Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Benzyl

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

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Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Benzyl, Amide, and Imide Complexes Renita Thim, H. Martin Dietrich, Martin Bonath, Cäcilia Maichle-Mössmer, and Reiner Anwander* Institut für Anorganische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany

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S Supporting Information *

ABSTRACT: The half-sandwich diiodide complexes [Cp*LnI2]x (Ln = Y, Lu), obtained in high yields from Cp*Ln(AlMe4)2 (Cp*= C5Me5) and 2 equiv of ISiMe3, reacted with 2 equiv of potassium benzyl KCH2Ph in THF to afford complexes Cp*Ln(CH2Ph)2(thf). Protonolysis of Cp*Ln(CH2Ph)2(thf) with 3,5-bis(trifluoromethyl)aniline (H2NC6H3(CF3)2-3,5 = H2NArCF3) in toluene gave rareearth-metal imide complexes [Cp*Ln(NC6H3(CF3)2-3,5)(thf)x]2 (Ln = Y (x = 2), Lu (x = 1)). The dimeric structure of [Cp*Ln(NC6H3(CF3)2-3,5)(thf)x]2 with two bridging imido ligands forming a planar Ln2N2 core was analyzed by X-ray crystallography. Treatment of Cp*Y(CH2Ph)2(thf) with H2NC6H3(CF3)23,5 in THF led to the monomeric bis(amide) complex Cp*Y(NHC6H3(CF3)2-3,5)2(thf)2. The reaction of Cp*Y(CH2Ph)2(thf) with 2,6-diisopropylaniline in toluene gave also the bis(amide) complex Cp*Y(NHC6H3iPr2-2,6)2(thf), whereas, in a THF solution, the formation of the labile mixed benzyl amide complex Cp*Y(HNC6H3iPr2-2,6)(CH2Ph)(thf) was observed.

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INTRODUCTION In the realm of current rare-earth-metal imide chemistry, various synthesis pathways have been established.1,2 Initially, Gordon and co-workers reported the formation of a dinuclear imido-bridged samarium complex via partial deprotonation of the primary anilide [Sm(NHAr)2(μ-NHAr)]2 with AlMe3 (Ar = C6H3iPr2-2,6).3 Similarly, Mindiola et al. obtained a Lewis acid stabilized scandium imide, evidencing an intermediate terminal ScNR bond.4 The first structurally characterized terminal scandium imide complex was described by Chen et al. and accessed via a sterically enforced deprotonation of a scandium methyl anilide complex using DMAP (N,Ndimethylaminopyridine).5 By adopting a similar strategy, we could obtain terminal yttrium and lutetium imide complexes.6 Recently, Schelter and co-workers synthesized the first terminal anionic Ce(IV) imide complex by trapping the involved alkali metal cation with 2.2.2-cryptand.7 Overall, the reaction of complexes of the type LLnR2 (L = bulky monoanionic anicillary ligand, R = alkyl,5,6,8−11 hydride12) with a primary amine seems a most rational and viable approach to discrete rare-earth-metal imide complexes. Since rare-earth-metal ions have the tendency to assemble into stable di- or polynuclear complexes with bridging imido ligands,9,13−18 such oligomerization can be counteracted by the use of bulky ancillary ligands, like β-diketiminato (nacnac) or tris(pyrazolyl)borato.5,6 Moreover, bulky chelating ligands were shown to favorably stabilize the highly polarized LnNR bond.11,19−22 Surprisingly, only a few fully characterized cyclopentadienylsupported rare-earth-metal imide complexes have been described. Hessen and co-workers could isolate a scandium imide complex by insertion of benzonitrile into a Sc−diene bond (Chart 1, A).23,24 Another approach exploits the © XXXX American Chemical Society

insertion of alkyl/arylnitriles into the Ln−H bond of hydrides (B).16 Chart 1. Selected Half-Sandwich Rare-Earth-Metal Imide Complexes

Heterobimetallic rare-earth/d-block metal imide complexes [Cp*Ir(μ-NtBu)(μ-CH2SiMe2CH2)Lu(C5Me4R)] (R = Me, SiMe3) (C) could be synthesized by the reaction of the halfsandwich rare-earth-metal alkyl complexes [(C5Me4R)Lu(CH2SiMe3)2(thf)] with the d-transition metal imide complex Cp*Ir(NtBu) (Cp* = C5Me5) via addition and concomitant C−H bond activation.25 Our group showed that saltReceived: June 18, 2018

