Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and

Sep 3, 2014 - ABSTRACT: Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts...
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Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors Noriyuki Suzuki,*,†,‡ Takao Yoshitani,† Shota Inoue,† Daisuke Hashizume,‡ Hajime Yoshida,§ Meguru Tezuka,§ Keisuke Ida,⊥ Sayoko Nagashima,⊥ Teiji Chihara,‡,⊥ Osamu Kobayashi,† Shinkoh Nanbu,† and Yoshiro Masuyama† †

Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan ‡ Materials Characterization Support Unit, RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan § Department of Applied Chemistry, Graduate School of Engineering, Saitama Institute of Technology, Fukaya, Saitama 369-0293, Japan ⊥ Graduate School of Science and Engineering, Saitama University, Shimo-Okubo, Sakura-Ku, Saitama City, Saitama 338-8570, Japan S Supporting Information *

ABSTRACT: Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts. Some [5]cumulene compounds reacted with zirconocene(II) species to afford 1zirconacyclopent-3-yne complexes that have five-membered cycloalkyne structures. Only a few [5]cumulene compounds afforded η2-coordinated complexes in the presence of neutral ligands such as trimethylphosphine and tert-butyl isocyanide. Interconversion between the five-membered structure and the η2-complex was observed. Investigation of [5]cumulene derivatives of various cycloalkylidene moieties indicated that the η2-complex was preferred when the [5]cumulene has bulkier substituents. A [5]cumulene with 2,2,6,6-tetramethylcyclohexylidene groups much preferred the 1-zirconacyclopent-3-yne structure to η2coordination. In sharp contrast, the η2-coordinated complex was favored for a [5]cumulene with 2,2,7,7-tetramethylcycloheptylidene groups in the presence of PMe3. Small differences in steric environments caused totally different reactivity in [5]cumulene complexes. DFT calculations on the formation enthalpy were consistent with the experimental results, although that cannot fully rationalize the difference.

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Scheme 1. η4-and η2-Triyne Complexes of Cp*2Zr and Cp*2Ti

INTRODUCTION Haptotropic shift in organometallic species of π-ligands has been extensively studied in cyclic polyenes, such as cyclopentadienyl, indenyl, and anthracenyl ligands.1 A reversible haptotropic shift has been applied for molecular switches.1a Fewer studies have been conducted for linear polyenes and polyynes.2 A chain-walk movement of a zirconium metal along the polyyne ligand has been proposed by Rosenthal and coworkers.3 They isolated 1-zirconacyclopenta-2,3,4-triene complex 2Zr and proposed that in solution it formed η2coordinated complexes 1Zr and 1Zr′ on the basis of NMR spectroscopy (Scheme 1). The bis(η 5 -pentamethylcyclopentadienyl)titanium analogue showed only η2-coordination fashion 1Ti, and this hexatriyne did not form 1titanacyclopenta-2,3,4-triene compounds with the Cp*2Ti moiety. They ascribed the different reactivity between 2Zr and 1Ti to the atomic size of the two metals and the steric repulsion between the tert-butyl groups and the pentamethylcyclopentadienyl moieties. Choukroun and co-workers reported η2-vanadocene complexes of tetraynes.4 They isolated 3 and 5 and determined their molecular structures (Scheme 2). They observed the © 2014 American Chemical Society

Received: May 19, 2014 Published: September 3, 2014 5220

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Scheme 2. Vanadocene Complexes of Tetrayne

Scheme 5. 1-Zirconacyclopent-3-yne 8 from [3]Cumulenes

Scheme 6. η2-Cyclohexa-1,2,3-triene Complex of Zirconocene 9 transformation from 3 to 5 by addition of vanadocene and vice versa by adding one more equivalent of tetrayne. They suggested that 1-vanadacyclopenta-2,3,4-triene 4 was an intermediate for that reaction. They have not, however, isolated or detected complex 4. A related work on diyne complexes of zirconium has been reported.5 In this reaction the transformation of a 1zirconacyclopenta-2,3,4-triene complex into bis(alkynyl) zirconocene was promoted by B(C6F5)3. The latter can be regarded as the result of an η2-diyne complex (Scheme 3).

zirconacyclopentynes 10 and 2 equiv of tert-butyl isocyanide.12 The product 12 suggested the possibility of η2-butatriene complexes 11 as intermediates in the insertion reactions of isocyanide into 1-zirconacyclopent-3-ynes 10, although species 11 was not detected (Scheme 7). Scheme 7. Insertion of Isocyanide into 1-Zirconacyclopent3-ynes 10

Scheme 3. Borane-Promoted Haptotropic Behavior of Diyne on Zirconium

Similar reactivity of metallacyclic allene complexes has been reported. Erker’s group and our group independently reported 1-metallacyclopenta-2,3-diene compounds.6,7 These five-membered metallacycloallene complexes can be prepared from lowvalent zirconocene and 1-en-3-yne compounds.8 Transformation of cycloallene complexes 6 to η2-1-en-3-yne complexes 7 was achieved by addition of ancillary ligands such as phosphine and isocyanide (Scheme 4).8

Thus, both the η2-coordinated mode and 1-metallacyclopent3-yne structure are known for [3]cumulene complexes. However, transformation between these two has not been observed. It is important to pursue the haptotropic shifts of [n]cumulene ligands in transition metal complexes and factors that affect the reactivity. Herein we report on zirconocene− hexapentaene complexes that show haptotropic behavior. The steric effects of the substituents on the reactivity are examined. Part of the results have been previously reported.13

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Scheme 4. Five-Membered Metallacycloallenes and η2-1-En3-yne Complexes

RESULTS AND DISCUSSION Interconversion between the Metallacycle and η2Complex of [5]Cumulene with tert-Butyl Groups. We previously reported that 1,1,6,6-tetrakis(4-ethylphenyl)hexa1,2,3,4,5-pentaene (13a)14 reacted with low-valent zirconocene species Cp2Zr(PMe3)2 to form the 1-zirconacyclopent-3-yne compound of 2,5-bisalkylidene moieties 14a.6c,15 In the present study, we found that the reaction of 3,8-di-tert-butyl-2,2,9,9tetramethyldeca-3,4,5,6,7-pentaene (13b),16 under similar conditions, afforded the phosphine-coordinated η2-π-complex 15b (92%) selectively, instead of the 1-zirconacyclopent-3-yne 14b (Scheme 8). In the 1H NMR spectroscopy of 15b, the cyclopentadienyl (= Cp) signal appeared at 5.45 ppm as a doublet (3JPH = 1.8 Hz) because of the coupling with 31P. The number of 13C signals assignable to the [5]cumulene ligand in the 13C NMR spectra indicated its unsymmetrical structure because of PMe3 coordination. Two signals of quaternary carbon atoms were observed at 195.66 (d, 3JPH = 1.9 Hz) and 200.95 ppm. These chemical shifts are typical for central carbon atoms of allene groups. The molecular structure of 15b was unambiguously determined by X-ray diffraction study (vide

