ACYLIDENEPHOSPHINES AND ALKYLIDENEPHOSPHINES .32. DI-CYCLO-HEXOYLPHOSPHINE AND DIADAMANT-1-OYLPHOSPHINE - KETO-ENOL-TAUTOMERISM AND STRUCTURE

Lithium dihydrogenphosphide . DME1) [12] and cyclo-hexoyl or adamant-1-oyl chloride react in a molar ratio of 3:2 to give lithium di-cyclo-hexoylphosphide . DME and the corresponding diadamant-1-oylphosphide . 2THF1) resp. Treatment of these two compounds with 85% tetrafluoroboric acid . diethylether adduct yields di-cyclo-hexoyl- (1b) and diadamant-1-oylphosphine (lc). In nmr spectroscopic studies of a 2 M solution of the liquid di-cyclo-hexoyl derivative 1 b over a range of 203 to 343 K, a strong temperature dependence of the keto-enol equilibrium is found; thermodynamic data characteristic for the formation of the enol tautomer (DELTA-H0) = -4.3 kJ . mol-1; DELTA-S0 = -9.2 J . mol-1 . K-1) are compared with those of 1,3-diketones. The enol tautomer of diadamant-1-oylphosphine (E-1c) as obtained from a benzene solution in thin colourless plates, crystallizes in the monoclinic space group P2(1)/c {a = 722.2(2); b = 1 085.5(4); c = 2 434.8(5) pm; beta = 96.43(2)-degrees at -100 +/- 3-degrees-C; Z = 4}. An X-ray structure analysis (R(W) = 0.033) shows bond lengths and angles to be almost identical within the enolic system (P-C 179/180; C-O 130/129; C-C(adamant-1-yl) 152/153 pm; C-P-C 99-degrees; P-C-O 124-degrees/124-degrees; P-C-C 120-degrees/120-degrees; C-C-O 116-degrees/116-degrees). The geometry of the very strong, but probably asymmetric O..H..O bridge is discussed (O-H 120/130; O..O 245 pm).