Article pubs.acs.org/Organometallics
Synthesis of (Imido)vanadium(V) Alkyl and Alkylidene Complexes Containing Imidazolidin-2-iminato Ligands: Effect of Imido Ligand on ROMP and 1,2-C−H Bond Activation of Benzene Kotohiro Nomura,* Bijal Kottukkal Bahuleyan, Ken Tsutsumi, and Atsushi Igarashi Department of Chemistry, Tokyo Metropolitan University, Minami Osawa 1-1, Hachioji, Tokyo 192-0397, Japan S Supporting Information *
ABSTRACT: A series of (imido)vanadium(V) alkylidene complexes containing an imidazolidin-2-iminato ligand of the type V(CHSiMe3)(NR)(X)(PMe3) (R = 2,6-Me2C6H3 (Ar, 3a), 1adamantyl (Ad, 3b), C6H5 (3c); X = 1,3-Ar′2(CH2N)2CN; Ar′ = 2,6-iPr2C6H3) have been prepared in n-hexane in the presence of PMe 3 from the corresponding dialkyl complexes V(NR)(CH2SiMe3)2(X) (2a−c). These alkylidene complexes (3a−c) exhibit catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene: the phenylimido analogue (3c) exhibits remarkable activity at 80 °C (e.g. a TOF value of 84800 h−1 (7070 turnovers after 5 min)), affording high-molecular-weight polymers with uniform molecular weight distributions. The reaction of the (arylimido)vanadium(V) dialkyl complex 2a with C6H6 afforded the phenyl complex V(NAr)(CH2SiMe3)(C6H5)(X) (4a) by 1,2-C−H activation via an alkylidene intermediate and the diphenyl complex V(NAr)(C6H5)2(X) as the final product. The activity by 3a−c for ROMP, the reactivity of 2a−c for formation of these alkylidenes by α-hydrogen elimination, and the reactivity of 2a−c toward benzene were highly affected by the nature of the imido ligand.
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INTRODUCTION Transition-metal alkyl and alkylidene (carbene) complexes are important reagents or intermediates in stoichiometric/catalytic organic reactions, as well as in olefin polymerization.1−5 Highoxidation-state early-transition-metal alkylidene complexes have attracted considerable attention,3−5 since they play essential roles as catalysts in olefin metathesis and Wittig-type or group transfer reactions,3−6 as demonstrated especially by molybdenum.3,4a,b,e Due to the promising characteristics (especially notable reactivity toward olefins) demonstrated by classical Ziegler type vanadium catalysts,2 the design of vanadium complex catalysts has been considered as an attractive target.2f,g,5 Our group has focused on the synthesis and reaction chemistry of (imido)vanadium(V) alkyl and alkylidene complexes,5,7,8 because their syntheses and reaction chemistry are of fundamental importance for a basic understanding in organometallic chemistry1,3−5 and might also lead to promising applications in catalysis. We recently demonstrated that ketimide-7a,e and aryloxo-modified7d,j vanadium(V) alkylidenes (Chart 1) exhibited unique reactivities in the ring-opening metathesis polymerization (ROMP) of norbornene (NBE). These alkylidenes were prepared by α-hydrogen elimination from the dialkyl analogues in C6D6 or n-hexane in the presence of PMe3 or NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene),5,7a,d−f known as a common approach for preparation of high-oxidation-state early-transition-metal alkylidenes.3−5 However, we faced difficulties for isolation of the desired alkylidenes in certain attempts (especially conducted in benzene). More recently,7h we realized that 1,2-C−H (or 1,2© XXXX American Chemical Society
Chart 1. Olefin Metathesis Active Vanadium(V) Alkylidenes7a,d−f
C−D) activation took place in the thermolysis of the imidazolin-2-iminato-modified dialkyl precursor (Scheme 1), 9,10 as exemplified by the reaction of V(NAr)(CH2SiMe3)2[1,3-Ar′2(CHN)2CN] (A; Ar = 2,6-Me2C6H3; Ar′ = 2,6-iPr2C6H3), in C6H6 (or C6D6) in the presence of PMe3. We thus demonstrated that an exclusive formation of the phenyl analogues V(NAr)(CH 2 SiMe 3 )(C 6 H 5 )[1,3Ar′2(CHN)2CN] (C) by 1,2-C−H (or 1,2-C−D) bond activation of C6H6 (or C6D6) with the dialkyl analogue (A) Received: September 28, 2014
A
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
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molecular-weight (co)polymers with uniform molecular weight distributions (Scheme 2).16 It also turned out that the activities were affected by both the imido ligand and the substituents on the anionic ligand: the 2,6-iPr2C6H3 (Ar′) analogues showed higher activities than the tBu analogues, and the arylimido analogue showed higher activities than the adamantylimido analogue.16 In this paper, we explore the syntheses of a series of (imido)vanadium(V) dialkyl complexes containing imidazolidin-2-iminato ligand types, V(NR)(CH 2 SiMe 3 ) 2 [1,3Ar′2(CH2N)2CN] (R = 2,6-Me2C6H3 (Ar, 2a), 1-adamantyl (Ad, 2b), C6H5 (2c)), and their reactions with benzene, including isolation of their alkylidene analogues V(CHSiMe3)(NR)[1,3-Ar′2(CH2N)2CN](PMe3) (3). We also explored the potential of these alkylidenes as the catalysts for ROMP of NBE. In particular, we wish to present a remarkable effect of the imido substituents toward the reactivity of the dialkyl analogues 2a−c in both α-hydrogen elimination and 1,2-C−H bond activation and that of the alkylidene analogues in the ROMP of NBE.17
Scheme 1. Reaction of Benzene with V(NAr)(CH2SiMe3)2[1,3-Ar′2(CHN)2CN] (A; Ar = 2,6Me2C6H3, Ar′ = 2,6-iPr2C6H3): Isolation of the Alkylidene and Benzyne Intermediates7h
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RESULTS AND DISCUSSION Synthesis of (Imido)vanadium(V) Dialkyl and Alkylidene Complexes. A series of (imido)vanadium(V) dichloride complexes, V(NR)Cl2(X) (R = 2,6-Me2C6H3 (Ar, 1a), 1adamantyl (Ad, 1b); X = 1,3-Ar′2(CH2N)2CN, Ar′ = 2,6-iPr2C6H3), were prepared according to the reported procedure16 by reactions of the (imido)vanadium(V) trichlorides V(NR)Cl3 with the corresponding lithium salt (instantaneously prepared in situ by treatment of 1,3Ar′2(CH2N)2CNH with n-BuLi). The phenyl analogue V(NC6H5)Cl2(X) (1c) could also be prepared by adopting an analogous method and was identified by 1H, 13C, and 51V NMR spectra and elemental analysis. Treatment of 1a−c with 2.0 equiv of LiCH2SiMe3 in toluene afforded the corresponding dialkyl analogues V(NAr)(CH2SiMe3)2(X) (2a−c) in high yields (Scheme 3), and the resultant complexes 2a−c were
