Synthesis, structure and coordination of the ambiphilic ligand (2-picolyl)BCy2.

The new pyridine-borane compound (2-picolyl)BCy2, readily prepared from 2-picolyllithium and ClBCy2, adopts a head-to-tail dimeric structure in the solid state as indicated by X-ray diffraction analysis and according to NMR and DFT studies, the dimeric form equilibrates in solution with a strained monomeric structure; the ambiphilic behavior of the new compound is illustrated by its bridging coordination to the (p-cymene)RuCl2 unit.

Synthesis and theoretical study of a series of dipalladium(I) complexes containing the Pd2(mu-CO)2 core.

The complex [PBu4]2[Pd2(mu-CO)2Cl4] has been prepared in high yields by carbonylation of [PBu4]2[Pd2Cl6]. Methanol, potassium acetate, or CO readily reacted under ambient conditions to quantitatively afford a series of dipalladium(I) complexes, namely [Pd2(mu-CO)2Cl3(OCH3)]2-, [Pd2(mu-CO)2Cl3(OC(O)CH3)]2-, [Pd2(mu-CO)2Cl3(CO)]-, and [Pd2(mu-CO)2Cl2(OCH3)(CO)]-, all of which have the Pd2(mu-CO)2 core preserved. All these complexes have been characterized by infrared and NMR spectroscopies; the high nu(CO) stretching wavenumbers observed and the diamagnetic character of these complexes prompted us to perform theoretical calculations to describe the electronic structure of the Pd2(mu-CO)2 core and to gain an intimate description of the Pd-CO bonds. The pairing of the two lonely electrons of the Pd d9 atoms is due to the delocalization along the CO bridging ligands.

Fluxionality and Isomerism of the Bis(dihydrogen) Complex RuH(2)(H(2))(2)(PCy(3))(2): INS, NMR, and Theoretical Studies.

To study the fluxionality of the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1), NMR spectra were recorded in Freons (mixture of CDCl(3), CDFCl(2), and CDF(2)Cl). 1 was found to remain fluxional at all temperatures, but the presence of CDCl(3) necessary for its solubilization induces its transformation into, first, RuHCl(H(2))(2)(PCy(3))(2) (3) and the new ruthenium(IV) dihydride RuH(2)Cl(2)(PCy(3))(2) (4). 4 is produced selectively in pure CDCl(3) but reacts further to give a mixture of chloro complexes. 4 was isolated from the reaction of 1 with aqueous HCl in Et(2)O and shows a fluxional process attributed to the interconversion between two symmetrical isomers. The activation parameters of this process were obtained by (1)H NMR line shape analysis, as well as those corresponding to the exchange between 3 and free dihydrogen. The fluxionality of the dihydrogen-hydride system is also evident at a much faster time scale than that of NMR studies in the inelastic neutron scattering observations of the rotation of the dihydrogen ligands. The geometries and relative energies of several isomers of complexes 1, 3, and 4 were studied using density functional theory (DFT) and MP2 methods, together with a few coupled-cluster (CCSD(T)) calculations. In contrast to what might have been expected, the two hydrides and the two H(2) units of 1 lie in the same plane, due to the attractive "cis effect" created by the hydrides. The two H(2) ligands adopt cis positions in the lowest-energy isomer. Rotation of the two dihydrogen ligands has been analyzed using DFT calculations. A slight preference for a C(2) conrotatory pathway has been found with a calculated barrier in good agreement with the experimental INS value. Two low-energy isomers of 4 have been characterized computationally, both of which have C(2)(v)() symmetry, consistent with the solution NMR spectra.