The structure of C5H5RFe+ (R = F,Cl, Br,I, O,OH, OCH3, C6H5, H) ions in the gas phase and the generation of their neutral counterparts by neutralization-reionization mass spectrometry

The structure of C₅H₅FeR^+˙ ions was studied by tandem mass spectrometry that included the neutralization-reionization (NR) method. Halogen-containing species (R = F, Cl, Br, I) showed fragmentation that was consistent with a structure that has the cyclopentadienyl ring and R as separate ligands at the metal atom (structure A). This structure also was identified for C₅H₅FeO⁺ and CpFeOH^+˙ ions, but these species also easily isomerized to metal-cyclopentadiene structure, RC₅H₅Fe^+˙ (B), followed by hydrogen rearrangement(s) and CO loss. B was the dominant structure of C₅H₅FeH^+˙ and C₅H₅FeC₆H^+˙₅ ions. All ions that have structure A showed recovery signals in their NR mass spectra that indicated that their stable neutral counterparts were generated. The NR mass spectra also provided complementary information about the structure of ions before neutralization and after reionization.     

三核过渡金属配合物〔M_3~ⅢO(OOCR)_6L_3〕 (M=Cr,Fe,Mn;R=CH_3,C_2H_5,CH_2NH_2;L=C_5H_5N,H_2O)的~1H NMR性质

采用１ＨＮＭＲ谱研究了通式为〔Ｍ３ⅢＯ（ＯＯＣＲ）６Ｌ３〕＋（Ｍ＝Ｃｒ,Ｆｅ,Ｍｎ;Ｒ＝ＣＨ３,Ｃ２Ｈ５,ＣＨ２ＮＨ２;Ｌ＝Ｃ５Ｈ５Ｎ,Ｈ２Ｏ）的一系列氧心三核过渡金属配合物,主要考察其１Ｈ化学位移随金属、配体、温度、溶剂等因素变化而变化的规律。结果表明,骨架金属对化学位移的影响最大,Ｍ３Ｏ中的３个金属离子间存在反铁磁交换相互作用。对Ｍｎ配合物中顺磁中心对化学位移和线宽的影响机制的研究表明,其１Ｈ各向同性位移主要由接触作用贡献     

Gas-phase derivatization of [C3H5]+ ions using tandem mass spectrometry methods A13C labelling study

The study of specifically ¹³C-labelled precursors sheds further light on the gas-phase chemistry of allyl and 2-propenyl cations. It is demonstrated that both species are formed from allyl and 2-propenyl bromide upon 70 eV electron impact ionization without skeletal reorganization. Gas-phase derivatization of the [C₃ H₅]⁺ ions with benzene facilitates, as suggested and observed earlier, the distinction of the two isomers using collision-induced dissociation of the Wheland complexes (or isomers thereof). The ¹³C labelling data clearly demonstrate that 64% of allyl cations survive the derivatization while 36% isomerize to 2-phenylpropyl cations; the latter are also formed via the reaction of 2-propenyl cation with benzene, protonation of α-methylstyrene and water loss from protonated 2-phenyl-2-propanol, respectively. Unimolecular loss of C₂H₄ from protonated allylbenzene proceeds via two competing reaction channels: one involves heterolysis of 1-phenylpropyl cations (～30%); the major pathway (～70%), however, involves decomposition via propylene benzenium ions.     

Transition-metal mediated heteroatom removal by reactions of FeL+ [L=O,C4H6, c-C5H6, c-C5H5, C6H6, C5H4(=CH2)] with furan,thiophene, and pyrrole in the gas phase

Reactions of Fe⁺ and FeL⁺ [L=O, C₄H₆, c-C₅H₆, C₅H₅, C₆H₆, C₅H₄(=CH₂)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe⁺, Fe(C₅H₅)⁺, and FeC₆H ₆ ⁺ yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺], as well as FeC₅H₄(=CH₂)⁺ and FeO⁺, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC₄H₆ ⁺, Fe(c-C₅H₆)⁺, and FeC₅H₄(=CH₂)⁺. In addition, FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C₅H₆)⁺ with pyrrole and thiophene is hydrogen-atom displacement, which implies D^O(Fa(N₅H₅)⁺-C₄H₄X)>D^O(Fe(C₅H₅)⁺-H)=46±5 kcal mol^?1. D^O(Fe⁺-C₄H₄S) and D^O(Fe⁺-C₄H₅N)=D^O(Fe⁺-C₄H₆)=48±5 kcal mol^?1. Finally, 55±5 kcal mol^?1=D^O(Fe⁺-C₆H₆)>D^O(Fe⁺-C₄H₄O)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mol^?1. FeO⁺ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D^O(Fe⁺-CS)>D^O(Fe⁺-C₄H₄S)≈48±5 kcal mol^?1 and D^O(Fe⁺-C₄H₅N)≈48±5 kcal mol^?1>D^O(Fe⁺-HCN)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mil^?1.     

