Two new carbene−rhodium complexes are reported that are active hydroformylation catalysts, giving very high selectivities for the branched isomer (>95:5) when vinyl arenes are used as substrates. The carbene analogue of Wilkinson's catalyst, [RhIMes(PPh3)2Cl] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), and the related carbonyl complex [RhIMes(PPh3)(CO)Cl] were both prepared, and the latter was fully characterized using spectroscopic and crystallographic means.

Reduction of [(triphos)NiCl2] (1) with an excess of NaBH4 in THF produces the paramagnetic Ni(I) complex [(triphos)Ni(eta2-BH4)] (2). X-ray crystallography shows 1 to be a square-planar Ni(II) species in which the phosphine ligand is bidentate, whereas 2 has pseudotetrahedral geometry at the Ni(I) center, with a tridentate phosphine and the borohydride ligand occupying a single coordination site. Density functional theory calculations show the unpaired electron in 2 to reside in an orbital located mainly on the Ni atom.

Reduction of [(η-C5Me5)VCl(μ-N)]2 with sodium amalgam in toluene gave the diamagnetic cubane [(η-C5Me5)V(μ3-N)]4, which was characterized by spectroscopy, chemical analysis, and X-ray crystallography. The cluster has short V-V and V-N distances (2.674(8) and 1.87(2) Å, respectively), indicative of a strong V-N bond. It can be reversibly reduced electrochemically to {[(η-C5Me5)V(μ3-N)]4}-.

A series of tripodal amidopyridine receptors capable of selective recognition of methylmethanetriacetic acid (MMTA) in organic solvents is described. Intramolecular hydrogen-bonding groups, built into some of the receptors, were designed as preorganization devices. Binding was studied by NMR titration, variable temperature NMR experiments, 2D-NMR, isothermal titration calorimetry, and single-crystal X-ray crystallography. The results reveal that a balancing act between inter- and intramolecular hydrogen-bonding interactions in the complexes governs both the dynamics and the geometry of binding. Receptor 1b (without intramolecular hydrogen-bonding groups) features a simple symmetric MMTA binding geometry with optimal enthalpic interactions. In sharp contrast, receptor 1a (with intramolecular hydrogen-bonding groups) reveals a temperature-dependent dual binding mode where MMTA can bind in two completely different geometries. The two solution binding geometries of 1a.MMTA were unraveled by NMR experiments and correlated to the X-ray structures.