Yttrium Dihydride Cation [YH₂(THF)₂]⁺_n: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Abstract

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.

Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium ansa-Metallocene Hydride Complex, [K(crypt)][(μ-CpAn)Y(μ-H)]2 (CpAn = Me2Si[C5H3(SiMe3)-3]2), with a 3.4 Å Yttrium–Yttrium Distance

“…The metrical parameters for 3 are similar to those of other Y­(III) hydrides. In particular, the Y···Y distance of 3.6311(5) Å in 3 falls within the typical values for other bimetallic bridging hydride complexes, including {[Me 2 Si­(C 5 H 4 ) 2 ]­Y­(THF)­(μ-H)} 2 [3.514(3) Å], {[Y­(Me 3 TACD)­(THF)­(μ-H)] 2 }­[B­(3,5-C 6 H 3 [CF 3 ] 2 ) 4 ] 2 [3.6203(9) Å, TACD = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane], [{(MeC 5 H 4 ) 2 Y­(THF)­(μ-H)} 2 ] [3.66(1) Å], [{(dadmb)­Y­(THF)­(μ-H)} 2 ] [3.6652(8) Å, dadmb = 2,2′-bis-[( tert -butyl-dimethylsilyl)­amido]-6,6′-dimethylbiphenyl], [{SiMe 2 (C 5 Me 4 )­(N t Bu)­Y­(THF)­(μ-H)} 2 ] [3.672(1) Å], [{(1,3-Me 2 -C 5 H 3 ) 2 Y­(THF)­(μ-H)} 2 ] [3.68(1) Å], and {Y­[(Me 3 Si) 2 NC­(N i Pr) 2 ] 2 (μ-H)} 2 [3.6825(5) Å] …”

Using Diamagnetic Yttrium and Lanthanum Complexes to Explore Ligand Reduction and C–H Bond Activation in a Tris(aryloxide)mesitylene Ligand System

“…The J YH = 93 Hz coupling constant is larger than, but consistent with, the J YH = 74.8, 81.7, and 82.0 Hz coupling constants reported for the terminal hydride complexes [(C 5 Me 4 SiMe 3 ) 2 YH­(THF)], [(C 5 Me 5 ) 2 YH­(THF)], and [(C 9 Me 7 ) 2 YH­(THF)], respectively. In contrast, for μ 2 -hydride complexes, J YH coupling constants have been reported in the range of 21.3–35 Hz. − The J YH coupling constants for μ 3 -hydrides are 16.3–18 Hz, − and they are 12.5 and 15.3 Hz for μ 4 -hydrides. , A 89 Y– 1 H heteronuclear multiple quantum coherence (HMQC) experiment showed a correlation between the hydride resonance at 7.81 ppm with a 89 Y resonance at −138.0 ppm in the 89 Y NMR spectrum of 2-Y / 3-Y . When CCl 4 is added to the NMR sample, the 7.81 ppm resonance disappears, and chloroform at 7.89 ppm grows in, which is consistent with the presence of a hydride ligand .…”

Correction to “Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium ansa-Metallocene Hydride Complex, [K(crypt)][(μ-CpAn)Y(μ-H)]2 (CpAn = Me2Si[C5H3(SiMe3)-3]2), with a 3.4 Å Yttrium–Yttrium Distance”

“…We are grateful to readers who have pointed out that there are shorter Y···Y distances in bimetallic complexes involving only Y­(III); for leading references see refs − . Statements regarding the 3.3992(6) and 3.4022(7) Å Y···Y distances in our complex should be altered to involve Y­(II) systems as described below.…”