Molybdenum Analogue Research Articles

Substituted metal carbonyls: IV. Studies of the synthesis and decomposition of singly-bridging 1,3-bis(diphenylphosphino)propanedimetal decacarbonyls of chromium, molybdenum and tungsten

Singly-bridging diphosphine complexes M 2(CO) 10(μ-dppp) (M  Cr, W; dppp  Ph 2P(CH 2) 3PPh 2) have been isolated in a facile synthesis via an oxidative decarbonylation of M(CO) 6 using trimethylamine- N-oxide as the initiator. The thermal decomposition of these complexes, together with the molybdenum analogue, have been studied in refluxing acetonitrile, benzene or toluene under N 2 or CO. The characterisations and thermal stabilities of these species are described and discussed. Conversion of the 1,3-bis(diphenylphosphino)propanedimetal decacarbonyl complexes of chromium, molybdenum and tungsten into the chelate M(CO) 4(η 2-dppp) is promoted by free dppp but inhibited by CO gas.

Borole derivatives: X. Syntheses of (η 5-borole)metal complexes via borole ammonia adducts. Complexes of the chromium group metals and the crystal and molecular structures of tetracarbonyl [η 5-(1-phenylborole)] chromium and its molybdenum analogue

The 1 H-Borole ammonia adducts C 4H 4BR · NH 3 (R = Me, Ph) (Ia,b) have been made by ammonia degradation of the (η 5-borole)carbonyliodocobalt complexes (C 4H 4BR)Co(CO) 2I (VIa,b). They are the simplest 1 H-borole derivatives obtained to date, and have been identified in solution by NMR spectroscopy. Reactions starting from Ia,b have given otherwise inaccessible (η 5-borole)metal complexes such as (η 5-C 4H 4BMe)Cr(CO) 4 (II) and (η 5-C 4H 4BPh)M(CO) 4 (III: M = Cr, IV: M = Mo, V: M = W). X-ray diffraction studies on III and IV show them to have distorted piano stool structures with bond lengths CrB,240.3(2) and MoB 253.4(4) pm. Site exchange processes within the M(CO) 4 groups are fast on the 13C NMR time scale even at 155 K.

Superconductivity and the Metal-Semiconductor Transition

Ceramic superconductors based on transition metal oxides have existed for many years but have attracted little attention due to their relatively low critical temperatures (T{sub c}). The perovskite structure has played a major role in the history of oxide superconductors. The first example of a perovskite superconductor was strontium titanate. Insulating behavior is normally found for SrTiO{sub 3}, but it can be reduced or doped to become a degenerate semiconductor which is superconducting. However, T{sub c} for strontium titanate superconductors is always below 1K. It was later found that a great variety of tungsten bronzes, A{sub x}WO{sub 3} where A = Na, K, Rb, Cs, NH{sub 4}, Ca, Sr, Ba, etc., are superconducting with T{sub c}'s as high as 6K. These structures may also be regarded as perovskite related. Analogous molybdenum bronzes, A{sub x}MoO{sub 3}, and rhenium bronzes, A{sub x}ReO{sub 3}, have also been prepared and found to be superconducting. A T{sub c} of 13K was discovered in the Ba(Pb,Bi)O{sub 3} perovskite system. This was particularly significant because 13K is the highest T{sub c} ever observed for a material not containing a transition metal. Ba(Pb,Bi)O{sub 3} was also the first superconductor discovered that could be processed by conventional ceramic processingmore » techniques, i.e. sintering in air. Finally, the authors have the discovery of high temperature superconductivity in the perovskite related systems La{sub 2-x}A{sub x}CuO{sub 4} (A = Ca, Sr or Ba) and RBa{sub 2}Cu{sub 3}O{sub 7} (R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu or Y).« less

Phosphinsubstituierte Chelatliganden, XXV [1] Diastereoselektive Komplexierung chiraler Phosphinothioformamide mit entferntem Asymmetriezentrum

