Phosphine Substitution Research Articles

Stabilization of Fully Reduced Iron−Sulfur Clusters by Carbene Ligation: The [FenSn]0 Oxidation Levels (n = 4, 8)

The all-ferrous [Fe4S4](0) state has been demonstrated in the fully reduced Fe protein of the Azotobacter vinelandii nitrogenase complex. We seek synthetic analogues of this state more tractable than the recently prepared but highly unstable cluster [Fe4S4(CN)4](4-) (Scott, Berlinguette, Holm, and Zhou, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Pr(i)2NHCMe2) has been found to stabilize the fully reduced clusters [Fe8S8(Pr(i)2NHCMe2)6] (4) and [Fe4S4(Pr(i)2NHCMe2)4] (5), which are prepared by cluster assembly or phosphine substitution of FenSn (n = 8, 16) clusters. Cluster 4 is also obtained by reaction of the carbene with all-ferrous [Fe7S6(PEt3)5Cl2] (3) and cluster 5 by carbene cleavage of 4. Detailed structures of 3 (monocapped prismatic), 4, and 5 are described; the latter two are the first iron-sulfur clusters with Fe-C sigma bonds. Cluster 4 possesses the [Fe8(mu3-S) 6(mu4-S)2] edge-bridged double cubane structure and 5 the cubane-type [Fe4(mu3-S)4] stereochemistry. The all-ferrous formulations of the clusters are confirmed by X-ray structure parameters and (57)Fe isomer shifts. Both clusters are stable under conventional aprotic anaerobic conditions, enabling further study of reactivity. The collective properties of 5 indicate that it is a meaningful synthetic analogue of the core of the fully reduced protein-bound cluster.

Square planar diphosphinoazine rhodium(I) amido carbonyl complexes with an unsymmetrical PNP′ pincer-type coordination

A series of novel diphosphinoazine rhodium amido carbonyl complexes [{R 2PCH C(Bu t )–NN C(Bu t )CH 2PR 2}Rh(CO)] ( R = Ph, Pr i , c-C 6H 11, Bu t ) was prepared by deprotonation of cationic diphosphinoazine rhodium amino carbonyl complexes. The complexes were characterized by NMR as were also their precursors. The crystal structures of two cationic and one neutral deprotonated complex were determined by X-ray diffraction showing the complexes to be essentially planar with mutual trans arrangement of phosphine groups and nitrogens trans to carbonyl ligands. Measurement of valence vibration frequencies of carbonyl groups in the complexes allowed to estimate the electron density on the rhodium centre. The ene-hydrazone ligand backbone (nitrogen covalently bonded) is more electron donating than the azine backbone (nitrogen bonded by electron pair donation) as expected. In the neutral series of complexes electron donation increases with phosphine substitution in the order Ph < Pr i = c-C 6H 11 < Bu t with the corresponding decrease of carbonyl valence vibration frequency. The tert-butyl cationic complex undergoes in a low yield an unusual diphosphinoazine bond cleavage with simultaneous oxidation of the metal resulting in a binuclear bis(iminophosphine)dirhodium complex [{(Bu t ) 2PCH 2C(Bu t ) NH}Rh(Cl) 2(μ-Cl)] 2 the structure of which was also determined by X-ray diffraction.

Computational Study of C−C Activation of 1,3-Dimesitylimidazol-2-ylidene (IMes) at Ruthenium: The Role of Ligand Bulk in Accessing Reactive Intermediates

Density functional theory calculations have been employed to model phosphine substitution in Ru(PPh3)3(CO)(H)2 to form Ru(IMes)(PPh3)2(CO)(H)2 (1mono) and Ru(IMes)2(PPh3)(CO)(H)2 (1bis), as well as the novel C(aryl)−C(sp3) intramolecular bond activation of the IMes ligand in 1bis. The computed ligand exchange energies show that 1bis is unstable with respect to displacement of IMes by PPh3 and will thus re-form 1mono over time. PPh3/IMes substitution also leads to a significant labilization of the PPh3 ligand trans to hydride, a result of increasing steric encumbrance upon the introduction of the bulky IMes ligands. The energetics of intramolecular C−C and C−H activation have been computed for both 16e Ru(IMes)n(PPh3)3-n(CO) and 14e Ru(IMes)n(PPh3)2-n(CO) species (n = 1 or 2) and indicate that the introduction of a second IMes ligand does not significantly promote the actual C−C activation step. Instead the need to have two IMes ligands present in the metal coordination sphere before C−C activation can occ...

