Aluminum ansa-indenyl compounds. Synthesis, structures, dynamic properties, and application in the synthesis of group 4 ansa-metallocenes

The synthesis, structures, dynamic properties, and indenyl transfer reactio ns of aluminum ansa-bis(indenyl) compounds are described. The reaction of 2 equiv of AlMe2Cl with 1 equiv of Li-2[(1-indenyl)(2)SiMe2], Li-2[(2-Me-1-i ndenyl)(2)SiMe2], Li-2[(2-Me-4,5-benz-1-indenyl)(2)SiMe2]. Et2O, Li-2[(2-Me -4-Ph-1-indenyl)(2)SiMe2]. Et2O, or Li-2[1,2-(3-indenyl)(2)-C2H4] in Et2O f ollowed by treatment with the appropriate Lewis base (L) affords {AlMe2(THF )(indenyl)}(2)SiMe2 (1), [{1-AlMe2(1,4-dioxane)(0.5)-2-Me-1-indenyl}(2)SiMe 2](n) (2a), {1-AlMe2(Et2O)-2-Me-4,5-benz-1-indenyl}(2)SiMe2 (3), {1-AlMe2(E t2O)-2-Me-4-Ph-1-indenyl}(2)SiMe2 (4a), {1-AlMe2(THF)-2-Me-4-Ph-1-indenyl}( 2)SiMe2 (4b), or 1,2-{3-AlMe2(THF)-1-indenyl}(2)-C2H4 (5), respectively, as colorless to pale yellow solids in 41-70% isolated yields. Compounds 2a an d 4b are isolated as the rac isomers, whereas 1 and 3 are isolated as rac/m eso mixtures from which the rac isomer can be separated by recrystallizatio n. Compound 5 was isolated as a single diastereomer of 1,2-(3-AlMe2(THF)-1- indenyl}(2)-C2H4. The molecular structures of rac-2a and rac-3 have been de termined by X-ray crystallography. Low-temperature NMR studies establish th at, in toluene-d(8), rac-1 exists as a 2/1 mixture of two isomers, ({1-AlMe 2(THF)-1-indenyl}{1-AlMe2(THF)-3-indenyl})SiMe2 (rac-1a) and {1-AlMe2(THF)- 1-indenyl}(2)SiMe2 (rac-1b), which interconvert rapidly on the NMR time sca le 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-Al Me2L-1-indenyl}(2)SiMe2 isomers; in these cases no other isomers are detect ed. rac-1, rac-3, and rac-4b isomerize to rac/meso mixtures slowly (days) a t ambient temperature and more rapidly (minutes) at 70 degrees C. Compounds 1 and 5 undergo slow partial disproportionation by ligand redistribution ( e.g. 1: 28% conversion, 2 days, 23 degrees C, benzene); the more highly sub stituted indenyl compounds 3 and 4b are more resistant to this process. Com pounds 1, 2, 3, 4a, and 5 react with Zr(NMe2)(4) and Hf(NMe2)(4) in benzene or toluene under mild conditions to yield the corresponding ansa-metalloce nes {(1-indenyl)(2)SiMe2}M(NMe2)(2) (6, M = Zr, rac/meso = 4/1; 7, M = Hf r ac/meso = 10/1), {(2-Me-1-indenyl)(2)SiMe2)Zr(NMe2)(2) (8, rac/meso = 3/4), {(2-Me-4,5-benz-1-indenyl)(2)SiMe2}Zr(NMe2)(2) (9, rac/meso = 9/10), {(2-M e-4-Ph-1-indenyl)2SiMe(2)}Zr(NMe2)(2) (10, rac/meso = 2/3) and {1,2-(3-inde nyl)(2)C2H4}M(NMe2)(2) (11, M = Zr, rac/meso = 7.3/1; 12, M = Hf, rac/meso = 7/1) in 70-90% NMR yields.