Exploring the limits of frustrated Lewis pair chemistry with alkynes: detection of a system that favors 1,1-carboboration over cooperative 1,2-P/B-addition.

The zirconocene complex [{(C₆F₅)₂B-(CH₂)₃-Cp}(Cp-PtBu₂)ZrCl₂] (6; Cp=cyclo-C₅H₄) was prepared by hydroboration of [(allyl-Cp)(Cp-PtBu₂)ZrCl₂] (5) with HB(C₆F₅)₂ ("Piers' borane"). It represents a frustrated Lewis pair (FLP) in which both the Lewis acid and the Lewis base were attached at the metallocene framework. Its reaction with 1-pentyne did not result in the 1,2-addition of or deprotonation reaction by the FLP, but rather in the 1,1-carboboration of the triple bond, thereby obtaining a Z/E mixture (1.2:1) of the respective organometallic substituted alkenes 7. The analogous reaction of 1-pentyne with the phosphorous-free system [{(C₆F₅)₂B-(CH₂)₃-Cp)}CpZrCl₂] (9) gave the respective 1,1-carboboration products ((Z)-10/(E)-10≈1.3:1).