Experimental and Computational Studies on an Actinide

Article pubs.acs.org/Organometallics

Experimental and Computational Studies on an Actinide Metallacyclocumulene Complex Bo Fang,†,§ Lei Zhang,†,§ Guohua Hou,† Guofu Zi,*,† De-Cai Fang,*,† and Marc D. Walter*,‡ †

Department of Chemistry, Beijing Normal University, Beijing 100875, China Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany

‡

S Supporting Information *

ABSTRACT: Reduction of (η5-C5Me5)2ThCl2 (1) with potassium graphite (KC8) in the presence of 1,4-diphenylbutadiyne (PhCCCCPh) yields the first actinide metallacyclocumulene, the thorium metallacyclopentatriene (η5C5Me5)2Th(η4-C4Ph2) (2). The structure and reactivity of 2 were investigated in detail; structural parameters and density functional theory (DFT) studies confirm the presence of a metallacyclopentatriene unit in 2. Furthermore, DFT computations also indicate a notable contribution of the 5f orbitals to the bonding of the metallacyclopentatriene Th−(η4-CCCC) moiety. While complex 2 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as isothiocyanates, carbodiimides, aldehydes, ketones, nitriles, pyridines, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, in comparison to group 4 metals, the thorium metallacyclopentatriene 2 exhibits distinctively different reactivity patterns.

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INTRODUCTION Metallacycles have rapidly developed from laboratory curiosities to important organometallic complexes with unusual reactivity, which can play an important role in catalytic processes. This also initiated interest in metallacyclopropenes, metallacyclopentadienes, and metallacyclopentatrienes (metallacyclocumulenes) of group 4 metallocenes,1,2 which can serve as precursors for main-group heterocycles or functionalized organic molecules.1−3 In general, these metallacycles are accessible from the reduction of Cp′2MCl2 in the presence of an alkyne or by the reaction of Cp′2M (Cp′ = substituted or unsubstituted η5-cyclopentadienyl) with alkynes.1,2 Nevertheless, while group 4 chemistry has flourished, the corresponding metallacyclic complexes of the actinide elements have remained largely neglected and therefore unexplored.4 This is surprising, given the recent renaissance of organoactinide chemistry and the potential in small-molecule activation.5 Within the actinide series thorium has a unique position with its 7s26d2 electronic ground state, which relates it to the group 4 elements. However, recent investigations demonstrated that 6d and 5f orbitals contribute to the bonding in organothorium complexes and therefore different reactivity patterns emerge.6 In the course of our investigations we have recently prepared the thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2)7 and the thorium metallacyclopentadiene (η5-C5Me5)2Th(η2-C4Ph4)8 and studied their reactivity with various unsaturated molecules such as aldehydes, ketones, CS2, carbodiimides, nitriles, isothiocyanates, organic azides, and diazoalkane derivatives.7,8 We are now extending © 2015 American Chemical Society

these investigations to the so far unknown actinide metallacyclocumulenes. Herein, the synthesis, electronic structure, and structure−reactivity relationship of the first actinide metallacyclocumulene, thorium metallacyclopentatriene (η5C5Me5)2Th(η4-C4Ph2) (2), is reported and the differences between the metallacyclopentatrienes of thorium and group 4 metals are pointed out.

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RESULTS AND DISCUSSION Synthesis of (η5-C5Me5)2Th(η4-C4Ph2) (2). Treatment of a 1:1 mixture of (η5-C5Me5)2ThCl2 (1) and 1,4-diphenylbutadiyne (PhCCCCPh) with an excess of KC8 in toluene solution gives orange crystals of the metallacyclopentatriene (η5-C5Me5)2Th(η4-C4Ph2) (2) in 80% yield (Scheme 1). In Scheme 1

Received: November 6, 2015 Published: November 19, 2015 5669

DOI: 10.1021/acs.organomet.5b00923 Organometallics 2015, 34, 5669−5681

Article

Organometallics contrast to the group 4 (η5-C5Me5)2M (M = Ti, Zr, Hf) fragment, 2k−q,9 no thorium metallacyclopropene (η 5 C5Me5)2Th(η2-1,2-PhC2CCPh) was isolated, which may be attributed to the larger ionic size of the Th4+ ion.10 While 2 is air and moisture sensitive, it can be stored without degradation under a dry nitrogen atmosphere. Complex 2 is soluble in and readily recrystallized from an n-hexane solution, and it was fully characterized by various spectroscopic techniques, elemental analysis, and single-crystal X-ray diffraction. The 1H NMR resonances with chemical shifts in the 0−10 ppm region are narrow and show well-resolved coupling patterns that are consistent with a diamagnetic molecule. Furthermore, the 13C NMR spectrum features a resonance at δ 205.6 ppm, corresponding to the coordinated [η 4-C(Ph)CC C(Ph)] fragment. Next the lability of the butatriene moiety was probed on the chemical and NMR time scale. In contrast to group 4 metallacyclopentatrienes,2k−q,9 variable-temperature (20−100 °C) 1H NMR investigations reveal neither dissociation nor isomerization of 2 to a three-membered η2metallacyclopropene. Furthermore, DFT computations show that the isomerization of η4-metallacyclopentatriene 2 to the isomeric three-membered η2-metallacyclopropene P2 is energetically unfavorable (Figure 1) and is therefore not observed

Figure 2. Molecular structure of 2 (thermal ellipsoids drawn at the 35% probability level).

angle C(27)−Th(1)−C(30) of 90.0(3)° is significantly larger than those in the thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) (32.6(1)°)7 and the thorium metallacyclopentadiene (η5-C5Me5)2Th(η2-C4Ph4) (74.1(1)°).8 The Th−C distances to the central carbon atoms C(28) and C(29) of 2.544(8) and 2.540(8) Å, respectively, are essentially identical with those for Th−C(27) (2.530(8) Å) and Th− C(30) (2.542(9) Å). For comparison, the corresponding Th−C distances in the metallacyclopentadiene (η5-C5Me5)2Th(η2C4Ph4) (2.465(2) Å)8 and the metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) (2.395(2) Å)7 are significantly shorter, but they can be compared to Th−C(sp2) σ-bond distances (2.420(3)−2.654(14) Å).11 The angles of 130.7(8)° for C(26)−C(27)−C(28) and 130.5(8)° for C(29)−C(30)− C(31) differ from 180° and approach a value of 120°, which is typical for sp2-hybridized carbon atoms. Nevertheless, the cumulene remains highly strained and the bond angles C(27)− C(28)−C(29) of 148.7(9)° and C(28)−C(29)−C(30) of 150.4(9)° differ markedly from 180°. These structural parameters are consistent with a thorium metallacyclopentatriene, and distinct reactivity can be expected in comparison to that of the metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2)7 and metallacyclopentadiene (η5-C5Me5)2Th(η2C4Ph4).8 Bonding Studies. To better understand the interaction between the thorium atom and the PhCCCCPh moiety, a computational study has been carried out at the DFT level of theory (B3PW91). DFT studies suggest that the PhCCCCPh fragment is coordinated to the (η5C5Me5)2Th moiety by two Th−C σ bonds and one in-plane π bond in an η4-σ,σ,π2 fashion, as illustrated in Figure 3. In addition, the optimized structure agrees well with the experimentally determined geometry of 2: e.g., for the Th− (η4-CCCC) moiety the calculated values are 2.538, 2.527, 2.527, and 2.538 Å for Th−C distances, 1.323, 1.310, and 1.323 Å for CC distances, and 90.6° for the largest C− Th−C angle, which compare well with the experimental values of 2.530(8), 2.544(8), 2.540(8), and 2.542(9) Å for Th−C, 1.321(11), 1.341(11), and 1.284(10) Å for CC, and 90.0(3)° for the C−Th−C angle. A natural bond orbital (NBO) analysis

