|
Phosphinimide ligands, also known as phosphorane iminato ligands, are any of a class of organic compounds of the general formula NPR3−. == Structure and Bonding == Phosphinimide ligands have the general formula NPR3−, where the R groups represent organic substituents or, in rare cases, halides or NR2 groups. A discrete ion of NPR3− is not known, but the ligand can be easily derived from neutral phosphinimine precursors.〔 Several coordination types have been observed for transition metal phosphinimide complexes including terminal, μ2-N-bridging, and μ3-N-bridging.〔 In the terminal bonding mode the ligand can have either a linear or a bent geometry at nitrogen, and in the μ2-N-bridging mode, four-membered M2N2 rings can be formed either in an unsymmetrical fashion or in a symmetrical fashion.〔〔 The preferred coordination type is largely dependent upon the oxidation state of the metal as well as, to a lesser extent, upon the ligand sphere of the metal and the steric and electronic properties of the R groups on phosphorus. Bonding modes (A) and (B) are primarily seen in complexes containing metals in high oxidation states, mode (E) is preferred by metals with low oxidation states, and modes (C) and (D) are preferred by metals with medium oxidation states.〔 In main group phosphinimide complexes, only terminal and μ2-N-bridging bonding modes are observed.〔 The terminally bound ligands are primarily of type (B) with M-N-P bond angles ranging from 120-150°, and often showing surprisingly short M-N bonds.〔 Both the M-N and N-P bond lengths actually come close to being double bonds. This bonding can best be described by a covalent single bond with an overlaying share of polar bonding. The μ2-N-bridging mode arises when the free electron pair at nitrogen gives rise to dimerization.〔 center These dimeric complexes yield different M-N bond lengths depending on the ligands present in the rest of the ligand sphere of M.〔 When the complex contains two or four identical ligands, nearly equal M-N distances are observed, whereas, when different or odd-numbered identical ligands are in the complex, the M-N distances are all of significantly different length.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phosphinimide ligands」の詳細全文を読む スポンサード リンク
|
