Nucleophilic substitution reactions of 1,4-dichlorobenzene chromium tricarbonyl with mono- and diphenoxides

The nucleophilic substitution reactions of 1,4-dichlorobenzene chromium tricarbonyl ( 1 ) with the phenoxide anion were investigated. The substitution of the first chlorine was very fast and gave the mono-substituted product in high yield. The substitution of the second chlorine group was significantly retarded by the presence of the phenoxy group incorporated during the first reaction and also due to the competing decomplexation reaction. The application of 1,4-dichlorobenzene chromium tricarbonyl ( 1 ) to the synthesis of new monomers was demonstrated by the preparation of 2,2′-bis[4-(4-chlorophenoxy)phenyl]propane ( 9 ). 2,2′-Bis[4-(4-chlorophenoxyl)phenyl]propane ( 9 ) was synthesized by a nucleophilic substitution reaction of 4,4′-isopropylidenediphenolate with 1,4-dichlorobenzene chromium tricarbonyl ( 1 ) followed by decomplexation with I₂. 2,2′-Bis[4-(4-chlorophenoxy)-phenyl]propane ( 9 ) was also synthesized via a three-step reaction starting from the nucleophilic substitution reaction of 4,4′-isopropylidenediphenol ( 7a ) with 1-chloro-4-nitrobenzene ( 10 ). 2,2′-Bis[4-(4-chlorophenoxy)phenyl]propane ( 9 ) was polymerized by a Ni(0)-catalyzed reaction to yield amorphous aromatic polyethers with number-average molecular weights of up to 11,200 g/mol. © 1993 John Wiley & Sons, Inc.     

A 13C-NMR. Study of naphthalene chromium complexes. Correlation with reactivity: Nucleophilic aromatic substitution reactions

The ¹³C-NMR. spectra of the series of complexes η⁶-naphthalene · CrL₃ (L? CO ( 1 ), PF₃ ( 2 ), PF₂OMe ( 6 ), P(OMe)₃ ( 3 ), C₁₀H₈ (= 3 L) ( 4 ) and PMe₃ ( 5 )) are reported. Definite assignments of the ¹³C-NMR. resonances were made through the synthesis of [2, 3, 6, 7-²H₄]-naphthalene complexes. The coordinated ring ¹³C-resonance are found to undergo a smooth transition to higher field with increasing donor character of the coligands L. A correlation of the coordination shifts with the reactivity of the coordinated naphthalene is proposed. In complexes containing strong acceptor ligands the naphthalene is activated to attack by nucleophiles. Sequential treatment of complexes 1–4 , 6 and [C₁₀H₈FeC₅H₅]⁺[PF₆]^? ( 7 ) with stabilized carbanions and I₂ or Ce(IV)-salt yields α-substituted naphthalenes in the case of 1 , 2 , 6 and 7 but not in the case of 3 and 4 . Treatment of 3 with an excess of HBF₄ results not in the expected metal protonation but in a novel ligand transformation to yield 6 .     

Nucleophilic and electrophilic promotion of ligand substitution reactions in oxo‐bridged,dinuclear chromium(III) complexes

Base hydrolysis reactions of [Cr(tmpa)(NCSe)]₂O²⁺, [Cr(tmpa)(N₃)]₂O²⁺, [Cr₂(tmpa)₂(μ−O)(μ−PhPO₄)]⁴⁺ and [Cr₂(tmpa)₂(μ−O)(μ−CO₃)]²⁺ follow the pseudo‐first‐order relationship (excess OH⁻): k_obsd=k_o+k_bQ_p[OH⁻]/(1+Q_p[OH⁻]). For the CO₃²⁻ complex, k_b(60°C)=(1.50±0.03)×10⁻² s⁻¹; ΔH‡=61±2 kJ/mol, ΔS‡=−99±7 J/mol K; Q_p(60°C)=(3.8±0.3)×10¹ M⁻¹; ΔH°=67±2 kJ/mol, ΔS°=230±7 J/mol K (I=1.0 M). An isokinetic relationship among k_OH(=k_bQ_p) activation parameters for five (tmpa)CrOCr(tmpa) complexes shows that all follow essentially the same pathway. Activated complex formation is thought to require nucleophilic attack of coordinated OH⁻ at the chromium‐leaving group bond in the k_b step, accompanied by reattachment of a tmpa pyridyl arm displaced by OH⁻ in the Q_p preequilibrium. Abstraction of both thiocyanate ligands was observed upon mixing [Cr(tmpa)(NCS)]₂O²⁺ with [Pd(CH₃CN)₄]²⁺ in CH₃CN solution. The proposed mechanism requires rapid complexation of both reactant thiocyanate ligands by Pd(II) (K_p(25°C)=(4.5±0.2)×10⁸ M⁻²; ΔH°=−32±6 kJ/mol, ΔS°=59±19 J/mol K) prior to rate‐limiting Cr NCS bond‐breaking (k₂(25°C)=(1.17±0.02)×10⁻³ s⁻¹; ΔH‡=98±2 kJ/mol, ΔS‡=27±5 J/mol K). Pd(II)‐assisted NCS⁻ abstraction is not driven by weakening of the Cr( )NCS⁻ bond through ligation of the sulfur atom to palladium, but rather by a favorable ΔS‡ resulting from the release of Pd(NCS)⁺ fragments and weak solvation of the activated complex in CH₃CN solution. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 351–356, 1999     

