Short Rh Research Articles

Structure and 119Sn Mössbauer-spectroscopic characterization of BaRhSn2

Abstract The stannide BaRhSn2 was synthesized by induction melting of an arc-melted RhSn2 precursor compound with barium in a sealed tantalum ampoule. The structure of BaRhSn2 was refined from single-crystal X-ray diffractometer data: MgCuAl2 type, Cmcm, a = 437.56(4), b = 1242.35(10), c = 767.30(6) pm, wR2 = 0.0845, 469 F 2 values and 16 variables. The rhodium and tin atoms form a two-dimensional [RhSn2] δ− polyanionic network with short Rh–Sn (273–274 pm) and Sn–Sn (303–312 pm) distances. The large barium atoms lead to a substantial orthorhombic distortion of the (lonsdaleite-related) tin substructure, forcing a break of the Sn–Sn bond in b direction. This change in the tin substructure is reflected in the 119Sn Mössbauer spectrum. The tin atoms exhibit a higher s electron density which is expressed in an increased isomer shift of δ = 2.08(1) mm s−1 as compared to the previously reported stannide CaRhSn2 with a three-dimensional [RhSn2] δ− polyanionic network and δ = 1.96(4) mm s−1.

Intermediate ytterbium valence in YbRhSn2

Abstract The stannide YbRhSn2 has been synthesized. An arc-melted Rh25Sn48 precursor sample was reacted with ytterbium in a sealed tantalum ampoule in an induction furnace. The structure of YbRhSn2 was refined from single-crystal X-ray diffractometer data: MgCuAl2 type, Cmcm, a = 433.10(3), b = 1076.63(8), c = 739.36(5) pm, wR2 = 0.0676, 444 F 2 values and 16 variables. The rhodium and tin atoms form a three-dimensional [RhSn2] δ− polyanionic network with short Rh–Sn (271–273 pm) and Sn–Sn (301–324 pm) distances. The tin substructure is an orthorhombically distorted lonsdaleite network. YbRhSn2 shows paramagnetic behavior with a reduced magnetic moment of 2.2(1) µB per ytterbium atom, classifying it as an intermediate-valent compound.

Pressure-induced formation of rhodium zigzag chains in the honeycomb rhodateLi2RhO3

We use powder x-ray diffraction to study the effect of pressure on the crystal structure of the honeycomb rhodate Li$_2$RhO$_3$. We observe low-pressure ($P$$<$$P_{c1}$ = 6.5 GPa) and high-pressure ($P$$>$$P_{c2}$ = 14 GPa) regions corresponding to the monoclinic $C2/m$ symmetry, while a phase mixture is observed at intermediate pressures. At $P$$>$$P_{c2}$, the honeycomb structure becomes distorted and features short Rh--Rh bonds forming zigzag chains stretched along the crystallographic $a$ direction. This is in contrast to dimerized patterns observed in triclinic high-pressure polymorphs of $\alpha$-Li$_2$IrO$_3$ and $\alpha$-RuCl$_3$. Density-functional theory calculations at various pressure conditions reveal that the observed rhodium zigzag-chain pattern is not expected under hydrostatic pressure but can be reproduced by assuming anisotropic pressure conditions.

Chelate Silylene-Silyl Ligand Can Boost Rhodium-Catalyzed C-H Bond Functionalization Reactions.

The first N-heterocyclic silylene (NHSi)-silane scaffold LSi-R-Si(H)Mes2 (1) (L=PhC(NtBu)2 ; R=1,12-xanthendiyl spacer; Mes=2,4,6-Me3 C6 H2 ) was synthesized and used to form the unique rhodium(III) complex (LSi-R-SiMes2 )Rh(H)Cl 2 through its reaction with 0.5 molar equivalents of [Rh(coe)2 Cl]2 (coe=cyclooctene). An X-ray diffraction analysis revealed that 2 has a (SiII SiIV )Rh(H)Cl core with three short Rh⋅⋅⋅H-C contacts with Me groups of the ligand 1, which cause a distorted pentagonal bipyramidal coordination of the Rh center. Unexpectedly, the reaction of 2 with tBuONa gives the new bis(silyl)hydridorhodium(III) complex 4. Due to the strong donor ability of the chelate SiII -SiIV ligand, 2 and 4 can act as highly efficient pre-catalysts in the Rh-mediated selective C-H functionalization of 2-phenylpyridines with C-C unsaturated organic substrates under mild reaction conditions.