Abstract For further studies of the diastereoselective complex formation of ambidentate chiral chelating ligands, we prepared the racemic phosphinothioformamides. Ph2P(X )C(S)NHC*HR 1R2, with X = 2e- (R1 = Ph,R2 = Et: 1a;R1 = Ph,R2 = iPr:2a; R2 = Me,R2 = Et:3a) and X = O (1b ,2b ) according to a previously reported route. The coordination of 1a -3a to CpM (CO)3Cl (M = Mo, W) in m ethanol gives the diastereomeric P.S-chelate complexes, (Mo: 4-6, W: 7-9). In solution, epimerisation proceeds to an equilibrium ratio of B/A = 1,5 in case of 4, 5, 7, and 8, but less than 1,1 with 6 and 9. A reduced diastereoselectivity (d.e. 10 -20%) is also observed during the formation of the analogous molybdenum complexes 10a-d with phosphine ligands derived from α-amino acid esters. Ph2PC(S)NHC*H(R)COOMe [R = Me (L-Ala), CH2Ph (L-Phe). CHMe2 (L-Val). Ph (D-phenylglycine)]. The results indicate a significant asymmetric induction despite of the four bond distance of the chiral centres.

Crystal and molecular structure of octacarbonyl[bis(bispentafluorophenylarsenido)] dimolybdenum, Mo2(CO)8[?-As(C6F5)2

The X-ray crystallographic structure determination of Mo2(CO)8[μ-As(C6F5)2]2 reveals that the compound crystallizes in the tetragonal space groupP421c witha=14.915(3),c=16.732(3) A,V=3722(1) A3, andZ=4. Least-squares refinement based on 1474 independent observed data [(Fobs)≥3σ(Fobs)] resulted in a finalR value of 0.038. The Mo-Mo distance of 3.132(1) A is longer than found in analogous phosphido-bridged molybdenum systems. The central Mo2As2 rhombus is nearly flat and the coordination geometry of the Mo atoms is essentially octahedral. An unusual staggering of the Mo(CO)4 groups by 15.8° and short intramolecular C6F5⋯CO contacts support the presence of a strong steric interaction between the Mo(CO)4 and As(C6F5)2 groups.

Monometallic, homo- and hetero-bimetallic complexes based on redox active tris(3,5-dimethylpyrazolyl)borato-molybdenum and -tungsten nitrosyls. Part 4. The effects of ligating atom type on the reduction potentials of monometallic complexes

The complexes [M(NO)(L)X(Y)][L = tris(3,5-dimethylpyrazolyl)borate; M = Mo, X = Cl, Y = OPh; M = W, X = Cl, Y = SPh; or M = W, X = Y = NC4H4, OPh, or SPh] have been prepared and characterised. The electrochemical properties of these compounds were investigated by cyclic voltammetry and compared with those of others in the series [M(NO)(L)X(Y)](M = Mo or W; X = Cl, Y = OPh, NHPh, or SPh; or X = Y = NC4H4, OPh, NHPh, or SPh). It was found that the thiophenolate complexes reduced at slightly more anodic potentials than their phenolate analogues while the arylamide complexes reduced at significantly more cathodic potentials. In general the tungsten complexes reduced at potentials ca. 0.45 V more cathodic than their molybdenum analogues.

Synthesis and reactivity of compounds of formula W(S)(OR) 4

In ethereal solutions, WSCl 4 and 4 equiv LiOR (R = Bu t or Pr i ) react to form compounds of formula W(S)(OR) 4. A single-crystal X-ray diffraction study of W(S)(O-Bu t ) 4 showed it to have a square-based pyramidal geometry with an apical sulfide ligand. Pertinent bond distances (Å) and angles (°) are: WS = 2.1396(13), WO(av.) = 1.886(3), SWO(av.) = 105.09(10), WOC(av.) = 143.47(27). The tert-butoxide compound is stable toward sulfur atom abstraction by phosphines, and neither compound has shown any tendency to undergo comproportionations with W 2(OR) 6 (R = Pr i or CH 2Bu t ) species to form compounds of formula W 3(μ 3-S)(OR) 10, in direct contrast to analogous molybdenum and tungsten oxo alkoxides.

