A neutron diffraction study of bis(cyclopentadienyl)(methyl)(methylene)tantalum(V) at 15 K

Takusagawa, Fusao; Koetzle, T. F.; Sharp, Paul R.; Schrock, Richard R.

doi:10.1107/s0108270187010527

Cited by 6 publications

(2 citation statements)

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“…(1) The Ta−CH 2 distances are slightly longer than a typical Ta−C σ bond (cf. the Ta−CH 3 distance of 2.268(1) Å in Cp 2 Ta(CH 2 )CH 3 or the Ta−CH 2 R distance of 2.29(1) Å in Cp 2 Ta(η 2 -C 8 H 8 )CH 2 CH 2 CH 3 ), as would be expected upon approaching an η 2 bonding mode (the Ta−C distances to the η 2 -C 8 H 8 ligand in the latter complex above are 2.33(2) and 2.32(1) Å). (2) The acute Ta−CH 2 −B bond angles (87.3(3)° and 87.6(3)° for 4 and 5 , respectively) suggest a Ta−B interaction and are markedly different from the analogous angles in I (125.1(3)°) and II (110.8(3)°), which are more consonant with sp 3 hybridization at carbon.…”

Section: Resultsmentioning

confidence: 75%

Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes

et al. 2001

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plus 1 equiv of H 3 CB(C 6 F 5 ) 2 . The pathway to 1 involves stepwise attack of borane first at the methylene group, followed by attack at the methyl group, which undergoes alkyl/hydride exchange with the second equivalent of HB(C 6 F 5 ) 2 . The product of HB(C 6 F 5 ) 2 addition to the methylene ligand, methyl hydride complex Cp 2 -Ta(CH 2 B(C 6 F 5 ) 2 )(µ-H)(CH 3 ), 2, can be intercepted by carrying out the reaction in hexane at low temperature, a medium in which it is nearly totally insoluble. This complex eliminates methane at higher temperatures in a first-order decomposition process (∆H q ) 20.4(5) kcal mol -1 and ∆S q ) -2.0(2) cal mol -1 K -1 ). The product, a borataalkene complex formulated as Cp 2 Ta[CH 2 B(C 6 F 5 ) 2 ], 3, is unstable and cannot be isolated. DFT calculations support its formulation and show that it is present as a singlet/triplet mixture, accounting for the observed paramagnetism of solutions containing 3. While 3 cannot be isolated or spectroscopically probed, it can be trapped if 2 is allowed to decompose in the presence of t BuNC or CO, giving the products Cp 2 Ta[η 2 -CH 2 B(C 6 F 5 ) 2 ](L) (L ) t BuNC, 4; CO, 5). Both of these compounds have been structurally characterized, and the structural and spectroscopic data for these compounds support an η 2 bonding description for the borataalkene ligand which is reminiscent of the commonly held Dewar-Chatt-Duncanson model for alkene bonding to transition metals. DFT calculations on 5 and the model complex Cp 2 Ta[η 2 -CH 2 BH 2 ](CO), 6, provide further support for this description. The facile conversion of this ligand from an η 2 to an η 1 bonding mode is proposed to account for some H/D exchange processes observed in both dihydride 1 and methyl hydride complex 2. Plausible mechanisms for both of these processes are proposed.

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Section: Resultsmentioning

confidence: 75%

Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes

et al. 2001

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“…Complexes bearing the simplest of carbenes, a methylidene “CH 2 ”, however, remain considerably scarce, owing to the high reactivity of M=CH 2 unit . This scarcity persists despite the pioneering discovery of the first methylidene complex, [Cp 2 Ta=CH 2 (CH 3 )] by Schrock nearly half a century ago . Coincidently, in 1974, the first Ti methylidene synthon, the Tebbe reagent [Cp 2 Ti(μ-CH 2 )(μ-Cl)Al(CH 3 ) 2 ], was also documented and then reported in the literature .…”

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A Vanadium Methylidene

Senthil,

Fehn,

Gau

et al. 2024

J. Am. Chem. Soc.

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Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH2)] (PNP = N[2-P i Pr2-4-methylphenyl]−, Ar = 2,6- i Pr2C6H3), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH3)] or [(PNP)V(=NAr)(CH3)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, H2CPPh3. Structural and spectroscopic analysis, including 13C enriched labeling of the methylidene ligand, unequivocally confirmed the terminal nature of a rare 3d methylidene complex, featuring a V=CH2 bond distance of 1.908(2) Å and a highly downfield 13C NMR spectral shift at 298 ppm. In the absence of the ylide, intermediate [(PNP)V=NAr] activates dinitrogen to form an end-on bridging N2 complex, [(PNP)V(=NAr)]2(μ2-η1:η1-N2), having a singlet ground state. Complex [(PNP)V(=NAr)(=CH2)] reacts with H3COTf to form [(PNP)V(=NAr)(OTf)], accompanied by the release of ethylene as evidenced by 1H NMR spectroscopy, and reactivity studies suggest a β-hydride elimination pathway.

