M-85 1 J. Chem. Thermodyytramics 1978, 10, 309-320
The thermochemistry compounds HENRY A. SKINNER University of Manchester,
of organometallic
Manchester
Ml3
9PL, U.K.
Being the second ROSSINI
LECTURE
delivered at the FIFTH INTERNATIONAL CONFERENCE ON CHEMICAL THERMODYNAMICS Under the Commission on Thermochemistry and Thermodynamics International Union of Pure and Applied Chemistry Ronneby, Sweden 25 August 1977
of the
1. hltroductio!l
Organometallic chemistry is one of the growth areas of chemical investigation at the present time, and has been so for the past two decades. Due mainly to the intensive efforts of inorganic preparative chemists, numerous new compounds, in particular of the transition metals, have been isolated and investigated in respect of their molecular structures and characteristic spectra. The thermochemist is now presented with an area for investigation almost unexplored, challenging his technical skills, and beginning to be met. Readers of the Bulletin of Chemical Thermodynamics will certainly have noticed the increasing size of the Index in recent years, no small part of which has been due to the number of entries classified as “organometallic compounds”. It is pertinent to recall that the very thorough compilation of thermochemical data, published by Bichowsky and Rossini’r) in 1936, made reference to five compounds only which might be classified as “organometallic” in character.
2. Types of organometallic compounds It is convenient to begin by listing the types of organometallic compounds for which thermochemical data have been determined, or are now becoming available. (1) METAL
ALKYLS
Berthelot”) reported measurements of the energy of combustion of dimethyl- and diethylmercury in 1899, but no data of real value appeared until after the end of World War II. By the mid-1960’s, enthalpies of formation had been determined for several OO21-9614/78/0401-0309 19
$02+OlO.
8 1978 Academic Press Inc. (London)
Ltd.
310
H. A.
SKINNER
alkyl and aryl compounds of metals from Groups IIB (Zn, Cd, Hg), IIIB (Ga, In), IVB (Ge, Sn, Pb), and VB (As, Sb, Bi) of the Periodic Table. At this time, the synthesis of alkyl derivatives of the transition metals had not been achieved, and indeed was predicted to be most improbable. (3) This no doubt induced greater effort, and alkyl derivatives of several transition metals (e.g. Ti, Zr, Hf, Ta, W, Re) have been obtained,(4,‘) reviving interest in this particular area of thermochemistry concerned with the strength of metal-carbon o-bonds. (2) METAL
CARBENES
The carbenes of certain transition metals are important bring about the catalytic metathesis of olefins, e.g.
because of their ability to
b + f\&-*/d g’ No thermochemical (3) METAL
OLEFIN,
M-C ab = I I fg C-C de
‘4 =Y
+
II
A f g
’ e
A d
e
(1)
data on these compounds have yet been reported. DIENE
AND
Thermal studies have been made on Ni, Ir, and on di-ene complexes (** ‘) Pd, Fe, MO, and Cr. Enthalpies of heptatriene tricarbonyls of Cr, MO, carbonyl.(gy lo) (4) METAL