Reduction of bis[(2-phosphinoethyl)tetramethyl-cyclopentadienyl]zirconium dichlorides: intramolecular C-H activation vs. stabilization of the low-valence metal center

Abstract

Reduction of the R2P-functionalized zirconocene dichlorides [C5Me4(CH2)2PR2] (C5Me5)ZrCl2 (R = Me (1) and Ph (2)) and [C5Me4(CH2)2PMe2][C5Me4(CH2)2PR2]ZrCl2 (R = Me (3) and Ph (4)) with amalgamated magnesium was studied. In the reduction of compounds 1 and 2, intramolecular C-H activation highly selectively afforded the fulvene hydride complexes Zr(H)(η5−C5Me5)[η5:η2(C,P)−(CH2)C5Me3CH2CH2PR2] (R = Me (7), Ph (8)); in the case of compound 2, the aryl hydride Zr(H)(η5:C5Me5)[η5:η1(C)−C5Me4CH2CH2PPh(o−C6H4)] (9) was also formed. The reduction of complexes 3 and 4 gave the ZrII derivatives Zr[η5:η1(P)− C5Me4CH2CH2PMe2]2 (12) and Zr[η5:η1(P)−C5Me4CH2CH2PMe2][η5:η1(P)−C5Me4CH2 CH2PPh2] (14) stabilized by two phosphine groups. The second product in the reduction of compound 4 was the fulvene hydride complex Zr(H)(η5−C5Me4CH2CH2PPh2)[η5:η2(C,P)−(CH2)C5Me3CH2CH2PMe2] (15). The reaction of compound 7 with an excess of MeI resulted selectively in replacement of the hydride ligand by iodide to give the complex ZrI(η5−C5Me5)[η5:η2(C,P)−(CH2)C5Me3CH2CH2PMe2] (10). In contrast, in the reaction of compound 7 with Me2Si(H)Cl, the Zr-CH2 bond underwent cleavage to give the chloride hydride complex Zr(H)Cl(η5−C5Me5)[η5:η1(P)−C5Me3(CH2SiMe2H)CH2CH2PMe2] (11). In the reaction of complex 12 with CO, a phosphine group was replaced by CO to form the complex Zr(CO)(η5−C5Me4CH2CH2PMe2)[η5:η1(P)−C5Me4CH2CH2PMe2] (13). The results obtained were compared with analogous reduction reactions of MeO-, MeS-, and Me2N-functionalized zirconocene dichlorides.