Dehydrohalogenation by a Germylene:  Conversion of Carbene Ligands into Carbynes at Ruthenium

Caskey, Stephen R.; Stewart, Michael H.; Ahn, Yi Joon; Johnson, Mark; Kampf, Jeff W.

doi:10.1021/om0508482

Cited by 17 publications

(16 citation statements)

References 21 publications

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“…The identity of 4a was confirmed by independent synthesis from hydride precursors; dihydrogen adduct 5a was characterized by in situ NMR analysis, including T 1(min) measurements. Facile β-elimination from methoxide, discussed in more detail below, disfavors formation of stable bis(alkoxide) or deprotonated carbyne products, as formed in the corresponding reactions of 1a with excess tert -butoxide or phenoxides. − …”

Section: Resultsmentioning

confidence: 99%

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

et al. 2012

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On exposure to NaOMe (≥3 equiv) in CH2Cl2–MeOH at 23 °C, the first-generation Grubbs catalyst RuCl2(PCy3)2(CHPh) (1a) is immediately transformed into the six-coordinate methoxyhydride complexes RuH(OMe)(CO)2(PCy3)2 (4a) and RuH(OMe)(CO)(H2)(PCy3)2 (5a). Complex 5a can be recycled into 4a under conditions conducive to removal of H2. The second-generation catalyst RuCl2(IMes)(PCy3)(CHPh) (1b; IMes = N,N′-bis(mesityl)imidazol-2-ylidene) reacts more slowly, requiring several hours even at 20 equiv of NaOMe, and terminates at five-coordinate RuH(OMe)(CO)(IMes)(PCy3) (3b). Experiments in the presence of added PCy3 reveal that consumption of 1a, but not 1b, proceeds via the four-coordinate intermediate formed by equilibrium loss of phosphine, a function of the lability of the PCy3 ligand at ambient temperatures. The poor accessibility of such an intermediate for 1b at 23 °C retards salt metathesis and inhibits further reaction of 3b. For the bis(PCy3) analogue 3a, fast transformation into 4a is proposed to involve reversible loss of PCy3, coordination of methanol, σ-metathesis of methanol at the hydride site to liberate H2, and β-elimination/decarbonylation of bound methoxide. Competitive uptake of H2 by 3a yields six-coordinate 5a (the dihydrogen adduct of 3a). Independent routes to RuH(OMe)(CO)2(L)(PCy3) (4a/b; a, L = PCy3; b, L = IMes) were developed: these involved sequential transformation of RuHCl(CO)(L)(PCy3) (2a/b) into the bis-carbonyl adducts RuHCl(CO)2(L)(PCy3) (7a/b) under CO, conversion of 7a/b into the more reactive triflates RuH(OTf)(CO)2(L)(PCy3) (8a/b), and reaction of 8a/b with equimolar NaOMe. Dihydride 6b was also prepared, by reaction of 8b with NaH.

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Section: Resultsmentioning

confidence: 99%

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

et al. 2012

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“…We decided to harness the elimination route in order to prepare a number of ruthenium benzylidyne complexes for structural and reactivity studies, particularly in catalytic reactions involving alkyne substrates. Some of these results have been communicated …”

Section: Introductionmentioning

confidence: 91%

Synthesis, Structure, and Reactivity of Four-, Five-, and Six-Coordinate Ruthenium Carbyne Complexes

et al. 2007

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Square-planar carbyne complexes of the form Ru(tCR)(PCy 3 ) 2 X (X ) F, Cl, Br, I, O 3 SCF 3 ) are prepared by net dehydrohalogenation of the Grubbs catalysts Ru(dCHR)(PCy 3 ) 2 Cl 2 followed by substitution of the chloride ligand (when X * Cl). The dehydrohalogenation can be effected in one step (R ) n-Bu, Ph, p-C 6 H 4 Me) by Ge(CH[SiMe 3 ] 2 ) 2 or in two steps via treatment with excess aryloxide such as NaO-p-C 6 H 4 -t-Bu followed by SnCl 2 . The latter route gives greater yields but is more restricted in scope. Addition of HCl (1 equiv) to Ru(tCR)(PCy 3 ) 2 X (X ) Cl, Br, I) affords Ru(dCHR)(PCy 3 ) 2 ClX; those with mixed halide ligand sets undergo rapid halide exchange in solution. Upon treatment with the appropriate oxidant, each Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X complex undergoes two-electron oxidation. Oxidation of Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X (X ) F, Cl, Br, I) by XeF 2 , C 2 Cl 6 , Br 2 , and I 2 , respectively, yields either six-coordinate bis-phosphine complexes Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X 3 (X ) F, Cl) or square-pyramidal mono-phosphine complexes Ru(tC-p-C 6 H 4 Me)(PCy 3 )X 3 (X ) Br, I) depending on the size of the halide ligands. Cationic square-pyramidal complexes of the form [Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X 2 ] + (X ) Cl, I) can be prepared from Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 Cl 3 by chloride abstraction using [Ph 3 C]BF 4 and from Ru(tC-p-C 6 H 4 -Me)(PCy 3 )X 3 by addition of PCy 3 . Hydride addition to Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 Cl 3 yields the carbene complex Ru(dCHR)(PCy 3 ) 2 Cl 2 , whereas fluoride addition affords the carbyne complex Ru(tC-p-C 6 H 4 -Me)(PCy 3 ) 2 Cl 2 F, results with important implications for metathesis of vinyl fluorides. X-ray structures of Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X 2 F (X ) F, Cl), [Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 Cl 2 ]BF 4 , and Ru(tC-p-C 6 H 4 -Me)(PCy 3 )I 3 reveal short RutC bonds in the 1.670(5)-1.714(3) Å range; when two PCy 3 ligands are present, they are mutually trans. The benzylidyne ligands occupy the apical sites in the two squarepyramidal complexes. Of the five-and six-coordinate complexes, only the two fluoride-containing complexes Ru(tC-p-C 6 H 4 Me)(PCy 3 ) 2 X 2 F (X ) F, Cl) display reactivity toward alkynes, serving as alkyne dimerization catalysts.

