Dppb Ligand Research Articles

Palladium-Catalyzed Ligand-Controlled Switchable Hetero-(5 + 3)/Enantioselective [2σ+2σ] Cycloadditions of Bicyclobutanes with Vinyl Oxiranes.

For nearly 60 years, significant research efforts have been focused on developing strategies for the cycloaddition of bicyclobutanes (BCBs). However, higher-order cycloaddition and catalytic asymmetric cycloaddition of BCBs have been long-standing formidable challenges. Here, we report Pd-catalyzed ligand-controlled, tunable cycloadditions for the divergent synthesis of bridged bicyclic frameworks. The dppb ligand facilitates the formal (5+3) cycloaddition of BCBs and vinyl oxiranes, yielding valuable eight-membered ethers with bridged bicyclic scaffolds in 100% regioselectivity. The Cy-DPEphos ligand promotes selective hetero-[2σ+2σ] cycloadditions to access pharmacologically important 2-oxabicyclo[3.1.1]heptane (O-BCHeps). Furthermore, the corresponding catalytic asymmetric synthesis of O-BCHeps with 94-99% ee has been achieved using chiral (S)-DTBM-Segphos, representing the first catalytic asymmetric cross-dimerization of two strained rings. The obtained O-BCHeps are promising bioisosteres for ortho-substituted benzenes.

Supramolecularly Dimeric Assemble of Planar Cu13 Clusters Controlled by the Length of Spacers of Diphosphine.

The controlled formation of dimeric clusters is challenging. Three copper(I) clusters, labeled as {Cu13[o-Ph(C≡C)2]6(L)4}(ClO4), were synthesized by using three different ligands, including 1,4-bis(diphenylphosphino)butane (dppb), 1,5-bis(diphenylphosphino)pentane (dpppe), and bis(diphenylphosphino)hexane (dpph). By increasing the flexibility of alkyl spacers in the diphosphine ligands, the relative positions of the phenyl rings could be optimized to achieve efficient packing with maximized intercluster interactions. In the crystal structures, cluster 1 with dppb ligands did not display interlocked structures. In contrast, cluster 2 with dpppe ligands formed supramolecularly interlocked polymers through weak π-π interactions and C-H···π interactions, while cluster 3 employing dpph ligands formed supramolecularly interlocked dimers with strong π-π interactions and C-H···π interactions. The supramolecular dimer of 3 was also evidenced by analyses through electrospray ionization mass spectrometry and transmission electron microscopy. Density functional theory calculation was used to understand the electronic structure and transitions. Supramolecularly interlocked polymers/dimers with rigid structures exhibited higher quantum efficiency. The solution of these clusters demonstrated remarkable aggregation-induced emission enhancements. This study presents unique examples of planar luminescent copper clusters, featuring the first serial dialkynyl-protected cluster. It underlines the importance of ligand flexibility in creating supramolecular cluster dimers.

Uniform Gold Nanoclusters Supported on Mesoporous Polymer Beads Decorated with Polyaminophosphine Patches for the Catalytic Reduction of 4-Nitrophenol

In the jigsaw puzzle of quality gold nanoclusters (AuNCs), those protected by weak ligands or coligands are still rarely available. Here, we provide an example in the case of supported AuNCs. Branched polyethylenimine (PEI, diameter of 1.86 nm) is introduced as discrete molecular patches onto the support of mesoporous polymer beads. Each patch is derived into polyaminophosphine with 2-(diphenylphosphino) benzaldehyde (dppb). The molecular patch is of nanoscale and uniform size. The polymer beads after PEI loading bear unimodal pores (3.9 nm), and the specific surface area is of 390 m2 g–1. AuNCs are obtained by mildly heating the mixture of the functionalized beads and aqueous chloroauric acids. Uniform AuNCs with a diameter of 1.2 ± 0.2 nm (∼53 Au atoms) are obtained when each PEI patch bears 17 dppb ligands, smaller than that of 3.5 nm in the absence of any dppb, suggesting that dppb enhances the nucleation of AuNCs. The heteroleptic AuNCs show ultrahigh catalytic performance (TOF = 391 h–1) for the reduction of 4-nitrophenol, where the dppb ligands hardly suppress the catalytic activity. The catalyst is well recoverable and durable for the reduction of 4-nitrophenol.

