ACYLIDENEPHOSPHINES AND ALKYLIDENEPHOSPHINES .33. LITHOXY-METHYLIDENEPHOSPHINE . DME AND LITHOXY-METHYLIDYNEPHOSPHINE . 2DME - SYNTHESES AND STRUCTURES

Lithium dihydrogenphosphide . DME1) and ethyl formate in a molar ratio of 2 : 1 react in 1,2-dimethoxyethane to give liquid lithium formylphosphide . DME in 87% yield. Since lithium complexed by the chelate ligand DME is bound to the oxygen atom of the carbonyl group, the compound has to be considered as lithoxy-methylidenephosphine . DME (1). According to x-ray structure analyses of crystalline derivatives [5, 61, molecules of this type dimerize forming a four membered Li-O-Li-O ring. Characteristic nmr-data show the presence of an E- and Z-isomer (delta-H-1-P: 3.87 and 4.49; 1J(HP): 150.8 and 136.5; delta H-1-C: 11.4 and 10.05; 2J(HP): 6.1 and 81.2 ; 3J(HH): 6.6 and 13.9; delta-P-31: 38.6 and 8.8; delta-C-13 = P: 225.0 and 215.4 ppm; 1J(C=P): 41.2 and 65.0 cps); in 1,2-dimethoxyethane an E : Z ratio of 1.86: 1 is found. In a similar reaction of lithium bis(trimethylsilyl)phosphide . 1.6 THF1) with excess dimethyl carbonate lithoxy-methylidynephosphine . 2 DME (2) is formed via an up to now poorly understood mechanism. The compound can also be prepared from lithium dihydrogenphosphide - DME; it crystallizes in the monoclinic space group P2(1)/n {a = 880.6(2); b = 1296.6(2); c = 1 267.4(2) pm; beta = 96.07(2)-degrees at -100 +/- 3-degrees-C; Z = 41. An x-ray structure analysis (R(w) = 0.052) gives a P-C distance of 155.5 pm which is typical for a triple bond. The C-0 bond length of 119.8 pm, however, is extremely short compared to the standard value of a single bond (139 pm). Angles of 178.50 and 170.7-degrees at the carbon and oxygen correspond with the expected linear configuration of the P=C-0-Li backbone of the molecule. Characteristic nmr-data are as follow: delta-P-31 -384.2; delta-C-13 166.6 ppm; 1J(c=p) 41.5 cps.