A fluorene-based diphosphinite ligand, its Ni, Pd, Pt, Fe, Co and Zn complexes and the first structurally characterized diphosphinate metal chelates

The diphosphinite ligand 9,9-(Ph2POCH2)2-fluorene (1) was reacted with group 10 metal dichlorides to form chelate complexes of formula [MCl2(1)] (MNi, 2; MPd, 3; MPt, 4) showing 8-membered metallocycles. Chloride abstraction from 3 with AgOTf afforded the dinuclear complex [M(μ-Cl)Pd(1)]2(OTf)2 (5), in which the ligand adopts a different conformation with respect of 3. In 5, the fluorene moiety and the phenyl groups display stabilizing interactions with the anion which is located close to the metal centre. With Fe(II), Co(II) and Zn(II) chlorides, the non-isolated intermediates [MCl2(1)] readily undergo oxidation to [MCl2(1ox)] (MFe, 6; MCo, 7; MZn, 8; 1ox = 9,9-(Ph2P(O)OCH2)2-fluorene) in which the diphosphinate ligand and the metal centre form 10-membered metallocycles. Complexes 6–8 are the first examples of structurally characterized diphosphinate metal chelates. The Zn(II) diphosphinite complex [ZnCl2(1)] (9) could be observed by NMR spectroscopy, along with the mixed phosphinite–phosphinate, mono-oxidized complex which is an intermediate in the formation of 8. Complex [ZnCl2(9.9-fluorene-dimethanol)(Ph2P(O)H)] (10) was also observed as hydrolysis product of 9. The X-ray molecular structures of 2, 3, 5.2OTf, 6, 7, 8 and 10 are reported.

The chelate complexes 2–4 were prepared from a fluorene-based diphosphinite ligand which has an adaptable bite angle. Reaction of 3 with AgOTf afforded the dinuclear cationic complex 5·OTf, which displays anion–cation host–guest contacts. Complexes 6–8 are formed by air oxidation of the intermediates [MCl2(1)] (M = Fe, Co, Zn) and represent the first examples of structurally characterized diphosphinate metal chelates. A mixed phosphinite–phosphinate complex is an intermediate in the formation of 8 from 9 and [ZnCl2(9.9-fluorene-dimethanol) (Ph2P(O)H)] (10) was also observed as an hydrolysis product of 9.Figure optionsDownload as PowerPoint slide