D.C. van Beelen

Aromatic leady(IV) compounds XIII. 13C FT-NMR investigations on alkylphenyllead(IV) compounds☆

Abstract The 13C FT-NMR data of several organolead compounds of the type Phn-PbR4-n (R = alkyl, cycloaklyl; n = 0−4) are reported. Substituent chemical shift parameters have been calculated for the triphenyllead group in alkyltriphenyllead compounds. Variations of the 207Pb−13C coupling constants are discussed in terms of changes of hybridisation and nuclear charge of the lead atom. Steric factors can also play an important role, especially in the compounds Ph3Pb(cyclo-CnH2n−1 n = 6, 7.

Aromatic lead(IV) compounds : X. H and C NMR spectroscopy of compounds ArnPb(OAc)4−n (n 14)

Abstract 1 H and 13 C NMR data are reported for the compounds Ar n Pb(OAc) 4− n ( n  14). The increase of the 207 Pb 1 H and 207 Pb 13 C coupling constants with the number of acetate groups is explained in terms of changes in hybridization and effective nuclear charge. The occurrence of solvent effects is discussed for C 6 H 5 Pb(OAc) 3 . The effects of the solvent depend primarily on the dielectric constant and the coordinating properties. In methanol, methanolysis may occur.

Some spectroscopic properties of cyclic organolead compounds I

Abstract The nuclear magnetic resonance and infrared properties of two new cyclic organolead compounds are discussed.

Cyclic organolead compounds : III. Synthesis and dynamic behaviour of 10,10-dimethylphenoxaplumbin and a twelve membered heterocyclic organolead compound C28H28O2Pb2☆

Abstract The synthesis of 10,10-dimethylphenoxaplumbin (II), a related twelve membered ring compound (III), and 2,2′-bis-(trimethyllead)diphenylether (IV) are reported. These compounds have been studied by NMR ( 1 H, 13 C and 207 Pb) and IR spectroscopy. The twelve membered cyclic organolead compound (III) exists in solution as an equilibrium mixture of different conformational isomers.

SYNTHESIS AND MULTINUCLEAR NMR PROPERTIES OF SIXMEMBERED HETEROCYCLIC ORGANOLEAD COMPOUNDS

Several six-membered heterocyclic organolead compounds were synthesized from the appropriate di-Grignard resp. organodilithio compounds and a (diorgano)lead dihalide. The compounds were investigated by multinuclear NMR spectroscopy. Variable temperature H NMR measurements revealed a conformational equilibrium. In the C and Pb NMR spectra specific effects caused by the presence of a lead atom in the ring system could be observed.

SYNTHESIS AND MULTINUCLEAR NMR PROPERTIES OF COMPOUNDS OF THE TYPE (C6H5)3PbR (R = ALKYL, ALKENYL, ALKYNYL)

The synthesis and multinuclear NMR properties of compounds of the type (C6H5)3PbR (R=alkyl, alkenyl, alkynyl) are reported. Introduction of a C=C or a C=C bond next to the lead atom leads to a high field shift of the lead chemical shift of ca. 60 ppm to 130 ppm, respectively, while there is also a distinct influence on the values of the lead-proton and lead-carbon coupling constants. This so called neighboring bond effect is discussed on the basis of the Fermi contact interaction. Several approaches to this interaction have been discussed referring to the present data and those published earlier. The spin density at the nucleus depends on the overlap integral, the ionicity of the bond or fraction of charge transferred, the s orbital participation and the ρ character of the bonding orbital. Introduct ion In several studies we have investigated aspects of the NMR spectroscopy of organolead compounds. In the case of C NMR spectroscopy it appeared that the Pb-C coupling constants could be explained within the framework of the Fermi contact interaction on the basis of variations in the hybridization of the lead-carbon bonds and the effective nuclear charge at the nuclei involved in the coupling mechanism. Several empirical factors, such as the introduction of polar groups or other characteristic substituents, variation of the coordination number of the lead atom, the introduction of bulky groups, and the bond angle in cyclic compounds, were found to affect the magnitude of the coupling constants [2-10]. In order to determine systematically the influence of multiple bonds on the NMR parameters we have investigated a number of compounds of the type (C6H5)3PbR, in which the group R represents an alkyl, alkenyl or alkynyl substituent. While many C NMR data have been published on alkynylalkyllead compounds, only limited data on alkynylaryllead compounds and limited NMR investigations on alkenylaryllead compounds have been carried out [11-26]. For 2 0 7 P b NMR, see ref. [27], As the present investigation concludes our studies on the NMR spectroscopy of organolead compounds, we shall discuss the new data and previously obtained results in the light of the various approaches of the Fermi contact interaction. Materials and Methods The H and C NMR spectra were recorded on a JEOL-PFT-100 NMR spectrometer, the Pb NMR spectra on a Bruker WH 90 multinuclear NMR spectrometer. Experimental details concerning the recording and assignments of the various spectra have been published elsewhere [6,28]. All reactions were carried out under dry nitrogen. Tetrahydrofuran (THF), used as solvent and reaction medium, was distilled from LiAIH4 before use. Although the synthesis of triphenyllead bromide has been described [29-31], we have used an alternative route (see below). The alkenyl halides were commercially available, with the exception of iso-butenyl bromide, which was synthesized from tbutanol [32], For more details on the preparation of the compounds see ref. [9]. ®Part XIV, seeref.[1]