Synthesis, transition metal chemistry and catalytic reactions of ferrocenylbis(phosphonite), [Fe{C5H4P(OC6H 3(OMe-o)(C3H5-p))2}2]

Article abstract of DOI:10.1039/c3dt50995h

The new metalloligand ferrocenylbis(phosphonite), [Fe(C₅H ₄PR₂)₂ (R = OC₆H₃(OMe-o) (C₃H₅-p))], (2), is synthesized by the reaction of bis(dichlorophosphino)ferrocene Fe(C₅H₄PCl ₂)₂ (1) with 4-allyl-2-methoxyphenol. The reactions of 2 with H₂O₂ and elemental sulfur or selenium afforded bischalcogenides, [Fe{C₅H₄P(E)(OC₆H ₃(OMe-o)(C₃H₅-p))₂}₂] (3, E = O; 4, E = S; 5, E = Se), in good yield. The bis(phosphonite) reacts with group 6 metal carbonyls and group 10 metal dichloride precursors to produce the chelate complexes [{M(CO)₄}Fe{C₅H₄P(OC ₆H₃(OMe-o)(C₃H₅-p)) ₂}₂}] (6, M = Mo; 7, M = W) and [(MCl₂) Fe{C₅H₄P(OC₆H₃(OMe-o)(C ₃H₅-p))₂}₂] (8, M = Pd; 9, M = Pt). The palladium(ii) complex [(PdCl₂)Fe{C₅H ₄P(OC₆H₃(OMe-o)(C₃H ₅-p))₂}₂] (8) is an efficient catalyst for the Suzuki-Miyaura cross-coupling reactions (TON up to 1.5 × 10⁵). The reaction of 2 with one equivalent of [RuCl₂(η⁶-p- cymene)]₂ yielded the binuclear complex [{Ru₂Cl ₄(η⁶-p-cymene)₂}Fe{C₅H ₄P(OC₆H₃(OMe-o)(C₃H ₅-p))₂}₂] (12) in good yield. Treatment of 2 with copper chloride in a 1:1 or 1:2 molar ratio resulted in the formation of a binuclear complex, [{(CuCl)Fe{C₅H₄P(OC₆H ₃(OMe-o)(C₃H₅-p))₂} ₂}₂] (13), whereas a similar reaction of 2 with CuBr and CuI in a 1:2 or 1:2.5 molar ratio yielded the novel butterfly-like deca-nuclear complexes [Cu₅(μ-X)₅{Fe{C₅H ₄P(OC₆H₃(OMe-o)(C₃H ₅-p))₂}₂}₂]₂ (14, X = Br; 15, X = I). The reaction of 2 with two equivalents of [AuCl(SMe₂)] afforded the digold complex [(AuCl)₂Fe{C₅H ₄P(OC₆H₃(OMe-o)(C₃H ₅-p))₂}₂] (16), with the ligand exhibiting bridged-bidentate mode of coordination. Additionally, some complexes were studied by cyclic voltammetry. The crystal structures of complexes 8, 9, 12, 15 and 16 were determined using X-ray diffraction studies.

Full text of DOI:10.1039/c3dt50995h

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Synthesis, transition metal chemistry and catalytic
reactions of ferrocenylbis(phosphonite),
Cite this: Dalton Trans., 2013, 42, 11695
[Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]†
Sowmya Rao,a Joel T. Magueb and Maravanji S. Balakrishna*a
The new metalloligand ferrocenylbis(phosphonite), [Fe(C5H4PR2)2 (R = OC6H3(OMe-o)(C3H5-p))], (2), is
synthesized by the reaction of bis(dichlorophosphino)ferrocene Fe(C5H4PCl2)2 (1) with 4-allyl-2-methoxy-
phenol. The reactions of 2 with H2O2 and elemental sulfur or selenium afforded bischalcogenides,
[Fe{C5H4P(E)(OC6H3(OMe-o)(C3H5-p))2}2] (3, E = O; 4, E = S; 5, E = Se), in good yield. The bis(phosphonite)
reacts with group 6 metal carbonyls and group 10 metal dichloride precursors to produce the chelate
complexes [{M(CO)4}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}] (6, M = Mo; 7, M = W) and [(MCl2)Fe{C5H4P-
(OC6H3(OMe-o)(C3H5-p))2}2] (8, M = Pd; 9, M = Pt). The palladium(II) complex [(PdCl2)Fe{C5H4P-
(OC6H3(OMe-o)(C3H5-p))2}2] (8) is an efficient catalyst for the Suzuki–Miyaura cross-coupling reactions
(TON up to 1.5 × 105). The reaction of 2 with one equivalent of [RuCl2(η6-p-cymene)]2 yielded the binuc-
lear complex [{Ru2Cl4(η6-p-cymene)2}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (12) in good yield. Treatment
of 2 with copper chloride in a 1 : 1 or 1 : 2 molar ratio resulted in the formation of a binuclear complex,
[{(CuCl)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2] (13), whereas a similar reaction of 2 with CuBr and CuI in
a 1 : 2 or 1 : 2.5 molar ratio yielded the novel butterfly-like deca-nuclear complexes [Cu5(µ-X)5{Fe{C5H4P-
(OC6H3(OMe-o)(C3H5-p))2}2}2]2 (14, X = Br; 15, X = I). The reaction of 2 with two equivalents of
[AuCl(SMe2)] afforded the digold complex [(AuCl)2Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (16), with the
ligand exhibiting bridged-bidentate mode of coordination. Additionally, some complexes were studied
by cyclic voltammetry. The crystal structures of complexes 8, 9, 12, 15 and 16 were determined using
X-ray diffraction studies.
Received 16th April 2013,
Accepted 18th June 2013
DOI: 10.1039/c3dt50995h
www.rsc.org/dalton
also chiral ligands,11 which have proven to be good catalysts
for many organic transformations.
Introduction
The synthesis of new ferrocenylphosphines which can be steri-
In recent years, molecular architecture and self-assembly of
cally and/or electronically tuned either at the ferrocenyl back- coordination polymers based on ferrocenyl scaffolds have
bone or at the phosphorus atoms is still of fundamental and attracted the attention of inorganic chemists.12 The coordi-
industrial interest.1,2 Especially electron rich or bulky palla- nation polymers based on self-assembly of Cu(I) ions with a
dium complexes of ferrocenyl phosphines differing by the variety of phosphorus, nitrogen, oxygen and sulfur donor
number and type of donor groups and also by the substitution ligands are well established.12 However, there are only a few
patterns are of great interest due to their exceptional catalytic reports on the chemistry of supramolecular compounds con-
properties.3–7 This has led to the development of numerous taining olefins as donor sites which have otherwise been suc-
ferrocenylphosphines, for example, simple monophosphines,8 cessfully applied in biochemistry, copper catalysis and also to
diphosphines (1,1′-, 1,2- or 1,3-disubstitution)9 or polyphos- construct metal–organic frameworks (MOFs).13 The first stable
phines10 with different steric and electronic properties and Cu(I)–olefin complex was reported in 1983 by Thompson and
co-workers.14 Generally, halogen atoms act as bridging ligands
in Cu(I)–olefin coordination polymers, whereas olefins act as
spacers.15 The ligands with the P–Fc–P framework exhibit both
bridging and chelating modes of coordination depending
upon the metal precursors, stoichiometry and the reaction
conditions. In this contribution, we report the synthesis of a
aPhosphorus Laboratory, Department of Chemistry, Indian Institute of Technology
Bombay, Powai, Mumbai 400 076, India. E-mail: krishna@chem.iitb.ac.in;
Fax: +91 22 2576 7152/2572 3480; Tel: +91 22 2576 7181
bDepartment of Chemistry, Tulane University, New Orleans, Louisiana 70118, USA
†CCDC 933867–933871. For crystallographic data in CIF or other electronic
new ferrocenylbis(phosphonite) with allylic substituents and
its transition metal chemistry and catalytic application in
format see DOI: 10.1039/c3dt50995h
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Suzuki–Miyaura carbon–carbon cross coupling reactions. The which is eventually utilized in making PvSe bonds. The mass
X-ray structures of several complexes including that of a novel spectrum of 3 shows a peak due to the cation at m/z 931.2 (M + 1).
decanuclear copper(I) complex and the electrochemical behav- The 1H assignments and microanalysis data are found to be
ior of a few compounds are also described.
consistent with the proposed structures in all cases.
