Synthesis and Structure of Titanium(III) Bis(decamethyltitanocene) Oxide

Bis­(decamethyltitanocene) oxide, [(Cp*₂Ti)₂O] (<b>1</b>; Cp* = η⁵-C₅Me₅) has been obtained as a yellow crystalline solid after reacting equimolar amounts of the hydride [Cp*₂TiH] and the hydroxide [Cp*₂Ti­(OH)]. The solid-state structure of <b>1</b> revealed a linear Ti–O–Ti arrangement and a mutual, nearly perpendicular orientation of the bent-sandwich titanocene moieties; the length of both Ti–O bonds amounted to 1.9080(3) Å. A unique structural feature was a close-to-eclipsed conformation of the cyclopentadienyl ligands, attributed to the high steric congestion of <b>1</b>. The molecule in toluene glass exhibited a triplet state EPR spectrum of rhombic symmetry, having zero field splitting <i>D</i> = 0.02159 cm^–1 and <i>E</i> = 0.00230 cm^–1. The ¹H NMR spectrum of <b>1</b> in toluene-<i>d</i>₈ displays a paramagnetic resonance at δ 4.3 ppm (Δν_1/2 ≈ 270 Hz). Compound <b>1</b> reacts with 1 molar equiv of water to give [Cp*₂Ti­(OH)]. In CD₂Cl₂, <b>1</b> is oxidized to yield the major product [(Cp*TiCl₂)₂O] and minor product [{Cp*Ti­(Cl)­O}₃]

'Voigtlaender'

Ethene complexes of titanocenes [Ti­(II)­(η²-C₂H₄)­(Cp′)₂] for Cp′ = η⁵-C₅Me₅ (<b>1</b>), η⁵-C₅Me₄<i>t</i>-Bu (<b>2</b>), η⁵-C₅Me₄SiMe₃ (<b>3</b>), and η⁵-C₅HMe₄ (<b>4</b>) were prepared by reduction of corresponding titanocene dichlorides with magnesium in THF in the presence of ethene. Thermolysis of <b>1</b>–<b>3</b> in toluene solution at a maximum of 100 °C resulted in elimination of ethane, affording cleanly doubly tucked-in titanocene compounds <b>5</b>–<b>7</b>, respectively. Experiments with <b>2</b> and <b>3</b> in NMR tubes proved that symmetrical isomers <b>6a</b> and <b>7a</b> were formed first, and these thermally isomerized to thermodynamically more stable asymmetrical isomers <b>6b</b> and <b>7b</b>. The energy difference between <b>7a</b> and <b>7b</b> calculated by DFT methods was 15.3 kJ/mol. Thermolysis of <b>4</b> in <i>m</i>-xylene required a temperature of 135 °C, affording a mixture of <b>8b</b> > <b>8a</b> and “dimeric dehydro-titanocene” <b>9</b> as a concurrent product of hydrogen abstraction. In contrast to thermolysis in solvents, heating of <b>1</b> and <b>2</b> in high vacuum to 135 °C resulted in sublimation of known titanocenes [Ti­(C₅Me₅)₂] (<b>10</b>) and [Ti­(η⁵-C₅Me₄<i>t</i>-Bu)₂] (<b>13</b>) (Chirik et al. <i>J. Am. Chem. Soc.</i> <b>2004</b>, <i>126</i>, 14688–14689), respectively. The former isomerized in hexane solution to the tucked-in hydride [TiH­{C₅Me₄(CH₂)}­(C₅Me₅)] (<b>10A</b>) as described by Bercaw (<i>J. Am. Chem. Soc.</i> <b>2004</b>, <i>126</i>, 14688–14689). A mixture of <b>10</b>/<b>10A</b> decayed within days to give major paramagnetic products [TiH­(C₅Me₅)₂] (<b>11</b>) and singly tucked-in titanocene [Ti­{C₅Me₄(CH₂)}­(C₅Me₅)] (<b>12</b>) and minor diamagnetic <b>5</b> and its so far unknown, less stable isomer [Ti­{C₅Me₄(CH₂)}₂] (<b>10B</b>), identified by NMR spectra and corroborated by DFT calculations. Solid <b>3</b> eliminated ethene at only 80 °C, leaving titanocene <b>14</b>, whereas compound <b>4</b> sublimed at 135 °C mostly without decomposition. Cocrystals of <b>10</b> with [TiCl­(C₅Me₅)₂] (1:2) (<b>10C</b>) afforded an X-ray single-crystal structure with linear geometry for <b>10</b>. The ethene complexes <b>1</b>–<b>4</b> differed in their reactivity toward but-2-yne: compounds <b>1</b> and <b>4</b> yielded the respective [Ti­(IV)­(η¹: η¹-CH₂CH₂CMeCMe)­(Cp′)₂] 2,3-dimethyltitanacyclopent-2-ene complexes <b>15</b> and <b>16</b>, whereas <b>2</b> and <b>3</b> replaced ethene with but-2-yne, affording the [Ti­(II)­(η²-MeCCMe)­(Cp′)₂] complexes <b>17</b> and <b>18</b>, respectively. Crystal structures of <b>2</b>, <b>4</b>, <b>10C</b>, <b>15</b>, <b>17</b>, and <b>18</b> have been determined by X-ray crystallography