Figure 1. Free energy profile (kcal/mol) for the isomerization of 2 and the reaction of 2 + PhNCS. [Th] = (η5-C5Me5)2Th.

experimentally. In addition, the exchange of the coordinated 1,4-diphenylbutadiyne by PhCCPh, MeCCMe, PhC CMe, or (p-tolyl)CC(p-tolyl) was investigated at elevated temperatures, but no exchange or insertion occurred for complex 2, in contrast to the more covalent group 4 metallacyclopentatrienes.2k−q,9 The molecular structure of 2 is shown in Figure 2, and selected bond distances and angles are given in Table 1. To the best of our knowledge, complex 2 represents the first structurally characterized actinide metallacyclocumulene. The C−C distances for C(27)−C(28), C(28)−C(29), and C(29)− C(30) are 1.321(11), 1.341(11), and 1.284(10) Å, respectively, and they agree with a delocalized cumulene fragment. The 5670


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Organometallics Table 1. Selected Distances (Å) and Angles (deg) for Compounds 2, 3, 5−7, and 10−12a compound

C(Cp)−Thb

C(Cp)−Thc

Cp(cent)−Thb

Th−X

Cp(cent)−Th−Cp(cent)

2

2.802(10)

2.759(9)−2.837(10)

2.532(9)

137.8(3)

90.0(3)d

3

2.798(15)

2.767(14)−2.844(15)

2.527(15)

134.5(4)

117.8(4)e

5 6 7 10

2.819(4) 2.827(6) 2.847(4) 2.823(5)

2.793(4)−2.843(4) 2.779(6)−2.880(6) 2.832(4)−2.868(4) 2.762(5)−2.875(4)

2.548(4) 2.560(6) 2.581(4) 2.553(5)

137.9(1) 129.6(2) 127.1(1) 144.6(1)

70.2(1) 105.8(2) 110.6(1) 98.8(1),f 32.9(1)g

11

2.820(4)

2.792(4)−2.848(4)

2.549(4)

132.8(1)

118.3(1)h

12

2.820(17)

2.764(16)−2.856(15)

2.549(16)

C(27) 2.530(8), C(28) 2.544(8) C(29) 2.540(8), C(30) 2.542(9) C(23) 2.743(14), C(24) 2.681(14) C(25) 2.618(15), S(1) 2.834(4) C(29) 2.508(4), N(1) 2.338(3) O(1) 2.157(4), O(2) 2.150(4) O(1) 2.172(3), O(2) 2.168(3) C(27) 2.589(4), O 2.302(3) N 2.483(4) C(21) 2.747(5), C(22) 2.625(4) C(23) 2.674(4), N(1) 2.499(3) N(1) 2.280(14), N(2) 2.269(12)

139.4(5)

105.2(5)

X−Th−X/Y

a

Cp = cyclopentadienyl ring. bAverage value. cRange. dThe angle C(27)−Th(1)−C(30). eThe angle S(1)−Th(1)−C(25). fThe angle C(27)− Th(1)−N. gThe angle O−Th−N. hThe angle C(21)−Th−N.

thorium metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2C 2Ph2) 7 and metallacyclopentadiene (η 5-C5 Me5) 2 Th(η2 C4Ph4).8 Tables 2 and 3 give the products for the thorium metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2) and metallacyclopentadiene (η5-C5Me5)2Th(η2-C4Ph4), respectively. In contrast to the thorium metallacyclopentadiene (η5C5Me5)2Th(η2-C4Ph4) (Table 3),13 complex 2 reacts readily with heterounsaturated organic substrates and behaves in this respect similarly to the thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) (Table 2).7 For example, insertion of 1 equiv of PhNCS into the thorium metallacyclopentatriene moiety of 2 yields the seven-membered heterocyclic complex (η5-C5Me5)2Th[SC(NPh)(C4Ph2)] (3) in quantitative conversion (Scheme 2). DFT computations reveal that the reaction of 2 with PhNCS to 3 is exergonic with ΔG = −35.4 kcal/mol and proceeds via transition state TS3 (Figure 1), in which the two forming bond distances of Th−S and C−C are 3.105 and 2.314 Å, respectively, which are ca. 0.28 and 0.83 Å longer than those in product 3. The barrier for this reaction was computed to be ΔG⧧(298 K) = 21.4 kcal/mol (30.4 kcal/mol in the gas phase), which can readily be overcome at the reaction temperature of 110 °C. Nevertheless, treatment of 2 with N,N′-diisopropylcarbodiimide under similar reaction conditions also yields a sevenmembered metallaheterocycle, (η5-C5Me5)2Th[N(CHMe2)C(NCHMe2)(C4Ph2)] (4) (Scheme 2), which can be observed spectroscopically (see the Experimental Section for details). However, under the reaction conditions 4 is unstable and converts by a [1,3]-Th migration to the five-membered metallaheterocycle (η 5 -C 5 Me 5 ) 2 Th[N(CHMe 2 )C( NCHMe2)C(Ph)C(CCPh)] (5) (Scheme 2). However, when complex 2 is exposed to p-ClPhCHO, the ninemembered metallaheterocycle (η5-C5Me5)2Th[OCH(p-ClPh)(C4Ph2)CH(p-ClPh)O] (6) (Scheme 2) is isolated irrespective of the amount of aldehyde (p-ClPhCHO) added. Presumably complex 2 converts initially with p-ClPhCHO to a sevenmembered metallaheterocycle followed by the insertion of another 1 equiv of p-ClPhCHO to give complex 6. Nevertheless, in contrast to the thorium metallacyclopropene [η51,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2),7 no pinacolate complex is formed on treatment of 2 with Ph2CO; instead, double insertion occurs to yield (η5-C5Me5)2Th[OCPh2(C4Ph2)CPh2O] (7) independent of the quantity of Ph2CO added (Scheme 2). Double insertion also occurs when 2 is exposed to PhCN to give the nine-membered heterocyclic complex (η5-

Figure 3. Plots of MOs for 2. The hydrogen atoms have been omitted for clarity.

reveals that two polarized Th−C σ bonds, σ(Th−C), are formed by a carbon sp2 hybrid orbital (84.6%; 31% s and 69% p) and a thorium hybrid orbital (15.4%; 16% 5f, 62% 6d, 8% 7p, and 14% 7s). This illustrates that 5f and 6d orbitals contribute notably to the bonding between the metallocene and C4Ph2 fragments. The other bonding interactions can be divided into two σ bonds, σ1(CC) and σ2(CC), and three π bonds, π1(CC), π2(CC), and π(CCCC). The σ1 bond is composed of a carbon sp2 hybrid orbital (48%; 30% s and 70% p) and a carbon sp hybrid orbital (52%; 53% s and 47% p), whereas the σ2 bond consists of pure sp hybrid orbitals (47% s and 53% p). In the in-plane π bond, π2(CC), pure carbon p orbitals (100% p) donate electron density to a vacant Th orbital. The two remaining π orbitals, π1(CC) and the delocalized π(CCCC), are also formed by pure p orbitals (100% p). However, in contrast to group 4 complexes,1k,12 there is no strong delocalization of the metallacyclopentatriene moiety. Reactivity Studies. We then investigated the intrinsic reactivity of 2 toward a set of unsaturated organic substrates and compared the reaction products to those obtained for the 5671