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“…The DFT calculations in combination with compliance constants lend further support to the view that PC single‐bond strengthening in conjunction with steric relief seems to be one driving force for geminal bond activation/cleavage processes. Although the fate of methylene and its derivatives could not be detected, it is of special interest that dehydroiodination24 is strictly preferred over dediiodination in the reaction of complex 1 and diiodomethane, which is in marked contrast to reactions induced by metals, for example, in the system Zn/CH 2 I 2 23…”

Section: Methodsmentioning

confidence: 99%

Dehydroiodination of Iodo‐ and Diiodomethane by a Transient Phosphinidene Complex

Özbolat¹,

Khan²,

Frantzius³

et al. 2007

Angew Chem Int Ed

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Dedicated to Professor Ulrich Zenneck on the occasion of his 60th birthday Molecular organophosphorus chemistry currently offers a wide variety of different methods of PÀC bond formation, but only a few provide selective PÀC bond cleavage in the absence of any reagents [1] or without valence isomerization.[2]Knowledge about unconventional decomposition pathways, however, can be crucial for the design of stable phosphinebased catalysts. (2)].[4] 3) Branched triorganyl phosphine oxides are known to decompose by carbon-to-oxygen b-H transfer at elevated temperatures, whereas trimethyl or triphenyl derivatives are stable up to around 700 8C [Scheme 1, Eq. (3)].[5] Herein, we report on experimental and theoretical investigations of unprecedented PÀC bondbreaking reactions of acyclic halo(diorgano)phosphine tungsten complexes, which, at the same time, represent novel examples for dehydroiodination reactions of "simple" alkyl iodides.Recently, we studied reactions of the thermally generated electrophilic terminal phosphinidene complex [(CO) 5 WPCH-(SiMe 3 ) 2 ] (2) with alkyl chlorides and bromides. Surprisingly, we observed formation of a dichloro(organo)phosphine complex upon reaction of 2 with carbon tetrachloride [6] (proving the reductive capability of 2) as well as insertion into the C À Br bond by reaction with benzyl bromide to yield a benzyl(bromo)organophosphine complex, the latter being stable under these conditions. [7] To get further insight into such reduction and insertion reactions we decided to treat 2 with a series of C 1 and C 2 alkyl halides. Herein, we report preliminary results using iodo-and diiodomethane.Reaction of 2H-azaphosphirene complex 1 [8] with an excess of iodomethane in toluene at 75 8C yielded three major products: complex 3 by insertion of terminal phosphinidene complex 2 into the CÀI bond of iodomethane, iodo-(organo)phosphine complex 4 by formal "loss" of CH 2 , [9] and {bis(trimethylsilyl)methyl}trimethylphosphonium triiodo(tetracarbonyl)tungstate 5 (Scheme 2). Whereas formation of complex 3 was anticipated, [7] the formation of complex 4 and phosphonium salt 5 was a great surprise. Complex 5 resulted from an oxidation process caused by methyl iodide, in which oxidative addition of methyl iodide to the tungsten center might be the primary step. According to 31 P NMR spectroscopic monitoring of the reaction the amount of 3 (and 4) constantly increased within the first 55 min, but then 3 decreased in favor of 5, whereas 4 remained approximately constant. Further studies on the reaction course revealed that toluene is not the proton source in the formation of complex 4, as evidenced by the reaction in deuterated toluene, which yielded again 4 and not the D isotopomer. Scheme 1. Examples of thermal PÀC bond-cleavage methods.

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Dehydrohalogenation by a Germylene: Conversion of Carbene Ligands into Carbynes at Ruthenium

Cited by 17 publications

References 21 publications

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

Synthesis, Structure, and Reactivity of Four-, Five-, and Six-Coordinate Ruthenium Carbyne Complexes

Dehydroiodination of Iodo‐ and Diiodomethane by a Transient Phosphinidene Complex

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