AlIylferrocenylselenide (2) is prepared from diferrocenyldiselenide (ISe) which was characterized along with its sulfur analog IS by X-ray structure analysis. In the crystal lattice the packing is determined by 'point-to-face' CH-"re interactions with close contacts between the CH re donors and cyclopentadienyl rings as the r e acceptors. Compound 2 is then used in the trapping of the primary butatrienylidene intermediate trans-[CIRu(dppm)2=C=C=C=CH2]+ . The isolated product, trans-[CI(dppmhRu=C=C= C(SeFc)(C4H7)]+ (3) (Fc = ferrocenyl), represents the first seleno-substituted allenylidene complex to be reported to date. Compound 3 is formed in a sequence involving regioselective addition of the selenium nucleophile to Cy followed by hetero-Cope-rearrangement of the allyl vinyl substituted SeRt cation. Its spectroscopic properties place 3 at an intermediate position between sulfur and arene substituted all-carbon aIIenylidene complexes of the same metal fragment. The selenoaIlenyli dene complex 3 contains a redox active ferrocenyl substituent attached to the heteroatom giving rise to reversible electrochemistry. ESR spectroscopy proves that electron transfer occurs from this site and its effect on the spectroscopic properties of 3 is probed by combining electrochemistry and IR or UV -vis/NIR spectroscopy by in situ techniques. In contrast, the reversible reduction primarily involves the aIlenyIidene ligand as ascertained by ESR spectroscopy. In situ spectro-electrochemical techniques reveal how the reduction affects the bonding within the unsaturated ligand.
Aminoallenylidene complexes tr(/ns-[CI(dppmhRuC 3 (NRR')(CH 3 W are obtained fr ? m the re � iosel � ctiv � addition of secondary amines to trans-[CI(dppm)2Ru=C=C=C=CH2l'. Un symmetrically substituted ammes give ns. e to ZI E isomeric mixtures. Dynamic 3 1p NMR spectroscopy gave an energy barrier of about 85 kJ mol-I for rotatIOn around the CN-bond pointing to a large contribution of the iminium alkynyl resonance form trans-[CI(dppmhRu-C=-C C(=NRR ')(CH 3)],. This is also indicated by the pronounced bond length alternation � ithin � he �uC 3 N-cha�n as is revealed by X-ray structure analysis of the Z isomer of the (benzylmethyl)methylamme denvatIve 2d. The Issue of NR2 rotation was also addressed by DFT calculations on the trans-[CI(dhpmhRuC 3 {N(CH 3)2}(CH 3 W model complex (dhpm = H2PCH2PH2). Upon rotation around the iminium type CN bond, the nitrogen lone pair and the It-system of the allenylidene ligand are decoupled, resulting in a significantly longer CN bond and a tetrahedrally coordinated nitrogen atom.
, L 2 = 2 PPh 3 or 1,1Ј-bis(diphenylphosphanyl)ferrocene (dppf), R = Ph or ferrocenyl] and their spectroscopic and electrochemical characteristics. Three of these compounds possess redox-active, ferrocenebased substituents or ligands − that are oxidized at lower potentials than the ruthenium center itself − attached either to the terminal carbon atom of the allenylidene ligand or to the ruthenium atom. The Fc/Ph-substituted complexes 3a and 3b provide unique examples of hindered rotation of the allenylidene substituent around the M=C bond. For 3a (L 2 = 2 PPh 3 ), two isomers differing in the orientation of the vertically aligned, unsymmetrically substituted allenylidene ligand are discernible even at 388 K. The dppf-substituted congener 3b has the allenylidene ligand in a horizontal orientation and exhibits a rotational barrier, as determined by dynamic 31 P NMR spectroscopy, of ∆G ϶ = 47 kJ/mol at T C = 238 K. The changes in the spectroscopic and electrochemical properties upon replacement of the PPh 3 by a dppf ligand and the Ph by an Fc moiety can be explained in terms of the bonding within these systems. These effects are attenuated when the ferrocene-based redox tags are oxidized, as shown by IR and
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.
Trapping of the primary butatrienylidene intermediate trans-[Cl(dppm) 2 RudCdCdCdCH 2 ] + with five-membered 2-(dimethylamino)methyl-substituted heterocycles provides an easy and efficient route to aminoallenylidene complexes with appended 2-methylene-2,3-dihydrofuran,-thiophene, or-selenophene moieties. Upon warming or acid catalysis isomerization to the aromatic 2-methylated isomers is observed.
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