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Organometallics Table 3. Reactivity of (η5-C5Me5)2Th(η2-C4Ph4)8,13

Table 2. Reactivity of [η5-1,2,4-(Me3C)3C5H2]2Th(η2C2Ph2)7,14

Scheme 2

C5Me5)2Th[NC(Ph)(C4Ph2)C(Ph)N] (8) (Scheme 2), again independent of the amount of PhCN used in the reaction. The thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) reacts with pyridine N-oxide by deprotonation of an α-C−H position to yield a thorium pyridyl alkenyl complex (Table 2),14 whereas a very different product is isolated from the reaction of 2. Here the O,N-oximato complex (η5-C5Me5)2Th[η2-O,N-σ-C-ONCH(CHCH)2C(Ph) C(CCPh)] (10) is formed (Scheme 3). A plausible reaction pathway to account for the formation of complex 10 includes a metallacyclopropene adduct, followed by nucleophilic attack of the coordinated pyridine N-oxide to give an eight-membered heterocyclic complex, (η5-C5Me5)2Th[κ2-{(2-C4H4NO)CHC(Ph)CCCPh}] (9), which can be observed spectroscopically (see the Experimental Section for details). However, complex 9 is unstable and converts by a [1,3]-Th migration and

C−N bond cleavage to product 10. DFT computations support this mechanistic proposal: Intermediate COM9 forms via the transition state TS9a, when pyridine N-oxide initially coordinates to 2 (Figure 4). In the next step pyridine Noxide inserts into the Th-(C4Ph2) moiety of COM9 via the transition state TS9b to yield the eight-membered metallaheterocycle 9. The formation of 9 from 2 + pyO is 5672


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Organometallics

mol. However, the final product 10 is more thermodynamically preferred (ΔG(298 K) = −6.0 kcal/mol) than 9 (ΔG(298 K) = −2.8 kcal/mol) (Figure 4), and the barrier for the formation of 10 from 9 is ΔG⧧(298 K) = 21.4 kcal/mol, which can be overcome at ambient temperature and is in accordance with the experimental observations. Unlike the thorium metallacyclopropene [η 5 -1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) (Table 2),14 complex 2 reacts with 4-(dimethylamino)pyridine (DMAP) to give the sevenmembered heterocyclic complex (η5-C5Me5)2Th[η6-{2-(4Me2NC4H3N)C−C(Ph)CCCHPh}] (11) (Scheme 4).

Scheme 3

Scheme 4

Similar to the pyridine N-oxide reaction, the following reaction pathway can be proposed: on coordination of DMAP complex 2 isomerizes to a DMAP metallacyclopropene adduct and after nucleophilic attack of the CN bond of the coordinated DMAP a seven-membered heterocyclic complex is formed, which then converts by a [1,5]-hydrogen migration to complex 11 (Scheme 4). In contrast to the thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2) and metallacyclopentadiene (η5C5Me5)2Th(η2-C4Ph4) complexes (Tables 2 and 3),7,8 no insertion or isomerization products are isolated from the reaction of 2 with 9-diazofluorene. In this case the diiminato complex (η5-C5Me5)2Th[NC(C12H8)]2 (12) is unexpectedly formed, irrespective of the amount of 9-diazofluorene added (Scheme 5). This reactivity has some resemblance to that observed for the thorium bipy complex [η 5 -1,2,4(Me3C)3C5H2]2Th(bipy) toward 9-diazofluorene.15 The 9diazofluorene reacts initially with 2 to displace 1,4-diphenylbutadiyne and to form the hydrazido complex (η5-C5Me5)2Th NNC(C12H8), but unlike the sterically more congested hydrazido complex [η5-1,2,4-(Me3C)3C5H2]2ThNNC(C12H8),15 the Cp* derivative is less sterically crowded and therefore more reactive. It immediately converts with a second molecule of 9-diazofluorene in a [2 + 2] cycloaddition reaction, followed by NN bond cleavage (N transfer) and N2 release to give the diiminato complex 12 (Scheme 5). A similar [2 + 2] cycloaddition was previously observed in the reaction of the imido complex [η5-1,2,4-(Me3C)3C5H2]2ThN(p-tolyl) with

Figure 4. Free energy profile (kcal/mol) for the reaction of 2 + pyO. [Th] = (η5-C5Me5)2Th.

energetically favorable (ΔG(298 K) = −2.8 kcal/mol) and proceeds with a reaction barrier of ΔG⧧(298 K) = 19.3 kcal/ 5673


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Organometallics

INT12c to form 12 is more thermodynamically preferred (ΔG(298 K) = −77.7 kcal/mol) and the conversion from INT12c proceeds via transition state TS12d with a low barrier (ΔG⧧(298 K) = 17.5 kcal/mol). However, in contrast to the thorium metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2C2Ph2)7 and the metallacyclopentadiene (η5-C5Me5)2Th(η2C4Ph4),8 there is no reaction of 2 with the sterically more encumbered organic azide Me 3 SiN 3 or diazoalkane Me3SiCHN2 even on heating at 100 °C for 1 week. In addition, only unreacted starting materials are observed when 2 is heated in the presence of alkyne RCCR (R = Me, Ph, ptolyl) at 100 °C for 1 week, which probably originates from the steric hindrance between the reaction partners. Complexes 3, 5−8, and 10−12 are stable under a dry nitrogen atmosphere, but they are moisture sensitive. They were characterized by various spectroscopic techniques and elemental analyses. In addition, the solid-state structures of 3, 5−7, and 10−12 were determined by single crystal X-ray diffraction analyses. The solid-state molecular structure of (η5C5Me5)2Th[SC(NPh)(C4Ph2)] (3) is shown in Figure 6.

Scheme 5

9-diazofluorene,16 which is followed by NN bond cleavage (N transfer) to yield a diazenido iminato complex. DFT investigations suggest that 2 initially reacts with 9-diazofluorene to give the intermediate INT12a, which proceeds via the transition state TS12a with a reaction barrier of ΔG⧧(298 K) = 24.8 kcal/mol (Figure 5). In the next step 1,4-diphenylbuta-

Figure 6. Molecular structure of 3. Thermal ellipsoids are drawn at the 35% probability level.

