Syntheses, structures, and dynamic properties of M(CO)2(η3-C3H5)(L–L)(NCBH3) (M = Mo, W; L–L = dppe, bipy, en)

Compounds M(CO)2(η3-C3H5)(L–L)(NCBH3) (L–L = dppe, M = Mo(1), W(2); L–L = bipy, M = Mo(3), W(4); L–L = en, M = Mo(5), W(6)) were prepared and characterized. The single crystal X-ray analyses of 2–6 revealed that the cyanotrihydroborate anion bonds to the metal through a nitrogen atom, the open face of the allyl group being pointed toward the two carbonyls (endo-isomer). In compounds 2, 5, and 6, the two donor atoms of the bidentate ligand occupy equatorial and axial positions, respectively. In the solid state structures of compounds 3 and 4 both nitrogen atoms of the bipy ligand occupy equatorial positions. The NMR spectroscopy reveals a fluxional behavior of compounds 1, 2, 5, and 6 in solution. Although the fluxional behavior of compounds 5 and 6 ceased at about −40 °C, that of compound 1 could not be stopped even at −90 °C. Their low temperature conformations are consistent with their solid state structures. Both the endo- and exo-isomers coexist in solution for compounds 3 and 4.