Trivinylphosphine and trivinylphosphine chalcogenides: stereochemical trends of 31P1H spin-spin coupling constants

Abstract

A combined theoretical and experimental study of the stereochemical behavior of (31)P-(1)H spin-spin coupling constants has been performed in the series of trivinylphosphine and related trivinylphosphine oxide, sulfide and selenide. Theoretical energy-based conformational analysis of the title compounds performed at the MP2/6-311G** level reveals that each of the four compounds of this series exists in the equilibrium mixture of five true-minimum conformers, namely s-cis-s-cis-s-cis, s-cis-s-cis-gauche, syn-s-cis-gauche-gauche, anti-s-cis-gauche-gauche and gauche-gauche-gauche, which were taken into account in the conformational averaging of (31)P-(1)H spin-spin couplings calculated at the second-order polarization propagator approach/aug-cc-pVTZ-J level of theory. All (31)P-(1)H spin-spin coupling constants involving phosphorus and either of the vinyl protons are found to demonstrate a marked stereochemical dependences with respect to the geometry of the coupling pathway and internal rotation of the vinyl group around the P-C bond which is of major importance in the stereochemical studies of the unsaturated phosphines and phosphine chalcogenides.

Recent advances in computational 31P NMR: Part 2. Spin–spin coupling constants

“…Relative energies are given in parentheses (kJ/mol), dihedral angles are shown on structures. Reproduced from Fedorov et al with the permission of John Wiley and Sons…”

“…In two related publications by Fedorov et al dealing with the calculation of geminal and vicinal phosphorus‐proton coupling constants, 2 J PH and 3 J PH , in trivinyl phosphine ( 1 ) and trivinyl phosphine chalcogenides ( 2 ‐ 4 ), it was found that each of the four compounds of this series existed in the equilibrium mixture of five true‐minimum conformers, namely, s‐cis‐s‐cis‐s‐cis , s‐cis‐s‐cis‐gauche , syn‐s‐cis‐gauche‐gauche , anti‐s‐cis‐gauche‐gauche , and gauche‐gauche‐gauche .…”

“…In followed from the later publication, that trivinylphosphine ( 1 ) provided the most remarkable dihedral angle dependence of all its three 31 P‐ 1 H couplings, and this should undoubtedly be attributed to the well‐known lone pair effect decreasing both vicinal couplings, 3 J (P,H A ) and 3 J (P,H B ), and increasing geminal coupling, 2 J (P,H X ), on going from the cisoidal to the transoidal orientation of the free rotating vinyl group in respect with the phosphorus lone pair. However, the most exciting finding of that study was that geminal coupling, 2 J (P,H X ), increased at that by as much as about 70 Hz which is, indeed, a very strong conformational effect. It was noteworthy that cisoidal , 3 J (P,H B ), and transoidal , 3 J (P,H A ), vicinal couplings differed considerably (accordingly , 20 and 40 Hz) in the cisoidal orientation of the vinyl group ( φ = 0°), whereas they were almost equal (about 14–15 Hz) in the transoidal conformation ( φ = 180°).…”

“…The corresponding dihedral angle dependences of 2 J (P,H X ), 3 J (P,H A ), and 3 J (P,H B ) were reported to be less pronounced in trivinylphosphine chalcogenides 2‐4 . The only exception was a marked decrease of 2 J (P,H X ) in trivinylphosphine oxide ( 2 ) on going from the cisoidal to the transoidal orientation of the vinyl group in respect to the C═O bond.…”

“…Apparently, this was due to the different participation of the C═O and C═X (X═S, Se) bonds in the hyperconjugative interactions with the adjacent C─H X and C═C bonds of the vinyl group. Localized equilibrium structures of all the discussed true‐minimum conformers of 1 ‐ 4 are shown in Figures and , whereas calculated spin–spin coupling constants 31 Р‐ 1 Н in this series are given in Table retrieved from the parent publication …”