Hexacoordinated Oligosilanes from a Hexacoordinated Silicon(IV) Complex Containing an O,N,N,O Salen-type and Thiocyanato-N Ligands

Two new neutral hexacoordinated silicon complexes with SiN4O2 (6) and SiN3O2C (7) coordinating frameworks were synthesized by reaction of the O,N,N,O-donor salen-type ligand 1,2-bis[[(2-hydroxy-4-methoxyphenyl)(phenyl)methylene]amino]ethane (H(2)salen*) with Si(NCS)(4) and HMeSi(NCS)(2), respectively. The complexes 6 [Si(salen*)(NCS)(2)] and 7 [Si(salen*)Me(NCS)] were studied in the solid-state by Si-29 and N-15 CP/MAS NMR and in solution by H-1, C-13, and Si-29 insensitive nuclei enhanced by polarization transfer (INEPT) NMR, UV/vis and FT-IR spectroscopy. Elemental analysis and single-crystal X-ray diffraction analysis were used to confirm the composition and structure for compounds 6 and 7. Both complexes contain the diahionic salen-type ligand coordinated in an equatorial fashion to the silicon center, while the axial positions are occupied by two thiocyanato-N ligands for 6 and one thiocyanato-N and one methyl ligand for 7. Complex 6, which contains two Si-NCS functional groups, was used as monomer to produce a mixture of linear oligosilanes with a hexacoordinated silicon backbone (formulated SCN-[Si(salen*)](n)-NCS, n = 2-8) 8, via a Wurtz-type coupling reaction. Oligomers 8 were identified by solid-state Si-29 cross polarization-magic angle spinning NMR and solution H-1 and Si-29 NMR spectroscopy, matrix assisted laser desorption ionization-time of flight (MALDI-TOF), gel-permeation chromatography (GPC), FT-IR, UV/vis spectroscopy and thermogravimetric analysis (TGA). Conclusive evidence of the oligomeric nature of 8 was provided by MALDI-TOF spectrometry and was supported by quantitative solution Si-29 NMR and GPC studies.