takes place via a vanadium(V) alkylidene intermediate, and a subsequent thermolysis in C6H6 (or C6D6) afforded the diphenyl complexes V(NAr)(C6H5)2[1,3-Ar′2(CHN)2CN] (D).7h,11−14 The corresponding vanadium(V) alkylidene complex B (proposed as a key intermediate in the reaction of the dialkyl analogue in C6D6 or C6H6) and vanadium(V) benzyne complex E (assumed as an intermediate in the latter reaction affording the diphenyl complexes) could be isolated from the reaction mixture by trapping with PMe3, and their structures were determined by X-ray diffraction analysis.7h Imidazolidin-2-iminato ligands,15 the 4,5-dihydro congeners of the imidazolin-2-iminato ligands,7h,9,10 are known to be suitable ancillary ligands which exhibit a similar stabilization by the zwitterionic resonance structures, affording strongly basic nitrogen donor ligands with a high π-electron release capability toward early transition metals and/or metals in a higher oxidation state:9,10,15 these have been used for the preparation of early-transition-metal complexes.15 More recently, we reported that (imido)vanadium(V) dichloride complexes containing 1,3-imidazolidin-2-iminato ligands, V(NAr)Cl2[1,3Ar′2(CH2N)2CN] (Scheme 2, shown at the right), showed high catalytic activities not only for ethylene polymerization but also for copolymerization of ethylene with norbonene (NBE) in the presence of Et2AlCl cocatalyst, affording ultrahigh-
Scheme 3. Synthesis of V(NR)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2a−c)
identified by 1H, 13C, and 51V NMR spectra and elemental analysis. The structure of the admantylimido analogue 2b was determined by X-ray diffraction analysis (Figure 1).18 X-ray diffraction analysis reveals that 2b has a distortedtetrahedral geometry around the vanadium atom.18 The V−C bond distances in V-CH2SiMe3 (V(1)−C(38) 2.0626(14) Å, V(1)−C(42) 2.0462(13) Å) are relatively close to that in V(NAr)(CHDSiMe 3 )(C 6 D 5 )[1,3-Ar′ 2 (CHN) 2 CN] (2.0680(16) Å), containing an imidazolin-2-iminato ligand,7h and that in the alkyl alkylidene complex V(CHSiMe3)(NAd)(CH 2 SiMe 3)(NHC) (2.069(3) Å, NHC = 1,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene)7f but somewhat longer than that in the trialkyl analogue V(NAd)(CH2SiMe3)3
Scheme 2. Ethylene (Co)polymerization with Vanadium(V) Dichloro Complexes with Imidazolin-2-iminato and Imidazolidin-2-iminato Ligands16
B
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
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Scheme 4. Synthesis of Vanadium(V) Alkylidene Complexes V(CHSiMe3)(NR)[1,3-(2,6-iPr2C6H3)2(CH2N)2C N](PMe3) (3a−c)
Figure 1. ORTEP drawing of V(N-adamantyl)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2b). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.18 Selected bond distances (Å): V(1)−N(1) 1.6539(10), V(1)−N(2) 1.7877(13), V(1)−C(38) 2.0626(14), V(1)−C(42) 2.0462(13), N(1)−C(1) 1.4443(15), N(2)−C(11) 1.2793(19), N(3)−C(11) 1.3906(15), N(4)−C(11) 1.3697(18), N(3)−C(12) 1.469(2), N(4)−C(13) 1.4642(19), C(12)−C(13) 1.5287(19), C(1)−C(2) 1.540(2). Selected bond angles (deg): N(1)−V(1)−N(2) 114.16(6), N(1)−V(1)−C(38) 103.64(6), N(1)−V(1)−C(42) 108.24(6), N(2)−V(1)−C(38) 107.31(6), N(2)−V(1)−C(42) 111.68(6), C(38)−V(1)−C(42) 111.57(6), V(1)−N(1)−C(1) 162.15(10), V(1)−N(2)−C(11) 169.25(9), V(1)−C(38)−Si(1) 122.65(8), V(1)−C(42)−Si(2) 119.16(6).
was also confirmed by X-ray crystallographic analysis as the syn isomeric structure.20 It is interesting to note that the reaction of 2a after 6 h in nhexane at 60 °C afforded the corresponding alkylidene 3a on the basis of the 51V NMR spectrum (Figure 2b), whereas the
(2.0267(18) Å).7f The V−N distances in both the imido and the imidazolidin-2-iminato ligands in 2b (V(1)−N(1) 1.6539(10) Å, V(1)−N(2) 1.7877(13) Å) are close to those in the dichloride analogue 1b (V(1)−N(1) 1.645(3) Å, V(1)− N(2) 1.749(2) Å) reported previously,16 and the V(1)−N(1) imido distance is also somewhat close to that in the trialkyl analogue (1.6317(14) Å).7f Both C(11)−N(3) and C(11)− N(4) distances (1.3906(15), 1.3697(18) Å, respectively) are apparently shorter than the N(3)−C(12) and N(4)−C(13) distances (1.469(2), 1.4642(19) Å, respectively) as well as the C(12)−C(13) distance (1.5287(19) Å), and the V(1)−N(2)− C(11) bond angle is rather linear (169.25(9)°), strongly suggesting that the imidazolidin-2-iminato ligand plays a role as a 5e donor (2σ,4π-electron donor), as demonstrated previously in imidazolin-2-iminato systems with high-oxidation-state early transition metals.7h,10,16 It should be noted that heating an n-hexane solution containing the dialkyl complexes 2a−c in the presence of PMe3 (excess >7 equiv) in a sealed reaction tube afforded the corresponding alkylidene complexes V(CHSiMe3)(NR)[1,3Ar′2(CH2N)2CN](PMe3) (R = Ar (3a), Ad (3b), C6H5 (3c)), by α-hydrogen abstraction (Scheme 4).19 The resultant complexes were identified by 1H, 13C, and 51V NMR spectroscopy and elemental analysis, and the structure of 3a
Figure 2. 51V NMR spectra monitoring the reaction of V(NR)(CH2SiMe3)2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6-Me2C6H3 (2a), 1-adamantyl (2b), C6H5 (2c)) in n-hexane in the presence of PMe3 (excess, >7 equiv): formation of vanadium(V) alkylidenes 3a−c. Detailed results monitoring the time course are given in the Supporting Information.19
percentage of the product was low even after 24 h if the reaction of the adamantylimido analogue 2b was conducted under similar conditions (Figure 2c): the reaction was not complete even after 72 h (Figure 2d) and reached completion after 7 days. Moreover, a similar reaction with the phenylimido analogue 2c required a temperature of 70 °C but the percentage of the product 3c was low even after 24 h (Figure 2e): the reaction reached completion after 9−10 days (at 70 C
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
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Table 1. Ring-Opening Metathesis Polymerization (ROMP) of Norbornene (NBE) in Benzene using V(CHSiMe3)(NR)[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6-Me2C6H3 (Ar, 3a), 1-Adamantyl (3b), C6H5 (3c))a run
cat. (amt/μmol)
amt of NBE/mmol
benzene/mL
NBE concnb
time/min
temp/°C
yield/mg
TONc
Mnd × 10−4
Mw/Mnd
1 2 3 4 5 6 7 8 9 10
3a (2.50) 3b (2.50) 3c (2.50) 3b (2.50) 3a (2.50) 3b (2.50) 3c (2.50) 3a (1.25) 3b (1.25) 3c (1.25)
10.0 10.0 10.0 10.0 5.0 5.0 5.0 2.5 2.5 2.5
5.0 5.0 5.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0
2.00 2.00 2.00 1.00 0.50 0.50 0.50 0.25 0.25 0.25
60 60 60 60 30 30 30 60 60 60
25 25 25 80 80 80 80 80 80 80
69 40 190 86 118 34 470 (>99)e 89 17 214 (90.7)e
293 170 806 365 500 145 2000 756 145 1820
1.89 0.34 10.7 0.67 10.9 0.43 24.1 14.9 0.85 51.3
2.6 2.0 3.5 1.9 2.5 2.1 2.3 2.0 1.9 2.3
a Conditions: in 5.0 or 10.0 mL of benzene. bInitial NBE concentration in mmol/mL. cTON (turnover number) = (mmol of NBE consumed)/ (mmol of V). dGPC data in THF vs polystyrene standards. eConversion of NBE in %.
