Reduction–oxidation properties of organotransition-metal complexes. Part 20. Oxidative and thermolytic cyclopropane ring-opening reactions; X-ray crystal structure of [Fe₂(CO)₆(η⁴:η′⁴-C₁₆H₁₈)]

Abstract

I TS Oxidation of [ Fe,( C O ) , ( T ~~: T ~' ~-C , , H ~~) ] (1 ) with ferrocenium hexafluorophosphate results in regioselective cyclopropane ring-opening and the formation of [Fe,(CO),(q5:q'5-Cl,H18)] *+ (2), a derivative of trans-l,2-bis(cycloheptadienyl)ethylene. The same hydrocarbon ligand is formed w h e n (1) is thermolysed to give the insoluble polymer [{Fe,(CO),(p-C0),(~5:~r5-C,,Hl,)},] (3). A n Xray diffraction study has shown that the regio-and stereo-specificity observed in the formation of (2) and (3) derives from the stereochemistry of (1). The molecule (1) as a whole has near t w ofold symmetry, but this is not crystallographically required. T w o ring systems comprising fused cyclopropane and cyclohepta-lr3-diene fragments are joined b y a single bond between the t w o apical cyclopropane atoms. Four atoms of each C, ring are essentially co-planar, giving an 'envelope' conformation to the ring, and are bonded to an Fe(CO), fragment; the remainder of the C, ring is also planar, and incorporates the two C atoms shared with the C, ring and the CH, group. The C, ring folds away from the metal atom, and there are further folds at the junction with the C, ring and again at the apex of the C, ring, all in the same sense. The C, symmetry thus confers an overall S shape on the dimeric species when viewed along the t w o -f o l d axis. Along the Fe Fe vector, b y contrast, the C, rings are seen nearly edgewise and the two C, rings are almost eclipsed. Crystals of [ Fe,( CO),(q4:q4-C16H,8)] (1) are triclinic, space group P i , and the structure has been refined to R 0.043 for 3 468 reflections measured at 293 K. Complex (3) undergoes metal-metal bond cleavage with iodine to yield [Fe,l,(CO)4(qs:~'5-C,6H,8)] ( 4) which may also be prepared from the reaction of (2) and iodide ion. Triphenylphosphine adds to the terminal carbon atoms, adjacent to the CH, groups, of the dienyl units of (2), giving the bis(phosphonium) salt [Fe,(CO),(q4:qr4-C16H18( PPh,),}] [PF,], (5).The stereospecific oxidative dimerisation of [Fe(CO),(q4cot)] (cot = cyclo-octatetraene) gives [Fe,(CQ),(q':?"-C16H,,)]2+ which reacts with [BH,]-to yield [Fe,(C0)6(q4:q'4-C,,H,,)] (1) (Scheme 1). We now report details3 of the oxidation and thermolysis of (I), to yield CFe2(CQ)6(r15:q'5-C16H 18)12 + (2) and [f Fe2(CO),(~-CQ)2(q5:q'5-C 6H s)>n] (3), respectively; an X-ray diffraction study of (1) has shown that the stereochemistry of the rruns-1,2bis(cycloheptadieny1)ethylene ligands of (2) and (3) derives from that of the 8,8'-bi(bicyclo[5. 1 .O]octa-2,4-diene) ligand of (1). The reactions of (2) with iodide ion and with PPh,, and the reaction of (3) with iodine, are also reported. Results and DiscussionThe addition of two equivalents of [Fe(q-C,H,),][PF,] to a solution of [Fe2(CO),(r74:r7'4-C~6H,8)] ( I ) in CH,CI, gave a white precipitate which, on recrystallisation from nitromethanediethyl ether, was characterised as [Fe,(CO),(q ':q"-C,6H1,)'1. ~~ ~ -~ ~~ ~ ~ * fruns-p-[ 2-5-q:2'-5'q-8.8'-Bi( bicycle[ 5.1 .O]octa-2,4-diene) ] -hexacarbon y ldi-ir...

Reduction–oxidation properties of organotransition-metal complexes. Part 22. Stereospecific oxidative cyclopropane ring opening and reductive cyclobutane ring formation in polycyclic hydrocarbon complexes of iron; X-ray crystal structures of [Fe2(CO)6(η5:η′5-C16H16)][PF6]2·CH3NO2and [Fe2(CO)6(η4:η′4-C16H16)]

“…The seven-membered rings consist once more of two approximately planar sections, one C( 5 [Fe(C0)3(q4-C1 gH 16)i: and CFedC0)6(q4 : q"-cl6Hl torsion angle relative to that in (3), to 47(2) [48 (2)]", and hence explain the increase in the 'H n.m.r. coupling constant J(H1H2) of (4) (4.5 Hz).…”