Reactions with transition metal derivatives
Results and discussion
Synthesis of transition metal complexes 6–11. Ferrocenylbis-
(phosphonite) is a potential bidentate ligand and it would be
interesting to explore its coordination behavior with various
transition metal derivatives. Treatment of 2 with one equi-
valent of [M(pip)2(CO)4] (M = Mo, W) in dichloromethane
afforded chelate complexes cis-[M(PFcP)(CO)4] (6, M = Mo; 7,
M = W) (Scheme 2) in moderate yields. The 31P NMR spectra of
complexes 6 and 7 show single resonances at 182.4 ppm and
157.1 ppm, respectively, with that of the tungsten complex
Synthesis of [Fe{η5-C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (2) and
its chalcogenides
Bis(dichlorophosphino)ferrocene is an excellent precursor for
the formation of P–C, P–N and P–O bonds via nucleophilic
substitution reactions at phosphorus centers. Recently, we
reported the synthesis of a thioether-functionalized ferrocenyl-
bis(phosphonite),16 Fe(C5H4PR)2 (R = –OC10H6–(µ-S)C10H6O–)
by the reaction of thiobis(2,2′-naphthol) with Fe(C5H4PCl2)2. In
the present study, the ferrocenylbis(phosphonite), [Fe{C5H4P-
(OC6H3(OMe-o)(C3H5-p))2}2] (2), was synthesized by the reac-
tion of Fe(C5H4PCl2)2 with eugenol (HOC6H3(OMe-o)(C3H5-p))
in the presence of triethylamine at 0 °C as a pale yellow crystal-
line solid in good yield, as shown in Scheme 1. Compound 2
(here onwards referred to as PFcP) is a moderately air stable
solid having the smell of eugenol and soluble in most organic
solvents. The 31P NMR spectrum of compound 2 exhibits a
single resonance at 168.8 ppm and the 1H NMR spectrum
shows two broad singlets at 4.54 and 4.69 ppm for the protons
of the ferrocenyl moieties. In order to assess the reactivity of
the phosphorus(III) centers and also to get an insight into their
σ-donor and π-acceptor properties, oxidation reactions were
carried out with H2O2 and elemental sulphur or selenium. The
ferrocenylbis(phosphonite) 2 reacts smoothly with H2O2 in
THF at 0 °C and with elemental sulfur or selenium in toluene
under refluxing conditions to afford the corresponding
bis(chalcogenides), [Fe{C5H4P(O)(OC6H3(OMe-o)(C3H5-p))2}2] (3),
[Fe{C5H4P(S)(OC6H3(OMe-o)(C3H5-p))2}2] (4) and [Fe{C5H4P(Se)-
(OC6H3(OMe-o)(C3H5-p))2}2] (5) (Scheme 1), in good yield. The
31P NMR spectra of bis(chalcogenides) 3–5 consist of single
resonances at 20.2 ppm, 83.9 ppm and 88.9 ppm, respectively,
with that for the bis(selenide) showing characteristic 77Se satel-
1
showing JWP coupling of 201 Hz. The IR spectra of complexes
6 and 7 show four νCO bands in the region (1900–2035 cm−1
)
as expected for a {M(CO)4} moiety with C2v symmetry.17,18 The
reaction of 2 with M(COD)Cl2 (M = Pd, Pt) in 1 : 1 molar pro-
portions afforded the corresponding chelate complexes,
[(PdCl2){Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}] (8) and [(PtCl2)-
{Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}] (9) in good yield. The
31P NMR spectra of 8 and 9 show single resonances at 117.7
and 90.6 ppm, respectively, which are considerably shielded
1
compared to that of the free ligand. The high value of JPtP
coupling of 4969 Hz in complex 9 is consistent with the
observed trend in the literature for cis-orientation of the phos-
phorus atoms around the platinum centre.19 In the 1H NMR
spectra of 8 and 9, two broad singlets are observed in the
region 4.36–4.95 ppm for the ferrocenyl protons. The struc-
tures of 8 and 9 were confirmed by single-crystal X-ray diffrac-
tion studies.
Treatment of [(η5-C5H5)Ru(PPh3)2Cl] with 2 in a 1 : 1 molar
ratio in dichloromethane afforded the mononuclear complex
[(η5-C5H5)RuCl{Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}]
(10)
(Scheme 2) in good yield. The 31P NMR spectrum of 10 con-
sists of a single resonance at 183.7 ppm which is considerably
deshielded compared to that of the free ligand with a
1
lites with a JPSe coupling of 911 Hz. The large coupling con-
stant indicates the larger s-character of the phosphorus lone
1
pairs. Usually the magnitude of JPSe increases with an
increase in electron withdrawing ability of the phosphorus
substituents and vice versa. The electron withdrawing groups
leave slightly less ‘p’ and more ‘s’ character in the lone pair
Scheme 1 (i) 4 ROH, Et3N, Et2O, −20 °C, 8 h, (i) H2O2, THF, 0 °C, 8 h, (ii) S8/Se8,
Toluene 110 °C, 24 h.
Scheme 2 (i) [M(CO)4(pip)2], (ii) [M(COD)Cl2], (iii) [(η5-C5H5)Ru(PPh3)2Cl], (iv)
0.5 [Pd(η3-C3H5)Cl]2, AgOTf, CH3CN.
11696 | Dalton Trans., 2013, 42, 11695–11708
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coordination shift of 14.9 ppm. The 1H NMR spectrum showed complex 13 is moderately air stable and sparingly soluble in
a single resonance at 4.14 ppm for the cyclopentadienyl most of the organic solvents. The 31P NMR spectrum of 13
protons. The reaction of [Pd(η3-C3H5)Cl]2 with two equivalents shows a single resonance at 134.4 ppm indicating that both
of 2 followed by one equivalent of AgOTf in dichloromethane the phosphorus atoms are equivalent. The product formation
at room temperature resulted in the formation of a cationic was found to be independent of stoichiometry of the reactants
complex [Pd(η3-C3H5)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]OTf as both 1 : 1 and 1 : 2 reactions led to the formation of the
(11). The 31P NMR spectrum of complex 11 shows a single same product.
1
resonance at 159.6 ppm and the H NMR spectrum shows the
Similar reactions of 2 with two equivalents of CuX in a
presence of allylic protons. The mass spectrum of 11 shows a dichloromethane–acetonitrile mixture afforded yellow crystal-
peak due to the cation at m/z 1044.5 (M+ − OTf).
line products of the type [Cu5(µ-X)5{Fe{C5H4P(OC6H3(OMe-o)-
Synthesis of transition metal complexes 12–16. An equi- (C3H5-p))2}2}2]2 (14, X = Br; 15, X = I). Surprisingly, the structure
molar reaction between 2 and [Ru(η6-p-cymene)Cl2]2 in dichloro- determined by single crystal X-ray diffraction of 15 does not
methane at room temperature yielded a dinuclear complex correspond to the expected compounds with composition
[Ru2Cl4(η6-p-cymene)2{Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}] [Cu2(µ-X)2(NCCH3)2(L)] typical of bisphosphine complexes of
(12) as described in Scheme 3. The 31P NMR spectrum of the type [Cu2(μ-I)2(NCCH3)2(μ-PNP)]22 but found to be decanu-
complex 12 shows a single resonance at 150.8 ppm. The clear complexes of the type [{Cu5(µ-X)5}{Fe{C5H4P(OC6H3(OMe-o)-
1H NMR spectrum of 12 shows two doublets at 5.30 and (C3H5-p))2}2}2]2 as shown in Scheme 3. Similar reactions of 2
3
5.04 ppm with a JHH coupling of 5.6 Hz for the aromatic with 2.5 equivalents of CuX (X = Br, I) yielded the complexes
protons of cymene. The methyl groups of the isopropyl moiety 14 and 15 in quantitative yields. The 31P NMR spectra of com-
appear as a doublet centered at 1.02 ppm with a 3JHH coupling plexes 14 and 15 show two broad singlets at 137.1 and
1
of 6.6 Hz, whereas the –CH proton appears as a septet at 132.8 ppm, respectively. The H NMR spectra of complexes 14
2.6 ppm. The structure of 12 was confirmed by a single-crystal and 15 consist of two broad singlets around 4.52–5.10 ppm for
X-ray structure determination.
the ferrocenyl protons. Because of the poor solubility, the
The reactions of bidentate ligands with group 11 metals signals in the 31P NMR spectra appeared broad and electro-
yield a diverse array of two or more coordinated complexes chemical studies could not be carried out. The ligand 2
with various coordination geometries whose structures vary on treatment with [AuCl(SMe2)] in a 1 : 2 molar ratio yielded
from simple mononuclear to coordination polymers and poly-
a
dinuclear complex [(AuCl)2{Fe{C5H4P(OC6H3(OMe-o)-
nuclear clusters.20,21 The structures of polynuclear copper(I) (C3H5-p))2}2}] (16) with the ligand exhibiting the bridging
complexes with μ2-, μ3- or μ4-bridging halides are affected by mode of coordination. The 31P NMR spectrum of 16 shows a
the number of donor atoms, the method of preparation and single resonance at 142.6 ppm. The complex 16 is found to be
also the nature of the solvent used for reactions and crystalliza- light-sensitive in solution but is moderately stable in the solid
tion. Treatment of 2 with one equivalent of CuCl in acetonitrile state. The structural composition of the complex was further
leads to the formation of a binuclear complex [{(CuCl)Fe- confirmed by 1H NMR data, elemental analysis and also by
{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2] (13) in good yield. The single-crystal X-ray study.
