The reaction of phosphines with [Fe2(CO)4L2(η5: η′5-C16H16)]2+[L = CO or P(OPh)3]; cyclopropane ring-opening of the bicyclo[5.1.0]octadienyl groups, and the X-ray crystal structure of [Fe2(CO)6{η4:η′4-C16H16(PPh3)2}][PF6]2·0.5C6H5Me

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Abstract
Tributylphosphine and [Fe2(CO)4L2(η5:η′5-C16H16)][PF6]2(1; L = CO) form the symmetrical bis(phosphonium)salt [Fe2(CO)6{η4:η′4-C16H16(PBun 3)2}][PF6]2(2) in which one phosphine ligand has added to the terminal carbon atom of each of the two dienyl units of the bis(bicyclo[5.1.0]octadienyl) carbon skeleton of (1; L = CO). By contrast, PPh3 and (1; L = CO) yield [Fe2(CO)6{η4:η′4-C16H16(PPh3)2}][PF6]2(3), X-ray studies of which show that the dication comprises two open C7 rings joined by a trans ethylenic bridge of four coplanar carbon atoms, and that the two phosphine ligands are bonded to the two carbon atoms adjacent to the bridgehead of one C7 ring. The remaining carbon atoms of this ring are η4-bonded to an Fe(CO)3 group. In the other C7 ring, however, four atoms adjacent to the bridgehead are η4-bonded to another Fe(CO)3 group while the other two atoms form an ethylenic moiety not bonded to the metal. The complex crystallises in the monoclinic space group P21/c, and the asymmetric unit comprises two molecules of the dication, four [PF6]– counter ions, and two half-molecules of solvent (toluene), one of which is disordered. The structure has been refined to R= 0.142 for 6 436 reflections [l 2.0σ(l)]. The high R value is a consequence of poor crystal quality: of 22 019 unique reflections measured, 15 583 were rejected. Cyclopropane ring opening also occurs on reacting [1; L = P(OPh)3] with PBun 3 or PPh3; the hydrocarbon ligand of the resulting complex [Fe2(CO)4{P(OPh)3}2(η4:η′5-C16H16L′)][PF6]2(4; L′= PBun 3 or PPh3) is related to that of (3). NaBH4 and (2) react to give [Fe2(CO)6(η4:η′4-C16H18)] but (3) is reduced to [Fe2(CO)6(η4:η′4-C16H16)](5), a complex of trans-1,2-di(cycloheptatrienyl)ethylene.

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