Stable borylene

Scheme 1 S.24 Formation of a stable borylene, boronium salt and radical cation [295].

Recently, the borylene complex [p-B(NMe2) (r 5-C5H5)Mn(CO)2 2] (1) was subject to detailed computational studies and the theoretically predicted and the experimentally derived structural parameters were found to be in very good agreement (Table I).117 Density functional theoretical studies have concluded that borylenes BX can be viable ligands in the design of transition metal complexes, which are thermodynamically stable with... 

Although this reaction represents only an alternative synthesis for the chromium species 24 it was conducted as an initial experiment since the expected product was known to be stable under the chosen conditions. Monitoring the progress of the transfer by nB-NMR spectroscopy proved that the borylene transfer was quantitative after 12 h at —30 °C in toluene and no boron containing byproducts were detected. A corresponding... 

The reaction of 15 with 2-aminopyridine yields a mixture of the amino-(chloro)boryl complex 19a and the base-stabilized borylene complex 20a [40]. 20a reacts readily with ethanol, leading to the corresponding ethoxyborylene complex 20b, which was crystallographically characterized. 19a is stable in boiling ethanol but reacts, in the presence of Ag[SbF6] in undried thf, to the hydroxyboryl complex 19b (Scheme 8). The key structural parameters of 19b and 20b are very similar, which leads to the very important conclusion that there is only little difference in the nature of the Os-B bond in these types of base-stabilized borylene and boryl complexes. 

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