Ring-Opening Polymerization of THF by Aryloxo-Modified

Jul 12, 2012 - A new vanadium(V)-alkylidene, V(CHSiMe3)(NAd)(OC6F5)(PMe3)2, prepared from ... elimination in n-hexane in the presence of PMe3 at 25 °...
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Ring-Opening Polymerization of THF by Aryloxo-Modified (Imido)vanadium(V)-alkyl Complexes and Ring-Opening Metathesis Polymerization by Highly Active V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 Kotohiro Nomura,*,†,‡ Ken Suzuki,† Shohei Katao,‡ and Yuichi Matsumoto‡ †

Department of Chemistry, Graduate School of Science and Engineering, 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 S Supporting Information *

ABSTRACT: Ring-opening polymerizations of THF using V(NR)(CH2SiMe3)(OAr)2 [R = 2,6-Me2C6H3, 1-adamantyl (Ad), Ph; Ar = 2,6-Me2C6H3, C6F5] proceeded in a living manner in the presence of [Ph3C][B(C6F5)4], affording high molecular weight polymers with low PDI (Mw/Mn) values: the observed activity (initiation efficiency) was affected by the arylimido and aryloxo ligands employed. A new vanadium(V)alkylidene, V(CHSiMe3)(NAd)(OC6F5)(PMe3)2, prepared from V(NAd)(CH2SiMe3)2(OC6F5) by α-hydrogen elimination in n-hexane in the presence of PMe3 at 25 °C, exhibited remarkable catalytic activity for ring-opening metathesis polymerization of norbornene: the activity at 25 °C was higher than those by the reported vanadium(V)-alkylidenes and ordinary Mo(CHCMe2Ph)(N-2,6-iPr2-C6H3)(OtBu)2.

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INTRODUCTION Classical Ziegler-type vanadium catalysts are known to display unique characteristics, exemplified by syntheses of high molecular weight linear polyethylene1 and amorphous polymers [applied to synthesis of ethylene/propylene/diene copolymers (called EPDM, synthetic rubbers)]2,3 with uniform molecular weight distributions and others.4 Due to the promising characteristics demonstrated above, development of new vanadium complex catalysts for controlled polymerization has been considered as an attractive target.5,6 We recently demonstrated that (arylimido)vanadium(V) complexes containing anionic donor ligands (aryloxo, phenoxyimine, etc.) exhibited remarkable catalytic activities for ethylene polymerization7 and ethylene/norbornene copolymerization.7b,c Moreover, we recently demonstrated that the catalyst containing the chelate (2-anilidomethyl)pyridine ligand can be tuned from a polymerization catalyst to a highly efficient ethylene dimerization catalyst by modification of the imido ligand.8 We also focused on synthesis and reaction chemistry of (imido)vanadium(V)-alkyl and -alkylidene complexes,9−11 because their syntheses and reaction chemistry are of fundamental importance for basic understanding in organometallic chemistry and might also lead to promising applications in catalysis. We recently demonstrated that the ketimide,10a,e the aryloxo10d-modified vanadium(V)-alkylidenes (Chart 1), exhibited unique reactivities in the ring-opening metathesis polymerization (ROMP) of norbornene (NBE). More recently, we demonstrated 1,2-C−H bond activation of benzene promoted by an imidazolin-2-iminato-modified © 2012 American Chemical Society

Chart 1. Selected Vanadium(V)-alkylidenes As Catalysts for Ring-Opening Metathesis Polymerization10a,d,e

vanadium(V)-alkylidene.10h These alkylidenes were prepared by α-hydrogen elimination from the dialkyl analogues in C6D6 or n-hexane in the presence of PMe3, known as a common approach to prepare high-oxidation-state early transition metal alkylidenes.12,13 In our recent short full article,14 various (imido)vanadium dialkyl complexes containing aryloxo ligands, V(NR)(CH2SiMe3)2(OAr) [R = 1-adamantyl (Ad), 2,6-Me2C6H3; Ar = Ph, 4-FC6H4, 2,6-F2C6H3, 2,6-Me2C6H3, C6F5], were employed as the catalyst precursors for ROMP of NBE in the presence of PMe3 (at 80 °C). It turned out that the activity was strongly affected by the aryloxo substituent (Scheme 1): the imido ligand also affected the activity. In particular, the (imido)vanadium(V) complexes containing a OC6F5 ligand exhibited notable activities at 80 °C, and the complexes showed Received: May 27, 2012 Published: July 12, 2012 5114

