Synthesis and Characterization of Hydride−Alkynyl, Allenylidene, Carbyne, and Functionalized-Alkynyl Complexes Containing the [Os( η 5 -C 5 H 5 )(P i Pr 3 ) 2 ] + Fragment: The Complex [Os( η 5 -C 5 H 5 )(CCCPh 2 )(P i Pr 3 ) 2 ]PF 6 , a New Type of Allenylidene Derivative from the Reactivity Point of View

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 )(C⋮CR)(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 ){C⋮CC(OH)MePh}(P i Pr 3 ) 2 ]PF 6 ( 4 ), which evolves into the hydride−enynyl complex [OsH( η 5 -C 5 H 5 ){C⋮CC(Ph) CH 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 ){C⋮CC(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 ){C⋮CC(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 )(C C CPh 2 )(P i Pr 3 ) 2 ]PF 6 ( 8 ), which affords the dicationic carbyne derivative [Os( η 5 -C 5 H 5 )(CCH CPh 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 ){C⋮CC(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 ){C⋮CC[CH 2 C(O)CH 3 ]Ph 2 }(P i Pr 3 ) 2 ( 11 ) and Os( η 5 -C 5 H 5 ){C⋮CC(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(C C CH 2 )(PH 3 ) ( 13 ) and [Os( η 5 -C 5 H 5 )(C C CH 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(CCH CH 2 )(PH 3 )] + ( 16; 267 kcal·mol - 1 ), [Os( η 5 -C 5 H 5 )(CCH CH 2 )(PH 3 ) 2 ] 2+ ( 17; 180 kcal·mol - 1 ), and [Os( η 5 -C 5 H 5 )(CCH CH 2 )(CO)(PH 3 )] 2+ ( 18; 157 kcal·mol - 1 ) involves a stabilization of the system.