Several Types Of Ruthenium, Rhodium Metal Organic Compounds Into The Key And The Reaction Mechanism Of Theoretical Research

Density functional theory (DFT) calculations at the B3LYP level are carried out to study and analyze the following three problems. Our major intention is to investigate the molecular structures, bonding, and mechanisms on the organometallic reactions mentioned below.(1) The complex, [Ru(η⁵-C₉H₇)k³(P,C,Q-Ph₂P(CH₂CRK:H₂)(PPh₃)][PF₆] (R=H, Me), containing a hemilabile ligand, Ph₂PCH₂CR=CH₂, has two isomers as the carbon-carbon double bond of the hemilablile ligand coordinates to the metal center with different orientations. The two isomers can interconvert each other. Our results of calculations reveal that the vinyl plane flips during the interconversion process, which is in contrast to the argument of J. Gimeno that the vinyl plane remains coordinating to the metal center during the interconversion process. Our major concern aims to explore the essential bonding character and find out the factors controlling the relative stability of the isomers. Based on molecular orbital symmetry consideration, we found that the π-antibonding of C=C bond (LUMO) interacts with the first HOMO of CpRu(PH₃)₂ fragment in isomer 1, while the π-antibonding of C=C bond (LUMO) with different orientation in isomer 2 interacts with the third HOMO of CpRu(PH₃)₂ fragment. More effective overlapping involved in isomer 1 leads to its higher stability than isomer 2.(2) The C-H bond energy of benzene and methane is about 110 and 95 kcal/mol, respectively, which means that the C-H bond of benzene is stronger than that of methane. However, a lot of experimental results confirmed transitional metal complexes could easily activate the C-H bond of benzene while not the C-H bond of methane. We theoretically investigate the mechanisms of H-CH₃ and H-C₆H₅ activation by CpRhPMe₃ under irradiation. Our calculatedresults show that the rate-determining step is the C-H bond breaking for the two cases. The reaction activation free energy is calculated to be 39.28 and 33.68 kcal/mol, respectively, for the activation of H-CH3 and H-C6H5, which is in agreement with the experimental observations. Stronger electron-withdrawing of phenyl group compared with hydrogen atom is responsible for relative easiness of the H-C6H5 activation.(3) In order to confirm complexes CpRu(PPh3)2SH and CpRu(PH3)2 S Si'Pr3 having similar reactivity, that is, both of them react with RNCS(R= Ph, 1-Naphth) to afford similar products, we comparatively propose and perform the mechanisms for both reactions. For the reaction of CpRu(PPh3)2SH with RNCS(R= Ph, 1-Naphth), two mechanisms are proposed. One is that one PPh3 ligand dissociates firstly from CpRu(PPh3)2SH to give a 16e intermediate, then the substrate RNCS react with the intermediate, undergoing hydrogen migration, to give the product. The other is that CpRu(PPh3)2SH reacts directly with RNCS to give a 18e intermediate in which a C-S bond is formed, then one PPh3 ligand dissociates from and the C=S sulfur atom coordinates to the metal center, giving the product. It is theoretically predicted that the rate-determining step is hydrogen migration, and the reaction activation free energy is calculated to be 36.04 and 38.13 kcal/mol, respectively, for both mechanisms. Based on calculated close reaction free energies for both mechanisms , a plausible prediction is given that either one of the two mechanisms cannot be excluded, in other words, both mechanisms coexist competitively. For the reaction of CpRu(PPh3)2 SSi'Pr3 and RNCS, only one mechanism is proposed. One PPh3 dissociates firstly from CpRu(PPh3)2SSi'Pr3, then RNCS reacts with the resulting intermediate, undergoing silyl migration, to give the product. The rate-determining step is the silyl migration with the reaction activation free energy being 16.37 kcal/mol. Apparently, the reaction of CpRu(PPh3)2SSi'Pr3 with RNCS is much morefavorable kinetically than CpRu(PPh3)2SH with RNCS. The similarity is that both reactions have similar rate-determining steps and the products have similar geometrical structures.