Publisher Summary This chapter reviews that the impact of 119Sn nuclear magnetic resonance (NMR) parameters, determined either by 119Sn NMR or in the NMR spectra of other nuclei, on tin chemistry is remarkable. Nowadays, tin chemical shifts coupling constants and nuclear spin relaxation, with respect to the physical principles, is growing. At the same time, the application of more or less sophisticated NMR techniques enables one to monitor the reactions, identify the unstable intermediates, discover their relevance for mechanistic implications, assign the structural features, investigate the intra- and intermolecular dynamic processes, or to compare the structures in the solid and liquid state. 119Sn NMR parameters, in addition to those of the more common nuclei, for example, 1H, 13C, or 31P, add to the attempts at a more complete description of the bonding situation. The chapter suggests that it must be emphasized that the great potential of modern NMR spectrometers can be exploited by a multinuclear approach to obtain a large self-consistent set of NMR data. This also includes the isotope induced chemical shifts and long-range coupling constants that have been neglected in the past.

Application of 119Sn NMR Parameters

The Coordination Chemistry of Tin Porphyrin Complexes

This article reviews the use of nuclear magnetic resonance methods of spin 1/2 metal nuclei to probe the metal binding site(s) in a variety of metalloproteins. The majority of the studies have invo...

NMR spectroscopic studies of I = 1/2 metal ions in biological systems

Free base stannyl porphyrins and free base porphyrin dimers have been successfully synthesized via copper-free Stille coupling in 21−67% yields. This approach provides an access to stannyl porphyrin synthons that were previously unavailable. Moreover, variation of the reaction conditions selectively provides access to either stannyl porphyrins or porphyrin dimers. Full 119/117Sn NMR analysis was used for characterization of the stannyl porphyrins and detailed 119Sn-1H-13C NMR analyses were carried out on a series of the starting tin reagents and the stannyl porphyrins. These investigations indicate that significant structural information can be gathered by use of commonly known NMR techniques. Photophysical properties of the novel porphyrins prepared including absorption, emission, and fluorescence lifetimes were investigated. The stannyl porphyrins emitted in the visible region, and in all cases large Stokes shifts were observed. The emission intensities of the stannyl porphyrins were 100-fold higher tha...

Synthesis of Stannyl Porphyrins and Porphyrin Dimers via Stille Coupling and Their 119Sn NMR and Fluorescence Properties

In order to obtain a better molecular understanding of inhibitory role of tin metal in the verdoheme ring opening process, hydrolysis of three possibly six, five, and four coordinate verdoheme complexes of tin(IV) and (II) have been studied using DFT method. The results of calculations indicate that, in excellent accord with experimental reports, hydrolysis of different possibly coordinated tin(IV) and (II) verdohemes does not lead to the opening of the macrocycle. Contrary to iron and zinc verdohemes, in five and four coordinate verdoheme complexes of tin(IV) and (II), formation of open ring helical complexes of tin are unfavorable both thermodynamically and kinetically. In these pathways, coordination of hydroxide nucleophile to tin metal due to the highly charged, exclusive oxophilicity nature of the Sn center, and high affinity of Sn to increase coordination state are proposed responsible as inhibiting roles of tin via the ring opening. While, in saturated six coordinate tin(IV) and (II) verdoheme complexes the ring opening of tin verdohemes is possible thermodynamically, but it is not predicted to occur from a kinetics point of view. In the six coordinate pathway, tin plays no coordination role and direct addition of hydroxide nucleophile to the positive oxo-carbon centers and formation of closed ring hydroxy compounds is proposed for preventing the verdoheme ring opening. These key points and findings have been corroborated by the results obtained from atomic charge analysis, geometrical parameters, and molecular orbital calculations. In addition, the results of inhibiting ring opening reaction of tin verdoheme complexes could support the great interest of tin porphyrin analogues as pharmacologic means of chemoprevention of neonatal jaundice by the competitive inhibitory action of tin porphyrins on heme oxygenase.

R S Deeb

Papers

1H and 119Sn magnetic resonance study of the SnIV protoporphyrin IX complex of equine myoglobin. Structure of the porphyrin-binding pocket.