Article pubs.acs.org/Organometallics
Synthesis and Reactivity of Palladium- and Platinum-Bridged Heterobimetallic [3]Trochrocenophanes Holger Braunschweig,* Maria Friedrich, Krzysztof Radacki, and Justin Wolf Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, D-97074, Würzburg Germany S Supporting Information *
ABSTRACT: Heterobimetallic [3]trochrocenophanes with PdCl2 and PtCl2 bridges were prepared in reasonable yields. The PdCl2 species possess, like their Pt analogues, poor solubility but can be made more soluble by ligand substitution. By reaction of Pd-bridged [3]trochrocenophanes with MeLi, both Cl atoms can be substituted by a Me group. Likewise, reaction of Pt-bridged complexes with LiCCPh leads to the expected disubstituted compound. Herein we present the synthesis of MCl2- and MR2-bridged (M = Pd, Pt; R = Me, CCPh) [3]trochrocenophanes, as well as some solid-state structures of these [3]trochrocenophanes.
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INTRODUCTION Heteroleptic metalloarenophanes have aroused increasing interest in the past few years owing to their unique structure, bonding, and reactivity patterns. A multitude of different bridging atoms and metalloarene moieties have now been successfully incorporated into novel heteroleptic [n]metalloarenophanes.1 In addition to main-group-elementbridged systems, transition-metal-bridged representatives were also introduced.1b Recently, novel ansa complexes featuring cyclooctatetraene ligand fragments in the metalloarene framework were reported for the first time.1c Due to recent synthetic efforts in the field of heteroleptic [n]metalloarenophanes, [1]and [2]metalloarenophanes ([M(η5-C5H4)(η7-C7H6)ERx] (M = Ti,1d,2 V,1a,2 Cr1b,j,l,3), [Mn(η5-C5H4)(η6-C6H5)ERx]1b,e,g) were prepared by simple salt-elimination reactions on the basis of the dilithiated species [M(η5-C5H4Li)(η7-C7H6Li)]·tmeda/ pmdta1a,l,6 and [Mn(η5-C5H4Li)(η6-C6H5Li)·pmdta.1g Highstrain representatives, for example, are precursors for metalcontaining macromolecules.1a,j,2a In contrast to the well-known heteroleptic [n]metalloarenophanes, few 1,1′-disubstituted heteroleptic species of the form [M(η 5 -C 5 H 4 ER x )(η 7 C7H6ERx)] (M = Ti4, Cr3,5) are known, although 1,1′bis(phosphanyl)troticenes were reported in 1989 (ERx = PPh2)4b and 1991 (ERx = PMe2).4a An improved synthesis of these 1,1′-bis(phosphanyl)troticenes was reported in 2009 with successful conversion to a couple of early/late heterobimetallic complexes, but without any further reactivity.6 Recently we have established a synthetic protocol for the related unsymmetrical 1,1′-bis(phosphanyl)trochrocene derivatives [Cr(η5C5H4PR2)(η7-C7H6PR2)] (1, R = Ph; 2, Cy; 3, Me) (Scheme 1) and their conversion to [3]trochrocenophanes by chelating a further metal by the phosphine substituents.5 So far, larger bridges in [n]trochrocenophanes (n > 2) have only been © 2012 American Chemical Society
Scheme 1. Unsymmetric 1,1′-Bis(phosphanyl)trochrocenes 1−3
accessible via subsequent B−B1l or Si−Si1i bond-activation chemistry. With these chelating ligands (1, R = Ph; 2, Cy; 3, Me) in hand, a wide range of P−M−P ansa bridges are accessible. Herein we present the first late-transition-metal complexes based on chelating 1,1′-bis(phosphanyl)trochrocenes and their reactivity and probe their applicability as C−C coupling catalysts using one established example, the Heck reaction.
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RESULTS AND DISCUSSION [3]Trochrocenophanes. By reaction of the aforementioned 1,1′-trochrocenophanes (1−3) with late-transition-metal dichloride complexes [(cod)PdCl2] (cod = 1,5-cyclooctadiene) or [(Ph3P)2PtCl2] in thf at slightly elevated temperatures (75 °C; 4, 3 h; 5, 20 min; 6, 30 min; 7, 2 h; 8, 5 h; 9, 1.5 h) the new [3]trochrocenophanes [Cr(η5-C5H4PR2)(η7-C7H6PR2)MCl2] (M = Pd, R = Ph (4), Cy (5), Me (6); M = Pt, R = Ph (7), Cy (8), Me (9)) were synthesized with liberation of cod and PPh3, respectively (Scheme 2). Received: November 14, 2011 Published: March 16, 2012 3027
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Scheme 2. Heterobimetallic [3]Trochrocenophanes 4−9
The reaction can be monitored by 31P NMR spectroscopy, revealing, in the case of 4, 5, 7, and 8, concomitant consumption of the starting material and formation of the product. However, 6 and 9 proved insoluble in common solvents such as pentane, benzene, toluene, thf, dmso, acetonitrile, and others; therefore, only the consumption of the starting material can be observed spectroscopically. In the case of 4, 5, 7, and 8, the products give rise to two doublets in the 31P NMR spectrum at higher field (Table 1), in comparison Table 1. 31P NMR Shifts (ppm) and 2JP,P Coupling Constants (Hz) of [3]Trochrocenophanes 4, 5, 7, and 8 (C6D6) 4 δ(31P) 2
JP,P JP,Pt
1
56.63 (P7), 22.51(P5) 20.1
5 70.54 (P7), 35.50 (P5) 21.1
7 34.59 (P7), 5.69 (P5) 8.9 not detected
Figure 1. Molecular structure of 5 in the solid state. Hydrogen atoms and ellipsoids of the cyclohexyl groups, as well as the disordered component, are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.
