Synthesis and Reactions of Ditantalum—Allyl Complexes Derived

Article pubs.acs.org/Organometallics

Synthesis and Reactions of DitantalumAllyl Complexes Derived from Intramolecular C−H Bond Activation of the Methylene of the Ethyl Group Bound to Ditantallacyclopentadiene Keishi Yamamoto, Haruki Nagae, Hayato Tsurugi,* and Kazushi Mashima* Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan S Supporting Information *

ABSTRACT: Reaction of a dinuclear tantallacyclopentadiene complex, Ta2Cl6(μ-C4Et4) (1), with PhSiH3 quantitatively afforded a polymeric dinuclear tantalum η3-allyl complex, {Ta2Cl5[μ-C4Et3(CHMe)]}n (2), whose η3-allyl moiety was derived from selective C−H bond activation of the methylene moiety of the ethyl group bound to the tantallacyclopentadiene fragment. Lewis bases, such as THF and PMe2Ph, coordinated to 2 to give Ta2Cl5(L)2[μ-C4Et3(CHMe)] (3: L = thf; 4: L = PMe2Ph). An insertion reaction of diphenylacetylene into the η3allyl moiety of 3 afforded the diphenylacetylene-incorporated complex 5. Similarly, unsaturated organic substrates, such as trimethylsilylacetylene, 2-vinylpyridine, and benzaldehyde, inserted into the η3-allyl moiety of 3 to afford the corresponding complexes 6−8.

■

INTRODUCTION Metal hydride species of early transition metals continue to attract interest due to their high reactivity to unsaturated organic compounds for insertion reactions,1 as exemplified by Schwartz’s reagent of zirconocene hydride,2 as well as the generation of a coordinatively unsaturated low-valent metal center by reductively eliminating dihydrogen or hydrocarbons from polyhydride complexes.3 On the basis of the high reactivity of M−H species, some hydride species of group 5 metals exhibit σ-bond metathesis reactions involving C−H bond activation to form a new organometallic species along with elimination of H2.4 As a representative early example, Rothwell et al. reported that a Ta−H bond cleaves a C−H bond of a 2,6-diphenylphenoxide ligand through σ-bond metathesis, giving the corresponding cyclometalated complex.5 Remarkably, intermolecular C−H bond activation of alkanes is accessible by surface-grafted Ta−H species, leading to the reformation of petroleum ether.6,7 Thus, the Ta−H species is considered to be a key intermediate for C−H bond activation to generate new M−C bonds, which are utilized for further transformations, such as insertion of unsaturated organic molecules and β-H elimination. In addition to M−H-mediated cyclometalation of the supporting ligands as well as intermolecular C−H bond activation reactions, direct C−H functionalization of the organometallic species is in high demand due to their applicability as new organometallic reagents for organic synthesis. For example, direct C−H functionalization of C5Me5 ligands was reported;8 however, the high stability of the cyclopentadienyl ligands made it difficult to apply to further organic synthesis. Thus, a direct C−H functionalization for more reactive organometallic species is needed. Recently, we isolated and characterized a dinuclear tantalum metallacyclo© XXXX American Chemical Society

pentadiene complex, Ta2Cl6 (μ-C 4Et4) (1), in which a tantallacyclopentadiene fragment coordinated to another tantalum center.9 We anticipated that introduction of a hydride ligand to the dinuclear tantalum center would induce C−H bond activation of the metallacyclopentadiene fragment to give an M−C bond, which is targeted for subsequent reactions with unsaturated organic molecules, as a new strategy for accessing a wide variety of functionalized metallacyclopentadiene species from one metallacyclopentadiene complex. Herein, we report that in situ-generated tantalum hydride species afforded a tantalum η3-allyl complex, {Ta2Cl5[C4Et3(CHMe)]}n (2), via a C−H bond cleavage at the methylene position of the ethyl group bound to the α-position of the tantallacyclopentadiene moiety of 1. Some reactions of the tantalum η3-allyl moiety to unsaturated compounds were disclosed as typical of the tantalum η3-allyl species.

■

RESULTS AND DISCUSSION Reaction of complex 1 with 2 equiv of PhSiH3, which is typically used as a hydride donor for early transition metal complexes, in toluene at 110 °C for 22 h did not afford any hydride complexes, but resulted in the precipitation of {Ta2Cl5[C4Et3(CHMe)]}n (2) in quantitative yield (eq 1). Monitoring the reaction in C6D6 by NMR spectroscopy revealed formation of H2 gas and PhSiH2Cl as a singlet signal at δH 5.06, suggesting the formation of a nascent Ta−H species during the reaction course. Characterization of polymeric complex 2 was hampered by its low solubility in noncoordinated solvents except for elemental analysis. On the Received: May 18, 2016

