Reactions of cerium complexes with transition metal nitrides: synthesis and structure of heterometallic cerium complexes containing bridging catecholate ligands

Abstract

In an attempt to synthesize heterometallic cerium nitrido complexes, we studied the reactions of cerium complexes supported by the Kläui tripodal ligand [Co(η⁵-C₅H₅){PO(OEt)₂}₃]⁻ (L_OEt⁻) with transition-metal nitrides. Whereas no reactions were found between Ce–L_OEt complexes and [Ru^VI(L_OEt)(N)Cl₂] (2), treatment of the Ce(IV) oxo complex [Ce^IV(L_OEt)₂(O)(H₂O)]·MeCONH₂ (1) with 2 resulted in reduction of both the Ce(IV) and Ru(VI) complexes, and formation of a heterometallic Ce(III)/Ru(III) complex with a bridging deprotonated acetamide ligand, [(L_OEt)₂(H₂O)Ce^III{μ-O,N-MeC(O)NH}Ru^III(L_OEt)Cl₂] (4), along with a minor product, [Ce^III(L_OEt)₂(NO₃)]. Ce(IV)–L_OEt complexes such as [Ce^IV(L_OEt)₂Cl₂] (3) can oxidize [Re^V(L_OEt)(N)(PPh₃)Cl] to give the Re(VI) nitride [Re^VI(L_OEt)(N)(PPh₃)Cl]⁺. Chloride abstraction of 3 by TlPF₆ followed by reaction with [PPh₄]₂[Mn^V(N)(CN)₄] afforded a diamagnetic red solid that is tentatively formulated as a heterometallic Ce(IV)/Mn(V) complex, [Ce(L_OEt)₂(H₂O){Mn(N)(CN)₄}] (5). Reactions of 3 with [ⁿBu₄N][M^VI(N)(cat)₂] (cat²⁻ = catecholate(2−)) afforded the Ce(III)/M(VI) complexes [(L_OEt)₂Ce^III{(μ-cat)₂M^VI(N)}] [M = Ru (6), Os (7)], in which the Ce(III) and M(VI) centers are bridged by two oxygen atoms of the two catecholate ligands. Similarly, the catecholate-bridged Ce(III)/Re(V) complex [(L_OEt)₂Ce^III{(μ-cat)₂Re^V(O)}] (8) was prepared from 3 and [Me₄N][Re^V(O)(cat)₂]. In CH₂Cl₂, 8 was air-oxidized to the Ce(III)/Re(VII) complex [Ce^III(L_OEt)₂(H₂O)₂][cis-{Re^VII(O)₂(cat)₂}] (9) with a cis-dioxo-Re(VII) counter-anion. The crystal structures of 4, 6, and 9 have been determined.