An Improved Synthesis for Novel Hexaruthenium Cluster Compound Bearing Two Quadruply-Bridging CO Ligands: Synthesis, Characterization, and X-Ray Structural Analysis of Ru 6(CO) 12(μ 3-H)(μ-CO) (μ 4-η 2-CO) 2[η 5-C 5H 4(SiMe 3)]