Unique Reactivity of (Arylimido)vanadium(V)–Alkyl Complexes with

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Unique Reactivity of (Arylimido)vanadium(V)
Alkyl Complexes with Phenols: Fast Phenoxy Ligand Exchange in the Presence of Vanadium(V)
Alkyls Kotohiro Nomura†,‡ and Yuichi Matsumoto‡ † ‡

Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan

bS Supporting Information ABSTRACT: Reactions of the aryloxo-modified (arylimido) vanadium(V) mono- or dialkyl complexes, V(NAr)(CH2SiMe3)2(OAr) or V(NAr)(CH2SiMe3)(OAr)2 (Ar = 2,6-Me2C6H3), with various phenols in C6D6 have been explored. The reaction of V(NAr)(CH2SiMe3)2(OAr) (1a) with ArOH in C6D6 did not take place at 25 °C even after 24 h, and the reaction affording V(NAr)(CH2SiMe3)(OAr)2 (2a) was complete after 50 h at 60 °C. In contrast, the reaction of 1a with C6F5OH took place rapidly at 25 °C, affording another monophenoxide, V(NAr)(CH2SiMe3)2(OC6F5) (1b), in addition to formation of the corresponding bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(OC6F5) (2b). The immediate ligand exchange was also observed when V(NAr)(CH2SiMe3)(OAr)2 (2a) was added to C6F5OH at 25 °C, affording 2b exclusively without reaction with the vanadium(V)
alkyl bond: further, subsequent reaction of 2b with C6F5OH or ArOH did not take place or was very slow at 25 °C. The exchange of 1a (in C6D6 at 25 °C) with various phenols (Ar0 OH) proceeded in the order Ar0 = C6F5 > 4-FC6H4 > C6H5 > 2,6-F2C6H3 . 2,6-Me2C6H3 (too slow or no reaction). The results clearly suggest that the reactions proceeded by coordination of phenols on the vanadium metal center.

’ INTRODUCTION Efficient carbon
carbon bond formation is one of the most important reactions in organic synthesis as well as in polymer synthesis, and metal
alkyl species are known to play essential roles. Synthesis and reaction chemistry of metal
alkyl complexes have thus been considered to be important not only for designing efficient catalysts but also for better understanding of organic reactions especially in terms of catalytic cycles or reactions pathways.1 Metal-catalyzed olefin coordination insertion polymerization plays an essential role in the production of polyolefins (polyethylene, polypropylene, etc.), and catalyst development is considered the core technology.2
7 Classical Ziegler-type vanadium catalysts are known to display unique characteristics, such as syntheses of high molecular weight linear polyethylene8 and amorphous polymers [applied to the synthesis of ethylene/propylene/diene copolymers (called EPDM, synthetic rubbers)9,10 with uniform molecular weight distribution, and ethylene/cyclic olefin copolymers (COC) with high transparency and thermal resistance].11 Due to the promising characteristics demonstrated above, development of new vanadium complex catalysts has thus been considered as an attractive target.5,7 However, successful examples that exhibit the above unique characteristics of vanadium had been limited until recently,5,7 and examples of synthesis and reaction chemistry of vanadium
alkyls were limited until recently,12
14 probably because these r 2011 American Chemical Society

vanadium
alkyls tend to be reactive and/or thermally labile and reductions to lower oxidation states often occurred in reactions with organometallic reagents.14 We focused on the synthesis and reaction chemistry of (imido)vanadium(V)
alkyl and alkylidene complexes,15,16 because these complexes exhibited remarkable catalytic activities for ethylene (co)polymerization or oligomerization7d,15,17,18 and unique reactivity in ring-opening metathesis polymerization.7d,15,16a,16d
16f Moreover, the vanadium(V)
alkylidene complexes could be prepared from the dialkyl analogues by Rhydrogen elimination in the presence of PMe3 or NHC.16a,d
f,h In order to establish a systematic synthetic route for the dialkyl analogues, we chose a route from the (arylimido)vanadium(V) trialkyl analogue, V(NAr)(CH2SiMe3)3 (Ar = 2,6-Me2C6H3), by treating with 1.0 equiv of substituted phenols/alcohols (Scheme 1).16d Most of the reactions with phenols/alcohols took place cleanly to afford the corresponding dialkyl complexes in high yields.16d However, the reaction even with an excess of 2,6-tBu2-4-MeC6H2OH (2.6 equiv) in C2D2Cl4 did not take place at 50 °C.16d We speculated that this is probably due to the steric bulk of both tert-butyl groups in the aryloxo ligand and three CH2SiMe3 ligands around V.19,20 Received: April 7, 2011 Published: June 17, 2011 3610

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Organometallics We also reported that a rapid scrambling between V(NAr)Me(NdCtBu2)(O-2,6-Me2C6H3) and V(NAr)Me(NdCtBu2)(O2,6-iPr2-4-tBuC6H2) was observed when V(NAr)Me(NdCtBu2)(O-2,6-Me2C6H3) was treated with 1.0 equiv of 4-tBu-2, 6-iPr2C6H2OH in CDCl3 at 25 °C (Scheme 2, within 30 min at 25 °C), and the solution finally gave three species in an approximately 1:2:1 ratio upon heating at 60 °C for 12 h.16c We Scheme 1. Reaction of V(NAr)(CH2SiMe3)3 with Phenols and Alcohols16d