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(Alkyl)‐ and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes

et al. 2006

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Alkylation of [TaCp*Cl4] (Cp* = η5‐C5Me5) with 3 equiv. of MgCl(CH2SiMe3) gives the chloridotris(trimethylsilylmethyl) complex [TaCp*Cl(CH2SiMe3)3] (1). TaCp*Cl2Me2 reacts with 2 equiv. of LiR (R = CH2Ph, CH2SiMe3) to give the mixed alkyl derivatives [TaCp*Me2R2] (R = CH2Ph, 2; CH2SiMe3, 3). The dimethyldineopentyl complex [TaCp*Me2(CH2CMe3)2] (4) was obtained by reaction of TaCp*Cl2(CH2CMe3)2 with 2 equiv. of LiMe. The treatment of a toluene solution of TaCp*Cl2Me2 with 2 equiv. of neophyllithium in a standard vacuum line gave a mixture of three compounds, [{TaCp*Me2(CH2CMe2Ph)}2(μ‐O)] (5), [TaCp*Me2(CH2CMe2–o‐C6H4‐κ2C,C)] (6) and [TaCp*Me(CH2CMe2Ph)(CH2)] (7), which were identified by NMR spectroscopy. However, when the reaction was carried out under rigorously anhydrous conditions, only complexes 6 and 7 were isolated. A chlorido(trimethylsilylmethyl)(trimethylsilylmethylidene) complex [TaCp*Cl(CH2SiMe3)(CHSiMe3)] (8) was prepared by heating 1 at 60 °C, or by leaving it at room temperature for a long time. A 3:2 (9/10) mixture of [TaCp*MeR(CHSiMe3)] (R = CH2SiMe3, 9; Me, 10) was obtained by thermal treatment of 3, which was accompanied by the evolution of CH4 and SiMe4. However, irradiation of a [D6]benzene solution of 3 with a sun lamp gave a mixture of 9 and [TaCp*(CH2SiMe3)R(CH2)] (R = Me, 11; CH2SiMe3, 12) in a 2:1:1 (9/11/12) ratio. When a [D6]benzene solution of 4 was heated at 60 °C, a mixture of the (alkyl)(neopentylidene) derivatives [TaCp*MeR(CHCMe3)] (R = Me, 13; CH2CMe3, 14) in a 4:1 (13/14) ratio was detected by NMR spectroscopy, while irradiation with a sun lamp produced a mixture ofalkylidene complexes [TaCp*(CH2CMe3)R(CH2)] (R = Me, 15; CH2CMe3, 16) in a 3:1 (15/16) ratio. On the other hand, the alkylation of TaCp*Cl2(CH2CMe3)2 with 2 equiv. of LiCH2SiMe3 gave the (alkyl)(alkylidene) complex [TaCp*(CH2CMe3)(CH2SiMe3)(CHCMe3)] (17) with the elimination of SiMe4, whereas the treatment of TaCp*Cl2(CH2SiMe3)2 with the appropriate reagent gave [TaCp*(CH2R)(CH2SiMe3)(CHR′)] (R = R′ = Ph, 18; R = CMe2Ph, R′ = SiMe3, 19) with the elimination of SiMe4 and CMe3Ph, respectively. All compounds were studied by IR and NMR spectroscopy, and the molecular structures of complexes 1, 4 and 5 were determined by X‐ray diffraction methods. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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A neutron diffraction study of bis(cyclopentadienyl)(methyl)(methylene)tantalum(V) at 15 K

Cited by 6 publications

References 6 publications

Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes

Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes

A Vanadium Methylidene

(Alkyl)‐ and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes

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A neutron diffraction study of bis(cyclopentadienyl)(methyl)(methylene)tantalum(V) at 15 K

Cited by 6 publications

References 6 publications

Reactions of Bis(pentafluorophenyl)borane with Cp2Ta(CH2)CH3: Generation and Trapping of Tantalocene Borataalkene Complexes

Reactions of Bis(pentafluorophenyl)borane with Cp2Ta(CH2)CH3: Generation and Trapping of Tantalocene Borataalkene Complexes

A Vanadium Methylidene

(Alkyl)‐ and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes

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Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes

Reactions of Bis(pentafluorophenyl)borane with Cp₂Ta(CH₂)CH₃: Generation and Trapping of Tantalocene Borataalkene Complexes