Metal-Metal Multiple Bonds in Early/Late Heterobimetallics Support Unusual Trigonal Monopyramidal Geometries at both Zr and Co

Reduction of Zr/Co heterobimetallic complexes lCo(MesNP(l)Pr(2))(3)ZrCl (1) and lCo((PrNPPr2)-Pr-l-Pr-l)(3)ZrCl (2) with excess Na/Hg under N-2), followed by subsequent benzene extraction to remove coordinated Na halide salts, leads to neutral two-electron reduced, dinitrogen-bound complexes (THF)Zr(MesNP(l)Pr(2))(3)Co-N-2 (4) and Zr((PrNPPr2)-Pr-l-Pr-l)(3)Co-N-2 (5). Upon halide loss, a THF solvent Molecule coordinates to the axial site of the Zr center in 4, while this axial site remains unoccupied in 5. X-ray crystallography reveals short Co-Zr distances in 4 and 5, indicative of metal-metal multiple bonding, and an unprecedented trigonal monopyramidal geometry about the Zr center in 5. Reduction of 4 under an Ar atmosphere (in the absence of N2) results in another unusual structure type: an unoccupied axial Co coordination site and a trigonal monopyramidal Co center in (THF)Zr(MesNP(l)Pr,)(3)Co (6). X-ray crystallography reveals that, in the absence of coordinated N2, the Co-Zr bond can attain full triple bond character with a Co-Zr distance of 2.14 angstrom, the shortest M-M distance in an early/late heterobimetallic complex reported to date. To further assess the electronic structure and bonding in 4, 5, and 6, calculations were performed on these molecules using DFT and the results of these theoretical investigations will be discussed.