"POLYHEDRAL CONTRACTION" OF TETRAMETHYLAMMONIUM CLOSO-CARBOUNDECABORATE UNDER ACTION OF TRIS(TRIPHENYLPHOSPHINE)RUTHENIUM DICHLORIDE

Abstract

In this paper the objectives were not only to investigate new promising methods leading to a deep structural rearrangement of carboranes and metallacarboranes but also to try to fix, to isolate and to characterize the intermediates. At the same time considerable attention is paid to the so-called "anti-wade" clusters formed during the reactions, the electronic structure of which does not correspond to their actually observed geometry. It is shown that the interaction of 11-vertex monocarbon closo-carboundecaborane with tris(triphenylphosphine)ruthenium dichloride leads to a series of new metallacarborane complexes. For the first time it was possible to control the process of "polyhedral contraction" of carborane {CB10} → (RuCB10} → {RuCB9} → {RuCB8} → {RuCB6} on the example of ruthenium complex and also to confirm experimentally each stage of the whole process. As a result of the reaction clusters of classical type and electron-deficient isocloso-/hypercloso-rutenacarborans {RuCB8}, {RuCB9} with 2n skeletal electrons were isolated. It is found that the interaction of tetramethylammonium closo-carboundecaborate with tris(triphenylphosphine)ruthenium dichloride proceeds in several stages. The first intermediate 12-vertex cluster is formed by mixing the initial reagents under heterogeneous conditions (methanol-THF, K2CO3, triethylbenzylammonium chloride) at room temperature for 10 hours. When the resulting complex is stirred in a mixture of methanol-THF solvents for 7 days at 20 °C, its almost quantitative transition to 11-vertex rutenacarborane was observed. Further transformation with the formation of a 10-vertex isocloso-rutenacarborane occurs when the methanol solution of this complex is boiled for 15 minutes. When the complex is boiled in methanol for 8 hours we obtained another extraordinary metallacarborane belonging to the rare 8-vertex pileo-clusters with a boron vertex built over the triangular face.