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thus assumed that both phenol scrambling and the phenol/ ketimide exchange reaction are preferred if the phenol approaches the electrophilic vanadium metal center trans to the Me group (forming pentacoordinated trigonal-bipyramidal intermediates shown in Scheme 2). In the course of syntheses of various (arylimido)vanadium(V)
alkyl complexes from the trialkyl analogue V(NAr)(CH2SiMe3)3, we recently realized that the reaction with 1.0 equiv of 2,6-Me2C6H3OH took place cleanly,16d but the subsequent reaction with additional phenol did not proceed at 25 °C: the reaction was complete after 50 h at 60 °C (Scheme 3).21 We also found that a rapid, immediate phenoxide ligand exchange of V(NAr)(CH2SiMe3)(OAr) (1a) with C6F5OH affording V(NAr)(CH2SiMe3)(OC6F5) (1b) occurred even at 25 °C. Therefore, in this report, we wish to introduce our explored results concerning the syntheses of various (imido)vanadium(V) mono- and dialkyl complexes containing phenoxide ligands and their reaction chemistry with various phenols.21

’ RESULTS AND DISCUSSION Figure 1 shows 51V NMR spectra for monitoring the reaction of V(NAr)(CH2SiMe3)3 (Ar = 2,6-Me2C6H3) with 2.0 equiv of ArOH (2,6-Me2C6H3OH) in C6D6.21 The reaction with 1.0 equiv of ArOH proceeded at 25 °C within 1 h to afford V(NAr)(CH2SiMe3)2(OAr) (1a) exclusively (Figure 1a,b), as reported previously.16d However, the subsequent reaction with ArOH did not take place at 25 °C even after 24 h (Figure 1b), and the reaction required 50 h at 60 °C for (almost) completion to afford the bis(phenoxide) V(NAr)(CH2SiMe3)(OAr)2 (2a) (Figure 1e). The sample preparation of 2a was conducted at Scheme 2. Reaction of V(NAr)Me(NdCtBu2)(O-2,6-Me2C6H3) with 2,6-iPr2-4-tBuC6H2OH16c

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Scheme 3

Figure 1.

51

V NMR spectra in the reaction of V(NAr)(CH2SiMe3)3 with 2.0 equiv of 2,6-Me2C6H3OH in C6D6.

70 °C for 4 days in benzene to afford 2a in 58% isolated yield, and the resultant complex (2a) was identified on the basis of NMR spectra and elemental analysis. Since the second reaction, the reaction of 1a with ArOH, proceeded very slow, we thus explored the reaction of 1a with various phenols. Note that the reaction of 1a with 1.0 equiv of C6F5OH in C6D6 afforded V(NAr)(CH2SiMe3)2(OC6F5) (1b, major)16d in addition to the bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(OC6F5) (2b), as the minor product even after mixing the solution at 25 °C (Scheme 4, Figure 2a,b). A sample of 2b for identification (NMR spectra and elemental analysis) was prepared independently from 1a by treating with 1.0 equiv of C6F5OH in n-hexane at 25 °C for 4 h (yield 82.3%, described in the Experimental Section). The fact that C6F5OH first reacts with ArOH by ligand exchange is promising, because the reaction with alkyl did not take place. This clearly suggests that, as proposed previously, the reaction with C6F5OH proceeded via a pentacoordinate trigonal-bipyramidal species by coordination of C6F5OH (Scheme 4, left in the assumed intermediate).16c,d,22

The immediate ligand exchange with OC6F5 affording the bis(phenoxide) 2b also occurred when to the C6D6 solution containing V(NAr)(CH2SiMe3)(OAr)2 (2a) was added 1.0 equiv of C6F5OH at 25 °C (Scheme 4 and Figure 2c): further reaction (with ArOH remaining) did not proceed or proceeded very slowly even after 18 h. This fact is also promising because the vanadium
alkyl in 2a does not react even with strong acidic phenol, C6F5OH (pKa = 5.49). This fact also clearly suggests that the reaction with C6F5OH proceeded via pentacoordinate trigonalbipyramidal species by coordination of C6F5OH (Scheme 4, right in the assumed intermediate).22 We simply estimated the stability of the assumed coordinated species (Scheme 5) in the ligand exchange reaction of 1a or 2a with C6F5OH (estimated by PM3 semiempirical calculation).22,23 The species formed by coordination of C6F5OH to the CNO or NOO face seems more stable than the others (CCO, CCN face or CCO, CNO face), probably due to the steric bulk of the CH2SiMe3 group and/or hydrogen bonding with the phenoxide: 3612

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Organometallics especially, the coordination of C6F5OH to the NOO face in 2a thus prohibits the reaction with alkyl. Figure 3 shows 51V NMR spectra (in C6D6 at 25 °C) in the reaction of 1a with 1.0 equiv of 4-FC6H4OH (Figure 3a
c) or C6H5OH (Figure 3d
f).24 Samples of V(NAr)(CH2SiMe3)2(O-4-F-C6H4) (1c), V(NAr)(CH2SiMe3)2(OC6H5) (1d), and V(NAr)(CH2SiMe3)2(O-2,6-F2C6H3) (1e) were prepared independently from V(NAr)(CH2SiMe3)3 by treating with 4-FC6H4OH, C6H5OH, or 2,6-F2C6H3OH by a procedure Scheme 4

