Hydroborato Ligand Research Articles

Electronic structure of tris(pyrazolyl)hydroborato [Tp] gallium complexes: density functional studies of monovalent Ga[Tp], terminal chalcogen complexes, Ga[Tp]E (E = O, S, Se or Te) and a GaI3 adduct, Ga2[Tp]I3

Density functional theory calculations have been made on gallium complexes supported by the tris(pyrazolyl)hydroborato ligand [Tp], Ga[Tp] I, Ga[Tp]E II (E = O a, S b, Se c or Te d) and Ga2[Tp]I3 III aimed at modelling the bonding in the recently reported tris(3,5-di-tert-butylpyrazolylhydroborato ([TpBut2]) gallium complexes, Ga[TpBut2] 1, the terminal chalcogen complexes Ga[TpBut2]E 2 (E = S b, Se c or Te d), and the adduct Ga2[TpBut2]I3 3. The calculated and observed structures are in good agreement. The gallium “lone pair” in Ga[Tp] has Ga–N antibonding character. The decrease in Ga–N bond lengths between Ga[Tp] and its adducts is associated with relief of this antibonding character. The bonding in Ga[Tp]E (E = O, S, Se or Te) is found to be almost entirely semipolar [[Tp]Ga+–E–] irrespective of the nature of the chalcogen element although the polarisation of charge decreases on descending the group. The GaI3 adduct is also best described by the resonance structure [Tp]Ga+–Ga–I3.

Asymmetric bis(pyrazolyl)hydroborato ligands via direct synthesis: structural characterization of thallium and zinc complexes †

Asymmetrically substituted bis(pyrazolyl)hydroborato ligands, in which the two pyrazolyl groups possess different substituents, have been synthesized by the direct reaction of a ca. 1∶1 molar mixture of the respective pyrazoles with LiBH4.

Bis- and Tris(pyrazolyl)hydroborato Ligands with Bulky Triptycyl Substituents: The Synthesis and Structural Characterization of Tl[Bp(Trip)] and Tl[Tp(Trip)

Bis- and tris(pyrazolyl)hydroborato complexes with bulky triptycyl substituents (Trip) in the 3-positions, Tl[BpTrip] and Tl[TpTrip], have been synthesized and structurally characterized by X-ray d...

Terminal Chalcogenido Complexes of Gallium Supported by Tris(3,5-di-tert-butylpyrazolyl)hydroborato Ligation: [TpBut2]GaE (E = Se, Te)

Terminal selenido and tellurido complexes of gallium supported by the tris(3,5-di-tert-butylpyrazolyl)hydroborato ligand, [TpBut2]GaE (E = Se, Te), have been prepared by oxidative addition of the elemental chalcogens to the three-coordinate gallium(I) complex [TpBut2]Ga. The positions of the equilibria involving chalcogenido transfer between [TpBut2]M (M = Ga, In) and Et3PSe demonstrate that the strengths of the X≈Se interactions decrease in the sequence [TpBut2]GaSe > Et3PSe > [TpBut2]InSe.

Formation of Hydrido–η3‐Allyl Complexes of IrIII by Sequential Olefinic CH Bond Activation and CC Coupling of Alkenyl and Olefin Ligands

AbstractThe bis(ethene) complex [Tp*Ir‐(C2H4)2] (1*) (Tp* = tris(3,5‐dimethyl‐1‐pyrazol‐1‐yl)hydroborato) undergoes thermal rearrangement to the hydrido–allyl complex [Tp*IrH(π3‐C3H4Me)] (6*), through the intermediacy of the hydrido–vinyl complex [Tp*IrH(C2H3)(C2H4)] (2*). The overall conversion of 1* into 6* corresponds formally to the dimerisation of ethene by an unprecedented pathway that involves sequential C–H bond activation of a coordinated olefin molecule and C–C bond formation by coupling of the resulting vinyl and ethene moieties. Similar transformations have been observed for monosubstituted olefins like propene and 1‐butene, while the internal alkene cis−2‐butene experiences allylic activation of an sp3 C–H bond, which provides an alternative route to 6*. The extension of these investigations to the analogous complexes of the unsubstituted tris(pyrazolyl)hydroborato ligand Tp is also reported. Mechanistic studies on the formation of the C–C bond by coupling of the vinyl and the olefin ligands suggest the participation of a vinylidene complex (formed by α‐H abstraction from the vinyl group), which then rearranges to an allene species. Evidence for the involvement of these and other key reaction intermediates is provided.