Carbon-bridged diphosphine ligands for chromium-catalysed ethylene tetramerisation and trimerisation reactions

The use of carbon-bridged diphosphine ligands in chromium-catalysed ethylene tri- and tetramerisation reactions has been investigated. Two- and three-carbon spacer ligands all showed activity for selective oligomerisation, with a structure–selectivity correlation between P–Cr–P bite angle and 1-octene:1-hexene ratio evident. Activated chromium complexes of single carbon spacer diphosphines were also shown to be effective tetramerisation catalysts, provided that the ligand is innocent under the conditions of catalyst activation. A catalyst with the bis(diphenylphosphino)benzene ligand was found to be exceptionally active, although the combined 1-hexene and 1-octene selectivity was lower than with the best diphosphinoamine (PNP) ligands. The yield losses to by-products can to an extent be minimised by the use of high reaction temperatures and pressures. Unlike with the PNP-based systems, attempts to activate the Cr/bis(diphenylphosphino)benzene catalyst in situ from a chromium salt and free ligand resulted in low activity and high polymer formation. The effect of different phosphine substitution on catalyst selectivity was explored. Steric constraints around the catalytic centre ( ortho-alkylphenyl phosphines) resulted in a shift towards 1-hexene formation, as with PNP catalysts. Additionally, the basicity of the phosphines appears to influence catalyst selectivity, with alkyl phosphines favouring trimerisation. An interplay between phosphine basicity and bridge structure is in evidence, however, as a catalyst containing a ligand with both basic phosphine atoms and a small bite angle was shown to be selective towards 1-octene.

Carbonyl(5-chloroquinolin-8-olato-κ2N,O)[tris(4-chlorophenyl)phosphine-κP]rhodium(I)

In the title compound, [Rh(C9H7ClNO)(C18H12Cl3P)(CO)], the phosphine ligand is trans to the N atom of the quinolinolate ligand. This indicates that changes in the electronic properties of the quinolinolate backbone have a negligible influence on the phosphine substitution. Important geometrical parameters are the quinolinolate bite angle of 80.15 (9)° and the Rh—P bond distance of 2.2478 (9) A, the effective cone angle (ΘE) for the phosphine ligand being 165°. Quinoline ligand-to-ligand π-stacking is in a tail-to-tail fashion with an inter­molecular distance of 3.26 A. The molecule also exhibits intramolecular C—H⋯Cl and C—H⋯O hydrogen bonds.

Experiments in Thermodynamics and Kinetics of Phosphine Substitution in (p-Cymene)RuCl2(PR3)

This manuscript describes a set of three experiments that investigates the thermodynamic and kinetic aspects of phosphine substitution at a Ru center. In the first experiment, the students synthesize a Ru organometallic complex containing a phosphine ligand. In the second, equilibria for phosphine substitution involving several different phosphines are studied. The equilibrium constants are converted into free energies of reactions which are compared with data from literature thermochemical studies. In the third experiment, the kinetics of the substitution of tris(p-fluorophenyl)phosphine is studied using variable-temperature (25�60 °C range) 19F NMR. The kinetic studies confirm that this reaction follows a simple first-order rate law. With some approximations, combining the data obtained here and the literature thermochemical data allow estimation of the strength of a bridging Ru�Cl bond in the starting material used in this laboratory set. The materials used in these experiments are relatively inexpensive and air-stable.

