Feil, Florian; Harder, Sjoerd:

Guanidinate complexes of heavier alkaline-earth metals (Ca, Sr): Syntheses, structures, styrene polymerization and unexpected reaction behavior.

In: European Journal of Inorganic Chemistry, (2005) ; Nr. 21, S. 4438-4443
ISSN: 1434-1948
Zeitschriftenaufsatz / Fach: Chemie
The guanidinate complex [Ca{(Cy)NC{N(SiMe3)2}N(Cy)}2] (1) can be prepd. in good yields and in cryst. purity by two different routes: (1) addn. of [Ca{N(SiMe3)2}2] to (Cy)N=C=N(Cy) or (2) addn. of KN(SiMe3)2 to (Cy)N=C=N(Cy) followed by a metathesis reaction of the obtained potassium guanidinate complex with CaI2. Crystn. from Et2O yielded 1.(Et2O) which shows a C2-sym. structure in the crystal. A Sr analog could be prepd. and also crystallizes as the mono-etherate [Sr{(Cy)NC{N(SiMe3)2}N(Cy)}2.(Et2O)] (2) with a very similar crystal structure. The Schlenk equil. between 1 and [Ca{a-(Me3Si)-o-(Me2N)benzyl}2.(THF)2] (3) in benzene does not completely favor the heteroleptic product. However, an excess of 1 yields predominantly the heteroleptic benzylcalcium complex [Ca{(Cy)NC{N(SiMe3)2}N(Cy)}{a-(Me3Si)-o-(Me2N)benzyl}] (4). Styrene polymn. with a mixt. of 1 and 3 results largely in atactic polystyrene of which the mol. wt. distribution shows a tailing in the lower range. This could be due to decompn. of the guanidinate ligand under the given polymn. conditions. It is shown that heating a mixt. of 1 and 3 gives the cryst. decompn. product [Ca{(Cy)N-C{N(SiMe3)2}-N(Cy)}{(Cy)(TMS)N}] which crystallizes as a dimer with bridging amide ligands.