Metal-rich clusters: synthesis, structure and bonding of metallaboranes featuring µ5-boride and triply bridging borylene units

Abstract

A series of metal-rich clusters of group 9 containing boride or borylene units have been isolated and structurally characterized. The thermolysis reaction of arachno-[IrCp*H2(B3H7)] (I) with [Ru3(CO)12] allowed to isolate the µ5-boride nido-[(IrCp*){Ru(CO)2}{Ru(CO)3}3(µ-H)5B2H2(μ5-B)] (1) and the tetrametallic cluster [(IrCp*)2{Ru(CO)2}{Ru(CO)3}(μ-CO)2(μ3-BH)] (2) with a µ3-coordinated triply-bridged borylene moiety. The geometry of cluster 1 can be derived from an eight-vertex closo-dodecadeltahedron by removal of one five-connected vertex followed by capping of a Ru(CO)3 moiety. The borylene moiety (BH) of cluster 2 is connected in a μ3-fashion to the deltahedral face of a tetrametallic tetrahedron (Ir2Ru2). To synthesize the Mn analogue of 2, thermolysis reaction with [Mn2(CO)10] was carried out, that afforded the trimetallic tetrahedral borylene [(IrCp*)2{MnH (CO)3}(μ-CO)2(μ3-BH)] (3) along with the known face-fused boride [{Ir(CO)2}3(IrCp*)3(μ3-CO)(μ-CO)(μ5-BH)] (4). Clusters 2 and 3 are the first triply-bridged borylenes having an Ir metal atom in the core. All these clusters were characterized by NMR (1H, 11B and 13C), infrared (IR) spectroscopies and mass spectrometry. The structure of cluster 1 was confirmed by X-ray diffraction analysis. In addition, density functional theory (DFT) calculations were conducted to interpret and study the nature of bonding and electronic structure of cluster 1.