Tripodal Phosphine Ligand Research Articles

Unveiling the mechanism of triphos-Ru catalysed C–O bond disconnections in polymers

Ruthenium complexes with facially coordinating tripodal phosphine ligands are privileged catalysts for a broad range of (de-)hydrogenation-based transformations. Among these, C–O bond hydrogenolysis holds potential for the depolymerisation of both the biopolymer lignin and epoxy resins applied in wind turbine blades, aircrafts and more. However, this methodology is poorly understood in mechanistic terms. Here, we present a detailed investigation on the triphos-Ru catalysed C–O bond scission on a molecular level. A combination of experimental, spectroscopical and theoretical studies elucidates the reactivity of the ruthenium trimethylenemethane precatalyst, revealing the key roles of ruthenium phenolates in both catalyst activation as well as the catalytic cycle itself. Furthermore, a Ru(0)/Ru(II) oxidative addition into the C–O bond is disclosed, with a triphos-Ru(0) dihydrogen complex as entry point. With the molecular nature of the operating triphos-Ru species and the thermodynamics and kinetics of the catalysis unravelled, improvements of established methods as well as design of related transformations may become possible.

Synthesis of New Chelating Phosphines Containing an Aryl Chloride Group

AbstractThe syntheses of bidentate and tripodal phosphine ligands containing aryl chlorides were achieved in 4 and 7 steps respectively, starting from diethyl malonate.

Synthesis and Reactivity of Copper(I) Complexes Based on C3‐Symmetric Tripodal HTIM(PR2)3 Ligands

We present the first example of non‐classical hydrogen bonding in CuI complexes. To this end, we have studied the coordination capacity of the tripodal phosphine ligands HTIM(PR2)3 {tris[1‐(di‐R‐phosphanyl)‐3‐methyl‐1H‐indol‐2‐yl]methane, R = Ph, iPr} towards copper, leading to a series of eight CuI complexes [{HTIM(PR2)3}CuX] [R = Ph (1–4), iPr (5–8); X = Cl–, I–, OTf–, BF4–]. An anagostic interaction in the CuI complexes has been proposed based on the results of 1H NMR, ultrahigh‐resolution X‐ray diffraction, and theoretical [atoms‐in‐molecules (AIM) and natural bonding orbital (NBO)] analyses of the electron density. Among the different synthesized complexes, [{HTIM(PPh2)3}CuOTf] (2) shows the strongest Cu···H–C interaction with a linear geometry (179.98°) and the shortest distance described so far [d(Cu–H) = 1.9 Å] in its toluene solvated form. Both parameters are characteristic of 3c–4e– interactions. In addition, we have found that these tripodal ligands exhibit unprecedented selectivity towards CuI ions. The synthesized HTIM(PR2)3CuI complexes have been found to be catalytically active and selective for the hydroboration of CO2 to formic acid.

Complexes of the tripodal phosphine ligands PhSi(XPPh2)3 (X = CH2, O): synthesis, structure and catalytic activity in the hydroboration of CO2.

The coordination chemistry of Fe(2+), Co(2+) and Cu(+) ions was explored with the triphosphine and triphosphinite ligands PhSi{CH2PPh2}3 (1) and PhSi{OPPh2}3 (2), so as to evaluate the impact of the electronic properties of the tripodal phosphorus ligands on the structure and reactivity of the corresponding complexes. The synthesis and characterization of the complexes [Fe(κ(3)-PhSi{CH2PPh2}3)(MeCN)3][OTf]2 (3) (OTf = O3SCF3), [Fe(κ(3)-PhSi{OPPh2}3)(MeCN)3][OTf]2 (3'), [Co(κ(2)-PhSi{CH2PPh2}3)Cl2] (4), [Co(κ(3)-PhSi{OPPh2}3)Cl2] (4'), [Cu(κ(3)-PhSi{CH2PPh2}3)Br] (5) and [Cu(κ(3)-PhSi{OPPh2}3)I] (5') were carried out. The crystal structures of 3, 3', 4, 4', and of the solvates 5·3THF and 5'·THF are reported. Complexes 3-5' were shown to promote the catalytic hydroboration of CO2 with (9-BBN)2 (9-BBN = 9-borabicyclo[3.3.1]nonane). While the iron and cobalt complexes of the triphosphine 1 are more active than the analogous complexes with 2, the opposite trend is observed with the copper catalysts. Overall, the copper catalysts 5 and 5' are both more reactive and more selective than the Fe and Co catalysts, enabling the formation of the acetal H2C(OBBN)2 with a high molar ratio of H2C(OBBN)2 : CH3OBBN up to 92 : 8.

