Two unusual closo-type ruthenaboranes: preparation, molecular structure, and nuclear magnetic resonance properties of [1,1,1 -(PPh3)HCl-1-RuB9H7-3,5-(PPh3)2] and [1,1 -(PPh3)2-1 -RuB10H8-2,5-(OEt)2]

Abstract

Reaction of arachno-[B₉H₁₄]^–- with [RuCl₂(PPh₃)₃] under mild conditions gives the orange 10 vertex ruthenadecaborane [1,1,1-(PPh₃)HCl-1-RuB₉H₇-3,5-(PPh₃)₂] in ca. 40% yield. The molecular structure is based on an ‘isocloso’C_3v 1 : 3 : 3: 3 RuB₉ stack with the nine-co-ordinate metal occupying the unique six-connected apical position. The electronic structure may be interpreted either on the basis of a ‘PSEPT-deficient’ 2n-electron cluster with the metal having a straightforward ‘conical’ three-orbital contribution, or as a ‘PSEPT-precise’(2n+ 2)-electron cluster with the metal having a four-orbital involvement, also conical, with the cluster. Similar bonding considerations apply to the red 11-vertex ruthenaundecaborane [1,1-(PPh₃)2-1-RuB₁₀H₈-2,5-(OEt)₂] which is obtained in a yield of 80% from the reaction of [RuCl₂(PPh₃)₃] with closo-[B₁₀H₁₀]^2– in refluxing ethanolic chloroform. The molecular structure is based on that of a closo-type C_2v 1 : 2 : 4 : 2 : 2 RuB₁₀ stack again with the metal occupying the unique six-connected apical position. Both compounds can be considered as having ‘isocloso’ structures derived from the complete capping of the open face of an arachno geometry to give a completely closed deltahedral cluster.