Stille cross-coupling of a racemic planar-chiral ferrocene and crystallographic trace analysis of catalysis intermediates and by-products

Article abstract of DOI:10.1002/hlca.200790083

A pressure-controlled procedure for the S_N1 reaction of rac-1-[(dimethylamino)methyl]-2-(tributylstannyl)ferrocene (1) to rac-1-(phthalimidomethyl)-2-(tributylstannyl)ferrocene (2) was developed. Pd⁰-Catalyzed Stille coupling of 2 with iodobenzene afforded rac-1-phenyl-2-(N-phthalimidomethyl)-ferrocene (5) in 74% yield; after trace enrichment by crystallization of the combined mother liquors, one single crystal of each, 5, catalysis intermediate trans-iodo(σ-phenyl) bis(triphenylarsino)palladium(II) (7), trans-diiodobis(triphenylarsino) palladium(II) (8), and rac-2,2′-bis(phthalimidomethyl)-1,1′- biferrocene (9) could be isolated by crystal sorting under a microscope and characterized by X-ray crystal structure analysis. Furthermore, 5 was deprotected to amine (11), which does even survive the Birch reduction to rac-1-(aminomethyl)-2-(cyclohexa-2,5-dienyl)ferrocene (12).

Full text of DOI:10.1002/hlca.200790083

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Helvetica Chimica Acta – Vol. 90 (2007)
Stille Cross-Coupling of a Racemic Planar-Chiral Ferrocene and
Crystallographic Trace Analysis of Catalysis Intermediates and By-products
by Immo Weber*1), Frank W. Heinemann, Panagiotis Bakatselos, and Ulrich Zenneck
Institut für Anorganische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg,
Egerlandstrasse 1, D-91058 Erlangen
Dedicated to the memory of Professor John K. Stille Ph.D.
A pressure-controlled procedure for the SN1 reaction of rac-1-[(dimethylamino)methyl]-2-(tribu-
tylstannyl)ferrocene (1) to rac-1-(phthalimidomethyl)-2-(tributylstannyl)ferrocene (2) was developed.
Pd0-Catalyzed Stille coupling of 2 with iodobenzene afforded rac-1-phenyl-2-(N-phthalimidomethyl)-
ferrocene (5) in 74% yield; after trace enrichment by crystallization of the combined mother liquors, one
single crystal of each, 5, catalysis intermediate trans-iodo(s-phenyl)bis(triphenylarsino)palladium(II)
(7), trans-diiodobis(triphenylarsino)palladium(II) (8), and rac-2,2’-bis(phthalimidomethyl)-1,1’-bifer-
rocene (9) could be isolated by crystal sorting under a microscope and characterized by X-ray crystal
structure analysis. Furthermore, 5 was deprotected to amine (11), which does even survive the Birch
reduction to rac-1-(aminomethyl)-2-(cyclohexa-2,5-dienyl)ferrocene (12).
1. Introduction. – Because of their unique properties, 1,2-disubstituted planar-chiral
ferrocenyl ligands gained a fundamental role in enantioselective catalysis over the past
decade [1a – h]. Mostly established by Togni and co-workers [1a – f], planar-chiral 1,2-
disubstituted ferrocenes are obtained in two steps starting from a ferrocene template
bearing a chiral auxiliary group, such as Ugiꢀs (R)- or (S)-[1-(dimethylamino)ethyl]-
ferrocene [1i]: The first ligating functionality is introduced via diastereoselective ortho
lithiation followed by electrophile quenching, the second by nucleophilic substitution
of the dimethylamino group. Enantioselective Pd0-catalyzed transformations [2a] are of
vast synthetic utility. Pedersenꢀs monodentate planar-chiral ferrocene ligands proved to
be highly active and enantioselective for Pd0-catalyzed hydrosilylation reactions [2b,c],
which contain an arene in ortho position to the donor group. Generally, coupling of
arene units with ferrocene cores have been achieved via Pd0-catalyzed Negishi [2b – e]
and Stille [3] cross-coupling reactions. Air-stable planar-chiral ortho-(tributylstannyl)-
ferrocenes are very attractive intermediates due to their synthetic versatility. Besides
Stille couplings with various aryl iodides, the stannyl group can be exchanged with BuLi
followed by quenching with electrophiles; direct halo exchange in the sense of an
ꢁUmpolungꢀ for coupling reactions is also possible [3b]. For catalytic applications, we
became also interested in planar-chiral ortho-substituted arylferrocene derivatives [4].
In a preliminary study, starting from rac-1-[(dimethylamino)methyl]-2-(tributylstan-
1
)
Present address: Kunststoff- und Metallwaren-Fabrik (KUM) GmbH & Co. KG, Abteilung
Forschung und Entwicklung, Essenbacher Strasse 2, D-91054 Erlangen (phone: þþ 49-(0)9131-
826823; fax: þþ 49-(0)9131-788629; e-mail: immo.weber@kum.net).
