The synthesis of NHC-PdCl(2)-3-chloropyridine (NHC=N-heterocyclic carbene) complexes from readily available starting materials in air is described. The 2,6-diisopropylphenyl derivative was found to be highly catalytically active in alkyl-alkyl Suzuki and Negishi cross-coupling reactions. The synthesis, ease-of-use, and activity of this complex are substantial improvements over in situ catalyst generation and all current Pd-NHC complexes. The utilization of complex 4 led to the development of a reliable, easily employed Suzuki-Miyama protocol. Employing various reaction conditions allowed a large array of hindered biaryl and drug-like heteroaromatic compounds to be synthesized without difficulty.

In order to gain insight into the electrochemical and conformational properties of the prototypical high polymeric poly(ferrocenylsilane), poly(ferrocenyldimethylsilane) [Fe(η-C5H4)2SiMe2] n 6, three series of oligo(ferrocenylsilanes) R-fc-[SiMe2-fc] n - 1-R‘ (fc = Fe(η-C5H4)2) 7 2 −7 9 (R = R‘ = H), 8 2 −8 7 (R = H and R‘ = SiMe3), and 9 2 −9 7 (R = R‘ = SiMe3) have been prepared and studied (the subscript n in the oligomer refers to the number of ferrocene units present). These species were prepared via the anionic ring-opening oligomerization of the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 5. Initiation with ferrocenyllithium FcLi (Fc = Fe(η-C5H5)(η-C5H4)) followed by quenching with H2O or SiMe3Cl afforded H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or H-fc-[SiMe2-fc] n - 1-SiMe3 (8 2 -7 ), respectively. Initiation with the dilithioferrocene complex fcLi·2/3TMEDA followed by quenching with H2O or SiMe3Cl similarly afforded the oligomers H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or alternatively the bis(silyl)-capped species Me3Si-fc-[SiMe2-fc] n - 1-SiMe3 (9 2 -7 ), respectively. The individual molecular compounds of these three series of oligomers 7 2 −7 9 , 8 2 −8 7 , and 9 2 −9 7 were isolated in pure form from the oligomeric mixtures by column chromatography and these were structurally characterized by 1H, 13C, and 29Si NMR spectroscopy, mass spectrometry, and in selected cases by elemental analysis. The structure of the linear pentamer 7 5 has also been determined by single crystal X-ray diffraction. The central portion of this species possesses a trans planar zigzag conformation in the solid state and appears to be a valuable model for the analogous conformation of the high polymer 6 in crystalline domains. The electrochemical behavior of each pure oligomer was studied by cyclic and differential pulse voltammetry and was found to depend on whether an odd or an even number of ferrocene units were present. For oligomer systems containing an odd number of iron centers two reversible redox processes of varying intensities at −0.02−0.00 V and 0.21−0.23 V (vs ferrocene) were observed with a redox splitting of 0.21−0.23 V. For oligomer systems containing an even number of iron centers larger then two, three reversible redox processes of varying intensities were observed at ca. 0.00, 0.13, and 0.24 V vs ferrocene. As the oligomer chain length increased, the electrochemical behavior for both the “odd” and “even” series approached that of the high polymer 6 for which two reversible redox processes at 0.00 and 0.24 V (vs ferrocene) of equal intensity exist. These results are completely consistent with the previously proposed theory that initial oxidation of 6 affords a product in which alternating iron sites are oxidized. Spectroelectrochemical experiments show an intervalence electron transfer absorption (1100−1350 nm, εmax ⩽ 150 M-1 cm-1) for partially oxidized oligo(ferrocenylsilanes) that is typical for class II mixed-valent compounds. Additionally, single crystals were obtained of the m...

A rational approach is needed to design hydrogenation catalysts that make use of Earth-abundant elements to replace the rare elements such as ruthenium, rhodium, and palladium that are traditionally used. Here, we validate a prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines, with isopropanol as the hydrogen donor, at turnover frequencies as high as 200 per second at 28°C. We present a direct synthetic approach to enantiopure ligands of this type that takes advantage of the iron(lI) ion as a template. The catalytic mechanism is elucidated by the spectroscopic detection of iron hydride and amide intermediates.

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.

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A high-yield route to the new complexes OsBr2(dppe)2 and trans-OsHBr(dppe)2 starting from (NH4)2[OsBr6] is described. The new 5-coordinate complexes [OsX(dppe)2]PF6 (X = Cl (8Os) and X = Br (9Os)) are prepared by reaction of cis-OsX2(dppe)2 with NaPF6. Complexes 8Os and 9Os consist of distorted trigonal bipyramidal cations with “Y”-shaped equatorial planes. They react in CH2Cl2 with H2 or HD (1 atm) to give complexes trans-[Os(H··H)X(dppe)2]PF6 (X = Cl (1OsPF6), X = Br (2OsPF6)) or trans-[Os(H··D)X(dppe)2]PF6, respectively. The last complexes have J(H,D) = 13.9 and 13.7 Hz, respectively. The BF4 - salts of these complexes, 1OsBF4 and 2OsBF4, respectively, are prepared by reacting trans-OsHX(dppe)2 with HBF4·Et2O or DBF4·Et2O. These complexes are characterized by NMR, IR, and FAB MS. The single-crystal X-ray and neutron diffraction studies of 1OsPF6 revealed an elongated H··H ligand with d HH = 1.11(6) (X-ray) or 1.22(3) Å (neutron) occupying one site in an octahedral complex. The X-ray diffraction study of 2OsBF4 produced a similar structure with d HH = 1.13(8) Å. One fluorine of the anion in each structure is positioned near the acidic H2 ligand. A linear relationship between d HH and J(H,D) for many dihydrogen complexes is used to indicate that complexes 1Os and 2Os have H−H distances of about 1.2 Å in solution. Plots of ln(T 1) versus inverse temperature for 1Os and 2Os are distorted from the usual “V” shape, suggesting that the rotational frequency of the H2 ligand is near that of the Larmor frequency. Therefore the d HH for 1Os is between the values of 1.04 and 1.31 Å calculated from the T 1(min) for fast and slow spinning H2, respectively. The chloride ligand in trans-[Os(H··H)Cl(L)2]+ buffers the effect of changing the cis ligands L from dppe to depe to dcpe so that there is little change in the H−H distance. Complexes 1Os and 2Os have pK a values of 7.4 and 5.4, respectively, while trans-[Os(H2)H(dppe)2]+ is much less acidic with a pK a of 13.6. These pK a values and some E 1/2 values are used to show that 1Os and 2Os are dihydride-like even though they have relatively short H−H distances. Properties of trans-[Os(H··H)Cl(depe)2]BF4 (3Os) are also reported.

Catechol borane reacts with the frustrated Lewis pairs tBu2RP (R = tBu, 2-C6H4(C6H5)) and B(C6F5)3 to give the species [(C6H4O2)BPtBu2R][HB(C6F5)3] that can formally be described as either borenium cation or boryl-phosphonium salts; the nature of these species was probed with DFT calculations.

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