Expanding the Scope: Monopentafulvene and -Benzofulvene

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Expanding the Scope: Monopentafulvene and -Benzofulvene Complexes of Zirconium and Hafnium Malte Fischer,† Tim Oswald,† Hanna Ebert, Marc Schmidtmann, and Rüdiger Beckhaus* Institut für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany S Supporting Information *

ABSTRACT: The reaction of Cp*MCl3 (M = Zr, Zr1; M = Hf, Hf1) with the reducing agent Na/Hg (20% Na) and with sterically encumbered pentafulvenes adamantylidenepentafulvene AdFv, 6,6′-di-p-tolylpentafulvene pTol2Fv, and benzofulvenes adamantylidenebenzofulvene AdBzFv, 10,10′-di-p-tolylbenzofulvene pTol2BzFv, and 10,10′-diphenylbenzofulvene Ph2BzFv yielded the corresponding pentafulvene complexes (η5-pentamethylcyclopentadienyl)metal(η5:η1-pentafulvene)chloride (Zr2a,b, Hf2a,b) and benzofulvene complexes (η5pentamethylcyclopentadienyl)metal(η5:η1-benzofulvene)chloride (Zr3a−c, Hf3a). This reductive complexation approach can be used in a multigram scale and mostly very good yields (up to 92%). In addition to NMR spectroscopic analyses, the pentafulvene complex Zr2b and benzofulvene complex Zr3b were characterized by Xray crystallography, showing mainly the π−η5:σ−η1 dianionic bonding mode together with slight influence of the π−η2:π−η3:σ−η1 bonding mode. By use of the prochiral benzofulvenes the corresponding complexes Zr3a−c and Hf3a are furthermore obtained in a diastereoselective manner.

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bis(η5:η1-pentafulvene)titanium via bis(η6-toluene)titanium by a fulvene-arene exchange reaction demonstrates the stronger πacceptor properties of the six-electron fulvene ligand compared with the arene ring.8 The π−η5:σ−η1 structure results from a stronger π-back-bonding from the exocyclic carbon atom of the fulvene moiety (Fv Cexo) to the metal. Additionally this coordination mode goes along with a change of polarity at the Fv Cexo. In other words, the Fv Cexo in metal complexes has a nucleophilic character in contrast to the free pentafulvenes, which possesses an electrophilic Cexo atom (Scheme 2).

INTRODUCTION Pentafulvenes feature a unique cross-conjugated electronic system, enabling a wide array of coordination modes to early and late transition metals strongly depending on the metal and the substitution patterns of the pentafulvenes.1,2 Generally, η2, η4 and η6 coordination modes are known, whereas for early transition metals the η6 coordination is dominating.3−6 This type of coordination occurs in two different resonance structures, either as a neutral olefinic fulvene fragment in a η2 (A, B), η2:η2 (C) or η2:η2:η2 (D) fashion or as dianionic fragment in a η5:η1 (E) and η2:η3:η1 fashion (F), respectively (Scheme 1).7 The partial dipolar character of pentafulvenes leads to excellent π-acceptor abilities and is therefore able to stabilize low-valent metal centers. In such a way, the first synthesis of

Scheme 2. Overview of the Cross-Conjugated Pentafulvene System and the Dianionic π−η5:σ−η1 Structure Leading to the “Umpolung” of the Fv Cexo Atom

Scheme 1. Different Coordination Modes of Pentafulvenes: Neutral η2-exo (A), Neutral η2-endo (B), Neutral η4 (C), Neutral η6 (D), Dianionic π−η5:σ−η1 (E), Dianionic π−η2:π−η3:σ−η1 (F)

The different coordination in pentafulvene complexes illustrates the high flexibility of the electronic properties of the fulvene ligands. The synthetic pathways to pentafulvene complexes range from heat- or light-induced deprotonation reactions of cyclopentadienyl ligands with alkyl substitution9−11 Received: November 16, 2017

© XXXX American Chemical Society

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DOI: 10.1021/acs.organomet.7b00832 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics to ligand exchange reactions.8 In the case of group 4 metals the reductive complexation of the corresponding fulvene ligand (mostly sterically encumbered) by either sodium or magnesium to various Ti(IV) and Zr(IV) precursors has proven itself to be a very effective method to generate mixed cyclopentadienyl/ fulvene titanium complexes12−15 (I), bisfulvene titanium complexes4,5 (II) and even zirconocene pentafulvene complexes16,17 (III) as shown in Scheme 3.

