Dihydrogen Bonding and Proton Transfer from MH and OH Acids to Group 10 Metal Hydrides [( t Bu PCP)MH] [ t Bu PCP = κ 3 ‐2,6‐( t Bu 2 PCH 2 ) 2 C 6 H 3 ; M = Ni, Pd]

The interactions of HA acids {indole, fluorinated alcohols, phenols, and [CpW(CO) 3 H] ( 2 )]} with the title hydrides [( t Bu PCP)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) 1··· HA 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 Δ H ≠ = 9.2 ± 0.4 and 6.5 ± 1.5 kcal mol –1 and activation entropies Δ S ≠ = –30 ± 1 and –35 ± 6 cal mol –1  K –1 , respectively. Calculations revealed the (η 2 ‐H 2 )‐like TS (Δ E ≠ = 9.3 kcal mol –1 ) for the reaction of 1b with p ‐nitrophenol and the [Pd(η 2 ‐H 2 )] + OAr – complex as a local minimum at around 5 kcal mol –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 (Δ E ≠ = 7.4 kcal mol –1 ) to yield the unusual µ,η 1:1 ‐H 2 end‐on complex. The µ,η 1:1 ‐H 2 molecule transforms easily into the more stable η 2 ‐H 2 side‐on tautomer, which eventually gives the bimetallic product after H 2 evolution.