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analogous to that reported previously16d and were identified on the basis of NMR spectra and elemental analyses. Corresponding bis(phenoxide) analogues V(NAr)(CH2SiMe3)(OAr)(O-4
FC6H4) (2c), V(NAr)(CH2SiMe3)(OAr)(OC6H5) (2d), and V(NAr)(CH2SiMe3)(OAr)(O-2,6-F2C6H3) (2e) were also prepared from 1a according to a procedure described in the Experimental Section (in benzene at 40 °C for 5 h) and the formations were confirmed by NMR spectra. The 51V NMR spectrum after adding 4-FC6H4OH was a mixture of V(NAr)(CH2SiMe3)2(O-4
F-C6H4) (1c, major) and the bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(O-4
F-C6H4) (2c), in addition to 1a (small amount): 2c became the major product after 6 h. A similar reaction profile was observed if 1a was treated with 1.0 equiv of C6H5OH: the spectrum after adding C6H5OH was a mixture of V(NAr)(CH2SiMe3)2(OC6H5) (1d, major), the bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(OC6H5) (2d), and 1a (small amount), and 2d became the major product after 7 h.24 The results are somewhat similar but strongly suggest that the reaction of 1a with 4-FC6H4OH or C6H5OH proceeded rather slowly compared to that with C6F5OH. In contrast, as shown in Figure 4, the initial reaction product was both 1a and V(NAr)(CH2SiMe3)2(O-2,6-F2C6H3) (1e) (Figure 4a), and formation of the bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(O-2,6-F2C6H3) (2e), proceeded rather slowly (Figure 4b).25 Taking into account the observed difference in reaction of 1a with various phenols, the relative reactivity would be summarized in the following order: C6F5OH (very fast) > 4-FC6H4OH, C6H5OH > 2,6-F2C6H3OH . 2,6-Me2C6H3OH (no reaction at 25 °C). In order to explore the reactivity of 2b toward C6F5OH, the reactions of 2a with various amounts of C6F5OH were explored as NMR tube experiments (Figure 5). As described above, the rapid ligand exchange occurred to afford 2b even

Figure 2. 51V NMR spectra (in C6D6 at 25 °C) in the reaction of (a, b) V(NAr)(CH2SiMe3)2(OAr) (1a) with 1.0 equiv of C6F5OH and (c, d) V(NAr)(CH2SiMe3)(OAr)2 (2a) with 1.0 equiv of C6F5OH. *Unidentified product. 3613

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Organometallics soon after addition of 1.0 equiv of C6F5OH: the conversion of 2a to 2b became exclusive by additions of 1.2 equiv of C6F5OH. The major reaction product was 2b even if 3.0 equiv of C6F5OH was added at 25 °C, and a small amount of V(NAr)(CH2SiMe3)(OC6F5)2 [2f, prepared independently from V(NAr)(CH2SiMe3)3 with 2.0 equiv of C6F5OH in n-hexane at 50 °C for 12 h (described in the Experimental Section)] was observed in the reaction mixture (Figure 5c, Scheme 6). This Scheme 5

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observation is also promising, not only because the formation of 2f from 2b was slow whereas very rapid conversion of 2a to 2b was observed, but also because the reaction between the remaining vanadium
alkyl and an excess amount of phenols still did not take place. We have shown that the reaction of V(NAr)(CH2SiMe3)2(OAr) (1a, Ar = 2,6-Me2C6H3) or V(NAr)(CH2SiMe3)(OAr) 2 (2a) with C6F5OH took place rapidly to afford V(NAr)(CH2SiMe3)2(OC6F5) (1b) and/or V(NAr)(CH2SiMe3)(OAr)(OC6F5) (2b), and the reaction with vanadium(V)
alkyl did not take place. The reaction of 1a with 4-FC6H4OH, C6H5OH, and 2,6-F2C6H3OH initially afforded the phenoxy ligand exchange product and then converted to the corresponding bis(phenoxide) analogues. These results clearly indicate that the ligand exchange proceeded by coordination of phenols into the vanadium metal center. Moreover, the rates of the phenoxy exchange were affected by the kind of phenols employed. We strongly believe that the results presented here are promising and should be useful for a better understanding especially in the field of organometallic chemistry of vanadium. We are still preparing a series of various (imido)vanadium(V) alkyls and alkylidenes. These will be introduced in the near future.