Reactions of D2 with 1,4‐Bis(diphenylphosphino) butane‐Stabilized Metal Nanoparticles‐A Combined Gas‐phase NMR, GC‐MS and Solid‐state NMR Study

AbstractThe reactions of three metal nanoparticle (MNP) systems Ru/dppb, RuPt/dppb, Pt/dppb (dppb=1,4‐bis(diphenylphosphino)butane) with gaseous D2 at room temperature and different gas pressures have been studied using 1H gas phase NMR, GC‐MS and solid state 13C and 31P MAS NMR. The main product is gaseous HD arising from the reaction of D2 with surface hydrogen sites created during the synthesis of the nanoparticles. In a side reaction, some of the dppb ligands are decomposed producing surface phosphorus species and gaseous partially deuterated butane and cyclohexane. These findings are fundamental for detailed studies of the reaction kinetics of these particles towards H2 or D2 gas.

Diverse Tp*-Capped W-Cu-S Clusters from One-Pot Assembly Involving in Situ Thiolation of Phosphines.

In the absence/presence of S8, the one-pot assembly of [Et4N][Tp*WS3] [1; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate] with [Cu(MeCN)4]PF6 and bis- or tetraphosphine ligands 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb), and N,N,N',N'-tetrakis(diphenylphosphinomethyl)ethylenediamine (dppeda) produces six W-Cu-S clusters, namely, [(Tp*WS3Cu2Cl)2(dppe)] (2), [Tp*WS3Cu4(dppp)2(μ4-Cl)(μ-Cl)]PF6·MeCN (3·MeCN), [(Tp*WS3Cu3)2(μ4-Cl)(μ-Cl)2(dpppS2)] (4), [(Tp*WS3Cu2Cl)2(dppbS2)]·2MeCN·2H2O (5·2MeCN·2H2O), [(Tp*WS3Cu3Cl2)2(dppbS2)] (6), and [(Tp*WS3Cu3)2(Ph2PS2)3(μ6-Cl)0.5](PF6)0.5·0.75CH2Cl2 (7·0.75CH2Cl2). Compounds 2-7 are characterized by elemental analysis, IR, UV-vis, (1)H and (31)P{(1)H} NMR, electrospray ionization mass spectrometry, and X-ray crystallography. For 2, the dppe ligand bridges a pair of butterfly-shaped [Tp*WS3Cu2] cores to form a double-butterfly-shaped structure. For 4, the dppp ligand is susceptible toward S association and forms an in situ generated dpppS2 ligand, supporting an octanuclear double-half-open-cubane structure and contrasting an analogous system wherein a pentanuclear motorcycle-shaped cationic cluster 3 is formed with the absence of S8. A longer dppb ligand readily converts to S-based ligands in 5 and 6, subsequently serving as bridges between a pair of a butterfly-shaped (5) and nest-shaped (6) clusters. Further use of a tetraphosphine ligand, dppeda, in the cluster formation, with the presence of S8, leads to an unexpected ligand degradation to give the [Ph2PS2](-) anions. Three [Ph2PS2](-) anions juxtapose a pair of nest-shaped cluster cores to yield an octanuclear cluster, 7, featuring a cage to encapsulate μ6-Cl(-). The third-order nonlinear-optical (NLO) properties of 2-7 in N,N-dimethylformamide, investigated using a Z-scan technique at 532 nm, show that 2-6 have a reverse saturable absorption, while 7 has a notable saturable absorption. All of 2-7 exhibit a self-focusing effect with hyperpolarizability γ values in the range of 4.71 × 10(-30)-1.02 × 10(-29) esu, which are 440-1000 times higher than that of 1. The formation of 4-7 from 1 through the in situ thiolation of phosphine ligands presents a new approach to the design and assembly of the W-Cu-S clusters with interesting structural arrays and better NLO properties.

