Carbenoid Reactions in Rhodium(II)-Catalyzed Decomposition of Iodonium Ylides

The intermediacy of metallocarbenes in decomposition reactions of iodonium ylides with [Rh₂(OAc)₄] was established by comparison with reactions of the corresponding diazo compounds. The sensitivity of the Rh^II-catalyzed intermolecular cyclopropane formation from substituted styrenes and bis(methoxycarbonyl)(phenyliodono)methanide ( 1a ) or dimethyl diazomalonate ( 1b ) is identical. The Hammett plot (with σ⁺) has a slope of ?0.47. Iodonium ylides and diazo compounds afford the same products in [Rh₂(OAc)₄]-catalyzed cyclopropane formations, cycloadditions, and intramolecular CH insertions, and exhibit the identical selectivity in intramolecular competitions for cyclopropane formation and insertion. The intramolecular CH insertion of the ylide 20c , when carried out in the presence of a chiral catalyst ([Rh₂{(?)-(S)-ptpa}₄]), results in formation of 21a having an ee of 67%, identical to the ee obtained with the diazo compound 20b .     

Enantioselectivity and cis/trans-Selectivity in Dirhodium(II)-Catalyzed addition of diazoacetates to olefins

The Rh¹¹-catalyzed carbenoid addition of diazoacetates to olefins was investigated with [Rh₂{(4S)-phox}₄] ( 1 ;phox = tetrakis[(4S)-tetrahydro-4-phenyloxazol-2-one]), [Rh₂{(2S)-mepy}₄] ( 2 ; mepy = tetrakis[methyl (2S)-tetrahydro-5-oxopyrrole-2-carboxylate]), and [Rh₂(OAc)₄] ( 3 ). While catalysis with 2 and 3 afford preferentially trans-cyclopropanecarboxylates, the cis-isomers are the major products with 1 . In general, the enantioselectivities achieved with 1 and 2 are comparable. Additions catalyzed by 1 are strongly sensitive to steric effects. Highly substituted olefins afford cyclopropanes in only poor yield. The preferential cis-selectivity observed in reactions catalyzed by 1 is attributed to dominant interactions between the ligand of the catalyst and the substituents of both olefin and diazoacetate, which overrule the steric interactions between olefin and diazoacetate in the transition state for carbene transfer.     

Zn(II) and Cu(II) unsymmetrical formamidine complexes as effective initiators for ring‐opening polymerization of cyclic esters

A series of Zn(II) and Cu(II) complexes were synthesized using unsymmetrical N,N′‐ diarylformamidine ligands, i.e. N‐(2‐methoxyphenyl)‐N′‐2,6‐dichorophenyl)‐formamidine ( L1 ), N‐(2‐methoxyphenyl)‐N′‐phenyl)‐formamidine ( L2 ), N‐(2‐methoxyphenyl)‐N′‐(2,6‐dimethylphenyl)‐formamidine ( L3 ) and N‐(2‐methoxyphenyl)‐N′‐(2,6‐diisopropylphenyl)‐formamidine ( L4 ). The complexes, [Zn₂( L1 )₂(OAc)₄] ( 1) , [Zn₂( L2 )₂(OAc)₄] ( 2 ), [Zn₂( L3 )₂(OAc)₄] ( 3 ), [Zn₂( L4 )₂(OAc)₄] ( 4 ), [Cu₂( L1 )₂(OAc)₄] ( 5 ), [Cu₂( L2 )₂(OAc)₄] ( 6 ), [Cu₂( L3 )₂(OAc)₄] ( 7 ) and [Cu₂( L4 )₂(OAc)₄] ( 8 ), were prepared via a mechanochemical method with excellent yields between 95 ‐ 98% by reacting the metal acetates and corresponding ligands. Structural studies showed that both complexes are dimeric with a paddlewheel core structure in which the separation between the two metal centres are 2.9898 (8) and 2.6653 (7) Å in complexes 3 and 7 , respectively. Complexes 1 – 8 were used in ring‐opening polymerization of ε‐caprolactone (ε‐CL) and rac‐lactide (rac‐LA). Zn(II) complexes were more active than Cu(II) complexes, with complex 1 bearing electron withdrawing chloro groups being the most active (k_app = 0.0803 h^‐1). Low molecular weight poly‐(ε‐CL) and poly‐(rac‐LA) ranging from 1720 to 6042 g mol^‐1, with broad molecular weight distribution (PDIs, 1.78 – 1.87) were obtained. Complex 2 gave reaction orders of 0.56 and 1.52 with respect to ε‐CL and rac‐LA, respectively.     