8
ideal 90°, except for the chelate angle (P1−Pd−P2 = 103.39(4) °). The trochrocene moiety in 5 is, as expected, not affected by bridging, which is reflected by the high deformation angle δ ≈ 178° (centroid−Cr−centroid) and the low tilt angle α ≈ 2°. Due to the cis conformation, the torsion angle C1−XCp−XCht− C2 (XCp/Cht = centroid of the C5H4/C7H6 ring) decreases to ≈34°, while in the nonbridged 1,1′-trochrocene 2, an anticlinal alignment (149°) can be found.5 In comparison to analogous metalloarenophanes,5−8 all revealed parameters are similar. The Pd−P bond lengths are very similar to those of the corresponding ferrocenophane [Fe(η5-C5H4PCy2)2PdCl2], with Pd−P1 = 2.305(1) Å and Pd−P2 = 2.292(1) Å (ferrocenophane: 2.287 Å).8 The geometrical parameters of 7 and 8 were confirmed by Xray diffraction analyses (Figure 2). Their structures are analogous to that of 5, although disorder in the trochrocene backbone and the cyclohexyl groups precludes their detailed discussion. Methylation of 4−6 and 9. Since we could not obtain acceptable 1H or 13C NMR data of the palladium-bridged compounds 4 and 5 or 31P NMR data of 6 and 9, due to the poor solubility of these complexes, we substituted the chloride ligands bound to the late-transition-metal center by methyl groups in order to enhance their solubility and to verify their spectroscopic properties (Scheme 3). The appropriate metal dihalide was cooled to −25 °C and treated with MeLi (5 equiv). After complete addition, the reaction mixture was stirred for 10 min at this temperature, warmed to ambient temperature, and stirred for an additional 12 h. All volatiles were removed under reduced pressure, and the resulting residue was washed with pentane at ambient temperature, extracted into toluene, and filtered. After removal of all volatile components, 11−13 were obtained as light blue solids and 10 as a brown solid, in adequate yields (30−48%).
38.33 (P7), 10.22 (P5) 6.1 3691 (P7), 3659 (P5)
to 1 and 2. The coupling constants are in the expected range, by comparison with analogous ferrocenophanes (1JP,Pt = 3778 Hz)7 and troticenophanes (2JP,P = 13.4 Hz, 1JP,Pt = 3780 (C5H4PPh2), 3812 Hz (C7H6PPh2)).6 The 1JP,Pt coupling constants of 7, as well as 1H and 13C NMR spectra of all PdCl2and PtCl2-bridged [3]trochrocenophanes, could not be measured due to their low solubility. In all cases the product precipitates directly after formation and cannot be redissolved. All products (4−9) were washed with thf and pentane at ambient temperature and dried in vacuo at 70 °C and could be isolated as analytically pure solids, as validated by elemental analysis. In the case of 7 and 9 the solid includes solvent molecules (7, thf; 9, 0.5 thf). The compounds 4−9 have very low solubility in most common organic solvents, virtually eliminating recrystallization as a method for obtaining good-quality crystals. The crystals used for X-ray crystallographic analyses were grown directly from the reaction solution. For this reason the data for 7 and 8 are not adequate for extensive discussion; however the X-ray data confirm the overall geometry of both compounds (see Figure 2). The crystallographic data of 5 are of good quality; however, the disorder of both rings in the trochrocene backbone prevents discussion of this part of the molecule. As previously shown for [3]trochrocenophanes bridged by M(CO)4 (M = Cr, Mo, W),5 both phosphorus atoms in 5 are eclipsed in order to allow bidentate coordination of the chelating diphosphine (Figure 1; C1−P1−Pd = 121.4(5)°, C2−P2−Pd = 120.0(6)°). Consequently, the phosphorus atoms are mutually cis at the square-planar palladium, reflected by the angles around Pd, which are all slightly smaller than the 3028
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Figure 2. Molecular structures of 7 (left) and 8 (right) in the solid state. Hydrogen atoms and ellipsoids of the phosphanyl substituents and minor disordered components are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.
