ABSTRACT
The assembly of dinuclear complexes with the ultimate smallest ditopic ligands based on side-on complexes of methyl substituted alkynes is presented. In fact, the coordination of Ru(II) and Ir(III) by a W alkyne complex based cyclometallating metalla-ligand causes close intermetallic electronic cooperation, which substantially changes the electrochemical and photophysical properties of the single isolated moieties.
ABSTRACT
Treatment of the side-on tungsten alkyne complex of ethinylethyl ether [Tp*W(CO)2(η2-C,C'-HCCOCH2CH3)]+ {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} (2a) with n-Bu4NI afforded the end-on ketenyl complex [Tp*W(CO)2(κ1-HCCO)] (4a). This formal 16 ve complex bearing the prototype of a ketenyl ligand is surprisingly stable and converts only under activation by UV light or heat to form a dinuclear complex [Tp*2W2(CO)4(µ-CCH2)] (6). The ketenyl ligand in complex 4a underwent a metal template controlled cyclization reaction upon addition of isocyanides. The oxametallacycles [Tp*W(CO)2{κ2-C,O-C(NHXy)C(H)C(Nu)O}] {Nu = OMe (7), OEt (8), N(i-Pr)2 (9), OH (10), O1/2 (11)} were formed by coordination of Xy-NC (Xy = 2,6-dimethylphenyl) at 4a and subsequent migratory insertion (MI) into the W-ketenyl bond. The resulting intermediate is susceptible to addition reactions with protic nucleophiles. Compounds 2a-PF6, 4a/b, and 7-11 were fully characterized including XRD analysis. The cyclization mechanism has been confirmed both experimentally and by DFT calculations. In cyclic voltammetry, complexes 7-9 are characterized by a reversible W(ii)/W(iii) redox process. The dinuclear complex 11 however shows two separated redox events. Based on cyclic voltammetry measurements with different conducting electrolytes and IR spectroelectrochemical (SEC) measurements the W(ii)/W(iii) mixed valent complex 11+ is assigned to class II in terms of the Robin-Day classification.
ABSTRACT
A pair of diastereomeric dinuclear complexes, [Tp'(CO)BrW{µ-η2 -C,C'-κ2 -S,P-C2 (PPh2 )S}Ru(η5 -C5 H5 )(PPh3 )], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp'(CO)(PhS)W{µ-η2 -C,C'-κ2 -S,P-C2 (PPh2 )S}Ru(η5 -C5 H5 )-(PPh3 )], in which valence trapped WIII /RuII and WII /RuIII cationic species are at equilibrium.
ABSTRACT
Furan and thiophene diarylmethenes are potential redox-active ligands for metal centers that could be exploited in the development of nontraditional, stoichiometric, and catalytic redox reactions. As such, we describe here the selective meso-deprotonations of dithiophene, difuran, and diimine-difuran diarylmethanes to form the π-conjugated anions, for which only the diimino-difuryl anion is truly isolable and studied by X-ray crystallography. In all cases, facile one-electron oxidation of these anions occurs, which allows the isolation of the neutral dithienyl and diimino-difuryl radicals. UV-Visible and time-dependent density functional theory studies reveal that the oxidation of the dithienyl anion to its radical is associated with an increase in the highest (singly) occupied molecular orbital-lowest unoccupied molecular orbital gap, evident through a hypsochromic shift of the main absorption band in the electronic spectrum, whereas oxidation of the diimino-difuryl anion causes only minor spectroscopic changes. Electrochemical studies support the stability of the radicals with respect to the anion, showing strongly negative oxidation potentials. The control of the redox activity of these diarylmethene carbanions through variation of the nature of the substituents, donor-atom, and the conjugated π-system and their potential as ligands for redox-inert metal centers makes them intriguing candidates as noninnocent partners for redox reactions.
