PART 16: TRANSITION METAL CARBYNE COMPLEXES FOR CSIR NET/GATE

In this lecture no. 16 I have explained the detailed concepts of transition metal carbyne complexes. The metal−ligand multiply bonded systems even extended beyond the doubly bonded Fischer and the Schrock carbenes to the triply bonded LnM≡CR type Fischer carbyne and the Schrock carbyne complexes. Similar to carbene that exists in a singlet and a triplet spin state, the carbyne also exists in two other spin states i.e in a doublet and a quartet form. Upon binding to the metal in its doublet spin state as in the Fischer carbene system, the carbyne moiety donates two electrons via its sp hybridized lone pair containing orbital to an empty metal d orbital to yield a LnM←CR type ligand to metal dative bond. It also makes a covalent π−bond through one of its singly occupied pz orbital with one of the metal d orbitals. The carbyne−metal interaction consist of two ligand to metal interactions namely a dative one and a covalent one that together makes the carbyne moiety a LX type of a ligand. In addition to these two types of ligand to metal bonding interactions, there remains an empty py orbital on the carbyne−C atom that can accommodate electron donation from a filled metal d orbital to give a metal to ligand π−back bonding interaction. Analogously, in the quartet carbyne spin state in the Schrock carbyne systems three covalent bonds occur between the singly occupied sp, py and pz orbitals of carbyne−C moiety with the respective singly occupied metal d orbitals. Similar to what has been observed earlier in the case of the Fischer carbenes and Schrock carbenes, the Fischer carbyne complexes are formed with metal centers in lower oxidation states for e.g. as in Br(CO)4W≡CMe, while the Schrock carbyne complexes are formed with metals in higher oxidation state, e.g. as in (t−BuO)3W≡Ct−Bu.
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