Scheme 3 (i) [Ru(η6-p-cymene)Cl2]2, (ii) CuCl, CH2Cl2–CH3CN (1 : 1 or 1 : 2), (iii) CuX, CH3CN (1 : 2 or 2 : 5), (iv) [AuCl(SMe2)].
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Molecular structures of complexes 8, 9, 12, 15 and 16. Per-
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spective views of the molecular structures of all the com-
pounds with the atom numbering schemes are shown in
Fig. 1–5. The crystallographic data and the details of the struc-
ture determinations are given in Table 1 while the selected
bond lengths and bond angles are listed in Table 2.
Crystals of 8 suitable for the single crystal X-ray diffraction
study were obtained by slow diffusion of petroleum ether into
a CH2Cl2 solution of complex 8. The palladium center adopts a
slightly distorted square planar geometry, with the two phos-
phorus atoms and two chlorines coordinating in a cis-fashion
as shown in Fig. 1. The distortions involve deviations in the
angles at Pd from 90° as noted below as well as slight
Fig. 3 Molecular structure of [Ru2Cl4(η6-p-cymene)2Fe{C5H4P(OC6H3(OMe-o)-
(C3H5-p))2}2] (12). All hydrogen atoms have been omitted for clarity.
tetrahedral deviations from planarity (dihedral angle Cl1–Pd1–
P1 vs. Cl2–Pd1–P2 = 3.7°). The bite angle of P1–Pd1–P2, 96.93(5)°
is slightly less than that in [PdCl2(dppf-P,P′)] [99.07°]23,24
but larger than those observed in [PdCl2(dppe-P,P′)] [85.8°],
[PdCl2(dppp-P,P′)] [90.6°], [PdCl2(dppb-P,P′)] [94.51°] and
[PdCl2(dpbp-P,P′)] [92.24°]. On the other hand, the Cl1–Pd1–
Cl2 angle of 89.48(4)° in complex 8 is slightly less than the
same observed in [PdCl2(dppe-P,P′)] [94.2°], [PdCl2(dppp-P,P′)]
[90.8°] but larger than the same in [PdCl2(dpbp-P,P′)] [88.21°],
[PdCl2(dppf-P,P′)] [87.8°], whereas comparable with the same
in [PdCl2(dppb-P,P′)] [89.78°].25–35 The Cl1–Pd1–P1 and Cl2–
Pd1–P1 bond angles are 83.89(5)° and 172.38(4)°, respectively.
The cyclopentadienyl rings in complex 8 adopt a staggered
conformation with a twist angle of 36.4°. The Pd1–P1 and
Pd1–P2 bond lengths are 2.243(15) and 2.255(11) Å, respect-
ively, which are slightly shorter than those observed for
[PdCl2(dppf-P,P′)] [2.283(1) and 2.301(1) Å].36
Fig. 1 Molecular structure of [(PdCl2)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (8).
All hydrogen atoms have been omitted for clarity.
The molecular structure of platinum complex 9 is very
similar to the palladium analogue. The platinum center
adopts a distorted square planar geometry (the dihedral angle
Cl1–Pt1–P1/Cl2–Pt1–P2 is 4.1°), with two chlorine atoms in
mutually cis dispositions. The P1–Pt1–P2 angle is 97.12(2)°,
while the Cl1–Pt1–Cl2 angle is 87.13(2)°. The P–Pt bond
lengths are 2.2268(5) Å and 2.2194(5) Å for P1–Pt1 and P2–Pt1,
respectively, which are slightly shorter than those found in
[Fe{η5-C5H4P(C2F5)2}2(PtCl2)] [Pt(1)–P(1), 2.2411(7) Å, Pt(1)–P(2),
2.2397(7) Å]. The Pt–Cl bond lengths of 2.3446(5) Å for Pt1–Cl1
and 2.3415(5) Å for Pt1–Cl2 are comparable but shorter than
those of the analogous complex [Fe{η5-C5H4P(C2F5)2}2(PtCl2)]
[Pt(1)–Cl(1), 2.306(8) Å, Pt(1)–Cl(2), 2.304(1) Å].37,38
Reddish brown crystals suitable for X-ray diffraction were
obtained by slow diffusion of a dichloromethane–petroleum
ether solution of 12 at room temperature. The ferrocenylbis-
(phosphonite) coordinates to the ruthenium atoms in a brid-
ging fashion with the ruthenium centers assuming a typical
three-legged “piano-stool” structure as shown in Fig. 3. The
Ru–P bond distance of 2.307(2) Å is comparable with those in
Fig. 2 Molecular structure of [(PtCl2)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (9).
All hydrogen atoms have been omitted for clarity.
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[(p-cymene)RuCl2(PH2Fc)]
[2.312(2)
Å],
[(η6-p-cymene)-
RuCl2{PH2(CH2Fc)}] [2.310(1) Å] and [(η6-p-cymene)RuCl2{PH-
(CH2Fc)2}] [2.296(2) Å] but is shorter than the 2.34–2.37 Å
bond lengths observed in similar complexes containing
tertiary phosphines.39 The Cl1–Ru1–P1, Cl2–Ru1–P1 and Cl1–
Ru1–Cl2 bond angles are 89.39(9)°, 90.31(9)° and 86.30(9)°,
respectively, which are comparable with those observed in ana-
logous complexes of tertiary phosphines. The Ru–C bond dis-
tances range from 2.175(12) Å (Ru1–C31) to 2.280(10) Å (Ru1–
C27) in which the Ru–C bonds (Ru1–C28, 2.251(10) Å) trans to
phosphine are longer than those trans to the chlorine atoms
(Ru1–C31, 2.175(12) Å). This is likely due to the greater
expected trans influence of phosphorus over chlorine as there
do not appear to be any unusually close contacts with the
p-cymene ligand which could otherwise be responsible.
The complex 15 consists of two pentameric [Cu5(μ-I)5] units
linked across a center of symmetry by Cu(η2-allyl) interactions.
It is very interesting to analyze the structure of 15 as the crystal
structure reveals that the [(CuI)10(PFcP)4] unit has unique
Cu5I5 cores as part of the 24-membered ring containing the
Cu(I)–olefin complex as depicted in Fig. 4. This core contains
four iodides bonded to three copper centers in a μ3-fashion
while the fifth iodide is bonded to two copper centers in a μ2-
fashion. The core can alternatively be considered to contain
four different rhombic [Cu2(µ-I)2] units. In the symmetrical
[Cu2(µ-I1,I3)Cu3] rhombic unit, Cu2 and Cu3 adopt a distorted
tetrahedral geometry with the coordination sites occupied by
one of the phosphorus atoms of the ligand 2 and three brid-
ging iodide atoms. The Cu–P bond lengths (Cu2–P1 = 2.208(3),
Cu3–P3 = 2.220(3) Å) are slightly shorter than the corres-
ponding distances observed in [Cu(µ-I)(dppf-P,P′)]2 (Cu–P =
2.28(1), 2.286(8) Å), where dppf chelates the copper centers.40
The Cu–I bond lengths vary appreciably, ranging from 2.6529(14)
Å (Cu2–I3) to 2.7140(13) Å (Cu3–I1), with an I1–Cu2–I3
angle of 109.79(5)°. In the [Cu3(µ-I1,I2)Cu5] rhombic unit,
both the copper centers adopt a distorted tetrahedral geome-
try. In the third [Cu1(µ-I4,I5)Cu5] unit, the geometry of one of
the copper(I) centers is trigonal planar being coordinated by
two bridging μ2-I atoms and one of the phosphorus atoms of
ligand 2 while the other is tetrahedrally coordinated by four
bridging μ2-I atoms. The Cu–I bond lengths in these units
differ significantly with those to the tetra-coordinated copper
[2.6276(15)–2.6538(15) Å] being longer than the Cu5–I bond
lengths [2.544(5)–2.5575(5) Å] of the tri-coordinated copper. An
increase in bond angle from 102.31(4)° [I4–Cu1–I5] to 117.09(3)°
[I4–Cu5–I5] arises due to the increase in the coordination
number from three to four. The Cu5–Cu1 distance of 2.4782(58) Å
is less than the sum of the van der Waals radii for the
Cu(I) ion indicating that the ligand supports a strong Cu⋯Cu
interaction.41 In the fourth [Cu3(µ-I2,I3)Cu4] rhombic unit,
copper center Cu4 adopts a distorted tetrahedral geometry
defined by two bridging μ2-I ligands, one phosphorus atom
and the center of the allylic CvC moiety of one of the substitu-
ents on the phosphorus atom of ligand 2. This is comparable
to the 4-coordinate geometry observed about copper in other
Cu(I) olefin coordination polymers. All the four separate Cu2I2
Fig. 4 Molecular
structure
of
[Cu5(µ-I)5{Fe{C5H4P(OC6H3(OMe-o)(C3H5-
p))2}2}2]2 (15): (a) without phosphorus substituents except coordinating allylic
group, (b) with all phosphorus substituents. All hydrogen atoms have been
omitted for clarity.
