Phosphorus ligand metallocenes

In recent years we have developed a new type of planar-chiral ligand system which is based on a phosphaferrocene skeleton equipped with an additional donor function Y [8]. This structure is closely related to the well-known ferrocene-type ligands in that a CH unit of the latter has been replaced by a P atom. The phosphaferrocene moiety serves as both a chiral metallocene-type backbone and as a donor group via the phosphorus atom lone pair. These new ligands are unique in their topological architecture and show interesting ligand properties. 

When the 7r-bonding ligand contains a sulfur or phosphorus atom, the redox properties of the corresponding complexes are much more like the corresponding metallocene. Thus the Fen(B10H10S)22- and Fen(B9H9 CHP)22 ions are more stable than the Fe(III) species. 

Perhaps the most interesting of all the phosphorus analogues of metallocenes is the first carbon-free metallocene, [( ri -P5)2Ti]. This complex, prepared by the reaction of [Ti(naphthalene)2l with P4, contains parallel, eclipsed P5 rings.The P5 ligand in this and other complexes functions as a weaker donor but substantially stronger acceptor than the cyclopentadienyl ligand. 

The direct reaction of white phosphorus with dinuclear metallocenes is the most useful entry to compose the planar cyclo-P5 ligand isolobal with the Cp anion [5] although Baudler et al. demonstrated that ionic metathesis may be used to prepare similar derivatives [90]. The pentaphosphacyclopentadienyl ligand... 

Other Lewis base derivatives are known as for example, with Et20, acetone, pyridine MeCN, BuNC. In the X-ray structure of the complex Cp2YbCl(Me2PCH2PMe2) (Tilley et al. 1983) where divalent Yb is oxidized by YbCls to the trivalent metallocene, Yb is coordinated to the two Cp ligands, to the chlorine and to one phosphorus of the dmpm ligand in a nearly tetrahedral arrangement. Yb-Cl bond length is 2.532(2), Yb-P is 2.941(3)A. 

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