Organometallic complexes with RSSR ligands: a new synthetic method

Reactions of [Me 2SSMe]BF 4 with metal thiolate complexes have been used to prepare new complexes with coordinated organic disulfide ligands. Complexes prepared include [CpFe(CO)(L)(PhSSMe)]BF 4 (L , PPh 3, PPh 2Me, PPh 2OMe, P(OPh) 3), [CpFe(CO) 2(MeSSMe)]BF 4 and [CpW(CO) 3(MeSSMe)[BF 4. A molybdenum analogue of the last compound and [Mn(CO) 5(MeSSMe)]BF 4 were identified in solution as products of this type of reaction, but these species were unstable and could not be isolated. Isomerization of [CpFe(CO){P(OPh) 3}(PhS-SMe)]BF 4 upon heating was noted. This synthetic method is easy and versatile, and is a useful alternative to other known routes to this type of complex.

An Investigation of Adduct Complexes of M(S2CNEt2)2(Co)2 (M=Mo,W) by 95Mo and 183W N.M.R-Spectroscopy

The seven-coordinate adducts M(S2CNEt2)2(CO)2L and [M(S2CNEt2)2(CO)2]2-μ-L (M = Mo, W;L below), derived from the 16-electron complexes M(S2CNEt2)2(CO)2, have been investigated by 95Mo and 183W n.m.r. spectroscopy. The molybdenum and tungsten adducts exhibit resonances in the regions from 310 to -430 and from -465.5 to -1500 ppm , respectively. All the resonances are shielded relative to those of the M(S2CNEt2)2(CO)2 precursors. The dependence of the nuclear shielding on L is as follows. For M = Mo: NH2NHSO2C6H4Me < Cl - < OPPh3 < μ- pyrazine < pyridine < NH2NHCOPh < NH2NMe2 < μ-NH2NHMe < μ-NH2NH2 < μ-NH2CH2CH2NH2 < NH3 < N3- < F- < AsPh3 < PPh3 < SbPh3 < PPh2Et < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3 < CO. For M = W: NH2NHCOPh < AsPh3 < Ph2PCH2PPh2 < PPh3 < PPh2Et < Ph2PCH2CH2PPh2 < PPh2Me < PMe3 < P( OPh )3 < P( OEt )3 < P( OMe )3 < CO. The OPPh3, halide and nitrogen-donor ligand adducts participate in a dynamic equilibrium with Mo(S2CNEt2)2(CO)2 on the n.m.r . time scale. The remaining adducts do not exhibit such behaviour. The chemical shifts of both the molybdenum and tungsten adducts are correlated with the π- acceptor ability of the ligand , L, and the stereochemistry of the adducts. A linear relationship between the chemical shifts of analogous molybdenum and tungsten complexes is observed; the equation of the line is δ(183W) = 1.46δ(95Mo)-857.5.

Chromium, molybdenum, and tungsten chlorophosphazenes: molecular structures of N3P3Cl5[Cr(CO)3(.eta.-C5H5)] and N3P3Cl4(C5H5)[Mo(CO)3(.eta.-C5H5)

Abstract : Cyclopentadienylchromium tricarbonyl anion reacts with hexachlorocyclotriphosphazene, (NPCl2)3, to form a metallophosphazene of formula N3P3Cl5Cr(CO)3(n-C5H5 (5). The reactions of the analogous molybdenum and tungsten anions with (NPCl2)3 are more complex and lead to the formation of metallophosphazenes of formula N3P3Cl4(C5H5)M-(CO)3(n-C5H5) (6a, M = Mo; 6b, M = W) in which the chlorine atom geminal to the metal has been replaced by a cyclopentadiene group. A key requirement for the success of these reactions is the use of a tetra-n-butlammonium counterion. The products are among the first chlorophosphazenes to contain metal-phosphorus side-group bonds. The structures of 5 and 6a were examined in detail by spectroscopic and X-ray diffraction techniques. In both compounds the N-P-N bond angle at the metal-bearing phosphorus is unusually narrow, being 112.3 (3) deg in 5 and 111.0 (3) deg in 6a. Moreover, an alternation of longer and shorter bond lengths is found for the P-N bonds located at increasing distances from the metal.

Tungsten(VI) and mixed tungsten, molybdenum(VI) complexes of tartaric acid

A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH4] ratios of 1∶1 and the third has the same ratio of 1∶2. This latter species cannot be that proposed by Avaloset al. (3) since both ligands in their structure would have to be present as unidentates. Recently we have shown(4) that high resolution1H and13C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH4. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species(4). In addition we have observed the formation of a mixed dimeric species [MoWO4{(+)-tart}2]4−, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH4 (5).

