12130-65-3Relevant articles and documents
New syntheses of ansa-metallocenes or unbridged substituted metallocenes by the respective reductive dimerization of fulvenes with Group 4 metal divalent halides or with Group 4 metal dichloride dihydrides
Eisch, John J.,Owuor, Fredrick A.,Shi, Xian
, p. 1325 - 1339 (2008/10/09)
Two unprecedented syntheses of Group 4 metallocenes from 6-substituted fulvenes have been discovered and developed into high-yielding processes. In the first route the di-n-butylmetal dichlorides of Ti, Zr and Hf are generated in toluene suspensions of LiCl at -78°C from the metal tetrachlorides and 2 equiv. of n-butyllithium. Bringing the Bun2MCl2 to 25°C and then heating at reflux for several hours gave complete conversion to slurries of MCl2 (M = Ti, Zr, Hf). Heating such slurries of MCl2 with 2 equiv. of 6-substituted or 6,6-disubstituted fulvenes gave high yields of ansa-metallocenes or substituted ethylene-bis(cyclopentadienyl)metallocene dichlorides (fulvenes: 6,6-dimethyl-, 6-phenyl-, 6-(1-naphthyl)-, 6-(9-anthryl)-). For 6-substituted fulvenes, both racemic- and meso-1,2-disubstituted ethylene-ansa-metallocene dichlorides are expected to form, but with M = Zr (or Ti), the actual racemic- to meso-ansa-metallocene dichloride ratios observed were: phenyl, 50:50; 1-naphthyl, 83:17; 9-anthryl, 100:0. Apparently for steric reasons 6,6-diphenylfulvene underwent no ansa-metallocene dichloride formation with ZrCl2 but rather produced bis(diphenylmethyl(cyclopentadienyl))zirconium dichloride. The second route to novel metallocenes involves generating Bun2MCl2 at -78°C in toluene slurry, as in the foregoing method, but then adding 2 equiv. of the 6-substituted or 6,6-disubstituted fulvene immediately thereafter at -78°C. Except with Bun2TiCl2, warming the reaction mixture to 25°C and then further heating at 65°C cause a smooth bis-hydrometallation by transfer to occur, giving good to very good yields of bis(substituted cyclopentadienyl)metal dichlorides (M = Zn, Hf). The instability of Bun2TiCl2, even at -78°C, rapidly led to a mixture of TiCl2 and Bun2TiCl2and hence to a mixture of ansa-titanocene dichlorides and unbridged, bis(substituted cyclopentadienyl) titanocene dichlorides. With a detailed study of the attainment and the stereochemistry of the formation of ansa-bridged complexes or metallocenes with acetophenone, benzylideneaniline and 6-arylfulvenes, a mechanistic model is developed involving either a three-membered metallocycle formed from MCl 2 or an open-face sandwich complex of the fulvene and MCl2. Such intermediates offer a rational steric explanation for the observed stereochemistry of ansa-bridge C-C bond formation. Finally, in comparative polymerizations of ethylene by such metallocenes, cocatalyzed by MAO, the superior catalytic activity of ansa-metallocenes in the order, Ti > Zr > Hf and of ansa-metallocenes over unbridged substituted metallocenes is attributed to the hyperconjugative stabilization afforded by the ansa σ C-C bond to the metallocenium cation at the active olefin-polymerization site.
Chemistry of (RC5H4)2TiS5. New information on its reactions with nucleophiles, syntheses and reactions of 1,4-[(RC5H4)2Ti]2S4, and a second isomer of (RC5H4)2TiS2C2(CO 2Me)2
Giolando, Dean M.,Rauchfuss, Thomas B.,Rheingold, Arnold L.,Wilson, Scott R.
, p. 667 - 675 (2008/10/08)
Described are a series of reactions of [(RC5H4)2TiSx]n (R = H, CH3, i-Pr; x = 5 (1, n = 1), 3 (2, n = 2), 2 (3, n = 2)). The reactions of 1 with organophosphines in the presence of acetylenes gives the dithiolenes (RC5H4)2TiS2C2R 2. In the absence of acetylenes desulfurization of 1 gives the dimers [(RC5H4)2Ti]2Sx (x = 4, 6). These dimers could not be prepared from (RC5H4)2TiCl2 and Li2Sx; however, reaction of (RC5H4)2TiCl2 and Li2S2 in the presence of CS2 gives high yields of 3. The oxidation of (RC5H4)2Ti(SH)2 also gives 3. The mechanisms of these reactions are discussed in light of corresponding work on 1,2-C6H4(SR)2 (R = H, Sx). The structure of 1,4-[(i-PrC5H4)2Ti]2S4 (3c) was determined by X-ray crystallography. It crystallizes in the monoclinic space group C2/c with a = 35.481 (10) ?, b = 10.976 (3) ?, c = 23.553 (6) ?, β = 130.74 (3)°, V = 6950 (3) ?3, and Z = 4 and refined to R = 0.052 and R(w) = 0.074. The analysis confirms the structure as an 1,4-M2S4 ring in the chair conformation. Whereas 1 reacts with electrophilic acetylenes to give dithiolenes, the corresponding ambient temperature reaction of 3 with dialkyl acetylenedicarboxylates (DEAD or DMAD) gives vinyl disulfides. The structure of the vinyl disulfide complex (CH3C5H4)2TiS2C 2(CO2CH2CH3)2 (4) was confirmed by X-ray diffraction (monoclinic, P21/n; a = 9.772 (2) ?, b = 14.573 (2) ?, c = 11.756 (2) ?, β = 100.25 (1)°, V = 1647.4 (5) ?3, and Z = 4; refinement to R = 0.0387 and R(w) = 0.0411). The TiSSCC ring adopts an envelope conformation. The formation of 4 from 3 occurs via a bimolecular pathway according to the following equation d[4]/dt = (4.2 × 10-3 M-1 s-1)[3][DMAD]. Compound 4 easily rearranges to give the dithiolene. Labeling studies (C5H5 vs. CH3C5H4; DMAD vs. DEAD; 32S vs. 34S) demonstrate the intramolecularity of this rearrangement. These findings suggest that other acetylene-metal sulfide reactions may proceed via this unexpected pathway.
ansa-METALLOCENE DERIVATIVES. V. SYNTHESIS OF TETRAMETHYLETHYLENE-BRIDGED TITANOCENE AND ZIRCONOCENE DERIVATIVES VIA REDUCTIVE FULVENE COUPLING
Schwemlein, Heinz,Brintzinger, Hans H.
, p. 69 - 74 (2007/10/02)
Titanocene and zirconocene derivatives with an interannular tetramethylethylene bridge can be made by reductive coupling of 6,6-dimethylfulvene with sodium amalgam, sodium anthracenide, or magnesium metal/CCl4 as reducing agents and subsequent reaction of
