Synthesis, electrochemistry, spectroelectrochemistry, and solid-state structures of palladium biferrocenylphosphines and their use in C,C cross-coupling reactions

Article

pubs.acs.org/Organometallics

Synthesis, Electrochemistry, Spectroelectrochemistry, and

Solid-State Structures of Palladium Biferrocenylphosphines and

Their Use in C,C Cross-Coupling Reactions

Manja Lohan, Bianca Milde, Silvio Heider, J. Matthaus Speck, Sabrina Krauße, Dieter Schaarschmidt,

̈

Tobias Ruffer, and Heinrich Lang*

̈

Faculty of Science, Institute of Chemistry, Department of Inorganic Chemistry, Chemnitz University of Technology,

Straße der Nationen 62, 09111 Chemnitz, Germany

S

* Supporting Information

ABSTRACT: The series of biferrocenyl-functionalized phosphines Bfc(PR₂)/Bfc(SePR₂)

(R = C₆H₅(6/14), C₆H₄-2-CH₃(7/15), ^cC₄H₃O (8/16), ^cC₆H₁₁(9/17); Bfc = 1′-biferrocenyl,

Fe(η⁵-C₅H₅)(η⁵-C₅H₄)Fe(η⁵-C₅H₄)₂) and biferrocenyl diphosphines bfc(PR₂)₂/bfc(SePR₂)₂

c

(R = C₆H₅(10/18), C₆H₄-2-CH₃(11/19), C₄H₃O (12/20), C₆H₁₁(13/21); bfc = 1′,1‴-

biferrocenyl, (Fe(η⁵-C₅H₄)₂)₂) have been prepared by consecutive synthesis methodologies. The

reaction of 6−9 with [Pd(Et₂S)₂Cl₂] (22) gave the appropriate palladium dichloride complexes

trans-[Pd(Bfc(PR₂))₂Cl₂] (R = C₆H₅(23), C₆H₄-2-CH₃(24), ^cC₄H₃O (25), ^cC₆H₁₁(26)). The

structures of 15, 16, 21, 23, and 25 in the solid state were determined by single-crystal X-ray

diffraction studies, showing that the structural parameters of these molecules correspond to those

of related seleno phosphines and phosphino palladium dichloride complexes. Additionally, all

complexes were characterized by cyclic voltammetry using [ⁿBu₄N][PF₆] and [ⁿBu₄N][B(C₆F₅)₄]

as supporting electrolytes. Phosphines 6−9 and seleno phosphines 14−17 show mostly

irreversible redox processes involving the phosphorus and the selenium atom, both being able to

form radicals leading to dimerization and other follow-up reactions. In contrast, palladium complexes 23−26 show in both

electrolyte solutions a reversible behavior, although the iron centers were oxidized at more positive potentials in comparison to

free Bfc or bfc phosphines. UV/vis/near-IR spectroelectrochemical measurements were carried out with 25 and 26. At potentials

between 300 and 700 mV IVCT bands typical for [Bfc]⁺are observed, reflecting intermetallic communication between the two

ferrocene moieties within the biferrocenyl phosphine units, two of which are present. No further bands were found, indicating

that no electronic communication between the biferrocenyl moieties along the P−Pd−P unit exists in the mixed-valent species.

The palladium complexes are suitable catalysts in the Suzuki reaction of 2-bromotoluene (27) or 4′-chloroacetophenone (28) with

phenylboronic acid (29). They can also be applied in the Heck C,C cross-coupling of iodobenzene (32) with tert-butyl acrylate (33).

1

31 77

Depending on the steric (estimated by the Tolman cone angle) and electronic properties (estimated by J _{P Se}) of the phosphine

ligands, the activity of the corresponding palladium complexes can be predicted. It was found that bulky and electron-rich cyclohexyl-

and o-tolyl-containing complexes are the most active catalysts in the appropriate Suzuki and Heck reactions.

derivatives.⁵⁸⁻⁶⁸Van Leeuwen and Widhalm applied, for example,

INTRODUCTION

■

enantiopure phosphorus-chiral 2,2′-bis(diarylphosphino)-1,1′-

biferrocenyls in palladium-promoted allylic substitution reac-

tions.^58,69,702,2″-Phosphino-substituted biferrocenes were inves-

tigated by Weissensteiner in asymmetric hydrogenations.⁵⁹

Furthermore, different trans-chelating 2,2″-bis[1-(diphenyl-

phosphino)alkyl]-1,1′-biferrocenes (TRAPs) were used in a wide

range of enantioselective catalysis by Ito, Sawamura, and

Kuwano.^{60−63,65,66}

Palladium-catalyzed C,C cross-coupling reactions, including the

Suzuki¹⁻⁸and Heck^1−4,8−11reactions, are essential transfor-

mations in organic and organometallic chemistry. They give access

to functionalized biaryls and aryl-substituted alkenes.¹²Therefore,

the development of new ligands which effect high conversions at

low catalyst loadings under mild reaction conditions have

accelerated during the last years. Hitherto, N-heterocyclic carbenes

and palladacycles were successfully applied in the synthesis of

efficient catalysts.^{1−4,13−28}Especially electron-rich and/or bulky

palladium-based catalysts, including mono- and bidentate fer-

rocenyl phosphines, are of great interest, due to the exceptional

properties of ferrocene as an electron-rich, stable, and structurally

easily modifiable molecule.²⁸⁻⁴⁴Although palladium complexes

with metallocenyl-containing mono- and diphosphine ligands have

been well investigated in C,C or C,N bond-forming reac-

tions,^6,34,45−57less is known about the use of biferrocene

Catalytic reactions are often affected by relatively small changes

in the electronic and/or spatial structure (i.e., Tolman cone angle)

of the appropriate palladium-complexed sandwich compounds.^34,71

Since the early work of Allen and Taylor, the existence of a rela-

1

³¹P⁷⁷Se

tion between the J

coupling constant and the electronic

Received: December 8, 2011

Published: March 13, 2012

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Scheme 1. Synthesis of Mono- and Diphosphanyl Biferrocenes Bfc(PR₂) and bfc(PR₂)₂and the Appropriate Seleno Phosphines

Bfc(SePR₂) and bfc(SePR₂)₂, Respectively

properties of phosphines has been well established.⁷²⁻⁷⁷An in-

(BfcH) at various temperatures by addition of 1 equiv of

1

t

ⁿBuLi or BuLi always gave next to the appropriate mono-

31 77

crease of J

of the appropriate seleno phosphine corresponds

P Se

to an increase in the s character of the phosphorus lone-pair orbital,

resulting in a decrease of basicity. This allows in a straightforward

way the prediction and design of specific, catalytically active

transition-metal complexes for homogeneous catalysis.^{38,39,44,78,79}

We herein report the synthesis, electrochemistry, structure,

and bonding of a series of novel monosubstituted biferroce-

nylphosphines and their use in selected palladium-promoted

C,C cross-coupling reactions.

metalated species multilithiated products.

In contrast, the symmetric biferrocenes bfc(PR₂)₂(10−13) are

formed in much higher quantities (67−80%) by applying the

reaction conditions described above but changing the stoichiom-

etry to 1:2 (Scheme 1). They were even more efficiently accessible

when diiodobiferrocene (bfcI₂)^82,83was used as starting material.

The orange biferrocenes 10−13 are less soluble than Bfc(PR₂)

(6−9). All molecules Bfc(PR₂) and bfc(PR₂)₂(6−13) are stable

toward air in the solid state and dissolve in common solvents such

as dichloromethane. However, solutions containing these mole-

cules oxidize easily to the corresponding phosphino oxides.

To first obtain information on the donor ability of the phos-

phorus atom in 6−13 toward transition-metal fragments, these

molecules were converted into the appropriate seleno phosphines

Bfc(SePR₂) (R = C₆H₅(14), C₆H₄-2-CH₃(15), 2-^cC₄H₃O

(16), ^cC₆H₁₁(17)) and bfc(SePR₂)₂(R = C₆H₅(18), C₆H₄-2-

RESULTS AND DISCUSSION

■

1. Synthesis and Characterization of Metallocenyl

Phosphines (6−13), Phosphine Selenides (14−21), and

Palladium Complexes (23−26). The mono- and diphos-

phanyl biferrocenes Bfc(PR₂) (R = C₆H₅(6), C₆H₄-2-CH₃(7),

c

2-^cC₄H₃O (8), C₆H₁₁(9); Bfc = 1′-biferrocenyl, Fe(η⁵C₅H₅)-

(η⁵C₅H₄)Fe(η⁵C₅H₄)₂) and bfc(PR₂)₂(R = C₆H₅(10),⁸⁰

c

CH₃(19), 2-^cC₄H₃O (20), C₆H₁₁(21)) on oxidation with

c

C₆H₄-2-CH₃(11), C₄H₃O (12), C₆H₁₁(13); bfc =1′,1‴-

biferrocenyl, (Fe(η⁵C₅H₄)₂)₂) were accessible by consecutive

reaction methodologies, as shown in Scheme 1. Treatment of

selenium in its elemental form in toluene at 100 °C (Scheme 1).

Seleno phosphines 14−21 could be isolated in almost quantitative

yield as orange solids (Experimental Section).

bfcBr₂(1)⁸¹with 1 equiv of BuLi in tetrahydrofuran at low

n

Complexation of phosphines 6−9 to palladium dichloride was

carried out by reacting them with [Pd(Et₂S)₂Cl₂] (22) in a molar

ratio of 2:1 at ambient temperature in dichloromethane. Thus

formed trans-[Pd(Bfc(PR₂))₂Cl₂] (R = C₆H₅(23), C₆H₄-2-CH₃

(24), C₄H₃O (25), C₆H₁₁(26)) could be isolated in excellent

yield (Experimental Section) (eq 1). As expected, seleno pho-

sphines 14−21 and palladium complexes 23−26 are stable toward

air and moisture both in the solid state and in solution.

The identity of all new compounds was confirmed by elemental

analysis, IR and NMR spectroscopy (¹H, ¹³C{¹H}, ³¹P{¹H}), and

ESI TOF mass spectrometry (Experimental Section). Additionally,

the electrochemical behavior of these molecules was determined

by cyclic voltammetric measurements. Moreover, the spectroelec-

trochemical behavior of 25 and 26 was determined using

UV/vis/near-IR spectroscopy. The molecular structures of 15, 16,

21, 23, and 25 in the solid state were determined by single-crystal

X-ray structure analysis. Suitable crystals for X-ray diffraction were

temperature followed by an addition of the appropriate

chlorophosphine R₂PCl (R = C₆H₅(2), C₆H₄-2-CH₃(3),

c

^cC₄H₃O (4), C₆H₁₁(5)) produced a mixture of Bfc(PR₂) and

bfc(PR₂)(Br) compounds. Repeating column chromatography

allowed in a time-consuming procedure the separation of the

appropriate products from the reaction mixture. For this

reason, we developed a consecutive synthesis strategy for the

preparation of the monophosphine biferrocenyls 6−9 (Scheme 1).

This methodology implies the use of an exact ratio of Bfc(PR₂)

and bfc(PR₂)(Br) (1:3, respectively). To this mixture was

added a slight excess of ⁿBuLi and EtOH (Experimental

Section) to solely give 6−9. After appropriate workup, these

orange solid materials could be obtained in moderate yields

(40−60%) (Experimental Section). Attempts to obtain higher

quantities of monolithiated 1 by lowering the temperature or

using solvent mixtures or longer reaction times did not result in

significantly higher yields. Monometalation of biferrocene

c

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obtained by slow diffusion of n-hexane into a concentrated dichloro-

methane solution containing 15, 16, 21, 23, or 25 at ambient

temperature. ORTEP diagrams are shown in Figure 1 (15, 16),

Figure 2 (21), and Figure 3 (23, 25). Selected bond distances (Å)

and angles (deg) are given in Tables 1 and 2. The crystal and

structure refinement data are summarized in Table S1 (Supporting

Information).

Compounds 15 and 16 crystallize in the monoclinic space group

P2₁(15) or P2₁/c (16), whereas 21, 23, and 25 crystallize in the

triclinic space group P1. The asymmetric units of 21 and 23

̅

contain half of the molecule with crystallographic C_isymmetry

about the center of the fulvalenide connectivity (21) or at the

palladium atom (23). The asymmetric unit of 25 contains 1.5

crystallographic independent molecules (for clarity, Figure 3 shows

only one molecule of 25).

Figure 2. ORTEP diagram (thermal ellipsoids are at the 50% probability

level) of the molecular structure of 21 along with the numbering scheme.

Hydrogen atoms are omitted for clarity. Symmetry transformations used

to generate equivalent atoms: −x + 1, −y, −z + 1 (center of inversion

C9−C9A).

In all compounds the biferrocenyl moieties show a trans con-

figuration; both iron atoms are oriented opposite to each other

with respect to the fulvalenide plane. The two C₅H₄rings of this

array are almost coplanar, with interplanar angles of 0.9 (15), 10.4

(16), 0.0 (21), 7.5 (23), 14.7 (with Fe1, Fe2), 5.6 (with Fe3,

Fe4), and 7.6° (with Fe5, Fe6) (25). The cyclopentadienyl rings

of individual ferrocenyl building blocks are rotated by 10.4 (Fe1),

20.3 (Fe2) (15), 4.8 (Fe1), 3.4 (Fe2) (16), 7.6 (21), 0.2 (Fe1),

6.3 (Fe2) (23), 0.2 (Fe1), 14.9 (Fe2), 12.4 (Fe3), 1.9 (Fe4), 8.2

(Fe5), and 2.4° (Fe6) (25), revealing a conformation between fully

eclipsed (0°) and staggered (36°). The phosphino substituents

and the biferrocenyl units are rotated by 91.3 (15), 145.7 (16),

153.2 (21), 134.9 (23), 143.7 (with Fe1, Fe2), 129.9 (with Fe3,

Fe4) and 133.7° (with Fe5, Fe6) (25) with respect to each other.

