Enhanced long-range Si center dot center dot center dot N interactions in organosilicon cations. A theoretical study

For the model organosilicon cation H3N . . . SiH3+, potential curves have b een calculated by density functional theory at the B3LYP level, by both MP2 and MP4 perturbation procedures and by a Coupled Cluster approach. Relativ e to the analogous potential curve for the uncharged adduct, H3N . . . SiH4 , a considerable increase of the long-range Si . . .N interaction accompani ed by bond shortening is predicted. For chemical comparison, the structure of the "double R2N-twister" dication salt, [C6H4(CH2NR2)(2)-Si-(R2NCH2)(2)C 6H4]Cl-++(2)-, reported in the literature as a non-crystalline solid, was o ptimized by DFT calculations and a minimum for the hexacoordinated organosi licon center with each two SI N bonds of different lengths was located. To test the reliability of the quantum chemical procedure, in addition the ana logous and structurally characterized dication salt, [(3-picoline)(4)SiH2]( ++)[Cl-. . . (HCCl3)(2)](2), which contains a hexacoordinated Si center wit h 4 equivalent Si N interactions, has been selected to reproduce its struct ure by DFT optimization. Both hexacoordinated, tetra-N-surrounded Si dicati ons, substantiate the increase of long-range Si N interactions as predicted by the potential curves for the model adduct H3N . . . SiH3+ based on high ly correlated calculations.