°C).19 These results clearly indicate that the reactivity in the αhydrogen elimination is highly dependent upon the nature of the imido ligand employed. One broad resonance ascribed to the alkylidene proton, V CHSiMe3, was observed at 15.20 (3a), 15.15 (3b), and 15.34 (3c) ppm, respectively, in the 1H NMR spectra in addition to a single resonance each in the 51V and 31P NMR spectra; this suggests the absence of syn/anti isomers in solution. A corresponding broad resonance ascribed to a carbon of the alkylidene was observed at 312 (3a), 310 (3b), and 302 (3c) ppm, respectively, and these are typical observations for nucleophilic carbene (alkylidene) complexes of the early transition metals.4,5 Since 3a possesses a syn isomeric form on the basis of the crystallographic analysis,20 the structures of these alkylidenes would be a syn form probably influenced by a rather bulky imidazolidin-2-iminato ligand. Effect of the Imido Ligand in the Ring-Opening Metathesis Polymerization (ROMP) of Norbornene (NBE) using V(CHSiMe3)(NR)[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6-Me2C6H3, 1-Adamantyl, C6H5). Table 1 summarizes the results in the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in benzene using V(CHSiMe3)(NR)[1,3-(2,6-iPr2C6H3)2(CH2N)2CN](PMe3) (R = 2,6-Me2C6H3 (3a), 1-adamantyl (3b), C6H5 (3c)). These alkylidenes 3a−c initiated the ROMP of NBE (Scheme 5), and
10) and, as demonstrated previously, this (thermal resistance of the active species) is one of the unique characteristics of using these alkylidenes as olefin metathesis catalysts (in comparison to Mo and Ru catalysts).5,7a The same trend/order for the effect of the imido ligand toward activity was observed in the ROMP at 80 °C, and the ROMP by 3c reached completion (runs 7 and 10) even at rather low NBE concentrations. The resultant polymers possessed a ring-opened structure containing a mixture of cis/trans olefinic double bonds, and a trend in the selectivity was not observed. Table 2 summarizes results in the ROMP of NBE by the phenylimido alkylidene 3c at 80 °C under various conditions. The ROMP (under rather low NBE concentration conditions, 0.25 mmol/mL) proceeded without significant deactivation (runs 13−15), affording rather high molecular weight polymers with uniform molecular weight distributions. The Mn values did not change (with uniform distributions) over the time course, suggesting that a certain degree of chain transfer occurs under these conditions. It should be noted that the activity increased at high NBE concentration (e.g. NBE concentration 0.25 mmol/mL (run 13) vs 0.50 (run 7) and 1.00 (run 14) mmol/ mL) and the ROMP was completed (>98% conversion) even when the amount of NBE charged was increased. The TOF value of 45000 h−1 (run 17) has thus been achieved by adding NBE to the reaction mixture under the same catalyst concentration conditions (runs 7 and 13−15): a TOF value of 84800 h−1 (7070 turnovers after 5 min) has been demonstrated by 3c under the rather optimized conditions (run 17). The remarkable activity at 80 °C, affording highmolecular-weight polymers with uniform molecular weight distribution, is noteworthy, because the observation shown here is different from those for conventional molybdenum and ruthenium catalysts (observed decreases in the activities at higher temperatures in most cases). C−H Bond Activation of Benzene using V(NR)(CH2SiMe3)2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6Me2C6H3, 1-Adamantyl, C6H5). It is noteworthy that the diphenyl complex V(NAr)(C6H5)2(X) (5a; Ar = 2,6-Me2C6H3, X = 1,3-(2,6-iPr2C6H3)2(CH2N)2CN) was cleanly isolated when the dialkyl complex 2a was heated in C6H6 at 70 °C for 1 day (Scheme 6),21 and 5a was identified by NMR spectra and elemental analysis. On the basis of 51V NMR spectra, the reaction was not complete at 60 °C (after 24 h) and an intermediate, probably the monophenyl complex expressed as 4a, was observed (integration ratio 4a:5a = 3:7, after 24 h at 60 °C).21 The intermediate could be expressed as V(NAr)-
Scheme 5. Ring-Opening Metathesis Polymerization (ROMP) of Norbornene by V(CHSiMe3)(NR)[1,3(2,6-iPr2C6H3)2(CH2N)2CN](PMe3) (3a−c)
the activity was strongly affected by the imido ligand employed. The activity at 25 °C (after 1 h, runs 1−3) increased in the order 3b (170 turnovers) < 3a (293) < 3c (806). The phenylimido analogue 3c showed activity higher than that of 3a,b, and the Mn value in the resultant ROMP polymer by the adamantylimido analogue 3b was low. The activities of 3a−c increased upon increasing the temperature at 80 °C (runs 4− D
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
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Table 2. Ring-Opening Metathesis Polymerization (ROMP) of Norbornene (NBE) using V(CHSiMe3)(NC6H5)[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (3c) in Benzene at 80 °Ca run
amt of 3c/μmol
NBE concnb
amt of benzene/mL
time/min
yield/mg
conversnc/%
TONd
TOFe/h−1
Mnf × 10−4
Mw/Mnf
11 12 13 7 14 15 16 17
2.50 2.50 2.50 2.50 2.50 2.50 1.25 1.25
0.25 0.25 0.25 0.50 1.00 2.00 1.00 2.00
10.0 10.0 10.0 10.0 5.0 5.0 5.0 5.0
15 30 60 30 15 5 15 5
154 204 232 470 469 883 447 832
65.3 86.4 >98 >99 >99 93.7 94.9 88.3
654 867 985 2000 1990 3750 3800 7070
2620 1730 985 4000 7960 45000 15200 84800
32.2 32.8 35.5 24.1 43.8 49.0 50.3 65.4
2.1 2.5 1.9 2.3 2.3 2.7 2.6 2.0
a
Conditions: in 5.0 or 10.0 mL of benzene. bInitial NBE concentration in mmol/mL. cConversion of NBE in %. dTON (turnover number) = (mmol of NBE consumed)/(mmol of V). eTOF (turnover frequency) in h−1. fGPC data in THF vs polystyrene standards.
