Phosphine Substitution Research Articles

Tuning a phosphine-substituted diimine ligand to afford an iron monocarbonyl complex

A series of low-valent iron complexes that feature a phosphine-substituted α-diimine (DI) ligand have been synthesized. Reduction of (Ph2PPrDI)FeBr2 with an excess of Na/Hg in the presence of carbon monoxide afforded the corresponding dicarbonyl complex, (Ph2PPrDI)Fe(CO)2. Through multinuclear NMR and single crystal X-ray diffraction analysis, this complex was found to possess a 3-coordinate DI ligand. Upon heating for 10 days at 110 °C while applying intermittent vacuum, (Ph2PPrDI)Fe(CO)2 was successfully converted to the corresponding monocarbonyl complex, (Ph2PPrDI)Fe(CO), which was found to feature a tetradentate chelate. Similar reactivity was explored using the analogous bis(tert-butyl)phosphine-substituted ligand, tBu2PPrDI. Addition of this chelate to FeBr2 afforded (tBu2PPrDI)FeBr2, and subsequent reduction yielded (tBu2PPrDI)FeBr, which was found to possess a tridentate DI ligand by single crystal X-ray diffraction. Performing the reduction of (tBu2PPrDI)FeBr2 in the presence of CO afforded the corresponding dicarbonyl complex, (tBu2PPrDI)Fe(CO)2. Like aryl-substituted (Ph2PPrDI)Fe(CO)2, alkyl-substituted (tBu2PPrDI)Fe(CO)2 was found to feature a pendant phosphine arm. However, heating (tBu2PPrDI)Fe(CO)2 under vacuum did not allow for phosphine substitution and conversion to the corresponding monocarbonyl complex, highlighting the importance of phosphine π-acidity for substitution and the stabilization of low-valent iron.

PNP‐Pincer Ligands Armed With Methyls: New Tools To Control Sterics and Non‐Innocence

AbstractThe widespread use of pyridine‐based PNP pincer ligands has inspired the concept of metal‐ligand cooperation (MLC), in which the reactivity at the deprotonated CH2 (or NH) arm of the ligand is proposed to play an important role. Several groups developed a family of PNP‐type pincer ligands with methylated arms which were initially introduced to test the effect of blocking MLC in catalysis, but eventually led to unexpected consequences such as stabilization of unusual oxidation states, beneficial catalytic activity, or selectivity. Analysis of the sterics imposed by introducing Me groups revealed that arm protection can be an efficient tool to control sterics around the metal as an alternative to phosphine substitution, leading to much greater steric hinderance above and below pincer's coordination plane. This Concept will describe several illustrative examples which contrast the reactivity of classical CH2/NH‐arm PNP pincers with their CMe2/NMe‐armed counterparts, in particular related to Ru‐catalyzed alcohol dehydrogenative coupling, Fe‐catalyzed hydrogenation, hydroboration, and alkyne semihydrogenation.

Modular synthesis of unsymmetric 1,3-diphosphinopropanes through sequential substitution reactions

Methods to synthesize diphosphines with different substituents on the two phosphorus centers are limited, particularly for the synthesis of unsymmetric bis(dialkylphosphine) ligands. Herein is reported a modular and high-yielding synthesis of borane-protected unsymmetric 1,3-bis(diphosphino)propanes containing either two dialkylphosphine moieties or one dialkylphosphine and one diphenylphosphine group. The method relies on sequential phosphine substitution on 1,3-dibromopropane. The borane-protected diphosphines are readily converted to bis(phosphonium salts), which serve as convenient preligands. Palladium(II) complexes of di-tert-butyl(3-(dicyclohexylphosphino)propyl)phosphine (tBuCyPP), di-tert-butyl(3-(diisobutylphosphino)propyl)phosphine (tBuiBuPP), and diisobutyl((3-(dicyclohexylphosphino)propyl)phosphine (CyiBuPP) have been prepared. The tBuiBuPP and CyiBuPP complexes have been structurally characterized and their structural properties compared to symmetric (1,3-diphosphinopropane)palladium dichloride structures.

