilized by further electrochemical and/or chemical oxidation to give phosphine oxides. The second independent electrochemical process is the reversible oxidation of these ferrocene/phosphine oxides to ferrocenium/phosphine oxides. There are further electrochemical processes associated with the irreversible oxidation of the carboxyl group.

Full text of DOI:10.1021/om950528q

Organometallics 1996, 15, 543-550
543
1′-(Dip h en ylp h osp h in o)fer r ocen eca r boxylic Acid a n d Its
P -Oxid e a n d Meth yl Ester : Syn th esis, Ch a r a cter iza tion ,
Cr ysta l Str u ctu r e, a n d Electr och em istr y
J aroslav Podlaha,* Petr Sˇteˇpnicˇka, J irˇ´ı Ludv´ık,† and Ivana C´ısarˇova´
Department of Inorganic Chemistry, Charles University, 12840 Prague, Czech Republic
Received J uly 10, 1995X
The ferrocene derivative (η5-C5H4PPh2)Fe(η5-C5H4COOH) (3), a potential hybrid phosphine
ligand with heteroannular soft and hard donor groups, was synthesized in 71% yield from
1-phenyl-1-phospha[1]ferrocenophane by ring opening with phenyllithium, followed by
reaction with carbon dioxide and acidification. Oxidation of 3 with hydrogen peroxide and
its esterification with diazomethane provided the derivatives, phosphine oxide 4 and methyl
ester 5, respectively. The new compounds were characterized by IR, UV/vis, MS, and NMR
1
1
spectroscopy, the degenerate H NMR spectra being assigned with the aid of selective H-
{1H} decoupling, 1H,1H-COSY, 13C HMQC, and J (P,C) from APT. The solid-state structures
n
of 3-5 were determined by single-crystal X-ray diffraction. Voltammetric measurements
of 3-5 and related monosubstituted derivatives in acetonitrile revealed that the phosphines
are first oxidized to the corresponding ferrocenium derivatives which are then the subject
of the intramolecular electron transfer from the phosphine group to iron, the resulting species
being immediately stabilized by further electrochemical and/or chemical oxidation to give
phosphine oxides. The second independent electrochemical process is the reversible oxidation
of these ferrocene/phosphine oxides to ferrocenium/phosphine oxides. There are further
electrochemical processes associated with the irreversible oxidation of the carboxyl group.
Sch em e 1
In tr od u ction
The coordination chemistry of phosphinoferrocenes
has been the subject of substantial investigation over
the past 2 decades. In particular, the heteroannular bis-
(phosphines) such as 1,1′-bis(diphenylphosphino)fer-
rocene attract much interest because their complexes
find synthetic applications in transition-metal-catalyzed
processes. Less attention has been paid to related
phosphinoferrocenes which posses a hard-donor func-
tional group instead of the second phosphine center.
These ligands belong to the class of “hybrid” phosphines
which are capable of coordinating by a number of ways
depending mainly on the metal hardness. Representa-
tive examples of such hard donors in phosphinofer-
rocenes include 2,2′-bipyridyl,1 Schiff bases,2 and mac-
rocycles3,4 as the hard donor functionality. In our
laboratory, tertiary phosphines with carboxyl group(s)
as the second donor have been studied.5 They are
formally analogous to the familiar amino polycarboxy-
lates and constitute two series, R3-nP(CH2COOH)n (n
) 1-3; R ) Ph, Me, Et, i-Pr) and [-CH2P(CH2COOH)n-
Ph2-n]2 (n ) 1, 2). These substituted phosphines form
secondary metal-carboxylate bonds which may be
cleaved reversibly on changing pH to open a coordina-
tion site on the metal, necessary for the induction of
catalytic activity. Moreover, the ligands and complexes
with n > 1 are often water-soluble and may be used as
selective and effective extractants of platinum metals
from organic into aqueous phase.6 In this paper, we
report the synthesis and properties of a new ligand
bearing the given combination of the donor groups on
the ferrocene backbone.
† Current address: J . Heyrovsky´ Institute of Physical Chemistry,
Academy of Sciences of the Czech Republic, 18223 Prague, Czech
Republic.
X Abstract published in Advance ACS Abstracts, December 1, 1995.
(1) Butler, I. R.; Kalaji, M.; Nehrlich, L.; Hursthouse, M.; Karaulov,
A. I.; Abdul Malik, K. M. J . Chem. Soc., Chem. Commun. 1995, 459.
(2) Houlton, A.; J asim, N.; Roberts, R. M. G.; Silver, J .; Cunningham,
D.; McArdle, P.; Higgins, T. J . Chem. Soc., Dalton Trans. 1992, 2235.
(3) Beer, P. D.; Nation, J . E.; McWhinnie, S. L. W.; Harman, M. E.;
Hursthouse, M. B.; Ogden, M. I.; White, A. H. J . Chem. Soc., Dalton
Trans. 1991, 2485.
(5) (a) Podlahova´, J .; Kratochv´ıl, B.; Podlaha, J .; Hasˇek, J . J . Chem.
Soc., Dalton Trans. 1985, 2393 and references therein. (b) Podlaha,
J .; J egorov, A.; Budeˇsˇ´ınsky´, M.; Hanusˇ, V. Phosphorus Sulfur 1988,
37, 87 and references therein. (c) Podlahova´, J .; Hartl, F.; Podlaha, J .;
Knoch, F. Polyhedron 1987, 6, 1987 and references therein.
(6) J egorov, A.; Podlaha, J . Catal. Lett. 1991, 8, 9.
(4) Grossel, M. C.; Goldspink, M. R.; Knychala, J . P.; Cheetham, A.
K.; Hriljac, J . A. J . Organomet. Chem. 1988, 352, C13.
0276-7333/96/2315-0543$12.00/0 © 1996 American Chemical Society

544 Organometallics, Vol. 15, No. 2, 1996
Podlaha et al.
