Reactivity patterns of the unsaturated tetrahedral cluster [Re4(µ3-H)4(CO)12]. Easy addition of four MeCN molecules and ‘ionic’ or ‘neutral’ fragmentation pathways of the spiked-triangle intermediate [Re4(µ-H)4(CO)12(NCMe)4]

Abstract

The unsaturated (56 valence electrons, v.e.s) tetrahedral cluster [Re₄(µ₃-H)₄(CO)₁₂]1 readily added four acetonitrile molecules, affording two isomers 2a and 2b of the 64 v.e.s [Re₄(µ-H)₄(CO)₁₂-(NCMe)₄] derivative, containing a spiked-triangle metallic skeleton. These isomers at room temperature rapidly underwent an ionic fragmentation to the known unsaturated triangular cluster anion [Re₃(µ-H)₄(CO)₉(NCMe)]^– and to the cation [Re(CO)₃(NCMe)₃]⁺. The rate of decomposition significantly increased at low [MeCN] concentration. Treatment of compounds 2a and 2b with the π-acidic ligand CO, in the absence of free acetonitrile, gave only neutral products. Monitoring by NMR spectroscopy has revealed the rapid stepwise substitution of the nitrile ligands, accompanied by fragmentation to the known saturated triangular clusters [Re₃(µ-H)₃(CO)_{12 –n}(NCMe)_n](n= 1–3) and to the mononuclear complexes [ReH(CO)_{5 –n}(NCMe)_n](n= 0 or 1). The novel, unstable, mononuclear hydride [ReH(CO)₄(NCMe)] has been obtained by treatment of [ReH(CO)₅] with Me₃NO in acetonitrile and by reaction of [ReH₂(CO)₄]^– with CF₃SO₃H, in acetonitrile. In the presence of free acetonitrile, compounds 2a and 2b reacted with CO more slowly and gave both anionic and neutral triangular clusters.