[M(CO)2(NO)], a new core in bioorganometallic chemistry: model complexes of [Re(CO)2(NO)] and [Tc(CO)2(NO)]

In this study selected bidentate (L²) and tridentate (L³) ligands were coordinated to the Re(I) or Tc(I) core [M(CO)₂(NO)]²⁺ resulting in complexes of the general formula fac-[MX(L²)(CO)₂(NO)] and fac-[M(L³)(CO)₂(NO)] (M = Re or Tc; X = Br or Cl). The complexes were obtained directly from the reaction of [M(CO)₂(NO)]²⁺ with the ligand or indirectly by first reacting the ligand with [M(CO)₃]⁺ and subsequent nitrosylation with [NO][BF₄] or [NO][HSO₄]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium (^99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO)₂(NO)]₂ and the mononuclear complexes [NEt₄][ReCl₃(CO)₂(NO)], [NEt₄][ReBr₃(CO)₂(NO)], [ReBr(PIC)(CO)₂(NO)], [NMe₄][Re(NO₃)₃(CO)₂(NO)], [Re(HIS)(CO)₂(NO)][BF₄], [⁹⁹Tc(HIS)(CO)₂(NO)][BF₄], [^99mTc(IDA)(CO)₂ (NO)] and [^99mTc(NTA)(CO)₂(NO)]. The chemical and physical characteristics of the Re and Tc-dicarbonyl-nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.     

Zinc-rich compounds of iron and cobalt: formation of [Fe2Zn(n)] (n = 2-4) and [Co2Zn3] cores

The reactions of heteroleptic GaCp*/CO containing transition metal complexes of iron and cobalt, namely [(CO)(3)M(μ(2)-GaCp*)(m)M(CO)(3)] (Cp* = pentamethylcyclopentadienyl; M = Fe, m = 3; M = Co, m = 2) and [Fe(CO)(4)(GaCp*)], with ZnMe(2) in toluene and the presence of a coordinating co-solvent were investigated. The reaction of the iron complex [Fe(CO)(4)(GaCp*)] with ZnMe(2) in presence of tetrahydrofurane (thf) leads to the dimeric compound [(CO)(4)Fe{μ(2)-Zn(thf)(2)}(2)Fe(CO)(4)] (1). Reaction of [(CO)(3)Fe(μ(2)-GaCp*(3))Fe(CO)(3)] with ZnMe(2) and stoichiometric amounts of thf leads to the formation of [(CO)(3)Fe{μ(2)-Zn(thf)(2)}(2)(μ(2)-ZnMe)(2)Fe(CO)(3)] (2) containing {Zn(thf)(2)} as well as ZnMe ligands. Using pyridine (py) instead of thf leads to [(CO)(3)Fe{μ(2)-Zn(py)(2)}(3)Fe(CO)(3)] (3) via replacement of all GaCp* ligands by three{Zn(py)(2)} groups. In contrast, reaction of [(CO)(3)Co(μ(2)-GaCp*)(2)Co(CO)(3)] with ZnMe(2) in the presence of py or thf leads in both cases to the formation of [(CO)(3)Co{μ(2)-ZnL(2)}(μ(2)-ZnCp*)(2)Co(CO)(3)] (L = py (4), thf (5)) via replacement of GaCp* with {Zn(L)(2)} units as well as Cp* transfer from the gallium to the zinc centre. All compounds were characterised by NMR spectroscopy, IR spectroscopy, single crystal X-ray diffraction and elemental analysis.     

First examples of [Rh(Bident)(CO)(L)] complexes where L is N-donor ligand: Molecular structure of [Rh(8-Oxiquinolinato)(CO)(NH3)]

Selective oxidation of one (trans to N) carbonyl group in [Rh(8-Oxiquinolinato)(CO)₂] with stoichiometric amount of Me₃NO in MeCN produces a solution containing [Rh(Oxq)(CO)(Me₃N)] and [Rh(Oxq)(CO)(MeCN)]. The ammonia complex, [Rh(Oxq)(CO)(NH₃)], has been prepared by action of NH₃ gas on this solution and characterized by IR, ¹H and ¹³C NMR, and X-ray data. Spectral parameters, ν(CO), δ¹³C, and ¹J(CRh), were measured in situ for a series of complexes [Rh(Oxq)(CO)(L)] (L = NAlk₃, Py, PBu₃, PPh₃, P(OPh)₃, C₈H₁₄) formed upon action of L on [Rh(Oxq)(CO)(NH₃)] in THF. A new ν(CO) and δ¹³C based scale of σ-donor/π-acceptor properties of ligands L is proposed including NH₃ and CO as the natural endpoints.     

