Functionalization, Fragmentation, and Expansion of cyclo-P₄R₂ Ligands

In this study, three isolobal complexes of the form [{L_nM}(η³-P₄R₂)]⁺ ({L_nM}  = {CpMo(CO)₂} (A), {Cp'''Ni} (B), {Cp'''Co}^- (C), R = Ph, iPr; Cp''' = 1,2,4-^tBu₃C₅H₂) are reacted with nucleophilic carbenes (L). While C does not show any reactivity, the cationic complexes A and B undergo addition reactions. The respective products [CpMo(CO)₂(η³-P₄R₂L)]⁺ (1a - d) and [Cp'''Ni(η^1:1-P₄R₂L)]⁺ (3a - d) show different geometries for the L-P₃PR₂ ligands. Their reactivity towards EtO^- results in either a simple addition (for 1) or a complex addition, ring-opening, rearrangement sequence (for 3). Moreover, [Cp'''Ni(η²-IDippPP(OEt)PPⁱPr₂)] (4) could be methylated by the reaction with MeOTf, which affords an iso-tetraphosphine ligand, marking the first example of complete functionalization of a polyphosphorus ligand to a complexed phosphine. Mechanistic studies shed light upon the fundamental principles, which differentiate the influence of the isolobal {CpMo(CO)₂}, {Cp'''Ni}, and {Cp'''Co}^- transition metal units. Lastly, 3a-d were chosen as model substrates for further nucleophilic functionalization. In this regard, 3 reacts with [CN]^- in a [3+1] fragmentation reaction affording the dimerized species [{Cp'''Ni}₂(μ,η^1:1:1:1-cyclo-P₄(PR₂)₂)] (6a: R = Ph, 6b: R  =  ⁱPr) together with IDippP-CN. In contrast, the reaction with [ECO]^- (E = P, As) led to an extension of the pnictogen framework yielding [Cp'''Ni(η^1:1-EP₄Ph₂IDipp)] (8a: E = P, 8b: E = As).