Phosphine substitution and linkage isomerization in cyclopentadienylruthenium bis(triphenylphosphine)thiocyanide and selenocyanide, CpRu(PPh3)2NCS and CpRu(PPh3)2SeCN.

The reaction between CpRu(PPh3)2NCS (1a) and PMePh2 yields CpRu(PPh3)(PMePh2)NCS (2a) while CpRu(PPh3)(PMePh2)Cl reacts with SCN- to form the S-bonded isomer, CpRu(PPh3)(PMePh2)SCN (2b). Compound 1a and the linkage isomers of 2 were characterized by X-ray crystallography. The kinetics of the reaction between 1a and PMePh2 under pseudo-first order conditions in THF and in fluorobenzene to form 2a are consistent with a dissociative interchange mechanism. Activation parameters for the reaction are: ΔH† = 15.7 ± 0.6 kcal mol-1 and ΔS† = -35 ± 2 cal mol-1 K-1 in THF vs. ΔH† = 24.8 ± 1.2 kcal mol-1 and ΔS† = -6 ± 4 cal mol-1 K-1 in C6H5F. In the presence of added SCN-, the rate of phosphine substitution is unchanged but a mixture of 2a and 2b is observed. The selenocyanate derivative, CpRu(PPh3)2SeCN (3b), crystallizes as the Se-bonded linkage isomer. Compound 3b reacts with PMePh2 under pseudo-first order conditions in fluorobenzene to form CpRu(PPh3)(PMePh2)SeCN (4b) at a much faster rate than 1a with activation parameters: ΔH† = 30.9 ± 4.8 kcal mol-1 and ΔS† = 22.4 ± 15.9 cal mol-1 K-1 with no evidence for linkage isomerization to the N-bonded products.

Monodentate phosphine substitution in [Pd(κ3-dppf)(PR3)][BF4]2 (dppf = 1,1'-bis(diphenylphosphino)ferrocene) compounds.

The ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf) is commonly employed in a variety of catalytic systems. There are a variety of coordination modes known for dppf, the least studied being the κ3 coordination mode, in which both phosphorus atoms and the iron atom of dppf interact with another metal center. One such compound is the previously reported [Pd(κ3-dppf)(PPh3)]2+. A series of related compounds, [Pd(κ3-dppf)(P(p-C6H4R)3)]2+ (R = OCH3, CH3, F and CF3), has been synthesized and characterized. The X-ray crystal structure of [Pd(dppf)(P(p-C6H4F)3)][BF4]2 was determined. Electrochemical and computational studies indicate that the electron donor ability of the P(p-C6H4R)3 ligands influences the properties of these compounds. Substitution reactions of the P(p-C6H4R)3 ligands have been examined, and, in general, the more electron donating P(p-C6H4R)3 ligands completely replace the less electron donating ones. The kinetics of the reaction of [Pd(κ3-dppf)(P(p-C6H4F)3)]2+ with P(p-C6H4OCH3)3 indicate that the reaction proceeds through a dissociative mechanism, contrary to the associative substitutions prevalent in square planar palladium(ii) chemistry.

Kinetics of phosphine substitution in CpRu(PPh3)2X (X = Cl, Br, I, N3, and NCO)

The kinetics of phosphine substitution in CpRu(PPh3)2X (X = Cl, Br, I, N3, and NCO) is consistent with a dissociative mechanism. The complexes react with chloroform to yield CpRu(PPh3)2Cl by a mechanism that involves phosphine loss.

One-pot reductive amination of carbonyl compounds with ammonia via ‘hydrogen borrowing’ using hydrido- and bis-ammine P,O(Me)-ruthenacycles

The novel cationic [RuH{PPh2(2-OMeC6H4)}2]BPh4 and neutral trans-[Ru(NH3)2{PPh2(2-OC6H4)}2] complexes were isolated from phosphine substitution reactions with [RuH(1,5-cod)(NH2NMe2)3]BPh4 and [RuCl(1,5-cod)(NH3)2(NH2NMe2)]BPh4 respectively. Ligand induced bisdemethylation of the pendent ether moieties of the phosphines occurred to give rise to the bis-phosphanylphenoxy moieties. Both complexes catalyzed the one-pot reductive amination of carbonyl compounds where excellent selectivity of aryl aldehydes over aryl ketones as precursors to the alcoholic species existed. Through substrate screening and 1H NMR studies, both steric and electronic effects of the substrates were found to influence the hydrogenation/amination mechanistic pathway, as well as direct the alcohol:amine selectivity.