The average Th−C(Cp) distance is 2.798(15) Å, and the angle Cp(cent)−Th−Cp(cent) is 134.5(4)°. The C−C distances C(22)−C(23), C(23)−C(24), and C(24)−C(25) within the butatriene are 1.347(19), 1.300(20), and 1.304(19) Å, respectively, which can be compared to those in 2 (1.321(11), 1.341(11) and 1.284(10) Å). The Th−C distances of 2.743(14) Å for C(23), 2.681(14) Å for C(24), and 2.618(15) Å for C(25) are longer than those found in 2 (2.530(8), 2.544(8), 2.540(8), and 2.542(9) Å). The Th−S distance of 2.834(4) Å can be compared to those found in [η51,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)C(S)S] (2.704(2) Å),17 [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)C(NPh)S] (2.709(1) Å),17 [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)C(SSiMe3)S](Cl) (2.890(3) Å),17 [(Ph2PS)2C]2Th(DME) (2.875(2), 2.909(2), 2.931(2) and 3.007(2) Å),6d [η5-1,2,4-(Me3C)3C5H2]2Th[(bipy)(SCPh2)] (2.754(1) Å),18 and [η5-1,3(Me3C)2C5H3]2Th[(bipy)(SCPh2)] (2.759(4) Å).18 The molecular structure of (η5-C5Me5)2Th[N(CHMe2)C( NCHMe2)C(Ph)C(CCPh)] (5) is shown in Figure 7. The Th4+ ion is η5 bound to two Cp rings and σ coordinated to

Figure 5. Free energy profile (kcal/mol) for the reaction of 2 + N2C(C12H8) + N2C(C12H8). [Th] = (η5-C5Me5)2Th and R = C12H8.

diyne dissociates from INT12a to yield the hydrazido complex INT12b via the transition state TS12b with a low barrier (ΔG⧧(298 K) = 11.2 kcal/mol). Subsequently, the hydrazido complex INT12b reacts with a second molecule of 9diazofluorene in a concerted [2 + 2] cycloaddition to INT12c. Furthermore, the formation of INT12c is energetically favorable (ΔG(298 K) = −4.4 kcal/mol) with a reaction barrier of ΔG⧧(298 K) = 20.6 kcal/mol. However, N2 loss from 5674


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Organometallics



two Cp ring and σ coordinated to two oxygen atoms of the dianions [OCH(p-ClPh)(C4Ph2)CH(p-ClPh)O]2− (for 6) and [OCPh2(C4Ph2)CPh2O]2− (for 7) in a distorted-tetrahedral geometry with average Th−C(Cp) distances of 2.827(6) and 2.847(4) Å for 6 and 7, respectively. The Cp(cent)−Th− Cp(cent) angles in 6 and 7 are 129.6(2) and 127.1(1)°, respectively, and the O−Th−O angles in 6 and 7 are 105.8(2) and 110.6(1)°, respectively. The C−C distances within the butatriene are 1.316(8), 1.271(8), and 1.313(8) Å for 6 and 1.324(5), 1.254(5), and 1.344(5) Å for 7, which are in the same range as those observed in complexes 2 and 3. The average Th−O distances are 2.154(4) Å for 6 and 2.170(3) Å for 7, which are slightly shorter than those found in [η5-1,2,4(Me 3 C) 3 C 5 H 2 ] 2 Th[O 2 CPh 2 ] (2.202(3) Å), 17 [η 5 -1,2,4(Me3C)3C5H2]2Th[(OCPh2)2] (2.182(2) Å),7 and [η5-1,2,4(Me 3 C) 3 C 5 H 2 ] 2 Th[N(p-tolyl)CH 2 C(Me)C(OMe)O] (2.197(9) Å).19 Figure 10 represents the molecular structure of (η5C 5 Me 5 ) 2 Th[η 2 -O,N-σ-C-ONCH(CHCH) 2 C(Ph) C(CCPh)] (10). The average Th−C(Cp) distance is 2.823(5) Å, and the angle Cp(cent)−Th−Cp(cent) is 144.6(1)°. The Th−C(27) distance of 2.589(4) Å is in the range of previously reported Th−C(sp2) σ bonds (2.420(3)− 2.654(14) Å).11 The C(28)−C(29) distance is 1.200(6) Å, consistent with a typical CC bond. The O−N distance of 1.364(5) Å, Th−O distance of 2.302(3) Å, Th−N distance of 2.483(4) Å, and N−Th−O angle of 32.9(1)° can be compared to the values found in (η5-C5Me5)2Th[η2-O,N-ONCH(CHCH)2Ph]2 with O−N distances of 1.372(5) and 1.365(5) Å, Th−O distances of 2.332(3) and 2.334(4) Å, Th−N distances of 2.577(4) and 2.519(5) Å, and N−Th−O angles of 31.98(12) and 32.39(12)°.20 The solid-state molecular structure of (η5-C5Me5)2Th[η6-{2(4-Me2NC4H3N)CC(Ph)CCCHPh}] (11) is shown in Figure 11. The C−C distances of 1.415(6) Å for C(21)− C(22), 1.227(6) Å for C(22)−C(23), 1.409(6) Å for C(23)− C(24), and 1.402(6) Å for C(24)−C(37) and the C(37)−N distance of 1.404(5) Å are consistent with a delocalization of the negative charge within the {2-(4-Me2NC4H3N)CC(Ph)CCCHPh} fragment. This, in addition to the larger chelate

one carbon atom and one nitrogen atom of the [N(CHMe2)C(NCHMe2)C(Ph)C(CCPh)] group with an average Th−C(ring) distance of 2.819(4) Å. The C(30)−C(31) distance of 1.215(6) Å is in the typical range of a CC bond. The Th−N (2.338(3) Å) and Th−C(29) distances (2.508(4) Å) are comparable to those found in [η5-1,2,4(Me 3C)3C5H2]2Th[N(C6H11)C(NC 6H11)(C 2Ph2)] with Th−N and Th−C distances of 2.309(6) and 2.530(8) Å, respectively.7 The molecular structures of (η5-C5Me5)2Th[OCH(p-ClPh)(C 4 Ph 2 ) C H ( p-C lPh)O] (6 ) an d ( η 5 -C 5 Me 5 ) 2 Th[OCPh2(C4Ph2)CPh2O] (7) are illustrated in Figures 8 and 9, respectively. In both complexes, the Th4+ ion is η5 bound to

Figure 8. Molecular structure of 6. Thermal ellipsoids are drawn at the 35% probability level. 5675


Article

Organometallics

Figure 12. Molecular structure of 12. Thermal ellipsoids are drawn at the 35% probability level. Figure 10. Molecular structure of 10. Thermal ellipsoids are drawn at the 35% probability level.

Cp rings and σ coordinated to two nitrogen atoms of the two iminato groups (NC(C12H8)) in a distorted-tetrahedral geometry with an average Th−C(Cp) distance of 2.820(17) Å, a Cp(cent)−Th−Cp(cent) angle of 139.4(5)°, and a N− Th−N angle of 105.2(5)°. The short Th−N distances (2.280(14) Å for N(1) and 2.269(12) Å for N(2)) and the angles Th−N(1)−C(21) (172.1(12)°) and Th−N(2)−C(34) (174.7(15)°) suggest some nitrogen π donation to the thorium atom.21 These structural parameters may be compared to those found in [η5-1,2,4-(Me3C)3C5H2]2Th[η2-NN(p-tolyl)][N C(C12H8)] with a Th−N distance of 2.275(2) Å and Th−N−C angle of 161.6(2)°16 and those in imidazolin-2-iminato thorium complexes with Th−N distances of 2.176(8)−2.235(9) Å and Th−N−C angles of 166.9(8)−173.7(4)°.24