Radiation reduction of binuclear Rh(II) complexes in aqueous-methanol solutions

Radiation reduction of binuclear [Rh₂(OAc)₂(phen)₂(H₂O)₂](OAc)₂, [Rh₂(OAc)(tpy)₂Cl₂]Cl·2H₂O and [Rh₂Cl₂(HCOO)₂(bpy)₂]·4H₂O complexes in aqueous-methanol solution have been studied. The reduction yields as equal to ca. 6 equiv/100eV and the rate constants of reactions: complex+e _solv ⁻ as equal to 2.9·10¹⁰, 3.2·10¹⁰ and 3.7·10¹⁰ M⁻¹·s⁻¹, respectively, have been determined. On the basis of electronic spectra it has been shown that Rh(II) compounds were reduced giving several Rh(I) complexes being in equilibrium. The mechanism of the processes has been discussed.     

Reaction of dirhodium(II) tetraacetate with S-methyl-L-cysteine

Abstract

The reaction of antitumor active dirhodium(II) tetraacetate, [Rh₂(AcO)₄], with S-methyl-L-cysteine (HSMC) was studied at the pH of mixing (=4.8) in aqueous media at various temperatures under aerobic conditions. The results from UV–vis spectroscopy and electrospray ionization mass spectrometry (ESI–MS) showed that HSMC initially coordinates via its sulfur atom to the axial positions of the paddlewheel framework of the dirhodium(II) complex, and was confirmed by the crystal structure of [Rh₂(AcO)₄(HSMC)₂]. After some time (48?h at 25?°C), or at elevated temperature (40?°C), Rh-SMC chelate formation causes breakdown of the paddlewheel structure, generating the mononuclear Rh(III) complexes [Rh(SMC)₂]⁺, [Rh(AcO)(SMC)₂] and [Rh(SMC)₃], as indicated by ESI–MS. These aerobic reaction products of [Rh₂(AcO)₄] with HSMC have been compared with those of the two proteinogenic sulfur-containing amino acids methionine and cysteine. Comparison shows that the (S,N)-chelate ring size influences the stability of the [Rh₂(AcO)₄] paddlewheel cage structure and its Rh^II–Rh^II bond, when an amino acid with a thioether group coordinates to dirhodium(II) tetraacetate.     

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

The synthesis of the reactive PN(C^H) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine ( 1^H ) and its versatile coordination to a Rh^I center is described. Facile C?H activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [Rh^I(CO)(κ³‐P,N,C‐ 1 )] ( 3 ), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D₁]formic acid. The addition of HBF₄ to 3 leads to rapid net protonolysis of the Rh?C bond to produce [Rh^I(CO)(κ³‐P,N,(C?H)‐ 1 )] ( 4 ). This species features a rare aryl C?H agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [Rh^I(CO)(κ²‐P,N‐ 1^Me )] ( 5 ). Variable‐temperature NMR spectroscopy indicates the involvement of a Rh^III intermediate through formal oxidative addition to give trans‐[Rh^III(CH₃)(CO)(I)(κ³‐P,N,C‐ 1 )] prior to C?C reductive elimination. The Rh^III–trans‐diiodide complex [Rh^I(CO)(I)₂(κ³‐P,N,C‐ 1 )] ( 6 ) has been structurally characterized as a model compound for this elusive intermediate.     

