Synthesis and crystal structure of [PPh4]2[Ir4(CO)10(CH2CO2Me)2] and [PPh4][Ir4(CO)11(CH2CO2Me)]. First examples of iridium clusters bearing an alkyl-like ligand

Abstract

The reaction of Na(Ir(CO){sub 4}) ((Na)1) with given amounts of BrCH{sub 2}COOMe in THF, followed by treatment with PPh{sub 4}Cl, gave high yields of the two novel clusters (PPh{sub 4}){sub 2}(Ir{sub 4}(CO){sub 10}(CH{sub 2}COOOMe){sub 2}) ((PPh{sub 4}){sub 2}2) and (PPh{sub 4})(Ir(CO){sub 11}(CH{sub 2}COOMe)) ((PPh{sub 4})3). The reaction takes place in two steps; the first compound formed is 2, which then reacts, in a slower reaction, with excess BrCH{sub 2}COOMe to afford 3. To the best of the authors' knowledge, 2 and 3 are among the first examples of clusters bearing an alkyl or alkyl-like substitutent. X-ray diffraction analysis of the clusters was carried out on crystals obtained by using PPh{sub 4}{sup +} as a countercation. Compound (PPh{sub 4}){sub 2}2 is triclinic. Both anions contain a tetrahedron of iridium atoms with three bridging CO ligands around a triangular basal face of the metal tetrahedron of iridium atoms with three bridging CO ligands around a triangular basal face of the metal tetrahedron, the alkyl-like substituents being axially bonded to the iridium atoms of this face. The reactivity of the sodium salt of (Ir(CO){sub 4}){sup {minus}} with BrCH{sub 2}COOMe was quite different from that, already reported by the authors, of the same anionmore » with PPN{sup +} (PPN{sup +} = (PPh{sub 3}){sub 2}N{sup +}) as a countercation. This latter reaction forms only mononuclear species. The possible role of Na{sup +} in the formation of the clusters is discussed.« less