The compounds Cp2M((PR)3) (M - Zr, R = Ph (1), Cy (2); M = Hf, R = Cy (3)) and CP*2Zr((PCy)3) (4) were prepared and characterized. These compounds were prepared by the known reactions of the metallocene dihalide with primary phosphide salts. Alternatively, activation of the P-H bonds of a primary phosphine by zirconocene yields 1, 2 and 4, respectively. Both stabilized metallocene(II) Cp2Zr(SMe2)2 and metallocene generated by in situ reduction were employed. Attempts to identify intermediates in these reactions have been undertaken. Reaction of Cp2ZrCl2 With the phosphide LiPHPh in the presence of NEt4Br affords the species [Cp2ZrBr((PPh)2)] [NEt4] (5). These results suggest a mechanism of formation of the M(PR)3 derivatives involving phosphinidene M = PR and M((PR)2) intermediates. Intervention in such a mechanism is also accomplished by the additional electron on V(IV). Thus reaction of Cp2V with PH2Ph yields Cp2V((PPh)2) (6). Although this reaction could not be halted at the intermediate phosphinidene, species 6 was also generated via the reaction of Cp2VMeCl with LiPHPh. In a similar reaction CP2V(PC6H2,4,6-Me3)2) (7) was generated in the reaction of Cp2V with PH2(C6H2,4,6-Me3). In contrast, reaction of the species [Cp2V]+ with PH2Ph led only to the formation of the 18-electron product [CP2V(PH2Ph)2]+(8). These results are described, and the implications of these results with particular reference to the mechanism of P-P bond formation are considered. Compounds 1, 2, 4-6, and 8 were characterized crystallographically. 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 crystallizes in space group P2(1)/n with a = 13.022(8) angstrom, b = 9.303(9) angstrom, 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 with a = 22.900(16) angstrom, c - 14.975(8) angstrom, V = 7853(5) angstrom3, 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, alpha = 93.44(3)-degrees, beta = 91.25(3)-degrees, gamma = 62.52(2)-degrees, V = 1469(2) angstrom3, and Z = 2. Compound 6 crystallizes in space 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 = 94.63(3)-degrees, beta = 105.96(2)-degrees, gamma = 98.04(2)-degrees, V = 1842(1) angstrom3, and Z = 2.