Bildung eines neuartigen C4-Liganden durch oxidative kupplung zweier metallgebundener alkinylgruppen

Titanocene – 1,4,6-tris(trimethylsilyl)hex-3-ene-1,5-diyne-3-yl complexes – crystal structures and their retro reaction

“…The differences in bond lengths and valence angles given in Table 1 are smaller than threefold esdÕs except for the angles C14-C15-C16 (171.8 (2) (5) Å indicates a large contribution of sp 2 hybridization. Similar bond lengths were found in 1,4-substituted g 3 -butenyne ligands bonded to transition metals, e.g., Ru [20], Os [21], W [22] and Fe [23], and in zirconocene-g 3 -propargyl complexes [24].…”

Quantitative Determination of the Regioselectivity of Nucleophilic Addition to η3-Propargyl Rhenium Complexes and Direct Observation of an Equilibrium between η3-Propargyl Rhenium Complexes and Rhenacyclobutenes

“…In repeating this work, we monitored the reaction of 1- t -Bu (0.030 M) with PPh 3 (0.063 M) in CD 2 Cl 2 by 1 H NMR spectroscopy, and found that metallacycle 11 was formed at −78 °C with characteristic low frequency doublets for the metal-bound CH 2 group at δ 0.14 and 1.1 (2 J = 12 Hz). When the sample was warmed to −20 °C, the conversion of metallacycle 11 to alkyne complex 12 was observed by 1 H NMR spectroscopy to be 80% complete within 2 h (Δ G ‡ ≈ 18.9(5) kcal mol −1 ).…”

“…Since the rhenacyclobutene is the only observed initial product and neither an η 2 -alkyne complex nor an η 2 -allene complex are initially seen, estimates of >20 can be placed on the regioselectivity. In some cases, the initially formed metallacyclobutene rearranged to a thermodynamically more stable η2-alkyne complex (ΔG° ≤ −2.3 kcal mol −1 ). The reaction was complete before the cold sample was inserted into the pre-cooled NMR probe; this requires a t 1/2 of less than a minute at −50 °C and Δ G ‡ (0.02 M ligand) ≤ 14.7 kcal mol −1 , Δ G ‡ (1.0 M ligand) ≤ 12.9 kcal mol −1 .…”

“…The regioselectivity of PMe 3 addition to 1- t -Bu was carefully determined by an indirect method: comparison of the rate of exchange of PMe 3 with deuterium labeled metallacycle 7-d 9 with the rate of rearrangement of metallacycle 7 to η2-alkyne complex 8 (Figure 6). The regioselectivity for addition of PMe 3 to the central carbon of 1- t -Bu was 480:1 (ΔΔ G ‡ = 3.2 kcal mol −1 ).…”

“…The first stable η 3 -propargyl complex, [(Me 3 P) 4 Os( η 3 -PhC≡CC=CHPh)][PF 6 ], was reported by Werner in 1985,2 and the first isolated η 3 -propargyl complex not having an exo -double bond [(C 6 Me 5 H)Mo(CO) 2 ( η 3 -CH 2 C≡CH)][BF 4 ] was reported by Kryvich in 1991 3…”