Diferrocenylmercury‐Bridged Diphosphine: A Chiral, Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox-active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2-fc(PPh2 )(SnMe3 ) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n-Bu4 N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg-Cl→Hgfc2 (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2 )2 ⋅HgCl2 where the bridging mercury atom acts as a σ-acceptor. Furthermore, a bis-[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10-2 and 1.4×10-2 e/a03 at the bond critical points.

Diferrocenylmercury‐Bridged Diphosphine: A Chiral, Ambiphilic, and Redox‐Active Bidentate Ligand

AbstractA diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2‐fc(PPh2)(SnMe3) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n‐Bu4N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc2 (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2)2⋅HgCl2 where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10−2 and 1.4×10−2 e/a03 at the bond critical points.

Equiatomic rare earth rhodium plumbides RERhPb (RE=Y, La–Nd, Sm, Gd–Lu) with ZrNiAl-type structure

Abstract The equiatomic plumbides RERhPb (RE=Y, La–Nd, Sm, Gd–Lu) were synthesized by induction melting of the elements in sealed niobium ampoules. The samples were characterized by X-ray powder diffraction, confirming their ZrNiAl-type structure, space group P6̅2m. Four structures were refined from single-crystal X-ray diffractometer data: a=769.42(5), c=415.60(3) pm, wR=0.0415, 343 F 2 values, 15 variables for LaRhPb, a=767.91(6), c=369.37(4) pm, wR=0.0798, 284 F 2 values, 15 variables for ErRhPb, a=767.01(8), c=366.21(4) pm, wR=0.0380, 341 F 2 values, 15 variables for YbRhPb and a=766.9(1), c=363.42(6) pm, wR=0.0699, 290 F 2 values, 15 variables for LuRhPb. The RERhPb plumbides contain two crystallographically independent rhodium atoms, both in tricapped trigonal prismatic coordination: Rh1@Pb3 RE 6 and Rh2@RE 6Pb3. Short Rh–Pb distances (277 and 284 pm in ErRhPb) are indicative of covalent Rh–Pb bonding. The crystal chemical details of the RERhPb series are compared with the silver plumbides REAgPb which show different transition metal-lead coloring. Temperature dependent magnetic susceptibility data show Pauli paramagnetism for YRhPb, LaRhPb and LuRhPb. An antiferromagnetic ground state below the Néel temperatures of 13.5, 21.0 and 6.9 K was found for PrRhPb, TbRhPb and DyRhPb, respectively. HoRhPb exhibits Curie-Weiss behavior in the observed temperature range.

The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4

AbstractThe gallides SrRh2Ga2, SrIr2Ga2, and Sr3Rh4Ga4 were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh2B2 type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR2 = 0.0218, 398 F2 values, 15 variables for SrRh2Ga2; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr2Ga2, and Na3Pt4Ge4 type, I$\bar{4}$3m, a = 777.4(2) pm, wR2 = 0.0234, 190 F2 values, 11 variables for Sr3Ir4Ga4. The gallides SrRh2Ga2 and Sr3Ir4Ga4 exhibit complex, covalently bonded three‐dimensional [Rh2Ga2] and [Ir4Ga4] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh2Ga2 and by 4 Ir + 8 Ga in Sr3Ir4Ga4. The structure of SrRh2Ga2 is discussed along with the monoclinic distortion variants HoNi2B2 and BaPt2Ga2 on the basis of a group‐subgroup scheme.

Bistable multifunctionality and switchable strong ferromagnetic-to-antiferromagnetic coupling in a one-dimensional rhodium(I)-semiquinonato complex.

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV-vis-NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium(I)-semiquinonato complex, [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3), where 3,6-DBSQ-4,5-(MeO)2(•-) represents 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound 3 comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh-Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228-207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C-H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound 3 exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature T(N) of 14.2 K. The electrical conductivity of 3 at 300 K is 4.8 × 10(-4) S cm(-1), which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation.

Terminal Imido Rhodium Complexes

AbstractCompounds of the late transition metals with MX multiple bonds (X=CR2, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second‐ and third‐row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP3)(NR)] (PhBP3=PhB{CH2PPh2}3) with a multiple and terminal RhN bond. These imido compounds result from reactions of organic azides with the corresponding rhodium(I) complex having a labile ligand, and display a pseudo‐tetrahedral core geometry with an almost linear Rh‐N‐C arrangement [177.5(2)°] and a short RhN bond [1.780(2) Å]. We also show that the RhN bond undergoes protonation at the nitrogen atom or addition of H2, and also engages in nitrene‐group transfer and cycloaddition reactions.

Terminal imido rhodium complexes.

