Phosphorus ring expansion at cobalt: targeted synthesis of P4, P5, and P7 ligands†

Abstract

We report the synthesis of extended polyphosphorus ligands through the condensation of CoP₃ and CoP₄ frameworks with P₁ and P₂ units. Tetraphosphido complexes [(L)Co(CN)(η³-P₄R₂)] (1a-R: L = PHDI; R = Cy, Ph; 1b-R: L = Ar*BIAN; R = Cy, N(iPr)₂) were obtained by treatment of the anionic cyclo-P₃ complexes [nBu₄N][(PHDI)Co(CN)(η³-P₃)] (H, PHDI = bis(2,6-diisopropylphenyl)phenanthrene-9,10-diimine) and [K(18c-6)][(Ar*BIAN)Co(CN)(η³-P₃)] (I, BIAN = 1,2-bis(arylimino)acenaphthene diimine with aryl being 2,6-dibenzhydryl-4-isopropylphenyl) with diorganochlorophosphanes (R₂PCl, R = Cy, Ph, or N(iPr)₂). Similar reactions of the cyclo-P₄ complex [K(18c-6)][(Ar*BIAN)Co(η⁴-P₄)] (K) yielded pentaphosphido complexes [K(18c-6)][(Ar*BIAN)Co(η⁴-P₅R₂)] (2b-R; R = tBu, N(iPr)₂). Importantly, we show that the previously reported cationic cyclo-tetraphosphane [(L_C)₄P₄][OTf]₄ (G[OTf]₄, L_C = 4,5-dimethyl-1,3-diisopropylimidazol-2-yl) can be used to introduce [L_C–P]⁺ and [L_C–P]₂²⁺ units. Depending on the stoichiometry and reaction conditions, the reaction of G[OTf]₄ with complex H furnishes complexes [(PHDI)Co(CN)(η³-P₄L_C)] (3a) and [(PHDI)Co(CN)(η³-P₅(L_C)₂)][OTf] (4a[OTf]) with η³-coordinated tetra- and pentaphosphido ligands. Expanding this strategy, the cyclo-P₅ and cyclo-P₇ complexes [(PHDI)Co(μ:η⁴,η¹-P₅L_C){W(CO)₅}] (5a-W(CO)₅) and [(PHDI)Co(μ₃:η²:η²,η¹,η¹-P₇L_C){W(CO)₅}₂] (6a-{W(CO)₅}₂) were isolated from the reaction of G[OTf]₄ with [K(18c-6)][(PHDI)Co(η⁴-P₄)] (J) upon addition of W(CO)₅(THF) to the reaction mixture. Intermediates en route to products 5a and 6a were detected by ³¹P{¹H} NMR spectroscopy. The Ar*BIAN complexes I and K afford structurally analogous compounds 3b to 6b. Compounds 3–6 were isolated as crystalline materials and characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy.