Mixed Cobaltacarboranes Incorporating η⁵-Pyrrolyl and Dicarbollide Ligands. Synthetic Routes, Structures, and Mechanistic Implications

Abstract

Mixed cobaltacarboranes [(η5-NC4H4)Co(7-R-8-R‘-7,8-C2B9H9)] containing η5-pyrrolyl and dicarbollide ligands have been synthesized. Reaction of [N(CH3)4][7-R-8-C4H4N-(CH2)3-7,8-C2B9H10] (R = CH3, C6H5) with K(t-BuO) and CoCl2 in dimethoxyethane leads to two complexes with the formulae [(η5-NC4H4)Co(7-R-8-C4H9-7,8-C2B9H9)] and [(η5-NC4H4)Co(7-R-8-C3H5-7,8-C2B9H9)] (R = CH3, C6H5). The 8-C4H9 and 8-C3H5 groups are produced as a result of the cleavage of the spacer joining the pyrrolyl and carborane moieties in the original ligand. The [N(CH3)4]+ ion is necessary to produce the 8-C4H9 substituent. An alternative and more efficient route to [(η5-NC4H4)Co(7-R-8-C3H5-7,8-C2B9H9)] (R = CH3, C6H5) involves the reaction of 1-Cl(CH2)3-2-R-1,2-C2B10H10 (R = CH3, C6H5) with K(NC4H4) and CoCl2 in dimethoxyethane. This last route can also be utilized to produce the simple [(η5-NC4H4)Co(7-R-8-R‘-7,8-C2B9H9)] compounds starting from closo-1-R-2-R‘-1,2-C2B10H10 compounds. The structures of those species have been proven by X-ray structural analyses of [(η5-NC4H4)Co(7-CH3-8-C4H9-7,8-C2B9H9)] and [(η5-NC4H4)Co(7-C6H5-8-C3H5-7,8-C2B9H9)].