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RESEARCH PRODUCT

N-Heterocyclic Phosphenium, Arsenium, and Stibenium Ions as Ligands in Transition Metal Complexes: A Comparative Experimental and Computational Study

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Reaction of 2-chloro-1,3,2-diazaarsolenes and -diazaphospholenes with Tl[Co(CO)4] gives instable complexes of type [Co(ER2)(CO)4] which decarbonylated to yield [Co(ER2)(CO)3]. Spectroscopic and X-ray diffraction studies revealed that the tetracarbonyl complexes can be formulated as ion pair for E = P and as covalent metalla-arsine for E = As, and the tricarbonyl complexes as carbene-like species with a formal E=Co double bond. A similar reactivity towards Tl[Co(CO)4] was also inferred for 1,3,2-diazastibolenes although the products were not isolable and their constitution remained uncertain. Evaluation of structural and computational data suggests that the weak and polarized Co–As bond in [Co(AsR2)(CO)4] can be characterized as an “inverse” ML donor-acceptor bond. The computational studies disclosed further η2(EN)-coordination of the EN2C2 heterocycle as an alternative to the formation of a carbene-like structure for [Co(ER2)(CO)3]. The η2-complex is less stable for E = P but close in energy for E = As and more stable than the carbene-like complex for E = Sb.