Regiospecificity in the reaction of [Fe2(η-C5H5)2(CO)4-n(CNMe)n] (n  02) with mercury(II) halides

The reactions of [Fe₂(η-C₅H₅)₂(CO)₂(L)(CNMe)] (L  CO or CNME) with HgX₂ (X  Cl, Br or I) give [Fe(η-C₅H₅)(CO)₂HgX] and [Fe(η-C₅H₅)(L)-(CNMe)X] as the sole products in ca. quantitative yields; this is consistent with the previously proposed mechanism for the reactions of electrophiles with polynuclear metal carbonyl derivatives.     

Some observations on the systems Co2(CO)8/sodium amalgam and Hg[Co(CO)4]2/sodium amalgam,and the effect of added LiBr

Co₂(CO)₈ and Hg[Co(CO)₄]₂ react sodium amalgam and/or mercury in ethereal solvents to give a variety of products. On treatment with aqueous M(o-phen)₃Cl₂(M  Fe, Ni), the anions [Co(CO)₄^?, [Co₃(CO)₁₀]^?, {Hg[Co(CO)₄]₃}^? and {Hg[Co(CO)₄]₂Cl}^? could be isolated as their [M(o-phen)₃]²⁺ salts. The effect of LiBr on the reacting systems was also investigated and the anion {Hg[Co(CO)₄]₂Br}^? isolated.     

Reactivity of Cyanide and Thiocyanate Towards the Nitrosyl Carbonyl [Co(CO)3(NO)]

The reaction of equimolar amounts of [Co(CO)₃(NO)] and [PPN]CN, PPN⁺ = (PPh₃)₂N⁺, in THF at room temperature resulted in ligand substitution of a carbonyl towards the cyanido ligand presumably affording the complex salt PPN[Co(CO)₂(NO)(CN)] as a reactive intermediate species which could not be isolated. Applying the synthetic protocol using the nitrosyl carbonyl in excess, the title reaction afforded unexpectedly the novel complex salt PPN[Co₂(μ-CN)(CO)₄(NO)₂] ( 1 ) in high yield. Because of many disorder phenomena in crystals of 1 the corresponding NBu₄⁺ salt of 1 has been prepared and the molecular structure of the dinuclear metal core in NnBu₄[Co₂(μ-CN)(CO)₄(NO)₂] ( 2 ) was determined by X-ray crystal diffraction in a more satisfactory manner. In contrast to the former result, the reaction of [PPN]SCN with [Co(CO)₃(NO)] yielded the mononuclear complex salt PPN[Co(CO)₂(NO)(SCN-κN)] ( 3 ) in good yield whose molecular structure in the solid was even determined and its composition additionally confirmed by spectroscopic means.     

[Fe2(μsb‐CO)(CO)3(NO)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)]: Synthese,Kristallstruktur und Koordinationsisomerie

[Fe₂(μ_sb‐CO)(CO)₃(NO)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)]: Synthesis, X‐ray Crystal Structure and Isomerization Na[Fe₂(μ‐CO)(CO)₆(μ‐P^tBu₂)] ( 1 ) reacts with [NO][BF₄] at —60 °C in THF to the nitrosyl complex [Fe₂(CO)₆(NO)(μ‐P^tBu₂)] ( 2 ). The subsequent reaction of 2 with phosphanes (L) under mild conditions affords the complexes [Fe₂(CO)₅(NO)L(μ‐P^tBu₂)], L = PPh₃, ( 3a ); η‐dppm (dppm = Ph₂PCH₂PPh₂), ( 3b ). In this case the phosphane substitutes one carbonyl ligand at the iron tetracarbonyl fragment in 2 , which was confirmed by the X‐ray crystal structure analysis of 3a . In solution 3b loses one CO ligand very easily to give dppm as bridging ligand on the Fe‐Fe bond. The thus formed compound [Fe₂(CO)₄(NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4 ) occurs in solution in different solvents and over a wide temperature range as a mixture of the two isomers [Fe₂(μ_sb‐CO)(CO)₃(NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4a ) and [Fe₂(CO)₄(μ‐NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4b ). 4a was unambiguously characterized by single‐crystal X‐ray structure analysis while 4b was confirmed both by NMR investigations in solution as well as by means of DFT calculations. Furthermore, the spontaneous reaction of [Fe₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 5 ) with NO at —60 °C in toluene yields a complicated mixture of products containing [Fe₂(μ‐CO)(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 6 ) as main product beside the isomers 4a and 4b occuring in very low yields.     