Fig. 5 Molecular structure of [(AuCl)2Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]
(16). All hydrogen atoms have been omitted for clarity.
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Table 1 Crystallographic information for compounds 8, 9, 12, 15 and 16
8
9
12
15
16
Formula
FW
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
50H52FeO8P2PdCl2
C50H52FeO8P2PtCl2
1164.70
Monoclinic
P21/c
14.9206(6)
19.1288(7)
18.0870(7)
90
113.349(1)
90
4739.5(3)
4
C70H80FeO8P2Ru2Cl4
1511.07
Triclinic
ˉ
P1
13.320(3)
14.572(3)
19.016(4)
78.967(3)
86.074(3)
84.913(3)
3603.5(13)
2
C200H208Cu10Fe4I10O32P8
5499.33
Triclinic
ˉ
P1
14.630(1)
16.1611(2)
24.111(2)
71.670(1)
80.188(1)
71.003(1)
5102.1(8)
1
C53H52FeO8P2Au2Cl2
1399.57
Triclinic
ˉ
P1
9.4474(10)
11.7473(13)
14.7451(16)
112.484(1)
103.393(1)
104.426(2)
1363.2(3)
1
1076.01
Monoclinic
P21/c
14.9965(13)
19.1024(16)
18.0574(15)
90
113.145(1)
90
4756.5(7)
4
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalc. (g cm−3
)
1.503
0.916
2208
1.632
3.488
2336
1.393
0.856
1552
1.790
2.936
2708
1.705
5.837
682
µ(Mo Kα) (mm−1
F(000)
)
T (K)
Θ range (°)
Total no. of reflns
100
1.5–26.4
37 771
100
1.8–29.1
83 317
195
2.2–26.9
70 854
100
1.2–26.8
74 797
100
2.0–28.0
35 219
No. of indep. reflns
R
9756 [Rint = 0.064]
0.0507
12 365 [Rint = 0.037]
0.0199
15 313 [Rint 0.101]
0.0614
21 465 [Rint = 0.092]
0.0649
11 159 [Rint = 0.036]
0.0450
wR2
S
0.1260
1.03
0.0479
1.04
0.1801
1.03
0.1720
0.99
0.1192
1.06
dimeric units are associated by additional sharing of their acid to yield the desired biaryls in high yields with low catalytic
bridging iodine atoms in a µ3 or µ4 fashion to form a “canopy” loadings at room temperature using methanol as a solvent. The
with the Cu4 and I4 and I5 functioning as the “legs” and Cu3 results are summarized in Table 3. It is important to achieve
and I1 as the “ridgepole”. Two of the resulting pentamers are good yields using minimum amounts of a catalyst; therefore we
linked together by dangling olefinic groups through one of the examined the effect of catalyst loading on the coupling between
copper atoms of each pentamer to give a novel decanuclear 4-bromoacetophenone and phenylboronic acid. Complete con-
complex [((Cu5(µ-I)5){Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2]2 version of the starting materials into biaryl was achieved with
(15). The allylic carbon–carbon (C16–C17) double bond dis- 1 mol% of the catalyst in half an hour or 0.1 mol% in 3 h; there-
tance is found to be 1.339(15) Å which is shorter than the fore a concentration of 0.1 mol% was selected as the optimal
CvC bond distance [1.41 Å] observed in [Cu2Cl2(cycloocta- concentration for catalytic loading. The Suzuki–Miyaura cross-
diene-1,5)2] and longer than the uncoordinated CvC bond coupling reaction is strongly influenced by the solvent and the
distance in complex 16 [1.302(17) Å] indicating an interaction base. While the reactions proceed with various bases (K3PO4,
of moderate strength.42–44
K2CO3, Cs2CO3, Et3N) and solvents (THF, MeOH, toluene), the
The molecular structure of 16 consists of
a
discrete best results were obtained with potassium carbonate as the
[(AuCl)2(μ-PFcP)] species having a crystallographically imposed base and methanol as the solvent. Higher conversion rates were
2-fold rotation symmetry with the 2-fold axis passing through realized when activated aryl bromides were used as substrates
the iron atom and the midpoint of the Au1–Au2 vector. The but low catalytic conversions were observed with heterocyclic
ligand coordinates to the metal centers in an open bridging bromides. In the coupling of 4-bromobenzonitrile with phenyl
mode with Au1–P1 and Au1–Cl1 bond distances of 2.2067(19) boronic acid, the highest TON of 1.5 × 105 (entry 7) was
and 2.289(2) Å, respectively, which are similar to those found in observed. The activity of catalyst 8 is found to be much superior
the analogous complexes [Au2Cl2(μ-dppf)]45 (Au–P = 2.226(1) compared to most commonly used catalysts, PdCl2(dppf) and
and Au–Cl = 2.282(1) Å) and [{Fe(C5H4PR)2-P,P′}Au2Cl2 (R = Pd2(dba)3/(dppf), which catalyze the reaction between 4-bromo-
–OC10H6(μ-S)C10H6O–)]16 (Au–P = 2.202(1) and Au–Cl = 2.284(1) acetophenone and phenylboronic acid in toluene at 70 °C
Å). The AuI centers adopt an approximately linear geometry with with 94 and 86% yields, respectively.46,47
a P1–Au1–Cl1 bond angle of 176.11(7)°. The P–Au–Cl units are
trans-oriented and therefore there is no aurophilic interaction.
Electrochemical studies
The cyclopentadienyl rings adopt a staggered conformation.
The significance of ferrocene based ligands is their potential
Suzuki–Miyaura cross-coupling reactions using the palla- ability to undergo a rapid and reversible redox process cen-
dium complex [(PdCl2)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] tered at the iron atom. The electrochemical behavior of ligand
(8). The palladium-catalyzed Suzuki–Miyaura cross-coupling 2 and its derivatives was investigated by cyclic voltammetry. All
reaction is one of the efficient methods for forming symmetric electrochemical data are shown in Table 4 and the voltammo-
and nonsymmetric biaryl compounds in organic synthesis. The grams are depicted in Fig. 6–8.
