Rinaldo Poli

The interaction of FeCl3 with PPh3 in chloroform. X-ray crystal structure of [Ph3PCH2PPh3][FeCl4]2

Abstract Interaction of FeCl3, and PPh3 in CHCl3 yields complex mixtures containing unstable adducts. The compound [Ph3PCH2PPh3][FeCl4]2·CHCl3 was isolated from the solution after the decomposed mixture had been allowed to interact with air. Crystal data: triclinic, space group P1, a = 11.459(4), b = 12.102(2), c = 18.109(4) A, α = 105.15(2), β = 102.14(2), γ = 94.91(2)°, V = 2347(2) A3, Z = 2, dc = 1.49 g cm−3, μ(Mo-Kα) = 13.49 cm−1, R = 0.045 (Rw = 0.054) for 487 parameters and 5256 observed reflections with F02 > 3 σ (Fo2).

Hydrotris(pyrazolyl)borate molybdenum chemistry: spin triplet 16-electron carbonyl derivatives of molybdenum (II), and the X-ray structure of the Mo(V) oxo compound {HB(3,5-Me2C3N2H)3} MoOI2

Abstract The hydrotris(3,5-dimethylpyrazolyl)borate complexes Tp ∗ Mo ( CO ) 2 X ( X = Cl, I ) are rare examples of 16-electron carbonyl derivatives with a spin triplet ground state, which exhibit relatively sharp contactshifted 1H NMR spectra. Oxidation of Tp∗MoI(CO)2 led to the isolation and crystallographic characterization of Tp∗MoOI2.

Dissociative phosphine exchange for cyclopentadienylmolybdenum(III) systems. Bridging the gap between Werner-like coordination chemistry and low-valent organometallic chemistry

Several phosphine exchange processes on 17-electron CpMoCl2(PR3)2 systems have been investigated. The exchange of two PPh3 ligands with either two PMe3 ligands or with Ph2PCH2PPh2 (dppe) is complete within a few minutes at −80 °C. Equally fast is the exchange of two PEt3 ligands with two PMe3 ligands. On the other hand, the exchange of two PEt3 ligands with dppe is much slower (t12 ≈ 15 min to a few hours at r.t.), with excess dppe accelerating the exchange and free PEt3 retarding it. The self-exchange reaction of PMe3 is extremely slow (less than 25% exchange at r.t. in 6 h at r.t.) and an analysis of the initial rate of this reaction shows a two-term rate law with one [PMe3]-dependent and one independent term. Finally, PMe3 self-exchange on Cp∗MoCl2(PMe3)2 proceeds over one order of magnitude faster than for the corresponding Cp system, with a substantially [PMe3]-independent rate law. All these data are indicative of a dominant dissociative exchange mechanism involving rupture of the MoPR3 bond in the slow step and formation of a 15-electron intermediate. The rate of phosphine dissociation qualitatively correlates with the MoP distance in the 17-electron starting complex. Only for the CpMoCl2(PMe3)2 system is phosphine dissociation sufficiently slowed down so that the alternative associative exchange pathway becomes competitive. Possible reasons for a low activation barrier in these dissociative exchanges are discussed.

Attempts to prepare the 17-electron (η5-C5H5)MoX2(dmpe) (XCl, Br, I; dmpe=bis(dimethylphosphino)ethane) compounds. Formation and X-ray molecular structure of (η5-C5H5)MoCl3(dmpe) and [(η5-C5H5)-Mo(dmpe)2][MoBr4(dppe)] (dppe=bis(diphenylphosphino)ethane)

