Scorpionate Ligand Research Articles

ChemInform Abstract: Dynamic Processes in Palladium and Platinum Complexes Coordinated on Scorpionate and Pyrazolylazine Type Ligands

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Yttrium and Neodymium Di- and Monohalide Complexes Based on Scorpionate (Poly(pyrazolyl)borate) Ligands

The syntheses of a series of well-characterized complexes of the type TpRYX2(solvent)n (1 and 2, R = H, X = Br, Cl, solvent = THF, n = 2; 4, R = Me, X = Cl, solvent = THF, n = 1; 5, R = Me, X = Cl, solvent = 3,5-dimethylpyrazole, n = 1; 7, R = Ph, X = Cl, solvent = THF, n = 1) and the novel solvent-free bis(poly(pyrazolylborate) complexes [(TpR)(BpR‘)YX] (8, R = R‘ =Me, X = Cl; 9, R = H, R‘ = Ph, X = Br) are presented. The data demonstrate that the steric, dynamic, and coordination behavior of these complexes are heavily influenced by the choice of scorpionate ligand substituents, showing the versatility of this ligand system for catalyst design. The coordinated THF solvent molecules of complexes 1, 2, and 4 are seen to undergo a dynamic solvation/desolvation equilibrium in solution that is fast on the NMR time scale. The position of this equilibrium is solvent-dependent and can be evaluated in complex 4 by observation of the line broadening of the 3-methyl resonance in the 1H NMR spectra taken in differe...

A new type of monoanionic “scorpionate” ligand. Synthesis, spectroscopic characterisation and dynamic behaviour of some niobium(III) complexes

The syntheses of novel scorpionate ligands in the form of the lithium derivative [{Li(H2O)(bdmpza)}4] 1 [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] or as the alcohol derivative 2,2-bis(3,5-dimethylpyrazol-1-yl)ethanol 2 (Hbdmpze) have been studied. These compounds are excellent precursors for the introduction of these scorpionate ligands into transition metal complexes. The complex [{NbCl3(dme)}n] (dme = 1,2-dimethoxyethane) reacted with 1 and 2, the latter with prior addition of BunLi, to give the binuclear complexes [{NbCl2(bdmpzx)}2] (x = a, 3; x = e, 4) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide]. Complex 3 reacted with 1 to give the complex [{NbCl(bdmpza)2}2] 5. In the same way the reaction of the mononuclear species [NbCl3(dme)(RCCR′)] with 1 and 2, the latter with prior addition of BunLi, gave the appropriate [NbCl2(bdmpzx)(RCCR′)] complexes [x = a, R = R′ = Me, 6; Et, 7; Ph, 8; or SiMe3, 9; R = Ph, R′ = Me, 10; R = Ph, R′ = Et, 11; R = Ph, R′ = SiMe3, 12; x = e, R = R′ = Me, 13; Et, 14; or Ph, 15; R = Ph, R′ = Me, 16; R = Ph, R′ = Et, 17; R = Ph, R′ = SiMe3, 18]. The structures of these complexes have been determined by spectroscopic methods. Variable-temperature NMR studies were carried out in order to study their dynamic behaviour in solution. The barriers to alkyne rotation have also been calculated. Reaction of 10 with LiCp′ (Cp′ = C5H4SiMe3) gave the mixed Cp–bdmpza complex [NbCp′Cl(bdmpza)] 19.

N,O-Polydentate Scorpionate Ligands.

New bis- and trispyrazolylborate (scorpionate) ligands derived from 3-(2,4-dimethoxyphenyl)pyrazole have been synthesized. They can function as N,O-polydentate donors, as was demonstrated in the structure of the octahedral complex Ni[Bp(2,4(OMe)2Ph)]2. The structure of Tl[Tp(2,4(OMe)2Ph)] has also been determined.

Influences of Ligand Environment on the Spectroscopic Properties and Disproportionation Reactivity of Copper−Nitrosyl Complexes

