Organometallic compounds cyclopentadienyl complexe

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

The chemistry of rhenium(I) is dominated by organometallic compounds which are not covered by this review. Thus, cyclopentadienyl and related compounds, where the organometallic part of the molecule dominate the properties will generally not be considered. Nevertheless, compounds with carbonyl or isocyanide co-ligands will be treated when they can be regarded as constituents of a typical coordination compound or the compounds are of fundamental interest in a radiopharmaceutical context such as the hexakis(isocyanide)rhenium(I) cations. For the same reason a separate section has been included which gives a brief summary of recent attempts to develop synthetic routes to tiicarbonylrhenium(I) complexes for nuclear medical applications. 

Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds, 18, 151 13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds, 12, 135 Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, I, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365... 

Optically active organometallic compounds in which the transition metal is the center of chirality have been known since 1969, when the first manganese compounds were reported1. In the meantime cyclopentadienyl and carbonyl transition metal complexes with 4, 5 and 6 ligands have been obtained in optically active form for the following types of compounds (Scheme 1) ... 

The cubane-like cluster [ Fe(/X3-S)(NO) 4] (68) is not formally an organometallic compound, but the structural changes observed when it is reduced, and the MO description of its bonding, are relevant to the cyclopentadienyl complexes described above. The nitrosyl complex contains 60 valence electrons, 8 less than [ Fe()U3-S)Cp 4], and is reduced in two consecutive one-electron steps to an isolable monoanion [68] , and to a dianion [68] . 

The 18-electron rule is not obeyed as consistently by these types of organometallic compounds as by the carbonyl and nitrosyl complexes and their derivatives. For example, in addition to ferrocene. M(i7 -C5H5)2 compounds are known for most of the other elements of the first transition series (M = V, Cr. Mn. Co, Ni) and these cannot obey the 18-electron rule. However, only ferrocene shows exceptional thermal stability (stable to 500 °C) and is not oxidized by air. Furthermore, cobaltocene, a 19-electron species, is readily oxidized to the 18-electron cobaltocenium ion, [Co(t7 -CjH5)2J, which reflects much of the thermal stability of ferrocene. Mixed cyclopentadienyl carbonyl complexes are common [(- j -C3H5)V(CO)J, [(tj -CjHj)-Cr(CO)3J2, [(77 -CjH5)Mn(CO)3], [(77- -C3H5)Fe(CO)2)2. [(t, -CjH5)Co(CO)2],... 

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