2,5-Dihydro-1,2,5-phosphasilaborole Derivatives: Determination of Signs of Coupling Constants [1J(31P,29Si), 2J(31P,31P), J(31P,13C), J(31P,1H)]

✍ Scribed by Bernd Wrackmeyer; Gerald Kehr; Roland Köster; Günter Seidel

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 418 KB
• Volume: 34
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199608)34:8<625::aid-omr932>3.0.co;2-q

✦ Synopsis

2,5-Dihydro-1,2,5-phosphasilaborole derivatives 1-3, 5 and 6 and the 1,2,5,6-tetrahydro-l,2,5-phosphasilaborin derivative 4 were studied with respect to the signs of coupling constants 'J(3'P,2gSi), 2J(3'P,31P), "J(3'P,'"C) (n = 1, 2, 3) and nJ(3'P,'H) (n = 2, 3, 4). The determination of relative coupling signs was achieved either by 1D selective 'H("P) heteronuclear double resonance or by various types of 2 D X-detected X/'H or 'H-detected 'H/X heteronuclear shift correlations (X = 13C, "'Si). The absolute signs were related to 'J("C,'H) > 0, using 2 D 'H-detected 1H/3'P('3C) or 'H/29Si("C) pseudo-BIRD HMQC experiments. The sign of 1J(31P,29Si) is positive ['K(3'P,29Si) < 01 in the phosphane adduct 2 where the ring phosphorus atom is three-coordinate. It becomes negative [ 1K(31P,29Si) > 01 for tetracoordinate phosphorus atoms as in the dimer 1, in the AICI, adduct 5 and in the transition metal complexes 3, 4 or 6, 6 , 6". The molecular structure of the Me,P adduct 2 in solution can be deduced on the basis of the large and positive coupling constant 2J(31P,31P) ( + 160.0 Hz) together with evidence from NOE difference spectra. All coupling constants nJ(31P,'3C) and "J(3'P,1H) in 1-6 possess a positive sign except 2J(31P,'H,,,) in 2, 2J(31P,'Hp,,) in 4 and 2J(31P,'Hp,z) in 6.