Synthesis, bonding and dynamic behavior of fac-[Mo(II)(CO)(2)(eta(3)-allyl)] derivatives

Cationic complexes [Mo(eta (3)-allyl)(CO)(2)(L-L)L ' ]PF6, (L-L=C6H5SCH2CH2 SC6H5. L ' = NCCH3 (1): bipy. NCCH3 (2): py. (NCCH3). (3), (NCCH3)(3) (4); dppe, NCCH3 (5) and the neutral analogues [Mo(eta (3)-allyl)(CO)(2)(L-L)X] (L-L = phen (6). bipy (7): X = Br) were synthesized. Complexes 2, 5, 6 and 7 were characterized by single crystal X-ray diffraction. Depending on the chelating ligand, these pseudo-octahedral complexes undergo different dynam ic processes in solution and NMR spectroscopic evidence was provided for th ose studies. The structural trends of the limiting structures depicted by t hese complexes as well as the pathways to their inter-conversion were analy zed by ab initio theoretical calculations. Both NMR data and the calculatio ns showed that for complex 2 the equatorial species predominates at room te mperature but that two forms differing only by the conformation of the ally l coexist. Lowering the temperature leads to the appearance of the equatori al-axial isomer. (C) 2001 Elsevier Science B.V. All rights reserved.