C6H6 at 60 °C after 48 h afforded a mixture of 2b, diphenyl complex 5b (which was isolated independently from the dichloro analogue (1b) with PhLi), and an intermediate expressed as 4b (assumed to be the monophenyl complex),21 although the percentage of 5b (via 4b) increased over time.21 Moreover, it should be noted that a reaction mixture of 2b or 2c in C6D6 at 60 °C after 24 h showed the starting complexes (in addition to tiny resonances probably due to an intermediate in the reaction with 2b) on the basis of 51V NMR spectra.21 These results suggest that the reactions with the adamantylimido and the phenylimido analogues 2b,c would be more difficult than that with the arylimido analogue 2a. The product in the reaction of 2b in C6D6 at 70−80 °C after 12 days was assumed to be the diphenyl complex V(NAd)(C6D5)2(X) (5b′) in high certainty on the basis of 1H and 51V NMR spectra21 and elemental analysis. On the basis of the above results, a C6H6 solution containing the dialkyl complex V(NAr)(CH2SiMe3)2(X) (2a) was first heated to 60 °C for 24 h (affording a mixture of 4a and 5a)21 and then heating was continued at 70 °C for another 24 h in the presence of PMe3 (Scheme 7). The 51V NMR spectrum of
Scheme 6. Reaction of V(N-2,6-Me2C6H3)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2a) with C6H6a
a
Detailed results monitoring NMR spectra are shown in the Supporting Information.21
Scheme 7. Reaction of 4a and 5a (Formed in Situ from 2a by Treating with C6H6 at 60 °C) with C6H6 in the Presence of PMe3 (at 70 °C)a
(CH2SiMe3)(C6H5)(X) (4a) in high certainty on the basis of its 1H and 51V NMR spectra in addition to those for the reported imidazolin-2-iminato analogue,7h,21 although our attempts to isolate analytically pure samples failed (probably due to a contamination of the diphenyl analogue 5a). The ratio (4a:5a on the basis of integration ratios in the 51V NMR spectra) was highly dependent upon the reaction time and the temperature;21 4a became the major product on the basis of 51 V NMR spectra, when the reaction was conducted at 50 °C (Scheme 6). Importantly, a similar reaction in C6D6 at 60 °C after 24 h afforded a product assumed to be the monophenyl complex 4a-d5 (on the basis of its 51V NMR spectrum),21 whereas the same reaction in C6H6 afforded 5a as the major product. Moreover, the reaction of 2a in C6H6 in the presence of PMe3 (excess) afforded the corresponding alkylidene 3a as the exclusive product (70 °C after 6 h).21 When these results were taken into account, as demonstrated previously,7h the reaction with benzene proceeded via 1,2-C−H bond activation via a vanadium(V) alkylidene intermediate (Scheme 6). This contrast is interesting, because the C−H bond activation with 2a took place at 50 °C and the reaction temperatures used here are apparently lower than those used for the imidazolin-2iminato analogue (which required 80 °C for several days to obtain the diphenyl complex from the monophenyl complex).7h A similar reaction of the (adamantylimido)vanadium dialkyl analogue V(NAd)(CH2SiMe3)2(X) (2b; Ad = 1-adamantyl) in
a
Detailed results monitoring NMR spectra are shown in the Supporting Information.21
the brown precipitates (which were obtained from a chilled (−30 °C) n-hexane solution after removal of volatiles from the reaction mixture) showed resonances due to the vanadium alkylidene V(CHSiMe3)(NAr)(X)(PMe3) (3a) and unidentified resonances at −485 and −488 ppm.21 The resonances (−485 and −488 ppm) are analogous to those reported for a benzyne complex of the imidazolin-2-iminato analogue, V(N2,6-Me 2 C 6 H 3 )(η 2 -C 6 H 4 )[1,3-Ar′ 2 (CHN)2 CN](PMe 3 ),7h and analogous resonances (due to the protons of benzyne) were also observed in the 1H NMR spectrum.21,22 These results suggest the formation of benzyne under these conditions. E
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
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Scheme 8. Summary of the Reaction of the (Arylimido)vanadium Dialkyl Complex 2a with Benzene
bond activation with 2a (containing the imidazolidin-2-iminato ligand) took place under rather mild conditions in comparison to those for the analogous dialkyl complex containing the imidazolin-2-iminato ligand.7h We believe that this is important information in terms of better ligand design. We are currently exploring the possibility of activation of other aromatic compounds by the dialkyl complex 2a and the utility of 3c as a ROMP catalyst: these will be reported in the near future.
However, our attempts to isolate the benzyne intermediate failed due to difficulty in separation. In contrast, the reaction of 5a in C6D6 in the presence of PMe3 (excess) at 70 °C afforded decomposition products, although a species at ca. −365 ppm was observed as a tiny trace in the 51V NMR spectrum.21 When these results are taken into account, it seems likely that the reaction products observed were derived from the monophenyl complex 4a and there is a possibility that the proposed benzyne complex was not formed from the diphenyl analogue 5a, although these assumptions are made on the basis of NMR spectra and should also consider the formation of paramagnetic species in situ as byproducts.
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EXPERIMENTAL SECTION
General Procedure. All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox unless otherwise specified. All chemicals used were of reagent grade and were purified by the standard purification procedures. Anhydrous grade toluene, n-hexane, and 1,2-dichloromethane (Kanto Chemical Co., Inc.) were transferred into bottles containing molecular sieves (mixture of 3 Å 1/16 and 4 Å 1/8, and 13X 1/16) under a nitrogen stream in the drybox and passed through a short alumina column under N2 prior to use. V(N-2,6-Me2C6H3)Cl2[1,3(2,6- i Pr 2 C 6 H 3 ) 2 (CH 2 N) 2 CN] (1a), 1 6 V(NAd)Cl 2 [1,3(2,6-iPr2C6H3)2(CH2N)2CN] (1b),16 and V(NPh)Cl317b were prepared according to previous reports. Elemental analyses were performed by using an EAI CE-440 CHN/ O/S Elemental Analyzer (Exeter Analytical, Inc.). All 1H, 13C, 31P, and 51 V NMR spectra were recorded on a Bruker AV500 spectrometer (500.13 MHz for 1H, 125.77 MHz for 13C, 202.5 MHz for 31P, 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), H3PO4 (δ 0.00, 31P), and VOCl3 (δ 0.00, 51V). Coupling constants and half-width values, Δν1/2, are given in Hz. 