A Red-Light-Driven CO-Releasing Complex: Photoreactivities and Excited-State Dynamics of Highly Distorted Tricarbonyl Rhenium Phthalocyanines

A complex comprising one [Re(CO)₃]⁺ unit and a phthalocyanine (Pc) ligand ( Re₁Pc ) is shown to function as a photo-induced CO-releasing molecule (photoCORM) in the presence of O₂ and a coordinative solvent under irradiation with red light, which can deeply penetrate living tissues. Transient absorption spectroscopic measurements indicate very short excited-state lifetimes and ultrafast intersystem crossing for Re₁Pc and Re₂Pc , which contains two [Re(CO)₃]⁺ units. The excited-state properties are ascribed to efficient spin–orbit coupling and large Franck–Condon factors originating from the complexes’ distorted structures, that is, unsymmetric coordination of [Re(CO)₃]⁺ unit(s), one of which was confirmed by single-crystal X-ray analysis of a symmetrically substituted Pc with two [Re(CO)₃]⁺ units. Re₁Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.     

Facile Synthetic Access to Rhenium(II) Complexes: Activation of Carbon–Bromine Bonds by Single‐Electron Transfer

The five‐coordinated Re^I hydride complexes [Re(Br)(H)(NO)(PR₃)₂] (R=Cy 1 a , iPr 1 b ) were reacted with benzylbromide, thereby affording the 17‐electron mononuclear Re^II hydride complexes [Re(Br)₂(H)(NO)(PR₃)₂] (R=Cy 3 a , iPr 3 b ), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded Re^II hydrides 3 in addition to Re^I carbene hydrides [Re(?CHR¹)(Br)(H)(NO)(PR₃)₂] (R¹=H 4 , Br 5 ; R=Cy a , iPr b ) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re^I dibromide complexes [Re(Br)₂(NO)(PR₃)₂(η²‐H₂)] (R=Cy 2 a , iPr 2 b ) were reacted with allyl‐ or benzylbromide, thereby affording the monophosphine Re^II complex salts [R₃PCH₂R′][Re(Br)₄(NO)(PR₃)] (R′=? CH?CH₂ 6 , Ph 7 ). The reduction of Re^II complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h^?1) or allylbromide (TOF: 3 a 575, 3 b 562 h^?1). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re^I complexes [Re(Br)₂(NO)(MeCN)₂(PR₃)] (R=Cy 8 a , iPr 8 b ), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h^?1). Single‐electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a , 6 a , 6 b , 7 a , 7 b , and 8 a were established by single‐crystal X‐ray diffraction studies.     

Highly soluble tetra lauryl alcohol substituted phthalocyanines; synthesis,electrochemistry, spectroelectrochemistry

The tetra peripherally β-substituted 2(3),9(10),16(17),23(24)-tetrakis undecyloxy phthalocyanine derivatives, M{Pc[O-(CH₂)₁₁CH₃)]₄} Pc: Phthalocyanine, [M: Zn(II)(2), Ga(III)(3), and Ti(IV)(4)], have been synthesized and characterized using FT-IR, ¹H, and ¹³CNMR, MS (MALDI-TOF), UV–vis, atomic force microscopy, electro and spectroelectro chemical and elemental analysis. The new synthesized complexes are soluble in both polar solvents and nonpolar solvents, such as THF, DMF, CHCl₃, CH₂Cl_2, benzene, and even hexane. Electrochemical and spectroelectrochemical measurements give common metal-based and/or Pc ring-based redox processes which support the proposed structures of the complexes. While titanium phthalocyanine exhibits metal- and Pc ring-based reduction and/or oxidation couples, gallium and zinc phthalocyanines give only Pc ring-based electron transfer processes.     

Synthesis of Re(I) complexes bearing tridentate 2,6-bis(7-azaindolyl)phenyl ligand with green emission properties

The Re(I) complexes bearing 2,6-bis(7^′-azaindolyl)phenyl ligand as a tridentate ligand were synthesized by treatment with Re₂(CO)₁₀. The structures of the complexes were confirmed by X-ray crystallography. Both 7-azaindolyl ligands of Re(I) complexes are present in butterfly forms. The Re-C_ipso bonds showed a partial double bond character by π back-donation between the phenyl moiety and Re atom. In THF solution at room temperature, these complexes exhibited green emission (λ_em=510 nm), which is considered to be attributable to MLCT (dz²(Re) →π^* (7^′-azaindolyl group)) transition containing π→π^* (7^′-azaindolyl group) transition.     

