Tetraphosphane Ligands Research Articles

Luminescence Thermochromism of Gold(I) Phosphane-Iodide Complexes: A Rule or an Exception?

A series of gold(I) iodide complexes 1-11 have been prepared from di-, tri-, and tetraphosphane ligands. Crystallographic studies reveal that the di- (1-7) and tetrametallic (11) compounds feature linearly coordinated gold(I) ions with short aurophilic contacts. Their luminescence behavior is determined by the combined influence of the phosphane properties, metal-metal interaction, and intermolecular lattice-defined interactions. The proposed variable contribution of 3 (X+M)-centered (X=halogen; M=metal) and 3 XLCT (halogen to ligand charge transfer) electronic transitions into the lowest lying excited state, which is influenced by supramolecular packing, is presumably responsible for the alteration of room-temperature emission color from green (λ=545 nm, for 11) to near-IR (λ=698 nm, for 2). Dinuclear compounds 6 and 7 exhibit distinct luminescence thermochromism with a blueshift up to 5750 cm-1 upon cooling. Such dramatic change of emission energy is assigned to the presence of two coupled triplet excited states of 3 ππ* and 3 (X+M)C/3 XLCT nature, the presence of which depends on both molecular structure and the crystal lattice arrangement.

Stabilisation effects of phosphane ligands in the homogeneous approach of sunlight induced hydrogen production.

Most of the systems for photochemical hydrogen production are not stable and suffer from decomposition. With bis(bidentate) tetraphosphane ligands the stability increases enormously, up to more than 1000 h. This stability was achieved with a system containing osmium(ii) as a light harvesting antenna and palladium(ii) as a water reduction catalyst connected with a bis(bidentate) phosphane ligand in one molecule with the chemical formula [Os(bpy)2(dppcb)Pd(dppm)](PF6)4. With the help of electrochemical measurements as well as photophysical data and its single crystal X-ray structure, the electron transfer between the two active metal centres (light harvesting antenna, water reduction catalyst) was analysed. The distance between the two active metal centres was determined to be 7.396(1) Å. In a noble metal free combination of a copper based photosensitiser and a cobalt diimine-dioxime complex as water reduction catalyst a further stabilisation effect by the phosphane ligands is observed. With the help of triethylamine as a sacrificial donor in the presence of different monophosphane ligands it was possible to produce hydrogen with a turnover number of 1176. This completely novel combination is also able to produce hydrogen in a wide pH-range from pH = 7.0 to 12.5 with the maximum production at pH = 11.0. The influence of monophosphane ligands with different Tolman cone angles was investigated. Monophosphane ligands with a large Tolman cone angle (>160°) could not stabilise the intermediate of the cobalt based water reduction catalyst and so the turnover number is lower than for systems with an addition of monophosphane ligands with a Tolman cone angle smaller than 160°. The role of the monophosphane ligand during sunlight-induced hydrogen production was analysed and these results were confirmed with DFT calculations. Furthermore the crystal structures of two important Co(i) intermediates, which are the catalytic active species during the catalytic pathway, were obtained. The exchange of PPh3 with other tertiary phosphane ligands can have a major impact on the activity, depending on the coordination properties. By an exchange of monophosphane ligands with functionalised phosphane ligands (hybrid ligands) the hydrogen production was raised 2.17 times.

Synthesis, Characterization of N-Pyrrolylphosphanes Based on Heterocyclic Amine Backbones and Their Application in Hydroformylation of 1-Octene

A new class of N-pyrrolylphosphanes based on new heterocyclic amines have been synthesized, characterized and applied in homogeneous rhodium-catalyzed hydroformylation of 1-octene. These ligands possessing strong π-acceptor properties effectively facilitate the olefin isomerization. The steric effect of ligands has also been examined. Large steric tetraphosphane ligand afforded better regioselectivity, and the L/B ratio of about 6.4 was obtained at low synthesis gas pressure (5 bar). New heterocyclic amines have been developed, and two type pyrrole-based ligands possessing strong π-acceptor and weak o-donor properties have been prepared. High regioselectivity has been achieved in the rhodium-catalyzed hydroformylation of terminal olefin.