ꢂ 2007 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 90 (2007)
835
nyl)ferrocene (1) [3c] (Scheme 1), we therefore explored the Stille coupling reaction of
a racemic planar chiral stannylated ferrocene because protocols reported in [3] vary in
detail (ligands, additives, solvents, temperature).
Scheme 1
a) In closed Schlenk tube in situ: 1. MeI (1.1 equiv.), DMF r.t.; 2. Et3N (0.4 equiv.), r.t.; 3. potassium
phthalimide (1.4 equiv.), 1008, 15 h. b) Catalyst mixture [Pd2(dba)3] · CHCl3 (0.025 equiv.)/AsPh3
(0.15 equiv.)/CuI (0.50 equiv.) PhI (1.9 equiv.), DMF, 708, 14 h. c) Hydrazine hydrate (10.4 equiv.),
EtOH, 708, 1 h. d) Li (12.5 equiv.)/liq. ammonia, EtOH, THF, À 788 ; 2. NH4Cl (13.8 equiv.).
a) Product not further purified.
2. Results and Discussion. – For the nucleophilic substitution reaction of the
dimethylamino group of 1 with potassium phthalimide to rac-1-(phthalimidomethyl)-
2-(tributylstannyl)ferrocene (2), Weissensteinerꢀs protocol [5a,b] was envisaged
(Scheme 2). A dialkylamino group of an 1,2-disubstituted planar-chiral ferrocene
derivative such as 1 is activated by permethylation and then substituted with
nucleophiles under reflux in a polar aprotic solvent (DMF, MeCN, etc.) in SN1 fashion,
which is well established to proceed via (h4 :h2)-fulvenium complexes [1a – c][1e,f].
Such complexes were isolated [5c]. However, this method is not easily applicable for
ferrocene derivatives with highly activating electron-donor substituents such as
trialkylstannyl groups, which are bulky at the same time. In the case here, the
corresponding energetically stabilized (h4 :h2)-fulvenium complex (4) (Scheme 2) is

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Helvetica Chimica Acta – Vol. 90 (2007)
Scheme 2. in situ SN1-Type Reaction Pathway of 1 to 2 via (h4 :h2)-Fulvenium Intermediate 4
a) Oxidative addition of iodobenzene to catalyst 6 (see Scheme 3). b) Transmetallation (often rate
limiting). c) Reductive elimination to coupling product 5 and backformation of 6.
readily formed from 3 under the extrusion of Me3N, but decomposes also faster than the
subsequent reaction with the nucleophile can occur, due to steric repulsion. Therefore,
these two antagonistic effects cannot be overcome by simple temperature control. To
outflank this dilemma, the Weissensteiner protocol was optimized to an in situ and
pressure-controlled procedure for the synthesis of rac-ferrocene derivative 2.
Ferrocene derivative 1 was directly N-permethylated in DMF with MeI (! 3),
followed by addition of potassium phthalimide and heating in a closed Schlenk tube.
Keeping the mixture under pressure in this way decelerates the formation of the
(h4 :h2)-fulvenium complex 4 sufficiently to give the potassium phthalimide enough
time to react since gaseous Et3N cannot escape the closed system. Choosing DMF as
solvent has the advantage that 2 is constantly removed because it separates as a second
and less polar liquid phase. With this method, racemic 2 was obtained in 84% yield after
purification. Quenching of excess MeI with Et3N after N-permethylation is essential.
Otherwise N-methylphthalimide forms which cannot be easily removed from the
desired reaction product leading to significant losses in yield.
The Stille cross-coupling of 2 with iodobenzene to rac-1-phenyl-2-(phthalimido-
methyl)ferrocene (5) was oriented on Curnowꢀs procedure [6a] for coupling electron-
rich and sterically demanding stannyl compounds with iodobenzene. A mixture of
5 mol-% Pd0 from 2.5 mol-% [Pd2(dba)3] · CHCl3/CuI/AsPh3 1:10 :3 (dba ¼
dibenzylideneacetone ¼ 1.5-diphenylpenta-1,4-dien-3-one) in DMF was also found to
be optimal here. The actual catalyst formed in situ is obviously bis(triphenylarsino)-
palladium(0) (6) (see Scheme 3 for a generally accepted catalytic cycle proposed on
coupling of 2 to 5). After recrystallization, racemic 5 was obtained in 74% yield.

Helvetica Chimica Acta – Vol. 90 (2007)
837
Scheme 3. Catalytic Cycle Proposed for the Stille Coupling of 2 to 5
Unfortunately, traces of other by-products could not be removed completely from 5,
also not by column chromatography, so a correct elementary analysis could not be
obtained. Crystallization of combined mother liquors succeeded at least in a trace
enrichment of these impurities, i.e., of 7 – 9 (Scheme 3). Single crystals of racemic 5
(Fig. 1, Table 1)2), catalysis intermediate (7) (Fig. 2, Table 2), diiodo complex (8)
(Fig. 3, Table 3) and of rac-2,2’-bis(phthalimidomethyl)-1,1’-biferrocene (9; Fig. 4,
3
`
Table 4) were obtained ꢁa la Pasteurꢀ by tedious sorting under a microscope ).
