Diastereoselective Synthesis of a Bis(tetrahydroindenyl)zirconocene Dichloride with “Ansa-Fused” Annulated Six-Membered Ring Systems:  A Specific Solution of the Synthetic rac-/meso-Group 4 Bent Metallocene Problem

Abstract

1-Phenyl-1,4-pentanedione (3) is selectively converted to the corresponding fulvene-ketone (4) by treatment with cyclopentadiene in the presence of pyrrolidine. Treatment with lithium dimethylcuprate results in selective CH 3 -addition at the fulvene carbon and subsequent ringclosure reaction to give 7, which in the presence of lithium diisopropylamide is rapidly dehydrated to yield the bicyclic fulvene 8. Its treatment with amalgamated calcium metal leads to reductive fulvene coupling and formation of the calcocene complex (10) of the substituted 7,7′-bi(tetrahydroindenyl) ligand. Only the respective rac-isomer is obtained. Hydrolysis of 10 followed by double deprotonation with butyllithium yields the corresponding 7,7′-bi(tetrahydroindenyl) dianion equivalent 16. In tetrahydrofuran, 16 is cleaved at the 7,7′-linkage with formation of the "monomeric" disproportionation products 11-Li and 12-Li, and treatment of 16 with zirconium tetrachloride in THF leads back to the formation of the fulvene 8. Transmetalation to zirconium is, however, cleanly achieved when 16 is treated with donor-ligand-free ZrCl 4 suspended in toluene. The corresponding diastereomerically pure rac-ansa-zirconocene dichloride 17 containing the ansa-bridge as part of the R-fused bi(tetrahydroindenyl) ligand system is obtained under these specific conditions. Complex 17 was characterized by X-ray diffraction, and the outcome of the preliminary propene polymerization experiments is reported.

Main‐Group Metallocenophanes

“…In addition to metallocenophanes of magnesium, there are several examples of metallocenophanes of the heavier alkaline earth metals calcium, strontium and barium, with the majority being calcocenophanes, 2 (Figure 4). [36–53] In contrast to magnesocenophanes, 1 , where the synthesis commonly involves metalation of an ansa ‐ligand system by deprotonation with dibutyl magnesium (Scheme 1), calcocenophanes, 2 , and strontiocenophane, 3 , are often prepared by oxidative coupling starting from the corresponding alkaline earth metal and a suitable fulvene (Scheme 5). [38–52] …”

Strategies for the Synthesis of Chiral Carbon‐Bridged Group IV ansa‐Metallocenes

“…As an alternative approach, the C2‐bridged ebi ligands were prepared through a double intramolecular Friedel–Crafts acylation reaction . A C7‐bridged ansa ‐zirconocene 64 was synthesized from the annulated fulvene 62 starting with a reductive calcium‐promoted dimerization, giving the corresponding calcocene in exclusive rac ‐selectivity that was hydrolyzed to give ligand precursor 63 in 51 % yield (Scheme b) . The reductive fulvene dimerization had been used before to access a related bis‐guaiazulene titanocene dichloride .…”

“…[63] AC 7-bridged ansa-zirconocene 64 was synthesized from the annulated fulvene 62 startingw ith ar eductivec alcium-promoted dimerization, giving the corresponding calcocene in exclusive rac-selectivity that was hydrolyzed to give ligand precursor 63 in 51 %y ield (Scheme 13 b). [64] The reductive fulvene dimerizationh ad been used before to access ar elated bis-guaiazulene titanocene dichloride. [7,65] Ac onversion of 63 into the dilithium salt and reaction with ZrCl 4 then affordedt he pure zirconocene dichloride 64.T he fulvene precursor 62 was prepared from 1-phenylpentane-1,4-dione in three steps.…”

Synthesis and structures of dinuclear iron, molybdenum and tungsten complexes derived from (PhCHCHPh)-coupled bis(cyclopentadiene)

“…Ligand CpPhCHCHPhCp (1) was synthesized followed the method of ShapiroÕs group (reductive coupling of phenylfulvene) [15] and ErkerÕs group [16] as a mixture of racemic and meso isomers (70:30). Fortunately, the pure meso isomer 1-meso suitable for X-ray crystallography was obtained while the crude 1 was recrystallized with pentane/CH 2 Cl 2 at À30°C.…”

“…Ligand CpPhCHCHPhCp (1) was synthesized followed the method of ShapiroÕs group [15] and ErkerÕs group [16] To a solution of ligand 1 (0.93 g, 3.0 mmol) in 50 mL of xylene was added Fe(CO) 5 (1.0 mL, 7.6 mmol), and the resulting mixture was refluxed for 24 h. After removal of solvent under reduced pressure, the residue, which was dissolved in a minimum of CH 2 Cl 2 and chromatographed on an alumina column using petroleum ether/CH 2 Cl 2 as an eluent. The first brown band affords oil, which could not be characterized.…”