A series of new metalloradical rhodium and iridium complexes [M(II)(cod)(N-ligand)](2+) in the uncommon oxidation state +II were synthesized by one-electron oxidation of their [M(I)(cod)(N-ligand)](+) precursors (M=Rh, Ir; cod=(Z,Z)-1,5-cyclooctadiene; and N-ligand is a podal bis(pyridyl)amine ligand: N,N-bis(2-pyridylmethyl)amine (dpa), N-(2-pyridylmethyl)-N-(6-methyl-2-pyridylmethyl)amine (pla), or N-benzyl-N,N-bis(6-methyl-2-pyridylmethyl)amine (Bn-dla). EPR spectroscopy, X-ray diffraction, and DFT calculations reveal that each of these [M(II)(cod)(N-ligand)](2+) species adopts a square-pyramidal geometry with the two cod double bonds and the two pyridine fragments in the basal plane and the N(amine) donor at the apical position. The unpaired electron of these species mainly resides at the metal center, but the apical N(amine) donor also carries a considerable fraction of the total spin density (15-18 %). Density functional calculations proved a valuable tool for the analysis and simulation of the experimental EPR spectra. Whereas the M(II)(olefin) complexes are quite stable as solids, in solution they spontaneously transform into a 1:1 mixture of M(III)(allyl) species and protonated M(I)(olefin) complexes (in the forms [M(I)(olefin)(protonated N-ligand)](2+) for M=Rh and [M(III)(H)(olefin)(N-ligand)](2+) for M=Ir). Similar reactions were observed for the related propene complex [M(II)(propene)(Me(2)tpa)](2+) (Me(2)tpa=N,N,N-tris(6-methyl-2-pyridylmethyl)amine). The decomposition rate of the [M(II)(cod)(N-ligand)](2+) species decreases with increasing N-ligand bulk in the following order: dpa>pla>Bn-dla. Decomposition of the most hindered [M(II)(cod)(Bn-dla)](2+) complexes proceeds by a second-order process. The kinetic rate expression v=k(obs)[M(II)](2) in acetone with k(obs)=k'[H(+)][S], where [S] is the concentration of additional coordinating reagents (MeCN), is in agreement with ligand-assisted dissociation of one of the pyridine donors. Solvent coordination results in formation of more open, reactive species. Protonation of the noncoordinating pyridyl group increases the concentration of this species, and thus [H(+)] appears in the kinetic rate expression. The kinetic data are in agreement with bimolecular hydrogen-atom transfer from M(II)(cod) to another M(II) species (DeltaH( not equal)=11.5+/-2 kcal mol(-1), DeltaS( not equal)=-27+/-10 cal K(-1) mol(-1), and DeltaG( not equal)(298 K)=19.5+/-5 kcal mol(-1)).

Complexation of [RhI(cod)]+ and [IrI(cod)]+ by the new pyridine‐amine‐pyrrole ligands Py–CH2–N(R)–CH2–Pyr–H (HLR; R = H, Bzl, Bu) and the corresponding pyridine‐amine‐pyrrolate ligands [Py–CH2–N(R)–CH2–Pyr]− (LR−; R = H, Bzl, Bu, CH2Py) has been investigated. The neutral ligands HLR (R = H, Bu, Bzl) give [(HLR)MI(cod)]+ (M = Rh, Ir) in which HLR acts as a didentate ligand via the pyridine nitrogen (NPy) and the amine nitrogen (NRamine). The crystal structures of [(HLH)MI(cod)]PF6 (M = Rh: [1]PF6 and M = Ir: [2]PF6) have been determined. Deprotonation of [(HLR)MI(cod)]+ (M = Rh, Ir; R = H, Bzl, Bu) results in the neutral complexes [(LR)MI(cod)] (M = Rh, Ir) of the mono‐anionic ligands LR− (R = H, Bzl, Bu). In square‐planar [(LH)MI(cod)] (M = Rh: 3, M = Ir: 4), LH− is didentate via NHamine and the pyrrolate nitrogen (NPyr). The X‐ray structures of 3 and 4 reveal that in both cases the uncoordinated NPy accepts a hydrogen bond from NHamine. The X‐ray structures of [(LBzl)MI(cod)] (M = Rh: 5, M = Ir: 6), show that LBzl− is didentate via Namine and NPyr for M = Rh and tridentate for M = Ir. In solution LBzl− is tridentate for both M = Rh and M = Ir. The neutral complexes [{Py–CH2–N(R)–CH2–Pyr}MI(cod)] (M = Rh, Ir) cannot be oxidised selectively with H2O2. This is in marked contrast to the previously observed selective oxidation of the corresponding cationic complexes [{Py–CH2–N(R)–CH2–Py}RhI(cod)]+. Rhodium complex 5 is an active catalyst for the stereoregular polymerisation of phenylacetylene, whereas iridium complex 6 is inactive.

Complexation of [Rh I (cod)] + and [Ir I (cod)] + by the new nitrogen (N Pyr ). The X-ray structures of 3 and 4 reveal that in both cases the uncoordinated N Py accepts a hydrogen pyridine-amine-pyrrole ligands Py-CH 2 -N(R)-CH 2 -Pyr-H (HL R ; R = H, Bzl, Bu) and the corresponding pyridine-amine-bond from N H amine . 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 pyrrolate ligands [Py-CH 2 -N(R)-CH 2 -Pyr] -(L R -; R = H, Bzl, Bu, CH 2 Py) has been investigated. The neutral ligands HL R and N Pyr for M = Rh and tridentate for M = Ir. In solution L Bzl is tridentate for both M = Rh and M = Ir. The neutral (R = H, Bu, Bzl) give [(HL R )M I (cod)] + (M = Rh, Ir) in which HL R acts as a didentate ligand via the pyridine nitrogen (N Py ) complexes [{Py-CH 2 -N(R)-CH 2 -Pyr}M I (cod)] (M = Rh, Ir) cannot be oxidised selectively with H 2 O 2 . This is in marked and the amine nitrogen (N R amine ). The crystal structures of [(HL H )M I (cod)]PF 6 (M = Rh: [1]PF 6 and M = Ir: [2]PF 6 ) have contrast to the previously observed selective oxidation of the corresponding cationic complexes [{Py-CH 2 -N(R)-CH 2 -been determined. Deprotonation of [(HL R )M I (cod)] + (M = Rh, Ir; R = H, Bzl, Bu) results in the neutral complexes Py}Rh I (cod)] + . Rhodium complex 5 is an active catalyst for the stereoregular polymerisation of phenylacetylene, whereas [(L R )M I (cod)] (M = Rh, Ir) of the mono-anionic ligands L R -(R = H, Bzl, Bu). In square-planar [(L H )M I (cod)] (M = Rh: 3, iridium complex 6 is inactive. M = Ir: 4), L H is didentate via N H amine and the pyrrolate Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands Fax: (internat.) ϩ31-24/ 355-3450 corresponding amines with NaBH 4 . Alkylation of the am-