Method for the preparation of halogen substituted methanes and ethanes

A method for the preparation of CH.sub.3 X or a mixture of CH.sub.3 X and XCH.sub.2 -CH.sub.3, wherein X is a halogen selected from the group consisting of chlorine, bromine, fluorine and iodine, comprising contacting CO, H.sub.2 and HX at a temperature below 200.degree. C. in the presence of a catalytic amount of a metal carbonyl complex having the formula M.sub.n (CO).sub.m, wherein M is a transition metal, n and m are the same or different and represent integers having a value of at least 1, said complex being capable of oxidatively adding H.sub.2 or HCl and further being in association with (1) at least one Lewis or Bronsted acid capable of coordinating the oxygen atom of said carbonyl moiety and (2) at least one Lewis base other than CO attached to the metal atom of the metal carbonyl complex capable of oxidatively adding hydrogen or HX or a metal carbonyl complex having the formula Z.sub.y [M.sub.n (CO).sub.m.sup.y- ] wherein M, n and m have the meanings set forth above, y is an integer having a value of at least l and Z is a cation or a cationic support ionically bonded to or in association with the transition metal anion.