Alkoxycarbonyl Groups in Metalloesters Showing Oxocarbenium‐like Structure and Alkylating Reactivity

The first series of Co/Ni bimetallic metalloesters bearing the novel oxocarbenium-like alkoxycarbonyl groups are synthesized and characterized. As triggered by the long O−C_alkyl bonds (1.522(11)~1.607(15) Å), the alkylating reactivity of the oxocarbenium-like alkoxycarbonyl groups toward a series of C/N/O-nucleophiles via the rare B_AL2 mechanism was examined at ambient conditions.

Abstract

In contrast to the well-documented acylating reactivity, the alkylating reactivity of the alkoxycarbonyl group, as signified by its oxocarbenium-like resonance structure, remains almost unexplored. Herein, the first series of Co/Ni dinuclear metalloesters exhibiting the novel oxocarbenium-like alkoxycarbonyl groups were synthesized and characterized. In these deformed alkoxycarbonyl groups, the C_carbonyl−O_alkoxyl bonds were contracted to 1.177(11)~1.191(9) Å with the elongations of the C_carbonyl=O_carbonyl bonds to 1.368(13)~1.441(9) Å. Meanwhile, the O−C_alkyl bonds were also elongated to 1.522(11) ~1.607(15) Å, and were by far the longest O−C_alkyl bonds reported for alkoxycarbonyl groups. As triggered by the long O−C_alkyl distances, the alkylating reactivity of the oxocarbenium-like methoxycarbonyl group towards a series of C/N/O-nucleophiles via the rare B_AL2 mechanism at ambient conditions was examined. Furthermore, the homo-etherifications of alcohols mediated by the Co/Ni dinuclear metalloesters were investigated. The yields followed the trend ethanol≫n-propanol≫n-butanol ≈n-pentanol, that closely related to the structure features of the alkoxycarbonyl groups in corresponding metalloesters: while the ethoxycarbonyl group showed the reactive oxocarbenium-like framework, the n-propoxycarbonyl group displayed the dioxocarbenium-like skeleton with a shorter O−C_alkyl bond; In comparison, the classical frameworks with unactivated alkyl moieties were observed for n-butoxycarbonyl and n-pentoxycarbonyl groups.

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