NEW COMPOUNDS OF ZIRCONIUM(II) AND HAFNIUM(II) - SYNTHESIS AND X-RAY CRYSTAL-STRUCTURES OF NOVEL DIMERS OF FORMULA M2X4(ETA-6-C6H5PME2)2(PME2PH)2

The reduction of MX4, where M = Hf; X = Br, and M = Zr; X = I, with Na/Hg amalgam, followed by addition of 2 equiv of PMe2Ph, yields the arene complex M2X4(eta-6-C6H5PMe2)2(PMe2Ph)2. An X-ray crystal structure determination indicated that the pyramidal M2X2P2 units are centered over and bound to the phenyl substituent of the phosphine on the adjacent metal center. Crystallographic parameters are as follows. Hf2Br4(eta-6-C6H5PMe2)2(PMe2Ph)2 (1): triclinic space group P1; a = 9.090 (4), b = 13.823 (3), c = 15.524 (6) angstrom, alpha = 101.50 (3)-degrees, beta = 93.18 (4)-degrees, V = 1890 (1) angstrom-3, and d(calc) = 2.160 g/cm3 for two crystallographically independent but essentially identical molecules in the unit cell. The structure was refined to R = 0.0525 and R(w) = 0.0584 with a data/parameter ratio of 8.5. Zr2I4(eta-6-C6H5PMe2)2(PMe2PH)2 (2): monoclinic space group P2(1)/c, a = 13.527 (4), b = 12.599 (2), c = 13.574 (3) angstrom, beta = 119.34 (2)-degrees, V = 2017 (2) angstrom-3, and d(calc) = 2.046 g/cm3 for Z = 2. The structure was refined to R = 0.0606 and R(w) = 0.0769 with a data/parameter ratio of 8.2. Molecular orbital calculations on the model complex ZrI2(PH3)2(C6H6), at the Fenske-Hall level, were conducted to elucidate the bonding between the metal center and arene ring. The calculations indicate that the HOMO is composed of a d(xy) delta-type orbital on the zirconium and a formerly e2-PI* orbital on the arene.