Hydroalumination and Hydrogallation Reactions with Tri(ethynyl)silanes – Generation of Compounds with up to Three Coordinatively Unsaturated Aluminium Atoms

Abstract

Hydroalumination or hydrogallation of tri(ethynyl)silanes, RSi(CϵC-Ar) 3 (1a, R = Ph, Ar = Ph; 1b, R = Me, Ar = Ph; 1c, R = Me, Ar = C 6 H 4 Me), with the element hydrides H-EtBu 2 (E = Al, Ga) in stoichiometric ratios of 1:1 to 1:3 at ambient temperature yielded the addition products (PhCϵC) 2 (R)Si[(tBu 2 E)C=C(H)Ph] (2, R = Ph, E = Ga; 3a, R = Me, E = Al; 3b, R = Me, E = Ga), (PhCϵC)(Me) Si[(tBu 2 E)C=C(H)Ph] 2 (4a, E = Al, 4b, E = Ga) and (Me)Si[(tBu 2 Al) C=C(H)Ar] 3 (5, Ar = Ph; 6, Ar = C 6 H 4 Me). Compounds 2-4 show

Hydroalumination of a Chlorotrialkynylsilane: Spontaneous Stepwise 1,3‐Dyotropic Rearrangement via an Intermediate Silyl Cation

“…The preferred coordination of the alkynyl group to Al1 may be favoured by its bonding to the electron‐withdrawing chlorine atom and its enhanced Lewis‐acidity. Dual hydroalumination of the trialkynes Me‐Si(CC‐C 6 H 5 ) 3 6 and Et 2 N‐Ge(CC‐CMe 3 ) 3 11 has been reported previously, but a similar dyotropic rearrangement was not observed. Interestingly, gallium compound 6 did not show the corresponding chlorine– tert ‐butyl exchange even when a solution of 6 in benzene was heated to 75 °C for two weeks.…”

“…[3] Recently, we observed unexpected activation processes after hydroalumination or -gallation of alkynylsilanes or -germanes. Dialkynyl derivative compounds afforded mixed alkenyl-alkynyl silanes [4][5][6][7] and germanes, [7][8][9] which have coordinatively unsaturated aluminium or gallium atoms in a geminal arrangement to silicon or germanium (A; Scheme 1). The a-carbon atoms of the unreacted alkynyl groups bear a relatively high negative partial charge and show a close intramolecular contact to the Lewisacidic aluminium or gallium atoms, which results in almost ideally planar E-C(vinyl)-E'-C(alkynyl) heterocycles (E = Si, Ge; E' = Al, Ga), a pyramidalisation of the Group 13 atoms, and relatively small endocyclic C-E-C angles (< 1008).…”

Poly‐Boron, ‐Silicon, and ‐Gallium Lewis Acids by Hydrometallation of 1,5‐ and 1,8‐Dialkynylanthracenes

“…Prominent examples include mercury,1 tin2 and silicon,3 for example, the trisilacyclohexane derivative reported by Brondani et al3a or the Si‐based crown ether analogue reported by Jung and Xia 3b. Remarkable progress in the field of poly‐Lewis acids based on aluminium4 and gallium [4e–4g,5] has been achieved by Uhl and co‐workers with hydroalumination4d–4f and hydrogallation reactions employing dialkylgallanes [4e,4f,5a–5c] and dichlorogallane as reagents,5d–5g respectively. The synthesis of dichlorogallane (HGaCl 2 ) 2 6 and its application in the hydrogallation of unsaturated substrates7 was first investigated by Schmidbaur and co‐workers.…”

Tridentate Lewis Acids: Boron‐, Silicon‐ and Gallium‐Functionalised Tris(dimethylsilyl)methanes

“…A prominent example of a mercury-based poly-Lewis acid was synthesised by Sartori and Golloch; [20] their tridentate Lewis acid is able to form complexes with carbonyl groups and acetylenes. [21] In addition to cyclic poly-Lewis acids, Uhl and co-workers have achieved outstanding progress in constructing multi-dentate Lewis acids through the hydrometallation of unsaturated substrates with dialkylgallium [22][23][24] and dialkylaluminium hydrides. [22,23,25] Further poly-Lewis acids based on chlorogallane groups [14] have been synthesised in reactions between dichlorogallane, (HGaCl 2 ) 2 , and unsaturated scaffolds.…”

“…[21] In addition to cyclic poly-Lewis acids, Uhl and co-workers have achieved outstanding progress in constructing multi-dentate Lewis acids through the hydrometallation of unsaturated substrates with dialkylgallium [22][23][24] and dialkylaluminium hydrides. [22,23,25] Further poly-Lewis acids based on chlorogallane groups [14] have been synthesised in reactions between dichlorogallane, (HGaCl 2 ) 2 , and unsaturated scaffolds. [26] Herein we report new trisilylmethane-based flexible scaffolds, their synthesis and efficient preparative functionalisation to afford a series of boron, gallium and electronegatively substituted silicon-containing tridentate Lewis acids.…”