Scheme 3. Methylation of 4−6 and 9
Hz; 11, δ 41.00, 15.75; 2JP,P = 17.4 Hz; 12, δ 9.73, −18.83; 2JP,P = 19.6 Hz). In 13 these signals can be found in an region analogous to that of 12 (13, δ 10.33, −18.06) and with a similar coupling constant of both P atoms (2JP,P = 11.2 Hz) and an additional coupling to 195Pt (1JP7,Pt = 1854 Hz, 1JP5,Pt = 1830 Hz). X-ray diffraction studies finally confirm the connectivity of 11 and 13 in the solid state (Figures 3 and 4). The trochrocene backbone in the solid-state structures of 5 and 11 suggests little variance. In 11 the coplanar arrangement of both rings is less affected, reflected by the deformation angle δ = 177.8° and the tilt angle α = 2.8° (C1−P1−Pd = 117.82(5) °, C2−P2−Pd = 122.50(5)°). The angles around Pd are similar: the bite angle and the angles containing P1 or P2 are mildly widened (P1−Pd−P2 (bite angle) = 104.28(1)°), while the remaining angle C3−Pd−C4 is reduced to 81.27(6)°. The coordination around Pd is no longer square planar, in that C3 and C4 lie slightly above and below an imaginary plane containing P1, Pd, and P2 (C4, 0.08 Å; C3, 0.28 Å). The distances between the phosphorus atoms and the ipso carbon atoms of the trochrocene moiety are similar to those of 2 (11, C1−P1 = 1.8125(16) Å, C2−P2 = 1.8494(15) Å; 2, C1−P1 = 1.8121(3) Å, C2−P2 = 1.853(2) Å).5 The palladium-containing bond distances are elongated compared to those of 5 (P1−Pd = 2.3242(5) Å, P2−Pd = 2.3469(4) Å) and the distances to the Me groups are comparable (C4−Pd = 2.1204(15) Å, C3−Pd = 2.1269(15) Å). As expected, the solid-state structure of 13 is similar to those of the previously discussed trochrocenophane derivatives and represents the first structural characterization of a 1,1′-
For complexes 10−13 the NMR spectroscopic data of the trochrocene moiety are very similar and differ insignificantly from those of the precursor 1,1′-trochrocenes 1−3.5 As previously described for metal−carbonyl-bridged [3]trochrocenophanes, the NMR data indicate the absence of any molecular ring strain. As a result, the signals for the C7H6 protons (10, δ 6.04 (2H), 5.25 (2H), 5.11 (2H); 11, δ 5.97 (2H), 5.51 (4H); 12, δ 5.57 (2H), 5.43 (2H), 5.28 (2H); 13, δ 5.67 (2H), 5.48 (2H), 5.27 (2H)) as well as the C5H4 protons (10, δ 4.03 (2H), 3.57 (2H); 11, δ 4.06 (2H), 3.81 (2H); 12, δ 3.70 (2H), 3.65 (2H); 13, δ 3.71 (2H), 3.66 (2H)) are shifted downfield in comparison to the parent molecule [Cr(η5C5H5)(η7-C7H7)] (δ 5.45 (7H), 3.66 (5H)), an effect previously noted for other 1,1′-disubstituted trochrocenes.3,5 The methyl groups are all detected in the expected range as multiplets; the Pd-bound Me groups are found in relatively similar positions (10, δ 1.15 (3H), 1.03 (3H), 11, δ 1.09 (3H), 0.98 (3H), 12, δ 1.02 (3H), 0.93 (3H)), while the Pt−Me groups are shifted downfield to δ 1.29 and 1.21 with the same integration ratio of 3:3. Like the 1H NMR parameters, the 13C NMR spectra resemble those of the nonbridged complexes 1− 3. While the Me groups bound to the metal center in 12 can be detected as doublets, the Me groups of 10 and 11 are detected as broad multiplets and one of the signals in 10 (δ 11.13 (br)) can only be identified by HMBC experiments. The separation of the 31P NMR signals of the two phosphorus nuclei is larger and the resonances are shifted to high field in comparison to the PdCl2 species (4−6). The coupling constants are similar and lie in the range of 20 Hz (10, δ 44.45, 17.12; 2JP,P = 21.3 3029
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around Pt is ideal square planar, with respect to the imaginary plane containing P1, Pt, and P2, in which C3 (0.03 Å) and C4 (0.00 Å) lie perfectly in this plane. All other angles and distances are in the expected range (P1−Pt = 2.2789(14) Å, P2−Pt = 2.2711(13) Å, C3−Pt = 2.103(5) Å, C2−Pt = 2.109(5) Å, P1−Pt−P2 = 102.29(5)°). Reaction of 7 and 8 with LiCCPh. Wong et al. demonstrated that ferrocene analogues of 7 and 8 undergo substitution of both Cl atoms by a phenylacetylide group via a CuI-catalyzed chloride-to-alkyne metathesis.9 Due to the low solubility of the metal dichloride systems, we substituted both Cl atoms by direct salt-elimination reaction of the dichloride precursor with LiCCPh. In the case of 7 and 8 a suspension of the dichloride complex was treated with 2 equiv of LiC CPh in benzene for 60 min at 75 °C. If these complexes are kept longer at this temperature, they decompose with loss of the nonbridged 1,1′-bis(phosphanyl)trochrocene. At lower temperatures (50 °C) the reaction takes longer, but with a similar extent of decomposition. Complexes 14 and 15 were isolated as brown (14) or light green (15) solids in yields of 37−59%. 31 P NMR spectra of 14 and 15 show two different sets of signals for the two nonequivalent phosphorus nuclei. In complex 14 they can be detected at δ 36.79 and 8.56 with a P−P coupling constant of 17.4 Hz and additional P−Pt coupling constants of 2319 Hz for the C5H4−P nucleus and 2338 Hz for the C7H6−P nucleus, respectively. The P nucleus bound to C5H4 in 15 can be detected at δ 10.35 with P−P coupling constant of 16.2 Hz and P−Pt coupling constant of 2327 Hz, while the P nucleus bound to C7H6 reveals a signal at δ 37.14 with the corresponding coupling constants of 16.2 Hz (P−P) and 2316 Hz (P−Pt). The 1H and 13C NMR data of 14 and 15 are nearly unaffected in comparison to those of the nonbridged counterparts 1 and 2, though with additional signals for the CCPh units. The quaternary C atoms could not be detected in the 13C NMR spectra; however, IR and UV−vis spectroscopy of 14 and 15 reveal signals for the CC vibrations in the expected range. The solid-state IR spectrum of 14 shows broad bands for the CC vibration at 2087 and 2117 cm−1; in 15 it can be detected at 2117 cm−1. This is in agreement with the analogous ferrocene complex [(dppf)Pt(CCPh)2], which shows two CC stretching vibrations at ca. 2112 and 2120 cm−1.9 UV−vis spectra, recorded in hexane, exhibit absorption bands with vibronic contibutions from the CCPh ligand around 257 and 328 nm (Figure 5, black line) for 14 and for 15 at 254, 265, and 311 nm (Figure 5, gray line), similar to data of other alkynyl platinum complexes.10 The absorption bands for 14 were difficult to detect due to its low solubility in hexane but can be found in regions similar to those detected for 15. Single crystals of 14 and 15 were obtained from C6D6 solutions at ambient temperature (Figure 6). Comparison of
Figure 3. Molecular structure of 11 in the solid state. Hydrogen atoms and ellipsoids of the cyclohexyl groups are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.