With regard to cumulative polyenes, [n]cumulenes, many examples of η2-π-coordinated [n]cumulene (n ≥ 3) complexes are known.9 We recently reported that [3]cumulenes (1,2,3butatrienes) react with group 4 metallocenes to form 1metallacyclopent-3-ynes 8, five-membered cycloalkynes (Scheme 5).10 Jones and co-workers have reported the η2-coordinated cyclohexa-1,2,3-triene-zirconium complexes 9 (Scheme 6).11 The 1-zirconacyclopent-3-yne structure of cyclohexa-1,2,3trienes has not been synthesized to date. Haptotropic interconversion between these two types of [n]cumulene complexes has been rarely mentioned. Rosenthal and co-workers reported the synthesis of complex 12 from 15221

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To examine the coordination behavior of 13b to a zirconocene moiety, we added a large excess (ca. 20 equiv) of trimethylphosphine to a benzene-d6 solution of 14b. Interestingly, 95% of 14b disappeared in 20 h, and 15b formed in 73% yield (Scheme 9). On the other hand, when crystals of 15b were dissolved in benzene-d6, leaving the solution to stand did not give 14b, and 15b gradually degraded instead. This implies that 15b did not liberate the PMe3 ligand. Addition of triethylborane gave rise to the formation of 14b in 1 h (60%). This is the first example of haptotropic interconversion between an η2-cumulene complex and a 1-metallacyclopent-3yne. The molecular structure of 14b was fundamentally the same as that of 14a bearing 4-ethylphenyl substituents. The zirconium and the six carbon atoms of the cumulene moiety are nearly coplanar. Four tert-butyl groups were almost located on that plane. In the structure of 15b, the [5]cumulene ligand bent away from the metal by 128.5° and 131.6°, showing its η2fashion. Bond lengths and angles around the Zr, C3, and C4 atoms in 15b resemble those in zirconium−alkene complexes.17 In contrast to 14b, the planes C7−C1−C11 and C15−C6− C19, which include two tert-butyl groups at the termini of the cumulene, were nearly perpendicular (75.1° and 83.8°, respectively) to the Zr and C1−C6 plane. These molecular structures show that the ligand is rotated about 90° during the interconversion between 14b and 15b. It is noteworthy that the distances Zr−C3 in 14b and Zr−C3 and Zr−C4 in 15b are in the same range. This suggests that the movement of C2−C3 and C5−C4 bonds during the haptotropic change seems like they pivot upon the C3 and C4 atoms, respectively. Coordination Behavior of the Complexes of [5]Cumulene with 4-Ethylphenyl Groups. Although starting from Cp2Zr(PMe3)2, the reaction with 13a gave 14a as the only product, and a phosphine adduct such as 15a was not obtained after recrystallization. However, the reaction needs 2 to 4 days to produce a good yield of 14a. Thus, we examined the products in the beginning of the reaction. After Cp2Zr(PMe3)2 and 13a were dissolved in toluene-d8 at room temperature (rt), the solution was immediately observed by NMR. Broad signals were found in the Cp region. 1H NMR observation at −40 °C suggested that, in the beginning of the reaction (ca. 1 h), the η2-π-complexes 15a and 15a′ were formed in 50% and 26% yield, respectively, accompanied by a small amount of 14a (4%) (Scheme 10). Two Cp-1H NMR doublets were observed at 5.39 and 5.29 ppm (3JPH = 1.6 Hz) in toluene-d8, and these coalesced at 20 °C (Figure 2). Because 13C NMR gave an unsatisfactory S/N ratio because of low concentration, we employed 13C-enriched 13a to assign the chemical shifts.6c The two signals of the central allene were at 196 and 199 ppm, which are typical for central allene carbons. Coupling constants (1JCC) with the adjacent 13C atoms were 116 and 111 Hz, respectively. Besides the signals assignable to 15a, other sets of signals due to 15a′ were observed. Quaternary carbons at 150 and 174 ppm were assigned to a “butatriene” part, and the smaller chemical shifts are consistent with the structure. Another isomer, 15a″, is possible, but it is unlikely taking account of its steric congestion, and the third isomer was not detected as far as we investigated. This indicates that 15a and 15a′ were in equilibrium in solution, and the equilibrium probably proceeded by “ligand-sliding”, not via 14a.9e,k,19 The “sliding”

Scheme 8. Reactions of Hexapentaenes and Cp2Zr(PMe3)2

infra). Prolonged stirring or heating did not result in the formation of 14b, showing that the η2-mode is much more favored than the five-membered metallacyclic structure for the tert-butyl-substituted [5]cumulene 13b. Interestingly, 14b could be prepared from 13b and low-valent zirconocene species generated from Cp2ZrCl2 and Mg in the absence of PMe3 (76%, Scheme 9). Complex 14b is stable enough, as well as 14a, in solution that no significant degradation was detected during the NMR measurement. Note that the reaction of 13b with Cp2ZrCl2/Mg in the presence of PMe3 gave 15b in good yield. The molecular structures of 14b was also characterized by X-ray analyses (Figure 1). Scheme 9. Formation of Zirconocene Complexes of 13b with or without PMe3 and Reversible Haptotropic Conversion in 14b and 15b

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Figure 1. Molecular structures of 14b (left) and 15b (right) drawn with 50% probability ellipsoids. Hydrogen atoms are omitted. Selected bond lengths (Å) and angles (deg): 14b, Zr−C2 2.393(2), Zr−C3 2.307(2), C2−C3 1.390(3), C3−C3* 1.258(2), C2−Zr−C2* 100.3(1), Zr−C2−C3 69.4(1), C2−C3−C3* 150.3(2); 15b, Zr−P 2.6916(7), Zr−C3 2.305(2), Zr−C4 2.246(2), C1−C2 1.326(3), C2−C3 1.303(3), C3−C4 1.445(3), C4−C5 1.303(3), C5−C6 1.318(3), C1−C2−C3 174.6(2), C2−C3−C4 128.5(2), C3−C4−C5 131.6(2), C4−C5−C6 178.3(2).

