Lorenza Marvelli

Reactivity of the [ReNR]3+ and [ReN]2+ cores toward bis(diphenylphosphino)amine and its derivatives. Synthesis and crystal structures

The complexes fac-[Re(NMe)Cl3{NH(PPh2)2-P,P′}]1, [ReNCl{NH(PPh2)2-P,P′}2]X (X = Cl 2 or BPh42a), [Re(NMe) Cl2{N(XPPh2)2-X,X′}(PPh3)](X = 0 3, S 4 or Se 8), [Re(NMe)Cl{N(XPPh2)2-X,X′}2](X = S 5 or Se 9), [ReNCl{N(SPPh2)2-S,S′}(PPh3)]6, [ReN{N(XPPh2)2-X,X′)2](X = S 7 or Se 10) and trans-[ReOCl2{N(OPPh2)2-O,O′}(AsPh3)]11 were obtained by treatment of [Re(NMe)Cl3(PPh3)2], [ReNCl2(PPh3)2] or [ReOCl3(AsPh3)2] with the appropriate ligand under different experimental conditions. The structures of complexes 1, 2a and 6 were determined by X-ray crystallography. In 1 and 2a the Re atom is six-co-ordinate in a distorted octahedral configuration, whereas in 6 the Re atom is five-co-ordinate square pyramidal with the N atom in the apical position.

Synthesis and Characterisation of tetrahedro-Tetraphosphorus Complexes of Rhenium – Evidence for the First Bridging Complex of White Phosphorus

Reaction of white phosphorus with [(triphos)Re(CO)2(OTf)] (1) in dichloromethane affords the new tetraphosphorus complex [(triphos)Re(CO)2(η1-P4)](OTf) (2) [triphos = MeC(CH2PPh2)3; OTf = OSO2CF3]. Compound 2 reacts with a second equivalent of 1 to give the binuclear complex [{(triphos)Re(CO)2}2(μ,η1,η1-P4)](OTf)2 (3) in which a tetrahedro-P4 ligand behaves as tethering unit between two [(triphos)Re(CO)2]+ moieties. Complexes 2 and 3 represent the first soluble metal complexes of the tetraphosphorus molecule where the P4 ligand has not undergone any major modification.

In situ IR and NMR study of the interactions between proton donors and the Re(I) hydride complex [{MeC(CH2PPh2)3}Re (CO)2H]. ReH…H bonding and proton-transfer pathways

Abstract The reactions of various proton donors (phenol, hexafluoro-2-propanol, perfluoro-2-methyl-2-propanol, monochloroacetic acid, and tetrafluoroboric acid) with the rhenium (I) hydride complex [(triphos)Re(CO)2H] (1) have been studied in dichloromethane solution by in situ IR and NMR spectroscopy. The proton donors from [(triphos)Re(CO)2H…HOR] adducts exhibiting rather strong H…H interactions. The enthalpy variations associated with the formation of the H-bonds (−ΔH = 4.4–6.0 kcal mol−1) have been determined by IR spectroscopy, while the H…H distance in the adduct [(triphos)Re(CO)2H…HOC(CF3)3] (1.83 A) has been calculated by NMR spectroscopy through the determination of the T1min relaxation time of the ReH proton. It has been shown that the [(triphos)Re(CO)2H…HOR] adducts are in equilibrium with the dihydrogen complex [(triphos)Re(CO)2(η2-H2)]+, which is thermodynamically more stable than any H-bond adduct.

Reactivity of rhenium(V) complexes containing different cores such as [ReO]3+, [ReNR]3+ and [ReN]2+ toward bis(diphenylphosphino)methane: synthesis and crystal structures

