Synthesis, molecular structures, and dynamics of primary and secondary fluoroalkyl complexes of palladium(II) with tetramethylethylenediamine (TMEDA) ligands.: Evaluation of the structural trans-influences of methyl and fluoroalkyl groups as ligands within the same coordination sphere

Reaction of (TMEDA)Pd(CH3)(2) (TMEDA = tetramethylethylenediamine) with primary perfluoroalkyl iodides gives a mixture of products that depend markedly on the choice of solvent. In hexanes, (TMEDA)PdMe(R-F) [R-F = n-C3F7 (1); n-C4F9 (2)] is afforded in about 50% yield, with (TMEDA)Pd(CH3)I (3) formed concurrently. In hexanes 3 precipitates from solution and does not react further, but with THF as the solvent 3 remains in solution and reacts with RFI ih the presence of light to give (TMEDA)PdI(R-F) [R-F = n-C3F7 (4); n-C4F9 (5)] and (TMEDA)PdI2, as well as 1 and 2, respectively. Treatment of either 1 or 2 with I-2 yields the corresponding iodide compounds 4 and 5, with elimination of CH3I, while an analogous reaction of 2 with concentrated HCl produces the chloride compound (TMEDA)PdCl-(C4F9) (8) In contrast, reaction of (TMEDA)Pd(CH3)(2) with the secondary iodide ICF(CF3)(2) gives only one fluoroalkyl product, (TMEDA)Pd(CH3)(i-C3F7) (6), in either hexanes or THF. Reaction of 6 with I-2 occurs with selective cleavage of the Pd-CH3 bond to give the iodide product (TMEDA)PdI(i-C3F7) (7). The solid-state structures of 1-5, 7, and 8 have been confirmed by X-ray crystallography. Examination of bond distances illustrates that fluoroalkyl ligands have smaller trans-influences than methyl ligands, but larger trans-influences than iodide or chloride ligands toward the N-donor TMEDA ligand. This results in a shorter, presumably stronger Pd-fluoroalkyl bond being trans to a shorter, presumably stronger Pd-N bond. The principal steric effect of the perfluoroisopropyl group in the solid state is to generate an almost planar TMEDA ring. The solution NMR data for 1, 2, 4, 5, and 8 show resonances due to diastereotopic CF2 groups below room temperature, with the CF2 group acting as a remote sensor for formation of a stereocenter at the metal due to slowing of the inversion of the puckered five-membered metallacycle formed by the TMEDA ligand and Pd. The other TMEDA complexes show the same behavior below room temperature, with the exception of (TMEDA)PdI(i-C3F7) (7), in which the TMEDA ring is presumably