(PHOSPHINOMETHYL)ALUMINUM COMPOUNDS - THE ROLE OF COLIGANDS AND X-RAY STRUCTURE DETERMINATIONS OF THE HETEROCYCLES (TMEDA)LICLALME2C(SIME3)2PME2 AND (ME)(CL)ALC(SIME3)2PME2SIME2C(SIME3)PME2

From the 1:1 reaction of R2AlCl (a, R = Cl; b, R = Me) with {Li[C(SiMe3)2(PMe2)]}2, six-membered heterocycles [R2AlC(SiMe3)2(PMe2)]2 (1a,b) are obtained. The 1:2 reaction for R = Cl involves a facile methyl migration from the silicon to aluminum and leads to the novel heterocycle (Me)(Cl)Al activated C-(SiMe3)2PMe2SiMe2C(SiMe3)PMe2 (2), exhibiting a number of unusual structural features, as shown by the X-ray structure determination of 2, which crystallizes from pentane (colorless crystals, triclinic, space group P1, a = 9.161 (1), b = 15.280 (2), and c = 11.832 (1) angstrom, alpha = 109.62 (1), beta = 74.57 (1), and gamma = 98.39 (1)-degrees, V = 1500.9 angstrom 3, Z = 2, R = 0.035 for 283 refined parameters and 4841 observables). A formal [3 + 2] cycloaddition is observed in the same 1:1 reaction in the presence of tetramethylethylenediamine (TMEDA) to give five-membered heterocycles (TMEDA)L activated iClAlR2C(SiMe3)2PMe2 (3a,b), incorporating five different elements within the ring. 3b crystallizes from pentane (colorless crystals, monoclinic, space group P2(1)/n, a = 8.915 (1), b = 18.887 (2), and c = 16.558 (2) angstrom, alpha = 90.0 (1), beta = 92.52 (1), gamma = 90.0 (1)-degrees, V = 2785.3 angstrom 3, Z = 4, R = 0.064 for 268 refined parameters and 3830 observables). An X-ray structure determination shows the ambidentate phosphinomethanide ligand to be bound to the lithium atom via phosphorus and to the aluminum atom via carbon. 3b thermally is converted to 1b by loss of TMEDA, whereas 3a is stable to thermolysis. In the presence of tetrahydrofuran (THF), the 1:1 reaction for R = Me gives rise to Me2(THF)Al[C(SiMe3)2(PMe2)] (4), which is also obtained from 3b and THF. As a byproduct, due to some traces of HCl, in the 1:1 reaction (R = Cl) the ylide complex Cl3AlC(SiMe3)2PMe2H (5) is identified spectroscopically and eventually can be isolated. 5 either is converted by further addition of HCl to [HC(SiMe3)2PMe2H][AlCl4] (6) or rearranges to its tautomer Cl3AlPMe2C(SiMe3)2H (7), thus constituting a novel example for an ylide half-arrow-right-over-half-arrow-left phosphane diadic relationship. 7 is also obtained directly from AlCl3 and HC(SiMe3)2(PMe2).