The First-principle Explorations Of The First Scandium Phosphinoalkylidene Complex

The mononuclear rare earth metal carbene complexes are of great interests in the applications of synthetic chemistry and coordination chemistry.However,the synthesis of the reactive mononuclear rare earth metal carbene complexes has remained a challenging problem in the last decades.The recently synthesized first scandium phosphinoalkylidene complex?LScPT?has attracted extensive attentions for its stability and high reactivity.Experimental studies revealed that the LScPT complex show rich chemical reactivity,for example activating pyridine and H₂ et al.In particular,an unusually short Sc-C bond was characterized in its molecular structure.The earlier theoretical work focused on the possible reaction paths,while left the important high reactivity of LScPT and the unusually short Sc-C bond unexplained.In this work,the molecular structure,electronic properties and bonding features of LScPT complex are investigated by first-principles method.The main contents and conclusions of this thesis are:1)The calculated band structure and density of states show that the HOMO orbital of the LScPT complex is dominated by C-2p orbitals?mesomethylene carbon in L?,mixed with small amount of Sc-3d and P-3p orbitals.2)The analysis of band orbitals for frontier orbitals establishes a triple-bond picture,d-p??,?,??,for the extremely short Sc-C bonding interactions.3)The crystal orbital Hamilton populations calculations reveal the triple-bond features of the short Sc-C bond and the strength of the Sc-C bond of the LScPT complex is nearly 1.6 times larger than that of the Sc-C bond of the NaCl-type ScC.4)The calculated valence Bader charge shows that the specific C atom on the Sc-C bond is highly charged,which makes the C atom on the Sc-C bond an active nucleophilic site for the attack of Lewis acids.On the other hand,the Sc atom is shown to be an electrophilic site and thus vulnerable to the attack of Lewis bases due to the empty Sc-3d yz/xz orbitals on the LUMO band.Our studies reveal the origin for the short Sc-C bond and the high reactivity occurring around the Sc-C bond.5)Our molecular calculations give consistent results with the solid calculations.