Cyclopentadienyl and its derivatives (Cp ligands) are among the most extensively utilized p ligands in organometallic chemistry. In most organometallic reactions of transitionmetal complexes, the h 5 -Cp ligand plays the role of a spectator that stays tightly bound in h 5 fashion to the metal center throughout the course of the reactions. [1] For example, ruthenium half-sandwich complexes [(h 5 -C 5 R 5 )RuXL 2 ] (R = H, Me; X = halide; L 2 = neutral ligands) are very effective catalysts for C À C bond-forming reactions, whereby the CpRu moiety remains intact. [2] Though Cp ligands are usually considered as inert groups, a few examples of C À C activation of Cp have been reported in titanocene, [3][4][5] cobaltocene, and chromocene complexes. [6] We report herein an unprecedented participation of a Cp in coupling and cycloaddition reactions with alkynes to give tricyclic compounds.
Reaction of [{h 5 :s-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )}Ru(NCCH 3 ) 2 ] (1) [7] with 3 equiv of ArC CH in toluene at room temperature afforded unexpected ruthenium complexes bearing a tricyclic moiety [{h 4 :s-Me 2 C(C 11 H 7 Ar 3 )(C 2 B 10 H 10 )}Ru(NCCH 3 )] (2 ad) in 68-76 % yields of isolated compounds (Scheme 1). [8] The 1 H NMR spectra of 2 a-d were similar. In addition to multiplets for aromatic protons in the range 7.6-7.2 ppm, two singlets for the Me 2 C protons at about 1.5 and 1.3 ppm, and one singlet for CH 3 CN protons at about 1.7 ppm, two singlets around 6.2 and 4.9 ppm assignable to vinyl protons H10 and H12, two doublets at about 3.4 and 1.0 ppm attributable to H8 and H14, and three doublets of doublets at approximately 4.8, 3.7, and 3.3 ppm corresponding to H7, H5, and H6, respectively, were observed in all 1 H NMR spectra. A characteristic resonance [9] for RuC14H at about À17 ppm was found in the 13 C NMR spectra of 2 a-d. All 11 B NMR spectra exhibited a 1:1:3 pattern.
When PhC CH was replaced by PhC CD in the above reaction, [{h 4 :s-Me 2 C(C 11 H 4 D 3 Ph 3 )(C 2 B 10 H 10 )}Ru(NCCH 3 )] ([D 3 ]-2 a) was isolated in 70 % yield with greater than 98 % deuterium incorporation (Scheme 1). [8] Its 1 H NMR spectrum showed that the resonances corresponding to H10, H12, and H14 had disappeared and one doublet attributable to H5 (instead of one doublet of doublets in 2 a) was observed, while all other signals were identical with those of 2 a. This result indicates that H10, H12, and H14 come from the alkyne.
The molecular structure of 2 a was confirmed by singlecrystal X-ray analysis. [10] The Ru atom is s-bound to C2 and C14, h 2 -bound to two double bonds, and coordinated to one CH 3 CN molecule in a distorted square-pyramidal geometry Scheme 1. Preparation of 2 a-d and [D 3 ]-2 a.