Reaction of Dimethylzirconocene with Alkylmagnesium Halides as a Potentially General Method for Preparing Zirconocene-Alkene Complexes

Abstract

Addition of one equivalent of RCH2CH2MgX to Cp2ZrMe2 (Cp = C5H5) in the presence of PMe3 led to a transmetalation reaction to afford zirconocene-alkene complexes Cp2Zr(RCH=CH2)(PMe3) in good yields along with the formation of MeMgX.

Selective Intermolecular Coupling of Alkynes with Nitriles and Ketones via β,β‘ Carbon−Carbon Bond Cleavage of Zirconacyclopentenes

“…Formation and Characterization of Zirconacyclopentenes. We have reported the formation of zirconocene−ethylene complex Cp 2 Zr(CH 2 CH 2 ) in situ when zirconocene dichloride was treated with 2 equiv of EtMgBr . When the zirconocene−ethylene complex thus formed was treated with alkynes, zirconacyclopentenes 1 were formed in >90% yields (Scheme , Table ) …”

“…For example, Cp 2 ZrBu 2 is converted into zirconocene−butene complex Cp 2 Zr(EtCHCH 2 ), which has been used as a zirconocene “Cp 2 Zr” equivalent, since the butene ligand is very labile. On the other hand, Cp 2 ZrEt 2 gives zirconocene−ethylene complex Cp 2 Zr(CH 2 CH 2 ) in a similar way; however, the behavior of the ethylene ligand is very different from the butene moiety of the zirconocene−butene complex in most cases. ,, The ethylene ligand reacts with various unsaturated compounds and is incorporated in the reaction products. We have preliminarily reported that Cp 2 ZrEt 2 reacted with alkynes to give zirconacyclopentenes 1 by the coupling of an alkyne with ethylene derived from Cp 2 ZrEt 2 .…”

Tandem Insertion of Halocarbenoids and Lithium Acetylides into Zirconacycles: A Novel Rearrangement to Zirconium Alkenylidenates by β‐Addition to an Alkynyl Zirconocene

“…Beta addition of the anion 20 to the bisA C H T U N G T R E N N U N G (alkynyl) zirconium 21 could give the zirconocene alkenylidenate complex 22. The known [18] rapid loss/re-addition of anions from zirconate complexes provides precedent for the fragmentation of 19. Although b-addition to a metal alkyne as suggested for the recombination of 20 and 21 is novel, for mid-late transition metals the isomerisation of alkyne to alkenylidene ligands is known.…”

“…[22] The normal test for a fragmentation/recombination mechanism would be a crossover experiment. Although aware that rapid exchange between organolithium species and organozirconocenes via ate complexes [18] was likely to invalidate the result, the experiment was tried (Scheme 7).…”

Synthesis of Cyclic 1-Alkenylboronates via Zr-Mediated Double Functionalization of Alkynylboronates and Sequential Ru-Catalyzed Ring-Closing Olefin Metathesis

“…Next our investigations focused on the regio-and stereoselective preparation of multisubstituted alkenylboronates through double allylation of zirconacyclopentenes (Scheme 2). 20 To our delight, upon treatment with Cp 2 ZrCl 2 /2EtMgBr (Takahashi's reagent), 21 1-alkynylboronate 1a afforded the zirconacyclopentene as an intermediate regioselectively, which was subjected to double allylation to give 2f and 2g in 53% and 58% yields, respectively. The obtained alkenylboronates 2aÀ2g are fully characterized by GC-MS, 1 H, and 13 C{ 1 H} NMR spectra as well as elemental analyses.…”