Manganese–Tin Triple Bonds: A New Synthetic Route to the Manganese Stannylidyne Complex Cation trans-[H(dmpe)2Mn≡Sn(C6H3-2,6-Mes2)]+ (dmpe = Me2PCH2CH2PMe2, Mes = 2,4,6-Trimethylphenyl)

Abstract

A new approach to the first complex featuring a manganese-tin triple bond that takes advantage of the propensity of dihydrogen complexes to eliminate H2 is reported. Reaction of the 18-valence-electron manganese dihydrogen hydride complex [MnH(η(2)-H2)(dmpe)2] (1) (dmpe = Me2PCH2CH2PMe2) with the organotin(II) chloride SnCl(C6H3-2,6-Mes2) (Mes = 2,4,6-trimethylphenyl) selectively afforded by H2 elimination the chlorostannylidene complex trans-[H(dmpe)2Mn═Sn(Cl)(C6H3-2,6-Mes2)] (2), which upon treatment with Na[B(C6H3-3,5-(CF3)2)4] and Li[Al(OC(CF3)3)4] was transformed quantitatively into the stannylidyne complex salts trans-[H(dmpe)2Mn≡Sn(C6H3-2,6-Mes2)]A [A = B(C6H3-3,5-(CF3)2)4 (3a), Al(OC(CF3)3)4 (3b)]. Complexes 2 and 3a/3b were fully characterized, and the structures of 2 and 3a were determined by single-crystal X-ray diffraction. Complex 2 features the shortest Mn-Sn double bond reported to date, a large Mn-Sn-Caryl bond angle, and a long Sn-Cl bond of the trigonal-planar-coordinated tin center. These bonding features can be rationalized in valence-bond terms by a strong contribution of the triply bonded resonance structure [LnMn≡SnR]Cl and were verified by a natural resonance theory (NRT) analysis of the electron density of the DFT-minimized structure of 2. Complex 3a features the shortest Mn-Sn bond reported to date and a linearly coordinated tin atom. Natural bond order and NRT analyses of the electronic structure of the complex cation in 3a/3b suggested a highly polar Mn-Sn triple bond with a 65% ionic contribution to the NRT Mn-Sn bond order of 2.25. Complex 3a undergoes reversible one-electron reduction, suggesting that open-shell stannylidyne complexes might be accessible using strong reducing agents.