Kinetic and Electrochemical Studies of the Oxidative Addition of Demanding Organic Halides to Pd(0): the Efficiency of Polyphosphane Ligands in Low Palladium Loading Cross-Couplings Decrypted

Oxidative addition (OA) of organic halides to palladium(0) species is a fundamental reaction step which initiates the C-C bond formation catalytic processes typical of Pd(0)/Pd(II) chemistry. The use of structurally congested polyphosphane ligands in palladium-catalyzed C-C bond formation has generated very high turnover numbers (TONs) in topical reactions such as Heck, Suzuki, Sonogashira couplings, and direct sp(2)C-H functionalization. Herein, the OA of aryl bromides to Pd(0) complexes stabilized by ferrocenylpolyphosphane ligands L1 (tetraphosphane), L2 (triphosphane), and L3 (diphosphane) is considered. The investigation of kinetic constants for the addition of Ph-Br to Pd(0) intermediates (generated by electrochemical reduction of Pd(II) complexes coordinated by L1-L3) is reported. Thus, in the OA of halides to the Pd(0) complex coordinated by L1 the series of rate constants kapp is found (mol(-1) L s(-1)): kapp(Ph-Br) = 0.48 > kapp(ClCH2-Cl) = 0.25 ≫ kapp(p-MeC6H4-Br) = 0.08 ≈ kapp(o-MeC6H4-Br) = 0.07 ≫ kapp(Ph-Cl). Kinetic measurements clarify the influence that the presence of four, three, or two phosphorus atoms in the coordination sphere of Pd has on OA. The presence of supplementary phosphorus atoms in L1 and L2 unambiguously stabilizes Pd(0) species and thus slows down the OA of Ph-Br to Pd(0) of about 2 orders of magnitude compared to the diphosphane L3. The electrosynthesis of the complexes resulting from the OA of organic halides to [Pd(0)/L] is easily performed and show the concurrent OA to Pd(0) of the sp(3)C-Cl bond of dichloromethane solvent. The resulting unstable Pd/alkyl complex is characterized by NMR and single crystal X-ray structure. We additionally observed the perfect stereoselectivity of the OA reactions which is induced by the tetraphosphane ligand L1. Altogether, a clearer picture of the general effects of congested polydentate ligands on the OA of organic halides to Pd(0) is given.

Synthesis and Application of Tetraphosphane Ligands in Rhodium‐Catalyzed Hydroformylation of Terminal Olefins: High Regioselectivity at High Temperature

A new class of substituted tetraphosphane ligands has been developed and applied in the rhodium-catalyzed regioselective hydroformylation of terminal olefins. The high regioselectivity (linear selectivity is above 97 % for 1-octene and 1-hexene) at high temperature (140 degrees C) shown by these tetraphosphane ligands is remarkable considering the low regioselectivity commonly observed under similar reaction conditions when other bisphosphane analogues are used. The steric and electronic effects of substituents on the diarylphosphane moiety have also been examined.

Direct Arylation of Heterocycles: The Performances of Ferrocene‐Based Polyphosphane Ligands in Palladium‐Catalyzed CH Bond Activation

AbstractThe palladium‐catalyzed direct arylation of alkylated‐ furan, thiophene, and thiazole and benzoxazole heterocycles with electronically and sterically deactivated bromoarenes was selectively and efficiently promoted by ferrocenyl polyphosphanes. In this CH bond activation reaction of heteroaromatics, the performances of polydentate di‐, tri‐, and tetraphosphane ligands were compared, showing that the triphosphane 1,1′,2‐tris(diphenylphosphino)‐4‐tert‐butylferrocene 3 was the most effective for the coupling. The introduction of more electron‐donating (iPr) or electron‐withdrawing (furyl) groups on the phosphorus atoms did not improve the ligand performances. The coordination behavior of 3 towards palladium(II) and other group 10 metals, NiII and PtII, was studied and the corresponding 1,2‐P chelating phosphorus complexes were isolated in high yields and fully characterized by multinuclear 1H, 13C, 31P NMR (3⋅PdCl2, 3⋅PtCl2) and X‐ray structures (3⋅NiBr2). It was found that the triphosphane ligand 3 was able to accommodate bidentate chelating cis coordination to group 10 metals, and additionally a much rarely described bis monodentate trans configuration. The combination of these two modes of coordination in a multimetallic species was clearly evidenced for the first time for a ferrocenyl polyphosphane. This versatility in bonding is a clear difference of coordination potential of this catalytically more efficient triphosphane compared to analogous ferrocenyl di‐ or tetraphosphanes.

