Syntheses of dinuclear carbonylates of the iron subgroup: (M sub 2 (CO) sub 8 ) sup 2 minus (M = Ru, Os) and (FeRu(CO) sub 8 ) sup 2 minus. Structures of (PPh sub 4 ) sub 2 (FeRu(CO) sub 8 )ter dot CH sub 3 CN and (PPh sub 4 ) sub 2 (Fe sub 2 (CO) sub 8 )ter dot 2CH sub 3 CN

The homonuclear dianions (Ru{sub 2}(CO){sub 8}){sup 2{minus}} and (Os{sub 2}(CO){sub 8}){sup 2{minus}} are prepared by a procedure that involves the reductive disproportionation of CO{sub 2} in its reaction with an alkali-metal salt of (M(CO){sub 4}){sup 2{minus}} (M = Ru, Os) to form M(CO){sub 5}, which then reacts with additional (M(CO){sub 4}){sup 2{minus}} in situ to give (M{sub 2}(CO){sub 8}){sup 2{minus}}. The dianion (FeRu(CO){sub 8}){sup 2{minus}} is prepared by a procedure with two distinct steps: (1) (Ru(CO){sub 4}){sup 2{minus}} reacts with CO{sub 2} in a 1:2 molar ratio to form Ru(CO){sub 5}; (2) (Fe(CO){sub 4}){sup 2{minus}} is then added to the system, and it reacts with Ru(CO){sub 5} to form (FeRu(CO){sub 8}){sup 2{minus}}. The dinuclear dianions are isolated as the tetraphenylphosphonium salts. They are air- and moisture-sensitive. From a single-crystal x-ray analysis, the structure of (PPh{sub 4}){sub 2}(FeRu(CO){sub 8}){center dot}CH{sub 3}CN has been determined.