Iridanonaborane chemistry. Some reactions of arachno-4-irida-nonaboranes: nuclear magnetic resonance investigations and the molecular structure of the nido nine-vertex species [2,2,2-(CO)(PMe3)2-nido-2-IrB8H11]

Abstract

arachno-4-Iridanonaboranes may be deprotonated with KH and subsequent reaction with cis-[PtCl₂(PMe₃)₂] yields arachno-6,9-dimetalladecaboranes such as the compound [(PMe₃)₂PtB₈H₁₀IrH(PMe₃)₂(CO)] which has been characterized by detailed multi-element single- and multiple-resonance n.m.r. spectroscopy. Mild thermolysis or u.v. photolysis of the arachno-4-iridanonaboranes yields the corresponding nido-2-iridanonaboranes which have been characterized by a single-crystal X-ray diffraction analysis of [(CO)(PMe₃)₂IrB₈H₁₁]; these are the first nido nine-vertex metallaboranes to be structurally characterized and the IrB₈ cluster is based on that of a bicapped Archimedean square antiprism with an equatorial five-connected vertex missing, and with the Ir atom on the open face. The arachno→nido-transformation by dihydrogen loss is quantitative and has been followed by ¹¹B n.m.r. spectroscopy. The kinetics are first order with ΔH^‡=ca. 130 kJ mol^–1 and ΔS^‡=ca. 30 J K^–1 mol^–1 for the compounds studied.