Donor-acceptor substituted ferrocenes. Novel structural motifs by intramolecular acid-base pairing

Article abstract of DOI:10.1016/0022-328X(95)05753-C

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 unusuall non-planar conformation.For its two halves meeting in the B...B line the angle was found to be 45.0 deg.The cyclodiborataphosphoniane bridge shows a dynamic behaviour with an activation barrier ΔG^excit=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.Keywords: Boron; Ferrocenylboranes; Aminoboranes; Push-pull-systems; Dynamic NMR spectroscopy