Accessing Spin-Crossover Behaviour In Iron(II) Complexes Of N-Confused Scorpionate Ligands

The first examples of a class of N-confused tris(pyrazolyl)methane ‘scorpionate’ ligands have been prepared. The magnetic properties of their iron(II) tetrafluoroborate complexes are dictated by changing one substituent per ligand rather than three as is typical for normal scorpionate ligands

Different coordination modes of an aryl-substituted hydrotris(pyrazolyl) borate ligand in rhodium and iridium complexes

Complexes TptolRh(C2H4)2 (1a) and TptolRh(CH2C(Me)C(Me)CH2) (1b) have been prepared by reaction of KTptol with the appropriate [RhCl(olefin)2]2 dimer (Tptol means hydrotris(3-p-tolylpyrazol-1-yl)borate). The two complexes show a dynamic behaviour that involves exchange between κ2 and κ3 coordination modes of the Tptol ligand. The iridium analogue, TptolIr(CH2C(Me)CHCH2) (2) has also been synthesized, and has been converted into the Ir(III) dinitrogen complex [(κ4-N,N',N'',C-Tptol)Ir(Ph)(N2) (3) by irradiation with UV light under a dinitrogen atmosphere. Compound 3 constitutes a rare example of Ir(III)-N2 complex structurally characterized by X-ray crystallography. Its N2 ligand can be easily substituted by acetonitrile or ethylene upon heating and denticity changes in the Tptol ligand, from κ4-N,N',N'',C (monometallated Tptol, from now on represented as Tptol′) to κ5-N,N′,N″,C,C″ (dimetallated Tp tol ligand, represented as Tptol″) have been observed. When complex 3 is heated in the presence of acetylene, dimerization of the alkyne takes place to yield the enyne complex [(κ5-N,N′,N′′,C,C′-Tp tol)Ir(CH2CHCCH), 7̧ in which the unsaturated organic moiety is bonded to iridium through the carbon-carbon double bond.Ministerio de Educación y Ciencia CTQ2007-62814Consolider-Ingenio 2010 CSD2007-00006Junta de Andalucía FQM-3151, FQM-672CONACYT 22934

Seven coordinate molybdenum and tungsten complexes containing Tpm and Tpm derivatives and the impact of ligand substitution on NMR chemical shifts

A series of known and new seven coordinate molybdenum and tungsten complexes of tris(pyrazolyl)methane (Tpm) and substituted Tpm, [TpmM(CO)3X]+, have been synthesized. Depending on the identity of X, (bromo, iodo, hydrido) and the substitution of the Tpm ligand, substantial chemical shift differences are observed for the hydrogen on the central carbon of the Tpm ligand. Factors impacting the chemical shift of the hydrogen on the central carbon of the Tpm ligand, such as the electron donating ability of the Tpm ligand and the electronegativity of the additional ligand on the metal, will be discussed

Theoretical investigation of the scope of sequential ligand tuning using a bifunctional scorpionate tris(1,2,4-triazolyl)borate-based architecture

The donor properties of a series of tripodal mixed N-donor/carbene ligands derived through sequential alkylation of hydrotris(1,2,4-triazolyl)borate have been investigated by density functional theory (DFT) methods. The structures of complexes of the form [Mo(L)(CO)3]- were optimized (L = [HB(1,2,4-triazolyl)n(1,2,4-triazol-5-ylidene)3-n]- (n = 0 – 3), hydrotris(pyrazolyl)borate, hydrotris(3,5-dimethylpyrazolyl)borate and hydrotris(imidazol-2-ylidene)borate) and nuCO frequencies for these complexes and partial charges of their Mo(CO)3 fragments were determined. Results show that ligand donation is highly tunable when compared to similar experimentally known ligands with a shift in the symmetric nuCO stretching mode of -39 cm -1 on going from the tris(1,2,4-triazolyl)borate complexes to that of the triscarbene hydrotris(1,2,4-triazol-5-ylidene) and an increase in partial charge (distributed multipole analysis) of the Mo(CO)3 fragment from -0.23 to -0.48

Reaction Chemistry of Silver(I) Trifluoromethanesulfonate Complexes of Nitrogen-Confused \u3cem\u3eC\u3c/em\u3e-Scorpionates

