Insight into the structures of [M(C5H4I)(CO)3] and [M2(C12H8)(CO)6] (M = Mn and Re) containing strong I...O and π(CO)–π(CO) interactions

The compounds tricarbonyl(η⁵‐1‐iodocyclopentadienyl)manganese(I), [Mn(C₅H₄I)(CO)₃], (I), and tricarbonyl(η⁵‐1‐iodocyclopentadienyl)rhenium(I), [Re(C₅H₄I)(CO)₃], (III), are isostructural and isomorphous. The compounds [μ‐1,2(η⁵)‐acetylenedicyclopentadienyl]bis[tricarbonylmanganese(I)] or bis(cymantrenyl)acetylene, [Mn₂(C₁₂H₈)(CO)₆], (II), and [μ‐1,2(η⁵)‐acetylenedicyclopentadienyl]bis[tricarbonylrhenium(I)], [Re₂(C₁₂H₈)(CO)₆], (IV), are isostructural and isomorphous, and their molecules display inversion symmetry about the mid‐point of the ligand C[triple‐bond]C bond, with the (CO)₃M(C₅H₄) (M = Mn and Re) moieties adopting a transoid conformation. The molecules in all four compounds form zigzag chains due to the formation of strong attractive I...O [in (I) and (III)] or π(CO)–π(CO) [in (I) and (IV)] interactions along the crystallographic b axis. The zigzag chains are bound to each other by weak intermolecular C—H...O hydrogen bonds for (I) and (III), while for (II) and (IV) the chains are bound to each other by a combination of weak C—H...O hydrogen bonds and π(Csp²)–π(Csp²) stacking interactions between pairs of molecules. The π(CO)–π(CO) contacts in (II) and (IV) between carbonyl groups of neighboring molecules, forming pairwise interactions in a sheared antiparallel dimer motif, are encountered in only 35% of all carbonyl interactions for transition metal–carbonyl compounds.     

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.     

In situ generation of H2Se and hydrothermal synthesis of new polynuclear rhenium carbonyl polyselenides

Two new polyselenide-bridged rhenium carbonyl complexes, [Re₅(CO)₁₈(Se₂)₃]⁻ and [Re₄(CO)₁₄(Se₂)(Se₅)], were obtained by hydrothermal reaction of [Re(CO)₅Cl] with in situ generated H₂Se and have been characterized by X-ray diffraction.     

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.     

Formation of a six-coordinate fac-[Re(CO)3]+ complex by the N-C bond cleavage of a potentially tetradentate ligand

The rhenium(I) compound fac-[Re(CO)₃(daa)].Hpab.H₂O (Hpab = N,N’-(1,2-phenylene)bis(2′-aminobenzamide); Hdaa = 2- amino-N-(2-aminophenyl)benzamide) was synthesized from the reaction of [Re(CO)₅Br] with two equivalent of Hpab in toluene. The monoanionic tridentate ligand daa was formed by the rhenium-mediated cleavage of an amido N-C bond of the potentially tetradentate ligand Hpab. The compound was characterized by IR spectroscopy and X-ray crystallography, and daa is coordinated as a diaminoamide via three nitrogen-donor atoms.     

Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato Complexes: Synthesis,Characterization, and Photophysical,Electrochemical, and Computational Studies

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)₃(N^N)(CNBR₃)], where N^N=bpy, 4,4′‐Me₂bpy, phen, 4,7‐Me₂phen, 2,9‐Me₂phen, 3,4,7,8‐Me₄phen; R=C₆F₅, C₆H₅, Cl, 4‐ClC₆H₄, 3,5‐(CF₃)₂C₆H₃, with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X‐ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD‐DFT calculations have been performed, which revealed that the lowest‐energy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π*(N^N)] and LLCT [π(CNBR₃)→π*(N^N)] transitions.     