Scheme 4. Syntheses of Monopenta- and Benzofulvene Complexes of Zirconium (Zr2a,b, Zr3a−c) and Hafnium (Hf2a,b, Hf3a)

Scheme 3. Selected Examples of Group 4 Fulvene Complexes I−IV Derived from the Reductive Complexation Route

This approach also offers the possibility to use prochiral benzofulvene ligands to prepare bisbenzofulvene titanium complexes in a diastereoselective manner (IV).5 Starting from these complexes, numerous subsequent transformations are reported, including small-molecule activation reactions, E−H bond activation reactions, insertion reactions of various electrophiles and their catalytic use in hydroamination and hydroaminoalkylation reactions, showcasing the unique reactivity, the synthetic potential, and the applications.18−25 As presented in Scheme 4, the access to bispentafulvene complexes II of the heavier congener zirconium has already been established. However, up to now the missing reductive approach to monofulvene complexes of zirconium or even hafnium has not been reported. Herein, we close the gap and present the convenient preparative access to monopenta- and benzofulvene complexes of zirconium, as well as the corresponding complexes of the heaviest congener hafnium.

observed due to repetitive purification steps to isolate an analytically pure product. Zr2a, Zr2b, Hf2a and Hf2b demonstrate high solubilities in aliphatic, aromatic and polar solvents. The structures of the complexes mentioned above are confirmed by means of single crystal X-ray diffraction of Zr2b. Suitable crystals were obtained from a saturated n-hexane solution at 4 °C. Complex Zr2b crystallizes in the monoclinic space group P21/n. The molecular structure (Figure 1) shows a 4-fold coordinated zirconium atom in a distorted tetrahedral coordination environment (Ct1−Zr1−Ct2 136.5°). The terminal Zr1−Cl1 bond length (2.4438(13) Å) is in the expected range of a single bond.4,26,27 The Zr−Cexo bond length (2.500(4) Å) is significantly elongated in comparison to a Zr− C(sp 3 ) single bond (2.26−2.36 Å) 26,27 and to other monopentafulvene complexes of the type Cp*(Fv)ZrR (Fv = C5Me4CH2, R = alkyl, aryl) reported in the literature due to sterically demanding substituents.28,29 Of high diagnostic value for a dianionic π−η5:σ−η1 fulvene coordination mode is the deviation (bend angle θ) of the Cexo−Cipso bond from the plane of the five-membered ring toward the metal center as well as

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RESULTS AND DISCUSSION The monopentafulvene complexes of zirconium Zr2a,b and Hafnium Hf2a,b were synthesized by reaction of Cp*MCl3 (M = Zr (Zr1), M = Hf (Hf1)) with an equimolar amount of the appropriate pentafulvene (AdFv, pTol2Fv) and 2 equiv of sodium mercury amalgam (20% Na) in tetrahydrofuran for approximately 24 h at room temperature. Whereas magnesium is a suitable reducing agent for the corresponding titanium complexes,12,14 zirconium and hafnium precursors require the use of sodium mercury amalgam. After purification the extremely air and moisture sensitive compounds Zr2a,b and Hf2a,b are obtained in good to very good yields as violet (Zr2a), red (Zr2b) and orange (Hf2a,b) solids (Scheme 4). In the case of Hf2a and Zr3a reduced yields of 29% and 37% are B


Article

Organometallics

Table 1. Comparison of the Structural Data of Zr2b, Ib and Va,b (Bond Lengths [Å]; Bond Angles [deg])a Zr2b Ib12 Va30 Vb28 a

M−Cexo

Cexo−Cipso

θ

Δ

2.500(4) 2.535(5) 2.389(8) 2.371(5)

1.461(5) 1.428(7) 1.468(9) 1.432(8)

32.7 29.2 36.3 36.3

0.327 0.29 0.370 0.382

Structures:

Figure 1. Molecular structure of complex Zr2b. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Zr1− Cl1 2.4438(13), Zr1−C16 2.500(4), Zr1−C11 2.280(4), Zr1−C12 2.417(4), Zr1−C13 2.579(4), Zr1−C14 2.556(4), Zr1−C15 2.383(4), C11−C16 1.461(5), C13−C14 1.386(6), Ct1−Zr1−Ct2 136.5, Σ∠C16 348.6 (C11−C16−C17 + C17−C16−C24 + C11−C16− C24) (Ct1 = centroid of C1A−C5A; Ct2 = centroid of C11−C15).

the ring slippage (Δ) toward the Cipso atom of the fivemembered ring (Scheme 5). Scheme 5. Representation of the Deviation (Bend Angle θ) of the Cexo−Cipso Bond from the Plane of the Five-Membered Ring toward the Metal Center and the Ring Slippage (Δ) toward the Cipso Atom of the Five-Membered Ring

Figure 2. 1H NMR spectrum (500 MHz, C6D6, rt) of complex Zr2b. Corresponding signals are highlighted by colored symbols.

