S.M. van der Kerk

The addition of methylborylene to acetylenes: Synthesis of 1,4-diboracyclohexa-2,5-dienes, and of a borirene and a diboretene derivative

Abstract The synthesis of 1,4-dimethyl-2,3,5,6-tetra- n -alkyl-1,4-diboracyclohexa-2,5-dienes from the reaction of di- n -alkylacetylenes with the methylborylene-generating system 2C 8 K/MeBBr 2 is described. A mechanism for these reactions is proposed. The addition of methylborylene to di- t -butylacetylene results in the formation of 1-methyl-2,3-di- t -butylborirene and of 1,3-dimethyl-2,4-di- t -butyl-1,3-diboretene.

Formation and some properties of the aromatic compound 1-methylborepin

Abstract The aromatic compounds 1-methylborepin (I) and 1-methyl-3,6-dideuteroborepin (XXII) are formed in the reactions between methylboron dibromide and the products of the hydrostannation of a 1/1 cis/trans mixture of 1,5-hexadiyn-3-ene (XIV) with diethylbromotin hydride and diethylbromotin deuteride, respectively. I and XXII are thermally unstable, yielding benzene and 1,4-dideuterobenzene, respectively, on decomposition.

1-methylborepin, its aromaticity and thermal decomposition

1-Methylborepin (I) is judged to be aromatic on the basis of a) the value of its Huckel MO resonance energy, b) the ring-current effect on its1H NMR spectrum, and c) its degree of aromaticity based on Julgs criterion. The thermal stabilities of hetero-conjugated monocyclic ring systems containing 5, 7, 9, and 11 ring atoms and B or N as the hetero atom are assessed to the basis of orbital symmetry considerations. Hetero-conjugated ring systems containing 2n + 1 ring atoms (2n being the number of ring carbon atoms) are predicted to be thermally stable when n is even, and thermally unstable when n is odd.

The reaction of methylborylene with cyclohexene and some other olefinic compounds

Abstract Some potential methylborylene-generating systems were investigated, using cyclohexene as the trapping agent. Methylborylene, generated by the system 2C 8 K/MeBBr 2 , reacts with cyclohexene to yield 2-methyl-2-boratricyclo-[7.4.0.0 3.8 ]-tridecane (MBTT) Ia . In the course of the work an isomer of MBTT was synthesized along a completely different route and compared with Ia . With the system 2C 8 K/MeBBr 2 , only cyclic olefins were converted to analogues of MBTT. An acyclic olefin and a conjugated diene yielded only haloboration products. Possible mechanisms leading to the formation of MBTT Ia are discussed.

THE ADDITION OF METHYLBORYLENE TO ACETYLENES

The synthesis of alkyl-substituted 1,4-dimethyl-1,4-diboracyclohexa-2,5-dienes from dialkylacetylenes and the system C8K/MeBBr2 is described.

The generation of the germanium dihalides

Abstract A method is described for the generation of GeX2 (X = F, Cl, Br, I) as uncoordinated monomers in the gas phase, free from impurities. These species were identified by UV photoelectron spectroscopy and mass spectroscopy.

Insertion of Methylborylene into c-h bonds

The insertion of methylborylene, MeB:, into C-H bonds in benzenechromium tricarbonyl and in ferrocene is described. Evidence is presented for the presence of B-H bonds in both insertion products. It is believed that in these and other reactions free methylborylene, MeB:, is involved.