Figure 4. Molecular structure of 13 in the solid state. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.
bis(dimethylphosphanyl)trochrocene (Figure 4). The deformation angle δ = 179.6° and the tilt angle α = 1.7° indicate an almost ideal parallel arrangement (C1−P1−Pt = 123.65(17)°, C2−P2−Pt = 120.50(17)°). The torsion angle (36.0°) is comparable to those detected in other [3]trochrocenophanes,5 as are the C−P distances at the trochrocene moiety (C1−P1 = 1.818(5) Å, C2−P2 = 1.830(5) Å). The coordination sphere Scheme 4. Synthesis of Alkynyl Platinum Complexes 14 and 15
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Catalytic Activity of 4−6. The first chelating metalloarenebackbone ligand used in cross-coupling reactions was dppf (16).11 Chiral derivatives have generated great interest in enantioselective processes, while the first asymmetric metalloarene-based ligand (N,N-dimethyl-1-[2(diphenylphosphanyl)ferrocenyl]ethylamine, ppfa),12 highly active when used as a ligand for catalysis, spurred research into further ferrocenyl-based ligand systems.13 Our recently reported 1,1′-bis(phosphanyl)trochrocenophanes5 are potential precursors for C−C coupling reactions. For this reason we investigated their catalytic activity and their product selectivity in one established example, the Heck coupling of bromobenzene with styrene to cis- and trans-stilbene. All catalysts (4−6 and 16) react with an excellent selectivity of >99% to trans-stilbene, while the extents of conversion vary (21−94%). The reactions were completed after comparatively short times, but with poor TON and TOF rates (Table 3) in comparison to those of common ligand systems. Given the poor performance of these catalysts in comparison with established systems,14 no further investigations were conducted with different educts or other coupling reactions.
Figure 5. UV−vis spectra of complex 14 (black) and 15 (gray) in hexane.
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the surroundings of the bridging metal with those of the analogous dppf complex9 shows that all geometric parameters are similar. The geometry around Pt is square planar with two CCPh groups bound mutually cis and CC distances in the expected range (14, C5−C6 = 1.191(5) Å, C3−C4 = 1.194(5) Å; 15, C5−C6 = 1.200(9) Å, C3−C4 = 1.1963 Å; [(dppf)Pt(CCPh)2], C5−C6 = 1.195(2) Å, C3−C4 = 1.199(2) Å). As shown for the [3]trochrocenophanes 5, 11, and 13, C−P−M angles are around 110−125° (14, C1−P1−Pt = 123.6(7)°, C2−P2−Pt = 114.7(3)°; 15, C1−P2−Pt = 123.3(2)°, C2−P2−Pt = 120.0(2)°). In comparison to the analogous ferrocene complex, all other angles and bond lengths are also in the expected range (Table 2). The trochrocene backbone in 14 shows partial disorder of the aromatic rings. In 15 a disordered component is located at C3/C4.
CONCLUSIONS In this contribution, we have reported the synthesis of latetransition-metal dichloride complexes to heterobimetallic metalloarenophanes. These PdCl2- and PtCl2-bridged [3]trochrocenophanes 4−9 can be converted to their soluble counterparts 10−15. By reaction of the PtCl2-bridged, Ph- and Cy-substituted bis(phosphanyl)trochrocenes (7 and 8) with LiCCPh the expected disubstituted complexes (14 and 15) can be synthesized. The Me-substituted counterparts 10−13 can be prepared analogously by reaction of 4−6 and 9 with MeLi. Additionally, the molecular structures of 5, 7, 8, 11, and 13−15 were determined by X-ray diffraction analyses. Thus, we have demonstrated that the metallocenophanes 1−3 can act as excellent ligands to late transition metals, analogous to the reactivity we recently observed with group 6 hexacarbonyls.5
Figure 6. Molecular structures of 14 (left) and 15 (right) in the solid state. Hydrogen atoms, ellipsoids of the phosphanyl substituents, and minor disordered components are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. 3031
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Table 2. Bond Distances (Å) and Angles (deg) for 14 and 15a 14 15 a
δ
α
torsion angle
P2−Pt−C3, C3−Pt−C5
P1−Pt−P2, P1−Pt−C5
Pt−P1
Pt−P2
Pt−C5
Pt−C3
∼178.9 178.12
∼2.6 3.21
∼37.7 31.25
88.39(19), 88.26(14) 88.78(19), 81.78(20)
100.62(3), 82.83(9) 103.85(6), 86.55(18)
2.3122(9) 2.3035(16)
2.3000(10) 2.3193(18)
