1,2-Disubstituted Aryl-Based Ferrocenyl Phosphines

Mar 14, 2013 - Martyna Madalska , Peter Lönnecke , Vladimir Ivanovski , and Evamarie Hey-Hawkins. Organometallics 2013 32 (20), 5852-5861...
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1,2-Disubstituted Aryl-Based Ferrocenyl Phosphines Martyna Madalska, Peter Lönnecke, and Evamarie Hey-Hawkins* Faculty of Chemistry and Mineralogy, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany S Supporting Information *

ABSTRACT: Ferrocenylaryl- or ferrocenylheteroarylphosphines [Fe{1-PPh 2 (spacer)-2-NMe 2 CH 2 C 5 H 3 }(C 5 H 5 )] (spacer = 1,4-phenylene (rac-6), 1,3-phenylene (rac-7), 4,4′biphenylene (rac-8), 2,5-thienylene (rac-9)) were prepared in a facile two-step sequence starting with Negishi cross-coupling between N,N-dimethylaminomethylferrocene and aryl halide phosphine oxides, Br-spacer-P(O)Ph2, followed by reduction with trichlorosilane. All products were characterized spectroscopically (1H, 13C, and 31P NMR, MS, FTIR), and rac-6, the corresponding phosphine oxide rac-2, and rac-9 were also characterized by X-ray crystallography. Furthermore, the redox properties of rac-2−9 were studied by cyclic voltammetry.

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INTRODUCTION Since the first reports on ferrocene in 1951−1952 by Kealey and Pauson,1 interest in ferrocene chemistry has remained intense and has placed this compound among the most important structural motifs in organometallic chemistry, materials science, and especially catalysis.2 A significant feature of ferrocene is its ability to undergo electrophilic substitution. In lithiation reactions it behaves as an electron-rich compound, leading to facile formation of lithioferrocene derivatives which can efficiently react with a broad range of electrophiles.3 Orthodirecting groups such as N,N-dimethylamino on the ferrocene framework direct the lithium atom to the ortho position and thus facilitate the preparation of 1,2-disubstituted ferrocenes.4 This opens the possibility to synthesize many novel compounds and is the reason for the significant role of ferrocene as a backbone or substituent in ancillary ligands: for example, phosphine ligands.5 Most of these ligands are based on a direct phosphorus−carbon (Cp) bond. There are only a few examples of tertiary phosphines with alkylene spacers6 and even fewer based on arylferrocene fragments,7 despite the fact that they show promising results in rhodium-catalyzed reactions. For example, a new family of chiral ligands with a phenylferrocenylethyl backbone, the so-called Walphos ligands [Fe{1-PR2CHMe-2-(2-PPh2C6H4)C5H3}(C5H5)] (R = Cy, 3,5-(CF3)2-C6H3, Ph, 3,5-Me2-4-OMe-C6H2), was developed by Weissensteiner et al.7d,8 Our research on new classes of ferrocenyl phosphines has focused on aryl-based ferrocenyl derivatives with different spacers between the ferrocene framework and the phosphorus atom. Here, the synthesis and characterization of ferrocenyl phosphines with phenylene, biphenylene, and thienylene spacers are reported.

subsequent introduction of the diphenylphosphine substituent by electrophilic substitution.7d,8a Our approach starts from N,N-dimethylaminomethylferrocene (1)9 and aryl halide phosphine oxides (Br-spacer-P(O)Ph2; spacer = 1,4-phenylene, 1,3-phenylene, 4,4′-biphenylene, 2,5-thienylene), which were prepared according to known methodologies,10 and yields ferrocenylaryl- (rac-6−8) and ferrocenylheteroarylphosphines (rac-9) in a straightforward two-step sequence (Scheme 1). The first step, formation of the new bond between two sp2hybridized carbon atoms, was achieved by palladium(0)catalyzed Negishi cross-coupling.11 None of the reagents are sensitive toward the rather basic reaction conditions, and since the Negishi reaction can be carried out with precursors obtained in situ, the number of synthetic steps can be lowered.12 Thus, ferrocenyl phosphine oxides rac-2−5 were obtained as orange solids in moderate yields (35−49%); unconverted N,N-dimethylaminomethylferrocene (1) can be recovered from the reaction mixture. These results are in agreement with related Negishi coupling reactions of various ferrocenyl derivatives.13 Unfortunately, it is difficult to identify which step of the reaction sequence is the limiting one. The lithiation reaction can be excluded, since the lithioferrocene derivative reacts with chlorodiphenylphosphine almost quantitatively. This suggests that either the transmetalation reaction or the C−C coupling process is inefficient. Chemical shifts of rac-2−5 in the 31P{1H} NMR spectra are typical for phosphine oxides. Signals of rac-2−4 are in the same range as that of triphenylphosphine oxide (in CDCl3, δ 29.8 ppm);14 that is, the ferrocenyl moiety is too distant from the phosphorus atom to influence its chemical shift. The 31P{1H} NMR signal of rac-5 is observed at δ 21.8 ppm due to the shielding effect of the thienylene spacer. As expected, the

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RESULTS AND DISCUSSION The protocol developed by Weissensteiner et al. requires the coupling reaction of ferrocenylamine and dibromobenzene and © XXXX American Chemical Society

Received: February 8, 2013

A

dx.doi.org/10.1021/om400117n | Organometallics XXXX, XXX, XXX−XXX

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Scheme 1. Two-Step Synthesis of 1,2-Disubstituted Ferrocenyl Phosphines

Figure 1. Molecular structures of rac-2 (left) and rac-6 (right); only one independent molecule and only one enantiomer (R enantiomer) is shown. Thermal ellipsoids are drawn at the 50% probability level for rac-2 and the 30% probability level for rac-6. Hydrogen atoms (other than H15) are omitted for clarity.

