95911-92-5Relevant academic research and scientific papers
Electron-rich hydrocarbon-metal complexes: Synthesis and electrochemical and NMR studies of (η4-trimethylenemethane)-and (η4-o-xylylene)iron complexes and their one-electron oxidation, paramagnetic derivatives. X-ray structure of the 17-electron (η4-trimethylenemethane)tris(trimethylphosphine)iron(1+) cation
Grosselin, Jean-Michel,Le Bozec, Hubert,Moinet, Claude,Toupet, Lo?c,K?hler, Frank H.,Dixneuf, Pierre H.
, p. 88 - 98 (2008/10/08)
Fe(η4-TMM)L3 complexes 3 (TMM is trimethylenemethane; L = PMe3 (a), L = PMe2Ph (b), L3 = MeC(CH2PMe2)3, (c)) were prepared directly from FeCl2, via addition of CH2=C(CH2Cl)2 to FeCl2L2/L and magnesium in tetrahydrofuran (THF). NMR studies of 3 indicate that the presence of phosphine ligands L favors an electron transfer from the iron toward the methylene carbons of the TMM ligand. Fe(η4-o-xylylene)L3 complexes 6a, 6b, and 6c were prepared either by addition of o-(ClMgCH2)2C6H4 to FeCl2(PMe3)2 (1a)/PMe3, FeCl2(PMe2Ph)2 (1b)/PMe2Ph, and FeCl2(P(OMe)3 (1c) or by addition of o-(ClCH2)2C6H4 to a mixture of 1a/PMe3 or 1b/PMe2Ph and magnesium. Complexes 6a and 6b were also obtained from the reaction of o-(BrMgCH2)C6H4CH3 with 1a/PMe3 and 1b/PMe2Ph, via a process relevant to δ(C-H) activation, whereas the same reaction performed with 1c led to the C-C bond formation product 0,0′ -CH3C6H4CH2CH2C 6H4CH3. NMR studies of complexes 6 demonstrated that both exocyclic C=C double bonds of the o-xylylene ligand are bonded to the iron atom. 3b reacted with FSO3Me, to give 3b+, which was easily reduced into 3b by hydride, and with NOBF4, to give Fe(NO)2(PMe2Ph)2 via 3b+. The 17-eIectron paramagnetic complexes 3a+(CF3SO3-) and 3b+(CF3SO3-) were isolated from the reaction of Ag(CF3SO3-) with 3a and 3b. The structure of 3a+(CF3SO3-) was determined at 128 K by an X-ray diffraction study [monoclinic, P21/c; a = 12.313 (2) A?; b = 11.016 (2) A?; c = 17.064 (3) A?; β = 103.1 (2)°; V = 2254.7 (6) A?3; Z = 4; R = 0.026; Rw = 0.024] and showed a piano-stool geometry for the cation 3a+ with an umbrella shape of the η4-TMM ligand. The paramagnetic 1H NMR shifts (δ) were measured for 3a+ (-213.5), 3b+ (-215.1), and 6a+ (-50.1, -11.3, -4.8), the lesser distortion in the planarity of the hydrocarbon ligand in 6a+ than in 3+ being related to a smaller observed shift in 6a+ than in 3+. Electrochemical studies established the electron-rich nature of both complexes 3 and 6: cyclic voltammetry showed a first reversible oxidation at low potential [E1/2 (V vs ECS) = -0.450 (3a), -0.365 (3b), -0.655 (3c), -0.610 (6a), -0.510 (6b), -0.100 (6c)] followed by an irreversible oxidation. The first oxidation is a one-electron process (coulometry), takes place more easily with electron donor phosphorus ligands, and occurs at lower potential for 6 than for 3.
