Tetrafluorobenzobarrelene Research Articles

Chiral NHC-Iridium Complexes and Their Performance in Enantioselective Intramolecular Hydroamination and Ring-Opening Amination Reactions

A series of chiral N-heterocyclic carbene (NHC)-iridium complexes of general formula [(NHC*)Ir(diene)Cl] bearing TFB (tetrafluorobenzobarrelene), TCB (tetrachlorobenzobarrelene), BB (benzobarrelene), and COD (cyclooctadiene) as diene ligands were synthesized and fully characterized. Chiral NHC ligands used were of the type previously reported from our group, with backbone stereocenters as well as axial chirality present. The cationic NHC-iridium complexes [(NHC*)Ir(diene)][PF6] were obtained via chloride abstraction from [(NHC*)Ir(diene)Cl] with AgPF6. X-ray crystallographic data for some of the neutral and cationic complexes were obtained and analyzed. The topographic steric bulk of the chiral NHC ligands was calculated using the SambVca 2.0 program. While attempting to get a single crystal of the unstable (Ra,Ra,S,S)-[(DiPh-2-SICyoctNap)Ir(BB)][PF6] complex, a decomposition product with an unexpected pincer-type NHC*-diene ligand was obtained. The series of chiral cationic NHC-iridium complexes were eit...

Racemic NHC–Iridium Complexes with Electron-Poor Diene Ligands and Their Reactivity in the Intramolecular Hydroamination Reaction

TFB (tetrafluorobenzobarrelene), TCB (tetrachlorobenzobarrelene), and BB (benzobarrelene) are introduced as alternative diene ligands to COD (1,5-cyclooctadiene) for NHC–iridium complexes of the ge...

Dihydrido and Trihydrido Diolefin Complexes Stabilized by the Os(PiPr3)2 Unit: New Examples of Quantum Mechanical Exchange Coupling in Trihydrido Osmium Compounds

The hexahydrido complex OsH6(PiPr3)2 (1) reacts with tetrafluorobenzobarrelene (TFB), 2,5-norbornadiene (NBD), and 1,3-cyclohexadiene to afford OsH2(η4-TFB)(PiPr3)2 (2), OsH2(η4-NBD)(PiPr3)2 (3), and OsH2(η4-cyclohexadiene)(PiPr3)2 (4), respectively. The protonation of 2 and 3 with HBF4 yields [OsH3(η4-TFB)(PiPr3)2]BF4 (5) and [OsH3(η4-NBD)(PiPr3)2]BF4 (6). The 1H NMR spectra of 5 and 6 in the hydrido region at low temperature display AM2X2 spin systems (X = 31P), which are simplified to AM2 spin systems in the 1H{31P} spectra. The values for JAM are temperature dependent, increasing from 13.1 to 35.9 Hz (5) and from 11.0 to 17.7 Hz (6) as temperature is increased from 190 to 230 K and from 180 to 240 K, respectively. The reaction of 4 with HBF4 leads to the cyclohexenyl complex [OsH2(η3-C6H9)(PiPr3)2]BF4 (7), which shows an agostic interaction between the osmium center and one of the two endo-CH bonds adjacent to the π-allyl unit. In solution complex 7 is fluxional. The fluxional process involves the exchange between the relative positions of the hydrido ligands and the endo-CH hydrogen atoms of the cyclohexenyl ligand and, at the same time, the exchange between the CH allyl and the exo-CH hydrogen atoms inside the cyclohexenyl ligand. The structure of 7 in the solid state has been determined by X-ray diffraction. The distribution of ligands around the osmium atom can be described as a piano stool geometry with the agostic hydrogen atom and the midpoints of the carbon−carbon bonds involved in the π-allyl unit forming the three-membered face, while both the hydrido and phosphine ligands lie in the four-membered face.

