The influence of ligand variation on the crystal properties of(η4-azadiene)Fe(CO)3-n(PR3)n (n=1, 2; R = Cy, Ph, OMe)

Compared to (eta(4)-azadiene)Fe(CO)(3) complexes the formal substitution of one or two CO ligands with phosphines or phosphites, respectively, leads to changes in the electronic structure of the organometallic compounds. The increased electron density at the iron atom brings about an out of plane position of H(C-3) of the azadiene chain which is necessary to stabilize the bonding between iron and C-3. The hydrogen atom is bent out of the plane of the azadiene ligand to a higher extend than in the corresponding Fe(CO)(3) derivatives. In all complexes with just one phosphorus containing ligand this ligand adopts the apical position in the square pyramidal coordination sphere of the iron atom. In addition, the number and nature of groups that may act as hydrogen donor or acceptor sites in intermolecular hydrogen bond systems building up the crystal structures is changed. The use of PCy3 or PPh3 mostly leads to the formation of dimers or chains by hydrogen bonding between the remaining CO ligands and C-H bonds either of the organic substituents of the azadiene or suitable C-H bonds of the organic moieties at the phosphine ligands. The use of one P(OMe)(3) leads to similar substructures which now are linked by additional hydrogen bonds involving both oxygen and hydrogen atoms of the phosphite ligands as hydrogen bond acceptor or donor sites. If two P(OMe)(3) ligands are present in the molecule the steric effect of these rather large ligands again leads to less complicated supramolecular architectures of the organometallic crystals which now in all cases occur as chains of dimers.