Synthetic and reaction chemistry of heteroatom stabilized boryl and cationic borylene complexes

The synthesis, spectroscopic and structural characterization of the aryloxy and amino functionalized chloroboryl complexes (eta(5)-C5R5)Fe(CO)(2)B(OMes)Cl (R = H, 2a; R = Me, 3a) and (eta(5)-C5H5)Fe(CO)(2)B((NPr2)-Pr-i)Cl (7a) are reported. Compound 2a is shown to be a versatile substrate for further boron-centred substitution chemistry leading to the asymmetric boryl complexes (eta(5)-C5H5)Fe(CO)(2)B(OMes)ERn[ERn = OC6H4t Bu-4, 2c; ERn = SPh, 2d] with retention of the metal-boron bond. The reactivities of 2a, 3a and 7a towards the halide abstraction agent Na[BAr4f] have also been examined, in order to investigate the potential for the generation of cationic heteroatom-stabilized terminal borylene complexes. The application of this methodology to the mesityloxy derivatives 2a and 3a gives rise to B-F containing products, presumably via fluoride abstraction from the [BAr4f](-) counter-ion. By contrast, amino-functionalized complex 7a is more amenable to this approach, and the thermally robust terminal aminoborylene complex [(eta(5)-C5H5)Fe(CO)(2)B((NPr2)-Pr-i)][BAr4f] (9) can be isolated in ca. 50% yield. The reactivity of 9 towards a range of nucleophilic and/or unsaturated reagents has been examined, with examples of addition, protonolysis and metathesis chemistries having been established.