Group trends thermodynamic stability

Reliable information on the thermodynamic stability of group 13/15 adducts is usually obtained by gas phase measurements. However, due to the lability of stibine and bismuthine adducts in the gas phase toward dissociation, temperature-dependent H-NMR studies are also useful for the determination of their dissociation enthalpies in solution [41b], We focussed on analogously substituted adducts t-BusAl—E(f-Pr)3 (E = P 9, As 10, Sb 11, Bi 12) since they have been fully characterized by single crystal X-ray diffraction, allowing comparisons of their thermodynamic stability in solution with structural trends as found in their solid state structures. 

These experimentally observed structural trends were confirmed by computational calculations on H3A1 and Me3Al adduct families. In each adduct family, the amount of increase of the M-X bond lengths and decrease of the X M-X bond angles (X = H, Me) compared to uncomplexed MX3 diminishes with the atomic number of the group 15 element. The structural trends very well reflect the trends observed for the thermodynamic stability of such adducts, as is illustrated in Tables XI and XII. 

Trends in stability or structure of related compounds can often be usefully rationalized from bond strength trends. The decline in 5(E-H) as a main group is descended leads to reduced thermodynamic stability of hydrides EHw (see Topic F2Y Double-bonded structures are much commoner with the... 

With few exceptions, transition metal complexes of terminal alkyl groups are more stable than those of isomeric secondary or tertiary alkyl groups. Consistent with this trend, the terminal alkylmetal hydride complexes of systems that undergo oxidative addition of C-H bonds are thermodynamically more stable than the branched alkylmetal hydride complexes. "- The oxidative addition of alkanes by the Cp Ir(PMe3) fragment is reversible, and this reversibility allowed for an evaluation of the thermodynamic stability of alkyl hydride complexes formed from a series of alkanes, as weU as from arenes. These data showed that the alkyl hydride complex formed from oxidative addition at the primary C-H bond leads to more stable products than those formed from... 

---