Synthesis of a sterically bulky diphosphine synthon and Ru(ii) complexes of a cooperative tridentate enamide-diphosphine ligand platformElectronic supplementary information (ESI) available. CCDC 1483798-1483805. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt02352e

In order to generate tridentate enamido diphosphine ligand platforms, we developed procedures for the preparation of t Bu 2 PCH 2 CH 2 P( t Bu)I, which involve low temperatures, pentane solvent and addition of 4 equiv. of t BuLi to Cl 2 PCH 2 CH 2 PCl 2 or 2 equiv. of t BuLi to known Cl( t Bu)PCH 2 CH 2 P( t Bu)Cl also at low temperatures in pentane; an alternate method involves the inverse addition of Cl( t Bu)PCH 2 CH 2 P( t Bu)Cl to 2 equiv. of t BuLi in pentane at 0 °C; all of these methods generate good yields of the tetraphosphine dimer ( t Bu 2 PCH 2 CH 2 P( t Bu)) 2 contaminated by small amounts of t Bu 2 PCH 2 CH 2 P t Bu 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 t Bu 2 PCH 2 CH 2 P( t Bu)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 KO t Bu 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. The preparation of the bulky diphosphine synthon 1 is described and used to generate a tridentate enamido diphosphine ligand platform that can be installed on Ru( ii ).