Comparative reactivity of triorganosilanes, HSi(OEt)3 and HSiEt3, with IrCl(CO)(PPh3)2. Formation of IrCl(H)2(CO)(PPh3)2 or Ir(H)2(SiEt3)(CO)(PPh3)2 depending on the substituents at Si

Reaction of HSi(OEt)₃ with IrCl(CO)(PPh₃)₂ (5:1 molar ratio) at room temperature for 1 h gives IrCl(H){Si(OEt)₃}(CO)(PPh₃)₂ (1), which is observed by the ¹H and ³¹P{¹H} NMR spectra of the reaction mixture. The same reaction, but in 20:1 molar ratio at 50 °C for 24 h produces IrCl(H)₂(CO)(PPh₃)₂ (2) rather than the expected product Ir(H)₂{Si(OEt)₃}(CO)(PPh₃)₂ (3) that was previously reported to be formed by this reaction. Accompanying formation of Si(OEt)₄, (EtO)₃SiOSi(OEt)₃, and (EtO)₂HSiOSi(OEt)₃ is observed. On the other hand, trialkylhydrosilane HSiEt₃ reacts with IrCl(CO)(PPh₃)₂ (10:1 molar ratio) at 80 °C for 84 h to give Ir(H)₂(SiEt₃)(CO)(PPh₃)₂ (4) in a high yield, accompanying with a release of ClSiEt₃.     

Time-resolved infrared study of reactive species produced by flash photolysis of the hydroformylation catalyst precursor Co2(CO)6(PMePh2)2

Flash photolysis with time-resolved infrared (TRIR) spectroscopy was used to elucidate the photochemical reactivity of the hydroformylation catalyst precursor Co₂(CO)₆(PMePh₂)₂. Depending on reaction conditions, the net products of photolysis varied significantly. A model is presented that accounts for the net reactivity with two initial photoproducts, the 17-electron species Co(CO)₃(PMePh₂) and the coordinatively unsaturated dimer Co₂(CO)₅(PMePh₂)₂. No evidence was found for photochemical formation of Co₂(CO)₆(PMePh₂). Time-resolved spectroscopic studies allowed for the direct observation of transient species and for kinetics studies of certain reactions; for example, the reactions of Co(CO)₃PMePh₂ with CO and with PMePh₂ gave the respective rate constants 1.5 × 10⁵ and 1.2 × 10⁷ M⁻¹ s⁻¹, while the analogous reactions with Co₂(CO)₅(PMePh₂)₂ gave the rate constants of 2.6 × 10⁶ M⁻¹ s⁻¹ and 3.9 × 10⁷ M⁻¹ s⁻¹.     

Syntheses and structures of the heterometallic clusters [(Ph3PAu)3Re(CO)4], [(Ph3PAu)4Re(CO)4], [(Ph3PAu)6AuRe2(CO)8], and [(Ph3PAu)6Re(CO)3]

The reaction of [HRe₃(CO)₁₂]²⁻ with an excess of Ph₃PAuCl in CH₂Cl₂ yields [(Ph₃PAu)₄Re(CO)₄]⁺ as the main product, which crystallizes as [(Ph₃PAu)₄Re(CO)₄]PF₆ · CH₂Cl₂ (1 · CH₂Cl₂) after the addition of KPF₆.The crystal structure determination reveals a trigonal bipyramidal Au₄Re cluster with the Re atom in equatorial position.If [(Ph₃PAu)₄Re(CO)₄]⁺ is reacted with PPh₄Cl, a cation [Ph₃PAu]⁺ is eliminated as Ph₃PAuCl, and the neutral cluster [(Ph₃PAu)₃Re(CO)₄] (2) is formed.It combines with excess [(Ph₃PAu)₄Re(CO)₄]⁺ to afford the cluster cation, [(Ph₃PAu)₆AuRe₂(CO)₈]⁺. It crystallizes from CH₂Cl₂ as[(Ph₃PAu)₆AuRe₂(CO)₈]PF₆ · 4CH₂Cl₂ (3 · 4CH₂Cl₂). In [(Ph₃PAu)₃Re(CO)₄] the metal atoms are arranged in form of a lozenge while in [(Ph₃PAu)₆AuRe₂(CO)₈]⁺ two Au₄Re trigonal bipyramids are connected by a common axial Au atom.The treatment of [(Ph₃PAu)₄Re(CO)₄]⁺ with KOH and Ph₃PAuCl in methanol yields the cluster cation [(Ph₃PAu)₆Re(CO)₃]⁺, which crystallizes with from CH₂Cl₂ as [(Ph₃PAu)₆Re(CO)₃]PF₆ · CH₂Cl₂ (4 · CH₂Cl₂). The metal atoms in this cluster form a pentagonal bipyramid with the Re atom in the axial position.     