Abstract The reaction of [Cp2Mo2Cl5]− with dmpe, followed by work-up in CH2Cl2 produced CpMoCl3(dmpe). From the reaction of CpMoBr2(dppe) (Cp=η5-C5H5) with dmpe the salt [CpMo(dmpe)2][MoBr4(dppe)] was isolated. Crystal data: CpMoCl3(dmpe): monoclinic, space group P21/n, a=8.1763(6), b=13.643(1), c=14.948(2) A, β=103.054(8)°, V=1624.3(6) A3, Z=4, Dc=1.71 g cm−3, R=0.046, Rw=0.070 for 155 parameters and 1876 observations with Fo2>3σ(Fo2); [CpMo(dmpe)2][MoBr4(dppe)]: monoclinic, space group P21/n, a=17.642(4), b=29.040(4), c=19.721(3) A, β=99.28(1)δ, V=9972(5) A3, Z=8, Dc=1.70 g cm−3, R=0.100, Rw=0.119 for 651 parameters and 3976 observations with Fo2>2.5σ(Fo2).

Further considerations on the structure and bonding in edge-sharing bioctahedral complexes

Abstract Extended Huckel MO calculations have been carried out on model compounds that mimic transition metal edge-sharing bioctahedral (ESBO) complexes of stoichiometry M 2 X 6 L 4 (X=anionic ligand with lone pairs for bridge-bonding and for π bonding, L=neutral 2-electron donor ligand), and for the corresponding mononuclear cis -MX 4 L 2 system. The widening of the cis -L eq -M-L eq angle (eq=equatorial) is shown to cause the narrowing of the opposite X-M-X angle which, for the ESBO complexes, disfavors the formation of a strong metal-metal interaction. The calculations also address the importance of the M-X π interactions in metal-metal bonded dimers. The X ax (ax=axial) ligands are shown to be better π donors than the X eq ligands for the configurations d 1 -d 1 through d 5 -d 5 , the differential between the π donating abilities in the two different positions being maximal for the d 1 -d 1 configuration. This effect is proposed to be responsible for the preference of d 1 -d 1 systems for the ESBO structure having all L ligands in equatorial positions, whereas the metal-metal bonded ESBO compounds of all other electronic configurations as well as all non-bonded ESBO complexes prefer the structure with two L eq on one metal and two L ax , on the other one on steric grounds. The MO model presented here is also in excellent agreement with the observed trends of M-Cl ax , M-Cl eq and M-Cl br (br=bridging) bond distances as a function of d n d- n configuration.

17-electron, four-legged piano stool CpMoX2L2 complexes (X=halogen, L=tertiary phosphine). EPR evidence for the existence of a second isomer in solution

Abstract Several 17-electron molybdenum(III) complexes of the type CpMoCl2L2 have been generated by either (1) reaction between CpMoCl2 and the appropriate L, (2) reaction between MoCl3(THF)3, the appropriate L and CpTl, and (3) phosphine exchange from CpMoCl2(PPh3)2. The iodide complexes CpMoI2L2 (L  PMePh2, PPh3) have been generated from the corresponding chloride and NaI. The complexes have been investigated by EPR (X-band and Q-band) and cyclic voltammetry. The four-legged piano stool structure is found by single crystal X-ray diffraction studies of the PMePh2 and PPh3 dichloride compounds. However, this structure equilibrates in solution with at least one other isomeric form which is observable for the PMe2Ph complexes by X-band EPR and for other complexes, including the previously reported CpMoCl2(dppe), by Q-band EPR. Phosphine exchange equilibria show a thermodynamic stability trend that parallels the phosphine σ-donor strength.

Synthesis, characterization, and reactivity of cyclopentadienyltrichloromolybdenum(IV). X-Ray structure of CpMoCl3[P(OCH2)3CEt]2 (Cp = η5-C5H5)

Abstract CpMoCl 3 has been generated by either oxidation of CpMoCl 2 with PhI·Cl 2 , reduction of CpMoCl 4 with TiCl 3 , or valence conproportionation of CpMoCl 2 and CpMoCl 4 . Low-energy IR spectroscopy and power X-ray diffraction establish that this material is different from a 1 : 1 mixture of CpMoCl 2 and CpMoCl 4 . The 18-electron adducts CpMoCl 3 (LL) (LL = Me 2 PCH 2 CH 2 PMe 2 , Ph 2 PCH 2 CH 2 PPh 2 ) and CpMoCl 3 [P(OCH 2 ) 3 CEt] 2 have been obtained by interaction with the appropriate free ligand, while the reaction with PMe 3 leads to decomposition with formation of several different products. The crystal structure of the cage phosphite complex shows a pseudo-octahedral configuration with a facial arrangement of the three chloride ions.

