The synthesis of mixed-valence dirhodium carbonyl complexes, and the X-ray crystal structures of [{Rh(CO)(PPh₃)(µ-RNNNR)}₂] and [{Rh(CO)(PPh₃)(µ-RNNNR)}₂][PF₆](R =p-tolyl)

Abstract

X-Ray structural studies on [{Rh(CO)(PPh,)(p-RNNNR)}p]Z+ (R = p-tolyl, z = 0 and 1) show that the mixed-valence cation is formed by electron-loss from a metal-metal anti-bonding orbital; the asymmetric compounds [Rh2(CO)2L(PPh3){p-PhNC(Me)NPh}2]z+ [L = P(OPh)3, AsPh3, etc., z = 0 and 11 result from the oxidatively induced substitution of [Rh2(CO)3(PPh3){p-PhNC(Me)NPh}21.

Synthesis of Paramagnetic Tetranuclear Rhodium and Iridium Complexes with the 2,6-Pyridinedithiolate Ligand. Redox-Induced Degradation to Diamagnetic Triiridium Compounds

“…Paramagnetic square-planar mononuclear rhodium(II) complexes ( n = 1), such as [Rh(C 6 Cl 5 ) 2 (PR 3 ) 2 ], [Rh(C 6 Cl 5 ) 2 (cod)], and [Rh(2,4,6-Pr i 3 C 6 H 2 ) 2 (tht) 2 ] (tht = tetrahydrothiophene), show typical g -values in the range 2.46−2.32. The mean g -values in mixed-valence face-to-face dinuclear rhodium complexes ( n = 2) with ancillary π-acceptor carbonyl ligands, such as [Rh 2 (μ-PhNC(Me)NPh) 2 (CΟ) 2 (PPh 3 ) 2 ] and [Rh 2 (μ-RNNNR) 2 (CΟ) 2 (PPh 3 ) 2 ] (R = p -tolyl), show values of 2.119 and 2.118, respectively . Slightly higher values are found for related dinuclear complexes with diolefins as auxiliary ligands such as [Rh 2 (μ-mhp) 2 (cod) 2 ], [Rh 2 (μ-chp) 2 (nbd) 2 ], and [Rh 2 (μ-mhp) 2 (nbd) 2 ] (mhp = 6-methyl-2-hydroxypyridinate, chp = 6-chloro-2-hydroxypyridinate, nbd = 2,5-norbornadiene) with mean g -values of 2.218, 2.181, and 2.178 in frozen solutions, respectively .…”

“…The mean g-values in mixed-valence face-to-face dinuclear rhodium complexes (n ) 2) with ancillary π-acceptor carbonyl ligands, such as [Rh 2 (µ-PhNC(Me)NPh) 2 (CΟ) 2 (PPh 3 ) 2 ] and [Rh 2 (µ-RNNNR) 2 (CΟ) 2 (PPh 3 ) 2 ] (R ) p-tolyl), show values of 2.119 and 2.118, respectively. 26 Slightly higher values are found for related dinuclear complexes with diolefins as auxiliary ligands such as [Rh 2 (µ-mhp) 2 (cod) 2 ], [Rh 2 (µ-chp) 2 (nbd) 2 ], and [Rh 2 (µ-mhp) 2 (nbd) 2 ] (mhp ) 6-methyl-2-hydroxypyridinate, chp ) 6-chloro-2-hydroxypyridinate, nbd ) 2,5-norbornadiene) with mean g-values of 2.218, 2.181, and 2.178 in frozen solutions, respectively. 10 The diolefin complexes [Rh 2 (µ-1,8-(NH) 2 C 10 H 6 )-(diolefin) 2 ] (diolefin ) cod, nbd, tfbb) also exhibit mean g-values in the range 2.149-2.141 in CH 2 Cl 2 at room temperature.…”

Crescent-Shaped Rhodium(I) Complexes with Bis(o-carboxymethylphenyl)triazenide

“…30 kV, 3-nitrobenzyl alcohol (NBA) was used as matrix. 1 H and 13 C{ 1 H} NMR spectra were recorded on a Bruker ARX 300 and on a Varian UNITY 300 spectrometers operating at 300.13 and 299.95 MHz for 1 H, respectively. Chemical shifts are reported in parts per million and referenced to SiMe 4 using the residual signal of the deuterated solvent as reference.…”

“…The high stability of the eight-membered "M 2 (µ-ArNNNAr) 2 " core in the homodinuclear complexes has allowed the development of a rich redox-chemistry involving a combination of theoretical studies with electrochemistry and ESR spectroscopy. 12 For example, the "face-to-face" dirhodium structure remained intact after one electron oxidation reaction 13,14 to the corresponding paramagnetic monocations (formally M(I)/ M(II) complexes), and a recent study 15 on dinuclear complexes with a family of triazenide ligands of the type (p-XC 6 H 4 )NNN(p-X′C 6 H 4 ) showed the marked influence of the X and X′ groups on the oxidation potential E o′ . Moreover, the geometrically asymmetric triazenido-bridged complex [(CO) 2 Rh(µ-ArNNNAr) 2 Rh(bipy)] 16 was found to be a precursor to a wide range of redox-active species, 17 allowing the observation of processes such as the redox-isomerization of a triazenide bridge "µ-(1κN 1 ,2κN 3 )-ArNNNAr" into "µ-(1κN 1 ,1:2κN 3 )-ArNNNAr" 18 and the equilibrium between the cores "Rh(II)(µ-ArNNNAr) 2 Rh(II)(CO)" and "Rh(III)-(µ-ArNNNAr) 2 (µ-CO)Rh(III)".…”

The oxidative conversion of the N,S-bridged complexes [{RhLL′(μ-X)}2] to [(RhLL′)3(μ-X)2]+ (X = mt or taz): a comparison with the oxidation of N,N-bridged analogues

“…than to paramagnetic monocations [{RhLL¢(m-X)} 2 ] + analogous to those isolated from the oxidation of N,N-bridged species such as [{Rh(CO)(PPh 3 )(m-X)} 2 ] (X = p-tolNNNtol-p 15 or 2-t-butylpyrazolyl 16 ).…”