Treatment of aminoalkynes (ynamines), Me3Si-CC-NR2 [NR2 = N(CH2CH2)2NMe, N(CHMe-CH2)2CH2], with dialkylaluminum hydrides, H-AlR′2 (R′ = CH2 tBu, iBu, tBu), afforded by hydroalumination the corresponding alkenyl derivatives R′2Al-(Me3Si)CC(H)-NR2 (3 to 6) in which the opposite Lewis functionalities adopted a cis-arrangement with the aluminum and nitrogen atoms on the same side of the resulting CC double bonds. Intramolecular Al–N interactions gave four-membered AlC2N heterocycles, but ring strain may cause relatively long Al–N distances of 2.07 to 2.15 Å. These compounds represent a new type of Lewis acid–base pairs, and we observed C–H bond activation by opening of the Al–N bond upon treatment with H-CC-C6H5. Compound 7 was isolated, which had the proton attached to nitrogen and the anionic ethynyl group bonded to aluminum. The formation of 7 is reversible in solution with an increasing dissociation into the starting compounds at elevated temperatures. Two different structural motifs were obtained upon reaction of the Lewis acid–base pairs with dicyclohexylcarbodiimide, which inserted selectively into the bond between the aluminum and the vinylic carbon atom. In the first compound (8) an amidinato ligand was formed, which coordinated the metal atom by both nitrogen atoms to give an AlCN2 heterocycle. A six-membered heterocycle (9) resulted from the insertion of only one CN double bond of the carbodiimide into the Al–C(vinyl) bond. 9 had an unchanged interaction of the metal atom with the α-nitrogen atom of the former ynamine. The latter compound may be considered an intermediate, and rearrangement to yield an amidinato compound analogous to 8 was indeed observed with extended reaction time.

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The vicinal frustrated P/B Lewis pair (FLP) Mes(2)PCH(2)CH(2)B(C(6)F(5))(2) reacts with 9-borabicyclo[3.3.1]nonane (9-BBN) by C(6)F(5)vs. H exchange at boron to give the new [B]-H functionalized FLP Mes(2)PCH(2)CH(2)B(H)(C(6)F(5)) (4) and 9-C(6)F(5)-BBN. The latter was characterized as an isonitrile adduct by X-ray diffraction. The new FLP 4 forms an adduct with pyridine and it undergoes clean hydroboration reactions with 1-pentyne or added styrene or dimesitylvinylphosphane. The products formed stable adducts with pyridine; two such examples were also characterized by X-ray crystal structure analysis. A similar alkyl vs. hydrogen exchange was observed upon treatment of an Al/N based Lewis pair, iBu(2)Al-(Me(3)Si)C=C(H)-N(CH(2)CH(2))(2)NMe (14), with 9-BBN.

The active Al/N Lewis pair, (Me C) Al-C(SiMe )=C(H)-N(CHMe-CH ) CH (2), reacted with isocyanates to afford a fascinating variety of products. One equivalent of Ph-N=C=O yielded by the release of H-C≡C-SiMe an urea-type ligand which coordinated the Al atom in a chelating manner (4). Dipp-N=C=O gave a similar product, but the bulky substituent hindered the approach of the N-aryl group to Al. A situation similar to that of frustrated Lewis pairs resulted in the coordination of the alkyne to the Al and N atoms (6) by C-H bond activation. Dual insertion was observed upon treatment of 2 with two equivalents of isocyanates (8 to 11). The preferred formation of cyclic oligomers is prevented by the specific cooperative properties of the Lewis pair. A metal-free dimeric isocyanate (13) was formed by hydrolysis. Replacement of the CMe groups in 2 by less bulky isobutyl groups (7) afforded the insertion of two isocyanate molecules into the Al-vinyl bonds without alkyne elimination. The resulting highly functionalised compound had a chain formed by two isocyanates and the organic backbone of the Lewis pair. Me C-N=C=O and 2 afforded a unique compound (14) in which an isocyanate ligand connects two molecules of 2 by the release of dimethylpiperidine. The combination of a C building block and two C groups gave an unsaturated branched C moiety by the simultaneous formation of two C-C bonds. The molecular structure showed an interaction between an Al atom and a C-C π-bond.

We have investigated the coordination of alkanide and alkynide anions to the coordinatively unsaturated aluminium atoms of the methylene-bridged dialuminium compound R 2 Al-CH 2 -AlR 2 [1, R = CH(SiMe 3 ) 2 ]. Treatment of 1 with the corresponding lithium derivatives in the presence of a small excess of TMEN (TMEN = tetramethylethylenediamine) yielded mono-adducts [M] + [R 2 Al-CH 2 -AlR 2 R'] -[2a, M = Li(TMEN) 2 , R' = Me; 2b, M = Li(TMEN) 2 , R' = n-Bu; 3a, M = Li(TMEN) 2 , R' = CϵC-SiMe 3 ; 3b, M = Li(TMEN) 2 , R' = CϵC-t-Bu; 3d, M = Li(DME) 3 , R' = CϵC-Ph; 3e, M = Li(TMEN) 2 , R' = CϵC-PPh 2 )] and bis-adducts [Li(TMEN) 2 ] + [LiCH 2 (AlR 2 R') 2 ] -[4a, R' = CϵC-CH 2 -NEt 2 ; 4b, R' = CϵC-t-Bu]. In the solid state the