Klaus Horchler

207Pb-NMR Parameters

Publisher Summary Inorganic lead compounds as stabilizers for polymers or as components in glasses, the toxicity of lead chemicals, and basic research in organolead chemistry are important topics of discussion. In lead chemistry, nuclear magnetic resonance (NMR) spectroscopy has become one of the prominent tools for studying lead compounds in solution, and it may also be valuable for studying various classes of solid lead compounds. This chapter aims to present the results of the study of 207 Pb NMR measurements performed in liquids. In addition, the chapter outlines some aspects of the solid-state 207 Pb NMR, as it is a rapidly growing area at present. Multinuclear magnetic resonance (mNMR) is used for obtaining consistent information on the systems under consideration. A larger set of 207 Pb NMR data helps in understanding the NMR parameters of the lighter magnetically active isotopes in Group IV of the periodic table, in particular for l19 Sn and 29 Si nuclei. Furthermore, 207 Pb NMR parameters serve as a crucial test for the validity of theoretical models, aiming at the description of chemical and physical properties of the heavy elements. Many old problems in the solid-state chemistry of lead can be tackled, taking advantage of the improvements in modern NMR instrumentation.

Silylmethyl and silylamino groups as ligands in tin(II), tin(IV), lead(II) and lead(IV) compounds - a multinuclear magnetic resonance study

Abstract We have studied tin(II), tin(IV), lead(II) and lead(IV) compounds of the type M[CH(SiMe3)2]2 (5), M[N(SiMe3)2]2 (6), M[N(SiMe3)SiMe2tBu]2 (7), Me3Mue5f8CH2ue5f8SiMe3 (1), Me3Mue5f8CH(SiMe3)2 (3), Me3Mue5f8NHue5f8SiMe2tBu (2), Me3Mue5f8N(SiMe3)2 (4), Me2M[N(SiMe3)2]2, (8) and (Me3M)2Nue5f8SiMe2tBu (9) by 13C, 15N, 29Si, 119Sn and 207Pb NMR spectroscopy. In some cases, two-dimensional (2-D) 13C/1H and 29Si/1H heteroscalar-correlated NMR spectra served for the comparison of the signs of the respective coupling constants [nJ(M 13C), 2J(M29Si) and nJ(M1H)]. The 13C and 15N NMR parameter of comparable compounds (replacement of the CH or CH2 fragment by a nitrogen atom or the NH group, respectively), show analogous trends. In the monomeric M(II) compounds (5, 6, 7) the peculiar electronic situation at the metal is reflected by the extreme deshielding of the metal nuclei (e.g. δ207 Pb for 5b = +9110 ppm), by the strongly deshielded 13C (5) and 15N nuclei (6, 7), as well as by large negative contributions to the reduced nuclear spin—spin coupling constants 1K(M13C) (5) and 1K(M15N) (6). In the M(II) compounds 5 the 119Sn and, in particular, the 207Pb longitudinal and transverse nuclear relaxation is dominated by the chemical-shift-anisotropy mechanism. This is also true for 6 and 7, in which the transverse relaxation rate is further increased by scalar relaxation of the second kind owing to partially relaxed scalar coupling 1J(M14N).

NMR parameters of alkynes

Article presentant des donnees RMN dun certain nombre dalcynes substitues, dorganometalliques et de metaux de transition ayant des triples liaisons C≡C a letat solide et en solution

Plumboles bearing organometallic substituents. Their synthesis and reaction mechanism, as studied by multinuclear magnetic resonance spectroscopy

Reaction of bis(trimethylsilylethynyl)dimethyllead (1) with trialkylboranes (2) gives the 3-dialkylboryl-4-alkyl-2,5-bis(trimethylsilyl)-1,1-dimethylplumboles (4). The course of the reactions was monitored by multinuclear NMR (1H, 11B, 13C, 29Si, 207Pb), and various intermediates were identified, including two non-cyclic bis(alkenyl)lead compounds (8, 9) and a zwitterionic species (5) in which a triorganolead cation is stabilized by intramolecular side-on coordination to the Cue5fcC bond of an alkylnylborate moiety. The presence of at least one trimethylsilylethynyl group is necessary for the formation of plumboles from zwitterionic compounds analogous to 5, as was shown by the synthesis of 3-diethylboryl-4-ethyl-1,1,5-trimethyl-2-trimethylsilylplumbole (11). Positive and negative signs of coupling constants 1J(207Pb13C) in the plumboles have been determined by two-dimensional 13C/1H heteronuclear shift correlations. Features of these data and of the δ207Pb values are compared with 119Sn NMR parameters of comparable tin compounds.

Dimeric cyclic bis(amino)stannylenes and -plumbylenes - a multinuclear magnetic resonance study

Abstract 1,3-Dialkyl-4,4,5,5-tetramethyl-1,3,4,5,2λ 2 -diazadisilastannolidines ( 3 ) and -plumbolidines ( 4 ) (alkyl= t Bu ( a ), i Pr ( b ), Et ( c )) and 5,5-dimethyl-1-trimethylsilyl-3-(R)-1,3,2λ 2 -diazastannolidines ( 5 ) and -plumbolidines ( 6 ) (R=Me 3 Si ( a ), i Pr ( b )) have been prepared. In the case of 3b , 4b , 3c and 4c monomer-dimer equilibria exist at room temperature and above. At low temperature ( 3c , 4c ) the mechanism (ring slippage) of the intramolecular rearrangement was established by dynamic 1 H and 13 C NMR. The heterocycles 5 and 6 are dimers in which the nitrogen atoms linked to less bulky substituents prefer selectively the bridging positions. The exchange reaction between ( 6b ) 2 and ( 1b ) 2 (dimeric 1.3-diisopropyl- 2,2-dimethyl-1,3,2,4λ 2 -diazasilastannetidine) leads preferably to dimers each built from two five- or from two four-membered rings rather than to dimers built from a five and a four-membered ring. Natural abundance 15 SN NMR has served to characterize some dimers. All compounds were characterized by 1 H, 13 C, 29 Si, 119 Sn and 207 Pb NMR data. Some of these measurements are severely hampered owing to dynamic processes.

UV photoelectron spectra and pseudopotential ab initio calculations of (CH3)3PbCCCH3

Abstract Gas-phase UV photoelectron spectroscopy (UPS) and pseudopotential ab initio calculations were used to analyse the electronic structure of (CH3)3PbCue5fcCCH3, with particular interest in the possible σ-π interaction between the π(Cue5fcC) system and the σ(Pbue5f8C) bonds. The results obtained, compared with the UPS data already known for the tin analogue, and with the pseudopotential calculations performed during the present work for both compounds, showed that the bonding is similar in the two molecules. In particular the σ-π interaction is quite weak and the HOMO has mainly π(Cue5fcC) character. The present interpretation is supported by the analysis of the NMR results.

Electronic structure of tetrahedral tin acetylides by pseudopotential ab initio calculation and gas-phase UV photoelectron spectroscopy

Abstract The electronic structure of highly symmetric tin acetylides was investigated by means of ab initio pseudopotential calculations and gas-phase UV photoelectron spectroscopy. Good agreement between calculated energy levels and experimental ionization energies was found, which allowed to the assignment of the outermost molecular orbitals.