A

DOI: 10.1021/acs.organomet.8b00420 Organometallics XXXX, XXX, XXX−XXX

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ambient temperature as revealed by a color change from yellow to slightly orange. The decomposition of 1 can be monitored by 1H NMR spectroscopy in a sealed J. Young NMR valve overnight at ambient temperature. Complexes 1 crystallize as discrete monomeric complexes but show slightly distinct coordination geometries due to the different size of the metal centers (Figure 1, Table 1). At first sight, the formally 6-

metathetical exchange of the AlMe4 unit in [La(AlMe4)(NC6H3iPr2-2,6)(DMAP)]2 by Cp′ (= C5H4SiMe3) leads to the respective half-sandwich imide complex (Chart 1, D).26 More recently, Sadow et al. employed a bulky oxazolinefunctionalized cyclopentadienyl ligand (BoMCptet = tetramethyl-cyclopentadienyl−bis(4,4-dimethyl-2-oxazoline)) to stabilize dimeric lutetium imide complexes [(BoMCptet)Lu(NCH2R)]2 (R = Ph; 1-C10H7) (E), accessed from the respective lutetium benzyl complex by protonolysis.27 It is noteworthy that Cui and co-workers provided evidence for a scandium terminal imide complex supported by a CpPN ligand by applying a Lewis base promoted proton abstraction of scandium anilide/alkyl complex (η5:κ1-C5H4−PPh2NAr)Sc(HNAr)(CH2SiMe3) (Ar = C6H3iPr2-2,6).10 Along these lines, Gordon and co-workers reported that the reaction between Cp*Lu(CH2SiMe3)2(thf) (Cp* = C5Me5) and 2,6diisopropylaniline gave mixed alkyl/anilide and bis(anilide) complexes instead of the imide species.28 Previous studies from our group revealed that the reaction between Cp*Ln(AlMe4)2 and potassium 2,4,6-tri-tert-butylphenylamide or 1-adamantylamine did not lead to the desired imide complexes.29 Herein, we aimed at a better understanding of the steric and electronic influence of the “reactive” group in such protonolysis reactions with amines, by changing the (CH2SiMe3)−/(AlMe4)− moiety to a benzyl group. We were also interested in the influence of the type of amine itself. Balancing these factors, we found that rare-earth-metal dibenzyl complexes supported by the pentamethylcyclopentadienyl ligand can act as suitable precursors for the synthesis of rare-earth-metal imide complexes.

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Figure 1. ORTEP representation of the molecular structures of 1a (top) and 1b (bottom, one of two independent molecules in the asymmetric unit is shown) with atomic displacement parameters set at the 30% level. Hydrogen atoms are omitted for clarity. Selected intramolecular distances and angles for complexes 1 are compiled in Table 1.

RESULTS AND DISCUSSION The half-sandwich rare-earth-metal dibenzyl complexes Cp*Ln(CH2Ph)2(thf) (Ln = Y (1a), Lu (1b)) were prepared by the reaction of [Cp*LnI2]x with 2 equiv of KCH2Ph in THF at ambient temperature (Scheme 1). Analytically pure diiodide

Table 1. Selected Interatomic Distances [Å] and Angles [deg] for 1

Scheme 1. Synthesis of Half-Sandwich Imide and Amide Complexes Derived from H2NC6H3(CF3)2-3,5

Ln1−C1 Ln1−C8 Ln1···C2 Ln1−O1 Ln1···Ct Ln1−C1−C2 Ln1−C8−C9

1a-Y

1b-Lu (molecule 1)a

2.437(2) 2.449(2) 2.709 2.338(1) 2.334 84.3(2) 107.8(2)

2.378(2) 2.386(2) 3.144 2.235(1) 2.269 107.1(1) 108.3(1)

a

Molecule 2 of the asymmetric unit and relevant metrical parameters are shown in the Supporting Information, Figure S23 and Table S1.

