Synthesis and Coordination Chemistry of an Enantiomerically Pure

Article pubs.acs.org/Organometallics

Synthesis and Coordination Chemistry of an Enantiomerically Pure Pentadienyl Ligand Ann Christin Fecker, Andreas Glöckner, Constantin G. Daniliuc,† Matthias Freytag, Peter G. Jones, and Marc D. Walter* Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany S Supporting Information *

ABSTRACT: The coordination chemistry of the enantiomerically pure dimethylnopadienyl ligand (Pdl*) with early to late transition metals is presented. Dimethylnopadiene is prepared by a Wittig reaction from (1R)-(−)-myrtenal, which is readily available from the chiral pool. Deprotonation of dimethylnopadiene with a Schlosser base gives K(Pdl*), which is a good starting material for the preparation of the early- to late-transition-metal open metallocenes [M(η5-Pdl*)2] (M = Ti, V, Cr, Fe) and mono(pentadienyl) complexes [(η5-Cp′)Fe(η5-Pdl*)] (Cp′ = 1,2,4-(Me3C)3C5H2), [(η7-C7H7)Zr(η5-Pdl*)], and [(η4-COD)Ir(η5-Pdl*)]. These complexes have been fully characterized by several spectroscopic techniques, elemental analysis, and X-ray crystallography. In all of these cases the Pdl* ligand exhibits excellent face selectivity upon metal coordination, because it coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Within the series of open metallocenes [M(η5-Pdl*)2] (M = Ti, V, Cr, Fe) the open ferrocene is the least thermally stable molecule and degrades to iron metal in solution. This instability is attributed to the severe steric demand of this ligand system in combination with the relatively small Fe2+ center.

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INTRODUCTION Metal cyclopentadienyl (Cp) and allyl complexes are well-known and have attracted significant attention over the years. While the cyclopentadienyl ligand is one of the most prominent spectator ligands in organometallic chemistry, the allyl ligand is often used in synthetic and catalytic applications.1 However, pentadienyls (Pdl) are well-established ligands for transition-metal complexes and they are interesting, as they can be considered as “open” cyclopentadienyl congeners.2−9 In contrast to cyclopentadienyl, this class of ligands can readily adopt multiple hapticities. This ability to isomerize between the η1, η3, and η5 coordination modes may be very beneficial chemically as well as catalytically, offering great flexibility to facilitate ligand association and dissociation processes in a manner similar to that displayed by indenyl ligands.10−12 Since the η5-bound pentadienyl is a better chelate than allyl, a wide variety of thermally stable complexes are accessible. In comparison to the cyclopentadienyl ring, the open pentadienyl system is a stronger δ acceptor for geometric and electronic reasons.6 With the open edge, the area enclosed by five pentadienyl carbon atoms is much larger than that of the cyclopentadienyl ring and the bond formation to these widely spread carbon atoms requires the metal atom to move more closely to the pentadienyl plane, thereby enhancing the orbital overlap. The pentadienyl LUMO is of low energy and is well suited for δ-type back-bonding interactions with metal orbitals of matching symmetry. If the terminal carbon atoms of the pentadienyl system approach each other, the LUMO is shifted to higher energy, because the corresponding orbital lobes are out of phase. These stronger bonding interactions in comparison to the cyclopentadienyl ligand might facilitate chiral introduction © 2013 American Chemical Society

enforced by an optically active pentadienyl ligand. Despite these advantageous properties, it is remarkable that chiral pentadienyl complexes have not been explored extensively.13 In contrast, enantiomerically pure cyclopentadienyl ligands have been known since 1978,14 and their development was primarily motivated by the belief that such ligands could play a valuable role in catalytic enantioselective synthesis, particularly for reactions or substrates where chiral phosphines are ineffective. To date, considerable success has been achieved with chiral metallocene complexes that catalyze the polymerization of alkenes,15,16 the hydrogenation of nonfunctionalized alkenes,17 and the hydrosilylation of ketones18 and act as chiral Lewis acid catalysts.19 Over the years a large number of pentadienyl complexes have been prepared, but these investigations have mainly focused on the parent ligand, C5H7, or alkyl- or trimethylsilyl-substituted derivatives such as 2,4-dimethylpentadienyl (2,4-Me2C5H5) and 1,5-(Me3Si)2C5H4.2−9 Additionally, a number of so-called edgebridged pentadienyl ligands such as cyclooctadienyl are known.20 However, the only enantiomerically pure pentadienyl ligand reported in the literature is dimethylnopadienyl (Pdl*), which has been used to prepare the half-open ruthenocene [(η5-C5Me5)Ru(η5-Pdl*)].13 Intrigued by this fact, we set out to explore the coordination chemistry of this ligand in greater detail. Herein, we report on the preparation and characterization of chiral open metallocenes with early to late transition metals and present a Received: December 10, 2012 Published: January 30, 2013 874

dx.doi.org/10.1021/om301189g | Organometallics 2013, 32, 874−884

Organometallics

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Scheme 1

Table 1. Crystallographic Data chem formula formula mass/amu cryst syst a/Å b/Å c/Å α/deg β/deg γ/deg unit cell vol/Å3 temp/K space group no. of formula units per unit cell, Z radiation type abs coeff, μ/mm−1 no. of rflns measd no. of indep rflns Rint final R1 values (I > 2σ(I)) final wR2(F2) values (I > 2σ(I)) final R1 values (all data) Final wR2(F2) values (all data) Flack parameter goodness of fit on F2 Δρ/e Å−3

4

5

6

7

C25H43KO6 478.69 orthorhombic 9.6598(3) 13.2279(3) 20.7805(7) 90 90 90 2655.29(14) 100(2) P212121 4

C26H38Ti 398.46 orthorhombic 12.1532(2) 14.9904(4) 24.2244(6) 90 90 90 4413.23(18) 100(2) P212121 8

C26H38V 401.50 orthorhombic 12.0837(2) 14.9805(2) 24.2167(2) 90 90 90 4383.70(10) 100(2) P212121 8

C26H38Cr 402.56 orthorhombic 12.0216(2) 14.8368(2) 24.5563(2) 90 90 90 4379.91(10) 100(2) P212121 8

Mo Kα 0.235 93305 6551 0.0651 0.0371

Mo Kα 0.396 165691 10516 0.0844 0.0347

Cu Kα 3.807 76005 8976 0.0297 0.0187

0.0683

0.0652

0.0553

9

10

C26H38Fe 406.41 monoclinic 8.7907(2) 11.5333(2) 11.5809(2) 90 111.230(2) 90 1094.45(4) 100(2) P21 2

C30H48Fe 464.53 orthorhombic 9.5922(2) 14.8818(4) 18.3651(4) 90 90 90 2621.60(11) 100(2) P212121 4

C20H26Zr 357.63 orthorhombic 8.0907(2) 10.9532(2) 18.8076(4) 90 90 90 1666.71(6) 100(2) P212121 4

C21H31Ir 475.66 monoclinic 8.3693(2) 24.3239(2) 9.5464(2) 90 115.328(2) 90 1756.59(6) 100(2) P21 4

Cu Kα 4.322 84454 8931 0.0331 0.0197

Cu Kα 5.548 10522 3548 0.0223 0.0243

Mo Kα 0.590 101445 6242 0.0633 0.0279

Mo Kα 0.652 66370 4670 0.0308 0.0142

Mo Kα 7.597 82625 8312 0.0236 0.0236

0.0501

0.0521

0.0615

0.0594

0.0350

0.0128

0.0458

0.0188

0.0199

0.0248

0.0334

0.0149

0.0130

0.0743

0.0684

0.0502

0.0522

0.0619

0.0614

0.0353

0.0305

0.00(3) 1.015 0.171/−0.182

−0.017(13) 1.042 0.265/−0.218

0.000(2) 1.039 0.182/−0.169

−0.002(2) 1.026 0.180/−0.259

−0.008(2) 1.055 0.227/−0.273

−0.022(10) 1.045 0.314/−0.218

−0.010(18) 1.061 0.269/−0.186

−0.003(4) 1.158 0.920/−0.685

comparison to the nonchiral analogues [M(η5-Pdl)2] and the classical metallocenes [M(η5-Cp)2].

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8

11

lithium pentadienyl complex [(tmeda)Li(1,5-(Me 3Si) 2-3(MeOC2H4)C5H4)].22 In [(tmeda)K(η5-2,4-Me2C5H5)] the U-shaped η5-2,4-dimethylpentadienyl anion is coordinated by two potassium cations to form a zigzag polymeric chain in the solid state.21 Unfortunately, the same crystallization strategy failed to provide single crystals of 3. Therefore, to increase the solubility of 3 in noncoordinating hydrocarbon solvents and also to derive structural information, the crown ether 18-crown-6 was added to a suspension of 3 in toluene and [K(18-crown-6)(η5-Pdl*)] (4) was isolated as orange single crystals (Table 1). An ORTEP diagram of 4 is shown in Figure 1, and selected bond distances and angles are given in the figure caption. The pentadienyl anion is coordinated to one K+ cation in a U-shaped η5-coordination mode, and the 18-crown-6 ether prevents the formation of a polymeric chain structure. The C−C distances (C1−C5) within the pentadienyl system exhibit a distinct short− long−long−short pattern, and the central carbon atom C3 has the shortest distance to the metal center: 3.0923(16) Å. The other distances are progressively longer: 3.1156(16) Å (C2), 3.1694(18) Å (C1), 3.2332(16) Å (C4), and 3.3063(18) Å (C5). These observations are consistent with a substantial contribution of the resonance structure (a) shown in Figure 2. The distance between the terminal carbon atoms C1 and C5 is 3.255 Å, and the metal−(ligand plane) separation is 2.758 Å.

