Solid state nuclear bromination with N-bromosuccinimide. Part 2. Experimental and theoretical studies of reactions with some substituted benzaldehydes

N-Bromosuccinimide reacts with aromatic aldehydes in the solid state to yield exclusively nuclear brominated products while a similar reaction in the solution phase produces a number of products under varied conditions. The reactivity and regioselectivity have been studied in terms of the energies of HOMO, HOMO–LUMO difference, reaction free energy, reaction conditions and crystal packing. Single crystal X-ray structural analysis of 3,4-dihydroxybenzaldehyde has been carried out. Crystal packing energies of some of the reactive and unreactive benzaldehydes indicate the importance of molecular bromine diffusion in the solid state

Some New Dicationic Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of ruthenium of the type $trans-[(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2$ $[dppe = Ph_2PCH_2CH_2PPh_2; R = CH_3, CH_3CH_2, CH_3CH_2CH_2, CH_2=CH, p-CH_3-C_6H_4-CH_2, C_6H_5, and (CH_3)_2N]$ have been prepared by the protonation reaction of the precursor hydrides, trans- $[(dppe)_2Ru(H)(RCN)][BF_4]$ using $HBF_4·OEt_2$. The variable temperature spin-lattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2$ -HD isotopomers indicate the intact nature of the H-H bond in these complexes. It was found that the spectroscopic and chemical properties of these derivatives are not very sensitive to the change in the trans nitrile ligand. The $pK_a$ values of the dihydrogen complexes have been determined using the equilibrium: trans- $[(dppe)_2Ru(H)(RCN)][BF_4] + HBF_4\cdot OEt_2 \rightleftharpoons trans- [(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2 + Et_2O$ by $^1H\hspace{2mm}NMR$ spectroscopy