The title compds., e.g., I were studied by multinuclear magnetic resonance both in the liq. (11B, 13C, 29Si, 119Sn NMR) and solid state (13C, 29Si, 119Sn CP/MAS NMR). Together with the results of the x-ray anal. of I-THF the NMR data allowed the assessment of structural features in soln. and in the solid state (e.g. the weakened coordinative Sn-O interactions in I-THF in soln.). The 1J(13C:13C) values in 4,5,5-triethyl-2,5-dihydro-1,2,2-trimethyl-3-trimethylsilyl- and -3-trimethylstannyl-1,2,5-oxoniastannaboratole and in some non-cyclic alkenes bearing organometallic substituents were measured using INEPT expts. based on 3J(13C1H) long-range coupling consts.