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Outstation, Hamburg, FRG) for measuring the EXAFS spectra.Registry No. [L4Fe4(M-0)2(M-OH)4]I4-3H20, 123567-48-6; [L4Fe4-(µ-0)2(µ-0 )4]( 04)4•3 20, 123567-50-0; [L2Fe2(acac)2^-0)]-(C104)2, 118486-84-3; LFeClj, 86823-88-3. Supplementary Material Available; Tables of complete crystallographic data, bond distances and angles, and thermal parameters (5 pages); a listing of structure factor amplitudes (43 pages). Ordering information is given on any current masthead page.

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The tantalum(II1) $-arene complexes (V~-CBR~)T~(DIPP)~C~ (DIPP = 2,&diisopropyl phenoxide) undergo facile one-electron reductions to afford the paramagnetic Ta(I1) arenes ( T~-C~~) T~( D I P P ) , .Thus, (&C& )Ta(DIPP)2Cl (l), itself prepared by the cyclotrimerization of E t C e E t , reacts with excess NaHg from the three-electron reduction of Ta(DIPP)2C13(OEtJ in the presence of E t C e E t . Similarly, ($-CeMee)Ta(DIPP)2 (4) is prepared upon reducing (tle-CeMe6)Ta(DIPP)2C1 (2) with excess NaHg. ($-C&tB)Ta(DIPP)2 (3) undergoes oneelectron oxidative addition reactions with CH2C12 to regenerate 1, with allyl bromide to afford ($-C6Eb)Ta(DIPP)2Br (5), and with CH3CH21 to provide (qe-C6EtJI'a(DIPP),I (7). ($-C,E )Ta(DIPP)2 (3) crystallizes in the monoclinic space group R 1 / c , with a = 12.396 (4) A, b of 1.31 g ~m -~. The @-arene ligand in 3 is characterized by a folded or boatlike distortion, with two carbons making a close approach to the metal. The arene also displays a C2, "twist-boat" deformation of the other four arene carbons. Molecular orbital calculations at the extended Hiickel and ab initio level on (q6-CeHe)Ta(OH), are used to investigate the bonding and geometric distortions for these molecules. It is found that the boatlike deformation of the benzene ligand is primarily due to maximization of the overlap between an s hybridized x 2 -y2 orbital at the metal and ?r* on benzene. The peculiar C2 deformation of the remaining four carbon atoms in the benzene ligand is tied to rotation of the ML2 unit about the metal-benzene axis. At the ab initio level, a fully optimized structure was found to lie 19.8 kcal/mol lower in energy than one where the benzene ligand was constrained to be planar.to affor 3 the maroon Ta(I1) complex ($-C6Eb)Ta(DIPP)2 (3) in high yield. Alternatively, 3 is prepared = 17.344 (6) 1 , c = 18.622 (4) A, and p = 99.11 (2)O, with V = 3953.3 A3 and 2 = 4 for a calculated density (1) (a) Silverthom, W. E. Adu. Organomet. Chem. 197S, 13,47. (b) Muetterties, E. L.; Bleeke, J. R.; Wucherer, E. J.; Albright, T. A. Chem.13 electrons, these molecules represent extremely electron deficient (q6-arene)ML2-type complexes. Further interest in these species arises since the arene ligand was assembled at the metal center by alkyne cyclization c h e m i s e " and since they represent rare examples of tantalum(I1) or-(8) ($B-Arene)FeL*: (a) Green, M. L. H.; Wong, L. L. J. Chem. SOC., Chem.