The complexes fac-[ReOCl3(dppm-P,P′)] (1a), mer-[ReOCl3(dppm-P,P′)] (1b), mer-[ReCl3(dppm-P,P′)(dppom-P)] (2), [ReCl4(dppom-P,O)] (3) and mer-[ReCl3(dppm-P,P′)PPh3] (4) (dppmPh2PCH2PPh2, dppomPh2PCH2P(O)Ph2) were obtained by reaction of [ReOCl3(PPh3)2] or [AsPh4][ReOCl4] and dppm under different experimental conditions. Complex 1b is probably obtained via the intermediate formation of complexes 2 or 4. The complexes fac-[Re(NCH3)Cl3(dppm-P,P′] (5), trans-[ReNCl2(dppm-P)PPh3] (6) and [ReNCl(dppm-P,P′)2]Cl (7) were also obtained starting from [Re(NCH3)Cl3(PPh3)2] and [ReNCl2(PPh3)2], respectively. The structures of 1a and 3 were determined by X-ray crystallography. Compound 1a is monoclinic, space group P21/c, with a=11.156(4), b=17.264(5), c=14.467(5) A and β=110.96(3)°. The molecular complex is distorted octahedral. Selected bond distances (A) are: ReO(oxide) 1.671(6), ReCl(trans to O) 2.452(3), ReCl(trans to P) 2.365(4) and 2.373(3), ReP 2.439(3) and 2.449(2). The PReP chelation angle is 69.2(1)°. Compound 3 is orthorhombic, space group Pccn, with a=34.843(5), b=8.242(2) and c=19.342(4) A. The molecular complex is roughly octahedral with the oxidized dppm ligand chelated through the P atom and the O atom of the PO group. Selected bond distances (A) are: ReCl(trans one other) 2.355 (mean), ReCl(trans to P) 2.353(3), ReCl(trans to O) 2.215(5), ReO 2.087(7). The PReO chelation angle is 80.7(2)°.

Reactivity of the [ReO]3+ core toward Ph2P(Se)NH(Se)PPh2

The salt K[N(PPh2Se)2] reacts with [ReOCl3(PPh3)2] or [AsPh4][ReOCl4] to give [ReO(Cl){N(PPh2Se)2}2]. In solution this compound tends to transform into [ReO(Cl)(Ph2PNPPh2Se)2], by loss of one Se atom from each ligand. Recrystallization from CH2Cl2–EtOH yielded [ReO(OEt)(Ph2PNPPh2Se)2] the crystal structure of which has been determined.

New rhenium complexes with phosphinite PPh2OR or phosphonite PPh(OR)2(R = Me, Et or Pri) ligands: synthesis and protonation of various polyhydrides

The rhenium complexes [ReOCl3L2] and [ReCl3L3][L = PPh2OMe, PPh2OEt, PPh2OPri, PPh(OEt)2 or PPh(OPri)2] were prepared by allowing [ReOCl3(AsPh3)2] to react with the appropriate amount of phosphinite or phosphonite. Treatment of [ReCl3L3] with CO and p-MeC6H4NC afforded the mer-trans-[ReCl(CO)3L2] and [ReCl2(p-MeC6H4NC)4L]BPh4 complexes, respectively. Treatment of [ReOCl3L2] with NaBH4 gave [Re2H8L4], but in the presence of phosphinite or phosphonite the trihydrides [ReH3L4] were obtained. Treatment of [ReCl3L3] with NaBH4 gave instead pentahydride complexes [ReH5L3]. All the multihydrides were characterised as ‘classical’ species by variable-temperature NMR spectroscopy (1H and 31P) and T1 measurements. Protonation of [Re2H8L4] and [ReH3L4] with HBF4·Et2O gave the classical hydride cations [Re2H9L4]+ and [ReH4L4]+, respectively, while similar treatment of [ReH5L3] gave a species formulated as containing an η2-H2 ligand, [ReH4(η2-H2)L3]+ on the basis of T1(min) evidence.

2-Oxacyclopentylidene, 2-Oxacyclohexylidene, and 2-Oxacycloheptylidene Rhenium Complexes by Reaction of ω-Alkynols with the [{MeC(CH2PPh2)3}Re(CO)2]+ Auxiliary

Various β-, γ-, and δ-alkynols have been reacted with the 16e− fragment [(triphos)Re(CO)2]+ generated in situ by H2 elimination from [(triphos)Re(CO)2(η2-H2)]BF4 [triphos = MeC(CH2PPh2)3]. Irrespective of the length of the alkyl chain between the C≡C and OH functional groups in the ω-alkynol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)Re(CO)2{=CCH2CH2CH2O}]BF4 and [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)2{=CCH2CH2CH2CH2O}]BF4 and[(triphos)Re(CO)2{=CCH2CH2CH2CH(Me)O}]BF4, and the 2-oxacycloheptylidene complex [(triphos)Re(CO)2{=CCH2CH2- CH2CH2CH2O}]BF4. The latter compound contains a unprecedented seven-membered oxacarbene ring. The rhenium-assisted δ-alkynol to 2-oxacyloheptylidene rearrangement proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO)2{C=C(H)CH2CH2CH2CH2OH}]BF4, which has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single crystal of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4. The structure of this complex consists of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]+ cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly distorted octahedral environment.