RESULTS AND DISCUSSION

Ligand Synthesis. The natural product (1R)-(−)-myrtenal (1) was treated with the Wittig salt [Ph3PCH(CH3)2]I and NaNH2 to give the enantiomerically pure dimethylnopadiene (2).13 Deprotonation of 2 with potassium tert-pentoxide (KOtPe) and n-butyllithium (n-BuLi) yields the potassium salt K(Pdl*) (3) as an extremely pyrophoric yellow powder (Scheme 1). Alternatively, a traditional Schlosser base (KOtBu and n-BuLi) can also be used to deprotonate 2. However, the low solubility of KOtBu in aliphatic solvents can cause product contamination with unreacted KOtBu and this problem is overcome by the very soluble KOtPe derivative. In addition, salt metathesis reactions with 3 prepared from KOtPe and n-BuLi are cleaner and give increased yields. Compound 3 is soluble in coordinating solvents, such as tetrahydrofuran, in which it forms dark red solutions, but it is only sparingly soluble in aromatic hydrocarbons and insoluble in aliphatic hydrocarbons. It is interesting to note that only very few group 1 complexes with pentadienyl fragments have been structurally authenticated, such as [(tmeda)K(η5-2,4Me2C5H5)]21 and more recently the donor-functionalized 875


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Table 3. 13C{1H} NMR Data of 3, 4, 5 (Major), 5′ (Minor), and 8−11 at Ambient Temperature in C6D6

a

compd

C1

C2

C3

C4

C5

3a 4 5 (major) 5′ (minor) 8b 9 10 11

75.7 77.5 64.2 68.4 46.0 43.0 78.0 51.7

143.0 143.0 118.3 113.1 98.7 89.8 129.9 99.3

82.5 83.1 112.6 114.8 84.1 82.0 93.6 96.4

149.4 150.1 134.3 136.6 115.2 111.5 144.4 122.9

84.1 82.0 87.5 86.7 67.9 54.3 86.0 48.5

In THF-d8. bIn C7H8.

18-electron rule. Because of the straightforward synthesis, most studies on open metallocenes have focused on the 2,4dimethylpentadienyl ligand, 2,4-Me2C5H5.3,4,6,7,27−30 However, the preparation of other open metallocenes of the first-row transition metals with the sterically more demanding and chiral pentadienyl ligand 3 should also be feasible. Open Titanocene/Vanadocene/Chromocene. The reaction of [TiCl3(thf)3] or [VCl3(thf)3] with 3 equiv of 3 in a toluene/ THF solvent mixture gives deep green solutions (Scheme 2). Single crystals of the open titanocene [Ti(η5-Pdl*)2] (5) and open vanadocene [V(η5-Pdl*)2] (6) were grown from concentrated pentane solutions at −30 °C. The reduction of the metal(III) chloride to a divalent species is induced by 1 equiv of 3, which presumably results in the corresponding coupled bis(pentadiene), as in many other cases.30 In addition, we have found that the analogous open chromocene [Cr(η5-Pdl*)2] (7) can readily be prepared as a green crystalline compound starting from CrCl2 and 2 equiv of 3. These open metallocenes 5−7 are air and moisture sensitive but can be stored without degradation under a dry nitrogen atmosphere. The open sandwich structure of these molecules was confirmed by single-crystal X-ray diffraction studies. Complexes 5−7 are isostructural and crystallize in the orthorhombic space group P212121 with two independent molecules in the asymmetric unit (Table 1). The open metallocenes 5−7 have approximate (noncrystallographic) C2 symmetry; as a representative example, the molecular structure of 5 is shown in Figure 3 and selected bond distances and angles are given in Table 4 (see the Supporting Information for the molecular structures of 6 and 7, Figures S1 and S2). To the best of our knowledge, these complexes represent the first structurally characterized enantiomerically pure open metallocenes. To differentiate the mutual orientations of two pentadienyl moieties, the conformation angle χ is defined as the angle between the two planes (centroid (C1−C5)−C3−M) and (centroid (C14−C18)−C16−M) (Scheme 3). In 5 the

Figure 1. ORTEP diagram of 4 with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): K−O(18-C-6) = 2.8242(11)−3.0343(12), K−C1 = 3.1693(18), K−C2 = 3.1156(16), K−C3 = 3.0923(16), K−C4 = 3.2332(16), K−C5 = 3.3063(18), C1−C2 = 1.369(3), C2−C3 = 1.423(2), C3−C4 = 1.418(2), C4−C5 = 1.371(2); C1−C2−C3 = 128.04(17), C2−C3− C4 = 129.62(16), C3−C4−C5 = 131.00(15).

Figure 2. Resonance structures of a metal-bound pentadienyl ligand.

The 1H and 13C{1H} NMR spectra of 3 and 4 were recorded in THF-d8 and C6D6, respectively (see Tables 2 and 3). The crown ether in 4 exhibits a single resonance at δ 3.23 and 70.0 in the 1H and 13C{1H} NMR spectra, respectively. The terminal hydrogen atom H5 is observed as a multiplet at δ 4.39−4.44, whereas those for the terminal carbon atom C1 and the central carbon atom C3 are shifted further downfield (H1a, 4.03 ppm; H1b, 3.81−3.85 ppm; H3, 3.74 ppm). This observation is consistent with the resonance structure shown in Figure 2a. No trace of the other possible diastereomer, in which the metal coordinates from the sterically more hindered site, was detected by NMR spectroscopy. This is accord with the coordination chemistry developed for the dimethylnopadiene ligand,23 since in most cases the neutral ligand and its functionalized derivatives react with complete diastereoselectivity to produce only a single transition-metal complex. Paquette and co-workers reported a similar π-facial selectivity with respect to Diels−Alder cycloadditions and metallocene formation of related cyclopentadienyl ligands.24−26 Preparation of [M(η5-Pdl*)2] Complexes. In contrast to their Cp analogues, open metallocenes of the first-row elements can exhibit enhanced stability even when they do not obey the

Table 2. 1H NMR Data of 3, 4, 5 (Major), 5′ (Minor), and 8−11 at Ambient Temperature in C6D6

a

compd

H1a (endo)

H1b (exo)

H3

H5

3a 4 5 (major) 5′ (minor) 8b 9 10 11

2.76, “d”, 1 H, J = 2.76 Hz 4.03, “d”, 1 H, J = 3.26 Hz −1.35, “d”, 2 H, J = 5.27 Hz 1.81−1.80, m, 2 H −2.07, br s, 2 H −1.21, “d”, 1 H, J = 3.52 Hz 1.87−1.82, m, 1 H 1.86−1.83, m, 1 H

3.27−3.22, m, 1 H 3.85−3.81, m, 1 H 0.56, dd, 2 H, J = 5.15 Hz, J = 2.64 Hz 3.50, dd, 2 H, J = 5.64 Hz, J = 2.38 Hz 1.17−0.99, m, 2 H 3.05, dd, 1 H, 2J = 3.60 Hz, 4J = 1.40 Hz 3.81, s, 1 H 3.62, “t”, 1 H, J = 1.64 Hz

3.11, “d”, 1 H, J = 2.01 Hz 3.74, “d”, 1 H, J = 2.01 Hz 6.32, “d”, 2 H, J = 2.51 Hz 6.58, “d”, 2 H J = 2.26 Hz 4.09, br s, 2 H 5.44, s, 1 H 3.84, m, 1 H 5.42−5.39, m, 1 H

3.78−3.73, m, 1 H 4.44−4.39, m, 1 H 1.91, “d”, 2 H, J = 3.76 Hz −1.28, “d”, 2 H, J = 5.77 Hz 2.14−1.98, m, 2 H 0.32, “d”, 1 H, J = 7.28 Hz) 2.78, “d”, 1 H, J = 4.9 Hz 1.73−1.66, m, 1 H

In THF-d8. bIn C7H8. 876


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Scheme 2

Figure 3. ORTEP diagrams of 5 (left) and 8 (right) with thermal displacement parameters drawn at 50% probability. Only one of the two independent molecules in the asymmetric unit is shown for 5.

Table 4. Selected Bond Distances (Å) and Angles (deg) for 5−8 [Ti(η5-Pdl*)2] (5) χ M−C(1/14) M−C(2/15) M−C(3/16) M−C(4/17) M−C(5/18) M−C(av) M−Pdl*planea C(1/14)−C(5/18)b

84.7 2.2264(18)/2.2246(18) 2.2698(17)/2.2809(18) 2.2912(17)/2.3019(18) 2.3050(17)/2.3000(17) 2.2370(17)/2.2894(18) 2.273 ± 0.032 1.585/1.542 3.166/3.208

χ M′−C′(1/14) M′−C′(2/15) M′−C′(3/16) M′−C′(4/17) M′−C′(5/18) M′−C′(av) M−Pdl*planea C′(1/14)−C′(5/18)b

86.1 2.2117(18)/2.2182(17) 2.2762(17)/2.2610(17) 2.2872(18)/2.2722(18) 2.2790(17)/2.2836(16) 2.2684(18)/2.2801(18) 2.264 ± 0.027 1.560/1.579 3.140/3.109

[V(η5-Pdl*)2] (6) Molecule 1 82.0 2.1803(11)/2.1809(11) 2.2434(11)/2.2462(11) 2.2604(11)/2.2583(11) 2.2672(11)/2.2537(10) 2.2027(11)/2.2485(11) 2.234 ± 0.032 1.5046/1.5401 3.123/3.095 Molecule 2c 87.4 2.1694(11)/2.1820(11) 2.2487(11)/2.2290(10) 2.2517(11))/2.2338(11) 2.2324(10)/2.2401(10) 2.2298(11)/2.2426(11) 2.226 ± 0.028 1.5177/1.5427 3.102/3.064

