Rare-earth metal methylidene complexes with Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3core structure

Schädle, Dorothea; Meermann-Zimmermann, Melanie; Maichle‐Mößmer, Cäcilia; Schädle, Christoph; Törnroos, Karl W.

doi:10.1039/c5dt02936h

Cited by 21 publications

(9 citation statements)

References 65 publications

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“…Two of the scandium centers are additionally connected to tetramethylaluminato groups, while the two Sc-CH 2 edges involving the third scandium metal are flanked by trimethylaluminum moieties. The [Ln 3 Me 3 ] six-membered ring structural motif has earlier been observed in the benzamidinato-supported scandium complex [{(NCN)Sc(μ 2 -Me)} 3 (μ 3 -Me)(μ 3 -CH 2 )] or, for other rare-earth metals, in the mixed methyl/methylidene compounds [{NSiMe 3 (Ar)} 3 Ln 3 (μ 3 -CH 2 )(μ 3 -Me)(μ 2 -Me) 3 (thf) 3 ] (Ln = Y, Ho, Lu; Ar = C 6 H 3 i Pr 2 -2,6) . The Sc–CH 2 distances (2.298(3)–2.442(2) Å) are comparable to those in the already known six-coordinate benzamidinate complex (2.346–2.399 Å) or Mindiola’s mononuclear Lewis-acid-stabilized six-coordinate scandium methylidene complex [(PNP)Sc(μ 3 -CH 2 ){(μ 2 -Me) 2 AlMe 2 } 2 ] (2.3167(17) Å) .…”

Section: Resultsmentioning

confidence: 99%

Trimethylscandium

2019

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The hitherto unknown homoleptic tetramethylaluminate complex [Sc(AlMe 4 ) 3 ] could be obtained by reacting the ate complex [Li 3 ScMe 6 (thf) 1.2 ] with AlMe 3 in the cold. It cocrystallizes with AlMe 3 as [Sc-(AlMe 4 ) 3 (Al 2 Me 6 ) 0.5 ] and decomposes at ambient temperature in n-pentane via multiple C−H bond activations to the mixed methyl/methylidene complex [Sc 3 (μ 3 -CH 2 ) 2 (μ 2 -CH 3 ) 3 (AlMe 4 ) 2 (AlMe 3 ) 2 ]. Donor-induced methylaluminate cleavage of [Sc(AlMe 4 ) 3 (Al 2 Me 6 ) 0.5 ] produced [ScMe 3 ] n in good yield, which could be derivatized with trimethyltriazacyclononane (Me 3 TACN) to form the structurally characterizable [(Me 3 TACN)ScMe 3 ]. Additionally, half-sandwich complex [Cp*Sc(AlMe 4 ) 2 ] and sandwich complex [Cp* 2 Sc(AlMe 4 )] were accessible by salt metathesis reactions from [Sc-(AlMe 4 ) 3 (Al 2 Me 6 ) 0.5 ] and KCp* (Cp* = C 5 Me 5 ). 45 Sc NMR spectroscopy was applied as a significant probe to evidence the existence of [ScMe 3 ] n . Compounds [(Me 3 TACN)ScMe 3 ] (+624.6 ppm) and [ScMe 3 (thf) x ] (+601.7 ppm) gave large 45 Sc NMR shifts, revealing the strong deshielding effect of the σ-bonded alkyl ligands on the scandium nuclei. Ultimately, cationized [Sc(AlMe 4 ) 3 (Al 2 Me 6 ) 0.5 ] was employed in isoprene polymerization, leading to polymers in high yields (>95%) and with high (>90%) cis-1,4-polyisoprene content.

