Formation and Reactivity of (Octaethyltetraazaporphyrinato)rhodium Complexes

Abstract

A series of (octaethyltetraazaporphyrinato)rhodium, (OETAP)Rh, complexes including (OETAP)Rh-I, (OETAP)Rh-CH[sub 3], and [(OETAP)Rh][sub 2] were prepared for comparison with the corresponding (octaethyltetraazaporphyrinato)rhodium, (OEP)Rh, derivatives. [(OETAP)Rh][sub 2] (1) reacts like [(OEP)Rh][sub 2] (2) with CH[sub 3]I, CH[sub 3]NC, (CH[sub 3]O)[sub 3]P, and CH[sub 2]=CH[sub 2] in forming (OETAP)Rh-CH[sub 3] and (OETAP)Rh-I, (OETAP)Rh(NC)(CH[sub 3]NC), (OETAP)Rh-P(O)(OCH[sub 3])[sub 2], and (OETAP)Rh-CH[sub 2]CH[sub 2]-Rh(OETAP), respectively, but reactions of 1 are invariably much slower than those of 2. [(OETAP)Rh][sub 2] fails to react with H[sub 2], CO, CH[sub 3]CHO, and CH[sub 3]C[sub 6]H[sub 5], 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][sub 2]. Dissolution of 1 in pyridine results in formation of a persistent OETAP anion radical complex of Rh(III), (OETAP[sup [sm bullet][minus]])Rh[sup III](py)[sub 2], which contrasts with 2 where disproportionation produces the (OEP)Rh[sup I] anion and the (OEP)Rh[sup III](py)[sub 2]cation. (OETAP)Rh-CH[sub 3] (RhC[sub 33]H[sub 43]N[sub 8]) crystallizes in the monoclinic system, space group P2[sub 1]/c. The X-ray crystal and molecular structure determination for (OETAP)Rh-CH[sub 3] reveals a smaller hole size and corresponding shortermore » Rh-N distances for the (OETAP)Rh derivative but virtually identical Rh-CH[sub 3] bond distances in comparison with (OEP)Rh-CH[sub 3]. 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.« less