ABSTRACT
The interaction of trans-W(N2)2(dppe)2 (1; dppe = 1,2-bis(diphenylphosphino)ethane) with relatively weak acids (p-nitrophenol, fluorinated alcohols, CF3COOH) was studied by means of variable temperature IR and NMR spectroscopy and complemented by DFT/B3PW91-D3 calculations. The results show, for the first time, the formation of a hydrogen bond to the coordinated dinitrogen, W-N≡N···H-O, that is preferred over H-bonding to the metal atom, W···H-O, despite the higher proton affinity of the latter. Protonation of the core metal-the undesirable side step in the conversion of N2 to NH3-can be avoided by using weaker and, more importantly, bulkier acids.
ABSTRACT
Dimethylamine-borane (DMAB) acid/base properties, its dihydrogen-bonded (DHB) complexes and proton transfer reaction in nonaqueous media were investigated both experimentally (IR, UV/vis, NMR, and X-ray) and theoretically (DFT, NBO, QTAIM, and NCI). The effects of DMAB concentration, solvents polarity and temperature on the degree of DMAB self-association are shown and the enthalpy of association is determined experimentally for the first time (-ΔH°assoc = 1.5-2.3 kcal/mol). The first case of "improper" (blue-shifting) NH···F hydrogen bonds was observed in fluorobenzene and perfluorobenzene solutions. It was shown that hydrogen-bonded complexes are the intermediates of proton transfer from alcohols and phenols to DMAB. The reaction mechanism was examined computationally taking into account the coordinating properties of the reaction media. The values of the rate constants of proton transfer from HFIP to DMAB in acetone were determined experimentally [(7.9 ± 0.1) × 10(-4) to (1.6 ± 0.1) × 10(-3) mol(-1)·s(-1)] at 270-310 K. Computed activation barrier of this reaction ΔG(theor)298 K(acetone) = 23.8 kcal/mol is in good agreement with the experimental value of the activation free energy ΔG(exp)270 K = 21.1 kcal/mol.
ABSTRACT
The reaction of ClAuPPh3 and 1,1'-biphenyl-2,2'-dithiol in the presence of trimethylbenzylammonium chloride and K2CO3 in a tetrahydrofuran/methanol solution gives the title complex, [Au2(C12H8S2)(C18H15P)2]. The molecule contains P-Au-S units which 'cross' with torsion angles of approximately 90 degrees [P-Au-Au-P = 86.23 (5) degrees and S-Au-Au-S = 95.62 (5) degrees]. The intra- and intermolecular Au.Au distances [3.9064 (3) and 6.3797 (5) A, respectively] are outside the range for typical Au...Au interactions. However, the Au atoms appear to be drawn together, leading to a significant bending of the P-Au-S angles [170.24 (5) and 169.52 (5) degrees].
