Synthesis and reactivity of low-coordinate phosphines

Abstract

The reaction of a series of chlorophosphines R(,2)NP(Cl)CH(,2)SiMe(,3) (6) (R = Me, Et, i-Pr) with lithium bis(trimethylsilyl)amide in ether gives the diaminophosphines R(,2)N{(Me(,3)Si)(,2)N}PCH(,2)SiMe(,3) (7), and in THF gives mixtures of 7 and the methylenephosphines R(,2)NP=CHSiMe(,3) (11). The chlorophosphine (Me(,3)Si)(,2)NP(Cl)CH- (SiMe(,3))CH=CHSiMe(,3) (13) can be dehydrohalogenated using DBU to give a mixture of a stable 1-phosphadience (Me(,3)Si)(,2)NP=C- (SiMe(,3))CH=CHSiMe(,3) (14) and an isomeric phosphyacyclobutene 15(' )Me(,3)SiN-P-C(SiMe(,3))=CH-CHSiMe(,3). The UV spectrum indicates that the 1-phosphadiene 14 may be conjugated. The methylene- phosphines R(,2)NP=C(SiMe(,3))(,2) (17, 18) (R = Me(,3)Si, Me(,2)N) are prepared by reaction of the silyl amide or dimethylaminotrimethyl- silane with (Me(,3)Si)(,2)C=PCl. The methylenephosphines react with MeOH to give 1,2-addition products; with trimethylsilylazide to give oxidization products; and with Fe(,2)(C)(,9) to give iron tetracarbonyl complexes. In the case where methylenephosphine 17 is coordinated to iron tetracarbonyl {(Me(,3)Si)(,2)NP=C(SiMe(,3))(,2)}Fe(CO)(,4) (33), X-ray crystal structure analysis indicates that the phosphine is equatorially substituted. The P-C bond length is 1.66 A. The P-C double bond is twisted 30.3(DEGREES) out of planarity.