Synthesis of a sterically bulky diphosphine synthon and Ru(II) complexes of a cooperative tridentate enamide-diphosphine ligand platform

In order to generate tridentate enamido diphosphine ligand platforms, we developed procedures for the preparation of tBu(2)PCH(2)CH(2)P(tBu)I, which involve low temperatures, pentane solvent and addition of 4 equiv. of tBuLi to Cl2PCH2CH2PCl2 or 2 equiv. of tBuLi to known Cl(tBu)PCH2CH2P(tBu)Cl also at low temperatures in pentane; an alternate method involves the inverse addition of Cl(tBu)PCH2CH2P(tBu) Cl to 2 equiv. of tBuLi in pentane at 0 degrees C; all of these methods generate good yields of the tetraphosphine dimer (tBu2PCH2CH2P(tBu)) 2 contaminated by small amounts of tBu(2)PCH(2)CH(2)PtBu(2) (dtbpe), which can be conveniently separated by sublimation. Subsequent oxidative cleavage of the P-P bond with I-2 or 1,2-diiodoethane results in the formation of the desired tBu(2)PCH(2)CH(2)P(tBu) I, which undergoes C-P bond formation when added to 1 equiv. of the lithium N-2,6-diisopropylphenylenamide of cyclopentylidene imine to generate the HNPP ligand precursor; this species exists as a tautomeric mixture of the corresponding enamine and imine, the ratio of which depends on workup conditions used. This enamine-imine mixture can be used directly to form Ru(II) species either directly with heating to generate the five-coordinate (NPP)RuCl(CO) via loss of H-2 or by inclusion of 1 equiv. of KOtBu to generate (NPP) RuH(CO). X-ray crystallographic studies confirm that the geometry in the solid state matches the solution spectroscopic data. Subsequent studies of (NPP) RuH(CO) indicate that it reacts with benzaldehyde, benzyl alcohol, and H-2 in a cooperative manner to generate a series of hydride carbonyls that have been characterized fully by NMR spectroscopy and X-ray crystallography.