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 pri mary perfluoroalkyl iodides gives a mixture of products that depend markedl y 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) forme d 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-C 4F9 (5)] and (TMEDA)PdI2, as well as 1 and 2, respectively. Treatment of ei ther 1 or 2 with I-2 yields the corresponding iodide compounds 4 and 5, wit h elimination of CH3I, while an analogous reaction of 2 with concentrated H Cl produces the chloride compound (TMEDA)PdCl-(C4F9) (8) In contrast, react ion of (TMEDA)Pd(CH3)(2) with the secondary iodide ICF(CF3)(2) gives only o ne fluoroalkyl product, (TMEDA)Pd(CH3)(i-C3F7) (6), in either hexanes or TH F. 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 structu res of 1-5, 7, and 8 have been confirmed by X-ray crystallography. Examinat ion of bond distances illustrates that fluoroalkyl ligands have smaller tra ns-influences than methyl ligands, but larger trans-influences than iodide or chloride ligands toward the N-donor TMEDA ligand. This results in a shor ter, presumably stronger Pd-fluoroalkyl bond being trans to a shorter, pres umably stronger Pd-N bond. The principal steric effect of the perfluoroisop ropyl 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 diastere otopic CF2 groups below room temperature, with the CF2 group acting as a re mote sensor for formation of a stereocenter at the metal due to slowing of the inversion of the puckered five-membered metallacycle formed by the TMED A ligand and Pd. The other TMEDA complexes show the same behavior below roo m temperature, with the exception of (TMEDA)PdI(i-C3F7) (7), in which the T MEDA ring is presumably