29Si and 13C NMR spectra of chloro- and fluoro-substituted linear permethylpolysilanes

²⁹Si and ¹³C NMR spectra are reported for the three halopolysilane series Me(SiMe₂)_nCl, Cl(SiMe₂)_nCl and F(SiMe₂)_nF, where n = 2 to 6. Except for the dihalodisilanes (XSiMe₂)₂, data for all of the compounds fit linear relationships based on substituent constants for chlorine or fluorine atoms in the α, β and γ positions. The effects of halogen substitution on ²⁹Si and ¹³C chemical shifts are rapidly attenuated along the polysilane chain, becoming negligible four atoms away from the halogen. The NMR data provide no evidence for long-range electronic transmission from chlorine or fluorine in halopermethylpolysilanes of the type suggested by other workers [1].     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Chemical shift correlations in the 13C, 17O and 31P NMR spectra of some Mo(CO)4((PPh2O)2Y(R)R′) (Y(R) = P(O), Si(Me); R′ = alkyl,haloalkyl, aryl) and [Mo(CO)4(PPh2O)2]2Si complexes

The syntheses and ¹³C, ¹⁷O, ²⁹Si and ³¹P NMR spectra of a series of Mo(CO)₄((PPh₂O)₂Y(R)R′) (Y(R) = P(O), Si(Me); R′=alkyl, haloalkyl, aryl) and [Mo(CO)₄(PPh₂O)₂]₂Si complexes are given. The chemical shift ranges of the cis and trans carbonyl ¹³C and ¹⁷O, phenyl C(1) ¹³C and ³¹P resonances are relatively large and, with the exception of the cis carbonyl ¹⁷O chemical shifts, the correlations between the chemical shifts of the various resonances are excellent. These correlations are consistent with the model of metal carbonyl ¹³C and ¹⁷O chemical shifts proposed by Bodner and Todd. In addition they allow the model to be extended to include the diphenylphosphinite ³¹P chemical shifts in these complexes. The excellent correlations may be due to the presence of the chelate ring which limits the rotation around the molybdenum-phosphorus bond and to the fact that all three groups directly bonded to the phosphorus remains constant.     

Fourier transform NMR studies of organometallic compounds. II—synthesis and NMR spectroscopy of propenyl and isopropenyl derivatives of silicon and lead

Isomeric mixtures of compounds Me_nM(CH?CHMe)_4?n (M=Si, Pb; n=0?3) have been prepared and studied, as well as pure Me₃M(CMe?CH₂) and mixtures containing propenyl isopropenyl residues bonded to silicon and lead. ¹H, ¹³C, ²⁹Si and ²⁰⁷Pb NMR data are presented; as previously observed for the corresponding tin compounds, the ²⁹Si and ²⁰⁷Pb shifts for the Me₃MC₃H₅ isomers can be used to calculate the shifts expected for the other isomers; while for lead the agreement is good, calculated and observed values for silicon diverge with decreasing n due, at least in part, to steric factors.     

CNDO/2 study of 29Si NMR chemical shifts

A CNDO-2 study of ²⁹Si NMR chemical shifts for compounds of the type (CH₃)_nSiX_4-n (X = H, F, Cl) is reported. The paramagnetic screening constants σ_p are given. The general variation in σ_p with n agrees fairly well with the variation of the observed chemical shifts for X = H and F, but the correlation is not so good for X = Cl.     

29Si and 13C NMR Studies of organofunctional di- and trisilanes

A series of di- and trisilanes of general structure Ph₃SiSiMe₂R and (Ph₃Si)₂SiR′R″ were synthesized, and the ²⁹Si and ¹³C chemical shifts and one-bond siliconsilicon coupling constants (¹J_SiSi) were measured. The coupling constants of the disilanes were found to be primarily dependent upon the inductive effect of the alkyl group, R, as measured by the Taft o^★ constant. In both series of compounds, increasing alkyl substitution at silicon led to a decrease in ¹J_SiSi.     

NMR study (1H, 13C and 29Si) of (CH3)4−x Si(CHCH2)x compounds where x = 0, 1, 2, 3, 4

The ¹H, ¹³C and ²⁹Si NMR spectra of the various methylvinylsilanes have been analysed with the aid of a special simulation program. From considerations of the chemical shifts and of the coupling constants ^2,3j_¹H-¹H, ¹J_¹³C-¹H, ¹J_{²⁹Si-¹³C} and ²J_{²⁹Si-C-¹H} it is shown that a mesomeric —M effect from the vinyl group to the Me—Si group is important, in very good agreement with previously published PES results [1–3]. The mesomeric interaction in this series is ascribed to a {d, σ^*—π} hyperconjugation in accordance with theoretical considerations [4].     

Silicon-29 NMR studies of polymethylhydrosiloxanes: Spin-lattice relaxation time (T1) measurements

²⁹Si NMR spectra of polymethylhydrosiloxanes, Me₃SiO[MeHSiO]_nSiMe₃ from n = 3 to 8 and 35, have been determined. Both chemical shifts and spin-lattice relaxation times (T₁) have been measured. The stereochemistry at the adjacent chiral MeHSiO unit influences the nearest neighbor ²⁹Si chemical shift. The effect of chain length and position of MeHSiO units on T₁ values for Me₃SiO[MeHSiO]_nSiMe₃ systems are discussed.     

