Structure–solid-state CPMAS 13C NMR correlation in palladacycle solvates (pseudo-polymorphs) with a transformation from Z′ = 1 to Z′ = 2

Abstract

The dinuclear µ-acetato-µ-benzophenone iminato palladium complex [{(C^∧N)Pd}₂(µ-OAc)(µ-NCPh₂)] (1) [C^∧N = N,N-dimethylbenzylamine-κN,κC)] is prepared by reaction of [{(C^∧N)Pd(µ-OAc)}₂] with benzophenone imine and [NBu₄]OH in ethanol. The dinuclear palladacycle 1 can crystallize with different solvents molecules as 1·1.5C₆H₅CH₃, 1·0.25C₆H₅CH₃ (Z′ = 2), 1·1.5C₆H₆ and 1·C₆H₁₄ (n-hexane) upon hexane diffusion into a toluene, benzene or CH₂Cl₂ solution, respectively. The structure of 1·0.25C₆H₅CH₃ with two palladacycle molecules and two partly occupied toluene molecules in the asymmetric unit (Z′ = 2) is a consequence of partial toluene solvent loss from 1·1.5C₆H₅CH₃ (Z′ = 1) as was followed by solid-state CPMAS ¹³C NMR. The transformation from Z′ = 1 to Z′ = 2 (crystal “on the way”?) toluene solvate can proceed in a solid-state single-crystal-to-crystal transition as evidenced from multiple single-crystal X-ray diffraction studies, also when the crystals are still in their mother liquor. During this transformation the remaining toluene crystal solvent becomes “locked in” (immobile from static ²H (D) NMR, only lost above 80° from TGA) and the crystals of 1·0.25C₆H₅CH₃ (Z′ = 2) remain crystalline in air in the absence of mother liquor or toluene, different from the other solvates. A rotational disorder of one of the benzene molecules in 1·1.5C₆H₆ (Z′ = 1) around its pseudo-six-fold axis is supported by the line-shape analysis of the static ²H (D) spectrum.