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 7 equiv) was heated in a sealed NMR tube at 60 °C for 1 day. The solution was then filtered through a Celite pad, and the filter cake was washed with n-hexane. The combined solution (filtrate and wash) was concentrated, and the chilled solution (−30 °C) gave brown microcrystals (47 mg, 0.064 mmol, yield 91%). 1H NMR (C6D6): δ 15.20 (s, 1H, CHSiMe3), 7.19−7.14 (m, 3H, Ar-H), 7.09−7.03 (m, 5H, Ar-H), 6.78 (t, 1H, J = 7.8, Ar-H), 3.41−3.25 (m, 4H, CH(CH3)2), 3.34 (s. 4H, CH2), 2.20 (s, 6H, ArCH3), 1.43 (d, 6H, J = 6.4, CH(CH3)2), 1.37 (d, 6H, J = 7.3, CH(CH3)2), 1.25 (d, 6H, J = 6.4, CH(CH3)2), 1.21 (d, 6H, J = 6.4, CH(CH3)2), 0.80 (d, 9H, J = 8.2, PMe3), 0.24 (s, 9H, CHSiMe3). 13C NMR (C6D6): δ 312 (broad), 148.8, 148.7, 136.2, 129.7, 128.6, 128.4, 127.2, 124.3, 124.1, 119.0, 47.8, 29.3, 29.1, 25.3, 24.6, 24.5, 24.4, 20.6, 19.4 (d, J = 24.4, PMe3), 2.2. 51V NMR (C6D6): δ 2 (Δν1/2 = 1241 Hz). 31P NMR (C6D6): δ 11.8. Anal. Calcd for C42H66N4PSiV: C, 68.45; H, 9.03; N, 7.60. Found: C, 68.42; H, 9.33; N, 7.30. Synthesis of V(CHSiMe3)(NAd)[1,3-(2,6-iPr2C6H3)2(CH2N)2C N](PMe3) (3b). The synthetic procedure of 3b is similar to that for 3a, except that V(NAd)(CH2SiMe3)2[1,3-(2,6-iPr2C6H3)2(CH2N)2C N] (2b; 50 mg, 0.064 mmol) and PMe3 (excess, >7 equiv) were heated in a sealed NMR tube at 60 °C for 7 days. Yellowish brown microcrystals (31 mg, 0.040 mmol, yield 63%) were obtained. 1H NMR (C6D6): δ 15.17 (s, 1H, CHSiMe3), 7.28−7.09 (m, 6H, ArH), 3.57−3.20 (m, 8H, CH2, CH(CH3)2), 2.08 (s, 3H, Ad-CH), 1.90 (s, 6H, Ad-CH), 1.72−1.62 (m, 6H, Ad-CH), 1.63 (d, 6H, J = 6.8, CH(CH3)2), 0.75 (d, 9H, J = 8.5, PMe3), 0.38 (s, 9H, CHSiMe3). 13 C NMR (C6D6): δ 310 (broad), 149.8, 149.3, 148.8, 148.5, 137.0, 136.5, 134.5, 129.0, 128.5, 124.8, 124.2, 124.1, 124.0, 48.5, 48.3, 47.8, 37.1, 30.8, 29.3, 29.2, 28.9, 25.6, 25.4, 25.3, 25.0, 24.8, 24.7, 24.2, 24.1, 19.7 (d, J = 22.7, PMe3), 3.6. 51V NMR (C6D6): δ −98 (Δν1/2 = 1056 Hz). 31P NMR (C6D6): δ 15.9. Anal. Calcd for C44H73N4Si2V: C, 68.80; H, 9.58; N, 7.29. Found: C, 68.47; H, 9.39; N, 7.03. Synthesis of V(CHSiMe3)(NC6H5)[1,3(2,6-iPr2C6H3)2(CH2N)2CN](PMe3) (3c). The synthetic procedure of 3c is similar to that for 3a, except that the dialkyl complex V(NC6H5)(CH2SiMe3)2(1,3-(2,6-iPr2C6H3)2(CH2N)2CN) (2c; 50 mg, 0.07 mmol) and PMe3 (excess, >7 equiv) were heated in a sealed NMR tube at 70 °C for 10 days. Brown microcrystals (29 mg, 0.041 mmol, yield 57%) were obtained. 1H NMR (C6D6): δ 15.45 (s, 1H, CHSiMe3), 7.22−7.17 (m, 3H, Ar-H), 7.12−7.08 (m, 5H, Ar-H), 6.93 (d, J = 7.3, Ar-H), 6.81 (t, 1H, J = 6.9, Ar-H), 3.40 (s. 4H, CH2), 3.38− 3.28 (m, 4H, CH(CH3)2), 1.50 (d, 6H, J = 5.8, CH(CH3)2), 1.49 (d, 6H, J = 5.8, CH(CH3)2), 1.26 (d, 6H, J = 6.30, CH(CH3)2), 1.24 (d, 6H, J = 6.30, CH(CH3)2), 0.74 (d, 9H, J = 8.15, PMe3), 0.30 (s, 9H, =CHSiMe3). 13C NMR (C6D6): δ 302 (broad), 148.8, 148.7, 136.0, 128.6, 128.3, 124.3, 124.2, 124.1, 124.0, 119.5, 47.7, 29.2, 29.1, 25.1, 24.8, 18.4 (d, J = 21.8, PMe3), 3.3. 51V NMR (C6D6): δ 0 (Δν1/2 = 942 Hz). 31P NMR (C6D6): δ 21.3. Anal. Calcd for C40H62N4PSiV: C, 67.77; H, 8.81; N, 7.90. Found: C, 67.85; H, 8.64; N, 7.90. Synthesis of V(N-2,6-Me2C6H3)(C6H5)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (5a). A C6H6 solution containing complex 2a (60 mg, 0.08 mmol) was heated to 70 °C in a sealed NMR tube under a nitrogen atmosphere. After 1 day, the solvent was then removed in vacuo, and the resultant residue was washed with cold n-hexane. A red solid (39 mg, 0.054 mmol) was obtained in a yield of 66%. 1H NMR (C6D6): δ 7.46 (d, 4H, J = 6.6, V-Ph-H), 7.27 (t, 2H, J = 7.6, Ar-H), 7.09 (d, 4H, J = 7.65, Ar-H), 6.98 (d, 2H, J = 7.3, Ar-H), 6.93−6.89 (m, 6H, V-Ph-H), 6.76 (t, 1H, J = 7.2, Ar-H), 3.41 (s, 4H, CH2), 3.37−3.29 (m, 4H, CH(CH3)2), 2.41 (s, 6H, ArCH3), 1.16 (d, 12H, J = 6.6, CH(CH3)2), 1.14 (d, 12H, J = 6.60, CH(CH3)2). 13C NMR (C6D6): δ 148.3, 134.8, 134.7, 129.5, 129.0, 128.6, 128.3, 127.5, 127.3, 126.3, 124.8, 123.1, 48.9, 29.2, 25.3, 23.9, 20.5. 51V NMR (C6D6): δ 155 (Δν1/2 = 925 Hz). Anal. Calcd For C47H55N4V: C, 77.44 (75.79 + VC, vanadium carbide); H, 7.88; N, 7.69. Found: (1): C, 75.82; H, 7.94; N, 7.82. Found (2): C, 75.40; H, 7.84; N, 7.77. The observed C values were somewhat low because of the incomplete combustion (by production of vanadium carbide), whereas both H and N observed values were close to the calculated values. Synthesis of V(NAd)(C6H5)2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (5b). Method 1. A C6H6 solution containing complex 2b (62 mg, 0.08
green solid was extracted with hot toluene. The solution was placed into a rotary evaporator to remove all volatiles. The remaining solid was then dissolved in a minimum amount of CH2Cl2 and layered with n-hexane. Green microcrystals were grown from the chilled solution (−30 °C) and collected in a yield of 80% (0.83 g, 1.27 mmol). 1H NMR (CDCl3): δ 7.37 (t, 2H, J = 7.65, Ph-H), 7.19 (d, 4H, J = 7.81, Ar-H), 7.11 (t, 2H, J = 7.63, Ph-H), 6.93 (t, 1H, J = 7.30, Ph-H), 6.89 (d, 2H, J = 7.86, Ar-H), 4.09 (s, 4H, CH2), 3.26−3.23 (m, 4H, CH(CH3)2), 1.34−1.25 (m, 24H, CH(CH3)2. 13C NMR (CDCl3): δ 146.1, 131.8, 130.5, 127.8, 125.5, 124.9, 124.2, 48.5, 29.7, 25.1, 23.7. 51 V NMR (CDCl3): δ −183 (Δv1/2 = 953 Hz). Anal. Calcd for C35H47Cl2N4V: C, 65.11; H, 7.34; N, 8.68. Found: C, 64.98; H, 7.19; N, 8.78. Synthesis of V(N-2,6-Me2C6H3)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2a). To a toluene solution containing V(N-2,6-Me2C6H3)Cl2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (1a; 206 mg, 0.32 mmol) was added LiCH2SiMe3 (60 mg, 0.64 mmol) at −30 °C. The reaction mixture was warmed slowly to room temperature and was stirred for 6 h. The solvent was then removed in vacuo, and the resulting residue was extracted with n-hexane. After the n-hexane was removed in vacuo, the resultant solids were dissolved in a minimum amount of n-hexane. The solution was cooled to −30 °C, and the brown microcrystals (204 mg, 0.55 mmol) were collected in a yield of 82%. 1H NMR (C6D6): δ 7.15−7.11 (m or t, 2H, Ar-H), 7.04 (d, 4H, J = 7.4, Ar-H), 7.01 (d, 2H, J = 7.6, Ar-H), 6.79 (t, 1H, J = 7.6, Ar-H), 3.39 (s, 4H, CH2), 3.41 (m, 4H, CH(CH3)2), 2.68 (s, 6H, ArCH3), 1.77 (d, 2H, J = 11.2, CH2SiMe3), 1.43 (d, 12H, J = 6.80, CH(CH3)2), 1.16 (d, 12H, J = 6.8, CH(CH3)2), 0.62 (d, 2H, J = 10.8, CH2SiMe3), 0.02 (s, 18H, CH2SiMe3). 