Synthesis and characterization of hydride-alkynyl, allenylidene, carbyne, and functionalized-alkynyl complexes containing the [Os(eta(5)-C5H5) ((PPr3)-Pr-i)(-)(2)](+) fragment: The complex [Os(eta(5)-C5H5)(C=C=CPh2)((PPr3)-Pr-i)(2)]PF6, a new type of allenylidene derivative from the reactivity point of view

Complex Os(eta(5)-C5H5)Cl((PPr3)-Pr-i)(2) (1) reacts with equimolecular mix tures of TlPF6 and alkynes such as phenylacetylene and cyclohexylacetylene to give [OsH(eta(5)-C5H5)(C drop CR)((PPr3)-Pr-i)(2)]PF6 (R = Ph (2), Cy (3 )). The structure of 2 in the solid state has been determined by X-ray diff raction analysis. The distribution. of ligands around the metallic center c an 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 TlPF6 leads to [OsH(eta(5)-C5H5){C drop CC(OH)-MePh}((PPr3)-Pr-i)( 2)]PF6 (4), which evolves into the hydride-enynyl complex [OsH(eta(5)-C5H5) {C drop CC(Ph)=CH2}((PPr3)-Pr-i)(2)]PF6 (5) in solution of chloroform. Trea tment of 1 with 1,1-diphenyl-2-propyn-1-ol and TIPF6 affords [OsH(eta(5)-C5 H5){C drop CC(OH)Ph-2}((PPr3)-Pr-i)(2)]PF6 (6), which reacts with KOH in me thanol to give the neutral compound Os(eta(5)-C5H5){C drop CC(OH)Ph-2}((PPr 3)-Pr-i)(2) (7) by extraction of the hydride ligand. The addition of 1 equi v of HPFs to the solutions of 7 leads to the allenylidene, [Os(eta(5)-C5H5) (C=C=CPh2)((PPr3)-Pr-i)(2)]PF6 (8), which affords the dicationic carbyne de rivative [Os(eta(5)-C5H5)(CCH=CPh2)((PPr3)-Pr-i)(2)](PF6)(2) (9) by reactio n with HPF6. The structure of 9 in the solid state has been also determined by X-ray diffraction analysis. In this case, the geometry around the osmiu m center is close to octahedral with the triisopropylphosphine ligands mutu ally cis disposed (P-Os-P = 105.12(8)degrees), Complex 8 also reacts with n ucleophilic reagents; the reaction with CH3Li gives Os(eta(5)-C5H5){C drop CC-(CH3)Ph-2}((PPr3)-Pr-i)(2) (10), whereas the reactions with acetone and methanol solutions of KOH afford Os(eta(5)-C5H5){C drop CC[CH2C(O)CH3]Ph-2} ((PPr3)-Pr-i)(2) (11) and Os(eta(5)-C5H5){C drop CC(OCH3)Ph-2}-((PPr3)-Pr-i )(2) (12), respectively. To understand the chemical behavior of 8, EHT-MO c alculations on the model compounds Os(eta(5)-C5H5)Cl(C=C=CH2)(PH3) (13) and [Os(eta(5)-C5H5)(C=C=CH2)L-(PH3)](+) (L = PH3 (14), CO (15)) have been als o carried out. The results suggest that the behavior of 8 as nucleophile is a consequence of the high electron density of the allenylidene ligand, whi le the behavior as gamma-electrophile is due to its cationic nature. In add ition, we have determined by ab initio calculations the energies of stabili zation by protonation of 13-15 with a naked proton. In the three cases the formation of the corresponding carbyne derivatives [Os(eta(5)-C5H5)Cl(CCH=C H2)(PH3)](+) (16; 267 kcal. mol(-1)), [Os(eta(5)-C5H5)(CCH=CH2)-(PH3)(2)](2+) (17; 180 kcal.mol(-1)), a nd [Os(eta(5)-C5H5)(CCH=CH2)(CO)(PH3)](2+) (18; 157 kcal.mol(-1)) involves a stabilization of the system.