The novel rhodium(I) complexes 2)(LL)] (LL = 2 CO, COD (1,5-cyclooctadiene), and NBD (norbomadiene); R = H and CH3; pz = 1-pyrazolyl; BBN = 9-borabicyclo[3.3.1]nonane) were synthesized and characterized in solution by one-and two-dimensional multinuclear NMR spectroscopy. The NMR spectra of all the compounds show that one of the methine protons (Hv) of the BBN moiety is considerably deshielded. Furthermore, their three-dimensional solution structures, as derived byspectroscopy, show that this proton is placed in proximity to the rhodium center. This is confirmed by the X-ray solid-state structure of [Rh|BBN(pz)2|(COD)] (space group Pnma, a = 12.940 ( 2), b = 13.697(2), c = 11.959 (2) A; Z = 4; R = 0.034, Rv = 0.041 for 1485 observed reflections), which shows that the Rh-H8 (corresponding to H1' above) separation in this compound is 2.42 (4) A. This interaction can be described as "agostic", albeit of the weak type, and might make a contribution to the lack of the inversion of the boatlike Rh(NN)2B ring which, however, is characteristic for the complexes [Rh{Ph2Bpz2}(LL)] (LL = 2CO, NBD, and COD).
The tunnel splitting of the librational ground state and the torsional frequencies of the dihydrogen ligand in Tp(Me)()2RhH(2)(eta(2)-H(2)) (Tp(Me)()2 = hydrotris(3,5-dimethylpyrazolyl)borate) were measured using inelastic neutron scattering spectroscopy. The barrier for the rotation of the H(2) ligand and its H-H separation, calculated from these data, are 0.56(2) kcal/mol and 0.94 Å, respectively. These values indicate that pi-back-donation from the Tp(Me)()2RhH(2) fragment to H(2) is relatively weak and/or the interaction between the coordinated dihydrogen molecule and the two cis-hydride ligands significantly lowers the barrier for H(2) rotation.
The H2 ligand in 1 is stabilized only by nitrogen ligands. 1H‐Detecting 2D‐(1H,103Rh)‐NMR spectroscopy, an NMR procedure in the preliminary phase of which a heteronuclear two‐spin coherence is excited, together with variation of the 1H‐transmitter frequency, made it possible to read directly from the spectrum both the chemical shift of the metal and the number of hydride ligands present.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.