Synthesis and Reactions of Sterically Encumbered, Heteroleptic Lanthanum Phosphides. Structural Characterization of [{(Me3Si)2CH}- (C6H4-2-CH2NMe2)P]2La(OR) and [{(Me3Si)2CH}- (C6H4-2-CH2NMe2)P]La(THF)[P(C6H4-2-CH2NMe2)- {CH(SiMe3)(SiMe2CH2)}] [R = i-Pr, t-Bu]

Metathesis between LaI 3 and 2 equiv of {R(C 6 H 4 -2-CH 2 NMe 2 )P}K gives the heteroleptic complex {R(C 6 H 4 -2-CH 2 NMe 2 )P} 2 LaI ( 1 ), which reacts in situ with 1 equiv of KOR‘ to give the corresponding mixed phosphide/alkoxide complexes {R(C 6 H 4 -2-CH 2 NMe 2 )P} 2 La(OR‘) [R = (Me 3 Si) 2 CH, R‘ = t -Bu ( 2 ), i -Pr ( 3 )]. A similar in situ reaction between 1 and 1 equiv of any of the alkali metal organometallics R‘K [R‘ = PhCH 2, Me 3 SiCH 2, (Me 3 Si) 2 CH] yields the cyclometalated product {([Me 3 Si] 2 CH)(C 6 H 4 -2-CH 2 NMe 2 )P}La(THF)[P(C 6 H 4 -2-CH 2 NMe 2 )[CH{SiMe 3 }{SiMe 2 CH 2 }] ( 4 ) and R‘H. Reaction between the homoleptic tris(alkyl) {(Me 3 Si) 2 CH} 3 La and 2 equiv of the secondary phosphine R(C 6 H 4 -2-CH 2 NMe 2 )PH yields 4 as the exclusive product, suggesting that the cyclometalation reaction is intramolecular in nature. Compounds 2 − 4 have been characterized by multielement NMR spectroscopy and X-ray crystallography. Variable-temperature 31 P and 1 H NMR spectra and 2-D NMR experiments reveal that 4 is subject to dynamic processes in toluene solution, which may be attributed to rapid, reversible inversion at phosphorus, which results in rapid equilibria between stereoisomers; La−C cleavage is slow on the NMR time scale.