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Scheme 1. Ring-Opening Metathesis Polymerization of Norbornene by V(NR)(CH2SiMe3)2(OAr) [R = 1-adamantyl (Ad), 2,6Me2C6H3] in the Presence of PMe314

moderate activities even at 25 °C. On the basis of these results, in this paper, we thus explored a possibility for isolation of the vanadium(V)-alkylidene-containing pentafluorophenoxy ligand as a promising catalyst in olefin metathesis polymerization.15 Moreover, we also demonstrated ring-opening polymerization of THF using a catalyst system consisting of V(NAd)(CH2SiMe3)(OAr)2 [Ar = 2,6-Me2C6H3 (1a), C6F5 (1b)] and [Ph 3 C][B(C 6 F 5 ) 4 ] for the first time with vanadium.14 Since the catalyst systems afforded ring-opened high molecular weight poly(THF)s with low PDI (Mw/Mn) values, we thus explored in more detail especially the effect of both imido and aryloxo ligands on the activity. Through these studies, we expect to obtain some important information for designing efficient catalysts for these two ring-opening polymerizations. 1. Ring-Opening Polymerization of THF by V(NR)(CH2SiMe3)(OAr)2 (R = Ad, 2,6-Me2C6H3, Ph; Ar = 2,6Me2C6H3, C6F5)−[Ph3C][B(C6F5)4] Catalyst Systems. As described above, we recently demonstrated that ring-opening polymerization (ROP) of tetrahydrofuran (THF) by V(NAd)(CH2SiMe3)(OAr)2 [Ar = 2,6-Me2C6H3 (1a), C6F5 (1b)] proceeded in a living manner in the presence of [Ph3C][B(C6F5)4] (Scheme 2).14 Since the reaction of V(N-2,6-

Table 1. Ring-Opening Polymerization of THF by V(NR)(CH2SiMe3)(OAr)2 [R = 1-adamantyl (Ad, 1), 2,6Me2C6H3 (2), Ph (3); Ar = 2,6-Me2C6H3 (a), C6F5 (b)]− [Ph3C][B(C6F5)4] Catalyst Systemsa complex c

1a 1ac 1ac 1ac 1bc 1bc 1bc 1bc 2a 2a 2a 2a 2b 2b 2b 2b 3a 3a 3a 3a

Scheme 2

time/min

yield/mg

Mnb × 10−4

Mw/Mnb

15 30 45 60 15 30 45 60 15 30 45 60 15 30 45 60 15 30 45 60

53 101 139 212 48 80 100 159 120 156 226 272 81 120 157 232 10 20 25 46

8.87 13.5 16.6 20.5 6.80 12.8 14.7 21.1 8.4 11.8 17.2 21.5 13.9 16.3 21.3 30.4 7.4 11.2 12.9 16.7

1.06 1.11 1.11 1.18 1.20 1.19 1.21 1.18 1.10 1.14 1.12 1.18 1.11 1.16 1.15 1.21 1.08 1.15 1.20 1.20

Reaction conditions: complex 40 μmol, [Ph3C][B(C6F5)4] 40 μmol, THF 5.0 mL, 25 °C. bGPC data in THF vs polystyrene standards. c Cited from ref 14. a

(CH2SiMe3)(OAr)2 (1a,b),14 V(N-2,6-Me2C6H3)(CH2SiMe3)(OAr)2 (2a,b),10i and V(NPh)(CH2SiMe3)(O-2,6-Me2C6H3)2 (3a), were prepared from the trialkyl analogues, V(NR)(CH2SiMe3)3, by treatment with the corresponding phenols (2 equiv). As shown in both Table 1 and Figure 1, the Mn values of the resultant polymers increased linearly upon increasing the polymer yields consistently with rather low PDI values in all cases (Figure 1a). Moreover, both the Mn values and the polymer yields increased over the time course under these conditions (Figure 1b). Therefore, these results strongly suggest that these polymerizations proceeded in a living manner. As far as we know, this is not only the first example of vanadium-initiated living ROP of THF but also a rare example for the synthesis of high molecular weight poly(THF) in a controlled manner. The ROP of THF by 2a did not take place when the reactions were conducted in the presence of [PhN(H)Me2][B(C6F5)4] or B(C6F5)3 in place of [Ph3C][B-