2.016(4) 2.021(6)
2.008(3) 1.971(3)
Only the major disordered component is discussed. Anal. Calcd for C16H22CrP2PdCl2 (505.61): C, 38.01; H, 4.39. Found: C, 37.15; H, 4.41. [Cr(η5-C5H4PPh2)(η7-C7H6PPh2)PtCl2] (7). A mixture of [Cr(η5C5H4PPh2)(η7-C7H6PPh2)] (1; 60 mg, 100 μmol) and [(Ph3P)2PtCl2] (82 mg, 100 μmol) in thf (1.5 mL) was heated (75 °C; 2 h) in an oil bath. The brown suspension dissolved and a dark brown solid precipitated. The solid was washed with pentane (3 × 3 mL), stirred with thf (2 × 3 mL; 12 h), washed with pentane (3 × 3 mL), and dried in vacuo at 70 °C (1 h). Complex 7 was isolated as a brown solid. Crystals suitable for X-ray analysis were obtained directly from the reaction mixture. Yield: 60 mg (71 μmol, 71%). 31 1 P{ H} NMR (162 MHz, THF): δ 5.69 (d, P5, 2JP5,P7 = 8.9 Hz), 34.59 (d, P7, 2JP7,P5 = 8.9 Hz). Anal. Calcd for C36H30CrP2PtCl2·thf (914.66): C, 52.53; H, 4.19. Found: C, 52.60; H, 4.19. [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)PtCl2] (8). Complex 8 was prepared similarly to 7, using [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)] (2; 60 mg, 100 μmol) and [(Ph3P)2PtCl2] (77 mg, 98 μmol) in thf (1.5 mL; 75 °C; 5 h). The blue-white suspension turned gray, and a brown solid precipitated. Complex 8 was isolated as a gray-brown solid. Crystals suitable for X-ray analysis were obtained directly from the reaction mixture. Yield: 57 mg (65 μmol, 67%). 31 1 P{ H} NMR (162 MHz, THF): δ 10.22 (d, P5, 2JP5,P7 = 6.1 Hz, 1 JP5,Pt = 3659 Hz), 38.33 (d, P7, 2JP7,P5 = 6.1 Hz, 1JP7,Pt = 3691 Hz). Anal. Calcd for C36H54CrP2PtCl2 (866.74): C, 49.89; H, 6.28. Found: C, 49.80; H, 6.52. [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)PtCl2] (9). Complex 9 was prepared similarly to 7, using [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)] (3; 45 mg, 140 μmol) and [(Ph3P)2PtCl2] (107 mg, 135 μmol) in thf (1 mL; 75 °C; 90 min). Yield: 42 mg (70 μmol, 50%) as a blue-black solid. Anal. Calcd for C16H22CrP2PtCl2·0.5thf (629.02): C, 34.34; H, 4.17. Found: C, 34.20; H, 4.01. [Cr(η5-C5H4PPh2)(η7-C7H6PPh2)PdMe2] (10). Complex 4 (100 mg, 133 μmol) in Et2O was cooled to −25 °C, and MeLi (1.6 M, 0.44 mL, 660 μmol) was added. After the mixture was stirred for 10 min at this temperature, the cooling bath was removed and stirring was continued at ambient temperature for 12 h. After removal of all volatiles, the remaining solid was washed with pentane (3 × 3 mL). The product was dissolved in toluene (∼10 mL), and after filtration and removal of all volatiles 10 could be obtained as a brown solid. Yield: 33 mg (46 μmol, 35%). 1 H NMR (500.1 MHz, C6D6): δ 1.03 (m, 3H, CH3), 1.15 (m, 3H, CH3), 3.57 (m, 2H, β-C5H4), 4.03 (m, 2H, α-C5H4), 5.11 (m, 2H, βC7H6), 5.25 (m, 2H, γ-C7H6), 6.04 (m, 2H, α-C7H6), 7.03−7.05 (m, 6H, C6H5), 7.06−7.09 (m, 6H, C6H5), 7.75 (m, 4H, C6H5), 8.06 (m, 4H, C6H5). 13C{1H} NMR (126 MHz, C6D6): δ 11.13 (br, CH3), 11.48 (s, CH3), 79.70 (d, β-C5H4, 3JC,P5 = 5.2 Hz), 81.57 (d, α-C5H4, 2 JC,P5 = 11.5 Hz), 86.62 (d, β-C7H6, 3JC,P7 = 9.7 Hz), 88.65 (s, γ-C7H6), 92.93 (d, α-C7H6, 2JC,P7 = 17.6 Hz), 129.71 (m, p-C6H5), 130.02 (m, pC6H5), 135.10 (d, o-C6H5, 2JC,P5 = 13.1 Hz), 136.53 (d, o-C6H5, 2JC,P7 = 13.2 Hz) (the remaining signals for C6H5 are obscured by the solvent signal; i-C6H5 not detectable). 31P{1H} NMR (202 MHz, C6D6): δ 17.12 (d, P5, 2JP5,P7 = 21.3 Hz), 44.45 (d, P7, 2JP7,P5 = 21.3 Hz). Anal. Calcd for C38H36CrP2Pd (713.06): C, 64.01; H, 5.09. Found: C, 63.45; H, 5.51. [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)PdMe2] (11). Complex 11 was prepared similarly to 10 using 5 (100 mg, 130 μmol) in Et2O (4 mL) and MeLi (1.6 M, 0.43 mL, 640 μmol). 11 was isolated as a blue solid. Crystals suitable for X-ray analysis were obtained from toluene/hexane at ambient temperature. Yield: 46 mg (62 μmol, 48%). 1 H NMR (500.1 MHz, C6D6): δ 0.98 (m, 3H, CH3), 1.09 (m, 3H, CH3), 1.11−2.64 (m, 44H, C6H11), 3.81 (m, 2H, β-C5H4), 4.06 (m,
Table 3. Results Using 0.4 mol % Catalyst 4 5 6 16
conversn (%)
trans/cis (%)
TONa
TOF (min−1)
TOF (h−1)
94 84 21 88
>99 >99 >99 >99
68 58 16 61
4.6 5.8 0.5 2
274 351 32 123
a
Carried out in an external experiment, with 6 mL total volume and with only one sample after 65 min.
