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.
The half-open rare-earth-metal aluminabenzene complexes[(1-Me-3,5-tBu 2 -C 5 H 3 Al)(m-Me)Ln(2,4-dtbp)] (Ln = Y, Lu) are accessible via as alt metathesis reaction employing Ln(AlMe 4 ) 3 and K(2,4-dtbp). Treatment of the yttrium complex with B(C 6 F 5 ) 3 and tBuCCH gives access to the pentafluorophenylalane complex [{1-(C 6 F 5 )-3,5-tBu 2 -C 5 H 3 Al}{m-C 6 F 5 }Y{2,4-dtbp}] and the mixed vinyl acetylide complex [(2,4-dtbp)Y(m-h 1 :h 3 -2,4-tBu 2 -C 5 H 4 )(m-CCtBu)-AlMe 2 ], respectively.Since the 1980s it has been known that pentadienyl ligands impart as tabilizing environment for the organometallic chemistry of alkali, alkaline-earth, transition, and rare-earth metals. [1] In comparison to the ubiquitous cyclopentadienyl congeners these "open variants" actively engage in distinct reaction paths,t he most prominent being the formation of metallabenzenes.T he feasibility of such metallacycles was initially shown for osmium by Elliot and co-workers in 1982 and later extended to the transition metals molybdenum, iridium, ruthenium, and nickel by the research groups led by Roper, Ernst, and Salzer. [2] In contrast to these aromatic transition-metal derivatives and the well-established borabenzene chemistry, [3] such ac ompound was only recently described for the Group 13 metal aluminum. In fact, the first isolation and subsequent characterization of the anionic aluminabenzene Li[1-Mes-2,6-C 5 H 3 Al] (Mes = 2,4,6-trimethylphenyl) was accomplished by Yamashita et al. in 2014 through as ophisticated reaction pathway employing asilyl-substituted diyne,DIBAL-H, and mesityllithium. [4] The same group also utilized the aforementioned aluminabenzene derivative in reactions with CpZrCl 3 ,C p*ZrCl 3 ,a nd ZrCl 4 , yielding distinct chlorido-bridged aluminabenzene-bearing complexes but at the expense of losing aromaticity in the aluminacycle to some degree. [5] Furthermore,n onbridged aluminabenzene complexes of the transition metals rhodium and iridium were published very recently by the Yamashita group as was az witterionic zirconium complex derived from an aluminacyclohexadiene and homoleptic benzyl ZrBn 4 . [6] These complexes also showed promising performances in C À Hb orylation and ethylene polymerization, respectively.Here we wish to report the formation of ad ianionic aluminabenzene ligand at rare-earth-metal centers according to an unprecedented reaction path, exploiting an alkylaluminate-mediated pentadienyl deprotonation and ring closure.A ccordingly,w hen we reacted the potassium salt of 2,4-di-tert-butylpentadiene K(2,4-dtbp) [1f] with rare-earthmetal tetramethylaluminates Ln(AlMe 4 ) 3 (Ln = Y, Lu) [7] at ambient temperature,w ew ere able to isolate the unusual "half-open" sandwich complexes [(1-Me-3,5-tBu 2 -C 5 H 3 Al)(m-Me)Ln(2,4-dtbp)] (1-Y,L n= Y) and 1-Lu (Ln = Lu) in high yields (Scheme 1). Complexes 1-Ln bear one 2,4-di-tertbutylpentadienyl ligand and one methyl-bridged 3,5-di-tertbutylaluminabenzene ligand, thus displaying another member of this rare family of metal-coordinated aluminabenzenes,...
Scandium mixed alkyls form readily via subsequent treatment of ScCl3 with Li[CH(SiMe3)2] and LiMe, as probed by 45Sc NMR spectroscopy.
Targeting the synthesis of rare‐earth‐metal pentadienyl half‐sandwich tetramethylaluminate complexes, homoleptic [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Lu) were treated with equimolar amounts of the potassium salts K(2,4‐dmp) (2,4‐dmp=2,4‐dimethylpentadienyl), K(2,4‐dipp) (2,4‐dipp=2,4‐diisopropylpentadienyl), and K(2,4‐dtbp) (2,4‐dtbp=2,4‐di‐tert‐butylpentadienyl). The reactions involving the larger rare‐earth‐metal centers lanthanum, cerium, praseodymium, and neodymium gave selectively the desired half‐sandwich complexes [(2,4‐dmp)La(AlMe4)2], [(2,4‐dipp)La(AlMe4)2], and [(2,4‐dtbp)Ln(AlMe4)2] (Ln=La, Ce, Pr, Nd) in high crystalline yields. Smaller rare‐earth‐metal centers yielded preferentially the sandwich complexes [(2,4‐dmp)2Ln(AlMe4)] (Ln=Y, Lu) and [(2,4‐dipp)2Y(AlMe4)]. Activation with fluorinated borate/borane co‐catalysts gave highly active catalyst systems for the fabrication of polyisoprene, displaying molecular weight distributions as low as Mw/Mn=1.09 and a maximum cis‐1,4 selectivity of 90.4 %. The equimolar reaction of half‐sandwich complex [(2,4‐dtbp)La(AlMe4)2] with B(C6F5)3 led to the isolation and full characterization of the single‐component catalyst {{(2,4‐dtbp)La[(μ‐Me)2AlMe(C6F5)]}[Me2Al(C6F5)2]}2. The reaction of the latter complex with 10 equivalents of isoprene could be monitored by 1H NMR spectroscopy. Also, a donor‐induced aluminato/gallato exchange was achieved with [(2,4‐dtbp)La(AlMe4)2] and GaMe3(OEt2) leading to [(2,4‐dtbp)La(GaMe4)2].
Die halboffenen Seltenerdmetall-Aluminabenzol-Komplexe[ (1-Me-3,5-tBu 2 -C 5 H 3 Al)(m-Me)Ln(2,4-dtbp)] (Ln = Y, Lu) sind über eine Salzmetathese-Reaktion unter Verwendung von Ln(AlMe 4 ) 3 und K(2,4-dtbp) zugänglich. Die Umsetzung des Yttrium-Komplexes mit B(C 6 F 5 ) 3 und tBuCCH ermçglicht den Zugang zum Pentafluorphenylalan-Komplex [{1-(C 6 F 5 )-3,5-tBu 2 -C 5 H 3 Al}{m-C 6 F 5 }Y{2,4-dtbp}] bzw.d em gemischten Vinylacetylid-Komplex [(2,4-dtbp)Y(m-h 1 :h 3 -2,4-tBu 2 -C 5 H 4 )(m-CCtBu)AlMe 2 ].
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