coordinate complexes Cp*Ln(CH2Ph)2(thf) seem to feature the same three-legged piano-stool geometry, involving two benzyl ligands, one thf molecule, and the Cp* ligand. However, in the yttrium case 1a, the coordination environment features an additional close contact of an ipso carbon atom of one benzyl group to the yttrium center (Y···C2, 2.709 Å, Figure 1, top). This is also clearly indicated by a rather acute Y1−C1− C2 angle of 84.3(2)° compared to the larger Y1−C8−C9 angle of 107.8(2)° (Table 1). A similar bending of one of the benzyl ligands was observed in isostructural complex Cp*Gd(CH2Ph)2(thf), which was synthesized using a 1:1:2 mixture of GdBr3, KCp*, and KCH2Ph, and crystallized from an nheptane/thf mixture.31 The Y−C(benzyl) distances of

precursors were obtained in high yields by treatment of Cp*Ln(AlMe4)2 (Ln = Y, Lu) with ISiMe3 in toluene, in analogy to the synthesis of [Cp*LaI2]x from a Cp*Ln[CH(SiMe3)2]2/ISiMe3 mixture, as reported by Schaverien in 1989.30 Complexes Cp*Ln(CH2Ph)2(thf) (1) are temperaturesensitive in a THF-d8 solution, decomposing already at B

DOI: 10.1021/acs.organomet.8b00420 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Table 2. Selected Yttrium Amide and Imide Complexes and Their Corresponding 89Y NMR Chemical Shifts Amide complexes Y[N(SiMe3)2]3 Y[N(SiMe3)2]3(OPPh3) Cp*Y(NHC6H3(CF3)2-3,5)2(thf)2 (3) Cp*Y(NHC6H3iPr2-2,6)(CH2Ph)(thf)2 (4) Cp*Y(NHC6H3iPr2-2,6)2(thf) (5) Ap′Y(NHC6H3iPr2-2,6)[CH(C3HN2Me2-3,5)2](thf) Imide complexes Y(AlMe4)(NMes*)]2 [(TptBu,Me)Y(NtBu)(AlMe3)] [Cp*Y(NC6H3(CF3)2-3,5)(thf)2]2 (2a) a

δexpt [ppm]

CNa

solvent

ref

570.0 (23 °C) 544.4 (23 °C) 154.2 249.4 233.0 336

3 4 7 7 7 7

CDCl3 C6D5CD3 C6D6 C6D6 C6D6 C6D6

34 34

396 426.2 216.5

4 5 7

C6D6 C6D5CD3 C6D6

9 8

b b b

35

b

b

CN = coordination number. This work. Ap′ = amidopyridinato.

2.437(2) Å and 2.449(2) Å in 1a are slightly shorter than those in 6-coordinate benzyl complex [Y(CH 2 Ph) 3 (thf) 3 ] (2.452(3)−2.463(3) Å).32 The significantly shorter Lu− C(benzyl) distances of 2.378(2) Å and 2.386(2) Å in 1b are comparable to those detected in 5-coordinate {BoMCptet}Lu(CH2Ph)2 (BoMCptet = MeC(4,4-dimethyl-2-oxazoline)2C5Me4) (2.367(7)−2.379(7)Å) and shorter than in [Lu(CH2Ph)3(thf)3] (2.404(7)−2.413(5) Å).27,33 There is no evidence for any significant interaction between the ipso carbon atoms of the benzyl ligands and the lutetium center, as suggested by the Lu···C2 distance of 3.144 Å) and the Lu−C(CH2)−Cipso angles of 107.1(1)° and 108.3(1)° (Table 1 and Figure 1, bottom). The 1H NMR spectrum of yttrium complex 1a shows the benzylic protons as a doublet at 1.88 ppm (2JYH = 2.1 Hz). This signal assignment could be also derived from a 1H−89Y HSQC NMR spectrum (δY = 448.6 ppm.34,35 Correspondingly, the 13C{1H}NMR spectrum exhibits a doublet at 54.9 ppm (1JYC = 32.3 Hz) for the benzylic carbon atoms. Having in mind the successful synthesis of the terminal imide complex [(TptBu,Me)Lu(=NC6H3(CF3)2-3,5)(DMAP)] (TptBu,Me = tris(3-tert-butyl-5-methyl-pyrazolyl)borato),6 we probed the reactivity of complexes 1 toward a comparatively highly Brønsted-acidic “fluorinated” aniline (Scheme 1). To our delight, the equimolar reaction of monomeric Cp*Ln(CH2Ph)2(thf) with H2NC6H3(CF3)2-3,5 in toluene gave the dimeric rare-earth-metal imide complexes [Cp*Ln(μ-NR)(thf)2]2 (Ln = Y (2a), x = 2; Lu (2b), x = 1; R = C6H3(CF3)23,5) in decent yields. The formation of compounds 2 was monitored by 1H NMR spectroscopy. After 18 h at ambient temperature, most of benzyl precursors 1 had converted into the new complex 2 with concomitant formation of toluene. Furthermore, the 1H NMR spectra did indicate the absence of the NH resonance. Complexes 2a and 2b are insoluble in nhexane and crystallized from a saturated THF solution at −35 °C. Single-crystal X-ray diffraction studies revealed the dimeric arrangements of [Cp*Y(NC6H3(CF3)2-3,5)(thf)2]2 (2a, Figure 2, top) and [Cp*Lu(NC6H3(CF3)2-3,5)(thf)]2 (2b, Figure 2, bottom). The Ln2N2 core structure with two bridging imido ligands resembles that found in complexes A, D, and E (Chart 1). Each yttrium center in 2a is formally 7-coordinated by a Cp* ligand, two thf molecules, and two imido ligands, adopting a four-legged piano-stool geometry. The Y−N imido bond lengths range from 2.222(4) Å to 2.304(4) Å (Table 3), being comparable to the respective distances in the yttrium imide complexes [Cp′Y(μ3-NCH2Ph)]4 (Cp′ = η5-

