Coordination chemistry and FLP reactivity of 1,1- and 1,2-bis-boranes

Coordination chemistry and frustrated Lewis pair (FLP) chemistry have been most commonly studied using monodentate Lewis acids. In this paper, we examine the corresponding reactions employing the 1,1- and 1,2-bis-boranes, PhCH 2 CH(B(C 6 F 5 ) 2 ) 2 1 and Me 3 SiCH(B(C 6 F 5 ) 2 )CH 2 B(C 6 F 5 ) 2 2 , respectively. Coordination of isocyanide to these species results in the formation of the products RCH(B(C 6 F 5 ) 2 CN t Bu)CH 2 (B(C 6 F 5 ) 2 CN t Bu) (R = Ph 3 , Me 3 Si 4 ). The rearrangement of 1 to give the 1,2-bis-borane adduct 3 was probed and attributed to a donor-induced retrohydroboration and subsequent hydroboration. The analogous reaction of 1 is evident in efforts to use the Gutman-Beckett method to assess its Lewis acidity. However, in combination with t Bu 3 P, bis-boranes 1 and 2 form FLPs and react with H 2 to give [ t Bu 3 PH][PhCH 2 CH(B(C 6 F 5 ) 2 ) 2 (μ-H)] 5a and [ t Bu 3 PH][Me 3 SiCH(B(C 6 F 5 ) 2 )CH 2 (B(C 6 F 5 ) 2 )(μ-H)] 6 , respectively. Reactions of 1 and 2 with various donors and PhCCH were shown to give deprotonation and addition products, depending on the nature of the base. However, in the case of 1 , products resulting from retrohydroboration, and subsequent hydroboration are evident. Several of these alkyne products are crystallographically characterized. The coordination, Lewis acidity and frustrated Lewis pair (FLP) chemistry of PhCH 2 CH(B(C 6 F 5 ) 2 ) 2 1 and Me 3 SiCH(B(C 6 F 5 ) 2 )CH 2 B(C 6 F 5 ) 2 2 are studied.