[Cr(η5-Pdl*)2] (7)

[Fe(η5-Pdl*)2] (8)

84.2 2.1928(12)/2.1968(12) 2.2124(11)/2.2004(12) 2.1997(12)/2.1952(12) 2.2115(11)/2.2059(11) 2.2144(12)/2.2470(11) 2.208 ± 0.016 1.538/1.553 3.0227/3.0207

72.5 2.134(2)/2.134(2) 2.0688(18)/2.0642(18) 2.0698(17)/2.0702(17) 2.1162(16)/2.1155(16) 2.1961(17)/2.1957(17) 2.117 ± 0.043 1.494/1.492 2.847/2.853

89.0 2.1847(11)/2.1929(11) 2.2036(12)/2.1907(11) 2.1917(11)/2.1726(11) 2.1862(11)/2.1910(11) 2.2305(12)/2.2466(11) 2.199 ± 0.023 1.542/1.556 3.0012/2.9850

a M−Pdl*plane is defined as the distance between the metal atom and the plane formed by C1−C5 and C14−C18, respectively. bC(1/14)−C(5/18) describes the distance of the open edges of the Pdl* ligand, i.e. the distances between C(1) and C(5) and C(14) and C(18), respectively. cThe prime (′) denotes the second independent molecule in the asymmetric units.

indicates a rather flat potential energy surface with respect to the conformation angle χ. The carbon atoms of the pentadienyl fragments (C1−C5/ C1′−C5′ and C14−C18/C14′−C18′) lie in an almost perfect plane, but steric interactions between the two pentadienyl ligands

orientation of the pentadienyl fragments is approximately staggered with χ = 84.7 and 86.1° for both independent molecules, respectively. For 6 and 7 the conformation angles are also very similar ([V(η5-Pdl*)2]/[V′(η5-Pdl*)2], χ = 82.0/87.4°; [Cr(η5-Pdl*)2]/[Cr′(η5-Pdl*)2], χ = 84.2/89.0°). Overall, this 877


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Scheme 3

the presence of another diastereomer in which the titanium is coordinated to the more sterically hindered site of the pentadienyl ligand (i.e., syn to the CMe2 bridge). The terminal hydrogen atom H5 (major) is observed as a pseudodoublet at δ 1.91, whereas the signal for the terminal hydrogen atom H5′ (minor) is shifted further upfield (δ −1.28). The protons attached to the terminal carbon atom C1 have also very different chemical shifts in both isomers δ −1.35 (H1a-major) and 0.56 (H1b-major), in comparison to δ 1.81 (H1a′ minor) and 3.50 (H1b′ minor). VT NMR studies were carried out on 5 to investigate if these two isomers interconvert on the NMR time scale. However, no significant line broadening of the 1H NMR resonances was observed when the sample was heated to 90 °C, but exchange peaks between these isomers can be identified in an EXSY NMR experiment (Figure 4). This suggests that these two species are

are responsible for a pronounced tilting of the two ligand planes with respect to each other. The tilt angles α for the two independent molecules of 5 in the asymmetric unit are 18.7 and 13.4°, respectively. However, for 6 and 7 the α values are significantly smaller ([V(η5-Pdl*)2]/[V′(η5-Pdl*)2], α = 14.7/ 10.6°; [Cr(η5-Pdl*)2]/[Cr′(η5-Pdl*)2], α = 15.4°/11.3°). In addition, the methyl (β-Me) groups at the C2/C2′ and C15/ C15′ positions are rotated slightly out of the ligand plane toward the metal atom to realize a better metal−ligand overlap ([Ti(η5-Pdl*)2]/[Ti′(η5-Pdl*)2], β-Me-2 = 8.8/8.4°; [V(η5Pdl*)2]/[V′(η5-Pdl*)2], β-Me-2 = 8.9/5.0°; [Cr(η5-Pdl*)2]/ [Cr′(η5-Pdl*)2], β-Me-2 = 8.3/6.8°; [Ti(η5-Pdl*)2]/[Ti′(η5Pdl*)2], β-Me-15 = 11.2/7.2°; [V(η5-Pdl*)2]/[V′(η5-Pdl*)2], β-Me-15 = 7.2/6.5°; [Cr(η5-Pdl*)2]/[Cr′(η5-Pdl*)2], β-Me-15 = 9.4/6.8°). Furthermore, the distances between the terminal carbon atoms C1−C5/C1′−C5′ and C14−C18/C14′−C18′ are significantly longer than the ca. 1.40 Å edge length of a cyclopentadienyl ligand. In addition, the average separation between the terminal carbon atoms decreases smoothly from 3.156 Å for [Ti(η5-Pdl*)2] to 3.096 Å for [V(η5-Pdl*)2] and 3.007 Å for [Cr(η5-Pdl*)2]. This difference can be explained by the smaller atomic radii of the last two.31 However, as a direct geometric consequence the pentadienyl planes C1−C5/C1′−C5′ and C14−C18/C14′−C18′ must approach the metal center more closely in order to realize comparable M−C bond distances as in classic metallocenes. The average Ti−C distances are 2.273(32)/ 2.264(27) Å and are longer than in 6 (2.234(33)/2.226(28) Å) and 7 (2.208(16)/2.199(23) Å). It is instructive to compare the metal−ligand plane separations in these open metallocenes to those of the corresponding metallocenes. These distances are 1.522/1.530 Å for 6 and 1.546/1.549 Å for 7 in comparison to 1.928(6) and 1.798(4) Å for [V(η5-C5H5)2] and [Cr(η5-C5H5)2], respectively. [Cr(η5-C5H5)2] and 7 have two unpaired electrons (S = 1). The difference between the open vanadocene and [V(η5-C5H5)2] is quite remarkable but can be rationalized by the different spin states of these molecules. The low-spin configuration of 6, μeff(300 K) = 2.1 μB, results in stronger metal− pentadienyl bonds (see the Supporting Information for details, Figure S3). This is also reflected in substantially shorter average V−C distances in 6 in comparison to those in [V(η5-C5H5)2] (2.280(5) Å).32a However, shorter V−C distances for pentadienyl vs cyclopentadienyl are also observed in the half-open vanadocene [(η5-C5H7)V(η5-C5H5)(L)] (L = CO, PEt3),32b which suggests that the bonding between V and pentadienyl is stronger (independent of spin states). The larger size and lower nuclear charges of the early transition metals seem especially important for generating stronger interactions with these metals. The 1H and 13C{1H} NMR spectra of the diamagnetic open titanocene 5 are interesting (see Tables 2 and 3), since two different C2-symmetric species, 5 (major) and 5′ (minor), are observed in a 10:1 ratio in solution. These species are also present in the crude reaction mixture. NOESY NMR experiments rule out

Figure 4. 1H EXSY NMR spectrum of 5 recorded at 90 °C in C7D8. The prime (′) denotes resonances corresponding to the minor isomer 5′.

conformational isomers and that there is a significant barrier for their interconversion. In addition, the ratio between 5 and 5′ is temperature dependent and the minor isomer 5′ is favored when the temperature is increased. The thermodynamic parameters of this equilibrium (Keq = [5]/[5′]) were derived from the ln Keq vs T−1 plot (see the Supporting Information for details): ΔH° = −1.0(1) kcal/mol and ΔS° = 1.1(2) eu. The entropy value ΔS° is close to zero and therefore consistent with an intramolecular process. Unfortunately, attempts to obtain structural information on the minor isomer by X-ray diffraction have so far been unsuccessful. 878


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All attempts to coordinate PMe3 or CO to the open metallocenes 5−7 failed, and only unreacted starting material was recovered. We attribute this to the significant steric hindrance imposed by the pentadienyl ligand system and hence the effective shielding of the metal atoms. Open Ferrocene. The open ferrocene [Fe(η5-Pdl*)2] (8) suffers from a significantly reduced thermal stability, and metallic iron is also formed during the synthesis of 8 starting from [FeBr2(dme)] (dme = dimethoxyethane) and 2 equiv of 3 in THF. Hence, crystals of 8 were only obtained in low yield from a saturated pentane solution. It is noteworthy that crystallized 8 decomposes at ambient temperature in solution and that, even in freshly prepared solutions, broadened NMR resonances are observed because of the presence of iron nanoparticles. In view of the synthesis of [Fe(η1-C5H5P)5] from [Fe(η5-2,4-Me2C5H5)2]33 and [Fe(PF3)5] from [Fe(η5-C5H7)2],34 the open ferrocene 8 might also serve as a suitable precursor for the preparation of low-valent iron complexes or nanoparticles under mild conditions.35 Bis(pentadienyl)iron ([Fe(η5-C5H7)2]) and bis(3-methylpentadienyl)iron ([Fe(η5-3-C6H9)2]) also form metallic iron particles, but at slower rates.29 The 1H NMR spectrum of 8 displays the terminal hydrogen atom H5 as a multiplet at δ 1.98−2.14. The hydrogen atom H3 is shifted downfield (δ 4.09), whereas the terminal hydrogen atoms at C1 are shifted further upfield (H1a, δ −2.07; H1b, δ 0.99−1.17) (see Tables 2 and 3). In contrast to the other chiral open metallocenes 5−7, 8 crystallizes in a different chiral space group (monoclinic, P21) with only one molecule in the asymmetric unit (Table 1 and Figure 3), and selected bond distances and angles are given in Table 4. The conformation angle χ is, at 72.46°, very different from those observed for 5−7. For comparison a nearly gauche-eclipsed conformation is adopted in [Fe(η5-2,4-Me2C5H5)2],29 [Fe(η5-1Me3Si-3-CH3C5H5)2],36 and [Fe(η5-c-C7H9)2]37 However, the average Fe−C distance of 2.117(43) Å is significantly longer than that in [Fe(η5-C5H5)2] (2.064(3) Å)38 and in the open ferrocene [Fe(η5-2,4-Me2C5H5)2] (2.089(3) Å),29 probably because of the steric strain imposed by the bulky pentadienyl ligand, Pdl*. For the same reasons as discussed above, a very close approach of the ligand plane to the metal is observed (1.493 Å), resulting in an increased interligand repulsion in comparison to that in the corresponding metallocenes. The van der Waals radii for carbon atoms and methyl groups are 1.7 and 2.0 Å, respectively,39 and therefore a series of nonbonded C...C contacts (C1−C17 = 3.093 Å, C1−C16 = 3.256 Å, C2−C16 = 3.199 Å, C2−C15 = 3.24 Å, C3−C15 = 3.181 Å, C3−C14 = 3.244 Å, C4−C14 = 3.079 Å, C5−C18 = 3.098 Å, C8−C14 = 3.173 Å, C1−C21 = 3.169 Å) are found in 8, which might explain the thermal instability and the formation of iron metal. Steric repulsion has also been invoked for the formation of the stable cyclopentadienyl radical [C5(CHMe2)5]• from the reaction of FeCl2 with [Li(OEt2)][C5(CHMe2)5].40 Half-Open Ferrocene. Half-open metallocenes offer the possibility of direct comparison between conventional Cp ligands and their open congeners within one molecule, thereby revealing the unique properties of pentadienyl ligands. However, the synthesis of half-open ferrocenes is usually hampered by the fact that “CpFeX” complexes are thermodynamically unstable; ligand redistribution to Cp2Fe and FeX2 takes place, and a mixture of compounds is usually obtained. In contrast, sterically demanding cyclopentadienyl ligands kinetically stabilize “CpFeX” complexes and facilitate the exploration of their reaction chemistry.41−49 Our ligand of choice is 1,2,4-(Me3C)3C5H2 (Cp′), which stabilizes unusual and low-coordinate molecules.46−54 To compare the features of the chiral pentadienyl ligand (Pdl*)

