Boron Lewis Acid‐Catalyzed Hydroboration of Alkenes with Pinacolborane: BArF3 Does What B(C6F5)3 Cannot Do!

The transition‐metal‐free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris[3,5‐bis(trifluoromethyl)phenyl]borane (BAr^F₃) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)borane (B(C₆F₅)₃) is reluctant to react. Unlike B(C₆F₅)₃, BAr^F₃ is found to engage in substituent redistribution with HBpin, resulting in the formation of Ar^FBpin and the electron‐deficient diboranes [H₂BAr^F]₂ and [(Ar^F)(H)B(μ‐H)₂BAr^F₂]. These in situ‐generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin‐derived anti‐Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle.     

Unprecedented Oxidative Addition and Metal‐Only Lewis Pair Chemistry of Antimony Trihalides

Reaction of the zero‐valent platinum complex [Pt(PCy₃)₂] with SbF₃ generates the cationic diplatinum stibenium complex [{(Cy₃P)₂Pt}₂(μ‐SbF₂)]⁺, the first unsupported metal‐only Lewis pair containing an antimony‐centered Lewis acid. In contrast, SbCl₃ undergoes oxidative addition to [Pt(PCy₃)₂], resulting in the dihalostibanyl complex trans‐[PtCl(SbCl₂)(PCy₃)₂], the first example of oxidative addition of an antimony–halide bond to a transition metal.     

Isolation and Structure of Germylene‐Germyliumylidenes Stabilized by N‐Heterocyclic Imines

The ditopic germanium complex FGe(NIPr)₂Ge[BF₄] ( 3 [BF₄]; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) is prepared by the reaction of the amino(imino)germylene (Me₃Si)₂NGeNIPr ( 1 ) with BF₃?OEt₂. This monocation is converted into the germylene‐germyliumylidene 3 [BAr^F₄] [Ar^F=3,5‐(CF₃)₂‐C₆H₃] by treatment with Na[BAr^F₄]. The tetrafluoroborate salt 3 [BF₄] reacts with 2 equivalents of Me₃SiOTf to give the novel complex (OTf)(GeNIPr)₂[OTf] ( 4 [OTf]), which affords 4 [BAr^F₄] and 4 [Al(OR^F)₄] [R^F=C(CF₃)₃] after anion exchange with Na[BAr^F₄] or Ag[Al(OR^F)₄], respectively. The computational, as well as crystallographic study, reveals that 4 ⁺ has significant bis(germyliumylidene) dication character.     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.     

A Theoretical Study of the Reductive Elimination of CH3EH3 from cis‐[Pt(CH3)(EH3)(PH3)2] (E = Si,Ge) in the Presence of Acetylene

The reaction mechanism of the elimination of CH₃EH₃ from the platinum complexes cis‐[Pt(CH₃) · (EH₃)(PH₃)₂] (E = Si, Ge) in the presence of acetylene has been studied using gradient‐corrected DFT calculations at the B3LYP level. The reaction proceeds in two steps. The first step is the formation of the acetylene complex [Pt(CH₃)(HCCH)(EH₃)(PH₃)] which occurs in a associative/dissociate pathway via the five‐coordinated intermediate [Pt(CH₃)(HCCH)(EH₃)(PH₃)₂]. The rate‐determining step is the elimination of CH₃EH₃ via a four‐coordinated transition state. The alternative mechanism via direct dissociation from the five‐coordinated intermediates has higher activation barriers. The calculated activation energies of the model reactions are in good agreement with experimental results. The silyl complex has a lower barrier for the elimination reaction than the germyl complex. The calculated transition states show that the reason for the lower barrier is the strength of the nascending C–Si bond, which is higher than the C–Ge bond. The results are in agreement with the postulated mechanism of Ozawa et al. (Organometallics, 1998 , 17, 1018).     

Trans-methyl-azido-bis(triisopropylphosphin)platin(II), [PtN3(CH3)(PiPr3)2]

Trans-methyl-azido-bis(triisopropylphosphine)platinum(II), [PtN₃(CH₃)(PⁱPr₃)₂] [PtN₃(CH₃)(PⁱPr₃)₂] has been prepared by reductive elimination of ethane from [Pt(CH₃)₃N₃]₄ in the presence of triisopropylphosphine at 80 °C. The complex is characterized by IR and NMR spectroscopy and by crystal structure determination, as well as by ab initio calculations. [PtN₃(CH₃)(PⁱPr₃)₂], which is in trans-configuration here, crystallizes in the monoclinic space group P2₁, Z = 2, and with the lattice dimensions a = 806.9(1), b = 1384.3(1), c = 1093.8(1) pm, β = 94.107(10)°.     

