An unusual cyclopentaannulation reaction: Thermolysis of an alpha,beta-unsaturated Fischer carbene complex anchored on a Fe-2(CO)(6)(mu-Se)(2) core

An unusual annulation of-a Fischer carbene complex anchored on a Fe-2(CO)(6)(mu-Se)(2) core is examined. Thermolysis of Fe-2(CO)(6){mu-SeC(Ph)=C(Se)[(OEt)C=Cr(CO)(5)]} in THF yields an unusual annulated product, [Fe-2(CO)(6)Se-2{mu-(CO)(3)Cr(eta(5)-C5H(CH2Ph)(Ph)(OEt))}] (1), as characterized by IR and H-1, C-13, and Se-77 NMR spectroscopies, and its structure has been established by single-crystal X-ray diffraction

Zirconium, hafnium, and tantalum amide silyl complexes: Their preparation and conversion to metallaheterocyclic complexes via gamma-hydrogen abstraction by silyl ligands

New transition metal silyl amide complexes (Me2N)(3)Ta[N(SiMe3)(2)](SiPh2But) (1) and (Me2N)M[N(SiMe3)(2)](2)(SiPh2But) (M = Zr, 2a, and Hf, 2b) were found to undergo gamma-H abstraction by the silyl ligands to give metallaheterocyclic complexes (Me2N)(3)Ta(NSiMe3SiMe2CH2) (3) and {(Me2N)[(Me3Si)(2)N]M(NSiMe3SiMe2CH2)}(2) (M = Zr, 4a, and Hf, 4b), respectively. The conversion of 1 to 3 follows first-order kinetics with DeltaH(double dagger) = 23,6(1.6) kcal/mol and DeltaS(double dagger) = 3(5) eu between 288 and 313 K. The formation of 4a from (Me2N)Zr[N(SiMe3)(2)](2)Cl (5a) and Li(THF)(2)SiPh2Bu1 (6) involves the formation of the intermediate 2a, followed by gamma-H abstraction. Kinetic studies of these consecutive reactions, a second-order reaction to give 2a and then a first-order y-H abstraction to give 4a, were conducted by an analytical method and a numerical method. At 278 K, the rate constants k(1) and k(2) for the two consecufive reactions are 2.17(0.03) x 10(-3) M-1 s(-1) and 5.80(0.15) x 10(-5) s(-1) by the analytical method. The current work is a rare kinetic study of the A + B --> C --> D (+ E) consecutive reactions. Kinetic studies of the formation of a metal laheterocyclic moiety M(NSiMe3SiMe2CH2) have, to our knowledge, not been reported. In addition, gamma-H abstraction by a silyl ligand to give such a metallaheterocyclic moiety is new. Theoretical investigations of the gamma-H abstraction by silyl ligands have been conducted by density functional theory calculations at the Becke3LYP (B3LYP) level, and they revealed that the formation of the metallacyclic complexes through gamma-H abstraction is entropically driven. X-ray crystal structures of (Me2N)(3)Ta[N(SiMe3)(2)](SiPh2But) (1), (Me2N)Zr[N(SiMe3)(2)](2)Cl (5a), and {(Me2N)[(Me3Si)(2)N]M(NSiMe3SiMe2CH2)}(2) (M = Zr, 4a, and Hf, 4b) are also reported

Novel OˆNˆN Pyrazolyl-imine and Imidazolyl-imine Pincer Palladium Complexes as Heck Coupling Catalysts

Five pyrazolyl and imidazolyl compounds, 2,4-di-tert-butyl-6-[2-pyrazol-1-yl-ethylimino-methyl]-phenol (L1), 2,4-di-tert-butyl-6-{[2- (3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L2), 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3), 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L4) and 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L5) were synthesized by condensation of the appropriate 2-hydroxybenzaldehyde and the corresponding alkylamine. Reactions of L1–L5 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] led to in situ deprotonation of the phenolic-OH proton to afford the pincer palladium complexes [Pd(L1)Cl] (1), [Pd(L1)Me] (2), [Pd(L2)Cl] (3), [Pd(L3)Cl] (4),[Pd(L4)Cl] (5) and [Pd(L5)Cl] (6). The tridentate coordination modes of the ligands were confirmed by the solid state structures of 1, 2, 3 and 4.H2O. Complexes 1–6 catalyzed the Heck coupling reactions of iodobenzene and butylacrylate. In addition, complex 4 catalyzed the Heck coupling reaction of butyl acrylate and bromobenzene; giving conversions as high as 70 %.Keywords: Pincer palladium complexes, pyrazolyl-imine, imidazolyl imine, aryl halides, Heck coupling catalyst

Silyl-substituted alkylidenes: preparation of the novel complexes and mechanistic studies of their formation from reactions of alkylidenes with silanes and silyl-to-alkylidyne migration

Alkylidene complexes (Me3SiCH2)(3)Ta(PMe3)=CHSiMe3 (1) and Me3SiCH2Ta(PMe3)(2)(=CHSiMe3)(2) (3a) were found to react with phenylsilanes H2SiR'Ph (R' = Me, Ph) and (PhSiH2)(2)CH2 to give disilyl-substituted alkylidenes (Me3SiCH2)(3) Ta=C(SiMe3)(SiHR'Ph) (2) and novel metallasilacyclobutadiene and metalladisilacyclohexadiene complexes. Silyl-substituted alkylidene complex ((BuCH2)-C-t)(2)W(=O)[=C(Bu-t)(SiPh2But)] (5a) was prepared from the reaction of O-2 with an equilibrium mixture ((BuCH2)-C-t)W(=CHBut)(2)(SiPh2But) (4b) <----> (Bu-t CH2)(2)W(dropCBu(t))(SiPh2But) (4a). Our recent studies of the preparation of these complexes and mechanistic pathways in the formation of these silyl-substituted alkylidene complexes are summarized. (C) 2002 Elsevier Science B.V. All rights reserved

Synthesis and variable coordination modes of a bis-thiophene-appended macrocycle in complex with cobalt(III)

The bis-thiophene appended cyclam derivative L (trans-6,13-dimethyl-6,13-bis(thiophene-3′-ylmethylamino)-1,4,8,11-tetraazacyclotetradecane) has been synthesised, characterised and complexed with Co. The crystal structure of the diprotonated ligand as its cyanoborohydride salt [HL][NCBH] is reported. Variable coordination modes to Co have been identified that find the ligand binding either as a tetradentate (cyclam-like) macrocycle in the structurally characterised complexes trans-[CoLCl]Cl and trans-[CoL(NCBH)(OH)]Cl or as a hexadentate in [CoL]Cl where both functionalised exocyclic amines coordinate in trans coordination sites. In this case, we have found that the structure of the hexadentate coordinated complex [CoL] is significantly tetragonally elongated due to steric effects of the thiophene rings and this also leads to a very large 500 mV anodic shift in the Co redox potential relative to the unsubstituted hexaamine complex of Co