FORMATION AND REACTIVITY OF (OCTAETHYLTETRAAZAPORPHYRINATO)RHODIUM COMPLEXES

A series of (octaethyltetraazaporphyrinato)rhodium, (OETAP)Rh, complexes including (OETAP)Rh-1, (OETAP)-Rh-CH3, and [(OETAP)Rh]2 were prepared for comparison with the corresponding (octaethylporphyrinato)-rhodium, (OEP)Rh, derivatives. [(OETAP)Rh]2 (1) reacts like [(OEP)Rh]2 (2) with CH3I, CH3NC, (CH3O)3P, and CH2=CH2 in forming (OETAP)Rh-CH3 and (OETAP)Rh-I, (OETAP)Rh(CN)(CH3NC), (OETAP)Rh-P(O)(OCH3)2, and (OETAP)Rh-CH2CH2-Rh(OETAP), respectively, but reactions of 1 are invariably much slower than those of 2. [(OETAP)Rh]2 fails to react with H-2, CO, CH3CHO, and CH3C6H5, which participate in prominent substrate reactions for 2. Reactivity and equilibrium studies indicate that a substantially larger Rh-Rh bond dissociation enthalpy for 1 compared with 2 is primarily responsible for the slower rates and reduced scope of substrate reactions for [(OETAP)Rh]2. Dissolution of 1 in pyridine results in formation of a persistent OETAP anion radical complex of Rh(III), (OETAP.-)Rh(III)(py)2, which contrasts with 2 where disproportionation produces the(OEP)Rh(I) anion and the (OEP)Rh(III)(py)2 cation. (OETAP)Rh-CH3 (RhC33H43N8) crystalllzes in the monoclinic system, space group P2(1)/c, with a = 9.889(2) angstrom, b = 22.660(4) angstrom, c = 14.781(3) angstrom, beta = 106.85(2)degrees, and Z = 4. The X-ray crystal and molecular structure determination for (OETAP)Rh-CH3 reveals a smaller hole size and corresponding shorter Rh-N distances for the (OETAP)Rh derivative but virtually identical Rh-CH3 bond distances in comparison with (OEP)Rh-CH3. Differences in the structures and reactivities of (OETAP)Rh and (OEP)Rh complexes are discussed in terms of the smaller hole size, lower energy of the pi* orbitals, and the doming of the OETAP ligand.