Phenylhydrazine Compounds of Aluminum and Gallium – from Adducts to Cyclic Hydrazides and Cages

Abstract

The reactions of trialkyl-element compounds (E ϭ Al, Ga) with hydrazines usually proceed by the intermediate formation of the simple adducts R 3 EǟNH 2 -N(H)-RЈ. However, only one adduct (1; R ϭ iPr, E ϭ Ga) could be isolated and characterized in the reactions of ER 3 compounds bearing relatively small substituents with phenylhydrazine. In all other cases fast secondary processes gave directly the corresponding dimeric hydrazides [R 2 EϪN(H)ϪN(H)-C 6 H 5 ] 2 (2 to 4; R ϭ Me, Et; E ϭ Al, Ga) by gas evolution below room temperature. In contrast, decomposition of the adduct 1 required boiling toluene to produce the hydrazide 5. Compounds 3 and 4 possess four-membered E 2 N 2 heterocycles Einleitung Elementorganische Aluminium-, Gallium-oder Indiumhydrazide stellen als leicht zugängliche Ausgangsverbindungen hervorragende Vorläufer für die thermolytische Abscheidung der entsprechenden Metallnitride dar [1]. Darüber hinaus besitzen sie aber beträchtliches wissenschaftliches Interesse, da die Hydrazinliganden ein bemerkenswertes Koordinationsverhalten aufweisen. Sie besitzen freie Elektronenpaare an miteinander verbundenen Stickstoffatomen und sind daher in der Lage, eine große Vielfalt unterschiedlicher Strukturmotive durch terminale bzw. 1,1oder 1,2-verbrückende Koordination von Metallatomen zu realisieren [2]. Die Darstellung solcher Erdmetallhydrazide gelingt auf unterschiedlichen Wegen durch Salz-, Wasserstoff-oder Alkaneliminierung. Der erste Schritt besteht im allgemeinen aus der Bildung von Addukten zwischen den Hydrazinmolekülen und den koordinativ ungesättigten

From tert‐Butylhydrazine Adducts of AlR3 (R = Me, CMe3) to Oligonuclear AlN Cage Compounds – Evidence for a Hydrazine Twist Across an Al3 Triangle

“…Bond lengths and angles are unexceptional and compare well to reported values of related aluminum-hydrazine adducts [Al1-N1 202.1(4), N1-N2 145.0(6) pm]. [5,7] Heating of 1a to 160°C resulted in the loss of isobutane (gas evolution at 155°C) and the formation of the aluminum hydrazide 2 in 72 % yield [Equation (2)]. Compound 2 has been obtained previously through salt elimination from the reaction of (Me 3 C) 2 AlClǟNH 2 -N(H)CMe 3 with nBuLi.…”

“…4 the Al-N distances between the six-membered heterocycles are slightly shorter than those within the cycles. [7] The N-N bond lengths (149.9 pm on average) are within the characteristic range for hydrazinediido ligands (see above). The molecular structure of compound 7 ( Figure 5 [8] This analogue shows disorder similar to that of the aluminum derivative 7.…”

“…www.eurjic.org The related aluminum and gallium derivatives [MeAlN(H)-NPh] 4 , [7] [Me 3 CAlN(H)-NMe] 4 , [6] [EtGaN(H)-NPh] 4 [7] and [MeGaN(H)-NCMe 3 ] 4 , [3,14] have recently been synthesized at elevated temperatures directly from the corresponding dimeric hydrazides. Intermediates similar to the above norbornane-like compound 5 may also exist, but have so far never been isolated or identified by spectroscopic methods.…”

“…[4] The hydrazine adducts were found to decompose spontaneously at room temperature, or upon slight warming, to yield the corresponding hydrazides featuring monoanionic hydrazide groups. [3,4,[6][7][8][9] These hydrazides are usually dimeric, with the exception of the sterically crowded monomeric compounds In[N(SiMe 3 )-NMe 2 ] 3 [10] and Me 3 C-Al[N(SiMe 3 )-N(H)SiMe 3 ] 2 , [11] and show a variety of structural motifs ranging from four-to six-membered heterocycles, [3,4,[6][7][8][9]12,13] and zero, one, or two endocyclic N-N bonds (Scheme 1). Transannular repulsion between partially charged metal and nitrogen atoms disfavors the formation of E 2 N 2 heterocycles, whereas electrostatic attraction between metal and nitrogen atoms and steric interactions between the substituents favor the creation of small heterocycles.…”

“…In the absence of steric influences the five-membered heterocycles were calculated to be thermodynamically favorable. [13] Experiments on the controlled thermolysis of hydrazides have given access to large EN cages such as [R-E-N(H)-NRЈ] 4 (R = Me, E = Al, RЈ = Ph; [7] R = Et, E = Ga, RЈ = Ph; [7] R = Me, E = Ga, RЈ = CMe 3 ; [8] R = iPr, E = Ga, RЈ = Ph; [8] R = Me, E = Ga, RЈ = CMe 3 or Ph [3,14] ), (Me 3 CGaNH) 8 [8] and very recently the unprecedented gallium compound (GaMe) 4 -(GaMe 2 ) 4 [N(H)-NMe] 4 (N 2 ) [15] that features as a unique structural motif a completely deprotonated tetraanionic N 2 4-group stabilized by six gallium atoms. These compounds and larger cages may, under thermolysis conditions, occur as intermediate compounds between the initially formed adducts and the corresponding element nitrides.…”