SYNTHETIC, STRUCTURAL, AND BONDING STUDIES OF PHOSPHIDO-BRIDGED EARLY LATE TRANSITION-METAL HETEROBIMETALLIC COMPLEXES

The mononuclear terminal phosphide complexes Cp2M(PR2)2(M = Zr, Hf; R = Et, Ph, Cy) are shown to act as chelating bis(phosphine) ligands to Ni, Pd, and Pt (M’) in compounds of the form Cp2M(μ-PR2)2M’Ln(n = 1, 2) and {Cp2M(μ-PR2)2}2M’. Reaction of Cp2M(PEt2)2with Ni(1,5-COD)2yields either Cp2M(μ-PEt2)2Ni(1,5-COD) or {Cp2M(μ-PEt2)2}2Ni depending on the stoichiometry employed. Analogous reactions with Pd(PPh3)4and Pt(PPh3)3yield mixtures of Cp2M(μ-PEt2)2M’(PPh3) and (Cp2M(μ-PEt2)2}2M’ (M’ = Pd, Pt) when the M/M’ ratio is <2. With bulkier substituents, Cp2M(PR2)2(R = Ph, Cy) react with Pt(1,5-COD)2and CpPd(η-2-Me-allyl) in the presence of phosphines and phosphites yielding only Cp2M-(μ-PR2)2M’L (L = PR’3, P(OR’)3). The M’L2complexes Cp2M(μ-PPh2)2M’(DMPE) were also prepared. The three classes of compounds were characterized by X-ray crystallography. The structure of Cp2Zr-(μ-PEt2)2Ni(μ-PEt2)2HfCp2(C2/c, Z = 8, a = 34.823 (4), b = 10.991 (2), c = 21.606 (3) Å, β = 105.65 (1)°) consists of two 16-e-d0metal centers coupled to a pseudotetrahedral 18-e-d10Ni center by PEt2bridges. The MP2Ni rings are nearly planar with an average M—Ni separation of 3.027 (1) Å. The structure of Cp2Hf(μ-PPh2)2Pd(PPh3) (C2/c, Z = 8, a = 27.701 (8), b = 10.654 (5), c = 30.330 (11) Å, β = 103.16 (5)°) consists of edge-shared, 16-e-pseudotetrahedral Hf(IV) and trigonal planar Pd(0) centers with a puckered HfP2Pd ring and a Hf-Pd separation of 2.896 (1) Å. In the structure of Cp2Hf(μ-PPh2)2Pd(DMPE) (C2/c, Z = 8, a = 25.361 (12), b = 19.584 (5), c = 18.814 (13) Å, β = 126.15 (5)°) the 16-e-Hf(IV) and 18-e-Pd(0) centers are pseudotetrahedral, the HfP2Pd ring is puckered and the Hf—Pd separation is 2.983 (1) Å. Extended Hückel molecular orbital calculations performed on the model complexes Cp2Zr(μ-PH2)2M’Ln(M’Ln= Pt(PH3), Pt(DMPE), Rh(η5-indenyl), Ni(μ-PH2)2ZrCp2, and Mo(CO)4) indicate the presence of M’ → Zr donor-acceptor metal-metal bonds that become weaker along the series. The calculations also predict low barriers to MP2M’ ring inversion for the Pt complexes, consistent with low-temperature1H and31P NMR spectroscopic observations. © 1990, American Chemical Society. All rights reserved.