Frustrated Lewis Pair Reactions at the [3]Ferrocenophane Framework

Condensation of the o-NH2-/alpha-NMe2-substituted [3]ferrocenophane 5 with aromatic aldehydes or ketones (PhC(R)=O) yields the corresponding organometallic Schiff bases 6 (R = H) and 7 (a, R = CH3; b, R = CF3). The o-imino/alpha-P(mesityl)(2) derivative 8 (R = CH3) was obtained by exchange with H-P(mesityl)(2). Its treatment with B(C6F5)(3) generated a frustrated Lewis pair that reacted with dihydrogen by replacement of the phosphine and reduction of the imine to give the o-PhCHMeNH-substituted [3]ferrocenophane 12. The ketimino functional group in 7a is cleanly reduced with H-2 in the presence of 10 mol % of the Lewis acid hexylB(C6F5)(2) to give the corresponding amine 14. The analogous reaction reaction of 7b yielded a 5:1 mixture of the amine diastereoisomers 13a,b. The imine 6 reacts with B(C6F5)(3) by intramolecular hydride abstraction and transfer from the NMe2 group to give the stabilized cyclic [3]ferrocenophane iminium salt 19. Treatment of the related o-PPh2/alpha-NMe2 [3]ferrocenophane system 20 with B(C6F5)(3) proceeded in a related way to yield the annelated heterocyclic phosphonium salt 22. The complexes 6 center dot HCl, 7b (R = CF3), 12, 13a, 14, 19, and 22 were characterized by X-ray diffraction.