Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Establishing the Coordination Chemistry of Antimony(V) Cations: Systematic Assessment of Ph4Sb(OTf) and Ph3Sb(OTf)2 as Lewis Acceptors

The coordination chemistry of the stiboranes Ph₄Sb(OTf) ( 1 a , OTf = OSO₂CF₃) and Ph₃Sb(OTf)₂ ( 3 ) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4‐methylpyridine‐N‐oxide (OPyrMe) and OPMe₃ enabled the characterization of [Ph₄Sb(OPyrMe)][OTf] ( 2 a ) and [Ph₄Sb(OPMe₃)][OTf] ( 2 b ), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph₃Sb(donor)₂][OTf]₂ [donor=OPMe₃ ( 6 a ), OPCy₃ ( 6 b , Cy=cyclohexyl), OPPh₃ ( 6 c ), OPyrMe ( 6 d )], [Ph₃Sb(dmap)₂(OTf)][OTf] ( 6 e , dmap=4‐(dimethylamino)pyridine) and [Ph₃Sb(donor)(OTf)][OTf] [donor=1,10‐phenanthroline ( 7 a ) or 2,2′‐bipy ( 7 b , bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid‐state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh₃ and products of phosphine oxidation.     

Cyclopolymerization of 1,5‐hexadiene catalyzed by various stereospecific metallocene compounds

Cyclopolymerization of 1,5‐hexadiene has been carried out at various temperatures in toluene by using three different stereospecific metallocene catalysts—isospecific rac‐(EBI)Zr(NMe₂)₂ [EBI: ethylenebis(1‐indenyl), Cat 1], syndiospecific Me₂C(Cp)(Flu)ZrMe₂ (Cp = 1‐cyclopentadienyl, Flu = 1‐fluorenyl, Cat 2), and aspecific CpZrMe₂ (Cp*: pentamethylcyclopentadienyl, Cat 3) compounds in the presence of Al(i‐Bu)₃ and [Ph₃C][B(C₆F₅)₄]—in order to study the effect of polymerization temperature and catalyst stereospecificity on the property and microstructure of poly(methylene‐1,3‐cyclopentane) (PMCP). The activities of catalysts decrease in the following order: Cat 1 > Cat 2 > Cat 3. PMCPs produced by Cat 1 are not completely soluble in toluene, but those by Cat 2 and Cat 3 are soluble in toluene. trans‐Diisotactic rich PMCPs are produced by Cat 1 and Cat 2, and cis‐atactic PMCP by Cat 3. The cis/trans ratio of PMCP by Cat 1 and Cat 2 is relatively insensitive to the polymerization temperature, but that by Cat 3 is highly sensitive to the polymerization temperature. Melting temperatures of PMCP produced increase with the cis to trans ratio of rings. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1520–1527, 2000     

Quinone complexes of aluminum: Synthesis and structures

Reactions of aluminum metal with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in various solvents gave aluminum tris-o-semiquinolate and catecholate. The metal catecholate underwent partial hydrolysis in the presence of water. The dimeric complex [(Cat)Al(OH)Bipy]₂ × 4C₂H₄Cl₂ (Cat is the 3,6-Q dianion and Bipy is 2,2-bipyridyne) with bridging OH groups was isolated and characterized by X-ray diffraction. A reaction of aluminum with o-quinone in the presence of molecular iodine yielded the dimeric catecholate iodide [(Cat)₂Al(Et₂O)₂]AlI₂. The structure of the latter was confirmed by X-ray diffraction. An aluminum catecholato-o-semiquinolate complex was obtained by an exchange reaction between [(Cat)₂Al(Et₂O)₂]AlI₂ and thallium o-semiquinolate.     

cis‐trans‐Isomerie bei (Me4Sb)2[Ph2Sb2I6]

cis‐trans‐Isomerism in (Me₄Sb)₂[Ph₂Sb₂I₆] Crystals of cis‐(Me₄Sb)₂[Ph₂Sb₂I₆] ( 1 a ) are formed by reaction of PhSbI₂ and Me₄SbI in ethanol/petroleum ether at –7 °C. In ethanol/acetone crystals of trans‐(Me₄Sb)₂[Ph₂Sb₂I₆] · acetone ( 1 b ) form. The X‐ray crystal structure analyses reveal that both isomers consist of tetrahedral cations and of dimeric anions with the geometry of two edge sharing tetragonal pyramids. The phenyl groups possess apical cis ( 1 a ) or trans ( 1 b ) positions relative to the I₂SbI₂SbI₂ plane. The acetone molecules in 1 b are non coordinating.     

