Homo- and Hetero-bimetallic Flexibly Linked Dinuclear Salphen Complexes

A modification of the previously developed synthetic approach towards dinuclear flexibly linked salphen complexes is successfully utilized for the preparation of heterodinuclear salphen dimers. A dinuclear salphen species with Pd(II) and Cr(III) centers bears a stronger structural resemblance to the related bis-Cr(III) compound than the corresponding mononuclear Cr(III) salphen complex. Therefore, it was considered as a more useful model for the comparison with the homobinuclear Cr(III) complex regarding the catalytic activity in the ring-opening polymerization of β-butyrolactone, for which a bimetallic catalytic mechanism seems to operate. The polymerization results again have shown a higher activity of the homobinuclear Cr(III) complex.