A

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Scheme 1. Proposed Mechanism for the Formation of 2 from 1 and PhSiH3

other hand, complex 2 was dissolved in THF to develop a green solution, from which the discrete THF adduct 3 was isolated in quantitative yield (eq 2). Complex 3 was characterized by NMR spectroscopy to hold a “Ta-(η3-allyl)” fragment as a consequence of C−H bond activation of a methylene proton of the ethyl group bound to the α-position of the tantallacyclopentadiene fragment of 1. The 1H NMR spectrum of 3 in THFd8 showed a doublet at δH 2.99 (3JH−H = 6.1 Hz) for CHCH3 and a quartet at δH 3.53 (3JH−H = 6.1 Hz) for CHCH3, together with three sets of two doublets of a quartet and a triplet for three ethyl groups. In the 13C{1H} NMR spectrum, a lower field signal at δC 89.8 (1JC−H = 149 Hz) was attributed to the allylic carbon bearing a methyl group. Compared with the chemical shift values and coupling constants of δC 56.1 (1JC−H = 149 Hz) for Cp2Ta(η3-CH2CHCH2)10 and δC 73.7 (1JC−H = 145 Hz) and 62.9 (1JC−H = 151 Hz) for Cp*Ta(η3PhCHCHCH2)2,11 complex 3 had two canonical forms, 3-A and 3-B, as schematically drawn in Figure 1: 3-A has a

polymeric compound 2 induced the cleavage of the polymeric structure of 2 to give 4 in 91% yield. Complex 4 was characterized by spectral measurements and X-ray diffraction analysis (vide inf ra). Notably, fluxional behavior of complex 4 was observed in the 31P{1H} NMR spectrum; one sharp singlet signal was detected at δP −2.3, and a broad signal was observed at δP −20.3 at 30 °C, the latter of which became a sharp singlet at −60 °C with keeping the other signal sharp, indicating that one of the two PMe2Ph ligands was labile, although assignment of each phosphine ligand was not accomplished. Figure 2 shows the molecular structure of 4, and selected bond distances and angles are summarized in Table 1. Complex

Figure 1. π-Allyl (3-A) and σ3-allyl (3-B) forms of the η3-allyl moiety in 3.

monoanionic η3-π-allyl structure, where the monoanionic πallyl moiety coordinated to the tantalum atom with an oxidation state of +3,10 whereas 3-B adopts a trianionic η3-σ3allyl structure bound to the tantalum atoms with the oxidation state of +5.11 The 1JC−H coupling constant is used to estimate the anionic character of the allyl ligand, as discussed for that of diene ligands in (C5R5)Ta(diene) (R = H, Me) complexes.12 According to the allylic 1JC−H value in complex 3, we concluded that both of the canonical forms, 3-A and 3-B, contributed to the structure of 3. Although the mechanism for the formation of 2, bearing the η3-allyl moiety, was uncertain, the reaction of 1 and PhSiH3 was proposed to progress according to the pathway outlined in Scheme 1: the first reaction produces the hydride intermediate A along with the formation of PhSiH2Cl, and then an intramolecular σ-bond metathesis between a C−H bond of methylene of an ethyl group and a nascent Ta−H bond occurs via transition state B, generating 2 along with the release of H2. The two THF ligands of 3 were labile enough to be replaced by PMe2Ph, producing the bis(PMe2Ph) adduct 4 in 96% yield (eq 3). Alternatively, the direct reaction of PMe2Ph with

Figure 2. Molecular structure of complex 4 with 50% thermal ellipsoids. All hydrogen atoms and solvent molecules are omitted for clarity.

4 has an η3-allyl moiety with a syn configuration. The C−C bond lengths and the Ta−C bonds of the η3-allyl moiety are good indicators to evaluate the π-back-donation from the tantalum to the η3-allyl moiety. Two allylic C−C bond lengths of C3−C4 (1.505(13) Å) and C4−C8 (1.427(11) Å) are longer than those (1.406(11) and 1.381(11) Å) found for the Ta(V) complex Cp*Ta(NSitBu3)(η3-C3H5)(η1-C3H5)11b while comparable to those (1.49(3) and 1.46(3) Å) found for the Ta(III) complex Cp*Ta(η3-PhC3H4)2.10 The bond lengths of Ta2−C3 (2.376(8) Å), Ta2−C4 (2.215(8) Å), and Ta2−C8 (2.346(9) Å) are longer than those (mean 2.25 Å) found for B

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

into the Ta-(η3-allyl) of 3 to give complex 6 in a regioselective manner in 33% yield. The 1H NMR spectrum of 6 showed a doublet due to TaC(SiMe3)CH at δH 8.04 (3JH−H = 2.0 Hz) and a quartet of doublets due to CHCH3 at δH 4.60 (3JH−H = 7.0 Hz, 3JH−H = 2.0 Hz). Two-dimensional NMR measurements such as 1H−1H COSY and 1H−13C{1H} HMBC revealed that the insertion of trimethylsilylacetylene into the Ta-(η3-allyl) moiety proceeded in a “head-to-tail” manner, which was confirmed by X-ray analysis of 6 (vide inf ra). In the 13 C{1H} NMR spectrum, a signal due to CHCH3 (δC 62.8) was observed in a similar magnetic field to that of 5. 2-Vinylpyridine also inserted into the Ta-(η3-allyl) moiety of 3 in a head-to-tail manner to give complex 7 in 95% yield, whereas 1-hexene and styrene did not, indicating that the pyridyl group was necessary for the insertion reaction as a directing group. In the 1H NMR spectrum of 7, a multiplet signal attributed to the CHCH3 moiety was observed at δH 3.90−3.98 with coupling to the adjacent methyl and methylene groups. In the 13C{1H} NMR spectrum of 7, a signal (δC 48.4) for CHCH3 shifted to a higher magnetic field compared with that (δC 89.8) of 3, indicating the disappearance of the Ta-(η3-allyl) moiety after the insertion reaction, as observed for complexes 5 and 6. Finally, we conducted a reaction of 3 with benzaldehyde to yield complex 8 in 55% yield. The 1H NMR spectrum of 8 exhibited a doublet due to TaOCHPh at δH 5.46 (3JH−H = 9.4 Hz) and a multiplet due to CHCH3 at δH 4.22−4.34. In the 13C NMR spectrum of 8, a signal for the carbonyl moiety of benzaldehyde disappeared with the appearance of a signal for the aliphatic carbon bound to the oxygen atom at δC 100.1, which was correlated to the doublet signal in the 1H NMR spectrum at δH 5.46. Signals for the α- and β-positions of the tantalacyclopentadiene were observed at δC 224.5 and 226.6 for the α-position and 114.3 and 120.0 for the β-position, which was observed in the same region as 5−7, suggesting that the tantalacyclopentadiene moiety was intact during the reaction with benzaldehyde. As summarized in Scheme 2, these reactions are rare examples of the direct C−H functionalization reactions adjacent to the metallacyclopentadiene moiety. The molecular structures of complexes 5, 6, and 7 were elucidated by X-ray diffraction studies, and the results are summarized in Figure 3 and Table 2. The molecular structure of complex 5 shows a dimeric structure with two bridging chloride ligands. Both of the tantalum atoms adopt a distorted octahedral geometry. The bond length (2.124(2) Å) of Ta2− C14 is typical for a Ta−C σ-bond, while the bond length

Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of 4 Ta1−Ta2 Ta1−C4 Ta2−C2 Ta2−C4 Ta1−Cl3 C1−C2 C3−C4 Ta1−P1 C1−Ta1−C4 C1−C2−C3 C3−C4−Ta1

2.9467(15) 2.062(7) 2.476(8) 2.215(8) 2.582(2) 1.458(10) 1.505(13) 2.727(3) 91.6(3) 119.5(8) 86.9(5)

Ta1−C1 Ta2−C1 Ta2−C3 Ta2−C8 Ta1−Cl4 C2−C3 C4−C8 Ta2−P2 Ta1−C1−C2 C2−C3−C4 Θa

2.074(9) 2.345(8) 2.376(8) 2.346(9) 2.525(2) 1.435(13) 1.427(11) 2.684(2) 88.8(5) 122.6(7) 56.11

Θ = the dihedral angle between the best planes of C1−Ta1−C4 and C1−C2−C3−C4.

a

Cp*Ta(η3-PhC3H4)2 and shorter than those (mean 2.40 Å) found for Cp*Ta(NSitBu3)(η3-C3H5)(η1-C3H5), suggesting that the degree of π-back-donation from tantalum to the η3-allyl moiety increases in the order Cp*Ta(η3-PhC3H4)2 > 4 > Cp*Ta(NSitBu3)(η3-C3H5)(η1-C3H5). The bond length of Ta−Ta (2.9467(15) Å) is longer than that of typical Ta−Ta single bonds (ca. 2.85 Å), while it is comparable to a dative interaction between the tantalum atom, as observed for other Ta2 complexes with a bridging metallacyclopentadiene ligand.9b Each tantalum atom is coordinated by PMe2Ph, which is consistent with the 31P{1H} NMR spectrum where two magnetically nonequivalent signals were observed (vide supra). With a new organometallic species, a tantalum allyl complex, in hand, we conducted a reaction of 3 with alkynes because our group previously reported a [4+2] cycloaddition of the tantallacyclopentadiene moiety with an external alkyne to form a tantallanorbornadiene complex.9a Treatment of 3 with diphenylacetylene (1.3 equiv) afforded complex 5 in 54% yield, where diphenylacetylene inserted into the Ta-(η3-allyl) moiety, although a [4+2] cycloaddition did not proceed, presumably due to the deformation of a tantallacyclopentadiene structure in 3. In the 1H NMR spectrum, a quartet appeared at δH 5.16 (3JH−H = 7.2 Hz) for the CHCH3, which shifted to a magnetically lower field than that (δH 3.53) of 3. In the 13 C{1H} NMR spectrum, a signal (δC 58.7) due to CHCH3 was observed in the lower field compared with those (δC 89.8 for 3; δC 82.9 for 4) of complexes 3 and 4. These NMR data indicated the disappearance of the tantalum allyl fragment after the insertion reaction. Similarly, trimethylsilylacetylene inserted

Scheme 2. Insertion Reactions of Unsaturated Substrates into the Ta-(η3-allyl) Moiety in Complex 3

C

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Figure 3. Molecular structures of (a) complex 5, (b) complex 6, and (c) complex 7 with 50% thermal ellipsoids. All hydrogen atoms are omitted for clarity.

(2.031(14), 2.011(14), 1.442(19), 1.43(2), and 1.44(2) Å) found for 1,9a indicating that complex 5 has a similar tantallacyclopentadiene structure to 1 by losing the strained η3-allyl moiety in complex 3. On the other hand, complex 6 adopts a monomeric structure, even though the geometric parameters for the bridging metallacycle moiety are almost the same as for complex 5. Ta1 possesses a distorted trigonal bipyramidal geometry with one κ1-Cl ligand and one μ-Cl ligand at apical positions, and Ta2 adopts a distorted octahedral geometry. We presumed that the electron-withdrawing phenyl group on C14 affected the Lewis acidity of the dinuclear Ta2 core, leading to the dimerization of the Ta2 unit by bridging one chloride ligand, whereas C14 for complex 6 is electron-rich due to the trimethylsilyl group, decreasing the Lewis acidity of Ta1 through the interaction between two tantalum atoms. The molecular structure of 7 reveals a monomeric Ta2 structure with additional coordination of the pyridine ring for Ta2. Ta1 adopts a pentacoordinated distorted trigonal bipyramidal geometry with one κ1-Cl ligand and one μ-Cl ligand at apical positions, while Ta2 possesses a heptacoordinated pentagonal bipyramidal geometry. Formation of tantallacyclopentane is observed for Ta−C4−C8−C13−C14, in which the bond length (1.499(17) Å) of C13−C14 is a typical C−C single bond, while that (2.267(14) Å) of Ta2−C14 is slightly longer than the tantalum−carbon σ-bond of tantallacyclopentane.14 The bond length (2.418(11) Å) of Ta2−C1 is much longer than that (2.319(13) Å) of 1, presumably due to the increased coordination number by the coordination of pyridine to Ta2.

Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) of 5−7 Ta1−Ta2 Ta1−C1 Ta1−C4 Ta2−C1 Ta2−C2 Ta2−C3 Ta2−C4 Ta2−C14 C1−C2 C2−C3 C3−C4 C4−C8 C8−C13 C13−C14 Ta2−N C1−Ta1−C4 Ta1−C1−C2 C1−C2−C3 C2−C3−C4 C3−C4−Ta1 Θa

5

6

7

2.9774(4) 2.025(2) 2.0322(19) 2.271(2) 2.409(2) 2.466(2) 2.356(2) 2.124(2) 1.464(3) 1.454(3) 1.443(3) 1.521(3) 1.507(3) 1.351(3)

2.9891(8) 2.027(2) 2.024(2) 2.285(2) 2.428(2) 2.501(2) 2.321(2) 2.129(2) 1.471(3) 1.432(3) 1.452(3) 1.513(3) 1.499(3) 1.336(3)

90.67(8) 92.49(14) 119.04(19) 119.92(17) 92.00(13) 50.45

89.48(9) 92.68(14) 119.2(2) 118.7(2) 91.95(13) 51.90

2.9832(10) 2.015(12) 2.044(12) 2.418(11) 2.427(12) 2.439(11) 2.349(11) 2.267(14) 1.438(16) 1.431(17) 1.420(16) 1.510(18) 1.537(18) 1.499(17) 2.258(11) 89.6(5) 97.9(8) 120.1(11) 119.8(10) 97.0(8) 38.39

Θ = the dihedral angle between the best planes of C1−Ta1−C4 and C1−C2−C3−C4.

a

■

(1.351(3) Å) of C13−C14 is typical for a CC bond, giving tantallacyclopentene for the Ta−C4−C8−C13−C14 ring.13 The tantallacyclopentadiene moiety of Ta−C1 (2.025(2) Å), Ta1−C4 (2.0322(19) Å), C1−C2 (1.464(3) Å), C2−C3 (1.454(3) Å), and C3−C4 (1.443(3) Å) is comparable to those

CONCLUSION The in situ-generated transient Ta−H species, which was formed from the reaction of 1 and PhSiH3, activated the C−H bond at the α-position of the ethyl group bound to the D