13C NMR (C6D6): δ 148.7, 135.7, 134.4, 129.9, 128.3, 127.5, 125.2, 123.5, 49.5, 29.6, 26.4, 24.7, 21.1, 2.9. 51V NMR (C6D6): δ 435 (Δν1/2 = 1023 Hz). Anal. Calcd for C43H69N4Si2V: C, 68.94; H, 9.28; N, 7.48. Found: (1): C, 68.31 (66.7 + VC, vanadium carbide); H, 9.30; N, 7.20. Found (2): C, 68.22 (66.7 + VC, vanadium carbide); H, 9.14; N, 7.48. The observed C values were somewhat low because of the incomplete combustion (by production of vanadium carbide), whereas both H and N observed values were close to the calculated values. Synthesis of V(NAd)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2b). The synthetic procedure of 2b is similar to that for 2a, except that V(N-Ad)Cl 2 [1,3(2,6-iPr2C6H3)2(CH2N)2CN] (1b; 338 mg, 0.5 mmol) was used instead of the arylimido analogue 1a. Orange microcrystals (331 mg, 0.43 mmol) were obtained in a yield of 85%. 1H NMR (C6D6): δ 7.16−7.12 (m, 2H, Ar-H), 7.08 (d, 4H, J = 7.6, Ar-H), 3.45 (s, 4H, CH2), 3.39 (m, 4H, CH(CH3)2), 2.20 (s, 6H, Ad−CH), 2.10 (s, 3H, Ad−CH), 2.08 (s, 6H, Ad-CH), 1.68 (d, 2H, J = 11.2, CH2SiMe3), 1.56 (d, 12H, J = 6.8, CH(CH3)2), 1.51 (d, 2H, J = 10.8, CH2SiMe3), 1.21 (d, 12H, J = 6.8, CH(CH3)2), 0.11 (s, 18H, CH2SiMe3). 13C NMR (C6D6): δ 148.9, 136.4, 129.7, 124.8, 49.1, 46.5, 37.3, 31.09, 29.6, 25.7, 3.2. 51V NMR (C6D6): δ 336 (Δν1/2 = 953 Hz). Anal. Calcd for C45H75N4Si2V: C, 69.36; H, 9.70; N, 7.19. Found: C, 69.59; H, 9.51; N, 7.04. Synthesis of V(NC6H5)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2c). The synthetic procedure of 2c is similar to that for 2a, except that V(NC 6 H 5 )Cl 2 [1,3(2,6-iPr2C6H3)2(CH2N)2CN] (1c; 185 mg, 0.3 mmol) was used instead of 1a. Brown microcrystals (177 mg, 0.23 mmol) were obtained in a yield of 82%. 1H NMR (C6D6): δ 7.32 (d, 2H, Ar-H), 7.14 (d, 4H, J = 7.6, Ar-H), 7.03 (d, 2H, J = 7.6, Ar-H), 6.82 (t, 1H, J = 7.6, Ar-H), 3.35 (s, 4H, CH2), 3.31 (m, 4H, CH(CH3)2), 1.75 (d, 2H, J = 11.2, CH2SiMe3), 1.47 (d, 12H, J = 6.8, CH(CH3)2), 1.17 (d, 12H, J = 6.8, CH(CH3)2), 0.42 (d, 2H, J = 10.8, CH2SiMe3), 0.06 (s, 18H, CH2SiMe3). 13C NMR (C6D6): δ 148.7, 135.7, 135.4, 129.9, 125.8, 125.1, 123.4, 49.1, 29.8, 25.6, 25.3, 3.0. 51V NMR (C6D6): δ 424 (Δν1/2 = 1124 Hz). Anal. Calcd for C41H65N4Si2V: C, 68.29; H, 9.09; N, 7.77. Found: C, 68.05; H, 9.32; N, 7.76. Synthesis of V(CHSiMe3)(N-2,6-Me2C6H3)[1,3(2,6-iPr2C6H3)2(CH2N)2CN](PMe3) (3a). A n-hexane solution containing the dialkyl complex V(N-2,6-Me2C6H3)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (2a; 50 mg, 0.07 mmol) and PMe3 G
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mmol) was heated to 70 °C in a sealed NMR tube under a nitrogen atmosphere. After 4 days, the solvent was then removed in vacuo, and the resultant residue was washed with cold n-hexane. The red solid (35 mg, 0.05 mmol) was obtained in a yield of 56%, but the resultant sample was not pure enough for elemental analysis, probably due to contamination of 5a (5b could not be isolated due to the copresence of 5a when the reaction was conducted at 60 °C). Method 2. To a toluene solution containing the dichloride complex 1b16 (203 mg, 0.3 mmol) was added PhLi (0.33 mL, 1.8 M in nhexane, 0.6 mmol) at −30 °C. The reaction mixture was warmed slowly to room temperature and was stirred for 6 h. The mixture was then filtered through a Celite pad, and the filter cake was washed with toluene. The combined solution (filtrate and the wash) was then removed in vacuo, and the resultant residue was washed with cold nhexane. The red solid (162 mg, 0.214 mmol) was obtained in a yield of 71%. 1 H NMR (C6D6): δ 7.48 (d, 4H, J = 6.9, V-Ph-H), 7.24 (t, 2H, J = 7.8, Ar-H), 7.09 (d, 4H, J = 7.4, Ar-H), 7.06−6.99 (m, 6H, V-Ph-H), 3.42 (s, 4H, CH2), 3.38−3.31 (m, 4H, CH(CH3)2), 2.02 (s, 6H, AdCH), 1.93 (s, 3H, Ad-CH), 1.56−1.46 (m, 6H, Ad-CH), 1.31 (d, 12H, J = 6.4, CH(CH3)2), 1.21 (d, 12H, J = 6.9, CH(CH3)2). 13C NMR (C6D6): δ 148.3, 135.4, 135.3, 129.2, 128.6, 127.5, 126.2, 124.7, 48.7, 44.9, 36.6, 30.2, 29.2, 25.2, 24.7. Anal. Calcd For C49H63N4V: C, 77.54 (75.95 + VC, vanadium carbide); H, 8.37; N, 7.36. Found: C, 76.44; H, 8.67; N, 7.06. A compound was isolated after the reaction of 2b in C6D6 at 80 °C for 12 days (method 1 in C6D6). Anal. Calcd for V(NAd)(C6D5)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (5b′): C, 76.53; H, 8.25; N, 7.29. Found: C, 74.99; H, 8.73; N, 7.44. The results also suggest the formation of a diphenyl analogue, although the observed C values were somewhat low because of incomplete combustion (by production of vanadium carbide), whereas both H and N observed values were close to the calculated values. The NMR spectra for monitoring the reaction and the final product are shown in the Supporting Information. ROMP of Norbornene (NBE). A typical reaction procedure is as follows. In a sealed Schlenk tube (50 mL scale) containing norbornene dissolved in benzene was placed a benzene solution containing the prescribed amount of complex. The tube was then immediately placed in an oil bath preheated to 25 or 80 °C, and the mixture was stirred for a prescribed time. The polymerization was then quenched by the addition of excess PhCHO, and the solution was stirred for an additional 1 h at room temperature. The mixture was then poured into methanol (ca. 100 mL). The resultant solid was collected by filtration, washed with methanol, and then dried in vacuo. Crystallographic Analysis. Measurements for 2b were carried out on a Rigaku RAXIS-RAPID Imaging Plate diffractometer with graphite-monochromated Mo Kα radiation. The crystal data and collection parameters of 2b, CIF files, and crystal structure report are given in the Supporting Information.18 All structures were solved by direct methods23 and expanded using Fourier techniques, and the nonhydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. All calculations were performed using the Crystal Structure24 crystallographic software package except for refinement, which was performed using SHELXL-97.25 Selected crystal collection parameters: C45H75N4Si2V, formula wt 779.23, yellow block, crystal size 0.200 × 0.160 × 0.140 mm, triclinic, space group P1̅ (No. 2), a = 10.8115(2) Å, b = 12.2653(3) Å, c = 18.3622(4) Å, α = 85.3288(7)°, β = 86.9167(7)°, γ = 72.4998(7)°, V = 2313.43(8) Å3, Z = 2, Dcalcd = 1.119 g/cm3, F000 = 848.00, T = 123 K, μ(Mo Kα) = 2.992 cm−1, 23220 reflections measured, 10558 unique reflections, R1(I > 2.00σ(I)) = 0.0408, wR2 = 0.1122, goodness of fit 1.167.