Stepwise reduction of the thiocarbonyl ligand: hydride transfer to CS: thioformyl,thioformaldehyde, methylthiolato,secondary carbene,formyl and iminoformyl complexes of osmium

The complexes OsHX(CS)L(PPh₃)₂ (X  Cl, Br; L  CO and X  Cl; L  CN-p-tolyl), which contain mutually cis hydrido and thiocarbonyl ligands, undergo transfer of the hydrido ligand to CS when treated with CO to give blue complexes containing the thioformyl ligand [OsCHS]. OsCl(CHS)(CO)₂(PPh₃)₂ reacts with borohydride to give the first metal complex of the thioformaldehyde monomer, viz. Os(η²-CH₂S)(CO)₂(PPh₃)₂, which reacts rapidly with HCl to give OsCl(SCH₃)(CO)₂(PPh₃)₂ and then, by a slower reaction, OsCl₂(CO)₂(PPh₃)₂ and CH₃SH. The ligands produced in this stepwise reduction have possible relevance as models for postulated intermediates in the Fischer—Tropsch synthesis. Synthetic routes to formyl [OsCHO], iminoformyl [OsCHNMe] and secondary carbene complexes [OsCHSMe, OsCHNMe₂, OsCHOMe] are also demonstrated.     

Potential inhibitors of DNA topoisomerase II: ruthenium(II) poly-pyridyl and pyridyl-azine complexes

In search of new DNA probes a series of new mono and binuclear cationic complexes [RuH(CO)(PPh₃)₂(L)]⁺ and [RuH(CO)(PPh₃)₂(-μ-L)RuH(CO)(PPh₃)₂]²⁺ [L=pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)aldimine (pbp) and p-biphenylene-bis(picoline)aldimine (bbp)] have been synthesized. The reaction products were characterized by microanalyses, spectral (IR, UV-Vis, NMR and ESMS and FAB-MS) and electrochemical studies. Structure of the representative mononuclear complex [RuH(CO)(PPh₃)₂(paa)]BF₄ was crystallographically determined. The crystal packing in the complex [RuH(CO)(PPh₃)₂(paa)]BF₄ is stabilized by intermolecular π-π stacking resulting into a spiral network. Topoisomerase II inhibitory activity of the complexes and a few other related complexes [RuH(CO)(PPh₃)₂(L)]⁺ {L=2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and 2,3-bis(2-pyridyl)-pyrazine (bppz)} have been examined against filarial parasite Setaria cervi. Absorption titration experiments provided good support for DNA interaction and binding constants have also been calculated which were found in the range 1.2 × 10³-4.01 × 10⁴ M⁻¹.     

Fast atom bombardment mass spectra of [(diars)Fe(CO)2(C(O)Me)(P-donor)]+ BF4− salts

Characteristic fast atom bombardment (FAB) mass spectra (8 keV, argon, glycerol matrix) have been obtained for an isostructural series of organometallic cations of the form cis,trans[(diars)Fe(CO)₂(C(O)Me)L]⁺ Bf₄ (L = phosphorus donor). The fast atom bombardment mass spectra (FABMS) obtained show relatively abundant fragments corresponding to the cationic portion of the complex [C⁺]. Extensive fragmentation also occurs via successive CO loss, phosphorus donor ligand cleavage, and ligand decomposition. Evidence for a rearrangement fragmentation corresponding to the process [Fe(C(O)Me)]⁺ → [FeMe]⁺ + CO is presented.     

