Randomization‐based statistical inference: A resampling and simulation infrastructure

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Mechanisms of d8 organometallic reactions involving acids and intramolecular assistence by nucleophiles

The most attractive and fundamental interaction between metal centers and organic molecules that could lead to new functionalization at carbon is direct activation of the C-H bonds of hydrocarbons. In particular, transition metal complexes have been used not only in pioneering studies of the synthesis or detection of complexes resulting from C-H activation, but also in cyclometalation chemistry. In most of the reactions reviewed here intramolecular assistance by a nucleophile plays a major role in the mechanism and/or in the stabilization of products, and thus they are relevant also to the development of a better understanding of cyclometalation reactions. This Account summarizes recent research that implicates the occurrence of electrophilic attack at the metal center in reactions leading to metal-electrophile bondin

Phenylpalladium(IV) Chemistry : Selectivity in Reductive Eli mination from Palladium(IV) Complexes and Alkyl Halide Transfer from Palladium(IV) to Palladium(II)

Methyl iodide, benzyl bromide, and benzyl iodide react with PdMePh(bpy) (bpy = 2,2'- bipyridyl) in acetone at 0 °C to form the isolable fuc-triorganopalladium(1V) complexes PdIMez- Ph(bpy) (3) and PdXMePh(CHzPh)(bpy) [X = Br (4), I (5)l. Complex 3 occurs as a mixture of isomers in a cu. 1:l ratio, involving the phenyl group in a position trans either to bpy (3a) or to iodine (3b), while complexes 4 and 5 are obtained as one isomer which, most likely, has the benzyl group trans to the halogen. The selectivity of reductive elimination from a metal bonded to three different groups could be studied for the first time. The complexes undergo facile reductive elimination in (CD3)zCO at 0 °C, in which PdIMezPh(bpy) gives a mixture of ethane and toluene in a 4:l molar ratio together with PdIR(bpy) (R = Ph, Me), whereas PdXMePh- (CHzPh)(bpy) (X = Br, I) gives exclusively toluene and PdX(CHZPh)(bpy). The analogous tmeda complex, PdMePh(tmeda) (tmeda = N,N,N',N'-tetramethylethylenediamine), reacts more slowly than PdMePh(bpy1 with alkyl halides. Methyl iodide reacts cleanly with PdMePh- (tmeda) at 0 °C in (CD3)zC0 to form ethane and PdIPh(tmeda), but the expected palladium(1V) intermediate could not be detected. Benzyl bromide does not react with PdMePh(tmeda) below the decomposition temperature of the latter under these conditions (50 °C, (CD&CO), while benzyl iodide reacts at 40 °C to give a complicated mixture of products of which ethane, diphenylmethane, ethylbenzene, toluene, and PdIR(tmeda) (R = Me, Ph) could be identified. Benzyl iodide reacts with PdMez(tmeda) at -30 °C in (CD3)zCO to form PdIMez(CHzPh)- (tmeda), for which lH NMR spectra showed the benzyl group to be trans to one of the N-donor atoms. However, PdIMez(CHzPh) (tmeda) is unstable and undergoes facile reductive elimination to form ethane and PdI(CH2Ph)(tmeda). Transfer of alkyl and halide groups from palladium- (IV) to palladium(I1) complexes occurs in (CD3)zCO at low temperatures for several reaction systems in which the resulting palladium(1V) complex is known to be more stable than the palladium(1V) reagent. There is a strong preference for benzyl group transfer from PdXMePh- (CHZPh)(bpy) to PdMez(L2) (X = Br, I; LZ = bpy, phen). The mechanism of the transfer reactions is discussed in terms of the mechanism suggested earlier for alkyl halide transfer from palladium(1V) to platinum(II), palladium(I1) to palladium(O), cobalt(II1) to cobalt(I), and rhodium(II1) to rhodium(1). These reaction systems involve nucleophilic attack by the lower oxidation state reagent at an alkyl group attached to the higher oxidation state reagent

Carbon-Oxygen Bond Formation at Metal(IV) Centers: Reactvity of Palladium(II) and Platinum(II) Complexes of the [2,6-(Dimethylaminomethyl)phenyl-N,C,N]- (Pincer) Ligand Towards Iodomethane and Dibenzoyl Peroxide; Structural Studies of M(II) and M(IV) Complexes

The presence of the [2,6-(dimethylaminomethyl)phenyl-N,C,N]- (pincer) ligand (NCN) in platinum(II) complexes has been used to generate stable organoplatinum(IV) complexes that model possible intermediates and reactivity in metal-catalyzed C-O bond formation processes. The complexes M(O2CPh)(NCN) [M ) Pd (1), Pt (2)] were obtained by metathesis reactions from the chloro analogues, and although 1 does not react with dibenzoyl peroxide, 2 does so to form Pt(O2CPh)3(NCN) (3) as a model intermediate for the acetoxylation of arenes by acetic acid in the presence of palladium(II) acetate and an oxidizing agent. The complex Pt(O2CPh)(NCN) (2) reacts with iodomethane in a complex manner to form PtI- (NCN) (6) and cis-Pt(O2CPh)2Me(NCN) (7). Complex 7 decomposes to form Pt(O2CPh)(NCN) (2) and MeO2CPh, probably via benzoate dissociation followed by nucleophilic attack by the benzoate ion at the PtIV-Me carbon atom. The Pd(II) analogue Pd(O2CPh)(NCN) (1) reacts with MeI to give PdI(NCN) (8) and MeO2CPh, for which the potential intermediacy of Pd- (IV) species could not confirmed by 1H NMR spectroscopy. The complex PtTol(NCN) (4) (Tol ) 4-tolyl) reacts with (PhCO2)2 to form cis-Pt(O2CPh)2Tol(NCN) (5), but, unlike the PtIVMe analogue 7, the PtIVTol complex 5 does not undergo facile C-O bond formation. X-ray structural studies of the isostructural square-planar complexes M(O2CPh)(NCN) (1, 2) and of the octahedral Pt(IV) complexes as solvates 3.1/2Me2CO, 5.Me2CO, and 7.Me2CO.H2O are reported. Complexes 5 and 7 have cis-PtC2 and cis-Pt(O2CPh)2 configurations