Nucleophilic substitution reactions of pyranose polytosylates

The 2,3,4-tri-toluenesulfonate ester derivatives of the methyl pyranosides of l-arabinose, d-ribose, d-lyxose, and d-xylose have been prepared, and their substitution reactions with various nucleophiles have been examined. For arabinose, xylose, and ribose, highly regioselective monosubstitutions were observed with benzoate, nitrite, and azide anions. These reactions have led to short and simple routes from d-xylose to l-arabinose derivatives, from l-arabinose to d-xylose derivatives, and from d-ribose to l-lyxose derivatives. The tritosylate derived from methyl alpha-d-lyxopyranoside was unreactive toward nucleophilic substitution reactions, giving instead a dihydropyran product arising from an initial E2 elimination reaction of the 2-tosylate.     

Nucleophilic substitution reactions in 4-halonitro-pyrazolecarboxylic acids

The reaction of 4-bromo-1-methyl-3-nitropyrazole-5- and 4-bromo-1-methyl-5-nitro-pyrazole-3-carboxylic acids with arylamines in aqueous solution in the presence of monovalent copper salts leads to the formation of 4-arylamino- and 4-hydroxy substituted nitropyrazolecarboxylic acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 328–330, March, 1986.     

Taft substituent constants for arene chromium dicarbonyl phosphine and arsine derivatives

A series of biphenyl, meta- and para-fluorobiphenyl complexes of chromiumtricarbonyl, chromiumdicarbonyltriphenylphosphine and chromiumdicarbonyltriphenylarsine have been prepared and their spectral and physical properties recorded. Taft substituent constants have been calculated for the coordinated arenes and the consequences of substituting a Group V ligand for a carbonyl are discussed.     

Nucleophilic substitution reactions in tetranitrodibenzo-18-crown-6

The nature of the reaction of a reagent with tetranitrodibenzo-18-crown-6 was found to depend on its basicity. This behavior was interpreted in the framework of the theory of hard and soft acids and bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 605–608, May, 1992.     

Indenyl effect in dissociative reactions. Nucleophilic substitution in iron carbonyl complexes: a case study

The mechanism of carbonyl substitution in [Fe(Ind)(CO)(2)I] (Ind = C(9)H(7)(-), indenyl) by P(OMe)(3) was investigated by means of DFT calculations. The most favourable path involves a spin crossover of the complex from the ground state singlet to the triplet potential energy surface (S = 1), followed by dissociative loss of CO, and phosphite addition to the coordinatively unsaturated intermediate, [Fe(Ind)(CO)I], with S = 1. In the final step, the system returns to the spin singlet surface, affording the product. This dissociative mechanism is in agreement with the experimental findings. Several pathways occurring exclusively along the singlet surface (S = 0) were explored, namely the expected associative mechanism, which is the most favourable among them, and the "pseudo" associative including the participation of solvent (n-octane). In all cases the corresponding energy barriers were significantly higher than the ones involved in the "spin forbidden" mechanism. The rate enhancement observed comparing the Ind complex with the cyclopentadienyl (Cp = C(5)H(5)(-)) analogue reflects the stability difference between the corresponding S = 0 and S = 1 species in the initial step. The larger number of π orbitals and the lower symmetry of the indenyl ligand, compared with Cp, results in a smaller HOMO-LUMO gap, in a more accessible triplet species, and in a smaller barrier for the spin crossover.     

Quantum-chemical study of donor-acceptor interactions in chelate dicarbonyl complexes of rhodium(I)

DFT calculations were used to analyze the electronic structures of 15 mono- and dicarbonyl rhodium(I) complexes with bidentate O,O-, N,N-, and N,O-donor ligands. The characteristics describing the metal-CO bond (bond length and spin-spin coupling constant J(CRh)) were found to depend on which of the donor atoms (N or O) is trans to the carbonyl group. Because of this, the trans-effect transmitted along the σ-bonds can be judged from the values of these characteristics. The characteristics whose values are determined by the populations of the π-antibonding orbitals of the CO groups primarily depend on the cis-partners in the coordination sphere.     