Scheme 10. Isomers of η2-Complexes of [5]Cumulene

between 15a and 15a′ is fast compared with the NMR time scale at rt. Signals for 15a and 15a′ disappeared with time, and 14a formed quantitatively in 4 days, showing that 15a/a′ spontaneously released PMe3 to transform into 14a. To our surprise, addition of excess PMe3 to 14a did not form any 15a, and 14a remained unreacted, as did complex 10 (Cp′ = C5H5). These facts indicate that the equilibrium lies toward the right in (14b + PMe3)/15b (Scheme 11), while it lies far toward the left in (14a + PMe3)/15a and in (10 + PMe3)/11. This is probably because of the steric demand of the tert-butyl groups. Effect of the Steric Bulkiness of [5]Cumulenes. To shed light on the different behavior between 14a/15a (R = 4EtC6H4−) and 14b/15b (R = t-Bu−), we investigated a few other [5]cumulene derivatives for comparison. We employed hexapentaenes with cyclopentylidene (13c), cyclohexylidene (13d), and cycloheptylidene moieties (13e). All of these compounds reacted with Cp2ZrCl2/Mg to give zirconacycles 14c−e in moderate to good yields (Scheme 12).20 These complexes 14c−e must show similar steric repulsion between their methyl groups and cyclopentadienyl rings to those of 14b. However, they should be slightly different according to the ring size, and the repulsion must be larger in the order 14e > 14d > 14c.

Figure 2. 1H NMR of Cp signals of η2-complexes 15a/15a′. Although the signal at 5.24 ppm (uk) is unidentified, it is possibly due to phosphine-coordinated dimeric species.18

Scheme 11. Equilibrium between 14 and 15

Complexes 14c−e were structurally characterized and showed fundamentally similar molecular structures to that of the tetra-tert-butyl complex 14b (vide infra, Table 1).21 Trimethylphosphine was added to the benzene-d6 solution of 14c to examine whether the η2-complex 15c was formed. Surprisingly, no reaction took place and 14c remained 5223

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Scheme 12. 1-Zirconacyclopent-3-ynes of [5]Cumulenes with Various Ring Sizes

Scheme 13. Haptotropic Shift and Steric Environments

the cyclopentadienyl ligands and four singlets for methyl groups were consistent with the structure of 15e. A doublet of PMe3 observed at 0.94 ppm downfield compared with free PMe3 showed its coordination to the metal. Complex 15e was alternatively prepared from Cp2ZrCl2/Mg and 13e in the presence of trimethylphosphine, and its structure was confirmed by X-ray crystallographic analyses. To examine the possibility of 15d, we monitored the reaction of 13d with Cp2Zr(PMe3)2 using 1H NMR. In this reaction two molecules of PMe3 have to be liberated from the zirconium atom before the formation of the five-membered complex 14d. After stirring the reaction mixture at rt for 24 h, 1H NMR observation suggested the clean formation of η2-coordinated complex 15d (Scheme 14). The Cp signal was coupled with

Table 1. Selected Bond Distances (Å) and Angles (deg) of 14b−e

Scheme 14. Temporary Formation of 15d

Zr−C2 Zr−C3 Zr−C4 Zr−C5 C2−C3 C3−C4 C4−C5 d1 d2 l1 l2 Zr−C2−C3 Zr−C5−C4 C2−Zr−C5 C2−C3−C4 C3−C4−C5

14b

14c (n = 2)a

14d (n = 3)

14e (n = 4)

2.393(2) 2.307(2)

2.374e 2.333e

1.390(3) 1.258(2)b

1.408e 1.267e

2.11(4) 2.16(3) 2.720(4)

2.37 2.39 2.509e

69.4(1)

71.08e

100.3(1)c 150.3(2)d

101.1e 148.4e

2.4260(17) 2.3163(17) 2.3168(17) 2.4159(16) 1.390(2) 1.253(3) 1.388(3) 2.23(3) 2.24(3) 2.663(2) 2.644(3) 68.7(1) 69.1(1) 99.38(6) 151.6(2) 151.1(2)

2.401(6) 2.308(6) 2.312(4) 2.392(4) 1.391(6) 1.267(7) 1.387(8) 2.20(9) 2.24(9) 2.723 2.715 69.2(3) 69.7(3) 100.4(2) 150.7(6) 149.9(5)

phosphine (5.58 ppm, 3JPH = 1.7 Hz, in THF/C6D6); four singlets for methyl groups at 1.23−1.40 ppm and one doublet for PMe3 at 0.89 ppm were observed. Complex 15d, however, was labile in solution. Our attempt to isolate 15d has been unsuccessful so far. After the recrystallization procedure, only 14d and unidentified decomposed products were observed with 1 H NMR in the solution, which suggests that the coordinated trimethylphosphine in 15d dissociated during the operation. These results indicated that the equilibrium position in Scheme 15 lies far to the left in the reaction from (14c−d + PMe3) to 15c−d, whereas it lies far to the right in the reaction from (14e + PMe3) to 15e (Scheme 15). Comparison of the Molecular Structures of 14b−e. To examine the structural differences among these complexes, structural data on the basis of X-ray diffraction analyses are compared in Table 1. These four complexes have similar structural features in their 1-zirconacyclopent-3-yne moieties. Steric repulsions between the cyclopentadienyl rings and the methyl groups on the terminal substituents must affect the haptotropic reactivity of

a

Ref 20. bC3−C3* bond distance. cC2−Zr−C2* angle. dC2−C3− C3* angle. eAverage values of two pseudoequivalent bonds in two independent molecules are shown.

unreacted even after 20 h at rt. Heating at 60 °C for 3 h did not produce any change, and no trace of 15c was observed. It should be noted that 14d, with a more sterically congested environment, also gave no 15d upon addition of PMe3 (Scheme 13). In sharp contrast to these results, addition of PMe3 to a solution of 14e gave η2-coordinated complex 15e in 23% at rt in 20 h accompanied by remaining 14e (58%). The formation of 15e reached 72% in 8 days with 1% of 14e remaining. A doublet at 5.46 ppm (3JPH = 1.7 Hz) that could be assigned to 5224

