Synthesis and reactivity of hydrogen-rich uranium-rhenium compounds; An unsuspected detrimental effect of alkali-metal halide on chemical metathesis

Reaction of [U(eta-C(5)Me(5))(2)Cl(thf)] and [K(thf)(2)][ReH6(PPh(3))(2)] did not afford the metathesis product with elimination of KCl but gave the anionic addition;compound [K(thf)(2)][Cl(eta-C(5)Me(5))(2)UH6Re(PPh(3))(2)] (thf = tetrahydrofuran); the borohydride analogue was similarly prepared. The bimetallic complexes [(eta-C(5)H(4)R)(3)UH6Re(PPh(3))(2)] (R = Bu(t) or SiMe(3)) could not be isolated from [U(eta-C(5)H(4)R)(3)Cl] and [K(thf)(2)][ReH6(PPh(3))(2)] because of their reverse cleavage by KCl which led to an equilibrium mixture; these hexahydrides were cleanly synthesized by reaction of [U(eta-C(5)H(4)R)(3)][BPh(4)] and [K(thf)(2)][ReH6(PPh(3))(2)].