The interaction of different proton donors with ionic (Bu4NBH4) and neutral (BH3NEt3, BH3P(OEt)3) boron hydrides was studied by IR and NMR spectroscopy in solution (CH2Cl2, C6H14, and C6D12). A close similarity was observed between the spectral and thermodynamic properties of these unusual BH···HX and those of classical H bonds. The typical characteristics of hydrogen bonding, such as linearity of the fragment H···HX, lengthening of X−H and H−B bonds, and strong electron redistribution, were confirmed by ab initio calculations.

The interaction of [NbCp(2)H(3)] with fluorinated alcohols to give dihydrogen-bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200-295 K, affording a clear picture of dihydrogen-bond formation when [NbCp(2)H(3)]/HOR(f) mixtures (HOR(f) = hexafluoroisopropanol (HFIP) or perfluoro-tert-butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen-bond energetics were determined to be 4.5+/-0.3 kcal mol(-1) for TFE (TFE = trifluoroethanol) and 5.7+/-0.3 kcal mol(-1) for HFIP. (1)H NMR studies of solutions of [NbCp(2)H(2)(B)H(A)] and HFIP in [D(8)]toluene revealed high-field shifts of the hydrides H(A) and H(B), characteristic of dihydrogen-bond formation, upon addition of alcohol. The magnitude of signal shifts and T(1) relaxation time measurements show preferential coordination of the alcohol to the central hydride H(A), but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride-proton distances based on T(1) data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp(2)H(3)] with a series of non-fluorinated (MeOH, CH(3)COOH) and fluorinated (CF(3)OH, TFE, HFIP, PFTB and CF(3)COOH) proton donors of different strengths showed dihydrogen-bond formation, with binding energies ranging from -5.7 to -12.3 kcal mol(-1), depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp(2)H(3)], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H(3)O(+), the proton transfer occurs without any barrier, and no dihydrogen-bonded intermediates are found. Proton transfer to [NbCp(2)H(3)] gives bis(dihydrogen) [NbCp(2)(eta(2)-H(2))(2)](+) and dihydride(dihydrogen) complexes [NbCp(2)(H)(2)(eta(2)-H(2))](+) (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen-bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp(2)(eta(2)-H(2))(2)](+) and the homoconjugated anion pair (CF(3)COO...H...OOCCF(3))(-) was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies.

The (carbonyl)dihydride complex [(triphos)Ru(CO)H2] (2) has been synthesized by reaction of the ruthenate [(triphos)RuH3]K (triphos = MeC(CH2PPh2)3) with ethanol saturated with CO. A single crystal X-ray analysis and IR and NMR experiments have shown that 2 adopts in both the solid state and solution an octahedral coordination geometry with a facial triphos ligand, two cis terminal hydrides, and a terminal carbonyl. The reaction of hexafluoro-2-propanol (HFIP) with 2 has been studied in CH2Cl2 solution by IR and NMR spectroscopy. The proton donor interacts with a terminal hydride of 2 forming a rather strong hydrogen bond. The resulting H-bonded adduct [{(triphos)Ru(CO)(H)H}···{HOCH(CF3)2}] (2a) has fully been characterized by in situ NMR and IR techniques. Compound 2a is in equilibrium with the nonclassical η2-H2 complex [(triphos)Ru(CO)H(H2)]+ (2b), which can independently be prepared by protonation of 2 with a strong protic acid at low temperature. Unequivocal characterization of the dihydrogen complex (2b) has been achieved by a multifaceted spectroscopic investigation (Tobs1min = 0.005 s (200 MHz), JH,D [Formula: see text] 30 Hz, DQCC = 78.3 kHz). A combined IR and NMR study of the proton transfer reaction involving 2 and HFIP in CH2Cl2 to give, first, the H-bonded adduct (2a) and, then, the dihydrogen complex (2b) has demonstrated that all these species are in equilibrium in the temperature range from 190 to 260 K. The thermodynamic parameters for the formation of 2a have independently been determined by NMR and IR methods, while those for the formation of 2b have been obtained by IR spectroscopy. An energetic profile for the reaction sequence 2 [Formula: see text] 2a [Formula: see text] 2b is proposed and discussed.Key words: hydrides, hydrogen bonding, ruthenium, IR spectroscopy, NMR spectroscopy.

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4-Hg)3 (1) is capable of binding closo-[B10H10]2- and closo-[B12H12]2- anions to form complexes [[(o-C6F4Hg)3](B10-H10)]2- (2), [[(o-C6F4Hg)3]2(B10H10)]2-(3), [[(o-C6F4Hg)3](B12H12)]2- (4), and [[(o-C6F4Hg)3]2(B12H12)]2- (5). According to IR data, the bonding of the [B10H10]2- and [B12H12]2- ions to the macrocycle in these complexes is accomplished through the formation of B-H-Hg bridges. Complexes 2, 3, and 5 have been isolated in analytically pure form and have been characterized by spectroscopic means. X-ray diffraction studies of 3 and 5 have revealed that these compounds have unusual sandwich structures, in which the polyhedral di-anion is located between the planes of two molecules of 1 and is bonded to each of them through two types of B-H-Hg bridges. One type is the simultaneous coordination of a B-H group to all three Hg atoms of the macrocycle. The other type is the coordination of a B-H group to a single Hg atom of the cycle. According to X-ray diffraction data, complex 2 has an analogous but half-sandwich structure. The obtained complexes 2-5 are quite stable; their stability constants in THF/acetone (1:1) at 20 degrees C have been determined as 1.0 x 10(2)Lmol(-1), 2.6 x 10(3)L(2)mol(2), 0.7 x 10(2)Lmol(-1), and 0.98 x 10(3)L(2)mol(-2), respectively.