Intramolecular C-H oxidative addition to iridium(i) triggered by trimethyl phosphite in N, N'-diphosphanesilanediamine complexes

The reaction of Ir(SiNP)(cod)]PF6] (1]PF6]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2) with trimethyl phosphite affords the iridium(iii) derivatives of the formula IrHClx(SiNP-H){P(OMe)3}2-x](1-x)+ (x = 0, 3+; x = 1, 6) containing the ¿3C, P, P'-coordinated SiNP-H ligand (SiNP-H = Si(CH2)(CH3){N(4-C6H4CH3)PPh2}2). The thermally unstable pentacoordinated cation Ir(SiNP){P(OMe)3}(cod)]+ (2+) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula IrClx(SiNP){P(OMe)3}2-x](1-x)+ (x = 0, 4+; x = 1, 7) should be firstly obtained from 2+ and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2+ on the outcome of the C-H oxidative addition reaction has also been investigated

Divergent reactivity of 2-vinylpyridine and 1-vinylpyrazole in rhodium-phosphine systems: C-H activation and dinuclear chemistry

The Rh-I-Rh-III mixed valence dinuclear complex Rh-2-Cl-2(mu-H)(mu-eta(2),kappa(2)-C, N-NC5H4-2-(Z)CH=CH)( PPhMe2)(3) has been prepared by reaction of [Rh(mu-Cl)(eta(2)-coe)(2)](2) with 2-vinylpyridine in the presence of dimethylphenylphosphine as a result of C-H activation of the terminal olefinic proton. The X- ray structure presents anagostic Rh center dot center dot center dot HC and pi-pi interactions between aromatic rings. In contrast, 1-vinylpyrazole does not undergo a C-H activation process, resulting in the formation of dinuclear species supported by 1 vinylpyrazole bridges. Anagostic Rh center dot center dot center dot HC interactions and CH center dot center dot center dot Cl hydrogen bonds are responsible for the 3D packing of the complex. El complejo dinuclear de valencia mixta RhI-RhIII Rh2-Cl2(µ-H)(µ-¿2,¿2-C,N-NC5H4-2-(Z)CH=CH)(PPhMe2)3 ha sido preparado por reacción de [Rh(µ-Cl)(¿2-coe)2]2 con 2-vinilpiridina en presencia de dimetilfenilfosfina, como resultado de la activación C-H del protón terminal de la olefina. La estructura de rayos-X presenta enlaces anagósticos Rh···HC, así como interacciones p-p entre anillos aromáticos. Por otro lado, la reacción con 1-vinilpirazol no da lugar a una activación C-H sino que se observa la formación de una especie dinuclear soportada por ligandos 1-vinilpirazol puente. Diferentes interacciones anagósticas Rh···HC y de enlace de hidrógeno CH···Cl son responsables del empaquetamiento tridimensional del complejo

Hydroformylation of synthetic naphtha catalyzed by a dinuclear gem-dithiolato-bridged rhodium(I) complex

This work focuses on the use of a gem-dithiolato-bridged rhodium(I) Rh 2(µ-S 2CBn 2)(cod) 2 complex (cod = 1,5-cyclooctadiene, Bn 2CS 2 2- = 1,3-diphenyl-2,2-dithiolatopropane) dissolved in toluene in the presence of monodentate phosphite P-donor ligand (P(OPh) 3) under carbon monoxide/hydrogen (1:1, syngas) atmosphere as an effective catalyst for hydroformylation of some olefins (oxo-reactions). The capability of this system to catalyze the hydroformylation of hex-1-ene, cyclohexene, 2,3-dimethyl-but-1-ene and 2-methyl-pent-2-ene and their quaternary mixture (synthetic naphtha) has been demonstrated. This innovative method to perform the in situ hydroformylation of the olefins present in naphthas to oxygenated products would be a promissory work for a future industrial catalytic process applicable to gasoline improving based on oxo-reactions. An important observation is that variation of CO/H 2 pressure (6.8-34.0 atm), temperature (60-80 oC), reaction time (2-10 h), rhodium concentration ((1.0-1.8)x10 -3 mol/L) affect hydroformylation reaction rates. Optimal conversion to oxygenated products were achieved under Rh = 1.8 x10 -2 mol/L, P(CO/H 2) = 34 atm (CO/H 2 = 1:1) at 80 oC for 10 h

Iridium(i) complexes bearing hemilabile coumarin-functionalised N-heterocyclic carbene ligands with application as alkyne hydrosilylation catalysts