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and 15d,e (for example 15d spontaneously converted into 14d), the DFT studies support that steric hindrance would be an important factor for the haptotropic shifts. Intermediacy in Double Insertion of Isocyanide. As shown in Scheme 7, Rosenthal and co-workers reported insertion of two molecules of tert-butyl isocyanide into zirconium−carbon bonds in 10 that afforded 12. They suggested η2-[3]cumulene complex 11 as an intermediate, that is, the species resulting from a haptotropic shift from 10. Complex 11 or its stabilized form such as adducts of ancillary ligands has not been detected to date.22 Complex 14b reacted with 2 equiv of tert-butyl isocyanide at rt to give the inserted product 16 in good yields. As reported for diazadiene complexes,23 the two Cp rings in 16 were observed to be inequivalent in NMR spectroscopy. The X-ray diffraction study showed that 16 has a similar molecular structure to 12, although the results were unsatisfactory to discuss detailed structural aspects. Addition of tert-butyl isocyanide to the [5]cumulene complex 14a, on the other hand, did not give the corresponding inserted products, even at 80 °C. The phosphine adduct 15b also reacted with 2 equiv of tertbutyl isocyanide to afford 16. It was interesting that the η2complex isocyanide adduct 17 was formed by the reaction of 15b with 1 equiv of tert-butyl isocyanide (Scheme 16). The

Scheme 15. Equilibria between Complexes 14 and 15

the complexes. The closest and the second closest distances between the hydrogen atoms of methyl groups and Cp rings are shown as d1 and d2, respectively. There are only small differences among 14b−e, although the order of d1,2 is 14c > 14d > 14e > 14b. The distances between the two carbon atoms directly attached to the termini of [5]cumulene moieties are shown as l1 and l2. Naturally, the larger the ring size of the substituents, the longer the values of l. Indeed, the l values are in the order 14b > 14e > 14d > 14c. Longer l values must mean more a sterically congested environment around the methyl and the Cp groups. It is surprising for us that there are quite small differences between the structural features in 14d and 14e in spite of their totally different reactivities. These results led us to perform DFT studies to compare the reactivity of 14d and 14e. DFT Calculation of the Haptotropic Shift. To obtain more information on the difference in haptotropic behavior between 14d ↔ 15d and 14e ↔ 15e, DFT calculations were performed (Figure 3).

Scheme 16. Insertion of tert-Butyl Isocyanide into 14b and 15b

molecular structure of 17 was unequivocally characterized (Figure 4). The [5]cumulene 13b coordinates to the zirconium atom in η2-fashion. The X-ray study showed that 17 had similar structural features to the η2-complex phosphine adduct 15b, although the angles C2−C3−C4 and C3−C4−C5 are slightly larger in 17 (133.5° and 135.1°) than those in 15b (128.5° and 131.6°). Treatment of 17 with an additional equivalent of tertbutyl isocyanide gave 16 in 42% yield. Formation of 17 could also be detected as an intermediate during the reaction of 14b with 2 equiv of tert-butyl isocyanide. Consumption of 14b and formation of 16 and 17 with time are depicted in Figure 5. 14b rapidly reacted to give 17 first, and then 16 grew after 3 h. Complex 16 grew at the expense of the amount of 17, reaching 82% in 18 h.

Figure 3. Energy gaps for haptotropic transformation.

In the haptotropic shift from 14 to η2-fashion IM, the energy gap (ΔE1) was significantly larger in 14d than in 14e. On the other hand, the energy gap for coordination of trimethylphosphine to IM was found to be only slightly larger in 15d than 15e. The calculated values are consistent with the experimental results that 14e changed to 15e by the addition of PMe3, but 14d did not. Although the difference in the energy gaps might not be large enough to fully rationalize the reactivity of 14d,e 5225

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EXPERIMENTAL SECTION

All manipulations were carried out under an inert atmosphere using Schlenk techniques or a glovebox. Anhydrous hexane and toluene were purchased from Kanto Chemical Co., Inc., and degassed prior to use. THF was dried over a Contour dry-solvent system. Zirconocene dichloride, tert-butyl isocyanide, trimethylphosphine, and 2,2,4,4tetramethyl-3-pentanone were purchased from Aldrich Chemical Co. and used as received. Hexachloro-1,3-butadiene was obtained from Wako Pure Chemical Industries, Ltd., and used without further purification. Compounds 13a,14 14a,6c and 14c20 were prepared as previously described. Bis(η 5 -cyclopentadienyl)zirconiumbis(trimethylphosphine) [Cp2Zr(PMe3)2] was prepared according to the literature.24 1,4-Bis(2,2,5,5-tetramethylcyclopentylidene)buta1,2,3-triene (13c)16 and 1,4-bis(2,2,6,6-tetramethylcyclohexylidene)buta-1,2,3-triene (13d)25 were prepared according to the literature. 1H and 13C NMR spectra were recorded on JEOL EX-270, AL-300, AL400, and ECP-500 spectrometers. Infrared spectra were recorded on TravelIR total reflection infrared spectroscopy equipment (SensIR Technologies) and a Shimadzu FTIR-8300. 3,8-Di-tert-butyl-2,2,9,9-tetramethyldeca-3,4,5,6,7-pentaene (13b). The title compound was prepared from 1,1,6,6-tetrakis(tertbutyl)-2,4-hexadiyne-1,6-diol according to the method reported by Iyoda et al.16 The starting 1,6-diols were prepared from 1,4-dilithio1,3-butadiyne26 and ketone as follows. In a thoroughly dried 200 mL round-bottom flask filled with argon, tetrahydrofuran (20 mL) was charged, and the contents were cooled to −78 °C. A hexane solution of n-butyllithium (1.58 M, 30.6 mmol) and hexachloro-1,3-butadiene (1.2 mL, 7.5 mmol) were added dropwise in this order. The mixture was warmed to rt and stirred for 20 h. The mixture was then cooled at −78 °C, and 2,2,4,4-tetramethyl-3-pentanone (2.6 mL, 15.1 mmol) was added dropwise. The reaction mixture was warmed to rt, stirred for 2 h, and then stirred at 70 °C for an additional 2 h. The solution was concentrated to about one tenth by volume, and diethyl ether and 1 N HCl was added. The aqueous layer was extracted with ether, and the organic layer was dried over magnesium sulfate and filtered. Volatiles were removed in vacuo, leaving 1,1,6,6-tetrakis(tert-butyl)2,4-hexadiyne-1,6-diol as white crystals in 95% yield. 1,4-Bis(2,2,7,7-tetramethylcycloheptylidene)buta-1,2,3-triene (13e). The title compound was synthesized in a similar manner to 13b using 2,2,7,7-tetramethylcycloheptanone.27 A THF (3 mL) solution of 1,4-bis(2,2,7,7-tetramethylcycloheptylidene)-2,3-dibromobuta-1,3-diene (150 mg, 0.29 mmol) was sonicated in the presence of activated zinc powder (164 mg, 2.5 mmol) at 40 °C for 3 h. The reaction mixture was filtered, and the volatiles were removed in vacuo from the filtrate. The residue was purified with column chromatography on silica gel (hexane) to give 13e as yellow crystals (100 mg, 97%). The molecular structure of 13e was determined by X-ray analysis (see the Supporting Information). 1H NMR (CDCl3, Me4Si, 500 MHz): δ 1.25 (s, 24H), 1.55, (m, 8H), 1.63 (m, 8H). 13C{1H} NMR (CDCl3, 125.8 MHz): δ 25.89 (CH3), 31.62 (CH2), 42.08 (q), 43.03 (q), 131.23 (q), 140.63 (q), 156.45 (q). IR (KBr): 661, 760, 957, 1007, 1134, 1161, 1242, 1275, 1362, 1387, 1474, 1992, 2855, 2922, 2963 cm−1. High-resolution mass spectrometry (FAB): calcd for C26H40 352.3130, found 352.3109. Preparation of 1,1-Bis(η5-cyclopentadienyl)-2,5-bis(di-tertbutylmethylidene)-1-zirconacyclopent-3-yne (14b). Dried magnesium powder (48 mg, 2 mmol) was suspended in THF (4 mL). To this mixture were added bis(η5-cyclopentadienyl)zirconium dichloride (Cp2ZrCl2, 146 mg, 0.5 mmol) and 13b (150 mg, 0.5 mmol), and the mixture was sonicated at 50 °C for 1 h. 1H NMR observation indicated the formation of the title compound in 76% yield in this stage. Volatiles were removed in vacuo, and the residue was dissolved in hexane and filtered. Solvent was slowly evaporated under argon flow, leaving complex 14b as yellow crystals (50%). 1H NMR (C6D6, Me4Si, 270 MHz): δ 1.61 (s, 18H), 1.66, (s, 18H), 5.38 (s, 10H). 13C{1H} NMR (C6D6, Me4Si, 67.8 MHz): δ 33.26 (CH3), 33.31 (CH3), 40.02 (q), 43.15 (q), 100.30 (CC), 105.87 (Cp), 156.78 (q), 163.35 (q). IR (neat, ATR): 789, 1013, 1225, 1358, 1478, 1574, 1912 (w), 2860, 2950 cm−1. Anal. Calcd for C32H46Zr: C 73.64, H 8.88. Found: C 73.75, H 9.02.

