The tris[(4-dimethylaminopyridyl)methyl]amine (TPMA) as a ligand for copper-catalyzed atom transfer radical polymerization (ATRP) is reported. In solution, the [Cu(TPMA)Br] complex shows fluxionality by variable-temperature NMR, indicating rapid ligand exchange. In the solid state, the [Cu(TPMA)Br][Br] complex exhibits a slightly distorted trigonal bipyramidal geometry (τ = 0.89). The UV-vis spectrum of [Cu(TPMA)Br] salts is similar to those of other pyridine-based ATRP catalysts. Electrochemical studies of [Cu(TPMA)] and [Cu(TPMA)Br] showed highly negative redox potentials (E = -302 and -554 mV vs SCE, respectively), suggesting unprecedented ATRP catalytic activity. Cyclic voltammetry (CV) in the presence of methyl 2-bromopropionate (MBrP; acrylate mimic) was used to determine activation rate constant k = 1.1 × 10 M s, confirming the extremely high catalyst reactivity. In the presence of the more active ethyl α-bromoisobutyrate (EBiB; methacrylate mimic), total catalysis was observed and an activation rate constant k = 7.2 × 10 M s was calculated with values of K ≈ 1. ATRP of methyl acrylate showed a well-controlled polymerization using as little as 10 ppm of catalyst relative to monomer, while side reactions such as Cu-catalyzed radical termination (CRT) could be suppressed due to the low concentration of L/Cu at a steady state.

The bis(dihydrogen) complex RuH2(H2)2(PCy3)2 (1) reacts with the disilanes (R2SiH)2X to produce the dihydride complexes [RuH2{(η2-HSiR2)2X}(PCy3)2] (with R = Me and X = O (2a), C6H4 (3), (CH2)2 (4), (CH2)3 (5), OSiMe2O (6)) and R = Ph, X = O (2b)). In these complexes, the bis(silane) ligand is coordinated to ruthenium via two σ-Si−H bonds, as shown by NMR, IR, and X-ray data and by theoretical calculations. 3, 4, and 6 were characterized by X-ray diffraction. In the free disilanes the Si−H bond distances and the J Si - H values are around 1.49 Å and 200 Hz, respectively, whereas in the new complexes the values are in the range 1.73−1.98 Å and 22−82 Hz, respectively for the σ-Si−H bonds. The importance of nonbonding H···Si interactions, which control the observed cis geometry of the two bulky PCy3 ligands, is highlighted by X-ray data and theoretical calculations. The series of bis(silane) model complexes, RuH2{(η2-HSiR2)2X}(PR‘3)2, with X = (CH)2, C6H4, (CH2) n , O, and OSiH2O, and with R and R‘ = H or Me, was investigated by density functional theory (DFT) by means of two hybrid functionals B3LYP and B3PW91. In the case of X = C6H4 three isomers were studied, the most stable of which has C 2 v symmetry and whose structure closely resembles the X-ray structure of 3. Calculated binding energies for the bis(silane) ligand to the RuH2(PH3)2 fragment vary from 130 to 192 kJ/mol, showing that in the more stable complexes, the Si−H bonds are bound more strongly than dihydrogen. The dynamic behavior of these complexes has been studied by variable temperature 1H and 31P{1H} NMR spectroscopy and exchange between the two types of hydrogen is characterized by barriers of 47.5 to 68.4 kJ/mol. The effect of the bridging group X between the 2 silicons is illustrated by reactions of compounds 2−6 with H2, CO, tBuNC. 3 is by far the most stable complex as no reaction occurred even in the presence of CO, whereas elimination of the corresponding disilane and formation of RuH2(H2)2(PCy3)2, RuH2(CO)2(PCy3)2, or RuH2(tBuNC)2(PCy3)2 were observed in the case of 2 and 4−6. The mixed phosphine complexes [RuH2{(η2-HSiMe2)2X}(PCy3)(PR3)] 3R−6R (with R = Ph and R = pyl) have been isolated in good yields (80−85%) and fully characterized by the addition of 1 equiv of the desired phosphine to 3−6. In the case of 4Ph, an X-ray determination was obtained. In the case of 2, elimination of the disiloxane was always observed. Addition of 1 equiv of a disilane to Ru(COD)(COT) in the presence of 2 equiv of the desired phosphine under an H2 atmosphere produces the complexes [RuH2{(η2-HSiMe2)2X}(PR3)2] (X = C6H4, R = Ph (3Ph2) and R = pyl (3pyl2); X = (CH2)2, R = Ph, 4Ph2; R = pyl, 4pyl2). 4Ph2 was also characterized by an X-ray structure determination.

