Titanium‐Mediated Rearrangement of Bis(alkynyl)boranes: B─C Activation versus C─H Activation

Abstract

Abstract Reactions between Rosenthal's titanocene (Cp 2 Ti) and decamethyltitanocene (Cp* 2 Ti) synthons with various bis(alkynyl)boranes were investigated. A series of titanium‐fused boracyclobutenes were obtained through the reaction of the Cp* 2 Ti synthon with (Me 3 Si) 2 NB(CCR) 2 or PhB(CCPh) 2 . This represents the first realization of approaching this structural motif via the rearrangement of bis(alkynyl)boranes within the coordination sphere of a d ‐block metal. These findings break the previous limitation that the boron substituent must be an amino group. Furthermore, the reaction of the Cp* 2 Ti synthon with (Me 3 Si)PhNB(CCPh) 2 or (Mes 2 B)PhNB(CCPh) 2 (Mes = 2,4,6‐trimethylphenyl) led to the formation of novel tethered metallocene complexes, in which the titanacyclopentadiene structure is linked to one of the cyclopentadienyl groups via a ─CH 2 ─BR─ bridge. Both experimental and theoretical studies provided insights into an unprecedented reaction mechanism. The process involves the initial formation of an η 2 ‐coordinated bis(alkynyl)borane intermediate, which was detected and analyzed by NMR spectroscopy and X‐ray diffraction analysis. This intermediate subsequently undergoes either B─C alkynyl bond activation or C Me ─H activation of the Cp* ligand, leading to the formation of two distinct types of products.