The catalysis intermediate 7 is isostructural to the analog phosphine complex trans-
[PdII(I)(Ph)(PPh3)2] in the solid state, but not isomorphous [6b]. Intermediate 7 shows
furthermore an extraordinary trans influence of the s-phenyl on the iodo ligand
because nearly all ligands are bent out of the square planar geometry compared with
the nearly perfect square planar structure of diiodo complex 8. Three possible
explanations for the formation of the racemic like-like ferrocene diastereoisomer 9,
2
)
Coupling product 5 crystallized so fast, even under slow solvent diffusion into a diluted solution,
that suitable crystals for X-ray structure analysis could be only obtained by slow crystallization from
the combined mother liquors.
After solvent removal, the combined mother liquors contained nearly exclusively iodobenzene and
5; in the NMR spectra of the crude product and of the combined mother liquors, PdII complexes 7
and 8 as well as by-product 9 could be only insufficiently identified due to signal overlap and very
low concentration (d 7 – 8, aromatic region, d 4 – 6, h5-cyclopentadienyl moieties). A full
spectroscopic analysis of 7 – 9 was not possible due to the low amount of material isolated.
3
)

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Helvetica Chimica Acta – Vol. 90 (2007)
Fig. 1. Thermal ellipsoid plot (50% probality) of racemic 5. The (P)-enantiomer is shown; for selected
bond distances and angles, see Table 1.
Table 1. Selected Bond Distances and Bond Angles of rac-5
Distance
[Š]
Bond angle
[8]
N(1)ÀC(11)
C(11)ÀC(10)
C(10)ÀC(9)
C(9)ÀC(20)
C(9)ÀFe(1)
C(10)ÀFe(1)
1.458(2)
1.513(2)
1.441(2)
1.486(2)
2.053(2)
2.047(2)
N(1)ÀC(11)ÀC(10)
C(11)ÀC(10)ÀC(9)
C(10)ÀC(9)ÀC(20)
C(9)ÀFe(1)ÀC(1)
C(9)ÀFe(1)ÀC(2)
C(10)ÀFe(1)ÀC(2)
C(10)ÀFe(1)ÀC(3)
111.2(2)
126.7(2)
128.6(2)
149.28(7)
169.08(7)
148.77(7)
169.26(7)
which bears two chiral planes and one chiral axis, can be given: i) intramolecular ipso
transmetallation of PdII intermediate 10 (Scheme 3) followed by reductive elimination
to catalyst 6 and by-product 9; ii) transmetallation of two molecules 2 on a
[PdII(AsPh3)2] complex similar to 8 evolved from oxidation followed again by
reductive elimination to 6 and 9; iii) or most likely, the formation of 9 is due to
transmetallation of two molecules 2 on traces of CuII resulting then in an Ullmann-type
reductive elimination [6c – e].
Complementary, it should be mentioned that the synthesis of 2,2’-diformyl-1,1’-
biferrocene via Ullmann coupling has been achieved by Nicolosi and co-workers [6e].
The last explanation (iii)) is also consistent with the fact that copper salts are often
required for Stille cross-coupling reactions which do not proceed otherwise. In this
sense, CuI or CuO might activate the SnÀC bond enabling transmetallation.
Furthermore, simple alkynes couple with iodoferrocenes just in the presence of copper
salts by using a palladium catalyst [6f]. Copper salts could also trap excess ligand, but
this is of debate because copper salts have to be added stoichiometrically also to Stille
coupling reactions with preformed Pd0 catalysts containing bidentate ligands [3b]. In

Helvetica Chimica Acta – Vol. 90 (2007)
839
Fig. 2. Thermal ellipsoid plot (50% probality) of catalysis intermediate trans-[PdII(I)(Ph)(AsPh3)2] (7).
H-Atoms are omitted for clarity; for selected bond distances and angles, see Table 2.
Table 2. Selected Bond Distances and Bond Angles of Catalysis Intermediate trans-[PdII(I)-
(Ph)(AsPh3)2] (7)
Distance
[Š]
Bond angle
[8]
Pd(1)ÀAs(1)
Pd(1)ÀAs(2)
Pd(1)ÀI(1)
Pd(1)ÀC(1)
2.4335(6)
2.4187(6)
2.6743(7)
2.010(5)
As(1)ÀPd(1)ÀAs(2)
C(1)ÀPd(1)ÀI(1)
C(1)ÀPd(1)ÀAs(2)
I(1)ÀPd(1)ÀAs(1)
171.77(2)
173.5(2)
83.9(2)
94.47(2)
our hands, using triphenylphosphine or 1,1’-bis(diphenylphosphino)ferrocene (dppf)
instead of triphenylarsine under otherwise identical reaction conditions did not lead to
any success here. All attempts to couple 1-iodo-2-(phthalimidomethyl)ferrocene with
stannyl building blocks under otherwise identical reaction conditions (5 mol-%
Pd0/CuI/AsPh3 1:10 :3 in DMF) failed as well.
