Carbon dioxide activation by low-valent pseudo-tetrahedral iron

Upon exposure to CO_2, pseudo-tetrahedral iron(I) supported by 1;PhBP^R_33;- ligands (where 1;PhBP^R_33; =1;PhB(CH_2PR2)_33;-, and R = CH_2Cy, ^iPr, and Ph) effects either the reductive cleavage of CO_2 via O-atom transfer or reductive coupling of CO_2 to give an oxalate. THF solns. of 1;PhBP^(CH2Cy)_33;Fe(I) gives rise to the structurally unprecedented- Fe_2(μ-O)(μ-CO), whereas 1;PhBP^(CH2Cy)_33;FePPh_3 gives a bridging oxalate species. In situ sodium/amalgam redns. of 1;PhBP^R_33;FeCl under an atm. of CO_2 again gives Fe_2(μ-oxalate) for R =CH_2Cy, but gives a Fe_2O species as the major product for both R = -^iPr and Ph