Antonio Palazzi

Essential role of the ancillary ligand in the color tuning of iridium tetrazolate complexes.

We report on the synthesis and physical chemical characterization of a class of heteroleptic mononuclear cyclometalated bis(phenylpyridine)iridium(III) complexes with tetrazolate chelate ligands, such as the deprotonated form of 2-(1 H-tetrazol-5-yl)pyridine ( PyTzH), 2-(1 H-tetrazol-5-yl)pyrazine ( PzTzH), and 5-bromo-2-(1 H-tetrazol-5-yl)pyridine ( BrPyTzH). The electrochemical and photophysical investigations of the resulting iridium(III) complexes revealed a rather wide span of redox and emission properties as a consequence of the nature of the ancillary tetrazolate ligand. In particular, within a series of the three neutral species, the emission observed changes from the blue-green of the pyridyltetrazolate complex to the red of that containing the pyrazinyltetrazolate ligand. The bromo-containing species, despite it displaying poor photophysical performances, is a synthetically attractive building block for the construction of polymetallic architectures. Moreover, the investigation of the reactivity toward electrophiles of one of the neutral mononuclear complexes, by methylation of the coordinated tetrazolate ligand, has also allowed further tuning of the electronic properties. In the latter case, the emission color tuning is also associated with a simple method for the conversion of a neutral species, a potentially triplet emitter for organic light-emitting devices, into the corresponding methylated cation, which might be used as a dopant for light-emitting electrochemical cell type devices or as a marker for biological labeling.

Preparation and reactivity of some new azido-bridged complexes of Pd(II) and Pt(II)

Abstract Azido-bridged complexes of Pt(II) and Pt(II) of the type [(dieneOCH 3 )MN 3 ] 2 (M = Pd, Pt) and[(π-allyl)PdN 3 ] 2 have been prepared by methathetical reaction from their chloro-bridged congeners. The bridging azido group in these new complexes reacts with carbon monoxide to give the corresponding cyanato-bridged complexes, whereas with CS 2 , CF 3 CN and SCNC 6 H 5 undergoes 1,3-cycloaddition to form thiatriazolate or tetrazolate groups bridging in dimeric complexes of the type [(diene)CH) 3 )M(N 3 CS 2 ) (M = Pd, Pt), [(π-allyl)Pd(N 3 CS 2 ] 2 ,[(π-allyl)Pd(N 3 CF 3 CN)] 2 and [(π-allyl)Pd(N 3 SCNC 6 H 5 )] 2 . Preliminary results on the termal decomposition of the CS 2 adducts and on the reaction with COS are reported and discussed.

Additions to the coordinated ethylene ligand in the [C5H5Fe(CO)2(C2H4)]+ complex

Abstract Reaction of [C5H5Fe(CO)2C2H4]+ with methylamine or methoxide ion (L) yields the stable σ-bonded carboniron complexes [C5H5Fe(CO)2(C2H4L)], which regenerate the original iron cationic complex when treated with hydrogen chloride. Reactions with other nucleophiles, such as N−3, NCO−, CN− have also been examined. With N−3 the nucleophilic attack occurs at the CO group to give the cyanato complex [C5H5Fe(CO)(C2H4)(NCO)], while with NCO− and CN− (X) ethylene is replaced to give [C5H5Fe(CO)2X] complexes.

Synthesis and reactivity of a new Fe(II) 5-(4-pyridyl)-tetrazolate complex and X-ray structure of its doubly protonated derivative.

Abstract The synthesis of the new Fe(II) complex [CpFe(CO)2(N4C–C5H4N)] (2) is described. 1H- and 13C-NMR spectroscopy data of (2) indicate the presence of interannular conjugation in the pyridyl-tetrazolate ligand, implying coplanarity between the two rings. Addition of electrophiles to 2 resulted in the formation of cationic complexes such as [CpFe(CO)2(4-MeN4C–C5H4N)][O3SCF3] (3), [CpFe(CO)2(4-HN4C–C5H4N)][O3SCF3] (4) and of the doubly protonated complex [CpFe(CO)2(4-HN4C–C5H4N–H)][O3SCF3]2 (5). In all cases, the out-of-plane rotation of the pyridyl ring occurred as a consequence of the quaternization of the N-4 of tetrazole ring. X-ray structure of complex 5 indicates a torsion angle of 20.9(2)° between the aromatic rings. Protonation reactions were found to be reversible and complexes 4–5 were easily converted into the starting complex 2 by addition of a base.

