Molybdenum–carbon functionalities supported by a quadridentate Schiff-base ligand: the reactivity of trans-dichloro[N,N′-bis(salicylidene)-o-phenylenediaminato]molybdenum(IV)‡

Abstract

The parent compounds trans-[Mo(salophen)Cl₂] 1 [salophen = N,N′-bis(salicylidene)-o-phenylenediamine dianion] and trans-[Mo(tbsalophen)Cl₂] 2 [tbsalophen = N,N′-bis(3,5-di-tert-butylsalicylidene)-o-phenylenediamine dianion] were obtained from the corresponding Schiff bases and [MoCl₄(MeCN)₂]. The alkylation of 1 proceeded very differently depending on the alkylating agent. The reaction with (PhCH₂)₂Mg led to the formation of trans-[Mo(salophen)(PhCH₂)₂] 3, containing two alkyl groups at the metal, while with Mg(mes)Br (mes = 2,4,6-Me₃C₆H₂) arylation occurred both at the imino carbons and at the metal, via a rather complex mechanism. Reduction of 1 led to an intermediate Mo(salophen), which was intercepted by PhCCPh. The plausible intermediate metallocyclopropene rearranged with the migration of one of the carbons to an imino group and dimerization of the monomeric unit. The salophen ligand displayed a bridging bonding mode in the dimer, containing a MoMo fragment and two bridging vinyl functionalities. The proposed structures are supported by three X-ray analyses.