Effect of the Alkali-Metal Cation on the Bonding Mode of 2,5-Dimethylpyrrole in Divalent Samarium and Ytterbium Complexes

The pyrrole ring η2-hapticity bridged binuclear tricarbonyl Mo(0) and W(0) complexes: catalysis of regioselective hydroamination reactions and DFT calculations

Following the report of the ferrocene structure, metal complexes containing the heteroatom-substituted cyclopentadienyl (Cp) analogue, that is the η⁵ pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in organometallics, the transition metal chemistry of the pyrrolyl ligand is still in the developing stage. In view of this, we carried out the reaction between the multidentate ligand 2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole (LH) and Mo(CO)₆ or [W(CO)₃(CH₃CN)₃] and isolated two new binuclear tricarbonyl Mo(0) and W(0) complexes, [Mo₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (1) and [W₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (2). Their X-ray structural analyses showed that the metal centers are bridged by the double bonds of the central pyrrole ring (μ-η²:η²), a rarely observed coordination mode. Interestingly, complex 1 is a catalyst precursor for the hydroamination reactions of phenylacetylene with a series of secondary amines at room temperature offering the regioselectively formed anti-Markovnikov product in excellent yields. In addition, DFT calculations were performed to understand the bonding nature of the pyrrole ring in 1 and 2 and to estimate the energy of six different conformations of LH.

Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes

Actinide complexes of a small-cavity, dipyrrolide macrocycle exhibit unusual bent metallocene-type binding, or bis(arene)-type binding, or both at once in a di-uranium adduct.

Dinitrogen Coordination and Cleavage Promoted by a Vanadium Complex of a σ,π,σ-Donor Ligand

The deprotonation of the tripyrrole MeTPH(2) [MeTPH(2) = 2,5-[(2-pyrrolyl)(C(6)H(5))2C](2)(MeNC(4)H(2))], containing one N-methylated pyrrolyl ring, was carried out with 2 equiv of KH. The corresponding dipotassium salt reacted with VCl(3)(THF)(3) to afford the complex [(MeTP)VCl(THF)].THF (1). While the two lateral pyrrolide rings are sigma-bonded, the central one is perpendicularly oriented in a sort of pi-fashion. However, the bond distances clearly indicated that only the quaternized N atom is forming a bonding contact. Subsequent reduction of 1 with Na yielded the corresponding divalent complex [(MeTP)V(THF)].(C(7)H(8))(0.5) (2) where the central N-methylated ring adopted a more regular pi-orientation. When treated with a strong Lewis acid (AlMe(3)), THF was extracted from the vanadium coordination sphere, forming the dinuclear dinitrogen complex [(MeTP)V(mu-N(2))](2).(C(7)H(8))(2.9) (3). Reduction of 3 with potassium graphite gave cleavage of dinitrogen, affording the mixed-valent nitride-bridged complex [(MeTP)V(mu-N)](2).(THF) (4).

F-block N-heterocyclic carbene complexes

N-Heterocyclic carbenes (NHCs) can bind as two-electron sigma-donor ligands to lanthanide and actinide metal cations. In this review we summarise how the incorporation of an anionic group (alkoxide or amido), to form heterobidentate NHC ligands, allows the synthesis of a range of f-block NHC adducts. The tethering group also allows the lability of the NHC group, and its subsequent reactivity, to be studied. We include a brief survey of the known, structurally characterised f-element-NHC bond distances, and a range of substrates that react to displace the metal-bound NHC group.

Divalent Molybdenum Complexes of the Dipyrrolide Ligand System. Isolation of a Mo2 Unit with a 45° Twist Angle

The preparation of divalent Mo complexes of dipyrrolide dianions was carried out by reacting Mo(2)(acetate)(4) with the dipotassium salts of Ph(2)C(2-C(4)H(3)NH)(2) and 2-[1,1-bis(1H-pyrrol-2-yl)ethyl]pyridine. The two reactions respectively afforded the diamagnetic [[Ph(2)C(C(4)H(3)N)(2)](2)Mo(2)(OAc)(2)[K(THF)(3)][K(THF)]].THF (1) and [[(2-C(5)H(4) N)(CH(3))C(2-C(4)H(3)N)(2)]Mo(OAc)[K(THF)]](2).THF (2). Both compounds retained two acetate units in the dimetallic structure. Conversely, the reaction of Me(8)Mo(2)Li(4)(THF)(4) with Et(2)C(2-C(4)H(3)NH)(2) afforded the paramagnetic dimer [[Et(2)C(C(4)H(3)N)(2)](4)Mo(2)Li(2)][Li(THF)(4)](2).0.5THF (3). The paramagnetism is most likely caused by the 45 degree rotation of the two Mo(dipyrrolide) units with respect to each other and which, in turn, is caused by the presence of two lithium cations in the molecular structure.

Dinuclear and Octanuclear Mn(II) Complexes with μ2-C, μ2-N(Pyrrolide), and μ-η1:η5-(Pyrrolide) Bridges: A Structural and Magnetic Study

Reaction of the dinuclear [(CH2SiMe3)(mu-CH2SiMe3)Mn(THF)]2 (1) with an equivalent amount of 1,1-dipyrrolylcyclohexane afforded two compounds depending on the solvent employed. Reaction carried out in THF afforded the dinuclear ([1,1-(mu-C4H3N)(C4H3N)C6H10]Mn(THF)2)2.2(THF) (2) while reaction in toluene yielded the octanuclear and cyclic cluster ([1,1-(mu,eta1:eta5-C4H3N)2C6H10]Mn)8.4(toluene) (3). The magnetism in all three cases is dominated by intramolecular antiferromagnetic exchange with strong coupling in 1 (J=-85 cm(-1)), and in 2 (J=-23.2 cm(-1)), whereas substantially weaker coupling through the sigma/pi-bonded dipyrrolide bridges (J=-3.3 cm(-1)) was observed within the cyclic and octameric 3.