Figure 2. ORTEP representation of the molecular structures of 2a (top) and 2b (bottom) with atomic displacement parameters set at the 30% level. Hydrogen atoms and the disorder in the thf molecules and CF3 groups are omitted for clarity. Selected intramolecular distances and angles for complexes 2 are compiled in Table 3.

C5Me4SiMe3) (2.193(3)−2.342(3) Å) and [Y(CH2SiMe3)(μ2NArBH3)]2 (Ar = 2,6-(3,5-Me2C6H3)2C6H3) (2.297(2) and 2.335(2) Å).16,18 The Lu−N bond lengths in formally 6coordinate 2b (2.149(2)−2.188(2) Å, Table 2) are similar to those found in the dimeric imide complexes [{BoMCptet}LuNCH2(1-C10H7)]2 (2.116(4)−2.163(4) Å)27 and [Lu(AlMe4)(NC6H2tBu3-2,4,6)]2 (2.071−2.249 Å)9 but markedly elongated compared to the one in 5-coordinate terminal imide complex [(Tp tBu,Me )Lu(=NC 6 H 3 (CF 3 ) 2 -3,5)(DMAP)] (1.991(5) Å).6 While the solid-state structure of compound 2a exhibits two thf molecules per yttrium center, one thf molecule is removed upon drying of a crystalline sample under C

DOI: 10.1021/acs.organomet.8b00420 Organometallics XXXX, XXX, XXX−XXX

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2.293(3) Å in 3 are comparable to those in the five-coordinate yttrium bis(amide) complexes LY(NHC6H3iPr2-2,6)2 (L = methoxy-modified iminato ligand), (NNSBzThH)Y(NHC6H3iPr2-2,6)2 (NNSBzThH = benzothiophenyl- substituted amidopyridinato ligand), and ApY(NHC6H3iPr2-2,6)2(bipy) (Ap = bulky amidopyridinato ligand) (2.194(6)−2.348(3) Å)/ 2.231(2)−2.236(3) Å/2.228(2)−2.269(2) Å).36−38 The NH moiety was observed as a broad resonance at 4.33 ppm in the 1H NMR spectrum and a stretch vibration at 3321 cm−1 in the IR spectrum. The 89Y chemical shift (Table 2) detected by 1H−89Y HSQC/HMQC studies for the formally 7coordinate yttrium center in 3 (154.2 ppm) is shifted to higher field compared to the likely 7-coordinate imide complex 2a (216.5 ppm). We next examined the reactivity of complex Cp*Y(CH2Ph)2(thf) (2a) toward 2,6-diisopropylaniline (H2NDipp). This sterically more bulky aniline was successfully applied in reactions with homoleptic Ln(AlMe4)3, affording mixed imide tetramethylaluminate complexes of the type [{Ln(AlMe4)(μ-NDipp)}2(AlMe3)]2 (Ln = Y, La, Ce, Nd).26 The reaction of 1a with 1 equiv of 2,6-diisopropylaniline in a toluene solution led not to the envisaged imide complex but rather to a mixture of products, in which we could identify one product as the bis(amide) complex Cp*Y(NHC6H3iPr22,6)2(thf)2 (5) (Scheme 2). Bis(amide) complex 5 can be

