N-15 NMR spectra of four series of amidines (R(2)R(3)N-CR(1)=NR(4); 24 compounds) in CDCl3 solutions have been recorded and the chemical shifts of both nitrogen atoms assigned. The relation between substitution at the three sites of the amidino [>N-C(=N-)-] group and the N-15 NMR chemical shifts of both nitrogen atoms is discussed on the basis of the results and the data accessible in the literature for seven other non-tautomerizing open-chain amidines.It is shown that, due to a strong conjugation in the amidino group, a substituent at either of the two nitrogen atoms exerts opposite effects on the shielding and thus on the chemical shifts of the amino and imino nitrogen atoms.The effect of substitution at either of the two nitrogen atoms depends on substituents at the other two sites i.e. at the second nitrogen and the amidino carbon atom For amidines containing a substituted phenyl ring at the imino (N-2) nitrogen atom-the chemical shifts of both nitrogen atoms correlate with the Hammett-type constants of substituents, but the slopes of the regression lines are opposite for both atoms, and depend on substituents at the amino (N-1) nitrogen atom.The results indicate that calculation of the N-15 NMR chemical shifts in tautomerizing amidines (i.e. containing a hydrogen atom at the amino nitrogen) on the basis of the shifts in the corresponding methylated model compounds may yield incorrect results, and that this is the most probable source of discrepancies in estimations of the tautomeric equilibria by the nitrogen NMR method.

15 N NMR spectra of four series of amidines (R2R3N–CR1NR4; 24 compounds) in CDCl3 solutions have been recorded and the chemical shifts of both nitrogen atoms assigned. The relation between substitution at the three sites of the amidino [〉N–C(N–)–] group and the 15N NMR chemical shifts of both nitrogen atoms is discussed on the basis of the results and the data accessible in the literature for seven other nontautomerizing open-chain amidines.It is shown that, due to a strong conjugation in the amidino group, a substituent at either of the two nitrogen atoms exerts opposite effects on the shielding and thus on the chemical shifts of the amino and imino nitrogen atoms.The effect of substitution at either of the two nitrogen atoms depends on substituents at the other two sites i. e. at the second nitrogen and the amidino carbon atom. For amidines containing a substituted phenyl ring at the imino (N2) nitrogen atom the chemical shifts of both nitrogen atoms correlate with the Hammett type constants of substituents, but the slopes of the regression lines are opposite for both atoms, and depend on substituents at the amino (N1) nitrogen atom.The results indicate that calculation of the 15N NMR chemical shifts in tautomerizing amidines (i.e. containing a hydrogen atom at the amino nitrogen) on the basis of the shifts in the corresponding methylated model compounds may yield incorrect results, and that this is the most probable source of discrepancies in estimations of the tautomeric equilibria by the nitrogen NMR method.