complex 8 was found to be an efficient catalyst for the C–C
The results (Table 4) demonstrate that ferrocenylbis(phos-
cross-coupling reactions of aryl bromides with phenylboronic phonite) (2) and its derivatives show reversible one electron
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Table 2 Selected bond distances (Å) and bond angles (°) for 8, 9, 12, 15 and 16
Compound 8
Compound 9
Bond length (Å)
Bond angle (°)
Bond length (Å)
Bond angle (°)
P1–Pd1
P2–Pd1
Pd1–Cl1
Pd1–Cl2
P2–O5
P2–O7
P1–O1
2.2434(15)
2.2550(11)
2.3322(11)
2.3391(14)
1.606(3)
1.605(3)
1.613(3)
P1–Pd1–P2
P1–Pd1–Cl1
P2–Pd1–Cl1
Cl1–Pd1–Cl2
O5–P2–O7
O1–P1–O3
96.93(5)
83.89(5)
179.17(5)
89.48(4)
106.61(17)
107.17(17)
P1–Pt1
P2–Pt1
Pt1–Cl1
Pt1–Cl2
P2–O5
P2–O7
P1–O1
P1–O3
2.2268(5)
2.2194(5)
2.3446(5)
2.3415(5)
1.6123(14)
1.6117(15)
1.6101(15)
1.6055(14)
P1–Pt1–P2
P1–Pt1–Cl1
P2–Pt1–Cl1
Cl1–Pt1–Cl2
O5–P2–O7
O1–P1–O3
97.12(2)
90.32(2)
171.50(2)
87.13(2)
106.64(8)
106.49(8)
P1–O3
1.605(3)
Compound 12
Compound 16
Bond length (Å)
Bond angle (°)
Bond length (Å)
Bond angle (°)
P1–Ru1
P1–O1
P1–O3
Ru1–Cl1
Ru1–Cl2
2.307(2)
1.629(6)
1.629(6)
2.403(3)
2.383(3)
O1–P1–O3
103.6(4)
106.1(3)
118.6(2)
86.30(9)
89.39(9)
90.31(9)
P1–Au1
P1–O1
P1–O3
Au1–Cl1
P1–C1
O1–C6
O3–C16
2.2067(19)
1.602(5)
1.596(5)
2.289(2)
1.769(7)
1.398(10)
1.464(9)
O1–P1–Au1
P1–Au1–Cl1
C1–P1–O1
C1–P1–O3
C1–P1–Au1
113.7(2)
176.11(7)
105.4(3)
98.3(3)
O1–P1–Ru1
O3–P1–Ru1
Cl1–Ru1–Cl2
P1–Ru1–Cl1
P1–Ru1–Cl2
118.6(3)
Compound 15
Bond length (Å)
Bond angle (°)
I1–Cu1
I1–Cu2
I2–Cu3
I1–Cu5
P1–Cu2
P2–Cu1
P3–Cu3
Cu2–I3
Cu3–I1
Cu3–I3
Cu3–I2
Cu5–I2
Cu1–I4
Cu1–I5
Cu5–I5
2.9031(15)
2.7021(16)
2.6653(14)
2.544(5)
2.208(3)
2.196(3)
P4–Cu4
P1–O1
P2–O5
C16–C17
C16–Cu4
C17–Cu4
P1–C1
2.230(3)
1.642(8)
1.627(7)
1.339(15)
2.302(9)
2.207(12)
1.782(9)
1.794(10)
2.033(10)
2.040(8)
2.041(10)
2.047(10)
2.047(9)
2.6149(14)
2.7303(14)
Cu4–C16–C17
Cu4–C17–C16
O1–P1–Cu2
Cu1–I4–Cu2
Cu2–I1–Cu3
Cu1–I5–Cu5
Cu3–I3–Cu4
Cu2–I4–Cu1
Cu4–I3–Cu2
P4–Cu4–C17
Cu3–I2–Cu4
I4–Cu1–I5
68.9(6)
76.7(7)
P4–Cu4–I2
P1–Cu4–I1
P1–Cu2–I4
P1–Cu2–I3
P2–Cu1–I5
P2–Cu1–I4
P4–Cu4–C17
C16–Cu4–C17
P4–Cu4–C16
C16–Cu4–I2
C17–Cu4–I2
110.27(8)
116.13(8)
112.30(9)
108.14(8)
123.03(9)
121.82(9)
130.8(3)
34.5(4)
115.3(3)
78.32(4)
69.53(4)
61.96(11)
72.83(4)
78.32(4)
113.87(5)
130.83
71.27(4)
102.31(4)
105.27(5)
105.26(4)
109.81(8)
2.220(3)
2.6529(14)
2.7140(13)
2.6803(15)
2.6653(14)
2.479(5)
2.6276(15)
2.6538(15)
2.557(5)
P2–C6
Fe1–C6
Fe1–C7
Fe1–C8
Fe1–C9
Fe1–C10
Cu4–I3
Cu4–I2
100.0(2)
101.8(3)
99.8(3)
I2–Cu3–I3
I2–Cu4–I3
I3–Cu4–P4
oxidation similar to the ferrocene–ferrocenium (FeII/FeIII) redox potential to a less positive value relative to the free
couple except that their E1/2 values are greater than that for a ligand is due to the effect of phosphorus coordination, which
FeII/FeIII couple. The redox pattern of the free ligand 2 makes the iron(II) center more electron rich. Cyclic voltamme-
resembles that of the 1,1′-bis(diphenylphosphino)ferrocene try of complex 12 exhibits a reversible single-electron oxidation
(dppf).48 The free ligand 2 is oxidized at E1/2 = 0.63 V, indicat- wave assigned to the RuII/RuIII oxidation at E1/2 = 1.05 V in
ing that its oxidation is slightly more difficult than that of CH2Cl2, as depicted in Fig. 7, which is comparable with the
ferrocene (E1/2 = 0.46 V), in line with the expected electron redox potentials reported for {[Ru(p-cymene)(TpmsPh)]Cl}
withdrawing effect of the substituents on the phosphorus [1.02 V] (Tpms
=
tris(pyrazolyl)methanesulfonate) and
atoms. The redox potentials shift to positive values for 3 and 5 {[Ru(benzene)(Tpms)]Cl} [1.07 V].49–51 In acetonitrile, complex 12
(E1/2 = 0.64 and 0.97 V, respectively) relative to the ligand 2 as displayed two pairs of redox waves corresponding to FeII/FeIII
depicted in Fig. 6. This is due to the oxidation of phosphorus and RuII/RuIII oxidations, where only one oxidation is clearly
centers which make them electron deficient.
In addition, palladium(II) complex 8 and ruthenium(II) to a lower electron donating ability of the η6-arene ligand, the
complex 12 have within each molecular entity two distinct electro- redox potential of the RuII/III couple in complex 12 [E1/2
seen and the other is quasi-reversible as shown in Fig. 8. Due
;
active sites, the ferrocenyl (Fc) group and the coordinated Fe: 0.52, Ru: 1.14 V] shifts to a higher value than that observed
metal center (Pd or Ru). The complex 8 shows a unique wave in the analogous complex [RuCl2(η6-C6Me6)(FcPPh2)] [E1/2; Fe:
on sweeping at anodic potential, which is attributed to the 0.03, Ru: 0.66 V].51 A shift of the RuII/III redox potential to a
FeII/FeIII couple and oxidation would not involve the formation higher value with a ferrocenyl bis(phosphonite) ligand also
of heterometallic mixed-valent intermediates. The shift in the corresponds to the oxidation which involves the change of a
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Table 3 Suzuki cross-coupling reactions using palladium complex 8
Entry
1
Aryl halide
Arylboronic acid
Conditiona
Product
Conv.b (%)
TONc
1000
0.1 mol%,
R.T., 3 h
100
2
3
4
0.1 mol%,
R.T., 3 h
90
87
86
900
870
860
0.1 mol%,
R.T., 3 h
0.1 mol%,
R.T., 4 h
5
0.1 mol%,
R.T., 24 h
21
210
6
7
8
0.005 mol%,
60 °C, 3 h
90
75
90
18 000
150 000
18 000
0.0005 mol%,
60 °C, 24 h
0.005 mol%,
60 °C, 1 h
9
0.05 mol%,
60 °C, 3.5 h
100
50
2000
10
0.0005 mol%,
60 °C, 2.5 h
100 000
a Aryl halide (0.5 mmol), aryl boronic acid (0.75 mmol), K2CO3 (1 mmol), MeOH (5 mL). b Conversion to coupled product determined by GC,
based on aryl halides; average of two runs; corrected with respect to internal standards such as mesitylene or dodecane. c (mol of product)/
(mol of catalyst).
Table 4 Electrochemical data for free ligand and its derivatives in CH2Cl2 at
298 K
Entry
Compounds
E1/2 (V)
1
2
3
4
5
[Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (2)
[Fe{C5H4P(O)(OC6H3(OMe-o)(C3H5-p))2}2] (3)
[Fe{C5H4P(Se)(OC6H3(OMe-o)(C3H5-p))2}2] (5)
[PdCl2Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (8)
[Ru2Cl4(η6-cymene)2Fe{C5H4P(OC6H3(OMe-o)(C3H5-
p))2}2] (12)
0.63
0.64
0.97
0.55
1.05
strongly electron-donating ferrocene substituent at the phos-
phorus center into an electron-withdrawing ferrocenium, thus
Fig. 6 Comparative cyclic voltammograms of ferrocenyl bis(phosphonite) 2
(violet), compounds 3 (red) and 5 (green) in CH2Cl2/0.1 M TBAP (tetrabutyl-
lowering the electron density at the ruthenium center and ammonium perchlorate) vs. SCE at a scan rate of 100 mV s−1
making the Ru-oxidation more difficult.
.
mode of coordination was observed in the case of ruthenium
and gold complexes. It is very interesting to analyze the struc-
tural features of the decameric copper complex 15 in which
Conclusions
The new ferrocenylbis(phosphonite) ligand shows both chelat- two pentameric moieties are linked by olefinic bonds. The for-
ing and bridging modes of coordination. It forms chelate com- mation of the complex 15 was due to the coordination of one
plexes with group 6 and group 10 metals, whereas the bridging of the olefinic groups that probably prevented the formation of
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(NEt2)2}2 and Fe{C5H4PCl2}2 (1) were prepared according to the
published procedures.59,60 CuI was purchased from Aldrich
Chemicals and used as such without further purification.
Other chemicals were obtained from commercial sources and
purified prior to use.
Instrumentation
The NMR spectra were recorded at the following frequencies:
400 MHz (1H), 100 MHz (13C), and 162 MHz (31P) using either
a Varian VXR 400 MHz or a Bruker AV 400 spectrometer. The
spectra were recorded in CDCl3 (or DMSO-d6) solutions with
CDCl3 (or DMSO-d6) as an internal lock; TMS and 85% H3PO4
were used as external standards for 1H and 31P{1H} NMR,
respectively. Positive shifts lie downfield of the standard in all
the cases. Infrared spectra were recorded on a Nicolet Impact
400 FT IR instrument in a KBr disk or a nujol mull. The micro-
analyses were performed using a Carlo Erba Model 1112
elemental analyzer. Mass spectra were recorded using Waters
Q-Tof micro (YA-105). The melting points of all compounds
were determined on a Veego melting point apparatus and are
uncorrected. Cyclic voltammetric (CV) and differential pulse
voltammetric (DPV) studies were carried out with a BAS
electrochemical system using a three electrode configuration
consisting of a glassy carbon (working electrode), platinum
wire (auxiliary electrode), and saturated calomel (reference
electrode) electrodes in dry dichloromethane using 0.1 M
tetrabutylammonium perchlorate (TBAP) as a supporting elec-
trolyte. GC analyses were performed on a Perkin Elmer Clarus
500 GC fitted with a FID detector and a packed column.
Fig. 7 Comparative cyclic voltammograms of ferrocenyl bis(phosphonite) 2
(blue), palladium complex 8 (red) and ruthenium complex 12 (green) in CH2Cl2/
0.1 M TBAP vs. SCE at a scan rate of 100 mV s−1
.