Figure 3. 51V NMR spectra (in C6D6 at 25 °C) in the reaction of V(NAr)(CH2SiMe3)2(OAr) (1a) with 1.0 equiv of (a
c) 4-FC6H4OH or (d
f) C6H5OH.24 3614

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’ EXPERIMENTAL SECTION

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General Procedure. All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox. Anhydrous grade toluene, benzene, n-hexane, and dichloromethane (Kanto Kagaku Co., Ltd.) were transferred into a bottle containing molecular sieves (a mixture of 3A 1/16, 4A 1/8, and 13X 1/16) in the drybox under N2 and were passed through a short alumina column under a N2 stream prior to use. Elemental analyses were performed by using a PE2400II Series (Perkin-Elmer Co.) instrument. All 1H, 13C, 19F, and 51V NMR

spectra were recorded on a JEOL JNM-LA400 spectrometer (399.65 MHz for 1H, 100.40 MHz for 13C, 376.17 MHz for 19F, and 105.31 MHz for 51V) or a Bruker AV500 spectrometer (500.13 MHz for 1H, 125.77 MHz for 13C, and 131.55 MHz for 51V). All spectra were obtained in the solvent indicated at 25 °C unless otherwise noted. Chemical shifts are given in ppm and are referenced to SiMe4 (δ 0.00 ppm, 1H, 13C), CFCl3 (δ 0.00,19F), and VOCl3 (δ 0.00, 51V). Coupling constants and halfwidth values, Δν1/2, are given in Hz. V(N-2,6-Me2C6H3)(CH2SiMe3)3, V(N-2,6-Me2C6H3)(CH2SiMe3)2(O-2,6-Me2C6H3) (1a), and V(N2,6-Me2C6H3)(CH2SiMe3)2(OC6F5) (1b) were prepared according to the reported procedure.16d

Figure 4. 51V NMR spectra (in C6D6 at 25 °C) in the reaction of V(NAr)(CH2SiMe3)2(OAr) (1a) with 1.0 equiv of 2,6-F2C6H3OH.24

Figure 5. 51V NMR spectra (in C6D6 at 25 °C) in the reaction of V(NAr)(CH2SiMe3)(OAr)2 (2a) with C6F5OH.24

Scheme 6

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Organometallics V(N-2,6-Me2C6H3)(CH2SiMe3)2(O-4-FC6H4) (1c). Into a n-hexane solution (30 mL) containing V(N-2,6-Me2C6H3)(CH2SiMe3)3 (216 mg, 0.50 mmol) was added 4-FC6H4OH (56 mg, 0.50 mmol) at
30 °C. The solution was stirred at room temperature for 5 h. The resultant solution was placed into a rotary evaporator to remove volatiles, affording a sticky brown liquid. Yield: 205 mg (90.0%). 1H NMR (C6D6): δ 0.17 (s, 18H, (CH3)3Si
), 1.98 (br, 2H, VCH2
), 2.53 (s, 6H, CH3), 2.80 (br, 2H, VCH2
), 6.57
6.90 (m, 7H). 13C NMR (C6D6): δ 2.0, 19.6, 115.5, 120.6, 126.4, 136.1, 157.69, 158.5. 19F NMR (C6D6): δ
121. 51V NMR (C6D6): δ 535 (Δν1/2 = 414 Hz). Anal. Calcd for C22H35FNOSi2V: C, 57.99; H, 7.74; N, 3.07. Found: C, 57.52; H, 7.64; N, 3.32. V(N-2,6-Me2C6H3)(CH2SiMe3)2(OC6H5) (1d). Synthesis of 1d was carried out by the same procedure as that for 1c except that C6H5OH (47 mg, 0.50 mmol) was added in place of 4-FC6H4OH. Yield: 208 mg (95.1%). 1H NMR (C6D6): δ 0.15 (s, 18H, (CH3)3Si
), 2.31 (br, 2H, VCH2
), 2.52 (s, 6H, CH3), 2.57 (br, 2H, VCH2
), 6.73 (t, 1H, J = 7.1 Hz), 6.77 (t, 1H, J = 7.1 Hz), 6.85 (d, 2H, J = 7.6 Hz), 6.95
7.04 (m, 4H). 13C NMR (C6D6): δ 2.0, 19.6, 86.8 (br), 119.3, 123.8, 125.6, 127.9, 127.3, 129.4, 135.4, 165.1. 51V NMR (C6D6): δ 530 (Δν1/2 = 436 Hz). Anal. Calcd for C22H36NOSi2V: C, 60.38; H, 8.29; N, 3.20. Found: C, 59.76; H, 8.50; N, 3.46. Synthesis of V(N-2,6-Me2C6H3)(CH2SiMe3)2(O-2,6-F2C6H3) (1e). Synthesis of 1e was carried out by the same procedure as that for 1c except that 2,6-F2C6H3OH (65 mg, 0.50 mmol) was added in place of 4-FC6H4OH. Yield: 214 mg (90.4%). 1H NMR (C6D6): δ 0.15 (s, 18H, (CH3)3Si
), 2.50 (br, 2H, VCH2
), 2.53 (s, 6H, CH3), 2.80 (br, 2H, VCH2
), 6.23 (m, 1H), 6.46 (t or dd, 2H, J = 7.8 Hz), 6.66 (t, 1H, J = 8.1 Hz), 6.77 (d, 2H, J = 7.5 Hz). 13C NMR (C6D6): δ 1.6, 19.2, 111.7 (m), 120.3 (t), 126.0, 135.7, 152.8, 155.3. 19F NMR (C6D6): δ
128.2. 51V NMR (C6D6): δ 620 (Δν1/2 = 344 Hz). Anal. Calcd for C22H34F2NOSi2V: C, 55.79; H, 7.24; N, 2.96. Found: C, 55.53; H, 6.94; N, 3.21. V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)2 (2a). Into a 50 mL scale sealed Schlenk tube in the drybox were added benzene (10 mL), V(N-2,6-Me2C6H3)(CH2SiMe3)3 (0.750 g, 1.74 mmol), and 2,6-Me2C6H3OH (0.425 g, 3.48 mmol) at room temperature. The solution was then heated at 70 °C for 4 days. After the reaction, the solution was passed through a Celite pad, and the filtercake was washed with nhexane. The combined filtrate and wash was placed in a rotary evaporator to remove volatiles. The resultant solid was dissolved in a minimum amount of n-hexane. The chilled solution (
30 °C) afforded deep red microcrystals (508 mg, yield 58.4%). 1H NMR (C6D6): δ 0.31 (s, 9H, (CH3)3Si
), 2.22 (s, 6H, CH3), 2.35 (s, 12H, CH3), 2.81 (br, 2H, VCH2
), 6.51 (t or dd, 1H), 6.58 (d, 2H, J = 7.7 Hz), 6.75 (t, 2H, J = 7.3 Hz), 6.91 (d, 4H, J = 7.7 Hz). 13C NMR (C6D6): δ 1.6, 17.7, 18.4, 71.4 (br), 122.7, 126.0, 126.5, 127.6, 128.5, 128.8, 135.7, 165.3. 51V NMR (C6D6): δ
37 (Δν1/2 = 389 Hz). Anal. Calcd for C28H38NO2SiV: C, 67.31; H, 7.67; N, 2.80. Found: C, 67.24; H, 7.72; N, 3.05. V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)(OC6F5) (2b). Into a n-hexane solution (20 mL) containing V(N-2,6-Me2C6H3)(CH2SiMe3)2(O-2,6-Me2C6H3) (1a, 0.233 g, 0.5 mmol) was added C6F5OH (0.92 g, 0.50 mmol) at
30 °C. The solution was stirred at room temperature for 4 h. The resultant solution was placed into a rotary evaporator to afford a sticky deep red liquid (231 mg, 82.3%). 1H NMR (C6D6): δ 0.31 (s, 9H, (CH3)3Si
), 2.22 (s, 6H, CH3), 2.35 (s, 12H, CH3), 2.82 (br, 2H, VCH2
), 6.50 (2H, J = XXX), 6.58 (d, 2H), 6.80 (br t, 1H), 6.85 (d, 2H, J = 6.7 Hz), 6.91 (br t, 1H). 13C NMR (C6D6): δ 1.0, 17.0, 18.1, 84.0 (br), 123.6, 126.4, 127.1, 128.7, 136.4, 137.2, 138.4, 139.1, 140.4, 165.1. 19F NMR (C6D6): δ
159.4 (d, 2F, J = 22 Hz),
165.1 (t, 2F, J = 21 Hz),
167.7 (t, 1F, J = 22 Hz). 51V NMR (C6D6): δ 66.3 (Δν1/2 = 415 Hz). Anal. Calcd for C26H29NO2SiV: C, 55.61 (53.47 + VC, vanadium carbide); H, 5.21; N, 2.49. Found: C, 54.77; H, 5.04; N, 2.56.

