Carbonylmetallates--A Special Family of Nucleophiles in Aromatic and Vinylic Substitution Reactions.

Carbonylmetallates, [M(CO)(n)L](-), anionic transition-metal carbonyl complexes, represent a large family of metal-centered nucleophiles, and studying carbonylmetallates allows us to understand the differences in the behavior of the metal-centered complexes versus heteroatom-based nucleophiles. The mechanisms of carbonylmetallate reactions with aryl- and alkenyl halides have been examined by employing radical and, especially, carbanion trapping techniques. Carbonylmetallates show a marked preference for halogenophilic attack, and nucleophilic substitution with carbonylmetallates is often not a direct process, but proceeds through the initial attack at halogen with subsequent coupling of carbanion and HalM(CO)(n)L intermediates.

A halogenophilic pathway in the reactions of transition metal carbonyl anions with [(η⁶-iodobenzene)Cr(CO)₃].

The paper provides the first example of formal nucleophilic substitution by the halogenophilic pathway in Cr(CO)3 complexes of haloarenes with metal carbonyl anions. All metal carbonyl anions examined attack [(η(6)-iodobenzene)Cr(CO)3] at halogen, which is shown by aryl carbanion scavenging with t-BuOH. The reaction with K[CpFe(CO)2] gives only the dehalogenated arene, but the reaction with K[Cp*Fe(CO)2] (Cp* = η(5)-C5Me5) results in nucleophilic substitution to give [(η(6)-C6H5FeCp*(CO)2)Cr(CO)3].

Dualism of Ion-Pairing Effects in Nucleophilic Vinylic Substitution with Transition-Metal Carbonyl Anions.

Ion pairing with cations has a marked but nonuniform effect on the chemistry of carbonylmetalate anions and can either inhibit or facilitate their reactions. A study of the effect of cation-solvating agents ([18]crown-6, hexamethylphosphoramide) on the reactions of carbonylmetalates [Na(K)][M(CO) L] with vinyl halides activated with strong electron-withdrawing groups, which at the same time could serve as hard donor centers for sodium or potassium cations is presented. The addition of a cation-solvating agent to the solution in THF produced a sharp drop in the rate of the reactions of Na[Re(CO) ] or K[Mn(CO) ] with the vinyl chlorides studied; the effect (k (THF)/k (THF+[18]crown-6)) increased along the series: PhCClC(CN) (4)<(Z)-PhC(CN)CHCl (17) View Article and Find Full Text PDF

Radical-chain oxidative addition mechanism for the reaction of an [Re(CO)5]- anion with α-bromostilbene.

E-α-Bromostilbene spontaneously reacts with Na[Re(CO)(5)] at 22 °C in THF to give Na[ReBr(CO)(4){Z-C(Ph)=CHPh}] and Na[Re(2)(CO)(9){Z-C(Ph)=CHPh}] as the main products. Z-α-Bromostilbene is less reactive, but gives the same products. The reaction is stimulated by visible light or a source of solvated electrons (NaK(2.

Lariat ethers with fluoroaryl side-arms: a study of CFmetal cation interaction in the complexes of N-(o-fluoroaryl)azacrown ethers.

New lariat ethers, N-(o-fluorophenyl)aza-15-crown-5 (F-A15C5) and N,N'-bis(o-fluorophenyl)diaza-18-crown-6 (F(2)-A(2)18C6), were prepared by the N-arylation of the corresponding azacrown ethers. The interaction of the ligands with metal cations was studied in solution by (1)H and (19)F NMR (in acetone-d(6)) and UV spectroscopy (MeOH) confirming the formation of complexes of F(2)-A(2)18C6 with K(+), Na(+), Ag(+), Ba(2+), Pb(2+) and of F-A15C5 with Na(+) and giving evidence of CFmetal cation interaction. Cation binding constants (beta, evaluated by UV titration method), demonstrate that F-A15C5 and F(2)-A(2)18C6 form more stable complexes than their fluorine-free analogs.