Studies of chelation : II. Phosphine complexes of molybdenum and manganese

Activation parameters have been obtained for the chelation of Mo(CO)₅dpe (dpe = Ph₂PCH₂CH₂PPh₂) and of Mo(CO)₅dmpe (dmpe = Me₂PCH₂CH₂PMe₂) to give cis-Mo(CO)₄dpe and cis-Mo(CO)₄dmpe respectively. The results are compared with those for the analogous chromium complexes and show that the enthalpy contribution determines the more rapid chelation in the molybdenum complexes. The preparation and properties of the chelate-bridged hetero-metallic complex (CO)₅ModmpeMn(CO)₄Br are reported. The reaction between Et₄N[Mn(CO)₄X₂] (X = Cl, Br) and bidentate ligands dpe, dmpe and ape (ape = Ph₂PCH₂CH₂AsPh₂) in the presence of either silver(I) tetrafluoroborate or Et₃OBF₄ produces cis-Mn(CO)₄X(bidentate) which is identified by infrared and mass spectrometry. At room temperature the Mn(CO)₄X(bidentate) complex is rapidly converted to the chelated fac-Mn(CO)₃X(bidentate) complex. The chelation process is approximately 10⁴ times more rapid than in the isoelectronic chromium(O) complexes. The preparation and characterisation of fac-Mn(CO)₃Br(dmpe), cis-Mn(CO)₄Br(PMe₃) and fac-Mn(CO)₃Br(PMe₃)₂ are reported.     

Oxo-molybdenum(IV) and tungsten(IV) complexes with phosphine and isocyanide ligands

The complexes [MOCl₂(dmpe)(PMe₃)] and [MOCl₂(dmpe)₂]Cl (M = Mo, W; dmpe = Me₂PCH₂CH₂PMe₂) have been prepared by reaction of the oxo compounds [MOCl₂(PMe₃)₃] with equivalent amounts of the dmpe ligand under appropriate conditions. The dark blue tungsten species [WOCl₂(dmpe)(PMe₃)] forms only slowly but reacts readily with more dmpe to afford [WOCl(dmpe)₂]Cl. This prevents isolation of the former in a pure form. The related isocyanide derivatives [MOCl₂(CNR)(PMe₃)₂], (M = Mo; R = CMe₃ and C₆H₁₁; M = W, R = CMe₃) have been obtained similarly by reaction of the [MOCl₂(PMe₃)₃] complexes with the stoichiometric amount of the isocyanide ligand, but attempts to prepare the carbonyl analogues, [MOCl₂(CO)(PMe₃)₂], have proved unsuccessful. The new compounds have been characterized by analytical and spectroscopic methods (IR, ¹H, ¹³C and ¹³P NMR spectroscopy).     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

Alternativ-Liganden. XXII. Rhodium(I)-Komplexe mit Donor/Akzeptor-Liganden des Typs Me2PCH2CH2SiXnMe3−(X = F,Cl, OMe)

Alternative Ligands. XXII. Rhodium(I) complexes with Donor/Acceptor Ligands of the Typs Me₂PCH₂CH₂SiX_nMe_3?n(X = F, Cl, OMe) Donor/acceptor ligand of the type Me₂PCH₂SiX_nMe_3?n react with [Rh(CO)₂Cl]₂ ( 1 ) to give the mononuclear complexes RhCl(CO)(PMe₂CH₂CH₂SiX_nMe_3?n)₂ ( 2-6 , Table 1) with planar geometry of the donor atoms, one exception being Me₂PCH₂CH₂CH₂SiCl₃, yielding the crystalline Rh^III-complex RhCl₂(CO)(PMe₂CH₂CH₂SiCl₂)(PMe₂CH₂CH₂SiCl₃) ( 7 ) by oxidative addition of one of the SiCl bonds to the Rh¹ precursor. Structures with Rh → Si interaction between the basic central atoms and the acceptor group SiX_nMe_3?n could be detected in the isolated products neither spectroscopically nor by X-ray diffraction of the two representatives RhCl(CO)(PMe₂CH₂CH₂SiF₃)₂ ( 2 ) and RhCl(CO)[PMe₂CH₂CH₂siF₃]₂ ( 2 ) and RhCl(CO) [PMe₂CH₂CH₂Si(OMe₃]₂ ( 6 ). The presence of such acid/base adducts in the reaction mixture is indicated for the more acidic acceptor groups SiX_nMe_3?n byv_co values near 1990cm^?1, (see Table 3). The complex RhCl(CO)PMe₃)(PMe₂CH₂CH₂SiF₃ ( 8 ) is obtained by the reaction of RhCl(CO)(PMe₃)₂ ( 9 ) with Me₂PCH₂SiF₃ and has been identified spectroscopically in a mixture with 2 and 9 .     