Oxorhenium(V)‐ and Tricarbonylrhenium(I) Complexes with Substituted Pyrazoles as Products of the Degradation of Hydrotrispyrazolylborates

Hydrotris(3, 5‐dimethylpyrazol‐1‐yl)borate and hydrotris(3‐phenylpyrazol‐1‐yl)borate decompose during reactions with [ReOCl₃(PPh₃)₂] and [NEt₄]₂[Re(CO)₃Br₃], respectively. The generated pyrazole ligands form complexes with the rhenium(V) oxo and the rhenium(I ) tricarbonyl cores. X‐ray crystal structures of the oxo‐bridged dimer [Cl(PPh₃)(O)Re(μ‐O)(μ‐Me₂pz)₂Re(O)(HMe₂pz)Cl] ( 1 ) and [Re(CO)₃(HPhpz)₂(Phpz)] ( 2 ) (HMe₂pz = 3, 5‐dimethylpyrazole, HPhpz = 3‐phenylpyrazole) show that the substituted pyrazoles can readily deprotonate and act as monodentate or bridging anionic ligands. Re‐N bond lengths between 2.09 and 2.14Å have been observed for the bridging and between 2.12 and 2.23Å for the terminal pyrazole ligands.     

Photoinduced synthesis of the mixed metal “manganese rhenium cubane” [Mn3Re(CO)12(SC6H5)4]

The photoinduced synthesis and spectroscopic properties of the new mixed metal compound [Mn₃Re(CO)₁₂(SC₆H₅)₄] by UV irradiation of a mixture of Mn₂(CO)₁₀, Re₂(CO)₁₀ with S₂(C₆H₅)₂ is described. No mixed sulphur/selenium compounds [M₄(CO)₁₂S_nSe_4?n(C₆H₅)₄] (M = Mn or Re, n = 1–3) could be obtained by analogous photoreactions.     

Heteronukleare Metallatomcluster der Typen X4−n[SnM(CO)4P(C6H5)3]n und M2(CO)8 [μ-Sn(X)M (CO)4P(C6H5)3]2 aus Umsetzungen von SnX2 mit M2(CO)8[P(C6H5)3]2 (X = Halogen; M = Mn,Re; n = 2, 3)

Heteronuclear Metal Atom Clusters of the Types X_4?n[SnM(CO)₄P(C₆H₅)₃]_n and M₂(CO)₈[μ-Sn(X)M(CO)₄P(C₆H₅)₃]₂ by Reaction of SnX₂ with M₂(CO)₈[P(C₆H₅)₃]₂ (X = Halogene; M = Mn, Re; n = 2, 3) The compounds of the both types X_4?n[SnM(CO)₄P(C₆H₅)₃]_n (n = 3; M = Mn; X = F, Cl, Br, I. n = 2: M = Mn, Re; X = Cl, Br, I) and M₂(CO)₈[μ-Sn(X)M(CO)₄P(C₆H₅)₃]₂ (M = Mn; X = Cl, I. M = Re; X = Cl, Br, I) are prepared by reaction of SnX₂ with M₂(CO)₈[P(C₆H₅)₃]₂ (M = Mn, Re). Their IR frequencies are assigned. In Re₂(CO)₈[μ-Sn(Cl)Re(CO)₄P(C₆H₅)₃]₂ the central molecule fragment contains a planar Re₂Sn₂ rhombus with a transannular Re? Re bond of 316.0(2) pm. Each of the Sn^IV atoms is connected with the terminal ligands Cl and Re(CO)₄P(C₆H₅)₃. These ligands are in transposition with respect to the Re₂Sn₂ ring. The mean values for the remaining bond distances (pm) are: Sn? Re = 274.0(3); Sn? Cl = 243(1), Re? C = 176(5), Re? P = 242.4(9), C? O = 123(5). The factors with an influence on the geometrical shape of such M₂Sn₂ rings (M = transition metal) are discussed.     

Reactions of coordinated molecules : XXV. The preparation of several bis[(hydroxy)(methyl)]carbenoid complexes of rhenium

When the rhenium(I) complexes, XRe(CO)₅ (where X is Cl, Br or I), are treated with two molar-equivalents of methyllithium, dianionic complexes of the type, fac-(OC)₃(X)Re[C(CH₃)O]₂^–, are formed. The diprotonation of these dianions with HX affords the neutral, bis-carbenoid complexes, fac-(OC)₃(X)Re[C(CH₃)(OH)]₂. When X is methyl, the reaction with methyllithium gives only a monoanion. The iodo, bis-carbenoid complex decomposes in solution with the elimination of acetaldehyde and with the formation of the known dimeric complex, [Re(CO)₄I]₂. The X-ray molecular structure determination of this dimeric complex is reported. The ^13C NMR data of the chloro and bromo biscarbenoid complexes are also presented.     