Scheme 4

with those of Cp′, the half-open ferrocene [(η5-Cp′)Fe(η5-Pdl*)] (9) was prepared from [(η5-Cp′)FeI]247 and 3 in THF (Scheme 4). Despite the presence of two bulky π ligands, 9 exhibits an enhanced thermal stability in comparison to the open ferrocene 8 and was isolated in good yield. The molecular structure of 9 is shown in Figure 5, and selected bond distances and angles are given in the figure caption. The carbon atoms of the pentadienyl (C1−C5) and the Cp′ (C14− C18) fragments form almost perfect planes. To reduce the steric interactions of the pentadienyl ligand with the sterically demanding CMe3 groups, the two planes are tilted with respect to each other by 7.3°. As shown for 8, the methyl group at the C2 position is displaced toward the iron center, but the tilt angle (6.5°) is less pronounced than in 8. In contrast, the CMe3 groups point away from the iron atom (by 12.7, 4.0, and 11.2°) to minimize steric repulsions. The average Fe−C(Pdl*) bond distance is 2.121(72) Å, longer than the Fe−C(Cp′) bond length at 2.107(27) Å but quite similar to the 2.117(43) Å found in 8. However, because of the unique properties of the pentadienyl ligand, the metal−(ligand plane) separation for the pentadienyl system (1.506 Å) is significantly shorter than for the cyclopentadienyl system (1.718 Å), consistent with previous results.12,37 In contrast to 8, 1H and 13C{1H} NMR spectra recorded in C6D6 solution are resolved (see Tables 2 and 3), and the terminal hydrogen atom H5 is observed upfield at δ 0.32, whereas the resonances for H1a and H1b are shifted to δ −1.21 and 3.05, respectively. Half-Open Trozircene. It was recently shown that [(η7C7H7)Zr(tmeda)Cl] is an ideal complex fragment for the incorporation of various monoanionic ligands, including achiral 879


Organometallics

Article

The Zr−C distances are uniform and range between 2.335(11) and 2.369(11) Å. In contrast, the Zr−C distances of the pentadienyl system are different, with the shortest distance of 2.429(10) Å being found between C10 and Zr, whereas the others become progressively longer. This short−longer−longest pattern is characteristic of pentadienyl ligands coordinated to a metal in a high oxidation state, and it is also reflected in a typical short− long−long−short pattern of the Pdl* C−C bond distances. The (η7-C7H7)Zr fragment provides an excellent platform to assess the size of η5-bound monoanionic ligands in a realistic manner, and cone angle measurements on a series of [(η7C7H7)Zr(η5-L)] (L= Cp, Ind, pyrrolyl (Pyr), imidazolyl (Im)) complexes were undertaken.61,65 For this purpose the angle θ, which describes the size of the ligand in the xy dimension, was defined.61 Interestingly, Pdl* is significantly larger than 2,4Me2C5H5 with θ = 134 vs 113°, and it is also slightly larger than Cp′ ligand (θ = 133°). Complex 10 and the other pentadienyl complexes are volatile enough to obtain EI mass spectra and, in addition to the molecular ion, species resulting from H2 loss were also observed, suggesting a pentadienyl-to-cyclopentadienyl conversion (see the Experimental Section for details). This is consistent with previous experiments describing such a conversion under highenergy conditions such as mass spectroscopy and thermolysis.66−70 However, [(η7-C7H7)Zr(η5-C5H7)] converts to [(η7-C7H7)Zr(η5C5H5)] and H2 under relatively mild conditions on sublimation or on heating in solution.55 Unfortunately, no pentadienyl-tocyclopentadienyl conversion was observed on heating of 10 in the solid state at 120 °C for several weeks followed by sublimation. Iridium(I) Pentadienyl Complex. Attempts to prepare open cobaltocenes [Co(η5-Pdl)2] have been unsuccessful, and instead reduction to Co(I) has been observed.71 However, cationic pentadienyl Co(III) complexes can be stabilized by a (η5-C5H5)Co or (η5-C5Me5)Co fragment.72,73 For the heavier cobalt congener iridium, iridium(I) heteropentadienyl complexes74 such as [(η4-COD)Ir(μ2-1-2,5-η-CH2CHCHCHSO)]2 and cationic iridium(III) pentadienyl complexes75 such as [(η5C5H5)Ir(η5-C5H5Me2-2,4)][BF4] have only recently been reported. Complex 3 was treated with [(η4-COD)Ir(μ-Cl)]2 in THF, forming the heteroleptic complex [(η4-COD)Ir(η5-Pdl*)] (11). Single crystals were grown from concentrated pentane solution at −30 °C (Scheme 4). Complex 11 crystallizes in space group P21 with two independent, but similar, molecules in the asymmetric unit. Figure 7 shows the molecular structure of one of these independent molecules, and selected bond distances and angles are given in the figure caption. No COD replacement was observed on addition of PMe3 or tris(2,4,6-trimethoxyphenyl)-phosphine to 11. However, preliminary experiments suggest that the COD moiety can be replaced by CO, and further experiments regarding the reaction chemistry are ongoing and will be reported in due course.

Figure 5. ORTEP diagram of 9 with thermal displacement parameters drawn at the 50% probability level. Selected bond distances (Å) and angles (deg): Pdl* ligand, Fe−C(1) = 2.0961(15), Fe−C(2) = 2.0602(15), Fe− C(3) = 2.0753(15), Fe−C(4) = 2.1307(14), Fe−C(5) = 2.2410(16), Fe− C(av) = 2.121 ± 0.072, Fe−plane(C(1)−C(5)) = 1.506; Cp′ ligand, Fe− C(14) = 2.1375(15), Fe−C(15) = 2.1236(15), Fe−C(16) = 2.0863(15), Fe−C(17) = 2.1132(14), Fe−C(18) = 2.0715(16), Fe−C(av) = 2.106 ± 0.027, Fe−plane(C(14)−C(18)) = 1.718; α(Pdl*−Cp′ planes) = 7.3.

pentadienyl ligands, into the cycloheptatrienyl (Cht) coordination sphere.55−65 With the Pdl* ligand in hand, we set out to extend this series to chiral derivatives. The potassium salt 3 reacts cleanly with [Zr(η7-C7H7)(Cl)(tmeda)] in THF to give [(η7C7H7)Zr(η5-Pdl*)] (10) as a wine red solid in moderate yield after sublimation at 135 °C (0.1 mbar) (Scheme 4). Single crystals were grown from concentrated pentane solutions at −30 °C. The molecular structure of 10 is shown in Figure 6, and

Figure 6. ORTEP diagram of 10 with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Pdl* ligand, Zr−C(8) = 2.5994(11), Zr−C(9) = 2.5131(10), Zr−C(10) = 2.4291(10), Zr−C(11) = 2.5513(10), Zr−C(12) = 2.6464(11), Zr−C(av) = 2.548 ± 0.083, Zr−plane(C(1)−C(5)) = 2.019; Cht ligand, Zr−C(1) = 2.3682(12), Zr−C(2) = 2.3651(12), Zr− C(3) = 2.3411(12), Zr−C(4) = 2.3353(11), Zr−C(5) = 2.3571(13), Zr−C(6) = 2.3689(11), Zr−C(7) = 2.3361(12), Zr−C(av) = 2.353 ± 0.015, Zr−plane(C(1)−C(7)) = 1.690; α(Pdl*−Cht planes) = 21.6.