Racemic ferrocene 5 was then deprotected with hydrazine to the free primary
amine 11 in 89% yield after chromatography (Scheme 1). Birch reduction [7] of 11
required ca. 12.5 equiv. of lithium. THF had to be used as a cosolvent due to the low
solubility of 11 in EtOH at low temperature. Nevertheless, cyclohexadienylferrocene
12 was obtained nearly pure in 96% yield without further purification. The ferrocene
backbone stayed intact during the Birch reduction. However, all attempts to induce 12
to react with RuCl3 to the corresponding ansa complex rac-dichloro{1-[(amino-
kN)methyl]-2-(h6-phenyl)ferrocene}ruthenium(II) under standard conditions (ammo-
nium salt, EtOH) [8] resulted in total decomposition. It was also tried to let 12 react

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Fig. 3. Thermal ellipsoid plot (50% probality) of trans-[PdII(I)2(AsPh3)2] (8). H-Atoms are omitted for
clarity; for selected bond distances and angles, see Table 3.
Table 3. Selected Bond Distances and Bond Angles of trans-[PdII(I)2(AsPh3)2] (8)
Distance
[Š]
Bond angle
[8]
Pd(1)ÀAs(1)
Pd(1)ÀI(1)
2.4356(3)
2.6060(3)
As(1)ÀPd(1)ÀAs(1A)a)
I(1)ÀPd(1)ÀI(1A)a)
As(1)ÀPd(1)ÀI(1)
180
180
88.04(1)
91.96(1)
I(1)ÀPd(1)ÀAs(1A)a)
a) Symmetry transformation: À x þ 1, À y þ 1, À z
with ꢁruthenium inkꢀ (preformed by refluxing RuCl3 in EtOH), without success. A brief
investigation of this ꢁblue inkꢀ by cyclovoltammetry (CV), which is said to consist only
of RuII ions, a widespread statement in textbooks, revealed that ꢁruthenium inkꢀ is a
ꢁliving solutionꢀ of RuIII species with standard potentials around 700 mV in the sense
that this solution dynamically changes in composition without reaching a defined
equilibrium. This is well above the standard potential of 450 – 500 mV typically found
for ferrocene derivatives, so the failure of this synthesis attempt is due to the oxidation
of the ferrocene moiety by RuIII. Therefore, further attempts to obtain the desired ansa
complex, even by variation of this method, were abandoned. Conclusively, for the
direct synthesis of [RuII(h6-arene)] complexes with RuCl3 in alcoholic solution, the
substituents attached at the cyclohexadiene derivatives must be capable to withstand an
oxidation potential above 700 mV.
3. Conclusions. – Although the originally anticipated synthesis of the ansa [RuII(h6-
arene)] complex had to fail, both, the in situ substitution of 1 to 2 and the Stille coupling
of 2 to 5 are of potential synthetic utility: A detour for the preparation of 1,2-
disubstituted planar-chiral ferrocene ligands via ortho-stannylated ferrocene analogs of
1 is indicated if the desired ortho substituents strongly deactivate the formation of the
corresponding (h4 :h2)-fulvenium complex or if they are prone for side reactions in the

Helvetica Chimica Acta – Vol. 90 (2007)
841
Fig. 4. Thermal ellipsoid plot (50% probality) of rac-2,2’-bis(phthalimidomethyl)-1,1’-biferrocene (9).
The (M,M,M)-diastereoisomer is shown; H-atoms are omitted for clarity; for selected bond distances
and angles, see Table 4.
Table 4. Selected Bond Distances and Bond Angles of rac-2,2’-Bis(phthalimidomethyl)-1,1’-biferrocene
(9)
Distance
[Š]
Bond angle
[8]
N(1)ÀC(11)
C(11)ÀC(10)
C(10)ÀC(9)
C(9)ÀC(28)
C(28)ÀC(29)
C(29)ÀC(30)
C(30)ÀN(2)
C(10)ÀFe(1)
C(9)ÀFe(1)
C(28)ÀFe(2)
C(29)ÀFe(2)
1.469(3)
1.502(4)
1.441(4)
1.472(4)
1.434(4)
1.501(4)
1.464(3)
2.041(3)
2.056(3)
2.060(3)
2.036(3)
N(1)ÀC(11)ÀC(10)
C(11)ÀC(10)ÀC(9)
C(10)ÀC(9)ÀC(28)
C(9)ÀC(28)ÀC(29)
C(28)ÀC(29)ÀC(30)
C(29)ÀC(30)ÀN(2)
C(9)ÀFe(1)ÀC(4)
C(9)ÀFe(1)ÀC(5)
C(10)ÀFe(1)ÀC(5)
C(28)ÀFe(2)ÀC(20)
C(29)ÀFe(2)ÀC(22)
113.0(2)
126.4(3)
125.2(2)
125.7(2)
126.0(3)
112.6(2)
127.2(2)
164.0(2)
153.1(2)
155.4(2)
166.1(2)
following nucleophilic substitution of the (dimethylamino)group. After nucleophilic
substitution at the fulvenic position, the originally desired ortho substituent can be
introduced via stannyl – lithio exchange followed by electrophile quenching or by a
Stille coupling with a haloarene, for example. Because catalysis intermediate 7 is
isostructural to the analog phosphine complex, the reason for the efficiency of the
catalyst mixture applied here (5 mol-% Pd0/CuI/AsPh3 1:10 :3) in DMF might be

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simply based upon the obviously inherent stability of catalyst 6 and of catalysis
intermediate 7. It is remarkable that 7 does not only withstand an aqueous workup with
an aqueous fluoride solution in air but also two crystallization cycles under aerobic
conditions.