Starting from either K2PtCl4 or K[PtCl3(C2H4)]•H2O (Zeise's salt), complexes (nBu4P)2[PtBr4] (1), nBu4P[PtBr3(C2H4)] (2), nBu4P[PtBr3(PhNH2)] (3), trans-[PtBr2(C2H4)-(PhNH2)] (4), cis-[PtBr2(C2H4)(PhNH2)] (5), and cis-[PtBr2(PhNH2)2] (6) have been obtained by efficient one-pot procedures. All have been fully characterized by microanalysis (C, H, N), multinuclear NMR spectrometry ( 1 H, 13 C, 195 Pt), UV-visible spectroscopy, and single crystal Xray diffraction. Compound 1 slowly loses Brin solution to yield (nBu4P)2[Pt2Br6] (1'), which has also been characterized crystallographically. The relative stability of the various compounds has been probed experimentally by NMR studies in several solvents and computationally by gas phase geometry optimizations followed by C-PCM calculations of the solvation effects in dichloromethane and aniline. The calculations also included the bis(ethylene) complexes [PtBr2(C2H4)2] in the trans (two different conformations 7 and 7') and cis (8) configurations.The solution experiments gave no evidence for a nucleophilic attack of aniline onto coordinated ethylene under mild conditions (T up to 68°C), setting a lower limit of 29 kcal mol -1 for the activation barrier of this process. Therefore, the relative energies computed for the other compounds suggest that all ethylene-containing complexes (2, 4, 5, 7 and 8) are viable candidates for the key nucleophilic addition step of the PtBr2-catalyzed ethylene hydroamination by aniline. Use of the isolated complexes 2, 4 or 5 in combination with nBu4Br as precatalysts for the ethylene hydroamination by aniline yields similar catalytic activities.

A new family of hexakis(ferrocenylethynyl)benzenes was synthesized by Negishi coupling from ethynylferrocenes and C(6)Br(6) and can be reversibly oxidized to stable hexaferrocenium salts (see picture, Ar(F)=[3,5-C(6)H(3)(CF(3))(2)]). Their cyclic voltammograms show a single six-electron wave, three distinct two-electron waves, or a cascade of six single-electron waves, depending on the electrolyte counterion and number of methyl substituents on the ferrocenyl groups.

Air-stable neutral and cationic palladium complexes bearing chiral phosphine-Nheterocyclic carbene ligands with planar chirality only have been prepared in moderate to good yields and characterized by NMR and X-ray diffraction studies. They are shown to catalyze the asymmetric coupling of aryl bromides with arylboronic acids in good yields and moderate enantioselectivities (up to 42% ee) with low catalyst loadings (0.1-0.5 mol%).N-Heterocyclic carbenes (NHCs) have received a great deal of attention recently and are now considered as ligands of choice for various catalytic reactions, 1 among which the Suzuki-Miyaura reaction using aryl bromides and less reactive aryl chlorides. 2 They have several advantages over phosphines, such as air and thermal stability of the resulting complexes. We have focused our attention

"Click" reactions between ethynylferrocene and mono-, bis-, and tris-azido aromatic derivatives yielded mono-, bis-, and tris-1,2,3-ferrocenyltriazoles (1, 2, and 3, respectively) as orange crystals. The X-ray crystal structure of the monoferrocenyltriazole compound 1 was solved with two nearly identical molecules within the asymmetric unit. In both molecules, the two Cp rings make a tilt angle of 2.1(3) degrees [0.7(3) degrees], and they are roughly eclipsed with a twist angle of 2.4(3) degrees [1.8(3) degrees]. Reaction of 1 with [PdCl2(PhCN)2] in dimethylsulfoxide (DMSO) yielded orange crystals of [PdCl2L2] (4; L=1), for which the X-ray crystal structure shows trans coordination to the nitrogen atom close to the ferrocene substitution. The Pd atom is located on an inversion center and displays a nearly perfect square planar environment. In DMSO-d6, 4 reversibly dissociates to regenerate 1, whose (1)H NMR spectrum is then observed. The 1H NMR study also shows that progressive addition of PdCl2 or [PdCl2(NCR)2] (R=Me or Ph) to DMSO-d6 solutions of 1 reversibly leads to the formation of 4 and the addition of excess PdII is necessary to lead to the complete disappearance of the signals of 1. The cyclic voltammograms of 1, 2, and 3 show the reversible oxidation wave of the ferrocenyl group, and that of 4 shows that this wave appears with increased intensity tentatively attributable to redox-catalyzed oxidation.

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The kinetics and mechanism of Catalytic Radical Termination (CRT) of n-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally. The tetradentate TPMA, TPMA* 1 , TPMA* 2 , TPMA* 3 and the newly synthesized tridentate N-propyl-N,N-bis(4-methoxy-3,5-dimethylpyrid-2-ylmethtyl)amine (BPMA* Pr ) as well as tridentate BPMA Me were used as ligands. L/Cu II X2 (X = Cl or OTf) complexes were characterized by cyclic voltammetry (CV), UV-Vis-NIR and X-ray diffraction. Polymerization of n-butyl acrylate (BA) initiated by azobisisobutylnitrile (AIBN)MeCN in the presence of a L/Cu I complex showed higher rates of CRT for more reducing L/Cu I complexes. The ligand denticity (tri-vs. tetradentate) had a minor effect on the relative polymerization kinetics but affected the molecular weights in a way specific for ligand denticity. Quantification of the apparent CRT rate coefficients, , showed larger values for more reducing L/Cu I complexes, which correlated with 2 the L/Cu II -R (R = CH(CH3)(COOCH3)) bond strength, according to DFT calculations.The bond strength is mostly affected by the complex reducing power and to a lesser degree by the ligand denticity. Analysis of kinetics and molecular weights for different systems indicates that, depending on the ligand nature, the ratedetermining step of CRT may be either the radical addition to L/Cu I to form the L/Cu II -R species or the reaction of the latter species with a second radical.