Diverse ring-opening reactions of rhodium η(4)-azaborete complexes

Sequential treatment of [Rh(COE)(2)Cl](2) (COE = cyclooctene) with P(i)Pr(3), alkyne derivatives and (t)BuN[triple bond, length as m-dash]BMes (Mes = 2,4,6-trimethylphenyl) provided functionalized rhodium η(4)-1,2-azaborete complexes of the form (η(4)-azaborete)RhCl(P(i)Pr(3)). The scope of this reaction was expanded to encompass alkynes with hydrogen, alkyl, aryl, ferrocenyl, alkynyl, azaborinyl and boronate ester substituents. Treatment of these complexes with PMe(3) led to insertion of the rhodium atom into the B–C bond of the BNC(2) ring, forming 1-rhoda-3,2-azaboroles. Addition of N-heterocyclic carbenes to azaborete complexes led to highly unusual rearrangements to rhodium η(2),κ(1)-allenylborylamino complexes via deprotonation and C–N bond cleavage. Heating and photolysis of an azaborete complex also led to rupture of the C–N bond followed by subsequent rearrangements, yielding an η(4)-aminoborylallene complex and two isomeric η(4)-butadiene complexes.