F igu r e 1. ORTEP plot of the molecule of 3 at 40%
probability level. For clarity, calculated hydrogen atoms
are omitted and only pivot and adjacent carbon atoms of
the rings are labeled.
F igu r e 2. ORTEP plot of the molecule of 4 at 40%
probability level. For clarity, calculated hydrogen atoms
are omitted and only pivot and adjacent carbon atoms of
the rings are labeled.
Resu lts a n d Discu ssion
Syn th esis. According to Scheme 1, ring opening7 of
1-phenyl-1-phospha- [1]ferrocenophane (1)8 with phen-
yllithium gave the lithiated derivative 2 which was
reacted in situ with excess solid carbon dioxide; the
subsequent acidification provided 1′-(diphenylphosphi-
no)ferrocenecarboxylic acid (3) in 71% yield. The stan-
dard oxidation of 3 with hydrogen peroxide in acetone
produced phosphine oxide 4 in 43% yield, and the
reaction of 3 with diazomethane in Et2O led to methyl
ester 5 in 71% yield (yields not optimized). Sodium salt
6 is formed by neutralization of 3 with sodium hydrogen
carbonate in ethanol or with sodium hydroxide in
aqueous ethanol, but it could not be isolated in pure
form (IR of a crude hygroscopic material in Nujol: 1345,
1540 cm-1, COO-). Attempts to isolate the K or Rb salt
were also unsuccessful, even in the presence of alkali-
metal complexing agents such as linear and cyclic
polyethers. Compounds 3-6 are soluble in polar or-
ganic solvents (6 also in water) to give orange solutions
(yellow for 6) which, for phosphines 3, 5, and 6, are
oxidized slowly in air. Solid samples of 3-5 are air-
stable; 3 and 5 are orange in color, and 4 is rusty red.
Cr ysta l Str u ctu r es. The solid-state structures of
compounds 3-5 were determined by single-crystal X-ray
diffraction. Since the position of the substituents on the
cyclopentadienyl rings is neither exactly anti-staggered
nor exactly syn-eclipsed, the molecules display planar
chirality in the crystal with both enantiomers present
in the racemic crystal. Further, the asymmetric unit
of 3 contains two symmetrically independent but chemi-
cally almost identical molecules labeled 1 and 2. The
arrangement of molecules (R)-3 (molecule 1), (R)-4, and
(R)-5 (Figures 1-3) is very similar. It consists of nearly
parallel cyclopentadienyl rings (the tilt angles are less
than 3°; see the Supporting Information for details)
bearing the heteroannular substituents in anti arrange-
F igu r e 3. ORTEP plot of the molecule of 5 at 40%
probability level. For clarity, calculated hydrogen atoms
are omitted and only pivot and adjacent carbon atoms of
the rings are labeled.
ment. All intramolecular bond distances and angles are
unexceptional; selected values are summarized in Table
1. There are significant conformational differences
between the three molecules. Major changes are en-
countered, of course, at the places where the molecules
differ chemically. As manifested by the dihedral angles
of the mean phenyl and cyclopentadienyl planes (Sup-
porting Information), the distortion of the approximately
tetrahedral environment of phosphorus reflects different
steric requirement of oxygen in 4 and of the electron
pair in 3 and 5. At the opposite end of the molecules,
the carboxyl groups are nearly coplanar with the parent
cyclopentadienyl rings but the carboxylate group in
ester 5 is turned over by 180° with respect to carboxylic
acids 3 and 4. There are further less obvious but
(7) (a) Seyferth, D.; Withers, H. P., J r. J . Organomet. Chem. 1980,
185, C1. (b) Seyferth, D.; Withers, H. P. Organometallics 1982, 1, 1275.
(8) Osborne, A. G.; Whiteley, R. H.; Meads, R. E. J . Organomet.
Chem. 1980, 193, 345.

1′-(Diphenylphosphino)ferrocenecarboxylic Acid
Organometallics, Vol. 15, No. 2, 1996 545
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles (d eg) for 3-5
3
molecule 1
molecule 2
4
5
(a) Bond Lengths
Fe-C in Cp (mean) 2.048(5)
C-C in Cp (mean) 1.42(1)
C-C in Ph (mean) 1.38(1)
2.04(1)
1.41(1)
1.38(1)
1.487(2)
2.037(7)
1.41(1)
1.380(9)
P-O(3)
P(1)-C(101)
P(1)-C(112)
P(1)-C(118)
C(111)-O(11)
C(111)-O(12)
1.820(5) P(2)-C(201)
1.842(5) P(2)-C(212)
1.837(4) P(2)-C(218)
1.228(5) C(211)-O(21)
1.314(5) C(211)-O(22)
1.814(5) P-C(01)
1.833(5) P-C(12)
1.830(4) P-C(18)
1.228(5) O(1)-C(11)
1.315(5) O(2)-C(11)
1.787(3) P-C(01)
1.795(3) P-C(12)
1.808(3) P-C(18)
1.200(4) O(1)-C(11)
1.318(4) O(2)-C(11)
O(2)-C(24)
1.808(2)
1.835(2)
1.839(2)
1.204(3)
1.333(3)
1.439(4)
(b) Bond Angles
C-C-C in Cp (mean) 108.0(6)
C-C-C in Ph (mean) 120(1)
108.0(5)
120.0(7)
124.3(3) O(1)-C(11)-O(2)
108.0(7)
120(1)
123.5(3)
117.0(3)
125.0(3)
111.4(2)
O(11)-C(111)-O(12)
123.2(5) O(21)-C(211)-O(22)
123.7(5) O(1)-C(11)-O(2)
C(11)-O(2)-C(24)