Compounds of the late transition metals with M=X multiple bonds (X=CR2, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second- and third-row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP3)(NR)] (PhBP3=PhB{CH2PPh2}3) with a multiple and terminal Rh=N bond. These imido compounds result from reactions of organic azides with the corresponding rhodium(I) complex having a labile ligand, and display a pseudo-tetrahedral core geometry with an almost linear Rh-N-C arrangement [177.5(2)°] and a short Rh-N bond [1.780(2) Å]. We also show that the Rh=N bond undergoes protonation at the nitrogen atom or addition of H2 , and also engages in nitrene-group transfer and cycloaddition reactions.

Unprecedented partial paddlewheel dirhodium methyl isocyanide compounds with unusual structural and electronic properties: a comprehensive experimental and theoretical study

A series of dirhodium acetonitrile compounds, namely cis-[Rh2(DTolF)2(CH3CN)6][BF4]2 (1) cis-[Rh2(F-form)2(CH3CN)6][BF4]2 (2), cis-[Rh2(NNN)2(CH3CN)6][BF4]2 (3) ([F-form]−: p-difluorophenylformamidinate, [NNN]−: p-ditolyltriazenide, [DTolF]−: p-ditolylformamidinate), cis-[Rh2[Ph2P(C6H4)]2(CH3CN)6][BF4]2 (4) and their unprecedented methyl isocyanide analogs 5–8, respectively, were synthesized and characterized by X-ray crystallography, cyclic voltammetry, NMR, electronic and infrared spectroscopies. The elongation of the Rh–Rh distances (∼0.07 A) and the bonds trans to eq CH3NC in 5–8vs.1–4 are in accord with the strong trans influence of isocyanide. The short Rh–C (CH3NC) distances in 5–8 are attributed to π-backbonding, whereas the short CN distances in CH3NC and the high energy ν(CN) stretches are attributed to appreciable σ-donation of CH3NC. Of particular note are the longer Rh–Rh bonds (∼2.76 A) that 8 exhibits and unprecedented short ax Rh–C distances in the same range as the eq Rh–C bonds (2.01–2.04 A) for CH3NC. TD-DFT calculations predict the lowest-energy LMCT transitions in the order 1 < 2 < 5 < 6, 3 < 7 and the HOMO–LUMO energy gaps to be greater in 5–7vs.1–3, respectively, findings corroborated by electrochemical and electronic spectral data. This trend is attributed to the stabilization of the HOMOs and destabilization of the LUMOs in 5–7. The π-backbonding in 5–8 stabilizes the Rh2(π*) orbitals and σ-donation from CH3NC destabilizes the Rh2(σ) orbitals, with the extreme case being 8 where Rh2(σ) becomes the HOMO. This fact accounts for the ∼20-fold increase in intensity of the HOMO Rh2(σ) → LUMO Rh2(σ*) transition for 8 (∼370 nm) vs.4, also in accord with TD-DFT calculations.

P(CH)P Pincer Rhodium(I) Complexes: The Key Role of Electron-Poor Imidazoliophosphine Extremities

The coordination chemistry of a potentially pincer-type dicationic meta-phenylene-bis(imidazoliophosphine) ligand 3 to neutral and cationic carbonylrhodium(I) centers has been investigated. Similarly to what was observed previously for its ortho-phenylene counterpart, 3 was found to bind to the RhCl(CO) fragment in a trans-chelating manner that makes possible a weak Rh-C(H) interaction, inferred from the nonbonding but relatively short Rh-C and Rh-H contacts observed in the solid state structure of the dicationic adduct (3)RhCl(CO) (5). Formation of the target PCP-type pincer complex could not be triggered despite multiple attempts to deprotonate the central C-H moiety in the initial dicationic adduct 5, or in the tricationic species [(3)Rh(CO)](+) (8) generated by abstraction of the chloride ion from 5. Complex 8 was identified on the basis of NMR and IR analyses as a Rh(I)-stabilized P(CH)P-intermediate en route to the anticipated classical PCP-type pincer complex. Analysis of the electronic structure of this intermediate computed at the density functional level of theory (DFT level) revealed a bonding overlap between a Rh d-orbital and π-orbitals of the m-phenylene ring. NBO analyses and calculated Wiberg indices confirm that this interaction comprises an η(1)-C-Rh bonding mode, with only secondary contributions from the geminal C and H atoms. Although the target PCP-type pincer complex could not be generated, treatment of the tricationic intermediate with methanol induced a P-CN(2) bond cleavage at both imidazoliophosphine moieties, resulting in the formation of a dicationic "open pincer" species, that is, a nonchelated bis((MeO)PPh(2))-stabilized aryl-Rhodium complex that is the κC-only analogue of the putative κP,κC,κP-PCP complex sought initially. Theoretical studies at the DFT level of experimental or putative species relevant to the final C-H activation process ruled out the oxidative addition pathway. Two alternative pathways are proposed to explain the formation of the "open pincer" complex, one based on an organometallic α-elimination step, the other based on an organic aromatization-driven β-elimination process.