Two new C-scorpionate ligands with a bis(3,5-dimethylpyrazol-1-yl)methyl group bound to the 3 position of either an N-tosyl (TsL*) or an N–H pyrazole (HL*) ring have been prepared. The silver(I) complexes of these new ligands and the two previously reported analogous ligands with unsubstituted bis(pyrazol-1-yl)methyl groups (TsL and HL) in both 1:1 and 2:1 ligand/metal ratios were investigated to explore the effects of ligand sterics on their physical and chemical properties. The structurally characterized derivatives of the type [Ag(L)2](OTf) are four-coordinate, where the confused pyrazolyl is not bound to the metal. On the other hand, three 1:1 complexes [Ag(L)](OTf) had all pyrazolyls bound, while the μ–κ1,κ1-TsL derivative had an unbound confused pyrazolyl. The molecularity of the latter four ranged from polymeric to dimeric to monomeric in the solid with increasing steric bulk of the ligand. The utility of these complexes in stoichiometric ligand-transfer reactions and in styrene aziridination was demonstrated. Thus, tricarbonylmanganese(I) complexes were prepared as kinetically inert models for comparative solution diffusion NMR studies. Also, [Fe(HL)2](OTf)2 was prepared for similar reasons and to compare the effects of anion on spin-crossover properties

The Characterization and Reactivity of Tris(4-methylpyrazolyl)methane and its Tungsten and Molybdenum Metal Complexes

The scorpionate ligand tris(pyrazolyl)borate (Tp) has contributed to the understanding of coordination and organometallic chemistry and has proven to be useful in the synthesis of metalloprotein models. Studies focusing on the similar ligand, tris(pyrazolyl)methane (Tpm), have recently been made possible with improved synthetic techniques. Characterization of the Tpm ligand and its metal derivatives, [TpmW(CO)3L]+ and [TpmMo(CO)3L]+, unveiled unexpected activity in the 1H NMR chemical shift of the methane hydrogen after the coordination of a seventh ligand. The more electronegative the seventh ligand was, the more downfield the chemical shift appeared. Various analogs of Tpm have since been synthesized that substitute methyl groups on different positions of the pyrazolyl rings and the effect of these substitutions on the methane hydrogen was examined. This work successfully synthesized an analog of Tpm(4-methyl) and its metal complexes of Tpm(4-methyl)W(CO)3 and Tpm(4-methyl)Mo(CO)3. The reactivity of Tpm(4-methyl)M(CO)3 (M = W or Mo) was observed and FTIR, 1H NMR, and 13C NMR were used for the characterization of [Tpm(4-methyl)M(CO)3L]+[X]- (L = H, I, or Br; X = counterion). The chemical shift of the methane hydrogen was further examined and determined to follow the same trend seen in the previously reported Tpm metal complexes

Synthesis and Characterization of a New Cyano-substituted Tris(pyrazolyl)borate and its Thallium(I) Complex

A new cyanoscorpionate - tris(4-cyano-3,5-diphenylpyrazolyl)borate (TpPh2,4CN) has been synthesized and characterized. The thallium complex of this ligand TlTpPh2,4CN has also been prepared and characterized by FT-IR, 1H NMR, and single-crystal X-ray-diffraction. The complex TlTpPh2,4CN crystalized in the monoclinic space group C2/c with unit cell a = 14.6697(10) Å, b = 13.9493(10) Å, c = 19.3347(12) Å, and b= 91.761(2)°. Structural comparison of TlTpPh2,4CN with analogous complexes demonstrated the effects of both steric and electron-withdrawing substituents on coordination geometry and the electronic properties of the metal ion. There were short contacts between the cyano groups and neighboring thallium ions that also indicated the ligand’s potential to form coordination polymers