The coordination geometry of the trans palladium complexes is

square planar with an rms deviation of 0.0265 Å (Pd1) (25). Due

to C_isymmetry no deviation from planarity for 25 (Pd2) and 23

with P−Pd−Cl bond angles between 86.6 and 92.3° is observed.

The analytical data are consistent with the formation of sym-

metrically and unsymmetrically substituted biferrocenes.^80,83−85

While IR spectra of the molecules Bfc(PR₂)/bfc(PR₂)₂, Bfc-

(SePR₂)/bfc(SePR₂)₂, and trans-[Pd(Bfc(PR₂))₂Cl₂] are

1

not very distinctive, the H NMR spectra of monophosphine

Figure 1. ORTEP diagrams (thermal ellipsoids are at the 50% probability level) of the molecular structures of 15 (left) and 16 (right) along with the

numbering scheme. Hydrogen atoms are omitted for clarity.

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Figure 3. ORTEP diagrams (thermal ellipsoids are at the 50% probability level) of the molecular structures of 23 (top) and 25 (bottom) along with

the numbering scheme. Hydrogen atoms are omitted for clarity. Symmetry transformations used to generate equivalent atoms: −x + 2, −y + 2, −z + 1

(center of inversion Pd1 (23)).

Table 1. Selected Bond Distances (Å) and Angles (deg) of 15, 16, and 21

Bond Distances

a

Compound 15

P1−Se1

C27−P1

Fe1−D2

2.1204(13)

1.830 (5)

1.6484(1)

C16−P1

C6−C11

Fe2−D3

1.811(5)

1.463(7)

1.6504(1)

C21−P1

Fe1−D1

Fe2−D4

1.831(5)

1.6548(1)

1.6434(1)

a

b

Compound 16

Compound 21

Bond Angles

P1−Se1

C25−P1

Fe1−D2

2.0864(11)

1.810(4)

1.6409

C16−P1

C6−C11

Fe2−D3

1.780(4)

1.459(5)

1.6465

C21−P1

Fe1−D1

Fe2−D4

1.791(4)

1.6593

1.6406

P1−Se1

C11−P1

Fe1−D2

2.1166(6)

1.842(2)

1.6450(3)

C1−P1

C9−C9A

1.801(2)

1.444(4)

P1−C17

Fe1−D1

1.841(2)

1.6506(3)

Compound 15

C16−P1−C21

Se1−P1−C16

104.6(2)

C16−P1−C27

Se1−P1−C21

103.6(2)

C21−P1−C27

Se1−P1−C27

110.7(2)

112.59(16)

110.66(16)

114.20(18)

Compound 16

C16−P1−C21

Se1−P1−C16

106.41(19)

117.24(15)

C16−P1−C25

Se1−P1−C21

103.72(17)

111.24(14)

C21−P1−C25

Se1−P1−C25

106.92(18)

110.60(14)

Compound 21

C1−P1−C11

Se1−P1−C1

104.87(10)

116.62(7)

C1−P1−C17

Se1−P1−C11

102.97(10)

C11−P1−C17

Se1−P1−C17

105.12(10)

114.91(8)

111.18(7)

b

a

D denotes the centroids of C₅H₄(D2, D3, D4) and the centroids of C₅H₅(D1). D denotes the centroids of C₅H₄(D1, D2).

derivatives Bfc(PR₂), Bfc(SePR₂), and trans-[Pd(Bfc-

structure. In the ¹H NMR spectra of complexes 23−26 a total of

seven signals were observed, one of which appears as a singlet for

(PR₂))₂Cl₂] show multiple resonances due to their unsymmetrical

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Table 2. Selected Bond Distances (Å) and Angles (deg) of 23 and 25

Bond Distances

a

Compound 23

P1−Pd1

C27−P1

Fe1−D1

Fe2−D4

2.3366(7)

1.820(2)

C18−P1

C10−C11

Fe1−D2

1.800(2)

1.463(3)

1.6470(4)

C21−P1

Pd−Cl1

Fe2−D3

1.819(2)

2.3035(6)

1.6554(4)

1.6547(4)

1.6487(3)

a

Compound 25

P1−Pd1

C25−P1

Fe1−D1

Fe2−D4

2.309(2)

1.791(8)

1.6357(11)

1.647(1)

C1−P1

C8−C11

Fe1−D2

1.787(8)

C21−P1

Pd−Cl1

Fe2−D3

1.800(8)

2.295(2)

1.656(1)

1.467(11)

1.6447(11)

Bond Angles

Compound 23

Cl1−Pd−Cl1A

P1−Pd1−Cl1A

Pd1−P1−C27

180.000(1)

93.41(2)

P1−Pd1−P1A

Pd1−P1−C18

180.000(1)

115.70(8)

P1−Pd1−Cl1

Pd1−P1−C21

86.59(2)

117.36(8)

110.23(8)

Compound 25

Cl1−Pd−Cl2

P1−Pd1−Cl2

Pd1−P1−C25

Pd1−P2−C29

178.52(8)

88.05(7)

111.1(3)

116.9(3)

P1−Pd1−P2

Pd1−P1−C1

P2−Pd1−Cl1

Pd1−P2−C53

178.13(8)

116.5(3)

87.18(7)

116.9(3)

P1−Pd1−Cl1

Pd1−P1−C21

P2−Pd1−Cl2

Pd1−P2−C49

92.28(7)

117.4(3)

92.53(7)

111.5(3)

a

D denotes the centroids of C₅H₄(D2, D3, D4) and denotes the centroids of C₅H₅(D1).

the C₅H₅unit (Figure 4, trans-[Pd(Bfc(PR₂))₂Cl₂]). The signals of

the biferrocenyl unit ranging from 3.85 to 4.35 ppm (Bfc(PR₂)),

(Experimental Section). Further signals were found, as is typical for

the included organic groups at phosphorus (Experimental

Section).^78,79,89

In the ³¹P{¹H} NMR spectra of phosphines Bfc(PR₂) a high-

field shift is observed in the series 9 (−7 ppm) > 6 (−16 ppm)

> 7 (−36 ppm) > 8 (−64 ppm), of which 9 is most shielded,

indicating the strong electron-donating character of the cyclohexyl

groups. The progress of the reaction of Bfc(PR₂) (6−9) with [Pd-

(Et₂S)₂Cl₂] (22) could be monitored by ³¹P{¹H} NMR spectro-

scopy, because coordination of the phosphorus atom to palladium

is accompanied by a characteristic downfield shift of the phos-

phorus resonance signal from −64.6 to −7.39 (6−9) to −14.2 to

+18.2 ppm (23−26) (Experimental Section). Changing the oxida-

tion state of the phosphorus atom from +III in 6−13 to +V in

14−21 induces a significant shift to lower field (50−65 ppm).

Generally the donor−acceptor character of phosphines toward

31

77

selenium can be quantified by the J _{P− Se}coupling constant. It was

1

31

77

found that an increasing J _{P− Se}coupling constant is significant for

electron-withdrawing groups at the phosphorus atom, due to the

increased s character of the orbital which is involved in the P−Se

Figure 4. Part of the ¹H NMR spectra (in CDCl₃, 298 K) of

complexes trans-[Pd(Bfc(PR₂))₂Cl₂] (23−26).

bonding.⁷²⁻⁷⁷A summary of the ³¹P{¹H} NMR chemical shifts of

1

³¹P−⁷⁷Se

molecules 6−13 and seleno phosphines 14−21 with J

3.9 to 4.55 ppm (Bfc(SePR₂)), and 3.95 to 4.7 ppm ([Pd-

(Bfc(PR₂))₂Cl₂]) show a shift to lower field, due to electron-

withdrawing P(V) species (14−21) or due to coordination of the

phosphorus atom to palladium (23−26). For the different organic

substituents bonded at the phosphorus atom, there is no direct

electronic influence on the protons of the biferrocenyl core. The

¹³C{¹H} NMR spectra of Bfc(PR₂), Bfc(SePR₂), and trans-[Pd-

(Bfc(PR₂))₂Cl₂] contain the corresponding carbon signals for the

unsymmetrically substituted Bfc unit between 60 and 90 ppm.⁸⁴

Characteristic for the complexes trans-[Pd(Bfc(PR₂))₂Cl₂] are the

pseudotriplet signals in the ¹³C{¹H} NMR spectra due to P−C

coupling, indicating the trans arrangement of the phosphine ligands

toward each other (Experimental Section).⁸⁶⁻⁸⁸For all symmetri-

cally substituted molecules bfc(PR₂)₂and bfc(SePR₂)₂four

coupling constants is given in Table 3. From this table it can be

seen that the electron-rich SeP(^cC₆H₁₁)₂units appear, as

expected, at low field (ca. 49 ppm), while SeP(^cC₄H₃O)₂species

containing electron-poor furyl units resonate at higher field (ca. −5

ppm). The coupling constants decrease in the series 16/20 < 14/

18 < 15/19 < 17/21, demonstrating that the phosphine featuring

a furyl ligand acts as an electron-withdrawing group and hence pos-

sesses less donor ability (Experimental Section).

Electronic and steric effects are related.^37,71Therefore, the Tol-

man cone angle, which is the apex angle of a cylindrical cone

centered 2.28 Å from the center of the phosphorus atom which

touches the van der Waals radii of the outermost atoms,^79,90,91is an

important value and was calculated for 23 and 25. Increasing the

angle between the phosphine substituents decreases the percent-

age of s character in the phosphorus lone pair.³⁷The Tolman cone

angle was calculated from the structural data obtained by X-ray

1

signal sets in the H NMR spectra and six resonances in the

¹³C{¹H} NMR spectra could be detected in the range expected

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Table 3. Chemical Shifts and J

Ferrocenyl Analogues 35−42, for Comparison

Article

1

³¹P−⁷⁷Se

Coupling Constants of Phosphines 6−13 and Corresponding Selenides 14−21 and

a

R

compd

Mc

δ(P(III)), ppm

compd

δ(P(V)), ppm

¹J

³¹P−⁷⁷

_Se, Hz

ref

C₆H₅

6

Bfc

bfc

Fc

−16.5

−16.09

−17.7

−36.8

−36.5

−64.6

−64.7

−64.4

−7.3

14

18

39

15

19

40

16

20

41

17

21

42

31.8

31.7

30.8

29.5

29.4

−5.2

−5.4

−5.3

49.8

48.8

732

10

35

7

733

715

714

717

768

769

700

699

80

89

2-CH₃-C₆H₄

2-^cC₄H₃O

^cC₆H₁₁

Bfc

bfc

Fc

11

36

8

79

89

Bfc

bfc

Fc

12

37

9

Bfc

bfc

Fc

13

38

−7.39

−8.4

a

Abbreviations and conditions: Bfc = 1′-biferrocenyl, bfc = 1′,1‴-biferrocenyl, Fc = 1′-ferrocenyl; measurements at 298 K in CDCl₃.

a

structure analysis of 23 and 25 using the programm STERIC.⁹²⁻⁹⁴

It was found that the biferrocenyl moiety has an remarkable

influence on the size of the Tolman cone angle. The Tolman cone

angle was calculated to be 190.4 (23) and 167.4° (25), indicating

that the furyl groups are less sterially demanding than phenyl

groups. For molecules 24 and 26 larger values are expected, due to

comparison with PR₃molecules investigated by Tolman⁷¹and

complexes of type [Pd((FcCC)PR₂)₂Cl₂] (R = C₆H₅, C₆H₄-2-

CH₃, 2,4,6-Me₃C₆H₂, ^cC₄H₃O, tBu, ^cC₆H₁₁).⁷⁸The obtained

electronic and steric parameters allow the design of catalytically

active palladium transition-metal complexes which can be used, for

example, in C,C cross-coupling reactions.^{38,39,44,78,79}Our results

suggest that in the latter series phosphine 9 and its corresponding

palladium dichloride complex 26 should be best suited for Suzuki

carbon−carbon couplings, while 8 with its more electron-with-

drawing character in 25 is thought to be less active. From Table 3 it

can be seen that the related ferrocenyl analogues Fc(PR₂) (R =

C₆H₅(35),^79,89C₆H₄-2-CH₃(36),⁷⁹^cC₄H₃O (37),⁷⁹^cC₆H₁₁

(FcCy);^79,89Fc = ferrocenyl, (Fe(η⁵-C₅H₄)(η⁵-C₅H₅)) and

Table 4. Redox Potentials of Biferrocenyl Phosphines 6−13

compd

E_ox, V

E_red, V

Bfc(PR₂)

E_ox,irrev, V

E_red,irrev, V

6

7

8

9

0.48

0.30

0.74

1.2

0.8

0.97

1.09

0.91

0.99

0.49

0.84

0.44

0.85

0.42

0.53

0.33

1.26

0.72

0.35

1.09

0.74

0.34

0.9

0.47

1.06

bfc(PR₂)₂

b

10

0.49

0.5

0.67

1.01

11

0.4

0.78

1.06

1.36

0.52

0.68

0.96

1.26

0.38

12

13

0.84

1.17

c

Fc(SePR₂) (R = C₆H₅(39), C₆H₄-2-CH₃(40), C₄H₃O (41),

0.42

0.83

0.54

1.00

0.31

0.13

R = ^cC₆H₁₁(42)) show similar shifts in the ³¹P{¹H} NMR spectra

1

31

77

with almost identical J

coupling constants.⁷⁹

P− Se

−0.8

2. Electrochemistry. The redox properties of all new

compounds have been studied by cyclic voltammetry (CV), square

wave voltammetry (SW), and spectroelectrochemistry (UV/vis/

near-IR spectroscopy) in dichloromethane solutions utilizing

[ⁿBu₄N][PF₆] (0.1 M) and [ⁿBu₄N][B(C₆F₅)₄] (0.1 M),

respectively, as supporting electrolyte. The cyclic voltammetric

measurements were carried out at 298 K with a scan rate of

100 mV s⁻¹. All data are summarized in Tables 4−7. All

potentials are referenced vs a saturated calomel electrode

(SCE) with the FcH/FcH⁺redox couple (E₀= 0.46 V) as

internal calibrant.⁹⁵

Figure 5 shows the CVs of 8 in different electrolyte solutions.