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Formation of V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)(O-4FC6H4) (2c). Into a 50 mL scale sealed Schlenk tube in the drybox were added benzene (5 mL), V(N-2,6-Me2C6H3)(CH2SiMe3)2(O-2,6Me2C6H3) (1a, 0.233 g, 0.50 mmol), and 4-FC6H4OH (0.056 g, 0.50 mmol) at room temperature. The solution was then heated at 40 °C for 5 h. After the reaction, the solution was placed in a rotary evaporator to remove volatiles. The solution was then passed through a Celite pad, and the filter cake was washed with n-hexane. The combined filtrate and wash was placed in a rotary evaporator to remove volatiles to afford a sticky brown liquid of 2c.24 Isolation of analytically pure 2c was not successful because of contamination of 2a, monophenoxides, and unidentified products [probably tris(phenoxide)s] in small amounts. 1 H NMR (C6D6): δ 0.28 (s, 9H, Me3Si
), 2.18 (s, 6H, CH3), 2.23 (s, 6H, CH3), 2.85 and 3.08 (br, 2H, VCH2
), 6.50
6.95 (br, 10H). 13C NMR (C6D6): δ 1.50, 17.3, 17.7, 18.5, 75.0 (br), 115.7, 115.9, 119.3, 122.7, 126.2, 126.4, 128.6, 135.9, 157.7, 159.6, 162.5, 165.2. 19F NMR (C6D6): δ
120.5. 51V NMR (C6D6): δ
28 (Δν1/2 = 363 Hz). Formation of V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)(OC6H5) (2d). The reaction procedure was the same as that for 2c except that C6H5OH (0.047 g, 0.50 mmol) was used in place of 4-FC6H4OH. After removal of the volatiles in vacuo, 2d was afforded as a sticky brown liquid.24 Isolation of analytically pure 2d was not successful because of contamination of 2a and unidentified products [probably tris(phenoxide)s] in small amounts. 1H NMR (C6D6): δ 0.30 (s, 9H, Me3Si
), 2.21 (s, 6H, CH3), 2.26 (s, 6H, CH3), 2.87 and 3.09 (br, 2H, VCH2
), 6.59 (br, 3H), 6.77 (br, 3H), 6.87 (br, 3H), 7.02 (br, 2H). 13C NMR (C6D6): δ 1.5, 17.3, 17.7, 18.5, 75 (br), 118.4, 122.6, 123.1, 126.3, 127.4, 128.6, 128.7, 129.5, 135.9, 165.1, 166.4. 51V NMR (C6D6): δ
32 (Δν1/2 = 383 Hz). Formation of V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)(O-2,6F2C6H3) (2e). The reaction procedure was the same as that for 2c except that 2,6-F2C6H3OH (0.056 g, 0.50 mmol) was used in place of 4-FC6H4OH. After removal of the volatiles in vacuo, 2e was afforded as a sticky brown liquid.24 Isolation of analytically pure 2e was not successful because of contamination of 2a and unidentified products in small amounts. 1H NMR (C6D6): δ 0.33 (s, 9H, Me3Si
), 2.22 (s, 6H, CH3), 2.31 (s, 6H, CH3), 2.81 and 3.14 (br, 2H, VCH2
), 6.21 (m, 1H), 6.49 (d, 2H), 6.51
6.59 (m, 3H), 6.73 (m, 1H), 6.87 (d, 2H). 13C NMR (C6D6): δ 1.2, 17.2, 17.7, 18.2, 111.7 (m), 120.4 (t), 122.7, 123.0, 126.4, 126.6, 127.6, 128.2, 128.6, 128.7, 135.7, 136.3, 152.7, 154.6. 19F NMR (C6D6): δ
129.2 (t, J = 6.7 Hz). 51V NMR (C6D6): δ 33 (Δν1/2 = 405 Hz). V(N-2,6-Me2C6H3)(CH2SiMe3)(OC6F5)2 (2f). Into an n-hexane solution (20 mL) containing V(N-2,6-Me2C6H3)(CH2SiMe3)3 (0.864 g, 2.0 mmol) was added C6F5OH (0.736 g, 4.0 mmol) at
30 °C. The solution was stirred at 50 °C for 12 h. The resultant solution was placed into a rotary evaporator to remove volatiles, and the resultant solid was dissolved with a minimum amount of n-hexane. The chilled (
30 °C) solution afforded deep red microcrystals (445 mg, 35.7%). 1H NMR (C6D6): δ 0.19 (s, 9H, Me3Si
), 2.17 (s, 6H, CH3), 6.50 (s, 3H). 13C NMR (C6D6): δ 0.7, 18.0, 127.8, 128.2, 135.4 (m), 137.1, 138.3 (m), 139.1 (m), 140.3 (m), 140.8 (m), 166.3 (m). 19F NMR (C6D6): δ
158.9,
164.6,
166.2. 51V NMR (C6D6): δ 176 (Δν1/2 = 513 Hz). Resonances of the proton and carbon ascribed to CH2SiMe3 were not observed (or very difficult to assign). Anal. Calcd for C24H20F10NO2SiV:C, 46.24; H, 3.23; N, 2.25. Found: C, 46.24; H, 3.20; N, 2.12. NMR Experiments for the Time Course in the Reaction of V(N-2,6Me2C6H3)(CH2SiMe3)2(O-2,6-Me2C6H3) (1a) with C6F5OH in C6D6. A typical procedure is as follows. Into a frozen C6D6 solution (ca. 0.4 mL) containing 1a (23.3 mg, 50 μmol) placed in the freezer (
30 °C) was added a C6D6 solution (ca. 0.1 mL) containing C6F5OH (9 mg, 1.0 equiv). The mixture was then monitored by 51V NMR to estimate the ratio between the starting material and the product by integration ratio of the resonances. (The measurements were started in less than 5 min.) 3616