Synthesis and structure of FeRu3(CO)13(μ-PPh2)2; A “64-electron” cluster complex with a planar triangulated rhomboidal array of metal atoms

The species FeRu₃(CO)₁₃(μ-PPH₂)₂, synthesized from Ru₃(CO)₁₂ and Fe(CO)₄(Ph₂PPPh₂),has been characterized both spectroscopically and via a single-crystal X-ray structural analysis. This complex crystallizes in the centrosymmetric triclinic space group P$\text{1}$ [No. 2, C_i¹] with a  10.066(3), b  12.899(3), c  17.003(4) Å, α  111.89(2), β  91.02(2), γ  102.00(2)°, V  1992.7(9) ų, Z  2, ?(obsd)  1.79(2) g cm^-3 and ?(calcd)  1.82 cm^-3. Diffraction data were collected with a Syntex P2₁ automated four-circle diffractometer and the structure was refined to R_F  6.0% and R_WF  3.6% for all 5213 reflections (R_F  3.8%, R_WF  3.6% for those 4140 reflections with |F_o|> 3σ(|F_o|).The metal atoms define a planar triangulated rhombus, with atoms Ru(1) and Ru(2) at the bridgehead, and Fe(1) and Ru(3) at the acute apices. Fe(1) is linked to four terminal carbonyl ligands and is associated with the heteronuclear bonds Fe(1)Ru(1)  2.861(1) Å and Fe(1)Ru(2)  2.868(1) Å. The ruthenium atoms are each bonded to three terminal carbonyl groups. The retheniumruthenium distances are Ru(1)Ru(2)  3.098(1), Ru(1)Ru(3)  3.147(1), and Ru(2)Ru(3)  3.171(1) Å. The structure is completed by Ph₂P bridges across the Ru(1)Ru(3) and Ru(2)(ru(3) vectors (<Ru(1)P(1)Ru(3)  84.89(5)° and <Ru(2)P(2)Ru(3)  85.56(6)°).     

Reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] with Alkyl Halides and Dihalides: Formation of the Alkyl- and the Dialkylantimony-Iron Carbonyl Complexes

The reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] (1) with RX (R = Me, Et, n-Pr; X = I) in MeCN form the monoalkylated antimony complexes [Et(4)N](2)[RSb{Fe(CO)(4)}(3)] (R = Me, 2; R = Et, 4; R = n-Pr, 6) and the dialkylated antimony clusters [Et(4)N][R(2)Sb{Fe(CO)(4)}(2)] (R = Me, 3; R = Et, 5; R = n-Pr, 7), respectively. When [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] reacts with i-PrI, only the monoalkylated antimony complex [Et(4)N](2)[i-PrSb{Fe(CO)(4)}(3)] (8) is obtained. The mixed dialkylantimony complex [Et(4)N][MeEtSb{Fe(CO)(4)}(2)] (9) also can be synthesized from the reaction of 2 with EtI. While the reaction with Br(CH(2))(2)Br produces [Et(4)N](2)[BrSb{Fe(CO)(4)}(3)] (10), treatment with Cl(CH(2))(3)Br forms the monoalkylated product [Et(4)N](2)[Cl(CH(2))(3)Sb{Fe(CO)(4)}(3)] (11) and a dialkylated novel antimony-iron complex [Et(4)N][{&mgr;-(CH(2))(3)}Sb{Fe(CO)(4)}(3)] (12). On the other hand, the reaction with Br(CH(2))(4)Br forms the monoalkylated antimony product and the dialkylated antimony complex [Et(4)N][{&mgr;-(CH(2))(4)}Sb{Fe(CO)(4)}(2)] (13). Complexes 2-13 are characterized by spectroscopic methods or/and X-ray analyses. On the basis of these analyses, the core of the monoalkyl clusters consists of a central antimony atom tetrahedrally bonded to one alkyl group and three Fe(CO)(4) fragments and the dialkyl products are structurally similar to the monoalkyl clusters, with the central antimony bonded to two alkyl groups and two Fe(CO)(4) moieties in each case. The dialkyl complex 3 crystallizes in the monoclinic space group P2(1)/c with a = 13.014(8) ?, b = 11.527(8) ?, c = 17.085(5) ?, beta = 105.04(3) degrees, V = 2475(2) ?(3), and Z = 4. Crystals of 12 are orthorhombic, of space group Pbca, with a = 14.791(4) ?, b = 15.555(4) ?, c = 27.118(8) ?, V = 6239(3) ?(3), and Z = 8. The anion of cluster 12 exhibits a central antimony atom bonded to three Fe(CO)(4) fragments with a -(CH(2))(3)- group bridging between the Sb atom and one Fe(CO)(4) fragment. This paper discusses the details of the reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] with a series of alkyl halides and dihalides. These reactions basically proceed via a novel double-alkylation pathway, and this facile methodology can as well provide a convenient route to a series of alkylated antimony-iron carbonyl clusters.     

