Abstract: Process for selective homogeneous catalytic hydrogenation of carboxylic acid anhydrides to ester or lactones at an improved rate and to obtain improved yields wherein the catalyst is a ruthenium trichlorostannate complex of the formula: ##STR1## wherein X is hydrogen, chlorine, bromine, iodine or lower alkyl; m is the integer 1 or 2; n is an integer of from 0 to 3 but when n is 2 or 3, X may be the same or different; M is P, As or Sb; R.sup.6, R.sup.7 and R.sup.8 independently are lower alkyl, cycloalkyl, aryl, benzyl or a bidentate legand; x is an integer of from 1 to 4 but when x is 2 or more, M may be the same or different; L is a neutral ligand, olefin, CO or (R.sup.9).sub.2 CO wherein R.sup.9 is lower alkyl; y is an integer of from 0 to 3 but when y is 2 or 3, L may be the same or different; and the sum of x and y is at least 2.