Density Functional Theory Calculations Support the Additive Nature of Ligand Contributions to the pKa of Iron Hydride Phosphine Carbonyl Complexes

The acid dissociation constant Ka of a transition-metal hydride complex is a key thermodynamic quantity for evaluating reactivity and stability of the complexes and their conjugate bases in stoichiometric and catalytic reactions. It can be estimated using a simple ligand acidity constant (LAC) empirical equation for a wide range of complexes. Here, we provide the first density functional theory (DFT) study that supports the additive nature of ligand contributions to the pKa of metal hydride complexes. Specifically, the pKa values of iron hydride complexes [FeH(CO)x(PR3)(5-x)]+ in either tetrahydrofuran or dichloromethane solutions are estimated using the LAC method and DFT calculations. There is a linear correlation between these two methods, and both predict a surprisingly linear increase in pKa over a wide range from approximately -15 for x = 5 to approximately 40 for x = 0. The LAC equation predicts that pKaTHF or pKaDCM increases by 9 units with the replacement of each CO ligand with a trialkylphosphine ligand in a stepwise fashion, whereas the DFT calculations predict the step size will be approximately 11. The two methods agree with pKDCM data available for x = 3 and qualitative data for x = 1 and 0, but further quantitative measurements over a wider range are needed to firmly establish the trend. The free energy of protonation and the energy of the highest occupied molecular orbital of Fe(CO)x(PR3)(5-x) (mainly nonbonding d electrons) increase linearly with phosphine substitution, and this increases the pKa value as observed.

Mixed-metal cluster chemistry. 37. Syntheses, structural, spectroscopic, electrochemical, and optical power limiting studies of tetranuclear molybdenum–iridium clusters

Tetrahedral Mo2Ir2(μ3-CO)(μ-CO)5(CO)4(η5-C5H5)2 (1) reacted with P(C6H4Me-4)3, P(C6H2Me2-3,5-OMe-4)3, and AsPh3 to afford the substitution products Mo2Ir2(μ-CO)3(CO)6(L)(η5-C5H5)2 [L = P(C6H4Me-4)3 (3), P(C6H2Me2-3,5-OMe-4)3 (4), AsPh3 (5)] in fair to good yields, while reaction of 1 with HC≡CSiPri3 proceeded by insertion into the Mo–Mo bond to give the pseudo-octahedral Mo2Ir2(μ4-η2-HC2SiPri3)(μ-CO)4(CO)4(η5-C5H5)2 (6) in fair yield. While MoIr3(μ-CO)3(CO)7(η5-C5H5) reacted with HC≡CSiMe3 to give a complex mixture of thus-far-uncharacterized products, its phosphine substitution product MoIr3(μ-CO)3(CO)5(PPh3)2(η5-C5H5) reacted with the same alkyne via insertion into a Mo–Ir bond to afford the pseudo-octahedral MoIr3(μ4-η2-HC2SiMe3)(μ-CO)3(CO)4(PPh3)2(η5-C5H5) (8) in good yield. Clusters 4, 5 (two isomers), 6 and 8 have been characterized by single-crystal X-ray diffraction studies. Cyclic voltammetric studies of Mo2Ir2(μ-CO)3(CO)6(PPh3)(η5-C5H5)2 (2), 3–6 and 8 confirmed the tuning of redox potentials upon phosphines/arsine introduction and alkyne modification. IR spectroelectrochemical studies of 2, 6, and 8 suggest decreasing proclivity for bridging carbonyl ligands following oxidation. Variable temperature 31P NMR studies of 3 and 4 revealed interconverting isomers in solution, the structures of which are assigned as analogues of the X-ray diffraction-confirmed isomers of 5. Studies of 2–5 using ns pulses and the open-aperture Z-scan technique revealed that all are optical limiters at wavelengths in the visible region.

