Ab initio SCF calculations were carried out to study the bonding in mirror-symmetric (C5H5)Ru(PH3)X where X = halide, OCH3, and OSiH3, With the goal of understanding the effect of X-group lone pairs on the Ru-X bonding. Comparison of these calculations to those where PH3 has been added, to give mirror-symmetric CpRu(PH3)2X (where X = OCH3), show that the Ru-X pi-bonding present in CpRu(PH3)(OCH3) is disrupted upon addition of PH3. Comparison to CpRu(PH3)2(CH3) shows the absence of such changes when the "pure-sigma" ligand CH3 is bound to ruthenium. Comparison to the case CpRu(PH3)(CO)(OCH3) reveals how the CO pi* orbital stabilizes the otherwise antibonding Ru-OCH3 molecular orbital and thereby leaves some Ru-O multiple bonding intact. Comparison calculations on mirror-symmetric CpRu(PH3)(OEH3) for E = C and Si show the latter to have a longer Ru-O distance and a much flatter energy surface for bending at oxygen.