SYNTHESIS AND X-RAY AND NEUTRON STRUCTURES OF ANTI-[L2RH2(H)2(MU-H)2](PF6)2 (L = 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE) AND A RELATED SPECIES CONTAINING A SYN-[RH2(H)2(MU-H)2]2+ CORE - ISOLATION OF [L2FE2(MU-H)3]BPH4

The macrocyclic ligands 1,4,7-trimethyl-1,4,7-triazacyclononane (L) and 1,2-bis(4,7-dimethyl-1,4,7-triaza-1-cyclononyl)ethane (Me4dtne) react with RhCl3.3H2O in ethanol affording the neutral complexes LRhCl3 (1) and [(Me4dtne)Rh2Cl6]2H2O (2). Aqueous suspensions of 1 and 2 react with NaBH4 yielding upon addition of KPF6 red-brown crystals of air- and moisture-stable anti-[L2Rh2(H)2(mu-H)2](PF6)2 (3) and syn-[(Me4dtne)Rh2(H)2(mu-H)2](PF6)2 (4), respectively, LFeCl3 and Li[AH4] were found to form red [L2Fe2(mu-H)3]BPh4 (5) in tetrahydrofuran. The structure of 3 has been determined by single-crystal X-ray (295 K) and neutron diffraction (20 K). Neutron data for 3: monoclinic space group P2(1)/c, a = 8.155(l) angstrom, b = 11.768(2) angstrom, c = 15.611(2) angstrom, beta = 92.156(8)-degrees, V = 1497.1(2) angstrom3, Z = 2, D(calcd) = 1.869 g/cm3. The [HRh(mu-H)2RhH]2+ core contains a planar Rh2(mu-H)2 ring (Rh-H(b) = 1.754(2) angstrom; Rh ... Rh = 2.595(2) angstrom); each rhodium center has a terminal hydride ligand in anti-position with respect to each other (Rh-H(t) = 1.536(2) angstrom). The terminal hydride exerts a pronounced structural trans influence on the Rh-N bond in trans position (Rh-N(trans) = 2.276(1) angstrom vs average Rh-N(cis) = 2.082(1) angstrom. In 4 the [HRh(mu-H)2RhH]2+ core is syn configurated due to the steric requirements of the strapped macrocycle. The solution behavior of 3 and 4 has been studied by H-1 NMR spectroscopy. 3 is a fluctional molecule, and in contrast, 4 is rigid at ambient temperature.