Metallaborane Heteroatom Incorporation Reactions: Metallacarboranes, Metallathiaboranes, and an Iridaazaborane from Iridanonaborane Precursors

Formation of metallaheteroboranes by insertion of heteroatoms into an existing metallaborane cluster, rather than adding the metal moiety to the heteroborane which is normally the case, has been achieved in the cases of carbon, nitrogen, and sulfur to produce nine-, ten-, and eleven-vertex metallaheteroborane clusters. Thus passage of acetylene through refluxing p -xylene solutions of either arachno -[(PMe 3 ) 2 (CO)HIrB 8 H 12 ] ( 1a ) or nido -[(PMe 3 ) 2 (CO)IrB 8 H 11 ] ( 2a ) afforded the 11-vertex cluster nido -[9,9,9-(PMe 3 ) 2 (CO)-9,7,8-IrC 2 B 8 H 11 ] ( 5a ) in up to 44% yield. With the cage substituted species arachno -[(PMe 3 ) 2 (CO)HIrB 8 H 11 Cl] ( 1b ), the analogous product is nido -[5-Cl-9,9,9-(PMe 3 ) 2 (CO)-9,7,8-IrC 2 B 8 H 10 ] ( 5b ) and the position of the Cl substituent in the product suggests that the acetylene moiety attacks across the open face of the intermediate nido -iridanonaborane species and that cage rearrangement does not occur during the course of the reaction. Similarly, reaction of 1a with H 2 S under identical conditions results in the formation nido -[2,2,2-(PMe 3 ) 2 H-2,6-IrSB 8 H 10 ] ( 9a ), closo -[2,2,2-(PMe 3 ) 2 H-2,1-IrSB 8 H 8 ] ( 10 ), and nido -[(PMe 3 ) 2 HIrS 2 B 8 H 8 ] ( 11a ) in overall yields of 13%, 7%, and 20%, respectively. Additionally, refluxing a solution of 1a and anhydrous hydrazine in xylene afforded a 10% yield of the novel iridaazanonaborane nido- [2,2,2-(PMe 3 ) 3 -2,9-IrNB 7 H 9 ] ( 12 ). The compound is the first metallaazanonaborane cluster to be described, and its formation indicates that methods similar to those used to generate azaboranes may be used on metallaboranes to generate metallazaboranes. In addition to characterization by a combination of 1 H, 31 P, and 11 B NMR and IR spectroscopy and high-resolution mass spectrometry, single-crystal X-ray diffraction studies were carried out on compounds 5a, 9a, 10, and 12 .