two signals for the hydrogen atoms of the methyl groups of the diastereotopic pTol moieties at 2.04 and 2.17 ppm, respectively (central metal atom as chiral center). Of high diagnostic value are the four chemical inequivalent signals of the hydrogen atoms of the coordinated five-membered ring of the pentafulvene ligand localized at 4.68, 5.24, 5.33, and 6.11 ppm. In comparison to the free pentafulvene ligand pTol2Fv the analogous signals are shifted toward higher field.31 This difference in the chemical shifts is the result of the noneven influence of the anisotropy cone of the Cp* ligand.5 The most important NMR parameters for complexes Zr2a, Zr2b, Hf2a and Hf2b are summarized in Table 2. Generally, the 1H and 13C NMR data are in good agreement to the titanium congeners Ia and Ib and to the free pentafulvenes AdFv and pTol2Fv. One exception is the 13C chemical shift of the Cexo. The titanium complexes Ia and Ib show a lesser high field shift of the Cexo atom (130.1 ppm Ia, 127.4 ppm Ib) than the zirconium and hafnium complexes (109.9 to 117.8 ppm). This is an evidence for a stronger M− Cexo π-back-bonding. In contrast to the pTol substituted titanium complex Ib the analogous zirconium and hafnium complexes Zr2b and Hf2b show no rotation of the pentafulvene ligand at room temperature and temperatures above along the M−pentafulvene axis.12 Due to the weak coordination of the Cexo atom to titanium of Ib in solution the olefinic π−η6 coordination mode D has a higher impact than in

In comparison to the titanium congener Ib the M−Cexo bond is slightly shortened (Ti−Cexo 2.535(5) Å; Ib),12 indicating a stronger M−Cexo π-back-bonding in Zr2b and consequentially a higher dianionic character of the pentafulvene ligand. The also higher deviation angle θ of Zr2b (32.7°) compared to Ib (29.2°) confirms this. The Cexo−Cipso bond length (1.461(5) Å) is a slightly shortened C(sp3)−C(sp2) single bond. The sum of angles around the Cipso atom (348.6°) of the pentafulvene moiety proves its sp3-hybridization. The ring slippage Δ of Zr2b adds up to 0.327 Å and is characteristic for a dianionic pentafulvene ligand. Due to the longer Zr1−C13 (2.579(4) Å) and Zr1−C14 (2.556(4) Å) bond lengths compared to Zr1− C11 (2.280(4) Å), Zr−C12 (2.417(4) Å), and Zr1−C15 (2.383(4) Å) bond lengths, together with the short C13−C14 bond length (1.386(6) Å) a slight contribution of the coordination mode F has to be considered (Scheme 1).28,30 The structural data is summarized in Table 1 together with other pentafulvene complexes reported in the literature. Compounds Zr2a, Zr2b, Hf2a and Hf2b are fully characterized by NMR analyses, and the spectroscopic data are consistent with the X-ray structure of Zr2b. The NMR data of Complex Zr2b is, due to their similarity, discussed exemplary for this substance class and the corresponding 1H NMR spectrum is shown in Figure 2. The NMR spectrum shows one signal for the hydrogen atoms of the methyl groups of the Cp* ligand at 1.68 ppm and C


Article

Organometallics Table 2. Selected NMR Parameters of Complexes Zr2a, Zr2b, Hf2a and Hf2b in Comparison to the Analogous Titanium Compounds Ia and Ib and Free Pentafulvenes AdFv and pTol2Fv (C6D6, rt, ppm)a C5Me5

C5H4

C5H4

Cexo

Cipso

Zr2a

1.78/12.0

131.3

1.68/11.6

109.9

130.1

Hf2a

1.82/11.8

117.8

128.0

Hf2b

1.72/11.5

111.0, 115.1, 115.7, 116.6 111.1, 114.1, 117.4, 118.8 109.3, 114.7, 114.8, 115.4 109.5, 113.8, 117.0, 117.5 115.8, 118.5, 119.4, 123.4 115.8, 116.7, 121.9, 124.5 119.8, 133.1

113.3

Zr2b

3.72, 5.25, 5.58, 6.07 4.68, 5.24, 5.33, 6.11 3.75, 5.38, 5.44, 5.97 4.68, 5.33 (m, 2H), 5.99 3.08, 4.63, 5.65, 6.68 4.21, 4.56, 5.98, 6.42 6.61 (m, 2H), 6.64 (m, 2H) 6.59 (m, 2H), 6.65 (m, 2H)

114.0

126.8

130.1

131.3

127.4

130.1

164.8

136.9

124.8, 132.4

152.2

144.2

Ia14 Ib12

a

AdFv32

−

pTol2Fv31

−

Figure 3. Molecular structure of complex Zr3c. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Zr1− Cl1 2.4381(7), Zr1−C20 2.526(2), Zr1−C11 2.294(2), Zr1−C12 2.347(2), Zr1−C13 2.478(2), Zr1−C14 2.639(2), Zr1−C19 2.542(2), C11−C20 1.461(3), C14−C15 1.419(3), C15−C16 1.352(4), C16− C17 1.424(3), C17−C18 1.368(3), C18−C19 1.421(3), C14−C19 1.432(3), Ct1−Zr1−Ct2 134.2, Σ∠C20 348.2 (C11−C20−C21 + C11−C20−C27 + C21−C20−C27) (Ct1 = centroid of C1−C5; Ct2 = centroid of C11−C114 + C19).

