Sigma metal-carbon

Pi and Sigma Transition Metal Carbon Compounds as Catalysts for the Polymerization of Vinyl Monomers and Olefins... 

Sigma-bond metathesis at hypovalent metal centers Thermodynamically, reaction of H2 with a metal-carbon bond to produce new C—H and M—H bonds is a favorable process. If the metal has a lone pair available, a viable reaction pathway is initial oxidative addition of H2 to form a metal alkyl dihydride, followed by stepwise reductive elimination (the microscopic reverse of oxidative addition) of alkane. On the other hand, hypovalent complexes lack the... 

Flood, Thomas C., Stereochemistry of Reactions of Transition Metal-Carbon Sigma Bonds, 12, 37. Floss, Heinz G., Stereochemistry of Biological Reactions at Proprochiral Centers, 15, 253. Freedman, T. B., Stereochemical Aspects of Vibrational Optical Activity, 17, 113. 

Green) Stereochemistry of Reactions of Transition Metal-Carbon Sigma Bonds 9 35... 

An aliphatic metal-carbon sigma bond, e. g., M-CH3, affords a fairly small C chemical shift, sometimes at negative d values. The relatively rare r allyl derivative, PdCl(q allyl)(PHOX), 61 [61], which is related to allylic alkylation chemistry, shows... 

Metal-Halogen Counpounds. One of the few examples of an olefin insertion into a metal-halogen compound has been reported by Tsuji. The reaction, which also supports the idea that sigma-bonded metal-carbon compounds are intermediates in the palladium chloride-olefin oxidation reaction, was the addition of carbon monoxide to the ethylene palladium chloride 7r-complex in nonaqueous solvents to produce a moderate yield of 3-chloropropionyl chloride (96). 

Equations 11, 12, and 13 constitute a process for the formation of the metal-carbon sigma bond. Carbonyl insertion may now occur as shown in Equation 14. 

Flood has recently published an excellent contribution which includes a review of the stereochemistry of insertion reactions of CO and S02 into metal-carbon sigma bonds. 

Figure 12.2 Some organometallic compounds with sigma-covalent metal-carbon bonds.

---