High-Temperature Single-Site Ethylene Polymerization Behavior of Titanate Complexes Supported by 1,3-Bis(3,5-dialkylpyrazol-1-yl)propan-2-olate Ligation

Titanate(1−) complexes Na[(THF)(κ1-O-bdbpzp)TiCl4] (1) and Na[(THF)(κ1-O-bdmpzp)TiCl4] (2) and titanate(2−) complexes [Na(THF)]2[(κ1-O-bdbpzp)2TiCl4] (4) and [Na(THF)]2[(κ1-O-bdmpzp)2TiCl4] (5) were obtained in good yield from reaction of Na[bdbpzp] or Na[bdmpzp] (sodium salt of 1,3-bis(3,5-di-tert-butylpyrazol-1yl)propan-2-ol or 1,3-bis(3,5-dimethylpyrazol-1yl)propan-2-ol) with TiCl4 (in the appropriate molar ratio) at 0−25 °C. Protonolysis of TiCl4 with 1 equiv of bdmpzpH furnished related zwitterionic titanate(1−) complex 3 that possessed a κ2-N,O-coordinated pyrazolyl-alkoxide with pendant pyrazolium group. Methylalumoxane (MAO) activation of 1−5 under high-temperature solution polymerization conditions produced active single-site ethylene polymerization catalysts that exhibit considerably higher thermal stability (especially 2/MAO, 3/MAO, and 5/MAO) than previously reported for Cp2TiCl2/MAO or Ti catalysts supported by related heteroscorpionate or scorpionate ligation

Highly Regioselective [2 + 2 + 2] Cycloaddition of Terminal Alkynes Catalyzed by η⁶-Arene Complexes of Titanium Supported by Dimethylsilyl-Bridged <i>p</i>-<i>tert</i>-Butyl Calix[4]arene Ligand

Two new Ti−η6-arene complexes [(DMSC)Ti{η6-1,2,4-C6H3(SiMe3)3}] (6) and [(DMSC)Ti{η6-1,3,5-C6H3But3}] (7) containing 1,2-alternate, Me2Si-bridged p-tert-butylcalix[4]arene (DMSC) ancillary ligand have been synthesized. The solid-state structure of 6 revealed a highly folded arene ligand [with a dihedral angle of 29.7(7)°] and suggests that 6 is better described as a 7-titananorbornadiene species. Both 6 and 7 are efficient catalysts for highly regioselective [2 + 2 + 2] cycloaddition of terminal alkynes to yield 1,2,4-substituted benzenes. Kinetic studies of the catalytic [2 + 2 + 2] cycloaddition of Me3SiC⋮CH revealed first-order dependence on [6] and [Me3SiC⋮CH]; and activation parameters, ΔH⧧ = 14 kcal/mol, and ΔS⧧ = −11 cal/mol K, that are consistent with an associative mechanism. The reaction rate is influenced by the steric requirements of both the alkyne and the η6-arene compound. The high selectivity for 1,2,4-substituted benzene may be understood in terms of the directing influence of the DMSC ligand

Highly Regioselective Alkyne Cyclotrimerization Catalyzed by Titanium Complexes Supported by Proximally Bridged <i>p-tert-</i>Butylcalix[4]arene Ligands

Highly Regioselective Alkyne Cyclotrimerization Catalyzed by Titanium Complexes Supported by Proximally Bridged p-tert-Butylcalix[4]arene Ligand

Highly Regioselective Alkyne Cyclotrimerization Catalyzed by Titanium Complexes Supported by Proximally Bridged <i>p-tert-</i>Butylcalix[4]arene Ligands

Highly Regioselective Alkyne Cyclotrimerization Catalyzed by Titanium Complexes Supported by Proximally Bridged p-tert-Butylcalix[4]arene Ligand

Synthesis and Reactivity of [(DMSC)Ti(η²-OCAr₂)L₂] Complexes (DMSC = Dimethylsilyl-Bridged <i>p-tert-</i>Butylcalix[4]arene Dianion, Ar = Aryl Group, and L₂ = Delocalized Diimine)

Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr2CAr2O)] (1, Ar = Ph; 2, Ar = p-MeC6H4; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η2-ketone complexes [(DMSC)Ti(η2-OCAr2)L2)] 3−6 (L2 = bpy, dmbpy, or phen). The ketone is weakly bound in 3−6, and it is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give intense green solutions and undergo a photochemically assisted transformation into 1-aza-5-oxa-titanacyclopentene derivatives 8−11, in which C−H activation of the heterocyclic diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has occurred. The reaction of 3−6 with one or more equivalents of appropriate ketone gave 8−11 in high yield. The compounds were characterized by NMR (1H and13C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9). The ease of transformation of [(DMSC)Ti{η2-OC(p-MeC6H4)2}L2] complexes (4, L2 = bpy; 5, L2 = dmbpy; 6, L2 = phen) into 9−11 tracks the facility of metal to diimine ligand charge transfer (MLCT) transition and increased in the order 5 4 ≪ 6. This transformation is suggested to occur by a mechanism that involves reversible coordination of ketone to titanium and a rate-limiting step that is dependent on ketone concentration

Synthesis and Reactivity of [(DMSC)Ti(η²-OCAr₂)L₂] Complexes (DMSC = Dimethylsilyl-Bridged <i>p-tert-</i>Butylcalix[4]arene Dianion, Ar = Aryl Group, and L₂ = Delocalized Diimine)

Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr2CAr2O)] (1, Ar = Ph; 2, Ar = p-MeC6H4; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η2-ketone complexes [(DMSC)Ti(η2-OCAr2)L2)] 3−6 (L2 = bpy, dmbpy, or phen). The ketone is weakly bound in 3−6, and it is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give intense green solutions and undergo a photochemically assisted transformation into 1-aza-5-oxa-titanacyclopentene derivatives 8−11, in which C−H activation of the heterocyclic diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has occurred. The reaction of 3−6 with one or more equivalents of appropriate ketone gave 8−11 in high yield. The compounds were characterized by NMR (1H and13C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9). The ease of transformation of [(DMSC)Ti{η2-OC(p-MeC6H4)2}L2] complexes (4, L2 = bpy; 5, L2 = dmbpy; 6, L2 = phen) into 9−11 tracks the facility of metal to diimine ligand charge transfer (MLCT) transition and increased in the order 5 4 ≪ 6. This transformation is suggested to occur by a mechanism that involves reversible coordination of ketone to titanium and a rate-limiting step that is dependent on ketone concentration

Reactivity of a Well-Characterized Titananorbornadiene (η⁶-Arene) Complex with Ketones and Aldehydes

The reaction between the titananorbornadiene complex [(DMSC)Ti(η6-1,2,4-(Me3Si)3C6H3)] (2) and ketones or aldehydes proceeds by insertion of a ketone or aldehyde molecule into a Ti−C bond of 2, yielding 2,5-dioxatitanacyclopentane or 2-oxatitanacycloheptene compounds. The intermediacy of a 2-oxatitanacycloheptene species en route to arene loss from 2 and the formation of 2,5-dioxatitanacyclopentane compounds are indicated

Synthesis, Characterization, and Reactivity of [LiC(SiMe₂H)₃]·2THF: Formation of 1,1,3,3-Tetramethyl-2,2,4,4-tetrakis(dimethylsilyl)- 1,3-disilacyclobutane, [Me₂SiC(SiMe₂H)₂]₂

Reaction of [HC(SiMe2H)3] with [(CH3)2CH]2NLi in tetrahydrofuran afforded [LiC(SiMe2H)3]·2THF (1) in excellent yield. Reactions of 1 with Me3SiCl, MeSiHCl2, HSiCl3 and MeSiCl3 at −78 °C gave [Me3SiC(SiMe2H)3] (2), [(HMeClSi)C(SiMe2H)3] (3), [(HCl2Si)C(SiMe2H)3] (4), and [(MeCl2Si)C(SiMe2H)3] (5), respectively. At room temperature, reaction between 1 and SiCl4 in toluene resulted in multiple products, including a new highly substituted 1,3-disilacyclobutane [Me2SiC(SiMe2H)2]2 (6). 6 was isolated in moderate yield from reaction of 1 with 2 equiv of SiCl4

Unusual Reductive Coupling of Alkynes and Ketones: Reactivity of Titanacycles Supported by Dimethylsilylcalix[4]arene (DMSC) Ligands

Reaction of [(DMSC)Ti{1,2,4-(Me3Si)3C6H3}] (1) with 1 equiv of bipyridine (bpy) or 4,4‘-dimethyl-2,2‘-dipyridyl (dmbpy) and a slight excess of RC⋮CH quantitatively produced [(DMSC)Ti(η2-RC⋮CH)(L2)] (L2 = bpy or dmbpy) (5−16). (DMSC)TiPh2 (17) reacted with ≥2 equiv of bpy or dmbpy to give (DMSC)Ti(bpy)2 (18) and (DMSC)Ti(dmbpy)2 (19), respectively. Both 1H and 13C NMR data, as well as X-ray crystallography in the case of [(DMSC)Ti(η2-HC⋮CBut)(bpy)] (7), support exo-orientation of the alkyne's non-H substituent in 5−16. Reaction of [(DMSC)Ti{1,2,4-(Me3Si)3C6H3}] (1) with a mixture of RC⋮CH and R2CO did not give the expected 5-oxa-1-titana-2-cyclopentene products but instead produced 2,7-dioxa-1-titana-4-cycloheptenes (20−25). The latter result may be understood in terms of the unique directing influence of the DMSC ligand

Strengthening of N−H···Co Hydrogen Bonds upon Increasing the Basicity of the Hydrogen Bond Acceptor (Co)

Low temperature crystal structures of (DABCO)H+Co(CO)4- (1) and (DABCO)H+Co(CO)3PPh3- (2) (DABCO = 1,4-diazabicyclooctane) indicate that both salts exhibit N−H···Co hydrogen bonding. IR and NMR data indicate that these hydrogen bonded species persist in nonpolar solvents such as toluene, but exist as solvent separated ions in more polar solvents. Replacement of the axial CO ligand by PPh3 leads to a shortening of the N···Co separation in the solid state from 3.437(3) to 3.294(6) Å. This change is accompanied by an increase in the angle between the equatorial carbonyl ligands. Thus, the crystallographic results suggest a strengthening of the N−H···Co hydrogen bond upon increasing the basicity of the metal center, the first observation of this type in the solid state. This assertion is supported by variable-temperature 1H and 13C NMR data in toluene-d8 solution which, discussed in the light of ab initio calculations, indicate that the barrier to a fluxional process involving cleavage of the N−H···Co hydrogen bond is greater in 2 than in 1. The crystal structures of 1 and 2 have been determined by X-ray diffraction at 135(5) and 123(5) K, respectively [1 monoclinic, P21/n (No. 14), a = 8.728(2), b = 23.333(5), c = 12.146(2) Å, β = 95.74(2)°, V = 2461.1(9) Å3, Z = 8, R(F) = 0.043, Rw(F) = 0.043, S(F) = 1.21; 2 orthorhombic, Pca21 (No. 29), a = 16.084(8), b = 8.874(3), c = 17.312(3) Å, V = 2471(1) Å3, Z = 4, R(F) = 0.065, Rw(F) = 0.060, S(F) = 1.16]