O(11)-C(111)-C(106)
O(12)-C(111)-C(106)
122.0(5) O(21)-C(211)-C(206)
114.8(5) O(22)-C(211)-C(206)
122.2(4) O(1)-C(11)-C(06)
114.1(5) O(2)-C(11)-C(06)
122.6(3) O(1)-C(11)-C(06)
113.1(3) O(2)-C(11)-C(06)
C(107)-C(106)-C(111) 124.2(4) O(207)-C(206)-C(211) 128.1(4) C(07)-C(06)-C(11) 123.6(3) C(07)-C(06)-C(11) 127.4(2)
C(110)-C(106)-C(111) 127.7(4) C(210)-C(206)-C(211) 124.1(4) C(10)-C(06)-C(11) 128.8(3) C(10)-C(06)-C(11) 124.6(3)
O(3)-P-C(01)
O(3)-P-C(12)
O(3)-P-C(18)
113.2(1)
113.7(1)
109.8(2)
C(101)-P(1)-C(112)
C(101)-P(1)-C(118)
C(112)-P(1)-C(118)
C(102)-C(101)-P(1)
C(105)-C(101)-P(1)
C(113)-C(112)-P(1)
C(117)-C(112)-P(1)
C(119)-C(118)-P(1)
C(123)-C(118)-P(1)
100.9(2) C(201)-P(2)-C(212)
100.2(2) C(201)-P(2)-C(218)
102.3(2) C(212)-P(2)-C(218)
123.6(3) C(202)-C(201)-P(2)
129.7(3) C(205)-C(201)-P(2)
117.3(4) C(213)-C(212)-P(2)
124.5(4) C(217)-C(212)-P(2)
124.0(3) C(219)-C(218)-P(2)
118.0(4) C(223)-C(218)-P(2)
101.3(2) C(01)-P-C(12)
100.2(2) C(01)-P-C(18)
102.4(2) C(12)-P-C(18)
123.8(3) C(02)-C(01)-P
129.4(3) C(05)-C(01)-P
118.4(4) C(13)-C(12)-P
124.6(4) C(17)-C(12)-P
124.0(3) C(19)-C(18)-P
118.6(4) C(23)-C(18)-P
106.4(1) C(01)-P-C(12)
106.6(1) C(01)-P-C(18)
106.8(1) C(12)-P-C(18)
124.0(2) C(02)-C(01)-P
128.7(2) C(05)-C(01)-P
118.4(2) C(13)-C(12)-P
123.0(2) C(17)-C(12)-P
118.2(3) C(19)-C(18)-P
122.8(3) C(23)-C(18)-P
101.5(1)
101.0(1)
101.5(1)
123.9(2)
129.5(2)
117.8(2)
124.2(2)
124.3(2)
117.4(2)
of hydrogen bonding, while the bulky PPh2 groups of
1,1′-bis(diphenylphosphino)ferrocene are exactly anti-
staggered. Clearly, the particular conformation of the
cyclopentadienyls rings is dictated by subtle factors of
which the crystal packing is undoubtedly imperative.
The interaction of molecules 3-5 and 5 in the crystalline
state differs, in fact, considerably. In 3, each of the two
independent molecules is linked to its centrosymmetric
partner through a 2-fold hydrogen bond, resulting in
dimers which are then packed at the normal van der
Waals distances. The molecules of phosphine oxide 4
are associated by intermolecular hydrogen bonding
[O‚‚‚O, 2.588(3) Å] between the carboxylic hydroxyl and
the PdO oxygen which links the molecules into zigzag
chains running along the crystallographic b direction.
Finally, the structure of ester 5 is molecular with no
contacts shorter than the sum of the van der Waals
radii. These different types of crystal packing are nicely
reflected on the mass spectra and mp’s (see Experimen-
tal Section).
F igu r e 4. Superposition of molecules 3 (thick lines) and
4 and 5 (thin lines) viewed from the side of the P-
substituted Cp ring.
significant differences between the three molecules in
the mutual position of the phosphine and carboxyl
substituents. Figure 4 depicts the superposition of the
appropriate fragments, oriented perpendicularly to the
cyclopentadienyl rings from the side of the P-substituted
ring (i.e., according to the chirality preference). It
appears that the anti-conformation of the substituted
cyclopentadienyls is exactly halfway between staggered
and eclipsed in phosphines 3 and 5 but, in contrast,
perfectly eclipsed in phosphine oxide 4. This is best
demonstrated by the torsion angle τ defined by the
P-bearing carbon C(01), the cyclopentadienyl centroids,
and the carboxyl-bearing carbon C(06). The value of τ
is 162.0(4)° for 3 and 161.8(4)° for 5 but 141.9(3)° for 4,
the theoretical τ’s being 180° for the fully staggered and
144° for the fully eclipsed anti-conformation. A search
of the Cambridge Structural Database for 1,1′-disub-
stituted ferrocenes (free of intramolecular steric con-
straints such as transannular links) revealed that the
syn- and anti-conformations of the 1,1′-substituents are
preferred but other arrangements are also quite com-
mon (see the Supporting Information for the data).
From the closely related compounds, the carboxyl
groups are exactly syn-eclipsed, possibly as the result
NMR Sp ectr a . The 1H and 31P NMR spectra of
compounds 3-5 and the 13C spectra of 3 are sum-
marized in Tables 2 and 3; atom labels are defined in
Chart 1 (hydrogens are labeled according to their
bonding carbons). In phosphine carboxylic acid 3, the
cyclopentadienyl protons of the P-substituted ring be-
have as an AA′BB′X spin system (X ) P) and those of
the COOH-substituted ring as an AA′BB′ system. The
signal of the carboxyl proton was not observed. The
spin-spin interactions deduced from the degenerate 1H
1
spectra by selective H{1H} decoupling were confirmed
by 1H T 1H correlations (1H,1H-COSY: 4.17 T 4.45; 4.34
1
T 4.76), 13C T H correlations (13C HMQC; see Table
3), and by the nJ (P,C) interaction constants (from APT).