Oxidative addition reaction of o-quinones to triphenylantimony: novel triphenylantimony catecholate complexes

New catecholate Sb(V) complexes triphenyl(3,6-di-tert-butylcatecholato)antimony(V) Ph₃Sb(3,6-DBCat) (1) and triphenyl(perchloroxanthrenecatecholato)antimony(V) Ph₃Sb(^OXCat_Cl) (2) were synthesized by the oxidative addition reaction of corresponding o-quinones (3,6-di-tert-butyl-o-benzoquinone and perchloroxanthrenequinone-2,3) with triphenylantimony. Catecholates 1 and 2 can alternatively be synthesized by reacting the appropriate thallium catecholate with triphenylantimony dichloride. The oxidative addition reaction of an equimolar ratio of 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone) and triphenylantimony yielded 4-(2-methyl-5-tert-butyl-cyclohexadien-1,5-dion-3,4-yl)-(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V) Ph₃Sb(Cat-Q) (3); in the case of a 1:2 molar ratio, complex 4,4′-di-[(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V)] Ph₃Sb(Cat-Cat)SbPh₃ (4) resulted. Complexes 1-4 were characterized by IR- and ¹H NMR spectroscopy. Molecular structures of 1, 2 and 4 were determined by X-ray crystallography to be a distorted tetragonal-pyramidal.     

Anion‐Controlled Switching of an X Ligand into a Z Ligand: Coordination Non‐innocence of a Stiboranyl Ligand

The tetravalent platinum stiboranyl complex [(o‐(Ph₂P)C₆H₄)₂(o‐C₆Cl₄O₂)Sb]PtCl₂Ph ( 2 ) has been synthesized by reaction of [(o‐(Ph₂P)C₆H₄)₂SbClPh]PtCl ( 1 ) with o‐chloranil. In the presence of fluoride anions, the stiboranyl moiety of 2 displays non‐innocent behavior and is readily converted into a fluorostiborane unit. This transformation, which is accompanied by elimination of a chloride ligand from the Pt center, results in the formation of [(o‐(Ph₂P)C₆H₄)₂(o‐C₆Cl₄O₂)SbF]PtClPh ( 3 ). Structural, spectroscopic, and computational studies show that the conversion of 2 into 3 is accompanied by a cleavage of the covalent Pt? Sb bond present in 2 and formation of a longer and weaker Pt→Sb interaction in 3 . These results show that this new Pt–Sb platform supports the fluoride‐induced metamorphosis of a stiboranyl X ligand into a stiborane Z ligand.     

Triaryl- and trialkylantimony(V) Bis(catecholates) based on 1,1′-spirobis[3,3-dimethylindanequinone-5,6]: Spectroscopic and electrochemical studies

A series of new binuclear bis(catecholate) antimony(V) complexes based on 1,1′-spirobis[3,3-dimethylindanequinone-5,6] with various substituents at the central antimony atoms, R₃Sb(Cat-Spiro-Cat)SbR₃ (I–IV) and R₃Sb(Cat^Br-Spiro-^BrCat)SbR₃ (V–VIII) (R = p-fluorophenyl, phenyl, p-tolyl, and ethyl), were synthesized. Spirobis(catecholates) I–III exhibit two one-electron oxidation waves on the cyclic voltammograms, whereas bromo-substituted spirobis(catecholates) V–VII undergo two-electron oxidation immediately at the first stage. The two-electron oxidation of the complexes results in the loss of one of the organoantimony fragments and the formation of mononuclear catecholate-quinone complexes (Q-Spiro-Cat)SbR₃ or (Q^Br-Spiro-^BrCat)SbR₃, respectively. An insignificant delocalization of the charge and spin between two redox centers is observed in the complexes. The nature of substituents at the antimony atom exerts an effect on the values of redox potentials of the complexes: more donating groups decrease the oxidation potentials of the catecholate fragments and more withdrawing groups increases these values.     