Reactions of cis-[dicarbonylbis(1,2-bis(dimethylphosphino)ethane)metal] compounds of chromium and molybdenum with organic electron acceptors; Tetracyanoethene, 1,2,4,5-tetracyanobenzene and 1,3,5-trinitrobenzene

Reaction between cis-[Mo(CO)₂(dmpe)₂] (dmpe =Me₂PCH₂CH₂PMe₂) and organic π-acids tetracyanoethene (TCNE), 1,2,4,5-tetracyanobenzene (TCNB) and 1,3,5-trinitrobenzene (TNB) proceeds via electron transfer from the metal complex, which is oxidised to the 17-electron trans-[Mo(CO)₂(dmpe)₂]⁺ ion, to the organic acceptor which is reduced to the radical anion. The final products of the reactions are characterised ascis-[Mo{C₂(CN)₃} (CO)₂(dmpe)₂] [CN], cis-[Mo{C₆H₂(CN)₄} (CO)₂(dmpe)₂] [C₆H₂(CN)₄]₈ and [Mo(CO)₂(dmpe)₂ · 2 C₆H₃(NO₂)₃] by analysis and spectroscopic (IR, NMR, ESR) measurements which are compared with those of cis-[MoX(CO)₂(dmpe)₂]X (X = Cl, Br, I) and fac, fac-[Mo₂Cl₄(CO)₄(dmpe)₃]. The reaction of cis-[Cr(CO)₂(dmpe)₂] with TCNE gives trans-[Cr(CO)₂(dmpe)₂]⁺ [TCNE]^? only.     

Alkyl complexes of palladium(II) with trimethylphosphine and 1,2-bis-(dimethylphosphino)ethane ligands

A number of neutral, mononuclear dialkylpalladium(II) tertiary phosphine complexes of geneal formula cis or trans-PdR₂(PMe₃)₂ and cis-PdR₂ (dmpe) [dmpe = 1,2-bis(dimethylphosphino)ethane], R = Me, CH₂Ph, CH₂CMe₂Ph, CH₂SiMe₃ have been obtained by interaction of magnesium reagents with palladium(II) acetate or trans-Pd(O₂CMe)₂(PMe₃)₂.     

Studies on some mono-η5-cyclopentadienyliron derivatives with chelate diphosphine ligands

The reactions between Fe(η⁵-C₅H₅)(LL)I (where LL = Ph₂PCH₂CH₂PPh₂, Me₂PCH₂CH₂PMe₂ or ()-DIOP) and TIBF₄ or TIPF₆ inpresence of olefins are described. Evidence is presented that the diphosphine ligands give rise to steric restrictions against coordination of olefins to the metal center.     

Synthesis,Structural Characterization and Reactivity of a Bis(phosphine)(silyl) Platinum(II) Complex

Treatment of 1,2‐C₆H₄(SiH₃)(SiH₃) ( 1 ) with Pt(dmpe)(PEt₃)₂ (dmpe=Me₂PCH₂CH₂PMe₂) in the ratio of 1:1 leads to the complex {1,2‐C₆H₄(SiH₂)(SiH₂)}Pt^II (dmpe) ( 2 ), which can react with proton organic reagent bearing hydroxy group with low steric hindrance to form a tetra‐alkoxy substituted silyl platinum(II) compound ( 3 ). Compounds 2 and 3 are the very rare examples of silyl transition‐metal complexes derived from this chelating hydrosilane ligand. To the best of our knowledge, there are only 6 examples of silyl metal complexes prepared from this ligand with such structural features registered in the Cambridge Structural Database, among them, only one silyl platinum(II) compound is presented. The structures of complexes 2 and 3 were unambiguously determined by multinuclear NMR spectroscopic studies and single crystal X‐ray analysis.     

