4,4-p-Biphenyl bis-phosphinidene: generation of a bis-W(CO)5 complex and ab initio calculation of its electronic structure
作者:Ngoc Hoa Tran-Huy、Hung Thanh Le、Francois Mathey、Minh Tho Nguyen
DOI:10.1039/b205813h
日期:2002.12.6
The (bis-7-phosphanorbornadiene-7-yl)-biphenyl was prepared from the reaction of the 4,4′-biphenyl dianion with the readily available 1-cyano-3,4-dimethylphosphole. The resulting complex was then used as a precursor of the 4,4′-p-biphenyl bisphosphinidene (P–C6H4–C6H4–P), which is trapped either by insertion reaction with MeOH leading to the bisphosphine complex or by [1+2] cycloaddition with diphenylacetylene, leading to the 4,4′-p-biphenyl bisphosphirene complex. Ab initio calculations on biphosphinidene were carried out using the CASSCF/CASPT2 method in conjunction with the 6-31G(d) basis set and both (12 electron–12 orbital) and (14 electron–14 orbital) active spaces that include all four lone pair orbitals of phosphorus atoms and the higher-lying phenyl p-orbitals. The calculated results pointed out that, in the ligand-free form, the parent 4,4′-p-biphenyl bis-phosphinidene (BPBP) exhibits a quintet ground electronic state (5A) having a twisted geometry, but with small quintet-singlet and quintet-triplet (5A < 1Ag < 3B1u) energy gaps of only 6 and 16 kJ mol−1, respectively. While the singlet and triplet states need to be treated by multi-reference wavefunctions, the lowest-lying quintet state 5A can essentially be described by HF-based single reference methods. In this high-spin state, BPBP is formed by a loose connection between two phenyl phosphinidenes in keeping the spin state of the P-atoms intact, leading to a weak coupling between phosphorus non-bonding electrons through the biphenyl moiety.
(双-7-膦降冰片二烯-7-基)-联苯是由4,4'-联苯二二阴离子与容易获得的1-氰基-3,4-二甲基磷的反应制备的。然后将所得络合物用作 4,4'-对联苯双膦亚膦 (P–C6H4–C6H4–P) 的前体,该前体通过与 MeOH 的插入反应形成双膦络合物或通过 [1+2 ] 与二苯乙炔环加成,形成 4,4'-对联苯双磷烯络合物。使用 CASSCF/CASPT2 方法结合 6-31G(d) 基组以及(12 电子 - 12 轨道)和(14 电子 - 14 轨道)活性空间(包括所有四个孤单轨道)对双膦亚胺进行从头计算磷原子的轨道对和较高位的苯基 p 轨道。计算结果指出,在无配体形式下,母体4,4'-对联苯双膦亚膦(BPBP)呈现出具有扭曲几何形状的五重基电子态(5A),但具有小的五重单线态和五重态三重态 (5A < 1Ag < 3B1u) 能隙分别仅为 6 和 16 kJ mol−1。虽然单重态和三重态需要通过多参考波函数处理,但最低五重态 5A 本质上可以通过基于 HF 的单参考方法来描述。在这种高自旋状态下,BPBP是由两个苯基次膦之间的松散连接形成的,以保持P原子的自旋状态完整,导致磷非键电子之间通过联苯部分产生弱耦合。