Dimerization of terminal alkynes catalyzed by chloro(η 5-pentadienyl) bis(triphenylphosphine)ruthenium(II) and kinetics of phosphine substitution

Exchange of PMe 2Ph for PPh 3 in (η 5-pentadienyl)ruthenium{bis(triphenylphosphine)}chloride, (η 5-C 5H 7)Ru(PPh 3) 2Cl ( 1) under first order conditions proceeds rapidly in THF at room temperature. A pseudo-first order rate constant of 17 ± 2 × 10 −4 s −1 is obtained for the reaction at 21 °C. The rate constant is essentially independent of the phosphine concentration. The activation parameters, Δ H † = 16.1 ± 0.4 kcal mol −1 and Δ S † = −16 ± 1 cal K −1 mol −1 differ from those reported for phosphine exchange in CpRu(PPh 3) 2Cl ( 2) and (η 5-indenyl)Ru(PPh 3) 2Cl ( 3). The reaction of 1 with PMe 2Ph is about 70 times faster than the reaction of 2 at 30 °C and some 40 times faster than the reaction of 3 at 20 °C. (η 5-C 5H 7)Ru(PPh 3) 2Cl( 1) is more active than the ruthenium(II) complexes 2, 3, and TpRu(PPh 3) 2Cl ( 4) in the catalytic dimerization of terminal alkynes with nearly quantitative conversion of PhCCH and FcCCH at ambient temperature in 24 h. The enhanced substitution rate is accompanied by >50% conversion of phenylacetylene to oligomeric products. Reaction of 1 with NaPF 6 in acetonitrile yields the cationic ruthenium(II) complex [(η 5-C 5H 7)Ru(PPh 3) 2(CH 3CN)][PF 6] ( 7). The latter complex is much less active in reactions with phenylacetylene than 1 but avoids the formation of oligomeric products.

Heats of Formation of Co(CO)2NOPR3, R = CH3 and C2H5, and Its Ionic Fragments

A joint threshold photoelectron photoion coincidence spectrometry (TPEPICO) and collision-induced dissociation (CID) study on the thermochemistry of Co(CO)(2)NOPR(3), R = CH(3) (Me) and C(2)H(5) (Et), complexes is presented. Adiabatic ionization energies of 7.36 +/- 0.04 and 7.24 +/- 0.04 eV, respectively, were extracted from scans of the total ion and threshold electron signals. In the TPEPICO study, the following 0 K onsets were determined for the various fragment ions: CoCONOPMe(3)(+), 8.30 +/- 0.05 eV; CoNOPMe(3)(+), 9.11 +/- 0.05 eV; CoPMe(3)(+) 10.80 +/- 0.05 eV; CoCONOPEt(3)(+), 8.14 +/- 0.05 eV; CoNOPEt(3)(+), 8.92 +/- 0.05 eV; and CoPEt(3)(+), 10.66 +/- 0.05 eV. These onsets were combined with the Co(+)-PR(3) (R = CH(3) and C(2)H(5)) bond dissociation energies of 2.88 +/- 0.11 and 3.51 +/- 0.17 eV, obtained from the TCID experiments, to derive the heats of formation of the neutral and ionic species. Thus, the Co(CO)(2)NOPR(3) (R = CH(3) and C(2)H(5)) 0 K heats of formation were found to be -350 +/- 13 and -376 +/- 18 kJ x mol(-)(1), respectively. These heats of formation were combined with the published heat of formation of Co(CO)(3)NO to determine the substitution enthalpies of the carbonyl to phosphine substitution reactions. Room-temperature values of the heats of formation are also given using the calculated harmonic vibrational frequencies. Analysis of the TCID experimental results provides indirectly the adiabatic ionization energies of the free phosphine ligands, P(CH(3))(3) and P(C(2)H(5))(3), of 7.83 +/- 0.03 and 7.50 +/- 0.03 eV, respectively.