Tetracarbonyl(trifluoromethyl)cobalt(I) [Co(CO)4(CF3)] as a Precursor to New Cobalt Trifluoromethyl and Difluorocarbene Complexes

An improved synthesis of the known trifluoromethyl cobalt compound Co(CO)4(CF3) (1), which gives significantly higher yields than previously reported methods, allows for an investigation of its carbonyl substitution chemistry. Treatment of 1 with P-donor ligands of varying denticity under thermal conditions afforded Co[P(O-o-tolyl)3](CO)3(CF3) (2), Co(DPPE)(CO)2(CF3) (3), and Co(P3)(CO)(CF3) (4) in high isolated yields [DPPE = Ph2PCH2CH2PPh2; P3 = PhP(CH2CH2PPh2)2]. The new cobalt N-heterocyclic carbene complex Co(SIPr)(CO)3(CF3) (5) [SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene)] was obtained by phosphine substitution from Co(PPh3)(CO)3(CF3), a known compound efficiently prepared from 1. Additionally, we report the synthesis of two rare cobalt difluorocarbene complexes ([Co] = CF2) produced by fluoride abstraction from 3 or 4. These results are relevant to our efforts to assess the reactivity of first-row metal perfluoroalkyl and fluorocarbene complexes.

Novel synthetic approach to charge-compensated phosphonio-nido-carboranes. Synthesis and structural characterization of neutral mono and bis(phosphonio) nido-ortho-carboranes.

A number of monosubstituted n-(triphenylphosphonio)-7,8-dicarba-nido-undecaboranes (2a, n = 1; 2b, n = 3; 2c, n = 5; 2d, n = 9) were prepared via a cross-coupling reaction between the tetrabutylammonium iodo-7,8-dicarba-nido-undecaborates (1a-d) and PPh3 in the presence of a Pd(PPh3)4 catalyst. The substitution rate was found to depend on the iodine position in the carborane cage. Under similar conditions, the reaction of 5,6-diiodo- (3) and 9,11-diiodo-7,8-dicarba-nido-undecaborate (5) anions exclusively yielded the monosubstitution products 5-iodo-6-(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (4) and 9-iodo-11-(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (6), respectively. The reaction of tetrabutylammonium 6,9-diiodo-7,8-dicarba-nido-undecaborate (7) exclusively produced the phosphine substitution product in the open face of the nido-carborane, 6-iodo-9-triphenylphosphonio-7,8-dicarba-nido-undecaborane (8). The addition of a base (Cs2CO3, NaH) to the reactions of 3 and 5 with PPh3 afforded the corresponding bis(triphenylphosphonio)-7,8-dicarba-nido-undecaboranes, 9 and 10. Compound 10 was also prepared from 6 using the general procedure. The reaction of the triiodocarborane tetrabutylammonium 5,6,9-triiodo-7,8-dicarba-nido-undecaborate (11) with excess PPh3 in the presence of Cs2CO3 and Pd(PPh3)4 only produced neutral 5-iodo-6,9-bis(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (12); no positively charged tris(phosphonio) species formed. The compositions of all prepared compounds were determined by multinuclear NMR spectroscopy and high-resolution mass spectrometry. The structures of compounds 2c, 6, 8, 9, and 12 were established by the X-ray diffraction analysis of single crystals.

Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N(3),C(2) ligands: synthetic, structural, reactivity, electrochemical and spectroscopic studies.

Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl)lithium (1a, Ar = Mes; 1b, Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of [Ir(cod)(μ-Cl)]2 yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex [Ir(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (3), 3H-H, a head-to-head (H-H) isomer of CS symmetry, and 3H-T, the thermodynamically preferred head-to-tail (H-T) isomer of C2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3H-H and 3H-T afforded the tetracarbonyl complexes [Ir(CO)2{μ-C3H2N2(Mes)-κC2,κN3}]24H-H and 4H-T, respectively. The reaction with PMe3, which gave only one complex, [Ir(CO)(PMe3){μ-C3H2N2(Mes)-κC2,κN3}]2 (5), demonstrates that the isomerization of the central core Ir[μ-C3H2N2(Mes)-κC2,κN3]2Ir from H-H to H-T on going from 4H-H to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d(7)-d(7) complex [Ir2(CO)2(PMe3)2(Me)I{μ-C3H2N2(Mes)-κC2,κN3}2] (6). The blue [Ir(C2H4)2{μ-C3H2N2(Mes)-κC2,κN3}]2 (7) and purple [Rh(C2H4)2{μ-C3H2N2(Dipp)-κC2,κN3}]2 (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3H-T, 4H-T and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3H-T undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(i)/Ir(ii) system. The energy of the intervalence band for the orange dirhodium complex [Rh(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (8) is shifted toward lower energies in comparison with 3H-T, reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(i)/Ir(ii) and Rh(i)/Rh(ii) systems. The molecular structures of 3H-H, 3H-T, 8 and 9 have been determined by X-ray diffraction.