In both electrolyte solutions compound 8 exhibits multiple redox

events, as is characteristic for ferrocenyl phosphines.^{79,80,96−103}

The assignment of the redox processes to the biferrocenyl unit or

to the phosphorus atom cannot be made unequivocally. A similar

behavior was found for all phosphines 6−13 (Tables 4 and 5). In

earlier studies it was stated that follow-up reactions such as

dimerization and irreversible oxidations, caused by traces of water

or oxygen, can occur at the phosphorus atom.¹⁰¹A mechanism for

the well-known dppf derivative was recently described by the

group of Pilloni.¹⁰⁴The presence of the lone pair of electrons on

each phosphorus atom leads to a phosphorus radical as a result of

a

Conditions: cyclic voltammetric data for 10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][PF₆] (0.1 M) as supporting electrolyte;

scan rate 100 mV s⁻¹; all potentials in V (ΔE_pin V) vs SCE (FcH/

FcH⁺as internal standard (E₀= 0.46 V)).⁹⁵Potentials obtained from

b

ref 80.

intramolecular electron transfer processes which can undergo

dimerization.^98,105

Kotz and Nivert reported about a reversible one-electron-redox

process for diphenylphosphino ferrocene on measurement to a

maximum of 0.8 V.¹⁰³However, irreversible oxidations occur on

measurement to higher potentials (1.3 V).¹⁰³Nevertheless, the

reversibility of the Fe(II)−Fe(III) oxidation in ferrocenyl phos-

phines was discussed intensively and many parameters were varied

(solvent, scan rate, electrolyte).^98,105−107Actually, it is known that

[ⁿBu₄N][PF₆] as supporting electrolyte favors the formation of ion

pairs of the type Fc⁺···PF₆⁻.^{104,108−112}The negative effect of ion

pairing was recently described by Geiger and co-workers.^113−115

They found that the electrolyte had a remarkable influence on the

in situ oxidized phosphorus centers. By using a weak coordinating

anion (=WCA) such as [B(C₆F₅)₄]⁻fewer follow-up reactions are

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6−13 were observed using [ⁿBu₄N][B(C₆F₅)₄] as supporting

electrolyte.

Table 5. Redox Potentials of Biferrocenyl Phosphines 6−9

a

and Seleno Phosphines 14−17 under Modified Conditions

To first get information on the donor ability of the pho-

sphorus atoms in 6−13 toward transition-metal fragments,

these molecules were converted into the appropriate seleno

phosphines 14−21. It was found that such molecules undergo

dimerization at the PSe bond^98,99in further oxidation pro-

cesses, resulting from an intramolecular electron transfer from a

selenium-centered radical. As expected, seleno phosphines

Bfc(SePR₂) (14−17) and bfc(SePR₂)₂(18−21) show

irreversible redox events in both electrolyte solutions with an

anodic shift, reflecting the fact that seleno phosphines with

phosphorus in the oxidation state +V are more difficult to

oxidize than the molecules containing phosphorus(III) (for

example, see Figure 6, compound 16). These results illustrate

that follow-up reactions take place (Table 5).

When the phosphorus atom is datively bonded to palladium,

follow-up processes are inhibited. The complexes trans-

[Pd(Bfc(PR₂))₂Cl₂] (23−26) show, applying standard con-

ditions ([ⁿBu₄N][PF₆]/dichloromethane), two reversible redox

events between 0.40 and 0.91 V, supporting the subsequent

oxidation of the iron centers exclusively (Table 6). In Figure 7

the cyclic voltammograms of 23−26 are depicted. It can be

seen that the outer iron atoms (Fe1) are much less influenced

by the PR₂group (E₀= 0.4−0.42 V) than those of the fer-

rocenyl units directly bonded to phosphorus (Fe2, E₀= 0.78−

0.91 V). Hence, the peak separation ΔE₀found for the

unsymmetrically substituted biferrocenyl unit is highly depend-

ent on the organic group R at phosphorus. ΔE₀decreases in the

series 25 > 23 > 24 > 26 (Table 7). For E_redvalues between

−0.74 and −1.3 V the reduction of Pd(II) to Pd(0) is

observed.^116,117The reduction potential decreases in the series

26 > 24 > 23 > 25. Furthermore, it can be seen that with

increasing electron density at phosphorus the Pd reduction is

shifted toward anodic potentials and is thus simplified.

compd

E_ox, V

E_red, V

Bfc(PR₂)

E_ox,irrev, V

E_red,irrev, V

6

7

8

9

0.45

0.63

0.32

0.49

0.91

0.35

0.52

0.39

0.93

1.03

0.4

0.94

0.56

1.23

0.36

0.62

0.47

1.13

0.34

0.98

0.55

Bfc(SePR₂)

14

15

16

0.42

0.43

0.28

0.34

1.08

0.92

0.93

0.45

0.98

0.65

0.69

0.57

0.33

0.23

17

0.42

0.33

0.69

a

Conditions: cyclic voltammetric data of 10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][B(C₆F₅)₄] (0.1 M) as supporting

electrolyte; scan rate 100 mV s⁻¹; all potentials in V (ΔE_pin V) vs

SCE (FcH/FcH⁺as internal standard (E₀= 0.46 V)).⁹⁵

Table 6. Redox Potentials of Complexes 23−26 under

Standard Conditions

a

[Mⁿ⁺]/[M⁽ⁿ⁺¹⁾⁺] E₀

(ΔE_p), V

[Fe²⁺]/[Fe³⁺] (Bfc) E₀

(ΔE_p), V

ΔE₀,

compd

M

mV

23

Pd

−1.2

0.404 (0.088)

0.86 (0.100)

0.413 (0.08)

0.87 (0.11)

0.42 (0.116)

0.91 (0.092)

0.4 (0.12)

466

457

490

380

24

25

26

Pd

−1.18

−1.3

−0.74

Cyclic voltammograms of 23−26 measured in electrolytes

with WCAs ([ⁿBu₄N][B(C₆F₅)₄]) are depicted in Figure 8.

Different from the aforementioned measurements, the second

redox process is split. This observation leads to the assumption

that both outer iron centers (Fe1) are oxidized at the same

potential, while the inner iron centers (Fe2) are oxidized at

different potentials (Figure 8). The separation ΔE₀₁between

the third and fourth redox processes depends on the organic

groups at phosphorus and increases in the series 24 < 25 ≈ 23

< 26. ΔE₀₂values found for the biferrocenyl unit in 23−26

increase in the opposite direction (Table 7). For an explanation

of ΔE₀₁and ΔE₀₂, see Figure 9.

0.78 (0.12)

a

Conditions: cyclic voltammetric data of 10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][PF₆] (0.1 M) as supporting electrolyte;

scan rate 100 mV s⁻¹; all potentials in V (ΔE_pin V) vs SCE (FcH/

FcH⁺as internal standard (E₀= 0.46)).⁹⁵

Table 7. Redox Potentials of Complexes 23−26 under

a

Modified Conditions

b

c

[Fe²⁺]/[Fe³⁺]

[Fe²⁺]/[Fe³⁺] ΔE₀₁,

ΔE₀₂,

compd E₀₁(ΔE_p), V E₀₂(ΔE_p), V E₀₃(ΔE_p), V]

mV

23

24

25

26

0.42 (0.07)

0.40 (0.08)

0.41 (0.1)

0.38 (0.07)

1.03 (0.05)

1.00 (0.05)

1.06 (0.1)

1.11 (0.05)

1.06 (0.13)

1.14 (0.08)

1.03 (0.02)

80

60

650

630

690

600

To investigate a possible electronic interaction between the

biferrocenyl moieties over the P−Pd−P bridge,^79,118,119

spectroelectrochemical experiments were carried out on

electron-poor 25 and electron-rich 26, as examples. Figure 10

displays that both species show absorption bands at low

energies at potentials above 300 mV, which reach a maximum

at around 700 mV. They can be assigned to the dicationic

species [25]²⁺and [26]²⁺, respectively, reflecting the existence

of two separate mono-oxidized biferrocenium species, one per

phosphane unit. Gaussian-shaped bands in the near-IR region

(5941 cm⁻¹([25]²⁺) and 4746 cm⁻¹([26]²⁺)) could be fitted

by deconvolution (Figure 11) representing the experimental

spectra. Their extinction coefficients and widths at half-height

are indicative of class II mixed-valent systems.¹²⁰Because of

the unsymmetrical structure, delocalization is less favored.^121−124

80

0.93 (0.03)

100

a

Conditions: cyclic voltammetric data of 10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][B(C₆F₅)₄] (0.1 M) as supporting

electrolyte; scan rate 100 mV s⁻¹; all potentials in V (ΔE_pin V) vs

SCE (FcH/FcH⁺as internal standard (E₀= 0.46 V)).⁹⁵ΔE₀₁= E₀₃

−

b

c

E₀₂. ΔE₀₂= E₀₃+ E₀₂/2 − E₀₁.

observed, as demonstrated for example for ferrocenyl phosphine

selenides and oxides.⁹⁹The combination of a solvent with a low

donor character, such as dichloromethane, and a WCA electrolyte

such as [ⁿBu₄N][B(C₆F₅)₄] gives almost ideal conditions for the

investigation of molecules with one or more ferrocenyl moieties

because of minimization of the nucleophilic attack and high

solubility. Nevertheless, no reversible processes for compounds

125

Therefore, the intensities are lower compared to those of [bfc]⁺

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Figure 5. Cyclic voltammograms of 8 (10⁻³M dichloromethane solutions at 298 K; scan rate 100 mV s⁻¹).⁹⁵

Figure 6. Cyclic voltammograms of 16 (10⁻³M dichloromethane solutions at 298 K; scan rate 100 mV s⁻¹).⁹⁵

Figure 7. Cyclic voltammograms of 23−26 (10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][PF₆] (0.1 M) as supporting electrolyte;

scan rate 100 mV s⁻¹).⁹⁵

Figure 8. Cyclic voltammograms of 23−26 (10⁻³M dichloromethane

solutions at 298 K; [ⁿBu₄N][B(C₆F₅)₄] (0.1 M) as supporting

electrolyte; scan rate 100 mV s⁻¹).⁹⁵

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catalyst loading of 0.1−0.25 mol % Pd at 100 °C in analogy to litera-

ture procedures published by Beletskaya (Experimental Section).³⁴

From parts a and b of Figure 12 it can be seen that all

biferrocenyl phosphines show a good performance at catalyst

loadings of 0.25 and 0.1 mol % with almost quantitative

conversions (Table 8). Complexes 25 and 26 are somewhat less

productive then 23 and 24. At lower catalyst loadings a reduced

activity for the furyl-containing system is found, which is in

agreement with the electron density at the phosphorus atom

(Table 3, Figure 12b). Due to the electronic and steric

properties of phosphines 6−9, palladium complexes 24 and 26

should show the highest performance in Suzuki cross-couplings,

since they possess large Tolman cone angles and high Lewis

basicity.^37,71,78,79The obtained results are in accordance with

the general statement that electron-rich and bulky phosphines

are suitable ligands in Suzuki C,C couplings.^40,41

Figure 9. Cyclic voltammogram and square wave voltammogram of 26

(10⁻³M dichloromethane solutions at 298 K; [ⁿBu₄N][B(C₆F₅)₄] (0.1 M)

as electrolyte; scan rate 100 mV s⁻¹; unreferenced).

In comparison with the analogous ferrocenylphosphine-based

complexes trans-[Pd(Fc(PR₂))₂Cl₂] (R = C₆H₅(43), C₆H₄-2-

and symmetrically substituted biferrocenes^83,85,125and the

absorptions possess broader bandwidths at half-height. Comparison

of both absorption bands reflects that the electronic interaction

between the two iron centers of each biferrocenyl moiety strongly

depends on the substituents at the phosphorus atom. While

absorptions for the electron-poor furyl derivative are located at

higher energies with low ε values (655 L mol⁻¹cm⁻¹) (Figure 10a),

absorptions of the more electron-rich cyclohexyl complex are red-

shifted with a significantly higher intensity (ε = 1100 L mol⁻¹cm⁻¹,

Figure 10b). In conclusion, the peak separation (ΔE₀₁), which

was found only in electrolytes with WCAs ([ⁿBu₄N][B(C₆F₅)₄]),

does not result from an electronic interaction between the iron

centers over the palladium bridge because no additional IVCT transi-

tion was observed for the appropriate tricationic species (Figure 10,

spectral series at the top). Therefore, this separation most likely

corresponds to electrostatic effects. Similar observations were made

for analogous ferrocenyl phosphine palladium complexes.⁷⁹

c

CH₃(44), C₄H₃O (45), C₆H₁₁(46); Fc = 1′-ferrocenyl,

Fe(η⁵C₅H₄)(η⁵C₅H₅)), complexes 23−26 are less active; how-

ever, a similar dependence of the catalytic performance and

the organic group at the phosphorus atom is characteristic.⁷⁹

The bidentate system [Pd(fc(P(C₆H₄-2-CH₃)₂)₂)Cl₂] (fc =

Fe(η⁵C₅H₄)₂) shows similar conversions at 100 °C with catalyst

loadings of 1 mol %.³⁴

4. Catalysis. The reactions of 2-bromotoluene (27) and 4′-

chloroacetophenone (28) with 1.3 equiv of phenylboronic acid

(29) to give the C,C cross-coupled biaryls 2-methylbiphenyl (30)

and 4-acetylbiphenyl (31), respectively, were used as standard

reactions to compare the catalytic activity of the newly synthesized

palladium complexes 23−26 (eq 2). The conversions were per-

formed in presence of 3 equiv of potassium carbonate as base in a

solvent mixture of dioxane and water (ratio of 2/1 v/v) with a

Due to the fact that the investigated palladium complexes 23,

24, and 26 show similar catalytic behavior for the conversion of

Figure 10. UV/vis/near-IR spectroelectrochemical measurements of 25 (left) and 26 (right), recorded in an OTTLE (optically transparent thin-

layer electrode) cell. Potentials are vs Ag/AgCl (10⁻³M dichloromethane solutions at 298 K; [ⁿBu₄N][B(C₆F₅)₄] (0.1 M) as supporting electrolyte).