Elaboration of the bis(pyrazolyl)hydroborato ligand [Bp Bu t,Pr i] into the NNO donor ligand, [(MeO)Bp Bu t,Pr i]: Structural characterization of a complex in which the [(MeO)Bp Bu t,Pr i] ligand models the binding of zinc to the peptide backbone in thermolysin

The bis(pyrazolyl)hydroborato ligand in (Bp Bu t ,Pr i)ZnMe is converted to the NNO donor ligand in [ η 3-(MeO)Bp Bu t , Pr i ]ZnMe by insertion of [CH 2O] into one of the BH bonds; structural characterization by X-ray diffraction confirms that the ligand binds to the zinc centre a in manner analogous to the binding of zinc to the peptide backbone in thermolysin.

Oxidative-Addition Reactions of a Monomeric Indium(I) Complex Supported byTris(3,5-di-t-butylpyrazolyl)-hydroborato Ligation, [TpBut2]In: The Syntheses and Structures of [TpBut2]InI2and [TpBut2]In(η2-S4)

The monomeric subvalent indium(I) complex supported by ligation of the tris(3,5-di-t-butylpyrazolyl)hydroborato ligand, [TpBu t 2 ]In, undergoes oxidative-addition reactions with elemental I2 and S8 to give the indium (III) complexes [TpBu t 2 ]InI2 and [TpBu t 2 ]In(η2-S4), respectively. [TpBu t 2 ]InI2 is monoclinic, P21/ n (No. 14), with a = 26.698(10) A, b = 10.801(3) A, c = 29.192(6) A, β = 92.07(3)°, V = 8412(4) A3 and Z = 8. [TpBu t 2 ]In(η2-S4) is monoclinic, C2/c (No. 15) with a = 38.150(8) A, b = 10.585(2) A, c = 23.984(3) A, β = 109.19(2)°, v = 9165(5) A3 and Z = 8.

Synthesis and Structure of a Magnesium Hydroxide Complex Supported by Tris(pyrazolyl)hydroborato Ligation, {[Tp(Ar,Me)]Mg(&mgr;-OH)}(2) (Ar = p-Bu(t)C(6)H(4)).

A well-defined magnesium hydroxide complex has been synthesized by using a tris(pyrazolyl)hydroborato ligand with p-tert-butylphenyl substituents. Specifically, the dinuclear complex {[TpAr,Me]Mg(μ-OH)}2 (Ar = p-ButC6H4) is prepared by the reaction of the magnesium alkyl derivative [TpAr,Me]MgMe with H2O.

The Synthesis and Structural Characterization of the Sterically Demanding Tris (3,5-di-t-butylpyrazolyl) hydroborato Ligand, [TpBut2]: A Highly Twisted, Propeller-Like, Ligand System

The synthesis of the new sterically demanding tris (3,5-di-t-butylpyrazolyl) hydroborato ligand, [TpBu2 t ], in which both the 3- and 5-positions of the pyrazolyl group are occupied by bulky t-butyl substituents is described. The structural character

The tris[3-(9-anthryl)pyrazol-1-yl]hydroborato ligand, [Tp Ant]: Compositional disorder between a vacancy and a chain of three atoms

A new tris(pyrazolyl)hydroborato ligand with anthryl susbtituents in the 3-position, tris[3-(9-anthryl)pyrazol-1-yl]hydroborate, [Tp Ant], has been synthesized by the reaction of KBH 4 with 3-(9-anthryl)pyrazole and characterized as the thallium derivative, Tl[Tp Ant]. The thallium reagent was used to prepare the cobalt and molybdenum derivatives, [Tp Ant]CoNCS and [Tp Ant]Mo(CO) 2( η 3-CH 2C(Me)CH 2). The molecular structure of [Tp Ant]CoNCS, contaminated with ca6% Tl[Tp Ant], has been determined by X-ray diffraction, thereby providing an example of compositional disorder between a vacancy and a chain of three atoms.

