Klaus Eichele Publication Abstracts 2020

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)(mu-Cl)(2)Li(thf)(2)](2)and Sc[CH(SiMe3)(2)](3)(mu-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)(mu-Me)(2)Li(thf)(2)](2)and Sc[CH(SiMe3)(2)](3)(mu-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 LiAlMe(4)separation occurred, aluminium complex Al[CH(SiMe3)(2)]Me-2(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe3)(2)}(2)(mu-Me)(2)Li(thf)(2)](2)and [Sc(CH2SiMe3)(4)][Li(thf)(4)] revealed the maximum downfield(45)Sc 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 attemptedviathe aryloxide route applying complexes Sc(OC(6)H(2)tBu(2)-2,6-Me-4)(3)and [Sc(OC(6)H(3)iPr(2)-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.

The benzo annulated cycloheptatriene PCP pincer ruthenium hydrido dicarbonyl complex syn-2 was prepared in one step by treatment of the ligand 1 with Ru-3(CO)(12). Protonation of syn-2 with the superacid [H(Et2O)(2)][BArF24] {[BArF24]- = tetrakis[bis(trifluoromethyl)phenyl]borate} initiates the highly stereoselective hydrogenation of one of the double bonds in the cycloheptatriene backbone. This results in the formation of the pentacoordinate cationic 16-electron dicarbonyl ruthenium complex 3. Hydrogenation of 3 with LiAlH4 generates the hydride complexes syn-4 and anti-4 which after protonation allow isolation of the symmetric 5. In 5 a second double bond of the cycloheptatriene backbone was hydrogenated. Complex 5 was also obtained directly by the reaction of 3 with hydrogen (1 bar). Storage of 5 under a hydrogen atmosphere yields two pairs of eta(2)-H-2 complexes (syn-7, anti-7) which are in a tautomeric equilibrium with their corresponding dihydrides (syn-8, anti-8). A stepwise transfer of the hydrides to the ligand backbone can be deduced from the distribution of deuterium along the seven membered ring after applying the deuterated reagents (D+, D-2). The observed stereochemistry suggests that the hydride transfer is controlled by conformational constraints.