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Figure 11. Deconvolution of near-IR absorptions of [25]²⁺(left) and [26]²⁺(right) using two Gaussian-shaped bands determined by

spectroelectrochemical measurements in an OTTLE cell.

Figure 12. Kinetic investigation of 23−26 in the Suzuki C,C cross-coupling of 27 with 29 (a, b) and of 23, 24, and 26 in the coupling of 28 with 29 (c).

bromoarenes, a less reactive substrate was applied, and hence

28 was reacted with PhB(OH)₂in presence of 0.5 mol % of

palladium catalyst. From Figure 12c it can be seen that 23

shows only a conversion of 10%; however, the palladium

complexes 24 and 26 proved to be more efficient. After 90 min

a complete conversion of 28 with 29 to 31 was observed for

catalysts 24 and 26 the latter complex of which shows the

highest activity with full conversion after 10 min (Table 8).

In addition to Suzuki C,C cross-couplings the performance of

transition-metal complexes 23−26 in the Heck reaction of

iodobenzene (32) with tert-butyl acrylate (33) to give (E)-tert-

butyl cinnamate (34) following the method described by Boyes

and Butler was studied³⁶(eq 3, Figure 13).

ethylamine as base with catalyst loadings of 0.5 mol % Pd to

investigate the productivity of 23−26. The data given in Figure 13a

reveal that the highest productivity is obtained with catalyst 24,

while the highest activity was found for 26. It can be seen that,

as for Suzuki couplings, sterically demanding and electron-rich

phosphines are best suited for the Heck reaction. A similar

behavior was found for appropriate monoferrocenyl phosphine

palladium complexes of the type [Pd(Fc(PR₂))₂Cl₂] (43−46)

(Figure 13b).⁷⁹In comparison with these species the bifer-

rocenyl derived catalysts possess a similar activity. With regard

to previous dppf-based catalysts reported by Butler and Boyes,

which are supported by addition of [CuI] and show high

activity at low catalyst loadings, the systems described here do

not require addition of [CuI].³⁶

The reactions were carried out in 1/1 (v/v) toluene/

acetonitrile mixtures at 80 °C in the presence of diisopropyl-

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Figure 13. Kinetic investigation of 23−26 (a) as well as 43−46⁷⁹(b) in the Heck reaction of 32 with 33 to give 34.

Table 8. Suzuki Reaction of Br-tol or Cl-AcPh with PhBOH

for comparison of the electrochemical behavior under different

conditions. In both electrolytes phosphines Bfc(PR₂)/bfc(PR₂)₂

possess multiple redox processes as are typical for ferrocenyl

phosphines.^{79,80,96−103}At higher potentials follow-up reactions

were detected, which most likely correspond to processes at the

phosphorus atom.

using Catalyst Loadings of 0.25 and 0.1 mol % and 23−26 as

a

the Palladium Source

For prevention of follow-up reactions during electrochemical

measurements, palladium complexes were investigated in which

the lone pair of electrons is part of the P−Pd bond. The

palladium complexes trans-[Pd(Bfc(PR₂))₂Cl₂] show a rever-

sible redox behavior in both supporting electrolytes and are, as

expected, more difficult to oxidize in comparison to phosphines

Bfc(PR₂). E₀values of the iron centers next to the phosphine

moiety decrease in the series 25 > 24 > 23 > 26, due to an

increase of electron density in the molecules. The outer iron

centers are much less influenced by the organic groups at phos-

phorus. Measurements in [ⁿBu₄N][B(C₆F₅)₄]/dichloromethane

solutions result in a separation of the second redox event, which is

attributed to the WCA (weak coordinating anion) effect.⁹⁹In

conclusion, the outer iron centers were oxidized at the same

potential, while the inner, phosphorus-bonded iron centers were

oxidized separately. In addition, UV/vis/near-IR spectroelectro-

chemical measurements were carried out with electron-poor 25

and electron-rich 26. IVCT bands could be observed in both

cases, reflecting intermetallic communication between the two

ferrocene units within the biferrocenyl phosphine moieties for the

dicationic species.¹²⁵During further oxidation no additional IVCT

bands were observed, which leads to the conclusion that electronic

communication over the P−Pd−P connectivity does not take

place. The IVCT band of electron-rich 26 in comparison to

electron-poor 25 is located at lower energy but with higher

extinction coefficients, revealing that the communication between

the iron centers in 26 is stronger than in 25.

All palladium complexes were tested as catalysts in C,C

cross-couplings. In the palladium-promoted Suzuki reaction of

2-bromotoluene or 4′-chloroacetophenone with phenylboronic

acid all complexes are active; however, the highest activity was

observed with the cyclohexyl- or o-tolyl-substituted phosphines.

This can be explained by their bulkiness and high σ donor

capability. Furthermore, it could be demonstrated that all pal-

ladium species are active in the Heck reaction of iodobenzene

with tert-butyl acrylate. In comparison to other species in the

literature³⁷the same dependence on the basicity of the phos-

phines as for the Suzuki reaction was observed. In summary, the

catalysts reported within this work are, in comparison with

current catalytic systems,^{2,13−15,23,24,26−33,129−131}less active but,

a

Results after 2 h.

In summary, in comparison with the bidentate ferrocenyl phos-

phines reported by Beletskaya, our catalysts are active in the

Suzuki reaction at lower catalyst loadings.³⁴Nevertheless,

compared with the catalyst systems to date based on, for example,

N-heterocyclic carbenes,^{13,15,23,25−28}palladacycles,^{21,22,126−130}or

bulky, electron-rich phosphines^{2,14,19,24,29−33,131}they are less

active.

CONCLUSIONS

■

Within this study a series of new biferrocenyl phosphine-based

transition-metal complexes of the type trans-[Pd(Bfc-

c

(PR₂))₂Cl₂] (R = C₆H₅, C₆H₄-2-CH₃, C₄H₃O, C₆H₁₁; Bfc =

1′-biferrocenyl) are reported. They have been synthesized by

reacting the phosphines Bfc(PR₂) with [Pd(Et₂S)₂Cl₂].

Phosphines Bfc(PR₂) together with their symmetric analogues

bfc(PR₂)₂(bfc = 1′,1‴-biferrocenyl) are accessible by a con-

secutive synthesis methodology starting from bfcBr₂. For the

classification of the σ donor ability of the appropriate phos-

phines Bfc(PR₂) the corresponding phosphine selenides

Bfc(SePR₂) have been synthesized upon addition of

1

³¹P−⁷⁷Se

selenium in its elemental form to Bfc(PR₂). High J

values are distinctive for electron-poor phosphines with less

donor capability.⁷²⁻⁷⁷Electrochemical studies of all bimet-

allocenyl-functionalized phosphines were carried out with two dif-

ferent supporting electrolytes ([ⁿBu₄N][PF₆], [ⁿBu₄N][B(C₆F₅)₄])

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n-butyllithium (1.89 mmol, 0.76 mL, 2.5 M in n-hexane) dropwise

at −70 °C. After the solution was stirred for 60 min at this temperature,

1 equiv of the appropriate chlorophosphine 2−5 was added. The

reaction mixture was stirred for 12 h at ambient temperature, and then

the solvent was removed under vacuum. The resulting residue was

purified by column chromatography and dried under vacuum. A mix-

ture of the title complexes and disubstituted bfc(Br)(PR₂) (R = C₆H₅,

in comparison with other metallocenyl diphosphine palladium

catalysts, show a higher activity under similar reaction condi-

tions.^34,36The corresponding monodentate ferrocenyl phos-

phines trans-[Pd(Fc(PR₂))₂Cl₂] show a somewhat higher (for

Suzuki) or quite similar activity (for Heck) under the same

conditions.⁷⁹

c

C₆H₄-2-CH₃, C₄H₃O, C₆H₁₁) was obtained in a molar ratio of 1:3

and was used without further purification in a second lithiation process

(vide supra). Therefore, the appropriate mixture was dissolved in 50

mL of tetrahydrofuran and was treated with an excess of a 2.5 M

solution of n-butyllithium at −70 °C. After 30 min of stirring at this

temperature, 1 equiv of EtOH was added in a single portion. The reac-

tion mixture was stirred for 1 h at ambient temperature. Afterward, all

volatile materials were evaporated. The resulting residue was purified

by column chromatography on alox and dried under vacuum. Com-

plexes 6−9 were isolated as orange solid materials.

Synthesis of Bfc(PPh₂) (6). Using the general procedure described

above, molecule 1 was reacted with n-butyllithium followed by the

dropwise addition of 417 mg (1.89 mmol) of 2. The resulting residue

was purified by column chromatography on alumina (column dimens-

ion 2.5 × 30 cm) using a diethyl ether/n-hexane mixture in a ratio of

1/5 (v/v). At first, unreacted 1 and then a mixture of the title complex

and bfc(Br)(PPh₂) (ratio 1/3) was eluted as a red oil. Yield: 800 mg

(average molecular weight 613.39 g/mol, 1.3 mmol), ³¹P{¹H} NMR

(CDCl₃, δ): −16.6 ppm. An 800 mg portion (1.3 mmol) of the

obtained mixture was dissolved in tetrahydrofuran and was sub-

sequently lithiated with 0.62 mL of n-butyllithium (1.56 mmol, 2.5 M

in n-hexane) and reacted afterward with 120 mg of EtOH at −70 °C.

The obtained crude product was subjected to column chromatography

on alumina (column dimension 2.5 × 30 cm) using diethyl ether/

n-hexane (ratio 1/5, v/v) as eluent. After removal of all solvents,

compound 6 could be obtained as an orange solid. Yield: 690 mg (1.24

mmol, 65.8% based on 1). Anal. Calcd for C₃₂H₂₇Fe₂P (554.22

EXPERIMENTAL SECTION

■

General Data. All reactions were carried out under an atmosphere

of nitrogen or argon using standard Schlenk techniques. Tetrahy-

drofuran, toluene, n-hexane, and n-pentane were purified by distillation

from sodium/benzophenone ketyl; dichloromethane was purified by

distillation from calcium hydride.

Instruments. Infrared spectra were recorded with a FT-Nicolet IR

1

200 spectrometer. The H NMR spectra were recorded with a Bruker

Avance III 500 spectrometer operating at 500.303 MHz in the Fourier

transform mode; the ¹³C{¹H} NMR spectra were recorded at 125.800

MHz. Chemical shifts are reported in δ (parts per million) downfield

from tetramethylsilane with the solvent as reference signal (¹H NMR,

CDCl₃, 7.26; ¹³C{¹H} NMR, CDCl₃, 77.00). ³¹P{¹H} NMR spectra

were recorded at 101.255 MHz in CDCl₃with P(OMe)₃as an external

standard (δ 139.0 ppm, relative to H₃PO₄(85%) with δ 0.00 ppm).

The abbreviation pt in the ¹H NMR spectra corresponds to

pseudotriplet. The melting points of analytically pure samples (sealed

off in nitrogen-purged capillaries) were determined using a

Gallenkamp MFB 595 010 M melting point apparatus. Microanalyses

were performed using a Thermo FLASHEA 1112 Series instrument.

Cyclic voltammograms were recorded in a dried cell purged with puri-

fied argon. Platinum wires served as working and counter electrodes. A

saturated calomel electrode in a separate compartment served as

reference electrode. For ease of comparison, all electrode potentials are

converted using the redox potential of the ferrocene−ferrocenium

couple [FcH]/[FcH⁺] (FcH = Fe(η⁵-C₅H₅)₂, E₀= 0.46 V) as internal

standard.⁹⁵Electrolyte solutions were prepared from dichloromethane

and [ⁿBu₄N][PF₆] (Fluka, dried under oil-pump vacuum). Measure-

ments on 1.0 mmol/dm³solutions of 6−9, 14−17, and 23−26 in dry

dichloromethane containing 0.1 mol/dm³of [ⁿBu₄N][B(C₆F₅)₄] as

supporting electrolyte were conducted in a three-electrode cell, which

utilized a Pt auxiliary electrode, a glassy-carbon working electrode

(surface area 0.031 cm²), and an Ag/Ag⁺(0.01 mmol/dm³[AgNO₃])

reference electrode (mounted on a Luggin capillary). The working

electrode was treated by polishing on a Buehler microcloth first with

1 μm and then with 1/4 μm diamond paste. The reference electrode was

constructed from a silver wire inserted into a solution of 0.01 mmol/

dm³[AgNO₃] and 0.1 mol/dm³[ⁿBu₄N][B(C₆F₅)₄] in acetonitrile, in

a Luggin capillary with a Vycor tip. This capillary was inserted into a

second Luggin capillary with Vycor tip filled with a 0.1 mmol/dm³

[ⁿBu₄N][B(C₆F₅)₄] solution in dichloromethane. Experimental

potentials were referenced against [FcH]/[FcH⁺]. Data were mani-

pulated on a Microsoft Excel worksheet to set the formal reduction

potentials of the [FcH]/[FcH⁺] couple to E₀= 0.46 V. Under our

conditions the [FcH]/[FcH⁺] couple was at around 0.21 V vs Ag/Ag⁺.