The 1,8-Bis(2′-pyridyl)-3,6-dithiaoctane Complex of Rhodium(III)

The tetradentate ligand 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) forms a pseudooctahedral structure with rhodium(III). The yellow racemic [Rh(Pdto)Cl2](CF3SO3) compound belongs to the Pbca space group with a = 13.566(15), b = 15.6588(16), c = 21.473(2) A, and Z = 8. The Rh–S bonds are shorter than is usual, while the pyridine rings are mutually trans and form an interplanar angle of 24°. The yellow racemic Rh(III) complex [Rh(Pdto)Cl2]+ possesses a pseudooctahedral structure with relatively short Rh–S bonds, in which the pyridine rings are mutually trans and form an interplanar angle of 24°.

Contrasting Reactivity of 2-Mesityl-1,8-Naphthyridine (Mes-NP) with Singly-Bonded [RhII–RhII] and [RuI–RuI] Compounds

Reaction of cis-[Rh2(CH3COO)2(CH3CN)6](BF4)2 with two equivalents of 2-mesityl-1,8-naphthyridine (Mes-NP) affords trans-[Rh2(CH3COO)2(Mes-NP)2](BF4)2 (1). X-ray structure reveals weak Rh–C(ipso) interaction, and a short Rh–Rh distance. The same ligand, in contrast, oxidatively cleaves the Ru–Ru bond in cis-[Ru2(CO)4(CH3CN)6](BF4)2 and results in trans-[Ru(Mes-NP)2(CH3CN)2](BF4)2 (2). Both compounds adopt trans geometry to relieve the steric strain. Compound 2 exhibits moderate activity for the alcohol oxidation and aldehyde olefination reactions.

RERhZn (RE = Y, Sm, Gd–Lu) compounds with TiNiSi type structure – Synthesis and magnetic properties

The TiNiSi type intermetallic compounds RERhZn (RE = Y, Sm, Gd–Lu) were synthesized by induction melting of the elements in sealed tantalum ampoules. They were characterized by X-ray powder diffraction. Five structures were refined from single crystal X-ray diffractometer data: Pnma, Z = 4, a = 699.7(2), b = 405.6(2), c = 816.9(2) pm, wR2 = 0.038, 628 F 2 values for SmRhZn, a = 696.1(2), b = 405.6(1), c = 811.9(3) pm, wR2 = 0.028, 886 F 2 values for GdRhZn, a = 692.8(1), b = 403.0(1), c = 809.5(2) pm, wR2 = 0.039, 562 F 2 values, for TbRhZn, a = 690.6(3), b = 401.50(9), c = 808.2(2) pm, wR2 = 0.036, 763 F 2 values, for DyRhZn, and a = 688.6(5), b = 399.6(4), c = 808.3(7) pm, wR2 = 0.048, 546 F 2 values for HoRhZn with 20 variables for each refinement. The rhodium atoms have coordination number 9 (5 RE + 4 Zn atoms) in the form of a tricapped trigonal prism. Together the rhodium and zinc atoms build up three-dimensional [RhZn] networks with short Rh–Zn (263–269 pm in GdRhZn) and Zn–Zn (296 pm in GdRhZn) distances. The gadolinium atoms bind to the [RhZn] network by Gd–Rh bonds (292–294 pm). Magnetic susceptibility measurements show Pauli paramagnetism for YRhZn and van Vleck paramagnetism for SmRhZn. The remaining RERhZn compounds are Curie–Weiss paramagnets which show magnetic ordering at low temperatures.

Rare earth metal-rich indides RE14Rh 3−xIn 3 ( RE=Y, Dy, Ho, Er, Tm, Lu)

