Studies on template effects, condensation reactions, oxida tive dehydrogenations, catalytic hydrogenations and ligand deprotonations have made it possible to synthesize almost any tetradentate macrocyclic ligand one might choose. The principle of multiple juxtapositional fixedness is ex plained and applied to metal binding in enzymes. The inflexibility of the metal ion site in the porphyrin ring is contrasted to those in synthetic macrocycles. TAAB, a related tetraazaannulene, can vary its inner site while other rings fold when the metal ion is too large. Many model compounds for high-spin, five-coordinate deoxyhemoglobin and deoxymyoglobin are presented. The Fe III -O-Fe III bridge is extremely hard to break when iron is bound to a tetraazaannulene (TAAB). Iron is a better catalyst for oxi dative dehydrogenation of its own ligand than is nickel.
The i.r. [(v(CO) and v(Fe-H)] and Mossbauer spectra of H,Fe(CO), in hexane at -78 and -196' are reported. The reaction between H,Fe(CO), and thiols proceeds by simultaneous loss of hydrogen and carbon monoxide t o the known thiolate-bridged complexes, [Fe(CO),SR], (R = Ph, CgF,, or Pr'). With triphenyl-phosphine and -arsine, hydrogen substitution occurs producing the complexes Fe(CO),L and Fe(CO),L, (L = Ph, P or Ph,As). Two unstable complexes were also isolated in low yield from the Ph,As reaction, one of which was identified by mass spectrometry as Fe(CO),H,AsPh,.A structure with bridging hydrogen atoms between iron and arsenic is suggested.
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