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adamantyl (Ad, 2b), C6H5 (2c)), NMR spectra for reactions of 2a−c with C6H6 or C6D6, including reference data for estimation/identification of complexes/intermediates, and crystal data and collection parameters of V(NAd)(CH2SiMe3)2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (2b). This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*K.N.: tel, +81-42-677-2547; fax, +81-42-677-2547; e-mail,
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This project was partially supported by a Grant-in-Aid for Scientific Research on Innovative Areas (″3D Active-Site Science”, No. 26105003) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. B.K.B. expresses his sincere thanks to the Japan Society for the Promotion of Science (JSPS) for postdoctoral fellowships (P11072), and A.I. expresses his heartfelt thanks to the JSPS for a predoctoral fellowship (26-7313). B.K.B. and K.N. express their thanks to Mr. Shohei Katao (Nara Institute of Science and Technology) for the crystallographic analysis of 2b. K.N. expresses his heartfelt thanks to Prof. Dr. Matthias Tamm (Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Braunschweig, Germany) and Dr. Bart Hessen (formerly University of Groningen, Groningen, The Netherlands) for fruitful discussions.
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REFERENCES
(1) (a) Crabtree, R. H. In The Organometallic Chemistry of the Transition Metals, 5th ed.; Wiley: Hoboken, NJ, USA, 2009; p 58. (b) Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier Science/Pergamon US: New York, 2006. (c) Synthesis of Organometallic Compounds: A Practical Guide; Komiya, S., Ed.; Wiley.: West Sussex, England, 1997. (d) Organometallics in Synthesis: A Manual, 3rd ed.; Schlosser, M., Ed.; Wiley: Hoboken, NJ, USA, 2013. (e) Astruc, D. Organometallic Chemistry and Catalysis; Springer-Verlag: Berlin, Heidelberg, Germany, 2007. (f) Steinborn, D. Fundamentals of Organometallic Catalysis; WileyVCH: Weinheim, Germany, 2012. (2) Related reviews for olefin polymerization catalysts including vanadium complexes: (a) Gambarotta, S. Coord. Chem. Rev. 2003, 237, 229. (b) Hagen, H.; Boersma, J.; van Koten, G. Chem. Soc. Rev. 2002, 31, 357. (c) Bolton, P. D.; Mountford, P. Adv. Synth. Catal. 2005, 347, 355. (d) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283. (e) Nomura, K. In New Developments in Catalysis Research; Bevy, L. P., Ed.; Nova Science Publishers: New York, 2005, 199. (f) Redshaw, C. Dalton Trans. 2010, 39, 5595. (g) Nomura, K.; Zhang, S. Chem. Rev. 2011, 111, 2342 and related references cited therein. (3) For examples, see: (a) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158. (b) Schrock, R. R. In Alkene Metathesis in Organic Synthesis; Fürstner, A., Ed.; Springer: Berlin, Germany, 1998; p 1. (c) Schrock, R. R. In Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, Germany, 2003; Vol. 1, p 8. (4) For examples, see: (a) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98. (b) Schrock, R. R. Chem. Rev. 2002, 102, 145. (c) Mindiola, D. Acc. Chem. Res. 2006, 39, 813. (d) Mindiola, D.; Bailey, B.; Basuli, F. Eur. J. Inorg. Chem. 2006, 16, 3135. (e) Schrock, R. R. Chem. Rev. 2009, 109, 3211. (5) Nomura, K.; Zhang, W. Chem. Sci. 2010, 1, 161.
ASSOCIATED CONTENT
S Supporting Information *
Text, figures, tables, and a CIF file giving NMR spectra for isolations of (imido)vanadium alkylidene complexes 3a−c from the dialkyl complexes V(NR)(CH2SiMe3)2[1,3(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6-Me2C6H3 (2a), 1H
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Organometallics
Article
Kitiyanan, B.; Tamm, M.; Nomura, K. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2575. (11) Related chemistry recently reported for the reaction of (PNP) V(CH2tBu)2 with C6D6 affording (PNP)V(C6D5)2 (PNP = N{2-PiPr24-Me-C6H3}2−) via intermolecular C−H bond activation of benzene: Andino, J. G.; Kilgore, U. J.; Pink, M.; Ozarowski, A.; Krzystek, J.; Telser, J.; Baik, M.-H.; Mindiola, D. Chem. Sci. 2010, 1, 351. They postulated that the double 1,2-C−H bond activation proceeds via a vanadium(III) alkylidene and a vanadium(III) benzyne intermediate, including isolation of the (oxo)vanadium(V) alkylidene (PNP)V(O) (CHtBu). (12) For example (examples of 1,2-C−H bond activation of benzene using Mo and W), see: (a) Pamplin, C. B.; Legzdins, P. Acc. Chem. Res. 2003, 36, 223. (b) Wada, K.; Pamplin, C. B.; Legzdins, P. J. Am. Chem. Soc. 2002, 124, 9680. (c) Wada, K.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.; Tsyba, I.; Bau, R. J. Am. Chem. Soc. 2003, 125, 7035. (d) van der Heijden, H.; Hessen, B. Chem. Commun. 1995, 145. (e) Tran, E.; Legzdins, P. J. Am. Chem. Soc. 1997, 119, 5071. (f) Adams, C. S.; Legzdins, P.; McNeil, W. S. Organometallics 2001, 20, 4939. (g) Adams, C. S.; Legzdins, P.; Tran, E. J. Am. Chem. Soc. 2001, 123, 612. (h) Adams, C. S.; Legzdins, P.; Tran, E. Organometallics 2002, 21, 1474. (i) Tsang, J. Y. K.; Buschhaus, M. S. A.; Legzdins, P.; Patrick, B. O. Organometallics 2006, 25, 4215. (13) For example (examples of 1,2-C−H bond activation of benzene using Ti), see: (a) McDade, C.; Green, J. C.; Bercaw, J. E. Organometallics 1982, 1, 1629. (b) van der Heijden, H.; Hessen, B. Chem. Commun. 1995, 145. (c) Cheon, J.; Rogers, D. M.; Girolami, G. S. J. Am. Chem. Soc. 1997, 119, 6804. (d) Bailey, B. C.; Fan, H.; Baum, E. W.; Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 16016. (e) Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2007, 129, 5302. (f) Bailey, B. C.; Fan, H.; Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2007, 129, 8781. (g) Fout, A. R.; Scott, J.; Miller, D. L.; Bailey, B. C.; Pink, M.; Mindiola, D. J. Organometallics 2009, 28, 331. (14) For example (examples of 1,2-C−H bond activation of benzene using Ta), see: (a) Chamberlain, L. R.; Rothwell, I. P.; Huffman, J. C. J. Am. Chem. Soc. 1986, 108, 1502. (b) Abbott, J. K. C.; Li, L.; Xue, Z. L. J. Am. Chem. Soc. 2009, 131, 8246. (15) (a) Kretschmer, W. P.; Dijkhuis, C.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2002, 608. (b) Nomura, K.; Fukuda, H.; Katao, S.; Fujiki, M.; Kim, H.-J.; Kim, D.-H.; Zhang, S. Dalton Trans. 2011, 44, 7842. (16) Nomura, K.; Bahuleyan, B. K.; Zhang, S.; Sharma, P. M. V.; Katao, S.; Igarashi, A.; Inagaki, A.; Tamm, M. Inorg. Chem. 2014, 53, 607. (17) Effect of imido ligands toward ethylene reactivity in (imido) vanadium(V) dichloride complexes containing the (2-anilidomethyl) pyridine ligand, V(NR)Cl2[2-ArNCH2(C5H4N)]: (a) Zhang, S.; Katao, S.; Sun, W.-H.; Nomura, K. Organometallics 2009, 28, 5925. (b) Zhang, S.; Nomura, K. J. Am. Chem. Soc. 2010, 132, 4960. (c) Nomura, K.; Igarashi, A.; Katao, S.; Zhang, W.; Sun, W.-H. Inorg. Chem. 2013, 52, 2607. (18) Structural analysis data, including a CIF file for complex 2b, are given in the Supporting Information. (19) Additional results for the reaction of 2a−c in n-hexane in the presence of PMe3 are given in the Supporting Information. (20) The structure of complex 3a is also supported by an X-ray crystallographic analysis, and the CIF file was deposited as a personal communication to the Cambridge Structural Database (CCDC 1025936). Due to the fact that some bonds (isopropyl group in the imidazolidin-2-iminato ligand, carbon in CHSiMe3 (alkylidene), and methyl group in SiMe3) possess disorder even after refinement and the crystal contains solvent (n-hexane) (R1 = 0.0972; wR2 = 0.2602; GOF = 1.022). (21) Additional results for reactions of the dialkyl complexes V(NR) (CH2SiMe3)2[1,3-(2,6-iPr2C6H3)2(CH2N)2CN] (R = 2,6-Me2C6H3 (2a), 1-adamantyl (2b), C6H5 (2c)) in C6H6 or C6D6 under various conditions are given in the Supporting Information.