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CONCLUSIONS In conclusion, with the thorium metallacyclopentatriene (η5C5Me5)2Th(η4-C4Ph2) (2), the first actinide metallacumulene was comprehensively studied. In analogy to the thorium metallacyclopropene7 and metallacyclopentadiene complexes,8 density functional theory (DFT) reveals that in addition to the 6d orbitals also the 5f orbitals contribute to the polarized Th− C σ bond of the Th−(η4-CCCC) fragment. As a consequence, while the coordinated butatrienes in the more covalent group 4 metallacyclopentatrienes are readily isomerized or exchanged with alkynes,2k−q,9 this is not observed for the thorium complex 2, in which the [η4-PhCCC CPh]2− moiety is prone to react as a nucleophile. However, the steric strain in the metallacycles also significantly modulates the reactivity, as illustrated by the products formed with heterounsaturated molecules. In contrast to the thorium metallacyclopentadiene (η5-C5Me5)2Th(η2-C4Ph4),13 but similar to the metallacyclopropene [η5-1,2,4-(Me3C)3C5H2]2Th(η2-C2Ph2),7 the thorium metallacyclopentatriene 2 shows single or double insertions of isothiocyanates, carbodiimides, aldehydes, and nitriles into the Th(η4-C4Ph2) moiety. However, in contrast to the thorium metallacyclopropene [η5-1,2,4(Me3C)3C5H2]2Th(η2-C2Ph2),7,14 Ph2CO also doubly inserts into the metallacyclopentatriene; exposure of 2 to pyridine derivatives such as pyridine N-oxide and DMAP results in a CN bond insertion into the Th−(C4Ph2) moiety. From there on the reaction pathways for the two substrates diverge: for pyridine N-oxide a [1,3]-Th migration and a C−N bond


size, also contributes to a Th−N distance of 2.499(3) Å, which is significantly longer than those found in [η 5 -1,2,4(Me3C)3C5H2]2Th(NHp-tolyl)2 (2.279(3) and 2.286(3) Å),21 [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)C(S)S] (2.347(6) Å),17 [η5-1,2,4-(Me3C)3C5H2]2Th[N(p-tolyl)C(NPh)S] (2.328(3) Å), 17 [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Th[N(p-tolyl)NNN(ptolyl)] (2.366(3) and 2.354(3) Å), 1 6 [η 5 -1,2,4(Me3C)3C5H2]2Th(bipy) (2.325(5) and 2.363(4) Å),15 and [η5-1,3-(Me3C)2C5H3]2Th(bipy) (2.326(7) and 2.325(7) Å).22 In addition, the Th−C distances of 2.747(5) Å for C(21), 2.625(4) Å for C(22), and 2.674(4) Å for C(23) are elongated and may be compared to those found in [η 5 -1,2,4(Me 3 C) 3 C 5 H 2 ] 2 ThMe 2 (2.480(3) Å) 21 and [η 5 -1,2,4(Me3C)3C5H2]2Th(CH2Ph)2 (2.521(3) and 2.527(3) Å),23 while they are close to those in 3 (2.743(14), 2.681(14), and 2.618(15) Å). The molecular structure of (η5-C5Me5)2Th[NC(C12H8)]2 (12) is shown in Figure 12. The Th4+ ion is η5 bound to two 5676


Article

Organometallics cleavage occur to form the thorium oximate (η5-C5Me5)2Th[η2O,N-σ-C-ONCH(CHCH)2C(Ph)C(CCPh)] (10), whereas for DMAP a [1,5]-hydrogen migration can occur to yield the amido complex (η 5 -C 5 Me 5 ) 2 Th[η 6 -{2-(4Me2NC4H3N)CC(Ph)CCCHPh}] (11). Furthermore, in contrast to the thorium metallacyclopropene7 and the metallacyclopentadiene,8 compound 2 reacts with 9-diazofluorene by substitution of the PhCCCCPh moiety, but the hydrazido intermediate (η5-C5Me5)2ThNNC(C12H8) is too reactive to be isolated or even observed; it reacts with another 1 equiv of 9-diazofluorene in a [2 + 2] cycloaddition reaction, followed by NN bond cleavage (N transfer) and N2 loss to give the diiminato complex (η5-C5Me5)2Th[NC(C12H8)]2 (12). Further efforts in unraveling the intrinsic reactivity of actinide metallacycles are ongoing and will be reported in due course.

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(phenyl C), 128.5 (phenyl C), 128.2 (phenyl C), 127.9 (phenyl C), 125.1 (ring C), 123.4 (phenyl C), 121.2 (phenyl C), 11.7 (CH3) ppm. IR (KBr, cm−1): 3024 (m), 2904 (s), 2854 (s), 1591 (s), 1562 (s), 1483 (s), 1442 (s), 1377 (s), 1205 (s), 1072 (s), 1026 (s), 846 (s), 756 (s), 691 (s). Anal. Calcd for C43H45NSTh: C, 61.49; H, 5.40; N, 1.67. Found: C, 61.54; H, 5.38; N, 1.65. Method B: NMR Scale. A C6D6 (0.3 mL) solution of PhNCS (2.7 mg, 0.02 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances of 3 were observed by 1H NMR spectroscopy (100% conversion) after the sample was heated at 110 °C for 2 days. Preparation of (η 5-C5Me5 ) 2Th[N(CHMe2 )C(NCHMe 2)C(Ph)C(CCPh)] (5). Method A. This compound was prepared as yellow crystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and iPrNCNiPr (32 mg, 0.25 mmol) in toluene (15 mL) at 110 °C and recrystallization from an n-hexane solution by a procedure similar to that for the synthesis of 3. Yield: 154 mg (74%). Mp: 178−180 °C. 1H NMR (C6D6): δ 7.74 (d, J = 7.2 Hz, 2H, phenyl), 7.53 (m, 2H, phenyl), 7.30 (t, J = 7.8 Hz, 2H, phenyl), 7.13 (m, 2H, phenyl), 7.09 (m, 1H, phenyl), 7.01 (m, 1H, phenyl), 4.49 (m, 1H, NCH), 3.74 (m, 1H, NCH), 2.05 (s, 30H, CH3), 1.34 (d, J = 6.3 Hz, 6H, CH(CH3)2), 1.16 (d, J = 6.0 Hz, 6H, CH(CH3)2) ppm. 13 C{1H} NMR (C6D6): δ 198.9 (ThC), 159.4 (NC), 158.3 (CPh), 144.0 (phenyl C), 131.0 (phenyl C), 128.6 (phenyl C), 128.5 (phenyl C), 127.8 (phenyl C), 127.0 (phenyl C), 126.5 (phenyl C), 126.2 (ring C), 122.4 (phenyl C), 112.0 (CCPh), 95.2 (CCPh), 48.2 (NCH), 42.6 (NCH), 26.2 (CH(CH3)2), 19.2 (CH(CH3)2), 11.8 (ring CH3) ppm. IR (KBr, cm−1): 3055 (m), 2960 (s), 2906 (s), 2141 (s), 1633 (s), 1595 (s), 1564 (s), 1440 (s), 1382 (s), 1263 (s), 1201 (s), 1145 (s), 1018 (s), 970 (s), 806 (s), 754 (s). Anal. Calcd for C43H54N2Th: C, 62.15; H, 6.55; N, 3.37. Found: C, 62.21; H, 6.52; N, 3.35. Method B: NMR Scale. A C6D6 (0.3 mL) solution of iPrNC i N Pr (2.5 mg, 0.02 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The NMR sample was maintained at 110 °C and monitored periodically by 1H NMR spectroscopy. After 4 h, resonances due to 5 (ca. 20%) along with those of unreacted 2 and i PrNCNiPr and (η5-C5Me5)2Th[N(CHMe2)C(NCHMe2)(C4Ph2)] (4) (ca. 15%; 1H NMR (C6D6) δ 7.67 (d, J = 8.2 Hz, 2H, phenyl), 7.43 (m, 2H, phenyl), 7.34 (m, 2H, phenyl), 6.96 (m, 3H, phenyl), 6.88 (m, 1H, phenyl), 5.63 (m, 1H, NCH), 4.63 (m, 1H, NCH), 1.92 (s, 30H, CH3), 1.63 (d, J = 6.0 Hz, 6H, CH(CH3)2), 1.33 (d, J = 6.3 Hz, 6H, CH(CH3)2) ppm) were observed by 1H NMR spectroscopy (total 35% conversion based on 2). After 2 days, only resonances of 5 were observed by 1H NMR spectroscopy (100% conversion). Nevertheless, complex 4 could not be isolated in pure form on a synthetic scale, since partial degradation to 5 was always observed. Preparation of (η 5-C 5Me 5) 2 Th[OCH(p-ClPh)(C 4Ph 2)CH(pClPh)O]·C6H6 (6·C6H6). Method A. This compound was prepared as colorless crystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and p-ClPhCHO (70 mg, 0.50 mmol) in toluene (15 mL) at 80 °C and recrystallization from a benzene solution by a procedure similar to that in the synthesis of 3. Yield: 192 mg (72%). Mp: 272−274 °C dec. 1H NMR (C6D6): δ 7.53 (d, J = 7.6 Hz, 4H, phenyl), 7.25 (d, J = 8.3 Hz, 4H, phenyl), 7.15 (s, 6H, C6H6), 7.12 (d, J = 8.3 Hz, 4H, phenyl), 7.05 (t, J = 7.7 Hz, 4H, phenyl), 6.90 (t, J = 7.4 Hz, 2H, phenyl), 6.73 (s, 2H, OCH), 1.89 (s, 30H, CH3) ppm. 13 C{1H} NMR (C6D6): δ 157.2 (CC), 143.8 (CPh), 137.2 (phenyl C), 133.5 (phenyl C), 131.2 (phenyl C), 128.9 (phenyl C), 128.8 (phenyl C), 128.5 (phenyl C), 128.1 (phenyl C), 128.0 (C6H6), 126.2 (phenyl C), 123.9 (ring C), 83.6 (OCH), 11.1 (CH3) ppm. IR (KBr, cm−1): 2922 (s), 2853 (s), 1950 (w), 1591 (m), 1560 (m), 1487 (s), 1444 (s), 1382 (s), 1261 (s), 1234 (s), 1088 (s), 1070 (s), 954 (s), 804 (s). Anal. Calcd for C56H56Cl2O2Th: C, 63.21; H, 5.31. Found: C, 63.16; H, 5.37. Method B. NMR Scale. A C6D6 (0.3 mL) solution of p-ClPhCHO (5.6 mg, 0.04 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances of 6 were observed by 1H NMR