Monometallic Ni(0) and Heterobimetallic Ni(0) /Au(I) Complexes of Tripodal Phosphine Ligands: Characterization in Solution and in the Solid State and Catalysis.

The tridentate chelate nickel complexes [(CO)Ni{(PPh2 CH2 )3 CMe}] (2), [(CO)Ni{(PPh2 CH2 CH2 )3 SiMe}] (6), and [Ph3 PNi{(PPh2 CH2 CH2 )3 SiMe}] (7), as well as the bidentate complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 PPh2 }] (3) and the heterobimetallic complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 Ph2 PAuCl}] (4), have been synthesized and fully characterized in solution. All (1) H and (13) C NMR signal assignments are based on 2D-NMR methods. Single crystal X-ray structures have been obtained for all complexes. Their (31) P CP/MAS (cross polarization with magic angle spinning) NMR spectra have been recorded and the isotropic lines identified. The signals were assigned with the help of their chemical shift anisotropy (CSA) data. All complexes have been tested regarding their catalytic activity for the cyclotrimerization of phenylacetylene. Whereas complexes 2-4 display low catalytic activity, complex 7 leads to quantitative conversion of the substrate within four hours and is highly selective throughout the catalytic reaction.

Modulating Sonogashira Cross‐Coupling Reactivity in Four‐Coordinate Nickel Complexes by Using Geometric Control

AbstractHerein, we present the synthesis of nickel complexes with tripodal phosphine ligands, CH3Si(CH2PPh2)3 and CH3C(CH2PPh2)3, and their application as catalysts in Sonogashira cross‐coupling reactions in water. Although both types of nickel complexes are based on similar tripodal ligands, the Si‐derived compounds adopt stable tetrahedral coordination geometries, whereas the C‐derived counterparts adopt a square‐planar coordination environment. This structural and electronic difference has an important effect on the catalytic properties of the complexes. Our study demonstrates that C‐derived complexes are catalytically inactive, whereas the complexes [CH3Si(CH2PPh2)3NiX2] (X = Cl–, Br–) are competent catalysts for cross‐coupling reactions of aryl halides with phenylacetylenes. This investigation reveals the importance of structural tuning on catalysis and strongly supports the theory that tetrahedral (PR3)2NiCl2 complexes are the active species in Sonogashira cross‐coupling reactions.

Reactivity of Ruthenium Phosphido Species Generated through the Deprotonation of a Tripodal Phosphine Ligand and Implications for Hydrophosphination

The fragmentation of the 1,1,2-tris(diphenylphosphino)ethane ligand in [RuCp*((Ph2P)2CHCH2PPh2)][PF6] (1) was explored through treatment with base under aprotic conditions. The neutral phosphido complex RuCp*(PPh2CH═CHPPh2)(PPh2) (2) with a (Z)-1,2-bis(diphenylphosphino)ethene (dppen) ligand was generated through a base-facilitated dehydrophosphination reaction. Installation of a bis(p-tolyl)phosphido ligand was attempted by combining bis(p-tolyl)phosphine with RuCp*(dppen)Cl in the presence of KOtBu, but surprisingly, the unsymmetrical diphenylphosphido compound RuCp*(Ph2PCHCHP(p-tol)2)(PPh2) (5) was generated instead. The ligand rearrangement reaction was driven by the greater electron density on the bis(p-tolyl)phosphido moiety. Density functional theory calculations showed that fragmentation to the 1,2-disubstituted ligand was thermodynamically favored over the 1,1-disubstituted ligand and that intramolecular phosphido exchange was kinetically accessible at room temperature. The greater basicity of th...

