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[SiMe 2 N(CH 2 Ph)] 3 Li 3 (THF) 2 (THF = tetrahydrofuran) and AlCl 3 in Et 2 O/hexanes leads to complete elimination of LiCl and formation of the corresponding tripodal triamido alane HC[SiMe 2 N(CH 2 Ph)] 3 Al·(THF) ( 1 ). On the other hand, the reaction of {MeC[CHN(SiMe 3 )] 3 Li 3 } 2 and AlCl 3 in Et 2 O/hexanes yields a LiCl-containing compound MeC[CH 2 N(SiMe 3 )] 3 AlCl[Li(Et 2 O)] ( 2 ). Alkane elimination involving [N 3 ]H 3 and 1 AlMe 3 produces diamido−amino aluminum methyl HC[SiMe 2 NHAr][SiMe 2 NAr] 2 AlMe [Ar = 4-MeC 6 H 4 ( 3 ), CH 2 Ph ( 4 )], while the reaction using ≥2 AlMe 3 gives amido−amino aluminum dimethyl [ArHNMe 2 Si](H)C[SiMe 2 NAr] 2 (AlMe 2 ) 2 (Ar = 4-MeC 6 H 4, 5 ) and [(Me 3 Si)HNCH 2 ](Me)C[CH 2 N(SiMe 3 )] 2 (AlMe 2 ) 2 ( 6 ). The H 2 -elimination route involves treatment of [N 3 ]H 3 with LiAlH 4 and AlH 3, affording [{HC[SiMe 2 N(4-MeC 6 H 4 )] 3 AlH}Li] 2 ( 7 ) and MeSi[SiMe 2 N(4-MeC 6 H 4 )] 3 AlH(AlH 2 ) ( 8 ), respectively. There is no reaction between [N 3 ]H 3 and Al[N(SiMe 3 ) 2 ] 3; however, the amine-elimination reaction using Sm[N(SiMe 3 ) 2 ] 3 produces tripodal triamido Sm complex {MeSi[SiMe 2 N(4-MeC 6 H 4 )] 3 Sm} 2 ( 9 ). Ligand exchange between tripodal borane HC[SiMe 2 N(4-MeC 6 H 4 )] 3 B and AlR 3 (R = Me, H) offers the first-step ligand exchange product HC[SiMe 2 N(4-MeC 6 H 4 )] 3 BMe(AlMe 2 ) ( 10 ) or the second-step ligand exchange product HC[SiMe 2 N(4-MeC 6 H 4 )] 3 AlH(BH 2 ) ( 11 ). Activation of dimethyl metallocenes LZrMe 2 by HC[SiMe 2 N(4-MeC 6 H 4 )] 3 B produces ligand redistribution products LZrMe[N(4-MeC 6 H 4 )SiMe 2 ](H)C[SiMe 2 N(4-MeC 6 H 4 )] 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 1 exhibits low activity for ring-opening polymerization (ROP) of propylene oxide, but high activity for ROP of ε-caprolactone (CL). Significantly, tripodal aluminum hydride 8 effects catalytic ROP of CL upon addition of benzyl alcohol as a chain-transfer reagent.