A Transformation of N‐Alkylated Anilines to N‐Aryloxamates

Transformation of N‐alkylated anilines to N‐aryloxamates was studied using ethyl 2‐diazoacetoacetate as an alkylating agent and dirhodium tetraacetate (Rh₂(OAc)₄) as the catalyst. The general applicability of the reaction as a synthetic method for N‐aryloxamates was studied with a number of substituted N‐alkylated anilines. The results revealed that the oxamate was formed by a radical reaction with molecular O₂ and Rh₂(OAc)₄ as initiator.     

Structure and properties of di-μ-acetato-dichlorobis(2,2′-bipyridine)dirhodium(II)-trihydrate

Reduction of [Rh₂(-OAc)₂(bpy)₂(H₂O)₂](OAc)₂ and [Rh₂Cl₂(-OAc)₂(bpy)₂] · 3H₂O complexes with ethanol and [Cr₂(OAc)₄(H₂O)₂] has been investigated using e.p.r. and u.v.–vis. spectra. The results indicate that stable complexes containing the [Rh₂ ³⁺] entity are not formed. The X-ray structure of [Rh₂Cl₂(-OAc)₂(bpy)₂] · 3H₂O has been determined. Coordination around the Rh atom is in the form of a distorted octahedron. The complex shows an almost ideal eclipsed conformation. The equatorial coordination sites are occupied by bridging carboxylato ligands and 2,2-bipyridine and axial positions by the Cl ligand and the rhodium atom. The Rh–Rh distance is 2.574 Å.     

The Enantioselectivity and the Stereochemical Course of Copper‐Catalyzed Intramolecular CH Insertions of Phenyliodonium Ylides

The Cu‐catalyzed intramolecular CH insertion of phenyliodonium ylide 1b was investigated at 0° in the presence of several chiral ligands. Enantioselectivities varied in the range 38–72%, and were higher than those resulting from reaction of the diazo compound 1c at 65°. The intramolecular insertion of the enantiomerically pure methyl diazoacetate (R)‐ 20 and of the corresponding phenyliodonium ylide (R)‐ 21 proceeded to (R)‐ 23 with retention of configuration with [Cu(hfa)₂] (hfa=hexafluoroacetylacetone=1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione) and [Rh₂(OAc)₄]. These results are consistent with a carbenoid mechanism for the Cu‐catalyzed insertion with phenyliodonium ylides. However, the insertion of the perfluorosulfonated phenyliodonium ylide (R)‐ 29 afforded with [Cu(hfa)₂] as well as with [Rh₂(OAc)₄] the cyclopentanone derivative 30 as a cis/trans mixture with only 56–67% enantiomeric excess.     

Variation of hydrogen‐bonded networks in hexa­fluoro­phosphate salts of amidate‐bridged dirhodium(II,III) complexes with axial aqua ligands

In diaqua­tetra‐μ‐acetamidato‐κ⁴N:O;κ⁴O:N‐di­rhodium(II,III) hexa­fluoro­phosphate, [Rh₂(C₂H₄NO)₄(H₂O)₂]PF₆, and diaqua­tetra‐μ‐acetamidato‐κ⁴N:O;κ⁴O:N‐di­rho­dium(II,III)hexa­fluoro­phosphate dihydrate, [Rh₂(C₂H₄NO)₄(H₂O)₂]PF₆·2H₂O, the cations and anions lie on inversion centers. Diaqua­tetra‐μ‐propionamidato‐κ⁴N:O;κ⁴O:N‐dirhodium(II,III) hexa­fluoro­phosphate dihydrate, [Rh₂(C₃H₆NO)₄(H₂O)₂]PF₆·2H₂O, and diaqua­tetra‐μ‐butyramidato‐κ⁴N:O;κ⁴O:N‐dirhodium(II,III) hexa­fluoro­phosphate, [Rh₂(C₄H₈NO)₄(H₂O)₂]PF₆, crystallize with two crystallographically independent complexes that lie on inversion centers. In all of the structures, the dirhodium units are hydrogen bonded to one another. The hydrogen‐bonded networks vary with the alkyl substituents.     