Spectroscopic and magnetic properties of an iodo CoI tripodal phosphine complex

Reaction of the tripodal phosphine ligand 1,1,1-tris((diphenylphosphino)phenyl)ethane (PhP3) with CoI(2) spontaneously generates a one-electron reduced complex, [(PhP3)Co(I)(I)] (1). The crystal structure of 1 reveals a distorted tetrahedral environment, with an apical Co-I bond distance of ~2.52 Å. Co(II/I) redox occurs at an unusually high potential (+0.38 V vs. SCE). The electronic absorption spectrum of 1 exhibits an MLCT peak at 320 nm (ε = 8790 M(-1) cm(-1)) and a d-d feature at 850 nm (ε = 840 M(-1) cm(-1)). Two more d-d bands are observed in the NIR region, 8650 (ε = 450) and 7950 cm(-1) (ε = 430 M(-1) cm(-1)). Temperature dependent magnetic measurements (SQUID) on 1 (solid state, 20-300 K) give μ(eff) = 2.99(6) μ(B), consistent with an S = 1 ground state. Magnetic susceptibilities below 20 K are consistent with a zero field splitting (zfs) |D| = 8 cm(-1). DFT calculations also support a spin-triplet ground state for 1, as optimized (6-31G*/PW91) geometries (S = 1) closely match the X-ray structure. EPR measurements performed in parallel mode (X-band; 0-15,000 G, 15 K) on polycrystalline 1 or frozen solutions of 1 (THF/toluene) exhibit a feature at g≈ 4 that arises from a (Δm = 2) transition within the M(S) = <+1,-1> manifold. Below 10 K, the EPR signal decreases significantly, consistent with a solution zfs parameter (|D|≈ 8 cm(-1)) similar to that obtained from SQUID measurements. Our work provides an EPR signature for high-spin Co(I) in trigonal ligation.

Ruthenium-catalysed hydrogenation of esters using tripodal phosphine ligands

The synthesis of a new tripodal phosphine ligand, N(CH 2PEt 2) 3, N-TriPhos Et is reported, and the use of tripodal ligands of this type, N(CH 2PR 2) 3 (R = Ph, Et), in conjunction with ruthenium for the catalysed hydrogenation of dimethyl oxalate (DMO) is reported and contrasted with catalysis using the MeC(CH 2PPh 2) 3 (TriPhos Ph) ligand. A different order of reaction with respect to the DMO substrate is found, and the rate is slower. A study of the kinetics and mechanism of the hydrogenation of DMO with Ru(acac) 3/TriPhos Ph is described, along with the effect of different additives to the system. The performance of Ru(acac) 3/TriPhos Ph/Zn system with unactivated ester substrates is probed and found to proceed significantly slower. Finally, based upon experimental observations, a mechanism is proposed for ester hydrogenation using ruthenium catalysts with tripodal phosphine ligands.

Ruthenium Hydride Complexes of the Hindered Phosphine Ligand Tris(3-diisopropylphosphinopropyl)phosphine

The synthesis and characterization of the novel hindered tripodal phosphine ligand P(CH(2)CH(2)CH(2)P(i)Pr(2))(3) (P(3)P(3)(iPr)) (1) are reported, along with the synthesis and characterization of ruthenium chloro and hydrido complexes of 1. Complexes [RuCl(P(3)P(3)(i)Pr)][BPh(4)] (2[BPh(4)]), RuH(2)(P(3)P(3)(i)Pr) (3), and [Ru(H(2))(H)(P(3)P(3)(iPr))][BPh(4)] (4[BPh(4)]) were characterized by crystallography. Complex 2 is fluxional in solution, and low-temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers.