Table 3. Selected Interatomic Distances [Å] and Angles [deg] for 2 Ln1−N1 Ln1−N2 Ln2−N1 Ln2−N2 Ln−O Ln1···Ct1 Ln2···Ct2 N1−C1 N2−C9 Ln1−N1−Ln2 Ln2−N2−Ln1 N1−Ln2−N2 N1−Ln1−N2

2a-Y

2b-Lu

2.222(4) 2.304(4) 2.231(4) 2.283(4) 2.392(3)−2.519(3) 2.447 2.418 1.363(6) 1.348(6) 103.4(2) 99.2(2) 78.8(2) 78.6(2)

2.187(2) 2.188(2) 2.149(2) 2.167(2) 2.267(2)−2.275(2) 2.301 2.316 1.366(3) 1.363(3) 97.19(9) 96.64(9) 83.75(9) 82.38(9)

reduced pressure, as evidenced by 1H NMR spectroscopy. The two thf molecules coordinating the dimeric lutetium complex 2b in the solid state are positioned trans with respect to the Lu2N2 plane and are retained after the same vacuum treatment. The reaction of compound 1a with 2 equiv of H2NC6H3(CF3)2-3,5 in toluene afforded the yttrium bis(amide) Cp*Y[NHC6H3(CF3)2-3,5]2(thf)2 (3) (Scheme 1). Interestingly, the reaction of 1a with 1 equiv of H2NC6H3(CF3)2-3,5 in THF gave also complex 3, however, in lower yields. In the solid state, complex 3 adopts a four-legged piano-stool geometry (Figure 3, Table 4). The Y−N bond lengths of 2.294(3) and

Scheme 2. Synthesis of Half-Sandwich Amide Complexes Derived from H2NC6H3iPr2-2,6

Figure 3. ORTEP representation of the molecular structure of 3 with atomic displacement parameters set at the 30% level. Hydrogen atoms (except NH) and the disorder in the thf molecules and CF3 groups are omitted for clarity. Selected intramolecular distances and angles for complex 3 are compiled in Table 4.

independently synthesized by treatment of 1a with 2 equiv of H2NC6H3iPr2-2,6 in toluene. The benzyl anilide species Cp*Y(CH2Ph)(HNC6H3iPr2-2,6)(thf)2 (4) could be obtained by the reaction of 1a with 1 equiv of 2,6-diisopropylaniline in a THF solution. The formation of mixed alkyl anilide and bis(anilide) complexes when aiming at rare-earth-metal imide complexes has been reported previously.28,38,39 Unfortunately, attempts to synthesize the desired imide complex in solvent mixtures failed. Complex 4 is temperature-sensitive as monitored by 1H NMR spectroscopic studies. Already after 5 min at ambient temperature, a solution of 4 in C6D6 turned from colorless to slightly yellow and the formation of small amounts of complex 5 was indicated by an additional NH resonance. Therefore, the NMR spectrum of 4 for full characterization was performed at −20 °C. By heating this solution for 72 h at 60 °C, the envisaged second intramolecular anilide deprotonation to the putative yttrium terminal imide complex did not occur. The molecular structures of complexes 4 and 5 were further confirmed by X-ray diffraction analysis (Figure 4, Table 4). The Y−N bond length of 2.250(3) Å in 7-coordinate 4 is

Table 4. Selected Interatomic Distances [Å] and Angles [deg] for 3, 4, and 5 Y1−N1 Y1−N2 Y1−O1 Y1−O2 Y−C23 Y1···Ct1 N1−C11 N2−C19/C23 N1−Y1−N2 N1−Y1−C23

3

4

5

2.294(3) 2.293(3) 2.378(2) 2.346(2)

2.250(3)

2.271(1) 2.258(1) 2.462(1) 2.399(1)

2.347 1.354(4) 1.349(4) 143.0(1)

2.419(2) 2.391(2) 2.498(3) 2.389 1.386(4)

2.396 1.385(2) 1.389(2) 85.30(5)

138.7(1)

D

DOI: 10.1021/acs.organomet.8b00420 Organometallics XXXX, XXX, XXX−XXX

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Scheme 3. Proposed Mechanistic Scenario of Amide/Imide Formation