A set of iridium(i) complexes of formula IrCl(¿C, ¿2-IRCouR')(cod) or IrCl(¿C, ¿2-BzIRCouR')(cod) (cod = 1, 5-cyclooctadiene; Cou = coumarin; I = imidazolin-2-carbene; BzI = benzimidazolin-2-carbene) have beeen prepared from the corresponding azolium salt and [Ir(µ-OMe)(cod)]2 in THF at room temperature. The crystalline structures of 4b and 5b show a distorted trigonal bipyramidal configuration in the solid state with a coordinated coumarin moiety. In contrast, an equilibrium between this pentacoordinated structure and the related square planar isomer is observed in solution as a consequence of the hemilability of the pyrone ring. Characterization of both species by NMR was achieved at the low and high temperature limits, respectively. In addition, the thermodynamic parameters of the equilibrium, ¿HR and ¿SR, were obtained by VT 1H NMR spectroscopy and fall in the range 22-33 kJ mol-1 and 72-113 J mol-1 K-1, respectively. Carbonylation of IrCl(¿C, ¿2-BzITolCou7, 8-Me2)(cod) resulted in the formation of a bis-CO derivative showing no hemilabile behaviour. The newly synthesised complexes efficiently catalyze the hydrosilylation of alkynes at room temperature with a preference for the ß-(Z) vinylsilane isomer. © The Royal Society of Chemistry

Variation on the p-acceptor ligand within a Rhi-N-Heterocyclic carbene framework: divergent catalytic outcomes for phenylacetylene-methanol transformations

A series of neutral and cationic rhodium complexes bearing IPr {IPr=1, 3-bis-(2, 6-diisopropylphenyl)imidazolin-2-carbene} and p-acceptor ligands are reported. Cationic species [Rh(¿4-cod)(IPr)(NCCH3)]+ and [Rh(CO)(IPr)(L)2]+ (L=pyridine, CH3CN) were obtained by chlorido abstraction in suitable complexes, whereas the cod-CO derivative [Rh(¿4-cod)(IPr)(CO)]+ was formed by the carbonylation of [Rh(¿4-cod)(IPr)(NCCH3)]+. Alternatively, neutral derivatives of type RhCl(IPr)(L)2 {L=tBuNC or P(OMe)3} can be accessed from [Rh(µ-Cl)(¿2-coe)(IPr)]2. In addition, the mononuclear species Rh(CN)(¿4-cod)(IPr) was prepared by cyanide-chlorido anion exchange, which after carbonylation afforded the unusual trinuclear compound [Rh{1¿C, 2¿N-(CN)}(CO)(IPr)]3. Divergent catalytic outcomes in the phenylacetylene-methanol transformations have been observed. Thus, enol ethers, arisen from hydroalkoxylation of the alkyne, were obtained with neutral Rh-CO catalyst precursors whereas dienol ethers were formed with cationic catalysts. Variable amounts of alkyne dimerization, cyclotrimerization or polymerization products were obtained in the absence of a strong p-acceptor ligand on the catalyst. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH Gmb

Preparation of Butadienylpyridines by Iridium-NHC-Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement

Iridium(I) N-heterocyclic carbene complexes of formula Ir(¿2O, O’-BHetA)(IPr)(¿2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1, 3-bis(2, 6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(¿2O, O’-BHetA)(¿2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(¿2O, O’-BHetA)(¿2N, C-C7H6N)(IPr) through the iridium(I) intermediate Ir(¿2O, O’-BHetA)(IPr)(¿2-C7H7N). The cyclometalated IrH(¿2O, O’-acac)(¿2N, C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z, E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z, 3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6p-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

Zwitterionic Rhodium and Iridium Complexes Based on a Carboxylate Bridge-Functionalized Bis-N-heterocyclic Carbene Ligand: Synthesis, Structure, Dynamic Behavior, and Reactivity

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp MIIICl{(MeIm)2CHCOO}] and [MI(diene){(MeIm)2CHCOO}] (Cp* = 1, 2, 3, 4, 5-pentamethylcyclopentadienyl; M = Rh, Ir; MeIm = 3-methylimidazol-2-yliden-1-yl; diene = 1, 5-cyclooctadiene (cod), norbornadiene (nbd)) were prepared from the salt [(MeImH)2CHCOO]Br and suitable metal precursor. The solid-state structure of both types of complexes shows a boat-shaped six-membered metallacycle derived of the ¿2C, C' coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp MIII complexes, whereas in the MI(diene) complexes it is at the flagpole position of the metallacycle. The complexes [RhI(diene){(MeIm)2CHCOO}] (diene = cod, nbd) exist as two conformational isomers in dichloromethane, bowsprit and flagpole, that interconvert through the boat-to-boat inversion of the metallacycle. An inversion barrier of ~17 kcal·mol-1 was determined by two-dimensional exchange spectroscopy NMR measurements for [RhI(cod){(MeIm)2CHCOO}]. Reaction of zwitterionic Cp MIII complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp MIIICl{(MeIm)2CHCOOMe}]+ or [Cp MIIICl{(MeIm)2CHCOOH}]+ (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [MI(diene){(MeIm)2CHCOOMe}]+ (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic MI(diene) complexes with methyl triflate. In contrast, reaction of [IrI(cod){(MeIm)2CHCOO}] with HBF4·Et2O (Et = ethyl), CH3OTf, CH3I, or I2 gives cationic iridium(III) octahedral complexes [IrIIIX(cod){(MeIm)2CHCOO}]+ (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from ¿2C, C' to ¿3C, C', O coordination of the bis-NHC ligand accompanying the oxidative addition prevents the coordination of the anions eventually formed in the process that remain as counterions

