Rapid Reversible Oxidative Addition of Group 14−Halide Bonds to Platinum(II):  Rates, Equilibria, and Bond Energies

Abstract

The reversible oxidative addition reactions of methyl(halogeno)tin and methyl(halogeno)germanium compounds to electron-rich platinum(II) complexes of the type [PtMe2(diimine)] have been studied. Complete kinetic and thermodynamic parameters have been obtained by VT 1H NMR for the reversible oxidative addition of Me3EX (E = Sn, X = Cl, Br, I) to [PtMe2(bpy- t bu2)] (bpy- t bu2 = 4,4‘-di-tert -butyl-2,2‘-bipyridyl) and related compounds, while partial data have been obtained for the reductive elimination of Me2SnCl2 from [PtClMe2(Me2SnCl)(bpy- t bu2)] and for the oxidative addition of Me3GeCl to [PtMe2(bpy- t bu2)]. UV−visible spectroscopic studies have also yielded equilibrium constants and ΔG° for the reversible oxidative addition reactions of Me3SnX (X = Cl, Br, I) to [PtMe2(diimine)]. Thermodynamic studies quantitatively establish the halogen effect on the oxidative addition reactions studied according to the favorability series I > Br > Cl. Kinetic studies clearly point to an SN2 mechanism for the reactions studied, and this is further supported by the observation of the cationic complex [PtMe2(Me3Sn)(bpy- t bu2){OC(CD3)2}]+ at low temperature in acetone-d 6. Extremely large second-order rate constants are observed for the oxidative addition of Sn−X bonds to dimethylplatinum(II) complexes, some being greater than 108 M-1 s-1, and it is established that rates follow the series Sn > Ge > Si > C and I > Br > Cl. Estimates have been made of the Pt−MMe3 bond dissociation energies for [PtXMe2(MMe3)(bpy- t bu2)], X = halide, and these are 233, 182, and 172 kJ mol-1 for M = Si, Ge, and Sn, respectively; the values are useful in rationalizing the chemistry of the Pt−M bonds.

Tetrel bonds, penta‐ and hexa‐coordinated tin and lead centres

“…This is in agreement with experimental observations, since the methylhalotin species Me 3 SnX (X = Cl, Br, I) react by an S N 2 pathway that requires a five‐coordinate tin structure in the transition state; for the germanium analogue Me 3 GeCl the variable‐temperature NMR spectra series shows a rate decrease of the S N 2 reaction; for the related silicon complexes 1 H NMR spectra have not shown any evidence of the S N 2 process. These observations were explained as partly resulting from size effects …”

Cationic thiolate and selenolate complexes of platinum(IV)

“…The 1 H NMR spectrum of 3a contained a single methylplatinum resonance, with the coupling constant ( 2 J Pt,Me = 66 Hz) in the range expected for methylplatinum(IV) complexes with methyl trans to nitrogen (8). The presence of a single methylplatinum resonance indicates that the product is formed by trans oxidative addition and so supports the structure shown in Chart 1.…”

Tetrel Bonding Interactions

“…We have devoted some attention to this “noncovalent carbon bonding” (see Section ), and so have several others . c, …”