Crystals of compound rac-2 were twinned and contain two independent molecules with the same configuration that differ slightly from each other in the asymmetric unit. In the asymmetric unit of compound rac-6, two independent molecules (both enantiomers) were found. The molecular structure of rac-2 is remarkably similar to that of rac-6. In both molecules, the planes of the cyclopentadienyl rings are almost parallel to each other (tilt angles are 1.0(2) and 1.7(2)° for rac-2 and 3.7(2) (S) and 1.2(2)° (R) for the two independent molecules of rac-6). The dihedral angles between the plane of the substituted cyclopentadienyl ring and the plane of the C6H4 spacer are 34.2(2) and 34.8(2)° in rac-2 and 32.1(2) (S) and 38.5(2)° (R) for the two independent molecules of rac-6, and the phenylene spacer is turned toward the amine substituent. The shortest distance between the corresponding atoms H15 and N1 is 254.6 pm (or N2−H46 = 258.8 pm in the second independent molecule) (rac-2) and 236.6 (S) and 241.0 pm (R) (rac-6), which is smaller than the sum of the van der Waals radii of these elements (264 pm).16 The molecular structure of rac-9 (Figure 2) exhibits a similar tilt angle between the planes of the cyclopentadienyl rings (1.9(2)°), but due to less steric hindrance the dihedral angle between the plane of the substituted cyclopentadienyl ring and the plane of the thienylene spacer (26.2(2)°) is smaller than the angles observed in rac-2 and rac-6 and the distance between H15 and N1 is 264.9 pm. Apparently, an energetically favored arrangement with a conjugated π system is prevented due to steric hindrance also in solution. Thus, the 13C{1H} NMR spectrum of rac-2 in C6D6 showed signals for nine nonequivalent carbon atoms (as

chemical shift is similar to that of (5-bromo-2-thienyl)diphenylphosphine oxide (δ 19.4 ppm).10d Reduction of phosphine oxides rac-2−5 with trichlorosilane in the presence of triethylamine afforded phosphines rac-6−9 (Scheme 1) in almost quantitative yield.7e,15 Refluxing overnight in toluene was sufficient to complete the reduction process. As expected, reduction of rac-2−5 to phosphines rac6−9 was accompanied by an upfield shift in the 31P{1H} NMR spectra (−5.1 to −6.0 ppm for rac-6 to rac-8 and to −19.3 ppm for rac-9). The molecular structures of compounds rac-2 and rac-6 (Figure 1) and rac-9 (Figure 2) were determined by singlecrystal X-ray crystallography (Table 1). The compounds crystallize in the centrosymmetric space groups P1̅ (rac-2 and rac-6) and P21/c (rac-9) with four molecules in the unit cell.

Figure 2. Molecular structure of rac-9 with thermal ellipsoids at the 30% probability level. Hydrogen atoms (other than H3 and H15) are omitted for clarity. Only one enantiomer (S) is shown. B

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Table 1. Selected Bond Lengths (pm) and Angles (deg) for rac-2, rac-6, and rac-9a rac-2

C2−C14 P1−C17 P1−C26 P1−C20 P1−O1 P1−C24 P1−C18 C33−C45 P2−C48 P2−C51 P2−C57 P2−O2

C17−P1−C26 C17−P1−C20 C20−P1−C26 O1−P1−C20 O1−P1−C26 O1−P1−C17 C17−P1−C24 C17−P1−C18 C18−P1−C24 C48−P2−C57 C48−P2−C51 C51−P2−C57 C57−P2−O2 C51−P2−O2 C48−P2−O2

Bond Lengths molecule 147.1(5) 178.8(3) 180.2(4) 180.3(4) 148.7(2)

rac-6 1 146.9(7) 182.2(5) 183.9(5) 183.2(5)

Table 2. Oxidation (Epa (V)) and Reduction (Epc (V)) Potentials of rac-2−5 Measured in 0.1 M (Bu4N)BF4/ CH2Cl2 with a Scan Rate of dE/dt = 100 mV/s

rac-9

145.8(2) 180.8(2)

2 147.7(6) 182.9(5) 183.7(5) 183.6(5)

1 102.0(2) 100.7(2) 102.7(2)

Epa(2)

0.716 0.982 0.602 0.746

1.281 1.471 0.734 0.896

Epa(3)

Epa(4)

1.937 1.150 1.329

1.799

Epa(5)

2.370

Epc(1)

Epc(2)

0.485 0.540 0.566 0.495

1.579

compd

Epa(1)

Epa(2)

Epa(3)

Epc(1)

Epc(2)