Investigations of Benzyl and Aryl Palladium Complexes with Pendant Hydroxy Substituents and Their Transformation into Benzolactones on Carbonylation

Reactions of 2-hydroxymethylbenzyl halides with Pd(PPh3)4 afford complexes Pd(CH2C6H4-2-CH2OH-κ2C1α,O)(PPh3)X (X = Br, 3; X = Cl, 4) containing bidentate 2-hydroxymethylbenzyl ligands. Further reactions of 3 or 4 with NaH produce the binuclear cyclocondensation product Pd2(μ-2-OCH2C6H4CH2)2(PPh3)2, 7, containing a central planar Pd2O2 unit incorporated into a system of five fused rings. Compound 7 undergoes phosphine substitution to form related binuclear products Pd2(μ-2-OCH2C6H4CH2)2(PAr3)2 {Ar = p-MeC6H4, 8; p-(MeO)C6H4, 9} but is cleaved by more electron-donating phosphines and by diphosphines to give mononuclear alkoxides Pd(OCH2C6H4CH2-κ2C1α,O)(P−P) (P−P = dppf, 10; dppe, 11). Compounds 3, 4, and 7−9 react readily with carbon monoxide to liberate the lactone 3-isochromanone via carbonyl insertion, and the acyl intermediate PdCl(COCH2C6H4-2-CH2OH)(PPh3), 12b, has been studied spectroscopically. Reactions of 2-halogenobenzenealkanols with Pd(PPh3)4 afford simple derivatives with monodentate aryl ligands, trans-Pd(C6H4-2-(CH2)nOH)(PPh3)2X (n = 1, X = Br, 15; n = 2, X = I, 17) and the known complex (n = 1, X = I, 14), which on reaction with NaH are also converted into binuclear products Pd2(μ-2-O(CH2)nC6H4)2(PPh3)2 {n = 1, 19a (previously reported) and n = 2, 20}; compound Pd2(μ-2-OCH2C6H4)2{P(C6H4-4-OMe)3}2, 25, is formed from 19a by phosphine exchange, and cleavage of 19a or 20 by diphosphines generates new mononuclear complexes 22−24 containing chelating alkoxide ligands. Carbonylations of these arylpalladium derivatives of 2-hydroxyalkylphenyl halides to form the respective benzolactones, phthalide and 3,4-dihydroisocoumarin, have been investigated. Crystal structures of mononuclear compounds 3, 4, 14, and 17, including intermolecular H-bonding interactions to halogen ligands in the solid state, and of binuclear compounds 7, 8, and 25 are reported and discussed. The new complexes are discussed in relation to the mechanism of Pd(0)-catalyzed syntheses of benzolactones from aromatic halo alcohols; in production of 3-isochromanone, the results support a process involving coordination of a hydroxyl group prior to reductive elimination of organic product but with CO insertion into the Pd−C rather than the Pd−O bond.

Effect of Phosphine Substitution on the Electronic Structure of Cobalt Tricarbonyl Nitrosyl

The He-I ultraviolet photoelectron spectra of a series of phosphine-substituted organometallic complexes, Co(CO) 2 NOL (L = CO, PMe 3 , PEt 3 , PPr 3 , PBu 3 , PCy 3 , PPh 3 , and P(OMe) 3 ) are reported. The first vertical ionization energy of the complexes was found to be 8.75 (CO), 7.85 (PMe 3 ), 7.69 (PEt 3 ), 7.47 (PPr 3 ), 7.49 (PBu 3 ), 7.71 (PCy 3 ), 7.58 (PPh 3 ), and 8.15 eV (P(OMe) 3 ) ′ 0.03 eV. Quantum chemical calculations at the HF, DFT (B3LYP), and EOMIP-CCSD levels of theory were employed to interpret both the trends in the series and the most important features of the spectra. Photoelectron spectra of some of the complexes are also reported at He-II photon energy. Intensity changes in the photoelectron bands between He-I and He-II photon energies are discussed on the basis of the orbital compositions.