(6) For examples (metathesis polymerization), see: (a) Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565. (b) Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, Germany, 2003; Vols. 1− 3. (c) Ring-Opening Metathesis Polymerisation and Related Chemistry; Khosravi, E., Szymanska-Buzar, T., Eds.; Kluwer: Dordrecht, The Netherlands, 2002. (d) Metathesis Chemistry; Imamoglu, Y., Dragutan, V., Eds.; Springer: Dordrecht, The Netherlands, 2007. (7) (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. (i) Nomura, K.; Matsumoto, Y. Organometallics 2011, 30, 3610. (j) Nomura, K.; Suzuki, K.; Katao, S.; Matsumoto, Y. Organometallics 2012, 31, 5114. (8) For other established examples of the synthesis and reaction chemistry of organovanadium complexes, see: (a) Basuli, F.; Kilgore, U. J.; Hu, X. L.; Meyer, K.; Pink, M.; Huffman, J. C.; Mindiola, D. J. Angew. Chem., Int. Ed. 2004, 43, 3156. (b) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2004, 126, 1924. (c) Basuli, F.; Bailey, B. C.; Brown, D.; Tomaszewski, J.; Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2004, 126, 10506. (d) Kilgore, U. J.; Sengelaub, C. A.; Pink, M.; Fout, A. R.; Mindiola, D. J. Angew. Chem., Int. Ed. 2008, 47, 3769. (e) Kilgore, U. J.; Sengelaub, C. A.; Sengelaub, H.; Fan, H.; Tomaszewski, J.; Karty, J. A.; Baik, M.-H.; Mindiola, D. J. Organometallics 2009, 28, 843. (f) Andino, J. G.; Kilgore, U. J.; Pink, M.; Ozarowski, A.; Krzystek, J.; Telser, J.; Baik, M.-H.; Mindiola, D. J. Chem. Sci. 2010, 1, 351. (9) Wu, X.; Tamm, M. Coord. Chem. Rev. 2014, 260, 116 (review article for transition metal complexes containing imidazolin-2-iminato ligands etc.). (10) (a) Tamm, M.; Beer, S.; Herdtweck, E. Z. Naturforsch., B 2004, 59b, 1497. (b) Tamm, M.; Randoll, S.; Bannenberg, T.; Herdtweck, E. Chem. Commun. 2004, 876. (c) Tamm, M.; Randoll, S.; Herdtweck, E.; Kleigrewe, N.; Kehr, G.; Erker, G.; Rieger, B. Dalton Trans. 2006, 459. (d) Beer, S.; Hrib, C. G.; Jones, P. G.; Brandhorst, K.; Grunenberg, J.; Tamm, M. Angew. Chem. 2007, 119, 9047; Angew. Chem., Int. Ed. 2007, 46, 8890. (e) Panda, T. K.; Randoll, S.; Hrib, C. G.; Jones, P. G.; Bannenberg, T.; Tamm, M. Chem. Commun. 2007, 5007. (f) Beer, S.; Brandhorst, K.; Grunenberg, J.; Hrib, C. G.; Jones, P. G.; Tamm, M. Org. Lett. 2008, 10, 981. (g) Stelzig, S. H.; Tamm, M.; Waymouth, R. M. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6064. (h) Panda, T. K.; Trambitas, A. G.; Bannenberg, T.; Hrib, C. G.; Randoll, S.; Jones, P. G.; Tamm, M. Inorg. Chem. 2009, 48, 5462. (i) Beer, S.; Brandhorst, K.; Hrib, C. G.; Wu, X.; Haberlag, B.; Grunenberg, J.; Jones, P. G.; Tamm, M. Organometallics 2009, 28, 1534. (j) Sharma, M.; Botoshanskii, M.; Bannenberg, T.; Tamm, M.; Eisen, M. S. C. R. Chim. 2010, 13, 767. (k) Trambitas, A. G.; Panda, T. K.; Bannenberg, T. C.; Hrib, G.; Daniliuc, C. G.; Jones, P. G.; Jenter, J.; Roesky, P. W.; Tamm, M. Inorg. Chem. 2010, 49, 2435. (l) Haberlag, B.; Wu, X.; Brandhorst, K.; Grunenberg, J.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2010, 16, 8868. (m) Panda, T. K.; Hrib, C. G.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2010, 695, 2768. (n) Trambitas, A. G.; Panda, T. K.; Tamm, M. Z. Anorg. Allg. Chem. 2010, 636, 2171. (o) Trambitas, A. G.; Yang, J.; Melcher, D.; Daniliuc, C. G.; Jones, P. G.; Xie, Z.; Tamm, M. Organometallics 2011, 30, 1122. (p) Glöckner, A.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg. Chem. 2012, 51, 4368. (q) Trambitas, A. G.; Melcher, D.; Hartenstein, L.; Roesky, P. W.; Daniliuc, C.; Jones, P. G.; Tamm, M. Inorg. Chem. 2012, 51, 6753. (r) Sharma, M.; Yameen, H. S.; Tumanskii, B.; Filimon, S.-A.; Tamm, M.; Eisen, M. S. J. Am. Chem. Soc. 2012, 134, 17234. (s) Nomura, K.; Fukuda, H.; Apisuk, W.; Trambitas, A. G.; Kitiyanan, B.; Tamm, M. J. Mol. Catal. A: Chem. 2012, 363−364, 501. (t) Shoken, D.; Sharma, M.; Botoshansky, M.; Tamm, M.; Eisen, M. S. J. Am. Chem. Soc. 2013, 135, 12592. (u) Apisuk, W.; Trambitas, A. G.; I
dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
Organometallics
Article
(22) It is interesting to note that the assumed benzyne complex (containing the imidazolidin-2-iminato ligand) might be formed under rather mild conditions (70 °C after 1 day) in comparison to those for the imidazolin-2-iminato analogue (required several days at 80 °C). The case is also similar to that for the formation of the monophenyl complex 4a from the dialkyl complex 2a via vanadium-alkylidene intermediate (Scheme 6).7h (23) SIR2008: (a) Burla, M. C.; Calandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Siliqi, D.; Spagna, R. J. Appl. Crystallogr. 2007, 40, 609. (b) Camalli, M.; Carrozzini, B.; Cascarano, G. L.; Giacovazzo, C. Cryst. Res. Technol. 2011, 46, 555. (24) CrystalStructure 4.0: Crystal Structure Analysis Package; Rigaku and Rigaku Americas, Tokyo 196-8666, Japan, 2000−2010. (25) SHELX97: Sheldrick, G. M. Acta Crystallogr., Sect. A 1997, A64, 112.
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dx.doi.org/10.1021/om500986m | Organometallics XXXX, XXX, XXX−XXX