Synthesis of dirhodium[3H]tetraacetate

Realizing a need for labeled dirhodium tetraacetate [Rh₂/OAc/₄] for binding studies by the equilibrium dialysis procedure, we have established a method for the preparation and purification of [³H]Rh₂/OAc/₄. This is obtained with a tritium label of a sufficiently high specific activity in the methyl group of acetate residues. The method consists of replacement of the existing acetate bridge by [³H]OAc^–. A typical preparation involves refluxing Rh₂/OAc/₄ with [³H]NaOAc in dry ethanol at 80°C for 6 h. The reaction time is critical for obtaining the product with a high specific activity. A simple purification of reaction products yields the compound of interest with a high specific activity, i. e., 315±10 Ci per mol of Rh₂/OAc/₄ and in satisfactory yield /87% of the starting material., This labeled material can be synthesized with greatly increased specific activity /of tritium in acetate groups/ by employing [³H]NaOAc without prior dilution. The labeled Rh₂/OAc/₄ is stable and yields a characteristic product with adenylic acid.     

Complexes of NS and NSO donor ligands. Nickel(II), copper(II) and cobalt(II) complexes of glyoxal bis(morpholineN-thiohydrazone) and diacetyl bis(morpholineN-thiohydrazone)

Summary Reactions of glyoxal bis(morpholineN-thiohydrazone), H₂gbmth, with NiCl₂·6H₂O, Ni(OAc)₂·4H₂O, Ni(acac)₂· H₂O, CuCl₂·2H₂O, Cu(OAc)₂·H₂O, Cu(acac)₂, CoCl₂· 6H₂O, Co(OAc)₂·4H₂O and Co(acac)₂·2H₂O yield complexes of the type [M(gbmth)], [M=Ni^II, Cu^II or Co^II]. Diacetyl reacts with morpholineN-thiohydrazide in the presence of nickel salts to yield [Ni^II(dbmth)], [Ni^II(dmth)(OAc)]H₂O and [Ni^II(Hdmth)(NH₃)Cl₂] involving N₂S₂ and NSO donor ligands. Copper and cobalt complexes of N₂S₂ and NSO donor ligands with compositions [Cu^II(dbmth)], [Co^II(dbmth)]·4H₂O and [Co^II(H₂dbmth)]Cl₂, have been isolated. The compounds have been characterised by elemental analyses, magnetic moments, molar conductance values and spectroscopic (electronic and infrared) data.     

Complexing behaviour of aromatic thioamides (ArCSNHCOR). Transition metal complexes of N-carboethoxy-4-chlorobenzene- and N-carboethoxy-4-bromobenzene thioamide ligands

N-Carboethoxy-4-chlorobenzene thioamide (Hcct or HL) and N-carboethoxy-4-bromobenzene thioamide (Hcbt or HL) react with bivalent (Ni, Co, Cu, Ru, Pd and Pt), trivalent (Ru and Rh) and tetravalent (Pt) transition metal ions to give [M^II(L)₂], [Ru^III(L)₃], [Rh^III(L)(HL)Cl₂] and [Pt(L)₂Cl₂] complexes, respectively. In the presence of pyridine, Co^II and Ni^II salts react with the ligands (HL) to give [M^II(L)₂Py] (M = Co and Ni) complexes. Soft metal ions abstract sulphur from the ligands to yield the corresponding sulphide, together with oxygenated forms of the ligands. All the metal complexes have been characterised by chemical analyses, conductivity, spectroscopic and magnetic measurements.     

