J.J. Zuckerman

Carbon-13 chemical shifts of substituted t-butylbenzenes, phenyltrimethylsilanes and phenyltrimethylgermanes

Abstract Carbon-13 NMR chemical shifts are reported for three series of Group IV aromatics p -XC 6 H 4 Y(CH 3 ) 3 where Y = C, Si and Ge. The shifts for the C(1), C(2), CH 3 and C(α) carbons correlate with the substituent parameters σ, and σ o R , and the slopes of the CH 3 correlations suggest roughly equal transmitting abilities for carbon and silicon. For a given substituent X, the shift of the C(1) carbon varies in the order C>Ge>Si expected from electronegativity considerations. The other ring carbon atoms experience smaller changes corresponding to their respective positions ortho , para , and meta to Y. The shifts of the C(4) and C(2, 6) carbons vary Si>Ge>C, in agreement (for X = N(CH 3 ) 2 with atomic charge values from published CNDO/2 calculations for carbon and silicon which indicate that while silicon exerts an electron-releasing effect through the σ-framework, there is a net π-withdrawal registered at the C(4) and C(2, 6) carbon atoms relative to Y = C.

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : II. (119Sn-13C) coupling constants and 13C chemical shifts of meta- and para-derivatives

Abstract Carbon-13 NMR data are reported for thirteen para - and meta -substituted phenyltrimethyltin compounds, RC 6 H 4 Sn(CH 3 ) 3 , where R = para -N(CH 3 ) 2 , para -OCH 3 , para -OC 2 H 5 , para -CH 3 , meta -CH 3 , -H, para -F, meta -OCH 3 , para -Cl, para -Br, meta -F, meta -Cl and para -Sn(CH 3 ) 3 . In the para -derivatives, correlation coefficients with Hammet σ-constants of greater than ca. 0.9 are obtained with the tin-carbon couplings to methyl, C 1 and C 4 carbons, and with the carbon-13 chemical shifts δ(C(1)). In the meta -derivatives, the couplings | J (Sn-CH 3 )|:, |: J (Sn-C(1))|:, |: J (Sn-C(3))|: and |: J (Sn-C(6))|:, and the shifts δ(C(1)) and δ(C(5)) correlate well with Hammett σ. In the para -derivatives, sensitivity to change in substituent falls off C(4) > C(3, 5) > C(1) > C(2, 6) > CH 3 as registered by the δ(C), while in the meta -derivatives δ(C) changes decrease C(3) > C(2), C(4) > C(1) > C(5), C(6) > CH 3 . The magnitudes of the tin coupling constants decrease C(1) > CH 3 > C(3, 5) > C(2, 6) > C(4) in the para -derivatives, while in the meta -series the order is C(1) > CH 3 > C(3), C(5) > C(2) > C(6) > C(4). The two sets of one-bond |: J (Sn-CH 3 )|: and |: J (Sn-C(1)|: values correspond closely to the 0.25/0.33 ratio of coefficients in the LCAO approach, and are interpreted in terms of s -electron redistributions at the tin atom with change in substituent.

119mSn Mössbauer and NMR study of trialkyltin acetates

Abstract Homologous series of trialkyltin acetates in which the methyl group of the acetate is successively chlorinated and fluorinated have been studied by infrared, 1 H and 19 FNMR and Mossbauer spectroscopies. Substitution by increasingly electron withdrawing groups leads to monotonic increase of the Mossbauer Isomer Shift ( IS ) and NMR J ( 117,119 SnC 1 H) values, and in the methyltin series, of the Mossbauer Quadrupole Splitting ( QS ) values. The data for these five-coordinated, solid-state structures indicate that the effect of halosubstitution is apparently registered predominantly at the carbonyl group whose coordination with tin changes the effective |Ψ 5s (0)| 2 by shielding. Halosubstitution weakens the donor power of the carbonyl, raising the IS ; and concentrates s -character in the tin-carbon bonds, raising J ( 117,119 SnC 1 H). Likewise, J ( 117,119 SnC 1 H) increases with halosubstitution for the apparently four-coordinated solution species signifying a concentration of s -character in the tincarbon bonds. Five-coordinated, monomeric species may be present in frozen solutions.

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : IV. Proton and carbon-13 NMR data for ortho-, 2,6-, and poly-substituted aryltrimethyltins☆

Abstract Proton and carbon-13 NMR data recorded in the Fourier transform mode are reported for ten ortho -substituted, six 2,6-disubstituted, and six miscellaneous polysubstituted aryltrimethyltin compounds. Although ¦ 1 J ( 13 C  1 H)¦ and ¦ 2 J ( 119 SnC 1 H)¦ coupling constants are rather insensitive to substituent variation, tin methyl proton chemical shifts reflect the increasing inductive effects as methyl-, chloro-, fluoro-, and trifluoromethyl-groups are brought into juxtaposition with the trimethyltin moiety. Resonances in the natural-abundance carbon-13 NMR spectra for the tin derivatives are assigned on the basis of additivity relationships, proton undecoupled spectra, and relative magnitudes of ¦ J ( 119 Sn 13 C)¦ and ¦ J ( 13 C  19 F)¦ coupling constants. Mutually deshielding γ-, δ-, and ϵ-effects in the carbon-13 chemical shifts of substituent carbons are rationalized in terms of steric crowding between the trimethyltin group and neighboring substituents. Deshieldings in ring carbons formally para - to conjugating substituents are discussed in terms of the steric inhibition of resonance model. Previous conclusions concerning lack of significant higher coordination at tin in aryltin derivatives bearing substituents with lone pair electrons are corroborated in this work.

