Boron-pnictogen multiple bonds: donor-stabilized P=B and As=B bonds and a hindered iminoborane with a B-N triple bond

Reaction of the hindered phosphino- and arsinoboranes, Ar*Pn(H)-B(Br)Tmp (Ar* = -C6H3-2,6-(C6H2-2,4,6-iPr3)2; Tmp = 2,2,6,6-tetramethylpiperidino; Pn = P and As, 1 and 3, respectively) with 4-dimethylaminopyridine, DMAP, afforded the boranylidenephosphane and arsane, Ar*Pn=B(DMAP)Tmp (Pn = P and As, 2 and 4) as deep red-purple solids. The analogous aminoboranes Ar'N(H)-B(X)Tmp (Ar' = -C6H3-2,6-(C6H2-2,4,6-Me3)2; X = Cl and Br; 5 and 6) did not display any reactivity with DMAP, but in the presence of the amide base, NaN(SiMe3)2], the clean formation of the uncomplexed iminoborane Ar'NBTmp (7) was observed. Attempts to generate an Sb=B bond were unsuccessful, as the required stibinoborane precursor, Ar*Sb(H)-B(Br)Tmp, could not be prepared; in place of clean Sb-B bond formation, the reduced product Ar*Sb=SbAr* was obtained. All compounds were characterized spectroscopically, and the X-ray crystal structures of 1, 2, 4, 6, and 7 were determined.