Single-flask synthesis of (C5H5)W(CO)3Cl from W(CO)6

(C₅H₅)W(CO)₃Cl has been prepared in >90% yield from W(CO)₆, cyclopentadiene, and CCl₄ in a single-flask synthesis involving the intermediates W(CO)₃(CH₃CN)₃ and (C₅H₅)W(CO)₃H.     

Sn-S and Ru-Ru bonds cleavage reactions between [Ph3SnS(CH2)3SSnPh3] and Ru3(CO)12: X-ray crystal structures of [Ph3SnS(CH2)3SSnPh3] and trans-[Ru(CO)4(SnPh3)2]

The organotin complex [Ph₃SnS(CH₂)₃SSnPh₃] (1) was synthesized by PdCl₂ catalyzed reaction between Ph₃SnCl and disodium-1,3-propanedithiolate which in turn was prepared from 1,2-propanedithiol and sodium in refluxing THF. Reaction of 1 with Ru₃(CO)₁₂ in refluxing THF affords the mononuclear complex trans-[Ru(CO)₄(SnPh₃)₂] (2) and the dinuclear complex [Ru₂(CO)₆(μ-κ²-SCH₂CH₂CH₂S)] (3) in 20 and 11% yields, respectively, formed by cleavage of Sn-S bond of the ligand and Ru-Ru bonds of the cluster. Treatment of pymSSnPPh₃ (pymS = pyrimidine-2-thiolate) with Ru₃(CO)₁₂ at 55-60 °C also gives 2 in 38% yield. Both 1 and 2 have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.     

Oxidative addition of methyl iodide to [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)]

The reaction rate of the oxidative addition and the following CO insertion step of methyl iodide with [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] is determined. The key finding is that while [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] oxidatively adds methyl iodide ca 300 times faster than the Monsanto catalyst, the CO insertion step is much slower. However, the rate-determining step of the oxidative addition reaction of the phosphorus-containing acetylacetonato-rhodium(I) complex, the carbonyl insertion step, is still in the same order or faster than the rate-determining oxidative addition step of iodomethane to [Rh(CO)₂I₂]⁻.     

Reactions of Zr(C5H5)(6,6-dmch)(PMe3)2 and Zr(6,6-dmch)2(PMe3)2 (dmch=dimethylcyclohexadienyl) with CO and alkynes

The reactions of Zr(C₅H₅)(6,6-dmch)(PMe₃)₂ and Zr(6,6-dmch)₂(PMe₃)₂ (dmch=dimethylcyclohexadienyl) with CO lead to the selective replacement of one PMe₃ ligand by CO. Both carbonyl complexes have been structurally characterized. Additionally, the reaction of the latter complex with PhC₂SiMe₃ leads to a similar replacement of one PMe₃ ligand, involving simple coordination of the alkyne, rather than any coupling to the dmch ligand.     

Electrochemical oxidation of Mo(CO)4(LL) and Mo(CO)3(LL)(CH3CN): Generation, infrared characterization, and reactivity of [Mo(CO)4(LL)] and [Mo(CO)3(LL)(CH3CN)] (LL = 2,2′-bipyridine, 1,10-phenanthroline and related ligands)