Reactions involving transition metals : XIX. Some reactions of perfluoronorbornadiene with low valent transition metal complexes

Perfluoronorbornadiene reacts with the compounds [M(PPh₃)₄] (M = Pt, Pd) and [IrCl(CO)(PMePh₂)₂] to give the adducts [(C₇F₈)M(PPh₃)₂] and [(C₇F₈)IrCl(CO)(PMePh₂)₂] in which one of the double bonds is coordinated to the metal atom. The platinum complex reacts further with [Pt(PPh₃)₄] to give [(C₇F₈){Pt(PPh₃)₂}₂] having both double bonds coordinated to a Pt atom. The carbonylmetal anions [M^?] react to form the mono-substitution products [(C₇F₇)M] (M = Mn(CO)₅, Re(CO)₅, Ir(CO)₂(PPh₃)₂, Rh(CO)₂(PPh₃)₂), but the use of an excess of [Fe(CO)₂(η-C₅H₆)]^? leads to substitution of one fluorine atom on each of the double bonds. The complex having M = Mn(CO)₅ reacts with [Pt(PPh₃)₄] to afford the derivative [(C₇F₇){Mn(CO)₄(PPh₃)}{Pt(PPh₃)₂}], and the compound where M = Ir(CO)₂(PPh₃)₂ undergoes an oxidative addition reaction with acetyl chloride. Oxidative coupling products have been isolated on UV irradiation of a mixture of perfluoronorbornadiene and [Fe(η⁴-CH₂CRCHCH₂)(CO)₃] (R = H, Me), and under similar conditions the reaction with Fe(CO)₅ affords [(C₇F₈)Fe(CO)₄] in very low yield.     

A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomerization of Acetylene to Vinylidene

Complex [PtMe₂(PMe₂Ar )] ( 1 ), which contains a tethered terphenyl phosphine (Ar =2,6‐(2,6‐ⁱ Pr₂C₆H₃)₂C₆H₃), reacts with [H(Et₂O)₂]BAr_F (BAr_F⁻=B[3,5‐(CF₃)₂C₆H₃]₄⁻) to give the solvent (S) complex [PtMe(S)(PMe₂Ar )]⁺ ( 2⋅S ). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C₂H₄) to afford the corresponding adducts, treatment of 2⋅S with C₂H₂ yielded instead the allyl complex [Pt(η³‐C₃H₅)(PMe₂Ar )]⁺ ( 6 ) via the alkyne intermediate [PtMe(η²‐C₂H₂)(PMe₂Ar )]⁺ ( 5 ). Deuteration experiments with C₂D₂, and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a Pt^II‐promoted HC≡CH to :C=CH₂ tautomerization in preference over acetylene migratory insertion into the Pt−Me bond.     

Synthetic and spectroscopic studies of some mono-hydrido-bridged complexes of platinum(II)

The mono-hydrido-bridged complexes (PEt₃)₂(Ar)Pt(μ₂-H)Pt(Ar)(PEt₃)₂]-[BPh₄] (Ar = Ph, 4-MeC₆H₄ and 2,4-Me₂C₆H₃) have been obtained by treating trans-[Pt(Ar)(MeOH)(PEt₃)₂][BF₄] with sodium formate and Na[BPH₄]. The cations [PEt₃)₂(Ar)Pt(μ₂-H)Pt(Ar^b')(PEt₃)₂]^b+ (Ar = Ph and Ar^b' - 2,4-Me₂C₆H₃ and 2,4,6-Me₃C₆H₂ have bee identified in solution. Their ^b1H- and ^b31P-NMR data are reported. The X-ray crystal structure of [(PEt₃)₂(Ph)Pt(μ₂-H)Pt(Ph)(PEt₃)₂][BPh₄] is reported.     

