C−C Coupling and C−H Bond Activation Reactions of Cyclopentadienyl−Osmium Compounds: The Rich and Varied Chemistry of Os(η5-C5H5)Cl(PiPr3)2 and Its Major Derivatives

Abstract

The six-coordinate osmium(IV) complex OsH2Cl2(PiPr3)2 reacts with cyclopentadienyl derivatives of s- or p-block elements to afford cyclopentadienyl−osmium complexes, including Os(η5-C5H5)Cl(PiPr3)2. One of the phosphine ligands of this compound is displaced by phenylmethylene, terminal alkynes, and 1,1-diphenyl-2-propyn-1-ol to give Os(η5-C5H5)Cl(CHPh)(PiPr3), Os(η5-C5H5)Cl(CCHR)(PiPr3), and Os(η5-C5H5)Cl(CCCPh2)(PiPr3), respectively, which give rise to half-sandwich carbyne, η3-allyl, η3-benzyl, and substituted olefin derivatives by reactions with electrophiles and nucleophiles. In the presence of chlorine extractors, the rupture of the Os−Cl bond of Os(η5-C5H5)Cl(PiPr3)2 is favored. The resulting metal fragment activates C(sp3)−H, C(sp2)−H, C(sp)−H, and P−H bonds. The C(sp)−H activation of terminal alkynes is the key step to the formation of [Os(η5-C5H5)(CCHR)(PiPr3)2]+ and [Os(η5-C5H5)(CCCPh2)(PiPr3)2]+. Mixed-ligand allenylidene derivatives of the type [Os(η5-C5H5)(CCCPh2)L(PiPr3)]+ are formed by addition of Lewis bases to the four-electron alkyne complex [Os(η5-C5H5){η2-HC⋮CC(OH)Ph2}(PiPr3)]+. The reactions of the carbonyl derivative [Os(η5-C5H5)(CCCPh2)(CO)(PiPr3)]+ with RXH (X = O, NR) molecules afford Fischer-type alkenylcarbene compounds. The complex Os(η5-C5H5)Cl(PiPr3)2 also reacts with group 14 element hydride compounds to give OsH(η5-C5H5)Cl(EPh3)(PiPr3) (E = Si, Ge, Sn). Treatment of OsH(η5-C5H5)Cl(EPh3)(PiPr3) (E = Si, Ge) with LiNu reagents (Nu = CH2CN, CH2C(O)CH3, alkyl, NR2, PPh2) yields four different types of compounds: OsH2(η5-C5H4EPh3)(Nu)(PiPr3), OsH2(η5-C5H4Nu)(EPh3)(PiPr3), and The formation of these derivatives has been rationalized on the basis of the tendency of the EPh3 and Nu ligands of OsH(η5-C5H5)(Nu)(EPh3)(PiPr3) to exchange their positions with the hydrogen atoms of the cyclopentadienyl ring and the stability of these species and OsH2(η5-C5H4EPh3)(Nu)(PiPr3) toward the reductive elimination of H−Nu. One of the phosphines of Os(η5-C5H5)Cl(PiPr3)2 can be also displaced by molecular hydrogen. The reaction leads to OsH2(η5-C5H5)Cl(PiPr3), which reacts with diphenylacetylene to yield Os(η5-C5H5)Cl(η2-PhC⋮CPh)(PiPr3). In methanol, the latter gives rise to the isopropenyldiisopropylphosphine derivative Os(η5-C5H5)Cl{[η2-CH2C(CH3)]PiPr2}, which affords dienylphosphine and iminophosphine compounds by reactions with terminal alkynes and benzonitriles, respectively.