Arsenic cyclopentadienyl complexes

In summary, there are quite a number of interesting cyclopentadienyl complexes with pendant arsenic ligands. However, all this has been found by a single... 

There is a recent review of two-coordinate phosphorus complexes.306 Malisch et a/.307 observed the reversible reaction (86), in which a metal-arsenic(III) double bond is formed, i.e. the M—As a bond is augmented by the arsenic lone pair to form a n bond system (since the cyclopentadienyl coligand is not coplanar with the M=As, the arsenic double bond is isolated). Complex (58) undergoes reactions typical of double bond molecules (Scheme 14). Phosphorus analogues have also been prepared (Scheme 15) the crystal structure of product (c) in Scheme 15 has been solved (59a). The d(W—P) of 2.181 A is shorter than the predicted rf(W=P) of 2.26 A, and the trigonal planar coordination of phosphorus indicates sp2 hybridization.308... 

The first cyclopentadienyl n complexes of phosphorus, arsenic, and antimony have been characterized only recently. The salt-like species LXXXV-LXXXVII containing a cationic n complex are prepared via halide ion abstraction from pentamethylcyclopentadienyl element halides according to Eq. (47) (248-250). 

The cyclopentadienyl reactions have been illustrated for early as well as late transition metals and also the actinides. It is remarkable that the reactions are very similar across the entire group. This methodology results often in sandwich-type complexes of the Et units and has been found successful for both phosphorus and arsenic, but only one example has been reported for antimony. There are no reports of bismuth metal reacting with cyclopentadienyl metal fragments. Neither Sb nor Bi readily form the soluble E4 species as do P and As, and so their reactivities may be limited by solubility factors (Table XLI). 

Phosphorus, arsenic, antimony, and bismuth ligands have been discussed in CCC (1987).153 Complexes containing bonds between scandium, yttrium, and phosphorus or arsenic have been reviewed,154 as have complexes with neutral phosphorus ligands.155 Many of the complexes described in these reviews contain organic substituents such as cyclopentadienyl or alkyl groups. 

This review covers the chemistry of cyclopentadienylmetal complexes, in which the cyclopentadienyl ligand bears a sidearm which includes a phosphorus, arsenic, or sulfur ligand. The pendant ligand has to be separated from the cyclopentadienyl part, that is. 

Organometallic compounds are those in which there is a metal-carbon bond. According to this definition, in the case of transition metals, this group of compounds includes not only metal carbonyls, olefin complexes, cyclopentadienyl, and other 7r-complexes, but also cyanide and fulminate compounds. Certain difficulties arise in defining the metal of the main group elements. Usually, organometallic compounds are comprised not only of compounds of typical metals, but also of metalloids such as boron, silicon, phosphorus, arsenic, selenium, etc. In compounds of metals as well as in those of metalloids, the bond is generally polarized as follows C. Consequently, the... 

Half-sandwich complexes of cobalt with intramolecular phosphorous coordination have been known for the cobalt atoms in oxidation state - -l and - -ll (see Sections 7.01.3.3 and 7.01.3.4). Butenschon has published a comprehensive review recently on cyclopentadienyl metal complexes bearing pendant phosphorous arsenic and sulphur ligands. Intramolecular coordination to the cobalt center via a substituted Cp ring also oecurred in a rare reaction which combined C-H and C-F activation at the same time, thus leading to the coupling between a pentafluorophenyl ring and a pentamethylcyclopentadienyl ring (see Scheme 10 above). 

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