Financial support by the Deutsche Forschungsgemeinschaft (SFB 583) and the Kunststoff- und
MetallwarenfabrikErlangen (KUM) GmbH & Co. KG is gratefully acknowledged. We are indebted to
´
´
Dr. Konrad Szaciłowski (Wydział Chemii, Uniwersytet Jagiellonski, Krakow, Poland) for CV measure-
ments and for helpful discussions. We are grateful to Professor Dr. Peter Gmeiner (Emil Fischer Zentrum
– Lehrstuhl für Pharmazeutische Chemie und Lebensmittelchemie, Friedrich-Alexander-Universität
Erlangen-Nürnberg) for providing access to a melting-point apparatus.
Experimental Part
1. General. All reactions were carried out under dry N2 by using conventional Schlenk and septum
techniques. All workups were performed in air. Solvents and chemicals were purchased from Acros,
Aldrich, Strem, and Merck. Solvents were dried and distilled under N2 according to standard techniques
prior to use: THF over sodium/benzophenone; DMF and Et3N over CaH2; EtOH over Mg. All other
chemicals were used as received. Racemic 1-[(dimethylamino)methyl]-2-(tributylstannyl)ferrocene (1)
was prepared by a slightly modified known procedure [3c]. Melting points: Büchi-530 melting point
apparatus, not corrected. Flash column chromatography (FC): silica gel F 60 from Fluka or Merck. TLC:
Merck-F-60 silica plates with a 364 nm fluorescence indicator. NMR Spectra: Jeol FT-JNM-EX-270
(270 MHz) and Bruker AMX-300 (300 MHz) spectrometers; in deuterated solvents and referenced to
the residual proton signal of the particular solvent. Mass spectra: Varian MAT-212 spectrometer.
Elemental analyses: Carlo-Erba elemental analyzer, model 1108.
2. rac-1-[(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)methyl]-2-(tributylstannyl)ferrocene (2). Caution!
All operations must be performed in a hood! To a suspension of racemic 1 (17.48 g, 32.84 mmol) in DMF
(35 ml) in a Schlenk tube capable to withstand a minimum pressure of 10 bar, MeI (2.30 ml, 5.34 g,
36.95 mmol) was added dropwise at r.t. The suspension was stirred for 30 min at r.t. until it became a clear
orange soln. and heat evolution ceased. Excess MeI was then quenched with Et3N (2.00 ml, 14.35 mmol).
Solid potassium phthalimide (8.19 g, 44.21 mmol) was added, and the suspension was diluted with DMF
(10 ml). The inhomogeneous mixture was stirred for 15 h at 1008 in the closed Schlenk tube to become a
nearly clear deep orange soln. after reaching the reaction temp. The endpoint of the reaction was
indicated by the separation of two liquid phases. Caution! Before opening, the Schlenk tube must slowly
cool down to room temperature! After such a cooling down to r.t., excess potassium phthalimide
precipitated. The mixture was diluted with Et2O, and excess potassium phthalimide was filtered off over a
D4-sinter with vacuum suction. The filter cake was washed with Et2O. The combined filtrate and washing
soln. was diluted with AcOEt and the soln. washed eight times with brine until free of DMF, dried
(MgSO4), and concentrated to give nearly pure 2 (19.08 g, 92%), which was purified by FC (substance
applied in eluent, hexanes/AcOEt 2 :1): 17.45 g of pure racemic 2. Red oil solidifying to a waxy
semicrystalline mass upon standing. M.p. 65 – 678 (rac.). 1H-NMR (CDCl3, 270 MHz): 7.79 (m, HÀC(4)
and HÀC(7) of C6H4(CO)2N); 7.66 (m, HÀC(5) and HÀC(6) of C6H4(CO)2N); 4.65 (d, 2J ¼ 14.53, 1 H,
CH2); 4.53 (m, 1 H, Cp); 4.43 (d, 2J ¼ 14.53, 1 H, CH2); 4.26 (ꢁtꢀ, 1 H, Cp); 4.11 (s, 5 H, Cp’); 3.91 (m, 1 H,
Cp); 1.60 – 1.52 (not resolved t, 3 MeCH2CH2CH2); 1.42 – 1.28 (not resolved tt, 3 MeCH2CH2CH2); 1.20 –
1.09 (not resolved qt, 3 MeCH2CH2CH2); 0.89 (t, 3J ¼ 7.27, 3 MeCH2CH2). 13C{1H}-NMR (CDCl3,
68 MHz): 167.78 (C6H4(CO)2N); 133.74 (C(5) and C(6) of C6H4(CO)2N); 132.08 (C(3a) and C(7a) of
2
C6H4(CO)2N); 123.08 (C(4) and C(7) of C6H4(CO)2N); 88.51 (d, J(C,Sn) ¼À 38.2, C(1) of Cp); 75.13
(d, J(C,Sn) ¼À 22.5, Cp); 71.98 (d, J(C,Sn) ¼ À28.2, Cp); 71.16 (d, J(C,Sn) ¼ À34.2, Cp); 70.48 (d,
2
1J(C,Sn) ¼ À29.9, C(2) of Cp); 68.66 (Cp’); 38.51 (CH2); 29.31 (MeCH2CH2CH2); 27.48 (d, J(C,Sn) ¼
1
À61.7, MeCH2CH2CH2); 13.68 (MeCH2CH2CH2); 10.95 (d, J(C,Sn) ¼ À320.8, MeCH2CH2CH2). FD-
MS (pos.; CHCl3): 634 (100, Mþ with respect to 56Fe). Anal.calc. for C31H41FeNO2Sn (634.23): C 58.71, H
6.52, N 2.21; found: C 58.47, H 6.75, N 2.20.

