Synthesis and characterization of alkylidyne complexes of group 6 transition metals (Cr, Mo and W)

Abstract

The N,N,N``,N``-tetramethylethylenediamine (TMEDA) substituted alkylidyne complexes, $Br(CO)_2$(tmeda)M≡CTol [M=Cr(1), Mo(2), W(3)], have been prepared from the reaction of $Br(CO)_4$M≡CTol with TMEDA. Complexes 1,2 and 3 exist as two diastereomers in solution. One of the diastereomers, trans,cis-$Br(CO)_2$(tmeda) Cr≡CTol (1a), has been structurally characterized via a single crystal X-ray diffraction study and the other, cis,trans-1b, charactrized by IR and NMR spectroscopic methods. An efficient synthetic method of chromium alkylidyne complexes, $Cp(CO)_2$Cr≡CTol (4) and Tp*$(CO)_2$Cr≡CTol (5) [Tp*=hydrotris (3,5-dimethyl pyrazol-1-yl)borato], has been developed. These complexes have been prepared from the reaction of $Br(CO)_2$(py)_2Cr≡CTol (6) with NaCp and KTp* in good yields. The first cluster - bound $C_{60}$ derivatives, $Os_3(CO)_{11}(\eta^2-C_{60})$ (7), $Os_3(CO)_{10}(NCMe)(η^2-C_{60})$ (10) have been synthesized. Spectroscopic data (IR and NMR) support that the $C_{60}$ ligand is coordinated to an osmium atom at an equatorial site of the triosmium cluster. Complex 7 has been characterized by a single crystal X-ray diffraction study, which shows the $η^2$-binding of the $C_{60}$ ligand to an osmium atom at a 6-6 fullerene double bond. Fluxional behavior of 8 in solution has been investigated by variable temperature $^{13}C$ NMR, which reveals the restricted cyclic in-plane motion of carbonyl and $C_{60}$ ligands. Electrochemistry of $C_{60}$-triosmium complexes (7, 9, and 10) has been studied by cyclic voltammetry. The first one-electron reductions of 7 and 9 are localized at the coordinated $C_{60}$ ligand. The electrons accepted via $C_{60}$ are transferred intramolecularly to the triosmium center, which is supported by the observation that the second and third reduction potiontials of 7 and 9 are more positived than those of $C_{60}$. The first and second reduction potential is more positive than that of $C_{60}$. This indicates that intramolecula...