Steric effects in 29Si and 13C NMR spectra of trimethylsilyl- and alkyl-substituted benzenes

²⁹Si and ¹³C NMR spectra of trimethylsilylbenzenes substituted at different positions by methyl and trimethylsilyl groups were investigated with special reference to steric interactions between the ortho-substituents. The steric effects, as measured by ¹³C and ²⁹Si chemical shifts, are generally smaller in trimethylsilyl- than in t-butyl-substituted compounds. Both nuclei follow the same general trends in the benzene derivatives.     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. 46 [1]. 29Si-NMR-chemische Verschiebungen von Trialkoxysilylthioderivaten der Permethylpolysilane

Contributions to the Chemistry of Silicon-Sulphur Compounds. 46. ²⁹Si-N.M.R. Chemical Shifts of Trialkoxysilylthio Derivatives of Permethylpolysilanes ²⁹Si-N.M.R. chemical shifts of trialkoxysilythio derivatives of permethylpolysilanes of the two series: α, ω-(RO)₃SiS(SiMe₂)_nSSi(OR)₃, n = 2, 3, 4, 6 and 1-(RO)₃SiS(SiMe₂)_nMe, n = 2, 4; R = i-Pr, t-Bu and also ³¹C-NMR shifts are given. The relationship of ²⁹Si-NMR chemical shift from the netto charge at the silicon atom q(Si) which value has been corrected according to the Sandorfy C quantum-chemical model is discussed. The greater reduction of the electron density at silicon in compounds with Si? X bond (X = S, P, Cl) has been explained by a conjugation of the lone of sulphur with the Si? X bonding pair.     

Tin-element exchange: Formation and multinuclear NMR characterisation of mixtures of the type C(SnMe3)n(MMe3)4-n (M = Si,Pb; n = 0–3)

Treatment of tetrakis(trimethylstannyl)methane with one equivalent of methyllithium followed by one equivalent of Me₃MCl gives mixtures of the type C(SnMe₃)_n(MMe₃)_4-n (M = Si, Pb; n = 0?3), which have been characterised by multinuclear (¹³C, ²⁹Si, ¹¹⁹Sn, ²⁰⁷Pb) NMR. The main component (ca. 40%) is in each case (Me₃Sn)₃ CMMe₃, but considerable amounts of the other tetrametallamethanes are also present.     

13C, 15N and 29Si nuclear magnetic resonance studies of some aminosilanes and aminodisilanes

¹³C, ¹⁵N (at natural abundance) and ²⁹Si NMR data (chemical shifts and coupling constants) are reported for aminosilanes R₂R′SiNHR¹ (1), bis(silyl)amines Me₂R′SiNHSiMe₃ (2), 1,2-bis(amino)-ethanes (3), bis(amino)silanes RR′Si(NHR¹)₂ (4), 1,2-bis(amino)tetramethyldisilanes (5) and 1,1,2,2-tetrakis(amino)dimethyldisilanes (6). The δ¹⁵N values depend more on the nature of the substituents R¹(H, alkyl, aryl) at the nitrogen atom (in the same way as for other amines) than on different substituents at the silicon atom. A linear correlation between ¹J(²⁹Si¹⁵N) and ¹J(²⁹Si¹³C) is proposed for silanes in which the SiN unit is replaced by the SiCH unit. This correlation comprises all ¹J(²⁹Si¹⁵N) values for aminosilanes R_4-nSi(N)n (n = 1–4) and—most likely—also for aminodisilanes, and it predicts ¹J(²⁹Si¹⁵N)>0 if the corresponding value |¹J(²⁹Si¹³C)|>25 Hz. For the first time a two-bond coupling across Si, ²J(²⁹Si ¹⁵N) = 6.9 Hz, has been observed for 6a. In the case of 6b (R¹ = ^sBu) all resonances for the diastereomers are resolved in the ¹⁵N and ²⁹Si NMR spectra in contrast to the ¹H and ¹³C NMR spectra.     

Cleavage of the carbon-silicon bonds in trimethylsilylacetylenes by trans[(PR3)2PtX(R′OH)]PF6 cations and formation of cationic alkoxycarbene complexes of platinum(II)

Cationic alkoxycarbene complexes of platinum(II) have been isolated in the reactions of trans-[(PR₃)₂PtX(R′OH)]PF₆ (X  H or Me; R′  Me or Et) with Me₃SiCCR′′ (R′′  H, Me or SiMe₃). In these reactions cleavage of the carbon-silicon bond by the nucleophilic attack of alcohol has been observed. These carbene complexes have been characterized by elemental analyses and by IR, ¹H and ¹³C NMR spectral data. ¹³C NMR chemical shift data for carbene carbon atoms suggest that the carbene carbon may be very positively charged.     