Synthesis of Titanium and Zirconium Complexes with 2-Pyridonate and 2, 6-Pyridinedithiolate Ligands

Treatment of complex Cp2TiCl2] with the lithium salt of 2-hydroxypyridine afforded complex Cp2Ti(Opy)2] (1), whereas the same synthetic strategy applied to the analogous zirconium compound Cp2ZrCl2] did not worked. However, the use of the metallocene Cptt 2ZrMe2] with protic ligands allowed directing the reactivity towards protonation of the methyl groups attached to zirconium. To check this approach we reacted Cptt 2ZrMe2] with methanol affording complex Cptt 2ZrMe(OMe)] (2), which was characterized in situ by NMR techniques. In the same line, the reaction of Cptt 2ZrMe2] with 2-hydroxypyridine gave complex Cptt 2Zr(Me)(Opy)] (3)//forcing the conditions of this reaction did not lead to the expected complex Cptt 2Zr(Opy)2], most probably due to the steric hindrance exerted by the bulky cyclopentadienyl ligands. Further reactions of complex 3 with ligands having acidic protons also led to the recovery of the starting complex. However, when shifting to the bifunctional ligand 2, 6-dimercaptopyridine py(SH)2] a double protonation of the methyl ligands in Cptt 2ZrMe2] occurred, allowing the isolation of mononuclear complex Cptt 2Zr(¿S, ¿S, ¿N-pyS2)] (4), upon evolution of methane. The molecular structure of complex 4 was determined by X-ray methods, showing the zirconium atom in a highly distorted trigonal bipyramidal arrangement//structural parameters indicate a conventional Zr-N bond, but rather weak Zr-S interactions

Mechanistic studies on the: N -alkylation of amines with alcohols catalysed by iridium(i) complexes with functionalised N-heterocyclic carbene ligands

Iridium(i) cyclooctadiene complexes featuring O- and N-donor functionalised NHC ligands efficiently catalyse the C-N coupling of amines with alcohols through a borrowing hydrogen mechanism. These catalysts have been applied for the N-alkylation of several aromatic and aliphatic primary amines with a range of alcohols including benzyl alcohol derivatives, straight-chain primary alcohols and secondary alcohols. The cationic complex [Ir(NCCH3)(cod){MeIm(2-methoxybenzyl)}]+ (cod = 1, 5-cyclooctadiene, MeIm = 3-methylimidazol-2-ylidene) having a rigid O-donor wingtip exhibits the best catalytic performance for the N-alkylation of aniline with benzyl alcohol giving a quantitative conversion to N-benzylaniline in 3 h. Experimental and theoretical studies at the DFT level on the N-alkylation of aniline with benzyl alcohol catalysed by the model compound [IrCl(cod)(IMe)] (IMe = 1, 3-dimethyl-imidazol-2-ylidene) support the participation of the iridium catalyst not only in the alcohol dehydrogenation and imine hydrogenation steps but also in the key step leading to the formation of the new C-N bond. Nucleophilic attack of an iridium-amido species generated in basic medium on the electrophilic aldehyde results in a hemiaminolate intermediate species from which the hemiaminal is released by alcoholysis. The free hemiaminal dehydrates to give the corresponding intermediate imine product that is hydrogenated by the iridium catalyst to the N-alkylated amine product. The iridium(i) complexes featuring functionalised NHC ligands are more active than [IrCl(cod)(IMe)] which highlights the positive influence of the functional group on the N-alkylation catalytic activity

A well-defined NHC-Ir(III) catalyst for the silylation of aromatic C-H bonds: Substrate survey and mechanistic insights

A well-defined NHC-Ir(iii) catalyst, [Ir(H)2(IPr)(py)3][BF4] (IPr = 1, 3-bis-(2, 6-diisopropylphenyl)imidazol-2-ylidene), that provides access to a wide range of aryl- and heteroaryl-silanes by intermolecular dehydrogenative C-H bond silylation has been prepared and fully characterized. The directed and non-directed functionalisation of C-H bonds has been accomplished successfully using an arene as the limiting reagent and a variety of hydrosilanes in excess, including Et3SiH, Ph2MeSiH, PhMe2SiH, Ph3SiH and (EtO)3SiH. Examples that show unexpected selectivity patterns that stem from the presence of aromatic substituents in hydrosilanes are also presented. The selective bisarylation of bis(hydrosilane)s by directed or non-directed silylation of C-H bonds is also reported herein. Theoretical calculations at the DFT level shed light on the intermediate species in the catalytic cycle and the role played by the ligand system on the Ir(iii)/Ir(i) mechanism