P n Ligands with Maximum Electron‐Donor Capacity, 7. – Three‐Component Reaction of P 4 ‐Phosphorus with [Cp x Rh(CO) 2 ] in the Presence of [Cr(CO) 5 THF] or [CpMn(CO) 2 THF]. – A Method of Studying the Pathway from Tetrahedral P 4 to the Planar cyclo ‐P 4 Ligand Herrn Professor Gerhard Fritz zum 75. Geburtstag gewidmet. The reaction of P 4 with [Cp x Rh(CO) 2 ] (Cp x = Cp′, Cp′′; Cp′ = η 5 ‐C 5 H 4 t Bu, Cp′′ = η 5 ‐C 5 H 3 t Bu 2 ‐1,3) in the presence of [Cr(CO) 5 THF] leads to [Cp x Rh(CO)(η 1:1 ‐P 4 ){Cr(CO) 5 } 4 ] ( 1a, b ), [Cp′′Rh(η 4 ‐P 4 ){Cr(CO) 5 } 3 ] ( 2b ), and [Cp′Rh(η 4 ‐P 4 ){Cr‐(CO) 5 } 4 ] ( 3a ). In the corresponding reaction with [CpMn‐(CO) 2 THF] no P 4 takes part, and [(Cp′′RhCO)(CpMnCO)(μ‐CO) 2 ] ( 4 ) is formed. An X‐ray structure determination of [Cp x Rh(CO)(η 1:1 ‐P 4 ){Cr(CO) 5 } 4 ] ( 1 ) and [Cp′Rh(η 4 ‐P 4 )‐{Cr(CO) 5 } 4 ] ( 3a ) indicates a stepwise (PP) bond cleavage as the transformation pathway from the P 4 tetrahedron to the cyclo ‐P 4 ligand by passing a bicyclotetraphosphane. In the cyclo ‐P 4 ligand complex 3a all P atoms are able to coordinate to [Cr(CO) 5 ] groups. However, in [Cp′′Rh(η 4 ‐P 4 ){Cr(CO) 5 } 3 ] ( 2b ) the additional t Bu group at the Cp x ligand sterically influences the coordination behavior of the P atoms, and only three of them are able to coordinate to [Cr(CO) 5 ] units. In these syntheses the [Cr(CO) 5 ] moieties promote the reaction and stabilise intermediates along the reaction pathway. Variable‐temperature 31 P{ 1 H}‐NMR measurements indicate for 2b the freezing of the Cp′′ rotation at low temperature and reveals a Δ G (at the coalescence temperature) of 36 kJ mol −1 . Surprisingly, in [(Cp′′RhCO)(CpMnCO)(μ‐CO) 2 ]‐( Rh‐Mn ) ( 4 ) the Cp x ligands are cis ‐oriented whereas in [(Cp*RhCO)(CpMnCO)(μ‐CO) 2 ]( Rh‐Mn ) a trans arrangement is observed. This indicates the unusual behavior of the Cp′′ ligand as a “rod” and not as an “enlarged disk” like Cp* in the crystal lattice of these compounds.

Primary and secondary phosphines (RPH2, R2PH; R = Aryl) react with the P4-Schwesinger Base 4 under formation of alkalimetalfree phosphides. P-31-NMR-investigations prove the existence of phosphine/phosphide equilibriums in the reaction solutions. The interaction of other Schwesinger Bases with alkyl- and arylphosphines is also described.

Primary and secondary phosphines (RPH2, R2PH; R = Aryl) react with the P4-Schwesinger Base 4 under formation of alkalimetalfree phosphides. 31P-NMR-investigations prove the existence of phosphine/phosphide equilibriums in the reaction solutions. The interaction of other Schwesinger Bases with alkyl-and arylphosphines is also described.

Dithiocarboxylation of CH‐Acidic Sulfoxides and ThioethersReaction of (arylsulfinyl)acetonitriles or (arylthio)acetonitriles 1 (X = SO, S) with carbon disulfide in the presence of sodium hydride and subsequent alkylation yield the open‐chain or cyclic ketene S,S‐acetals 3 or 4, respectively. Using two equivalents of an α‐CH‐acidic halo compound as alkylating agent, thiophenes 5 are formed. Treatment of 3a with 2‐mercaptoethanol affords the 1,3‐oxathiolane 6. The 1H‐NMR spectra of phenylsulfinyl‐substituted compounds 3b, 4a, 4b, 5a and 6 show a typical AB system for the methylene group caused by the chiral sulfoxide group.

AbstractFerrocenyltriethylstannane des Typs RSnEt3 [R = Et3SnC5H4FeC5H4, C5H5FeC5H3(2−CH2NMe2), C5H5FeC5H3(2‐CH2NC5H10), C5H5FeC5H3(2‐CH2OMe), MeOCH2C5H4FeC5H4] wurden aus Et3SnCl und den entsprechenden Ferrocenyllithium‐Derivaten synthetisiert und mittels ihrer 1H‐, 13C‐, 119Sn‐NMR‐ und IR‐Spektren sowie elementaranalytisch charakterisiert. Aus den Kopplungskonstanten 1J(119Sn13CEt) wurde der elektronische Einfluß der substituierten Ferrocenylreste abgeschätzt.