_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

General survey
elements are rapidly attacked, although Me 2 Hg and the derivatives of the
Group IVB elements are inert. Many (e.g. Me 2 Zn, Me 3 In, Me 3 Sb) are spontaneously
inflammable in air. Kinetic instability to oxidation may be associated
with the presence of empty low-lying orbitals, e.g. Sp in Me 3 In, or of a nonbonding
pair of electrons e.g. Me 3 Sb. In contrast, the Group IVB alkyls possess
neither of these features and behave as saturated compounds.
Most transition metal derivatives too are sensitive to oxygen and it is
customary and often obligatory to handle them under an inert atmosphere of
nitrogen or argon.
1.5.3 Stability to hydrolysis
Hydrolysis of an organometallic compound often involves nucleophilic attack by
water and hence is facilitated by the presence of empty low-lying orbitals on the
metal atom. In agreement with this, the organic derivatives of the elements of
Groups IA and IIA and ofZn, Cd, Al, Ga and In are readily hydrolysed. The rate of
hydrolysis is dependent on the polarity ofthe M-C bond; where this is high (e.g.
Me 3 Al), rapid attack by water occurs, whereas Me 3 B is unaffected by water at
room tempera ture, even though an empty 2p orbital is present on the boron atom.
The alkyls and aryls ofGroup IVB and VB elements, however, are kinetically inert
ta hydrolysis by water. In these compounds the metal atom is surrounded by a
filled shell of eight electrons, so that nucleophilic attack is no longer favoured. The
majority of the neutral organic derivatives of transition elements are inert to
hydrolysis. Organo-lanthanides, however, are extremely susceptible, on account
of the polar character of the bonding, the large size of the central atom and the
presence of many low lying empty orbitals, all of which aid coordination of a
nucleophile.
1.5.4 General features relating to stability; jilled shells of electrons
It is well known that much of carbon chemistry is controlled by kinetic factors; for
example diamond would change spontaneously into graphite and ethyne into
benzene at room tempera ture and atmospheric pressure if thermodynamics were
controlling. In addition, all organic compounds are thermodynamically unstable
to oxidation and exist in the presence of air only because no suitable low energy
oxidation mechanism is available.
This 'kinetic stability' of carbon compounds has a variety of causes, notably the
Juli use of the faur valence orbitals (sp 3 ) in carbon, leading to the common
maximum coordination number of faur (exceptions e.g. Me 4 Li 4 , (Me 3 Al) 2 in
which the coordination number rises to 5-7 are discussed in Chapter 3) and the
high energy of empty antibonding orbitals into which electrons could be donated
in the case of nucleophilic attack.
Expansion of the coordination number above faur commonly occurs in
compounds of silicon and of other main group elements of the 2nd and later
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