ACYLPHOSPHINE AND ALKYLIDENEPHOSPHINES .31. BIS(2,4,6-TRIMETHYLBENZOYL)PHOSPHINE AND BIS(2,4,6-TRIMETHYLBENZOYL)ARSINE - SYNTHESES AND STRUCTURES

Lithium bis(2,4,6-trimethylbenzoyl)phosphide.2THF (1a) and the homologous arsenide 1b [16] are prepared from lithium bis(trimethylsilyl)phosphide . 2THF1) and lithium dihydrogenarsenide . 2THF, resp, and 2,4,6-trimethylbenzoyl chloride in a molar ratio of 3:2. Subsequent reaction with tetrafluoroboric acid . diethylether adduct results in an exchange of lithium with hydrogen and formation of bis(2,4,6-trimethylbenzoyl)phosphine (2a) and the corresponding arsine 2 b in nearly quantitative yields. Characteristic nmr parameters for the keto and enol tautomer could be obtained from a larger number of derivatives [19]. X-ray structure determination of the two isotypic compounds 2a and 2b (space group F d d 2; a = 1 486.1 (4)/1 501.7(4); b = 2975.8(12)/3 000.6(6); c = 827.9(2)/822.7(2) pm at - 100-degrees +/- 3-degrees-C; Z = 8; R(w) = 0.034/0.040) show enol tautomers with very short symmetrical O..H..O-bridges (O..O 243/245 pm) to be present in the solid state. Due to their special position the molecules are of point symmetry 2; characteristic bond lengths and angles are: P-C177; As-C 190; C-O 126/128; C-C (arene) 150/147; O-H 122/128 pm; C-P-C 98-degrees; C-As-C97-degrees; P-C-O 125-degrees; As-C-O 123-degrees; P-C-C 117-degrees; As-C-C 118-degrees; C-O-H 99-degrees/116-degrees; O-H-O 173-degrees/146-degrees. The different geometry of the two enol rings is discussed in detail.