CO reduction by calcium and ytterbium hydride complexes with a bulky monodentate carbazolyl ligand

The bulky monodentate carbazolyl ligand 1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazole ($^{dtbp}$Cbz) was employed in the synthesis of monomeric heteroleptic amido carbazolyl complexes of Ca and Yb. For both central metal atoms, dimeric hydride complexes [($^{dtbp}$Cbz)Ca(benzene)H]$_2$, [($^{dtbp}$Cbz)Ca(THF)H]$_2$, [($^{dtbp}$Cbz)Yb(benzene)H]$_2$ and [($^{dtbp}$Cbz)Yb(THF)H]$_2$ were obtained, which show remarkably poor solubility in organic solvents. The characteristic hydride $^1$H NMR resonance of [($^{dtbp}$Cbz)Ca(benzene)H]$_2$ was observed at 2.07 ppm, and for the first time, characteristic vibrational modes of the Ca$_2$H$_2$ and Yb$_2$H$_2$ moiety are discussed. Despite their poor solubility, the hydride complexes could be reacted with CO to yield the corresponding ethenediolate complexes.