Mo(CO)₄(LL) complexes, where LL = polypyridyl ligands such as 2,2′-bipyridine and 1,10-phenanthroline, undergo quasi-reversible, one-electron oxidations in methylene chloride yielding the corresponding radical cations, [Mo(CO)₄(LL)]⁺. These electrogenerated species undergo rapid ligand substitution in the presence of acetonitrile, yielding [Mo(CO)₃(LL)(CH₃CN)]⁺; rate constants for these substitutions were measured using chronocoulometry and were found to be influenced by the steric and electronic properties of the polypyridyl ligands. [Mo(CO)₃(LL)(CH₃CN)]⁺ radical cations, which could also be generated by reversible oxidation of Mo(CO)₃(LL)(CH₃CN) in acetonitrile, can be irreversibly oxidized yielding [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ after coordination by an additional acetonitrile. Infrared spectroelectrochemical experiments indicate the radical cations undergo ligand-induced net disproportionations that follow first-order kinetics in acetonitrile, ultimately yielding the corresponding Mo(CO)₄(LL) and [Mo(CO)₂(LL)(CH₃CN)₃]²⁺ species. Rate constants for the net disproportionation of [Mo(CO)₃(LL)(CH₃CN)]⁺ and the carbonyl substitution reaction of [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ were measured. Thin-layer bulk oxidation studies also provided infrared characterization data of [Mo(CO)₄(ncp)]⁺ (ncp = neocuproine), [Mo(CO)₃(LL)(CH₃CN)]⁺, [Mo(CO)₃(LL)(CH₃CN)₂]²⁺ and [Mo(CO)₂(LL)(CH₃CN)₃]²⁺ complexes.     

CO-loss and geometric isomerization in the frozen matrix photochemistry of cis-Fe(CO)4X2, where X = Br and I, cis-[Et4N][Mn(CO)4Br2], cis-Mn(CO)4(PBu3)Br, and Mn(CO)3(PBu3)2Br

Photolysis of cis-Fe(CO)₄X₂, where X = Br and I, results in low energy, facile rearrangement to the trans isomer with no evidence of CO-loss. In contrast, the isoelectronic cis-Mn(CO)₄Br₂ anion exhibits CO-loss upon photolysis with only weak evidence for the trans isomer. The photolysis of Mn(CO)₅Br, Mn(CO)₄Br(PBu₃) and Mn(CO)₃Br(PBu₃)₂ have also been examined in frozen matrices.     

Kinetics study of the substitution reaction of fac-[Fe(CN)2(CO)3I] with PPh3

Substitution reaction of fac-[Fe^II(CN)₂(CO)₃I]⁻ with triphenylphosphine (PPh₃) produced mono phosphine substituted complex cis-cis-[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh₃. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻][PPh₃]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (k_BT/h)exp(−ΔH^≠/RT + ΔS^≠/R) with ΔH^≠ = 119(4) kJ mol⁻¹ and ΔS^≠ = 102(10) J mol⁻¹ K⁻¹. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.     

Synthesis of fac-[Os(CO)3(L)Me2] (L = THF or MeCN) and some reactions with PPh3 and trityl salts

The reaction of cis-[Os(CO)₄Me₂] with Me₃NO in the THF or MeCN yields the complexes fac-[Os(CO)₃(L)Me₂] (where L = THF or MeCN). Whereas the THF complex is unstable and only characterised spectroscopically, fac-[Os(CO)₃(MeCN)Me₂] has been isolated as a white solid and fully characterized by both analytical and spectroscopic methods. These complexes fac-[Os(CO)₃(L)Me₂] are shown to be useful intermediates. Thus, reaction with PPh₃ gives fac-[Os(CO)₃(PPh₃)Me₂] in good yield.Reactions of fac-[Os(CO)₃(L)Me₂] (L = CO or MeCN) with CPh₃PF₆ or B(C₆F₅)₃ have been investigated. Whereas cis-[Os(CO)₄Me₂] showed no reaction with either CPh₃PF₆ or B(C₆F₅)₃, the reaction of fac-[Os(CO)₃(MeCN)Me₂] with CPh₃PF₆ in CH₂Cl₂ occurred over 16 h at room temperature to give an unstable cationic product and CPh₃Me. The reaction was monitored by both IR and NMR spectroscopies. When this reaction of fac-[Os(CO)₃(MeCN)Me₂] was carried out in the presence of a trapping ligand such as MeCN, the stable cationic product [Os(CO)₃(MeCN)₂Me]⁺ could be isolated and identified spectroscopically.     

