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Synthesis, Coordination Properties, and Catalytic Use of Phosphinoferrocene Carboxamides Bearing Donor-Functionalized Amide Substituents Petr Štěpnička,* Barbora Schneiderová, Jiří Schulz, and Ivana Císařová Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 12840 Prague 2, Czech Republic S Supporting Information *

ABSTRACT: Phosphinoferrocene carboxamides bearing donor-functionalized substituents at the amide nitrogen, Ph2PfcCONH(CH2)nY (Y/n = NMe2/2 (1), NMe2/3 (2), PPh2/2 (3), and PPh2/3 (4); fc = ferrocene-1,1′-diyl), were obtained by amide coupling reactions of 1′(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) with the respective amines and structurally characterized. Amide 1 was further converted to the corresponding ω-azoniaalkyl amidophosphine [Ph2PfcCONHCH2CH2NMe3]X (7; X = Cl/I). Amides 1 and 3, possessing the shorter ethane-1,2-diyl linker, reacted smoothly with [PdCl2(cod)] (cod = cyclocta-1,5-diene) to give the respective trans-chelate complexes, trans-[PdCl2(Lκ2P,Y)] (8: L = 1; 9: L = 3). The homologous donors 2 and 4 showed more complicated coordination behavior, affording mixtures of several Pd(II) complexes under similar conditions. Compounds 1, 3, and 7 were further evaluated as ligands for Pdcatalyzed Suzuki−Miyaura cross-coupling using 4-bromoacetophenone and phenylboronic acid as model substrates. In dioxane, the yields of the coupling product decreased in the order 3 > 1 > 7, presumably due to different donor ability of these ligands (type of donor atoms; PP > PN > PN+). The catalytic performance in pure water was different: The yields were generally lower and the order of ligands changed to 3 > 7 > 1.

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INTRODUCTION Inspired by the rich chemistry and various applications of simple (organic) phosphino-carboxamide ligands,1 we have decided to prepare the analogous donors derived from ferrocene and study their coordination properties and prospective catalytic applications. Prior to our work, there were only a few reports dealing with compounds of such type, the prominent examples being Trost-type diphosphine diamides obtained from planar-chiral 2-(diphenylphosphino)ferrocene-1carboxylic acid,2 several C2-symmetric diphosphine diamides,3 and reaction intermediates used for the preparation of other phosphinoferrocene compounds.4 In analogy with the synthesis of their purely organic analogues, the phosphinoferrocene carboxamides are readily accessible via amidation reactions of phosphinoferrocene carboxylic acids with amines mediated by peptide coupling agents,5 though other routes also proved viable.6 Compounds derived from 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf)7 as the archetypal representatives8 now include simple amides suitable for use as organometallic synthons9 or hybrid10 multidonor ligands, in which the amide unit is used as a relatively stable and structurally well-defined connecting group allowing conjugation of the phosphinoferrocenyl unit11 with various functional moieties (see Chart 1). The latter compounds include dendrimer-like molecules tested in C−C bond-forming reactions,12 polar compounds derived from amino acids, aminosulfonic acids, and hydroxyamines potentially applicable in catalytic transformations performed in polar and/or aqueous media13 as well as multidonor ligands bearing © XXXX American Chemical Society

Chart 1

donor-functionalized pendant groups at the amide nitrogen.14 Phosphino-amides derived from ferrocene-based phosphinocarboxylic acids other than Hdpf remain still rather uncommon.15 Our previous studies with Hdpf amides prepared from pyridyl- and phosphino-substituted amines (I−III14a,b and IV14c in Scheme 1) have shown that some of these donors can coordinate in a trans-chelating manner. The 2-pyridyl amides appear particularly attractive in this regard because the majority of trans-spanning donors16 reported to date are symmetrical diphosphines in which the P-donor moieties are brought into Special Issue: Ferrocene - Beauty and Function Received: April 4, 2013

A

dx.doi.org/10.1021/om400282z | Organometallics XXXX, XXX, XXX−XXX

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coupling agents. Following isolation by column chromatography, the amides were obtained in good yields as rusty orangebrown, amorphous solids or slowly crystallizing oils that tenaciously retain traces of solvents used during the chromatographic purification. 1 H and 13C{1H} NMR spectra of compounds 1−4 comprise the expected signals due to the 1,1′-disubstituted ferrocene moiety and its phosphine substituent. Also seen are characteristic signals of the (CH2)n spacers and their attached terminal groups. 31P{1H} NMR spectra of 1 and 2 display one signal at δP ca. −17. The phosphorus resonances of the diphosphines are observed at δP −16.9 and −20.9 and at δP −16.9 and −15.7 for 3 and 4, respectively. The compounds give rise to pseudomolecular ions in their ESI mass spectra ([M + Z]+, where Z = H, Na, or K, and [M − H]−) and show characteristic amide bands in the IR spectra (νNH; amide I at ca. 1630 cm−1 and amide II around 1540 cm−1). Compound 1 was further employed in the preparation of the cationic, Me3N+-substituted amidophosphine 7 (Scheme 3).

Scheme 1

positions suitable for trans-chelation with the aid of a rigid organic backbone. The related donor unsymmetric ligands remain rare. Considering the particular combination of the uniquely flexible ferrocene moiety whose cyclopentadienyl rings are known to rotate practically freely17 and the methylene spacers with the more rigid parts (CONH and aromatic rings) in the molecules of I and IV, which readily form trans-chelate complexes with Pd(II), we set out to prepare analogous donorsubstituted amides with an increased flexibility and to study their coordination properties. To this end, we have synthesized a series of Hdpf amides from amines substituted by diphenylphosphino and dimethylamino groups in the terminal position of an aliphatic chain (Scheme 1, bottom). This contribution reports the preparation of such compounds and results of our investigation into their coordination behavior toward palladium(II). Also reported are the preparation of an analogous phosphinoamide modified with a polar ammonium tag and the results of catalytic testing of the compounds prepared as ligands for Pd-catalyzed Suzuki−Miyaura reaction of model substrates.

Scheme 3. Synthesis of the Cationic Phosphine 7

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Phosphines bearing the highly polar, positively charged ammonium moieties have been studied mostly as prospective water-soluble ligands possibly allowing for performing transition-metal-catalyzed organic transformations in aqueous reaction media. The direct synthesis of donors of this type from the corresponding phosphine-amines is typically hampered by a competitive alkylation at phosphorus, which deactivates the “main” donor atom. Hence, alternative preparative routes had to be devised based on the use of temporary protecting groups and appropriate reaction intermediates and on carefully designed (sequenced) synthetic reaction pathways.18,19 Even in our case the attempted direct alkylation of 1 with one molar equivalent of methyl iodide in acetonitrile rather expectedly afforded an inseparable mixture of P- and Nmonoalkylated products as well as the P,N-dialkylated derivative. Therefore, the phosphine group in 1 was protected prior to the alkylation by converting the free phosphine into the corresponding phosphine sulfide 5, which was then smoothly alkylated to give intermediate 6 (Scheme 3). In the last step, the free phosphine moiety was regenerated via desulfuration with Raney nickel. However, also this standard method required a careful optimization. When carried out in methanol, the desulfuration was accompanied by a reductive removal of

RESULTS AND DISCUSSION Synthesis and Characterization of the Amidophosphine Ligands. Phosphinoferrocene amides modified with amide substituents bearing N- or P-donor groups in the terminal position, compounds 1−4 (Scheme 2), resulted readily upon reacting Hdpf7a with the appropriate amines in the presence 1-hydroxybenzotriazole and 1-ethyl-3-[3(dimethylamino)propyl]carbodiimide as the common peptide Scheme 2. Preparation of Hdpf Amides 1−4a

a

Legend: EDC = 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, HOBt = 1-hydroxybenzotriazole. B


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2. Selected geometric data are summarized in Table 1. Generally, the structures confirm the formulation, and the

the entire phosphorus substituent, providing inseparable mixtures of [FcCONH(CH2)2NMe3]I (Fc = ferrocenyl) and phosphine 7. Gratifyingly, changing the solvent to acetonitrile suppressed the unwanted side reaction, and the desired product 7 was isolated in a reasonable yield (34% after crystallization) and in good purity.20 The compound was isolated as a mixed anion salt (90% chloride/10% iodide). Attempts to fully exchange the anion by repeated washing with saturated NaCl solution were not successful. Sulfidation of the phosphine moiety in 1 is clearly manifested through a low-field shift of the 31P NMR resonance (5: δP +42.4), whereas the alkylation at nitrogen results in an increase in the intensity of the signal due to NMe protons and its shift to a lower field. The ESI mass spectra of phosphines 6 and 7 are dominated by the signals of the respective cations (i.e., [M − halide]+) and further display fragments resulting from an elimination of NMe3 The molecular structures of 5−7 as determined by singlecrystal X-ray diffraction analysis are presented in Figures 1 and

Table 1. Selected Distances and Angles for 5−7 (in Å and deg) parametera

5

6

7

Fe−Cg1 Fe−Cg2 ∠Cp1,Cp2 τ P−S P−C1 P−C12 P−C18 C6−C11 C11−O C11−N1 O−C11−N1 φ C25−N2 N2−C26 N2−C27 N2−C28 N1−C24−C25−N2

1.6434(9) 1.6498(9) 0.6(1) −149.3(1) 1.9638(7) 1.789(2) 1.815(2) 1.817(2) 1.486(3) 1.229(2) 1.348(2) 122.9(2) 14.2(2) 1.462(2) 1.458(3) 1.459(2) n.a. −171.5(1)

1.6555(9) 1.6570(9) 1.0(1) 90.2(2) 1.9470(9) 1.787(2) 1.813(2) 1.813(3) 1.488(3) 1.231(3) 1.348(3) 121.7(2) 9.2(2) 1.515(3) 1.504(3) 1.503(3) 1.495(3) −75.7(2)

1.656(2) 1.660(2) 2.3(2) −84.1(3) n.a. 1.818(3) 1.834(3) 1.838(4) 1.478(5) 1.237(4) 1.352(5) 121.2(3) 6.1(4) 1.517(4) 1.503(5) 1.500(5) 1.496(4) 74.4(4)

a Cp1 and Cp2 are the cyclopentadienyl ring planes C(1−5) and C(6− 10), respectively. Cg1/2 denote their respective centroids. τ is the torsion angle C1−Cg1−Cg2−C6; φ is the dihedral angle subtended by the amide plane {C11, O, N1} and the plane of its parent cyclopentadienyl ring Cp2. n.a. = not applicable.

geometry of their ferrocenecarboxamido moieties does not differ significantly from that found in other structurally characterized Hdpf-based amides.13,14 The ferrocene units in 5−7 are regular, showing similar Fe−C distances (ca. 2.03− 2.07 Å in the whole series) and, accordingly, an insignificant tilting. In the case of 5, the substituents in positions 1 and 1′ assume an anticlinal staggered conformation (cf. the ideal value τ = 144°), and the amide plane is rotated by ca. 14° with respect to the plane of its bonding cyclopentadienyl ring so that the amide nitrogen is oriented to the side of the phosphorus

Figure 1. View of the molecular structure of phosphine sulfide 5 showing the atom-labeling scheme. Displacement ellipsoids enclose the 30% probability level.

