Reversible Dihydrogen Activation in Cationic Rare‐Earth‐Metal Polyhydride Complexes

Abstract

Dihydrogen activation by metal alkyl complexes via s-bond metathesis is a facile non-redox reaction and a common method for the preparation of rare-earth [1] and early-transition-metal hydrido complexes. [2] The intramolecular CÀH bond activation has been reported for metal alkyl or hydride complexes to give so-called "tucked-in" or "tucked-over" cyclometalated complexes with concomitant liberation of alkane or dihydrogen, [3] predominantly in metallocenes of early transition metals [2b, 4] and f-block elements. [5] The metallocene hydrides of zirconium [6] and samarium [5d] and tris-(amido) actinide hydrides [7] reversibly form the hydrido complex and the cyclometalated complexes by addition and removal of dihydrogen.We have reported a bimetallic trivalent rare-earth-metal complex with two bridging hydrido ligands that adds dihydrogen across a metal-carbon bond and a metal-metal axis. [8] The reverse liberation of dihydrogen by CÀH bond activation was not observed. [9] We have now obtained a rare-earth-metal hydrido complex capable of reversibly binding and releasing dihydrogen under mild conditions. No change in the oxidation state of the metals is involved, as addition and release occur by s-bond metathesis involving a metal-carbon bond. Notably, hydrogenolysis in the solid state was also observed in a single-crystal to single-crystal transformation.The cationic dialkyl lutetium complex [Lu(CH 2 SiMe 3 ) 2 -(thf) 3 ][A] (A = B{3,5-C 6 H 3 (CF 3 ) 2 } 4 ) [10] was treated with the neutral NNNN-type macrocyclic ligand 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (Me 4 TACD = Me 4 [12]aneN 4 ) to give the THF-free dialkyl complex [(Me 4 TACD)Lu-(CH 2 SiMe 3 ) 2 ][A] (1-Lu) in quantitative yield (Scheme 1). Scheme 1. CÀH bond activation in cationic bis(alkyl) complex 1-Lu to give complex 2-Lu.Scheme 2. Preparation of dicationic trihydrido complex 3-Lu.

Molecular Calcium Hydride: Dicalcium Trihydride Cation Stabilized by a Neutral NNNN‐Type Macrocyclic Ligand

“…On the basis of these observations,w ep ropose the deuteration of the cationic calcium hydride 3 to the deuterated complex [D 3 ]-3 via an intermediate dideuterium complex A. [9] Ad issociated complex B [20] may also be formed (Scheme 3). Deuterium is activated either by the Lewis acidic calcium center in A or by s-bond metathesis in complex B to give the neutral dicalcium monodeuteride trihydride C under release of DSiPh 3 .T he silane DSiPh 3 [3,5] B(C 6 F 5 ) 3 catalyzed hydrogenation (4 atm of H 2 )of1,1'-DPE showed full conversion at 50 8 8Cafter 48 h, [21] whereas B(C 6 F 5 ) 3 -catalyzed transfer hydrogenation of 1,1'-DPE was complete at 25 8 8Ca fter 8h.…”

“…[9] The 1 HNMR spectrum of 2 in [D 8 ]THF at 25 8 8Cs hows two sharp singlets at d = 2.18 and 2.50 ppm for the protons of (12 vs.3min for a0 .1m solution). Compound 3 is soluble in THF (t 1/2 % 12 h), but insoluble in aromatic and aliphatic hydrocarbons and was characterized by elemental analysis and NMR spectroscopy (Scheme 2).…”

“…(8), Ca1-N3 2.590(6), Ca1-N4 2.674(7), Ca2-N5 2.589(6), Ca2-N6 2.670(7), Ca2-N7 2.612(6), Ca2-N8 2.587(6). [9] Thec onversion of 3 into [D 3 ]-3 followed pseudo-first-order kinetics with k H (H 2 ) = 2.82(3) 10…”

Molekulares Calciumhydrid: Dicalciumtrihydrid‐Kation, stabilisiert durch einen neutralen makrocyclischen NNNN‐Liganden

“…[5] Während Bis(triphenylsilyl)calcium [Ca(SiPh 3 ) 2 (THF) 4 ]( 1) mit Wasserstoff anscheinend kolloidales Calciumdihydrid bildet, [6] sollte sich Me 4 TACD-gebundenes Bis(triphenylsilyl)calcium als Vorstufe für das molekulare Calciumdihydrid [CaH 2 (Me 4 TACD)] (Me 4 TACD = 1,4,7,4,7, (SiMe 3 ) 3 } 2 (THF) 3 ]. [8] Der kleine Si1-Ca1-Si1'-Winkel von 85.68 (5) [4] (Ca···Ca = 3.3551(10) ) und vergleichbar zu denen in zweikernigen Lanthanoidtrihydriden [Ln 2 H 3 ]( Ln = Yu nd Lu; Ln···Ln = 2.93-3.75 ), [9,11] obwohl der Radius des Ca 2+ -Ions (1.06 b ei KZ = 7) grçßer als der des Y 3+ -Ions (0.96 b ei KZ = 7) und des Lu 3+ -Ions (0.86 b ei KZ = 6) ist. [12] Die Stabilität des kationischen Calciumhydrids 3 wurde anhand einer NBO-Analyse über DFT-Rechnungen auf dem gleichen Niveau wie für 2 bewertet.…”

“…[19] Wurde das kationische Calciumhydrid 3 Aufgrund dieser Beobachtungen schlagen wir vor,d ass die Deuterierung des kationischen Calciumhydrids 3 zum deuterierten Komplex [D 3 ]-3 über einen Diwasserstoffkomplex A als Zwischenstufe abläuft. [9] Auch ein dissoziierter Komplex B [20] [3,5] B(C 6 F 5 ) 3 katalysierte die Hydrierung von 1,1'-DPE mit quantitativer Umsetzung nach 48 hb ei 50 8 8C( unter 4a tm H 2 -Druck, [21] wobei die mit B(C 6 F 5 ) 3 katalysierte Tr ansferhydrierung von 1,1'-DPE bei 25 8 8Cnach 8h zum gleichen Umsatz führte). [22] Die mit einem kationischen NHC-Galliumchlorid katalysierte Tr ansferhydrierung von 1,1'-DPE führte nach 1h bei 20 8 8Cn ur zu 67 %U msatz.…”