Synthesis and Properties of the Indenyl Ruthenium(II) Complex [Ru{(E)-.eta.1-C(CCPh):CHPh}(.eta.5-C9H7)(.kappa.2-P-dppm)] (dppm = bis(diphenylphosphino)methane). An Organometallic Intermediate in the Catalytic Dimerization of Phenylacetylene.