Figure 4. Molecular structure of 17. Selected bond lengths (Å) and angles (deg): Zr−C23 2.3083(18), Zr−C3 2.2772(18), Zr−C4 2.2578(16), C1−C2 1.326(2), C2−C3 1.291(2), C3−C4 1.441(2), C4−C5 1.290(2), C5−C6 1.323(2), C1−C2−C3 177.84(18), C2− C3−C4 133.45(15), C3−C4−C5 135.13(18), C4−C5−C6 177.64(17).

Figure 5. Formation of 16 and 17 from 14b and tert-butyl isocyanide at rt in C6D6.

The reaction of 15b and 2 equiv of tert-butyl isocyanide was also observed by 1H NMR in C6D6. The Cp signal of 15b was observed at 5.45 ppm as a doublet (3JPH = 1.8 Hz), and it decreased after 1 h at rt (conv 86%). The Cp singlet of 17 appeared later at 5.60 ppm (62%) accompanied by the inequivalent Cp singlets of 16 at 5.63 and 5.92 ppm (19%). After 3 h, 17 and 16 were formed in 49% and 42% yield, respectively, with 91% conversion of 15b. Complex 17 was obtained in 92% yield after 21 h, when 17 decreased to 2% (15b: conv 94%). This suggests that the phosphine ligand in 15b was replaced by tert-butyl isocyanide followed by insertion. These results clearly indicate that a ligand-induced haptotropic shift from 14b to 17 was the first step in the insertion of isocyanides.

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CONCLUSION Zirconocene complexes of 1,6-tetrasubstituted [5]cumulene compounds showed two types of coordination modes, a fivemembered 1-zirconacyclopent-3-yne structure and η2-coordinated complexes. Haptotropic interconversion between the former and the latter was observed for [5]cumulenes of bulkier substituents such as tert-butyl groups, while five-membered structures were much favored for [5]cumulenes with less bulky substituents. A critical difference in the haptotropic reactivity was observed between two compounds of very similar steric environment, but with a very small difference in the steric bulkiness. The haptotropic shift from five-membered metallacycle to η2-complex was suggested in the double insertion reaction of isocyanide into zirconium−carbon bonds. 5226