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

PPhMeMe), 1.82 (d, 3J = 5.6 Hz, 3H, CHCH3), 2.68 (dq, 2J = 14.1 Hz, 3 J = 7.2 Hz, 1H, CHHCH3), 3.04−3.29 (m, 4H, 3 CHHCH3, CHCH3), 4.03 (dq, 2J = 14.7 Hz, 3J = 7.2 Hz, 1H, CHHCH3), 4.15 (dq, 2J = 14.7 Hz, 3J = 7.2 Hz, 1H, CHHCH3), 6.89−7.03 (m, 6H, PPhMe2), 7.30−7.37 (m, 2H, PPhMe2), 7.37−7.45 (m, 2H, PPhMe2). 13 C{H} NMR (100 MHz, C6D6, 30 °C): δ 11.8, 12.1, 13.5, 14.5, 14.8, 15.6, 17.1, 17.4, 21.5 (CH2CH3), 23.5 (CH2CH3), 30.3 (CH2CH3), 82.9 (d, 2JC−P = 6.0 Hz, CHCH3), 107.6 (CβCH2CH3), 122.8 (CβCH2CH3), 122.9 (PPhMe2), 125.7 (PPhMe2), 129.5 (d, 2JC−P = 39.0 Hz, PPhMe2), 129.6 (br d, 2JC−P = 15.6 Hz, PPhMe2), 131.0 (d, 2 JC−P = 8.2 Hz, PPhMe2), 131.8 (br d, 2JC−P = 9.6 Hz, PPhMe2), 135.4 (d, 2JC−P = 32.5 Hz, PPhMe2), 202.7 (TaCαCHCH3), 221.8 (d, 2JC−P = 7.6 Hz, TaCαCH2CH3). One carbon signal for the phenyl ring was overlapped with C6D6 resonances. 31P{1H} NMR (162 MHz, C6D6, 30 °C): δ −20.3 (br s), −2.3 (s). Anal. Calcd for C28H41Cl5P2Ta2: C, 34.36; H, 4.22. Found: C,34.73; H, 3.75. Due to the small amount of phosphine-derived impurity, the value of hydrogen was slightly out of range (±0.4%). Synthesis of Ta2Cl5[C4Et3(CHMeCPhCPh)] (5). A solution of complex 3 (300 mg, 0.354 mmol) and diphenylacetylene (82.0 mg, 0.460 mmol) in toluene (20 mL) was heated at 80 °C for 2 h. After all volatiles were removed under reduced pressure, the yellow-red residue was extracted by toluene (10 mL). The solution was concentrated to 1 mL, and then hexane (10 mL) was added to form yellow precipitates. The precipitates were washed by hexane (3 mL × 3) and then dried under reduced pressure to give complex 5 (170 mg, 0.193 mmol) in 54% yield, mp 180−183 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 1.04 (t, 3J = 7.5 Hz, 3H, CH2CH3), 1.20 (t, 3J = 7.2 Hz, 3H, CH2CH3), 1.27 (t, 3J = 7.6 Hz, 3H, CH2CH3), 1.46 (d, 3J = 7.2 Hz, 3H, CHCH3), 2.54 (dq, 2J = 14.3 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 3.03−3.28 (m, 4H, CH2CH3), 3.56 (dq, 2J = 15.9 Hz, 3J = 7.9 Hz, 1H, CHHCH3), 5.16 (q, 3J = 7.2 Hz, 1H, CHCH3), 6.71−6.86 (m, 10H, Ph), 6.96 (br s, 2H, Ph). 13C{H} NMR (100 MHz, C6D6, 30 °C): δ 13.7 (CH2CH3), 15.7 (CH2CH3), 16.6 (CH2CH3), 21.0 (CHCH3), 23.6 (CH2CH3), 24.0 (CH2CH3), 35.2 (CH2CH3), 58.7 (CHCH3), 113.1 (CβCH2CH3), 124.8 (CβCH2CH3), 128.55 (Ph), 128.59 (Ph), 129.0 (Ph), 129.5 (Ph), 136.8 (Ph), 139.4 (Ph), 162.0 (TaCPhCPh), 224.9 (CαCHCH3), 229.4 (CαCH2CH3), 229.9 (TaCPhCPh), two signals for the Ph ring were overlapped by the solvent signal. Anal. Calcd for C26H29Cl5Ta2(C6H6)0.5: C, 37.87; H, 3.51. Found: C, 37.95; H, 3.33. Synthesis ofTa2Cl5[C4Et3(CHMeCHCSiMe3)] (6). To a solution of complex 3 (300 mg, 0.354 mmol) in toluene (15 mL) was added a solution of trimethylsilylacetylene (34.8 mg, 0.354 mmol) in toluene (5 mL) at −40 °C. After the reaction mixture was stirred at room temperature for 30 min, all of the volatiles were removed under reduced pressure. The red-brown residue was extracted by hexane (40 mL). The extracted solution was concentrated to 3 mL, and then the solution was kept at −40 °C to form brown precipitates. Dryness of the precipitates afforded complex 6 (95.0 mg, 0.118 mmol) as a brown powder in 33% yield, mp 80−82 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 0.32 (s, 9H, SiMe3), 0.97 (t, 3J = 7.5 Hz, 3H, CH2CH3), 1.01 (t, 3J = 7.6 Hz, 3H, CH2CH3), 1.10 (t, 3J = 7.5 Hz, 3H, CH2CH3), 1.25 (d, 3J = 7.0 Hz, 3H, CHCH3), 2.49 (dq, 2J = 14.3 Hz, 3J = 7.5 Hz, 1H, CHHCH3), 2.69 (dq, 2J = 14.2 Hz, 3J = 7.6 Hz, 1H, CHHCH3), 2.90 (dq, 2J = 14.2 Hz, 3J = 7.6 Hz, 1H, CHHCH3), 3.02−3.17 (m, 2H, CH2CH3), 3.29 (dq, 2J = 16.0 Hz, 3J = 7.5 Hz, 1H, CHHCH3), 4.60 (qd, 3J = 7.0 Hz, 3J = 2.0 Hz, 1H, CHCH3), 8.04 (d, 3J = 2.0 Hz, 1H, TaC(SiMe3)CH). 13C{H} NMR (100 MHz, C6D6, 30 °C): δ 0.5 (SiMe3), 13.9 (CH2CH3), 15.6 (CH2CH3), 16.7 (CH2CH3), 19.2 (CHCH3), 23.2 (CH2CH3), 23.7 (CH2CH3), 35.0 (CH2CH3), 62.8 (CHCH 3 ), 112.2 (CβCH 2 CH 3 ), 124.4 (CβCH 2 CH 3 ), 164.8 (CHCSiMe3), 226.1 (CαCHCH3), 229.4 (CαCH2CH3), 234.5 (CHCSiMe3). Anal. Calcd for C17H29Cl5SiTa2: C, 25.50; H, 3.65. Found: C, 25.90; H, 3.43. Synthesis of Ta2Cl5[C4Et3(CHMeCH2CHPy)] (7). A solution of complex 3 (300 mg, 0.354 mmol) and 2-vinylpyridine (74.5 mg, 0.709 mmol) in toluene (20 mL) was heated at 80 °C for 6 h. After all volatiles were removed under reduced pressure, the yellow residue was washed with hexane (5 mL × 2). Drying the residue under reduced

tantallacyclopentadiene fragment of 1 to produce polymeric complex 2, bearing a Ta-(η3-allyl) fragment. Lewis base ligands, such as THF and PMe2Ph, solubilized the polymeric structure of 2 to afford discrete Ta-(η3-allyl) complexes 3 and 4. As direct C−H functionalization reactions adjacent to the metallacyclopentadiene moiety, we demonstrated insertion reactions of diphenylacetylene, trimethylsilylacetylene, 2-vinylpyridine, and benzaldehyde into the Ta-(η3-allyl) moiety to give the corresponding products 5−8.

