Establishment of syntheses of metal-rich metallaborane clusters using borane-Lewis base adducts

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The purpose of this project was to establish new methods for the syntheses of metallaboranes with large M/B ratios using activation of borane-Lewis base adducts by transition metal complexes which we have developed recently. Reactions of organometallic ruthenium complexes with BH_3-THF gave cluster compounds with the Ru_2B_3, RU_2B_4, RuB_4 frameworks, and further reactions of these clusters with phosphines gave RU_2B_2, RuB_3 clusters with larger M/B ratios.The reaction of BH_3-THF with [Cp^*RuCl]_4 gave nido-[(Cp^*Ru(μ-H)}_2B_3H_7] (1), and 1 further reacted with BH_3-THF to give nido-[(Cp^*Ru(μ-H)}_2B_4H_9] (2). Reaction of 1 with phosphine derivatives underwent degradation and rearrangement of cluster frameworks, and the reaction modes depended on the nature of phosphines. In the reactions with PHPh_2 or P(OPh)_3 1 gave arachno-[(Cp^*_2Ru_2PR_3)(μ-H)_2B_3H_7] (3) adding phosphine to the basal metal. Reaction with P(OR)_3 underwent dehydrogenation rearragement to give nido-[(Cp^*_2Ru_2(μ-P(OR)_2}(μ-H)_2B_3H_5(OR)] (4). Reactions with PR_3, stronger bases gave [(Cp^*Ru)_2(μ-H)(PR_3)B_2H_5] (5) with elimination of BH_3-PR_3. Reaction using phenyl phosphines provided [(Cp^*Ru)_2(μ-PR_2)(B_2H_2)] (6) accompanied with benzene elimination and rearagement of the framework. NMR measurement showed the fraxional property of the cluster flamework of 6. Reaction of 5 with excess PR_3, underwent total degradation of the cluster to form mononuclear compounds, although 6 did not show any such reaction.Reaction of BH_3-THF and [(C_6Me_6)RuCl_2]_2 with a bulky ligand, C_6Me_6, afforded arachno-[(C_6Me_6)RuB_4H_<10>] (7) which contained only one metal fragment. Reaction of 7 with PMe_3 arachno-[(C_6Me_6)Ru(PMe_3)(B_3H_7)] (8) accompanied with the elimination of BH_3-PMe_3. This also shows that the reaction of the cluster with phosphine provides a route to the change of the M/B ratio.