Mechanistic Study on Ligand-Controlled Rh(I)-Catalyzed Coupling Reaction of Alkene-Benzocyclobutenone

Recently, Dong’s group [Angew. Chem., Int. Ed. 2012, 51, 7567–7571; Angew. Chem., Int. Ed. 2014, 53, 1891–1895] reported the ligand-controlled selectivity of Rh-catalyzed intramolecular coupling reaction of alkene-benzocyclobutenone: the direct coupling product (i.e., fused-rings) was formed in the DPPB-assisted system (DPPB = PPh2(CH2)4PPh2), while the decarbonylative coupling product (i.e., spirocycles) was generated in the P(C6F5)3-assited system. To explain this interesting selectivity, density functional theory (DFT) calculations have been carried out in the present study. It was found that the direct and decarbonylative couplings experience the same C(acyl)–C(sp2) activation and alkene insertion steps. The following C–C reductive elimination or β-H elimination–decarbonylation–reductive elimination leads to the direct or decarbonylative coupling reaction, respectively. The coordination features of different ligands were found to significantly influence C–C reductive elimination and decarbonylation step. The requisite phosphine dissociation of DPPB ligand from Rh center for the decarbonylation step is disfavored, and thus, the reductive elimination and direct coupling reaction are favored therein. By contrast, a free coordination site is available on the Rh center in the P(C6F5)3-assisted system, facilitating the decarbonylation process together with the generation of related decarbonylative coupling product.

Nickel(II) thiolates derived from transmetallation reaction of [Zn(Tab)4](PF6)2 with Ni(II) ions and their catalytic activity toward the C[sbnd]N coupling reactions

Reactions of NiCl2·6H2O or Ni(ClO4)2·6H2O with 2,2′-bipyridine (2,2′-bipy), or 2-bis(diphenylphosphino)ethane (dppe) or 1,4-bis(diphenylphosphino)butane (dppb) followed by addition of [Zn(Tab)4](PF6)2 (1) resulted in the formation of one trinuclear cationic complex [(2,2′-bipy)4Ni3(μ-Tab)4]Cl0.5(PF6)5.5 (2), one mononuclear cationic complex [Ni(Tab)2(dppe)](PF6)2 (3), and one dinuclear cationic complex [Ni2(dppb)(μ-Tab)2(Tab)2](PF6)2(ClO4)2 (4). Complexes 2–4 were characterized by elemental analysis, IR, UV–vis, 1H and 31P NMR, and single-crystal X-ray diffraction. In the [(2,2′-bipy)4Ni3(μ-Tab)4]6+ hexacation of 2, the central Ni(II) atom is connected to two [Ni(2,2′-bipy)2]2+ fragments by two pairs of μ-Tab ligands, forming a linear trinuclear cationic structure. The Ni(II) center of the dication of 3 is tetrahedrally coordinated by two S atoms from two Tab ligands and two P atoms of one dppe ligand. Complex 4 has a dimeric cationic structure in which two [(Tab)Ni]2+ species are linked by a pair of μ-Tab ligands and one dppb ligand. Complexes 2–4 displayed high catalytic activity toward the cross-coupling reactions of arylboronic acids and amines to produce N-arylated amines.

μ-Butane-1,4-diylbis(di-phenyl-phos-phane)-κ(2) P:P']bis-{[butane-1,4-diylbis(di-phenyl-phosphane)-κ(2) P,P']copper(I)} bis-(hexa-fluorido-phosphate) diethyl ether disolvate.

In the centrosymmetric dinuclear copper(I) complex cation of the title compound, [Cu2(C28H28P2)3](PF6)2·2C4H10O, the CuI atom is bonded to three P atoms of two butane-1,4-diylbis(di­phenyl­phosphane) (dppb) ligands with a triangular coordination geometry. One of these P atoms belongs to a bridging dppb ligand [Cu—P = 2.2381 (5) Å] and two belong to a chelating dppb ligand [Cu—P = 2.2450 (6) and 2.2628 (5) Å]. The bridging dppb ligand lies on an inversion centre. In the crystal, the cation and the PF6 − anion are linked by C—H⋯F inter­actions, forming a tape along [110]. The cation and the diethyl ether solvent mol­ecule are also linked by a C—H⋯O inter­action.

