Mixed isocyanide-1,4-diaza-1,3-butadiene complexes of molybdenum and tungsten-II. Species of the type [M(CO) 3(CNR)(R′-DAB)] 1+,0,1−

Abstract

Listen

Translate article

The complexes M(CO) 4(R′-DAB) (M = Mo or W; R′-DAB = R′NCHCHNR′; R′ = i-Pr, t-Bu, Cy or p-tol) undergo substitution of a single CO ligand by isocyanide ligands RNC (R = Me, CHMe 2, CMe 3, C 6H 11 or xylyl), in refluxing toluene to give fac-M(CO) 3(CNR)(R′-DAB). Synthesis of the latter complexes can also be achieved, at ambient temperature, through the use of the nitrile complexes, Mo(CO) 3(NCMe) 3 and W(CO) 3(NCEt) 3: the method involves substitution of the nitrile ligands first by R′-DAB, then by RNC. The intermediate compounds Mo(CO) 3(NCMe)(R′-DAB) and W(CO) 3(NCEt)(R′-DAB) have also been isolated and characterized. Oxidation of dark blue-purple Mo(CO) 3(NCMe)( t-Bu-DAB) and Mo(CO) 3(CNR)( t-Bu-DAB)(R = Me or CMe 3) with [Cp 2Fe]PF 6 in dichloromethane solution produces the paramagnetic (17-electron), orange complexes [Mo(CO) 3(NCMe)( t-Bu-DAB)PF 6 and [Mo(CO) 3(CNR)( t-Bu-DAB)]PF 6, respectively. The molybdenum cations, [Mo(CO) 3(NCMe)( t-Bu-DAB)]PF 6 and [Mo(CO) 3(CNCMe 3)( t-Bu-DAB)]PF 6, react with two and one equivalent of tert-butyl isocyanide, respectively, to yield dark red cis, trans-[Mo(CO) 2(CNCMe 3) 2) t-Bu-DAB)]PF 6. Reduction of cis, trans-[Mo(CO) 2(CNCMe 3) 2)( t-Bu-DAB)]PF 6 with cobaltocene in acetone yields the analogous dark blue zerovalent species cis, trans-Mo(CO) 2(CNCMe 3) 2( t-Bu-DAB). The compounds [Mo(CO)(CNR) 4( t-Bu-DAB)](PF 6) 2 and Mo(CO) 3(CNR)( t-Bu-DAB) are produced, via a disproportionation reaction, when solutions of the cations [Mo(CO) 3(CNR)( t-Bu-DAB)] + (R = Me or CMe 3) are reacted with ∼three equivalents of RNC. On the other hand, the reaction between tert-butyl isocyanide and [Mo(CO) 3(CNCMe 3)( i-Pr-DAB)] + gives seven-coordinate [Mo(CNCMe 3) 5( i-Pr-DAB)](PF 6) 2 and Mo(CO) 3(CNCMe 3)( i-Pr-DAB). The ligand-based reduction of the complexes M(CO) 3(CNR)(R′-DAB) (M = Mo or W) is readily accessible in THF upon addition of one molar equivalent of THF-soluble LiEt 3BH to yield solutions that contain the radical anions [M(CO) 3(CNR)(R′-DAB)] −.. The complexes synthesized in this work have been characterized on the basis of their spectroscopic and electrochemical properties, including ESR spectral studies on the paramagnetic 17- and 19-electron complexes.