546 Organometallics, Vol. 15, No. 2, 1996
Ta ble 2. 1H a n d 31P NMR Da ta for 3-5
1H chem shifta for protons (multiplicity,b rel intensity)
Podlaha et al.
compd
2, 5
3, 4
2′, 5′
3′, 4′
others
31P chem shiftc
3
4
5
4.76 (t, 2H) 4.34 (t, 2H) 4.17 (q, 2H) 4.45 (t, 2H)
5.06 (t, 2H) 4.31 (t, 2H) 4.60 (q, 2H) 4.37 (q, 2H) phenyl, 7.43-7.64 (m, 6H), 7.67-7.79 (m, 4H)
4.71 (t, 2H) 4.17 (t, 2H) 4.13 (q, 2H) 4.39 (t, 2H)
phenyl, 7.30-7.37 (m, 10H)
-17.6
+32.9
-17.4
phenyl, 7.29-7.42 (m, 10H); methyl, 3.17 (s, 3H)
a
b
Measured at room temperature in C[2H]Cl3 with TMS as internal standards. s ) singlet, t ) triplet, and q ) quadruplet. c Measured
at room temperature in C[2H]Cl3 with 85% aqueous H3PO4 as external standards.
Ta ble 3. 13C NMR Sh ifts a n d Heter on u clea r
Cor r ela tion s for 3
and 1,1′-(diphenylphosphino)ferrocene,10 may be clas-
sified as belonging to three groups labeled A-C.
Process Asthe main anodic reactionsis in all cases
the reversible one-electron oxidation of the ferrocene
skeleton yielding the corresponding ferrocenium. It can
be subdivided into processes A1 and A2 (Figures 5 and
6). In contrast to the oxidation of phosphines (com-
pounds FcPPh2, 3, and 5) where both processes A1 and
A2 are involved, only the reversible process A2 takes
place for phosphine oxides (FcP(O)Ph2 and 4).
1H correlation
signal
δ(13C)a (multb)
(from 13C HMQC)
Cp
1
70.4 (s)
2, 5
3, 4
1′
2′, 5′
3′, 4′
71.4 (s)
4.76
4.34
73.4 (d, J ) 1.5 Hz)
78.4 (d, J ) 9.2 Hz)
74.4 (d, J ) 14.5 Hz)
73.3 (d, J ) 3.0 Hz)
4.17
4.45
Ph
138.4 (d, J ) 9.9 Hz)
133.5 (d, J ) 19.8 Hz)
128.3 (d, J ) 6.9 Hz)
128.7 (s)
From the comparison of the redox behavior of analo-
gous PIII and PV derivatives (FcPPh2, FcP(O)Ph2 and 3,
4, respectively), it is evident that process A2 in the case
of PIII compounds corresponds to the single ferrocene-
ferrocenium redox process for phosphine oxides. It
follows that the phosphine oxides are generated in situ
from PIII derivatives during the first anodic A1 reaction.
If the switching potential in CV of phosphines lies
close to the anodic peak of A1 (but before A2), a small
cathodic peak corresponding to A1 redox couple appears
and gains in intensity with increasing sweep rate. If
the switching potential is more positive by 200-250 mV
(i.e., after A2), the reversible couple of anodic/cathodic
peaks belonging to A2 dominates and, simultaneously,
the cathodic peak of A1 becomes smaller. Short elec-
trolysis at the switching potential during CV causes this
peak to disappear totally. These observations are
indicative of a subsequent chemical oxidation which
follows the first electron transfer.
i
o
m
p
7.30-7.37
CdO
177.2 (s)
Measured at room temperature in C[2H]Cl3, indirect internal
a
b
reference C[2H]Cl3 (δ 77.0). s ) singlet and d ) doublet.
As summarized in Scheme 2, the first process for
phosphine-substituted ferrocenes is the oxidation of FeII
to FeIII (A1). The resulting ferrocenium is the subject
of the intramolecular electron transfer from the phos-
phine group to iron (via cyclopentadienyl), the resulting
species being immediately stabilized by further one-
electron oxidation (electrochemical and/or chemical by
traces of oxygen or water11) to give phosphine oxide.
The phosphine oxides originated in this way manifest
themselves as the reversible redox system A2 (Figure
6). The proposed mechanism is in agreement with the
high susceptibility of ferrocene derivatives to electro-
philic substitution.12
F igu r e 5. Cyclic voltammograms of 3. Curves a-c cor-
respond to different switch potentials, and dotted lines, to
measurement after electrolysis at potentials labeled by
double arrows.
Ch a r t 1
The redox potentials of RDE voltammetric waves for
process A are shifted in the positive direction against
the unsubstituted ferrocene by +190, +170, and +50
mV for FcCOOH, FcP(O)Ph2, and FcPPh2, respectively.
This remarkable positive shift is undoubtedly caused
Further discussion of NMR spectra is presented as
Supporting Information.
(9) (a) Little, W. F.; Reilley, C. N.; J ohnson, J . D.; Sanders, A. P. J .
Am. Chem. Soc. 1964, 86, 1382. (b) Scholl, H.; Sochaj, K. Electrochim.
Acta 1991, 36, 689.
(10) Pilloni, G.; Longato, B.; Corain, B. J . Organomet. Chem. 1991,
420, 57.
(11) Acetonitrile is known to be notoriously difficult to dry below
10 ppm level (see, e.g.: Burfield, D. R.; Lee, K. H.; Smithers, R. H. J .
Org. Chem. 1977, 42, 3060); this amount corresponds, however, to the
same order of molar concentration as that of the compounds studied.
(12) Rosenblum, M.; Santer, J . O.; Glenn, H. W. J . Am. Chem. Soc.
1963, 85, 1450.