Figure 2. Views of the molecular structures of compounds 6 (left) and 7 (right) showing the atom-labeling scheme and displacement ellipsoids at the 30% probability level. C


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and 9 display all the expected signals, though some are markedly broadened. This broadening is indicative of a limited molecular mobility at room temperature resulting obviously from spatial constraints imposed by the chelate coordination. It expectedly becomes more pronounced upon cooling, while sharpening of the signals is seen at higher temperatures (for VT 1 H NMR spectra of 8, see Supporting Information, Figure S2). The 31P NMR resonances of 8 and 9 appear shifted to lower fields as compared with the free ligands [8: δP 24.2 (s); 9: a pair of doublets at δP 9.7 and 15.9]. The value of the two-bond coupling constant 2JPP of 571 Hz determined for the latter complex corresponds with the data reported for trans[PdCl2(PR3)2] (R = Me: 541 Hz; R = Et: 640 Hz),25 thereby corroborating the trans-P,P arrangement. The ESI mass spectra of the chelate complexes lack the signals due to the (pseudo)molecular ions. Instead, fragments attributable to [M − Cl − HCl]+ (and also [M + Na − HCl]+ for 8) are observed as the heaviest positively charged species. The molecular structure of complex 8 is shown in Figure 3. Selected distances and angles are given in Table 2. The Pd-

substituent and inward of the ferrocene unit. The nitrogen substituents at the C24−C25 bonds are found in an anti conformation, and the entire amide substituent extends away from the rest of the molecule. In contrast, compounds 6 and 7 adopt an intermediate conformation at the ferrocene unit and show a smaller departure of the C5H4 and CON subunits from a coplanar arrangement. Although the amide nitrogen is oriented again toward the side of the phosphorus group, it is the oxygen that appears closer to the iron atom. The positively charged pendants are directed toward the same direction (i.e., toward the phosphinylated cyclopentadienyl ring) having the nitrogen atoms at the C24−C25 bond in a synclinal orientation. Finally, the polarized N−C bonds in 6 and 7 are ca. 0.05 Å longer than those in 5,21 presumably due to an absence of a bonding contribution (delocalization) from the lone pair at nitrogen and, perhaps, also owing to an increased steric crowding around the quarternized nitrogen atom. It is also noteworthy that whereas the individual molecules of 5 assemble into centrosymmetric dimers via N1−H1N···S hydrogen bonds (N1···S = 3.468(2) Å, angle at H1N = 162°), the NH protons in the ammonium salts 6 and 7 form N1− H1N···X hydrogen bonds toward the nearest anion (6: N1···I = 3.606(2) Å, angle at H1N = 139°; 7: N1···Cl = 3.180(3) Å, angle at H1N = 142°). Simplified packing diagrams for 5−7 are available as Supporting Information, Figure S1. Preparation and Structural Characterization of Pd(II) Complexes. In view of the intended catalytic testing, compounds 1−4 were studied as ligands for the soft Pd(II) ion.22 The complexation reactions were performed at 1:1 ligand-to-metal ratio to avoid the formation of the usual bisligand diphosphine complexes using [PdCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) as the palladium precursor. The reactions were monitored in situ by 31P NMR spectroscopy and by electrospray ionization (ESI) mass spectrometry. The reaction studies revealed that donors 1 and 3 rapidly (within minutes) and cleanly replace the diene ligand in the precursor complex to afford the respective trans-chelates 8 and 9 (Scheme 4). These complexes were subsequently isolated by crystalScheme 4. Preparation of Complexes 8 and 9a

Figure 3. PLATON plot of the molecule of complex 8. Displacement ellipsoids are scaled to the 30% probability level.

a

donor distances in 8 compare well with the data reported for the structurally related complex trans-[PdCl2(I-κ2N,P)]14a (for the structure of I, see Scheme 1). The exception is the Pd−N2 bond length, which is ca. 0.1 Å shorter in 8 than the Pd−N distance found in the reference compound. This difference may well reflect the different nature of the N-donor moieties present in the ligands. On the other hand, the P−Pd−N2 or the ligand bite angle of 172.7(1)° is similar to that reported for the mentioned pyridyl-amide complex (173.67(5)°), which in turn corresponds with the structural similarity (atom connectivity) of both P,N-chelate ligands (Ph2PfcC(O)NH-C-C-N; fc = ferrocene-1,1-diyl). The palladium and its four ligating atoms in 8 are coplanar within ca. 0.07 Å,26 but the central atom is moved slightly toward the amide unit and toward Cl1 (the Cl1−Pd−(P/N2) angles are less acute that the Cl1−Pd−(P/N2) angles). When viewed along the N2···P line, the NC3 and PC3 moieties appear

cod = η2:η2-cyclocta-1,5-diene.

lization in experiments performed on a larger scale (0.5 mmol), resulting in air-stable, red crystalline solids. It should be noted that with the exception of several compounds prepared from ligands I and IV and from some ferrocene-based P,N(heterocycle) donors,23 all structurally characterized Pd(II) complexes bearing phosphinoferrocene P,P- and P,N-ligands as chelating ligand adopt a cis geometry.24 Complexes 8 and 9 were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. In addition, their molecular structures were determined by single-crystal Xray diffraction analysis. The 1H NMR spectra of complexes 8 D


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Table 2. Selected Distances and Angles for Complex 8 (in Å and deg)a Distances Pd−Cl1 Pd−P Fe−Cg1 P−C1 P−C12 P−C18 N1−C24 C25−N2

2.312(1) 2.243(1) 1.654(2) 1.806(4) 1.821(4) 1.827(4) 1.451(5) 1.487(7)

Pd−Cl2 Pd−N2 Fe−Cg2 C6−C11 C11−O C11−N1 N2−C26 N2−C27

2.300(1) 2.223(3) 1.651(2) 1.478(6) 1.236(5) 1.352(5) 1.466(7) 1.479(7)

Angles Cl1−Pd−P Cl2−Pd−P P−Pd−N2 ∠Cp1,Cp2 O−C11−N1

92.42(4) 85.60(4) 172.7(1) 5.1(2) 122.6(4)

Cl1−Pd−N2 Cl2−Pd−N2 N1−C24−C25−N2 τ φ

92.98(9) 89.10(9) −54.6(5) 64.1(3) 20.0(5)

Parameters Cg1/2, Cp1/2, τ, and φ are defined as for compounds 5− 7 (see footnote a in Table 1). a

Figure 4. PLATON plot of molecule 1 in the structure of complex 9. Displacement ellipsoids enclose the 30% probability level. Note: Atomic labels in molecule 2 are obtained by changing the first digit to 2 (heavy atoms other than C) or by adding 50 to the numerical part of the corresponding atomic label in molecule 1 (carbon atoms).

nearly eclipsed (mutual rotation: ca. 12°)27 and the P−C1 and N−C25 bonds in the chelate ring are syn to each other. The closure of the chelate ring results in conformational rearrangements of the ferrocene ligand. The donor substituents at the cyclopentadienyl rings are inclined toward each other, assuming a conformation near synclinal eclipsed (ideal value: τ = 72°). The ferrocene cyclopentadienyls are tilted by ca. 5° and the amide moiety is twisted by 20° so that the nitrogen atom is located at the side of the phosphorus substituent and below the Ph2Pfc unit. Finally, the 2-(dimethylamino)ethyl substituent is directed to the side and above the amide plane, with the N1− C24−C25−N2 torsion angle being −54.6(5)°. Complex 9 crystallizes with two structurally independent molecules and a triclinic space group symmetry of P1. The independent molecules differ only marginally, mainly by the orientation of the phosphorus-bound phenyl rings (for an overlap of the two independent molecules, see Supporting Information, Figure S3). View of molecule 1 is presented in Figure 4. Geometric data for both molecules are summarized in Table 3. The coordination planes PdCl2P2 in the molecules of 9 are somewhat twisted, the maximum deviations from the mean plane being ca. 0.12 and 0.14 Å for molecules 1 and 2, respectively. The ligand bite angles of 172.83(3)° (molecule 1) and 169.85(3)° (molecule 2) are similar to the P−Pd−P′ angle determined for [PdCl2(IV-κ2P,P′)] (171.91(3)°; for the structure of IV, see Scheme 1), possessing a longer yet less flexible spacer group.14c In both compounds, the Cl1−Pd−P1/ 2 angles are more opened than the Cl2−Pd−P1/2 angles and may thus reflect steric demands of the bulky chelating ligands as well as the formation of intramolecular N−HN···Cl1 hydrogen bonds (N···Cl = 3.340(3) Å for molecule 1 and 3.384(3) Å for molecule 2). Similarly to 8, the trans-chelate coordination in 9 requires a preorganization of the donor moieties. The ferrocene cyclopentadienyls in coordinated 3 are found to be near synclinal eclipsed and are slightly tilted (by ca. 8.7(2)° and 6.6(2)° in molecules 1 and 2, respectively). The rotation of the amide planes (ca. 10° in both molecules) in 9 is considerably lower than that in 8, presumably due to the presence of a longer spacer separating the donor atoms (N−C bond is shorter than the C−P bond). The substituents at the flexible ethane-1,2-diyl