Synthesis and structures of triphenylantimony oximates

The reactions of triphenylantimony or trimethylantimony with tert-butyl hydroperoxide in the presence of acetone oxime, acetophenone oxime, cyclohexanone oxime, or benzaldehyde oxime afforded monomeric triorganoantimony oximates Ph₃Sb(ON=CMe₂)₂, Ph₃Sb(ON=CMePh)₂, Ph₃Sb[ON=C(CH₂)₅]₂, Ph₃Sb(ON=CHPh)₂, and Me₃Sb(ON=CMe₂)₂ in 87—96% yields. X-ray diffraction analysis demonstrated that Ph₃Sb(ON=CMe₂)₂ and Ph₃Sb(ON=CHPh)₂ have trigonal-bipyramidal structures. An analogous reaction with dimethylglyoxime gave rise to polymeric triphenylantimony dioximate in 96% yield. The reaction with butane-2,3-dione monoxime yielded chelate cyclic bis(triphenylantimony) oxides.     

Binuclear Triphenylantimony(V) Catecholate Based on Redox-Active Bis-<Emphasis Type="Italic">o</Emphasis>-Benzoquinone,a Bis-Catechol-Aldimine Derivative

The oxidative addition of bis-o-benzoquinone Q–(CH=N–N=CH)–Q (L), in which two 3,5-ditert-butyl-o-benzoquinones are linked to each other in positions 6 via the CH=N–N=CH group, to triphenylstibine gave a new binuclear triphenylantimony(V) bis-catecholate complex, Ph₃Sb(Cat–(CH=N–N=CH)–Cat)SbPh₃ (I). Recrystallization of I from a methanol–trichloromethane mixture resulted in an additional coordination of a methanol molecule to each antimony atom to give the binuclear complex, (CH₃OH)Ph₃Sb(Cat–(CH=N–N=CH)–Cat)SbPh₃(CH₃OH) (I · 2CH₃OH), the crystals of which (I · 2CH₃OH) · 2CH₃OH · CHCl₃ (II) contain additionally two methanol solvate molecules, which fix the geometry of the nitrogen-containing bridging group, and a trichloromethane molecule. The molecular structure of compound II in the crystalline state was determined by X-ray diffraction (CIF file CCDC no. 1560840).     

Trans Influence of Triphenylstibine: Crystal Structures of cis‐[PtBr2(SbPh3)2], trans‐[PtBr(Ph)(SbPh3)2], [NMe4][PtBr3(SbPh3)], and cis‐[PtBr2(SbPh3)(PPh3)]

The work reports the unexpected reaction of diphenyldibromo antimonates (III) with PtCl₂ and cis‐[PtCl₂(PPh₃)₂]. The reaction gives triphenylstibine containing Pt^II complexes viz. cis‐[PtBr₂(SbPh₃)₂] ( 1 ), trans‐[[PtBr(Ph)(SbPh₃)₂] ( 2 ), [NMe₄][PtBr₃(SbPh₃)] ( 3 ), and cis‐[PtBr₂(PPh₃)(SbPh₃)] ( 4 ). All the complexes were characterised by elemental analyses, IR, Raman, ¹⁹⁵Pt NMR, FAB mass spectroscopy and X‐ray crystallography. A plausible mechanism via the phenyl migration is proposed for the formation of these complexes. The average Pt–Br distance in 1 is 2.456(2) Å, in 2 2.496 Å(trans to Ph) while in 3 it is 2.476 Å (trans to Sb) implying a comparable trans influence of Ph₃Sb and Ph₃P.     

Free radical fixation by tin(IV) diphenylcatecholate complexes

The reactions of sodium and thallium catecholates CatM₂ (Cat is the 3,6-di-tert-butylpyrocatechol dianion; M = Na, T1) with tin diphenyl dichloride afford new tin catecholate complexes Ph₂SnCat · THF (I) and Ph₂SnCat (II). The molecular structure of pentacoordinated complex I is determined by X-ray diffraction analysis. The synthesized complexes are capable of fixating both short-lived (PhC(O)O^., (CH₃)₂NC(S)S^., and NC(CH₃)₂C^.) and stable free radicals (aroxyl, nitroxyl, triphenylmethyl, and phenoxazinyl) to form stable o-semiquinone tin derivatives.     