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten–triiridium clusters

Reaction of WH(CO) 3(η-C 5Me 5) with IrCl(CO) 2(4-H 2NC 6H 4Me) affords WIr 3(μ-CO) 3(CO) 8(η-C 5Me 5) in low yield. A structural study reveals a WIr 2-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr 3(CO) 11(η-C 5H 5) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr 3(CO) 11(η-C 5H 5) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. 13C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr 3(CO) 11(η-C 5H 5) and the related tetrahedral cluster W 2Ir 2(CO) 10(η-C 5H 5) 2 are very fast and involve all carbonyls on the clusters. DFT calculations on MIr 3(CO) 11(η-C 5H 5) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener.

Synthesis and Thermal Rearrangement of Tetramethyldisilane‐bridged Bis(cyclopentadienyl) Diiron Complexes with Bis (phosphine) Substitution

AbstractPhotolysis of (Me2SiSiMe2) [C5H4Fe (CO)2]2 with a series of bis‐(phosphine) ligands Ph2P(CH2)n PPh2 (n = 1–4) leads to the formation of the corresponding diiron complexes with intramolecular and intermolecular bis (phosphine) substitution. When these complexes were heated in refluxing xylene, only in the complexes with intermolecular bis (phosphine) substitution the thermal rearrangement reaction occurred.

Synthesis and reactions of cubane-type iron-sulfur-phosphine clusters, including soluble clusters of nuclearities 8 and 16.

A family of soluble, reduced iron-sulfur clusters with nuclearities 4, 8, and 16 having tertiary phosphine ligation and based on the Fe(4)S(4) cubane-type structural motif has been synthesized. The results of this investigation substantially extend and improve the results of our original work on iron-sulfur-phosphine clusters (Goh, C.; Segal, B. M.; Huang, J.; Long, J. R.; Holm, R. H. J. Am. Chem. Soc. 1996, 118, 11844). A general property of this cluster family is facile phosphine substitution. The clusters [Fe(4)S(4)(PR(3))(4)](+) are precursors to monosubstituted [Fe(4)S(4)(PR(3))(3)X] (X = Cl-, RS-), homoleptic [Fe(4)S(4)(SR)(4)](3-), and all-ferrous monocubanes [Fe(4)S(4)(PR(3))(4)] (R = Pr(i), Cy, Bu(t); generated in solution). In turn, [Fe(4)S(4)(PPr(i)()(3))(3)(SSiPh(3))] and [Fe(4)S(4)(PPr(i)(3))(4)] can be transformed into the dicubanes [Fe(8)S(8)(PPr(i)()(3))(4)(SSiPh(3))(2)] and [Fe(8)S(8)(PPr(i)((3))(6)], respectively. Further, the tetracubanes [Fe(16)S(16)(PR(3))(8)] are also accessible from [Fe(4)S(4)(PR(3))(4)] under different conditions. X-ray structures are described for [Fe(4)S(4)(PCy(3))(3)X] (X = Cl-, PhS-), [Fe(8)S(8)(PPr(i)(3))(4)(SSiPh(3))(2)], [Fe(8)S(8)(PPr(i)()(3))(6)], and [Fe(16)S(16)(PCy(3))(8)]. The monosubstituted clusters show different distortions of the [Fe(4)S(4)](+) cores from idealized cubic symmetry. The dicubanes possess edge-bridged double cubane structures with an Fe(2)(mu(4)-S)(2) bridge rhomb and idealized C(2)(h)() symmetry. The ready cleavage of these clusters into single cubanes is considered a probable consequence of strained bond angles at the mu(4)-S atoms. Tetracubanes contain four individual cubanes, each of which is implicated in two bridge rhombs so as to generate a cyclic structure of idealized D(4) symmetry. Redox properties and Mössbauer spectroscopic parameters are reported. The species [Fe(4)S(4)(PR(3))(4)] (in solution), [Fe(8)S(8)(PR(3))(6)], and [Fe(16)S(16)(PR(3))(8)] are the only synthetic all-ferrous clusters with tetrahedral iron sites that have been isolated. Their utility as precursors to other highly reduced iron-sulfur clusters is under investigation.

