Quantum Mechanical Hydrogen Exchange Coupling in [(C5H5)Ir(L)H3]+ Complexes (L = PH3, CO). A Combined ab Initio/Tunneling Dynamics Study

Quantum mechanical exchange in a transition metal hydride complex: NMR data for [cp(PPh3)IrH3]+ fitted by a two-dimensional model

“…The importance of the hydrogen pair lift-off in the proposed two-step mechanism has been confirmed by quantum chemical results published by Jarid et al 10 For the rotational angle fixed at its equilibrium value, they found a minimum energy path describing a mutual approach of the two hydrogen atoms, combined with a displacement of their midpoint away from the metal center, as illustrated in Fig. 1.…”

“…While their potential energy surface does not confirm the existence of a metastable dihydrogen state, the exchange relies, as suggested by Limbach et al 8 on a promotion of the system from the classical dihydride equilibrium configuration towards a nonclassical dihydrogen configuration where the rotation is facilitated by a substantially reduced rotational barrier. Based on a noncyclic one-dimensional reaction path on their potential surface, Jarid et al 10 found positive tunnel splittings for the three lowest vibrational states and a Boltzmann average in qualitative agreement with observations.…”

“…A second motional variable ␤ is used to describe an MH 2 bending mode that merges into a lift-off motion at short H•••H distance. The common z coordinate of the two hydrogen atoms is related to their distance r HH by a function fitting the minimum energy path obtained by Jarid et al 10 when fixing the rotational angle at one of its two equilibrium values ͑see Ϫ2 . This term diverges as the distance r HH ϭ2r 0 sin␤ decreases the value d HH ϭ0.74 Å for a free hydrogen molecule ͑see Fig.…”

“…Theoretical explanations of the anomalous J coupling have been proposed by a number of authors [5][6][7][8][9][10][11] who agree on pairwise proton exchange as the dominant tunneling mechanism, an assumption that is also supported by the observed isotope effect: In complexes deuterated in one of the two equivalent Y sites, the tunneling interaction due to exchange of the remaining two protons is larger in magnitude by only 4%-8% than that observed in the normal isotopic species. 3 Zilm and Millar 5 considered localized vibrational states for each of the two protons and related the tunnel interaction J ex to the overlap of the two wave functions.…”

Structure and coordinate bonding nature of the manganese–σ–borane complexes

“…Theoretical calculations have also been carried out to substantiate the presence of g 2 -dihydrogen [9,[31][32][33][34][35][36][37] and g 2 -silane [15,[18][19][20][38][39][40][41] coordination to many different transition metal centers, but less attention has been paid to r-borane complexes. Ab initio calculations have been performed for r-borane complexes [(g 5 -C 5 H 5 )Ti{H-B(OH) 2 } 2 ] and [(g 5 -C 5 H 5 )Ti{HB(H) 2 r-borate complexes [(g 5 -C 5 H 5 ) 2 Nb{H 2 B(OH) 2 }] [42], [(g 5 -C 5 H 5 )Nb{H 2 B(C 8 H 14 )] and [(g 5 -C 5 H 5 )Nb{H 2 B(H) 2 }] [43].…”