Reactivity of OsH2Cl2(PiPr3)2toward Diolefins: New Reactions Involving C−H and C−C Activation and C−C and C−P Bond Formation Processes

The dihydrido-dichloro complex OsH2Cl2(PiPr3)2 (1) reacts with 1,5-cyclooctadiene in toluene under reflux to give the isopropenylphosphine derivative OsCl2(η4-COD){[η2-CH2C(CH3)]PiPr2} (2), which has been characterized by X-ray diffraction analysis. The coordination geometry around the osmium atom of 2 can be rationalized as a highly distorted octahedron. The distortion is due to the ring constraint imposed by the bidentate isopropenylphosphine ligand, which acts with a bite angle of 56.0(1)°. In toluene at 85 °C, the reaction of 1 with 1,5-cyclooctadiene leads to the hydrido compound OsHCl2(η4-C8H11PiPr3)(PiPr3) (3). The molecular structure of this complex has also been determined by an X-ray investigation. The X-ray diffraction analysis of 3 demonstrates the η4-binding mode of the carbocyclic ligand [C8H11PiPr3]+. The coordination geometry around the osmium center can be rationalized as a distorted octahedron with the triisopropylphosphine, a chlorine atom, and the carbocyclic ligand forming the equatorial plane. Complex 3 reacts with 1,5-cyclooctadiene and 2,5-norbornadiene (NBD) to give 2 and OsCl2(η4-NBD){[η2-CH2C(CH3)]PiPr2} (8), respectively. Complex 8 can also be obtained, under refluxing toluene, from 1 and 2,5-norbornadiene. Similarly, the reaction of 1 with tetrafluorobenzobarrelene (TFB) affords a mixture of the propenylphosphine isomers OsCl2(η4-TFB){(η2-CH2CHCH2)PiPr2} (9) and OsCl2(η4-TFB){[η2-CH2C(CH3)]PiPr2} (10), which can also be prepared from 3 and tetrafluorobenzobarrelene. The molecular structure of 9 has been determined by X-ray diffraction analysis. The coordination geometry around the osmium can be described as a distorted octahedron, and as for 2, the distortion is mainly due to the ring constraint imposed by the bidentate olefin−phosphine ligand, which in this case acts with a bite angle of 74.8(1)°.

Dinuclear rhodium-rhodium and rhodium-palladium complexes with different bridging ligands. Crystal structure of [Rh 2(μ-SPPh 2)(μ-Cl)(COD) 2

Homo- and hetero-dinuclear complexes of general formulae [Rh 2(μ-SPPh 2)(μ-Cl)(diolefin) 2] (diolefin = 1,5-cyclooctadiene (CO (1), tetrafluorobenzobarrelene (TFB) (2)) and [RhPd( μ-SPPh 2)( μ-Cl)(diolefin) η 3-C 3H 5)] (diolefin = COD (4), 2,5-norbornadiene (NBD) (5)), containing one chloride anion and one thiophosphinito group as bridging ligands, have been synthesised by redistribution reactions starting from the corresponding homo-bridged compounds [Rh 2(μ-SPPh 2) 2(diolefin) 2, [Rh 2(μ-Cl) 2(diolefin) 2] or [Pd 2( μ-Cl) 2( η 3-C 3H 5) 2]. The structural X-ray analysis carried out for one member of this series, [Rh 2(μ-SPPh 2)(μ-Cl)(COD) 2], has shown the bridging P, S-coordination of the thiophosphinito ligand. The intermetallic separation, 3.291(2) Å, excludes any significant direct metal-metal interaction.

Hydrosilylation of phenylacetylene catalyzed by [Ir(COD)( η2- iPr 2PCH 2CH 2OMe)][BF 4

