76498-73-2Relevant articles and documents
Kinetic study of cycloaddition reactions of transition metal-propargyl and -η1-allyl complexes with p-toluenesulfonyl isocyanate
Bell, Priscilla B.,Wojcicki, Andrew
, p. 1585 - 1592 (2008/10/08)
Reactions between transition metal-propargyl complexes (MCH2C≡CR) and various unsaturated electrophiles have been examined with a view to finding a system that is readily amenable to a kinetic study under ambient conditions. The reaction between MCH2Gs≡CR and p-toluenesulfonyl isocyanate (TSI), which proceeds cleanly, with no observable intermediates, to the [3+2] cycloadducts MC=C(R)C(O)N[S(O)2C6H4CH3-p]CH 2, was followed kinetically by infrared and, in some cases, 1H NMR spectroscopy, mostly in CH2Cl2 at 25.0°C. The cycloaddition is first order in each of MCH2C≡CR and TSI; for a given R, the bimolecular rate constants decrease as a function of M in the order η5-C5H5Cr(NO)2 > η5-C5H5Fe(CO)2 > η5-C5H5Mo(CO)3 > η5-C5H5W(CO)3 > Mn(CO)5, spanning 2 orders of magnitude. Replacement of a CO in η5-C5H5Mo(CO)3CH 2C≡CC6H5 or Mn(CO)5CH2C≡CC6H5 with a better σ-bonding ligand (L) leads to an acceleration in the rate of the addition, which depends on ligand basicity, viz., L = P(C6H5)3 > P(OC6H5)3 > CO. Methylpropargyl complexes (MCH2C≡CCH3) react 16-30 times as rapidly as the corresponding phenylpropargyl complexes (MCH2C≡CC6H5). Solvent influence on the rate of the reactions of η5-C5H5Mo(CO)3CH 2C≡CCH3 and η5-C5H5Fe-(CO)2CH 2C≡CC6H5 with TSI in toluene, chlorobenzene, CH2Cl2, or CH3CN is very small; the activation parameters for the first-mentioned reaction in toluene are Ea = 11.5 kcal/mol, ΔH? = 10.9 kcal/mol, and ΔS? = -31 eu. These data do not distinguish between a two-step dipolar mechanism and a concerted one, but the former is favored on the basis of the earlier stereochemical studies. The related reaction of η5-C5H5Fe(CO)2CH 2C(R)=C(R′)R″ with TSI to give η5-C5H5Fe(CO) 2C(R)C(R′)(R″)C(O)N[S(O)2C6H 4CH3-p]CH2 was also investigated kinetically in CH2Cl2 at 25.0°C; the bimolecular rate constants decrease as a function of the η1-allyl ligand in the order CH2CH=CHCH3 > CH2CH=C(CH3)2 > CH2CH=CH2 ? CH2CH=CHC6H5, indicating that both steric and electronic effects are contributing. Surprisingly, structurally related η5-C5H5Fe(CO)2CH 2O≡CR and η5-C5H5Fe(CO)2CH 2CH=CHR″ (R = R″) cycloadd TSI at comparable rates.
