Rhodium(I) Complexes of N-Aryl-Substituted Mono- and Bis(amidinates) Derived from Their Alkali Metal Salts

Article abstract of DOI:10.1002/ejic.201800349

The synthesis and characterization of several rhodium(I) complexes of amidinate and linker-bridged bis(amidinate) ligands are presented. The amidinate ligands for the mononuclear complexes CH₃{C(NMes)₂Rh(cod)} (1), CH₃{C(NDipp)₂Rh(cod)} (2), and HCC{C(NDipp)₂Rh(cod)} (3) (cod = 1,5-cyclooctadiene) were synthesized by reacting the corresponding organometallic precursor [Rh(cod)Cl]₂ with the alkali metal amidinates CH₃{C(NR)₂Li} L1Li (R = Mes = 2,4,6-Me₃C₆H₂) and L2Li (R = Dipp = 2,6-iPr₂C₆H₃). Analogously, the alkynyl-functionalized sodium amidinate (HCC{C(NDipp)₂Na}·2DME, L3Na) could be further deprotonated and reacted with carbodiimine to form the alkyne-bridged bis(amidinate) CC{C(NDipp)₂Na(thf)}₂ (L4Na), which serves as suitable starting material for the synthesis of CC{C(NDipp)₂Rh(cod)}₂ (4). The bis(amidinate) ligands for the corresponding para- (5) and meta- (6) phenylene-bridged complexes p-/m-C₆H₄{C(NMes)₂Rh(cod)}₂ were accessible through the reaction of phthalic acids with trimethylsilyl polyphosphate and mesitylamine and subsequent deprotonation of the obtained amidines. Tetramesityl oxalamidinate was used to synthesize the dinuclear complex {C(NMes)₂Rh(cod)}₂ (7) and its carbonylation product {C(NMes)₂Rh(CO)₂}₂ (8). All compounds under study were fully characterized by various spectroscopic methods. In particular the alkali metal salt of the linker-bridged bis(amidinate) L5Na forms a one-dimensional coordination polymer in the solid state. Reaction of L5Na and L6Na with [Rh(cod)Cl]₂ leads to dinuclear complexes in which the metal–metal distance can be adjusted, enabling us to study their reactivity, including possible cooperative effects in catalysis.