Reaction of η-enone and enal-platinum(0) complexes with Lewis acidic compounds

Reaction of η²-enone and enal-platinum(0) complexes Pt(CH₂CHCOR)(PPh₃)₂ (R=H, Me) with Lewis acidic compounds BX₃ (X=F, C₆F₅) afforded adducts formed by coordination of boron to oxygen of the carbonyl group. The X-ray structure determination of the adduct formed from B(C₆F₅)₃ and η²-methylvinylketone complex showed no strong interaction between Pt and carbonyl carbon. In contrast to the inability of the palladium(0) η²-enone complexes to form any Me₃Al adduct, η²-cyclohexenoneplatinum(0) complex formed an isolable adduct with Me₃Al, the structure of which was also confirmed by X-ray analysis. The NMR spectral parameters (Pt-C, Pt-P and P-P coupling constants) of these adducts were compared with those of the original η²-enone or enal-platinum(0) complexes as well as the ordinary η³-allylplatinum cation [Pt(PPh₃)₂(MeCHCHCH₂)]⁺.     

Aromatic Osmacyclopropenefuran Bicycles and Their Relevance for the Metal‐Mediated Hydration of Functionalized Allenes

The aromatic osmacyclopropenefuran bicycles [OsTp{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(PⁱPr₃)]BF₄ (Tp=hydridotris(1‐pyrazolyl)borate) and [OsH{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(CO)(PⁱPr₃)₂]BF₄, with the metal fragment in a common vertex between the fused three‐ and five‐membered rings, have been prepared via the π‐allene intermediates [OsTp(η²‐CH₂=CCHCO₂Et)(OCMe₂)(PⁱPr₃)]BF₄ and [OsH(η²‐CH₂=CCHCO₂Et)(CO)(OH₂)(PⁱPr₃)₂]BF₄, and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(PⁱPr₃)₂]⁺ metal fragment is a key intermediate in the [OsH(CO)(OH₂)₂(PⁱPr₃)₂]BF₄‐catalyzed regioselective anti‐Markovnikov hydration of ethyl buta‐2,3‐dienoate to ethyl 4‐hydroxycrotonate.     

High selectivity for l-cysteine residue at axial solvated site of trigonal-bipyramidal palladium(II) complex with tripodal tetradentate phosphine

The five-coordinate trigonal-bipyramidal palladium(II) and platinum(II) complexes with sulfur-coordinated glutathione at the axial position, [Pd(gluta)(pp₃)](BF₄) and [Pt(gluta)(pp₃)](PF₆) (gluta = glutathionate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), were prepared and characterized by ³¹P NMR spectroscopy. The dimeric square-planar platinum(II) complex [Pt(pp₃)]₂(PF₆)₄ gave the monomeric five-coordinate solvated complex, [Pt(pp₃)(CH₃CN)]²⁺, in acetonitrile. Extraction experiments for amino acids from the aqueous solution to the chloroform layer were carried out by using [Pd(pp₃)(CH₃CN)]²⁺, [Pt(pp₃)(CH₃CN)]²⁺, and [Pd(p₃)(CH₃CN)]²⁺ (p₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine) as extractants. High selectivity for the thiolate sulfur atom in l-cysteinate was observed at the solvated coordination site in [Pd(pp₃)(CH₃CN)]²⁺. The selectivity was applied to extraction of l-cysteinate from a mixture of some amino acids and, further, the reduced form of glutathionate from a mixture of the reduced and oxidized forms of glutathione.     

From Ion‐Like Ethylzinc Aluminates to [EtZn(arene)2]+[Al(ORF)4]− Salts

Attempts to prepare previously unknown simple and very Lewis acidic [RZn]⁺[Al(OR^F)₄]^? salts from ZnR₂, AlR₃, and HO?R^F delivered the ion‐like RZn(Al(OR^F)₄) (R=Me, Et; R^F=C(CF₃)₃) with a coordinated counterion, but never the ionic compound. Increasing the steric bulk in RZn⁺ to R=CH₂CMe₃, CH₂SiMe₃, or Cp*, thus attempting to induce ionization, failed and led only to reaction mixtures including anion decomposition. However, ionization of the ion‐like EtZn(Al(OR^F)₄) compound with arenes yielded the [EtZn(arene)₂]⁺[Al(OR^F)₄]^? salts with arene=toluene, mesitylene, or o‐difluorobenzene (o‐DFB)/toluene. In contrast to the ion‐like EtZn(η³‐C₆H₆)(CHB₁₁Cl₁₁), which co‐crystallizes with one benzene molecule, the less coordinating nature of the [Al(OR^F)₄]^? anion allowed the ionization and preparation of the purely organometallic [EtZn(arene)₂]⁺ cation. These stable materials have further applications as, for example, initiators of isobutene polymerization. DFT calculations to compare the Lewis acidities of the zinc cations to those of a large number of organometallic cations were performed on the basis of fluoride ion affinity. The complexation energetics of EtZn⁺ with arenes and THF was assessed and related to the experiments.     