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EXPERIMENTAL SECTION
All manipulations were conducted either under an atmosphere of dry argon or in vacuo using standard Schlenk line or glovebox techniques. Solvents were dried according to standard procedures, degassed, and stored under argon over activated molecular sieves. C6D6 was degassed by three freeze−pump−thaw cycles and stored over molecular sieves. NMR spectra were acquired on a Bruker AMX 400 or a Bruker Avance 500 NMR spectrometer. 1H and 13C{1H} NMR spectra were referenced to external TMS via the residual protons of the solvent (1H) or the solvent itself (13C). 31P NMR spectra were referenced to 85% H3PO4. Microanalyses (C, H, N) were performed on a Leco Instruments elemental analyzer, type CHNS 932. IR spectra in the solid state were acquired on a JASCO FT/IR-6200 spectrometer in an Innovative Technology PureLab glovebox using a PIKE HWG Accessory. UV−vis spectra were measured on a JASCO V-660 UV− vis spectrometer as hexane solutions. [Cr(η5 -C 5 H 4 PPh 2 )(η7 C 7 H 6 PPh 2 )], 5 [Cr(η 5 -C 5 H 4 PCy 2 )(η 7 -C 7 H 6 PCy 2 )], 5 [Cr(η 5 C5H4PMe2)(η7-C7H6PMe2)],5 and [(Ph3P)PtCl2]15 were prepared according to published procedures. LiCCPh was prepared by reaction of BuLi with HCCPh in hexane (0 °C). MeLi (1.6 M in Et2O) was purchased from Sigma-Aldrich, and [(cod)PdCl2], styrene, and bromobenzene were obtained commercially, degassed, and used without further purification. NaOAc was dried at 80 °C under reduced pressure. The phosphorus atoms are defined as P5 (η5-C5H4R) and P7 (η7-C7H6R). [Cr(η5-C5H4PPh2)(η7-C7H6PPh2)PdCl2] (4). A mixture of [Cr(η5C5H4PPh2)(η7-C7H6PPh2)] (1; 60 mg, 100 μmol) and [(cod)PdCl2] (27 mg, 95 μmol) in thf (1.5 mL) was heated for 3 h to 75 °C in an oil bath. The brown mixture turned red, and a green solid was formed, which was washed with pentane (3 × 2 mL) and dried in vacuo at 70 °C. Thus, 4 was isolated as a green solid. Yield: 63 mg (85 μmol, 89%). 31 1 P{ H} NMR (162 MHz, thf): δ 22.51 (d, P5, 2JP5,P7 = 20.1 Hz), 56.63 (d, P7, 2JP7,P5 = 20.1 Hz). Anal. Calcd for C36H30CrP2PdCl2 (753.89): C, 57.35; H, 4.01. Found: C, 56.65; H, 4.43. [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)PdCl2] (5). Complex 5 was prepared similarly to 4, using [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)] (2; 60 mg, 100 μmol) and [(cod)PdCl2] (26 mg, 89 μmol) in thf (1.5 mL; 75 °C; 20 min). The blue reaction mixture changed to green, and 5 was isolated as a green solid. Crystals suitable for X-ray analysis were obtained directly from the reaction mixture. Yield: 54 mg (69 μmol, 77%). 31 1 P{ H} NMR (162 MHz, THF): δ 35.50 (d, P5, 2JP5,P7 = 21.1 Hz), 70.54 (d, P7, 2JP7,P5 = 21.1 Hz). Anal. Calcd for C36H54CrP2PdCl2 (778.08): C, 55.57; H, 7.00. Found: C, 55.53; H, 7.10. [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)PdCl2] (6). Complex 6 was prepared similarly to 4, using [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)] (3; 40 mg, 120 μmol) and [(cod)PdCl2] (34 mg, 120 μmol) in thf (1.5 mL; 75 °C; 30 min). Complex 6 was isolated as a brown solid. Yield: 34 mg (68 μmol, 56%). 3032
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Organometallics
Article
