RESUMEN
The yttrium gallabenzene complex [(1-Me-3,5-tBu2 -C5 H3 Ga)(µ-Me)Y(2,4-dtbp)] is accessible from Y(GaMe4 )3 and K(2,4-dtbp) via a tandem salt metathesis/methane elimination (2,4-dtbp=2,4-di-tert-butyl-pentadienyl). The pentadienyl ligand in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] (E=Al, Ga) is easily displaced by salt metathesis with KC5 Me5 and KTpMe,Me (TpMe,Me =tris(pyrazolyl-Me2 -3,5)borato) affording [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(TpMe,Me )] and [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(C5 Me5 )]. The yttrium center in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] readily forms adducts with neutral Lewis bases like 4-DMAP (4-dimethylaminopyridine), PMe3 , DMPE (1,2-bis(dimethylphosphino)ethane), and DME (1,2-dimethoxyethane). In stark contrast, addition of TMEDA (N,N,N',N'-tetramethylethylenediamine) results in methyl/pentadienyl exchange between aluminum and yttrium resulting in [(1-(2,4-dtbp)-1-Me-3,5-tBu2 -C5 H3 Al)Y(Me)(tmeda)]. The bonding features of the newly synthesized complexes are analyzed by single-crystal X-ray diffraction (SCXRD) and heteronuclear (89 Y, 31 P) NMR spectroscopy.
RESUMEN
Depending on the molar ratio employed, the reaction of ScCl3(thf)3 with Li[CH(SiMe3)2] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe3)2}2(µ-Cl)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(µ-Cl)Li(thf)3, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe3)2}2(µ-Me)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(µ-Me)Li(thf)3. Aiming at homoleptic {Sc[CH(SiMe3)2]3} both of the mixed [CH(SiMe3)2]/Me complexes were treated with AlMe3. Although LiAlMe4 separation occurred, aluminium complex Al[CH(SiMe3)2]Me2(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe3)2}2(µ-Me)2Li(thf)2]2 and [Sc(CH2SiMe3)4][Li(thf)4] revealed the maximum downfield 45Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe3)2]3} was also attempted via the aryloxide route applying complexes Sc(OC6H2tBu2-2,6-Me-4)3 and [Sc(OC6H3iPr2-2,6)3]2 along with Li[CH(SiMe3)2] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe3)2] in the solid state.
RESUMEN
The hitherto unknown homoleptic tetramethylaluminate complex [Sc(AlMe4)3] could be obtained by reacting the ate complex [Li3ScMe6(thf)1.2] with AlMe3 in the cold. It cocrystallizes with AlMe3 as [Sc(AlMe4)3(Al2Me6)0.5] and decomposes at ambient temperature in n-pentane via multiple C-H bond activations to the mixed methyl/methylidene complex [Sc3(µ3-CH2)2(µ2-CH3)3(AlMe4)2(AlMe3)2]. Donor-induced methylaluminate cleavage of [Sc(AlMe4)3(Al2Me6)0.5] produced [ScMe3]n in good yield, which could be derivatized with trimethyltriazacyclononane (Me3TACN) to form the structurally characterizable [(Me3TACN)ScMe3]. Additionally, half-sandwich complex [Cp*Sc(AlMe4)2] and sandwich complex [Cp*2Sc(AlMe4)] were accessible by salt metathesis reactions from [Sc(AlMe4)3(Al2Me6)0.5] and KCp* (Cp* = C5Me5). 45Sc NMR spectroscopy was applied as a significant probe to evidence the existence of [ScMe3]n. Compounds [(Me3TACN)ScMe3] (+624.6 ppm) and [ScMe3(thf)x] (+601.7 ppm) gave large 45Sc NMR shifts, revealing the strong deshielding effect of the σ-bonded alkyl ligands on the scandium nuclei. Ultimately, cationized [Sc(AlMe4)3(Al2Me6)0.5] was employed in isoprene polymerization, leading to polymers in high yields (>95%) and with high (>90%) cis-1,4-polyisoprene content.
RESUMEN
Aluminabenzene complex [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(2,4-dtbp)] (2,4-dtbp = 2,4-di-tert-butylpentadienyl) reacts with LiN(SiHMe2)2 according to a methyl/silylamido exchange and formation of [(1-Me-3,5-tBu2-C5H3Al){µ-N(SiHMe2)2}Ln(2,4-dtbp)] which engages in a donor(THF)-dependent reversible Ln-to-Al-pentadienyl migration. The reaction of [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(2,4-dtbp)] with [CPh3][B(C6F5)4] results in pentadienyl group abstraction affording cationic complex [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(benzene)][B(C6F5)4] which acts as a single-component catalyst in isoprene polymerization.
RESUMEN
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)2 Ln(AlMe4 )] (Ln=Y, Lu) and [(2,4-dipp)2 Y(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(C6 F5 )3 led to the isolation and full characterization of the single-component catalyst {{(2,4-dtbp)La[(µ-Me)2 AlMe(C6 F5 )]}[Me2 Al(C6 F5 )2 ]}2 . The reaction of the latter complex with 10â equivalents of isoprene could be monitored by 1 Hâ 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 ].
RESUMEN
The half-open rare-earth-metal aluminabenzene complexes [(1-Me-3,5-tBu2 -C5 H3 Al)(µ-Me)Ln(2,4-dtbp)] (Ln=Y, Lu) are accessible via a salt metathesis reaction employing Ln(AlMe4 )3 and K(2,4-dtbp). Treatment of the yttrium complex with B(C6 F5 )3 and tBuCCH gives access to the pentafluorophenylalane complex [{1-(C6 F5 )-3,5-tBu2 -C5 H3 Al}{µ-C6 F5 }Y{2,4-dtbp}] and the mixed vinyl acetylide complex [(2,4-dtbp)Y(µ-η1 :η3 -2,4-tBu2 -C5 H4 )(µ-CCtBu)AlMe2 ], respectively.