Bond Activation in Iron(II) and Nickel(II) Complexes of Polypodal Phosphanes

A pyridine-derived tetraphosphane ligand (donor set: NP4) has been found to undergo remarkably specific C-P bond cleavage reactions, thereby producing a ligand with an NP3 donor set. The reaction may be reversed under suitable conditions, with regeneration of the original NP4 ligand. In order to investigate the mechanism of this reaction, the NP3 donor ligand C5H3N[CMe(CH2PMe2)2][CMe2(CH2PMe2)] (11) was prepared, and its iron(II) complex 4 generated from Fe(BF4)2 ・6H2O, with methyl diethylphosphinite (7) as an additional monodentate ligand. Ligand 11 has, in addition to the NP3 donor set, one methyl group in close contact with the iron center, reminiscent of an agostic M・ ・ ・H-C interaction. Depending on the stoichiometric amount of iron(II) salt, a side product 15 is formed, which has a diethylphosphane ligand instead of the phosphinite 7 coordinated to iron(II). While attempts to deprotonate the metal-coordinated methyl group in 4 were unsuccessful, the reaction was shown to occur in an alternative complex (18), which is similar to 4 but has a trimethylphosphane ligand instead of the phosphinite 7. The reaction of complex 15 with CO gave two different products, which were both characterized by single-crystal X-ray diffraction. One (19) is the dicarbonyl iron(II) complex of the triphosphane ligand 11, the other (3) is the carbonyl iron(II) complex of the tetraphosphane C5H3N[CMe(CH2PMe2)2]2 (1). This suggests an intermolecular mechanism for the C-P bond formation in question.

Tetrapodal pentadentate ligands: Single site reactivity and bond activation in iron(II) complexes

Tetrapodal pentadentate ligands occupy five coordination positions in a coordination octahedron, thereby providing the metal ion with a square-pyramidal "coordination cap": In such complexes, all reactivity is focused on a single coordination site. The review highlights recent advances in the coordination chemistry of iron. With a variety of NN(4) ligands, the concept is being used to model non-heme active sites in biomolecules. Tetraphosphane ligands (donor set: NP(4)) undergo, depending on the solvent, remarkably specific P-C bond activation reactions, which may be reversed under suitable conditions.

Synthesis and Characterization of Linear Tetranuclear Silver(I) Complexes Bridged by Tetraphosphane Ligands

AbstractReactions of AgOTf with meso‐bis[(diphenylphosphanylmethyl)phenylphosphanyl]methane (dpmppm) afforded[Ag4(OTf)2(μ‐OTf)(μ‐dpmppm)2{(CH3)2CO}](OTf) (1) and [Ag4(OTf)2(μ‐OTf)(μ‐dpmppm)2(RNC)2](OTf) {R = Xyl (2a), Mes (2b), tBu (2c)}. When AgOTf was treated with dpmppm in air in the presence of tBuNC, cleavage of the C–Cl and P–C bonds occurred to give [Ag4(μ‐Cl)(μ‐dpmppm)2(tBuNC)4](OTf)3 (3) and [Ag4(μ‐Ph2PO2)(μ‐dpmppm)2(tBuNC)3](OTf)3 (4). Reaction of AgOCOCF3 with dpmppm resulted in [Ag4(OCOCF3)2(μ‐OCOCF3)(μ‐dpmppm)2](CF3COO) (5). By treatment of AgPF6 with dpmppm, [Ag4(μ‐dpmppm)2(tBuNC)4](PF6)4 (6) and [Ag4(PO2F2)2(μ‐dpmppm)2(tBuNC)2] (PF6)2 (7) were obtained. Wheareas complexes 1–3 possess a {Ag4(μ‐dpmppm)2}4+ core in which the Ag4 strings are rather bent with two dpmppm ligands arranged in a syn fashion, complexes 4–7 have linear Ag4 strings supported by two dpmppm ligands arranged in an anti fashion. These results suggest that the dpmppm‐supported tetrasilver(I) strings are quite flexible and labile and thus are potentially important in promoting organic reactions as a result of the multimetallic centers.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Stereoselective Synthesis of the First Chatt‐Type Bis(dinitrogen)‐Molybdenum(0) Complex with a Tetraphosphane Ligand

AbstractThe first Chatt‐type Mo0 dinitrogen complex with a tetraphosphane ligand has been prepared and characterized by NMR as well as infrared and Raman spectroscopy. Importantly, the employed reaction route allows the stereospecific synthesis of this complex as trans‐[Mo(N2)2(meso‐prP4)] (prP4 = a tetraphos ligand with a central propylene bridge). The stereoselectivity in the reaction course is induced by the oxido‐iodido‐molybdenum(IV) precursor [Mo(O)I(prP4)]+ which directs both phenyl groups of the bridging P atoms of prP4 into a meso configuration. The paper establishes a general strategy to synthesize mononuclear Mo0 dinitrogen and related molybdenum complexes with multidentate phosphane ligands which has not been possible to date. Moreover, the obtained molybdenum tetraphos N2 complex should exhibit a higher thermodynamic stability in the reactions of the Chatt cycle of synthetic nitrogen fixation than the conventional bis(diphos) complexes, due to the linkage of the two diphosphane units by an alkyl bridge. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Tetra‐ and Triphosphane Pyridine Podands and Their Cobalt(II) and Nickel(II) Complexes