Helvetica Chimica Acta – Vol. 90 (2007)
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3. rac-1-[(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)methyl]-2-phenylferrocene (5). Caution! All op-
erations must be performed in a hood! All glassware for this reaction must be cleaned in a base bath before
use and rinsed with dist. H2O only (not with acid or acetone!!), and heated in an oven at 2008 overnight!
The reaction tolerates traces of moisture, but air must be vigorously excluded. Into a Schlenk tube were
weighed under air first 2 (8.209 g, 12.943 mmol), then [Pd2(dba)3] · CHCl3 (335 mg, 0.324 mmol), then
CuI (1.235 g, 6.485 mmol), and finally AsPh3 (595 mg, 1.943 mmol), in this order. After three
evacuation – N2 flushcycles, the mixture was suspended in DMF (55 ml), and then freshly distilled
iodobenzene (2.80 ml, 5.096 g, 24.979 mmol) was added. The mixture was stirred for 14 h at 708 until
precipitation of ꢁpalladium blackꢀ indicated the endpoint of the reaction. Alternatively, the reaction was
monitored by TLC (hexanes/AcOEt 2 :1; Rf(2) 0.56 and Rf(5) 0.42). After cooling to r.t., KF (ca. 2.2 g)
and then dist. H2O (ca. 20 ml) were added into the open flask, whereupon the mixture became warm and
was stirred for 30 min at r.t. to ensure total cleavage of all organostannane compounds. All solid residues
of the black suspension were filtered off over a D3 sinter with cellulose flakes by vacuum suction. The
filter cake was washed with AcOEt. The combined filtrate and washing soln. was diluted with AcOEt and
the soln. washed eight times with brine until free of DMF, dried (MgSO4), and concentrated to give an
orange microcrystalline squash (ca. 10.91 g) containing nearly exclusively iodobenzene and 5. The crude
product was dissolved in a minimum amount of hot AcOEt, the soln. was layered with pentane, and
crystallization was completed overnight at À 308. After a second recrystallization of the same kind finally
nearly pure racemic 5 (4.012 g, 74%) was obtained as deep orange crystals. After recrystallization, the
product was not free of catalyst or ligand traces, so it must also be considered as potentially toxic! The
combined mother liquors were crystallized at À 308 from AcOEt only to give a crystal mixture mostly
consisting of racemic 5. From this mixture, one single crystal of racemic 5, one of intermediate trans-
[PdII(I)(Ph)(AsPh3)2] (7), one of trans-[PdII(I)2(AsPh3)2] (8) and one of rac-2,2’-bis[(1,3-dihydro-1,3-
dioxo-2H-isoindol-2-yl)methyl)]-1,1’-biferrocene (9) were isolated under a microscope by crystal color
and shape, which were all suitable for X-ray crystal-structure determination (see below). Crystal sizes
[mm]: 0.35 ꢀ 0.13 ꢀ 0.11 (5), 0.11 ꢀ 0.10 ꢀ 0.07 (7), 0.18 ꢀ 0.18 ꢀ 0.09 (8), and 0.28 ꢀ 0.14 ꢀ 0.08 (9). 5:
1
M.p. 1468 (rac.). H-NMR (CDCl3, 270 MHz): 7.84 – 7.79 (m, HÀC(4) and HÀC(7) of C6H4(CO)2N);
7.66 (2m, HÀC(5) and HÀC(6) of C6H4(CO)2N, and 2 Ho of Ph); 7.43 – 7.26 (m, 2 Hm and 1 Hp of Ph);
4.90 (d, 2J ¼ 14.8, 1 H, CH2); 4.70 (d, 2J ¼ 14.8, 1 H, CH2); 4.39 (ꢀdꢀ, 2 H, Cp); 4.20 (ꢁtꢀ, 1 H, Cp); 4.12 (s,
5 H, Cp’). 13C{1H}-NMR (CDCl3, 68 MHz): 167.95 (C6H4(CO)2N); 137.58 (Cipso of Ph); 133.89 (C(5) and
C(6) of C6H4(CO)2N); 131.95 (C(3a) and C(7a) of C6H4(CO)2N); 129.63 (Cm of Ph); 127.96 (Co of Ph);
126.52 (Cp of Ph); 123.22 (C(4) and C(7) of C6H4(CO)2N); 87.96 (C(2) of Cp); 82.35 (C(1) of Cp); 70.17
(Cp’); 69.17 (Cp); 68.83 (Cp); 67.26 (Cp); 36.09 (CH2). FD-MS (pos.; CHCl3): 422 (100, Mþ with respect
to 56Fe). A correct elementary analysis could not be obtained.
