SYNTHESIS AND CHARACTERIZATION OF THE HOMOLEPTIC ARYLOXIDES [M(O(2,4,6-T-BU3C6H2))2]2 (M = MN, FE), THE ADDUCTS [MN(OCPH3)2(PY)2] AND [FE(OCPH3)2(THF)2], AND THE MIXED COMPLEX [FE(N(SIME3)2)(MU-O(2,4,6-T-BU3C6H2))]2 - EVIDENCE FOR PRIMARILY IONIC M-O BONDING

The characterization of several aryloxide and alkoxide derivatives of manganese and iron is reported. They were synthesized by treatment of the amides [M{N(SiMe3)2}2]2 (M = Mn, Fe) with the appropriate alcohol or phenol, in the presence or absence of donor molecules, to give the title compounds. Thus, the reaction of [M{N(SiMe3)2}2]2 (M = Mn, Fe) with 2 equiv of HOMes* (Mes* = 2,4,6-t-Bu3C6H2) gave [Mn(OMes*)2]2 (1) or [Fe(OMes*)2]2 (2). The intermediate species [Fe{N(SiMe3)2}(mu-OMes*)]2 (3) was isolated by using 1 equiv of HOMes*. The base adducts Mn(OCPh3)2(py)2 (4) (py = pyridine) and Fe(OCPh3)2(THF)2 (5) were isolated by treatment of the amide with 2 equiv of HOCPh3 in the presence of the base. The X-ray crystal structures of 1-3 show them to be dimers with aryloxide bridging. They were further characterized by IR spectroscopy. Variable-temperature H-1 NMR spectroscopy shows that the bridging is quite strong and in the case of 2 is > 15 kcal mol-1. The structures of 4 and 5 have very distorted 4-fold coordination at the metals. In all compounds the M-O bonding appears to be primarily ionic with little evidence for a strong M-O pi interaction. Crystal data with Mo K-alpha (lambda = 0.71069 angstrom) at 130 K: 1, a = 14.201 (6) angstrom, b = 28.677 (11) angstrom, c = 18.515 (8) angstrom, beta = 103.30 (3)-degrees, Z = 4, space group P2(1)/c, 6851 data with I > 2-sigma-(I), (R) = 0.07; 2, a = 14.343 (6) angstrom, b = 27.110 (9)-degrees, c = 21.121 (8) angstrom, beta = 101.51 (3)-degrees, Z = 4, space group P2(1)/c, 5035 data with I > 2.5-sigma-(I), R = 0.77; 3, a = 10.194 (3) angstrom, b = 12.376 (6) angstrom, c = 12.558 (3) angstrom, alpha = 74.73 (3)-degrees, beta = 65.93 (2)-degrees, gamma = 84.61 (3)-degrees, Z = 1 (dimer), space group P1BAR, 5308 data with I > 2-sigma-(I), R = 0.040; 4, a = 9.613 (3) angstrom, b = 10.614 (3) angstrom, c = 21.543 (5) angstrom, alpha = 79.88 (2)-degrees, beta = 78.70 (2)-degrees, gamma = 62.86 (2)-degrees, Z = 2, space group P1BAR, 4103 data with I > 2-sigma-(I), R = 0.077; 5, a = 19.078 (4) angstrom, b = 9.562 (3) angstrom, c = 23.454 (3) angstrom, beta = 119.06 (1)-degrees, Z = 4, space group C2/c, 2936 data with I > 3 sigma(I), R = 0.039.