Mononuclear Phenolate Diamine Zinc Hydride Complexes and Their Reactions With CO₂

Abstract

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (1)/methoxy (2)/nitro (3)]-6-{[(2′-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes 4–6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes 7–9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes 10–12. The new complexes 4–12 have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (d8-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(μ-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes 13–15. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer–dimer equilibrium that is dominated by the mononuclear species at 298 K.

Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex

“…Reported zinc-based catalysts for the hydrosilylation of CO 2 . [14][15][16][17] Furthermore,a lso in the AT-IR spectrum the ZnÀHstretching vibration is found at 1769 cm À1 as asharp signal. [14] In the solid state,t he hydrido compound is moderately stable at ambient atmosphere whereas in solution it is sensitive towards moisture and decomposes to yet unidentified products.H owever,i nd ichloromethane,a lso in absence of moisture, 2 is only stable below À30 8 8C, while at room temperature it decomposes in the course of 4-6 h, predominantly forming [k 4 -C,N,S,S-Tntm]Zn(Pn) (4,P n = 6-tertbutyl-3-thiopyridazine;S upporting Information, Figures S8-S10, S19).…”

Mononuclear Heteroscorpionate Zwitterionic Zinc Terminal Hydride: Synthesis, Reactivity, and Catalysis for Hydrosilylation of Aldehydes

“…18 In the 1 H NMR spectrum in benzene-d 6 , the terminal hydride (Zn−H) resonance appears at 5.38 ppm, which is close to the corresponding zwitterionic tris(substituted-pyrazoyl) hydroborate zinc hydrides (δ 5.36 ppm for Tp tBu ZnH, 4a 5.26 ppm for Tp p-Tol, Me ZnH 4b ), but shifts obviously downfield as compared with those in many other neutral mononuclear zinc hydrides reported previously (3.99− 5.02 ppm). 5e, 10 The molecular structure of complex 2 was well resolved by a single-crystal X-ray diffraction study (Figure 1, left), where the heteroscorpionate ligand moiety caps the zinc ion with three nitrogen atoms in the κ 3 -coordination mode, appearing as a mononuclear structure bearing a single zinc terminal hydride species. The terminal Zn(1)−H(1) bond length is 1.57(4) Å, falling in the normal range for mono zinc hydride complexes reported previously.…”

Reaction Mechanisms of CO2 Reduction to Formaldehyde Catalyzed by Hourglass Ru, Fe, and Os Complexes: A Density Functional Theory Study

“…As an abundant and non-toxic C 1 -building block, carbon dioxide can be reduced to various chemicals, such as carbon monoxide [1], methanol [2], formaldehyde [3], acetals [4,5], formic acid [5], formate [6,7], formamides [8], methylamines [8], formamidines [8], imines [3] and methane [9]. Recently, Beller and co-workers [10] reported the methylation of aromatic C-H bonds using CO 2 and H 2 with the assistance of a ruthenium triphos catalyst.…”