Cyclic voltammograms were recorded in the negative direction at the

starting potentials using a Voltalab 3.1 potentiostat (Radiometer)

equipped with a DEA 101 digital electrochemical analyzer and an IMT

102 electrochemical interface. Spectroelectrochemical measurements

were carried out in an OTTLE cell similar to that described previously

by Hartl,¹³²from solutions in dichloromethane containing 0.1 mol/

dm³of [ⁿBu₄N][B(C₆F₅)₄] as supporting electrolyte using a Varian

Cary 5000 spectrometer. High-resolution mass spectra were recorded

using a micrOTOF-QII Bruker Daltonik workstation (ESI-TOF).

Reagents. All starting materials were obtained from commercial

suppliers and used without further purification. Dibromobiferrocene,⁸¹

bis(diphenylphosphanyl)biferrocene,⁸⁰chlorophosphines

(3−5),^133−135and [Pd(Et₂S)₂Cl₂]¹³⁶were prepared according to published

procedures.

g/mol): C, 69.34; H, 4.91. Found: C, 69.22; H, 4.91. Mp: 136 °C. IR

1

(KBr, cm⁻¹): ν

̃

1436 (w, ν_P−C); 1457, 1473 (w, ν_CC). H NMR

(CDCl₃, δ): 3.90 (pq, J_HH= 1.8 Hz, 2 H, C₅H₄), 3.96 (s, 5 H, C₅H₅),

4.04 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.13 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄),

4.15 (pt, J_HH= 1.74 Hz, 2 H, C₅H₄), 4.25−4.26 (dt, J_HH= 4.2 Hz, 1.8

Hz, 4 H, C₅H₄), 7.3−7.31 (m, 6 H, C₆H₅), 7.33−7.37 (m, 4 H, C₆H₅).

¹³C{¹H} NMR (CDCl₃, δ): 66.43 (C₅H₄), 67.32 (C₅H₄), 67.73

(C₅H₄), 69.06 (C₅H₄), 69.17 (s, C₅H₅), 72.7, 72.73 (d, J_CP= 3.87 Hz,

C₅H₄−P), 73.88, 74 (d, J_CP= 14.69 Hz, C₅H₄−P), 75.82, 75.87 (d,

J_CP= 6.2 Hz, C_i/C₅H₄), 83.0 (C_i/C₅H₄), 84.84 (C_i/C₅H₄), 128.07,

128.12 (d, J_CP= 6.67 Hz, C_m/C₆H₅), 128.39 (C_p/C₆H₅), 133.42,

133.57 (d, J_CP= 19.17 Hz, C_o/C₆H₅), 139.26, 139.34 (d, J_CP= 9.6 Hz,

C_i/C₆H₅). ³¹P{¹H} NMR (CDCl₃, δ): −16.55 ppm (s). This compound

was stirred for 1 week in acetone in air to prove its oxidation sensitivity,

yielding a 1/1 mixture of Bfc(PPh₂) and Bfc(OPPh₂). ³¹P{¹H} NMR

(CDCl₃, δ): 28.94 ppm (s).

Synthesis of Bfc(P(2-CH₃C₆H₄)₂) (7). Acoording to the general

procedure described earlier, compound 1 was reacted with n-butylli-

thium followed by the addition of 470 mg (1.89 mmol) of 3 in a single

portion. The resulting residue was purified by column chro-

matography on alumina (column dimension 2.5 × 30 cm) using a

1/2 (v/v) toluene/n-hexane mixture. At first, 1 was eluted. Then the

title complex together with bfc(Br)(P(2-CH₃C₆H₄)₂) in a 1/3 molar

ratio was eluted as a red oil. Yield: 600 mg (average molecular weight

641 g/mol, 0.93 mmol), ³¹P{¹H} NMR (CDCl₃, δ): −36.9 ppm. A

600 mg portion (0.93 mmol) of the mixture was lithiated with 0.44 mL

of n-butyllithium (1.22 mmol, 2.5 M in n-hexane) and was then reacted

with 85 mg of ethanol as described earlier. The obtained residue was

subjected to column chromatography on alumina (column dimension

2.5 × 30 cm) using toluene/n-hexane (ratio 1/2, v/v) as eluent. After

removal of all volatiles, 7 was obtained as an orange solid. Yield: 520 mg

(0.89 mmol, 47% based on 1). Anal. Calcd for C₃₄H₃₁Fe₂P (582.27 g/

mol): C, 70.13; H, 5.36. Found: C, 69.99; H, 5.33. Mp: 146−148 °C

1

General Procedure for the Synthesis of Bfc(PR₂). To a solution

of 1.0 g (1.89 mmol) of 1′,1‴-dibromobiferrocene (1) dissolved in

50 mL of dry tetrahydrofuran was added 1 equiv of a 2.5 M solution of

dec. IR (KBr, cm⁻¹): ν

̃

1446 (m, ν_P−C); 1559 (m, ν_CC). H NMR

(CDCl₃, δ): 2.53 (s, 6 H, CH₃), 3.94 (s, 5 H, C₅H₅), 3.95 (pq, J_HH

=

3.7 Hz, 1.8 Hz, 2 H, C₅H₄), 4.06 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.1 (pt,

2321

dx.doi.org/10.1021/om201220w | Organometallics 2012, 31, 2310−2326

Organometallics

Article

J_HH= 1.8 Hz, 2 H, C₅H₄), 4.17 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.19 (pt,

J_HH= 1.8 Hz, 2 H, C₅H₄), 4.22 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 6.9−7.06

(m, 4 H, C₆H₄CH₃), 7.15−7.21 (m, 4 H, C₆H₄CH₃). ¹³C{¹H} NMR

(CDCl₃, δ): 21.42 (d, J_CP= 21.79 Hz, CH₃), 66.32 (C₅H₄), 67.13

(C₅H₄), 67.68 (C₅H₄), 68.84 (C₅H₄), 69.14 (s, C₅H₅), 72.8, 72.85 (d,

J_CP= 4.16 Hz, C₅H₄−P), 74.46, 74.58 (d, J_CP= 15.44 Hz, C₅H₄−P),

75.64, 75.68 (d, J_CP= 5.4 Hz, C_i/C₅H₄), 83.04 (C_i/C₅H₄), 84.7 (C_i/

C₅H₄), 125.5 (s, C₆H₄CH₃), 128.3 (s, C₆H₄CH₃), 129.79, 127.83 (d,

J_CP= 5.08 Hz, C₆H₄CH₃), 133.4, (C₆H₄CH₃), 137.85, 137.94 (d, J_CP= 10.7

Hz, C_i/C₆H₄CH₃), 141.54, 141.75 (d, J_CP= 26.36 Hz, C_i/C₆H₄CH₃).

³¹P{¹H} NMR (CDCl₃, δ): −36.84 ppm (s). HRMS (ESI-TOF): m/z

calcd for C₃₄H₃₁Fe₂P ([M]⁺) 582.0858, found 582.0822 (100%).

Synthesis of Bfc(P(2-^cC₄H₃O)₂) (8). Compound 1 was reacted with

n-butyllithium followed by the dropwise addition of 380 mg (1.89

mmol) of 4 as described for the preparation of 6. The resulting residue

was purified by column chromatography on alumina (column dimens-

ion 2.5 × 30 cm) using toluene/n-hexane (ratio 1/2, v/v). Along with

1, a mixture of the title complex and bfc(Br)(P(2-^cC₄H₃O)₂) in a 1/3

molar ratio was eluted as a red oil. Yield: 700 mg (average molecular weight

593.3 g/mol, 1.17 mmol). ³¹P{¹H} NMR (CDCl₃, δ): −64.79 ppm. A 700

mg portion (1.17 mmol) of the obtained mixture was dissolved in tetra-

hydrofuran and was lithiated with 0.56 mL of n-butyllithium (1.4 mmol, 2.5

M in n-hexane). Afterward, it was reacted with 107 mg of ethanol. The

obtained crude product was purified by column chromatography on

alumina (column dimension 2.5 × 30 cm) using toluene/n-hexane (ratio

1/2, v/v) as eluent. After removal of all volatiles compound 8 was obtained

as an orange solid. Yield: 609 mg (1.14 mmol, 60.3% based on 1). Anal.

Calcd for C₂₈H₂₃Fe₂O₂P (534.14 g/mol): C, 62.96; H, 4.34. Found: C,

(C_i/C₅H₄). ³¹P{¹H} NMR (CDCl₃, δ): −7.39 ppm (s). HRMS (ESI-

TOF): m/z calcd for C₃₂H₃₉Fe₂P ([M + nH]⁺) 567.1562, found 567.1544.

General Procedure for the Synthesis of bfc(PR₂)₂. To 50 mL

of a tetrahydrofuran solution containing 1.0 g (1.89 mmol) of 1 was

added 2 equiv of a 2.5 M solution of n-butyllithium (3.78 mmol, 1.5

mL, 2.5 M in n-hexane) dropwise at −70 °C. After the reaction

mixture was stirred for 60 min at −70 °C, 2 equiv of the appropriate

chlorophosphine was added. The reaction mixture was stirred for 12 h

at ambient temperature and was then concentrated in vacuo to

dryness. The resulting residue was purified by column chromatography

on alumina using toluene as eluent.

Synthesis of bfc(P(2-CH₃C₆H₄)₂)₂(11). According to the general

procedure described above, molecule 1 was reacted with n-butyllithium

followed by addition of 940 mg (3.78 mmol) of chlorodi-o-tolyl-

phosphine (3) in a single portion. The title complex was obtained as an

orange solid. Yield: 1.0 g (1.2 mmol, 66% based on 1). Anal. Calcd for

C₄₈H₄₄Fe₂P₂(794.5 g/mol): C, 72.56; H, 5.58. Found: C, 72.78; H, 5.44.

1

Mp: 210 °C. IR (KBr, cm⁻¹): ν

̃

1449 (m, ν_P−C); 1559 (m, ν_CC). H

NMR (CDCl₃, δ): 2.44 (s, 12 H, CH₃), 3.83 (pq, J_HH= 3.7, 1.8 Hz, 4 H,

C₅H₄), 3.92 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 4.00 (pt, J_HH= 1.8 Hz, 4 H,

C₅H₄), 4.05 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 6.89−6.97 (m, 8 H,

C₆H₄CH₃), 7.06−7.12 (m, 8 H, C₆H₄CH₃). ¹³C{¹H} NMR (CDCl₃, δ):

21.32, 21.49 (d, J_CP= 22 Hz, CH₃), 67. 07 (C₅H₄), 68.95 (C₅H₄), 72.81,

72.84 (d, J_CP= 3.8 Hz, C₅H₄−P), 74.35, 74.47 (d, J_CP= 15.6 Hz, C₅H₄−

P), 75.65, 75.7 (d, J_CP= 6 Hz, C_i/C₅H₄), 83.86 (C_i/C₅H₄−P), 125.54

(C₆H₄CH₃), 128.36 (C₆H₄CH₃), 129.78, 129.82 (d, J_CP= 4.7 Hz,

C₆H₄CH₃), 133.41 (C₆H₄CH₃), 137.8, 137.89 (d, J_CP= 4.7 Hz,

C₆H₄CH₃), 141.52, 141.73 (d, J_CP= 26.3 Hz, C₆H₄CH₃). ³¹P{¹H} NMR

(CDCl₃, δ): −36.8 ppm (s). HRMS (ESI-TOF): m/z calcd for

C₄₈H₄₄Fe₂P₂([M]⁺) 794.1614, found 794.1586 (100%).

63.03; H, 4.375. Mp: 179 °C dec. IR (KBr, cm⁻¹): ν

̃

1006 (m, ν_C−O); 1457

1

2

(w, ν_P−C); 1559 (w, ν_CC); 3094 (m, ν_{C(sp )−H}). H NMR (CDCl₃, δ):

3.96 (s, 5H, C₅H₅), 4.0 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.12 (pt, J_HH= 1.5

Hz, 2 H, C₅H₄), 4.15 (pt, J_HH= 1.7 Hz, 2 H, C₅H₄), 4.22 (pt, J_HH= 1.7 Hz,

4 H, C₅H₄), 4.3 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 6.38 (m, 2 H, C₄H₃O), 6.66

(m, 2 H, C₄H₃O), 7.62 ppm (d, J_HH= 1.6 Hz, 2 H, C₄H₃O). ¹³C{¹H}

NMR (CDCl₃, δ): 65.4 (C₅H₄), 66.21 (C₅H₄), 66.73 (C₅H₄), 67.9 (C₅H₄),

68.1 (s, C₅H₅), 71.7, 71.9 (d, J_CP= 5.54 Hz, C₅H₄−P), 73.52, 73.67 (d,

J_CP= 18.2 Hz, C₅H₄−P), 109.5 (d, J_CP= 6 Hz, C₄H₃O), 118.5, 118.7 (d,

J_CP= 23 Hz, C₄H₃O), 145.5 (d, J_CP= 2 Hz, C₄H₃O). ³¹P{¹H} NMR

(CDCl₃, δ): −64.6 ppm (s).

