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