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, PhCH2CH(B(C6F5)2)21 and Me3SiCH(B(C6F5)2)CH2B(C6F5)22, respectively. Coordination of isocyanide to these species results in the formation of the products RCH(B(C6F5)2CNtBu)CH2(B(C6F5)2CNtBu) (R = Ph 3, Me3Si 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 tBu3P, bis-boranes 1 and 2 form FLPs and react with H2 to give [tBu3PH][PhCH2CH(B(C6F5)2)2(µ-H)] 5a and [tBu3PH][Me3SiCH(B(C6F5)2)CH2(B(C6F5)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.

Probing B-X to B-H conversions and applications in C-F bond activation catalysis.

Herein we exploit a catalytic amount of [Ph3C]+ to initiate B-X to B-H bond conversion with Et3SiH. This was applied to 6 haloboranes. However, 9-X-9-borabicyclo[3.3.1]nonane (B-X-9-BBN, X = F, Br) reacts directly with silane. Thus, C-F bond activation of benzyl fluorides in the presence of arenes afforded the Friedel-Crafts (FC) products using B-H-9-BBN in the presence of Et3SiH. This catalysis was probed with a range of arenes and several benzyl fluoride derivatives. The protocol is simple, cheap and a convenient route to 1,1-diarylmethanes from benzyl fluorides in good to excellent yields (up to 99%) under mild conditions.

Reactions of a Lewis acidic methylene phosphonium cationic adduct with olefins.

Efforts to deprotonate the halophosphonium cations [Ph2P(X)Me]+ (X = F, Cl) generated species of the form [Ph2(X)PC(H)PPh2Me][X']. The derivative where X = O3SCF3 provides access to a methylene phosphonium cation. The coordinated triflate anion can be replaced by Et3PO and dimethylaminopyridine (DMAP). In addition, the cation reacts with the olefins R2CCH2 (R = Ph, Me) and PhMeCCH2. While Ph2CCH2 was shown to give the species [Ph2(Ph2CCH)PCH2PPh2Me][O3SCF3]2 with a pendant vinyl group, reactions with methyl substituted olefins undergo additional isomerization to form [Ph2(RCH2CCH2)PCH2PPh2Me][O3SCF3]2 (R = Ph, Me) featuring pendant allyl moieties.