Chemistry of thiocarbonyl complexes of the type π-(C5H5)Fe(CO)(CS)(L)+

Abstract Cationic thiocarbonyl complexes of the type π-(C 5 H 5 )Fe(CO)(CS)(L) + have been prepared from π-(C 5 H 5 )Fe(CO) 2 (CS) + and various group V A ligands. The loss of CO in the substitution reaction suggests that the strength of the Fe(CS) bond is greater than that of the Fe(CO) bond. The 13 C n.m.r. spectra of these new thiocarbonyl derivatives indicate that the deshielding of the thiocarbonyl resonance increases as the infrared stretching force constant of the CS group decreases; the shielding of the carbonyl resonance of π-(C 5 H 5 )Fe(CO)(CS)(P(C 6 H 5 ) 3 ) + relative to the π-(C 5 H 5 )Fe(CO) 2 (P(C 6 H 5 ) 3 ) + is attributed to the increased π-acceptor ability of CS relative to CO. The reactions of π-(C 5 H 5 )Fe(CO)(CS)(L) with various nucleophiles such as NH 2 R, CH 3 O − , N 3 − , NH 2 NH 2 have been studied; in all the cases reported the nucleophilic addition occurs, at the carbon of the thiocarbonyl group, in line with the 13 C n.m.r. chemical shift of the thiocarbonyl which indicates a large deshielded carbon resonance. The nucleophilic reactions studied can be summarized as follows: reaction with NH 2 R with formation of π-(C 5 H 5 ) Fe(CO)(L)(CNR) + ; reaction with N 3 − and NH 2 NH 2 leading to π-(C 5 H 5 )Fe(CO)(L)(NCS); reaction with CH 3 O − yielding thiocarbonyl derivatives π-(C 5 H 5 )Fe (CO)(L)(C(S)OCH 3 ).

Reactions of cyclopentadienyliron carbonyl derivatives with azide ion

Abstract The complex (π-C 5 h 5 )Fe(CO)(PPh 3 )(NCO) has been prepared by treatment of the salt [(π-C 5 H 5 )Fe(CO) 2 (PPh 3 )]PF 6 with hydrazine or with azide ion. The kinetics of the reaction between axide ion and the salts [(π-C 5 H 5 )Fe(CO) 2 (L)]PF 6 , where L=CO, PPh 3 , or C 2 H 4 have been studied spectrophotometrically, and in each case the reaction has been shown to be first order with respect to the salt and the azide ion. The rate constants for the sequence L=CO, PPh 3 , and C 2 H 4 are in the ratio 1/67/300. It is suggested that an acyl azide is formed as an intermediate by nucleophilic attack of azide ion on the carbonyl group, and rearranges to the corresponding isocyanate with loss of nitrogen.

Reactions of (cyclopentadienyl)nitrosyldicarbonylmanganese cation with amines

Abstract The [(XC5H4)Mn(CO)(NO)L]+ complexes react with primary alkylamines to give carboxamido complexes, where X = H, CH3; L = CO, P(C6H5)3. In the case of L = CO, the carboxamido complexes may be isolated, whereas with L = P(C6H5)3 the reversibility of the reactions permits the isolation only of the starting materials when the solutions are evaporated to dryness. This diminished tendency to form carboxamido complexes is related to the decreased electron density on the carbonyl carbon going from L = CO to L = P(C6H5)3. The presence of the coordinated NO group does not change the reactivity of the cationic complexes towards amines.

Electrophilically promoted cyanide abstraction in diiron cyano(amino) alkylidene complexes: molecular structure of [Fe2(CO)2(η-C5H5)2(µ-CO){µ-CN(CH2)4CH2}][(OC)5WCNW(CO)5]

