Aluminum <i>ansa</i>-Indenyl Compounds. Synthesis, Structures, Dynamic Properties, and Application in the Synthesis of Group 4 <i>ansa</i>-Metallocenes

Abstract

The synthesis, structures, dynamic properties, and indenyl transfer reactions of aluminum ansa -bis(indenyl) compounds are described. The reaction of 2 equiv of AlMe 2 Cl with 1 equiv of Li 2 [(1-indenyl) 2 SiMe 2 ], Li 2 [(2-Me-1-indenyl) 2 SiMe 2 ], Li 2 [(2-Me-4,5-benz-1-indenyl) 2 SiMe 2 ]·Et 2 O, Li 2 [(2-Me-4-Ph-1-indenyl) 2 SiMe 2 ]·Et 2 O, or Li 2 [1,2-(3-indenyl) 2 -C 2 H 4 ] in Et 2 O followed by treatment with the appropriate Lewis base (L) affords {AlMe 2 (THF)(indenyl)} 2 SiMe 2 ( 1 ), [{1-AlMe 2 (1,4-dioxane) 0.5 -2-Me-1-indenyl} 2 SiMe 2 ] n ( 2a ), {1-AlMe 2 (Et 2 O)-2-Me-4,5-benz-1-indenyl} 2 SiMe 2 ( 3 ), {1-AlMe 2 (Et 2 O)-2-Me-4-Ph-1-indenyl} 2 SiMe 2 ( 4a ), {1-AlMe 2 (THF)-2-Me-4-Ph-1-indenyl} 2 SiMe 2 ( 4b ), or 1,2-{3-AlMe 2 (THF)-1-indenyl} 2 -C 2 H 4 ( 5 ), respectively, as colorless to pale yellow solids in 41−70% isolated yields. Compounds 2a and 4b are isolated as the rac isomers, whereas 1 and 3 are isolated as rac / meso mixtures from which the rac isomer can be separated by recrystallization. Compound 5 was isolated as a single diastereomer of 1,2-{3-AlMe 2 (THF)-1-indenyl} 2 -C 2 H 4 . The molecular structures of rac - 2a and rac - 3 have been determined by X-ray crystallography. Low-temperature NMR studies establish that, in toluene- d 8, rac - 1 exists as a 2/1 mixture of two isomers, ({1-AlMe 2 (THF)-1-indenyl}{1-AlMe 2 (THF)-3-indenyl})SiMe 2 ( rac - 1a ) and {1-AlMe 2 (THF)-1-indenyl} 2 SiMe 2 ( rac - 1b ), which interconvert rapidly on the NMR time scale at room temperature. In contrast, similar studies establish that rac - 2b (in THF- d 8 ) and rac - 3 and rac - 4b (in toluene- d 8 ) exist as the rac -{1-AlMe 2 L-1-indenyl} 2 SiMe 2 isomers; in these cases no other isomers are detected. rac - 1, rac - 3, and rac - 4b isomerize to rac / meso mixtures slowly (days) at ambient temperature and more rapidly (minutes) at 70 °C. Compounds 1 and 5 undergo slow partial disproportionation by ligand redistribution (e.g. 1: 28% conversion, 2 days, 23 °C, benzene); the more highly substituted indenyl compounds 3 and 4b are more resistant to this process. Compounds 1, 2, 3, 4a, and 5 react with Zr(NMe 2 ) 4 and Hf(NMe 2 ) 4 in benzene or toluene under mild conditions to yield the corresponding ansa -metallocenes {(1-indenyl) 2 SiMe 2 }M(NMe 2 ) 2 ( 6, M = Zr, rac / meso = 4/1; 7, M = Hf, rac / meso = 10/1), {(2-Me-1-indenyl) 2 SiMe 2 }Zr(NMe 2 ) 2 ( 8, rac / meso = 3/4), {(2-Me-4,5-benz-1-indenyl) 2 SiMe 2 }Zr(NMe 2 ) 2 ( 9, rac / meso = 9/10), {(2-Me-4-Ph-1-indenyl) 2 SiMe 2 }Zr(NMe 2 ) 2 ( 10, rac / meso = 2/3) and {1,2-(3-indenyl) 2 -C 2 H 4 }M(NMe 2 ) 2 ( 11, M = Zr, rac / meso = 7.3/1; 12, M = Hf, rac / meso = 7/1) in 70−90% NMR yields.