Heterobimetallic Nitrido Complexes of Group 8 Metalloporphyrins

Heterobimetallic nitrido porphyrin complexes with the [(L)­(por)­M–N–M′(LOEt)­Cl2] formula {por2– = 5,10,15,20-tetra­phenyl­porphyrin (TPP2–) or 5,10,15,20-tetra­(p-tolyl)­porphyrin (TTP2–) dianion; LOEt– = [Co­(η5-C5H5)­{P­(O)­(OEt)2}3]−; M = Fe, Ru, or Os; M′ = Ru or Os; L = H2O or pyridine} have been synthesized, and their electrochemistry has been studied. Treatment of trans-[Fe­(TPP)­(py)2] (py = pyridine) with Ru­(VI) nitride [Ru­(LOEt)­(N)­Cl2] (1) afforded Fe/Ru μ-nitrido complex [(py)­(TPP)­Fe­(μ-N)­Ru­(LOEt)­Cl2] (2). Similarly, Fe/Os analogue [(py)­(TPP)­Fe­(μ-N)­Os­(LOEt)­Cl2] (3) was obtained from trans-[Fe­(TPP)­(py)2] and [Os­(LOEt)­(N)­Cl2]. However, no reaction was found between trans-[Fe­(TPP)­(py)2] and [Re­(LOEt)­(N)­Cl­(PPh3)]. Treatment of trans-[M­(TPP)­(CO)­(EtOH)] with 1 afforded μ-nitrido complexes [(H2O)­(TPP)­M­(μ-N)­Ru­(LOEt)­Cl2] [M = Ru (4a) or Os (5)]. TTP analogue [(H2O)­(TTP)­Ru­(μ-N)­Ru­(LOEt)­Cl2] (4b) was prepared similarly from trans-[Ru­(TTP)­(CO)­(EtOH)] and 1. Reaction of [(H2O)­(por)­M­(μ-N)­M­(LOEt)­Cl2] with pyridine gave adducts [(py)­(por)­M­(μ-N)­Ru­(LOEt)­Cl2] [por = TTP, and M = Ru (6); por = TPP, and M = Os (7)]. The diamagnetism and short (por)­M–N­(nitride) distances in 2 [Fe–N, 1.683(3) Å] and 4b [Ru–N, 1.743(3) Å] are indicative of the MIVNM′IV bonding description. The cyclic voltammograms of the Fe/Ru (2) and Ru/Ru (4b) complexes in CH2Cl2 displayed oxidation couples at approximately +0.29 and +0.35 V versus Fc+/0 (Fc = ferrocene) that are tentatively ascribed to the oxidation of the {LOEtRu} and {Ru­(TTP)} moieties, respectively, whereas the Fe/Os (3) and Os/Ru (5) complexes exhibited Os-centered oxidation at approximately −0.06 and +0.05 V versus Fc+/0, respectively. The crystal structures of 2 and 4b have been determined.