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CONCLUSIONS A series of open metallocenes [M(η5-Pdl*)2] (M = Ti, V, Cr, Fe) and mono(pentadienyl) complexes [(η5-Cp′)Fe(η5-Pdl*)] (Cp′ = 1,2,4-(Me3C)3C5H2), [(η7-C7H7)Zr(η5-Pdl*)], and [(η4-COD)Ir(η5-Pdl*)] can be prepared with the enantiomerically pure dimethylnopadienyl ligand. It is noteworthy that, in all of these complexes, the Pdl* ligand exhibits excellent face selectivity upon metal coordination, since it coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Because of the severe steric demand of Pdl* in

selected bond distances and angles are given in the figure caption. As was found for the half-open ferrocene, the Pdl* ligand exclusively coordinates from the sterically less hindered site to avoid repulsive interactions with the seven-membered Cht ring. The carbon atoms C1−C7 of the Cht ligand form an almost perfect plane and coordinate in a η7 fashion to the zirconium atom. 880


Organometallics

Article

Synthesis of Dimethylnopadiene (2).

Compound 2 had been previously reported,13 but we utilized a slight variation of the reported procedure for its isolation. A suspension of [Ph3PCH(CH3)2]I (24.5 g, 56.7 mmol) and NaNH2 (2.21 g, 56.7 mmol) in THF (250 mL) was stirred at ambient temperature. The suspension turned brown after a few minutes, and stirring was continued for 4 h until no further NH3 evolution was observed. (1R)-(−)-Myrtenal (1; 8.51 g, 56.7 mmol) was added, and the solution was stirred for 12 h at ambient temperature. The orange solution was poured into a diethyl ether/water mixture (100 mL/100 mL). The ether phase was separated, and the water phase was extracted with three portions of diethyl ether (30 mL). The collected organic phases were washed with a 40% aqueous NaHSO3 solution (20 mL) and dried over NaHCO3, yielding a pale yellow solution. After removal of the solvent, pentane (250 mL) was added to precipitate Ph3PO. Filtration, removal of the solvent, and column chromatography (silica) (pentane, Rf = 0.860) yielded a colorless oil. Yield: 8.16 g (46.3 mmol, 82%). Bp: 84−86 °C/7.9 mbar. Anal. Calcd for C13H20: C, 88.56; H, 11.43. Found: C, 86.01; H, 10.88. The EI mass spectrum showed a molecular ion at m/z 176 amu. GC: 22.64 min. 1H NMR (400 MHz, CDCl3, 298 K): δ 5.57−5.53 (m, 1 H, H3), 5.38−5.34 (m, 1 H, H5), 2.42−2.37 (m, 1 H, H8a), 2.37−2.26 (m, 2 H, H6) 2.19 (dt, 1 H, H9, J = 5.65 Hz, J = 1.51 Hz), 2.12−2.06 (m, 1 H, H7), 1.78 (br s, 3 H, H1), 1.76 (br s, 3 H, H13), 1.23 (s, 3 H, H12), 1.21 (d, 1 H, H8b, J = 8.53 Hz), 0.89 (s, 3 H, C-11) ppm. 13C{1H} NMR (101 MHz, CDCl3, 298 K): δ 145.7 (C, C4), 133.0 (C, C2), 126.4 (CH, C3), 120.7 (CH, C5), 47.0 (CH, C9), 40.8 (CH, C7), 37.9 (C, C10), 32.0 (CH2, C6) 31.8 (CH2, C8), 27.0 (CH3, C13), 26.6 (CH3, C12), 21.4 (CH3, C11), 20.1 (CH3, C1) ppm. The EI mass spectrum showed a molecular ion at m/z 177 amu. The parent ion isotopic cluster was simulated (calcd %, obsd %): 176 (100, 100), 177 (14, 14). Synthesis of K(pdl*) (3).

Figure 7. ORTEP diagram of 11 with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg) of molecule 1: Ir−C1 = 2.266(3), Ir−C2 = 2.249(3), Ir−C3 = 2.302(3), Ir−C4 = 2.285(3), Ir−C5 = 2.193(3), Ir−C(av) = 2.259 ± 0.042, Ir−plane(C(1)−C(5)) = 1.634, C1−C2 = 1.369(3), C2−C3 = 1.423(2), C3−C4 = 1.418(2), C4−C5 = 1.371(2); C1−C2− C3 = 128.04(17), C2−C3−C4 = 129.62(16), C3−C4−C5 = 131.00(15).

combination with the relatively small Fe(II) ion, the open ferrocene [Fe(η5-Pdl*)] is thermally unstable and decomposes to iron metal in solution. The synthesis of a myrtenal-derived ligand library and its application in homogeneous catalysis are ongoing and will be reported in due course.

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EXPERIMENTAL SECTION

General Considerations. All experiments were carried out under an atmosphere of purified nitrogen, either in a Schlenk apparatus or in a glovebox. The solvents were dried and deoxygenated by distillation under a nitrogen atmosphere from sodium benzophenone ketyl (tetrahydrofuran) and by a MBraun GmbH solvent purification system (toluene, pentane). The following starting materials were prepared according to the literature: CrCl2,76 [FeBr2(dme)],77 [(η5-Cp′)FeI]2,47 [Ir(COD)Cl]2,78 KOtPe,79 [TiCl3(thf)3],80 [VCl3(thf)3],81 and [(η5C7H7)Zr(tmeda)Cl].55 Other commercial reagents such as n-BuLi (Acros), 18-crown-6 ether (Acros), [Ph3PCH(CH3)2]I (Sigma Aldrich), (1R)-(−)-myrtenal (1) (Sigma Aldrich), and NaNH 2 (Acros) were used as received without further purification. NMR spectra were recorded on a Bruker DRX 400 spectrometer at 400 MHz (1H) or 101 MHz (13C). All chemical shifts are reported in δ units with reference to the residual protons of the deuterated solvents, which are internal standards, for proton and carbon chemical shifts. Gas chromatography was performed with Hewlett-Packard (5890 Serie II), using a 35 m × 0.25 mm glas capillary column coated with Cyclodex-B. Magnetic susceptibility data were recorded from 5 to 300 K on a Quantum Design MPMS XL7 SQUID magnetometer.82 Elemental analyses were performed on a vario MICRO cube elemental analyzer (MS Finnigan MAT 8400-MSS I and Finnigan MAT 4515). X-ray Diffraction Studies. Data were recorded at 100 K on Oxford Diffraction diffractometers using monochromated Mo Kα or mirrorfocused Cu Kα radiation (Table 1). The structures were refined anisotropically using the SHELXL-97 program.83 Hydrogen atoms at C1, C3, and C5 of the pentadienyl ligands were located in difference syntheses and refined isotropically, in some cases using distance restraints. For 9 the hydrogens of the Cp′ ring and for 10 the hydrogens of the C7H7 ring were treated in the same way (for further details, see the Supporting Information). Other H atoms were included using rigid methyl groups or a riding model. The absolute configuration was confirmed by the Flack parameter.

A solution of potassium tert-pentoxide (4.08 g; 32.3 mmol) in pentane (250 mL) was prepared. At −78 °C dimethylnopadiene (2; 6.00 g, 34.0 mmol) was added to form a deep red suspension, to which n-BuLi (1.6 M in hexane, 22.3 mL, 35.7 mmol) was added. The reaction mixture was warmed to room temperature and stirred for 12 h at ambient temperature. During this time the color of the mixture changed slowly to yellow. After filtration, the yellow precipitate was washed with pentane (3 × 30 mL) and dried under high vacuum. Yield: 7.23 g (33.72 mmol, 90%). Compound 3 was a highly pyrophoric yellow solid. Despite several attempts, no reliable elemental analysis was obtained, but a representative 1H NMR spectrum is shown in the Supporting Information (Figure S5). 1H NMR (400 MHz, THF-d8, ambient): δ 3.78−3.73 (m, 1 H, H5), 3.27−3.22 (m, 1 H, H1b), 3.11 (“d”, 1 H, H3, J = 2.01 Hz), 3.08 (“d”, 1 H, H1a, J = 2.76 Hz), 2.58 (dt, 1 H, H6b, J = 15.81 Hz, J = 3.01 Hz), 2.46 (dt, 1 H, H6a, J = 15.73 Hz, J = 2.82 Hz), 2.26 (dt, 1 H, H8b, J = 8.20 Hz, J = 5.65 Hz), 2.07−1.99 (m, 1 H, H7), 1.78 −1.74 (m, 1 H, H9), 1.73 (s, 3 H, H13), 1.28 (d, 1 H, H8a, J = 8.28 Hz), 1.21 (s, 3 H, H12), 0.91 (s, 3 H, H11) ppm. 13C{1H} NMR (101 MHz, THF-d8, ambient): δ 149.4 (C, C4), 143.0 (C, C2), 84.1 (CH, C5), 82.5 (CH, C3), 75.7 (CH2, C1), 53.9 (CH, C9), 42.5 881