Reaction of Mo(CO)4(NCCH3)2 and 7-aza-2-Tosylnorbornadiene

Reaction of Mo(CO)₄(NCCH₃)₂ and 7-aza-2-tosylnorbornadiene (7-azaNBD) yielded five air-stable Mo complexes. One is Mo(CO)₄(η⁴-7-azaNBD), in which the molybdenum atom is chelated by the two π-bonds of 7-azaNBD. The other four are isomers of Mo(CO)₂(η²-7-azaNBD)₂, in which the molybdenum atoms are chelated by the nitrogen atom and one of the two double bonds of 7-azaNBD. In one pair of the isomers, the metal binds to C(2)C(3) of both 7-azaNBD ligands; whereas in the other pair of isomers the metal binds to C(2)C(3) of one 7-azaNBD ligand and C(5)C(6) of another ligand. All structures were fully characterized by NMR spectra. A single crystal of compound 4 was analyzed by X-ray diffraction analysis, which was found to be monoclinic with a = 8.4199, b = 23.984, c = 16.395 Å, and β = 99.99°.     

An SC-MEH molecular orbital study of HCo(CO)4 and Co(CO)4

The Self Consistent Modified Extended Hückel (SC-MEH) molecular orbital method has been applied to the HCo(CO)₄ and Co(CO)₄ molecules. The results show that the highest occupied orbitals are predominantly ligand in character, which is at variance with other published calculations. Computation of the UV and photoelectron spectra, bond energy and some associated parameters, and magnetic hyperfine parameters of Co(CO)₄ have been carried out and found to be in exceptionally good agreement with experiment. The reported results also provide an acceptable rationalization for the observed photolysis and homolytic activity of the HCo(CO)₄ molecule.     

A rare example of a di-cationic hydrido carbonyl tetra-nuclear cluster, [H2Rh2Pt2(CO)7(PPh3)3]

Addition of excess CF₃CO₂H (HTFA) to [Rh₂Pt₂(CO)₇(PPh₃)₃], I, under nitrogen results in the formation of a salt (X²⁺ Y²⁻), which contains only the second example of a di-cationic carbonyl hydride tetra-nuclear cluster, [H₂Rh₂Pt₂(CO)₇(PPh₃)₃]²⁺, X²⁺, and a presently partially characterized polymetallic anion Y²⁻. The di-cation X²⁺ has been characterized by mass spectrometry and a variety of multinuclear NMR methods. Since there is no difference in the electron count for I and X²⁺, it is probable that both I and X²⁺ adopt similar butterfly metallic frameworks with a Rh-Rh hinge; in X²⁺, there are two bridging hydrides to the same wing-tip Pt but the phosphine site occupancies on the Rh₂Pt₂-framework in I and X²⁺ are different.     

Equilibrium, solid state behavior and reactions of four and five co-ordinate carbonyl stibine complexes of rhodium. Crystal Structures of trans-[Rh(Cl)(CO)(SbPh3)2], trans-[Rh(Cl)(CO)(SbPh3)3] and trans-[Rh(I)2(CH3)(CO)(SbPh3)2]

The crystal structures of the four-coordinate trans-[Rh(Cl)(CO)(SbPh₃)₂] (1) and the five-coordinate trans-[Rh(Cl)(CO)(SbPh₃)₃] (2) are reported, as well as the unexpected oxidative addition product, trans-[Rh(I)₂(CH₃)(CO)(SbPh₃)₂] (3), obtained from the reaction of 2 with CH₃I. The formation constants of the five-coordinate complex were determined in dichloromethane, benzene, diethyl ether, acetone and ethyl acetate as 163±8, 363±10, 744±34, 1043±95 and 1261±96 M⁻¹, respectively. While coordinating solvents facilitate the formation of the five-coordinate complex, the four-coordinate complex could be obtained from diethyl ether due to the favorable low crystallization energy. The tendency of stibine ligands to form five-coordinate rhodium(I) complexes is attributed mainly to electron deficient metal centers in these systems, with smaller contributions by the steric effects. The average effective cone angle for the SbPh₃ ligand in the three crystallographic studies was determined as 139° with individual values ranging from 133 to 145°.     