Electr och em istr y. Compounds 3-5 and related
monosubstitued ferrocenes were studied by voltammetry
with a rotating disk platinum electrode (RDE) and by
cyclic voltammetry (CV) with a stationary platinum
electrode. There are several redox processes involved
(Figure 5; Table 4) which, in analogy to the known
electrochemical behavior of monosubstituted ferrocenes9

1′-(Diphenylphosphino)ferrocenecarboxylic Acid
Organometallics, Vol. 15, No. 2, 1996 547
Ta ble 4. Electr och em ica l Beh a vior of 3-5 a n d Rela ted Der iva tivesa
cyclic voltammetry
A2
voltammetry on RDE
A1
B
C
A1
A2
B
compd
FcH
FcCOOH
FcP(O)Ph2
Epa
Epc
Epa
Epc
Epc
Epa
E1/2
E1/2
E1/2
0.47
0.65
0.39
0.60
0.44
0.63
-0.97
0.33
-0.81
0.64
0.65
0.98
0.98
0.88
0.59
0.60
0.90
0.90
0.80
0.61
0.63
FcPPh2
0.52
0.78
0.47
0.69
0.49
0.75
3
4
5
-0.99
-0.75
0.39
0.54
-0.80
-0.66
0.93
0.78
0.68
0.75
a
All values in V; see text for definition of processes A-C; potentials referred to SCE.
ipa(A1) is constant. It appears that the process C is the
ferro/ferri redox system of the ferrocene derivative
bearing the reduced carboxyl group. The difference
between the reduction potential of the process B and
the oxidation potential of the process C is nearly
constant for all compounds having the carboxyl group
[Epa(C) - Epc(B) is 1.30 V for FcCOOH and 1.29 V for
both 3 and 4], and therefore, it is likely that analogous
products are formed in this process. The only difference
is in the absolute potential values which are shifted in
accordance with the electronic effects of the substituents
(Figure 6).
F igu r e 6. Trends in potentials of processes A-C.
In summary, the electrochemical results reflect the
well-known phenomenon that, in substituted ferrocenes,
the changes of the electron density located at the
substituents are easily mediated through the fully
conjugated π-electron system of the ferrocene skeleton.
Such coupling of the redox centers is of crucial impor-
tance in the recent field of supramolecular electrochem-
istry.14,15
Sch em e 2
Exp er im en ta l Section
Gen er a l Con sid er a tion s. NMR spectra: 1H (200.06
MHz), 31P{1H} (80.98 MHz) on a Varian Unity 200
instrument; 2D (1H observed at 499.843 MHz) and APT
(13C observed at 125.697 MHz) experiments on a Varian
Unity 500 instrument; the standards were internal TMS
by the electron-withdrawing effect of the substituents.
Diphenylphosphinyl and carboxyl group are strong
electron acceptors which diminish the electron density
at the ferrocene skeleton, thus making its oxidation
more difficult. The lower value of the shift of the
potential for FcPPh2 is explainable by the weaker
electron-accepting properties of the PPh2 group (-I but
+M substituent). For disubstituted ferrocenes 3-5, the
redox potentials of process A are shifted vs ferrocene
by +310, +490, and +310 mV, respectively, thus point-
ing to the additivity of contributions of the substituents.
The shifts are, however, by about 20% higher than the
sum of the voltammetrically determined contributions
of the monosubstituted derivatives, which may be
explained by the absence of the “electron-buffering”
effect of the unsubstituted Cp ring. Nevertheless, the
1
for H, the solvent signal for 13C (C[2H]Cl3, δ 77.0), and
external 85% aqueous H3PO4 for 31P. All spectra were
recorded in C[2H]Cl3 at room temperature (2D experi-
ments at a probe temperature of 30 °C). Mass spectra
were measured on a J EOL D-100 instrument (EI, 80
eV). Exact m/z values were obtained by the peak-match
method with perfluorokerosene as the internal stan-
dard. IR spectra were measured in Nujol mulls between
KBr windows in the range of 400-4000 cm-1 on an FT
IR ATI Mattson Genesis instrument. UV/vis spectra
were recorded in DME solutions on a Specord M40 (Carl
Zeiss, J ena, Germany) instrument. The mp’s are uncor-
rected. Electrochemical measurements were carried out
at room temperature in an argon atmosphere with (3-
8) × 10-4 M acetonitrile solutions containig 0.05 M Bu4-
NPF6 as the supporting electrolyte. The standard three-
electron system consisted of a stationary platinum disk
electrode of 2 mm diameter, an auxiliary platinum wire
electrode, and a saturated calomel electrode (to which
all potentials are referenced) separated from the solu-
tion by a double salt bridge. In RDE measurements,
1
redox potentials of process A [from CV as /2(Epa + Epc)]
display linear corelation with Hammett’s σp constants13
of the substituents.
For the compounds containing carboxyl two further
processes were observed. Process B is, most likely, the
irreversible reduction of the carboxylic group.
Process C is the reversible oxidation of the product
generated by the process B. After the electrolysis at a
negative potential (-1.2 V) the oxidation peak on CV
gains in intensity but, simultaneously, the anodic peak
of the process A1 diminishes such as the sum ipa(C) +
(14) Texeira, M. G.; Roffia, S.; Bignozzi, C. A.; Paradisi, C.; Paolucci,
F. J . Electroanal. Chem. 1993, 345, 243.
(13) Exner, O. Correlations in Organic Chemistry (in Czech); SNTL
Alfa Publishers: Prague, 1981.
(15) Medina, J . C.; Goodnow, T. T.; Rojas, M. T.; Atwood, J . T.; Lynn,
B. C.; Kaifer, A. E.; Gokel, G. W. J . Am. Chem. Soc. 1992, 114, 10583.

548 Organometallics, Vol. 15, No. 2, 1996
Podlaha et al.
Ta ble 5. Cr ysta llogr a p h ic Da ta for 3-5
the platinum disk electrode rotated at 500 rpm.
A
Multipurpose Polarograph GWP 673 (ZWG, Berlin, East
Germany) linked to an X-Y recorder served for the
registration of voltammograms as well as the poten-
tiostat for electrolyses. The potential was scanned at
500 and 250 mV min-1 for RDE and CV measurements,
respectively.