Transition metal-main group metal bond. VI. 199Hg NMR and 57Fe mössbauer study of (η 5-C 5H 5)(CO) 2FeHgX [X = Cl,Br,I,S 2COC 2H 5, S 2CN(C 2H 5) 2, S 2P(OC 2H 5) 2 and Fe(CO) 2(η 5-C 5H 5)]complexes.

The 199Hg NMR and 57Fe Mössbauer spectra of iron-mercury bounded complexes are reported, compared with the 199Hg NMR data for analogous molybdenum and tungsten compounds and discussed in terms of the polarization of the metal-metal bonds.

Synthesis of chloro(trimethylphosphine)tris(trimethylsilylmethyl)tungsten(IV); synthesis and molecular structure of di-µ-chloro-bis[dicarbonyl(trimethylphosphine)(1—2-η-trimethylsilylmethylcarbonyl)tungsten(II)

The interaction of [MgCl(CH2SiMe3)] or [Mg(CH2SiMe3)2] with [WCl4(PMe3)2] yields the five-co-ordinate paramagnetic tungsten(IV) alkyl [WCl(CH2SiMe3)3(PMe3)] which reacts with carbon monoxide to give an η2-acyl dimeric complex [{WCl(1—2-η-COCH2SiMe3)(CO)2(PMe3)}2]. The crystal structure of the latter has been determined from three-dimensional X-ray diffraction data collected by counter methods. It crystallizes in the monoclinic space group P21/c, isomorphous with the molybdenum analogue, with a= 8.420(3), b= 10.449(3), c= 19.300(4)A, β= 90.59(2)°, and Z= 2. The final R value was 0.016 for 1 218 independent observed reflections. The molecule exists as a chloride-bridged dimer with an η2-acyl linkage. The tungsten–carbon(acyl) bond length is 2.029(7)A and the tungsten–oxygen(acyl) distance is 2.289(5)A.

Structural studies of technetium complexes. III. The crystal structure of Tris[2-aminobenzenethiolato(2 - )-S, N]technetium(VI) : a trigonal-prismatictechnetium geometry

Tris[2-aminobenzenethiolato(2–)-S,N]technetium(VI), Tc(NHC6H4S)3, has been prepared by the reaction of ammonium pertechnetate with 2-aminobenzenethiol in 0.1 M hydrochloric acid solution at room temperature. The crystal structure of Tc(NHC6H4S)3 has been determined by single-crystal X-ray diffraction methods at 17�C. Crystals are orthorhombic, space group P212121, with a 10.696(2), b 11.363(1), c l5.220(2) �, and Z 4. Automatic diffractometry has provided significant Bragg intensities for 1413 independent reflections, and the structure of the correct enantiomorph has been refined by full-matrix least-squares methods to R 0.044. The compound, which is isostructural with the molybdenum analogue, consists of discrete molecules of Tc(NHC6H4S)3. The environment about the technetium atom closely approximates a trigonal-prismatic geometry. This is the first example where this geometry has been established with technetium. Differences in detail between the structures of TC(NHC6H4S)3 and its molybdenum analogue are discussed. In particular the S3N3 coordination polyhedron in TC(NHC6H4S)3is contracted and the distortions from ideal trigonal-prismatic geometry are less than in the molybdenum analogue.

Tricarbonyl (triquinacene)-molybdenum and-tungsten

Triquinacene reacts with hexacarbonylmolybdenum to give tricarbonyl(triquinacene)molybdenum, and with tris(acetonitrile)tricarbonyltungsten to give tricarbonyl(triquinacene)tungsten, whereas efforts to synthesize the corresponding chromium complex, tricarbonyl(triquinacene)chromium, were unsuccessful. The molybdenum complex was characterized by 1 H and 13 C NMR spectroscopy, mass spectra, and a single crystal X-ray structure determination. The tungsten complex is thermally less stable and more susceptible to oxidation than its molybdenum analogue and was characterized by the mass spectrum and the 1 H NMR spectrum. The crystal structure of the tricarbonyl(triquinacene)molybdenum is compared to that for the free ligand. Besides the expected lengthening of the C=C bonds, the complex shows a deepening of the triquinacene “basket”, presumably to give better overlap of the C=C bonds with molybdenum orbitals.