Epc(3)

rac-6 rac-7 rac-8 rac-9

0.539 0.757 0.654 0.557

0.672 0.861 0.965 0.821

1.194

0.374 0.529 0.503 0.456

0.607a) 0.706 0.859 0.661

1.084

1.219

The presence of electron-withdrawing substituents in the ferrocenyl framework shifts the oxidation potential Epa(1) corresponding to FeII/FeIII toward higher values in comparison with unsubstituted ferrocene (Epa = 0.496 V). Moreover, additional Epa processes could be observed. The differences between the Epa(1) values of PIII and PV ferrocene derivatives are caused by the less pronounced electron-accepting properties of the −PPh2 group in comparison to −P(O)Ph2.18 Different redox mechanisms are expected to take place in the redox reactions of ferrocenyl phosphine and phosphine oxide derivatives. The oxidation and reduction processes observed for rac-2−9 are in good agreement with those reported for 1,1′(diphenylphosphino)ferrocenecarboxylic acid and its P V analogue, 1,1′-(diphenylphosphine oxide)ferrocenecarboxylic acid.19 The first oxidation process is the oxidation of FeII. An intramolecular electron transfer from the phosphorus(III) atom via the cyclopentadienyl ligand to the generated FeIII ion results in a FeII−PIV species, which is immediately stabilized by a further one-electron oxidation of phosphorus, yielding phosphine oxide. This process can occur either by an electrochemical path or as chemical oxidation caused by traces of oxygen or water.20 In the cyclic voltammogram of rac-6, Epa(1) = 0.539 V, Epa(2) = 0.679 V, and Epa(3) = 1.194 V are observed. According to the previously described mechanisms, the first value (Epa(1)) corresponds to the oxidation of FeII. Epa(2) can be assigned to the oxidation of FeII in the in situ generated ferrocenyl phosphine oxide. Podlaha et al. observed only two oxidation steps.19 However, in that case, the phosphine group had no neighboring group on the cyclopentadienyl ring. This suggests that additional oxidation processes take place due to a subsequent reaction in which the methylene(N,N-dimethylamino) group is involved.

102.6(7) 98.8(7) 102.3(7) molecule 108.8(2) 108.1(2) 105.8(2) 110.9(2) 111.9(2) 111.2(2)

Epa(1)

rac-2 rac-3 rac-4 rac-5

Table 3. Oxidation (Epa (V)) and Reduction (Epc (V)) Potentials of rac-6−9 Measured in 0.1 M (Bu4N)BF4/ CH2Cl2 with a Scan Rate of dE/dt = 100 mV/s

184.0(2) 183.9(2) molecule 147.4(5) 180.7(4) 181.4(4) 180.9(4) 148.5(2) Bond Angles molecule 108.5(2) 107.9(2) 106.1(2) 111.7(2) 110.9(2) 111.5(2)

compd

2 103.6(2) 99.9(2) 105.3(2)

a

Given for both independent molecules in the asymmetric unit for rac2 and rac-6.

doublets due to P−C coupling), while in the case of free rotation around the C2−C14 bond (Figure 1, left), only eight signals (four for the phenylene spacer and four for the phenyl substituents) should be observed in the range between 120 and 150 ppm. As can be concluded from the values of the coupling constants, three of them are carbon atoms bonded directly to the phosphorus atom (131.2 (d, 1JCP = 104.9 Hz), 134.4 (d, 1 JCP = 102.6 Hz), 134.5 ppm (d, 1JCP = 102.6 Hz)); that is, the two phenyl rings (C20−C25 and C26−C31) are nonequivalent. When rac-2 was dissolved in CDCl3, even 12 separate signals were observed in the 13C{1H} NMR spectrum in the aromatic region. In this case, five signals, one of which consists of two overlapping signals, can be assigned to carbon atoms directly bonded to phosphorus (129.3 (d, 1JCP = 105.9 Hz), 129.4 (d, 1JCP = 105.9 Hz), 132.9 (d, 1JCP = 112.8 Hz), 132.8 (2 overlapping signals, d, 1JCP = 95.0 Hz), 132.7 ppm (d, 1 JCP = 112.8 Hz)). As rac-2 is a planar-chiral compound, hindered rotation of the phenylene−diphenylphosphine oxide unit (C17−P1 bond) leads to axial chirality, and thus two diastereoisomers of rac-2 are observed. The redox properties of rac-2−9 were studied by cyclic voltammetry, and the oxidation (Epa) and reduction potentials (Epc) are given in Tables 2 and 3.17

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CONCLUSION Aryl- or heteroaryl-based ferrocene derivatives rac-6−9 were prepared by a facile two-step synthetic route. We have shown that a palladium-catalyzed Negishi cross-coupling reaction can be employed for the first step, formation of a C−C bond between the ferrocenyl framework and the aryl phosphine oxide. The resulting phosphine oxides were successfully reduced with a mixture of trichlorosilane and triethylamine. C

