Vier- und fünffach koordinierte Organometall-Phosphankomplexe von Aluminium, Gallium, Indium und Thallium / Four- and Five-Coordinate Organometal Phosphine Complexes of Aluminum, Gallium, Indium, and Thallium

Abstract

The organometal phosphine complexes ML3 (L = [o-(Ph2PCH2)C6H4]-; M = Al3+, Ga3+, In3a+) are obtained from MC13 and the lithiated ligand in diethyl ether. Tl[o-(Ph2PCH2)C6H4]3 is prepared from T1C1 by a disproportionation reaction. M1 species could not be detected with L as ligand. Al[o-(Ph2PCH2)C6H4]3 is the first triorganoaluminum bis(phosphine) adduct where C3P2 pentacoordination at aluminum has been definitely proven for both the solution (δ(27Al) =131 ppm, w1/2 = 12 kHz) and the solid state (d(Al–P) = 2.676(3)/2.782(2) A). The trigonal-bipyramidal coordination geometry (C3P2) at Al is achieved by two of the anionic phosphines acting as chelating ligands, spanning equatorial (C atoms) and axial sites (P atoms), while the third phosphine is only carbon-bonded. Like AlL3, the heavier congeners ML3 (M = Ga, In, Tl) are stereochemically nonrigid molecules in solution. Surprisingly, in the solid state only InL3 resembles the aluminum complex (C3P2 penta-coordination) while GaL3 and T1L3 contain four-coordinate metal centers (C3P). This may be rationalized by the noticeably less polar Ga–P bonds as compared to Al–P and In–P bonds, while in T1L3 the span of the ligand is not sufficient to allow for chelating coordination at a five- (or six-)coordinate Tl center.