Synthese und dynamisches Verhalten von [Rh2(μ-H)3H2(PiPr3)4]+. Beiträge zur Reaktivität des Tetrahydridodirhodium-Komplexes [Rh2H4(PiPr3)4]

Synthesis and Dynamic Behaviour of [Rh₂(μ-H)₃H₂(PiPr₃)₄]⁺. Contributions to the Reactivity of the Tetrahydridodirhodium Complex [Rh₂H₄(PiPr₃)₄] An improved synthesis of [Rh₂H₄(PiPr₃)₄] ( 2 ) from [Rh(η³-C₃H₅)(PiPr₃)₂] ( 1 ) or [Rh(η³-CH₂C₆H₅)(PiPr₃)₂] ( 3 ) and H₂ is described. Compound 2 reacts with CO or CH₃OH to give trans-[RhH(CO)(PiPr₃)₂] ( 4 ) and with ethene/acetone to yield a mixture of 4 and trans-[RhCH₃(CO)(PiPr₃)₂] ( 5 ). The carbonyl(methyl) complex 5 has also been prepared from trans-[RhCl(CO)(PiPr₃)₂] ( 6 ) and CH₃MgI. Whereas the reaction of 2 with two parts of CF₃CO₂H leads to [RhH₂(η²-O₂CCF₃) · (PiPr₃)₂] ( 8 ), treatment of 2 with one equivalent of CF₃CO₂H in presence of NH₄PF₆ gives the dinuclear compound [Rh₂H₅(PiPr₃)₄]PF₆ ( 9a ). The reactions of 2 with HBF₄ and [NO]BF₄ afford the complexes [Rh₂H₅(PiPr₃)₄]BF₄ ( 9b ) and trans-[RhF(NO)(PiPr₃)₂]BF₄ ( 11 ), respectively. In solution, the cation [Rh₂(μ-H)₃H₂(PiPr₃)₄]⁺ of the compounds 9a and 9b undergoes an intramolecular rearrangement in which the bridging hydrido and the phosphane ligands are involved.     

Synthesis,Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2]

The synthesis of [Ir₂Rh₂(CO)₁₂] ( 1 ) by the literature method gives a mixture 1 /[IrRh₃(CO)₁₂] which cannot be separated using chromatography. The reaction of [Ir(CO)₄]^? with 1 mol-equiv. of [Rh(CO)₂(THF)₂]⁺ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir₂Rh₂(CO)₅(μ₂-CO)₃(norbornadiene)₂] which were analysed using X-ray diffraction. The ground-state geometry of 1 in solution has three edge-bridging CO's on the basal IrRh₂ face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D- and VT-¹³C-NMR. Substitution of CO by X^? in 1 takes place at a Rh-atom giving [Ir₂Rh₂(CO)₈(μ₂-CO)₃X]^? (X = Br, I). Substitution by bidentate ligands gives [Ir₂Rh₂(CO)₇(μ₂-CO)₃(η⁴-L)] (L = norbornadiene, cycloocta-1,5-diene) where the ligand L is chelating a Rh-atom of the basal IrRh₂ face. Carbonyl substitution by tridentate ligands gives [Ir₂Rh₂(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C₃ axis on the apical Ir-atom.     

Synthesis,electrochemical and e.p.r. spectral studies of binuclear copper(II) complexes with new pentadentate L-proline-based binucleating ligands

