Synthesis and Characterization of a Series of 1, 2‐Phenylenedioxoborylcyclopentadienes

Treatment of 1, 2‐C 6 H 4 O 2 BCl [B(CAT)Cl], 4‐ tert ‐butyl‐1, 2‐phenylenedioxo‐chloro‐borane [B(CAT t )Cl] ( 1 ) or its 3, 5‐Bu t 2 ‐analogue [B(CAT tt )Cl] ( 2 ) with the appropriate Me 3 Si‐cyclopentadienyllithium compound afforded in good yield C 5 H 4 (BCAT)SiMe 3 ( 3 ), C 5 H 4 (BCAT t )SiMe 3 ( 4 ), C 5 H 4 (BCAT tt )SiMe 3 ( 5 ), C 5 H 3 (BCAT)(SiMe 3 ) 2 ( 6 ), C 5 H 3 (BCAT t )(SiMe 3 ) 2 ( 7 ), C 5 H 3 (BCAT tt )(SiMe 3 ) 2 ( 8 ), or Me 2 Si{μ‐C 5 H 3 (BCAT)(SiMe 3 )} 2 ( 9 ). Compounds C 5 H 3 (SiMe 3 )(1, 4‐BCAT) 2 ( 10 ), its B(CAT t ) 2 ( 11 ) or B(CAT tt ) 2 ( 12 ) analogues were prepared from C 5 H 3 (SiMe 3 )(SnMe 3 ) 2 and B(CAT)Cl, 1 , or 2 , respectively. Single crystal X‐ray diffraction on crystalline 3 and 6 established their structures. In toluene‐d 8 , 3 , 4 and 5 exist as mixtures of up to 5 isomers. Compounds 6 — 12 exist as only single isomers, compound 9 shows inequivalent cyclopentadienyl rings at 223 K which exchange with each other via a sigmatropic [1, 5]‐trimethylsilyl shift exchange process at higher temperatures.