Diazaallyls of group 4 metals based on trans-1,2-diaminocyclohexane

Amination of 1-bromo-2-methylpyridine with trans-1,2-diaminocyclohexane gives the corresponding bis(aminopyridine) H2L1. Conversion of the same diamine to the N,N′-bis(amino-4,4-dimethylthiazoline) H2L2 is also completed in three steps. The analogous aminooxazoline is however inaccessible, although the aminocyclohexane analogue is prepared readily. The proligand H2L1 forms bis(aminopyridinato) alkyl complexes of the type [ZrL1R2] (R = CH2Ph, CH2But). The molecular structure of the neopentyl complex shows that the chiral backbone leads to a puckering of the N4Zr coordination sphere, which contrasts with the related cyclohexyl-bridged Schiff-base complexes which are essentially planar. [ZrL2(CH2But)2] – the first aminothiazolinato complex – is formed similarly. A comparison of the structures of [ZrL1(CH2But)2] and [ZrL2(CH2But)2] indicates that the latter has a fully delocalised N–C–N system, rather similar to a bis(amidinate). Reaction of H2L2 with [Ti(NMe2)4] gives [TiL2(NMe2)2] which appears to be C2-symmetric like the above complexes according to NMR spectra, but has one uncoordinated thiazoline unit in the solid state. This is a result of increased ring strain at the smaller titanium metal centre.

Graphical abstractBis(aminopyridinato) and bis(aminothiazolinato) ligands based on 1,2-diaminocyclohexane give complexes of zirconium in which the N4M unit is distorted from planarity by the presence of the chiral backbone. For the smaller metal Ti, X-ray crystallography shows that the constrained architecture leads to coordination of three N atoms only.Figure optionsDownload full-size imageDownload as PowerPoint slide