(a) Crystal Parameters
formula
MW
cryst system
space group
a, Å
C23H19FeO2P
414.05
C23H19FeO3P
430.05
C24H21FeO2P
428.06
monoclinic
P21/c (No. 14)
8.4113(8)
triclinic
P1h (No. 2)
5.9189(6)
13.814(1)
23.234(2)
86.852(6)
82.980(8)
77.640(7)
1920.3(3)
4
monoclinic
P21/c (No. 14)
12.738(1)
12.4813(8)
12.388(1)
b, Å
c, Å
17.2130(2)
14.1817(9)
1′-(Diph en ylph osph in o)fer r ocen ecar boxylic Acid
(3). In a dry argon atmosphere, phenyllithium (28 mL
of 1.8 mol dm-3 solution in 70:30 v/v cyclohexane/diethyl
ether, 50.4 mmol) was added with cooling (solid carbon
dioxide/i-PrOH bath) to a stirred precooled solution of
17,8 (7.5 g, 25.7 mmol) in diethyl ether (400 mL). After
being stirred for 30 min with cooling and then for 40
min without cooling, the reaction mixture was cooled
again, poured onto powdered solid carbon dioxide (110
g, excess), and allowed to stand overnight. The subse-
quent operations were carried out in air. The reaction
mixture was extracted by 5% aqeous sodium hydroxide
(250 mL in four portions), and the combined extracts
were acidified toward Congo Red with ice-cold 6 M
aqueous HCl. The precipitated crude product was
washed with ice-cold 1% aqueous HCl and dissolved in
chloroform (350 mL). The solution was dried with
magnesium sulfate and evaporated to dryness at re-
duced pressure. After crystallization from 50% v/v
aqueous acetic acid by slow cooling of hot concentrated
solution to 0 °C, washing with petroleum ether presatu-
rated with acetic acid and then with petroleum ether,
and drying over sodium hydroxide, pure 3 (7.6 g, 71%)
was obtained as orange plates, mp 164.5-166 °C. Anal.
Calcd for C23H19FeO2P: C, 66.69; H, 4.62. Found: C,
66.6; H, 4.5. IR in Nujol [cm-1 (relative intensity), as-
signment]: 497 (s), 823 (m), 1090 (m), Fc; 1025 (m), 1153
(s), Ph; 1666 (s), COOH. MS (direct inlet, 170-180 °C;
m/z, relative intensity, elemental composition, MW
calcd/found): 414 (M+•, 100%, C23H19FeO2P, 414.0472/
414.0484); 386 ([M - CO]+•, 7%, C22H19FeOP, 386.0523/
386.0514); 370 ([M - CO2]+•, 33%, C22H19FeP, 370.0574/
370.0520); 321 (18%, C17H14FeOP, 321.0132/321.0102);
293 (28%, C16H14FeP, 293.0182/293.0174). UV/vis [λmax
(nm), ꢀ (m2 mol-1)]: 443 (23).
R, deg
â, deg
96.994(8)
95.360(6)
γ, deg
V, Å
Z
1954.8(3)
4
2044.3(2)
4
1.391
d(calcd), g/cm3
d(measd),
1.433
1.43
1.462
1.45
g/cm3
a
µ(Mo, KR),
0.884
0.875
0.832
mm-1
temp, K
cryst size, mm
296(2)
296(2)
296(2)
0.07 × 0.18 ×
0.08 × 0.21 ×
0.20 × 0.32 ×
0.29
0.25
0.70
color
orange
rusty red
orange
(b) Data Collection
scan limits (θ),
deg
data collcd
h
k
l
reflcns collcd
reflcns unique
reflcns obsd
(Fo g 4σ(Fo))
std reflcns
var in stds, %
0-25
0-24
0-25
-6, 7
-16, 16
0, 28
-14, 14
-14, 0
-14, 14
6119
-9, 9
0, 20
0, 16
3864
3582
2762
6720
6720
3059
3725
2021
3 after every 1 h
2
4
2
(c) Refinement
R(F), %b
R(wF), %c
GOFd
∆/σ(max)
∆(F), e/Å3
No/Nv
4.07
3.06
3.24
7.99
1.038
-0.001
-0.43; 0.23
3582/262
7.92
6.59
1.110
0.001
(0.28
6701/495
1.050
0.001
-0.22; 0.24
3059/257
a
b
Flotation in aqueous ZnBr2. R(F) ) ∑(|Fo| - |Fc|)/∑|Fo| for
observed reflections. c R(wF) ) ∑(w1/2(|Fo| - |Fc|)/w1/2|Fo|); w )
[σ2(Fo2) + w1P2 + w2P]-1; P ) [max(Fo2) + 2Fc2]/3; w1 (w2) ) 0.0337
d
(0.87) for 3, 0.0364 (0.10) for 4, and 0.0453 (0.60) for 5. GOF )
(∑(w||Fo| - |Fc||)/(No - Nv))1/2
.
in boiling methanol (30 mL) and crystallized on addition
of water (30 mL) to the hot solution and slow cooling.
The product was washed with petroleum ether presatu-
rated with methanol and then with petroleum ether and
dried in air to give 5 (0.30 g, 71%) as orange flakes, mp
118.5-119.5 °C. Anal. Calcd for C24H21FeO2P: C,
67.31; H, 4.94. Found: C, 67.4; H, 4.9. IR (as above):
490 (m), 830 (s), 1090 (m), Fc; 1026 (m), 1145 (s), Ph;
1′-(Dip h en ylp h osp h in oyl)fer r ocen eca r b oxylic
Acid (4). A solution of 30% aqueous hydrogen peroxide
(2 mL, excess) was added to a stirred solution of 3 (0.20
g, 0.48 mmol) in acetone (15 mL). After 1 h at room
temperature, a further 1 mL of the H2O2 solution was
added and the mixture was refluxed for 90 min. The
solution was evaporated at reduced pressure, the prod-
uct was extracted into chloroform, and the extract was
evaporated and crystallized as for 3 to give 4 (90 mg,
43%) as rusty red prismatic crystals, dec 195 °C without
melting. Anal. Calcd for C23H19FeO3P: C, 64.21; H,
4.45. Found: C, 64.1; H, 4.5. IR (as above): 491 (m),
834 (s), 1099 (m), Fc; 1025 (s), 1150 (m), Ph; 1110-1200
(s), PdO; 1696-1703 (s), COOH. MS not measured
(decomposition on attempted direct inlet). UV/vis (as
above): 442 (saturated solution).