In studies of the chemistry of new copper−nitrosyl complexes supported by tris(3-(trifluoromethyl)-5-methylpyrazol-1-yl)hydroborate (TpCF3,CH3) and tris(3-mesitylpyrazol-1-yl)hydroborate (TpMs,H), significant effects of the scorpionate ligand substituents on the properties of the {CuNO}11 unit were found that have implications for environmental influences on similar species in biological and catalytic systems. The copper(I) complexes TpMs,HCu(THF) and TpCF3,CH3Cu(CH3CN) were structurally characterized by X-ray crystallography, and their respective CO and NO adducts were studied by FTIR, EPR, NMR, and/or UV−vis spectroscopies in solution. Both nitrosyl complexes disproportionate in the presence of excess NO to N2O and TpR,R‘Cu(NO2); an X-ray structure of the latter product supported by TpCF3,CH3 was determined. Unlike previously studied paramagnetic [CuNO]11 compounds that exhibit EPR signals with g < 2.0 and large ANO values at temperatures below ∼40 K (Ruggiero, C. E.; Carrier, S. M.; Antholine, W. E.; Whittaker, J. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 1993, 115, 11285−11298), TpMs,HCu(NO) is EPR silent at 4.2 K and exhibits an NMR spectrum (238 K, toluene-d8) with sharp signals. Peak assignments for the NMR spectrum were deduced from integrated intensities, temperature-dependent isotropic shifts, and the nuclear relaxation rates. The unique NMR spectral behavior for the TpMs,H complex, which only differs from those of analogues with simple phenyl substituents by virtue of the shape of the substrate binding pocket enforced by the mesityl methyl groups, suggests that caution should be exercised in characterizing such adducts in proteins and heterogeneous systems; subtle environmental effects may determine the applicability of EPR versus NMR methods. The electron-withdrawing effects of the trifluoromethyl substituents in TpCF3,CH3Cu(NO) perturb ν(NO) and the Cu(I) → NO MLCT energy in the respective FTIR and UV−vis spectra and induce a significant slowing of its disproportionation rate. These results, in conjunction with those obtained from kinetic and spectroscopic studies on the TpMs,H system, support a mechanism for the disproportionation involving generation of the CuNO adduct from NO and the Cu(I) precursor in a preequilibrium step, followed by electrophilic attack of a second NO molecule on the adduct that is rate-controlling.

Coordination Chemistry of Homoscorpionate Ligands with 3-Cyclopropyl Substituents

In a quest for precisely sterically tuned ligand systems, the new scorpionate ligands hydrotris(3-cyclopropylpyrazol-1-yl)borate, TpCpr, and tetrakis(3-cyclopropylpyrazol-1-yl)borate, pz*TpCpr, have been synthesized. They readily form octahedral homoleptic and heteroleptic complexes with first-row transition metal compounds, but their [M(TpCpr)(X)] complexes are unstable with respect to the octahedral ones. The complex [Mo(TpCpr)(CO)2(η3-CH2CMeCH2)] was also prepared. Structures of the paramagnetic [Co(TpCpr)2], [Co(pz*TpCpr)2], and [Co(TpCpr)(TpPh)] complexes have been determined by 1H NMR and those of [Fe(TpCpr)2] and [Fe(pz*TpCpr)2], as well as that of [Co(TpCpr)(TpPh)], by X-ray crystallography, indicating facile accommodation of six cyclopropyl groups in the equatorial belt of octahedral complexes. In its coordination behavior, TpCpr is quite different from TpiPr and resembles TpMe.

Ferrocene-Based Tris(1-pyrazolyl)borates: A New Approach to Heterooligometallic Complexes and Organometallic Polymers Containing Transition Metal Atoms in the Backbone.

Starting from mono- and bifunctional ferrocene-based tris(1-pyrazolyl)borates, a novel route to oligonuclear complexes is presented, which incorporates transition metal centers differing substantially in their chemical nature. Both binuclear organometallics FcB(pz)(3)ML(n)() (Fc: ferrocenyl. pz: 1-pyrazolyl. ML(n)(): Tl, 1-Tl; Mo(CO)(3)Li, 1-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 1-Mo; ZrCl(3), 1-Zr) and trinuclear complexes 1,1'-fc[B(pz)(3)ML(n)()](2) (fc: ferrocenylene. ML(n)(): Tl, 2-Tl; Mo(CO)(3)Li, 2-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 2-Mo) have been prepared. The trinuclear compound [FcB(4-SiMe(3)pz)(3)](2)Fe, 1-FeSi, has been investigated as a model system for organometallic coordination polymers, consisting of the bifunctional linker 1,1'-fc[B(pz)(3)](2)(2)(-) and transition metal ions M(n)()(+). X-ray crystallography shows 1-Tl to establish a polymeric structure in the solid state, while 1-Mo features the usual tridentate coordination mode of the scorpionate ligand (C(25)H(25)BFeMoN(6)O(2); a = 8.756(1) Å, b = 12.154(1) Å, c = 12.927(1) Å, alpha = 105.26(1) degrees, beta = 102.29(1) degrees, gamma = 105.09(1) degrees; triclinic space group P&onemacr;; Z = 2). With the exception of 1,2-Tl, the anodic oxidation of the ferrocene moiety is generally reversible; cyclic voltammetry measurements indicate the two Mo centers in 2-Mo and the two Fc moieties in 1-FeSi to be noncommunicating.