Dihydrogen Bonding and Proton Transfer from MH and OH Acids to Group 10 Metal Hydrides [((PCP)-P-tBu)MH] [(PCP)-P-tBu = kappa(3)-2,6-(tBu(2)PCH(2))(2)C6H3; M = Ni, Pd]статья
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Аннотация:The interactions of HA acids {indole, fluorinated alcohols, phenols, and [CpW(CO)(3)H] (2)]} with the title hydrides [((PCP)-P-tBu)MH] [M = Ni (1a), Pd (1b)] have been studied by a combination of spectroscopic (variable-temperature IR, NMR, UV/Vis) and computational (DFT/M06, AIM) methods in THF and toluene. The formation of the dihydrogen bond (DHB) 1HA is the first step in a process leading to proton transfer and H-2 evolution. The DHBs of 1 with 2 are much weaker than those of 1 with NH or OH acids, but the former complexes are more reactive. Kinetic studies of the reactions of 4-(4-nitrophenylazo)phenol and [CpWH(CO)(3)] with 1b in THF gave activation enthalpies H = 9.2 +/- 0.4 and 6.5 +/- 1.5 kcalmol(-1) and activation entropies S = -30 +/- 1 and -35 +/- 6 calmol(-1)K(-1), respectively. Calculations revealed the ((2)-H-2)-like TS (E = 9.3 kcalmol(-1)) for the reaction of 1b with p-nitrophenol and the [Pd((2)-H-2)]+OAr- complex as a local minimum at around 5 kcalmol(-1) above the DHB adduct. In the reaction of 1b with 2, both the acidic WH and hydridic NiH or PdH bonds undergo heterolytic cleavage (E = 7.4 kcalmol(-1)) to yield the unusual mu,(1:1)-H-2 end-on complex. The mu,(1:1)-H-2 molecule transforms easily into the more stable (2)-H-2 side-on tautomer, which eventually gives the bimetallic product after H-2 evolution.