Phosphine substituted Ru 3(μ-dppm)(CO) 10: structural trends within [Ru 3(μ-dppm)(PR 3)(CO) 9] (R=Et, Ph, Cy and Pr i)

The complexes [Ru 3(μ-dppm)(PR 3)(CO) 9] (R=Et, Ph, Cy, Pr i } were prepared from [Ru 3(μ-dppm)(CO) 10] by simple phosphine substitution reactions at room temperature and their structures determined by single crystal X-ray studies. Variations in the RuRu bond adjacent to the phosphine ligand suggest the enhanced reactivity of [Ru 3(μ-dppm)(CO) 10] over the parent carbonyl [Ru 3(CO) 12] to be consequent on the inability of [Ru 3(μ-dppm)(CO) 10] to effectively relieve steric congestion imposed by the presence of the bulky, bidentate dppm ligand.

Reactions of tungsten phosphonium carbyne complexes with aryloxide nucleophiles to form aryloxycarbyne and η 2-ketenyl complexes

Tungsten phosphoranylideneketene complexes of the type Tp′(CO)( p-OC 6H 4R)W(η 2-(C,C)OCCPR′ 2Ph) (R=NO 2, R′=Me ( 6a); R=NO 2, R′=Ph ( 6b); R=CN, R′=Me ( 7a); R=CN, R′=Ph ( 7b); R=Cl, R′=Ph ( 8b)) have been synthesized from phosphonium carbyne precursors in a reaction that reflects coupling of carbonyl and carbyne ligands. In addition to these products, aryloxycarbyne complexes Tp′(CO) 2WCO( p-C 6H 4NO 2) ( 9a), Tp′(CO) 2WCO( p-C 6H 4CN) ( 9b), and Tp′(CO) 2WCO( p-C 6H 4Cl) ( 9c)) have been prepared via substitution of the phosphonium carbyne phosphine with an aryloxide nucleophile. The product ratio of substitution at the carbyne carbon to carbonyl–carbyne coupling can be tuned by variation of the aryloxide para-substituent. Aryloxy carbyne complexes are the favored products with stronger nucleophiles, while weaker nucleophiles result in a mixture of aryloxy carbyne complexes and η 2-ketenyl coupled complexes. Formation of η 2-ketenyl complexes is favored for the least nucleophilic aryloxides. Ketenyl complexes 6a and 6b were methylated at the ketenyl oxygen to form cationic alkyne complexes [Tp′(CO)( p-OC 6H 4NO 2)W(η 2-(C,C)CH 3OCCPR 2Ph)][OTf] (R=Me ( 10a), R=Ph ( 10b)). The structures of η 2-ketenyl complexes 6a and 7b and the structure of cationic alkyne complex 10a were determined by X-ray crystallography.

Fluxional processes and structural characterization of μ 3-η 2,η 2,η 2-C 60 triosmium cluster complexes, Os 3(CO) 9− n(PMe 3) n(μ 3-η 2,η 2,η 2-C 60) ( n=1, 2, 3)

The title complex, Os 3(CO) 6(PMe 3) 3(μ 3-η 2,η 2,η 2-C 60) ( 3), has been prepared by decarbonylation of Os 3(CO) 9(μ 3-η 2,η 2,η 2-C 60) with three equivalents of Me 3NO in the presence of excess PMe 3 ligand. The solid-state structures of Os 3(CO) 7(PMe 3) 2(μ 3-η 2,η 2,η 2-C 60) ( 2) and 3 have been determined by single-crystal X-ray diffraction studies. Compound 2 has two inequivalent equatorial phosphine ligands on adjacent osmium atoms and compound 3, with a distorted C 3 symmetry, has one equivalent equatorial phosphine ligand on each osmium center. The fluxional processes of Os 3(CO) 8(PMe 3)(μ 3-η 2,η 2,η 2-C 60) ( 1), 2, and 3 have been examined by variable-temperature 13C- and 31P-NMR studies. Only one isomer exists in solution and a restricted ligand rotation on each phosphine-substituted osmium center appears to occur for all three compounds, 1– 3. Activation barriers for the carbonyl exchange process increase with increasing phosphine substitution, presumably, due to the steric effect of the phosphine ligands.

