N-Heterocyclic Carbene Adducts of Alkynyl Functionalized 1,3,2-Dithioborolanes

Abstract

Alkynyl functionalized boron compounds are versatile intermediates in the areas of medicinal chemistry, materials science, and optical materials. In particular, alkynyl boronate esters [R1−C≡C−B(OR2)2] are of interest since they provide reactivity at both the alkyne entity, with retention of the B−C bond or alkyne transfer to electrophilic substrates with scission of the latter. The boron atom is commonly well stabilized due to (i) the extraordinary strength of two B−O bonds, and (ii) the chelate effect exerted by a bifunctional alcohol. We reasoned that the replacement of a B−O for a B−S bond would lead to higher reactivity and post-functionalization in the resulting alkynyl boronate thioesters [R1−C≡C−B(S2X)]. Access to this poorly investigated class of compounds starts form chloro dithioborolane cyclo-Cl−B(S2C2H4) as a representative example. Whereas syntheses of three coordinate alkynyl boronate thioesters [R1−C≡C−B(S2X)] proved to be ineffective, the reactions of NHC-adducts (NHC = N-heterocyclic carbene) of cyclo-Cl-B(S2C2H4) afforded the alkyne substituted thioboronate esters in good yield. The products NHC−B(S2C2H4)(C≡C-R1) are remarkably stable towards water and air, which suggests their use as boron-based building blocks for applications akin to oxygen-based boronate esters.

Dual-Band, Efficient Self-Powered Organic Photodetectors with Isotype Subphthalocyanine-Based Heterojunctions toward Secure Optical Communications

“…The detailed synthetic process is described Supporting Note 1, and the related nuclear magnetic resonance (NMR) spectra can be found in Figures S1–S3 (Supporting Information). These phenoxy-BSubPcs containing B–O bonds have environmental stability due to their hydrophobic properties . The thermostability of all SubPc derivatives was evaluated via thermal gravimetric analysis (TGA) tests, as shown in Supporting Information Figure S4.…”

Benzyl Borane NHC Adducts: Beyond B−C Bond Scission

“…The latter could be silylated (with SiMe 3 )a tt he C1 positiona nd afforded Lewis base-stabilized 2-boranaphthalene (6)w ith elimination of silyl halides. For investigations of reactive benzyl boranes we concentrated on the N-heterocyclicc arbene (NHC) adduct of the parent benzylb orane (8), which can be obtained froma mine-borane adduct (7). [6a-c] NHC-stabilized derivatives of benzylb oranes are currentlyu nknown, which is surprising in view of the various advantages provided by this class of strong s-donor ligands, in particular in the area of main-groupc hemistry.…”

“…[6a-c] NHC-stabilized derivatives of benzylb oranes are currentlyu nknown, which is surprising in view of the various advantages provided by this class of strong s-donor ligands, in particular in the area of main-groupc hemistry. [8] We employed the NHC ligand IiPr [IiPr = DC{N(iPr)CH} 2 ]i nt he formation of a robust adduct of the parent benzyl borane BnBH 2 and wish to demonstrate results of the reactivity at currently unaddressed functional sites in benzyl boranes. Due to the incompatibleb ehavior of the auxiliary NMe 3 ligand towards someo ft he reported transformations, it was exchanged with the NHC ligand.…”

“…Ellipsoids are drawn at the 50 %p robability level. Hydrogen atoms and second molecule in the asymmetric unit are omittedf or clarity.Selected bond lengths []a nd angles [8]: B1ÀC1 1.576(7), B1ÀC10 1.561(7), B1ÀI1 2.115(6), B2ÀC101.642 (8), B2ÀI2 2.267(6), B2ÀI3 2.252(5), B2ÀI4 2.266 (6);C 1-B1-C10 123.4(5), C1-B1-I1 112.8(4), B1-C10-B2 110.4(4), C10-B2-I21 10.9(3), C10-B2-I3 113.4(3), C10-B2-I4 110.3 (4).…”

“…Molecular structure of compound 12.E llipsoids are drawn at the 50 %p robability level. Hydrogen atoms are omitted for clarity.S elected bond lengths []a nd angles[8]: B1ÀC1 1.635(7),B1 ÀC10 1.618(7),B 1 ÀBr1 2.083(5), B1ÀBr2 2.042(5);C 1-B1-C10 109.5(4), C1-B1-Br1 110.5(3), C1-B1-Br2 114.2(3).…”