Reactivity of the Anionic Carbonyltrirhenium Cluster [Re3(µ‐H)3(µ3‐ampy)(CO)9]− − Synthesis of Neutral Phosphane and Alkenyl Derivatives

Protonation of the trinuclear anionic rhenium cluster [HNEt3][Re3(µ-H)3(µ3-ampy)(CO)9] (1) (Hampy = 2-amino-6-methylpyridine) with [HOEt2][BF4] at low temperature leads to dihydrogen and the neutral unsaturated dihydride derivative [Re3(µ-H)2(µ3-ampy)(CO)9]. The low thermal stability of this compound (it undergoes decomposition above 5 °C) has prevented its isolation as a pure solid. The compound [Re3(µ-H)3(CO)12] is the major product obtained when the protonation of 1 is carried out under CO. Protonation of 1 in the presence of phosphanes or alkynes gives the neutral derivatives [Re3(µ-H)2(µ3-ampy)(PR3)(CO)9] (2: R = Ph; 3: R = p-tolyl) or [Re3(µ3-H)(µ3-ampy)(µ-RC=CHR′)(CO)9] (4: R = R′ = Ph; 5: R = R′ =Et; 6a: R = Ph, R′ = H; 6b: R = H, R′ = Ph). In 2 and 3, the phosphane ligand is in an equatorial position on an Re atom of the NH-bridged Re−Re edge, cis to a hydride ligand and far away from the other hydride ion. In compounds 4−6, the alkenyl ligand, which arises from the insertion of the corresponding alkyne into an Re−H bond, is attached to two metal atoms in a µ-η1:η2 fashion, spanning the same Re−Re edge as the NH fragment of the ampy ligand. The hydride ligand of compounds 4−6 coordinates in a triply bridging fashion, capping the Re3 triangle. Compounds 4−6 represent the first examples of trirhenium clusters containing alkenyl ligands.