The synthesis of [HB]3,5-(Bu tph) 2pz] 3] − (Bu tph = p-C 6H 4Bu t), a new tris(pyrazolyl)hydroborato ligand: the crystal and molecular structure of Tl{η 3-HB[3,5-(Bu tph) 2pz] 3}

The synthesis of a new sterically demanding tris(pyrazolyl)hydroborato ligand, [HB[3,5-(Bu tph) 2pz] 3] − (Bu tph = para-C 6H 4Bu t), is reported. The potassium derivative is prepared by the direct reaction of KBH 4 with 3,5-bis( para-tert-butylphenyl)pyrazole. Metathesis with TlNO 3 converts the potassium derivative to the thallium complex Tl{η 3-HB[3,5-(Bu tph) 2pz] 3}. The crystal and molecular structures of the pyrazole derivative [3,5-(Bu tph) 2pz] 2ZnI 2 and the thallium derivative Tl{η 3-HB[3,5-(Bu tph) 2pz] 3} have been determined.

Structural and spectroscopic studies on four-, five-, and six-coordinate complexes of zinc, copper, nickel, and cobalt: Structural models for the bicarbonate intermediate of the carbonic anhydrase catalytic cycle

The molecular structures and electronic spectra of a series of four-, five-, and six-coordinate complexes of cobalt, nickel, copper, and zinc, stabilized by tris(pyrazolyl)hydroborato ligands, have been determined. The structural variations that are observed for the series of nitrate and carbonate complexes reveal that the preference for bidentate coordination of these ligands increases across the series Zn < Co ⪡ Cu and Ni.

The synthesis and electrochemistry of some high-oxidation-state rhenium complexes containing the tris(3,5-dimethylpyrazolyl) hydroborato ligand and a heterobimetallic complex containing both rhenium and molybdenum centres

[ReL *O 3] ( 1) [L * = HB(3,5-Me 2C 3N 2 H) 3] is readily prepared by reaction of Re 2O 7 with KL * in THF. Complex 1 is reduced by triphenylphosphine in the presence of excess Me 3SiCl in THF at room temperature to give [ReL *O(OH)Cl] ( 2). This reaction yields an inseparable mixture of 2 and [ReL *OCl 2] ( 3) when carried out under reflux. Reaction of 2 with an excess of thiophenol, 2-methoxythiophenol, 4-nitrothiophenol, 4-hydroxythiophenol or 4-aminothiophenol in THF in the presence of triethylamine affords the thiophenolato derivatives [ReL *O(OH)SAr)] [Ar = C 6H 5 ( 4), C 6H 4-2-OCH 3 ( 5), C 6H 4-4-NO 2 ( 6), C 6H 4-4-OH ( 7) or C 6H 4-4-NH 2 ( 8), respectively]. Reaction of a mixture of 2 and 3 with an excess of thiophenol in toluene in the presence of triethylamine yields both 4 and [ReL *O(SC 6H 5) 2] ( 9). A heterobimetallic complex, [ReL *O(OH){SC 6H 4-4-O}Mo(NO)L *Cl] ( 10), is formed when 7 is reacted with [Mo(NO)L *Cl 2] in toluene in the presence of triethylamine. The new rhenium(V) complexes 2 and 4–10 undergo both reduction and oxidation processes which are in many cases reversible or quasi-reversible.

A mononuclear zinc hydroxide complex stabilized by a highly substituted tris(pyrazolyl)hydroborato ligand: analogies with the enzyme carbonic anhydrase

A mononuclear zinc hydroxide complex stabilized by a highly substituted tris(pyrazolyl)hydroborato ligand: analogies with the enzyme carbonic anhydrase

Tris(pyrazolyl)hydroborato]magnesium alkyl derivatives: synthetic and structural studies