Amino Group Functionalized N‑Heterocyclic 1,2,4-Triazole-Derived Carbenes: Structural Diversity of Rhodium(I) Complexes

The synthesis of the amino group functionalized NHC precursor 1-<i>tert</i>-butyl-4-(2-((dimethylamino)­methyl)-phenyl)-3-phenyl-4<i>H</i>-1,2,4-triazol-1-ium perchlorate has been developed. The generation and bonding properties of the NHC ligand have been evaluated in reactions toward three Rh­(I) complexes[Rh­(COD)­Cl]₂, [Rh­(cyclooctene)₂Cl]₂, and [Rh­(ethylene)₂Cl]₂, respectively. For the first complex, [(NHC)­RhCl­(COD)], the coordination of the dangling amino group was not observed because of the fully occupied coordination neighborhood of the Rh atom. On the other hand, in the case of [(NHC)­RhCl­(ethylene)], [(NHC)­RhCl­(cyclooctene)], [(NHC)­Rh­(COD)]⁺[BF₄]⁻, and [(NHC)­RhCl­(CO)] a strong intramolecular coordination of the amino nitrogen atom was revealed, thus forming the unusual seven-membered diazametallacycle. All of the products of these reactions were characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction analysis

Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

Titanocene hydride [Cp*₂TiH] (Cp* = η⁵-C₅Me₅) (<b>1</b>) readily inserts simple internal alkynes R¹CCR² into its Ti–H bond, yielding titanocene alkenyl Ti­(III) compounds of two structural types. The less sterically congested products [Cp*₂Ti­(R¹CCHR²)] (<b>2a</b>–<b>e</b>) contain a σ¹-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R¹ = SiMe₃; R² = SiMe₃, <b>4a</b>; CMe₃, <b>4b</b>; and Ph, <b>4c</b>) possess a remarkable Ti–H agostic bond of the σ¹-bonded alkenyl group. This feature is consistent with solution EPR spectra of <b>4a</b>–<b>4c</b> showing a doublet due to coupling of the hydrogen nucleus with the Ti­(III) d¹ electron. Compound <b>1</b> reacts with one molar equivalent of conjugated buta-1,3-diynes (RCC)₂ to give η³-butenyne complexes (R = SiMe₃, <b>5a</b>; CMe₃, <b>5b</b>). The Ti­(III) complexes <b>2a</b>–<b>2e</b> and <b>5a</b> and <b>5b</b> were oxidatively chlorinated with PbCl₂ to give Ti­(IV) chloro-alkenyl complexes [Cp*₂TiCl­(R¹CCHR²)] <b>3a</b>–<b>3e</b> and chloro-alkenynes <b>6a</b> and <b>6b</b>, respectively. ¹H and ¹³C NMR spectra of <b>3a</b>–<b>3e</b> and <b>6a</b> and <b>6b</b> revealed that these compounds form equilibria of two atropisomers differing by the <i>anti</i>- and <i>syn</i>-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (<b>a</b>) and (<b>b</b>), respectively. Compound <b>1</b> reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (<b>7</b>) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (<b>8</b>). In toluene-<i>d</i>₈ solutions <b>7</b> dissociated at 80 °C and <b>8</b> at room temperature to give [Cp*Ti­(C₅Me₄CH₂)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti­(C₅Me₄CH₂)]. Compound <b>1</b> was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for <b>3d</b>(<b>a</b>), <b>3e</b>(<b>a</b>), <b>4a</b>–<b>4c</b>, <b>5a</b>, <b>6b</b>, and <b>7</b>