Cyanoalkyl Complexes of Platinum (II). I. Preparation and Spectroscopic Properties

The oxidative addition of XRCN to PtL₄ yields cis-and/or trans-PtX(RCN)L₂ (X = Cl, Br; R = (CH₂)_n, n = 1, 2, 3; L = PPh₃, PPh₂CH₃, AsPh₃). L is readily displaced by more basic phosphines or by a diphosphine. In each case the trans complex is the thermodynamically more stable isomer and cis-trans isomerization catalyzed by free L occurs in dichloromethane. Insertion of CO in the σ Pt? C bond takes place quantitatively in the case of cyanoethyl and cyanopropyl. Abstraction of X by AgBF₄ gives cis or trans cationic complexes with N-bonded CN group.     

cis-trans Isomerization of bis(Dialkylsulfide)Dihaloplatinum(II) Complexes in Solution

The equilibrium energetics and the kinetics of cis-trans isomerization of some bis(dialkylsulfide)dihaloplatinum(II) complexes have been examined by ¹H-NMR. spectroscopy. The isomers are stable in chloroform but each form isomerizes to an equilibrium mixture when free dialkylsulfide is added. The cis to trans process is endothermic and the position of the equilibrium is markedly dependent on the nature of the donor atoms and of the solvent. The rate of isomerization of Pt(Me₂S)₂Cl₂ is first order in complex and in Me₂S. The isomerization proceeds by a double displacement mechanism as it is shown that the tris(dimethylsulfide)chloroplatinum(II) cation is an isolable intermediate of the reaction. When free Me₂S is added to trans-Pd(Me₂S)₂Cl₂, isomerization does not occur and one observes instead a fast ligand exchange. Its mechanism is the usual associative one for substitutions in square planar d⁸complexes.     

Alkyl,hydrido and related compounds of ruthenium with trimethylphosphine and bis(1,2-dimethylphosphino)ethane. X-ray crystal structures of cis-hydridoethyltetrakis(trimethylphosphine)-ruthenium(II) and ethylene tetrakis-(trimethylphosphine)ruthenium(0)

The interaction of trans-RuCl₂(PMe₃)₄ with R₂Mg, depending on the reaction conditions and the alkyl groups gives either (C₂H₄)Ru(PMe₃)₄ or cis-Ru(H)(C₂H₅)(PMe₃)₄ for R = ethyl, and cis-Ru(H)(ⁿC₃H₇(PMe₃)₄ for R = n-propyl. The interaction of Et₂Mg with trans-RuX₂(dmpe)₂ (X = Cl, CO₂Me) gives either cis-Ru(Et₂)dmpe)₂ for X = Cl or trans-Ru(Et)₂(dmpe)₂ for X = CO₂Me. NMR data for (C₂H₄)Ru(PMe₃)₄ suggest that ethylene is bound in the η² or metallocyclopropane form, which is confirmed by a single-crystal X-ray diffraction study. This shows a relatively long carbon-carbon bond distance of 1.44(1)Å between the “ethylene” carbons. The structure of cis-Ru(H)(C₂H₅)(PMe₃)₄ has also been confirmed by a single-crystal X-ray diffraction study. Possible mechanisms for the observed reactivities are considered.     

