Two pathways of proton transfer reaction to (triphos)Cu(η¹-BH₄) via a dihydrogen bond [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane]

Abstract

The interaction of the η(1)-tetrahydroborate copper(i) complex (triphos)Cu(η(1)-BH4) () with proton donors [CF3CH2OH (TFE), (CF3)2CHOH (HFIP), (CF3)3COH (PFTB), PhOH, p-NO2C6H4OH (PNP), p-NO2C6H4N[double bond, length as m-dash]NC6H4OH (PNAP), CF3OH] was a subject of a combined IR spectroscopic and theoretical investigation. Spectral (Δν) and thermodynamic (ΔH) parameters of dihydrogen bond (DHB) formation were determined experimentally. The terminal hydride ligand (characterized by the basicity factor Ej(BH) = 0.87 ± 0.01) is found to be a site of proton transfer which begins with nucleophilic substitution of BH4(-) by the alcohol oxygen atom on the copper center (BH pathway). The activation barrier computed for (CF3)2CHOH in CH2Cl2 - ΔG = 20.6 kcal mol(-1) - is in good agreement with the experimental value (ΔG = 20.0 kcal mol(-1)). An abnormal dependence of the reaction rate on the proton donor strength found experimentally in dichloromethane is explained computationally on the basis of the variation of the structural and energetic details of this process with the proton donor strength. In the second reaction mechanism found (CuH pathway), DHB complexes with the initial ROH coordination to the bridging hydride lead to B-Hbr bond cleavage with BH3 elimination. "Copper assistance" via the CuO interaction is not involved. This mechanism can be evoked to explain the occurrence of proton transfer in coordinating solvents.

Competition between the Hydride Ligands of Two Types in Proton Transfer to [{κ3‐P‐CH3C(CH2CH2PPh2)3}RuH(η2‐BH4)]

“…No significant changes to the geometry or electron‐density distribution of the borohydride fragment were found for the model (Figure S10, Tables S1 and S2). Previously, such an approach was successfully applied in the investigation of the DHB intermediates and alcoholysis reactions of (Triphos)Cu(η 1 ‐BH 4 )[9a] and [(PP 3 )RuH(η 1 ‐BH 4 )]. [9b]…”

“…Previously, such an approach was successfully applied in the investigation of the DHB intermediates and alcoholysis reactions of (Triphos)Cu(η 1 ‐BH 4 )[9a] and [(PP 3 )RuH(η 1 ‐BH 4 )]. [9b]…”

“…The treatment of metal tetrahydridoborate complexes with acids results in the loss of the BH 4 – ligand and the formation of mono‐ or dinuclear species . The data obtained in our studies of the interactions of alcohols with copper and ruthenium tetrahydridoborates (Scheme ) show the increase of BH 4 – reactivity entailed by complexation to metal centers . The presence of various hydride sites in these complexes [terminal B–H (BH term ), bridging B–H–M (BH br ), and terminal M–H bonds] leads to the formation of a large variety of dihydrogen‐bonded complexes, but only a few of the conceivable DHB complexes are real intermediates of the alcoholysis process .…”

“…The presence of various hydride sites in these complexes [terminal B–H (BH term ), bridging B–H–M (BH br ), and terminal M–H bonds] leads to the formation of a large variety of dihydrogen‐bonded complexes, but only a few of the conceivable DHB complexes are real intermediates of the alcoholysis process . As part of our investigations into noncovalent interactions (hydrogen and dihydrogen bonds) and the reactivity of transition‐metal tetrahydridoborates towards alcoholysis (Scheme ), herein we report a combined computational (DFT) and spectroscopic [variable‐temperature (VT) FTIR, NMR] analysis of the interactions of the mixed hydrido–tetrahydridoborate ruthenium(II) complex [(Triphos)RuH(η 2 ‐BH 4 )] [ 1 , Scheme ; Triphos = κ 3 ‐ P ‐CH 3 C(CH 2 CH 2 PPh 2 ) 3 ][8c], with fluorinated alcohols of various acidic strengths. Mechanistic studies on the alcoholysis of metal tetrahydridoborates are of interest in view of the catalytic activities of these complexes.…”

Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of [(µ2-dppm)2Cu2(η2-BH4)2] Dichloromethane Solvate

“…Our studies of intermolecular interactions of BH4 − [65,66] and several metal tetrahydroborates [67][68][69][70] with proton donors have shown the versatility of dihydrogen bonded (DHB) complexes formed and their crucial role in the reactivity of these compounds. In particular, we have shown that the formation of bifurcate DHB complexes involving both bridging and terminal hydride hydrogens of (Ph3P)2Cu(η 2 -BH4) (Scheme 2) is prerequisite for the subsequent proton transfer and dimerization to occur [67].…”