Deaggregation of Zinc Dihydride by Lewis Acids Including Carbon Dioxide in the Presence of Nitrogen Donors

Abstract

Thermally sensitive polymeric zinc dihydride [ZnH2] n can conveniently be prepared by the reaction of ZnEt2 with [AlH3(NEt3)]. When reacted with CO2 (1 bar) in the presence of chelating N-donor ligands L n = N,N,N′,N′-tetramethylethylenediamine (TMEDA), N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA), N,N,N′,N″,N′′-pentamethyldiethylenetriamine (PMDTA), and 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (Me4TACD), insertion into the Zn–H bond readily occurred. Depending on the denticity n, formates [(L n )­Zn­(OCHO)2] were isolated and structurally characterized, either as a molecule (L n = TMEDA, TMPDA, PMDTA) or a charge-separated ion pair [(L n )­Zn­(OCHO)]­[OCHO] (L n = Me4TACD). The reaction of [ZnH2] n with the mild Lewis acid BPh3 in the presence of chelating N-donor ligands L n gave a series of hydridotriphenylborates, either as a contact ion pair [(L2)­Zn­(H)­(HBPh3)] (L2 = TMEDA, TMPDA) or a separated ion pair [(L n )­Zn­(H)]­[HBPh3] (L n = PMDTA, Me4TACD). In the crystal, the contact ion pair [(TMEDA)­Zn­(H)­(HBPh3)] showed a bent Zn–H–B bridge indicative of a delocalized Zn–H–B interaction. In contrast, a linear Zn–H–B bridge for [(TMPDA)­Zn­(H)­(HBPh3)] was observed, suggesting a contact ion pair. In THF solution, both complexes show an exchange with free BPh3 as well as [HBPh3]−. DFT calculations suggest the presence of [HBPh3]− anion with a highly polarized B–H bond that interacts with the Lewis acidic zinc hydride cation [(L2)­Zn­(H)]+. The hydridotriphenylborates [(L n )­Zn­(H)­(HBPh3)] underwent CO2 insertion to give (formato)zinc (formoxy)­triphenylborate complexes [(L n )­Zn­(OCHO)]­[(OCHO)­BPh3] (L n = TMPDA, PMDTA, Me4TACD). For L n = TMEDA, a dinuclear complex [(L n )2Zn2(μ-OCHO)3]­[(OCHO)­BPh3] was isolated. Hydridotriphenylborates [(L n )­Zn­(H)­(HBPh3)] catalyzed the hydrosilylation of CO2 (1 bar) by n BuMe2SiH in THF at 70 °C to give formoxysilane and (methoxy)­silane.

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)‐Centre: Labile Mono‐ and Bis(hydridogallyl)zinc Complexes

“…A Schlenk flask was charged with [ZnH 2 ] n (14.5 mg, 0.215 mmol)[ 20a , 21a ] and [(BDI)Ga] ( I ) (100 mg 0.205 mmol). [24] TMEDA (117 mg, 1.0 mmol) and benzene (5 mL) were added and the reaction mixture was rapidly stirred, resulting in the formation of a bright yellow solution.…”

Dihydrogen Cleavage by a Zinc–Zinc Bond of a Heteroleptic Dizinc(I) Cation

“…All solvents were degassed before use. [ZnH 2 ] n , 37 ] − (1b, 200 mg, 0.192 mmol) in THF (10 mL) was added to a Schlenk flask charged with Zn 2 (C 5 Me 5 ) 2 (92.8 mg, 0.231 mmol) at room temperature and stirred rapidly for one h to give a clear colorless reaction mixture. The reaction mixture was filtered, and the filtrate was concentrated in vacuo.…”

“…The 11 B NMR spectra of 5a−c recorded at 25 °C display an upfield shifted broad peak 6) Å). 37 The Zn2−H1−B1 angle in 5a (130°) and 5b (149°) showed the oblique arrangement of the Zn−H−BPh 3 fragment which brings the BPh 3 moiety in close vicinity to the Zn2 center (Zn2•••B1 distance 2.819(2) Å for 5a, 2.948(5) Å for 5b), which is essential for the stabilization of the Cp*Zn−Zn(HBPh 3 ) unit (Table 1). In contrast, the Zn2−H1−B1 angle in 5c (162°) is directed away from the oblique arrangement, which eventually results in a smaller interaction correlating with an increased Zn2•••B1 distance (3.046(2) Å; see SI for details).…”

Heterobimetallic Hydrides with a Germanium(II)‐Zinc Bond

“…Additional references cited within the Supporting Information. [37,39,[50][51][52][53][54][55][56][57][58][59][60]…”