Me2C6H3)(Me)(NCtBu2)2 with [Ph3C][B(C6F5)4] in THF exclusively afforded a cationic complex, [V(N-2,6-Me2C6H3)(NCtBu2)2(THF)]+[B(C6F5)4]−,10c the facts (occurrence of ring-opening polymerization) are thus in unique contrast. The resultant polymers possessed high molecular weights with rather low PDI (Mw/Mn) values; therefore, we explored the polymerization using a series of V(NR)(CH2SiMe3)(OAr)2 [R = 1-adamantyl (Ad, 1), 2,6-Me2C6H3 (2), Ph (3); Ar = 2,6Me2C6H3 (a), C6F5 (b)] under rather low catalyst concentration conditions to explore the ligand effect toward the activity as well as the initiation efficiency. The results are summarized in Table 1. These alkyl complexes, V(NAd)5115

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Figure 1. Plots of (a, left) Mn values and Mw/Mn values vs polymer yields and (b, right) polymer yields and Mn values vs time course in ring-opening polymerization of THF by V(NR)(CH2SiMe3)(OAr)2 [R = 1-adamantyl (Ad, 1), 2,6-Me2C6H3 (2), Ph (3); Ar = 2,6-Me2C6H3 (a), C6F5 (b)]− [Ph3C][B(C6F5)4] catalyst systems. Plots of (a) 1a (▲,△), 1b (⧫,◇), 2a (■,□), 2b (●,○), 3a (+,× ) for Mn × 10−4, Mw/Mn, respectively; (b) 2a (■,□), 2b (●,○), 3a (+,× ) for Mn × 10−4, polymer yield, respectively. Detailed conditions are shown in Table 1.

simple comparison to estimate the relative rate. The results are thus summarized in Table 2. Although 2b showed the largest values, no significant differences were observed among the other complexes (1a,b, 2b, 3a). These results would suggest that both imido and aryloxo ligands affected the initiation efficiency in most cases except 2b. 2. Synthesis and Structural Analysis of V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 and Its Use As the Catalyst for Ring-Opening Metathesis Polymerization of Cyclic Olefins. 2-1. Synthesis and Structural Analysis of V(CHSiMe3)(NAd)(OC6F5)(PMe3)2. V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) was cleanly isolated in moderate isolated yield (38%) when an n-hexane solution containing V(NAd)(CH2SiMe3)2(OC6F5) was added to PMe3 in excess amount (at −30 to 25 °C, Scheme 3). The resultant complex (4) was

(C6F5)4]. Monitoring the reaction of 2a with [PhN(H)Me2][B(C6F5)4] showed no significant changes in the 1H, 51V, and 19 F NMR spectra even after 24 h (in C6D6 at 25 °C), suggesting no reaction took place under these conditions. The polymer yields in the ROP using various complexes after 60 min increased in the order 3a ≪ 1b < 1a < 2b < 2a. The polymer yields by using the phenylimido analogue (3a) were much lower than those by the others, although the resultant polymers possessed relatively high molecular weights (Mn = (7.4−16.7) × 104). The arylimido analogues (2a,b) showed relatively better THF consumption than the adamantylimido analogues (1a,b): the Mn values of the resultant polymers prepared by V(N-2,6-Me2C6H3)(CH2SiMe3)(OC6F5)2 (2b) were higher than those by the others. These results also suggest that the catalytically active (propagating) species were formed partially in these catalyses. Table 2 summarizes observed TOF values (min−1) calculated on the basis of polymer yields. Since it is possible to simply

Scheme 3

Table 2. Summary of Reaction Rates in Ring-Opening Polymerization of THF

a

complex

TOFa/ min−1

Nassumedb/μmol

relative ratec

1a 1b 2a 2b 3a

1.15 0.87 1.71 1.31 0.23

0.750 0.623 1.32 0.733 0.179

1.53 1.40 1.30 1.79 1.28

identified by 1H, 13C, 19F, 31P, and 51V NMR spectra and elemental analysis, and the structure was determined by X-ray crystallography (Figure 2). Only one broad resonance ascribed to vanadium(V)-alkylidene was observed at 16.09 ppm in the 1 H NMR spectrum and at 329 ppm in the 13C NMR spectrum. These data strongly suggest the formation of the alkylidene species. In contrast, 4 showed a large (−188 ppm) in addition to a small resonance (−133 ppm) in the 51V NMR spectrum.16 Two possibilities might be considered for explaining the observed results (51V NMR spectrum): (i) PMe3 is partly dissociated in solution as observed in the other (arylimido)vanadium(V)-alkylidenes containing aryloxo,10d ketimide ligands,10a,e or (ii) the resultant alkylidene is present as a syn/anti mixture in an appropriate ratio in solution. We assume the latter possibility at this moment, because no significant changes in the 51V NMR spectra were observed in the presence of even 20 equiv of PMe3.16 An attempt to isolate the alkylidene in the

