Pyrrolyl substituted allenylidene complexes of ruthenium

Abstract

7// 6854/65Pyrrolyl 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 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.

Electron-donor/acceptor properties of carbynes, carbenes, vinylidenes, allenylidenes and alkynyls as measured by electrochemical ligand parameters

“…Most of the electrochemical studies of allenylidene complexes have been performed with the trans-{RuCl(dppm) 2 } + center [92][93][94][95][96] (in a few cases with the analogous dppe [86,94] or depe [94] sites) which has allowed to establish the following order of net electron acceptance: arylallenylidenes @C@C@CRR 0 (P L = À0.15 to À0.31 V, E L = 0.61-0.47 V vs. NHE) > selenoallenylidenes @C@C@C(SeR) (alkyl) (P L = À0.22 to À0.26 V, E L = 0.55-0.51 V vs. NHE) > thioallenylidenes @C@C@C(SR)(alkyl) (P L = À0.26 to À0.31 V, E L = 0.51-0.47 V vs. NHE) > aminoallenylidenes (P L = À0.39 to À0.84 V, E L = 0.41-0.0 V vs. NHE), pyrollyl or indolyl substituted allenylidenes (P L = À0.53 to À0.65 V, E L = 0.28-0.18 V vs. NHE). This order reflects the electronic effects of the groups at the C c which are transmitted to the binding metal center through the allenylidene unsaturated carbon chain.…”

Density Functional Study of Butadiyne to Butatrienylidene Isomerization in [Ru(HC≡CC≡CH)(PMe3)2(Cp)]+

“…This increasing activity toward longer chain cumulynidene complexes has also stirred interest in the stabilization of longer chain cumulenes by metal centers and in the possible isomerization mechanisms for their formation from stable unsatured organic molecules. − …”

“…Following the pioneering work of Selegue and Bruce, , in the last few years several groups have reported a series of reactions that have been rationalized as proceeding via butatrienylide intermediates, formed in situ from the reaction of 1,3-butadiynes with electron-rich Ru(II) metal complexes with a labile ligand, − such as [Ru(thf)(PR 3 ) 2 Cp] + , cis -RuCl 2 (dppm) 2 , and cis -RuCl 2 (dppe) 2 . However, due to their excessive reactivity, the corresponding [Ru(CCCCH 2 )(PR 3 ) 2 Cp] + , [ cis -Ru(CCCCH 2 )(dppm) 2 Cl] + , and [ cis -Ru(CCCCH 2 )(dppe) 2 Cl] + butatrienylidene complexes have never been isolated along this route because they easily add a nucleophile at the C γ carbon, leadingdepending on the nucleophileto functionalized allenylidenes or ethynyl complexes.…”

OC151: Cervical length and relaxin as predictors of preterm birth

“…There are two resonance forms of transition‐metal allenylidenes: an allenylidene form A and a metal‐propargyl‐cation form B (Scheme 3) 16. Electron‐donating groups on the C γ center (R 1 or R 2 ) tend to increase the contribution of form B, which is reflected in the 13 C NMR spectra of complexes 4 – 8 .…”