Proton reactivity of butterfly oxo and sulfido clusters and structural characterization of HFe3Mn(CO)10(dmpm)(μ4-O)

Phosphine substitution for CO in the butterfly oxo cluster [Fe3Mn(CO)12(μ4-O)]− (1) produces the bis-phosphine clusters [Fe3Mn(CO)10(PR3)2(μ4-O)]− (R=OCH3 (2a), CH3 (2b)) and [Fe3Mn(CO)10(dmpm)(μ4-O)]− (3). In the presence of the strong acid, HSO3CF3, the oxo cluster 1 is not protonated, 3 is protonated at the Fe-Fe backbone of the butterfly, and [Fe3Mn(CO)12(μ4-S)]− (5) loses CO and Mn upon protonation to yield H2Fe3(CO)9(μ3-S) and a manganese containing by-product. The structure of the protonated cluster HFe3Mn(CO)10(dmpm)(μ4-O) (4), determined by single-crystal X-ray diffraction, compared with its parent, 1, compound 4, has elongated metal-metal bonds, a smaller dihedral angle (111° compared to 113°), and shorter wingtip metal-to-oxo ligand distances. Additionally, the carbonyl ligands on 4 shift to accommodate the hydride ligand on the hinge iron metals and the bidentate phosphine ligand spanning the hinge and wingtip iron atoms. The butterfly clusters were characterized by 1H NMR, variable temperature 13C NMR, 31P NMR, and infrared spectroscopy. Crystal data for 4: monoclinic (Cc), a=7.917(2), b=18.541(2), c=16.196(1) Å, β=95.41(1)°, Z=4, R (Rw)=0.022 (0.029).

Mixed chloride/amine complexes of dimolybdenum(II,II). 6. Stepwise substitution of amines by tertiary phosphines and vice versa: stereochemical hysteresis.

The substitution reactions of primary amines by tertiary phosphines in quadruply bonded dimolybdenum(II,II) complexes Mo2Cl4(NH2R)4 have been studied. The exchange reaction has been shown to result at room temperature in disubstituted species Mo2Cl4(NH2R)2(PR3)2 (PR3 = PMe3, NH2R = NH2Prn (1a), NH2But (2a), NH2Cy (3a); PR3 = PMe2Ph, NH2R = NH2Cy (4a)), while heating is needed to obtain fully substituted complexes Mo2Cl4(PR3)4. The crystal structure of disubstituted products has been investigated by X-ray crystallography and revealed that they all belong to the alpha-isomer, having both phosphine groups at the same Mo atom. Crystal data are as follows: for 1a, tetragonal space group I4(1/a) with a = 17.737(2) A, c = 15.6915(6) A, and Z = 8; for 3a, monoclinic space group P2(1) with a = 10.963(3) A, b = 10.117(2) A, c = 13.323(4) A, beta = 90.05(2) degrees, and Z = 2; for 4a, triclinic space group P1 with a = 9.329(3) A, b = 10.206(2) A, c = 18.975(3) A, alpha = 85.45(2) degrees, beta = 87.10(1) degrees, gamma = 80.88(1) degrees, and Z = 2. The substitution processes for the direct and reverse reactions have been monitored by 31P NMR. They both proceed in a stepwise manner; however, a stereochemical hysteresis is taking place, i.e., the back reaction, the substitution of phosphines by amines, goes through another isomer of Mo2Cl4(NH2R)2(PR3)2, having phosphine ligands on different Mo atoms. This beta-isomer is more thermodynamically stable and can be obtained by thermal conversion of the alpha-form. All chemical equilibria studied in the paper have been explained as governed by a higher trans effect of PR3 groups compared to NH2R groups.