■

EXPERIMENTAL SECTION

General Procedures. All manipulations involving air- and moisture-sensitive tantalum complexes were performed either under argon by using the standard Schlenk techniques or in an argon-filled glovebox. Complex 1 was prepared according to the literature.9a Alkynes, PhSiH3, 2-vinylpyridine, and PPhMe2 were purchased from TCI or Aldrich and distilled over CaH2 before use. Anhydrous hexane, toluene, and THF were purchased from Kanto Chemical and further purified by passage through activated alumina under positive argon pressure as described by Grubbs et al.15 Benzene, benzene-d6, toluened8, and THF-d8 were distilled over CaH2 and degassed before use. 1H NMR (400 MHz) and 13C{1H} NMR (100 MHz) spectra were measured on Bruker AVANCEIII-400 and JEOL JNM-ESC400 spectrometers. Assignment of 1H and 13C NMR peaks for some complexes were facilitated by 2D 1H−1H COSY, 2D 1H−13C HMQC, and 2D 1H−13C HMBC spectra. GC-MS measurements were performed using a DB-1 capillary column (0.25 mm × 30 m) on a Shimadzu GCMS-QP2010Plus. All melting points were measured in sealed tubes under an argon atmosphere. Elemental analyses were recorded by using PerkinElmer 2400 at the Faculty of Engineering Science, Osaka University. Synthesis of {Ta2Cl5[C4Et3(CHMe)]}n (2). To a solution of complex 1 (300 mg, 0.406 mmol) in toluene (3 mL) was added a solution of PhSiH3 (101 μL, 0.819 mmol) in toluene (1 mL). After the reaction mixture was heated at 110 °C for 22 h, green precipitates formed. The supernatant was decanted, and then the green precipitates were washed with hexane (5 mL × 2). Dryness of the residue under reduced pressure gave complex 2 (284 mg, 0.404 mmol) as a green powder in 99% yield, mp 333−335 °C (dec). Anal. Calcd for C12H19Cl5Ta2: C, 20.52; H, 2.73. Found: C, 20.75; H, 2.49. Synthesis of Ta2Cl5[C4Et3(CHMe)](thf)2 (3). Complex 2 (300 mg, 0.427 mmol) was dissolved in THF (5 mL), and then the green solution was stirred at room temperature for 30 min. THF was removed under reduced pressure to give complex 3 (358 mg, 0.423 mmol) as a green powder in 99% yield, mp 331−333 °C (dec). 1H NMR (400 MHz, THF-d8, 30 °C): δ 1.19 (t, 3J = 7.5 Hz, 3H, CH2CH3), 1.44 (t, 3J = 7.7 Hz, 3H, CH2CH3), 1.52 (t, 3J = 7.6 Hz, 3H, CH2CH3), 1.74−1.80 (m, 8H, β-THF), 2.73 (dq, 2J = 14.0 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 2.99 (d, 3J = 6.1 Hz, 3H, CHCH3), 3.15 (dq, 2J = 14.0 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 3.39−3.60 (m, 2H, CHHCH3), 3.53 (q, 3J = 6.1 Hz, 1H, CHCH3), 3.59−3.68 (m, 8H, α-THF), 3.80 (dq, 2J = 14.7 Hz, 3J = 7.3 Hz, 1H, CHHCH3). 13C{H} NMR (100 MHz, C6D6, 30 °C): δ 13.8 (CH2CH3), 15.5 (CH2CH3), 15.6 (CHCH3), 17.6 (CH2CH3), 22.3 (CH2CH3), 23.6 (CH2CH3), 33.9 (CH 2 CH 3 ), 89.8 (CHCH 3 ), 111.5 (CβCH 2 CH 3 ), 119.2 (CβCH2CH3), 205.8 (TaCαCHCH3), 224.7 (TaCαCH2CH3). Anal. Calcd for C20H35Cl5O2Ta2: C, 28.37; H, 4.17. Found: C, 28.08; H, 3.80. Synthesis of Ta2Cl5[C4Et3(CHMe)](PMe2Ph)2 (4). To a solution of complex 3 (200 mg, 0.236 mmol) in toluene (5 mL) was added PMe2Ph (97.9 mg, 0.709 mmol) via a syringe. After the reaction mixture was stirred at room temperature for 20 min, all volatiles were removed under reduced pressure. The green residue was washed with hexane (5 mL × 2) to give a green powder of 4 (222 mg, 0.227 mmol) in 96% yield, mp 164−166 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 1.39 (t, 3J = 7.1 Hz, 3H, CH2CH3), 1.43 (t, 3J = 7.1 Hz, 3H, CH2CH3), 1.52−1.61 (m, 9H, CH2CH3 and 2 PPhMeMe), 1.63 (d, 2 JP−H = 8.7 Hz, 3H, PPhMeMe), 1.72 (d, 2JP−H = 8.7 Hz, 3H, E