Table 3. Selected Distances and Angles for the Two Crystallographically Independent Molecules of Complex 9 (in Å and deg)a molecule 1 Pd1−Cl11 Pd1−Cl12 Pd1−P11 Pd1−P12 Cl11−Pd1−P11 Cl11−Pd1−P12 Cl12−Pd1−P11 Cl12−Pd1−P12 P11−Pd1−P12 Fe−Cg11 Fe−Cg12 ∠Cp11,Cp12 τ1 P11−C1 P12−C25 C11−O1 C11−N1 O1−C11−N1 φ1 N1−C24−C25−P12

molecule 2 2.3164(8) 2.2935(9) 2.3343(9) 2.3379(9) 91.85(3) 91.20(3) 88.12(3) 89.36(3) 172.83(3) 1.647(2) 1.654(2) 8.7(2) −69.8(2) 1.802(3) 1.832(4) 1.228(4) 1.351(5) 122.9(4) 10.0(4) −63.5(4)

Pd2−Cl21 Pd2−Cl22 Pd2−P21 Pd2−P22 Cl21−Pd2−P21 Cl21−Pd2−P22 Cl22−Pd2−P21 Cl22−Pd2−P22 P21−Pd2−P22 Fe−Cg21 Fe−Cg22 ∠Cp21,Cp22 τ2 P21−C51 P22−C75 C61−O2 C61−N2 O2−C61−N2 φ2 N2−C74−C75−P22

2.3151(9) 2.2883(8) 2.3333(8) 2.3464(9) 93.91(3) 91.85(3) 85.67(3) 89.28(3) 169.85(3) 1.655(2) 1.660(2) 6.6(2) −74.9(2) 1.807(3) 1.843(4) 1.222(4) 1.347(4) 122.5(3) 9.6(4) −61.7(4)

a

The ring planes are defined as follows: Cp11 = C(1−5), Cp12 = C(6−10), Cp21 = C(51−55), Cp22 = C(56−60). Cgn are the respective centroids. Parameters τ and φ are defined similarly to compounds 5−7 (see footnote a in Table 1).

linker assume a gauche conformation, similar to the conformation of the N−C−C-N moiety in 8. Unlike the P,Nchelate 8, however, the PC3 units in 9 are practically staggered, presumably owing to higher steric demands of the bulky phosphine moieties. Reaction tests performed with ligands 2 and 4 possessing the longer propane-1,3-diyl spacer revealed much more complicated coordination behavior of these ligands. Thus, the reaction of [PdCl2(cod)] with one molar equivalent of 2 yielded a E


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mixture of several Pd-2 species, among which one of the products markedly dominated (Figure 5). The composition of

Figure 5. 31P{1H} NMR spectra of the [PdCl2(cod)]−2 mixture (Pd:2 = 1:1) as recorded after 1 and 24 h of reaction in CDCl3. (N.B. The preparative experiments were performed in dichloromethane.) Figure 6. 31P{1H} NMR spectra of the [PdCl2(cod)]−4 mixture (Pd:4 = 1:1) as recorded after 1 and 24 h of reaction in CDCl3. Red diamonds denote the signals due to dimeric complex 10b, which separates from the reaction mixture. Signals due to an AB spin system of another Pd-4 species are also indicated (2JPP = 568 Hz). (N.B. The preparative experiments were performed in dichloromethane.)

the reaction mixture did not practically change upon extending the reaction times (cf. the 31P{1H} NMR spectra recorded after 1 h and 1 day in Figure 5), but all attempts at isolating any defined (single) product from this mixture by crystallization failed. It is noteworthy that similar differences have been noted for the homologous ligands I and III, which afforded transchelate complex [PdCl2(I-κ2P,N)] and dimer [PdCl2(μ-III)]2, respectively, after crystallization.14a Trans-chelate Pd(II) complexes were isolated also with the analogous (2Ph2PC6H4)CH2O(CH2)nPy ligands (Py = 2-pyridyl; n = 2 and 3). However, the complex featuring the more flexible ligand (n = 3) was accompanied by a trinuclear side-product and was shown to isomerize partially to the symmetric, ligand-bridged dimer [Pd2Cl4L2].28 According to NMR monitoring, the course of the reaction between equimolar amounts of [PdCl2(cod)] and diphosphine 4 proved to be even more complicated. Unlike the previous case, however, the complex reaction mixture resulting immediately after mixing of the starting materials simplified over time (two major species detected; see Figure 6) and, upon the addition of hexane, deposited red crystals of a pure Pd-4 complex, which was structurally characterized as the symmetric, ligand-bridged dimer 10b (Scheme 5). Considering the donor properties of ligand 4, one can expect the formation of a monopalladium chelate complex (10a in Scheme 5) and two dimers: a symmetric (or head-to-tail) one and an unsymmetric (head-to-head/tail-to-tail) one. The gradual change in composition of the (kinetic) reaction mixture is completed within less than 1 day and suggests a fluxional nature of the species involved in the equilibrium, which can thus shift in favor of the thermodynamically preferred species. On the other hand, the isolation of complex 10b from the reaction in a yield that does not correspond with the initial composition of the reaction solution may reflect a relatively lower solubility of this compound (monomer vs dimer). The dimer, which separates preferentially from the reaction mixture, can be continuously replenished in the solution via the dynamic equilibrium among the Pd-4 complexes. NMR data for the isolated pure complex 10b (δP 15.8 and 15.929) were used to identify the second major component in

Scheme 5. Anticipated Equilibrium between the Monopalladium Chelate 10a and the Symmetric Dimer 10ba

a

Unsymmetric dimer as a third most plausible species is not shown in this scheme (cod = η2:η2-cyclocta-1,5-diene).

the equilibrated reaction mixture. On the basis of a comparison of the observed 2JPP coupling constants that are ca. 568 Hz for the “unknown” species and 571 Hz for the structurally characterized complex 9 resulting from the homologous ligand 3, the other dominant species was tentatively formulated as the monopalladium P,P-chelate 10a. The formulation of dimer 10b was unambiguously corroborated by single-crystal X-ray diffraction analysis (Figure 7). The center of the complex molecule in the crystal structure coincides with the crystallographic inversion center, which renders only half of the complex molecule structurally F


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Figure 8. Kinetic profiles for the model coupling reaction performed in dioxane at 90 °C in the presence of catalysts generated from palladium(II) acetate and ligands 1, 3, and 7.

phosphines are rapidly converted to active catalysts (see the initial reaction rates). However, whereas the catalyst based on the cationic monophosphine 7 lost its activity within ca. 2 h, those resulting from ligands 1 and 3 remained active during the whole experiment (6 h). This probably reflects the different donor properties of the ligands, among which compound 7 can be expected to coordinate in a P-monodentate fashion, whereas both neutral donors can act as chelating ligands and thus increase the stability of palladium intermediates. In line with this explanation, diphosphine 3, comprising two soft donor atoms, shows systematically better results than the mixed-donor ligand 1 (cf. the kinetic profiles in Figure 8 and conversions after 6 h: 100% for 3 and 91% for 1). When the reaction was performed similarly in water (on water),31 practically quantitative yields of the coupling product were obtained with all the Pd(OAc)2/L catalysts (L = 1, 3, and 7; 0.1 mol % Pd) after 6 h at 90 °C (Table 4). No decrease in

Figure 7. PLATON plot of the complex molecule in the structure of 10b·2Et2O showing 30% probability displacement ellipsoids. The second half of the molecule (including P2′) is generated by the crystallographic inversion. For the sake of clarity, all hydrogen atoms and carbons in the phenyl rings (except for the pivotal atoms) were omitted. Selected distances and angles (in Å and deg): Pd−Cl1 2.294(1), Pd−Cl2 2.3102(9), Pd−P1 2.336(1), Pd−P2′ 2.328(1), Cl1−Pd−P1 92.61(5), Cl1−Pd−P2′ 91.65(5), Cl2−Pd−P1 87.63(4), Cl2−Pd−P2′ 88.02(4); Fe−Cg1 1.647(2), Fe−Cg2 1.650(2), C11−O 1.235(6), C11−N 1.356(6), O−C11−N 121.8(4). Note: The ring planes are defined similarly to compounds 5−7.

independent. Because of a lack of a steric strain resulting from trans-chelate formation, the palladium and its four ligating atoms in 10b are coplanar within less than 0.05 Å. However, similarly to 9, the Cl−Pd−P1/2′ interligand angles involving one of the chloride ligands (Cl1) are less acute that for the other chloride (Cl2). Since the Cl1···Cl2 and P1···P2′ vectors subtend a nearly ideal angle of 90.34(3)°, the interligand angles seem to correspond with a minor displacement of the Pd atom from the center of the dimer toward Cl1. Nonetheless, the sum of interligand angles (359.9°) rules out any significant tetrahedral distortion of the coordination sphere. The ferrocene units in ligand 10b adopt a sterically relaxed conformation near anticlinal eclipsed with τ = −135.0(3)° and are tilted by 4.1(3)°. The rotation of the amide moiety from the plane of its parent cyclopentadienyl ring is only 4.7(6)°. Catalytic Evaluation. Catalytic properties of phosphines 1, 3, and 7 were evaluated in the Suzuki−Miyaura crosscoupling30 of phenylboronic acid with 4-bromoacetophenone to give 4-acetylbiphenyl (Scheme 6). The reactions were performed in dioxane using 0.1 mol % of Pd catalysts generated in situ by mixing palladium(II) acetate with the appropriate ligand (0.12 mol %) and anhydrous potassium carbonate as the base. Kinetic profiles for the reactions performed at 90 °C in dioxane are presented in Figure 8. The data indicate that all

Table 4. Summary of Catalytic Results Obtained with Pd(OAc)2/L (L = 1, 3, and 7) in Watera ligand

yieldb after 2 h [%]

yieldb after 6 h [%]

1 3 7

94 96 94

94 97 94

a

Reaction of 4-bromoacetophenone (5.0 mmol), phenylboronic acid (6.0 mmol), and K2CO3 (12 mmol) in water (20 mL) at 90 °C for 2 h performed with Pd catalysts generated by mixing separately palladium(II) acetate (0.1 mol.%) with the respectively ligand (0.12 mol %). For further details, see the Experimental Section. bIsolated yield of 4acetylbiphenyl.

the yields was observed after shortening the reaction time to 2 h. This led us to test also the toluene−water biphase system, possibly allowing for catalyst recovery. The results presented in Figure 9 as kinetic profiles clearly indicate a relatively worse performance of all Pd(OAc)2/L catalysts in this reaction medium. The system based on diphosphine 3 afforded the best results, achieving a 67% yield after 6 h. Notably, the catalyst based on the cationic ligand 7 performed better than its analogue, resulting from its neutral counterpart 1, and also showed the least relative decrease in activity as compared to the reaction performed in dioxane, presumably owing to its higher polarity and solubility in the aqueous system.

