Complex Os(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 (1) reacts with equimolecular mixtures of TlPF 6 and alkynes such as phenylacetylene and cyclohexylacetylene to give [OsH(η 5 -C 5 H 5 )(CtCR)(P i Pr 3 ) 2 ]PF 6 (R ) Ph (2), Cy (3)). The structure of 2 in the solid state has been determined by X-ray diffraction analysis. The distribution of ligands around the metallic center can be described as a four-legged piano-stool geometry with the hydride and alkynyl ligands mutually transoid. The reaction of 1 with 2-phenyl-3-butyn-2-ol and TlPF 6 leads to [OsH(η 5 -C 5 H 5 ){CtCC(OH)-MePh}(P i Pr 3 ) 2 ]PF 6 (4), which evolves into the hydride-enynyl complex [OsH(η 5 -C 5 H 5 ){Ct CC(Ph)dCH 2 }(P i Pr 3 ) 2 ]PF 6 (5) in solution of chloroform. Treatment of 1 with 1,1-diphenyl-2-propyn-1-ol and TlPF 6 affords [OsH(η 5 -C 5 H 5 ){CtCC(OH)Ph 2 }(P i Pr 3 ) 2 ]PF 6 (6), which reacts with KOH in methanol to give the neutral compound Os(η 5 -C 5 H 5 ){CtCC(OH)Ph 2 }(P i Pr 3 ) 2 ( 7) by extraction of the hydride ligand. The addition of 1 equiv of HPF 6 to the solutions of 7 leads to the allenylidene, [Os(η 5 -C 5 H 5 )(CdCdCPh 2 )(P i Pr 3 ) 2 ]PF 6 (8), which affords the dicationic carbyne derivative [Os(η 5 -C 5 H 5 )(CCHdCPh 2 )(P i Pr 3 ) 2 ](PF 6 ) 2 (9) by reaction with HPF 6 . The structure of 9 in the solid state has been also determined by X-ray diffraction analysis. In this case, the geometry around the osmium center is close to octahedral with the triisopropylphosphine ligands mutually cis disposed (P-Os-P ) 105.12(8)°). Complex 8 also reacts with nucleophilic reagents; the reaction with CH 3 Li gives Os(η 5 -C 5 H 5 ){CtCC-(CH 3 )Ph 2 }(P i Pr 3 ) 2 (10), whereas the reactions with acetone and methanol solutions of KOH afford Os(η 5 -C 5 H 5 ){CtCC[CH 2 C(O)CH 3 ]Ph 2 }(P i Pr 3 ) 2 (11) and Os(η 5 -C 5 H 5 ){CtCC(OCH 3 )Ph 2 }-(P i Pr 3 ) 2 (12), respectively. To understand the chemical behavior of 8, EHT-MO calculations on the model compounds Os(η 5 -C 5 H 5 )Cl(CdCdCH 2 )(PH 3 ) (13) and [Os(η 5 -C 5 H 5 )(CdCdCH 2 )L-(PH 3 )] + (L ) PH 3 (14), CO ( 15)) have been also carried out. The results suggest that the behavior of 8 as nucleophile is a consequence of the high electron density of the allenylidene ligand, while the behavior as γ-electrophile is due to its cationic nature. In addition, we have determined by ab initio calculations the energies of stabilization by protonation of 13-15 with a naked proton. In the three cases the formation of the corresponding carbyne derivatives [Os(η 5 -C 5 H 5 )Cl(CCHdCH 2 )(PH 3 )] + (16; 267 kcal‚mol -1 ), [Os(η 5 -C 5 H 5 )(CCHdCH 2 )-(PH 3 ) 2 ] 2+ (17; 180 kcal‚mol -1 ), and [Os(η 5 -C 5 H 5 )(CCHdCH 2 )(CO)(PH 3 )] 2+ (18; 157 kcal‚mol -1 ) involves a stabilization of the system.

The allenylidene complex [Ru(η5-C5H5)(CCCPh2)(CO)(PiPr3)]BF4 (1) reacts with diethylamine and piperidine to give the azoniabutadienyl derivatives [Ru(η5-C5H5){C(CHCPh2)NEt2}(CO)(PiPr3)]BF4 (2) and (3), respectively. The molecular structure of 2 has been determined by X-ray crystallography. The geometry around the ruthenium center is close to octahedral with the cyclopentadienyl ligand occupying three sites of a face. The Ru−Cα bond length is 2.063(6) Å, whereas the Cα−N distance is 1.306(7) Å. Treatment of 2 and 3 with sodium methoxide produces the deprotonation of the CHCPh2 fragment to afford the aminoallenyl derivatives Ru(η5-C5H5){C(NEt2)CCPh2}(CO)(PiPr3) (4) and (5). Complex 1 also reacts with n-propylamine and aniline. In this case, the reaction products are [Ru(η5-C5H5){C(CHCPh2)NHnPr}(CO)(PiPr3)]BF4 (6) and [Ru(η5-C5H5){C(CHCPh2)NHPh}(CO)(PiPr3)]BF4 (7). Treatment of 6 and 7 with sodium methoxide produces the deprotonation of the nitrogen atom of the unsaturated η1-carbon ligand, to give the azabutadienyl compounds Ru(η5-C5H5){C(CHCPh2)NnPr}(CO)(PiPr3) (8) and Ru(η5-C5H5){C(CHCPh2)NPh}(CO)(PiPr3) (9), respectively. The ellipticities of the Ru−Cα and Cα−N bonds of the model compounds [Ru(η5-C5H5){C(CHCH2)NH2}(CO)(PH3)]+ (10), Ru(η5-C5H5){C(NH2)CCH2}(CO)(PH3) (11), and Ru(η5-C5H5){C(CHCH2)NH}(CO)(PH3) (12) have been studied using the AIMPAC series of programs. The obtained values are 0.07 and 0.12 (10), 0.05 and 0.07 (11), and 0.07 and 0.10 (12), respectively.

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