A series of solvent-free, monomeric, (tris pyrazolyl)hydroborato)magnesium alkyl derivatives, {η 3 -HB-(3-Bu t pz) 3 }MgR and {η 3 -HB(3,5-Me 2 pz) 3 }MgR (3-Bu t pz=3-C 3 N 2 Bu t H 2 ; 3,5-Me 2 pz=3,5-C 3 N 2 Me 2 H; R=CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 , C(CH 3 ) 3 , CH 2 (CH 2 ) 2 CH 3 , CH 2 Si(CH 3 ) 3 , CH=CH 2 , C 6 H 5 ), have been prepared by the reaction of the appropriate dialkylmagnesium compound with either the potassium or thallium derivatives of the respective tris(pyrazolyl)hydroborato ligand. The molecular structures of the complexes have been determined by X-ray diffraction, which shows that in each case the complexes are monomeric with 4-coordinate magnesium centers and η 3 -coordinate tris(pyrazolyl)hydroborato ligands

Ligand redistribution reactions of tris(3,5-dimethylpyrazolyl)hydroboratomagnesium alkyl derivatives: crystal structure of {η 3-HB(3,5-Me 2pz) 3} 2Mg

Tris(pyrazolyl)hydroboratomagnesium alkyl derivatives {η 3-HB(3,5-Me 2pz) 3}-MgR (3,5-Me 2pz = 3,5-C 3N 2Me 2H; R = CH 3, CH 2CH 3, (CH 2) 3CH 3, CH(CH 3) 2, C(CH 3) 3, CHCH 2, C 6H 5) undergo ligand redistribution reactions, analogous to the Schlenk equilibrium, to give the bis complex {η 3-HB(3,5-Me 2pz) 3} 2Mg. In contrast, magnesium alkyl derivatives of the more sterically demanding tris(3-t-butylpyrazolyl)hydroborato ligand, {η 3-HB(3-Bu tpz) 3}MgR (3-Bu tpz = 3-C 3N 2Bu tH 2), are stable with respect to the formation of {η 3-HB(3-Bu tpz) 3} 2Mg.

Poly(pyrazolyl)hydroborato and poly(pyrazolyl)methane aluminium alkyl derivatives

Bis- and tris(pyrazolyl)hydroborato aluminium methyl derivatives, {η 3-HB(3,5- Me 2pyz) 3}Al(CH 3) 2, {η 2 -HB(3-Bu tpyz) 3}Al(CH 3) 2 and {η 2-H 2B(3-Bu tpyz) 2}Al(CH 3) 2 have been prepared by metathesis of Al(CH 3) 3 with either K{HB(3,5-Me 2pyz) 3}, Tl{HB(3- Bu tpyz) 3} or K{H 2B(3-Bu tpyz) 2}, respectively. In contrast to the formation of these 1 : 1 complexes, the isostructural but neutral ligand HC(pyz) 3 readily coordinates three equivalents of (CH 3) 3Al giving {HC(pyz) 3}[Al(CH 3) 3] 3. 1H NMR studies provide evidence for the formation of the mono- and bis-complexes {HC(pyz) 3}[Al(CH 3) 3] and {HC(pyz) 3} [Al(CH 3) 3] 2 as products of the reaction of HC(pyz) 3 with less than three equivalents of Al(CH 3) 3. The aluminium-carbon bonds of {η 3 -HB(3,5-Me 2pyz) 3}Al(CH 3) 2 are readily cleaved by H 2O to give {η 3-HB(3,5-Me 2pyz) 3}Al(OH) 2 and CH 4. However, the reaction of {η 3-HB(3,5-Me 2pyz) 3}Al(CH 3) 2 with D 2O gives CH 4 in addition to CH 3D and thus demonstrates that a secondary process involving coupling of the aluminium-methyl ligand with one of the hydrogen atoms of the pyrazolyl methyl group must be competitive with the direct reaction of the aluminium-carbon bond with D 2O. The complex {η 2-H 2B(3- Bu tpyz) 2}Al(CH 3) 2 undergoes a unimolecular rearrangement of the bis(3-t-butylpyrazolyl)hydroborato ligand to give the more stable isomer, {η 2 -H 2B(3-Bu tpyz)(5-Bu tpyz)} Al(CH 3) 2. The kinetics of this rearrangement are first-order with the activation parameters Δ h ‡ = 34.5(8) kcal mol −1 and Δ s ‡ = 6(2) e.u. and the proposed mechanism consists of steps involving a 1,2-shift of the t-butylpyrazolyl group.