Electronically unsaturated three-coordinate chloride and methyl complexes of iron, cobalt, and nickel

Three-coordinate organometallic complexes are rare, especially with the prototypical methyl ligand. Using a hindered, rigid bidentate ligand (L), it is possible to create 12-electron methyliron(II) and 13-electron m ethyl cobalt(l 1) complexes. These complexes are thermally stable, and H-1 NMR spectra suggest that the low coordination number is maintained in solution. Attempts to create the 14-electron LNiCH3 led instead to the three-coordinate nickel(l) complex LNi(THF). Single crystals of LMCH3 are isomorphous with the new three-coordinate chloride complexes LNiCl and LCoCl. Along with the recently reported LFeCl (Smith, J.M.; Lachicotte, R.J.; Holland, P. L. Chem. Commun. 2001, 1542), these are the only examples of three-coordinate iron(II), cobalt(II), and nickel(II) complexes with terminal chloride ligands, enabling the systematic evaluation of the effect of coordination number and metal identity on M-Cl bond lengths. Electronic structure calculations predict the ground states of the trigonal complexes.