Cyclisation of Allenylidene Ligands to Indenyl Groups on Ruthenium Clusters

Thermolysis of Ru₃ cluster complexes containing diarylallenylidene and dppm ligands results in phenyl migration from dppm to the allenylidene with concomitant H migration and C–C bond formation reactions to give several complexes each containing a cluster-bound indenyl group. In initially-formed complexes 3 or 6, the diarylindenyl group is attached to the cluster by two localized C=C double bonds of one aryl group and a benzylic interaction of the remaining C=C double bond combined with one carbon of the five-membered ring. Thermal rearrangement of these complexes with concomitant loss of CO gives 4 or 7, respectively, in which the indenyl group is more symmetrically bonded to the cluster by two C=C double bonds from the six-membered ring and an ⁵-interaction from the five-membered ring, both of the indenyl ligand. The X-ray crystal structure determination of Ru₃( ₃-PPhCH₂PPh₂)( ₃-C₉H₅Ph₂)(CO)₅ (4) is reported. A related reaction was found between Ru₃(-H)(-CCCPh₂)(-OH)(CO)₉ and Co₂(CO)₈, which afforded CoRu₃( ₃-C₉H₆Ph) (-CO)₄(CO)₅ (8), also structurally characterized, in which the indenyl group caps the Ru₃ face of a CoRu₃ tetrahedron; unusually, there are four CO groups bridging the three Co–Ru bonds.     

Reactions of Ruthenium–Allenylidene Complexes Tethering a Cyclopropyl Group

Two cyclopropyl allenylidene complexes [Ru]=CCC(R)(C₃H₅) ([Ru]=[RuCp(PPh₃)₂], Cp=Cyclopentadienyl; R=thiophene ( 2a ) and R=Ph ( 2b )) are prepared from the reactions of [Ru]Cl with the corresponding 1‐cyclopropyl‐2‐propyn‐1‐ol in the presence of KPF₆. Thermal treatment, halide‐anion addition, and palladium‐catalyzed reactions of 2a and 2b all lead to a ring expansion of the cyclopropyl group, giving the vinylidene complexes 4a and 4b , respectively, each with a five‐membered ring. This ring expansion proceeds by C C bond formation between Cβ of the cumulative double bond and a methylene group of the cyclopropyl ring. In the reaction of 2a with pyrrole, consecutive formation of two C C bonds, one between C‐2 of pyrrole and Cγ of 2a and the other between C‐3 of pyrrole and Cα, results in the formation of 6a . The reaction proceeds by addition of pyrrole and 1,3‐proton shifts. The hydrogenation of 2a by NaBH₄ is carried out in different solvents. The cumulative double bonds are reduced regioselectively to give a mixture of 7a and 8a . Interestingly, use of different solvents leads to different ratios of 7a and 8a . Presence of a protic solvent like methanol in dichloromethane or chloroform solution increases the yield of 8a , thus revealing that both the rates of hydroboration and deboronation increase. The structures of two new complexes 4a and 6a have been firmly established by X‐ray diffraction analysis.     

Synthesis of Allenylidene Lithium and Silver Complexes,and Subsequent Transmetalation Reactions

Alpha, beta, gamma! Amino substituents in alpha and beta positions allow the isolation of free carbenes, but even in the gamma position, their strong π‐electron‐donating properties permit the synthesis of allenylidene lithium adducts and silver complexes (see picture), which are ideal precursors for the preparation of various transition‐metal–allenylidene complexes.

     

Homobimetallic Ruthenium-Ethylene,Vinylidene, Allenylidene,and Indenylidene Catalysts for Olefin Metathesis

Summary: Following the discovery of bimetallic ruthenium scaffold ( 1 ), two new homobimetallic ruthenium-N-heterocyclic carbene complexes ( 2 , 3 ) were synthesized and found highly suitable for promoting ROMP, RCM, and CM reactions. Results from this study indicated that the ethylene ligand was highly labile and that adding a small amount of a terminal alkyne to the reaction media had a beneficial influence on the metathetical activity. These observations prompted us to further investigate the role of the alkyne co-catalyst. Thus, homobimetallic ruthenium-arene complexes bearing vinylidene ( 4 , 5 ), allenylidene ( 6 ), and indenylidene ( 7 ) ligands were prepared from complex 1 and propargyl alcohol derivatives. Their catalytic activities were probed in several types of olefin metathesis reactions, and they were found valuable intermediates for the safe and efficient one-pot synthesis of the Hoveya–Grubbs isopropoxybenzylidene catalyst ( 8 ).     

Chiral Ruthenium–Allenylidene Complexes That Bear a Fullerene Cyclopentadienyl Ligand: Synthesis,Characterization, and Remote Chirality Transfer

Ruthenium complexes that bear both a fullerene and an allenylidene ligand, [Ru(C₆₀Me₅)((R)‐prophos)=C?C?CR¹R²]PF₆ (prophos=1,2‐bis(diphenylphosphanyl)propane), were prepared by the reaction of [Ru(C₆₀Me₅)Cl((R)‐prophos)] and a propargyl alcohol in better than 90 % yields, and characterized by ¹H, ¹³C, and ³¹P NMR, IR, and UV/Vis/NIR spectroscopy and MS. Cyclic voltammograms of these complexes showed one reversible or irreversible reduction wave due to the allenylidene part, and two reversible reduction waves due to the fullerene core. Nucleophilic addition of RMgBr or RLi proceeded regioselectively at the distal carbon atom of the allenylidene array. The reaction took place with a 60:40–95:5 level of diastereoselectivity with respect to the original chirality in the (R)‐prophos ligand, which is located six atoms away from the electrophilic carbon center.     

Determination of the mechanism of the oxidation of the trichloromethyl radical by the photolysis of chloral in the presence of oxygen

The photooxidation of chloral was studied by infrared spectroscopy under steady-state conditions with irradiation of a blackblue fluorescent lamp (300 nm < λ < 400 nm, λ_max = 360 nm) at 296 ± 2 K. The products were hydrogen chloride, carbon monoxide, carbon dioxide, and phosgen. The kinetic results reveal that the reaction proceeds via chain reaction of the Cl atom: The results lead to the conclusion that mechanism (B) is confirmed to be more likely than mechanism (A), which was favored at one time by Heicklen for the mechanism of the oxidation of trichloromethyl radicals by oxygen molecules: The ratio of the initial rates of CO and CO₂ formation gave k₇/k₆ = 4.23M^?1, and the lower limit of reaction (5) was found to be 3.7 × 10⁸M^?1 sec^?1.