Synthesis and reactivity of poly(pyrazol-1-yl) borate derivatives of cyclopalladation systems,including structural studies of Pd{2-CH2C6H4P(o-tolyl)2-C,P}{(pz)3BH-N,N'} andPd(C6H4C5H4NC2,N'){(pz)3BH-N,N'}

The cyclopalladated complexes Pd{2-CH{2}C{6}H{4}P(o-tol){2}}{(pz){n}BH{4}{-}{n}} and Pd(C{6}H{4}C{5}H{4}N-C}2{, N'){(pz){n}BH{4}{-}{n}} [n=2, 3; pz=pyrazol-1-yl] have been synthesised from the corresponding halide bridged cyclometallated dimers; the crystal structures of the complexes for which n=3 have been determined. The complexes Pd{2-CH{2}C{6}H{4}P(o-tol){2}}{(pz){n}BH{4}{-}{n}} (n=2, 3) and [Pd{2-CH{2}C{6}H{4}P(o-tol){2}}(@m-O{2}CMe)]{2} are unreactive towards oxidation by alkyl halides, iodobenzene and 4-bromoanisole

Selectivity in reductive elimination and organohalide transfer from methyl(aryl)benzyl-palladium(IV) complexes of bidentate nitrogen donor ligands, PdBrMe(Ar)CH2Ph)(L2)

Oxidative addition of iodoarenes to bis(dibenzylideneacetone)palladium(0) in the presence of N, N,N',N'-tetramethylethylenediamine (tmeda) affords PdIAr(tmeda) (Ar = 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 4-Me(O)CC{6}H{4}, 4-O{2}NC{6}H{4}, 3-MeOC{6}H{4}) in high yield. Some of these complexes (Ar = 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 3-MeOC{6}H{4}) react with LiMe to form PdMeAr(tmeda), and the methyl(aryl)palladium(II) complexes react with 2,2'-bipyridyl (bpy) or 1,10-phenanthroline (phen) to afford PdMeAr(L{2}); PdMePh(phen) may be obtained similarly. All of the diorganopalladium(II) complexes of bpy and phen react with benzyl bromide to form PdBrMeAr(CH{2}Ph)(L{2}) but a complex could not be isolated for Ar = 3-MeOC{6}H{4}, L{2} = bpy. The isolated palladium(IV) complexes react with PdMe{2}(bpy) at -20}o{C in (CD{3}){2}CO to selectively transfer benzyl bromide to give PdMeAr(L{2}) and PdBrMe{2}(CH{2}Ph)(bpy) respectively. The complexes PdBrMeAr(CH{2}Ph)(bpy) (Ar = Ph, 4-MeC{6}H{4}, 4-MeOC{6}H{4}) undergo selective reductive elimination of Ar-Me in CDCl{3} to form PdBr(CH{2}Ph)(L{2}), but PdBrMeAr(CH{2}Ph)(phen) (Ar = Ph, 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 3-MeOC{6}H{4}) give mixtures of PdBr(CH{2}Ph)(phen) and Me-Ar together with lesser amounts of PdBrMe(phen) and Ar-CH{2}Ph (ca. 10-20%)

Selectivity in reductive elimination from dialkyl(aryl)palladium(IV) complexes, and the observation of benzyl halide transfer from palladium(IV) to palladium(II) : The X-ray structure of methyl(phenyl)(2,2'-bipyridyl)-palladium(II)

The first arylpalladium(IV) complexes, [PdXMePhR(bpy)] (bpy = 2,2'-bipyridyl), have been isolated upon oxidative addition of methyl iodide or benzyl bromide to the organopalladium(II) reagent [PdMePh(bpy)]. These dialkyl(aryl)palladium(IV) complexes undergo reductive elimination in solution at ca. 0°C: [PdBrMePh(CH2Ph)(bpy)] decomposes quantitatively into [PdBr(CH2Ph)(bpy)] and toluene whereas [PdIMe2Ph(bpy)] gives ethane and toluene in 4:1 ratio together with the corresponding complexes [PdIR(bpy)] (R = Me or Ph). The reaction of methyl iodide with [PdMePh(tmeda)] at 0°c yields ethane and [PdIPh(tmeda)] without detection of a palladium(IV) intermediate. No reaction of [PdMePh(tmeda)] with benzyl bromide was observed. The first demonstration that organic groups can be transferred from palladium(IV) to palladium(II) is reported. The molecular structure of [PdMePh(bpy)] in the solid state has been determined