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’ ASSOCIATED CONTENT

bS

Supporting Information. Selected NMR spectra (in C6D6 at 25 °C) for additional explanation. These materials are available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

Tel: +81-42-677-2547. Fax: +81-42-677-2547. E mail: ktnomura@ tmu.ac.jp.

’ ACKNOWLEDGMENT This research was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas (No. 19028047, “Chemistry of Concerto Catalysis”) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and The Ube Foundation. ’ REFERENCES (1) (a) In The Organometallic Chemistry of the Transition Metals, 5th ed.; Crabtree, R. H., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2009; p 58. (b) In Comprehensive Organometallic Chemistry III; Crabtree, R. H.; Mingos, D. M. P., Eds.; Elsevier Science/Pergamon US: New York, USA, 2006. (c) In Synthesis of Organometallic Compounds: A Practical Guide; Komiya, S., Ed.; John Wiley & Sons, Inc.: West Sussex, England, 1997. (d) In Organometallics in Synthesis: A Manual, 2nd ed.; Schlosser, M., Ed.; John Wiley & Sons Ltd.: West Sussex, England, 2002. (e) In Organometallic Chemistry and Catalysis; Astruc, D., Ed.; SpringerVerlag: Berlin, Germany, 2007. (2) (a) Mason, A. F.; Coates, G. W. In Macromolecular Engineering; Matyjaszewski, K.; Gnanou, Y.; Leibler, L., Eds.; Wiley-VCH: Weinheim, Germany, 2007; Vol. 1, p 217. (b) Metal Catalysts in Olefin Polymerization, Topics in Organometallic Chemistry 26; Guan, Z., Ed.; Springer Verlag: Berlin, 2009. (3) For selected review articles for metallocenes and linked halfmetallocenes (constrained geometry type), see: (a) Brintzinger, H. H.; Fischer, D.; M€ulhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b) Kaminsky, W. Macromol. Chem. Phys. 1996, 197, 3903. (c) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 143. (d) Suhm, J.; Heinemann, J.; W€orner, C.; M€uller, P.; Stricker, F.; Kressler, J.; Okuda, J.; M€ulhaupt, R. Macromol. Symp. 1998, 129, 1. (e) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587. (f) Braunschweig, H.; Breitling, F. M. Coord. Chem. Rev. 2006, 250, 2691. (g) Cano, J.; Kunz, K. J. Organomet. Chem. 2007, 692, 4411. (4) For review articles on half-metallocenes, see: (a) Stephan, D. W. Organometallics 2005, 24, 2548. (b) Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. J. Mol. Catal. A 2007, 267, 1. (c) Nomura, K. Dalton Trans. 2009, 8811.(d) Nomura, K.; Liu, J. Dalton Trans., in press (Web released on Mar 15, 2011). (5) For selected review articles for non-metallocenes, see: (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 429. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283. (c) Bolton, P. D.; Mountford, P. Adv. Synth. Catal. 2005, 347, 355. (6) For special issues, see: (a) Frontiers in Metal-Catalyzed Polymerization (special issue): Gladysz, J. A., Ed.; Chem. Rev. 2000, 100 (4). (b) Metallocene Complexes As Catalysts for Olefin Polymerisation: Alt, H. G., Ed.; Coord. Chem. Rev. 2006, 250 (1
2), 1. (c) Metallocene Complexes As Catalysts for Olefin Polymerization (special issue): Alt, H. G., Ed.; Coord. Chem. Rev. 2006, 250 (1
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in Catalysis Research; Bevy, L. P., Ed.; NOVA Science Publishers: New York, USA, 2005; p 199. (d) Redshaw, C. Dalton Trans. 