Bimodal substitution behavior in the reaction of N,N’-diisopropylformamidine with [Os3(CO)10(NCMe)2]: Kinetics and molecular structures of the formamidinate-substituted clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri], HOs3(CO)10[μ-NPriC(H)NPri], and HOs3(CO)9[μ3-NPriC(H)NPri

Abstract

The dinitrogen donor N,N’-diisopropylformamidine [PriN=C(H)NHPri] reacts with the triosmium cluster Os3(CO)10(NCMe)2 at room temperature to yield the isomeric clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri] (1) and HOs3(CO)10[μ-NPriC(H)NPri] (2) in a 1:2.8 ratio. 1 contains an edge-bridging iminocarbamoyl ligand, while 2 contains a bridging formamidinate ligand. Thermolysis of 1 yields 2 plus the face-capped cluster HOs3(CO)9[μ3-NPriC(H)NPri] (3). The decarbonylation of 2 to 3 + CO confirms the molecularity of the observed reaction steps. The three products have been fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures for 1-3 have been determined by X-ray crystallography. The kinetics for the thermolysis reaction were investigated over the temperature range 342–383 K, and the concentration versus time profiles for the conversion of 1 → 2 → 3 + CO have been successfully modeled using two consecutive, irreversible first-order reactions. The bonding in clusters 1-3 have been examined by DFT, and these data support cluster 1 as the kinetic substitution product and cluster 2 as the thermodynamically favored isomer.