Organometallics

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green crystals (82 mg, 0.20 mmol, 43%). Mp: 178.4−178.5 °C. Anal. Calcd for C26H38Cr: C, 77.57; H, 9.51. Found: C, 77.53; H, 9.51. The EI mass spectrum (70 eV) showed a molecular ion at m/z 402 amu with the following isotopic cluster distribution: 396 (1), 397 (1), 398 (4), 399 (1), 400 (13), 401 (5), 402 (100), 403 (41), 404 (11). Simulated distributions (in %): for C26H38Cr, 400 (5), 401 (2), 402 (100), 403 (39), 404 (10); for C26H36Cr, 398 (5), 399 (2), 400 (100), 401 (39), 402 (10); for C26H34Cr, 396 (5), 397 (2), 398 (100), 399 (39), 400 (10). Synthesis of [Fe(η5-Pdl*)2] (8). A solution of [FeBr2(dme)] (143 mg, 0.47 mmol) and 3 (200 mg, 0.93 mmol) in toluene (15 mL) and THF (1 mL) was stirred for 4 h at ambient temperature and evaporated to dryness. The brown solid residue was extracted with pentane (3 mL). The extract was concentrated and cooled to −30 °C to give brown crystals (54.2 mg, 0.13 mmol, 28%). Mp: 120 °C. Anal. Calcd for C26H38Fe: C, 76.84; H, 9.42. Found: C, 76.63; H, 9.61. 1H NMR (400 MHz, C7D8, 298 K): δ 4.09 (br s, 2 H, H3), 2.92 (“d”, 2 H, H6, J = 15.08 Hz), 2.54 (br s, 4 H, H6 and H8), 2.26 (br s, 2 H, H9), 2.19 (“s”, 2 H, H7), 2.14−1.98 (m, 4 H, H5 and H8), 1.91 (br s, 6 H, H13), 1.44 (br s, 6 H, H12), 1.17−0.99 (m, 8 H, H1b and H11), −2.07 (br s, 2 H, H1a) ppm. 13C{1H} NMR (101 MHz, C7D8, 298 K): δ 115.2 (2 C, C4), 98.7 (2 C, C2), 84.1 (2 CH, C3), 67.9 (2 CH, C5), 51.7 (2 CH, C9), 46.0 (2 CH2, C1), 42.2 (2 CH, C7), 38.7 (2 C, C10), 36.2 (2 CH2, C8), 32.7 (2 CH2, C6), 26.7 (2 CH3, C12), 25.9 (2 CH3, C13), 22.1 (2 CH3, C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 406 amu with the following isotopic cluster distribution: 402 (7), 403 (1), 404 (20), 405 (3), 406 (100), 407 (25), 408 (3). Simulated distributions (in %): for C26H38Fe, 404 (6), 405 (2), 406 (100), 407 (30), 408 (4); for C26H36Fe, 402 (6), 403 (2), 404 (100), 405 (30), 406 (4); for C26H34Fe, 400 (6), 401 (2), 402 (100), 403 (30), 404 (4). Synthesis of [(η5-Cp′)Fe(η5-Pdl*)] (9).

(CH, C7), 38.8 (C, C10), 32.99 (CH2, C6), 32.97 (CH2, C8), 28.2 (CH3, C13), 27.3 (CH3, C12), 21.8 (CH3, C11) ppm. Synthesis of (18-Crown-6)potassium Dimethylnopadienide (4). A saturated solution of 18-crown-6 (123 mg, 0.47 mmol) in toluene (0.5 mL) was added to 3 (100 mg, 0.47 mmol). A few drops of pentane were carefully layered onto the toluene solution, and diffusive mixing at −30 °C overnight resulted in 48 mg (0.10 mmol, 22%) of red/orange crystals. Anal. Calcd for C25H43O6K: C, 62.73; H, 9.05. Found: C, 62.77; H, 8.82. 1H NMR (400 MHz, C6D6, 298 K): δ 4.44−4.39 (m, 1 H, H5), 4.03 (“d”, 1 H, H1a, J = 3.26 Hz), 3.85−3.81 (m, 1 H, H1b), 3.74 (“d”, 1 H, H3, J = 2.01 Hz), 3.23 (s, 24 H, 18-crown-6), 3.15−3.01 (m, 2 H, H6), 2.55−2.46 (m, 2 H, H7 and H8a), 2.36 (br dt, 1 H, H9), 2.26 (s, 3 H, H13), 1.89−1.82 (m, 1 H, H8b), 1.63 (s, 3 H, H12), 1.54 (s, 3 H, H11) ppm. 13C{1H} NMR (101 MHz, C6D6, ambient): δ 150.1 (C, C4), 143.0 (C, C2), 83.1 (CH, C3), 82.0 (CH, C5), 77.5 (CH2, C1), 70.0 (CH2, 18-crown-6), 54.2 (CH, C9), 42.9 (CH, C7), 40.0 (C, C10), 33.9 (CH2, C6), 31.4 (CH2, C8), 29.6 (CH3, C13), 28.0 (CH3, C12), 22.1 (CH3, C11) ppm. Synthesis of [Ti(η5-Pdl*)2] (5). A solution of [TiCl3(thf)3] (115 mg, 0.31 mmol) and 3 (200 mg, 0.93 mmol) in toluene (15 mL) and THF (1 mL) was stirred for 4 h at ambient temperature and evaporated to dryness. The solid residue was extracted with pentane (3 mL), and the filtered extract was concentrated and cooled to −30 °C to give green crystals (75 mg, 0.189 mmol, 61%). Anal. Calcd for C26H38Ti: C, 78.37; H, 9.61. Found: C, 77.89; H, 9.27. The NMR spectra showed two isomers 5 and 5′ in the ratio 10:1. 1H NMR (400 MHz, C6D6, 298 K, major product (5)): δ 6.32 (d, 2 H, H3, J = 2.51 Hz), 2.97 (dt, 2 H, H9, J = 5.71 Hz, J = 1.17 Hz), 2.93−2.82 (m, 4 H, H6), 2.14 (“sept”, 2 H, H7, J = 2.89 Hz”), 2.04 (“dt”, 2 H, H8b, J = 9.29 Hz, J = 5.96 Hz), 1.91 (“d”, 2 H, H5, J = 3.76 Hz), 1.85 (s, 6 H, H13), 1.80 (s, 6 H, H11), 1.49 (s, 6 H, H12), 0.56 (dd, 2 H, H1b, J = 5.15 Hz, J = 2.64 Hz), −0.78 (d, 2 H, H8a, J = 9.29 Hz), −1.35 (d, 2 H, H1a, J = 5.27 Hz) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 134.3 (2 C, C4), 118.3 (2 C, C2), 112.6 (2 CH, C3), 87.5 (2 CH, C5), 64.2 (2 CH2, C1), 55.4 (2 CH, C9), 40.9 (2 CH, C7), 39.5 (2 C, C10), 33.8 (2 CH2, C8), 32.5 (2 CH2, C6), 28.7 (2 CH3, C13), 26.5 (2 CH3, C12), 22.7 (2 CH3, C11) ppm. 1H NMR (400 MHz, C6D6, 298 K, minor product (5′)): δ 6.58 (d, 2 H, H3′, J = 2.26 Hz), 3.50 (dd, 2 H, H1b′, J = 5.64 Hz, J = 2.38 Hz), 2.59 (s, 6H, H13′), 2.38 (dt, 2 H, H9′, J = 5.64 Hz, J = 1.16 Hz), 1.88−1.86 (m, 2 H, H8b′), 1.81 − 1.80 (m, 2 H, H1a′), 1.68−1.63 (m, 2 H, H7′), 1.63−1.50 (m, 4 H, H6′), 1.22 (s, 12 H, H11′ and H12′), −1.17 (d, 2 H, H8a′, J = 9.03 Hz), −1.28 (d, 2 H, H5′, J = 5.77 Hz) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 136.6 (2 C, C4′), 114.8 (2 CH, C3′), 113.1 (2 C, C2′), 86.7 (2 CH, C5′), 68.4 (2 CH2, C1′), 55.0 (2 CH, C9′), 40.6 (2 CH, C7′), 38.3 (2 C, C10′), 36.1 (2 CH2, C8′), 31.2 (2 CH2, C6′), 29.1 (2 CH3, C13′), 26.3 (2 CH3, C11′ or C12′), 22.2 (2 CH3, C12′ or C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 398 amu with the following isotopic cluster distribution: 392 (5), 393 (2), 394 (9), 395 (4), 396 (19), 397 (15), 398 (100), 399 (32), 400 (12), 401 (2). Simulated distributions (in %): for C26H38Ti, 396 (11), 397 (13), 398 (100), 399 (35), 400 (13), 401 (2); for C26H36Ti, 394 (11), 395 (13), 396 (100), 397 (35), 398 (13), 399 (2); for C26H34Ti, 392 (11), 393 (13), 394 (100), 395 (35), 396 (13), 397 (2). Synthesis of [V(η5-Pdl*)2] (6). A solution of [VCl3(thf)3] (116 mg, 0.31 mmol) and 3 (200 mg, 0.93 mmol) in THF (15 mL) was stirred for 4 h at ambient temperature. The solvent was removed under dynamic vacuum, and the solid residue was extracted with pentane (3 mL) and filtered. The extract was concentrated and cooled to −30 °C to give dark green crystals (50 mg, 0.13 mmol, 40%). Mp: 192.2−192.8 °C. Anal. Calcd for C26H38V: C, 77.77; H, 9.54. Found: C, 77.41; H, 9.58. The EI mass spectrum (70 eV) showed a molecular ion at m/z 401 amu with the following isotopic cluster distribution: 397 (6), 398 (3), 399 (5), 400 (3), 401 (100), 402 (26), 403 (4). Simulated distributions (in %): for C26H38V, 401 (100), 402 (28), 403 (4); C26H36V: 399 (100), 400 (28), 401 (4); for C26H34V, 397 (100), 398 (28), 399 (4). Synthesis of [Cr(η5-Pdl*)2] (7). A solution of CrCl2 (57 mg, 0.47 mmol) and 3 (200 mg, 0.93 mmol) in THF (15 mL) was stirred for 4 h at ambient temperature. The solvent was removed under dynamic vacuum, and the solid residue was extracted with pentane (3 mL) and filtered. The extract was concentrated and cooled to −30 °C to give dark

