Zirconocene Derivatives with Phosphinomethanide Ligands: Synthesis, Reactions, and Molecular Structures of Cp₂Zr(Cl)[C(PMe₂)(X)(Y)] (X =H, Y = PMe₂, SiMe₃; X = Y = SiMe₃

From Cp₂ZrCl₂and the appropriate lithium phosphinomethanides, the novel complexes Cp₂Zr(Cl)[C-(PMe₂)(X)(Y)] (X =H, Y = PMe₂(4); X = H, Y = SiMe₃(5); X = Y = SiMe₃ (6)) are obtained as crystalline solids and characterized by spectroscopy and by X-ray structure determinations. 4: monoclinic, P2₁/n, a = 16.080 (2) Å, b = 14.047 (1) Å, c = 17.003 (2) Å, β = 116.64 (1)°, V = 3432.9ų, Z = 8, T = −35 °C, R_w= 0.030, w = 1/σ²(F_°). 5: monoclinic, P2₁/c, a = 15.687 (2) Å, b = 15.898 (2) Å, c = 16.165 (2) Å, β = 111.16 (1)°, V = 3759.6 ų, Z = 8, T = −35 °C, R_w= 0.061. 6·0.5(toluene): monoclinic, P2₁/c, a = 18.585 (2) Å, b = 8.809 (1) Å, c = 16.102 (2) Å, β = 103.93 (1)°, V = 2558.6 ų, Z = 4, T = −40 °C, R_w= 0.053. In all three complexes 4–6, the zirconium atom as part of a metallaphosphacyclopropane ring is the most prominent structural feature. Whereas the Zr–P (4,2.621 (1)/2.632 (1) Å 5, 2.634 (1)/2.616 (1) Å 6, 2.606 (1) Å) as well as the Zr–Cl (4, 2.569 (1)/2.576 (1) Å; 5, 2.558 (1)/2.572 (1) Å 6, 2.554 (1) Å) and the Zr–D distances (where D denotes the centroid of the cyclopentadienyl rings; 4, 2.42/2.22 and 2.22/2.24 Å;5, 2.24/2.24 and 2.23/2.24 Å; 6, 2.23/2.26 Å) are nearly equal, the Zr-C(1) distances differ considerably in going from 4 (2.413 (2)/2.408 (2) Å) to 5 (2.401 (5)/2.423 (5) Å) and to 6 (2.607 (1) Å), due to steric congestion. Consequently, 6 exists in solution as an η¹(P)-coordinated 16e complex, as may be deduced from NMR data. Complex 4 exists in solution as an equilibrium mixture of isomers 4 and 4a, the latter exhibiting a chelating P,P-coordination of the diphosphinomethanide ligand, thus forming the four-membered heterocycle Zr–P–C–P. At elevated temperatures, all phosphorus nuclei equilibrate, obviously via a common intermediate of 4 and 4a. Complexes 4 and 5 do not react with CO at ambient temperature and pressure, whereas 6 decomposes above 0 °C in solution.