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3)

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.     

A metallocene-complexed dibismuthene: Cp2Zr(BiR)2 (Cp = C5H5; R = C6H3-2,6-Mes2)

The zirconocene-complexed dibismuthene, Cp2Zr(BiR)2 (Cp = C5H5; R = C6H3-2,6-Mes2), was prepared by the reaction of sodium metal with Cp2ZrCl2 and RBiCl2. The air- and moisture-sensitive dark reddish/brown compound is the first organometallic compound containing Bi-Zr bonds and the only example of a ZrBi2 ring. Moreover, our computations on associated model systems offer insight into the nature of the interaction of the heaviest dipnictene with a metallocene center.     

Structure of gas phase [C5H6]+˙ ions

Charge-stripping spectra have been used to differentiate ionized cyclopentadiene from its acyclic isomers. The minimum amounts of translational energy lost during the charge-stripping processes and the relative charge-stripping efficiencies, which are also structurally important parameters, have been measured for these ionic species. [C₅H₆]⁺˙ ions, formed by dissociative ionization of various precursors in the ion source are found, usually, to be a mixture of cyclic and acyclic ions. In contrast, [C₅H₆]⁺˙ ions, derived from the dissociation of metastable molecular ions from a series of organic compounds, have the cyclopentadienyl structure. This structure was confirmed by collision-induced dissociation of ions formed in the first field-free region of a triple sector mass spectrometer.     

A tandem mass spectrometric investigation of (C2H5)2X+ ions (X = Cl,Br, I): The involvement of classical and nonclassical ethyl structures therein

The formation of diethyl halonium ions (C₂H₅)₂X⁺ (X = Cl, Br, I) by a variety of ion-molecule reactions is described. The dissociation characteristics (metastable and collision-induced dissociation mass spectra) of these ions and their isomers were studied in detail. Some of the neutral fragmentation products were examined by their collision-induced dissociative ionization mass spectra. The participation of classical (1, CH₃CH₂X⁺CH₂CH₃) and nonclassical forms of the ions was considered. Dissociation reactions for which loss of positional identity of H-D atoms took place, for example C₂H₄ loss (a common fragmentation of metastable ions) and C₂H₅ ⁺ formation, were interpreted as involving nonclassical ions, 2. It was concluded that the ion-molecule reactions produced both ion structures, but in different halogen-dependent proportions. For (C₂H₅)₂C1⁺ ions, 2 is the major species, for (C₂H₅)₂Br⁺ both 1- and 2-type ions are generated, whereas for (C₂H₅)₂I⁺ the classical form 1 must be the predominant structure.     

m -Terphenyl derivative of titanium(III): Cp2TiR (Cp=C5H5; R =2,6-(4-MeC6H4)2C6H3)

The title compound, Cp₂TiR (Cp=C₅H₅; R=2,6-(4-MeC₆H₄)₂C₆H₃), 1, was prepared by reaction of RLi with [Cp₂TiCl]₂. Compound 1 was characterized by elemental analysis, EPR, and single crystal X-ray crystallography. The title compound crystallizes in the monoclinic space group C2/c with the following unit cell dimensions: a=11.1466(7) Å, b=16.4429(11) Å, c=13.0786(8) Å; b=106.2040(10)^°;V=2301.9(3) ų. The EPR spectrum of 1 displays two signals, a high field signal at g=1.979 and a lower field signal at g=1.959. Significantly, 1 is a sterically encumbered m-terphenyl-stabilized trivalent titanocene paramagnetic complex and may be a practical one-electron reducing reagent.     

