Forming Adducts with Unsaturated Hydrocarbons

In Group 14 (IV), carbon serves as a Lewis base in a few of its compounds. In general, saturated ahphatic and aromatic hydrocarbons are stable in the presence of BF, whereas unsaturated ahphatic hydrocarbons, such as propjdene or acetylene, are polymerized. However, some hydrocarbons and their derivatives have been reported to form adducts with BF. Typical examples of adducts with unsaturated hydrocarbons are 1 1 adducts with tetracene and 3,4-benzopyrene (39), and 1 2 BF adducts with a-carotene and lycopene (40). 

Cycloaddition with unsaturated hydrocarbons such as alkenes and alkynes have been explored (68-74). Schrauzer and Mayweg (74) first reported that M(sdt)2 (M = Ni, Pd, Pt) reacts with alkynes and alkenes via cycloaddition to the dithiolene ligand. With alkynes, dithiane is formed via decomposition of the adduct (Scheme 7). 

This unique reactivity was subsequently utilized in the functionalization of unsaturated hydrocarbon substrates with CO (Scheme 39) [285, 286]. In the course of these studies the stereospecific synthesis of a diolato unit was observed via a samarium-mediated CO and CH (alkene) activation. A bridging trans-5,10-dihydroindeno[2,l-a]-5,10-diolate ligand forms terminal Sm-O bonds in [Cp Sm]2(O2C16H10) and its THF adduct. Two molecules of CO are formally inserted into the carbon carbon double bond of l,2-di-2-pyridylethene to form a terminal bisenolate moiety [286] (Table 18). 

Besides facilitating such displacement reactions THF and other solvents aid the reaction of metals with organic compounds. The preparation of unsaturated hydrocarbon-metal adducts is immeasurably more rapid in such ethers. Thus, although lithium and biphenyl react very slowly in diethyl ether to form a 1 1 adduct (several days), the same reaction in THF proceeds momentarily (compare Section II.G). 

No 2 1 adducts could be detected in the complex mixtures produced by interaction of the nitroxide with perfluorinated acetylenes, although they are believed to be formed initially the main reaction paths proposed in the case of perfluorobut-2-yne, which yields the two mono-carbonyl products (43) and (44) as well as perfluorobiacetyl, are presented in Scheme 29. Acetylene itself, stated previously to yield AlV-bistrifluoromethylhydroxyl-amine and unsaturated hydrocarbons, is attacked only slowly at room temperature to give (CF3)2NOH, (CF3),NH, (CF3)2NON(CFs)2, [(CFa)jN-0]2CH-CO O N(CF3)2, and unidentified liquid products but no (CFa),N 0-C0 C0 0 N(CF3)2, the product expected (see p, 226) if any... 

General methods of obtaining functionalized HRs with carboxylic groups include thermal grafting with initiators forming free radicals, or with cationic catalysts of the Friedel-Crafts type. Also included are cationic co-oligomerization of unsaturated hydrocarbons or of some Diels-Alder adducts (obtained from dienic hydrocarbons) with MA or other filodienes with carboxylic functions [155,1561. 

It may be more surprising for a similar reaction to take place with saturated hydrocarbon polymers such as polypropylene (PP) and polyethylene (PE) since the level of unsaturation in these cases is insufficient. It was shown, however, that in such cases binding is achieved in two stages. Most of the adduct is formed during the first minute of processing when the applied shear is... 

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