Reactions of small boranes with ruthenium phosphine hydrides: Oligomerisation of monoborane-tetrahydrofuran to a nido-hexaruthenaborane

Reaction of [Ru(PPh3)4H2] with BH3 · thf at room temperature gives borane oligomerisation with the formation of the 6-vertex metallaborane nido -2-[Ru(PPh3)2(H)B5H10] (1). This cluster is also formed by reaction of [Ru(PPh3)4H2] with nido -B5H9. Compound (1) is readily deprotonated by KH in thf at the unique basal B–H–B bridge to give View the MathML sourcenido-2-[Ru(PPh3)2(H)B5H9-][K+] (2). In contrast to [Ru(PPh3)4H2] reaction of [cis-Ru(PMe3)4H2] with BH3 · thf gives initially the known borohydride [Ru(PMe3)3(H)(η2-BH4)] which reacts with excess BH3 · thf to give the 5-vertex metallaborane nido-2-[Ru(PMe3)3B4H8] (3). Reaction of [cis-Ru(PMe3)4H2] with nido-B5H9 also gives (3) and nido-2-[Ru(PMe3)3B9H13] (4). [cis-Ru(PMe3)4H2] is conveniently prepared in high yield in a one-pot synthesis by the sodium amalgam reduction of RuCl3 · 3H2O in thf with excess PMe3 under dinitrogen.