Complexes of the bis(trimethylsilyl)-benzamidinato ligand 'siam': Synthesis and X-ray structures of (siam)2M, (siam) (siamH) MX (M = Ni, Pd), (siam)2MnI and (siam) ReO3, and their reactivity towards CO2

Article abstract of DOI:10.1016/s0020-1693(98)00167-4

Complexes with the bis(trimethylsilyl)-benzamidinato ligand 'siam' of the type (siam)₂M (M = Ni (2), Pd (3)), (siam) (siamH) NiBr (4a), (siam) (siamH)PdCl (4b) and (siam)₂MnI (5) were prepared by reaction of (siam)₂Mg(thf)₂ (1) with the corresponding metal halides and addition of water or iodine, respectively. The reaction of (siam)₂Zn with Re₂O₇ yielded (siam)ReO₃ (6). X-ray analysis of 1-6 revealed that siam acts as a bidentate ligand forming four-membered chelate rings in all complexes. In 2 four nitrogen atoms show a distorted tetrahedron; in contrast, 3, 4a and 4b are square planar complexes. In both 4a and 4b siamH is coordinated as a monodentate ligand. The Mn(III) complex 5 exhibits a trigonal bipyramidal coordination of the four amidinato nitrogens and the iodo ligand, which occupies an equatorial position. The Re(VII) complex 6 shows an irregular trigonal bipyramidal coordination. In all compounds the bond lengths and angles in the amidinato ligand are comparable and exhibit typical values. The reaction of 2 with excess CO₂ gave a green dimeric complex 7 in which one Ni(II) centre is octahedral and the other is square pyramidal coordinated. X-ray analysis revealed that 5 mol CO₂ per 2 mol nickel are inserted in N-Si bonds forming new types of tridentate bridging ligands which contain N-COOSiMe₃ groups.