Synthesis and Structure of Titanium(III) Bis(decamethyltitanocene) Oxide

Bis­(decamethyltitanocene) oxide, [(Cp*₂Ti)₂O] (<b>1</b>; Cp* = η⁵-C₅Me₅) has been obtained as a yellow crystalline solid after reacting equimolar amounts of the hydride [Cp*₂TiH] and the hydroxide [Cp*₂Ti­(OH)]. The solid-state structure of <b>1</b> revealed a linear Ti–O–Ti arrangement and a mutual, nearly perpendicular orientation of the bent-sandwich titanocene moieties; the length of both Ti–O bonds amounted to 1.9080(3) Å. A unique structural feature was a close-to-eclipsed conformation of the cyclopentadienyl ligands, attributed to the high steric congestion of <b>1</b>. The molecule in toluene glass exhibited a triplet state EPR spectrum of rhombic symmetry, having zero field splitting <i>D</i> = 0.02159 cm^–1 and <i>E</i> = 0.00230 cm^–1. The ¹H NMR spectrum of <b>1</b> in toluene-<i>d</i>₈ displays a paramagnetic resonance at δ 4.3 ppm (Δν_1/2 ≈ 270 Hz). Compound <b>1</b> reacts with 1 molar equiv of water to give [Cp*₂Ti­(OH)]. In CD₂Cl₂, <b>1</b> is oxidized to yield the major product [(Cp*TiCl₂)₂O] and minor product [{Cp*Ti­(Cl)­O}₃]

Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

Titanocene hydride [Cp*₂TiH] (Cp* = η⁵-C₅Me₅) (<b>1</b>) readily inserts simple internal alkynes R¹CCR² into its Ti–H bond, yielding titanocene alkenyl Ti­(III) compounds of two structural types. The less sterically congested products [Cp*₂Ti­(R¹CCHR²)] (<b>2a</b>–<b>e</b>) contain a σ¹-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R¹ = SiMe₃; R² = SiMe₃, <b>4a</b>; CMe₃, <b>4b</b>; and Ph, <b>4c</b>) possess a remarkable Ti–H agostic bond of the σ¹-bonded alkenyl group. This feature is consistent with solution EPR spectra of <b>4a</b>–<b>4c</b> showing a doublet due to coupling of the hydrogen nucleus with the Ti­(III) d¹ electron. Compound <b>1</b> reacts with one molar equivalent of conjugated buta-1,3-diynes (RCC)₂ to give η³-butenyne complexes (R = SiMe₃, <b>5a</b>; CMe₃, <b>5b</b>). The Ti­(III) complexes <b>2a</b>–<b>2e</b> and <b>5a</b> and <b>5b</b> were oxidatively chlorinated with PbCl₂ to give Ti­(IV) chloro-alkenyl complexes [Cp*₂TiCl­(R¹CCHR²)] <b>3a</b>–<b>3e</b> and chloro-alkenynes <b>6a</b> and <b>6b</b>, respectively. ¹H and ¹³C NMR spectra of <b>3a</b>–<b>3e</b> and <b>6a</b> and <b>6b</b> revealed that these compounds form equilibria of two atropisomers differing by the <i>anti</i>- and <i>syn</i>-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (<b>a</b>) and (<b>b</b>), respectively. Compound <b>1</b> reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (<b>7</b>) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (<b>8</b>). In toluene-<i>d</i>₈ solutions <b>7</b> dissociated at 80 °C and <b>8</b> at room temperature to give [Cp*Ti­(C₅Me₄CH₂)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti­(C₅Me₄CH₂)]. Compound <b>1</b> was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for <b>3d</b>(<b>a</b>), <b>3e</b>(<b>a</b>), <b>4a</b>–<b>4c</b>, <b>5a</b>, <b>6b</b>, and <b>7</b>

Reactivity of a Titanocene Pendant Si–H Group toward Alcohols. Unexpected Formation of Siloxanes from the Reaction of Hydrosilanes and Ph₃COH Catalyzed by B(C₆F₅)₃

