Khalil J. Asali

Half sandwich iron S-bonded mono-thiocarbonate complexes: structure of CpFe(CO)2SCO2Et

Abstract The synthesis and characterization of mononuclear iron complexes containing mono-thiocarbonate ligands are described. The new compounds of general formula CpFe(CO)2SCO2R [R=Et (1), iso-Bu (2), Ph (3), 4-C6H4NO2 (4), Me (5)] were prepared by reacting the iron sulfides (μ-Sx)[CpFe(CO)2]2 (x=2, 3) with the corresponding chloroformates (ROCOCl). These new complexes have been characterized by elemental analyses and spectroscopic methods. The crystal structure of CpFe(CO)2SCO2Et, 1, has been determined by single crystal X-ray diffraction analysis.

Synthesis, Characterization, and Some Properties of 4-Vinylpyridine-Cr(CO)5 Containing Polymers

The polymerization of 4-vinylpyridine (4VP) and 4-vinylpyridine chromium pentacarbonyl [(4VP)Cr(CO)5] was performed under N2 atmosphere at 60–80°C temperature range. Different percent of feed (%PF) of Cr(CO)5 groups were anchored into poly(4-vinylpyridine) (P4VP) by addition of the intermediate Cr(CO)5THF, which was generated photochemically from Cr(CO)6 in THF, to the polymer at ambient temperature. The determined percent of anchoring (%PA) has shown that the maximum anchored Cr(CO)5 groups was 40% (w/w) with respect to P4VP, and the optimum percent of anchoring was 20% (w/w). The rate of polymerization (Rp) and the activation energy (Ea) of 4VP in the absence and in the presence of 16.7% Cr(CO)5(4VP) were determined. Thermal analysis has shown various changes in the properties of the 4VP polymers after modification of the polymer by Cr(CO)5 groups. The X-ray diffraction and the melting enthalpy derived from the DSC thermogram revealed that the synthesized poly[(CO)5Cr(4VP)] has a crystallinity of about 40%, whereas no crystallinity was observed for pure P4VP.

Octahedral metal carbonyls : XLVIII. Kinetics and mechanism of reactions of hexacarbonyltungsten(0) with bis(triphenylphosphine)imminium pseudo halides☆

Hexacarbonyltungsten(0) reacts with [(Ph3P)2N]+[X]−([PPN]+[X]−) salts (X− = CN−, OCN−, SCN−) in chlorobenzene at 90–120°C to afford [PPN]+[W-(CO)5(X)]− (X− = OCN−, SCN−) and [PPN]+2[cis-W(CO)4(CN)2]2− products. Rate data taken over this temperature range support a rate-law, —d[W(CO)6]/dt = k2 [W(CO)6][PPN+X−] The data are consistent with a mechanism involving initial attack of the anionic nucleophiles (which exist in chlorobenzene as contact ion pairs) at a carbonyl carbon of the substrate. Additional studies of reactions of[PPN]+[SCN]− reveal that at no time is a coordinatively-unsaturated species formed during the substitution process. It is likely that the same is true for the other pseudo-halides as well. It appears probable that most reactions of anionic nucleophiles with M(CO)6 species (M = Cr, Mo, W) involve interaction at carbon, in contrast to results for uncharged Lewis bases (L) such as phosphines and phosphites, for which the bimolecular path is best described as a dissociative interchange. The pseudohalides are “labilizing” ligands, and thus [cis-W(CO)4(L)(X)]− species are formed from [W(CO)5(X)]− substrates under mild conditions (ca. 60°C) via an unimolecular process. The inability to produce [W(CO)4(X)2]2− products (X− = OCN−, SCN−) thus results from thermodynamic considerations.

Dinuclear group VIB metal carbonyl complexes bridged by bis(diphenylphosphino)alkanes

Reactions of the intermediate W(CO)5THF, generated photochemically from W(CO)6 in THF, with Ph2P(CH2)nPPh2 [ = PP; n = 2 (dppe), 4 (dppb), 6 (dpph), 10 (dppd)] at room temperature in THF solutions gave exclusively bimetallic complexes of the (CO)5WPPW(CO)5 type. In addition, complexes bridged by diphosphine ligands of the (CO)4(pip)MPPM(pip)(CO)4 type (pip = piperidine; M = Mo, W) were prepared by stirring the (CO)4M(pip)2 complexes with bis(diphenylphosphino)alkanes in CH2Cl2 solution at ambient temperatures. These new bis(diphenylphosphino)alkane-bridged complexes were characterized by i.r., 1H- and 31P-n.m.r. spectroscopies, as well as by elemental analysis.

Bimetallic Complexes with Bridging Dithiaalkane Ligands: Preparation and Kinetic Study

Reactions of M(CO)5THF, which was generated photochemically from M(CO)6 in THF, with (CH3)3CS(CH2)nSC(CH3)3 (=SS; n=5, 6; M=W, Cr) at room temperature afforded exclusively the bimetallic complexes (CO)5MSSM(CO)5. These new complexes with dithiaalkane bridging ligands have been characterized by IR and 1H NMR spectroscopies and elemental analysis. Kinetic studies of ligand-exchange reactions in these complexes in chlorobenzene (=CB) solutions employing tri(iso-propyl)phosphite (=L) as an incoming nucleophile indicated that the bridging ligand SS is replaced by L to afford finally (CO)5MP(O-i-Pr)3 as the sole reaction product. The kinetic data have also confirmed that replacement of SS by L under pseudo-first-order reaction conditions is dissociative and proceeds via a mechanism which involves initial M-S bond breaking followed by other steps. First order rate constants and activation parameters for these reactions have been determined.

