The chemical reactivity of hydride complexes can be predicted using bond strengths for homolytic and heterolytic cleavage of bonds to hydrogen. To determine these bond strengths, thermodynamic constants describing the stability of H(+), H˙, H(-), and H2 are essential and need to be used uniformly to enable the prediction of reactivity and equilibria. Due to discrepancies in the literature for the constants used in water, we propose the use of a set of self-consistent constants with convenient standard states.

Reaction of triphenylmethylium tetrakis-(pentafluorophenyl)borate, [Ph 3 C][B(C 6 F 5 ) 4 ], with excess neat triethylsilane affords triethylsilylium(triethylsilane) tetrakis(pentafluorophenyl)borate, [(Et 3 Si) 2 (μ-H)][B(C 6 F 5 ) 4 ](1), identified by X-ray crystallography. In chlorobenzene and fluorobenzene, 1 is observed in solution. When 1 is dissolved in benzene or toluene, the evolved gas was shown to be hydrogen. Isotope labeling experiments demonstrate that the hydrogen arises from the reaction of Et 3 SiH with the silylium complex of the arene solvent.

Hydrogen activation by nickel: A tBuPCP pincer ligand facilitates formation of cationic Ni(II) dihydrogen and terminal dinitrogen complexes. The compounds have been characterized by X-ray crystallography and NMR spectroscopy. Addition of base promotes heterolytic cleavage of H(2) to form the corresponding neutral hydride complex.

The preparation and isolation of the first palladium dihydrogen complex is described. NMR spectroscopy reveals a very short H-H bond length, but the hydrogen molecule is activated toward heterolytic cleavage. An X-ray crystal structure suggests that proton transfer to the (tBu) PCP (κ(3)-2,6-((t)Bu2PCH2)2C6H3) pincer ligand is possible. The basicity of the ipso-carbon atom of the pincer ligand was investigated in a related complex.

Abstract:The preparation and isolation of the first palladium dihydrogen complex is described. NMR spectroscopyr eveals av ery short H À Hb ond length, but the hydrogen molecule is activated towardh eterolytic cleavage.A nX -ray crystal structure suggests that proton transfer to the tBu PCP (k 3 -2,6-( t Bu 2 PCH 2 ) 2 C 6 H 3 )p incer ligand is possible.T he basicity of the ipso-carbon atom of the pincer ligand was investigated in ar elated complex.