Bimodal substitution behavior in the reaction of N,N '-diisopropylformamidine with [Os-3(CO)(10)(NCMe)(2)]: Kinetics and molecular structures of the formamidinate-substituted clusters HOs3(CO)(9)[mu-C(O)(NPrC)-C-i(H)NPri], HOs3(CO)(10)[mu-(NPrC)-C-i(H)NPri], and HOs3(CO)(9)[mu(3)-(NPrC)-C-i(H)NPri]

摘要

The dinitrogen donor N,N'-diisopropylformamidine [(PrN)-N-i-C(H)NHPri] reacts with the triosmium cluster Os-3(CO)(10)(NCMe)(2) at room temperature to yield the isomeric clusters HOs3(CO)(9)[mu-C(O)(NPrC)-C-i(H)NPri] (1) and HOs3(CO)(10)[mu-(NPrC)-C-i(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)[mu(3)-(NPrC)-C-i(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. (C) 2021 Elsevier B.V. All rights reserved.