In the presence of the complexes [Ir(diolefin)( η 2- iPr 2PCH 2CH 2NMe 2)][BF 4] (diolefin = 1,5-cyclooctadiene (COD) ( 1) or tetrafluorobenzobarrelene (TFB) ( 2)) and [Ir(diolefin)( η 2- iPr 2PCH 2CH 2OMe)][BF 4] (diolefin = COD ( 3) or TFB ( 4)), phenylacetylene undergoes reaction with triethylsilane. In all experiments carried out PhCHCH 2, PhCCSiEt 3, cis-PhCHCH(SiEt 3), trans-PhCHCH(SiEt 3) and Ph(SiEt 3)CCH 2 were obtained. An investigation in detail for the catalyst 3 suggests that, under catalytic conditions, the complexes [IrH(C 2Ph)(COD)( η 2- iPr 2PCH 2CH 2OMe)]BF 4 ( 5) and [IrH(SiEt 3)(COD)( η 2- iPr 2PCH 2CH 2OMe)]BF 4 ( 6) are formed. Complex 5 is the key intermediate for the formation of PhCCSiEt 3, while 6 is the species leading to cis-PhCHCH(SiEt 3). The isomer trans-PhChCH(SiEt) 3) is formed by isomerization of cis-PhCHCH(SiEt 3). The mechanisms of formation of these compounds are discussed.

Heteronuclear and heterovalent diphenylphosphido-bridged complexes of rhodium, iridium and ruthenium. Crystal structure of [(C 5Me 5)ClRh(μ-Cl)(μ-PPh 2)Rh(COD)] · [formula omitted]Et 2O (COD = 1,5-cyclooctadiene)

Mononuclear complexes of formulae [LMCl 2(HPRR′)], [LCMl(HPR 2) 2]BF 4 and [LM(acac)(HPR 2)]BF 4 (M = Rh, Ir; L = C 5Me 5. M = Ru; L = p-Cymene; R = Ph, H; R′ = H; Hacac = acetylacetone, but not in all possible combinations) have been prepared from the corresponding [{(LMCl} 2(μ-Cl) 2] or [LMCl(acac)] and HPRR′. Complexes [LMCl 2(HPPh 2)] [L = C 5Me 5; M = Rh (I), Ir (IV), L = p-Cymene; M = Ru (VII)] react with [M′(μ-OMe)(diolefin)] 2 (M′ = Rh; diolefin = tetrafluorobenzobarrelene (TFB), 1,5-cyclooctadiene (COD). M′ = Ir; diolefin = COD) to yield diphenylphosphido-bridged complexes of formula [LMCl 2(μ-PPh 2)M′(diolefin)]. The structure of [(C 5Me 5)ClRh(μ-Cl)(μ-PPh 2)Rh(COD)]· 1 2 Et 2O has been determined by X-ray diffraction methods. The complex consists of two moieties. (C 5Me 5)RhCl and Rh(COD), doubly-bridged by a diphenylphosphido group and a chlorine atom. The two rhodium atoms are separated by 3.3657(6) Å.

Synthesis and catalytic activity of heterodinuclear Ru-Ir and Ru-Rh complexes. Crystal structure of [H(CO)(PPh 3) 2Ru(μ-Cl)(μ-pz)Ir(TFB)] (pz = pyrazolate, TFB = tetrafluorobenzobarrelene)

Reactions of the ruthenium compounds [RuHCl(CO)(PR 3) n ] (R = Ph, n = 3; R = iPr, n = 2) with pyrazole C 3H 4N 2 (Hpz) give the complexes [RuHCl(CO)(Hpz)(PR 3) 2]. Treatment of these complexes with a hydrogen abstractor (methoxide ion or acetylacetonate (acac)), such as [M(μ-OMe)(diolefin)] 2 (M = Ir, Rh; diolefin = cycloocta-1,5-diene (COD), tetrafluorobenzobarrelene (TFB)) or [Pd(acac)(η 3-C 3H 5)] has given the heterobinuclear complexes [H(CO)(PR 3) 2Ru(μ-Cl)(μ-pz)ML 2] (R = Ph; M = Ir or Rh, L 2 = COD or TFB; R = iPr, M = Rh, L 2 = TFB; R = Ph, M = Pd, L 2 = C 3H 5). The structure of [H(CO)(PPh 3) 2Ru(μ-Cl)(μ-pz)Ir(TFB)] has been established by an X-ray diffraction study. The species is binuclear, with a pyrazolate group and a chlorine atom as bridging ligands. The intermetallic separation is 3.8907(6) Å. The reduction of cyclohexanone by hydrogen transfer from isopropanol catalyzed by [H(CO)(PPh 3) 2Ru(μ-Cl)(μ-pz)M(diolefin)] (M = Ir, Rh; diolefin = COD, TFB) is also reported.