Synthesis, Characterization, and Interconversion of the Rhenium Polyhydrides [ReH3(η4-NP3)] and [ReH4(η4-NP3)]+ {NP3 = tris[2-(diphenylphosphanyl)ethyl]amine}

The rhenium(III) dichloride complex [ReCl2(η4-NP3)]Cl (1) was prepared from [ReCl3(CH3CN)(PPh3)2] by treatment with the tripodal tetradentate ligand N(CH2CH2PPh2)3 (NP3) in ethanol. The reaction of 1 with LiAlH4 in THF gave the rhenium(III) trihydride [ReH3(η4-NP3)] (2), which was converted into the rhenium(V) tetrahydride [ReH4(η4-NP3)]BPh4 (3) by protonation in CH2Cl2 with HBF4·OMe2, followed by a metathetical reaction with NaBPh4. The classical polyhydride nature of 2 and 3, as well as the overall molecular structures in solution, were determined by NMR spectroscopy, 1H NMR relaxation, and IR spectroscopy. The polyhydride complexes 2 and 3 are stereochemically nonrigid in solution, and the thermodynamic parameters associated with the fluxional processes were determined by variable-temperature NMR studies. A single-crystal X-ray analysis of 3 has shown the complex cation [ReH4(η4-NP3)]+ to be eight-coordinated by the four donor atoms of NP3 and by four terminal hydride ligands in a distorted dodecahedral geometry. An in situ IR study in CH2Cl2 has shown that the protonation of 3 occurs regioselectively at the metal center with no formation of a dihydrogen complex. Kinetic hydrogen bond products of the formula [(η4-NP3)H3Re···HOR] (ROH = C2H5OH, CFH2CH2OH, CF3CH2OH) were intercepted by IR spectroscopy at low temperature. The thermodynamic parameters associated with the formation of the hydrogen bond adducts were determined by either IR spectroscopy applying the Iogansen equation or van’t Hoff plots of the formation constant vs. temperature.

Rhenium(III) and rhenium(V) complexes stabilized by the potentially tetradentate ligand tris(2-diphenylphosphinoethyl)amine

The reaction of the rhenium(V) nitrido complex [Re(N)Cl2(PPh3)2] with the tripodal ligand N(CH2CH2PPh2)3 (NP3 )i n THF gave [Re(N)Cl2( 2 -P,P-NP3)] (1) in which NP3 acts as a tridentate ligand using the nitrogen and two phosphorus donors for coordination. Refluxing 1 in a polar solvent such as ethanol produced [( 4 -NP3)Re(N)Cl]Cl (2) in which NP3 acts as a tetradentate ligand. Treatment of complex [Re(O)Cl3(AsPh3)2] containing the [ReO] 3 + core with NP3 in THF yielded [ReCl3{ 3 -N,P,P(N{CH2CH2Ph2}2{CH2CH2P(O)Ph2})}] (3). Complexes 1 and 3 have been characterized by single-crystal X-ray analyses.

Organometallic radiopharmaceuticals: rhenium(I) carbonyl complexes of natural bile acids and derivatives

Abstract The precursor [Re(CO)3(PPh3)2Cl] reacts with natural bile acids to give new carboxylato–carbonyl(phosphine) rhenium(I) complexes [Re(CO)2(PPh3)2(L)] (HL=natural bile acids). Coupling reactions between the carboxylic group of bile acids with the NH2 moiety of 2-aminothiazole, 2-(2-aminoethyl)pyridine and hydrazine form derivatives which coordinate the metal ion through the deprotonated amidic group. For a comparison, the carboxylato–rhenium(I) complex [NEt4][Re(CO)3Cl(L1)] (HL1=3α,7α,12α-trihydroxy-5β-cholic acid) was synthesized starting from the [Re(CO)3Cl3]2− precursor. The complex [Tc(CO)3(PPh3)2Cl] reacts with HL1 to form the corresponding carboxylato–carbonyl compound [Tc(CO)2(PPh3)2(L1)]. No difference in reactivity is observed with respect to the reactions carried out with the Re(I) starting materials. The complexes were characterized by elemental analyses, IR and NMR spectra, and a few also by mass spectrometry. An octahedral geometry may be assigned to these complexes. The two phosphine ligands are located in the axial position, and the two cis-CO groups having in trans the chelating ligand define the equatorial plane.