Organometallic Chemistry

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