The configuration of the tin-centered radical R3Sn (R = 2,4,6-tri-i-propyphenyl) as studied by ESR

Persistent and Stable Radicals of the Heavier Main Group Elements and Related Species

“…128 Reduction of the corresponding tin halide, Sn(Cl)-(C 6 H 3 -2,6-Mes 2 ), did not afford an isolable radical but produced a red solution from which the diamagnetic cluster Sn 8 (C 6 H 3 -2,6-Mes 2 ) 4 could be isolated. 129 130a In THF at room temperature, the EPR spectra of the two compounds were essentially identical, with signals at g ) 2.0069 and hyperfine couplings to 117 Sn and 119 Sn of a( 117/119 Sn) ) 8.3/8.5 G, consistent with the location of the unpaired electron in a p-or π-orbital. X-ray crystallography showed that the [Ar*SnSnAr*] •radical anion is trans-bent, with Sn-Sn distances of 2.8123(9) and 2.7821( 14) Å and Sn-Sn-C angles of 95.2(1) and 97.3(2)°.…”

“…In addition, variable-temperature data for the ‚SnTrip 3 radical showed that the hyperfine coupling to 119 Sn decreases markedly with increasing temperature, indicating that the radical has pyramidal geometry. 117 If the geometry were planar, the hyperfine splitting constant would be expected to increase with increasing temperature, since increasing the amplitude of the out-of-plane vibration increases the scharacter of the singly occupied orbital, which, in turn, is proportional to the isotropic interaction. A frozen (-140 °C) toluene solution EPR spectrum allowed the a | , a ⊥ , g | , and g ⊥ components of the axially symmetric A and g tensors to be determined.…”

“…In the wake of these results, several other persistent germanium- or tin-centered radicals with half-lives that vary from minutes to years were generated. Radicals with a variety of bulky substituents, such as −CH 2 CMe 2 Ph, −CH 2 CMe 3 , CH 2 SiMe 3 , −C 6 H 2 -2,4,6-Me 3 , − −C 6 H 3 -2,6-Me 2 , −C 6 H 2 -2,4,6-Et 3 , −C 6 H 2 -2,4,6-Pr i 3 , − 1-adamantyl, −N(GeMe 3 ) 2 , and −N(GeEt 3 ) 2 , were obtained of the type ·Si(SiMe 3 - n Et n ) 3 ( n = 1, 2, or 3), ·Si(SiPr i 3 ) 3 , ·Si(SiMe 2 Bu t ) 3 , and Si(SiMe 2 SiMe 3 ) 3 could be synthesized by hydrogen abstraction from the silane, or by oxidation or reduction of the sodium or halide derivatives in solution.…”

“…For the methyl-substituted (i.e., Mes) species, a Δ H diss of 49(2) kcal mol -1 was estimated for the Sn−Sn bond, whereas the values for the Et and Pr i aryl derivatives were 26.6(2.0) and 8.5(1) kcal mol -1 . In addition, variable-temperature data for the ·SnTrip 3 radical showed that the hyperfine coupling to 119 Sn decreases markedly with increasing temperature, indicating that the radical has pyramidal geometry . If the geometry were planar, the hyperfine splitting constant would be expected to increase with increasing temperature, since increasing the amplitude of the out-of-plane vibration increases the s-character of the singly occupied orbital, which, in turn, is proportional to the isotropic interaction.…”

Thermodynamic, Kinetic, Structural, and Computational Studies of the Ph3Sn–H, Ph3Sn–SnPh3, and Ph3Sn–Cr(CO)3C5Me5Bond Dissociation Enthalpies

“…In most of the cases, reasonable agreement between the different values obtained by independent means is observed. However, in several cases such as the enthalpy of formation of Ph 3 SnSnPh 3 , a marked lack of agreement in the results of almost 25 kcal/mol was found. , In addition to the combustion experiments, photoacoustic calorimetric, , threshold photoelectron–photoion coincidence, appearance potential, ,,− gas-phase acidity, kinetics, and variable-temperature electron spin resonance (ESR) studies were performed to derive Sn–H, Sn–Sn, and Sn–M (M = transition metal) bond dissociation enthalpies (BDE).…”