1710 (s), CdO. MS (direct inlet at 120 °C): 428 (M+•
,
100%, C24H21FeO2P, 428.0628/428.0638); 413 ([M -
CH3]+, 25%, C23H18FeO2P, 413.0394/413.0383); 397 ([M
- OCH3]+, 2%); 351 ([M - C6H5]+, 7%, C18H16FeO2P,
351.0237/351.0232); 321 (50%, C17H14FeOP, 321.0132/
321.0131). UV/vis: 445 (25).
X-r a y Str u ctu r e Deter m in a tion s of 3-5. An
orange, platelike crystal of 3 was grown from 50%
aqueous acetic acid by slow cooling. A rusty red
prismatic crystal of 4 was selected from the preparative
batch. An orange prismatic crystal of 5 was grown from
methanol presaturated with heptane by slow evapora-
tion. The crystals were mounted on glass fibers with
epoxy cement. All measurements were carried out on
an Enraf Nonius CAD4 diffractometer at 23 °C using
graphite-monochromated Mo KR radiation (λ ) 0.710 73
Å). Data were collected by ω-2θ scans. Absorption was
neglected. Further crystallographic details are sum-
Meth yl 1′-(Dip h en ylp h osp h in o)fer r ocen eca r box-
yla te (5). A solution of diazomethane in diethyl ether
(approximately 2-fold excess) was added to a solution
of 3 (0.41 g, 0.99 mmol) in diethyl ether (20 mL), and
the mixture was stirred at room temperature for 30 min
and then refluxed for further 30 min. After evaporation
at reduced pressure, the crude product was dissolved

1′-(Diphenylphosphino)ferrocenecarboxylic Acid
Organometallics, Vol. 15, No. 2, 1996 549
Ta ble 6. F r a ction a l Atom ic Coor d in a tes (×104) a n d Equ iva len t Isotr op ic Disp la cem en t P a r a m eter sa (Å2 ×
103) for 3
x
y
z
U(eq)
x
y
z
U(eq)
Fe(1)
P(1)
O(11)
O(12)
368(1)
-1142(2)
-1751(6)
2060(6)
145(7)
1841(1)
93(1)
1046(1)
2011(1)
258(1)
39(1)
43(1)
53(1)
56(1)
38(1)
43(1)
51(1)
52(1)
45(1)
40(1)
48(1)
54(1)
58(1)
49(1)
43(1)
43(1)
62(2)
82(2)
82(2)
79(2)
65(2)
39(1)
50(1)
60(1)
68(2)
77(2)
58(1)
39(1)
P(2)
O(21)
O(22)
962(2)
2788(6)
5858(6)
3119(7)
2853(8)
4849(9)
6368(8)
5332(8)
2858(8)
3854(8)
2293(10)
314(9)
4906(1)
712(3)
2989(1)
4742(1)
5007(1)
3181(2)
3160(2)
3337(2)
3467(2)
3373(2)
4700(2)
4763(2)
4605(2)
4446(2)
4498(2)
4812(2)
3273(2)
3766(2)
4016(2)
3778(3)
3286(3)
3036(2)
2244(2)
1997(2)
1426(2)
1108(2)
1338(2)
1903(2)
-92(26)
5101(17)
42(1)
55(1)
56(1)
36(1)
43(1)
52(1)
52(1)
44(1)
40(1)
46(1)
57(1)
55(1)
47(1)
43(1)
47(1)
62(2)
83(2)
83(2)
80(2)
63(2)
40(1)
49(1)
58(1)
67(2)
76(2)
58(1)
113(23)
33(13)
4285(3)
3803(3)
1164(3)
2161(3)
2794(4)
2214(4)
1208(4)
2590(3)
2227(4)
1191(4)
892(4)
1759(4)
3629(4)
-917(3)
-1311(4)
-2036(5)
-2386(5)
-2014(5)
-1284(4)
-19(3)
1202(3)
3834(3)
2837(3)
2200(4)
2786(4)
3792(4)
2413(3)
3242(4)
4102(4)
3812(4)
2776(4)
1368(4)
5914(3)
6319(4)
7040(4)
7381(5)
7010(4)
6288(4)
5018(3)
4593(4)
4675(4)
5206(4)
5626(5)
5534(4)
4537(54)
592(33)
-8(1)
C(201)
C(202)
C(203)
C(204)
C(205)
C(206)
C(207)
C(208)
C(209)
C(210)
C(211)
C(212)
C(213)
C(214)
C(215)
C(216)
C(217)
C(218)
C(219)
C(220)
C(221)
C(222)
C(223)
H(91)
C(101)
C(102)
C(103)
C(104)
C(105)
C(106)
C(107)
C(108)
C(109)
C(110)
C(111)
C(112)
C(113)
C(114)
C(115)
C(116)
C(117)
C(118)
C(119)
C(120)
C(121)
C(122)
C(123)
Fe(2)
1817(2)
1838(2)
1666(2)
1536(2)
1627(2)
305(2)
-1141(8)
393(9)
2628(9)
2498(8)
-31(8)
-2083(9)
-1431(9)
978(10)
1861(9)
15(9)
1201(8)
919(11)
2659(13)
4653(12)
4954(10)
3213(9)
-821(7)
690(8)
502(2)
556(2)
399(2)
237(2)
649(8)
3826(8)
1996(8)
857(9)
191(2)
1725(2)
1233(2)
983(2)
1602(13)
3492(13)
4661(11)
3906(10)
1906(8)
4096(8)
4699(9)
3097(11)
931(11)
336(9)
1216(3)
1711(3)
1960(2)
2758(2)
3005(2)
3576(2)
3897(2)
3660(2)
3096(2)
3954(1)
413(4)
311(4)
-214(4)
-626(5)
-538(4)
3158(1)
786(9)
-598(10)
-2114(10)
-2225(9)
3256(1)
1918(99)
6215(68)
H(92)
a
U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.