AbstractThe reaction of the 2,6‐diethylpyridine‐derived tetraphosphane ligand C5H3N[CMe(CH2PMe2)2]2 (1Me) with nickel(II) or cobalt(II) perchlorate or tetrafluoroborate in methanol produces complexes of approximate square‐pyramidal geometry (NP4 coordination). The nickel complexes are diamagnetic, with NMR spectral features (31P) that reflect a tetrahedral distortion of diametrically opposite phosphorus donors; this is also found in the solid state. In terms of bond lengthsand angles, all complexes differ significantly from theiranalogues containing the phenyl‐substituted ligand C5H3N[CMe(CH2PPh2)2]2. The ligand 1Me is readily and completely oxidised to the corresponding tetrakis(phosphane oxide) upon reaction with NO. Slow oxidation of the cobalt(II) tetrafluoroborate complex of 1Me with aerobic oxygen in acetonitrile produces a trinuclear cobalt complex containing two equivalents of partially oxidised ligand (C2‐symmetrical; donor set: [PMe2]2[P(O)Me2]2). Four phosphane oxide oxygen atoms coordinate the central cobalt(II) ion in tetrahedral fashion, whereas the lateral cobalt(II) ions are in a square‐pyramidal environment provided by two PMe2 donors and three acetonitrile ligands in each case. The reaction of the cobalt(II) perchlorate complex of 1Me with carbonmonoxide gives an octahedral, 19‐valence‐electron dicarbonyl complex in which one of the dimethylphosphanyl groups is uncoordinated. A structural relative of 1Me, C5H3N[CMe(CH2PMe2)2][CMe2(CH2PMe2)] (2), which contains one fewer dimethylphosphanyl donor, can be prepared in a straightforward manner from 2‐ethyl‐6‐isopropylpyridine in a four‐stage process. In a series of mononuclear nickel(II) complexes, 2 employs only its three phosphane donors which, together with a monodentate ligand (acetonitrile, acetamide, or bromide), provide a tetragonal coordination environment for the metal ion which is intermediate between square planar and tetrahedral. The acetamide complex is generated from the acetonitrile complex by slow hydrolysis of the coordinated ligand. Full spectroscopic details for the complexes, as well as X‐ray structure analyses, are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Characterization, and Electrochemical Properties of Novel Transition Metal–Fullerene Complexes Containing Di‐ and Tetraphosphane Ligands

AbstractThis paper reports the synthesis, characterization, and some properties of transition metal–fullerene complexes containing trans‐1,1′‐bis(diphenylphosphanyl)ethylene (dppet, trans‐Ph2PCH=CHPPh2) and N,N,N′,N′‐tetra(diphenylphosphanylmethyl)ethylene diamine (dppeda, [(Ph2PCH2)2NCH2]2), including [(η2‐C60M)(dppet)2] (M = Pt 1, Pd 2), [(η2‐C60M)(dppet)]2 (M = Pt 3, Pd 4), [(η2‐C60Pd)(η2‐C60Pt)(dppet)2](5), [(η2‐C60Pd)(η2‐C70Pd)(dppet)2] (6), [(η2‐C70Pd)(dppet)]2 (7), [(η2‐C60M)(dppeda)] (M = Pt 8, Pd 9), and [(η2‐C60M)2(dppeda)] (M = Pt 10, Pd 11). Interestingly, while complexes 1, 2, 8, and 9 are the first examples of metallacyclopropafullerene diphosphane ligands containing fullerene cores, complexes 3–7, 10, and 11 are the first group 10 metal‐containing, dumbbell‐shaped bisfullerenes. All the complexes 1–11 were characterized by elemental analysis, spectroscopy, and, particularly for 4 and 5, by X‐ray crystallography and cyclic voltammetry. Pathways for the formation of 1–11 are suggested. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Two Organometallic Fragments Inclusioned in a 1,3-Alternate Calix[4]arene Tetraphosphane: Evidence for Transition Metal−Arene Interaction through the Cavity

The preparation of an 1,3-alternate calix[4]arene tetraphosphane ligand, 25,26,27,28-tetrakis{2-(diphenylphosphino)ethoxy}calix[4]arene (4), is described. Ligand 4 is obtained in four steps in 17% overall yield. Reaction of 4 with AgBF4 produced the encapsulated two silver complex [Ag2{(P,P,P,P)-tetraphencalix[4]arene}](BF4)2. The solid-state structure shows that the encapsulated silver undergoes a substantial pi-interaction by two opposite arene rings. Rhodation of 4 employing [Rh(cot)2]BF4 yielded the encapsulated complex with a bent coordination mode. Two organometallic fragments inclusioned inside a 1,3-alternate calix[4]arene tetraphosphane was also achieved by the reaction of 4 with [PtH(PPh3)2 (thf)]+. Full characterization includes X-ray structural studies of compounds 4-6.