Scheme 6. Model Suzuki−Miyaura Reaction

G


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spacers behave similarly to their more rigid analogues obtained from 2-(aminomethyl)pyridine or 2-(diphenylphosphino)benzylamine, affording smoothly trans-chelate complexes of the type trans-[PdCl2(L)]. Introduction of the longer propane1,3-diyl spacer such as in 2 and 4 renders the amides more flexible, which in turn markedly complicates their coordination behavior. This in turn suggests that a rigid backbone is not a necessary prerequisite for the design of donors capable of traversing the trans position in the coordination sphere of a metal ion. However, careful attention has to be paid to the choice of spacer between the donor groups, particularly when it comprises flexible parts. Furthermore, reaction tests performed with the former donors (1 and 3) and their N-alkylated analogue 7 revealed the catalytic performance to change with both the polarity (solubility) and the nature of additional donor atoms (PP vs PN and PN+) available in these ligands.

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Figure 9. Kinetic profiles for the model coupling reaction performed in water at 90 °C in the presence of catalysts generated from palladium(II) acetate and ligands 1, 3, and 7.

EXPERIMENTAL SECTION

Materials and Methods. All syntheses were performed under an argon atmosphere and with exclusion of direct daylight. Dichloromethane and chloroform were dried over anhydrous potassium carbonate and distilled under argon. Dioxane was dried over sodium metal and distilled similarly. Hdpf was prepared as described elsewhere.7a Other chemicals and solvents utilized during crystallizations and chromatography were used without any further purification (Sigma-Aldrich; solvents from Lachner). NMR spectra were measured with a Varian UNITY Inova 400 spectrometer (1H, 399.95; 13C, 100.58; 31P, 161.90 MHz) at 25 °C unless noted otherwise. Chemical shifts (δ/ppm) are given relative to internal tetramethylsilane (1H and 13C) or to external 85% aqueous H3PO4 (31P). In addition to the standard notation of the signal multiplicity, vt and vq are used to distinguish virtual multiplets arising from the AA′BB′ and AA′BB′X spin systems of the amide- and phosphorus-substituted cyclopentadienyl rings, CpC and CpP, respectively (fc = ferrocene-1,1′-diyl). The multiplicity of signals in the 13C{1H} NMR spectra is specified only for nonsinglet signals. IR spectra were recorded with an FT-IR Nicolet 6700 instrument in the range 400−4000 cm−1. Electrospray ionization mass spectra (ESI-MS) were recorded on a Bruker Esquire 3000 spectrometer. The samples were dissolved in dichloromethane and diluted with methanol in large excess. High-resolution (HR) ESI-MS measurements were performed with an LTQ Orbitrap XL instrument (Thermo Fisher Scientific). Electron ionization mass spectra (EI-MS) were obtained with a GCT Premier (Waters) spectrometer. Preparation of the Amidophosphine Ligands. 1-(Diphenylphosphino)-1′-{[(2-(dimethylamino)ethyl)amino]carbonyl}ferrocene (1). Neat 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC; 264 mg, 1.7 mmol) was added to a suspension of Hdpf (414 mg, 1.0 mmol) and 1-hydroxybenzotriazole (149 mg, 1.1 mmol) in dry dichloromethane (15 mL) while stirring and cooling in an ice bath, whereupon the solids quickly dissolved to give an orange-red solution. The resulting mixture was stirred for 30 min at 0 °C and then treated with neat 2-(dimethylamino)ethylamine (96 mg, 1.1 mmol). After the addition, the stirring was continued for 15 min at 0 °C and then at room temperature overnight. The reaction mixture was quenched by addition of 10% aqueous citric acid and stirring for another 5 min. The organic layer was separated, washed with saturated aqueous NaHCO3, dried over MgSO4, and evaporated under vacuum. The residue was purified by chromatography over neutral alumina using dichloromethane−methanol (20:1, v/v) as the eluent. Subsequent evaporation afforded 1 as an orange oil, which solidified upon prolonged standing. Yield: 474 mg, 98%. 1 H NMR (CDCl3): δ 2.25 (s, 6 H, NMe2), 2.46 (t, 2 H, 3JHH = 6.0 Hz, CH2NMe2), 3.42 (virtual q, 2 H, J ≈ 6 Hz, NHCH2), 4.11 (vq, 2 H, J′ = 1.9 Hz), 4.18 (vt, 2 H, J′ = 1.9 Hz), 4.41 (vt, 2 H, J′ = 1.8 Hz), 4.58 (vt, 2 H, J′ = 1.9 Hz) (4 × CH of fc); 6.37 (t, 1 H, 3JHH = 5.0 Hz, NH), 7.29−7.40 (m, 10 H, PPh2). 31P{1H} NMR (CDCl3): δ −17.1 (s). 13C{1H} NMR (CDCl3): δ 36.82 (CH2), 45.22 (NMe2), 58.05

Recyclability tests on the biphase system were performed only with the most polar, cationic ligand, 7. The reactions were performed similarly to other reaction tests except that 1 mol % of the catalyst prepared from Pd(OAc)2 and 1.2 or 2.4 eqivalents of ligand 7 was used. After heating to 90 °C for 2 h, the organic phase was separated, and the aqueous layer was washed with toluene and then mixed with fresh reagents and toluene. In the first run, the catalyst prepared from 2.4 molar equiv of 7 achieved a complete conversion, while the “Pd(OAc)2/L” system showed a 93% conversion. During the following runs, both catalytic systems gradually lost their activity (Figure 10). Although the system containing more

Figure 10. Recyclability tests for the model Suzuki−Miyaura reaction performed in the toluene−water biphase mixture with catalysts prepared in situ from Pd(OAc)2 (1 mol %) and different amounts of phosphine 7 (1.2 mol %, yellow bars; 2.4 mol %, blue bars).

phosphine performed in the most cases slightly better, there is no clear trend distinguishing the catalysts that differ only by the amount of the supporting phosphine ligand.

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CONCLUSION Amidation of Hdpf with aliphatic amines bearing potentially donating substituents in the terminal position affords the corresponding organometallic phosphinocarboxylic amides suitable for use as multidonor ligands. When reacted with [PdCl2(cod)], compounds 1 and 3 possessing ethane-1,2-diyl H


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(CH2), 69.39 (fc CHC), 71.48 (fc CHC), 72.92 (d, JPC = 4 Hz, fc CHP), 74.30 (d, JPC = 14 Hz, fc CHP), 128.24 (d, 3JPC = 7 Hz, PPh2 CHmeta), 128.67 (PPh2 CHpara), 133.44 (d, 3JPC = 20 Hz, PPh2 CHortho), 138.55 (d, 3JPC = 9 Hz, PPh2 Cipso), 169.81 (s, CO). Signals due to ferrocene Cipso were not observed. IR (Nujol): ν 3327 w, 3040 w, 1631 s, 1583 w, 1539 s, 1304 m, 1259 w, 1219 w, 1194 m, 1182 m, 1157 s, 1070 w, 1053 w, 1032 m, 996 w, 950 m, 877 w, 845 w, 833 w, 814 m, 744 s, 698 s, 639 w, 593 w, 569 w, 504 s, 489 m, 452 w, 439 w cm−1. ESI-MS: m/z 507 ([M + Na]+), 485 ([M + H]+); 483 ([M − H]−). HR-ESI-MS: calcd for C27H30N2OP56Fe ([M + H]+) 485.1440, found 485.1439. Anal. Calcd for C27H29FeN2OP·0.2CH2Cl2 (501.3): C 65.16, H 5.91, N 5.59. Found: C 65.30, H 6.03, N 5.56 (the presence of residual CH2Cl2 was confirmed by 1H NMR spectroscopy). 1-(Diphenylphosphino)-1′-{[(3-(dimethylamino)propyl)amino]carbonyl}ferrocene (2). This was prepared similarly from Hdpf (414 mg, 1.0 mmol), HOBt (150 mg, 1.2 mmol), EDC (234 mg, 1.5 mmol), and 3-(dimethylamino)propylamine (115 mg, 1.1 mmol) and was isolated by column chromatography (neutral alumina, dichloromethane−methanol, 20:1, v/v). Yield: 403 mg, 81%; orange, viscous oil. 1 H NMR (CDCl3): δ 1.70 (quintet, 3JHH = 6.3 Hz, 2 H, CH2CH2CH2), 2.26 (s, 6 H, NMe2), 2.43 (t, 3JHH = 6.3 Hz, 2 H, CH2NMe2), 3.42 (virtual q, J ≈ 6 Hz, 2 H, CH2NH), 4.10 (vq, J′ = 1.9 Hz, 2 H), 4.20 (vt, J′ = 2.0 Hz, 2 H), 4.39 (vt, J′ = 1.9 Hz, 2 H), 4.54 (vt, J′ = 1.9 Hz, 2 H) (4 × CH of fc); 7.29−7.40 (m, 11 H, PPh2 and NH). 31P{1H} NMR (CDCl3): δ −16.9 (s). 13C{1H} NMR (CDCl3): δ 25.99 (CH2), 39.70 (CH2), 45.52 (NMe2), 59.03 (CH2), 69.02 (CHC fc), 71.64 (CHC fc), 73.02 (d, JPC = 2 Hz, CHP fc), 74.04 (d, JPC = 13 Hz, CHP fc), 128.25 (d, 3JPC = 7 Hz, PPh2 CHmeta), 128.67 (s, PPh2 CHpara), 133.47 (d, 2JPC = 20 Hz, PPh2 CHortho), 138.57 (d, 1JPC = 10 Hz, PPh2 Cipso), 169.49 (CO). Signals due to ferrocene Cipso were not found. IR (neat): ν 3307 br m, 3069 m, 2943 m, 2859 m, 2817 m, 2766 m, 1634 vs, 1549 vs, 1464 m, 1435 m, 1300 vs, 1192 m, 1161 s, 1068 m, 1027 s, 998 w, 833 s, 744 s, 699 s, 499 vs, 452 m cm−1. ESI-MS: m/z 521 ([M + Na]+), 499 ([M + H]+); 497 ([M − H]−). HR-ESI-MS: calcd for C28H32N2OP56Fe ([M + H]+) 499.1596, found 499.1598. Anal. Calcd for C28H31FeN2OP·0.15CH2Cl2 (511.1): C 66.15, H 6.17, N 5.48. Found: C 66.12, H 6.27, N 5.56. The amount of clathrated solvent was verified by 1H NMR spectroscopy. 1-(Diphenylphosphino)-1′-{[(2-(diphenylphosphino)ethyl)amino]carbonyl}ferrocene (3). This was obtained analogously from Hdpf (0.840 g, 2.0 mmol), HOBt (0.298 g, 2.2 mmol), EDC (0.539 g, 3.5 mmol), and 2-(diphenylphosphino)ethylamine (0.512 g, 2.2 mmol). Following the aqueous workup and evaporation, it was isolated by chromatography on silica gel with dichloromethane− methanol (20:1, v/v) as the eluent. Yield: 1.14 g, 91%; yellow-orange solid. 1 H NMR (CDCl3): δ 2.35 (br t, 3JHH ≈ 6.8 Hz, 2 H, PCH2), 3.44 (br dt, 3JHH ≈ JPH ≈ 7 Hz, 2 H, NHCH2), 4.07 (vq, J′ = 1.8 Hz, 2 H), 4.20 (vt, J′ = 1.9 Hz, 2 H), 4.42 (vt, J′ = 1.8 Hz, 2 H), 4.50 (vt, J′ = 1.9 Hz, 2 H) (4 × CH of fc); 5.97 (br t, 3JHH = 5.2 Hz, 1 H, NH), 7.27− 7.48 (m, 20 H, 2 × PPh2). 31P{1H} NMR (CDCl3): δ −16.9 and −20.8 (2 × s). 13C{1H} NMR (CDCl3): δ 28.70 (d, 1JPC = 13 Hz, PCH2), 36.93 (d, 2JPC = 20 Hz, NCH2), 69.48 (fc CHC), 71.42 (fc CHC), 72.77 (d, 3JPC = 4 Hz, fc CHP), 74.35 (d, 2JPC = 13 Hz, fc CHP), 128.29 (d, 3JPC = 6 Hz, PPh2 CHmeta), 128.60 (d, 3JPC = 6 Hz, PPh2 CHmeta), 128.77 (PPh2 CHpara), 128.79 (PPh2 CHpara), 132.76 (d, 2JPC = 20 Hz, PPh2 CHortho), 133.62 (d, 2JPC = 20 Hz, PPh2 CHortho), 137.70 (d, 1JPC = 11 Hz, PPh2 Cipso), 138.54 (d, 1JPC = 10 Hz, PPh2 Cipso), 169.74 (CO). The signals of ferrocene Cipso were probably obscured by the solvent. IR (Nujol): ν 3330 w, 2670 w, 1628 vs, 1583 w, 1534 vs, 1295 s, 1158 m, 1092 w, 1068 w, 1026 m, 998 w, 815 w, 740 s, 695 vs, 504 s cm−1. ESI-MS: m/z 648 ([M + Na]+), 664 ([M + K]+); 624 ([M − H]−). HR-ESI-MS: calcd for C37H34NOP256Fe ([M + H]+) 626.1460, found 626.1461. Anal. Calcd for C37H33FeNOP2·0.1CH2Cl2 (633.9): C 70.29, H 5.28, N 2.21. Found: C 70.16, H 5.20, N 2.17. The amount of residual solvent was confirmed by 1H NMR spectroscopy.