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1,1-Bis(η 5-cyclopentadienyl)-2,5-bis(2,2,6,6-tetramethylcyclohexylidene)-1-zirconacyclopent-3-yne (14d). The title compound was prepared in a similar manner to that described for 14b using 13d (0.5 mmol, 162 mg). Recrystallization from hexane solution gave the title compound 14d as yellow crystals (107 mg, 44%). 1H NMR (C6D6, Me4Si, 300 MHz): δ 1.58 (s, 12H), 1.68, (s, 12H), 1.65−1.73 (m, 12H), 5.41 (s, 10H). 13C{1H} NMR (C6D6, 75.6 MHz): δ 18.77 (CH2), 32.08 (4C, CH3), 32.89 (4C, CH3), 39.24 (CH2), 40.90 (CH2), 41.46 (q), 41.48 (q), 100.38 (CC), 105.91 (Cp), 156.09 (q), 162.31 (q). IR (KBr): 679, 795, 980, 1015, 1069, 1184, 1234, 1358, 1377, 1447, 1462, 1597, 1925, 2862, 2920 cm−1. Anal. Calcd for C34H46Zr: C 74.80, H 8.49. Found: C 74.83, H 8.63. 1,1-Bis(η 5-cyclopentadienyl)-2,5-bis(2,2,7,7-tetramethylcycloheptylidene)-1-zirconacyclopent-3-yne (14e). The title compound was prepared similarly to 14b using 13e (0.09 mmol, 33 mg) (yellow crystals, 34 mg, 63%; 88% by 1H NMR). 1H NMR (C6D6, Me4Si, 300 MHz): δ 1.47−1,55 (m, 4H), 1.61−1.76 (m, 18H), 1.64 (s, 12H), 1.72 (s, 12H), 1.81−1.85 (m, 4H), 5.40 (s, 10H). 13C{1H} NMR (C6D6, Me4Si, 75.6 MHz): δ 25.62 (CH2, 4C, two signals overlapped), 32.56 (CH3), 33.56 (CH3), 43.88 (CH2, 4C, two signals overlapped), 45.80 (q, 4C, two signals overlapped), 100.42 (q, CC), 106.13 (Cp), 157.70 (q), 164.65 (q). IR (KBr): 648, 679, 795, 1018, 1096, 1169, 1261, 1358, 1381, 1454, 1574, 1925, 2858, 2924 cm−1. Anal. Calcd for C36H50Zr: C 75.33, H 8.78. Found: C 74.98, H 9.17. Ziconocene-η 2-hexapentaene Complex−Trimethylphosphine Adduct (15b) from Cp2Zr(PMe3)2. Cp2Zr(PMe3)2 (20 mg, 0.054 mmol) and 13b (16.2 mg, 0.054 mmol) were dissolved in benzenze-d6 (1 mL), and the mixture was stirred for 1 h at rt. The formation of 15b in 92% yield was observed by 1H NMR spectroscopy. Ziconocene-η 2-hexapentaene Complex−Trimethylphosphine Adduct (15b) from 14b. To a solution of 14b (23.5 mg, 0.045 mmol) in benzene-d6 (0.4 mL) was added trimethylphosphine (76 mg, 1.0 mmol) at rt. The mixture was observed by 1H NMR spectroscopy using pyrene as internal standard. Formation of 15b was detected (12%) after 1 h. After 20 h, 95% of 14b was consumed and 15b was formed in 73% yield. Preparation of 15b from Cp2ZrCl2/Mg. Magnesium powder (25.3 mg, 1.04 mmol) was thoroughly dried under vacuum in a Schlenk tube. Zirconocene dichloride (145 mg, 0.50 mmol) and 13b (153 mg, 0.51 mmol) were added, and the mixture was suspended in THF (3 mL) at rt. Trimethylphosphine (114 mg, 1.5 mmol) was added, and the mixture was sonicated at 50 °C for 1 h. 1H NMR observation using toluene as internal standard showed quantitative formation of 15b at this stage. The volatiles were removed in vacuo, and the residue was dissolved in hexane and filtered. The filtrate was concentrated and cooled at −20 °C to give the title compound as yellow needle crystals (120 mg, 40%). 1H NMR (C6D6, Me4Si, 500 MHz): δ 0.92 (d, 2JP−H = 6.9 Hz, 9H), 1.43 (s, 18H), 1.57 (s, 18H), 5.45 (d, 3JP−H = 1.8 Hz, 10H). 13C{1H} NMR (C6D6, C6D5H = 128 ppm, 125.8 MHz): δ 16.77 (d, J = 17.3 Hz), 34.00, 34.25, 36.03 (q), 36.65 (q), 97.38 (q, J = 23.0 Hz), 102.99, 103.32 (d, J = 9.6 Hz), 109.68, 112.59, 195.66 (d, J = 1.9 Hz), 200.95. IR (neat, ATR): 2948, 2906, 1870, 1478, 1355, 1281, 1208, 1198, 1011, 947, 791 cm−1. Anal. Calcd for C35H55PZr: C 70.30, H 9.27. Found: C 70.06, H 9.32. Ziconocene-η 2-hexapentaene Complex−Trimethylphosphine Adduct (15e) from 14e. To a solution of 14e (25.7 mg, 0.045 mmol) in benzene-d6 (0.4 mL) was added trimethylphosphine (76 mg, 1.0 mmol) at rt. The mixture was observed by 1H NMR spectroscopy using pyrene as an internal standard. The formation of 15e in 23% yield was detected after 20 h with 58% of 14e remaining. Formation of 15e reached 72% in 8 days with 1% of 14e remaining. 15e: Selected chemical shifts for 1H NMR (THF/C6D6, Me4Si): δ 1.00 (d, J = 6.5 Hz), 1.28 (s, 6H), 1.31 (s, 6H), 1.46 (s, 6H), 1.48 (s, 6H), 5.46 (d, J = 1.7 Hz, 10H). Full data in C6D6 are shown below. Preparation of Zirconocene-η2-hexapentaene Complex− Trimethylphosphine Adduct (15e) from Cp2ZrCl2/Mg. Magnesium powder (48.6 mg, 2.0 mmol) was thoroughly dried under vacuum in a Schlenk tube. Zirconocene dichloride (148 mg, 0.5 mmol) and 13b (178 mg, 0.51 mmol) were added, and the mixture was

suspended in THF (3 mL) at rt. Trimethylphosphine (114 mg, 1.5 mmol) was added, and the mixture was sonicated at 50 °C for 1 h. 1H NMR observation using toluene as internal standard showed the formation of 15b in 90% yield at this stage. The volatiles were removed in vacuo, and the residue was dissolved in hexane and filtered. The filtrate was concentrated and cooled at −30 °C to give the title compound as yellow needle crystals (165 mg, 50%). 1H NMR (C6D6, Me4Si, 500 MHz): δ 0.94 (d, 2JP−H = 6.9 Hz, 9H), 1.34 (s, 6H), 1.38 (s, 6H), 1.54 (s, 12H), 1.66−1.94 (m, 16H), 5.46 (d, 3JP−H = 1.7 Hz, 10H). 13C{1H} NMR (C6D6, Me4Si, 125.8 MHz): δ 16.86 (d, JPC = 18 Hz), 26.73 (CH2), 26.95 (CH2), 32.27 (CH3), 33.31 (CH3), 34.11 (CH3), 34.34 (CH3), 38.93 (q), 39.51 (q), 45.49 (CH2), 45.52 (CH2), 97.11 (q, J = 23.0 Hz), 103.04 (Cp), 108.13 (q), 111.47 (q), 128.39 (q), 195.95 (J = 2.4 Hz), 202.19. IR (KBr): 667, 729, 787, 953, 1015, 1134, 1165, 1242, 1285, 1304, 1377, 1450, 1470, 1871, 2855, 2920 cm−1. Anal. Calcd for C39H59PZr: C 72.05, H 9.15. Found: C 71.81, H 9.09. Observation of 15a and 15a′. Bis(η5-cyclopentadienyl)zirconiumbis(trimethylphosphine) (13 mg, 0.035 mmol), 13a (14.6 mg, 0.03 mmol), and pyrene (3.9 mg, 0.077 mmol as internal standard) were dissolved in toluene-d8 (0.6 mL) at rt in an NMR tube, and the mixture was immediately observed by 1H NMR spectroscopy. At room temperature, a broad signal was observed at 5.4 ppm. When the sample was cooled to −40 °C, this broad signal split into two doublets at 5.39 and 5.29 ppm, which were assignable to the Cp protons of 15a (50%) and 15a′ (26%), respectively. A small amount of 14a was also observed at 5.35 ppm (4%). There were two doublets at 0.67 and 0.92 ppm that were assigned to coordinated trimethylphosphines. These Cp and P(CH3)3 signals coalesced at 20 °C again, showing that the change is reversible. This type of haptotropic shift in cumulene complexes has been reported for platinum and rhodium complexes.6,7,9e,k Presumably, the equilibrium between 15a/15a′ proceeded by “ligand-sliding”, not via 14a. Since satisfactory 13C NMR spectra were not obtained due to low concentration and short measurement time, we conducted a reaction using the 13C-enriched hexapentaene 13a (13a*) that has four 13C atoms at the central cumulene moiety in order to confirm the structure. Compound 13a* was prepared as previously reported.6c The 13C-enriched acetylene was monolithiated with n-BuLi and reacted with di(4-ethylphenyl)ketone. Obtained progargylic alcohol was dimerized using copper(II) acetate, followed by reduction with SnCl2. Each signal was assigned on the basis of the 13C−13C coupling constants. Assignments and the coupling constants are shown below. 15a: 1H NMR (toluene-d8, −40 °C): δ 0.67 (d, JPH = 7 Hz, 9H, PMe3), 5.39 (d, JPH = 1.6 Hz, 10H, Cp). Chemical shifts (ppm) and coupling constants (in parentheses, Hz) in 13C and 31P NMR. The atom label “13C” represents enriched atoms. Italic digits show JPC.