(amide) complex (3 or 5) along with dibenzyl complex 1 (c), prevails if intramolecular deprotonation is hindered. Moreover, 1 equiv of amine per metal center can add across the Ln− N(imido) bond in complex 2 to yield also the bis(amide) complex (d), as observed for the formation of complexes 3 and 5 in THF-d8. It seems that the arylamine with bulky iso-propyl substituents at 2- and 6-positions are not accessible for an efficient intramolecular deprotonation (although the benzylic and amido ligands are cis-positioned) and hence formation of the desired imide complex cannot occur. In contrast, the use of highly Brønsted acidic but sterically less demanding H2NC6H3(CF3)2-3,5 (electron-withdrawing CF3 groups in 3,5positions) seems ideally suited. The progress of the reaction is also directed by the used solvent: in this study, imide formation was not observed when using THF as the solvent, most likely disfavoring the second deprotonation.

Figure 4. ORTEP representation of the molecular structures of 4 (top) and 5 (bottom) with atomic displacement parameters set at the 30% level. Hydrogen atoms (except NH) are omitted for clarity. Selected intramolecular distances and angles for complexes 4 and 5 are compiled in Table 4.

comparable to those detected in alkyl amide yttrium complexes as the 5-coordinated LY(NHC6H3iPr2](CH2SiMe3) (L = N(Ph2PNC6H3iPr2)2) (2.230(5) Å) and 6-coordinated ApY(CH2SiMe3)(NHC6H3iPr2-2,6)(dme)2 (Ap = bulky amidopyridinato ligand) (2.250(3) Å).11,38 Unsurprisingly, the Y− C(benzyl) bond length of 2.498(3) Å is slightly longer than in 6-coordinate precursor Cp*Y(CH2Ph)2(thf) (1a: 2.437(2) and 2.449(2) Å). Due to steric saturation of the yttrium center in 4, a close Y···Cipso contact like in 1a was not observed. Complex 5 adopts a four-legged piano-stool geometry in the solid state (Figure 4, bottom; Table 4), while the Y−N bond lengths of 2.271(1) and 2.258(1) Å match those of complex 3. The 1H NMR chemical shift of the NH moiety was observed at 4.53 ppm, at slightly lower field compared to complex 3 (4.33 ppm). The 89Y NMR signal (Table 1) detected by 1H−89Y HSQC/HMQC studies in complex 5 (233.0 ppm) is shifted to lower field in contrast to complex 3 (154.2 ppm). The amido ligands in complex 5 are arranged in a cisoid fashion (N1− Y1−N2, 85.30(5)°) contrary to their transoid arrangement in complex 3 (N1−Y1−N2, 143.0(1)°). The successful isolation of mixed benzyl amide complex 4, bis(amide) complexes 3 and 5 as well as imide complexes 2 allows us to speculate about a likely mechanistic scenario, in which the solvent (donor vs arene) and substitution pattern on the arylamine (2,6 vs 3,5) are crucial factors (Scheme 3). The reaction proceeds presumably via a sequence of toluene elimination (a) to yield mixed benzyl amide intermediate I1 (or complex 4), while intramolecular elimination of another molecule of toluene and concomitant dimerization affords the envisaged imide complex 2 (b). The side-reaction of intermediate I1 via ligand rearrangement, yielding the bis-

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CONCLUSION Rare-earth-metal half-sandwich benzyl complexes Cp*Ln(CH2Ph)2(thf) (Ln = Y, Lu) can display suitable precursors for the synthesis of imide complexes. However, the formation of imide derivatives according to a protonolysis reaction is highly dependent on the nature of the amine and the solvent employed. While use of the fluorinated aniline H2NC6H3(CF3)2-3,5 in toluene led to the dimeric rare-earth-metal imide complexes [Cp*Ln(NC6H3(CF3)2-3,5)(thf)x]2, the reaction in THF gave the bis(amide) complex Cp*Y(NHC6H3(CF3)23,5)2(thf)2. Similarly, the reaction of Cp*Y(CH2Ph)2(thf) with the sterically bulky H2NC6H3iPr2-2,6 resulted only in the isolation of the bis(amide) complex. Interestingly, the mixed amide/benzyl compound Cp*Y(NHC6H3iPr2-2,6)(CH2Ph)(thf) 2 could be detected in the reaction of Cp*Y(CH2Ph)2(thf) with H2NC6H3iPr2-2,6 in either a THF or a toluene solution, featuring a likely intermediate en route to the imide derivative.

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EXPERIMENTAL SECTION

General Considerations. All operations were performed in a glovebox with rigorous exclusion of air and water (MBraun 200B,