Further studies on organonickel compounds: the synthesis of some new alkyl-, acyl- and cyclopentadienyl-derivatives and the crystal structure of trans-[Ni(CH2SiMe3)2(PMe3)2]

The complex [NiCl₂(PMe₃)₂] reacts with one equivalent of mg(CH₂CMe₃)Cl to yield the monoalkyl derivative trans-[Ni(CH₂CMe₃)Cl(PMe₃)₂], which can be carbonylated at room temperature and pressure to afford the acyl [Ni(COCH₂CMe₃)Cl(PMe₃)₂]. Other related alkyl and acyl complexes of composition [Ni(R)(NCS)(PMe₃)₂] (R = CH₂CMe₃, COCH₂CMe₃) and [Ni(R)(η-C₅H₅)L] (L = PMe₃, R = CH₂CMe₃, COCH₂CMe₃; L = PPh₃, R = CH₂CMe₂Ph) have been similarly prepared. Dialkyl derivatives [NiR₂(dmpe)] (R = CH₂SiMe₃, CH₂CMe₂Ph; dmpe = 1,2-bis(dimethylphosphine)ethane, Me₂PCH₂ CH₂PMe₂) have been obtained by phosphine replacement of the labile pyridine and NNN′N′-tetramethylethylenediamine ligands in the corresponding [Ni(CH₂SiMe₃)₂(py)₂] and [Ni(CH₂CMe₂Ph)₂(tmen)] complexes. A single-crystal X-ray determination carried out on the previously reported trimethylphosphine derivative [Ni(CH₂SiMe₃)₂(PMe₃)₂] shows the complex belongs to the orthorhombic space group Pbcn, with a = 14.345(4), b = 12.656(3), c = 12.815(3) Å, Z = 4 and R 0.077 for 535 independent observed reflections. The phosphine ligands occupy mutually trans positions P-Ni-P 146.9(3)° in a distorted square-planar arrangement.     

Synthesis and structural characterization of the electron rich complexes Co(η-C5Me5)(R2PCH2CH2PR2) (R = Me,Ph); photoelectron spectroscopic studies of some pentamethylcyclopentadienylphosphinecobalt complexes

The compounds Co(η-C₅Me₅)(R₂PCH₂CH₂PR₂), (R = Me, Ph) have been prepared and characterized. X-Ray diffraction studies of Co(η-C₅Me₅)-(Me₂PCH₂CH₂PMe₂) show the two phosphorus atoms and the ring centroid to have a trigonal coordination around the cobalt. Photoelectron spectral studies show Co(η⁵-C₅Me₅)(R₂PCH₂CH₂PR₂) to have rather low first ionization energies of around 5.1 eV, indicating that the metal centre has a very electron rich nature.     

Synthesis and structure of a dmpe-substituted dinuclear complex bridged by a substituent-free gallium atom: Electronic effect of metal fragment on the iron–gallium bonding

A dinuclear complex bridged by a substituent-free gallium atom, Cp¹(dmpe)Fe–Ga–Fe(CO)₄ (1b: Cp¹ = η-C₅Me₅, dmpe = Me₂PCH₂CH₂PMe₂), was synthesized by the reaction of Cp¹Fe(dmpe)GaCl₂ with K₂[Fe(CO)₄]. Crystal structure analysis of complex 1b showed that the geometry around the gallium atom is essentially linear and the two Fe–Ga bonds are significantly shorter than those of usual single bonds, indicating the multiple bonding character of the Fe–Ga bonds. Comparison of the structure and IR data of 1b and those of Cp¹(dppe)Fe–Ga–Fe(CO)₄ (1a: dppe = Ph₂PCH₂CH₂PPh₂) revealed that the Fe–Ga bond is sensitive to the electronic character of the metal fragment. The Fe–Ga bond is shortened upon introducing a more π-basic metal fragment.     

Immobilization, Characterization, and Preliminary Reactivity Studies of Halfsandwich Ruthenium Complexes on Silica