Instability of 15-electron Cp☆MoCl2L (L = 2-electron donor) derivatives. X-ray structure of Cp☆MoCl2(PMe2Ph)2 and [Cp☆MoCl2(PMe2Ph)2]AlCl4

Abstract The complex Cp★MoCl2(PMe2Ph)2 (Cp★ = η5C5Me5) has been obtained in good yield from Cp☆MoCl4, PMe2Ph2, and Na in the appropriate stoichiometric ratio, and it is also obtained by a ligand redistribution process after reduction of Cp☆MoCl3- (PMe2Ph) with Na. This compound is oxidized by the CH2Cl2 solvent in the presence of AlCl3 to afford the salt [Cp☆MoCl2(PMe2Ph)2AlCl4. Both compounds have been characterized crystallographically and by 1H-NMR spectroscopy. The reasons for the instability of 15-electron Cp☆MoCl2L complexes are discussed. The 1H-NMR resonance data for Cp ☆ MoCl 2 L 2 ( L = PMe 3 , PMe 2 Ph ) and [Cp☆MoCl2(PMe2Ph)2]+ are also discussed.

Metal-metal bonding in pentamethylcyclopentadienylmolybdenum(IV) dinuclear compounds: chloride abstraction from non-bonded Cp∗2Mo2Cl6 to afford bonded [Cp∗2Mo2Cl5]+

Chloride abstraction from Cp∗2Mo2Cl6 (Cp∗ = η5C5Me5) is accomplished by interaction with the Lewis acid AlCl3 to afford the structurally characterized salt [Cp∗2Mo2Cl5]+[AlCl4]−. Crystal data: triclinic, space group P1, a = 8.3903(13), b = 15.797(3), c = 24.036(2) A; α = 86.766(11), β = 80.916(10), γ = 81.616(14)°, V = 3110.5(8) A3, Dc = 1.726 Mg m−3, μ(Mo Kα) = 1.618 mm−1, R = 0.0637. The structure exhibits two four-legged piano stools joined by three bridging Cl atoms. The MoMo distance of 2.866(2) A is significantly longer than all other reported bonded Mo(IV)-Mo(IV) distances and longer than the single bond (σ2δ∗2δ2) distance in the related Mo(III) complexes [(ring)MoCl2]2 (ring = substitute cyclopentadienyl ring). The reasons for this lenthening are analyzed and discussed on the basis of structural data and Fenske-Hall MO calculations. [Cp∗2Mo2Cl5]+ reacts rapidly with Cl− to afford [Cp∗MoCl4]− and exhibits a reversible one-electron oxidation to a neutral Cp∗2Mo2Cl5 species at −0.13 V versus ferrocene/ferricinium. The non-existence of a metal-metal bonded isomeric form of the Cp∗2Mo2Cl6 parent compound is also discussed.

Synthesis, structure and properties of the face-sharing bioctahedral Mo2X6(PMe2Ph)3 (X = Br, I) compounds

Abstract The title compounds were obtained by reacting the corresponding MoX3(THF)3 complexes with PMe2Ph in a 2 : 3 ratio in refluxing toluene. The compounds assume a face-sharing, bioctahedral structure with three bridging halide ligands, the coordination geometries being completed by one terminal halide and two phosphines for one metal centre, and by two terminal halides and one phosphine for the other one. A comparison with the known chloride analogue shows that the metal-metal separation increases in the order Cl