Coordination chemistry of 2-pyrimidinolate: synthesis and characterization of a neutral tetrameric rhodium(I) derivative

A novel metal-organic complex of analytical Rh(COD)(2-pymo) formulation (COD=1,5-cyclooctadiene, 2-Hpymo=2-hydroxypyrimidine) has been prepared by reacting [Rh(COD)Cl]2 with 2-Hpymo. While direct syntheses in a variety of solvents (acetone, toluene or methanol) typically afforded amorphous powders, recrystallization from methanol allowed to perform a single crystal data collection on the CH3OH solvate. The crystal structure of the latter [tetragonal, P-42c, a=13.9780(2), c=14.4980(10) Å, V=2832.7(6) Å3] contains cyclic [Rh(COD)(2-pymo)]4 tetramers, in which distorted square planar metal atoms are bridged by η1-μ2-N,N′-exo-bidentate 2-pymo ligands in 1,3-alternate disposition. Upon dissolving both the amorphous and the crystalline (solvated) species in CD2Cl2, variable temperature NMR spectra confirmed the presence of identical (tetrameric) species, thus excluding the existence of other oligomers of different nuclearity in the amorphous powders.