DONOR-ACCEPTOR SUBSTITUTED FERROCENES. NOVEL STRUCTURAL MOTIFS BY INTRAMOLECULAR ACID-BASE PAIRING

On the basis of intramolecular donor-acceptor pairing, a convenient way to realize important structural motifs in organometallic chemistry is presented. Ferrocene, bearing a (phosphino)boryl substituent (BRPPh2) at each of its cyclopentadienyl rings, was found to establish a novel type of ansa-structure through interannular head-to-tail bonding (1). This B2P2 bridge adopts an unusual non-planar conformation. For its two halves meeting in the B⋯B line the angle was found to be 45.0°. The cyclodiborataphosphoniane bridge shows a dynamic behaviour with an activation barrier ΔG‡ = 70 kJ mol−1 for the breaking of a PB bond. When the boron and phosphorus atoms are not directly attached to each other, but separated by an amino group (BRNPhPPh2), no donor-acceptor pairing takes place (2,3). The ligand properties of 1 and 2 towards the Cr(CO)5 fragment have been investigated.