The effect of guest molecules on the conformation and molecular assembly of the fac-[RuCl3(NO)(dppb)] complex

This paper describes the occurrence of two crystalline solvate forms of the nitrosyl ruthenium complex fac-[RuCl3(NO)(dppb)] (dppb=1,4-bis(diphenylphosphino)butane), and the role of acetone and chloroform inclusions on molecular conformations and molecular assemblies. These two crystal forms were identified by X-ray diffraction and infrared spectroscopy, and compared with the known crystal structure of the complex, without the solvent. Using the FT-IR technique, it was possible to assign the bands characteristics of the nitrosyl stretching and the solvents. An interesting structural aspect occurring in both solvate forms is that the solvent inclusion modifies the molecular conformation of the dppb ligand and the molecular assembly. Due to the similar total volume of guest solvents, the unit cell parameters are similar, resulting in an isostructural arrangement with small differences in the intermolecular interactions, with caged guest solvents, that interact with the complex by hydrogen bonds.

Carborane Complexes of Ruthenium(III): Studies on Thermal Reaction Chemistry and the Catalyst Design for Atom Transfer Radical Polymerization of Methyl Methacrylate

The heating of the 18-electron complex [3,3-(dppb)-3-H-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (3) in benzene at 80 °C in the presence of a small amount of CCl(4) as initiator afforded paramagnetic 17-electron species [3,3-(dppb)-3-Cl-closo-3,1,2-RuC(2)B(9)H(11)] (4) along with minor amounts of two P-phenylene ortho-cycloboronated derivatives [3-Cl-3,3,8-{Ph(2)P(CH(2))(4)PPh-μ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (5) and [3,7-Cl(2)-3,3,8-{Ph(2)P(CH(2))(4)PPh-μ-(C(6)H(4)-ortho)}-closo-3,1,2-RuC(2)B(9)H(10)] (6) in total yield of ca. 80%. The heating of either 3 or 4 in toluene at 95 °C in the absence of CCl(4) led to the selective formation of 5, which was isolated in 64% and 46% yield, respectively. Thermolysis of 3 at higher temperatures (boiling toluene, 110 °C) gives novel paramagnetic species [3-Cl-3,3,7,8-{Ph(2)P(CH(2))(4)P-μ-(C(6)H(4)-ortho)(2)}-closo-3,1,2-RuC(2)B(9)H(9)] (7) featuring bis(ortho-cycloboronation) of both P-phenyl groups at the same phosphorus atom of the ruthenium-bound dppb ligand. All new paramagnetic complexes 4-7, as well as starting diamagnetic species 3, were characterized by single-crystal X-ray diffraction and, in addition, by EPR spectroscopic studies of odd-electron complexes. Ruthenacarboranes 3-5 and 7 all display high efficiency as catalysts for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Complex 5 gave the best catalyst performance in terms of polydispersity; the PDI (M(w)/M(n)) of the polymer samples is as low as 1.15.

Reactions of a gold(i) thiolate complex [Au(Tab)2]2(PF6)2(Tab = 4-(trimethylammonio)benzenethiolate) with diphosphine ligands

