Addition of PhC≡CH to hypho-type species [(R'H 2 N)B 8 H 1 1 NHR] proceeds readily with the displacement of R'NH 2 to give corresponding N-bridged arachno ten-vertex species [6,9-μ-(NHR)-5-Ph-arachno-5,10-C 2 B 8 H 1 0 ] (15-34%), for which DFT structural and GIAO 1 1 B nuclear shielding calculations suggest the syn configurations that have the R and Ph groupings on the same side of the molecule.