The reaction of bis(phenyldimethylphosphine)bis(diphenylsilyl)platinum(II) with acetylenes

The synthesis and the reactions of cationic complexes of rhodium(I) and iridium(I) of the type [M(NN′)(COD)]⁺ and [M(NN′)(CO)₂]⁺ (NN′  Schiff bases of pyridine-2-aldehyde; COD  cis,cis-1,5-cyclooctadiene) are reported.     

Synthesis and reactivity of formamidinato rhodium(I) complexes

The syntheses of [Rh(diol)(formamidine)]₂ complexes (diol  cycloocta-1,5-diene (1); diol  norbornadiene (2); formamidine  N,N′-di-p-tolylformamidine) are reported. These complexes are dimeric and contain the bridging formamidino ligand. They react with CO, dppe and PPh₃ with displacement of the diene ligand to yield the known [Rh(CO)₂(formamidine)]₂, [Rh(dppe)₂]⁺ and [Rh(PPh₃)₂(formamidine)], respectively; the last complex, in which the formamidine acts as a chelating ligand, was isolated only as the O₂ adduct. With HCl or HBF₄ aqueous 1 and 2 do not form hydrides but instead the formamidino cation [p-tolyl-NHCHNHtolyl-p]⁺ and the complexes [Rh(diol)X]₂ (X  Cl, F); a possible scheme for the reaction with HCl is proposed. The [Rh(C₈H₁₂)(formamidine)]₂ complex reacts with heterocumulenes as CS₂, SO₂, PhNCS and PhNCO with diene displacement; the only product isolated was [Rh(CS₂)₂(formamidine], to which a polymeric structure is assigned.     

Substitution reactions of [MBr(π allyl)(CO)2(LL)] complexes (M = Mo,W; L-L = 2,2 -bipyridine 1,2-bis(diphenylphosphine)ethane) with xanthates and dithiocarbamates

The complexes [MBr(π-allyl)(CO)₂(bipy)] (M = Mo, W, bipy = 2,2′-bipyridine) react with alkylxanthates (M^IRxant), and N-alkyldithiocarbamates (M^IRHdtc) (M^I = Na or K), yielding complexes of general formula [M(S,S)- (π-allyl)(CO)₂(bipy)] (M = Mo, (S,S) = Rxant (R = Me, Et, t-Bu, Bz), RHdtc (R = Me, Et); M = W, (S,S) = Extant). A monodentate coordentate coordination of the (S,S) ligand was deduced from spectral data. The reaction of [MoBr(π-allyl)(CO)₂(bipy)] with MeHdtc and Mexant gives the same complexes whether pyridine is present or not. The complexes [Mo(S,S)(π-allyl)(CO)₂(bipy)] ((S,S) = MeHdtc, Mexant) do not react with an excess of (S,S) ligand and pyridine.No reaction products were isolated from reaction of [MoBr(π-allyl)(CO)₂(dppe)] with xanthates or N-alkyldithiocarbamates.     

Acyl-platinum(II) and -palladium(II) complexes derived from 2-hydroxybenzaldehyde derivatives. X-ray structure of [Pt(OC6H4CO) (P(p-CH3C6H4)3)2]