Organoantimony compounds : VIII. Cleavage of Sb—O—Sb bonds in μ—oxybis(triphenyl -chloroantimony) and triphenylantimony oxide by methanol and acetylacetone

SbOSb bonds in (Ph₃ClSb)₂O and PH₃SbO are cleaved readily by methanol and acetylacetone. The reactions provide convenient synthetic routes for Ph₃Sb(OMe)Cl, Ph₃Sb(OMe)₂, Ph₃Sb(acac)Cl, and Ph₃Sb(acac)OH. Characterization of these compounds by infrared, Raman, and ¹H NMR spectral measurements is reported.     

Structural,Spectroscopic and Computational Examination of the Dative Interaction in Constrained Phosphine–Stibines and Phosphine–Stiboranes

A series of phosphine–stibine and phosphine–stiborane peri‐substituted acenaphthenes containing all permutations of pentavalent groups ?SbCl_nPh_4–n ( 5 – 9 ), as well as trivalent groups ?SbCl₂, ?Sb(R)Cl, and ?SbPh₂ ( 2 – 4 , R=Ph, Mes), were synthesised and fully characterised by single crystal diffraction and multinuclear NMR spectroscopy. In addition, the bonding in these species was studied by DFT computational methods. The P–Sb dative interactions in both series range from strongly bonding to non‐bonding as the Lewis acidity of the Sb acceptor is decreased. In the pentavalent antimony series, a significant change in the P–Sb distance is observed between ?SbClPh₃ and ?SbCl₂Ph₂ derivatives 6 and 7 , respectively, consistent with a change from a bonding to a non‐bonding interaction in response to relatively small modification in Lewis acidity of the acceptor. In the Sb^III series, two geometric forms are observed. The P–Sb bond length in the SbCl₂ derivative 2 is as expected for a normal (rather than a dative) bond. Rather unexpectedly, the phosphine–stiborane complexes 5 – 9 represent the first examples of the σ⁴P→σ⁶Sb structural motif.     

Interconversion of Molybdenum Imido and Amido Complexes by Proton‐Coupled Electron Transfer

Interconversion of the molybdenum amido [(^PhTpy)(PPh₂Me)₂Mo(NHtBuAr)][BArF²⁴] (^PhTpy=4′‐Ph‐2,2′,6′,2“‐terpyridine; tBuAr=4‐tert‐butyl‐C₆H₄; ArF²⁴=(C₆H₃‐3,5‐(CF₃)₂)₄) and imido [(^PhTpy)(PPh₂Me)₂Mo(NtBuAr)][BArF²⁴] complexes has been accomplished by proton‐coupled electron transfer. The 2,4,6‐tri‐tert‐butylphenoxyl radical was used as an oxidant and the non‐classical ammine complex [(^PhTpy)(PPh₂Me)₂Mo(NH₃)][BArF²⁴] as the reductant. The N?H bond dissociation free energy (BDFE) of the amido N?H bond formed and cleaved in the sequence was experimentally bracketed between 45.8 and 52.3 kcal mol^?1, in agreement with a DFT‐computed value of 48 kcal mol^?1. The N?H BDFE in combination with electrochemical data eliminate proton transfer as the first step in the N?H bond‐forming sequence and favor initial electron transfer or concerted pathways.     

Synthesis,characterization and biological activity of a novel binuclear organotin complex,Ph3Sn(HL)·Ph2SnL [L = 3,5‐Br2‐2‐OC6H2CHNCH(i‐Pr)COO]

A 1:1 reaction of triphenyltin chloride with potassium N‐[(3,5‐dibromo‐2‐hydroxyphenyl)methylene] valinate in benzene under reflux leads to the formation of a novel mixed organotin binuclear complex, Ph₃Sn(HL)·Ph₂SnL [L = 3,5‐Br₂‐2‐OC₆H₂CH?NCH(i‐Pr)COO], by means of a facile phenyl–tin bond cleavage process. The X‐ray structure reveals that there are two distinct types of carboxylate coordination mode and trans‐O₂SnC₂N and trans‐O₂SnC₃ in distorted trigonal bipyramidal geometries. The complex displays good in vitro cytotoxicity and antibacterial activities. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental and theoretical investigation of topological and energetic characteristics of Sb complexes reversibly binding molecular oxygen

