[ECCE]-Coordinated (E = P, As) Ruthenium Complexes in Different Oxidation States: Ru(I) (E = P), Ru(II) (E = P, As) and Ru(III) (E = As)

Targeting Ru(III) and Ru(I) η2-alkyne complexes, 2,2’-(iPr2E)2-substituted diphenylacetylenes (1-E, E = P, As) were employed for the prepara-tion of [ECCE]-coordinated Ru(II) complexes, which were examined with respect to 1e− oxidation and reduction. Starting from [(η6-cymene)RuCl2]2 and 1-E, ligand cyclization reactions (via attack of one iPr2E moiety at the alkyne) were observed and found to afford cyclic aryl ylidic mesoionic carbenes (2-E). Attempts to ring-open these complexes were unsuccessful for E = P, but found to proceed smoothly for E = As, which led to the isolation of cis-[AsCCAs]RuCl2(MeCN) (3-As). To also gain access to the corresponding [PCCP]-coordinated derivative (3-P), the reactions between 1-E (E = P, As) and cis-(MeCN)2(COD)RuCl2 ∙ 2 MeCN were examined, which led to the envisioned complexes 3-E for E = As and E = P. Compounds cis-[ECCE]RuCl2(MeCN) (3-E) and their carbonyl derivatives cis-[ECCE]RuCl2(CO) (5-E) were oxidized using PhICl2, which led to an oxidative dichlorination of the alkyne in the case of 5-E. The latter dichlorination was found to occur trans-selective to afford complexes of the type [trans-E(Cl)C=C(Cl)E]RuCl2(CO) (6-E), while unselective oxidation processes set in upon treatment of 3-E with PhICl2. Although the envisioned Ru(III) complexes [ECCE]RuCl3 (7-E) were detectable for E = P and E = As, only the arsa-derivative 7-As was obtained in a pure form, namely via oxidation of cis-[ECCE]RuCl2(THT) (8), which is accessible for E = As only. Upon reduction of compounds 3-E, a hitherto unprecedented Ru(I) η2-alkyne complex, [PCCP]RuCl (9), was obtained for E = P, while multi-ple attempts to also isolate the corresponding arsa-derivative met with failure. The former square planar Ru(I) complex (9) was characterized comprehensibly and examined in detail by means of DFT and CASSCF calculation. Upon treatment of 9 with TlPF6, a diamagnetic µ-Tl-bridged compound (10) with a nearly linear Ru−Tl−Ru array was formed and isolated in high yields. Careful analysis of the bonding situation suggested that the Ru−Tl−Ru moiety in 10 is best interpreted in terms of a 3c-4e− bond.