Fig. 8 Cyclic voltammogram of ruthenium complex 12 in CH3CN/0.1 M TBAP
vs. SCE at a scan rate of 100 mV s−1
.
Synthesis of [Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (2). A
mixture of eugenol (6.76 g, 0.041 mol) and triethylamine
(4.38 g, 0.043 mol) in diethyl ether (50 mL) was added drop-
wise to a solution of ferrocenyldihalophosphane 1 (4.0 g,
0.010 mol) also in diethyl ether (30 mL) at −20 °C under a
nitrogen atmosphere. After the completion of the addition, the
reaction mixture was stirred for 8 h at room temperature and
then filtered through Celite to remove amine hydrochloride
salt. The solvent was removed under reduced pressure to
obtain 2 as a pale yellow solid having the smell of eugenol.
The residue was dissolved in hot petroleum ether and kept at
room temperature to give an analytically pure crystalline pale
yellow product 2. Yield: 70% (6.48 g). Mp: 178–179 °C. Anal.
Calcd for C50H52FeO8P2: C, 66.82; H, 5.83. Found: C, 66.73; H,
5.75. 1H NMR (400 MHz, CDCl3): δ 3.31 (d, CH2, 8H, 3JHH = 6.8
Hz), 3.74 (s, OCH3, 12H), 5.04 (m, CH2, 8H), 5.89–5.98 (m, CH,
4H), 6.63 (m, C6H3, 4H), 6.68 (s, C6H3, 4H), 7.09 (d, C6H3, 4H,
3JHH = 7.9 Hz), 4.54 (s, 4H, Fc), 4.69 (s, 4H, Fc). 31P{1H}NMR
(162 MHz, CDCl3): δ 168.8 (s). MS (EI): m/z = 899.7 (M + 1).
Synthesis of [Fe{C5H4P(O)(OC6H3(OMe-o)(C3H5-p))2}2] (3). A
a simple dinuclear complex with either a rhombic [Cu2(μ-I)2]
unit or a tetranuclear complex with a cuboid [Cu4(μ-I)4] frame-
work. The structure 15 is a rare example with iodides perform-
ing as 4e, 6e and 8e donors.
The electrochemical behavior consists of one reversible
electron oxidation process for selected compounds at slightly
higher potential than for ferrocene itself. The palladium
complex 8 was employed in Suzuki–Miyaura C–C cross-coup-
ling reaction and the catalytic efficiency is found to be superior
to most of the commonly used catalysts with TON up to
1.5 × 105 with very low catalyst loading. Further catalytic reac-
tions are under active investigation in our laboratory.
Experimental
General procedures
All experimental manipulations were performed using stan-
dard vacuum-line and Schlenk techniques under a nitrogen 30% aqueous solution of H2O2 (0.003 g, 0.01 mL, 0.090 mmol)
atmosphere unless otherwise stated. All the solvents were in THF (6 mL) was added dropwise to a well-stirred THF solu-
purified by conventional procedures and distilled prior to tion (10 mL) of 2 (0.040 g, 0.045 mmol) at 0 °C. The reaction
use. The compounds [M(CO)4(NHC5H10)2] (M = Mo, W),52 mixture was slowly warmed to room temperature and stirred
[Ru(η6-p-cymene)Cl2]2,53 [M(COD)Cl2] (M = Pd, Pt),54 [AuCl- for 8 h. The solvent was removed under reduced pressure to
(SMe2)],55 [CuX] (X = Cl, Br),56 [(η5-C5H5)Ru(PPh3)2Cl],53 [Pd(η3- give a sticky residue. The residue was dissolved in 3 mL of
C3H5)Cl]2,57 bis(diethylamino)-chlorophosphine,58 Fe{C5H4P- CH2Cl2, layered with 1 mL of petroleum ether and kept at
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−20 °C to afford 3 as an analytically pure product. Yield: 88% 143–145 °C (dec). Anal. Calcd for C54H52FeO12P2W: C, 54.29;
(0.036 g). Mp: 177–178 °C. Anal. Calcd for C50H52FeO10P2: C, H, 4.39. Found: C, 53.83; H, 4.26. 1H NMR (400 MHz, CDCl3): δ
3
64.50; H, 5.63. Found: C, 64.73; H, 5.55. 1H NMR (400 MHz, 3.31 (d, CH2, 8H, JHH = 6.4 Hz), 3.87 (s, OCH3, 12H), 5.05 (m,
CDCl3): δ 3.35 (d, CH2, 8H, 3JHH = 6.4 Hz), 3.64 (s, OCH3, 12H), CH2, 8H), 5.89–5.98 (m, CH, 4H), 6.59 (s, C6H3, 4H), 6.68 (m,
3
5.09 (m, CH2, 8H), 5.79–5.92 (m, CH, 4H), 6.66 (m, C6H3, 4H), C6H3, 4H), 7.32 (d, C6H3, 4H, JHH = 7.2 Hz), 4.27 (s, 4H, Fc),
3
6.72 (s, C6H3, 4H), 7.12 (d, C6H3, 4H, JHH = 7.2 Hz), 4.44 (s, 4.72 (s, 4H, Fc). IR (KBr disk): 1922 (br), 2029 cm−1
.
31P{1H}
4H, Fc), 4.88 (s, 4H, Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 20.2 NMR (162 MHz, CDCl3): δ 157.1 (s 1JWP = 201 Hz).
(s). MS (EI): m/z = 931.2 (M + 1).
Synthesis of [{PdCl2}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]
Synthesis of [Fe{C5H4P(S)(OC6H3(OMe-o)(C3H5-p))2}2] (4). A (8). A solution of Pd(COD)Cl2 (0.012 g, 0.039 mmol) in dichloro-
mixture of 2 (0.134 g, 0.149 mmol) and elemental sulfur methane (5 mL) was added dropwise to a solution of 2
(0.009 g, 0.298 mmol) in 15 mL of toluene was refluxed for (0.035 g, 0.039 mmol) also in dichloromethane (5 mL) with
12 h. The solution was cooled to room temperature and fil- constant stirring. The reaction mixture was allowed to stir for
tered through Celite to remove unreacted sulfur. The solvent 4 h to give a clear yellow solution. The solution was concen-
was removed under reduced pressure to give a pale yellow trated to 4 mL, saturated with 2 mL of petroleum ether and
residue. The residue was dissolved in 4 mL of CH2Cl2, layered stored at room temperature for several days to give an analyti-
with 1 mL of petroleum ether and stored at room temperature cally pure product 8 as a pale yellow crystalline solid. Yield:
for 2 days to get an analytically pure pale yellow crystalline 85% (0.036 g). Mp: 171–172 °C. Anal. Calcd for
product 4. Yield: 85% (0.121 g). Mp: 147–148 °C. Anal. Calcd C50H52FeO8P2PdCl2: C, 55.81; H, 4.87. Found: C, 55.47; H,
for C50H52FeO8P2S2: C, 62.37; H, 5.44; S, 6.66. Found: C, 63.03; 4.73. 1H NMR (400 MHz, CDCl3): δ 3.25 (d, CH2, 8H, 3JHH = 6.8
1
H, 5.55; S 6.12. H NMR (400 MHz, CDCl3): δ 3.36 (d, CH2, 8H, Hz), 3.69 (s, OCH3, 12H), 5.03 (m, CH2, 8H), 5.85–5.92 (m, CH,
3JHH = 6.2 Hz), 3.69 (s, OCH3, 12H), 5.07 (m, CH2, 8H), 4H), 6.48 (s, C6H3, 4H), 6.68 (m, C6H3, 4H), 7.30 (d, C6H3, 4H,
5.90–5.97 (m, CH, 4H), 6.65 (m, C6H3, 4H), 6.74 (s, C6H3, 4H), 3JHH = 7.6 Hz), 4.38 (s, 4H, Fc), 4.95 (s, 4H, Fc). 31P{1H}NMR
3
7.12 (d, C6H3, 4H, JHH = 7.6 Hz), 4.78 (s, 4H, Fc), 4.94 (s, 4H, (162 MHz, CDCl3): δ 117.7 (s).
Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 83.9 (s).