Template Synthesis of Tetracarbene Platinum(II) Complexes with Five- and Six-Membered-Ring N-Heterocyclic Carbenes

Reaction of 2 equiv of 2-azidoethyl isocyanide and the tetraphosphine platinum(II) complexes [1a–c](X)2 (a, PR3 = PMe3; b, PR3 = PMe2Ph; c, PR3 = PMePh2) yielded via phosphine substitution and template-controlled cyclization of the isocyanide ligands the trans-di(NH,NH-NHC) complexes [2a–c](X)2. Treatment of [2c](PF6)2 with an additional 2 equiv of 2-azidoethyl isocyanide gave the tetracarbene complex [3](PF6)2, bearing four protic NH,NH-NHC ligands derived from a five-membered heterocycle. The same template synthesis utilizing 3-azidopropyl isocyanide and complex [1c](PF6)2 gave the dicarbene complex [5](PF6)2 and, after addition of 2 equiv more of 3-azidopropyl isocyanide, the tetracarbene complex [6](PF6)2 with four protic NH,NH-NHC ligands derived from a six-membered heterocycle. The intermediate trans-di(NH,NH-NHC) platinum(II) complex [5](PF6)2 also reacts with 2 equiv of 2-azidoethyl isocyanide to give the tetracarbene complex [7](PF6)2, bearing two five-membered-ring NHCs and two six-membered-ring NHCs.

Relative binding affinities of fluorobenzene ligands in cationic rhodium bisphosphine η6–fluorobenzene complexes probed using collision-induced dissociation

A range of cationic rhodium bisphosphine η6-fluorobenzene (fluorobenzenes = C6H6−nFn, n = 1–3) and related complexes have been synthesized and characterized. These complexes act as useful organometallic precursors for catalysis or further synthetic elaboration. The relative binding affinity of the arene ligands has been investigated using Electrospray Ionisation Mass Spectrometry (ESI–MS) and two different collision-induced dissociation (CID) techniques. The influence of arene fluorination upon arene binding affinity is discussed as well as the comparison of different bis–phosphine ligands with regard to bite angle and phosphine substitution. We show that this simple technique allows fast and easy comparison of the binding affinity of arene ligands to cationic organometallic fragments.

Bioinspired Hydrogenase Models: The Mixed-Valence Triiron Complex [Fe3(CO)7(μ-edt)2] and Phosphine Derivatives [Fe3(CO)7-x (PPh3) x (μ-edt)2] (x = 1, 2) and [Fe3(CO)5(κ2-diphosphine)(μ-edt)2] as Proton Reduction Catalysts.

The mixed-valence triiron complexes [Fe3(CO)7–x(PPh3)x(μ-edt)2] (x = 0–2; edt = SCH2CH2S) and [Fe3(CO)5(κ2-diphosphine)(μ-edt)2] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an anti arrangement of the dithiolate bridges, and PPh3 substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF4·Et2O, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe3(CO)5(PPh3)2(μ-edt)2]+ and [Fe3(CO)5(κ2-diphosphine)(μ-edt)2]+, species which also result upon oxidation by [Cp2Fe][PF6]. The electrochemistry of the formally Fe(I)–Fe(II)–Fe(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe3(CO)5(PPh3)2(μ-edt)2] is oxidized at −0.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between −1.47 V for [Fe3(CO)7(μ-edt)2] and around −1.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe2(CO)6(μ-edt)], [Fe3(CO)7(μ-edt)2] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron–iron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.

