Synthesis, structure, and reactivity of fluorous phosphorus/carbon/phosphorus pincer ligands and metal complexes
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Reactions of the diphosphine 1,3-C6H4(CH2PH2)(2) and fluorous alkenes H2C=CHRfn (R-fn = (CF2)(n-1)CF3; n = 6, 8) at 75 degrees C in the presence of AIBN give the title ligands 1,3-C6H4(CH2P(CH2CH2Rfn)(2))(2) (3-R-fn) and byproducts 1,3-C6H4(CH3)(CH2P(CH2CH2Rfn)(2)) (4-R-fn) in 1:3 to 1:5 ratios. Workups give 3-R-fn in 4-17% yields. Similar results lre obtained photochemically. Reaction of 1,3-C6H4(CH2Br)(2) and HP(CH2CH2Rf8)(2) (5) at 80 degrees C(neat, 1:2 mol ratio) gives instead of simple substitution the metacyclophane [1,3-C6H4(CH2P(CH2CH2Rf8)(2)CH2-1,3-C6H4CH2P(CH2CH2Rf8)(2)CH2](2+) 2Br(-), which upon treatment with LiAlH4 yields 3-R-f8 (20%), 4-R-f8, and other products. Efforts to better access 3-R-f8, either by altering stoichiometry or using various combinations of the phosphine borane (H3B) PH(CH2CH2Rf8)(2) and base, are unsuccessful. Reactions of 3-R-fn with Pd(O2CCF3)(2) and [IrCl(COE)(2)](2) (COE = cyclooctene) give the palladium and iridium pincer complexes (2,6,1-C6H3(CH...2P(CH2CH2Rfn)(2))(2)) Pd(O2CCF3) (10-R-fn; 80-90%) and (2,6,1-C6H3(CH2P(CH2CH2Rf8)(2))(2)) Ir(Cl)(H)(11-R-f8; 29%), which exhibit CF(3)C(6)F(11)3toluene partition coefficients of gt 96 : lt 4. The crystal structure of 10-R-f8 shows CH2CH2Rf8 groups with all-anti conformations that extend in parallel above and below the palladium square plane to create fluorous lattice domains. NMR monitoring shows a precursor to 11-R-f8 that is believed to be a COE adduct.
Source:Dalton Transactions, 2005, 13, 2275-2283
- Royal Soc Chemistry, Cambridge