ORGANOMETALLIC OXIDES - PREPARATION AND PROPERTIES OF THE TETRAHEDRAL (TD) CUBANE [(ETA-C5(CH3)5)CR(MU-3-O)]4 AND COMPARISON WITH THE D2 [(ETA-C5H5)CR(MU-3-O)]4 AND D2D [(ETA-C5H4CH3)CR(MU-3-O)]4

The cubane [(eta-C5(CH3)5)Cr(mu-3-O)]4 (3) was prepared by the reaction between (eta-C5(CH3)5)2Cr (4) and N2O (1:1 molar ratio) in toluene at 80-degrees-C. The structures of 3 and 4 have been determined by X-ray diffraction. 3: M(r) = 813.0, triclinic, P1BAR, a = 10.876 (2) angstrom, b = 10.923 (2) angstrom, c = 18.105 (2) angstrom, alpha = 83.75 (1)-degrees, beta = 83.89 (1)-degrees, gamma = 66.86 (1)-degrees, Z = 2, R = 0.060, R(w) = 0.080 for 4121 observed reflections and 463 refined parameters. 4: M(r) = 322.45, orthorhombic, Ccmm, a = 8.6857 (5) angstrom, b = 14.7842 (8) angstrom, c = 29.2031 (15) angstrom, Z = 8, R = 0.079, R(w) = 0.092 for 816 observed reflections and 100 parameters. 3 has T(d) symmetry, the six Cr-Cr distances averaging 2.834 (2), and the Cr-O distances, 1.945 (5) angstrom. The Cr-O-Cr angles average 93.5 (2); the O-Cr-O angles, 86.4 (2)-degrees. 3 is antiferromagnetic, the magnetic moment increasing from 1.10 at 4.5 to 1.94-mu-B at 84.5 K; at 295 K the moment was 3.74-mu-B. The physical and chemical properties of 3 are compared to those of [(eta-C5H5)Cr(mu-3-O)]4 (1), which has D2 symmetry, and to [(eta-C5H4CH3)Cr(mu-3-O)]4, which has D(2d) symmetry. It is concluded that the eta-C5R5 ring does not influence the [Cr(mu-3-O)]4 core. Whereas 1 lost all eta-C5H5 ligands rapidly on treatment with O2, 3 was essentially inert to it.