15a′: 1H NMR (toluene-d8, −40 °C): δ 0.92 (d, JPH = 7 Hz, 9H, PMe3), 5.29 (d, JPH = 1.6 Hz, 10H, Cp) ppm. Chemical shifts and coupling constants (in parentheses) in 13C and 31P NMR. The label “13C” represents enriched atoms. Italic digits show JPC. Although the isomer 15a″ is possible, its sterically congested structure seems unlikely. We concluded that the species must be 15a′ according to the coupling constants JPC between the zirconium-coordinated carbon atoms and phosphorus atom.10 5227

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of full-matrix least-squares refinement on F2 was based on 3211 observed reflections and 171 variable parameters. All calculations were performed using the CrystalStructure30 crystallographic software package. Crystallographic data are summarized in the Supporting Information. CIF data were deposited in the Cambridge Structural Database (CCDC-679733). X-ray Diffraction Analyses of 14d. Crystals were obtained by evaporation of solvent from a hexane solution. An orange platelet crystal (0.30 × 0.20 × 0.05 mm) was mounted on a polyaminde film [MicroMounts (MiTegen)] and coated with paraffin. All data were collected on a Rigaku Mercury CCD area detector with graphitemonochromated Mo Kα radiation at 93 K. The structure was solved by direct methods28 and expanded using Fourier techniques.30b The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined isotropically. The final cycle of full-matrix least-squares refinement on F2 was based on 6402 observed reflections and 501 variable parameters. All calculations were performed using the CrystalStructure31 crystallographic software. Crystallographic data are summarized in the Supporting Information. CIF data were deposited in the Cambridge Structural Database (CCDC-991966). X-ray Diffraction Analyses of 14e. Crystals were obtained by recrystallization from a hexane solution. A yellow platelet crystal (0.20 × 0.15 × 0.03 mm) was mounted on a polyaminde film [MicroMounts (MiTegen)] and coated with paraffin. All data were collected on a Rigaku Mercury CCD area detector with graphite-monochromated Mo Kα radiation at 93 K. The structure was solved by direct methods32 and expanded using Fourier techniques. The non-hydrogen atoms were refined anisotropically. Some hydrogen atoms were refined isotropically, and the rest were refined using the riding model. The final cycle of full-matrix least-squares refinement on F2 was based on 5286 observed reflections and 382 variable parameters. All calculations were performed using the CrystalStructure33 crystallographic software package except for refinement, which was performed using SHELXL97.30b Crystallographic data are summarized in the Supporting Information. CIF data were deposited in the Cambridge Structural Database (CCDC-991967). X-ray Diffraction Study of 15b. Single crystals were obtained by recrystallization from a hexane solution. A yellow crystal (0.48 × 0.03 × 0.01 mm) was mounted in a loop and coated with paraffin. All measurements were made on a Rigaku Saturn 70 CCD area detector with graphite-monochromated Mo Kα radiation at 90 K. The structure was solved by direct methods28 and expanded using Fourier techniques.29 The non-hydrogen atoms were refined anisotropically. Hydrogen atoms on the cyclopentadienyl ring were refined isotropically, and the rest were located at calculated positions and refined using the riding model. The final cycle of full-matrix least-squares refinement on F2 was based on 9185 observed reflections and 375 variable parameters. All calculations were performed using the CrystalStructure30a,34 crystallographic software package. Crystallographic data are described in the Supporting Information. CIF data were deposited in the Cambridge Structural Database (CCDC699032). X-ray Diffraction Study of 15e. Single crystals were obtained by recrystallization from a hexane solution. A yellow platelet crystal (0.15 × 0.12 × 0.03 mm) was mounted on a polyamide film [MicroMounts (MiTegen)] and coated with paraffin. All measurements were made on a Rigaku Mercury CCD area detector with graphite-monochromated Mo Kα radiation at 194 K. The structure was solved by direct methods35 and expanded using Fourier techniques. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms on the cyclopentadienyl ring were refined isotropically, and the rest were located at calculated positions and refined using the riding model. The final cycle of full-matrix least-squares refinement on F2 was based on 6030 observed reflections and 381 variable parameters. All calculations were performed using the CrystalStructure33 crystallographic software package except for refinement, which was performed using SHELXL-97.30b Crystallographic data are summarized in the Supporting Information. CIF data were deposited in the Cambridge Structural Database (CCDC-991968).

Preparation of 16: Insertion Reaction of tert-Butyl Isocyanide to 14b. Caution!: tert-Butyl isocyanide is highly toxic and must be handled with care in a fume hood. To a solution of 14b (58 mg, 0.11 mmol) in toluene (1 mL) was added tert-butyl isocyanide (28 mg, 0.33 mmol) at rt, and the mitxture was stirred for 22 h. 1H NMR observation using 1,4-dioxane as internal standard indicated formation of 16 in 83% yield at this stage. Volatiles were removed in vacuo, and the residue was dissolved in hexane and filtered. The filtrate was concentrated and cooled at −30 °C to give 16 as yellow, thin needle crystals (46 mg, 61%). The molecular structure was confirmed by Xray diffraction study, although the refinement was unsatisfactory. 1H NMR (C6D6, Me4Si, 270 MHz): δ 1.35 (s, 18H), 1.41 (s, 18H), 1.44 (s, 18H), 5.63 (s, 5H), 5.92 (s, 5H). 13C{1H} NMR (C6D6, Me4Si, 67.8 MHz): δ 32.86 (CH3), 32.92 (CH3), 33.19 (CH3), 36.84 (q), 37.19 (q), 57.86 (q, NC), 104.44, 109.11 (Cp × 2), 109.90 (q), 120.20 (q), 127.44 (q), 189.38 (q). IR (neat, ATR): 2958, 2908, 1480, 1459, 1360, 1204, 1021, 787, 726 cm−1. Anal. Calcd for C42H64N2Zr: C 73.30, H 9.37, N 4.07. Found: C 73.11, H 9.44, N 3.98. Preparation of 16 from 15b. Complex 15b (7 mg, 0.0117 mmol) was dissolved in benzene-d6 (0.5 mL) and tert-butyl isocyanide (2.9 mg, 0.035 mmol) was added at rt. Formation of 16 and 17 was observed by 1H NMR spectroscopy.