5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin axial complexes of rhenium: Synthesis and reactions in protic solvents

The spectral (UV–Vis, IR, and NMR ¹H) properties and the state of oxorhenium(V) complexes with 5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin H₂P (O=Re(X)P) in protic solvents have been studied depending on the axial trans-ligand X^– (X = Cl, OPh, or OH). The O=Re(Cl)P, O=Re(OPh)P, and O=Re(OH)P in AcOH and CF3COOH are subjected to reaction of substitution their axial ligands with solvent molecules or anions, while remaining stable to the dissociation of M–N bonds and to oxidation both to the macrocyclic ligand and to the central metal cation. Quantitative parameters of the coordination of molecular oxygen by O=Re(Cl)P in 17.4–18.2 M H₂SO₄ to form O=Re(O₂)P⁺ · Cl^– have been obtained, these parameters being independent of the initial H₂SO₄ concentration. The character of peripheral functional substituents in H₂P has been shown to be responsible for the stability of the studied oxo complexes to chemical oxidation in aerated acids.     

Einführung eines terminalen Halogenoliganden in diorgano-verbrücke Dirhenium- und Molybdän-Rhenium-Komplexanionen in Gegenwart eines Amidinkations

Insertion of a Terminal Halogeno Ligand into Diorgano-bridged Dirhenium and Rhenium-Molybdenum Complex Anions in the Presence of an Amidin Cation and the Isomerization Processes The equimolar reaction of in situ generated anion Anions Re₂(μ-PCy₂)(CO)₈^? (Re? Re) in the presence of a steric expansive amidine cation DBUH⁺ with bromine and iodine in tetrahydrofuran solution gave the two isomers Re₂(PCy₂)(CO)₈X (Re? Re) and Re₂(μ-PCy₂)(μ-X)(CO)₈ (X = Br, I), of which the isomer with a terminal X ligand as major product was formed under maintenance of the Re? Re bond. The monotropic isomerization process of Re₂(μ-PCy₂)(CO)₈I runs thermically relative slowly, but more rapid in photochemical and electrochemical processes. The analogeous reaction of the heterometallic anion ReMo(η⁵-C₅H₅)(μ-PPh₂)(CO)₆^? with iodine delivers opposite to the former reaction mainly the bridged isomer ReMo(η⁵-C₅H₅)(μ-PPh₂μ-I)(CO)₆ besides ReMo(η⁵-C₅H₅)(μ-PPh₂)(CO)₆I. The obtained complexes were characterized by means of v(CO) and ³¹P NMR spectroscopic measurements. Single-crystal analyses led to the subsequent metal—metal bond lengths: Re? Re of 308.0(1) pm in Re₂(μ-PCy₂)(CO)₈Br and Re? Mo of 313.6(1) pm in ReMo(η⁵-C₅H₅)(μ-PPh₂)(CO)₆I.     

Coordination behaviour of the multidentate Schiff base 2,6-bis(2-hydroxyphenyliminomethyl)pyridine towards the fac-[Re(CO)3] and [ReO] cores

The seven-coordinate rhenium(III) complex cation [Re^III(dhp)(PPh₃)₂]⁺ was isolated as the iodide salt from the reaction of cis-[Re^vO₂I(PPh₃)₂] with 2,6-bis(2-hydroxyphenyliminomethyl)pyridine (H₂dhp) in ethanol. In the complex fac-[Re(CO)₃(H₂dhp)Br], prepared from [Re(CO)₅Br] and H₂dhp in toluene, the H₂dhp ligand acts as a neutral bidentate N,N-donor chelate. The complexes were characterized by elemental analysis, infrared and ¹H NMR spectroscopy and X-ray crystallography.     