Mass spectrometry of π-complexes of transition metals XI. Manganese and rhenium vinylidene complexes

The mass spectra of (π-C₅H₅)_nM_n(CO)(L)₁(L′) (M = Mn, Re; L = CO, P(C₆H₅)₃, P(OC₆H₅)₃; L′ is a vinylidene ligand) are reported and characterised by strong dehydrogenation of the rhenium complexes. In bimetallic analogues, the ReRe bond is stronger than the MnMn.     

Stepwise Degradation of Trifluoromethyl Platinum(II) Compounds

The action of moisture on the homoleptic organoplatinum(II) compound [NBu₄]₂[Pt(CF₃)₄] ( 1 ) gives rise to the carbonyl derivative [NBu₄][Pt(CF₃)₃(CO)] ( 2 ), which is itself moisture stable. However, treatment of compound 2 with HCl(aq) results in the formation of [NBu₄][cis‐Pt(CF₃)₂Cl(CO)] ( 3 ), which undergoes degradation of an additional CF₃ group by further treatment with HCl(aq) in large excess, affording [NBu₄][cis‐Pt(CF₃)Cl₂(CO)] ( 4 ). The carbonyl derivatives 2 – 4 are fairly stable species, in which the CO ligand, however, can be readily extruded by reaction with trimethylamine N‐oxide (ONMe₃). Thus, compound 2 reacts with ONMe₃ in the presence of a number of neutral or anionic ligands affording a series of singly or doubly charged derivatives with the general formulae [NBu₄][Pt(CF₃)₃(L)] [L=CNtBu ( 5 ), PPh₃ ( 6 ), P(o‐tolyl)₃ ( 7 ), tht ( 8 ; tht=tetrahydrothiophene)] and [NBu₄]₂[Pt(CF₃)₃X] [X=Cl ( 9 ), Br ( 10 ), I ( 11 )], respectively. Compound 2 also reacts with ONMe₃ and pyridin‐2‐thiol (C₅H₅NS) giving rise to the five‐membered metallacyclic derivative [NBu₄][Pt(CF₃)₂(CF₂NC₅H₄S‐κC,κS)] ( 12 ), which can be viewed as a difluorocarbene species stabilized by intramolecular base coordination. On the other hand, treatment of compound 3 with ONMe₃ in the presence of C₅H₅NS yields the four‐membered metallacyclic compound [NBu₄][Pt(CF₃)₂(NC₅H₄S‐κN,κS)] ( 13 ). The geometries of the metallacycles in compounds 12 and 13 are compared. In the absence of any additional ligand, compound 3 undergoes dimerization producing the dinuclear species [NBu₄]₂[{Pt(CF₃)₂}₂(μ‐Cl)₂] ( 14 ). Halide abstraction in the latter compound with AgClO₄ in THF yields the solvento compound cis‐[Pt(CF₃)₂(thf)₂] ( 15 ). The highly labile character of the THF ligands in compound 15 makes this species a convenient synthon of the “cis‐Pt(CF₃)₂” unit.     

Trindenyl[tris(rheniumtricarbonyl)]

Trindene is combined with KH and [Re(CO)₃(THF)Br]₂ (THF = tetrahydrofuran) in THF to yield the first trinuclear half-sandwich complex of the trindene trianion, (trindenyl)[Re(CO)₃]₃, in 50% yield. Two of the rhenium carbonyl units are rigidly held in close proximity and the carbonyl ligands on adjacent metals are vibrationally coupled. Both cis and trans isomers of the dirhenium complex, (trindenyl)[Re(CO)₃]₂, are also isolated from the above reaction in low yield.     

Tricarbonyl complexes of rhenium(I) and technetium(I) with thiourea derivatives

fac-[M(CO)₃X₃]²⁻ complexes (M=Re, X=Br; M=Tc, X=Cl) react with thiourea derivatives under formation of stable rhenium(I) and technetium(I) complexes. The composition of the products can be controlled by the steric requirements of the ligands and their ability to form chelates.The products of reactions with tetramethylthiourea, Me₄tu (I), N,N-diethylthiocarbamoylbenzamidine, H₂Et₂tcb (II), and morpholinylthiocarbamoylbenzamidine, H₂morphtcb (III), have been studied by X-ray crystallography showing that the products belong to three different structural types. A mononuclear complex of the composition fac-[Re(CO)₃Br(Me₄tu)₂] has been isolated with tetramethylthiourea, whereas the thiocarbamoylbenzamidines deprotonate and act as N,S-chelating ligands. This results in the formation of a dimeric [Tc(CO)₃(HEt₂tcb-N,S)]₂ complex with a central, almost square Tc₂S₂ unit and a monomeric compound of the composition [Tc(CO)₃(Hmorphtcb-N,S)(H₂morphtcb-S)]. The latter compound contains a neutral, S-bonded morpholinylthiocarbamoylbenzamidine in the unusual imine form in addition to a chelate-bonded Hmorphtcb⁻ ligand.     

