Neutral and cationic di(tert-butyl)cyclopentadienyltitanium, zirconium and hafnium complexes - Dynamic NMR study of the ligand-free cations [M(1,3-Bu-t(2)-eta(5)-C5H3)(eta(5)-C5H5)(CH3)](+) (M=Zr, Hf)

Group 4 metal complexes containing the di(tert-butyl)cyclopentadienyl ligand (1,3-B-t(u)-eta(5)-C5H3) have been synthesized. The reaction of a mixture of 1,3- and 1,4-di( tert-butyl)cyclopentadiene isomers with KH in THF at -78 degrees C gives the salt K+[(1,3-(Bu2C5H3)-Bu-t)](-)(THF)(1-3) 2 as a white solid. Treatment of 2 with chlorotrimethylsilane in a 1:1 molar ratio gives the air-stable trimethylsilylcyclopentadienyl derivative Si(1,3-(Bu2C5H3)-Bu-t)(CH3)(3) 3. The silyl derivative 3 is an excellent precursor for monocyclopentadienyl trichlorotitanium and zirconium compounds M(1,3-Bu-t(2)-eta(5)-C5H3)Cl-3 [M = Ti (4), Zr (5)]. Addition of a stoichiometric amount of water in the presence of NE3, to a toluene solution of 4 affords the oxo trimer compound [Ti(1,3-Bu-t(2)-eta(5)-C5H3)Cl(mu-O)(3) 6. The reaction of 4 with 2 equiv. of LiMe affords the chloro dimethyl derivative Ti(1,3-Bu-t(2)-eta(5)-C5H3)Cl(CH3)(2) 7. The mixed dicyclopentadienyl compounds M(1,3-Bu-t(2)-eta(5)-C5H3)(C5H5)Cl-2 [M = Ti (8); Zr (9)] were prepared by reaction of complexes 4 and 5 respectively with TI(C5H2). Treatment of complexes (8) and (9) with the appropriate alkylating reagent and molar ratio, in hexane at -78 degrees C, gives the chloro alkyl derivatives M(1,3-Bu-t(2)-eta(5)-C5H3)(C5H5)CIR [M = Ti, R = Me (10); M = Zr, R = Me (11), Bz (12)] or the dialkyl complexes M(1,3-Bu-t(2)-eta(5)-C5H3)(C5H5)R-2 [M = Ti, R = Me (13); M = Zr, R = Me (14), Bz (15), Nf (16)]. When 8 reacts with 2 equiv. of MgBz(2)(THF)(2) or LiCH2CMe2Ph the metallacyclic complexes Ti(1-Bu-t-3-CMe2CH2-eta(5)-C5H3)(C5H5)R [R = Bz (17); Nf (18)] were isolated as red oils at room temperature, with the elimination of toluene or tert-butyl benzene respectively. The previously reported cationic mono 1,3-di(tert-butyl)cyclopentadienyl dibenzyl zirconium species [Zr(1,3-Bu-t(2)-eta(5)-C5H3)(CH2Ph)(2)](+) (19) can be stabilized by reaction with (BuNC)-Bu-t or PMe3, in CD2Cl2 at -78 degrees C, and the formation of the new cationic species [Zr(1,3-Bu-t(2)-eta(5) C5H3)(L)(CH2Ph)(2)](+) [L = (BuNC)-Bu-t (20); PMe3 (21)] was identified by NMR spectroscopy. The reaction of B(C6F5)(3) with the monocyclopentadienyl trimethyl derivatives M(1,3-Bu-t(2)-eta(5)-C5H3)(CH3)(3) [M = Ti (22), Zr (23)], in the presence of PMe3, gives the cationic species [M(1,3-Bu-t(2)-eta(5)-C5H3)(PMe3)(2)(CH3)(2)](+) [M = Ti (24); Zr (25)], obtained as orange-yellow solids, stable at room temperature. The reaction of B(C6F5)(3) with the metallocene dimethyl derivatives M(1,3-Bu-t(2)-eta(5)-C5H3)(eta(5)-C5H5)(CH3)(2) [M = Zr (14); Hf (26)1, in a 1:1 molar ratio and in hydrocarbon solvents gives the cationic derivatives [M(1,3-Bu-t(2)-eta(5)-C5H3)(eta(5) C5H3)(CH3)](+)[(CH3)B(C6F5)(3)](-) [M = Zr (27); Hf (28)] as yellow oils which can be stored for weeks under an inert atmosphere. When the same reactions of (14) and (26) with B(C6F5)(3) are carried out in 2:1 molar ratio at room temperature, the complexes [[M(1,3-Bu-t(2)-eta(5)-C5H3)(eta(5)-C5H5)Me](2)(mu-Me)][MeB(C6F5)(3)] [M - Zr (29), If (30)] can be obtained as a mixture of syn- and anti-isomers as shown by NMR spectroscopic observations. The formation of (29) and (30) implies the stabilization of the 14-electron cationic intermediate by interaction with one methyl group of the neutral complexes (14) and (26). Complexes (27) and (28) undergo heterolytic dissociation of the Metal-MeB(C6F5)(3) bonds, leading to the formation of the free [M(1,3-Bu-t(2)-eta(5)-C5H3)(eta(5)-C5H5)(CH3)](+) 14-electron species, verified by H-1 DNMR spectroscopy. When compound (27) was heated at 50 degrees C the metallacyclic cation[Zr(1-Bu-t-3-CMe2CH2-eta(5)-C5H3)(eta(5)-C5H5)](+) (31) was formed. The alkyl derivatives synthesized and reported herein, activated with MAO, B(C6F5)(3) or [Ph-3][B(C6F5)(4)], polymerize ethylene with very tow activity. The molecular structure of [Ti(1,3-Bu-t(2)-eta(5)-C5H3)Cl(mu-O)](3) 6 has been determined by X-ray diffraction methods. (C) 1997 Elsevier Science S.A.