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-PPh(2)) 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 degrees. The cyclodiborataphosphoniane bridge shows a dynamic behaviour with an activation barrier Delta G double dagger=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-PPh(2)), no donor-acceptor pairing takes place (2,3). The ligand properties of 1 and 2 towards the Cr(CO)(5) fragment have been investigated.