Carbon disulfide reacted with the cyclometalated ruthenium complex [RuH(η 2 -CH 2 PMe 2 )(PMe 3 ) 3 ] (1) at low temperature to yield the dithioformate complex [Ru(η 1 -SC(S)H)(η 2 -CH 2 PMe 2 )(PMe 3 ) 3 ] (4), where the CS 2 inserts into the metal hydride bond. On warming, complex 4 rearranges to give the known complex [Ru(S 2 CHPMe 2 CH 2 -κ 3 S,S,C)(PMe 3 ) 3 ] (3), where the CS 2 is inserted in a metal phosphorus bond. Further reaction of this complex with excess CS 2 over a period of days resulted in insertion of a second CS 2 unit into one Ru−S bond to yield [Ru(SC(S)SCH(-S)PMe 2 CH 2 -κ 3 S,S,C)(PMe 3 ) 3 ] (5). Complex 5 was characterized crystallographically and by multinuclear NMR spectroscopy. In contrast, reaction of [RuH(η 2 -CH 2 PMe 2 )(PMe 3 ) 3 ] (1) with CO 2 resulted in insertion of CO 2 into the Ru−C bond to give [RuH(OC(O)CH 2 PMe 2κ 2 O,P)(PMe 3 ) 3 ] (2). Low-temperature NMR spectroscopic studies did not show any evidence for prior formation of a formate complex.