−1

TOF (min ) = [(mmol of THF consumed)/(mmol of V charged)]/ time (min), average between 30 and 60 min. bAssumed number of polymer chains calculated based on Mn value and polymer yield (after 30 min). cRelative propagation rate (min−1) simply estimated by TOF/Nassumed for comparison.

assume the number of polymer chains (Nassumed, amount of catalyst initiated for the ROP) from both the polymer yields and Mn values, it would thus be possible to estimate the actual relative propagation rates by each catalyst (on the basis of TOF and Nassumed). This is because the Nassumed values would be considered as a percentage of the formed active species in situ. Although the actual number of polymer chains (amount of actual catalyst) employed here should not be accurate from the real values because these Mn values were estimated by GPC versus polystyrene standards, these values should be used for 5116

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140.47(13)°, N(1)−V(1)−C(17) 106.25(16)°, O(1)−V(1)− C(17) 113.28(15)°, total 360°]. The results thus indicate that two phosphorus atoms are positioned in a trans form. The V(1)−C(17) bond distance [1.845(4) Å] is shorter than those in V(CHSiMe3)(NAr′)(NCtBu2)(PMe3) [1.860(2) Å]10a and V(CHSiMe3)(NAr′)[1,3-(2,6-iPr2C6H3)2(CHN)2CN](PMe3) [1.866(5) Å],10h but longer than V(NAd)(CHSiMe3)(CH2SiMe3)(NHC) [1.829(3) Å, NHC = 1,3(2,6- iPr2C6H3) 2(CHN)2C].10f The V−P bond distances [2.4869(10), 2.4665(11) Å] are apparently longer than those in V(CHSiMe3)(NAr′)[1,3-(2,6-iPr2C6H3)2(CHN)2CN](PMe3) [2.4202(14) Å]10h and V(CHSiMe3)(NAr′)(N CtBu2)(PMe3) [2.4331(7) Å],10a probably because these phosphine ligands are placed in a trans form. The SiMe3 group is positioned syn (major) probably due to a rather small adamantylimido ligand versus a rather sterically crowded pentafluorophenoxy substituent in a N−C−O plane. 2-2. Ring-Opening Metathesis Polymerization of Norbornenes by V(CHSiMe3)(NAd)(OC6F5)(PMe3)2. It should be noted that the isolated V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) exhibited remarkable catalytic activities for the ROMP of norbornene: the polymerization reached completion within 10 min even under low catalyst concentration conditions (runs 3− 5), whereas the activities were low when the ROMP by the corresponding dialkyl analogue, V(NAd)(CH2SiMe3)2(OC6F5), was conducted in the presence of PMe3 (runs 1, 2).14 The resultant polymers prepared by 4 possessed rather high molecular weights with unimodal molecular weight distributions (Mw/Mn = 2.1−2.2, runs 3−5, suggesting a possibility of chain transfer).16 The ROMP of NBE by the reported V(CHSiMe 3)(NAr′)(NCtBu2)(PMe3) (5) 10a and V(CHSiMe 3 )(NAr′)(O-2,6- i Pr 2 C 6 H 3 )(PMe 3 ) (6)10d was also carried out for comparison (Table 3, Scheme 4), but the observed activities of 5 and 6 were low under these conditions. Complex 6 afforded a polymer with narrow molecular weight distribution, because the ROMP by 6 generally proceeded in a living manner under these conditions (run 6).10d Moreover, the ROMP by known Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 (7)12,17,18 was also conducted under the same conditions (run 8), but the conversion (63%) was lower than that by 4 under the same conditions (run 8 vs run 5), although the resultant polymer possessed narrow distributions (Mw/Mn = 1.02). These results clearly indicate that the present vanadium(V)-alkylidene (4) exhibits one of the highest levels of activity among these complex catalysts.

