A two-step synthesis of K2[Fe(CO)3(PR3)] (PR3 = PPh3, PMe2Ph, and PMe3) from the corresponding Fe(CO)4(PR3) has been developed. Treatment of Fe(CO)4(PR3) with a methanolic solution of [Et4N]OH provided the corresponding monohydrides HFe(CO)3(PR3)-. Deprotonation of monohydrides by K[sec-Bu3BH] in refluxing tetrahydrofuran gave 50-70% isolated yields (based on Fe(CO)4(PR3)) of the thermally stable but exceedingly air-sensitive salts K2[Fe(CO)3(PR3)], which were characterized by elemental analysis, infrared spectra, and reactivity patterns. These are the first isolated salts containing (phosphine)carbonylmetalate dianions and are extremely reactive. They quickly deprotonated acetonitrile to give essentially quantitative yields of HFe(CO)3(PR3)- and reacted with triphenylstannyl chloride to provide Ph3SnFe(CO)3(PR3)-. Ligand exchange reactions of K2[Fe(CO)3(PPh3)] with CO and P(OMe)3 readily occurred at room temperature and gave 80-90% isolated yields of K2[Fe(CO)4] and K2[Fe(CO)3(P(OMe)3)]. The latter salt contains the first isolated (phosphite)carbonylmetalate dianion and was characterized by elemental analyses and infrared spectra as a triphenyltin derivative, (Ph3Sn)Fe(CO)3(P(OMe)3)-. Treatment of [Et4N][HFe(CO)3(PPh3)] with hot ethanol provided low yields (ca. 10%) of the bridging phosphide salt [Et4N][Fe2(CO)6(μ-CO)(μ-PPh2)]. Full details on the molecular structure of this anion, which has been mentioned previously in the scientific literature (Kyba, E. P.; Davis; R. E.; Clubb, C. N.; Liu, S. T.; Palacios, H. A. O.; McKennis, J. S., Organometallics 1986, 5, 869), are reported for the first time. Crystal data: triclinic, space group P1̅ (No. 2); a = 11.140 (1) Å, b = 13.982 (4) Å, c = 10.161 (3) Å; a = 105.30 (2)°, β = 103.33 (2)°, γ = 77.21 (2)°, V = 1464 (1) Å3; Z = 2; R = 0.034; Rw= 0.039.