Pyrrolyl substituted allenylidene complexes of ruthenium
7// 6854/65 Pyrrolyl a nd indo lyl substituted allenylidene complexes of ruthenium have been prepared from the trappi ng of cati o nic Irans-[Cl(dppmhRu = C= C = C = CH 2 j+ with vari ous pyrroles or N-methylindole. T he react io n is rationalized as involving regioselective attack of the organometallic electrophile on the electron-rich heterocycle followed by proton mi gration to the terminal = CH 1 entity of the interm ediate butenynyl substituted a-complex. Pyrrolyl substituted a llenylidene
... tuted a llenylidene complexes have spectroscopic and electrochemical properties interm edi ate between those of amino and aryl substituted congeners a nd ca n thus be regarded as vinylogous aminoallenylidene complexes. We present spectroscopic evidence that the pyrrole It-system is efficiently incorporated into the meta llabu tatriene chrom opho re including resonance Raman spectroscopy. According to our results, the respective fro ntier orbi tals are delocalized across the entire ClRuC)(pyrrolyl) entity which defies a ny classification of the individual redox events as metal or liga nd centered redox processes. This iss ue has been specifically addressed by spectroe lectrochemistry. The structure of the l-methylindole-3-yl compl ex has bee n determined by X-ray crystallography. Bond parameters along the ruth en ium-a ll enylidene cha in a re intermed iate between those of amin o a nd aryl substituted co ngeners and suppo rt our conclusions drawn from th e spectroscopic results. While still electron rich, pyrrolyl subst ituted alknylid cnc complexes a re easily deprotonatcd to their conj ugate bases, which a re substituted butenynyl complexes. This has been exempli lied with the tetrahydroindole derived complex 3f.