E.I. Fedin

A 19F NMR study of electronic effects in organomercury, -tin and -lead derivatives of some fluorophenols and fluorothiophenols

Abstract A number of organomercury, -tin and -lead derivatives of m- and p-fluoro-substituted phenols and thiophenols of the type RnMOAr and RnMSAr have been prepared. The 19F chemical shifts relative to fluorobenzene have been measured in various solvents for all these compounds. On the basis of the data obtained, the electronic features of the substituents RnMO and RnMS have been studied and compared with those of OH, CH3O, SH and CH3S groups. The influence of various factors on the electronic effect of the organometallic substituent and on its solvent susceptibility is discussed. The coordinating abilities of the substituents (C2H5)3SnO and (C2H5)3-SnS in solution have been compared with those of the OH and SH groups.

A 19F NMR study of steric hindrance and intramolecular coordination in organo-mercury, -tin and -lead derivatives of 2,6-dimethyl-4-fluorothiophenol and 2,6-dibromo-4-fluorothiophenol

Abstract Some organomercury, -tin and -lead derivatives of 2,6-dimethyl-4-fluorothiophenol and 2,6-dibromo-4-fluorothiophenol of the general type RpMSAr have been prepared. The fluorine chemical shifts of the compounds realtive to internal fluorobenzene and the 19F SCS values for the corresponding substituents have been determined and discussed in terms of steric hindrance and intramolecular coordination, the behaviour of the organometallic substituents RnMS in these respects being compared with that of the SH and CH3S groups. The anomalously low steric requirements of RnMS groups, as well as the differences in the strength of intramolecular coordination and its influence on the acceptor power of the metal atom, in the compouds of mercury, tin and lead have been demonstrated.

A 19F NMR study of electronic effects in some organo-antimony and organobismuth compounds containing metal—heteroatom bonds

Abstract The 19 F NMR technique has been used to study the ground-state electronic effects of univalent organo-antimony and -bismuth substituents in compounds of the type (C 6 H 5 ) n MSC 6 H 4 F-3, (C 6 H 5 ) n MSC 6 H 4 F-4, (C 6 H 5 ) 4 SbOC 6 H 4 F-3, (C 6 H 5 ) 4 SbOC 6 H 4 F-4 and (4-FC 6 H 4 ) 2 SbX, where (C 6 H 5 ) n M = (C 6 H 5 ) 2 Sb, (C 6 H 5 ) 2 Bi and (C 6 H 5 ) 4 Sb, X = C 6 H 5 S, CH 3 COO, Cl, Br. It has been found that the electron-donating effect of the sulphur-containing groups increases in the order: (C 6 H 5 ) 2 SbS 6 H 5 ) 2 BiS 6 H 5 ) 4 SbS, the substituents (C 6 H 5 ) 4 SbS and (C 6 H 5 ) 4 SbO being the most electron-releasing among the (C 6 H 5 ) n MS and (C 6 H 5 ) n MO groups containing heavy non-transition metals. From the viewpoint of solvent susceptibility of their electronic effects the (C 6 H 5 ) 2 SbS, (C 6 H 5 ) 2 BiS and (C 6 H 5 ) 4 SbS groups resemble the (C 6 H 5 ) 3 SnS and (C 6 H 5 ) 3 PbS substituents, and differ from the C 6 H 5 HgS group, whereas the (C 6 H 5 ) 4 SbO substituent differs in this respect from all other (C 6 H 5 ) n MO groups. The low conjugating ability of the (C 6 H 5 ) 2 SbS substituent and slight influence of steric hindrance upon its electronic effect have been explained by the operation of conformational factors. It has been established that the electronic interactions across the antimony—heteroatom bonds are mainly of inductive character and that the order of electron withdrawal for the ArSbX substituents can be reversed on transfer from an inert to coordinating solvent.

The 19F NMR spectra of some fluoroaryl mercurials and the electronic effect of mercury substituents

A number of new fluoroaryl mercurials have been prepared, and for the compounds indicated the 19F NMR spectra have been recorded in chloroform, tetrahydrofuran and dimethyl sulphoxide. The values of σ1 and σOR for mercury substituents have been derived from the fluorine shielding parameters. The dependence of the electronic effect of mercury substituents upon the solvent, the nature of the groups on mercury, steric hindrance and possible intramolecular coordination is discussed.

A Comparative 19F NMR study of electronic effects in some fluoroaryl compounds of antimony and bismuth and in their carbon and nitrogen analogues

Abstract A number of m - and p -fluorophenyl compounds of type Ar 2 QC 6 H 4 F (Q = Sb, Bi, N and CH; Ar = C 6 H 5 , C 6 H 4 F) have been prepared. The l0 F chemical shifts relative to fluorobenzene have been measured in cyclohexane, chloroform and pyridine for all these compounds. On the basis of the data obtained, the electronic nature of the Ar 2 Sb and Ar 2 Bi substituents has been studied and compared with that of the corresponding (C 6 H 5 ) 2 N and (C 6 H 5 ) 2 CH groups. The electronic effect of the Ar 2 Sb and Ar 2 Bi substituents has been shown to be mainly inductive, its solvent susceptibility being in most cases close to zero relative to both electron- and proton- donating solvents.