Synthesis and Reactivity of [(PhB(CH2PPh2)3-κ3P)Ru(NCMe)3]PF6 and Its Potential as a Transfer Hydrogenation Catalyst

The acetonitrile ligands in [(PhB(CH2PPh2)3-κ3P)Ru(NCMe)3]PF6 (1) (which contains a facially coordinated anionic tripodal phosphine ligand) are labile and are rapidly replaced by other ligands, although the steric profile of the phosphine ligand limits the size and the number of the incoming ligands. Complex 1 and some of its derivatives proved to be very efficient and rapid transfer hydrogenation precatalysts and yielded turnover frequencies (TOFs) greater than those typically observed for most other ruthenium-based catalysts.

The preparation of multimetallic complexes using sterically bulky N-centred tripodal dialkyl phosphino ligands

Sterically bulky monodentate and bidentate phosphines have been widely used as ligands for metal complexation and catalyst formation. Bulky tridentate phosphine ligands are however much rarer and have not been widely investigated even though they may be considered attractive ligands for coordination chemistry studies and catalysis. Here we report the synthesis of two new N-centred tripodal phosphine ligands bearing bulky cyclohexyl and tert-butyl groups. The coordination chemistry of the cyclohexyl triphosphine ligand N(CH 2PCy 2) 3 ( 4) was investigated and found to react with Mo and W hexacarbonyls preferentially forming bidentate metal tetracarbonyl complexes [Mo(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] ( 6) and [W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] ( 7) over the expected facial capping tridentate complexes. The steric bulk of the cyclohexyl groups on the phosphorus atoms is sufficient to prevent the third arm of the ligand from coordinating and adopting the required geometry for facial coordination. This ‘steric control’ at the metal centre results in the third arm remaining freely available for further metal coordination. The coordination chemistry of this free phosphine arm on complexes 6 and 7 was investigated further and used to prepare a series of gold, platinum and silver multimetallic complexes. The X-ray crystal structures of the resulting mixed bi and trimetallic complexes [W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}AuCl] ( 8), [[Mo(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] 2(μ-PtCl 2)] ( 9) and [[W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] 2(μ-Ag)]ClO 4 ( 11) are reported.

Spin-State Tuning at Pseudotetrahedral d7Ions: Examining the Structural and Magnetic Phenomena of Four-Coordinate [BP3]CoII−X Systems