2H, α-C5H4), 5.51 (m, 4H, β/γ-C7H6), 5.97 (m, 2H, α-C7H6). 13 C{1H} NMR (126 MHz, C6D6): δ 5.69 (m, CH3), 6.54 (m, CH3), 26.62 (d, C6H11, JC,P = 5.7 Hz), 27.46−27.56 (m, C6H11), 28.20−28.31 (m, C6H11), 29.84 (br, C6H11), 30.11 (br, C6H11), 30.47 (br, C6H11), 34.78 (d, C6H11, JC,P = 14.4 Hz), 35.11 (d, C6H11, JC,P = 16.8 Hz), 78.30 (d, β-C5H4, 3JC,P5 = 3.4 Hz), 79.99 (d, α-C5H4, 2JC,P5 = 7.5 Hz), 86.03 (d, β-C7H6, 3JC,P7 = 8.2 Hz), 88.47 (s, γ-C7H6), 90.28 (br, αC7H6). 31P{1H} NMR (202 MHz, C6D6): δ 15.75 (d, P5, 2JP5,P7 = 17.4 Hz), 41.00 (d, P7, 2JP7,P5 = 17.4 Hz). Anal. Calcd for C38H60CrP2Pd (737.25): C, 61.91; H, 8.20. Found: C, 62.92; H, 8.19. [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)PdMe2] (12). Complex 12 was prepared similarly to 10 using 6 (65 mg, 130 μmol) in Et2O (4 mL) and MeLi (1.6 M, 0.43 mL, 640 μmol). Complex 12 was isolated as a light blue solid. Yield: 23 mg (50 μmol, 38%). 1 H NMR (500.1 MHz, C6D6): δ 0.93 (m, 3H, Pd−(CH3)), 1.02 (m, 3H, Pd−(CH3)), 1.18 (d, 6H, CH3, 2JH,P5 = 6.5 Hz), 1.52 (d, 6H, CH3, 2 JH,P7 = 6.3 Hz), 3.65 (m, 2H, β-C5H4), 3.70 (m, 2H, α-C5H4), 5.28 (m, 2H, β-C7H6), 5.43 (m, 2H, γ-C7H6), 5.57 (m, 2H, α-C7H6). 13 C{1H} NMR (126 MHz, C6D6): δ 5.13 (d, Pd−(CH3), 1JC,P = 12.9 Hz), 6.04 (d, Pd−(CH3), 1JC,P = 12.8 Hz), 15.24 (d, P5−(CH3)2, 1JC,P5 = 21.6 Hz), 15.72 (d, P7−(CH3)2, 1JC,P7 = 18.8 Hz), 78.20 (d, α-C5H4, 2 JC,P5 = 11.0 Hz), 79.02 (d, β-C5H4, 3JC,P5 = 5.0 Hz), 85.03 (br, iC5H4), 87.06 (d, β-C7H6, 3JC,P7 = 9.5 Hz), 88.08 (s, γ-C7H6), 89.51 (d, α-C7H6, 2JC,P7 = 17.2 Hz), 98.42 (br, i-C7H6). 31P{1H} NMR (202 MHz, C6D6): δ −18.83 (d, P5, 2JP5,P7 = 19.6 Hz), 9.73 (d, P7, 2JP7,P5 = 19.6 Hz). Anal. Calcd for C18H28CrP2Pd (464.01): C, 46.55; H, 6.08. Found: C, 45.44; H, 5.96. [Cr(η5-C5H4PMe2)(η7-C7H6PMe2)PtMe2] (13). Complex 13 was prepared similarly to 10 using 9 (76 mg, 130 μmol) in Et2O (4 mL) and MeLi (1.6 M, 0.43 mL, 640 μmol). 13 was isolated as a light blue solid. Crystals suitable for X-ray crystallographic analysis were obtained in C6D6 at ambient temperature. Yield: 21 mg (38 μmol, 30%). 1 H NMR (500.1 MHz, C6D6): δ 1.21 (m, 3H, Pt−(CH3)), 1.29 (m, 3H, Pt−(CH3)), 1.31 (d, 6H, CH3, 2JH,P5 = 7.9 Hz, 3JH,Pt = 22.4 Hz), 1.66 (d, 6H, CH3, 2JH,P7 = 7.6 Hz, 3JH,Pt = 22.1 Hz), 3.66 (m, 2H, βC5H4), 3.71 (m, 2H, α-C5H4), 5.27 (m, 2H, β-C7H6), 5.48 (m, 2H, γC7H6), 5.67 (m, 2H, α-C7H6). 13C{1H} NMR (126 MHz, C6D6): δ 3.92 (m, Pt−(CH3)), 4.74 (m, Pt−(CH3)), 15.27 (s, CH3, 1JC,P5 = 32.8 Hz), 15.51 (s, CH3, 1JC,P7 = 33.3 Hz), 77.96 (d, α-C5H4, 2JC,P5 = 10.9 Hz), 78.95 (d, β-C5H4, 3JC,P5 = 5.7 Hz), 83.97 (br, i-C5H4), 86.92 (br, β-C7H6), 88.21 (br, γ-C7H6), 89.14 (br, α-C7H6), 97.26 (br, iC7H6). 31P{1H} NMR (202 MHz, C6D6): δ −18.06 (d, P5, 2JP5,P7 = 11.2 Hz, 1JP5,Pt = 1830 Hz), 10.33 (d, P7, 2JP7,P5 = 11.2 Hz, 1JP7,Pt = 1854 Hz). Anal. Calcd for C18H28CrP2Pt (553.44): C, 39.05; H, 5.10. Found: C, 38.35; H, 5.28. [Cr(η5-C5H4PPh2)(η7-C7H6PPh2)Pt(−CCPh)2] (14). Complex 7 (40 mg, 47 μmol) and LiCCPh (10 mg, 100 μmol) in benzene (0.6 mL) were heated in an oil bath (75 °C, 1 h). The red reaction mixture was covered with pentane (1 mL) and cooled to −50 °C. After a solid had precipitated, the solution was decanted. The solid was washed with pentane (3 × 3 mL) and dissolved in benzene (3 mL). After filtration and removal of all volatiles 14 was obtained as a red-brown solid. Crystals suitable for X-ray crystallographic analysis were obtained in C6D6 at ambient temperature. Yield: 17 mg (17 μmol, 37%). 