A CONVENIENT SYNTHETIC STRATEGY TOWARD HEAVY ALKALI-METAL BIS(TRIMETHYLSILYL)PHOSPHIDES CRYSTAL-STRUCTURES OF THE LADDER-TYPE POLYMERS [A(THF)P(SIME3)(2)]INFINITY (A = K, RB, CS)

A series of highly reactive heavy alkali metal phosphides was prepared by treating trimethylsilyl-substituted phosphines with alkali metal t ert-butyl alcoholates. The compounds are formed in excellent yield and purity, and the side product can be easily removed in a vacuum. The h igh synthetic potential of this reaction route was further shown by ut ilizing excess alkali metal tert-butyl alcoholates in reaction with si lyl substituted phosphines. In all cases, only monometalated products were isolated. In the course of this work the crystal structures of th e bis(trimethylsilyl)phosphides [K(thf)P(SiMe3)(2)](infinity) 1a, [Rb( thf)P(SiMe3)(2)](infinity), 1b, and [Cs(thf)P(SiMe3)(2)](infinity), 1c , were obtained. The compounds display polymeric ladder-type structure s. Compounds 1a,b are isomorphous, while compound Ic displays a slight ly altered local geometry. Despite small differences in local geometry , the coordination spheres for the phosphorus atoms and the alkali met al are fairly similar. The five coordinate phosphorus atoms are connec ted to three alkali metal centers in addition to two trimethylsilyl gr oups. The alkali metals are four coordinate with ligations to three ph osphorus centers in addition to one thf oxygen donor. Compounds la-c w ere characterized using elemental analysis, NMR spectroscopy, and X-ra y crystallography. Crystal data with Mo K alpha (lambda = 0.710 75 Ang strom) at 150 K are as follows: 1a, a = 6.4261(2) Angstrom, b = 12.411 9(2) Angstrom, c = 21.5447(4) Angstrom, V= 1718.41(7) Angstrom(3), Z = 4, orthorhombic, space group p2(1)2(1)2(1), 3427 independent reflecti ons, R1 (all data)= 0.0351; 1b, a = 6.5338(2) Angstrom, b = 12.5664(3) Angstrom, c 21.5537(5) Angstrom, V= 1769.70(8) Angstrom(3), Z = 4, or thorhombic, space group P2(1)2(1)2(1), 4195 independent reflections, R 1 (all data) = 0.0776; 1c, a = 11.3515(1) Angstrom, b = 22.3445(3) Ang strom, c = 7.2501(1) Angstrom, beta = 96.017(1)degrees V = 1828.81(4) Angstrom(3), Z = 4, monoclinic, space group P2(i)/c, 4343 independent reflections, R1 (all data) = 0.0811.