Coordination of bidentate aniline derivatives to the fac-[Re(CO)3] core

A series of rhenium(I) tricarbonyl complexes, containing bidentate derivatives of aniline, was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)₃(Hpda)₂]Br was isolated. The neutral complex [Re(CO)₃(Hapa)Br] was formed with 2-aminodiphenylamine (Hapa) as ligand. 2-Aminophenol (Hopa) also produced the neutral ‘2+1’ complex [Re(CO)₃(opa)₂(Hopa)], but with 2-mercaptophenol (Hspo) the bridged dimer [Re₂(CO)₇(spo)₂] was found. In the complex [Re(CO)₃(Htpn)Br] (Htpn = N′-{(2-methylthio)benzylidene}benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthio sulfur and imino nitrogen atoms only, with a free amino group.     

Unexpected Molecular Structure of a Putative Rhenium-Dioxo-Benzocarbaporphyrin Complex. Implications for the Highest Transition Metal Valence in a Porphyrin-Type Ligand Environment

A combination of quantum chemical calculations and synthetic studies was used to address the possibility of very high (>6) valence states of transition metals in porphyrin-type complexes. With corrole as a supporting ligand, DFT calculations ruled out Re(VII) and Ir(VII) dioxo complexes as stable species. Attempted rhenium insertion into benzocarbaporphyrin (BCP) ligands on the other hand led to two products with different stoichiometries – Re[BCP]O and Re[BCP]O₂. To our surprise, single-crystal structure determination of one of the complexes of the latter type indicated an Re^VO center with a second oxygen bridging the Re−C bond. In other words, although the monooxo complexes Re[BCP]O are oxophilic, the BCP ligand cannot sustain a trans-Re^VII(O)₂ center. The search for metal valence states >6 in porphyrin-type ligand environments must therefore continue.     

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The novel complexes CpRe(CCHPh)(CO)₂ and Cp₂Re₂(μ-CCHPh)(CO)₄ containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)₂Re[CC(Ph)C(Ph)CH₂]Re(CO)₂Cp were obtained in the reaction of CpRe(CO)₃ with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η¹-bonded to one Re atom and η²-bonded to the other.     

Re4(CO)12[μ3-InRe(CO)5]4 und Re2(CO)8[μ-InRe(CO)5]2-cluster aus dem reaktionssystem In/Re2(CO)10 in xylol

The thermally stable solids Re₂(CO)₈[μ-InRe(CO)₅]₂ and Re₄(CO)₁₂[μ₃-InRe(CO)₅]₄ could be obtained by treatment of In with Re₂(CO)₁₀ in a bomb tube. A mechanism of the formation of the latter cluster from the first one is proposed. Compared with Re₂(CO)₈[μ-InRe(CO)₅]₂, Re₄(CO)₁₂[μ₃_InRe(CO)₅]₄ shows in polar solvents an unusual high stability, which can be explained by the higher coordination number of In with rhenium carbonyl ligands. Re₄(CO)₁₂-[μ₃-InRe(CO)₅]₄ dissolves monomerically in acetone, where as Re₂(CO)₈[μ-InRe(CO)₅]₂ dissociates yielding Re(CO)₅^? anions. Single-crystal X-ray analyses of Re₄(CO)₁₂[μ₃-InRe(CO)₅]₄ establish the metal skeleton. The central molecular fragment Re₄(CO)₁₂ contains a tetrahedral arrangement of four bonded Re atoms [ReRe 302.8 (5) pm]. The triangles of this fragment are capped with a μ₃-InRe(CO)₅ group each [InRe(terminal) 273.5 (7) pm; InRe (polyhedral) 281.8 (7) pm]. The bridging type of In atoms with the Re₄ tetrahedron and the metal skeleton was realized for the first time. By treating Re₄(CO)₁₂[μ₃-InRe(CO)₅]₄ with Br₂ the existence of Re(CO)₅ ligands could be proved by isolating BrRe(CO)₅.     

