Derivatization of an especially electron-rich diborane

Abstract

Starting with electron-rich ditriflato-diborane B2(hpp)2(OTf)2 (hpp = 1,3,4,6,7,8 hexahydro-2H-pyrimido[1,2-α]pyrimidinate), novel symmetric and unsymmetric diboranes B2(hpp)2X2 and B2(hpp)2XY with X,Y = Br, NCS, N3 or OTf are synthesized by substitution reactions...

Bistriazoles Connected Through a B−B Bridge, Synthesized by Highly Selective Dipolar Cycloaddition Reactions of a Diazido‐diborane(4)

“…Figure 3 illustrates the solid‐state structures; selected bond lengths are collected in Table 1. The B−B bond lengths in the three crystallized bistriazoles (1.713 and 1.714 Å) fall into a typical region for B−B single bonds, being significantly longer than the B=B double bond in diborene compounds [45–48] . The lengths of the B−N bonds to the triazole rings (1.552 and 1.557 Å) are similar to previously reported B−N bonds to triazole groups (1.567 Å), [36] and only slightly larger than the lengths of B−N bonds to the bridging hpp substituents.…”

“…The BÀ B bond lengths in the three crystallized bistriazoles (1.713 and 1.714 Å) fall into a typical region for BÀ B single bonds, being significantly longer than the B=B double bond in diborene compounds. [45][46][47][48] The lengths of the BÀ N bonds to the triazole rings (1.552 and 1.557 Å) are similar to previously reported BÀ N bonds to triazole groups (1.567 Å), [36] and only slightly larger than the lengths of BÀ N bonds to the bridging hpp substituents. Moreover, all BÀ N bond lengths fall into a typical range for sp 3 hybridized boron atoms.…”

“…The knowledge about the chemistry of diazido-diborane(4) compounds is scarce; only a few stable compounds are known up to date. The remarkable stability of [B(hpp)(N 3 )] 2 (9), reported recently by our group, [45] stands out and was used in this work to synthesize the first bistriazoles connected by a BÀ B bridge. At high temperatures (120 °C), terminal alkynes react with 9 in dipolar 1,3-cycloaddition reactions; the reactions are strictly regioselective, leading exclusively to the 1,4-substituted bistriazoles.…”

“…[43] Recently, we reported the reaction of the ditriflato diborane [B(hpp)OTf] 2 (8) (hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2α]pyrimidinate) [44] with nBu 4 NN 3 to give the diazido diborane [B(hpp)(N 3 )] 2 9 (see Lewis structure in Scheme 2). [45] Since test experiments showed that it has an exceptionally high temperature stability, we thought of evaluating the chemistry of this electron-rich diazido diborane(4). Here we focus on its reaction with alkynes, giving convenient, first access to bis-1,4-triazoles connected by a BÀ B bridge.…”

Synthesis of Symmetrically and Unsymmetrically Substituted Cationic Diborane(4) Compounds with Distinct Structural Motifs and Properties

“…Additional experiments with 2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) gave similar results (see Supporting Information for details). The cations are tetracoordinate at the boron atoms; therefore substitution reactions following an S N 1‐type mechanism [18] are hampered by the firmly bound three guanidinate groups.…”