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 [(LC)4P4][OTf]4 (G[OTf]4, LC = 4,5-dimethyl-1,3-diisopropylimidazol-2-yl) can be used to introduce [LC–P]+ and [LC–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-P4LC)] (3a) and [(PHDI)Co(CN)(η3-P5(LC)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-P5LC){W(CO)5}] (5a-W(CO)5) and [(PHDI)Co(μ3:η2:η2,η1,η1-P7LC){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.