Synthesis of [{PtCl2}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]
[Fe{C5H4P(Se)(OC6H3(OMe-o)(C3H5-p))2}2] (9). Compound 9 was synthesized by a procedure similar to
Synthesis
of
(5). Compound 5 was synthesized by a procedure similar to that of 8 using Pt(COD)Cl2 (0.03 g, 0.08 mmol) and 2 (0.064 g,
that of 4 using ligand 2 (0.054 g, 0.060 mmol) and elemental 0.08 mmol). The analytically pure product 9 was obtained as a
selenium (0.009 g, 0.120 mmol). Yield: 83% (0.053 g). Mp: pale yellow powder from a mixture of dichloromethane and
158–160 °C. Anal. Calcd for C50H52FeO8P2Se2: C, 56.83; H, petroleum ether. Yield: 73% (0.068 g). Mp: 162–163 °C. Anal.
1
4.96. Found: C, 56.33; H, 4.75. H NMR (400 MHz, CDCl3): δ Calcd for C50H52FeO8P2PtCl2: C, 51.56; H, 4.50%. Found: C,
3
3.33 (d, CH2, 8H, JHH = 6.6 Hz), 3.72 (s, OCH3, 12H), 5.07 (m, 51.42; H, 4.63%. 1H NMR (400 MHz, CDCl3): δ 3.36 (d, CH2,
3
CH2, 8H), 5.88–5.96 (m, CH, 4H), 6.67 (m, C6H3, 4H), 6.72 (s, 8H, JHH = 6.6 Hz), 3.64 (s, OCH3, 12H), 5.03 (m, CH2, 8H),
3
C6H3, 4H), 7.15 (d, C6H3, 4H, JHH = 7.8 Hz), 4.81 (s, 4H, Fc), 5.82–5.89 (m, CH, 4H), 6.50 (s, C6H3, 4H), 6.65 (m, C6H3, 4H),
3
4.91 (s, 4H, Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 88.9 (s, 7.33 (d, C6H3, 4H, JHH = 7.8 Hz), 4.36 (s, 4H, Fc), 4.94 (s, 4H,
1JPSe = 911 Hz).
Synthesis
Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 90.65 (s), 1JPtP = 4969 Hz.
Synthesis of [{(η5-C5H5)RuCl}Fe{C5H4P(OC6H3(OMe-o)(C3H5-
of
[{Mo(CO)4}Fe{C5H4P(OC6H3(OMe-o)(C3H5-
p))2}2] (6). A dichloromethane solution (6 mL) of p))2}2] (10). A toluene (4 mL) solution of [(η5-C5H5)Ru-
[Mo(CO)4(pip)2] (0.016 g, 0.042 mmol) was added dropwise to (PPh3)2Cl] (0.029 g, 0.041 mmol) was added to a solution of 2
a solution of 2 (0.038 g, 0.042 mmol) in the same solvent (4 mL) (0.036 g, 0.041 mmol) also in toluene (6 mL). The reaction
with constant stirring. The pale yellow reaction mixture was mixture was then refluxed for 4 h, and the orange solution was
stirred for 4 h at room temperature. The solvent was removed then concentrated to 5 mL, and saturated with 2 mL petroleum
under vacuum and the residue was washed with petroleum ether to give 10 as an analytically pure orange product. Yield:
ether to afford an analytically pure yellow solid product 6. 76% (0.034 g). Mp: 194–195 °C (dec). Anal. Calcd for
Yield: 78% (0.037 g). Mp: 150–152 °C (dec). Anal. Calcd for C55H57ClFeO8P2Ru: C, 60.03; H, 5.22. Found: C, 60.37; H, 5.37.
3
C54H52FeO12P2Mo: C, 58.60; H, 4.74. Found: C, 58.74; H, 5.04. 1H NMR (400 MHz, CDCl3): δ 3.25 (d, CH2, 8H, JHH = 6.0 Hz),
3
1H NMR (400 MHz, CDCl3): δ 3.21 (d, CH2, 8H, JHH = 6.8 Hz), 3.80 (s, OCH3, 12H), 4.99 (m, CH2, 8H), 5.85–5.91 (m, CH, 4H),
3
3.88 (s, OCH3, 12H), 5.05 (m, CH2, 8H), 5.90–5.98 (m, CH, 4H), 6.62 (m, C6H3, 4H), 7.04 (s, C6H3, 4H), 7.38 (d, C6H3, 4H, JHH
6.66 (m, C6H3, 4H), 6.68 (s, C6H3, 4H), 7.32 (d, C6H3, 4H, = 6.8 Hz), 4.55 (s, 4H, Fc), 4.97 (s, 4H, Fc). 31P{1H}NMR
3JHH = 7.6 Hz), 4.27 (s, 4H, Fc), 4.71 (s, 4H, Fc). IR (KBr disk): (162 MHz, CDCl3): δ 183.6 (s).
1927 (br), 2034 cm−1
.
31P{1H}NMR (162 MHz, CDCl3): δ 182.4 (s).
Synthesis of [{(η3-C3H5)Pd}Fe{C5H4P(OC6H3(OMe-o)(C3H5-
Synthesis of [{W(CO)4}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] p))2}2(OTf)] (11). A solution of [Pd(η3-C3H5)Cl]2 (0.006 g,
(7). Compound 7 was synthesized by a procedure similar to 0.017 mmol) in dichloromethane (5 mL) was added dropwise
that of 6 using [W(CO)4(pip)2] (0.011 g, 0.023 mmol) and 2 to a solution of 2 (0.030 g, 0.033 mmol) also in dichloro-
(0.020 g, 0.023 mmol). The analytically pure product 7 was methane (5 mL) with constant stirring. The reaction mixture
obtained as a pale yellow powder from a mixture of dichloro- was stirred for 2 h and then a solution of AgOTf (0.004 g,
methane and petroleum ether. Yield: 83% (0.018 g). Mp: 0.017 mmol) in acetonitrile was added. After stirring for 2 h,
11704 | Dalton Trans., 2013, 42, 11695–11708
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3
the solvent was concentrated under vacuum to 2 mL and then 4H, JHH = 7.8 Hz), 6.76 (s, C6H3, 4H), 4.76 (s, 4H, Fc), 5.08 (s,
layered with petroleum ether to give an analytically pure 4H, Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 137.1 (br, s).
product 11 as a pale yellow crystalline solid. Yield: 78%
Synthesis
of
[Cu5(µ-I)5{Fe{C5H4P(OC6H3(OMe-o)(C3H5-
(0.031 g). Mp: 155–157 °C. Anal. Calcd for C54H57F3- p))2}2}2]2 (15). A solution of cuprous iodide (0.013 g,
FeO11P2PdS: C, 54.26; H, 4.81; S, 2.68. Found: C, 54.22; H, 0.069 mmol) in acetonitrile (5 mL) was added to a solution of
1
4.61; S, 2.32. H NMR (400 MHz, CDCl3): δ 3.35 (d, CH2, 8H, 2 (0.031 g, 0.034 mmol) in dichloromethane (5 mL). After stir-
3JHH = 6.4 Hz), 3.82 (s, OCH3, 12H), 4.04 (m, br, CH2, 2H), ring for 4 h, the resulting solution was concentrated to 2 mL,
4.86 (m, br, CH2, 2H), 5.08 (m, CH2, 8H), 5.81–5.85 (m, br, CH, layered with 1 mL petroleum ether and stored at room temp-
1H), 5.85–5.95 (m, CH, 4H), 6.66 (m, C6H3, 4H), 6.77 (s, C6H3, erature for several days to afford analytically pure yellow 15
3
4H), 7.16 (d, C6H3, 4H, JHH = 6.8 Hz), 4.64 (s, 4H, Fc), crystals suitable for X-ray diffraction analysis. Yield: 65%
5.10 (s, 4H, Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 159.6 (s). (0.121 g). Mp: 208–211 °C (dec). Anal. Calcd for C200H208Cu10-
MS (EI): m/z = 1044.5 (M+ − OTf).
Fe4I10O32P8: C, 43.68; H, 3.81. Found: C, 44.03; H, 3.69. 1H
Synthesis of [{Ru2Cl4(η6-p-cymene)2}Fe{C5H4P(OC6H3(OMe-o)- NMR (400 MHz, CDCl3): δ 3.69 (s, OCH3, 12H), 3.31 (d, CH2,
(C3H5-p))2}2] (12). A solution of [Ru(η6-p-cymene)Cl2]2 8H, JHH = 6.4 Hz), 5.07 (m, CH2, 8H), 5.88–5.98 (m, CH, 4H),
3
3
(0.016 g, 0.026 mmol) in dichloromethane (4 mL) was added 6.61 (m, C6H3, 4H), 6.85 (d, C6H3, 4H, JHH = 7.0 Hz), 6.69 (s,
dropwise to a solution of 2 (0.023 g, 0.026 mmol) also in C6H3, 4H), 4.52 (s, 4H, Fc), 5.03 (s, 4H, Fc). 31P{1H}NMR
dichloromethane (6 mL). The reaction mixture was allowed to (162 MHz, CDCl3): δ 132.8 (br, s).
stir at room temperature for 4 h. The resulting blood-red solu-
Synthesis of [(AuCl)2Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]
tion was concentrated to 3 mL followed by the addition of pet- (16). A dichloromethane solution of AuCl(SMe2) (0.015 g,
roleum ether to give a red precipitate of 12. Red crystals were 0.051 mmol) was added dropwise to a solution of 2 (0.023 g,
obtained upon recrystallization from a 1 : 1 dichloromethane– 0.026 mmol) also in dichloromethane (6 mL). The reaction
petroleum ether mixture. Yield: 81% (0.029 g). Mp: 185–186 °C mixture was allowed to stir at room temperature for 4 h. The
(dec). Anal. Calcd for C70H80Cl4FeO8P2Ru2: C, 55.64; H, 5.34. resulting yellow solution was concentrated to 2 mL, followed
Found: C, 55.37; H, 5.37. 1H NMR (400 MHz, CDCl3): δ 1.02 (d, by layering with petroleum ether and stored at room temp-
3
CH3, 12H, JHH = 6.6 Hz), 2.6 (sept, CH, 2H), 3.52(d, CH2, 8H, erature for several days to give analytically pure pale yellow
3JHH = 6.6 Hz), 3.81 (s, OCH3, 12H), 4.98 (m, CH2, 8H), 5.04 (d, crystals of 16. Yield: 76% (0.026 g). Mp: 134–135 °C. Anal. Calcd
C6H4, 4H, 3JHH = 5.6 Hz), and 5.30 (d, C6H4, 4H, 3JHH = 5.6 Hz), for C50H52FeO8P2Au2Cl2: C, 44.04; H, 3.84. Found: C, 43.84; H,
5.80–5.89 (m, CH, 4H), 6.62 (m, C6H3, 4H), 6.67 (s, C6H3, 4H), 3.71. 1H NMR (400 MHz, CDCl3): δ 3.37 (d, CH2, 8H, 3JHH = 6.8
3
6.79 (d, C6H3, 4H, JHH = 7.84 Hz), 4.46 (s, 4H, Fc), 4.55 (s, 4H, Hz), 3.79 (s, OCH3, 12H), 4.97 (m, CH2, 8H), 5.91–5.98 (m, CH,
Fc). 31P{1H}NMR (162 MHz, CDCl3): δ 150.8 (s).
4H), 6.69 (m, C6H3, 4H), 6.76 (s, C6H3, 4H), 7.07 (d, C6H3, 4H,
Synthesis of [{(CuCl)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2] 3JHH = 7.0 Hz), 5.07 (s, 4H, Fc), 4.97 (s, 4H, Fc). 31P{1H}NMR
(13). A solution of cuprous chloride (0.005 g, 0.052 mmol) in (162 MHz, CDCl3): δ 142.6 (s).
acetonitrile (3 mL) was added to a solution of 2 (0.023 g,
Catalysis
0.026 mmol) in dichloromethane (5 mL). The mixture was
allowed to stir at room temperature for 4 h. The solvent was In a two-necked round-bottom flask under a nitrogen atmos-
evaporated to give an oily product which on repeated washing phere was placed an appropriate amount of catalyst solution
with petroleum ether and drying under vacuum for extended and 5 mL of methanol was added to it. The correct amount of
times gave an analytically pure pale yellow product 13. Yield: the catalyst was added as a methanol solution made up by
70% (0.036 g). Mp: 211–212 °C (dec). Anal. Calcd for multiple volumetric dilutions of stock solutions. After stirring
C
100H104Fe2O16P4Cu2Cl2: C, 60.19; H, 5.25. Found: C, 60.37; H, for 5 min, aryl bromide (0.5 mmol), arylboronic acid
1
5.34. H NMR (400 MHz, CDCl3): δ 3.73 (s, OCH3, 12H), 3.31 (0.75 mmol), and K2CO3 (0.138 g, 1 mmol) were introduced
(d, CH2, 8H, JHH = 6.4 Hz), 5.06 (m, CH2, 8H), 5.81–5.98 (m, into the reaction flask. The mixture was heated at 60 °C for the
3
3
CH, 4H), 6.69 (m, C6H3, 4H), 6.64 (d, C6H3, 4H, JHH = 7.92 required time under a nitrogen atmosphere (the course of reac-
Hz), 6.69 (s, C6H3, 4H), 5.10 (s, 4H, Fc), 4.60 (s, 4H, Fc). 31P{1H} tion was monitored by GC analysis), following which the
NMR (162 MHz, CDCl3): δ 134.4 (br, s).
solvent was removed under reduced pressure. The residue was
Synthesis of [Cu5(µ-Br)5{Fe{C5H4P(OC6H3(OMe-o)(C3H5- diluted with H2O (8 mL) and Et2O (8 mL) followed by extrac-
p))2}2}2]2 (14). This was synthesized by a procedure similar to tion twice with 6 mL of Et2O. The combined organic fractions
that of 13 using cuprous bromide (0.010 g, 0.067 mmol) and 2 were dried (MgSO4), stripped of the solvent under vacuum,
(0.030 g, 0.033 mmol). The analytically pure pale yellow crystal- and the residue was redissolved in 5 mL of dichloromethane.
line product 14 was obtained by keeping the saturated CH2Cl2– An aliquot was taken with a syringe and subjected to GC ana-
petroleum ether (1 : 1 mixture) solution of 14 at room temp- lysis. Yields were calculated versus aryl bromides.
erature for two days. Yield: 73% (0.121 g). Mp: >220 °C (dec).
X-ray crystallography
Anal. Calcd for C200H208Cu10Fe4Br10O32P8: C, 47.76; H, 4.17.
1
Found: C, 47.19; H, 3.89. H NMR (400 MHz, CDCl3): δ 3.54 (s, Crystals of each of the compounds 8, 9, 12, 15 and 16 suitable
OCH3, 12H), 3.38 (d, CH2, 8H, JHH = 6.4 Hz), 5.12 (m, CH2, for X-ray crystal analysis were mounted on a Cryoloop with a
3
8H), 5.80–5.98 (m, CH, 4H), 6.56 (m, C6H3, 4H), 6.98 (d, C6H3, drop of Paratone oil and placed in the cold nitrogen stream of
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the Kryoflex attachment of the Bruker APEX CCD diffracto- Ms. V. Lakshmi, Department of Chemistry IIT Bombay, for
meter. A full sphere of data was collected using 606 scans in ω their assistance in using the BAS electrochemical system.
(0.3° per scan) at φ = 0, 120 and 240° (8 and 15) or 3 sets of
400 frames, each of width 0.5° in ω, collected at φ = 0.00, 90.00
and 180.00° and 2 sets of 800 frames, each of width 0.45° in φ,
References
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APEX2 program suite.61 The raw data were reduced to F2 values
using SAINT+ software62 and a global refinement of unit cell
parameters using ca. 4626–9954 reflections chosen from the
full data set was performed. Crystals of 12 and 16 proved to be
twinned as determined by CELL_NOW63 and were integrated
using the two-component option in SAINT. In the case of 16,
refinement was done with the single-component reflection file
and the offending solvent was squeezed out. Multiple
measurements of equivalent reflections provided the basis for
an empirical absorption correction as well as a correction for
any crystal deterioration during the data collection (SADABS64a
for 8, 9 and 15; TWINABS64b for 12 and 16). The structures 8,
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program package.65 The structures were solved by direct
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Cyclic voltametric procedure
Cyclic voltammetric (CV) and differential pulse voltammetric
(DPV) studies were carried out with an electrochemical system
utilizing the three electrode configuration consisting of a
glassy carbon (working electrode), platinum wire (auxilary elec-
trode) and saturated calomel (reference electrode) electrodes.
The experiments were done in dry dichloromethane using 0.1
M tetrabutylammonium perchlorate as a supporting electro-
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anodic peak potentials. All potentials were calibrated versus
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internal standard, taking E1/2 (FcII/FcIII) = 0.46 V, vs. SCE.66
Acknowledgements
We are grateful to the CSIR, New Delhi for funding. We also
thank the Department of Chemistry Instrumentation Facilities,
IIT Bombay, for spectral and analytical data and J.T.M. thanks
the Louisiana Board of Regents for the purchase of the CCD
diffractometer and the Chemistry Department of Tulane Uni-
versity for support of the X-ray laboratory. S.R. thanks CSIR, 11 V. E. Albrow, A. J. Blake, R. Fryatt, C. Wilson and
New Delhi, for SRF. We thank Prof. M. Ravikanth and
S. Woodward, Eur. J. Org. Chem., 2006, 2549–2557.
11706 | Dalton Trans., 2013, 42, 11695–11708
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Paper
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