A density functional theory investigation on intramolecular hydrogen transfer of the [Os3(CO)11P(OMe)3(Ru(n5- C5H5))2] cluster

The reduction of [Os3(CO)11P(OMe)3] and subsequent ionic coupling of the reduced species with [Ru(n5- C5H5) (CH3CN)3]+ resulted in the formation of [Os3(CO)11P(OMe)3(Ru(n5-C5H5))2] which can be converted to spiked tetrahedral cluster, [HOs3(CO)11P(OMe)3Ru 2(n5-C5H5)(C5H 4)] via the intramolecular hydrogen transfer. Due to the unavailability of a suitable single crystal, the PW91/SDD and LDA/SDD density functional methods were used to predict possible structures and the available spectroscopic information (IR, NMR) of [Os3(CO)11P(OMe) 3(Ru(n5-C5H5))2]. The most probable geometry found by constrained search is the isomer (a2) in which the phosphite, P(OMe) 3, occupies an axial position on one of the two osmium atoms that is edge bridged by the Ru(CO)2(n5-C5H 5) unit. By using the most probably geometry, the predicted infrared frequencies and 1H, 13C and 31P NMR chemical shifts of the compound are in the same range as the experimental values. For this type of complex, the LDA/SDD method is appropriate for IR predictions whereas the OPBE/IGLO-II method is appropriate for NMR predictions. The activation energy and reaction energy of the intramolecular hydrogen transfer coupled with the structural change of the transition metal framework were estimated at the PW91/SDD level to be 110.32 and -0.14 kcal/mol respectively.