Phosphine substitution reactions of (η5-cyclopentadienyl)ruthenium bis(triarylphosphine) chloride, CpRu(PAr3)2Cl {PAr3 = PPh3, P(p-CH3C6H4)3, P(p-FC6H4)3, P(p-CH3OC6H4)3, and PPh2(p-CH3C6H4)}: a tale of two mechanisms.

The kinetics of phosphine substitution in CpRu(PAr3)2Cl by PMePh2 under pseudo-first order conditions in CDCl3 have been measured for PAr3 = PPh3, 1a, PPh2(p-tol), 1b, P(p-tol)3, 1c, P(p-CH3OC6H4)3, 1d, and P(p-FC6H4)3), 1e. Activation parameters characteristic of a dissociative pathway (ΔH(†) = 110-124 ± 2 kJ mol(-1), ΔS(†) = 16-44 ± 5-12 J mol(-1) K(-1)) are observed for all five compounds. The rate of substitution in CpRu(PAr3)2Cl (1a) and CpRu[P(p-FC6H4)3]2Cl (1e) is independent of added chloride ion and decreases in the presence of excess PAr3, however, the rate of substitution in CpRu[P(p-CH3OC6H4)3]2Cl (1d) is first order in added chloride ion and is less dependent on added PAr3. A mechanism involving [CpRu(PAr3)2(PMePh2)](+)[Cl](-) intermediates contributes to the substitution in 1b-d.

Generation of σ,π-furyl and thienyl ligands at di-iron centers via facile phosphorus–carbon bond cleavage: Synthesis and molecular structures of [Fe2(CO)6(μ-η1,η2-C4H3E){μ-P(C4H3E)2}] (E = O, S)

Treatment of [Fe3(CO)12] with tri(2-furyl)phosphine (PFu3) or tri(2-thienyl)phosphine (PTh3) in dichloromethane at 40°C leads to facile phosphorus–carbon bond scission affording di-iron furyl- and thienyl-bridged complexes [Fe2(CO)6(μ-η1,η2-C4H3E){μ-P(C4H3E)2}] (1E=O, Fu; 3E=S, Th) in good yields, together with smaller amounts of the phosphine-substituted [Fe2(CO)5(μ-η1,η2-C4H3E){μ-P(C4H3E)2}{P(C4H3E)3}] (2E=O, 4E=S). When the same reactions were carried out at room temperature, small amounts of the tri-iron clusters [Fe3(CO)11{P(C4H3E)3}] (5E=O, 6E=S) were isolated in which the coordinated phosphine(s) remain intact. Thermolysis of [Fe3(CO)11{P(C4H3E)3}] at 40°C in dichloromethane gave [Fe2(CO)6(μ-η1,η2-C4H3E){μ-P(C4H3E)2}], which also undergo phosphine substitution under similar conditions. However, both of these processes are too slow to account for the reaction product ratios and yields observed in the room temperature reactions. In contrast, addition of catalytic amounts of Na+[Ph2CO] to 5 resulted in the rapid formation of 1. We therefore propose that these reactions may occur via a radical-initiated mechanism proceeding through the initial formation of the 49-electron radical anions [Fe3(CO)11{P(C4H3E)3}]. The crystal structures of [Fe2(CO)6(μ-η1,η2-Fu)(μ-PFu2)] (1), [Fe2(CO)5(μ-η1,η2-Fu)(μ-PFu2)(PFu3)] (2), [Fe2(CO)6(μ-η1,η2-Th)(μ-PTh2)] (3) and [Fe3(CO)11(PFu3)] (5) have been determined. The di-iron complexes all show the expected cis arrangement of three-electron donor ligands, short iron–iron distances consistent with a 34-valence electron count, and, in 2, the phosphine is coordinated to the π-bound iron atom and lies trans to the metal–metal bond. Close inspection of the bonding parameters within the Fe2C2E core reveals that these alkenyl species are quite different to those without electron-withdrawing substituents. The tri-iron cluster 5 has two independent molecules in the asymmetric unit. Each contains two bridging carbonyls and the molecules differ in the relative positions of these carbonyls and the coordinated phosphine ligand, the latter lying in the equatorial plane in both molecules.