Synthesis of bfc(P(2-^cC₄H₃O)₂)₂(12). As described earlier,

compound 1 was reacted with n-butyllithium and then 760 mg (3.78

mmol) of chlorodifurylphosphine (4) were added dropwise. The product

was obtained as an orange solid. Yield: 1.0 g (1.43 mmol, 75% based

on 1). Anal. Calcd for C₃₆H₂₈Fe₂O₄P₂(698.24 g/mol): C, 61.92; H, 4.04.

Found: C, 62.03; H, 3.997. Mp: 180 °C dec. IR (KBr, cm⁻¹): ν

̃

1007

1

2

(m, ν_C−O); 1458 (m, ν_P−C); 1556 (w, ν_CC), 3091 (w, ν_{C(sp )−H}). H

NMR (CDCl₃, δ): 3.98 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 4.09 (pt, J_HH= 1.5

Hz, 4 H, C₅H₄), 4.18−4.2 (m, 8 H, C₅H₄), 6.38−6.39 (m, 4 H, C₄H₃O),

6.65−6.66 (m, 4 H, C₄H₃O), 7.62 (d, J_HH= 1.5 Hz, 4 H, C₄H₃O).

¹³C{¹H} NMR (CDCl₃, δ): 67.47 (C₅H₄), 69.2 (C₅H₄), 72.6 (C_i/C₅H₄),

72.88, 72.92 (d, J_CP= 5.3 Hz, C₅H₄−P), 74.68, 74.83 (d, J_CP= 18 Hz,

C₅H₄−P), 84.07 (C_i/C₅H₄), 110.65 (d, J_CP= 6 Hz, C₄H₃O), 119.8 (d,

J_CP= 23.3 Hz, C₄H₃O), 146.7 (s, C_i/C₄H₃O), 152.68 ppm (d, J_CP= 8.4

Hz, C₄H₃O. ³¹P{¹H} NMR (CDCl₃, δ): −64.74 ppm (s).

Synthesis of Bfc(P(^cC₆H₁₁)₂) (9). Using the procedure described

above, compound 1 was reacted with n-butyllithium followed by dropwise

addition of 440 mg (1.89 mmol) of chlorodicyclohexylphosphine (Cy).

The crude product was purified by column chromatography on alumina

(column dimension 2.5 × 30 cm) using toluene/n-hexane (ratio 1/2, v/v).

At first, 1 was eluted. Then a 1/3 mixture of the title complex and

bfc(Br)(P(^cC₆H₁₁)₂) was eluted as a red oil. Yield: 680 mg (average

molecular weight 625.47 g/mol, 1.08 mmol), ³¹P{¹H} NMR (CDCl₃, δ):

−7.46 ppm. A 680 mg portion (1.08) of the mixture was dissolved in

tetrahydrofuran as described above and was than lithiated with 0.5 mL of

n-butyllithium (1.3 mmol, 2.5 M in n-hexane) and reacted with 100 mg of

ethanol. The crude product was subjected to column chromatography on

alumina (column dimension 2.5 × 30 cm) using a toluene/n-hexane

mixture (ratio 1/2, v/v) as eluent. After removal of all volatile materials

compound 9 could be obtained as an orange solid. Yield: 500 mg

(0.88 mmol, 46% based on 1). Anal. Calcd for C₃₂H₃₉Fe₂P·¹/₂C₆H₁₄

(566.31 g/mol): C, 68.90; H, 7.60. Found: C, 68.82; H, 7.70. Mp: 157 °C.

Synthesis of bfc(P(^cC₆H₁₁)₂)₂(13). Using the procedure described

above, molecule 1 was reacted with n-butyllithium and then with 880

mg (3.78 mmol) of chlorodicyclohexylphosphine (5). The title

compound 13 was obtained as an orange solid. Yield: 1.1 g (1.14

mmol, 76% based on 1). Anal. Calcd for C₄₄H₆₀Fe₂P₂(762.58 g/mol):

C, 69.30; H, 7.93. Found: C, 69.05; H, 7.86. Mp: 192 °C. IR (KBr,

1

cm⁻¹): ν

̃

1448 (m, ν_P−C). H NMR (CDCl₃, δ): 1.02−1.08 (m, 4 H,

C₆H₁₁), 1.13−1.29 (m, 18 H, C₆H₁₁), 1.63−1.67 (m, 7 H, C₆H₁₁),

1.7−1.76 (m, 11 H, C₆H₁₁), 1.85−1.87 (m, 4 H, C₆H₁₁), 3.94 (4 H,

C₅H₄), 4.04 (4 H, C₅H₄), 4.13 (4 H, C₅H₄), 4.33 (4 H, C₅H₄).

¹³C{¹H} NMR (CDCl₃, δ): 26.46 (CH₂/C₆H₁₁), 27.28, 27.33 (d, J_CP

=

6.2 Hz, CH₂/C₆H₁₁), 27.35, 27.41 (d, J_CP= 7.6 Hz, CH₂/C₆H₁₁),

30.23, 30.34 (d, J_CP= 13.3 Hz, CH₂/C₆H₁₁), 30.34, 30.43 (d, J_CP

̃

IR (KBr, cm⁻¹): ν 1447.5 (m, ν_P−C). ¹H NMR (CDCl₃, δ): 0.88

=

(CH₃/C₆H₁₄), 1.26 (CH₂/C₆H₁₄), 1.14−1.28 (m, 10 H, C₆H₁₁),

1.64−1.77 (m, 10 H, C₆H₁₁), 1.87−1.9 (m, 2 H, C₆H₁₁), 3.96 (2 H,

C₅H₄), 3.98 (s, 5 H, C₅H₅), 4.06 (pt, J_HH= 1.7 Hz, 2 H, C₅H₄), 4.14

(pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.17 (pt, J_HH= 1.7 Hz, 2 H, C₅H₄), 4.32

(pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.38 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄).

¹³C{¹H} NMR (CDCl₃, δ): 14.14 (CH₃/C₆H₁₄), 22.70 (CH₂/C₆H₁₄),

25.45 (CH₂/C₆H₁₁), 26.26, 26.32 (d, J_CP= 7.2 Hz, CH₂/C₆H₁₁), 26.33, 26.4

(d, J_CP= 8.3 Hz, CH₂/C₆H₁₁), 29.21, 29.32 (d, J_CP= 14 Hz, CH₂/C₆H₁₁),

29.32, 29.39 (d, J_CP= 7.7 Hz, CH₂/C₆H₁₁), 32.4, 32.49 (d, J_CP= 11.3 Hz,

CH/C₆H₁₁), 65.51 (C₅H₄), 66.35 (C₅H₄), 66.67 (C₅H₄), 68.71 (s, C₅H₅),

68.4 (C₅H₄), 70.33 (C₅H₄−P), 71.52, 71.61 (d, J_CP= 11 Hz, C₅H₄−P),

75.28, 75.41 (d, J_CP= 16.4 Hz, C_i/C₅H₄), 82.52 (C_i/C₅H₄), 83.42

11.3 Hz, CH₂/C₆H₁₁), 33.42, 33.51 (d, J_CP= 11.6 Hz, CH/C₆H₁₁),

67.56 (C₅H₄), 69.42 (C₅H₄), 71.37, 71.39 (d, J_CP= 2.5 Hz, C₅H₄−P),

73.54, 72.63 (d, J_CP= 11.4 Hz, C₅H₄−P), 84.07 (C_i/C₅H₄). ³¹P{¹H}

NMR (CDCl₃, δ): −7.39 ppm (s). HRMS (ESI-TOF): m/z calcd for

C₄₄H₆₀Fe₂P₂([M + nH]⁺) 763.2944, found 763.2915 (90%); ([M +

nH]²⁺) 382.1508, found 382.1485 (100%).

General Procedure for the Preparation of Bfc(SePR₂) and

bfc(SePR₂)₂. To a toluene solution (20 mL) containing 100 mg of

monophosphines 6−9 (0.18 mmol) or diphosphines 10−13 (0.13 mmol)

was added 1.2 (for monophosphines) or 2.4 equiv (for diphosphines) of

elemental selenium in a single portion, and the reaction mixture was stirred

for 5 h at 100 °C. After the respective reaction mixture was cooled to

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ambient temperature, it was filtered through a pad of Celite to remove the

excess elemental selenium. After filtration all volatile materials were removed

under vacuum to afford the appropriate compounds as orange solids.

Synthesis of Bfc(SePPh₂) (14). Using the general procedure

described above, 6 was reacted with 21.3 mg (0.27 mmol) of selenium.

Molecule 14 was obtained as an orange solid. Yield: 100 mg (0.15 mmol,

87.79% based on 6). Anal. Calcd for C₃₂H₂₇Fe₂PSe·¹/₆CH₂Cl₂(633.18 g/

(d, J_CP= 4.6 Hz, CH₂/C₆H₁₁), 26.25, 26.27 (d, J_CP= 2.8 Hz, CH₂/

C₆H₁₁), 36.05, 36.4 (d, J_CP= 44.5 Hz, CH/C₆H₁₁), 65.54 (C₅H₄),

66.93 (C₅H₄), 66.95 (C₅H₄), 68.26 (s, C₅H₅), 69.95 (C₅H₄), 71.2 (C_i/

C₅H₄), 71.69, 71.76 (d, J_CP= 8.1 Hz, C₅H₄−P), 71.77, 71.83 (d, J_CP

=

6.5 Hz, C₅H₄−P), 81.33 (C_i/C₅H₄), 84.81 (C_i/C₅H₄). ³¹P{¹H} NMR

³¹P⁷⁷Se

(CDCl₃, δ): 49.87 ppm (J

= 700 Hz). HRMS (ESI-TOF): m/z

calcd for C₃₂H₃₉Fe₂PSe ([M]⁺) 646.0652, found 646.0634.

mol): C, 59.82; H, 4.26. Found: C, 59.79; H, 4.26. Mp: 215 °C dec. IR

Synthesis of bfc(SePPh₂)₂(18). According to the procedure

described above, molecule 10 was reacted with 25.6 mg (0.325 mmol)

of selenium. Compound 18 was obtained as an orange solid. Yield: 100

mg (0.11 mmol, 85.8% based on 10). Anal. Calcd for C₄₄H₃₆Fe₂P₂Se₂

(896.31 g/mol): C, 58.96; H, 4.05. Found: C, 59.12; H, 3.98. Mp:

1

(KBr, cm⁻¹): ν

̃

574 (m, ν_PSe); 1433 (w, ν_P−C); 1475 (w, ν_CC). H

NMR (CDCl₃, δ): 3.95 (s, 5 H, C₅H₅), 4.16 (4 H, C₅H₄), 4.25 (pq, J_HH

=

1.8 Hz, 2 H, C₅H₄), 4.33 (2 H, C₅H₄), 4.35 (pt, J_HH= 1.8 Hz, C₅H₄),

4.54 (pt, J_HH= 2.4, 1.98 Hz, 2 H, C₅H₄), 5.30 (CH₂/CH₂Cl₂), 6.47−6.48

(m, 2 H, C₆H₅), 7.07−7.09 (m, 2 H, C₆H₅), 7.68 (2 H, C₆H₅). ¹³C{¹H}

NMR (CDCl₃, δ): 53.52 (CH₂/CH₂Cl₂), 65.36 (C₅H₄), 66.81 (C₅H₄),

66.90 (C₅H₄), 68.19 (C₅H₅), 69.5 (C₅H₄), 70.38 (C_i/C₅H₄), 73, 73.09

(d, J_CP= 10 Hz, C₅H₄−P), 73.17, 73,27 (d, J_CP= 12.5 Hz, C₅H₄−P),

80.98 (C_i/C₅H₄), 85.03 (C_i/C₅H₄), 127.10, 127.20 (d, J_CP= 12.6 Hz, C_o/

C₆H₅), 130.13, 130.16 (d, J_CP= 3.4 Hz, C_m/C₆H₅), 131.03, 131.12 (d,

J_CP= 10.9 Hz, C_p/C₆H₅), 132.37, 133 (d, J_CP= 78.6 Hz, C_i/C₆H₅). ³¹P{¹H}

150 °C dec. IR (KBr, cm⁻¹): ν

̃

572, 531 (m, ν_PSe); 1432 (w, ν_P−C); 1475

(w, ν_CC). ¹H NMR (CDCl₃, δ): 4.13 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄),

4.2 (pt, J_HH= 1.9 Hz, 4 H, C₅H₄), 4.22 (pq, J_HH= 1.8 Hz, 4 H, C₅H₄),

4.25 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 7.38−7.41 (m, 8 H, C₆H₅), 7.44−

7.46 (m, 4 H, C₆H₅), 7.65−7.69 (m, 8 H, C₆H₅). ¹³C{¹H} NMR

(CDCl₃, δ): 66.97 (C₅H₄), 69.74 (C₅H₄), 72.93, 73.01 (d, J_CP= 10 Hz,

C₅H₄−P), 73.19, 73.29 (d, J_CP= 12.5 Hz, C₅H₄−P), 83.07 (C_i/C₅H₄),

³¹P⁷⁷

127.13, 127.23 (d, J_CP= 12.2 Hz, C_o/C₆H₅), 130.19, 130.22 (d, J_CP

=

NMR (CDCl₃, δ): 31.8 ppm (J _Se= 731.18 Hz). HRMS (ESI-TOF): m/z

calcd for C₃₂H₂₇Fe₂PSe ([M]⁺) 633.9713, found 633.9690 (100%).