The rare earth ( RE) metal-rich indides RE 14Rh 3– x In 3 ( RE=Y, Dy, Ho, Er, Tm, Lu) can be synthesized from the elements by arc-melting or induction melting in tantalum crucibles. They were investigated by X-ray diffraction on powders and single crystals: Lu 14Co 3In 3 type, space group P4 2/ nmc, Z=4, a=961.7(1), c=2335.5(5) pm, w R2=0.052, 2047 F 2 values, 62 variables for Y 14Rh 3In 3, a=956.8(1), c=2322.5(5) pm, w R2=0.068, 1730 F 2 values, 63 variables for Dy 14Rh 2.89(1)In 3, a=952.4(1), c=2309.2(5) pm, w R2=0.041, 1706 F 2 values, 63 variables for Ho 14Rh 2.85(1)In 3, a=948.6(1), c=2302.8(5) pm, w R2=0.053, 1977 F 2 values, 63 variables for Er 14Rh 2.86(1)In 3, a=943.8(1), c=2291.5(5) pm, w R2=0.065, 1936 F 2 values, 63 variables for Tm 14Rh 2.89(1)In 3, and a=937.8(1), c=2276.5(5) pm, w R2=0.050, 1637 F 2 values, 63 variables for Lu 14Rh 2.74(1)In 3. Except Yb 14Rh 3In 3, the 8 g Rh1 sites show small defects. Striking structural motifs are rhodium-centered trigonal prisms formed by the RE atoms with comparatively short Rh– RE distances (271–284 pm in Y 14Rh 3In 3). These prisms are condensed via common corners and edges building two-dimensional polyhedral units. Both crystallographically independent indium sites show distorted icosahedral coordination. The icosahedra around In2 are interpenetrating, leading to In2–In2 pairs (309 pm in Y 14Rh 3In 3).

Rhodium Dimers with 2,2-Dimethyl-1,3-diisocyano and Bis(diphenylphosphino)methane Bridging Ligands

Four rhodium dimers have been synthesized with a bridging diisocyanide ligand, dmb (2,2-dimethyl-1,3-diisocyanopropane): [Rh2(dmb)4](BPh4)2, [Rh2(dmb)4Cl2]Cl2, [Rh2(dmb)4I2](PF6)2, and [Rh2(dmb)2(dppm)2](BPh4)2 (dppm = bis(diphenylphosphino)methane). The complexes have been characterized by elemental analysis and mass spectrometry, as well as UV-visible, IR, and 1H NMR spectroscopies. X-ray crystal structures of the rhodium(I) complexes, [Rh2(dmb)4](BPh4)2 . 1.5CH3CN (3.2330(4), 3.2265(4) A) and [Rh2(dmb)2(dppm)2](BPh4)2.0.5CH3OH . 0.2H2O (3.0371(5) A), confirm the existence of short Rh...Rh interactions. The metal-metal separation for the rhodium(II) adduct, [Rh(2)(dmb)4Cl2]Cl2.6CHCl3 (2.8465(6) A), is consistent with a formal Rh-Rh bond. For the two luminescent rhodium(I) dimers and six previously investigated diisocyano-bridged dimers with and without dppm ligands, the intense spin-allowed dsigma-->psigma absorption band maximum shifts to longer wavelengths with decreasing Rh...Rh separation, and there is an approximate correlation between band energy and the inverse of the metal-metal separation cubed. Both [Rh2(dmb)4]2+ and [Rh2(dmb)4(dppm)2]2+ undergo oxidative addition in the presence of iodine. In the conversion of [Rh2(dmb)4]2+ to [Rh2(dmb)4I2]2+, the observed intermediate is tentatively assigned to a tetramer composed of two rhodium dimers. In the case of [Rh2(dmb)2(dppm)2]2+, no intermediate was detected.

Photochromic Rh(II) complexes based on 1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Reaction of [Rh 2(O 2CC(CH 3) 3) 4] with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene ( cis-dbe) or closed-dbe in benzene and dichloromethane yielded three novel Rh(II) complexes. Their structures were characterized and photochromic properties were studied. X-ray crystallographic analyses revealed that the coordination environments of the three metal complexes are quite different. Complex 2 exhibits a 1-D infinite chain structure with two cyano groups of the ligand bridging two metal ions while in complexes 1 and 3 the metal ions have a direct interaction with at least one of the sulfur atoms of the two bisthienylethene molecules. Closed-dbe of complex 3 was transferred to the ring-open form in the crystalline phase upon photoexcitation with 529 nm light. It underwent a photocycloreversion reaction although the metal atom is coordinated to the thienyl group. The irreversible cyclization reaction was presumably attributed to the fixed rotation of thienyl rings, short Rh S distance and steric hindrance of anions.

The valence structure analysis for dirhodium(II) tetracarboxylato complexes with nitric oxide as axial ligand

Density functional theory has been used to study the trans-influence of Rh–Rh and Rh–L bonds in dirhodium(II) tetracarboxylates with axial ligands L=H 2O, pyridine, CO, triphenylphosphine, NO and NO 2. The absence of the chemical bond between metal atoms in Rh 2(μ-O 2CR) 4(NO) 2 complexes and the formation of two covalent Rh–NO bonds explain the very long Rh–Rh and very short Rh–N distances in these compounds.