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(s), 72.6 (s), 82.1 (s), 86.3 (s), 128.2 (d, 3JCP = 11.9 Hz), 129.0 (d, JCP = 12.2 Hz), 131.2 (d, 4JCP = 2.2 Hz), 131.2 (d, 1JCP = 104.9 Hz), 131.9 (d, 2JCP = 9.8 Hz), 132.2 (d, 3JCP = 9.6 Hz), 134.4 (d, 1JCP = 102.6 Hz), 134.5 (d, 1JCP = 102.6 Hz), 143.6 (d, 4JCP = 3.1 Hz) ppm. 13 C{1H} NMR (CDCl3, 100 MHz): δ 45.0 (s), 58.2 (s), 68.2 (s), 70.6 (s), 71.0 (s), 72.9 (s), 82.5 (s), 86.2 (s), 128.5 (d, 3JCP = 12.2 Hz), 128.9 (d, 3JCP = 12.2 Hz), 129.3 (d, 1JCP = 105.9 Hz), 129.4 (d, 1JCP = 105.9 Hz), 131.8 (d, 2JCP = 9.7 Hz), 131.8 (d, 4JCP = 2.2 Hz), 132.1 (d, 3 JCP = 9.9 Hz), 132.7 (d, 1JCP = 112.8 Hz), 132.8 (2 overlapped signals d, 1JCP = 95.0 Hz), 132.9 (d, 1JCP = 112.8 Hz), 143.9 (d, 4JCP = 2.7 Hz) ppm. EI MS: m/z (relative intensity, %) 519 (100) [M]+, 504 (14), 475 (90), 462 (7), 438 (12), 409 (20), 355 (28), 257 (9), 238 (27), 229 (21), 201 (23), 183 (20), 152 (40), 133 (13), 121 (72), 77 (28), 58 (64). Anal. Calcd for C31H30FeNOP: C, 71.69; H, 5.82; N, 2.70. Found: C, 72.03; H, 6.21; N, 2.66. (3-Diphenylphosphine oxide)phenyl-2-N,N-dimethylaminomethylferrocene (rac-3). rac-3 was obtained by a Negishi coupling reaction starting from N,N-dimethylaminomethylferrocene (1) and (3bromophenyl)diphenylphosphine oxide. The same procedure as in the synthesis of rac-2 was used. rac-3 was obtained as an orange-red viscous oil (almost solid) in 49% yield. 1 H NMR (CDCl3, 400 MHz): δ 2.06 (s, 6H), 3.02 (d, 1H, 2JHH = 12.8 Hz), 3.48 (d, 1H, 2JHH = 12.8 Hz), 3.87 (s, 5H), 4.20 (s, 1H), 4.26 (s, 1H), 4.40 (s, 1H), 7.18−7.05 (m. 7H), 7.36 (t, 1H, 2JHH = 15.9 Hz), 7.54−7.46 (m, 4H), 7.94 (d, 1H, 2JHH = 7.7 Hz), 8.01 (d, 1H, 2JHH = 7.6 Hz) ppm. 31P{1H} NMR (CDCl3, 161 MHz): δ 29.3 ppm. 13C{1H} NMR (C6D6, 100 MHz): δ 44.7 (s), 58.1 (s), 67.2 (s), 70.2 (s), 70.9 (s), 72.2 (s), 82.3 (s), 87.0 (s), 128.1 (d, overlapped signals, JCP not determined), 128.3 (d, 2JCP = 11.8 Hz), 129.7 (d, 3JCP = 9.9 Hz), 131.3 (d, 4JCP = 2.5 Hz), 131.3 (d, 4JCP = 2.8 Hz), 132.2 (d, 3 JCP = 9.6 Hz), 133.3 (d, 2JCP = 10.8 Hz), 133.3 and 134.0 (d, 1JCP =103.3 Hz), 134.2 and 134.3 (d, 1JCP = 103.3 Hz), 134.3 and 134.4 (d, 1 JCP = 102.6 Hz), 140.0 (d, 2JCP = 12.3 Hz), 140.0 (d, 3JCP = 12.3 Hz) ppm. EI MS: m/z (relative intensity, %) 519 (100) [M]+, 504 (23), 476 (73), 409 (20), 355 (14), 243 (19), 238 (38), 199 (38), 152 (20), 133 (9), 121 (38), 77 (10), 58 (34), 43 (11). (4-Diphenylphosphine oxide)biphenyl-2-N,N-dimethylaminomethylferrocene (rac-4). rac-4 was obtained by a Negishi coupling reaction starting from N,N-dimethylaminomethylferrocene (1) and (4′-bromobiphenyl-4-yl)diphenylphosphine oxide. The same procedure as for the synthesis of rac-2 was used. rac-4 was obtained as an orange-red powder in 43% yield. Mp: 169−172 °C. 1H NMR (CDCl3, 400 MHz): δ 2.21 (s, 6H), 3.13 (d, 1H, 2JHH = 12.8 Hz), 3.69 (d, 1H, 2JHH = 12.4 Hz), 4.06 (s, 5H), 4.26 (t br, 1H, 3JHH = 2.5 Hz), 4.33 (t br, 1H, 3JHH = 1.6 Hz), 4.53 (t br, 1H, 3JHH = 1.85 Hz), 7.51− 7.47 (m, 4H), 7.58−7.55 (m, 4H), 7.75−7.69 (m, 8H), 7.84−7.82 (m, 2H) ppm. 31P{1H} NMR (CDCl3, 161 MHz): δ 28.9 ppm. 13C{1H} NMR (CDCl3, 100 MHz): δ 45.1 (s), 58.1 (s), 67.6 (s), 70.1 (s), 72.0 (s), 77.2 (s), 82.3 (s), 87.1 (s), 126.8 (s), 126.8 (d, 2JCP = 13.1 Hz), 128.5 (d, 2JCP = 12.1 Hz), 129.7 (s), 130.8 and 130.9 (d, 1JCP = 105.6 Hz), 131.9 (d, 4JCP = 2.5 Hz), 132.1 (d, 3JCP = 9.6 Hz), 132.6 (d, 3JCP = 10.4 Hz), 132.8 (d, 1JCP = 104.7 Hz), 137.2 (s), 139.4 (s), 144.5 (d, 4 JCP = 2.7 Hz) ppm. EI MS: m/z (relative intensity, %) 595 (100) [M]+, 580 (20), 551 (72), 538 (36), 485 (25), 428 (8), 351 (8), 297 (23), 275 (39), 228 (19), 201 (20), 183 (23), 149 (20), 121 (34), 77 (23), 58 (64). Anal. Calcd for C37H34FeNOP: C, 74.63; H, 5.75; N, 2.35. Found: C, 75.13; H, 5.98; N, 2.30. (5-Diphenylphosphine oxide)thienyl-2-N,N-dimethylaminomethylferrocene (rac-5). rac-5 was obtained by a Negishi coupling reaction starting from N,N-dimethylaminomethylferrocene (1) and (5bromothienyl)-2-diphenylphosphine oxide. The same procedure as for the synthesis of rac-2 was used. rac-5 was obtained as an orange-red powder in 35% yield. Mp: 82−84 °C. 1H NMR (CDCl3, 400 MHz): δ 2.16 (s, 6H), 3.08 (d, 1H, 2JHH = 12.8 Hz), 3.76 (d, 1H, 2JHH = 12.4 Hz), 4.04 (s, 5H), 4.26 (t, 1H, 3JHH = 4.9 Hz), 4.32 (s br, 1H), 4.55 (s br, 1H), 7.21−7.18 (m, 1H), 7.34−7.33 (m, 1H), 7.50−7.47 (m, 4H), 7.56−7.55 (m, 2H), 7.81−7.74 (m, 4H) ppm. 31P{1H} NMR (CDCl3, 161 MHz): δ 21.8 ppm. 13C{1H} NMR (CDCl3, 100 MHz): δ 45.0 (s), 58.0 (s), 67.8 (s), 70.21 (s), 70.7 (s), 72.4 (s), 78.9 (s), 82.8 (s), 126.2 (d, 2JCP = 12.2 Hz), 128.4 (d, 3JCP = 11.1 Hz), 130.9 (d, 1JCP =

