Synthesis, structure, and reactivity of fluorous phosphorus/carbon/phosphorus pincer complexes derived from P(CH2)5P backbones

Reactions of the diphosphine H2P(CH2)5PH2 and fluorous alkenes H2CCHRfn (excess; Rfn = (CF2)n−1CF3; n = a, 6; b, 8; c, 10) at 60 °C in the presence of AIBN give the precursors (RfnCH2CH2)2P(CH2)5P(CH2CH2Rfn)2 (2a–c; 68–74%). These react with Pd(O2CCF3)2 in CF3C6F5 at 80 °C to give the title complexes (5a–c, 51–18%). Addition of LiCl to 5b gives (6b, 97%); subsequent reaction with MeLi affords the corresponding methyl complex (97%). A solvate of 6b is crystallographically characterized. The structure exhibits CH2CH2Rf8 groups with nearly anti C–C–C–C conformations, extending in parallel above and below the palladium square plane to create fluorous lattice domains. Reactions of 2b and other metal complexes are described; in the cases of (PhCN)2PdCl2 or (COD)2PtCl2 (CF3C6H5, room temperature), bimetallic species in which two MCl2 moieties are bridged by two diphosphines appear to form. The CF3C6F11/toluene partition coefficients of 2a–c and 5a–c establish high fluorophilicities; despite the lower fluorine weight%, those of 5a–c are slightly greater ((97.4–99.7):(2.6–0.3) versus (95.3–99.3):(4.7–0.7)).

The diphosphines 2a–c are prepared via free radical chain additions to H2CCHRfn to H2P(CH2)5PH2 and elaborated to a variety of pincer complexes, one of which (X/n = Cl/8) is crystallographically characterized.Figure optionsDownload as PowerPoint slide