CATALYTIC ACTIVATION OF H-2 AND C-H BONDS BY ELECTRON-DEFICIENT RUTHENIUM(II) PORPHYRINS

The Ru-2 and RuNi derivatives of -bis(10,15,20-trimesityl-5-porphyrina to)anthracene recently reported cofacial diporphyrin ligand comprising two hindered porphyrins spanned by an anthracene bridge-have been syn thesized. Both Ru-2(DPAHM) and RuNi(DPAHM) are extremely reactive spec ies that apparently contain 14-electron Ru-(II) centers and, as is the case for their monoporphyrin analog, (5,10,15,20-tetramesitylporphyri nato)rut [Ru(TMP)], must be rigorously protected from oxygen. nitrogen , and other ligating agents. in addition, these electron-deficient Ru( II) porphyrins all appear to bind aromatic solvents such as benzene an d toluene, the weakest ligating solvents in which these Ru(II) porphyr ins have been found soluble. Ru(TMP) and its metallodiporphyrin analog s, Ru-2(DPAHM) and RuNi(DPAHM), catalyze H-2/D-2 exchange in benzene s olution and as solids. When adsorbed on a particularly nonpolar carbon support, these Ru(II) porphyrins all manifest significant activity wi th respect to catalytic H-2/D-2 exchange [approximately 40 turnovers s (-1), when normalized for Ru(II) content]. In addition, these molecule s slowly catalyze the exchange of H-2 into deuterated aromatic hydroca rbons and, in the absence of solvent, the exchange of Dr into CH4. Kin etic studies of H-2/D-2 exchange catalyzed by these Ru(II) porphyrins on carbon supports indicate that exchange is likely to be effected by one face of a single Ru(TMP) moiety. The activity of each supported ca talyst was suppressed by the presence of ligands, either exogenous(CO irreversibly and N-2 reversibly) or from polar functionalities on the surface of the supporting matrix.