This synthetic approach should also be applicable for other derivatives as well as for diastereomerically pure ligands starting from Ugi’s amine, (S)- or (R)-[Fe(NMe2CHMeC5H3)(C5H5)].21 Compounds rac-6−9 combine the advantages of aryl-based phosphines with the properties of the ferrocenyl moiety and should therefore be suitable ligands in catalytic processes. These studies are now under way.

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EXPERIMENTAL SECTION

General Considerations. All manipulations were carried out by standard Schlenk techniques under an atmosphere of dry, high-purity nitrogen. Toluene, THF, and dichloromethane were dried with an MB SPS-800 Solvent Purification System and stored over activated 4 Å molecular sieves. Et3N was distilled from MgSO4. Deuterated solvents for NMR spectroscopy were purchased from Eurisotop and Chemotrade GmbH. CDCl3 was distilled from P2O5 and stored over activated 4 Å molecular sieves. C6D6 was dried with sodium, filtered, and stored over potassium mirror. The compounds N,N-dimethylaminomethylferrocene (1), 9 [PdCl2(PPh3)2],22 (4-bromophenyl)diphenylphosphine oxide,10a (3bromophenyl)diphenylphosphine oxide,10b (4′-bromobiphenyl-4-yl)diphenylphosphine oxide, 1 0 c and (5-bromo-2-thienyl)diphenylphosphine oxide10d were synthesized according to literature procedures. Other chemicals were obtained from commercial sources and used as supplied. Spectra were recorded on a Bruker AVANCE DRX 400 NMR spectrometer at 400.13 (1H NMR), 161.98 (31P NMR), or 100.61 MHz (13C NMR). TMS was used as an internal standard for the 1H NMR spectra, and spectra of other nuclei were referenced to TMS on the δ scale.23 The signals of the 13C NMR spectra were assigned by 13 C{31P} experiments. EI mass spectra were recorded on a ZAB-HSQVG12-520 Analytical Manchester spectrometer or a MASPEC II spectrometer; ESI mass spectra were recorded on a Bruker-Daltonics FT-ICR-MS APEX II. FTIR spectra were recorded on a Perkin-Elmer Spectrum 2000 spectrometer. C, H, N analyses were performed with a Heraeus VARIO EL Analyzer. Air-sensitive samples were prepared in a glovebox. Melting points were determined in sealed glass capillaries under nitrogen and are uncorrected. (4-Diphenylphosphine oxide)phenyl-2-N,N-dimethylaminomethylferrocene (rac-2). At −78 °C, 4.9 mL of nBuLi in n-hexane (1.66 M, 8.23 mmol, 1 equiv) was added dropwise to a solution of 2.0 g (8.23 mmol) of N,N-dimethylaminomethylferrocene (1) in 20 mL of THF. The reaction mixture was stirred overnight at room temperature. In the next step, 1.94 g of dry ZnCl2 (8.64 mmol, 1.05 equiv) was added at 0 °C. The obtained orange suspension was then stirred at room temperature for 4 h. One equivalent of nBuLi in n-hexane (4.9 mL, 1.66 M, 8.23 mmol) was added to a suspension of 0.29 g (0.41 mmol, 5 mol %) of [PdCl2(PPh3)2] in THF. The obtained dark purple solution was added to the suspension of the ferrocenyl zinc derivative followed by addition of 2.8 g (8.23 mmol, 1 equiv) of (4-bromophenyl)diphenylphosphine oxide in 20 mL of THF. The reaction mixture was heated to reflux for 20 h under an inert atmosphere. THF was removed under reduced pressure. The remaining solid was dissolved in CH2Cl2, water was added, and the mixture was extracted with CH2Cl2. The organic phase was dried with MgSO4. The solvent was evaporated under reduced pressure, and the dark brown crude product was purified by column chromatography (silica gel, eluent acetone/Et3N 1000/1) to give a brown oil consisting of rac-2 and N,N-dimethylaminomethylferrocene (1). Compound 1 was distilled off under reduced pressure (6 × 10−3 mbar) at 140 °C. The remaining brown powder was dissolved in Et2O, the solution was filtered, and the solvent was evaporated under reduced pressure to give rac-2 as an orange powder in 47% yield. Crystals suitable for X-ray diffraction were obtained by recrystallization from acetone. Mp: 160−163 °C. 1H NMR (CDCl3, 400 MHz): δ 2.16 (s, 6H), 3.07 (d, 1H, 2JHH = 12.8 Hz), 3.64 (d, 1H, 2JHH = 12.8 Hz), 4.02 (s, 5H), 4.27 (s, 1H), 4.32 (s, 1H), 4.53 (s, 1H), 7.47−7.85 (m, 14H) ppm. 31P{1H} NMR (CDCl3, 161 MHz): δ 29.4 ppm. 13C{1H} NMR (C6D6, 100 MHz): δ 44.6 (s), 58.2 (s), 67.5 (s), 70.3 (s), 71.3 D