Re(I) Complexes as Backbone Substituents and Cross-Linking Agents for Hybrid Luminescent Polysiloxanes and Silicone Rubbers

This study focuses on the synthesis of hybrid luminescent polysiloxanes and silicone rubbers grafted by organometallic rhenium(I) complexes using Cu(I)-catalyzed azido-alkyne cycloaddition (CuAAC). The design of the rhenium(I) complexes includes using a diimine ligand to create an MLCT luminescent center and the introduction of a triple C≡C bond on the periphery of the ligand environment to provide click-reaction capability. Poly(3-azidopropylmethylsiloxane-co-dimethylsiloxane) (N₃-PDMS) was synthesized for incorporation of azide function in polysiloxane chain. [Re(CO)₃(MeCN)(5-(4-ethynylphenyl)-2,2′-bipyridine)]OTf (Re1) luminescent complex was used to prepare a luminescent copolymer with N₃-PDMS (Re1-PDMS), while [Re(CO)₃Cl(5,5′-diethynyl-2,2′-bipyridine)] (Re2) was used as a luminescent cross-linking agent of N₃-PDMS to obtain luminescent silicone rubber (Re2-PDMS). The examination of photophysical properties of the hybrid polymer materials obtained show that emission profile of Re(I) moiety remains unchanged and metallocenter allows to control the creation of polysiloxane-based materials with specified properties.     

Bifunctional activation of amine-boranes by the W/Pd bimetallic analogs of “frustrated Lewis pairs”

The reaction between basic [(PCP)Pd(H)] (PCP = 2,6-(CH₂P(t-C₄H₉)₂)₂C₆H₄) and acidic [LWH(CO)₃] (L = Cp (1a), Tp (1b); Cp = η⁵-cyclopentadienyl, Tp = κ³-hydridotris(pyrazolyl)borate) leads to the formation of bimolecular complexes [LW(CO)₂(μ-CO)⋯Pd(PCP)] (4a, 4b), which catalyze amine-borane (Me₂NHBH₃, ^tBuNH₂BH₃) dehydrogenation. The combination of variable-temperature (¹H, ³¹P{¹H}, ¹¹B NMR and IR) spectroscopies and computational (ωB97XD/def2-TZVP) studies reveal the formation of an η¹-borane complex [(PCP)Pd(Me₂NHBH₃)]⁺[LW(CO₃)]⁻ (5) in the first step, where a BH bond strongly binds palladium and an amine group is hydrogen-bonded to tungsten. The subsequent intracomplex proton transfer is the rate-determining step, followed by an almost barrierless hydride transfer. Bimetallic species 4 are easily regenerated through hydrogen evolution in the reaction between two hydrides.

Bimetallic complexes [LW(CO)₂(μ-CO)⋯Pd(PCP)] cooperatively activate amine-boranes for their dehydrogenation via N–H proton tunneling at RDS and H₂ evolution from two neutral hydrides.     

[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.     

Synthesis,Crystal Structure and Spectroscopic Characterisation of Mono‐ and Dinuclear 5,5‐Diethylbarbiturato Complexes of Chromium(0) and Rhenium(I)

Addition of 5,5‐diethylbarbituric acid (H₂debarb, 1 ) to [CpCr(NO)₂Cl], [Re(CO)₅Br] or [(PPh₃)Re(CO)₄Br] in the presence of triethylamine and AgO₃SCF₃ (= AgOTf) resulted in the mono‐barbiturato complexes [CpCr(NO)₂(Hdebarb)] ( 2 ), [PPh₃Re(CO)₄(Hdebarb)] ( 3 ) and [Re(CO)₅(Hdebarb)] ( 4 ), respectively. Bis‐barbiturato complex [{(CO)₅Re}₂(debarb)] ( 5 ) with a doubly deprotonated barbiturate dianion formed when a molar ratio of metal complex to ligand of 2:1 was used. In the case of the rhenium complexes, AgO₃SCF₃ must be used additionally to cleave off bromide. All of the complexes were fully characterised by means of IR, mass and ¹H, ¹³C and ³¹P NMR spectra and elemental analysis. In addition, their solid‐state structures were determined by single‐crystal X‐ray diffraction studies. The complexes exhibit distorted pseudo‐tetrahedral ( 2 ) or pseudo‐octahedral ( 3 – 5 ) configuration around the metal atom. In all complexes the ring system of the Hdebarb ligand is essentially planar.     

