SYNTHESIS AND 2D NMR-STUDIES OF (BIS(PYRAZOLYL)BORATO)RHODIUM(I) COMPLEXES WITH WEAK RH...H...C INTERACTIONS AND THE X-RAY CRYSTAL-STRUCTURE OF ((CYCLOOCTANE-1,5-DIYL)BIS(PYRAZOL-1-YL)BORATO)(1,5-CYCLOOCTADIENE)RHODIUM

The novel rhodium(I) complexes [Rh{BBN(3-R-pz)2}(LL)] (LL = 2 CO, COD (1,5-cyclooctadiene), and NBD (norbornadiene); 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 H-1 NMR spectra of all the compounds show that one of the methine protons (H-1') of the BBN moiety is considerably deshielded. Furthermore, their three-dimensional solution structures, as derived by H-1-NOESY spectroscopy, 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) angstrom; Z = 4; R = 0.034, R(w) = 0.041 for 1485 observed reflections), which shows that the Rh-H8 (corresponding to H-1' above) separation in this compound is 2.42 (4) angstrom. 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).