A novel zirconium-catalyzed hydroalumination of olefins

Principle of Activation of Electrophiles by Electrophiles through Dimeric Association—Two Are Better than One

“…For Zr-catalyzed hydroalumination, (iBu) 3 Al ± Cl 2 ZrCp 2 is a synthetically more useful, superior reagent system, and it satisfactorily hydroaluminates various monosubstituted alkenes. [35] This work, published in 1980, appears to represent the first report on Zr-catalyzed hydrometalation. A mechanism involving the formation of iBuZrCp 2 Cl by transmetalation and its H-transfer hydrozirconation of alkenes via a 6-membered transition state was initially proposed.…”

“…A mechanism involving the formation of iBuZrCp 2 Cl by transmetalation and its H-transfer hydrozirconation of alkenes via a 6-membered transition state was initially proposed. [35] However, a recent study has shown that neither (iBu) 3 Al nor iBuZrCp 2 Cl alone is capable of readily hydrometalating alkenes in high yields, strongly indicating that bimetallic activation must be required. The rate of the reaction of 1-alkenes with (iBu) 3 Al and Cl 2 ZrCp 2 (5 mol %) is independent of alkene concentration, which is consistent with the formation of a hydridozirconocene derivative, for example 25, in the rate-determining step, but is not compatible with a direct six-centered process via 26 (Scheme 13).…”

“…Interestingly, a reagent combination consisting of (iBu) 2 AlH and a catalytic amount (10 mol %) of Cl 2 ZrCp 2 is totally ineffective as a hydroaluminating agent under comparable conditions. [35] Hydrozirconations of alkenes and alkynes are commonly carried out with preformed HZrCp 2 Cl, [34] which can be obtained as a pure reagent. However, its preparation is somewhat cumbersome, and various procedures for its in situ generation have been devised that use LiAlH 4 , [36,37] NaAl-H 2 (OCH 2 CH 2 OCH 3 ) 2 , [35] LiBH(sBu) 3 , [36,38] and so on.…”

“…[35] Hydrozirconations of alkenes and alkynes are commonly carried out with preformed HZrCp 2 Cl, [34] which can be obtained as a pure reagent. However, its preparation is somewhat cumbersome, and various procedures for its in situ generation have been devised that use LiAlH 4 , [36,37] NaAl-H 2 (OCH 2 CH 2 OCH 3 ) 2 , [35] LiBH(sBu) 3 , [36,38] and so on. However, one of the least expensive and cleanest is iBuZrCp 2 Cl, readily preparable in b 90 % yield by treating Cl 2 ZrCp 2 with 1 ± 1.1 equiv of tBuMgCl.…”

“…In view of the facile Zr-catalyzed hydroalumination of alkenes with (iBu) 3 Al (Scheme 13), [35] even if isoalkylaluminum derivatives are produced by the desired carboalumination, they would be competitively consumed in the hydroalumination reaction shown in Scheme 13. This has indeed been recently confirmed.…”