Reactions of a gold(i) thiolate complex [Au(Tab)(2)](2)(PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) with equimolar 1,2-bis(diphenylphosphine)ethane (dppe), 1,3-bis-(diphenylphosphine)propane (dppp) or 1,4-bis-(diphenylphosphine)butane (dppb) in MeOH-DMF-CH(2)Cl(2) gave rise to three polymeric complexes [Au(2)(Tab)(2)(dppe)](2)(PF(6))(4)·2MeOH (1·2MeOH), [Au(2)(Tab)(2)(dppp)]Cl(2)·0.5MeOH·4H(2)O (2·0.5MeOH·4H(2)O), and [Au(4)(μ-Tab)(2)(Tab)(2)(dppb)](PF(6))(4)·4DMF (3·4DMF), respectively. Analogous reaction of 1 with dppb in DMF/C(2)H(4)Cl(2) produced one tetranuclear complex [Au(2)(μ-Tab)(Tab)(2)](2)Cl(4)·2DMF·4H(2)O (4·2DMF·4H(2)O). Complexes 1-4 were characterized by elemental analysis, IR spectra, UV-vis spectra, (1)H and (31)P{(1)H} NMR and single crystal X-ray analysis. Compounds 1 and 2 consist of [Au(Tab)](2) dimeric fragments that are bridged by dppe or dppp ligands to form a 1D linear chain extending along the a axis. For 3, each [Au(4)(Tab)(2)(μ-Tab)(2)] fragment is linked by a pair of dppb ligands to afford another 1D chain extending along the c axis. For 4, the four [Au(Tab)](+) fragments are linked by two Au-Au bonds and two doubly bridging Tab ligands to form a {[Au(Tab)](4)(μ-Tab)(2)} chair-like cyclohexane structure. Hydrogen-bonding interactions in 2 and 4 lead to the formation of interesting 2D hydrogen-bonded networks. The luminescent properties of 1-4 in solid state were also investigated.

Vapochromic and Mechanochromic Tetrahedral Gold(I) Complexes Based on the 1,2‐Bis(diphenylphosphino)benzene Ligand

Tetrahedral gold(I) complexes containing the diphosphane ligand (dppb=1,2-bis(diphenylphosphino)benzene), [Au(dppb)(2)]X [X=Cl (1), Br (2), I (3), NO(3) (4), BF(4) (5), PF(6) (6), B(C(6)H(4)F-4)(4) (7)], and the ethanol and methanol adducts of complex 4, 8, and 9, were prepared to analyze their unique photophysical properties. These complexes are classified into two categories on the basis of their crystal structures. In Category I, the complexes (1-5) have relatively-small counter anions and two dppb ligands are symmetrically coordinated to the central Au(I) atom, and display an intense blue phosphorescence. Alternatively, the complexes (6-9) in Category II have large counter anions and two dppb ligands asymmetrically coordinated to Au(I) atom, and display a yellow or yellow orange phosphorescence. The difference in the phosphorescence color of the complexes between the Category I and II is ascribed to the change in the structure of the cationic moiety in the complex. According to DFT calculations, the symmetry reduction caused by the large counter anion of the complex in Category II gives the destabilization of HOMO (σ*) levels, leading to the red-shift of the emission peak. We have demonstrated that the symmetry reductions are responsible for the phosphorescence color alteration caused by external stimuli (volatile organic compounds and mechanical grinding).

Phosphorescence Color Alteration by Changing Counter Anions on Tetrahedral Gold(I) Complexes; Intra‐ and Interligand π–π Interactions

AbstractTetrahedral gold(I) complexes containing the diphosphaneligand [dppb = 1,2‐bis(diphenylphosphanyl)benzene], [Au(dppb)2]X {X = Cl (1), BF4 (2) and PF6 (3)}, were prepared and characterized by X‐ray structural analysis. Complexes 1 and 2 have almost the same structure with two dppb ligands, which are symmetrically coordinated to the Au atom in the crystal. However, the two dppb ligands of 3 are asymmetrically bound to the gold(I) stom in the crystal. Both colorless complexes 1 and 2 exhibit intense blue phosphorescence with peak maxima at 481 nm (Φp = 0.86) for 1 and 490 nm (Φp = 0.90) for 2, respectively. The pale yellow complex 3 shows weak yellow‐orange phosphorescence with a peak maximum at 596 nm (Φp = 0.04). A small conformational change in the crystal, which is caused by changing the counter anion, dramatically alters the optical properties of the tetrahedral gold(I) complexes in the solid state. The difference in the absorption and phosphorescence spectra between 1 and 3 has been interpreted on the basis of molecular arrangement including packing structures of the complexes and time‐dependent density functional theory (TD‐DFT) calculations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Driving forces in substitution reactions of octahedral complexes: The influence of the competitive effect