Reactions of [Os3(CO)10(MeCN)2] with ethynyl thiophenes: The formation of linked clusters

The reaction of 2 equiv. of [Os₃(CO)₁₀(MeCN)₂] with R-CC-L-CC-R (R = H, L = (C₄H₂S); R = SiMe₃, L = (C₄H₂S-C₄H₂S), (C₄H₂S-C₄H₂S-C₄H₂S), (C₄H₂S)-(C₁₄H₈)-(C₄H₂S)) affords the series of linked clusters [{Os₃(CO)₁₀}(HCC(C₄H₂S)CCH){Os₃(CO)₁₀}] (1), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (2), [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S-C₄H₂S-C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (4) and [{Os₃(CO)₁₀}(Me₃SiCC(C₄H₂S)-(C₁₄H₈)-(C₄H₂S)CCSiMe₃){Os₃(CO)₁₀}] (6) as the major products. The complexes have been characterised by a range of spectroscopic methods and, in the case of 1 and 2 by single crystal X-ray crystallography. The alkyne groups cap the osmium triangles in the expected μ₃-η²-||-bonding mode and each triangle is coordinated by nine terminal and one μ₂-carbonyl group. Solution UV-Vis spectra of the complexes were similar to those observed for the free ligands consistent with there being little delocalisation between the cluster units and the thiophene groups.     

Reinvestigation of the visible absorption bands of the 2,2′-bipyrimidine complexes W(CO)4(bpym) and (μ-bpym)[M(CO)4]2 (M=Mo, W) with resonance Raman spectroscopy; the emission spectrum of (μ-bpym)[Mo(CO)4]2

The character of the two lowest energy transitions of W(CO)₄(bpym) and (μ-bpym)[M(CO)₄]₂ (M=Mo, W) were established with resonance Raman spectroscopy. According to these spectra the two bands belong to MLCT transitions to different π* orbitals of the bpym ligand. Contrary to expectations it is not the first (lowest energy) but the second and more intense electronic transition which, according to the resonance Raman spectra, is directed to the lowest lying π* orbital (b_2u*, LUMO) of these complexes. This interpretation explains the different band intensities and the untypically low g values of the ESR signals of corresponding anion radicals. Excitation of (μ-bpym)[Mo(CO)₄]₂ in CH₂Cl₂ at 400 nm produced a weak emission with an onset at 700 nm. According to the excitation spectrum, this emission originates from the lowest MLCT-excited state of the complex.     

Kinetics and mechanism of CO substitution of [η-CpFe(CO)3]PF6 with PPh3 in the presence of substituted pyridine N-oxide

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Comparative properties of fluorous phosphine ligand complexes: W(CO)5L. Crystal structure of W(CO)5P(C6H4-4-CH2CH2(CF2)7CF3)3

The compounds W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ (1) and W(CO)₅P(CH₂CH₂(CF₂)₅CF₃)₃ (2) were synthesized in order to probe the electronic and physical effects of ligation by perfluorocarbon substituted tertiary phosphine ligands in a W(CO)₅L complex. The π-accepting ability of the fluorous phosphines was found to rank with non-fluorous comparators as P(CH₂CH₂(CF₂)₅CF₃)₃ > P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ > PPh₃ > P(p-tolyl)₃ > P(n-octyl)₃. The X-ray crystal structure of W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ shows strong intermolecular association of fluorous components but confirms that the para fluorocarbon subtituents have an insignificant effect on the tungsten coordination environment. Partition coefficients (toluene/perfluoromethylcyclohexane) were measured for compounds 1 and 2.     

O-Alkylthio- and O-alkylselenooxalate iron complexes: Structures of CpFe(CO)2ECOCO2Me and [CpFe(CO)2ECO]2

When the iron sulfide complexes (μ-S_x)[CpFe(CO)₂]₂ (x = 2, 3) are treated with O-alkyl oxalyl chlorides ROCOCOCl the complexes CpFe(CO)₂SCOCO₂R (1) [R = Me (a), Et (b)] are obtained. Similarly, the complexes CpFe(CO)₂SeCOCO₂R (2) are obtained from the analogous iron selenide (μ-Se)[CpFe(CO)₂]₂ reaction with the same reagents. Treatment of the iron selenide with half equivalent of oxalyl chloride produces the dimeric complex [CpFe(CO)₂SeCO]₂ (3). The new complexes, 1, 2 and 3, have been characterized by elemental analyses, IR and ¹H NMR spectroscopy. The solid state structures of 1a, 2a, 3 and [CpFe(CO)₂SCO]₂ (4) were determined by an X-ray crystal structure analysis.