X-ray photoelectron spectra of inorganic molecules: XXX . Organometallic derivatives of tungsten(O) and tungsten(II)

The W 4 f binding energies of various carbonyl-containing complexes of tungsten are reported. Comparisons between W II complexes containing the [(η 3-allyl)W(CO) 2] moiety and neutral derivatives of the type W(CO) 6- x L x are made. The absence of a clear-cut correlation between the W 4 f binding energies and the value of x in W(CO) 6- x L x is discussed and these results compared with those obtained for the analogous molybdenum complexes.

ChemInform Abstract: REACTIONS OF DIPHENYLPHOSPHINE AND METHYLDIPHENYLPHOSPHINE WITH (η3‐ALLYL)DICARBONYLCHLOROBIS(METHYL CYANIDE)MOLYBDENUM AND ‐TUNGSTEN: MECHANISTIC IMPLICATIONS IN THE REDUCTIVE ELIMINATION OF ALLYL HALIDES

AbstractDie tert. Phosphine reagieren mit den Titelkomplexen (II) im molaren Verhältnis von 2:1 in Methanol zu den Substitutionsprodukten (I) und von 3:1 in Acetonitril unter reduktiver Eliminierung von Allylhalogeniden zu den mer‐Komplexen (III).

Reactions of diphenylphosphine and methyldiphenylphosphine with (?3-allyl)dicarbonylchlorobis(methyl cyanide)molybdenum and-tungsten: Mechanistic implications in the reductive elimination of allyl halides

Reactions of L = PHPh2 or PMePh2 with [MCl(CO)2(η3-C3H4R)(MeCN)2] (M = Mo, R = H or Me; M = W, R = H) in MeOH involve initial substitution to give [MCl(CO)2(η3-C3H4R)L2]. In MeCN, an excess of tertiary phosphine readily causes reductive elimination of allyl halide with the formation ofmer-[M(CO)2(MeCN)L3]. The molybdenum analogue can also be produced in high yields by reacting PMePh2 with either [Mo(CO)2(η3-C3H5)(MeCN)3]BF4 or Ph4As[Mo2Cl3(CO)4(η3-C3H5)2]. During these reactions, the new [MCl2(CO)2(η3-C3H5)(PMePh2)]− anions were formed and isolated as their σ-allylphosphonium salts. Under forcing conditions, reactions involving PHPh2 also resulted in elimination of the allyl group giving high yields ofcis-M(CO)2(PHPh2)4. The relevance of these observations on the mechanism of the reduction process are discussed.

Di-η 5-cyclopentadienylmetal complexes with nitrogen donor atom ligands: New imidazole, N-methylimidazole, pyrazole and 2,2′-bisimidazole complexes of molybdenum and tungsten

Reactions of the tetrahedral metallocene derivatives [M(η-C 5H 5) 2X 2], [M(η-C 5H 5) 2HX] and [M(η-C 5H 5) 2H 3][PF 6] (M = Mo, W; X = halogen) with ligands imidazole, N-methylimidazole, pyrazole and 2,2′-bisimidazole give a wide range of new mono- and bi-nuclear complexes. The p K a values for some of the coordinated ligands and the ESR spectra of some molybdenum(V) complexes obtained by oxidation of their molybdenum(IV) analogues are also presented and discussed.

Studies on the reactivity of oxodihalobis(diethyldithiocarbamato) molybdenum(VI) and tungsten(VI) complexes

The complexes OMoX 2L 2 (L = S 2)CNEt 2) 2 react with Na 2S 2O 4 to yield OMoL 2 (X = Cl), with PhNCO to yield (PhN)MoX 2L 2 (X = Cl), with PPh 2Et to give MoX 2(PPh 2Et)L 2 (X = Cl, Br), and with OMol 2 to produce OMoXL 2 (X = Cl, Br). The epr spectra of OMoXL 2 display halogen superhyperfine splitting [A( 35,37Cl) = ∼3 gauss; A(bb]79,81Br) = 12.3 gauss). Reaction of WCl 6 with NaL in MeOH yields the new complex OWCl 2L 2 which either does not react at all or gives no characterizable products with the above reagents. The results demonstrate the lack of atom transfer ability of tungsten(VI) relative to its molybdenum analog.