New Rhenium(V) Nitrofuryl Semicarbazone Complexes.Crystal Structure of [ReOCl2(PPh3)(3‐(5‐Nitrofuryl)acroleine semicarbazone)]

The synthesis and characterization of the first two Re complexes with semicarbazone ligands is presented. Selected ligands are 5‐Nitro‐2‐furaldehyde semicarbazone (Nitrofurazone) ( L1 ) and its derivative 3‐(5‐Nitrofuryl)acroleine semicarbazone ( L2 ). Complexes of general formula [Re^VOCl₂(PPh₃) L ], where L = L1 and L2 , were prepared in good yields and high purity by reaction of [Re^VOCl₃(PPh₃)₂] with L in ethanol or methanol solutions. The complexes formula and molecular structures were supported by elemental analyses and electronic, FTIR, ¹H, ¹³C and ³¹P NMR spectroscopies. In addition, the crystal and molecular structure of [Re^VOCl₂(PPh₃) L2 ] was determined by X‐ray diffraction methods. [ReOCl₂(PPh₃)(3‐(5‐Nitrofuryl)acroleine semicarbazone)] crystallizes in the space group P‐1 with a = 11.2334(2), b = 11.3040(2), c = 12.5040(2) Å, α = 81.861(1), β = 63.555(1), γ = 83.626(1)°, and Z = 2. The Re(V) ion is in a distorted octahedral environment, equatorially coordinated to a deprotonated semicarbazone molecule acting as a bidentate ligand through its carbonylic oxygen and azomethynic nitrogen atoms, to an oxo ligand and a chlorine atom. The six‐fold coordination is completed by another chlorine atom and a triphenylphosphine ligand at the axial positions.     

Azafullerene C59N–Phthalocyanine Dyad: Synthesis,Characterisation and Photoinduced Electron Transfer

The synthesis of a new azafullerene C₅₉N–phthalocyanine (Pc) dyad is described. The key step for the synthesis of the C₅₉N–Pc dyad was the formation of the C₅₉N‐based carboxylic acid, which was smoothly condensed with hydroxy‐modified Pc. The structure of the C₅₉N–Pc dyad was verified by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, UV/Vis spectroscopy and MS measurements. The photophysical and electrochemical properties of the C₅₉N–Pc dyad were investigated in both polar and non‐polar solvents by steady state and time‐resolved photoluminescence and absorption spectroscopy, as well as by cyclic voltammetry. Different relaxation pathways for the photoexcited C₅₉N–Pc dyad, as a result of changing the solvent polarity, were found, thus giving rise to energy‐transfer phenomena in non‐polar toluene and charge‐transfer processes in polar benzonitrile. Finally, the detailed quenching mechanisms were evaluated and compared with that of a C₆₀–Pc dyad, which revealed that the different excited‐state energies and reduction potentials of the two fullerene spheres (i.e. C₅₉N vs. C₆₀) strongly diverged in the deactivation pathways of the excited states of the corresponding phthalocyanine dyads.     

Heterometallatom-Koordinationsverbindungen Re2(μ-PPh2)2[mer-(CO)3]2-trans-[InX2(H2O)]2 und neue halogenhaltige drei- und vierkernige Rheniumcluster aus Reaktionen zwischen Re2[μ-PPh2)2(CO)8] und InX3 (X = Cl,Br, I)

