Organometallic compounds in organic synthesis—part 17

Nucleophilic addition to coordinated cyclic .pi.-hydrocarbons: mechanistic and synthetic studies

“…Our mechanistic studies of Pand N-donor nucleophile addition to coordinated x-hydrocarbons suggest that (1) the mechanism is bimolecular with no initial interaction at the metal; (2) the transition state is usually an early one; (3) nucleophile basicity is important; (4) single electron transfer is not important mechanistically; (5) in the absence of steric effects relative nucleophilic reactivities are electrophile independent and are the same as for addition to free carbonium ions. There may be isolated exceptions to these conclusions, but we believe that such exceptions will prove to be rare.…”

“…39 The kinetically favored addition (fex) to the C6H7 ligand has a much lower AHi value (32 kJ mol-1) than the subsequent iodide substitution process (AH2* = 91 kJ mol-1). In certain cases, such as the reactions of trialkylphosphines with cations Mn(CO)3(?j-C6H6)+ and Mo(CO)3(?j-C7H7)+, where only carbonyl or ^-hydrocarbon displaced products were isolated by others,13,40 (2) [Fe(CO)2(N-0)(C4H4)]PF6; (3) [Ru(C6H6)2](PF6)2; (4) [Cr(CO)3(C7H7)]BF4; (5) [Fe(CO)(NO)(PPh3)(C4H4)]PF6; (6) [Mn(CO)3(C6H6)]PF6.…”

Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

“…104,105 Silyl enol ethers readily react with the (tricarbonyl)ironcomplexed cyclohexadienylium (27) and the 2-phenyl-[1,3]-dithian-2-ylium ion (28), which are positioned below most enol ethers in Figure 8 (Scheme 19). [106][107][108] Highly reactive Co 2 (CO) 6 -complexed propargyl cations (with E in the range of +1 to -1, 16 generated from the corresponding propargyl methyl ethers or acetates by BF 3 •OEt 2 -mediated ionization) have been reported to react with the silyl enol ethers 1b and 9c even at 0 °C in dichloromethane to yield, after aqueous workup, α-substituted ketones. 109 Silyl enol ethers have also been used for the synthesis of α-heteroatom-substituted carbonyl compounds.…”

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

“…A few other electrophiles, not covered by sections A−C above, react with allylsilanes, mostly with unsurprising stereochemical control. Thus the irontricarbonyl cationic complex 874 , the homochiral irontetracarbonyl cationic complex 875 , and the chromiumtricarbonyl complex 876 559 are all attacked anti to the metal (Scheme ).

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