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Liquid‐ and solid‐state (CP‐MAS) 13 C and 207 Pb nuclear magnetic resonance study of two triorganolead methoxides and a stabilized triorganolead cation
Author(s) -
Wrackmeyer Bernd,
Horchler Klaus,
Sebald Angelika,
Merwin Lawrence H.
Publication year - 1990
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260280515
Subject(s) - chemistry , chemical shift , solid state nuclear magnetic resonance , heteronuclear molecule , crystallography , coupling constant , nmr spectra database , solid state , magic angle spinning , spectral line , analytical chemistry (journal) , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , stereochemistry , organic chemistry , physics , particle physics , astronomy
Liquid‐ and solid‐state NMR data ( 13 C, 207 Pb) are reported for three organolead compounds, Me 3 PbOMe (1) and two comparable heterocycles, 5,5,4‐tricyclopentyl‐2,5‐dihydro‐1,2,2,3‐tetramethyl‐1,2,5‐oxoniaplumbaboratol (2) and ( E )‐2‐dimethyl‐3‐diisopropyl(propinyl)borata‐4‐methyl‐2‐pentene (3); 2 contains a bridging methoxy group, and a triorganolead cation is stabilized by a bridging alkynyl group in 3. Compound 1 is shown to be associated in solution and forms chains in the solid state with bridging methoxy groups. The 207 Pb CP‐MAS NMR spectrum of 1 shows that there is a single lead site with near‐axial symmetry. Two‐dimensional heteronuclear 13 C/ 1 H shift correlations were used to obtain the relative signs of numerous J ( 207 Pb 13 C) and J ( 207 Pb 1 H) coupling constants. In the case of 2 and 3 the 1 J ( 207 Pb 13 C Me ) coupling constants have a negative sign. This indicates an extremely distorted tetrahedral surrounding of the lead atom. The isotropic 207 Pb chemical shifts of 2 and 3 are almost identical in the solid state and in solution. Therefore, the structures in the solid state are fully retained in solution. Quantitative analysis of the spinning side‐band pattern of the 207 Pb CP‐MAS spectra gave similar chemical shift anisotropies, Δσ( 207 Pb‐1133) ppm (2) and ‐1223 ppm (3), and also similar tensorial components of σ( 207 Pb), indicating that the basic structures of the two heterocyclic systems are comparable except for the bridging unit.