Structures:

The benzofulvene complexes Zr3a−c and Hf3a are characterized by NMR measurements. Characteristically for this compound class is the single set of signals, showing that Zr3a−c and Hf3a are obtained in a diastereomerically pure fashion. The chirality arises from the fact that the monosubstituted benzofulvenes AdBzFv, pTol2BzFv and Ph2BzFv exhibit enantiotopic faces, leading to the occurrence of one planar chiral element for each monobenzofulvene complex Zr3a−c and Hf3a together with the chiral metal atom (Scheme 6).

Zr2b and Hf2b, where the dianionic coordination mode E is dominant (Scheme 1). After the successful reductive approach to the monopentafulvene complexes, we wanted to expand the reductive complexation route to bulky monobenzofulvene complexes. The monobenzofulvene complexes of zirconium Zr3a−c and Hafnium Hf3a are also synthesized by the reductive complexation route with sodium amalgam and are obtained in moderate to good yields as brown (Zr3a) or red (Zr3b,c, Hf3a) solids (Scheme 4). However, the Hf analogs of Zr3b and Zr3c could not be prepared in a satisfactory manner. Complexes Zr3a−c and Hf3a are thoroughly characterized by NMR analyses and single-crystal X-ray diffraction. The molecular structure of the monobenzofulvene zirconium complex Zr3c is shown in Figure 3. Suitable single crystals were obtained from a saturated toluene solution of Zr3c at −26 °C. Complex Zr3c crystallizes in the monoclinic space group I2/ a. As expected the central zirconium atom is in a distorted tetrahedral coordination environment (Ct1−Zr1−Ct2 134.2°) and the terminal Zr1−Cl1 (2.4381(7) Å) is typical of a single bond. The Zr1−Cexo bond length (2.526(2) Å) is an elongated Zr−C(sp3) single bond, indicating weaker M−Cexo π-backbonding than in Zr2b, and the Cipso atom is sp3-hybridized (sum of angles 348.2°). Furthermore, the deviation angle θ (33.3°) and the ring slippage (0.390 Å) are indicative for the dianionic π−η5:σ−η1 bonding mode. As for Zr2b the difference in the bond lengths between Zr1−C19/Zr1−C14 (2.542(2) Å/ 2.639 Å) and Zr1−C11/Zr1−C12/Zr1−C13 (2.294(2) Å/ 2.347(2) Å/2.478(2) Å) shows a slight contribution of the coordination mode F. Additionally, located double bonds are found in the annulated six-membered ring system of the benzofulvene moiety (C14−C15 1.419(3) Å, C15−C16 1.352(4) Å, C16−C17 1.424(3) Å, C17−C18 1.368(3) Å, C18−C19 1.421(3) Å).

Scheme 6. Enantiotopic Faces of Planar Chiral Benzofulvene Ligands

The configuration of Zr3c can be determined directly from the obtained crystal structure (Scheme 7). Hence, Zr3c possesses a (R,pR/S,pS)-configuration in the solid state.33 Due to high similarities in the chemical shifts of Zr3a−c and Hf3a (Table 3), they are discussed exemplary for compound Zr3b (Figure 4). The 1H NMR spectrum of the C1 symmetric complex Zr3b shows two signals for the methyl groups of the chemically inequivalent pTol groups at 2.10 and 2.17 ppm and one signal for the Cp* ligand at 1.68 ppm, respectively as well as distinct signals in the low field for the aromatic hydrogen atoms. Of high diagnostic value are the signals of the C5H2 moiety, leading to two doublet signals in the 1H NMR spectrum at 4.80 and 5.60 ppm (2JHH = 3.1 Hz). Those signals are shifted significantly to higher field compare to the free benzofulvene pTol2BzFv.13 The Cexo atom (110.3 ppm) of Zr3b is also shifted to higher field in the 13C NMR spectrum in comparison to pTol2BzFv and is in the same range as in Zr2a,b and Hf2a,b. D


Article

Organometallics

fulvene complexes Zr3a−c and Hf3a are obtained in a diastereoselective manner. The herein presented complexes expand the scope of fulvene complexes, and due to the nucleophilic character of the Cexo atom various follow-up chemistry can be expected.

