Page 242 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

P1: GJC/GLE P2: GNB Final Pages
Encyclopedia of Physical Science and Technology EN011A-544 July 25, 2001 18:30

Organometallic Chemistry

Robert H. Crabtree
Yale University

I. Main Group Organometallic Compounds
II. Transition Metal Organometallic Compounds

GLOSSARY ligands and have more types of reactions available to them
than do the main group metals.
Back donation Donation by the metal of one or more of
its electron pairs into the ligand. Since an empty ligand
orbital is required to allow this to happen, the ligand I. MAIN GROUP ORGANOMETALLIC
must usually be unsaturated, that is, have double or COMPOUNDS
triple bonds.
Main group metals Metals from groups 1, 2, and 11–15 A. With Metal Carbon Bonds
of Mendeleev’s periodic table, such as Li, Mg, Al, Pb.
We will look at the main group cases first, the most im-
Organometallic compound A compound containing a
portant organometallic derivatives of which are the alkyls,
metal-carbon bond.
such as LiMe, MeMgBr, PbEt 4 , and similar species (Me =
Transition metals Metals from groups 3–10 of
methyl, CH 3 ;Et = ethyl, C 2 H 5 ). They are usually prepared
Mendeleev’s periodic table, such as Ti, Fe, W, Pt.
either by treating an alkyl halide with the metal, or by the
reaction of a metal halide with an alkylating agent, often
an organometallic compound such as LiMe.
ORGANOMETALLIC CHEMISTRY is the study of
substances that contain an organic compound or frag- MeI + Li = LiMe + LiI (1)
ment bound to a metal atom or ion by a metal-carbon
LiMe + CuCl = LiCuMe 2 + LiCl (2)
(M–C) bond. By tradition, compounds containing a metal-
hydrogen (M–H) bond are also included in organometallic The most electropositive metals, such as Na and K, tend
chemistry. In certain non-English-speaking nations, such to form ionic organometallic species, and therefore the
as Russia, the scope of the subject is extended beyond the best known are ones in which the anion of the organic
metals and is called “organo-element chemistry.” fragment is unusually stable because the negative charge
Organometallic compounds behave somewhat differ- is delocalized over many atoms of the organic anion. For
−
ently depending on the type of metal involved. The main example, Na[Ph 2 CO] contains the [Ph 2 CO] radical an-
group metals are groups 1, 2, and 11 12, and the heavier ion; the unpaired electron carrying the negative charge is
elements of 13–15, and the transition metals are groups delocalized over the whole Ph 2 CO molecule. There is no
3–10. The transition metals can bind a wider range of M C bond per se, because the compound is ionic. These

529