Activation of Strong Boron–Fluorine and Silicon–Fluorine σ‐Bonds: Theoretical Understanding and Prediction

The oxidative addition of BF₃ to a platinum(0) bis(phosphine) complex [Pt(PMe₃)₂] ( 1 ) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF₃ to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol^?1, respectively) and require large Gibbs activation energies (ΔG°^≠=56.3 and 38.9 kcal mol^?1, respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF₃ to 1 in the presence of a second BF₃ molecule occurs with ΔG°^≠ and ΔG° values of 10.1 and ?4.7 kcal mol^?1, respectively. ΔG°^≠ becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF₃, occurs from the dissociating fluoride to the second non‐coordinated BF₃. This CT interaction stabilizes both the transition state and the product. The B?F σ‐bond cleavage of BF₂Ar^F (Ar^F=3,5‐bis(trifluoromethyl)phenyl) and the B?Cl σ‐bond cleavage of BCl₃ by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF₄ to 1 easily occurs in the presence of a second SiF₄ molecule via the formation of a hypervalent Si species.     

Titanium(IV) Cations with Trigonal Monopyramidal Geometry: Unusual Lewis Acids Supported by a Triaryl Triamidoamine Ligand

Protonolysis of the titanium alkyl complex [Ti(CH₂SiMe₃)(Xy-N₃N)] (Xy-N₃N=[{(3,5-Me₂C₆H₃)NCH₂CH₂}₃N]³⁻) supported by a triamidoamine ligand, with [NEt₃H][B(3,5-Cl₂C₆H₃)₄] or [PhNMe₂H][B(C₆F₅)₄] afforded the cations [Ti(Xy-N₃N)][A] (A⁻=[B(3,5-Cl₂C₆H₃)₄]⁻ ( 1[B(Ar^Cl)₄] ; B(Ar^Cl)₄=tetrakis(3,5-dichlorophenyl)borate); A⁻=[B(C₆F₅)₄]⁻ ( 1[B(Ar^F)₄] ; B(Ar^F)₄=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate). These Lewis acidic cations were reacted with coordinating solvents to afford the cations [Ti(L)(Xy-N₃N)][B(C₆F₅)₄] ( 2-L ; L=Et₂O, pyridine and THF). XRD analysis revealed a trigonal monopyramidal (TMP) geometry for the tetracoordinate cations in 1[B(Ar^X)₄] and trigonal bipyramidal (TBP) geometry for the pentacoordinate cations in 2-L . Variable-temperature NMR spectroscopy showed a dynamic equilibrium for 2-Et₂O in solution, involving the dissociation of Et₂O. Coordination to the titanium(IV) center activated the THF molecule, which, in the presence of NEt₃, underwent ring-opening to give the titanium alkoxide [Ti(O(CH₂)₄NEt₃)(Xy-N₃N)][B(3,5-Cl₂C₆H₃)₄] ( 3 ). Hydride abstraction from C_β,eq of the triamidoamine ligand arm in [Ti(CH₂SiMe₃)(Xy-N₃N)] or [Ti(NMe₂)(Xy-N₃N)] with [Ph₃C][B(3,5-Cl₂C₆H₃)₄] led to the diamidoamine–imine complex [Ti(R){(Xy-N=CHCH₂)(Xy-NCH₂CH₂)₂N}][B(3,5-Cl₂C₆H₃)₄] (R=CH₂SiMe₃ ( 4 a ); R=NMe₂ ( 4 b )). Hydride addition to 4 b with [Li(THF)][HBPh₃] gave [Ti(NMe₂)(Xy-N₃N)], whereas KH deprotonated further to give [Ti(NMe₂){(Xy-NCH=CH)(Xy-NCH₂CH₂)₂N}] ( 5 ). XRD on single crystals of 3 and 4 b confirmed the proposed structures.     