Electronic structure, spin-state, and geometrical relationships for a series of pseudotetrahedral Co(II) aryloxide, siloxide, arylthiolate, and silylthiolate complexes supported by the tris(phosphino)borate [BP(3)] ligands [PhBP(3)] and [PhBP(i)()(Pr)(3)] ([PhB(CH(2)PPh(2))(3)](-) and [PhB(CH(2)P(i)()Pr(2))(3)](-), respectively) are described. Standard (1)H NMR, optical, electrochemical, and solution magnetic data, in addition to low-temperature EPR and variable temperature SQUID magnetization data, are presented for the new cobalt(II) complexes [PhBP(3)]CoOSiPh(3) (2), [PhBP(3)]CoO(4-(t)()Bu-Ph) (3), [PhBP(3)]CoO(C(6)F(5)) (4), [PhBP(3)]CoSPh (5), [PhBP(3)]CoS(2,6-Me(2)-Ph) (6), [PhBP(3)]CoS(2,4,6-(i)()Pr(3)-Ph) (7), [PhBP(3)]CoS(2,4,6-(t)()Bu(3)-Ph) (8), [PhBP(3)]CoSSiPh(3) (9), [PhBP(3)]CoOSi(4-NMe(2)-Ph)(3) (10), [PhBP(3)]CoOSi(4-CF(3)-Ph)(3) (11), [PhBP(3)]CoOCPh(3) (12), [PhBP(i)()(Pr)(3)]CoOSiPh(3) (14), and [PhBP(i)()(Pr)(3)]CoSSiPh(3) (15). The low-temperature solid-state crystal structures of 2, 3, 5-10, 12, and 15 are also described. These pseudotetrahedral cobalt(II) complexes are classified as featuring one of two limiting distortions, either umbrella or off-axis. Magnetic and spectroscopic data demonstrate that both S = (1)/(2) and S = (3)/(2) ground-state electronic configurations are accessible for the umbrella distorted structure type, depending on the nature of the X-type ligand, its denticity (eta(1) versus eta(3)), and the tripodal phosphine ligand employed. Off-axis distorted complexes populate an S = (1)/(2) ground-state exclusively. For those four-coordinate complexes that populate S = (1)/(2) ground states, X-ray data show two Co-P bond distances that are invariably shorter than a third Co-P bond. The pseudotetrahedral siloxides 2, 10, and 11 are exceptional in that they display gradual spin crossover in the solid state. The diamagnetic cobalt(III) complex {[PhBP(3)]CoOSiPh(3)}{BAr(4)} ({16}{BAr(4)}) (Ar = Ph or 3,5-(CF(3))(2)-C(6)H(3)) has also been prepared and structurally characterized. Accompanying electronic structure calculations (DFT) for complexes 2, 6, and {16}(+) support the notion of a close electronic structure relationship between these four-coordinate systems and octahedral, sandwich, and half-sandwich coordination complexes.

Coordinatively and Electronically Unsaturated Zwitterionic Iron Silyl Complexes Featuring the Tripodal Phosphine Ligand [PhB(CH2PiPr2)3]-

A series of 14-electron, coordinatively unsaturated Fe(II) silyl complexes featuring the anionic, tripodal phosphine ligand [PhB(CH2PiPr2)3]- have been prepared and characterized; preliminary reactivity studies indicate that at least one such complex can undergo redox processes to generate isolable Fe(I) species with concomitant loss of the silyl ligand.

Tridentate phosphine ligands with novel linker-units

The synthesis of two novel types of tripodal phosphine ligands containing vinyl and alkynyl linker functions in their ligand backbones are reported. Using pentaerythritol (1) as the starting material the functionalized phosphines H2CCH–CH2OCH2C(CH2PPh2)3 (6), Me3SiCC–CH2OCH2C(CH2PPh2)3 (10) and HCC–CH2OCH2C(CH2PPh2)3 (11) were obtained in good yield in 4–5-step syntheses. H2CCH–CH2OCH2C(CH2PPh2)3 (6) and the silyl protected alkinyl derivative (CH3)3Si–CC–CH2OCH2C(CH2PPh2)3 (10) were reacted with one molar equivalent of [Mo(CO)3(MeCN)3] to yield the yellow-brown, air stable triphosphine–molybdenum complexes [{H2CCH–CH2OCH2C(CH2PPh2)3}Mo(CO)3] (12) and [{(CH3)3Si–CC–CH2OCH2C(CH2PPh2)3}Mo(CO)3] (13) the latter of which was characterized by X-ray diffraction.

Synthesis and characterization of Ni-, Pd- and Pt-complexes of functionalized, tripodal phosphine ligands