1-(Diphenylphosphino)-1′-{[(3-(diphenylphosphino)propyl)amino]carbonyl}ferrocene (4). This was prepared similarly from Hdpf (414 mg, 1.0 mmol), HOBt (149 mg, 1.2 mmol), EDC (237 mg, 1.5 mmol), and 3-(diphenylphosphino)propylamine (331 mg, 1.4 mmol). The reaction mixture was worked up as above, and the crude product was purified by chromatography on silica gel using dichloromethane− methanol (50:1, v/v) as the eluent. The first major band containing the product was evaporated to afford 4 as a yellow-orange solid (499 mg, 78%). A second band due to 1H-1,2,3-benzotriazol-1-yl 1′(diphenylphosphino)-1-ferrocenecarboxylate (unreacted active ester)32 was discarded. 1 H NMR (CDCl3): δ 1.61−1.73 (m, 2 H, CH2), 2.06−2.13 (m, 2 H, CH2), 3.38 (virtual q, J ≈ 6.7 Hz, 2 H, NCH2), 4.03 (vq, J′ = 1.9 Hz, 2 H), 4.20 (vt, J′ = 1.9 Hz, 2 H), 4.39 (vt, J′ = 1.8 Hz, 2 H), 4.52 (vt, J′ = 1.9 Hz, 2 H) (4 × CH of fc); 5.71 (t, 3JHH = 5.8 Hz, 1 H, NH), 7.28−7.45 (m, 20 H, 2 × PPh2). 31P{1H} NMR (CDCl3): δ −15.7 and −16.9 (2 × s). 13C{1H} NMR (CDCl3): δ 25.48 (d, JPC = 11 Hz, CH2), 26.47 (d, JPC = 17 Hz, CH2), 40.50 (d, JPC = 13 Hz, CH2), 69.39 (CHC fc), 71.41 (CHC fc), 72.79 (d, JPC = 4 Hz, CHP fc), 74.35 (d, JPC = 15 Hz, CHP fc), 128.29 (d, 3JPC = 7 Hz, PPh2 CHmeta), 128.47 (s, PPh2 CHpara), 128.53 (s, PPh2 CHpara), 128.72 (d, 3JPC = 9 Hz, PPh2 CHmeta), 132.71 (d, 2JPC = 18 Hz, PPh2 CHortho), 133.62 (d, 2 JPC = 20 Hz, PPh2 CHortho), 138.3−138.5 (m, PPh2 2 × Cipso), 169.67 (s, CO). Signals due to ferrocene Cipso were not found. IR (Nujol): ν 3280 m, 2725 w, 1624 vs, 1584 w, 1542 vs, 1305 m, 1160 m, 1095 w, 1068 w, 1026 m, 999 w, 835 m, 739 s, 696 vs, 502 s cm−1. ESI-MS: m/ z 679 ([M + K]+), 663 ([M + Na]+), 641 ([M + H]+); 639 ([M − H]−). HR-ESI-MS: calcd for C38H36NOP256Fe ([M + H]+) 640.1616, found 640.1617. Anal. Calcd for C38H25FeNO2P·0.15CH2Cl2 (652.2): C 70.25, H 5.46, N 2.15. Found: C 70.17, H 5.59, N 2.22. The amount of residual solvent was verified by 1H NMR spectroscopy. 1-(Diphenylphosphinothioyl)-1′-{[(2-(dimethylamino)ethyl)amino]carbonyl}ferrocene (5). Phosphine 1 (1.452 g, 3.0 mmol) and elemental sulfur (99 mg, 3.1 mmol) were mixed in toluene (30 mL). The resulting solution was heated at 80 °C for 90 min and then allowed to stand at room temperature overnight. The reaction mixture was evaporated under vacuum, and the residue was purified by column chromatography (silica gel; CH2Cl2−methanol, 10:1 v/v). A single orange band was collected and evaporated under vacuum, leaving 5 as an orange solid. Yield: 1.145 g, 91%. 1 H NMR (CDCl3): δ 2.28 (s, 6 H, NMe2), 2.56 (t, 3JHH = 6.5 Hz, 2 H, CH2NMe2), 3.48 (apparent q, J ≈ 6.2 Hz, 2 H, NHCH2), 4.01 (vt, J′ = 2.0 Hz, 2 H), 4.35 (vq, J′ = 2.0 Hz, 2 H), 4.59 (vq, J′ = 1.8 Hz, 2 H), 4.87 (vt, J′ = 2.0 Hz, 2 H) (4 × CH of fc); 7.25 (br t, 3JHH ≈ 6 Hz, 1 H, NH), 7.42−7.55 (m, 6 H, PPh2), 7.67−7.75 (m, 4 H, PPh2). 31 1 P{ H} NMR (CDCl3): δ 42.4 (s). 13C{1H} NMR (CDCl3): δ 37.34 (CH2), 45.42 (NMe2), 58.23 (CH2), 70.82 (CHC fc), 71.32 (CHC fc), 73.37 (d, JPC = 10 Hz, CHP fc), 74.91 (d, JPC = 13 Hz, CHP fc), 76.22 (d, 1JPC = 98 Hz, C-P fc), 78.65 (C-CONH fc), 128.35 (d, 2JPC = 13 Hz, PPh2 CHmeta), 131.52 (d, 4JPC = 3 Hz, PPh2 CHpara), 131.60 (d, 2 JPC = 10 Hz, PPh2 CHortho), 133.81 (d, 1JPC = 87 Hz, PPh2 Cipso), 169.26 (CO). IR (Nujol): ν 3364 m, 1646 vs, 1583 w, 1530 s, 1439 m, 1346 w, 1305 w, 1239 m, 1222 w, 1195 w, 1181 w, 1167 m, 1101 m, 1063 w, 1033 w, 1025 m, 998 w, 861 w, 842 w, 826 m, 777 w, 764 m, 699 s, 661 m, 630 w, 614 w, 545 m, 510 m, 507 w, 498 m, 440 m, 472 w, 458 w, 448 w cm−1. ESI-MS: m/z 517 ([M + H]+), 539 ([M + Na]+); 515 ([M − H]−). HR-ESI-MS: calcd for C27H30N2OPS56Fe 517.1160, found 517.1160. Anal. Calcd for C27H29FeN2OPS (516.4): C 62.79, H 5.66, N 5.43. Found: C 62.41, H 5.62, N 5.28. 1-(Diphenylphosphinothioyl)-1′-{[(2-(trimethylazonia)ethyl)amino]carbonyl}ferrocene iodide (6). Neat iodomethane (0.88 g, 6.2 mmol) was introduced dropwise to a solution of phosphine sulfide 5 (1.006 g, 1.9 mmol) in dry acetonitrile (20 mL). The clear reaction mixture was stirred at room temperature for 75 min and then poured into diethyl ether (ca. 40 mL). The resulting mixture was allowed to stand in a freezer overnight before the precipitated product was filtered off, washed with diethyl ether and pentane, and, finally, dried under vacuum. Yield: 1.186 g (93%), an orange solid. 1 H NMR (CD3CN): δ 3.14 (s, 9 H, NMe3), 3.50, (t, 3JHH = 6.5 Hz, 2 H, CH2NMe3), 3.71 (qt, 3JHH = 6.3 Hz, 4JHH = 1.6 Hz, 2 H, I


