Dialumenes – arylvs.silyl stabilisation for small molecule activation and catalysis

Abstract

Ligand controlled reactivity: a trans-bent and twisted geometry enables dihydrogen activation and enhanced catalytic activity for NHC-stabilised dialumenes.

Recent advances in low oxidation state aluminium chemistry

“…4) was synthesised in an analogous fashion to 4, with crystallographic analysis revealing a trans-bent and twisted geometry with nearly perpendicular arrangement of the NHC groups. 37 This was notably different to 4, whose NHC groups were orientated parallel to each other. The Al-Al bond length of 2.4039(8)Å was also slightly longer than in 4.…”

Reversible Dissociation of a Dialumene**

“…Like I and II, [3] 1 can react with alkenes and alkynes to form 4-membered aluminacycles.T reatment of 1with ethene (1 atm) at room temperature results in rapid (5-20 mins) conversion to dialuminacyclobutane 4 by formal [2+ +2] cycloaddition of the Al=Al and C=Cb onds.S imilarly,d iphenylacetylene reacts with 1 to form dialuminacyclobutene 5 (Scheme 2). 31 P{ 1 H} NMR spectroscopy of 4 and 5 reveals distinct signals for three diastereomers in each case.T his is aresult of the "locking" of the stereogenic aluminium centres enforced by their cyclic structures (4: d 11.6 (d, 3 J PP = 12 Hz), 11.5 (s), 11.5 (s), 11.4 (d, 3 J PP = 12 Hz);, 5: d 11.0 (br s), 10.7 (s), 10.4 (s), 10.3 (br s). ;s ee SI).…”

Main Group Multiple Bonds for Bond Activations and Catalysis

“…It was found that dialumene( 7)a cts as ap re-catalyst which forms carbonate 15 upon addition of CO Very recently,asecond neutral NHC-stabilised dialumene (16)w as isolated. [45] This differed to compound 7,d ue to the use of an aryl supporting ligand,w hichr esulted in a trans-bent and twisted geometry.T he influence of the different ligands on the dialumene geometry was largelyt he result of the steric demands of the ligand.I nt erms of the electronics, the silyl ligand resultsinanalmost neutral Al 2 core whilst the aryl dialumene core is highly polarised, which can be attributed to the relative differences in electronegativities. Notably, this results in am uch more reactive dialumene and reactivity towards ste-rically more demanding substrates is now possible due to the increased flexibility in the trans-bent and twisted structure.…”

“…Very recently, a second neutral NHC‐stabilised dialumene ( 16 ) was isolated [45] . This differed to compound 7 , due to the use of an aryl supporting ligand, which resulted in a trans ‐bent and twisted geometry.…”