EXPERIMENTAL SECTION

General Procedures. All reactions and product manipulations were carried out under an atmosphere of dry dinitrogen with rigid exclusion of air and moisture using standard Schlenk or cannula techniques or in a glovebox. All organic solvents were freshly distilled from sodium benzophenone ketyl immediately prior to use. 1,4Diphenylbutadiyne was purified by sublimation prior to use. KC8,25 (η5-C5Me5)2ThCl2 (1),8 and 9-diazofluorene26 were prepared according to literature methods. All other chemicals were purchased from Aldrich Chemical Co. and Beijing Chemical Co. and used as received unless otherwise noted. Infrared spectra were recorded in KBr pellets on an Avatar 360 Fourier transform spectrometer. 1H and 13 C{1H} NMR spectra were recorded on a Bruker AV 400 spectrometer at 400 and 100 MHz, respectively. All chemical shifts are reported in δ units with reference to the residual protons of the deuterated solvents, which served as internal standards, for proton and carbon chemical shifts, but they also served as the internal standard in our NMR investigations. Melting points were measured on an X-6 melting point apparatus and were uncorrected. Elemental analyses were performed on a Vario EL elemental analyzer. Preparation of (η5-C5Me5)2Th(η4-C4Ph2) (2). KC8 (1.42 g, 10.5 mmol) was added to a toluene (20 mL) solution of (η5-C5Me5)2ThCl2 (1; 2.00 g, 3.5 mmol) and 1,4-diphenylbutadiyne (0.71 g, 3.5 mmol) with stirring at room temperature. After this solution was stirred for 1 day at room temperature, the solvent was removed. The residue was extracted with n-hexane (10 mL × 3) and the extract filtered. The volume of the filtrate was reduced to 10 mL; orange crystals of 2 were isolated when this solution was kept at room temperature for 1 week. Yield: 1.97 g (80%). Mp: 208−210 °C dec. 1H NMR (C6D6): δ 8.11 (d, J = 7.0 Hz, 4H, phenyl), 7.38 (t, J = 7.7 Hz, 4H, phenyl), 7.15 (m, 2H, phenyl), 1.83 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 205.6 (ThCPh), 149.2 (PhCC), 138.1 (phenyl C), 134.0 (phenyl C), 129.2 (phenyl C), 128.1 (phenyl C), 122.6 (ring C), 11.3 (CH3) ppm. IR (KBr, cm−1): 3024 (m), 2922 (s), 2857 (s), 1600 (m), 1490 (s), 1444 (s), 1381 (s), 1072 (s), 1028 (s), 783 (s). Anal. Calcd for C36H40Th: C, 61.35; H, 5.72. Found: C, 61.44; H, 5.68. Preparation of (η5-C5Me5)2Th[SC(NPh)(C4Ph2)] (3). Method A. A toluene solution (5 mL) of PhNCS (34 mg, 0.25 mmol) was added to a toluene (10 mL) solution of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) with stirring at room temperature. After the solution was stirred at 110 °C for 2 days, the solvent was removed. The residue was extracted with benzene (10 mL × 2) and the extract filtered. The volume of the filtrate was reduced to 3 mL; red crystals of 3 were isolated when this solution was kept at room temperature for 1 week. Yield: 164 mg (78%). Mp: 232−234 °C dec. 1H NMR (C6D6): δ 8.31 (d, J = 7.6 Hz, 2H, phenyl), 7.75 (d, J = 7.3 Hz, 2H, phenyl), 7.42 (m, 4H, phenyl), 7.28 (t, J = 7.7 Hz, 2H, phenyl), 7.22 (t, J = 7.6 Hz, 2H, phenyl), 7.09 (t, J = 7.3 Hz, 2H, phenyl), 7.02 (t, J = 7.1 Hz, 1H, phenyl), 1.88 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 194.3 (ThCPh), 186.5 (CN), 179.3 (ThC(Ph)C), 152.7 (ThC(Ph)C C), 139.3 (CPh), 137.6 (phenyl C), 135.0 (phenyl C), 134.7 (phenyl C), 130.6 (phenyl C), 129.5 (phenyl C), 129.2 (phenyl C), 128.8 5677


