Resonance raman study of (η2-TCNE)M(CO)5 (M = Cr, W; TCNE = tetracyanoethene). Evidence for an olefin-complex → metallacyclopropane transition upon low-energy metal-to-ligand charge-transfer excitation

Electrochemical, Spectroscopic, and Structural Evidence for the Mild Hydrolysis of Tetracyanoethylene, TCNE, To Form the 2,3,3-Tricyanoacrylamidate Ligand: Isolation of an Unexpected Quadruply-Bonded Polymeric Material [Mo2(O2CCMe3)3((NC)2CC(CN)CONH)]∞

Under strictly anhydrous conditions, no reaction occurs between Mo(2)(O(2)CCMe(3))(4) and tetracyanoethylene, TCNE, at room temperature, but after addition of 1 equiv of water, a reaction proceeds to form [Mo(2)(O(2)CCMe(3))(3)((NC)(2)CC(CN)CONH)], 1. The compound contains a quadruple-bonded Mo(2) unit and the 2,3,3-tricyanoacrylamidate anion as a ligand (TC3A), a very unusual hydrolyzed form of TCNE. Two different solid-state structures were obtained after crystallization of 1. Crystals obtained from CH(2)Cl(2) consist of a two-dimensional network, and crystals grown from a C(6)H(6) solution form a 1-D chain motif. In both cases, the TC3A ligand acts as a polydentate ligand involving a bidentate OCN bridging unit and two CN groups. The electrochemical and spectroscopic (IR, UV/vis/near-IR, NMR, EPR) properties of 1 support the formulation in solution as a discrete 1:1 complex of the TC3A donor ligand and a Mo(2) unit with no charge transfer. The coordinated TC3A ligand exhibits redox properties similar to those of free TCNE.