Reactivity of tungsten(0) and molybdenum(0) pentacarbonyl thiobenzoate anions: thiobenzoate as a cis-CO labilizing ligand

The [Et4N][M(CO)5SCOPh] complexes (1a, M = Mo; 2a, M = W) have been prepared at ambient temperatures by reacting the photogenerated M(CO)5 THF intermediate with [Et4N][SCOPh] in THF. Kinetic studies of the reactions of the anions [M(CO)5SCOPh]− with the tri(iso-propyl)phosphite (L) ligand under pseudo-first-order conditions indicate that these reactions are first-order in substrate and are independent of the P(OPr-i)3 concentration. It is thus envisaged that these CO substitutions proceed via a mechanism which involves initial cis-M—CO bond-breaking, followed by fast attack of the incoming nucleophile on the resulting intermediate to give [cis-M(CO)4{P(O-Pri)3}SCOPh]−. This facile displacement of cis-CO indicates the labilizing nature of the thiobenzoate ligand, most probably by virtue of distal oxygen atom participation. Activation parameters for the reactions are: [M(CO)5SCOPh]− + L → cis-[M(CO)4(L)SCOPh]− + CO M = Mo, ΔH‡ = 24.6(2) kcal mol−1, ΔS‡ = 8.2(6) eu; M = W, ΔH‡ = 28.4(2) kcal mol−1, ΔS‡ = 11.3(5) eu. Kinetic data and the mechanism of these ligand-substitutions are discussed.

Novel Anionic Heterocyclic Thiolate Complexes of Group VIB Metal Carbonyls: Synthesis and Reactivity

The syntheses and characterization of novel Group VIB metal carbonyl complexes containing heterocyclic thiolate ligands is described. The reactions of the photogenerated intermediate, M(CO)5THF (M = W, Mo, Cr), with the thiolate anions RS− in [(n‐Bu)4N][SR] [SR− = 2‐mercaptobenzimidazolyl (a), 2‐mercaptobenzothiazolyl (b), 2‐mercaptobenzoxazolyl (c)], afforded exclusively [(n‐Bu)4N][M(CO)5SR] in fairly good yields. Homo‐ and heterobimetallic complexes of the type [(n‐Bu)4N][M(CO)5(μ‐SR)M′(CO)5] (M, M′ = W, Mo, Cr), in which both the exocyclic S‐atom and the endocyclic N‐atom are involved in coordination to two metal centers, have been prepared by the reaction of [(n‐Bu)4N][M(CO)5SR] with M′(CO)5·THF at ambient temperatures. The methods of preparation and characterization of these complexes are described. CO‐substitution reactions in [(n‐Bu)4N][W(CO)5SR] [SR− = (b) and (c)] with tri(iso‐propyl)phosphite (L) afforded the complexes [(n‐Bu)4N][cis‐W(CO)4(SR){P(OPr‐i)3}] as the sole reaction product. The kinetics of CO dissociation from the pentacarbonyl anions under pseudo‐first‐order conditions confirm that these reactions are first‐order in substrate and independent of the entering group (L) concentration. The facile CO dissociation in these complexes is another example of neighboring‐group participation in assisting cis‐CO loss in octahedral metal carbonyls. From the kinetics data, the anionic ligands (b) and (c) are classified as cis‐CO labilizing groups. Rate constants and activation parameters for the CO‐substitution reactions in these complexes are reported.

Bimetallic group 6 metal tetracarbonyls doubly bridged by bisphosphine and/or dithiaalkane ligands

A series of [W(CO)4]2(μ-dppa)(μ-DTA) type complexes [dppa = Ph2P(CH2)nPPh2, n = 2(dppe), 4(dppb), 6(dpph), 10(dppd); DTA = tBuS(CH2)mStBu, m = 3(DTN), 4(DTD), 5(DTUD), 6(DTDD)] containing doubly bridged bisphosphine and dithiaalkane ligands have been prepared by stepwise replacement of piperidine (pip) from cis-W(CO)4(pip)2 complex. In addition, complexes of general formulae [W(CO)4]2(μ-dppa)2 and [Mo(CO)4]2(μ-DTA)2 have been prepared by similar methods. These new complexes have been characterized by i.r. spectroscopy and elemental analysis.

Kinetics and mechanism of ligand substitution reactions in [cis-M(CO)4(amine)(EPh3)] complexes (M = Mo, W; amine = pyridine, piperidine; E = As, Sb)

Abstract Group 6 metal carbonyls [cis-M(CO)4(amine)(EPh3)] (M = Mo, W; amine = piperidine (pip), pyridine (py); E = As, Sb) have been prepared and characterized. These complexes react thermally in chlorobenzene solutions with phosphine or phosphite ligands (= L) to give cis- and trans-M(CO)4(L)(EPh3) products. Kinetics of amine substitution by L in these complexes, under pseudo-first-order conditions, indicate that these reactions proceed by a rate law that is first-order in concentration of the metal complex. Rate constants and activation parameters for these reactions have been determined and are discussed. Competition studies for the [M(CO)4(EPh3)] intermediates show that these intermediates are highly reactive and react almost indiscriminately with various incoming nucleophiles with slight preference for more basic ones.

μ-(2,2,9,9-tetramethyl-3,7-dithiadecane) decacarbonylditungsten(0)

The title compound crystallizes in the centrosymmetric triclinic unit cell, a = 6.6662(8) Å, b = 8.8584(6) Å, c = 13.574(2) Å, α = 71.468(7)°, β = 82.182(9)°, γ = 75.270(7)°, Z = 1. Refinement converged at R = 0.0396 for 1383 observed reflections. The molecule consists of two W(CO)5 fragments bridged centrosymmetrically by the 2,2,9,9-tetramethyl-3,7-dithiadecane ligand.