Hydrocarbon bridging groups

Air oxidation of coal causes a significant decrease in the concentration of aliphatic bridges as determined by acid-catalyzed transalkylation of coal with phenol. Infrared analysis of the raw and oxidized coals indicate that the hydrocarbon bridges are converted to carbonyl groups. Plausible explanations have been offered for the formation of carbonyl groups from aliphatic bridges. 

Whereas the synthesis of zeolite occurs in nature and in the laboratory under strongly basic conditions (pH 9-11), they are widely used as catalysts in hydrocarbon chemistry under their acidic form. In order to obtain acidic zeolites, the alkali cations (K, Li, Na, Ca, etc.) are first exchanged by NH4+C1 followed by heating which, after release of ammonia, leaves the proton loosely attached to the framework on the Si-O-Al bridging group (Figure 2.19). 

The reactivity of osmium with terminal alkynes can be used to prepare bimetallic complexes. When an osmium hydride reacts with a terminal aUcyne that is part of a ruthenium complex, the product is a Ru-Os bimetallic complex with a hydrocarbon bridge (Scheme 16). Another bimetallic complex, [Cp(PPh3 )20s=C=C=CH-C=C-0s(PPh3)2Cp]+, resulted from the reaction between [CpOs(PPh3)2]+ with HC=CCH(OH)C=CH followed by alumina. The unsaturated C5 bridging group is V-shaped. 

Aliphatic hydrocarbon moieties are present in significant amounts within the Murchison macromolecular material and several pyrolysis studies have indicated that these entities exist within or around the aromatic network as hydroaromatic rings and short alkyl substituents or bridging groups (e.g., Hayatsu et al., 1977 Holtzer and Oro, 1977 Levy et al., 1973). 

A broad variety of aza-oxa coronands is known with ferrocene units bonded as side groups to the macrocycle in various modes. The ferrocene units can be connected by hydrocarbon bridges, 32-35, or by functional groups, 36-38 [80-84]. 

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