The synthesis, reduction, optical and e.p.r. spectral properties of a series of new binuclear copper(II) complexes, containing bridging moieties (OH^–, MeCO₂ ^–, NO₂ ^–, and N₃ ^–), with new proline-based binuclear pentadentate Mannich base ligands is described. The ligands are: 2,6-bis[(prolin-1-yl)methyl]4-bromophenol [H₃L¹], 2,6-bis[(prolin-1-yl)methyl]4-t-butylphenol [H₃L²] and 2,6-bis[(prolin-1-yl)methyl]4-methoxyphenol [H₃L³]. The exogenous bridging complexes thus prepared were hydroxo: [Cu₂L¹(OH)(H₂O)₂] · H₂O (1a), [Cu₂L²(OH)(H₂O)₂] · H₂O (1b), [Cu₂L³(OH)(H₂O)₂] · H₂O (1c), acetato [Cu₂L¹(OAc)] · H₂O (2a), [Cu₂L²(OAc)] · H₂O (2b), [Cu₂L³(OAc)] · H₂O (2c), nitrito [Cu₂L¹(NO₂)(H₂O)₂] · H₂O (3a), [Cu₂L²(NO₂)(H₂O)₂] · H₂O (3b), [Cu₂L³(NO₂)(H₂O)₂] · H₂O (3c) and azido [Cu₂L¹(N₃)(H₂O)₂] · H₂O (4a), [Cu₂L²(N₃)(H₂O)₂] · H₂O (4b) and [Cu₂L³(N₃)(H₂O)₂] · H₂O (4c). The complexes were characterized by elemental analysis and by spectroscopy. They exhibit resolved copper hyperfine e.p.r. spectra at room temperature, indicating the presence of weak antiferromagnetic coupling between the copper atoms. The strength of the antiferromagnetic coupling lies in the order: NO₂ N₃ OH OAc. Cyclic voltammetry revealed the presence of two redox couples Cu^IICu^II Cu^IICu^I Cu^ICu^I. The conproportionality constant K _con for the mixed valent Cu^IICu^I species for all the complexes have been determined electrochemically.     

6‐(Diazomethyl)‐1,3‐bis(methoxymethyl)uracil,Synthesis and Transformation into Annulated Pyrimidinediones

6‐(Diazomethyl)‐1,3‐bis(methoxymethyl)uracil ( 5 ) was prepared from the known aldehyde 3 by hydrazone formation and oxidation. Thermolysis of 5 and deprotection gave the pyrazolo[4,3‐d]pyrimidine‐5,7‐diones 7a and 7b . Rh₂(OAc)₄ catalyzed the transformation of 5 into to a 2 : 1 (Z)/(E) mixture of 1,2‐diuracilylethenes 9 (67%). Heating (Z)‐ 9 in 12n HCl at 95° led to electrocyclisation, oxidation, and deprotection to afford 73% of the pyrimido[5,4‐f]quinazolinetetraone 12 . The Rh₂(OAc)₄‐catalyzed reaction of 5 with 3,4‐dihydro‐2H‐pyran and 2,3‐dihydrofuran gave endo/exo‐mixtures of the 2‐oxabicyclo[4.1.0]heptane 13 (78%) and the 2‐oxabicyclo[3.1.0]hexane 15 (86%), Their treatment with AlCl₃ or Me₂AlCl promoted a vinylcyclopropane–cyclopentene rearrangement, leading to the pyrano‐ and furanocyclopenta[1,2‐d]pyrimidinediones 14 (88%) and 16 (51%), respectively. Similarly, the addition product of 5 to 2‐methoxypropene was transformed into the 5‐methylcyclopenta‐pyrimidinedione 18 (55%). The Rh₂(OAc)₄‐catalyzed reaction of 5 with thiophene gave the exo‐configured 2‐thiabicyclo[3.1.0]hexane 19 (69%). The analoguous reaction with furan led to 8‐oxabicyclo[3.2.1]oct‐2‐ene 20 (73%), and the reaction with (E)‐2‐styrylfuran yielded a diastereoisomeric mixture of hepta‐1,4,6‐trien‐3‐ones 21 (75%) that was transformed into the (1E,4E,6E)‐configured hepta‐1,4,6‐trien‐3‐one 21 (60%) at ambient temperature.     

Highly regio- and diastereoselective three-component reaction of acyclic/cyclic donor–acceptor carbenoids for the synthesis of angularly fused furocoumarins and spirooxindolylfurocoumarins

A highly regio- and stereoselective method has been developed for the synthesis of spiro[furo[3,4-c]chromene-1,3′-indoline]-2′,4(9bH)-dione derivatives via a three component reaction of cyclic diazoamide and aldehyde with methyl 2-oxo-2H-chromene-3-carboxylate, 3-acetyl-2H-chromen-2-one and 3-benzoyl-2H-chromen-2-one using 3 mol % of Rh₂(OAc)₄. Similarly, acyclic diazoesters also undergo smooth coupling with carbonyl compounds and 3-substituted coumarin in the presence of 1 mol % of Rh₂(OAc)₄ to afford a novel series of tetrahydro-1H-furo[3,4-c]chromene-1-carboxylates in 78–88% yield with high regio- and stereo-selectivity for the first time.     