A 19F NMR investigation of the transmission of electronic effects through tin-aromatic carbon bonds

A number of triaryl(4-fluorophenyl)tin compounds have been prepared. The fluorine chemical shifts relative to fluorobenzene as an internal standard have been measured for all these compounds in chloroform, and a linear relationship between these values and the Σσo values for the substituted phenyl groups attached to the tin atom has been demonstrated. The results obtained suggest that the transmission of electronic effects from one aromatic ring to another in compounds of the type Ar4Sn occurs mainly by an inductive mechanism. In conjunction with the data on similar systems containing other bridging atoms, the results obtained provide a quantitative measure of the relative ability of tin-aromatic carbon bonds to transmit electronic effects.

A 19F NMR study of the transmission of electronic effects in triarylantimony and triarylbismuth compounds. A comparison with the nitrogen- and carbon-containing analogues

Abstract A 19F NMR study of the transmission of electronic effects has been made for the systems Ar2EC6H4F-4 (E = Sb, Bi, CH, N). The fluorine chemical shifts obtained are correlated with the polar constants (Σσo and Σσ) of the substituents, suggesting that electronic effects are transmitted through the SbCar, BiCar and CCar bonds predominantly by an inductive mechanism, whereas the transmission through the NCar bonds is contributed to significantly by classical resonance effects due to competitive conjugation of the lone pair with the aromatic rings, and the substituents therein. A dual parameter correlation of the fluorine chemical shifts with the inductive (σI) and resonance (σoR and σR) parameters of the substituents in the aromatic rings has led to similar conclusions. The inductive transmission through the bridging Sb and Bi atoms has been assigned to the absence of conjugation of lone pair and vacant d-orbitals of the metals with π-electron systems of the aromatic rings. On the basis of the values of the ϱ coefficients for the correlation equations obtained it has been established that the transmitting ability of the BiCar bonds is close to that of the CalCar bonds and considerably lower than the transmitting ability of the NCar bonds.

The synthesis and 19F NMR spectra of some derivatives of (4-fluorophenyl)dimethyltin

Abstract A number of (4-fluorophenyl)dimethyltin compounds and their carbon analogues have been prepared, and the fluorine chemical shifts for these compounds relative to fluorobenzene as an internal standard have been determined in cyclohexane, chloroform and pyridine. It has been shown that the electron-accepting capacity of the Sn-(CH3)2X substituents (where X is a heteroatom) increases in chloroform solution and decreases in pyridine solution relative to the value in cyclohexane, pyridine inhibiting transmission of electronic effects through the tin atom. Correlation between the 19F chemical shifts and the σ1 and Σσ0 values for the groups on the metal atom has been found, indicating that the electronic interactions between the substituents and the tin atom are mainly inductive in nature. The abilities of Sn(CH3)2 and C(CH3)2 bridging groups to transmit such electronic effects have been shown to be similar.

A PMR study of relative strength of chelate rings in the C6H5Hg, (C6H5)3Sn and (C6H5)3Pb derivatives of some nitrogen-containing thiols

Abstract The equilibrium constants for the exchange reactions involving the C 6 H 5 Hg, (C 6 H 5 ) 3 Sn and (C 6 H 5 ) 3 Pb derivatives of 2,6-dimethylthiophenol, 1-thionaphthol, 8-mercaptoquinoline, 2-mercaptopyridine and 2-dimethylaminothiophenol in chloroform have been determined by the PMR technique. The analysis of the data obtained allowed elucidation of the relative strength of chelate rings in the organometallic derivatives of the nitrogen-containing thiols studied.

A 19F NMR study of the transmission of electronic effects in triarylphosphines

Abstract The nature and efficiency of transmission of electronic effects of substituents through the bridging phosphorus atom in systems of the Ar 2 PC 6 H 4 F-4 type have been investigated by 19 F NMR. Correlation of the obtained data on the fluorine chemical shifts in triarylphosphines with those in the correspondingtriarylmethanes and tetraarylsilanes indicated that the bridging phosphorus atom shows a higher transmitting ability than carbon and silicon. On the basis of the data on two-parameter correlation of the fluorine chemical shifts with the inductive (σ I ) and resonance (σ R ) parameters of the substituents in the aromatic rings for systems with bridged phosphorus, carbon, silicon, tin, nitrogen, and bismuth atoms it has been established that phosphorus occupies an intermediate position between nitrogen and bismuth as regards the nature of transmission of electronic effects, i.e. interactions through the PC ar bonds occur both by an inductive and, to some extent, a resonance mechanism.