Scheme 7. Chirality of the Monobenzofulvene Complexes and Priorities for IUPAC Nomenclature Illustrated by an Example

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Table 3. Selected NMR Parameters of Complexes Zr3a−c, Hf3a in Comparison to Free Benzofulvenes AdBzFv and pTol2BzFv (C6D6, rt, ppm) C5Me5 Zr3a Zr3b Zr3c Hf3a AdBzFv5 pTol2BzFv13

1.79/12.2 1.68/11.8 1.67/11.7 1.72/11.6 − −

C5H2 3.73, 4.82, 4.82, 4.84, 6.84, 6.85,

5.59 5.62 5.61 5.66 6.73 7.09

C5H2

Cexo

Cipso

101.1, 114.2 99.1, 113.6 99.3, 113.5 98.3, 112.0 127.0, 128.5 124.4, 125.2

114.6 110.3 110.4 114.7 159.9 145.4

134.2 134.3 134.2 133.4 131.3 137.2

EXPERIMENTAL SECTION

General Considerations. All reactions were carried out under an inert atmosphere of argon or nitrogen with rigorous exclusion of oxygen and moisture using standard gloveboxes or Schlenk techniques. Solvents were dried according to standard procedures over Na/K alloy with benzophenone as indicator and distilled under a nitrogen atmosphere. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III 500 spectrometer (1H 500.1 MHz; 13C 125.8 MHz). The NMR chemical shifts were referenced to residual protons of the solvent (benzene-d6) or the internal standard TMS. IR spectra were recorded on a Bruker Tensor 27 spectrometer using an attenuated total reflection (ATR) method. Melting points were determined using a “Mel-Temp” by Laboratory Devices, Cambridge. The mass spectra were measured with a Finnigan MAT 95 instrument. Synthesis and Characterization of Compounds. Cp*ZrCl3,34 Cp*HfCl 3 35 and the fulvenes adamantylidenepentafulvene (AdFv),32,36 6,6′-di-p-tolylpentafulvene (pTol2Fv),31 adamantylidenebenzofulvene (AdBzFv), 5 10,10′-di-p-tolylbenzofulvene (pTol2BzFv)13 and 10,10′-diphenylbenzofulvene (Ph2BzFv)37 were prepared according to published procedures. General Procedure. Cp*MCl3 (1 equiv), the corresponding fulvene (1 equiv) and sodium mercury amalgam (2 equiv) were placed in a Schlenktube and suspended in thf. The resulting reaction mixture was stirred at room temperature until all sodium mercury amalgam has been consumed and mercury has formed. Subsequent filtration using a porous glass filter frit (P4) with Celite and removal of the solvent afforded the desired complexes. Synthesis of Zr2a. Prepared as mentioned in General Procedure starting with 2.5 g Cp*ZrCl3 (7.5 mmol), 1.49 g AdFv (7.5 mmol) and 1.73 g sodium mercury amalgam (15.0 mmol) and isolated as violet solid, 3.17 g (92%), mp 144 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.42−2.48 (adamantyl), 1.78 (s, 15 H, C5Me5), 3.72 (m, 1 H, C5H4), 5.25 (m, 1 H, C5H4), 5.58 (m, 1 H, C5H4), 6.07 (m, 1 H, C5H4) ppm. 13 C NMR (125 MHz, benzene-d6) δ = 12.0 (C5Me5), 28.9 (Ad CH), 29.9 (Ad CH), 33.3 (Ad CH), 35.7 (Ad CH), 38.8 (Ad CH2), 38.8 (Ad CH2), 42.8 (Ad CH2), 45.4 (Ad CH2), 111.0 (C5H4), 113.3 (Fv Cexo), 115.1 (C5H4), 115.7 (C5H4), 116.6 (C5H4), 120.2 (C5Me5), 131.3 (Fv Cipso) ppm. IR (ATR) ṽ = 2901 (s), 2847 (m), 1488 (w), 1448 (m), 1377 (m), 1261 (m), 1098 (m), 1060 (m), 1023 (m), 947 (w), 852 (w), 802 (s), 744 (m), 760 (m), 685(s) cm−1. MS (EI, 70 eV) m/z (%) = 458 (100) [M]+, 199 (17) [AdFv + H]+, 135 (99) [Cp*]+. Synthesis of Zr2b. Prepared as mentioned in General Procedure starting with 2 g Cp*ZrCl3 (6.00 mmol), 1.55 g pTol2Fv (6.00 mmol) and 1.38 g sodium mercury amalgam (12.00 mmol) and isolated as red-violet solid, 2.7 g (88%), mp 145 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.69 (s, 15 H, C5Me5), 2.05 (s, 3 H, pTol CH3), 2.17 (s, 3 H, pTol CH3), 4.69 (m, 1 H, C5H4), 5.24 (m, 1 H, C5H4), 5.34 (m, 1 H, C5H4), 6.12 (m, 1 H, C5H4), 6.95 (m, 4 H, pTol CH), 7.19 (m, 2 H, pTol CH), 7.45 (m, 2 H, pTol CH) ppm. 13C NMR (125 MHz, benzene-d6) δ = 11.6 (C5Me5), 21.0 (pTol CH3), 21.0 (pTol CH3), 109.9 (Fv Cexo), 111.1 (C5H4), 114.2 (C5H4), 117.4 (C5H4), 118.8 (C5H4), 120.9 (C5Me5), 126.8 (pTol CH), 128.5 (pTol CH), 129.6 (pTol CH), 130.1 (Fv Cipso), 133.1 (pTol CH), 133.9 (quat. pTol C), 136.3 (quat. pTol C), 141.6 (quat. pTol C), 142.1 (quat. pTol C) ppm. IR (ATR) ṽ = 2914 (w), 2862 (w), 1508 (m), 1447 (m), 1378 (m), 1261 (w), 1185 (w), 1110 (m), 1022 (m), 806 (s), 763 (s), 746 (m), 685 (m), 596 (s) cm−1. MS (EI, 70 eV) m/z (%) = 518 (60) [M]+, 384 (56) [M − Cp*]+, 291 (23) [M − Cp* − pTol]+, 259 (19) [pTol2Fv + H]+, 135 (6) [Cp*]+. Synthesis of Hf2a. Prepared as mentioned in General Procedure starting with 1 g Cp*HfCl3 (2.38 mmol), 472 mg AdFv (2.38 mmol) and 548 mg sodium mercury amalgam (4.76 mmol) and isolated as

