New Hydrazide Based Tricyclic Pentacoordinate Siliconium Ions –A Facile Route to the Synthesis of Spherical Shaped Sr5(PO4)2SiO4

Hydrazide based phosphine linkers were prepared by the condensation reaction of hydrazide of the type RC(O)NHNH2 (R = t‐BuPh) with dppe (1,2‐bis (diphenylphosphino)ethane) to produce the corresponding product of the type RCONHN=PPh2CH2CH2PPh2 = NNHCOR (2). The silylation product RC (OSiMe3) = N‐N=PPh2‐CH2CH2PPh2 = N‐N=C (OSiMe3)R (3) derived from 2 reacts with halosilanes to yield novel hypercoordinate silicon (IV) complexes (4–7). All the products are well characterized by the spectroscopic and analytical data. The DFT calculations indicate that both charge density and electronegativity of the atoms surrounding a magnetically active nucleus have an effect on the chemical shift values. An increase in the electronegativity of the substituted atoms is reflected by the natural hybrids, which causes deshielding of the magnetic Si and P nuclei from the external magnetic field to an increasing level. As a consequence of this, the 29Si and 31P NMR chemical shifts increase for 4–7 thus augmenting the experimental interpretations. Since the phosphorus hydrazide based hypercoordinate Si (IV) complexes are the rich sources of P, and Si directly from a single molecule, the present work also demonstrates the preparation of spherically shaped strontium phosphosilicate (Sr5(PO4)2SiO4) by the sol–gel method.