The syntheses and first structural characterization of terminal (diisopropylamino)borylene complexes are reported. The 11B NMR chemical shifts for these novel systems (I B 93.8 and 90.2 for [Cpa??Fe(CO)2(BNiPr2)][BArf 4 ], 3, and [CpRu(CO)2(BNiPr2)][BArf 4 ], 4, respectively) are ca. 40 ppm downfield of those measured for the boryl precursor complexes,consistent with observations for related trimethylsilyl and cyclohexylamino substituted compounds. Structurally, the linearity of the M a?? B a?? N fragment in each case and the marked shortening of the M a?? B bonds (cf. the single bonds found in boryl complexes CpFe(CO)2(BNiPr2)Cl, 1b, and CpRu(CO)2(BNiPr2)Cl, 2) reflect the fact that the M a?? B bond order in borylene systems 3 and 4 is between one and two.