To a solution of 3 (33 mg, 0.154 mmol) in THF (15 mL) was added a solution of [(η5-Cp′)FeI]2 (64 mg, 0.077 mmol) in THF (5 mL). The mixture was stirred for 4 h at room temperature. The brown solution was separated from a light yellow precipitate by filtration, the solvent was removed under dynamic vacuum, and the remaining solid was extracted with pentane (3 mL). The extracts were cooled overnight at −30 °C to yield brown-red crystals (51 mg, 0.109 mmol, 71%). Mp: 174.2− 175.0 °C. Anal. Calcd for C30H48Fe: C, 77.23; H, 10.80. Found: C, 77.16; H, 10.00. 1H NMR (400 MHz, C6D6, ambient): δ 5.44 (s, 1 H, H3), 3.91 (d, 1 H, H17 or C24, J = 2.20 Hz), 3.05 (dd, 1 H, H1b, J = 3.60 Hz, J = 1.40 Hz), 2.54−2.42 (m, 3 H, H6, H8 and H9), 2.27 (d, 1 H, H17 or H24, J = 2.08 Hz), 2.04 (s, 3 H, H13), 1.89−1.99 (m, 2 H, H6 and H7), 1.85 (s, 1 H, H8), 1.83 (s, 9 H, H20 or H23), 1.49 (s, 9 H, H23 or H20), 1.32 (s, 3 H, H11 or H12), 1.16 (s, 9 H, H16), 0.82 (s, 3 H, H12 or H11), 0.32 (d, 1 H, H5, J = 7.28 Hz), −1,21 (d, 1 H, H1a, J = 3.52 Hz) ppm. 13C{1H} NMR (101 MHz, C6D6, ambient): δ 111.5 (C, C4), 104.2 (C, C18 or C21), 100.4 (C, C14), 97.6 (C, C21 or C18), 89.8 (C, C2), 82.0 (CH, C3), 71.2 (CH, C17 or C24), 64.7 (CH, C24 or C17), 54.3 (CH, C5), 51.6 (CH, C9), 43.0 (CH2, C1), 41.4 (CH, C7), 39.3 (C, C10), 35.3 (3 × CH3, C20 or C23), 34.9 (CH2, C8), 33.7 (3 × CH3, C23 or C20), 33.5 (C, C19 or C22), 33.1 (C, C22 or C19), 32.6 (CH2, C6), 32.0 (3 × CH3, C16), 30.2 (C, C15), 26.2 (CH3, C11 or C12), 25.7 (CH3, C13), 21.5 (CH3, C12 or C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 464 amu with the following isotopic cluster distribution: 460 (1), 461 (2), 462 (15), 463 (6), 882


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464 (100), 465 (24), 466 (8). Simulated distributions (in %): for C30H48Fe, 462 (6), 463 (2), 464 (100), 465 (35), 466 (5); for C30H46Fe, 460 (6), 461 (2), 462 (100), 463 (35), 464 (5). Synthesis of [(η7-C7H7)Zr(η5-Pdl*)] (10).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

Westfälische Wilhelms-Universität Münster, Organisch-Chemisches Institut, Corrensstrasse 40, 48149 Münster, Germany. [(η7-C7H7)ZrCl(tmeda)] (0.5 g, 1.497 mmol) was dissolved in THF (30 mL). Slow addition of K(Pdl*) (0.337 g, 1.572 mmol) in THF (10 mL) at −78 °C resulted in a red solution, which was stirred for 4 h. After solvent removal, sublimation at 135 °C (0.1 mbar) afforded a wine red solid (0.245 g, 0.69 mml, 46%). Single crystals were grown from a concentrated toluene/pentane solution at −20 °C. Mp: 174.5−175.5 °C. Anal. Calcd for C20H26Zr: C, 67.2; H, 7.33. Found: C, 67.0; H, 7.44. 1H NMR (400 MHz, C6D6, ambient temperature): δ 5.16 (s, 7 H, C7H7), 3.84 (m, 1 H, H3), 3.81 (s, 1 H, H1b), 2.78 (d, J = 4.9 Hz, 1 H, H5), 2.63 (dd, 1 H, H6b, J = 16.8 Hz, J = 3.4 Hz), 2.33−2.26 (m, 2 H, H6a and H8b), 1.99 (“sept“, 1 H, H7), 1.91 (s, 3 H, H13), 1.87−1.82 (m, 2 H, H1a and H9), 1.35 (d, 1 H, H8a, J = 9.3 Hz), 1.19 (s, 3 H, H12), 0.81 (s, 3 H, H11) ppm. 13C{1H} NMR (101 MHz, C6D6, ambient): δ 144.4 (C4), 129.9 (C2), 93.6 (C3), 86.0 (C5), 82.8 (C7H7), 78.0 (C1), 51.7 (C9), 41.1 (C7), 39.2(C10), 35.3 (C8), 32.4 (C6), 27.7 (C13), 26.2 (C12), 21.3 (C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 356 amu with the following isotopic cluster distribution: 354 (47), 355 (22), 356 (100), 357 (43), 358 (49), 359 (11), 360 (33), 361 (6), 362 (5), 363 (0). Simulated distributions (in %): for C20H26Zr, 356 (100), 357 (43), 358 (40), 359 (7), 360 (34), 361 (7), 362 (5), 363 (1); for C20H24Zr, 354 (100), 355 (43), 356 (40), 357 (7), 358 (34), 359 (7), 360 (5), 361 (1). Synthesis of [(η4-COD)Ir(η5-Pdl*)] (11).

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS M.D.W. acknowledges the current financial support by the TU Braunschweig through the “Zukunftsfonds” and by the Deutsche Forschungsgemeinschaft (DFG) through the Emmy-Noether program (WA 2513/2-1). M.D.W. is grateful to W. C. Heraeus GmbH for a generous gift of IrCl3. We thank Dr. Greg Nocton (Laboratoire Hétéroélement et Coordination Ecole polytechnique/CNRS, Palaiseau Cedex) for magnetic susceptibility measurements (SQUID).

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A solution of [(COD)Ir(μ-Cl)]2 (85 mg, 0.13 mmol) and 3 (54 mg, 0.25 mmol) in 15 mL of THF was stirred for 24 h at ambient temperature and then evaporated to dryness. The brown solid residue was extracted with 3 mL of pentane. Concentration of the extract and cooling to −30 °C resulted in orange crystals. Yield: 72 mg (0.15 mmol, 61%). Mp: 122.8−123.1 °C. Anal. Calcd for C21H31Ir: C, 53.2; H, 6.57. Found: C, 52.87; H, 6.55. 1H NMR (400 MHz, C6D6, 298 K): δ 5.42−5.39 (m, 1 H, H3), 4.24 (br s, 2 H, COD), 3.76−2.16 (br m, 6 H, COD), 3.62 (t, 1 H, H1b, J = 1.64 Hz), 2.67−2.60 (m, 1 H, H8b), 2.37 (t, 1 H, H9, J = 5.90 Hz), 2.02 (br s, 2 H, COD), 1.98−1.91 (m, 2 H, H7 and H8a), 1.86−1.83 (m, 1 H, H1a), 1.82−1.75 (“ddd”, 1 H, H6b), 1.73−1.66 (m, 2 H, H6a and H5), 1.52 (br s, 2 H, COD), 1.32 (s, 3 H, H13), 1.31 (s, 3 H, H12), 0.98 (s, 3 H, H11) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 122.9 (C, C4), 99.3 (C, C2), 96.4 (CH, C3), 51.7 (CH2, C1), 50.9 (CH, C9), 48.5 (CH, C5), 43.2 (CH, C7), 39.2 (C, C10), 38.1 (CH2, C8), 26.3 (CH3, C12), 25.1 (CH2, C6), 22.8 (CH3, C13), 22.2 (CH3, C11) ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 476 amu with the following isotopic cluster distribution: 472(29), 473 (19), 474 (78), 475 (25), 476 (100), 477 (22), 478 (3). Simulated distributions (in %): for C21H31Ir, 474 (60), 475 (14), 476 (100), 477 (23), 478 (3); for C21H29Ir, 472 (60), 473 (14), 474 (100), 475 (23), 476 (3).

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REFERENCES

(1) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science: Sausalito, CA, 2010. (2) Kreiter, C. G. Adv. Organomet. Chem. 1986, 26, 297. (3) Ernst, R. D. Chem. Rev. 1988, 88, 1255. (4) Ernst, R. D. Struct. Bonding (Berlin) 1984, 57, 1. (5) Yasuda, H.; Nakamura, A. J. Organomet. Chem. 1985, 285, 15. (6) Ernst, R. D. Comments Inorg. Chem. 1999, 21, 285. (7) Ernst, R. D. Acc. Chem. Res. 1985, 18, 56. (8) Powell, P. Adv. Organomet. Chem. 1986, 26, 125. (9) Stahl, L.; Ernst, R. D. Adv. Organomet. Chem. 2007, 55, 137. (10) Calhorda, M. J.; Romão, C. C.; Veiros, L. F. Chem. Eur. J. 2002, 8, 868. (11) Veiros, L. F.; Calhorda, M. J. Dalton Trans. 2011, 40, 11138. (12) Glöckner, A.; Bannenberg, T.; Ibrom, K.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Walter, M. D.; Tamm, M. Organometallics 2012, 31, 4480. (13) Bosch, H. W.; Hund, H.-U.; Nietlispach, D.; Salzer, A. Organometallics 1992, 11, 2087. (14) Cesarotti, E.; Kagan, H. B.; Goddard, R.; Krüger, C. J. Organomet. Chem. 1978, 162, 297. (15) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 12114. (16) Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (17) Giardello, M. A.; Conticello, V. P.; Brard, L.; Gagne, M. R.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10241. (18) Willhoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 2642. (19) Odenkirk, W.; Bosnich, B. J. Chem. Soc., Chem. Commun. 1995, 1181. (20) Kulsomphob, V.; Tomaszewski, R.; Yap, G. P. A.; Liable-Sands, L. M.; Rheingold, A. L.; Ernst, R. D. J. Chem. Soc., Dalton Trans. 1999, 3995. (21) Gong, L.; Hu, N.; Jin, Z.; Chen, W. J. Organomet. Chem. 1988, 352, 62. (22) Solomon, S. A.; Bickelhaupt, F. M.; Layfield, R. A.; Nilsson, M.; Poater, J.; Solà, M. Chem. Commun. 2011, 47, 6162. (23) Salzer, A.; Schmalle, H.; Stauber, R.; Streiff, S. J. Organomet. Chem. 1991, 408, 403. (24) Paquette, L. A.; McKinney, J. A.; McLaughlin, M. L.; Rheingold, A. L. Tetrahedron Lett. 1986, 27, 5598. (25) Paquette, L. A.; Gugelchuk, M.; McLaughlin, M. L. J. Org. Chem. 1987, 52, 4732.