Heterometallic Coordination Compounds Re₂(μ-PPh₂)₂[mer-(CO)₃]₂-trans-[InX₂(H₂O)]₂ and New Halogene Containing Three- and Four-Nuclear Rhenium Clusters from Reactions between Re₂(μ-PPh₂)₂(CO)₈ and InX₃ (X = Cl, Br, I) In sealed glass tubes equimolar amounts of Re₂(μ-PPh₂)₂(CO)₈ and InX₃ (X = Cl, Br, I) were reacted in the presence of xylene at 220°C to two types of products. The first type comprised the heterometallic coordination compounds Re₂(μ-PPh₂)₂(CO)₆[InX₂(H₂O)]₂ (X = Cl, Br, I) (yield 60%), and the second halogene containing rhenium complexes Re₃(μ₃-H)(μ₃-X)(μ-PPh₂)₃(CO)₆ (unsaturated three-membered metal ring with 46 VE) and Re₄(μ-H)(μ-X)(μ-PPh₂)₄(μ₄-PPh)(CO)₈ and additionally those substances as cis-IRe(CO)₄(PPh₂H), Re₂(μ-PPh₂)(μ-X)(CO)₈ (X = Cl, Br), Re₂(μ-I)₂[μ-(PPh₂)₂O](CO)₆ and Re₄(μ-Cl)₂(μ-PPh₂)₄(μ₄-PPh)(CO)₈ (four-membered metal ring with 66 VE with three Re? Re bonds) which have been observed in one or two of the three reaction systems. A proposal of the reaction course is discussed. The single X-ray analysis of Re₂(μ-PPh₂)₂[mer(CO)₃]₂-trans[InI₂(H₂O)]₂ · 2 Me₂CO shows for the two fold phosphido bridged dirhenium molecular fragment with 34 VE a Re? Re bond of 294.6(1) pm. From two possible transpositions of both In? Re bond vectors, the one found advantageously has sterical reasons. The average In? Re single bond length is 271.1(1) pm. The corresponding determination of the unsaturated three-membered ring compound Re₃(μ₃-H) (μ₃-Cl)(μ-PPh₂)₃(CO)₆ showed three Re? Re bond lenghts of comparable size, of which the mean value of 281.9(1) pm was significantly shortened by π electron delocalization effect compared to that of a saturated phosphido bridged three-membered rhenium ring compound. As it was recognized by further comparison, the structural data of the common molecular fragments in the three examined three-membered rhenium ring clusters (X = Cl, Br, I) are not dependent on the different kind of halogeno ligand atoms. Finally, the crystal structure determination of the substance Re₄(μ-H)(μ-Br)(μ-PPh₂)₄(μ₄-PPh)(CO)₈ shows the presence of square-pyramidal Re₄(μ₄-P) atomic arrangement, of which the planar basic plane has a sequence of up- and downwards orientated four diphenylphosphido bridging groups. The four measured Re? Re single bond lengths (mean value 302.7(3) pm change with the different kind of bridging atoms. The structural features observed are compared with those of a corresponding iodine derivative.     

Die Gasmolekeln Re3Cl9, Re3Br9 und Re3J9. Halogenaustausch und Fragmentierung

The Gaseous Molecules Re₃Cl₉, and Re₃I₉. Halogen Exchange and Fragmentation The mass spectrum of Re₃I₉ is communicated and compared with the spectra of Re₃Cl₉ and Re₃Br₉. The fragmentation corresponds with the stability of the bonds Re? Cl, Re? I, and Re? Re. In the mixed halides Re₃Cl_9?nX_n (X = Br, I) the observed abundance of molecules with n = 0–9 may be described statistically using the same weight for all the 9 positions of halogen. No difference of the 3 bridging halogens and the 6 terminal halogens can be seen regarding the halogen exchange at 300°C.     

Spectroscopic and Molecular Docking Study of the Interaction between Neutral Re(I) Tetrazolate Complexes and Bovine Serum Albumin

Re(I) complexes have potential in biomedical sciences as imaging agents, diagnostics and therapeutics. Thus, it is crucial to understand how Re(I) complexes interact with carrier proteins, like serum albumins. Here, two neutral Re(I) complexes were used (fac-[Re(CO)₃(1,10-phenanthroline)L], in which L is either 4-cyanophenyltetrazolate (1) or 4-methoxycarbonylphenyltetrazole ester (2) , to study the interactions with bovine serum albumin (BSA). Spectroscopic measurements, calculations of thermodynamic and Förster resonance energy transfer parameters, as well as molecular modelling, were performed to study differential binding between BSA and complex 1 and 2 . Induced-fit docking combined with quantum-polarised ligand docking were employed in what is believed to be a first for a Re(I) complex as a ligand for BSA. Our findings provide a basis for other molecular interaction studies and suggest that subtle functional group alterations at the terminal region of the Re(I) complex have a significant impact on the ability of this class of compounds to interact with BSA.     

Zur Koordinationschemie des Rhenium(VII). IV. t-Butylperrhenat

On the coordination chemistry of rhenium(VII). IV. t-Butylperrhenate t-Butylperrhenate is obtained in good yield form Re₂O₇ and di-t-butylether (data of an improved instruction for the preparation of the either) or from Re₂O₇ and t-butanol. The colourless crystals are decomposed already at ?40°C. The position of Re? O valence vibrational bands in the IR spectra of t-butylperrhenate and trimethylsilylperrhenate indicate a high formal bonding number at rhenium(VII) in these compounds. They do not add dimethylformamide as a mere ligand, but interact with it to form DMF complexes of Re₂O₇.     