Nucleophilic substitution reactions of alpha-chloroacetanilides with benzylamines in dimethyl sulfoxide

Kinetic studies of the reactions of alpha-chloroacetanilides (YC6H4NRC(=O)CH2Cl; R = H (5) and CH3 (6)) with benzylamines (NH2CH2C6H4X) were carried out in dimethyl sulfoxide at 55.0 degrees C. The Br?nsted betaX values were in the range from 0.6 to 0.9 and cross-interaction constants phoXY were positive: phoXY = +0.21 and +0.18 for 5 and 6, respectively. The rates were faster with 6 than with 5 and inverse secondary kinetic isotope effects involving deuterated benzylamine (ND2CH2C6H4X) nucleophiles, kH/kD < 1.0, were obtained. Based on these and other results, a stepwise mechanism with rate-limiting expulsion of the chloride leaving group from a zwitterionic tetrahedral intermediate, T+/-, is proposed. In this mechanism, a prior carbonyl addition to T+/- is followed by a bridged type transition state to expel the chloride. An enolate-like transition state in which the developing negative charge on C(alpha) delocalizes toward the carbonyl group (nC-->pi*(C=O) interaction) is not feasible for the present series of reactions due to a stronger charge transfer involving the lone pair on the anilino nitrogen (nAN-->pi*(C=O) interaction).     

Nucleophilic substitution reactions of aryl dithioacetates with pyridines in acetonitrile

Kinetic studies of the pyridinolysis (XC(5)H(4)N) of aryl dithioacetates (CH(3)C(=S)SC(6)H(4)Z) are carried out in acetonitrile at 60.0 degrees C. A biphasic Br?nsted plot is obtained with a change in slope from a large value (beta(X) congruent with 0.9) to a small value (beta(X) congruent with 0.4) at pK(a) degrees = 5.2, which is attributed to a change in the rate-limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, T(+/-), in the reaction path as the basicity of the pyridine nucleophile increases. A clear-cut change in the cross-interaction constants rho(XZ) from a large positive value (rho(XZ) = +1.34) to a small negative value (rho(XZ) = -0.15) supports the mechanistic change proposed.     

Nucleophilic aromatic substitution reactions of 1,2-dihydro-1,2-azaborine

Could go either way: The addition of nucleophiles to the parent 1,2-dihydro-1,2-azaborine and subsequent quenching with an electrophile generates novel substituted 1,2-azaborine derivatives. Mechanistic studies are consistent with two distinct nucleophilic aromatic substitution pathways depending on the nature of the nucleophile.     

Nucleophilic substitution reactions of aryl N-phenyl thiocarbamates with benzylamines in acetonitrile

The aminolysis reactions of aryl N-phenythiocarbamates (PhNHC(=O)SC(6)H(4)Z; 3b) with benzylamines (XC(6)H(4)CH(2)NH(2)) in acetonitrile are studied. Rates are much faster than the corresponding reactions of aryl N-phenylcarbamates (PhNHC(=O)OC(6)H(4)Z; 3a). The rate increase from 3a to 3b is greater than that expected from substitution of thiophenoxide for phenoxide leaving group in the stepwise aminolysis reactions of esters. This large rate increase and the similar change in the aminolysis rates that are reported to occur from aryl ethyl carbonate (EtOC(=O)OC(6)H(4)Z; 2a) to aryl ethylthiocarbonate (EtOC(=O)SC(6)H(4)Z; 2b) lead us to conclude that the aminolysis of 3b proceeds by a concerted mechanism in contrast to a stepwise process for 3a. The negative rho(XZ) values (-0.63) and violation of the reactivity-selectivity principle (RSP) support the proposed mechanism. The large beta(X) values (1.3-1.5) obtained are considered to indicate a large degree of bond making in the transition state, which is consistent with the relatively large kinetic isotope effects (k(H)/k(D) > 1.0) observed.     

Nucleophilic substitution in nitrofluorenones

The reaction of 2,4,5,7-tetranitrofluorenone with amines, thiols, and phenol in a polar aprotic solvent led to the preferable substitution of the nitro group in the position 2, and in the reaction of 2,4,7-trinitrofluorenone first the nitro group in the position 4 was replaced. The different regioselectivity is due evidently to the steric hindrances to the nucleophilic attack on the atom C⁴ caused by the nitro group in the position 5 of tetranitrofluorenone.