Platinum(II) and palladium(II) complexes containing chelating acyl ligands have been synthesized from salicylaldehyde, 2-hydroxynaphthaldehyde and 2-hydroxy-3-methoxybenzaldehyde. The platinum(II) complexes [Pt(acyl)L₂], acyl  OC₆H₄CO, OC₁₀H₆CO, O(m-CH₃OC₆H₃CO), L  tertiary phosphine, 1/2 diphenylphosphinoethane, can be isolated with both monodentate and chelating diphosphines, whereas for palladium only the compounds with chelating phosphines are readily obtainable. The reactions of [Pt(OC₆H₄CO)L₂] with HCl afford trans-[PtCl(OHC₆H₄CO)L₂], L  monodentate tertiary phosphine and cis-[PtCl(OHC₆H₄CO)L₂], L2  1,2-bis-diphenylphosphinoethane, in which the metal—carbon bond remains intact. The structure of [Pt(OC₆H₄CO)-(P(p-CH₃C₆H₄)₃)₂] has been determined by X-ray diffraction methods and found to have the expected square planar structure. Some relevant bond lengths and angles are: PtP; 2.271(4) and 2.348(5) Å; PtC; 1.96(2) Å and PtO; 2.07(1) Å; PPtP  101°, CPtO  82°.     

Zur koordination mehrfunktioneller thioether in cyclopentadienyleisen-komplexen

[C₅H₅Fe(CO)₂thf]⁺ reacts with the ligands LL and LLL to give the cations [C₅H₅Fe(CO)₂LL]⁺ (LL = RS(CH₂)_nSR, 1,4-dithiane) and [C₅H₅Fe(CO)₂LLL]⁺ (LLL = 1,3,5-trithiane, tris(methylmercapto)methane) containing monodentate coordinated sulfur ligands. In a similar way, sulfur ligand bridged dinuclear dications [(C₅H₅Fe(CO)₂)₂(μ-LL)]²⁺ and [(C₅H₅Fe(CO)₂(μ-LLL)]²⁺ and tri-nuclear trications [(C₅H₅Fe(CO)₂)₃(μ-LLL)]³⁺ are formed. Irradiation of the mononuclear cations gives the chelate complexes [C₅H₅Fe(CO)(η²-LL)]⁺.     

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C5H5Mn(CO)2L und C5H5Cr(CO)(NO)L

The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C₅H₅Mn(CO)₂L and C₅H₅Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent ¹H NMR spectra. The olefinic ligand is arranged preferably in a position where the CC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The ¹H NMR spectra of C₅H₅Cr(CO)(NO)(trans-CH₃OOCCHCHCOOCH₃) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C₅H₅Mn(CO)₂L complexes (ΔG^≠(T_C) 11–12 kcal mol^?1) than in the isoelectric C₅H₅Cr(CO)(NO)L compounds (ΔG^≠(T_C) 15–20 kcal mol^?1).     

Exploring the nitrosyl-approach: “Re(CO)2(NO)”- and “Tc(CO)2(NO)”-complexes provide new pathways for bioorganometallic chemistry

Nitrosylation reactions are rare in the context of low valent Re(I)- and Tc(I)-tricarbonyl complexes so far. We herein describe a method for the conversion of a “M(CO)₃-moiety” (M = Re, Tc) into a dicarbonyl-nitrosyl moiety “M(CO)₂NO”, the synthesis of important precursor complexes and intermediates and possible applications for this new kind of Re- and Tc-chemistry.The behavior of the complex [ReCl₃(CO)₂(NO)]⁻ in water was studied in detail and compared to that of [ReCl₃(CO)₃]²⁻. Contrary to the conversion of [ReCl₃(CO)₃]²⁻ to the mixed aquo-carbonyl complex [Re(OH₂)₃(CO)₃]⁺ in water, one chloride remains initially bound to the metal center in the dicarbonyl-nitrosyl complex, making [ReCl(OH₂)₂(CO)₂(NO)]⁺ the main species for further reactions. In this context, we isolated and characterized the complex [Re(μ₃-O)(CO)₂(NO)]₄. Examples of complexes with different bi- and tridentate ligands based on ReCl₃(CO)₂(NO)]⁻ are discussed.For the development of potential new radiopharmaceuticals we also adapted the nitrosylation technique to the n.c.a. level with ^99mTc. [^99mTc(OH₂)₃(CO)₃]⁺ served as starting material to form a ^99mTc(CO)₂(NO)-core. Labelling reactions with ligands such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA) and diethylenetriamine pentaacetic acid (DTPA) were performed, resulting in the complexes [^99mTc(IDA)(CO)₂(NO)], [^99mTc(NTA)(CO)₂(NO)] and [^99mTc(DTPA)(CO)₂(NO)]. In this way, the “nitrosyl-approach” adds a new and challenging synthetic tool to the already established organometallic chemistry of Re- and Tc-tricarbonyl complexes.