Insertion of CO and CNR into Tantalum−Methyl Bonds of Imido(pentamethylcyclopentadienyl)tantalum Complexes. X-ray Crystal Structures of [TaCp*(NR)Me{η²-C(Me)NR}] and [TaCp*Cl(O){η²-C(Me)NR}] (R = 2,6-Me₂C₆H₃)

Abstract

TaCp*Cl 2 {N(2,6-Me 2 C 6 H 3 )}] reacts with 2 equiv of LiMe at -78 °C to give the imido dimethyl complex TaCp*Me 2 {N(2,6-Me 2 C 6 H 3 )} (1) in almost quantitative yield, whereas the monomethyl imido derivatives [TaCp*MeX{N(2,6-Me 2 C 6 H 3 )}] (X ) Cl (2), OC 6 H 3 Me 2 (3)) can be prepared by addition of HX (X ) Cl, OC 6 H 3 Me 2 ) to toluene solutions of [TaCp*Me-(NR){NR(CMedCMe 2 )}] (R ) 2,6-Me 2 C 6 H 3 ) with elimination of the corresponding imine RNdCMeCHMe 2 . Complex 1 reacts with CO to give the dinuclear ene diolate complex [TaCp*{N(2,6-Me 2 C 6 H 3 )Me}] 2 {µ-η 2 -OC(Me)dC(Me)O} (5) via intermolecular coupling between two acyl carbon atoms of the intermediate η 2 -acyl complex TaCp*Me{N(2,6-Me 2 C 6 H 3 )}{η 2 -C(Me)dO} ( 4). However, when the same reaction was carried out with the chloro imido methyl derivative 2, the unexpected oxo 7) was obtained via the barely stable intermediate η 2 -acyl complex [TaCp*Cl-{N(2,6-Me 2 C 6 H 3 )}{η 2 -C(Me)dO}] (6). The analogous reaction of [TaCp*Cl 2 Me 2 ] with CO leads to the formation of the dichloro oxotantalacyclopropane complex [TaCp*Cl 2 (η 2 -CMe 2 O)] ( 8), but the acyl intermediate species was not observed. Similarly, the azatantalacyclopropane complexes [TaCp*XMe(η 2 CMe 2 -NR)] react with 1 equiv of CO to form the stable enolate derivatives [TaCp*X(NR){OC(Me)dCMe 2 }] (X ) Cl (9), Me (10); R ) 2,6-Me 2 C 6 H 3 ). The stable 18-electron imido η 2 -iminoacyl derivatives [TaCp*X(NR){η 2 -C(Me)dNR}] (X ) Me (11), Cl (12), OC(Me)dCMe 2 (13); R ) 2,6-Me 2 C 6 H 3 ) are formed when the isocyanide RNC (1 equiv) is added to toluene solutions of the imido complexes 1, 2, and 10, respectively. All compounds were characterized by IR and NMR ( 1 H and 13 C), and the molecular structures of 7 and 11 were studied by X-ray diffraction methods.

η2‐Iminoacyl and η2‐Acyl Monocyclopentadienyl Tantalum Complexes Bearing Oxo and Oxo‐Borane Ligands

“…It was observed that for monocyclopentadienyl imido tantalum derivatives addition of a second CNR molecule into the iminoacyl compounds [TaCp*(NR)X{η 2 -C(Me)=NR}] (R = 2,6-Me 2 C 6 H 3 , tBu; X = Cl, Me) resulted in differing behaviours depending on the R group of the imido ligand. No reaction was found for R = 2,6-Me 2 C 6 H 3 , [10] whereas a second insertion occurred for R = tBu. [20] Conversely, the imido complexes [TaCp*MeX(NR)] (R = 2,6-Me 2 C 6 H 3 , tBu; X = Cl, Me) reacted with CO to give the dinuclear compound [TaCp*(NR)Me] 2 {µ-η 2 -OC-(Me)=C(Me)O} for X = Me [10] and one of the few mononuclear derivatives [TaCp*Cl(O){η 2 -C(Me)=NR}] containing a terminal tantalum-oxo double bond for X = Cl.…”

“…[1] For a given metal atom, the stability and further evolution of these compounds are determined by the nature of the ancillary ligands. Many reaction pathways may follow to give a broad variety of products: [1] (a) migratory insertion of a second alkyl or aryl group to give η 2 -imine or η 2 -ketene complexes; [2][3][4][5] (b) intra-or intermolecular coupling of iminoacyl or acyl units affording diaza-or dioxobutene complexes; [6,7] (c) transfer of the NR or O moieties to the metal centre; [8][9][10][11] (d) insertion of a second CNR [12][13][14][15][16] or CO [17] molecule into the new M-C bond formed after the first insertion process and (e) hydrogen migration. [18,19] We reported the results of our studies on the insertion reactions of CNR into the Ta-C(methyl) bond of monocyclopentadienyl complexes of the type [TaCp*Cl x Me 4-x ] [8][9][10] for which processes (a) and (c) were observed.…”

“…Similar reactions with imido compounds of the type [TaCp*MeX(NtBu)] (X = Cl, Me, OR, NHtBu) gave . [20] With regard to the CO insertion reactions, double migration of the alkyl group [process (a)] was observed for [TaCp*Cl 2 Me 2 ], [10] whereas the coupling of the acyl groups [process (b)] occurred for [TaCp*Me 2 (NR)] (R = 2,6-Me 2 C 6 H 3 ) to give the dinuclear compound [TaCp*(NR)Me] 2 {µ-η 2 -OC(Me)=C(Me)O}, [10] and ligand exchange [process (c)] for complexes [TaCp*ClMe(NR)] (R = 2,6-Me 2 C 6 H 3 , [10] tBu) [11] led to the oxo compounds [TaCp*Cl(O){η 2 -C(Me)=NR}]. Furthermore, the η 2 -(methyl)acyl complexes remained elusive and were only detected as intermediates by NMR spectroscopy, whereas the related η 2 -iminoacyl complexes are stable.…”

“…[20] Conversely, the imido complexes [TaCp*MeX(NR)] (R = 2,6-Me 2 C 6 H 3 , tBu; X = Cl, Me) reacted with CO to give the dinuclear compound [TaCp*(NR)Me] 2 {µ-η 2 -OC-(Me)=C(Me)O} for X = Me [10] and one of the few mononuclear derivatives [TaCp*Cl(O){η 2 -C(Me)=NR}] containing a terminal tantalum-oxo double bond for X = Cl. [10,11] The versatility and potential applications of all these results determined by the R and X substituents of the imido complexes [TaCp*MeX(NR)] led us to extend our studies to similar insertion reactions of CNR and CO into the Taalkyl bonds of the related oxo-borane compounds [TaCp*X 2 {O·B(C 6 F 5 ) 3 }] that have recently been isolated. [21] Results and Discussion [21][22][23][24][25][26][27][28][29][30][31] and the 1 H NMR spectra with the monosubstitution of only one of the alkyl ligands.…”

Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using α,β‐Unsaturated Carbonyl Ligands

“…[36][37][38][39][40] However, the insertion reaction was not observed, rather displacement of the coordinated MMA and MA ligands (Scheme 4) gave the carbonyl derivatives [NbCp R Cl 2 (CO) 2 ] 2 [Cp R = C 5 H 4 SiMe 2 Cl (9), Cp R = C 5 H 4 SiMe 3 (10)] for the reaction with CO, although we could not characterize the corresponding organometallic species resulting from the reaction with CNAr (Scheme 4). Therefore, the formally Nb V starting compounds 2-3 undergo a reductive decoupling to the Nb III derivatives.…”