Group 13 and lanthanide complexes supported by tridentate tripodal triamine ligands: Structural diversity and polymerization catalysis

Several different synthetic approaches to a total of 13 novel B, Al, and Sm complexes derived from the tridentate tripodal triamine ligand [N-3]H-3 with a neopentane, trisilylmethane, or trisilylsilane backbone and different N-substituents, as well as applications of the selected complexes to polymerization catalysis, are reported. Salt metathesis between HC[SiMe2N(CH2Ph)](3)Li-3(THF)(2) (THF = tetrahydrofuran) and AlCl3 in Et2O/hexanes leads to complete elimination of LiCl and formation of the corresponding tripodal triamido alane HC[SiMe2N(CH2Ph)](3)Al center dot(THF) (1). On the other hand, the reaction of {MeC[CH2N(SiMe3)](3)Li-3}(2) and AlCl3 in Et2O/hexanes yields a LiCl-containing compound MeC[CH2N(SiMe3)](3)AlCl[Li(Et2O)] (2). Alkane elimination involving [N-3]H-3 and 1 AlMe3 produces diamido-amino aluminum methyl HC[SiMe2NHAr][SiMe2NAr](2)AlMe [Ar = 4-MeC6H4 (3), CH2Ph (4)], while the reaction using >= 2 AlMe3 gives amido-amino aluminum dimethyl [ArHNMe2Si](H)C[SiMe2NAr](2)(A]Me-2)(2) (Ar = 4-MeC6H4, 5) and [(Me3Si)HNCH2](Me)C[CH2N(SiMe3)](2)(AlMe2)(2) (6). The H-2-elimination route involves treatment of [N-3]H-3 with LiAlH4 and AlH3, affording [{ HC[SiMe2N(4-MeC6H4)](3)AIH}Li](2) (7) and MeSi[SiMe2N(4-MeC6H4)](3)AIH(AIH(2)) (8), respectively. There is no reaction between [N-3]H-3 and AI[N(SiMe3)(2)](3); however, the amine-elimination reaction using Sm[N(SiMe3)(2)](3) produces tripodal triamido Sm complex IMeSi[SiMe2N(4-MeC6H4)13SM12 (9). Ligand exchange betwe.en tripodal borane HC[SiMe2N(4MeC(6)H(4))](3)B and AIR(3) (R =Me, H) offers the first-step ligand exchange product HC[SiMe2N(4-MeC6H4)](3)BMe(AlMe2) (10) or the second-step ligand exchange product HC[SiMe2N(4-MeC6H4)](3) AIH(BH2) (11). Activation of dimethyl metallocenes LZrMe2 by HC[SiMe2N(4-MeC6H4)](3) B produces ligand redistribution products LZrMe[N(4-MeC6H4)SiMe2](H)C[SiMe2N(4-MeC6H4)](2)BMe [L = Cp-2 (12), rac-Et(Ind)(2) (13)]. Besides characterizations by NMR and elemental analysis of the above new complexes, six of them (2, 4, 5, 8, 9, and 13) have also been structurally characterized by X-ray single-crystal diffraction studies. "Activated" metallocene complexes 12 and 13 are inactive for ethylene or propylene polymerization. Complex I exhibits low activity for ring-opening polymerization (ROP) of propylene oxide, but high activity for ROP of c-caprolactone (CL). Significantly, tripodal aluminum hydride 8 effects catalytic ROP of CL upon addition of benzyl alcohol as a chain-transfer reagent.