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics pressure gave complex 7 (273 mg, 0.338 mmol) in 95% yield, mp 180−183 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 1.23−1.34 (m, 12H, CH2CH3), 1.37 (d, 3J = 6.6 Hz, 3H, CHCH3), 1.49−1.65 (m, 2H, TaCHCH2 and TaCHCHH), 2.82 (dq, 2J = 14.3 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 3.18 (dq, 2J = 15.0 Hz, 3J = 7.4 Hz, 1H, CHHCH3), 3.27−3.58 (m, 4H, 3 CHHCH3 and TaCHCHH), 3.90− 3.98 (m, 1H, CHCH3), 4.54 (dq, 2J = 15.0, 3J = 7.4 Hz, 1H, CHHCH3), 6.12 (d, 3J = 7.7 Hz, 1H, py), 6.33 (t, 3J = 7.7 Hz, 1H, py), 6.91 (t, 3J = 7.7 Hz, 1H, py), 9.40 (d, 3J = 7.7 Hz, 1H, py). 13C{H} NMR (100 MHz, C6D6, 30 °C): δ 13.6 (CH2CH3), 14.3 (CH2CH3), 16.4 (CH2CH3), 24.0 (CH2CH3), 24.1 (CH2CH3), 27.5 (CHCH3), 34.0 (CH2CH3), 41.0 (TaCHCH2), 48.4 (CHCH3) 73.2 (TaCHCH2), 114.6 (CβCH2CH3), 120.3 (CβCH2CH3), 121.6 (py), 122.8 (py), 140.8 (py), 143.1 (py), 169.6 (py), 233.7 (TaCαCH2CH3), 235.5 (TaCαCHMe). Anal. Calcd for C19H26Cl5NTa2: C, 28.26; H, 3.25; N, 1.73. Found: C, 28.31; H, 3.14; N, 1.74. Synthesis of Ta2Cl5[C4Et3(CHMeCHPhO)] (8). To a solution of complex 3 (300 mg, 0.354 mmol) in toluene (15 mL) was added a solution of benzaldehyde (56.7 mg, 0.354 mmol) in toluene (5 mL). The color changed from green to orange. After the reaction mixture was stirred at room temperature for 1 h, the solution was concentrated to 1 mL under reduced pressure. Hexane (10 mL) was added to the solution to form yellow precipitates. The precipitate was washed with hexane (5 mL × 3) and then dried under reduced pressure to afford complex 8 (140 mg, 0.173 mmol) as a yellow powder in 55% yield, mp 120−123 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 0.89 (m, 6H, CH2CH3), 1.18−1.27 (m, 6H, CH2CH3 and CHCH3), 2.63 (dq, 2 J = 14.4 Hz, 3J = 7.0 Hz, 1H, CHHCH3), 2.86−2.78 (m, 2H, CH2CH3), 3.10 (dq, 2J = 15.3 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 3.28 (dq, 2J = 14.4 Hz, 3J = 7.3 Hz, 1H, CHHCH3), 3.53 (td, 3J = 15.3 Hz, 2 J = 7.7 Hz, 1H, CHHCH3), 4.22−4.34 (m, 1H, CHCH3), 5.46 (d, 3J = 9.4 Hz, 1H, CHPh) 6.89−6.93 (m, 2H, Ph), 6.98−7.07 (m, 3H, Ph). 13 C{H} NMR (100 MHz, C6D6, 30 °C): δ 13.2 (CH2CH3), 14.2 (CH2CH3), 16.8 (CH2CH3), 22.9 (CHCH3), 23.9 (CH2CH3), 24.7(CH2CH3), 33.6 (CH2CH3), 59.8 (CHCH3), 100.1 (CHPh), 114.3 (CβCH2CH3), 120.0 (CβCH2CH3), 126.1 (Ph), 128.9 (Ph), 129.0 (Ph), 140.8 (Ph), 224.5 (CαCHCH3), 226.6 (CαCH2CH3). Anal. Calcd for C19H25O1Cl5Ta2: C, 28.22; H, 3.12. Found: C, 28.24; H, 2.52. X-ray Crystallographic Analysis. All crystals were handled similarly. The crystals were mounted on the CryoLoop (Hampton Research Corp.) with a layer of light mineral oil and placed in a nitrogen stream at 113(1) K. Measurements were made on a Rigaku R-AXIS RAPID imaging plate area detector or a Rigaku AFC7R/ Mercury CCD detector with graphite-monochromated Mo Kα (0.710 75 Å) radiation. Crystal data and structure refinement parameters were listed in Table SI2. The structures of tantalum complexes were solved by direct methods (SHELXS-97 for 7; SHELXS-2013 for 4, 5, 6).16 The structures were refined on F2 by the full-matrix least-squares method, using SHELXL-97 or 2013. H atoms were included in the refinement on calculated positions riding on their carrier atoms. The function minimized was [∑w(Fo2 − Fc2)2] (w = 1/[σ2(Fo2) + (aP)2 + bP]), where P = (Max(Fo2,0) + 2Fc2)/3 with σ2(Fo2) from counting statistics. The functions R1 and wR2 were (∑||Fo| − |Fc||)/∑|F0| and [∑w(Fo2 − Fc2)2/∑(wFo4)]1/2, respectively. The ORTEP-3 program was used to draw the molecules.17 Crystals of complexes 4, 5, and 7 were obtained from a benzene solution diffused with hexane at room temperature. Crystals of complex 6 were grown from saturated pentane solution at −40 °C.

■

■

Crystallographic data for complexes 4−7 and NMR spectra of complexes 3−8 (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail (H. Tsurugi): [email protected]. Tel: +816-6850-6247. *E-mail (K. Mashima): [email protected]. Tel: +81-6-6850-6245. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS K.Y. acknowledges financial support from a JSPS Research Fellowship for Young Scientists and JSPS Japanese-German Graduate Externship Program. H.T. acknowledges financial support from JSPS KAKENHI Grant No. JP15KT0064. This work was supported by JSPS KAKENHI Grant No. JP15H05808 in Precisely Designed Catalysts with Customized Scaffolding.

