Dative ligands with more than one donor atom s Metal complexes Metal dihydrogen complexes  Discovered in 1984 by Kubas: M(CO)3(PR3)2(H2) (M = Mo, W; R = Cy, i-Pr) dH-H = 0.84 Å (0.74 Å in free H2); dW-H = 1.75 Å nHH = 2690 cm-1; nHD = 2360 cm-1 dHH = -4.21 (24 Hz wide), dHD = -4.21 (8 Hz wide, 1:1:1 triplet, JHD = 33 Hz, JHD (HD gas) = 43 Hz)  Bonding Good p acceptors (CO, NO) are effective in stabilizing the H2 ligand. Reference: Kubas, G. J. et al. J. Am. Chem. Soc. 1984, 106, 451 2 Complexes of Anionic, Multiple-Carbon Ligands Discovery of ferrocene  1948: Miller, Tebboth, Tremain report that olefins in the presence of Fe salts form FeC10H10  1951: Keally, Pauson, and Miller oxidized C5H5MgBr with FeCl3:  Wilkinson/Woodward (Harvard) and Fischer (Munich) report the correct structure: Fe(h5-C5H5)2  1973 Nobel prize Geoffrey Wilkinson and Ernst Otto Fischer on sandwich compounds 4 Sandwich complexes  They usually follow the 18 e rule  1st row TMs: electron counts from 15 to 20 are known because of the favorable metallocene structure  18 e rule does not apply to lanthanides and actinides 5 Synthesis of metallocenes 6 Cyclopentadienyl (Cp) complexes: orbitals in Cp- Fe Bonding is covalent, there is very little charge separation. Cp: orbital combinations for two ligands Metallocenes, MCp2 HOMO of FeCp2, dz2 (nonbonding) Most important interaction: e1g C-C bond in Cp is 1.44 Ǻ (C6H6, 1.35 Ǻ); H atoms of Cp are bent downwards. Reactivity Electrophilic aromatic substitution: faster than for benzene Reactions of paramagnetic metallocenes Uranocene: Streitwieser, 1968 U-C: 2.647(10); C-C: 1.392(13) Å K. N. Raymond et al. Inorg. Chem. 1972, 11, 1083 COT2- vs. benzene COT2- HOMO Benzene LUMO d bonding in uranocene UCl4 + 2 K2C8H8 U(g) + 2 C8H8 e2u* THF MVS U e3u e2u e2u • UV-PES studies show that bonding in uranocene has 5f and 6d contributions. • e2u interaction shown can only occur via f orbitals. C. Elschenbroich; A. Salzer Organometallics, 2nd ed., VCH, Weinheim, 1992, p. 363