Half-sandwich hydride complexes of ruthenium with bidentate phosphinoamine ligands: proton-transfer reactions to [(C5R5)RuH(L)] [R = H, Me; L = dippae, (R,R)-dippach

The complexes [(C5R5)RuH(dippae)] [R = H (1a), Me (2a); dippae = 1,2-bis(diisopropylphosphinoamino)ethane] and [(C5R5)RuH((R,R)-dippach)] [R = H (1b), Me (2b); (R,R)-dippach = (R,R)-1,2-bis(diisopropylphosphinoamino)cyclohexane] have been prepared and characterized. The cationic ruthenium(IV) dihydride derivatives [(C5R5)RuH2(dippae)][BPh4] [R = H (3a), Me (4a)] and [(C5R5)RuH2((R,R)-dippach)][BPh4] [R = H (3b), Me (4b)] are also reported. No significant intramolecular interaction between the amino protons and the hydrogen atoms bound to the metal has been observed in any of these compounds. The X-ray crystal structure of 4a was determined. The proton-transfer processes over the monohydrides 2a and 2b with HBF4.OEt2 have been studied by NMR spectroscopy. Dicationic dihydride complexes [CpRuH2(LH)]2+ [LH = dippaeH+ (5a), (R,R)-dippachH+ (5b)] and [Cp*RuH2(LH)]2+ [LH = dippaeH+ (6a), (R,R)-dippachH+ (6b)] result respectively from the protonation of either the monohydrides 1a,b or 2a,b or the dihydrides 3a,b or 4a,b at one of the NH groups of the phosphinoamine ligands by an excess of HBF4. These dicationic derivatives exhibit fluxional behavior in solution. In the course of the protonation of 1a with HBF4.OEt2, a cationic dihydrogen complex and a dihydrogen-bonded derivative have been identified as intermediates by NMR spectroscopy. Another dihydrogen species, namely, [CpRu(H...HOOCPh)((R,R)-dippach)], was also identified in the course of the reaction of 1b with benzoic acid in toluene-d8. The reaction of 1a with 0.5 equiv of 1,1,1,3,3,3-hexafluoroisopropanol generates a hydride species having a very short (T1)min of 6.5 ms at 400 MHz, an experimental fact for which no satisfactory explanation has yet been found.     

Über den Phosphandiyl‐Transfer von invers‐polarisierten Phosphaalkenen R1P=C(NMe2)2 (R1 = tBu,Cy, Ph,H) auf Phospheniumkomplexe [(η5‐C5H5)(CO)2M=P(R2)R3] (R2 = R3 = Ph; R2 = tBu,R3 = H; R2 = Ph,R3 = N(SiMe3)2)

Phosphanediyl Transfer from Inversely Polarized Phosphaalkenes R¹P=C(NMe₂)₂ (R¹ = tBu, Cy, Ph, H) onto Phosphenium Complexes [(η⁵‐C₅H₅)(CO)₂M=P(R²)R³] (R² = R³ = Ph; R² = tBu, R³ = H; R² = Ph, R³ = N(SiMe₃)₂) Reaction of the freshly prepared phosphenium tungsten complex [(η⁵‐C₅H₅)(CO)₂W=PPh₂] ( 3 ) with the inversely polarized phosphaalkenes RP=C(NMe₂)₂ ( 1 ) ( a : R = tBu; b : Cy; c : Ph) led to the η²‐diphosphanyl complexes ( 9a‐c ) which were isolated by column chromatography as yellow crystals in 24‐30 % yield. Similarly, phosphenium complexes [(η⁵‐C₅H₅)(CO)₂M=P(H)tBu] (M = W ( 6 ); Mo ( 8 )) were converted into (M = W ( 11 ); Mo ( 12 )) by the formal abstraction of the phosphanediyl [PtBu] from 1a . Treatment of [(η⁵‐C₅H₅)(CO)₂W=P(Ph)N(SiMe₃)₂] ( 4 ) with HP=C(NMe₂)₂ ( 1d ) gave rise to the formation of yellow crystalline ( 10 ). The products were characterized by elemental analyses and spectra (IR, ¹H, ¹³C‐, ³¹P‐NMR, MS). The molecular structure of compound 10 was elucidated by an X‐ray diffraction analysis.     

Reactivity of the inversely polarized phosphaalkenes RP=C(NMe2)2 (R = tBu, Me3Si, H) towards arylcarbene complexes [(CO)5M=C(oEt)Ar] (Ar= Ph, M = Cr, W; Ar = 2-MeC6H4, 2-MeOC6H4, M = W)

The reaction of the arylated Fischer carbene complexes [(CO)5M=C(OEt)Ar] (Ar=Ph; M = Cr, W; 2-MeC6H4; 2-MeOC6H; M = W) with the phosphaalkenes RP=C(NMe2), (R=tBu, SiMe3) afforded the novel phosphaalkene complexes [[RP=C(OEt)Ar]M(CO)5] in addition to the compounds [(RP=C(NMe2)2]M(CO)5]. Only in the case of the R = SiMe3 (E/Z) mixtures of the metathesis products were obtained. The bis(dimethylamino)methylene unit of the phosphaalkene precursor was incorporated in olefins of the type (Me2N)2C=C(OEt)(Ar). Treatment of [(CO)5W=C(OEt)(2-MeOC6H4)] with HP=C(NMe2)2 gave rise to the formation of an E/Z mixture of [[(Me2N)2CH-P=C(OEt)(2-MeOC6H4)]W(CO)5] the organophosphorus ligand of which formally results from a combination of the carbene ligand and the phosphanediyl [P-CH(NMe2)2]. The reactions reported here strongly depend on an inverse distribution of alpha-electron density in the phosphaalkene precursors (Pdelta Cdelta+), which renders these molecules powerfu] nucleophiles.     

