An Aluminum–Nitrogen Based Lewis Pair as an Effective Catalyst for the Oligomerization of Cyanamides: Formation of Acyclic CN Oligomers Instead of Thermodynamically Favored Cyclic Aromatic Trimers

Cooperative Activation of Isocyanates by Al–N‐Based Active Lewis Pairs and the Generation of a C5 Chain by Simultaneous Formation of Two C–C Bonds

“…The Lewis acid catalysed oligomerisation of isocyanates leads usually to the formation of trimeric compounds with N 3 C 3 heterocycles . Lewis pairs prevent the formation of such thermodynamically strongly favoured cyclic products by the cooperative activation of the substrates via their Lewis acidic and basic functionalities as confirmed by quantum chemical calculations . Acyclic oligomers such as the isocyanate dimers reported in this article are highly interesting and potentially applicable in various secondary transformations.…”

“…Four‐membered heterocycles resulted from direct Al−N interactions, but relatively long Al−N distances and acute endocyclic Al−C=C angles (∼90°) confirmed a considerable ring strain. Cleavage of the Al−N bonds results in a situation similar to that of FLPs, and we observed typical FLP reactions with C−H bond activation for a terminal alkyne or particularly interesting the unprecedented oligomerisation of cyanamides to form acyclic oligoimines . In the latter reaction, cooperativity between the Lewis functionalities prevents the thermodynamically highly favored trimerisation with the formation of heterocyclic C 3 N 3 R 3 compounds (triazines) .…”

“…Cleavage of the Al−N bonds results in a situation similar to that of FLPs, and we observed typical FLP reactions with C−H bond activation for a terminal alkyne or particularly interesting the unprecedented oligomerisation of cyanamides to form acyclic oligoimines . In the latter reaction, cooperativity between the Lewis functionalities prevents the thermodynamically highly favored trimerisation with the formation of heterocyclic C 3 N 3 R 3 compounds (triazines) . The insertion of a carbodiimide ( 3 ) represents another aspect of this chemistry .…”

Reactivity of a Monomeric Aluminium Hydrazide towards Isocyanates and Isothiocyanates: Active Lewis Pair Behaviour versus Classical Insertion Reactions

“…For compound 1 the Al–N bond lengths in the ring differed considerably [181.7(2) vs. 200.8(2) pm], and the Wiberg bond indices were calculated to 0.24 and 0.13 . Cleavage of the relatively weak donor–acceptor bonds resulted in a situation similar to that of FLPs,, and indeed treatment of 1 with phenyl isocyanate afforded an adduct ( 2 ; Scheme ) in which the oxygen atom was coordinated to aluminium, while the carbonyl carbon atom was attached to the β‐nitrogen atom of the hydrazide . The constitution of 2 resembles that of typical FLP–isocyanate adducts reported in the literature , .…”

Non-conventional Lewis Acids and Bases in Frustrated Lewis Pair Chemistry

“…Despite this dative interaction, these bonds are labile and can activate small molecules including CO 2 and isocyanates [62]. In an unprecedented result, they reported the hydroalumination of an ynamine to give a N/Al FLP system [63]. This compound was also found to contain a weak dative bond, and thus it activated alkynes and carbodiimides (Scheme 18).…”