The tripodal ether, ester and cyano functionalized phosphine ligands (tdppcymome) ( a), (tdppcyme) ( b), and (tdppcycn) ( c), respectively, of the cyclohexane backbone type cis,cis-1,3,5-(PPh 2) 3-1,3,5-(R) 3-C 6H 5 (tdppcyR) (with R=–CH 2OCH 3, –COOCH 3, –CN) are each treated with the cyclooctadiene complexes M(COD)Cl 2 ( 1, 2) (M=Pt, Pd) and NiCl 2 ( 3). The potentially tridentate ligands form with these transition metals four-coordinated, bidentate dichloro complexes cis-M II(η 2-tdppcyR)Cl 2 ( 1a– c, 2a– c, 3a– c), in which two diphenylphosphino donor groups are bound to the metal center, and one phosphorus remains uncoordinated. Treatment of the ether functionalized complex 1b with SnCl 2 a bimetallic platinum tin complex cis-Pt(tdppcyme)Cl(SnCl 3) ( 1e) is obtained. Detailed NMR investigations were undertaken to characterize structural properties. The platinum and palladium complexes have square-planar coordination geometries, whereas the nickel compounds show a different behavior with a temperature-dependent change from square-planar to tetrahedral arrangements. For Ni(tdppcyme)Cl 2 ( 3b) a single-crystal X-ray structure determination was performed which established the η 2-coordination of the phosphine ligand and the square-planar geometry of the nickel complex in the solid state. The cyclohexane backbone of the ligand prefers the boat conformation.

ChemInform Abstract: Synthesis of Immobilizable and Water‐Soluble Tripodal Phosphine Ligands Supported by Organometallic Protection Groups

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereochemical and Electronic Control of Functionalized Tripodal Phosphines. Reactivity of the Adamantane-Type Ir(tripod)(CO)Cl (tripod = cis,cis-1,3,5-(PPh2)3-1,3,5-X3C6H6; X = H, COOMe, CN) Complexes toward H+, H2, CO, and C2H41

Treatment of the tripodal phosphine ligand cis,cis-1,3,5-tris(diphenylphosphino)-1,3,5-tris(methoxycarbonyl)cyclohexane (tdppcyme) (2) with Ir(PPh3)2(CO)Cl gives the carbonyl chloro complex Ir(tdppcyme)(CO)Cl (2a). NMR spectroscopic investigations prove a dynamic equilibrium between a square-planar (2a‘) and a trigonal-bipyramidal (2a) complex with two and three phosphine groups coordinated to iridium, respectively. This is in contrast to the comparable complexes Ir(tripod)(CO)Cl (1a, 3a) [tripod = cis,cis-1,3,5-tris(diphenylphosphino)cyclohexane (tdppcy) (1), cis,cis-1,3,5-tricyano-cis,cis-1,3,5-tris(diphenylphosphino)cyclohexane (tdppcycn) (3)] which only exist in the trigonal-bipyramidal form. The three compounds Ir(tripod)(CO)Cl (1a−3a), which only differ in the functionalization of the ligand backbone, display altered basicity and thus different reaction patterns. The carbonyl chloro complexes 1a−3a are readily protonated by the strong acid HBF4 to give the octahedral cations 1b−3b. The weaker acid N...

The Mo(CO)3 Fragment as an Organometallic Protection Group in the Synthesis of Functionalized Tripodal Phosphine Ligands

Treatment of Mo(CO)6 with cis,cis-1,3,5-tris(diphenylphosphino)-1,3,5-tris(methoxycarbonyl)cyclohexane (tdppcyme) (L) at elevated temperatures gives Mo(CO)3(tdppcyme) (1) in high yield. The ester g...

Synthesis and X-ray molecular structure of cis, cis-1,3,5-Tris(diphenylphosphino)- 1,3,5-tris(methoxycarbonyl) cyclohexane

The novel tripodal phosphine ligand cis, cis-1,3,5-tris(diphenylphosphino)-1,3,5-tris(methoxycarbonyl)cyclohexane (tdppcyme) ( 2) has been synthesized. 1H, 13C and 31P NMR spectroscopy shows that in solution the sterically demanding diphenylphosphine groups occupy equatorial positions on the cyclohexane ring. An X-ray crystal investigation confirms this result for the solid state. Treatment of tdppcyme with Mo( η 6-C 7H 8)(CO) 3 gives Mo(tdppcyme)(CO) 3 ( 3), with octahedral molybdenum coordination.