Chemistry of the lanthanides with pyrazolylborate ligands

In the work presented in this thesis we have established the utility of the substituted tris-(pyrazolyl)borates as ancillary ligands for the lanthanides. Compounds of formula (TpME2)2LnOTf have been synthesized. For the larger lanthanides, the triflate group is coordinated to the metal, [(TpME2)2LnOTf] (Ln = La and Nd), whilst for the smaller elements ion pair complexes are formed, [(Tp ME2)2Ln]+[OTf]- (Ln = Y, Dy and Yb); the structures of the Nd and Yb complexes have been determined. For lanthanides of intermediate ionic radius (Ln = Sm), there are good indications that these two structural forms coexist in CDCI3. Attempts to derivatise these complexes were not successful. Reduction of (TpME2)2LnOTf (Ln = Sm, Eu and Yb) gave [(TpME2)2Ln]; 1 the related [(Tp ME2-4-Et)2Ln] complexes were also prepared. [(TpME2) 2Ln] (Ln = Eu and Yb) were characterised by X-ray crystallography and found to be isomorphous. Initial reactivity studies showed that [(Tp ME2)2Ln] and [(TpME2-4-Et)2Ln] were significantly less reactive than the decamethyllanthanocenes. They were found to react with TCNQ and TCNE and in the case of the Yb complexes, the products were simple charge transfer salts; the X-ray crystal structure of [(TpME2) 2Yb]+[TCNE]- was determined. The hydrolysis product [(TpME2)Sm{(pzMe2)2B(H)([μ-O)}]2.(THF)2 was also characterised crystallographically. Reaction of [(TpME2-4-Et)2Ln] with NO gave nitrito complexes and the structure of [(TpME2-4-Et)2Sm(η2-O2N)] was determined by X-ray crystallography. It was not possible to isolate stable half sandwich complexes of the divalent lanthanides with these 3-Me substituted tris-(pyrazolyl) borates. In contrast, the stable monomeric complexes [Tp3-t-Bu-5-MeSml(THF)2] .(Et2O)0.5 and [Tp3-t-Bu-5iMeYbl(THF)] were prepared and characterised crystallographically.3 These compounds could be desolvated, and pyridine and isonitrile adducts were prepared; the X-ray crystal structures of [Tp3-t-Bu-5-MeLnl(3,5-Me2py)2] and [Tp3-t-Bu-5-MeLnl(CNBut)] have been determined. [Tp3-t-Bu-5-MeYbBH4(THF)] was prepared by reaction of [Tp3-t-Bu-5-MeYbl(THF)] with NaBH4. This compound decomposes on heating to give at least two new products, the nature of which remains to be established

Picolyl−NHC Hydrotris(pyrazolyl)borate Ruthenium(II) Complexes: Synthesis, Characterization, and Reactivity with Small Molecules

Ruthenium(II) hydrotris(pyrazolyl)borate chloro complexes bearing picolyl-functionalized N-heterocyclic carbenes [TpRu- (κ2-C,N-picolyl-RI)Cl] (picolyl-MeI = 3-methyl-1-(2-picolyl)imidazol-2- ylidene) (1a), picolyl-iPrI = 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), picolyl-Me45DClI = 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol- 2-ylidene (1c), picolyl-PhI = 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1d), picolyl-MeBI = 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e)) have been synthesized and characterized. Furthermore, cationic carbonyl derivatives 2a−e have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands (picolyl-RI) via infrared spectroscopy. Also, the reactivity of the 16-electron species [TpRu(κ2-C,N-picolyl-RI)]+, in situ generated using NaBArF 4 (ArF = 3,5-bis(trifluoromethyl)phenyl) as a halide scavenger, toward N2, CH3CN, H2, CH2CH2, S8, and O2 was studied indicating a strong influence of the NHC wingtip and backbone substituents in the product distribution. The crystal structures of [TpRu(κ2- C,N-picolyl-iPrI)Cl] (1b), [TpRu(κ2-C,N-picolyl-MeI)CO][BArF 4] (2a), [TpRu(κ2-C,N-picolyl-PhI)CO][BArF 4] (2d), [{TpRu(κ2- C,N-picolyl-MeI}2(μ-N2)][BArF 4]2 (3′a), [{TpRu(κ2-C,N-picolyl-PhI)}2(μ-N2)][BArF 4]2 (3′d), [TpRu(κ2-C,N-picolyl-iPrI)(η2- CH2CH2)][BArF 4] (5b), and [{TpRu(κ2-C,N-picolyl-MeI)}2(μ-S2)][BArF 4]2 (6) are reported

Syntheses and Characterization of a New Cyano-Substituted Bis(pyrazolyl)borate and its Thallium (I) Complex

Scorpionates are versatile and flexible ligands with a wide range of applications including catalysis, C-H bond activation, formation of new class of materials, and mimicking enzymatic reactions. This is as a result of its steric and electronic properties, and due to the relative ease with which the 3, and 5-positions of the pyrazole ring can be functionalized. In this work, we report the synthesis of a new class of scorpionate ligands known as cyanoscorpionates which can crosslink various metal centers. Thus, bis (4-cyano-3,5-diphenylpyrazolyl)borate BpPh2,4CN was synthesized and fully characterized by 1H NMR and FT-IR. Coordination of bis (4-cyano-3,5-diphenylpyrazolyl)borate BpPh2,4CN to thallium (I) metal was performed and characterized and we are looking to elucidating its molecular structure by X-ray crystallography in future