The reaction of cis-[RuCl 2(P–P)(N–N)] type complexes (P–P = 1,4-bis(diphenylphosphino)butane or (1,1′-diphenylphosphino)ferrocene; N–N = 2,2′-bipyridine or 1,10-phenantroline) with monodentate ligands (L), such as 4-methylpyridine, 4-phenylpyridine and benzonitrile forms [RuCl(L)(P–P)(N–N)] + species. Upon characterization of the isolated compounds by elemental analysis, 31P{ 1H} NMR and X-ray crystallography it was found out that the type of the L ligand determines its position in relation to the phosphorus atom. While pyridine derivatives like 4-methylpyridine and 4-phenylpyridine coordinate trans to the phosphorus atom, the benzonitrile ligand (bzCN), a good π acceptor, coordinates trans to the nitrogen atom. A 31P{ 1H} NMR experiment following the reaction of the precursor cis-[RuCl 2(dppb)(phen)] with the benzonitrile ligand shows that the final position of the entering ligand in the complex is better defined as a consequence of the competitive effect between the phosphorus atom and the cyano-group from the benzonitrile moiety and not by the trans effect. In this case, the benzonitrile group is stabilized trans to one of the nitrogen atoms of the N–N ligand. A differential pulse voltammetry experiment confirms this statement. In both experiments the [RuCl(bzCN)(dppb)(phen)]PF 6 species with the bzCN ligand positioned trans to a phosphorus atom of the dppb ligand was detected as an intermediate complex.

Ni-catalyzed regioselective three-component coupling of alkyl halides, arylalkynes, or enynes with R–M (M = MgX′, ZnX′)

A new method for the regioselective three-component cross-coupling of alkyl halides, alkynes, or enynes with organomagnesium or organozinc reagents in the presence of a nickel catalyst and a dppb ligand has been developed.

Facile Ligand Oxidation and Ring Nitration in Ruthenium Complexes Derived from a Ligand with Dicarboxamide-N and Phosphine-P Donors

The reaction of the tetradentate dicarboxamide ligand 1,2-bis-N-[2'(diphenylphosphanyl)benzoyl]diaminobenzene (dppbH(2)) with RuCl(3) in DMF or ethanol results in metal-mediated ligand oxidation and formation of the diamagnetic Ru(II) complex [(dppQ)Ru(Cl)(2)] (1) with N(2)P(2) chromophore. The o-phenylenedicarboxamide portion of the dppb(2-) ligand is oxidized to a o-benzoquinonediimine (bqdi) moiety in [(dppQ)Ru(Cl)(2)]. Presence of oxygen accelerates the ligand oxidation process. Unlike other tetradentate dicarboxamide ligands with pyridine-N, phenolato-O, or thiolato-S donors, dppb(2-) provides stability to the +2 oxidation state of ruthenium and facilitates oxidation of the coordinated ligand frame. Results of spectroscopic and redox studies strongly support the +2 oxidation state of Ru in 1. Exposure of 1 to NO(g) does not lead to formation of any metal nitrosyl; instead, the bqdi ring is nitrated to afford [(NO(2)dppQ)Ru(Cl)(2)] (2).

Effects of ligands on the rhodium-catalyzed hydroformylation of acrylate

The hydroformylation of butyl acrylate in toluene was studied. Ligands were found to impact significantly on the reaction rates and selectivities. When combined with rhodium, ligands with large bite angles displayed higher activities. Whilst 1,4-bis(diphenylphosphino)butane (dppb) was found to be a best choice, a modified, electron-deficient dppb ligand led to considerably higher catalytic activities in comparison with the electron-rich analogues. Other parameters were also examined, including ligand/rhodium ratios, and concentrations of the catalyst and olefin.

