Abstract:The reactivity of [Mo(NPh)Cl 2 (o-(Me 3 SiN) 2 C 6 H 4 ‚THF)] (1) with β-hydrogen-containing Grignard reagents was examined. Reaction of 1 with 2 equiv of RMgCl (R ) CH 2 CH 2 Ph, CH 2 CH 2 CH 3 , CH 2 CH(CH 3 ) 2 , CH 2 CH 2 CH 2 CH 3 , and CH(CH 3 )CH 2 CH 3 ) gave Mo(IV) olefin complexes of the type [Mo(NPh)(η 2 -olefin)(o-(Me 3 SiN) 2 C 6 H 4 )] (olefin ) styrene (2a), propene (2b), isobutene (2c), 1-butene (2d), and 2-butene (2e)). The crystal structure of 2a is reported. Reaction of 1 with 2 equiv of eth… Show more
“…This is consistent with the general observation of increasing metal−ligand multiple-bond stability on going from group 4 to the middle transition elements . Notwithstanding this general observation, Legzdins 26,27 for example has shown that certain tungsten imides undergo cycloaddition reactions with isocyanates, while Jensen and Børve have suggested on the basis of DFT calculations that bis(imido)chromium alkyl cations might undergo cycloaddition reactions with ethylene at a CrNR linkage. , On the other hand, the diamide-supported imido molybdenum and tungsten complexes studied comprehensively by Boncella show no apparent reactions at the MNR bonds. − 1 Previously Reported Transition Metal Imido Compounds Containing the N 2 N P y Ligand …”
Section: Introductionsupporting
confidence: 72%
“…28,29 On the other hand, the diamide-supported imido molybdenum and tungsten complexes studied comprehensively by Boncella show no apparent reactions at the MdNR bonds. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] We recently described the synthesis and structure of the six-coordinate imidotungsten dimethyl compound W(NPh)(N 2 N py )Me 2 (1) (type III in Chart 1) and its isotopomers W(NPh)(N 2 N py )(CD 3 ) 2 (1-d 6 ) and W(NPh)-(N 2 N py )( 13 CH 3 ) 2 (1-13 C 2 ). 3 Neither 1 nor its dichloride analogue W(NPh)(N 2 N py )Cl 2 shows any well-defined reactivity with unsaturated substrates.…”
Me(L)] + (L ) MeCN (4 + ) or THF (5 + )). For comparison the neutral tantalum derivatives Ta(N t Bu)(N 2 N py )R (R ) Me (6) or η 1 -allyl (7)) were synthesized by reaction of Ta(N t Bu)(N 2 N py )Cl(py) with MeLi or (allyl)MgCl. Compound 6, valence isoelectronic with 2 + , was crystallographically characterized. Although both 2 + and 6 possess trigonal bipyramidal geometries at the metal, the methyl ligand in 2 + lies in the equatorial plane (with NPh trans to pyridyl), whereas in 6 the opposite arrangement of methyl and imido ligands is found. Reaction of 1 with 0.5 equiv of BAr F 3 gave the fluxional Me-bridged cation [{W(NPh)(N 2 N py )Me} 2 (µ-Me)] + (8 + ); 8 + was also formed by direct reaction of 1 with 2 + . The methyl cation 2 + underwent facile methyl group exchange with Cp 2 ZrMe 2 and ZnMe 2 as established by spin saturation transfer and deuterium labeling studies. Although a stable intermediate was not spectroscopically observed for either reaction, for the latter case a likely adduct was identified by DFT calculations on a model system and features coordination of Zn to the imido nitrogen and a Zn-Me‚‚‚W interaction. Reaction of 2 + with AlMe 3 formed [W{MeC(2-C 5 H 4 NAlMe)(CHNSiMe 3 )(CH 2 NSiMe 3 )}(µ-NPh)Me 2 ] + (9 + ) and CH 4 by deprotonation of a CH 2 linkage of N 2 N py . DFT (B3PW91) calculations on model systems of the type M(NR){HC(2-C 5 H 4 N)(CH 2 SiH 3 ) 2 }(X) (X ) Cl, Me) showed that there is an unambiguous electronic preference for the imido ligand to lie trans to the pyridyl nitrogen. This geometry allows optimal π-donation from the imido and the amido nitrogen atoms. Inclusion of the steric bulk of the SiMe 3 groups and the R group (Ph or t Bu) on the imido ligand through ONIOM(B3PW91:UFF) calculations showed that the underlying electronic preference for the imido ligand to be trans to pyridyl can be reversed because of increased steric repulsions between the imido and amido N-substituents in this isomer. These cause a misdirection of the amido lone pair π-donation, which in turn destabilizes the metal-imido ligand π-bonding.