New Bimetallic Ni–Rh Carbonyl Clusters: Synthesis and X-ray Structure of the [Ni7Rh3(CO)18]3?, [Ni3Rh3(CO)13]3? and [NiRh8(CO)19]2? Cluster Anions

The reaction of the [Ni₆(CO)₁₂]²⁻ dianion with [Rh(COD)Cl]₂ (COD = cyclooctadiene) in acetone affords a mixture of bimetallic Ni–Rh clusters, mainly consisting of the new [Ni₇Rh₃(CO)₁₈]³⁻ and [Ni₈Rh(CO)₁₈]³⁻ trianions. A study of the reactivity of [Ni₇Rh₃(CO)₁₈]³⁻ led to isolation of the new [Ni₃Rh₃(CO)₁₃]³⁻ and [NiRh₈(CO)₁₉]²⁻ anions. All these new bimetallic Ni–Rh carbonyl clusters have been isolated in the solid state as tetrasubstituted ammonium salts and have been characterised by elemental analysis, X-ray diffraction studies, ESI-MS and electrochemistry. The unit cell of the [NEt₄]₃[Ni₇Rh₃(CO)₁₈] salt contains two orientationally-disordered ν₂-tetrahedral [Ni₇Rh₃(CO)₁₈]³⁻ trianions with occupancy factors of 0.75 and 0.25. Besides, their inner Ni₃Rh₃ octahedral moieties show two cis sites purely occupied by Rh atoms, two trans sites purely occupied by Ni atoms and the remaining two cis sites are disordered Ni and Rh sites with respective occupancy fraction of 0.5. At difference from the parent [Ni₇Rh₃(CO)₁₈]³⁻, the octahedral [Ni₃Rh₃(CO)₁₃]³⁻ displays an ordered distribution of Ni and Rh atoms in two staggered triangles. The [NiRh₈(CO)₁₉]²⁻ dianion adopts an isomeric metal frame with respect to that of the [PtRh₈(CO)₁₉]²⁻ congener. As a fallout of this work, new high-yield synthesis of the known [Ni₆Rh₃(CO)₁₇]³⁻ and [Ni₆Rh₅(CO)₂₁]³⁻, as well as other currently-investigated bimetallic Ni–Rh clusters have been obtained.     

Double deoxygenation of PPN(NO2) using metal carbonyl clusters of cobalt,rhodium, and iridium

The reaction of PP(NO₂) with M₄(CO)₁₂ (M = Co, Rh) gives the nitrido clusters [M₆N(CO)₁₅]^? in 13 and 21% yields, respectively. A high yield synthesis (77%) of [Rh₆N(CO)₁₅)]^? directly from Rh₆(CO)₁₆ and PPN(NO₂) is also presented. PPN(NO₂) reacts with Ir₄(CO)₁₂ to give the new isocyanato cluster, [Ir₄(NCO)(CO)₁₁]^? in 34% yield, while the direct synthesis of this isocyanate product occurs in 77% yield from PPN(N₃) and Ir₄(CO)₁₂. Modifications of published procedures for the preparation of [N(C₂H₅)₄]₂ [Ir₆(CO)₁₅] and Ir₆(CO)₁₆ are reported that allow shorter reaction times and give higher yields. The reaction of Ir₆(CO)₁₆ with one equivalent of PPN(NO₂) generates a new cluster, PPN[Ir₆(CO)₁₅(NO)], in 57% yield which is proposed to contain a bent nitrosyl ligand. An additional equivalent of PPN(NO₂) gives (PPN)₂[Ir₆(CO)₁₅] in 84% yield with the evolution of N₂O as well as CO₂.