Application des spectrographies RMN 13C et 1H a l'etude de derives cycliques du silicium et germanium,interactions pπdπ

The properties of 1-sila- and 1-gemma-cyclopent-2-(or -3-)enes with various substituents have been investigated by ¹³C and ¹H NMR spectroscopies. Values of chemical shifts and coupling constants in olefinic cyclic systems and in aromatic or ethylenic substituents attached to the hereto atom suggest the presence of a mesomeric p_πd_π interaction, particularly for the silicon atom. Studies at low temperatures given conformational data, which have been compared with data from the literature.     

NMR study of organosilicon compounds. III—Silicon-29, nitrogen-14, carbon-13 and proton NMR spectra of silylakylamines

²⁹Si, ¹⁴N ¹³C and ¹H NMR data are presented for a series of homologous (methylethoxysilyl)alkylamines of the type (CH₃)_3?n(C₂H₅O)_nSi(CH₂)_mNH₂(n=o to 3; m = 1 to 4). The measured ¹³C and ¹H chemical shifts correlate with the total net charges Q_A on the corressponding atoms, estimated by the Del Re method. ¹⁴N and ²⁹Si chemical shifts which do not show simple linear relationships to the charges are found to correlate with the relative basicities of the compounds. The influence of the remote substituent (? NH₂ and others) on the ₂₉Si chemical shifts is shown to depend on the number and nature of substituents directly on the silicon atom. Argyments for d-orbital participation in the Si? O bounds are given. The chemical shifts of ²⁹Si, ¹⁴N and ₁₃C nuclei are not consistent with the fromation of intramolecular ‘long bonds’ between the solicon and nitrogen atoms in aliphatic silymethylamines.     

High resolution CPMAS 13C NMR of organometallic solids. Observation of J coupling to tin

Chemical shift and ¹J(^117,119Sn, ¹³C) data from cross polarization magic angle spinning (CPMAS) proton-decoupled solid-state ¹³C NMR experiments are given for the methyltin carbon in (Me₂SnS)₃, Me₃SnOAc, Me₂S(acetylacetonate)₂, Me₂SnCl₂· 2(dimethylsulfoxide), and amorphous (Me₂SnO)_n. The relationship between the magnitude of the coupling constant and the coordination at tin is examined by reference to X-ray structure data. The tin-methyl ¹³C chemical shift was sensitive to slight variations in bond angles and bond lengths. The presence of isotopically abundant NMR-active nuclei in the molecule broadens lines, and can prevent resolution of the J coupled interaction.     

29Si-Chemische Verschiebungen in Alkoxy(amino)silanen

²⁹Si Chemical Shifts of Alkoxy(amino)silanes The ²⁹Si NMR spectra of a series of alkoxy(amino)silanes (RO)_nMe_3?nSiNHC₆H₄X (n = 1–3) have been measured and are discussed by means of relative paramagnetic screening constants σ*, calculated by a simplified quantum-chemical model. The Hammett plots of the silicon chemical shift show both positive and negative slopes with changes of the number of electronegative atoms (O, N) attached to silicon. The steric and electronic shift contributions of the alkoxy groups are given.     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.     

Reversible crotylstannation of carbonyl compounds. Crotylstannation ability of Bu3-nClnSnCH2CHCHCH3 (n = 0, 1, 2) compounds towards acetone and benzaldehyde and 13C NMR characterization

The crotylstannation reaction:

has been found to be reversible. The compounds trans/cis-Bu_3-nCl_n SnCH₂CH= CHCH₃ (n = 0, 1, 2) have been prepared by elimination reactions of organostannoxy compounds,Bu_3?nCl_nSn—O—C(Me)(i-Pr)CH(Me)CHCH2, which were synthesized by means of transalkoxylation between Bu_3-nCI_nSn(OMe) compounds and threo/erithro-2,3,4-trimethyl-5-hexen-3-ol. Under the conditions used the elimination occurs stereospecifically and with complete allylic rearrangement. The ability of the organostannoxy compounds to yield crotyl butylchlorotins via elimination increases in the order, Bu₃Sn—O—C < Bu₂ClSn—O—C < BuCI₂Sn—O—C. In the addition reactions, the sequence of increasing reactivity is Bu₃SnCrot < CIBu₂SnCrot < CI₂BuSnCrot (Crot = crotyl). The ¹³C NMR spectra of the compounds made reveal that the chemical shifts of the allylic carbon atoms are related to the inductive effects of the chloro-substituents.     

Structure of novel N-fluorosilylmethyl-N-isopropylureas

Novel N-isopropyl-N',N'-dimethyl-N-(silylmethyl)ureas Me₂NC(O)N(Prⁱ)CH₂SiMe_nX_3–n (X = OEt, F; n = 0–2) were synthesized, and their structure was confirmed by ¹H, ¹³C and ²⁹Si NMR spectroscopy. According to NMR data, the silicon atom of the fluorosilanes (X = F) is pentacoordinated. The X-ray diffraction analysis of the (trifluorosilyl)methylcontaining urea showed that it exists as (O–Si) chelate with intramolecular dative bond C=O→Si (1.880 Å).