4. rac-1-(Aminomethyl)-2-phenylferrocene (11). A suspension of 5 (5.814 g, 13.80 mmol) and of
hydrazine hydrate (7.00 ml, 7.210 g, 144.03 mmol) in EtOH p.a. (100 ml) was refluxed for 75 min at 958.
White phthalazine-1,4-dione started to precipitate once the reaction temp. was reached. After cooling to
r.t., Et2O was added, the solid phthalazine-1,4-dione sucked off and washed with Et2O, and the red soln.
combined with the washing soln. concentrated. The residue was redissolved in Et2O and the org. phase
washed once with brine (made alkaline with NaOH), dried (MgSO4), and concentrated to give crude
product (4.031 g, quant.) which was purified by FC (hexanes/CH2Cl2 1:5 þ 10% Et3N): 3.584 g (89%) of
pure racemic 11. Red oil. 1H-NMR (CDCl3, 270 MHz): 7.57 – 7.50 (m, 2 Ho of Ph); 7.36 – 7.19 (2m, 2 Hm
and Hp of Ph); 4.44 (ꢁtꢀ, 1 H, Cp); 4.33 (ꢁtꢀ, 1 H, Cp); 4.21 (ꢀtꢀ, 1 H, Cp); 4.09 (s, 5 H, Cp’); 3.82 (d, 2J ¼ 14.1,
1 H, CH2); 3.76 (d, 2J ¼ 14.1, 1 H, CH2); 1.60 (br. s, NH2). 13C{1H}-NMR (CDCl3, 68 MHz): 138.30 (Cipso
of Ph); 128.64 (Cm of Ph); 127.90 (Co of Ph); 126.04 (Cp of Ph); 88.13 (C(1) of Cp); 86.41 (C(2) of Cp);
69.64 (Cp’ and Cp); 68.18 (Cp); 66.56 (Cp); 40.22 (CH2). FD-MS (pos.; CHCl3): 292 (100, [M þ H]þ with
respect to 56Fe). Anal. calc. for C17H17FeN (291.17): C 70.13, H 5.88, N 4.81; found: C 70.12, H 5.92, N
4.79.
5. rac-1-(Aminomethyl)-2-(cyclohexa-2,5-dienyl)ferrocene (12). To freshly condensed liquid ammo-
nia (130 ml) was canuled a precooled soln. of racemic 11 (2.254 g, 7.74 mmol) in EtOH (10 ml) and THF
(45 ml) at À 788. Then Li (670 mg, 96.53 mmol) was added, and the soln. was stirred vigorously at À 788.
The blue color of solvated electrons persisted for 1 h before the reaction was quenched with NH4Cl
(5.703 g, 106.62 mmol). After evaporation of ammonia, the residue was poured into brine (made alkaline

844
Helvetica Chimica Acta – Vol. 90 (2007)
with NaOH), the aq. phase extracted twice with Et2O, and the combined org. phase dried overnight
(Na2SO4) and concentrated: 2.184 g (96%) of racemic 12 (free of any starting material by NMR). Red oil
1
which was not further purified. H-NMR (CDCl3, 270 MHz): 6.00 – 5.76 (2m, HÀC(2) and HÀC(6) of
C6H7); 5.76 – 4.48 (2m, HÀC(3) and HÀC(5) of C6H7); 4.15 (m, 1 H, Cp); 4.10 (s, 5 H, Cp’); 4.04 (m,
HÀC(1) of C6H7); 4.00 (ꢀtꢀ, 1 H, Cp); 3.96 (m, 1 H, Cp); 3.63 (d, 2J ¼ 14.2, 1 H, CH2); 3.54 (d, 2J ¼ 14.2,
1 H, CH2); 2.68 – 2.65 (m, CH2(4) of C6H7). 13C{1H}-NMR (CDCl3, 68 MHz): 128.85 (C(3) or C(5) of
C6H7); 128.1 (C(5) or C(3) of C6H7); 124.41 (C(2) or C(6) of C6H7); 123.17 (C(6) or C(2) of C6H7); 91.07
(C(2) of Cp); 87.91 (C(1) of Cp); 68.65 (Cp’); 67.65 (Cp); 67.44 (Cp); 65.58 (Cp); 39.84 (CH2); 33.90 (C(1)
of C6H7); 25.92 (C(4) of C6H7). FD-MS (pos.; CHCl3): 294 (100, [M þ H]þ with respect to 56Fe).