■

REFERENCES

(1) (a) Kaesz, H. D.; Saillant, R. B. Chem. Rev. 1972, 72, 231−281. (b) Crabtree, R. H. Acc. Chem. Res. 1990, 23, 95−101. (c) Harrod, J. F. Coord. Chem. Rev. 2000, 206−207, 493−531. (d) McGrady, G. S.; Guilera, G. Chem. Soc. Rev. 2003, 32, 383−392. (e) Hoskin, A. J.; Stephan, D. W. Coord. Chem. Rev. 2003, 233−234, 107−129. (f) Fegler, W.; Venugopal, A.; Kramer, M.; Okuda, J. Angew. Chem., Int. Ed. 2015, 54, 1724−1736. (g) Nishiura, M.; Fang, G.; Zhomin, H. Acc. Chem. Res. 2015, 48, 2209−2220. (2) (a) Schwartz, J.; Labinger, J. A. Angew. Chem., Int. Ed. Engl. 1976, 15, 333−340. (b) Fernández-Megía, E. Synlett 1999, 1999, 1179. (3) (a) Ballmann, J.; Munhá, R. F.; Fryzuk, M. D. Chem. Commun. 2010, 46, 1013−1025. Related references are cited therein. For a representative example, see: (b) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120, 11024−11025. (c) Fryzuk, M. D.; MacKay, B. A.; Patrick, B. O. J. Am. Chem. Soc. 2003, 125, 3234−3235. (d) Shaver, M. P.; Fryzuk, M. D. J. Am. Chem. Soc. 2005, 127, 500− 501. (e) MacKay, B. A.; Munha, R. F.; Fryzuk, M. D. J. Am. Chem. Soc. 2006, 128, 9472−9483. (f) Ballmann, J.; Pick, F.; Castro, L.; Fryzuk, M. D.; Maron, L. Organometallics 2012, 31, 8516−8524. (g) Kawaguchi, H.; Matsuo, T. J. Am. Chem. Soc. 2003, 125, 14254−14255. (h) Watanabe, T.; Ishida, Y.; Matsuo, T.; Kawaguchi, H. J. Am. Chem. Soc. 2009, 131, 3474−3475. (4) Mashima, K. In Comprehensive Organometallic Chmistry III; Crabtree, R. H.; Mingos, M. P., Eds.; Elsevier Ltd., Vol. 5, p 101. (5) Mulford, D. R.; Clark, J. R.; Schweiger, S. W.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1999, 18, 4448−4458. (6) (a) Coperet, C.; Chabanas, M.; Saint-Arroman, R. P.; Basset, J.M. Angew. Chem., Int. Ed. 2003, 42, 156−181. (b) Basset, J.-M.; Coperet, C.; Soulivong, D.; Taoufik, M.; Cazat, J. T. Acc. Chem. Res. 2010, 43, 323−334. (7) (a) Vidal, V.; Theolier, A.; Thivolle-Cazat, J.; Basset, J.-M. Science 1997, 276, 99−102. (b) Maury, O.; Lefort, L.; Vidal, V.; ThivolleCazat, J.; Basset, J.-M. Angew. Chem., Int. Ed. 1999, 38, 1952−1955. (c) Soulivong, D.; Coperet, C.; Thivolle-Cazat, J.; Basset, J.-M.; Maunders, B. M.; Pardy, R. B. A.; Sunley, G. J. Angew. Chem., Int. Ed. 2004, 43, 5366−5369. (d) Basset, J.-M.; Coperet, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Roux, E. L.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J.; Taoufik, M.; Thivolle-Cazat, J. J. Am. Chem. Soc. 2005, 127, 8604−8605. (8) (a) Pinkas, J.; Císařová, I.; Gyepes, R.; Horácě k, M.; Kubišta, J.; Č ejka, J.; Gómez-Ruiz, S.; Hey-Hawkins, E.; Mach, K. Organometallics 2008, 27, 5532−5547. (b) Montalvo, E.; Miller, K. A.; Ziller, J. W.; Evans, W. J. Organometallics 2010, 29, 4159−4170. (c) Takase, M. K.; Siladke, N. A.; Ziller, J. W.; Evans, W. J. Organometallics 2011, 30,

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00402. Crystallographic data (CIF) F

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics 458−465. (d) Schmiege, B. M.; Fieser, M. E.; Ziller, J. W.; Evans, W. J. Organometallics 2012, 31, 5591−5598. (9) (a) Yamamoto, K.; Tsurugi, H.; Mashima, K. Chem. - Eur. J. 2015, 21, 11369−11377. (b) Yamamoto, K.; Tsurugi, H.; Mashima, K. Organometallics 2016, 35, 1573−1581. (10) Gibson, V. C.; Parkin, G.; Bercaw, J. E. Organometallics 1991, 10, 220−231. (11) (a) Mashima, K.; Yamanaka, Y.; Gohro, Y.; Nakamura, A. J. Organomet. Chem. 1993, 455, C6−C8. (b) Antonelli, D. M.; Leins, A.; Stryker, J. M. Organometallics 1997, 16, 2500−2502. (12) (a) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.; Nakamura, A.; Kai, Y.; Kanehisa, H.; Kasai, N. J. Am. Chem. Soc. 1985, 107, 2410−2422. (b) Mashima, K.; Tanaka, Y.; Nakamura, A. Organometallics 1995, 14, 5642−5651. (13) Wallace, K. C.; Liu, A. H.; Davis, W. M.; Schrock, R. R. Organometallics 1989, 8, 644−654. (14) Churchill, M. R.; Youngs, W. J. Inorg. Chem. 1980, 19, 3106− 3112. (15) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518−1520. (16) Sheldrich, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112. (17) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

G

DOI: 10.1021/acs.organomet.6b00402 Organometallics XXXX, XXX, XXX−XXX