Formation of Dinuclear Ruthenacyclopentenyl Complexes from Reactions of Cp*Ru(μ-SPri)2RuCp* (Cp* = η5-C5Me5) with Terminal Alkynes and Subsequent Ring-Opening Reaction Induced by ButNC To Give Diruthenium μ-Alkenyl Complexes

Ruthenium-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohols with Oxygen-, Nitrogen-, and Phosphorus-Centered Nucleophiles

The scope and limitations of the ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with heteroatom-centered nucleophiles are presented. Oxygen-, nitrogen-, and phosphorus-centered nucleophiles such as alcohols, amines, amides, and phosphine oxide are available for this catalytic reaction. Only the thiolate-bridged diruthenium complexes can work as catalysts for this reaction. Results of some stoichiometric and catalytic reactions indicate that the catalytic propargylic substitution reaction proceeds via an allenylidene complex formed in situ, whereby the attack of nucleophiles to the allenylidene C(gamma) atom is a key step. Investigation of the relative rate constants for the reaction of propargylic alcohols with several para-substituted anilines reveals that the attack of anilines on the allenylidene C(gamma) atom is not involved in the rate-determining step and rather the acidity of conjugated anilines of an alkynyl complex, which is formed after the attack of aniline on the C(gamma) atom, is considered to be the most important factor to determine the rate of this catalytic reaction. The key point to promote this catalytic reaction by using the thiolate-bridged diruthenium complexes is considered to be the ease of the ligand exchange step between a vinylidene ligand on the diruthenium complexes and another propargylic alcohol in the catalytic cycle. The reason why only the thiolate-bridged diruthenium complexes promote the ligand exchange step more easily with respect to other monoruthenium complexes in this catalytic reaction should be that one Ru moiety, which is not involved in the allenylidene formation, works as an electron pool or a mobile ligand to another Ru site. The catalytic procedure presented here provides a versatile, direct, and one-step method for propargylic substitution of propargylic alcohols in contrast to the so far well-known stoichiometric and stepwise Nicholas reaction.

Metal-Metal Bonding in Pentanuclear Bow-Tie Metal Sulfido Clusters. Synthetic and Structural Studies on the Cationic Pentanuclear Clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](n)()(+) (M = Fe, Co, Ni; n = 1, 2)

Reactions of [CpMCl(&mgr;(2)-SH)(2)MCpCl] (1, M = Ir; 2, M = Rh; Cp = eta(5)-C(5)Me(5)) with excess FeCl(2).4H(2)O in THF gave the paramagnetic trinuclear clusters [(CpM)(2)(&mgr;(3)-S)(2)FeCl(2)] (3, M = Ir; 4, M = Rh), which were further converted into the dicationic 78e(-) pentanuclear bow-tie cluster [(CpIr)(2)(&mgr;(3)-S)(2)Fe(&mgr;(3)-S)(2)(IrCp)(2)](2+) (5) by treatment with NaBPh(4). When complex 1 was allowed to react with CoCl(2) and NiCl(2).6H(2)O or Ni(cod)(2) (cod = cyclooctadiene), the related pentanuclear 79e(-) and 80e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](2+) (6, M = Co; 7, M = Ni) were obtained directly, respectively. Cyclic voltammograms of 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) showed two reversible reduction waves at -0.25 to -0.43 V and -1.04 to -1.34 V. In both redox couples, the redox potential was in the order Fe < Co < Ni. One-electron reduction of clusters 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) with Co(eta(5)-C(5)H(5))(2) gave the corresponding monocationic pentanuclear 79-81e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](+) (8, M = Fe; 9, M = Co; 10, M = Ni). The molecular structures of 3, 4, 5[BPh(4)](2).CH(2)Cl(2), 6[CoCl(3)(NCMe)](2), 7[NiCl(4)].CH(2)Cl(2), 8[BPh(4)], 9[BPh(4)], and 10[BPh(4)] were unambiguously determined by X-ray diffraction study. The structures of the pentanuclear bow-tie cluster cores remarkably changed stepwise as the core electrons increased from 78 to 81. Two of the M-Ir (M = Fe, Co) bonds in the 79e(-) clusters 6 and 8 show significant elongation in comparison with the Fe-Ir bonds in the 78e(-) cluster 5. Two different types of the bow-tie structures were observed for the 80e(-) clusters 7 and 9. Cluster 7 has a Z-shaped metal core with only two Ni-Ir bonds, while in cluster 9, the six metal-metal bonds in the bow-tie structure are retained with slight elongation of the Co-Ir bonds in comparison with the corresponding dication 6. The 81e(-) cluster 10 has two normal Ni-Ir bonds and one long Ni-Ir bonding interaction with the fourth nonbonding Ni-Ir contact. This structural variation is interpreted in terms of the total electron counts and molecular orbital calculations of the clusters.