Metal fragment addition and substitution reactions of [Ru3(CO)9BH5] and [Ru3H(CO)9(B2H5)]: molecular structures of [WRu3(cp)H(CO)11(BH)] and [MoRu3(cp)H3(CO)11](cp =η-C5H5)

Abstract

The photochemical reactions of [{M(cp)(CO)₃}₂](M = Mo or W, cp =η-C₅H₅) with [Ru₃(CO)₉BH₅]1 or [Ru₃H(CO)₉(B₂H₅)]2 have been investigated. The observed cluster products arise by either the addition of a {(cp)M(CO)₂} fragment to the Ru₃B cluster core of 1 with associated hydrogen loss or by substitution of one {(cp)M(CO)₂} for a {BH₂} fragment in either 1 or 2 and, for M = W only, by the substitution of two {BH₂} fragments. An assessment as to whether the reaction pathways may be reasonably described in terms of isolobal fragment replacement is presented; Fenske–Hall quantum-chemical calculations are used to show that some degree of semi-bridging character from the Group 6 metal carbonyl ligands to the triruthenium framework necessarily follows as the {(cp)M(CO)₂}(M = Mo or W) fragment is introduced in place of the {BH₂} unit in 1. Two products have been characterized by single-crystal X-ray crystallography: [MoRu₃(cp)H₃(CO)₁₁]4, monoclinic, space group P2₁/c, a= 16.668(5), b= 14.575(6), c= 18.319(4)Å, β= 102.85(2)°, Z= 8; R(F)= 0.0408; [WRu₃(cp)H(CO)₁₁(BH)]5, monoclinic, space group P2₁/c, a= 17.328(6), b= 7.641(3), c= 17.924(8)Å, β= 114.92(3)°, Z= 4, R(F)= 0.1210. Compound 4 exhibits a tetrahedral metal core and is related to 1 by the replacement of an apical {BH} unit and one endo-hydrogen atom by a {(cp)Mo(CO)₂} group. Compound 5 consists of a butterfly framework of metal atoms with the tungsten atom occupying a wingtip site and is the first heterometallic butterfly cluster containing a semi-interstitial boron atom to be structurally characterized. Partial structural data have been obtained for a third product, [W₂Ru₃(cp)₂(CO)₁₃] and the presence of a trigonal bipyramidal cluster core with two equatorial tungsten site has been confirmed. This isomer is found not to be that which is dominant in solution.