The synthesis of 2-silanorcaranes

Abstract 2,2-Dimethyl-2-silanorcarane has been prepared by the stepwise reduction of 7,7-dibromo-2,2-dimethyl-2-silanorcarane with tri-n-butyltin hydride. Treatment of the dibromonorcarane with silver ion or pyrolysis with quinoline releases hydrogen bromide and decomposs the ring system. Trimethyl(dimethylamino)stannane reduces the dibromo compound to a 1.5/1 mixture of the endo - and exo -isomers of 7-bromo-2,2-dimethy-2-silanorcarane in the first known reaction of the tinnitrogen bond to proceed by a radical mechanism. β-Elimination of bromine is favored endo ⪢ exo in the mass spectrometer. The 7,7-dibromo compound is prepared by a series of steps which include the hydrosilation of 5-chloro-1-pentyne by trichlorosilane, the intramolecular Barbier cyclization of the product, the methylation of the resulting 1,1-dichloro-1-sila-2-cyclohexene, and the action of a dihalocarbene generated from phenyl(tribromomethyl)mercury on this silacyclohexene. The dibromonocarane is formed in 50% yield, but a side reaction produces 5-(dimethylbromosilyl)-1-pentene, which was identified as its hydrolysis product, [CH 2 CH)CH 2 ) 3 Si(CH 3 ) 2 ] 2 O. Deuteration experiments establish that the process of ring-opening is concerted, and the observation of resonances due to a transient β-addition product in the NMR leads to the proposal of an HBr-addition β-elimination mechanism for ring-opening which appears to apply to several examples of unsaturated sila- and germacarbocycles in general. Hydrostannation of 5-chloro-1-pentyne by dimethyltin hydride chloride leads to the dimethylchlorostannyl-substituted 5-chloro-1-pentene which undergoes alkyl group redistribution to form a mixture of alkyltin chlorides.

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group

Abstract Proton NMR data at 100 MHz are reported for thirteen para - and meta -substituted phenyltrimethyltin compounds, XC 6 H 4 Sn(CH 3 ) 3 , where X = para -N(CH 3 ) 2 , para -OCH 3 , para -OC 2 H 5 , para -CH 3 , meta -CH 3 , -H, para -F, meta -OCH 3 , para -Cl, para -Br, meta -F, meta -Cl and para -Sn(CH 3 ) 3 . Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon [ 1 J ( 13 C 1 H)] and tin [ 2 J (SnC 1 H)]. Solvent effects and other extraneous factors invalidate comparisons of ϱ values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ϱ[C(1)Sn] > ϱ [SnC] > ϱ [CH]. Satisfactory correlations ( r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, 2 J (SnC 1 H) and the constituent, one-bond 1 J (Sn 13 C) and J ( 13 C 1 H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, 1 J (Sn 13 C) and 1 J ( 13 C 1 H) is lower ( r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and 119 Sn Mossbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para -trimethyltin group of −0.14, and the significance of this value is discussed.

Structural studies in main group chemistry III. Tin-119m mössbauer investigation of some tin-nitrogen bonded compounds

Abstract The tin-119m Mossbauer data are presented for several classes of organotin- nitrogen bonded compounds, including N-stannylamines, -imines, -amides, and -carbamates. Thc structures of the N,O-bis(trialkylstannyl)carbamates are discussed. Those derivatives possessing the Sn-NR-C(O)X group are intermolecularly associated via carbonyl→tin coordination, the strength of the coordination varying with X in the manner H ≈ OSnR3 > OR.

NMR J(Sn−13 C) coupling constants in substituted aryltrimethyltins

Abstract NMR one-bond J(Sn−13C) values have been measured for both the methyltin and C1 phenyltin bonds in thirteen meta- and para-substituted aryltrimethyltin compounds.

Solid-state association in organotin compounds containing bulky organic groups. Tricyclohexyltin hydroxide

Abstract Tricyclohexyltin hydroxide is shown to share the hydroxy-bridged polymeric structure of its methyl analogue on the basis of the ambient temperature 119m Sn Mossbauer spectrum, similar QS value and its ν(OH) in the infrared. Fragments larger than the parent molecular ion are observed in the mass spectrum, but these may arise from a rapid dehydration/condensation to bis(tricyclohexyltin) oxide.

Tin-119m Mössbauer spectra of trimethyltin phosphines used as ligands in transition metal carbonyl complexes

Abstract Tin 119m Mossbauer Quadrupole Splitting (Q.S.) data for several trimethyltin amines, phosphines, arsines, stibines and sulfides are compared with the larger values found for the transition metal carbonyl complexes of the phosphine and sulfide derivatives which reveal the polarizing effect of donor action by the adjacent group V or VI atom.