Organouranium Complexes with Phosphinine-Based SPS Pincer Ligands. Variations with the Substituent at the Phosphorus Atom

Abstract

Reaction of [K(Et2O)][SPSMe] with [U(Cp*)(BH4)3] or [U(COT)(BH4)2(THF)] in THF gave the expected substitution products [U(Cp*)(BH4)2(SPSMe)] (1) and [U(COT)(BH4)(SPSMe)] (2), respectively. Protonolysis of 2 with [NEt3H][BPh4] afforded the cationic complex [U(COT)(SPSMe)(NEt3)][BPh4] (3), which was transformed into [U(COT)(SPSMe)(L)][BPh4] [L = OPPh3 (4) or HMPA (5)]. Changing [K(Et2O)][SPSMe] with [Na][SPSOMe] in its reaction with [U(COT)(BH4)2(THF)] afforded a mixture of complexes, among which [U(COT)(BH4)(SPSH)] (6) was deposited as red crystals of a THF solvate. Complex 6 was isolated in 79% yield from the reaction of [U(COT)(BH4)2(THF)] and SPS in the presence of a catalytic amount of NaBH4; the key intermediate of the reaction is [Na(THF)x][SPSH·BH3], formed by addition of NaBH4 to SPS, which reacts with [U(COT)(BH4)2(THF)] to give 6 and NaBH4. The X-ray crystal structures of 1·4.5C6H12, 2·THF, 5·Et2O, and 6·1.5THF indicate that the central moiety of the SPS ligand can be considered as a classical phosphine, the anionic charge being stabilized by delocalization over the five carbon atoms of the phosphahexadienyl anion and negative hyperconjugation into the two Ph2PS pendant arms. The X-ray crystal structures of [{U(COT)(S2PPh2)(μ-OMe)}2] and [{U(COT)}4{U(THF)3}2(μ3-S)8], which resulted from decomposition of the SPS ligand, are also presented.