Figure 4. 1H NMR spectrum (500 MHz, C6D6, rt) of complex Zr3b. Corresponding signals are highlighted by colored symbols; 1.40 and 3.57 ppm: residue of thf.

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CONCLUSION Convenient syntheses of four monopentafulvene complexes Zr2a,b and Hf2a,b as well as of four monobenzofulvene complexes Zr3a−c and Hf3a of the heavier group 4 elements zirconium and hafnium have been established. The reductive complexation of the corresponding pentafulvene (AdFv, pTol2Fv) and benzofulvene (AdBzFv, pTol2BzFv, Ph2BzFv) ligands with Na/Hg (20%) allows the syntheses of the abovementioned complexes in high yields and in a multigram scale by using Cp*MCl3 (M = Zr, Zr1; M = Hf, Hf1) as the metal precursor compounds. In all cases the coordination mode of the fulvene ligand is best described as π−η5:σ−η1 (dianionic). By utilizing the prochiral benzofulvene ligands the monobenzoE


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Organometallics orange solid, 374 mg (29%), mp 124 °C dec 1H NMR (500 MHz, benzene-d6) δ = 1.65−2.55 (adamantyl), 1.82 (s, 15 H, C5Me5), 3.75 (m, 1 H, C5H4), 5.38 (m, 1 H, C5H4), 5.44 (m, 1 H, C5H4), 5.97 (m, 1 H, C5H4) ppm. 13C NMR (125 MHz, benzene-d6) δ = 11.8 (C5Me5), 29.0 (Ad CH), 29.8 (Ad CH), 32.9 (Ad CH), 35.6 (Ad CH), 38.8 (Ad CH2), 38.9 (Ad CH2), 39.0 (Ad CH2), 43.3 (Ad CH2), 45.9 (Ad CH2), 109.3 (C5H4), 114.7 (C5H4), 114.8 (C5H4), 115.4 (C5H4), 117.0 (Fv Cipso)118.8 (C5Me5), 128 (Fv Cexo)* ppm. * remaining “Fv Cexo” signal is overlapped by solvent signal. IR (ATR) ṽ = 2902 (s), 2848 (m), 1486 (w), 1448 (m), 1378 (m), 1354 (w), 1099 (m), 1060 (m), 1026 (m), 808 (s), 762 (s), 723 (m), 696 (m) cm−1. Synthesis of Hf2b. Prepared as mentioned in General Procedure starting with 1.2 g Cp*HfCl3 (2.86 mmol), 737 mg pTol2Fv (2.86 mmol) and 657 mg sodium mercury amalgam (5.72 mmol) and isolated as orange solid, 1.34 g (77%), mp 153 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.72 (s, 15 H, C5Me5), 2.07 (s, 3 H, pTol CH3), 2.22 (s, 3 H, pTol CH3), 4.68 (m, 1 H, C5H4), 5.33 (m, 2 H, C5H4), 5.99 (m, 1 H, C5H4), 6.99 (m, 4 H, pTol CH), 7.38 (m, 2 H, pTol CH), 7.47 (m, 4 H, pTol CH) ppm. 13C NMR (125 MHz, benzened6) δ = 11.5 (C5Me5), 20.9 (pTol CH3), 21.1 (pTol CH3), 109.5 (C5H4), 113.8 (C5H4), 114.0 (Fv Cexo), 117.0 (C5H4), 117.5 (C5H4), 119.4 (C5Me5), 126.8 (Fv Cipso), 127.5 (pTol CH), 128.2 (pTol CH), 129.2 (pTol CH), 134.0 (quat. pTol C), 134.2 (pTol CH), 135.9 (quat. pTol C), 141.9 (quat. pTol C), 143.3 (quat. pTol C) ppm. IR (ATR) ṽ = 2961 (w), 1699 (w), 1652 (w), 1559 (w), 1509 (m), 1148 (w), 1377 (w), 1261 (w), 1182 (w), 1109 (w), 1021 (m), 807 (s), 763 (s), 722 (s), 575 (s) cm−1. MS (EI, 70 eV) m/z (%) = 608 (100) [M]+, 474 (51) [M − Cp* + H]+, 381 (26) [M − Cp* − pTol]+. Synthesis of Zr3a. Prepared as mentioned in General Procedure starting with 300 mg Cp*ZrCl3 (0.90 mmol), 224 mg AdBzFv (0.90 mmol) and 209 mg sodium mercury amalgam (1.80 mmol) and isolated as brown solid, 168 mg (37%), mp 144 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.39−2.91 (adamantyl), 1.79 (s, 15 H, C5Me5), 3.72 (d, 2JHH = 3.0 Hz, 1 H, C5H2), 5.57 (d, 2JHH = 3.0 Hz, 1 H, C5H2), 6.83 (m, 2 H, C6H4), 7.11 (m, 1 H, C6H4), 7.64 (m, 1 H, C6H4) ppm. 13C NMR (125 MHz, benzene-d6) δ = 12.2 (C5Me5), 28.8 (Ad CH), 30.0 (Ad CH), 34.1 (Ad CH), 37.2 (Ad CH), 38.6 (Ad CH2), 38.7 (Ad CH2), 38.8 (Ad CH2), 43.9 (Ad CH2), 45.7 (Ad CH2), 101.1 (C5H2), 114.6, (Fv Cexo), 115.2 (C5H2), 120.1 (C5Me5), 120.9 (quat. C6H4), 122.6 (C6H4), 124.5 (C6H4), 127.6 (C6H4), 128 (quat. C6H4)*, 130.1 (C6H4), 134.2 (Fv Cipso) ppm. * remaining “quat. C6H4” signal is overlapped by solvent signal. IR (ATR) ṽ = 2900 (m), 2845 (m), 1444 (w), 1376 (w), 1346 (w), 1098 (w), 1020 (w), 955 (w), 833 (w), 755 (m), 764 (m), 744 (w) cm−1. MS (EI, 70 eV) m/z (%) = 508 (100) [M]+, 248 (91) [AdBzFv]+, 135 (6) [Cp*]+. Synthesis of Zr3b. Prepared as mentioned in General Procedure starting with 1 g Cp*ZrCl3 (3.00 mmol), 926 mg pTol2BzFv (3.00 mmol) and 691 mg sodium mercury amalgam (6.00 mmol) and isolated as red solid, 1.26 g (74%), mp 148 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.68 (s, 15 H, C5Me5), 2.10 (s, 3 H, pTol CH3), 2.17 (s, 3 H, pTol CH3), 4.80 (d, 2JHH = 3.1 Hz, 1 H, C5H2), 5.60 (d, 2JHH = 3.1 Hz, 1 H, C5H2), 6.31 (m, 1 H, C6H4), 6.54 (m, 1 H, C6H4), 6.76 (m, 1 H, pTol CH), 6.82 (m, 1 H, C6H4), 6.95 (m, 3 H, pTol CH), 7.02 (m, 1 H, pTol CH), 7.12 (m, 1 H, C6H4), 7.49 (m, 2 H, pTol CH), 7.77 (m, 1 H, pTol CH) ppm. 13C NMR (125 MHz, benzened6) δ = 11.8 (C5Me5), 21.0 (pTol CH3), 21.1 (pTol CH3), 99.1 (C5H2), 110.3 (Fv Cexo), 113.6 (C5H2), 119.5 (quat. C6H4), 120.7 (C5Me5), 122.9 (C6H4), 125.0 (C6H4), 127.2 (quat. C6H4), 128.4 (pTol CH), 128.5 (C6H4), 129.7 (C6H4), 130.1 (pTol CH), 134.0 (quat. pTol C), 134.3 (Fv Cipso), 134.6 (pTol CH), 135.7 (pTol CH), 136.5 (quat. pTol C), 143.7 (quat. pTol C), 143.8 (quat. pTol C) ppm. IR (ATR) ṽ = 2911 (w), 1565(w), 1509 (w), 1433 (m), 1377 (w), 1110 (w), 1021 (w), 764 (m), 573 (m) cm−1. MS (EI, 70 eV) m/ z (%) = 569 (100) [M]+, 434 (41) [M − Cp* + H]+, 341 (12) [M − Cp* − pTol]+, 308 (99) [pTol2BzFv]+. Synthesis of Zr3c. Prepared as mentioned in General Procedure starting with 1 g Cp*ZrCl3 (3.00 mmol), 842 mg Ph2BzFv (3.00 mmol) and 691 mg sodium mercury amalgam (6.00 mmol) and isolated as red solid, 1.43 g (88%), mp 150 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.67 (s, 15 H, C5Me5), 4.82 (d, 2JHH = 3.0 Hz, 1 H,