“…This is consistent with the general observation of increasing metal−ligand multiple-bond stability on going from group 4 to the middle transition elements . Notwithstanding this general observation, Legzdins 26,27 for example has shown that certain tungsten imides undergo cycloaddition reactions with isocyanates, while Jensen and Børve have suggested on the basis of DFT calculations that bis(imido)chromium alkyl cations might undergo cycloaddition reactions with ethylene at a CrNR linkage. , On the other hand, the diamide-supported imido molybdenum and tungsten complexes studied comprehensively by Boncella show no apparent reactions at the MNR bonds. − 1 Previously Reported Transition Metal Imido Compounds Containing the N 2 N P y Ligand …”
Section: Introductionsupporting
confidence: 72%
“…28,29 On the other hand, the diamide-supported imido molybdenum and tungsten complexes studied comprehensively by Boncella show no apparent reactions at the MdNR bonds. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] We recently described the synthesis and structure of the six-coordinate imidotungsten dimethyl compound W(NPh)(N 2 N py )Me 2 (1) (type III in Chart 1) and its isotopomers W(NPh)(N 2 N py )(CD 3 ) 2 (1-d 6 ) and W(NPh)-(N 2 N py )( 13 CH 3 ) 2 (1-13 C 2 ). 3 Neither 1 nor its dichloride analogue W(NPh)(N 2 N py )Cl 2 shows any well-defined reactivity with unsaturated substrates.…”
Me(L)] + (L ) MeCN (4 + ) or THF (5 + )). For comparison the neutral tantalum derivatives Ta(N t Bu)(N 2 N py )R (R ) Me (6) or η 1 -allyl (7)) were synthesized by reaction of Ta(N t Bu)(N 2 N py )Cl(py) with MeLi or (allyl)MgCl. Compound 6, valence isoelectronic with 2 + , was crystallographically characterized. Although both 2 + and 6 possess trigonal bipyramidal geometries at the metal, the methyl ligand in 2 + lies in the equatorial plane (with NPh trans to pyridyl), whereas in 6 the opposite arrangement of methyl and imido ligands is found. Reaction of 1 with 0.5 equiv of BAr F 3 gave the fluxional Me-bridged cation [{W(NPh)(N 2 N py )Me} 2 (µ-Me)] + (8 + ); 8 + was also formed by direct reaction of 1 with 2 + . The methyl cation 2 + underwent facile methyl group exchange with Cp 2 ZrMe 2 and ZnMe 2 as established by spin saturation transfer and deuterium labeling studies. Although a stable intermediate was not spectroscopically observed for either reaction, for the latter case a likely adduct was identified by DFT calculations on a model system and features coordination of Zn to the imido nitrogen and a Zn-Me‚‚‚W interaction. Reaction of 2 + with AlMe 3 formed [W{MeC(2-C 5 H 4 NAlMe)(CHNSiMe 3 )(CH 2 NSiMe 3 )}(µ-NPh)Me 2 ] + (9 + ) and CH 4 by deprotonation of a CH 2 linkage of N 2 N py . DFT (B3PW91) calculations on model systems of the type M(NR){HC(2-C 5 H 4 N)(CH 2 SiH 3 ) 2 }(X) (X ) Cl, Me) showed that there is an unambiguous electronic preference for the imido ligand to lie trans to the pyridyl nitrogen. This geometry allows optimal π-donation from the imido and the amido nitrogen atoms. Inclusion of the steric bulk of the SiMe 3 groups and the R group (Ph or t Bu) on the imido ligand through ONIOM(B3PW91:UFF) calculations showed that the underlying electronic preference for the imido ligand to be trans to pyridyl can be reversed because of increased steric repulsions between the imido and amido N-substituents in this isomer. These cause a misdirection of the amido lone pair π-donation, which in turn destabilizes the metal-imido ligand π-bonding.
“…Complexes 1a and 1b were synthesized according to published procedures. 12 A representative synthesis of 2: to a green pentane solution of freshly generated 1b (1.07 g, 2.18 mmol) was added an excess of pyridine (0.51 g, 6.54 mmol). Upon addition of pyridine, 2 precipitated from solution and was isolated by filtration in 90% yield.…”
The compounds [Mo(NPh)(h 2 -olefin){o-(Me 3 SiN) 2 C 6 H 4 }] (olefin = propene 1a or isobutene 1b) react with excess pyridine affording the Mo(IV) bis-pyridine complex, [Mo(N-Ph)(Py) 2 {o-(Me 3 SiN) 2 C 6 H 4 }] 2 which when heated to 90 °C in toluene undergoes a C-N bond cleavage reaction and is converted to 3, a bimetallic molybdenum species; the crystal structures of both 2 and 3 are reported.
“…in A, [8] they are approximately 1.95 Å (Scheme 2). Several molybdenum DAD complexes have been described in the literature, with examples given by B-E. [9][10][11][12] Type B [9] represents a four-electron Lewis base adduct of the diazadiene ligand that is coordinated to a formally sixvalent molybdenum center, which is characterized by perfectly planar N atoms and long Mo-N distances of ca. 2.40 Å, short N-C distances of ca.…”
Section: Molecular Structure Ofmentioning
confidence: 99%
“…However, due to its low-lying π* orbitals, neutral DAD can easily be reduced by more electron-rich metal centers to form the coordinated radical anion [DAD] - [14] and the ene-diamido [DAD] 2-ligands. [1,6,10,11,15,16] Examples of molybdenum complexes with a fully reduced DAD moiety are C [10] and D. [11] The structural parameters of their MN 2 C 2 units are similar to that of the phenylene-1,2-diamido system E [12] (Table 2). Typically, flat [15] and folded [16] ene-diamido units (MN 2 C 2 ) are known.…”
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