Mechanistic Pathways For N2o Elimination From Trans-R3sn-O-N=N-O-Snr3 And For Reversible Binding Of Co2 To R3sn-O-Snr3 (R = Ph, Cy)

The rate and mechanism of the elimination of N2O from trans-R3Sn-O-N=N-O-SnR3 (R = Ph (1(Ph)) and R = Cy (1(Cy))) to form R3Sn-O-SnR3 (R = Ph (2(Ph)) and R = Cy (2(Cy))) have been studied using both NMR and IR techniques to monitor the reactions in the temperature range of 39-79 degrees C in C6D6. Activation parameters for this reaction are Delta H-double dagger = 15.8 +/- 2.0 kcal.mol(-1) and Delta S-double dagger = -28.5 +/- 5 cal.mol(-1).K-1 for 1(Ph) and Delta H-double dagger = 22.7 +/- 2.5 kcal.mol(-1) and Delta S-double dagger = -12.4 +/- 6 cal.mol(-1).K-1 for 1(Cy). Addition of O-2, CO2, N2O, or PPh3 to sealed tube NMR experiments did not alter in a detectable way the rate or product distribution of the reactions. Computational DFT studies of elimination of hyponitrite from trans-Me3Sn-O-N=N-O-SnMe3 (1(Me)) yield a mechanism involving initial migration of the R3Sn group from O to N passing through a marginally stable intermediate product and subsequent N2O elimination. Reactions of 1(Ph) with protic acids HX are rapid and lead to formation of R3SnX and trans-H2N2O2. Reaction of 1(Ph) with the metal radical center dot Cr(CO)(3)C5Me5 at low concentrations results in rapid evolution of N2O. At higher center dot Cr(CO)(3)C5Me5 concentrations, evolution of CO2 rather than N2O is observed. Addition of 1 atm or less CO2 to benzene or toluene solutions of 2(Ph) and 2(Cy) resulted in very rapid reaction to form the corresponding carbonates R3Sn-O-C(=O)-O-SnR3 (R = Ph (3(Ph)) and R = Cy (3(Cy))) at room temperature. Evacuation results in fast loss of bound CO2 and regeneration of 2(Ph) and 2(Cy). Variable temperature data for formation of 3(Cy) yield Delta H-o = -8.7 +/- 0.6 kcal.mol(-1), Delta S-o = -17.1 +/- 2.0 cal.mol(-1).K-1, and Delta(o)(G298K) = -3.6 +/- 1.2 kcal.mol(-1). DFT studies were performed and provide additional insight into the energetics and mechanisms for the reactions.