SYNTHESIS, STRUCTURE, AND BONDING IN ZIRCONOCENE PRIMARY PHOSPHIDO (PHR-), PHOSPHINIDENE (PR2-), AND PHOSPHIDE (P3-) DERIVATIVES

The syntheses of the Zr primary phosphido complexes CP2Zr(PH(C6H2-2,4,6-t-Bu3))Cl (1) and CP2Zr(PH(C6H2-2,4,6-Me3))CI (2) from the appropriate LiPHR and 1 equiv Of CP2ZrCl2 are described. In reactions of PH2(C6H2-2,4,6-Me3) or PH2SiMe3 with CP2ZrHCl, the respective bridging-phosphinidene derivatives (Cp2ZrCl)2(mu2-PC6H2-2,4,6-Me3) (3) and CP2Zr(mu2-PSiPh3)-(mu2-eta1:eta5-C5H4)ZrCpCl (4) are obtained. These products are planar at phosphorus, indicative of Zr-P pi-bonding. Reaction of PH(C6H2-2,4,6-t-BU3) with excess CP2ZrHCl results in the formation of the planar, trinuclear phosphide complex (CP2Zr)2(mu2-Cl)(mu3-P)(ZrCp2Cl)(5). This species 5 is also generated from the addition of PH(C6H2-2,4,6-t-Bu3) to a mixture of CP2ZrCl2 and Mg. The mixed-valent product 5 is paramagnetic, exhibiting an EPR spectrum typical of Zr(III)-P species. Under similar reaction conditions, but with prolonged exposure to Mg, the diamagnetic phosphide derivative (CpZr(mu2-eta1:eta5-C5H4))3(mu3-P) (6) is obtained. In contrast to 5, the geometry at phosphorus in 6 is pyramidal. The terminal phosphinidene complexes Cp2Zr(P(C6H2-2,4,6-t-Bu3))(PMe3) (7) and CP2Zr(P(C6H2-Me3))(PMe3) (8) are generated via the reaction of 1 or 2 with KH and PMe3. The reaction mechanisms operative in the formation of these phosphinidene or phosphide complexes are discussed. MO calculations were performed on models of the terminal and bridging phosphinidene complexes as well as the planar and pyramidal trinuclear phosphide complexes. These studies provide insights regarding the structure and bonding in these compounds. Cumulatively, this work implies that phosphinidene species are generally highly reactive, exhibiting the ability to induce C-H and P-C activation. Crystallographic data are reported herein for compounds 1, 4, and 5. Compound 1: space group P2(1)/a with a = 16.179(15) angstrom, b = 10.167(4) angstrom, c = 17.515(6) angstrom, beta = 105.88(5)-degrees, V = 2771 (5) angstrom3, and Z = 4. Compound 4: space group P1BAR with a = 11.159(8) angstrom, b = 16.434(13) angstrom, c = 10.490(8) angstrom, alpha = 95.49(7)-degrees, beta = 111.63(6)-degrees, gamma = 71.73-degrees, V = 2771(5) angstrom3, and Z = 2. Compound 5: space group P2(1)/a with a = 15.683(6) angstrom, b = 10.379(4) angstrom, c = 17.250(6) angstrom, beta = 93.28(4)-degrees, V = 2802(2) angstrom3, and Z = 4.