The reaction of [Cp­(η⁵-C₅H₄CH₂SiMe₂H)­TiCl₂] (<b>1</b>; Cp = η⁵-C₅H₅) and methanol in the presence of catalytic amounts of B­(C₆F₅)₃ afforded a complex with a pendant silyl ether group, [Cp­(η⁵-C₅H₄CH₂SiMe₂OMe)­TiCl₂] (<b>2</b>), in good yield. The analogous reaction of <b>1</b> and Ph₃COH resulted in the unexpected formation of [CpTiCl₂{μ-η⁵:η⁵-(C₅H₄)­CH₂SiMe₂OSiMe₂CH₂(C₅H₄)}­TiCl₂Cp] (<b>4</b>). The formation of siloxanes from the reaction of 2 equiv of hydrosilane with Ph₃COH mediated by B­(C₆F₅)₃ has a general applicability and proceeds in two consecutive steps: (i) transfer of the hydroxyl group from the trityl moiety to the silicon atom and (ii) silylation of the silanol formed in situ with the second equivalent of hydrosilane. The different hydrosilane reactivity toward Ph₃COH in comparison with other alcohols can be attributed to the easy generation of the borate salt [Ph₃C]⁺[(C₆F₅)₃B­(μ-OH)­B­(C₆F₅)₃]⁻ (<b>5</b>) under catalytic conditions. The intramolecular Si–H and Ti–Cl exchange in <b>1</b> is catalyzed by B­(C₆F₅)₃ in the presence of no alcohol. This process affords presumably a transient titanocene hydrido chloride, which is either chlorinated to give [Cp­(η⁵-C₅H₄CH₂SiMe₂Cl)­TiCl₂] (<b>3</b>) in CD₂Cl₂ or decomposes into several paramagnetic Ti­(III) species in toluene-<i>d</i>₈. Complex <b>3</b> was independently synthesized from <b>1</b> and Ph₃CCl in a good yield

Reactivity of Tin(II) Guanidinate with 1,2- and 1,3-Diones: Oxidative Cycloaddition or Ligand Substitution ?

A series of tin­(IV) guanidinates were prepared by a (4+1) oxidative cycloaddition of four 1,2-diones (3,5-di-<i>tert</i>-butyl-<i>o</i>-benzoquinone, 3,4,5,6-tetrachloro-1,2-benzoquinone, 9,10-phenanthrenedione, 1,2-diphenylethanedione) or by an oxidative addition of a C–Br bond (from 2-bromo-1,3-diphenylpropane-1,3-dione followed by rearrangement) and a Cl–Cl bond (Cl₂ generated from (dichloro-λ³-iodanyl)­benzene) with {<i>p</i>Tol-NC­[N­(SiMe₃)₂]­N-<i>p</i>Tol}₂Sn (<b>1</b>). The reactivity of five pentane-1,3-diones and dimethyl malonate with compound <b>1</b> was assessed on the basis of the effect of 1,3-diones on the reaction mechanism in comparison with 1,2-diones. In contrast with oxidation reactions observed for compounds containing conjugated CO bonds, the reactions of the tin­(II) guanidinate with 1,3-diones revealed a high ability for ligand substitution. All the tin compounds prepared were characterized, and ligand substitution reactions were monitored using ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The molecular structures of one tin­(II) and five tin­(IV) guanidinato complexes investigated were determined by X-ray diffraction. All tin­(IV) compounds display six- or seven-coordination. The UV–vis absorption spectra were recorded and simulated by TDDFT methods in order to get insight into the origin of the nontypical colors of the target tin­(IV) diolato-guanidinates and their keto-functionalized precursors

Oxidative Additions of Homoleptic Tin(II) Amidinate

Seven tin­(IV) amidinates were prepared and isolated from the reactions of tin­(II) bisamidinate [Cy–NC­(<i>n</i>Bu)­N–Cy]₂Sn with a series of various 1,2-diones ((4 + 1) oxidative cycloaddition mechanism) and chlorine/oxygen molecules, respectively. The ligand substitution effect of (non)­symmetric 1,3-diones to starting stannylene as well as intermolecular CO₂ activation via prepared dimeric stannoxane is also reported. All the prepared tin containing compounds as well as ligand substitution reactions were investigated by the multinuclear NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopic techniques. Molecular structures of one tin­(II) and seven tin­(IV) amidinates investigated were determined by X-ray diffractions and also evaluated by DFT methods. The UV–vis absorption spectra of all desired colored tin­(IV) diolates and its diketo precursors were recorded and simulated by TD-DFT methods