Yttrium porphyrin complexes

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Porphyrin complexes of yttrium, lanthanum, cerium, praesodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and thorium can be synthesized using this method. 

Aluminium alkoxides (especially aluminium isopropoxide), dialkylalumi-nium alkoxides, yttrium alkoxides, zinc alkoxides, aluminoxanes, zincoxanes, bimetallic -oxoalkoxides, aluminium porphyrins and aluminium Schiff s base complexes are the most representative coordination catalysts, containing multi-nuclear or mononuclear species, for lactone polymerisations (Table 9.5). 

Double decker complexes involving yttrium with a porphyrin and the 2,3-naphthalocyaninato (nc) group (8) have been prepared by the reaction of yttrium acac, porphyrin, and naphthalo-nitrile in the presence of l,8-diazabicyclo[5,4,0]undec-7-ene (DBU).147 148 These complexes have been studied spectroscopically and electrochemically and in the case of the Y(nc)(oep) complex the crystal structure has been determined. In Y(nc)(oep) the yttrium is eight-coordinate and sits between the two ligand planes that are separated by 2.7 A. The complex Y(nc)2 has also been prepared by the reaction of yttrium acac and naphthalonitrile in the presence of DBU.149... 

Y[N(SiMe3)2]3 with ttp in coordinating solvents such as thf or bis(2-methoxyethyl)ether (9) give complexes in which the yttrium lies well above the N4 plane of the porphyrin.150... 

The porphyrin precursor octaethylporphrinogen (oepg) (10) has been used to form a yttrium complex [Li(thf)2][(oepg)Y(OEt)Li(thf)]. The ethoxide group, which is believed to arise from cleavage of thf, acts as a bridge between the yttrium and one lithium cation.146... 

Among the multinuclear and mononuclear active species evaluated for lactone polymerization, those effective for the polymerization of P-lactones implying an O-acyl scission (Scheme 9.16a) are aluminum and dialkylaluminum alkoxides, yttrium alkoxides, zinc alkoxides, aluminoxanes, zincoxanes, bimetallic g-oxoalkoxides and aluminum porphyrins of the (TPP)AIOR type [50]. However, aluminum porphyrins such as (TPP)AICI or (TPP)A10C(0)R and aluminum SchifFs base complexes such as (Sal)AlCl (where Sal = salcenato group) are able to promote lactone polymerization by O-alkyl scission (Scheme 9.16b) [50]. 

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