Heteroallylic compounds

Scheme 3.23 Hetero-Cope (hetero-Claisen) rearrangement in vinylalkynyl ruthenium complexes formed by addition of heteroallyl compounds to C3 of complex 10.

Within the variety of the designed ligands, bulky heteroallylic compounds have been described. Such complexes usually contain the benzamidinate fragment in a chelating coordination mode. 

Because the C(1)—P(1) bond in 64 is shortened, the (Me2N)PC(SiMe3) group is a strong 7t-donor in this compound and the mesomeric structures 64b and 64c give a good description of the heteroallyl anion113. 

In coordination compounds with heteroallyls ZC(X)S (X = S, O) the resonance structure (2) is of great importance. Ions with the fragment Z C(X)Y can also be dinegative, e.g. (3). These ligands can be thought to stem from the heteroallyls when Z = Z H via the loss of an H atom and a shift of the lone pair left on Z into the Z —C bond. 

Table 1 shows the assignment of the various lanthanide elements in the numbering of the compounds in this article. As usual, scandium and yttrium have been included because of their chemical similarity with the lanthanides. Not included was the radioactive promethium for which no complex containing heteroallylic ligands has so far been reported. 

Although some Ti(III)-allyl complexes have been fully characterized spectroscopically [ 109,110], well-characterized Zr(III)-allyl compounds in the solid state have not been reported in the literature. On the basis of previous results obtained in our laboratory, it was very attractive and conceptually important to find a route to synthesize simple monomeric Group 4 early transition metal allyl complexes and to compare their catalytic activity to that of the well-characterized heteroallylic octahedral early transition metal compounds. Here we report the synthesis and solid-state X-ray structural characteristics of a Zr(III) bulky bis-allylic complex, and its catalytic activity in the polymerization of a-olefins [111]. 

An X-ray structure analysis of red rodlets isolated from an 1,2-dimethoxyethane/npentane solution at -5 shows the compound to crystallize as a Z-isomerie neutral complex (Fig. 10). P-C and C-N bond lengths of 176.9 and 132.3 pm respectively are in good agreement with the formation of an electronically stabilized mesomeric heteroallyl anion. Lithium primarily bound to nitrogen and two oxygen atoms of the 1,2-dimethoxyethane ligand increases its coordination number from 3 to 4 or probably 5 by interactions with the i/7JO-carbon of the phenyl substituent and phosphorus. 

Transition metal complexes containing heteroallyl ligands, such as those in structures (7.79), have been less studied than metal allyl compounds. " Complexes con-... 

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