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The synthesis and reactivity of ring-substituted cycloheptatrienyl complexes of the chromium triad metals
Başlık:
The synthesis and reactivity of ring-substituted cycloheptatrienyl complexes of the chromium triad metals
Yazar:
Roberts, Andrew, author.
ISBN:
9780355977950
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (216 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
Three synthetic routes to ring-substituted cycloheptatrienyl complexes [M(CO)3 (eta7-C7H6R)]-+. (M = Cr, Mo or W) have been developed:- substitution at the metal coordinated ring of [M(CIO)3(eta7- C7-C7H7)]+, coordination of a substituted cycloheptatriene 7-R-C7H7 to give [M(CO)3(eta6-(7-R)C7H7}] followed by H- abstraction, and finally direct reaction of substituted cycloheptatrienyl ions [C7H6R]+ with the tris(nitrile) complexes [M(CO)3(NCR')3] (M = Mo, R' = Me; M = W, R' = Prn). By use of a combination of these alternative routes the ring-substituted complexes [M(CO)3 (eta7-C7H6R)]+ (M = Cr, R = C6H4CH3-4, CetaCPh; M = Mo, R = Me, But C6H4CH3-4, C6H4F-4, C=CPh; M = W, R = Me, C6H4F-4) have been obtained. Treatment of [M(CO)3(eta7-C7H6R)]+ (M = Mo or W) with NaX (X = halide) affords [MX(CO)2 (eta7-C7H6R)] (M = Mo, R = Me, C6H4CH3-4 or C6H4F-4; M = W, R = Me). The effect of ring substitution on the stability, structure and fluxional properties of trihapto bonded cycloheptatrienyl complexes has been investigated. The acetonitrile complexes [Mo(CO)2(NCMe)(eta7-C7H6R)]+ (R = Me or C6H4Me-4) have been obtained by reaction of [MoI(CO)2(eta7-C7H6R)] with Ag[BF4] in NCMe followed by dissolution of the reaction mixture in CH2C12. When redissolved in NCMe, [Mo(CO)2(NCMe) (eta7-C7H6R)]+ exist in equilibrium with [Mo(CO)2(NCMe)3(eta3-C7H6R)]+ but the equilibrium composition is R-dependent with the % composition of [Mo(CO)2(NCMe) (eta7-C7H6R)]+ enhanced (with respect to R = H) by R = Me and diminished by R = C6H4CH3-4. The % composition of [Mo(CO)2(NCMe)(eta7-C7H6R)]+ also increases with increased temperature. Reaction of [MoI(CO)2(eta7-C7H6C6H4F-4)] with NaCp yields [Mo(CO)2(eta3-C7H6C6H4F-4)Cp] which exhibits an increased activation energy for the [1,2] shift of the metal group around the coordinated cycloheptatrienyl ring by comparison with [Mo(CO)2(eta3-C7H7)Cp]; limiting low temperature 1H NMR studies on [Mo(CO)2(eta3-C7H6C6H4F-4)Cp] reveal that the C6H4F-4 substituent becomes localised at an uncoordinated terminal diene carbon of the cycloheptatrienyl ring. The bis(phosphine) complexes [MoX(CO)2(P-P)(eta3-C7H6R)] [P-P = dppe (Ph2PCH2CH2PPh2) or dmpe (Me2PCH2CH2PMe2), X = I or Cl, R = Me or C6H4F-4] are synthesised by reaction of [MoX(CO)2(eta7-C7H6R)] with P-P. The X-ray crystal structure of [MoCl(CO)2(dPPe)(eta3-C7H6C6H4F-4)] reveals a pseudo-octahedral molecular geometry with cis carbonyl ligands and one phosphorus of the dppe ligand located trans to the cycloheptatrienyl ring; the C6H4F-4 substituent is again located on a terminal diene carbon. Variable temperature 31P, 1H and 13C NMR investigations establish only a small effect of ring substitution on the two fluxional processes exhibited by [MoX(CO)2(P-P)(eta3-C7H6R)]. The mixed arene cycloheptatrienyl sandwich complexes [M(eta6-C6H6-nMen) (eta7-C7H6R)]+ (M = Cr, R = H or C6H4CH3-4, n = 1 or 3; M = Mo, R = Me or C6H4F-4, n = 1) were synthesised by reflux of [M(CO)3(eta7-C7H6R)+-in C6H6-nMen; in the case of the Cr derivatives, the yield and ease of preparation are substantially improved by a cycloheptatrienyl ring-substituent. Cyclic voltammetric investigations reveal a reversible one-electron oxidation where M = Cr but a corresponding irreversible process for the Mo analogues. Chemical oxidation of [Cr(eta6-C6H5Me)( eta7-C7H6C6H4CH3-4)]+ with [FeCp2]+ affords the stable radical dication [Cr(eta6-C6H5Me)(eta7-C7H6C6H4CH3-4)]2+. The chromium complexes [Cr(eta6-C6H5Me)( eta7-C7H6C6H4CH3-4)]z+ (z = 1 or 2) are unreactive towards arene displacement but the Mo analogues [Mo(eta6-C6H5Me) (eta7-C7H6R)r (R = Me or C6H4F-4) provide convenient syntheses of [Mo(L)(dppe) (eta7-C7H6R)]+ (L = Ca-CBut or NCMe).
Notlar:
School code: 1543
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(683831.1) | 683831-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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