A bulky tris(carbene)borate ligand allows several lowvalent iron carbonyl complexes to be isolated. One-electron reduction of the cationic iron(II) complex [PhB(MesIm) 2), as determined by structural and spectroscopic methods. This complex can in turn be reduced to provide the anionic dicarbonyl complex [K][PhB(MesIm) 3 Fe(CO) 2 ] (3), which crystallizes as a dimer in which the potassium cation coordinates in a side-on fashion to one CO ligand. Protonation of 3 yields the weakly acidic iron hydride PhB(MesIm) 3 Fe(CO) 2 H (4), which can also be isolated by treating the κ 3 -coordinated alkylborohydrido complex PhB-(MesIm) 3 Fe(κ 3 -BH(CH 2 CH 3 ) 3 ) (5) with CO. The strong donor ability of the tris(carbene)borate ligand results in significant reduction of the CO bonds, as measured by IR spectroscopy.