Bridging Pseudohalides in Palladacycles as a Source of Different Assemblies

The reaction of [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐Cl)]2 (CH2NC5H10 = piperidinomethyl) with KSCN led to the centrosymmetric dimer [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐SCN‐κ1S,κ1N)]2, which features side‐on bridging thiocyanate ligands. However, the analogous reaction of the chlorido‐bridged starting material with NaN3 yielded the dimer [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐N3‐κ1κ1N)]2, in which the azido ligands exhibit end‐on coordination. This complex persists as a mixture of cis and trans isomers in solution. Lastly, the square tetrametallic complex [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐CN‐κ1C,κ1N)]4 was obtained from the reaction between the parent chlorido‐bridged complex and AgCN. In solution, this compound forms an equilibrium between the tetra‐ and trimetallic species. Thermodynamic data (equilibrium constants and free energies in CDCl3 and C6D6, and enthalpy and entropy in CDCl3) were determined and show that the formation of the trimetallic isomer is thermodynamically disfavored [Keq = (1.93 ± 0.07) × 10–4 mol L–1 and ΔGeq = 20.83 ± 0.11 kJ mol–1 in CDCl3, Keq = (4.5 ± 0.2) × 10–5 mol L–1 and ΔGeq = 24.40 ± 0.14 kJ mol–1 in C6D6] and that the variation in the enthalpy and entropy are positive (ΔH = 75 ± 5 kJ mol–1 and ΔS = 186 ± 15 J mol–1 K–1 in CDCl3). Coordination of pseudohalides to the soft metal center of a silapalladacycle leads to different bridging modes depending on the pseudohalide. With cyanide, a molecular square is formed, which in solution is in equilibrium with the corresponding triangular species.