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H), 5.37 (br s, 2 H) (4 × CH of fc); 7.31−7.38 (m, 4 H, PPh2), 7.39− 7.45 (m, 2 H, PPh2), 7.62−7.70 (m, 4 H, PPh2), 7.75 (t, 3JHH = 5.2 Hz, 1H, NH). 1H NMR (CDCl3, 50 °C): δ 2.69 (d, 3JPH = 3.0 Hz, 6 H, NMe2), 2.98 (virtual q, J′ = 5.0 Hz, 2 H, NHCH2), 3.70 (br d, 2 H, 3 JHH = 4.6 Hz, CH2NMe2), 4.55 (vt, 2 H, J′ = 2.0 Hz, 2 H), 4.71 (vq, J′ = 1.6 Hz, 2 H), 4.89 (br s, 2 H), 5.37 (vt, J′ = 1.9 Hz, 2 H) (4 × CH of fc); 7.29−7.36 (m, 4 H, PPh2), 7.37−7.44 (m, 2 H, PPh2), 7.61−7.70 (m, 4 H, PPh2), 7.73 (br t, 3JHH = 4.0 Hz, 1 H, NH). 31P{1H} NMR (CDCl3, 25 °C): δ 24.2 (s). ESI-MS: m/z 647 ([M + Na − HCl]+), 589 [M − HCl − Cl]+). Anal. Calcd for C27H29Cl2FeON2PPd·0.1CHCl3 (673.6): C 48.32, H 4.35, N 4.16. Found: C 48.40, H 4.31, N 4.00. Complex 9. This was prepared similarly from 3 (0.313 g, 0.50 mmol) and [PdCl2(cod)] (0.143 g, 0.50 mmol) in dichloromethane (5 mL) and subsequently recrystallized from dichloromethane−diethyl ether. Yield: 0.320 g (80%), red crystalline solid. 1 H NMR (CDCl3, 25 °C): δ 2.87 (br s, 2 H, NCH2), 3.84 (br s, 2 H, CH2P), 4.42 (vt, J′ = 2.0 Hz, 2 H), 4.74 (br s, 2 H) and 5.34 (br s, 2 H) (3 × CH of fc); 7.28−7.48 (m, 1 H, PPh2), 7.56−7.72 (m, 8 H, PPh2), 7.74 (t, 1 H, 3JHH = 4.6 Hz, NH). The fourth signal due to ferrocene CH protons is too broad to be observed at this temperature. 1 H NMR (CDCl3, 50 °C): δ 2.87 (br s, 2 H, NCH2), 3.84 (br d, 2JPH = 19.4 Hz, 2 H, CH2P), 4.39 (vt, J′ = 2.0 Hz, 2 H), 4.71 (br s, 2 H), 4.74 (br s, 2 H), 5.34 (br s, 2 H) (4 × CH of fc); 7.37−7.47 (m, 12 H, PPh2), 7.68−7.71 (m, 8 H, PPh2), 7.73 (br t, 3JHH = 4.4 Hz, 1 H, NH). 31 1 P{ H} NMR (CDCl3, 25 °C): δ 9.7 and 15.9 (2× d, 2JPP = 571 Hz). ESI-MS: m/z 730 ([M − Cl − HCl] + ). Anal. Calcd for C37H33Cl2FeONP2Pd·0.2CHCl3 (826.6): C 54.04, H 4.05, N 1695. Found: C 54.16, H 3.89, N 1.62. Complex 10b. This was prepared from 4 (96 mg, 0.15 mmol) and [PdCl2(cod)] (43 mg, 0.15 mmol) in dichloromethane (5 mL) and isolated as described above for 8. Yield: 96 mg (78%), red solid. 1 H NMR (CDCl3): δ 1.80, 2.63, and 3.62 (3 × br s, 2H, CH2); 4.30, 4.54, 4.65, and 4.81 (4 × br s, 2 H, fc); 6.63 (br s, 1 H, NH), 7.29− 7.44 (m, 12 H, PPh2), 7.46−7.53 (m, 4 H, PPh2), 7.77−7.84 (m, 4 H, PPh2). 31P{1H} NMR (CDCl3): δ 15.8 and 15.9 (2 × s). ESI-MS: m/z 1657 ([Pd2Cl4(4)2 + Na]+), 1597 ([Pd2Cl4(4)2 − HCl]+), 744 ([Pd(4 − H)]+). Anal. Calcd for C38H35Cl2FeONP2Pd·0.4CHCl3 (864.5): C 53.35, H 4.13, N 1.62. Found: C 53.57, H 4.10, N 1.52. Catalytic Tests. A Schlenk tube was charged with 4-bromoacetophenone (0.995 g, 5.0 mmol), phenylboronic acid (0.732 g, 6.0 mmol), potassium carbonate (1.659 g, 12 mmol), diethylene glycol dimethyl ether (internal standard; 0.336 g, 2.5 mmol), and a stirring bar. Dry dioxane was introduced, and the reaction vessel was flushed with argon, sealed with a septum, and transferred to an oil bath maintained at 90 °C. Meanwhile, the catalyst was prepared in a separate vial by mixing palladium(II) acetate (1.1 mg, 0.10 mol %) and the appropriate ligand (0.12 mol %) in dioxane (ca. 1 mL) and stirring for 10 min. This solution was added to the reaction mixture, which was then monitored by 1H NMR spectra. Reaction mixtures for reactions in water were prepared in the same manner except that deionized water (20 mL) was used as the solvent and the reaction was performed without the internal standard. The catalyst was prepared in dioxane as described above. After heating to 90 °C for 2 or 6 h, the reaction mixture was cooled and extracted carefully with diethyl ether. The combined ethereal extracts were washed with brine, dried over anhydrous MgSO4, and evaporated under vacuum. The crude product was purified by chromatography on silica gel using hexane−diethyl ether (3:1 v/v) mixture as the eluent. The conversions (Table 4) were determined by integration of the 1H NMR spectra. Reaction mixtures used for evaluation of the toluene−water biphase system consisted of 4-bromoacetophenone (0.398 g, 2.0 mmol), phenylboronic acid (0.293 g, 2.4 mmol), potassium carbonate (0.663 g, 4.8 mmol), mesitylene (internal standard; 0.080 g, 2/3 mmol), toluene (5 mL), and water (5 mL). The catalyst (0.10 mol % Pd(OAc)2 + 0.12 mol % ligand) was prepared as given above in pure dioxane (for 1 and 2) or in dioxane−water (for 7) and introduced into the preheated reaction mixture. The recyclation experiments were performed similarly using 1 mol % of the Pd catalyst (i.e., 1 mol % of

NHCH2), 4.14 (vt, J′ = 2.0 Hz, 2 H, fc), 4.41 (vq, J′ = 2.0 Hz, 2 H), 4.64 (vq, J′ = 1.8 Hz, 2 H), 4.77 (vt, J′ = 2.0 Hz, 2 H) (4 × CH of fc); 7.46−7.55 (m, 5 H, PPh2 and NH), 7.55−7.62 (m, 2 H, PPh2), 7.68− 7.76 (m, 4 H, PPh2). 31P{1H} NMR (CD3CN): δ 42.5 (s). 13C{1H} NMR (CD3CN): δ 34.57 (NHCH2), 54.36 (t(1:1:1), 1JNC = 4 Hz, NMe3), 65.88 (t(1:1:1), 1JNC = 3 Hz, CH2NMe3), 71.17 (CHC fc), 73.17 (CHC fc), 74.99 (d, JPC = 10 Hz, CHP fc), 75.41 (d, JPC = 13 Hz, CHP fc), 77.20 (d, 1JPC = 97 Hz, C−P fc), 78.41 (C-CONH fc), 129.56 (d, 2JPC = 12 Hz, PPh2 CHo), 132.41 (d, 3JPC = 11 Hz, PPh2 CHm), 132.74 (d, 4JPC = 3 Hz, PPh2 CHp), 135.04 (d, 1JPC = 87 Hz, PPh2 C i p s o ), 170.60 (CO). ESI-MS: m/z 531 ([Ph 2 P(S)fcCONHCH2CH2NMe3]+), 472 ([531 − NMe3]+). Anal. Calcd for C28H32FeIN2OPS (658.3): C 51.08, H 4.90, N 4.26. Found: C 50.86, H 4.77, N 3.99. 1-(Diphenylphosphino)-1′-{[(2-(trimethylazonia)ethyl)amino]carbonyl}ferrocene Chloride/Iodide (7). A reaction flask was charged with an aqueous slurry of active Raney nickel (ca. 1.5 g; Raney 2400 from Sigma-Aldrich), flushed with argon, and sealed. The water was removed via cannula, and the solid was washed successively with dry methanol and acetonitrile (2 × 5 mL each). Then, a solution of phosphine sulfide 6 (0.318 g, 0.48 mmol) in dry acetonitrile (10 mL) was added, and the resulting heterogeneous mixture was stirred at room temperature overnight, filtered, and evaporated under vacuum. The residue was taken up with dichloromethane (200 mL), and the solution was extracted with saturated aqueous NaCl (200 mL, deoxygenated by bubbling with argon). The organic layer was separated, filtered, and evaporated. The orange residue was purified by column chromatography over alumina using dichloromethane− methanol (3:1, v/v) as the eluent. Subsequent evaporation and crystallization from ethanol−diethyl ether by liquid-phase diffusion afforded 7 as an orange crystalline solid. Yield: 0.112 g (40%). 1 H NMR (CDCl3): δ 3.42 (s, 9 H, NMe3), 3.83−3.96 (m, 4 H, CH2CH2N), 4.10 (vt, J′ = 1.7 Hz, 2 H), 4.18 (vt, J′ = 2.0 Hz, 2 H), 4.45 (vt, J′ = 1.8 Hz, 2 H), 4.98 (vt, 3JHH = 2.0 Hz, 2 H) (4 × CH of fc); 7.28−7.39 (m, 10 H, PPh2), 8.82 (br t, 3JHH = 5.4 Hz, 2 H, NH). 31 1 P{ H} NMR (CDCl3): δ −17.6 (s). 13C{1H} NMR (CDCl3): δ 34.76 (NHCH2), 54.38 (NMe3), 66.00 (CH2NMe3), 69.86, 72.21, 72.98, 74.19 (d, JPC = 13 Hz) (4 × CH of fc); 75.88 (s, C-CONH fc), 128.25 (d, 3JPC = 5 Hz, PPh2 CHm), 128.63 (PPh2 CHp), 133.49 (d, 2 JPC = 20 Hz, PPh2 CHo), 138.3−138.7 (m, PPh2 CHipso), 171.51 (s, CO). The signal due to ferrocene C-P probably overlaps with the solvent resonance. IR (Nujol): ν 3172 w, 1642 s, 1522 m, 1302 m, 1188 w, 1160 w, 1089 w, 1071 w, 1058 w, 1023 w, 1006 w, 956 w, 873 w, 836 w, 827 w, 813 w, 754 w, 745 m, 699 m, 638 w, 567 w, 533 m, 520 w, 496 w, 476 w, 447 w cm−1. ESI-MS: m/z 499 ([M − Cl]+; i.e., the cation), 440 ([M − NMe 3 − Cl] + ). Anal. Calcd for C28H32FeN2OPCl0.9I0.1 (544.0): C 61.82, H 5.93, N 5.15, Cl 5.87, I 2.33, P 5.69, Fe 10.27. Found: C 61.33, H 5.75, N 5.03, Cl 5.72, I 2.75, P 5.67, Fe 9.94. NMR Study of the Complexation Reactions with Ligands 1− 4. Equimolar amounts of the respective ligand (1−4, 0.01 mmol) and [PdCl2(cod)] (2.9 mg, 0.01 mmol) were dissolved in CDCl3 (ca. 0.6 mL). The resulting solution was analyzed by 1H and 31P{1H} NMR spectroscopy immediately after mixing and then after standing for 1 h, 1 day, and 1 week. Spectra recorded for 1/[PdCl2(cod)] and 3/ [PdCl2(cod)] revealed clean formation of the respective trans-chelates under concomitant liberation of cod. The homologous ligands 2 and 4 afforded complicated mixtures, whose composition changed with time (see above). Preparation of Palladium(II) Complexes. Complex 8. Ligand 1 (0.242 g, 0.50 mmol) was added to a solution of [PdCl2(cod)] (0.143 g, 0.50 mmol) in dichloromethane (5 mL). The resulting mixture was stirred for 30 min and then evaporated under vacuum. The solid residue was dissolved in ethyl acetate, and the solution was layered with hexane. Crystallization over several days afforded the product as a red crystalline solid, which was filtered off, washed with diethyl ether and pentane, and dried under vacuum. Yield: 0.281 g (85%). 1 H NMR (CDCl3, 25 °C): δ 2.69 (d, 3JPH = 3.0 Hz, 6 H, NMe2), 2.98 (virtual q, 3JHH = 5.0 Hz, 2 H, NHCH2), 3.71 (br s, 2 H, CH2NMe2), 4.58 (vt, J′ = 2.0 Hz, 2 H), 4.73 (br s, 2 H), 4.91 (br s, 2 J


