Implementation of Ln(AlMe4)3 as Precursors in Postlanthanidocene Chemistry

Abstract

cis-2,5-Bis[N,N-((2,6-diisopropylphenyl)amino)methyl]tetrahydrofuran (H2BDPPthf) was obtained from LiNH(2,6-iPr2C6H3) and cis-2,5-bis((tosyloxy)methyl)tetrahydrofuran in high yield and employed as a new [NON]2- ancillary ligand for rare-earth metal centers. The reaction of H2BDPPthf with homoleptic tetramethylaluminates Ln(AlMe4)3 (Ln = Y, Nd, La) quantitatively yielded heterobimetallic complexes (BDPPthf)Ln(AlMe4)(AlMe3) via alkane elimination. X-ray structure analysis of (BDPPthf)Ln(AlMe4)(AlMe3) (Ln = Y, La) revealed different coordination modes of BDPPthf, AlMe4-, and AlMe3. The yttrium derivative displays an η2-coordination of BDPPthf and insertion of AlMe3 into one of the Ln−N anilido bonds to form a novel [LnIII(μ-Me)2AlMe(NR2)] moiety. In contrast, BDPPthf coordinates the larger lanthanum center in an η3 fashion involving a heterobridging [La(μ-NR2)(μ-Me)AlMe2] moiety. The AlMe4- ligand adopts an unusual distorted μ:η3- (La) and a routine μ:η2-coordination mode (Y) depending on the size of the metal center. The intrinsic [NON]2- ligand functionality for the first time implied the formation and structural identification of a kinetically favored aluminate/HR protonolysis product (Y), whereas the thermodynamically favored Ln−amido contact is found for the lanthanum derivative. All organolanthanide complexes were fully characterized by NMR and FTIR spectroscopy and elemental analysis.