2010, 39, 5595. (e) Nomura, K.; Zhang, S. Chem. Rev. 2011, 111, 2342. (8) (a) Carrick, W. L. J. Am. Chem. Soc. 1958, 80, 6455. (b) Carrick, W. L.; Kluiber, R. W.; Bonner, E. F.; Wartman, L. H.; Rugg, F. M.; Smyth, J. J. J. Am. Chem. Soc. 1960, 82, 3883. (c) Phillips, G. W.; Carrick, W. L. J. Polym. Sci. 1962, 59, 401. (9) (a) Junghanns, E.; Gumboldt, O.; Bier, G. Makromol. Chem. 1962, 58, 18. (b) Natta, G.; Mazzanti, G.; Valvassori, A.; Sartori, G.; Fiumani, D. J. Polym. Sci. 1961, 51, 411. (10) For example: Christman, D. L.; Keim, G. I. Macromolecules 1968, 1, 358. (11) (a) Doi, Y.; Ueki, S.; Keii, T. Macromolecules 1978, 12, 814. (b) Doi, Y.; Koyama, T.; Soga, K. Makromol. Chem. 1985, 186, 11. (12) For structural characterizations and reaction chemistry of V(III),(IV) methyl complexes, see: (a) Hessen, B.; Teuben, J. H.; Lemmen, T. H.; Huffman, J. C.; Caulton, K. G. Organometallics 1985, 4, 946. (b) Hessen, B.; Lemmen, T. H.; Luttikhedde, H. J. G.; Teuben, J. H.; Petersen, J. L.; Jagner, S.; Huffman, J. C.; Caulton, K. G. Organometallics 1987, 6, 2354. (c) Hessen, B.; Meetama, A; Teuben, J. H. J. Am. Chem. Soc. 1989, 111, 5977. (d) Gerlach, C. P.; Arnold, J. Organometallics 1996, 15, 5260. (e) Aharonian, G.; Feghali, K.; Gambarotta, S.; Yap, G. P. A. Organometallics 2001, 20, 2616. (f) Feghali, K.; Harding, D. J.; Reardon, D.; Gambarotta, S.; Yap, G.; Wang., Q. Organometallics 2002, 21, 968. (g) Choukroun, R.; Lorber, C.; Donnadieu, B. Organometallics 2002, 21, 1124. (h) Liu, G.; Beetstra, D. J.; Meetsma, A.; Hessen, B. Organometallics 2004, 23, 3914. (13) Examples for structurally characterized V(V) alkyls: (a) de With, J.; Horton, A. D.; Orpen, A. G. Organometallics 1990, 9, 2207. (b) Murphy, V. J.; Turner, H. Organometallics 1997, 16, 2495. (14) Examples: (a) Preuss, F.; Ogger, L. Z. Naturforsch. 1982, 37B, 957. (b) Devore, D. D.; Lichtenhan, J. D.; Takusagawa, F.; Maatta, E. J. Am. Chem. Soc. 1987, 109, 7408. (c) Preuss, F.; Becker, H.; Kraub, J.; Sheldrick, W. J. Z. Naturforsch. 1988, 43B, 1195. (d) Preuss, F.; Becker, H.; Wieland, T. Z. Naturforsch. 1990, 45B, 191. (e) Solan, G. A.; Cozzi, P. G.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1994, 13, 2572. (f) Chan, M. C. W.; Cole, J. M.; Gibson, V. C.; Howard, J. A. K. Chem. Commun. 1997, 2345. (15) Nomura, K.; Zhang, W. Chem. Sci. 2010, 1, 161. (16) (a) Yamada, J.; Nomura, K. Organometallics 2005, 24, 2248. (b) Yamada, J.; Fujiki, M.; Nomura, K. Organometallics 2005, 24, 3621. (c) Yamada, J.; Fujiki, M.; Nomura, K. Organometallics 2007, 26, 2579. (d) Nomura, K.; Onishi, Y.; Fujiki, M.; Yamada, J. Organometallics 2008, 27, 3818. (e) Zhang, W.; Yamada, J.; Nomura, K. Organometallics 2008, 27, 5353. (f) Zhang, W.; Nomura, K. Organometallics 2008, 27, 6400. (g) Zhang, W.; Katao, S.; Sun, W.-H.; Nomura, K. Organometallics 2009, 28, 1558. (h) Zhang, S.; Tamm, M.; Nomura, K. Organometallics 2011, 30, 2712. (17) For example, see: (a) Nomura, K.; Sagara, A.; Imanishi, Y. Macromolecules 2002, 35, 1583. (b) Wang, W.; Nomura, K. Macromolecules 2005, 38, 5905. (c) Wang, W.; Nomura, K. Adv. Synth. Catal. 2006, 348, 743. (d) Onishi, Y.; Katao, S.; Fujiki, M.; Nomura, K. Organometallics 2008, 27, 2590. (e) Zhang, S.; Nomura, K. Organometallics 2009, 28, 5925. (18) Zhang, S.; Nomura, K. J. Am. Chem. Soc. 2010, 132, 4960. (19) For examples, see: (a) Lubben, T. V.; Wolczanski, P. T.; van Duyne, G. D. Organometallics 1984, 3, 977. In this report, the reaction of Zr(CH2Ph)4 with 1.14 equiv of tBu3COH in benzene under reflux conditions for 7 h afforded Zr(CH2Ph)3(OCtBu3), whereas synthesis of Zr(CH2Ph)3(OCtBu3) by the reaction of Zr(CH2tBu)4 with tBu3COH in benzene required 30 h at 93
95 °C.(b) It has been known that certain chromium(IV)
tetra(alkyl)s are stable even in alcohols under reflux conditions. (20) For recent examples, see: (a) Nicholas, P.; Ahn, H. S.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 4325. (b) McKittrick, M. W.; Jones, C. W. J. Am. Chem. Soc. 2004, 126, 3052. (c) Rhers, B.; Salameh, A.; Baudouin, A.; Quadrelli, E. A.; Taoufik, M.; Coperet, C.; Lefebvre, F.; Basset, J.-M.; Solans-Monfort, X.; Eisenstein, O.; Lukens, W. W.; Lopez, L. P. H.; Sinha, A.; Schrock, R. R. Organometallics 2006, 25, 3554. 3617