Organometallics

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Pd(OAc)2 and 1.2 mol % of 7) at 90 °C for 2 h. Before the second and the following runs, the reaction mixture was cooled to room temperature and the organic phase was carefully removed. The aqueous residue was washed with toluene (3 × 5 mL) and then reused with fresh reagents (2.0 mmol of 4-bromotoluene, 2.4 mmol of phenylboronic acid, and 4.8 mmol of K2CO3) and toluene (5 mL). The toluene solutions were washed with brine, dried over MgSO4, and evaporated. The coupling product was isolated by column chromatography, and the conversion determined from 1H NMR spectra (see above). X-ray Crystallography. Single crystals suitable for X-ray diffraction analysis were grown by liquid-phase diffusion from ethyl acetate−hexane (5: orange prism, 0.13 × 0.15 × 0.25 mm3; 8: red prism, 0.10 × 0.13 × 0.28 mm3), chloroform−diethyl ether (9: red prism, 0.10 × 0.13 × 0.18 mm3), and from acetone−diethyl ether (10b·2Et2O: red plate, 0.05 × 0.13 × 0.13 mm3) or, alternatively, by cooling solutions in warm acetonitrile (6: orange bar, 0.08 × 0.10 × 0.35 mm3; 7: orange plate, 0.07 × 0.10 × 0.23 mm3). Full-set diffraction data (±h ± k ± l, 2θmax = 52−55°, completeness ≥99.6%) were collected with a Nonius KappaCCD diffractometer equipped with a Cryostream Cooler (Oxford Cryosystems). The measurements were performed at 150(2) K using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). If appropriate, the data were corrected for absorption by methods included in the diffractometer software. Further details on the data collection, structure solution, and refinement are available as Supporting Information (Table S1). The structures were solved by direct methods (SHELXS9733 or SIR-9734) and refined by full-matrix least-squares routines based on F2 (SHELXL9733). The non-hydrogen atoms were refined with anisotropic displacement parameters except for the partly disordered solvent molecules in the structure of 10b·2Et2O, which were refined isotropically. The amide hydrogens (NH) were located on the difference electron density maps and refined as riding atoms. All other hydrogen atoms were included in their calculated positions and refined similarly. Geometric calculations were performed with a recent version of the Platon program.35

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Deng, W.-P.; Hou, X.-L.; Dai, L.-X. J. Organomet. Chem. 2001, 637− 639, 845. (f) Longmire, J. M.; Wang, B.; Zhang, X. J. Am. Chem. Soc. 2002, 124, 13400. For small dendritic amido-amines obtained from (S p )-2-(diphenylphosphino)ferrocene-1-carboxylic acid, see: (g) Lamač, M.; Tauchman, J.; Dietrich, S.; Císařová, I.; Lang, H.; Štěpnička, P. Appl. Organomet. Chem. 2010, 24, 326. (3) Zhang, W.; Shimanuki, T.; Kida, T.; Nakatsuji, Y.; Ikeda, I. J. Org. Chem. 1999, 64, 6247. (4) Representative examples: (a) Zhang, W.; Yoneda, Y.; Kida, T.; Nakatsuji, Y.; Ikeda, I. Tetrahedron: Asymmetry 1998, 9, 3371. (b) Deng, W.-P.; You, S.-L.; Hou, X.-L.; Dai, L.-X.; Yu, Y.-H.; Xia, W.; Sun, J. J. Am. Chem. Soc. 2001, 123, 6508. (c) Drahoňovský, D.; Císařová, I.; Štěpnička, P.; Dvořaḱ ová, H.; Maloň, P.; Dvořaḱ , D. Collect. Czech. Chem. Commun. 2001, 66, 588. (5) (a) El-Faham, A.; Albericio, F. Chem. Rev. 2011, 111, 6557. (b) Valeur, E.; Bradley, M. Chem. Soc. Rev. 2009, 38, 606 , and references therein.. (6) The alternative synthetic routes are represented by directed (usually diastereoselective) ortho-lithiation of tertiary ferrocenecarboxylic amides (6a−f) and the reactions of lithiated phosphinoferrocenes with isocyanates (6g): (a) Tsukazaki, M.; Tinkl, M.; Roglans, A.; Chapell, B. J.; Taylor, N. J.; Snieckus, V. J. Am. Chem. Soc. 1996, 118, 685. (b) Jendralla, H.; Paulus, E. Synlett 1997, 471. (c) Laufer, R. S.; Veith, U.; Taylor, N. J.; Snieckus, V. Org. Lett. 2000, 2, 629. (d) Metallinos, C.; Szillat, H.; Taylor, N. J.; Snieckus, V. Adv. Synth. Catal. 2003, 345, 370. (e) Stavrakov, G.; Philipova, I.; Ivanova, B.; Dimitrov, V. Tetrahedron: Asymmetry 2010, 21, 1845. (f) Philipova, I.; Stavrakov, G.; Chimov, A.; Nikolova, R.; Shivachev, B.; Dimitrov, V. Tetrahedron: Asymmetry 2011, 22, 970. (g) Štěpnička, P.; Solařová, H.; Lamač, M.; Císařová, I. J. Organomet. Chem. 2010, 695, 2423. (7) (a) Podlaha, J.; Š těpnička, P.; Císařová, I.; Ludvík, J. Organometallics 1996, 15, 543. (b) Štěpnička, P. Eur. J. Inorg. Chem. 2005, 3787. (8) Hdpf-amides represent an entry among functional analogues of the ubiquitous 1,1′-bis(diphenylphoshino)ferrocene: Štěpnička, P. 1′Functionalised Ferrocene Phosphines: Synthesis, Coordination Chemistry and Catalytic Applications. In Ferrocenes: Ligands, Materials and Biomolecules; Štěpnička, P., Ed.; Wiley: Chichester, 2008; Chapter 5, p 177. (9) Meca, L.; Dvořaḱ , D.; Ludvík, J.; Císařová, I.; Štěpnička, P. Organometallics 2004, 23, 2541. See also refs 4a and 4c. (10) For an overview of the chemistry of hybrid phosphine ligands, see: (a) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem. 1999, 48, 233. (b) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27. (11) For books and review articles summarizing the chemistry of phosphinoferrocene donors, see: (a) Ferrocenes: Ligands, Materials and Biomolecules; Štěpnička, P., Ed.; Wiley: Chichester, 2008. (b) Ferrocenes: Homogeneous Catalysis, Organic Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; Wiley-VCH: Weinheim, 1995. (c) Atkinson, R. C. J.; Gibson, V. C.; Long, N. J. Chem. Soc. Rev. 2004, 33, 313. (d) Barbaro, P.; Bianchini, C.; Giambastiani, G.; Parisel, S. L. Coord. Chem. Rev. 2004, 248, 2131. (e) Goméz Arrayás, R.; Adrio, J.; Carretero, J. C. Angew. Chem., Int. Ed. 2006, 45, 7674. (12) Kühnert, J.; Lamač, M.; Demel, J.; Nicolai, A.; Lang, H.; Štěpnička, P. J. Mol. Catal. A: Chem. 2008, 285, 41. (13) (a) Lamač, M.; Tauchman, J.; Císařová, I.; Štěpnička, P. Organometallics 2007, 26, 5042. (b) Schulz, J.; Císařová, I.; Štěpnička, P. J. Organomet. Chem. 2009, 694, 2519. (c) Tauchman, J.; Císařová, I.; Štěpnička, P. Organometallics 2009, 28, 3288. (d) Tauchman, J.; Císařová, I.; Štěpnička, P. Eur. J. Org. Chem. 2010, 4276. (e) Tauchman, J.; Císařová, I.; Štěpnička, P. Dalton Trans. 2011, 40, 11748. (f) Schulz, J.; Císařová, I.; Štěpnička, P. Organometallics 2012, 31, 729. (g) Tauchman, J.; Therrien, B.; Süss-Fink, G.; Štěpnička, P. Organometallics 2012, 31, 3985. (h) Schulz, J.; Císařová, I.; Štěpnička, P. Eur. J. Inorg. Chem. 2012, 5000. (i) Tauchman, J.; Süss-Fink, G.; Štěpnička, P.; Zava, O.; Dyson, P. J. J. Organomet. Chem. 2013, 723, 233.

