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

The six-coordinate osmium(IV) complex OsH 2 Cl 2 (P i Pr 3 ) 2 reacts with cyclopentadienyl derivatives of s- or p-block elements to afford cyclopentadienyl−osmium complexes, including Os(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 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(η 5 -C 5 H 5 )Cl( CHPh)(P i Pr 3 ), Os(η 5 -C 5 H 5 )Cl( C CHR)(P i Pr 3 ), and Os(η 5 -C 5 H 5 )Cl( C C CPh 2 )(P i Pr 3 ), respectively, which give rise to half-sandwich carbyne, η 3 -allyl, η 3 -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(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 is favored. The resulting metal fragment activates C(sp 3 )−H, C(sp 2 )−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(η 5 -C 5 H 5 )( C CHR)(P i Pr 3 ) 2 ] + and [Os(η 5 -C 5 H 5 )( C C CPh 2 )(P i Pr 3 ) 2 ] + . Mixed-ligand allenylidene derivatives of the type [Os(η 5 -C 5 H 5 )( C C CPh 2 )L(P i Pr 3 )] + are formed by addition of Lewis bases to the four-electron alkyne complex [Os(η 5 -C 5 H 5 ){η 2 -HC⋮CC(OH)Ph 2 }(P i Pr 3 )] + . The reactions of the carbonyl derivative [Os(η 5 -C 5 H 5 )( C C CPh 2 )(CO)(P i Pr 3 )] + with RXH (X = O, NR) molecules afford Fischer-type alkenylcarbene compounds. The complex Os(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 also reacts with group 14 element hydride compounds to give OsH(η 5 -C 5 H 5 )Cl(EPh 3 )(P i Pr 3 ) (E = Si, Ge, Sn). Treatment of OsH(η 5 -C 5 H 5 )Cl(EPh 3 )(P i Pr 3 ) (E = Si, Ge) with LiNu reagents (Nu = CH 2 CN, CH 2 C(O)CH 3, alkyl, NR 2, PPh 2 ) yields four different types of compounds: OsH 2 (η 5 -C 5 H 4 EPh 3 )(Nu)(P i Pr 3 ), OsH 2 (η 5 -C 5 H 4 Nu)(EPh 3 )(P i Pr 3 ), and The formation of these derivatives has been rationalized on the basis of the tendency of the EPh 3 and Nu ligands of OsH(η 5 -C 5 H 5 )(Nu)(EPh 3 )(P i Pr 3 ) to exchange their positions with the hydrogen atoms of the cyclopentadienyl ring and the stability of these species and OsH 2 (η 5 -C 5 H 4 EPh 3 )(Nu)(P i Pr 3 ) toward the reductive elimination of H−Nu. One of the phosphines of Os(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 can be also displaced by molecular hydrogen. The reaction leads to OsH 2 (η 5 -C 5 H 5 )Cl(P i Pr 3 ), which reacts with diphenylacetylene to yield Os(η 5 -C 5 H 5 )Cl(η 2 -PhC⋮CPh)(P i Pr 3 ). In methanol, the latter gives rise to the isopropenyldiisopropylphosphine derivative Os(η 5 -C 5 H 5 )Cl{[η 2 -CH 2 C(CH 3 )]P i Pr 2 }, which affords dienylphosphine and iminophosphine compounds by reactions with terminal alkynes and benzonitriles, respectively.