A Dimeric Gallium Hydrazide as an Active Lewis Pair – Complexation and Activation of Me₂GaH and Various Heterocumulenes

Abstract

Treatment of the dimeric gallium hydrazide [Me2Ga‐N(2‐Ad)‐NC5H10]2 (5) with Me2GaH resulted in the formation of an adduct 6 by Ga–N bond cleavage and coordination of the metal hydride via a Ga–N and a 3c–2e Ga–H–Ga bond. This reaction reflects the typical behavior of frustrated Lewis pairs. Reactions with heterocumulenes R–N=C=X (R = Ph, CMe3, Dipp, X = O; R = Ph, X = S) or X=C=X (X = O, S) resulted in the formation of the cyclic Ga–N insertion products Me2Ga–N(R)C(O)N(2‐Ad)‐NC5H10 (7a–c), Me2GaS2C‐N(2‐Ad)‐NC5H10 (8) or Me2GaX2C‐N(2‐Ad)‐NC5H10 [X = O (9); S (10)] in moderate to good yields. Three different structural motifs were observed in the solid state: Five‐membered GaNCN2 heterocycles with exocyclic C=O bonds for compounds 7a–c, four‐membered GaSCN or GaSCS heterocycles for compounds 8 and 9 (chelating coordination of the Ga atoms by SCN and CS2 ligands) and an eight‐membered (GaOCO)2 heterocycle for the dimeric CO2 insertion product 10. Treatment of 5 with PhCN or Ph2CO resulted in a completely different reaction and afforded a dimeric Ga imide 11a or an alcoholate 11b. These reactions may start by retro‐hydrogallation with the formation of H10C5N–N=C(C9H14) and Me2GaH and proceed by addition of the metal hydride to the polar multiple bonds of the nitrile or ketone.

New Ga/N‐based Active Lewis Pairs, Trifunctional Ga–Ga Compounds, Reactions with Cyanamide and Dual Insertion of Isocyanate

“…In contrast, ALPs based on Al and N atoms ( 1 and 2 ) led to cleavage of the Al‐N donor‐acceptor bonds or the insertion of the isocyanate groups into M–C or M–N bonds (M = Al, Ga) ,. [6a], [6c], [8b] Reaction of 7a with equimolar quantities of Ph–N=C=O afforded a pale yellow oil. Its main component is likely (2,6‐Me 2 C 5 H 8 N)–C(H)=C(SiMe 3 )C(NPh)(O)Ga t Bu 2 , which resembles the carbodiimide insertion product 3 (Scheme ) and results from insertion into the Ga–C(vinyl) bond (Scheme ).…”

“…Hydroalumination of hydrazones, or ynamines afforded two classes of Al/N‐based Lewis pairs. Hydrazones gave monomeric Al hydrazides with AlN 2 heterocycles, ( 1 ; Scheme ), while ynamines yielded enamines with Al and N in vicinal positions and AlC 2 N heterocycles ( 2 ) . Ring strain facilitates cleavage of the Al–N bonds and allows both compounds to behave as active Lewis pairs (ALPs).…”

Cooperative activation of azides by an Al/N-based active Lewis pair – unexpected insertion of nitrogen atoms into C–Si bonds and formation of AlCN3 heterocycles

“…A class of compounds closely related to the Al/P FLPs contain Al or Ga and N atoms. Weak bonding interactions between the Lewis acidic metal and the Lewis basic N atoms result in strained four- [11][12][13][14] or three-membered heterocyles [15][16][17][18]. Cleavage of the relatively weak donor-acceptor bonds in the presence of suitable substrates results in a reactivity similar to that of FLPs.…”

An Unprecedented Ga/P Frustrated Lewis Pair: Synthesis, Characterization, and Reactivity

“…Although aluminumh as also been explored as a Lewis-acidic site in the past few years, [8] the use of the heavier galliuma saLewis acid in FLPs was rare. [9,10] Herein, we report as traightforward one-step synthesis of an unprecedentedG a/P FLP,i nw hich the Lewis acidic Ga center is tetra-coordinated with aN!Ga donor-acceptor bond. Density functional theory (DFT) calculations and reactivity toward several substrates were investigated.…”

“…2019, 25,14295 -14299 www.chemeurj.org 2019 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim centers in thesep roducts were penta-coordinated, which is novel in the addition products of other FLP systems. [9,10] In addition, compound 2 was also reacted with the dimeric species[ IrCl(COD)] 2 ,f rom which the addition product 8 was isolated in 67 %y ield. The 31 P{ 1 H} NMR spectra showed as ingle signal at 23.6 ppm, consistentw ith the formulation of bimetallic product.…”