Syntheses, Reactivity, and Stereochemistry of η3-Allyl Dithio-Molybdenum Complexes: Crystal Structures of endo-[Mo(η3-C3H5)(η2-S2CNC4H8)(CO)(η2-dppe)], endo-[Mo(η3-C3H5){η2-S2P(OEt)2}(CO)(η2-dppe)], exo-, endo-[Mo(η3-C3H5)(η2-S2CNC4H8)(CO)(η2-dppm)], and endo-[Mo(η3-C3H5){η2-S2P(OEt)2}(CO)(η2-dppm)

Abstract

The reactions of η3-allyldicarbonyldithiomolybdenum(II) compounds [Mo(η3-C3H5)(CO)2(η2-L2)(X)] (L2, X = S2CNC4H8 (1a); S2CNEt2 (1b); S2P(OEt)2, CH3CN (1c)) with diphos in refluxing acetonitrile give a mixture of endo and exo complexes [Mo(η3-C3H5)(η2-L2)(CO)( η2-diphos)] (diphos: dppe = {1,2-bis(diphenylphosphino)ethane} (2−4); dppm = {bis(diphenylphosphino)methane} (5−7); dppa = {bis(diphenylphosphino)amine} (8−10)). The orientations of endo and exo are defined for the open face of the allyl group and carbonyl group in the same direction in the former and opposite directions in the latter. In solution, both the endo and the exo isomers are present in dithiocarbamate Mo complexes, whereas only the endo conformer is present in dithiophosphate dppe and dppa Mo complexes. The variable-temperature 1H and 31P{1H} NMR experiments and X-ray crystal structures of endo-[Mo(η3-C3H5)(η2-S2CNC4H8)(CO)(η2-dppe)] (2), endo-[Mo(η3-C3H5){η2-S2P(OEt)2}(CO)(η2-dppe)] (4), exo- and endo-[Mo(η3-C3H5)(η2-S2CNC4H8)(CO)(η2-dppm)] (5), and endo-[Mo(η3-C3H5){η2-S2P(OEt)2}(CO)(η2-dppm)] (7) are used to elucidate the allyl rotation mechanism and the two orientations. The activation barriers of interconversion were determined to be 61.5 ± 0.4 (3) and 65.1 ± 0.4 kJ mol-1 (5). X-ray analysis on 5 shows that the unit cell contains two independent molecules, endo and exo, which differ mainly by the orientation of the allyl group with respect to the carbonyl group. This is the first example of such a conformation in the crystal structure of the Mo(η3-C3H5)(η2-L) derivative.