Organo-Transition-Metal Compounds

Carbon-13 chemical shifts of transition metal carbonyls [471, 473] decrease as one proceeds down a given group of the periodic table, as demonstrated for the triad Cr(CO)6, Mo(CO)e, and W(CO)e in Table 4.71. Substitution of CO by cyclopentadienide and other organic ligands deshields the carbonyl carbon nuclei. This is exemplified by iron pentacarbonyl (211 ppm) in comparison to cyclopentadienylirondicarbonyl-dimer, which displays one avaraged carbonyl signal ( 240 ppm) at room temperature [488] due to rapid cis-trans isomerization and intramolecular bridged-terminal carbonyl interconversion  

Transition metal compounds with covalent carbon-metal bonds include organo-zinc, organo-cadmium, and organo-mercury compounds. Carbon-13 shifts of the methyl derivatives (Table 4.71) indicate a heavy atom deshielding. Diphenylmercury displays carbon shifts similar to those of phenyllithium and phenylmagnesium bromide (Table 4.53). 

Carbon-13-mercury coupling constants (199Hg with I = 1/2 and 16.8% natural abundance) follow relations known from other carbon couplings. One-bond carbon-mercury 

Three-bond carbon-mercury couplings are larger for transoid in comparison to cisoid coupling routes, as shown for the endo-exo pair of 2-norbornylmercury acetate, and met a 

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The stabilities of the [ML2R2] phosphines increase from Ni to Pt and for Ni" they are only isolable when R is an o-substituted aiyl. Those of Pt", on the other hand, are amongst the most stable cr-bonded organo-transition metal compounds while those of Pd" occupy an intermediate position. 

Organometallic chemistry (see p. 1199) is not particularly extensive even though gold alkyls were amongst the first organo-transition metal compounds to be prepared. Those of Au are the most stable in this group, while Cu and Ag (but not Au ) form complexes, of lower stability, with unsaturated hydrocarbons. 

Optical induction in organo-transition metal compounds and asymmetric catalysis. H. Brunner, Acc. Chem. Res., 1979,12, 250-257 (85). 

It is to be hoped that measurements will be made in the near future which will put more substantial flesh on the skeleton of known bond enthalpy contributions in organo-transition metal compounds, so that a better understanding of the energetics of reactions such as olefin disproportionation (metathesis) and hydroformylation may be achieved. 

Organo-Transition Metal Compounds, Primary Photoprocesses of (Bock and von Gustorf). 

Organo-Transition Metal Compounds Containing Perfluorinated Ligands ... 

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