Distance and Scalar HH-Coupling Correlations in Transition Metal Dihydrides and Dihydrogen Complexes

Abstract

The bond-valence bond-length concept has been applied to derive a correlation between the hydrogen−hydrogen and the metal−hydrogen distances in the nonclassical dihydrogen complexes and classical transition metal dihydrides. The parameters of this correlation are similar to those for strong hydrogen-bonded systems. The predicted correlation is supported by 18 neutron structures of transition metal dihydrides or dihydrogen complexes and 2 neutron structures of transition metal trihydride complexes. It is also shown that the bond-valence bond-length concept can also be used to establish a correlation between the dihydrogen distance r HH in dihydrogen/dihydride complexes and the scalar coupling constants J HH/J HD/J HT in the different isotopomers of these complexes.

The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers

“…There is an almost complete continuum from complexes with distances close to that of free H 2 , through "stretched" dihydrogen complexes, to complete oxidative addition where the H···H separation exceeds 1.8 . [25,26] The polyhydride cation [OsH 5 (PMe 2 Ph) 3 ]…”

Activation of Molecular Hydrogen

“…A more sophisticated analysis of the relationship between HD coupling and d HH has recently been reported by Chaudret, Limbach, and coworkers, which allows for reliable values for d HH to be extracted from HD coupling. 134 A slightly different nonlinear relationship was reported by Heinekey and coworkers ( Figure 5.6). 135 Implicit in the extraction of d HH from values of J HD is the assumption that molecular structure is independent of mass.…”

Elongated Dihydrogen Versus Compressed Dihydride Complexes: The Temperature Dependence of the H–D Spin–Spin Coupling Constant as a Criterion To Distinguish between Them

“…With the aim of discerning the existence of "compressed dihydride complexes" as different entities from elongated dihydrogen complexes, a thorough comparative theoretical study has been undertaken on complexes [Cp*Ru-(dppm)(H 2 )] + (R HÀH = 1.10 , neutron diffraction [3] ) and [CpRe(CO) 2 2 + would fit this description. Both kinds of complexes should show isotope geometric effect when the HH unit is substituted by heavier types, such that the R HÀH distance would be decreased in elongated dihydrogen complexes and increased in compressed dihydride complexes.…”

“…Moreover, and surprisingly enough for a family of complexes with so few members, different opposing behaviors have been observed: 1 J HD either increases or decreases with temperature. By virtue of a well-established inverse relationship between 1 J HD and R HÀH , [2] this temperature dependence of 1 J HD has found prompt interpretation in terms of shortening or lengthening of R HÀH with temperature.…”

“…In particular, different behavior is predicted with respect to 1) the sign of the isotope geometric effect on the HÀH distance at 0 K, 2) the temperature dependence of the HÀH distance, and 3) the temperature dependence of the HÀD spin-spin coupling constant in 1 H NMR spectroscopy. 2 + (dmpm = bis(dimethyl)phosphinomethane) (2). [7] This complex was first described as a stretched dihydrogen complex, in which 1 J HD increased with the temperature, which has a comparatively large R HÀH distance of 1.49 , estimated from T 1(min) relaxation time measurements.…”