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Section: Resultsmentioning

confidence: 99%

Trimethylscandium

2019

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“…The Y–C(CH 2 ) distances in complexes 4-Y X can be compared to those of complex VI Y (see Figure , 2.345(5)–2.424(4) Å), V Y (2.283(4)–2.477(3) Å), and (NCN dipp ) 3 Y 3 (μ-Me) 3 (μ 3 -CH 2 )(μ 3 -CCTMS) (2.382(6)–2.418(6) Å), which tend to be shorter. Overall, trimetallic rare-earth-metal methylidene complexes as depicted in Figure show similar average Ln–C(CH 2 ) bond lengths considering the different ionic radii of the rare-earth-metal centers: e.g., II Sc 2.367 Å, II Er 2.388 Å, II Lu 2.376 Å, IV Tm 2.346 Å, VI Nd 2.475 Å, VI Ho 2.391 Å, and VI Lu 2.347 Å …”

Section: Resultsmentioning

confidence: 85%

“…So far, two structural motifs of rare-earth-metal methylidene complexes have been utilized in methylidene transfer reactions, comprising cubane-like tetrametallic [(L)Ln(CH 2 )] 4 ( I ; Ln = smaller-sized expensive rare-earth metals only) and trimetallic complexes L 3 Ln 3 (μ-X) 3 (μ 3 -X)(μ 3 -CH 2 )(THF) n ( II – VI ) with L being a monoanionic ligand and X being either a methyl or halogenido moiety (Figure ). − …”

Section: Introductionmentioning

confidence: 99%

“…For example, the generation of the cubane-like lutetium complex stabilized by the trimethylsilyl-substituted cyclopentadienyl ligand C 5 Me 4 SiMe 3 (Cp′) was achieved by C–H-bond activation of the dimethyl precursor [Cp′Lu(CH 3 ) 2 ] 3 via release of CH 4 . Such reactive Ln–Me moieties are also easily generated via alkyl exchange in [(L)Ln(R) 2 ] ( II , R = CH 2 C 6 H 4 NMe 2 , L = PhC(NC 6 H 3 i Pr 2 -2,6) 2 for Ln = Sc, Y, Er, Lu; III , L = (C 6 H 4 NMe 2 )CH 2 C(NC 6 H 3 i Pr 2 -2,6) 2 for Ln = Lu; IV , R = CH 2 SiMe 3 , L = C 5 Me 4 SiMe 3 , Ln = Tm) ,, with AlMe 3 or through donor-induced cleavage of tetramethyl-aluminate in (L)Ln(AlMe 4 ) 2 ( V Y , L = C 5 Me 5 , Ln = Y; VI , L = N(C 6 H 3 i Pr 2 -2,6)(SiMe 3 ), Ln = Y, Nd, Ho, Lu; II , L = PhC(NC 6 H 3 i Pr 2 -2,6) 2 , Ln = Sc, Lu) for bridging methyl groups ,,, or [(L)Ln(AlMe 4 ) x (Cl) y ] z ( V , L = C 5 Me 5 , Ln = Y with x = y , z = 2, La with 2 x = y , z = 6) for bridging chlorido units . In all cases inter- or intramolecular C–H-bond activation will afford the desired dianionic methylidene moiety.…”

Section: Introductionmentioning

confidence: 99%

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A Rare-Earth-Metal Ensemble of the Tebbe Reagent: Scope of Coligands and Carbonyl Olefination

et al. 2020

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Treatment of the half-sandwich complexes Cp R Ln-(AlMe 4 ) 2 (Cp R = C 5 Me 5 , C 5 Me 4 SiMe 3 ; Ln = Y, La, Lu) with the mild halogenido transfer reagents SiMe 3 X (X = Cl, Br, I) resulted in efficient and selective halogenido/tetramethylaluminato exchange. Depending on the size of the rare-earth metal, dimeric [Cp R Ln-(AlMe 4 )(μ-X)] 2 (Ln = Y, Lu) and decametallic [Cp R 3 La 3 (AlMe 4 ) 2 (μ-X) 4 ] 2 could be obtained. Donor (THF)-induced tetramethylaluminato cleavage gave access to "methyl-free" mixed methylidene/halogenido complexes Cp R 3 Ln 3 (μ-X) 3 (μ 3 -X)(μ 3 -CH 2 )(THF) 3 for yttrium (X = Cl, Br) and lanthanum (X = Cl, Br, I) in good yields. Additionally, mixed methylidene/halogenido Y(III) complexes could be obtained via methyl/halogenido exchange employing (C 5 Me 5 ) 3 Y 3 (μ-Me) 3 (μ 3 -Me)(μ 3 -CH 2 )(THF) 2 and SiMe 3 X via tetramethylsilane elimination. All methylidene complexes were probed in olefination reactions and found to act as efficient Schrock-type nucleophilic carbenes converting ketones and aldehydes into the respective terminal alkenes. Such reactivity is as high as that of the prominent Tebbe reagent but is less tolerant toward sterically demanding and functionalized substrates (such as esters). In contrast to the Tebbe reagent, complexes Cp R 3 Ln 3 (μ-X) 3 (μ 3 -X)(μ 3 -CH 2 )(THF) 3 polymerize δ-valerolactone in an efficient manner, generating polylactones with molecular weight distributions M w /M n as low as 1.13. Moreover, the bromido variant of the Tebbe reagent, Cp 2 Ti(μ-CH 2 )(μ-Br)AlMe 2 , is described, underlying similar synthesis limitations: that is, the coformation (and hence cocrystallization) of the trivalent species Cp 2 Ti(μ-Br) 2 AlMe 2 .