The reactions of the µ-cyano(amino)alkylidene complexes [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)(NR2)}][cp η5-C5H5, NR2 [graphic omitted]H21a or NMe21b] with [W(CO)5(thf)](thf = tetrahydrofuran), MeSO3CF3 and HSO3CF3 electrophiles promotes µ-C–CN bond cleavage with formation of the corresponding [Fe2(CO)2(cp)2(µ-CO)(µ-CNR2)]+3. In the case of [W(CO)5(thf)] the unexpected salts [Fe2(CO)2(cp)2(µ-CO)(µ-CNR2)][(OC)5WCNW(CO)5] have been prepared and characterized by the crystal structure of 3a[NR2= [graphic omitted]H2]. The structure [monoclinic, space group P21/n,a= 11.196(3), b= 17.389(3), c= 17.938(3)A, β= 95.19(2)°, Z= 4, R= 0.032] contains ordered cations and anions. Distances of interest are Fe–µ-C(N) 1.875(6), C–N 1.280(8)A in the cation and W–C(N) 2.184(8), W–N(C) 2.187(7) and C–N 1.15(1)A in the anion, where the cyanide ligand symmetrically bridges two W(CO)5 units. Electrophilic addition to phosphorus in [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)(PEt2)}]2 has been observed and the adduct [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)[PEt2W(CO)5]}]4 spectroscopically characterized. The different reactivity of 1 and 2 with electrophilic reagents is attributed to the strong tendency to CN double-bond formation.

Formation of metal carbonyl derivatives of monothiocarbamates and dithio-carbamates from CS2 and COS

The reaction of (C5H5)Fe(CO)2CONHCH3 with CSX (X = O, S) gives (C5H5)Fe(CO)2SC(X)NHCH3, where the mono or dithio-carbamate act as monodentate ligands. In the case of carbon disulfide small variable quantities of (C5H5)Fe(CO)S2CNHCH3 are obtained depending on reaction conditions. The carbamoyl derivatives (C5H5Re(CO)(NO)CONHCH3, cis-(CO)4M(NH2CH3)CONHCH3 (M = Mn, Re) react with CS2 to give (C5H5)Re(CO)(NO)S2CNHCH3 and (CO)4MS2CNHCH3 respectively. The mechanism of thiocarbamate formation is discussed on the basis of chemical evidence which indicates nucleophilic attack of the N-carbamoylic atom on the carbon of the CSX reagents.

The μ-sulfonium–methylidene diiron complexes [Fe2{μ-C(X)SMe2}(μ-CO)(CO)2(Cp)2]SO3CF3 (X=CN, H) as precursors of μ-alkylidene complexes

Abstract The reactions of [Fe 2 {μ-C(X)SMe 2 }(μ-CO)(CO) 2 (Cp) 2 ]SO 3 CF 3 (X=CN 2a , H 2b ; Cp=η-C 5 H 5 ) with Li 2 Cu(CN)R 2 (R=Me, Bu n , Ph, CCC 6 H 4 Me-4, C 4 H 3 S) give the neutral μ-alkylidene complexes [Fe 2 {μ-C(X)R}(μ-CO)(CO) 2 (Cp) 2 ] ( 3 ) arising from nucleophilic attack at the bridging carbon and SMe 2 displacement. Likewise, 2a , b react with the sodium salt of dimethylmalonate, diethylmalonate, ethylacetoacetate, 2,4-pentanedione, dibenzoylmethane and benzylcyanide, resulting in the formation of the corresponding functionalized μ-alkylidene complexes [Fe 2 {μ-C(X)R}(μ-CO)(CO) 2 (Cp) 2 ] ( 5 – 7 ) (X=CN, H; R=CH(COOMe) 2 , CH(COOEt) 2 , CH(COOMe)(COMe), CH(COMe) 2 , CH(COPh) 2 , CH(Ph)CN). The dichetone adducts [Fe 2 {μ-C(X)CH(COR) 2 }(μ-CO)(CO) 2 (Cp) 2 ] (X=CN, H; R=Me, Ph) undergo deacylation upon treatment with alumina, leading to the formation of the complexes [Fe 2 {μ-C(X)CH 2 C(O)R}(μ-CO)(CO) 2 (Cp) 2 ]. Reactions of 2a , b with LiBu or PhLi result in the formation the metallacycles [Fe 2 {μ-C(X)S(Me) CH 2 }(μ-CO)(C O)(CO)(Cp) 2 ] (X=CN, 4a ; H 4b ) which arise from the deprotonation of an SMe group and the intramolecular addition at a terminally coordinated carbonyl. Finally, a comparison of the reactivity of 2a , b with that of the μ-carbyne diiron complexes [Fe 2 (μ-CX)(μ-CO)(CO) 2 (Cp) 2 ]SO 3 CF 3 (X=H, SMe, NMe 2 ) is presented.