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113.8 Hz), 131.9 (d, 2JCP = 10.2 Hz), 132.1 (d, 4JCP = 2.5 Hz), 133.1 (d, 1JCP = 109.5 Hz), 137.3 (d, 3JCP = 10.4 Hz), 152.7 (d, 4JCP = 5.1 Hz) ppm. EI MS: m/z (relative intensity, %) 525 (100) [M]+, 481 (96), 468 (6), 415 (15), 361 (6), 324 (9), 241 (20), 202 (15), 133 (6), 121 (15), 77 (6), 58 (22). Anal. Calcd for C29H28FeNOPS: C, 66.29; H, 5.37; N, 2.67. Found: C, 66.54; H, 5.48; N, 2.60. (4-Diphenylphosphino)phenyl-2-N,N-dimethylaminomethylferrocene (rac-6). A 5.3 mL portion (38.5 mmol, 20 equiv) of Et3N and 3.8 mL (38.5 mmol, 20 equiv) of SiHCl3 were added to a toluene solution of 1 g (1.92 mmol) of rac-2. The suspension was heated to reflux overnight under an inert atmosphere. After the mixture was cooled to room temperature, 10 mL of a NaOH solution in degassed water (30%) was added and the mixture was stirred at 60 °C for 2 h. The two phases were separated under an inert atmosphere, and the water phase was extracted twice with dry Et2O. The organic phase was dried with MgSO4 and filtered, and the solvent was evaporated under vacuum. The obtained orange wax was purified by flash column chromatography (eluent acetone with 1 mL of Et3N per liter) to give rac-6 as an orange solid in 96% yield. Crystals suitable for X-ray diffraction were obtained by recrystallization from Et2O. Mp: 69−73 °C. 1H NMR (C6D6, 400 MHz): δ 2.09 (s, 6H), 2.83 (d, 1H, 2 JHH = 12.4 Hz) 3.64 (d, 1H, 2JHH = 12.8 Hz), 3.85 (s, 5H), 4.03 (t, 1H, 3JHH = 5.0 Hz), 4.10 (t, 1H, 3JHH = 3.4 Hz), 4.38 (s, 1H), 7.08− 7.05 (m, 6H), 7.52−7.45 (m, 6H), 7.93 (d, 2H, 2JHH = 7.1 Hz) ppm. 31 1 P{ H} NMR (C6D6, 161 MHz): δ −5.8 ppm. 13C{1H} NMR (C6D6, 100 MHz): δ 44.7 (s), 58.2 (s), 67.2 (s), 70.2 (s), 70.8 (s), 72.3 (s), 82.1 (s), 87.2 (s), 128.5 (d, 4JCP = 5.3 Hz), 128.5 (d, 3JCP = 6.8 Hz), 129.4 (d, 3JCP = 6.9 Hz), 133.7 (d, 2JCP = 18.7 Hz), 133.9 (d, 2JCP = 19.7 Hz), 133.9 (d, 2JCP = 19.7 Hz), 134.8 (d, 1JCP = 11.5 Hz), 137.9 (d, 1JCP = 12.2 Hz), 138.0 (d, 1JCP = 12.2 Hz), 140.3 (s) ppm. EI MS: m/z (relative intensity, %) 503 (100) [M]+, 460 (23), 274 (41), 183 (33), 163 (12), 152 (18), 121 (41), 91 (36), 58 (52). Anal. Calcd for C31H30FeNP: C, 73.96; H, 6.01; N, 2.78. Found: C, 74.25; H, 6.32; N, 3.02. (3-Diphenylphosphino)phenyl-2-N,N-dimethylaminomethylferrocene (rac-7). rac-7 was synthesized by using the same procedure as for the synthesis of rac-6. rac-7 was obtained as an orange powder in 96% yield. Mp: 59−61 °C. 1H NMR (C6D6, 400 MHz): δ 2.09 (s, 6H), 2.87 (d, 1H, 2JHH = 12.8 Hz), 3.61 (d, 1H, 2JHH = 12.4 Hz), 3.78 (s, 5H), 3.97 (t, 1H, 3JHH = 4.9 Hz), 4.09 (t, 1H, 3JHH = 3.4 Hz), 4.28 (t, 1H, 3JHH = 3.5 Hz), 7.18−7.04 (m, 7H), 7.37 (t, 1H, 2JHH = 15.5 Hz), 7.54−7.46 (m, 4H), 7.94 (d, 1H, 2JHH = 7.7 Hz), 8.02 (d, 1H, 2JHH = 7.6 Hz) ppm. 31P{1H} NMR (C6D6, 161 MHz): δ −5.1 ppm. 13C{1H} NMR (C6D6, 100 MHz): δ 44.7 (s), 58.1 (s), 67.0 (s), 70.1 (s) 70.5 (s), 71.8 (s), 82.4 (s), 87.8 (s), 128.2 (d, 3JCP = 8.0 Hz), 128.5 (d, 3JCP = 7.2 Hz), 128.6 (d, 3JCP = 6.6 Hz), 129.6 (s), 131.7 (d, 2 JCP = 22.8 Hz), 133.9 (d, 2JCP = 19.5 Hz), 134.0 (d, 2JCP = 19.5 Hz), 135.00 (d, 1JCP = 16.8 Hz), 137.2 (d, 1JCP = 11.8 Hz), 137.9 (d, 1JCP = 12.3 Hz), 138.1 (d, 1JCP = 12.5 Hz), 139.8 (d, 3JCP = 6.2 Hz) ppm. EI MS: m/z (relative intensity, %) 503 (100) [M]+, 459 (33), 339 (11), 274 (37), 257 (11), 230 (20), 183 (27), 152 (16), 121 (35), 58 (29). Anal. Calcd for C31H30FeNP: C, 73.96; H, 6.01; N, 2.78. Found: C, 74.21; H, 6.35; N, 2.98. (4-Diphenylphosphino)biphenyl-2-N,N-dimethylaminomethylferrocene (rac-8). rac-8 was synthesized by using the same procedure as for the synthesis of rac-6. rac-8 was obtained as an orange powder in 96% yield. Mp: 123−127 °C. 1H NMR (C6D6, 400 MHz): δ 2.19 (s, 6H), 2.91 (d, 1H, 2JHH = 12.4 Hz), 3.77 (d, 1H, 2JHH = 12.4 Hz), 3.91 (s, 5H), 7.38−7.34 (m, 12H), 7.55 (d, 2H, 2JHH = 8.4 Hz), 7.60 (d, 2H, 2JHH = 7.5 Hz), 7.79 (d, 2H, 2JHH = 8.4 Hz) ppm. 31P{1H} NMR (C6D6, 161 MHz): δ −6.0 ppm. 13C{1H} NMR (C6D6, 100 MHz): δ 45.1 (s), 58.1 (s), 67.3 (s), 70.0 (s), 70.1 (s), 71.9 (s), 82.1 (s), 87.4 (s), 126.5 (s), 126.86 (d, 3JCP = 6.9 Hz), 128.5 (d, 3JCP = 7.0 Hz), 128.7 (s), 129.6 (s), 133.8 (d, 2JCP = 19.4 Hz), 134.2 (d, 2JCP = 19.4 Hz), 135.8 (d, 1JCP = 10.8 Hz), 137.2 (d, 1JCP = 10.8 Hz), 137.9 (s), 138.6 (s), 141.2 (s) ppm. EI MS: m/z (relative intensity, %) 580 (60) [M]+, 535 (100), 523 (19), 470 (18), 334 (20), 289 (19), 267 (30), 183 (63), 163 (40), 121 (96), 58 (98). Anal. Calcd for C37H34FeNP: C, 76.69; H, 5.91: N, 2.42. Found: C, 76.38; H, 6.10; N, 2.29.

