Diversity in complexation of [Rh-I(cod)](+) and [Ir-I(cod)](+) by pyridine-amine-pyrrole ligands

Complexation of [Rh-I(cod)](+) and [Ir-I(cod)](+) by the new pyridine-amine -pyrrole ligands Py-CH2-N(R)-CH2-Pyr-H (HLR; R = H, Bzl, Bu) and the corres ponding pyridine-amine-pyrrolate ligands [Py-CH2-N(R)-CH2-Pyr](-) (L-R(-); R = H, Bzl, Bu, CH2Py) has been investigated. The neutral ligands HLR (R = H, Bu, Bzl) give [(HLR)M-I(cod)](+) (M = Rh, Ir) in which HLR acts as a did entate ligand via the pyridine nitrogen (N-Py) and the amine nitrogen (N-am ine(R)). The crystal structures of [(HLH)M-I(cod)]PF6 (M = Rh: [1]PF6 and M = Ir: [2]PF6) have been determined. Deprotonation of [(HLR)M-I(cod)](+) (M = Rh, Ir; R = H, Bzl, Bu) results in the neutral complexes [(L-R)M-I(cod)] (M = Rh, Ir) of the mono-anionic ligands L-R(-) (R = H, Bzl, Bu). In squar e-planar [(L-H)M-I(cod)] (M = Rh: 3, M = Ir: 4), L-H(-) is didentate via N- amine(H) and the pyrrolate nitrogen (N-Pyr). The X-ray structures of 3 and 4 reveal that in both cases the uncoordinated N-Py accepts a hydrogen bond from N-amine(H). The X-ray structures of [(L-Bzl)M-I(cod)] (M = Rh: 5, M = Ir: 6), show that L-Bzl(-) is didentate via N-amine and N-Pyr for M = Rh an d tridentate for M = Ir. In solution L-Bzl(-) is tridentate for both M = Rh and M = Ir. The neutral complexes [{Py-CH2-N(R)-CH2-Pyr}M-I(cod)] (M = Rh, Ir) cannot be oxidised selectively with H2O2. This is in marked contrast t o the previously observed selective oxidation of the corresponding cationic complexes [{Py-CH2-N(R)-CH2-Py}Rh-I(cod)](+). Rhodium complex 5 is an acti ve catalyst for the stereoregular polymerisation of phenylacetylene, wherea s iridium complex 6 is inactive.