HETEROCYCLIC-SYSTEMS CONTAINING ANTIMONY(III)-VIII - HYPERVALENCY BY INTRAMOLECULAR 1,5-CHELATION SB-CENTER-DOT-CENTER-DOT-CENTER-DOT-N IN RINGS RSB[(CH2)(3)](2)NR' (NR' = NME, NBZ, NBUI) AND COMPARISON TO ANALOGOUS COMPOUNDS OF AS-III, BI-III, GE-IV AND SN-IV

Eleven antimony compounds RSb[(CH2)(3)](2) NR' and eight germanium com pounds R2Ge[(CH2)(3)](2) NR' (some combinations of R = Cl, I, NCS, OSi Ph3, Ph, and NR' = NMe, NBz, NBui) have been synthesized by diGrignard reactions and subsequent treatment with AgSCN, Ph3SiONa or PhLi. The compounds were compared to 14 Sn, 1 As, 5 Sb and 4 Bi analogues taken from the literature. Evidence is provided for 1,5-chelation Sb ... N v ia crystal structure determinations (5 + 1 (lit) Sb compounds), C-13- and Si-29-NMR chemical shifts;Sb-121 and I-127 Mossbauer data (11 and 3 Sb compounds, respectively), cyclic voltammetry (9 Sb compounds) and semi-empirical MO calculations on the Extended Huckel level (8 presen t compounds and 4 models). The ligand sequence (Cl < I < NCS) holds fo r an increasing approach N ... Sb. The effect of electronegativity and the effect of n- or pi --> sigma charge transfer into the LUMO at Sb are counteractive. The intramolecular donor strength increases in the following order: NBu' < NBz < NMe. Simultaneously a decrease of the a bsolute value of the Sb-121 quadrupole coupling constant from Mossbaue r spectroscopy occurs. The postulation of a control of the Sb ... N ch elation by frontier orbital interactions is supported by the CV result s in CH2Cl2 at a Au/Hg electrode. It is proved by scan rate dependence that the observed reversible reduction/oxidation process is diffusion controlled, and by coulometry that the reduction takes place by trans fer of one electron. (C) 1998 Elsevier Science Ltd. All rights reserve d.