The zero-valent iron phosphine [Fe(N 2 )(dmpe) 2 ] (2) reacts with CO 2 to form the(3) through the reductive coupling of two molecules of carbon dioxide. The formation of metalacycle 3 proceeds through a stepwise reaction with carbon dioxide to form, initially, the isolable 1), which reacts with a second molecule of CO 2 to form the 5-membered metalacycle. This sequence represents the first experimental evidence for the formation of a κ 2 C,O-FeC 2 O 4 metalacycle via an η 2 (C,O)-CO 2 precursor. Isotopic labeling was used to demonstrate that the initial coordinated CO 2 molecule forms the metal-bound carbonyl moiety in the metalacycle, while the second molecule of CO 2 forms the carbonyl β to the iron center. The metalo-2,4-dioxolane-3,5-dione cis-[Fe(C(O)OC(O)O-κ 2 C,O)(dmpe) 2 ] (3) breaks down with loss of CO to yield the iron carbonate cis-[Fe(CO 3 -κ 2 O,O)(dmpe) 2 ] (5). In the presence of a CO scavenger such as [Fe(N 2 )(dmpe) 2 ], CO is trapped to give [Fe(CO)(dmpe) 2 ] (4). This is the first direct experimental evidence for a κ 2 C,O-C 2 O 4 metalacycle being a key intermediate in the reductive disproportionation of CO 2 to CO and CO 3 2− .

The acetylido iron hydride trans-[FeH(CCH)(depe) 2 ] reacts with an excess of CO 2 at ambient pressure and temperature to form a five-membered metalalactone cis-[Fe(OC(O)CHCH-κ 2 C,O)(depe) 2 ]. The reaction appears to proceed by electrophilic addition of CO 2 to the β-carbon of the coordinated acetylide and cyclization to form the metalalactone product. At low temperature, a second molecule of CO 2 is incorporated to give a carboxy-substituted metalalactone cis-When the initial metal acetylido hydride is substituted at the β-acetylenic carbon, the addition of CO 2 results in a metalalactone where the substituent is in the position adjacent to the carbonyl in the metalalactone ring.

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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.