In-depth NMR and IR study of the proton transfer equilibrium between [{(MeC(CH₂PPh₂)₃}Ru(CO)H₂] and hexafluoroisopropanol

Abstract

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.

Selective B–H versus N–H Bond Activation in Ammonia Borane by [Ir(dppm)2]OTf

“…No boron-containing species was present, as shown by the absence of 11 B NMR signals. The classical dihydrides 2 (T 1min = 490.4 ms, 257 K; 566.2 ms, 308 K for 2a and 2b, respectively) [21][22][23][24] were also obtained independently by gently bubbling H 2 ( A small amount of dark precipitate was formed during the reaction and was found to be insoluble in most common organic solvents and poorly soluble in polar solvents such as dmso and MeCN. Preliminary 11 B NMR and IR analyses suggest the formation of (poly)borane derivatives.…”

Isotopomeric diols by “one-pot” Ru-catalyzed homogeneous hydrogenation of dicarboxylic acids

“…The complex Ru(triphos)(acac) 2 is initially formed that reacts with hydrogen, giving an hydride, as suggested by Tenuissen et al [14] The hydride reacts with the alcohol as solvent giving a solvento species as reported by Bakhmutov and co-workers [15] for fluorinated alcohols. This solvento species may interacts and subsequently reacts with the acid substrate giving the addition of the Ru-H moiety to the CO group.…”

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

“…The low solubility of the ion-paired complex in hexane prevented us from determining the equilibrium thermodynamic parameters of the proton transfer step. The enthalpies and entropies of both the dihydrogen bond and the molecular hydrogen complex formation steps have been obtained for [(triphos)-Re(CO) 2 H]/PFTB, [21] [(triphos)Ru(CO)H 2 ]/HFIP, [22] [PP 3 OsH 2 ]/TFE, [23] and [RuH 2 (dppm) 2 ]/HFIP [24] systems (triphos = CH 3 C(CH 2 PPh 2 ) 3 ; PP 3 = P(CH 2 CH 2 PPh 2 ) 3 ; dppm = Ph 2 PCH 2 PPh 2 ; HFIP = hexafluoroisopropanol, TFE = 2,2,2-trifluoroethanol). The protonation of these hydrides is exothermic and exoentropic, the equilibrium shifting toward cationic dihydrogen complexes upon cooling.…”