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(21) Part of these results were presented at the 24th International Conference on Organometallic Chemistry (ICOMC), Taipei, Taiwan, July 2010 (poster presentation). (22) According to a simple estimation of the stability of the proposed pentacoodinated species, [V(NAr)(CH2SiMe3)2(OAr)(C6F5OH)], by simple energy evaluations [equilibrium geometry at the ground state with semiempirical PM3, geometry optimization, RHF/PM3D Spartan ’08 for Windows (Wavefunction Inc.)], the coordination of C6F5OH to the CNO face seems favored [ΔE = 6.45 kcal/mol (coordination to CCN face), 9.14 kcal/mol (coordination to CCO face)]. Moreover, the stability of [V(NAr)(CH2SiMe3)(OAr)2(C6F5OH)] in the coordination of C6F5OH to the bis(phenoxide) (2a), the species by coordination of C6F5OH onto the NOO face, seems favored over the coordination onto the COO face (ΔE = 30.61 kcal/mol) or CNO (ΔE = 43.49 kcal/ mol) face. Although these data are based on a simple evaluation at the semiempirical PM3 level, these data assume that coordination onto the CNO or NOO face should be favored to induce the ligand exchange. (23) We previously received a comment from a reviewer16c about the possibility of the arylimido ligand acting as a proton shuttle, and we cannot neglect this possibility at this stage. (24) Selected NMR spectra for monitoring the reactions and additional explanations are shown in the Supporting Information. (25) As shown in Figure 4c, experimental descriptions for syntheses of the bis(phenoxide) analogues (2c
e), and in the Supporting Information, we observed the formation of 2a as the minor product. These might be due to the presence of an equilibrium of coordination and dissociation of phenol in the reaction mixture.16g

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