SYNTHESIS OF BIMETALLIC COMPLEXES OF MOLYBDENUM-CONTAINING BIS(ETA-5-CYCLOPENTADIENYL)DIMETHYLSILANE OR BIS(ETA-5-TETRAMETHYLCYCLOPENTADIENYL)DIMETHYLSILANE BRIDGES - CRYSTAL-STRUCTURE OF [(MO(CO)3CL)2-MU-(ETA-5-C5H4)2SIME2]

Reaction of (arene)Mo(CO)3 (arene = xylene, mesitylene) and (C5R4H)2SiMe2 in THF (THF = tetrahydrofuran) at room temperature gives the bimetallic complexes [(MO(CO)3H)2(mu-(eta5-C5R4)2SiMe2)] (R = H (2), Me (2*)). From 2 or 2*, other dimetallic complexes of molybdenum are obtained in high yields. Reaction of 2 with aqueous H2O2 leads to the dimeric carbonyl [(Mo(CO)3)2(mu-(eta5-C5H4)2SiMe2)](Mo-Mo) (3). Complex 2 reacts with NaH to give the anion [(Mo(CO)3)2(mu-(eta5-C5H4)2SiMe2)]2- isolated as its sodium (4) or tetrabutylammonium (5) salt. Reaction of 4 with p-CH3C6H4SO2N(NO)CH3 (Diazald) leads to the nitrosyl derivative [(Mo(CO)2(NO))2(mu-(eta5-C5H4)2SiMe2)] (6), whose oxidation with PCl5, Br2, or I2 gives the halo complexes [(MoX2(NO))2(mu-(eta5-C5H4)2SiMe2)] (X = Cl (7), Br (8), I (9)), respectively. Complexes 2 and 2* are easily transformed into the halides [(Mo(CO)3Cl)2(mu-(eta5-C5R4)2SiMe2)] (R = H (10), Me (10*)) when dissolved in CCl4 and can be also oxidized by PCl5 to the tetrahides [(MoCl4)2(mu-(eta5-C5R4)2SiMe2)] (R = H (11), Me (11*)). The variable-temperature H-1 NMR spectra of complexes 7-9 in solution support an 18e structure with two bridging and two terminal halides with fast interchange at room temperature (H-1 NMR scale) between cis and trans isomers through a 16e intermediate. The solid-state structure of 10 has been determined by a single-crystal X-ray analysis. It crystallizes in the triclinic space group P1BAR with Z = 2 in an unit cell of dimensions a = 7.934(3) angstrom, b = 12.305(3) angstrom, c = 13.166(3) angstrom, alpha = 112.32(1)-degrees, beta = 105.48(1)-beta, and gamma = 90.34(1)-degrees. The structure has been solved from diffractometer data by a combination of heavy atom, direct methods, and Fourier synthesis and refined by full-matrix least squares on the basis of the 4493 observed reflections to R = 0.037 and R(w) = 0.055. The coordination around the molybdenum atoms is ''four-legged piano stool'', all the angles and distances having the usual values for this type of structure. The molybdenum atoms are exo with respect to the Cp-Si-Cp system, allowing the metals to be situated at a very long distance, 6.491 angstrom.