Summary. The complexes [RuCp(CH₃CN)₂(Ph₂PCH₂CH₂Si(OMe)₃)]PF₆ and [RuCp(CH₃CN) (Ph₂PCH₂CH₂Si(OMe)₃)₂]PF₆ were obtained in good yields by treatment of [RuCp(CH₃CN)₃]PF₆ with 1 and 2 equivs of Ph ₂PCH₂CH₂Si(OMe)₃. Both free Ph ₂PCH₂CH₂Si(OMe)₃ and the two complexes were grafted onto the surface of powdered silica. The surface coverage was determined independently by ³¹P solid state NMR and IR spectroscopy. IR data revealed that for Ph ₂PCH₂CH₂Si(OMe)₃ and the complexes 52, 52, and 18 molecules, respectively, were immobilized per 100nm² of SiO₂ surface. Similar values were obtained from ³¹P MAS NMR measurements. With the immobilized first complex the catalytic redox isomerization of allyl alcohol to propanal has been studied by means of IR spectroscopy and ¹H NMR spectroscopy showing the quantitative formation of aldehyde. While in the first cycle satisfactory turnover numbers were achieved, the subsequent cycles showed only low conversions to aldehyde presumably due to decomposition of the complex. The immobilized second complex was catalytically inactive.Received February 25, 2003; accepted March 24, 2003 Published online August 18, 2003     

The preparation of mono(η5-pentamethylcyclopentadienyl) compounds of tantalum(V)

The synthesis and characterization of (η⁵-C₅Me₅)TaCl₄, (η⁵-C₅Me₅)TaCl₄L (L  PMe₃, P(OMe)₃, Ph₂PCH₂CH₂PPh₂), (η⁵-C₅Me₅)TaMe₄, and (η⁵-C₅Me₅)Ta(CH₂Ph)₂(CHPh) is described. NMR studies of the bis(1,2-diphenylphosphino)ethane (dppe) adduct show exchange of free and ligated dppe, possibly via dissociation of the ligand from a monodentate compound.     

Metallocenyl cations : IV. cymantrenyl carbenium ions containing two phosphine ligands

Cymantrene carbinols (I) with two phosphine ligands (PP) have been synthesized. Carbinols I (where PP is the chelate diphosphine Ph₂PCH₂CH₂PPh₂ or Ph₂PCH₂CH₂CH₂PPh₂) form the corresponding carbenium ions (II), stabilized by manganese, in the presence of CH₃COOH. The phosphorus atosm of the chelate diphosphine ligands become non-equivalent in the carbenium ions. IR spectra and ³P and ¹³C NMR spectra have been recorded, and the nature of the non-equivalence and of the structure of cymantrenyl carbenium ions are discussed. In the presence of CF₃COOH carbinols i (where PP = 2PMe₂(C₆H₄CH₃-p or 2PPH₂Me) are protonated at the metal atom.     

Emissive Annular Digold(I) Compounds Containing Diphosphine and Dithiolate Ligands

Molecular structures of three emissive annular digold compounds [Au₂(dmpm)(dtc)]Cl (dmpm = Me₂PCH₂PMe_2,dtc = S₂CNEt₂), 1 , [Au₂(dppm)(dtc)]PF₆, (dppm = Ph₂PCH₂PPh₂),₂,and [Au₂(dppe)(dtc)]-(PF₂) (dppe = Ph₂P(CH₂)₂PPh₂), 3, were determined. All three compounds are dimetallacycles having two gold atoms bridged by a dithiolate ligand and a diphosphine ligand, the geometry around each gold atom being almost linear. All the dimetal lacy die rings are slightly distorted from planarity with intramolecular Au-Au distances shorter than 3.0 Å. Compound 1 forms a polymeric chain through intermolecular Au-Au contacts (3.061 ? 3.135 Å). Compound 2 forms a tetramer through intermolecular Au-Au interactions (Au-Au distances ranging from 3.086 to 3.222 ). Compound 3 is monomeric. All of the compounds luminesce at 77 K in the solid state. Emissions originating from ³LMCT from dtc ligand to Au excited states are assigned. The emission maxima of 1 ? 3 are at 541,535 and 520 nm respectively and are blue shifted as the number of Au-Au interactions is decreased.     