Steric and electronic effects on the heterolytic H2‐splitting by phosphine‐boranes R3B/PR′3 (R = C6F5, Ph; R′ = C6H2Me3, tBu,Ph, C6F5, Me,H): A computational study

The steric and electronic effects exerted by the substituents R/R′ on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃ [R = C₆F₅ ( 1 ), Ph ( 2 ); R′ = C₆H₂Me₃ ( a ), tBu ( b ), Ph ( c ), C₆F₅ ( d ), Me ( e ), H ( f )] have been studied by performing quantum mechanical density functional theory and RI‐MP2 calculations. Energy decomposition analyses based on the block‐localized wavefunction method show that the nature of the interaction between R₃B and PR′₃ is strongly dependent on the B? P distance. With short B? P distances (～2.1 Å), the strength of Lewis pairs results from the balance among various energy terms, and both strong and weak dative bonds can be found in this group. However, at long B? P distances (>4.0 Å), the correlation and dispersion energy (ΔE_corr) dominates. In other words, the van der Waals (vdW) interaction rules these weakly bound complexes. No ion‐pair structures of 1f and 2c – 2f can be located as they instantly converge to vdW complexes R₃B···H₂···PR′₃. We thus propose a model, which predicts that when the sum (E_hp) of the hydride affinity (HA) of BR₃ and the proton affinity (PA) of PR′₃ is higher than 340.0 kcal/mol, the ion‐pair [R₃BH^?][HPR′] can be observed, whereas with E_hp below this value, the ion pair would instantly undergo the combination of proton and hydride with the release of H₂. The overall reaction energies ( 1a – 1e and 2a – 2b ) can be best described by a fitting equation with HA(BR₃), PA(PR′₃), and the binding energy ΔE_b(BR₃/PR′₃) as predictor variables: ΔE_R([R₃BH^?][HPR′]) = ?0.779HA(BR₃) ? 0.695PA(PR′₃) ? 1.331 ΔE (BR₃/PR′₃) + 245.3 kcal/mol. The fitting equation provides quantitative insights into the steric and electronic effects on the thermodynamic aspects of the heterolytic H₂‐splitting reactions. The electronic effects are reflected by HA(BR₃) and PA(PR′₃), and ΔE_b can be significantly influenced by the steric overcrowding. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

气相中二氯苯的双电荷离子[C6H4CI2]^2+和[C6H3CI]^2+的动能谱研究

本文利用质量分析离子动能(MIKES)和碰撞诱导解离(CID)技术, 研究了邻、间、对二氯苯分子在电子轰击质谱(EIMS)中产生的[C6H4CI2]^2+和[C6H4CI]^2+双电荷离子的单分子电荷分离(CS)反应。根据测定和CS反应的动能释放值T和由此估算的反应过渡态的电荷间距的最小值R, 推测过渡态的结构。有趣的是, 可以利用双电荷离子[C6H4CI2]^2+的分解反应区分二氯苯的位置异构体。     

Structure and Bonding in Stannadiphospholes and their Dianions SnC2P2R2m (R=H,tBu m=0, −2): A Comparative Study with C5H5+ and C5H5− Analogues