Cooperativity in Rh2 Complexes: High Catalytic Activity and High Regioselectivity in the Hydroformylation of Olefins

A breakthrough in tailor-made homogeneous catalysts has been achieved by Stanley et al., who synthesized the rac-Rh2 complex 1 with a new tetraphosphane ligand, which catalyzes the hydroformylation of olefins with a high activity and extremely selectively. The combination of these important catalytic properties is traced back to the intramolecular interaction of the two Rh centers fixed by the ligand matrix.

Macrocyclic polyphosphane ligands. Cobalt(II) and nickel(II) complexes of the γ and ε diastereoisomers of 4,7,13,16-tetraphenyl-4,7,13,16-tetraphospha-1,10-dithiacyclo-octadecane(L1) and the crystal structure of [Co(ε-L1)][BPh4]2·EtOH

The chiral configuration of the title diastereoisomer, ε-L1, has been ascertained by the X-ray crystal-structure determination of its cobalt(II) complex [Co(ε-L1)][BPh4]2·EtOH. The complex crystallises in the monoclinic space group P21/c, with a= 14.590(3), b= 13.004(3), c= 40.972(9)Å, β= 91.80(4)°, and Z= 4. Least-squares refinement gave R= 0.114 for 1 241 observed reflections. The cobalt atom is six-co-ordinated by two sulphur and four phosphorus atoms of the macrocycle forming a distorted cis-octahedral geometry. The nickel complexes are attributed a similar stereochemistry on the basis of their electronic spectra. The stereochemistry of the cobalt and nickel complexes of γ-L1 has been investigated by electronic spectroscopy. The γ-L1 isomer behaves as a quadridentate tetraphosphane ligand, the two sulphur atoms being unco-ordinated.

31P and 1H NMR characterization of stereoisomeric macrocyclic nickel(II) complexes with a tetraphosphane ligand

Several studies on metal complexes formed by macrocyclic ligands have shown that these compounds provide stimulating examples for studying the conformational properties of the molecules. Recent synthetic developments in this laboratory have provided some ideal ligands for investigating the configurational properties of polyphosphane macrocyclic complexes. As an example, the results of 31P and 1H NMR investigations on some stereoisomeric nickel(II) derivatives of the 4,7,13,16-tetraphenyl-1,10-dioxa-4,7,13,16-tetraphoscyclooctadecane {∣18∣aneP 4O 2} are here reported. The ∣18∣aneP 4O 2 ligand can exist in five basic structural forms (Fig. 1), as determined by the distribution of phosphorus atom configurations with respect to the aliphatic chains spanning the phosphorus atoms themselves. Three of these forms [(a), (b), and (c)] are nonenantiomeric, whereas (d) and (e) forms exist together their respective enantiomers. The five forms are interconvertible diastereoisomers; however, because of their high temperature of ▪ Fig. 1. The five possible diastereoisomers of ∣18∣aneP 4O 2 ligand. racemization, they can, in principle, be isolated as free ligands at room temperature. Two isomeric forms I and II of the ∣18∣aneP 4O 2 ligand have been isolated and their nickel(II) tetrafluoroborate derivatives have been synthesized and characterized. Conductometric, magnetic and spectroscopic measurements indicate that the latter compounds contain square planar {Ni(∣18∣aneP 4O 2)} 2+ cations, the nickel(II) ion being coordinated to the four phosphorus atoms. The 31P NMR spectrum of isomer I is reported in Fig. 2 and shows a pattern of ▪ Fig. 2. 31P NMR spectrum at 30 °C of d 6-DMSO solution of {Ni(∣18∣aneP 4O 2I)} 2+ resonances which indicates the presence of four nonequivalent phosphorus atoms. The (d) configuration, therefore, is proposed for this stereoisomer. Both 1H and 31P NMR spectra indicate a symmetric configuration for isomer II. Since form 1H NMR trace it appears that the ethylenic chains spanning the phosphorus atoms adopt the gauche conformation, only configurations (b) and (e) can be proposed for this stereoisomer. Preliminary X-ray diffractometric data indicate that the configuration (b) is to be assigned to the isomer II. Attempts to isolate and characterize all the possible isomers are actually in progress.