The reaction of the alkali metal salt of several hydrotris(pyrazolyl)borate anions (Tp3R,4R,5R) with RhCl3·3H2O in MeOH gave complexes of the type [Tp3R,4R,5RRhCl2(MeOH)] (Tp3R,4R,5R=TpMe, TpMe2, TpMe,4Me, TpMe2,4Cl, TpiPr and TpiPr,4Br). While the reaction of Na[TpMe2] with [RhCl3(MeCN)3] in MeCN gave [TpMe2RhCl2(PzMe2H)] (18), that of Na[TpCF3,Me] gave [TpCF3,MeRhCl2(MeCN)]. The X-ray crystal structure of 18 (space group P1̄, a=10.949(8), b=11.415(8), c=24.16(2)Å; α=95.40(7), β=91.39(7), γ=115.37(5)°; Z=4, R=0.032, Rw=0.035 for 3813 observed reflections) shows that the rhodium atom has an octahedral geometry. The reaction of Na[TpMe,Ph] with RhCl3·3H2O or [RhCl3(MeCN)3] gave mer-[RhCl3(PzPh,Me)3] while M[TpCF3,CF3] (M=Na or Tl) did not react with either rhodium substrate. The complexes [Tp3R,4R,5RRhCl2(L)] (L=MeOH and MeCN) react with Cl− in CHCl3 forming the corresponding [Tp3R,4R,5RRhCl3]− anions (Tp3R,4R,5R=Tp, TpMe, TpMe2, TpMe2,4Me, TpMe2,4Cl, TpiPr, TpiPr,4Br, TpCF3,Me). The X-ray crystal structure of [PPh4][TpMe2RhCl3] ([PPh4] [25]) (space group P21/c, a=16.301(1), b=9.9830(6), c=26.337(1)Å; β=101.97(3)°; Z=4, R=0.052, Rw=0.060 for 4264 observed reflections) shows octahedral coordination at rhodium. A molecular modeling study using the structural data for 25 indicates that steric interactions between (a) the CF3-substituents in position 5 on the pyrazolylborate and (b) the CF3-substituents in position 3 and the other ligands present in the coordination sphere, may prevent the formation of rhodium(III) complexes with TpCF3,CF3.

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 new B-substituted pyrazolylborates Na[MeTp(Me)] and Na[MePhBp(Me)] were synthesised by reacting the organyl boronic and borinic esters MeB((OPr)-Pr-i)(2) and MePhB((OPr)-Pr-i), respectively, with a mixture of 3-Me-pyrazole and its Na-salt. In methanol, the trispyrazolylborate compound containing a B-Me bond is significantly less stable than the corresponding compound containing a B-H bond: Na[MeTp(Me)] appears to be reasonably stable for longer periods only in DMSO and carefully dried acetonitrile. The new rhodium(I) complexes MeTp(Me)Rh(LL), LL = 2 CO and NBD (norbornadiene), were synthesised and fully characterised, whereas MeTp(Me)Rh(LL), LL = COD (1,5-cyclooctadiene), could only be studied in solution as it decomposes rapidly to Rh-2(pz(Me))(2)(COD)(2). The tris-pyrazolylborate complexes exist in solution as isomeric mixtures with kappa(2) and kappa(3)-bonded Tp ligands. IR, C-13-, N-15-, and Rh-103 NMR spectroscopies show that these forms are in a rapid equilibrium, the penta-coordinated complex being favoured for LL = 2 CO whereas the four-coordinated form predominates when LL = COD and NBD. However, MeTp(Me)Rh(NBD) [space group C2/c, a = 11.842(7), b = 17.452(9), c = 19.84(1) Angstrom; beta = 105.37(4); Z = 8; R = 0.029, R(w) = 0.027 for 4779 observed reflections] is a five-coordinated complex in the solid state with a distorted trigonal-bipyramidal structure, one olefinic double-bond occupying an equatorial and the other an axial position. The new bis-pyrazolylborate complexes MePhBp(Me)Rh(LL), LL = 2 CO, NBD and GOD, exist in solution in the form of single, stereochemically rigid isomers. Two-dimensional NOE spectroscopy shows that, in each case, the phenyl substituent occupies the pseudo-axial position of the boat-like six-membered chelate ring and is positioned above the rhodium centre.

Rhodium(I) complexes of the type Tp(3R,4R,5R)Rh(LL) (LL = 2 CO, NBD (norbornadiene), COD (1,5-cyclooctadiene), 3R = 4R = 5R = H; 3R = Me, 4R = 5R = H; 3R = Me, Ph, CF3, 4R = H, 5R = Me; 3R = Me, 4R = Me, Cl, 5R = Me; 3R = Pr-i, 4R = Br, 5R = H) were synthesized and fully characterized. Isomeric forms of three types were identified in solution for these compounds: type A, square planar complexes in which the Rh(NN)(2)B six-membered ring has a boat conformation, the third pyrazolyl ring being free and occupying an equatorial position; type B, compounds with a coordination geometry and chelate ring as above, but having the third pyrazolyl ring in an axial position, i.e., an arrangement which can easily form penta-coordinate complexes; type C, five-coordinate species which, however, on the NMR time scale, are in a fast exchange with those of type B. In the carbonyl complexes (LL = 2 CO), compounds of type C can be distinguished from the forms A and B by IR spectroscopy, The dynamic equilibria between the corresponding isomeric structures, A, B, and C, are solvent-dependent and can be shifted completely toward the forms B and C by placing a methyl substituent in the 5-position of each pyrazole. For compounds possessing COD as a co-ligand, the formation of square-planar complexes of type B, with kappa(2)-bonded pyrazolylborates is preferred, as indicated by Rh-103 NMR spectroscopy, whereas both four- and five-coordinate species are present in compounds having NBD as a co-ligand, their relative contributions being dependent on the substituents bn the pyrazolyl rings. The X-ray crystal structure of the compound Tp(Me)-Rh(NBD) (space group P2(1)/c, a = 18.152(3), b = 16.732(4), c = 20.591(4) Angstrom; beta = 141.793(7); Z = 8; R = 0.0457, R(w) = 0.0412 for 3904 observed reflections) shows that the tris(pyrazolyl)borate ligand is kappa(3)-bonded and the rhodium atom has a distorted trigonal bipyramidal structure (type C), the two olefinic double bonds being in an equatorial and an axial position, respectively.

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).

(1H, 103Rh) and (1H, 103Rh){2H} inverse correlation techniques, which profit from the presence of a magnetically active central metal nucleus, were applied to the complex [RhY2(Y2){HB(3,5‐Me2pz)3}] (Y = H or D; pz = pyrazolyl) containing both ‘classical’ and ‘non‐classical’ hydrogen ligands. The sample examined was a mixture of all species ranging from the perprotio to the perdeuterio compound. It is shown that the large isotope chemical shifts of the Rh nucleus can be used to separate the 1D 1H and 1H{2H} NMR spectra of the different H/D isotopomers. The observed isotope effects are discussed.

AbstractThe Rh hydride complex (V) is synthesized as shown and characterized by NMR spectroscopy.

Nur durch Stickstoffliganden wird der H2‐Ligand in 1 stabilisiert. 1H‐detektierte 2D‐(1H, 103Rh)‐NMR‐Spektroskopie, ein NMR‐Experiment, bei dem während der Präparationszeit heteronucleare Zwei‐Spin‐Kohärenzen angeregt werden, ermöglicht durch Variation der 1H‐Senderfrequenz, sowohl die chemische Verschiebung des Metallatoms als auch die Zahl der Hydridoliganden direkt aus dem Spektrum abzulesen.magnified image