Synthesis of Bfc(SeP(2-CH₃C₆H₄)₂) (15). According to the pro-

cedure earlier described, 7 was reacted with 20.35 mg (0.25 mmol) of

selenium. The title compound 15 was obtained as an orange solid.

Yield: 100 mg (0.15 mmol, 89% based on 7). Anal. Calcd for

C₃₄H₃₁Fe₂PSe (661.23 g/mol): C, 61.757; H, 4.725. Found: C, 61.37;

3 Hz, C_m/C₆H₅), 131, 131.09 (d, J_CP= 10.8 Hz, C_p/C₆H₅), 132.26

31

(C_i/C₆H₅). P{¹H} NMR (CDCl₃, δ): 31.7 ppm (J

= 733 Hz).

³¹P⁷⁷Se

Synthesis of bfc(SeP(2-CH₃C₆H₄)₂)₂(19). Compound 11 was

reacted with 24.8 mg (0.31 mmol) of selenium. Compound 19 was

obtained as an orange solid. Yield: 110 mg (0.11 mmol, 92% based on

11. Anal. Calcd for C₄₈H₄₄Fe₂P₂Se₂·¹/₂CH₂Cl₂(952.42 g/mol): C,

H, 4.85. Mp: 185 °C dec. IR (KBr, cm⁻¹): ν

̃

558, 575 (m, ν_PSe); 1448

58.55; H, 4.55. Found: C, 58.3; H, 4.62. Mp: 200 °C dec. IR (KBr,

1

cm⁻¹): ν

̃

574, 558 (m, ν_PSe); 1448 (m, ν_P−C); 1559 (m, ν_CC). H

(m, ν_P−C); 1559 (m, ν_CC). ¹H NMR (CDCl₃, δ): 1.99 (s, 6 H, CH₃),

3.93 (s, 5 H, C₅H₅), 4.1 (2 H, C₅H₄), 4.13 (bs, 2 H, C₅H₄), 4.24 (2 H,

C₅H₄), 4.29 (2 H, C₅H₄), 4.3 (bs, 2 H, C₅H₄), 7.11−7.18 (m, 4 H,

C₆H₄CH₃), 7.37 (bm, 4 H, C₆H₄CH₃). ¹³C{¹H} NMR (CDCl₃, δ):

21.75 (m, CH₃), 65.27 (C₅H₄), 66.83 (C₅H₄), 66.9 (C₅H₄), 68.19

(s, C₅H₅), 70.07 (C₅H₄), 72.9 (C₅H₄−P), 73.03 (C₅H₄−P), 75

(C_i/C₅H₄), 81.08 (C_i), 84.88 (C_i), 125.27, 125.37 (d, J_CP= 12.5 Hz,

C₆H₄CH₃), 127.21 (C₆H₄CH₃), 130.33 (C₆H₄CH₃), 130.61, 130.7

(d, J_CP= 10.19 Hz, C₆H₄CH₃), 138.9, 139 (d, J_CP= 8.1 Hz,

NMR (CDCl₃, δ): 1.97 (bs, 12 H, CH₃), 4.2 (bs, 8 H, C₅H₄), 4.23 (bs,

8 H, C₅H₄), 5.30 (CH₂/CH₂Cl₂), 7.09−7.12 (m, 4 H, C₆H₄CH₃),

7.15−7.17 (m, 4 H, C₆H₄CH₃), 7.24 (bs, 4 H, C₆H₄CH₃), 7.36 (bs,

4 H, C₆H₄CH₃). ¹³C{¹H} NMR (CDCl₃, δ): 21.6 (m, CH₃), 53.52

(CH₂/CH₂Cl₂), 67.96 (C₅H₄), 71.3 (C₅H₄), 73.95 (C₅H₄−P), 74.0

(C₅H₄−P), 74.4 (C_i/C₅H₄, 84.0 (C_i), 126.3, 126.39 (d, J_CP= 13 Hz,

C₆H₄CH₃), 128.2 (C₆H₄CH₃), 129.0 (C₆H₄CH₃), 131.66, 131.74

(d, J_CP= 10.1 Hz, C₆H₄CH₃), 139.9, 140 (d, J_CP= 9.3 Hz, C_i/C₆H₄CH₃).

³¹P{¹H} NMR (CDCl₃, δ): 29.42 ppm (J

= 718 Hz).

C_i/C₆H₄CH₃). ³¹P{¹H} NMR (CDCl₃, δ): 29.5 ppm (J _Se= 715 Hz).

³¹P⁷⁷Se

³¹P⁷⁷

Synthesis of Bfc(SeP(2-^cC₄H₃O)₂) (16). As described earlier, 8

was reacted with 22 mg (0.28 mmol) of selenium. 16 was obtained as

an orange solid. Yield: 110 mg (0.179 mmol, 99.6% based on 8). Anal.

Calcd for C₂₈H₂₃Fe₂O₂PSe (613.10 g/mol): C, 54.85; H, 3.78. Found:

Synthesis of bfc(SeP(2-^cC₄H₃O)₂)₂(20). As described earlier, 12

was reacted with 28.2 mg (0.35 mmol) of selenium. Compound 20

was obtained as an orange solid. Yield: 119 mg (0.14 mmol, 99.2%

based on 12). Anal. Calcd for C₃₆H₂₈Fe₂O₄P₂Se₂·¹/₂(n-hexane)

(856.16 g/mol): C, 52.08; H, 3.98. Found: C, 51.99; H, 4.05. Mp:

C, 55.0; H, 3.9. Mp: 200 °C dec. IR (KBr, cm⁻¹): ν

̃

585, 595

200 °C dec. IR (KBr, cm⁻¹): ν

̃

578, 569 (m, ν_PSe); 1014 (m, ν_C−O);

(m, ν_PSe); 1002 (m, ν_C−O); 1454 (w, ν_P−C); 1556 (w, ν_CC), 3084

1

1458 (m, ν_P−C); 1559 (w, ν_CC), 3096 (m, ν_{C(sp )−H}). ¹H NMR

(CDCl₃, δ): 0.88 (CH₃/C₆H₁₄), 1.26 (CH₂/C₆H₁₄), 4.16 (pt, J_HH= 1.8

Hz, 4 H, C₅H₄), 4.23 (pq, J_HH= 1.8 Hz, 4 H, C₅H₄), 4.36 (pt, J_HH= 1.8

Hz, 8 H, C₅H₄), 4.5 (pq, J_HH= 2.4 Hz, 1.9 Hz, 4 H, C₅H₄), 6.47−6.49

(m, 4 H, C₄H₃O), 7.08 (pt, J_HH= 2.6 Hz, 4 H, C₄H₃O), 7.68 ppm (4 H,

C₄H₃O). ¹³C{¹H} NMR (CDCl₃, δ): 14.14 (CH₃/C₆H₁₄), 22.70 (CH₂/

C₆H₁₄), 32.01 (CH₂/C₆H₁₄), 67.14 (C₅H₄), 69.7 (C₅H₄), 70.23 (C_i/

C₅H₄), 72.78, 72.9 (d, J_CP= 14.5 Hz, C₅H₄−P), 72.96, 73.0 (d,

2

(m, ν_{C(sp )−H}). H NMR (CDCl₃, δ): 3.95 (s, 5 H, C₅H₅), 4.16 (pq,

J_HH= 1.7, 3.0 Hz, 2 H, C₅H₄), 4.26 (pq, J_HH= 1.8, 3.6 Hz, 2 H, C₅H₄),

4.33 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.36 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄),

4.55 (pq, J_HH= 2, 4.4 Hz, 2 H, C₅H₄), 6.48−6.49 (m, J_HH= 1.6, 3.3

Hz, 2 H, C₄H₃O), 7.09−7.1 (m, 2 H, C₄H₃O), 7.68−7.7 ppm (m, 2 H,

C₄H₃O). ¹³C{¹H} NMR (CDCl₃, δ): 65.44 (C₅H₄), 66.85 (C₅H₄),

66.96 (C₅H₄), 68.21 (C₅H₅), 69.43 (C₅H₄), 69.93 (C_i/C₅H₄), 70.73

(C_i/C₅H₄), 72.7, 72.8 (d, J_CP= 14.8 Hz, C₅H₄−P), 73.06, 73.15 (d,

J_CP= 11.5 Hz, C₅H₄−P), 80.96 (C_i/C₅H₄, C₅H₄−P), 85.29 (C_i/C₅H₄,

C₅H₄−P), 109.05, 109.98 (d, J_CP= 9.6 Hz, C₄H₃O), 120.89, 121.07

(d, J_CP= 21.8 Hz, C₄H₃O), 145.89, 146.79 (d, J_CP= 114.2 Hz,

C_i/C₄H₃O), 147.11, 147.17 (d, J_CP= 6.9 Hz, C₄H₃O). ³¹P{¹H} NMR

J_CP= 11.4 Hz, C₅H₄−P), 83.35 (C_i/C₅H₄), 110.01, 110.08 (d, 3J_CP

9.5 Hz, C₄H₃O), 120.9, 121.12 (d, 2J_CP= 21.9 Hz, C₄H₃O), 145.78,

=

146.68 (d, J_CP= 114 Hz, C_i/C₄H₃O), 147.18, 147.23 (d, J_CP= 7 Hz,

31

C₄H₃O). P{¹H} NMR (CDCl₃, δ): −5.4 ppm (J

= 769 Hz).

³¹P⁷⁷Se

Synthesis of bfc(SeP(^cC₆H₁₁)₂)₂(21). Applying the general

procedure described earlier, 13 was reacted with 25.8 mg (0.32

mmol) of selenium. 21 was obtained as an orange solid. Yield: 100 mg

(0.108 mmol, 83.6% based on 13). Anal. Calcd for C₄₄H₆₀Fe₂P₂Se₂

(920.5 g/mol): C, 57.41; H, 6.56. Found: C, 57.50; H, 6.60. Mp:

̃

³¹P⁷⁷Se

(CDCl₃, δ): −5.2 ppm (J

= 768 Hz). HRMS (ESI-TOF): m/z

calcd for C₂₈H₂₃Fe₂O₂PSe ([M]⁺) 613.9298, found 613.9278 (100%).

Synthesis of Bfc(SeP(^cC₆H₁₁)₂) (17). Molecule 9 was reacted with

21 mg (0.26 mmol) of selenium as stated earlier. Compound 16 was

obtained as an orange solid. Yield: 100 mg (0.15 mmol, 91% based on 9).

Anal. Calc. for C₃₂H₃₉Fe₂PSe (645.27 g/mol): C, 59.56; H, 6.091.

160 °C dec. IR (KBr, cm⁻¹): ν 549 (m, ν_PSe); 1441 (m, ν_P−C). ¹H NMR

Found: C, 59.8; H, 6.05. Mp: 165 °C dec. IR (KBr, cm⁻¹): ν

̃

554, 533

(CDCl₃, δ): 1.22−1.27 (m, 18 H, C₆H₁₁), 1.54 (2 H, C₆H₁₁), 1.65−

1.67 (m, 4 H, C₆H₁₁), 1.80−1.83 (m, 8 H, C₆H₁₁), 1.93−1.97 (m, 12

H, C₆H₁₁), 4.16 (4 H, C₅H₄), 4.22 (4 H, C₅H₄), 4.41 (pt, J_HH= 1.78

Hz, 4 H, C₅H₄), 4.55 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄). ¹³C{¹H} NMR

(CDCl₃, δ): 24.79 (CH₂/C₆H₁₁), 25.35, 25.36 (d, J_CP= 1.4 Hz, CH₂/

C₆H₁₁), 25.40, 25.45 (d, J_CP= 5.7 Hz, CH₂/C₆H₁₁), 25.51, 25.55

(d, J_CP= 5 Hz, CH₂/C₆H₁₁), 26.23, 26.26 (d, J_CP= 3.2 Hz, CH₂/

C₆H₁₁), 36.02, 36.37 (d, J_CP= 44.5 Hz, CH/C₆H₁₁), 67.34 (C₅H₄),

70.26 (C₅H₄), 71.77, 71.8 (d, J_CP= 3.6 Hz, C₅H₄−P), 71.84, 71.88

(m, ν_PSe); 1448 (m, ν_P−C). ¹H NMR (CDCl₃, δ): 1.22−1.27 (m, 9 H,

C₆H₁₁), 1.64−1.66 (m, 2 H. C₆H₁₁), 1.79−1.82 (m, 4 H, C₆H₁₁), 1.9−

1.98 (m, 7 H, C₆H₁₁), 3.97 (s, 5 H, C₅H₅), 4.15 (pq, J_HH= 1.59, 1.66

Hz, 2 H, C₅H₄), 4.18 (pt, J_HH= 1.76 Hz, 2 H, C₅H₄), 4.23 (pq, J_HH

=

1.6, 1.7 Hz, 2 H, C₅H₄), 4.38 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄), 4.39 (pt,

J_HH= 1.8 Hz, 2 H, C₅H₄), 4.47 (pt, J_HH= 1.8 Hz, 2 H, C₅H₄). ¹³C{¹H}

NMR (CDCl₃, δ): 24.8 (CH₂/C₆H₁₁), 25.37, 25.38 (d, J_CP= 1.7 Hz,

CH₂/C₆H₁₁), 25.41, 25.45 (d, J_CP= 5.4 Hz, CH₂/C₆H₁₁), 25.52, 25.55

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(d, J_CP= 4.8 Hz, C₅H₄−P), 83.3 (C_i/C₅H₄). ³¹P{¹H} NMR (CDCl₃, δ):

4.55 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 4.57 (4 H, C₅H₄), 5.30 (CH₂/

CH₂Cl₂). ¹³C{¹H} NMR (CDCl₃, δ): 26.37 (CH₂/C₆H₁₁) 27.55 (CH₂/

C₆H₁₁), 27.68 (CH₂/C₆H₁₁), 28.85 (CH₂/C₆H₁₁), 30.07 (CH₂/C₆H₁₁),

36.75 (pt, J_CP= 11 Hz, CH/C₆H₁₁), 53.52 (CH₂/CH₂Cl₂), 66.43

(C₅H₄), 67.74 (C₅H₄), 67.82 (C₅H₄), 69.24 (C₅H₅), 71.02 (C₅H₄), 72.86

(C₅H₄−P), 75.14 (pt, J_CP= 4.6 Hz, C_i/C₅H₄−P), 83.2 (C_i/C₅H₄), 85.07

(C_i/C₅H₄). ³¹P{¹H} NMR (CDCl₃, δ): 18.2 ppm (s). HRMS (ESI-

TOF): m/z calcd for C₆₄H₇₈Fe₄P₂PdCl₂([M]⁺) 1308.1409, found

1309.1366; ([M]²⁺) 655.0696, found 655.0665; C₆₄H₇₈Fe₄P₂PdCl ([M]⁺)

1273.1722, found 1273.1560.