Preparation of IrH(diene)L 2 compounds via methoxyiridium complexes: Catalysts for hydrogen transfer reactions

Hydrido-diene complexes of general formula IrH(diene)L 2 (diene = tetrafluorobenzobarrelene (TFB), 1,5-cyclooctadiene (COD); L = PPh 3; L 2 = bis(1,2-diphenylphosphino)ethane (dppe), bis(1,3-diphenylphosphino)propane (dppp)) have been obtained by decomposition of methoxyiridium complexes. The related IrH(diene)(AsPh 3) 2 complexes have been prepared from iridium chloro-diene compounds. The catalytic activity of IrH(COD)L 2 complexes in hydrogen transfer reactions from alcohols to cyclohexanone is described.

Fluorinated barrelene-ruthenium(II) complexes with anionic chelating ligands

Reaction of ruthenium(III) chloride with the barrelene diolefins (tetrafluoro-benzobarrelene (TFB) or (trimethyltetrafluorobenzobarrelene) (Me 3 TFB) leads to the formation of the polymeric complexes [RuCl 2(barrelene)] n . These compounds react with anionic chelating ligands with formation of new hexacoordinated neutral complexes of the general formulae [Rh(chelate) 2(barrelene)], where chelate = acetylacetonate, tropolonate, salicylal-dehydate and 8-oxyquinolinate. The IR and 1H NMR spectra of the complexes are given and discussed.

Dinuclear rhodium(I) compounds containing diolefins and the 1,6-bis(2′-benzimidazolyl)-2,5-dithiahexane ligand

The reactions of 1,6-bis(2′-benzimidazolyl)-2,5- dithiahexane (LH 2) with [RhCl(diolefin)] 2 and with [Rh(diolefin) 2] + yield dinuclear compounds of formula [Rh 2Cl 2(diolefin) 2(LH) 2)] and [Rh 2- (diolefin) 2(LH 2) 2] 2+ respectively. Used diolefins are tetrafluorobenzobarrelene (TFB) and cyclooctadiene (COD). The dinuclear nature has been established by spectroscopic methods and molecular weight determinations. Addition of triethylamine to [Rh 2CI 2(TFB) 2− (LH 2)] results in the formation of [Rh 2(L)(TFB) 2] 2. This latter compound reacts with [Au(PPh 3)(Me 2CO)][ClO 4] to yield the polynuclear species [Rh 2(L)(TFB) 2[Au(PPh 3) 2] n[ClO 4] 2n. The ligand LH 2 coordinates through its imidazole nitrogens to the RH ions, whereas the thioether S-atoms are coordinating to the Au ions, as deduced from spectroscopic measurements.

Durene-rhodium(I) complexes. Crystal structures of the complexes [Rh(durene)(diolefin)]ClO 4 (diolefin  tetrafluorobenzobarrelene or trimethyltetrafluorobenzobarrelene)

The crystal structures of [Rh(durene)(diolefin)ClO 4 (diolefin  tetrafluorobenzobarrelene (TFB) and trimethyltetrafluorobenzobarrelene (Me 3TFB)) have been solved by standard X-ray single crystal methods. The compounds crystallize in the space groups R 3 c for the unmethylated TFB compound and P2 1/ n for the methylated one. The cell dimensions are 25.7586(5), 17.0059(4) Å and 12.6686(6), 11.5565(3), 16.7269(8) Å, β  104.023(5)°, respectively. The refinement was taken to R values of 0.04 and 0.06, respectively. The arene in the TFB derivative has a distorted inverted boat conformation which becomes a skew one in the Me 3TFB compound. These puckering seems to be related to the tendency of rhodium(I) to achieve square-planar coordination.