EARLY METAL-MEDIATED P-P BOND FORMATION IN CP2M((PR)2) AND CP2M((PR)3) COMPLEXES

The compounds Cp2M((PR)3) (M - Zr, R = Ph (1), Cy (2); M = Hf, R = Cy (3)) and CP2Zr((PCy)3) (4) were prepared and characterized. These com pounds were prepared by the known reactions of the metallocene dihalid e with primary phosphide salts. Alternatively, activation of the P-H b onds of a primary phosphine by zirconocene yields 1, 2 and 4, respecti vely. Both stabilized metallocene(II) Cp2Zr(SMe2)2 and metallocene gen erated by in situ reduction were employed. Attempts to identify interm ediates in these reactions have been undertaken. Reaction of Cp2ZrCl2 With the phosphide LiPHPh in the presence of NEt4Br affords the specie s [Cp2ZrBr((PPh)2)] [NEt4] (5). These results suggest a mechanism of f ormation of the M(PR)3 derivatives involving phosphinidene M = PR and M((PR)2) intermediates. Intervention in such a mechanism is also accom plished by the additional electron on V(IV). Thus reaction of Cp2V wit h PH2Ph yields Cp2V((PPh)2) (6). Although this reaction could not be h alted at the intermediate phosphinidene, species 6 was also generated via the reaction of Cp2VMeCl with LiPHPh. In a similar reaction CP2V(P C6H2,4,6-Me3)2) (7) was generated in the reaction of Cp2V with PH2(C6H 2,4,6-Me3). In contrast, reaction of the species [Cp2V]+ with PH2Ph le d only to the formation of the 18-electron product [CP2V(PH2Ph)2]+(8). These results are described, and the implications of these results wi th particular reference to the mechanism of P-P bond formation are con sidered. Compounds 1, 2, 4-6, and 8 were characterized crystallographi cally. Compound 1 crystallizes in space group P2(1)/a with a = 8.159(5 ) angstrom, b = 36.838(22) angstrom, c = 8.338(5) angstrom, beta = 100 .09(6)-degrees, V - 2467(3) angstrom3, and Z = 4. Compound 2 crystalli zes in space group P2(1)/n with a = 13.022(8) angstrom, b = 9.303(9) a ngstrom, c = 23.127(10) angstrom, beta = 93.25(5)-degrees, V = 2797(3) angstrom3, and Z = 4. Compound 4 crystallizes in space group, I4/m wi th a = 22.900(16) angstrom, c - 14.975(8) angstrom, V = 7853(5) angstr om3, and Z = 16. Compound 5 crystallizes in space group P1BAR with a = 11.557(3) angstrom, b = 12.455(5) angstrom, c = 11.527(4) angstrom, a lpha = 93.44(3)-degrees, beta = 91.25(3)-degrees, gamma = 62.52(2)-deg rees, V = 1469(2) angstrom3, and Z = 2. Compound 6 crystallizes in spa ce group P2(1)/n with a 15.399(2) angstrom, b = 19.876(5) angstrom, c = 6.2129(9) angstrom, beta = 90.02(1)-degrees, V = 1901.5(5) angstrom3 , and Z = 4. Compound 8 crystallizes in space group P1BAR with a = 11. 103(3) angstrom, b = 16.121(5) A, c = 10.895(4) angstrom, alpha = 94.6 3(3)-degrees, beta = 105.96(2)-degrees, gamma = 98.04(2)-degrees, V = 1842(1) angstrom3, and Z = 2.