³¹P⁷⁷Se

49.8 ppm (J

= 700.5 Hz). HRMS (ESI-TOF): m/z calcd for

C₄₄H₆₀Fe₂P₂Se₂([M]⁺) 922.1207, found 922.1199.

General Procedure for the Synthesis of [Pd(Bfc(PR₂))₂Cl₂]. To

a dichloromethane solution (50 mL) containing 1 equiv of the phosphines

6−9 was added 0.5 equiv of [Pd(Et₂S)₂Cl₂] (22) in a single portion, and

the reaction mixture was stirred for 5 h at 25 °C. Subsequently, the solvent

was reduced in volume to 3−5 mL and addition of n-hexane (20 mL)

caused the precipitation of the appropriate product, which was then washed

with n-hexane (2 × 10 mL) and dried under oil pump vacuum.

General Procedure for the Suzuki Reaction. A 500 mg portion

(2.92 mmol) of 2-bromotoluene or 464 mg (3.00 mmol) of 4′-

chloroacetophenone, 470 mg (3.85 mmol) of phenylboronic acid, 1.21 g

(8.76 mmol) of K₂CO₃, and 114 mg (0.50 mmol) of acetylferrocene

were dissolved in 12 mL of a dioxane/water mixture (ratio 2/1, v/v).

After addition of 0.25 or 0.1 mol % (reaction of 2-bromotoluene) or

0.5 mol % (reaction of 4′-chloroacetophenone) of the appropriate

catalyst 23, 24, 25, or 26, the reaction mixture was stirred for 2 h at

100 °C. Samples (1 mL) were taken after 2.5, 5, 10, 20, 30, 60, 90, and

120 min and filtered through silica gel with diethyl ether as eluent. All

volatiles were evaporated under reduced pressure, and the conversions

Synthesis of [Pd(Bfc(PPh₂))₂Cl₂] (23). Using the general procedure

described above, 64.5 mg (0.18 mmol) of 22 were reacted with 200

mg (0.36 mmol) of 6. Complex 23 was obtained as a red solid. Yield:

210 mg (0.16 mmol, 90.7% based on 22). Anal. Calcd for C₆₄H₅₄Fe₄-

P₂PdCl₂·¹/₂CH₂Cl₂(1285.76 g/mol): C, 58.32; H, 4.17. Found: C,

58.56; H, 4.27. Mp: 214.5 °C. IR (KBr, cm⁻¹): ν

̃

1436 (w, ν_P−C);

1474, 1483 (m, ν_CC). H NMR (CDCl₃, δ): 3.99 (s, 10 H, C₅H₅),

4.14 (4 H, C₅H₄), 4.18 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 4.35 (pt, J_HH

1

=

1.8 Hz, 4 H, C₅H₄), 4.47 (4 H, C₅H₄), 4.54 (pt, J_HH= 1.8 Hz, 4 H,

C₅H₄), 4.67 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄), 5.30 (CH₂/CH₂Cl₂),

7.35−7.44 (m, 12 H, C₆H₅), 7.61−7.65 (m, 8 H, C₆H₅). ¹³C{¹H}

NMR (CDCl₃, δ): 53.52 (CH₂/CH₂Cl₂), 65.19 (C_i/C₅H₄), 66.6

(C₅H₄), 67.89 (C₅H₄), 67.94 (C₅H₄), 69.2 (C₅H₅), 71.04 (C₅H₄),

774.32 (C₅H₄), 76.04 (C₅H₄), 127.7 (pt, J_CP= 5.4 Hz, C₆H₅), 129.9

(C₆H₅), 130.04 (C₆H₅), 134.19 (C₆H₅). ³¹P{¹H} NMR (CDCl₃, δ):

15.42 ppm (s).

1

were determined by H NMR spectroscopy.

General Procedure for the Heck Reaction. A 612 mg portion

(3.0 mmol) of iodobenzene, 397 mg (3.1 mmol) of tert-butyl acrylate,

415 mg (3.2 mmol) of EtNⁱPr₂, and 114 mg (0.50 mmol) of acetyl-

ferrocene were dissolved in 15 mL of a toluene/acetonitrile mixture

(1/1 (v/v)). After addition of 0.5 mol % of the appropriate catalyst 23,

24, 25, or 26, the reaction mixture was stirred for 10 h at 80 °C.

Samples (1 mL) were taken every 1 h, and all volatiles were evaporated

Synthesis of [Pd(Bfc(P(2-CH₃C₆H₄)₂))₂Cl₂] (24). Following the

general procedure stated earlier, 76.7 mg (0.21 mmol) of 22 were

reacted with 250 mg (0.43 mmol) of 7. Complex 24 was obtained as a

red solid. Yield: 230 mg (0.17 mmol, 81.6% based on 22). Anal. Calcd

for C₆₈H₆₂Fe₄P₂PdCl₂(1341.87 g/mol): C, 60.86; H, 4.65. Found: C,

1

under reduced pressure and the conversions determined by H NMR

spectroscopy.

59.84; H, 4.601. Mp: 173 °C dec. IR (KBr, cm⁻¹): ν

̃

1448 (m, ν_P−C);

Crystallography. Crystal data for 15, 16, 21, 23 and 25 are

presented in the Supporting Information. All data were collected on a

Oxford Gemini S diffractometer with graphite-monochromatized

Mo Kα radiation (λ = 0.710 73 Å) (21, 23, 25) and graphite-

monochromated Cu Kα radiation (λ = 1.541 84 Å) (15, 16) at 100 K

using oil-coated shock-cooled crystals. The structures were solved by

direct methods using SHELXS-97 or SIR-92 and refined by full-matrix

least-squares procedures on F²using SHELXL-97.^137,138All non-

hydrogen atoms were refined anisotropically, and a riding model was

employed in the refinement of the hydrogen atom positions.

1

1559 (m, ν_CC). H NMR (CDCl₃, δ): 2.37 (s, 12 H, CH₃), 3.97 (s,

10 H, C₅H₅), 4.14 (4 H, C₅H₄), 4.17 (pt, J_HH= 1.6 Hz, 4 H, C₅H₄),

4.28 (pt, J_HH= 1.7 Hz, 4 H, C₅H₄), 4.36−4.37 (m, 8 H, C₅H₄), 4.65 (4 H,

C₅H₄), 7.14−7.20 (m, 8 H, C₆H₄CH₃), 7.30−7.33 (m, 4 H,

C₆H₄CH₃), 7.9−7.94 (m, 4 H, C₆H₄CH₃). ¹³C{¹H} NMR (CDCl₃, δ):

23.96 (pt, J_CP= 3.5 Hz, CH₃), 66.44 (C₅H₄), 67.88 (C₅H₄), 68.01

(C₅H₄), 69.25 (s, C₅H₅), 72.2 (C₅H₄), 74.4 (pt, J_CP= 4.48 Hz, C₅H₄),

77.4 (pt, J_CP= 6 Hz, C₅H₄), 82.74 (C_i/C₅H₄), 85.3 (C_i/C₅H₄), 124.9 (pt,

J_CP= 5.2 Hz, C₆H₄CH₃), 130.2 (s, C₆H₄CH₃), 131 (pt, J_CP= 4 Hz,

C₆H₄CH₃), 134.9 (s, C₆H₄CH₃), 142.31, 142.35 (d, J_CP= 5.65,

C_i/C₆H₄CH₃). ³¹P{¹H} NMR (CDCl₃, δ): 11.42 ppm (s).

ASSOCIATED CONTENT

Synthesis of [Pd(Bfc(P(2-^cC₄H₃O)₂))₂Cl₂] (25). A 67 mg portion

(0.187 mmol) of 22 was reacted with 200 mg (0.374 mmol) of 8,

applying the procedure described above. Complex 25 was obtained as

a red solid. Yield: 230 mg (0.181 mmol, 97% based on 22). Anal.

Calcd for C₅₆H₄₆Fe₄O₄P₂PdCl₂·¹/₄CH₂Cl₂(1266.84 g/mol): C, 53.32;

■

S

* Supporting Information

CIF files giving crystallographic data for the three reported

X-ray crystal structures and tabulated crystal and intensity

collection data for 15, 16, 21, 23, and 25. This material is

available free of charge via the Internet at http://pubs.acs.org.

Crystallographic data for complexes 15, 16, 21, 23, and 25 have

also been deposited with the Cambridge Crystallographic Data

Centre (CCDC: 838776 (23), 838777 (21), 838778 (25),

838779 (15) and 838780 (16)) and can be obtained free of

charge from the CCDC via http://www.ccdc.cam.ac.uk/data_

request/cif.

H, 3.69. Found: 53.25, 3.76. Mp: 126.6 °C dec. IR (KBr, cm⁻¹): ν

̃

2

1007 (m, ν_C−O); 1455 (m, ν_P−C); 1555 (m, ν_CC); 3104 (m, ν_{C(sp )−H}).

¹H NMR (CDCl₃, δ): 3.97 (s, 10 H, C₅H₅), 4.16 (pt, J_HH= 1.8 Hz,

4 H, C₅H₄), 4.22 (4 H, C₅H₄), 4.38 (pt, J_HH= 1.8 Hz, 4 H, C₅H₄),

4.58 (pt, J_HH= 1.7, 1.8 Hz, 8 H, C₅H₄), 4.61 (pt, J_HH= 1.7, 1.8 Hz,

4 H, C₅H₄), 4.67 (4 H, C₅H₄), 5.30 (CH₂/CH₂Cl₂), 6.47 (m, 4 H,

C₄H₃O), 7.04, 7.05 (d, J_HH= 3.4 Hz, 4 H, C₄H₃O), 7.71 (m, 4 H,

C₄H₃O). ¹³C{¹H} NMR (CDCl₃, δ): 53.52 (CH₂/CH₂Cl₂), 65.6

(C₅H₄), 66.8 (C₅H₄), 66.98 (C₅H₄), 68.2 (C₅H₅), 69.9 (C₅H₄), 70.81

(C_i/C₅H₄), 71.33 (C_i/C₅H₄), 73.2 (C₅H₄−P), 74.1 (C₅H₄−P), 85

(C_i/C₅H₄), 109.7 (C₄H₃O), 122.3 (C₄H₃O), 146.4 (pt, J_CP= 3.2 Hz,

C₄H₃O). ³¹P{¹H} NMR (CDCl₃, δ): −14.2 ppm (s).

AUTHOR INFORMATION

■

Corresponding Author

Synthesis of [Pd(Bfc(P(^cC₆H₁₁)₂))₂Cl₂] (26). A 79 mg portion (0.22

mmol) of 22 was reacted with 250 mg (0.44 mmol) of 9 as described

earlier. Complex 26 was obtained as a red solid. Yield: 250 mg (0.19

mmol, 86.7% based on 22). Anal. Calcd for C₆₄H₇₈Fe₄P₂PdCl₂·¹/₄CH₂Cl₂

*E-mail: heinrich.lang@chemie.tu-chemnitz.de.

Notes

The authors declare no competing financial interest.

(1309.95 g/mol): C, 57.96; H, 5.94. Found: C, 58.06; H, 6.17. Mp:

1

220 °C dec. IR (KBr, cm⁻¹): ν

̃

1447 (m, ν_P−C). H NMR (CDCl₃, δ):

ACKNOWLEDGMENTS

■

1.26−1.33 (m, 16 H, C₆H₁₁), 1.69−1.8 (m, 16 H, C₆H₁₁), 2.05−2.08 (m,

4 H, C₆H₁₁), 2.33−2.35 (m, 4 H, C₆H₁₁), 2.5−2.6 (m, 4 H, C₆H₁₁), 3.98

(s, 10 H, C₅H₅), 4.12 (4 H, C₅H₄), 4.18 (pt, J_HH= 1.76 Hz, 4 H, C₅H₄),

4.38 (pt, J_HH= 1.78 Hz, 4 H, C₅H₄), 4.51 (pt, J_HH= 1.75 Hz, 4 H, C₅H₄),

We are grateful to the Deutsche Forschungsgemeinschaft and

to the Fonds der Chemischen Industrie for generous financial

support.

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Article

(40) Liu, S.-Y.; Choi, M. J.; Fu, G. C. Chem. Commun. 2001, 2408−

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dx.doi.org/10.1021/om201220w | Organometallics 2012, 31, 2310−2326

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Synthesis, electrochemistry, spectroelectrochemistry, and solid-state structures of palladium biferrocenylphosphines and their use in C,C cross-coupling reactions

DOI: 10.1021/om201220w

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Full text of DOI:10.1021/om201220w

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