ASSOCIATED CONTENT

S Supporting Information *

Diagrams depicting the H-bonding interaction in the structures of 5−7, 1H VT NMR spectra of complex 8, an overlap of the crystallographically independent molecules of 9, a tabular summary of relevant crystallographic data, and complete crystallographic data in the standard CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Czech Science Foundation (grant no. 13-08890S) and the Ministry of Education, Youth and Sports of the Czech Republic (project no. MSM0021620857) is gratefully acknowledged.

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REFERENCES

(1) Štěpnička, P. Chem. Soc. Rev. 2012, 41, 4273. (2) (a) You, S.-L.; Hou, X.-L.; Dai, L.-X.; Cao, B.-X.; Sun, J. Chem. Commun. 2000, 1933. (b) Longmire, J. M.; Wang, B.; Zhang, X. Tetrahedron Lett. 2000, 41, 5435. (c) You, S.-L.; Hou, X.-L.; Dai, L.-X.; Zhu, X.-Z. Org. Lett. 2001, 3, 149. (d) You, S.-L.; Hou, X.-L.; Dai, L.-X. J. Organomet. Chem. 2001, 637−639, 762. (e) You, S.-L.; Luo, Y.-M.; K


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(14) (a) Kühnert, J.; Dušek, M.; Demel, J.; Lang, H.; Štěpnička, P. Dalton Trans. 2007, 2802. (b) Kühnert, J.; Císařová, I.; Lamač, M.; Štěpnička, P. Dalton Trans. 2008, 2454. (c) Štěpnička, P.; Krupa, M.; Lamač, M.; Císařová, I. J. Organomet. Chem. 2009, 694, 2987. (15) (a) Feng, X.; Pugin, B.; Kusters, E.; Sedelmeier, G.; Blaser, H.-U. Adv. Synth. Catal. 2007, 349, 1803 (amides from carboxylated Josiphos). (b) Lamač, M.; Císařová, I.; Štěpnička, P. Eur. J. Inorg. Chem. 2007, 2274 (amides of (R,Rp)-2-[1-(diphenylphosphino)ethyl] ferrocenecarboxylic acid). (c) Lamač, M.; Císařová, I.; Štěpnička, P. New J. Chem. 2009, 33, 1549 (amides from planar-chiral, monocarboxylated 1,1′-bis(diphenylphosphino)ferrocene). See also refs 2 and 4. (16) (a) Freixa, Z.; Leeuwen, P. W. N. M. Coord. Chem. Rev. 2008, 252, 1755. (b) Bessel, C. A.; Aggarwal, P.; Marschilok, A. C.; Takeuchi, K. J. Chem. Rev. 2001, 101, 1031. (17) The energy barrier for the rotation of the cyclopentadienyl rings in the gas phase was estimated to be as low as ca. 4 kJ mol−1 (see references below). Both the reaction studies and structural investigations suggest that the conformation mobility of ferrocene is maintained at least partly in its derivatives unless the ferrocene unit becomes heavily substituted or bridged. (a) Haaland, A. Acc. Chem. Res. 1979, 12, 415. (b) Gardner, A. B.; Howard, J.; Waddington, T. C.; Richardson, R. M.; Tomkinson, J. Chem. Phys. 1981, 57, 453. (18) (a) Pinault, N.; Bruce, D. W. Coord. Chem. Rev. 2003, 241, 1. (b) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643. (c) Aqueous-Phase Organometallic Catalysis, 2nd ed.; Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim, 2004. (19) Selected examples for [Ph2PCH2CH2NMe3]X (amphos): (a) Smith, R. T.; Baird, M. C. Transition Met. Chem. 1981, 6, 197. (b) Smith, R. T.; Baird, M. C. Inorg. Chim. Acta 1982, 62, 135. (c) Smith, R. T.; Ungar, R. K.; Sanderson, L. J.; Baird, M. C. Organometallics 1983, 2, 1138. Amphos analogues: (d) Peiffer, G.; Chhan, S.; Bendayan, A.; Waegell, B.; Zahra, J.-P. J. Mol. Catal. 1990, 59, 1. (e) Bitterer, F.; Kucken, S.; Stelzer, O. Chem. Ber. 1995, 128, 275. (f) Hessler, A.; Kucken, S.; Stelzer, O.; Blotevogel-Baltronat, J.; Sheldrick, W. S. J. Organomet. Chem. 1995, 501, 293. (g) Papagni, A.; Trombini, C.; Lombardo, M.; Bergantin, S.; Chams, A.; Chiarucci, M.; Miozzo, L.; Parravicini, M. Organometallics 2011, 30, 4325. (20) The compound is typically contaminated by the corresponding phosphine oxide (ca. 5%), which cannot be efficiently removed by column chromatography or crystallization. (21) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1. (22) Hartley, F. R. The Chemistry of Platinum and Palladium; Applied Science: London, 1973. (23) (a) Butler, I. R.; Kalaji, M.; Nehrlich, L.; Hursthouse, M.; Karaulov, A. I.; Malik, K. M. A. Chem. Commun. 1995, 459. (b) Hildebrandt, A.; Wetzold, N.; Ecorchard, P.; Walfort, B.; Rüffer, T.; Lang, H. Eur. J. Inorg. Chem. 2010, 3615. (24) Selected P,N-chelates: (a) Van Der Steen, F. H.; Kanters, J. A. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1986, 42, 547. (b) Richards, C. J.; Hibbs, D. E.; Hursthouse, M. B. Tetrahedron Lett. 1995, 36, 3745. (c) Ahn, K. H.; Cho, C.-W.; Baek, H.-H.; Park, J.; Lee, S. J. Org. Chem. 1996, 61, 4937. (d) Mernyi, A.; Kratky, C.; Weissensteiner, W.; Widhalm, M. J. Organomet. Chem. 1996, 508, 209. (e) Woo, T. K.; Pioda, G.; Rothlisberger, U.; Togni, A. Organometallics 2000, 19, 2144. (f) Liptau, P.; Seki, T.; Kehr, G.; Abele, A.; Fröhlich, R.; Erker, G.; Grimme, S. Organometallics 2003, 22, 2226. (g) Metallinos, C.; Zaifman, J.; Van Belle, L.; Dodge, L.; Pilkington, M. Organometallics 2009, 28, 4534. (h) Štěpnička, P.; Schulz, J.; Klemann, T.; Siemeling, U.; Císařová, I. Organometallics 2010, 29, 3187. (i) Schuecker, R.; Zirakzadeh, A.; Mereiter, K.; Spindler, F.; Weissensteiner, W. Organometallics 2011, 30, 4711. Representative examples of P,P-chelates: (j) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K. J. Am. Chem. Soc. 1984, 106, 158. (k) Hierso, J.-C.; Fihri, A.; Amardeil, R.; Meunier, P.; Doucet, H.; Santelli, M.; Donnadieu, B. Organometallics 2003, 22, 4490. (l) Hagopian, L. E.; Campbell, A. N.; Golen, J. A.; Rheingold, A. L.; Nataro, C. J. Organomet. Chem. 2006, 691, 4890. (m) Cortes, J. G. L.;

Ramon, O.; Vincendeau, S.; Serra, D.; Lamy, F.; Daran, J.-C.; Manoury, E.; Gouygou, M. Eur. J. Inorg. Chem. 2006, 5148. (n) Wang, Y.; Weissensteiner, W.; Spindler, F.; Arion, V. B.; Mereiter, K. Organometallics 2007, 26, 3530. (o) Wang, Y.; Sturm, T.; Steurer, M.; Arion, V. B.; Mereiter, K.; Spindler, F.; Weissensteiner, W. Organometallics 2008, 27, 1119. (p) Buergler, J. F.; Togni, A. Organometallics 2011, 30, 4742. (q) Štěpnička, P.; Císařová, I.; Schulz, J. Organometallics 2011, 30, 4393 and ref 24f. (25) Analogous cis complexes exert much smaller coupling constants. Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition Metal Phosphane Complexes. In NMR Basic Principles and Progress; Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer: Berlin, 1979; Vol. 16, Chapter E, p 65, and references therein. (26) The largest distance from the least-squares plane of 0.068(1) Å is seen for the phosphorus atom. (27) See the dihedral angles C25−N2−P−C1 = −12.5(3)°, C26− N2−P−C12 = −10.7(3)°, and C27−N2−P−C18 = −12.3(3)°. (28) Tani, K.; Yabuta, M.; Nakamura, S.; Yamagata, T. J. Chem. Soc., Dalton Trans. 1993, 2781. (29) The signals observed at δP 15.8 and 15.9 can also be the central lines of a four-line AB spin system pattern. We did not observe clearly any satellite lines. Nonetheless, the intensity of such lines can be expected to be very low considering the relatively small chemical shift difference and a large 2JPP interaction constant. (30) Miyaura, N. In Metal-Catalyzed Cross-Coupling Reactions, 2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004, Vol. 1, Chapter 2, p 41. (b) Miayura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (c) Suzuki, A. J. Organomet. Chem. 1999, 576, 147. (d) Miyaura, N. Top. Curr. Chem. 2002, 219, 11. (31) (a) Chanda, A.; Fokin, V. V. Chem. Rev. 2009, 109, 725. (b) Butler, R. N.; Coyne, A. G. Chem. Rev. 2010, 110, 6302. (32) Štěpnička, P.; Schulz, J.; Císařová, I.; Fejfarová, K. Collect. Czech. Chem. Commun. 2007, 72, 453. (33) Sheldrick, G. M. Acta Crystallogr. A, Fundam. Crystallogr. 2008, 64, 112. (34) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115. (35) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.

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