Article

Organometallics spectroscopy (100% conversion) after the sample was heated at 80 °C for 2 days. In this transformation, only one resonance due to PhCHO (δ 6.73 ppm) was observed: i.e., no other isomer was detected. Reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2) with p-ClPhCHO: NMR Scale. A C6D6 (0.3 mL) solution of p-ClPhCHO (2.8 mg, 0.02 mmol) was placed in a J. Young NMR tube charged with (η5C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 6 along with those of unreacted 2 were observed by 1H NMR spectroscopy (50% conversion based on 2) on heating at 80 °C for 2 days. Preparation of (η5-C5Me5)2Th[OCPh2(C4Ph2)CPh2O]·0.5C6H6 (7·0.5C6H6). Method A. This compound was prepared as colorless crystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and Ph2CO (91 mg, 0.50 mmol) in toluene (15 mL) at 85 °C and recrystallization from a benzene solution by a procedure similar to that in the synthesis of 3. Yield: 238 mg (86%). Mp: 296− 298 °C dec. 1H NMR (C6D6): δ 7.87 (m, 8H, phenyl), 7.57 (d, J = 7.5 Hz, 4H, phenyl), 7.21 (t, J = 7.4 Hz, 8H, phenyl), 7.15 (m, 7H, phenyl and C6H6), 6.94 (t, J = 7.6 Hz, 4H, phenyl), 6.86 (t, J = 7.3 Hz, 2H, phenyl), 1.89 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 159.3 (CC), 149.9 (CPh), 145.0 (phenyl C), 139.3 (phenyl C), 133.8 (phenyl C), 131.2 (phenyl C), 129.6 (ring C), 129.4 (phenyl C), 128.0 (C6H6), 127.6 (phenyl C), 125.5 (phenyl C), 124.7 (phenyl C), 94.5 (OC), 11.7 (CH3) ppm. IR (KBr, cm−1): 3057 (m), 2922 (s), 1952 (w), 1595 (m), 1487 (s), 1442 (s), 1382 (s), 1259 (s), 1209 (s), 1083 (s), 1051 (s), 964 (s), 779 (s). Anal. Calcd for C65H63O2Th: C, 70.45; H, 5.73. Found: C, 70.52; H, 5.65. Method B: NMR Scale. A C6D6 (0.3 mL) solution of Ph2CO (7.3 mg, 0.04 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances of 7 were observed by 1H NMR spectroscopy (100% conversion) after the sample was heated at 85 °C for 2 days. Reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2) with Ph2CO: NMR Scale. A C6D6 (0.3 mL) solution of Ph2CO (3.7 mg, 0.02 mmol) was placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 7 and unreacted 2 were observed by 1H NMR spectroscopy (50% conversion based on 2) on heating at 85 °C for 2 days. Preparation of (η5-C5Me5)2Th[NC(Ph)(C4Ph2)C(Ph)N] (8). Method A. This compound was prepared as red microcrystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and PhCN (52 mg, 0.50 mmol) in toluene (15 mL) at room temperature and recrystallization from a benzene solution by a procedure similar to that in the synthesis of 3. Yield: 191 mg (84%). Mp: 176−178 °C dec. 1 H NMR (C6D6): δ 7.63 (m, 8H, phenyl), 7.13 (m, 4H, phenyl), 7.07 (t, J = 7.4 Hz, 2H, phenyl), 6.98 (m, 4H, phenyl), 6.87 (t, J = 7.4 Hz, 2H, phenyl), 1.98 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 170.2 (NC), 161.9 (CPh), 143.5 (CC), 138.7 (phenyl C), 137.8 (phenyl C), 129.6 (phenyl C), 129.3 (phenyl C), 128.7 (phenyl C), 128.5 (phenyl C), 125.6 (phenyl C), 124.6 (phenyl C), 123.3 (ring C), 11.1 (CH3) ppm. IR (KBr, cm−1): 3055 (m), 2962 (s), 2906 (s), 1948 (w), 1611 (m), 1598 (s), 1489 (s), 1442 (s), 1382 (s), 1259 (s), 1072 (s), 1020 (s), 798 (s). Anal. Calcd for C50H50N2Th: C, 65.92; H, 5.53; N, 3.08. Found: C, 65.95; H, 5.50; N, 3.15. Method B. NMR Scale. A C6D6 (0.3 mL) solution of PhCN (4.2 mg, 0.04 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances of 8 were observed by 1H NMR spectroscopy (100% conversion in 10 min). Reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2) with PhCN: NMR Scale. A C6D6 (0.3 mL) solution of PhCN (2.1 mg, 0.02 mmol) was placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 8 and unreacted 2 were observed by 1H NMR spectroscopy (50% conversion based on 2). Preparation of (η5-C5Me5)2Th[η2-O,N-σ-C-ONCH(CHCH)2C(Ph)C(CCPh)] (10). Method A. This compound was prepared as red crystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and pyridine N-oxide (24 mg, 0.25 mmol) in toluene (15 mL) at room temperature and recrystallization from a benzene