Perfluormethyl-element-liganden XII. Zweikernkomplexe des rheniums: Re2(CO)8XY [1]

The reaction of Re₂(CO)₁₀ with E₂(CF₃)₄ (E = P, As) yields the binuclear complexes Re₂(CO)₈[E(CF₃)₂]₂ with two E(CF₃)₂ bridges. The complexes Re₂(CO)₈E(CF₃)₂I (E = P, As) and Re₂(CO)₈As(CF₃)₂Cl, containing two different bridges, are formed in the reactions of Re₂(CO)₁₀ with (CF₃)₂EI (E = P, As) and (CF₃)₂AsCl, respectively. A series of new binuclear complexes is obtained on substitution of iodine in the compounds Re₂(CO)₈E(CF₃)₂I (E = P, As) by SCH₃, SCF₃, SeCF₃, P(CH₃)₂ and H. The binuclear complexes Re₂(CO)₈(E′CF₃)₂ having two E′CF₃ bridges (E′ = S, Se) are obtained reacting Re(CO)₅I With Hg(E′CF₃)₂. At room temperature the mononuclear complex Re(CO)₅SeCF₃ is obtained. Substitution of iodine in Re₂(CO)₈I₂ by SCF₃ also yields the symmetrical compound Re₂(CO)₈(SCF₃)₂; reduction with NaBH₄ gives the binuclear hydride Re₂(CO)₈HJ. - IR and NMR spectra (¹H, ¹⁹F) of the new complexes are reported and discussed.     

μ‐Oxo‐bis{{2,2′‐[2,2‐di­methyl­propane‐1,3‐diyl­bis­(nitrilomethyl­idyne)]­diphenolato}­oxo­rhenium(V)}

The title compound, [Re₂O₃(C₁₉H₂₀N₂O₂)₂], is a hexacoordinate complex containing an [Re₂O₃]⁴⁺ core with a linear O=Re—O—Re=O bridge. The distorted octahedral coordination of the Re^V atom is achieved by an N₂O₂ donor set from the tetradentate imine–phenol ligand. The overall charge of the compound is neutral due to deprotonation of the phenol groups, and the terminating and bridging O atoms. The Re=O and Re—O bond distances of the [Re₂O₃]⁴⁺ core are 1.699 (4) and 1.911 (1) Å, respectively. The Re—O and Re—N bond distances of the equatorial plane are in the ranges 2.024 (4)–2.013 (4) and 2.128 (5)–2.120 (5) Å, respectively.     

Synthesis and reactions of isocyanate and carbamoyl complexes of rhenium

Re(CO)₂(NO)(PPh₃)₂ reacts with aroyl azides RCON₃ (R = C₆H₅, p-CH₃C₆H₄) in benzene to form isocyanate complexes of formula Re(CO)(NO)-(PPh₃)₂(RCONCO) (I). When the reaction is carried out in protic solvents such as ethanol, carbamoyl derivatives of formula Re(NCO)(NO)(PPh₃)₂-(CONHCOR) (II) are obtained, which give Re(NCO)(NO)(PPh₃)₂(CO)(NHCOR) when dissolved in chloroform, a terminal carbonyl ligand being formed from the carbamoyl group.I can be transformed into II by reaction with gaseous HCl, via [Re(CO)-(NO)(PPh₃)₂ {C(OH)=NCOR}]⁺Cl^- followed by anion exchange with NaN₃. II reacts with mineral acids HX (X = Cl, BF₄) to give amide derivatives of formula [Re(NCO)(NO)(PPh₃)₂(CO)(NH₂COR)]⁺ X^- which when X = Cl can be easily transformed into Re(NCO)(NO)(PPh₃)₂(CO)Cl, the amide ligand being removed. Both the protonation reactions of I and II are reversible. IR and ¹H NMR data of the new compounds and the mechanisms of formation of I and II are reported and discussed.