1 H NMR (500.1 MHz, C6D6): δ 3.52 (m, 2H, β-C5H4), 3.97 (m, 2H, α-C5H4), 4.99 (m, 2H, β-C7H6), 5.25 (m, 2H, γ-C7H6), 5.93 (m, 2H, α-C7H6) 6.85−6.90 (m, 2H, CC−C6H5), 6.94−6.99 (m, 4H, CC−C6H5), 7.02 (m, 6H, P5−(C6H5)2), 7.06 (m, 6H, P7− (C6H5)2), 7.18−7.21 (m, 4H, CC−C6H5), 7.83−7.87 (m, 4H, P5(C6H5)2, 8.20−8.24 (m, 4H, P7−(C6H5)2). 13C{1H} NMR (126 MHz, C6D6): δ (CC not detected), 80.30 (d, β-C5H4, 3JC,P5 = 6.4 Hz), 81.89 (d, α-C5H4, 2JC,P5 = 11.5 Hz), 86.68 (br, β-C7H6), 89.19 (s, γC7H6), 93.11 (br, α-C7H6), 125.14 (br, CC−C6H5), 127.74 (m, CC−C6H5), 130.42 (m, p-C6H5), 130.71 (m, p-C6H5), 131.77 (s, CC−C6H5), 135.38 (d, o-C6H5, 2JC,P5 = 11.4 Hz), 136.96 (d, oC6H5, 2JC,P7 = 11.3 Hz). 31P{1H} NMR (202 MHz, C6D6): δ 8.56 (d, P5, 2JP5,P7 = 17.4 Hz, 1JP5,Pt = 2319 Hz), 36.79 (d, P7, 2JP7,P5 = 17.4 Hz,
JP7,Pt = 2338 Hz); UV−vis: λ ∼257, ∼328 nm. IR (solid): 2087 (br), 2117 (br) cm−1, ν(CC). Anal. Calcd for C52H40CrP2Pt (973.90): C, 64.13; H, 4.14. Found: C, 64.95; H, 4.41. [Cr(η5-C5H4PCy2)(η7-C7H6PCy2)Pt(−CCPh)2] (15). Complex 9 (40 mg, 46 μmol) and LiCCPh (10 mg, 92 μmol) in benzene (0.6 mL) were heated in an oil bath (75 °C, 1 h). The reaction mixture was covered with pentane (1 mL), and after a solid had precipitated, the solution was decanted. The solid was washed with pentane (3 × 3 mL) and dissolved in thf (3 mL). After filtration and removal of all volatiles 15 was obtained as a green-brown solid. Crystals suitable for X-ray analysis were obtained in C6D6 at ambient temperature. Yield: 29 mg (27 μmol, 59%). 1 H NMR (500.1 MHz, C6D6): δ 1.41−2.86 (m, 44H, C6H11), 3.76 (m, 2H, β-C5H4), 4.04 (m, 2H, α-C5H4), 5.48 (m, 4H, β/γ-C7H6), 6.00 (m, 2H, α-C7H6), 6.98 (m, 2H, CC−C6H5), 7.11 (m, 4H, C C−C6H5), 7.72 (m, 2H, CC−C6H5), 7.78 (m, 2H, CC−C6H5). 13 C{1H} NMR (126 MHz, C6D6): δ (CC not detected), 26.43 (m, C6H11), 27.35−27.48 (m, C6H11), 28.18 (m, C6H11), 29.68−29.87 (m, C6H11), 30.15−30.22 (m, C6H11), 30.53 (br, C6H11), 36.12 (m, C6H11), 78.90 (m, β-C5H4), 80.30 (m, α-C5H4), 86.13 (m, β-C7H6), 88.95 (s, γ-C7H6), 90.63 (br, α-C7H6), 125.40 (m, CC−C6H5), 128.41 (s, CC−C6H5), 131.36 (br, CC−C6H5), 131.45 (br, C C−C6H5). 31P{1H} NMR (202 MHz, C6D6): δ 10.35 (d, P5, 2JP5,P7 = 16.2 Hz, 1JP5,Pt = 2327 Hz), 37.14 (d, P7, 2JP7,P5 = 16.2 Hz, 1JP7,Pt = 2316 Hz). UV−vis: λ 254, 265, 311 nm. IR (solid): 2117 (br) cm−1, ν(CC). Anal. Calcd for C52H64CrP2Pt·C6H6 (1076.20): C, 64.73; H, 6.56. Found: C, 64.38; H, 6.91. Typical Catalytic Reaction. Bromobenzene (2.38 mmol, 250 μL), styrene (4.80 mmol, 550 μL), NaOAc (2.86 mmol, 234 mg), and catalyst (9.52 μmol) were treated with DMSO (5 mL) and heated to 135 °C. After selected periods samples were taken and filtered. Exactly 100 μL of the filtrate was added to an Alox I column (height 3 cm; diameter 0.5 cm), and the column was eluted with toluene (2 mL). Dodecane (9 μmol, 2 μL) was added to the eluate, filled up to exactly 2 mL with toluene, and analyzed by GC/MS. 1
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ASSOCIATED CONTENT
S Supporting Information *
Text and CIF files giving crystal structure data for 5, 7, 8, 11, 13, and 14. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC-853604 (5), CCDC853605 (7), CCDC-853606 (8), CCDC-853607 (11), CCDC853608 (13), CCDC-853609 (14) and CCDC-853610 (15) also contain supplementary crystallographic data for this paper.16 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.
REFERENCES
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