Chemistry of tricarbonylrhenium(I) chelates of azopyrimidines, azoimidazoles and anion radicals thereof

The azopyrimidine and azoimidazole ligands (general abbreviations, RL) used in the present work are 2-(p-R-C₆H₄NN)C₄H₃N₂, RL_pm (R=H, Cl) and 2-(p-R-C₆H₄NN)-1-(Me)C₃H₂N₂, RL_im (R=Me, Cl), respectively. The reaction of Re(CO)₅Cl with a slight excess of RL in boiling benzene has furnished blue-violet complexes of type Re(CO)₃Cl(RL) which have been spectrally characterized. In Re(CO)₃Cl(HL_pm) and Re(CO)₃Cl(ClL_im) the Re-N^h, Re-N^a distances are 2.173(6), 2.136(6) Å and 2.150(5), 2.166(5) Å, respectively (N^h and N^a are heterocyclic and azo N atoms, respectively). Their N-N lengths (1.271(8), 1.281(7) Å) implicate relatively weak Re-azo(π^*) back-bonding. In the lattice of Re(CO)₃Cl(HL_pm), pair-wise C-H?O hydrogen bonding between symmetry related molecules is present (C?O; 3.264(9) Å, H?O; 2.460(10) Å; C-H?O; 130.6(5)°). The lattice of Re(CO)₃Cl(ClL_im) also consists of centrosymmetric dimers held by aromatic π-π stacking between parallely placed pendant aryl rings (centroid?centroid distance, 3.781(9) Å). Extended Hückel calculations reveal that the LUMO of Re(CO)₃Cl(RL) is ∼60% azo in character. One-electron quasireversible electrochemical reduction occurs near −0.1 and −0.4 V vs. SCE in the cases of Re(CO)₃Cl(RL_pm) and Re(CO)₃Cl(RL_im), respectively. The redox orbital is believed to be to the above noted LUMO. Electrogenerated Re(CO)₃Cl(RL⁻) underwent spontaneous solvolytic chloride displacement in MeCN furnishing Re(CO)₃(MeCN)(RL⁻) which has been isolated. The latter in turn reacted with imidazole and triphenyl phosphine furnishing Re(CO)₃(C₃H₄N₂)(RL⁻) and Re(CO)₃(PPh₃)(RL⁻), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)₃Cl(RL) but for shifts to lower frequencies by 10-40 cm⁻¹. All the three radical anion systems are one-electron paramagnets (1.7-1.8 μ_B). The unpaired electron is primarily localized in a predominantly azo-π^* orbital. A small metal contribution (^{185, 187}Re, I=5/2) is present and both Re(CO)₃(MeCN)(RL⁻) and Re(CO)₃(C₃H₄N₂)(RL⁻) display six-line EPR spectra (A∼28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)₃(PPh₃)(RL⁻) seven nearly equispaced lines are observed due to virtually equal coupling with metal and ³¹P (I=1/2) nuclei. The g values of the radical species span the range 2.0033-2.0066.     

Photochemical reactions of allyl and crotyl halides with cyclopentadienyl-chromium, -molybdenum and -tungsten complexes

[MoCl(CO)₃(η⁵-C₅H₅)] on photolysis with allyl or crotyl halides C₅H₄RX gives Mo^IV complexes [MoX₂(CO)(η³-C₃H₄R)(η⁵-C₅H₅)] (R = H, X = Cl, Br, I; R = Me, X = Cl, Br). [WCl(CO)₃(η⁵-C₅H₅)] under similar conditions gives trihalides [WX₃(CO)₂(η⁵-C₅H₅)] (X = Cl, Br) on reaction with C₃H₅Cl and C₃H₅Br while [WCl(CO)₃(η⁵-C₅H₄SiMe₃)] and [CrI(CO)₃(η⁵-C₅H₅)] react with allyl chloride to give [WCl₃(CO)₂(η⁵-C₅H₄SiMe₃)] and [CrCl₂(η⁵-C₅H₅)] respectively.