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for 4−11 and figures giving the 1H NMR spectrum of 3, an ln K vs T plot for 5/5′, and solid-state magnetic susceptibility vs T data for 6 and 7. This 883


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(26) Paquette, L. A.; Moriarty, K. J.; McKinney, J. A.; Rogers, R. D. Organometallics 1989, 8, 1707. (27) Campana, C. F.; Ernst, R. D.; Wilson, D. R.; Liu, J.-Z. Inorg. Chem. 1984, 23, 732. (28) Newbound, T. D.; Freeman, J. W.; Wilson, D. R.; Kralik, M. S.; Patton, A. T.; Campana, C. F.; Ernst, R. D. Organometallics 1987, 6, 2432. (29) (a) Wilson, D. R.; Ernst, R. D.; Cymbaluk, T. H. Organometallics 1983, 2, 1220. (b) Wilson, D. R.; DiLullo, A. A.; Ernst, R. D. J. Am. Chem. Soc. 1980, 102, 5928. (30) Ernst, R. D.; Freeman, J. W.; Swepston, P. N.; Wilson, D. R. J. Organomet. Chem. 1991, 402, 17. (31) Shannon, R. D. Acta Crystallogr. 1976, A32, 751. (32) (a) Haaland, A. Acc. Chem. Res. 1979, 12, 415. (b) Gedridge, R. W.; Hutchinson, J. P.; Rheingold, A. L.; Ernst, R. D. Organometallics 1993, 12, 1553. (33) Elschenbroich, C.; Nowotny, M.; Behrendt, A.; Harms, K.; Wocadlo, S.; Pebler, J. J. Am. Chem. Soc. 1994, 116, 6217. (34) Severson, S. J.; Cymbaluk, T. H.; Ernst, R. D.; Higashi, J. M.; Parry, R. W. Inorg. Chem. 1983, 22, 3833. (35) Tuchscherer, A.; Georgi, C.; Roth, N.; Schaarschmidt, D.; Rüffer, T.; Waechtler, T.; Schulz, S. E.; Oswald, S.; Gessner, T.; Lang, H. Eur. J. Inorg. Chem. 2012, 4867. (36) Trakarnpruk, W.; Arif, A. M.; Ernst, R. D. J. Organomet. Chem. 1995, 485, 25. (37) Basta, R.; Wilson, D. R.; Ma, H.; Arif, A. M.; Herber, R. H.; Ernst, R. D. J. Organomet. Chem. 2001, 637−639, 172. (38) Bohn, R. K.; Haaland, A. J. Organomet. Chem. 1966, 5, 470. (39) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell University Press: Ithaca, NY, 1960. (40) Sitzmann, H.; Boese, R. Angew. Chem., Int. Ed. Engl. 1991, 30, 971. (41) Sitzmann, H.; Dezember, T.; Kaim, W.; Baumann, F.; Stalke, D.; Kärcher, J.; Dormann, E.; Winter, H.; Wachter, C.; Kelemen, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 2872. (42) Wallasch, M.; Wolmershäuser, G.; Sitzmann, H. Angew. Chem. 2005, 117, 2653. (43) Wallasch, M. W.; Weismann, D.; Riehn, C.; Ambrus, S.; Wolmershäuser, G.; Lagutschenkov, A.; Niedner-Schatteburg, G.; Sitzmann, H. Organometallics 2010, 29, 806. (44) Weismann, D.; Sun, Y.; Lan, Y.; Wolmershäuser, G.; Powell, A. K.; Sitzmann, H. Chem. Eur. J. 2011, 17, 4700. (45) Pammer, F.; Sun, Y.; Pagels, M.; Weismann, D.; Sitzmann, H.; Thiel, W. R. Angew. Chem., Int. Ed. 2008, 17, 3271. (46) Walter, M. D.; Grunenberg, J.; White, P. S. Chem. Sci. 2011, 2, 2120. (47) Walter, M. D.; White, P. S. New J. Chem. 2011, 35, 1842. (48) Walter, M. D.; White, P. S. Dalton Trans. 2012, 41, 8506. (49) Walter, M. D.; White, P. S. Inorg. Chem. 2012, 51, 11860. (50) Krinsky, J. L.; Stavis, M. N.; Walter, M. D. Acta Crystallogr., Sect. E 2003, 59, m497. (51) Ren, W.; Zi, G.; Fang, D.-C.; Walter, M. D. J. Am. Chem. Soc. 2011, 133, 13183. (52) Ren, W.; Zi, G.; Fang, D.-C.; Walter, M. D. Chem. Eur. J. 2011, 17, 12669. (53) (a) Ren, W.; Zi, G.; Walter, M. D. Organometallics 2012, 31, 672. (b) Ren, W.; Lukens, W. W.; Zi, G.; Maron, L.; Walter, M. D. Chem. Sci. 2013, DOI: 10.1039/C2SC22013J. (54) Maekawa, M.; Römelt, M.; Daniliuc, C. G.; Jones, P. G.; White, P. S.; Neese, F.; Walter, M. D. Chem. Sci. 2012, 3, 2972. (55) Glöckner, A.; Bannenberg, T.; Tamm, M.; Arif, A. M.; Ernst, R. D. Organometallics 2009, 28, 5866. (56) Glöckner, A.; Tamm, M.; Arif, A. M.; Ernst, R. D. Organometallics 2009, 28, 7041. (57) Glöckner, A.; Arif, A. M.; Ernst, R. D.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg. Chim. Acta 2010, 364, 23. (58) Glöckner, A.; Bannenberg, T.; Büschel, S.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2011, 17, 6118. (59) Glöckner, A.; Kronig, S.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2012, 723, 181.

(60) Glöckner, A.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg. Chem. 2012, 51, 4368. (61) Glöckner, A.; Bauer, H.; Maekawa, M.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Sun, Y.; Sitzmann, H.; Tamm, M.; Walter, M. D. Dalton Trans. 2012, 41, 6614. (62) Glöckner, A.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Tamm, M. Chem. Commun. 2012, 48, 6598. (63) Glöckner, A.; Tamm, M. Chem. Soc. Rev. 2013, 42, 128. (64) Glöckner, A.; Cui, P.; Chen, Y.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. New J. Chem. 2012, 36, 1392. (65) Kreye, M.; Glöckner, A.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Tamm, M.; Walter, M. D. Dalton Trans. 2012, 42, 2192. (66) Pillet, S.; Wu, G.; Kulsomphob, V.; Harvey, B. G.; Ernst, R. D.; Coppens, P. J. Am. Chem. Soc. 2003, 125, 1937. (67) Scheins, S.; Messerschmidt, M.; Gembicky, M.; Pitak, M.; Volkov, A.; Coppens, P.; Harvey, B. G.; Turpin, G. C.; Arif, A. M.; Ernst, R. D. J. Am. Chem. Soc. 2009, 131, 6154. (68) Mann, B. E.; Manning, P. W.; Spencer, C. M. J. Organomet. Chem. 1986, 312, C64. (69) Kralik, M. S.; Rheingold, A. L.; Ernst, R. D. Organometallics 1987, 6, 2612. (70) Kirss, R. U.; Quazi, A.; Lake, C. H.; Churchill, M. R. Organometallics 1993, 12, 4145. (71) Wilson, D. R.; Ernst, R. D.; Kralik, M. S. Organometallics 1984, 3, 1442. (72) Witherell, R. D.; Ylijoki, K. E. O.; Stryker, J. M. J. Am. Chem. Soc. 2008, 130, 2176. (73) Butovskii, M. V.; Englert, U.; Herberich, G. E.; Kirchner, K.; Koelle, U. Organometallics 2003, 22, 1989. (74) Gamero-Melo, P.; Melo-Trejo, P. A.; Cervantes-Vasquez, M.; Mendizabal-Navarro, N. P.; Paz-Michel, B.; Villar-Masetto, T. I.; Gonzalez-Fuentes, M. A.; Paz-Sandoval, M. A. Organometallics 2012, 31, 170. (75) Müller, J.; Schiller, C.; Escarpa Gaede, P.; Kempf, M. Z. Anorg. Allg. Chem. 2005, 631, 38. (76) Köhler, F. H.; Prössdorf, W. Z. Naturforsch. 1977, 32b, 1026. (77) Kölle, U.; Fuss, B.; Khouzami, F.; Gersdorf, J. J. Organomet. Chem. 1985, 290, 77. (78) Herde, J. L.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974, 15, 18. (79) Lochmann, L.; Trekoval, J. J. Organomet. Chem. 1987, 326, 1. (80) Jones, N. A.; Liddle, S. T.; Wilson, C.; Arnold, P. L. Organometallics 2007, 26, 755. (81) Manzer, L. E. Inorg. Synth. 1982, 21, 135. (82) Walter, M. D.; Schultz, M.; Andersen, R. A. New J. Chem. 2006, 30, 238. (83) (a) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structure from Diffraction Data; University of Gö ttingen, Göttingen, Germany. (b) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

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