(5-Diphenylphosphino)thienyl-2-N,N-dimethylaminomethylferrocene (rac-9). rac-9 was synthesized by using the same procedure as for the synthesis of rac-6. rac-9 was obtained as an orange powder in 93% yield. Crystals suitable for X-ray diffraction were obtained by recrystallization from Et2O. Mp: 39−41 °C. 1H NMR (C6D6, 400 MHz): δ 2.10 (s, 6H), 2.84 (d, 1H, 2JHH = 12.4 Hz), 3.77 (d, 1H, 2JHH = 12.4 Hz), 3.86 (s 5H), 3.93 (t, 1H, 3JHH = 4.9 Hz), 4.04 (s, 1H), 4.36 (s, 1H), 7.10−7.04 (m, 6H), 7.26−7.23 (m, 1H), 7.58− 7.52 (m, 5H) ppm. 31P{1H} NMR (C6D6, 161 MHz): δ −19.3 ppm. 13 C{1H} NMR (C6D6, 100 MHz): δ 44.6 (s), 58.2 (s), 67.2 (s), 70.1 (s), 70.6 (s), 72.0 (s), 80.7 (s), 82.8 (s), 126.7 (d, 3JCP = 7.1 Hz), 128.4 (d, 3JCP = 6.7 Hz), 128.6 (s), 133.3 (two overlapping doublets, 1 JCP = 19.6 Hz and 1JCP =19.7 Hz), 136.2 (d, 2JCP = 27.9 Hz), 136.9 (d, 1 JCP = 25.6 Hz), 138.6 (d, 2JCP = 9.6 Hz), 138.7 (d, 3JCP = 9.9 Hz), 150.1 (s) ppm. EI MS: m/z (relative intensity, %) 509 (52) [M]+, 465 (17), 324 (17), 280 (19), 183 (8), 121 (26), 91 (100), 58 (29). Anal. Calcd for C29H28FeNPS: C, 68.37; H, 5.54; N, 2.75. Found: C, 68.83; H, 5.90; N, 2.80. Cyclic Voltammetry Studies. Cyclic voltammetry measurements were performed with a standard three-electrode cell (volume 10 mL) on a single-channel SP-50 potentiostat which was coupled with ECLab Software designed by BioLogic Science Instruments. The working electrode (WE) was a platinum disk (diameter 2 mm) sealed in Teflon, a platinum wire was used as the reference electrode (RE), and a platinum plate was used as the counterelectrode (CE). The voltammograms were recorded in dry CH2Cl2 with (Bu4N)BF4 as supporting electrolyte. Potentials were calibrated by using ferrocene as an external standard.