Figure 2. ORTEP drawing for V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4). Selected bond distances (Å): V(1)−C(17) 1.845(4), V(1)−P(1) 2.4869(10), V(1)−P(2) 2.4665(11), V(1)−N(1) 1.660(3), V(1)− O(1) 2.003(3), N(1)−C(1) 1.442(5). Selected Bond Angles (°): P(1)−V(1)−O(1) 80.01(8), P(2)−V(1)−O(1) 81.39(8), P(2)− V(1)−C(17) 91.82(11), P(1)−V(1)−C(17) 94.13(11), P(2)− V(1)−N(1) 97.44(10), P(1)−V(1)−N(1) 97.82(10), N(1)−V(1)− C(17) 106.25(16), O(1)−V(1)−C(17) 113.28(15), P(1)−V(1)− P(2) 161.35(4), O(1)−V(1)−N(1) 140.47(13), V(1)−N(1)−C(1) 173.3(3).

presence of PPh3 in place of PMe3 recovered 4. The conditions adopted here (25 °C for 3 h) should be a unique contrast to those for isolation of reported (arylimido)vanadium(V)alkylidenes, V(NAr′)V(CHSiMe3)(X)(PMe3)n [Ar′ = 2,6Me 2 C 6 H 3 ; X = NC t Bu 2 , 10a O-2,6- i Pr 2 C 6 H 3 , 10d 1,3(2,6-iPr2C6H3)2(CHN)2CN10h], which required heating (at 60−80 °C) for promotion of α-hydrogen elimination. The crystallographic result (Figure 2) indicates that 4 displays a distorted trigonal-bipyramidal geometry around the vanadium atom consisting of two phosphorus axes [bond angles: P(1)−V−P(2) 161.35(4) o , P(1)−V(1)−O(1) 80.01(8)°, P(1)−V(1)−N(1) 97.44(10)°, P(1)−V(1)−C(17) 91.82(11)°] and a plane consisting of the aryloxo, alkylidene, and adamantylimido ligand [bond angles: O(1)−V(1)−N(1)

Table 3. Ring-Opening Metathesis Polymerization of Norbornene by V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4), V(CHSiMe3)(N-2,6-Me2C6H3)(NCtBu2)(PMe3) (5), V(CHSiMe3)(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3)(PMe3) (6), and Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 (7)a run

catalyst (μmol)

NBE/concb

time/min

conv/%

TONc

TOF/h−1

Mnd × 10−4

Mw/Mnd

1e 2e 3 4 5 6 7 8

V(NAd)(CH2SiMe3)2(OC6F5) + PMe3 (5.0) V(NAd)(CH2SiMe3)2(OC6F5) + PMe3 (5.0) V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) (2.5) V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) (2.5) V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) (1.0) V(CHSiMe3)(N-2,6-Me2C6H3)(NCtBu2)(PMe3) (5) (1.0) V(CHSiMe3)(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3)(PMe3) (6) (1.0) Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 (7) (1.0)

0.44 0.89 0.22 0.22 0.44 0.44 0.89 0.44

60 60 5 10 3 60 60 10

2 28 92 97 95 7 7 63

9 117 1576 1657 2020 149 149 1340

9 117 18 900 9900 40 300 149 149 8040

1.4 5.5 28 35 95 42 3.1 19

2.0 2.8 2.2 2.1 2.1 2.4 1.1 1.02

a Reaction conditions: catalyst 1.0 μmol, norbornene 2.12 mmol, benzene solvent 2.4 mL (runs 2, 7) or 4.8 mL (runs 1, 5, 6, 8) or 9.6 mL (runs 3, 4), 25 °C. bInitial NBE conc (mmol/mL). cTON (turnovers) = NBE reacted (mmol)/vanadium complex charged (mmol). dGPC data in odichrolobenzene vs polystyrene standards. eCited from ref 14.

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etc.). 16 However, the attempted ROMP of 2,3-bis(carbomethoxy)norborn-5-ene (NBEDE) did not take place or afforded negligible amount of product. Although the present vanadium(V)-alkylidene (4) may not be effective for norbornenes with the ester functionality, these results clearly indicate that the present catalyst (4) should be useful for certain applications.