Acyl and α-Ketoacyl Complexes of Pt(II) with Weak Donor Ligands

Treatment of trans-Pt(COCOPh)(Cl)(PPh₃)₂ (1a) with AgBF₄in THF led to the formation of a metastatic complex trans-[Pt(COCOPh)(THF)(PPh₃)₂](BF₄) (2) which readily underwent ligand substitution to give a cationic aqua complex trans-[Pt(COCOPh)(OH₂)(PPh₃)₂](BF₄) (5a). Complex 5a has been characterized spectroscopically and crystallographically. Analogous reaction of trans-Pt(COCOOMe)(Cl)(PPh₃)₂ (1b) with Ag(CF₃SO₃) in dried CH₂C1₂ was found first to yield a methoxyoxalyl triflato complextrans-Pt(COCOOMe)(OTf)(PPh₃)₂ (6). Attempts to crystallize the triflato product in CH₂-cl₂hexane under ambient conditions also afforded an aqua complex of the triflate salt f/wu-[Pt(COCOOMe)(OH₂)(PPhj)₂](CF₃SO₃) (5b). Complex 5a in a noncoordinating solvent such as CH₂C1₂ or CHCl₃ suffered spontaneous decarbonylation to form first cis-[Pt(COPh)(CO)(PPh₃)₂l(BF₄) (3a) then the thermodynamically stable isomer trans-[Pt(COPh)(CO)(PPh₃)₂](BF₄) (3b). Crystallization of complex 3b under ambient conditions resulted in an aqua benzoyl complex trans-[Pt(COPh)(OH₂)(PPh₃)₂](BF₄) (7). The replacement of the H_2O ligand in complex 7 by CO was done simply by bubbling CO into the solution of 7. The single crystal structures of 5b and 7 have been determined by X-ray diffraction. The distances of the Pt-O bonds in 5a, 5b, and 7 support that the aqua ligand is a weak donor in such cationic aquaorganoplatinum(lI) complexes, in agreement with their lability to the substitution reactions.     

Reactions of dimethyldivinylsilane,dimethyldivinyltin and allyltrimethyltin with diethylene (tertiary) phosphine)platinum complexes

The compounds [Pt(C₂H₄)₂(PR₃)] [PR₃ = P-tBu₂Me, P(C₆H₁₁)₃, PPh₃] react dimethyldivinylsilane or dimethyldivinyltin to give chelate complexes [Pt{(CH₂CH)₂MMe₂} (PR₃)] (M = Si or Sn). allyltrimethyltin reacts with various diethylene (tertiary phosphine)platinum compounds with cleavage of the allyl group to afford complexes [Pt(SnMe₃)(η³-C₃H₅)(PR₂)]. The NMR spectra (¹³C, ¹H and ³¹P) of the new compounds have been recorded, and the data are discussed in terms of the structures proposed.     

Reversible carbon–boron bond formation at platinum centers through σ-BH complexes

A reversible carbon–boron bond formation has been observed in the reaction of the coordinatively unsaturated, cyclometalated, Pt(ii) complex [Pt(I^tBuⁱPr′)(I^tBuⁱPr)][BAr^F], 1, with tricoordinated boranes HBR₂. X-ray diffraction studies provided structural snapshots of the sequence of reactions involved in the process. At low temperature, we observed the initial formation of the unprecedented σ-BH complexes [Pt(HBR₂)(I^tBuⁱPr′)(I^tBuⁱPr)][BAr^F], one of which has been isolated. From −15 to +10 °C, the σ-BH species undergo a carbon–boron coupling process leading to the platinum hydride derivative [Pt(H)(I^tBuⁱPr–BR₂)(I^tBuⁱPr)][BAr^F], 4. Surprisingly, these compounds are thermally unstable undergoing carbon–boron bond cleavage at room temperature that results in the 14-electron Pt(ii) boryl species [Pt(BR₂)(I^tBuⁱPr)₂][BAr^F], 2. This unusual reaction process has been corroborated by computational methods, which indicate that the carbon–boron coupling products 4 are formed under kinetic control whereas the platinum boryl species 2, arising from competitive C–H bond coupling, are thermodynamically more stable. These findings provide valuable information about the factors governing productive carbon–boron coupling reactions at transition metal centers.

