Inorganic Chemistry, Vol.33, No.7, 1292-1296, 1994
Bis(Cyclopentadienyl)Zirconium and Hafnium Macrocyles Containing Siloxane Bridges - Synthesis of ((Eta-5-C5H5)2M(Eta-OSI(C6H5)2O))2 (M=zr, HF) and Crystal-Structure and EHMO Study for M=zr
The reaction of Cp2MMe2 (M = Zr, Hf) with Ph2Si(OH)2 yields the eight-membered ring [Cp2M(mu-OSiPh2O)]2 (M = Zr (1), Hf (2)). 1 crystallizes in the space group P1BAR with a = 10.410(9) angstrom, b = 12.140(6) angstrom, c = 16.318(5) angstrom, alpha = 94.26(3)degrees, beta = 103.42(5)degrees, gamma = 93.16(6)degrees, and Z = 2. The crystal structure reveals that the ring is not planar. The Cp2Zr units are bent 20-degrees out of the Si2O4 Plane to give a "chaise longue conformation; however, in solution the molecule is fluxional on the NMR timescale. The zirconium-oxygen distances of 1.974(2) and 1.983(2) angstrom are significantly longer than those reported in other Zr-O-Si compounds. EHMO calculations suggest that the Zr-O bond order may be rationalized in terms of an in-plane pi-system.