Reactions of the dirhenium(III,III) complex cis-Re2(μ-O2CMe)2Cl4(H2O)2 that lead to the dirhenium(III,II) complexes Re2(μ-O2CMe)Cl4(PR3)2 and tetrarheniumcyclodiyne clusters of the type Re4(μ-O)4Cl4(PR3)4

The reaction of cis-Re2(μ-O2CMe)2Cl4(H2O)2 1 with P(C6H4OMe-p)3 gives the tetranuclear complex Re4(μ-O)4Cl4[P(C6H4OMe-p)3]4 14 along with the salt [(C6H4OMe-p)3PMe]2Re2Cl8 15. Compound 14 is the first symmetrical, neutral, tetrarheniumcyclodiyne type cluster that contains phosphine ligands. Complexes of this same type with PPh3 (16) and PMe2Ph (17) have been prepared by alternative methods but have poor solubility properties. The paramagnetic complex Re2(μ-O2CMe)Cl4(PPh3)2 2, which is prepared from 1 by reaction with PPh3, undergoes phosphine substitution reactions when treated with dichloromethane solutions of other phosphines. Simple non-redox reactions can occur upon reaction of 2 with monodentate and bridging bidentate phosphines to afford complexes of the types Re2(μ-O2CMe)Cl4(PR3)2 [PR3 = PBz3 3, P(C6H4OMe-p)3 4 or PMePh2 5] and trans-Re2(μ-O2CMe)Cl4(μ-PP)2 [PP = dppm 9, Ph2PNHPPh2 10 or (Ph2P)2CCH2 11]. However, reactions that lead either to reduction to dirhenium(II) complexes or Re–Re bond cleavage are encountered in the case of the reactions of 2 with PMePh2, PMe2Ph, PCy3 and dppe; these have led to the isolation of Re2Cl4(PMePh2)4 6, Re2Cl4(PMe2Ph)4 7, mer-trans-ReOCl3(PCy3)2 8, α-Re2Cl4(dppe)2 12, and trans-[ReO2(dppe)2]Cl 13. The structures of compounds 3, 8, 13, 14 and 15 have been determined by X-ray crystallography.

Photoelectron Spectra of Trimethylphosphine-Substituted Tungsten Carbonyls: Ligand Field Effects, Ligand Additivity Effects, and Core-Valence Ionization Correlations.

High-resolution broad-scan gas-phase photoelectron spectra using synchrotron radiation (including valence, inner valence, and core levels) are reported for a series of trimethylphosphine-substituted tungsten carbonyls: W(CO)(6), W(CO)(5)PMe(3), cis-W(CO)(4)(PMe(3))(2), trans-W(CO)(4)(PMe(3))(2), and fac-W(CO)(3)(PMe(3))(3). The inner valence and core level spectra are interpreted by comparison with the published spectra of W(CO)(6) and other metal carbonyls. High-resolution valence level spectra of these complexes are also obtained by He I radiation. Fine structure, resulting from spin-orbit splitting, ligand field splittings, and vibrational coupling is resolved in the spectra of both W 5d and W 4f regions. Ligand field splittings on both the W 5d and W 4f levels increase in the order W(CO)(6) approximately fac-W(CO)(3)(PMe(3))(3) < W(CO)(5)PMe(3) </= cis-W(CO)(4)(PMe(3))(2) < trans-W(CO)(4)(PMe(3))(2). For the first time, the phosphorus 2p spin-orbit components of the phosphine complexes have been resolved. The binding energies (or ionization potentials) in the spectra of both W 5d valence level and W 4f core level regions are shifted almost linearly to lower energy with each successive step of ligand substitution. The shift per phosphine substitution is 0.66 +/- 0.03 eV for the W 5d ionizations and 0.76 +/- 0.03 eV for the W 4f ionizations (DeltaE(valence)/DeltaE(core) = 0.86 +/- 0.03). Similar linear shift trends are also found in the phosphorus 2p core level and phosphorus valence "lone-pair" ionizations. These data confirm the ligand additivity model predictions for these complexes.