Extremely large one-bond31P13C and two-bond31P18O isotope shifts in [(H3C)2CH]3SiOCP, a new representative of λ3-phosphaalkynes, and isotope shifts of several derivatives and some λ3-phosphaalkenes

Remarkably Large 15N, 13C and 18O Isotope NMR Shifts of the Mono-coordinate Phosphorus Atoms in the Compounds (Me3 Si)iPrNCP, K+[iPrNCP]-and KOCP · 2 DME (DME = 1,2-Dimethoxyethane)

“…Strikingly, the geminal 31P 15N coupling constant for the NC!P fragment of compound 1 (15.1 Hz) exceeds that of 2 (3.3 Hz) by approximately a fac tor of five (see Table 1). By contrast, the ^(P C 1) coupling in 1 (18.2 Hz) is smaller than that of 2 (45.7 Hz) by a factor of 2.5, the latter being in the range of A3-phospaalkynes containing a C3C-C'P fragment (cf The 31P singlet of potassium phosphanetriyl methoxide (3) dissolved in 1,2-dimethoxyethanedio is, in comparison to the similar ion pair (dme)2Li-0 -C =P (4), 7.36 ppm upfield at -390.11 ppm and forms the < 531P high-field maxi mum for all currently known A3-phosphaalkynes [3,16]. In both compounds the chemical shifts of the carbon C 1 directly bound to phosphorus (169.17 vs. 166.46 ppm) differ by only 2.71 ppm; by con trast, the 170 NMR spectra exhibit singlets (+175.7 and +146.2 ppm) differing by about 30 ppm (see Table 1 and [3] Table 1 Table 1).…”

“…The programs Bruker WIN1D-NMR, version 6.0 and WIN2D-NMR version 6.01 were available for spec tra interpretation. Isotope shifts "_i31P(X) over n bonds, X = 13C, 15N, 180 and 29Si, are defined as usual [3,29]; the measurement accuracy is < ± 1 ppb (cf. [3,25,30]).…”

“…However, com pounds containing low-coordinate phosphorus were recently found to exhibit31P13C isotope shifts which exceeded values of phosphanes as well as four-and six-membered heterocycles with <r4 A5-phosphorus atoms [1 , 4 -7 ] by approximately two orders of magnitude [3]. 31P I5N Isotope shifts of two-coordi nate phosphorus atoms directly bound to nitrogen, determined from various azaphospholes, are also significantly larger than values of the <j4\ 5P, a4X5P' dimethylamino-substituted P-C-P fragment in a dihydro-A5-phosphete with an sp3-hybridized carbon [4,8 ].…”

“…Furthermore, several reports on 31P I80 iso tope shifts in phosphorus-oxygen compounds with l80 enriched oxygen directly adjacent to a <j4A5-phosphorus atom have been published [1, 2, 9, 10]. In contrast, unusually large 31P 180 isotope effects over two bonds in both of the A3-phosphaalkynes 'Pr3 S i-0-C = P and (dme)2 L i-0-C = P were observed without lsO enrichment [3]; the values exceed those previously known over one bond substantially.…”

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“…l.c. [8,11,16]). Im 1 H-NMRSpektrum von 3 zeigt das Triplett von Tripletts von H a , das als X-Teil eines AA'MM'X-Spinsystems (A, A' = P; M, M' = H b,c ) nach 1.…”