Ferrocene tethered boramidinate frustrated Lewis pairs: stepwise capture of CO 2 and CO.

The synthesis and reactivity of novel ferrocene tethered boramidinate frustrated Lewis pairs (FLPs), capable of the sequential capture of small molecules, is reported. Reactions of 1,1'-dicarbodiimidoferrocenes with different boranes provides access to metallocene tethered FLPs. The reactivity of the boramidinate moieties can be tuned by the nature of the carbodiimido substituents (alkyl vs. aryl) and the borane used in the reduction (9-borabicyclo[3.3.1]nonane [(C 8 H 14 ) 2 BH] 2 vs. bis-pentafluorophenyl borane [(C 6 F 5 ) 2 BH] 2 ). The boramidinate FLP arms do not engage in intramolecular reactions, allowing for independent small molecule capture by each FLP. By careful synthetic control, sequential capture of different gaseous small molecules (CO 2 and CO or CO 2 and CN t Bu) by the same bis(boramidinate)ferrocene molecule has been demonstrated.