Activation of 2-Propyn-1-ol Derivatives by Indenylruthenium(II) and -osmium(II) Complexes: X-ray Crystal Structures of the Allenylidene Complexes [M(CCCPh2)(η5-C9H7)(PPh3)2][PF6]·CH2Cl2 (M = Ru, Os) and EHMO Calculations