6. Crystal Structure Determinations4). Crystal parameters, data collection, and structure refinement
details are summarized in Table 5. Intensity data were collected at 100 K on a Bruker-Nonius-KappaCCD
diffractometer (MoKa radiation, l 0.71073 Š, graphite monochromator). All structures were solved by
direct methods [9] and refined by full-matrix least-squares procedures on F2. All non-H-atoms were
refined with anisotropic displacement parameters. Absorption corrections were performed on the basis
of multiple scans with SADABS [9c]. All H-atoms were placed in positions of optimized geometry; their
isotropic displacement parameters were tied to the equivalent isotropic displacement parameters of their
Table 5. Crystallographic Data for 5, 7, 8 and 9 · 0.65 AcOEt. All measured at 100 K.
5
7
8
9 · 0.65 AcOEt
Empirical formula
Mr
C25H19FeNO2
421.26
C42H35As2IPd
922.84
C36H30As2I2.Pd C40.6H33.2Fe2N2O5.3
972.64
745.59
Crystal system
Space group
a [Š]
b [Š]
c [Š]
orthorhombic
Pbca (no. 61)
16.318(2)
7.9306(6)
29.038(3)
90
orthorhombic triclinic
monoclinic
P21/C (no. 14)
13.310(2)
7.3722(6)
34.450(3)
90
97.95(1)
90
3347.9(6)
4
¯
Pbca (no. 61)
19.503(2)
10.846(2)
33.315(3)
90
90
90
7047(2)
8
P1 (no. 2)
10.1917(7)
12.6708(9)
13.1838(9)
84.614(8)
77.726(7)
78.764(6)
1629.3(2)
2
a [8]
b [8]
90
90
g [8]
V [Š3]
Z
3757.9(7)
8
1.489
0.825
1744
1 [g/cm3] (calc.)
1.740
1.983
1.479
0.917
1541
m [mmÀ1
F (000)
]
3.296
4.504
3616
928
Tmin; Tmax
0.763; 0.910
0.654; 0.790
0.469; 0.667
0.750; 0.929
2q interval [8]
Lim. indices
7.1 ꢁ 2q ꢁ 555.8 7.3 ꢁ 2q ꢁ 54.2 6.5 ꢁ 2q ꢁ 55.8 7.0 ꢁ 2q ꢁ 51.4
À 21 ꢁ h ꢁ 21;
À 10 ꢁ k ꢁ 10;
À 38 ꢁ l ꢁ 38
37177
À 24 ꢁ h ꢁ 25; À 13 ꢁ h ꢁ 13;
À 13 ꢁ k ꢁ 13; À 16 ꢁ k ꢁ 16;
À 16 ꢁ h ꢁ 16;
À 8 ꢁ k ꢁ 8;
À 42 ꢁ l ꢁ 42
38439
À 41 ꢁ l ꢁ 42
51608
7744
À 17 ꢁ l ꢁ 17
35711
7759
Coll. refl.
Indep. refl.
4474
6250
Obs. refl. (I0 ꢂ 2s(I))
No. ref. param.
wR2 (all data)
R1 (I0 ꢂ 2s(I))
GooF (on F2)
3677
262
0.0700
0.0304
6022
415
0.0893
0.0449
1.115
6408
373
0.0488
0.0219
1.026
4956
494
0.1076
0.0459
1.030
1.022
Max.; min. res. electr. density 0.330; À 0.275
1.863; À 0.910 0.837; À 0.930 0.857; À 0.933
4
)
CCDC-618850 (for 5), CCDC-618851 (for 7), CCDC-618852 (for 8), and CCDC-618853 (for 9 ·
0.65 AcOEt) contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif.

Helvetica Chimica Acta – Vol. 90 (2007)
845
corresponding carrier atoms by a factor of 1.2 or 1.5, resp. Compound 9 crystallized with ca.
0.65 molecules of AcOEt per formula unit, which are disordered; two preferred positions could be
refined, which are occupied by 44.5(6)% and 20.5(6)% in the crystal. The unit cell of the Pd-complex 8
contains two symmetry-independent molecule halves in the asymmetric unit, which are each located on
crystallographic inversion centers. For PdII intermediate 7, the highest maximum of residual electron
density is located in trans position to the iodo ligand. Distance and location of this maximum suggest that
the crystal structure contains traces of the corresponding diiodo complex 8 of not more than 3%.
Attempts to consider these traces by a disorder model did not lead to satisfying results.
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Received August 30, 2006