A series of luminescent Cu(i) mixed-ligand complexes containing 2,9-dimethyl-1,10-phenanthroline and simple diphosphine ligands

A series of Cu(I) mixed-ligand complexes containing dmp (2,9-dimethyl-1,10-phenanthroline) and one of simple diphosphine ligands (Ph2P(CH2)nPPh2) were prepared. Among the complexes, [Cu(dppp)(dmp)]PF6 (n=3) and [Cu2(dppb)2(dmp)2](PF6)2 (n=4) were characterized by X-ray structure analyses. The dppp complex has been characterized as a mononuclear complex, while [Cu2(dppb)2(dmp)2]2+ exists as a dinuclear complex in which two dppb ligands bridge between the two Cu(I) atoms. Although the distorted tetrahedral structures around the central metals of the two complexes are similar, the P-Cu-P angles are different between the two complexes. All of the series of complexes show photoluminescence in solution, and the intensity of the luminescence increases with n (n=2-4). The non-radiative rate constants of the complexes decrease markedly with n although radiative rate constants of the complexes are similar.

Scope, mechanism and diene inhibition of isomerization of allylic alcohols to saturated ketones catalyzed by ruthenium(II)-cyclopentadienyl complexes

The isomerization of 3-buten-2-ol to butanone catalyzed by Ru(II)Cp-complexes (Cp = η 5-cyclopentadienyl) with phosphine and amine ligands is described. The reaction catalyzed by [RuCp(MeCN) 3](PF 6) and two equivalents of triphenylphospine is first order in substrate with a k ini of 0.43 h −1 and an initial TOF of 13,000 h −1. The catalyst precursor complex [RuClCp(dppb)] (dppb = bis(diphenylphosphino)butane) has been characterized by X-ray diffraction. This compound features a seven-membered ring incorporating the ruthenium centre and the dppb ligand. Combination of two equivalents of primary, secondary or tertiary amines and [RuCp(MeCN) 3](PF 6) results in active catalyst precursors. Within each group, increasing the bulk of the ligand gives lower isomerization rates. The combined effects of optimal p K a, nucleophilicity and steric bulk make RuCp-complexes with secondary amines the most active precursors. With di- n-butylamine, 745 turnovers can be reached after 1 h. 31P NMR spectra indicate that the resting state in the catalytic cycle is a complex in which 3-buten-2-ol is η 2-coordinated through the alkene moiety. This implies that coordination of the oxygen moiety and concomitant β-hydrogen abstraction is the rate-limiting step. A counterintuitive result is that allylic alcohols bind stronger to RuCp complexes with phosphine ligands than dienes. Inhibition of the catalyst appears to be a result of interaction of the diene with a ruthenium–allyl alcohol complex, which is sufficiently strong to prevent coordination of the oxygen moiety of the allylic alcohol. This hinders orientation of the allylic alcohol substrate in a suitable way to undergo β-hydrogen abstraction, thereby blocking isomerization catalysis.

1,2‐Bis‐N‐[2′‐(diphenylphosphanyl)benzoyl]diaminobenzene, a New Chelating Ligand with Versatile Coordination Properties

Abstract1,2‐Bis‐N‐[2′‐(diphenylphosphanyl)benzoyl]diaminobenzene (dppbH; 1) was prepared by peptidic coupling and shown to exist, in the solid state, in the form of hydrogen‐bonded dimers by single‐crystal X‐ray structure analysis. As expected, 1 reacts with [MCl2(cod)] (M = Pd, Pt; cod = cyclooctadiene) to form square‐planar complexes. However, in the case of palladium [PdCl2(dppbH)] (2) is obtained, while in the case of platinum [Pt(dppb)] (3) is formed. Thus, the nature of the metal induces a completely different coordination mode: In 2, the dppbH ligand only coordinates through the two phosphorus atoms, while in 3 a dppb ligand, formed by deprotonation of the two amino functions in dppbH, coordinates through the two phosphorus atoms and through the two nitrogen atoms. The single‐crystal X‐ray analyses of the two square‐planar complexes reveal 2 to contain the two phosphorus atoms in a trans coordination mode and 3 to contain the two phosphorus atoms in a cis coordination mode. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)