title: Expansion of iridaborane clusters by addition of monoborane. Novel metallaboranes and mechanistic detail.
abstract: This work reports the results of a thermally driven cluster expansion of arachno-1-{eta5-C5Me5IrH2}B3H7, 1, with BH3.THF. In addition to the previously reported product, arachno-1-{eta5-C5Me5IrH}B4H9, 2, formed at lower temperatures, reaction at 100 degrees C permits the isolation of four new iridaboranes. Two products, nido-1-(eta5-C5Me5Ir)B5H9, 3, and nido-3-(eta5-C5Me5Ir)B9H13, 4, contain a single Ir atom and five and nine framework boron atoms, respectively. One, nido-3,4-(eta5-C5Me5Ir)2B8H12, 5, contains two Ir atoms and eight framework boron atoms. Their structures are predicted by the electron counting rules to be a nido-iridahexaborane, 3, nido-iridadecaborane, 4, and nido-diiridadecaborane, 5. The accuracy of these predictions in each case is established experimentally by spectroscopic characterization in solution and structure determinations in the solid state. A less stable metallaborane has been identified and the available spectroscopic and crystallographic information are consistent with the formulation nido-3,4-(eta5-C5Me5Ir)2B8H13(eta-BH2), 6, i.e., a species containing an exopolyhedral bridging BH group. These new observations, along with earlier ones on ruthenaborane cluster systems, are used to fully define a general mechanism for a cluster expansion reaction, i.e., addition of borane to form an exopolyhedral adduct followed by cage insertion.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Madras, Chennai, 600036, India.
authors.forename: Sundargopal
authors.initials: S
authors.lastname: Ghosh
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Noll
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Fehlner
mesh_terms: D001880:Boranes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007495:Iridium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D012015:Reference Standards; D013696:Temperature
chemical_list: D001880:Boranes; D009942:Organometallic Compounds; D007495:Iridium