Methylenephosphanyl Comple:r.es of Chromium., Molybdenum, Tungsten, Iron and Nickel -Syntbesis and ReacUvity "The reacHon of the functionalized Pie double bond systems x -P", qR)SiMe l [R = SiMel and X = Cl (la), Cp· (5a) or R -Pb and X = Br (1 b), Cp· (S b)1 wilh alkali carbonylmetallates or earbonyl eomplexes of group 6, 8. and 10 metals leads to thc formation of the transition metal-substituted phosphaalkenes J{M}-P= C(R)SiMeJ 3a -j and 4a -i J, in which the P-C fragment aets as a one-eleetron donor. Depending on the nuc1eophilicity of the tnm~ition m .. t ..

The allyl anion (I) and, in particular, the metal-stabilized ~3complexes are among the best explored carbanion systems.' In contrast, little is known about the phosphaallylic systems in which one carbon atom is replaced by a twofold coordinated phosphorus center (II, 111) (Scheme I). While the 2-phosphaallyl complexes ( 5 ) The coordination of lithium by thrce dme molecules is known: Baker, T.; Krusic, P. J.; Tulip, T. H.; Calabrcae, J. C.; Wreford, S . S . J. Am. Chem. Soc. 1983,105,6763. Altwood, J. L.; Rogers, R. D.; Vann Bynum, R. Cryst. Struct. Commun. 1!%4,40,1812. Schumann,H.;Nickel,S.;Hahn,E.;Heeg, M. J. Organometallics 1985, I , 800. Schumann, H.; Nickel, S.; Loebel, J.; Pickardt, J. Organometallics 1988, 7, 2004.

A phosphindolyllithium complex or a lithium salt with a phosphindolyl anion? Both the ease of the synthesis and the structure of compounds 1 are surprising: the unit cell of crystalline 1 b contains two independent molecules in which lithium is coordinated in an η5 fashion in one and an η3 fashion in the other—this indicates the transition from the complex to the anion.

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