Journey from Mo-Mo quadruple bonds to quintuple bonds

Abstract

(Chemical Equation Presented) Heating K4Mo2Cl 8 and 2 equiv of Li[RC(NDipp)2] (R = H, Ph; Dipp = 2,6-i-Pr2C6H3) in tetrahydrofuran (THF) at 60°C gives two paddlewheel type quadruply bonded dimolybdenum complexes, Mo2(μ -Cl)[Cl2Li(OEt2)][μ- η2-RC(N-2,6-i-Pr2C6H3) 2]2 (R = H (1), Ph (2)). The Mo-Mo bond lengths of 1 and 2 are 2.0875(4) and 2.0756(8) Å, respectively, indicating typical Mo-Mo quadruple bonds. Reduction of 1 and 2 by two electrons results in the isolation of their corresponding Mo-Mo quintuple bonded complexes, Mo2[μ- η2-RC(N-2,6-i-Pr2C6H3) 2]2 (R = H (3), Ph (4)), and the Mo-Mo bond lengths dramatically decrease to 2.0187(9) Å (3) and 2.0157(4) Å (4), a consequence of the formation of the second δ bond and representing the shortest metal-metal bonds beyond the first row elements. The Mo-Mo quintuple bonding characters are corroborated by DFT calculations at the level of BP86/def2-TZVP and BP86/def2-TZVPP. © 2009 American Chemical Society.