Ruthenium η 4 -trimethylenemethane complexes containing two different tridentate phosphine ligands have been synthesized. The formation of the complexes using [Ru(η 4 -COD)(η 3 -CH 2 CMeCH 2 ) 2 ] as the metal precursor occurred via elimination of isobutene. An intermediate species has been isolated in which the ligand coordinates with only two phosphorus atoms. Furthermore, protonation of the trimethylenemethane ligand gave rise to a cationic methylallyl complex.

The facile one-step synthesis of five new bis(diisopropylphosphinomethyl)amine ligands RN(CH2DIP)2 (DIP = diisopropylphosphine, R = Me–, iPr–, PhCH2–, 2-ThCH2–, and 2-FuCH2−) based on the use of the air-stable phosphonium salt [DIP(CH2OH)2]Cl is presented. The phosphonium salt cleanly reacts with primary amines to afford amine-bridged bisphosphine ligands with variable backbone substitution in good yields. These DIP ligands are useful model systems for their chiral bisphospholane analogues. The coordination chemistry of neutral nickel(II) complexes [(RDIP)NiCl2], [(RDIP)Ni(CH3)2], [(iPrDIP)Ni(Cl)CH2Si(CH3)3], and [(RDIP)Ni(CH2Ph)2], as well as coordinatively unsaturated cationic nickel(II) complexes [(RDIP)Ni(THF)CH3]+BArF– and [(RDIP)NiCH2Ph]+BArF–, has been studied by spectroscopic and X-ray diffraction methods. The cationic methyl complexes reacted cleanly with 2-butyne and 1,1-dimethylallene, yielding allylic complexes [(RDIP)Ni(pmcb)]+BArF– and [(RDIP)Ni(tma)]+BArF–, respectively (pmcb: η3-1,2,3,4,4-pentamethylcyclobutenyl; tma: η3-2,3,3-trimethylallyl). Nickel(0) complexes [(BzDIP)Ni(trans-stilbene)] and [(RDIP)Ni(C2H4)] were synthesized in one step from the corresponding dichloro complexes and have been fully characterized and analyzed by X-ray diffraction methods. [(MeDIP)Ni(C2H4)] reacted with phenyl-2-thiophenecarboxylate, yielding [(MeDIP)Ni(OPh)(2-Th)] and [(MeDIP)Ni(CO)2] in a 2:1 ratio. Both complexes were also synthesized via alternative routes. The phenolato-thienyl complex represents an intermediate in the catalytic cycle of a recently reported decarbonylative arylation of azoles. Complexes [(RDIP)Ni(C2H4)] were shown to be active catalysts for this reaction.

The modular one-pot synthesis of a large family of bi- and tridentate 2,5-dimethyl- and 2,5-diphenyl-substituted phospholanes employs air-stable chiral phospholanium chloride salts and primary amines or NH(4)Cl as starting materials. These were transformed into the C(2)-symmetric dimethyl- and diphenylphospholane ligands, which reacted with [Rh(cod)(2)]BF(4) (cod=1,5-cyclooctadiene) to yield the rhodium complexes [Rh(L)(cod)]BF(4) (L=bisphospholane ligands). The corresponding trisphospholane complexes, 11 and 12, were obtained in high yields (81 and 92%, respectively), and fully characterised by NMR spectroscopy, mass spectrometry and elemental analysis. Whilst in the C(3)-symmetric complex 11, containing the tridentate 2,5-dimethylphospholane, the ligand is bound symmetrically, different coordination behaviour was found for the diphenyl-substituted complex 12, in which the coordination of only two of the three phospholane moieties to the metal centre was observed. A DFT study at the B3PW91 level established minimum energy structures consistent with experimental findings in solution and in the solid state. The non-coordinated phospholane unit present in 12 allowed further modification of the complex through the coordination of Au(I)-X (X=Cl, C(6)F(5) and tris(trifluoromethyl)phenyl ((F)Mes)) fragments to the pendant phosphane. To investigate the potential of the new ligands, the enantioselective hydrogenation of a series of prochiral olefins as benchmark substrates, using isolated Rh complexes as catalysts, was studied. The substrates included methyl esters of three dehydro-α-acetamido acids and two itaconic acid derivatives. In general good to excellent enantioselectivities (of up to >99% ee) were observed. Ligand backbone modification by coordination of bulky Au-X substituents to the free phospholane unit in complex 12 led to an outstanding enhancement of the catalyst performance and there was a clear correlation between the properties of the complex periphery and the enantioselectivity.