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“…External donor stabilization was exploited for complexes Cp*ScMe 2 (OP t Bu 3 ) ( VII ), [N(SiMe 3 )(Dipp)]LuMe 2 (THF) 2 ( VIII ), and [(Dipp)NC(Me ) CHC(Me)N(Dipp)]ScMe 2 (THF) ( IX ) …”

Section: Introductionmentioning

confidence: 99%

Mixed Methyl Aryloxy Rare-Earth-Metal Complexes Stabilized by a Superbulky Tris(pyrazolyl)borato Ligand

2019

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Various mixed methyl aryloxide complexes Tp tBu,Me LnMe(OAr) (Ln = Y, Lu) were obtained in moderate to high yields according to distinct synthesis protocols dependent on the metal size and sterics of the phenolic proligand. The reaction of Tp tBu,Me LuMe 2 and Tp tBu,Me YMe(AlMe 4 ) via protonolysis with 1 or 2 equiv HOC 6 H 2 tBu 2 -2,6-Me-4 in n-hexane gave the desired complexes Tp tBu,Me LnMe(OAr). Corresponding treatment of Tp tBu,Me LuMe 2 with the sterically less demanding HOC 6 H 3 Me 2 -2,6, HOC 6 H 3 iPr 2 -2,6 and HOC 6 H 3 (CF 3 ) 2 -3,5 led to the formation of the bis(aryloxy) lutetium complexes Tp tBu,Me Lu(OAr) 2 . Application of a salt-metathesis protocol employing Tp tBu,Me LnMe(AlMe 4 ) and the potassium aryloxides KOAr made complexes Tp tBu,Me LnMe(OAr) accessible for the smaller aryloxy ligands as well. All complexes were analyzed by X-ray crystallography to compare the terminal Ln−Me bond lengths and to evaluate the implication of the methyl/aryloxy coordination for the exact cone angles Θ°of the [Tp tBu,Me ] ancillary ligand. Treatment of Tp tBu,Me LnMe(AlMe 4 ) (Ln = Lu, Y) with HOC 6 H 2 tBu 2 -2,6-Me-4 in the presence of 4-(dimethylamino)pyridine (dmap) produced ion-separated complexes [Tp tBu,Me LnMe(dmap) 2 ]-[Me 3 AlOC 6 H 2 tBu 2 -2,6-Me-4)]. The thermal instability of Tp tBu,Me LuMe(OC 6 H 2 tBu 2 -2,6-Me-4) was revealed by the formation of (Tp (tBu-H)/(tBu)2,Me )Lu(OC 6 H 2 tBu 2 -2,6-Me-4) via intramolecular C−H-bond activation.

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Rare-earth metal methylidene complexes with Ln₃(μ₃-CH₂)(μ₃-Me)(μ₂-Me)₃core structure

Cited by 21 publications

References 65 publications

Trimethylscandium

Trimethylscandium

A Rare-Earth-Metal Ensemble of the Tebbe Reagent: Scope of Coligands and Carbonyl Olefination

Mixed Methyl Aryloxy Rare-Earth-Metal Complexes Stabilized by a Superbulky Tris(pyrazolyl)borato Ligand

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