The potential energy surfaces of both neutral and dianionic SnC₂P₂R₂ (R=H, tBu) ring systems have been explored at the B3PW91/LANL2DZ (Sn) and 6‐311+G* (other atoms) level. In the neutral isomers the global minimum is a nido structure in which a 1,2‐diphosphocyclobutadiene ring (1,2‐DPCB) is capped by the Sn. Interestingly, the structure established by X‐ray diffraction analysis, for R=tBu, is a 1,3‐DPCB ring capped by Sn and it is 2.4 kcal mol^?1 higher in energy than the 1,2‐DPCB ring isomer. This is possibly related to the kinetic stability of the 1,3‐DPCB ring, which might originate from the synthetic precursor ZrCp₂tBu₂C₂P₂. In the case of the dianionic isomers we observe only a 6π‐electron aromatic structure as the global minimum, similarly to the cases of our previously reported results with other types of heterodiphospholes. 1 , 4 , 19 The existence of large numbers of cluster‐type isomers in neutral and 6π‐planar structures in the dianions SnC₂P₂R₂^2? (R=H, tBu) is due to 3D aromaticity in neutral clusters and to 2D π aromaticity of the dianionic rings. Relative energies of positional isomers mainly depend on: 1) the valency and coordination number of the Sn centre, 2) individual bond strengths, and 3) the steric effect of tBu groups. A comparison of neutral stannadiphospholes with other structurally related C₅H₅⁺ analogues indicates that Sn might be a better isolobal analogue to P⁺ than to BH or CH⁺. The variation in global minima in these C₅H₅⁺ analogues is due to characteristic features such as 1) the different valencies of C, B, P and Sn, 2) the electron deficiency of B, 3) weaker pπ–pπ bonding by P and Sn atoms, and 4) the tendency of electropositive elements to donate electrons to nido clusters. Unlike the C₅H₅⁺ systems, all C₅H₅^? analogues have 6π‐planar aromatic structures as global minima. The differences in the relative ordering of the positional isomers and ligating properties are significant and depend on 1) the nature of the π orbitals involved, and 2) effective overlap of orbitals.     

Evolved gas analysis of Ti(C5H5)2Cl2 by means of Li+ ion attachment mass spectrometry

Characterization of the compound Ti(C(5)H(5))(2)Cl(2) was studied using Li(+) ion attachment mass spectrometry (IAMS) as an analytical methodology. Since this target compound is used as an anticancer drug in the treatment of leukemia, accurate and rapid monitoring methods for the determination of titanium drugs in a hospital environment are desirable. A quadrupole mass spectrometry system along with a Li(+) ion attachment technique and a direct inlet probe (DIP) produced the Li(+) adduct of Ti(C(5)H(5))(2)Cl(2), Ti(C(5)H(5))(2)Cl(2)Li(+). The DIP also was used to study the temperature-resolved behavior of this compound. The slope of the plot of signal intensity of Ti(C(5)H(5))(2)Cl(2)Li(+) versus temperature for Ti(C(5)H(5))(2)Cl(2) sublimation from 60 to 100 °C was used to determine an apparent activation energy (E(a)) of 124.43 kJ/mol for the sublimation of Ti(C(5)H(5))(2)Cl(2). This value is comparable to the reported value of 118.8 kJ/mol for molar enthalpy of sublimation of Ti(C(5)H(5))(2)Cl(2). These results demonstrate that the IAMS methodology can be used to study the enthalpy of sublimation for d-metal complex materials.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

Electrosynthesis of Rh2(dpf)4(R) where dpf = N,N'-diphenylformamidinate anion and R = CH3, C2H5, C3H7, C4H9 or C5H11

The electrosynthesis of Rh(2)(dpf)(4)(R) where dpf is the N,N'-diphenylformamidinate anion and R = CH(3), C(2)H(5), C(3)H(7), C(4)H(9) or C(5)H(11) was carried out in THF containing 0.2 M tetra-n-butylammonium perchlorate (TBAP) and one of several alkyl iodides represented as RI. The initial step in the reaction involved a one-electron reduction of the Rh(2)(4+) unit in Rh(2)(dpf)(4) to its Rh(2)(3+) form followed by a homogeneous reaction involving electrogenerated [Rh(2)(dpf)(4)](-) and the alkyl iodide in solution to give Rh(2)(dpf)(4)(R). The homogeneously generated Rh(2)(5+) product was then immediately reduced by a second electron at the potential where [Rh(2)(dpf)(4)(R)](-) is generated, giving [Rh(2)(dpf)(4)(R)](-) which contains a Rh(2)(4+) center as a final product of an electrochemical ECE mechanism. The electrosynthesized [Rh(2)(dpf)(4)(CH(3))](-) derivative could be reoxidized to Rh(2)(dpf)(4)(CH(3)) on the reverse potential sweep and both forms of the CH(3) bonded derivative were in situ characterized by cyclic voltammetry combined with UV-visible and/or ESR spectroscopy. The reversible Rh(2)(4+/3+) process of Rh(2)(dpf)(4) is located at E(1/2) = -1.11 V in THF, 0.2 M TBAP while the electrogenerated Rh(2)(dpf)(4)(R) products are substantially easier to reduce, with E(p) values for the Rh(2)(5+/4+) couples ranging from -0.50 to -0.54 V vs. SCE depending upon the specific R group.