Monocationic bis(hydrocarbyl)yttrium complexes [YR 2 (THF) 2 ][A] (R = CH 2 SiMe 3 , CH 2 C 6 H 4 -o-NMe 2 ; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH 2 (THF) 2 ] n [A] n . The mixture composition as well as the nuclearity n depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a closo-type tetrahedral [YH 2 (THF) 2 ] 4 4+ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis (diphenylmethoxy) cation [Y(OCHPh 2 ) 2 (THF) 4 ][AlR 4 ]. The reaction of this cluster with the (NNNN)-type macrocycle Me 4 TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y 2 (μ-H) 4 (Me 4 TACD) 2 ][A] 2 , analogous to the previously characterized lutetium derivative. NH-acidic (Me 3 TACD)H gave the dinuclear dihydride dication [Y 2 (μ-H) 2 (Me 3 TACD) 2 (THF) 2 ][A] 2 .
■ INTRODUCTIONIn contrast to interstitial rare-earth metal hydrides of the type LnH n (n = 2, 3), molecular hydrides of these large, electropositive, and Lewis acidic metals are commonly stabilized as bis-or mono(cyclopentadienyl) hydride complexes [Ln(η 5 -C 5 R 5 ) n H 3−n ] (n = 2, 1). 1 They are easily prepared by σ-bond metathesis of the corresponding hydrocarbyl compounds [Ln(η 5 -C 5 R 5 ) n R′ 3−n ] (n = 2, 1) with dihydrogen or phenylsilane. 1 Cationic hydrocarbyl complexes of the rare-earth metals [LnR 2 (THF) 2 ][A] are easily accessible by protonolysis of the parent neutral complexes with Brønsted acidic ammonium salts of weakly coordinating borate anions or with Lewis acidic boranes, tris(alkyl)aluminum, and trityl salts. 3 In the presence of weakly coordinating neutral donor ligands L, hydrogenolysis with dihydrogen or phenylsilane should lead to cationic dihydrides of the formula [LnH 2 (L) n ] + . We describe here details of the long quest for yttrium compounds of the type [YH 2 (L) n ] + , solely coordinated by neutral donor ligands such as tetrahydrofuran (THF), tetrahydropyran (THP), or crown ethers, 2 as well as the characterization of an (NNNN)-type macrocycle-stabilized dimer [Y 2 (μ-H) 4 (Me 4 TACD) 2 ] 2+ featuring a quadruple hydride bridge.