Studies with the rhenacarborane Cs[Re(CO)3(η5-7,8-C2B9H11)]:: Surprising reactivity with a range of metal ligand fragments

The rhenacarborane salt Cs[Re(CO)(3)(eta(5)-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)(eta(5)-2,3,10-(mu-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 beta-B-H bond in the coordinating CCBBB face of the cage, while the source of the remaining two B-H-Ru bonds is in the Bs belt. The anion of salt 1 also binds exopolyhedral [Rh(PPh3)(2)](+) and [Rh{Fe(eta-C5H4PPh2)(2)}](+) fragments in the complexes [Re(CO)(3)(eta(5)-5, 10-(mu-H)(2)-exo-(RhL2)-7,8-C2B9H9)] (L-2 = (PPh3)(2) (3a), {Fe(eta-C5H4PPh2)(2)} (3b)). Reaction of 1 with the salts [M(CO)(2)(THF)(eta-C5H5)] [BF4] (M = Fe, Ru) and [Fe(CO)(2)(THF)(eta-C5Me5)][BF4] gives the complexes [Re(CO)(3)(eta(5)-n-(mu-H)-exo-{M(CO)(2)(eta-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)(eta-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) Angstrom). The compounds [ReM(mu-10-H-)eta(5)-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 beta-B-H-M interactions. In solution the complexes 5 are highly dynamic on the NMR time scale, even at low (-90 degrees C temperatures.