Acyl- and alkylidenephosphanes. XXXV. Bis[N-(trimethylsilyl)iminobenzoyl]phosphanides of lithium and zinc-syntheses as well as NMR spectroscopic, structural, and quantumchemical studies

From the reaction of bis (tetrahydrofuran)lithium bis(trimethylsilyl)phosph anide with two equivalents of benzonitrile in 1,2-dimethoxyethane, the yell ow dme complex (2a) of lithium bis [N-(trimethylsilyl)iminobenzoyl]phosphan ide (2) was obtained in 69% yield. However, the intermediate {1-[N-lithium- N-(trimethybilyl)amido]benzylidene)trimethylsilylphosphane (1), formed by a n analogous 1:1 addition in diethyl ether, turned out to be unstable and as a consequence could be characterized by nmr spectroscopic methods only; at tempts to isolate the compound failed, but small amounts of the neutral com plex 2b, with the ligands benzonitrile and tetrahydrofuran coordinated to l ithium, precipitated. The reaction of compound 2 with zinc(II) chloride in diethyl ether gives the orange-red spiro-complex zinc bis{bis[N-(trimethyls ilyl)iminobenzoyl]phosphanide} (3); this complex is also formed from bis[N- (trimethylsilyl)iminobenzoyl]phosphane (4), easily amenable by a lithium hy drogen exchange of 2a with trifluoroacetic acid [18], and zinc bis[bis(trim ethylsilyl)amide]. As derived from nmr spectroscopic studies and x-ray structure determination s, compounds 2a (delta(31)P +63.3 ppm; P2(1)/n; Z = 4; R-1 = 0.067}, 2b (de lta(31)P +63.3 ppm; P2(1)/c; Z = 4; R-1 = 0.063), 3 (delta(31)P +58.2 ppm; C2/c; Z = 4; R-1 = 0.037) and 4 (delta(31)P +58.1 ppm [18]} exist as cyclic 3-imino-2 lambda(3)sigma(2)-phosphapropenylamides and -propenylamine, resp ectively, in solution as well as in the solid state. Unlike hydrogen deriva tive 4 the bis[N-(trimethylsilyl)iminobenzoyI]phosphanide fragments N,N'-co ordinating either a lithium or a zinc cation are characterized by almost co mpletely equalized bond lengths; typical mean distances and angles are: P c hemical anion C 180.3 and 178.7; C chemical anion N 130.5 and 131.8; N-Si 1 75.3 and 179.3; N-Li 202.3; N-Zn 203.5 pm; C chemical anion P chemical anio n C 108.8 degrees and 110.5 degrees P chemical anion C chemical anion N 130 .9 degrees and 132.9 degrees; C chemical anion N-Li 113.0 degrees, C chemic al anion N-Zn 117.4 degrees; N-Li-N 104.6 degrees; N-Zn-N 108.8 degrees. Al terations in the shape of the six membered chelate rings, caused by an exch ange of the 3-imino-2 lambda(3)sigma(2)-phosphapropenylamide or related 2 l ambda(3)sigma(2)-phospha-1,3-dionate units for the corresponding phosphorus free ligands, are discussed in detail. The results of quantumchemical DFT- B3LYP calculations coincide very well with the experimentally obtained find ings.