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Studies with the Rhenacarborane Cs[Re(CO)35-7,8-C2B9H11)]:  Surprising Reactivity with a Range of Metal Ligand Fragments

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journal contribution
posted on 28.10.1999, 00:00 by Dianne D. Ellis, Paul A. Jelliss, F. Gordon A. Stone
The rhenacarborane salt Cs[Re(CO)3(η5-7,8-C2B9H11)] (1) has been synthesized in excellent yield using a new procedure. Treatment of CH2Cl2 solutions of 1 with [RuCl2(PPh3)3] yields the exo-closo complex [Re(CO)3(η5-2,3,10-(μ-H)3-exo-{RuCl(PPh3)2}-7,8-C2B9H8)] (2a). In this molecule a [RuCl(PPh3)2]+ moiety is exopolyhedrally bound via three B−H⇀Ru bonds to a closo-3,1,2-ReC2B9 system. An X-ray diffraction study revealed that one of these agostic interactions utilizes a β-B−H bond in the coordinating face of the cage, while the source of the remaining two B−H⇀Ru bonds is in the B5 belt. The anion of salt 1 also binds exopolyhedral [Rh(PPh3)2]+ and [Rh{Fe(η-C5H4PPh2)2}]+ fragments in the complexes [Re(CO)3(η5-5,10-(μ-H)2-exo-(RhL2)-7,8-C2B9H9)] (L2 = (PPh3)2 (3a), {Fe(η-C5H4PPh2)2} (3b)). Reaction of 1 with the salts [M(CO)2(THF)(η-C5H5)][BF4] (M = Fe, Ru) and [Fe(CO)2(THF)(η-C5Me5)][BF4] gives the complexes [Re(CO)3(η5-n-(μ-H)-exo-{M(CO)2(η-C5R5)}-7,8-C2B9H10)] (M = Fe, R = H, n = 10 (4a); M = Ru, R = H, n = 10 (4b); M = Fe, R = Me, n = 10 (4c), 9 (4d)) with isomers 4c and 4d formed as an inseparable mixture. An X-ray structural study on 4b revealed that there was no Re−Ru bond and that an exo-[Ru(CO)2(η-C5H5)]+ fragment is bound to the rhenacarboranyl anion by a single unsupported B−H⇀Ru interaction with an unusually long B−Ru distance (2.695(13) Å). The compounds [ReM(μ-10-H-η5-7,8-C2B9H10)(CO)3(PPh3)] (M = Cu (5a), Ag (5b)) were isolated from the reaction of 1 with sources of the fragments [M(PPh3)]+ (M = Cu, Ag). X-ray structure determinations of both species 5 revealed the presence of direct Re−M (M = Cu, Ag) connectivities bridged by carborane β-B−H⇀M interactions. In solution the complexes 5 are highly dynamic on the NMR time scale, even at low (−90 °C) temperatures.