Syntheses, structures, and anticancer activity of novel organometallic ruthenium–maltol complexes

Organometallic ruthenium complexes containing two dehydrogenated maltol ligands Ru3(CO)8(2L–2H) 1, Ru3(CO)7PPh3(2L–2H) 2, [Ru3(CO)7 (2L–2H)]2(dppm or dppe) 3,4 (L = Maltol) have been synthesized and characterized. The in vitro anticancer activity of compounds 1–4 against seven types of human cancer cell lines was assessed and compared to clinically used drug cisplatin. The anticancer activity of compound 1 (Fig. 3) is many times more potent than cisplatin against seven types of human cancer cell lines. There is a correlation between substituting a CO ligand in 1 with different phosphines decreases the activity following the order 1 > 2 > 3 > 4. The X-ray crystal structures of complexes 1 and 2 are reported. The single crystal X-ray diffraction structure of 1 consists of a triangular ruthenium metal framework in which a Ru–Ru bond is bridged by two maltolate ligands with their two oxygen atoms in a μ−η2-bonding mode. The dihedral angle between Ru3 and maltol planes is 40.2°. The two ruthenium atoms bridged by maltol ligands each have two carbonyl ligands and the third ruthenium atom is bonded to four carbonyl ligands. The greatest structural difference between 1 and 2 is the angle between the best planes of the two coordinated C6H5O3−1 ligands; in 1 it is 27.1° while in 2 it is 42.8°. It is interesting to note that the phosphine substitution occurs at the ruthenium atom not bound by maltol ligands.

Photocatalytic properties of new cyclopentadienyl and indenyl rhodium(I) carbonyl complexes with water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA) and tris(2-cyanoethyl)phosphine

Reactions of [( η 5-R)Rh(CO) 2] (R = cp, ind) with water-soluble phosphines (L = 1,3,5-triaza-7-phosphaadamantane and tris(2-cyanoethyl)phosphine) give the new rhodium(I) complexes of the types [Rh( η 5-cp)(CO)(PTA)] ( 1), [Rh( η 5-cp)(CO)(P(CH 2CH 2CN) 3)] ( 2), [Rh( η 5-ind)(CO)(PTA)] ( 3) and [Rh( η 5-ind)(CO)(P(CH 2CH 2CN) 3)] ( 4) in isolated yields of 52–75%. All these compounds have been fully characterized by IR, 1H, 31P{ 1H} and 13C{ 1H} NMR, FAB-MS spectroscopies and elemental analyses. Reactivity for the substitution of phosphine is greater for [( η 5-ind)Rh(CO)(L)] comparing to [( η 5-cp)Rh(CO)(L)] because of a flexibility of the indenyl ligand to undergo facile η 5– η 3 coordinative isomerizations. The obtained complexes are active catalyst precursors for the dehydrogenation of propan-2-ol, octane and cyclooctane under photoassisted conditions without any organic hydrogen transfer acceptors, giving TOFs of 26–56 using 3 as precatalyst.

A simple synthesis of trans-RuCl(CCR)(dppe)2 complexes and representative molecular structures

Abstract The five-coordinate complex [RuCl(dppe)2]OTf ([2]OTf) is obtained in high yield by the sequential reduction of RuCl3 · nH2O to RuCl2(PPh3)3, subsequent phosphine substitution to give trans-RuCl2(dppe)2 (trans-1) and finally chloride abstraction (AgOTf, CH2Cl2). The use of [2]OTf as an entry point to mono-acetylide complexes trans-RuCl(C CC6H4R-4)(dppe)2 (3) is described, and represents an alternative route to the long-standing methods based on cis-RuCl2(dppe)2 (cis-1), which is always prepared as a mixture with the more thermodynamically stable trans isomer when prepared by phosphine substitution reactions of RuCl2(dmso)4. The molecular structures of [2]OTf, trans-RuCl(C CC6H4OMe-4)(dppe)2 (3b), trans-RuCl(C CC6H4Me-4)(dppe)2 (3c) and trans-RuCl(C CC6H4CO2Me-4)(dppe)2 (3e) are described. A facile and reproducible synthesis of cis-1 is also reported.