solution by a procedure similar to that in the synthesis of 3. Yield: 162 mg (81%). Mp: 128−130 °C dec. 1H NMR (C6D6): δ 8.09 (d, J = 5.4 Hz, 1H, phenyl), 7.81 (d, J = 7.4 Hz, 2H, phenyl), 7.52 (d, J = 7.5 Hz, 2H, phenyl), 7.32 (m, 3H, phenyl), 7.01 (d, J = 7.6 Hz, 2H, phenyl), 6.90 (m, 3H, CH), 6.32 (t, J = 9.9 Hz, 1H, CH), 5.36 (m, 1H, CH), 2.09 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 207.2 (ThC), 159.6 (NC), 144.4 (CCPh), 141.1 (phenyl C), 140.5 (phenyl C), 134.3 (phenyl C), 132.7 (phenyl C), 131.2 (phenyl C), 129.0 (phenyl C), 128.7 (phenyl C), 128.1 (phenyl C), 127.0 (alkenyl C), 124.9 (ring C), 118.6 (alkenyl C), 111.7 (alkenyl C), 102.2 (alkenyl C), 82.2 (PhCC), 75.0 (PhCC), 11.6 (CH3) ppm. IR (KBr, cm−1): 2906 (s), 2854 (s), 2119 (m), 2048 (m), 1593 (s), 1487 (s), 1440 (s), 1377 (s), 1026 (s), 775 (s). Anal. Calcd for C41H45NOTh: C, 61.57; H, 5.67; N, 1.75. Found: C, 61.62; H, 5.61; N, 1.72. Method B: NMR Scale. A C6D6 (0.3 mL) solution of pyridine Noxide (1.9 mg, 0.02 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The NMR sample was maintained at room temperature and monitored periodically by 1H NMR spectroscopy. After 4 h, resonances due to 10 (ca. 40%) along with those of unreacted 2 and (η5-C5Me5)2Th[κ2-{2-C4H4NO)CHC(Ph)C CCPh}] (9) (ca. 20%; 1H NMR (C6D6) δ 8.40 (d, J = 7.6 Hz, 2H, phenyl), 8.16 (d, J = 7.4 Hz, 1H, pyridyl), 7.68 (m, 5H, phenyl), 7.21 (m, 4H, phenyl and pyridyl), 6.74 (t, J = 7.4 Hz, 1H, pyridyl), 6.22 (m, 1H, pyridyl), 5.74 (br s, 1H, pyridyl), 2.03 (s, 30H, CH3) ppm) were observed by 1H NMR spectroscopy (total 60% conversion based on 2). After 1 day, only resonances of 10 were observed by 1H NMR spectroscopy (100% conversion). Nevertheless, complex 9 could not be isolated in pure form on a synthetic scale, since partial degradation to 10 was always observed. Preparation of (η5-C5Me5)2Th[η6-{2-(4-Me2NC4H3N)CC(Ph)C CCHPh}] (11). Method A. This compound was prepared as red crystals from the reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and DMAP (31 mg, 0.25 mmol) in toluene (15 mL) at 110 °C and recrystallization from a benzene solution by a procedure similar to that in the synthesis of 3. Yield: 174 mg (84%). Mp: 110− 112 °C dec. 1H NMR (C6D6): δ 8.03 (d, J = 7.4 Hz, 2H, phenyl), 7.38 (m, 3H, phenyl), 7.23 (m, 3H, phenyl), 6.99 (m, 3H, phenyl and pyridyl), 6.54 (d, J = 2.4 Hz, 1H, pyridyl), 5.55 (dd, J = 6.8 Hz, 2.5 Hz, 1H, pyridyl), 4.64 (s 1H, PhCH), 2.39 (s, 6H, N(CH3)2), 1.95 (s, 15H, CH3), 1.77 (s, 15H, CH3) ppm. 13C{1H} NMR (C6D6): δ 171.5 (ThCC), 152.3 (ThCC), 145.7 (aryl C), 143.9 (aryl C), 143.8 (aryl C), 137.8(aryl C), 135.2 (aryl C), 134.5 (aryl C), 129.3 (aryl C), 126.5 (aryl C), 126.0 (aryl C), 125.6 (aryl C), 124.9 (aryl C), 123.4 (ring C), 121.6 (ring C), 95.0 (pyridyl C), 94.6 (pyridyl C), 80.3 (CPh), 71.4 (ThCHPh), 38.6 (N(CH3)2), 11.6 (CH3) 11.5 (CH3) ppm. IR (KBr, cm−1): 3053 (m), 2900 (s), 2857 (s), 1982 (w), 1606 (s), 1593 (s), 1483 (s), 1377 (s), 1263 (s), 1209 (s), 983 (s), 914 (s), 758 (s), 698 (s). Anal. Calcd for C43H50N2Th: C, 62.46; H, 6.09; N, 3.39. Found: C, 62.45; H, 6.13; N, 3.35. Method B: NMR Scale. A C6D6 (0.3 mL) solution of DMAP (2.5 mg, 0.02 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances of 11 were observed by 1H NMR spectroscopy (100% conversion) after the sample was heated at 110 °C for 2 days. Preparation of (η5-C5Me5)2Th[NC(C12H8)]2 (12). Method A. This compound was prepared as red crystals from the reaction of (η5C5Me5)2Th(η4-C4Ph2) (2; 176 mg, 0.25 mmol) and 9-diazofluorene (96 mg, 0.50 mmol) in toluene (15 mL) at 110 °C and recrystallization from a benzene solution by a procedure similar to that in the synthesis of 3. Yield: 183 mg (85%). Mp: 266−268 °C dec. 1 H NMR (C6D6): δ 7.88 (t, J = 4.2 Hz, 4H, aryl), 7.47 (t, J = 4.2 Hz, 4H, aryl), 7.23 (m, 8H, aryl), 2.00 (s, 30H, CH3) ppm. 13C{1H} NMR (C6D6): δ 170.5 (NC), 143.6 (aryl C), 137.7 (aryl C), 131.0 (aryl C), 129.3 (aryl C), 123.7 (ring C), 122.2 (aryl C), 120.1 (aryl C), 11.4 (CH3) ppm. IR (KBr, cm−1): 3059 (m), 2962 (s), 1641 (s), 1598 (s), 1442 (s), 1382 (s), 1259 (s), 1087 (s), 1018 (s), 792 (s). Anal. Calcd for C46H46N2Th: C, 64.32; H, 5.40; N, 3.26. Found: C, 64.45; H, 5.43; N, 3.35. 5678


Organometallics

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Method B. NMR Scale. A C6D6 (0.3 mL) solution of 9diazofluorene (7.7 mg, 0.04 mmol) was slowly placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). The resonances due to 12 and those of PhCCCCPh (1H NMR (C6D6) δ 7.35 (d, J = 6.8 Hz, 4H, phenyl), 6.87 (m, 6H, phenyl) ppm) were observed by 1H NMR spectroscopy (100% conversion) after the sample was heated at 110 °C for 3 days. Reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2) with 9-diazofluorene. NMR Scale. A C6D6 (0.3 mL) solution of 9-diazofluorene (3.8 mg, 0.02 mmol) was placed in a J. Young NMR tube charged with (η5C5Me5)2Th(η4-C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.2 mL). Resonances of 12, PhCCCCPh and unreacted 2 were observed by 1H NMR spectroscopy (50% conversion based on 2) when heated at 110 °C for 3 days. Reaction of (η5-C5Me5)2Th(η4-C4Ph2) (2) with RCCR (R = Me, Ph, p-tolyl), Me3SiN3 or Me3SiCHN2. NMR Scale. An excess amount of RCCR (R = Me, Ph, p-tolyl), Me3SiN3, or Me3SiCHN2 was placed in a J. Young NMR tube charged with (η5-C5Me5)2Th(η4C4Ph2) (2; 14 mg, 0.02 mmol) and C6D6 (0.5 mL). In each case, the sample was monitored periodically by 1H NMR spectroscopy. No changes in the 1H NMR spectrum were observed on heating at 100 °C for 1 week. X-ray Crystallography. Single-crystal X-ray diffraction measurements were carried out on a Bruker Smart APEX II CCD diffractometer at 100(2) K using graphite-monochromated Mο Kα radiation (λ = 0.71073 Å). An empirical absorption correction was applied using the SADABS program.27 All structures were solved by direct methods and refined by full-matrix least squares on F2 using the SHELXL program package.28 All hydrogen atoms were geometrically fixed using the riding model. The crystal data and experimental data for 2, 3, 5−7, and 10−12 are summarized in the Supporting Information. Selected bond lengths and angles are given in Table 1. Computational Methods. All calculations were carried out with the Gaussian 09 program (G09),29 employing the B3PW91 functional, plus a polarizable continuum model (PCM) (denoted as B3PW91PCM), with the standard 6-31G(d) basis set for C, H, N, O, and S elements and Stuttgart RLC ECP from the EMSL basis set exchange (https://bse.pnl.gov/bse/portal) for Th,30 to fully optimize the structures of reactants, complexes, transition state, intermediates, and products and also to mimic the experimental toluene solvent conditions (dielectric constant ε = 2.379). All stationary points were subsequently characterized by vibrational analyses, from which their respective zero-point (vibrational) energies (ZPEs) were extracted and used in the relative energy determinations; in addition, frequency calculations were also performed to ensure that the reactant, complex, intermediate, product, and transition state structures resided at minima and first-order saddle points, respectively, on their potential energy hypersurfaces. In order to consider the dispersion effect for the reactions 2 + PhNCS and 2 + N2C(C12H8) + N2C(C12H8), singlepoint B3PW91-PCM-D331 calculations, based on B3PW91-PCM geometries, have been performed.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for G.Z.: [email protected]. *E-mail for D.-C.F.: [email protected]. *E-mail for M.D.W.: [email protected]. Author Contributions §

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant Nos. 21472013, 21172022, 21272026, and 21373030), and the Deutsche Forschungsgemeinschaft (DFG) through the Emmy-Noether and Heisenberg programs (WA 2513/2 and WA 2513/6, respectively).

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00923. Additional experiments, crystal parameters for compounds 2, 3, 5−7, and 10−12, and computational details (PDF) Cartesian coordinates of all stationary points optimized at the B3PW91-PCM level (XYZ) X-ray crystallographic data for compounds 2, 3, 5−7, and 10−12 (CIF) 5679


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Experimental and Computational Studies on an Actinide

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