The experimental distribution of electron density in Ph(3)(4,5-OMe-3,6-Bu(t)-Cat)Sb·MeCN (1*) and Ph(3)(4,5-N(2)C(4)H(6)-3,6-Bu(t)-Cat)Sb·MeOH (2*) complexes was studied. According to atoms in molecules theory, the Sb-C(Ph), Sb-O(catecholate), and Sb···N(O) bonds are intermediate, whereas the O-C and C-C bonds are covalent, respectively. The energy of the Sb···N(MeCN) and Sb···O(MeOH) bonds are 7.0 and 11.3 kcal/mol according to the Espinosa equation. Density functional theory and Hartree-Fock calculations were carried out for a series of catecholate and amidophenolate complexes of antimony(V). It was shown that such calculations reliably reproduce geometrical and topological parameters and therefore can be used for a criterion search of dioxygen reversible binding by the catecholate and amidophenolate complexes of antimony(V). It was found that the "critical" value of the HOMO energy vary in the range from -5.197 to -5.061 eV for reversible binding of dioxygen complexes. This can serve as a thermodynamic criterion to predict the possibility of the dioxygen reversible binding by the catecholate and amidophenolate complexes of Sb(V). The HOMO energies correlate with the conversion of the catecholate and amidophenolate complexes in corresponding spiroendoperoxide derivatives as well. The contribution of the atom orbitals of the carbon atoms in the five-membered metallocycle to HOMO in complexes with different substitutes in the 4- and 5-positions of the catecholate ligand allows predicting the place of dioxygen addition.     

Kinetics and Mechanism Comparison between Cr/Ti‐Based Bimetallic and Ti‐Based Monometallic Catalysts for Ethylene Polymerization

Two (SiO₂/MgR₂/MgCl₂)·TiCl_x model catalysts are made by refluxing TiCl₄ with 0.35 wt% Cr modified silica gel/alkyl Mg adducts or silica gel/alkyl Mg adducts, which are named as Cr/Ti‐based bimetallic Cat‐1 and Ti‐based monometallic Cat‐2, respectively. The kinetics, active center counting, morphology, and polymer characterizations are studied to disclose the effect of low loading Cr active sites on the Cr/Ti‐based bimetallic Cat‐1 polymerization under mild conditions. The activity of Cat‐1 is 120.4% higher than that of Cat‐2, with a 114.1% higher [C*]/[M] value. Morphology results show the Cat‐1 fragmentation in the first 3 min is highly accelerated, which helps to release buried clustered Ti sites. Differential scanning calorimetry results show that low‐temperature heat absorbing shoulder of polyethylene (PE) from Cat‐2 demonstrates the signal of low crystallinity polymer made by Cat‐2 during the first 60 s, verifying the fluffy polymer in morphology results. GPC results show PE from Cat‐1 has a higher M_w in the first 3 min while a lower M_w in the end. The Cat‐1, which release active sites faster, has a high M_w in the early time. Lower M_w in the 900 s attributes to the effect of relative lower M_w polymer made by Cr sites, compared with Cat‐2.     

An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

With the intent to demonstrate that the charge of Z‐type ligands can be used to modulate the electrophilic character and catalytic properties of coordinated transition metals, we are now targeting complexes bearing polycationic antimony‐based Z‐type ligands. Toward this end, the dangling phosphine arm of ((o‐(Ph₂P)C₆H₄)₃)SbCl₂AuCl ( 1 ) was oxidized with hydrogen peroxide to afford [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl₂]⁺ ([ 2 a ]⁺) which was readily converted into the dicationic complex [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl]²⁺ ([ 3 ]²⁺) by treatment with 2 equiv AgNTf₂. Both experimental and computational results show that [ 3 ]²⁺ possess a strong Au→Sb interaction reinforced by the dicationic character of the antimony center. The gold‐bound chloride anion of [ 3 ]²⁺ is rather inert and necessitates the addition of excess AgNTf₂ to undergo activation. The activated complex, referred to as [ 4 ]²⁺ [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuNTf₂]²⁺ readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong σ‐accepting properties of the dicationic antimony ligand and its activating impact on the gold center.