Synthesis, Structure, and Reactivity of Peralkylcyclopentadienyl ansa-Metallocenes of Samarium: Effect of Steric Crowding on the Reactivity of Tris(peralkylcyclopentadienyl)samarium Complexes

Tris(peralkylcyclopentadienyl)samarium complexes containing two rings connected by a Me 2 Si group were synthesized for comparison with (C 5 Me 5 ) 3 Sm. SmI 3 reacts with Me 2 Si(C 5 Me 4 K) 2 in THF to make Me 2 Si(C 5 Me 4 ) 2 SmI(THF) ( 1 ) in >90% yield. 1 reacts with KC 5 Me 5 in toluene to make Me 2 Si(C 5 Me 4 ) 2 Sm(C 5 Me 5 ) ( 2a ) and in THF to make Me 2 Si(C 5 Me 4 ) 2 Sm(C 5 Me 5 )(THF) ( 2b ). 1 reacts with KC 5 Me 4 Et, KC 5 Me 4 n Pr, and KC 5 Me 4 i Pr in toluene to make Me 2 Si(C 5 Me 4 ) 2 Sm(C 5 Me 4 Et) ( 3 ), Me 2 Si(C 5 Me 4 ) 2 Sm(C 5 Me 4 n Pr) ( 4 ), and Me 2 Si(C 5 Me 4 ) 2 Sm(C 5 Me 4 i Pr) ( 5 ), respectively. In contrast to the reactivity of (C 5 Me 5 ) 3 Sm, complexes 2a and 3 − 5 do not ring-open THF, do not reduce 1,3,5,7-C 8 H 8 or Ph 3 P Se, and do not polymerize ethylene at 50 psi. Structural data were obtained on 1, 2a, 2b, and 4 . The (ring centroid)−metal−(ring centroid) angles of the Me 2 Si(C 5 Me 4 ) 2 units in each structure range from 115.2° ( 2b ) to 123.3° ( 1 ) and have average Sm−C(ring) distances of 2.70(6) Å ( 1 ), 2.82(10) Å ( 2a ), 2.92(14) Å ( 2b ), and 2.83(10) Å ( 4 ). The average Sm−C(C 5 Me 4 R) distance is 2.77(3) Å in 2a, 2.82(4) Å in 2b, and 2.78(3) Å in 4 . The β-carbon of the propyl substituent in 4 is oriented toward samarium at a distance of 3.36 Å.