Electronic communication between tungsten alkylidyne and metal isocyanide complex fragments across phenyleneethynylene bridges

Heteronuclear metal complexes of the type [X(CO)2(LL)Wtriple bond; length of mdashC(–C6H4–Ctriple bond; length of mdashC)p–C6H4–Ntriple bond; length of mdashC–]nMLm (X = Cl, Br; LL = tmeda, dppe; p = 0–3; n = 1 for Cr(CO)5, n = 2 for ReX(CO)3, PdCl2, PdI2, and PtI2) have been prepared. The molecular structure of one example, [Cl(CO)2(tmeda)Wtriple bond; length of mdashC–C6H4–Ntriple bond; length of mdashC–]2PdI2, was determined by X-ray crystallography. The extent of electronic communication between the tungsten alkylidyne and the metal isocyanide centers was probed by various spectroscopic techniques. In the parent systems (p = 0), the electronic changes due to modification of the isocyanide metal complex fragments could be distinguished clearly by the 13C NMR chemical shift of the alkylidyne carbon atom and the d → π∗ and π → π∗ electronic transitions of the metal alkylidyne system. However, only residual effects could be discerned for the longer systems using these spectroscopic probes. Probes based on the emission property of the tungsten alkylidyne fragment proved to be the most useful in distinguishing long-range effects in those cases where the isocyanide metal complex fragment is capable of quenching the emission. This is the case for MLm = PdCl2 and PdI2. Partial quenching effects were still observed at the longest investigated distance between the metal centers of about 3.1 nm. The available evidence suggests that the quenching mechanism is electron transfer.