0000000000309358
AUTHOR
Luciano Canovese
Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-Pyridyl complexes [M(dmtc)(C5H4N-Cn)(L)] (M Pd, Pt; dmtc dimethyldithiocarbamate; n 2,4; L
Abstract A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes [M(dmtc)C 5 H 4 N- C 2 )(L)] (M Pd or Pt; L PMe 3 , PEt 3 or PPh 3 ) and [Pd(dmtc)C 5 H 4 N- C 4 )(L)] (L PMe 3 or PPh 3 ) on organic halides XCH 2 R (X Cl or Br; R CHCH 2 , COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives [M(dmtc)1-CH 2 R)C 5 H 4 N- C 2 (L)] + and [Pd(dmtc)(1-CH 2 R)(C 5 H 4 N- C 4 (L)] + , respectively. The kinetics obey a second-order rate law: rate k 2 [XCH 2 R][Complex]. A similar rate law is observed for the analogous reactions involving 4-dimethyl-aminopyridine (4-dmapy) as the nucleophile. The effects of solvent and leaving group, a…
Mechanism of aminocarbene formation by nucleophilic attack on isocyanide ligands in platinum(II)2-pyrazyl and 4-pyridyl complexes
Abstract The reactions of 2-pyrazyl and 4-pyridyl isocyanide complexes [Pt(CNC 6 H 11 )(C 4 H 3 N 2 - C 2 )(dppe)ClO 4 and [Pt(CNC 6 H 11 )(C 5 H 4 N- C 4 ) (dppe)]ClO 4 ( 1 ) with amines involving the formation of aminocarbene derivatives have been studied kinetically in 1,2-dichloroethane by UV—VIS techniques. The kinetics obey the simple second-order rate law rate = k 2 [ 1 ][amine]. Low activation enthalpies and highly negative activation entropies for the k 2 term are observed. A mechanism is proposed involving direct nucleophilic attack of the amine on the isocyanide carbon with concomitant proton transfer from the amine to the isocyanide nitrogen assisted by the heterocyclic nitrogen…
Organometallic nucleophiles.A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium (II) and platinum (II)
Abstract The reactions of the 2- and 4-pyridyl complexes [MX(C 5 H 4 N C n )(dppe)] and trans -[MX(C 5 H 4 N C n )(PPh 3 ) 2 ] (M Pd, Pt; X Cl, Br; n = 2, 4)- involving halide displacement from the organic halides XCH 2 R (X Cl, Br; R CN, Ph, CH CH 2 ) by the pyridyl nitrogen have been studied kinetically by conductivity in acetone or acetonitrile at 25°C. The kinetic data fit the second-order rate law rate k 2 [XCH 2 R][complex], in agreement with an S N 2 process at saturated carbon. The higher rates are displayed by the 2-pyridylplatinum derivatives with X Br in both the metal complex and the organic halide. The higher nucleophilic power of the 2-pyridyl complexes compare…
Mechanism of oxidative allyl transfer from allylic ammonium cations to palladium(0) α-diimine complexes
Abstract The palladium(0) complex [Pd(η2-fn)(NN′)] (1, fn = fumaronitrile; NN′ = C5H4N-2-CH=NC6H4OME-4) reacts slowly and reversibly with A + CH 2 CH=CH 2 (2a, A = NEt 3 ; 2 b , A = C 5 H 5 N ) to yield the cationic η3-allypalladium(II) derivative [ Pd (η[ 3 - C 3 H 5 )( N N ′)] + (3) the free amine A and fn. The equilibrium constant Ke is (2.6 ± 0.1) × 10−3 for 2a and 1.0 ± 0.4 for 2b. Kinetic studies of these oxidative allyl-transfer reactions show that the rates increase with increasing concentration of 2 and with decreasing concentration of fn. A stepwise mechanism is proposed which involves slow and reversible displacement of fn by 2 to give a labile intermediate [ Pd (η 2 - CH…
Phenylation of cationic allylpalladium(II) complexes by tetraphenylborate anion. A mechanistic study
Abstract The mechanism of the reaction of allyl complexes [Pd(η3-2-R′C3H4)(NN′)]+ (NN′ = α-diimine ligand) wiht BPh4− in the presence of activated olefins (ol), yielding the products [Pd(η2-ol)(NN′)] and PhCH2C(R′)CH2, has been investigated. The results are interpreted in terms of extensive association between the cationic substrate and the BPh4− anion in a tight ion-pair, followed by rate-determining phenyl transfer to the palladium center and fast reductive elimination of allylbenzene.
Isomer Distribution and Interconversion in Cationic Allylpalladium(II) Complexes with 2-(Iminomethyl)pyridine Ligands
The complexes [Pd(η3-allyl)(N-N‘)]ClO4 [allyl = 2-butenyl or 3-methyl-2-butenyl, N-N‘ = C5H3(6-R)N-2-CHNR‘ (R = H, R‘ = Me, CMe3, C6H4OMe-4; R = Me, R‘ = C6H4OMe-4) and C5H4N-2-CH2NMe2] are present in solution with different isomers, the structures of which may be assigned by an 1H NMR criterion based on chemical shift changes of the pyridine H(6) and/or of the allylic methyl protons, as confirmed also by 2D 1H NMR spectra. The isomer distribution depends mainly on the steric requirements of both the allyl and N-N‘ ligands: for [Pd(η3-3-methyl-2-butenyl)(N-N‘)]ClO4 the predominant isomer (ca. 100%) has a structure with the allylic methyl groups cis to the coordinated pyridine nitrogen when…