Reversible Dissociation of a Dialumene**

Abstract

Dialumenes are neutral Al I compounds with Al = Al multiple bonds.Wereport the isolation of an amidophosphinesupported dialumene.O ur X-ray crystallographic,s pectroscopic,a nd computational DFT analyses reveal al ong and extreme trans-bent Al=Al bond with alow dissociation energy and bond order.Insolution, the dialumene can dissociate into monomeric Al I species.Reactivity studies reveal two modes of reaction:asdialumene or as aluminyl monomers.

Trapping of a Transient Base‐Stabilised Alumylene and Alumylene‐Type Reactivity of a Self‐Stabilising Dialumene towards Organic Azides

“…The C1−C2 bond length in 7 at 1.361(2) Å indicates a clear double bond (Figure 2). The Al−C1 (1.9271(16) Å) and Al1−C2 (1.9199(16) Å) bonds lengths are similar to those of other such aluminocyclopropenes (Al−C C=C ∼1.84–1918 Å) [7,27] but shorter than the Al−C vinyl bond (1.9773(13) Å) in 6 and the Al−C Ter bond (1.9926(14) Å) in 7 . Furthermore, the C1−Al1−C2 angle is 41.43(7)°, significantly smaller than in organic cyclopropene (49.9°) [28] or borirenes (54.59–56.75°) [29] but comparable to those of other aluminacyclopropenes [7,29] …”

“…Furthermore, some of these cycloaddition reactions have been observed to be reversible in nature [24b–c] . Reversibility has also been observed in the dissociation of doubly Lewis‐base‐stabilised dialumenes into transient dicoordinated alumylenes [7,26] . In this work, we report direct evidence for the presence of dicoordinate 4 in the reaction medium by trapping with alkynes.…”

“…Alumylenes have been reported to undergo [1+2] cycloadditions with alkynes such as diphenylacetylene, phenylacetylene and bis(trimethylsilyl)acetylene to give aluminacyclopropenes [27] . Using this strategy, Cowley trapped an in‐situ‐generated alumylene resulting from the reversible dissociation of an aminophosphine‐stabilised dialumene [7] . Inspired by these results, we carried out the reduction of 1 in the presence of diphenylacetylene and phenylacetylene, which yielded an intractable mixture of products.…”

“…In 2018 and 2019, our group reported successively two monomeric Al I species, one stabilised by a very bulky η 5 ‐Cp 3t ligand (Cp 3t =1,3,5‐tri‐tert‐butylcyclopentadienyl, III ) [4] and another by two π‐accepting cyclic alkyl(amino)carbenes (CAACs), displaying 36 % singlet diradical (Al III ) character ( IV ) [5] . Recent additions to this compound family are Liu's carbazolyl‐substituted base‐stabilised alumylene [6] and Cowley's transient aminophosphine‐supported alumylene [7] . Beyond these base‐stabilised dicoordinate alumylenes, monocoordinate base‐free alumylenes have also been reported recently by Power, stabilised by a very bulky terphenyl substituent ( V ), [8] and by the Liu and Hinz groups independently, employing a bulky carbazolyl substituent ( VI ) [9] .…”

[2+4] Cycloaddition Product of an Amidinate Substituted Dialumene with Toluene

“…Since then several dialanes have been reported [5] . However, only a few Al−Al multiply bonded compounds are known [6–8] …”