Syntheses and molecular structures of two boride cluster anions: octahedral [Rh2Ru4(CO)16B]– and double-prismatic [Rh3Ru6(CO)23B2]–

Abstract

The compounds [N(PPh₃)₂][Rh₂Ru₄(CO)₁₆B]1 and [N(PPh₃)₂][Rh₃Ru₆(CO)₂₃B₂]3 were isolated after treating [N(PPh₃)₂][Ru₃(CO)₉BH₄] with [{Rh(CO)₂Cl}₂] for 1 h. The neutral cluster [Rh₂Ru₄H(CO)₁₆B]2 was also isolated. The crystal structure of 1 has been determined: monoclinic, space group P2₁/n, a= 16.370(5), b= 10.330(3), c= 33.532(9)Å, β= 96.33(2)°, Z= 4. The core of 1 is octahedral with the two rhodium atoms in a trans arrangement; the boron atom is sited at the centre of the octahedron. The crystal structure of 3 has also been determined: triclinic, space group P, a= 10.666(2), b= 17.540(4), c= 18.658(3)Å, α= 91.06(2), β= 104.15(2), γ= 92.54(2)°, Z= 2. The cluster core consists of two, face-sharing prisms with one square face capped by a rhodium carbonyl fragment; each prismatic cavity contains a boron atom and B–B separation is 1.80(2)Å. The structure of cluster 3 is novel both as far as the environment of the boron atoms and the geometry of the metal skeleton are concerned but it is related to a series of previously characterised carbido clusters.