Ta ble 7. F r a ction a l Atom ic Coor d in a tes (×104) a n d
Equ iva len t Isotr op ic Disp la cem en t P a r a m eter sa
(Å2 × 103) for 4
Ta ble 8. F r a ction a l Atom ic Coor d in a tes (×104) a n d
Equ iva len t Isotr op ic Disp la cem en t P a r a m eter sa
(Å2 × 103) for 5
x
y
z
U(eq)
x
y
z
U(eq)
Fe
P
O(1)
O(2)
9035(1)
6775(1)
12254(2)
11559(2)
7275(2)
7465(2)
8008(2)
8486(2)
8262(3)
7630(2)
10615(2)
10142(2)
9657(2)
9820(2)
10406(2)
11169(2)
6668(2)
7290(2)
7237(3)
6584(3)
5967(3)
6010(2)
5448(2)
4967(3)
3935(3)
3399(3)
3867(3)
4887(2)
11835(27)
2672(1)
1343(1)
3495(2)
4273(2)
642(2)
2578(2)
3138(3)
4044(3)
4062(3)
3159(3)
2668(3)
1753(2)
1150(3)
1675(3)
2614(3)
3514(2)
731(2)
-163(2)
-642(3)
-247(3)
625(3)
1120(3)
1688(2)
1063(3)
1295(4)
2132(4)
2741(3)
2536(3)
4706(27)
8687(1)
7882(1)
7131(2)
8758(2)
7119(2)
8164(2)
7395(3)
7918(3)
8991(3)
9160(3)
8627(2)
8077(3)
8835(3)
9841(3)
9722(2)
8086(3)
9175(2)
9473(2)
10470(3)
11167(3)
10880(3)
9897(3)
7300(3)
6455(3)
6000(3)
6398(4)
7227(4)
7676(3)
8451(27)
37(1)
38(1)
60(1)
64(1)
51(1)
37(1)
44(1)
53(1)
56(1)
47(1)
39(1)
46(1)
52(1)
57(1)
49(1)
41(1)
38(1)
45(1)
55(1)
55(1)
56(1)
47(1)
45(1)
63(1)
82(1)
86(2)
75(1)
58(1)
48(11)
Fe
P
O(1)
O(2)
7101(1)
3785(1)
10636(2)
8421(2)
5199(3)
5043(4)
6375(5)
7349(4)
6649(3)
8683(6)
7236(3)
7003(4)
8259(4)
9308(4)
9373(3)
4981(3)
5495(3)
6460(3)
6893(3)
6371(3)
5425(3)
2500(2)
2557(3)
1462(3)
311(3)
3260(1)
2094(1)
4658(2)
5259(1)
2708(1)
3532(2)
3816(2)
3190(2)
2505(2)
3956(2)
3913(2)
3125(2)
2688(2)
3191(2)
4643(2)
1216(1)
1067(1)
433(2)
8527(1)
8342(1)
8911(1)
8296(1)
9029(2)
9097(2)
9676(2)
9968(2)
9576(2)
7944(2)
7340(2)
7090(2)
7528(2)
8057(2)
8436(2)
8206(2)
7322(2)
7180(2)
7911(2)
8785(2)
8934(2)
9253(2)
10150(2)
10775(2)
10508(2)
9621(2)
8994(2)
8783(3)
9439(30)
8597(29)
8600(27)
49(1)
43(1)
80(1)
72(1)
45(1)
63(1)
82(1)
81(1)
57(1)
52(1)
55(1)
70(1)
79(1)
70(1)
57(1)
41(1)
51(1)
61(1)
59(1)
54(1)
48(1)
41(1)
53(1)
62(1)
65(1)
66(1)
56(1)
102(2)
123
O(3)
C(01)
C(02)
C(03)
C(04)
C(05)
C(06)
C(07)
C(08)
C(09)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
H(24A)
H(24B)
H(24C)
C(01)
C(02)
C(03)
C(04)
C(05)
C(06)
C(07)
C(08)
C(09)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
H(99)
-65(2)
65(1)
700(1)
1785(1)
2098(2)
1880(2)
1343(2)
1020(2)
1237(2)
5964(2)
5914(23)
6345(26)
6141(25)
239(3)
1325(3)
8924(7)
9073(48)
8256(51)
10088(49)
123
123
a
U(eq) is defined as one-third of the trace of the orthogonalized
Uij tensor.
a
U(eq) is defined as one-third of the trace of the orthogonalized
Uij tensor.
marized in Table 5. The structures were solved by
combination of heavy atom and direct methods (SHELXS-
8616 ) and refined by a full-matrix least-squares proce-
dure based on F2 (SHELXL9317). Hydrogen atoms of
cyclopentadienyl and phenyl groups were fixed in
calculated positions [C-H ) 0.96 Å, Uiso(H) ) 1.2Uiso(C)];
those of carboxyl and methyl groups found from the
difference maps were refined isotropically. The final
(17) Sheldrick, G. M. SHELXL93: A computer program for crystal
structure refinement; University of Go¨ttingen, Germany, 1993.
(16) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.

550 Organometallics, Vol. 15, No. 2, 1996
Podlaha et al.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 3-5, including tables of H coordinates and thermal
parameters, anisotropic thermal parameters of non-H atoms,
complete bond distances and angles, and least-squares planes
and atomic deviations therefrom and unit cell diagrams,
Cambridge Crystallographic Database search tables including
GSTAT query and statistics, and text providing detailed
discussion of NMR spectra (22 pages). Ordering information
is given on any current masthead page.
difference Fourier map had no peaks of chemical
significance. Scattering factors were those implemented
in the SHELX programs. Positional parameters are
given in Tables 6-8.
Ack n ow led gm en t. Financial support for this work
was given by the Grant Agency of the Czech Republic
through Grant Nos. 203/93/0244, 203/93/2463, and 203/
93/0154.
OM950528Q