15b 17 16 1 h 14% 62% 19% 3 h 8.5% 49% 42% 21 h 6.4% 2% 92% Zirconocene-η2-hexapentaene Complex−tert-Butyl Isocyanide Adduct (17). Caution!: tert-Butyl isocyanide is highly toxic and must be handled with care in a f ume hood. To a solution of 15b (25 mg, 0.042 mmol) in toluene (1 mL) was added tert-butyl isocyanide (3.3 mg, 0.040 mmol) at rt. The mixture was stirred for 0.5 h at rt, and the volatiles were removed in vacuo. The residue was dissolved in hexane and filtered. The filtrate was concentrated and cooled at −20 °C to give the title compound as yellow block crystals (11.5 mg, 45%). 1H NMR (C6D6, Me4Si, 500 MHz): δ 1.00 (s, 9H), 1.44 (s, 18H), 1.57 (s, 18H), 5.60 (s, 10H). 13C{1H} NMR (C6D6, Me4Si, 125.8 MHz): δ 30.26 (CNC(CH3)3), 34.10, 34.12, 35.95 (q), 36.61 (q), 56.70 (CNCMe3), 97.55 (q), 98.36 (q), 102.81 (Cp), 109.62 (q), 112.05 (q), 189.36 (CN), 196.13 (q), 198.05 (q). IR (ATR, neat): 2946, 2861, 2175, 1891, 1476, 1355, 1208, 1177, 1011, 787 cm−1. Anal. Calcd for C37H55NZr: C 73.45, H 9.16, N 2.31. Found: C 73.20, H 9.34, N 2.14. Formation of 16 from 14b. Complex 14b (16.5 mg, 0.0316 mmol) was dissolved in benzene-d6 (0.6 mL), and tert-butyl isocyanide (5.4 mg, 0.065 mmol) was added at rt. Formation of 16 and 17 was monitored by 1H NMR spectroscopy using toluene as internal standard (see the text). X-ray Diffraction Analyses of 14b. Crystals were obtained by slow evaporation of solvent from a hexane solution. A yellow block crystal (0.15 × 0.10 × 0.05 mm) was mounted in a loop and coated with paraffin. All data were collected on a Rigaku Saturn 70 CCD area detector with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) at 90 K. The structure was solved by direct methods28 and expanded using Fourier techniques.29 The non-hydrogen atoms were refined anisotropically. Some hydrogen atoms were refined isotropically, and the rest were refined using the riding model. The final cycle 5228

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X-ray Diffraction Study of 16. The molecular structure of 16 was confirmed by X-ray diffraction study, although the refinement was unsatisfactory. A colorless crystal having approximate dimensions of 0.10 × 0.02 × 0.02 mm was mounted on MicroMounts (MiTegen) and fixed with epoxy resin. Data were collected on a Rigaku RAXIS V imaging plate area detector with Si(111) monochromated radiation (λ = 0.800 Å) at 90 K at SPring-8 (BL26B1). The structure was solved by direct methods.36 The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined using the riding model. The asymmetric units consist of two crystallographically independent molecules of 16, which have almost the same structure. The final cycle of full-matrix least-squares refinement on F2 was based on 10 538 observed reflections and 866 variable parameters. All calculations were performed using the CrystalStructure30a,34 crystallographic software package. Final R values were not satisfactory probably because one of the molecules has a disordered structure in its tert-butyl groups. Crystallographic data are summarized in the Supporting Information, and the CIF data were deposited in the Cambridge Structural Database (CCDC-699033). X-ray Diffraction Study of 17. A yellow block crystal having approximate dimensions of 0.51 × 0.14 × 0.15 mm was mounted on MicroMounts (MiTegen) and coated with liquid paraffin. Data were collected on a Rigaku Saturn 70 CCD area detector with graphitemonochromated Mo Kα radiation at 90 K. The structure was solved by direct methods28 and expanded using Fourier techniques.29 The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined isotropically. The final cycle of full-matrix least-squares refinement on F2 was based on 10 240 observed reflections and 573 variable parameters. All calculations were performed using the CrystalStructure30a,34 crystallographic software package. Crystallographic data are described in the Supporting Information, and the CIF data were deposited in the Cambridge Structural Database (CCDC-699034).

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COMPUTATIONAL METHODS

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ASSOCIATED CONTENT

REFERENCES

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All molecular structures were fully optimized using the density functional theory (DFT) at the Becke and Lee, Yang, and Parr (B3LYP) level of theory.37 Dunning’s D9538 basis set was used for C, H, and P, and the zirconium atom was treated with the Stuttgart/ Dresden effective core potential (SDD).39 Energy minima were verified by vibrational frequency analysis. All these ab initio calculations were performed with use of the electronic structure program Gaussian 09.37c Using 8 CPU-cores of Intel Xeon E5-2680 and 8 GB ram (CONCURRENT SYSTEM, TS3DR-E5 model) at Sophia University, it took about two week to obtain all results.

S Supporting Information *

1

H and 13C NMR spectra of 13−17, details on X-ray diffraction studies on 13e, 14b, 14d, 14e, 15b, 15e, 16, and 17. This material is available free of charge via the Internet at http:// pubs.acs.org.

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Article

AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financially support from a Grant-in-Aid for Scientific Research (B, 22350022; C, 26410058), Japan Interaction in Science & Technology Forum, and Asahi Glass Foundation is gratefully acknowledged. The authors thank Ms. K. Yamada (RIKEN CEMS) and Ms. S. Machishima (Sophia Univ.) for assistance with elemental analysis. The authors are grateful to Ms. E. Okano and Ms. Y. Shimizu for assistance with NMR analyses and mass spectrometry, respectively. 5229

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Organometallics

Article

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