C5H2), 5.62 (d, 2JHH = 3.0 Hz, 1 H, C5H2), 6.18 (m, 1 H, C6H4), 6.53 (m, 1 H, C6H4), 6.83 (m, 1 H, C6H4), 6.90 (m, 2 H, C6H5), 7.07−7.18 (m, 6 H, C6H5, C6H4), 7.54 (m, 2 H, C6H5), 7.84 (m, 1 H, C6H5) ppm. 13C NMR (125 MHz, benzene-d6) δ = 11.7 (C5Me5), 99.3 (C5H4), 110.4 (Fv Cexo), 113.5 (C5H2), 119.2 (quat. C6H4), 120.9 (C5Me5), 122.9 (C6H4), 124.9 (C6H5), 125.0 (C6H4), 127.1 (C6H5), 127.2 (quat. C6H4), 127.8 (C6H5), 127.9 (C6H5), 128.5 (C6H4), 129.1 (C6H5), 129.5 (C6H4), 134.2 (Fv Cipso), 134.8 (C6H5), 135.8 (C6H5), 146.2 (quat. C6H5), 146.7 (quat. C6H5) ppm. IR (ATR) ṽ = 3026 (w), 2905 (w), 1596 (w), 1492 (w), 1449 (w), 1378 (w), 1078 (w), 1028 (w), 796 (w), 773 (w), 754 (m), 740 (m), 700 (s) cm−1. MS (EI, 70 eV) m/z (%) = 540 (100) [M]+, 406 (31) [M − Cp* + H]+, 280 (41) [Ph2BzFv]+. Synthesis of Hf3a. Prepared as mentioned in General Procedure starting with 500 mg Cp*HfCl3 (1.19 mmol), 367 mg pTol2BzFv (1.19 mmol) and 274 mg sodium mercury amalgam (2.38 mmol) and isolated as red solid, 633 mg (81%), 150 °C. 1H NMR (500 MHz, benzene-d6) δ = 1.72 (s, 15 H, C5Me5), 2.11 (s, 3 H, pTol CH3), 2.22 (s, 3 H, pTol CH3), 4.84 (d, 2JHH = 2.9 Hz, 1 H, C5H2), 5.66 (d, 2JHH = 2.9 Hz, 1 H, C5H2), 6.42 (m, 1 H, C6H4), 6.52 (m, 1 H, C6H4), 6.80 (m, 1 H, C6H4), 6.98 (m, 4 H, pTol CH), 7.04 (m, 1 H, pTol CH), 7.11 (m, 1 H, C6H4), 7.47 (m, 2 H, pTol CH), 7.86 (m, 1 H, pTol CH). ppm. 13C NMR (125 MHz, benzene-d6) δ = 11.6 (C5Me5), 20.9 (pTol CH3), 21.2 (pTol CH3), 98.3 (C5H2), 112.0 (C5H2), 114.7 (Fv Cexo), 115.0 (quat. C6H4), 119.3 (C5Me5), 122.7 (C6H4), 125.0 (C6H4), 128 (quat. C6H4)*, 128.7 (pTol CH), 128.8 (C6H4), 129.8 (C6H4), 130.0 (pTol CH), 133.4 (Fv Cipso), 134.1 (quat. pTol C), 135.5 (pTol CH), 136.1 (quat. pTol C), 136.8 (pTol CH), 143.8 (quat. pTol C), 144.6 (quat. pTol C) ppm. * remaining “quat. C6H4” signal is overlapped by solvent signal. IR (ATR) ṽ = 2971 (w), 2909 (w), 1505 (m), 1447 (m), 1377 (m), 1304 (w), 1260 (w), 1109 (m), 1066 (m), 1021 (m), 809 (s), 795 (m), 741 (m), 698 (m), 651 (m), 573 (s) cm−1. MS (EI, 70 eV) m/z (%) = 658 (29) [M]+, 311 (100) [pTol2BzFv) + 3H]+, 309 (28) [pTol2BzFv) + H]+.

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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.7b00832. Supporting figures and tables (PDF) Accession Codes

CCDC 1584537−1584538 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Rüdiger Beckhaus: 0000-0003-3697-0378 Author Contributions †

M.F. and T.O. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the DFG Research Training Group 2226 is kindly acknowledged. We kindly thank Friederike Kirschner for the Table of Contents drawing. F


Article

Organometallics

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(30) Schock, L. E.; Brock, C. P.; Marks, T. J. Organometallics 1987, 6, 232−241. (31) Jeffery, J.; Probitts, E. J.; Mawby, R. J. J. Chem. Soc., Dalton Trans. 1984, 11, 2423−7. (32) Miller, S. A.; Bercaw, J. E. Organometallics 2002, 21 (5), 934− 945. (33) For detailed description, see the Supporting Information. (34) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793− 799. (35) Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hillhouse, G. L.; Bercaw, J. E. Organometallics 1985, 4, 97−104. (36) Abrams, M. B.; Yoder, J. C.; Loeber, C.; Day, M. W.; Bercaw, J. E. Organometallics 1999, 18, 1389−1401. (37) Kice, J. L.; Parham, F. M. J. Am. Chem. Soc. 1958, 80, 3792− 3797.

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