NOVEL METALLACYCLES VIA NUCLEOPHILIC AMINOMETHYLATION - S(CYCLOPENTADIENYL)-1,3-DIAZA-5-ZIRCONACYCLOHEXANE AND RELATED ORGANOMETALLIC HETEROCYCLES

The doubly lithiated aminals bis(lithiomethyl(methylamino))methane [Li CH2N(Me)](2)CH2 (1a) and bis(lithiomethyl-isopropylamino)methane [LiCH 2N(i-Pr)](2)CH2 (1b) react with Cp- and Cp- (Cp* = C5Me5) substituted zirconocene chlorides in toluene to give Cp2ZrCH2N(R)CH2N(R)CH2 (2a, R = Me; 2c, R = i-Pr) and Cp2ZrCH2N(R)CH2N(R)CH2 (2b, R = Me; 2d, R = i-Pr). An interaction of the nitrogen atoms of the metallacycles with the zirconium centers in the solid state (2a, 2b) and in solution (2a , 2c) is deduced from structural studies and from the H-1 NMR spectra at variable temperatures (Delta G double dagger = 65.7 +/- 0.6 kJ mol( -1) for the ring inversion process in 2c), Isonitriles CNR (R = t-Bu, Me) and CO insert in one of the zirconium methylene sigma-bonds of 2b and 2d and yield CpZr-2[N(R-2)CCH2N(R-1)CH2N(R-1)CH2] (3a, R-1 = Me, R-2 = t-Bu; 3b, R-1 = i-Pr, R-2 = t-Bu; 3c, R-1, R-2 = Me) and the zir conium enolates CpZr-2(H)[OC=CHN(R)CH2N(R)CH2] (4a, R = Me; 4b, R = i -Pr), respectively. Further insertion of isonitriles does not occur. C omplexes 2a and 2c are unaffected by isonitriles or CO. The molecular structures of 2a, 2b, and 3a have been studied by X-ray diffraction. T he resulting structural information of the complexes 2a and 2b provide s valuable insight into the nature of the Zr <-- N interaction within the metallacycles, which is discussed briefly.