Synthesis of [Ethylene-1-(η⁵-4,5,6,7-tetrahydro-1-indenyl)-2- (η⁵-4‘,5‘,6‘,7‘-tetrahydro-2‘-indenyl)]titanium Dichloride, the Elusive Isomer of the Brintzinger-Typeansa-Titanocenes

Abstract

We present a short synthesis of 1-(2-indenyl)-2-(3-indenyl)ethane (5) and a method for its conversion to the ansa-metallocene [ethylene(eta5-inden-1-yl)(eta5-inden-2-yl)]titanium dichloride (13). The synthetic strategy applied to prepare bisindene 5 relies on the efficient alkylation of 2-(phenylsulfonyl)indane followed by HMPA-assisted E1cB-elimination of phenylsulfinate. This tandem sequence circumvents the predisposition of indene to undergo C(1)-alkylation and enables access to C(2)-substituted indenes. The key step in the synthesis of the title ansa-titanocene (4) features a previously unreported equilibration step to generate the bis(indenide anion) of 5. Complexation with TiCl4.(THF)2 followed by hydrogenation of the product metallocene furnishes ansa-titanocene 4.

Synthetic approaches to multifunctional indenes

“…However, an attempt to convert the (3-indenyl)ethylsulfonate 11 into the advanced inden-5-amine 9 was ineffective, resulting in the formation of the spiro indene 12 instead, and hence this route was not studied further (Scheme 2 and Supporting Information File 1). It should be mention that the propensity of several 3-substituted indenes, appropriately fitted with leaving groups, to undergo spirocyclization has been previously reported [26–27]. …”

Enantioselective Hydrogenations with Chiral Titanocenes

“…Ethylene-bridged ansa -bis(tetrahydroindenyl)titanium dichloride 15 was obtained by Brintzinger from the corresponding ligand [24]. Its isomers with different positions of the ethylene bridge in the indene ring and different substituents (R=Me, Bz) were prepared by Nantz and coworkers [25,26,27]. Complexes 15 and 18 are chiral, and 16 is an achiral meso -like compound.…”

“…In the case of 18 , use of TiCl 3 ·3THF for the metalation of the indene ligand was unsuccessful [27]. Replacing the chloride by Ti(NMe 2 ) 4 in the synthesis of 15 resulted in initial metallocene formation, but the product decomposed shortly in the reaction mixture.…”

Aliphatic Nucleophilic Substitutions: Problematic Electrophiles

“…Although the reactivity of epoxides toward organometallic reagents can be enhanced by the addition of Lewis acids [241,243,251,296], this can also lead to cleavage of other ethers present in the reaction mixture, for example THF or Et 2 O [238,240]. Strong Lewis acids, for example trityl cations [297], can also enhance the amount of products resulting from rearranged epoxides.…”

“…Carbon nucleophiles which do not readily trigger the rearrangement of epoxides include lithiated dithianes [295,304], lithiated sulfones [238], lithiated diarylphosphine oxides [240,305], lithium enolates [306], and allylic organolithium or organomagnesium compounds [298,[307][308][309][310] (Scheme 4.67). 105 Scheme 4.67.…”