Scheme 4

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CONCLUDING REMARKS In this paper, we explored the effect of imido and aryloxo ligands in the ring-opening polymerization of tetrahydrofuran by V(NR)(CH2SiMe3)(OAr) [R = 1-adamantyl (1), 2,6Me2C6H3 (2), Ph (3); Ar = 2,6-Me2C6H3 (a), C6F5 (b)] in the presence of [Ph3C][B(C6F5)4]. The ROP proceeded in a living manner in all cases, and the polymer yields by the arylimido analogues were higher than the adamantylimido analogues (1a,b). It was thus assumed that both imido and aryloxo ligands affect the initiation efficiency in most cases except 2b, which afforded polymers with high molecular weights. V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4) was cleanly isolated from V(NAd)(CH2SiMe3)2(OC6F5) by α-hydrogen elimination. Complex 4 exhibited much higher catalytic activities for ring-opening metathesis polymerization of norbornene than V(CHSiMe3)(N-2,6-Me2C6H3)(NCtBu2)(PMe 3 ) (5) 10a and V(CHSiMe 3 )(N-2,6-Me 2 C 6 H 3 )(O2,6-iPr2C6H3)(PMe3) (6):10d 4 showed higher activity than the known Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 (7) under the same conditions. The ROMP of dicyclopentadiene, 5-vinyl-2-norbornene, and 5-ethylidene-2-norbornene by 4 was complete within 15 min to afford high molecular weight ringopened polymers with uniform distributions. The results clearly indicate that 4 should be a highly effective catalyst for ROMP of norbornene derivatives. We believe that this is potentially important information for designing vanadium complex catalysts for efficient olefin polymerization. Since the arylimido analogue showed higher activities than the adamantylimido analogues in ROMP of NBE by the dialkyl analogues in the presence of PMe3,14 we are exploring the possibility of isolation of the analogous V(CHSiMe3)(N-2,6-Me2C6H3)(OC6F5)(PMe3)n, although our initial attempt was unsuccessful. Our explored results including isolation of more active catalysts and their applications will be introduced in the near future.

ROMPs of various norbornene derivatives were thus employed in the presence of 4 under similar conditions (Scheme 5), and the results are summarized in Table 4. The Scheme 5

Table 4. Ring-Opening Metathesis Polymerization of Various Norbornenes by V(CHSiMe3)(NAd)(OC6F5)(PMe3)2 (4)a monomer

time/min

yield/%

TONb

Mnc × 10−4

Mw/Mnc

DCP VNBE ENBE DENBE

10 15 15 180

99 98 98

424 414 416

5.4 8.5 6.0

2.0 1.8 2.1

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EXPERIMENTAL SECTION

General Procedure. All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox. Anhydrous grade toluene, benzene, and n-hexane (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 an alumina short column under a N2 stream prior to use. Elemental analyses were performed by using an EAI CE-440 CHN/O/ S elemental analyzer (Exeter Analytical, Inc.). All 1H, 13C, 19F, 31P, and 51 V NMR spectra were recorded on 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 half-width values, Δν1/2, are given in Hz. V(N-2,6-Me2C6H3)(CH2SiMe3)(O-2,6-Me2C6H3)2 (2a),10i V(N-2,6-Me 2 C 6 H 3 )(CH 2 SiMe 3 )(OC 6 F 5 ) 2 (2b), 10i V(NAd)(CH2SiMe3)(O-2,6-Me2C6H3)2 (1a),14 and V(NAd)(CH2SiMe3)2(OC6F5)14 were prepared according to the reported procedure. The synthetic procedure including isolation of V(NAd)(CH2SiMe3)(OC6F5)2 (1b) was partly described in ref 14. V(CHSiMe 3 )(N-2,6-Me 2 C 6 H 3 )(NC t Bu 2 )(PMe 3 ) (5), 10a V-

a Reaction conditions: 4 5.0 μmol, monomer 2.12 mmol, benzene solvent 4.8 mL, 25 °C, monomer 2.12 mmol. bTON (turnovers) = monomer reacted (μmol)/vanadium complex charged (μmol). cGPC data in o-dichlorobenzene vs polystyrene standards.

polymerizations of dicyclopentadiene (DCP), 5-vinyl-2-norbornene (VNBE), and 5-ethylidene-2-norbornene (ENBE) were complete within 15 min to afford high molecular weight polymers with uniform distributions. 1H NMR spectra in the resultant polymers strongly suggested that the resultant polymers possessed ring-opened structures, suggesting that these polymerizations proceeded in a ring-opening metathesis fashion (resonances ascribed to olefininc protons of the ringopened polymers at ca. 5.0−5.5 ppm and vinyl group in VNBE, 5118

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(CHSiMe3)(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3)(PMe3) (6),10e and Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 (7)17 were also prepared according to the reported procedures. Molecular weights and the molecular weight distributions of the resultant polymers were measured by gel-permeation chromatography (GPC). HPLC grade THF was used for GPC and was degassed prior to use. GPC was performed at 40 °C on a Shimadzu SCL-10A using a RID-10A detector (Shimadzu Co. Ltd.) in THF (containing 0.03 wt % of 2,6-di-tert-butyl-p-cresol, flow rate 1.0 mL/min). GPC columns (ShimPAC GPC-806, 804 and 802, 30 cm × 8.0 mm diameter, spherical porous gel made of styrene/divinylbenzene copolymer, ranging from