Vanadium(II) alkyls. Synthesis and X-ray crystal structures of trans-VMe2(dmpe)2 and cis-V(CH2SiMe3) 2(dmpe)2

Treatment of the vanadium(II) tetrahydroborate complex trans-V(η¹-BH₄)₂(dmpe)₂ with (trimethylsilyl) methyllithium gives the new vanadium(II) alkyl cis-V(CH₂SiMe₃)₂(dmpe)₂, where dmpe is the chelating diphosphine 1,2-bis(dimethylphosphino)ethane. Interestingly, this complex could not be prepared from the chloride starting material VCl₂(dmpe)₂. The CH₂SiMe₃ complex has a magnetic moment of 3.8 μ_B, and has been characterized by ¹H NMR and EPR spectroscopy. The cis geometry of the CH₂SiMe₃ complex is somewhat unexpected, but in fact the structure can be rationalized on steric grounds. The X-ray crystal structure of cis-V(CH₂SiMe₃)₂(dmpe)₂ is described along with that of the related vanadium(II) alkyl complex trans-VMe₂(dmpe)₂. Comparisons of the bond distances and angles for VMe₂(dmpe) ₂, V---C = 2.310(5) Å, V---P = 2.455(5) Å, and P---V---P = 83.5(2)° with those of V(CH₂SiMe₃)₂(dmpe)₂, V---C = 2.253(3) Å, V---P = 2.551(1) Å, and P ---V---P = 79.37(3)° show differences due to the differing trans influences of alkyl and phosphine ligands, and due to steric crowding in latter molecule. The V---P bond distances also suggest that metal-phosphorus π-back bonding is important in these early transition metal systems. Crystal data for VMe₂(dmpe)₂ at 25°C: space group P2₁/n, with a = 9.041(1) Å, b = 12.815(2) Å, c = 9.905(2) Å, β = 93.20(1)°, V = 1145.8(5) ų, Z = 2, R_F = 0.106, and R_wF =0.127 for 74 variables and 728 data for which I 2.58 σ(I); crystal data for V(CH₂SiMe₃)₂(dmpe)₂ at −75°C: space group C2/c, with a = 9.652(4) Å, b = 17.958(5) Å, c = 18.524(4) Å, β = 102.07(3)°, V= 3140(3) ų, Z = 4, R_F = 0.033, and R_wF = 0.032 for 231 variables and 1946 data for which I 2.58 σ(I).     

Alternativ-Liganden. XXIV. Rhodium(I)-Komplexe mit P-Donor-und Sn- bzw. B-Akzeptor-Liganden

Alternative Ligands. XXIV. Rhodium(I) Complexes with P-Donor and Sn- or B-Acceptor Ligands Donor/acceptor ligands of the type Me₂PCH₂CH₂SnMe₃ (1) , (Me₂PCH₂CH₂)₂SnMe₂ (2) , and Me₂PCMe=CMeBMe₂ (3) , respectively, have been prepared by hydrostannlation of Me₂PVi with Me₃SnH or Me₂SnH₂ and by a multistep synthesis via Na[Me₃BH], Na[Me₃BC?;CMe] using Me₂PCI as partner, respectively. The new ligands were used to produce the Rh(I) complexes RhCI(CO)(Me₂PCH₂CH₂SnMe₃)₂ (5) , RhCI(CO)(Me₂PCH₂CH₂)₂SnMe₂ (7), and RhCI(CO)(Me₂PCMe=CMeBMe₂)₂ (8) by reactions of Rh(CO)₂CH₂ (4) with the corresponding ligands. In addition, the VASKA type compounds RhCI(CO)(Me₂PVi)₂ (6) and RhCI(CO)(PMe₃)₂ were prepared in order to test an alternative route to 5 or to from the known adduct RhCI(CO)(PMe₃)₂. BBr₃ (9) . RhBr(CO)(PMe₃)₂ (10) and the binuclear system [RhBr(CO)PMe₃]₂ (11) were identified spectroscopically after working up the 1:1 reaction mixture of RhCI(CO)(PMe₃)₂ and BBr₃. Reasonable pathways are suggested for their formation. ?Metallbase”?/acceptor interaction show up, on the one hand, in following reactions in case of the ligands with Sn acceptors, on the other hand, in significant changes of spectroscopic data for 8 . New compounds of sufficient stability were characterized by analytical (C, H) and spectroscopic (MS, IR. NMR) investigations.