Table 4. Crystal Data and Structure Refinement Details for Compounds rac-2, rac-6, and rac-9 formula fw T (K) cryst syst space group a (pm) b (pm) c (pm) α (deg) β (deg) γ (deg) V (nm3) Z Dc (Mg m−3) μ (mm−1) F(000) cryst size (mm3) θ range (deg) ranges of h,k,l

no. of indep rflns GOF (F2) final R1 (all data) wR2 (all data) residual electron density (e Å−3) a

E

rac-2

rac-6

rac-9

C31H30FeNOP 519.38 130(2) triclinic P1̅ 1006.63(6) 1494.6(1) 1678.9(1) 96.048(6) 90.550(5) 99.252(5) 2.4783(3) 4 1.392 0.698 1088 0.23 × 0.15 × 0.04 2.78−26.37 −12 ≤ h ≤ 12 −18 ≤ k ≤ 18 −20 ≤ l ≤ 20 17123 (R(int) = 0)a 0.935 R1 = 0.0598 wR2 = 0.1132 R1 = 0.1227 wR2 = 0.1259 1.036 and −0.434

C31H30FeNP 503.38 130(2) triclinic P1̅ 948.42(9) 1285.1(1) 2265.4(2) 81.326(7) 82.564(8) 71.866(9) 2.5840(4) 4 1.294 0.665 1056 0.3 × 0.1 × 0.05 3.03−25.03 −10 ≤ h ≤ 11 −15 ≤ k ≤ 14 −26 ≤ l ≤ 26 9116 (R(int) = 0.0629) 0.989 R1 = 0.0684 wR2 = 0.1295 R1 = 0.1318 wR2 = 0.1582 0.635 and −0.407

C29H28FeNPS 509.40 130(2) monoclinic P21/c 1539.27(2) 1289.96(2) 1288.58(2) 90 102.034(2) 90 2.50237(6) 4 1.352 0.768 1064 0.2 × 0.15 × 0.1 3.13−30.51 −20 ≤ h ≤ 21 −18 ≤ k ≤ 16 −18 ≤ l ≤ 18 7629 (R(int) = 0.0326) 1.027 R1 = 0.0365 wR2 = 0.0743 R1 = 0.0530 wR2 = 0.0809 0.397 and −0.277

Twinned crystal. dx.doi.org/10.1021/om400117n | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

X-ray Structure Determinations. Suitable crystals were mounted on a glass needle with perfluoro polyalkyl ether and cooled under a nitrogen stream. Crystallographic measurements were made with a Gemini diffractometer (Agilent Technologies). Data were collected by using monochromated Mo Kα radiation (λ = 71.073 pm). Structure solution was carried out with SIR92 (for rac-2 and rac-6) and SHELXS-97 (rac-9).24 Anisotropic refinement of all non-hydrogen atoms used SHELXL-97.24 All hydrogen atoms of rac-2 and rac-6 were calculated on idealized positions; for rac-9, all H atoms were located in difference Fourier maps calculated at the final stage of the structure refinement. The crystal of rac-2 was found to be twinned (twin law by rows: −1.00,0.00,0.00; 0.48,1.00,0.19; 0.00,0.00,−1.00). In rac-6, one cyclopentadienyl ring (C6−C10) was found to be disordered over two positions (ratio 0.51(1):0.49(1)). ORTEP25 was used for visualization. Crystal data and details of data collection and refinement are given in Table 4.

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ASSOCIATED CONTENT

S Supporting Information *

Text, figures, and CIF files giving detailed assignments of NMR and MS data and IR spectroscopic data for compounds rac-2−9 and crystallographic data for rac-2, rac-6, and rac-9. This material is available free of charge via the Internet at http:// pubs.acs.org. CCDC 922458 (rac-2), 922459 (rac-6) and 922460 (rac-9) contain supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was funded by the European Union and the Free State of Saxony (Europäischer Sozialfonds (ESF) Nachwuchsforschergruppe “Katalyse”, doctoral grant for M.M., project number 080937615). Support from the Graduate School BuildMoNa (funded by the Deutsche Forschungsgemeinschaft and the EU COST Action CM0802 PhoSciNet) is gratefully acknowledged. We thank Chemetall GmbH and BASF SE for generous donations of chemicals.

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