Comparison Of Binuclear Phospholyl And 1,3-Diphosphacyclobutadiene Sandwich Compounds Chromium Carbonyl Derivatives With Their Cyclopentadienyl And Cyclobutadiene Sandwich Analogues:Role Of Phosphorus Lone Pair

Recently,transition metal carbonyl compounds have been a highlight in organometallic chemistry and other relecant fields.In this paper,BP86 and M06-L,two common and efficient density functional?DFT?theory methods,are used to study the effect of lone electrons of phosphorus atom on the structures of binuclear phospholyl chromium carbonyl derivatives??C₄H₄P?₂Cr₂?CO?_n?n=6,5,4,3??and diphosphacyclobutadiene sandwich compounds??Me₂C₂P₂?₂Cr₂?CO?_n?n=6,5,4,3??.The main results are as follows:The low energy structures of?C₄H₄P?₂Cr₂?CO?_n?n=6,5,4,3?are studied with two DFT methods?BP86 and M06-L?.It is found that the lowest energy structure 6S-1,4S-1 and 3T-1of?C₄H₄P?₂Cr₂?CO?_n?n=6,4,3?have two five-electron donor terminal?⁵-C₄H₄P rings.For?C₄H₄P?₂Cr₂?CO?₅,apart from the similar one five-electron donor terminal?⁵-C₄H₄P ring,there is another seven-electron donor bridging?⁵,?¹-C₄H₄P ring in the lowest energy structure5S-1 state.The bridging?⁵,?¹-C₄H₄P ring is a seven-electron donor through five?electrons giving to one chromium atom and two-electrons giving to the other chromium atom through a P?Cr coordination bond from the phosphorus lone pair.However,the relative energies of the structures without bridging?⁵,?¹-C₄H₄P ring among all low energy structures of?C₄H₄P?₂Cr₂?CO?₅ are slightly higher than that of 5S-1.This means that compared with?bond,the phosphorus lone pair has a greater influence on the stability of the dichromic carbonyl complex of?C₄H₄P?₂Cr₂?CO?_n?n=6,5,4,3?.For the low energy structures of?Me₂C₂P₂?₂Cr₂?CO?_n?n=6,5,4,3?,there is no two-electrons giving to the two chromium atoms through a P?Cr coordiantion bond from the phosphorus lone pair in the lowest energy structures 3T-1 and 4T-1 of?Me₂C₂P₂?₂Cr₂?CO?_n?n=4,3?.As for?Me₂C₂P₂?₂Cr₂?CO?_n?n=6,5?,however,the structures of the lowest energetic6S-1 and 5T-1 of?Me₂C₂P₂?₂Cr₂?CO?_n?n=6,5?is very interesting due to the phosphorus lone pair.The two lowest energy structures have two bridging?⁴,?¹-Me₂C₂P₂ rings,bonding to one of the two Cr atoms through the ring?electrons and the other Cr through the lone pair of a phosphorus atom.Moreover,both structures do not have bonding between the metal atoms due to the very long Cr-Cr distance.This reveals that Cr atoms with 4 terminal CO groups in 6S-1 and 5T-1 have the favorite 18-electron configurations.