FURTHER-STUDIES OF THE REACTIVITY OF CYCLOPENTADIENYL, SUBSTITUTED CYCLOPENTADIENYL AND INDENYL LIGANDS WITH M2CL2(NME2)(4) (M=MO OR W) - CRYSTAL AND MOLECULAR-STRUCTURES OF MO-2(C9H7)(2)(NME2)(4) AND W-2(C5H4ME)(2)(NME2)(4)

Metathetic:reactions employing 1,2-M2Cl2(NMe2)(4) compounds (M = Mo or W) and the sodium or lithium salts of cyclopeptadienyl (Cp), methylcy clopentadienyl, indenyl (C9H7) and bis(methyl)bis(cyclopentadienyl)sil yl, Me2Si(C5H4)(2)(2-), anions carried out in hydrocarbon or ether sol vents have led to the isolation of orange, hydrocarbon-soluble, air-se nsitive crystalline solids of formula 1,2-M2R2(NMe2)(4). In solution t he NMR data are consistent with C-2 symmetry and restricted rotation a bout the M-N bonds. The complexes where R = C5H5 show only one CH reso nance in their H-1 NMR spectra consistent with ring whizzing. The soli d-state and molecular structures of Mo-2(C9H7)(2)(NMe2)(4) and W-2(C5H 4Me)(2)(NMe2)(4) reveal that the indenyl and C5H4Me ligands are eta(3) -bonded to the M=M6+ moiety with three M-C distances within the range 2.35 to 2.52 Angstrom and two distinctly larger ca. 2.75-2.80 Angstrom . The M-M distances, 2.252(1) Angstrom (M = Mo) and 2.345(1) Angstrom (M = W) and M-N distances, 1.96 to 1.99 Angstrom, are similar to those for 1,2-M2R2(NMe2)(4) compounds, where R = alkyl or aryl. The linked Cp complex W-2(C5H4)(2)SiMe2(NMe2)(4) was found to show similar struct ural features although the molecular structure suffered from disorder. The data reported, together with previous results, show that cyclopen tadienyl ligands compete favorably with the NMe2 ligand as sigma(2) pi (3) donors, eta(3)-C-5. The eta(5)-C-5 mode is not favoured (on electr onic grounds) because this would require disruption of the M-M triple bond in the presence of four Me2N sigma(2) pi(2) donors.