A reversible carbon–boron bond formation has been observed in the reaction of the coordinatively unsaturated, cyclometalated, Pt(ii) complex [Pt(I^tBuⁱPr′)(I^tBuⁱPr)][BAr^F], 1, with tricoordinated boranes HBR₂.     

Über das Donor‐Verhalten von Bis(pyrazolyl)‐Schwefel‐Derivaten

The Donor Properties of Bis(pyrazolyl)‐Sulfur Derivatives From the reactions of bis(pyrazolyl)sulfane S(pz)₂ ( 1 ) with the fluoro Lewis acids BF₃ and AsF₅ in liquid SO₂ the 1:2‐adducts S(pz·BF₃)₂ ( 2 ) and S(pz·AsF₅)₂ ( 3 ) are obtained. 1 reacts with [Co(SO₂)₄(FAsF₅)₂] to give the doubly bridged FAsF₄F dimeric complex [Co{S(pz)₂}(FAsF₅)(SO₂)(μ‐FAsF₄F)]₂ ( 5 ). From F₂S(pz)₂ and [Ni(SO₂)₆](AsF₆)₂, the fluorocubane [Ni₄F₄{S(pz)₂}₄(μ‐FAsF₄F)₂](AsF₆)₂·4SO₂ ( 8 ) is isolated. The X‐ray structures of the compounds 2 , 3 , 5 and 8 are reported.     

Reaction site diversity in the reactions of titanium hydrazides with organic nitriles, isonitriles and isocyanates: Ti=N(α) cycloaddition, Ti=N(α) insertion and N(α) -N(β) bond cleavage

We report a range of new transformations of the diamide–amine supported Ti?NNPh₂ functional group with a variety of unsaturated substrates, along with DFT studies of the key mechanisms. Reaction of [Ti(N₂N^py)(NNPh₂)(py)] ( 4 , N₂N^py=(2‐NC₅H₄)CMe(CH₂NSiMe₃)₂; py=pyridine) with MeCN gave the dimeric species [Ti₂(N₂N^py)₂{μ‐NC(Me)(NNPh₂)}₂] through a [2+2] cycloaddition process. Reaction of 4 or [Ti(N₂N^Me)(NNPh₂)(py)] ( 5 , N₂N^Me=MeN(CH₂CH₂NSiMe₃)₂) with fluorinated benzonitriles gave the terminal hydrazonamide complexes [Ti(N₂N^R){NC(Ar)NNPh₂}(py)] (R=py or Me; Ar=2,6‐C₆H₃F₂ or C₆F₅). DFT studies showed that this proceeds through an overall [2+2] cycloaddition–reverse cycloaddition, resulting in net insertion of ArCN into the Ti?N_α bonds of the respective hydrazides. Reaction of 4 with a mixture of MeCN and PhCCMe gave the metallacycle [Ti(N₂N^py){NC(Me)C(Ph)C(Me)NNPh₂}] by sequential coupling of Ti?NNPh₂ with PhCCMe and then MeCN. A related product, [Ti(N₂N^py){NC(Me)C(Ar^F)C(H)NNPh₂}], was formed by insertion of MeCN into the Ti? C bond of the isolated azatitanacyclobutene [Ti(N₂N^py){N(NPh₂)C(H)C(Ar^F)}] (Ar^F=3‐C₆H₄F). Reaction of 4 with two equivalents of B(Ar)₃ (Ar=C₆F₅) formed the zwitterionic borate [Ti(N₂N^py){η²‐N(NPh₂)B(Ar)₃}] by electrophilic attack at N_α. Compounds 4 and 5 reacted with tBuNC and/or XylNC (Xyl=2,6‐C₆H₃Me₂) to give the N_α? N_β bond cleavage products, [Ti(N₂N^R)(NCNR′)(NPh₂)] (R=py or Me; R′=tBu or Xyl), containing metallated carbodiimide ligands. DFT studies of these reactions found an initial addition of RNC across Ti?N_α followed by N_β coordination, and finally complete N_α transfer from the NNPh₂ to the RNC fragment. Reaction of 5 with Ar′NCE (E=O, S, Se; Ar′=2,6‐C₆H₃iPr₂) gave the [2+2] cycloaddition products [Ti(N₂N^Me){N(NPh₂)C(NAr′)O}(py)] and [Ti(N₂N^Me){N(NPh₂)C(NAr′)E}] (E=S or Se), which did not undergo further transformation of the Ti? N? NPh₂ moiety.